Graphene2014 poster book 1 by Phantoms Foundation

Poster Book Vol. 1

OREWORD

On behalf of the Organising, Scientific and Local Committees we take great pleasure in welcoming you to Toulouse for the fourth edition of the Graphene International Conference & Exhibition. A plenary session with internationally renowned speakers, extensive thematic workshops in parallel, one-to-one meetings (Brokerage Event) and a significant industrial exhibition featuring current and future Graphene developments will be highlighted at the event. Graphene 2014 is now an established event, attracting global participants intent on sharing, exchanging and exploring new avenues of graphene-related scientific and commercial developments. The event is raising great interest and is now considered as the Graphene meeting point in 2014. We truly hope that Graphene 2014 serves as an international platform for communication between science and business. We are also indebted to the following Scientific Institutions, Companies and Government Agencies for their help and/or financial support: Phantoms Foundation, Université Catholique de Louvain, ICN2 (ICN-CSIC), Centre National de la Recherche Scientifique, CEMES, CIRIMAT, Université de Montpellier 2, LCC Ensiacet, Université de Bordeaux, Grafoid Inc., Aixtron, Thermo Scientific, Fondation AIRBUS Group, AIRBUS, HORIBA Scientific, The Nano, EXtreme measurements & Theory (NEXT) project, ONERA, Donostia International Physics Center (DIPC) & Materials Physics Center (CFM), SO Toulouse, Galeries Lafayette, Mairie de Toulouse, EuroPhysics Letters (epl), INSA Toulouse, Solvay, Center for Nanostructured Graphene, GDRI: Graphene-Nanotubes, American Elements, PRACE, Université Toulouse III, Paul Sabatier, Groupe Français d’Etude des Carbones (GFEC), Région Midi-Pyrénées, European Physical Society (EPS), Cambridge University Press and Air France / KLM. We also would like to thank all the exhibitors and participants that join us this year. One thing we have for granted: very few industries, one way or another, will escape from the influence of Graphene and the impact on businesses is here to stay. Hope to see you again in the next edition of Graphene 2015 to be held during ImagineNano event (www.imaginenano.com) in Spain.

Graphene 2014 Organising Committee

Graphene2014

May 06-09, 2014 Toulouse (France)

Sergiu Amarie

Uriel Sierra, Zoraida González, Matías Blanco, Clara Blanco, M. Victoria Jiménez, Javier Fernández-Tornos, Jesús J. Pérez-Torrente, Luis A. Oro and Rosa Menéndez

Patricia Alvarez

C. Botas, R. Santamaria, R. Menendez, D. Martin-Yerga, A. Costa-Garcia

Patricia Alvarez

C.F. Gutierrez-Gonzalez, A. Smirnov, A. Centeno, A. Fernández, V.G. Rocha, R. Torrecillas, A. Zurutuza and J.F. Bartolome

Beatriz Alonso

Burcu S. Okan, Lale I. Şanlı, Vildan Bayram, Begüm Yarar

Selmiye Alkan Gürsel

V.V.Luchinin

Nickolay Alekseyev

Seunghee Jeong, Zhigang Wu, Shi-Li Zhang and Zhi-Bin Zhang

Patrik Ahlberg

C. Mukherjee, S. Fregonese, C. Maneux, T. Zimmer

Jorge Daniel Aguirre Morales

Bing Li, Kazukuni Tahara, Willem Vanderlinden, Kunal S. Mali, Stefan De Gendt, Yoshito Tobe, Steven De Feyter

Jinne Adisoejoso

Gian Franco Tantardini, Rocco Martinazzo

Simona Achilli

authors

Germany

Spain

Turkey

Russia

Sweden

France

Belgium

Italy

country

Spectroscopies and microscopies

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Quantum transport

topic

poster title

"From Nanoscale Chemical Identification to Real-Space Mapping of Graphene Plasmons"

"Preparation of coke-based graphenes and their application in batteries and catalysis"

"Electrochemical characterization of graphene oxides using screen-printed electrodes"

"Wear behavior of electroconductive graphene/alumina composite"

"Graphene based Electrodes for PEM Fuel Cells"

"Calculation of electronic properties of graphene grown on faceted SiC surface as on optimal matrix for the graphene synthesis"

"Graphene/Galinstan Contacts for Reliable Liquid Interconnects"

"Analytical Study of Performances of Monolayer and Bilayer Graphene FETs based on Physical Mechanisms"

"Self-Assembled Air-Stable Supramolecular Porous Networks on Graphene"

"Hydrogen-dimer lines and electron waveguides on graphene"

Only Posters submitted by fully registered participants are listed below: 351 (as of 24/04/2014)

osters list: alph abet ic al orde r

Roberto Y. Sato Berrú, Doroteo Mendoza López

Claudia Bautista Flores

Gerardo G. Naumis

Jose Eduardo Barrios Vargas

Nara R. S. Basso, Fabiana Fim, Thuany Maraschin, Giovani Pavoski

Griselda Barrera Galland

Felipe M Perez, Na Ni, Paulado V Pereira, Robert C Maher, Esther Garcia-Tuñon, Salvador Eslava, Cecilia Mattevi, Eduardo Saiz

Suelen Barg

Sébastien Bonhommeau, Jean-Baptiste Verlhac, Dario Bassani

Hugo Bares

Philippe Serp, Pierre Lecante, Wolfgang Bacsa

Revathi Bacsa

Tilmar Kümmell, Wolf Quitsch, Sebastian Matthis, Tobias Litwin

Gerd Bacher

Stefano Leoni, Gotthard Seifert

Igor Baburin

Fethullah Gunes, David Alamarguy, Alexandre Jaffré, José Alvarez, Jean-Paul Kleider and Mohamed Boutchich

Hakim Arezki

Ayaka Sasabuchi, Shigeru Yamauchi

Takashi Aoyama

A. Grozdanov, P. Paunovic and A.T. Dimitrov

Beti Andonovik

Gunst, D. Stradi & M. Brandbyge

Nick Papior Andersen

C. Androulidakis, G. Tsoukleri, J.Parthenios, I. Polyzos,K. Papagelis, C.Galiotis

Georgios Anagnostopoulos

A.Dimoulas, E. Xenogiannopoulou, P. Tsipas, D. Tsoutsou,S. Kassavetis, E. Golias, C. Grazianetti, D. Chiappe, A. Molle, M. Fanciulli

Sigiava Aminalragia Giamini

authors

Mexico

Spain

Brazil

France

Germany

France

Japan

Macedonia

Denmark

Greece

country

Spectroscopies and microscopies

Quantum transport

Growth, synthesis techniques and integration methods

Chemistry of Graphene

Growth, synthesis techniques and integration methods

Other 2 dimensional materials

Applications (gaz sensors, composites, nanoelectronic devices...)

Chemistry of Graphene

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Quantum transport

Spectroscopies and microscopies

Other 2 dimensional materials

topic

"Charge transfer between graphene and fullerene C60"

"Pseudo-gap opening and Dirac point confined states in doped graphene"

"A Few Layer Graphene Material Prepared by Thermal Reduction of GO"

"Graphene Complex Cellular Networks"

"Direct Liquid-Phase Exfoliation of Graphite via Diels-Alder reaction"

"Large scale catalytic synthesis of few layer graphene: structure and mechanism of formation"

“Electrical control ofexcitons and trions in MoS2 monolayer and bilayer crystals”

"A novel route towards carbon-based materials for hydrogen storage: packings of carbon nanotubes and graphene–carbon nanotubes composites"

"Nitric Acid doping of epitaxial graphene on SiC(0001) substrate"

"Schottky diode characteristics of ZnO/graphene/Cu heterojunctions"

"Determining graphene layers number distribution by XRD data"

"DFT-NEGF calculations of gated graphene nano-structures"

“Monitoring stress transfer characteristics under tension in simply supported and embedded graphenes”

“Growth and Characterization of Graphene-like 2D Nanolattices of Silicene and AlN”

poster title

Louise Brooks

Y. Dappe, M. Andersen, R. Balog

Xavier Bouju

Simon M.-M. Dubois, Jean-Christophe Charlier

Andrés Rafael Botello Méndez

Thorben Casper, Jorge Pedrós, Javier Martínez, Fernando Calle

Alberto Boscá Mojena

G.M. Junior, P. Alpuim, M.F. Cerqueira

Jérôme Borme

Ledjane Silva Barreto, Jing Kong

Gabriela Borin Barin

Konstantin A. Milakin, Markus Pesonen, Aleksandr N. Ozerin, Vladimir G. Sergeyev and Tom Lindfors

Zhanna Boeva

Achim Richter, Maksym Miski Oglu, Barbara Dietz, Tobias Klaus, Dominik Smith, Lorenz von Smekal

Manon Bischoff

Charles Agnès, Florence Duclairoir, Lionel Dubois

Gérard Bidan

Ji-Hua Xu, Fabrizio Castellano, Miriam S. Vitiello, Alessandro Tredicucci, Harvey E. Beere, David A. Ritchie, Vaidotas Miseikis, Camilla Coletti

Federica Bianco

Sinead Winters, Claudia Backes, Aoife Ryan, Mathias O. Senge, Georg S. Duesberg

Nina Berner

M. Spina, J. Jacimovic, P. R. Ribic, A. Walter, D.Y. Oberli, E. Horvath, L. Forró, A. Magrez

Laurent Bernard

D. Mendoza

Jose Luis Benítez

M. Fabiane, D. Y. Momodu, S. Khamlich, J. K. Dangbegnon, N. Manyala

Abdulhakeem Bello

authors

USA

France

Belgium

Spain

Portugal

Brazil

Finland

Germany

France

Italy

Ireland

Switzerland

Mexico

South Africa

country

Chemistry of Graphene

Spectroscopies and microscopies

Quantum transport

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Quantum transport

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Chemistry of Graphene

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

topic

"Graphene on Press"

"Adsorption and STM characterization of polycyclic aromatic hydrocarbons on graphite/graphene"

"The effect of a third nearest neighbor tight binding model on the pseudo-magnetic field in graphene"

"Method for electrical evaluation of graphene using a GFET structure"

"Multiple Use of High Purity Copper Foils as Catalyst Substrates for Graphene Growth"

"Pre-Patterned CVD Graphene: Influence of ALD deposition parameters on Al2O3 and graphene layers"

"Dispersible composite of exfoliated graphite and polyaniline with improved electrochemical activity for sensor applications"

"Testing the index theorem for graphene and C60 molecules"

"One-pot reduction and diazonium functionalization of graphene oxide"

"THz saturable absorption in graphene"

"Noncovalent functionalization of graphene with large organic molecules"

"Functionalized graphene grown by oxidative dehydrogenation chemistry"

"Control of the Optical transmittance in Multilayer Graphene using a bias Voltage"

"Three dimensional graphene composite electrodes for electrochemical applications"

poster title

Ali Çelik, Ender Suvaci and Emmanuel Flahaut

Yasemin Çelik

P. Trinsoutrot, M. Brignone, H. Vergnes, B. Caussat, D. Pullini

Brigitte Caussat

Luca Artiglia, Emanuele Cavaliere, Marco Favaro, Stefano Agnoli, Alexey Barinov, Silvia Nappini, Elena Magnano, Federica Bondino, Luca Gavioli and Gaetano Granozzi

Mattia Cattelan

Mikkel Kongsfelt, Daniel Tejero, Steen U. Pederson, Kim Daasbjerg, Liv Hornekær

Andrew Cassidy

Xavier Cartoixà

Jorge Pedros, Jürgen Schiefele, Fernando Sols, , and Francisco Guinea

Fernando Calle

J. Martinez, A. Ladron de Guevara, D. J. Choi, A. Bosca, J. Pedros

Fernando Calle

Niclas Lindvall, MartinB. B. S.Larsen and Peter Bøggild

Alberto Cagliani

Michael Shtein and Oren Regev

Matat Buzaglo

Filippo Pizzocherro, Michael Hilke, Eric Whiteway, Peter Bøggild, Peter Uhd Jepsen

Jonas Buron

Pawel Potasz, Arkadiusz Wójs

Pawel Bugajny

authors

Turkey

France

Italy

Denmark

Spain

Denmark

Israel

Denmark

Poland

country

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

Spectroscopies and microscopies

Chemistry of Graphene

Quantum transport

Applications (gaz sensors, composites, nanoelectronic devices...)

Chemistry of Graphene

Spectroscopies and microscopies

Nanoelectromechanical systems

topic

"Anisotropic mechanical and thermal properties of graphene nanosheets/alumina composites"

"Development of a multi-steps CVD process to produce bilayers graphene for anode of Organic Light Emitting Diodes"

"The nature of the Fe-Graphene interface at the nanometer level"

"Thermally activated chemical functionalization of graphene under ultra-high vacuum conditions"

"Electronic Transport in Graphene / Ni(111) contacts from first principles"

"Coupling light into graphene plasmons with the help of surface acoustic waves"

"Graphene flexible electronic device for lighting LEDs"

"Defect-Oxygen assisted direct write technique for nanopatterning graphene"

"Critical Parameters in Exfoliating Graphite into Graphene"

"Non-Drude CVD graphene terahertz conductance dynamics"

"Analysis of optical properties of symmetric graphene quantum dots"

poster title

Chang-Soo Han

Wook Choi

Dong Hee Shin, Sung Kim, Chang Oh Kim, Jong Min Kim, Ju Hwan Kim, Kyeong Won Lee

Suk-Ho Choi

Qingyun Zhang, Udo Schwingenschlog

Yingchun Cheng

N. Vermeulen and J. E. Sipe

JinLuo Cheng

Irene Calizo, Angela R. Hight Walker

Guangjun Cheng

Johan Biscaras and Abhay Shukla

Zhesheng Chen

Zhibo Liu,Wenshuai Jiang, Wei xin, Fei Xing, Peng Wang, Bin Dong, Xiaoqing Yan, Yongsheng Chen, Jianguo Tian

Xudong Chen

David JimĂŠnez

Ferney A. Chaves R.

Philippe Gaillard, Pavel Moskovskin, StĂŠphane Lucas and Luc Henrard

Thomas Chanier

Chabi, Zhuxian Yang, Chuang Peng, Yongde Xia, Yanqiu Zhu

Sakineh Chabi

Lu Hua Li,Morteza Aramesh,Hualin Zhan,Kate Fox,Desmond Lau,Ying Chen and Steven Prawer

Jiri Cervenka

Irene Palacio, Alexandre Gloter, Meredith S. Nevius, Alberto Zobelli, Muriel Sicot, Daniel Malterre, Claire Berger, Walter de Heer, Edward H. Conrad, Amina Taleb-Ibrahimi, Antonio Tejeda

Arlensiu Celis

authors

Korea

Saudi Arabia

Belgium

USA

France

China

Spain

Belgium

Australia

France

country

Applications (gaz sensors, composites, nanoelectronic devices...)

Magnetism and Spintronics

Quantum transport

Chemistry of Graphene

Other 2 dimensional materials

Applications (gaz sensors, composites, nanoelectronic devices...)

Quantum transport

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

topic

"Graphene-Embedded Nanopore Device"

"Photoresponsivity characterization of all-graphene p-n vertical-junction photodetectors at various doping concentrations"

"Valley polarization in magnetically doped single layer transition metal dichalcogenide"

"Theoretical study of the third order optical nonlinearity of graphene"

"Fe-catalyzed Etching of Graphene and Few-layer Graphene"

"High performance photo-detector based on few layer InSe"

"The Design and Fabrication of Twisted Multilayer Graphene with Fine Tunable Rotated Angle"

"Theoretical Study of the Contact Resistance in MetalGraphene Junctions"

"Graphene on copper: ab initio modelisation and growth"

"Synthesizing 3D graphene foam with direct etching for energy storage applications"

"Atomically thin carbon and boron nitride films as anticorrosive coatings"

"Structural Origin Of The Band-Gap In Armchair Graphene Nanoribbons"

poster title

D. Lopez-Cortes, E. C. Romani, D. G. Larrudé, I. C. S. Carvalho, H. B. Ribeiro, M. A. Pimenta, and F. L. Freire Jr

Christiano de Matos

P. Trinsoutrot, H. Vergnes, B. Caussat

Laetitia Dardenne

M. Svec, P. Merino, C. González, E. Abad, P. Jelinek, and J. A. Martin-Gago

Yannick Dappe

S. Noel , F. Houzé , D. Alamarguy , A. Jaffré

Kevin Dalla Francesca

Mohammed S. El-Bana, Hasti Shajari, Simon J. Bending

Sara Dale

Maria C. Paiva, M. Fernanda Proença, Florinda Costa, António José Fernandes, Marta A. C. Ferro, Paulo E. C. Lopes, Mariam Debs, Manuel Melle-Franco, Francis L. Deepak

Eunice Cunha

Francois Peeters

Lucian Covaci

Carlos Celedon

Andrea Cortes

Alberto Fina, Zhidong Han, Guido Saracco

Samuele Colonna

Maria Sarno, Claudia Cirillo, Massimiliano Polichett

Paolo Ciambelli

Abhilash Sasidharan, G. Siddaramana Gowd, Shantikumar Nair, Manzoor Koyakutty

Girish Chundayil Madathil

Wang, W.; Wubs, M.; Jauho, A.-P.; Mortensen, N.A.

Thomas Christensen

authors

Brazil

France

Portugal

Belgium

Chile

Italy

India

Denmark

country

Growth, synthesis techniques and integration methods

Spectroscopies and microscopies

Other 2 dimensional materials

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

Spectroscopies and microscopies

topic

"Graphene ablation by an optical fiber delivered laser"

"Graphene synthesis on copper from ethylene by Catalytic Chemical Vapor Deposition"

"van derWaals interactions mediating the cohesion of fullerenes on graphene"

"Morphological and electrical characterizations of graphene exfoliated by liquid way"

"Superconductivity in 2D NbSe2 Field Effect Devices"

"Production of Pyrrolidine – Functionalized Graphene in Solution"

"Andreev quantum dots in graphene-superconductor hybrid devices"

"CVD synthesis of graphene from acetylene on copper foil"

"Graphene nanoplatelets for thermally conductive polymer nanocomposites"

"Highly magnetic core-shell graphene coated Fe/Co nanoparticles"

"In vivo biodegradation of graphene: A Confocal Raman Microscopy study"

"Comparisons between Classical, Semiclassical, and Quantum Plasmonics in Graphene Nanodisks"

poster title

Jean-Christophe Charlier

Simon Dubois

Ekarat Detsri

Stephan Dubas

Guido Burkard

Matthias Droth

M. Suchea, I.V. Tudose, G. Kenanakis, E Koudoumas

Emmanuel Drakakis

Artem Shelaev, Mikhail Yanul, Eugenii Kuznetsov, Sergey Timofeev, Sergey Lemeshko and Victor Bykov

Pavel Dorozhkin

Jiri Cervenka

Nikolai Dontschuk

V. Hung Nguyen, M. Chung Nguyen, H. Viet Nguyen

Philippe Dollfus

Yalei Wang, A. Mark Fox and Gillian A. Gehring

Wala Dizayee

Abdulakim Ademi, Anita Grozdanov, Beti Andonovic,Gennaro Gentile, Maurizio Avella and Perica Paunovi

Aleksandar Dimitrov

Z. Ji, K. A. Velizhanin, C. Sheehan, M. Sykora, and S. K. Doorn

Enkeleda Dervishi

J.-L. Codron, C. Boyaval, X. Wallart, D. Vignaud

Geetanjali Deokar

Giancarlo Vincenzi, Fabio Coccetti

George Deligeorgis

Simona Achilli, Fausto Cargnoni, Davide Ceresoli, Gian Franco Tantardini, Mario Italo Trioni

Elisabetta del Castillo

authors

Belgium

Thailand

Germany

Greece

Russia

Australia

France

Macedonia

USA

France

Italy

country

Quantum transport

Applications (gaz sensors, composites, nanoelectronic devices...)

Magnetism and Spintronics

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Applications (gaz sensors, composites, nanoelectronic devices...)

Magnetism and Spintronics

Spectroscopies and microscopies

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Quantum transport

topic

"Layer-by-layer deposition of anionic graphite oxide and polyaniline into thin films with cationic poly(diallyl dimethyl ammonium chloride)" "A first-principles investigation of h-BNC nanostructures: electronic structure, stability of the edges, electronic scattering at the interfaces"

"Exchange coupling between localized defect states in graphene nanoflakes"

"Graphene based paint-like composites for electromagnetic shielding in the GHz frequency range"

"Nano-Raman (Tip Enhanced Raman) and co-localized AFM-Raman characterization of graphene and related materials"

"Graphene-molecule interactions and the potential for selective chemical sensing by graphene FET's"

"Strategy of strain engineering to improve performance of graphene transistors"

"Magneto- Optics Properties of Graphite"

"Spectroscopic Characterization of Graphene Synthesized by Electrolysis in Molten Electrolytes"

"Synthesis of graphitic nano-discs with unique optical properties"

"CVD graphene growth on Ni films and transfer"

"On the Kinetic Inductance of Graphene Devices"

"Spin asymmetric band gap in graphene by Fe adsorption"

poster title

V. S. Amaral, J. G. Correia, J. N.Gonçalves, A.Gottberg, K. Johnston, Yacine Kadi

Abel Fenta

Chuanbin Sun, Wei Feng

Yiyu Feng

I. Verzhbitskiy, C. Woods, C. Rice, J.-J. Pireaux, C. Casiraghi

Alexandre Felten

A. Kardakova, I. Gayduchenko, B.M. Voronov, M. Finkel, T.M. Klapwijk, and G. Goltsman

Georgy Fedorov

Barbaros Ozyilmaz, Antônio H. C. Neto

Guilhermino Fechine

Boris Fainberg

C. P. Ewels, Ph. Wagner, X. Rocquefelte, O. Stephan, K March, M. Kociak, R. Arenal, A. Loiseau, M. Scardamaglia, P. Pochet, R. Snyders, C. Bittencourt

Dogan Erbahar

M.M. Mahmoodian

Matvey Entin

Philippe Carbonnière, and Michel Rérat

Khaled Elkelany

Sara Costa, Otakar Frank, Martin Kalbac

Johan Ek Weis

Li He, Ziyu Wang, Peter Hodgson, Mainak Majumder, Lingxue Kong

Ludovic Dumee

H. Amara, Th. Mercier, L. Henrard

François Ducastelle

authors

Portugal

China

Belgium

Russia

Brazil

Israel

Turkey

Russia

France

Czech Republic

Australia

France

country

Spectroscopies and microscopies

Chemistry of Graphene

Applications (gaz sensors, composites, nanoelectronic devices...)

Chemistry of Graphene

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Quantum transport

Quantum transpor

Spectroscopies and microscopies

Applications (gaz sensors, composites, nanoelectronic devices...)

Chemistry of Graphene

topic

"Atomic local studies on graphene using isolated ad-atom probes"

"Solvothermal exfoliation of fluorographene by the intercalation of organic solvents for lithium primary batteries"

"The effect of hydrogen plasma on the chemical and structural modification of graphene"

"Photothermoelectric Response in Asymmetric Nanostructured Carbon Devices Exposed to THz Radiation"

"Challenges in Graphene-Polymer Interactions"

"Photon-Assisted Tunneling through Molecular Conduction Junctions with Graphene Electrodes"

"Nitrogen segregation in nanocarbons"

"Enhancement of optical transitions in graphene by attraction between electrons and holes"

"Piezoelectricity of BN-doped Graphene mono-, bi-, and trilayer(s), and their corresponding bulk structures: An ab initio description"

"Raman Mapping of Fluorinated Labelled Bilayer Graphene"

"Development of graphene corrosion resistant coatings across porous stainless steel materials"

"Nitrogen doping and the Coulomb impurity problem in graphene"

poster title

Erol Zekovic, David Mackenzie, Jose Caridad, Alberto Cagliani, Tim Booth and Peter Bøggild

Lene Gammelgaard

Eoin Murray, Sepidar Sayyar, Gordon G. Wallace and David L. Officer

Sanjeev Gambhir

Stephan Hofmann and Gehan A. J. Amaratunga

Dona Thanuja Lakmali Galhena

I. Zsoldos, I. Laszlo

David Fulep

Martin Gmitra, Jaroslav Fabian

Tobias Frank

Florence Mouchet, Stéphanie Cadarsi, JeanCharles Arnault, Hugues GirarrdI, C. MenardMoyon, Izabela Janowska, Alberto Bianco, Emmanuel Flahaut, Eric Pinelli and Laury Gauthier

Emmanuel Flahaut

Yasemin Celik, Ender Suvaci

Emmanuel Flahaut

R. Lo Nigro, F. Roccaforte, S. Ravesi,F. Giannazzo

Gabriele Fisichella

F. Giannazzo, G. Greco, S. Ravesi, F. Roccaforte

Gabriele Fisichella

Martina Datteo, Cristiana Di Valentin

Lara Ferrighi

M. Z. Iqbal, Jonghwa Eom

Núria Ferrer-Anglada

Luis Segura, Noel Rodriguez, , Akiko Ohata, Carlos Marquez, Francisco Gamiz

Cristina Fernandez

authors

Denmark

Australia

Hungary

Germany

France

Italy

Spain

country

Applications (gaz sensors, composites, nanoelectronic devices...)

Chemistry of Graphene

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

Magnetism and Spintronics

Other 2 dimensional materials

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Chemistry of Graphene

Applications (gaz sensors, composites, nanoelectronic devices...)

topic

"Influence of individual process steps on graphene device characteristics"

"Organic Dispersions of Highly Reduced Chemically Converted Graphene"

"Graphene Oxide and Activated Carbon Composites for High-Power Supercapacitors"

"Preparation of carbon nanotube Y-junctions from graphene nanoribbons"

"Ab initio studies of fluorinated graphene"

“Toxicity evaluation in Xenopus laevis tadpoles exposed to carbon based nanoparticles under normalized conditions”

"Few-layer Graphene Sheets by Liquid Phase Exfoliation in a Low Boiling Point Solvent: A Comparative Study of Three Different Graphite-based Starting Materials"

"Large-area graphene from catalytic metals to arbitrary substrates by electrochemical delamination and transfer printing"

“Current transport in graphene/AlGaN/GaN heterostructures”

"Boosting Graphene Reactivity with Oxygen by Boron Doping: DFT Modeling of the Reaction Path"

"Stable p-doping in graphene using deep UV irradiation"

“Direct Electrical Characterization of Graphene-OnInsulator by Multiple-PointContact Configuration”

poster title

Alfonso Álvarez, Néstor Perea-López, Olga Martin, Juan Baselga, Mauricio Terrones

Viviana Jehova Gonzalez Velazquez

L. Rosales, M. Pacheco, A. Ayuela

Jhon W. González Salazar

V. V. Brus, G. V. Troppenz, X. Zhang, K. Hinrichs, J. Rappich, and N. H. Nickel

Marc A. Gluba

Virginia D. Wheeler, Luke O. Nyakiti, Rachael L. Myers-Ward, Charles R. Eddy, Jr., D. Kurt Gaskill, Olga Kazakova

Cristina Giusca

M.Losurdo,G.V.Bianco, P.Capezzuto and G.Bruno

Maria Michela Giangregorio

Shishir Kumar, N.Ravishankar, S.Raghavan

Priyadarshini Ghosh

Agnieszka Kuc, Nourdine Zibouche, Thomas Heine

Mahdi Ghorbani Asl

Joseph N Grima, Szymon Winczewski, Michael C. Grech, Ruben Gatt, Reuben Cauchi1, Daphne Attard and Jaros?aw Rybicki

Ruben Gatt

A.Centeno, B.Alonso, A. Fernández, C.F. Gutierrez-Gonzalez, R. Torrecillas, A. Zurutuza

Victoria Garcia Rocha

J. Fernández-Rossier

Noel Garcia

Kian Ping Loh

Libo Gao

Udo Schwingenschlögl

Li-Yong Gan

authors

Spain

Germany

Italy

India

Germany

Malta

Portugal

Singapore

Saudi Arabia

country

Applications (gaz sensors, composites, nanoelectronic devices...)

Quantum transport

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Growth, synthesis techniques and integration methods

Other 2 dimensional materials

Chemistry of Graphene

Applications (gaz sensors, composites, nanoelectronic devices...)

Magnetism and Spintronics

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

topic

"Graphene functionalized with TiO2 for Nanocomposites"

"Resonances induced by Hydrogen-like ad-atoms in graphene-like ribbons"

"Charge transport along and across integrated large-area graphene"

"Tuneable humidity gating of graphene’s electronic properties"

"Work function of metal-doped CVD graphene by Kelvin Probe Force Microscopy"

"Role of Defect Density of Cu Substrate on Graphene Nucleation"

"Strain and defect modulations of electronic structure in transition-metal dichalcogenides"

"Introduction of Auxetic Behaviour in Graphene"

"Graphene/alumina (G/Al2O3) composites by Spark Plasma Sintering; a simple, fast and upscalable method"

“Edge States in bilayer and trilayer graphene nanoribbons”

"Spontaneous Transfer of Wafer-scale Graphene by Capillary Bridges"

"First-principles analysis of MoS2/Ti2C and MoS2/Ti2CY2 (Y=F and OH) all-2D semiconductor/metal contacts"

poster title

Bor-Kae Chang, and Chih-Chen Chang

Kun-Ping Huang

Hsiang-En Chen, Ching-Yuan Su

Chi-Hsien Huang

Ute Schmidt, Thomas Dieing and Olaf Hollricher

Hailong Hu

Zhongfu Zhou, Jianshu Yu, Simon Cooil, Andrew Evans, Neville Greaves

Di Hu

Huan Feng

Shifeng Hou

Alf Mews

Michael Höltig

Alexander Zöpfl, Masoumeh Sisakthi, Christoph Strunk

Thomas Hirsch

Patrik Ahlberg, Shun Yu, Zhi-Bin Zhang, Nima Jokilaakso, Xindong Gao, Andreas Larsson, Amelie Eriksson Karlström, Shi-Li Zhang

Malkolm Hinnemo

Stephen A. Shevlin and Zheng Xiao Guo

Xiaoyu Han

A. Shakouri, H.K. Taylor, S. Haigh, A. Rooney, M. T. Cole, M.S. Ferreira, W.I. Milne, G.S. Duesberg

Toby Hallam

Ana Tomova, Dejan Dimitrovski, Perica Paunovic, Aleksandar Dimitrov

Anita Grozdanov

Jesper Goor Pedersen and Antti-Pekka Jauho

Søren Schou Gregersen

Micah Green

M. Pisarra, G. Falcone, P. Riccardi, A. Sindona

Mario Gravina

authors

Taiwan

Singapore

USA

Germany

Sweden

Ireland

Macedonia

Denmark)

USA

Italy

country

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Applications (gaz sensors, composites, nanoelectronic devices...)

Chemistry of Graphene

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Quantum transport

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

topic

"Directly Growing Graphene Film on Quartz by Low Pressure Microwave Plasma Torch Chemical Vapor Deposition"

"Large-Scale Graphene Oxide Sheet by Low Damage Plasma Treatment"

"Highest resolution confocal Raman-AFM-SNOM: advantages and new insights for the characterization of novel 2D materials"

“Towards Imaging Single Molecules on Graphene Substrate”

"Electroless Deposition of Silver Nanoparticles on Graphene Oxide surface and Its Applications for Hydrogen Peroxide Detection"

"Electrochemical deposition of different metals on few-layer graphene sheets for fuel cell applications"

"Comparison of Different Graphene Materials in Amperometric Sensors"

"Functionalization of Graphene towards Dual-Mode BioSensing"

"First-principles study of nitrogen-doped and defective graphene"

"Controlled folding of 2D materials: Grafin Printing"

"UV and ZETA Spectroscopic characterization of MWCNTs"

"Graphene on Antidot Lattice"

"Intermolecular Interactions in Colloidal Graphene Dispersions and Composites"

"The π plasmon of graphene on transition metals in timedependent density functional theory"

poster title

Aron W. Cummings, Ferney Chaves, Dinh Van Tuan, Jani Kotakoski, Stephan Roche

David Jiménez

Seung Yol Jeong, Doo Jae Park, Hyun Joon Jeong, Eun-Kyung Suh, Geon-Woon Lee, Young Hee Lee, Mun Seok Jeong

Hyun Jeong

Ho Young Kim, Hyun Jeong, Joong Tark Han, Seung Yol Jeong, Kang-Jun Baeg, Mun Seok Jeong, Geon-Woong Lee

Hee Jin Jeong

Anpan Han, Kim Daasbjerg

Bjarke Jensen

Paweł Potasz, Arkadiusz Wójs

Blazej Jaworowski

Andrew J. Pollard, Bonnie J. Tyler, Helena Stec, Steve J. Spencer, Ling Hao, Debdulal Roy, Alex G. Shard, Ian S. Gilmore

JT Janssen

J. Ostrowska, L. Lipinska, Z. Sieradzki, M. Puchalski, E. Skrzetuska, I. Krucinska, M. Rogala, I. Wlasny, Z. Klusek

Joanna Jagiello

Pierre Trinsoutrot, Anatoli Mitioglu, Véronique Conédéra, Matthieu Pierre, Bertrand Raquet, Michel Goiran, Hugues Vergnes, Brigitte Caussat, Walter Escoffier

Fabrice Iacovella

A.G. Shulga, P.J. Zomer, N. Tombros, D. Bartesaghi, S.Z. Bisri, M.A. Loi, L.J.A. Koster and B.J. van Wees

Everardus Huisman

Sun Liping, Ma Fangwei, Li Qiang, Huo Lihua

Zhao Hui

Amir Moradi Golsheikh

Nay MIng Huang

authors

Spain

Korea

Denmark

Poland

France

Netherlands

China

Malaysia

country

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

Magnetism and Spintronics

Chemistry of Graphene

Quantum transport

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

topic

"How does graphene polycrystallinity impact on the performance of graphene based transistors?"

"Enhanced light output power of GaN UV-LED by a simple passivation with graphene oxide"

"One-step transfer and integration of multifunctionality in CVD graphene by TiO2/graphene oxide hybrid layer"

“How to set up CVD for Graphene Synthesis”

"Magnetic properties of graphene nanoflakes with KaneMele spin-orbit coupling"

"Graphene Contamination Removal Using Argon Cluster Etching"

"Reduction of graphene oxide layers printed on different substrates"

"Transport properties of disordered CVD graphene in the strong localized regime"

"High Gain Hybrid Graphene-P3HT Phototransistors"

"Graphene oxide induced rapid synthesis of a-MnO2 nanorod and the electrochemical performance"

"One-pot sonochemical synthesis of reduced graphene oxide uniformly decorated with ultrafine silver nanoparticles"

poster title

Chang-Soo Han

Ju Tae Kim

Kyeong Won Lee, Jong Min Kim, Dong Hee Shin, Sung Kim, Suk-Ho Choi

Ju Hwan Kim

Hyo Jung Kim, Junichiro Kono, Pulickel M. Ajayan, Mun Seok Jeong

Ji-Hee Kim

Anastasia Tyurnina, Jean-Pierre Simonato, Jean Dijon, Denis Rouchon, Denis Mariolle, Nicolas Chevalier, and Olivier Renault

HoKwon Kim

Wonsuk Jung, Donghwan Kim, Joonkyu Park, Taeshik Yoon, Jongho Choi, Taek-Soo Kim, Soohyun Kim, Yong Hyup Kim, Chang-Soo Han

Donghwan Kim

Dukhyun Lee, Mijung Lee, Sangik Lee, Chansoo Yoon, Dayea Oh, Baeho Park

Cheol Kyeom Kim

D. Mele, M. M. Belhaj, I. Colambo, E. Pallecchi, D. Vignaud and H. Happy

Mohamed Salah Khenissa

A. Zugarramurdi, M. Debiossac, P. LuncaPopa, A. Mayne, A. Momeni, A.G. Borisov, P. Roncin

Hocine Khemliche

Nicolás Otero, Claude Pouchan

Panaghiotis Karamanis

Xavier Cartoixà

Ferran Jovell

Yann Tison, Yann Girard, Cyril Chacon, Vincent Repain, Patrick Le Fèvre, Antonio Tejeda, Amina Taleb, Sylvie Rousset, Sergey Babenkov, Victor Aristov, Olga Molodtsova, Ed Conrad, Robert Sporken, Luc Henrard, Jacques Ghijsen and Jérôme La

Frederic Joucken

authors

Korea

France

Korea

France

Spain

Belgium

country

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Other 2 dimensional materials

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Other 2 dimensional materials

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

topic

"Silver nanowire - Graphene oxide hybrid transparent conductive thin film for high mechanical stability and flexibility"

"Electrical and optical characterization of field-effect transistors containing graphene layers doped with HNO3, AuCl3, and RhCl3"

"Ultrafast Detection of Carrier Relaxation in Graphene Quantum dots"

"Photoemission Electron Microscopy Investigation of Iodine Doped Graphene"

"Superstrong encapsulated monolayer graphene and prevention of water permeation by strong adhesion between graphene and SiO2"

"Local Anodic Oxidation of Graphene Using Atomic Force Microscope and its Effect on Electrical Properties"

"Graphene Field Effect Transistors on SiC with T-Shaped Gate: Homogeneity and RF performance"

"Atomic and topographic corrugations of graphene on 6HSiC(0001) derived from Grazing Incidence Fast Atom Diffraction"

"White-graphene sections confined in Graphene nanoflakes. Toward a novel class of 2-D systems bearing extaordinary first order dipolar/octupolar non-linear optical responses"

"Band Gap Engineering in Graphene Nanomeshes"

"Nitrogen doped graphene studied by STM/STS and Photoemission Spectroscopy"

poster title

Johann Coraux, Maurizio De Santis, Simon Lamare, Laurence Magaud, Frédéric Chérioux

John Landers

D. Jiménez, and J.L. González

Gerhard Martin Landauer

J. Fernández-Rossier

Jose Lado

Shih-Hao Chan, Jia-Wei Chen, Sheng-Hui Chen

Chien-Cheng Kuo

M. Otyepka, R. Zboril

Kasibhatta Kumara Ramanatha Datta

Francesco Piana, Jürgen Pionteck

Beate Krause

Bulushev D., Chuvilin A., Bulusheva L.G., Okotrub A.V.

Victor Koroteev

Dominik Smith, Lorenz von Smekal

Michael Körner

Emil B. Pedersen, Kyoko Shimizy, Steen U. Pedersen, Kim Daasbjerg

Mikkel Kongsfelt

Cristina E. Giusca, Francesco Perrozzi, Luca Ottaviano, Emanuele Treossi, Vincenzo Palermo, Olga Kazakova

Stephanie Kitchen

Byung-Chul Moon, Min-Chae Jang

Yangsoo Kim

Dong Hee Shin, Sung Won Hwang, Suk-Ho Choi

Sung Kim

authors

France

Spain

Portugal

Taiwan

Czech Republic

Germany

Russia

Germany

Denmark

Korea

country

Other 2 dimensional materials

Applications (gaz sensors, composites, nanoelectronic devices...)

Magnetism and Spintronics

Growth, synthesis techniques and integration methods

Applications (gaz sensors, composites, nanoelectronic devices...)

Other 2 dimensional materials

Magnetism and Spintronics

Chemistry of Graphene

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

topic

“Convergent Fabrication of a Perforated Graphene Network with Air-Stability”

"Compact modeling of external parasitics of graphene field-effect transistors"

"Magnetic edge anisotropy in graphene-like honeycomb crystals"

"Derivation of approximately model for CVD graphene growth"

"Carbon Dot Modified Graphene Oxide with Tunable Fluorescence for Selective Cell Labeling"

"Effect of the chemical structure and processing conditions on the morphology and electrical conductivity TPU/EG composites"

"MoS2/carbon nanostructures based hybrid materials"

"Investigating topological phase transitions in graphene through Monte Carlo simulations"

Introducing the Versatile Carboxylate Handle on Graphene by Reductive Carboxylation"

"Electrostatic transparency of graphene oxide sheets"

"Formaldehyde Sensing Properties of Conducting PolymerFunctionalized Carbon Nanocomposites"

"Structural and optical properties of N-doped graphene quantum dots"

poster title

Hong Ngee Lim

Lin Zhou, Qin Xie, Xuefeng Guo, Zhongfan Liu

Lei Liao

Yoann Olivier, David Beljonne

Jian Xiang Lian

Alexander J. Marsden, Robert J. Young, Ian A. Kinloch, Neil R. Wilson

Zheling Li

Jing He

Yang Li

Andres R. Botello-Mendez, Jean-Christophe Charlier

Aurelien Lherbier

Seong Hun Yu, Yu Seong Gim, Euyheon Hwang and Jeong Ho Cho

Youngbin Lee

Ju Hwan Kim, Soo Seok Kang, Dong Hee Shin, Sung Kim, Suk-Ho Choi

Kyeong Won Lee

C.K. KiM, M.J. Lee, D.Y. Oh, S.I. Lee, C.S. Yoon and B. H. Park

Duk Hyun Lee

Mikoushkin V.M., Shnitov V.V., Lebedev S .P. , Likhachev E. V, Yakimova R ,Vilkov O. Yu

Alexander Lebedev

Nguyen Dang Luong, Jukka Seppälä

Hoang Sinh Le

Thomas Olsen, Kristian S. Thygesen

Simone Latini

authors

Malaysia

China

Belgium

China

Belgium

Korea

Russia

Finland

Denmark

country

Applications (gaz sensors, composites, nanoelectronic devices...)

Chemistry of Graphene

Spectroscopies and microscopies

Magnetism and Spintronic

Quantum transport

Applications (gaz sensors, composites, nanoelectronic devices...)

Other 2 dimensional materials

Quantum transport

Chemistry of Graphene

Other 2 dimensional materials

topic

"Graphene Reinforced With Polypyrrole Nanoparticles For Energy Storage Application"

"Periodic modification of graphene via strain-induced localized reaction"

“Electronic structure of graphene nanoribbons delimited by sp3 defect lines: A density functional theory study”

"Analyzing Monolayer Graphene Edge-on by Raman Spectroscopy"

"Theory of Vacancy-Induced Intrinsic Magnetic Impurity with Quasi-Localized Spin Moment in Graphene"

"Electronic and transport properties of unbalanced sublattice Nitrogen-doping in Graphene"

"Ultrahigh performance of dye molecule enhanced graphene photodetector"

"Effect of rapid thermal annealing in vacuum on the structural and optical properties of MoS2 flakes in solution"

"Loading direction dependence of graphene thickness measured using atomic force microscope"

"Bilayer graphene grown on 6H-SiC (0001) substrate by sublimation: Size confinement effect"

"Modification of graphene oxide for polyurethane composite by combination of isocyanate and diisocyanate"

"Modelling Excitons in Atomically Thin Semiconductors"

poster title

Jianfeng Liu, Kazunari Sasaki

Stephen Lyth

Peter Siemroth, Sigurd Schrader

Helge Lux

X. Wang, A. Wolff, J. Kitzmann, W. Mehr, M. Arens, and G. Lupina

Mindaugas Lukosius

Carlos Bueno-Alejo, Suzana M. Andrade, Roberta Viana Ferreira, Bruno Machado, Revathi Bacsa, Philippe Serp

St茅phane Louisia

Cristina G贸mez-Navarro, Vincenzo Parente, Francisco Guinea , Mikhail I. Katsnelson, Francesc P茅rez-Murano and Julio G贸mezHerrero

Guillermo Lopez-Polin

C. De Angelis, A.-D. Capobianco, S. Boscolo, M. Midrio

Andrea Locatelli

Yanfeng Zhang, Zhongfan Liu

Mengxi Liu

Jijun Zhao

Lizhao Liu

Po-Hsun Ho, Yun-Chieh Yeh, Chun-Wei Chen

Yi-Ting Liou

Jie Sun, and August Yurgens

Niclas Lindvall

Younal Ksari, Jai Prakash, Luca Giovanelli, Jean-Marc Themlin

Yu-Pu Lin

authors

Japan

Germany

France

Spain

Italy

China

Taiwan

Sweden

France

country

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

Nanoelectromechanical systems

Applications (gaz sensors, composites, nanoelectronic devices...)

Spectroscopies and microscopies

Chemistry of Graphene

Applications (gaz sensors, composites, nanoelectronic devices...)

Growth, synthesis techniques and integration methods

topic

"Electrochemistry on Defective Graphene Foam: Nonprecious Catalysis"

"Synthesis of Graphene on dielectric substrates using a modified filtered vacuum arc system"

"Seed-free Si growth on transferred graphene by ICP Chemical Vapor Deposition"

"Synthesis and characterization of gold nanoparticles/graphene hybrid materials"

"Mechanical properties of graphene with defects created by ion bombardment"

"Efficient modelling of graphene-based optical devices"

"Atom-resolved study of CVD graphene on Rh substrates and its intriguing properties by STM/STS"

"First-principles study of the structure and mechanical properties of graphene oxide"

"Self-encapsulated doped graphene/silicon Schottky junction solar cell with high efficiency and excellent stability"

"Non-catalytic chemical vapor deposition of nanocrystalline graphene on insulating and semi-conducting substrates"

"A versatile plasma-based method for the nitrogen doping of graphene"

poster title

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Self-Assembled Air-Stable Supramolecular Porous Networks on Graphene 1

Li Bing , Kazukuni Tahara , Jinne Adisoejoso , Willem Vanderlinden , Kunal S. Mali , Stefan De 3,4, 2 1 Gendt Yoshito Tobe , Steven De Feyter 1

Department of Chemistry, Division of Molecular Imaging and Photonics, KU Leuven-University of 2 Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium, Division of Frontier Materials Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, 3 Japan,3Department of Chemistry, Division of Molecular Design and Synthesis, KU Leuven-University of 4 Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium, IMEC, Kapeldreef 75,B-3001 Leuven, Belgium. tobe@chem.es.osaka-u.ac.jp steven.defeyter@chem.kuleuven.be Functionalization and modification of graphene at thenanometer scale is desirable for many applications. Supramolecular assembly offers an attractive approach in this regard, as many organic molecules form well-defined patterns on surfaces such as graphite via physisorption. Here we show that ordered porous supramolecular networks with different pore sizes can be readily fabricated on different graphene substrates via self-assembly of dehydrobenzo[12]annulene (DBA) derivatives at the interface between graphene and an organic liquid. Molecular resolution scanning tunneling microscopy (STM) and atomic force microscopy (AFM) investigations reveal that the extended honeycomb networks are highly flexible and that they follow the topological features of the graphene surfacewithout any discontinuity, irrespective of the step-edges present in the substrate underneath. We also demonstrate the stability of these networks under liquid aswell as ambient air conditions. The robust yet flexible DBA network adsorbed on graphene surface is a unique platform for further functionalization and modification of graphene. Identical network formation irrespective of the substrate supporting the graphene layer and the level of surface roughness illustrates the versatility of these building blocks.[1] References [1] B.Li, K. Tahara, J. Adisoejoso, W. Vanderlinden, K.S. Mali, S. De Gendt, Y. Tobe, S. De Feyter, ACS Nano, 7, (2013) 10764

Self Assembly of DBA-DA25 on E-G/SiC graphene under ambient conditions.

Analytical Study of Performances of Monolayer and Bilayer Graphene FETs Based on Physical Mechanisms J.D. Aguirre-Morales, C. Mukherjee, S. Fregonese, C. Maneux and T. Zimmer IMS Laboratory, UMR CNRS 5218, Cours de la Libération ± 33405 Talence Cedex, Bordeaux, France jorge.aguirre@ims-bordeaux.fr Abstract Following the recents works of K.S. Novoselov and A.K. Geim [1] in 2004, the semiconductor industry has been attracted to carbon-based technologies in order to maintain the trend on low-cost and still reducible transistor structures. From circuit point of view, monolayer and bilayer Graphene FETs (GFETs) are being studied for high performance applications. Although monolayer graphene presents an energy band structure where there is no bandgap, its high thermal and electrical conductivity makes it suitable for high-frequency applications. On the other hand, bilayer graphene presents a tunable bandgap by the application of an electric field perpendicular to the layer which allows the design of more flexible GFET structures. In this paper, we report the evidence of a tunable bandgap on bilayer graphene based on physical equations and the expected performances of these devices are compared with monolayer graphene FETs. The presented results are based on GFET structures with an HfO2 top gate dielectric (İr = 16) and a SiO2 back gate dielectric İr = 3.9) as in [4]. The gate length is fixed to 1 µm -2 and the width to 2.1 µm. Residual carrier density npuddle is considered to be 1.5e12 cm and the net -2 doping concentration to -5e12 cm . Access resistances RS and RD DUH VHW WR EH HTXDO WR 2 Electron and hole mobilities are set to 1500 cm /V s. For the simulations shown below, the effect of a tunable bandgap on a AB-stacking bilayer graphene (Figure 1) due to the applied electric field has been taken into account. Figure 2 shows the low energy bands for bilayer graphene for two different values of the applied potential energy. When the applied potential energy is zero (U = 0 eV) there is no bandgap (E gap = 0), on the other hand when the applied potential energy is non-zero (i.e. U = 1 eV), the presence of a non-zero energy band gap can be observed. Figure 3 shows the Energy band gap Egap under the average electrical displacement field generated by the applied bias voltages [2]. A variation on Egap within [0 to 250 meV] can be noted. For the purpose of a comparative study, the monolayer and bilayer GFETs are compared via numerical simulations. Based on [3] and [4], a model for monolayer GFET has been developed where access resistances, the effect of puddles on carrier density and doping concentration are taken into account. In the case of bilayer GFETs a model based on physical equations [5] has been developed. Figure 4 shows a comparison of the IDS-VGS plot for bilayer and monolayer GFETs under the same bias conditions VDS = [-1.5, -1.0, -0.5] V and a back-gate voltage VBG = -40 V. Higher currents on bilayer GFETs can be observed from Figure 4 and a higher transconductance gm reflecting a better current modulation in the channel by the gate voltage. Figure 5 shows the typical ID-VDS characteristic for both bilayer and monolayer GFETs under the same bias conditions Vgs = [0 to 3.0] V and VBG = -40 V. Higher currents and higher output conductance gds are observed in the case of bilayer GFETs. The effect of a backgate voltage VBG is shown in Figure 6 from which it can be observed that the current modulation stays constant for all VBG as the ambipolar point (VDirac) moves along de x-axis. Extraction of small-signal parameters from both the GFETs allows us to calculate the cut-off frequency fT as a function of gate length (Figure 7). Higher cut-off frequencies, fT, can be observed for bilayer graphene for all gate lengths. Scaling down gate lengths for both bilayer and monolayer GFETs show an increase in fT. Thus, from our study, we can infer some important conclusions about the possible future of GFETs as bilayer graphene offers higher cut-off frequencies and a tunable band gap over monolayer devices. Even if voltage gain (AV = gm/gds) is higher in bilayer graphene FETs, it is still to be improved for future high-performance applications. Acknowledgements This work (part of the GRADE project) was supported by the European Commission through the Seventh Framework Program for Research and Technological Development and by the French National 5HVHDUFK $JHQF\ $15 WKURXJK WKH 3 1 ³*5$&<´ SURMHFW References [1] K. S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, Firsov and A.A. Firsov, Science, 5696 (2004) pp. 666-669. [2] Y. Zhang, T. Tang, C. Girit, Z. Hao, M. Martin, A. Zetti, M. Crommie, Y. Shen and F. Wang, Nature, 459(2009), pp. 820-823. [3] S. Fregonese, M. Magallo, C. Maneux, H. Happy and T. Zimmer, IEEE Transactions on Nanotechnology, 4 (2013), pp. 539-546. [4] S.A. Thiele, J.A. Schaefer and F. Schwierz, Journal of Applied Physics, 9 ( 2010), p. 094505. [5] M. Cheli, G. Fiori, G. Iannaccone, IEEE Transactions on Electron Devices, 12 (2009), pp. 29792986.

Figures

Figure 1: AB ± stacking bilayer graphene

Figure 3: Bandgap variation under average electrical displacement fields

Figure 4: IDS(VGS) for monolayer (red) and bilayer (blue) GFETs for VDS = [-1.5, -1.0, -0.5] V, VBG = -40 V and RS = RD

Figure 6: IDS(VGS) for monolayer (red) and bilayer (blue) GFETs for VDS = -1.0 V, VBG = [0 to -60] V and RS = RD .

Figure 2: Low energy bands for bilayer graphene for two values of the applied potential energy

Figure 5: IDS(VDS) for monolayer (red) and bilayer (blue) GFETs for VGS = [-3 to 0],VBG = -40 V and RS = RD .

Figure 7: fT as a function of gate length (L) for monolayer (red) and bilayer (blue) GFETs for VDS = 1.0 V, VBG = -40 V, VGS = 0.5 V and RS = RD

Graphene/Galinstan Contacts for Reliable Liquid Interconnects Patrik Ahlberg, Seunghee Jeong, Zhigang Wu, Shi-Li Zhang and Zhi-Bin Zhang Uppsala University, P.O. Box 534, SE-751 21 Uppsala, Sweden patrik.ahlberg@angstrom.uu.se Abstract Shortly after its discovery graphene has been shown to possess extraordinary chemical stability and also the ability to work as a protective membrane for gases such as helium and hydrogen [1]. This has inspired us to investigate the inertness of graphenes towards galinstan as well as graphene as diffusion barrier to protect the ordinary metals used in interconnection from the attack of galinstan. The application concerns flexible and stretchable electronics where the galinstan is used as interconnects. Galinstan, a Ga-In-Sn alloy, is a relatively new material but has already found many applications. One example is that it can act as a non-toxic replacement for mercury. The alloy has a large liquid window of o o 6 temperature ranging from -19 C up to 1300 C. It has a high conductivity of 3.46x10 S/m at room teperature [2]. This makes galinstan ideal to be used in stretchable and bendable electronics. It unfortunately has the drawback of being highly reactive with some metals that are ordinarily used in interconnects. For instance, aluminum is fully reacted within days were as tungsten can survive up to a year [3][4]. Al and galinstan interdiffuse into each other. Redox reactions between Al and water occur when water is present at the galinstan surface, resulting in insulating aluminum oxides and hydroxides [4]. We show here that graphene can both act as diffusion barrier and survive in direct contact with the galinstan. In this work the graphene was synthesized in our home-made chemical vapour deposition (CVD) system. The graphene is produced according to the todayÂśV RUGLQDULO\ XVHG SURFHGXUH WKDW argon, hydrogen and methane flow over a copper foil in a furnace at 1000 Â°C under medium vacuum. When the foil has cooled and removed from the furnace it is subsequently spin coated with poly(methyl methacrylate) (PMMA). Two different techniques of transfer were employed. The first transfer process constitutes etching the copper with FeCl3, removing etchant residue from the PMMA/graphene stack in DI water and finally attaching the PMMA/graphene stack onto a substrate. It was however found that this transfer method carried a significant amount of chlorine with it, which etched the aluminum substrate. The second procedure starts from the first layer of any stacks of graphene. To the PMMA/graphene/Cu-foil a cut mask of a plastic foil was glued on and this stack was immersed in a NaOH solution. The graphene system was connected to a cathode and a platinum piece acted as anode, Hydrolysis was performed until the graphene is separated from the Cu foil [5]. The graphenepolymer structure was cleaned in DI water. At this point in both processes the samples were heated, followed by acetone wash to get clean graphene. The galinstan from Geratherm Medical was used as received. All aluminum films were deposited by means of sputtering on microscope slide glass. After applying a drop of galinstan on Al, it shows quickly that the galinstan attacks the underlying Al (see figure 1a and b). The Al below the droplet was quickly dissolved and a black layer formed on the surface and around the edge of the droplet. The black layer was later confirmed to be aluminum oxide by energy-dispersive X-ray spectroscopy (EDS) and Raman spectroscopy (not shown here) [3]. Initial testing showed that a graphene film of three layers and beyond is required to act as a barrier for the drop casted galinstan (see figure 1c). To electrically evaluate the effect of graphene as a diffusionbarrier, three samples were prepared. Two of them are covered 1 and 4 layers of graphene, respectively, in the middle region from side to side. A channel of galinstan was air brushed within the graphene area (see figure 2a). A sample without graphene is used as reference. The resistance of the samples were monitored as a function of time using the measurememt configuration as shown in Fig 2a. It is found that for the spray-coated galinstan, the tiny galinstan droplets of high momentum impact the weak spots of the graphene layer which leads to the patchways for galinstan to reach the underlying Al. This can be evidenced by the reaction spots of galinstan/Al visualized from the rear side after 0.5 hour (see figure 2b). After around 2 hours, the reaction spots evolves to a line (figure 2c). The untouched graphene however blocks the supply of moisture and thus prevents the Al from the gallium facilitated oxidation. This results shows that graphene works as efficient diffusion barrier towards galinstan and holds promising application in liquid interconnects in stretchable electronics.

References [1] J. Scott Bunch , Scott S. Verbridge , Jonathan S. Alden , Arend M. van der Zande , Jeevak M. Parpia , Harold G. Craighead and Paul L. McEuen, Nano Lett., 2008, 8 (8), pp 2458±2462 [2] N.B. Morley, J. Burris, L.C. Cadwallader and M.D. Nornberg, Rev. of Sci. Instr. 79, 056107, (2008) [3] J. Ziebarth, J. Woodall, R. Kramer and G Choi, , Int. J. Hydrogen Energy, 36, 5271, (2011) [4] S. H. Mannan and M. P. Clode, IEEE Transaction on advanced packaging, 27, 508-514, (2004) [5] César J. Lockhart de la Rosa, Jie Sun , Niclas Lindvall, Matthew T. Cole, Youngwoo Nam, Markus Löffler, Eva Olsson, Kenneth B. K. Teo and August Yurgens, Appl. Phys. Lett. 102, 022101 (2013) Figures

Figure 1: a) Galinstan on Al after it has reacted and precipitated aluminum oxide on the surface. b) Picture a seen from beneath the sample c) Galinstan on four layers of graphene 6 month after deposition. d) Raman curves of the graphene, lowest single layer graphene on SiO2, middle 3 layer graphene on Al, top 3 layer graphene that has been under galinstan for several months.

Figure 2: Spraycoated sample seen from beneath while the resistivity is being measured. a) Sketch of set up. b) 4 layer sample seen from beneath 30min after deposition. c) same sample as in b 2 hours after deposition. d) Resistivity over time of unprotected sample e) 4 layer graphene protected sample.

Calculation of electronic properties of graphene grown on faceted SiC surface as on optimal matrix for the graphene synthesis N.I.Alekseyev, V.V.Luchinin St.-Petersburg ElectroTechnical University LETI, Center for MicroTechnology and Diagnostics, 197376, ul.Prof.Popova,5, St.Petersburg, Russia NIAlekseyev@yandex.ru Abstract It is known that one of the challenges of the digital graphene-based electronics is a difficulty of creating the bandgap ÇťEg in the graphene. Almost none of the ways to generate ÇťEg (graphene nanoribbons NR, stretched graphene, chemical fictionalization, partial reduction of the graphene oxide GO) cannot be considered as satisfactory for the industrial production of graphene. The arising difficulties are connected here with obtaining a predictable quantity of ÇťEg and, at the same time, with high and predictable quantity of the carrier mobility within a particular technology. Having an experience in the research of SiC, the authors offer for SiC-Graphene based GHYLFHV WKH FRQFHSW RI WKH JUDSKHQH JURZWK RQ DFFRUGLQJO\ SUHSDUHG V\VWHP RI 6L& IDFHV ÂłIDFHWHG 6L& VXUIDFHÂ´ FDOFXODWHG E\ VRPH DOJRULWKP 7KLV DOJRULWKP RIIHUV D VWUXFWXUH RI 6L& FRPSOLFDWHG surface, optimized with using the quantum chemistry methods, analytic methods and non-equilibrium thermodynamics apparatus.. $ FRQYHQLHQW DSSDUDWXV IRU DQDO\WLFDO DSSURDFK WR WKH SUREOHP LV WKH *UHHQÂśV IXQFWLRQV PHWKRG LQ QRGDO UHSUHVHQWDWLRQ XQGHU ZKLFK WKH *UHHQÂśV IXQFWLRQs matrix elements are looked for in 1 9DQQLHÂśV IXQFWLRQ EUDFNHWV . In this formalism the known linear dispersion law for the infinitive graphene turns to trivial 2 exercise for the Microelectronics Chair sudents . The method was mastered by us, then, on several testing calculations: dispersion laws and DOS calculations for the graphene nanoribbons of different width and chirality, and for various 0 0 graphene superstructures ((ÂĽ [ÂĽ 5 ÂĽ [ÂĽ 5 etc.). , SODQ WR WHOO DERXW WKH UHVXOWV RI WKH *UHHQÂśV IXQFWLRQ DSSOLFDWLRQ WR WKH HOHFWURQ SURSHUWLHV calculation for some faceted SiC surfaces. Within the analytical approach the bandwidth ÇťEgÂ? LV LQGXFHG E\ WKUHH IDFWRUV (Fig.1): by the substrate, by the graphene surface curvature on the faceting-generated SiC protrusions (i.e., the features of the surface), by the superstructure, generated by the system of protrusions.. So, in the zero approximation the ÇťEg is giveb by one dimension quantity (e.g., the protrusion height) and by aspect ratio. In more realistic calculation (density function theory DFT approach) the faceting details and the indexes of the arisen crystallographic planes is taken into account. In my report I will show the results of the electronic properties calculation for the graphene, built on such faceted surface. The principal result is that ÇťEg, determined by the second and by the third factors, can reach 0.5 Âą 0.7 eV even without immediate contribution of the surface to be substantial for using the graphene on such faceted SiC surface in digital electronics devices. We succeeded to show, then, that the graphene islands nucleation over the SiC surface SURWUXVLRQV OHDGV WR DQ DGGLWLRQDO IUHHGRP LQ DOLJQLQJ WKH LVODQGÂśV HGJHV DQG WKHLU PXWXDO RULHQWDWLRQ DW WKH PRPHQW RI WKHLU VWDFNLQJ +HUHZLWK WKH LQVWDELOLWLHV WKDW JHQHUDWH ÂłWHUUDFH ÂąVWULSÂ´ structures of the resulting graphene, are compensate. So, an opportunity arises to synthesize practically ideal graphene with minimal reduction in mobility as compared with the ideally smooth graphene. The detailed analysis of all such opportunities is a subject of our further research.

Graphene

Fig.1. Faceted surface of 2H ± SiC and the graphene grown on this surface The planes 1 and 2 are {1127} and {1122}. References 1..J.M.Ziman. Principles of the theory of solids. Cambridge University Press. 1972. 471 P. 2. S.Y.Davidov. On the charge transfer in the system of adsorbed molecules±graphene monolayer± SiC-substrate. Technical Physics (Russ.). 2011. Vol.45, Iss.5

Graphene based Electrodes for PEM Fuel Cells 6HOPL\H $ *Â UVHO , Burcu S. Okan /DOH , ĂšDQOĂ&#x2022; , Vildan Bayram %HJÂ P <DUDU 1,2

6DEDQFĂ&#x2022; 8QLYHUVLW\, Nanotechnology Research and Application Center (SUNUM), Istanbul, Turkey 2 6DEDQFĂ&#x2022; 8QLYHUVLW\ )DFXOW\ RI (QJLQHHULQJ DQG 1DWXUDO 6FLHQFHV ,VWDQEXO 7XUNH\

selmiye@sabanciuniv.edu

Abstract A polymer electrolyte membrane (PEM) fuel cell is an electrochemical device in which hydrogen is oxidized at the anode electrode and oxygen is reduced at the cathode electrode [1]. Membrane electrode assembly (MEA), consisting of a proton exchange membrane, catalyst layers, and gas diffusion layers (GDL), is regarded as the heart of the PEM fuel cell). Typically, these components are fabricated individually and then pressed together at high temperatures and pressures. The first generation of PEM fuel cell used platinum (Pt) supported on carbon black as the catalyst layer that exhibited excellent long-term performance at a prohibitively high cost [2]. These conventional 2 catalyst layers generally featured expensive platinum loadings of 4 mg/cm , the loading is improved up 2 to 0.04 mg/cm [3]. However, the cost of catalyst layer still is the major barrier to the commercialization of PEM fuel cells [4]. Thus in our study we have aimed to manufacture low platinum loaded catalyst layers. In our study, graphene nanosheets (GNS) were separated from graphite by an improved, safer and mild method including the steps of oxidation, thermal expansion, ultrasonic treatment and chemical reduction (Figure 1) [5, 6]. In the one way direction of the study, Pt was impregnated onto GNS or graphene oxide (GO) by in-situ nucleation to provide dispersed and uniform catalyst structure (Figure 2). In addition, Pt deposited samples were exposed to thermal shock to improve the crystallinity. The effect of annealing time, annealing temperature and catalyst loading was investigated on the growth of Pt nanoparticles. The structural changes and the surface morphologies of the samples were examined by Raman Spectroscopy, X-ray Diffraction (XRD), Thermogravimetric Analysis, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques. Since electrospinning is an established technique for generating nanofibers [7] and very promising to fabricate new catalyst layers with high activity, high poisoning resistance and good durability in PEM fuel cells [8], it can increase Pt utilization through an enhancement of the three-phase boundary. Therefore, we expected that electrospun Pt/graphene plays an important role as catalyst support by mitigating CO poisoning risks and reducing cost. In order to do that, as a second direction in the study, Poly(vinyl pyrrolidone) (PVP) was used as a carrier binder and solution of PVP/Pt/GN was electrospun onto carbon paper. Moreover, PVP and synthesized Pt/GN and Pt/GO nanoparticles were also imposed onto carbon paper and a gas diffusion electrode was formed. The physical tests of resultant gas diffusion electrodes were accomplished by SEM, TEM and electrical conductivity measurements according to four-point probe technique. Moreover, to be able to compare with commercial electrode performances, MEAs were prepared from resultant electrodes in our study. Performances of the MEAs are still under investigation in fuel cell system. References [1] M.S. Wilson, J.A. Valerio, S. Gottesfeld, Electrochim. Acta 40 (1995) 355Âą363. [2] G.S. Kumar, M. Raja, S. Parthasarathy, Electrochim. Acta 40 (1995) 285Âą290. [3] D. Fofana, S. K. Natarajan, J. Hamelin, P. Benard, Energy 64 (2014), 398-403. [4] www1.eere.energy.gov/hydrogenandfuelcells/pdfs/fy14_budget_request_rollout.pdf [5] B. 6DQHU ) 2N\D\ < <Â UÂ P )XHO 89 (2010) 1903-10. [6] % 6DQHU ) 'LQF < <Â UÂ P Fuel 90 (2011) 2609-16. [7] D.H. Reneker, I. Chun, Nanotechnology 7 (1996) 216Âą223. [8] H.J. Kim, Y.S. Kim, M.H. Seo, S.M. Choi, W.B. Kim, Electrochem. Commun. 11 (2009) 446Âą449. 1

Figure1: SEM image of graphene nanosheets

Intensity

126

0 PtGO

Intensity

138

Pt (111)

Pt (200)

0 10

Figure 2: XRD spectrum of synthesized Pt/GO nanoparticles

Wear behavior of electroconductive graphene/alumina composite 1

B. Alonso , C.F. Gutierrez-Gonzalez , A. Smirnov , A. Centeno , A. FernĂĄndez , V.G. Rocha , R. 2 1 3 Torrecillas , A. Zurutuza and J.F. Bartolome 1

Graphenea S.A. Tolosa Hiribidea 76 E-20018 Donostia-San SebastiĂĄn, Spain. Centro de InvestigaciĂłn en Nanomateriales y NanotecnologĂa (CINN). Principado de Asturias Consejo Superior de Investigaciones CientĂficas (CSIC) - Universidad de Oviedo (UO). Parque TecnolĂłgico de Asturias, 33428 Llanera, (Asturias), Spain. 3 Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones CientĂficas (CSIC), C/ Sor Juana InĂŠs de la Cruz, 3, 28049 Madrid, Spain. 4 Centre for Advanced Structural Ceramics, Department of Materials, Imperial College London, London SW7 2AZ, United Kingdom b.alonso@graphenea.com 2

Abstract In the last few years, graphene has emerged as a promising reinforcement material to improve wear resistance in composite materials. Although there are many research articles in the graphene/polymer composite field, there are only a few examples in the literature where the tribological properties of graphene/ceramic composites have been analysed (1,2). The present work has studied, for the first time, to the best of our knowledge, the dry sliding behaviour of an alumina/graphene composite (3) against alumina in air. Under the adopted testing conditions, the reduction in the wear rate of almost twice the alumina value was observed once the graphene platelets were added to the monolithic material. Additionally, it was appreciated a reduction of the friction coefficient of about 10% that was attributed to the presence of the graphene platelets and the role that they play in the tribological system. These adhered platelets act as a self-lubricating layer when fixed to the contact surface between the composite and the alumina ball, during the experiment, that acts as counterpart material References [1] Belmonte M, RamĂrez C, GonzĂĄlez-JuliĂĄn J, Schneider J, Miranzo P, Osendi MI. Carbon 2013;61:431-435. > @ +YL]GRĂŁ 3 'XV]D - %DOi]VL & 7ULERORJLFDO SURSHUWLHV RI 6L 1 -graphene nanocomposites J. Eur. Ceram. Soc. 2013;33:2359-2364. [3] Centeno A, Rocha VG, Alonso B, FernĂĄndez A, Gutierrez-Gonzalez CF, Torrecillas R, et al. J. Eur. Ceram. Soc. 2013;33:3201-3210.

Electrochemical characterization of graphene oxides using screen-printed electrodes

C. Botas, P. Alvarez, R. Santamaria, R. Menendez, D. Martin-Yerga, A. Costa-Garcia 1

Instituto Nacional del Carb贸n INCAR-CSIC, P.O. Box 73, 33080, Oviedo, Spain Department of Physical and Analytical Chemistry, Faculty of Chemistry, University of Oviedo, 33006 Oviedo, Spain

Costa@uniovi.es The development of novel nanomaterials such as graphene has opened a new field of study in the field of electrochemical sensing[1]. These materials provide very interesting properties when used as transducers of electrochemical sensors such as a large surface area, a high electron transfer ability or a high potential window, among others beneficial properties. However, both the structural and electrochemical characterization of these nanomaterials is crucial since the results obtained in applications of electrochemical sensing rely heavily on the synthesis and the functional groups of these materials[2]. Therefore, the characterization should be as complete as possible to find the best conditions and the most suitable graphene for different electrochemical sensing applications. In this work, the electrochemical characterization of screen-printed electrodes modified with several graphene oxides (GO-SPEs) and electrochemical reduced graphene oxides (ERGO-SPEs) was carried out. A study was performed to check the suitability of these graphene materials for electrochemical sensing. The methodology for the fabrication of the GO-SPEs and ERGO-SPEs was: a drop of graphene oxide (in ethanol/water) was deposited onto the working electrode of the SPE and left to dry until complete evaporation. Electrochemical reduction of the deposited GO film was optimized using different currents and reduction times to generate electrochemically reduced graphene oxide (ERGO). The electrochemical behavior and electrochemical characteristics of the ERGO-SPEs were studied using cyclic voltammetry for a model analyte (dopamine in H2SO4 0.1 M). As shown in Figure 1, the electrochemical reduction of GO, improved the different analytical parameters such as the peak intensity (ip) and the separation between the peak potentials. This improvement of the electrochemical redox behavior allows the dopamine system become a reversible situation starting from an irreversible situation when unmodified SPEs or modified with GO were used. Furthermore, it was found that the electrochemical process is controlled by diffusion of dopamine on the ERGO since the peak current follow a linear trend with the square root of the scan rate. A study by X-ray photoelectron spectroscopy (XPS) was performed to verify the functional groups that were reduced in the formation of the better ERGO film (Figure 2). This study showed that this ERGO had a greater amount of Csp2 and Csp3 with a significant reduction of the C-O-C groups, in relation to the initial GO. This study shows how some graphenes are most suitable than others to detect a target analyte and how the best conditions must be found to get outstanding results in electrochemical sensing.

References [1] M. Pumera, A. Ambrosi, A. Bonanni, E.L.K. Chng, H.L. Poh, Graphene for electrochemical sensing and biosensing, TrAC Trends Anal. Chem. 29 (2010) 954卤965.

[2] A. MartĂn, A. Escarpa, Graphene: the cutting-edge interaction between chemistry and electrochemistry, TrAC Trends Anal. Chem. (2014), in press.

Figures Figure 1: Cyclic voltammetry of a solution containing 0.1 mM dopamine in H2SO4 using a) unmodified SPE, b) GO-SPE, c) ERGO-SPE.

Figure 2: XPS spectra of A) GO and B) ERGO materials.

Preparation of coke-based graphenes and their application in batteries and catalysis a

Uriel Sierra, Zoraida GonzĂĄlez, Patricia Ă lvarez, MatĂas Blanco, Clara Blanco, M. Victoria b b b b a JimĂŠnez, Javier FernĂĄndez-Tornos, JesĂşs J. PĂŠrez-Torrente, Luis A. Oro and Rosa MenĂŠndez,* Instituto Nacional del CarbĂłn INCAR-CSIC, P.O. Box 73, 33080, Oviedo, Spain. Departamento de QuĂmica InorgĂĄnica, Instituto de SĂntesis QuĂmica y CatĂĄlisis HomogĂŠnea-ISQCH, Universidad de Zaragoza-C.S.I.C., 50009-Zaragoza, Spain

rosmenen@incar.csic.es Graphene materials have recently attracted increasing interest due to the excellent physico-chemical properties that they can exhibit.[1] One interesting application is as electrodes in vanadium redox flow batteries (VRFBs). These are promising large-scale energy storage devices in which the electrodes must be carefully selected since they support the chemical reactions necessary for the operation of the battery. In this regard, graphenes obtained by thermal treatment of graphite oxide exhibited an excellent performance due to their high electrical conductivity and a high mechanical stability.[2] The use of graphene at industrial scale in conventional applications is however conditioned by the amounts required and the associated cost.[3] We have recently reported the possibility to replace the graphite by coke as precursor in the preparation of graphene oxides by chemical methods. Furthermore, the characteristics of the materials obtained from coke and from graphite were comparable. The advantages of the procedure proposed lie mainly in the possibility to use a product (coke) which is largely available and cheaper than synthetic graphite, which requires temperatures above 2000 Âş C for its preparation. Following with these investigations, the main objectives of this work are to obtain thermally reduced graphenes from cokes and to demonstrate that their performance in VRFB devices is equivalent to that obtained for graphenes. In the present study, a commercial carbochemical coke (C), graphitizable, with a well-developed microtexture of large anisotropic domains is used as the raw material for graphene oxide and graphene preparation. For comparative purposes, graphene-like materials were also prepared from (i) the graphite obtained after treating the same coke C at 2000Â°C (CG) and (ii) from a commercial graphite (SG, ALDRICH). Coke oxide and graphene oxides are prepared by a modified Hummers method. Graphenes were then produced by thermal exfoliation/reduction of the coke oxide and the graphite oxides at 1000ÂşC in a single step, yielding TRG-C, TRG-CG and TRG-SG from coke C and graphites CG and SG, respectively. It is worth mentioning that, in the case of the samples from coke, a slightly larger amount of KMnO4 was required during the oxidation step, to facilitate the subsequent thermal exfoliation. TEM studies of the TRGs evidenced the presence of monolayers in all cases (Figure 1), with the typical wrinkled structure currently observed for this kind of graphenes. The reconstruction of the Csp2 structure after the thermal treatment was observed in all cases, the DWRPLF & 2 UDWLR LQFUHDVLQJ IURP Â§ LQ WKH *2V XS WR Â§ LQ WKH 75*V DV GHWHUPLQHG E\ ;36 7KH Csp2 content raises in the three cases to values above 77 % (Figure 2), well in the range of the values obtained for this type of materials in the literature. All these results also confirm the similarities among samples independently of their origin (cokes or graphites) and confirm that cokes can be excellent candidates to prepare graphenes with standard characteristics and avoiding the use of high temperatures. In order to confirm the suitability of graphenes from cokes as other standard graphenes, TRG-C was therefore used as active electrode material in the positive half-cell of a VRFB. This material exhibits a similar performance to those graphenes obtained from graphites. Thus, the CVs recorded on the CRBTR1000 electrode display similar electrochemical activity and kinetic reversibility towards the vanadium redox reactions.

The catalytic activity of these coke-based graphenes was also tested in catalysis. For that we developed a covalent bonding of organometallic complexes (Iridium N-heterocyclic carbenes (NHC)) to the graphenes through their OH-groups. Our proposed strategy proceeds, in a first step, with the functionalization of the GO via the formation of carbonate groups, from the surface hydroxylic groups with p-nitrophenylchloroformate. Those p-nitro groups can be easily displaced in a second step by another nucleophilic center such as the OH-ending of the imidazolium salt (1) producing p-nitrophenol. To the best of our knowledge, this strategy has not been employed before with carbonaceous supports, and proceeds with similar reactivity and selectivity in the case of using graphenes form cokes or from graphites. The catalytic activity of the supported catalyst was tested in hydrogen transfer reactions. References [1] Haddadi-Asl V, Kazacos M, Skyllas-Kazacos M.. J Appl Polymer Sci 25 (1995) 29Âą33. [2] Park S, Ruoff RS. Chemical methods for the production of graphenes. Nature Nanotechnol. 2009, 4, 217Âą24. [3] Patent P201330348. Figures:

Figure 1: TEM images of TRGs from a) coke (TRG-C), b) carbochemical graphite TRG-CG and c) commercial graphite (TRG-SG).

Figure 2: XPS C1s spectra and deconvoluted curves of TRGs from a) coke (TRG-C), b) carbochemical graphite (TRG-CG) and c) commercial graphite (TRG-SG).

From Nanoscale Chemical Identification to Real-Space Mapping of Graphene Plasmons Sergiu Amarie Neaspec GmbH, Bunsenstr. 5, Martinsried(Munich), Germany sergiu.amarie@neaspec.com The performance of the next-generation electronic devices based on Graphene is strongly influenced by the structure-function relationship. A novel technique which combines the best of two worlds, the high spatial resolution of Atomic Force Microscopy (AFM) and the analytical power of infrared spectroscopy makes now possible the nanoscale mapping of such nano-devices. The spatial resolution of about 10nm of our unique NeaSNOM microscope opens a new era for modern nano-analytical applications such as chemical identification, free-carrier profiling and plasmonic vector near-field mapping. Recent research highlights including contact-free direct access to local conductivity, electron mobility and intrinsic doping via plasmon interferometry imaging demonstrated the power of the NeaSNOM microscope [1-4]. 7KH ([SHULPHQW LQYROYHV ODXQFKLQJ SODVPRQV IURP WKH 1HD6120ÂśV WLS KDYLQJ WKHP propagate, reflect from the graphene edge, and influence the backscattering amplitude. Two unique properties of the NeaSNOM microscope were instrumental for this success: (i) the high spatial resolution of <20nm allowed to easily resolve the plasmon standing waves which have periods as small as 100 nm, and (ii) more subtle, the highly confined light at the tip helps to efficiently launch the plasmons, giving theP WKH PRPHQWXP ÂłNLFNÂ´ QHHGHG -times that of plasmons. Using plasmon interferometry, NeaSNOM microscope can investigate losses in graphene by exploring real-space profiles of plasmon standing waves formed between the tip of our nano-probe and the edges of the samples (Fig1.). Plasmon dissipation quantified through this analysis is linked to the exotic electrodynamics of graphene. New technical developments of the NeaSNOM microscope enables now real-space graphene mapping of big area scans at high-resolution and industrial speeds (Fig2). An outlook of further several application potential of nanoscale chemical mapping by local infrared spectroscopy will be presented elsewhere: x Quantitative measurement of local infrared absorption and dielectric function; x Semiconductor free carrier distribution [6]; x Graphene used as H2 storage

x x x

Nanoscale phase transition [5]; Free carrier dynamics (ultrafast plasmonics); Bio-medical nano-imaging [7,8];

References [1] Z. Fei, A. S. Rodin, W. Gannett, S. Dai, W. Regan, M. Wagner, M. K. Liu, A. S. McLeod, G. Dominguez, M. Thiemens, Antonio H. Castro Neto, F. Keilmann, A. Zettl, R. Hillenbrand, M. M. Fogler and D. N. Basov, Nature Nanotechnology 8 (2013) 821. [2] J. Chen, M. L. Nesterov, A. Y. Nikitin,S. Thongrattanasiri, P. AlRQVR-*RQ]iOH] 7 0 6OLSFKHQNR ) Speck, M. Ostler, T. Seyller, I. Crassee, F. H. L. Koppens, L. Martin-Moreno, F. J. GarcĂa de Abaj, A. B. Kuzmenko and R. Hillenbrand Nano Letters 13 (2013) 6210. [3] Z. Fei, A. S. Rodin, G. O. Andreev, W. Bao, A. S. McLeod et al. Nature 487 (2012) [4] J. Chen, M. Badioli, P. Alonso-GonzĂĄlez, S. Thongrattanasiri, F. Huth, R. Hillenbrand & F. H. L. Koppens Nature 487 (2012) 82. [5] M. M. Qazilbash, M. Brehm, Byung-Gyu Chae, P.-C. Ho, G. O. Andreev, Bong-Jun Kim, Sun Jin Yun, A. V. Balatsky, M. B. Maple, F. Keilmann, Hyun-Tak Kim and D. N. Basov Science 318 (2007) 1750. [6] M. K. Liu, M. Wagner, E. Abreu, S. Kittiwatanakul, A. McLeod, Z. Fei, M. Goldflam, S. Dai, M. M. Fogler, J. Lu, S. A. Wolf, R. D. Averitt, and D. N. Basov Physical Review Letters 111 (2013) 096602. [7] I. Amenabar, S. Poly, W. Nuansing, E.H. Hubrich, A.A. Govyadinov, F. Huth, R. Krutokhvostov, L. Zhang, M. Knez, J. Heberle, A.M. Bittner and R. Hillenbrand, Nature Communications, 4 (2013) 2890. [8] S Amarie, P Zaslansky, Y Kajihara, E Griesshaber, WW Schmahl and F Keilmann, Beilstein Journal of Nanotechnology 3 (2012) 312.

Figures

NeaSNOM correlative AFM-IR microscopy. Contact-free direct access to local conductivity, electron mobility and intrinsic doping via plasmon interferometry imaging. Fig1.

Fig2. Epitaxial grown grapheme. NeaSNOM measurements with 10nm resolution of near-field phase (left) and near-field amplitude components (right).

Growth and Characterization of Graphene-like 2D Nanolattices of Silicene and AlN 1

A. Dimoulas , E.

Xenogiannopoulou1, P. Tsipas1, D. Tsoutsou1, S. Kassavetis1, E. Golias1,

S.A. Giamini1, C. Grazianetti2,3, D. Chiappe2, A. Molle2, M. Fanciulli2,3 1DWLRQDO &HQWHU IRU 6FLHQWLILF5HVHDUFK Âł'HPRNULWRVÂ´ $WKHQV *UHHFH 2 Laboratorio MDM, IMM-CNR, I-20864, Agrate Brianza (MB), Italy 3 Dipartimento di Scienza dei MaterLDOL 8QLYHUVLWj GHJOL 6WXGL GL 0LODQR %LFRFFD ,-20126, Milano, Italy Contact@E-mail: dimoulas@ims.demokritos.gr 1

Abstract (Arial 10) The outstanding properties of graphene have opened the way to search for other two-dimensional (2D) sp2 hybridized materials. 7KH JUDSKHQHÂśV ÂłFRXVLQVÂ´ VLOLFHQH DQG JHUPDQHQH WKH ' VHPLFRQGXFWRU 0R6 DQG WKH LQVXODWLQJ KH[DJRQDO %1 DUH FRQVLGHUHG WR EH WKH PDLQ ÂłLQJUHGLHQWVÂ´ FRPSOHPHQWLQJ semi-metallic graphene in new electronic devices. The main idea is that 2D graphite-like materials could couple weakly between each other through Van der Waals forces maintaining the integrity of each layer and preserving their good physical properties near ideal, normally obtained in their free standing form. Silicene, has recently attracted intense attention, mainly due its compatibility with current Si-based nanoelectronic devices. As free-standing silicene does not exist in nature, there is an increasing effort to realize it on suitable substrates. Remarkably, silicon wets the Ag(111) surface forming a 2D honeycomb network topology with a variety of superstructures and buckling configuration [1]. In the present work the electronic band structure of monolayer (4x4) silicene on Ag(111) (Fig. 1) is imaged by angle resolved photoelectron spectroscopy [2]. A dominant hybrid surface metallic band is observed to be located near the bulk Ag sp-band which is also faintly visible. The two-dimensional character of the hybrid band has been distinguished against the bulk character of the Ag(111) sp-band by means of photon energy dependence experiments (Fig. 2). The surface band exhibits a steep linear dispersion around the KAg point and has a saddle point near the MAg point of Ag(111) resembling the pband dispersion in graphene (Fig. 3). To integrate silicene on suitable electronic devices, there is a need to be developed on dielectric substrates. It is predicted that silicene is stable when encapsulated between two thin graphite-like hexagonal AlN layers [3]. The possibility to grow stable silicene on insulating substrates such as hexagonal AlN could be a major technological breakthrough. Ultrathin (sub-monolayer to 12 monolayers) AlN nanosheets are grown epitaxially by plasma assisted molecular beam epitaxy on Ag(111) single crystals [4]. Electron diffraction (Fig. 4) and scanning tunneling microscopy (Fig. 5) provide evidence that AlN on Ag adopts a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN. This claim is further supported by ultraviolet photoelectron spectroscopy (Fig. 6) indicating a reduced energy bandgap as expected for hexagonal AlN. This work was supported by the 2D-NANOLATTICES (Grant No. 270749) of the Future and Emerging Technologies (FET) program of the European Commission 7th Framework Program. References [1] M. Xu, T. Liang, M. Shi, and H. Cheng, Chemical Reviews 113 (2013) 3766. [2] D. Tsoutsou, E. Xenogiannopoulou, E. Golias, P. Tsipas, and A. Dimoulas, Appl. Phys. Lett. 103 (2013) 231604. > @ 0 +RXVVD * 3RXUWRLV 9 9 $IDQDVÂśHY DQG $ 6WHVPDQV $SSO 3K\V /HWW 97 (2010) 112106. [4] P. Tsipas, S. Kassavetis, D. Tsoutsou, E. Xenogiannopoulou, E. Golias, S. A. Giamini, C. Grazianetti, D.Chiappe, A. Molle, M. Fanciulli, and A. Dimoulas, Appl. Phys. Lett. 103 (2013) 251605.

Figures

Figure 1: (a) RHEED diffraction patterns of the clean and Ag(111)/Si (1ML) and Ag(111)/Si (3ML) samples obtained

along the 1 1 2 and

>1 10@

azimuth of

Ag(111) surface. Blue and red arrows indicate the diffraction streaks of Ag(111) and Ag(111)/Si superstructure, respectively.

Figure 2: Energy vs. k//x dispersion for k//y=0 for the Ag(111)/Si (1ML) structure acquired by ARPES along the īȀAg with different excitation energies hv: (a) HeI 21.22eV, (b) NeI 16.67eV and (c) ArI 11.62eV. The dispersing bulk Ag sp-band is indicated by blue line, while the invariant surface band SB is marked by red line. Figure 4: (a) RHEED patterns of bare Ag(111) and AlN/Ag(111) structures along [1-10] azimuth of silver. The overall streaky pattern shows that AlN grows epitaxially on the Ag(111) substrates. (b) RHEED and (c) intensity patterns of 4 ML-thickAlN/Ag(111) and wurtzite 200nmAlN/Si(111) structures along [11-2] azimuth of silver. For illustration purposes, in fig. 4(b) and (c) we have shifted the pictures in order for the first order left streaks to be aligned. A slightly larger lattice constant is determined for the ultrathin layer which is characteristic of its graphitic structure.

Figure 3: (a) and (b) Energy vs. k//x dispersion for k//y=0, recorded along the ī0Ag direction of the Ag(111) SBZ for the clean Ag(111) and Ag(111)/Si (1ML) samples, respectively; (c) constant energy contours kx-ky (EB=-0.45eV) for the Ag(111)/Si (1ML) sample; (d) Energy vs. k//y dispersion for k//x c-1 along the ī0Ag for Ag(111)/Si (1ML) sample and (e) Saddle point schematic.

Figure 5: (a) STM topography (100x100 nm2) of 2D triangleshaped islands epitaxially grown on Ag(111) substrates, Vtip=0.8 V, I=1 nA; (b) magnification (20.5x20.5 nm2) of a single AlN island and line profile along the green line; (c) atomic resolution (2.5x2.5 nm2) STM topography inside an island (see green contour in panel (b)).

Figure 6: HeI valence band spectra of the AlN(bulk)/Si(111) and AlN(12ML)/Ag(111) samples. The smaller VBM of the 12ML-AlN/Ag comparing to the bulk w-AlN/Si sample could be an indication of the smaller energy bandgap, which is expected for a graphite-like hexagonal AlN phase.

Monitoring stress transfer characteristics under tension in simply supported and embedded graphenes 1

1,2

G. Anagnostopoulos , C. Androulidakis , G. Tsoukleri , J. Parthenios , I. Polyzos , 1,3 1,2,3* K. Papagelis , C. Galiotis 1 Institute of Chemical Engineering and High Temperature Chemical Processes, Foundation for Research and Technology Âą Hellas (FORTH), P.O. BOX 1414, Patras 265 04, Greece 2 Interdepartmental Programme in Polymer Science & Technology, University of Patras, Patras 26504, Greece 3 Department of Materials Science, University of Patras, Patras 26504, Greece c.galiotis@iceht.forth.gr Abstract In this work, we investigate the stress/strain transfer mechanism under tension in simply-supported and embedded graphene flakes on polymer substrates (mechanical exfoliation of HOPG and transferred onto a cantilever PMMA ÂąSU8 beam in the simply-supported flakes, while in the embedded case the flake is covered by a thin layer of PMMA) using a four point bending apparatus and the cantilever beam approach, in tandem with Raman spectroscopy. In both cases, the mechanical apparatuses were placed above a piezoelectric nanopositioning stage (Thorlabs, max 301) At each applied strain level, a PDSSLQJ ČŚ2D ČŚG profiles) across specific lines on 1LG flakes is made, starting from the edges up to distance > 4Č?m with a step of 100 nm. In the case of simply-supported flake (Č&#x153;exc. QP ČŚ2D shifts (Fig.1) from the edge towards the middle, indicating stress transfer from the substrate to the graphene. However, close to edges (a distance ~ 1.5 Č?m) fluctuations of the 2D values are observed, which are more intense at lower levels, implementing the presence of additional influences [1], [2]. Similar results are also confirmed at figure 2, where a correlation between ČŚ2D & ČŚG slopes with the distance. For a distance < 1.5 Č?m the ratio of ČŚ2D/ ČŚG is different than ~ 2.2 [3], which imply doping effects or friction besides mechanical effects [1], [2], [4], [5]. For a distance > 1.5 Č?m, it seems that the ČŚ2D follows a linear profile, which has almost the -1 same slope value for all applied strain levels (~ 2.0 cm /cm) 2610

0 0.00% 0.20% 0.40% 0.60% 0.80%

-10

-20

-30

-40

-50 6000

2580

2570

2560

2550 0

1000

2000

3000

4000

5000

-50

6000

1000

2000

3000

4000

5000

-1

-1 ČŚ2D [cm ]

ČŚ2Dslope [cm /%]

2590

5DWLR RI ČŚ 2D WR ČŚG slopes

1 -10

ČŚGslope [cm /%]

2600

Distance [nm]

Fig. 1: The ČŚ2D distributions for various levels of externally applied tensile strain.

Fig.2: The strain sensitivity of ČŚ2D and ČŚG bands as a function of the distance from the edge of the simply Âą supported flake, and their corresponding ratio ČŚ2D / ČŚG In the case of embedded flake (Č&#x153;exc. = 514.5 nm), the maximum applied strain was up to 0.8%. At 0% applied strain residual strain of about -0.2% (Fig.3), due to a) initial deposition process, b) the shrinkage -1 of the upper layer and c) the roughness of substrate. The position of ČŚ2D is almost constant at 2690 cm all along the mapping line. The profile of ČŚ2D showed an initial plateau up to 1500 nm from the edges and after that the behavior becomes similar to the simply supported. For a distance > 1500 nm, the ČŚ2D -1 profile becomes more linear, which has a slope of ~4.0 cm /% and appears to be the same for all the applied levels. At higher levels (0.60%), the ČŚ2D profile becomes less linear. Furthermore, the ČŚG is splitted into the ČŚG- and ČŚG+ components at 0.30% of applied strain, implying an efficient stress transfer. In Table 1 & 2, the average values of ČŚ2D ČŚG as a function of the applied strain for both examined cases are presented. Finally, as it is also observed at the simply-supported case, at the edges the slopes of ČŚ2D ČŚG as well as the their ratio are much different from the expected one [3], while at distances > 4000 nm, the strain sensitivity of ČŚ2D ČŚG appears to be similar with our previous works [3], -1 reaching a value of 53.8 cm /% (Fig.4) [1]

Table 1: The slopes of ČŚ2D ČŚG for the simply-supported case Simply-supported Applied strain (%)

2D Av. Value

G Av. Value

0 0.2

G (-) Av. Value

2577.1 2581.7

1.0 2.7

1578.4 1578.0

0.4 1.2

0.4 0.6

2575.3 2567.9

0.8 1

2562.7 2555.7

G(+) Av. Value

2.1 2.5

1573.8 1568.1

1.3 1.4

1580.0 1577.2

0.9 0.8

4.2 1.3

1564.1 1559.8

2.2 1.0

1575.8 1574.3

1.1 0.4

Table 2: The slopes of ČŚ2D ČŚG for the embedded case Embedded Applied strain(%)

G (-)

Av. Value

0 0.05

2690.1 2683.0

2.2 3.2

1594.1 1590.9

0.8 1.5

0.1 0.3 0.4 0.5

2679.2 2672.1 2671.4 2664.0

3.5 6.8 8.2 8.0

1589.8

1.9

0.6 0.7

2660.8 2650.1

0.8

2663.3

G(+)

Av. Value

1585.7 1584.6 1586.9

5.7 5.2 6.0

1589.3 1585.6 1587.4

1.1 6.3 1.3

8.5 1.2

1577.1 1571.9

9.7 1.5

1591.1 1589.1

7.4 4.5

9.3

1581.6

6.5

1601.6

7.3

2700 Applied strain (cantilever)

2690

2670

9 -10

-10

2650

-20

2640

-30

-40

-50

-60

-70

-80

-90

1500

2000

2500

3000

0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3

3500

4000

Applied strain (cantilever)

0.00 % 0.30 % 0.60 %

-100 0

500

1000

1500

2000

2500

3000

3500

4000

2000

4000

6000

8000

10000

-100 12000

5DWLR RI ČŚ2D WR ČŚG slopes

1000

-1

500

-1

ČŚG slope [cm /%]

2630

Applied strain (cantilever) [%]

2660

ČŚ2D slope [cm /%]

-1

ČŚ2D [cm ]

0.00 % 0.30 % 0.60 %

2680

7 6 5

Distance [nm]

Fig.3: Distributions of 2D peak and strain for various level of applied strain (cantilever) as a function the distance (max. 3000 nm away from the edge of the flake) References

Fig.4: The strain sensitivity of ČŚ2D and ČŚG bands as a function of the total measured distance from the edge of the embedded flake, and their corresponding ratio ČŚ2D / ČŚG

[1] Busuttil, K.; Geoghegan 0 +XQWHU & $ /HJJHWW * - Âł&RQWDFW 0HFKDQLFV RI 1DQRPHWHU-Scale 0ROHFXODU &RQWDFWV &RUUHODWLRQ EHWZHHQ $GKHVLRQ )ULFWLRQ DQG +\GURJHQ %RQG 7KHUPRG\QDPLFVÂ´ J. Am. Chem. Soc. 133 (2011), 8625Âą8632 [2] Bhushan, B.; Israelachvili, J. N.; Landman, 8 Âł1DQRWULERORJ\ )ULFWLRQ :HDU DQG /XEULFDWLRQ DW WKH $WRPLF 6FDOHÂ´ Nature 374 (1995), 607Âą616. [3] Tsoukleri G., Parthenios J., Papagelis K., Jalil R., Ferrari A. C., Geim A. K., Novoselov K. S., Galiotis C., Small 5(21) (2009), 2397Âą2402 [4] Casiraghi C., Physica Status Solidi-Rapid Research Letters 3(6) (2009): 175-177. [2]

[5] Casiraghi C, Hartschuh A., Qian H., Piscanec S., Georgi C., Fasoli A., Novoselov K., Basko D., Ferrari A., Nano Letters 9(4) (2009): 1433-1441

[3]

DFT-NEGF calculations of gated graphene nano-structures N. P. Andersen, T. Gunst, D. Stradi & M. Brandbyge Dept. of micro and nanotechnology & Center for Nanostructured Graphene (CNG), Tech. Univ. of Denmark, build. 345ø, 2800 Kongens Lyngby, Denmark nickpapior@gmail.com

Abstract First-principles modeling of electrostatic gating is important for characterization of transistor-like systems at the atomic scale. In 2D materials, such as graphene, one can control the Fermi level and electronic states involved in transport by gating, as well as achieve gate/device separations on the order of a few Angstroms due to the thinness of graphene [1–3]. We use DFT-NEGF calculations by considering a variety of technologically relevant 2D structures of different chemical and physical characteristics. Specifically we focus on the interplay between charge accumulation/depletion and the electric field in these. To accomplish this task we have implemented a gating feature in the SIESTA package which can be used to simulate homogeneous and inhomogeneous charge distributions, thus allowing us to model electrostatic gates but also trapped charges without resorting to empirical parameters [4–6]. Our implementation gives results consistent with ∞-dielectric medium calculations in the homogeneous case [7]. We consider the effect of gating a graphene nanoconstriction with hydrogen terminated edges connecting two graphene leads. Such constrictions are known to have electronic resonances due to the diffraction barrier at abrupt interfaces [8]. We examine how a gate can be used to tune the position of the electronic resonances, however less linearly than expected, and hereby changing what states drive the current through the device. In Fig. 1(left figures) we show the charge density redistribution for a non-gated and a gated (p-type) nanoconstriction. Interestingly, the left-right symmetry is broken and the potential profile is concentrated where the resistivity dipoles are mostly dominant as can be seen in Fig. 1(right figures). This effect can be traced back to the difference between the density of states in the two leads when a gate is applied. One can therefore utilize a gate to engineer the local potential drop across such constrictions. Additionally, we will compare the effect of gating with that of donor and acceptor adatoms and examine the role of a gate on functionalization and adatoms in the device.

References [1]

C. Berger, Z. Song, T. Li, X. Li, A. Y. Ogbazghi, R. Feng, Z. Dai, A. N. Marchenkov, E. H. Conrad, P. N. First, and W. A. de Heer. The Journal of Physical Chemistry B. 108 (52). (2004), pp. 19912–19916.

[2]

E. Castro, K. Novoselov, S. Morozov, N. Peres, J. dos Santos, J. Nilsson, F. Guinea, A. Geim, and A. Neto. Physical Review Letters. 99 (21). (2007), p. 216802.

[3]

Y. Zhang, V. W. Brar, C. Girit, A. Zettl, and M. F. Crommie. Nature Physics. 5 (10). (2009), pp. 722–726.

[4]

J. M. Soler, E. Artacho, J. D. Gale, A. Garc´ıa, J. Junquera, P. Ordej´ on, and D. S´ anchez-Portal. Journal of Physics: Condensed Matter. 14 (11). (2002), pp. 2745–2779.

[5]

M. Brandbyge, J.-L. Mozos, P. Ordej´ on, J. Taylor, and K. Stokbro. Physical Review B. 65 (16). (2002), pp. 1–17.

[6]

N. P. Andersen et al. To be published. (2014).

[7]

M. Otani and O. Sugino. Physical Review B. 73 (11). (2006), p. 115407.

[8]

T. Gunst, J.-T. L¨ u, P. Hedeg˚ ard, and M. Brandbyge. Physical Review B. 88 (16). (2013), p. 161401.

Figure 1: Charge redistribution with respect to Vbias = 0 V (left figures) and potential drop (right figures) of the nano-constriction device upon application of a Vbias = 0.5 V. Top panel shows the case for no doping n = 0e and bottom panel show n = −0.5e (p-type).

Determining graphene layers number distribution by XRD data

B. Andonovic, A. Grozdanov, P. Paunovic and A.T. Dimitrov )DFXOW\ RI 7HFKQRORJ\ DQG 0HWDOOXUJ\ 8QLYHUVLW\ Âł6W &\ULO 0HWKRGLXVÂ´ 6NRSMH Rudjer Boskovic 16, 1000 Skopje, Republic of Macedonia beti@tmf.ukim.edu.mk

An equation that uses Laue functions and a model which includes graphene thickness distribution were used to calculate XRD intensities of the curves that exhibit good fitting to the XRD intensities curves of the studied graphene samples. The subject of this study is graphene samples produced by different electrochemical procedures: electrolysis in aqueous electrolyte and electrolysis in molten salts. In both electrochemical procedures, reverse change of the applied potential was applied. The employed equation parameters make it possible to calculate the n-layer graphene regions coverage of the graphene samples, and the average value for number of graphene layers. Graphene produced in molten salts has shown better structural characteristics and lower number of layers. Key words: Graphene, electrochemical production, XRD analysis, layers.

Schottky Diode characteristics of ZnO/graphene/Cu heterojunctions formed by direct bonding technique Takashi Aoyama, Ayaka Sasabuchi, Shigeru Yamauchi, Takao Komiyama, Yasunori Chonan, and Hiroyuki Yamaguchi Electronics & Information Systems, Akita Prefectural Univ. Yuri-honjo, Akita 015-0055, Japan aoyama@akita-pu.ac.jp Abstract Schottky barrier heights between graphene and semiconductors have been already reported for GaAs, Si, SiC and ZnO [1-5]. Generally, surface treatments for semiconductors significantly affect the Schottky barrier heights. Oxide semiconductors, however, are free from oxidation in the atmosphere at room temperature (RT). On the other hand, direct bonding technique at RT can afford ideal heterojunctions by minimizing additional thermal effect on the respective material [6, 7]. We investigated Schottky barrier diodes formed by graphene and ZnO (oxide semiconductor) using direct bonding technique in the atmosphere at RT. Single layer graphene on Cu foils formed by CVD was purchased from Graphene Platform Co. Ltd. Figure 1 shows two schematic Schottky diode structures formed by direct bonding technique in the atmosphere at RT. The ZnO was either single crystals (+c plane) or polycrystalline films formed on sapphire substrates by pulsed laser deposition (PLD). The VI/II ratios of the ZnO films were changed by applying bias voltages on the grid inserted between the substrate and the ZnO target in PLD [5, 6]. The ZnO surfaces were cleaned by only organic solvent (acetone) and deionized water. Figure 2 shows a Raman spectrum of the graphene on the Cu foil where the peak intensity ratio of I2D/IG was approximately 3, indicating a monolayer thickness. Figure 3 shows I-V characteristics of ZnO/Cu heterojunctions for ZnO single crystals under different bonding pressures. As the pressure was increased, both the forward and the reverse currents increased. Figure 4 shows the effect of the bonding pressure on the forward currents. As the pressure was increased, the currents increased first 2 and they were saturated for the pressure of more than about 300 g/cm . This implies that reliable heterojunction characteristics can be obtained by our direct bonding technique. Figure 5 shows I-V characteristics of the ZnO/Cu and ZnO/graphene/Cu heterojunctions for single crystals under a bonding 2 pressure of 300 g/cm . The difference of work functions between graphene (4.5 eV) and Cu (4.65 eV) is only 0.15 eV and the forward currents were almost the same values. Figure 6 shows I-V characteristics of ZnO/Cu and ZnO/graphene/Cu heterojunctions for polycrystalline ZnO films. The forward currents tended to be straight and this suggested that the currents changed from the thermionic emission for single ZnO crystals to tunneling currents for polycrystalline films. The deep energy levels in the polycrystalline films played important roles in the tunneling mechanism. The threshold voltage was decreased by inserting graphene and the forward currents were increased. Figure 7 shows the forward currents of the heterojunctions for polycrystalline ZnO films with different defect densities. As the VI/II ratios of the ZnO films deviated from the stoichiometric composition (1:1), the forward currents were increased by a factor between 2 and 3. This indicates that the tunneling currents were caused mainly by the deep energy levels of vacancies and interstitial atoms in the ZnO films [8] and, they were also affected by the difference between the Fermi energy surfaces of graphene and Cu.

References [1] B. J. Coppa and R. F. Davis, Appl. Phys. Letters 82, 401 (2003) [2] S. Tngay, T. Schumann, and A. F. Hebard, Appl. Phys. Letters 95, 222103(2009) [3] S. Lee, Y. Lee, D. Kim, E. Song, and S. Kim, Appl. Phys. Letters 102, 242114 (2013) [4] E. L. H. Mayes, D. G. McCulloch, and J. G. Partridge, Appl. Phys. Letters 103, 182101(2013) [5] C. Yim, N. McEvoy, and G. Duesberg, Appl. Phys. Letters 103, 193106 (2013) [6] H. Abe, M. Fujishima, T. Komiyama, Y. Chonan, H. Yamaguchi, and T. Aoyama, Phys. Status Solidi C, 9, 1396 (2012) [7] K. Komatsu, Y. Seno, T. Komiyama, Y. Chonan, H. Yamaguchi, and T. Aoyama, Phys. Status Solidi C, 10, 1280 (2013) [8] Y. Seno, D. Konno, T. Komiyama, Y. Chonan, H. Yamaguchi, and T. Aoyama, AIP Conf. Proc., 1583, 327 (2014)

Fig. 1 Schematic heterojunction structures

Fig. 3 I-V curves of ZnO/Cu under different DB pressures

Fig. 5

Fig. 2 Raman Spectrum of graphene on Cu foil

Fig. 4 Effect of DB pressure on the forward currents of ZnO/Cu junction

I-V curve of ZnO/graphene/Cu for single crystal ZnO

Fig. 7 Effect of VI/II ratio of ZnO on forward currents

Fig. 6

I-V curve of ZnO/graphene/Cu for polycrystalline ZnO

Nitric Acid doping of epitaxial graphene on SiC(0001) substrate Fethullah Gunes, David Alamarguy, Hakim Arezki, Alexandre JaffrĂŠ, JosĂŠ Alvarez, Jean-Paul Kleider and Mohamed Boutchich

LGEP, CNRS UMR8507, SUPELEC, Univ Paris-Sud, Sorbonne UniversitĂŠs-UPMC Univ Paris 06, 11 rue Joliot-Curie, Plateau de Moulon, 91192 Gif-sur-Yvette Cedex, France mohamed.boutchich@lgep.supelec.fr Abstract Chemical doping by surface charge transfer is an effective way to modulate grapheneâ&#x20AC;&#x2122;s electrical properties through p or n-type doping. Nitric Acid (HNO3) is an efficient acidic doping agent that 1,2 manipulates work function (WF) of graphene . Although HNO3 is known as a p-type dopant for CVDgraphene increasing the conductivity by surface charge transfer, it may behave different on intrinsically n-type epitaxial graphene on SiC(0001) surface due to the difference in surface potentials 3. In this work, the doping behavior of HNO3 solutions with several concentrations on n-type epitaxial graphene was investigated. Three different concentrations of 15 vol%, 30 vol%, and 70 vol% of HNO3 solutions in DI water were applied on the surface of epitaxial graphene and compared with pristine samples. The samples used for each concentration were separately measured by Raman spectroscopy before and after doping to avoid errors due to the structural differences on each sample affecting the peak positions. In Figure1, Raman results show that after the 15 vol% of HNO3 resulted in no-change in Gband position and a red-shift at higher concentrations. 2D-band positions of Raman spectra all exhibit a 4,5 red-shift after doping regardless the concentration indicating n-type doping behavior . D-band intensities of Raman spectroscopy are increased after doping with concentration of HNO3 above 15 vol%. AFM image in Figure 2 shows the surface morphology of SiC(0001) consist of micron size parallel steps. To confirm Raman spectroscopy results, ultraviolet photoelectron spectroscopy (UPS) (Fig.2) and X-ray photoelectron spectroscopy (XPS) (Fig.3) were utilized to investigate the chemical environment of the graphene surface and to observe the change in WF for each concentration. The UPS results clearly confirmed the trend as it was observed in Raman spectroscopy where WF is decreasing at all concentrations. It is worth noting that considering Raman and UPS results (Fig.2), Fermi level shifted up more severely into the conduction band in the case of 30 vol% HNO3 than that of 70 vol% HNO3 doping. It is also noteworthy that doping of epitaxial graphene on SiC could be more complex than that of CVDgraphene doping due to strong covalent bonding with the substrate. Acidic solutions could interact with the SiC that may result in decoupling of graphene by strong oxidation. This complex behavior of WF changes could be implemented into apparent compensation effects from two simultaneous chemical reactions of oxidation/nitrogenation which occur via: i) stronger nitrogenation for concentrations below 50 vol% HNO3, and weaker for concentrations above 50 vol% HNO3, ii) increasing oxidative effect as the concentration of HNO3 is increasing as demonstrated by the O1s XPS data.

References > @ *Â QHĂş ) et al. ACS Nano 4 (2010) 4595â&#x20AC;&#x201C;4600. [2] Bae, S. et al. Nature Nanotechnology 5 (2010) 574â&#x20AC;&#x201C;578. [3] Ohta, T. et al. Physical Review Letters 98, (2007) 206802. [4] Voggu, R. et al. J. Phys.: Condens. Matter 20 (2008) 472204. [5] Panchakarla, L. S. et al. Advanced Materials 21 (2009) 4726â&#x20AC;&#x201C;4730.

Figures: Fig.1

Fig.2

Fig.3

A novel route towards carbon-based materials for hydrogen storage: packings of carbon nanotubes and graphene–carbon nanotubes composites Igor A. Baburin, Stefano Leoni, Gotthard Seifert Email: Igor.Baburin@chemie.tu-dresden.de Technische Universität Dresden, Physikalische Chemie, 01062 Dresden

Carbon-based materials proposed so far for hydrogen storage (graphite intercalated with fullerenes, carbon foams, nanotube bundles, etc.) perform only modestly [1]. Their hydrogen uptake usually amounts up to Ң3.0–7.0 wt.% at 77 K, quite far from the target value set by the US Department of Energy (6 wt.% at ambient conditions). Having in mind that in experiments carbon nanotubes (CNTs) are usually obtained as mixtures of tubes (often of different sizes and orientations), we suggest a new way of looking at the arrangements of CNTs, namely to consider their entangled assemblies (referred to as packings of CNTs). We modeled three-dimensional arrangements of CNTs with three and four orientations of tube axes, by matching cylinder packings known in crystallography (see the Figure). We considered different packings built up from (6,0) zigzag and (5,5) armchair carbon nanotubes. Their energetic and mechanical properties were studied with the density-functional-based tight-binding method (DFTB) [2]. Dispersion correction was included to account for inter-tube van der Waals interactions. Overall, (6,0) tube packings turned out to be slightly more stable than the fcc packing of C60 fullerenes while packings of (5,5) armchair tubes approach the stability of diamond [2]. The least dense (ȡ=0.2–0.3 g/cm3) nanotube packings (packing types + Ȉ, Ȉ*, see the Figure, bottom left and right) have relatively high bulk moduli (8.8 and 18.0 GPa, resp.) that is remarkable for porous structures. Hydrogen adsorption was investigated by means of classical Grand Canonical Monte Carlo (GCMC) simulations. + Ȉ packings of (6,0) and (5,5) tubes show technologically relevant (absolute) H2 uptake, namely, 17.5 and 19.0 wt.% at 100 bar (T = 77 K), respectively [2]. Even at room temperature +Ȉ packing of (5,5) tubes can adsorb up to 5.5 wt.% of hydrogen at 100 bar, that approaches the Department of Energy (DOE) target value of 6 wt. %. To optimize further the performance of nanotube packings, we consider more eclectic arrangements (e.g. with 6 or 12 orientations of tube axes) as well as graphene – CNTs composites. Our preliminary results indicate that more eclectic arrangements of CNTs can show relatively high total hydrogen uptake (~12 wt. % at T=77 K) at moderate pressures (~up to 20 bar). The calculations on hydrogen storage in graphene – CNTs composites are currently in progress.

References: [1] K. Spyrou, D. Gournis, P. Roudolf, ECS Journal of Solid State Science and Technology, 2, M3160 (2013). [2] B. Assfour, S. Leoni, G. Seifert, I. A. Baburin, Advanced Materials 23, 1237 (2011).

Electrical control of excitons and trions in MoS2 monolayer and bilayer crystals Tilmar K체mmell, Wolf Quitsch, Sebastian Matthis, Tobias Litwin, Gerd Bacher Werkstoffe der Elektrotechnik and CENIDE, Universit채t Duisburg-Essen, 47057 Duisburg, Germany gerd.bacher@uni-due.de Ultrathin crystals based on transition metal dichalcogenides form a new fascinating class of materials. Large direct band gaps allow for optoelectronic device concepts, the sub-nanometer thickness is attractive for ultrathin flexible electronics and the unique band structure could evoke new components for spintronics or valleytronics [1]. MoS2 flakes that can be realized easily by mechanical exfoliation have seen intensive research during the last couple of years, yet main aspects are still unclear. A central question concerns the possibility to manipulate the emission properties by e.g. electric fields. Indeed, charged excitons (trions) that are well known from semiconductor quantum dots could be observed in electrically contacted flakes recently up to room temperature [2]. These findings are limited to monolayers up to now. However, few layer structures have seen growing experimental attention: They are a kind of a link between true two dimensional and bulk semiconductors, and some controversy exists whether significant photoluminescence can be expected from bilayers [3-5]. Up to now no detailed information is available at all on the exciton-trion control in MoS2 bilayers. In our contribution, we study the interplay between trions and excitons in MoS2 bilayers in comparison with monolayers. Flakes were exfoliated mechanically and deposited on Si/SiO2 (90 nm) substrates. The thickness (layer number) is determined by Raman spectroscopy. Micro-photoluminescence measurements at T = 5 K (Fig. 1) reveal at first a common feature between mono- and bilayer emission: In contrast to the first theories, the dominating emission in both structures stems from the direct band 0 gap (A transition), and in both cases, this emission is split into a higher energy line A and a lower energy line A with Lorentzian line profile and an HQHUJ\ VHSDUDWLRQ RI 퓨( 5 meV. As the MoS2 flakes 0 are intrinsically negatively doped, we attribute A to an exciton and A to a negatively charged trion [2]. For the first time, we see these two lines not only in monolayers but also clearly separated in bilayers, due to the relatively small linewidth of 30 meV (exciton) and 50 meV (trion). However, significant differences are recorded as well: In monolayers a strong influence of defect-bound excitons is found, while these are absent in bilayers and instead emission from the indirect band gap is visible, in agreement with theory. In order to elucidate the exciton-trion interplay in detail, contact lines to the flakes were defined by electron beam lithography and evaporation of Ti-Au. The Si substrate serves as back gate contact. Micro-PL measurements were performed under variation of the gate voltage Ug which leads to an agglomeration (depletion) of excess electrons for positive (negative) Ug. In PL emission, this effect can be monitored easily in the bilayer structures, where the emission shows a clear shift from the trionic to the excitonic component, if Ug changes from positive to negative values (Fig. 2, right). In contrast, the monolayer shows a high disposition to defect luminescence: A switching is here only possible from trion emission to bound excitons, when Ug is decreased (Fig.2, left). To suppress the bound states, the analysis was expanded up to 300 K. At room temperature, we actually find an opposite behaviour: Switching between exciton and trion can now be observed easily in the monolayer. In the bilayer only exciton and indirect transition can be detected independent of Ug, indicating less robust trions in bilayer as compared to monolayer MoS2.

References [1] Q. Wang, K. Kalantar-Zadeh, A. Kis, J. N. Coleman , M. Strano, Nat. Nanotech. 7, 699 (2012) [2] K. Mak, K. He, C. Lee, G. Lee, J. Horne, T. Heinz, J. Shan, Nat. Mat. 12, 207 (2013) [3] A. Splendiani, L. Sun, Y. Zhang, T. Li, J. Kim, C.-Y. Chim, G. Galli, F. Wang, Nano Lett 10, 1271 (2010) [4] K. Mak, C. Lee, J. Hone, J. Shan, and T. Heinz, Phys. Rev. Lett. 105 (2010). [5] S. Wu, J. Ross, G.-B. Liu, G. Aivazian, A. Jones, Z. Fei, W. Zhu, D. Xiao, W. Yao, D. Cobden, X. Xu, Nat. Phys. 9, 149 (2013)

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Fig 1.: Photoluminescence from MoS2 monolayer and bilayer. The symbols represent A ; exciton, A : negative trion, B: transition between conduction band and split-off valence band, I: indirect band gap, Xbound: exciton bound to defects.

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Large scale catalytic synthesis of few layer graphene: structure and mechanism of formation 1

Revathi Bacsa, Ignacio Cameán, Alberto RAMOS , Ana B.Garcia, 3 1 Wolfgang Bacsa, Philippe SERP 1 Laboratoire de Chimie de Coordination UPR CNRS 8241, composante ENSIACET, Toulouse University, 118 Route de Narbonne, 31077 Toulouse Cedex 4, France 2 Instituto Nacional del Carbón, CSIC, Francisco Pintado Fe 26, 33011-Oviedo, Spain 3 Centre d’élaboration des matériaux et d’études structurales CNRS, 29 Rue Jeanne-Marvig, BP 4347, 31055 Toulouse, France Following the report of the unique electronic, mechanical and thermal properties of graphene, a number of processes have been developed for the large scale production of graphene nanoparticles 1 and films . Among the bottom up methods, chemical vapor deposition (CVD) has been the most widely 2 used . While the application of single layer graphene in electronics and display applications has been well demonstrated, it is becoming evident that for larger volume applications such as in composites, electrochemical and energy applications, few layer graphene (FLG) containing 2-10 layers are ideal candidates since they combine the properties of graphene at the same time being robust and easy to handle. To enable the wide availability of FLG at low cost, a breakthrough in the form of a selective, large scale, cheap process for the production of FLG is desirable. We report here, a large scale 3 substrate free fluidized bed catalytic chemical vapor deposition process for FLG powder production . In a typical experiment, FLG was produced by decomposition of ethylene in the 600°C-800°C range on a nanocrystalline (5-20 nm grain size) ternary oxide powder catalyst of the type ABO3 (where A and B are Fe, Ni, Co, Cu, Mn ). The carbon deposited at the end of the reaction was purified by dissolving the catalyst in acid. Using a judicious combination of A and B and appropriate growth parameters, it has been observed that the thickness of the FLG flakes could be varied between 3-20 layers. This process can operate on both fixed bed and fluidized bed reactors. The FLG flakes were heat treated in argon atmospheres at temperatures varying from 2200°C-2700°C to study the variation of domain size and crystallographic ordering. These variations were studied using TEM, XRD and Raman spectroscopy.

200 nm

Figure 1 (a) TEM image of FLG and (b) edge of FLG under high resolution. Inset shows fourier transformed image of zone shown by red arrow. 1(c) Raman spectrum of FLG prepared by FB-CVD High resolution TEM showed thin flakes of varying thicknesses from 2-8 nm with flake sizes in the 200 nm range. Electron diffraction of the flakes showed highly crystalline graphene layers (Fig. 1). It is observed that at the end of 10s, the number of layers is in the 1-5 range. A rough estimate of the average thickness can be obtained from the full width at half maxima of the 002 reflection in the X-ray powder diffraction image. Upon heat treatment at 2800°C in argon atmosphere, it was observed that domaine sizes increased showing a preferential development of the bi-dimensional structure but influenced the stacking order only marginally. Figure 1.c shows Raman spectra in the region of the 2D band recorded with two excitation energies at the same sample spot. The 2D spectral band caused by second-order double resonant scattering between two zone-boundary phonons (TO-derived) is sensitive to the presence of neighbouring layers -1 and stacking order (4). The 2D band width (HWHM: 37-42 cm ) is symmetric and not much broader -1 than the Raman G band (HWHM: 29 cm ) indicating the presence of single graphene layers with little interaction with neighbouring layers. The distinct combinational bands appearing as side bands in the region of the 2D band are defect and size induced. The relative narrow line shape shows the good crystallinity of the FLG. The differences in the spectral bands as a function of excitation wavelength are due to the variation of the dispersive behaviour of the D’ band compared to the D band. Conclusions A new process for the large scale preparation of FLG using FB-CVD has been developed. The yield and thickness are determined by a variety of parameters including a) catalyst composition b) crystallite size of the catalyst and c) the reaction conditions of the CCVD process (temperature, time, the nature of the carbon source and its partial pressure). A description of the synthesis and structure-property correlation in FLG powders prepared by this process will be presented. A possible mechanism for the selective growth of FLG, under reaction conditions where normally multiwalled carbon nanotubes are formed, will be proposed. The effect of heat treatment at 2800°C on the crystallographic ordering and Raman spectra will also be presented in detail. References 1. Bonaccorso, F., et al., Production and processing of graphene and 2d crystals. Materials Today, 2012. 15(12): p. 564-589. 2. Reina, A., et al., Large Area, Few-Layer Graphene Films on Arbitrary Substrates by Chemical Vapor Deposition. Nano Letters, 2008. 9(1): p. 30-35. 3. R. Bacsa, P. Serp, Graphene production method and graphene obtained by said method WO 2013093350 A1. 4. Pimenta, M.A., Dresselhaus, G., Dresselhaus, M.S., Cançado, L.G., Jorio A., Saito R., Studying disorder in graphite-based systems by Raman spectroscopy, Physical Chemistry Chemical Physics 9 (2007) : p. 1276-1291.

Direct Liquid-Phase Exfoliation of Graphite via Diels-Alder reaction Hugo Barès, Sébastien Bonhommeau, Jean-Baptiste Verlhac, Dario Bassani Institut des Sciences Moléculaires, CNRS UMR 5255 – Université de Bordeaux, 351, Cours de la Libération, 33405 Talence, France hugo.bares@u-bordeaux.fr Since the discovery of the electronic properties of graphene in 2004,1 many techniques to produce graphene films have been developed. The most common methods are Chemical Vapor Deposition (CVD )2,3 and through micromechanical1 or chemical4 exfoliation of graphite. The latter are very cost effective and suitable for large-area device fabrication but generate defects and residual stress in the material that is deleterious to its performance. In particular, liquid-phase exfoliation of graphite requires the use of surfactants, or non-volatile and/or halogenated solvents that are impractical to remove following deposition. Likewise, chemical reduction of water-soluble graphite oxide does not lead to materials with the same electrical properties of pristine graphene due to the presence of residual defects. We developed a process for the chemically-assisted exfoliation of graphite based on a reversible cycloaddition reaction.5 This approach is highly efficient even in volatile organic solvents that are otherwise ineffective for exfoliation of graphite. The method relies on the Diels –Alder reaction between graphite and reactive dienes assisted by mild sonication. The formation of a “butterfly” adduct in which two sp3 centers are present on the graphene skeleton is used to separate and solubilize functionalized graphene sheets. Because the Diels-Alder reaction is fully reversible, and that the adducts cannot migrate, gentle heating is sufficient to return the chemically modified graphene to its pristine state. Thermogravimetric analyses, TEM, and confocal Raman spectroscopy were used to investigate the transformation and its consequences on the physical and electronic properties of graphene.

References [1] Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A., Science, 306 (2004) 666. [2] Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Kim, K. S.; Ahn, J.!H.; Kim, P.; Choi, J.!Y.; Hong, B. H., Nature, 457 (2009) 706. [3] Reina, A.; Jia, X.; Ho, J.; Nezich, D.; Son, H.; Bulovic, V.; Dresselhaus, M. S.; Kong, J., Nano Letters, 9, (2009) 30. [4] Lotya, M.; Hernandez, Y.; King, P. J.; Smith, R. J.; Nicolosi, V.; Karlsson, L. S.; Blighe, F. M.; De, S.; Wang, Z. M.; McGovern, I. T.; Duesberg, G. S.; Coleman, J. N., Journal of the American Chemical Society, 131 (2009) 3611. [5] BNT217097FR00 Figure

Graphene Complex Cellular Networks 1

Suelen Barg , Felipe M Perez , Na Ni , Paula do V Pereira , Robert C Maher , Esther Garcia-TuĂąon , 1

Salvador Eslava , Cecilia Mattevi , Eduardo Saiz

Centre for Advanced Structural Ceramics, Department of Materials, Imperial College London, London SW7 2AZ, United Kingdom. 2 Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom. suelen.barg@imperial.ac.uk

Abstract The advance of a wide range of key and emergent technologies demands the creation of complex three-dimensional architectures that scale in structure and function, can reversibly respond to external environments or store and transport energy. Graphene is an ideal nano-scale building block that if properly integrated into these complex structures has the potential to form novel platforms for a wide range of functional systems. However, to achieve this goal we need to develop ways for the controlled assembly of three-dimensional materials using a two-dimensional building block. In this work, we have developed a mesoscale self-assembly strategy for the manufacturing of ultra-light ( 1 mg cm-3) chemically modified graphene CMG cellular networks. The approach is based on the use of soft templates and the controlled segregation of CMG to liquid interfaces allowing for manipulation of the structure at multiple levels. We can control the densities of the materials over two orders of -3 magnitude, from 1 to 200 mg cm , cell shape (from lamellar, polyhedral to spherical) and sizes (~7 to over 60 m) at the micro-level to the cell walls topography, porosity and chemistry at the micro to nanolevel. Further, due to the intrinsic flexibility of emulsions, it is possible to extrude CMG wires with cellular architectures showing promise for the fabrication of complex structures at the macroscale. As a result 2 -1 we show it is possible to tune properties like surface area (up to 3280 Âą 287 m g ), elasticity, specific strength, energy loss coefficient, electrical conductivity, and organic absorption capabilities (above 600 grams per gram of material). This opens up new opportunities to explore applications in numerous fields of key technological areas including energy damping, compression tolerant supercapacitors, catalyzers or any application where separation, absorption, or filtration is required.

A Few Layer Graphene Material Prepared by Thermal Reduction of GO 1

Nara R. S. Basso , Fabiana Fim , Thuany Maraschin , Giovani Pavoski , Griselda B. Galland 1 2

PontifĂcia Universidade CatĂłlica do Rio Grande do Sul, Av. Ipiranga, 6681,Porto Alegre\RS, Brasil. Universidade Federal do Rio Grande do Sul, Av. Bento GonĂ§alves, 9500, Porto Alegre\RS, Brasil. nrbass@pucrs.br

Abstract Graphene shows a wide range of application due to its electrical, optical and mechanical properties and several methods of preparation have been developed in the last ten years. However, to prepare large graphene quantities with a relatively small number of defects is still a challenge. Physical and chemical exfoliation of graphite has been mentioned as an appropriate method to prepare graphene or few layer graphene materials for many applications, such as nanocomposites, sensors and electronic devices [1]. The aim of this work is to show the results concerning to preparation of few layer graphene material by thermal reduction of graphite oxide (GO). The energic oxidation of graphite using modified Staudenmaier methodology resulted in GO [2]. Two different types of graphite were evalueted: graphite flake (FK) and graphite nanosheets (GNS). It was also evaluated different times of oxidation (24, 48, 72 and 96h) and different reduction temperature of GO (600, 700 and 1000ÂşC). The samples were characterized by XRD, Raman spectroscopy and TEM. The Figure 1a shows the XRD patterns of GNS and FK. It is possible to observe the interlayer spacing along the c-axis (d-002) at 25Âş and (d-004) at 55Âş as sharp peaks for FK. The less intense peak at 25Âş and absence of peak at 55Âş indicates that GNS sample is exfoliated. The formation of GO is indicated by the increase of the interlayer spacing along the c-axis (d002) due the insertion of various oxygen-containing functional groups in the graphite structure. The Fig. 2a shows the XRD patterns of GO prepared from GNS oxidation during 96h. The formation of GO was confirmed by peak at 11.3Â° corresponding to the d-spacing of 0.81nm. When the 2 GNS graphite is oxidized, the delocalized electronic structure is disrupted, i.e. in the sp bonding networks of the graphite. Therefore is very important restoring the Ę&#x152;-network by reduction reaction, so that the electrical conductivity is restored again. A manner to restore the Ę&#x152; -network is by the thermal reduction. Therefore the GO was submitted to different thermal treatments. Figure 2a shows the XRD patterns to GO samples oxidized during 96h and GO that had different thermal treatment (GO6, GO7 and GO10; these were heated at 600, 700 and 1000 Â°C, respectively). According to Fig. 2a it can be seen that the increases in the reduction temperature decreases the intensity of the peaks characteristic of GO at 11 . GO6 and GO7 showed a smaller peak of starting material, GNS, about 24Â°. It shows that the heating restore the organization of graphitic structure, but it was not verified for higher temperatures. Figure 2b shows the Raman results for GO thermally reduced. The main Raman features of graphene -1 -1 -1 and graphite are the G band ( 1580 cm ), the D band ( 1350 cm ) and the 2D band ( 2670 cm ). The 2 the D band is related to crystal defects. The G band originates from in-plane vibration of sp carbon atoms and the 2D band corresponds to the second order overtone of the D band. For single layer graphene (SLG) the 2D band is a sharp and symmetric peak while it becomes broader when grapheme 2 thickness increases from SLG to few layer graphene[3]. The Figure 2b shows that a sp carbon network was restored, but with many defects. No peak is observed in the 2D band region indicating that amount 3 of graphene, if it is presence, is very small relative to amount of sp carbon. On the other hand, best results were obtained with GO prepared from FK. The Fig. 3 shows as example the results when FK was oxidized during 24 or 72h and the resulting GO was reduced at temperature of 600, 700 e 100Â°C. The X-ray diffraction spectrum shows the peak relative to the d-spacing at 25Â° and no GO characteristic peak at 11Â°, Fig. 3a and 3b. The less intense and broader peaks observed for SFK24H7, SFK24H6, SFK72H7 and SFK72H6 Indicate a great exfoliation. The interlayer distances (d002) between graphenes and the crystal VL]H & ZHUH HVWLPDWHG XVLQJ %UDJJÂśV /DZ DQG 6FKHUUHUÂśV (TXDWLRQ UHVSHFWLYHO\ and it was estimated that the crystal has 10-15 stacked graphene sheets. It can be seen in the Raman spectra that the graphite structure was recovered and the defects are similar to those existing at starting graphite, FK, Fig. 3a and 3b. The band 2D of SFK24H6 and SFK72H6 indicates that a stacking of few layer of graphene was obtained. The TEM image supports these results, Fig. 4. References [1] M. Cai, D. Thorpe, D. H. Adamson, H. C. Schniepp. J. Mater. Chem, 22 (2012), 2492. [2] M. Harrera-Alonso, A. A. Abdala, M. J. MacAllister, I. Akay, R.K. 3UXGÂśKRPPH /DQJXLPLU 23 (2007), 10644. [3] Z. Ni, Y. Wang, T. Yu, Z. Shen. Nano Res, 1 (2008), 273.

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Pseudo-gap opening and Dirac point confined states in doped graphene1 J.E. Barrios-Vargas†‡, Gerardo G. Naumis† †

Depto. de Física-Química, Instituto de Física, Universidad Nacional Autónoma de México (UNAM), Apdo. Postal 20-364, 01000 México D.F., México. ‡

Theoretical and Computational Nanoscience Group, Catalan Institute of Nanoscience and Nanotechnology (ICN2) Campus de la UAB, Edifici ICN2 08193 Bellaterra, Spain. jebarrios@fisica.unam.mx jose.barrios@icn.cat

Abstract The appearance of a pseudo-gap and the buildup of states around the Dirac point for doped graphene can be elucidated by an analysis of the density of states spectral moments. Such moments are calculated by using the Cyrot-Lackmann theorem2, which highlights the importance of the network local topology. Using this approach, we sum over all disorder realizations up to a certain radius to show how the spectral moments change. As a result, the spectrum becomes unimodal, however, strictly localized states appears at the Dirac point. Such states are important for the magnetic properties of graphene, and are calculated as a function of the doping concentration. By removing these states in the count of the spectral moments, it is finally seen that the density of states increases its bimodal character and the tendency for a pseudogap opening. This result is important to understand the trends in the magnetic and electronic properties of doped graphene. In graphene with vacancies, the same ideas can also be useful to isolate in a rough way which effects are due solely to topology. References [1] J.E. Barrios-Vargas, Gerardo G. Naumis, Solid State Communications, 162 (2013) pp. 23-27. [2] F. Cyrot-Lackmann, J. Phys. Chem. Solids, 29 (7) (1968), pp. 1235-1243.

Charge transfer between graphene and fullerene C60 1

Claudia Bautista Flores , Roberto Y. Sato BerrĂş , Doroteo Mendoza LĂłpez

Instituto de Investigaciones en Materiales, Centro de Ciencias Aplicadas y Desarrollo TecnolĂłgico, Universidad Nacional AutĂłnoma de MĂŠxico, 04510, Distrito Federal, MĂŠxico claudiabautistaf@iim.unam.mx, doroteo@unam.mx 2

Abstract: Graphene consists of only one layer of carbon atoms, thus the system is under the influence of surrounding area; it had been probed experimentally that electrical properties of graphene undergo limitations when it is on top of SiO2/Si substrate [1], which is the common substrate used in optical observations and in field effect transistors measurements. Another way to modify electrical properties of graphene, is doping it with other atoms (substitutional doping), adsorbed molecules on its surface (surface transfer doping) [2] or electrochemical top gating [3]. These processes permit us to obtain p and n-type graphene. p-type doping drives the Fermi level of graphene below the Dirac points, and ntype drives the Fermi level above the Dirac points. Functionalization of graphene increases applications of this material, particularly in thin film transistors, optoelectronics and transparent conducting films, for example. On the other hand, fullerene C60, a three dimensional structure of carbon atoms, presents some interesting physical properties, it can create electron-hole pairs after excitation with light. In this context we are interested in charge transfer between these two materials, graphene (or few layers of graphene, FLG) and C60 films deposited on its surface. To this end, we performed Raman spectroscopy and in situ electrical measurements. Raman spectroscopy is a powerful tool in characterization of graphene; the shapes, intensities and positions of peaks are used to determine the number of layers, strain, doping, disorder, types of edge, and so on. Raman fingerprint of graphene is characterized by three mean peaks: D peak at around -1 1350 cm due to the breathing modes of six-atom rings and requires defects for its activation; G peak -1 at 1585 cm corresponds to the high frequency E2g phonon at the Brillouin zone center, and the D peak -1 overtone 2D peak at around 2690 cm [4]. In surface transfer doping of graphene samples, position of G and 2D peaks, Pos(G) and Pos(2D) respectively, upshift for p-type doping but for n-type doping, Pos(G) downshifts while Pos(2D) upshifts [2]. We obtained FLG fiOPV E\ &9' WHFKQLTXH XVLQJ Č?P thick copper foils, methane as the carbon precursor and ambient pressure. After CVD process, FLG film was removed from the Cu foil by etching in an aqueous solution of iron nitrate, then the samples were transferred to SiO2/Si substrates to be analyzed by Raman scattering, and glass substrates were used to perform electrical measurements. We used a Nicolet Almega XR Spectrometer, 532 nm of laser excitation for Raman measurements. The FLG sample mainly consists of graphene and many isolated regions with few layers. We selected just graphene zones in FLG films for Raman measurements. In Figure a), Pos(2D) versus Pos(G) of graphene are plotted, with and without fullerene C60 deposited on graphene surface. As it is shown in -1 this figure, Pos (2D) of graphene upshifts about 20 cm , and this is because of the electrical influence of -1 C60 [5], on the other hand, Pos(G) upshifts about 10 cm , indicating p type doping. For electrical characterization two parallel silver strips were evaporated on FLG film to form Ohmic contacts, then fullerene C60 film was thermally evaporated on FLG, at the same time electrical conductivity was in situ monitored in darkness. In Figure b) current versus thickness of C60 on FLG is shown. When molecules of C60 are depositing on FLG, the current increases up to a thickness of about 70 Ă&#x2026;; for thickness higher than this value, current do not change any more. After evaporation of C60 on FLG, the electrical conductivity decreases upon exposition of the sample to monochromatic light of 514.5 nm (see figure c). This was an ex situ measurement in a different vacuum chamber. Since we observe both Pos(G) and Pos(2D) upshift, we can suppose that electrons flow from graphene to C60, thus C60 induce p-doping in graphene [6]. The intensity ratio of G and 2D peaks (I(2D)/I(G)) is also sensitive to doping [3], I(2D)/I(G) decreases for increasing charge concentration, and the same variations have been observed for our samples, from 3.5 in pristine graphene to 1.5 in graphene with fullerene C60 film Our tentative description, in order to reconcile electrical observations with Raman results, is as follows. We know that using CVD technique, contaminants from solvent of copper, or water originates p type graphene samples. Thus, Fermi level is below the Dirac point in our pristine samples. Since in situ measurements show an increase of conductivity when C60 is deposited on FLG film surface; which means that the hole density increases, now Fermi level of FLG film downshift even more with respect to Fermi level in initial sample. When light is on, a decrease in the electrical conductivity means that hole concentration are decreasing, and now Fermi level upshifts, but never above the Dirac point of initial FLG film, thus maintaining the p-type doping character.

Finally, we effectively found that fullerene C60 induce p type doping on graphene. Of course more measurements are needed in order to understand and describe the behavior of our system under illumination. References [1] Jian Hao Chen, Chaun Jang, Shudong Xiao, Masa Ishigami, Michael S. Fuhrer, Nature Nanotechnology, 4 (2008) 206. [2] Hongtao Liu, Yungi Liu and Daoben Zhu, Journal of Materials Chemistry, 1 (2011) 3253. [3] A. Das, S. Pisana, B. Chakraborty, S. Piscanec, S. K. Saha, U. V. Waghmare, K. S. Novoselov, A. K. Geim, A. C. Ferrari, A. K. Sood, Nature Nanotechnology, 4 (2008) 210. [4] Andrea C. Ferrari and Denis M. Basko, Nature Nanothechnology, 4 (2013) 235. [5] Rui Wang, Shengnan Wang, Xiaowei Wang, Jakob A. S. Meyer, Per Hedegard, Bo W. Laursen, Zhihai Cheng, and Xiaohui Qiu, Small, 14 (2013) 2420. [6] Jongweon Cho, Joseph Smerdon, Li Gao, Ozgun Suzer, Jeffrey R. Guest, and Nathan P. Guisinger, Nano Letters, 6 (2012) 3018.

Figures

a) Position of G and 2D peaks of graphene with and without thermally evaporated fullerene C60; b) Conductivity of FLG film versus thickness of C60 in darkness; c) Behavior of electrical conductivity of FLG film with C60 under illumination; for this experiment we used a 514.5 nm of laser excitation and 10 mW of Intensity.

Three dimensional graphene composite electrodes for electrochemical applications 1

A. Bello , M. Fabiane , D. Y. Momodu , S. Khamlich , J. K. Dangbegnon , N. Manyala 1

Department of Physics, Institute of Applied Materials, SARChI Chair in Carbon Technology and Materials, University of Pretoria, Pretoria 0028, South Africa Email: bellohakeem@gmail.com

Abstract In the emerging field of energy storage technology, the development of efficient energy storage devices with both high energy and power densities is highly desirable. The performance of these devices is closely related to material properties used for the fabrication of the device[1–3]. In our work few-layers graphene was synthesized on a nickel foam template by chemical vapour deposition (CVD). The resulting three-dimensional (3D) graphene was loaded with metal oxides (MnO2) nanostructures using hydrothermal techniques coupled with microwave irradiation. The composites were characterized and investigated as electrode material for electrochemical capacitors. Raman spectroscopy measurements performed on both 3D graphene and the composite material show that the 3D graphene network consisted of mostly few layers, while structural and morphological characterization, performed with X-ray diffractometry (XRD) and scanning electron microscopy (SEM), respectively, reveal the presence of the MnO2 in the 3D architecture. The electrochemical characterizations including cyclic voltammetry (CV), constant current experiment (charge-discharge) and long term cycling (stability) using a 6 M KOH aqueous electrolyte show that the composite electrodes materials exhibit excellent properties as a pseudocapacitive material with a high specific capacitances value of 305 Fg

-1

at a current density of 1 Ag , with 84% retention of the initial

capacitance after 1000 cycles in a three electrode configuration, while a symmetric coin cell devices -1

-1

exhibited a specific capacitance of 240 Fg , maximum energy and power densities of 8.3 Whkg and -1

20 Wkg

with no capacitance loss after 1000 galvanostatic discharge cycles. These results

demonstrate that composites made using 3D graphene are versatile and show considerable promise as electrode materials for electrochemical applications.

References [1]

P. Simon, Y. Gogotsi, Materials for electrochemical capacitors, Nat. Mater. 7 (2008) 845–854.

[2]

Y. Fang, B. Luo, Y. Jia, X. Li, B. Wang, Q. Song, et al., Renewing functionalized graphene as electrodes for high-performance supercapacitors., Adv. Mater. 24 (2012) 6348–55.

[3]

Z. Chen, W. Ren, L. Gao, B. Liu, S. Pei, H. Cheng, Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapour deposition, Nat. Mater. 10 (2011) 424–428.

Figures

Raman spectra of (a) the 3D graphene and (b) composite of 3D graphene and MnO2

Electrochemical performance of the composite electrode material (a) CV and (b) CD

Control of the Optical transmittance in Multilayer Graphene using a bias Voltage J.L. Benítez and D. Mendoza Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México. Apartado Postal 70-360, 04510 México D. F., México. doroteo@unam.mx, jlbentz2@gmail.com The search for new materials, particularly nanomaterials, has been intensively studied in the last two decades. Due to the fascinating physical properties that the family of materials based on carbon present, graphene, a two dimensional crystalline arrangement in the shape of honeycomb, is one of the most studied. The physical properties such as optical, electronic and thermal properties of this material become ideal for a wide range of applications. The optical absorption of graphene at normal incidence is 2.3% in the frequency range from visible to infrared (1). However, the optical absorption of graphene can be controlled by a gate voltage, enabling the construction of electro optical modulators (2). In this work, the modulation of the optical transmittance of the multilayer graphene (MG) through a bias voltage of the form across two coplanar electrodes (3) is studied (see figure 1). The multilayer graphene is synthesized by CVD technique, and later, placed on glass substrates. The experiment consists in passing light through the MG while the sample is biased with an electrical signal at frequency using a function generator ( see figure 1b). For illumination, different laser and white light sources were used. The transmitted light is detected by a photodiode and an electrometer which provides a direct physical measurement of transmittance, it is also important to mention that experiments have been done in reflection mode. The measurements were made in vacuum. One of the results can be seen in figure 2a, the variation of the modulated transmittance respect to the background is small and the values varie from 1% to 5 % depending on the experimental conditions. This was obtained from the numerical Fast Fourier Transform (FFT) (figure 2b) to know the frequencies present in measurement signal. In the Fourier analysis, we found that the fundamental frequency appears and also higher harmonics, in all cases the second harmonic is the most intense. The observed effect appears to be a universal phenomenon because it works with monochromatic and white light, with a DC bias, and in the reflection mode as well. Due to optical conductivity of graphene is a function of temperature, there is a possibility that modulation in optical transmittance in MG is a consequence of Joule effect. The electric field generated by the bias voltage is not discarded either. The observed phenomenon opens the possibility of using this effect in the transmission of information by optical means and for the generation of electrical signals with higher frequencies than that of the excitation signal.

References [1]. R. R. Nair, P. Blake, A. N. Grigorenko, K. S. Novoselov, T. J. Booth, T.Stauber, N. M. R. Peres, and A. K. Geim.,Science 320, (2008)1308 . [2]. Liu Ming, Yin Xiaobo, Ulin-Avila Erick, Geng Baisong, Zentgraf Thomas, Ju Long, Zhang, Feng Wang and Xiang Zhang. Nature 774,(2011) 64. [3]. J.L. Benitez and D. Mendoza, Appl. Phys. Lett. 103, (2013) 083116.

Figures

Figure 1. (a) Schematic of the electrical connections and (b) illustration of the set-up for the experimental measurements.

Figure 2. (a) Transmitted light intensity modulated using an amplitude of 11.2 V and a frequency of , (b) FFT frequency spectrum obtained from the transmittance measurements.

Functionalized Graphene Grown by Oxidative Dehydrogenation Chemistry Laurent S. BERNARD, Massimo Spina, Jacim Jacimovic, Primoz R. Ribic, Arnaud Walter, Daniel Y Oberli, Endre Horvath, László Forró and Arnaud Magrez Laboratory of Physics of Complex Matter, FSB Station 3, 1015 Lausanne, Switzerland laurent.bernard@epfl.ch Abstract We report on a highly efficient growth of graphene using dehydrogenation of acetylene by an oxidative reaction with carbon dioxide. In few seconds, large-area of copper foil used as catalyst of the UHDFWLRQ LV IXOO\ FRYHUHG ZLWK JUDSKHQH 7KH \LHOG RI WKH UHDFWLRQ FDQ EH DV KLJK DV Å 7KLV PHWKRG allows the growth of multilayered graphene with misoriented layer stacking. This could be the result of functional (carboxylic, hydroxyl, epoxy) groups, taking the role of catalytic centers, attached to the surface of the layers. The thickness of graphene is controlled by the growth duration. The presence of the functional groups is useful for further chemical manipulations but they have limited impact on the electrical and optical properties of the graphene films. The as-synthesized bilayer graphene has a 2

-1

mobility of positive charge carriers of 2300 cm /V .s at room temperature. The high quality of the oxidative dehydrogenation product makes this process an attractive alternative to produce high quality graphene by chemical vapor deposition. References Laurent S. Bernard et al, CARBON. Doi number : 10.1016/j.carbon.2013.12.032 This work is supported by the European Commission (FP7, Marie-&XULH ,71 ³1$0$6(1´ . Figures

Figure 1. Raman (a) and UV-Vis (b) spectra of graphene

Figure 2. (a,b) Raman maps of the intensity ratio of the 2D band

materials obtained at various C2H2/CO2 fluxes for 2 min. Raman

to the G band and the D band to the G band, respectively. (c,d)

Raman maps of the FWHM of the 2D band and the G band,

function of the growth duration with a C2H2/CO2 flux of 0.02 l/h.

respectively. (e) Raman spectrum of the blue spot corresponding to a monolayer graphene area. (f) Mean raman spectrum of the 900 spectra recorded to build the maps. (g) Raman spectrum of the green spot corresponding to a defective trilayer graphene area.

Figure 3. (a) Schematic view of the graphene based field effect transistor built for mobility measurement. The channel is a bilayer graphene obtained by ODH. (b) Ids(Vg) characteristics of the transistor (the length and the width equal 50 Âľm) at different V ds (legend in colour). (c) Evolution of holes mobility with the width at a given length (50 Âľm).

Noncovalent functionalization of graphene with large organic molecules 1

Nina C. Berner , Sinead Winters , Claudia Backes , Aoife Ryan , Mathias O. Senge , Georg S. 1 Duesberg 1

CRANN and School of Chemistry, Trinity College Dublin, Dublin 2, Ireland 2 School of Physics, Trinity College Dublin, Dublin 2, Ireland 3 SFI Tetrapyrrole Laboratory and School of Chemistry, Trinity College Dublin, Dublin 2, Ireland nberner@tcd.ie

Since the isolation of single layer graphene by mechanical exfoliation [1] and the subsequent discovery and demonstration of its outstanding electronic and mechanical properties [2], graphene has attracted a very high level of interest. Its exceptionally high charge carrier mobility, combined with its high surface area and biocompatibility, make it a particularly promising material for gas and biomolecular sensing applications [3]. However, the pristine graphene surface is chemically inert and therefore requires further functionalization to enable molecular recognition, i.e. sensor selectivity. Noncovalent functionalization by Ę&#x152;-interactions is an attractive strategy to introduce functional groups on the surface since it does not adversely affect the electronic properties of the graphene backbone [4]. With the goal of identifying the most suitable organic molecular compound for the fabrication of graphene-based biosensing devices, we investigated the wet-chemical deposition and adsorption characteristics of several different perylene bisimide and porphyrin compounds on large-area chemical vapor deposition (CVD) grown graphene. We further demonstrate the subsequent bioconjugate functionalization of some of those organic molecular thin films for the application in a quintessential selective biosensing device. References [1] Novoselov, K. S. et al., Science 306 (2004) 666 [2] Geim, A. K., Novoselov, K. S., Nature Mat. 6 (2007) 183 [3] Shao, Y. et al., Electroanalysis 22 (2010) 1027 [4] Mann, J. A., Dichtel, W. R., Phys. Chem. Lett. 4 (2013) 2649

Figure: (a) Schematic of the noncovalent functionalization of graphene with an example of a large organic molecule, (b) Raman spectra of several different large organic molecules adsorbed on CVD graphene.

THz saturable absorption in graphene (1)

Federica Bianco,

(1)

Ji-Hua Xu,

(1)

Fabrizio Castellano, Miriam S. Vitiello, (2) Harvey E. Beere, David A. Ritchie, (3) (3) Vaidotas Miseikis, Camilla Coletti

(2)

(1)

Alessandro Tredicucci,

(1)

NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, P.za S. Silvestro 12, 56127 Pisa (Italy) (2) Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom) (3) CNI@NEST, Istituto Italiano di Tecnologia, P.za S. Silvestro 12, 56127 Pisa (Italy) federica.bianco@nano.cnr.it Abstract Since the first graphene monolayer device reported by Novolosev et al. in 2004 [1], the number of applications of graphene enormously increased, both in photonics and electronics [2]. This extraordinary rise of graphene-based devices can be attributed to its unique electronic and optical properties that make graphene a remarkable material. Thanks to its characteristic linear Dirac-like band structure, graphene possesses a huge (2.3% per single atomic layer), flat, wavelength independent linear optical absorption in a broad range of frequencies [3] and an extremely high third-order nonlinear response [4-6]. The combination of such properties with the fast carrier dynamics [7] enables the use of graphene as ultrafast broadband saturable absorber. In fact, once a strong incident light exceeds an intensity threshold, the photogenerated carriers block further absorption (Pauli blocking principle) causing an increase of the material transparency. The bleaching of the absorption with relatively low intensity threshold and its broadband spectral range makes graphene competitive against the commonly used semiconductor saturable absorber mirrors [8] in ultrafast pulsed laser fabrication. Graphene-based mode-locked lasers have been successfully demonstrated at 800 nm [9], in the near infrared [10-14] and at 2500 nm [15]. Interestingly, theoretical studies have predicted further stronger nonlinearity of graphene in the microwave [16] and THz regions [17]. This opens the possibility of novel THz lasers (e.g. graphenemode-locked THz quantum cascade laser), as well as of detection and amplification in graphene devices [18]. Currently, graphene saturable absorption has been studied in the microwave range [19], but no experimental data have been reported in THz regime yet. In this work we show experimental results on the saturable absorption properties of graphene in the THz regime. The samples are graphene layers grown on the carbon-face of silicon carbide substrates with approximately 25 (sample 1) and 90 layers (sample 2 and sample 3, fabricated with two different recipes). Raman characterization (Fig. 1.a,b,c) shows a mainly single lorentzian shape of the 2D peak indicating loosely stacked layers. The presence of defects-induced D peak is expected to influence the nonsaturable component of the graphene absorption. The non-linear properties of the samples are investigated by open-aperture z-scan technique. A laser beam, emitted at 2.9 THz by a quantum cascade laser operating in pulsed regime (15% duty cycle, corresponding to 300 kHz frequency and 500 ns pulse width) and modulated at 4 Hz by a square function (50% duty cycle), is focalized with a beam waist of about 170 µm onto the sample. The transmitted beam is detected by thin film-based single element thermopile detector (2M from Dexter) for several positions of the sample along the optical axis. The normalized z-scan trace is then analyzed by assuming the simple two levels saturable absorber model and taking into account the temporal shape of the pulses train:

T ( z) =

1 (1 − α NS − T0

αs I ( z) 1+ 0 Is

)

(1)

where T0 is the transmission in linear regime, αNS and αs are the non-saturable and saturable components of the absorption, respectively. I0 is the beam intensity along the optical axis and Is is the saturation intensity threshold, i.e. the intensity value at which the saturable absorption is reduced to 1/2. In all the samples the experiments show an increase of the transmission, as shown in Fig. 1.d,e. This corresponds to about 4% in sample 1 and 10% in samples 2 and 3. The saturation intensity is estimated 2 to be tens of W/cm , that is 4 orders of magnitude lower than that in the telecommunication window [10], as expected from the much lower density of states in the THz. Unlike the shorter wavelengths region, where the non-saturable component is strongly influenced by the number of the layers, here the saturation of the absorption appears to be mainly influenced by the amount of defects in the graphene.

References [1] K.S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva and A. A. Firsov, Science, 306 (2004) 666-669. [2] F. Bonaccorso, Z. Sun, T. Hasan and A. C. Ferrari, Nature Photonic, 4 (9) (2010) 611-622. [3] R. R. Nair, P. Blake, A. N. Grigorenko, K. S. Novoselov, T. J. Booth, T. Stauber, N. M. R. Peres and A. K. Geim, Science, 320 (2008) 1308. [4] H. Zhang, S. Virally, Q. Bao, L. K. Ping, S. Massar, N. Godbout and P. Kockaert, Optics Letters 37 (2012) 1856-1858. [5] H. Yang, X. Feng, Q. Wang, H. Huang, W. Chen, A.T. S. Wee and W. Ji, Nano Lett. 11 (2011) 26222627. [6] E. Hendry, P. J. Hale, J. Moger, A. K. Savchenko and S. A. Mikhailov, Phys. Rev. Letter 105 (2010) 097401. [7] F. T. Vasko, Phys. Rev. B 82 (2010) 245422. [8] U. Keller, Nature 424 (2003) 831-838. [9] I. H. Baek, H. W. Lee, S. Bae, B. H. Hong, Y. H. Ahn, D. I. Yeom and F. Rotermund, Appl. Phys. Express 5 (3) (2012) 032701. [10] Q. L. Bao, H. Zhang, Y. Wang, Z. H. Ni, Z. X. Shen, K. P. Loh and D. Y. Tang, Adv. Funct. Mater. 19 (19) (2009) 3077-3083. [11] Q. Bao, H. Zhang, Z. Ni, Y. Wang, L. Polavarapu, Z. Shen, Q.-H. Xu, D. Tang and K. P. Loh, Nano Res. 4 (3) (2011) 297-307. [12] P. L. Huang, S.-C. Lin, C.-Y. Yeh, H.-H. Kuo, S.-H. Huang, G.-R. Lin, L.-J. Li, C.-Y. Su and W.-H. Cheng, Opt. Express 20 (3) (2012) 2460-2465. [13] Z. Sun, T. Hasan, F. Torrisi, D. Popa, G. Privitera, F. Wang, F. Bonaccorso, D. M. Basko and A. C. Ferrari, ACS Nano 4 (2) (2010) 803-810. [14] Z. Sun, D. Popa, T. Hasan, F. Torrisi, F. Wang, E. J. R. Kelleher, J. C. Travers, V. Nicolosi and A. C. Ferrari, Nano Res. 3 (9) (2010) 653-660. [15] M. N. Cizmeciyan, J. W. Kim, S. Bae, B. H. Hong, F. Rotermund, and A. Sennaroglu, Opt. Lett. 38 (3) (2013) 341-343. [16] S.A. Mikhailov and K. Ziegler, J. Phys. Condens. Matter 20 (2008) 384204. [17] K. Yang, S. Arezoomandan and B. Sensale-Rodriguez, Terahertz Science and Technology 6 (4) (2013) 223-233. [18] A. Tredicucci and M. S. Vitiello, Selected Topics in Quantum Electronics, IEEE Journal of, 20 (1) (2014) 130-138. [19] Z. Zheng, C. Zhao, S. Lu, Y. Chen, Y. Li, H. Zhang and S. Wen, Opt. Express 20 (2012) 2320123214. Figures

Figure 1: a, b, c) Raman spectra of the sample 1, 2, 3, respectively; d, e) z-scan traces of the sample 1 2 and 3 with a pump beam at 2.9 THz and intensity at the focal point of about 223 mW/cm , respectively. The red line is the fitting curve based on Eq. (1).

One-pot reduction and diazonium functionalization of graphene oxide a

Charles AgnĂ¨s , Florence Duclairoir , Lionel Dubois , GĂŠrard Bidan a

Univ. Grenoble Alpes, CEA, INAC, Laboratoire de Chimie Inorganique et Biologique, UMR-E3 CEAb UJF, INAC/DIR, F-38054, Grenoble, cedex 9, France. gerard.bidan@cea.fr The expectations around graphene come from huge potentialities for various applications (RF WUDQVLVWRU ELR VHQVRUVÂŤ Graphene high specific surface, mechanical resistance and conductivity make it specifically attractive for energy related applications [1]. Its interfacing with various compounds has been shown to make it more processable, to tune its electrical/optical properties and to create functional materials [2]. In this presentation, the fabrication of graphene using the chemical exfoliation route consisting on the oxidation of graphite followed by its reduction will be presented. A wide range of reduction techniques have been described in the literature and the laboratory uses mainly chemical reducing agent (hydrazine, Fe and SnCl2 Âą [3]). The oxidation/reduction confirmation and extent are assessed thanks to XRD, XPS, TGA characterization. In turn the exfoliation degree can be identified by specific surface area determination as well as by microscopic analyses (SEM, TEM). The rGO obtained displays a large surface area (Fig. 1) and its degree of exfoliation is important. These graphene derivatives have all been modified by diazonium functionalizationÂą aiming at passivating the graphene surface with carboxylic acid functions and decreasing its hydrophobicity. Diazonium chemistry on chemically exfoliated graphene is more often performed on rGO as this reaction is known to proceed in presence of a reducing agent which is the role played by rGO in the reaction. However rGO is more complicated to disperse than GO. The idea presented here is to functionalize GO by diazonium chemistry in presence of Fe to reduce GO into rGO and initiate the diazonium grafting at the same time. Based on XPS, TGA and BET results, the interest of such ÂłRQHSRW UHGXFWLRQ IXQFWLRQDOL]DWLRQÂ´ will be highlighted. The use of such chemistry to introduce molecular entities chosen to target the formation of a graphene framework will also be presented. These specific compounds have been chosen as to possess two anchoring sites. The idea is to develop a graphene matrix held together by these molecular pillars. Different pillar lengths and number of equivalents have been tested. The characterization of these matrices will be discussed. References [1] S. Yang, R. E. Bachman, X. Feng and K. MĂźllen, Acc. Chem. Res., 46 (2013) 116. [2] T. Kuila, S. Bose, A. K. Mishra, P. Khanra, N. H. Kim and J. H. Lee, Prog. Mat. Sci., 57 (2012) 1061. [3] N. A. Kumar, S. Gambarelli, F. Duclairoir, G. Bidan and L. Dubois, J. Mater. Chem. A, 1 (2013) 2789.

Fig. 1: SEM (left) and TEM (right) images of rGO

Testing the index theorem for graphene and C60 molecules Manon Bischoff, Barbara Dietz-Pilatus, Tobias Klaus, Maksym Miski-Oglu, Achim Richter, Dominik Smith, Lorenz von Smekal Theoriezentrum, Institut fur ¨ Kernphysik, TU Darmstadt, Schloßgartenstraße 2, 64289 Darmstadt, Germany manon@theorie.ikp.physik.tu-darmstadt.de Abstract To introduce a positive Gaussian curvature into a planar sheet of graphene, one cuts a segment with opening angle π/3 from the hexagonal lattice and attaches the open ends to one another. This amounts to introducing a single pentagon into the lattice which acts as a topological defect. To obtain a fullerene C60 molecule, one needs to introduce 12 pentagons. Mathematically, the curvature can be described by two gauge fields: One gauge field is used to describe the curved topology, which can be represented by magnetic monopoles, and the other gauge field is used to describe the mixing of the two sublattices. The topological index of the Dirac operator on the curved manifold can then be calculated using the Euler characteristic of the manifold. The analytical index of the Dirac operator is the difference of the number of its zero energy states at the two Fermi points. The Atiyah-Singer index theorem gives a connection between the topological index and the analytical index: It states that they are the same [1]. We propose to test the index theorem, using experimental results obtained from microwave billiards. Planar graphene has been simulated successfully with a microwave billard in Refs. [2, 3]. The plan is to apply a similar methodology to the case of a C60 fullerene molecule. The billard, in this case, is a microwave resonator whose cavity has the form of the 60 carbon atoms. In collaboration we will analyze the excitation spectrum of the fullerene molecule and verify that the index theorem is fulfilled in these experiments. References [1] J. K. Pachos and M. Stone, “An Index Theorem for Graphene,” Int. J. Mod. Phys. B21:5113-5120 (2007), arxiv:cond-mat/0607394 [2] B. Dietz, M. Miski-Oglu, N. Pietralla, A. Richter, L. von Smekal, J. Wambach and F. Iachello, “Lifshitz and Excited State Quantum Phase Transitions in Microwave Dirac Billiards,” Phys. Rev. B 88, 104101 (2013) arXiv:1304.4764 [cond-mat.mes-hall]. [3] S. Bittner, B. Dietz, M. Miski-Oglu, and A. Richter, “Extremal transmission through a microwave photonic crystal and the observation of edge states in a rectangular Dirac billiard,” Phys. Rev. B 85, 064301 (2012)

Dispersible composite of exfoliated graphite and polyaniline with improved electrochemical activity for sensor applications 1,2

Zhanna A. Boeva , Konstantin A. Milakin , Markus Pesonen , Aleksandr N. Ozerin , Vladimir G. 2 1 Sergeyev and Tom Lindfors 1

Åbo Akademi University, Process Chemistry Centre, Department of Chemical Engineering, Laboratory of Analytical Chemistry, Biskopsgatan 8, Turku/Åbo, Finland 2 Polymer Division, Chemistry Department, M.V. Lomonosov Moscow State University, Leninskie gory 1, build. 3, Moscow, Russian Federation 3 Åbo Akademi University, Department of Natural Sciences and Center for Functional Materials, Physics, Porthansgatan 3, Turku/Åbo, Finland 4 Institute of Synthetic Polymeric Materials, Russian Academy of Sciences, 70, Profsoyuznaya street, Moscow, Russian Federation. jboyeva@gmail.com The combination of conducting polymers with carbon materials possesses a fabrication of new composite materials having physic-chemical properties arising from the both components. Due to similar nature of the conjugation structures of carbon materials and conducting polymers some of these properties can be enhanced due to synergetic effect occurs in the composites. Polyaniline (PANI) is one of the most studied intrinsically conducting polymers with excellent environmental stability, good electrical conductivity and the possibility of chemical modification.

In this work, we report the synthesis of a dispersible composite material consisting of PANI and the exfoliated graphite platelets of either the graphite or the graphene grade (Figure 1). The properties of the composite material - such as solubility - are mostly determined by PANI and the FTIR and Raman spectra are dominated by the conducting polymer bands.

Cyclic voltammetry (CV) with the use of the ruthenium and iron couples (pH 9.5 and pH 7.8, respectively) has shown that the composite materials are electroactive at alkaline pH in contrast to conventional PANI prepared without graphene or graphite. This indicates that the graphene/graphite platelets form electrically conducting network within the PANI matrix (Figure 2).

This composite material is readily dispersible in N-methylpyrrolidone and it can be therefore casted or printed onto a substrate or an electrode and further used as an ion-to-electron transducer in solidcontact ion-selective electrodes or as an indicator electrode for the detection of biological molecules. We show that the incorporation of graphene or graphite platelets in the composite materials improved the electroactivity of the PANI-graphene/graphite composites at pH 10 in contact with aqueous electrolyte solutions. The CVs revealed also that the voltammetric current response of the composite materials was three times higher than for conventional PANI in ascorbic acid solutions (Figure 3).

Figures 4

4x10

exfoliated graphite few-layered graphene

I, relative units

3x10

2x10

1x10

0 10

Scattering angle, Figure 1. XRD pattern of the exfoliated graphite of the graphite and the few-layered graphene grades

PANI PANI-graphene PANI-graphite Glassy carbon

j / uA cm

-40

-80 -0.6

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E/V Figure 2. The cyclic voltammograms of the conventional PANI, PANI-graphene and PANI-graphite films casted onto glassy carbon electrode (GCE), and the bare GCE in 1 mM [Ru(NH3)6]Cl2 with 0.1 M KNO3 as the background electrolyte at pH 9; Reference electrode: Ag/AgCl; Counter electrode: GCE; Scan rate: 50 mV/s

pH 0

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PANI PANI-graphene PANI-graphite

-20 -30 -0.2

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PANI PANI-graphene PANI-graphite

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Figure 3. The cyclic voltammograms of the conventional PANI, PANI-graphene and PANI-graphite films at different pH. Reference electrode: Ag/AgCl; Counter electrode: GCE; Substrate: SnO2-glass with 15 nm layer of Pt. Scan rate: 50 mV/s

Pre-Patterned CVD Graphene: Influence of ALD deposition parameters on Al 2O3 and graphene layers 1,2

Gabriela Borin Barin , Ledjane Silva Barreto , Jing Kong

Materials Science and Engineering Department, Federal University of Sergipe, Marechal Rondon, ave. São Cristóvão, Sergipe 49000-100, Brazil 2 Department of Electrical Engineering and Computer Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States gabriela.borin@gmail.com

Abstract Fabrication of graphene nanostructures is of importance for both investigating their intrinsic physical properties and applying them into various functional devices. Our group has been developing studies on direct synthesis of graphene from an area-selectively passivated catalyst substrate in order to generate patterned graphene of high quality. Here we present a further study on this subject focusing on ALD deposition of Al2O3 to produce patterned graphene through area-selective CVD growth. We present the influence of number of cycles and purging time on Al2O3 deposition uniformity and graphene quality. The deposited Al2O3 films and the graphene layers are investigated in terms of morphology and electrical properties. It was obtained an optimized condition, in which was possible to prepare uniform Al2O3 layers with negligible mobility, and defect-free graphene with sheet resistance around 320 ohm/square. Introduction Pre-patterned graphene could potentially produce higher quality graphene devices since the patterning step is carried out before the graphene is synthesized and the risk of contamination is minimized [1,2]. We here use ALD to generate patterned graphene through area-selective CVD growth. The method relies on the passivation of defined areas of copper foil and the subsequent selective growth of graphene in the unpassivated regions. Our group already developed works on this subject, in order to obtain high quality patterned graphene with low cost and high resolution. Hoffman et al reported the possibility of barrier guided CVD generates high quality graphene on pre- patterned substrates, and thus open up the possibility to efficiently produce interconnects for a wide application [3]. Thus, this present work focuses on a further study on pre-patterned graphene, centering on the influence of ALD deposition parameters on graphene and passivation layers quality. Experimental Procedure In order to protect selected areas of the copper foil during Al 2O3 deposition was used a PMMA mask. The pattern was draw using a shadow mask and a brush. The deposition of Al2O3 was carried out using a homebuilt ALD system. In each cycle trimethylaluminum and water were released for 15ms. As a purge gas was used nitrogen and the temperature during the deposition was 150ͼC. It was used 120 and 200 cycles and 30 sec and 45 sec of purging time. After the deposition the PMMA mask was dissolved in acetone with sonication for 2 hours. Graphene growth was carried out in a LPCVD furnace at 1000 ϶C for 30 minutes flowing 50 sccm of hydrogen and 20 sccm of methane. Graphene transfer was carried out using wet transfer technique. Results and Discussion Increasing the purging time from 30 seconds to 45 seconds it seems to influence both graphene and Al2O3 quality. It is known that increasing the purging time in the same number of cycles it is possible to remove non-reacted reactants much more efficiently. AFM phase images of graphene showed that the graphene grown after the deposition with 30 seconds of purge contain more impurities than the graphene grown after the deposition with 45 seconds. The PMMA mask did not protected the cooper foil efficiently when more reactants are present in the chamber. It was observed the presence of two phases on 1(a) while on 1(d) we can observe a smooth graphene surface free of impurities. Increasing the number of cycles and purging time it was possible to obtain better uniformity of Al2O3 layers, the best result was achieved with 200 cycles and 45 sec of purge, showed by optical microscopy in figure 2. Insert Figure 1 and 2

Comparing the sheet resistance of the graphene layers and the passivation layer in which condition, it was observed that the best result for the graphene layer was 328 ohm/square while the worst was found around 2927 ohm/square. Regarding the sheet resistance of the passivation layer all the conditions 2 presented values greater than 1000 ohm/square, with electrical mobility ranging between 19-60 (cm /(V s), but on the deposition condition of 120cycles/45 seconds which was not found any mobility. This behavior can allow the direct integration of resistive elements in graphene circuits during growth, since the passivation layer is isolating graphene areas from one another. Insert Figure 3

Conclusion In this work the influence of parameters of ALD deposition of Al2O3 on pre-patterned graphene was reported. The best results were obtained using 200 cycles and 45 seconds of purge, with an uniform Al2O3 layer with negligible mobility, and defect-free graphene with sheet resistance around 320 ohm/square. References [1] Safron,N.S.; Kim, M.; Gopalan, P.; Arnold, M.S.. Adv. Mater, v. 24 (2012) p. 1041-1045. [2] Kim, K.S.; Zhao, Y.; Jang, H.; Yoon, S.; Kim, J.; Kim, K.; Ahn, J.;Kim, P.; Choi, J.; Hong, B.; Nature, v. 457 (2009), p. 706-710. [3] Hofmann, M. Hsieh, Y-P, Hsu, A.L., Kong, J., Nanoscale, v. 6 (2014), p. 289-292. Figures

(b)

(a)

(c)

(d)

Figure1:. AFM images of graphene layer grown after the Al2O3 deposition with: (a)120 cycles with 30 seconds purge, (b) 120 cycles with 45 seconds of purge, (c) 200 cycles with 30 seconds purge, (d)200 cycles with 45 seconds purge.

(a)

(b) (a)

(c)

(d)

(b)

Figure2: Optical images of Al2O3 layers deposited with different conditions (a) 120 cycles with 30 seconds of purge, (b) 120 cycles with 45 seconds of purge, (c) 200 cycles with 30 seconds of purge, (d) 200 cycles with 45 seconds of purge

Al2O3 layer

Mobility (cm /(V s)

120/30

120/45

200/30

200/45

Figure 3. Electrical properties of graphene and Al2O3 passivation layer

Multiple Use of High Purity Copper Foils as Catalyst Substrates for Graphene Growth G.M. Junior1, P. Alpuim1,2, M.F. Cerqueira2, J. Borme1 1INL

± International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga, Braga, Portugal ± Centre of Physics of the University of Minho, Campus de Gualtar, Braga, Portugal Jerome.Borme@inl.int

2CFUM

Abstract Graphene is a new material with unique properties, discovered in 2004 by Nobel Prize for Physics A. Geim and K. Novoselov, that has a high potential for high-tech applications. However, the use of the material on an industrial scale requires its manufacture over large areas without loss of its superlative electronic properties, like those observed in graphene obtained by exfoliation of graphite at a small scale. One of the most promising techniques for large area fabrication (hundreds of square centimeters or even square meters) of graphene is by hot wall chemical vapor deposition assisted by a metal catalyst [1,2]. Among the possible CVD catalysts copper has distinct advantages over other transition metals because it is abundant and, not least, carbon is practically insoluble in it, which makes the growth of atomic monolayer graphene (SLG) on a copper surface self-limited [3]. In the case of transition metal catalysts with high solubility of carbon, severe segregation of C atoms to the inner surface of the metal occurs during cooling, originating multiple layers of graphene (MLG) [1] instead of SLG that readily forms on copper. In order to lower costs, large-area deposition of graphene on copper foil would gain a lot if it were possible to recover and reuse the copper sheet in successive depositions. One way to meet this goal is the use of an electrolytic technique for separating the graphene sheet (covered by a temporary polymeric substrate, PMMA) from its native Cu substrate [4]. Using the graphene covered Cu sheet as a cathode in an electrolytic bath containing a dilute solution of potassium sulfate or persulfate, leads to the release of the graphene sheet / PMMA from the Cu surface due to hydrogen bubbling at the Cu / graphene interface as a result of water electrolysis. Before being reusable, however, it is necessary to recover the copper surface since Cu oxides that form during electrolysis have a melting temperature above the graphene growth temperature on Cu catalyst. Two processes for cleaning the Cu surface were studied: a microwave oxygen plasma step for removing any residual PMMA, followed by removal of oxides, nitrides and other copper compounds possibly formed during the growth and transfer steps, by the use of an aqueous bath of hydrochloric acid or acetic acid; or direct immersion of the used Cu substrates in one of these acids. Cu is finally DQQHDOHG DW § C in a reducing atmosphere of hydrogen and argon before it can be reused as catalyst in a new CVD process run of graphene. This work studies the chemical surface contamination of pure copper (fresh Cu sheets with purity of 99.999 %) after growth and removal of graphene and its evolution after each cleaning and/or annealing step. The results of the chemical analysis are interpreted taking into account the observations obtained by SEM images of the sample surface after each step of the treatment. The structure of the subsequent graphene layers deposited on the recovered Cu substrates is then compared, using Raman spectroscopy. For each of the above mentioned cleaning routes samples were collected after successive immersion times, were studied and compared. Figure 1 shows the evolution of surface morphology after 7, 20 and 30 min of immersion in HCl (2%wt). In this series, samples were not exposed to O2 plasma before entering the acidic bath. It can be seen that Cu compounds are progressively dissolved with immersion time in HCl. The insert suggests the presence of cubic Cu(I) oxide. Figure 2 shows the evolution of the Cu surface during cleaning in AcOH for 1, 6 and 18.5 hours. The insert shows that, after 6 hours of immersion, there were still cubic crystallites present on the surface although they disappeared after 18.5 hours of annealing. The evolution of the Cu surface took place in a much longer time scale using AcOH cleaning than using HCl. Figure 3 shows the Raman spectra of two samples immediately after transfer from native Cu recycled foils using PMMA temporary substrates. The CVD process was done at 1020 °C using methane and hydrogen for graphene growth. The recycled substrates were placed side by side in the reactor center zone. It can be seen that in a) the graphene 2D peak (Raman shift = 2695 cm -1) is absent while in b) it is prominent and fitted to a single Gaussian with FWHM = 35 cm -1 which is proof of the presence of singlelayer graphene (SLG) [5]. Most of other prominent peaks in the figure are attributable to the PMMA that covers the surface. Fig.3-a) corresponds to the cleaning procedure shown in Fig.1 whereas fig.3-b) corresponds to the cleaning procedure using AcOH shown in Fig.2. In order to reach a definite conclusion about the quality of the cleaning procedures statistics is needed for all cleaning routes. This will be the next step in this work.

References [1] K. S. Kim, Y. Zhao, H. Jang, S. Y. Lee, J. M. Kim, K. S. Kim, J.-H. Ahn, P. Kim, J.-Y. Choi and B. H. Hong, Nature, 457 (2009) 706. [2] X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, L. Colombo, and R. S. Ruoff, Science, 324 (2009) 1312. [3] X. Li, W. Cai, L. Colombo and R. S. Ruoff, Nano Lett., 9 (2009) 4268. [4] Y. Wang, Y. Zheng, X. Xu, E. Dubuisson, Q. Bao, J. Lu, and K. P. Loh, ACSNano, 5 (12) (2011) 9927. [5] A.C. Ferrari, D.M. Basko, Nature Nanotechnology, 8 (2013) 235. Figures

Fig.1 ± Cu surface morphology after 7, 20 and 30 min of immersion in HCl. Insert is a high magnification (300k x) micrograph of the first image, showing the cubic symmetry of the crystallites covering the surface.

Fig.2 ± Cu surface morphology after 1, 6 and 18.5 hours of immersion in acetic acid. Insert is a high magnification (50k x) micrograph of the second image, showing the cubic symmetry of the crystallites covering the surface.

Fig.3 ± Raman spectra of samples after transfer from native Cu recycled catalyst onto Si/SiO2 substrate. a) corresponds to the cleaning procedure shown in Fig.1 whereas b) corresponds to the cleaning procedure using AcOH shown in Fig.2. In a) the graphene 2D peak (at 2695 cm-1) is absent while in b) it is prominent and fitted to a single Gaussian with FWHM = 35 cm-1.

Method for electrical evaluation of graphene using a GFET structure Alberto Boscá, Thorben Casper, Jorge Pedrós, Javier Martínez, Fernando Calle. Instituto de Sistemas Optoelectrónicos y Microtecnología, UPM, E.T.S.I. de Telecomunicación, Av. Complutense 30, Madrid, Spain alberto.bosca@upm.es Abstract In this work, we explain a method to characterize graphene using electrical measurements in graphene field-effect transistors (GFET) devices. Our goal is to obtain the material electronic properties from the output characteristics of one GFET device. For the previous purpose, we will need to apply a physical model that allows us to correlate the electronic behavior of a GFET with the material properties. There are several models used for graphene. Some of them are based strongly on solid state physics [1], [2], including even quantum effects at high magnetic fields. Others are more focused on FET devices [3]. The model used in this work is based on first principles and is described thoroughly in [4]. The main advantage of this model is that most of the equations are directly derived from the energymomentum dispersion relation from graphene, so it is straightforward to obtain the carrier concentration and the current in terms of the gate voltage (Vg) of the transistor, and even local characteristics along the channel. Also, the temperature is an explicit parameter on the equations, and the shifts in the Dirac point are explained with a fixed surface charge. With this model we are able to obtain a quick characterization of the material electrical properties from just a transistor structure (Fig. 1). The fitting to this model is done by using the measured IDS vs. VG curves of a real device. All the relevant parameters, such as the oxide capacitance (Cox), voltage applied (VDS), gate metal work function, gate length (Lg), and width (w), among others must be introduced in the model. For fitting the experimental measurements into the model, we work with the transconductance (gm), in order to extract some fundamental values from the shape, such as the maximum and minimum transconductance, the Dirac point, or the curve slope in several voltage ranges, as detailed in Fig.2. Using these parameters from real data, we use the model to obtain the electron and hole mobilities, the total serial resistance and the total density of fixed charge. We have used different measurements from previous publications, like suspended devices [5] (see Fig. 3), and CVD graphene transistors [3] (see Fig. 4). We have also achieved a better fit to the experimental data using a mobility distribution that depends on the carrier concentration [6]. In Fig. 5 we show that with this addition to the initial model, the fit to our CVD- graphene devices is optimized. Acknowledgements This work was supported by the Ministerio de Economía y Competitividad, projects TEC 2010-19511 Readi and CSD 2009-00046 RUE. References [1] K.S. Novoselov, A.K. Geim et al., Nature, 438 (2005) 197. [2] S. Adam, E. Hwang et al., PNAS, 104 (2007) 18392. [3] H. Wang, A. Hsu et al., IEEE Transactions on Electron Devices, 58 (2011) 1523 . [4] J. Champlain, Journal of Applied Physics, 109 (2011) 084515. [5] K. Bolotin, K. Sikes et al., Physical Review Letters, 101 (2008) 1. [6] Y. Zhang, Y. Tan et. al., Nature, 438 (2005) 201.

Figures

Fig. 1: Sample with CVD-graphene transistor devices used for batch-fitting to the model.

Fig. 3: Fit for a suspended graphene device in [5] at low temperature.

Fig. 2: Relevant parameters obtained from real data transconductance.

Fig. 4: Model applied to a CVD graphene transistor from reference [3].

Fig. 5: Comparison between the experimental and simulated a) IDS vs. VGS and b) gm vs. VGS curves.

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Adsorption and STM characterization of polycyclic aromatic hydrocarbons on graphite/graphene Y. Dappe [1], M. Andersen [2], R. Balog [2], X. Bouju [3] [1] CEA Saclay, IRAMIS, SPEC/SPCSI, B창t. 462, F-91191 Gif sur Yvette Cedex, France [2] Interdisciplinary Nanoscience Center and Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark [3] CEMES-CNRS, 29 rue Jeanne Marvig, BP 94347, F-31055 Toulouse Cedex, France xavier.bouju@cemes.fr

Polycyclic aromatic hydrocarbons (PAH) molecules such as benzene, coronene or hexabenzocoronene (HBC) constitute building blocks for more complex molecules. The use of PAH as molecular skeletons in combination with chemical functionalization leads to molecule of high interest for molecular electronics for example. Consequently, the study of these building blocks and their interaction with metallic surfaces or graphitic materials is of fundamental importance. The characterization of their structural and electronic properties is a prerequisite for more complex studies like electronic transport. In that manner, this work is focused on these two aspects, using Density Functional Theory (DFT) for structural aspects, and Scanning Tunneling Microscopy (STM) image calculations for the characterization. In addition, since the interaction between these molecules and graphene is dominated by weak and van der Waals interactions, this constitutes also a model system for the study of dispersion interactions. Even though several approaches have been elaborated recently, these interactions remain complicated to handle, especially at the microscopic level. This is mainly due to the long-range character of the noncovalent bonding, in opposition with the short-range character of ab initio methods. Here our purpose is, following an intermolecular perturbation theory combined with DFT [1], to determine accurately the structural properties of PAH adsorbed on graphene. Then, starting from the adsorption geometries of benzene, coronene, and hexabenzocoronene on a graphene layer, we have calculated STM images in order to compare with experimental results. As the diffusion barrier of studied PAH molecules is relatively weak, we explore the influence of the tip on the imaging process. We show that, according to the tip-sample distance, the probe induces a displacement of the molecule when it is scanned above the substrate. We thus determine the conditions for an efficient threshold.

References [1] Y. J. Dappe, M. A. Basanta, F. Flores, J. Ortega, Phys. Rev. B 74 (2006) 205434. Y. J. Dappe, J. Ortega, F. Flores, Phys. Rev. B 79 (2009) 165409.

Figure

STM image calculations of benzene (a,b) coronene (c) and hexabenzocoronene on graphite.

Graphene On Press Louise Brooks, Senior Associate Vorbeck Materials 8306 Patuxent Range Road, Jessup, MD USA louise,.brooks@vorbeck.com Abstract Vorbeck Materials Corp. is a recognized leader in the manufacture of graphene and commercialization of technologies using Vor-x®, Vorbeck's patented graphene material developed at Princeton University. In 2009, 9RUEHFN ODXQFKHG WKH ZRUOG¶V ILUVW FRPPHUFLDO JUDSKHQH SURGXFW ZLWK 9RU-LQN FRQGXctive inks, which harness the exceptional conductivity of graphene into highly cost-effective, ultra-flexible and robust inks and coatings for printed electronics. We will discuss the latest advancements in Vor-x and Vor-ink and their applications including: - products already in a retail environment - expanded applications in sensors, heaters, and wearable electronics - advanced elastomers and energy-storage applications

Effects of using 2D-material buffer layer on the wire bonding graphene based devices Nirushan Udayakumar, Apratim Chakraborty, Mehrdad Irannejad, Andrew Brzezinski, Mustafa Yavuz Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, ON, N2L 3G1, Canada mehrdad.irannejad@uwaterloo.ca Abstract As the size of transistors and electronic devices decrease, the packaging of these components becomes a challenge and nano-wire bonding is one of the main challenges that with packaging of such devices. A challenge that is faced with wire bonding is the stress delivered to the bond pad during the bonding process. This stress can cause mechanical damage or deformation to the pad [1] and entire structure. The impact of this stress can be measured by monitoring the displacement of the structures within the device. In this work, the effects of wire bonding of various sizes and materials using different bonding methods were investigated numerically using technique of finite element analysis (FEA) and optimum parameters were acquired to achieve the minimum mechanical stress. The effects of the stress to the bond pad and subsequent layers were analyzed by incorporating a graphene monolayer on top of the silicon substrate. Figure 1 shows a schematic numerical layout which a wire being bonded to the top of 150 nm thick gold pad. The subsequent layers under the metal pad are graphene, MoS2 as buffer layer and a silicon substrate. The effects of adding the graphene and MoS2 layer were studied and displacement surface plot of different structures are shown in figure 2. From this figure, a 2-dimensional profile, it can be seen that the magnitude of displacement in the structure is decreased by adding the graphene layer. Further reduction was also observed on adding the MoS2 layer, which can be attributed to increases of mechanical strength and flexibility [2]. The size of the wire was also varied from 8 microns to 20 microns. It was determined that the largest size, 20 microns, caused the smallest amount of displacement and stress in the structure. This is most likely attributed to the same amount of force and stress being distributed over a larger surface area. Aluminum and copper wires are materials that are commonly used in wire bonding [3]. Using FEA, it was determined that copper resulted in a lower displacement and stress distribution when compared to an aluminum one. Figure 3 shows the displacement in the z-direction as the graphene and the MoS2 layers were added into the structure. As can be seen from this figure, displacement was decreased through the layers as the graphene and MoS2 layers were incorporated. Figure (3b) shows the effects of using graphene on the displacement reduction in the structure, while in Figure (3c), the effects of using MoS2 buffer layer, on the displacement absorption were reported as appearance of a peak in the displacement profile at z=20 nm.

References [1] Qin, I et al., Microelectronics Reliability, 1 (2011) 60-66. [2] Pu et al., Nano Letters, 12 (2012) 4013-4017 [3] Murali et al., J Materials Science, 42 (2007) 615-623

Figures

Figure 1:The schematic structure of graphene multilayer (1.5 nm thickness) on a silicon substrate, with a layer of 20 nm MoS2 between the two as a buffer layer, with a gold contact pad (150 nm thickness) on top of the graphene to perform the bonding with a 20 micron copper wire.

Figure 2 : Displacement distribution (Âľm) in (a) the substrate with gold pad, (b) graphene layer added between substrate and gold pad and (c) using MoS2 buffer layer between substrate and graphene. a)

Figure 3: The displacement versus height of structure to show the amount of displacement occurring in each layer from the top of the substrate to the top of the gold film. (a) Substrate with gold pad, (b) added substrate-graphene layerâ&#x20AC;&#x201C;gold and (c) using MoS2 buffer layer between substrate and graphene.

Analysis of optical properties of symmetric graphene quantum dots 3DZHรก %XJDMQ\ 3DZHรก 3RWDV] $UNDGLXV] :yMV :URFรกDZ 8QLYHUVLW\ RI 7HFKQRORJ\ :\EU]HฤชH :\VSLDฤ VNLHJR :URFรกDZ 3RODQG pawel.bugajny@onet.eu

Abstract We investigate optical properties of symmetric graphene quantum dots (GQD) [1] using the theory of representation of point groups. We classify symmetry of electronic states in the energy spectra obtained within tight-binding model (TB) of GQD with different sizes and edge termination [citations]. This allows us to determine allowed optical transitions. We next analyze the influence of edge effects on optical properties by studying structures with similar sizes, and zigzag and armchair edges. Optical transitions between edge-type and bulk-type states are investigated. A comparison between analytical and numerical results is presented. Absorption spectra for symmetric graphene quantum dots for different sizes and edges are shown. References [1] Z.Z. Zhang, K. Chang, F.M. Peeters, Phys. Rev. B, 77 (2008) 235411. [2] T. Yamamoto, T. Noguchi, K. Watanabe, Phys. Rev. B, 74 (2006) 121409. [3] A. D. Guclu, P. Potasz, P. Hawrylak, Phys. Rev. B 82 (2010) 155445. [4] M. Ezawa, Phys. Rev. B 76 (2007) 245415. [5] J. Fernandez-Rossier, J. J. Palacios, Phys. Rev. Lett. 99 (2007) 177204. [6] J. Akola, H. P. Heiskanen, M. Manninen, Phys. Rev. B 77 (2008) 193410. [7] W. L. Wang, O. V. Yazyev, S. Meng, E. Kaxiras, Phys. Rev. Lett. 102 (2009) 157201. [8] P. Potasz, A. D. Guclu, P. Hawrylak, Phys. Rev. B 81 (2010) 033403. [9] D. Subramaniam, F. Libisch, Y. Li, C. Pauly, V. Geringer, R. Reiter, T. Mashoff, M. Liebmann, J. Burgdorfer, C. Busse, T. Michely, R. Mazzarello, M. Pratzer, M. Morgenstern, Phys. Rev. Lett. 108 (2012) 046801. [10] S.K. Hamalainen, Z. Sun, M. P. Boneschanscher, A. Uppstu, M. Ijas, A. Harju, D. Vanmaekelbergh, P. Liljeroth, Phys. Rev. Lett. 107 (2011) 236803.

Non-Drude CVD graphene terahertz conductance dynamics Jonas D. Buron1, Filippo Pizzochero1, Michael Hilke2, Eric Whiteway2, Peter BĂ¸ggild1, Peter Uhd Jepsen3 1

DTU Nanotech - Department of micro- and nanotechnology, Technical University of Denmark, Ă&#x2DC;rsteds Plads, Kongens Lyngby, Denmark 2 Department of physics, McGill University, 3600 rue University, MontrĂŠal (QuĂŠbec) H3A 2T8, Canada 3 DTU Photonics - Department of photonics engineering, Technical University of Denmark, Ă&#x2DC;rsteds Plads, Kongens Lyngby, Denmark jcdb@nanotech.dtu.dk

Abstract Using ultra-broadband terahertz time-domain spectroscopy (THz-TDS), we report on the first observation of Non-drude equilibrium charge carrier dynamics in a large-area graphene film grown by chemical vapour deposition on copper foil. Sheet conductance spectra for CVD graphene films grown under 2 different sets of growth conditions are obtained by ultra-broadband THz-TDS based on terahertz air wave photonics as well as conventional THz-TDS based on photoconductive antennas, spanning the entire frequency range from 0.1 to 15 THz associated with intraband optical conductance. In the case of CVD graphene grown under optimized conditions, a Drude intraband conductance spectrum is observed, while a conductance spectrum showing distinct non-Drude characteristics are observed in the case of less optimized CVD graphene growth. The observations are interpreted in the framework of the Drude-Smith model[1] for restricted nanoscopic carrier movement caused by preferential carrier backscattering on extended electronic barriers. The sheet conductance is extracted from an analysis of the Fresnel coefficients of reflection and transmission for the sample geometry. For the pulse transmitted directly through the sample and the 1st roundtrip echo, the sheet conductance is given as

V s ,1 Z

V s ,2 Z

respectively, where T film (Z )

nA 1 nA Z0 T film Z

r nA nA2 4nA nBT film Z nA2 2nA nB 2T film Z

2nB Z 0T film Z

Esub graphene Z Esub Z , nA

nsub 1 , nB

nsub 1 and Z0 377: is

the vacuum impedance. To improve the S/N ratio of measurements on a graphene film with a lower THz response, the 1st roundtrip echo was in one case analyzed. We observe that the complex sheet conductance spectrum of a high quality CVD graphene film grown under optimized conditions on a copper substrate and transferred to a SiO2/high-resistivity-silicon substrate intimately follows the Drude model, as seen from the data in figure 1(a) and (b). In contrast, the complex sheet conductance spectrum of a CVD graphene film grown under less optimized conditions on a copper substrate and transferred to a SiO2/high-resistivity-silicon substrate, shows distinct features that cannot be reproduced by the Drude model, as seen from the data in figure 1(c) and (d). These features, which include a slight, but distinct suppression of the real conductance from DC to around 2 THz and an imaginary conductance that goes slightly negative in the same region, have commonly also been observed in nano-disordered, nano-defected or nano-patterned systems such as e.g. semiconductor nano-crystal systems[2]Âą[5]. We therefore suggest an analogous interpretation of the observed conductance spectrum in terms of restricted nanoscopic carrier movement via preferential carrier back-scattering within the Drude-Smith framework. The conductance spectrum measured for high quality CVD graphene grown under optimized conditions agrees extremely well with the Drude model, allowing an accurate determination of the carrier scattering time W=68 fs and VDC=2.19 mS, corresponding to a mean free path of approx. 61 nm and carrier mobility and carrier density of approx. P 2500cm2 Vs and N 5.45 u1012 cm 2 , respectively, under the assumption of transport limited by long-range scattering on charged impurities. In contrast, the conductance spectrum for the CVD graphene grown under less optimized conditions shows a good fit with the Drude-Smith model given by

V Z

WD 1 iZW

c Âş ÂŞ ÂŤÂŹ1 1 iZW ÂťÂź ,

with a Drude weight WD=1.54 mS , a carrier scattering time W=43 fs and a back-scattering parameter c=-0.60. The Drude-Smith model describes a suppression of DC and low frequency conductance as well

as a negative low frequency imaginary conductance as a consequence of charge carrier localization caused by preferential back-scattering on extended electronic barriers on the characteristic probing length scale of the measurement, given as L D 2S f , as illustrated in Figure 2. For frequencies between 0.1-15 THz L is on the order of 5-100 nm in the investigated films. Likely origins of extended electronic barriers on this length scale in the graphene film include crystal domain boundaries, sub-unity growth coverage and transfer-related damages such as e.g. rips, fractures or ripples. References 1 9 6PLWK Âł&ODVVLFDO JHQHUDOL]DWLRQ RI WKH 'UXGH IRUPXOD IRU WKH RSWLFDO FRQGXFWLYLW\ Â´ Phys. Rev. B, vol. 64, no. 15 (2001), p. 155106. [2] D. G. Cooke, A. N. MacDonald, A. Hryciw, J. Wang, Q. Li, A. Meldrum, and F. A. Hegmann, Âł7UDQVLHQW WHUDKHUW] FRQGXFWLYLW\ LQ SKRWRH[FLWHG VLOLFRQ QDQRFU\VWDO ILOPV Â´ Phys. Rev. B, vol. 73, no. 19 (2006), p. 193311. [3] ' * &RRNH $ 0HOGUXP DQG 3 8KG -HSVHQ Âł8OWUDEURDGEDQG WHUDKHUW] FRQGXFWLYLW\ RI 6L nanocrystal fiOPV Â´ Appl. Phys. Lett., vol. 101, no. 21 (2012), p. 211107. [4] *RUGRQ 0 7XUQHU DQG 0DWWKHZ & %HDUG DQG & $ 6FKPXWWHQPDHU Âł&DUULHU /RFDOL]DWLRQ DQG Cooling in Dye-6HQVLWL]HG 1DQRFU\VWDOOLQH 7LWDQLXP 'LR[LGH Â´ $PHULFDQ &KHPLFDO 6RFLHW\ no. 45 (2002), p. 11716-11719. [5] M. C. Beard, G. M. Turner, J. E. Murphy, O. I. Micic, M. C. Hanna, A. J. Nozik, and C. A. 6FKPXWWHQPDHU Âł(OHFWURQLF &RXSOLQJ LQ ,Q3 1DQRSDUWLFOH $UUD\V Â´ Nano Lett., no. 12 (2003), pp. 1695Âą1699. Figures

[1]

Figure 1: Ultra-broadband terahertz time-domain spectroscopy of CVD graphene sheet conductance. Terahertz transients transmitted through HR-silicon wafers and (a) high quality CVD graphene on HR-silicon, grown under optimized conditions and (c) CVD graphene on HR-silicon, grown under less optimized conditions. Complex, frequency-dependent sheet conductance extracted from time-domain measurements for (b) high quality CVD graphene on HR-silicon, grown under optimized conditions and (d) CVD graphene on HR-silicon, grown under less optimized conditions.

Figure 2: Preferential carrier backscattering on extended defects (e.g. crystal domain boundaries, transfer-induced rips, wrinkles, incomplete growth in CVD graphene) with a characteristic length scale smaller than or similar to the probing length scale of the THz-TDS experiment gives rise to suppression of low frequency conductance and negative imaginary conductance, as described by the Drude-Smith model [1].

Critical Parameters in Exfoliating Graphite into Graphene Matat Buzaglo, Michael Shtein and Oren Regev Department of Chemical Engineering and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva, Israel matat.buzi@gmail.com Abstract Dispersing graphite into few-layers graphene sheets (GS) in water is very appealing as an environmental-friendly,

low-cost,

low-energy

source

graphene.

Very

high

-1

concentrations in water (0.7 mg·mL ) are obtained by optimizing the nature of dispersant and the type of ultra-sonic generator. We employed a wide range of dispersant types: anionic, cationic, and nonionic surfactants and found no clear trend in GS concentration with the polarity of the head-group of the dispersant or the solution surface tension. In contrast, the nature of the hydrophobic part is critical for an efficient dispersion. Triton X-100 gave the highest GS concentration because it includes a benzene rinJ ZLWK VWURQJ ʌ-ʌ LQWHUDFWLRQV ZLWK the aromatic structure of GS. We found that a multi-step sonication procedure involving both tip and bath sources considerably enhances the yield of exfoliated GS. Tip sonication (TS) and bath sonication (BS) differ considerably in the power they supply. Therefore, the trivial assumption would be that the substantially higher power of TS would be more efficient than the weak BS. Fig. 1a compares the efficiency of either TS or BS alone, or their combination (TBT). Clearly, in terms of integrated sonication energy, TS alone is the least efficient option, and the weaker BS leads to much higher GS concentration. Still, combining the two sources gives the highest GS concentration. This marked difference is ocularly visible: a much darker supernatant (higher GS concentration) is obtained by TBT than by BS alone (Fig. 1a, inset). Although the BS contribution to the total energy is rather small (~1% of the total energy), it has a substantial contribution to the final GS concentration (40%) as shown in Fig. 1b. Both Raman spectroscopy and transmission electron microscopy indicate few-layers graphene patches with typical size of ~0.65ȝP LQ RQH GLPHnsion and ~0.35µm in the other (Fig. 2).

Reference [1] Matat Buzaglo, Michael Shtein, Sivan Kober, Robert Lovrincic, Ayelet Vilan and Oren Regev, Phys. Chem. Chem. Phys., 15 (12) (2013), 4428 - 4435.

Figures

Figure 1 - Optimization of sonication procedure, dispersant and energy/volume. (a) GS concentrations upon bath sonication (BS), tip sonication (TS) and tip-bath-tip sonication (TBT). Inset: Image of the supernatant of the GS dispersions after centrifugation; (b) Concentration of GS (with TX-100) as a function of integrated sonication energy/volume, as measured by UV-vis absorption. These solutions were treated by TBT cycles.

Figure 2 - Indication for few layers of graphene showing a) Room temperature TEM micrographs of GS stacks from GS-TX-100. The diffraction pattern (inset) indicates that the GS are less than 5 layers thick,

b) the Raman spectra of graphene film on quartz substrate

at 514 nm. Inset shows a zoom-up of the 2D peak.

Defect-Oxygen assisted direct write technique for nanopatterning graphene Alberto Cagliani1, Niclas Lindvall2, Martin B. B. S. Larsen1 and Peter Bøggild1 DTU Nanotech ± Center for Nanostructured Graphene (CNG) and Department of Micro- and Nanotechnology, DTU, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark 2 Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, SE-412 96 Gothenburg, Sweden 1

Alberto.Cagliani@nanotech.dtu.dk

Abstract In recent years, nanopatterned graphene has been attracting considerable attention due to the possibility of tuning the graphene electronic properties in many different ways through controlled patterning. It has been theoretically predicted that by properly shaping the nanopattern, graphene can display several new interesting properties such as a magnetic dipole or a strong anisotropy in the transport regime [1][2]. One of the most important modifications that can be created by nanopatterning is a band gap in the density of states of graphene by cutting graphene into nanoribbons [3] or creating an antidot lattice [4]. For all these applications the nanopattern features has to be 20 nm and below, which imposes stringent requirements for the resolution of the patterning techniques to be used. So far, the most used nanopatterning techniques which can achieve critical dimensions below 20nm in graphene are e-beam lithography and block copolymer lithography [3][5]. The main common issue with these techniques is that they require graphene to be in contact with a polymer, which inevitably alters the properties of graphene. One of the most used polymer to achieve under 20nm features in e-beam lithography is HSQ [3], which is known for doping graphene and it is very hard to remove [3][6]. PMMA is also used, but it presents similar problems of unwanted residues difficult to fully remove [7]. On the other hand Block copolymer process often involves the deposition of a SiO2 layer on top of graphene creating defects in the graphene lattice [5]. Thiele et al. recently demonstrated the possibility of etching graphene without any mask. They etched graphene with an e-beam combined with an oxygen rich atmosphere using an environmental SEM [9]. Unfortunately E-SEMs are not widely available and are costly. Here, we present a new nanopatterning technique that does not require any polymer and also does not require an environmental SEM, but only an EBL system and an oven that operates in air at atmospheric pressure. In Figure 1a the positive two-step direct write nanopatterning process is illustrated. The EBL system was used to irradiate the samples, writing the patterns that had to be etched into graphene. The e-beam irradiation is used to selectively damage the graphene crystal lattice in the exposed areas. In order to quantify the defect density induced by the irradiation Raman spectroscopy was used and in Figure 1b the ratio I(D)/I(G) is reported as a function of the irradiation dose. As 2 2 expected the I(D)/I(G) ratio is increasing starting from the lowest dose (0.185 C/cm ) till 0.7 C/cm , 2 indicating that the defect density increases with the dose. For doses larger than 0.7 C/cm till ~3 C/cm2 the ratio decreases due to the high density of defects that destroys the hexagonal carbon rings (characteristic length between defects is approximately few nanometers). In this range the nanocrystalline structure is turned into an amorphous structure with increasing sp 3 content. For higher doses the ratio is influenced by the e-beam induced deposition of amorphous carbon on the irradiated areas and it does not decrease. Figure 2a shows one of the samples after direct write, where 4x4 Pm squares have been written with different doses. The Figure 2b presents a Raman Map of the I(D)/I(G) ratio, showing how the damage is localized in the squares. Figure 2c presents the optical images of the etching sequence of this sample etched in air at 435 oC. After 16 minutes the etching is completed for the three different doses as shown in Figure 2d where the map of the 2D peak intensity is reduced over 10 times inside the squares. Figure 3a presents the SEM images of two squares written with 5 C/cm 2 2 and 10 C/Cm as the etching proceed. The graph in Figure 3b shows the remaining graphene in the written areas after 12 minutes of etching as a function of the dose. It is evident how a larger dose leads to faster etch rate. This novel nanopatterning technique has been employed to pattern nanoholes with a diameter of 40 nm and lines down to 40 nm in width (see Figure 4). References [1] Yang, H.-X.; Chshiev, M.; Boukhvalov, D. W.; Waintal, X.; Roche, S. Phys. Rev. B 84 (2011) 214404. [2] J. G. Pedersen; A. W. Cummings, and Roche S., in print for Phys. Rev. Lett.. [3] Han, M.; Özyilmaz, B.; Zhang, Y.; Kim, P. Phys. Rev. Lett., 98 (2007) 206805. [4] T. G. Pedersen, C. Flindt, J. Pedersen, A-P. Jauho, N.A. Mortensen and K. Pedersen Phys. Rev. Lett., 100 (2008) 136804 . [5] Bai, J.; Zhong, X.; Jiang, S.; Huang, Y.; Duan, X., Nat. Nanotechnol., 5 (2010) 190±4. [6] K. Brenner and R. Murali, Appl. Phys. Lett., 96 (2010) 063104. [7] Lin, Y.-C.; Lu, C.-C.; Yeh, C.-H.; Jin, C.; Suenaga, K.; Chiu, P.-W. Nano Lett., 12 (2012) 414±9. [8] Thiele, C.; Felten, A.; Echtermeyer, T. J.; Ferrari, A. C.; Casiraghi, C.; v. Löhneysen, H.; Krupke, R. Carbon N. Y., 64, (2013) 84±91.

Figure 1. (a) Illustration of the direct write nanopatterning method. (b) I(D)/I(G) as a function of the dose use after the direct write.

Figure 2. (a) SEM image of one of the sample after direct write. (b) I(D)/I(G) Raman map of the sample. (c) Optical images illustrating the etching sequence of the sample. (d) I(2D) Raman map after etching for 16 minutes.

Figure 3. (a) SEM images illustrating the etching sequence for different two doses. (b) The percentage of remaining graphene after 12 minutes of etching is plot as a function of the dose. The I(D)/I(G) ratio is also reported

Figure 4. Nanoholes in a square pattern with 40 nm diameter and lines down to 40 nm in width etched into graphene.

Graphene flexible electronic device for lighting LEDs 1

J. Martinez , A. Ladron de Guevara , D. J. Choi , A. Bosca , J. Pedros , F. Calle

1 ISOM - UPM, E.T.S.I.Telecomunicacion, Madrid, Spain 2 Division of Materials Science and Engineering, Hanyang University, Seoul, Korea javier.martinez@upm.es

Abstract

Graphene, has attracted increasing attention in recent years [1] due to its excellent mechanical, 2 -1 optical and electrical properties. Its high theoretical surface area (2630 m g ) and high electrical conductivity make it an attractive material for many industrial applications [2]. Also is a flexible transparent material that can be used for solar cells, light emitting diodes (LEDs, OLEDs), touchscreens and LCD displays [3].And in the near future, its flexibility will let to create foldable and wearable devices[4]. A layer of graphene can be prepared by several techniques: by mechanical exfoliation from graphite, by precipitation on a silicon carbide surface, by reduction of exfoliated graphene oxide, and by chemical vapor deposition growth on Cu or Ni. The most used one is the CVD, and the synthesized graphene is commonly grown on a flat metal foil or thin film. This method provides high quality graphene, and can also fabricate 3D graphene structures using metallic foams. The large area and porosity of this 3D graphene structures, makes them an ideal material for flexible 2 electronics. In order to create this structures, we used a 1 x1 cm Ni foam as the catalytic template to form graphene layers by plasma-enhanced CVD (PECVD). After this step, the Ni was removed by a wet etching in HCl acid, obtaining a soft graphene foam with the same porous size. Figure 1 shows an image of the foam by scanning electron microscopy (SEM). This graphene foam has a very high conductivity and can used for flexible electronics. The graphene foams were coated partially with PMMA for mechanical stability and sealed inside a plastic container with an electrolyte and two electrical contacts. This flexible device can store energy when is polarized by a positive bias and can light up several commercial LEDs as it is shown in the Figure 2.

Acknowledgements. This work has been partially supported by Ministerio de EconomĂa y Competitividad (Project No. TEC 2010-19511) and technical advice from Repsol.

References

[1] B. Luo, S. Liu, L. Zhi, Small 8 (2012) 630. [2] M. D. Stoller, S. Park, Y. Zhu, J. An, R. S. Ruoff, Nano Letter, 8 (2008) 3498. [3] X. Cao, Y. Shi, W. Shi, G. Lu, X. Huang, Q. Yan, Q. Zhang, and H. Zhang, Small 7 (2011) 3163. [4] M. F. El-Kady, V. Strong, S. Dubin, R. B. Kaner, Science 335 (2012) 1326

Figures

Figure 1. SEM picture of the graphene 3D foam

Figure 2. Picture of the flexible device lighting up 3 LEDs

Coupling light into graphene plasmons with the help of surface acoustic waves 1,2

2,3

1,2

Jorge Pedrós , Jürgen Schiefele , Fernando Sols , Fernando Calle , and Francisco Guinea

Instituto de Sistemas Optoelectrónicos y Microtecnología, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain 2 Campus de Excelencia Internacional, Campus Moncloa UCM-UPM, Ciudad Universitaria s/n, 28040 Madrid, Spain 3 Departamento de Física de Materiales, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain 4 Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain j.pedros@upm.es

Abstract Surface plasmon polaritons (hereafter plasmons) are essentially light waves trapped to the surface of a conductor due to their interaction with conduction electrons. The strong spatial confinement of the electromagnetic field and its coupling to charge carriers allow for the manipulation of light at subwavelength scales (beyond the diffraction limit of classical optics), opening the possibility to integrate electronics and optics at the nanoscale. Further promising plasmonic applications include, for example, the control of quantum-optics devices, single molecule detection, nanomedicine, metarmaterials, and light harvesting. Recently, the possibility to use graphene for plasmonic devices has received considerable attention [1,2]. In comparison to conventional conductors, graphene offers unique possibilities for tuning its plasmonic properties. However, in the experiments realized so far, graphene plasmon laser coupling required either complex near-field techniques or the patterning of micro- or nanoscale arrays for far-field coupling, where edge scattering reduces the localized plasmon lifetime, hindering the potential of the graphene plasmonic applications. Thus, an efficient method to excite propagating graphene plasmons for the development of integrated and scalable graphene plasmonic devices is still needed. In order to overcome this problem, we have recently proposed a method to couple far-field radiation into propagating graphene plasmons by periodically deforming a continuous graphene sheet with an electrically generated surface acoustic wave (SAW) [3]. This mechanisms allows to create a tunable optical grating without the need of any patterning, thus eliminating the edge scattering. An interdigital transducer (IDT) on a piezoelectric film is used to launch the SAW across the graphene sheet, as shown in Figure 1. By diffraction at the grating, incident laser light can overcome the momentum mismatch and excite propagating plasmons in the graphene sheet. Independently, another research group arrived at a similar proposal using an external mechanical vibrator [4]. Both works have been highlighted in synopsis articles published in the popular science magazines Physics [5] and Chemistry World [6]. In this contribution, we will briefly review the potential applications of graphene plasmonics and the different methods used so far for the generation of graphene plasmons. We will then present the details of our novel approach that allows to benefit from the simple optics of the far-field coupling technique while permitting to excite propagating plasmons in continuous graphene, otherwise impeded in patterned graphene sheets that only allows localized plasmons affected by edge scattering. Moreover, the use of an integrated transducer to generate the waves enables the fabrication of graphene plasmonic devices by the microelectronics industry. In addition, our approach permits to switch the laser-plasmon coupling electrically via the high-frequency signal at the IDT as well as to take advantage of the IDT technology for developing many different plasmon functionalities. For example, curved IDTs creating interfering SAWs, could easily be used for plasmon focusing.

References [1] F. H. L. Koppens, D. E. Chang, and F. J. Garcia de Abajo, “Graphene plasmonics: A platform for strong light-matter interactions”, Nano Letters, 11 (2011) 3370. [2] A. N. Grigorenko, M. Polini, and K. S. Novoselov, " Graphene plasmonics", Nat. Photonics 6 (2012) 749.

[3] J. Schiefele, J. PedrĂłs, F. Sols, F. Calle, and F. Guinea, â&#x20AC;&#x153;Coupling light into graphene plasmons through surface acoustic wavesâ&#x20AC;?, Phys. Rev. Lett., 111 (2013) 237405. [4] M. Farhat, S. Guenneau, and H. BaJFĂ&#x2022; ÂłExciting graphene surface plasmon polaritons through light and sound interplayâ&#x20AC;?, Phys. Rev. Lett., 111 (2013) 237404. [5] â&#x20AC;&#x153;Flexing some graphene muscleâ&#x20AC;?, Synopsis published in Physics (APS), December 2013, http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.111.237404 [6] â&#x20AC;&#x153;Vibrations couple light to grapheneâ&#x20AC;?, Synopsis published in Chemistry World (RSC), December 2013, http://www.rsc.org/chemistryworld/2013/12/vibrations-couple-light-graphene-plasmons

Figures

Figure 1: Sketch of the proposed device for coupling laser light into propagating graphene plasmons.

Electronic Transport in Graphene / Ni(111) contacts from first principles Xavier CartoixĂ 'HSDUWDPHQW GÂś(QJLQ\HULD (OHFWUzQLFD 8QLYHUVLWDW $XWzQRPD GH %DUFHORQD %HOODWHUUD 6SDLQ Xavier.Cartoixa@uab.cat Abstract Graphene microwave applications require an ultralow graphene-metal contact resistance in order to reduce extrinsic RC times that impact on the intrinsic performance of graphene field effect transistors (GFETs) [1]. For device applications, it is desirable to have a contact resistance (Rc) lower than 100 Č?Ă&#x201A;Č?P ZKLOH ODUJHU YDOXHV DUH WKRXJKW WR EH D OLPLWLQJ IDFWRU on the GFET performance [2,3]. Recent experimental developments have achieved this landmark value [4]. Injection of electrons from the metal into the GFET channel can be thought of as a succession of two steps: 1) injection from the metal into the graphene in contact with the metal, and 2) injection from the graphene in contact with the metal into the channel. Both steps will give rise to contributions towards Rc termed Ri (for interface, step 1) and Rg (for graphene, step 2). First principles calculations can provide insight on the fundamental processes at hand, identifying the limiting factors for efficient electron transfer from the contact into graphene. We will present ab initio calculations of ballistic transport in a Graphene / Ni(111) junction. It has been shown experimentally that graphene can be grown epitaxially on such a metal surface [5], thus providing an ideal testbed for first-principle calculations. We acknowledge financial support by the Spanish Ministerio de EconomĂa y Competitividad under Project No. TEC2012-31330. Also, the research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement No. 604391 Graphene Flagship.

References [1] J. S. Moon and D. K. Gaskill, IEEE Trans. Microwave Theory Tech. 59, (2011) 2702. [2] A. Venugopal, L. Colombo and E. M. Vogel, Appl. Phys. Lett. 96, (2010) 013512. [3] Bo-Chao Huang, Ming Zhang, Yanjie Wang and Jason Woo, Appl. Phys. Lett. 99, (2011) 032107. [4] J. S. Moon, M. Antcliffe, H. C. Seo, D. Curtis, S. Lin et al., Appl. Phys. Lett. 100, (2012) 203512. [5] Y. Gamo, A. Nagashima, M. Wakabayashi, M. Terai and C. Oshima, Surf. Sci. 374 (1997) 61.

Figures

Fig. 1: Relaxed Graphene / Ni(111) structure to study Rg.

Fig. 2: Spin-resolved line conductivity corresponding to the structure in Fig. 1.

Thermally activated chemical functionalization of graphene under ultra-high vacuum conditions 1

Andrew Cassidy , Mikkel Kongsfelt , Daniel Tejero , Steen U. Pederson , Kim Daasbjerg , Liv 1 HornekĂŚr 1

Dep. Physics and Astronomy, Aarhus University, Denmark 2 Dep. Chemistry, Aarhus University, Denmark amc@phys.au.dk

Abstract Although there are multiple reactions available to form carbon-carbon bonds at the graphene basal plane, many of these pathways rely on electron transfer between the graphene sheet and the reactant molecule. The distribution of electron-hole puddles in graphene grown on either SiC or metallic substrates has, consequently, been shown to have a large effect on the success of many of these reactions, in particular reactions involving diazonium salts. In an attempt to circumvent the influence of electron-hole puddles, here we introduce a thermally activated reaction, namely the decomposition of triazenes, to form carbon-carbon bonds at the graphene surface. All experiments were conducted under ultra-high vacuum (2E-10 mbar) and the reaction steps were followed using a combination of scanning tunneling microscopy and mass spectrometry. Graphene samples were prepared by chemical vapor deposition upon an Ir(111) surface. Triazene molecules, prepared locally, were deposited onto the graphene surface under vacuum and heated until decomposition. This in situ, surface-science approach gives a unique insight into the details of the reaction between the aryl radicals and the carbon surface. Indirect evidence from the STM shows that the graphene basal plane was successfully functionalized.

The nature of the Fe-Graphene interface at the nanometer level. Mattia Cattelan, Luca Artiglia, Emanuele Cavaliere, Marco Favaro, Stefano Agnoli, Alexey Barinov, Silvia Nappini, Elena Magnano, Federica Bondino, Luca Gavioli and Gaetano Granozzi Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131, Padova, Italy mattia.cattelan.1@studenti.unipd.it Abstract The study of the interface between Graphene (G) and metals is gaining more and more interest thanks to the growing industrial application of G in flexible electronics [1] and future use in high frequency transistors and thin film logic devices. G is also emerging as the ideal platform for future spintronics since it combines long spin lifetime and excellent electron velocity [2],[3]. In this context, the possibility to manipulate the local properties of the G/metal interface by the introduction of other species through the intercalation process, represents an easy method to obtain tailored interfaces [4],[5]. The aim of our work is to study how Fe interacts with the G/Pt(111) system either after in-situ UHV deposition at room temperature (RT) or at T=600 K. In this way two complementary systems can be investigated: supported Fe nanoparticles (NPs) (i.e. Fe/G/Pt(111)) and intercalated Fe layers (i.e. G/Fe/Pt(111)). Moreover, the oxidation of these systems was investigated by dosing oxygen at RT in -6

the range of 10 mbar. To understand the electronic properties of G in contact with Pt(111) and Fe, photoemission spectroscopy from core-levels, near edge x-ray absorption fine structure (NEXAFS) and angle resolved photoelectron spectroscopy (ARPES) were carried out using synchrotron radiation. We also performed scanning tunneling microscopy (STM) to obtain a precise view of G lattice morphology at the atomic scale. G was grown on Pt (111) by dosing of C2H4 at 1100 K obtaining a quasi free-standing layer [6]; Fe was deposited on G/Pt(111) by physical vapor deposition (PVD) at RT. Fig. 1a,b,c,d shows the evolution of the C 1s photoemission line as a function of the Fe coverage (0, 0.5, 1 and 1.5 equivalent ML). Three different components can be clearly identified: the peak at 284.16 eV is due to the unperturbed G atoms 2

(as for G/Pt(111)), whereas the two components at 284.40 eV and 285 eV are associated to the sp 3

atoms in contact with Fe and to a partial rehybridization of G to sp driven by the strong Fe-C interaction [7], respectively. STM data acquired upon Fe deposition at RT show a rough G morphology, in good agreement with the XPS data and the hypothesis of a G local rehybridization. The intercalated system, G/Fe/Pt(111), was prepared by depositing Fe at 600 K or heating the Fe/G/Pt(111) system at this temperature. In this case STM data (Fig. 3) show the formation of ML thick islands of Fe on the Pt surface, covered by a continuous unperturbed layer of G. This extraordinary continuity suggests that the combination of these two metals can be one of the best choices for future spintronic studies and devices. The flatness of the Fe layer intercalated below G was confirmed also by photoemission (Fig. 1f): the peak at 284.16 eV, which is the fingerprint of G in contact with Pt(111) is completely suppressed. ARPES measurements show major differences in the G band distribution for G/Pt(111) and G/Fe interfaces. In the G/Pt(111) case (Fig. 2a), G is scarcely interacting with the Pt 5d states; around the K SRLQW WKH Ę&#x152; EDQG RI * KDV D OLQHDU GLVSHUVLRQ DV LQ TXDVL IUHH-standing layer [8]. On the contrary, when G is in contact with Fe, either in the Fe/G/Pt(111) (Fig. 2b) or G/Fe/Pt(111) (Fig. 2d) case, a relevant

K\EULGL]DWLRQ RI LWV Ę&#x152; EDnd with Fe 3d states can be observed. At about 4 eV the band deviates from the linear dispersion typically observed around the K point, and it bends remaining pinned at about 2.6 eV below the Fermi level. Similar features in C 1s and ARPES spectra are reported in the literature for G interacting with other not-noble d-metals, such as Ni(111) [4]. To study the oxidation of our system O2 was dosed on Fe/G/Pt(111), obtaining a defective oxide referenced as FeOx. Both photoemission from core levels and ARPES show that this oxide does not interact with G. In the C 1s photoemission line related to FeOx(1.5 ML)/G/Pt(111) (Fig. 1e), we observed a decrease of the component of Fe/G and an increase of the one related to unperturbed G. Surprisingly, also the component at 285 eV is strongly suppressed after oxidation, demonstrating that the local 3

hybridization to sp is reversible. From ARPES measurements it is clear the absence of an interaction between the FeOx and G 7KH Ę&#x152; band is no more hybridized with the Fe 3d states (Fig. 2c), it has very similar structure of the G/Pt(111) (Fig. 2a). The attempt to oxidize the G/Fe/Pt(111) system with O 2 at RT was unsuccessful, indicating that this system can be a good platform to grow arrays of intercalated ferromagnetic islands that could be protected from air oxidation. References [1] Goki E., Giovanni F., ... Chhowalla M., Nat. Nanotechnol., 3 (2008) 270. [2] Tombros N., Jozsa C., ... & van Wees B. J., Nature, 448 (2007) 571. [3] Seneora P., Dlubaka B., ... & Fert A., MRS Bulletin,37 (2012) 1245. [4] Voloshina E. N., Generalov $ ÂŤ & Dedkov Y. S., New J. Phys., 13 (2011) 113028. [5] Sicot M., Leicht P.,.. & Fonin M., ACS Nano, 6 (2012) 151. [6] Sutter P., Sadowski J. T., Sutter E., Phys. Rev. B, 80 (2009) 245411. [7] Knudsen J., Feibelman P. J., ... & Michely T., Phys. Rev. B, 85 (2012), 035407. [8] Politano A., Marino A. R., ...& Chiarello G., Carbon, 50 (2011), 734. Figures

Figure. (1) C 1s photoemission line (hv=550 eV) deconvoluted into single chemical shift components for (a) G/Pt(111) system (b,c,d) after Fe deposition, (e) oxidation and (f) intercalation at 600 K. (2) ARPES acquisition in the ÄŤ WR . direction of G for (a) G/Pt(111) system (b) after Fe deposition, (c) oxidation and (d) intercalation at 600 K. Dashed red line are for the theoretical position of the G K point in a free-standing layer. (3) STM image of a Fe island on Pt(111) intercalated below a G layer.

Development of a multi-steps CVD process to produce bi-layers graphene for anode of Organic Light Emitting Diodes 1 2 1 1 2 P. Trinsoutrot , M. Brignone , H. Vergnes , B. Caussat , D. Pullini 1

Université de Toulouse, Laboratoire de Génie Chimique, ENSIACET/INP Toulouse UMR CNRS 5503, 4 allée Émile Monso, BP 44362, 31432 Toulouse Cedex 4, France. 2 Group Materials Labs, Centro Ricerche Fiat, Orbassano, Italy. *daniele.pullini@crf.it - brigitte.caussat@ensiacet.fr

Graphene is one of the most interesting candidates for the next generation of transparent conductive electrodes (TCEs) for electrical devices, because of its unique electronic structure. Furthermore, the optical transparency of graphene films surpasses that of conventional TCEs such as indium tin oxide (ITO) [1]. However, graphene anode for Organic Light Emitting Diodes (OLEDs) still presents several problems owing to its low work function and high sheet resistance [1], which may be related to a poor control of graphene quality. Chemical vapor deposition (CVD) on copper from methane seems to be the most efficient approach to form high quality transferable graphene for opto-electronic applications, due to the potential for commercially viable production at large scale. However, CVD processes need to be optimized for obtaining selective single or bilayers growth, as well as highly crystalline, full coverage, large area domains [2]. Indeed, CVD graphene films are typically composed of relatively small polycrystalline flakes. A high density of grain boundaries degrades the properties of graphene [2]. Thus, it is desirable to prepare large single-crystal graphene to minimize the impact of defects existing at grain boundaries. The most recent studies of the literature show that this objective can be met by using very low concentration of methane (<100 ppm), but in these conditions, it is difficult to obtain a full coverage of the substrate [3]. The most efficient way to obtain a continuous high quality monolayer of graphene seems to use a multi-steps process, first involving a very low methane concentration in order to form strictly monolayer graphene flakes with low nucleation density. Then, methane concentration is progressively increased, to counterbalance the decrease of the active catalytic copper surface [3]. In the present study, a two-step process then a three-steps one have been developed only differing by the third step, in order to produce graphene for OLED application. Methane diluted into 2

hydrogen and argon was used on copper foils (25 µm thick, 99,999% Alfa Aesar) of 2x2 cm . The operating temperature was fixed at 1,000°C and the total pressure was of 700 Torr. The hydrogen on methane inlet molar ratio was fixed to 800 for steps 1 and 2. The CH4 concentration was of 10 ppm for step 1 and 40 ppm for step 2, and their duration was of 60 min for each one. For step 3, only 5 min long, the CH4 concentration was of 9,000 ppm and the H2/CH4 ratio of 10. Optical microscope and Raman spectroscopy measurements (confocal Raman microscope Labram – Horiba Yvon Jobin) were carried out to investigate the quality and extend of graphene sheets. -1

-1

After the two first steps, graphene was strictly monolayer (2D (~2,670 cm )/G (~1,582 cm ) -1

peaks average ratio equal to 7), with no disorder-induced D-peak (~1,350 cm ), but it was formed of discontinuous flakes of several tens of microns. This is why a third step was added. Optical micrographies indicated that graphene fully covers the Cu substrate after step 3. Raman spectra taken on different points of the three-steps sample are given in Fig. 1a. The 2D/G peaks average ratio is of 1.4, corresponding to bi-layers graphene. The average D/G ratio is of 0.06, showing excellent graphene crystalline quality. So, it appears that for these conditions, a quite high CH4 concentration is necessary for the third step, to counterbalance the decrease of the active copper surface, thus maintaining a steady-state carbon ad-atoms supply to get full graphene coverage.

(a)

(b)

Figure 1: (a) Raman spectra after step 3 – (b) Schematic representation of a graphene OLED

The three-steps sample has been used for OLED fabrication. After transferring graphene on glass, a hole transporting layer, a water mixture of [poly(3,4-ethylenedioxithyophene) poly(styrene sulfonate)] PEDOT:PPS, was dissolved in 25%w isopropanol and deposited on the graphene surface by spin coating and dried at 50°C for 10 min (thick ness ≈50 nm), as shown in Fig. 1b. The quantity of isopranol used is significantly larger than that used in the standard ITO-OLED to allow the colloid to properly wet the hydrophobic surface of graphene. A light emitting polymer (Merck PDY 132) was then deposited by spin coating at 1,800 rpm (thickness ≈100 nm). The cathode, made of three metal layers (CA, Al, Ag, total thickness ≈300 nm) was evaporated in vacuum chamber. The device was packaged with an epoxy resin layer and a thin glass substrate. The prototype fabricated in this way lighted up as shown in Fig. 2. The figure shows a first example of OLED working device made from said emitting polymer. As a matter of fact, an outline for the future is to improve the graphene transferring process on such hydrophobic surface in order to limit the presence of corrugations and wrinkles. Indeed, they could have created a thickness inhomogeneity of each layer of the emitting sandwich, which most likely is the main reason for the limited lighting area in this experiment.

Figure 2: The graphene based OLED prototype

Acknowledgements: This work has been supported by the European project FP7-NMP Grenada (GRaphenE for NAnoscaleD Applications). References

[1] S. Shin, J. Kim, Y.H. Kim, S.I. Kim, Current Applied Physics, 13 (2013) S144-S147. [2] S. Chen, H. Ji, H. Chou, Q. Li, H. Li, J.W. Suk, R. Piner, L. Liao, W. Cai, R.S. Ruoff, Adv. Mater., 25 (2013) 2062-2065. [3] Q. Li, H. Chou, J.H. Zhong, J.Y. Liu, A. Dolocan, J. Zhang, Y. Zhou, R.S. Ruoff, S. Chen, W. Cai, Nano Lett., 13 (2013) 486-490.

Anisotropic mechanical and thermal properties of graphene nanosheets/alumina composites

Yasemin Ă&#x2021;elik1, Ali Ă&#x2021;elik1, (QGHU 6XYDFĂ&#x2022;1 and Emmanuel Flahaut2,3 ybozkaya@anadolu.edu.tr

Anadolu 8QLYHUVLW\ 'HSDUWPHQW RI 0DWHULDOV 6FLHQFH DQG (QJLQHHULQJ (VNLĂşHKLU 7XUNH\ 2 UniversitĂŠ de Toulouse, UPS, INP, Institut Carnot Cirimat, 118, route de Narbonne, F-31062 Toulouse cedex 9, France 3 CNRS, Institut Carnot Cirimat, F-31062 Toulouse, France

Graphene is a good candidate as a filler material for nanocomposite applications due to its unique electrical, thermal and mechanical properties, as well as its two-dimensional (2D) nature and high aspect ratio. Therefore, it has attracted attention not only in polymer-matrix composites, but also in ceramic-based composites [1-4]. In this study, graphene-based dispersions with a relatively high concentration ( 1.3 mg/mL) were prepared in isopropyl alcohol (IPA) within a short sonication time (90 min) by utilizing a high surface area nanographite powder as a starting material. The dispersion of graphene nanosheets in a low boiling point solvent such as IPA is an advantage for composite applications due to its easy removal from the system. Graphene nanosheets ZHUH LQFRUSRUDWHG LQWR ÄŽAl2O3 powder with 0, 3, 5, 7 and 10 vol.% contents. The resulting graphene/Al2O3 powders were sintered by spark plasma sintering (SPS) at 1300-1500Â°C (depending on the graphene content) and at 50 MPa for 5 min. Hardness and fracture toughness values of the prepared composites were measured from Vickers indentations and the corresponding crack-length measurements of both through-thickness (parallel to the SPS pressing axis) and in-plane (perpendicular to the SPS pressing axis) directions. Similarly, through thickness and in-plane thermal diffusivity measurements were performed from room temperature up to 600 C in N2 atmosphere. Besides the measured anisotropic mechanical and thermal properties of the graphene nanosheet/alumina composites, microstructural evaluation of alumina with graphene content, which was investigated by scanning electron microscopy, will be discussed in this presentation.

References [1] Miranzo, P., Garcia, E., Ramirez, C., Gonzalez-Julian, J., Belmonte, M., Osendi, M.I., J. Eur. Ceram. Soc., 32 (2012) 1847-1854 [2] Fan, Y., Jiang, W., and Kawasaki, A., Adv. Funct. Mater., 22 (2012) 3882-3889 [3] Liu, J., Yan, H. and Jiang, K., Ceram. Int., 39 (2013) 6215-6221 [4] Centeno, A., Rocha, V.G., Alonso, B., Fernandez, A., Gutierrez-Gonzalez, C.F., Torrecillas, R. and Zurutuza, A., J. Eur. Ceram. Soc., 33 (2013) 3201-3210

Structural Origin Of The Band-Gap In Armchair Graphene Nanoribbons A. Celis1,2, I. Palacio1, A. Gloter2, M. S. Nevius3, A. Zobelli2, M. Sicot 4, D. Malterre4, C. Berger3, W. de Heer3, E.H. Conrad3, A. Taleb-Ibrahimi1, A. Tejeda 1,2 1Synchrotron

SOLEIL, Saint-Aubin 91192, Gif-sur-Yvette, France de Physique des Solides, UMR 8502 Université Paris Sud 91405, Orsay, France 3 School of Physics, The Georgia Institute of Technology 30332-0430, Atlanta, USA 4Institut Jean Lamour, Faculté des Sciences et Technologies, BP 70239, F-54506, Vandoeuvre-lès-Nancy, France

2Laboratoire

Abstract Armchair graphene nanoribbons (GNRs) have shown the presence of a tunable band-gap, a requirement for the production of electronic devices. The appearance of the gap relies on the edge regularity of the ribbon, which is not achieved by lithography. However, sidewall ribbons induced by lithographing and annealing the Si-face of SiC are expected to have well defined edges 1. A deep understanding of the morphology of these GNRs will allow not only to link its atomic structure to its electronic properties, but also to improve the future carbon-based electronic devices. In this work we make use of Scanning Tunneling Microscopy (STM) and High Resolution cross-sectional Transmission Electron Microscopy (HR-XTEM) to present a detailed morphological characterization of these ribbons. Our aim is to address the unknown origin of the gap opening that has already been observed in photoemission2. The gap could be driven by either an sp3 hybridization, quantum confinement or by strain at the curved edge of the ribbon. Through our study it has been found that an sp3 hybridization is the responsible for band-gap opening. References [1] M. Sprinkle et al., Nature Nanotechnology, 5 (2010) 727. [2] J. Hicks et al., Nature Physics, 9 (2013) 49.

Atomically thin carbon and boron nitride films as anti-corrosive coatings Jiri Cervenka,1 Lu Hua Li,2 Morteza Aramesh,1 Hualin Zhan,1 Kate Fox,1 Desmond Lau,1 Ying Chen,2 1 and Steven Prawer 1

School of Physics, The University of Melbourne, Melbourne, VIC, Australia Institute for Frontier Materials, Deakin University, Geelong, VIC, Australia 3 Plasma Nanoscience Centre Australia, CSIRO, Lindfield, NSW, Australia

jiric@unimelb.edu.au Materials corrosion and degradation causes a serious problem in many important technological fields of modern society, and therefore the development of new improved anti-corrosive coatings is getting increasingly important. Application of effective anti-corrosive coatings poses considerable technical challenges, in particular when very thin protective coatings are required. For this reason, investigation of chemical resistance of two-dimensional (2D) materials is scientifically and technologically extremely valuable. From a scientific point of view, it allows to test some of the most fundamental processes happening at interfaces of composite materials, while addressing and helping to solve some of the problems in different technological applications.

In this study, we examine corrosion resistance of atomically thick materials, boron nitride (BN), graphene and diamond-like carbon (DLC), in various gaseous and liquid environments. The oxidation behavior of hexagonal BN and graphene nanosheets (1Âą4 layers) is examined using heating in air [1]. BN films are found to have higher oxidation resistance than graphene, which makes them more preferable for high-temperature applications. Atomic force microscopy and Raman spectroscopy analyses showed that monolayer BN nanosheets can sustain up to 850 Â°C. The starting temperature of oxygen doping/oxidation of BN nanosheets only slightly increases with an increasing number of layers and strongly depends on the exact heating conditions. The detailed oxidation mechanism of BN has been found different from graphene. Elongated etch lines have been observed on the oxidized monolayer BN nanosheets, indicating that the BN nanosheets are first cut along the chemisorbed oxygen chains and then the oxidative etching occures perpendicularly to these lines.

The main advantage of thin carbon films for anti-corrosive applications lies in their multi-functional properties, such as tunable electrical conductivity, surface chemistry and excellent biological, chemical and corrosion resistance. To fully utilize these unique properties in various nano- and bimomedical applications, it is first important to homogenously deposit atomically thin carbon coatings on different nanostructured materials. We have developed a new plasma-induced coating method that allows effective surface modification of the entire surface of nanoporous materials by homogenous ultrathin (25 nm) carbon layers. This method allows fabrication of hybrid carbon-alumina materials with well 3

ordered nanoporous structure and variable pore size. Higher sp content in the deposited carbon layers 2

has been found beneficial for anti-corrosion applications, providing better protection than sp -rich carbon layers. Our measurements show that ultrathin DLC coatings on nanoporous alumina templates possess excellent corrosion resistance to all tested harsh chemical (acid/alkaline) environments even at high temperatures (up to 200 Â°C). These highly resistant amorphous carbon layers could be converted to single, double and multilayer graphene layers respectively by using a low-temperature graphitization process. This process allows integration of graphene with well ordered nanoporous structures and holds promise for the development of novel sensor membrane devices.

References

[1] L. H. Li, J. Cervenka, K. Watanabe, T. Taniguchi and Y. Chen, ACS Nano, Article ASAP DOI: 10.1021/nn500059s

Synthesizing 3D graphene foam with direct etching for energy storage applications 1

Sakineh Chabi , Zhuxian Yang , Chuang Peng , Yongde Xia , Yanqiu Zhu*

College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, Devon, UK Department of Chemical and Environmental Engineering, University of Nottingham Ningbo Campus, Ningbo, 315100 China *y.zhu@exeter.ac.uk

Abstract In this study, a general strategy for the synthesis of 3D graphene foams using chemical vapor deposition method and Nickel template was developed using a direct etching process. Large scale,4 2 cm , flexible graphene foams, without using PMMA or further acetone dissolving process, were obtained. The as-prepared graphene foam has a very high surface area (approaching theoretically maximum values and is higher than all reported values), and also shows a very low density of ca. 3 mg/ 3 cm which is believed to be originated from the robust interconnected 3D structures. All these features make it an excellent scaffold for 3D electrode in energy storage applications. In a traditional architecture of energy storage devices, there is always a compromise between energy density and power density mainly due to the limitations of two dimension (2D) structure of the electrodes [1]. It is hoped that a 3D graphene-based structure could offer both high energy and power densities by providing short pathways for electron and ions.-1 The structural, morphological and performance of the resulting graphene foams were characterized and assessed by using SEM (Fig1), Raman spectroscopy (Fig2) EDX, TEM, cyclic voltammetry (CV) tests, OCP-time and A.C Impedance techniques. After the complete removal of the nickel template, which was confirmed by EDX analysis and TGA test, the Raman spectroscopy study shows that the as-prepared samples are not made of a single layer graphene but consisted of a few layers of graphene sheets. The almost symmetric characteristics of the -1 2D (~2700 cm ) peak presented in Fig 2 confirm the graphene features of the samples [2]. In a graphite spectrum, a hump at the left side of 2D peak is normally visible [2]. The stability and cycleability of graphene foams were investigated by electrochemistry tests in a three electrode cell. The graphene foams were used directly as the working electrode, without using binder or other carbon additive. Binders such as PVDE are insulator and affect negatively the efficiency of the electrodes [3]. The tests revealed an excellent capacity retention and mechanical stability, even after 20000 cycles no capacity fading was observed. This capacity retention is attributed mainly to the strong interconnected 3D architecture, the hierarchical porous structure and large surface areas of the foam. References

[1] J. W. Long , B. Dunn , D. R. Rolison , H. S. White , Chem. Rev. 104 (2004) 4463. [2] Yu, Qingkai, et al. Applied Physics Letters 93 (2008) 113103. [3]. J. Jiang , Y. Li , J. Liu , X. Huang , C. Yuan , X. W. Lou , Adv. Mater, 24 (2012) 5166

Figures

(b) (a) Figure 1: a,b SEM images of graphene foams.

intensity(a.u)

40000 30000

20000 10000 0

500

1500

2500

3500

Raman shift(cm-1)

Figure 2 Raman spectroscopy of graphene foam.

CV Current(A)

7.00E-06 2.00E-06 1000 -3.00E-06

20000

-8.00E-06 0.8 0.6

1st 0.4

0.2

Potential (V vs Ag/AgCl)

Figure 3 cyclic voltammetry of graphene foam in KCl solution.

Graphene on copper: ab initio modelisation and growth Thomas Chanier, Philippe Gaillard, Pavel Moskovskin, StĂŠphane Lucas and Luc Henrard

Department of Physics, University of Namur, rue de Bruxelles 61, B-5000 Namur, Belgium thomas.chanier@gmail.com

Abstract Chemical Vapor Deposition is one of the more promising methods for the large scale production of graphene. Precise and reliable investigations at the atomic scale, supported by multiscale simulations, is must for better understanding of the growth processes. We report ab-initio density functional theory calculation of graphene on copper (111). We compared different functionals for the exchange correlation potential: the local density approximation, the generalized gradient approximation and van der Waals corrected functional that take into account more properly the interface between graphene and copper. We determined the stability of the different adsorption sites of single carbon and carbon clusters in order to mimic the initial step of graphene growth on copper (111). We also considered a perfect graphene sheet on copper considering the different configurations fcc-hcp, top-fcc, top-hcp and the bridge configurations bridge-top, bridge-fcc, bridge-hcp. Our results give a thorough insight on the initial stages of graphene growth on copper (111). Large scale Kinetic Monte-Carlo simulations, based on activation energies for more stable adsorption sites and on the diffusion barriers obtained by ab-initio calculations are reported.

Top view of the supercells after relaxation: top (blue), grey (fcc), yellow (hcp) adsorption sites, (a) fcc-hcp, (b) top-fcc, (c) top-hcp, (d) bridge-top, (e) bridge-fcc and (f) bridge-hcp graphene configuration.

Contribution (oral)

Contact Resistivity Model of Metal-Graphene Junctions Based on Bardeen-Transfer-Hamiltonian Method 1*

Ferney A. Chaves , David Jiménez , Aron W. Cummings , and Stephan Roche 1

2,3

Departament d’Enginyeria Electrònica, Escola d’Enginyeria, Universitat Autònoma de Barcelona, Campus UAB, 08193 Bellaterra, Spain. 2 ICN2 – Institut Català de Nanociència i Nanotecnologia, Campus UAB, 08193 Bellaterra, Spain. 3 ICREA, Institució Catalana de Recerca i Estudis Avançats, 08070 Barcelona, Spain. * ferneyalveiro.chaves@uab.cat

Abstract While graphene-based technology shows great promise for a variety of electronic applications, including radio-frequency devices [1], the resistance of the metal-graphene contact is a technological bottleneck for the realization of viable graphene electronics [2]. One of the most important factors in determining the resistance of a metal-graphene junction is the contact resistivity. Despite the large number of experimental works that exist in the literature measuring the contact resistivity [3], a simple model of it is still lacking. In this paper we present a comprehensive analytical model for the contact resistivity of these junctions, based on the Bardeen Transfer Hamiltonian method [4]. This model unveils the role played by different electrical and physical parameters in determining the specific contact resistivity, such as the chemical potential of interaction, the work metal-graphene function difference, and the insulator thickness between the metal and graphene. In addition, our model reveals that the contact resistivity is strongly dependent on the bias voltage across the metal-graphene junction. This model is applicable to a wide variety of graphene-based electronic devices, and thus is useful for understanding how to optimize the contact resistance in these systems.

REFERENCES [1] Schwierz, F. Graphene Transistors: Status, Prospects, and Problems. Proceedings of the IEEE 2013, 101, 1567-1584 [2] Novoselov, K.S.; Geim, A.K.; Mozorov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666. [3] Nagashio, K.; Toriumi, A. Density-of-States Limited Contact Resistance in Graphene Field-Effect Transistors. Jap. Journal Appl. Phys. 2011, 50, 070108. [4] Bardeen, J. Tunnelling from a Many-Particle Point of View. Phys. Rev. Lett. 1961, 6, 57. FIGURE

The Design and Fabrication of Twisted Multilayer Graphene with Fine Tunable Rotated Angle 1

Xudong Chen , Zhibo Liu *,Wenshuai Jiang , Wei xin , Fei Xing , Peng Wang , Bin Dong , Xiaoqing 2 2 1 Yan , Yongsheng Chen , Jianguo Tian 1

The Key Laboratory ofWeak Light Nonlinear Photonics, Ministry of Education, Teda Applied Physics 2 School and School of Physics, Nankai University, Tianjin 300457, China, The Key Laboratory of Functional Polymer Materials and Center for Nanoscale Science & Technology, Institute of Polymer Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China. rainingstar@nankai.edu.cn

Abstract: The properity of few-layer graphene is determined by the ratation angles and interactions between layers. The theoretical calculation will guide the design and fabrication of the rotated graphene. It has been demonstrated that strong interlayer interactions will occur in the low rotation-angle regime. Strong Raman G band enhancement is observed at specific angle, which depend on the energy of the excitation laser. The rotated graphene used in experiments are commonly grown by the CVD method, and then the twisting angles are identiified by TEM analysis. However, the control of the twisting angle could be hard to be achieved by this method. To find the sample whose rotation angle is closing to the designed angle, a great number of rotated graphene need to be prepared. In addition, only double-layer graphene with large scale can be prepared by this method. In order to achieve the designed rotationangle and specific shaps, a new process based on the transfer of microcleaving graphene and femtosecond laser microfabrication is developed. The deviation of the rotation angle fabricated by this method is lower than 0.1o. This method based on microcleaving graphene could achieve the fabrication of the rotated graphene with more than two layers, which will great promote the study of the rotated graphene in theory and application. References [1] C. R. Dean, A. F. Young, I. Meric, C. Lee, L. Wang, S. Sorgenfrei, K. Watanabe, T. Taniguchi, P. Kim, K. L. Shepard & J. Hone, Nat. Nanotech., 5 (2010) 722-726. [2] A. K. Geim & I. V. Grigorieva, Nature, 499 (2013) 419-425. [3] X. Chen, Z. Liu, W. Jiang, X. Yan, F. Xing, P. Wang, Y. Chen & J. Tian, Sci. Rep., 3 (2013) 3216. [4] R. W. Havener, H. Zhuang, L. Brown, R. G. Hennig, & J. Park, Nano Lett., 12 (2012) 3162-3167. [5] K. Kim, S. Coh, L. Z. Tan, W. Regan, J. M. Yuk, E. Chatterjee, M. F. Crommie, M. L. Cohen, S. G. Louie & A. Zettl, Phys. Rev. Lett., 108 (2012) 246103. [6] R. He, T. Chung, C. Delaney, C. Keiser, L. A. Jauregui, P. M. Shand, C. C. Chancey, Y. Wang, J. Bao &Y. P. Chen, Nano Lett., 13 (2013) 3594-3601.

High performance photo-detector based on few layer InSe 1,2

Zhesheng Chen , Johan Biscaras , Abhay Shukla

Institut de Minéralogie et de Physique des Milieux Condensés, CNRS-UMR7590, Université Pierre et Marie Curie, Paris 75252, France 2 School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, PR China * Corresponding author: abhay.shukla@upmc.fr Abstract Since graphene was first discovered in 2004, few layered materials have generated considerable enthusiasm in the nanotechnology and condensed matter physics communities because of the possibility of obtaining ideal two-dimensional (2D) materials with exotic properties [1-2]. For example, monolayer MoS2 with direct bandgap has shown outstanding promise for applications in photo-detection and memory device [3-4]. However, monolayer Indium selenide (InSe) which is a III-VI semiconductor with an indirect bandgap is expected to make a transition towards a direct bandgap compound when the number of layers increases to five layers [5]. Moreover, it is expected that few layer InSe should also show promising photo-electronic properties. We prepare few layer InSe using the anodic bonding method [6], and charcaterize it by transmission electron microscopy (TEM) and Raman spectroscopy to analyze the structure and polytype of samples. From the TEM data, the hexagonal structure is determined which corresponds to ȕ RU İ SRO\W\SH 4 -1 Combined with Raman data ( Ƚ 3 $¶¶2) mode at 199cm ) the İ SRO\W\SH LV ILQDOO\ FRQILUPHG [7]. Eight layer InSe is then transferred to SiO2/Si substrate followed by electron beam lithography and electrode evaporation to fabricate 2D photo-detector device. The response time, on-off ratio, responsivity as well as external quantum efficiency (EQE) are analyzed with a 532nm laser as the light source. The 3 response time is less than 150ms with complete rise or decay, and on-off ratio is larger than 10 which -2 shows fast response properties. In addition, the responsivity and EQE are 7.5×10 A/W and 17.5% under the source-drain voltage at 10V without back gate, respectively. Finally the back gate is applied to enhance the performance of 2D InSe photodetector. As a result the photocurrent increases with the responsivity and EQE higher than 2 A/W and 460% respectively when 50V back gate is applied.

References [1] Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, Grigorieva I V and Firsov A A, Science (2004) 666. [2] Geim A K and Novoselov K S, Nat. Mater. (2007) 183. [3] Lopez-Sanchez O, Lembke D, Kayci M, Radenovic A and Kis A, Nat. nanotechnol. (2013) 497. [4] Roy K, Padmanabhan M, Goswami S, Sai T P, Ramalingam G, Raghavan S and Ghosh A, Nat. nanotechnol. (2013) 826 [5] Mudd G W, Svatek S A, Ren T, Patanè A, Makarovsky O, Eaves L, Beton P H, Kovalyuk Z D, Lashkarev G V, Kudrynskyi Z R and Dmitriev A I, Adv. Mater. (2013) 5714. [6] Chen Z, Gacem K, Boukhicha M, Biscaras J and Shukla A, Nanotechnol. (2013) 415708. [7] Carlone C, Jandl S and Shanks H R, Solid State Commun. (1981) 123.

Figures

Figure 1. Optical images and AFM of few layer InSe during transfer process (a) on glass, (b) on SiO 2/Si coated with polymer after transfer (c) on SiO2/Si after polymer dissolved and (d) AFM image of few layer InSe after transfer process.

Figure 2. Eight layered InSe photo-detector performances on SiO2/Si (a), (b), (c) and (d), respectively. (a) Optical image of InSe photo-detector prepared on SiO2/Si (b) Photoresponse time during photocurrent rise and decay with laser switching on and off, and a bias voltage of 10V. (c) Ids-Vds characterization of InSe with source-drain sweep from -10V to 10V and no back gate voltage. (d) Ids-Vgs characterization of InSe with back gate sweep from -40V to 50V and Vds at 10V.

Fe-catalyzed Etching of Graphene and Few-layer Graphene Guangjun Cheng, Irene Calizo, Angela R. Hight Walker Physical Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, MS 8443, Gaithersburg, MD 20899, USA guangjun.cheng@nist.gov Fe-catalyzed etching of graphite and few-layer graphene (FLG) has been used to create channels with desired crystalline edges [1,2]. Due to the strong Fe-C interaction, graphene can be etched through either carbon hydrogenation or carbon dissolution into Fe alone. In this work, we investigated the Fecatalyzed etching of graphene and few-layer graphene (FLG) in forming gas (10% H2/90% N2) or N2. Fe thin films were deposited onto mechanically exfoliated graphene and FLG flakes on Si/SiO2 substrates using a sputtering technique. When the thin film was rapidly annealed in either gas environment, particles were produced due to the dewetting of the films [3], and etching of graphene and FLG occurred. Low-voltage scanning electron microscopy (LVSEM) and Raman spectroscopy have been used to characterize the etched graphene and FLG regions. The combined microscopic and spectroscopic evidence reveals the strikingly different carbon residues in etched graphene and FLG regions produced in these two different gas environments, thus providing an insight into the catalytic mechanisms.

Figure 1a shows an optical image of mechanically exfoliated graphene and FLG regions on a Si/SiO2 substrate before depositing a Fe thin film. Figures 1b-1c show the representative Raman spectra of SULVWLQH JUDSKHQH DQG )/* FROOHFWHG DURXQG * DQG *â&#x20AC;Ť Ţ&#x2013;â&#x20AC;ŹSHDNV UHVSHFWLYHO\ $V WKH QXPEHU RI JUDSKHQH OD\HUV 1 LQFUHDVHV WKH LQWHQVLW\ RI * SHDN LQFUHDVHV )LJXUH E )LJXUH F VKRZV WKH FKDQJH RI *â&#x20AC;Ť Ţ&#x2013;â&#x20AC;Ź peak in position, shape, and intensity as the number of graphene layers graphene changes. The exact numbers of the graphene layers ranging from 1 to 7 (1L to 7L labeled in Figure 1a) are determined by the fact that the integrated area of G peak increase almost linearly as the number of graphene layers increases. After annealing the Fe thin film at 950 oC for 30s in a forming gas environment, the LVSEM image (Figure 1d) of the area in Figure 1a reveals that the dewetting of the Fe thin film takes place and the particles have been produced in the graphene, FLG, and substrate regions. The particles in the 1L, 2L, and 3L graphene regions are more densely distributed than those in the 6L and 7L graphene regions. The Raman spectra (Figure 1e) collected from the post-annealing graphene and FLG regions change significantly from those from their pristine counterparts. For monolayer graphene, after -1

annealing the Fe thin film, a peak ~1350 cm (the D peak) appears and both the G and G' peaks are significantly attenuated and broadened. The appearance of the D peak in the spectrum collected from the post-annealing graphene region, together with the significant reduction in the intensity of G and G' 2

peaks, suggests that the graphene is severely etched but that there exists sp carbon in the etched graphene region. For the spectrum collected from post-annealing bilayer graphene region, D and G peaks are also clearly observed. Interestingly, for the spectra collected from the post-annealing 3L to 7L JUDSKHQH UHJLRQV QR ' * DQG *â&#x20AC;Ť Ţ&#x2013;â&#x20AC;ŹSHDNV DUH REVHUYHG +RZever, we notice that all the Raman spectra collected from

the

post-annealing

graphene

and

FLG

regions exhibit

upward-sloping

photoluminescence (PL) background. As the number of graphene layers increases, the PL slope increases.

Etched graphene and FLG were also observed for the Fe film annealed in N2, suggesting that this graphene etching process can also occur through a carbon diffusion process. However, the Raman

spectra collected from post-annealing graphene and FLG regions in N2 still exhibit strong Raman G and *Âś SHDNV even with the presence of the D peak and no up-sloping PL background. LVSEM images reveal the visible graphene and FLG residues among the particles. We attribute the strong PL background from the carbon residues in the etched graphene and FLG regions produced in forming gas to the formation of hydrogenated amorphous carbon [4]. Therefore, our results provide insights into the catalytic roles which Fe particles play during the carbon hydrogenation in the dissociation of hydrogen into hydrogen atoms and in the production of hydrogenated amorphous carbon.

References [1] Tomita, A.; Tamai, Y. J. Phys. Chem. 78 (1974), 2254. [2] Datta, S.S.; et al, Nano Letters 8 (2008), 1912. [3] Carl V. Thompson, Annu. Rev. Mater. Res. 42 (2012), 399. [4] Ferrari, A. C.; Robertson, J. Phys. Rev. B 61 (2000), 14095. Figures

Figure 1. (a) Optical images of pristine graphene and few-layer graphene (FLG) on a Si/SiO2 substrate. (b,c) Representative micro-Raman spectra of graphene and FLG in the regions of G and *Ó&#x152;peaks, respectively. (d) LVSEM image of post-annealing graphene and FLG regions in forming gas. (e) Representative micro-Raman spectra collected from post-annealing graphene and FLG regions in forming gas.

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Valley polarization in magnetically doped single layer transition metal dichalcogenides Yingchun Cheng, Qingyun Zhang, Udo.Schwingenschlรถgl PSE Division, KAUST, Thuwal 23955-6900, Kingdom of Saudi Arabia yingchun.cheng@kaust.edu.sa Abstract The fields of electronics and spintronics require an active control and manipulation of the charge and spin degrees of freedom [1]. Valleytronics, on the other hand, is very new field that relies on the property that the conduction/valence bands have two or more minima/maxima at equal energy but different momenta. For valleytronics devices it is necessary to induce valley polarization, i.e., control the number of electrons in each valley, typically by strain [2] or a magnetic field [3, 4]. In general, twodimensional materials have raised a lot of interest both for fundamental and applied reasons. Examples are semiconductor quantum wells [5], noble metal surfaces [6], graphene [7], and topological insulators [8]. Semiconducting single layer transition metal dichalcogenides MX2 with M = Mo, W and X = S, Se, Te and D3h point group have caught attention, because they display distinctively different physical properties as compared to their bulk compounds with D6h point group. There exists a crossover from an indirect band gap in multilayers to a direct band gap in the single layer limit [9-12], see Fig. 1(a). In the latter the conduction and valence band edges are located at the K points of the two-dimensional hexagonal Brillouin zone, see Fig. 1(c). These two inequivalent valleys constitute a binary index for low energy carriers, which gives rise to a valley Hall effect and valley dependent optical selection rules for interband transitions at the K points [13-15]. It has been demonstrated that optical pumping with circularly polarized light can achieve a dynamic valley polarization in single layer MoS2 [16-18]. From application point of view, the equilibrium valley polarization in single layer MX2 is more important, which has not been investigated till now experimentally or theoretically. The interplay between spin orbit coupling and ferromagnetism in two-dimensional materials gives rise to a variety of unconventional phenomena, such as the quantum anomalous Hall effect [19-22]. In addition, it recently has been put forward that dichalcogenides doped with magnetic transition metal atoms form a promising platform for two-dimensional dilute magnetic semiconductors [23-25]. However, these studies did not take into account the spin orbit coupling, which interconnects the spin and valley physics, making it desirable to investigate the effects of the exchange field induced by magnetic doping. We propose in this work a method to control the valley polarization by magnetic doping, see Fig. 1(b,d, and e). Various possible Mn doping sites in single layer MoS2 are studied to investigate the influence of the exchange field on the electronic structure by first-principles calculations. We will argue that the strength of the spin orbit coupling together with the exchange energy determine the valley polarization, which can be inverted by modifying the spin polarization. References [1] S. A. Wolf, D. D. Awschalom, R. A. Buhrman, J. M. Daughton, S. von Molnar, M. L. Roukes, A. Y. Chtchelkanova, and D. M. Treger, Science 294 (2001) 1488. [2] O. Gunawan, Y. P. Shkolnikov, K. Vakili, T. Gokmen, E. P. De Poortere, and M. Shayegan, Phys. Rev. Lett. 97 (2006) 186404. [3] Y. P. Shkolnikov, E. P. De Poortere, E. Tutuc, and M. Shayegan, Phys. Rev. Lett. 89 (2002) 226805. [4] Z. W. Zhu, A. Collaudin, B. Fauque , W. Kang, and K. Behnia, Nature Phys. 8 (2012) 89. [5] M. Kohda, T. Bergsten, and J. Nitta, J. Phys. Soc. Japan 77 (2008) 031008. [6] S. LaShell, B. A. McDouall and E. Jensen, Phys. Rev. Lett. 77 (1996) 3419. [7] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov, Science 306 (2004) 666. [8] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82 (2010) 3045. [9] A. Splendiani, L. Sun, Y. Zhang, T. Li, J. Kim, C.-Y. Chim, G. Galli, and F. Wang, Nano Lett. 10 (2010) 1271. [10] K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, Phys. Rev. Lett. 105 (2010) 136805. [11] Z. Y. Zhu, Y. C. Cheng, and U. Schwingenschlรถgl, Phys. Rev. B 84 (2011) 153402. [12] Y. C. Cheng, Z. Y. Zhu, M. Tahir, and U. Schwingenschlรถgl, EPL 102 (2013) 57001. [13] D. Xiao, W. Yao, and Q. Niu, Phys. Rev. Lett. 99 (2007) 236809.

[14] W. Yao ,D. Xiao, and Q. Niu, Phys. Rev. B 77 (2008) 235406. [15] D. Xiao, G.-B. Liu, W. X. Feng, X. D. Xu, and W. Yao, Phys. Rev. Lett. 108 (2012) 196802. [16] H. L. Zeng, J. F. Dai, W. Yao, D. Xiao, and X. D. Cui, Nature Nanotech. 7 (2012) 490. [17] K. F. Mak, K. L. He, J. Shan, and T. F. Heinz, Nature Nanotech. 7 (2012) 494. [18] T. Cao, G. Wang, W. P. Han, H. Q. Ye, C. R. Zhu, J. R. Shi, Q. Niu, P. H. Tan, E. G. Wang, B. L. Liu, and J. Feng, Nature Comm. 3 (2012) 887. [19] X.-L. Qi, R. D. Li, J. D. Zang, and S.-C. Zhang, Science 323 (2009) 1184. [20] R. Yu, W. Zhang, H.-J. Zhang, S.-C. Zhang, X. Dai, and Z. Fang, Science 329 (2010) 61. [21] I. Garate and M. Franz, Phys. Rev. Lett. 104 (2010) 146802. [22] Z. H. Qiao, S. Y. A. Yang, W. X. Feng, W.-K. Tse, J. Ding, Y. G. Yao, J. Wang, and Q. Niu, Phys. Rev. B 82 (2010) 161414(R). [23] Y. C. Cheng, Z. Y. Zhu, W. B. Mi, Z. B. Guo, and Schwingenschlögl, Phys. Rev. B 87 (2013) 100401. Figures

Figure 1. Schematic view of the band structure of single layer MoS2 near the K and K¶ points: (a) pristine without spin orbit coupling, (b) with exchange field and without spin orbit coupling, (c) pristine with spin orbit coupling, and (d) with exchange field and with spin orbit coupling. (e) Same as (d) but with inverted spin polarization.

Photoresponsivity characterization of all-graphene p-n vertical-junction photodetectors at various doping concentrations Dong Hee Shin, Sung Kim, Chang Oh Kim, Jong Min Kim, Ju Hwan Kim, Kyeong Won Lee, SukHo Choi Department of Applied Physics, Kyung Hee University, Yongin 446-701, Korea sukho@khu.ac.kr Abstract Previous studies of photocurrent (PC) in graphene have demonstrated photoresponse near metallic contacts [1], at the interface between single-layer and bilayer regions [2], at lateral-type p-n junctions [3], or in the heterostructures with two-dimensional semiconductors [4]. Here, we firstly fabricate and characterize vertical-type graphene p-n junctions for photodetection. Single-layer graphene was synthesized by using chemical vapor deposition, and transferred on SiO 2/Si substrates. For the formation of graphene p-n junction, a solution of benzyl viologen (BV) was first dropped and 2

spin-coated on the 10 x 10 mm graphene/SiO2/p-type Si wafer, and then annealed at 100 C for 10 2

min to make graphene uniformly n-type. Subsequently, a 5 x 5 mm bare graphene was transferred on 1/4 area of the n-graphene/SiO2/p-type Si wafer, a solution of AuCl3 was dropped and spin-coated on the surface of graphene, and similarly annealed. As a result, the graphene p-n vertical junction was formed on the 1/4 area of the SiO2/p-type Si wafer. 1-mm-diameter Ag electrodes were deposited on the top of both n- and p-graphene layers to complete the graphene p-n device. The p-n junctions were fabricated for various n doping concentrations at a fixed highest p-doping concentration. The devices were named as D1

D5 when doping time (tD) in the BV exposure was 0.5, 1, 2, 3, and 4 min,

respectively. The dark current (DC)-voltage (I-V) curves are symmetric and linear in the forward/reverse directions with respect to zero voltage for D1 to D3 devices, indicating no rectifying behaviors at the p-n junctions, consistent with Klein-tunneling effect [5]. The I-V characteristics of these devices are almost not varied even under illumination at various photon wavelengths from 300 to 1000 nm. For tD > 2 min, the DC is greatly reduced over the full range of bias voltage, with the current reduction being stronger under forward bias than under reverse bias. The dark I-V curves show non-linear properties with varying bias voltage, indicating rectifying behaviors. The graphene p-n junction-based photodetectors (GPDs) shows strong PC responsivity in the UV-visible-near IR ranges, as shown in Fig. 1. High detectivity is achieved in the broad spectral range from ultraviolet to nearinfrared and the photoresponse is almost invariant even after 6 months since the GPDs were fabricated, as shown in Fig. 2. The GPD structures permit a large PC flow by the tunneling of charge carriers through the interlayer formed between the p and n graphene layers at higher n doping concentrations. These results are discussed based on possible physical mechanisms. References [1] J. Park, Y. H. Ahn, and C. Ruiz-Vargas, Nano Lett. 5 (2009) 1742Âą1746.

[2] X. Xu, N. M. Gabor, J. S. Alden, A. M. van der Zande, and P. L. McEuen, Nano Lett. 2 (2010) 562566. [3] N. M. Gabor, J. C. W. Song, Q. Ma, N. L. Nair,T. Taychatanapat, K. Watanabe, T. Taniguchi, L. S. Levitov, and P. Jarillo-Herrero, Science, 6056 (2011) 648-652. [4] L. Britnell, R. M. Ribeiro, A. Eckmann, R. Jalil, B. D. Belle, A. Mishchenko, Y.-J. Kim, R. V. Gorbachev, T. Georgiou, S. V. Morozov, A. N. Grigorenko, A. K. Geim, C. Casiraghi, A. H. Castro Neto, and K. S. Novoselov Science, 6138 (2013) 1311-1314. [5] A. F. Young and P. Kim, Nature Phys. 3 (2009) 222-226.

Figures

Fig. 1. Spectral responsivities of D4 device under forward-bias voltages from 1 to 3 V.

Fig. 2.Time-dependent responsivities of D4 device under different bias voltages for photon wavelengths of 600 nm.

Graphene-Embedded Nanopore Device Wook Choi, Chang-Soo Han Department of Mechanical Engineering, Korea University, Seoul 136-701, South Korea cshan@korea.ac.kr

Over the past decade, various researches for nano-channel and nanopore have been tried.

[1]

Especially, nanopore-based sensor has been studied for the detection of bio molecules or chemicals without any amplification or label. [2] Graphene is very suitable material to nanopore device, because its thickness is very effective to detect nanoscale material.

[3]

Here, we demonstrate Graphene-embedded

nanopore device. Firstly, we prepared the transmission electron microscopy (TEM) grid with shallow area of silicon nitride in the center of the device. CVD-grown monolayer graphene is transferred onto silicon nitride substrate, and performed the atomic layer deposition process for Al2O3 dielectric layer. Then, TEM sculpting has been tried to create single artificial nanopore with sub 10 nm size. [4] Using this nanopore, we measured the ion transport through the hole by using patch clamp instrument.

References [1]

C. Dekker, Nature nanotechnology, 2 (2007) 209-215.

[2]

Y.-R. Kim, J. Min, I.-H. Lee, S. Kim, A.-G. Kim, K. Kim, K. Namkoong, C. Ko, Biosensors & bioelectronics, 22 (2007) 2926-2931.

[3]

G. Schneider, S. Kowalczyk, V. Calado, G. Pandraud, H. Zandbergen, L. Vandersypen, C. Dekker, Nano letters, 10 (2010), 3163-3167.

[4]

, Applied Physics Letters, 93 (2008) 113107.

Comparisons between Classical, Semiclassical, and Quantum Plasmonics in Graphene Nanodisks Thomas Christensen,1, 2, ∗ Weihua Wang,1, 2, ∗ Martijn Wubs,1, 2 Antti-Pekka Jauho,2, 3 and N. Asger Mortensen1, 2 1

Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark Center for Nanostructured Graphene, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark 3 Department of Micro- and Nanotechnology, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark 2

We study the transitions from classical, semiclassical, and quantum plasmonic behavior in graphene nanodisks in the quasistatic limit. Specifically, we investigate four hierarchies of approximation: 1. Local-reponse approximation (LRA), embodying the traditional approach in plasmonic light-matter interaction. 2. Hydrodynamic response, adapted to the response of graphene, including the first nonlocal correction to its optical response. 3. Real-space random phase approximation (RPA) formulation with electron states calculated from the Dirac-Weyl equation, with infinite mass and zigzag boundary conditions (BCs). 4. Real-space RPA with electron states calculated from a nearest-neighbor tight-binding (TB) treatment. See Figure 1 for a summary of the considered hierarchies. Levels 1 and 2 constitute bulk response approximations, while levels 3 and 4 take the finite extent of the graphene structure into consideration with different precision: in the Dirac-Weyl treatment, the Hamiltonian is that of bulk graphene in the low-energy regime with boundary conditions accounting approximately for the topology and extent of the structure, whilst the TB treatment accounts naturally for the atomistic features of the structure. Additionally, levels 3 and 4 also naturally include the effects of energy level quantization and nonlocality. Graphene nanodisks are considered, which allows semi-analytical treatments for approaches 1 through 3. Additionally, nanodisks, with their nontrivial edgeconfigurations, highlight the importance of edge

LRA

Hydrodynamic

σbulk (ω )

σbulk (r − r′ , ω )

states in TB treatments. The treatment of edge-states is completely absent in the bulk descriptions, i.e. in the LRA and hydrodynamics, but can be qualitatively accounted for in the Dirac-Weyl approach with zigzag BCs. Below we explicate the essence of the four approaches: 1. Local-response approximation: Taking the localresponse limit of the low-energy dispersion ǫ = ±~vF k response result, the conductivity of graphene is given by:1 σbulk (ω ) = σD (ω ) + σI (ω ),

with intra- (Drude) and inter-band contributions

2ǫF − ~ω

ie 2 ǫF ie 2

. σD (ω ) = , σI (ω ) = log

π~(ω + i γ ) 4π~ 2ǫF + ~ω

with Fermi level ǫF and loss rate γ. 2. Hydrodynamic reponse in graphene: A Taylor approximation of the low-energy response result to first non-vanishing component in momentum, k , yields (neglecting loss): βD2 2 βI2 2 σ (k , ω ) ≃ σD (ω ) 1 + 2 k + σI (ω ) 1 + 2 k , (2) ω ω p where the plasma velocities βD = 3/4vF and βI = p 1/2vF differ. Neglecting this difference and letting βI → βD , which induces only a small error since the Drude contribution is usually dominant, allows recasting the response as a single hydrodynamic equation for the current J and electric field E: J(r, ω ) +

Dirac-Weyl RPA

Hˆ = vF σ (∗) · pˆ & BCs

TB RPA

Hˆ = γ

† an† bm + bm an

hn,mi

FIG. 1: Schematic illustration of the considered levels of approximation in our treatment.

(1)

βD2 ∇k ∇k · J(r, ω ) = σD (ω )E(r, ω ). 2 ω

(3)

In both hydrodynamic and local descriptions we solve the electrostatic problem due to an incident wave using a semi-analytical polynomial expansion technique.2 3. Dirac-Weyl and RPA: The Dirac-Weyl equation for uncoupled Dirac valleys can be cast as a twoˆ spinor equation Hψ = ǫψ with the Hamiltonian Hˆ κ = vF σ · pˆ for the K-valley (and Hˆ = vF σ ∗ · pˆ for the K′ valley), and spinor components associated with the A- and B-sublattice.3 BCs corresponding to zigzag, armchair, and mass confinement can be imposed. Here we focus on the comparison of zigzag4 and

2 mass confinement.5 Application of BCs discretizes the allowed states {ǫ, ψ}ln with angular and radial quantum numbers l and n. Additionally, an infinitely degenerate band of zero-energy edge-states exist for the zigzag BC. The non-interacting polarizability, χ0 , is computed in a real-space formulation according to:6 χ0 (r, r′ ; ω ) = 2

κll ′ nn′

flκ′ n′ − flnκ ~ω + i ~η − (ǫκln − ǫκl ′ n′ )

(4)

κ† κ† ′ κ ′ × [ψ κ† l ′ n′ (r)ψ ln (r)][ψ ln (r )ψ l ′ n′ (r )],

with the summation extending also over the valley index κ, with Fermi-Dirac functions flnκ , and with electron relaxation-rate η = γ/2. 4. Tight-binding and RPA: The TB Hamiltonian, including only nearest-neighbor interaction with P energy γ, reads as Hˆ = γ hj,j ′ iaˆ j† bˆ j ′ + bˆ j†′ aˆ j , with A- and B-sublattice annihilation (creation) operators (†) (†) aˆ j and bˆ j for 2p orbitals at site j and position rj . Diagonalization of this Hamiltonian yields the electron states. The polarizability is evaluable at the lattice sites, i.e. it takes a discrete representation in real-space χ0 (rj , rj ′ ; ω ). It is determined following the scheme in Eq. (4), but with the summation running over the TB states.6 The interaction with external potentials φext , for both the Dirac-Weyl and TB approaches, is introduced by self-consistently coupling the total potential φ and charge ρ through the equations ρ(r) = Rthe 0induced R χ (r, r′ )φ(r′ ) dr′ and φ(r) = φext (r)+ V (r, r′ )ρ(r′ ) dr′ , with V(r, r′ ) denoting the Coulomb interaction, thereby applying the RPA.

radii, being distinct but qualitatively similar in the Dirac-Weyl and TB approaches. These features are due in part to near-zero energy edge states and in part due to energy level quantization. (b) Assessing the role of nonlocality in the optical response. We find excellent agreement between the Dirac-Weyl and hydrodynamic approaches at larger radii, both exhibiting quantitatively identical blueshifts compared with the LRA result. These predictions of blueshifts, however, stand in contrast with the predictions of TB which predict minor redshifts6 of the dipole resonance. (c) The sensitivity of TB calculations to atomistic configuration variations, for fixed radii, and sensitivity to polarization-angle. We consider the ensemble-averaging of TB optical spectra and compare with the continuum approaches. We hope that our comparisons of the different hierarchies of approximation will offer new insight into the nature of quantum plasmonic effects in graphene nanostructures. Additionally, we aim to showcase the applicability of the continuum DiracWeyl approach, and the feasibility of including the effects of nonlocality and energy quantization in a single continuum scheme. In geometries with welldefined edges, such as zigzag or armchair, we predict that the Dirac-Weyl approach will generally agree very well with TB calculations, but at a reduced numerical cost and with a more transparent interpretation.

Acknowledgments

In our comparison of the above four approaches for graphene nanodisks we examine and focus on the following aspects: (a) The emergence of nonclassical features in the optical response of nanodisks at small

The Center for Nanostructured Graphene is sponsored by the Danish National Research Foundation, Project DNRF58. This work was also supported by the Danish Council for Independent Research - Natural Sciences, Project 1323-00087.

∗

2 3

T. Christensen and W. Wang contributed equally to this work. L. A. Falkovsky and A. A. Varlamov, Eur. Phys. J. B 56, 281 (2007). A. Fetter, Phys. Rev. B 33, 5221 (1986). A. Castro Neto, F. Guinea, N. Peres, K. Novoselov, and A. Geim, Rev. Mod. Phys. 81, 109 (2009).

L. Brey and H. Fertig, Phys. Rev. B 73, 195408 (2006). M. Berry and R. Mondragon, Proc. R. Soc. Lond. A 412, 53 (1987). S. Thongrattanasiri, A. Majavacas, and F. Garc´ıa de Abajo, ACS Nano 6, 1766 (2012).

In vivo biodegradation of graphene: A Confocal Raman Microscopy study Girish Chundayil Madathil, Abhilash Sasidharan, G. Siddaramana Gowd, Shantikumar Nair, Manzoor Koyakutty Amrita Centre for Nanosciences & Molecular Medicine, Amrita Vishwa Vidyapeetham University, Cochin, India- 682 041 manzoork@aims.amrita.edu Abstract The use of graphene based nanomaterials for biomedical applications is gaining huge interest. For its meaningful clinical translation, a proper knowledge about toxico-kinetics of graphene and its interaction with biological components is highly essential. In this study, using confocal Raman microscopy, we have investigated the fate of graphene in vivo, in intravenously injected mouse models up to 3 months. 3D Raman images of graphene localized in tissue sections from organs such as lung, liver, kidney and spleen were created by k-means cluster analysis (KCA) imaging, which revealed the size of aggregated graphene nanoparticles in tissues as 1-10 Âľm. Raman spectroscopic profile of graphene related structural disorder occurred over 3 months from tissue embedded graphene were monitored by DQDO\]LQJ WKH IRUPDWLRQ RI GHIHFW UHODWHG 'Âś EDQG line broadening of D and G bands (Č˝D Č˝G) , increase in ID/IG ratio and overall intensity reduction. KCA imaging enabled to observe the defects in graphene aggregates within a spatial resolution of ~312 nm and showed that the structural disorders were mostly th evident on the edges of graphene aggregates from 8 day onwards and grew towards inner regions over 3 months. Immuno-histopatholgy (CD68 macrophage specific antibody) analysis reveals that defective graphene aggregates were found from tissue bound macrophages of lung, liver and spleen. 2 This suggests the possible enzymatic biodegradation of graphene caused by the breakage of sp C-C 3 network in graphene leading to more number of amorphous or sp carbons. Furthermore, in vitro studies conducted on macrophage cell lines showed similar defect related spectral characteristics from macrophage engulfed graphene that confirms the possible macrophage mediate biodegradation of graphene. References [1] Girish C M, Abhilash S, Gowd G S, Shantikumar N, Manzoor K, Adv. Healthcare Mater., 2 (2013) 1489. [2] Dresselhaus M S, Jorio A, Hofmann M, Dresselhaus G, Saito R, Nano Lett., 10 (2010) 751. [3] Ferrari A C, Robertson J, Phil. Trans. R. Soc. Lond. A, 362 (2004) 2477. [4] Kagan V E, Konduru N V, Feng W, Allen B L, Conroy J, Volkov Y, Vlasova I I, Belikova N A, Yanamala N, Kapralov A, Tyurina Y Y, Shi J, Kisin E R, Murray A R, Franks J, Stolz D, Gou P, Seetharaman J K, Fadeel B, Star A, Shvedova A A, Nature 5 (2010) 354. Figures

Fig 1: 3D image of graphene embedded liver tissue section. z-stack images (x,y,z: 70,70,2.8 Âľm) from 7 planes with an inter-planar distance of 400 nm were acquired and created using KCA (graphene in red and tissue in blue).

Fig 2: CD68 stained images (A,a), Raman images (B,C,b,c) and Raman spectra (D, d) of 5 different spots on graphene aggregate from tissue after 24 hour (A,B,C,D) and 3 months (a,b,c,d) of intravenous administration of graphene. Raman spectra from the edges of graphene aggregates from 3 months tissue section clearly indicates the spectral features related to biodegradation of graphene.

Highly magnetic core-shell graphene coated Fe/Co nanoparticles 1,2

Maria Sarno , Claudia Cirillo , Massimiliano Polichetti 1

2,3

and Paolo Ciambelli

1,2

Department of Industrial Engineering, Research Centre NANO_MATES, Department of Physics University of Salerno, via Giovanni Paolo II, 134, 84084 Fisciano, Italy msarno@unisa.it

Introduction. Graphene coated magnetic nanoparticles (GCMNP) are object of a lot a research addressed to improve chemical and thermal stability and biocompatibility of magnetic nanoparticles (MNPs), in view of the exploitation of their properties in different applications including catalytic, environmental, biological, biomedical and electronic. Carbon covering has many advantages over other coatings, such as much higher chemical and thermal stability, easy functionalization. Typically, a two step process (MNP synthesis and then coating) is performed, however producing GCMNPs in a single step is a fascinating challenge [1]. Among different strategies suggested to prepare MNPs, Chemical Vapor Deposition (CVD) is the easiest one to be scaled up towards an economically viable production [2]. In fact, little attention has been devoted to the effect of process parameters in the preparation of stable MNPs, to obtain a quality controlled product and this is even more rare for GCMNPs. For a given catalyst and carbon source the CVD products strongly depend of the operating conditions and the selective and controlled coating process is still to be understood and optimized. Moreover, little attention has been devoted to investigate the influence of the support on the GCMNPs characteristics. Finally, insight into the formation mechanism is a critical issue to improve the control of the synthesis process. Herein, we report the preparation of stable core-shell graphene-coated magnetic nanoparticles (GCMNPs) via Catalytic Chemical Vapor Deposition (CCVD) of methane at atmospheric pressure. The magnetic properties of the nanoparticles have been also investigated. Materials and methods. The Co, Fe catalyst (50 wt.% of each metal) was prepared by wet LPSUHJQDWLRQ RI JLEEVLWH Ȗ-Al(OH)3) powder [3]. The experimental plant for the synthesis was equipped with on-line analyzers (Uras 26, ABB) that permit the monitoring of the inlet and outlet reactor concentrations of the reactants. To characterize the reaction products various techniques were employed as follows: transmission electron microscopy (TEM) (FEI Tecnai electron microscope operating at 200 kV), scanning electron microscopy (SEM) (LEO 1525 microscope), Raman spectroscopy ((Renishaw inVia; 514 nm excitation wavelength), thermogravimetric analysis (TG-DTG) (SDTQ 600 Analyzer (TA Instruments)) coupled with a quadrupole mass detector, X-ray diffraction analysis (Bruker D8 X-ray diffractometer) and N2 adsorption±desorption at 77 K. Results The change of process parameters: total flow rate, hydrocarbon methane partial pressure and catalyst weight in the synthesis process, has shown that the selective covering of nanoparticles and the control of the coating thickness can be obtained by feeding the hydrocarbon in a suitable carrier, preventing the unwanted homogeneous decomposition and increasing the conversion of methane.

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Figure 1. TEM images of nanoparticles covered by 1-2 layers graphene. X.ray diffraction patterns and Raman Spectrum of GCMNPs. The best result, consisting of nanoparticles covered by two graphene layers and free of other carbon species is shown in Figure 1. The nanoparticles have an average diameter of 4.12 nm with a 0.86 nm standard deviation, as measured for ~400 nanocrystals) and are covered by 1-2 layers of graphene (see the HRTEM in the Figure 1). In Figure 1, the X-ray diffraction pattern of GCMNPs is also shown. The peaks at 44.87°, 65.32° and 82.75° are typical of a crystalline body-centered-cubic Co/Fe alloy. It is important to note the absence of the (002) diffraction peak due to the stacking of AB graphite. In the Raman spectrum of GCMNPs the most prominent features of the sp2 carbon materials, which are

NQRZQ DV WKH * EDQG DQG WKH *Âś RU ' EDQG ZHUH REVHUYHG DW FP and approximately 2700 cm , respectively, using 514 nm excitation wavelength. The thermal stability was investigated by thermogravimetric analysis in flowing air, finding the nanoparticles are stable up to 350Â°C. The X-ray diffraction analysis after three weeks was found to be identical to that shown in Figure 1. To understand the mechanism of the carbon coverage, the concentrations of CH4, C2H2, C2H4 and H2 in the effluent stream have been monitored during the nanoparticles synthesis via on-line analyzers. The relevant profiles are shown in Figure 2. The methane conversion and hydrogen yield were calculated by assuming that the methane conversion to carbon and hydrogen was the primary reaction: CH4ÄşC+2 H2. The agreement between the CH4 conversion (x_CH4) and the H2 yield (R_H2) curves (Figure 2) confirms that the catalyst resulted in the selective formation of carbon and hydrogen. The evolution of the concentration profiles of the exhaust gases in the presence of non-impregnated gibbsite indicates a lack of methane decomposition in the absence of the catalysts in these operating conditions. Starting with the hydrogen produced from the catalytic decomposition of methane during the GCMNP1 test, the total deposited carbon was calculated to be 7.5 mg, which corresponds to a mean deposited carbon mass of 0.025 mg/sec a very close to the saturation threshold limit for the Co/Fe alloy, gC/gFeCo = 0.45 at.% at 800Â°C corresponding to 0.026 mg of carbon. Therefore, after the formation of GCMNPs during the pretreatment step, carbon saturation was achieved in approximately 1 sec. After 1 sec, carbon begins to cover the nanoparticle via carbon supersaturation and continuous precipitation from the cluster to form the graphitic structure. When the reaction was terminated, the catalyst remains active, and the carbon coverage phenomenon terminates when complete coverage of the GCMNP is achieved resulting in inactivation of the metal. The residual carbon mass inside the GCMNPs, which precipitated during the cooling phase, will contribute to the complete coverage of the metal [2]. It is important to note that there is no methane conversion in the absence of the metal catalyst on the support. -1

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Figure 2. On line analysis and CH4 conversion and H2 yield during GCMNPs synthesis. In Figure 3 we present the hysteresis loops of the nanoparticles at T= 5 K and T= 300 K. A saturation magnetization of 230 e.m.u./g for the sample, the highest Ms obtained for nanocrystal, can be measured. The presented hysteresis loops, are coherent with a superparamagnetic behavior.. 0,6

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Figure 3. Magnetic hysteresis loops at T=5K and 300 K for GCMNPs. Conclusion. Stable core-shell graphene-coated GCMNPs have been prepared by CCVD. Monodispersed 4.1 nm diameter body-centered-cubic-FeCo nanoparticles are coated by 1-2 layers of graphene. An Ms value of 230 e.m.u./g has been measured for the graphene-coated nanoparticles References 1. A.H. Lu, E.L. Salabas, F. SchĂźth, Angew. Chem. Int. Ed., 46 (2007) 1222-1244. 2. W.S. Seo, J.H. Lee, X. Sun, Y. Suzuki, D. Mann, Z. Liu, M. Terashima, P.C. Yang, M.V. Mcconnell, D.G. Nishimura, H. Dai, Nat. Mater. 5 (2006) 971Âą976. 3. M. Sarno, D. Sannino, C. Leone, P. Ciambelli, J. Mol. Catal. A-Chem. 357 (2012) 26-38.

Graphene nanoplatelets for thermally conductive polymer nanocomposites 1

Samuele Colonna , Alberto Fina , Zhidong Han , Guido Saracco

1- Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino Âą Sede di Alessandria, V.le Teresa Michel, 5, 15121 Alessandria, Italy 2- School of Materials Science and Engineering, Harbin University of Science and Technology, Linyuan Road 4, Dongli District, 150040, Harbin China samuele.colonna@polito.it Abstract Thermally conductive polymer composites offer new possibilities for replacing metal parts in low temperature heat exchangers, thanks to the polymer advantages such as light weight, corrosion resistance and ease of processing. The search for polymer based materials that conduct heat well has become essential for several applications, thanks to the following benefits: x x

x x

Superior corrosion resistance, which is an intrinsic property of the polymer matrix, allowing to attain durable components with no maintenance required Large design flexibility for an intensive exploitation of the available volume beyond the limitations of state-of-art heat exchangers; new heat-conductive polymers will enable new heat exchanger designs and manufacturing routes thereby potentially opening new application opportunities. Significant cost reduction of the innovative materials compared to metal materials used in highly corrosive contexts which will turn into a cost reduction for the complete appliances Weight reduction

Current interest to improve the thermal conductivity of polymers is focused on the selective addition of nanofillers with high thermal conductivity. Unusually high thermal conductivity makes carbon nanotubes (CNTs) and graphene nanoplatelets (GNP) the best promising candidate particles for thermally conductive composites [1-4]. However, to exploit the potential of such nanoparticles, both the dispersion of nanoparticles and the properties of thermal interfaces between nanoparticles has to be carefully designed and controlled [1] Thermal transport in CNTs and graphene can be dominated by the intrinsic properties of the strong sp2 carbon lattice, rather than by phonon scattering on boundaries or by disorder, giving rise to extremely high K values. Indeed, for graphene, the phonon mean-free path was estimated to be ~775 nm near room temperature, which evidences for very weak phonon scattering on the single particle. However, the intrinsic K strictly depends on the boundaries for the particles, especially in terms of support or inclusion into a matrix of a different material. Furthermore, the conductivity of graphene materials strictly depends on the number of layers and defectivity (partial oxidation, incomplete graphitization etc.) When graphene is embedded in polymer nanocomposites, the large surface area of the nanoparticles, maximizes the extent of polymer/particle interfacial area. Furthermore, in the case of percolating network, the number of contact points between particles increases with decreasing particle size. It is therefore reasonable to expect a significant role of the interfaces in thermal conductivity of nanocomposites. From a theoretical point of view, the scattering of phonons in composite materials is mainly due to the existence of an interfacial thermal barrier from acoustic mismatch. In a simplified model, the transmission of a phonon between two phases depends on the existence of common vibration frequencies for the two phases. Thus, it was supposed that only low frequency phonon modes of graphene are effective when GNP interact with a matrix only via weak dispersion forces Another source of interfacial resistance is the imperfect physical contact between GNP and matrix, which primarily depends on surface wettability

Due to the very low mean free path for phonons in the polymer (a few angstroms) compared to the mean free path on GNP (hundreds of nanometers), the theoretical scenario of perfectly dispersed GNP having no contact with each other and exchanging heat with the surrounding matrix does not appear to be convenient when aiming at efficient heat conduction. Indeed, preferential conduction of thermal energy along particles forming a percolating network is the basic idea behind the use of highly conductive and high aspect ratio nanoparticles such as GNP However, contact area between adjacent CNTs is relatively small and a significant temperature drop can be assumed for each contact point, which has previously been taken into account by considering GNP as a nano-plate coated with a very thin interfacial thermal barrier layer.[5] To overcome current limitations in thermal conductivity of graphene-based nanocomposites, different routes are being pursued in this PhD thesis, including: - Combination with cofillers (graphite, alumina, boron nitride) - non-covalent functionalization to promote dispersion during melt compounding and thermal contact between particles - Predispersion of GNP in liquid moieties (e.g. plasticizer) before melt compounding Recent achievements will be described in this paper. References [1] Zhidong Han, Alberto Fina, Prog. Polym. Sci., 36 (2011) 914Âą944. [2] Alexander A. Balandin, Nat. Mater., 10 (2011) 569Âą81. [3] Khan M. F. Shahil, Alexander A. Balandin, Nano Lett., 12 (2012) Ă . [4] Chih-Chun Teng, Chen-Chi M. Ma, Chu-Hua Lu, Shin-Yi Yang, Shie-Heng Lee, Min-Chien Hsiao, Ming-Yu Yen, Kuo-Chan Chiou, Tzong-Ming Lee, CARBON, 49 (2011) 5107 Âą5116. [5] Ke Chu, Cheng-chang Jia, Wen-sheng Li, Appl. Phys. Lett., 101 (2012) 121916

CVD synthesis of graphene from acetylene on copper foil 1

1,2

Andrea Cortés , Carlos Celedón , Universidad Técnica Federico Santa María, Departamento de Física, Avenida España 1680, Valparaíso-Chile, 2 Instituto Balseiro (U. N. de Cuyo and CNEA), Avenida Bustillo 9500, Bariloche-Argentina,

andrea.cortes@usm.cl

Abstract The challenges of graphene synthesis for its application at an industrial level are closely related to the synthesis of good quality material (good electrical properties and stability) and the ability to transfer it onto large areas without changing its physical properties. The study involves methods of synthesis that have been recently developed and which can be properly scaled to an industrial level, such as is the case of chemical vapor deposition (CVD) CVD synthesis is both simple and inexpensive. It allows the production of graphene over large areas. It involves the decomposition of gaseous hydrocarbons (CH 4, C2H2, CH3OH, among others) at elevated temperature. The metallic substrate acts as a catalyst for the decomposition reaction leaving carbon on the surface. However, it has been difficult to control the number of grown graphene layers. In recent years there has been extensive use of Cu as a catalyst, because it provides a better control of the number of graphene layers, which in turn is directly related to the low solubility of carbon in copper [1,2]. The growth of graphene onto copper foil substrates by CVD was employed. The gases applied in the synthesis were acetylene as a carbon source and hydrogen. Both for 20min growth time at 1000°C and low pressure. In the experiments, during the growth process, the acetylene flux is stays constant, while the hydrogen flow varied during the first 5 minutes of synthesis. Raman spectroscopy (Ȝ = 532 nm) shows that a bilayer of graphene was obtained in all tests. However for the 5min/60+15min/120 hydrogen flux process, a better quality bilayer was obtained, Figure 1.

References [1] M. H. Rümmeli, A. Bachmatiuk, A. Scott, F. Börrnert, J. H. Warner, V. Hoffman et al. ACS Nano, 4 (2010) 4206-4210. [2] J. Hofrichter, B. N. Szafranek, M. Otto, T. J. Echtermeyer, M. Baus, A. Majerus et al. Nano Lett., 10 (2010) 36-42.

Figure

Figure 1. Raman spectra of bilayer graphene synthesized by CVD process.

Andreev quantum dots in graphene-superconductor hybrid devices Lucian Covaci, Francois Peeters University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium lucian@covaci.org Although graphene is not intrinsically superconducting, Cooper pairs from a superconducting contact can diffuse through it. The superconducting proximity effect was observed experimentally in graphene Josephson junctions with contacts made of various superconducting materials like Al, Pb, Nb and even layered materials like NbSe2 [1,2]. When the energy of the electrons in the graphene layer is below the superconducting gap of the contacts, they will be bound in the normal region. These are the well known Andreev bound states. We consider a graphene layer deposited on top of a superconducting surface such that the graphene layer can be considered to be partially freestanding and/or strained. It was recently shown that strain has a peculiar effect on the electronic properties in graphene, namely that it will coupled exactly like a gauge field [3,4]. Under certain conditions it is thus possible to have strong pseudo-magnetic fields and even pseudo-Landau levels coexisting with superconducting correlations [5]. By using an efficient numerical method [6] we solve the Bogoliubov-de Gennes equations for a tight binding model of the graphene layer. We show that in the regions where the sheet is freestanding, bound states due to Andreev reflections appear, thus forming Andreev quantum dots. We provide various ways to manipulate the energy states inside the dots, and further more devise inter-dot coupling.

References: [1] H. B. Heersche, P. Jarillo-Herrero, J. B. Oostinga, L. M. K. Vandersypen, and A. F. Morpurgo, Nature (London) 446, 56 (2007). [2] A. Kanda, T. Sato, H. Goto, H. Tomori, S. Takana, Y. Ootuka, and K. Tsukagoshi, Physica C 470, 1477 (2010). [3] F. Guinea, M. I. Katsnelson, and A. K. Geim, Nat. Phys. 6, 30 (2009). [4] N. Levy, S. A. Burke, K. L. Meaker, M. Panlasigui, A. Zettl, F. Guinea, A. H. C. Neto, and M. F. Crommie, Science 29, 544 (2010). [5] L. Covaci and F. M. Peeters, Phys. Rev. B 84, 241401(R) (2011). [6] L. Covaci, F. M. Peeters, and M. Berciu, Phys. Rev. Lett. 105, 167006 (2010).

Production of Pyrrolidine Âą Functionalized Graphene in Solution 1

Eunice Cunha , Maria C. Paiva , M. Fernanda ProenĂ§a , Florinda Costa , AntĂłnio JosĂŠ Fernandes , 4 5 6 7 6 Marta A. C. Ferro , Paulo E. C. Lopes , Mariam Debs , Manuel Melle-Franco , Francis L. Deepak

Institute for Polymers and Composites/I3N, University of Minho, Campus de AzurĂŠm, 4800-058 GuimarĂŁes, Portugal, 2 Department of Chemistry, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal 3 Physics of Semiconductors, Optoelectronics and Disordered Systems/I3N, University of Aveiro, 3810193 Aveiro, Portugal 4 CICECO, Ceramics and Glass Engineering Deptartment, University of Aveiro, 3810-193 Aveiro, Portugal 5 Pole for Innovation in Polymer Engineering (PIEP), University of Minho, Campus de AzurĂŠm, 4800-058 GuimarĂŁes, Portugal, 6 International Iberian Nanotechnology Laboratory (INL), Av. Mestre JosĂŠ Veiga, 4715-330 Braga, Portugal 7 Computer Science and Technology Center, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal eunice.cunha@dep.uminho.pt

Abstract The formation of stable graphene solutions is a topic of great interest that has been the focus of recent investigations. The approaches proposed comprise the exfoliation of graphite in high boiling point solvents [1], the formation of graphene oxide (GO) followed by its reduction in solution (RGO), [2,3] or the formation of graphene nanoribbons (GNR) from carbon nanotubes (CNT) using an oxidation approach similar to that used for the formation of GO. Recently, the IRUPDWLRQ RI *15 ZDV REVHUYHG ÂłLQ VLWXÂ´ E\ XQ]LSSLQJ RI FDUERQ QDQRWXEHV XQGHU XOWUDhigh vacuum scanning tunneling microscopy (UHV STM) [4]. The CNT under observation were functionalized by the 1,3-dipolar cycloaddition reaction [5], and the functionalization route seems to be responsible for the unzipping of the CNT under these conditions. The present work demonstrates the formation, in solution, of graphene nanoribbons by unzipping of functionalized carbon nanotubes and graphene sheets (GS) through exfoliation of functionalized graphite. CNT and graphite were functionalized by 1,3-dipolar cycloaddition reaction, binding pyrrolidine-type groups to their surface. The solutions containing the functionalized GNR and GS presented the characteristic UV-visible spectra of graphene solutions. The graphene ribbons or flakes deposited by solvent evaporation on a Si surface were characterized by Raman spectroscopy and observed by transmission electron microscopy (TEM). Image analysis demonstrated that the assembled graphene formed regular stacks with an interlayer spacing of approximately 0.50 nm. TEM evidence is presented in Figure 1. The X-ray diffraction analysis showed a graphene-to-graphene interlayer distance of approximately 0,56nm. Molecular modeling was used to study the crystalline stacking of pyrrolidine functionalized GNRs, yielding interlayer distances in the range of 0.50 to 0.51 nm, for functionalized graphene with 50-70 surface C atoms per functional group. These results are in agreement with TEM observation and X-ray diffraction analysis. The assembled graphene could re-dissolve in the solvent to form stable solutions.

References [1] - &ROHPDQ 8 .KDQ $ 2Âś1HLOO 0 /RW\D 6 'H 6PDOO 6 (2010) 864. [2] D. Li, M. B. Muller, S. Gilje, R. B. Kaner, and G. G. Wallace, Nature Nanotech, 3 (2008) 101. [3] G. Wang, B. Wang, J. Park, J. Yang, X. Shen, and J. Yao, Carbon, 47 (2009) 68. [4] M. C. Paiva, W. Xu, M. F. ProenĂ§a, R. M. Novais, E. LĂŚgsgaard, F. Besenbacher, Nano Letters, 10 (2010) 1764. [5] M. C. Paiva, F. Simon, R. M. Novais, T. Ferreira, M. F. ProenĂ§a, W. Xu, F. Besenbacher, ACS Nano 4, (2010) 7379.

Acknowledgments The authors are thankful to the Institute of Nanostructures, Nanomodelling and Nanofabrication for project Grafitran (PEst-C/CTM/LA0025/2011). M. Melle-Franco acknowledges support by the 3RUWXJXHVH Âł)XQGDomR SDUD D &LrQFLD H D 7HFQRORJLDÂ´ WKURXJK WKH SURJUDP &LrQFLD DQG WKH project SeARCH (Services and Advanced Research Computing with HTC/HPC clusters) funded under contract CONC-REEQ/443/2005, and FCT for PhD grant SFRH/BD/87214/2012.

Figure 1. TEM micrograph of GNR formed in ethanol by unzipping of functionalized CNT, (a); FFT performed on the area within the square frame in micrograph a) (b); magnification of the image area in the square frame in micrograph a), showing the regular pattern (c).

Superconductivity in 2D NbSe2 Field Effect Devices Sara E. C. Dale, Mohammed S. El-Bana, Hasti Shajari, Simon J. Bending Department of Physics, University of Bath, Bath, BA2 7AY, UK S.Dale@bath.ac.uk

Two dimensional transition metal dichalcogenides (TMD) have become an increasing area of interest since the isolation of graphene. These materials exhibit a variety of electronic ground states, such as superconducting, semiconductor and metallic, and the electronic behavior of monolayer TMDs differs from that of bulk materials due to changes in their band structure.

Niobium diselenide commonly exists in two crystalline forms, 2H and 4H, depending on the stacking of the niobium diselenide molecular layers. In 2H-NbSe2, one layer of niobium atoms is sandwiched between two layers of selenide atoms which have coordination numbers of 6 and 3 respectively. It is a superconductor with a Tc of 7.2K but recent studies have found T c to decrease upon decreasing the thickness of the 2H-NbSe2 flake [1]. Here we report on 2H-NbSe2 field effect transistors made from few layer flakes and measure their resistive superconducting transitions as a function of applied gate potential and layer thickness [2].

Resistance measurements on all 2H-NbSe2 flakes showed several superconducting transitions which were attributed to disorder in stacking between layers. Flakes thinner than eight molecular layers were not found to be conducting in our experiments. The onset Tc of thicker flakes was found to be only slightly lower than the bulk value, and reduced slightly for positive gate voltages (electron doping).

These preliminary results show that the superconducting critical temperature of these 2D materials can be tuned in our field effect transistors and we are now extending our studies to higher doping levels and a broader range of TMD materials.

References [1] [2]

N. E. Staley, J. Wu, P. Eklund, Y. Liu, L. Li, Z. Xu, Physical Review B, 80 (2009) 184505. M. S. El-Bana, D. Wolverson, S. Russo, G. Balakrishnan, D. Mck Paul, S. J. Bending, Superconductor Science and Technology, 26 (2013) 125020.

Figures

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T (K) Figure 1. (a) AFM image of a NbSe2 flake with Cr/Au contacts (b) Resistance versus temperature curve showing three distinct superconducting transistions in a 10.37 nm flake.

Morphological and electrical characterizations of graphene exfoliated by liquid way

K. Dalla Francesca1 , S. Noel1 , F. Houzé1 , D. Alamarguy1 , A. Jaffré1 1

Laboratoire de Génie Electrique de Paris, UMR CNRS-Supélec 8507, Université Paris-Sud 11 et UPMC,11 rue Joliot Curie, Plateau de Moulon, 91192 Gif sur Yvette, France

Graphene is a relatively new material with very high potential for technological innovation through its electrical, mechanical and thermal exceptional properties. The liquid exfoliation methods of graphene sheets has been known for some years; the characteristics of the obtained suspensions strongly depend on the experimental parameters. These parameters govern, the number of sheets in solution, their thicknesses and dimensions and their structural and electrical properties when deposited on a substrate. In this work we show the influence of the liquid phase exfoliation conditions such as solvent choice, sonication duration and temperature

Figure 1: Schematic topography on a local resistance measurements, with a CP-AFM (module "Resiscope")

By changing the solvent allowing the deposition of and by performing the exfoliation at its boiling temperature we have been able to obtain suspensions to deposit graphene like sheets of interesting properties on various type of substrates(Au, Si, dopped Si). CP-AFM (Resiscope module developed at LGEP) and confocal micro-Raman techniques were used to study: the morphology, electrical and structural properties of sheets. Graphene like sheets with very few defects (as measured by the ratio of the intensity D peak over G peak) and good conductance (as measured with PtIr CP-AFM) were observed. First attempts to characterize even covering films from the overlapping of these sheet have been made by performing electrical measurements with a "Van Der Pauw" like technique and show sheet resistance values as low as 85 /sqr.

Further work involves optimization of the deposition technique in order to elaborate low cost graphene like film for a large rangs of applications.

Figures 2: CP-AFM of a "graphene like" sheets deposited on a gold surface with a PtIr tip with an applied force 70nN

Figure 3: Raman spectra of the above "graphene like sheet" (532nm laser source)

van derWaals interactions mediating the cohesion of fullerenes on graphene Y.J. Dappe, M. Svec, P. Merino, C. GonzĂĄlez, E. Abad, P. JelĂnek, and J. A. Martin-Gago CNRS-CEA Saclay/SPEC, BĂ˘t. 462, Gif sur Yvette, France yannick.dappe@cea.fr Fullerenes on single-layer epitaxial graphene are a model system where to study very faint interactions at a molecular level. By means of variable temperature scanning tunneling microscopy from 40K to ambient temperatures we have been able to grow ordered fullerene layers exclusively bound by van der Waals interactions. The adsorption geometry of the molecules was computationally confirmed only if van der Waals and weak interactions had been included in the calculation formalism. In the context of these interactions, mutual orientation of fullerenes in their close-packed arrangement is found to be an important factor for the total energy. Observation of collective movements of some islands point out the weak coupling to the substrate and the important role of the Van der Waals cohesion forces within. References [1] 0 Ă˘YHF 3 0HULQR < - 'DSSH & *RQ]iOH] ( $EDG 3 -HOtQHN - -A. M. Gago, Physical Review B 86, (2012) 121407(R). [2] Y.J. Dappe, J. Ortega and F. Flores, Physical Review B 79, (2009) 165409. Figures

Figure 1: 3D representation of 20x20 nm2 STM topography on C60 islands and their corresponding profiles.

Graphene synthesis on copper from ethylene by Catalytic Chemical Vapor Deposition P. Trinsoutrot, L. Dardenne, H. Vergnes, B. Caussat* Université de Toulouse, Laboratoire de Génie Chimique, ENSIACET/INP Toulouse/ UMR CNRS 5503, 4 allée Émile Monso, BP 44362, 31432 Toulouse Cedex 4, France. * Brigitte.Caussat@ensiacet.fr Graphene is a promising material thanks to its physical properties and presents many potential applications for example as transparent electrodes in the field of OLED, solar cells or sensitive flat displays. However its production at low cost and large scale with controlled characteristics remains elusive. This is the reason why its synthesis has still to be improved in order to control its crystallinity and its number of layers over large areas. Catalytic CVD (Chemical Vapor Deposition) appears to be the most promising commercially 2 viable process, since it allows forming cm scale areas of good quality graphene. However, most high quality CVD graphene is at present grown at temperatures close to 1,035°C on copper catalytic substrates from methane. This temperature is very close to the melting point of Cu (~1,085°C), and then creates intense Cu evaporation and then condensation fluxes upon cooling, which can affect the reproducibility of graphene synthesis and also decrease the samples quality and the reactor lifetime [1]. Some attempts have been made to decrease the synthesis temperature of graphene using alternative precursors like toluene, benzene, ethylene or acetylene [1-3]. Ethylene seems to be a good candidate to replace methane since it is cheap and easy to handle, and presents a higher reactivity than methane [1-2]. High quality graphene has already been obtained using ethylene on Cu foils at 850°C [12], but only at low total pressure (max. 100 Pa) and without a complete analysis of the key synthesis parameters influence. In the present study, the influence of the main deposition conditions on the graphene crystalline quality and number of layers has been analyzed using ethylene diluted into hydrogen and argon on 2 copper foils (25 µm thick, 99,999% Alfa Aesar) of 2x2 cm . The operating temperature was varied between 700 and 850°C, the hydrogen on ethylene inlet molar ratio between 1.5 and 14 and the total pressure between 3 and 700 Torr, as detailed in Table 1. The ethylene partial pressure was maintained at 30 mTorr for all experiments conducted at the total pressure of 3 Torr and was equal to 7 Torr at 700 Torr of total pressure. Optical microscopy and Raman spectroscopy measurements (confocal Raman microscope Labram – Horiba Yvon Jobin) with a laser excitation wavelength of 532 nm were carried out to investigate the quality and extend of graphene sheets. For each sample, at least three Raman analyses were performed at various points of the surface. The number of graphene layers was estimated from the -1 -1 2D (~2,670 cm )/G (~1,582 cm ) Raman peaks average ratios. The graphene crystalline quality was -1 deduced from the average ratio between the disorder-induced D-peak (~1,350 cm ) and the G peak. Table 1 details the ratios obtained for the various conditions tested. Table 1: 2D/G and D/G ratios measured for the various conditions tested

2D/G ratio D/G ratio

700°C

750°C

800°C

850°C

H2/C2H4=7

H2/C2H4=14

700 Torr

H2/C2H4=1.5 3 Torr

750°C 3 Torr

750°C

0.23

0.47

0.84

1.1

1.4

1.1

0.19

1.76

1.87

1.1

0.45

1.3

2.3

2.75

H2/C2H4=7

First, for all the conditions tested, graphene is continuous and uniform on the whole substrates surface.

Figure 1a presents the Raman spectra obtained at 3 Torr for the various temperatures studied. It appears that the best graphene quality is obtained at 850Â°C and corresponds to bi-layer graphene. So, these results confirm that the use of ethylene allows decreasing the synthesis temperature of 250Â°C in comparison with methane. These results are close to those obtained by other authors [1,2]. At 700Â°C, the 2D peak has very low intensity and is quite large, which could indicate the presence of amorphous carbon. Between 750 and 850Â°C, the 2D/G peak ratio increases with the temperature, meaning that the number of graphene layers decreases, whereas an opposite trend is observed for the D/G peak ratio. So, at 750 and 800Â°C, the amount of defects is much higher than at 850Â°C and graphene is multi-layers. These results could be explained by the fact that at low temperature, the etching activity of hydrogen and its catalytic role for ethylene dehydrogenation are reduced. Knowing that ethylene is highly reactive, this could lead to a higher number of graphene layers presenting more crystalline defects. Then, the influence of the hydrogen on ethylene ratio has been studied at 750Â°C and 3 Torr of total pressure, as detailed in Figure 1b. The best results in terms of defects and of number of layers have been obtained for the intermediate H2/C2H4 ratio of 7. When the hydrogen partial pressure is lower or is higher than that of this ratio, the amount of defects increases. This could be explained by the fact that if the H2 concentration is too high, graphene can be damaged by the etching activity of H2 [4]. At the opposite, if the H2 concentration is too low, an effect similar to that observed when the temperature is too low could appear. Lastly, the influence of the total pressure (or ethylene partial pressure) has been investigated at 750Â°C, as detailed in Table 1. The number of layers and the amount of crystalline defects notably increase with the total pressure. It is likely that at high ethylene pressure, the high ethylene reactivity generates a high concentration of carbon ad-atoms on the copper surface. The temperature tested here being not high enough to compensate this high carbon flux by the hydrogen etching activity, graphene is multi-layers with numerous defects. In conclusion, ethylene allows decreasing of 250Â°C the temperature of graphene synthesis on copper in comparison with methane, but the operating conditions must be selected with great attention to form good quality graphene, due to the high reactivity of this precursor.

Figure 1: Raman spectra - a) influence of the temperature - b) influence of the H2/C2H4 ratio

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Acknowledgements: This work has been supported by the European project FP7-NMP Grenada (GRaphenE for NAnoscaleD Applications). References [1] Wirtz C., Lee K., Hallam T., Duesberg G.S., Chem. Phys. Lett., 595-596 (2014) 192. [2] Celebi K., Cole M.T., Teo K.B.K., Park H.G., Electrochem. Solid State Lett., 15(1) (2012) K1. [3] Gao L., Guest J.R., Guisinger N.P., Nano Lett., 10 (2010) 3512. [4] Losurdo M., Giangregorio M.M., Capezzuto P., Bruno G., J. Phys. Chem., 13 (2011) 20836.

Graphene ablation by an optical fiber delivered laser 1

C. J. S. de Matos , D. Lopez-Cortes , E. C. Romani , D. G. Larrudé , I. C. S. Carvalho , H. B. Ribeiro , 3 2,4 M. A. Pimenta , and F. L. Freire Jr. 1 MackGraphe, Mackenzie Presbyterian University, R. da Consolação 896, São Paulo, Brazil 2 Physics Department, PUC-Rio, R. Marquês de São Vicente 225, Rio de Janeiro, Brazil 3 Physics Department, UFMG, Av. Antônio Carlos 6627, Belo Horizonte, Brazil 4 CBPF, Rua Dr. Xavier Sigaud 150, Rio de Janeiro, Brazil. cjsdematos@mackenzie.br Nano and micropatterning graphene is of ultimate importance for graphene-based electronic, photonic and plasmonic devices. In the majority of the reported work, patterning is achieved via optical or electron-beam lithography, with the latter offering nanometer-scale spatial resolution. However, lithography is a multi-step and high cost process. Importantly, it requires a resist to be deposited onto graphene, which can be a source of contamination. Laser ablation, on the other hand, is an attractive, single-step, alternative patterning method, which requires significantly less instrumentation and involves no direct contact with the sample. Laser ablation has been successfully used to generate holes and patterns in graphene [1-6], with feature sizes as small as ~0.5 µm [3,6]. Most reports to date describe graphene ablation using femtosecond lasers [1-4,6], with some mentioning the use of a controlled, inert, atmosphere [4] and the appearance of an intense Raman D band around the hole [1,2,5]. Outside the graphene area, fiber delivered-laser beams have been responsible for a technological revolution in micropatterning and microcutting, allowing for simpler and more flexible optical setups [7]. However, the fiber delivery of femtosecond laser pulses, such as those used so far for graphene ablation, is challenging because fiber chromatic dispersion and optical nonlinearity tend to degrade the pulses. Fiber beam delivery became even more attractive with the development of photonic crystal fibers (PCFs) [8], which allow for, e.g., delivery via an air-core [9] or a large modal area fiber, thus increasing the waveguide damage threshold. In addition, PCFs with exotic cross sectional profiles can present modal distributions that are not possible with conventional fibers.

Here, we present a graphene laser ablation setup that uses fiber delivery of a nanosecond laser beam. The fabricated hole´s edges do not present a significant D band in the Raman spectrum, meaning a predominance of zig-zag edges. The setup was designed to produce on graphene an optical image of the fiber’s modal profile, with the ablated region closely reproducing this profile. As a proof of principle experiment, 2 cores of a 3-core PCF were simultaneously excited and imaged onto a graphene sample, resulting in the immediate creation of a 2.4-µm-wide microribbon between the two generated holes.

The ablated graphene samples used in this work were synthesized by the chemical vapor deposition (CVD) (and more specifically high-vacuum CVD) method on copper foil substrate using methane [10]. The samples were then transferred to silica substrates using a wet transfer method with Poly-(methyl methacrylate) (PMMA) as a support film [11]. To ensure the quality of the growth and transfer processes, the silica substrate was optically inspected before and after PMMA removal, and Raman spectroscopy measurements were performed on the transferred graphene. For ablation, a Q-switched Nd:YAG laser was employed which delivered 0.7 ns pulses at 1064 nm with a repetition rate of 1 kHz. The pulses were launched into an optical fiber using an objective lens. At the fiber output a pair of 10× objective lenses collimated and subsequently imaged the fiber output modal distribution onto the graphene samples. Two types of optical fibers were employed: a standard telecommunications fiber (STF), in which case the fundamental mode (Gaussian-like intensity profile with a ~15-µm full width 1/e modal diameter) was excited; and a 3-core PCF, in which case two cores were simultaneously excited.

Figure 1 shows the results obtained with the STF and an average power of ~1 mW. Figure 1(a) shows an optical microscopy image of the sample after ablation. A round superficial hole is clearly observed. Ablation can be further confirmed and better observed via comparison of the confocal mapping of the 2D Raman band before (Fig. 1(b)) and after ablation (Fig. 1(c)). No graphene residue could be detected in the hole´s region. The ablated region shape, as well as its dimensions (~14 µm diameter), closely matches that of the fiber mode. The Raman spectra at the ablation edge (see insets) exhibit minimal Dband intensity. To demonstrate ablation with more complex modal structures, a 3-core PCF (Fig. 2(a)) was used. Modes were simultaneously excited in two cores (see inset). The average power into the graphene sample was ~0.5 mW. Figure 2(b) shows the 2D Raman band mapping of the ablated region, confirming the presence of two holes. The distance between hole centers is ~7.4 µm (c.f. 5-µm hole distance), indicating a small level of defocusing. Nevertheless, a 2.4-µm-wide, 7.5-µm-long microribbon is carved between holes, which can be lengthened by beam scanning and can be attractive for microdevice fabrication. Other hole´s shapes can also be obtained with other specialty PCFs.

The authors acknowledge FAPESP, MackPesquisa, CNPq, FAPERJ and CAPES for partial funding and Prof. C. M. B. Cordeiro for providing the photonic crystal fiber.

References [1] G. Kalita et al., Matterials Lett., 65 (2011) 1568. [2] M. Currie et al., Appl. Phys. Lett., 99 (2011) 211909. [3] J.-H. Yoo et al., Appl. Phys. Lett., 100 (2012) 233124. [4] W. Zhang et al., Appl. Phys. A, 109 (2012) 291. [5] V. Kiisk et al., Appl. Surf. Sci., 276 (2013) 133. [6] B. Wetzel et al., Appl. Phys. Lett., 104 (2013), 241111. [7] J. Nilsson and D. N. Payne, Science, 332 (2011) 921. [8] J. C. Knight, Nature, 424 (2003) 847. [9] J. D. Shephard et al., Optics Express, 12 (2004) 717. [10] X. Li et al., Science, 5 (2009) 1312. [11] J. W. Suk et al., ACS Nano, 5 (2011) 6916. Figures

Fig. 1. (a) Optical image of the ablated region. 2D Raman band mapping before (b) and after (c) ablation. Insets show individual Raman spectra taken at the indicated positions.

Fig. 2. (a) Scanning electron microscopy image of the PCF cross section (inset: excited modal profile). (b) 2D Raman band mapping showing the two ablated holes and a graphene microribbon in between.

Spin asymmetric band gap in graphene by Fe adsorption Elisabetta del Castillo, Simona Achilli, Fausto Cargnoni, Davide Ceresoli, Gian Franco Tantardini, Mario Italo Trioni Chemistry Department, University of Milano and CNR-ISTM, Via Golgi 19, 20133 Milano, Italy elisabetta.delcastillo@unimi.it Abstract The high mobility of graphene charge carriers, together with its small spin-orbit coupling, make graphene a very appealing material for spintronics applications [1]. However, due to the intrinsic spinunpolarized electronic structure of a pristine sheet, it is necessary to modify the electronic structure of graphene in such a way that the transport properties of the two spin channels become different. One of the possible ways to achieve this goal is to adsorbe magnetic impurities. In this work we study by first principles Fe atoms adsorbed on single graphene layer at different coverages using the density functional theory (DFT) approach implemented in the SIESTA package [2]. At very high coverages the electronic properties of the system are essentially determined by the Fe adlayer. The spectrum comprises a completely filled majority d-band and a partially filled minority one. In such a way we obtain a significant spin polarization but we loose the high correlation length typical of graphene. A feature observable at all coverages is a downshift of the graphene bands, much more evident for the minority spin component. This shift is related to a spin dependent charge transfer from Fe to graphene, the total amount of which we estimated to be 0.66 e using the Bader charge analysis. Another interesting effect is the formation of band gaps in the cells that are 3n times larger than the graphene unit cell (see Fig. 1). A first kind of gap is due to the folding of the two high symmetry points K and K′ of the pristine Brillouin zone to Γ. In these cases the presence of defects, in our case the Fe adatom, removes the degeneracy and induces a band-gap opening in both spin components [3]. Besides, we observe a second kind of gap present only in the minority spin component. This gap is approximately 0.6 eV (∼1 eV for the 3×3 supercell) and always comprises the Fermi level, changing the electronic behaviour of the system from a zero-gap semiconductor to an insulator but for one spin component only. The trend of this gap as a function of the decreasing coverage is shown in Fig. 2. We expect that the presence of this gap could influence the transport properties of the system. To explore the effects of this peculiar electronic structure on the transport properties we considered a graphene--Fe@graphene--graphene junction. The calculations were performed using the TranSIESTA code [4], which combines the non-equilibrium Green’s function (NEGF) technique with DFT. From the spin-resolved transmission function T(ε) shown in Fig. 3 we can see that the behaviour of the majority spin component is very similar to the pristine graphene case around the Fermi level (the very small dip observable at 0.4 eV above EF is the signature of a Fe 4s state that does not hybridize with the substrate). Conversely, in the minority component we observe an extended region (∼1 eV) around the Fermi level where the T(ε) is practically nil. In this energy range the tunnel effect is the only possible ballistic propagation mechanism. In Fig. 4 are reported the currents for the different spin components. The minority current is negligible for low voltages and remains of lower intensity with respect to the majority one for all the considered voltage range. Consequently, the ratio between the spin polarized currents shows very large values (> 2 10 ) for voltages lower than 0.5 eV and is still considerable even for higher voltages. This strong spin asymmetry of the I-V characteristic makes this system a prototypical one for future spintronic applications.

References [1] O.V. Yazyev, M.I. Katsnelson, Phys. Rev. Lett. 100, (2008) 047209. [2] J.M. Soler, E. Artacho, J.D. Gale, A. García, J. Junquera, P. Ordejón, and D. Sánchez-Portal, J. Phys.: Condens. Matter 14, (2002) 2745. [3] R. Martinazzo, S. Casolo and G.F. Tantardini, Phys. Rev. B. 81, (2010) 245420. [4] M. Brandbyge, J.-L. Mozos, P. Ordejón, J. Taylor, and K. Stokbro, Phys. Rev. B 65, (2002) 165401.

Figures 4

0.8 up

down

Minority Spin

0.6

Energy - EF (eV)

1 0 -1 -2

0.4 0.2 0.0 -0.2

-3

-0.4

-4 M Γ

K MM Γ

100

Number of C atoms per Fe adatom Fig. 1: Spin resolved DOS and band structure for the 3×3 supercell. For comparison, the grey line represents pristine graphene.

Fig. 2: Gap width as a function of the number of the graphene unit cells for the 3n supercells.

6 up

T(E)

2 0 -2 -4

Spin up current Spin down current

I(V) (arb. units)

2 0 -2 -4

down

-6

-3

-2

-1

Energy - EF (eV) Fig. 3: Spin dependent transmission coefficient. For comparison, the brown line represents the T(ε) for pristine graphene.

-6

-4

-2

0 Voltage (V)

Fig. 4: Spin dependent current.

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CVD graphene growth on Ni films and transfer Geetanjali Deokar, J.-L. Codron, C. Boyaval, X. Wallart, D. Vignaud Institute of Electronics Microelectronics and Nanotechnology, University of Lille 1 Av. Poincaré CS 60069 59652 Villeneuve d'Ascq Cedex, France geetanjali.deokar@iemn.univ-lille1.fr The graphene growth onto metal foils and thin films is currently the leading method for producing large, continuous graphene films. Due to the small lattice mismatch between Ni (111) and graphene, for epitaxial and homogeneous growth of graphene, Ni (111) is a promising substrate. However, on Ni graphene growth occurs via segregation of carbon, which is a difficult process to understand and control. We present here graphene growth on Ni films by using a rapid thermal annealing chemical vapor deposition set-up. The Ni film was annealed prior to graphene growth. It results in major Ni film surface grains with (111) preferred orientation after pre-growth annealing at 870°C, as confirmed by electron backscattered diffraction measurements (EBSD, Fig.1 a). A uniform and full layer graphene growth on the in-situ pre-annealed Ni films was achieved by controlling the deposition time, temperature, methane gas flow and, cooling rate. The as-produced graphene quality and number of layer was examined by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Further, the as-grown graphene was transferred to SiO2/Si substrates by using a wet chemical transfer process with polymethyl methacralyte (PMMA) as a support layer. XPS and Raman measurements of the transferred graphene sample do not show the presence of PMMA residues or any metallic contamination (including Ni). Hall-effect measurements were performed on 2 the graphene/SiO2/Si sample using the Van Der Pauw geometry and showed p-type mobility 1200 cm -1 -1 12 -2 V s and carrier concentration 3.9 10 cm . The as-grown and transferred large area good quality graphene represent an important step towards the fabrication of large-scale high-quality graphene

Ni/SiO2/Si

Gr/Ni/SiO2/Si

1 µm P 0DS 6WHS P *ULG [

Fig.1 a) EBSD mapping of 200 nm Ni films on SiO2/Si substrate annealed at 870 C in Ar and H2 with 10 Torr system pressure showing major (111) Ni surface grain orientation, b) Few layer graphene grown on pre-annealed Ni films, c) Optical image of the same graphene transferred to Si/SiO2 substrate using a wet chemical transfer process and in the inset corresponding sample photo

Gr/SiO2/Si

15 µm

Synthesis of graphitic nano-discs with unique optical properties E. Dervishi, Z. Ji, K. A. Velizhanin, C. Sheehan, M. Sykora, and S. K. Doorn Center for Integrated Nanotechnologies, Materials Physics and Application Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA enkeleda@lanl.gov Abstract Nano-graphene sheets with interesting optical and electronic properties have been extensively studied for a wide range of application areas including spintronics, electronics, photovoltaics, sensors, 1-6 diodes, bio-nano (as drug delivery agents with low-toxicity properties) and nano-composites. Most of the current synthesis methods involve a top-down technique using various chemical routes to control 3,7-10 the size and shape of nano-structures. In this work, we present a straightforward synthesis of nanographene discs via chemical vapor deposition. The size and morphology of these nano-materials can be controlled by varying the synthesis conditions. More specifically, a shorter reaction time was found to yield nano-discs with smaller dimensions (below 30 nm), while larger structures with 100-200 nm lateral 11,12 dimensions were synthesized using methane for 30 minutes. The purified structures were functionalized with carboxylic groups and characterized by various microscopy and spectroscopy techniques. The optical properties of the nano-discs are strongly dependent on their morphology and the presence/type of functional groups on their surface. These carbon nano-structures with interesting optical properties can be potential candidates in energy storage and opto-electronic devices.

References [1] J. K. Kim et al., ACS Nano, 7 (8) (2013), 7207±7212. [2] Y. Zhang et al., ACS Nano, 4 (6) (2010), 3181-3186. [3] L. Li et al., Nanoscale, 5 (2013), 4015±4039. [4] M. Mahmood et al., Journal of Materials Chemistry B, 1 (2013), 3220-3230. [5] X. Sun et al., Nano Res., 1(3) (2008), 203-212. [5] S. Pruneanu et al., CHEMPHYSCHEM, 13(16) (2012), 3632-3639. [6] A. R. Biris et al., Carbon, 50 (6) (2012), 2252-2263. [7] H. Tetsuka et al., Adv. Mater., 24 (2012), 5333±5338. [8] S. Kim et al., ACS Nano, 6 (9) (2012), 8203±8208. [9] S. H. Jin et al., ACS Nano, 7(2) (2013), 1239±1245. [10] K. A. Ritter et al., NATURE MATERIALS, 8 (2009), 235-242. [11] E. Dervishi et al., Chemical Communications, 27 (2009), 4061-4063. [12] E. Dervishi et al., Journal of Materials Science, 47 (4) (2012), 1910-1919. Figures (a) Absorption (a.u.)

(b)

200

300

400

500

600

700

Wavelength (nm)

(a) Absorption spectra of the nano-graphene discs synthesized via chemical vapor deposition. (b) SEM image (STEM mode) of the nano-discs dispersed in acetonitrile.

Spectroscopic Characterization of Graphene Synthesized by Electrolysis in Molten Electrolytes Aleksandar Dimitrov 1, Abdulakim Ademi2Anita Grozdanov 1, Beti Andonovic1,Gennaro Gentile3, Maurizio Avella DQG 3HULFD 3DXQRYLĂź 3

1-Faculty of Technology and 0HWDOOXUJ\ 8QLYHUVLW\ Âł6WV &\ULO DQG 0HWKRGLXVÂ´ 5XJHU%RĂŁNRYLĂź 6WU 6NRSMH 2- Ministry of Environment and Physical Planning, 1000 Skopje, 3-Institute for Chemistry and Technology of Polymers, ICTP-CNR, FabricatoOlliveti, Napoli aco@tmf.ukim.edu.mk

Abstract Production of graphene in semi industrial scale is of great importance for its industrial applications and industrial development in general.In this study, our main goal was producing larger amounts of graphene, by electrolysis in molten electrolytes, in the laboratory conditions as a first step towards semi-industrial production.The obtained results are promising. Here we present the results obtained from the physical characterization of applying Raman spectroscopy, XRD, Zeta and UV spectroscopy on graphene produced by electrolysis into molten salts using non stationary current regime. Raman spectroscopy was useful for determining of the number of the layers of the graphene. The Raman spectra, D, G and 2D bend, and ratio between it show that the produced graphene has high oriented structure, and thickness of several layers (1-2 nm). Furthermore, XRD results show that dominant structure is few layered, and the average value for number of graphene layers is about 5. UV absorption spectroscopy was used to characterize grapheme/SDS suspensions since they can be related with transitions of aromatic C-C bonds, and a shoulder at about 350 nm which can be attributed to transitions of C=O bonds. Zeta measurements of the grapheme samples have confirmed that the surface chare was negative.

Key words:

Graphene, Molten salts, Graphite, Electrolysis, Raman, XRD, ZP

Magneto- Optics Properties of Graphite 1,2

Wala Dizayee , Yalei Wang , A. Mark Fox and Gillian A. Gehring 1

Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK 2

Department of Science, Salahaddin University, Erbil, Iraq

Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education and School of Chemistry and Materials Science, Shanxi Normal University, Linfen 041004, P. R. China w.dizayee@sheffield.ac.uk

Abstract: Faraday rotation is one of the most important magneto-optical phenomena and is used in spintronics research where is used to study the polarization of electron spins [1]. In this work we prepare thin graphite films in order to measure the Faraday rotation for graphite in the visible region of the spectrum order to compare it with theory [2]. We used two techniques to produce thin films. Pulsed laser deposition using an excimer XeCl laser with an operating wavelength of 308 nm produced the best films. Films were also grown using spin coating, but this produced poor quality films that appeared dark. The magneto-optic spectrum is measured using the method of Sato [3] during which the magnetic circular dichroism MCD is measured simultaneously with the Faraday rotation. There are no available calculations of the MCD for graphite. A xenon lamp (150W), with an energy range of (1.5-4.5 eV) been used for our measurements and an electromagnet with an attainable maximum field of 1.8T. The magnetic field is perpendicular to the plane of the sample and parallel to the direction of incidence. A Dektak surface profiler is employed in order to measure the samples thickness. In addition, the thicknesses of the films have been estimated from the optical absorption using parameters taken from the bulk, by taking account of the reflections from the front and back sides of the film [4] as shown in Figure1. Both measurements showed that the thickness is dependent on the deposition time. The surface topography and the structural changes of the films were characterized by scanning electron microscopy (SEM), and AFM scanning probe microscopy shown in Figure2. The SEM measurements show a flat surface topography, however a height variation of (Âą5nm) was detected by AFM for a film of thickness approximately (20nm). The XRD shows two peaks, one for small crystallites of graphite (002) and the second for the sapphire substrate (Figure3) [5]. Results for the Faraday rotation and MCD in the range 1.5eV to 4.5eV will be presented and compared with the theory.

References: [1] A. Zarifi, ISRN Condensed Matter Physics, 2013 (2013) 843702. [2] T.G. Pedersen, Physical Review B, 68 (2003) 245104. [3] K. Sato, Japanese Journal of Applied Physics, 20 (1981) 2403-2409. [4] G.E. Jellison, Jr., J.D. Hunn, and Ho Nyung Lee, Physical Review B, 76 (2007) 085125. [5] L. Tang, Y. Wang, Yueming Li, H. Feng, Jin Lu, and Jinghong Li, Advanced Functional Materials, 19 (2009) 2782-2789. Figures:

100

Thickness (Lo)(nm) Thickness (Dektak)(nm)

90 80

Thickness (nm)

70 60 50 40 30 20 10 0 0

Time Deposition (min)

Figure1: Graphite film Thickness by Dektak (Green) and optical density (Red).

Graphite Film (1min) 500

002

Sapphire

Intensity (cps)

400

300

200

100

2theta (Degree)

Figure3: XRD spectrum of synthesized Graphite thin films.

Figure2: AFM for Graphite (1min)

Strategy of strain engineering to improve performance of graphene transistors V. Hung Nguyen

1,2,3

, M. Chung Nguyen , H. Viet Nguyen , and P. Dollfus

Institute of Fundametal Electronics, CNRS, Univ. of Paris-Sud, Orsay, France 2 L_Sim, SP2M, UMR-E CEA/UJF Grenoble 1, INAC, Grenoble, France 3 Center for Computational Physics, Institute of Physics, VAST, Hanoi, Vietnam philippe.dollfus@u-psud.fr Graphene, even with excellent transport properties, still have serious drawbacks for practical applications. In particular, its gapless character makes it difficult to turn off the current in graphene transistors and leads to a poor saturation of current. Many efforts of bandgap engineering have been made to overcome these limitations. For instance, they consist in cutting 2D graphene sheets into 1D nanoribbons [1], Bernal-stacking of graphene on hexagonal boron-nitride substrate [2], nitrogen-doped graphene [3], creating graphene nanohole lattice [4], and Bernal-stacking bilayer graphene [5]. However, each of these techniques still has its own issues. Beyond expected applications in electronics, graphene also shows remarkable mechanical properties, i.e., it is amenable to a large strain of over 20% [6]. This suggests many possibilities of strain engineering to modulate the electronic properties of graphene and graphene nanostructures [7]. To open a bandgap in 2D graphene, a strain larger than ~ 23% is however required [8]. In this work, we consider the effect of uniaxial strain on the transport characteristics of the transistors based on unstrained/strained graphene junction. By means of numerical simulation, we will show that with only a moderate strain of 5%, the use of this strain hetero-channel can greatly improve the performance of graphene transistors. Our calculations are based on the tight-binding model constructed in [8]. The strain causes the changes 11 , in the C-C bond vectors as rij 1 MS rij 0 where Ms is a diagonal matrix with MS

MS22

is the strain and

= 0.165 is the Poisson ratio. The hopping parameters between

nearest neighbor atoms are defined as tij

t0 exp

3.37 rij

rij 0

1 . This tight binding model is

VROYHG XVLQJ WKH *UHHQÂśV IXQFWLRQ PHWKRG VHOI FRQVLVWHQWO\ ZLWK WKH 3RLVVRQÂśV HTXDWLRQ 7KH WUDQVSRUW quantities are then determined after the self-consistency is obtained. The simulated devices are schematized in Fig. 1. In Fig. 2, we first investigate the transport properties of graphene strain junctions. It is shown that a uniform strain does not change the gapless character of graphene. However, a significant conduction gap Eg opens in the strain junctions, i.e., Eg 360 meV for the strain of 5% and can have a higher value for larger strain. Using this kind of strained junction, we demonstrate as displayed in Fig. 3 that the performance of graphene transistors can be significantly improved by a strain of a few %. In particular, a 5

high ON/OFF ratio of over 10 can be obtained for a strain of 5%. Moreover, in the graphene tunneling device, the subthreshold swing can reach a value lower than 30 mV/dec. In the normal graphene transistors, the performance is additionally improved in terms of current saturation (with even a possible negative differential conductance, see Fig. 4) and hence high voltage gain is reached. Finally, we found as shown in Fig. 5 that the tunneling transistors exhibit interesting non-linear effects such as gate controllable negative differential conductance and strong current rectification. In summary, we present an alternative approach to improve the performance of graphene transistors by using strain engineering. This type of strain engineering may be also useful for other devices based on graphene-like materials and for other applications.

References [1] M. Y. Han et al., Phys. Rev. Lett. 98, 206805 (2007) [2] N. Kharche et al., Nano Lett. 11, 5274 (2011) [3] A. Lherbier et al., Nano Lett. 13, 1446 (2013) [4] J. Bai et al., Nat. Nanotechnol. 5, 190 (2010) [5] Y. Zhang et al., Nature 459, 820 (2009) [6] C. Lee et al., Science 321, 385 (2008) [7] Y. Lu and J. Guo, Nano Res. 3, 189 (2010) [8] V. M. Pereira et al., Phys. Rev. B 80, 045401 (2009)

Figures gate

Fig. 3. Transfer characteristics of graphene FETs with different applied strains.

insulator strained graphene

source

unstrained graphene

drain

substrate

Fig. 1. Schematic view of simulated graphene transistors. The gate length is 80 nm and the length of the transition region (yellow zone) is 9 nm.

Fig. 4. ID-VDS characteristics of graphene FETs: strain junction ( = 5 %) compared to unstrained case ( = 0).

8 6 4 Vgs = 0.1 V

0.35 V

Vgs = 0.1 V

2 0 -2 -4 -0.1

Fig. 2. Conductance as a function of energy (top) and conduction gap as a function of the strain (bottom) in strained/unstrained junctions.

0.0

0.1

0.2

0.3

Fig. 5. ID-VDS characteristics of graphene tunneling FETs with

Graphene-molecule interactions and the potential for selective chemical sensing by graphene FET’s Nikolai Dontschuk and Jiri Cervenka School of Physics, The University of Melbourne

Graphene’s two dimensional nature, highly sensitive unique electrical properties and low intrinsic noise characteristics make it a prime candidate for the creation of a new generation of molecular sensors. Sensors that could provide single molecule sensitivity and selective determination of the sensed molecules. DNA sequencing technology is an area that stands to benefit greatly from such advances in sensing technology. As such we have seen a number of theoretical models for DNA relying on graphenes ability to sense and distinguish between DNA bases (or base pairs) as that pass near the graphene surface[1, 3]. Despite the promise of such models the underlying assumption, that graphene is sensitive enough to the physical absorption of molecules for single molecule selective sensing, has not been shown experimentally. Current theory uses Boltzmann transport theory to describe changes in graphene’s conductivity due to the presence of charge scattering sites [4]. Whilst strong agreement with experiment has been shown for molecules which undergo interger charge transfer with the graphene for many molecules physically absorbing to graphenes surface only partial charge transfer is observed, making such theories inadequate. In order to start addressing the validity of this assumption about graphene’s sensitivity we have undertaken experiments observing the changes in single layer CVD graphene on 90 nm SiO2 field effect transistors (FETs) when nucleobase molecules are absorbed on the graphene surface. To avoid potential environmental contamination our experiments were carried out in the ultra high vacuum systems of the soft X-ray beamline at the Australian synchrotron. This also allowed for the use of XPS techniques to monitor the quantity of molecules absorbed on our devices. Here we report on the results of these measurements, in particular on the potential of graphene to be used as a selective molecular sensor for genome sequencing applications.

[1] S. K. Min, W. Y. Kim, Y. Cho, and K. S. Kim, Nature Nanotechnology 6, 162 (2011). [2] A. Girdhar, C. Sathe, K. Schulten, and J.-P. Leburton, Proceedings of the National Academy of Sciences 110, 16748 (2013).

2 [3] K. K. Saha, M. Drndi, and B. K. Nikoli, Nano Letters 12, 50 (2012). [4] E. H. Hwang, S. Adam, and S. D. Sarma, Phys. Rev. Let. 98, 186806 (2007).

Contribution (Poster) Nano-Raman (Tip Enhanced Raman) and co-localized AFM-Raman characterization of graphene and related materials Pavel Dorozhkin, Artem Shelaev, Mikhail Yanul, Eugenii Kuznetsov, Sergey Timofeev, Sergey Lemeshko and Victor Bykov NT-MDT Co., Build. 100, Zelenograd Moscow, Russia dorozhkin@ntmdt.com Co-localized AFM-Raman studies of graphene and related materials are presented. While Raman is used to indicate number of layers in graphene, advanced AFM modes characterize its various physical properties as a function of number of layers. We show how number of layers in graphene affects its surface potential (work function), friction coefficient, elastic modulus, capacitance, conductivity, charge distribution, Raman and Rayleigh light scattering etc. Results for graphene flakes are qualitatively compared to those for carbon nanotubes of different diameters. AFM surface potential measurements are performed at different environmental humidity, indicating effect of water adsorption. Measurements in vacuum and at different temperatures are reported. The new Hybrid mode (fast force-distance curve AFM measurements together with co-localized Raman mapping) is used to characterize adhesion and stiffness of pure and contaminated graphene samples with nm-scale resolution. Nano-Raman (Tip Ehanced Raman) characterization of graphene, graphene oxide and carbon nanotubes is presented characterizing sample structure and defects. Spatial resolution of nano-Raman maps comes close 10 nm. References [1] www.ntmdt.com/afm-raman Figures

Fig. 1. Characterization of contaminated graphene monolayer by intermittent contact AFM, AFM stiffness measurement (HybriD mode) and Raman imaging.

Contribution (Poster)

Fig. 2. Nano-Raman (Tip Enhanced Raman) mapping of graphene oxide D-band. Scan size: 1x1 Âľm.

Fig. 3. Graphene surface potential maps at different environmental humidity (from 10% to 80%).

Graphene based paint-like composites for electromagnetic shielding in the GHz frequency range M. Suchea

1, 2

, I. V. Tudose

1, 2

, G. Kenanakis

1, 3

, E Koudoumas

1, 4

, E. Drakakis

Center of Materials Technology and Photonics, School of Applied Technology, Technological Educational Institute of Crete, 710 04 Heraklion, Crete, Greece 2 Â´$O , &X]DÂ´ 8QLYHUVLW\ RI ,DVL %XOHYDUGXO &DURO , ,DVL 5RPDQLD 5RPDQLD 3 Institute of Electronic Structure & Laser (IESL), Foundation for Research and Technology (FORTH) Hellas, P.O. Box 1385, Heraklion 70013, Crete, Greece 4 Electrical Engineering Department, School of Applied Technology, Technological Educational Institute of Crete, 710 04 Heraklion, Crete, Greece edrakakis@staff.teicrete.gr Nowadays, wireless communication systems have resulted in an increased electromagnetic (EM) radiation background, which can influence biological systems as well as the operation of all electronic devices. This is known as electromagnetic interference (EMI), an effect that can cause malfunction of, as an example, sensitive medical devices and robotic systems or even become harmful to life. As a result, both systems and operators need protection in cases where they are close to EM radiation sources. Therefore, it is necessary to develop materials offering EM shielding at particular frequencies used in wireless systems. Since the shielding materials must possess good electrical conductivity, metals such as aluminum, copper and steel are the most common and active materials used for EM shielding. However, there are several limitations in the applicability of metal in EM shielding applications since they are heavy, not easily handled/applied and they suffer from corrosion. As a result, the scientific community is trying to develop new EM shielding materials, a trial that has been significantly supported by the advances in materials science and nanotechnology. Among other materials, polymer composites containing carbonbased fillers (e.g., graphite, carbon black, carbon fibers, and carbon nanofibers) have been investigated 1 for use in EM shielding applications owing to their unique combination of electrical conduction, flexibility, light weight and corrosion resistance. However, so far the results did not allow yet an extensive use of composite materials in commercial applications and further research is required regarding materials, growth methods and understanding of the EM shielding mechanisms. More recently, graphene has been suggested as an ideal candidate for the formation of 2 polymer/graphene nanocomposites with improved mechanical and electrical properties and its possible 3 use in various applications including EM shielding have been studied. It is the purpose of our work to investigate the applicability of graphene based paint-like composites in EM shielding for the frequency range of 2-24 GHz. The samples used were based on paint-like compositions deposited on foam board. During preliminary tests, the composition was optimized regarding the polymeric binder employed, since some binders were observed to diminish both the conductivity and the EM shielding performance of the final coating. In all cases, water soluble binders were chosen in order to get an environmental friendly EM shielding material. Some binders were found suitable as dispersing agents but they were promoting foaming of composition. Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (named PEDOT:PSS) was finally proved to be the most promising binder. Although it possesses barely acceptable binding properties, its remarkable conductivity allowed the use of fairly large amounts in order to compensate for the low binding capacity. In the present study compositions based on graphene flakes, HCl doped polyaniline and PEDOT:PSS dispersed in distilled water were examined. The dispersed solid phase was kept around 10% by mass in order to obtain a reasonably thin paste that can be deposited on foam board. Regarding the transmission measurements, these were performed in free space, using a HewlettPackard 8722 ES vector network analyzer and four sets of microwave standard-gain horn antennas covering the range 3-24GHz. Prior to every measurement, an absorbing chamber was created using typical microwave absorbers (ECCOSORB AN-77, Emerson & Cuming Microwave Products, Inc., Randolph, MA) over all surfaces except the top, and each sample was placed in the middle of each set of horn antennas. For the scopes of this work, graphene flakes/HCl doped polyaniline/PEDOT:PSS coatings of various concentrations and thicknesses deposited on foam board were tested regarding their EM shielding applicability. Their basic characteristics such as structural, morphological and electrical properties were also investigated and their correlation with the EM shielding performance was examined. Acknowledgements: This project is implemented through the Operational Program "Education and Lifelong Learning" action Archimedes III and is co-financed by the European Union (European Social Fund) and Greek national funds (National Strategic Reference Framework 2007 - 2013).

References

[1] Y. L. Yang, M. C. Gupta, K. L. Dudley, R. W. Lawrence, Nano Lett, 5(11) (2005) 2131.

[2] B. Shen,W. Zhai, D. Lu, W. Zheng and Q. Yan, Polym Int., 61 (2012) 1693.

[3] W. Song, M. Cao, M. Lu, S. Bi, C. Wang, J. Liu, J. Yuan, L. Fan, Carbon, 66 (2014) 67.

Figures

Transmission (dB)

-20 -40 -60 0

-20 -40 -60 5

Frequency (GHz)

A typical example of GHz electromagnetic shielding in paint-like graphene composites

Exchange coupling between localized defect states in graphene nanoflakes Matthias Droth and Guido Burkard University of Konstanz, 78464 Konstanz, Germany matthias.droth@uni-konstanz.de Graphene nanoflakes are interesting because electrons are naturally confined in these quasi zerodimensional structures, thus eluding the need for a bandgap [1,2]. Defects inside the graphene lattice lead to localized states and the spins of two such localized states may be used for spintronics. We perform a tight-binding description on the entire system and, by virtue of a Schrieffer-Wolfftransformation on the bonding and antibonding states, we extract the coupling strength between the localized states [3]. The coupling strength allows us to estimate the exchange coupling, which governs the dynamics of singlet-triplet spintronics. [1] S. Phark et al., ACS Nano, 5 (2011) 8162. [2] D. Subramaniam et al., Phys. Rev. Lett., 108 (2012) 046801. [3] G. Burkard and A. Imamoglu, Phys. Rev. B, 74 (2006) 041307(R).

Layer-by-layer deposition of anionic graphite oxide and polyaniline into thin films with cationic poly(diallyl dimethyl ammonium chloride) Stephan Thierry Dubas, Ekarat Detsri The Petroleum and Petrochemical College Chulalongkorn University, soi Chula 12 phyathai rd pathumwan, Bangkok, Thailand Stephan.d@chula.ac.th Abstract In this work, anionic polyaniline (PANI) prepared from the interfacial polymerization of aniline in the presence of polystyrene sulfonate was assembled into layer-by-layers with anionic graphite oxide (GO) using poly(diallyldimethyl ammonium chloride as cationic counter polyelectrolyte. The graphite oxide was produce using a the hummer method and were deposited as anionic counterpart with cationic polyelectrolytes poly(diallyldimethyl ammonium chloride) (PDADMAC). A glass slide substrate was dipped in either solution in a sequential fashion to produce thin films of increasing thickness as a function of the number of deposited layers. The sequence was composed of (PDADMAC-GOPDADMAC-PANI)n and repeated needed. The increase in UV-Visible absorbance were record using a spectrophotometer as a function of the number of deposited layers and suggested that constant amount of graphene and polyaniline were deposited in each layer which is typical of the layer by layer process. Polyaniline is a pH dependant conducting polymer which electrical and optical properties varies from a doped to un-doped state leading to a color change from green in acid to purple in base. The electrical and optical properties of the composite films were evaluated as a function of pH and using a 4 point probe setup and a spectrophotometer. These composite films could be of interest for the fabrication of electro-optical sensors which would present optical and electrical properties varying as a function of pH for example in food sensing technology. References [1] Ekarat Detsri, Stephan Thierry Dubas, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 444 (2014) Pages 89-94 [2] Chularat Iamsamai, Apinan Soottitantawat, Uracha Ruktanonchai, Supot Hannongbua, Stephan Thierry Dubas, Carbon, 6 (2011) Pages 2039-2045

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Nitrogen doping and the Coulomb impurity problem in graphene 1

H. Amara, Th. Mercier, L. Henrard, and F. Ducastelle 1 2

/DERUDWRLUH GÂś(WXGH GHV 0LFURVWUXFWXUHV 21(5$-CNRS, BP 72, 92322 ChĂ˘tillon Cedex, France Physics Department (PMR), University of Namur (FUNDP), B-5000 Namur, Belgium francois.ducastelle@onera.fr

Abstract The introduction of local defects such as vacancies or doping impurities is a well-documented way to tune the electronic properties of graphene. In such a context, nitrogen is a natural substitute for carbon in the honeycomb structure due to both its ability to form sp2 bonds and its pentavalent character. Several experiments have shown that, as expected, substitutional nitrogen behaves as a donor whereas it seems to become an acceptor when nitrogen atoms are associated with vacancies (pyridinic configurations). In the substitutional case it is generally found, by comparing the estimated doping rate with the measured variation of the Fermi level, that about half of the electron provided by nitrogen is delocalized [1-2]. From the theoretical side the problem of a single localized potential due to a vacancy or impurity is easy to solve within the usual tight-binding description of graphene [3]. For strong enough potentials a resonance generally occurs close to the Dirac point a few tenths of eV above it in the case of a donor impurity such as nitrogen, just at the Dirac point for an unrelaxed vacancy (Fig. 1)[4], or very close to it for an hydrogen adatom. Within the TB scheme the position of the resonance depends on the potential, parametrized using ab initio data. One problem is that these self-consistent calculations use supercells whose size if not large enough to avoid spurious interactions between images of the impurity [5]. Furthermore, by construction the unit cells in these calculations are neutral so that no precise information concerning the screening of the additional charge of the nitrogen atom is obtained. From a more general point of view the screening of a Coulomb potential in graphene is still problematic because of the possibility of a so-called "atomic collapse" beyond a critical value of the coupling constant. It is believed that in graphene this critical regime can occur for excess chages of the order of unity. Unfortunately a complete satisfactory self-consistent treatment of screening is still not available so that it is not obvious whether, at very low doping, graphene behaves as a semi-conductor or a metal [6]. We have investigated this problem by studying the screening effects induced by different forms of potentials for a single impurity. For potentials of finite range we show exactly that no screening at all can occur at long distance whereas at short range a significant screening is present. More precisey we have calculated the Mulliken charges on each site of very big boxes using the recursion method and found that actually almost perfect screening is attained on the first shells, but this is counterbalanced at longer distance so that finally the screening charge vanishes for sufficienly weak potentials (Fig.2). Here again there are critical values of the coupling constant corresponding to the passage of a bound state at the Dirac point. Then the asymptotic screening charge is at least equal to two (spin included) so that satisfactory screening seems impossible for an odd excess charge, unless a bound state is locked at the Dirac point. From self-consistent band calculations we already know that the position of the resonance depends on the size of the used supercells (and therefore of the impurity concentration)[7] but we do not know what is the limit at infinite dilution. We have undertaken ab initio calculations to check this point and also to verify that the screening charges found in these calculations where neutrality is imposed (through a variation of the Fermi level) are consistent with our tight-binding calculations. We will also indicate how this discussion of screening effects can be extended to more complex situations (impurity pairs, pyridinic configurations) and can be used to understand recent scanning tunnel spectroscopy observations. References [1] L. Zhao, R. He, K. T. Rim, T. Schiros, K. S. Kim, H. Zhou, C. GutiĂŠrrez, S. P. Chockalingam, C. J. Arguello, L. Palova et al., Science 333, 999 (2011). [2] F. Joucken, Y. Tison, J. Lagoute, J. Dumont, D. Cabosart, B. Zheng, V. Repain, C. Chacon, Y. Girard, A. R. Botello-Mendez, S. Rousset et al., Phys. Rev. B 85, 161408 (2012). [3] M. I. Katsnelson, Carbon in Two Dimensions Cambridge University Press (2012). [4] F. Ducastelle, Phys. Rev. B 88 (2013) 075413.

[5] Ph. Lambin, H. Amara, F. Ducastelle, and L. Henrard, Phys. Rev. B 86 (2012) 045448. [6] V. Kotov, B. Uchoa, V. Pereira, F. Guinea, and A. H. Castro Neto, Rev. Mod. Phys. 84 (2012) 1067. [7] Z. Hou, X. Wang, T. Ikeda et al., Phys. Rev. B 87 (2013) 165401.

Figures

Fig. 1. Local density of states at zero energy in the presence of a vacancy.

Fig. 2. Excess Mulliken charge around a nitrogen atom as a function of distance for a short range potential: local charge (above) and integrated charge (bottom). The latter one is equal to one close to the impurity and to zero at long distance

Development of graphene corrosion resistant coatings across porous stainless steel materials Ludovic F. Dumée

1,2*

, Li He , Ziyu Wang , Peter Hodgson , Mainak Majumder , Lingxue Kong

1 Institute for Frontier Materials, Deakin University, Pigdons road, 3216 Waurn Ponds, Victoria ± Australia 2 Institute for Sustainability and innovation, Victoria University, Hoppers Lane, 3030 Werribee, Victoria ± Australia 3 Department of Mechanical and Aerospace Engineering, Monash University, Bayview Avenue, 3168 Clayton, Victoria ± Australia ludovic.dumee@deakin.edu.au Abstract The development of novel alternatives to current metal anti-corrosion technologies, including hexavalent chromium coating or electro-galvanization, are desperately sought to develop more environmentally friendly and cheaper corrosion resistant materials. These include new materials able to atomically bind with metals and able to improve interfaces with surrounding media or surface properties without compromising the metal thermal or electromechanical properties. Graphene offers highly promising perspectives for the development of active platforms with potential applications in nano-electronics, molecular separation, high strength composite, and surface coating industries [1, 2]. Recently, graphene oxide (GO) and graphene, either deposited or directly grown onto pre-formed surfaces have shown to act as highly efficient impermeable barriers reducing adverse effects of ion or gas diffusion across materials prone to degradation by electro-chemical reactions [3, 4]. Metal based materials are particularly prone to surface oxidation at the liquid/gas interface and leads to premature degradation through surface erosion or de-alloying, changes of surfaces wetting and sharp loss of mechanical integrity. In this paper, we demonstrated for the first time the growth of 3D networks of graphene nano-flakes across porous stainless steel substrates. The composition of two different austenitic stainless steel (SS) materials (SS304 and SS316) on the graphene growth stability and metal materials response to the growth conditions was also investigated. We demonstrate the controlled formation of high purity graphene from single sheets (Figure 1) to complex nano-flakes by Raman spectroscopy, contact angle, XPS, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (Figure 2) homogeneously across the porous stainless steel supports. The presence of the graphene was shown to enhance the materials corrosion resistance by up to 3 fold and electrical conductivity by 2 folds without otherwise altering the properties of the stainless steel. This new approach is opening the route to the facile fabrication of advanced surface coatings with potential applications in thermal exchangers, separation, specific adsorption and bio-compatible materials fabrication. References 1. Novoselov, K.S., et al., A roadmap for graphene. Nature, 2012. 490(7419): p. 192-200. 2. Gaikwad, A.V., et al., Carbon nanotube/carbon nanofiber growth from industrial by-product gases on lowand high-alloy steels. Carbon, 2012. 50(12): p. 4722-4731. 3. Mayavan, S., T. Siva, and S. Sathiyanarayanan, Graphene ink as a corrosion inhibiting blanket for iron in an aggressive chloride environment. RSC Advances, 2013. 3(47): p. 24868-24871. 4. Prasai, D., et al., Correction to Graphene: Corrosion-Inhibiting Coating. ACS Nano, 2012. 6(5): p. 4540-4540.

Figures

Figure 1 Representative high magnification SEMs of the formation of individual graphene sheets on the surface of the stainless steel. Scale bars are 500 nm

Figure 2 EDS mapping and SEM of a FIB milled cross section of a 900 C, 15 min, 20 ccm hybrid stainless steel graphene sample. The scale bar on the SEM is 5 Âľm and all elemental maps are equally scaled up

Raman Mapping of Fluorinated Labelled Bilayer Graphene Johan Ek Weis, Sara Costa, Otakar Frank, Martin Kalbac J. HeyrovskĂ˝ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., 'ROHMĂŁNRYD &=-18223 Prague 8, Czech Republic. e-mail: johan.ekweis@jh-inst.cas.cz Graphene bilayers can either be stacked in Bernal (AB) stack or in a random orientation (turbostratic) and the properties can change depending on the stacking order. The stacking order can be -1 determined by Raman spectroscopy [1], namely observing the 2D band, at around 2700 cm (at 2.41 eV). However, to distinguish the contributions of each layer can be difficult, since they yield very similar Raman signals. In order to be able to differentiate between the two layers, isotopically labelled bilayer graphene was studied. That is, one layer consists of 12C atoms and the other layer of 13C atoms. The different mass of the two layers results in a frequency shift of the Raman peaks, which clearly can be seen in the Raman spectrum. Because of the synthesis process (CVD), both labelled bilayers and bilayers containing only one isotope can be found on the same sample. The samples were fluorinated using XeF2 crystals. Using a WITec system to record high resolution Raman maps of bilayer structures a lot of information can be obtained. For example, the different isotopic regions can clearly be distinguished (Figure A), as well as regions of different stacking order (Figure B) and with or without the defect band, D band (Figure C). It was also observed that both types of stacking order can be found within the same grain. Monolayer graphene was found to be significantly more sensitive to fluorination than bilayers. For bilayers doped by fluorination it was found that AB regions presented D bands with lower intensities than turbostratic regions. Therefore, the fluorination process is more effective for turbostratic bilayer graphene. [1] Fang, W.; Hsu, A. L.; Caudillo, R.; Song, Y.; Birdwell, A. G. et al. Nano Lett. 13 (2013) 1541-1548.

-1

Figure A: Intensity map of the spectral region 1560-1620 cm . The yellow areas show regions with 13 bilayer graphene containing both isotopes, orange areas highlight C bilayer whereas darker areas represent monolayer graphene. Figure B: Spectral width of the 2D peak originating from 13C bilayer. Bright areas highlight AB stacked 13 regions, whereas dark areas show turbostratic regions. Monolayer C and bilayer regions containing 12 C are shown in black and are not fitted in this image. 13

Figure C: Intensity of the C D peak in all bilayers. Comparing this image with Figure B, it can be seen that the D peak is larger in turbostratic than in AB regions. A high intensity of D band can also be observed in the edges of the grains, were more structural defects are present.

Piezoelectricity of BN-doped Graphene mono-, bi-, and trilayer(s), and their corresponding bulk structures: An ab initio description. Khaled E. El-Kelany,1,2 Philippe Carbonnière,1 and Michel Rérat1 Equipe de Chimie Physique, IPREM UMR5254, Université de Pau et des Pays de l’Adour, 64000 Pau, France 2 Chemistry Department, Faculty of Science, Minia University, Minia 61519, Egypt khaled.el-kelany@univ-pau.fr 1

Abstract In the present work, we report the results of ab initio quantum mechanical techniques to the study of BN-doped graphene sheets and their corresponding bulk structures. The simulation of mono-, bi-, and tri-graphene layer(s) doped by BN as well as the corresponding bulk structures, is here explored. The structural, energetic, elastic and piezoelectric properties of these sheets in addition to the corresponding bulk structures are computed and analyzed. Both direct and converse - coupled with elastic compliance - piezoelectricity are computed and interpreted in terms of electronic and nuclear contributions. All the calculations are performed using the CRYSTAL14 program [1]. Graphene in its metallic or semi-metallic state is not intrinsically piezoelectric due to its centrosymmetric crystal structure. Here, we show that merely by substituting some C-C pairs by B-N one, graphene can act as a piezoelectric material. We find that at certain concentration of BN, graphene sheets can acquire piezoelectric coefficient that is nearly 16 times larger than the well-known piezoelectric quartz or 4 times larger than that of 2D h-BN. Piezoelectricity is a macroscopic property, so the corresponding bulk structures are also considered. The obtained piezoelectric coefficients have the same order of magnitude as that for 2D structures, although both graphite and BN bulk structures are non-piezoelectric materials. References [1] Dovesi, R.; Saunders, V. R.; Roetti, C.; Orlando, R.; Zicovich-Wilson, C. M.; Pascale, F.; Civalleri, B.; Doll, K.; Harrison, N. M.; Bush, I. J.; D’Arco, P.; Llunell, M.; Causà, M.; Noël, Y. CRYSTAL14 User's Manual. University of Torino: Torino, 2014.

Enhancement of optical transitions in graphene by attraction between electrons and holes. M.V. Entin, M.M. Mahmoodian Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, pr. Lavrent’eva 13, Novosibirsk, 630090 Russia mahmood@isp.nsc.ru Abstract Graphene is known to have a remarkable optical absorption coefficient πα determined by the finestructure constant α. This value is found in the Born approximation and it does not take into account the single-electron spectrum reconstruction due to the interaction. Electron-hole interaction is important factor mediating on the optical transitions. In bulk gapped semiconductors with central c and v bands the influence of e-h interaction is connected with the Sommerfeld factor Z = |ψ(0)|2 which is determined by the electron-hole envelope function ψ(r) at zero distance between electron and hole. The attraction between them strongly enhances the probability of transition near the absorption threshold. The absorption threshold behavior proportional to electron-hole DOS p ν(hω − Eg ) ∝ hω − Eg is replaced by Zν(hω − Eg ), where q 2π hχ 2(hω − Eg )/m, Z= , q = e2 q(1 − e−2π/q ) m is a e-h pair reduced mass, χ is a dielectric constant of medium, e is an electron charge, ω is the light frequency, Eg is the bandgap. As a result, the absorption at the threshold has a gap, instead vanishing. The parameter 2π/q is a dimensionless interaction constant which determines the interaction correction value. The Bohr energy me4 /(χ2 h2 ) plays role of a characteristic energy: at large detuning from the threshold the transition probability goes to the Born result for non-interacting particles. The purpose of the present study is to find the e-h-interaction-induced correction to the absorption coefficient κ of graphene. The conic gapless electron spectrum of graphene determines energyindependent dimensionless constant of e-h interaction g = e2 /(χhs), where s is an electron velocity. Besides, in free-suspended graphene this constant has large order. We found that κ obtains the additional Sommerfeld factor Z = |ψ(0)|2 originating from e-h interaction of the unbounded pair, that essentially enhances the absorption at small frequencies. The consideration is limited by the case g ≪ 1. The enhancement of the exciton effect results from singular behavior of the envelope wave function at small interparticle distance. The two-particle problem for electron and hole pair can be transformed to the basis of free electron and hole wave functions: 1 ipe re pex + ipey √ e , (1) |pe i = −pe 2pe 1 phx − iphy √ |ph i = (2) eiph rh . ph 2ph Matrix element of e-h interaction potential V (r) = −e2 /(χr), r = re − rh , in the basis of |pe , ph i = |pe i|ph i is Vpe ,ph ,p′e ,p′h = hp′e , p′h |V (re − rh )|pe , ph i.

(3)

For zero summary momentum pe = −ph = p Vp,p′ =

B(p, p′ ) , 4p2 p′2

B(p, p′ ) = (pp′ + pp′ ) + [p × p′ ]2 .

(4)

The integral Schrödinger equation (H0 + V )ψ = εψ for the envelope function of the relative motion in the momentum representation takes form: Z d2 p′ V (p − p′ )B(p, p′ )ψ(p′ ) = εψ(p). (5) 2spψ(p) + (2π)2 Here V (q) =

2π e2 q χ.

Integrating over polar angle in Eq. (5) we get Z gsp 2spψ(p) − w(x)ψ(xp)dx = εψ(p), 2 1

(6)

where ( 1 4x 4x 2 w(x) = (x + 1)2 K − − (x − 1) E − + 2π|x − 1| (x − 1)2 (x − 1)2 ) n

4x 4x x, x ≪ 1,

x − 1 K −E ≃ 2 2 1, x ≫ 1, (x + 1) (x + 1) K(x) and E(x) are the complete elliptic integrals. If 2sp ≫ ε we can rewrite Eq. (6) as g ψ(p) = 4

(7)

w(x)ψ(xp)dx

ε/2sp

and solve it in an iterative manner with zero order approximation ψ (0) (p) = δ(2sp − ε). The result reads ψ(p) = ψ (0) (p) +

g 4ε

2sp ε

g/4−2

(8)

and ψ(r) = ψ

(0)

(r) 1 +

2s εr

g/4 #

(9)

The wave function goes to infinity at r → 0. To limit the divergency, we set r = a, where a is the g/4 2 lattice constant. Hence, Z = |ψ(0)/ψ (0) (0)|2 = 1 + h¯4s and the absorption coefficient is παZ. ωa

If g ln h¯4s ωa ≫ 1, the absorption coefficient is much larger than α. Note, that there is another interaction-induced contribution to the absorption coefficient caused by the renormalization of single-electron energy [1]. In our opinion, if g ln h¯4s ωa ≫ 1 this contribution is less essential than e-h-attraction-induced. At the same time our result differs from that of [1], may be due non-correct collection of powers of g ln h¯4s ωa made in [1]. As a result, the absorption coefficient grows at ω → 0, instead dropping predicted in [1]. We should emphasize that the singularity of the absorption coefficient results from the singularity of the conic spectrum. In analogy with the electron-electron scattering [2] and exciton formation [3], one could expect that the trigonal correction to the single-electron spectrum essentially corrects the absorption coefficient behavior. In fact, it is not the case. One can show that just conic character of the spectrum makes trigonal corrections inessential near the threshold. This research is supported by the grants of RFBR No 13-02-12148 and 14-02-00593. References [1] E. G. Mishchenko, Phys. Rev. Lett. 98 (2007) 216801. [2] L. E. Golub, S. A. Tarasenko, M. V. Entin, L. I. Magarill, Phys. Rev. B 84 (2011) 195408. [3] M. M. Mahmoodian and M. V. Entin, Europhys. Lett. 102 (2013) 37012.

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Photon-Assisted Tunneling through Molecular Conduction Junctions with Graphene Electrodes Boris D. Fainberg Faculty of Sciences, Holon Institute of Technology, 5810201, Holon, Israel and School of Chemistry, Tel-Aviv University, 69978 Tel-Aviv, Israel fainberg@hit.ac.il The field of molecular-scale electronics has been rapidly advancing over the past two decades, both in terms of experimental and numerical technology and in terms of the discovery of new physical phenomena and realization of new applications. In particular, the optical response of nanoscale molecular junctions has been the topic of growing experimental and theoretical interest in recent years. A way of the control of the current through molecular conduction nanojunctions is the well-known photon-assisted tunneling (PAT) [1,2]. The main idea is that an external field periodic in time with IUHTXHQF\ Ȧ FDQ LQGXFH LQHODVWLF WXQQHOLQJ HYHQWV ZKHQ WKH HOHFWURQV H[FKDQJH HQHUJ\ TXDQWD Ȧ ZLWK the external field. Here we propose and explore theoretically a new approach to coherent control of electric transport via molecular junctions, using either both graphene electrodes or one graphene and another one - a metal electrode (that may be an STM tip) [3]. Our approach is based on the excitation of dressed states of the doped graphene electrode with electric field that is parallel to its surface (Fig.1), having used unique properties of graphene, like strongly non-linear electromagnetic (EM) response [4], linear dependence of the density of states on energy, and the gapless spectrum that can change under the action of external EM field. We have calculated a semiclassical wave function of a doped graphene under the action of EM excitation and the current through a molecular junction with graphene electrodes using non-equilibrium Green functions. Fig.2 show photon assisted current for a molecular junction with one graphene electrode and another one - a metal electrode for large momenta (far from the Dirac point). One can see the steps when the potential of the graphene electrode achieves the values corresponding to the photon energy, the doubled photon energy etc. The steps are found on the background that decreases linearly for a n-doped graphene electrode and increases linearly for a pdoped electrode when the potential of the graphene electrode increases. This is related to the linear dependence of DOS on energy. We have also shown that using graphene electrodes can essentially enhance currents evaluated at side-band energies ‫׽‬n԰Ȧ LQ PROHFXODU QDQRMXQFWLRQV WKDW LV UHODWHG WR

the modification of the graphene gapless spectrum under the action of external EM field. We have

calculated the corresponding quasienergy spectrum (Fig.3) that is accompanied with opening the gap

induced by intraband excitations (for the interband transition contributions to the gap in an undoped graphene see [5] and references there). The quasienergy shows a quadratic dependence on momentum near the gap (solid line in Fig.3) that gives rise to slow falling down Fourier-harmonics with the harmonics index. Since the n-doped graphene is a well-defined Fermi liquid, we estimate the imaginary part of its the self-energy for the excitations of n԰Ȧ DERYH WKH )HUPL HQHUJ\ 7KH HVWLPDWHV VKRZ WKDW D UDSLG UHOD[DWLRQ RI WKH )HUPL GLVWULEXWLRQ WR WKH ³GUHVVHG´ )ORTXHW VWDWHV VHHPV D reasonable assumption. Recently Floquet states of surface Dirac fermions of a topological insulator have been observed experimentally [6]. A side benefit of using doped graphene electrodes is the polarization control of photocurrent related to the processes occurring either in the graphene electrodes or in the molecular bridge. The latter processes are accompanied by surface plasmon excitation in the graphene sheet that makes them more efficient. Our results illustrate the potential of graphene contacts in coherent control of photocurrent in molecular electronics, supporting the possibility of single-molecule devices.

References [1] G. Platero and R. Aguado, Phys. Rep., 395 (2004) 1. [2] S. Kohler, J. Lehmann, and P. Hanggi, ibid., 406 (2005) 379. [3] B. D. Fainberg, Phys. Rev. B, 88 (2013) 245435. [4] E. Hendry, P. J. Hale, J. Moger, A. K. Savchenko, and S. A. Mikhailov, Phys. Rev. Lett., 105 (2010) 097401. [5] H. L. Calvo, H. M. Pastawski, S. Roche, and L. E. Torres, Appl. Phys. Lett., 98, (2011) 232103. [6] B. H.Wang, H. Steinberg, P. Jarillo-Herrero, and N. Gedik, Science, 342 (2013) 453.

Figures

Fig.1. Molecular bridge (thick horizontal line) between left (L) and right (R) graphene electrodes with applied voltage bias.External electromagnetic field acts on the electrodes.

Fig.2. Current in the case of large momenta for n-GRSHG Č?! solid) and p-GRSHG Č? GDVKHG graphene electrode as a function of applied voltage bias.

Fig.3. Quasienergies for momentum parallel (solid line) and perpendicular (dashed line) to electric field as functions of unperturbated energy vp weighted per the work done by the electric field during one fourth of period.

Challenges in Graphene-Polymer Interactions 1

Guilhermino J. M. Fechine, Barbaros Ozyilmaz, Antônio H. C. Neto

Mackgrafe - Graphene and Nano-Materials Research Center ± Mackenzie, Presbyterian University, 2 Rua da Consolação, 896, CEP 01302-907, São Paulo/SP, Brazil; Graphene Research Centre ± GRC, National University of Singapore, 2 Science Drive 2, 117551, Singapore guilherminojmf@mackenzie.br 1

Few years passed since the Academy announced the Nobel Prize Winners for Andre Geim and Novoselov, it was in 2010. In that time the world started to know the existence of this material The chemical structure prints in graphene interesting characteristics that have never seen in others materials such as <RXQJ¶V modulus of 1 TPa and tensile strength of 130 GPa , room-temperature electron 1

-1

-1 2

mobility of 2.53x10 cm V S

allied to a great ability to sustain extremely high densities of electric

-1 4

current , thermal conductivity above 3,000WmK

, optical absorption at the infrared limit of exactly

ʌĮ and a complete impermeability to any gases 6. 5

Nowadays, there are a lot of methods to produce graphene with different dimensions and purity. 7

Mechanical exfoliation of graphite , chemical exfoliations, synthesis on SiC and chemical vapor 8

deposition (CVD) are methods used to obtain graphene which one with its own characteristic . Therefore, for numerous application is need transfer graphene from metal foils to several target substrates, mainly polymeric films. The most used methodology to transfer large-area CVD graphene to hard and soft substrates like Si/SiO2 wafer and polymeric films has several steps and consume hours, it is called wet transfer. Spincoating of polymer, etching of metal and transfer graphene to target substrate are the steps for the complete technique. In 2010, a new technology of graphene transfer was introduced, ³roll-to-roll transfer 9

process´ . This technology enables a transfer of large-area of graphene to polymeric substrates using a thermal release tape (TRT) as a supporting layer. Other different approaches have been done using a 10

similar method such as call hot lamination 14

fractal evolution

and nano-imprinter

or direct transfer . Layer-by-layer , clean-lifting , surface

are examples of very specific methodologies developed to

transfer graphene to different substrates. 16,17

Theoretical calculations

and experimental analysis

have been used to obtain the binding energy of

graphene grown on metals, values are from 30 to 45 meV. Graphene transfer methodology could be choose from these results, since that the binding energy has to be overcome for a completely transfer. After graphene be transferred to a target substrate, the interaction between them must have studied. Adhesion energy of monolayer and multilayer graphene after transferred to hard substrate like silicon 2

oxide was obtained by using of Pressurized blister test, 0.45 and 0.31 J/m , respectively . In addition to the adhesion energy, the evaluation of the interface between graphene and substrate may be performed at the molecular level. The evaluation of graphene doping is an example for that, as showed for Meric et al12. However, evaluation of interactions of graphene on polymeric substrate is still a field to be explored. Since that numerous applications of graphene are related with polymeric substrate as a support (solar cells, touch panels, biomaterials and so on) the understanding of graphene-polymer interactions has an important role. The Figure 1 shows several points that must be taken into account to a good evaluation of the graphene-polymer interaction. As can see on Figure 1, the graphene-polymer interaction is essentially related with the source of the graphene, transfer methodology used and the chemical

structure of the polymer as well. The challenges to be overcome in graphene-polymer interactions are how can be obtained values of adhesion force and what is the best tools to understand the interface of these materials in molecular level.

Figure 1 ± Evaluation of graphene-polymer interactions

References 1. Lee, C., Wei, X., Kysar, J. W. & Hone, J. Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 321, 385±8 (2008). 2. Mayorov, A. S. et al. Micrometer-scale ballistic transport in encapsulated graphene at room temperature. Nano Lett. 11, 2396±9 (2011). 3. Moser, J., Barreiro, a. & Bachtold, a. Current-induced cleaning of graphene. Appl. Phys. Lett. 91, 163513 (2007). 4. Balandin, A. a. Thermal properties of graphene and nanostructured carbon materials. Nat. Mater. 10, 569±81 (2011). 5. Nair, R. R. et al. Fine Structure Constant Defines. 320, 2008 (2008). 6. Bunch, J. S. et al. Impermeable Atomic Membranes from 2008. 3±7 (2008). 7. Bae, S., Kim, S. J., Shin, D., Ahn, J.-H. & Hong, B. H. Towards industrial applications of graphene electrodes. Phys. Scr. T146, 014024 (2012). 8. Novoselov, K. S. et al. A roadmap for graphene. Nature 490, 192±200 (2012). 9. Bae, S. et al. Roll-to-roll production of 30-inch graphene films for transparent electrodes. Nat. Nanotechnol. 5, 574±8 (2010). 10. Verma, V. P., Das, S., Lahiri, I. & Choi, W. Large-area graphene on polymer film for flexible and transparent anode in field emission device. Appl. Phys. Lett. 96, 203108 (2010). 11. Martins, L. G. P. et al. Direct transfer of graphene onto flexible substrates. Proc. Natl. Acad. Sci. U. S. A. 110, 17762±7 (2013). 12. Meric, I. et al. Current saturation in zero-bandgap, top-gated graphene field-effect transistors. Nat. Nanotechnol. 3, 654±9 (2008). 13. Wang, D.-Y. et al. Clean-lifting transfer of large-area residual-free graphene films. Adv. Mater. 25, 4521±6 (2013). 14. Yu, Y. et al. Surface fractal evolution induced rubbing for rapid room temperature and transfer-free fabrication of graphene on flexible polymer substrate. Appl. Phys. Lett. 103, 011601 (2013). 15. Lock, E. H. et al. High-quality uniform dry transfer of graphene to polymers. Nano Lett. 12, 102±7 (2012). 16. Vanin, M. et al. Graphene on metals: A van der Waals density functional study. Phys. Rev. B 81, 081408 (2010). 17. Khomyakov, P. a. et al. First-principles study of the interaction and charge transfer between graphene and metals. Phys. Rev. B 79, 195425 (2009). 18. Yoon, T. et al. Direct measurement of adhesion energy of monolayer graphene as-grown on copper and its application to renewable transfer process. Nano Lett. 12, 1448±52 (2012). 19. Koenig, S. P., Boddeti, N. G., Dunn, M. L. & Bunch, J. S. Ultrastrong adhesion of graphene membranes. Nat. Nanotechnol. 6, 543±6 (2011).

Photothermoelectric Response in Asymmetric Carbon Nanotube Devices Exposed to THz Radiation *,Âś

Âś

*,Âś

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G. Fedorov , A. Kardakova , I. Gayduchenko , B.M. Voronov , M. Finkel , T.M. Klapwijk , and G. Âś Goltsman 15& Âł.XUFKDWRY ,QVWLWXWHÂ´ 0RVFRZ .XUFKatov square, Russia Âś

Physics Department, Moscow State Pedagogical University, Moscow, 119991, Russia Email: Â&#x201A; .DYOL ,QVWLWXWH RI 1DQRVFLHQFH Delft University of Technology, 2600 AA Delft, Netherlands gefedorov@mail.ru

Abstract This work reports on the voltage response of asymmetric carbon nanotube devices to subTHz radiation at the frequencies of 140 GHz through 2.5 THz 7KH GHYLFHV FRQWDLQ &17ÂśV ZKLFK DUH over their length partially suspended and partially Van der Waals bonded to a SiO2 substrate, causing a difference in thermal contact. Different heat sinking of CNTs by source and drain gives rise to temperature gradient and consequent thermoelectric power (TEP) as such a device is exposed to the sub-THz radiation. Sign of the DC signal, its power and gate voltage dependence observed at room temperature are consistent with this scenario. At liquid helium temperature the observed response is more complex. DC voltage signal of an opposite sign is observed in a narrow range of gate voltages at low temperatures and under low radiation power. We argue that this may indicate a true photovoltaic UHVSRQVH IURP VPDOO JDS OHVV WKDQ PH9 &17ÂśV DQ HIIHFW QHYHU UHSRUWHG EHIRUH While it is not clear if the observed effects can be used to develop efficient THz detectors we note that the responsivity of our devices exceeds that of CNT based devices in microwave or THz range reported before at room temperature. Besides at 4.2 K notable increase of the sample conductance (at least fourfold) is observed. Better efficiency could be obtained by using graphene or graphene nanoribbons with a bandgap of few meV. Such ribbons should have a width of about 100 nm and are easy to fabricate. Based on our results we suggest schematics of efficient optoelectronic devices based on graphene nanoribbons. To further understand our data we calculated the TEP dependence on gate voltage within a model based on ballistic transport in a 1D semiconducting channel. Importantly our model is applicable both to carbon nanotubes and graphene nanoribbons. .

The effect of hydrogen plasma on the chemical and structural modification of graphene 1

A. Felten , I. Verzhbitskiy , C. Woods , C. Rice , J.-J. Pireaux , C. Casiraghi

Research Center in Physics of Matter and Radiation (PMR), University of Namur, Namur, Belgium 2 Physics department, Free University Berlin, Germany 3 School of Physics and Astronomy, University of Manchester, UK 4 School of Chemistry and Photon Science Institute, Manchester University, UK alexandre.felten@unamur.be

Abstract

Graphene based devices fabrication is currently impeded by its metallic behavior and its lack of reactivity making it hard to create graphene based transistors or sensors. In order to overcome this problem, various approaches to tune and control the electronic properties of graphene have been considered. Among them, plasma treatment has been shown to be a very interesting and controllable way of chemically modifying graphene.[1-3] Furthermore, it has the advantage over other processes to be easily implemented in the electronic device production line. In this work, we investigated the controlled modification of graphene using hydrogen (H2) rf-plasma treatment.[1,3] Structural changes induced on the graphene flakes are first monitored using Raman spectroscopy.[2,3] It is found that changing the plasma parameters (i.e. pressure, power, exposure time and position of the sample in the plasma chamber) allows fine tuning of the modification induced on the graphene. For example, figure 1 shows the Raman spectra of monolayer graphene for different exposure time (figure 1a) and different positions of the sample inside the plasma chamber (figure 1b). We can see that these two parameters affect greatly the amount of defects induced on the graphene. In addition, it is noticed that the hydrogen pressure is another particularly important parameter to take into account. Defect formation kinetics under plasma is also found to vary with the number of graphene layers (see figure 1c). Surprisingly, at specific conditions, bilayer and trilayer graphene seem to be more reactive than monolayer graphene (higher intensity and larger FWHM of the D peak are recorded) and layer-bylayer thinning of multilayer graphene is occurring. In order to support the Raman results, complementary measurements performed using micro-focused X-ray photoelectron spectroscopy (micro-XPS) and atomic force microscopy (AFM) are performed. The first technique give us information on the chemical state and the carbon content of mono and bilayer graphene after hydrogenation, while the latter allows visualization of the structural damages induced on the graphene sheets. In conclusion, we carefully studied the hydrogenation of graphene inside a low temperature plasma. We show that graphene modification is strongly dependent on the plasma parameters (pressure, power, exposure time and position of the sample) as well as on its number of layers. This work sheds light to the complex process that is a hydrogen plasma which allows in turn controlled tuning of the functionalization of graphene.

References [1] A. Felten, A. Eckmann, J.-J. Pireaux, R. Krupke, C. Casiraghi, Nanotechnology, 24 (2013) 355705. [2] A. Felten, B. Flavel, L. Britnell, A. Eckmann, P. Louette, J.-J. Pireaux, M. Hirtz, R. Krupke, C. Casiraghi, Small, 9 (2013) 631. [3] A. Eckmann, A. Felten, A. Mishchenko, L. Britnell, R. Krupke, K.S. Novoselov, C. Casiraghi, Nanoletters, 12 (2012) 3925.

Figures

Figure 1. (a) Evolution of Raman spectra of monolayer graphene upon increasing hydrogen plasma exposure. (b) Raman spectra of monolayer graphene modified under hydrogen plasma placed at different positions in the plasma chamber. Positions 1, 2 and 3 correspond respectively to inside the discharge, outside the discharge (20 cm away from position 1) and further away from the discharge (40 cm away from position 1). (c) Raman spectra of mono- and bilayer graphene modified at the same time under the same plasma conditions.

Solvothermal exfoliation of fluorographene by the intercalation of organic solvents for lithium primary batteries Yiyu Feng, Chuanbin Sun, Wei Feng School of Materials Science and Engineering, Tianjin Key Laboratory of Composite and Functional Materials, Tianjin University, Tianjin 300072, China fengyiyu@tju.edu.cn Abstract Fluorographene (FG), a kind of graphene derivatives, is considered as one of important candidate materials for advanced technological applications because of its distinctive magnetic, electrical and electronic properties. Generally, FG nanosheets can be synthesized by severely fluoridizing graphene using many fluoride reagents or laser irradiation. Recently, a solvothermal-assisted exfoliation shows a great potential for the preparation of high-quality single- or few-layer nanomaterials. High temperature and pressure reduce the free energy, weaken van der Waals attraction between adjacent layers and promote the intercalation of solvent molecules into interlayers, resulting in the efficient exfoliation. Furthermore, F-graphite shows a wide lamellar space of 0.71 nm and a weak bonding energy of 9.36 kJ mol-1 [1], which favor the intercalation of molecules. In this paper, high-quality FG was prepared by the solvothermal exfoliation of F-graphite through the intercalation of acetonitrile and chloroform, which was demonstrated by wrinkled few-layered microstructures and the poor regularity along the stacking direction. The electrochemical performance of FG nanosheets was tested as the cathode material of Libattery at different current densities. Compared with F-graphite, FG cathode displayed an excellent electrochemical performance with an improved discharge voltage, specific capacities and rate capability. Figure 1 illustrates the preparation of FG nanosheets by the intercalation and exfoliation. FG-1 (intercalated by acetonitrile (ACN)) and FG-2 (intercalated by chloroform) prepared by the solvothermal intercalation exhibit a high yield of production up to 15%, which is almost three-fold higher than that of FG prepared only by ultrasonication. Elemental composition and the nature of chemical bonds of FG nanosheets were studied by C1s XPS spectra (Figure 2) deconvoluted to several symmetrical peaks. Compared with FG-1 with five peaks at 285.3, 284.5, 289.0, 291.0 and 292.0 eV, FG-2 exfoliated by chloroform exhibits a new peak at 288.4 eV in C1s spectra corresponding to semi-ionic C–F bonds [2]. This bond is also confirmed by F1s spectra with two peaks at 688.4 and 690.0 eV associated with semiionic C–F bonds and covalent C-F bonds, respectively [3]. Meanwhile, a minor shift of the peak from 689.0 eV to 688.6 eV also reflects the partial transformation of covalent C-F bonds to semi-ionic C-F bonds. It is probably due to the formation of C-H•••F hydrogen bonds (H-bonds) between chloroform molecules and F atoms of F-graphite. Figure 3a displays specfic capacities of FG nanosheets at different current densities. A remarkable increase specific capacities of FG cathode is obtained due to the improved Li+ diffusion rate into interlayers of FG with a large space. FG-2 with semi-ionic C-F bonds shows a high specific capacity of 520 mAh g-1 at 1C, which is 2.5-fold higher than that of FG-1. Moreover, FG-2 also shows a specific capacity of 413 mAh g-1 at 2C and 228 mAh g-1 at 3C. FG-1 fails to discharge at 3C. The discharge capacity of FG-2 at current densities from 0.1C to 2C outperforms that of FG nanosheets synthesized using F2/He in previous studies [4]. Figure 3b indicates that all samples show high energy densities and low power densities at low discharge rates ( 0.1 C) while the average power density of Li-battery using FG nanosheets is enhanced at high discharge rates. The increase in discharge rates leads to decreased energy densities due to the drop of the output potential as well as the discharge capacity. FG-2 shows a dramatic increase in energy density and power density compared with FG-1 and Fgraphite. A maximum power density value of 4038 W kg-1 is obtained for Li-battery using FG-2 nanosheets, which is almost four times higher than F-graphite (1136 W kg-1). FG nanosheets were prepared by the solvothermal-assisted exfoliation of F-graphite based on the intercalation of low-boiling-point organic solvents (ACN, chloroform) without any stabilizer or modifier. This exfoliation shows a high-yield production of FG nanosheets up to 15 wt.%. The partial transformation from covalent C-F bonds to semi-ionic C-F bonds in FG nanosheets exfoliated by chloroform was studied. Compared with FG-1, significant improvement of rate capability was obtained for FG-2 with semi-ionic C-F bonds. FG-2 nanosheets exhibited a high specific capacity of 520 mAh g-1 at 1C, which is 2.5-fold higher than that of FG-1 and 5 times as much as that of F-graphite. Moreover, high-quality exfoliated FG nanosheets can be utilized for Li-battery with high rate capability and discharge voltage. FG-2 showed a maximum power density of 4038 W kg-1 at 3C. Results indicate that

the solvothermal exfoliation by low-boiling-point solvents is a facile and high-yield approach to prepare high-purity FG nanosheets. References [1] A. Hamwi, J. Phys. Chem. Solids, 57 (1996) 677. [2] H. Touhara, F. Okino, Carbon, 38 (2000) 241. [3] P. F. Fulvio, S. S. Brown, J. Adcock, R. T. Mayes, B. Guo, X. G. Sun, Shannon M. Mahurin, G. M. Veith, S. Dai, Chem. Mater., 23 (2011) 4420. [4] P. Meduri, H. Chen, J. Xiao, J. J. Martinez, T. Carlson, J. G. Zhang, Z. D. Deng, J. Mater. Chem. A, 1 (2013) 7866. Figures

Figure 1 A schematic illustration of the preparation of FG nanosheets by the intercalation and exfoliation.

Figure 2 High-resolution XPS spectra of (a) C1s and (b) F1s of FG-2.

Figure 3 (a) specific capacities and (b) the Ragone plots giving the variation of energy density vs. power density of Li-battery at different current densities

ATOMIC LOCAL STUDIES ON GRAPHENE USING ISOLATED AD-ATOM PROBES 1,2

1,2

5,6

A.S. Fenta , V. S. Amaral , J. G. Correia , J. N.Gonçalves , A.Gottberg , K. Johnston , Yacine Kadi 1

Department of Physics University of Aveiro, 3810-193 Aveiro, Portugal 2

CICECO, University of Aveiro, 3810-193 Aveiro, Portugal

Centro de Ciências e Tecnologias Nucleares (C2TN), Instituto Superior Técnico, Universidade de Lisboa, 2686-953 Sacavém, Portugal 4 5

CERN, EN-STI-RBS Div, 1211 Geneva 23, Switzerland

Technische Physik, Universitaet Saarlandes, 66041 Saarbrucken, Germany 6 7

CERN, PH Div, 1211 Geneva 23, Switzerland

CERN, PH-UOP Div, 1211 Geneva 23, Switzerland fenta@ua.ptl

Abstract The one-atom-thick crystal - graphene, uniquely combines extreme mechanical strength, exceptionally high electronic and thermal conductivities, as well as many other exotic properties, all of which make it highly interesting for fundamental physics and numerous applications. Its properties strongly depend on surface and interface nanoscale interactions, where new physical models should apply aiming their understanding and control. In the present work we investigate the mechanisms of adhesion of ad-atoms on the surface, alone or when forming clusters, preferably in regions of structural defects (of different kinds), their capture processes, adsorption and migration of atoms. The aim is to investigate electronic, magnetic or catalytic properties. Understanding how the adsorption could be controlled would contribute to the development of innovative devices based on graphene. Experimental works are accompanied by theory and computational models generally based on density functional theory and/or molecular dynamics calculations, providing an important support for studying the electronic properties. In this context, our experimental observables are the hyperfine parameters of add-atoms on graphene, measured with the nuclear spectroscopy PAC (Perturbed Angular Correlations) technique. PAC allows to probe at the atomic scale the add-atoms interactions without interfering with the graphene electronic structure, thereby providing unique information, which is impossible to obtain by electron spectroscopy and electron microscopy techniques such as, AFM or STM, not exempted from interactions between the tip and the surface test or ad-atoms therein. By PAC measurements it can be determined the electric field gradient (EFG) and magnetic hyperfine field (MHF) at atomic scale, electronic structure and magnetic environment of ad-atoms. The EFG provides structural information, location of the probe, stability, and bond (ionic, covalent bonding, van der Waals). The MHF translates properties correlated with the electronic spin configuration. In this presentation we will present first results of the PAC hyperfine parameters obtained in graphene grown at different substrates as a function of different temperatures and different probing elements, 111m

Cd and

199m

Hg. To complement the experimental studies, ab initio simulations, using the software

Wien2k and VASP, with the self-consistent LAPW+lo and PAW methods to solve the Kohn-Sham

equations and GGA/LDA approximations, have been implemented to simulate the charge density distribution of ad-atoms on graphene for different probe isotopes. This is the first step to attain the next objective that is to understand the Cd, and Hg (our PAC probes) interactions at the graphene layer. Minima of energy for the ideal bond-length, the hyperfine parameters and the charge distributions in the unit cells will be presented. These are preliminary experimental and simulation results of a large portfolio of experiments and ideas, which are envisaged to come.

References [1]A. K. Geim, Graphene: Status and Prospects, Science, 324, 1530-1534, 2009; [2]H.H. Bertschat, H. Granzer, K. Potzger, S. Seeger, A. Weber , W.-D. Zeitz, Surface and interface studies with ASPIC, Hyperfine Interactions, 129, 475Âą492, 2000; [3]O. Yazyev, Hyperfine Interactions in Graphene and Related Carbon Nanostructures Nanolett., 8, 1011, 2008; [4]D. W. Boukhvalov and M. I. Katsnelson, Destruction of graphene by metal adatoms, Appl. Phys. Lett. 95, 023109, 2009; Z K

Figures

R(t) 0,0 0,1

E JUDSKHQH 6L 7 /7 Ë' H'

0,0 5

time (ns)

2000 4000

EFG1

Z (54) Mrad/s Z = 1310 K (0,07) K = 0,04 Z EFG1K Z = 1310 (54) Mrad/s K = 0,04 (0,07) EFG2

sqrt(P(w)) (arb.units)

FT 2

o /7 Ë' H' (a) graphene- Si, T=3 C, p D1eD3 0,1 E JUDSKHQH 6L 7

Fig.1 Âą First PAC results, on graphene/Si with

199m

Hg probe. We can observe 2

different

local

environments,

characterized by EFG1 and EFG2.

Z = 1071 (24) Mrad/s K = 0.35 (0.01)

: (Mrad/s)

Fig.2 Âą Ab initio simulation with VASP. Variation of electric

field

principal component gradient,

Vzz,

of and

asymmetry parameter, Č&#x2DC; = (vyy-vxx)/vzz, of Cd (at the H site) as a function of displacement relative to the equilibrium position, along the c axis. It is possible to assign a linear behavior for Vzz, which is sensitive to variations of the order of picometer.

Direct Electrical Characterization of Graphene-On-Insulator by Multiple-Point Contact Configuration Luis Segura, Noel Rodriguez, Cristina Fernandez, Akiko Ohata, Carlos Marquez, Francisco Gamiz Nanoelectectronics Laboratory, CITIC-UGR, Dept. of Electronics, University of Granada, Spain noel@ugr.es; fgamiz@ugr.es Abstract The experimental characterization of the physical properties of graphene has been the subject of a large number of manuscripts devoted to research results of this promising material [1]. When the characterization targets electrical parameters, microsized graphene sheets with ad hoc fabricated contacts (electrodes) have been extensively used [2]. From an industrial monitoring perspective, this task requires complex post-processing of the samples, which takes time and cost. We propose an alternative method for the electrical characterization of as-fabricated large CVD graphene-On-Insulator samples. The experimental setup is based on a four/two-probe measurement system with conductive chuck as schematized in Figure 1. The validity of this contact-based technique for testing large graphene samples is successfully demonstrated in the conductivity curves shown in Figure 2. The voltage between needles 2 and 3 in Figure 1.a is measured as a function of the substrate voltage, VSub, when a constant current is forced between probes 1 and 4 (four-probe configuration, current form factor ʌ/ln2 [3]). The thickness of the SiO2 layer is 90nm and the size of the monolayer of graphene is 1cm×1cm. Substrate silicon is highly P-type doped. This method has been further simplified by employing a two-point contact configuration. Special caution must be paid in this case to the contact resistance (Rc) consequence of the simultaneous measurement of the voltage while the current is flowing. In the case of our experiment, Tungsten-Carbide tips were used leading, potentially, to a large Rc value due to the similar graphene work-function [4]. In a first stage, we studied the impact of the probe pressure on the sample (Figure 3). At a given bias point, the current level saturates at a pressure of 50g on 25µm-radius tips (250MPa). Once the minimum measurement pressure is set, the total resistance curve as a function of the probe separation allows the extraction of the contact resistance (Rtot=ȡs-Gr d/W+ Rc) when d=0. ȡs-Gr is the sheet resistance of graphene obtained previously by four-probe measurements; W, the equivalent width of the current flow and d the separation between probes (on first approach we have assumed a linear relation between resistance and probe separation). Further exploitation of the two-needle configuration requires the determination of the form factor for the current flow between the needles (fg~d/W). fg can be evaluated by combining the resistivity extracted from four-probe measurements and the slope of the total resistance versus the distance between the probes of Figure 4 (under linear approach). The result is shown in Figure 5. One useful application of the technique is the fast monitoring of graphene quality by extracting parameters such as the carrier mobility. The results obtained for two graphene samples (clean and contaminated) are presented in Figure 6. As the number of defects increases, graphene mobility values reduce dramatically more than 60%. This method can be used for vendors and research laboratories for the fast characterization of samples. Acknowledgements This work has been partially funded by the Spanish Government through project TEC-2011-28660. Thanks are given to AMO-GmbH and Graphenea for sample supplying and Prof. A. Toriumi from University of Tokyo and Prof. S. Cristoloveanu from INP-Grenoble for useful discussions. References [1] R. Ruoff, IEEE Nanotechnology Materials and Devices Conference, Invited. 2013. [2] A. D. Franklin, S.-J. Han, A.A. Bol, V. Perebeinos, IEEE Electr. Dev. Letters, 33(1), 2012, 17-19 [3] D. K. Schroder, Semiconductor Material and Device Characterization, John Wiley & Sons, 3rdEd. (2006). [4] K. Nagashio, T. Nishimura, K. Kita, A. Toriumi, Applied Physics Letters, 97(14), 2010, 143514-3

Figures

Figure 1. Schematic experimental setup. (a) Fourprobe Kelvin measurement, probes 1 and 4 are used to source and drain the current; 2 and 3 for voltage measurement. (b) Two-point contact measurement, only two probes on the graphene are used to drive the current while the voltage is simultaneously measured or applied.

Figure 3. Current flow between probes (two-point contact configuration, Figure 1.b, d=1mm) as a function of the needle pressure. The current remains saturated above 50 grams. Further pressure increase only contributes to damage the underneath SiO2 layer until physical breakdown. Substrate voltage is 0V.

Figure 5. Form factor of the current flow for twopoint contact configuration extracted combining fourprobe and two-probe measurements. For large probe separation (d>1mm), the form factor, fg, can be approximated by 0.25.

Figure 2. Conductivity as a function of the substrate voltage obtained from four-probe contact measurements with two probe separations. The probes are located far away from the graphene borders [3] (current form factor Ę&#x152;/ln2). The conductivity values are independent of the probe separation and decrease until the Dirac point is achieved.

Figure 4. Total resistance between probes (two-point contact configuration) as a function of the probe separation. Linear regression for d=0 allows the extraction of the contact resistance. Tungsten Carbide needles, tip radius 25Âľm. Two substrate voltages are presented.

Figure 6. Carrier mobility extracted by the proposed two-point contact configuration for clean and contaminated samples of graphene. As observed, the mobility extracted for the contaminated sample dramatically decreases. The actual microscope images of the graphene surface are shown inside the bars.

Stable p-doping in graphene using deep UV irradiation 1,2

M. Z. Iqbal , N. Ferrer-Anglada , Jonghwa Eom

Applied Physics Dept., Universitat PolitĂ¨cnica de Catalunya, J. Girona 3-5, 08034 Barcelona, Spain 2 Dept. of Physics and Graphene Research Institute, Sejong University, Seoul 143-747, South Korea nuria.ferrer@upc.edu Abstract Graphene has been recognized as an important material for electronic devices due to its unique electronic properties such as ambipolar transport [1, 2].However, due to its zero band gap it is essential to modulate the Fermi level, opening a gap in the electronic structure. It can be achieved by different methods [3], between them doping with various molecules. But often doping degrades the carrier mobility of grapheme [4-6]. It is highly desirable to develop a way to tune the doping level without reducing the mobility of graphene. Theoretically, it has been described that oxygen molecules react with graphene in the presence of UV light to produce oxygen containing groups [7], these oxygen atoms form a stable structure on the sites of pristine graphene and induce p-type doping [8,9]. In the present work we used CVD grown graphene exposed to deep ultraviolet (DUV) light during different times up to 100 min. We analyzed the samples by Raman spectroscopy and transport measurements. By Raman spectroscopy we analyzed the shift of G and 2D peak frequencies and the intensity ratios of these peaks as a function of DUV light exposure time, the blue shift of G and 2D peak positions increases with increasing the exposition time. This fact is interpreted as an increasing p-doping [10-12, 1]. The minor change of ratio of D/G peak intensity implies a negligible change in the defects before and after DUV light exposure, the small ratio peak intensity D/G indicates a low defect density. The p-doping of CVD grown graphene is confirmed by transport measurements. The back gate voltage dependent resistivity for single layer graphene is analyzed as function of DUV light exposure time, the maximum resistivity corresponding to the Dirac point is shifted toward positive gate voltage with increasing the DUV light exposure time, see figure 1. Figure 1(a) shows the resistivity as a function of the back gate voltage (Vg), before and after DUV exposure for a different period of time. The Dirac point (VDirac) of the pristine CVD grown graphene is found around zero Volt. After being exposed to DUV light for a desired time, the VDirac moves towards a positive Vg, increasing with increasing DUV exposure time, up to ŕ¸? 35 V for 100 minutes of DUV exposure. The shift towards positive gate voltage, indicating p-type doping, is probably due to the formation of holes as the result of the photo-oxidation of graphene layer with DUV light exposure [13]. Figure 1 (b) shows the charge carrier concentration as a function of DUV light exposure time at different gate voltage, figure 1 (c) shows the mobility as a function of DUV light exposure time at different gate voltage. Inset shows the Dirac point shift as function of DUV light exposure time. Our work demonstrates by Raman spectroscopy and transport measurements a strong and stable pdoping in CVD grown graphene film with deep ultraviolet (DUV) light. References [1] Geim AK, Novoselov KS, Nat Mater, 6(3) (2007) 183. [2] Das Sarma S, Adam S, Hwang EH, Rossi E, Rev Mod Phys., 83(2) (2011) 407. [3] Iqbal MW, Singh AK, Iqbal MZ, Eom J, J Phys-Condens Mat., 24 (2012), 33. [4] Singh AK, Iqbal MW, Singh VK, Iqbal MZ et al., J Mater Chem., 22(30) (2012) 15168. [5] Dong XC, Fu DL, Fang WJ, Shi YM, Chen P, Li LJ, Small, 5(12) (2009) 1422. [6] Chen Y, Gao B, Zhao JX, Cai QH, Fu HG., J Mol Model,18(5) (2012) 2043. [7] Cheng YC, Kaloni TP, Zhu ZY, Schwingenschlogl U, Appl Phys Lett., 7 (2012) 101. [8] Dai JY, Yuan JM, Phys Rev B, 16, (2010) 81.

[9] Xu ZP, Xue K., Nanotechnology, 4 (2010) 21. [10] Shin HJ, Choi WM, Choi D, Han GH et al., J Am Chem Soc., 132(44) (2010)15603. [11] Tongay S, Berke K, Lemaitre M, Nasrollahi Z et al., Nanotechnology, 22(42) (2011). [12] Luo ZT, Pinto NJ, Davila Y, Johnson ATC, Appl Phys Lett., 100 (2012) 25. [13] Liu H, Ryu S, Chen Z, Steigerwald ML, Nuckolls C, Brus LE, Journal of the American Chemical Society, 131(47) (2009) 17099. Figures

6 4

Vg=-40V Vg=-20V Vg=-10V Vg=40V Vg=50V Vg=60V

(b)

Pristine 3 min 5 min 10 min 15 min 20 min 25 min 30 min 45 min 60 min 75 min 100 min

-2

(a) n (10 cm )

Resistivity k

2 -60

-40

-20

Vg (V)

100

DUV Exposure Time (min)

Dirac Point Shift (V)

Vg=-40V Vg=-20V Vg=-10V Vg=40V Vg=50V Vg=60V

40 30 20 10

Mobility (10 cm /V sec)

0 0

100

DUV Exposure Time (min)

0 0

100

DUV Exposure Time (min) Figure 1 (a) Resistivity as a function of back gate voltage (Vg) for the single layer CVD grown graphene before and after DUV light for different exposure time. (b) Charge carrier concentration as a function of DUV light exposure time at different gate voltage. (c) Mobility as a function of DUV light exposure time at different gate voltage. Inset shows the Dirac points shift as function of DUV light exposure time.

Boosting Graphene Reactivity with Oxygen by Boron Doping: DFT Modeling of the Reaction Path. Lara Ferrighi, Martina Datteo, Cristiana Di Valentin Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca Via Cozzi 55 20125 Milano, Italy. lara.ferrighi@unimib.it Abstract Graphene (G) reactivity toward oxygen is very poor, which limits its use as electrode for the oxygen reduction reaction (ORR). Contrarily, boron-doped graphene (BG) was found to be an excellent catalyst for the ORR[2,3,4,5]. Through a density functional study, comparing molecular (circumcoronene) and periodic approaches (in a 4x4 or 8x8 cell) and different functionals (B3LYP vs PBE), we show how substitutional boron in the carbon sheet can boost the reactivity with oxygen leading to the formation of bulk borates covalently bound to graphene (BO 3±G, see Fig. 1) in oxygen-rich conditions. These VSHFLHV DUH KLJKO\ LQWHUHVWLQJ LQWHUPHGLDWHV IRU WKH 2ő2 EUHDNLQJ VWHS LQ WKH UHGXFWLRQ SURFHVV RI 2 2 to form H2O as they are energetically stable. In this talk we show the reaction energies for molecular oxygen dissociation on BG are negative (exothermic processes, see Fig.2), in net contrast with pure G where reaction energies are highly positive (endothermic processes). The stability of oxygenated BG species is enhanced when the boron atom is directly bound to oxygen. We highlight the reaction products of O 2 with both G and BG, finding the same conclusions with all methods used, which definitely consolidates our results. We show that BG sheets can be much more easily oxidized than G ones and depending on the oxygen conditions the extent of oxidation of the boron-doped species can be different, but, at common oxygen pressures, borates are the most stable. The existence of oxygenated B species was proved before by XPS measurements; [2,3] however, their role in the chemistry of B-doped graphene has been totally overlooked and underestimated. We believe that our results are not only relevant in the context of ORR but could be more generally useful for the interpretation of nonmetal doped graphene based catalysis. References [1] Ferrighi L, Datteo M, Di Valentin C., J. Phys. Chem. C, 118 (2014), 223±230 [2] Sheng, Z.-H.; Gao, H.-L.; Bao, W.-J.; Wang, F.-B.; Xia, X.-H., J. Mater. Chem., 22 (2012) 390± 395 [3] Cattelan, M.; Agnoli, S.; Favaro, M.; Garoli, D.; Romanato, F.; Meneghetti, M.; Berinov, A.; Dudin, P.; Granozzi, G., Chem. Mater., 25 (2013), 1490± 1495 [4] Wang, H.; Zhou, Y.; Wu, D.; Liao, L.; Zhao, S.; Peng, H.; Liu, Z., Small, 9 (2013), 1316± 1320 [5] Yang, L.; Jiang, S.; Zhao, Y.; Zhu, L.; Chen, S.; Wang, X.; Wu, Q.; Ma, J.; Ma, Y.; Hu, Z., Angew. Chem., 123 (2011), 7270± 7273 Figures

Fig.1 Formation of stable bulk borates, from boron doped graphene and oxygen.

Fig.2 Energy profile for molecular oxygen physi-/chemisorption on BG. Top and side views of the balls and sticks 4 Ă&#x2014; 4 models.

Current transport in graphene/AlGaN/GaN heterostructures F. Giannazzo1, G. Fisichella1,2, G. Greco1, S. Ravesi3, F. Roccaforte1 1

CNR-IMM, Strada VIII, 5, Catania, Italy Department of Electronic Engineering, University of Catania, Italy 3 STMicroelectronics, Catania, Italy filippo.giannazzo@imm.cnr.it

Graphene (Gr) attracted a huge interest for many device applications, due to many interesting electrical and optical properties. Its main limitation as channel material in MOSFETs is the high off-state current, due to the absence of a bandgap, which hampers its use for switching applications. In the last years, novel device concepts have been proposed to overcome these limitations, like Gr/semiconductor junctions [1] or even heterostructures of Gr layers separated by ultrathin dielectric barriers [2]. These exploit the peculiar properties of the Gr 2DEG (finite density of states, atomic thickness), and the interaction of the 2DEGs in close proximity. In this context, novel devices formed by Gr with semiconductor heterostructures, including an ordinary 2DEG, can be very interesting. In this work, we investigated the electronic properties of Gr/AlGaN/GaN heterostructures, that can be interesting for high power and high frequency applications. Gr, deposited by CVD on Cu, was transferred on high quality Al0.25Ga0.75N/GaN, with ~25 nm thick AlGaN barrier layer. The vertical current transport from Gr to the buried 2DEG was characterized at nanoscale using current measurements by conductive atomic force microscopy (CAFM) and capacitance measurements by scanning capacitance microscopy (SCM) [3]. From these analyses, performed both on Gr-coated and bare AlGaN/GaN regions using different AFM tips metal coatings, the Gr/AlGaN barrier height was extracted, as well as the variation of the carrier densities of Gr and AlGaN/GaN 2DEG as a function of the gate bias. Novel device concepts based on the properties of vertical Gr/AlGaN/GaN heterostructures will be discussed.

References [1] H. Yang, J. Heo, S. Park, H. J. Song, D. H. Seo, K.-E. Byun, P. Kim, I. Yoo, H.-J. Chung, K. Kim, Science, 336 (2012) 1140-1142. [2] L. Britnell, R. V. Gorbachev, R. Jalil, B. D. Belle, F. Schedin, A. Mishchenko, T. Georgiou, M. I. Katsnelson, L. Eaves, S. V. Morozov, N. M. R. Peres, J. Leist, A. K. Geim, K. S. Novoselov, L. A. Ponomarenko, Science, 335, (2012) 947-950. [3] F. Giannazzo, S. Sonde, V. Raineri, and E. Rimini, Nano Lett., 9 (2009) 23.

Large-area graphene from catalytic metals to arbitrary substrates by electrochemical delamination and transfer printing G. Fisichella1,2, R. Lo Nigro1, F. Roccaforte1, S. Ravesi3, F. Giannazzo1 1

CNR-IMM, VIII Strada, 5, 95121, Catania, Italy, Department of Electronic Engineering, University of Catania, Viale A. Doria 6, 95125 Catania, Italy, 3 STMicroelectronics, Stradale Primosole, 50, 95121, Catania, Italy gabriele.fisichella@imm.cnr.it

Graphene growth on catalytic metals (Cu, Ni, Pt, Ru,…) by CVD followed by transfer currently represents one of the most viable roots to large area graphene-based electronics. Beyond catalyst and growth condition optimisation, transfer represents a critical step of this approach, with a strong impact on the final quality and uniformity of graphene on the target substrate. The typically adopted method to separate graphene from the growth substrate, i.e. chemical etching of the metal (typically in FeCl3 for Ni or Cu) while using a sacrificial polymer film (typically PMMA) as the graphene support, presents several drawbacks (metal contaminations remaining from the metal substrate and/or from the etchant, polymer residues on graphene) and limitations (difficult or not possible etching in the case of noble metal substrates). Furthermore, metal waste by etching raises the process cost in view of an industrial scaleup, so that approaches for reusing the metal substrate in several growth cycles are highly desirable. Recently, graphene has been effectively separated from the growth substrate without metal etching, using the mechanical action of hydrogen bubbles generated at graphene/metal interface [1] in an electrochemical process using electrolytes like NaOH and KOH [2]. This approach potentially solves the metal contaminations issues, allows reusing the substrate for unlimited number of growth, without limitations to the kind of catalytic metal. In this work, the influence of the critical parameters involved in the electrochemical delamination (such as the electrolyte molar concentration, the cell overvoltage,..) on the structural and electrical quality of transferred graphene was investigated. An optimised transfer-printing method, allowing a fine control of pressure and temperature ramps applied between the polymer/graphene stack and the target substrate, was developed for graphene transfer on different substrates, such as SiO2, Si, GaN, AlGaN, SiC or soft materials (PEN). Furthermore, specific functionalization/derivatization treatments [3] have been developed to optimise the graphene adhesion on each kind of substrate. Different combinations of support polymers and solvents (for final graphene cleaning) have been considered. The nanoscale morphological and electrical properties of the transferred graphene will be investigated by advanced scanning probe techniques [4], the structural and chemical properties by atomic resolution STEM and EELS [5]. Finally, the average electrical properties on large area will be tested by electrical measurements on proper device structures (FETs, TLM and VdP structures). [1] Y. Wang, et al., ACS Nano 5, 9927–9933 (2011). [2] C. J. L. de la Rosa, et al., Appl. Phys. Lett 102, 022101 (2013). [3] G. Fisichella, et al., Beilstein J. Nanotechnol. 4, 234–242 (2013). [4] F. Giannazzo, et al., Nano Lett. 11, 4612–4618 (2011). [5] G. Nicotra, et al., ACS Nano, 7, 3045–3052 (2013).

Few-layer Graphene Sheets by Liquid Phase Exfoliation in a Low Boiling Point Solvent: A Comparative Study of Three Different Graphite-based Starting Materials

Yasemin Ă&#x2021;elik (QGHU 6XYDFĂ&#x2022; and Emmanuel Flahaut 1

2,3

ybozkaya@anadolu.edu.tr

$QDGROX 8QLYHUVLW\ 'HSDUWPHQW RI 0DWHULDOV 6FLHQFH DQG (QJLQHHULQJ (VNLĂşHKLU 7XUNH\ UniversitĂŠ de Toulouse, UPS, INP, Institut Carnot Cirimat, 118 route de Narbonne, F-31062 Toulouse cedex 9, France 3 CNRS, Institut Carnot Cirimat, F-31062 Toulouse, France 1 2

Graphene is a promising material in many applications due to its unique electrical, thermal and mechanical properties. However, these properties and the yield of graphene show variations depending on which graphene production route is used. Liquid phase exfoliation routes may allow one to produce graphene in large scale for applications such as nanocomposites, thin films and conductive inks. The critical point in liquid phase exfoliation is to be able to increase graphene concentration as much as possible while maintaining the quality of graphene flakes. Graphite can be exfoliated into high-quality graphene sheets (with <5 layers) in 1-methyl-2-pyrrolidone (NMP) due to well matched surface energy between graphene and the solvent [1]. Therefore, it is one of the most widely preferred organic solvent for sonication assisted liquid-phase exfoliation of graphene from graphite. However, high boiling point ( 204 C at 760 mm Hg) of NMP makes it difficult to be completely removed from the system and the residual solvent can be detrimental for composites. Moreover, this may cause problems during flake deposition onto a substrate, since agglomeration tends to occur during the slow solvent evaporation [2]. Hence, exfoliating graphite in a low boiling point solvent to give graphene dispersions with a concentration as high as possible would facilitate incorporation of graphene into composites and deposition onto substrates. In this study, three different graphite-based materials (expandable graphite and two different nano-graphite powders) were investigated as starting powders for the liquid phase exfoliation in isopropyl alcohol (IPA) (82.5 C boiling point) within relatively short sonication times (up to 120 min). The prepared dispersions were analyzed and compared in terms of their graphene concentration, stability, number of graphene layers, quality and the electrical conductivity of the prepared graphene-

based materials using techniques such as UV-Vis absorption spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM) and Four Point Probe method.

References [1] Hernandez, Y. et al., Nat. Nanotechnol., 3(9) (2008), 563-568 [2] 2Âś1HLOO $ .KDQ 8 1LUPDOUDM 3 1 %RODQG - DQG &ROHPDQ - 1 - 3K\V &KHP &, 115 (2011) 5422-5428

Toxicity evaluation in Xenopus laevis tadpoles exposed to carbon based nanoparticles under normalized conditions 1, 2*

1,2

Florence MOUCHET , StĂŠphanie CADARSI , Jean-Charles ARNAULT , Hugues GIRARD , C. 4 5 4 6, 7 1, Menard-Moyon , Izabela JANOWSKA , Alberto BIANCO , Emmanuel FLAHAUT , Eric PINELLI 2 1, 2 and Laury GAUTHIER UniversitĂŠ de Toulouse ; UPS, INP ; EcoLab (Laboratoire GÂśpFRORJLH fonctionnelle et environnement) ; (16$7 $YHQXH GH OÂś$JURELRS{OH )-31326 Castanet-Tolosan

CNRS ; EcoLab (Laboratoire GÂśpFRORJie fonctionnelle et environnement) ; F-31326 Castanet-Tolosan

CEA, Diamond Sensors Laboratory, Centre d'Etudes de Saclay ; F-91191 Gif sur Yvette, France 4

CNRS, Institut de Biologie MolĂŠculaire et Cellulaire, UPR 3572, Immunopathologie et Chimie ThĂŠrapeutique, F-67084 Strasbourg Cedex

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UniversitĂŠ de Toulouse, INP, UPS, Institut Carnot CIRIMAT (Centre Inter-universitaire de Recherche et GÂś,QJpQLHULH GHV 0DWpULDX[ 805 &156 F-31062 Toulouse cedex 9 7

CNRS, Institut Carnot CIRIMAT, F-31062 Toulouse, France

*Email contact: florence.mouchet@orange.fr Due to their promising potential in numerous industrial applications because of their exceptional properties, some carbon nanoparticles (nanocarbons) such as carbon nanotubes (CNT), graphene (G), nano diamond (ND) and carbon black (CB) are expected to get into the environment (normal conditions of use, end of life) and especially to be found into the aquatic compartment because of its capability to concentrate pollution. Nevertheless, ecotoxicological data are still scarce, especially on aquatic organisms. The aim of the present work is to contribute to the ecotoxicological assessment in the aquatic compartment by comparing 4 different nanocarbons: CNT, few-layer graphene (FLG), ND and CB. The investigation of their environmental hazard was conducted according to an international standardized bioassay procedure (IS0, 2006) using a sensitive and relevant biological model, the amphibian larvae (Xenopus laevis). Few different endpoints were assessed: (i) acute toxicity (mortality), (ii) chronic toxicity (growth inhibition) and (ii) genetic toxicity (induction of micronucleated erythrocytes). The results, depending on the nature of the nanocarbon, showed moderate toxicity since growth inhibition was only observed at very high concentrations (10 and 50 mg/L). The chronic toxicity observed in larvae exposed to high concentrations of nanocarbons would be limited to physical effects (gill clogging and/or abrasive effects and or nutrients deprivation). Key Words: Nanocarbons, carbon nanotubes, graphene, nano diamond, carbon black, ecotoxicity, amphibian Xenopus laevis Presentation preference: poster presentation

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Preparation of carbon nanotube Y-junctions from graphene nanoribbons 1

D. Fulep , I. Zsoldos , I. Laszlo 1

Faculty of Technology Sciences, Szechenyi Istvan University - H-9126 Gyor, Hungary, EU Department of Theoretical Physics, Institute of Physics, Budapest University of Technology and Economics H-1521 Budapest, Hungary, EU zsoldos@sze.hu

Abstract The mass production of fullerenes and nanotubes faces the problem of their selective production. Special kind of graphene patterns was presented earlier which can be used as initial structures for fullerenes, nanotubes and other carbon nanostructures. Quantum chemical molecular dynamics calculations have proved that these structures transform in a self-organizing way into the desired structures [1-2]. In this work the conditions and the process of graphene based self-organizing transformation for carbon nanotube Y-junctions were studied. Our results can initiate new experimental researches for improving the existing carbon nanostructure productions and to develop a new, structure-selective nanolithography of carbon nanotube Y-junction. References [1] I. Laszlo and I. Zsoldos, EPL, 99 (2012) 63001 [2] I. Laszlo and I. Zsoldos, Phys. Status Solidi B 249, No. 12, (2012) 2616Âą2619

Figure 1: The self-organizing way does not result in a Y-junction when only one graphene pattern (left side) is used as an initial structure and the structure develops wrong (right side).

Figure 2: The Y-junction can develop perfect (right side) when two graphene patterns are used as initial structures which are placed below each other appropriately (left side)

Graphene Oxide and Activated Carbon Composites for High-Power Supercapacitors Â&#x201A;

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D. Thanuja L. Galhena, Stephan Hofmann and Gehan A. J. Amaratunga

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Â&#x201A; &HQWUH RI $GYDQFHG 3KRWRQLFV DQG (OHFWURQLFV 'HSDUWPHQW RI (QJLQHHULQJ 8QLYHUVLW\ RI &DPEULGJH 9 J. J. Thomson Ave., CB3 0FA, Cambridge, UK. E-mail: dtlg2@cam.ac.uk

Abstract Supercapacitors are gaining increasing attention for complementing or replacing batteries and they are highly desirable in applications where high power and long cycle life of energy storage devices are needed. Activated carbons (AC) are the most promising electrodes in the supercapacitor industry presenting the best performances/cost compromise. Recently, graphene, with a two dimensional carbon nanostructure, has emerged as a new class of promising electrode material in supercapacitors, due to its outstanding properties such as high electric conductivity, high surface area, good mechanical properties and chemical inertia. Among the various approaches to producing graphene materials, here we focus on reduced exfoliated graphene oxide (r-GO) derived from chemically synthesised graphene oxide (GO). However, the graphene materials prepared by either chemical or thermal reduction of the graphene oxide always exhibits a relatively low electrochemical performance due to the agglomeration of graphene sheets and does not reflect the intrinsic capacitance of an individual graphene nano-sheet. To exploit the potential electrochemical applications for graphene, a particularly attractive option is to design and develop composites of graphene with other materials. In this study, we present an approach to synthesize a composite of reduced graphene oxide (r-GO) with activated carbon and its use as an electrode material in supercapacitors. To the best of our knowledge, a few studies on the preparation of GO/AC composites have been reported so far. Graphene oxide was synthesised using vein graphite by a modified Hummers method and then mixed with activated carbon to prepare a homogeneous composite. The composite was thermally reduced to convert GO in to r-GO. The morphology and chemical structure of the materials were characterized by means of Electron microscopy, Raman spectroscopy, X-ray diffraction and Fourier Transform Infrared Spectroscopy. Thermal properties were investigated using Thermo Gravimetric Analysis. The electrochemical properties of as obtained composites with different mass ratios were investigated, together with their individual components (GO, r-GO and AC) for comparison. For electrochemical characterisation, two-electrode symmetrical supercapacitor cells were constructed and characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Tetraethylammonium tetrafluoroborate (TEABF4) in Propylene Carbonate (PC) was used as the electrolyte. The CV curves were measured from 0 to 1 V with various scan rates ranging from 10 to 1000 mV s

and the CV data were used to calculate the specific capacitances of the

electrodes. The results showed that the as-prepared composites exhibited an improved electrochemical performance as compared to pure r-GO or AC. This improvement can be attributed to the synergistic effect of AC and r-GO. The maximum specific capacitance observed for the r-GO/ AC composite was -1

115.6 F/g at a scan rate of 10 mV s . The near-rectangular CV curves at ultrafast sweep rate of 1000 -1

mV s indicated very efficient charge transfer within the composite electrodes. The incorporation of rGO into AC, not only provides the vacancies to accommodate ions, but also forms a promising network structure to conductively bridge the spaces between the AC particles, which can facilitate rapid transport

of the electrolyte ions within the electrode materials, leading to a high-rate performance of the supercapacitor. Within the composite, r-GO plays the role of both the binder and the conductive additive increasing the specific capacitance and the power density of the devices.

References [1] Hummers Jr., W. S., Offeman, R. E, J. Am. Chem. Soc., 80 (1958), 1339±1339 [2] Stoller, M. D. and Ruoff, R. S., Energy Environ. Sci., 3 (2010), 1294±1301 [3] Choi, H.-J. et al., Nano Energy, 1 (2012), 534±551. [4] Liu, C., Yu, Z., Neff, D., Zhamu, A. & Jang, B. Z., Nano letters 10 (2010), 4863±4868 [5] Zhu, Y. et al., Science (New York, N.Y.), 332 (2011), 1537±1541 [6] Jeong, H.-K. et al., Chemical Physics Letters, 470 (2009), 255±258 [7] Lee, I. et al., Journal of Applied Physics, 112 (2012), 033701

Figures

Figure 1. Electrochemical performance of r-GO/AC composite electrode in TEABF4 / AN solution -CV curves at various scan rates.

Organic Dispersions of Highly Reduced Chemically Converted Graphene Sanjeev Gambhir, Eoin Murray, Sepidar Sayyar, Gordon G. Wallace and David L. Officer ARC Centre of Excellence for Electromaterials Science (ACES), Intelligent Polymer Research Institute, Australian National Fabrication Facility, Innovation Campus, University of Wollongong, NSW 2500, Australia sanjeev@uow.edu.au There have been a number of reports of dispersions of chemically converted graphene (CCG) in organic solvents but they are either functionalized materials,1 mixtures of organic solvents with water2,3 or contain stabilizers4,5 and surfactants5 that affect the properties of the graphene.

We report here a simple, systematic approach to the reduction of graphene oxide (GO) that affords dispersions of chemically converted graphene (CCG) in organic solvents with decreasing basal plane defects is reported. The extent of reduction can be controlled and optimized resulting in the most highly reduced dispersible chemically converted graphene (hrCCG) having an O1S/C1S ratio of 0.06 (Table 1), which approaches that of graphite. The hrCCG dispersion in anhydrous dimethylformamide (DMF) was stable for several months at a concentration of 0.5 â&#x20AC;&#x201C; 0.6 mg mL-1 (Fig. 1). This process was found to be easily scalable and could be exploited for the large scale production of hrCCG in DMF and its dispersion in other anhydrous organic solvents. This study demonstrates that the stability of the graphene dispersion is critically dependent on the exfoliation process. The improved elimination of basal defects and the restoration of aromaticity as evident from XPS C1s, Raman, XRD spectra and TGA analysis (Fig. 2, a-d) and while maintaining dispersion stability on a large scale in an anhydrous organic solvent, greatly increase the potential of this material for a wide variety of applications.

References (1)

Cao, Y.; Feng, J.; Wu, P. Carbon 48 (2010) 1683.

(2)

Lomeda, J. R.; Doyle, C. D.; Kosynkin, D. V.; Hwang, W.-F.; Tour, J. M. J. Am. Chem. Soc. 130 (2008) 16201.

(3)

Park, S.; An, J.; Jung, I.; Piner, R. D.; An, S. J.; Li, X.; Velamakanni, A.; Ruoff, R. S. Nano Letters 9 (2009) 1593.

(4)

Georgakilas, V.; Bourlinos, A. B.; Zboril, R.; Steriotis, T. A.; Dallas, P.; Stubos, A. K.; Trapalis, C. Chem. Commun. 46 (2010) 1766.

(5)

Liang, Y.; Wu, D.; Feng, X.; Muellen, K. Adv. Mater. 21 (2009) 1679.

(6)

Moon In K, Lee J, Ruoff Rodney S, Lee H. Reduced graphene oxide by chemical graphitization. Nat Commun. (2010);1(6):73.

(a)

(c)

(d)

(b)

Fig. 1. (a) A comparison of the nominal particle size and dispersion stability of (i) aqueous CCG and anhydrous DMF-dispersed (ii) rCCG and (iii) hrCCG; (b) Zeta potential for CCG(i), rCCG(ii) and hrCCG (iii); (c) Atomic force microscope (AFM) image of hrCCG with (d) height profile (b)

(a)

(d)

(c)

Fig. 2. (a) High resolution XPS C1s spectra; (b) Raman Spectra; (c) XRD spectra; (d) TGA analysis of (i) CCG, (ii) rCCG, (iii) hrCCG and (iv) graphite powders.

Table 1. Correlation of XRD, XPS and Raman spectroscopy results of chemically reduced graphene samples with microanalysis and their corresponding electrical properties. XRD

Raman

Microanalysis

XPS

Sample

Conductivity -1

d-spacing o [A ]

D band -1 [cm ]

G band -1 [cm ]

ID/IG

O1S/C1S [At.%]

O1S/C1S [(Wt.%]

O/C [Wt.%]

[S cm ]

CCGaq

3.87

1328.5

1585.8

1.52

0.22

0.29

0.30

25.0

rCCGDMF

3.69

1326.6

1581.9

1.66

0.11

0.15

0.19

28.0

hrCCGDMF

3.64

1328.5

1581.3

1.90

0.06

0.075

0.10

99.4

Graphite

3.33

1580

0.05

Influence of individual process steps on graphene device characteristics Lene Gammelgaard, Erol Zekovic, David Mackenzie, Jose Caridad, Alberto Cagliani, Tim Booth and Peter BĂ¸ggild Centre for Nanostructured Graphene (CNG), Technical University of Denmark, 2800 Kgs. Lyngby, Denmark lene.gammelgaard@nanotech.dtu.dk Abstract The electrical properties of graphene-based electronic devices may be significantly affected by complex fabrication processes [1], including photolithography and electron-beam lithography (EBL). These involve chemicals, polymers, heating in various atmospheres, electron irradiation etc. [2]. Since electrical measurements are most often performed after the device has been subjected to several physical processes and chemicals, the role of individual processing steps on features like gate voltage hysteresis and residual doping can be difficult to assess. Stencil lithography enables the production of devices entirely without the use of resist, chemicals or heat [3]. We use stencil shadow masks for deposition of electrical contacts on mechanically exfoliated graphene flakes to form two-terminal electrical devices, see Fig. 1 (a-b). The great advantage of this strategy is the avoidance of additional contamination, which creates a clean starting point and makes it possible to investigate the change in the electrical behavior due to individual processing steps. We have systematically tested the effect on charge carrier mobility, doping level and gate voltage hysteresis due to various chemicals, heating and polymers such as polymethyl methacrylate (PMMA), see Fig. 1 (c). PMMA is a polymer often used as resist in EBL processes and for transfer of graphene between different substrates [4]. We find that the p-type doping and hysteresis induced by this EBL-like process can be strongly reduced by thermal annealing. This approach enables systematical, well-controlled study of individual process steps in a graphene fabrication cycle, which is critical for optimization, fault-finding and commercialization of graphene-based electronic devices.

References [1] Bao et al., Nano Research, Volume 3, Issue 2, (2010), 98 - 102. [2] Copper et al., ISRN Condensed Matter Physics, Volume 2012 Article ID 501686 (2012) 56 pages. [3] Gray er al., RCA Review (RCA Corporation), 20 (3) (1959), 413 - 425. [4] Reina et al., J. Phys. Chem. C, 112 (46) (2008) 17741 - 17744.

Figures (a)

(c)

(b)

Figure 1: Schematic drawing of (a) the fabrication of stencil devices and (b) the devices after dissolution of polymer. In (c) the effect of electron-beam lithography with PMMA as resist is mimicked. Electrical measurements are performed between every fabrication step. 1: A hysteresis of 5 V is observed after deposition of stencil electrodes. 2: The hysteresis is reduced after a 30 minutes temperature anneal (TA) in nitrogen atmosphere, at 250°C. 3: After a bake in ambient air at 200°C the graphene is found to be heavily p-doped. This step is typically used in electron-beam lithography fabrication to create better adhesion between substrate and PMMA. 4: The PMMA is applied and removed, which leaves PMMA residues on the graphene. 5: Doping and hysteresis is reduced after temperature anneal with same parameters as in 2. The optical image in (c) shows the measured graphene stencil device. The scale bar is 10µm.

First-principles analysis of MoS2/Ti2C and MoS2/Ti2CY2 (Y=F and OH) all-2D semiconductor/metal contacts Li-Yong Gan and Udo Schwingenschlรถgl Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia liyong.gan@kaust.edu.sa Semiconductors/metals heterostructures play a key role in modern electronic and photonic devices [1], being more crucial than the semiconductors themselves. Particularly, coherent and passivated interfaces govern the properties of high mobility transistors, solid state lasers, light emitting devices, and solar cells, since interfacial defects can severely degrade the performance [2]. Single-layer transition metal dichalcogenides (TMDCs), especially monolayer MoS2, exhibit many promising prospects in electronics and optoelectronics due to their exotic electronic, optical, mechanical, chemical, and thermal properties, as compared to their bulk counterparts [3-6]. Integration of MoS2 with other 2D materials to form 2D hybrid systems can give rise to remarkable electronic properties, and thus attract increasing interest [7, 8]. Very recently, new families of 2D graphene-like carbides and carbonitrides, so-called MXenes, have been synthesized from layered Mn+1AXn (n=1, 2, and 3) [9, 10], in which A represents elements mainly from groups IIIA and IVA. These materials display not only structural similarity to graphene but also show a high electrical conductivity, which may allow enhancing TMCD electronic devices by forming MoS2/MXenes heterojunctions. First-principles calculations are used to explore the geometry, bonding, and electronic properties of MoS2/MXenes semiconductor/metal contacts, taking Ti2C and Ti2CY2 (Y = F and OH) as prototypes [11]. The structure of the interfaces is determined for the first time. The three kinds of interfaces, MoS 2/Ti2C, MoS2/Ti2CF2, and MoS2/Ti2C(OH)2, can be divided into two classes according to the calculated energetics. Strong chemical bonds form in MoS2/Ti2C, while a much weaker interaction (that is not sensitive to the specific geometry) is found in the latter two interfaces. The metal induced states significantly modify the electronic structure of MoS2 in the case of MoS2/Ti2C. The fact that a metallic character emerges shows that deposition of Ti 2C on MoS2 can lead to conductive MoS2. In both the MoS2/Ti2CF2 and MoS2/Ti2C(OH)2 interfaces the semiconducting nature is preserved for the physisorbed MoS2. The bond alignment implies weak and strong n-type doping of the MoS2 in MoS2/Ti2CF2 and MoS2/Ti2C(OH)2 with corresponding n-type Schottky barrier heights of 0.85 and 0.26 eV. The MoS2/Ti2CF2 interface is found to be close to the Schottky limit with negligible charge transfer at the interface. At the MoS2/Ti2C(OH)2 interface a 2.50 eV discontinuity between the vacuum levels on the two sides of the interface indicates that the barrier in this case is mainly due to the interface dipole induced by charge rearrangement.

References [1] I. Popov, G. Seifert, and D. Tománek, Phys. Rev. Lett., 108 (2012) 156802. [2] G. Eda, T. Fujita, H. Yamaguchi, D. Voiry, M. Chen, and M. Chhowalla, ACS Nano, 6 (2012) 7311. [3] Q. H. Wang, K. Kalantar-Zadeh, A. Kis, J. N. Coleman, and M. S. Strano, Nat. Nanotech., 7 (2012) 699. [4] D. Xiao, G.-B. Liu, W. Feng, X. Xu, and W. Yao, Phys. Rev. Lett., 108 (2012) 196802. [5] S. Bertolazzi, J. Brivio, and A. Kis, ACS Nano, 5 (2011) 9703. [6] A. Castellanos-Gomez, M. Poot, G. A. Steele, H. S. J. van der Zant, N. Agraït, and G. RubioBollinger, Adv. Mater., 24 (2012) 772. [7] Y. Li, H. Wang, L. Xie, Y. Liang, G. Hong, and H. Dai, J. Am. Chem. Soc., 133 (2011) 7296. [8] K. Chang and W. Chen, Chem. Commun. 47, 4252 (2011). [9] M. Naguib, M. Kurtoglu, V. Presser, J. Lu, J. Niu, M. Heon, L. Hultman, Y. Gogotsi, and M. W. Barsoum, Adv. Mater., 23 (2011) 4248. [10] M. Naguib, O. Mashtalir, J. Carle, V. Presser, J. Lu, L. Hultman, Y. Gogotsi, and M. W. Barsoum, ACS Nano, 6 (2012) 1322. [11] L.-Y. Gan, Y.-J. Zhao, D. Huang, and U. Schwingenschlögl, Phys. Rev. B, 87 (2013) 245307.

Figures

Side views of the six non-equivalent stacking patterns of the MoS2/Ti2C(OH)2 interface.

Energy level alignments of MoS2/Ti2CF2, and MoS2/Ti2C(OH)2,heterostructures.

Spontaneous Transfer of Wafer-scale Graphene by Capillary Bridges Libo Gao & Kian Ping Loh Graphene Research Centre and Department of Chemistry, National University of Singapore, 6 Science Drive 2, 117546, Singapore. phygaol@nus.edu.sg Abstract Graphene has attracted worldwide interest since its experimental discovery [1,2] but the preparation of large area, continuous graphene film on insulating substrate such as SiO 2/Si wafers, free from growth-related morphological defects or transfer-induced cracks and folds, remains a formidable challenge [3]. Chemical vapour deposition (CVD) growth of graphene on Cu foils [4-7] has emerged as a powerful technique due to its compatibility with industrial scale roll-to-roll technology [6]. However, the polycrystalline nature and microscopic roughness of Cu foils means that such roll-to-roll transferred films are not devoid of cracks and folds [6,7]. High fidelity transfer or direct growth of high quality graphene films on arbitrary substrate is needed to enable wide ranging applications in photonics or electronics such as transistors, flexible electronics, on-chip biosensors and tunneling barriers [3]. The direct growth of graphene film on insulating substrate like SiO2/Si wafer is certainly useful, but current research efforts remain grounded at the proof-of-concept stage where only discontinuous nano-sized islands can be obtained [8]. Here we develop a unique face-to-face (F2F) transfer method for wafer-scale graphene films that can uniquely accomplish both the growth and transfer steps on one wafer [9]. This spontaneous transfer method relies on nascent gas bubbles and capillary bridges between graphene film and underlying substrate during etching of the metal catalyst, which is analogous to the method used by tree frogs to remain attached on submerged leave [10,11]. In contrast to the previous wet [4,5,12-14] or dry [6,7] transfer results, the F2F transfer is non-handcrafted and compatible with any size and shape, and enjoys the benefit of a much reduced density of transfer defects compared to the conventional transfer method. Most importantly, the non-handcrafted and wafer-compatible nature of this method suggests that it is automation compatible and industrially scalable. Interestingly, it shows that water has the ability to infiltrate between graphene and the wafer substrate, thus allowing the addition of different surfactants for modifying the interfacial tension and reducing the corrugations in graphene film. Although there are many potential applications of the roll-to-roll transfer method due to its amenability to flexible devices [6], LW PXVW EH QRWHG WKDW WR GDWH PRVW GHYLFHV RSHUDWH RQ ÂłVWLIIÂ´ VXEVWUDWH VXFK DV VLOLFRQ DQG D QRQhandcrafted, batch-processed transfer method serving this technology segment is definitely needed. The F2F transfer method will be very useful as an enabler for rapidly emerging graphene-on-silicon platforms that have shown excellent promises such as Schottky barristor and optical modulator. Finally, the F2F transfer method should be applicable to all CVD growth using metal catalyst-coated wafer, such as h-BN and other transition metal chalcogenide films. References [1] Novoselov, K. S. et al. Science 306 (2004) 666-669; [2] Novoselov, K. S. et al. Proc Natl Acad Sci USA 102 (2005) 10451-10453; [3] Novoselov, K. S. et al. Nature 490 (2012) 192-200; [4] Li, X. S. et al. Science 324 (2009) 1312-1314; [5] Gao, L. B. et al. Appl. Phys. Lett. 97 (2010) 183109; [6] Bae, S. K. et al. Nat. Nanotechnol. 5 (2010) 574-578; [7] Kang, J. et al. ACS Nano 6 (2012) 5360-5365; [8] Chen, J. Y. et al. J. Am. Chem. Soc. 133 (2011) 17548-17551;

[9] Gao, L. B. et al. Nature 505, (2014) 190-194; [10] Federle, W., Barnes, W. J. P., Baumgartner, W., Drechsler, P. & Smith, J. M. J R Soc Interface 3 (2006) 689-697; [11] Persson, B. N. J. J. Phys.: Condens. Matter. 19 (2007) 376110; [12] Reina, A. et al. Nano Lett. 9 (2009) 30-35; [13] Kim, K. S. et al. Nature 457 (2009) 06-710; [14] Gao, L. B. et al. Nat. Commun. 3 (2012) 699.

Figure 1 Illustration of F2F transferring graphene mediated by capillary bridges.

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Graphene/alumina (G/Al2O3) composites by Spark Plasma Sintering; a simple, fast and upscalable method a,b

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V.G. Rocha , A.Centeno , B.Alonso , A. Fernández , C.F. Gutierrez-Gonzalez , R. Torrecillas , A. c Zurutuza a Department of Materials, Exhibition Road, London SW7 2AZ, United Kingdom b ITMA Materials Technology, Parque Tecnológico de Asturias, 33428 Llanera, Spain c Graphenea S.A. Tolosa Hiribidea 76, E-20018 Donostia-San Sebastián, Spain d Centro de Investigación en Nanomateriales y Nanotecnología (CINN) (CSIC ± Universidad de Oviedo ± Principado de Asturias), Parque Tecnológico de Asturias, 33428 Llanera, Spain e Moscow State University of Technology (STANKIN), Vadkovskij per. 1, Moscow, Moscow Oblast, Russian Federation v.garcia-rocha@imperial.ac.uk Abstract Tough and electroconductive ceramics have a great potential to solve a wide number of material related challenges in high technology applications such as power generation, aerospace, transportation and military applications. The development of very complicated shapes and high accuracy components is especially challenging for ceramic materials due to their high hardness, low fracture toughness which has very often limited their applications. The reinforcement of ceramic materials with electroconductive second phases appears as an interesting alternative for manufacturing by Electro Discharge Machining (EDM) complex shape components from hard materials. However, low resistivity FP) of the material is required to be shaped using this technology. In this work, graphene is incorporated in the alumina (Al2O3) matrix in order to make it electroconductive and improve it mechanical properties. An outstanding dispersion of Graphene Oxide (GO) in the alumina matrix was achieved using a colloidal method and its consolidation by spark plasma sintering (SPS) allowed, in one-step, the in situ reduction of the GO during the sintering process. The sintered discs were cut along two directions: perpendicular and parallel to the pressure direction applied in SPS, as shown in Fig 1. Evaluation and optimisation of the graphene thermal reduction by SPS was performed by Raman spectroscopy [1,2]. Moreover, Raman spectroscopy is shown to be a powerful technique to study the orientation of the graphene in the G/Al2O3 composites. As it can be seen in Fig. 2 spectra there are important different peak intensities depending on the analysed orientation. The signal intensity in the surface perpendicular to the pressure direction applied in SPS (Fig. 2a) is much lower than in the parallel surface (Fig. 2b) indicating preferential orientation of the graphene in the composite. Raman parameters were determined in order to get further insight and to reveal the anisotropic structure of the composite. As a result of the reduction process, non-conductive graphene oxide is transformed into a conductive material. Electrically conductive composites in both directions were achieved with an unexpected low amount of graphene. The percolation threshold of the as prepared composites was found to be around 0.22 wt%, indicated by the exponential decrease of the electrical resistivity up to 8 9 orders of magnitude in comparison to the monolithic alumina (15 vs 10 FP The presence of graphene enhanced the mechanical properties of the raw alumina by nearly 50%. The resulting Rcurves are shown in Fig. 3 and the clearly show the higher fracture resistance of the G/Al 2O3 composite compared to the monolithic Al2O3. For the alumina, the initial fracture resistance is approximately 3.6 1/2 1/2 MPa m , however this value only rises up to 4.4 MPa m showing a very soft R-curve behaviour that it may be caused by the crack bridging between the ceramic grains. The graphene nanoplatelets lying in the crack plane behind the tip act as ligaments bridging the two crack surfaces, which provide a stable 1/2 crack growth until a steady-state toughness of 7 MPa m approximately. The fracture toughness improvement was meant to be due to crack bridging reinforcement mechanism. This mechanism is confirmed using Scanning Electron Microscopy (Fig 3).

References [1] Ferrari AC, Meyer JC, Scardaci V, Casiraghi C, Lazzeri M, Piscanec S, et al.. Phys Rev Lett 97 (2006) 187401. [2] Malard LM, Pimenta MA, Dresselhaus G, Dresselhaus MS. . Phys Rep 473 (2009) 51±87.

Figures

Figure 1. Image of SPS furnace and sketch of the sintered disc and the applied pressure

Figure 2. Raman spectrum of the 2-G/Al2O3 composite collected at two different orientations: (a) perpendicular to the pressure direction applied in SPS and (b) parallel to the pressure direction applied in SPS.

Figure 3. Comparison of the R-curves measured in the Al2O3 and G/Al2O3 materials (left). SEM observations of the reinforcement mechanisms of the G/Al2O3 composite (right).

Introduction of Auxetic Behaviour in Graphene 1

Joseph N Grima , Szymon Winczewski , Michael C. Grech , Ruben Gatt , Reuben Cauchi , 1 2 Daphne Attard 1

Metamaterials Unit, Faculty of Science, University of Malta, Msida MSD 2080, Malta auxetic@um.edu.mt 2

Faculty of Applied Physics and Mathematics, Gdansk University of Technology, ul. Narutowicza 11/12, 80-233 Gdansk, Poland

Abstract Auxetics are materials which exhibit the unconventional property of expanding laterally upon the application of a uniaxial stress, i.e. have a negative Poisson's ratio [1]. The property of auxeticity, despite being uncommon, results in various highly desirable macroscopic properties such as enhanced indention resistance [2]. Auxetics may be used in various practical applications ranging from smart tunable filters [3] to biomedical devices [4]. Examples of auxetics reported so far include foams [5,6], various zeolites and silicates [7,8], some liquid crystalline polymers [9] and various mechanical systems [10]. In all of these cases, this anomalous behaviour results from the particular nano/micro/macro structure of the system, and the way this deforms upon the application of uniaxial stress. Although auxeticity has so far been reported in a number of hypothetical carbon based systems [12], so far, little progress has been done at identifying realistic carbon-based auxetics which exhibit such behaviour. Here we report the results of force-field based simulations on defective graphene systems which suggest that graphene can be made to exhibit auxetic behavior through the introduction of randomly dispersed vacancy-type defects. For example, constant stress molecular dynamics simulations performed using the AIREBO (Adaptive Intermolecular Reactive Empirical Bond Order) potential [13] on defective graphene having double vacancies of the 5-8-5 type provide clear evidence that a negative Poisson's ratio may be obtained through the use of such defects (see Fig. 1a), as opposed to pristine graphene which was predicted to exhibit conventional characteristics (see Fig. 1b). Similar trends were also found using other forms of vacancy defects, or using other force-fields and modeling methodologies. This lowering of the Poisson's ratio may have various practical implications and can be explained by the fact that the introduction of vacancy-type defects transform a relatively planar graphene sheet to a much more 'crumpled' form (see fig. 2a) which has the geometric features that permit manifestation of in-plane auxeticity. In fact, the simulations suggest that upon application of uniaxial stress, the 'crumpled' sheet re-flattens out with the result that it expands in the lateral direction. This mechanism is not dissimilar to that manifested at the macro-scale by a crumpled paper [14], which can be regarded as a disordered form of the egg-rack model [15] which also exhibits a negative Poisson's ratio as it unfolds when uniaxially stretched, see Fig. 2b.

References [1] [2] [3] [4]

K.E. Evans, M.A. Nkansah, I.J. Hutchinson and S.C. Rogers, Nature, 353 (1991) 124 K.E. Evans, Endeavour, 15 (1991) 170-174 A. Alderson, J. Rasburn, K.E. Evans and J.N. Grima, Membrane Technology 137 (2001) 6-8. R Gatt, R Caruanaŕ¸&#x20AC; Physica Status Solidi b 2 (2014) DOI: 10.1002/pssb.201470109 [5] R. Lakes, Science, 235 (1987) 1038-1040 [6] J.N. Grima, D. Attard, R. Gatt and R.N. Cassar, Advanced Engineering Materials, 11 (2009) 533-535 [7] A. Yeganeh-Haeri, D.J. Weidner and J.B. Parise, Science, 257 (1992) 650-652 [8] J.N. Grima, R. Jackson, A. Alderson and K.E. Evans, Advanced Materials, 12 (2000) 1912-1918 [9] R.H. Baughman and D.S. GalvĂŁo, Nature, 365 (1993) 735-737 [10] C.B. He, P.W. Liu, P.J. McMullan and A.C. Griffin, Physica Status Solidi B, 242 (2005) 576-584 [11] J.N. Grima and K.E. Evans; Journal of Materials Science Letters, 19 (2000) 1563-1565 [12] Sihn, Sangwook, Varshney, Vikas. Roy, Ajit K., Farmer, Barry L. Carbon, 2(2012) 603-611 [12] Stuart, Tutein, Harrison, J Chem Phys, 112(2000), 6472-6486 [13] Grech M.C., University of Malta, 2013 [14] Grima, J. N., Williams, J. J., Gatt, R., Evans, K. E., Molecular Simulation, 13(2005) 907-913

Figures

(a)

(b)

Figure 1: (a) A typical strain-strain curve as simulated by the AIREBO force-field for a system having 3% double-vacancy 585 type defects and (b) A typical simulated strain-strain curve for a system having no defects. Note that these graphs in suggest that in the defective system, an extension in the x-direction due to a uniaxial strain in the same direction results in an expansion in the y-direction (i.e. a negative Poisson's ratio) whilst in the non-defective system, an extension in the x-direction due to a uniaxial strain in the same direction results in a shrinkage in the y-direction (i.e. a positive Poisson's ratio).

Figure 2: (a) The effect of uniaxial stress on defective graphene with 3% 585 defects. Note that as a tensile uniaxial stress is applied, the sheet becomes more planar and exhibits in-plane auxetic properties. (b) the â&#x20AC;&#x2DC;crumpled paperâ&#x20AC;&#x2122; model which illustrates the mechanism which results in the auxetic effect in defective graphene (image taken from Grech 2013).

Strain and defect modulations of electronic structure in transition-metal dichalcogenides

Agnieszka Kuc, Mahdi Ghorbani-Asl, Nourdine Zibouche, Thomas Heine Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany Email: a.kuc@jacobs-university.de In 2011, transition-metal dichalcogenides (TMCs) have started their renaissance as potential materials for nano- and opto-electronics due to their extraordinary electronic properties arising from quantum confinement (exfoliation). Though known for over 40 years, bulk 3D TMCs are no threat to traditional silicon-based electronics. The situation has changed in 2011, when Nicolosi and co-workers have shown that 3D TMCs are easy to process using liquid exfoliation and large-area single layers can be produced at low costs. Exfoliation to monolayers changes significantly electronic properties of TMCs. Kis and co-workers utilized this phenomenon and in the beginning of 2011 they produced the first fieldeffect transistor (FET) based on MoS2 monolayer. Shortly after, a logical circuits and amplifiers were produced. Silicon-based FETs often suffer from heat dissipation. Therefore, to improve nanoelectronic devices one could replace silicon with materials that perform better at smaller scale, such as layered TMCs. In this work, we show that electronic properties of TMC layered and tubular materials can be tuned by mechanical deformations (so-called straintronics). Tensile strain applied to the material affects strongly electronic structure and transport properties, resulting in the semiconductor-metal transition for elongations as large as 10%. It also does have a strong effect on the phonon dispersion, causing â&#x2C6;&#x2019;1 softening of the in-plane E modes by ~3 cm per percent of strain, and of the out-of-plane A modes by â&#x2C6;&#x2019;1 ~1 cm per percent of strain (see Figure top panel). Hence, Raman spectroscopy qualifies as an excellent tool to monitor tensile tests of TMDs, both in 2D and in tubular forms.[1] Electronic properties are also strongly changed in the presence of defects, such as point vacancies or grain boundaries (see Figure bottom panel). As in the pristine TMC monolayer transport is almost direction-independent, local defects change the situation completely, reducing conductance in some cases by more than 50%.[2] References [1] Ghorbani-Asl, Zibouche, Wahiduzzaman, Oliveira, Kuc, Heine, Sci. Rep., 3, (2013) doi:10.1038/srep02961 [2] Ghorbani-Asl, Enyashin, Kuc, Seifert, Heine, PRB, 88, (2013), 245440

Role of Defect Density of Cu Substrate on Graphene Nucleation 2

Priyadarshini Ghosh, Shishir Kumar, N. Ravishankar, S. Raghavan 1

1, 2

Centre for Nano Science and Engineering, Materials Research Centre, Indian Institute of Science, Bangalore, India priyadarshini@ipc.iisc.ernet.in shkumar@tcd.ie nravi@mrc.iisc.ernet.in sraghavan@mrc.iisc.ernet.in

Abstract The unique properties of large area graphene are crucially dependent on its grain size.

[1,5]

Microstructural design for the desired grain size requires a fundamental understanding of graphene nucleation and growth. For chemical vapor deposition of graphene on copper surface, the nucleation can be controlled by controlling the copper surface defect density and gas-phase supersaturation of carbon precursor. Here, we show that graphene nucleation density closely follows copper surface defect density under low supersaturations. We were able to control the latter by annealing copper prior to graphene growth. Nucleation density of graphene was estimated from the scanning electron microscope (SEM) images of isolated graphene grain in early stages of growth. The surface defect density was quantified by etch-pit measurements and by grain-misorientation plots. Among surface defects, dislocations are most potent graphene nucleation sites, as they are activated at the lowest supersaturation of gas-phase carbon precursor. As a proof, we generate dislocations in copper surface by indentation and show that nucleation of graphene occurs only at those locations and nowhere else. To summarize these findings, we have sketched a supersaturation plot, incorporating two basic growth parameters, temperature and flow rate of carbon precursor and identify the defect dominated growth regime. This study not only will help in understanding the basic of nucleation of graphene on copper but also to engineer the desired microstructure of graphene. . Reference: [1]. Kim , K., Lee, Z., regan, W., Kisielowski, C., Crommie, M. F., Zettl, A., ACS Nano,3 (2011), 2142-2146 [2]. Mattevi, C., Kim, H., Chhowalla, M., J. Mater. Chem., 21 (2011), 3324Âą3334 [3]. Yan, Z., Lin, J., Peng, Z., Sun, Z., Zhu, Y., Li, L., Xiang, C., Samuel, E. L. c., Kittrell, C., Tour, J. M., ACS Nano,6 (2012), 9110-9117. [4]. Kim, H., Mattevi, C., Calvo, M. R., Oberg, J. C., Artiglia, L., Agnoli, S., Hirjibehedin, C. F., Chhowalla, M., Saiz, E., ACS Nano, 6 (2012), 3614-3623. [5]. Chen, S.,Ji, H.,Chou, H., Li, Q.,Li, H., Suk, J. W., Piner, R., Liao, L., Cai, W., Ruoff, R. S., Adv. Matr.,14 (2013),2062-2065

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Work function of metal-doped CVD graphene by Kelvin Probe Force Microscopy M.M.Giangregorio, M.Losurdo,G.V.Bianco, P.Capezzuto and G.Bruno Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, via Orabona 4, 70126 Bari, Italy michelaria.giangregori@ba.imip.cnr.it Abstract In graphene-based electronic devices, graphene employed as a channel material or as an electrode material always contacts a metal, and the charge transfer between graphene and metal is a critical parameter because it strongly affects the performance of the devices. The optimization of the metal-graphene contact resistance depends on the metal, on the conduction mode of graphene on metal, and on graphene work function. Specifically, a high work function of graphene (p-doping) leads to better injection efficiency from metal to graphene while for FET applications the decrease of the graphene work function (n-doping) is highly desirable because it leads to an increase of the field emission current by over two orders of magnitude [1-2]. Therefore, a better understand and study of the work function of graphene under metal, W G-M, is essential for the realization of graphene-based electronic devices. Despite the significance of the work function, mainly theoretical calculations have been reported and a few direct observations on how the work function of graphene is affected by different metals. Here, we report on the measurement of the work function of graphene deposited by Chemical Vapor Deposition (CVD) in contact with different metals using the Kelvin probe force microscopy (KPFM). We use an Autoprobe CP (Thermomicroscope) to record the sample topography and the amplitudemodulated Kelvin probe force microscopy (KP-EFM) signal in a single-pass mode. [3-4]. We used a conductive tip, Au-coated Si, with a frequency of 80kHz to scan in non-contact mode [5-6] the sample surface, following its topography. The oscillating potential, Vac, applied to the tip is 5V at a frequency of 13kHz. The samples were electrically connected to the ground of the microscope (the sample stage). All measurements were collected in air at room temperature. Prior the imaging, all samples are cleaned and measured soon after the deposition, in order to improve the reproducibility and accuracy of the SP measurements that are affected by the surface of the sample (contaminations, uniformity or charging) [7]. All measurements are repeated in different points, using samples and in time in order to set the baseline for the sensitivity of our KPEFM measurements. Specifically, we present results on metal-on-graphene (figure 1a) and graphene-on-metal (figure 1b). We discuss the effect of the metal thickness, patterning and nanostructure on the graphene work function variation. We consider metals (Au, Ag, Al, Ga) able to induce p-type and n-type doping of graphene.

Acknowledge th 7KH DXWKRUV DFNQRZOHGJH IXQGLQJ E\ WKH (XURSHDQ &RPPXQLW\ÂśV Framework Programme under agreements no. 314578 MEM4WIN.

References [1] F.Xia, V.Perebeinos, Y.Lin, Y.Wu, Ph.Avouris, Nature Nanotechnology, 6 (2011) 179. [2] F.LĂŠonard, A.A.Talin, Nature Nanotechnology, 6 (2011) 773. [3] W.Melitz, J.Shen, A.C.Kummel, S.Lee, Surface Science Reports, 66 (2011) 1. [4] V.Palermo, M.Palma, P.SamorĂŹ, Advanced Materials 18 (2006) 145. [5] C.Bustamante, D.Keller, Physics Today, 48 (1995) 32. > @ + 7DNDQR - 5 .HQVHWK 6 6 :RQJ - & 2Âś%ULHQ 0 ' 3RUWHU &KHPLFDO 5HYLHZ 99 (1999) 2845. [7] H.Sugimura, Y.Ishida, K.Hayashi, O.Takai, N.Nakagiri, Applied Physics Letters 80 (2002) 1459.

(a)

(b) GRAPHENE

CPD G

METAL SUBSTRATE

EF = WG-M Âą WG

G on M

CPD

WFG= 4.7eV

CPD

Figure 1: Configurations used during the KPFM measurements for (a) metal-on-graphene and (b) graphene-on-metal.

Synthesis and structure of graphene-POSS hybrid aerogels 1,

Enrique Giménez Alfonso C Cárcel , Senlong Gu , Vicente Compañ , Sadhan Jana 1

Instituto de Tecnología de Materiales, Universidad Politécnica de Valencia, E 46022, (SPAIN) 2 Department of Polymer Engineering. The University of Akron, OH 44325, Akron (USA) enrique.gimenez@mcm.upv.es

Abstract Aerogels are extremely porous materials with large pore volume, high surface area and low bulk 1 densities[ ]. Recently, graphene aerogels have attracted attention due to their extraordinary characteristics and their potential application in many fields, such us thermal insulation, oil absorption, 2-4 energy storage, catalyst supports, and supercapacitors [ ]. However, the aerogel-based application performance strongly depends on the morphology and structure of the graphene aerogels. Different strategies have been developed to fabricate graphene-based 3D framework. In this work, we propose 5 the preparation of three-dimensional self-assembly of graphene by mild chemical reduction[ ] and in situ simultaneous deposition of polyhedral oligomeric silsesquioxane (POSS) on graphene sheets (Fig.1). Tetra-silanol phenyl-POSS (tetra-POSS) has been employed to functionalize graphene sheets(Fig. 1b), just before gelling and supercritical drying. The morphology and structure of the graphene-POSS hybrid aerogel was investigated by scanning electron microscopy) and X-ray powder diffraction tests. From the SEM inspection of the graphene aerogel (Fig.2a), a well-defined and interconnected 3D porous network is observed, and the pore walls consist of thin layers of stacked graphene sheets. However, the addition of low amounts of POSS resulted in aerogels with large pores and lower densities (Fig. 2b). The porous property of the resulting aerogels was investigated by nitrogen adsorption/desorption tests. The type IV nitrogen adsorption/desorption isotherms of hybrid aerogels showed a distinct hysteresis loop in the P/P0 range of 0.4 ௅1.0, implying the presence of relatively large macropores and mesopores in the frameworks (Fig.3). Furthermore, the mesopore size calculated by the BJH method ranged from 2.0 to 3.5nm with a narrow distribution (inset in Fig.3). The thermal stability, together with mechanical properties of the hybrid aerogels, was analyzed by thermal gravimetric analysis as well as compression tests. The results showed that the incorporation of low loading levels of POSS can significantly enhance the thermal stability, the compression strength DQG <RXQJ¶V PRGXOXV RI WKH UHVXOWLQJ hybrid aerogels. These results demonstrate that graphene-POSS hybrid aerogels prepared by supercritical CO2 drying of the graphene-POSS hybrid hydrogel precursors possess macro-and mesoporous structures with lower densities and higher compressive stress than neat graphene aerogel.

Acknowledgements The authors gratefully acknowledge financial support received from Spanish Ministry of Economy and Competitiveness (Project MAT2010/21494-C03) References [1] S. S. Kistler, Nature, 127 (1931) 741. [2] Y. X. Xu, K. X. Sheng, C. Li and G. Q. Shi, ACS Nano, 4 (2010) 4324. [3] H. Qian, AR Kucernak, E.S. Greenhalgh, A. Bismarck, M. Shaffer, ACS Appl.Mater. Interfaces, 5 (2013) 6113. [4] Z. P. Chen, W. C. Ren, L. B. Gao, B. L. Liu, S. F. Pei, H. M. Cheng, Nat. Mater. 10 (2011) 424. [5] W. Chen, L. Yan, Nanoscale, 3 (2011) 3132.

Figures

0 wt%

0.5 wt%

1 wt%

2 wt%

5 wt%

Figure 1: (a) Photographs of as-prepared 3D-graphene aerogels with different content of tetra-POSS; b) Chemical structure of Tetra-POSS

(a)

(b)

Figure 2: Cross-sectional SEM images of graphene aerogel( a) and graphene-1%wt POSS aerogel (b).

Figure 3: Nitrogen sorption isotherms and BJH (Barrett-Joyner-Halenda) adsorption pore size distribution curve (inset) of graphene aerogel.

Tuneable humidity gating of graphene¶V electronic properties 1

Cristina E. Giusca , Virginia D. Wheeler , Luke O. Nyakiti , Rachael L. Myers-Ward , 2 2 1 Charles R. Eddy, Jr. , D. Kurt Gaskill , Olga Kazakova 1

National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, United Kingdom 2 U.S. Naval Research Laboratory, Washington, DC 20375, United States of America 3 Texas A&M University, Galveston, TX 77553, United States of America cristina.giusca@npl.co.uk

Abstract An important concern regarding graphene-based devices that are normally operated in ambient environments is that water and gas molecules reacting with graphene have an influence on devices performance and reliability. The presence of water is inevitable when graphene is exposed to air [1] and understanding its interaction with graphene is important in order to fully exploit possibilities for design and fabrication of graphene devices and sensing platforms. Significant effort has been dedicated to both theoretical and experimental investigation of water on graphitic surfaces. However, in spite of these intense activities, a complete understanding of the water-graphene interaction is still lacking. From electronic properties point of view, water acts as a pdopant, leading to a shift of the Fermi level in graphene and significantly affecting the electrical transport properties [2,3]. The information obtained from transport measurements is generalized over the entire device and is not correlated with the exact morphology of graphene, the presence of local adsorbates or structural defects. In the current work, we employ scanning Kelvin probe microscopy (SKPM) to study the effect that water has on the electronic properties of epitaxial graphene, directly correlated with the local structural information, in an attempt to provide a systematic evaluation of the impact of ambient exposure on epitaxial graphene. We study the influence of relative humidity (RH=0-70%) changes on the surface potential of single-, bi- and tri-layer epitaxial graphene (1LG, 2LG and 3LG, respectively) and demonstrate the reversible process of water vapour adsorption and desorption on the various graphene domains. A sequence of representative surface potential images of epitaxial graphene characterised by in-situ SKPM under various environments (ambient, vacuum and humid conditions) is displayed in Figure 1. In ambient conditions (Figure 1a), the surface potential map shows regions with two main distinct contrast levels: a bright one, given by two parallel stripes, associated with 2LG, superimposed on a dark contrast background of 1LG. This is furthermore highlighted by the corresponding histogram associated with the surface potential map (Figure 1e), displaying a bi-modal surface potential distribution. It is important to note that the topography (not shown here) acquired simultaneously with the surface potential image does not distinguish between the 1LG and 2LG and is mainly dominated by SiC parallel terraces with edges that promote the growth of subsequent layers. Following ambient exposure, the sample was annealed at 150°C, under vacuum conditions (P = -6 6 × 10 mbar). Contrast inversion is observed in the associated surface potential image (Figure 1b) and the related histogram (Figure 1f), where 1LG now displays brighter contrast than 2LG. The contact potential difference, ¨VCPD, measured between the 2LG and 1LG changes sign compared to ambient and is consistent with lower carrier (electron) concentration in 2LG compared to 1LG in vacuum, ne(2LG)<ne(1LG). The opposite is observed in ambient, i.e. higher carrier concentration for 2LG in comparison to 1LG, ne(2LG)>ne(1LG). The observed effect is explained in terms of an increase of the electron concentration in both 1LG and 2LG on ambient-vacuum transition due to desorption of environmental p-dopants. VCPD values of 1LG and 2LG reproducibly restored to initial values whenever re-exposing the sample to ambient, indicating that the properties of graphene are strongly influenced by surface charge imposed by atmospheric adsorbates. In the next set of experiments following vacuum annealing, the sample was exposed first to dry nitrogen at atmospheric pressure and then to varying humidity levels, ranging between 10% and 70%. Only the images acquired under the lowest (10%) and the highest (70%) humidity atmospheres are shown in Figure 1c and Figure 1d, respectively. The initially QHJDWLYH YDOXH RI ¨VCPD between 2LG and 1LG of the vacuum annealed sample gradually decreases in absolute value with increasing humidity, passes through 0 at ~ 50% humidity and reaches a positive value for 70% humidity levels. As shown in Figure 1d, 2LG inverts contrast at 70% humidity, although not reaching the level observed in ambient, indicating that other factors in addition to water can significantly affect the surface potential and the electronic properties of graphene. The above observations will be presented, discussing in detail the charge transfer at graphenewater interface, as well as doping levels of 1LG compared to those of 2LG and 3LG upon water

adsorption/desorption, taking into account the interplay between carrier concentrations in graphene, the underlying substrate and atmospheric adsorbates. The results demonstrate the importance of surface studies of graphene in ambient, as well as at elevated temperature and humidity conditions in order to fully understand the underlying physical phenomena and control the electronic properties of proposed graphene devices. References [1] K. Xu, P. Cao, J.R. Heath, Science 329 (2010) 1188. [2] A.N. Sidorov, K. Gaskill, M. Buongiorno Nardelli, J.L. Tedesco, R.L. Myers-Ward et al., J. Appl. Phys. 111 (2012) 113706. [3] Y. Yang, K. Brenner, R. Murali, Carbon, 50, (2012) 1727. Figures ambient

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Figure 1: Sequence of surface potential images collected on the same region of the graphene sample, while environmental conditions were changing in the following order: ambient (a), vacuum after 2 annealing at 150Â°C (b), 10% humidity (c), 70% humidity (d). The scan size is (10x10) Č?P for all images. (e)-(h) Histograms showing relative VCPD values between individual layers correspond to images (a-d), respectively.

Charge transport along and across integrated large-area graphene M. A. Gluba, V. V. Brus, G. V. Troppenz, X. Zhang, K. Hinrichs, J. Rappich, and N. H. Nickel Helmholtz-Zentrum Berlin fĂźr Materialien und Energie GmbH, Institut fĂźr Silizium Photovoltaik, KekulĂŠstr. 5, 12489 Berlin, Germany marc.gluba@helmholtz-berlin.de Abstract Pronounced polycrystallinity and substrate interaction lead to a remarkable variation of the effective mobility and the concentration of charge carriers in chemical vapor deposited graphene. The aim to integrate this material into large-area devices such as solar cells, displays, and touch screens creates a growing interest in the mechanisms of charge transport along and across embedded carbon monolayers. In this work we present a detailed investigation on charge transport in buried graphene encapsulated by silicon layers of different crystallinity, as well as the transport barriers across the graphene/silicon heterojunction. To elucidate the governing charge-scattering mechanisms in buried layers, graphene was grown by chemical vapor deposition (CVD) and transferred to glass substrates. Subsequently, a capping layer of 300nm amorphous silicon was deposited and subsequently crystallized using electron beam crystallization (Fig 1a). Raman backscattering measurements performed at the buried interface confirm that the carbon monolayer withstands the deposition and crystallization process. Temperature dependent Hall-effect measurements reveal a significant impact of the crystallinity of the silicon layer on the transport properties of the encapsulated graphene electrode [1]. Vertical current transport was studied by transferring the CVD-grown graphene layers to hydrogenterminated single crystalline silicon. The heterojunction resembles the current-voltage characteristics of a Schottky contact and is sensitive to illumination with white light. However, the graphene/silicon heterojunction degrades noticeably and strong interface recombination impedes the extraction of photogenerated carriers. In contrast, methyl-passivated graphene/silicon heterojunctions (Fig. 1b) show remarkably low interface recombination with a defined transport barrier. The impact of this barrier as well as limiting mechanisms for lateral charge transport will be discussed in terms of graphene electrodes implemented in large-area silicon-based devices. References [1] M. A. Gluba, D. Amkreutz, G. V. Troppenz, J. Rappich, and N. H. Nickel, Applied Physics Letters 103 (2013) 073102. [2] V. V. Brus, M. A. Gluba, X. Zhang, K. Hinrichs, J. Rappich, and N. H. Nickel, Physica Status Solidi A (2014) DOI 10.1002/pssa.201330265. Figures

Fig. 1. a) Schematic depiction of encapsulated graphene structures. b) Device structure of a lightsensitive graphene/silicon heterojunction. To reduce interface recombination the silicon surface was passivated using a monolayer of methyl groups.

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Graphene functionalized with TiO2 for Nanocomposites. 1

Viviana Jehová González , Alfonso Álvarez , Néstor Perea-López , Olga Martin , Juan Baselga , 1, 2, 3 Mauricio Terrones Universidad Carlos III de Madrid, Avda. De la Universidad, 30. Leganes (Madrid), Spain. Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA. Research Center for Exotic Nanocarbons (JST), Shinshu University, Wakasato 4-17-1, Nagano 380853, Japan. Department of Chemistry, Department of Materials Science and Engineering and Materials, Research Institute, The Pennsylvania State University, University Park, PA 16802, USA jbaselga@ing.uc3m.es

Abstract [1]

Graphene has attracted great interest since their discovery in 2004 by Geim and Novoselov , [2] its excellent mechanical (Young’s modulus ~1TPa and strength 130GPa ), electrical (quantum hall [3] 2 [4] mobility of suspended graphene 230,000cm Vs ), thermal conductivity (between 3080effects -1 -1 [5,6] [7] 5150Wm K ) and optical properties makes it promising for variety of applications in the areas such [8] [9] [10] [11] as solar-cells, energy storage, sensors and nanocomposites. TiO2 nanoparticles have a [12] extraordinary photocatalytic properties and thermoplastic polymer was a good stable holder to engineering application.

Here, we present a method to prepare sensor nanocomposites based on graphene oxide, GO, sheets functionalized with TiO2, GOTiO2. GOTiO2 sheets were characterized by high resolution transmission electron microscopy, HRTEM (figure 1), thermogravimetry analysis, TGA and Raman techniques. [13]

Nanocomposites were prepared mixing (three-roll milling ) the nanoparticles with two thermoplastic polymers: polystyrene, PS, and polyvinylene fluoride, PVDF. The sensors were characterized by scanning electron microscopy, SEM, dynamic mechanical thermal analysis, DMTA, to evaluate the mechanical properties, differential scanning calorimetry, DSC , X ray diffraction, XRD, electrical conductivity and field emission measurements. Their response as laser photosensors (figure 2) was evaluated at two wavelengths, red and green (5mW) using a Keithley source-meter as shown in figure 3.

References [1] Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, Grigorieva IV, Firsov AA, Science, 306 (2004) 666–9. [2] Lee C, Wei XD, Kysar JM, Hone J, Science, 321 (2008) 385–8. [3] Novoselov K, Jiang Z, Zhang Y, Morozov S, Stormer H, Zeitler U, Maan J, Boebinger G, Kim P, Geim A, Science, 315 (2007) 1379. [4] Bolotin KI, Sikes KJ, Jiang Z, Klima M, Fudenberg G, Hone J, Kim P, Stormer HL, Solid State Communications, 146 (2008) 351-355. [5] Teweldebrhan D, Balandin AA, Appl Phys Lett, 94 (2009) 013101. [6] Ghosh S, Calizo I, Teweldebrhan D, Pokatilov EP, Nika DL, Balandin AA, Bao W, Miao F, Lau CN, Appl Phys Lett, 92 (2008) 151911. [7] Nair R, Blake P, Grigorenko A, Novoselov K, Booth T, Stauber T, Peres N, Geim A, Science, 320 (2008) 1308. [8] Wang X, Zhi L, Mullen K, Nano. Lett. 8 (2008) 3498. [9] Stoller MD, Park S, Zhu Y, An J, Ruoff RS, Nano. Lett. 8 (2008) 323. [10] Schedin F, Geim AK, Morozov SV, Hill EW, Blake P, Katnelson MI, Novoselov KS, Nat. Mater. 6 (2007) 652. [11] Ganguli S, Roy AK, Anderson DP, Carbon 46 (2008) 806–17. [12] Fujishima A, Honda K, Nature 238 (1972) 37–8. [13] Thostenson ET, Chou TW, Carbon 44 (2006) 3022-3029.

Figure 1. HRTEM image of a)GO and b) GO with TiO2 nanoparticles on its surface.

Figure 2. Photosensor of a sample of nanocomposite with graphene oxide.

Figure 3. Photosensor response for all the nanocomposites when a Laser Red and Green is positioned on the sample the cycle correspond to turn off and on, respectively.

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Intermolecular Interactions in Colloidal Graphene Dispersions and Composites Micah J. Green Texas Tech University, MS3121, Lubbock, TX, USA micah.green@ttu.edu Abstract One of the most exciting challenges in chemical engineering is the development of industrially scalable production and processing techniques for nanomaterials. Our research group has studied intermolecular interactions in the process of dispersing graphene from graphite without covalently functionalizing the JUDSKHQH EDVDO SODQH WKLV ÂłSULVWLQH Â´ XQIXQFWLRQDOL]HG JUDSKHQH KROGV SURPLVH IRU DSSOLFDWLRQV UDQJLQJ from nanofilled structural materials to electrochemical adsorption and sensing. In particular, our group has shown that both polyvinylpyrrolidone (PVP) as well as pyrene derivatives can naturally absorb to the graphene surface, create repulsive (steric and electrostatic) forces, and prevent aggregation [1,2]. This allows for graphene dispersion in a range of solvents and polymer without disrupting the graphene basal plane. Such dispersions are stable against aggregation even when subjected to freeze drying or pH changes (Figure 1). The interactions between graphene and pyrene derivatives can be tuned by the type and number of functional groups and counterions on the dispersant. We have recently shown that PVP and pyrene can serve as a graphene anchor in novel ÂłGHVLJQHU GLVSHUVDQWVÂ´ WKDW SUHFLVHO\ WDLORU JUDSKHQH-matrix interactions in polymer nanocomposites. We have demonstrated that pristine graphene can be used a filler for epoxy composites (Figure 2), polyvinyl alcohol films and nanofibers, as well as a variety of hydrogels (Figure 3) and aerogels (Figure 4) [3-7]. These composites consistently show enhanced modulus, strength, and electrical conductivity. Many of these processing steps have attracted interest from industry and may potentially be generalized to the broader family of two-dimensional nanomaterials, including Boron Nitride nanosheets and metal dichalcogenides. References [1] Wajid, A.S., Das, S., Irin, F., Ahmed, H.S.T., Shelburne, J.L., Parviz, D., Fullerton, R.J., Jankowski, A.F., Hedden, R.C., Green, M.J., Carbon, 50 (2012) 526-534 > @ 3DUYL] ' 'DV 6 $KPHG + 6 7 ,ULQ ) %KDWWDFKDULD 6 *UHHQ 0 - ÂłACS Nano, 6 (2012) 8857Âą8867 [3] Das, S., Irin, F., Ahmed, H.S.T., Cortinas, A.B., Wajid, A.S., Parviz, D., Jankowski, A.F., Kato, M., Green, M.J., Polymer, 53 (2012) 2485-2494 [4] Wajid, A.S., Ahmed, H.S.T., Das, S., Irin, F., Jankowski, A.F., Green, M.J., Macromolecular Materials and Engineering, 298 (2013) 339-347 [5] Das, S., Wajid, A.S., Bhattacharia, S.K., Wilting, M.D., Rivero, I.V., Green, M.J., Journal of Applied Polymer Science, 128 (2013) 4040-4046 [6] Irin, F., Das, S., Atore, F.O., Green, M.J., Langmuir, 29 (2013) 11449Âą11456 [7] Das, S., Irin, F., Ma, L., Bhattacharia, S.K., Hedden, R.C., Green, M.J., 5 (2013) 8633Âą8640

Figures

Figure 1: PVP-wrapped graphene may be (a) freeze-dried and (b) readily redispersed, indicating the graphene basal plane is aggregation resistant.

Figure 2: 0.46 wt% PVPgraphene in epoxy

Figure 3: Graphene-loaded polyacrylamide physically-crosslinked gels

Figure 4: Graphene-polymer aerogels can be backfilled with thermoset to create an aerogeltemplated, ultralow percolation threshold nanocomposite.

Graphene on Antidot Lattice SĂ¸ren Schou Gregersen, Jesper Goor Pedersen and Antti-Pekka Jauho DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, DTU, Building 345 East, DK-2800 Kongens Lyngby, Denmark sorge@nanotech.dtu.dk Abstract In recent years, graphene antidot lattices (GALs) have received great attention due to their ability to strongly alter the electronic properties of graphene, in some cases inducing a sizable electronic band gap [1]. Concurrently, bilayer graphene (BLG) has been studied as an alternative way of achieving semiconducting graphene-based structures, with a band gap tunable via an inter-layer bias [2]. While many studies have focused on combinations of pristine graphene and GAL structures, resulting in, e.g., GALbased waveguides [3], focus has so far been on structures retaining the single-layer nature of graphene. We propose instead a structure consisting of bilayer graphene, wherein one of the layers is periodically perforated, while the other one remains pristine, see Fig. 1. This results in a GAL vertically coupled to single-layered graphene (SLG), which we denote as GOAL (Graphene On Antidot Lattice). Using a nearest-neighbor tight-binding calculations, we demonstrate that if the isolated GAL has a band gap, the resulting GOAL behaves as a hybrid between single-layer and bilayer graphene, with properties tunable via the gap of the GAL layer. In particular, in the absence of an inter-layer bias, the gap in the GAL layer forces the electrons to localize predominantly in the graphene layer, resulting in properties resembling single-layer graphene. However, we find that introducing a bias via shifted on-site energies results in a tunable band gap, similar to the case of BLG. The combined structure thus retains the linear bands of graphene in absence of bias, yet maintains a sizable and tunable band gap when an inter-layer bias is applied, see Fig. 2. Using recursive Green's techniques we examine single-electron transport between semi-infinite BLG leads though a central GOAL region. We find that the device exhibits SLG-like transport within the gap of the GAL layer, albeit with slight modulations, including a non-zero transport at the Fermi energy, see the upper panel of Fig. 3. By expressing the bond currents in a recursive fashion similar to the recursive calculation of the transport coefficient, we are able to efficiently calculate the bond currents of large systems. These confirm that the current is restricted mostly to the graphene layer of GOAL as shown in the middle and lower panel of Fig. 3. The linear bands at zero bias and sizeable gap at non-zero bias of GOAL suggests a powerful platform material for probing SLG-like properties. Unlike SLG, GOAL has the possibility to open and tune band gaps selectively throughout the material by appropriately applying inter-layer biasing. References [1] T. G. Pedersen, C. Flindt, J. G. Pedersen, N. A. Mortensen, A.-P. Jauho & K. Pedersen, Phys. Rev. Lett. 100(2008) 136804. [2] E. McCann & M.,Koshino, Reports Prog. Phys. 76 (2013) 56503. [3] J. G. Pedersen, T. Gunst, T. Markussen & T. G. Pedersen, Phys. Rev. B 86(2012) 245410.

Figures Fig. 1. The material design. A layer of GAL (blue) coupled through BLG couplings to a layer of graphene (gray). The figure displays the hexagonal carbon-carbon bonds characteristic of graphene. Similar to BLG, GOAL turns semi-conducting with a nonzero inter-layer bias applied.

Fig. 2. The electronic band structure of PG (gray), GOAL with zero bias (black), and GOAL with non-zero bias (red). The GOAL materials have the triangular lattice GAL{7,3} [1]. These band structures are calculated from a TB model using BLG TB-parameters, only nearest neighbors, and uniform bias across all atoms with opposite signs in the two layers. Fig. 3. Upper panel: The single electron transport coefficient of pristine graphene (black) and GOAL (red) between semi-infinite BLG leads. Both the leads and the device are periodic yielding an infinite 2D system. The GOAL has the lattice GAL{6,3} [1] and has a width allowing at least 9 lines of antidots. Also shown is the point-ofinterest for the bond transport calculation below. Middel and lower panel: The single electron transport bond currents throughtout the graphene layer (middel) and antidot layer (bottom). The currents are displayed by summing outgoing current vectors of each atom in every hexagon in the respective layers. Note that the current in the antidot layer is practically zero, hence no visible arrows.

UV and ZETA Spectroscopic characterization of MWCNTs Anita Grozdanov1, Ana Tomova1, Dejan Dimitrovski1, Perica Paunovic1, 1 Aleksandar Dimitrov , 1- Faculty of Technology and Metallurgy, University Ss Cyril and Methodius in Skopje, Republic of Macedonia anita@tmf.ukim.edu.mk Multiwalled carbon nanotubes (MWCNTs), unique nanomaterials with extraordinary mechanical, electronic and optical properties, have attracted the material industry and academic society. According to Iijima, an ideal carbon nanotube consists of multiple rolled layers of graphite, derived from unusual carbon structure by metal oxidation catalyst. Owing to their great possibilities, MWCNTs are expected to substitute a variety of classical materials in the near future. However, MWCNTs with their high van der Waals force, surface area, high aspect ratio inevitably cause self-aggregation. The improvement of dispersion has become a challenge to maximize the properties of MWCNTs. In order to overcome self-aggregation, chemical modification of MWCNTs surface or utilization of surfactants is regarded as an effective way to improve their wettability and adhesion to host matrix materials. When surfactants are employed in MWCNT dispersions, surfactant molecules work by adsorption at the interface and self-accumulation into supramolecular structures, which help CNT dispersion retain a stable colloidal state. Coulombic or hydrophobic attraction plays a key role in achieving stable colloidal systems in ionic or nonionic surfactants, respectively. Functionalization of two types of MWCNTs obtained by pyrolisis and chemical vapour deposition was performed in acid (HNO3) and alkali (NH4OH+H2O2) media. In this work, UV-vis and ZETA potential measurement techniques of MWCNTs have been analysed in details. Zeta potential measurements were carried out with a 1cm cell on a Zeta Potential Analyzer from Brookhaven Instruments &RUSRUDWLRQ Č?O 0:17 GLVSHUVLRQ ZDV SXW LQWR WKH FHOO DQG GLOXWHG WR ml water in the presence of SDS surfactant. The experiments were repeated at least three times for averaging. UV-vis spectrum were recorded using Variant spectrophotometer in quartz cell with a path length of 1cm. The results have shown that nn improved dispersion stability results for oxidized MWCNTs in polar media. When the CNTs are modified with carboxylic anion groups, the dispersion stability in polar solvents was significantly enhanced due to the combination of polarÂąpolar affinity and electrostatic repulsion. The presence of electrostatic repulsion was found from the conductivity and zeta potential of the modified MWCNTs. Keywords: MWCNTs, Zeta potential, UV spectroscopy, Functionalization

Controlled folding of 2D materials: Grafin Printing Toby Hallam, A. Shakouri, H.K. Taylor, S. Haigh, A. Rooney, M. T. Cole, M.S. Ferreira, W.I. Milne, G.S. Duesberg Centre for Research on Adaptive Nanostructures and Nanodevices Trinity College Dublin hallamt@tcd.ie Abstract Graphene and other two-dimensional materials exhibit an overwhelming abundance of novel electronic and mechanical properties.[1, 2] In the last few years significant inroads have been made on shaping, patterning, doping and processing of these materials to create novel technological applications. However, such approaches have generally ignored the ability for flat 2D materials to fold and crease, while typically considered any such deformations to be unwanted.[3] This is in fact surprising, since the ability to fold graphene is actually one of the few properties that are entirely unique to 2D materials; a truly new avenue that 3D materials are in no way capable of following. At the current state of the art the only attempts at studying electronic transport through folds in 2D materials have been in graphene via isolation of accidental, naturally formed wrinkles. Such approaches rely heavily on luck and painstaking processes of locating the wrinkles and aligning electrodes to where they happen to occur. This lack of control over crease formation and precise morphology has severely KDPSHUHG V\VWHPDWLF LQYHVWLJDWLRQ RI IROGHG JUDSKHQHÂśV WKHRUHWically predicted properties.[4, 5] To address this issue we have developed a novel transfer-printing technique, grafin printing, to controllably introduce free-standing folds and pleats into graphene and other 2-dimensional materials.[6] This technique, when combined with the growing body of theoretical work on the properties of folded 2D materials offers a route to fundamental science, new device architectures and faster, more compact electronics.[7, 8]

Figures

References [1] CoopHU '5 'Âś$QMRX % *KDWWDPDQHQL 1 +DUDFN % +LONH 0 +RUWK $ HW DO ([SHULPHQWDO Review of Graphene. ISRN Condensed Matter Physics. 2012;2012:56. [2] Butler SZ, Hollen SM, Cao L, Cui Y, Gupta JA, GutiĂŠrrez HR, et al. Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene. ACS Nano. 2013;7(4):2898-926. [3] Lanza M, Wang Y, Bayerl A, Gao T, Porti M, Nafria M, et al. Tuning graphene morphology by substrate towards wrinkle-free devices: Experiment and simulation. Journal of Applied Physics. 2013;113(10):104301-7. [4] Zhu W, Low T, Perebeinos V, Bol AA, Zhu Y, Yan H, et al. Structure and Electronic Transport in Graphene Wrinkles. Nano letters. 2012;12(7):3431-6. [5] Wu Q, Wu Y, Hao Y, Geng J, Charlton M, Chen S, et al. Selective surface functionalization at regions of high local curvature in graphene. Chemical Communications. 2013;49(7):677-9. [6] Hallam T, Cole MT, Milne WI, Duesberg GS. Field Emission Characteristics of Contact Printed Graphene Fins. Small. 2014;10(1):95-9. [7] Britnell L, Gorbachev RV, Jalil R, Belle BD, Schedin F, Mishchenko A, et al. Field-Effect Tunneling Transistor Based on Vertical Graphene Heterostructures. Science. 2012;335(6071):947-50. [8] Costa AT, Ferreira MS, Hallam T, Duesberg GS, Castro Neto AH. Origami-based spintronics in graphene. EPL. 2013;104(4):47001.

First-principles study of nitrogen-doped and defective graphene Xiaoyu Han, Stephen A. Shevlin and Zheng Xiao Guo

Department of Chemistry, University College London, Gower St, London, WC1E 6BT * z.x.guo@ucl.ac.uk Since the discovery of graphene, many efforts have been made to tailor this 2D material of a Diraccone bandgap structure without disturbing the high electron mobility.[1] However, fundamental understanding of the potential and the effect of doping and defect is still lacking. Here we present a systematic study of nitrogen doping on defective graphenes based on Density Functional Theory (DFT). Up to 6 adjacent carbon vacancies (VC), nitrogen dopants (NC), and defect complexes (nVC+mNC) were considered. In both pure vacancy defects and vacancy-doping complex scenarios, the geometries undergo a Jahn-Teller like distortion driven by the unterminated dangling bonds on carbon atoms. The pure nitrogen substitution defects have the lowest formation energy, particularly with one nitrogen substitution. When a vacancy defect exists, the nitrogen atoms prefer to substitute the positions around the vacancy. These defect complexes also have significant effect on its own electronic properties. In the 2VC+4NC defect configuration, the bandgap can be opened to 0.25 eV. -6 The Fermi velocity of this defective graphene is 0.48Ă&#x2014;10 m/s, comparable to pristine graphene. Such insight is very important for the design of electronic devices, graphene-based catalysts and energy storage materials. Reference: [1] ; :DQJ HW DO Âł1-'RSLQJ RI *UDSKHQH 7KURXJK (OHFWURWKHUPDO 5HDFWLRQV ZLWK $PPRQLDÂ´ Science 324 (2009): 768-771. Figures:

Figure 1: The nVC+mNC complex defective graphene configurations. (Blue atoms are nitrogen, and graphene is the grey framework.)

Figure 2: The charge difference of the 2VC+4NC defective graphene on the left (yellow represents the charge accumulated and blue is decreased area. Isosurface is set to 0.002 a 0-3, where a0 is the Bohr radius) and its band structure is shown on the right.

Functionalization of Graphene towards Dual-Mode Bio-Sensing 1

Malkolm Hinnemo , Patrik Ahlberg , Shun Yu , Zhi-Bin Zhang , Nima Jokilaakso , Xindong Gao , 3 3 1 Andreas Larsson , Amelie Eriksson Karlström , and Shi-Li Zhang 1 Department of Engineering Sciences, Uppsala University, SE-75121 Uppsala, Sweden malkolm.hinnemo@angstrom.uu.se 2 Deutsches Elektronen-Synchrotron, D-22607 Hamburg, Germany 3 School of Biotechnology, KTH, SE-10044 Stockholm, Sweden Abstract We are developing and investigating an Immunological Ion Sensitive Field Effect Transistor (Im-ISFET) based on graphene grown by CVD and subsequently transferred to desired substrates including transparent foils as in Fig. 1. This Im-ISFET allows us to measure both the current (I-V measurement) through the graphene and the capacitance (C-V measurement) on its surface [1].The measurement setup is schematically shown in Fig. 2. Through C-V measurement, the potential drop over the Electrical Double Layer (EDL) and the capacitance of it are obtained simultaneously. This gives more information about the adsorption of molecules on the graphene surface, and will forward our understanding of the binding of targets to the graphene surface which in turn will give us a deeper understanding of what the measured signals may tell. Performing C-V measurement with Si-based structures is difficult since a thick oxide layer is necessary to prohibit uncontrolled redox reactions on the surface. This oxide layer has a much smaller capacitance than the EDL capacitance. When measured in series with the EDL capacitance, the oxide capacitance dominates and renders the EDL capacitance undetectable. The use of graphene as the channel material overcomes this challenge. Graphene is much more chemically inert and does not need passivation against electrolytes. A capacitance measurement then only contains two terms: the quantum capacitance of graphene and the EDL capacitance. These two capacitance components are of the same order of magnitude and this enables capacitance measurement of the binding process. Our focus in this work is on DNA sensing. To make a DNA sensor, it is necessary to bind the DNA probe to the graphene surface via a linker layer. We have employed two different approaches to achieve this layer. One approach is to rely on a self-assembled monolayer (SAM) of an organic molecule 1-pyrenebutanoic acid succinimidyl ester (PYR-NHS)[2]. PYR-NHS has a pyrene group that binds to graphene through pi-pi stacking[3], and a carboxylic group activated by a succinimidyl ester that binds to the probe DNA. The functionalization is done through wet chemistry at room temperature and can be combined with in situ electrical measurements to characterize the coverage of the PYRNHS. The coverage is also measured by AFM, XPS, SEM, and fluorescence measurement. The fluorescence experiment is carried out by attaching the probe DNA onto a predetermined pattern and then measuring the fluorescence intensity of the labeled target DNA. The selectivity of DNA binding is characterized by measuring the fluorescence intensity on the spots with and without the probe DNA, as seen in Fig. 3. Characterization of the films will also be performed through XPS and SEM. Another approach is to deposit a thin layer of Au on graphene. The Au layer is so thin that it becomes non-percolating islands spread over the graphene surface. Thiol-based chemistry is then used to attach the DNA probe to the Au. The thiol-chemistry is well established for attaching organic molecules to Au in biochemistry. We have deposited Au layers of different nominal thicknesses by electron-beam evaporation, in order to find a suitable thickness window for sensing. The Au layers are characterized using SEM, grazing incident small angle x-ray scattering (GISAXS) and electrical measurements. An example of the GISAXS measurement is shown in the upper panel of Fig. 4, while the setup and working principle are illustrated in the lower panel of Fig. 4. References [1] Chen, S., et al., Applied Physics Letters, 101 (2012) 154106/1-3. [2] Ohno, Y., et al., Journal of the American Chemical Society, 132 (2010) 18012±3. [3] Chen, R. J., et al., Journal of the American Chemical Society, 123 (2001) 3838±9.

Figures

Figure 1: Graphene transferred onto a PET substrate.

Figure 2: Schematic of the electrical measurement setup as well as the capacitor model with the graphene quantum capacitance Cq and the EDL capacitance CEDL in series.

Į Figure 3: Florescence measurement results with the matrix of round spots representing where the probe DNA has been deposited. The stronger light intensity indicates a higher concentration of target DNA at these spots than anywhere else initially without probe DNA.

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Figure 4: Schematic (lower) of the GISAXS measurement setup and an actual GISAXS image of the sample surface. The intensity and at what output angle the intensity peak is located give information about what kind of layers there are, while the spread out in the y-direction gives information about the lateral structure of the surface.

Comparison of Different Graphene Materials in Amperometric Sensors Alexander ZĂśpfl1, Masoumeh Sisakthi2, Christoph Strunk2, Thomas Hirsch1 1

Institute of Analytical Chemistry, University of Regensburg, UniversitĂ¤tsstrasse 31, 93053 Regensburg, Germany 2 Institute of Experimental and Applied Physics, Micro- and Nanophysics, University of Regensburg, UniversitĂ¤tsstrasse 31, 93053 Regensburg, Germany thomas.hirsch@ur.de

Abstract Carbon nanomaterials, especially graphene has become in focus for amperometric chemical and biosensors. Advantages in contrast to classical amperometric sensors, consisting of conductive polymers and transition-metal-complexes as mediators, can be found in the excellent conductivity and the large surface-to-volume-area of the 2-D carbon nanomaterial. Lower detection limits, broader detection range as well as higher selectivity have been reported [1,2]. On the other hand, the electrochemical properties of the graphene depend a lot on the preparation method of this highly advanced material. The defect density has a considerable effect on the electronic properties of graphene, with a higher concentration of defects resulting in lower electrical conductivity [3]. Whereas graphene flakes obtained by the Scotch-tape method are nearly defect-free, graphene fabricated by chemical vapor deposition (CVD) contains structural defects, and chemically reduced graphene oxide consists of a highly disturbed sp2 carbon lattice containing many functional groups. These three most popular preparation methods require varying amounts of effort, and result in materials differing in size, quality and uniformity of coverage. For an application as sensor material practical considerations such as differences in the ease of synthesis, transfer, and electrical contacting for the various types of graphene must be taken into account for future widespread industrial applications and mass production. Here we have systematically evaluated and compared three differently prepared graphene materials using optical microscopy to study their varying morphology, Raman microscopy to obtain chemical and structural information, and electrochemical methods to characterize the electron transfer properties and the sensor behavior. We studied the ability to detect hydrogen peroxide of all three graphene types in comparison to classical graphite electrode (Fig. 1). The immobilization of enzymes to the graphene is discussed. In essence it turned out that for practical biosensor applications graphene obtained from CVD modified with an antidote lattice performed by plasma etching seems to be favorable. References [1] T. Kuila, S. Bose, P. Khanra, A. K. Mishra, N. H. Kim, J. H. Lee, Biosens. Bioelectron., 26 ( 2011), 4637. [2] Y. Liu, X. Dong, and P. Chen, Chem. Soc. Rev., 41 (2012), 2283. [3] A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, A. K. Geim, Rev. Mod. Phys., 81 (2009), 109. Figures Figure 1:

Principle of an amperometric sensor based on graphene materials.

Electrochemical deposition of different metals on few-layer graphene sheets for fuel cell applications Michael Höltig, Alf Mews Institute of Physical Chemistry, University of Hamburg, 20146 Hamburg, Germany Few-layer graphene (FLG) sheets are highly electrical conductive, have good chemical inertness and a high surface-to-volume ratio. These properties make them a promising candidate as building block and support material for electrical application of high interest like fuel cells and lithium-ion batteries. We have grown FLG sheets directly on conductive substrates (glass with 50 nm goldlayer, 4 cm²) via plasma enhanced chemical vapor deposition at temperatures of

650 °C with acetylene as carbon

precursor. The morphology of the FLG sheets was analyzed by SEM and Raman spectroscopy and was tuneable by chosing synthesis parameters. Standard electrochemical deposition with aqueous metal salt solutions on FLG sheets is difficult and unfavourable because the very sharp edges of the structure would lead to inhomogeneous deposition of mainly large metal particles. Therefore we have invented a non-aqueous method which allows electrochemical deposition of many different metals (e.g. Ni, Co, Bi, Cu, Ag, Pd, Au, Ti) as homogeneous dense (nano particle) layer even on FLG sheets. We have especially investigated samples with large silver nano particles for surface enhanced Raman spectroscopy and with a dense layer of small palladium nanoparticles as catalyst for fuel cell apllications. Cyclovoltammetric (CV) measurements for ethanol oxidation in alkaline solution showed a very high catalyst activity, high cycle stability and current density for the FLG supported Pd nano particle layer. The loading of palladium catalyst was varied and could be correlated to its catalytic characteristics.

Figure 1: Typical SEM image and Raman spectrum of synthesized FLG sheets.

Figure 2: SEM image of FLG sheets densely covered with Pd nano particles and CV measurement of ethanol oxidation in alkaline solution (1 mol/L; 0.1 V/s scan speed).

Electroless Deposition of Silver Nanoparticles on Graphene Oxide surface and Its Applications for Hydrogen Peroxide Detection Shifeng Hou, Huan Feng Chemistry & Biochemistry Department, Montclair State University, 1 Normal Ave, NJ, USA, 07058 Hous@mail.montclair.edu Metal-graphene hybrid materials have received much attention due to their applications in fuel cells, batteries, and chemical or biosensors. Gaphene decorated with metal nanoparticles exhibits special electrical, thermal, mechanical, optical, and catalytic properties. The typical approaches to synthesize metal-graphene nanocomposites include the utilizing electrochemical, chemical vapor deposition, thermal and chemical reduction. Herein, a new process to decorate GO with silver nanoparticles was developed through the electroless deposition technique. This process was performed by treated GO with a series of metal solutions, initially with Sn2+, then with Ag+. And finally, Ag nanoparticles were deposited on GO surfaces (Ag-NPs/GO) (Figure 1). 2+

As expected, both Sn -GO and Ag-NPs/GO exhibited good solubility in aqueous solution, the color of 2+ Sn/GO is black color and Ag-NPs/GO solution exhibits little bite yellow color. The binding of Sn on GO 2+ surface is through the electrostatic force between ÂąCOO , ÂąO and Sn . And the small size of Ag-NPs on GO surface does not change the suspension properties of GO, so the introduction of Ag-NPs does not affect its hydrophilic properties of GO surface. And thus both Sn/GO and Ag-NPs/GO suspension exhibit a very state property. From Uv-Vis spectra, a strong adsorption peak at 402 nm assigned to Ag-NPs/GO is observed, suggesting the formation of Ag-NPs onto GO surface. And the wavelength of 402 nm refers to about 10 nm of Ag-NPs. These data confirm that the particle size of GO is about 10 nm. It is well known that the Ag-NPs exhibit high catalytic activity for reduction of H2O2, and then the cyclic voltammetery of H2O2 on Ag-NPs/GO electrode was then investigated. It is well known that GC had no reduction towards the redution of the reduction of H2O2 is pretty weak. Figure 2 shows the results of cyclic voltammetry of various concentrations of H2O2 at Ag-NPs-GO/GC electrode. The cyclic voltammogram demonstrates that the reduction peaks for H2O2 results a linear relation between the peak currents versus the concentrations. These observations indicate that the Ag-NP/GO exhibits catalytic ability for H2O2 reduction. Figure 3 depicts a typical currentÂątime plot of the Ag-NPs/GO/GC in N2-saturated 0.1 M PBS buffer on successive step change of H2O2 concentrations. When H2O2 was added into PBS solution, the response of Ag-NPs/GO/GC to H2O2 reaches a stable value rapidly. At the applied SRWHQWLDO RI Ă 40 V, the reduction currents of H2O2 increased dramatically and achieved 95% of the steady state current within 10s, indicating a fast amperometric response behavior and proved that the Ag-NPs/GO exhibit notable catalytic ability for H2O2 reduction. Its potential applications for the detection of hydrogen peroxide were WHVWHG ZLWK D OLQHDU UDQJH IURP Č?0 WR P0 DQG WKH GHWHFWLRQ OLPLW ZDV HVWLPDWHG WR EH Č?0 In conclusions, electroless deposition technique can provide a convenient and efficient method of metal nanoparticle deposited onto GO surface. This process was successful in producing Ag-NPs deposited on GO surface. The Ag-NPS/GO was of particular interest due to its capability of being utilized as a H2O2 sensor. Overall, this study provides an initiation point for further examination of the various metal deposited Go nanocomposites as excellent modules for potential sensor systems, produced in a fast, convenient, and cost effective manner.

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References 1. Guo S, Wen D, Zhai Y, Dong S, Wang E (2010) Platinum nanoparticle ensemble-on-graphene hybrid nanosheet: one-pot, rapid synthesis, and used as new electrode material for electrochemical sensing. ACS Nano, 2010, 4, 3959±3968. 2. Li J, Liu CY. , Ag/graphene heterostructures: synthesis, characterization and optical properties. Eur J Inorg Chem, 2010, 1244±1248. 3. Lightcap IV, Kosel TH, Kamat PV, Anchoring semiconductor and metal nanoparticles on a twodimensional catalyst mat. Storing and shuttling electrons with reduced graphene oxide. Nano Lett., 2010, 577±583. 4. Liu S, Tian J, Wang L, Li H, Zhang Y, Sun X., Stable aqueous dispersion of graphene nanosheets: noncovalent functionalization by a polymeric reducing agent and their subsequent decoration with Ag nanoparticles for enzymeless hydrogen peroxide detection. Macromolecules, 2010, 10078±10083. 5. Lu W, Liao F, Luo Y, Chang G, Sun X., Hydrothermal synthesis of well-stable silver nanoparticles and their application for enzymeless hydrogen peroxide detection. Electrochim Acta, 2011, 2295±2298.

References [1] Authors, Journal, Issue (Year) page. Figures

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Highest resolution confocal Raman-AFM-SNOM: advantages and new insights for the characterization of novel 2D materials 1*

Hailong Hu , Ute Schmidt , Thomas Dieing and Olaf Hollricher

WITec Pte. Ltd. 25 International Business Park, #05-109G German Center, 609916 Singapore 2

WITec GmbH, Lise-Meitner Str. 6, 89081 Ulm Germany (www.witec.de) *

Email address: hailong.hu@witec.biz

Abstract The unique chemical, mechanical, electrical, and optical properties of two dimensional

materials, like graphene[1-3], h-BN[4], MoS2[5], etc, lead to their many application possibilities such as: single molecule detectors, new high-strength low-weight materials, design of new semiconductor devices, to name but a few. An important goal however, is the detection of such few angstrom-thick two dimensional sheets and precisely determine the number of layers forming the 2D flake. The aim of this contribution is to show how the combination of confocal Raman, AFM and SNOM can contribute to the characterization of such small materials and devices. In the past two decades, AFM (Atomic Force Microscopy) was one of the main techniques used to characterize the morphology of nano-materials spread on nanometer-flat substrates. From such images it is possible to gain information about the physical dimensions of the material, without additional information about their chemical composition, crystallinity or stress state. On the other hand, Raman spectroscopy is known to be used to unequivocally determine the chemical composition of a material. By combining the chemical sensitive Raman spectroscopy with high resolution confocal optical microscopy, the analyzed material volume can be reduced below ~250 and 800 in lateral and vertical dimensions, thus leading to the ability to acquire Raman images with diffraction limited resolution from very flat surfaces [6, 7]. Using SNOM (Scanning Near-field Optical Microscopy) technology, it will furthermore be shown how the transparency of different graphene sheets is changing as a function of the number of layers with a lateral resolution well below the diffraction limit. With the combination of confocal Raman microscopy with AFM and SNOM, the high spatial and topographical resolution obtained with an AFM can be directly linked to the chemical information about 2D materials provided by confocal Raman spectroscopy and their optical properties obtained with SNOM. A representative characterization for MoS2 with various layers by a confocal Raman-AFM measurement is illustrated in Fig. 1. References

[1] J. Lee, K. S. Novoselov, K. S. Shin, ACS nano 5 (2011) 608 [2] D. A. Schmidt, T. Ohta, T. E. Becheem, Phys. Rev. B 84 (2011) 235422 [3] P. Wei, N. Liu, H. R. Lee, E. Adjianto, L. Ci, B. D. Naab, Nano Letters 13 (2013) 1890 [4] A. G. F. Garcia, M. Neumann, F. Amet, J. R. Williams, K. Watanabe, T. Taniguchi and D. Goldhaber-Gordon, Nano letters. 12 (2012) 4449-4454. [5] B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti and A. Kis, Nature nanotechnology. 6, (2011) 147Âą150 [6] P. Lasch, A. Hermelink. and D. Naumann. Analyst 134, (2009) 1162-1170. [7] Jungen, V. N. Popov, C. Stampfer, C. Durrer, S. Stoll, and C. Hierold. Physical Review 75, (2007) 405.

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Figure 1. (a) Optical image of MoS2 sheet with various layers on SiO2/Si substrate. (b) Color coded Raman image based on Raman spectra of MoS2 as shown in (c), Red: 2 layers; Green: 3 layers; Blue: 6 layers; Magenta: 3+3 layers. With increasing number of MoS2 layers, the peak position of A1g mode gradually shifts to higher wavenumbers. Importantly, comparing to 6 layers, it is the first time to observe the additional blue shift of A 1g mode in 3+3 folded layers. (d) The correlated AFM topography image of the selected area (green dashed frame in (b)) for Raman study. The insert indicates the height profile of MoS2 sheet along the green line. The combination of Raman and AFM techniques could benefit to a comprehensive understanding about chemical and topographic properties of such sub-nm-thick 2D materials, like sample quality, stacking order, domains in CVD growth, edge chirality etc. (Samples: courtesy of Dr. Sun Linfeng, Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore.)

Large-Scale Graphene Oxide Sheets by Low Damage Plasma Treatment 1

Hsiang-En Cheng , Ching-Yuan Su and Chi-Hsien Huang

Department of Materials Engineering, Ming Chin University of Technology, New Taipei City, Taiwan 2 Gradiuate Institute of Energy Engineering, National Central University, Taoyuan, Taiwan chhuang@mail.mcut.edu.tw

Abstract Although graphene is a promising material for a variety of applications, the development of graphene-based devices will require higher control over its surface functionalization. Plasma treatment is a major tool in VLSI processes that can react chemically with various materials. A number of groups have used plasma treatment to functionalize graphene surfaces. However, even multilayer graphene can be etched away within a few seconds in a conventional plasma environment due to the presence of energetic ions and vacuum ultraviolet (VUV) irradiation [1,2]. Both species in plasma have energy higher 2 than that of the C–C bonds of sp -hybridized C atoms in graphene, thereby easily breaking the lattice of graphene and destroying the honeycomb-like C nanostructure. As a result, the etching rate is generally too fast to allow precise control of functionalization. To overcome this issue, we developed a method— low-damage oxygen plasma treatment (O–LDPT) to functionalize CVD-grown graphene sheet. As shown schematically in Fig. 1, by inserting a complementary filter into a parallel plate plasma system, the ions and VUV can be efficiently shielded by the filter, allowing only radicals, which have the highest reactivity among plasma-generated species, to diffuse through the filter with extremely low kinetic energy and reach the nanomaterials to gently functionalize them [3]. Raman and XPS measurements revealed that oxidative functionalities were formed on the graphene surfaces in a highly controllable manner, as shown in Fig. 2 and 3, respectively, through variation of the treatment time ranging from 0 to 7 min. Contact angle (CA) measurements exhibited the high hydrophilicity (CA ~23°) of the large-scale graphene after O–LDPT while maintaining the featured bands of graphene in the Raman spectra. We confirmed that low damage occurred during this process by exposing double-layer graphene (DLG) samples to O-LDPT and then measuring their current-voltage (I–V) characteristics. We fabricated two-terminal devices with oxidized DLGs as the channel, as presented schematically in the inset of Figure 5. For comparison, the devices with DLGs O2-plasma were also prepared. The representative I-V curves of devices with various conditions as displayed in Figure 5. The I–V curve of the DLG that had not been subjected to treatment was linear, indicating conductive characteristics. The current level of the untreated SLG was almost identical to that of the DLG (not shown here). First, we examined the degree of oxidation after conventional plasma treatment using the same processing conditions for 1 min. The current level decreased dramatically. On the contrary, after exposing the DLG samples to O-LDPT for up to 5 min, the I–V curves remained linear. These curves for the devices incorporating the oxidized DLGs all featured almost the same current level; in addition, these values were only slightly lower than that of the DLG that had not been subjected to oxidation. These results suggest that only the top graphene layer of the DLG was oxidized during O-LDPT, implying an ultra-low-damage plasma process even when the exposure time was as high as 5 min, thereby allowing the bottom graphene layer of the DLG to remain conductive. The result indicates that the bottom layer of the graphene sheet was almost unaffected, even when a massive number of oxidative functionalities had been introduced onto the top layer of the graphene sheet. When the treatment time reached 7 min, the current level decreased significantly, leading to higher electrical resistance. We believe that this relatively long treatment time resulted in more defects near the grain boundaries, where oxygen radicals preferentially attack boundary edges. It leads to diffusion of oxygen radicals through top graphene and reach the bottom graphene layer for partial oxidation. Accordingly, our developed LDPT process is a promising technique for the surface modification of graphene, potentially enhancing its interfacial compatibility with the versatile dielectric materials employed nowadays in IC processes. References [1] B. Ozyilmaz, et al., Appl. Phys. Lett., 91 (2007) 192107. [2] C.-H. Hsien, et al., Carbon, 61 (2013) 229. [3] C.-H. Hsien, et al., Nanotechnology 23 (2012) 475201.

Figures

Fig. 1. (a)Schematic representation of the LDPT system. (b) Enlarged view of the dashed red rectangle in (a).

Figure 2 Representative Raman spectra as a function of treatment time.

Figure 4 Contact angles of oxidized SLG samples exposed to O-LDPT for various treatment times.

Figure 3 (a) XPS spectra of SLG samples oxidized through O-LDPT for various treatment times.

Fig.5. I-V curves of devices (inset) incorporating DLGs oxidized by O-LDPT for various treatment time.

Directly Growing Graphene Film on Quartz by Low Pressure Microwave Plasma Torch Chemical Vapor Deposition Kun-Ping Huang, Bor-Kae Chang, Chih-Chen Chang Mechanical and Systems Research Lab., Industrial Technology Research Institute, Bldg. 22, 195, Sec. 4, Chung Hsing Rd., Chutung, 31040, Taiwan, R. O. C. kphuang@itri.org.tw Abstract Traditional methods to prepare graphene film for transparent conducting electrodes involve the wet etching of the metal catalyst and the transfer of the graphene film [1], which can degrade the film through the creation of wrinkles, cracks, or tears. The resulting films may also be obscured by residual metal impurities and polymer contaminants. The electron cyclotron resonance chemical vapor deposition (ECR CVD) method can directly grow nanographene film temperature on SiO2[2], but its sheet resistance is as high as 20k /႒. Here, it is shown that directly growing graphene film on quartz can be achieved by low pressure microwave plasma torch chemical vapor deposition (LPMPT CVD). Raman spectra (Fig. 1) can confirm 2~3 layers graphene film [3], and sheet resistance is 6k /႒. References [1] Keun Soo Kim, Yue Zhao, Houk Jang, Sang Yoon Lee, Jong Min Kim, Kwang S. Kim, Jong-Hyun Ahn, Philip Kim, Jae-Young Choi, and Byung Hee Hong, Nature Lett., 457 (2009) 706. [2] Henry Medina, Yung-Chang Lin, Chuanhong Jin, Chun-Chieh Lu, Chao-Hui Yeh, Kun-Ping Huang, Kazu Suenaga, John Robertson, and Po-Wen Chiu, Adv. Funct. Mater., 22 (2012) 2123. [3] Andrea C. Ferrari, Solid State Commun. 143 (2007) 47. Figures

Figure 1. Raman spectra of LPMPT-CVD graphene grown on quartz. The spectra were taken by 532 nm laser excitation.

One-pot sonochemical synthesis of reduced graphene oxide uniformly decorated with ultrafine silver nanoparticles Huang Nay-Ming & Amir Moradi Golsheikh Low Dimensional Materials Research Centre, Physics Department, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia..edu.y Abstract Reduced graphene oxide (rGO) uniformly decorated with silver nanoparticles (AgNPs) is synthesized through a simple ultrasonic irradiation of the aqueous solution containing silver ammonia complex (Ag(NH3)2OH) and graphene oxide (GO). The results of X-ray diffraction, Fourier-transform infrared transmission spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy confirmed the simultaneous formation of cubic-phase AgNPs and the reduction of GO through the ultrasonication process. The size of the nanoparticles could be tuned by adjusting the volume ratio of the precursors and the ultrasonic irradiation time. Transmission electron microscope images show a uniform distribution of ultrafine spherical AgNPs with a narrow size distribution on the rGO sheets, which could only be achieved using silver ammonia complex instead of silver nitrate as the precursor. The average particle size of silver with the narrowest size distribution is 4.57 nm. The particle size and its distribution are directly proportional to the ultrasonic irradiation time. The rGO/Ag nanocomposites is highly stable in aqueous solution and render it to many potential applications.

Figure 2. (A) UV-Vis absorption spectra of GO and AgNPs-rGO (the inset shows the photograph of the solution of GO and Ag(NH3)2OH before and after ultrasonic irradiation), (B) time evolution of UV-Vis absorption spectra of AgNPs-rGO.

Figure 6. TEM images and size distribution diagrams of AgNPs-rGO prepared using the solution with GO (1.0 mg/mL) to Ag(NH3)2OH (0.04 M) volume ratios of 8 (a and b), 4 (c and d), 2 (e and f) as well as the solution with GO (1.0 mg/mL) to AgNO3 (0.04 M) volume ratio of 4 (g and h) with the same ultrasonic irradiation time of 5 min.

Graphene oxide induced rapid synthesis of a-MnO2 nanorod and the electrochemical performance Zhao Hui, Sun Liping, Ma Fangwei, Li Qiang, Huo Lihua School of Chemistry and Materials Science, Heilongjiang Univeristy, Harbin, China Zhaohui98@yahoo.com ÄŽ-MnO2 nanorods were rapid prepared by hydrothermal treatment of KMnO4, GO (graphene o

oxide)and sulfuric acid at 120 C for 3 h. The nanorods have a diameter of 10~20 nm and a length of 300~400 nm. The introduce of GO reduces the preparation temperature of ÄŽ-MnO2 QDQRURGV DQG VKRUWHQ WKH UHDFWLRQ WLPH 7KH HOHFWURFKHPLFDO UHVXOWV LQGLFDWH WKDW ÄŽ-MnO2 nanorods show fine capacitive behavior in neutral aqueous electrolyte (1 molÂˇL -1

-1

Na2SO4),When the scan rates were 2 mVÂˇs and 5 mVÂˇs , the specific capacitances were 276 FÂˇg and 240 FÂˇg UHVSHFWLYHO\ 7KLV ÄŽ-MnO2 nanorods is a potential electrode material for -1

-1

electrochemical capacitors. References [1] Simon P, Gogotsi Y., Nat. Mater., 7 (2008) 845-854. [2] Cheng F Y, Chen J, Gou X L, et al., Adv. Mater., 17 (2005) 2753-2756.

Figure 1, ÄŽ-MnO2 that hydrothermal treated at different times with/without the addition of GO. (a) XRD patterns; (b) Raman spectrum

Figure 2, (a) Galvanostatic charge/discharge curves at different current density (inset was the cycle life at current density of 1 mAÂˇcm ), (b) Nyquist plots of ÄŽ-MnO2 nanorods prepared by -2

hydrothermal treatment at 120 C for 3hrs

High Gain Hybrid Graphene-P3HT Phototransistors E.H. Huisman, A.G. Shulga, P.J. Zomer, N. Tombros, D. Bartesaghi, S.Z. Bisri, M.A. Loi, L.J.A. Koster and B.J. van Wees Zernike Institute for Advanced Materials, Nijenborgh 4, 9747 AG, Groningen, The Netherlands E.H.Huisman@rug.nl Abstract We present data on graphene field-effect transistors with P3HT (poly(3-hexylthiophene-2,5-diyl), an organic semiconducting polymer) applied on top of the graphene channel. Our data shows that the organic polymer provides an effective gating field to the graphene when light is applied. This observation is similar to the observation of ultrahigh gain in hybrid PbS colloidal quantum dot - graphene phototransistors [1]. Our findings demonstrate that the observed light-induced gating can also be applied to other semiconductor-graphene interfaces. References

[1] G. Konstantatos, M. Badioli, L. Gaudreau, J. Osmond, M. Bernechea, F. Pelayo, G. de Arquer, F. Gatti, F. H. L. Koppens Nature Nanotechnology 7 (2012) 363.

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165

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Left Panel. Schematic sideview of a device. Right panel. Temporal response of the current through a hybrid graphene-P3HT transistor made out of mechanically exfoliated graphene on top of boron nitride.

Responsivity (A/W)

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Transport properties of disordered CVD graphene in the strong localized regime 1

Fabrice Iacovella , Pierre Trinsoutrot , Anatoli Mitioglu , Véronique Conédéra , Matthieu Pierre , 1 1 2 2 1 Bertrand Raquet , Michel Goiran , Hugues Vergnes , Brigitte Caussat and Walter Escoffier 1

Laboratoire National des Champs Magnétiques Intenses, University of Toulouse, UPS, INSA, CNRS-UPR 3228, 143 av. De Rangueil, F-31400 Toulouse, France

ENSIACET-INP de Toulouse, Laboratoire de Génie Chimique, UMR CNRS 5503, 4 allée Emile Monso, F-31432 Toulouse, France 3

Laboratoire d'Analyse et d'Architecture des Systèmes, University of Toulouse, UPS, INSA, INP, ISAE, UT1, UTM, 7 avenue du colonel Roche, F-31077 Toulouse Cedex 4, France fabrice.iacovella@lncmi.cnrs.fr

The Chemical Vapor Deposition (CVD) of graphene is nowadays one of the most promising methods for the production of large scale graphene films [1]. The growth is first initiated onto transition metal substrates (Cu, Pt.) before being transferred onto an insulating wafer. High quality and homogeneous graphene films can be obtained this way, displaying amazing electronic properties such as the anomalous Quantum Hall Effect at low temperature and high magnetic field [2]. On the other hand, achieving high quality graphene films requires states-of-the art techniques and when the ideal set of parameters is not fulfilled, one may end up with a variety of disordered graphene devices with interesting electronic properties. We investigated the extreme limit of a highly disrupted multi-layer graphene film showing high electrical resistance. We demonstrate that electronic conduction occurs through hopping between localized sites, provided the drain-source voltage remains higher than a temperature-dependent threshold value. An exhaustive data analysis concludes that the sample can be assimilated as an array of very tiny graphene dots (~6nm in diameter) weakly interacting each other. The presence of such few-layer graphene islands is confirmed thanks to Raman spectroscopy [3]. In the strongly localized regime, the magneto-conductance (MC) happened to be unusual, being first positive up to 6T and then negative by about 50% up to the maximum experimental magnetic field (55T) (cf fig. 1). While the positive MC is nicely explained through magnetic field delocalization induced processes [4], the negative MC, on the other hand, remains unsettled. The reentrance of the Quantum Hall Effect, at high field and low carrier density, constitutes a stimulating hypothesis. This assumption is further reinforced through investigations of another similar sample with intermediate disorder, where the Hall mobility reads 1000 cm²/(V.s). At low carrier density and very high magnetic field, the MC is strongly negative because of the onset of the n=0 Landau level degeneracy lifting. The galvanometric properties display reproducible oscillations of the magneto-resistance which shifts towards higher/lower magnetic field when the carrier density is changed. These are interpreted as Shubnikov-de Haas oscillations which herald the establishment of the QHE (cf fig. 2). It is worth noticing, though, that precise quantized values of the Hall resistance are not achieved even at the highest magnetic field. Actually, such an observation is puzzling since it challenges the roEXVWQHVV RI WKH TXDQWXP VWDWH IRU ILOOLQJ IDFWRU Ȟ LQ low mobility graphene samples decorated with multi-layer patches [5]. These antagonist results can be brought back together of one considers the presence of connected multi-layer islands, which set the electronic properties of the sample in between those of graphene and graphite. [1] Avouris and Christos, Materials Today, 15 (3) (2012) 86-97. [2] Cao et al, App. Phys. Lett., 96 (1) (2010) 122106. [3] Vassiouk et al, Nanotechnology, 22 (27) (2011) 275716. [4] Lo et al, Nanotechnology, 24 (16) (2013) 165201. [5] Nam et al, App. Phys. Lett., 103 (23) (2013) 233110.

MC (%)

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-60 0 10 20 30 40 50 60

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=3 0V

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Figure 1: Magneto-conductance in ultra-disordered graphene sample for different bias voltage. The magneto-conductance is positive up to ~6T before turning negative. This effect is amplified at higher temperature (see insert) and higher bias voltage.

Vg=-40V Vg=-30V Vg=-20V Vg=-10V Vg=+0V

(k ) XX

(k )

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Reduction of graphene oxide layers printed on different substrates 1

J. Jagiello , J. Ostrowska , L. Lipinska , Z. Sieradzki , M. Puchalski , E. Skrzetuska , I. Krucinska , M. 4

Rogala , I. Wlasny , Z. Klusek 1

Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland 2

Electrotechnological Company QWERTY Ltd., Siewna 21, 94-250 Lodz, Poland

Department of Material and Commodity Sciences and Textile Metrology, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland

Department of Solid State Physics, Faculty of Physics and Applied Informatics, University of Lodz, Pomorska 149/153, 90-236 Lodz, Poland

joanna.jagiello@itme.edu.pl

Graphene exhibits superior electrical conductivity, high surface area and a broad electrochemical window that may be particularly advantageous for electronic application. In addition, graphene can be prepared in the form of a colloidal suspension with adjustable solubility and thus is suitable for printable electronics in an industrial scale and offers both transparency and good conductivity at the same time [1]. The most common form of graphene used as nanoelectronic components are graphene oxide (GO) and reduced graphene oxide (rGO). Although GO is not electrically conductive, it can be reduced to graphene thermally, chemically or photothermally. Chemical reduction of GO is the most common technique for the restoration of the graphene electronic structure [2,3]. In this work the results of reduction of GO layers are presented. Water suspension of graphene oxide was printed on four types of substrates: glass, flexible polyester foil (Autostat CT5), para-aramid (Kevlar) fabric and polyester fabric. GO layers were deposited with inkjet method. Graphene oxide was reduced by chemical methods with the use of various reducers: HI, HBr, KBH4, NaH2PO2 with NaHSO3, NH4I and H2SO4. Different substrates require the use of appropriate reducers which do not react with the material and do not destroy its structure. We recorded Raman and XPS spectra for the samples to investigate the reduction efficiency. As it is -1

shown in Fig.2., the D peak (1337 cm ) increased after reduction indicating the elimination of oxide groups from GO sheets and forming rGO. The sheet resistance varies from WHQV NÂ&#x; Ć&#x2018; WR IHZ NÂ&#x; Ć&#x2018; References [1] Lorenzo Grande, Vishnu Teja Chundi, Di Wei, Chris Bower, Piers Andrew 7DSDQL 5\KlQHQ Particuology 10 (2012) 1 [2] Xiaojuan Tian, Santanu Sarkar, Aron Pekker, Matthew L. Moser, Irina Kalinina, Elena Bekyarova, Mikhail E. Itkis, Robert C. Haddon, Carbon 72 (2014) 82 [3] Linh T. Le, Matthew H. Ervin, Hongwei Qiu, Brian E. Fuchs, Woo Y. Lee, Electrochemistry Communications 13 (2011) 355

Figures

Intensity (a.u.)

Fig.1. SEM images of GO printed on foil (left image) and on Kevlar fibers (right image).

1400

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1800

2000

2200

2400

2600

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Raman shift (cm-1)

1600

1800

2000

2200

2400

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Fig.2. Raman spectra of GO (on the left) and rGO (on the right).

Presented work is supported by the National Centre for Research and Development under the project GRAFTECH/NCBR/15/25/2013.

Graphene Contamination Removal Using Argon Cluster Etching

Andrew J. Pollard, Bonnie J. Tyler, Helena Stec, Steve J. Spencer, Ling Hao, Debdulal Roy, Alex G. Shard, Ian S. Gilmore, National Physical Laboratory, Teddington, TW11 0LW, UK andrew.pollard@npl.co.uk

Abstract

As graphene starts to progress from the research laboratory towards industrial applications, the requirement to overcome the practical problems related to 2-D materials, such as quality, reproducibility and contamination, increasingly needs to be met. An emerging global graphene industry requires large-scale production of graphene material that still achieves the exceptional properties demonstrated in smaller scale experiments. Chemical vapour deposition (CVD) growth methods can produce large-scale graphene sheets utilising roll-to-roll processing, however, the transfer steps required to remove CVD graphene from sacrificial metal substrates and subsequent electronic device manufacturing steps lead to inhomogeneous polymer contamination. This polymer residue from photoresists and transfer polymers cause undesired reductions in conductivity and irreproducibility in the production of graphene devices. Although heating graphene surfaces can improve the consistency of these devices, we show with high-sensitivity secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) that this does not fully remove the contamination present. However, we reveal that argon cluster ion beam etching, which is commonly used in the semiconductor industry, can be used to remove contamination from graphene layers whilst minimising any damage to the graphene lattice itself. Confocal Raman spectroscopy investigations reveal an impact energy of less than 1 eV per atom in the cluster is required. Optimised conditions for sputter profiling the organic overlayers whilst minimising graphene lattice damage will be presented and the effect on conductivity, as measured using a large-scale and contactless microwave dielectric resonator perturbation technique, is discussed.

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How to set up CVD for Graphene Synthesis Bjarke Bror Egede Jensen, Anpan Han, Kim Daasbjerg Aarhus University, Department of Chemistry and Interdisciplinary Nanoscience Center, Langelandsgade 140, DK-8000 Aarhus C, Denmark. bbj@newtec.dk Abstract The emergence of graphene has revealed a new versatile platform of materials, which are now being studied in almost every corner of science. However, new coming groups who wish to start a graphene program may rely on low quality production methods or expensive commercially available graphene, to get started. Chemical vapour deposition has proved to be a durable way of growing graphene due to the ability of several metals to catalyse the synthesis at high temperatures. Especially Cu has shown great potential for producing large area monolayer graphene, and a lot of effort has in recent years been put into understanding and optimising the procedure. Here we report on setting up low pressure chemical vapour deposition with the aim of growing graphene, and what considerations to make regarding safety. Furthermore, graphene was grown on Cufoil and characterised using Atomic Force Microscopy, Optical Microscopy and Raman Microscopy. Figures

Figure 1: Optical microscopy of graphene on Cu using differential interference contrast.

One-step transfer and integration of multifunctionality in CVD graphene by TiO2/graphene oxide hybrid layer 1

1,2

Hee Jin Jeong , Ho Young Kim , Hyun Jeong , Joong Tark Han , Seung Yol Jeong , Kang-Jun Baeg , 2 1 Mun Seok Jeong , Geon-Woong Lee 1

Nano Carbon Materials Research Group, Korea Electrotechnology Research Institute (KERI), 2 Changwon 641-120, Republic of Korea, Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS), Department of Energy Science, Sungkyunkwan University, Suwon, 440-746, Republic of Korea wavicle11@keri.re.kr Introduction For application in optoelectronic or electronic devices, graphene produced by CVD is to be transferred from the transition metal substrate to an insulating substrate. Poly(methylmethacrylate) (PMMA) has been widely used as the supporting material for graphene transfer. After the complete removal of copper, the graphene film coated with PMMA is placed on the desired substrate and the PMMA layer is removed using acetone. However, this process typically damages the graphene layer because of crack 1

or ripple formation and tearing. Moreover, it is difficult to completely remove the PMMA support layer. Another crucial challenge in graphene-based optoelectronic devices is to reduce environmental stability. When graphene is exposed to moisture or other chemical molecules, the conductivity of graphene films is significantly decreased because the graphene can readily interact with adsorbents, resulting in reduced long term stability. To avoid this impurity scattering, additional treatments such as top coating of polymeric material, chemical welding, and thermal welding into the polymeric substrate have been introduced. The permeability of gas molecules is mostly inversely proportional to the thickness of the polymeric layer. However, if the thickness of the polymeric layer is increased for reducing the gas permeability, the conductivity of the graphene film may be significantly reduced because of the intrinsically insulating property of the polymeric layer. Thus, thin semiconducting metal oxides films with low gas permeabilities may be suitable candidates as protection layers for graphene-based optoelectronic devices.

Materials and methods Monolayer graphene was grown by low pressure CVD of methane (99.96%) at 1050 °C on a 100 m thick 3 × 5 cm polycrystalline copper foil. The as-grown graphene film was transferred onto the target substrate by a TiO2 sol-mediated transfer method. A TiO2 sol, which acted as a supporting layer, was prepared using titanium isopropoxide (TIP) / acetylacetone (acac) (1:2 molar ratio), HCl, and water, 2

which were stirring at 60 °C for 10 h. 10 mL of the TiO2 sol was spin-coated at 1000 rpm for 1 min. A 50 nm thick TiO2 layer was finally obtained by curing the TiO 2 sol at various temperatures for 1 h. Next, the copper foil was etched away by soaking in a 0.2 M solution of ammonium persulfate for 3 h and then, the resulting graphene/TiO2 film was transferred onto an arbitrary substrate.

Results and discussion In order to examine the effect of the TiO2 layer as a protective layer, we measured the changes in the sheet resistance of the graphene/GO/TiO2 film with 30% GO coverage when exposed to conditions of high humidity (relative humidity of 80%) and temperature (80 °C) over a period of time, as shown in Figure 1. The environmental stability along with the transparency and conductivity are crucial for the application of graphene-based transparent electrodes. For comparison, the changes in the sheet

resistances of a graphene film without the GO/TiO 2 coating and a graphene film doped with gold were also measured. After 100 h, the sheet resistance of the undoped graphene film was increased by approximately 21% with respect to its initial value. This might have been caused by the selective adsorption of water molecules on the graphene domain boundaries, which acted as scattering centers in the carrier transport. Also, the adsorbed water molecules could open the band gap of the graphene film, -

which could have resulted in a decrease in the conductivity. Meanwhile, the sheet resistance of the Au

doped graphene film distinctively increased over time. Although the Au doping could effectively enhance the carrier density of graphene and thus, the electrical conductivity could be significantly increased, the marked increase in the sheet resistance might have resulted from the hygroscopic property of the Cl

ions.

Conclusion Electrical conductivity, environmental stability, and photocatalytic properties of graphene were significantly enhanced by simply introducing TiO 2 as a supporting layer for graphene transfer. TiO 2 also simultaneously acted as a passivation layer and a p-type doping layer. TiO2 could efficiently support the GO-modified graphene layer during etching of the underlying copper and graphene transfer because TiO2 strongly interacted with the oxygen functional groups of the graphene/GO film. The simple introduction of this multifunctional TiO2 layer can make graphene suitable for application in a variety of devices including FETs, gas sensors, touch panels, photo detectors, and solar cells.

References 1. X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, L. Colombo, R. S. Ruoff, Science, 324 (2007) 1312. 2. J. T. Han, B. G. Kim, M. Yang, J. S. Kim, H. J. Jeong, S. Y. Jeong, S.-H. Hong, G.-W. Lee, ACS Appl. Mater. Interfaces, 3 (2011) 2671. Figures

Figure 1. Long term environmental stability measured at 80 째C under a relative humidity of 80 % of bare graphene, Au-doped graphene, and the graphene/GO/TiO2 film.

Enhanced light output power of GaN UV-LED by a simple passivation with graphene oxide 1)

Hyun Jeong , Seung Yol Jeong , Doo Jae Park , Hyun Joon Jeong , Eun-Kyung Suh , 2) 1) Â&#x201A; Geon-Woon Lee , Young Hee Lee , Mun Seok Jeong 1)

Center for Integrated Nanostructure Physics, Institute of Basic Science, Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea 2) Nano Carbon Materials Research Group, Korea Electrotechnology Research Institute, Changwon, 641-120, Korea 3) School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756, Republic of Korea mjeong@skku.edu Abstract GaN-based ultraviolet (UV) LEDs are widely used in numerous applications, including white light pump sources, high-density optical data storage, medical equipment, and counterfeit bill detection[1,2]. However, low hole injection rate in p-type region due to poorly activated holes and spontaneous polarization leads to insufficient light emission efficiency[3]. Therefore, improving hole injection rate is a key step towards high performance UV-LEDs to expand their uses[4]. Here, we report a new method for enhancing light output power of UV-LEDs by increasing hole injection rate in p-type region. This was achieved by simply passivating graphene oxide (GO) on top of the fully fabricated LED. The dipole field formed by the passivated GO and indium tin oscide (ITO) junction enhanced hole injection rate in p-type region and simultaneously increased hole concentration by about 60%. This not only improved the homogeneity of electroluminescence intensity in active layers but also enhanced light output power to about 60% in linear current region and almost twice in saturated current region due to the delayed hole saturation. Our simple approach of overcoming the limited carrier concentration of p-type GaN using GO passivation method disrupts the current state of the art technology and will be useful for high-efficiency UV-LED technology. In one sentence summary, we developed a simple passivation method using GO nanosheets to enhance light output power of GaN-based UV-LED by about 60% where the spontaneous polarization in p-type GaN hole injection layer is suppressed by forming a strong dipole layer in GO nanosheets. References [1] Khan, A., Balakrishnan, K. & Katona, Nature Photon. 2 (2008) 77-84. [2] Oto, T., Banal, R.G., Kataoka, K., Funato, M. & Kawakami, Y. Nature Photon. 4 (2010) 767-770. [3] Nakamura, S. & Chichibu, S.F. Introduction to nitride semiconductor blue lasers and light emitting diodes. (Taylor & Francis, London ; New York; 2000). [4] Gotz, W., Johnson, N.M. & Bour, D.P. Appl. Phys. Lett. 68, 3470-3472 (1996).

Figures

Figure 1. Enhancement of LED performance by GO coating. a, The light output power versus injection current of conventional (black curve), l-GO-coated (red curve), and h-GO-coated (blue curve) UV-LEDs. The light output power increased by approximately 60% when the conventional UV-LED was coated with h-GO. b,c, Photograph of UV-LED/h-GO of the electroluminescence at an injection current of 1 mA (b) and 5 mA (c). d, I-V characteristics of the devices used in a. No significant change in the samples was observed. e, Energy band diagram of active region in UV-LED when device are applied forward bias. f, Transmittance spectra of sapphire/ITO with h-GO (red curve) and without h-GO (black curve). The change in the transmittance between two samples was negligible. g, Schematic diagram of the electric polarization in the ITO and p-type GaN regions induced by the GO nanosheets. h,i, Energy band diagram of p-type GaN (h) without and (i) with h-GO, which schematically explains the relaxation of spontaneous polarization. j, THz transmittance spectra of the p-type GaN/ITO with GO nanosheets (red curve) and without GO nanosheets (black curve).

How does graphene polycrystallinity impact on the performance of graphene based transistors ? David Jiménez1, Aron W. Cummings2, Ferney Chaves1, Dinh Van Tuan2, Jani Kotakoski3,4, Stephan Roche2,5 1

Departament d'Enginyeria Electrònica, Escola d'Enginyeria, Universitat Autònoma de Barcelona, 08193-Bellaterra, Spain 2 ICN2, Institut Català de Nanociencia i Nanotecnologia, Campus UAB, 08193 Bellaterra (Barcelona), Spain 3 Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Wien, Austria 4 Department of Physics, University of Helsinki, P.O. Box 43, 00014 University of Helsinki, Finland 5 ICREA, Institució Catalana de Recerca i Estudis Avançats, 08070 Barcelona, Spain. david.jimenez@uab.es Abstract The chemical vapor deposition (CVD) technique for growing wafer-scale graphene on metallic substrates1-4 produces a polycrystalline pattern. This is because the growth of graphene is simultaneously initiated at different nucleation sites, leading to samples with randomly distributed grains of varying lattice orientations.5 It has recently been predicted that the electronic properties of polycrystalline graphene differ from those of pristine graphene (PG), where the mobility scales linearly with the average grain size.6 Based on these results, we report on how the electronic properties of polycrystalline graphene (Poly-G) impact the behavior of graphene-based devices. For such a purpose, we have developed a drift-diffusion transport model for the graphene field-effect transistor (GFET), based on a detailed description of electronic transport in polycrystalline graphene7. This model allows us to determine how a graphene sample’s polycrystallinity alters the electronic transport in GFETs, enabling the prediction and optimization of various figures of merit for these devices. Specifically, we concentrate our study on the effect that Poly-G has on the gate electrostatics and I-V characteristics of GFETs. We find that the source-drain current and the transconductance are proportional to the average grain size, indicating that these quantities are hampered by the presence of grain boundaries (GBs) in the Poly-G. Besides, our simulations also show that current saturation is improved by the presence of GBs, and the intrinsic gain is insensitive to the grain size. We have found that the presence of GBs produces a severe degradation of both the maximum frequency and the cutoff frequency, while the intrinsic gain remains insensitive to the presence of GBs (Fig. 1). These results indicate that GBs play a complex role in the behavior of graphene-based electronics, and their importance depends on the application of the device. Overall, polycrystallinity is predicted to be an undesirable trait in GFETs targeting analog or RF applications. We acknowledge support from SAMSUNG within the Global Innovation Program. The research leading to these results has received funding from Ministerio of Economía y Competitividad of Spain under the project TEC2012-31330 and MAT2012-33911, and from the European Union Seventh Framework Programme under grant agreement n°604391 Graphene Flagship.

References [1] X. S. Li, W. W. Cai, J. H. An, S. Kim, J. Nah, D. X. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, L. Colombo, R. S. Ruoff, Science 324, 1312–1314 (2009). [2] A. Reina, X. Jia, J. Ho, D. Nezich, H. Son, V. Bulovic, M. S. Dresselhaus, J. Kong, Nano Lett. 9, 30 (2009). [3] X. S. Li, C. W. Magnuson, A. Venugopal, J. H. An, J. W. Suk, B. Y. Han, M. Borysiak, W. W. Cai, A. Velamakanni, Y. W. Zhu, L. F. Fu, E. M. Vogel, E. Voelkl, L. Colombo,R. S. Ruoff, Nano Lett. 10, 4328– 4334 (2010). [4] S. Bae, H. Kim, Y. Lee, X. F. Xu, J. S. Park, Y. Zheng, J. Balakrishnan, T. Lei, H. R. Kim, Y. I. Song, Y. J. Kim, K. S. Kim, B. Ozyilmaz, J. H. Ahn, B. H. Hong, S. Iijima, Nat. Nanotechnol. 5, 574– 578 (2010).

[5] P. Y. Huang, C. S. Ruiz-Vargas, A. M. van der Zande, W. S. Whitney, M. P. Levendorf, J. W. Kevek, S. Garg, J. S. Alden, C. J. Hustedt, Y. Zhu, J. Park, P. L. McEuen, D. A. Muller, Nature 469, 389 (2011). [6] D. V. Tuan, J. Kotakoski, T. Louvet, F. Ortmann, J. C Meyer, S. Roche, Nano Lett. 13, 1730-1735 (2013). [7] D. JimĂŠnez, A. W. Cummings, F. Chaves, D. Van Tuan, J. Kotakoski, S. Roche, Applied Physics Letters, 104, 043509 (2014).

Fig. 1. Output characteristics (a) and output conductance (b) of a graphene field-effect transistor considering polycrystalline graphene with different GB average size. (c) Intrinsic gain as a function of the drain voltage. (d) Intrinsic maximum and cutoff frequency for the simulated transistor assuming a channel length of 100 nm.

Nitrogen doped graphene studied by STM/STS and Photoemission Spectroscopy 1

Frédéric Joucken , Yann Tison , Yann Girard , Cyril Chacon , Vincent Repain , Patrick Le Fèvre , 3 3 2 4 4 4 Antonio Tejeda , Amina Taleb , Sylvie Rousset , Sergey Babenkov , Victor Aristov , Olga Molodtsova , 5 1 1 1 2 Ed Conrad , Robert Sporken , Luc Henrard , Jacques Ghijsen and Jérôme Lagoute Contact: frederic.joucken@unamur.be 1

PMR, Université de Namur, Namur, Belgique MPQ,STM team, Université Paris-Diderot, Paris, France, 3 Ligne Cassiopée, Synchrotron Soleil, Saint-Aubin, France 4 Beamline P04, PETRAIII, Hamburg 5 GeorgiaTech, Atlanta, USA 2

Tuning the electronic properties of low dimensional carbon materials is a current challenge for the development of carbon based technology. Doping by insertion of foreign atoms in the atomic lattice is a promising strategy to reach the control of the electronic structure of carbon materials. Nitrogen atoms are good candidates for chemical doping due to their suitable atomic radius and the additional electron that they contain as compared to carbon. They can adopt different local environments (graphitic-like, pyridiniclike) which can have various effects on the electronic structure [1]. For the particular doping method we use (i.e. exposure of the epitaxially grown graphene to an atomic nitrogen flux), we combine STM imaging and tunnelling spectroscopy [2] with Angled-Resolved Photoemission Spectroscopy (performed at the Cassiopée beamline at the synchrotron Soleil), to correlate the configuration of the nitrogen atoms in the graphene lattice with their observed effect on the band structure and compare it with the result of DFT-based calculations. We also evaluate the number of charge carriers brought by each doping atom and its evolution as a function of the nitrogen concentration. We will point out difficulties in determining those quantities arising when one is dealing with heavily doped samples. A direct comparison between STS measurements and ARPES measurements will reveal the importance of taking into account the gap in the STS spectra induced by the absence of the phonon-mediated channel, as put forward by Zhang et al. [3] Finally, XPS results and in particular the puzzling evolution of the N1s peak relative intensity as a function of the photon energy, which is not what one expects for nitrogen present at the extreme surface, will be presented and discussed.

References [1] B. Zheng, P. Hermet, L Henrard, ACS Nano, 7 (2010) 4165 [2] F. Joucken et al., Phys. Rev. B 85, (2012) 161408(R) [3] Y. Zhang et al., Nature Phys. 4, (2008) 627

Band Gap Engineering in Graphene Nanomeshes Ferran Jovell, Xavier CartoixĂ 'HSDUWDPHQW GÂś(QJLQ\HULD (OHFWUzQLFD 8QLYHUVLWDW $XWzQRPD GH %DUFHORQD %HOODWHUUD 6SDLQ Ferran.Jovell@uab.cat Abstract Despite having an extremely high carrier mobility [1], the straightforward use of graphene in digital electronics industry is precluded, among other factors, by its semimetallic character. Thus, great efforts have been made in order to open a gap in graphene and render it a semiconductor. These include adding an extra dimension of confinement, obtaining graphene nanoribbons (GNRs) [2], electrostatic patterning [3], chemical decoration [4], etc. Another possibility that has been reported in order to open a gap in graphene is the use of nanolithographic patterning to define an antidot lattice [5,6], also called a graphene nanomesh (GNM), where a periodic arrangement of (possibly passivated) holes is defined onto a graphene layer. We will present first-principles studies of the effect of hole shape, size, pitch, passivation and lattice type on the band structure of GNMs. We acknowledge financial support by the Spanish Ministerio de EconomĂa y Competitividad under Project No. TEC2012-31330. Also, the research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement No. 604391 Graphene Flagship.

References [1] Xu Du, Ivan Skachko, Anthony Barker and Eva Y. Andrei, Nature Nanotechnology (2008), 3:491 495 [2] L. Brey and H. A. Fertig, Phys. Rev. B (2006) 73:235411 [3] Jeroen B. Oostinga, Hubert B. Heersche, Xinglan Liu, Alberto F. Morpurgo & Lieven M. K. Vandersypen, Nature Materials (2007) 7:151 Âą 157 [4] Xiaochen Dong, Yumeng Shi, Yang Zhao, Dongmeng Chen, Jun Ye, Yugui Yao, Fang Gao, Zhenhua Ni, Ting Yu, Zexiang Shen, Yinxi Huang, Peng Chen, and Lain-Jong Li, Phys. Rev. Lett. (2009) 102:135501 [5] Jingwei Bai, Xing Zhong, Shan Jiang, Yu Huang and Xiangfeng Duan, Nature Nanotechnology (2010) 5, 190 Âą 194. [6] H. Sahin and S. Ciraci, Phys. Rev. B (2011) 84, 035452.

Figures

Fig. 1: Relaxed 6x6 graphene supercell with C12 holes (12 C atoms removed) in a hexagonal lattice arrangement.

Fig. 2: Band diagram corresponding to the structure in Fig. 1. The band with low dispersion right above the Fermi level corresponds to hole edge states.

Fig. 3: Wavefunction isosurface plot for the LUMO in Fig. 2. Its low dispersion in the band diagram and the preferential localization of the wavefunction indicate that it is an edge state. Blue (red) indicates positive (negative) phase.

White-graphene sections confined in Graphene nano-flakes. Toward a novel class of 2-D systems bearing extraordinary first order dipolar/octupolar non-linear optical responses P. Karamanis*, NicolĂĄs Otero, Claude Pouchan Groupe de Chimie ThĂŠorique et RĂŠactivitĂŠ, ECP, IPREM CNRS-UMR 5254, UniversitĂŠ de Pau et de 3D\V GH OÂś$GRXU +pOLRSDUF 3DX 3\UpQpHV DYHQXH GX 3UpVLGHQW $QJRW 3$8 &HGH[ Âą France. Panaghiotis.Karamanis@univ-pau.fr Abstract A proof-of-concept about a novel way of designing two dimensional based systems of exceptionally large first order non-linear optical (NLO) activity is presented. The proposed route has been inspired by the recent advances in synthesis of a novel type of graphene hybrid in which finite sections of Âłwhite grapheneÂ´ (c.c hexagonal boron nitride, h-BN) are confined in larger sections of pure graphene. The so called graphene/h-BN hybrids have been grown already as a part of numerous attempts to open the zero band gab of graphene at the Fermi level by creating asymmetric electron and hole conduction with simultaneous negative-type (with Nitrogen) and positive-type (with Boron) chemical doping [1-3]. In this communication it is demonstrated by means of quantum chemical methods, (Ab initio, Density Functional) that finite sections of such hybrids can be utilized to assemble a very handy toolbox of

2-dimensional

graphene

based

nanoobjects

characterized

extraordinary

first

order

hyperpolarizabilities. In particular, it will be revealed that such two dimensional architectures, are extremely promising for applications where high rated octupolar first hyperpolarizabilities are required. Octupolar molecules, bearing large octupolar NLO responses have been the subject of intense studies in the past mainly by Lehn, Zyss and co-worker[4-5] as very promising candidates for NLO materials allowing one to optimize the trade of between transparency and efficiency, achieving at the same time a non symmetric crystallization due to the absence of permanent electric dipole moment. A representative collection of the model systems to be discussed is given in Fig. 1. Among them one can distinguish h-BN-C222 which in its pristine form can be obtained from cyclodehydrogenation of polyphenylenes. Such systems containing small B24N24 domains embedded in graphene are feasible to synthesize using a single step CVD route [2]. As it will be shown, their NLO properties may reach easily 5

an order of magnitude of 10 atomic, while, with the proper modification, the threshold of 10 atomic units can be crossed. The resolved polarization mechanism points out that the charge transfer process in the excited states, responsible for the predicted responses, relies heavily on the particularities of the BN-graphene hetero-junction. What is more, the outcomes of extended structure-property investigation in systems up to 4.5 nm performed in our lab expose a remarkable correlation between of the position and the shape of the BN section in the hybrid flake and the delivered NLO response. Secondary parameters (but also important) are the total shape and size of the flake itself.

References [1] L. Ci, L. Song, C. Jin, D. Jariwala, D. Wu, Y. Li, A. Srivastava, Z. F. Wang, K. Storr, L. Balicas, F. Liu, and P. M. Ajayan, Nature Materials, 9, (2010) 430. [2] S. M. Kim, A. Hsu, P. T. Araujo, Y.-H. Lee, T. Palacios, M. Dresselhaus, J.-C. Idrobo, K. K. Kim, and J. Kong,Â´ 1DQR /HWW 13, (2013) 933. [3] G. Bepete, D. Voiry, M. Chhowalla, Z. Chiguvare, and N. J. Coville, Nanoscale, 5, (2013) 6552. [4] J. Zyss, I. Ledoux, Chem. Rev. 94, (1994) 77.

[5] [1]T. Verbiest, K. Clays, C. Samyn, J. Wolff, D. Reinhoudt, and A. Persoons, J. Am. Chem. Soc., 116, (1994) 9320.

Figure. 1. Structures of hybrid h-BN/graphene flakes and correlations between structure and first hyperpolarizability.

Graphene based materials for energy storage and conversion systems Emine Kayhan, Co-Authors TUBITAK MAM Energy Institute, Baris Mah. Dr. Zeki Acar Cad. No:1 P.K. 21, Kocaeli, TURKEY emine.kayhan@tubitak.gov.tr Graphene has attracted intense scientific interest due to its exceptional electrical, mechanical and chemical properties over the last couple of years. This strictly two-dimensional (2D) material has 1 potential applications in advanced electronic devices and composite materials. The challenge is to produce large area defect-free graphene necessary for electronic applications while bulk-production at gram scale of graphene with defects enabling anchoring sites for nanoparticles is required for applications like catalysis2. Graphene finds potential applications as an electrode material in electrochemical applications such as batteries and supercapacitors. Layered nature of graphene acts as a barrier against aggregation of nanoparticles in the electrode material. To illustrate, the use of chemically derived graphene (or reduced graphene oxide (CDG or RGO)) based materials as anode or cathode in Li-ion and metal-air battery technology promotes the improvement in the recent field due to the large surface-to-volume ratio and highly conductive nature of graphene. The formation of nanopores and disorders in the CDG through chemical synthesis promotes as lithium insertion active sites that are crucial in battery and supercapacitor technology. So the process fastens in the presence of graphene in the electrode (Figure 3 1, A) . In addition, both anode and cathode of a battery might become bendable due to the flexibility 4 feature of graphene (Figure 1, B) . Herein, we report chemical synthesis of graphene that is established by oxidation of graphite to graphite oxide (GO) and followed by reduction process. Prior to reduction, GO is N-doped and B-doped in order to provide defects on the surface. Then, doped-GO is introduced to porous nickel foam to get 3D-porous doped GO. The aim of the work is to synthesize graphene/metal (Si, Sn and Ge), graphene/metal oxide nanoparticles (SnO2, FexOy, CoxOy, MnxOy and CuxOy) and graphene/polimer (polyaniline and polypyrrole) based hybrid materials and use them as anode active in lithium-ion battery, as cathode active material in metal-air battery and as electrode in supercapacitor. References [1] E. Kayhan, R. M. Prasad, A. Gurlo, O. Yilmazoglu, J. Engstler, E. Ionescu, S. Yoon, A. Weidenkaff and J. J. Schneider, Chemistry ± A European Journal, 18 (2012) 14996-15003. [2] Ö. Metin, E. Kayhan, S. Özkar and J. J. Schneider, International Journal of Hydrogen Energy, 37 (2012) 8161-8169. [3] X. Zhao, C. M. Hayner, M. C. Kung and H. H. Kung, Advanced Energy Materials, 1 (2011) 10791084. [4] N. Li, Z. Chen, W. Ren, F. Li and H.-M. Cheng, Proceedings of the National Academy of Sciences, 109 (2012) 17360-17365.

Figures

Figure 1: Examples of CDG graphene-based electrodes in Li-ion battery. A. Si/Graphene as an anode3 B. Flexible Li4Ti5O12 /Graphene Anode and LiFePO4 /Graphene Cathode4

Atomic and topographic corrugations of graphene on 6H-SiC(0001) derived from Grazing Incidence Fast Atom Diffraction 1

1,2

H. Khemliche , A. Zugarramurdi , M. Debiossac , P. Lunca-Popa , A. Mayne , A. Momeni , A.G. 1 1 Borisov , P. Roncin 1

Institut des Sciences Moléculaires d'Orsay, CNRS/Université Paris-Sud, F-91405 Orsay, France 2 Université de Cergy-Pontoise, 33 Boulevard du Port, F-95031 Cergy, France hocine.khemliche@u-psud.fr

Abstract The exceptional properties of graphene and the prospect to use it as the new material for next generation micro- and nano-electronic devices are still waiting for major advances in the production methods in terms of scaling and cost. Current efforts to develop an effective process for producing large samples of high quality graphene could be made easier if characterization techniques, which provide reliable information on sensitive properties such as geometric corrugation, domain size, number of layers and their relative orientation, were able to operate in situ or if possible in real time during the growth process. Supported graphene most often exhibits a Moiré superstructure that originates from local anchoring of the graphene layer onto the substrate. The corresponding corrugation, of geometric origin and which provides a good estimate of the coupling strength between the carbon layer and the substrate, has a strong influence on the graphene properties. For instance the relationship between corrugation and thermal stability of graphene/Re(0001) has been demonstrated [1]. Yet precisely quantifying the corrugation of the Moiré has not become systematically accessible. As an illustration, figures of the superstructure corrugation of graphene grown on Ru(0001) differ substantially whether you consider density-functional-theory calculations [2], STM [3], XRD [4] or Helium Atom Scattering (HAS) [5]. Here we propose another method, Grazing Incidence Fast Atom Diffraction (GIFAD) [6,7], to reliably derive both atomic and geometric corrugations with high sensitivity. Physically, GIFAD is very similar to the technique used by Borca et al. [5]. However GIFAD uses helium atoms in the keV energy range in a scattering geometry comparable to that of RHEED; the diffraction pattern is recorded at once on a position sensitive detector and the image captured by a CCD camera. Figure 1 shows diffraction patterns measured with 300 eV He on a single layer graphene grown on 6HSiC(0001). The intrinsic atomic corrugation is observed along the zig-zag (right-hand side) direction, while the topographic corrugation of the Moiré superstructure is observed along the armchair (left-hand side) direction. We measure a period of 2.13 Å for graphene atomic structure; the period measured along the armchair direction yields a value of 16 Å, i.e. the 13x13 phase of graphene, which is of the SiC(0001) [8]. commensurate with the GIFAD probes the interaction potential, averaged along the beam direction, between the incident He atom and the surface. We describe the He-surface interaction using a Lennard-Jones He-C pair-wise potential [9] that has been optimized to reproduce HAS data on graphite. We have considered a graphene layer frozen at its equilibrium position [10] and calculated the diffracted intensities with a close coupling code described in [11]. Without any adjustment, the calculated diffraction probabilities in the zig-zag direction are comparable to the measured values, thus providing confidence on the validity of the potential. The Moiré structure is introduced by modulating the atom vertical positions on a 13x13 superlattice according to a model-corrugation adjusted to the ab initio data reported by Varchon et al. [12]. In this case, the calculated diffraction probabilities along the armchair direction do not reproduce the experimental data. However a good agreement is achieved if the Moiré corrugation from Varchon et al. is scaled by a factor 0.7. Figure 2 shows the atomic structure that best fits our diffraction data, the corresponding geometric corrugation is 0.275 0.02 Å. These results demonstrate the capability for GIFAD for resolving the structure of epitaxial graphene. The GIFAD sensitivity, together with its ability to operate at high temperatures makes this technique a good candidate for real time monitoring of graphene growth. References [1] E. Miniussi et al. Phys. Rev. Lett. 106, (2011) 216101 [2] D. E. Jiang, M. H. Du, and S. Dai, J. Chem. Phys. 130, (2009) 074705 [3] S. Marchini, S. Günther, and J. Wintterlin, Phys. Rev. B 76, 075429 (2007)

[4] D. Martoccia, M. Bjรถrck, C.M. Schleptz, T. Brugger, S.A. Pauli, B.D. Patterson, T. Greber and P.R. Willmott, New J. Phys 12, 043028 (2010) [5] Borca et al., New Journal of Physics 12, (2010) 093018 [6] H. Khemliche, P. Rousseau, P. Roncin, V.H. Etgens, and F. Finocchi, Appl. Phys. Lett. 95, (2009) 151901 [7] H. Winter, and A. Schller, Prog. Surf. Sci. 86, (2011) 169. [8] C. Riedl, C. Coletti, and U. Starke, J. Phys. D: Appl. Phys. 43, (2010) 374009 [9] W.E. Carlos, and M.W. Cole, Surf. Sci. 91, (1980) 339 [10] J.R. Manson, Theoretical Aspects of Atom-Surface Scattering, edited by E. Hulpke, Springer Series in Surface Sciences, Vol.27 (Springer-Verlag, Berlin, 1992) [11] A. Zugarramurdi, and A.G. Borisov, Phys. Rev. A 87, (2013) 062902 [12] F. Varchon, P. Mallet, J.-Y. Veuillen, and L. Magaud, Phys. Rev. B 77, (2008) 235412

Figures

Fig. 1. Diffraction patterns measured with 300 eV He along the armchair (left) and ziz-zag (right) directions. The bottom profile is the horizontal projection of the diffraction pattern.

Fig. 2. Constant-height image of the He-graphene potential-map following optimization on the experimental diffraction data.

Graphene Field Effect Transistors on SiC with T-Shaped Gate: Homogeneity and RF performance M. S. Khenissa, D. Mele, M. M. Belhaj, I. Colambo, E. Pallecchi, D. Vignaud and H. Happy Institute of Electronics Micro and Nanotechnologies, Avenue Henri Poincaré, Villeneuve d¶Ascq, France ms.khenissa@ed.univ-lille1.fr Abstract Due to its very high carrier mobility, carrier saturation velocity, large critical current density [1-3], and the ultrathin body allowing channel length scaling without the non-ideal short channel effect [4-5], graphene has attracted enormous attention in recent years for radiofrequency transistor applications for postsilicon electronics [6]. Here we present field effect transistors (FETs) fabricated on a 1/4 of 2-inch graphene wafer where the homogeneity of the GFETS realized across the whole substrate was studied. Epitaxial graphene is synthesized on semi-insulating 4H-SiC wafers by thermal decomposition. The graphene is grown in a UHV chamber on the Si-face of the substrate at 1150° C under a Si flux. The number of layers and the quality of the graphene are characterized by Raman spectroscopy. As shown -1 in figure (1), the characteristic Raman spectrum of graphene includes a narrow G-peak (1580 cm ) and -1 a single Lorentzian 2D-peak (2685 cm ). The number of layers is estimated from the intensities ratio I2D/IG to be around 4 layers. Structures for the Hall Effect Measurements were fabricated to measure the Hall mobility µ and the sheet carrier concentration ns at 300° K in a Bridge configuration. The values of mobility and the sheet carrier concentration are respectively 780 cm2/v.s and 8.7 10+12 /cm2. The contact and sheet resistivity of the Ni/Au (10nm/40nm) stacking were determined by the Transmission Line Method. The values were extracted from the curve shown in figure 2, ȡc = 2.1 x 10-6 /cm2 and ȡsh = 800 /sq. We fabricated GFETs with a T-shaped gate to reduce the gate access resistance. The fabrication process flow is shown in the schematic diagram of figure (3-a). The graphene was patterned by e-beam lithography. The source and drain contacts of Ni/Au were obtained by e-beam evaporation metal deposition and standard lift-off. After the deposition of 2 nm of Al which was left to oxidize in air, 10 nm of Al2O3 were deposited by ALD at 300° C, to be used as a high k gate dielectric. We employed a standard trilayer resist E-beam lithography to realize T-shaped gates. Finally, coplanar accesses were realized. Figure (3-b) shows a scanning electron microscope (SEM) image of a full device and a cross section of a 170 nm T-shaped gate. The devices were characterized both at DC and microwave frequency. The output characteristics of a graphene FET with Lg = 170 nm and W = 12 µm using are shown in figure (4) and the evolution of the transconductance gm is shown in figure (5). An output current of 25 mA as well as a transconductance of 2.6 mS are achieved at Vd = 2 V. The RF performances of our GFET transistors were characterized by measuring S-parameters with a power network analyzer PNA (HP AGILENT 8510C) over the frequency range of 0.05 to 67 GHz under ambient conditions. The calibration of the measurement to the probe tips was performed by using LRRM calibration method. Based on our graphene layer, the typical bias condition are for the gate electrode Vgs= -3 V, and for the drain electrode Vds= 3 V since this condition provides gm= 2.9 mS, as confirmed by DC measurement. Figure 6 presents both of the extrinsic (before de-embedding) and intrinsic (after de-embedding) current gain (H21) and maximum available gain (MAG) frequency response of the same graphene RF transistor measured on DC. Figures 7 and 8 shows the number of the devices providing ft and fmax in each range of frequency. We can remark that the majority of devices feature frequencies between 21 GHz and 34 GHz for ft and between 12 GHz and 21 GHz for fmax reflecting the homogeneity of our graphene and technological process. An intrinsic cut-off frequency ft as high as 43 GHz has been obtained and the maximum value of fmax is 23 GHz. References [1] Novoselov, K. S. et al. Nature, 438 (2005) 197±200. [2] Zhang, Y. B., Tan, Y. W., Stormer, H. L. & Kim, Nature, 438 (2005) 201±204. [3] Berger, C. et al. Science, 312 (2006) 1191±1196. [4] H. Xu, ACS Nano., vol. 5, n°3 (2012) 2340 -2347. [5] S.-J. Han, IEEE Electron Device Lett., vol. 32 (2011) 812 -814. [6] Wu et al., Proc. IEEE, vol. 101, no 7 (2013) 1620-1637. [7] N. Meng, IEEE Transactions on Electron Devices, vol. 58, n°6 (2011) 1594 ± 1596

Figures

figure 1 : Raman spectra of Si-face few-layer graphene on SiC showing the G and 2D graphene peaks.

figure 2 : Resistance versus distance R(d) curve for a TLM structure.

figure 4 : Output characteristics of a graphene FET with Lg= 180 nm and W= 12 Âľm

figure 3 : a) process flow for GFET fabrication b) scanning electron microscope (SEM) image of a full device and a cross section of T-shaped gate

fmeasured fmax = 23 GHz ft_intr = 33 GHz

figure 5 : Number of devices in each range of gm transconductences, a value of 2.9 mS has been achieved.

figure 7 : Number of devices in each range of fmax frequencies, a maximum oscillation frequency fmax of 23 GHz has been obtained.

figure 6 : GFET Current and power gain versus frequency for the device with Lg= 170 nm and W= 12 Âľm Bias point Vgs= -3 V, Vds= 2 V with ft = 33 GHz and fmax = 19.5 GHz.

figure 8 : Number of devices in each range of ft frequencies, an intrinsic cut-off frequency ft of 43 GHz has been obtained

Local Anodic Oxidation of Graphene Using Atomic Force Microscope and its Effect on Electrical Properties. Cheol Kyeom Kim, Dukhyun Lee, Mijung Lee, Sangik Lee, Chansoo Yoon, Dayea Oh, Baeho Park 1

Department of physics, Konkuk University, 120 neungdong-ro, Gwangjin-gu, seoul, korea herskiss84@gmail.com Abstract

Graphene has generated great interest since its discovery in 2004 due to its unusual and potentially useful electrical, chemical, mechanical, and optoelectronic properties. However, a major challenge in graphene research is to develop reliable and facile methods for tuning its properties for applications in electronics, optics, and sensing. In particular, numerous approaches for adjusting the electrical properties of graphene have been investigated, including electrical gating, size constriction, and the generation of defect states. In this study, we have formed graphene oxide (GO) lines with different widths on exfoliated graphene under different conditions by using atomic force microscope (AFM) lithography.[1] Local current and friction force images were obtained between adjacent two gold contacts using AFM before and after formation of a GO line which separated the graphene into two parts. Such functionalization with oxygencontaining groups has been demonstrated to be an effective method for changing the chemical potential or even opening a band gap.[2] Furthermore, the tunneling effect of the G/GO/G junction was observed in GO line with a few tens of nanometers width.[3] References [1] Ik-Su Byun, ACS Nano, 5 (8), pp 6417Âą6424(2011). [2] Satoru Masubuchi, Nano Lett., 11 (11), pp 4542Âą4546(2011). [3] Gwan-Hyoung Lee, Appl. Phys. Lett. 99, 243114 (2011) Figures

Superstrong encapsulated monolayer graphene and prevention of water permeation by strong adhesion between graphene and SiO2 1

Wonsuk Jung , Donghwan Kim Joonkyu Park , Taeshik Yoon , Jongho Choi , Taek-Soo Kim , 1 3 2 Soohyun Kim , Yong Hyup Kim , Chang-Soo Han 1. Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea 2. School of Mechanical Engineering, Korea University, Seoul, Republic of Korea 3. School of Mechanical and Aerospace Engineering, Seoul National University, Seoul, Republic of Korea cshan@korea.ac.kr Abstract 1

We report a superstrong adhesive of monolayer graphene by modified anodic bonding . In this bonding, graphene plays the role of a superstrong and ultra-thin adhesive between SiO2 and glass substrates. -2 As a result, monolayer graphene presented a strong adhesion energy of 1.4 Jm about 310% that of -2 2 van der Waals bonding (0.45 Jm ) to SiO2 and glass substrates . This flexible solid state graphene adhesive can tremendously decrease the adhesive thickness from about several tens of mm to 0.34 nm for epoxy or glue at the desired bonding area. As plausible causes of this superstrong adhesion, we suggest conformal contact with the rough surface of substrates and generation of CÂąO chemical bonding between graphene and the substrate due to the bonding process, and characterized these properties using optical microscopy, atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Additionally, this thermo-electrostatic bonding method could increase the adhesion energy of graphene to the substrate for reducing the influence of water permeation between graphene and its substrate. We characterized humidity effects on graphene using resistance measurements, atomic force microscopy and Raman spectroscopy. The results indicated that the strongly bonded graphene could be used to significantly reduce water permeation and improve device 3 durability . References [1] W. Jung, T. Yoon, J. Choi, S. Kim, Y. H. Kim, T.-S. Kim and C.-S. Han, Nanoscale, 6 (2014) 547. [2] S. P. Koenig, N. G. Boddeti, M. L. Dunn, J. Scott Bunch, Nature Nanotech., 6 (2011) 543 [3] W. Jung, J. Park, T. Yoon, T.-S. Kim, S. Kim and C.-S. Han, Small, online published,PMID:24339270 (2013) Figures

Fig. 1 Modified anodic bonding using monolayer graphene adhesive: (a) schematic description of the newly suggested bonding method. (b) The case of strong bonding shows the transparent graphene area on the SiO2. (c) On the other hand, if the sample is not bonded or has low bonding energy, there is a NewtonÂśs ring at the graphene area. (d) This cross-sectional image shows the composition of the sample and flexible interaction of graphene between the glass and SiO2/Si.

Fig. 2 After 8585 humidity test (85 C, 85 % relative humidity), while non-bonded samples exhibited significant changes in properties, the bonded graphene samples maintained their initial properties.

Photoemission Electron Microscopy Investigation of Iodine Doped Graphene 1

HoKwon Kim , Anastasia Tyurnina , Jean-Pierre Simonato , Jean Dijon , Denis Rouchon , Denis 1 1 1 Mariolle , Nicolas Chevalier , and Olivier Renault 1 CEA, LETI, Minatec Campus, 38054 Grenoble, France, 2 CEA, LITEN, Minatec Campus, 38054 Grenoble, France. hokwon.kim@cea.fr Abstract Graphene has a great potential in a wide range of electronic applications such as electrochemical cells, photovoltaics, and flexible transparent displays due to its exceptional properties. The large surface area, high charge carrier mobility, exceptional mechanical strength, and chemical stability of graphene make it especially promising as an electrode material. Large scale proof-of-concept devices such as photovoltaic cells, organic electrochemical cells, and supercapacitors have already been demonstrated by high quality large area graphene produced by chemical vapor deposition (CVD) [1] and solution based methods [2]. The current challenge in the area of graphene based electrodes is that intrinsic graphene itself has a low electrical conductivity due to its low density of states at the Fermi level giving sheet resistance as high as ~ Nȍ [3]. In order to address this issue, various doping methods have been investigated that can significantly increase the charge carrier concentrations in graphene. One of the common doping methods is the chemical modification of graphene where covalent functionalization by hole/electron donating species such as fluorine, nitrogen, and hydrogen improves the conductivity of the chemically modified graphene [4]. However, this method introduces crystalline defects through the 2 disruption of sp hexagonal lattice that alter the electronic structure and reduce the carrier mobility values limiting the doping effectiveness. An alternative approach is the attachment of surface adsorbates through physisorption that leads to surface charge transfer between the dopant and graphene. Weakly interacting molecules such as H2SO4, HNO3, HCl, and Br2 have been investigated as promising candidates for physisorbed dopants [5-7], although the high-temperature and long-term stability of the weakly adsorbed dopants remains an issue [6]. Here, we employ iodine as physisorbed dopants for increasing the hole concentration of graphene produced by CVD method. Iodine has been demonstrated to be a stable and effective dopant for conductive polymers and carbon nanotubes [8, 9]. For graphene, it has been recently shown that iodine can increase the conductivity of single layer graphene film by a factor of 4 [10]. Raman spectroscopy and X-ray Photoelectron Spectroscopy analyses have shown that the doping on graphene is enabled by the formation of anionic charge transfer complexes which mainly consist of I3- and I5- molecules [7]. So far, however, little is known about detailed doping mechanism and the thermal stability of the iodine complexes. Towards this end, we have employed spectroscopic X-ray photoelectron emission microscopy (XPEEM) on a NanoESCA instrument to analyze at high spatial- and energy resolution the chemical nature of graphene iodine interaction and the effect of in-situ thermal annealing on the transferred CVD graphene 2-probe device on SiO2/Si substrate (Fig. 1a). The work function mapping measurements performed by UV photoemission threshold spectroscopy and Kelvin force microscopy (KFM) before and after I2 doping on an heterogeneous area consisting of single (1L) and folded bilayer (2L) graphene domains have shown that iodine can strongly p-dope graphene with a greater effect on the double layer regions (Fig. 1b, c). This is corroborated by I 3d5/2 core level imaging of the same area where the double layer has significantly larger concentration of iodine (Fig. 1d). We also confirm the presence I3 and I5 anionic charge transfer complexes via high energy resolution core level spectroscopy for both 1L and 2L graphene. Further work function and core level analysis of iodine doped graphene immediately followed by in-situ annealing (Fig. 2) has shown that iodine on graphene is stable up to 250 °C where most of iodine is removed at annealing temperature greater than 300 °C, although a significant removal of iodine is observed for 2L graphene starting from 100 °C. Surprisingly, after the complete removal of iodine, the work function of the annealed graphene does not return to that of the graphene sample before the doping treatment. This is ascribed to the residual hydrocarbons due to exposure of the sample in air that appear to act as unintentional n-type dopants in our samples prior to doping [11]. Our work on the doping mechanism and the thermal stability of iodine on graphene provides guidelines for controllably tuning the electronic properties of graphene as well as evaluating potential dopants for graphene based systems for practical applications.

Acknowledgement: The XPEEM and KFM measurements were performed at the Nanocharacterization Platform (PFNC). References [1] L. Gomez De Arco, Y. Zhang, C.W. Schlenker, K. Ryu, M.E. Thompson, C. Zhou, ACS Nano, 4 (2010) 2865-2873. [2] L.L. Zhang, R. Zhou, X.S. Zhao, J. Mater. Chem., 20 (2010) 5983-5992. [3] A. Lherbier, X. Blase, Y.-M. Niquet, F. Triozon, S. Roche, Phys. Rev. Lett., 101 (2008) 036808. [4] H. Liu, Y. Liu, D. Zhu, J. Mater. Chem., 21 (2011) 3335-3345. [5] S. Bae, H. Kim, Y. Lee, X. Xu, J.-S. Park, Y. Zheng, J. Balakrishnan, T. Lei, H. Ri Kim, Y.I. Song, Y.J. Kim, K.S. Kim, B. Ozyilmaz, J.-H. Ahn, B.H. Hong, S. Iijima, Nat. Nanotechnol., 5 (2010) 574-578. [6] W. Zhao, P. Tan, J. Zhang, J. Liu, Phys. Rev. B, 82 (2010) 245423. [7] N. Jung, A.C. Crowther, N. Kim, P. Kim, L. Brus, ACS Nano, 4 (2010) 7005-7013. [8] L. Grigorian, K.A. Williams, S. Fang, G.U. Sumanasekera, A.L. Loper, E.C. Dickey, S.J. Pennycook, P.C. Eklund, Phys. Rev. Lett., 80 (1998) 5560-5563. [9] A.B. Kaiser, Reports on Progress in Physics, 64 (2001) 1. [10] S.W. Chu, S.J. Baek, D.C. Kim, S. Seo, J.S. Kim, Y.W. Park, Synthetic Metals, 162 (2012) 16891693. [11] B.H. Kim, S.J. Hong, S.J. Baek, H.Y. Jeong, N. Park, M. Lee, S.W. Lee, M. Park, S.W. Chu, H.S. Shin, J. Lim, J.C. Lee, Y. Jun, Y.W. Park, Sci. Rep., 2 (2012). Figures (a)

(b)

SiO2

Au (c)

W. F. 5.0

I3d5/2

(d)

4.9

4.8 4.7 4.6 4.5 (eV)

Fig. 1. (a) Optical microscope image of transferred graphene film on Si/SiO 2 with circular Au electrodes for electrical measurements. Scale bar = 200 µm. (b) Energy-filtered secondary electron PEEM image of the area defined by the green rectangle in a) with regions of 1L, overlapped 2L graphene, Au electrode, and exposed SiO2 substrate. hQ = 6.2 eV, D2 lamp; Ek = 4.9 eV; field of view (FOV) = 98 µm. (c) Work function (W. F.) map of the identical region in b). FOV = 98 µm. (d) Integrated I3d 5/2 core level (E b ~ 619 eV) peak area image on the identical area as Fig. 1 b). hQ = 1486.6 eV; FOV = 67 µm.

2.5

work function (eV)

4.6 2.0

4.5 1.5

4.4

1.0

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4.2

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WF before doping

4.1

0.0

as doped

100 C

150 C

200 C

250 C

iodine atomic concentration (%)

3.0

1L 2L

4.7

300 C

Fig. 2. Annealing temperature dependence of work function and iodine concentration for 1L and 2L graphene regions.

Ultrafast Detection of Carrier Relaxation in Graphene Quantum dots 1

1,2

Ji-Hee Kim , Hyo Jung Kim , Junichiro Kono , Pulickel M. Ajayan , Mun Seok Jeong

1,2

Center for Integrated Nanostructure Physics, Institute of Basic Physics, Sungkyunkwan University, Suwon, Republic of Korea 2 Department of Energy Science, Sungkyunkwan University, Suwon, Republic of Korea 3 Department of Electrical and Computer Engineering, Rice University, Houston, TX, USA 4 Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX, USA kimj@skku.edu

Abstract Graphene quantum dots (GQDs) have been recently fabricated with the size smaller than 4 nm using acidic exfoliation and etching of pitch carbon fibers, leading to bandgap opening at the K-point [1]. While fabricated GQDs, however, one cannot expect pure GQDs due to oxidation or other functional groups. Therefore the carrier dynamics in GQDs is affected by those defects. For further optical and optoelectronic applications, it is important to investigate the dynamics of both photoexcited carriers and defects that might interrupt the carrier relaxation in GQDs. Transient absorption (TA) spectroscopic technique is one of the powerful tools to study the dynamics of carriers and defects [2,3]. Using femtosecond TA technique, we have studied the photoexcited carrier distribution, and the unusual photo-bleaching behavior by detects, such as hydroxyl groups, which occurred on the femtosecond time scale. We performed TA spectroscopy with different excitation energies, tuned by using an optical parametric amplifier (OPA) which pumped by a Ti:sapphire regenerative amplifier of 1-kHz repetition rate. The pulse duration of OPA was around 200 fs, and 5 Č?J energy per pulse were used. TA signal was probed by white light continuum (WLC) in visible range from 450 to 750 nm (1.65 eV~2.75 eV). In order to generate WLC, the Ti:sapphire amplifier with 800 nm (1.55 eV) center wavelength was focused on a sapphire window. Figure 1 shows spatially and temporally resolved TA map in GQDs, excited above resonance and at resonance, respectively. Above resonance shown in Fig. 1(a), snapshots of hot carrier distribution in GQDs after laser excitation can be obtained by photo-induced absorption. At resonance shown in Fig. 1(b), the strong photobleaching behavior is shown in earlier delay time. The bleached energy state appears below 400 meV from the excitation energy. The energy difference corresponds to the energy of hydroxyl groups. It implies that the photoexcited carriers might be captured at the site of hydroxyl groups, and it takes less than 1 picosecond. In order to understand this behavior, we compared our data obtained from GQDs with that from large size of pristine graphene. We also annealed GQD o o sample at 200 C, and 600 C to remove the defects. Furthermore, we measured the excitation power dependence, and the carriers decay within 1 ~ 10 picosecond when the excitation power is higher References [1] Juan Peng, Wei Gao, Bipin Kumar Gupta, Zheng Liu, Rebeca Romero-Aburto, Liehui Ge, Li Song, Lawrence B. Alemany, Xiaobo Zhan, Guanhui Gao, Sajna Antony Vithayathil, Benny Abraham Kaipparettu, Angel A. Marti, Takuya Hayashi, Jun-Jie Zhu, and Pulickel M. Ajayan, Nano Lett., 12 (2012) 844. [2] Qun Zhang, Hongju Zheng, Zhigan Geng, Shenlong Jiang, Jing Ge, Kaili Fan, Sai Duan, Yang Chen, Xiaping Wang, and Yi Luo, J. Am. Chem. Soc, 135 (2013) 12468. [3] Sreejith Kaniyankandy, S. N. Achary, Sachin Rawalekar, and Hirendra N. Ghosh, J. Phys. Chem. C 115 (2011) 19110.

Figures

Figure 1 Spatially and temporally resolved transient absorption map in graphene quantum dots, excited (a) above resonance of 350 nm (3.54 eV), and (b) at resonance of 520 nm (2.38 eV), respectivley. Č?- energy per pulse were used.

Electrical and optical characterization of field-effect transistors containing graphene layers doped with HNO3, AuCl3, and RhCl3 Ju Hwan Kim, Kyeong Won Lee, Jong Min Kim, Dong Hee Shin, Sung Kim, Suk-Ho Choi Department of Applied Physics, Kyung Hee University, Yongin 446-701, Korea sukho@khu.ac.kr Abstract Doping graphene is currently one of the most important issues to be solved in the fundamental studies and applications of graphene. Tuning of electrical and optical properties in graphene, of great importance to realize graphene-based electronics/photonics, can be done by doping because the doping leads to a shift of the Fermi level. Chemical doping extensively employed to make graphene nor p-type by using various adsorbates involves charge transfer between the adsorbates and the graphene [1]. For instance, HNO3, AuCl3, and RhCl3 have been widely used as a p-type dopant in which electrons are extracted from graphene into the adsorbates [2]. There have been several reports on fabrication and characterization of doped graphene layers [2-4], but very few attempts have been made to study how the doping effect varies depending on the kind of dopant. Here, we employ three dopants, HNO3, AuCl3, and RhCl3 to fabricate p-type graphene layers and compare their structural and electrical properties. Large-scale single-layer graphene was synthesized by using chemical vapor deposition, and subsequently transferred to 300 nm SiO2/p-type Si wafers used as the back gate of graphene field-effect transistors (GFETs). The Cr/Au source and drain electrodes of 0.1 mm length and 0.3 mm separation for GFETs were deposited on the graphene films by using a mask in a RF magnetron sputtering. Single-layer graphene sheets were identified by an optical microscope, and chemically doped with HNO3, AuCl3, and RhCl3 at a concentration of 10mM. By HNO3, AuCl3, and RhCl3 doping, the sheet resistance decreased from 750 to 500, 220, and 350 ohm/sq, and the work function increased from 4.58 to 4.7, 4.8, and 5.2 eV, respectively, indicating p-type graphene [2,5]. To study the influence of the HNO3, AuCl3, and RhCl3 doping on the Raman spectra of graphene films, they were measured under a 532 nm (2.33 eV) laser excitation. As shown in Fig. 1, Raman spectra of the transferred layers exhibited three intense features, D, G, and 2D peaks at

1350,

1580, and

-1

2700 cm , respectively, uniquely characteristic of undoped graphene films. The G and 2D bands -1

were blue-shifted from 1587 to 1592, 1602, and 1596 cm and from 2682 to 2685, 2689, and 2688 -1

cm , respectively, by HNO3, AuCl3, and RhCl3 doping. By currentÂąvoltage measurements, the transfer characteristics (drain current ISD vs back-gate voltage VDG) of the GFETs were compared before and after HNO3, AuCl3, and RhCl3 doping. The threshold voltages of the graphene GFETs were at VDG ~ 6, 30, 58, and 70 V before and after HNO3, AuCl3, and RhCl3 doping, respectively, as shown in Fig. 2. These results are discussed based on possible physical mechanisms. References [1] H. Liu, Y. Liu, and D. Zhua, J. Mater. Chem. 10 (2011) 3253Âą3496

[2] K. C. Kwon , K. S. Choi, and S. Y. Kim, Adv. Funct. Mater. 22 (2012) 4724-4731 [3] K. K. Kim, A. Reina, Y. Shi, H. Park, L.-J. Li, Y. H. Lee, and J. Kong, 28 (2010) 28205. [4] H.-J. Shin, W. M. Choi, D. Choi, G. H. Han, S.-M. Yoon, H.-K. Park, S.-W. Kim, Y. W. Jin, S. Y. Lee, J. M. Kim, J.-Y. Choi, and Y. H. Lee, J. Am. Chem. Soc. 44 (2010) 15603±15609 [5] S. Das, P. Sudhagar, E. Ito, D.-Y. Lee, S. Nagarajan, S. Y. Lee, Y. S. Kang, and W. Choi, J. Mater. Chem. 38 (2012) 20490-20497 Figures

Fig. 1. Raman spectra of undoped and doped graphene layers on SiO2. The doping was done at 10 mM with three different dopants, HNO3, AuCl3, and RhCl3.

Fig. 2. ISD±VBG curves of GFETs containing pristine and doped graphene layers. The doping was done at 10 mM with three different dopants, HNO3, AuCl3, and RhCl3.

Silver nanowire - Graphene oxide hybrid transparent conductive thin film for high mechanical stability and flexibility Ju-Tae Kim, Chang-Soo Han School of Mechanical Engineering, Korea University, Seoul 136-713, Korea cshan@korea.ac.kr Abstract Silver nanowire (Ag NW) network film as transparent conductive electrode is a promising candidate for replacement of indium tin oxide (ITO) film. Also, this film is suitable as an electrode for organic photovoltaics (OPVs), organic light emitting diodes (OLEDs), flexible displays and touch panel. Flexibility and mechanical stability of nanowire films are still problematic to apply to the device. Graphene oxide (GO) could be easily synthesized through the controlled chemical oxidation of graphite. Oxygen functional groups render GO stable and induce homogeneous colloidal suspensions in aqueous and various polar organic solvents. The polar site of GO can induce a strong electrostatic interaction between it and the metal. In this study, we used GO for enhancing the adhesion between Ag NWs. Vacuum filtration process was firstly used to fabricate thin film with mixture of GO and Ag NWs of 50nm diameter. Next, by using welding process, we diminished the contact resistance of Ag NW network without other treatment. We characterized the physical properties of the NWs and transparent film before and after the compression process in terms of scanning electron microscopy (SEM), 4 point probe and UV-visible spectrometer. References [1] D. R. Dreyer, S. Park, C. W. Bielawski, R. S. Ruoff, Chemical Society Reviews, 39 (2010) 228-240. [2] Y. S. Yun, D. H. Kim, B. Kim, H. H. Park, H. J. Jin, Synthetic Metals, 162 (2012) 1364-1368. [3] J. Lee, P. Lee, H. Lee, D. Lee, S. S. Leea, S. H. Ko, Nanoscale, 4 (2012) 6408.

Structural and optical properties of N-doped graphene quantum dots 1

Sung Kim , Dong Hee Shin , Sung Won Hwang , Suk-Ho Choi

Department of Applied Physics, Kyung Hee University, Yongin 446-701, Korea Advanced Development Department, Samsung Electronics Co., Ltd, Yongin 446-711, Korea sukho@khu.ac.kr

Abstract Graphene quantum dots (GQDs) are atomically-thick, conductive nanosheets of sp

hybridized carbons, which exhibit size-, shape-, and edge-dependent electrical/optical properties. [1-3] Therefore, it is essential to be able to engineer the size and edge state of GQDs by their functionalization because this can alter the energy states of GQDs as that of graphene, thereby controlling their properties. Nitrogen (N) atom, having a comparable atomic size and five valence electrons for bonding with carbon atoms, has been widely used for chemical doping of carbon nanomaterials. For instance, doping of graphene with substituent N heteroatoms could effectively modulate the band gap of graphene, thereby exhibiting novel properties for device applications. [4-5] In this work, we studied the effect of N atoms on the structural and optical properties of N-doped GQDs (NGQDs) prepared by hydrothermal cutting of graphene sheets and subsequent hydrazine treatment. Figs. 1(a) and (b) show typical transmission electron microscopy (TEM) images of GQDs and NGQDs. Inset of Fig. 1(a) shows a high-resolution TEM (HRTEM) image of a typical GQD, indicating high crystalline structure with a lattice parameter of 0.244 nm, corresponding to (1120) lattice fringes of graphene. [3,6] It is also possible to see the hexagonal unit cell of GQDs in the magnified HRTEM image, [7] demonstrating that the GQDs consist of graphene. The average sizes of GQDs and NGQDs analyzed from the TEM images are estimated to be 5.03 Âą 0.05 and 5.55 Âą 0.05 nm, respectively. The NGQDs are not only n-type but also larger than undoped GQDs while the edgerelated defects are reduced, resulting from the bonding of the increased pyridinic N atoms with C atoms at the edge of GQDs, as confirmed by Raman spectroscopy and x-ray photoelectron spectroscopy. Fig. 2(a) and (b) show absorption and photoluminescence (PL) spectra of GQDs and NGQDs in the UV to visible ranges. The absorption band of GQDs is peaked at ~300 nm, and after doping they show an additional absorption peak at ~354 nm, originating from the impurity energy level formed by the N doping, as confirmed by electron energy loss spectroscopy. The GQDs emit bright blue PL peaked at 418 nm, and after hydrazine treatment the PL emission is redshifted by ~15 nm and its decay becomes slower, resulting from the N-related impurity level. References [1] N. Mohanty, D. Moore, Z. Xu, T.S. Sreeprasad, A. Nagaraja, A. A. Rodriguez, and V. Berry, Nat. Commun. 3 (2012) 844. .

[2] K. A. Ritter and J. W. Lyding, Nat. Mater. 8 (2009) 235±242. [3] F. Liu , M.-H. Jang , H. D. Ha , J.-H. Kim , Y.-H. Cho, and T. S. Seo, Adv. Mater. 25 (2013) 3657± 3662. [4] H. Liu, Y. Liu, and D. Zhua, J. Mater. Chem. 21 (2011) 3335±3345. [5] F. Cervantes-Sodi, G. Csányi, S. Piscanec, and A. C. Ferrari, Phys. Rev. B 77 (2008) 165427. [6] Y. Liu, and P. Wu, ACS Appl. Mater. Interfaces 5 (2013) í [7] S. Kim, S. W. Hwang, M.-K. Kim, D. Y. Shin, D. H. Shin, C. O. Kim, S. B. Yang, J. H. Park, E. Hwang, S.-H. Choi, G. Ko, S. Sim, C. Sone, H. J. Choi, S. Bae, and B. H. Hong, ACS Nano 6 (2012) 8203±8208.

(b)

25 nm Fig. 1. Transmission electron microscopy images of (a) GQDs and (b) NGQDs.

0.4

(a)

GQDs NGQDs

0.3 0.2 0.1

200 300 400 500 600 700 Wavelength (nm)

1.2

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GQDs NGQDs

0.9 0.6 0.3 0.0

15 nm

DI water

25 nm

Normalized PL intensity (arb. units)

(a)

Absorption (arb. units)

Figures

400 500 600 Wavelength (nm)

700

Fig. 2. (a) Absorption and (b) photoluminescence spectra of GQDs and NGQDs in the UV to visble ranges.

Formaldehyde Sensing Properties of Conducting Polymer-Functionalized Carbon Nanocomposites Yangsoo Kim*, Byung-Chul Moon, Min-Chae Jang, Dept. of Nanoscience and Engineering, Inje University, 607 Obangdong, Gimhae 621-749, Korea *cheykim@inje.ac.kr Abstract There is a growing demand for room temperature chemical sensor detecting volatile organic compounds (VOCs), specifically formaldehyde, with a high sensitivity and selectivity. Polyethyleneimine (PEI) was reported to be effective in sensing formaldehyde due to the interactive affinity between formaldehyde molecules and amine groups of PEI [1]. Multi-walled carbon nanotube (MWNT) and graphene oxide (GO) were chosen as a carbonaceous platform nanomaterial for detecting formaldehyde in this work. PEI was attached to acyl chloride group-modified MWNTs and GOs, respectively. Then the prepared MWNT-PEI and GO-PEI were respectively surrounded with conducting polymer by carrying out an insitu chemical oxidative polymerization. Intrinsically conducting polymers (ICPs) such as polypyrrole (PPy), poly(3,4-ethylenedioxy thiophene) (PEDOT) and polyaniline (PANI) were used for the conducting polymer non-covalent functionalization of MWNT-PEI and GO-PEI. Then the obtained ICPfunctionalized carbon nanocomposites were used as a chemiresistor for the detection of formaldehyde in the closed gas sensing system. Both MWNT-PEI/PEDOT and GO-PEI/PEDOT showed the most excellent sensitivity and selectivity to formaldehyde among the ICP-functionalized carbon nanocomposites. The reason for the enhanced formaldehyde sensing response of them was addressed based on the characterization results. A characterization of ICP-functionalized carbon nanocomposites was made by using Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffractometer, theromogravimetric analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. References [1] X. Wang, B. Ding, M. Sun, J. Yu, and G. Sun, Sensors & Actuators B: Chemical, 144 (2010) 11-17.

60 (Formaldehyde @36ppm)

GO-PEI/PEDOT

(R-R0)/R0 Ă&#x2014; 100

20 GO-PEI GO-PEI

120

180(360)

420

Time

Figure 1. Relative resistance increase of ICP-functionalized MWNT(Left) and GO(Right) nanocomposites when exposed to 36 ppm of formaldehyde.

480

540

Figure 2. TEM microphtographs of PEDOT-functionalized MWNT(Left) and GO(Right) nanocomposites.

110

100

MWNT-COCl 90

Weight(%)

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100

200

300

400

500

600

700

100

200

300

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Temperature( C)

. Figure 3. TGA thermograms of PEDOT-functionalized MWNT (Left) and GO (Right) nanocomposites.

. Figure 4. Experimental setup for formaldehyde sensing.

700

Electrostatic transparency of graphene oxide sheets 1

Cristina E. Giusca , Francesco Perrozzi , Luca Ottaviano , Emanuele Treossi , Vincenzo Palermo 1 Olga Kazakova 1

National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, United Kingdom 2 'LSDUWLPHQWR GL )LVLFD 8QLYHUVLWj GHOOÂś$TXLOD & CNR-63,1 826 /Âś$TXLOD 9LD 9HWRLR /Âś$TXLOD ,WDO\ 3 CNR-ISOF, Via Gobetti 101, 40129 Bologna, Italy - Laboratorio MIST.E-R, Via Gobetti 101, 40129 Bologna, Italy 4 CNR-ISOF, Via Gobetti 101, 40129 Bologna, Italy cristina.giusca@npl.co.uk Abstract *UDSKHQHÂśV GLVRUGHUHG DQDORJXH JUDSKHQH R[LGH (GO), has originally been regarded as a precursor for cost-effective graphene production on a large scale but has become particularly attractive for practical applications based on its intrinsic chemical and electronic structure [1]. As a result of the chemical oxidation and exfoliation of graphite, the as-synthesised GO is an inhomogeneous system consisting of hydroxyl and epoxies functional groups covalently attached to the basal plane of graphene, and carboxylic groups at the edges. The functional groups are randomly adsorbed, giving GO a 2 disordered appearance of small, separated sp clusters of 1 to 5 nm lateral size, embedded within an 3 sp matrix. Due to its defective nature, GO does not retain all of the fundamental two-dimensional properties observed in graphene, however chemical [1, 2], thermal [3], or photo-reduction approaches [4] are usually employed to controllably transform GO into a graphene-like material. For graphene layers, the interaction with the underlying substrate has been extensively studied by theoretical and experimental works [5] and it was found to affect the conductivity, doping level or to significantly impact the noise level in graphene devices. At the same time, the influence of the supporting substrate on the electronic properties of GO and its reduced form has remained largely unexplored. The role of the substrate is important for applications where electronic properties of GO are especially targeted, such as transparent conducting films, sensors and electrochemical devices. In the current study, we probe the interaction of GO of varying reduction degrees with insulating and metallic surfaces using scanning Kelvin probe microscopy (SKPM) and Raman spectroscopy. GO sheets were prepared via the Hummers method and deposited by spin coating on three different substrates: SiO2 on Si(100), Al2O3 on Si(100) and Au. Reduction of GO sheets was achieved by thermally annealing the samples in ultra-high vacuum, at 300Â°C and 600Â°C, respectively, for insulating substrates and at 200Â°C for samples on Au substrates. Individual GO sheets were electrically characterized using SKPM, which also provided information on sample morphology, as well as a clear determination of the number of layers. Representative examples of SKPM showing topography and surface potential maps are presented in Figure1a and 1b, respectively, for a reduced GO sheet deposited on SiO2 and annealed in UHV at 300Â°C. The lower section of the GO sheet is one-layer thick and the upper section is folded with doublefolded edges, as highlighted by topographical cross-sectional profiles (not shown). The topography does not show significant differences between the one- and two-layer areas, however noticeable differences are seen in the surface potential data. A relatively uniform surface potential is measured across the two layer region, whereas significant local variations are observed on the single layer section, of up to 260 mV between the bright and dark regions of the GO layer. The local variations in surface potential are common to all single-layer GO sheets in the reduced form, on both insulating substrates. However, this is not observed on the as-produced GO of monolayer thickness, or on the GO sheets deposited on the metallic substrate. The observed electronic non-uniformities of the surface potential are associated with charged impurities trapped in the oxide layer, inducing perturbations of carrier density and altering the electronic properties of GO. The absence of work function variations on the two-layer section is attributed to more effective screening of charge impurities through charge redistribution effects among the layers. Raman spectroscopy mapping, which shows a uniform response across all monolayer GO sheets on all supporting substrates investigated, brings further evidence that the surface potential inhomogeneity is substrate-related and not associated with defect distribution on the surface of GO sheets. A representative image of a Raman G-band intensity map taken on the same GO sheet investigated by SKPM is shown in Figure 1c. Individual Raman spectra display two prominent peaks at -1 -1 ~1350 cm and at ~1590 cm , corresponding to the well-known D- and G-band, respectively, as illustrated in Figure 1d. The intensity ratio of D- with respect to G-band is a measure of disorder and it can be used to estimate the crystallite size of the graphitic domains. For the GO sheet shown in Figure 1a, a value of 9 nm is found for the size of ordered graphitic regions (surrounded by defective areas),

corresponding to a much lower size than that of patches observed in the surface potential images. Decrease of the intensity ratio ID/IG is generally observed upon thermal reduction, as illustrated in Figure 1e for samples investigated in this study. The 2D-band region is significantly different from that of conventional graphene which is dominated by a single, narrow peak. Here, for both pristine and reduced GO, 4 relatively broad and low intensity peaks are observed, associated with defect-activated bands in these structures. The in-plane variations of surface potential associated with subsurface charged impurities for one-layer GO will be discussed in detail for all investigated substrates, in parallel with complete screening effects of two-layer and thicker GO layers. The study provides a useful account of the limitations that GO device performance could face when attempting to tune the electronic structure of GO via chemical functionalization. References [1] K.P. Loh, Q. Bao, G. Eda, M. Chhowalla, Nat. Chem. 2(12), (2010) 1015. [2] Y. Shi, X. Dong, P. Chen, J. Wang, L.-J. Li, Phys. Rev. B 79, (2009), 115402. [3] X. Wang, L. Zhi, K. MĂźllen, Nano Lett. 8(1), (2008) 323. [4] S. Prezioso, F. Perrozzi, M. Donarelli, F. Bisti, S. Santucci, L. Palladino, M. Nardone, E. Treossi, V. Palermo, L. Ottaviano, Langmuir 28(12), (2012), 5489. [5] Y. Zhang, V. W. Brar, C. Girit, A. Zettl, M. F. Crommie, Nat.Phys. 5 (2009) 722. Figures (a)

(d)

(c)

GO/Si 300C-GO/Si 600C-GO/Si

1.05

(e)

1L ID/IG 2L ID/IG

0.8

1.00

0.95

0.6

ID/IG

Raman Intensity (a.u.)

1.0

(b)

0.90 0.4

2D D+G G*

G+D'

0.85

0.2

0.80 1000

1500

2000

2500

Raman shift (cm-1)

3000

3500

pristine 300C 600C onSiO2 on SiO2 on SiO2

pristine 300C 600C 200C on Al2O3 on Al2O3 on Al2O3 on Au

Sample

Figure1: Topography (a) and surface potential (b) map of a reduced GO sheet on SiO2/Si substrate. 2 Scan size is (41x41) Č?P . (c) G-band intensity map of the same flake as recorded by Raman spectroscopy. (d) Representative Raman spectra taken on one-layer GO flakes with different degrees of reduction. The un-indexed peak corresponds to the substrate. (e) Intensity ratio ID/IG for one-layer and two-layer GO, for all samples investigated in this study.

Introducing the Versatile Carboxylate Handle on Graphene by Reductive Carboxylation Mikkel Kongsfelt, Emil B. Pedersen, Kyoko Shimizy, Steen U. Pedersen, Kim Daasbjerg Aarhus University, Department of Chemistry and Interdisciplinary Nanoscience Center, Langelandsgade 140, DK-8000 Aarhus C, Denmark kongsfelt@chem.au.dk Abstract The use of graphene has been suggested for as widespread applications as molecular electronics, drug [1] delivery systems, anti-corrosive coatings, polymer reinforcements, and much more. For all of these diverse applications to be viable, chemical tools are needed to handle graphene in its various forms and control its [2] [3] properties in detail. Reduction of aryldiazonium salts, both spontaneously and electrochemically, has been [4] [5] the preferred tool to carry out functionalization so far, although hydrogenation , fluorination and plasma[6] modification are possibilities as well. The great advantage of the diazonium procedure is that it allows modification of graphene with a large variety of functional groups. Unfortunately, these reactions are rather uncontrolled, usually resulting in large multilayer structures on top of the graphene sheets. In this work we introduce a new method to functionalize CVD grown graphene on copper and nickel [7] substrates with the carboxylate group using an electrochemical procedure developed for graphite and glassy [8] carbon . Electrochemical reduction of graphene generates a highly negatively charged polynucleophilic substrate with intercalated positively charged tetrabutylammonium ions, which in a second step may react with added carbon dioxide to form carboxylate groups (Figure 1). For the multilayered graphene samples on nickel the separation of the individual graphene sheets by intercalation permits carboxylation to be carried out between the graphene layers. Excellent control on the functionalization degree is obtained through repetitive use of the outlined stepwise procedure. The carboxylate groups which are introduced directly into the basal plane of graphene are versatile chemical handles for further chemical functionalization. At the same time the small size of the carboxylate group [9] compared to, e.g., the arylic multilayers derived from diazonium functionalization , makes them ideal candidates for developing useful sensors. As a proof of concept, we show that these carboxylate groups can be utilized for further functionalization through attachment of Bovine Serum Albumine proteins using an EDC-NHS coupling reaction. The proteins are attached in a well-dispersed manner across the graphene sheets, as investigated by transmission electron microscopy. References [1]

[2] [3] [4]

[5] [6] [7] [8]

a) C. Chung, Y.-K. Kim, D. Shin, S.-R. Ryoo, B. H. Hong, D.-H. Min, Accounts of Chemical Research 46 (2013), 2211-2224; b) R. S. Edwards, K. S. Coleman, Nanoscale 5 (2013), 38-51; c) D. Prasai, J. C. Tuberquia, R. R. Harl, G. K. Jennings, K. I. Bolotin, ACS Nano 6 (2012), 1102-1108. E. Bekyarova, M. E. Itkis, P. Ramesh, C. Berger, M. Sprinkle, W. A. de Heer, R. C. Haddon, Journal of the American Chemical Society, 131(2009), 1336-1337. a) L. Gan, D. Zhang, X. Guo, Small 8 (2012), 1326-1330; b) M. Lillethorup, M. Kongsfelt, M. Ceccato, B. B. E. Jensen, B. JĂ¸rgensen, S. U. Pedersen, K. Daasbjerg, Small, 2013 R. Balog, B. Jorgensen, L. Nilsson, M. Andersen, E. Rienks, M. Bianchi, M. Fanetti, E. Laegsgaard, A. Baraldi, S. Lizzit, Z. Sljivancanin, F. Besenbacher, B. Hammer, T. G. Pedersen, P. Hofmann, L. Hornekaer, Nat Mater, 9(2010), 315-319. J. T. Robinson, J. S. Burgess, C. E. Junkermeier, S. C. Badescu, T. L. Reinecke, F. K. Perkins, M. K. Zalalutdniov, J. W. Baldwin, J. C. Culbertson, P. E. Sheehan, E. S. Snow, Nano Letters, 10 (2010), 3001-3005. N. Amirhasan, C. Mirco, V. Tom, P. Geoffrey, C. Francesca, H. v. d. V. Marleen, H. Johan, M. H. Marc, G. Stefan De, F. S. Bert, Nanotechnology, 21 (2010), 435203. C. Dano, J. Simonet, Journal of Electroanalytical Chemistry, 564 (2004), 115-121. J. Simonet, Electrochemistry Communications 21 (2012), 22-25.

[9]

R. L. McCreery, Chemical Reviews, 108 (2008), 2646-2687.

Figures

Figure 1. The two steps involved in the functionalization of multilayer graphene using carbon dioxide: 1) Graphene sheets are reduced to enforce intercalation of positively charged counter ions between and underneath the negatively charged layers and 2) reaction with added carbon dioxide to form graphene-functionalized carboxylates.

Investigating topological phase transitions in graphene through Monte-Carlo simulations Michael KĂśrner, Dominik Smith, Lorenz von Smekal

Theoriezentrum, Institut fĂźr Kernphysik, TU Darmstadt, SchloĂ&#x;gartenstraĂ&#x;e 2, 64289 Darmstadt, Germany koerner@theorie.ikp.physik.tu-darmstadt.de

Abstract It has been shown within the framework of the tight-binding theory, that the density of states of non-interacting graphene exhibits Van Hove singularities which divide the band structure into regions governed by the relativistic Dirac equation and by the non-relativistic Schroedinger equation [1]. When the Fermi surface crosses these points (driven by a chemical potential) a topological neck-disrupting Lifshitz transition occurs which is manifest as a divergence of the number susceptibility. It is our goal to investigate the effect of interactions on this transition through Hybrid-Monte-Carlo simulations using a code which has been successfully applied in studies of the semi-metal insulator phasetransition [2, 3]. This code is based on the framework which was developed in Ref. [4]. Since a regular chemical potential causes a Fermion signproblem (a complex Fermion determinant which cannot be interpreted as a probability PHDVXUH ZH LQVWHDG FRQVLGHU D Â´VWDJJHUHGÂ´ SRWHQWLDO ZKLFK KDV D GLIIHUHQW sign for the two spin orientations of the electrons.

References

[1] B. Dietz, M. Miski-Oglu, N. Pietralla, A. Richter, L. von Smekal, J. Wambach and F. Iachello, Âł/LIVKLW] DQG ([FLWHG 6WDWH 4XDQWXP 3KDVH TransitionV LQ 0LFURZDYH 'LUDF %LOOLDUGV Â´ 3K\V 5HY B 88, 104101 (2013) arXiv:1304.4764 [cond-mat.mes-hall]. > @ ' 6PLWK DQG / YRQ 6PHNDO Âł0RQWH-Carlo simulation of the tight-binding model of graphene ZLWK SDUWLDOO\ VFUHHQHG &RXORPE LQWHUDFWLRQV Â´ LQ SUHSDUDWLRQ > @ ' 6PLWK DQG / YRQ 6PHNDO Âł+\EULG 0RQWH-Carlo simulation of interacting tight-binding PRGHO RI JUDSKHQH Â´ DU;LY > @ 5 %URZHU & 5HEEL DQG ' 6FKDLFK Âł+\EULd Monte Carlo simulation on the graphene KH[DJRQDO ODWWLFH Â´ 3R6 /$77,&( [arXiv:1204.5424]; [arXiv:1101.5131].

MoS2/carbon nanostructures based hybrid materials 1

Victor Koroteev , Bulushev D. , Chuvilin A. , Bulusheva L.G. , Okotrub A.V.

1. NIIC SB RAS, Lavrentiev ave. 3, 630090, Novosibirsk, Russian Federation 2. Ecole Polytechnique FeÂ´deÂ´rale de Lausanne, LGRC-EPFL, CH-1015, Lausanne, Switzerland 3. CIC nanoGUNE, Donostia Âą San Sebastian, Spain koroteev@niic.nsc.ru 2D materials and hybrid structures based on them are attracting attention of material scientists over the last years. Theoretical and experimental studies show that catalytic activity, magnetic properties and conductivity of layers MoS2 are attributed to edge atoms, and basal atoms are not participating in such processes[1, 2]. The edges in MoS2 are not fully coordinated and, thus, thermodynamically stable, which leads to formation of closed shell structures[3]. To control appearance of edges in MoS2 LWÂśV necessary to put the particles on the substrate. Graphene substrates are promising, because they allow tuning of their own surface chemical states, conductivity and band structure, widening the range of properties and applications. MoS2 could exist in various polymorphic forms, which have different electronic properties and layers structure[4]. Recent studies show, that appearance of 1T polymorph structures could drastically enhance catalytic activity of hybrid structures, and participate in Li-intercalation[5, 6]. In this work, we investigate MoS2 nanoparticles on few layer graphene formation and LWÂśV structure depending on temperature. All the samples were obtained using high temperature technique, implying MoS 3 deposition on graphene in suspension with further annealing in vacuum at 500-800Â°C. The materials were studied using transmission electron microscopy, Raman spectroscopy, optical absorption spectroscopy and Xray photoelectron spectroscopy. HRTEM images of the product obtained at 500Â°C LV SUHVHQWHG RQ )LJ D E ,WÂśV FOHDUO\ VHHQ that dark spots are nanometer-sized clusters of molybdenum sulfide. Cluster structure is different from 2H- or 1T-MoS2. There is no clear hexagonal structure, the clusters look like flat laying on graphene, but not spherically shaped. Histogram on fig 1(b) shows size distribution of MoSx nanoclusters. The distribution is close to normal with Feret diameter mean value ~ 1 nm. Synthesis temperature increase results in cluster agglomeration. At 600Â°C they compose of 2-3 layers with MoS2 structure and lateral size of ~ 2 nm. At 800Â°C MoS2 forms particles with lateral size of size ~20 nm (Fig. 1 (c)) and 5-10 layers thickness. No clusters are observed at this temperature. Raman measurements show that FWHM (full width at half maximum) of MoS2 E2g and A1g lines decrease with synthesis temperature. It clearly indicates MoS2 mean particles size increase with synthesis temperature increase. Catalytic activity of the samples in hydrogen production by formic acid decomposition reaction was studied. Prior to measurements, the samples were treated with H2 at 350Â°C during 1 hour. Formic acid decomposition starts at 100Â°C for the samples with the smallest particle size and reaches 100% at 250Â°C. With sample synthesis temperature increase, the curve shifts by 50Â°C and conversion rate reaches 1 at 300Â°C for the samples obtained at 800Â°C. The result clearly indicates catalytic activity and active site concentration decrease with synthesis temperature decrease. Formic acid decomposition products mostly compose of CO2, hydrogen and methyl formate. When decomposition temperature reaches, 200Â°C traces of CO are observed, due to non-catalytic decomposition. This work is supported by Russian Foundation of Basic Research grant Ę&#x2039; -03-31633. References: [1] J.V. Lauritsen, J. Kibsgaard, S. Helveg, H. Topsoe, B.S. Clausen, E. Laegsgaard, F. Besenbacher, Nat Nano, 2 (2007) 53Âą58. [2] R. Shidpour, M. Manteghian, Chemical Physics, 360 (2009) 97Âą105. [3] J.J. Hu, J.H. Sanders, J.S. Zabinski, Journal of Materials Research, 21 (2006) 1033Âą1040 DOI: 10.1557/jmr.2006.0118. [4] F. Wypych, K. Sollmann, R. SchĂśllhor, Materials Research Bulletin, 27 (1992) 545Âą553 DOI: 10.1016/0025-5408(92)90142-M. [5] M.A. Lukowski, A.S. Daniel, F. Meng, A. Forticaux, L. Li, S. Jin, Journal of the American Chemical Society, 135 (2013) 10274Âą10277 DOI: 10.1021/ja404523s. [6] T. Stephenson, Z. Li, B. Olsen, D. Mitlin, Energy Environ. Sci., 7 (2014) 209Âą231 DOI: 10.1039/C3EE42591F.

Count

60 40 20 0 0

Feret diameter (nm) c)

Figure 1. HR TEM images of MoS2 nanometer-sized particles obtained at different temperatures: 500째C (a, b). HR TEM image of MoS2 nanoparticles obtained at 800째C (c).

Effect of the chemical structure and processing conditions on the morphology and electrical conductivity TPU/EG composites Beate Krause, Francesco Piana, JĂźrgen Pionteck Leibniz-Institut fĂźr Polymerforschung Dresden e.V., Hohe Str. 6, 01069 Dresden, Germany pionteck@ipfdd,.de Abstract With the aim to produce electrically conductive composites, we analysed the influence of the processing conditions and chemical structure of thermoplastic poly(urethane) (TPU) on the electrical percolation threshold concentration in thermoplastic poly(urethane) / expanded graphite (TPU/EG) composites. For that, TPU with varying hard segment (HS) structure and HS content have been synthesized (Table 1). Commercial products (Elastollan series of Elastogran, BASF group) with same HS structure but different soft segments (SS) and varying composition Âą and therefore different hardness - have been used (S60A15 (hardness: 63 Shore A), 1185A (87 shore A, 36 shore D), and C74D50 (73 Shore D). &RQGXFWLYLWLHV Äą KDYH EHHQ GHWHUPLQHG RQ FRPSUHVVLRQ PRXOGHG SODWHV Table 1: Structure and composition of self-made TPU Molar HS content Č&#x2013; PC composition (wt.%) (mN/m) wt.% (DI / BD / PTHF) MDI-2 MDI 2/1/1 17 41 <10 MDI-5 MDI 5/4/1 45 45 <8 H12-MDI-2 H12-MDI 2/1/1 17 39 8 H12-MDI-5 H12-MDI 5/4/1 46 42 <8 IPDI-5 IPDI 5/4/1 44 41 6 Monomers: MDI: Âś-methylenebis(phenyl isocyanate); H12-MDI: methylenebis(cyclohexyl isocyanate); IPDI: isophorone diisocyanate; BD: 1,4-butanediole: PTHF: poly(tetrahydrofuran) (Mn = 1400 g/mol) Name

Isocyanate

Melt mixing, solution casting and in-situ polymerization have been compared. The in-situ polymerization is limited in regard to the filler amount which can be incorporated into the polymer matrix. At the maximum filler concentration of 2 % only MDI-2 and IPDI-5 showed some electrical conductivity. The observed percolation concentrations (PC) of composites prepared by melt mixing of synthesized TPU are in between 6 and 10 wt.%. In both cases no correlation between chemical structure, composition, physical properties, e.g. surface tension Č&#x2013; HVWLPDWHG IURP 3DUDFKRU PHWKRG [1]), to the electrical behavior could be found. Solution blending resulted in composites with more than 10 wt.% filler contents. The use of these materials as masterbatch for melt mixing with pure TPU was not beneficial in regard to conductivity and percolation concentration when compared to direct melt mixing of TPU with EG. Melt mixing of the commercial products at processing conditions where a homogeneous composites is obtained resulted in different PC with the lowest one of < 2 wt.% for TPU C74D50, the hardest polymer with the highest HS content and highest degree of crystallinity (Figure 1). However, when changing the processing conditions (melt mixing temperature, compression moulding temperature, and rotational speed of the mixer) of the TPU 1185A/EG composites the primary observed PC of ca. 4 wt.% could be shifted to < 2 wt.% (Figure 2, [2], the same which was observed for TPU C74D50 composites without optimization the processing conditions. Thus, again no correlation between structure and electrical properties can be proven till now. It should be mentioned, that at the conditions optimized in regard to electrical conductivity a very inhomogeneous material was obtained. Furthermore, the conductivities determined with two different electrode systems revealed increased resistance in the surface near regions. Overall, the conductivities of the composites are rather small if compared to that of EG. Acknowledgements We are grateful for the support of the project by the Deutsche Forschungsgemeinschaft (DFG) and to SGL Carbon for providing the expanded graphite.

References [1] D. W. Van Krevelen: Properties of Polymers, Elsevier Science, Amsterdam, 1997. [1] F. Piana, J. Pionteck, Comp. Sci. Tech. 80 (2013) 39-46.

[S/cm]

-4

10 -6 10 -8 10 -10 10 -12 10 -14 10 -16 10 -18 10 -20 10

TPU C74D50 TPU 1185A TPU S60A15 0

EG [Ma.%] Figure 1: Electrical conductivity of TPU/EG composites prepared by melt mixing at standard conditions in dependence on EG content.

-4

-6

[S/cm]

-8

-10

-12

-14

10 11

EG [Ma.%] Figure 2: Successive shift of electrical percolation concentration of TPU 1185A/EG composites prepared at standard conditions (black squares) by optimizing the processing conditions melt mixing temperature (red circles), compression moulding temperature (blue uptriangles) and rotational speed (pink downtriangles).

Carbon Dot Modified Graphene Oxide with Tunable Fluorescence for Selective Cell Labeling K. K. R. Datta, M. Otyepka, R. Zboril

Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University in Olomouc, Slechtitelu 11, 783 71 Olomouc, Czech Republic.

Abstract: Assembly of positively charged carbon dots (CD) over negatively charged graphene oxide (GO) was achieved by non-covalent approach. These hybrids are highly fluorescent and energy transfer occurs IURP 4&'ÂśV WR *2 7KH IOXRUHVFHQFH RI WKH K\EULGV FDQ EH WXQHG E\ VXLWDEOH PRGLILFDWLRQ RI *2 L H E\ changing the surface chemistry of GO. These hybrids act as selective cellular labels towards Mouse fibroblasts NIH3T3 cells.

Derivation of approximately model for CVD graphene growth Shih-Hao Chan1,2, Jia-Wei Chen1,2, Sheng-Hui Chen1,2, Chien-Cheng Kuo1,2,3* Film Technology Center , National Central University, Chung-Li (32001), Taiwan 2Department of Optics and Photonics, National Central University, Chung-Li (32001), Taiwan 3Graduate Institute of Energy Engineering , National Central University, Chung-Li (32001), Taiwan *cckuo@ncu.edu.tw 1Thin

The aim in this study is controlling the nucleation density of graphene seed, furthermore, pursuing a lower sheet resistance by reducing the quantity of grain boundaries. We developed a simple derivation of approximately model for graphene growth under different hydrogen flow rate, ranging from 10 to 50 sccm. The morphology of graphene edge was become smoother with a high concentration of hydrogen flow rate. The growth parameters, CH4 and temperature, are 0.5 sccm and 1070oC with ambient chemical vapor deposition (APCVD). The lowest sheet resistance of single layer graphene was 310 ȍ ˎ and the average transmittance is 97.7 % between 350 -1000 nm wavelengths.

Coverage Area of Graphene Domains Hexagonal Domain

Coverage Area of Graphene Domains (a) 10 sccm

(b) 20 sccm

Copper

Graphene

(e) 50 sccm

(d) 40 sccm

Dendritic Domain

Hydrogen can etch the weak C-C and the C-H bond.

Graphene

Copper

H2 flow rate 10 20 30 40 50 (sccm) Nucleation Density 3.22x10-4 2.45x10-4 2.33x10-4 2.01x10-4 1.72x10-4 ȝP-2)

Carbon Growth Rate

Transfer Process (2) Copper removal

(1) Supporting layer and etching

(3) Clean

PMMA Graphene Copper

PMMA

Graphene

Copper

(NH4)2S2O8 (Ammonium persulfate)

O2 plasma

Rinse in DI water for 15 min (10 times)

(4) Supporting layer removal Acetone bath (50oC) SiO2 Graphene

SiO2 thin film

Derivation of the Approximately model

Nanosphere template Glass substrate

Summary

t = growth time L= circumference A= average araea r = average radius The average area is the secondorder function of the growth time and growth rate of carbon atoms.

Department of Optics and Photonics National Central University

Graphene Substrate

ITO electrode 30 min

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Compact modeling of external parasitics of graphene field-effect transistors Gerhard Martin Landauer1,*, David JimĂŠnez2,**, JosĂŠ Luis GonzĂĄlez3 1Department

of Electronics Engineering, Universitat PolitĂ¨cnica de Catalunya, 08034 Barcelona, Spain dâ&#x20AC;&#x2122;Enginyeria ElectrĂ˛nica, Escola dâ&#x20AC;&#x2122;Enginyeria, Universitat AutĂ˛noma de Barcelona, 08193 Bellaterra, Barcelona, Spain 3DACLE/Lair, CEA/Leti, 38054 Grenoble, France gerhard.landauer@upc.edu

2Departament

Abstract Graphene is a promising candidate for future high-performance RF applications [1]. Its potential to substitute conventional silicon technology has been demonstrated with devices such as a graphene fieldeffect transistor (GFET) with an intrinsic cut-off frequency of 427 GHz [2]. Recently, research on graphene-based RF electronics has been extended to the circuit level and basic building blocks such as mixers [3] and amplifiers [4] have been reported. This scenario leads to a demand for accurate compact models for circuit design engineers. These models have to cover not only the intrinsic device, but also the bias-dependent and performance-degrading extrinsic elements. In this work we develop a compact model of the extrinsic part of a typical GFET structure. It is implemented in Verilog-A and usable with conventional circuit simulators. We assume a double-gate GFET structure with a channel of pristine monolayer graphene (Fig. 1). The intrinsic channel is covered by a high-Č&#x203A;/metal gate stack and modeled such as proposed in [5]. The extrinsic model consists of the contact resistances Rm-g and Rg-c at the metal-graphene interface, the access resistance Rc of the graphene contact layer between the electrodes and the intrinsic device, and fringe capacitances Cc,x between the electrodes and this graphene layer (Fig. 2). Rm-g and Rg-c are due to two consecutive tunneling processes at the metal-graphene interface. In compact models these resistances have up to now been empirically approximated [6, 7]. We implemented them following the description of the underlying physical processes given in [8] and using a combination of power-law and linear curve fitting (Fig. 3). Rc is due to the finite resistance of the extrinsic graphene layer. In a novel approach we split this region into segments and consider each of them as an individual triple-gate GFET device, which is weakly coupled to the gate and source/drain electrodes as well as to the back-gate (Figs. 4 and 5). There is a low voltage drop over the individual segments, which implies Fermi-levels close to the Dirac point. We have developed a drain current description which is accurate under these low-voltage conditions and have validated it by comparison to experiments [9] (Fig. 6). Simulations show that the extrinsic resistances have a strong impact on device current Id (Fig. 7). When simply regarding the intrinsic device, a variation of the back-gate voltage Vbs only leads to a shift in the point of minimum current. By considering Rm-g, Rg-c, and Rc, a decrease in Id can be observed. An efficient method to mitigate these parasitic resistances is to induce additional charge carriers in the extrinsic graphene layer by increasing Vbs (Fig. 8). For instance, a change in Vbs from 0 to 20 V yields a decrease RI WKH RYHUDOO FRQWDFW UHVLVWDQFH IURP WR NČ?Ä Â&#x2014;P These high Vbs values have been obtained for a back-gate oxide thickness of 300 nm. Vbs could be strongly reduced by for instance using a state-ofthe-art FDSOI oxide thickness of 25 nm. Based on these results, our work indicates the need for accurately modeling the GFETâ&#x20AC;&#x2122;s external resistances. Furthermore, applying a back-gate potential allows to significantly reduce them. References [1] F. Schwierz, Proc. IEEE, 101 (2013) 1567-1584. [2] R. Cheng et al., Proc. Natl. Acad. Sci. U.S.A., 109 (2012) 11588-11592. [3] Y. Wu et al., Proc. IEEE, 101 (2013) 1620-1637. [4] S.-J. Hand et al., Nano Lett., 11 (2011) 3690-3693. [5] D. JimĂŠnez, IEEE Trans. Electron Devices, 58 (2011) 4049-4052. [6] H. Wang et al., IEEE Trans. Electron Devices, 58 (2011) 1523-1533. [7] O. Habibpour, J. Vukusic, and J. Stake, IEEE Trans. Electron Devices, 59 (2012) 968-975. [8] F. Xia, Nat. Nanotech., 6 (2011) 179-184. [9] H. Wang et al., IEEE IEDM, San Francisco, USA (2010). [10] S.A. Thiele, J.A. Schaefer, and F. Schwierz, J. Appl. Phys., 107 (2010) 094505. * G.M. Landauer acknowledges the support of an FI grant of the Government of Catalonia and the European Social Fund as well as the support of the Spanish Ministry of Science and Innovation under project TEC2008-01856 with additional participation of FEDER funds. ** D. JimĂŠnez acknowledges funding from the Ministerio de EconomĂa y Competitividad of Spain under the project TEC2012-31330, and from the European Union Seventh Framework Programme under grant agreement nÂş604391 Graphene Flagship.

Figures

Fig. 1: Cross-section of the modeled dual-gate GFET. The channel consists of pristine single-layer graphene and is connected to the electrodes with an extrinsic graphene layer.

Fig. 2: Equivalent circuit of the GFET showing extrinsic resistances and capacitances. The distributed model of the graphene contact layer is shown in a symbolized form.

Fig. 3: Contact resistance Rm-g +Rg-c at the metal-graphene interface vs. Fermi levels Efm and Efg under the metal electrode and at the beginning of the extrinsic graphene contact layer, respectively. Curve fitting is used.

Fig. 4: Splitting of the graphene contact layer into N segments. Each one is described as an individual weakly coupled GFET and modeled with high accuracy at low voltage drops.

Fig. 5: Segment-to-electrode outer-fringe capacitance Cc,x for a geometry with Lc =Lg =Ls =Ld =1 Âľm and 100 nm contact height. Results were obtained with an EM field simulator and implemented in the model using power-law fitting.

Fig. 7: GFET transfer characteristics considering the metalgraphene contact resistance Rm-g+Rg-c and graphene contact layer resistance Rc. The impact of both components, of only Rc, and of not considering any extrinsics is shown.

Fig. 6: Low-voltage GFET model with high accuracy close to the Dirac point. A validation against measurement data for Vds = 10 mV [9] shows a gain in accuracy close to the point of minimum current when comparing to previous models [5], [10].

Fig. 8: Metal-graphene interface (Rm-g+Rg-c) and graphene contact layer (Rc) resistances at drain (solid line) and source (dashed line) side vs. back-gate voltage Vbs. Values are given for a back-gate oxide thickness of 300 nm.

Convergent Fabrication of a Perforated Graphene Network with Air-Stability 1

J. Landers , J. Coraux , M. De Santis , S. Lamare , L. Magaud , F. ChĂŠrioux

University of Grenoble Alpes, Institut NEEL, F-38042 Grenoble, France CNRS Institut FEMTO-ST, UniversitĂŠ de Franche-ComtĂŠ, CNRS, ENSMM, 32 Avenue de l'Observatoire F- %HVDQŕ¤&#x160;RQ )UDQFH john.landers@grenoble.cnrs.fr

Abstract The strategic synthesis of two-dimensional organic nanostructures has emerged in recent years[1] as one of the most actively pursued topics in nanotechnology[2-3]. Two-dimensional (2D) porous frameworks synthesized at a surface under conditions of ultra high vacuum (UHV) have drawn special attention due to the potentially different properties that they may possess with respect to their hermetic counterparts such as the ability to open a bandgap as well as the occurrence of flat bands leading to magnetic behavior[4]. Of particular interest are efforts towards the generation of a fully carbon backbone, such as porous graphene, through covalent self assembly, i.e through a bottom-up approach, where the size and shape of the pore can be uniformly controlled by reacting precursor molecules together at a surface. This strategy is a versatile way to produce different assemblies, for instance the long-sought after graphene antidot lattice[4], as well as in applications where size selectivity is crucial (e.g. for catalysis or optical absorption). Nevertheless, the applicability of these constructs is limited by their stability at higher temperatures (up to 700K) and atmospheric pressure (exposure to air). Herein we report a new synthesis procedure based on a convergent approach via a triple aldolisation, which we use to create nanoporous networks of graphene on Au(111) under UHV[5]. Using UHV scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we show that a nanoporous graphene network fully covers the surface and we identify intermediate states in the growth process. In addition the network is stable up to 800K under UHV. Finally, we have successfully demonstrated that the network is stable at higher pressures, including argon backed -5 pressures of 10 mbar, but most remarkably, without a protective layer, the structure remains intact after exposure to air. References [1] L. Grill, M. Dyer, L. Lafferentz, M. Persson, M. V. Peters, S. Hecht. Nat. Nanotechnol. 2 (2007) 687. [2] M. Bieri, M. Treier, J. M. Cai, K. Ait-Mansour, P. Ruffieux, O. Groning, P. Groning, M. Kastler, R. Rieger, X. L. Feng, K. Mullen, R. Fasel. Chem. Commun. 46 (2009) 6919-6921. [3] Y. Q. Zhang, N. Kepcija, M. Kleinschrodt, K. Diller, S. Fischer, A. C. Papageorgiou, F. Allegretti, J. Bjork, S. Klyatskaya, F. Klappenberger, M. Ruben, J. V. Barth. Nat. Commun. 3 (2012) 1286-1283. [4] T.G. Pedersen, C. Flindt, J. Pedersen, N.A. Mortensen, A.P. Jauho, K. Pedersen. Phys. Rev. Lett. 100 (2008) 136804. [5] J. Landers, J. Coraux, M. De Santis, S. Lamare, L. Magaud, F. ChĂŠrioux. Angew. Chem. Int. Ed. (2014). (submitted)

Figure 1: (Left) Scanning tunnel microscopy (STM) topograph of a fully conjugated carbon network synthesized on Au(111). (Right) Density functional theory (DFT) calculations showing the stable structure on Au(111). Middle inset shows the reaction based on a novel convergent approach via triple aldolisation.

Modelling Excitons in Atomically Thin Semiconductors Simone Latini, Thomas Olsen, Kristian S. Thygesen Center for Atomic-Scale Materials Design, Department of Physics Technical University of Denmark Fysikvej 311, 2800 Kgs. Lyngby simola@fysik.dtu.dkl Despite the numerous extraordinary properties of pristine graphene, its application to (opto)-electronics is problematic due to the lack of a band gap. This issue inevitably requires the systematic research for ew materials which combine a strong 2D nature and a semiconducting behaviour. As soon as a band gap is opened, excitonic effects start to play a fundamental role on the optical properties determining, for example, the onset of the optical transitions. The Bethe-Salpeter Equation (BSE) is nowadays the most refined method to quantitatively describe excitons but its applicability is limited to relatively simple systems because of its computational complexity. Here we propose a simple method to estimate the energy of the lowest bound exciton based on a modified Mott-Wannier model. For 2D semiconductors the dielectric function turns out to be strongly dependent on the wave vector and therefore the definition of the value for the dielectric constant to plug into the hydrogenic model has to be revised. This is done accounting for a quasi-2D picture of the exciton. The validity of the method is checked thoroughly benchmarking the binding energies and exciton radii for a large variety of 2D materials against the values obtained from the solution of the BSE. Our method has the merit to both keep the computational cost low and to provide a straightforward physical intuition on excitonic effects.

Modification of graphene oxide for polyurethane composite by combination of isocyanate and diisocyanate Le Hoang Sinh, Nguyen Dang Luong, Jukka Seppälä* The authors are equally distributed Aalto University, School of Chemical Technology, Department of Biotechnology and Chemical Technology, P.O. Box 16100, 00076 Aalto, Espoo, Finland

jukka.seppala@aalto.fi Abstract Utilization of graphene oxide (GO) in polymer composites has attracted both academic and industrial interest because it can produce a dramatic improvement in properties at very low filler content [1, 2]. Surface modification of GO is required to obtain good dispersion of GO in polymer matrix. Moreover, suitable modification method can introduce desired function groups, and thus, GO either has strong interaction with polymer or reacts with polymer to create covalent bonding with polymer. Functionalization of GO by treatment with isocyanate, which could be carried out in mild condition, is the most common method to modify GO for polymer composite. Modification of GO with several different isocyanate compounds was first reported by Stankovich et al.[3]. However, they did not successfully introduce a high reactive functional group into GO surface. Chemical treatment of GO with diisocyanate was also reported by Zhang et al. [4]. Unfortunately, GO sheets were crosslinked to form lamellar porous structures via reaction of diisocyanate with the carboxyl and hydroxyl groups on both sides of the sheets. Here, we report on modification of GO by combination ethyl isocyanate (EI) and 4,4methylenebis(phenyl isocyanate) (MDI) with molar ratio of 1:1. Then, composites of the modified GO and polyurethane (PU) were synthesized via in situ polymerization method. To our knowledge, this is the first report on combination of isocyanate and diisocyanate to modify GO. The modified GO readily forms a stable colloidal dispersion in all polar aprotic solvents, such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethylsulfoxide (DMSO). The free isocyanate groups, which come from MDI, can react with hydroxyl groups of diols/ polyols to create strong covalent bonding between GO sheets and polyurethane. As expected, addition of very low GO content produced a dramatic improvement in mechanical properties of PU. In particular, the tensile VWUHQJWK DQG <RXQJ¶V PRGXOXV significantly increased from 8.9 MPa and 2.6 MPa for pristine polyurethane to 19.3 MPa and 4.7 MPa for composite containing 0.03 wt% GO content, respectively, without losing of elongation at break. Notably, all composite films with 0.2 mm in thickness still had good transparency up to 0.1 wt% of GO content. References [1] Tapas Kuilla, Sambhu Bhadra, Dahu Yao, Nam Hoon Kim, Progress in Polymer Science, 35 (2010) 1350-1375. [2] Jeffrey R. Potts, Daniel R. Dreyer, Christopher W. Bielawski, Rodney S. Ruoff, Polymer, 52 (2011) 525. [3] Sasha Stankovich, Richard D. Piner, SonBinh T. Nguyen, Rodney S. Ruoff, Carbon, 44 (2006) 33423347. [4] Dan-Dan Zhang, Sheng-Zhen Zu, Bao-Hang Han, Carbon, 47 (2009) 2993-3000.

Figures

Figure 1. Scheme of modification of GO (a) and preparation of polyurethane/ graphene oxide composites (b).

PU/iGO 0.01wt%

PU/iGO 0.03wt%

PU/iGO 0.05wt%

Figure 2. Photographs of pristine PU and composite films.

PU/iGO 0.1wt%

Bilayer graphene grown on 6H-SiC (0001) substrate by sublimation: Size confinement effect Lebedev A.A.1,5), Mikoushkin V.M.1), Shnitov V.V.1), Lebedev S .P. 1,5), Likhachev E.V 1), Yakimova R 2) 3,4) , Vilkov O.Yu. 1)

Ioffe Institute, 194021, St. Petersburg, Russia Linkoping University, S-581 83, Linkoping, Sweden 3) Technische Universität Dresden, D-01062 Dresden, Germany 4) Institute of Physics, St. Petersburg State University, 199034, St. Petersburg, Russia 5) Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics, Russia, Saint-Petersburg , 197101 Kronverksky pr., 49 e-mail: E-mail: shura.lebe@mail.ioffe.ru 2)

The epitaxial growth technology based on high temperature annealing of SiC substrates seems to be to posess a real potential for mass production of wafer-scaled and high quality graphene films [1]. Despite the rapidly (quickly) increasing number of publications developing fundamental and applied aspects of this technology, it is still far from being accomplished. In this work we demonstrate that our original technique of substrate pre-growth treatment may promote considerable progress in this field. Graphene grown on silicon carbide substrate by sublimation method was used in our research. o The growth was carried out in inductively heated furnace at temperature of 2000 C and at an ambient argon pressure of 1 atm. Experiments was performed on nominally on-axis, n-type 6H-SiC wafers with polished Si (0001) face purchased from Cree Corp. Preliminary high-vacuum annealing of SiC substrate was used before graphene growth for removing distorted surface layer after polishing [2] Properties of the film thus grown were studied ³H[ VLWX´ by atomic force microscopy (AFM), Raman spectroscopy, low energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and near edge x-ray absorption fine structure (NEXAFS) spectroscopy. AFM study showed that substrate surface consists of flat and wide (~1 m) terraces covered with sufficiently large and continuous graphene domains. Numerous LEED patterns (see example in the figure) obtained from different points of the sample demonstrate concurrent presence of a well-ordered graphite (1×1) pattern and ¥ î ¥ 5 SDWWHUQ LQKHUHQW WR WKH XQGHUOying buffer layer [1] and, thereby, evidence mainly bilayer character of the grown film. XPS and NEXAFS data obtained on synchrotron BESSY II (Berlin) allowed us to specify a chemical composition and electronic structure of graphene film grown and confirm its high quality and mostly bilayer nature. In particular, the bilayer character of the film was confirmed (also by low energy electron diffraction experiments as well as - ɩɨɜɬɨɪ) by the 0.2 eV film charging due to charge transfer to substrate, which is typical for bilayer films [2-3]. Considering the bilayer as a quantum well with SiC bandgap wall, one can assume appearance of the van Hove singularities in the density of states because of size confinement in normal direction. Indeed, two peaks are seen in the graphene valence band spectrum near the Fermi level. Their energies are E1= 0.5 - 0.2 = 0.3 eV and E2= 1.5 0.2 = 1.3 eV, taking into account 0.2 eV spectrum shift due to charching the layer. The energy ratio (E2/E1 ~ 4 = n1/n2) and values agree with calculated ones for quantum well mentioned. The research was partially financially supported by the Russian-German Laboratory at BESSY II, by the FASR contract 02.740.11.0108 and by Government of Russian Federation, Grant 074-U01.. References [1] Hass J., de Heer W. A., Conrad E. H. Phys. J. Phys.: Condens Matter, 20, (2008) 323202. [2] Lebedev S.P. Petrov V.N., Kotousova I.S., Lavrent`ev A.A., Dement`ev P.A., Lebedev A.A., Titkov A.N., Mater. Sci. Forum, v.679-680, (2011) . 437-440, [3] D Ohta T., Bostwik A., McChesney J.L. at al., Phys. Rev. Lett. 98, (2007) 206802 [4] Virojanadara C., Yakimova R., Zakharov A.A.,at al., J. Phys. D: Appl. Phys 43, (2010) 374010.

Fig. 1. LEED pattern of graphene film grown on SiC substrate subjected to pre-growth treatment..

Fig. 2. Valence band density of states spectra of SiC substrate,

bilayer graphene film and phyrolytic graphite.

Quantum Hall Effect in Chemically Functionalized Graphene: Defect-Induced Critical States and Breakdown of Electron-Hole Symmetry Nicolas Leconte, Frank Ortmann, Alessandro Cresti, Jean-Christophe Charlier, and Stephan Roche UniversitĂŠ catholique de Louvain (UCL), Institute of Condensed Matter and Nanoscience (IMCN), NAPS, Chemin des ĂŠtoiles 8, 1348 Louvain la Neuve, Belgium nicolas.leconte@uclouvain.be Unconventional magneto-transport fingerprints in the quantum Hall regime (with applied magnetic field from one to several tens of Tesla) in chemically functionalized graphene are reported [1]. The scattering potential induced by the impurities is modeled by tight-binding parameters extracted from ab initio calculations [2], which, in turn, are used inside an efficient real space order N method [3] to calculate the dissipative conductivity [4] under high field. Upon chemical adsorption of monoatomic oxygen (from 0.5% to few percents), the electron-hole symmetry of Landau levels is broken, while a double-peaked conductivity develops at low-energy, resulting from the formation of critical states conveyed by the random network of defects-induced impurity states. Scaling analysis suggests an additional zero-energy quantized Hall conductance plateau, which is here not connected to degeneracy lifting of Landau levels by sublattice symmetry breakage. This singularly contrasts with usual interpretation, and unveils a new playground for tailoring the fundamental characteristics of the quantum Hall effect.

References [1] N. Leconte, F. Ortmann, A. Cresti, J.-C. Charlier, and S. Roche, submitted (2014) [2] N. Leconte; A. Lherbier, F. Varchon, P. Ordejon, S. Roche, and J.-C. Charlier, Phys. Rev. B 84 (2011) 235420; N. Leconte, J. Moser, P. Ordejon, H.H. Tao, A. Lherbier, A. Bachtold, F. Alsina, C.M.S. Torres, J.-C. Charlier, and S. Roche, ACS Nano 4 (2010) 4033 [3] H. Ishii, F. Triozon, N. Koboyashi, K. Hirose, and S. Roche, C.-R. Physique 10 (2009) 283 [4] D. Soriano, N. Leconte, P. Ordejon, J.-C. Charlier, J.J. Palacios, and S. Roche Phys. Rev. Lett. 107 (2011) 016602; N. Leconte, D. Soriano, S. Roche, P. Ordejon, J.-C. Charlier, and J.J. Palacios, ACS Nano 5 (2011) 3987 Figures

0.5

0.75

E2 E4

!(G0)

(G0)

(a)

E3 1% 80T E1

1% - 80T

(b) E5

0 -0.075 -0.05 -0.025

0.025

0.05

120

L (nm)

0.4

800

E (Kelvin)

!(G0)

0.6

600 400 200

0.2 0

(d) 5T 20T 40T 60T 80T

0 0

40 60 B (T)

-0.075

-0.05

-0.025 E (eV)

0.025

Loading direction dependence of graphene thickness measured using atomic force microscope D. H. Lee, C.K. KiM, M.J. Lee, D.Y. Oh, S.I. Lee, C.S. Yoon and B. H. Park* Division of Quantum Phases and Devices, School of Physics, Konkuk University, Seoul, 143-701, Korea corealeo@gmail.com Abstract After discovery of graphene using micromechanical cleavage technique[1], extremely many researches have been carried out so far due to its outstanding material characteristics such as electrical[2,3], mechanical[4,5] properties and so on. However, thickness of monolayer graphene, i.e. distance between surfaces of monolayer grapheme and substrate, has been experimentally determined in a wide range of 0.3 nm to 1.5 nm using scanning tunneling microscope (STM) or atomic force microscope (AFM) with atomic-scale resolution while it is theoretically predicted as 0.34 nm. Identification of exact thickness of monolayer grapheme is very important issue for application of grapheme to nano-devices whose performance strongly depends on dimensions of constituent materials, however, it has been rarely performed so far. We investigated AFM topographic images of graphene, of which thickness was determined by AFM tapping and contact mode. Thickness of graphene was observed as almost constant using AFM tapping mode, however, that identified using AFM contact mode showed strong dependence on sample rotation angle with certain periodicity. From analysis of torsion images and topographies, we suggest that the variation originates from effect of intrinsic ripple of graphene. References [1] Novoselov, K. S., Geim A. K., Morozov, S. V.; Jiang,D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science, 2004, 306, 666. [2] Novoselov, K. S. et al. Two-dimensional atomic crystals. Proc. Natl. Acad. Sci. USA, 2005, 102, 10451-10453. [3] Novoselov, K. S. et al. Two-dimensional gas of massless Dirac fermions in graphene. Nature, 2005, 438, 197200. [4] J. S. Choi, J.-S. Kim, I.-S. Byun, D. H. Lee, M. J. Lee, B. H. Park, C. Lee, D. Yoon, H. Cheong, K. H. Lee, Y.W. Son, J. Y. Park, and M. Salmeron, Science 2011. 333, 607. [5] Kwe Xu, Peigen Cao, James R.Heath, Science 2010, 329, 5996. Figures

Figure 1. (A) optical image of graphene smaple.(inset : AFM image in red square sector), (B) (A) raman spectra of each red and blue spot on opical image. (C) \AFM image altered variously through loading direction in red square sector.( 0degree to 330degree respectively 30 degree step), (D) Height graph of sample altered through loading direction.(red sircle : monolayer graphene height, blue sircle : bilayer graphene height, black sircle : differnece between bilayer and monolayer graphene)

Effect of rapid thermal annealing in vacuum on the structural and optical properties of MoS2 flakes in solution Kyeong Won Lee, Ju Hwan Kim, Soo Seok Kang, Dong Hee Shin, Sung Kim, Suk-Ho Choi Department of Applied Physics, Kyung Hee University, Yongin 446-701, Korea sukho@khu.ac.kr Abstract Recently, top-down and bottom-up methods have been developed to fabricate single-layer (1L) MoS2 nanosheets. The top-down method focuses on the mechanical [1-2] and solution-based exfoliation [3-4] of bulk MoS2 crystals. Although the mechanical exfoliation of MoS2 can produce the pristine 1L MoS2 with high quality, its yield and reproducibility are low. The solution-based exfoliated MoS2 is often accompanied by residual chemicals from the solution used, which in turn affects the properties of MoS2 nanosheets [3]. In the previous studies, a thermal annealing method has been used in layer thinning and etching of mechanically exfoliated MoS2 for achieving single-layer MoS2 from multi-layer MoS2 [1]. In this work, MoS2 flakes of ~ 400 nm lateral size in ethanol solution were used to investigate the thermal annealing mechanism of MoS2 flakes. For single-layer MoS2 nanosheets, MoS2 flakes solution was dropped on the whole surface of 100 nm SiO 2 substrate and subsequently, MoS2 flakes were heated by rapid thermal annealing at various temperatures from 100 o

to 500 C under vacuum for 10 min. The annealed samples were characterized by optical microscopy, Raman spectroscopy, and atomic force microscopy (AFM). Fig. 1 shows the optical images of MoS2 nanosheets on 100 nm SiO2 /Si, in which different color contrast represents different layer thickness of MoS2. [5] Fig. 1 (a) shows the MoS2 flakes before thermal annealing, which consists mainly of 6L nanosheets. Subsequently, thermal annealing was performed at 200 째C for 10 min. The formation of 2L MoS2 nanosheet by thinning was observed after thermal annealing, as shown in Fig 1 (b). Raman spectra of the transferred layers exhibited two intense features, E -1

1 2g

and A1g peaks at

cm , respectively, uniquely characteristic of MoS2 film. The two Raman modes,

1 E 2g

384 and

403

and A1g, exhibited

sensitive thickness dependences, with the frequency of the former decreasing and that of the latter increasing with thickness [6]. The annealing behaviors show several intriguing characteristics. Most strikingly, we find that the E12g vibration softens (blue shifts), while the A1g vibration stiffens (red shifts) with increasing annealing temperature, as shown in Fig 2. This Raman analysis reveals optimum o

annealing temperature of 200 C for the synthesis of smallest-layer-number and best-quality MoS2. The thickness of MoS2 estimated by AFM was consistent with the Raman results. As a result of thermal annealing, the MoS2 nanosheet is thinned, possibly due to its oxidation to form MoO 3. Possible mechanisms are proposed to explain the formation processes of MoS2 nanosheets from MoS2 flakes during the annealing. References

[1] H. Li, Z. Yin, Q. He, H. Li, X. Huang, G. Lu, D. W. H. Fam, A. I. Y. Tok, Q. Zhang, and H. Zhang,

Small, 1 (2012) 63-67 [2] K. S. Novoselov, D. Jiang, F. Schedin, T. J. Booth, V. V. Khotkevich, S. V. Morozov, and A. K. Geim, Proc. Natl. Acad. Sci. USA, 30 (2005) 10451-10453 [3] Z. Zeng, Z. Yin, X. Huang, H. Li, Q. He, G. Lu, F. Boey, and H. Zhang, Angew. Chem. Int. Ed. 47 (2011) 11093-11097 > @ - 1 &ROHPDQ 0 /RW\D $ 2Âś1HLOO 6 ' %HUJLQ 3 - .LQJ 8 .KDQ . <RXQJ $ *DXFKHU 6 'H R. J. Smith, I. V. Shvets, S. K. Arora, G. Stanton, H.-Y. Kim, K. Lee, G. T. Kim, G. S. Duesberg, T. Hallam, J. J. Boland, J. J. Wang, J. F. Donegan, J. C. Grunlan, G. Moriarty, A. Shmeliov, R. J. Nicholls, J. M. Perkins, E. M. Grieveson, K. Theuwissen, D. W. McComb, P. D. Nellist, and V. Nicolosi, Science, 6017 (2011) 568-571 [5] H. Li, G. Lu, Z. Yin, Q. He, H. Li, Q. Zhang, and H. Zhang, Small 5 (2012) 682-686 [6] Changgu Lee, Changgu Lee, Hugen Yan, Louis E. Brus, Tony F. Heinz, James Hone, and Sunmin Ryu, Acs Nano, 5 (2010) 2695-2700.

Figures

Fig. 1. Optical images of MoS2 flacks before (a) and after (b) thermal annealing in vacuum for 10 min at 200 Â° C

Fig. 2. Raman spectra of MoS2 flakes for various annealing temperatures together with the spectrum before thermal annealing

Ultrahigh performance of dye molecule enhanced graphene photodetector 1

1,3

Youngbin Lee , Seong Hun Yu , Yu Seong Gim , Euyheon Hwang 1

1,2

and Jeong Ho Cho

SKKU Advanced Institute of Nanotechnology (SAINT), School of Chemical Engineering, Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea, Youngbin1987@gmail.com

Abstract We present a novel graphene photodetector with broad spectral photo-response fabricated by using dye molecules for the realization of high performance optoelectronic device. We report the ultrahigh performance of a hybrid photodetector of dye molecules and graphene, covering wavelengths in the infrared to ultraviolet range with high quantum efficiencies. The main causes underlying the high performance of the hybrid photodetector are the enhancement of the absorption of light in graphene and the implementation of photocurrent gain. Due to the strong light absorption and the gain mechanism arising from dye molecules the hybrid photodetector generates much higher photocurrents (~ mA at zero gate voltage) than a pure graphene photodetectors (where the current is ~ pA) from the same amount of light. The proposed dye molecule sensitized graphene photodetectors, showing excellent weak signal detection with high responsivities (~100 A/W), uniform photoresponse, high speeds (~ millisecond), and broad spectral bandwidths (400 nm < Ȝ < 1000 nm) can be applied to graphene based optoelectronic devices. References [1] Bonaccorso, F., Sun, Z., Hasan, T. & Ferrari, A. C., Nature Photon., 4 (2010), 611±622. [2] Mueller, T., Xia, F. & Avouris, P., . Nature Photon., 4, (2010), 297±301. [3] Konstantatos G., et. al., Nature Nanotechnol., 7, (2012), 363-368

Figures

Figure 1. (a) Schematic illustration of dye molecule enhanced graphene photodetector. (b). Optical image of fabricated device. Inset denotes incident laser beam to the active area of photodetector. (c) Transfer characteristics of dye molecule enhanced graphene photodetector with respect to various wavelength of incident laser with fixed power of 1mW. (d) Photocurrent of dye molecule enhanced graphene photodetector as a function of wavelength of incident laser.

Electronic and transport properties of unbalanced sublattice Nitrogen-doping in Graphene Aurelien Lherbier, Andres R. Botell-Mendez, and Jean-Christophe Charlier Universite catholique de Louvain, IMCN, Chemin des ĂŠtoiles 8, 1348, Louvain-la-Neuve, Belgium aurelien.lherbier@uclouvain.be Abstract The incorporation of foreign atoms into the carbon honeycomb lattice has been widely investigated in order to modify the electronic and chemical properties of carbon-based materials [1,2]. In contrast with conventional materials, the effect of foreign atoms in a 2D material, such as graphene, is expected to depend significantly on the position and surrounding of each atom due to the quantum confinement of the electrons [2]. Recent scanning tunneling microscopy and spectroscopy studies of nitrogen doped 2 graphene have revealed how the incorporation of this foreign atom into the sp lattice occurs. Joucken and coworkers showed that the exposure of graphene to a nitrogen plasma flux after synthesis leads to a homogeneous distribution of substitutional atoms [3]. However, when a nitrogen source is introduced during the CVD growth of graphene, the nitrogen incorporation exhibits a preferential accommodation within one of the two triangular sublattice that compose the honeycomb lattice [4,5,6]. This wayward incorporation of nitrogen atoms into graphene is not hitherto understood [5]. Nevertheless, the consequences of this peculiar atom arrangement on the electronic and transport properties of graphene are addressed in this work. Electronic structure and transport properties of nitrogen-doped graphene with a single sublattice preference are investigated using both first-principles techniques and a real-space Kubo-Greenwood approach [7]. Such a break of the sublattice symmetry leads to the appearance of a true band gap in graphene electronic spectrum. A band gap opening due to an ordered superlattice of dopants has already been discussed [8,9]. However, such a periodic doping configuration is rather difficult to envisage experimentally. In this work, we demonstrate the robustness of the band gap opening for the case of a random distribution of dopants in the same sublattice. In addition, a natural spatial separation of both types of charge carriers at the band edge is observed, leading to a highly asymmetric electronic transport. For such N-doped graphene systems, the carriers at the conduction band edge present outstanding transport properties with long mean free paths, high conductivities and mobilities. This phenomenon is explained by a non-diffusive regime, and originates from a low scattering rate. The fact that corresponding electrons reside mainly in the unaltered sublattice explains such low scattering rate. The presence of a true band gap along with the persistence of carriers traveling in an unperturbed sublattice suggest the use of such doped graphene in GFET applications, where a high I ON/IOFF ratio is needed. The present simulations should encourage more investigation and specific measurements on N-doped graphene samples where such an unbalanced sublattice doping has been observed. References [1] P. Ayala, R. Arenal, A. Loiseau, A. Rubio, and T. Pichler, Rev. Mod. Phys. 82 (2010) 1843. [2] M. Terrones, A. Filho, A. Rao. Doped Carbon Nanotubes: Synthesis, Characterization and Applications in Carbon Nanotubes Springer (2008) 531. [3] F. Joucken, Y. Tison, J. Lagoute, et al. Phys. Rev. B 85 (2012) 161408(R). [4] L. Zhao, R. He, K.T. Rim et al., Science 333 (2011) 999. [5] A. Zabet-Khosousi, L. Zhao, L. Palova et. al., JACS 136 (2014) 1391. [6] R. Lv, Q. Li, A.R. Botello-Mendez et al., Nature Scientific Reports 2 (2012) 586. [7] A. Lherbier, A. R. Botello-Mendez, J.-C. Charlier, Nano Lett.13 (2013), 1446. [8] R. Martinazzo, S. Casolo, and G.F. Tantardini, Phys. Rev. B 81 (2010) 245420. [9] S. Casolo, R. Martinazzo, and G.F. Tantardini, J. Phys. Chem. C 115 (2011) 3250.

Figures

Figure 1. STM images of nitrogen doped graphene obtained by incorporation of N during growth: (a) single substitution [4], and (b) double substitution [6]. (c) Calculated semiclassical conductivities in graphene for various concentrations of N dopants randomly distributed in one sublattice [7].

Theory of Vacancy-Induced Intrinsic Magnetic Impurity with Quasi-Localized Spin Moment in Graphene Yang Li, Jing He, and Su-Peng Kou Department of Physics, Beijing Normal University, Beijing, 100875 spkou@bnu.edu.cn Abstract In this paper, by considering the Hubbard model on a honeycomb lattice, we developed a theory for the intrinsic magnetic impurities (MIs) with the quasi-localized spin moments induced by the vacancies in graphene. Because the intrinsic MIs are characterized by the zero modes that are orthotropic to the itinerant electrons, their properties are much different from those of Anderson MIs with the well-localized spin moments. References [1] K. S. Novoselov, et.al, Science, 306, 666(2004). [2] K. S. Novoselov, et.al, Nature, 438, 197(2005). [3] C. Neto A H,et.al, Rev. Mod. Phys. 81, 109(2009). [4] S Das Sarma, et. al, Rev. Mod. Phys. 83,407(2011). [5] S. A. Awschalom, et. al, Science, 294,1488(2001). [6] V. M. Pereira, et. al, Phys. Rev. Lett. 96, 036801(2006). [7] O. V. Yazyev, L. Helm, Phys. Rev. B75,125408(2007). [8] F. Ducastelle, Phys. Rev. B 88,075413(2013). [9] R. R. Nair, et. al, Nature Phys. 8, 199(2012). [10] Hong X, et. al, Phys. Rev. Lett. 108 226602(2012). [11] M. A. H. Vozmediano, et al, Phys. Rev. B 72,155121(2005); V. V. Cheianovand V. I. )DOÂśNR Phys. Rev. Lett.,97,226801(2006); V. K. Dugaev, et al, Phys. Rev. B 74,224438(2006); S. Saremi, Phys. Rev. B 76,184430(2007); L. Brey et al, Phys. Rev. Lett. 99, 116802(2007); E. H wang, et al,Phys. Rev. Lett. 101,156802(2008); J. E. Bunder et al, Phys. Rev. B 80,153414(2009); P. Venezuela, et al, Phys. Rev. B 80,241413(R)(2009); A. M. Black-SchaĆĄer, Phys. Rev. B 81,205416(2010); M. Sherafati, et al, Phys. Rev. B 83,165425(2011); S .R. Power, et al, Phys. Rev. B 83,155432(2011); B. Uchoa, et al, Phys. Rev. Lett. 106,016801;(2011); H. Lee, et al, Phys. Rev. B 85,075420(2012). S. R. Power, M. S. Ferreira, Crystals, 3 (1),49(2013). [12] B. Uchoa, et al, Phys. Rev. Lett. 106,016801(2011) M. A. Cazalilla, et al, arXiv: 1207.3135. [13] L. Fritz, M. Vojta, Rep. Prog. Phys. 76,032501(2013). [14] J. H. Chen, et. al, Nature Phys. 7, 535(2011). [15] For the case with a little next nearest neighbor hopping, the wave-function around a lattice-defect slightly permeates onto A sub-lattice. And the energy of the localized states shifts from zero to a Âżnite value. [16] Black-SchaĆĄer, Phys. Rev. B 82,073409(2010). [17] L. Pisani, et al, New J. Phys. 10,033002(2008). Figures

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Electronic structure of graphene nanoribbons delimited by sp3 defect lines: A density functional theory study J. X. Lian, Y. Olivier, D. Beljonne Laboratory for Chemistry of Novel Materials, University of Mons, 20 place du parc, Mons, Belgium E-mail: jian.lian@umons.ac.be

Abstract Graphene has been touted as the miracle material because of both its exceptional mechanical and electronic properties. However, owing to its semimetallic properties (absence of a band gap) its applications in electronic remain limited. Graphene nanoribbons (GNRs) appears as a particularly interesting alternative. Indeed, the electronic structure of GNRs can be tuned from a metallic to a 1-4 semiconductor behavior through a tailored quantum confinement and edge effects. To provide semiconducting properties to graphene with sufficiently large gaps, sub-5nm GNRs are required in order 1-3 to reach graphene-based FETs with proper on/off ratio at room temperature. 2 3 The formation of covalent bonds transforms the sp carbons of graphene to sp , opening a band gap 5 and generating semiconducting regions. This approach has been successfully applied for other carbon 6,7 nanostructures such as fullerenes and carbon nanotubes. In this work, we perform Density Functional Theory (DFT) calculations of the geometric and electronic structures of stripped graphene delineated by chemical defects. We show that the bonding of hydrogen atoms on specific carbon atoms along the armchair direction effectively breaks the ʌ-delocalization and opens a band gap. The density and the positions of such defects at the surface of graphene have been varied while simultaneously probing the influence on the electronic structure of the resulting periodical disruption in ʌ-conjugation. References [1] Raza, H., & Kan, E. C., Phys. Rev. B 77, 245434 (2008). [2] Son, Y. W., Cohen, M. L., & Louie, S. G., Phys. Rev. Lett. 97, 216803 (2006). [3] Han, M. Y., Ozyilmaz, B., Zhang, Y. & Kim, P., Phys. Rev. Lett. 98, 206805 (2007). [4] Li, X. L., Wang, X. R., Zhang, L., Lee, S. & Dai, H. J. Science 319, 1229±1232 (2008). [5] M. Quintana, et al., Phys. Stat. Sol. B 247, 2645 (2010) [6] M. Maggini, G. Scorrano, M. Prato, J. Am. Chem. Soc. 115, 9798 (1993) [7] P. Singh, M. Prato, et al., Chem. Soc. Rev. 38, 2214 (2009)

Acknowledgements This work is done in the frame of the project UPGRADE, which acknowledges the financial support of the Future and Emerging Technologies (FET) programme within the Seventh Framework Programme for Research of the European Commission, under FET-Open grant number: 309056

Periodic modification of graphene via strain-induced localized reaction Lei Liao, Lin Zhou, Qin Xie, Xuefeng Guo*, Zhongfan Liu

Center for Nanochemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China Corresponding author: guoxf@pku.edu.cn, zfliu@pku.edu.cn Abstract

Chemical modification has been regarded as an efficient and scalable method to tune the band structure of graphene. Because of the high energy barrier of the reaction, only a few species with high reactivity could react with graphene. Furthermore, these species react randomly with graphene and/or damage the main structure of graphene, potentially lowering the electrical properties. Thus, a new method for gaining selective modification of graphene in a controllable way is desirable. Here, we reported a controllable method to realize periodic chemical modification of graphene via the strain-induced localized reactivity. Experiments proved that graphene with the higher compress strain showed a higher reactivity. This fact was further strengthened by the DFT simulation which demonstrated that the energy barrier of the strained area was much lower than that of the flat area. Therefore, we developed an approach to introduce a periodic strain by transferring CVD-grown graphene onto a substrate with designed periodic patterns. Comprehensive characterizations including SEM, Raman spectroscopy, AFM and EFM confirmed that periodic modification was achieved after chemical reaction. To summarize, an efficient method to control periodic modification of graphene via the strain-induced localized reactivity was reported here. This method obviously provides a controllable approach to modify graphene, which opens up an avenue of applications toward functional optoelectronic devices and sensors. References [1] H. Liu, S; L. E. Brus; et al. J. Am. Chem. Soc. 131 (2009), 17099-17101. [2] A. K. Geim; K. S. Novoselov; et al. Science, 323 (2009), 610-613. Figures

Fig.1 (left) the scheme of periodic strained graphene on a patterned substrate. (right) the SEM image of periodic modified graphene.

Graphene Reinforced With Polypyrrole Nanoparticles For Energy Storage Application Hong Ngee Lim Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia janet_limhn@yahoo.com Abstract A binary nanocomposite film comprising polypyrrole (PPy) nanoparticles decorated graphene was realized using an Fe(III)-assisted electrochemical deposition approach. In the absence of Fe(III), graphene sheets were completely enveloped by PPy. With the inclusion of Fe(III) as a catalyst, the growth of PPy was controlled, which resulted in nano-sized PPy embedded uniformly on the surface of graphene sheets. The PPy nanoparticles act as spacer to hinder WKH Ę&#x152;-Ę&#x152; VWDFNLQJ RI QHLJKERXULQJ JUDSKHQH VKHHWV, causing the random orientation of the graphene sheets that gives rise to a highly porous structure. Without Fe(III), the nanocomposite film consists of largely PPy, indicating continuous growth of pyrrole monomers on the existing PPy during electrodeposition. In contrast, the PPy matrix was replaced with PPy nanoparticles in the presence of Fe(III) during electrodeposition, which suggests that Fe(III) encouraged the nucleation of PPy on the graphene sheets. The unique porous three-dimensional structure is likely to find application as an electrode material for energy storage application. Figures a

FESEM images showing cross sectional views of graphene/PPy prepared (a) in the absence and (b) in the presence of Fe(III). TEM image shows decoration of graphene with PPy nanoparticles.

A versatile plasma-based method for the nitrogen doping of graphene Yu-Pu Lin, Younal Ksari, Jai Prakash, Luca Giovanelli, Jean-Marc Themlin Aix-Marseille UniversitĂŠ, CNRS, IM2NP, UMR 7334, 13397 Marseille, France yu-pu.lin@im2np.fr Abstract The chemical doping of graphene, which influences its electronic and chemical properties (opening band-JDS DOWHULQJ FDUULHUV GHQVLWLHV HWFÂŤ , is currently a critical aspect in graphene research and development. [1] In particular, the nitrogen doping of graphene has attracted intensive attention due to a relative facility for nitrogen to substitute carbon atoms in the honeycomb lattice of graphene.[2] The doping nitrogen may be bound in various configurations, such as in graphitic-like, pyridinic-like or pyrrolic-like configuration (see figure 1a), depending on the presence of any neighbor vacancies.[2] Moreover, the N-doped graphene has also been reported to exhibit superior performance over the pristine material in several applications (field-effect transistors, batteries, fuel cells, super-capacitors, and biosensors).[3-8] Though, methods to realize a reliable and controlled doping have still to be mastered, if graphene is to enter the realms of practical devices. The substrate on which the pristine graphene is grown also plays an important role in the fabrication of graphene-based devices. Epitaxial monolayers grown on the Si-termination of SiC are a promising route to produce high-quality graphene on wafer-size area on top of a semi-insulating substrate, especially when the graphene monolayer can be effectively decoupled from the substrate (and the so-called buffer layer) by foreign atom intercalation.[9] However, there is only a very limited number of published works devoted to the nitrogen-doping of epitaxial graphene layers grown on SiC. Most of these studies consist of simulations, and the reported experimental realizations are still in their infancy: additional efforts are thus necessary in order to obtain control and reproducibility of graphene chemical doping by N atoms. In this work, we present an effective, versatile plasma-based method for the nitrogen-doping of graphene grown on 6H-SiC(0001). By using a tunable hybrid plasma source, the graphene monolayers are exposed to a stream of low-energy nitrogen ions and/or to a neutral flow of thermalized nitrogen species. A thermal annealing is applied during (or after) nitrogen doping to reduce the defects created by the plasma exposure. The electronic properties of the nitrogen-doped graphene are investigated using angle-resolved inverse photoemission spectroscopy (ARIPES). This technique reveals the energy and dispersion of the unoccupied electronic states of graphene, in particular the Ę&#x152;* states which form the upper Dirac cone at the K points of its Brillouin zone. We used the shift of these Ę&#x152;* states upon nitrogen exposure to estimate the magnitude of the n-type doping. The results show that low-energy nitrogen ions (5~35 eV) cause an n-type doping (up to 0.4 eV), as shown in figure 1b, associated to a majority of graphitic-N (up to 8.7%), as revealed by XPS (figure 1c). On the other hand, thermalized neutral nitrogen species, at even lower energy, rather form pyridinic-N (figure 1c) in the presence of defects, and induce nearly neutral doping with respect to the pristine one (figure 1b). In brief, we show how a simple plasma-based technique can be used in a versatile way to control the bonding environment of nitrogen atoms in graphene. It will certainly be of great interest for the processing of future graphene-based nano-devices using widespread technologies like plasmaprocessing.

References [1] [2] [3] [4] [5] [6] [7] [8] [9]

H. Liu, Y. Liu, and D. Zhu, Journal of Materials Chemistry 21 (2011) 3335-3345. H. Wang, T. Maiyalagan, and X. Wang, ACS Catalysis 2 (2012) 781-794. D. Wei, Y. Liu, Y. Wang, H. Zhang, L. Huang, and G. Yu. Nano Letters, 9 (2009) 1752-1758. M. D. Stoller, S. Park, Y. Zhu, J. An, and R. S. Ruo, Nano Letters 8 (2008) 3498. S. Yang, X. Feng, X. Wang, and K. Mullen, Angewandte Chem. International Edition 50 (2011) 5339. D. Pan, S. Wang, B. Zhao, M. Wu, H. Zhang, Y. Wang, and Z. Jiao, Chem. Mater. 21 (2009) 3136. H. M. Jeong, J. W. Lee, W. H. Shin, Y. J. Choi, H. J. Shin et al, Nano Lett. 11 (2011) 2472. Y. Wang, Y. Shao, D. W. Matson, J. Li, and Y. Lin ACS Nano 4 (2010) 1790-1798. C. Riedl, C. Coletti, T. Iwasaki, A. A. Zakharov, and U. Starke, Phys. Rev. Lett. 103 (2009) 246804.

Figures

Figure 1. (a) Schematic representation of the three principal configurations of doping nitrogen in graphene: Pyridinic-N, Pyrrolic-N and Graphitic-N. (b) Linear extrapolation of the Ę&#x152;* states obtained by ARIPES for pristine graphene (circle), NG-ion (square) and NG-atom (rhombus) with respect to k // along the ÄŤ-K direction of the graphene Brillouin Zone. (c) N 1s XPS spectra of the studied NG samples. The top two spectra are characteristic of the monolayer graphene exposed to nitrogen ion species of 35 and 5 eV for 10 min. NG-atom is the same pristine graphene exposed to neutral species for 10 min.

Non-catalytic chemical vapor deposition of nanocrystalline graphene on insulating and semiconducting substrates Niclas Lindvall, Jie Sun, and August Yurgens Chalmers University of Technology, SE-41296, Gothenburg, Sweden niclas.lindvall@chalmers.se There are various ways of producing large-scale graphene, all resulting in different kinds of material suitable for different applications. Catalytic chemical vapor deposition (CVD) of graphene on Cu is the most common way to produce high-quality graphene for electronics [1]. It relies, however, on the successful transfer of graphene from metal catalyst to the desired, typically insulating or semiconducting, substrate. This transfer is often related to issues with metal residues, adhesion problems, and holes in the graphene film. Hence, a transfer-free method of growing graphene is desirable. We grow nanocrystalline graphene non-catalytically on practically any high-temperature compatible substrate. Hence, there is no transfer involved in the process. The main difference from CVD of graphene on Cu is the significantly higher partial pressure of carbon precursor gas, typically C2H2. At the growth temperature of 1000 °C, we grow similar graphene films on Si 3N4, SiO2, HfO2, and GaN [2-5]. This process is not self-limiting, and the thickness of the film can be controlled form nominally monolayer to hundreds of nm by the process parameters. The films are characterized by Raman spectroscopy, transmission electron microscopy, and electrical measurements. They exhibit very small crystal domains in the order of 10 nm and electrical mobility in the order of 10 cm2/Vs. However, they also exhibit high mechanical strength, uniformity over optical length-scales, and show optical properties similar to pristine graphene. Such properties make it a promising candidate for applications including transparent heaters, transparent conductives, and membranes [6-8]. Especially, we use it as a current spreading layer in GaN devices. References [1] J. Sun, N. Lindvall, M. Cole, K. Angel, T. Wang, K. Teo, D. Chua, J. Liu, and A. Yurgens, IEEE Trans Nanotechnol 11/2 (2012), pp 255-260. [2] J. Sun, M. T. Cole, S. A. Ahmad, O. Bäcke, T. Ive, M. Löffler, N. Lindvall, E. Olsson, K. B. K. Teo, J. Liu, A. Larsson, A. Yurgens, and Å. Haglund, IEEE Trans Semicond Manuf 25/3 (2012), pp 494-501. [3] J. Sun, N. Lindvall, M. T. Cole, T. Wang, T. J. Booth, P. Boggild, K. B. K. Teo, J. Liu, and A. Yurgens, J Appl Phys 111/4 (2012), p. 044103. [4] J. Sun, N. Lindvall, M. T. Cole, K. B. K. Teo, and A. Yurgens, Appl Phys Lett 98/25 (2011), p. 252107. [5] N. Lindvall, J. Sun, G. Abdul, and A. Yurgens, Micro Nano Lett 7/8 (2012), pp 749-752. [6] J. Sun, M. T. Cole, N. Lindvall, K. B. K. Teo, and A. Yurgens, Appl Phys Lett 100/2 (2012), p. 022102. [7] N. Lindvall, A. Kalabukhov, and A. Yurgens, J Appl Phys 111/6 (2012), pp 064904-064904. [8] K. Xu, C. Xu, Y. Y. Xie, J. Deng, Y. X. Zhu, W. L. Guo, M. M. Mao, M. Xun, M. X. Chen, L. Zheng, and J. Sun, Appl Phys Lett 103/22 (2013).

Self-encapsulated doped graphene/silicon Schottky junction solar cell with high efficiency and excellent stability 1

Yi-Ting Liou, Po-Hsun Ho, Yun-Chieh Yeh, Chun-Wei Chen

Department of Materials Science and Engineering, National Taiwan University, No.1, Sec. 4, Roosevelt 5G 'DÂśDQ 'LVW Taipei, Taiwan etyiting@gmail.com

In this work, a high-efficiency graphene-silicon Schottky junction solar cell device has been demonstrated. With hybrid p-dopant (N-Fluorobenzenesulfonimide, NFSI) and antireflective materials (Poly(methyl methacrylate), PMMA) as a self-encapsulated doping layer, we are able to fabricate highefficiency graphene/Si solar cells with an efficiency up to 12% The self-encapsulated doping layer not only demonstrates efficient doping effect but also shows excellent antireflection function. The graphene/Si solar cell device based on this novel self-encapsulated doping layer also exhibits excellent air stability. This simple technique using the self-encapsulated doping layer provides a promising potential to develop high-efficiency graphene/Si Schottky junction solar cell device with excellent airstability.

First-principles study of the structure and mechanical properties of graphene oxide Lizhao Liu, Jijun Zhao

Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Dalian University of Technology), Ministry of Education, Dalian 116024, China lizhao_liu@mail.dlut.edu.cn; zhaojj@dlut.edu.cn Abstract Graphene oxide (GO) is a layered graphene with oxygen-contained functional groups, which plays an important role in synthesis of graphene from chemical reduction [1]. Also, due to abundant functional groups, GO shows promising applications in chemical engineering, energy storage, environmental science, and ELRWHFKQRORJ\ +RZHYHU LWÂśV YHU\ GLIILFXOW WR GHWHrmine atomistic structure of GO due to its nonstoichiometry since the oxygen-contained groups and their arrangements across the carbon network vary much more in different synthesis conditions. Using spectroscopic techniques, such as solid-state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), X-ray absorption nearedge spectroscopy (XANES), and Raman spectroscopy, the types of oxygenated functional groups in GO can be determined [2]. Now it is commonly accepted that GO bears epoxy (C-O-C) and hydroxyl (COH) on its basal plane. However, how are the epoxy and hydroxyl distributed spatially over the graphene plane? Numerous experimental measurements suggest that they are distributed amorphously; while theoretical simulations show that the epoxy and hydroxyl prefer to form ordered structure to lower the total energy. To address this controversial issue and gain a deeper insight into the structural characteristics of GO, we considered the possibility of amorphous structural models of GO and compared them with the ordered structures by using the plane-wave pseudopotential technique implemented in the CASTEP program [3]. Then, employing Vienna ab initio simulation package (VASP), we further studied the mechanical properties of GO for both the amorphous and ordered GO models [4]. According to some confinement rules, we randomly placed epoxy and hydroxyl groups on the basal graphene layer to construct GO models with tunable oxygen coverage (R) and ratio of hydroxyl to epoxy (OH : O) [3]. Then we compared the amorphous GO with the ordered structure proposed previously [5, 6]. It was found that formation of hydroxyl groups on graphene basal is easier than that of epoxy due to the effects of hydrogen bonds. At the same stoichiometry, ordered GO presents better thermodynamic stability than the amorphous one. But, when the coverage is less than 5%, amorphous GO can have comparable stability to the ordered GO. For the case of fixed OH : O ratio but different Rs, optimized GO models with low energies always contain some local ordered structures. Similarly, for the case of constant R but different OH : O ratios, local ordered structures also exist in the energetically preferable GO models, as shown in Fig. 1. This can be attributed to formation of hydrogen bonds between the ordered functional groups, which can lower the energy and stabilize the GO structure. Therefore, the real GO sample fabricated in experiments may be in a local ordered but long-range amorphous pattern. On the other hand, for both the amorphous and ordered GO models, increasing the R will lead to a large band gap, as shown in Fig. 2, which provides an effective approach to tune the electronic properties of GO. In addition, through comparing mechanical properties between the ordered and amorphous GO models, it was found that at the same stoichiometry, ordered GO has larger YoungÂśs modulus, intrinsic strength and critical failure strain than those of the amorphous GO, as shown in Table 1 [4]. Increase of the R will degrade the YoungÂśs modulus and intrinsic strength of GO. Generally, mechanical properties of GO depend mainly on the R and spatial distribution of functional groups (ordered or amorphous). Change of OH : O ratio only slightly fluctuate the YoungÂśs modulus. Particularly, GO shows significant strain-tuned electronic properties. Under uniaxial tensile strain, band gap of the GO gets shrinked with the strain due to weakening of C-O hybridization, as shown in Fig. 3. Therefore, in addition to change of R, external strain is another effective way to tune the electronic properties of GO. References [1] Pei S., Cheng H.-M. Carbon 50 (2012) 3210-3228. [2] Chen D., Feng H., Li J. Chemical Reviews 112 (2012) 6027-6053. [3] Liu L., Wang L., Gao J., Zhao J., Gao X., Chen Z. Carbon 50 (2012) 1690-1698. [4] Liu L., Zhang J., Zhao J., Liu F. Nanoscale 4 (2012) 5910-5916. [5] Wang L., Lee K., Sun Y.-Y., Lucking M., Chen Z., Zhao J.-J., Zhang S.-B. ACS Nano 3 (2009) 29953000.

[6] Wang L., Sun Y.-Y., Lee K., West D., Chen Z.-F., Zhao J.-J., Zhang S.-B. Physical Review B 82 (2010) 161406. Table 1 For the case of OH : O = 2.00 but different Rs, comparison of Young¶s modulus (E), intrinsic strength (Ĳc) and critical failure strain (İc) between the ordered and amorphous GO models, along with that of the graphene (R = 0%) for reference, where the van der Waals distance is taken to be 7 Å. R 0% 10% 20% 40% 50%

E (GPa)

Ordered GO Ĳc (GPa)

İc

495 469 454 421 408

47.8 46.3 44.4 40.0 38.6

20% 18% 17% 16% 16%

E (GPa)

Amorphous GO Ĳc (GPa)

İc

495 431 395 367 325

47.8 40.9 37.5 33.1 27.9

20% 13% 13% 13% 10%

Figure 1. Local ordered structures in amorphous GO models. (a) has OH : O = 2.00 and R = 70%; (b) has OH : O = 0.22 and R = 50%; and (c) has OH : O = 8.00 and R = 50%.

Figure 2. Increase of band gap with enlarging R for both ordered (a) and amorphous (b) GO.

Figure 3. Shrinkage of band gap under uniaxial tensile strain for the ordered GO (a) and release of charge due to weakening of C-O hybridization under strain (b).

Atom-resolved study of CVD graphene on Rh substrates and its intriguing properties by STM/STS Mengxi Liu

1, a

, Yanfeng Zhang

1, 2

, Zhongfan Liu

Center for Nanochemistry (CNC), College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China

Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing, 100871, China a

liumx-cnc@pku.edu.cn

Abstract: Chemical vapor deposition (CVD) is the most popular method to prepare large-scale and highly uniform graphene films on metal substrates. However, the atomic-scale structure, the stacking order, as well as the defect states was seldom reported due to the corrugated nature of the polycrystalline metal substrates.

[1-3]

We tried to address this issue by using Rh foils and Rh(111) as substrates, and explore

the different graphene growth behaviors mainly by virtue of scanning tunneling microscopy/ spectroscopy (STM/STS) characterizations.

[4, 5]

Interestingly, a templated growth of singlecrystalline

graphene by the Rh(111) lattice is obtained under (ultrahigh vacuum chemical vapor deposition) UHVCVD conditions at 600 Â°C, which is characterized with the formation of a uniform graphene moirĂŠ. In comparison, monolayer and randomly stacked few-layer graphene is achieved under the atmosphere pressure chemical vapor deposition (APCVD) condition at 1000 Â°C, via different quenching processes on both Rh foils and Rh(111) (Figure 1). On the basis of evidences hereinbefore, we proposed a surface catalysis and a segregation mechanism for graphene growth at 600 Â°C and 1000 Â°C, respectively. Moreover, randomly stacked bilayer or few layer graphene usually exhibit various moirĂŠ patterns, on which angel-dependent van hove singularities (VHSs) was observed by STM/STS.

[6]

In addition, since

the distinguished thermal expansion coefficient of graphene and Rh foils, high-density wrinkles and [5]

ripples are formed on graphene. Along a wrinkle, states condensed into well-GHÂżQHG SVHXGR-Landau OHYHOV ZKLFK PLPLF WKH TXDQWL]DWLRQ RI PDVVLYH FKLUDO IHUPLRQV LQ D PDJQHWLF ÂżHOG RI DERXW 7 We [7]

propose that this work is expected to contribute greatly to understand the growth mechanism, the atomic scale structures, as well as the intriguing physical properties like VHSs and high-temperature zero-field quantum valley Hall effect of graphene on polycrystalline metal substrates.

References [1] Y.F. Zhang, T. Gao, Y.B. Gao, S.B. Xie, Q.Q. Ji, K. Yan, H.L. Peng and Z.F. Liu, ACS Nano, 5, (2011), 4014. [2] T. Gao, S.B. Xie, Y.B. Gao, M.X. Liu, Y.B. Chen, Y.F. Zhang and Z.F. Liu, ACS Nano, 5, (2011), 9194. [3] Y.F. Zhang, T. Gao, S.B. Xie, B.Y. Dai, L, Fu, Y.B. Gao, Y.B. Chen, M.X. Liu and Z.F. Liu, Nano Research, 5, (2012), 402. [4] M.X. Liu, Y.B. Gao, Y.F. Zhang, Y. Zhang, D.L. Ma, Q.Q. Ji, T. Gao, Y.B. Chen, and Z.F. Liu, Small, 9, (2013), 1360. [5] M.X. Liu, Y.F. Zhang, Y.B. Chen, Y.B. Gao, T. Gao, D.L. Ma, Q.Q. Ji, Y. Zhang, C. Li, and Z.F. Liu., ACS Nano, 6, (2012), 10581.

ยง

[6] W. Yan , M.X. Liu , R.F. Dou, L. Meng, L. Feng, Z.D. Chu, Y.F. Zhang, Z.F. Liu, J.C. Nie, L. He., Physical Review Letters, 109, (2012), 126801. [7] W. Yan, W. Y. He, Z. F. Chu, M. X. Liu, L. Meng, R. F. Dou, Y. F. Zhang, Z. F. Liu, C. J. Nie and L. He, Nature Communications, 4, (2013), 2159.

Figures

Figure 1. Singlecrystalline and polycrystalline graphene were obtained on Rh(111) under UHV and APCVD conditions at different growth temperature, respectively.

Efficient modelling of graphene-based optical devices Andrea Locatelli, Costantino De Angelis UniversitĂ degli Studi di Brescia, via Branze 38, Brescia 25123, Italy E-mail: andrea.locatelli@unibs.it Antonio-Daniele Capobianco UniversitĂ degli Studi di Padova, via Gradenigo 6/b, Padova 35131, Italy Stefano Boscolo, Michele Midrio UniversitĂ degli Studi di Udine, via delle Scienze 208, Udine 33100, Italy Abstract In the last years the unique optical properties of graphene have attracted the attention of the scientific community, and novel graphene-based photonic, plasmonic and optoelectronic devices have been proposed for a plethora of applications [1, 2]. In this framework, numerical and analytical modelling play a crucial role both for design and analysis purposes. As a matter of fact, well-established models for the complex bi-dimensional linear conductivity of graphene have been reported in the literature (see e.g. [3, 4]), and a strong third-order optical nonlinear response has also been predicted both theoretically and experimentally [5, 6]. Nevertheless the analysis of graphene-based optical devices remains quite challenging from the numerical point of view. Indeed, it was demonstrated that graphene layers can be accurately modeled in conventional full-wave solvers by treating them as volumetric media with known conductivity and proper atomic thickness (< 1 nm) [7, 8], but the required fine discretization of these ultra-thin layers results in a huge computation burden. In order to overcome this limitation, a different and more efficient approach to this kind of problem has recently been proposed. In fact, it was demonstrated that all the effects induced by the presence of graphene layers embedded in dielectric media can be modeled by discontinuities of the magnetic field which take into account the surface currents flowing on the graphene layers. In this way, the whole analysis is greatly simplified and a more relaxed discretization step can be used. By applying this technique, amplitude equations for surface plasmons in graphene have been derived [9], and the peculiar properties of directional couplers composed of a pair of graphene layers have been thoroughly studied, both in the linear [10] and in the nonlinear regime [11]. In particular, in Ref. [10] we have calculated the dispersion relations of the supermodes of a symmetric graphene plasmonic coupler by illustrating a procedure which allows to treat the more general case of asymmetric structures. Graphene layers can also be sandwiched within conventional slab waveguides in order to electrically tune the optical properties of these structures. In this context, we have demonstrated that also the nonlinear phase shift which is induced by the strong third-order nonlinearity of graphene can be incorporated into a boundary condition for the tangential magnetic field, and we discussed the existence of nonlinear modes sustained by graphene layers in dielectric waveguides [12]. Moreover, we have shown that the beat length of dielectric couplers can be controlled by inserting graphene layers in the middle of those structures and then tuning the bias voltage in order to vary the dielectric constant of graphene, thus shifting only the effective index of the even supermode [13]. Last, but not least, we have recently proposed to exploit the idea of modelling the graphene as a purely bi-dimensional sheet which imposes a boundary condition on the magnetic field to realize a novel ultrafast field propagator tailored for graphene-based devices [14]. The algorithm is derived from the well known Beam Propagation Method (BPM), which has been widely used in the last decades for the analysis of wave propagation in photonic devices. The key point of the method is the finite-difference formulation of the second-order derivative, which allows to discretize the discontinuous magnetic field by including in the diffractive operator all the effects which stem from the presence of the graphene layers, thus avoiding to resort to sub-nanometer sampling steps. The novel BPM has been validated first by demonstrating the undistorted propagation of the even and the odd supermodes of the graphene coupler described in [10, 11], as it is possible to verify in Fig. 1. Then, a single waveguide has been excited and the field evolution along the coupler has been evaluated by propagating the input field with the reformulated BPM technique. In Fig. 2 we demonstrate the high tunability of this kind of structure by reporting results obtained by slightly varying the chemical potential of the two layers. In Fig. 3 a systematic comparison between the beat length calculated by using the BPM and analytical results obtained from the solution of the dispersion relations is depicted. The excellent agreement between numerical and analytical results constitutes a strong validation of the proposed technique. The results that we illustrate are fundamental to show that the novel BPM algorithm allows ultrafast and accurate analysis of complex photonic devices wherein graphene layers are introduced in order to exploit the high tunability of their optical parameters. These findings open the way to the realization of a brand new class of field propagators specifically tailored for the analysis of graphene-based structures.

References [1] Q. Bao, and K. P. Loh, ACS Nano, 6 (2012) 3677. [2] F. Xia, H. Yan, and P. Avouris, Proc. IEEE, 101 (2013) 1717. [3] G. W. Hanson, IEEE Trans. Antennas Propagat., 56 (2008) 747. [4] T. Stauber, N. M. R. Peres, and A. K. Geim, Phys. Rev. B, 78 (2008) 085432. [5] S. A. Mikhailov, and K. Ziegler, Journ. Phys.: Condens. Matter, 20 (2008) 384204. [6] E. Hendry, P. J. Hale, J. Moger, A. K. Savchenko, and S. A. Mikhailov, Phys. Rev. Lett., 105 (2010) 097401. [7] M. Midrio, S. Boscolo, M. Moresco, M. Romagnoli, C. De Angelis, A. Locatelli, and A.-D. Capobianco, Opt. Express, 20 (2012) 23144. [8] A. Locatelli, A.-D. Capobianco, M. Midrio, S. Boscolo, and C. De Angelis, Opt. Express, 20 (2012) 28479. [9] A. V. Gorbach, Phys. Rev. A, 87 (2013) 013830. [10] A. Auditore, C. De Angelis, A. Locatelli, and A. Aceves, Opt. Lett., 38 (2013) 4228. [11] D. A. Smirnova, A. V. Gorbach, I. V. Iorsh, I. V. Shadrivov, and Y. S. Kivshar, Phys. Rev. B, 88 (2013) 045443. [12] A. Auditore, C. De Angelis, A. Locatelli, S. Boscolo, M. Midrio, M. Romagnoli, A.-D. Capobianco, and G. Nalesso, Opt. Lett., 38 (2013) 631. [13] A. Locatelli, A.-D. Capobianco, G. Nalesso, S. Boscolo, M. Midrio, and C. De Angelis, Opt. Commun., 318 (2014) 175. [14] A.-D. Capobianco, A. Locatelli, S. Boscolo, C. De Angelis, and M. Midrio, submitted to IEEE Photon. Technol. Lett., (2014). Figures

Fig. 1. Magnitude of the magnetic field at the input of the coupler (blue lines) and after BPM propagation (red lines). Blue and red lines are almost overlapped. a) Even supermode. b) Odd supermode.

Fig. 2. Field evolution along the coupler evaluated by using the BPM algorithm when chemical potential is Âľc = 0.1 eV (left) and Âľc = 0.16 eV (right).

Fig. 3. Beat length of the coupler as a function of the chemical potential evaluated from BPM simulations (red circles) and from the dispersion relations of the supermodes (solid line).

Mechanical properties of graphene with defects created by ion bombardment 1

1,2

Guillermo López-Polín , Cristina Gómez-Navarro , Vincenzo Parente , Francisco Guinea , Mikhail I. 4 5 1,2 Katsnelson , Francesc Pérez-Murano and Julio Gómez-Herrero 1

Depto. de Física de la Materia Condensada, Universidad Autónoma de Madrid, 28049, Madrid, Spain. 2 Centro de Investigación de Física de la Materia Condensada, Universidad Autónoma de Madrid, 28049, Madrid. 3 Instituto de Ciencia de Materiales, CSIC, 28049, Madrid, Spain 4 Radboud University Nijmegen, Institute for Molecules and Materials, Heyendaalseweg 135, NL-6525AJ Nijmegen, The Netherlands 5 Instituto de Microelectrónica de Barcelona, CSIC, 08193 Bellaterra, Spain. guillermo.lopezpolin@uam.es

Abstract Pristine graphene sheets exhibits superior mechanical properties very promising for applications; they are very light, flexible, stiff, and strong [1]. One of the main challenges for transferring graphene to real application is the large scale production. Currently all the routes to obtain graphene in large scale (CVD, Graphene oxide) produce layers with different kind of defects (grain boundaries, point defects). These defects have been demonstrated to lower the stiffness and strength of the layers [2, 3]. Unfortunately, the fact that these defects are created in a non-controlled manner during sample preparation prevents systematic studies on mechanical properties with defects. Our approach in this work is to introduce defects in a pristine membrane in a controlled manner by Ar+ ion bombardment, creating mainly atomic monovacancies. For a precise characterization of the defect type and density we use Raman spectroscopy and STM. The stiffness and strength with defect density are then measured by AFM nanoindentations (Fig.1). Counter intuitively, we find that the stiffness of graphene increases with defect content until a vacancy content of ~0.2%, where it doubles its initial value. For higher irradiation doses the elastic modulus slowly decreases with defects inclusion. The initial increase in stiffness can be explained in the framework of statistical mechanics of 2D membranes, where the elastic coefficients are predicted to depend with the momentum of flexural modes [4]. In contrast to the elastic trend, the fracture strength decreases with defect density according to standard fracture continuum models.

References [1] C. Lee, X. D. Wei, J. W. Kysar, J. Hone, Science, 321 (2008), 385 [2] C. Gomez-Navarro, M. Burghard, K. Kern, Nano Letters, 8 (2008), 2045 [3] C.S. Ruiz-Vargas et al., Nano Letters, 11 (2011), 2259. [4] J. A. Aronovitz, T. C. Lubensky, Physical Review Letters, 60 (1988), 2634

Figures

Figure 1. Scheme of a AFM nanoindentation on a free-standing graphene membrane.

Synthesis and characterization of gold nanoparticles/graphene hybrid materials a

Carlos Bueno-Alejo , Suzana M. Andrade , Roberta Viana Ferreira Bruno Machado , Revathi Bacsa c c Stéphane Louisia , Philippe Serp

Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal b Departamento de Química, Universidade Federal de Minas Gerais, Campus Pampulha, 31270-901 Belo Horizonte, Minas Gerais, Brazil c Laboratoire de Chimie de Coordination UPR CNRS 8241, composante ENSIACET, Toulouse University, 4, Allée Monso-BP 44362 31030 Toulouse, France Philippe.Serp@ensiacet.fr

Abstract In recent years, graphene has been utilized as a support material to anchor a large variety of 1 nanoparticles including noble metals such Pt, Au, Pd and oxides such TiO2, ZnO and CeO2 . Such 2 composites are expected to have superior electronic or optical properties . Gold nanoparticles (AuNP) are one of the most interesting nanostructures, having found many applications in fields such as medicine, sensors, and catalysis. Due to their small size, these particles show some properties that differ from those of the bulk. Among those properties, the presence of a surface plasmon band in the visible region of the electromagnetic spectrum makes these materials suitable for many attractive 3 applications in catalysis, optics and nanobiotechnology . For these applications, an optimization of the gold particle size, the distribution of particle sizes and their dispersion on the graphene surface is desirable. In this communication, we report the synthesis and characterization of gold nanoparticles dispersed on few layer graphene (FLG) wherein we have compared a number of deposition methods. Different graphene derivatives such as purified FLG flakes (GP), functionalized FLG (FGP), defunctionalized FLG (DFGP), N-doped FLG (NGP) and fully oxidized graphene (GO) have been investigated as support. All 4 the supports were prepared by in house CVD process by the catalytic decomposition of ethylene . Nitrogen doping was carried out using a mixture of ethylene and ammonia as precursors. The FLG flakes were purified by dissolving the catalyst in 35% HCl at 25°C and characterized by SEM, TEM and Raman spectroscopy. Nitrogen doping was confirmed by chemical analysis and XPS. Prior to gold deposition, the surfaces of the FLG were functionalized by boiling in 65% HNO 3 at 120°C for 3-6h (FGP) 7KH H[WHQW RI IXQFWLRQDOL]DWLRQ ZDV GHWHUPLQHG E\ WKH %RHKP¶V WLWration and XPS. From the several methods available for the preparation of AuNP on graphene derivatives we have 5 chosen the following ones: a) a modification of the literature sonolytic method , which consists in the sonication of the support and the Au salt in aqueous suspensions, b) an impregnation/reduction method developed by us, and c) the simple mixing of pre-synthesized AuNP with the support. The size and dispersion control of the AuNP were assessed from TEM images. The interaction between the gold nanoparticles and the support was further investigated using Raman analysis. Nitrogen doping was found to have a strong influence on the particle density and size distribution (Fig.1).Very fine particles in the size range of 1-3 nm were observed even though some particles were much bigger in size even up to 20 nm.

200 nm

Figure 1. Gold particles deposited on FGP (left) and NGP (right) References

1. B.F. Machado, P. Serp, Catal. Sci. Technol. 2 (2012) 54. 2. C. Xu, X. Wang, J. Zhu, J. Phys. Chem. C 112 (2008) 19841. 3. V. Georgakilas, D. Gournisb, V.Tzitziosa, L. Pasquato, D. M.Guldie, M. Prato, J. Mater. Chem. 26 (2007) 2679. 4. R. Bacsa, P. Serp, WO 2013093350A1. 5. K. Vinodgopal, B. Neppolian, Ian V. Lightcap, Franz Grieser, Muthupandian Ashokkumar Prashant V. Kamat, J. Phys. Chem. Lett. 1 (2010) 1987.

Acknowledgments: Project PTDC/Qui-Qui/117498/2010 funded by FCT is acknowledged.

Seed-free Si growth on transferred graphene by ICP Chemical Vapor Deposition a

M. Lukosius , X. Wang , A. Wolff , J. Kitzmann , W. Mehr , M. Arens , and G. Lupina

IHP, Im Technologiepark 26, 15236 Frankfurt (Oder), Germany SENTECH Instruments, Schwarzschildstr. 2, 12489 Berlin, Germany lukosius@ihp-microelectronics.com

Abstract Large area graphene synthesis on the target substrates as well as the depositions of reliable thin dielectric/semiconducting layers on top of the graphene are key challenges in order to realize the complete potential of graphene in novel microelectronic devices like vertical field effect transistors [1], graphene base transistors [2], or photodetectors [3], to name a few. Due to the hydrophobic nature of graphene [4] and the lack of dangling bonds, the depositions of dielectric/semiconductors are hindered, which leads to the formation of discontinuous films, where dielectrics preferably grow on defects or steps [5]. In order to better nucleate the growth of the dielectrics on graphene, several surface treatments have been investigated, including the evaporation of metal seeding layers [6] or covering graphene with polymers [7]. Unfortunately, these treatments can lead to the degradation of the electrical properties or make the technological processes more complicated. Recently, we have reported on the MBE depositions of smooth and closed Si layers on transferred graphene [8]. Zhu reported that Si 3N4 can be grown directly on graphene by PECVD at 400 째C at low plasma power [9], although it is known that graphene is sensible to plasma processes. In this work, we examine the possibility to grow amorphous Si directly on graphene by inductively coupled plasma enhanced chemical vapour deposition (ICPECVD). Up to now, direct depositions of Silicon by ICPECVD on graphene have not been reported yet. Commercially available graphene was transferred (by using standard graphene transfer technique) from Cu foils on to the Si (100) wafers, covered with 100 nm SiO2 layers. After the transfer, the samples were annealed at 500 째C for 1 hour in order to remove the residual polymer contamination. Depositions of Si have been performed at 100 째C using silane (SiH4) and hydrogen (H2) gases. The plasma power was kept at 50 W in all the experiments. Raman spectroscopy was done by a Renishaw inVia microscope using 514 nm laser light and 1800 lines/mm grating. Atomic force microscopy (AFM) and Scanning electron microscopy (SEM) were used to examine the surfaces of the grown Si layers. In the first step, 10 or 50 nm amorphous Silicon has been grown on the transferred graphene. The optical image of the sample with 10 nm Si is shown in Fig.1, where a clear interface between the graphene and SiO2 was visible. No evidence of any cracking or peeling of the top Si layer was observed. Figure 2 shows the SEM image of the same 10 nm Si layer, grown on graphene. It can be seen, that the layer was continuous and completely closed. A more detailed surface analysis was performed by AFM, where two regions, Si grown on graphene (Fig. 3) and Si grown on SiO2 (Fig. 4) have been investigated. It is clearly visible, that the surface of Si, grown on graphene is rougher than the one grown on SiO 2. The extracted root mean square (RMS) values were 1,2 nm and 0,5 nm, respectively. The growth of Si was also confirmed by Raman spectroscopy (Fig. 5), where a-Si modes were detected on graphene as well as on SiO2. Figure 6 compares Raman spectra of graphene before and after Si deposition. The typical Raman spectrum of the transferred graphene is indicated by the green line in Fig. 6. As can be seen, transfer procedure does not influence graphene quality, as a negligible D mode was measured. However, the Si deposition process partially destroys graphene, since rather high D signal was detected, as can be seen in the red line in Fig. 6. This can be explained by the fact that plasma has a negative influence on the graphene layer; therefore the plasma assisted growth of Si must be further optimized. The development of low temperature ICPECVD Si process on graphene is vital for the back end of line fabrication of novel graphene devices. References [1] L. Britnell et .al., Science, 335 (2012) 947. [2] W. Mehr et. al., IEEE Electron Dev. Lett., 33 (2012) 691. [3] P. LV et .al., IEEE Electron Dev. Lett., 34 (2013) 1337. [4] C. N. Rao et. al. Angew. Chem. Int. Ed., 48 (2009) 7752. [5] B. Lee et. al., Appl. Phys. Lett., 92 (2008) 203102. [6] S. Kim et. al. Appl. Phys. Lett., 98 (2011) 133106. [7] D. Farmer et. al., Nano Lett., 9 (2009) 4474. [8] G. Lupina et. al. Appl. Phys. Lett., 103 (2013) 263101. [9] W. Zhu et. al., Nano Lett., 10 (2010) 3572.

Figures

a-Si / SiO

a-Si/Graphene/SiO

Fig. 1. Optical image of the a-Si, grown on graphene.

Fig. 3. AFM of 10 nm Si, grown on graphene.

Fig. 5. Raman spectra before (black line) and after depositions of Si on graphene (red line) and SiO2 (blue line).

Fig. 2. Tilt-view SEM image after deposition of 10 nm Si.

Fig. 4. AFM of 10 nm Si, grown on SiO2.

Fig. 6. Raman spectra from graphene after transfer (greeen line) and after Si deposition (red line).

Synthesis of Graphene on dielectric substrates using a modified filtered vacuum arc system 1

Helge Lux , Peter Siemroth , Sigurd Schrader 1 2

Technical University of Applied Sciences Wildau, BahnhofstraĂ&#x;e 1, 15745 Wildau, Germany Arc Precision GmbH, BahnhofstraĂ&#x;e 1 / Halle VII, 15745 Wildau, Germany

Contact Email: lux@th-wildau.de

Abstract Here we present a reliable process to deposit graphene directly on silicon oxide, quartz, and mica (muscovite) using a solid carbon source. The process uses a pulsed filtered vacuum arc system to deposit a small but well defined amount of carbon homogeneously on heated substrates. The substrates are tilted with respect to the particle beam and a noble gas provides an inert atmosphere. To prevent the buildup of agglomerations during the coating process a filtered arc system is used. Filtered arc evaporators produce a nearly droplet-free plasma stream of ionized atoms with particle energies of some tens of eV. By this way, carbon atoms will slightly be implanted and fixed at their place of arrival. Consequently, they cannot move over the surface and there cannot grow islands as it normally accrues with atoms or molecules of thermal energies. In the present system, a pulsed filtered vacuum arc system is used to deposit a precisely defined amount of carbon atoms, needed to produce a full covered graphene layer. The Raman spectrum is 2 GRPLQDWHG E\ WKH FKDUDFWHULVWLF SHDNV Âł'Â´ Âł*Â´ DQG Âł 'Â´ ZKLFK DUH WKH W\SLFDO VLJQDWXUHV RI VS hybridized graphitic carbon (Figure 1, blue line). The 2D peak (Figure 2) is split into four components: 2D1B, 2D1A, 2D2A, 2D2B. This is characteristic for -1 multilayer graphene between two and five layers [1]. The position of the 2D-peak at 2700 cm is shifted to a higher wavenumber as expected for few-layer graphene on silicon oxide [1,2]. The homogeneity of the graphene is shown by measuring the intensity of the 2D band over an area of (100 Âľm x 100 Âľm). The resulting false color picture shows neither holes nor any partial inhomogeneity (Figure 3, insert). 3 The best carbon layers have a surface resistance of 3Âˇ10 Â&#x2020;, measured by means of a 4-wire van-derPauw arrangement. The specific resistivity is found to be 1.5 Âľ cm, and is independent on the number of layers The filtered vacuum arc technology provides a completely metal free process for the graphene fabrication on insulating substrates. It can be used as a stable, large area graphene production, which is compatible to established CMOS and other semiconductor fabrication.

References [1] A. C. Ferrari, J. C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri, F. Mauri, S. Piscanec, D. Jiang, K. S. Novoselov, S. Roth and A. K. Geim, Raman Spectrum of Graphene and Graphene Layers, PHYSICAL REVIEW LETTERS, 97, (2006) [2]Ying ying Wang, Zhen hua Ni, Ting Yu, Ze Xiang Shen, Hao min Wang, Yi hong Wu, Wei Chen and Andrew Thye Shen Wee, Raman Studies of Monolayer Graphene: The Substrate Effect, J. Phys. Chem. C, 112, pp.10637Âą10640 (2008)

Figures

Figure 1: Comparison of Raman spectra of different carbon layers. Conventional ta-C layer (green) split into its 2 FRPSRQHQWV ³'´ DQG ³*´ RUDQJH OLQH $QQHDOHG WD-C layer on quartz (red line); graphene, deposited on heated quartz (blue line).

Figure2: 2D-Peak of graphene split in four components, insert: Large area scan of 2D-intensity (100 µm x100 µm)

Electrochemistry on Defective Graphene Foam: Non-precious Catalysis Stephen Matthew Lyth, Jianfeng Liu, Kazunari Sasaki International Institute for Carbon Neutral Energy Research, Kyushu University, Fukuoka, Japan lyth@i2cner.kyushu-u.ac.jp

Many industrial processes rely on catalysts to improve efficiency and yield of chemical reactions. Such catalysts are often platinum-group, or rare-earth metals which are and expensive and limited resource. Research in to non-precious catalysts is an active and crucial research field. Nitrogen-doped carbons are a promising class of new non-precious catalysts, due to their extremely low cost, ease of synthesis, large accessible surface area, and their ability to be tailored for different applications. Nitrogen-doped 1

carbons have catalytic activity for photocatalytic water splitting, oxidation of hydrocarbons, and photocatalytic CO2 conversion.

Specifically in electrocatalysis, nitrogen-doped carbons (doped with transition metals) have been extensively explored as cathode catalysts for polymer electrolyte membrane fuel cells (PEMFCs). Recently the power density of PEMFCs using these Fe/N/C catalysts is approaching that of platinum electrocatalysts, although the durability is still an issue. Replacing Pt with Fe/N/C in PEMFCs would drastically reduce the cost of such systems, significantly increasing market-place penetration, and contributing to a more carbon-neutral society. 4

However, the mechanism of these non-precious catalysts is still in debate. Specifically, it is unclear what the exact role of the transition metal is; whether it plays an active role in oxygen reduction, or acts to generate active sites during synthesis. Does nitrogen only catalyze 2-electron oxygen reduction, or can it catalyze a 4-electron process, like platinum? By investigating this debate, we aim to throw light on the nature of the active site in such materials, and therefore we will be able to engineer better nonprecious catalysts. Our approach is to synthesize, understand, and optimize a simplified catalyst system; completely iron-free nitrogen-doped carbons. 5

To this end we have investigated carbon nitride, carbon-black-supported pyrolysed carbon nitride, and 7

carbon nanotube-supported pyrolysed carbon nitride. However iron contamination and surface area were always issues in such materials. We turned to nitrogen-doped graphene foam to negate these problems.

8,9

We synthesize nitrogen-doped, defective graphene foam by combustion of nitrogen-containing sodium ethoxide, followed by washing, heat treatment, and sieving. The resulting material is a threedimensional carbon structure, with large micron-scale pores separated by cell walls of ~ 1 nm thickness 2

(Figure 1a). The surface area is around 700 m /g. The nitrogen content is less than 1 at% measured by CHN elemental analysis, in amine, pyridinic, tertiary (graphite-like), and pyrrole configuration (X-ray photoelectron spectroscopy, Figure 1b). We observe high oxygen reduction activity compared with other metal-free nitrogen-doped carbon catalysts by virtue of the three-dimensional structure, and the large surface area. The onset potential is 0.85 V vs RHE, and the electron transfer coefficient is 3.5, indicating a mix of 2- and 4-electron transfer during the oxygen reduction reaction, in the absence of iron. The Tafel slope shows two linear regions, which also supports the fact that 4-electron oxygen reduction can occur in nitrogen-doped carbon, in the absence of iron. Additionally, we have discovered that these catalysts are effective at the similar process of electrochemical reduction of carbon dioxide to carbon monoxide. This could be a useful process in reducing CO2 emissions and mitigating climate change. Our CO2 reduction catalysts are more effective than the current state-of-the-art, which is Ag nanoparticles.

In summary, we have synthesized a three-dimensional nitrogen-doped defective graphene foam, with large surface area. This was applied as a metal-free electrocatalyst for oxygen reduction, and 4-electron transfer was observed, supported by the Tafel slope. This material was also applied as an electrocatalyst for CO2 reduction, and showed better activity than the current state-of-the-art silver

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Figure 1. (a) Scanning electron microcopy of the nitrogen-doped defective graphene foam. (b) XPS N1s signal. (c) Linear sweep voltammograms at various rotation speeds. (d) Tafel slope displaying 2 linear regions, indicating a 4electron oxygen reduction reaction.

References [1] Maeda, K.; Wang, X. C.; Nishihara, Y.; Lu, D. L.; Antonietti, M.; Domen, K. J Phys Chem C 2009, 113, 4940. [2] Wang, Y.; Wang, X. C.; Antonietti, M. Angew Chem Int Edit 2012, 51, 68. [3] Dong, G. H.; Zhang, L. Z. J Mater Chem 2012, 22, 1160. [4] J-. P Dodelet, Electrocatalysis in Fuel Cells, Lecture Notes in Energy, 9, 271, Springer (2013). [5] S. M. Lyth, et al., J. Phys. Chem. C 113, 20148 (2009) [6] S. M. Lyth, et al., Journal of The Electrochemical Society 158, B194 (2011) [7] S. M. Lyth, et al., Journal of Nanoscience and Nanotechnology, 4887-4891 (2012) [8] J. Liu, K. Sasaki, S. M. Lyth, ECS Transactions, 58 (1), 1529-1540 (2013)