TNT2012 Abstract Book (posters)

Magnetic domain structure of Co ultra-thin islands on Ru M.Abuin

1,2,3

4

1,2

3

1,3

1

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, B. Santos , A. Mascaraque , M. Maicas , L. Pérez , E. Miralles , A. Quesada , A. T. 5 5 6 N´Diaye , A. K. Schimd and J. de la Figuera

1

Dpto. Física de Materiales, Universidad Complutense de Madrid, 28040 Madrid, Spain Unidad Asociada IQFR (CSIC)-UCM, Madrid 28040, Spain 3 Instituto de Sistemas Optoelectrónicos y Microtecnología, Universidad Politécnica de Madrid, 28040 Madrid, Spain 4 Elettra-Sincrotrone Trieste S.C.P.A., 34149 Basovizza, Trieste, Italy 5 Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 6 Instituto de Química-Física “Rocasolano”, CSIC, Madrid 28006, Spain m.abuin@fis.ucm.es Abstract 2

Magnetic thin films often present different properties than bulk materials [1]. For example thin films can present larger magnetic anisotropies (up to one order of magnitude larger [2, 3]) than the bulk.

These differences arise from the increasing importance of the surface contribution to the magnetic anisotropy when the thickness of a film is reduced.This surface term does not depend of the number of layers, but only on the topological and crystallographic structure of the interface between the substrate and the ferromagnetic film grown on it. Therefore, a good characterization of the surface is crucial for a proper understanding of the magnetic properties of thin films. For example, the discrepancies regarding the magnetization easy-axis in Co/Au(111) reported by Allenspach [4] and Pommier [5] were attributed to differences in the growth mode of the films. Another example is the Curie temperature of Co monolayers, reported to be the same as for bulk, while later work attributed the result to a coverage determination problem[6].

In this work we correlate the magnetic domain structure of Co islands on Ru, measured by spinpolarized low-energy electron microscopy (SPLEEM) with micromagnetic calculations. Three atomic layers thick triangular islands of Co were grown on Ru(0001) by molecular beam epitaxy in-situ in the SPLEEM chamber. Thein-plane magnetized triangular Co islands present two different stacking sequences,reflected in their triangular shape with two different orientations. After applying a magnetic field in a given direction, distinctly different magnetization patterns areobserved on the two island families. One island set has very wide domain walls whilethe other has much thinner walls, indicating their different magnetic anisotropy.Furthermore, the types of islands with narrower domain walls present a pattern witha given chirality.Some tests were performed with the micromagnetic simulation package OOMMF [7] to understand the interplay of applied field direction and island orientation. The simulation reproduces nicely the experimentally observed pattern (Figure 1). Following the micromagnetic simulations for different orientations of the islands relative to the applied magnetic field clarifies the origin of the domain pattern. The local magnetization on the island tends to align with the edges of the triangular island as the external field is removed.

References [1] F. Huang, M. T. Kief, G. J. Mankey, and R. F. Willis.49 (1994) Phys. Rev. B. 3962.

[2] M. T. Johnson, P. J. H.Bloemen, F. J. A. den Broeder, and J. J. de Vries, 59 (1996) Rep. Prog. Phys.

1409-1458.

[3] D Sander, 16 (2004) J. Phys-condens. Mat.R603-R636.

[4] R. Allenspach, M. Stampanoni, and A. Bischof, 65 (1990) Phys. Rev. Lett. 3344.

[5] J. Pommier, P. Meyer, G. P_enissard, J. Ferr_e, P. Bruno, and D. Renard., 65(1990) Phys. Rev.Lett.

2054.

[6] C. M. Schneider, P. Bressler, P. Schuster, J. Kirschner, J. J. de Miguel, and R. Miranda., 64 (1990) Phys. Rev. Lett., 1059.

[7] M.J. Donahue and D.G. Porter.Oommf user's guide, version 1.0.(1999) Interagency Report NISTIR 6376.

Figures

Figure 1. SPLEEM image acquired of 3 ML fcc Co islands. (b) Micromagnetic simulation of a configuration that reproduces the experimental picture. The grey level corresponds to the component of the magnetization along the upper-right islands edge. The arrows indicate the magnetization vector. (c) Single state triangular islands with two orientations. (d) Relaxed configuration after removing the field where the chirality of the pattern depends on the relative orientation of the island and the applied magnetic field.

SYNTHESIS AND CHARACTERIZATION OF NANOFILLERS BASED ON MODIFIED CLAY MATERIALS S. Albeniz*, M.A. Vicente**, R. Trujillano**, S.A. Korili*, A. Gil* * Department of Applied Chemistry, Building Los Acebos, Public University of Navarra, Campus of ArrosadĂ­a E-31006 Pamplona, Spain. ** Department of Inorganic Chemistry, Faculty of Chemical Science, Square of Merced, University of Salamanca, E-37008 Salamanca, Spain

The development of nanoscience and nanotechnology has allowed a new interest on clay materials. This interest is based on the size of the clay layers, as well as in their interlayer spacing size, being able to act as nanomaterials. Moreover, clays have the ability to incorporate in their interlayer spaces other molecules, giving rise to a large number of new materials with a variety of applications [1].

The main aim of this work is to synthesize materials based on clays that can be used as nanofillers of plastic matrices. It is intended to improve the properties of new materials with the presence of the nanoclay on the plastic matrix, such as mechanic properties, fire resistance or gas permeability, and that can acts as a screen effect against UV radiation.

The most common clay materials and polymers that constitute plastic matrices are not miscible.

Therefore, it is necessary to find organic molecules, as well as the conditions and the ratios, which allow the compatibility of the two materials. In this work, a clay supplied by The Clay Science Society of Japan has been used. The organic molecules used as surfactant have been: Arquad 2HT-75 (Fluka), octadecylamine (Aldrich), 3-aminopropyltriethoxysilane (Aldrich), trimethyloctadecylammonium bromide (Aldrich) and tetraethoxysilane (Alfa Aesar). In presence of organic molecules, it is achieved the reduction of clay surface energy and the increase of the interlayer space. Thus, it is achieved the well dispersion of silicate layers into the plastic matrix [2,3].

The techniques used to characterize the synthesized materials have been: X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, chemical analysis and scanning electron microscopy. In this work, the most important results found will be presented and discussed.

References

[1] D. Zhang, C.-H. Zhou, C.-X. Lin, D.-S. Tong, W.-H. Yu. Synthesis of clay minerals. Applied Clay Science, 50 (2010), 1-11.

[2] N.G. Shimpi, S. Mishra. Studies on effect of improved d-spacing of montmorillonite on properties of poly (vinyl chloride) nanocomposites. Journal of Applied Polymer Science, 119 (2011), 148-154.

[3] M. Moghri, M. Akbarian. Effects of nanoclay and additives on the fusion characteristics and thermal stability of poly (vinyl chloride) nanocomposites. Journal of Vinyl and Additive Technology, 15 (2009), 92-98.

Electronic Spectra of Calcium Carbonate Porous Nanostructured Material E.L. Albuquerque, U.L. Fulco, C.A. Barboza, and E. Moreira Departamento de BiofĂ­sica e Farmacologia, UFRN, 59072-970 Natal-RN, Brazil contact e-mail: eudenilson@gmail.com

Abstract For a long time silicon has been kept off from optoelectronic applications due to its indirect band gap, which drastically diminishes light emission efficiency. This setting changed, however, when light emission and optical devices based on nanostructured porous silicon [1] and silicon quantum dots [2] were achieved. Binding electrons and holes inside these structures greatly increases the probability of radiative recombination.

On the other hand, calcium carbonate (CaCO3) is a cheap material with a wide range of applications, whose versatility is mainly due to its use in various fields of industry such as paper, rubber, plastics, and paint industries as a coating pigment, filler, or extender, food, and horticulture. With the recent developments in materials manipulation at nanoscale, nanostructured CaCO3 particles have been investigated and produced for different purposes. Furthermore, CaCO3 applications are determined by a great number of strictly defined parameters, such as the average particle size, the particle size distribution and morphology, specific surface area, brightness, oil adsorption, chemical purity, etc.

Concerning bio-applications, many types of micro- and nanoparticles (mostly organic although some inorganic) have been investigated for the use in drug delivery systems [3,4].

On the other hand, porous materials have been the subject of intensive research because of their potential applications in optoelectronics, biotechnology, pharmaceutics, catalysis, etc. Particularly, CaCO3 has shown to be specially useful as a carrier for several substances, such as insulin and hydrophilic compounds, because of its easy production and slow biodegradability [3,4]. Unfortunately, the binding of substances adsorbed in the surface of solid CaCO3 is weak. This suggests that the inclusion of pores in solid CaCO3 particles might enhance its binding efficiency by increasing the available surface for adsorption of other substances. In fact, porous CaCO3 were synthesized and used for capsule preparation. Thus, the versatility of CaCO3 combined with the electronic properties presented by nanostructured porous materials may lead to interesting and innovative applications to a wide range of fields [5]. In particular, luminescence can be helpful in tracking the remaining porous CaCO3 in body fluids when used for drug delivery.

It is the aim of this work to investigate the optical properties of porous CaCO3 by means of computer simulations. A schematic diagram displaying a rectangular porous CaCO3 nanoparticle is shown in Fig. 1(a)-(b) with its respective size distribution of pores. The electronic structure calculation is performed within the effective mass framework.

Figure 2 displays the interband oscillator strength for several combinations of the porosities p and pore diameter D. As we can see, the energy separations between transitions are very small. This is a consequence of the energy state dependence as a power law scale. Even though we have investigated only the ten lowest states in both conduction and valence bands, we expect that this behavior is also true for a higher number of states. Due to the small energy difference between adjacent states, absorption and luminescence spectra are expected to be very strong and broad even at low temperatures. The authors expect to stimulate experimental efforts to confirm these predictions.

Acknowledgements: Thanks are due to the Brazilian Research Agencies CAPES (Procad and Rede NanoBioTec), CNPq (INCT-Nano(Bio)Simes and Casadinho-Procad) and FAPERN/CNPq (Pronex).

References: [1] E.L. de Oliveira et al, J. Appl. Phys. 103 (2008) 103716.

[2] E.L. de Oliveira et al, Appl. Phys. Lett. 94 (2009) 103114.

[3] J. Kreuter, Colloidal Drug Delivery Systems, Marcel Dekker, New York, 1994.

[4] R. Arshady, in Microspheres, Microcapsules and Liposomes: Preparation and Chemical Applications, edited by R. Arshady, Citus, London, 1999, Vol. I, p. 279.

[5] D. Nave and S. Rosenwaks, J. Appl. Phys. 95, (2004) 8309.

Figure 1. Schematic representation of the porous nanoparticles simulated in this work (a) and its respective size distribution of pores (b). The shaded area represents CaCO3. The pores content is modeled as vacuum.

Figure 2. Interband oscillator strength (in arbitrary units) for porous CaCO3 nanoparticles with porosities p = 0.3, 0.4, and 0.5. The average pore diameters are D = 1 nm (solid circle), 2 nm (open circle), and 3 nm (triangle). Each point in this graph were averaged over 40 samples.

Proposal of a low-cost, mask-less procedure for patterning electrodes of organic devices at nanoscale using electro-discharges R. Mallavia (1), A. L. Alvarez, C. Coya, J. Jimenez-Trillo (2), M. Garcia-Velez, G. Alvarado Dpt. Tecnología Electrónica, ESCET, Universidad Rey Juan Carlos, Móstoles, 28933 Madrid (Spain); (1) Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, 03202 Elche, Alicante (Spain) (2) Dpt. Ingeniería de Circuitos y Sistemas, EUIT Telecomunicación, UPM, 28031 Madrid (Spain) angelluis.alvarez@urjc.es Abstract We have recently proposed a novel subtractive technique that enables patterning of conductive thin layers by means of a biased probe with a low continuous (DC) voltage source, taking advantage of the arc-voltaic principles [1]. This technique resembles electro-discharge machining (EDM), commonly used in industry to cut, make holes and conform metal blocks. However, in EDM high voltage (kilovolts) pulses are generated in order to create sparks between a probe and the metal piece. Every spark drives a metal local region to the boiling point, and next the residual metal is removed by an additional gas or liquid flux. In our case, the spark is created by gradually approaching a biased probe at low DC voltage (< 20 V) to the conductive surface, employing a high precision micropositioner. For that purpose we have built a home-made system, consisting of an assembly of three micropositioners (XYZ) with resolution below 100 nm and absolute reproducibility of 1 m. At a sufficiently short distance (< 1 µm), breakdown of the air electric permittivity between probe and conductor substrate is achieved, and an electric arc is created. A specifically designed electronic circuit provides charge to keep the arc until material is removed and an insulating crater appears below the probe.

The crater size is of the order of the tip diameter, and defines a roughly circular insulating region. When tip rests on this region and next slides on the surface, it approaches the boundary of the circular insulating zone, so a lateral spark will appear which removes a new crown of material, and so on. In such a way, the probe is leaving an insulating path as it travels across the metal surface (Fig. 1). If the probe depicts a closed loop, it is able to electrically insulate the inner region from the outer one, so this opens the chance to pattern tracks and pads for circuits.

By oscilloscope monitoring the voltage between probe and substrate, we observe that sharp voltage drops may be associated with the sparks (Fig. 2). This process takes place in a few µs, what allows a fast motion of the probe during operation (tens mm/s), ensuring scalability to large areas.

In this contribution, correlation between the size of the features and the operating conditions are analyzed (Fig. 3) on different materials and substrates (gold, aluminium, and semiconducting oxides like indium-tin oxide, ITO, or graphene oxide). Preliminary results are obtained with commercial probes with tip diameter > 30 µm. Scalability to nanometer diameters using, for example, atomic force microscope probes is discussed. Comparison between this technique and similar patterning procedures used in organic electronics like ink-jet printing (additive technique) or laser ablation (subtractive technique) is discussed. Whereas the previous techniques are difficulty scaled to nanometer size because physical limitations of liquid drops and laser waist size respectively, arc-erosion appears to be only limited by the tip diameter, as well as its positional control, two technological issues of feasible implementation.

Another interesting feature is that layers like aluminium may be patterned at low voltages (2 - 3 V) whereas transparent conductive oxides such as ITO requires in general higher operating voltages (1012 V). This procedure allows working on stacked layers as long as the patterning voltage for the top layer is significantly lower than that for the bottom one. This property is useful for certain field effect transistor architectures, as well as the columns-rows arrangement of displays.

As an application, organic light emitting displays have been performed on electrodes patterned with this technique. For this purpose, solution processed active layers have been used to reinforce the concept of low-cost manufacturing. Thus, water-soluble conjugated polyelectrolyte layers have been casted on top and bottom of commercial semiconducting polymers in organic solvents. In particular we have combined a blue-emitting, cationic polyfluorene derivative, poly{9,9-bis[6’-(N,N,Ntrimethylammonium)hexyl] fluorene-co-1,4-phenylene} dibromide (PNMe), synthesized in our lab, together with a red-emitting, commercial Poly(2-methoxy-5-(3'-7'-dimethyloctyloxy)-1,4-

phenylenevinylene), (MDMO-PPV), in the following conventional structure: ITO (100 nm) / PEDOT:PSS (50 nm) / MDMO-PPV (130 nm) / PNMe (70 nm) / Ca / Al (100 nm). Electroluminescence from both materials has been recorded as shown in Fig. 4, revealing interesting physical aspects, for example, that electron-hole recombination zone is wide and extends over both layers. This confirms the robustness of this procedure, which results very promising to face development of micro- and nanoorganic devices.

References [1] J. Jimenez-Trillo, A. L. Alvarez, C. Coya, E. Cespedes, A. Espinosa, Thin Solid Films 520 (2011) pp.

1318-1322.

Figures

Fig.1. Sketch of a electrically biased tip sliding in contact with a conductive surface, leaving an insulating path of a similar width as the tip diameter.

Fig.2. Monitored voltage at the tip during motion.

The falls mean discharge processes. Tip speed was 1 mm/s, so a time division is equivalent to a 500 nm path.

0.000024

m )

MDMO_PPV

EL emission

(WSrnm

-1

-2

1.2 mA 300 A 0.000016

PNMe 0.000008

0.000000 400

Fig.3. Lines eroded on an ITO surface at 12 V using two different probes with tip diameter of 50 µm (up) and 130 µm (down)

500

600

700

Wavelength (nm)

Fig.4. Electroluminescence recorded from a 2 x 2 passive matrix display, with an active bilayer consisting of a blue-emitting cationic polifluorene derivative, PNMe, and a red-emitting poly(phenylene vinylene) derivative, MDMO-PPV. Spectra at driving currents from 300 µA to 1.2 mA are shown. Luminance ranges from 20 to 140 2 cd/m , respectively.

Evaluation of the Cytotoxic and Genotoxic Potential of TiO2 Nanoparticles 1

2

1

1

1

2

Banu Barutca , Gunes Alp Yakaboylu , Hatice Genc , Kenan Isik , A. Tansu Koparal , Ender Suvaci ¹Department of Biology, Faculty of Sciences, Anadolu University, Eskisehir, Turkey ²Department of Materials Science and Engineering, Anadolu University, Eskisehir, Turkey barutcabn@gmal.com

Along with the development of nanotechnology and its rapid advances, many nanomaterial containing consumer products has begun to take a place in human daily lives. Current statistics suggest that there are more than 1000 product lines like personal, commercial, medical, military use, cosmetics or products like clothes, electronics, sporting goods, sunscreens, are available world wide that take benefits of nanotechnology [1,2,3]. Despite that rapid development and common use of commercial products, that made by nanotechnologic strategies, impact of the nanoparticles on human health is still the main discussion topic [4].

TiO2 is the main ingredient in many commercial sunscreens due to its property of UV absorption and colorless [5,6]. On the other hand properties of nanoparticles such as small size, large spesific surface area and high number per given mass are the reason of the toxicological concern in biological systems.

As for TiO2 nanoparticles, an important sunscreen component, it is essential to highlight the 2 adverse effects on skin. With a surface of well over 2m , the skin, which is the largest organ of the body, can create an important portal route for entry of nanoparticles such as TiO 2 by using of sunscreens [7].

Thus, penetration of TiO2 nanoparticles within the skin and interaction with the skin cells are considerable discussion points [8]. In this study TIG-114 (human skin fibroblast) cells were used to guide dermal response of TiO2 nanoparticles.

Especially for <25nm NPs there are indeed concerns about their toxicological effects because of their high surface area and ability of penetration. This study is focused on the cytotoxic and genotoxic differences between commercial anatase TiO2 (<25nm) and synthesized rod-like TiO2 (<25nm) nanoparticles on TIG-114 (human skin fibroblast) cell line. Micron-sized agglomerates of TiO2 nanoparticles in rod-like shape were synthesized. Although rod-like particles can exhibit similar properties with TiO2 nanoparticles as having high UV-protection ability, they may also have less toxic effect on human health and low possibility of penetration to living cells. To demonstrate this hypothesis several in vitro techniques were studied. MTT and Neutral Red (NRU) assays were used to determine the cytotoxicity. To contrast the mitochondrial membran potential JC-1 (5,5’6,6’-tetrachloro-1,1’3,3’tetraethylbenzimidazol-carbocyanine iodide) staining, a hallmark method to indicate the early apoptoticureagent, was performed. Finally to show DNA damage, alkaline single-cell microgel electrophoresis (comet) assay was used.

The results showed that both TiO2 nanoparticles, commercial anatase TiO2 (<25nm) and synthesized rod-like TiO2 (<25nm) nanoparticles did not cause cytotoxicity on TIG 114 cells at treated concentrations (1.25, 2.5, 5, 10, 20, 40, 50, 80, 100, 200 µg/ml) (Fig. 1). And also JC-2 staining results showed in Fig.2. Dose depend DNA damage was observed both TiO2 Nanoparticles in Fig.3.

Commercial anatase TiO2 was more genotoxic compared to synthesized rod-like TiO2 (<25nm) nanoparticles. As a result, TiO2 did not induce apoptosis and cytotoxicity but induced genototoxicity on TIG 114 cells.

References [1]Hu, X., Cook, S., Wang, P., Hwang, H, Science of Total Environment.407 (2009) 3070-3072.

[2]Shukla, R.K., Sharma, V., Pandey, A.K., Singh, S., Sultana, S., Dhawan, A., Toxicology in Vitro. 25 (1) (2011) 231-241.

[3]Hsiao, IL., Huang, Y., Science of Total Environment. 409 (7) (2011) 1219-1228.

[4]Liu, S., Xu, L., Zhang, T., Ren, G., Yang, Z., 2010. Toxicology. 267, 172-177.

[5] Suh, W.H., Kenneth, K.K., Stucky, G.D., Suh, Y., Progress in Neurobiology, 87 (2009) 133-170.

[6] Nohynek, G., Antignac, E., Re, E., Toutain, H., Toxi. and Appl. Pharmacol., 243, (2010) 239-259.

[7] Lademann, J., Weigmann, H., Rickmeyer, C., Barthelmes, H., Schaefer, H., Mueller, G., Sterry, W., Skin Pharmacol. Appl. Skin Physiol, 12, (1999) 247-256.

[8] Newman, M.D., Stotland, M., Ellis, J.I., American Academy of Dermatology, Inc, (2009).

180

Commercial anataseTiO2

Commercial anatase-TiO2

140

160

Cell Viability by NRU (% Control)

Cell Viability by MTT (% Control)

Synthesized rod-like anatase-TiO2 120

100

80

60

40

20

0

Synthesized rod-like TiO2

140 120 100 80 60 40 20 0

0

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Concentration (µg/ml), t=24 hrs

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Concentration (µg/ml), t=24 hrs

Figure 1 Dose dependent cell viability results of TiO 2 (<25nm) commercial and synthesized rod like TiO2 (<25nm) on TIG 114 cells by MTT and NRU assay.

Figure 2. Fluorescencent microscopy results of JC-1 staining on TIG-114 cells. a)control, b)control (ultra pure water) and after exposed to commercial TiO2 particles at b)10 µg/ml, c) 20 µg/ml, d) 40 µg/ml and synthesized rod like TiO2 particles at h)10 µg/ml, c) 20 µg/ml, d) 40 µg/ml for 24 hours.

Figure 3. The morphology of the TIG 114 cells a)negative control (ultra pure water), b)positive control (H2O2) and after exposed to TiO2 particles at c)10 µg/ml, d) 20 µg/ml, e) 40 µg/ml and synthesized rod like TiO2 particles at f)10 µg/ml, g) 20 µg/ml, h) 40 µg/ml for 24 hours.

Acknowledgements The financial support for this study from The Scientific and Technological Research Council of Turkey (TUBITAK) (Project Number: 109M585) and Anadolu University Scientific Research Projects Commission (Project Number : 1101F020) was gratefully acknowledged.

Morphological changes of gel–type functional polymers after intermatrix synthesis of polymer stabilized silver nanoparticles Julio Bastos-Arrieta1, Maria Muñoz1, Dmitri N Muraviev1*, Patricia Ruiz2 1 Department of Chemistry, Autonomous University of Barcelona, 08193 Bellaterra, Barcelona, Spain 2 MATGAS Research Center (Carburos Metálicos/Air Products, CSIC, UAB), Campus de la UAB, 08193, Bellaterra, Barcelona, Spain dmitri.muraviev@uab.cat Abstract Ion exchange materials find numerous large-scale industrial applications in various fields, such as water treatment processes, catalysis and some others. The efficiency of the use of ion exchangers in some instances can be substantially improved by tailored modification of commercially available ion exchange materials with, for example, functional metal nanoparticles (FMNPs).[1] The modification of ion exchangers with FMNPs can be carried out by using the Intermatrix Synthesis (IMS) technique coupled with the Donnan exclusion effect. Such a combination allows for production of polymer-metal nanocomposites with the distribution of FMNPs near the surface of the polymer what appears to be the most favorable in their practical applications. This technique has been used to modify the polymers with cation exchange functionality with FMNPs by using the procedure, which includes the following sequential stages: 1) immobilization (sorption) of metal or metal complex ions (FMNP precursors) onto the functional groups of the polymer, and 2) their chemical or electrochemical reduction.

The use of the functional polymers as supports for the metal nanoparticles (MNPs) and metal oxide nanoparticles has in this sense, one more important advantage dealing with the possibility to synthesize the catalyst nanoparticles directly at the “point of use”, i.e. inside the supporting polymer. In the case of the metal catalyst nanoparticles (MCNPs) this results in the formation of the catalytically-active polymermetal nanocomposites.[2–5] The antibacterial features of Ag-MNPs represent one of the hot topics of investigation in the noble metals research. The unusual properties of nanometric scale materials in comparison with those of their macro counterparts give in many instances a number of advantages in their practical applications. For example, Ag-MNPs are widely used due to their more efficient antimicrobial activity in comparison with bulk silver. Some of our previous studies dealt with the IMS of Ag-NPs on different polymer matrices and their application for bactericide water treatment. [6–8] In the present work we present the results of IMS of Ag-MNPs in Purolite® C100E sulfonic ion exchange polymer having the gel-type structure. It has been shown that the modification of the gel – type matrix with Ag-MNPs leads to the increase of its cross-linking, what results in the increase of its surface area and the appearance of nanoporosity, as it is shown in Fig. 1 and Table 1. As it is clearly seen in Fig. 1a, the morphology of the initial MNPs-free polymer is absolutely smooth but it dramatically changes after IMS of Ag-MNPs (see b,c,d,e) what can be explained by interaction of Ag-NPs with the polymer chains leading to a sort of additional cross-linking of the polymer. This results in the appearance of nanopores (see Fig. 1e) in the polymer gel. Ag-MNPs are located on the polymer surface and do not form any visible agglomerations (see Fig. 1f). All these features of the nanocomposites obtained are important for their practical applications in catalysis, in sensors and bactericide water treatment. .

References [1]

P. Barbaro and F. Liguori, “Ion exchange resins: catalyst recovery and recycle.,” Chemical reviews, vol. 109, no. 2 (2009) pp. 515-29.

[2]

J. Bastos-Arrieta, A. Shafir, A. Alonso, M. Muñoz, J. Macanás, and D. N. Muraviev, “Donnan exclusion driven intermatrix synthesis of reusable polymer stabilized palladium nanocatalysts,” Catalysis Today, 2012.(in press)

[3]

D. N. Muraviev, P. Ruiz, M. Muñoz, and J. Macanás, “Novel strategies for preparation and characterization of functional polymer-metal nanocomposites for electrochemical applications,” Pure and Applied Chemistry, vol. 80, no. 11,(2008) pp. 2425-2437,

[4]

P. Ruiz, M. Muñoz, J. Macanás, and D. N. Muraviev, “Intermatrix Synthesis of Polymer−Copper Nanocomposites with Tunable Parameters by Using Copper Comproportionation Reaction,” Chemistry of Materials, vol. 22, no. 24 (2010), pp. 6616-6623

[5]

A. Alonso, A. Shafir, J. Macanás, a. Vallribera, M. Muñoz, and D. N. Muraviev, “Recyclable polymer-stabilized nanocatalysts with enhanced accessibility for reactants,” Catalysis Today,.

2012.(in press)

[6]

A. Alonso, J. Macanás, G. L. Davies, and Y. K. Gun, “Nanocomposites with Most Favorable Distribution of Catalytically Active and Biocide Nanoparticles,” 2010.

[7]

A. Alonso et al., “Environmentally-safe bimetallic Ag@Co magnetic nanocomposites with antimicrobial activity.,” Chemical communications (Cambridge, England), vol. 47, no. 37(2011), pp. 10464-6,

[8]

A. Alonso et al., “Characterization of fibrous polymer silver/cobalt nanocomposite with enhanced bactericide activity.,” Langmuir: the ACS journal of surfaces and colloids, vol. 28, no. 1(2012) pp. 783-90,

(A)

(D)

(B)

(C)

(E)

(F)

Fig.1: High resolution SEM images of C100E (a) and C100E modified with Ag-NPs. Magnification a=b<c<d<e<f.

Table 1: BET surface area analysis for C100E and C100E modified with Ag-NPs +

Sample

Time of Ag loading (min)

Surface Area (BET) m2/g

Average Pore diameter(nm)

C100E

-

0.91

1.87

5

1.15

2.25

10

1.09

4.44

C100E with AgNPs C100E with AgNPs

Unintended Consequences of Focused Ion Beam Milling on Nanostencil Lithography 1

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J.R. Bates , Y. Miyahara , J. A. J. Burgess , O. Iglesias-Friere and P. Grutter

1

1

McGill University, Montreal, Quebec, Canada University of Alberta, Edmonton, Alberta, Canada 3 Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid, Spain batesj@physics.mcgill.ca 2

Abstract Sub-micron device features may be fabricated using standard lift-off techniques including electron beam lithography, interference lithography, extreme UV and x-ray lithography. An alternative to these fabrication techniques is nanostencil lithography. Nanostencil lithography avoids possible contamination sources such as resist coatings, solvents and etching and also has the possibility of fabrication and measurement being performed while maintaining ultra high vacuum (UHV) conditions. Stencil lithography can be used in static [1] or dynamic mode [2] and is used for a variety of different applications such as magnetic nanostructures [2], fabrication of in situ interconnects [3], molecular beam epitaxial deposition through a stencil mask [4] and defining clean metal patterns [5].

Focused ion beam (FIB) milling, a common fabrication technique to make nanostencil masks, has the unintended consequence of gallium ion implantation surrounding milled features in silicon nitride membranes [6]. In this work, we demonstrate that FIB-milled nanostencils can lead to a substantial change in structure and chemical composition of resulting nanostructures deposited by electron beam evaporation when compared to the starting material. We present characterization with transmission electron microscopy (TEM), electron energy loss spectroscopy, energy dispersive x-ray spectroscopy, magnetic force microscopy (MFM) and Kelvin probe force microscopy (KPFM) to demonstrate the surprising influence of FIB-milled nanostencils on deposited nanostructures. This effect is attributed to implanted gallium ions in the nanostencil surrounding milled features, and could provide a means for tuneable control over the growth of magnetic nanostructures with varying iron content and film morphologies. The effect may also be mitigated by thinning the nanostencil using a reactive ion etch which may remove the gallium ions.

References [1] O. Vazquez-Mena, L. G. Villanueva, V. Savu, K. Sidler, P. Langlet, and J. Brugger, Nanotechnology 20, 415303 (2009).

[2] L. Gross, R. R. Schlittler, G. Meyer, A. Vanhaverbeke, and R. Allenspach, Applied Physics Letters 90, 093121 (2007).

[3] H. Guo, D. Martrou, T. Zambelli, J. Polesel-Maris, A. Piednoir, E. Dujardin, S. Gauthier, M. A. F. van den Boogaart, L. M. Doeswijk, and J. Brugger, Applied Physics Letters 90, 093113 (2007).

[4] G. H. Dohler, G. Hasnain, and J. N. Miller, Applied Physics Letters 49, 704 (1986).

[5] J. Brugger, J. Berenschot, S. Kuiper, W. Nijdam, B. Otter, and M. Elwenspoek, Microelectronic engineering 53, 403 (2000).

[6] G. Spoldi, S. Beuer, M. Rommel, V. Yanev, A. J. Bauer, and H. Ryssel, Microelectronic Engineering 86, 548 (2009).

Figures

Figure 1. Simultaneously acquired non-contact frequency shift topography (a) and Kelvin probe microscopy images (b) of nanostencil fabricated using FIB milling. Charged regions around FIB milled holes are observed and attributed to gallium implanted from the FIB processing.

Figure 2. MFM image of a permalloy nanostructure made using a FIB milled nanostencil. Image was taken in a 60 mT in-plane applied field at a lift height of 70 nm. White dotted line indicates location of nanostructure. Inset is a non-contact atomic force microscopy topography image of the nanostructure with a z-scale of 25 nm.

Figure 3. (a) Bright field TEM image of stencil used to make nanostructures. Two regions of permalloy growth are observed. Columnar growth is observed near the FIB milled holes (zone 1), and normal permalloy growth is observed far from the FIB milled holes (zone 3).

RAMAN EFFECT IN CARBON NANOTUBES FILLED WITH NANOWIRES E. Belandria Centro de Estudios Avanzados en Optica, Universidad de los Andes, Mérida, Venezuela E. Flahaut CIRIMAT-LCMIE, UMR CNRS 5085, Université Paul Sabatier, 118 Route de Narbonne, 31077 Toulouse Cedex 4, France J. González Centro de Estudios de Semiconductores, Facultad de Ciencias, Universidad de los Andes, Mérida 5251, Venezuela DCITIMAC-Malta Consolider Team, Universidad de Cantabria, Santander, Spain Unpolarized Raman spectra of radial and tangential modes on DWCNTs filled with 1D nanowires of different materials, were studied at room temperature. The G-band of the nanotubes can be used as measurement of factor filling. In the low wavenumber region we observed several phonons which correspond to the inner and outer radial modes of DWNTs, and the confined phonons of nanowires are observed.

Keywords: carbon nanotubes; nanowires; confinement; raman effect.

Phototoxicity induced by Iron-doped LiNbO3 nanoparticles in human tumor cells 1

3

4

2

1

A. Blázquez-Castro , J. Espada , J.C. Stockert , F. Agulló-López , A. García-Cabañes , and M. 1 Carrascosa 1. Department of Physics of Materials, Autonomous University of Madrid, 28049, Madrid, Spain 2. Center for Microanalysis of Materials (CMAM), Autonomous University of Madrid, 28049, Madrid, Spain 3. Institute for Biomedical Research “Alberto Sols”, High Council for Scientific Research (CSIC)Autonomous University of Madrid, 28029, Madrid, Spain 4. Department of Biology, Autonomous University of Madrid, 28049, Madrid, Spain alfonso.blazquez@uam.es Abstract As it is well known that the Bulk Photovoltaic Effect (BPE) appears in certain crystalline materials (usually ferroelectrics) that show an asymmetric cell unit arrangement [1]. This spatial pattern produces a directional electronic drift when electrons are excited to the conduction band as a result of visible light absorption by the material. This drift induces a charge carrier separation and generates an electric field between the illuminated edges of the crystal.

5 Reported measurements of this electric field show values as high as 10 V/cm in iron-doped LiNbO3, the material employed in our experiments [2].

In this communication, preliminary results regarding the use of photovoltaic fields generated in Fe:LiNbO3 nanoparticles for damaging human tumor cells in culture will be presented. These results are an extension of those we have previously obtained after exposing eukaryotic cell cultures to both macroscopic and microscopic crystals of iron-doped LiNbO3 in the presence of visible light [3]. Also, they are in line with recently published results of pyroelectric damage to prokaryotic cells that showed a reduced viability when incubated with LiNbO3 nanoparticles and then exposed to temperature cycles [4].

Iron-doped LiNbO3 nanoparticles were obtained by grounding a crystalline sample in an agate mortar until a very fine powder was produced. This powder was suspended in a phosphate buffered solution (PBS) for 24 h to separate the submicrometric fraction present in the original sample. This submicrometric fraction remained in suspension in the liquid, while the coarser particles precipitated. An example of the obtained particles is shown in Figure 1.

Human tumor cells (HeLa cell line) were cultured and grown on Petri dishes. After reaching a certain degree of confluence, the cell cultures were exposed to the iron-doped LiNbO3 nanoparticles. Immediately some cell cultures were also exposed to visible light provided by the water-filtered output of a halogen lamp, while others were kept in the dark. Cell morphology was evaluated 24 h after treatment as a measure of cell damage. Controls showed a normal morphology, with the typical spread polygonal shape of HeLa cells (Figure 2A). Cells exposed to iron-doped nanoparticles and visible light showed, in general, a certain degree of retraction, as can be seen in Figure 2B, which is an early sign of cell damage. Also, there are some cells that display the typical late apoptotic cell death morphology. These cells show a collapsed and smaller cell body, with increased surface roughness. Some examples of apoptotic cells are indicated by arrows in Figure 2B. These results are the first obtained in regard to the phototoxic activity of iron-doped LiNbO3 nanoparticles. Further research is underway to expand the results in this new area of the BPE applied to the life sciences.

This work has been supported by MICIN under grants MAT2008-06794-C03 and MAT201128379-C03-01.

References [1] B. Sturman and V.M. Fridkin, The Photovoltaic and Photorefractive Effects in Noncentrosymmetric Materials, Gordon & Breach Science Publishers, Amsterdam (1992) [2] E.M. de Miguel, J. Limeres, M. Carrascosa and L. Arizmendi, J. Opt. Soc. Am. B 17 (2000) 1140.

[3] A. Blázquez-Castro, J.C. Stockert, B. López-Arias, A. Juarranz, F. Agulló-López, A. GarcíaCabañes and M. Carrascosa, Photochem. Photobiol. Sci. 10 (2011) 956.

[4] E. Gutmann, A. Benke, K. Gerth, H. Böttcher, E. Mehner, C. Klein, U. Krause-Buchholz, U. Bergmann, W. Pompe and D.C. Meyer, J. Phys. Chem C 116 (2012) 5383.

Figures

Figure 1. Scanning electron microscopy (SEM) image showing the size and shape of the irondoped LiNbO3 particles employed in the biological experiments.

Figure 2. Cell damage and death induced after exposure of cell cultures to iron-doped LiNbO3 nanoparticles followed by illumination with visible light. Control cell cultures are shown on the left (Fig.2A). These cells appear with a normal morphology. On the right an image of cells 2 exposed to iron-doped LiNbO3 nanoparticles and visible light (light irradiance 267 mW/cm ) for 60 min. Many cells show a certain degree of body retraction (arrowheads), which denotes some amount of cell damage. Also, there are some dead apoptotic cells (arrows). The combined treatment of nanoparticles and light results in tumor cell death. Scale bar: 100 µm.

Preparation and characterization of polypropylene/ MgAl2O4.MgO nanocomposites a

a, b

Bahareh Borhani , Mohsen Mohsen-Nia

*

a

Department of Chemistry, University of Kashan, Kashan, 87317-51167, Iran Division of Chemistry and Chemical Engineering, Caltech, Pasadena, California, USA

b

*e-mail: moh.moh@cheme.caltech.edu Abstract The polymer/inorganic nanocomposites have attracted much attention for research and industrial uses in recent decades because of their enhanced thermal and mechanical properties, improved barrier properties, optical properties and reduced flammability [1]. Recently, there has been considerable interest in the preparation of nanocomposites based on layered materials as guests and polymers as hosts [2].

These layered materials include silicates, manganese oxides, titanates and phosphates. Among the many inorganic solids, magnesium aluminate spinel (MgAl2O4) system has long been considered as an important ceramic material due to its superior mechanical, chemical and thermal properties [3, 4].

In this work, The MgAl2O4.MgO spinel nanoparticles were prepared. The spinel nanoparticles were used to prepare polypropylene (PP)/ MgAl2O4.MgO nanocomposites via the melt compounding method.

The thermal, flammability and mechanical properties of the prepared nanocomposites were studied and the obtained results were reported in detail.

In order to analysis of the resulting product, X-ray analysis has been used to confirm the dispersion of MgAl2O4.MgO nanoparticles in the PP matrix. These patterns showed the structural changes of the samples with the loading of PP/MgAl2O4.MgO [Fig.1].

The morphological nanostructure of PP/ MgAl2O4.MgO in this study was ascribed by SEM in Fig.2.

Observation from SEM image showed that nanoparticles (MgAl2O4.MgO spinel) have a well dispersion in the PP matrix.

The influence of MgAl2O4 content on the mechanical properties of PP/ MgAl2O4 nanocomposites also was studied. According to the obtained results, the mechanical properties of the nanocomposites have enhanced with increasing the MgAl2O4.MgO content.

The limited oxygen index (LOI) value of PP was found to slightly improve with the addition of the MgAl2O4.MgO nanoparticles. These increases of the LOI values allow improvements on the inflammability of PP matrix by the effect of MgAl2O4.MgO nanoparticles.

The thermal properties of PP/MgAl2O4.MgO nanocomposites samples were also studied. It was observed that the thermal properties of the prepared nanocomposites were improved with the addition of the MgAl2O4.MgO nanoparticles to PP matrix.

Results showed that due to the well dispersion of PP/MgAl2O4.MgO nanoparticles in the polymer matrix, the polymer/ MgAl2O4.MgO nanocomposites have so better characteristics than pure PP. References [1] Sh. Lv,W. Zhou, H. Miao, W. Shi, Progress in Organic Coatings , 65 (2009) 450–456.

[2] L. Hu, Y. Yuan, W. Shi, Materials Research Bulletin, 46 (2011) 244–251.

[3] H. Revero´n, D. Gutie´rrez-Camposa, 1, R.M. Rodrı´guez, J.C. Bonassin, Materials Letters, 56 (2002) 97– 101.

[4] M.M. Amini, M. Mirzaee, N. Sepanj, Materials Research Bulletin, 42 (2007) 563–570.

Fig.1. XRD pattern of PP/ MgAl2O4. MgO nanocomposites

Fig.2. SEM images of sample of PP/ MgAl2O4. MgO nanocomposites

Size Dependent Differential Immune Response with Poly-Îľ-caprolactone Nanoparticles-An in vitro study C.K.Prashant, Madhusudan Bhatt, Manoj Gautam, A.K.Dinda* All India Institute of Medical Sciences,Ansari Nagar,New Delhi, India *amit_dinda@yahoo.com Abstract The present study aimed at developing poly-Îľ-caprolactone nanoparticles (PCL NP) in two size ranges viz 60nm and 450 nm, entrapping the antigens mycobacterial early secreted antigenic target 6 (ESAT 6) and tetanus toxoid (TT) separately in them and studying the effect of the size variation of PCL NP after internalization by human blood monocyte derived macrophages (hmoM) on antigen presentation by them to autologous CD4+ T cells and CD8+ T cells respectively. Macrophages belong to the mononuclear phagocytic system and function as antigen presenting cells. Targeting them with cellbased vaccination strategies using antigens entrapped in nanoparticles may provide mechanisms whereby modulation of the type of immune response elicited through subsequent interactions with the adaptive immune system can be controlled. The development of an effective immune response thus depends on effective presentation of antigenic peptides on MHC class I and MHC class II molecules which in turn dictate mucosal, humoral and cell-mediated immunity which may be required together or separately to deal with a particular infection depending on its nature.

The aim of many vaccine development programs has been to generate a strong T cell response which requires the presentation of antigenic peptides on MHC molecules for T- cell stimulation. Therefore the challenge for an effective vaccine is to induce long-lived central memory CD8+ T cells as well as CD4+ helper T cells [1].

PCL NP were successfully synthesized in the two size ranges of 60nm and 450nm and the sizes were determined using transmission electron microscopy and DLS. Zeta potential of 60nm particles was -3mv and that of 450nm was -14mv. They were entrapped with antigens of interest viz ESAT 6 and TT. The particles with highest entrapment efficiency were taken for antigen presentation assays. Cell viability assay done on human monocytic cell line, THP1 with MTT assay showed that the synthesized PCL NP were perfectly biocompatible and they also did not create significant ROS generation as determined by H2DCFDDA assay.

The results of in vitro antigen presentation assays using human monocyte derived macrophages (hmoM) indicated that irrespective of whether the pure antigen alone generates a Th1 or Th2 type of response, 60 nm PCL NP cause M1 polarization of the macrophages and generate a Th1 type immune response. 450nm PCL NP on the other hand, cause M2 polarisation of the macrophages and skews the T cell polarization towards Th2 type. This is clearly indicated by the ELISA results. When void 60nm PCL NP are incubated with hmoM for 72h and the supernatant is assayed for cytokines, we found significant amounts of IL12 and small amounts of IL 10 (p<.001). When the macrophages were incubated with void 450nm PCL NP, they caused copious amounts of IL 10 secretion with nonsignificant amounts of IL12 (p<.05).

When either ESAT 6 or TT entrapped 60nm PCL NP are used in the antigen presentation assays, CD4+ T cells produce IFN gamma in significant amounts (p<0.001). When 450nm antigen entrapped PCL NP are used, CD4+T cells produce significant amounts of IL 4 and IL 10 (p<0.05). When compared to the antigen entrapped particles, pure ESAT 6 causes IFN gamma secretion while TT and alum adsorbed TT produce IL4 and IL 10 respectively during antigen presentation assays.

The results are important in the light of modulating immune response to antigens with implications in vaccine design. Here, the study indicates that sub-nanometer PCL NP of about 60 nm diameter efficiently induce Th1 polarisation and cross-presentation of antigens. This may be important when a strong cell mediated immunity (CMI) may be needed against the antigen of interest. Sub-micron size PCL NP of about 450nm, on the other hand, cause Th2 polarisation and boost humoral immune responses, much like alum. Thus we observe that the nature of material used and the size of the particles formed affect the adjuvant properties of particulate delivery systems for vaccination.

References [1] Berzofsky, J. A.; Ahlers, J. D.; Janik, J.; Morris, J.; Oh, S.; Terabe, M.; Belyakov, I. M., JCI 114(4), (2004) 450 - 462

Transmission electron microscopic images of PCL NP

a) 60nm PCL NP

b) 450nm PCL NP

Cytokine production by macrophages when incubated with a) void 60nm PCL NP b) void 450nm PCL NP

Cytokine production by CD4+T cells when incubated with ESAT 6 loaded a) 60nm PCL NP b) 450nm PCL NP

Cytokine production byCD4+ T cells when incubated with TT loaded a) 60nm PCL NP b) 450nm PCL NP

Cytokine production by CD8+ T cells when incubated with ESAT 6 or TT loaded 60nm PCL NP

Ultrasensitive Non-Chemically Amplified Negative-Tone Electron Beam Lithography Resist V. Canalejas-Tejero,1 S. Carrasco,2 F. Navarro-Villoslada2, M.C. Capel-Sánchez3, J.L. García Fierro3, M.C. Moreno-Bondi2*, C.A. Barrios1* 1

Instituto de Sistemas Optoelectrónicos y Microtecnología (ISOM), ETSI Telecomunicación, Universidad Politécnica de Madrid, CEI-Moncloa, 28040 Madrid, Spain.

2

Optochemical Sensors and Applied Photochemistry Group (GSOLFA). Department of Analytical Chemistry, Faculty of Chemistry, Universidad Complutense, CEI-Moncloa, 28040 Madrid, Spain.

3

Grupo de Energía y Química Sostenibles (EQS). Instituto de Catálisis y Petroleoquímica (ICPCSIC). C/ Marie Curie 2, Cantoblanco, 28049 Madrid, Spain. * carlos.angulo.barrios@upm.es; mcmbondi@quim.ucm.es

Abstract Electron-beam lithography1 (EBL) is a well-known and powerful technique for top-down nanofabrication approaches2. However, EBL has some disadvantages for mass production like a low processing speed.

Highly sensitive EBL resists are therefore desirable as they reduce the writing time considerably.

We have developed and characterized a new negative-tone EBL resist with an extremely high sensitivity. The resist is based on the dual copolymer mixture poly(2-hydroxyethyl methacrylate-co-2methacrylamidoethyl methacrylate) (poly(HEMA-co-MAAEMA)) and has been synthesized using free radical polymerization of 2-hydroxyethyl methacrylate and 2-aminoethyl methacrylate (9:1 monomer feed ratio) with further methacryloylation of the amine side-chain groups.

The poly(HEMA-co-MAAEMA) resist exhibits a crosslinking threshold dose as low as 0.5 μC/cm2 (Fig. 1), which is one order of magnitude smaller than those of commercially-available EBL negative resists.

Unlike the latter, the high sensitivity of our copolymer mixture does not arise from a chemical amplification process induced by a photoacid generator, but caused by the presence of a large proportion of double bonds (~10%) into the resist composition, which increases the probability of electron-induced bond breakage significantly.

The copolymer mixture has been analyzed by 1H NMR (Fig. 2). In addition, exposed and non-exposed resist films have been characterized by X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy to study the polymerized species.

Our resist possesses a contrast value as low as 1.2 (Fig. 1), making it particularly suitable for achieving grey (3D) lithography3, and a half-pitch resolution of 100 nm. Dual-tone behaviour occurs at high electronic doses; in particular, the polymeric resist becomes positive for doses in the range of 5 – 10 mC/cm2.

Exposed resist patterns show good adherence to silicon substrates without the assistance of adhesion promoters or thermal treatments, and have been shown to be adequate for use as a mask for both wet (HF+HNO3+AcOH solution) and dry (SiF6-based Reactive Ion Etching) etching of Si. The presented resist is highly transparent in the visible, which, along with its aforementioned 3D fabrication capability, makes it suitable as a structural material for the implementation of micro- and nano-optical components, such as microlenses (see Fig. 3).

Acknowledgements: The authors gratefully acknowledge financial support from MICINN (TEC201010804-E, CTQ2009-14565-C03-03 and TEC2008-06574-C03-03), and the Moncloa Campus of International Excellence (CEI).

References [1] R. Fabian Pease and Stephen Y. Chou, Proceedings of the IEEE, 96, 2 (2008), 248-270.

[2] George M. Whitesides, Small, 2, 1 (2005), 172-179.

[3] Chen J-K, Ko F-H, Chen H-K and Chou C-T, J. Vac. Sci., Technol. B, 22 (2004), 492-500.

Figures

Remaining thickness (nm)

1000 D100

800 600 50 keV, MeOH as developer D0 = 0,14 C/cm2 D50 = 0,52 C/cm2 D100 = 0,89 C/cm2 Contrast = 1,24

400 200 0 D0 0

2

4

6

8

10

12

2 Dose (C/cm )

Fig. 1. Contrast curve for the poly(HEMA-co-MAAEMA) resist exposed at 50 keV and developed by methanol at room temperature.

Fig. 2. . 1H NMR spectra of the poly(HEMA-co-MAAEMA) copolymer.

Fig. 3. poly(HEMA-co-MAAEMA) resist dome fabricated by exposing concentric circles with gradual doses from 0.5 to 50 µC/cm2. Dome height: 1.3 µm. Horizontal scale bar equals 10 µm.

Conductance Quantization in Resistive Switching 1,2

3

1

4

1

1

Shibing Long , Carlo Gagli , Xavier Cartoixà , Riccardo Rurali , Enrique Miranda , David Jiménez , 3 2 1 Julien Buckley , Ming Liu and Jordi Suñé 1Departament d’Enginyeria Electrònica, Universitat Autònoma de Barcelona, Bellaterra, Spain Lab of nanofabrication and Novel Device Integration, Institute of Microelectronics, Chinese Academy of Sciences, Beijing, China 3 CEA-LETI, Grenoble, France 4 Institut de Ciència de Materials de Barcelona, CSIC, Bellaterra, Spain.

2

Xavier.Cartoixa@uab.es Abstract Many different transition metal oxides show resistive switching properties which have been attributed to the formation and reversible partial rupture of a nanoscale conducting filament (CF) [1]. In this work we focus on the conduction properties of these CFs in Pt/HfO2/Pt structures operated in the unipolar mode.

In these samples, the RESET transition is progressive until the CF conductance decreases to a value close to the quantum of conductance, Go=2e2/h, and it finalizes with an abrupt conductance drop of several orders of magnitude. This final drop corresponds to the opening of a spatial gap (potential barrier) in the CF. Abrupt conductance transitions of the order of Go between well-defined discrete states are found in the final stages of the RESET transient (Fig. 1). The behavior is completely analogous to that reported in metallic point contacts using mechanically controllable break junctions, STM contact-retraction experiments and the current induced local oxidation of nanoscale constrictions [2].

These results are evidence of conductance quantization or of structural changes at the atomic scale (i.e. single atom displacements from/to the CF). The temperature dependence is of metallic type for lowresistance CFs, while it is thermally activated when the CFs is in the high-resistance state. The transition from one regime to the other takes place for a CF conductance of the order of Go. A compact phenomenological model for the CF conduction based on the Quantum Point Contact concept is also shown to nicely fit the current-voltage characteristics both in the low and high resistance states. All these experimental results suggest that a CF with conductance of the order of Go is the natural boundary between the ON and OFF resistive switching states. For conductance above this limit, the CF supports at least one quasi-1D extended quantum state. Below this boundary, a spatial gap exists in the CF, the conduction takes place by tunneling or hopping and hence, it is strongly non-linear.

We have also carried out first principles calculations of the transport properties of metal-HfO2-metal structures where filaments composed of oxygen vacancies are present, in order to determine whether theory supports transport through vacancy paths. We have found that vacancy paths in both the monoclinic (crystalline) and amorphous phase of HfO2 are capable of sustaining conductive channels in the HfO2 energy gap region, though the gap is not completely closed at the path diameters that we have addressed. In particular, Fig. 2 shows the transmission coefficient of a metal/amorphousHfO2/metal structure for vacancy paths of different thicknesses. We can observe that the stoichiometric oxide still presents a transport gap even in its amorphous phase. As expected, transmission is more favored with increasing path width. Note that full transport calculations are needed in order to obtain transmission curves: the density of states (DOS) alone is not sufficient for qualitative predicting of the transmission properties, since it does not contain information about the spatial extent of the states (cf. inset in Fig. 2).

References

[1] R. Waser, R. Dittmann, G. Staikov and K. Szot, Adv. Mater., 21 (2009) 2632.

[2] N. Agraït, A. Levy Yeyati and J.M. van Ruitenbeek, Phys. Rep. 377 (2003) 81.

Figures Normalized conductance of CF (Gcf/G0)

5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0.5

0.6

0.7

0.8 0.9 Applied voltage (V)

1

1.1

1.2

Fig. 1. Evolution of CF conductance in the last stage of 100 switching successive RESET cycles of Pt/HfO2/Pt capacitors. Discrete levels at Go, 2Go are revealed. If plotted in a conductance histogram, peaks at 3Go and 4Go also become evident.

Fig. 2. Transmission coefficient for a metal/amorphous-HfO2/metal structure for vacancy paths of different diameters. The inset overlaps the transmission curve and the density of states (DOS) for the structure with the widest vacancy path.

Hysteresis loops and magnetic susceptibility for different orientation angle of oriented carbon nanotubes using VSM and SQUID

Arisbel Cerpa,1 Daniel Calle,2 Elizabetta Agostinelly,3 Gaspare Varvaro,3 Viviana Negri,2,4 Sebastián Cerdán,2 Paloma Ballesteros4 1

Department of Electromechanical and Materials Universidad Europea de Madrid, C) Tajo s/n, Villaviciosa de Odón-28670, Spain (arisbel.cerpa@uem.es) 2 LIERM, Institute of Biomedical Research “Alberto Sols”, CSIC, Madrid-28029, Spain 3 Institute of Structure of Material,CNR. Roma-00016, Italia 4 Laboratory of Organic Synthesis and Molecular Imaging by Magnetic Resonance, UNED, Madrid28040, Spain

Abstract

Single-Walled Carbon Nanotubes (SWNTs) are potentially useful systems for this purpose since they align with the magnetic field and depict different magnetic properties in the longitudinal and axial directions, preserving anisotropic relaxivity in the NMR [1]. We have reported that exogenous SWNTs are able to induce selectively the anisotropic diffusion of water molecules in the surrounding medium in a manner detectable by MRI methods [2]. Here we report the first measurements to our knowledge of directional relaxivity of SWNTs suspensions trapped in agarose gels using VSM and SQUID magnets.

In this study we have used untreated (CVD) SWNTs oxidized with HNO3 for 24 and 48 hours containing residual catalytic paramagnetic metals [2]. We determined the hysteresis loops and the virgin curve of untreated and oxidized SWNTs during 24 and 48 hours by vibrating sample magnetometer (VSM) and Superconducting Quantum Interference Device (SQUID). The studies were done with oriented SWNTs in an agarose matrix. The measured were obtained at T=100 K and T= 5 K using a VSM and SQUID respectively. The main magnetic properties studies were following: saturation magnetization (Ms), remnant magnetization (Mr), coercive field (Hc) and magnetic susceptibility for different orientation angle.

All the hysteresis loops were obtained using VSM and SQUID equipments showing a paramagnetic behaviour. Figure 1A and 1B depict the oriented suspensions of oxidized SWNTs for 24 and 48 hours which show anisotropic orientation (SQUID).The magnetization ratio (Mr/Ms) and coercitivy value change with the orientation angle for different samples studied. The same behaviour was detected as measured by VSM. Figure 1C shows that the values of magnetic susceptibility decrease as increase orientation angle. These features confirm the results described by T.A. Searles et al. [3].

References [1] J.Tumpane, N. Karousis, N. Tagmatarchis, B. Nordén. Alignment of Carbon Nanotubes in Weak Magnetic Fields. Angewandte Chemie 2008, 47: 5148-5152.

[2] V. Negri, A. Cerpa, P. López-Larrubia, L. Nieto-Charques, S. Cerdán, P. Ballesteros. Nanotubular Paramagnetic Probes as Contrast Agents for Magnetic Resonance Imaging Based on the Diffusion Tensor. Angewandte Chemie 2010, 49: 1813-1815.

[3] T. A. Searles, E. H. Haroz, Y. Imanaka , T. Takamasu , and J. Kono. Diameter dependence of the magnetic susceptibility anisotropy in metallic carbon nanotubes. Phys. Rev. Lett 2010, 105: 017403(1)017403(4)

Figure 48 h

D4 â&#x20AC;&#x201C; 48 hrs CNTs in serum

2,80E-007

2,40E-007

2,00E-007

Suscept, X (emu)

24 h

1,60E-007

SWNTs 24 h 1,20E-007

8,00E-008

SWNTs 48 h

4,00E-008 0

20

40

60

80

Angulo de orientaciĂłn

A

B

C

Figure 1. A, B: Hysteresis loops of oriented carbon nanotubes (SWNTs) in agarose for different orientation angle as measured by SQUID. C: Magnetic susceptibility of oriented SWNTs in agarose for different oxidation times as measured by VSM.

100

Coloring of injection molded plastic plate by surface nanostructures without pigment Doo-Sun Choi, Yeong-Eun Yoo, Jae-Sung Yoon Korea Institute of Machinery and Materials, #171, Jang-dong, Yusung-gu, Daejeon-city, Korea choids@kimm.re.kr Abstract Painting is a typical method for coloring diverse articles. Another common way is molding the plastic articles directly without painting using thermoset resin compounded with pigments or dye through compounding process. Coloring methods like these are based on chemical pigments or dye.

Compared to these colors, some colors in the nature arise from nanostructure, not from the pigment.

For example, the wing scales of butterfly are showing very diverse colors result of the scales micro- and nanostructure[1].

One of typical structures of the wing scales of butterfly is shown in Fig. 1, which consists of multi-layer micro- and nanostructure[2]. These multi-layer structures are very efficient for coloring, but very difficult to realize for engineering applications.

Instead of applying the same structures in nature to engineering applications, some variants should be introduced for mass production. As a variant, a multi-step nanostructure is designed to investigate the coloring effect for plastic articles injection molded.

A model for structures is designed to have three steps as shown in Fig. 2. For moldability of nanostructures and the article itself with nanostructures on the surface, no undercut structure is used and all structures are designed to be intaglio. This intaglio structure turns out to be better for durability of surface structures which is one of drawbacks of nanostructures A pattern master and nickel stamper(Fig. 3)is fabricated to be applied for injection molding of nanostructured plastic plates. A black colored PMMA(Poly MethylMetha Acrylate) is injection molded to see the color effect with the nanostructures. The injection molded nanostructures and the color of the area with nanostructures are shown in Fig. 4 and Fig. 5. As shown in Fig. 4, the nanostructures molded at higher mold temperature are replicated better.

As a result of this study, we could see the possibility of coloring with nanostructures without pigment.

References [1] Pete Vukusic and J. Roy Sambles, “Photonic structures in biology”, Nature, 2003, Vol. 424 14 [2] L. P. Biró et al. “Role of photonic-crystal-type structures in the thermal regulation of a Lycaenid butterfly sister species pair”, Physical Review, 2003, E 67, 021907 [3] Y.E. Yoo et al., “Injection molding of a nanostructured plate and measurement of its surface properties”, Curr. Appl. Phys., 2009, Vol. 9 e12-e18,

Figures

FIG. 1: Structures of the wing scales of butterfly.

FIG. 2: A three-step model design for structural coloring

FIG. 3: Pattern master(left) and stamper(right) for three-step model design for structural coloring

FIG. 4: Injection molded nanostructures at different mold temperature [mold temp. : 40oC (left), 150oC (right)]

FIG. 5: Structural color for injection molded nanostructures

High Frequency Epitaxial Graphene Fields Effect Transistors (GFET) on SiC. 1

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1

D. Mele , E. Pichonat , S. Frégonèse , A. Ouerghi and H. Happy 1

IEMN (UMR CNRS 8520), Avenue Poincaré - 59652 Villeneuve d'Ascq Cedex - BP69 - France 2 IMS (CNRS UMR 5218), Université Bordeaux, 33405 Talence Cedex - France.

3 LPN (CNRS), Route de Nozay, 91400 Marcoussis - France david.mele@ed.univ-lille1.fr

Abstract Since 2004, graphene has generated considerable interest in Physics. This revolutionary material for which discovery Novoselov’s group in Manchester [1] received the Nobel Prize in Physics (2010) can be described as a two-dimensional single layer carbon crystal, arranged on a honeycomb lattice. It comprehends unique characteristics relevant to many researchers in various domains, especially in microelectronics for its potentially high carrier mobility even at room temperature. Owing to its 2D lattice, graphene is considered a semimetal -its band gap and its density of state (DOS) at Fermi level are both nil. Moreover at K and K’ point the dispersion relation is linear and electrons are thus considered as relativistic massless particles and can theoretically reach a electron mobility of 100,000 cm²/V.s [1], [2].

In order to process devices on full wafer and pave the way for industrial graphene based transistors, we have decided to work on epitaxial graphene growths by thermal decomposition of Si-face silicon carbide. This sample was produced by the Laboratory for Photonics and Nanostructures (LPN CNRS).

The graphene layer is characterized by a mapping of the full width at half maximum 2D Raman peak (FWHM) and shown in figure 1. The sample is estimated to be composed of a full mono or bilayer of graphene.

Based on the technological process describe in [3], top-gated epitaxial graphene field effect transistor (GFET) on SiC substrate (shown in figure 2) are patterned by successive steps of electron beam lithography and standard lift-off process with Ni/Au (50 / 300nm) ohmic contacts. After protecting the full active area with a negative hydrogen silsesquioxane (HSQ) resist, the excess of graphene surface was then etched by O2 RIE. The improvement of gate oxide quality was also a challenge in this work. We decided to use Al2O3 deposit by an Atomic Layer Deposition technique. To achieve a uniform deposition of this oxide on the hydrophobic surface of the carbon crystal [4], [5], we had to deposit by evaporation thin aluminium as seed layer (~2nm) which is oxidized in ambient before ALD. Static measurements show the transfer characteristics and the Dirac point (on the figure 3) of a device at low VDS. Due to the interaction with the substrate, the Dirac point is shifted to a negative VGS. Drain current versus source-drain voltage described by the figure 4 doesn’t show saturation characteristics, this is due to the semi-metal behavior of graphene. S parameters measurements were performed in microwave range from 250MHz to 40GHz on a Agilent E8361A. In order to obtain the extrinsic parameters, the influence of parasitic capacitances is removed from the S parameters measurements with an “open” deembedding structure which only includes the pads and the coplanar accesses of the device [6]. Extrinsic cut-off frequency (ft_extr) has been extracted from H21_extr. We report high frequency performances with an extrinsic cut-off frequency of 25GHz and the maximum oscillation frequency 19GHz at VDS=3V and VGS=-2.8V for a transconductance Gm=275mS/µm (see figure 5).

References [1] K.S. Novoselov et al., Science, 306 (2004) 666-669.

[2] F. Schwierz, Nature Nanotechnology, 5 (2010) 487-496.

[3] Meng et al., IEEE Transactions on Electrons Devices, 58 (2011) 1594-1596 [4] D.B. Farmer et al., Nano Letters, 6 (2006) 699.

[5] Wang at al., Journal of the American Chemical Society, 130 (2008) 8152–8153.

[6] L. Nougaret et al., Applied Physics Letters, 94 (2009) 243505.

Figures G

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Figure 1: FHMW Raman mapping of epitaxial graphene on SiC (sample #G129).

Figure 2 : SEM of one final GFET device.

Figure 3: Dirac point voltage extracted from drain current versus gate voltage for a small VDS=100mV.

Figure 4: Measured output characteristics (drain current versus source-drain voltage) of a graphene transistor (LG = 100 nm, W DS=12µm and LDS=0.6µm) for various top-gate voltages. ( from -6V to 0V).

Figure 6: HF characteristics of GFET for LG = 100 nm, W DS=12µm and LDS=1.1µm. Extrinsic |H21|_extrinsic (red line) and maximum oscillation gain (green line) for VDS=3V and VGS=-2.8V. The dashed lines correspond to the ideal slopes of -20 dB/decade for |H21|.

Electroplating and magneto-structural characterization of multilayered Co50Ni50/Co80Ni20 nanowires from single electrochemical bath in anodic alumina templates V. M. Prida1, V. Vega1, L. Iglesias1, J. García1, D. Görlitz2, K. Nielsch2, E. Díaz Barriga-Castro3, R. Mendoza-Résendez4, A. Ponce5, C. Luna3 1 2 3

Departamento de Física, Universidad de Oviedo, Calvo Sotelo s/n, 33007- Oviedo (Spain)

Institute of Applied Physics, University of Hamburg, Jungiusstraβe 11, 20355-Hamburg (Germany).

Centro de Investigación en Ciencias Físico Matemáticas / Facultad de Ciencias Físico Matemáticas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, 66450-Nuevo León (México)

4

Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, 66450-Nuevo León (México) 5

Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, 78249-Texas (USA) vmpp@uniovi.es

Abstract Co-Ni alloy nanowires are outstanding magnetic materials that can exhibit either a soft or a hard magnetic behavior depending on the Co content in the alloy.[1,2] The combination of low magnetocrystalline anisotropy of fcc Ni and high magnetocrystalline anisotropy of hcp Co, together with the high solubility of Co atoms in the crystalline lattice of Ni and vice-versa, for a wide range of relative concentrations, allows for the design of a material composition with tunable magnetic properties. [3] Additionally, the anomalous electroplating behaviour of the Co-Ni alloys results in a preferential deposition of Co atoms with respect to the Ni ones, although Ni2+ ions have a slightly higher deposition potential than Co2+ ions. [4] This effect becomes predominant at low deposition potentials (-0.8V vs.

Ag/AgCl ref. electrode), but it is greatly reduced as the electrode potential is increased up to -1.4V vs.

Ag/AgCl ref. electrode.

By using the anomalous electrodeposition behaviour of Co-Ni alloys we have produced multilayered CoNi nanowires from a single Watts-type electrochemical bath containing Co2+ and Ni2+ ions. Hard-Anodic Aluminum Oxide (H-AAO) nanoporous alumina membranes were employed as templates to obtain highly ordered arrays of Co-Ni multilayered nanowires with a diameter of about 150 nm. The composition of each layer was modified by carefully adjusting the pulsed electrodeposition potential between -0.8V and -1.4V vs. Ag/AgCl reference electrode.[5] The nanowires morphology, crystalline structure and chemical composition were characterized by Scanning Electron Microscopy (SEM, JEOL-6610LV), High-Resolution Transmission Electron Microscopy (HR-TEM, FEI-Titan 80-300kV), Selected Area Electron Diffraction (SAED) and Electron Dispersive X-ray Spectroscopy (EDX). Magnetic hysteresis loops were measured in a Vibrating Sample Magnetometer (VSM, Quantum Design-Versalab) under a magnetic field of ± 30 kOe, applied in both parallel and perpendicular directions with respect to the nanowires long axis.

Our studies reveal that the nanowires are composed of a stack of 40 multilayers with an average length of about 350 nm and approximated compositions of Co50Ni50 and Co80Ni20 in each layer. Figure 1 displays a TEM image of nanowires after being released from the H-AAO template. The compositional contrast indicates the different composition of the multilayers, whereas SAED spectra (insets in Figure 1) demonstrate that nanowires exhibit a differenced crystalline structure between each layer, corresponding to fcc or hcp phases in the Co50Ni50 or Co80Ni20 layers, respectively.

The hysteresis loops depicted in Figure 2 show small coercive field values of HC = 150 and 194 Oe for the parallel and perpendicular directions, respectively. The reduced remanence (mr = Mr/MS) in both directions takes values close to 0.04. These results point out that the array of nanowires does not clearly show an easy magnetization axis, indicating that the shape magnetic anisotropy of the system is strongly competing with the magnetocrystalline anisotropy and dipolar interactions among adjacent barcode nanowires having layers with different compositions and crystalline structures.

References [1] Talapatra S, Tang X, Padi M, Kim T, Vajtai R, Sastry G V S., Shma M, Deevi S C, Ajayan, P M, J. Mater. Sci. 44 (2009) 2271.

[2] Vivas L G, Vรกzquez M, Escrig J, Allende S, Altbir D, Leitao D C, Araujo J P, Phys. Rev. B 85 (2012) 035439.

[3] Cheng S L, Huang C N, Synth. React. Inorg., Met.-Org., Nano-Met. Chem. 38 (2008) 475.

[4] Tian L, Xu J, Qiang C, Appl. Surf. Sci. 257 (2011) 4689.

[5] Clime L, Zhao S Y, Chen P, Normandin F, Roberge H, Veres T, Nanotechnology 18 (2007) 435709.

Figures

Figure 1: HR-TEM image of multilayered Co50Ni50/Co80Ni20 nanowires. The insets show SAED spectra of two layers with different compositions, evidencing the change in their crystalline structures.

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Parallel Perpendicular

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Magnetic Field (kOe) Figure 2. Hysteresis loops of multilayered Co50Ni50/Co80Ni20 nanowires in the parallel and perpendicular directions with respect to the nanowires long axis. The inset shows an enlargement at the low field region.

TOPIC: Nanomagnetism and Spintronics

Observation of low-field magnetoresistance in graphene at room temperature 1

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2

2

1

1

Chenxing Deng , Weiwei Lin , Xiaoyang Lin , Kaili Jiang , Dafiné Ravelosona , Claude Chappert , 1 Weisheng Zhao .

1

Institut d'Electronique Fondamentale, Université Paris-Sud - CNRS, 91405 Orsay, France Department of Physics and Tsinghua-Foxconn Nanotechnology Research Center, Tsinghua University, 100084 Beijing, China chenxing.deng@u-psud.fr

2

Abstract Graphene is a highly attractive material because it exhibits quantum properties of two-dimensional electron gas (2DEG) [1-9]. In particular, graphene has high carrier mobility, weak spin-orbit coupling and long spin lifetime [6-9]. The magnetic dependence of electronic transport in graphene is important to the fundamental physics and potential application. The magnetoresistance (MR) and quantum Hall effect (QHE) of graphene has been studied in large magnetic field and low temperature [3-5].

We have studied low-field magnetoresistance in single-layer graphene (SLG) at room temperature (RT). The SLG was synthesized by chemical vapor deposition (CVD) on copper foil and transferred to Si wafer. The size of the graphene is about 1 cm. The gold wires were patterned as the electrodes on the graphene, and electronic properties were studied using four-point measurements with the constant current mode. The magnetic field was applied perpendicular to the film. Figure 1 shows the MR curve in the SLG at low field range of 25 mT. The resistance R of SLG shows hysteresis behavior with the applied field. The R difference at zero magnetic field between the ascending and descending branches ΔRH=0 depends on the injected current (gate voltage), as shown in Fig. 2, and has a maximum about 100 Ω (0.5% of R) at the injected current of 0.05 mA which is close to the Dirac point of the SLG (about 1 V gate voltage).

The Dirac point in graphene depends on the defect or impurity [7,8]. The edge states with defect or impurity can result in weak ferromagnetic behavior [7]. We suggest that the observed low-field magnetoresistance behavior is related to the defect or impurity in the SLG. Our results can extend better understanding of the magnetic and electronic properties of graphene.

References [1] K. S. Novoselov et al., Science, 306 (2004) 666-669.

[2] C. Berger et al., J. Phys. Chem. B, 108 (2004) 19912-19916.

[3] K. S. Novoselov et al., Nature 438 (2005) 197-200.

[4] Y. Zhang et al., Nature 438 (2005) 201-204.

[5] C. Berger et al., Science, 312 (2006) 1191-1196.

[6] N. Tombros et al., Nature 448 (2007) 571-574.

[7] A. H. Castro Neto et al., Rev. Mod. Phys. 81 (2009) 109-162.

[8] S. Das Sarma et al., Rev. Mod. Phys. 83 (2011) 407-470.

[9] B. Dlubak et al., Nature Phys. (2012) DOI: 10.1038/NPHYS2331.

Figures 22.30

R (k)

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Figure 1. Low magnetic field dependence of resistance in the graphene with the injected current of 0.05 mA.

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22.15

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30

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RH=0 (k)

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Figure 2. (a) Resistance of SLG as a function of the injected current at zero magnetic field for the ascending and descending branches, respectively. (b) The resistance difference at zero magnetic field between the ascending and descending branches ΔRH=0 dependence on the injected current.

Spin selective transport through helical molecular systems Elena Díaz1, R. Gutierrez2, R. Raaman3 and G. Cuniberti2 1Departamento 2Institute

de Física de Materiales, Universidad Complutense, E-28040 Madrid, Spain for Materials Science, Dresden University of Technology, D-01062 Dresden, Germany 3Department of Chemical Physics, Weizmann Institute, 76100 Rehovot, Israel elenadg@fis.ucm.es

Abstract The concept of spintronic devices operating without a magnetic field has been proposed some time ago for solid state devices in which the spin-orbit coupling (SOC) is large [1, 2]. In recent years, a new type of magnet-less spin selective transmission e ffect has been reported [3–7]. It was found that electron transmission through self-assembled monolayers (SAM) of chiral molecules is highly spin selective at room temperature. These findings are so far surprising as organic molecules typically have a small SOC that cannot support significant splitting between the spin states. Although it has been suggested both by theory [8, 9] and experiments [10] that there is a cooperative contribution to the value of the SOC, making this quantity larger in molecules or nanotubes than in a single carbon atom, the values calculated or experimentally found are still relatively small [8–11], e.g. few meV for nanotubes [10]. Hence, even including this cooperative contribution, the spin polarization (SP) in electron transmission through SAMs of chiral molecules [6, 7] seems to be too high to be rationalized by such SOC values.

Recently, a theoretical model based on scattering theory has been proposed for explaining the spin selectivity of chiral molecules [12]. Although the results are in qualitative agreement with the experimental observations, they could not explain them using reasonable SOC values.

In this work [13], a minimal model is presented, describing electron transmission through a helical potential, see Fig. 1. Main goal of the model is to highlight the role of some crucial parameters, which will lead to a high SP while still keeping a moderate SOC strength. Although the recent transport experiments on DNA SAMs [7] are our main motivation, the model is generic enough to encompass other molecular systems with chiral symmetry. In short, there are two main key factors in the model allowing for a high SP: i) Lack of inversion symmetry due to the chiral symmetry of the scattering potential, and ii) Narrow electronic band widths in the helical system, i.e. the coupling between the units composing the helical structure is relatively weak. A physically meaningful estimation of the SOC is further obtained by taking into account that first, in the present study the electric field acting on the electron needs to include the effective influence of all the electrons belonging to a molecular unit [7, 14], and second, due to proximity effects, the Coulomb interaction between the transmitted electron and those in the molecular unit scales as 1/R for short distances R. References [1] B. Datta, and S. Das, Appl. Phys. Lett., 56 (1990) 665.

[2] J.P. Lu, J.B. Yau, S.P. Shukla, M. Shayegan, L.Wissinger, U. R¨ssler, and R. Winkler, Phys. Rev. Lett.,(1998) 81 1282.

[3] K. Ray, S. P. Ananthavel, D. H. Waldeck, and R. Naaman, Science, 283 (1999) 814.

[4] R. Naaman, and Z. Vager, MRS Bul., 35 (2010) 429.

[5] S. G. Ray, S. S. Daube, G. Leitus, Z. Vager, and R.Naaman, Phys. Rev. Lett., 96 (2006) 036101.

[6] B. Goehler, V. Hamelbeck, T. Z. Markus, M. Kettner,G. F. Hanne, Z. Vager, R. Naaman, and H. Zacharias,Science, 331 (2011) 894.

[7] Z. Xie, T. Z. Markus, S. R. Cohen, Z. Vager, R. Gutierrez, and R. Naaman, Nano Letters, 11 (2011) 4652.

[8] D. Huertas-Hernando, F. Guinea, and A. Brataas, Phys.Rev. B, 74 (2006) 155426.

[9] A. De Martino, R. Egger, K. Hallberg, and C. A. Balseiro, Phys. Rev. Lett., 88 (2002) 206402.

[10] F. Kuemmeth, S. Ilani, D. C. Ralph, and P. L. McEuen,Nature, 452 (2008) 448.

[11] E. I. Rashba, Sov. Phys. Solid State, 2 (1960) 1109.

[12] S. Yeganeh, M. A. Ratner, E. Medina, and V. Mujica, J.Chem. Phys., 131 (2009) 014707.

[13] R. Gutierrez, E. Díaz, R. Raaman and G. Cuniberti, Phys. Rev. B, 85 (2012) 081404(R).

[14] G. Bihlmayer, S. Bl¨ gel, and E. V. Chulkov, Phys. Rev. B, 75 (2007) 195414.

Figures

FIG. 1. A charge q in spin state σ is moving along through helical electric field. The parameters a, b and ∆z are the radius and the pitch of the helix and the spacing of the z-component of the position vector of the charges distributed along it, respectively. The helical field induces a magnetic field B in the rest frame of the charge and hence influences its spin state.

FIG. 2. Top panel: Schematic representation of the tight-binding model. The two channels interact via the SOC (framed region). To the left and right of the spin scattering region, both channels are independent and are modeled by semi-infinite chains. Bottom panel: Energy dependence of the SP P (E) for L0 =3 helical turns, and for injected electrons polarized with their spin pointing up (P10 ), down (P01 ), or unpolarized (P11 ). A spin-filter e ffect takes place only for energies near the band edges, where all SPs have the same sign.

Development of new Polymer-Metal-Nanocomposites based on activated foams and textile fibers and their catalytic evaluation.

1, *

1

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2,3

1

B. Domènech , K. Ziegler , J. Macanás , F. Carrillo , M. Muñoz , D.N. Muraviev

1

1

Analytical Chemistry Division, Chemistry Department, Universitat Autònoma de Barcelona, Campus UAB, 08193 Bellaterra, Spain.

2 Department of Chemical Engineering, Universitat Politècnica de Catalunya, UPC, C/Colom 1, 08222, Terrassa, Spain 3 INTEXTER, Universitat Politècnica de Catalunya, UPC, C/Colom 15, 08222, Terrassa, Spain Berta.Domenech@uab.cat

Abstract Nowadays research in Green Chemistry, Catalysis and Water Treatment fields has undergone an important intensification, focusing much interest and acting as a basis for the development of new techniques and materials. For instance, there is a general endeavor to develop environmentally friendly catalysts [1]. In this sense, the synthesis of Polymer-Metal-Nanocomposites (PMNCs) obtained by the incorporation of Metal Nanoparticles (MNPs) in polymeric matrices has demonstrated to be an attractive approach in the design of these catalytically active species [2].

There are two main reasons for that: i) it has been proved that MNPs are especially effective catalysts, mainly due to their large percentage of surface atoms [3,4]; ii) by stabilizing these MNPs in a polymeric matrix, it is possible to prevent their escape to the reaction medium, thus providing an easy separation of the catalyst what, in turn, allows the possibility to reuse the catalytic species without losing efficiency [1,5].

Accordingly, special efforts are focused nowadays to the development of new nanocomposites which can enlarge the basis of suitable materials intended to be used in a wide range of applications such as: water disinfection, catalysis, energy storage, electrochemical sensors and biosensors, etc. [6,7].

0 In this presentation we report the ion-exchange mediated synthesis of silver nanoparticles (Ag -NPs) in different polymeric matrices such as polyurethane foams, and polyacrylonitrile or polyamide fibers. This synthetic methodology refers to a group of methods that can be generally classified as Inter-Matrix Synthesis (IMS) technique [8]. The main feature of IMS is the dual function of the matrix, which provides 0 a confined medium for the synthesis (preventing Ag -NPs uncontrollable growth and aggregation) as well as it retains the MNPs, avoiding their release.

Anyhow, in order to apply the IMS technique, there are some requirements for the parent polymer such as: chemical compatibility with the MNPs surface, enough flexibility of the polymer chain segments, adequate swelling ratio, adequate hydrophilicity, etc. Yet, above all the mentioned features, the most + important one is that the polymer must bear functional groups (e.g. R-SO3 , R-COO , R-NR3 , …) which + act as nanoreactors able to bind and retain the nanoparticle ion precursors (e.g. Ag ), while allow the ion diffusion through the matrix. Regarding this issue, and taking into account the nature of some of the chosen matrices, it was essential to activate the support material to obtain an acceptable value of Ion Exchange Capacity. Therefore, in this work different chemical pretreatments have been tested to ensure 0 an effective Ag -NPs loading.

Finally, in order to evaluate the catalytic activity of the different developed PMNCs, a model catalytic reaction was carried out in batch experiments: the reduction of p-nitrophenol in presence of sodium borohydride and metallic catalyst [9,10].

References [1] Rothenberg, G., Wiley-VCH Verlag GmbH & Co. KGaA., (2008) p. 1-38.

[2] Pomogailo, A., Kestelman, V.N., Metallopolymer nanocomposites. Springer (2005).

[3] Roduner, E., Chemical Society Reviews. 35(7) (2006) p. 583-592.

[4] Campelo, J.M., Luna, D., Luque, R., Marinas, J.M., Romero, A.A., ChemSusChem, 2(1) (2009) p.

18-45.

[5] Macanás, J., Ruiz, P., Alonso, A., Muñoz, M., Muraviev, D.N., Ion Exchange-Assisted Synthesis of Polymer Stabilized Metal Nanoparticles, in Ion Exchange and Solvent Extraction, CRC Press. (2011) p. 1-44.

[6] Milev, A.S., Kannangara, G.S.K., Wilson, M.A., Nanotechnology, in Kirk-Othmer Encyclopedia of Chemical Technology, Wiley (2000).

[7] Thayer, A.N., C&EN Houston, Chemical & Engineering News, 80(29)(2002) p. 17-19.

[8] Muraviev, D.N., Macanás, J., Farre, M., Muñoz, M., Alegret, S., Sensors and Actuators B-Chemical, 118(1-2) (2006) p. 408-417.

[9] Dotzauer, D.M., Dai, J., Sun, L., Bruening, M. L., Nano Letters, 6(10) (2006) p. 2268-2272.

[10] Domènech, B., Muñoz, M., Muraviev, D.N., Macanás, J., Catalysis Today (2012) (In press, DOI/10.1016/j.cattod.2012.02.049).

Figures

0

Figure 1. Typical Scanning Electron Microscopy images of polyacrylonitrile fibres containing Ag -NPs.

0

Figure 2. Typical Scanning Electron Microscopy images of polyamide fibres containing Ag -NPs.

0

Figure 3. Typical Scanning Electron Microscopy images of polyurethane foam containing Ag -NPs.

NANO FABRICATION OF FinFETS TO FORM NANO SCALED INTEGRATED CIRCUIT CHIPS NILAY KETAN DOSHI BIRLA INSTITUTE OF TECHNOLOGY, PILANI – DUBAI nilaykdoshi@gmail.com ABSTRACT Semi-conducting, metallic and insulating nanowires are today’s building blocks in nanotechnology. Due to their small size, anisotropy and cost effectiveness it is viable to integrate Nano scaled elements into Nano IC chips. Strategies have emerged to position nanowires and Nano circuits on substrates to allow integration of Nano electronic devices. In this paper we describe the fabrication and assembly of Nano devices to form functional IC chips on a nanometer scale. Several methods have been developed from nanofabrication based on selfassembled alumina templates, using biomolecules for self-assembly of engineered Nano-scale devices and Nano structuring of ceramic surfaces by ways of unconventional lithographic methods, electron beam induced deposition, electron-ion beam lithography and electron beam direct writing[3].

We will begin by a review of the basic structure of IC chips and their varying properties using different materials and then move on to how these properties differ at a Nano scale. Hence we will describe how the basic components such transistors ( FinFETs ) can be engineered using various lithographic and non-lithographic methods. Hence implementing a majority gate and a 21 MUX by using both gates of FinFET[2] transistors as inputs is presented. Simulation results show that FinFET logic implementation has significant advantages over static CMOS logic and pass transistor logic in terms of power consumption and cell area therefore aiming at the end result which includes Nano-scaled IC chips which provide optimum efficiency and are cost effective[1].

KEYWORDS Nano-scaled IC chips, nanofabrication, nanowires, lithographic methods, semiconductor quantum dots, electron-ion beam, metal dot array, ceramic surfaces, biomolecules, alumina templates, optimum efficiency, cost effective.

REFERENCES [1] Michael C. Wang, Princeton University, “Low Power, Area Efficient FinFET Circuit Design“, Proceedings of the World Congress on Engineering and Computer Science 2009 Vol I WCECS 2009, October 20-22, 2009, San Francisco, USA [2] Jong-Ho Lee,” Fabrication and Characterization of bulk FinFETs for Future Nano-Scale CMOS Technology”, 2nd US-Korea NanoForum, LA [3] Ben G. Streetman, Sanjay Kumar Bannerjee, “Solid State Electronic Devices – Sixth

Editionâ&#x20AC;&#x153;, Pratence Hall of India

Fig 1(a) : Schematic of nano fabricating FinFETS with double fin gates.

Fig 1(b) : Graph of drain current vs the drain source voltage.

Compressive Buckling of Boron Nitride Nanotubes with Hydrogen Storage Salman Ebrahimi-Nejad, Ali Shokuhfar, Amin Hosseini-Sadegh, Abolfazl Zare-Shahabadi Faculty of Mechanical Engineering, K.N. Toosi University of Technology, 19991-43344 Tehran, Iran EbrahimiNejad@dena.kntu.ac.ir Abstract Energy and environment are two of the most significant issues for the world in the next 50 years [1]. Energy consumption is intimately linked with CO2 emission, a major human contributor to undesirable climate change. The simplest solution to both problems lies in the use of alternative green energy sources, such as hydrogen. Hydrogen is the most abundant element on the earth and an ideal alternative energy source; it has the highest energy content per weight, it is versatile and renewable, and it is easily produced anywhere without the current geopolitical dependencies [1, 2].

However, under ambient conditions, hydrogen is a very low density gas: 10 times lower than air, demanding efficient storage systems to enable exploiting the available energy. The US Department of Energy (DOE) recently set the 2015 automotive hydrogen storage target of system gravimetric and volumetric densities of 5.5 %wt and 40 g of H2/L [3]. Despite significant efforts, the solution has not yet been found.

Cryogenic liquid hydrogen, compressed gaseous hydrogen and metal hydrides have been investigated as possible hydrogen storage forms [4], which, however, have drawbacks such as low capacity, safety problems, or impractical release temperatures. Since the discovery of carbon nanotubes (CNTs) in 1997 [5], they were considered as a promising candidate for gas adsorption and many theoretical and experimental studies investigated the hydrogen storage capacity of these carbon nanostructures.

However, detailed investigations conclude that high hydrogen storage capacity at ambient conditions, which meets the DOE targets for vehicular fuel cells, cannot occur in bare carbon nanotubes [1, 2].

The structure of Boron nitride nanotubes (BNNTs) [6, 7], which are made from group-III and -V elements neighboring C in the Periodic Table, is very similar to that of CNTs and they can be imagined as rolled up hexagonal BN layers or as CNTs in which alternating B and N atoms entirely substitute for C atoms [8]. BNNTs have outstanding physical and mechanical properties [9] and, compared to CNTs, have an enhanced chemical and high-temperature stability and exhibit superior mechanical properties at high temperatures and enhanced resistance to oxidization. Their diameters can also reach hundreds of nanometers, much greater than that of CNTs, suitable for hydrogen storage applications.

Therefore, BNNTs have been tested as a new material for hydrogen storage and studies have revealed that they have better hydrogen storage characteristics and are a better hydrogen storage medium than CNTs, which is partly explained by the increased tube-hydrogen interactions due to the polar nature of their bonds. Furthermore, Tang et al. [10], revealed an implicit relation between the structure of BNNTs and their hydrogen storage behavior, and showed that BNNTs with a collapsed structure could store up to 4.2 %wt hydrogen at room temperature.

This work investigates the effect of hydrogen storage on the mechanical properties of BNNTs (Figure 1).

Molecular dynamics simulations have been performed to study the buckling behavior of BNNTs under uniaxial compressive loading with different percentages of hydrogen storage (Figure 2). The structural stability and compressive resistance properties of these nanotubes were investigated in a hydrogen environment and the critical buckling loads and critical buckling strains of the nanotubes and their susceptibility were determined.

References [1] G. E. Froudakis, Materials Today, 14 (2011) 324-328,.

[2] C. Liu, Y. Chen, C.-Z. Wu, S.-T. Xu and H.-M. Cheng, Carbon, 48 (2010) 452-455.

[3] Energy Efficiency and Renewable Energy website of the U.S. Department of Energy (DOE). www1.eere.energy.gov/hydrogenandfuelcells/storage/pdfs/targets_onboard_hydro_storage_explanat ion.pdf (2012).

[4] M. Becher, M. Haluska, M. Hirscher, A. Quintel, V. Skakalova, U. Dettlaff-Weglikovska, X. Chen, M. Hulman, Y. Choi, S. Roth, V. Meregalli, M. Parrinello, R. Ströbel, L. Jörissen, M. M. Kappes, J. Fink, A. Züttel, I. Stepanek and P. Bernier, Comptes Rendus Physique 4 (2003) 1055-1062.

[5] S. Iijima, Nature, 354 (6348) (1991) 56-58.

[6] D. Golberg, Y. Bando, C. C. Tang, and C. Y. Zhi, Adv. Mater. 19 (2007) 2413.

[7] C. Zhi, Y. Bando, C. Tang, and D. Golberg, Mat. Sci. Eng. R 70 (2010) 92.

[8] A. Shokuhfar, S. Ebrahimi-Nejad, A. Hosseini-Sadegh, A. Zare-Shahabadi, Phys. Status Solidi A, DOI:10.1002/pssa.201127678, (2012).

[9] J. B. Yoo, J. H. Han, S. H. Choi, T. Y. Lee, C. Y. Park, T. W. Jeong, J. H. Lee, S. G. Yu, G. S. Park, W. K. Yi, H. S. Kim, Y. J. Baik, and J. M. Kim, Physica B 323 (2002) 180.

[10] C. Tang, Y. Bando, X. Ding, S. Qi, D. Golberg, J Am Chem Soc 124 (2002) 14550.

Figures

Figure 1

Figure 2

Influence of metallic nanostructures on the optical properties of dye-doped polymer thin films a

a

a

M. Enculescu , E. Matei , I. Enculescu , C. Trautmann

b

a

National Institute of Materials Physics, PO Box MG-7, 77125, Magurele-Bucharest, Romania b GSI, Helmholtz Centre, Planckstr. 1, D-64291, Darmstadt, Germany mdatcu@infim.ro The fabrication of complex micro and nano-scaled architectures attracted a great interest during

the last decades. The devices that are based on polymers are gaining attention considering the possible applications, especially the ones requiring the processing on large areas with low costs. Polymer thin films doped with dyes or metal particles were intensively studied [1, 2]. One of the most used methods for obtaining of polymer thin films is spin coating. Polymers doped with dyes are successfully used as modern light sensing materials, white light diodes [3, 4], light amplifiers [5] or waveguides [6].

Our purpose is to produce polymer thin films that are doped with different dyes and codoped with metallic nanowires and present controllable optical properties. Thus, thin films of polyvinylpyrrolidone (PVP) doped with dyes from blue-green (coumarins) and orange-red (sulphorhodamines, rhodamines) domains of the spectrum were produced by spin coating. The dye-doped polymer thin films are codoped with nickel nanowires obtained by template method. The template method is a versatile method to produce nanostructures with controlled properties. Polycarbonate (PC) foils of thickness 30 μm were irradiated with swift heavy ions of high kinetic energies (11.4 MeV/nucleon) at the UNILAC linear accelerator of GSI, Darmstadt. By subsequent chemical etching, the tracks were transformed into pores.

The pores inside the PC membranes were filled with Ni nanowires via electrochemical deposition. The membranes were fully dissolved in order to obtain a suspension of Ni nanowires.

We evaluated the optical and morphological properties of both dye-doped polymer films and dyedoped polymer films containing nickel nanowires.

Acknowledgements This work was supported by a grant of the Romanian National Authority for Scientific Research, CNCS – UEFISCDI, project PN-II-RU-TE-2011-3-0107, contract no. 37/2011.

References [1] T. Xu, G. Chen, C. Zhang, Z. Hao, X. Xu, J. Tian, Optical Materials 39 (2008) 1349 [2] R. Abargues, K. Abderrafi, E. Pedrueza, R. Gradess, J. Marques-Hueso, J. L. Valdes, J. MartınezPastora, New Journal of Chemistry 33 (2009) 1720 [3] H. K. Lee, T.-H. Kim, J. H. Park, J.-K. Kim, O O. Park, Organic Electronics 12 (2011) 891 [4 T.-H. Kim, H. K. Lee, O O. Park,* B. D. Chin, S.-H. Lee, J. K. Kim Advanced Functional Materials 16 (2006) 611 [5] K. Yamashita, T. Kuro, K. Oe, Applied Physics Letters 88 (2006) 241110 [6] H. Yanagi, H. Miyamoto, A. Ishizumi, S. Tomita, K. Yamashita, Applied Physics Letters 96 (2010) 263304

Figures

Fig. 1. Optical transmission microscopy images of dye-doped PVP films containing nickel nanowires.

7

Emission intensity (a.u)

Transmission intensity (%)

100 80 60 PVP PVP +Rh6G PVP+Ni PVP+Rh6G+Ni

40 20 0 500

1000

Wavelength (nm)

1500

6 PVP+Rh6G PVP+Rh6G+Ni

5 4 3 2 1 0 520

560

600

640

680

Wavelength (nm)

Fig. 2. (a) Transmission spectra of PVP films deposited by spin coating on 1 mm thick microscope glass; (b) Emission spectra, excited with 500 nm, of Rh 6G doped PVP films with and without Ni nanowires.

Effects of a Plasmonic Nanostructure on Kerr Nonlinearity in a Four-Level Quantum System Sofia Evangelou, Vassilios Yannopapas, Emmanuel Paspalakis Materials Science Department, University of Patras, Patras 265 04, Greece evaggelou_sofia@yahoo.gr, paspalak@upatras.gr Abstract Recent studies have revealed that several nonlinear optical phenomena can be strongly modified in quantum systems near plasmonic nanostructures. Examples of these phenomena include upconversion processes [1], second harmonic generation [2], Kerr nonlinearity [3],four-wave mixing [4], nonlinear optical rectification [5], induced transparency [6,7], and gain without inversion [7,8].

In this work we continue our study on the effects of the presence of a plasmonic nanostructure (see Fig. 1, left) on the optical properties of a four-level double-V-type quantum system (see Fig. 1, right). In the quantum system under study the transitions |2⟩, |3⟩ to |1⟩ are in energies that are influenced by the surface plasmons of the metallic nanostructure while the transitions |2⟩, |3⟩ to |0⟩ are in quite different energies and are not influenced by the surface plasmons, so they interact with free space vacuum. This quantum system shows quantum interference in spontaneous emission near the plasmonic nanostructure [9-12]. In a previous study [6], we have shown that this system can also exhibit induced transparency and slow light when it interacts with a weak probe laser field. Here, we study the effects of the plasmonic nanostructure on Kerr nonlinearity.

For the plasmonic nanostructure we consider a two-dimensional array of metal-coated silica nanospheres (see Fig. 1, left), where the metallic part is described by a Drude-type dielectric function 2 2 ε(ω) = 1 - ωp /(ω +iω/τ), where ωp is the plasma frequency and τ is the relaxation time of the conduction-band electrons of the metal. We calculate the relevant decay rates with a rigorous electromagnetic Green's tensor technique, using a layer-multiple-scattering method for electromagnetic waves [9-11,13,14] (see results in Fig. 2). It is evident that the spontaneous decay rate for a dipole oriented parallel to the surface of the plasmonic nanostructure is suppressed relative to vacuum and exhibits significant suppression in the frequency region from 0.6ω/ωp to 0.7ω/ωp, with the actual value becoming significantly smaller that the free space decay rate. In the same frequency region the spontaneous decay rate for a dipole oriented perpendicular to the surface of the plasmonic nanostructure is also suppressed but it remains larger than the free space decay rate.

The quantum system is initially in state |0⟩ and interacts with a linearly polarized probe laser field, which couples the lowest state |0⟩ with states |2⟩ and |3⟩. We use a density matrix methodology for the theoretical description of the optical properties of the laser field. Assuming a weak laser field, the density matrix elements can be calculated analytically up to third order with respect to the electric field (3) amplitude. We use the relevant density matrix elements and determine the Kerr nonlinearity χ . The (3) imaginary and real part of χ are displayed in Fig. 3. Fig. (a) is in the absence of the plasmonic nanostructure, while figs. (b), (c) and (d) are in the presence of the plasmonic nanostructure. We see (3) that due to the presence of the plasmonic nanostructure, both the real and imaginary part of χ are significantly modified. This modification depends on the distance of the quantum system from the plasmonic nanostructure.

References [1] R. Esteban, M. Laroche, and J.-J. Greffet, J. Appl. Phys. 105, (2009) 033107.

[2] Y. Pu, R. Grange, C.-L. Hsieh, and D. Psaltis, Phys. Rev. Lett. 104, (2010) 207402.

[3] V. Yannopapas, Opt. Commun. 283, (2010) 1647.

[4] J.-B. Li, N.-C. Kim, M.-T. Cheng, L. Zhou, Z.-H. Hao, and Q.-Q. Wang, Opt. Express 20, (2012) 1856.

[5] I. Thanopulos, E. Paspalakis, and V. Yannopapas, Phys. Rev. B 85, (2012) 035111.

[6] S. Evangelou, V. Yannopapas, and E. Paspalakis, (2012), submitted.

[7] A. Hatef and M. R. Singh, Phys. Rev. A. 81, (2010) 063816.

[8] S. M. Sadeghi, Nanotechnology 21, (2010) 455401.

[9] V. Yannopapas, E. Paspalakis, and N. V. Vitanov, Phys. Rev. Lett. 103, (2009) 063602.

[10] S. Evangelou, V. Yannopapas, and E. Paspalakis, Phys. Rev. A 83, (2011) 023819.

[11] S. Evangelou, V. Yannopapas, and E. Paspalakis, Phys. Rev. A 83, (2011) 055805.

[12] Y. Gu, L. Wang, P. Ren, J.-X. Zhang, T.-C. Zhang, O. J. F. Martin, and Q.-H. Gong, Nano Lett. 12, (2012) 2488.

[13] R. Sainidou, N. Stefanou, and A.Modinos, Phys. Rev. B 69, (2004) 064301.

[14] V. Yannopapas and N. V. Vitanov, Phys. Rev. B 75, (2007) 115124.

Figures

Figure 1: Left: (a) Metallic nanoshell made from a silica core of radius Sc and metal coating of thickness S-Sc. (b) Square lattice of metallic nanoshells (monolayer) with period α. (c) Side view of the monolayer where d is the distance of the quantum emitter from the surface of a nanoshell. Right: The quantum system under study is a double-V-type system.

Figure 2: The spontaneous emission rate for a dipole which is normally oriented (a) [parallel oriented (b)] with respect to the plasmonic nanostructure as a function of the emitter frequency for various distances d from the plasmonic nanostructure (with exact values of d shown in the inset). Γ0 is the decay rate in the vacuum.

Figure 3: The real part (dashed curve) and imaginary part (solid curve) of Kerr nonlinearity [in units 4 3 3 2Nμ /(3ћ ε0Γ0 )], where N is the atomic density. Here, the central Bohr frequency (calculated from state |0> to the middle of states |2> and |3>) is ω = 0.632ωp, the frequency difference of the upper levels is ω32 = Γ0 and in (b) d = 0.5c/ωp, (c) d = 0.4c/ωp, and (d) d = 0.3c/ωp. The detuning is defined as δ = ωlas – ω. The spontaneous decay rates from states |2⟩ and |3⟩ to |0⟩ are taken zero.

Effect of noble metal nanoparticles on the glass transition temperature of poly(t-butylacrylate) composites Sara Fateixa, Ana L. Daniel-da-Silva, Noémi Jordão, Ana Barros-Timmons, Tito Trindade Department of Chemistry and CICECO, University of Aveiro, Portugal sarafateixa@ua.pt

Abstract In the last years the understanding of the effect of nanofillers on the behavior of polymer based nanocomposites became essential for the development of new materials with innovative properties [1,2]. However, few studies have been reported on the impact of metal nanoparticles (NPs) used as fillers on the thermal behavior of polymers [3,4].

The aims of the research reported here was the study of the effect of organically capped colloidal metal nanoparticles (NPs), prepared by a modification of the polyol method [5], on the glass transition temperature (Tg) of the polymer poly(tert-butyl acrylate) (PtBA). This polymer matrix was selected due to our interest on the optical properties of PtBA nanocomposites namely as new platforms for sensing devices [6, 7].

The nanocomposites were prepared by two distinct methods: i) cast films of blends of metal NPs and PtBA obtained from tetrahydrofuran (THF) mixtures and further evaporation of the solvent; ii) polymerization using miniemulsions (in situ method) in the presence of the metal NPs. The presence of the metal NPs in all the nanocomposites was confirmed by visible spectroscopy performed on the samples, namely by monitoring the surface plasmon resonance (SPR) of the nanometal. Microscopy analysis of the nanocomposites prepared by the in situ method shows that the polymer is coating the metal nanoparticles (Figure 1).

The influence of the inorganic fillers on the glass transition temperature of the polymer (Tg) by varying the chemical nature of the filler, average particle size, and metal content, were investigated by differential scanning calorimetry (DSC). This study showed slightly differences on the Tg of the polymer depending on the method employed in the composite preparation. On the other hand, the incorporation of metal (Au or Ag) nanoparticles in the PtBA matrix had a marked effect on the Tg due to the presence of metal/polymer interfaces which can promote polymer chains mobility. The chemical nature of the nanofillers used seemed to have similar effects on the Tg of the PtBA. On the other hand, the average particle size and amount of metal NPs strongly influenced the Tg of the polymer. These results have been interpreted in terms of effects on the polymer chains mobility, namely by considering the influence of the metal NPs on the intermolecular forces between the PtBA segments.

References [1] J. A. Balmer, A. Schmid, S. P. Armes, J. Mater. Chem., 18 (2008) 5722.

[2] F. Faupel, V. Zaporojtchenko, T. Strunskus, M. Elbahri, Adv. Eng. Mater. 12 (2010) 1177 [3] V. V. Vodnik, J. V. Vuković, J. M. Nedeljković, Colloid Polym. Sci., 287 (2009) 847 [4] Y. Sun, Z. Zhang, K-S.Moon, C. P. Wong, J. Polym. Sci. B: Polym. Phys., 42 (2004) 3849 [5] F. Fievet, J. P. Lagier; M. Figlarz, MRS Bull., 14 (1989) 29 [6] M A Martins, S. Fateixa, A. V. Girão, S. S. Pereira, T. Trindade, Lagmuir., 26 (2010) 11412 [7] S. Fateixa, A. V. Girão, H. I. S. Nogueira, T. Trindade, J. Mater. Chem., 21 (2011) 15629

Figure 1

Figure 1: Optical spectra of nanocomposites prepared by miniemulsion polymerization: a) Ag/PtBA (11nm, 0.8 wt% Ag); b) Au/PtBA(11nm, 0.8 wt% Au), photographs and TEM images of the respective nanocomposites.

Study of weather effect on pvdf/pmma based blend coatings ageing: influence of artificial ageing (xenotest) and neutral saline fog 1

1

2

1

F. Z.BENABID , F.ZOUAI , M.E. Cagiao , S.BOUHELAL and D. BENACHOUR

1

(1)Laboratoire des matériaux polymériques multiphasiques, Département de génie des procédés, Faculté des sciences de l’ingénieur, Université ferhat Abbas, Sétif, Algeria e-mail: fzbenabid@yahoo.fr (2) Departamento de Fisica Macromolecular, Instituto de Estructura de la Materia, Serrano, 119.28006 Madrid, Espana.

Fluorined and polyacrylic polymers are widely used in restorating historical monuments. PVDF provides easier implementing, high photo and chemical resistance.

In spite of its higher physical properties and lower cost compared to PVDF, use of PMMA as surface protecting agent of building stones is limited because of its low photo-resistance.

However, PVDF/PMMA blends are very interesting materials developped recently in architectural restoration works field, involving the cheaper and the most effective method to produce high performance new polymer materials.

After mixing the two polymers at different contents in the appropriate solvant (DMF), the films undergo exposure to artificial ageing and saline fog.

The results obtained allowed to observe by mean of several tests the behaviour of both polymers systems at different contents.

The set of results revealed that adding PVDF to PMMA improved the properties of the latter namely the resistance during exposure to natural and artificial ageing and saline fog.

PVDF/PMMA blend systems at 70/30 respectively were in accordance with literature reports as the most available formulation to be used.

Keywords: PVDF, PMMA, COATING, RESISTANCE, WEATHER ATTACK.

Optical and structural properties of Al doped ZnO nano-structured films formed

by Sol-Gel processing 1

2

2

1

Carole FAUQUET , Anna REYMERS , Vladimir GEVORGYAN , Alain RANGUIS , Damien 1 1,3 1 CHAUDANSON , Artak KARAPETYAN , Wladimir MARINE 1

CNRS, UMR7325, 13288, Marseille, France, Aix-Marseille Univ., CINaM, 13288, Marseille, France Russian-Armenian (Slavonic) University, 375051, H.Emin st.123, Yerevan, Armenia 3 Institute for Physical Research of NAS of Armenia, Ashtarak-2, 0203, Armenia fauquet@cinam.univ-mrs.fr 2

Abstract Zinc Oxide (ZnO) is a direct-gap and unipolar n-type semiconductor with a band gap of 3.3 eV and a large exciton binding energy of 60 meV at room temperature [1]. It has been extensively investigated for a variety of applications in electronics, optoelectronics, electrochemical, and electromechanical devices, such as light emitting devices [2-4], transparent conducting layers, and as conducting-window layer in thin film solar cells [5]. Moreover since the discovery of UV lasing emissions from ZnO nanowires [6], much attention has been paid to the stimulated emission from ZnO nanostructures.

Sol-Gel processing is one of the most promising methods of ZnO thin films preparation for different applications. It is important to highlight that this method allows to obtain high quality crystalline films with precise control of the stoichiometry, high degree of purity and doping homogeneity of the films.

In this work we report optical and structural investigations of Al doped ZnO nanostructured films, prepared by Sol-Gel optimized technique. Two series of samples were studied. Both were annealed at 500°C, while the second was further ann ealed at 600°C for 30 min. High resolution SEM observations show that both films are formed of 40-50 nm nanocrystallites while the surface of the second film is further decorated by nanorods of approximately 800 nm length. The nanocrystallites and the randomly distributed nanorods can be seen in the AFM images (see Figure 1).

The samples photoluminescence was recorded by using CW one photon He-Cd laser excitation at 325 nm and by two photons femtosecond pulsed laser excitation at 700 nm.

Both series show the characteristic excitonic band of ZnO under one photon excitation. However, with two photon excitation, the second series shows high intensity excitonic band and random lasing behaviour.

References [1] Look, D. C., Mat. Sci. Eng. B-.Adv. 2001, 80, 383–387.

[2] Wang, Z. L., Chinese Sci. Bull. 2009, 54, 4021–4034.

[3] Heo, Y. W.; Norton, D. P.; Tien, L. C.; Kwon, Y.; Kang, B.S.; Ren, F.; Pearton, S. J.; LaRoche, J. R., Mat. Sci. Eng. R 2004, 47, 147.

[4] G. C.; Yi, C. R.; Wang, W. I,. Park, Semicond. Sci. Technol, 2005, 20, S22–S34.

[5] Wei, Y. G.; Xu, C.; Xu, S.; Li, C.; Wu, W. Z.; Wang, Z. L., Nano Lett. 2010, 10, 2092–2096.

[6] Huang, M. H.; Mao, S.; Feick, H.; Yan, H. Q.; Wu, Y. Y.;Kind, H.; Weber, E.; Russo, R.; Yang, P. D., Science 2001, 292, 1897–1899.

a

b

Fig. 1: 18 Âľm x18 Âľm tapping mode AFM image of the ZnO film from second series. a) error signal image and b) topographical image.

3D nanostructuring of nanoporous anodic alumina for photonic applications Mohammad Mahbubur Rahman, Gerard Macias Sotuela, Maria Alba, Lluís F. Marsal, Josep Pallarès and Josep Ferré-Borrull Departament d'Enginyeria Electrònica, Elèctrica i Automàtica Universitat Rovira i Virgili Avda. Països Catalans 26, 43007 Tarragona, Spain josep.ferre@urv.cat

Abstract The nanoporous anodic alumina (NAA) has attracted significant attention due to its self-assembled, densely packed and nanoscale-ranged porous structure. In the adequate fabrication conditions the twodimensional pore pattern shows a characteristic interpore distance which can be of the order of the wavelength of visible light [1, 2], what makes it possible to control light inside the material. The low absorption coefficient, excellent thermal stability, the wide electronic band gap (7–9.5 eV) and easy handling of the NAA has made it a potential candidate for two-dimensional photonic crystal (2D PC) in the visible and infrared range [3]. Furthermore, quasi-random nanostructures based on NAA have been demonstrated to show photonic stop bands for all in-plane propagation directions [4, 5]. If this in-plane 2D photonic stop band could be combined with vertical optical confinement provided by a periodic change of refractive index in the direction parallel to the pores, then 3D confinement of light could be achieved. The ability of the porous materials to confine light in a small volume make them good candidate for sensing, LED light extraction, laser light generation. Recently, three-dimensional structuring or multilayer (in-depth) structures or Bragg’s stakes of NAA have been introduced, where attention was paid on the fabrication of Bragg mirrors based on NAA having cyclic porosity with the depth by applying a cyclic voltage with carefully chosen voltage profiles[6, 7]. However, the control over the optical properties of the layers obtained on every cycle is not studied in depth.

In this communication we will present a different approach to obtaining photonic stop bands for light propagating along the direction of the pores by an in-depth structuring of NAA. As in previous works, we apply a periodic voltage although we introduce a subsequent pore widening step which increases the refractive index contrast between the different layers, what permits to improve the optical performace of the structure. In order to fabricate in-depth structured NAA with significant optical properties, it is necessary to have different layers with the highest possible refractive index contrast. However, it is known that in the self-ordering regime of pore growth, porosity depends weakly on the applied voltage [8, 9]. Thus, if a periodic voltage is applied to obtain in-depth structured NAA, the different layers will have a small refractive index contrast. Although porosity of as-anodized layers is very similar for all anodization voltages, interpore distance, and consequently pore diameter, depend on the applied voltage. This difference in pore diameter induces a difference in the etching rate in the pore widening step, which results in an increase of the refractive index contrast. Figure (1) shows the effective refractive index of the porous NAA estimated from ellipsometric measurements of single-layer structures as a function of the pore widening time. The structures were fabricated by anodization in 0.3M oxalic acid at 4ºC and at applied voltages of 20 V, 30V, 40V and 50 V, at which 2D self-assembly of the pores takes place. It can be seen that the refractive index is very similar for all voltages and for the asproduced layers, while the refractive index decreases and the differences between voltages increase with increasing pore widening time.

With this result in mind, it is possible to modulate the thickness and refractive index only by changing the anodization voltage, whereas the acid electrolyte or concentration and anodizing temperature are kept constant. Figure (2a) shows the first five anodization voltage cycles and the corresponding current transient for an in-depth structured NAA. After the first anodization at 40 V and removal of the alumina layer to obtain the self-ordering of the pores, a second anodization starts at 20 V and it lasts until a charge of 2 C, in this way, a self-ordered layer of vertical pores is obtained. After this, a voltage cycle is applied for 150 times. Each cycle consists of a linear ramp from 20 V to 50 V, at a rate of 0.5 V/s and a subsequent ramp from 50 V to 20 V at 0.1V/s. The current transients shows that with the continuous change in the anodizing voltage induces a change in etching current in which modulates the size of the pores within the cycles.

Figure (2b) depicts the relectance spectra of the NAA structure obtained with this cyclic voltage for the as-produced structure and for the same structure after 9 minutes of pore widening with a solution of 5%wt H3PO4. The spectrum of the as-produced sample shows an unstable behaviour around 682 nm.

However, the spectrum of the same sample after pore widening shows a stop band: a range of

wavelengths (725nm to 639nm) where reflectance is increased with respect the surrounding values in the spectrum. The onset of the stop band is a consequence of the increase in refractive index contrast for the different voltages applied. Further studies are required to calibrate the position of the stop band and its width with the applied voltages and charges.

References [1] A. P. Li, F. Müller, A. Birner, K. Nielsch, and U. Gösele, J. Appl. Phys. 84 (1998) 6023.

[2] L. Vojkuvka, L. F. Marsal, J. Ferre-Borrull, P. Formentin, and J. Pallares, Superlattices Microstruct. 44 (2008) 577.

[3] Jinsub Choi, Yun Luo, Ralf B. Wehrspohn, Reinald Hillebrand, Jörg Schilling and Ulrich Gösele, J. Appl. Phys. 94 (2003) 4757.

[4] Ivan Maksymov, Josep Ferré-Borrull, Josep Pallarès, Lluis F. Marsal, Photonics and Nanostructures, Fundamentals and Applications, in press, available online: http://dx.doi.org/10.1016/j. photonics.2012.02.003.

[5] Mohammad Mahbubur Rahman, Josep Ferré-Borrull, Josep Pallarès, Lluis F. Marsal, Phys.

Status Solidi C 8 (2011) 1066–1070.

[6] Dusan Losic, Mickael Lillo, and Dusan Losic Jr, Small 5 (2009) 1392–1397.

[7] Yan Su, Guang Tao Fei, Yao Zhang, Peng Yan, Hui Li, Guo Liang Shang, Li De Zhang, Materials Letters 65 (2011) 2693–2695.

[8] K. Nielsch, J. Choi, K. Schwim, R.B. Wehrspohn, U. Gösele, Nano Lett. 2 (2002) 677-680.

[9] Sachiko Ono, Noboru Masuko, Surface and Coatings Technology 169 –170 (2003) 139– 142.

Acknowledgements This work was supported by the Spanish Ministry of Science under the projects TEC2009-09551, HOPE CSD2007-00007 (Consolider-Ingenio 2010), and FR2009-0005.

Figures

Figure 1: effective refractive index of the NAA layer for the wavelength λ=750nm as a function of the pore widening time, for NAA made under different anodization voltages.

Fig 2: a) first five cycles of periodic anodization voltage used to produce an in-depth structured NAA with DBR structure and the corresponding current, b) reflectance spectra of the as-produced in-depth structured NAAand for the same structure after 9 minutes of pore widening.

Gold-Catalyzed Growth of Colloidal Cadmium Chalcogenide Worm-like Nanostructures Albert Figuerola,a Víctor Fernàndez-Altable,a and Andrea Falqui b a

Dept.Inorganic Chemistry, University of Barcelona, Martí i Franqués 1-11, 08028 Barcelona, Spain b Istituto Italiano di Tecnologia, via Morego 30, 16163 Genoa, Italy albert.figuerola@qi.ub.es

Abstract Semiconductor inorganic nanocrystals are promising materials for a variety of applications, such as photovoltaics, photocatalysis, and opto-electronics. Cadmium chalcogenides (CdX, where X = S, Se or Te) are among the most well known semiconductor nanocrystals: quantum dots, nanorods, tetrapods, and recently also octapods have been extensively studied from a synthetic point of view as well as their properties and performance tested in several devices.1 Elongated CdX nanocrystals show unique properties as compared to their spherical analogues due to the confinement of their excitons in two dimensions. They enhance charge carriers separation after light illumination, which can be of special interest in any of the applications mentioned above. The selective growth of metal domains on the tips of CdX nanorods has been devised as an alternative strategy to improve the separation of the carriers.

Unfortunately, the selectivity in the Au growth onto the tips of CdX nanorods is relatively poor and can only be improved by a subsequent irradiation or thermal treatment.2 In this work, the possibility of obtaining elongated hybrid metal-semiconductor nanostructures has been investigated for the case of gold and cadmium chalcogenides by using spherical Au nanocrystals and CdX quantum dots as starting materials in high boiling point solvents. This approach opens up the possibility of obtaining elongated CdX nanostrutures epitaxially grown on Au nanocrystals, which circumvents the use of seeded-growth techniques and/or expensive surfactant molecules usually required in order to induce anisotropy during CdX growth. The growth mechanism is based on the surfactant-assisted dismantling of the initial CdX spherical nanocrystals followed by their Au-catalyzed recrystallization, which leads to well-defined Au-CdX head-tail nanoworms with a precise and reproducible location of each domain in the crystal. These results suggest a sort of Solution-Liquid-Solid growth mechanism as the one observed previously by Buhro et al. and Korgel et al. for other systems.3 The reaction temperature and the amount of quantum dots injected allow to tune the aspect ratio of the final nanoworms. Their crystallinity and their Au-CdX epitaxy have been assessed by means of high resolution TEM analysis and XRD, while their optical properties have been checked by UV-Visible absorption and photoluminiscence measurements.

References [1] L. Carbone et al. Nano Lett., 7 (2007) 2942 and H. Steinberg et al. Nano Lett. 10 (2010) 2416.

[2]. G. Menagen et al. J. Am. Chem. Soc. 131 (2009) 17406 and A. Figuerola et al. Nano Lett.10 (2010) 3028.

[3] A. T. Heitsch et al. Nano Lett. 9 (2009) 3042 and H. Yu et al. J. Am. Chem. Soc. 125 (2003) 16168.

Figure. a) Au-CdSe head-tail nanoworms of lengths around 100 nm; b) Au-CdSe head-tail nanoworms of lengths around 300 nm; c) Au-CdTe head-tail nanoworms of lengths around 200 nm.

Preparation of PlatinumNanoparticles-Graphene Modified Electrode and Sensitive Determination of Paracetamol a( )

Hayati Filik * , Gamze Çetintaş, Asiye Aslıhan Avan, Serkan Naci Koç, İsmail Boz Istanbul University, Faculty of Engineering, Department of Chemistry, 34320 Avcılar Istanbul, Turkey filik@istanbul.edu.tr Onyl three graphene (GR) based chemical sensors were reported for the determination of paracetamol (4'-hydroxyacetanilide, N-acetyl p-aminophenol, acetaminophen) (PCT). Kang’s group investigated the electrochemical behaviors of PCT on GR-modified electrodes by cyclic and square-wave voltammetry.

The results showed that the GR modified elektrode exhibited excellent electrocatalytic activity to PCT in alkaline medium (pH=9.5) [1]. Bahramipur and Jalali investigated the electrochemical behavior of PCT at the GR paste electrode [2]. Yin and co-workers fabricated the GR-chitosan composite film modified glassy carbon electrode and used to determine PCT [3]. In this study, aminopolysaccharide chitosan was used as a polymer binder in order to improve the film adhesion to the substrates.

However, the electrochemical behavior and voltammetric detection of PCT using noble metal nanoparticle GR/GC modified electrode has not yet been reported. Metal nanoparticles, especially the noble-metal nanoparticles, have attracted considerable attention in constructing electrochemical or optical sensors due to their novel chemical and physical properties [4,5]. Previous studies have recommended that Pt nanoparticles have a good electrocatalytic activity among other metal nanoparticles.

First, a graphene-modified glassy carbon electrode was fabricated by a simple drop-casting method.

Then,

Pt

nanopaticles

were

electrodeposited

on

this

electrode

surface

to

form

a

Pt

nanoparticles/graphene modified electrode (Pt/GR/GC), and used in the electrochemical detection of PCT. The electrochemical behaviors of PCT on Pt/GR/GC modified electrodes were investigated by cyclic voltammetry and square-wave voltammetry (SWV). A cyclic voltammetry (CV) was used to investigate the electrochemical behavior of PCT on the bare GCE, GR/GCE and Pt/GR/GCE in 0.1 M -1

ammonia buffer solution at a scan rate of 100 mV s , respectively. Fig. 1 depicts cyclic voltammograms of PCT on the bare GCE, GR/GCE and Pt/GR/GCE in 0.10 M ammonia buffer solution (pH 9.5). On the bare GCE (Fig. 1blue), PCT shows an irreversible redox behavior with small and undefined redox signals. At a bare GCE, PCT shows a quasi-reversible behavior with relatively weak redox current peaks at Epa= 0,389 V and Epc= - 0.72 V (vs. SCE). The peak potential separation (ΔEp=Epa-Epc) was as large as 317 mV. On the GR/GCE, the anodic and cathodic peak currents of PCT are significantly increased. According to the experimental results, the oxidation peak of PCT shifted negatively to 375 mV, and the reduction peak shifted positively to -44 mV at the GR/GCE (Fig. 1red). The value of ΔEp decreased to 331 mV, clearly indicating that the oxidation of PCT become more reversible at the GR/GCE. Futher, Pt nano particles were electrodeposited onto surface of GR/GCE. The oxidation peak of PCT shifted negatively to 264 mV, and the reduction peak shifted positively to 186 mV at the GR/GCE (curve black). It can be seen that the oxidation overpotential of PCT becomes lower than that on GR/GCE with a negative shifted of 78 mV. So, significantly increased redox peak currents, reduced oxidation potential and greatly increased electron transfer rate of of PCT at the Pt/GR/GCE. As can be seen in Fig 1, oxidation peak signal significantly increases to 36 µA,

which is 2.6 (36:14=2.6) times higher than that on GR/GCE. These results demonstrated that the electrochemical reactivity of PCT is remarkably improved on the Pt/GR/GCE.

Fig. 1 Cyclic voltammograms of PCT on the bare GCE (blue), GR/GCE (red) and Pt/GR/GCE (black) in 0.10 M ammonia buffer solution (pH 9.5).

The voltammetric determination of PCT was carried out using square-wave voltammetry (SWV). The calibration curve for PCT shows two linear segments: the first linear segment increases from 0.04 to -9

1.0 and second linear segment increases up to 10 µM. The detection limit was determined as 2.0×10 mol L

-1

using SWV. Finally, the proposed method was successfully used to determine PCT in

pharmaceutical preparations. The developed method can be used for the detection of PCT and paminophenol simultaneously without interference of each other.

Fig. 2. Square wave voltammograms of Pt/GR/GCE in 0.1M pH 9.5 acetate buffer solution containing different concentrations of PCT (a–n): 0.04, 0.06, 0.08, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 4.0,6.0,8.0,10 µM).

References [1] X. Kang, J. Wang, H. Wu, J. Liu, I. A. Aksay, Y. Lin, Talanta 81 (2010) 754.

[2] H. Bahramipur, F. Jalali, African J. Pharm. Pharmacol. 6 (2012) 1298.

[3] H. Yin, Q. Ma, Y. Zhou, S. Ai, L. Zhu, Electrochim. Acta 55 (2010) 7102.

[4] H. Jiang, Small 7 (2011) 2413 .

[5] Y. Wang, Z. Li, J. Wang, J. Li, Y. Lin, Trends Biotechnol. 29 (2011) 205.

Electrical properties of ZnO single nanowires contacted by FIBID and EBL a

a

a

a

a

Camelia FLORICA , Georgia IBANESCU , Elena MATEI , Nicoleta PREDA , Monica ENCULESCU , b a Maria Eugenia Toimil Molares , Ionut ENCULESCU a

National Institute of Materials Physics, PO Box MG-7, 77125, Magurele-Bucharest, Romania b GSI, Helmholtz Centre, Planckstr. 1, D-64291, Darmstadt, Germany camelia.florica@infim.ro

Abstract Semiconductor nanowires are used for building electronic devices like chemical or biological sensors, nwFETs, memories, light emitting diodes. In order to properly use the nanowires for such applications, the understanding of the transport properties in this kind of nanostructures becomes more and more important. To our knowledge, there is no evidence in the literature of the electrical properties of single zinc oxide nanowires grown electrochemically.

In this paper we investigate the electrical properties of ZnO nanowires grown electrochemically by the template method [1]. Contacting a single nanowire was a barrier that has been overcome using different lithographic techniques. Interdigitated electrodes made from different materials (Pt, Al) were deposited on Si/SiO2 substrates using photolithography combined with thermal vacuum evaporation. The contact between the nanowire and the interdigitated electrodes was made by e-beam lithography (EBL) and by focused ion beam induced deposition (FIBID) of platinum stripes.

The quantitative analysis of the current-voltage measurements gave us information about the intrinsic parameters of the ZnO nanowires such as conductivity, mobility or concentration of impurities. By fitting the curves using the metal-semiconductor-metal (M-S-M) model [2] the effective potential barrier was computed. A comparison between the two methods of contacting the semiconducting nanowires was made in order to select the one that is most suitable for being used in applications.

Our results are comparable with electrical measurements made on ZnO nanowires prepared by other methods such as high-temperature thermal evaporation process [3], vapor-liquid-solid process [4, 5] or electric field assisted nucleation [6].

Acknowledgements This work was supported by CNCS â&#x20AC;&#x201C; UEFISCDI, project EUROCORES 5EUROC/2011 and by CNDI â&#x20AC;&#x201C; UEFISCDI, project number PN-II-PT-PCCA-2011-3.2-1017.

References [1] C. Tazlaoanu, L. Ion, I. Enculescu, M. Sima, M. Enculescu, E. Matei, R. Neumann, R.Bazavan, D. Bazavan, S. Antohe, Physica E 40 (2008) 2504 [2] Z. Zhang, K. Yao, Y. Liu, C. Jin, H. Liang, Q. Chen and L.-M. Peng, Advanced Functional Materials, 17 (2007) 2478 [3] Q. Yang, X.Guo, W. Wang, Y. Zhang, S. Xu, D. H. Lien, and Z.L. Wang, ACS Nano, 4 (2010) 6285 [4] G. D. Yuan, W. J. Zhang, J. S. Jie, X. Fan, J. A. Zapien, Y. H. Leung, L. B. Luo, P. F. Wang, C. S. Lee, S. T. Lee, Nano Letters 8 (2008) 2591 [5] Jr H. He, Cheng L. Hsin, Jin Liu, Lih J. Chen, and Zhong L. Wang, Advanced Materials 19 (2007) 781 [6] Y. J. Kim, H. Shang and G. Cao, Journal of Sol-Gel Science and Technology 38 (2006) 79

Figures

Caracteristicile I V ale nanofirelor de ZnO

FIB C1007

Current A

a

I [A]

b 1.

10 6

5.

10 7

U [V] 2

1

1

5.

2

10 7

Caracteristicile I V ale nanofirelor de ZnO c

d

Voltage V

Current

A

1.

10 8

I [A]

5.

10 9

C1003

U [V] 6

4

2

2

5.

10 9

1.

10 8

4

6

Voltage V

SEM images of a single ZnO nanowire contacted using FIBID (a) and EBL (c) and their corresponding electrical characteristics (b) and (d)

Investigation of Plastic and Elastic Deformations of Gold Nanowires under Uniaxial Strain with Point-Contact Spectroscopy 1

1

Tamanaco Francisquez, Carlos Sabater , and Carlos Untiedt 1

1

Department of Applied Physics, University of Alicante, San Vicente del Raspeig, Alicante, Spain

Gold nanowires have been fabricated with the help of a motorized mechanically controllable 1 break-junction at low temperatures by repeated indentation between two gold leads . During the formation 2 and rupture of the nanowires, point contact spectroscopy was carried out at different conductance values of the gold nanowire formation/rupture cycle and at different strains along stable conductance plateaus.

2 2 The derivatives of the differential conductance (d I/dV versus V) display the characteristic gold pointcontact spectroscopy spectrum features of phonon excitations, which shift upon stretching the nanowire along the conductance plateaus, similar to previously reported shifts of the features in atomic 3,4 5 wires/contacts and molecular junctions . We also observed a direct correlation between the plastic 6 deformation length of the nanowire, estimated from a slab deformation model , and the magnitude of the features (TA and LA phonon peaks) in the point-contact spectroscopy curves.

1

Agraït, N., Yeyati, A. & van Ruitenbeek, J. “Quantum properties of atomic-sized conductors”. Physics Reports 377, 81-279 (2003).

2

Jansen, A., Gelder, A. & Wyder, P. “Point-contact spectroscopy in metals”. Journal of Physics C: Solid State Physics 13, 6073 - 6118 (1980).

3

Agraït, N., Untiedt, C., Rubio-Bollinger, G. & Vieira, S. “Onset of Energy Dissipation in Ballistic Atomic Wires”. Physical Review Letters 88, 216803 (2002).

4

Böhler, T., Edtbauer, a & Scheer, E. “Point-contact spectroscopy on aluminium atomic-size contacts: longitudinal and transverse vibronic excitations”. New Journal of Physics 11, 013036 (2009).

5

Djukic, D. et al. “Stretching dependence of the vibration modes of a single-molecule Pt-H_2-Pt bridge”.

Physical Review B 71, 161402R (2005).

6

C Untiedt, S. Vieira, G Rubio Bollinger, and N Agraït, Physical Review B 56, 2154-2160 (1997).

Influence of silver nanoparticles on in vitro wound healing model a

a

b

c

a

Jana Franková , Adéla Galandáková , Hana Vágnerová , Bohumil Zálešák , Jitka Ulrichová a

Palacký University Olomouc, Faculty of Medicine and Dentistry, Department of Medical Chemistry and Biochemistry, Hněvotínská 3, Olomouc, Czech Republic b

Palacký University Olomouc, Faculty of Science, Department of Organic chemistry, 17. listopadu 1192/12, Olomouc, Czech Republic

c

University Hospital Olomouc, Department of Plastic and Aesthetic Surgery, I.P. Pavlova 6, Olomouc, Czech Republic e-mail: frankova0@seznam.cz

Abstract The complex and multiple processes leading to wound healing are controlled by cytokines, growth factors and matrix metalloproteinases within the healing wound. It begins with homeostasis follow by inflammation, cell proliferation and tissue remodelling. Due to the importance of inflammation properties in wound healing, some products and their components have been tested for antiinflammatory properties. For the centuries silver has been known for its antibacterial and antiinflammatory properties. As a metal, silver is relatively inert and is poorly absorbed by mammalian and bacterial cells. In the presence of wound fluid and other secretion, it readily ionizes and becomes highly reactive in binding to protein and cell membrane [1]. Therefore we tested two types of nanosilver solution (metallic silver and ionic silver) for comparison of different wound healing properties.

Normal human dermal fibroblasts (NHDF) were used in our study. Cells were isolated from tissue section from plastic surgery with the informed consent of the Ethical committee of the University Hospital Olomouc and the patient’s consent. According to the MTT (3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) test we selected three non-toxic concentrations for in vitro wound healing model. For study of wound healing in vitro the modified scratch assay [2] was used and the tested solutions were added for 24 and 48 hours incubation periods. To detect pro-inflammatory, antiinflammatory parameters and matrix metalloptroteinases, the Bio-plex suspension array system, ELISA and western blot were used.

The difference between the influence of silver nano particles on the wound healing process in vitro, anti-inflammatory cytokines and matrix metalloproteinases will be discussed.

Acknowledgement: This work was supported by grants FT-TI2/205

and LF 2012 010.

References [1] Atiyeh BS, Costagliola M, Hayek SN, Dibo SA, Burns, 33 (2007) 139-148.

[2] Wolf NB, Kőchler S, Radowski MR, Blaschke T, Kramer KD, Weindl G, Kleuser B, Haag R, SchäferKorting M, European Journal of Pharmaceutics and Biopharmaceutisc, 73 (2009) 34-42.

Electronic Transport in Quasiperiodic Graphene p–n–p Junctions 1

1

U.L. Fulco , E.L. Albuquerque and M.S. Vasconcelos 1

2

Departamento de Biofísica e Farmacologia, UFRN, 59072-970, Natal-RN, Brazil 2 Escola de Ciências e Tecnologia, UFRN, 59072-970, Natal-RN, Brazil contact e-mail: umbertofulco@gmail.com

Abstract Since the pioneering work of Novoselov et al. [1], graphene has been hailed as a promising candidate material for future microelectronic devices (for a review see [2]). Graphene is a sheet of crystal carbon that behaves as a ballistic conductor with a long mean free path that can be locally gated. In addition, graphene can carry spin currents, and supercurrents at room temperature. Although graphene is, in many respects, similar to carbon nanotubes, from the experimental standpoint the planar character of this material makes it more amenable to microelectronics and nanoelectronic applications. Hence, the researches about the electronic structure and electronic tunneling in arrangements of this material could affect the engineering of computers, mobile phones, security devices and medical applications devices [3].

On the other hand, the interaction of carriers with electrostatic barriers in this system is strongly influenced by Klein tunneling (i.e. the perfect transmission of carriers through potential barriers at normal incidence). This effect has been studied for periodic potentials and the effect of disorder on the charge transport through multiple barriers has been considered. These results have highlighted the interplay between disorder and resonance effects on the carrier transmission through multiple barriers, which can influence the overall conductivity of graphene-based devices [4].

In this work we investigate the interaction of charge carriers in graphene with a series of p–n–p junctions arranged according to a deterministic quasiperiodic substitutional Fibonacci sequence.

Quasiperiodic systems are structures that can be classified as intermediate between ordered and disordered systems. Among the examples of quasiperiodic systems are artificial nanostructured materials with deterministic disorder, whose dynamic properties have common features, such as a fractal Cantor-like spectrum of elementary excitations.

The quasiperiodic sequence of p–n–p junctions in graphene gives rise to a potential landscape with quantum wells and barriers of different widths, allowing the existence of quasi-confined states. Spectra of quasi-confined states are calculated for several generations of the Fibonacci sequence as a function of the wavevector component parallel to the barrier interfaces. Our results show that, as the Fibonacci generation is increased, the dispersion branches form energy bands are distributed as a Cantor-like set (see Fig. 1). Besides, we obtain the electronic tunneling probability as a function of energy, whose transmission peak for small incidence angles is typical of Klein tunneling. The angular dependence of the transmission spectra is shown in Fig. 2 for carriers with energy E = 50 meV and potential barriers, whose height is U0 = 100 meV. Observe that, in addition to the large transmission peak for small incidence angles, the presence of a large number of sharp peaks, which arise due to resonance effects.

As the generation number increases, there is also an increase in the density of these transmission peaks, due to the resonant coupling with the bands of quasibound states in the structures.

Acknowledgements: Thanks are due to the Brazilian Research Agencies CAPES (PROCAD and Rede NanoBioTec), CNPq (INCT-Nano(Bio)Simes and Casadinho-Procad) and FAPERN/CNPq (Pronex).

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.

[2] A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. Geim, Rev. Mod. Phys. 81, (2009) 109.

[3] A. K. Geim and K. S. Novoselov, Nat. Mater. 6 (2007) 183.

[4] J. M. Pereira Jr., F. M. Peeters, A. Chaves, and G. A. Farias, Semicond. Sci. and Tech. 25 (2010) 033002.

Figure 1: The distribution of the energy levels for the quasiperiodic graphene p–n–p Fibonacci structure (12th generation) as a function of the generation number m for the y-component wavevector ky = 0.11 −1 nm .

Figure 2: Angular dependence of the transmission for a quasiperiodic graphene p–n–p structure, corresponding to the 12th Fibonacci generation, for E = 50 meV and U0 = 100 meV.

Biological effects induced by silver and gold nanoparticles: in vitro study. a

a

b

c

a

Adéla Galandáková , Jana Franková , Klára Habartová , Bohumil Zálešák , Jitka Ulrichová a

Palacký University Olomouc, Faculty of Medicine and Dentistry, Department of Medical Chemistry and Biochemistry, Hněvotínská 3, Olomouc, Czech Republic b

Palacký University Olomouc, Faculty of Science, Department of Organic Chemistry, 17. listopadu 1192/12, Olomouc, Czech Republic

c

University Hospital Olomouc, Department of Plastic and Aesthetic Surgery, I.P. Pavlova 6, Olomouc, Czech Republic E-mail: galandakova.a@seznam.cz

Abstract Nanotechnology allows an efficient exploitation of the antimicrobial properties of silver and gold in the form of nanoparticles. These are commonly used in applications such as preservatives in cosmetics, textiles, water purification systems, coatings in catheters and wound dressings. Wide spread use of nanoparticles has increased the risk of nanoparticle-induced toxic effects in the environment and in humans [1]. Recent reports in nanotoxicology suggest that the interaction and distribution patterns of the nanomaterials are diverse in different cell types [2]. In response, many studies investigating the effects of various types of silver and gold nanoparticles in different test systems are now emerging in the scientific literature.

The aim of our study was to compare the toxicity of two types of silver nanoparticles (colloidal metallic and ionic solutions) and gold nanoparticles (colloidal gold solution). Furthermore, we studied the influence of these nanoparticles on the selected parameters of inflammation.

As the model cell system we have used normal human dermal fibroblasts (NHDF). These cells have diverse functions like wound repair and production of cytokines. They are known to play a role in wound healing process which makes them a suitable model for inflammation studies. NHDF were isolated from skin specimens with the informed consent of the Ethical Committee of the University Hospital in 5

2

Olomouc and the patient’s written consent. NHDF (1x10 cells/cm ) were grown in Dulbecco’s modified Eagle’s medium supplemented with 10 % fetal calf serum in humidified atmosphere with 5% (v/v) CO2 at 37°C. At confluence, the nanoparticles (0.1- 200 pp m) in serum-free medium were applied for 24 h. Cell viability was evaluated by activity of cellular dehydrogenases. The pro- and anti-inflammatory parameters were monitored in the collected media by Bio-plex suspension array system and by specific ELISA kits. The expression of pro- and anti-inflammatory markers in the cells was evaluated by western blot analysis.

The different effect of silver and gold nanoparticles on the selected pro- and anti-inflammatory parameters in normal human dermal fibroblasts will be discussed.

Acknowledgement: This work was supported by Ministry of Trade and Commerce (FT-TI2/205).

References [1] Singh S, Nalwa HS, Journal of nanoscience and nanotechnology, 7 (2007) 3048-3070.

[2] Xia T, Kovochich M, Liong M, Zink JI, Nel AE, American Chemical Society nano, 2 (2008) 85-96.

Modeling of Diffusion Process in Nanosized Perovskite LaCoO3 Powder Catalysts A. Galdikasa, N. Bionb, S. Royerb, D. Duprezb, D. Sidabraa a

Physics Department, Kaunas University of Technology, 50 Studentu st. Kaunas, Lithuania b University of Poitiers, CNRS – IC2MP UMR 7285 – 4 rue Michel Brune, Poitiers, France Catalytic properties of nanosized perovskite LaCoO3 powders are considered experimentally and theoretically. For the purpose of the use of those catalysts in automotive exhaust gas conversion the kinetics of oxygen atom transport processes from/to gas phase and catalyst are experimentally analyzed by isotopic oxygen exchange method. Molecular oxygen isotope 18O2 gas is introduced into reactor with powder of catalyst. The process of exchange is performed at temperature 400oC. As a result of oxygen exchange between gas as catalyst the molecular species of oxygen 18O2, 18 16 O O and 16O2 appears in gas phase which kinetics is registered by mass spectrometer.

Three types of LaCoO3 samples differently prepared [1,2] are considered. The Sbet and powder particle size of those samples were following: first type 3.9 m2/g, 1000 nm, second type 3.8 m2/g, 11nm and third type 66 m2/g, 11nm. Small surface are and small powder size of second type catalyst shows that each powder particle contains grains which size is around 11 nm and can be considered as polycrystals. First and third type powder particles can be considered as monocrystalline.

The obtained experimental kinetic curves of partial pressures of oxygen species are fitted by proposed real time kinetic model based on rate equations. Model includes processes of chemical reactions (complex and simple heteroexchange) and diffusion of oxygen inside powder nanoparticles. The diffusion process is introduced considering the bulk diffusion adapted for powder catalysts [3] and diffusion by grain boundaries (for second type catalyst).

Considering possible reactions of type IOJOg+IOJOs=IOJOs+IOJOg where I and J =16 and/or 18 the concentration variation of 18O2, 16O2 and 16O18O species in the gas phase and on the catalyst oxide surface is described by rate equations using mass action law dni / dt = k ∑ ni c j (where ni is the concentration of i-th type species in gas phase, r is r

the number of reactions and ci is surface concentration) with reaction rate constant k determined by Arrhenius law k = A exp(−Q / kT ) .

Considering bulk diffusion for powder catalysts with cubic shape grains it is necessary to take into account the fact that the area of each layer (S(K)) decreases and tends to zero as one goes deeper and deeper into the oxide bulk. So, these areas were calculated 2 according to the following expression: S B( K ) = S ox (1 − 2( K − 1)a / d ox ) (K is number of monolayer, a is monolayer thickness and dox is size of grain). The variation of the atomic concentration in oxygen atoms in one given layer K of the oxide is calculated according to the second Fick’s law.

2 ( K −1) ( K −1) (K ) (K ) (K ) ( K +1) dci / dt = ( D / a )( B ci − c i − B ci + ci , where D = Do exp(−QD / kT ) is the diffusion coefficient and coefficients B describe

(

)

(

)

geometrical B

(K )

=S

(K )

factor /S

( K +1)

of

, if c

(K) i

monolayers −c

(K +1) i

B ( K ) = S ( K +1) / S ( K ) , if c (K) − c i(K +1) ≥ 0 i

or

< 0.

Fig. 1. Experimental (points) and calculated (lines) time dependencies of partial pressures of oxygen species 18O2 (p36), 18O16O (p34) and 16O2 (p32) in gas phase during isotopic oxygen exchange process: left - for second type catalysts (see text) and right for third type catalysts.

Calculated curves are in a good agreement with experimental points for all three types of catalysts. In Fig. 1 the experimental (points) and calculated (lines) time dependencies of partial pressures of oxygen species 18O2, 18O16O and 16O2 in gas phase during isotopic oxygen exchange process is presented. Two figures represent the cases of polycrystalline (left) and monocrystalline (right) powder particles. In the case of polycrystalline powder particles both bulk and grain boundary diffusion takes place, while in monocrystalline case only bulk diffusion occurs. This assumption is realized in model. From the calculated results the kinetic (exchange rate constants, diffusion coefficients of bulk and grain boundary diffusion) and thermodynamic (activation energies of exchange reactions and diffusion) parameters are obtained.

Acknowledgement: This research was funded by a grants (No.: TAPLZ 04/2012 and No.: MIP 118/2011) from the Research Council of Lithuania.

References: [1] S. Royer, F. Berube, H. Alamdari, R. Davidson, S. McIntyre, S. Kaliaguine, Appl.

Catal. A 282 (2004) 273.

[2] S. Royer, D. Duprez, S. Kaliaguine, J. Catal., 234 (2005) 364.

[3] A. Galdikas, D. Duprez, C. Descorme, Appl. Surf. Sci., 236 (2004) 342.

Terahertz Time Domain Spectroscopy for molecules inspection: water vapor and drugs 1

2

2

Enrique García-García , Yahya Moubarak Meziani , Jesús Enrique Velázquez-Pérez and Jaime 3 Calvo-Gallego 1

Centro de Lásers Pulsados (CLPU), Edificio M3, Parque Científico USAL; Calle Adaja s/n, 37185 Villamayor, Salamanca, Spain 2 Departamento de Fisica Aplicada, Plaza de la Merced s/n, Universidad de Salamanca, 37008 Salamanca, Spain 3 Escuela Politécnica Superior de Zamora, Avda. Cardenal Cisneros, 34, Universidad de Salamanca, 49022 Zamora, Spain egarcia@clpu.es Abstract In this paper we report on an experimental study of the spectral response of different compounds in the THz range. We set up a THz Time Domain Spectroscopy System (TDS) that uses a Ti:Sapphire femtosecond laser and a pair of LTD GaAs photoconductive antennas for THz generation and detection.

The THz TDS set up was validated through the matching of the main lines of the water vapor spectra in the 0.1-3THz range against the HITRAN database. Finally, the THz spectra of two commercial chemical compounds (paracetamol and ibuprofen) were obtained; the large difference found between the two spectra will easily allow to distinguish between both substances. Further work will be necessary to understand the fingerprints of those substances.

Introduction −1 −1 Terahertz radiation is located in the spectral region 0.1-10 THz (3 mm - 30 μm, 3 cm - 300 cm ) between the microwave and the infrared part of the electromagnetic spectrum. The interest in this spectral region comes from the fact that many substances have a “fingerprint” within this region. Several studies performed on different materials, from medical drugs to explosives, have showed this unique behavior [1-4]. Experiments carried out by Grichkowsky et al [5] showed the potential for THz spectroscopy of photoconductive switches by resolving in time the THz pulse transmitted through a sample, following the Time Domain Spectroscopy (TDS) scheme.

System Description.

We set up of a THz-TDS system where the emission and detection are performed by photoconductive antennas [6] (low temperature grown GaAs) triggered by ultra‐short laser pulses. A substrate lens fabricated from high resistance Silicon is attached to the backside of each antenna to guide the THz radiation toward the detector. Figure1 shows the optical layout of the system. The pumping laser pulse is a Ti:Sapphire oscillator at 780-810 nm, 60-80 fs and 50‐150 mW output power at 80 MHz pulse repetition rate. The system covers a range from 100 GHz until 3 THz (limited by the absorption of a pair of low density polyethylene focalization lenses) and the emitted power of the THz radiation is around 10 μW. The antenna is polarized in DC to obtain an internal electric field of 4kV/cm. When the fs pulse the first antenna, a bunch of free carriers is generated and then accelerated under the stationary electric field.

The relaxation of the free carriers generates the terahertz pulse. Detection follows the same principle but, instead of applying an external DC bias, the incoming THz radiation creates a field in the second antenna that provides a DC voltage. Both processes, emission and detection, are generated in a pump and probe scheme, thus both processes are coherent. The detection is achieved by sweeping the delay of one of the laser pulse arms. The signal measured in the detector is proportional to the THz electric field itself, instead of to its amplitude. Therefore, via Fourier analysis we can extract both the spectral amplitude and phase of the pulse. This allows the extraction of the complex electrical permittivity without carrying a Kramers-Kronig analysis [7]. A typical temporal and spectral profile is shown in Fig.2. Fourier transform allows us to extract the THz transmitted electrical field on a sample when we evaluate the ratio between the sample and reference measurements.

Experimental results Measurement of water vapor has been performed by determining the transmitted electrical field on air with a relative humidity close to 40%. The result can be seen in Fig. 3. The decay of the spectra when the frequency increases exhibits several peaks that have been correlated with the absorption lines of 20 2 water (only for lines with an intensity ≥10 cm/(molecule cm )) obtained from HITRAN's database.

We also present the transmission spectra for two different commercial drugs, in particular paracetamol and ibuprofen, in Fig.4. The excipient may also have an influence on the obtained spectra and generate

some of the observed peaks. On the other hand, there is a large difference between the spectra of both samples that indicates the ability of the technique to distinguish between drugs in the studied THz range. Further work will be carried out to understand the position and intensity of different peaks. We believe that this method could bring new information on nanoscale materials, like nanoparticles, nanowires, etc.

Summary and Conclusions We have performed several studies of TDS on different samples. We have been able to correctly obtain the absorption lines of water from vapor from 0.1 THz up to 3 THz in agreement with well-established data bases. Additionally, we have experimentally shown that the technique allows the discrimination between different chemical substances. Future work will try to develop a THz-TDS system using nanometric Field Effect Transistors as source/detector of THz radiation.

Acknowledgemets This work was partly funded by Ministerio de Ciencia e Innovacion (MICINN) under Grant TEC200802281 and Junta de Castilla y Le贸n under Grant SA061A09.

References [1] R. Woodward, B. Cole, V. Wallace, R. Pye, D. Arnone, E. Linfield, and M. Pepper, Physics in Medicine and Biology, 47 no. 21, (2002), 385.

[2] K. Kawase, Y. Ogawa, Y. Watanabe, and H. Inoue, Opt. Express, 11 no. 20, (2003), 2549.

[3] Shen, T. Lo, P. Taday, B. Cole, W. Tribe, and M. Kemp, Appl. Phys. Lett., 86, (2005), 241116 [4] B. Ferguson and X. Zhang, Nat. Mater., 1 no. 1, (2002), 26 [5] M. van Exter and D. Grichkowsky, Phys. Rev. B 41, (1990), 12140.

[6] P.R. Smith, D.H. Auston, and M.C. Nuss, IEEE J. of Quantum Electronics, 24, (1988), 255.

[7] S. Nashima, O. Morikawa, K. Takata, and M. Hangyo, J. Appl. Phys., 90, No. 2, (2001), 837 Figures

Figure 1: Scheme of the THz-TDS system.

Figure 2: Temporal (up) and spectral (bottom) profile of the THz electrical field transmitted on air.

Figure 3: Water vapor power spectrum. The vertical lines are the absorption lines of water with an intensity bigger or equal than 10^20 cm/(molecule cm^2) from HITRAN's database

Figure 4: Transmission spectra of two different drugs.

Gold Nanoparticle Decoration of Carbon Nanotubes and Graphene: Synthesis, PhysicalChemical Characterization, and Applications Andrés Seral-Ascasoa, Asunción Luquinb, Rosa Garrigac. Mariano Lagunab, Germán F. de la Fuented, and Edgar Muñoza a

b

Instituto de Carboquímica ICB-CSIC, Miguel Luesma Castán 4, 50018 Zaragoza, Spain Instituto de Síntesis Química y Catálisis Homogénea, Universidad de Zaragoza-CSIC, Zaragoza, Spain c Departamento de Química Física, Universidad de Zaragoza, 50009 Zaragoza, Spain d Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, Zaragoza, Spain rosa@unizar.es

Abstract Carbon nanostructured materials such as carbon nanotubes and graphene are attracting much attention due to their outstanding structural and physical properties.[1,2] Metal nanoparticle-decoration can provide additional functionalities to these nanocarbons.[3-5] Several chemical and physical methods are being used for the synthesis of these metal-carbon nanohybrids. On the other hand, the fascinating properties of gold nanoparticles have begun to be efficiently utilized for a variety of applications such as in photonics, catalysis, and sensor devices.[6-8] Therefore, gold nanoparticle decoration of carbon nanotubes and graphene can provide promising nanohybrid materials for a whole plethora of technological applcaitions.[9,10] In this work, we present chemical routes for gold nanoparticle decoration of carbon supports including carbon nanotubes and graphene. Our chemical methodology allows controlling the gold nanoparticle content of the synthesized nanohybrids, the gold nanoparticle size and uniform coating on the carbon supports used. Our results show that the structural properties and dispersibility of the of the carbon supports strongly affect the gold nanoparticle decoration process, Applications for these goldnanoparticle decorated carbon nanostructured materials are presented and discussed.[11] References [1] .R. H. Baughman, A. A. Zakhidov, W. A. de Heer, Science 297 (2002) 787.

[2] E. H. L. Falcao, F. Wudl, J. Chem. Technol. Biotechnol.. 82 (2007) 524 [3] I. Sayago, E. Terrado, M. Aleixandre, M. C. Horrillo, M. J. Fernández, J. Lozano, E. Lafuente, W. K. Maser, A. M. Benito, M. T. Martínez, J. Gutiérrez, E. Muñoz, Sens. Actuators B 122 (2007) 75.

[4] E. Lafuente, E. Muñoz, A. M. Benito, W. K. Maser, M. T. Martínez, F. Alcalde, L. Ganborena, I. Cendoya, O. Miguel, J. Rodríguez, E. P. Urriolabeitia, R. Navarro, J. Mater. Res. 21 (2006) 2841.

[5] L. Calvillo, M.J. Lázaro, E. García-Bordejé, R. Moliner, P.L. Cabot, I. Esparbé, E. Pastor, J.J. Quintana, J. Power Sources 169 (2007) 59.

[6] P.K. Sudeep, S.T. Shibu Joseph, K. George Thomas, J. Am. Chem. Soc. 127 (2005), 6516.

[7] G. Li, J. Edwards, A. F. Carley, G. J. Hutchings, Cat. Today 114 (2006), 369.

[8] L. M. Liz-Marzán, Langmuir 22 (2006) 32.

[9] J. John, E. Gravel, A. Hagège, H. Li, T. Gacoin, E. Doris, Angew. Chem. Int. Ed. 50 (2011) 7533.

[10] Y. Cao, R. Yuan, Y. Chai, L. Mao, H. Niu, H. Liu, Y. Zhuo, Biosens. Bioelectronics 31 (2012) 305.

[11] A. Seral-Ascaso et al, submitted.

Cell Internalizing and pH-responsive Chitosan Nanoparticles for Improved Delivery of DNA Biopharmaceuticals VM Gaspar1, F Sousa1, RO Louro2, JA Queiroz1, IJ Correia1 1

CICS-UBI - Centro de Investigação em Ciências da Saúde, Universidade da Beira Interior, Portugal

2

Instituto de Tecnologia Química e Biológica - Universidade Nova de Lisboa, Oeiras, Portugal vm.gaspar@fcsaude.ubi.pt

Abstract Non-viral gene therapy currently arises as an exceptionally promising approach for the treatment of a wide spectrum of incurable pathologies that have striking worldwide occurrence, such as cancer or HIV. However, regardless of its unique therapeutic potential, the translation of nucleic acid-based pharmaceuticals onto realistic clinical applications remains largely hindered. Such fact, is a direct consequence of a rather inefficient ability of the available nanoparticulated delivery systems to tackle major cellular barriers and deliver the genetic material into the nucleus. Hence, the design and development of improved nanocarrier systems remains a key challenge to be overcome when therapeutic application is envisioned. In order to surpass these limitations, herein we synthesised a novel biocompatible and bioresorbable chitosan nanoparticulated gene delivery carrier functionalized with amino acid moieties. This bioinspired conjugation takes advantage not only of chitosan complexation of nucleic acids [1], but also, of the amino acid specific DNA binding [2] and biological activity at the nano-bio interface. The functionalization of chitosan was promoted by the selective amidation of the primary amine residues of the polymer backbone, thus allowing its coordination with two amino acid residues. The amino acid conjugation with the polymer backbone was confirmed by 1

Fourier transform infrared and H NMR spectroscopy (Figure 1). Moreover, under precise formulation conditions the synthesized polymer had the ability to condense plasmid DNA biopharmaceuticals and spontaneously assemble into stable nanoparticulated polyplexes with 105 nm, positive surface charge density and spherical morphology (Figure 2), characteristics that are crucial to improve cellular uptake and transfection. In fact, the obtained flow cytometry data also revealed that the nano carriers were efficiently internalized by malignant cells, a fact that is associated with the grafting of cell-penetrating amino acid residues in the polymeric chain (Figure 3). Additionally, the characterization of nanoparticle cytotoxic profile showed that cellular transfection and gene delivery occurs without eliciting any deleterious effect on normal cellular metabolism and cell morphology. After cellular entry, the carriers demonstrated their ability to escape from degradative endosomal/lysosomal trafficking pathways and promoted a remarkable increase in therapeutic transgene expression in comparison to the native material. Collectively, these important findings emphasise the relevance of amino acids as novel biocompatible functionalization materials for gene delivery systems, and thus opening the possibility to design a new generation of specifically tailored and proficient nanoparticles for gene-based therapies.

References [1] Gaspar et al., J. Control. Release, 2011, 156: 212–222.

[2] Sousa et al, J. Gene Med 2009; 11: 79–88.

Figures

1

Figure 1. H 1D NMR spectra of chitosan-Hist-Arg.

Figure 2. Scanning electron microscopy image of chitosan-amino acid nanoparticles.

Figure 3. Confocal laser scaning microscopy analysis of nanoparticle cellular uptake

Zein nanoparticles as a carrier system for terpinen-4-ol 1

1

1

2

Vanderléia Gava Marini , Silvia Maria Martelli , Clarice Fedosse Zornio ,Thiago Caon , Cláudia Maria Oliveira 2 1 Simões and Valdir Soldi 1 - Department of Chemistry, Federal University of Santa Catarina, Florianópolis, Brazil.

2 – Department of Pharmaceutical Sciences, Federal University of Santa Catarina, Florianópolis, Brazil. vanderleiagm@gmail.com

The terpinen-4-ol (T4OL) is the major component of the Tea Tree Oil (TTO), which is extracted from leaves of Melaleuca alternifolia, a native plant to Australia. T4OL has shown anti-inflammatory effect, antibacterial, antifungal and an anticancer activity in human melanoma cell lines (M14) [1] and lung cancer cells have also been showed in recent studies [2]. Due to its intrinsic properties, T4OL can cause allergic reactions when applied directly in the skin, limiting its use. The main challenge of developing new systems containing TTO or its pure components to the treatment of human body is that the system must be effective and safe. In this sense, encapsulation can be used alternatively to reduce this topical irritation. Nanoparticle delivery has been an approach widely used to optimize skin local therapies [3]. Nanoparticles prepared from biopolymers represent an interesting alternative due to its high biocompatibility and biodegradability. Some proteins can be used as wall material, since they have the characteristic of being amphiphilic, which is a major driving force for the self-assembly, essential to the formation of nanoparticles. Given that zein, a prolamin fraction of corn protein, has long been recognized for its coating ability for the encapsulation of bioactive compounds [4], the main objective of this work was to evaluate the its potential as a carrier for T4OL, aiming an topical application in skin. Zein nanoparticles were obtained by the antisolvent precipitation process (dessolvation). Zein was solubilized in a binary system ethanol/water (87:13), and then T4OL was added in the solution and they were mixed for 30 min. For each sample, 3 mL of zein solution containing T4OL was dropped at a constant rate of 6 mL/h in 9 mL of an aqueous solution, containing the selected amount of surfactant (tetradecyl-trimethylammonium bromide – TTA), under magnetic stirring at 1000 rpm. The organic solvent was eliminated by evaporation under reduced pressure. The freshly prepared nanoparticle dispersions were submitted to particle size, zeta potential by photon correlation spectroscopy and laser-Doppler anemometry, respectively, using a Zetasizer Nano Series (Malvern Instruments, Worcestershire, UK), and morphologic analysis (Transmittion electron microscopy – TEM). The resulting suspensions were centrifuged at 4000 rpm for 30 min in Amicon ultra-filter (cellulose regenerated membrane with a molecular weight cut of 100 kDA) to calculate the efficiency of encapsulation (EE). The supernatants were removed, diluted in 87% v/v ethanol and the T4OL content was analyzed by HPLC. The EE was calculated as the amount of T4OL added in the zein solution in relation to that present in the supernatant (did not encapsulate). Since many factors influence the obtention of nanoparticles, the first step of this study included a fractional factorial experimental design (3/1/9) in that three factors were varied (concentrations of the protein, the active compound and surfactant), as shown in Table 1. The experimental design and the statistical analysis (ANOVA) were performed using Statistica Software ® version 7.0 to determine the significance of the factors studied. The responses analyzed were the particle size, polydispersity (PDI), zeta potential (mV) and EE. The response surface methodology was used to analyse the effect of the three factors on encapsulation efficiency. All experiments were performed in random order and duplicate. Zein nanoparticles showed diameters ranging from 59.5 to 95.5 nm and PDI in the range of 0.09 to 0.32 and zeta values rangin from 33.5 mV to 57.7 mV. No significant effect in the analyzed factors (concentration of zein, T4OL and TTA) on the size and polydispersity of nanoparticles was observed. This result can be explained in terms of the polymer chain lenght, since zein used in this study comprises a family of proteins composed by , , and - zein, with molecular weights ranging from 10-25 kDa.

Table 1: Factors evaluated in the experimental design and obtained results* Experimen t

Zein (mg/mL)

1

T4OL (% w/w zein)

TTA (% aqueous phase)

Size (nm)

PDI

Zeta (mV)

91.96 0.15 ± 0.01 33.5 1.93 2 87.62 ± 20 20 0.5 0.32 ± 0.04 57.7 5.79 3 59.53 ± 20 30 0.3 0.18 ± 0.02 48.5 1.27 4 67.13 ± 35 10 0.5 0.22 ± 0.01 55.1 0.48 5 85.96 ± 35 20 0.3 0.11 ± 0.01 46.1 0.80 6 84.39 ± 35 30 0.1 0.15 ± 0.01 45.7 1.03 7 92.31 ± 50 10 0.3 0.09 ± 0.03 50.8 0.74 8 89.52 ± 50 20 0.1 0.12 ± 0.01 48.5 0.70 9 95.53 ± 50 30 0.5 0.09 ± 0.03 45.0 2.15 *T4OL: Terpinen-4-ol; TTA: Tetradecyl trimethyl ammonium bromide; PDI: polydispersity 20

10

0.1

Encapsulation Efficiency (%) 63.7 60.8 85.8 82.0 78.1 85.0 93.2 85.7 93.1

The morphology of empty zein nanoparticles is shown in Figure 1a. Nanoparticles with or without T4OL present a compact spherical structure. Concerning the encapsulation efficiency (EE), the Pareto chart showed that only the zein concentration affected the EE significantly (ANOVA, p <0.05) (Figura1b), TTA and T4OL did not affected EE significantly in the concentration range studied. Figure 1c shows the influence of TTA/Zein proportion in EE fitted by the linear regression model expressed in Equation 1. The model is limited to the studied concentration range.

2

EE (%) = 58.86 + 0.641 [zein] R 0.60012 (±7.33) (±0.198)

(1)

Although zein has increased the EE in a concentration-dependent manner, for concentrations higher than 50 mg/mL, an aggregation of this protein was observed. Thus, it is not possible to carried out experiments with zein in high concentrations.

a

b

c

Figure 1: a) Morphology of an empty zein nanoparticle; b) Pareto chart showing the influence of factors on the EE of T4OL in zein particles and c) Response surfaces for the EE of T4OL (30% w/w zein) as a function of the concentration of the TTA and zein.

References

[1] A Calcabrini, A Stringaro, L Toccacieli, et al., Journal of Investigative Dermatology, 122 (2004) 349.

[2] C-S Wu, Y-J Chen, JJW Chen, et al., Evidence-Based Complementary and Alternative Medicine, (2012)1.

[3] TW Prow, JE Grice, LL Lin, et al., Advanced Drug Delivery Reviews, 63 (2011) 470.

[4] S Quispe-Condori, MDA Saldana, F Temelli, Lwt-Food Science and Technology, 44 (2011) 1880.

Photonics based on carbon nanotubes M. Gicquel-Guézo(1), Q. Gu(1), F. Grillot(1), S. Loualiche(1), J. Le Pouliquen(1), T. Batte(1), O. Dehaese(1),A. Le Corre(1),L. Bramerie(2), D. Bosc(2),L. Bodiou(2), J.-C. Simon(2), Y. Battie(3), A. Loiseau(4),B. L. Liang(5), D.L. Huffaker(5) (1)

FOTON, UMR CNRS 6082, INSA, Avenue des Buttes de Coësmes CS 14315 35043 Rennes Cedex, France (2) FOTON, UMR CNRS 6082, ENSSAT, 6 rue de Kerampont BP 80518 22305 Lannion Cedex, France (3) LPMD, Université Paul Verlaine, Ile du Saulcy BP 8079,4 57021 Metz, France (4) LEM, UMR CNRS 104, ONERA, 29 Avenue de la division Leclerc, 92322 Châtillon Cedex, France (5) Electrical Engineering Department, University of California at Los Angeles, Los Angeles, CA 90095, USA maud.gicquel@insa-rennes.fr

The bit rate request for optical telecommunications networks is continuously growing, in order to provide high speed internet all over the world. However, in long-haul optical fibers the quality of information transmission requires all-optical regeneration of the telecom signal, as it is damaged through its propagation. Our work focuses on designing efficient all-optical devices based on ultrafast dynamics and nonlinear optical properties of nanomaterials. We have highlighted nonlinear optical properties of carbon nanotubes (CNT), in direct comparison with quantum wells (QW) [1,2,3]: CNT present ultrafast absorption dynamics and large 1Dexcitonic nonlinearities. We aim at demonstrating the huge potential of CNT-based optical devices for high-bit-rate telecom applications, as simple-process and low-cost solution in comparison with QW-based devices [4]. Furthermore, we have reported a special behavior of CNT light emission with temperature: from 77K to room temperature, no shift of emission wavelength is observed [2], in contradiction with well-known Varshni’s law for semiconductor materials [5]. This behavior confers great interest to CNT for new photonics sources with higher performances. Thus, we will present our research studies on passive as well as active photonics devices based on CNT for telecom applications.

[1] Nong et al., Appl. Phys. Lett. 96, 061109 (2010).

[2] Nong et al., Jpn. J. Appl. Phys. 50, 040206 (2011).

[3] Gicquel-Guézo et al., Carbon 49, 2971 (2011).

[4] Gicquel-Guézo et al., Appl. Phys. Lett 85, 5926 (2004).

[5] Y. P. Varshni, Physica (Amsterdam) 34, 149 (1967).

Controlled synthesis of si nanowires on si substrates 1

1

2

1

A. Gómez , T. Campo , F. Márquez , E. Elizalde , C. Morant

1

1

Departamento de Física Aplicada, Universidad Autónoma de Madrid, 28049, Madrid (Spain) 2 School of Science and Technology, Universidad del Turabo, 00778PR, USA arancha.gomez@estudiante.uam.es

Abstract One-dimensional semiconductor nanostructures have recently attracted intense research attention due to their novel physical properties. In this study, we present a simple procedure for the synthesis of silicon nanowires (SiNws), with diameters of 30 nm and lengths up to several micrometers.

We have used crystalline Si (100) substrates, covered by a thin film of gold. The nanowires were synthesized by thermal treatment, without any Si gas source, at ambient conditions with a flux of hydrogen and argon. A systematic investigation of the processing parameters has been made, and revealed that temperature, hydrogen flow rate, catalyst and substrate morphology are critical for the growth of SiNws. Furthermore, in this work we show that the use of different coatings on the Si substrate improves the SiNws growth. TiN-coating gives vertically aligned SiNws and silica nanospheres-coating produces a high density of SiNws. The synthesized SiNws have been characterized by FESEM and HRTEM microscopies, X-ray diffraction, and X-ray photoelectron spectroscopy. It has been demonstrated that the nanowires have a Si core and an external oxidized shell, indicating that an oxide assisted growth mechanism could be responsible for the formation of the Si Nws. Related to the investigation of surface morphology of the Si substrate, we have successfully demonstrated that selective SiNws growth could be induced by local indentations on the Si substrate.

The local pressure caused by the indentation process generates metastable Si, which enhances the catalyst aggregation in the indented areas and SiNws grow within indents. We have also achieved a simple method to grow SiNws on selective areas by depositing the Au catalyst exclusively on selected positions of different substrates by using masks.

References [1] T. Yasui, Y. Nakai, Y. Onozuka, Thin Solid Films, 516 (2008) 859–862.

[2] F. Márquez, C. Morant, V. López, F. Zamora, T. Campo, E. Elizalde, Nanoscale Research Letters, 6:495 (2011) Figures

a)

b)

Figure 1. The roughnes of the substrate surface promotes the growth of SiNws forests (a).

Microindentations made on Si substrates before the Au deposition provide localized SiNWs growth on the created cracks (b).

a)

b)

Figure 2. TiN-coating gives vertically aligned SiNws (a) and silica nanospheres-coating produces a

high density of SiNws (b). a)

b)

Figure 3. TEM image of SiNws obtained by the TiN-coating procedure(a) and its chemical analysis (b).The copper element comes from the SiNws support.

a)

b)

Figure 4. The deposition of Au catalyst exclusively in patterned areas, allows a selective growth of SiNws on gold covered TiN/Si substrates (a) and on the edges of gold covered Si(111) surfaces (b). Circle patterns of 1 Îźm diameter.

Non-conservative electric and magnetic optical forces on semiconductor particles 1 2 1 Raquel Gómez-Medina , Manuel Nieto-Vesperinas and Juan José Sáenz 1 Dpto. Física de la Materia Condensada and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, Campus de Cantoblanco, Madrid 28049, Spain.

2 Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas (CSIC), Campus de Cantoblanco, Madrid 28049, Spain. r.gomezmedina@uam.es

The basic ideas behind the developments of optical manipulation are relatively simple for objects much smaller than the wavelength of light. However, when particles are not very small, they may develop not only electric dipoles but also magnetic dipoles and higher-order multipoles, in response to light’s electromagnetic field. The dipolar electric and magnetic response of lossless dielectric spheres made of both low and moderate permittivity materials has been recently analyzed [1, 2]. Interestingly, the light scattered by some semiconductor (as Si or Ge) nanoparticles of appropriate size is perfectly described by dipolar electric and magnetic fields, being quadrupolar and higher order contributions negligible in this frequency range.

The time averaged force on a dipolar magnetodielectric particle, characterized by its electric and magnetic polarizabilities, has been recently shown to be given by the sum of three terms [3-5], the force exerted by the incident field on the induced electric dipole, the force on the induced magnetic dipole and the force due to the interaction between both dipoles that is related to the interference between the fields radiated by electric and magnetic dipoles and the asymmetry in the scattered intensity distribution [4, 5].

As we will show, this force is a combination of conservative and non-conservative steady forces that can rectify the flow of magnetodielectric particles in an optical vortex wave-field [5] spinning the particles either in or out of the whirls sites leading to trapping or diffusion (see Fig. 1). This may permit the exploration of new forms of controlled atom motion in optical lattices [6] and even the manipulation of transparent objects such as biological macromolecules by using semiconductor nanospheres, similar to those discussed above, as pulling probes attached to them.

References [1] A. García-Etxarri, R. Gómez-Medina, L. S. Froufe-Pérez, C. López, L. Chantada, F. Scheffold, J. Aizpurua, M. Nieto-Vesperinas and J. J. Sáenz, Opt. Express, 19 (2011) 4815-4826.

[2] R. Gómez-Medina, B. García-Cámara, I. Suárez-Lacalle, F. González, F. Moreno, M. NietoVesperinas and J. J. Sáenz, J. Nanophoton. 5 (2011) 053512.

[3] M. Nieto-Vesperinas, R. Gómez-Medina, and J. J. Sáenz, J. Opt. Soc. Am. A, 28 (2011) 54-60.

[4] M. Nieto-Vesperinas, J. J. Sáenz, R. Gómez-Medina, and L. Chantada, Opt. Express, 18 (2010) 11428-11443.

[5] R. Gómez-Medina, M. Nieto-Vesperinas and J. J. Sáenz, Phys. Rev. A, 83 (2011) 033825.

[6] R. Gómez-Medina, L. S. Froufe- Pérez, M. Yépez, F. Scheffold, M. Nieto-Vesperinas and J. J. Sáenz, Phys. Rev. A, 85 (2012) 035802.

ky/2

(a)

ky/2

(b)

Figure 1. Nonconservative forces on a Si sphere of radius 230nm placed at the intersection region of two standing waves with a dephasing =/2 for a wavelength =1600nm, slightly below (blue-shifted) the magnetic dipolar resonance. Arrows in (a) and (b) point along the total force lines. (a) Contour maps of the modulus of the normalized total force. (b) Contour maps of the normalized electric field intensity.

Notice that equilibrium (zero force) positions correspond to electric field maxima. (Adapted from Ref. [5]).

“Nanocomposites based on poly(ether imide) by the addition of a poly(butylene terephthalate)/carbon nanotube masterbatch: Electrical conductivity and mechanical performance” Imanol González, José Ignacio Eguiazábal Department of Polymer Science and Technology and POLYMAT UPV/EHU, Paseo Manuel de Lardizábal 3, 20018 San Sebastián, Spain imanol.gonzalez@ehu.es Abstract Polymer nanocomposites (PNs) based on carbon nanotubes (CNTs) show exceptional properties resulting from the mixed polymer matrix and the nanostructured CNTs. These properties, mainly physical and mechanical, are clearly superior to those of conventional microcomposites.

Several processing methods have been employed to produce thermoplastics/CNT nanocomposites, such as melt mixing [1], in-situ polymerization [2], solution processing [3], etc.

Among these methods, melt mixing of CNTs with thermoplastic polymers using conventional processing techniques is particularly desirable, because the process is fast, simple, free of solvents and contaminants, and available for the plastic industry [4]. In this way, the use of precompounded, largely dispersed master-batches (usually containing 10–20 wt.% CNTs) produced in “ad hoc” machinery is advantageous for processing, as hazardous contact with the nano-sized inclusions is reduced to the minimum, and dispersion is close to the optimum.

Poly(ether imide) (PEI) is a high performance thermoplastic with high thermal stability and remarkable modulus of elasticity and tensile strength. It performs successfully in electrical and electronics industry, in aircraft applications and in the automotive market. Development of highly performing electrically conductor PNs based on PEI via melt processing is challenging in their processing and dispersion. This is due to the high processing temperature and melt viscosity of the PEI that hinder the dispersion of the CNTs. Widely dispersed PNs based on organoclays have been obtained by blending the desired matrix with a master-batch of a polymer that is both miscible with the matrix and able to disperse the organoclay. This technique collects together the advantages of the presence of the nanostructured filler and those conferred by blending. Moreover, it is especially effective when the production of the nanostructured master-batch lends advantages, such as easier processing or improved dispersion. It is known that PEI is fully miscible with poly(butylene terephthalate) (PBT) over the entire composition range. Moreover, highly dispersed PBT/multiwall carbon nanotube (MWCNT) master-batches are commercially available at very competitive prices.

Therefore, they could be used to disperse the MWCNTs and produce PEI-rich nanocomposites.

In this work, we have obtained melt processed PEI nanocomposites using a commercial PBT/MWCNT master-batch. The MWCNT content in ternary PEI/PBT/MWCNT PNs rich in PEI varied from 0 to 5 wt.%. The PNs were prepared in a twin-screw extruder-kneader and processed by injection moulding. The electrical conductivity was measured by means of an impedance analyzer and the processability by means of the melt pressure at the output of the extruder. The morphologies were analysed by transmission electron microscopy (TEM). The phase structure of the PNs was characterized by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC), and the mechanical properties were measured by means of tensile tests.

The nanostructural analysis conducted by TEM confirmed that the MWCNTs were efficiently dispersed in the new PEI/PBT matrix, mainly in the form of single tubes (Figure 1). The DC conductivity of the PNs increased abruptly in more than 7 decades with the addition of only 1 wt.% MWCNT, indicating the presence of the percolation threshold. The value of percolation critical exponent (t: 1.92) was consistent with that reported by the percolation theory for a three dimensional percolation structure (Figure 2). The processability of PEI clearly improved after PBT-MWCNT master-batch addition, decreasing the pressure at the output end of the extruder by half in the 5%-PN. With respect to the mechanical properties, the Young’s modulus increased significantly with increasing MWCNT content. The increase was 27% with respect to the corresponding PEI/PBT blend matrix in the PN with 5wt.% MWCNT. This is due to the large interfacial area-to-dispersed phase volume ratio characteristic of well-dispersed MWCNT PNs. The ductility of the PNs decreased after MWCNT addition, from 60% for pure PEI to around 7%

in the PNs, as a consequence of the stiffness increase caused by the filler presence.

Nevertheless, all PNs broke after yielding, indicating their ductile nature.

Acknowledgements: The financial support of the “Spanish Ministerio de Economía y Competitividad” (Project nº MAT2010-16171), the Basque Government (IT-234-07) and the University of the Basque Country (UFI 11/56) is gratefully acknowledged.

References [1] W.D. Zhang, L. Shen, I.Y. Phang and T. Liu, Macromolecules, 2 (2004) 256.

[2] T. Liu, Y. Tong and W. D. Zhang, Composites Science and Technology, 3-4 (2007) 406.

[3] J. Foster, S. Singamaneni, R. Kattumenu and V. Bliznyuk, Journal of Colloid and Interface Science, 1 (2005) 167.

[4] O. Breuer and U. Sundararaj, Polymer Composites, 6 (2004) 630.

Figures

Figure 1. TEM photomicrograph of the PEI based PN with 2% MWCNT.

Figure 2. DC electrical conductivity of PEI based PNs vs. MWCNT content at a frequency of 20 Hz. The insert shows log(σDC) versus log(p-pc) and the solid line corresponds to the best fit.

H diffusion in nanoestructured as compared to massive W 1

1,2

1

1

3

3

1

R. Gonzalez‐Arrabal , N. Gordillo , M. Panizo‐Laiz , A. Rivera , F. Munnik , K. Saravanan , and J. M. Perlado

1

Instituto de Fusión Nuclear, ETSI de Industriales, Universidad Politécnica de Madrid, C/ José Gutierrez Abascal, 2, E‐28006 Madrid, Spain.

2 CEI Campus Moncloa, UCM‐UPM 3 Helmholtz‐Zentrum Dresden‐Rossendorf, PO.Box 10119, D‐01314 Dresden, Germany.

One of the challenges in the design of the future nuclear power plant is to develop materials capable to resist in the hostile environment of a fusion reactor. Because of its low sputtering yield, low‐activation with a high melting point, high thermal conductivity, and low thermal expansion, tungsten is one of the most attractive materials proposed for first wall applications in the nuclear fusion reactors [1‐3]. Even when W is assumed to be the best candidate as plasma facing material (PFM), some limitations have been identified that have to be defeated in order to fulfil specifications i. e one of the important point of concern is the light species behaviour. Light species (mainly H, D, T and He), which are present in the plasma in magnetic confinement fusion (MC) and which result from the explosion in inertial confinement fusion (IC), are implanted in the near surface region of PFM. The concentration of light species in W can lead to formation of bubbles which notably degrade its mechanical properties [4] and heat load performance. Moreover, the degradation is enhanced by the fact that ion implantation is accompanied by the production of thermal vacancies in MC and ion‐induced damage in IC. In particular, in IC reactors with direct drives (HiPER), the mayor threats comes from the simultaneous arrival of a great diversity of energetic particles (mainly D, T, He and C) short time after the explosion and the subsequent arrival of a high neutron flux (with energies of up to 14 MeV/neutron).

In this work we focus on the study of hydrogen behavior in nanoestructured films (see N. Gordillo et al. contribution to this conference) as compared to massive W. For this purpose resonant nuclear reaction (RNRA) experiments are carried out by using the 1H(15N,αγ)12C nuclear reaction in nanoestructured and massive W samples implanted with (i) H at an energy of 170 keV and (ii) sequentially implanted with C at an energy of 665 keV and H at 170 keV. Implantations were carried out at a fluence of 5x1016 at/cm2 and at two different temperatures RT and 400ºC. RNRA data evidence that the highest H retention is observed for the samples sequentially implanted with C and H, being the lower one measured for the massive samples implanted only with H. In general, the H retention is higher for nanoestructured than for massive samples. Moreover, increasing the irradiation temperature up to 400ºC drives the H to completely out diffusion in nanoestructured as well as, in massive samples. The role of microstructure and radiation‐induced damage on light species behaviour will be discussed.

References [1] C. H. Wu et al. J. Nucl. Mater. 220‐222 (1995) 860 [2] G. Federic et al. J. Nucl. Mater. 266‐269 (11999) 14 [3] M. Kaufmann et al. Fusion Engineering and Design 82 (2007) 521‐527 [4] K. Shinohara, A. Kawakami, S. Kitajima, Y. Nakamura, M. Kutsuwada, Journal of Nuclear Materials 179–181 (1991) 246–249

Localization of states on graphene-type lattices C. González-Santander1, F. Domínguez-Adame1, R. A. Römer2 1

GISC, Departamento de Física de Materiales, Universidad Complutense de Madrid, E-28040, Spain 2 Department of Physics and Centre for Scientific Computing, University of Warwick, Coventry, CV4 7AL, United Kingdom cglezsantander@fis.ucm.es

Abstract The electronic properties of charged particles in two-dimensional (2D) systems under arbitrary disorder have attracted much attention in the last years. Not only from the theoretical point of view, because the scaling theory predicts that all states are localized in 2D, but also whether there are experimentally achievable true 2D systems. Graphene has been proposed as the most suitable material to address these questions [1-4]. Most of the numerical studies claim that, as expected, disorder induces localization in graphene. The detailed features of the localized behaviour depend on the precise numerical approaches employed for evaluating, e.g. the single-particle wavefunctions or the conductivity of the graphene samples. A few papers even propose that graphene can support a localized to extended transition [3,4]. Therefore, the problem of localization in 2D systems, and specifically in graphene, is still under debate and resembles somewhat the discussion of 2D localization of the mid 1980's.

In this work we proposed a novel approach based on a combination of the transfer matrix method and the power method for diagonalizing Hermitian matrices. Our methods allows to study 2D samples of size MxM directly without having to use quasi-1D geometries. We apply the method to both a simple square lattice (SQ) and a hexagonal lattice, representing a graphene sample, with zigzag (ZZ) and armchair (AC) edges. Our calculation is based on the Anderson tight-binding Hamiltonian for an electron in a lattice with compositional disorder. The on-site potentials are randomly distributed according to a uniform distribution with width W. Fig. 1 shows the localization lengths for (a) SQ and (b) ZZ lattices as a function of energy, E, for different disorders, W, ranging from W=1 to 10, for systems with 104 lattice sites. Results have a relative error equal or smaller than 2.5%, which is obtained averaging over at least 500 disorder configurations.

For comparison it should be noted that all lengths are given in units of the nearest neighbour distance, and therefore is different for each lattice, according to its topology. When the strength of the disorder increases the localization length found to decrease as expected because the wavefunctions become more localized. This effect is so robust that under strong disorder the localizations lengths are one order of magnitude smaller than the system size. However, for weaker disorders the localization lengths are bigger than the system size. Hence these states appear as extended, when actually this is a finite size effect.

A truly localized to extended transition can be studied from the dependence of the reduced localization length = /M on the width M. In the localized regime decreases with M since remains finite in the thermodynamic limit. On the other hand, increases for extended states. At the transition is constant.

In order to describe a system with infinite width and length it is necessary to extrapolate the computed data of with M. This can be done through a finite size scaling (FSS) procedure [5], assuming that =f( /M) where is the scaling parameter. In Fig. 2 is plotted as a function of /M for (a) SQ and (b) ZZ lattice at E=0. Results show that it is possible within the accuracy of our data to find a scaling function with only the localized branch. Even more, the SQ and ZZ data can be combined into a single such localized FSS curve. The presence of this one branch is a sign of the complete localization of states for large systems and hence the absence of an Anderson transition. Similar results are obtained for AC graphene-type lattice.

References [1] S.-J. Xiong and Y. Xiong Physical Review B, 76 (2007) 214204.

[2] G. Scubert, J. Schleede and H. Fehske Physical Review B, 79 (2009) 235116.

[3] M. Amini, S. A. Jafari and F. Shahbazi EPL, 87 (2009) 37002.

[4] M. Hilke arXiv:0912.0769v1 (2009) [5] A. MacKinnon and B. Kramer, Z. Phys. B Condensed Matter, 53 (1983) 1.

Micellar approach for the design of new up-converting nanophosphors and superparamagnetic nanoparticles for optical imaging and in vivo MRI. H. Groult [a]

[a,b]

, J. Ruiz-Cabello

[a,b]

[a,b]

and F. Herranz

Unidad de Imagen Avanzada. Centro nacional de Investigaciones Cardiovasculares (CNIC).

Madrid (Spain) hugo.groult@cnic.es [b]

Ciber de enfermedades respitorias (CIBERES). Bunyola, Mallorca (Spain).

Abstract Molecular Imaging, the observation of physiological events at cellular and molecular levels, offers remarkable opportunities for the understanding of the pathologic biological pathways and for diseasesâ&#x20AC;&#x2122; early diagnostic. Among others, the development of nanoparticles (NPs) as molecular imaging agents has particularly contributed to this advancement. Their small size confers new or improved physicochemical properties as well as an unusual chemical 1 platform with high tailoring possibilities. This unique tool can lead to the development of multimodal and theranostic agents which answer the challenging demands of the innovative imaging systems like high selectivity, good resolution, 2 and the achievement with one single probe of distinct complementary information.

We especially studied two classes of nanoparticles. First, Ultrasmall Superparamagnetic iron oxide (USPIOs) widely described as very efficient contrast agents for magnetic resonance imaging (MRI) and second, Upconverting 2 nanophosphors (UCNPs), a new type of nanomaterial for in vivo fluorescence imaging. It presents the unique feature to convert low energy near infrared (NIR) light into higher visible light and/or NIR emission throw two or three 3 sequential photon absorption, together with energy transfers. This singular property overcomes the drawbacks of classical luminescent probes (tissue damaged, high energy radiation, auto-fluorescence of the biological tissues and low penetration depth) and confers very attractive advantages for a UCNP-based fluorescence imaging: excitation 4 less harmful, no auto-fluorescence, high penetration depth, no toxicity and low cost techniques. NaYF4 : Yb0,18,Er0,02 3 provides the best upconverting fluorescence and it is also the golden standard in UCNPs chemistry.

The conventional method consists first in the synthesis of the nanoparticles in organic solvent and then turns 5,6 them hydrophilic for in vivo applications. Many approaches exist to assure hydrophilic coatings to the nanoparticles.

The most used are the ligand exchange or the direct chemical modification of the hydrophobic surfactant.( Herranz F., Morales M.P., Roca A.G., Desco M., Ruiz-Cabello J. 2008 Chemistry- A European Journal, 14(30), 9126-9130. ) Also a widely popular one consists in the formulation of amphiphilic bilayer organic structure such as micelles, liposome or solid lipid 7 nanoparticles.

The different NPs (USPIO and UCNPs) were first prepared in organic solvent coated with OA (oleic acid). The NPs were fully characterized especially in term of magnetic properties for the USPIOs and fluorescence for the UCNPs. We successfully improved the fluorescence of the UCNPs by a factor of five covering the core with a passive shell of the same material without the dopants.

8 Then, following a nanoemulsion method , these precursors were turned hydrophilic by creation of different micelles. Four coating were assessed: three amphiphilic polymers (polysorbate 20, polysorbate 80, poloxamer 407) and a phospholipid (phosphatidylcholine). They have been selected in particular for they known biocompatibility and 9 antibiofouling properties [figure 1]. Using the same method, we also stabilized the NPs with the oleic acid binding sites of a biopolymer. One very interesting candidate is the biopolymer coated NaGdF4 : Yb,Tm ; a nanophosphor which present the advantages to have a multimodal core. Indeed, in addition to the NIR to NIR upconverting fluorescence, the gadolinium provides a good r1 relaxivity for MRI and can serve as agent for computer tomography (CT) The different USPIOs and UCNPs hydrophilic micelles we have synthesized have been fully characterized.

We checked first the size; shape and crystallinity by dynamic light scaterring (DLS), transmission electronic microscopy (TEM) and X-ray diffraction (XRD). Composition of the coatings was then confirmed with FTIR. Specific characterizations for each type of NPs were then carried on; on one hand magnetic susceptibility and relaxometry for USPIOs, on other hand fluorescence emission in vitro and confocal microscopy of cell cultures for UCNPs. Finally we have carried out several in vivo experiments to check their behaviour as blood pool contrast agents showing circulation times between one and two hours. Regarding the high stability and long circulation times in the blood, we believe that these assemblies can be very useful as contrast agents for multimodal imaging in vivo.

Figures

A)

B)

Figure 1. A) Synthetic methodology for the micelle preparation. a) sonication, stirring b) hexane evaporation, centrifugation, dialysis. B) Hydrodynamic size of the micelles prepared.

A)

B) (1) (2)

(3)

C)

Figure 2. Example of characterizations of UCNPs NaYF4 Yb,Er micelles. A) Hydrodynamic size of polysorbate 20 coated UCNP micelle; inset TEM picture of polysorbate 20 coated UCNP micelle. B) Infrared spectra of polysorbate 20 (1), polysorbate 80 (2) and phosphatidylcholine (3) coated UCNP micelles C) Fluorescence emission spectra of the UNCP micelles under 980 nm wavelength excitation; inset photograph of the visible fluorescence emission of OA coated NaYF4 Yb,Er under a 980 nm wavelength excitation

References [1] Cheon, J. & Lee, J.-H., Accounts of Chemical Research, 41 (2008) 1630.

[2] Mccarthy, J. & Weissleder, R. Advanced Drug Delivery Reviews, 60 (2008) 1241.

[3] Haase, M. & Sch채fer, H., Angewandte Chemie International Edition, 50 (2011) 5808.

[4] Zhou, J., Liu, Z. & Li, F., Chemical Society Reviews, (2012).

[5] Yu, W. W., Falkner, J. C., Yavuz, C. T. & Colvin, V. L., Chemical Communications, (2004) 2306.

[6] Wang, F. & Liu, X., Chemical Society Reviews, 38 (2009) 976.

[7] Mulder, W. J. M. et al., Accounts of Chemical Research, 42 (2009) 904.

[8] Park, J. et al., Journal of Materials Chemistry, 19 (2009) 6412.

[9] Gupta, A. K. & Curtis, A. S. G., Journal of Materials Science, 15 (2004) 493.

Liquid-phase epitaxial growth on nanoporous substrates Jan Grym, Dušan Nohavica, Petar Gladkov Institute of Photonics and Electronics AS CR, v.v.i., Chaberska 57, Praha 8, Czech Republic grym@ufe.cz Abstract There is a limited number of III-V semiconductor substrates which are available at acceptable quality and cost. Restriction to lattice-matched systems would greatly limit the number of applications.

Development of vapor phase growth techniques allowed to precisely control the layer thickness and uniformity on the atomic level. Still, when the critical layer thickness is exceeded, misfit dislocations are created having negative impact on the performance, reliability and lifetime of semiconductor devices [1].

A number of defect engineering approaches are available to gain control over the generation of defects during heteroepitaxial growth. One of the approaches consists in the growth on a porous substrate to accommodate elastic strains at the heteroepitaxial interface [2]. An essential step in successful application of porous substrates in epitaxial growth is to achieve control over their properties: the surface roughness, pore size, orientation, density and depth.

We report on the growth of In(x)Ga(1-x)As on porous GaAs and InP substrates by the liquid phase epitaxy technique (LPE) and compare results with those achieved by metal-organic vapor phase epitaxy. InGaAs is a material widely used in electronic and optoelectronic devices such as high electron mobility transis-tors [3], laser diodes [4], infrared detectors [5], and photovoltaic cells [6]. The InGaAs system is flexible in terms of the range of optical wavelengths that can be emitted and absorbed; by varying the indium concentration, emission or detection wavelengths ranging from 1.1 to 3 μm can be achieved.

The pore etching was carried out in an electrochemical cell containing a fluoride-iodide [7] and chloride aqueous electrolytes using a three-electrode configuration. The LPE growth took place in a standard horizontal apparatus from 690-750°C with the initial supersaturation corresponding to 1-13°C. The porous structures before and after the epitaxial growth were characterized by Nomarski differential interference contrast microscopy (NDICM), scanning electron microscopy (SEM), atomic force microscopy (AFM), low temperature photoluminescence (PL), x-ray diffraction (XRD) and transmission electron microscopy (TEM).

We show how the thickness of the nanoporous layer, the melt composition, the supersaturation, the growth temperature, and the heat treatment in high-purity hydrogen influence the growth mechanism, the surface morphology, and the structural and optical properties of the layers. We demonstrate that pores are capable of accommodating strain at the interface. The layers grown on porous substrates show higher thickness. Moreover, the pore annihilation under the influence of stress takes place at the boundary of InAs grains in the heterostructure InAs/InP. The work was supported by the project P108/10/0253 of the Czech Science Foundation.

References [1] H. Foll, J. Carstensen, S. Frey, J. Nanomater. 2006, 1-10 (2006).

[2] S. Mahajan, Acta Mater. 48, 137-149 (2000) [3] S. Ahmad, IETE Tech. Rev. 14, 397-410 (1997).

[4] F. Bugge, U. Zeimer, R. Staske, B. Sumpf, G. Erbert, M. Weyers, J. of Crystal Growth 298, 652-657 (2007).

[5] J. B. D. Soole, H. Schumacher, IEEE J. Quantum Electron. 27, 737-752 (1991).

[6] J. F. Geisz, S. Kurtz, M. W. Wanlass, J. S. Ward, A. Duda, D. J. Friedman, J. M. Olson, W. E. McMahon, T. E. Moriarty, J. T. Kiehl, Appl. Phys. Lett. 91, 012108 (2007).

[7] V. Ulin, S. Konnikov, Semiconductors 41, 832-844 (2007).

Figures

a

b

c

d

e

f

SEM micrographs of a porous GaAs substrate treated at 690째C (a) cross-section, (b) surface, 750째C (c) cross-section, (d) surface and cross-section of InGaAs layers grown at low (e) and high (f) supersaturation.

Nanocrystals in the Manufacture of Target for Inertial Confinement Fusion.

Carlo Guerrero1, Manolo Perlado1 and Santiago Cuesta-Lopez2 Instituto de Fusión Nuclear, Universidad Politécnicade Madrid, Madrid – España 2 Universidad de Burgos. Plaza Misael Bañuelos s/n. 09002, Burgos - España

1

The efficiency of power generation in inertial confinement fusion is related, among other phenomena, to development in the manufacture of deuterium tritium target, in particular the solid layer of this material (DT ice). The requirements for the target manufacture are several, within the most salient this roughness and thickness variation of the solid layer [1], these are related to the hydrodynamic instabilities that occur at the time of compression, decreasing the efficiency ignition and burning of fuel, for example the Rayleigh-Taylor instability [2].

One of the ways to reduce these instabilities is the growth of nanocrystals in the solid layer of DT-ice, thus obtained solid structures more rigid and with a speed of sound propagation uniform [3]. In this work we present a simulation methodology [4] which is obtained by varying the speed of sound, to the solid structures of atomic isotopes of hydrogen in high pressure conditions. These simulations are performed for different grain sizes. The study is a first step in the analysis of the relationship between the growth of nanocrystals and ignition efficiency.

References: [1] B.J. Kozioziemski, D.S. Montgomery, J.D. Sater, J.D. Moody, C. Gautier, J.W. Pipes. Solid deuterium–tritium surface roughness in a beryllium inertial confinement fusion shell. Nucl. Fusion 47 1–8 (2007).

[2] Abbas Ghasemizad, Hanif Zarringhalam and Leila Gholamzadeh. The Investigation of Rayleigh-Taylor Instability Growth Rate in Inertial Confinement Fusion. J. Plasma Fusion Res. SERIES, Vol. 8 (2009) [3] E.M. Bringa, A. Caro, M. Victoria and N. Park. The Atomistic Modeling of Wave Propagation in Nanocrystals. JOM Journal of the Minerals, Metals and Materials Society. Volume 57, Number 9, 67-70, (2005).

[4] C.Guerrero, S. Cuesta-López, J.M. Perlado. “Structural propieties of hydrogen isotopes in solid phase in the context of inertial fusion target manufacturing”. Eur. Phys. Journal Web of conferences.

Proceedings of the Seventh Conference on Inertial Fusion Sciences and Applications (IFSA 2011).

In press (2012).

Efficient Gene Delivery Nanovectors Based on Functionalization Of Single wall Carbon Nanotubes (SWNT) with Polyethylenimine (PEI) Azadeh Hashem Niaa,b, M.Ramezanib*, M. Rahimizadeha, H. Eshghia, Kh. Abnoosb a

Faculty of Science, Department of Chemistry, Ferdowsi University, Mashhad, Iran

b

Nanomedicine Lab, Pharmaceutical Research Center, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran

*RamezaniM@mum.ac.ir

Abstract: Carbon nanotubes (CNTs) have found their uses in the biological sciences at molecular and cellular levels. Studies interfacing CNTs with biological molecules indicate that such interfaces can be established while the functions of biological molecules are preserved. We used functionalization procedures to improve the solubility and biocompatibility of SWNT. PEI ( polyethyleneimine) have been extensively searched for its binding ability to plasmid due to positive surface charge of its porotonated amine groups in biologic pH and different vectors are synthesized by modifying PEI molecules to improve its viability . By attaching PEI to the surface of SWNT, synthesized vectors will be able to bind plasmid efficiently and internalize the cell without causing allergic reactions and can be used as delivery vehicles for gene delivery purpose.

Keywords: Single wall Carbon Nanotube, Functionalization, Polyethyleneimine, Gene Delivery Introduction Since the discovery of SWNT in 1993 as a new allotrope of carbon, lot of attention has been focused on this magic one dimensional (1D) carbon structure [1]. They have been subjected to wide researches, due to their potential application, ranging from gas storage [2],field effect transistors, biosensors and catalyst support. Their poor solubility limits their application for biological purposes which can be overcamed by functionalization.

Attachment of PEI, polymer known for its excellent in vivo and in vitro gene delivery [4], via different linkers onto the surface of CNT not only leads to aqueous solubility but improves the transfection efficiency with respect to polymer.

Two different reactions are used to attach the succinct linker to the surface of SWNT: A- Attachment via Esterification Reactions After Hydroxylation of SWNT, esterification with succinc anhydride provided us with succinic spacer. Then PEI attachment carried out by amidation reaction. Three other vectors are synthesized and named S1.8,S10, S25 repectively.

Experimental Three different approaches were used for attachment of PEI to the surface of SWNT, as follows: 1- Direct Attachment PEI is attached directly via amide bond to the Carboxyl groups introduced in first step. Three nanovectors are synthesized using PEI with different molecular weights: 1800, 10000, 25000 Dalton , named V1.8,V10, V25.

2-Attachment using SUCCINC ACID linker

B- Attachment via Friedel- Craft Acylation: Succinct anhydride is attached to SWNT through a carbonyl group via Friedel- carft acylation and attachement of PEI is carried out by amide bond formation. Three other vectors are synthesized and named Ac1.8, Ac10, Ac25 respectively.

Results and Discussion Characterization of structures were carried out by FT-IR technique. Size and zeta potential of vector were determined using Malvern Zeta sizer.

Condensation Assay Vector were investigated for their binding ability to plasmid using Ethidium Bromide method.

Transfection Gene delivery and transfection efficiency of vectors were evaluated using pRL-CMV in N2A cells by luciferase assay(Promega). results are summarized in Figure1, 2, 3.

MTT ASSAY Cell viabilities were by evaluated MTT assay(Fig 4,5,6 ).

Conclusions Data from zeta potential shows that all structures bear positive charges, due to the cationic polymer on the surface. Size of nanovectors lay in the range of 90-130 nm (Fig 7).

In each set best results were obtained in the case of vector synthesized based on PEI 1800 and comparing the attachment mode of PEI onto the surface, vectors with succcinc linker were much more efficient in transfection. In the case of Ac1.8, at C/P=6 transfection is increased 65 times and for S1.8 at C/P=8, 8 fold increasement in transfection is observed. Vectors showed no cytotoxicity, especially for the vector with succinic linker which viability exceeds 100 percent.

It seems that the lower the size of polymer , the more polymer molecules are attached to a specific area of SWNT surface and transfection increases compare to polymer.

1.00E+09 8.00E+08 6.00E+08 4.00E+08 2.00E+08 0.00E+00

PEI25 V25 S25 Ac25 C/P=0.8 C/P=4

C/P=6

C/P=8

Fig3: Transfection results for vector based on PEI 25 kD.

100 80 60 40 20 0

PEI 1800 V1.8 S1.8 Ac1.8 C/P=4

C/P=6

C/P=8

Fig 4: Viability of vectors based on PEI 1800D

100 80

PEI 25

60

V25

40

S25

20

Ac25

0 C/P=4

C/P=6

C/P=8

Fig 5: Viability of vectors based on PEI 10KD

References [1] Iijima,S.;Ichihashi,T., Nature(London), 363( 1993),603- 605.

[2] EoghanP.Dillon,ChristopherA. Crouse, and Andrew R.Barron,s ,Acs Nano,2 (2008), 156-164.

[3] KeWua,CraigA.Meyers, Brain Research 1008 (2004) 284â&#x20AC;&#x201C;287.

100 80

PEI 25

60

V25

40

Figures

S25

20 3.00E+07

PEI1800

2.00E+07

Ac25

0 C/P=4

C/P=6

C/P=8

V1.8

1.00E+07

S1.8

0.00E+00

Ac1.8 C/P=4

C/P=6

C/P=8

Fig6: Viability of vectors based on PEI 25 kD

40 30 20

Fig1:Transfection results for vector based on PEI1800 D.

10 3.00E+07 PEI10 2.00E+07

V10

1.00E+07

S10

0.00E+00

Ac10 C/P=4

C/P=6

C/P=8

Fig2:Transfection results for vector based on PEI 10 kD.

0

Size(nm) Zeta Potential Fig7:Size(nm) and Zeta potential

300 250 200 150 100 50 0

Solvent-induced Delamination of a Multifunctional Two Dimensional Coordination Polymer Cristina Hermosaa, Almudena Gallegoa, Oscar Castillob, Isadora Berlangaa, Carlos Gómezc, Eva Mateod, José I. Martíneze , Fernando Florese, Andrew Houltonf, Benjamin R. Horrocksf, Cristina GómezNavarrog, Julio Gómez-Herrerog, Salome Delgadoa,and Félix Zamoraa a

Departamento de Química Inorgánica, Universidad Autónoma de Madrid, E-28049 Madrid, Spain, Departamento de Química Inorgánica, Universidad del País Vasco, E–48080 Bilbao, Spain, cInstituto de Ciencia Molecular, Parque Científico de la Universidad de Valencia, E-46980 Paterna, Valencia, Spain, dCentro de Astrobiología (CSIC-INTA), Madrid, Spain, eDepartamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain, fSchool of Chemistry, Newcastle University, NE1 7RU, Newcastle, United Kingdom, gDepartamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain. cristina.hermosa@uam.es b

Abstract Low dimensional carbon structures have attracted great attention in the last years due to their amazing properties and low dimensionality [1]. However, while many of the extraordinary properties of these carbon-based materials are due to its restricted chemistry and structural simplicity, in many cases this is not an advantage but a limitation. For applications where more complex structures are required alternative materials are mandatory.

Thus, a new revolution can be envisioned in materials science by extending this successful dimensional variability of carbon allotropes to other compounds with higher structural capabilities and a broad panel of properties. A good example of this tendency can be coordination polymers (CPs), and their subclass metal-organic frameworks (MOFs) [2]. CP can be defined by an organometallic polymer structure containing metal cation centers linked by ligands. Although little has been done so far regarding 2D forms of CP [3], up to now most works reported ultrasound assisted exfoliation of laminar 3D materials (top-down approach) or vacuum deposition of organic molecules on metal ions to generate MOFs (bottom-up approach). However, chemical or solvent exfoliation (without the use of other external forces) of 3D-layered materials is very little described.

In this work, solvent-assisted delamination of multifunctional 2D MOF [Cu(µ-pym2S2)(µ-Cl)]n·X (X = MeOH or H2O) is reported. Molecular thick layer of this compound with large lateral sizes and good structural integrity are isolated just by immersion of the laminar crystals in water. We determine that this unprecedented behavior is a direct consequence of its structure, characterized by interlayer cavities that can be filled by different solvent molecules producing delamination in a simple and reproducible way.

DFT calculations confirm the tendency of the solvents to induce delamination of the compound.

We have evaluated the macroscopic effect of the solvent on the monocrystals by means of Scanning Electron Microscopy (SEM) and the material incorporated to the suspension as a function of time by Atomic Force Microscopy (AFM). According to AFM and XPS data, the isolated layers reach an atomic thickness and structure consistent with the starting bulk material, confirming structural integrity.

We have been able to measure optical properties of the isolated single/few-layers. The electrical characterization of the single layers is currently under evaluation. Preliminary experiments carried out

by EFM on layers adsorbed on SiO2 suggest electrical conductivity.

Therefore we conclude that multifunctional laminar coordination polymers with suitable structurally design can be considered as a source of multifunctional 2D-materials with high potential applications alternatives to graphene.

References [1] Geim, A. K.; Novoselov, K. S. Nature Materials,6 (2007) 183.

[2] Carne, A.; Carbonell, C.; Imaz, I.; Maspoch, D. Chemical Society Reviews, 40 (2011) 291.

[3] Amo-Ochoa, P.; Welte, L.; González-Prieto, R.; Sanz Miguel, P. J; Gómez-García, C. J.; Delgado, S.; Gómez-Herrero, J.; Zamora, F.; Chemical Communications, 19 (2010) 3262.

Figures

(1) (2)

(1) (2)

CH3OH H2 O

6,195Å 5.903Å

(b)

Figure1. Compounds [Cu(µ-pym2S2)(µ-Cl)]n·X (X ≡ MeOH or H2O) are isostructural (a) A fragment of the crystal structure. (b) Perpendicular view of the sheets and (c) side view showing pile up of two sheets.

Figure 2. Scanning electron microscopy micrographies of the time evolution of crystals immersed in water. The image of the crystal surface before immersion is characterized by a flat surface. After 1 h in water, the crystal surface shows a significant evolution characterized by formation of a rough crystal surface with scale-like structures on the surface. (b)

3.5 Z[nm]

(a)

2

0 0

600

X[nm]

Z[nm]

2

0 0

X[µm]

2

Figure 3. AFM topographies and heights profiles obtained upon drop-casting adsorption on (a) mica and (b) HOPG of the suspensions formed by treatment crystals with water at 4 days.

Z[nm]

3

0

0

X[µm]

3

Figure 4. Fluorescence image of isolated flakes on SiO2 and AFM topography of one of these with its height profile.

Single wall carbon nanotubes as highly sensitive nano-electromechanical hybrid systems: driving, braking, detection D. Schmid, P. Stiller, C. Strunk, and Andreas K. Hüttel Institute for Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany andreas.huettel@ur.de

Abstract Single wall carbon nanotubes are not only excellent electrical conductors or semiconductors. Edges with dangling bonds, which could lead to unpredictable electronic behaviour, are intrinsically absent because of the closed tube structure. The nanotubes can be grown defect-free at considerable lengths, and are chemically stable. Additionally, the bonds of the carbon lattice cause large mechanical stability, with a Young's modulus significantly exceeding that of stainless steel.

Recent research has shown the mechanical quality factor of a suspended carbon nanotube nano5 electromechanical resonator to rise above Q~10 at cryogenic temperatures [1]. At these high values, mechanical motion can be excited by minute driving forces. At the same time, the electronically nonlinear behaviour of the quantum dot forming inside the carbon nanotube enables detection of the mechanical motion.

With this, we present a rich system where single-electron tunneling directly couples to and influences mechanical motion [2,3]. A dc current alone is sufficient to excite vibration via feedback effects [2-4]. In turn, the mechanical vibrations can be suppressed with a magnetic field [4] by means of eddy current dissipation. The interaction between mechanical and electronic system can be directly used for sensing applications; the quantum dot provides a clean few-carrier system. As a perspective, future experiments may show a carbon nanotube as a system mesoscopic or quantum mechanically coherent in both electronic and mechanical aspects.

References [1] A. K. Hüttel, G. A. Steele, B. Witkamp, M. Poot, L. P. Kouwenhoven, and H. S. J. van der Zant, “Carbon nanotubes as ultra-high quality factor mechanical resonators”, Nano Letters 9 (2009), 2547.

[2] G. A. Steele, A. K. Hüttel, B. Witkamp, M. Poot, H. B. Meerwaldt, L. P. Kouwenhoven, and H. S. J. van der Zant, “Strong coupling between single-electron tunneling and nanomechanical motion”, Science 325 (2009), 1103.

[3] A. K. Hüttel, H. B. Meerwaldt, G. A. Steele, M. Poot, B. Witkamp, L. P. Kouwenhoven, and H. S. J. van der Zant, “Single electron tunneling through high-Q single-wall carbon nanotube NEMS resonators”, physica status solidi (b) 247 (2010), 2974.

[4] D. R. Schmid, P. L. Stiller, Ch. Strunk, and A. K. Hüttel, “Magnetic damping of a carbon nanotube NEMS resonator”, New Journal of Physics (accepted), arXiv:1203.2319 (2012).

Figures

(a) Scanning electron micrograph of a suspended, ultra-clean carbon nanotube lying across a trench between metallic contacts. (b) Abrupt switching effects in the differential conductance of the embedded quantum dot, caused by mechanical feedback. (c) Electromechanical damping in an externally applied magnetic field.

Growth of high yield metallic-free horizontally aligned single wall carbon nanotubes nucleated from fullerene

1,2

Imad Ibrahim,

1 2

1

1

1

Alicja Bachmatiuk, Bernd B체chner, Mark H. R체mmeli, Gianaurelio Cuniberti

2

IFW Dresden, P.O. Box 270116, 01171 Dresden, Germany Technische Universit채t Dresden, D-01062, Dresden, Germany imad.ibrahim@ifw-dresden.de

Abstract Since the pioneering work in 1991 by Iijima,[1] single wall carbon nanotubes (SWCNTs) have attracted widespread attention.[2,3,4] Their exceptional electrical and physical properties motivate intense research in order to integrate them in to different applications.[5] Typical applications include, field effect transistors,[6] thin film transistors,[7] logic circuits,[8] and bio, environmental and medical sensors.[9] Horizontally aligned SWCNTs, where spatial position, orientation, yield are controlled, are essential for large-scale electronics.[10, 11] Different methods, such as laser ablation and arc-discharge can be used to grow SWCNTs which can be aligned post-synthesis using different techniques.[12] However, such routes provide short and defective aligned SWCNTs. In the contrast, chemical vapor deposition (CVD) can be used to grow long, defect-free and clean horizontally aligned SWCNTs in a single step,[13] in addition to its simplicity and up-scalability.[14] Accordingly, CVD has become the most promising and common method for growing aligned SWCNTs on different substrates over a wide range of growth parameters.[15,16] Nevertheless, there are still challenges that should be overcome prior to integrating horizontally aligned SWCNTs in nanoelectronic applications, including the growth of tubes with a homogenous diameter, chirality and electrical properties. Growth of metallic-free horizontally aligned SWCNTs is also advantageous due to avoidance of metal diffusion into the chip which can lead to device degradation. Metal-free SWCNTs were grown on scratched or treated quartz and silicon substrates nucleated from SiO2 nanoparticles,[17] Al2O3 and TiO2.[18]. More recently, growth of catalyst-free SWCNTs was demonstrated. Cloning short carbon nanotubes working as seeds in CVD reaction is an example.[19] It is shown also that functionalized open caps fabricated from fullerenebased structures may nucleate the carbon nanotube growth.[20] In this study, we grow metallic-catalyst-free horizontally aligned SWCNTs nucleated by functionalized hemispherical caps prepared from different fullerene-based structures. Pristine fullerene (C60) were dispersed in different solvents; including, toluene, acetone, ethanol and methanol, and sonicated over night to ensure better dispersion. Drops of fullerene solvents were loaded to stable temperature (ST-) cut single crystal quartz substrates. The ST-cut quartz substrates were subjected to thermally annealed prior the CVD in order to have very smooth surface, which has been shown to enhance the yield of the later grown tubes.[11] The loaded substrates were treated under different conditions resulting functionalized hemispherical opened-caps, followed by the CVD reaction using ethanol as the carbon precursor.

The yield of the grown tubes is tuned and enhanced by changing the thermal pre-treatment temperature, period and environment for the fullerene structure prior the CVD reaction. We found that an optimized thermal treatment period leads to higher yields, indicating that such pre-treatment produces higher numbers of hemispherical caps appropriate for tube nucleation. Moreover, treating the fullerene structures in low oxygen environments (e.g argon) increases the tube yield. In figure 1.a, one can see the plot of the CNTs yield variation based on the thermal treatment period. It is shown in the plot that the yield goes through a maximum with thermal period of 75 minutes; farther treatment decreases the achieved yield due to excess destruction of the fullerene clusters. The environment in which the thermal treatment is performed is another important factor which strongly affects the yield of the grown CNTS. Thermal treatment of the fullerene clusters in a low oxygen environment slows down the burning rate leaving more fullerene segments attached to the clusters. Figure 1.b summarizes the effect of this parameter on the as-grown tubes yield. In addition, the choice of solvent in which the fullerenes are dispersed affects the formed fullerene cluster size and possible functionalization, and hence affect the tubes yield. It was found that despite toluene being the best dispersion solvent for fullerenes as compared to other solvents, it gave the lowest yield of grown tubes. While acetone gave the highest yield although it is a bad solvent for fullerene dispersion. This suggests that the choice of solvent affects the size of the formed fullerene cluster, which dramatically increases the effective area where successful nucleation can take place and also determines the possible functional groups which can be attached to the opened fullerene. Characterization of the as-grown tubes with (AFM) shows that an existed tip (cluster) at one end of the tube, as shown in figure 2. Characterization of many such

tubes with AFM allowed us to plot the tubes diameter distribution as well as the corresponding cluster diameter as shown in the insert in figure 2. One can see that the obtained CNTs diameter distribution is quantized in well defined steps. In addition, there is no direct relation between the tube and the cluster diameters. Also, the AFM data suggest that the grown tubes are single wall CNTs, which is also confirmed with Raman spectroscopy. Systematic studies of the fullerene structure after different treatment steps as well as after tubes growth allow us to speculate a nucleation and growth mechanism for such metal-free SWCNTs. References [1] S. Iijima, Nature 354 (1991) 56.

[2] P. Avouris, Acc. Chem. Res. 35 (2002) 1026.

[3] V. N. Popov, Mater. Sci. Eng, R 43 (2004) 61.

[4] Q. Cao, J. A. Rogers, Adv. Mater. 21 (2009) 29.

[5] R. Saito, G. Dresselhaus, M. S. Dresselhaus, Physical properties of carbon nanotubes. Imperial College press: London, 1998 [6] S. J. Tans, A. R. M. Verschueren, C. Dekker, Nature 393 (1998) 49.

[7] S. J. Kang, C. Kocabas, T. Ozel, M. Shim, N. Pimparkar, M. A. Alam, S. V. Rotkin, J. A. Rogers, Nature nanotechnol. 2 (2007) 230.

[8] Z. Chen, J. Appenzeller, Y. M. Lin, J. Sippel-Oakley, A. G. Rinzler, J. Tang, et al, Science 311 (2006) 1735.

[9] M. Briman, E. Artukovic, L. Zhang, D. Chia, L. Goodglick, G. Gruner, Small 3 (2007) 758.

[10] N. Ishigami, H. Ago, K. Imamoto, M. Tsuji, K. Iakoubovskii, et al, J. Am. Chem. Soc. 130 (2008) 9918.

[11] I. Ibrahim, A. Bachmatiuk, F. Börrnert, J. Blüher, S. Zhang, et al, Carbon 49 (2011) 5029.

[12] R. Krupke, S. Linden, M. Rapp, F. Hennrich, Adv. Mater. 18 (2006) 1468.

[13] S. J. Kang, C. Kocabas, T. Ozel, M. Shim, N. Pimparkar, M. A. Alam, S. V. Rotkin, J. A. Rogers, nature nanotech. 2 (2007) 230.

[14] S. Dittmer, J. Svensson, E. E. B. Campbell, Current Applied Physics 4 (2004) 595.

[15] C. Kocabas, S.-H. Hur, A. Gaur, M. A. Meit, M. Shim, J. A. Rogers, Small 1 (2005) 1110.

[16] Z. Jin, H. Chu, J. Wang, J. Hong, W. Tan, Y. Li, Nano Lett. 7 (2007) 2073.

[17] B. Li, X. Cao, X. Huang, G. Lu, Y. Huang, et al, small 5 (2009) 2061.

[18] S. Huang, Q. Cai, J. Chen, Y. Qian, L. Zhang, J. Am. Chem. Soc. 131 (2009) 2094.

[19] Y. Yao, C. Feng, J. Zhang, Z. Liu, Nano Lett. 9 (2009) 1673 [20] I. Ibrahim, A. Bachmatiuk, M. H. Rümmeli, U. Wolff, A. Popov, et al, Phys. Status Solidi B 248 (2011) 2467.

Figures

Figure 1: Grown tubes yield dependency on the thermal treatment a) period b) environment

Figure 2: CNT height distribution of the fullerene-nucleated CNTs, (inset) AFM image for cluster at the end of fullerene-nucleated SWCNT

The Effect of Electrochemical Methods on The Shape of Zinc Oxide Nanostructures 1

1

G. Imamoglu , Y.Sahin , E. Suvaci

2

1

Anadolu University Department of Chemistry, Faculty of Science, Eskisehir, TURKEY

2

Anadolu University Department of Materials Science and Engineering, Eskisehir, TURKEY ggimamoglu@hotmail.com

The ability to control and manipulate the physical and chemical properties of materials has been one of the challenging issues for chemistry and materials researchers. These properties are strongly related to two crucial geometrical parameters: size and shape. Now, chemists are exploring many ways to obtain such control at the nanometer scale. Various shapes of materials have been synthesized, such as nanotube, nanorod, nanobelt, nanoplate, and nanoparticles, flower-like pattern, etc. Recently, three-dimensional (3D) superstructures composed of 1D and 2D nanoscale building blocks have been the subject of increasing interest in material synthesis and device fabrication because of their unique collective properties and practice applications [1-3]. Self-assembly process is probably the simplest synthetic route to 3D superstructure[4].

Zinc oxide (ZnO), with a direct band gap of 3.37 eV and almost high exciton binding energy (60 meV) at room temperature, displays excellent piezoelectric, catalysis and new optical properties and has wide range of applications in optical and electronic devices [5,6]. It appeared as a promising semiconductor candidate for chemical sensors [7], field effect transistor (FETs) [8] and ultraviolet light emitting devices [9]. Also, ZnO is employed in solar energy conversion due to its stability against photocorrosion and similar photochemical properties as of TiO2 [10].

ZnO can be easily processed into various nanostructures due to its nature in chemistry. To date, numerous ZnO nanostructures with different sizes and morphologies such as nanowires, nanorods, nanotubes, nanosheets, polypods and nanohedgehogs and nanoflowers have been successfully synthesized through different methods. Recently, ZnO nanoflowers have been used for different applications such as photocatalytic, biomedical , electron emitter, field emission, and solar cells [11].

Zinc oxide (ZnO) has a large application potential owing to the diverse physical properties and the fine-tuning in the preparation process [12]. A variety of physical and chemical methods have been successively employed to fabricate ZnO physical methods like vapor-phase, thermal reduction, pyrolysis, chemical vapor deposition (CVD) and chemical approaches such as precipitation, high temperature hydrotermal synthesis and sol-gel, are very popular among all.

In this work, Zn metal was used as a working electrode in the electrochemical studies.

Different electrolte solutions were tested for polarisation of Zn. Cyclic voltammetry (CV) and voltage controlled coulometry techniques were used as an electrochemical methods. Shape and size of ZnO, nanoflowers and nanopowders, can be easily controlled in our experiment conditions. The effect of applied potentials and tempatures on sizes and morphologies of ZnO nanoparticles have also been investigated. Moreover, anodization of a Zn foil was investigated method for producing various nanostructures of ZnO powder, in air atmosphere. ZnO nanopowders are synthesized with voltage controlled coulometry techniques in temperature controlled cells. Particles are characterized with scanning electron microscopy (SEM) , x-ray diffractometer (XRD).

Acknowledgements The financial support for this study from The Scientific and Technological Research Council of Turkey (TUBITAK) (Project Number: 109M585) and Anadolu University Scientific Research Projects Commission (Project Number : 1101F020) was gratefully acknowledged.

References [1] N. Mira, M. Salavati-Niasaria,, F. Davarc, Preparation of ZnO nanoflowers and Zn glycerolate nanoplates using inorganic precursors via a convenient rout and application in dye sensitized solar cells, Chemical Engineering Journal 181– 182 (2012) 779– 789 [2] J. Zhao, X. Wang, J. Liu, Y. Meng, X. Xu, C.Tang, Controllable growth of zinc oxide nanosheets and sunflower structures by anodization method, Materials Chemistry and Physics 126 (2011) 555–559 [3] J. S. Hu, Y. G. Guo, H. P. Liang, L. J. Wan, and L. Jiang, J. Am. Chem. Soc. 127, 17090 (2005).

[4] G. M. Whitesides and M. Boncheva, Proc. Natl. Acad. Sci. USA 99, 4769 (2002).

[5] S.J. Pearton, D.P. Norton, K. Ip, Y.W. Heo, T. Steiner, Prog. Mater. Sci. 50 (2005) 293.

[6] V.A. Coleman, C. Jagadish, Thin Films and Nanostructures, Elsevier Ltd., 2006, pp. 1–20.

[7] X. Xu, X.W. Sun, Field emission from zinc oxide nanopins, Appl. Phys. Lett. 83 (2003) 3806– 3808.

[8] M.S. Arnold, P. Avouris, Z.W. Pan, Z.L. Wang, Field-effect transistors based on single semiconducting oxide nanobelts, J. Phys. Chem. B 107 (2003) 659–663.

[9] X. Duan, Y. Huang, R. Agarwal, C.M. Lieber, Single-nanowire electrically driven lasers, Nature 421 (2003) 241–245.

[10] A.E. Suliman, Y. Tang, L. Xu, Preparation of ZnO nanoparticles and nanosheets and their application to dye-sensitized solar cells, Sol. Energy Mater. Sol. Cells 91 (2007) 1658–1662.

[11]A. Moezzi, A. M. McDonagh, M. B. Cortie, Zinc oxide particles: Synthesis, properties and applications, Chemical Engineering Journal 185– 186 (2012) 1– 22.

[12] G. Boschloo, T. Edvinsson, A. Hagfeldt, T. Soga (Eds.), Nanostructured Materials for Solar Energy Conversion, Elsevier, 2006, p. 227.

Figure 1. Scanning electron micrographs of ZnO obtained by electrochemical method in diffrerent experimental conditions.

Microwave-induced resistance oscillations and zero-resistance states in 2D bilayer systems 1

2

Jesus IĂąarrea and Gloria Platero Escuela PolitĂŠcnica Superior, Universidad Carlos III, LeganĂŠs, Madrid, 28911,Spain 2 E Instituto de Ciencia de Materiales, CSIC, Cantoblanco, Madrid, 28049, Spain

1

In the last decade it was discovered that when a Hall bar (a 2DES with a uniform and perpendicular magnetic field (B)) is irradiated with microwaves, some unexpected effects are revealed, deserving special attention from the condensed matter community: microwave-induced (MW) resistance oscillations (MIRO) and zero resistance states (ZRS) [1]. These remarkable effects show up at low B and high mobility samples, especially ZRS where ultraclean samples are needed. Different theories have been proposed to explain these striking effects but the physical origin is still being questioned. To shed some light on the physics behind them, a great effort has been made, especially from the experimental side, growing better samples, adding new features and different probes to the basic experimental setup, etc. One of the most interesting setups, carried out recently, consists in using samples with two or three occupied subbands [2]. These samples are either based in a double quantum well structure or just one single but wide quantum well. The main difference in the longitudinal magnetoresistance (Rxx) of a two-subband sample is the presence of magneto-intersubband oscillations (MISO).

In this work, we theoretically study magneto-resistance of a Hall bar being illuminated with MW radiation when two electronic subbands participate in the transport. We apply the theory developed by the authors, the MW-driven electron orbits model [3], which we extend to a twosubband scenario. According to this theory, when a Hall bar is illuminated, the electron orbit centers of the Landau states perform a classical trajectory consisting in a harmonic motion along the direction of the current. Thus, the whole 2DES moves periodically at the MW frequency altering dramatically the scattering conditions and giving rise eventually to MIRO and ZRS. In a double subband scenario the situation gets more complicated but with a richer physics. On the one hand, due to the presence of MW, we have two 2DES (two subbands) moving harmonically at the MW-frequency. On the other hand, we have two possible scattering processes with charged impurities: intra and inter-subband. We then calculate the two corresponding elastic impurity scattering rates, obtaining that the intra one is, approximately, three times larger than the inter-subband. This means first, that the current is mainly supported by intra-subband scattering processes.

Secondly and more important, the competition between intra and inter-subband scattering events under the presence of radiation alters significantly the transport properties of the sample. This is reflected in the magnetoresistance profile through a strong and peculiar interference effect. As in experiments, our calculated results recover the presence of new features regularly spaced through the whole MIRO's profile, mainly two shoulders at minima and narrower peaks (see Fig.). Within the same theory, we have obtained also ZRS in same position of experiments and with the same MW-frequency dependence. Finally, we have studied the influence of MWpower (P) and temperature (T) on MIRO's of the two subband sample and the obtained results are also in reasonable agreement with experimental result.

References [1] R. G. Mani, J. H. Smet, K. von Klitzing, V. Narayanamurti, W. B. Johnson, and V. Umansky, Nature(London), 6, 420, 646 (2002) [2] S. Wiedmann, G.M. Gusev, O.E. Raichev, A.K. Bakarov, and J.C. Portal, Phys. Rev. Lett., 105, 026804, (2010) [3] J. Inarrea and G. Platero, Phys. Rev. Lett. 94, 016806, (2005); J. Inarrea and G. Platero, Phys. Rev. B 72,193414 (2005)

Off-resonance magnetoresistance spike in irradiated ultraclean 2DES Jesus IĂąarrea Escuela PolitĂŠcnica Superior, Universidad Carlos III, LeganĂŠs, Madrid, 28911,Spain When a Hall bar (a 2DES with a uniform and perpendicular magnetic field (B)) is irradiated with microwaves, some unexpected effects are revealed deserving special attention: microwave-induced (MW) resistance oscillations (MIRO) and zero resistance states (ZRS) [1]. These remarkable effects show up at low B and high mobility samples, especially ZRS where very clean samples are needed.

Different theories have been proposed to explain these striking effects but the physical origin is still being under debate. To shed some light on the physical origin, a great effort has been made, especially from the experimental side, growing better samples and adding new features to the basic experimental setup.

Very recently an even more striking experimental result on this field, has been obtained when using ultraclean samples, i.e., samples with extremely high mobilities [2]. These results show a colossal spike in the manetoresistance of the 2DES under MW radiation and weak magnetic field. But the most striking and unexpected feature is that the spike shows up on the second harmonic of the MW frequency, i.e., at w=2wc, where w is the MW frequency and wc is the cyclotron frequency. The large spike was expected to show up at the cyclotron resonance condition, w=w c . To date there has not yet been presented any theoretical approach to try to explain such a surprising effect.

In this work, we theoretically study magnetoresistance of a Hall bar being illuminated with MW radiation when the Hall bar is supported on a ultra-clean GaAs sample. We apply the theory developed by the authors, the MWdriven electron orbits model [3], which we extend to an ultra-clean or high mobility sample.

According to this theory, when a Hall bar is illuminated, the electron orbit centers of the Landau states perform a classical trajectory consisting in a harmonic motion along the direction of the current. Thus, the 2DES moves periodically at the MW frequency altering dramatically the scattering conditions and giving rise eventually to MIRO and ZRS. An ultraclean sample implies that the Landau levels are very narrow or that the quantum life time is very long. This has an important influence in our theory. On the one hand, our theory proposes an acoustic phonon emission (inelastic process) which damps the electron motion. But ultraclean samples give rise to a acoustic phonon emission bottleneck effect. Then, when electrons are damped by the interaction with phonons do not have final states where to get to due to the extremely narrow Landau levels.

This produces the bottleneck effect and the damping decreases giving rise to the colossal spike.

On the other hand, these samples produce an increase in the scattering rate of electrons with charged impurities, (this is an elastic process with mainly supports the current). And it is due to the increase in the final states of the scattering process when Landau levels are very narrow.

The outcome is a smaller transport scattering time that it is perceived by the scattered electrons as a smaller MW frequency. Importantly, the spike is shifted to smaller magnetic fields and MIRO and ZRS are shifted too. According to our theory, in the very high mobility samples used in experiments the shift corresponds to the conditions of w=2wc. In our calculated results we have obtained the spike at the experimental obtained position but also, when the sample is less clean (lower mobility) we obtain MIRO

and ZRS in the older positions [1] (see Fig.). Finally, the calculated results are in reasonable agreement with experiments.

References [1] R. G. Mani et al., Nature(London), 6, 420, 646 (2002) [2] Yanhua Dai et al., Phys. Rev. Lett., 105, 246802, (2011); A.T. Hatke et al., Phys. Rev. B 83, 121301(R), (2011) [3] J. Inarrea and G. Platero, Phys. Rev. Lett. 94, 016806, (2005); J. Inarrea and G. Platero, Phys. Rev. B 72,193414 (2005)

High efficiency electrodes based on nanostructured materials for energy devices Rosalinda Inguanta, Serena Randazzo, Maria Chiara Mistretta, Salvatore Piazza, Carmelo Sunseri UniversitĂ degli studi di Palermo, Dipartimento di Ingegneria Chimica, Gestionale, Informatica, Meccanica, Viale delle Scienze, 90128, Palermo rosalinda.inguanta@unipa.it

Abstract In the last years we have focused our attention on the electrochemical synthesis of nanostructured materials for energy. The synthesis procedure is a typical bottom-up procedure and it is based on the electrodeposition of metals, alloys, pure and mixed oxides inside the pores of nanostructured membranes acting as templates [1-4]. After dissolution of the template, a more or less ordered array (in dependence on the template) of either nanowires or nanotubes is obtained. Their aspect ratio (length/width) can be adjusted by controlling the electric charge passed during the synthesis and high values can be achieved.

Both anodic alumina and polycarbonate membranes are currently used as templates in dependence of the desired morphology. Anodic alumina membranes can be produced by anodizing aluminum in aqueous solutions where the anodic oxide is scarcely soluble. In these conditions, well ordered structures are formed with cylindrical channels perpendicular to the surface and located at the centre of an array of hexagonal cells. The diameter of channel and the size of cell depend on the nature of the anodizing solution, applied voltage and temperature, while the thickness can be changed with the passed electrical charge. Consequently, it should be possible to tailor membranes with morphological features suitable for every specific applications. Track-etch polycarbonate membranes are constituted by circular pores with uniform diameter which are randomly distributed. The smallest pore diameter may -2 reach 5 nm while pore population is about 10(7á11) pores m . In general, the pores show a cigar-like structure and are not perpendicular to the surface.

As regard the morphology of nanostructures its depends on that of template, in particular for the case of anodic alumina membrane, ordered arrays of parallel nanowires are obtained, while interconnected structures are fabricated by polycarbonate templates. In this last case, the advantage consists in a better mechanical stability of the nanostructures, in particular at high aspect ratios. Tubular structures can also be obtained by electrodeposition into the pores of anodic alumina membranes. The tubular structures of nano/microcrystalline materials hold great potential for various applications due to their high porosity, large specific surface-to-volume ratio. For instance, the development of new functional materials with high porosity is required for optimized performances of dye-sensityzed photovoltaic cells, dimensionally stable anodes, metal-ion batteries, electrochemical supercapacitors, hydrogen storage devices, bio-sensors, and gas sensors. In contrast to randomly orienented nanotubes, high density and well-aligned nanotube arrays may provide enhanced and smart functionality.

Different types of materials were fabricated with attention toward those useful for energy applications [512]. For instance, for photovoltaic solar energy conversion, nanowires of CIGS (copper, indium, gallium selenide) were deposited and the procedure for in-situ growth of the p-n junction CIGS/ZnS is currently investigated. For electrochemical storage of energy, SnCo alloy was synthetized and tested as anode of Li-ion batteries, while nanostructures of LiFePO4 were fabricated for application as cathodes. Also Pb and PbO2 nanowires were fabricated for new generation of lead-acid batteries, featured by high utilization degree of active material and a very high charge and discharge rates (up to 10C). In addition, new electrolytes for both Li-ion and lead-acid batteries are under development. Nanostructured materials of interest in the field of water electrolysers were also fabricated and characterized. In particular we have developed nanostructured electrodes, with very large active area, constituted of PdCo alloys (cathode) and RuO2 (anode), to be used for H2 and O2 evolution reaction respectively. In fact, PdCo alloy is a valid alternative to Pt for H2 evolution, whilst ruthenium oxide is one of the most active catalysts for O2 evolution.

Here, we describe the electrochemical deposition of different nanostructures into nanoporous template, leading to regular arrays of either nanowires or nanotubes. In particular the attention will be focused on nanomaterials for batteries (Figure 1). Scanning electron microscopy was used in order to characterize the morphology of the different nanostructures, consisting of perfectly cylindrical wires or tubes, with an having uniform diameter throughout length. Crystallographic structure and chemical composition were also investigated by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy. The influence of different parameters, like temperature, solution composition and pH of solution, on growth and morphology of metal oxide nanostructures was studied, whilst nanostructures length was controlled by the electrodeposition time.

References 1 R. Inguanta, M. Butera, C. Sunseri, S. Piazza, “Fabrication of Metal Nano-Structures Using AAM Grown in Phosphoric Acid Solutions: Tailoring Template Morphology” App. Surf. Sci. 253, 5447 (2007). 2 R. Inguanta, S. Piazza, C. Sunseri, “Influence Of The Electrical Parameters On The Fabrication Of Copper Nanowires Into AAM Templates” App. Surf. Sci. 255, 8816 (2009).

[3] R. Inguanta, G. Ferrara, S Piazza, C. Sunseri “Nanostructures Fabrication by Template Deposition in AAM” Chem. Engin. Trans. 17, 957 (2009).

[4] R. Inguanta, G. Ferrara, S Piazza, C. Sunseri “Fabrication and characterization of metal and metal oxide nanostructures grown by metal displacement deposition into AAM” Chem. Engin. Trans., 24, 199 (2011).

[5] R. Inguanta, S. Piazza, C. Sunseri, “Growth and Characterization of ordered PbO 2 nanowire arrays” J. Electroch. Soc. 155, K205 (2008).

[6] G. Ferrara, R. Inguanta, S. Piazza, C. Sunseri, “Characterization of Sn-Co nanowires grown into AAM template” Electroch. Solid State Lett. 12, K17 (2009).

[7] R. Inguanta, E. Rinaldo, S. Piazza, C. Sunseri, “Lead Nanowires For Microaccumulators Obtained Through Indirect Electrochemical Template Deposition” Electroch. Solid State Lett. 13, K1 (2010).

[8] R. Inguanta, P. Livreri, S. Piazza, C. Sunseri, “Fabrication and Photoelectrochemical Behavior of Ordered CIGS Nanowire Arrays for Application in Solar Cells” Electroch. Solid State Lett. 13, K22 (2010).

[9] G. Ferrara, R. Inguanta, S. Piazza, C. Sunseri, “Electrosynthesis of Sn-Co nanowires in AAM” J. Nanosc. Nanotech. 10, 8328 (2010).

[10] R. Inguanta, F. Vergottini, G. Ferrara, S. Piazza, C. Sunseri, “Effect of temperature on the growth of -PbO2 nanostructures” Electroch. Acta 55, 8556 (2010).

[11] G. Ferrara, L. Damen, C. Arbizzani, R. Inguanta, S. Piazza, C. Sunseri, M. Mastragostino “SnCo Nanowire array as negative electrode for lithium-ion batteries” J. Power Sources 196, 1496 (2011).

[12] R. Inguanta, G. Ferrara, P. Livreri, S. Piazza, C. Sunseri, “Ruthenium Oxide Nanotubes via Template Electrosynthesis” Current Nanoscience 11, 210 (2011).

Figures

Fig. 1 Nanostructured lead dioxide electrode.

Graphene stru tures with ir ular shape: a study of the in uen e of topologi al defe ts in transport properties Esther JĂłdar1, Antonio PĂŠrez Garrido1 and Fernando Rojas1,2 1 2

Dpto. FĂ­si a Apli ada, Antiguo Hospital de Marina, Campus Muralla del Mar. UPCT, Cartagena 30202 Mur ia, Spain.

Departamento de FĂ­si a TeĂłri a, Centro de Nano ien ias y Nanote nologĂ­as. UNAM, Apdo. 356, Ensenada Baja California 22830 MĂŠxi o. esther.jferrandez up t.es

Abstra t We investigate the transport properties of graphene layers with ir ular shapes (quantum dots) and several kind of topologi al defe ts. An example is drawn in the Figure 1, whi h shows a pentagonal defe t. For dynami al relaxation we use a Terso -Brenner potential in order to get their 3D arrangement. We he k that variations in bond lengths are lower than 5%. We al ulate the density of states of these stru tures and he k that it shows several peaks asso iated with quasi-bound states. Other authors have made similar studies but onsidering di erent geometries: Zhang et al. [1, 2] worked on transport with narrow ballisti ribbon of graphene with zigzag edges in luding topologi al defe ts. Carpio et al. [3] studied just ele troni properties in a similar stru ture but with dislo ations onsisting of heptagon pentagon pairs in an hexagon latti e.

In our al ulations we employ a tight-binding model whi h only takes into a ount one Ď&#x20AC; -orbital per atom. The overlap energy between nearest neighbors is taken as t = â&#x2C6;&#x2019;2.66 eV where se ond-neighbor intera tions are negle ted. Intera tions with media sorrounding the graphene layer are not onsidered. We al ulate ele troni properties of our graphene stru tures, as density of states and transmission fun tion using the Green's

Ë&#x2020; Ë&#x2020;L â&#x2C6;&#x2019; ÎŁ Ë&#x2020; R â&#x2C6;&#x2019;1 , fun tion method [4], using the standard expression G(E) = E IË&#x2020; â&#x2C6;&#x2019; HË&#x2020;n â&#x2C6;&#x2019; ÎŁ and the formalism developed by LĂłpez San ho et al. [5]. The latter has the advantage that onverges very fast and has been applied to graphene layers by other authors (see. e. g. [6]). We also al ulate the eigen-energies En and eigen-fun tions Ψn , in order to P obtain the parti ipation number Pn : Pnâ&#x2C6;&#x2019;1 = m |Ψn (m)|4 , whi h gives a measure of the wavefun tion extension and help to nd out the lo alized or extended nature of an ele troni state.

With the formalism developed above we show that density of states shows several peaks asso iated with both the pressen e of quasi-bound states (due to the ir ular on nement) and lo alized edge states due to ir ular boundaries of the nite latti e.

These results are manifested in the peak stru ture in the transmission fun tion and are he ked al ulating the lo al density of states and parti ipation number obtained dire tly from the eigenstates. We observe a hange in the available quasi-bound states due to the defe ts presen e and new peak of the transmission fun tion. *Thanks to DGAPA proje t PAPPIT IN112012 for nan ial support and sabbati al s holarship.

Referen es [1] Yanyang Zhang, Jiang-Ping Hu, B. A. Bernevig, X. R. Wang, X. C. Xie and W. M. Liu, Phys. Rev. B 78 (2008) 155413.

[2] Yan-Yang Zhang, JiangPing Hu, B. A. Bernevig, X. R. Wang, X. C. Xie and W. M. Liu, Phys. Status Solidi A 207 (2010) 2726.

[3] Ana Carpio, Luis L. Bonilla, Fernando de Juan and Mar铆a A. H. Vozmediano, New Journal of Physi s 10 (2008) 053021.

[4] S. Datta Ele troni Transport in Mesos opi Systems (Cambridge University Press, Cambridge 1995).

[5] M. P. L贸pez San ho, J. M. L贸pez San ho and J. Rubio, J. Phys. F: Met. Phys. 14 (1984) 1205.

[6] T. C. Li and Shao-Ping Lu, Phys. Rev. B 77 (2008) 085408.

Figures

Figure 1: Geometry of the graphene sheet studied in this work. Note the pentagonal defe t pla ed at its entre. This stru ture is onne ted to 2 semi-in nite graphene leads, whi h are partially shown in the gure.

The Effect of Vacancy Defects on Electron Scattering in Carbon Nanotubes S.L.T Jones1,2, G. Greene-Diniz1, G. Fagas1, M.G. Haverty3, S. Shankar3, 3 1 C. Martinez-Lacambra , J.C. Greer 1

Electronic Theory Group, Tyndall National Institute, Cork, Ireland Department of Chemistry, University College Cork, Cork, Ireland 3 Intel Corporation, Santa Clara, California, USA sarah.jones@tyndall.ie

2

Abstract There has been much interest in carbon nanotubes (CNTs) in recent years due to their unique physical properties. Their defect free ballistic transport makes them an ideal material for use in nanoelectronic devices [1]. However, due to their low dimensionality introduction of defects can result in dramatic changes in both chemical and physical properties [2]. Because of their quasi-one dimensional structure, charge carriers propagate primarily along the CNT axis and consequently scattering at defects cannot be avoided. A detailed understanding of CNT defects is therefore of critical importance for the wide spread adoption of CNTs in technological applications.

The most widely observed defects in CNTs are mono- and divacancies (defects with one or two atoms respectively missing at the defect site) [3] and consequently these defects are the focus of this work. We consider two configurations for the divacancy defect, the first consisting of an octagon bordered by two pentagons (585) and the second formed by three pentagons and three heptagons (777555). In particular, we consider large diameter CNTs (up to ~4.2 nm) in this work. We use density functional theory (DFT) as implemented by OpenMX [4] to calculate the formation energies for mono(Emono) and divacancy (Elatdivac, Evertdivac, E777555) defects in armchair (AC) and zig-zag (ZZ) CNTs and graphene. We then use TIMES [5] to calculate transport properties (without self-consistency) from DFT electronic structure calculations. Transport results are therefore subject to the same limitations as standard DFT calculations.

For AC and ZZ CNTs, Elatdivac < Evertdivac < 2Emono (i.e. the formation of the lateral divacancy is least unfavourable) consistent with results previously reported for small diameter CNTs [6]. The formation energies for the 585 defects are smaller than for the 777555 defects for the ZZ CNTs studied, while E777555 is smaller than the 585 defect formation energies for the (30,30) AC CNT confirming the estimation from an exploration based on continuum mechanics for this crossover made by Amorim et al [7]. Thus at larger diameters (and hence less curvature) 777555 defects are more easily formed than 585, as is the case in zero-curvature graphene.

In all cases, the introduction of a defect results in decreased transmission relative to the pristine CNT, with the greatest reduction occurring for the 777555 defect (Figure 1). Of particular significance is the drop in transmission to ~0.1G close the Fermi level for the (30,30)-CNT. This large scattering would necessarily have to be considered in applications involving large diameter CNTs, as it is in such case this defect becomes relatively more stable than the 585. We estimate the mean free path () using the independent scattering approximation. As the CNT diameter increases,  increases significantly for fixed defect concentration, this is attributed to the diminishing scattering resistance (which is proportional to the ratio of the defect scattering concentration to the CNT diameter).

References [1] R.H. Baughman, A.A. Zakhidov and W.A. de Heer Science 297 (2002) 787.

[2] L. Valentini, F. Mercuri, I. Armentano, C. Cantalini, S. Picozzi, L. Lozzi, S. Santucci, A. Sgamellotti and J.M. Kenny, Chem Phys. Lett.387 (2004) 356.

[3] A.V. Krashninnikov, K. Norland and J. Keinonen, Phys Rev B 65 (2002) 245403.

[4] http://www.openmx-square.org [5] G. Fagas and J.C. Greer Nano Lett. 9 (2009) 1856.

[6] B. Biel, F.J. Garcia-Vidal, A. Rubio and F. Flores J. Physics-Condensed Mater. 20 (2008) 294214.

[7] R.G. Amorim, A. Fazzio, A. Antonelli, F.D. Novaes, and A.J.R. da Silva Nano Lett. 7 (2007) 2459.

Figures

(i)

(iii)

(ii)

(iv)

Figure 1. Conductance spectra for zigzag semiconducting tubes (graphs (i) and (ii) for (20, 0) and (30, 0) respectively) and armchair metallic tubes (graphs (iii) and (iv)for (20, 20) and (30, 30) respectively). Note the greater amount of scattering for the 555777 configuration of the divacancy defect.

Acknowledgments We acknowledge support of this work from the Irish Research Council for Science Engineering and Technology (IRCSET), Science Foundation Ireland (SFI) and the Irish Centre for High End Computing (ICHEC). This work is partially funded by Intel Corp.

Quantum Effects At Field Emission From Carbon Quasi-1D Cathodes 1

1

1

2

1

1

Kosakovskii G.G. , Gulyaev Yu.V. , Kosakovskaya Z.Ya. , Blagov E.V. , Latyshev Yu.I. , Orlov A.P. , 1 Smolovich A.M. 1 Kotelâ&#x20AC;&#x2122;nikov Institute of Radio Engineering and Electronics of the RAS, Mokhovaya 11-7, Moscow, 125009 Russia 2 Institute of Nanotechnology Microelectronics of the RAS, office 107 32A, Zone "B", Leninsky Prospekt, Moscow, 119991 Russia german_kos@mail.ru

A low threshold voltage and anomalous large currents of field emission from nanotube cathodes was observed by various researchers. Traditionally, current-voltage (I-V) characteristics of field emission of carbon nanocathodes are interpreted by Fowler-Nordheim model.[1-3] It is known that the FowlerNordheim model was developed for 3D-metal cathodes with having the quasi-continuous spectre of electrons , where and are the function of density states (DOS) and the kinetic energy of electrons, respectively. Therefore the Fowler-Nordheim relationship for emission current is continuously rising too on all energy range and grows exponentially.

But carbon nanotube is a quantum wire and a quantum-dimensional effects should be observed in their electron transport. Many various researchers marked a low correlation between data of a field emission from carbon nanotube cathodes and Fowler-Nordheim equation [4-6].This phenomena has not still an explanatory model. In our work the influence of the quantum-dimensional phenomena on field emission from carbon nanotube cathods was studied theoretical and experimental.

It was shown theoretically the full spectrum of electronic states of single wall carbon nanotube (SWNT) includes of the continuous and the discrete parts. The distribution function can be written as

where , m and l are the wave function, the electron mass and length of electronâ&#x20AC;&#x2122;s orbit of nanotube, respectively. The general form of DOS for the continuously part of electron spectra can be written as 3D crystal. The general form of DOS of the discrete part is given as (2) is Fermi energy. The DOS of the quantum electrons contains the Van Hove singularity.. As the electron spectrum is mixed the position of Fermi level will be to determine the domination part of the electron spectrum. The electron density and conductivity of nanotube are increased rapidly near the Van Hove singularity. As the electron spectrum is mixed the position of Fermi level determines the domination part of the electron spectrum ( the continuous or the discrete part). In accordance to (2) and (3) the emission current from nanotube catod doesn't correspond to the Fawler-Nordgeim law and can be written as (3) The electron density and conductivity of nanotube are increased rapidly near the Van Hove singularity.

The change of emission current conforms with the change of nanotube conductivity and the sharp peaks appear on the current-voltage characteristic Result of quantization is also presence of the threshold of the start of field emission on the I-V characteristics.

The I-V characteristics at field emission from quasi-1D carbon cathodes (carbon thin multi-walled nanotubes; vertically aligned carbon nanotube arrays; graphene nanoribbons) were experimentally measured using scanning electron microscope Carl Zeiss NEON 40 (Fig.1). For all types of cathodes the voltage thresholds for the start of electron emission are detected in the field emission I-V characteristics (Fig.2 ). The voltage thresholds are a clearly marked on Fowler-Nordgeim plot (Fig2b).

Also when the magnitude of cathode voltage greater-than the voltage threshold we can see the sharp peaks with a small full width (less 100mV) at half maximum on I-V characteristics. The emission current at peak's maximum was several times as much than it follows from Fowler-Nordgeim relationship. The

appearance of sharp peaks on I-V characteristics are connected with the high electron localization near features of Van Hova in the electron spectrum of carbon nanocathodes.

Possible mechanism of field emission from quasi-1D carbon cathodes will be discussed.

References [1] Forbes R.G., Sol. State Electronics, 45 (2001) 779–808.

[2] Wang X., Lin Z. et al., J. Phys. D: Appl. Phys., 40 (2007) 4775–4778.

[3] Sveningsson M., Morjan R.-E. et. al. Appl. Phys., A73 (2001) 409–418.

[4] D. Lovall et al., Phys. Rev. B, 61(8) (2000) 5683 [5] M.J. Fransen, Th.L. van Rooy, P., Kruit., Applied Surface Science, 146 (1999) 312–327 [6] Stetsenko B.V., Shchurenko A.I. Problems of Atomic Sci.and Techn., 1, Plasma Physics.(2009)136

Figures

1

2

Fig.1. SEM image of the experimental setup for field emission: (1) is single multi-walled nanotube with 14 nm diameter and length 1,5 mkm; (2) is tungsten anode .

Fig.2. Field-emission current vs voltage curve from single multi-walled carbon nanotubes(a) and Fowler–Nordeim plot (b).

Modified graphene and graphite oxide dispersions in petroleum fractions.

Wojciech Krasodomski, Michał Krasodomski, Michał Wojtasik, Kamil Pomykała Oil and Gas Institute, Lubicz 25A, Cracow, Poland wojciech.krasodomski@inig.pl Abstract This presentation exhibits results of research on the synthesis of modified structure graphite oxide (GO) and graphene, and their tendency to form dispersions in hydrocarbon fractions represented by diesel oil fraction and base oil SN 400. GO was obtained by modified method described by Hummer [1]. Graphite oxide consists of covalently attached oxygen-containing groups such as hydroxyl, epoxy (oxirane), carbonyl and carboxyl groups.

Scheme 1 The presence of these functional groups makes GO susceptible to various chemical modifications.

Organophilic graphite oxide and graphene nanosheets dispersions were prepared by multistep process according scheme 1. The used reagents and obtained structures were depicted in table below.

Graphite oxide functional group -COOH -COOH -COOH

Reaction with SOCl2 + + -

Modified GO structure formed in reaction with SOCl2 GO-COCl GO-COCl -

Reagent X R-NH2 R-ONa propylene oxide

Modified GO/graphene structure formed in reaction with reagent X GO-CONH2R GO-COOR GO-COO(CH(CH3)-CH2O)nH

C-OH C-OH C-OH C-OH C-OH

+ + -

GO-Cl GO-Cl -

R-NH2 R-ONa R-NCO (R-CO)2O propylene oxide

GO-NH-R GO-O-R GO-NH-COR GO-OOC-R GO-O-(CH(CH3)-CH2O)nH

oxirane oxirane

-

-

R-ONa R-NH2

GO-C(OR)-C(OH)-GO GO-C(NHR)-C(OH)-GO

The organophilic graphite oxide based products were characterized by FTIR spectroscopy.

Obtained dispersions properties were characterized by the Zeta Sizer, the Turbiscan measurements.

The dispersions of nanomaterials in diesel oil were hard to obtain, and their stability was poor.

In the dispersion of modified graphene oxide in the diesel oil in most cases during reduction a significant decreasing the number and size of dispersed particles were observed. Dispersions in lubricant base oil SN 400 are more stable. During the reduction is not observed a significant decrease the number and size of suspended particles.

References [1] W.S. Hummers, R.E. Offeman, J. Am. Chem. Soc. 80 (1958) 1339.

Figures Scheme 1

The features of carrier transport in the ferromagnetic semiconductor quantum well structures 1,2

1

1,2

2

1

A. Kudrin , O. Vikhrova , Yu. Danilov , I. Kalentieva , B. Zvonkov

1. Physico-Technical Research Institute of University of Nizhny Novgorod, Nizhny Novgorod, Russia 2. Department of Physics of University of Nizhny Novgorod, Nizhny Novgorod, Russia kudrin@nifti.unn.ru The Mn delta-doped GaAs layers are the subject of intensive studying by a number of research groups involved in the development of semiconductor spintronic devices [1-2]. One of the interesting areas of their application is a light-emitting diode, which produces circularly polarized light. In [3,4] it has been shown to us that Mn delta-doped GaAs layer itself possesses ferromagnetic properties.

In GaAs structures only with single Mn delta-doped layer ferromagnetic properties were revealed by carrier transport investigations [3,4]. Galvanomagnetic measurements at low temperatures showed the presence of anomalous, planar Hall effect, anisotropic and negative magnetoresistance, that evidence about a ferromagnetism. In this paper we present the investigation of the peculiarity of the carrier transport in GaAs structures containing InGaAs quantum well in addition to Mn delta-doped layer.

The structures were grown by the combined method of metal-organic chemical vapor deposition and pulse laser sputtering. Firstly a set of undoped layers was grown on i-GaAs (001) substrate by vapor-phase epitaxy at 600°С: 0.25 μm buffer GaAs layer, 10 nm thick InхGa1-хAs quantum well and 3 nm GaAs spacer layer. Then 0.2 monolayer thick Mn delta-doped layer and 20 nm thick GaAs cap layer were deposited at 400°C using laser sputtering of metallic Mn and undoped GaAs targets, respectively.

The In content was varied in range from x = 0.1 to 0.3 for different structures. Also the reference structure only with a single Mn delta-doped layer was fabricated.

The structure only with a single Mn delta-doped layer demonstrates at 10 K nonlinear Hall resistance dependence on magnetic field (RH(H)) with hysteresis loop (coercive field ≈ 90 Oe) and saturation at magnetic field about 2000 Oe (Fig 1, dependence 1). This indicates the presence of clear ferromagnetic properties and domination of anomalous Hall effect in RH(H) dependences.

The structures with a quantum well beside Mn delta-layer demonstrate at 10 K differ character of the Hall resistance dependence. The shape of the RH(H) curves depends on indium content in InGaAs layer and consequently on the energy depth of a quantum well (Fig 1). With increasing In content the contribution from normal Hall effect increase. For the structure with the most deep quantum well the RH(H) dependence is linear, consequently, it determines by normal Hall effect (Fig 1, dependence 3). Is it indicates about the absence or weakening of ferromagnetic properties? In our opinion ferromagnetic properties of structures with Mn delta-doped layer have no direct relation to presence of InGaAs quantum well and its depth and related to intrinsic ferromagnetism of a Mn deltalayer. The insertion of a quantum well leads to appearance of an additional conducting channel for free charge carriers (holes). The distribution of charge carriers in a structure depends on quantum well depth. Fig. 2 shows calculated band diagrams and carrier distribution at 77 K for the structure only with single Mn delta-layer (Fig 2a) and for the structures with Mn delta-layer and deep quantum well (Fig 2b).

For the structure only with single Mn delta-layer all carriers are localized in the ferromagnetic region of delta-doped layer (Fig 2a) and only these carriers determine the transport properties of the structure. In contrast to this case, for the structure with deep quantum well (with In content is 0.3, Fig. 2b) the most part of free carriers is localized in the region of quantum well. Inasmuch as mobility of carriers localized in deep InGaAs quantum well at low temperatures is high, these carriers determine the transport properties of the structure. At the same time the carriers localized in region of Mn layer can determine the ferromagnetic properties of the structure. As the transport of carriers localized in InGaAs quantum well leads to predominance of the normal Hall effect, the question about the degree of spin polarization of these carriers still remains open.

The work was supported by the Grant of President of Russian Federation (МК-5198.2012.2) and Grant of Russian Foundation for Basic Research (RFBR-11-02-00645а).

[1] A.M. Nazmul, T. Amemiya, Y. Shuto, S. Sugahara, M. Tanaka, Phys. Rev. B., 95 (2005), pp.

017201-1-4.

[2] S.V. Zaitsev, V.D. Kulakovskii, M.V. Dorokhin, Yu.A. Danilov, P.B. Demina, M.V. Sapozhnikov, O.V. Vikhrova, B.N. Zvonkov, Physica E., 41 (2009), pp. 652-654.

[3] O.V. Vikhrova, Yu. A. Danilov, M.V. Dorokhin, B.N. Zvonkov, I.L. Kalent’eva, A.V. Kudrin, Tech.

Phys. Lett., 35 (2009), pp.643-646.

4. A.V. Kudrin, O.V. Vikhrova, Yu.A. Danilov, Tech. Phys. Lett., 36 (2010), pp.511-513.

3

200

2

RH, Ohm

100

1 0

-100

-200 -4000

-2000

0

2000

4000

H, Oe Fig. 1. Magnetic field dependences of Hall resistance at 10 K. 1 - The structure without InGaAs quantum well, 2 - The structure with InGaAs quantum well (In content is 0.15), 3 - The structure with InGaAs quantum well (In content is 0.3).

19

1,5x10

18

5,0x10

EV

20 30 d, nm

40

0,0

GaAs

In0.3Ga0.7As

GaAs

19

1,5x10

0,0

1,0x10

EV

-3

19

b

p, cm

-3

1,0

E, eV

E, eV

a

10

EC

1,2 19

1,0x10

p, cm

1,4

0,0

1,4

EC

18

5,0x10

-0,2 10

20

30

40

0,0

d, nm

Fig. 2. Calculated band diagrams and carrier distribution at 77 K. a - The structure without InGaAs quantum well, b - The structure with deep InGaAs quantum well (In content is 0.3).

Molecular modeling of aromatic interactions between pyrene derivatives and carbon nanotubes 1

Isabel Lado Touriño,

2,3

3

2

Viviana Negri, Sebastián Cerdán and Paloma Ballesteros 1

1

Department of Mechanics and Materials Universidad Europea de Madrid, C) Tajo s/n, 28670 Villaviciosa de Odón, Spain misabel.lado@uem.es 2 Laboratory of Organic Synthesis and Molecular Imaging by Magnetic Resonance, Faculty of Sciences, UNED, 28040-Madrid, Spain, 3 LIERM, Institute of Biomedical Research “Alberto Sols”, CSIC, 28029-Madrid, Spain,

Abstract Magnetic Resonance Imaging (MRI) is the most useful method for clinical diagnosis. Effectiveness of diagnosis by MRI is joined to the design of new MR sequences as well as the development of new 1 Contrast Agents (CAs) increasing the quality, resolution and specificity of the MR images. In a previous work we have used paramagnetic carbon nanotubes and diffusion weighted MR imaging methods to 2 investigate the preferred direction of blood flow. To increase solubility and paramagnetic character of MWNTs we have designed and synthesized a new generation of CAs based on labeled Gd(III) MWNTs through π−π stacking interactions with pyrene derivatives. Here, we present the results obtained from a theoretical study of the interactions between (6, 6) armchair nanotubes and several pyrene derivatives.

We have placed pyrene, aminopyrene and nitropyrene molecules in different orientations over a (6, 6) 3 CNT surface (see figure 1) and performed DFT calculations to get a good understanding of the noncovalent functionalization of the outer surface of carbon nanotubes by these molecules. The analysis of the calculated binding energies, electrostatic potential surfaces (figure 2) and Mulliken charges can help us to shed some light on the way these aromatic systems interact.

References [1] Meerbach, A. E.; Toth, E. Eds. In the chemistry of contrast agents in medical magnetic resonance imaging. John Wiley & Sons, Ltd., Chichester, 2001.

[2] Negri, V., Cerpa, A.; López-Larrubia, P.; Nieto-Charques, L.; Cerdán, S.; Ballesteros, P.., Angewandte Chemie Int. Ed. 49 (2010) 1813-1815.

[3] Parr, Robert G; Yang, Weitao, Density-Functional Theory of Atoms and Molecules. Oxford: Oxford University Press (1994).

Figure 1. Parallel and perpendicular orientations of aminopyrene and nitropyrene relative to a (6, 6) CNT surface.

Figure 2. Electrostatic potential surfaces of isolated (a) and interacting (b) molecules. Blue colour indicates positive charge regions. Red colour indicates negative charge regions. Level contour: 0.009 kJ/mol.

Mesoporous Silica Nanoparticles (MSNs) as MRI/PET Dual-Modality Imaging Probes 1,2,3,4* 1,2,3,4 1,2,3,4 3,4** Myriam Laprise-Pelletier , Jean-Luc Bridot , Rémy Guillet-Nicolas , Freddy Kleitz ,Marc1,2,4** André Fortin 1 Centre Hospitalier Universitaire de Québec Axe Métabolisme, Santé Vasculaire et Rénale (AMSVR-CHUQ) 2 Department of Mining, Metallurgy and Materials Engineering, Université Laval, 3 Department of Chemistry, Université Laval 4 Centre de Recherche sur les Matériaux Avancés (CERMA), Université Laval, Canada, G1V 0A6 * M.Sc.Student:myriam.laprise-pelletier.1@ulaval.ca,**Professors: Marc-Andre.Fortin@gmn.ulaval.ca, Freddy.Kleitz@chm.ulaval.ca INTRODUCTION: Gadolinium-based nanoparticles have been developed as ‘positive-T1’ contrast agents for magnetic resonance imaging (MRI) procedures. Paramagnetic elements, such as gadolinium, decrease the 1 relaxation time of H protons in biological tissues, inducing signal enhancement in MRI. The main advantage of MRI over other biomedical imaging modalities, is the possibility to perform whole-body anatomical resolution imaging, and the achievement of high contrast effects in low density tissues.

However, high Gd concentrations are needed in order to reach MRI cell tracking detection thresholds, about a factor of 1000 compared with radioisotope concentrations needed to perform nuclear imaging scans (e.g. with positron emission tomography, PET). Mesoporous silica nanoparticles (MSNs) are promising materials currently being developed as cell labels and for drug delivery applications [1]. Labeling MSNs with paramagnetic chelates and radioactive isotopes would enable the detection with both MRI and PET, of small amounts of labeled cells and particles delivered for therapeutic use. This would provide an efficient way to quantify the local amount of MSN delivered in vivo, a very important biological data in the perspective of establishing quantitative diagnostic and/or therapy with drug eluting MSNs. The development 64 of such particles require an adequate labeling with Gd and Cu, followed by a rapid purification step to get rid of unreacted metal salts that could be potentially toxic to cells and to biological tissues.

MATERIALS AND METHODS: In this work, MSNs were functionalized with DTPA, a chelator of both Gd 64 and Cu that is efficiently excreted by the kidneys upon detachment from nanoparticles. Dialysis, the most common method for purifying magnetic nanoparticles, is long and therefore not suited in the case of fast radioactive decays. It also produces large amounts of radioactive aqueous waste. Because the half-life of 64 Cu is very short (12.7 h), size exclusion chromatography (SEC) [2] was used as a rapid purification method to clear-off excess of Gd and Cu. One (1mL) samples of labeled MSNs were chromatographied on a G-25 Sephadex-filled column. The total elution volume was 200 ml and fractions of 500 µl were collected 1 1 and analyzed by H-NMR (Figure 1). H-NMR (Bruker minispec 60mq) is commonly used for measuring the longitudinal and transversal (T1, T2) relaxation times of MRI contrast agents, which is a direct indication of Gd concentration (high Gd concentrations results in short T2 in Figure 1). Finally, purified particles were imaged with transmission emission microscopy (TEM) and their hydrodynamic size measured with dynamic light scattering (DLS). MRI was also used in order to quantify the contrast enhancement properties of the purified colloidal suspensions.

RESULTS: MSNs were successfully and efficiently eluted in 35 minutes by SEC (Figure 1). The eluted particles extracted from the Gd:MSNs elution peak (Figure 1, left in the graph) and visualised in TEM, had a mean diameter in the range (150-200 nm; Figure 2 a,b). The hydrodynamic diameter of the colloids was 230 nm ± 83 (Figure 2.c). Relaxivities (r1 and r2) were extracted from T1 and T2 values, and provided a r2/r1 ratio corresponding to 2.14. This value, as well as T1-weighted MRI images of the solutions (Figure 1.b), confirmed the behavior of these particles as “positive” contrast agents. As expected from the theory of signal enhancement in spin echo MRI sequences, the most concentrated suspensions demonstrated signal inflexion. This is a satisfactory indication in the perspective of using these particles only in dilute concentrations.

CONCLUSION: Gd-DTPA-labeled MSNs are efficient “positive” MRI contrast agents. They can be rapidly and efficiently purified by SEC, which is crucial for the labeling of MSNs with short-lived radioactive metals 64 (e.g Cu) used in PET/MRI procedures for molecular and cellular imaging.

References [1] Guillet-Nicolas, R.; Bridot, J.-L.; Seo, Y.; Fortin, M.-A.; Kleitz, F. Advanced Functional Materials, 21 (2011) 4653-4662.

[2] Hagel, L. Protein Purification: Principles, High Resolution Methods, and Applications, John Wiley and Sons, Inc., Hoboken, (2011) 51-91.

Figures

a)

b)

Figure 1: a) SEC profile: transverse relaxation times (T2) measured on 500 µl-fractions of eluted Gd-labeled MSNs nanoparticle suspensions used in MRI studies. Short T2s reflect the strong presence of Gd in the collected fractions. The first peak correspond to Gd-labeled MSNs shown in Figure 2, and the right part of 3+ the graph, to residual Gd ions. b) T1-weighted MR images of MSNs, measured with a 1 T small-animal MRI system (M2M, Aspect Imaging; matrix: 256x256; repetition time 600 ms ; echo time:11.6 ms; dwell time:16 ; slice thickness:1.9 mm; interslice: 0.1 mm; field of view: 70 mm; 3 excitations; T = 25°C).

Figure 2: a,b) TEM images of purified MSNs and c) DLS b) 40 kX and c) DLS profiles for the same material, in 150 mM NaCl nanopure water.

Thin Films of Polyelectrolytes with Adsorbed Gold Nanoparticles.

1

2

1

Angel Leiva , Marcela Urzúa , Maximiliano Pino and Deodato Radic´

1

1

Departamento de Química Física, Facultad de Química. Pontificia Universidad Católica de Chile, Casilla 302, correo 22. Santiago, Chile. Phone: (56)-2-6864041 Fax: (56)-2-6864744.

2 Departamento de Química, Facultad de Ciencias, Universidad de Chile, Santiago, Chile. aleivac@uc.cl

Abstract Nanocomposed films constituted by gold nanoparticles immobilized onto polyelectrolytes were obtained and studied. To obtain the films, polyelectrolytes derived from Poly (maleic anhydride-alt-styrene) containing in the side chains aryl and amine-alkyl groups were adsorbed onto amino terminated silicon wafer surfaces. The effects of the chemical nature of the side chains and ionic strength on the amounts of adsorbed polyelectrolytes were studied by ellipsometry [1]. The adsorption of polyelectrolytes increases with increasing ionic strength in agreement with the screening-enhanced adsorption regime; the results are discussed considering the steric hindrance of the side chains and flexibility of the polymers [2].

A spontaneous adsorption process of nanoparticles onto polyelectrolyte films took place when these last were immersed in a gold nanoparticles suspension [3,4]. The adsorption was qualitatively evaluated by SEM and AFM and showed dependence on chemical structure of polyelectrolytes. Figure shows an image of the adsorbed nanoparticles and the size distribution obtained by transmission electron microscopy (TEM) and dynamic light scattering (DLS) respectively.

References [1] M.D. Urzúa, X.G.Briones, L.P.Carrasco, M.V. Encinas, and D.F.S. Petri, Polymer 51 (2010) 3445.

[2] X. G. Briones, M. V. Encinas, D. F. S. Petri, J. E. Pavez, R. A. Tapia, M. Y. Pedram, and M. D. Urzúa. Langmuir 27 (2011) 13524.

[3] A. Leiva, C. Saldías, C. Quezada, A. Toro-Labbé, F.J. Espinoza-Beltrán, M. Urzúa, L. Gargallo, D. Radic, European Polymer Journal 45 (2009) 3035.

[4] C. Saldías, A. Leiva, C. Quezada, P. Jaque, L. Gargallo, D. Radic, European Polymer Journal 47 (2011) 1866.

The authors acknowledge Fondecyt projects 1120119 and 1100240 by partial financing of research

Figure 1.

TEM image and size distribution of gold nanoparticles

Shell structures in aluminum nanocontacts at elevated temperatures José Luis Costa-Krämer, Natalia León, Carlo Guerrero y Marisel Díaz Departamento de Mecánica, Universidad Simón Bolívar, Caracas, Venezuela nleon@usb.ve Abstract Aluminum nanocontact conductance histograms are studied experimentally from room temperature up to near the bulk melting point. The dominant stable configurations for this metal show a very early crossover from shell structures at low wire diameters to ionic subshell structures at larger diameters. At these larger radii, the favorable structures are temperature-independent and consistent with those expected for ionic subshell (faceted) formations in face-centered cubic geometries. When approaching the bulk melting temperature, these local stability structures become less pronounced as shown by the vanishing conductance histogram peak structure.

References [1] Yanson AI, Yanson IK, van Ruitenbeek JM, Nature, 400 (1999)144.

2. Yanson AI, Yanson IK, van Ruitenbeek JM, Phys Rev Lett, 87 (2001) 216805 3. Yanson AI, van Ruitenbeek JM, Yanson IK, Low Temp Phys, 27 (2001) 807 4. Díaz M, Costa-Krämer JL, Medina E, Hasmy A, Serena PA, Nanotechnology, 14 (2003) 113 5. Gülseren O, Ercolessi F, Tosatti E, Phys Rev B, 51 (1995) 7377 6. Gülseren O, Ercolessi F, Tosatti E, Phys Rev Lett, 80 (1998) 3775 7. Bilalbegović G, Phys Rev B, 58 (1998) 15412 8. Kondo Y, Takayanagi K, Science, 289 (2000) 606 9. Bilalbegović G, Solid State Commun, 115 (2000) 73 10. Wang B, Yin S, Wang G, Buldum A, Zhao J, Phys Rev Lett, 86 (2001) 2046 11. Kang JW, Hwang HJ, J Phys: Condens Matter, 14 (2002) 2629 12. Rodrigues V, Fuhrer T, Ugarte D, Phys Rev Lett, 85 (2000) 4124 13. Rodrigues V, Ugarte D, Phys Rev B, 63 (2001) 073405 14. Brack M, Rev Mod Phys, 65 (1993) 677 15. Martín TP, Phys Rep, 273 (1996) 199 16. Mares AI, Urban DF, Bürki JB, Grabert H, Stafford CA, van Ruitenbeek JM, Nanotechnology, 18 (2007) 265403 17. Díaz M, Costa-Krämer JL, Serena PA, Medina E, Hasmy A, Nanotechnology, 12 (2001) 118 18. Hasmy A, Medina E, Serena PA, Phys Rev Lett, 86 (2001) 5574 19. Yannouleas C, Bogachek EN, Landman U, Phys Rev B, 57 (1998) 4872 20. García-Martin A, Torres JA, Sáez JJ, Phys Rev B, 54 (1996) 13448 21. Lermé J, Pellarin M, Vielle JL, Baguenard B, Broyer M, Phys Rev Lett, 68 (1992) 2818 22. Medina E, Díaz M, León N, Guerrero C, Hasmy A, Serena PA, Costa-Krämer JL, Phys Rev Lett, 91 (2003) 026802 23. Oshima Y, Koizumi H, Mouri K, Hirayama H, Takayanagi K, Kondo Y, Phys Rev B, 65 (2002) 21401 Figures Figure 1 Temperature dependence of conductance histograms up to 7 G0 for Al nanowires. The histograms has been normalized to the total number of individual conductance traces (> 1,000 in all cases). The applied bias voltage between electrodes was 90 mV.

Figure 2 Positions of the main peaks in Al conductance histograms. Positions of the main peaks in Al conductance histograms (obtained from Figure 1) plotted against their sequential or peak index number m. Different straight lines and the value of their slopes are also displayed.

Plasma-liquid Electrochemistry : a Fast Method for Synthesizing Magnetic Nanoparticles Mathieu Létourneau

1,2,3

1

, Christian Sarra-Bournet , Myriam Laprise-Pelletier

1,2,3

1,2,3

, Marc-André Fortin

1

Axe métabolisme, santé vasculaire et rénale, Centre de recherche du Centre hospitalier universitaire de Québec (AMSVR-CRCHUQ), Groupe de recherche en imagerie moléculaire (GRIM), 10 rue de l'Espinay, Québec, QC G1L 3L5, Canada 2 Départment de génie des mines, de la métallurgie et des matériaux, Université Laval, Québec, QC G1V 0A6, Canada 3 Centre de recherche sur les matériaux avancés (CERMA), Université Laval, Québec, QC G1V 0A6, Canada mathieu.letourneau.2@ulaval.ca INTRODUCTION: Iron oxide nanoparticles (NPs) are a widely used contrast agent in magnetic resonance imaging (MRI). In general, these colloids are synthesized by thermal decomposition reactions, which require at least 24 hours as well as the work of a skilled chemist. As-synthesized particles covered with fatty acids are only dispersible in organic solvents.[1] A ligand exchange procedure is then needed to enable their aqueous dispersion. Such complex colloidal synthesis and ligand exchange steps can hardly be automated. New dual imaging scanners combining positron emission tomography and magnetic resonance imaging (PET/MRI) [2] are now available for clinical use. Dual MRI and PET acquisitions are expected to provide high anatomical resolution (in MRI) and high sensitivity (PET), an optimal combination for the development of new molecular and cellular tracking applications.

In this context, new imaging probes are necessary, requiring the integration of PET-detectable radioisotopes to 1 magnetic nanoparticles (e.g. FeOx; modifying H proton relaxation times). The synthesis procedure must fit within the decay time frame of common positron emitters (typically hours). Here we report a plasma-liquid electrochemistry technique allowing the fast synthesis of ultra-small metallic nanoparticles, within minutes.[3] MATERIALS AND METHODS: In brief, plasma-liquid electrochemistry consists in the generation of atmospheric microplasma pointing at the surface of an aqueous solution containing metallic salts and ligands. In the plasma, electrons and ions are accelerated toward the surface, reducing metal ions in the solution and inducing the nucleation and growth of nanoparticles. The plasma acts as the cathode, and the anode is a graphite rod immersed in the liquid (Figure 1). The nanoparticles generated within 5 minutes at the plasma-liquid interface, are readily dispersed in water and covered with biocompatible ligands such as dextrane and dimercaptosuccinic acid (DMSA)).

This is a significant advantage compared to the thermal decomposition method, and it would enable the doping of nanoparticles with fast decaying positron emitters used for PET, such as 64Cu (t½=12.7 hrs). To keep the time advantage offered by this technique, a rapid purification step is required. We have compared two purification techniques in this work: 1) dialysis, which removes the excess of ions and ligand molecules by osmotic exchange, and 2) size exclusion chromatography, in which nanoparticles pass through the column faster than ions and ligand molecules. The hydrodynamic diameter of the nanoparticles was assessed by dynamic light scattering (DLS) and size distributions of the nanoparticle cores were measured by transmission electron microscopy (TEM).

1 Relaxometric properties of the purified contrast media were characterised by H NMRD (T1 and T2 measurement) and 1-Tesla MRI. RESULTS AND DISCUSSION: TEM micrographs revealed the presence of ultra-small particles of mean diameters in the range 2-3 nm (Figure 2.a,b). The colloids had hydrodynamic diameters of 4 - 5 nm (Figure 3). The purified iron oxide NP suspensions shorten the longitudinal (T1) and transversal (T2) relaxation time of water, as showed in Table 1. Relaxometric ratios (r2/r1) of 2.67 to 3.75, as well as MRI assessments (Figure 4), confirmed the “positive” contrast enhancement effect achieved with these colloidal suspensions. Finally, preliminary results showed that iron oxide NPs could be synthesized via plasma-liquid electrochemical method with other ligand molecules, such as DMSA. CONCLUSION: Plasma-liquid electrochemistry allows the synthesis of ultra-fine and narrow nanoparticulate systems, with impact on the relaxation time of water allowing their use as contrast agents in MRI. The rapidity and simplicity of the technique could offer the possibility to synthesize magnetic and radioactive NPs for PET/MRI, upon demand. Finally, applications in internal radiotherapy are also being investigated.

References [1] [2] [3]

Yin, M.; O'Brien, S., Journal of the American Chemical Society, 34 (2003) 10180.

Judenhofer, M. S.; Wehrl, H. F.; et al., Nature Medicine, 4 (2008) 459.

Richmonds, C.; Sankaran, R. M., Applied Physics Letters, 13 (2008).

Figures and Tables

Figure 1. Plasma-liquid electrochemistry apparatus for nanoparticle synthesis.

Figure 2. TEM micrograph (200 keV) of a) FeOx-dextran nanoparticles purified by dialysis, b) by chromatography, and c) TEM of FeOx-DMSA nanoparticles (120 keV) purified by dialysis (inset : size distribution, measured with ImageJ).

Figure 3. DLS measurement after dialysis and chromatography.

Table 1. Longitudinal and transversal relaxation times (T1, T2) of aqueous NP suspensions.

Product FeOx-dextran (dialysis)

FeOx-dextran (chromatography) FeOx-DMSA (dialysis)

T1 (ms) 1663 ± 5 2014 ± 9 1511 ± 5

T2 (ms) 766.6 ± 0.5 1214 ± 1 477.3 ± 0.3

r2/r1 3.22 2.67 3.75

Figure 4. T1-weighted MRI measurements of dextran-covered nanoparticle suspensions purified by a) dialysis and b) chromatography.

The sequence is SE 2D with 1.9 mm slice thickness (0.1 mm gap), FOV = 70mm (200x200), 1 NEX with TR/TE: 1000/10.8 ms; total acquisition time: 200 seconds.

Thermal properties of the S-layer protein from Lactobacillus salivarius Liliana Lighezan1, 3, Ralitsa Georgieva2 and Adrian Neagu3 1

Faculty of Physics West University of Timisoara, Timisoara, Romania; The Stephan Angeloff Institute of Microbiology, Bulgarian Academy of Sciences, Sofia, Bulgaria; 3 Center for Modeling Biological Systems and Data Analysis, Department of Functional Sciences, Victor Babes University of Medicine and Pharmacy, Timisoara, Romania 2

llighezan@physics.uvt.ro, ralica_nedkova@mail.ru and neagu@umft.ro

Abstract Surface layer (S-layer) proteins have been identified in outermost structures of the cell envelope in many organisms, such as bacteria and archaea [1, 2]. They display intrinsic self-assembly property, forming monomolecular crystalline arrays with oblique, square or hexagonal symmetry [3, 4].

The biological functions of S-layer proteins are not completely understood. It is assumed that Slayer proteins act as protective coats, cell shape determinants, molecular and ion traps, adhesion sites for exoenzymes and structures involved in cell adhesion and surface recognition [3, 4].

Isolated S-layer proteins possess the unique ability to recrystallize into regular monomolecular arrays, on solid supports, on liquid surface-interfaces, on lipid films and liposomes, or in suspension.

The ability to self-assemble into regular lattices, with pores of identical size and morphology (of about 1 to 10 nm), facilitates the use of S-layer proteins in biotechnological applications, such as the control of the architecture of biomimetic surfaces [5, 6]. S-layer proteins are also used in the production of isoporous ultrafiltration membranes, in the construction of supporting structures for the controlled immobilization or incorporation of functional molecules (antigens, antibodies, ligands, enzymes) required for biosensors [7, 8]. Moreover, S-layer proteins are used to produce matrices for the formation of ordered arrays of metal clusters or nanoparticles, required in molecular electronics and nonlinear optics [9]. Also, they are used for drug targeting, being involved in the formation of supporting and stabilizing matrices for functional lipid membranes, liposomes and emulsomes [10, 11]. In recent applications, S-layer proteins were used to obtain encapsulated drugs [12] and as drug microcarriers [13]. For all these nanobiotechnological purposes, as well as for their biological functions, the thermal stability of the S-layer proteins under high temperature conditions is very important.

In this study, the S-layer protein has been isolated from Lactobacillus salivarius 16 strain of human origin, and purified by cation-exchange chromatography. Using circular dichroism (CD) spectroscopy, we have investigated the structure and the thermal properties of the S-layer protein.

The far UV circular dichroism spectra indicate that the secondary structure of the S-layer protein consists mainly of irregular motifs, but it can also contain small fractions of α-helices and βsheets. The near UV circular dichroism spectra show that the tertiary structure of the S-layer protein is determined by a high content of hydrophobic amino acids, such as Trp, Tyr and Phe, bound into a local chiral environment, which tend to compact the protein's tertiary structure.

According to the far UV CD spectra taken at different temperatures, the thermal denaturation of the secondary structure of the S-layer protein takes place in the temperature range between 40 °C and 80 °C and is partially reversible. The shape of the thermal denaturation ellipticity curve in the far UV domain (at a wavelength of 203 nm) is concentration-dependent and it also depends slightly on the heating rate (figure 1). The curve shows the existence of a metastable intermediate state in the protein denaturation pathway (figure 1 b). The thermal denaturation of the tertiary structure of protein occurs in the same temperature range, between 40 °C and 80 °C, and is partially reversible, too. The temperature dependence of the CD signal in the near UV domain (at a wavelength of 285 nm) reveals the presence of an intermediate state, at about 60 °C, in a good agreement with the temperature dependence of the CD signal in the far UV domain for the protein concentration of 0.25 mg/ml (at a wavelength of 203 nm). So, during thermal denaturation, the protein changes its secondary and tertiary structure simultaneously. After the heating of the protein up to 90 °C and, subsequently, its cooling down to 10 °C, the secondary and tertiary structures of the S-layer protein are partially recovered.

By fitting the thermal denaturation curves with sigmoidal functions, we have determined the temperature dependence of the population fractions of the native, intermediary and denatured states.

We have also determined the transition rates and free energy variations.

Taken together, our CD spectroscopy results concerning the thermal behavior of the S-layer protein from Lactobacillus salivarius 16 strain could be important for the use of S-layer proteins in nanobiotechnological applications, as well as for a better understanding of the protein's structure and function.

References [1] Messner P and Sleytr U B, Adv. Microbiol. Physiol. 33 (1992) 213-275.

[2] Sleytr U B and Messner P, Ann. Rev. Microbiol. 37 (1983) 311-339.

[3] Sara M and Sleytr U B, S-layer proteins J. Bacteriol. 182 (2000) 859-868.

[4] Sleytr U B and Beveridge T J, Trends Microbiol. 7 (1999) 253-260.

[5] Debabov V G, Molec. Biology 38 (2004) 482-493.

[6] Schuster B, Pum D, Sara M and Sleytr U B, Mini-Reviews in Medicinal Chemistry 6 (2006) 909-920.

[7] Neubauer A, Pum D, Sleytr U B, Biosensors and Bioelectronics 11 Issue 3 (1996) 317-325.

[8] Schleicher S R, Kainz B, Köstler S, Suppan M, Bizzarri A, Pum D, Sleytr U B, Ribitsch V, Biosensors and Bioelectronics 25 (2009) 797-802.

[9] Sleytr U B, Egelseer E M, Nicola I, Pum D and Schuster B, FEBS Journal 274 (2007) 323-334.

[10] Schuster B, NanoBiotechnology 1 (2005) 153-164.

[11] Schuster B and Sleytr U B, Curr. Nanosc. 2 (2006) 143-152.

[12] Habibi N, Pastorino L, Soumetz F C, Sbrana F, Raiteri R, Ruggiero C, Colloids and Surfaces B: Biointerfaces 88 (2011) 366-372.

[13] Ilk N, Egelseer E M, Sleytr U B, Current Opinion in Biotechnology 22 (2011) 824-831.

Figures

Figure 1. The temperature dependence of the ellipticity of the S-layer protein from Lactobacillus salivarius 16 strain, recorded at the fixed wavelength of 203 nm, for samples with different concentrations and different heating rates: (a) for two samples with the same concentration of 0.125 mg/ml and different heating rates, of 0.5 °C/min and 1°C/min; (b) for two samples with the same concentration of 0.25 mg/ml and different heating rates, of 0.5 °C/min and 1°C/min; (c) for two samples with different concentrations of 0.125 mg/ml and 0.5 mg/ml, and the same heating rate, of 1°C/min.

Fluctuation Relations for Spintronics Rosa L´opez, Jong Soo Lim∗ , and David S´anchez Institut de F´ısica Interdisciplinar i de Sistemes Complexos IFISC (CSIC-UIB)

The steady-state fluctuation theorem concerns the relative ratio of positive entropy production to negative entropy production. In the context of the full counting statistics, using a variant of the steady-state fluctuation theorem, fluctuation relations which generalize fluctuation-dissipation relations in linear response regime were derived [1]. In the presence of an applied magnetic field B, however, the fluctuation theorem is not valid any more because the micro-reversibility condition is not satisfied in nonequilibrium. Nevertheless, employing the microreversibility condition only at equilibrium and probability conservation, a kind of fluctuation relations was derived [2].

Here [3], we examine the role of the spin degrees of freedom in formulating fluctuation relations. The fact that the steady-state fluctuation theorems rely on the assumption of a local balance condition is observed. We then show that in some cases the presence of magnetic interactions violates this local balance condition. For illustrative purpose, we consider a quasilocalized level coupled to chiral and helical edge modes and demonstrate that the fluctuation theorem is not a priori satisfied when magnetic interactions are present. Importantly, nevertheless, we derive the fluctuation relations and verify them in an illustrative case.

References [1] K. Saito and Y. Utsumi, Phys. Rev. B 78, 115429 (2008).

[2] H. F¨orster and M. B¨uttiker, Phys. Rev. Lett. 101, 136805 (2008).

[3] R. L´opez, J.S. Lim, and D. S´anchez, Phys. Rev. Lett. 108, 246603 (2012). ∗

J.S. Lim, e-mail: lim.jongsoo@gmail.com, Tel.: +34-971259828

Antifolates-Modified Iron Oxide Nanoparticles for Targeting Cancer Cells 1

1

1

2

2

2

K. López , M. N. Piña , J. Morey , R. Alemany , B. O. Vögler , F. M. L. Barceló 1

2

Supramolecular Chemistry Research Group, Clinical and Translational Research Group.

University of the Balearic Islands Cra. de Valldemossa Km 7.5, 07122 Palma de Mallorca, Balearic Islands, Spain kenia.lopez@uib.es

Iron oxide nanoparticles have been used, in the last years, as a suitable platform for contrast enhancement in magnetic resonance imaging and as a drug carrier. The identification of specific agents or drugs that can be effectively release from the nanoparticles inside the 1 target cells is nowadays a strategy in development .

Folic acid (FA) is an effective tumor targeting to conjugate with nanoparticles due to 2 folate receptors which are overexpressed on the cell membranes of many cancer cells . It also 3 has been described the use of antifolates joined to the surface of nanoparticles . Antifolates are antimetabolites structurally similar to FA used in cancer chemotherapy. The best known is Methotrexate (MTX), but there are others like Raltitrexed (RTX) and Pemetrexed (PMX) whose effects on these kinds of cells have not been reported yet.

In this work we report the synthesis of iron oxide nanoparticles functionalized with RTX and PMX using as a linker 3-Aminopropyltrietoxysilane (APTES). As shown in figure 1, the nanoparticles, in a first synthetic step, were modified with APTES following with the conjugation of RTX or PMX respectively, through one of the carboxylic acids, establishing an amide bond.

These new nanoparticles have been characterized by TEM, FTIR and MALDI TOF/TOF. The potential biological applications of the free drugs (RTX, PMX) and the functionalized nanoparticles (NP-APTES-RTX, NP-APTES-PMX) were evaluated via MTT assay using lung carcinoma cells (A549), which are known to be folate-expressing cancer cells. Cells were incubated with different concentrations of the drugs and the respective nanoparticles at o 37 C from 24 to 96 hours. The results are presented in figures 2 and 3. Concentrations between 25 nM to 1 µM of the free drugs were used. There is a high in vitro differential citotoxicity from free RTX to PMX. A concentration of 50 nM of free RTX produce after 96 h about a 70% reduction in cell viability, however, a similar cytotoxicity from free PMX is only achieved when using a concentration of 1 µM after the same time. Analogous results were obtained after the incubation of NP-APTES-RTX and NP-APTES-PMX with cancer cells. Concentrations between 0.001 to 0.01 mg Fe/mL were examined. The highest concentration of NP-APTES-PMX used only reduces cell viability in a 10% though the same concentration of NP-APTES-RTX reduces it about a 90%.

[1a] M. F. Kircher, U. Mahmood, R. S. King, R. Weissleder, L. Josephson, Cancer Res. 63 (2003), 8122-8125. [1b] D. K. Nagesha, B. D. Plouffe, M. Phan, L. H. Lewis, S. Sridhar, S. K. Murthy, J. Appl. Phys. 105 (2009), 07B317-1-07B317-3.

[2a] K. J. Landmark, S. DiMaggio, J. Ward, C. Kelly, S. Vogt, S. Hong, A. Kotlyar, A. Myc, T. P. Thomas, J. E. Penner-Hahn, J. R. Baker, M. M. Banaszak, B. G. Orr, ACSNano, 2 (2008), 773783. [2b] S. Santra, C. Kaittanis, J. Grimm, J. M. Perez, Small, 5 (2009), 1862-1868. [2c] G. Zuber, L. Zammut-Italiano, E. Dauty, J. P. Behr, Angew. Chem. Int. Ed. 42 (2003), 2666-2669.

[2d] H. S. Yoo, T. G. Park, J. Control. Release, 100 (2004), 247-256.

[3] N. Kohler, C. Sun, J. Wang, M. Zhang, Langmuir, 21 (2005), 8858-8864.

Figure 1. Synthesis of NP-APTES-RTX and NP-APTES-PMX.

Cell viability (% viable)

MTT assay for RTX and NP-APTES-RTX

RTX 25nM

100

RTX 50nM 75

RTX 100nM

Figure 2. Determination of cytotoxicity of free RTX and NP-APTES-RTX at different concentrations.

Nanoparticles without functionalization (NP) were also tested.

RTX 1uM 50

0,001 mg Fe/mL 0,005 mg Fe/mL

25

0,01 mg Fe/mL NP 1 mg Fe/mL

0 24

48

72

96

t (h)

MTT assay for PMX and NP-APTES-PMX

Cell viability (% viable)

100

PMX 50nM PMX 100nM

75 PMX 1uM PMX 10uM

50

0,001 mg Fe/mL 0,005 mg Fe/mL

25

0,01 mg Fe/mL 0 24

48

72 t (h)

96

NP 1 mg Fe/mL

Figure 3. Determination of cytotoxicity of free PMX and NP-APTES-PMX at different concentrations.

Nanoparticles without functionalization (NP) were also tested.

Study of the transport properties frequency dependence of multilayer graphene by Impedance Spectroscopy

I.Lorite, A. Ballestar, J. Baryola-Quiquia, P. Esquinazi lorite@physik.uni-leipzig.de

University of Leipzig, Superconductivity and magnetism Division, LinnĂŠstraĂ&#x;e 5 04103 Leipzig, Germany

Multigraphene is a system quite close to the ideal graphite whose properties has been the object of i

discussion for more than 60 yeras . Experimental evidences indicate that high quality graphite is a multilayers graphene system with nearly decoupled 2D planes structure. Multigraphene presents interesting electronic and transport properties such as the Dirac physics, tunable band gap due to the broken symmetry by additional layers, electron interaction effects, long electron mean free path, high 2

ii

electron mobility, 15.000cm V with low carrier densities .

Despite to the efforts to understand transport properties of graphene many questions about the behavior of multigraphene system under an applied ac remain unanswered. It is important to obtain a clear understanding of the frequency dependence features and the relation to microscopic parameter and behavior at different temperatures. Complex impedance is an useful tool which can provide valuable information to differentiate the transport characteristics of the materials.

A detailed analysis in the range of 100Hz-1Mhz was performed for multilayer graphene at different temperature. Multigraphene presents an inductive behavior temperature dependent. This behavior is in well agreement with the theoretical predictions which present a parallel contribution of semiconducting graphene layers with low carrier density and the one from metallic like behavior due to iii

charge inhomogeneities in the internal interfaces . i

Wallace P R; Phys. Rev. 71 (1947) 622 S. Dusari, J. Quiquia, P. Esquinazi and N. Garcia; Physic Rew. B. 83 (2011) 125402 iii N.Garcia, P. Esquinazi, J. Baryola-Quiqui and S. Dusari, New Journal of Physics, 14 (2012) 053015 ii

New selective drugs based on carbon nanohorns 1,2

3

3

1

2

María Isabel Lucío , Giulio Fracasso , Marco Colombatti , María Antonia Herrero , Maurizio Prato 1 and Ester Vázquez .

1

Departamento de Química Orgánica-IRICA, Facultad de Química,Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain 2 Dipartamento di Scienze Farmaceutiche, Università degli Studi di Trieste, Piazzale Europa 1, 34127Trieste, Italy 3 Section of Immunology, Department of Pathology and Diagnostics, University of Verona, c/o Policlinico ‘G.B.Rossi’, L.go L.A.Scuro 10, I-37134 Verona, Italy.

MIsabel.Lucio@alu.uclm.es

Carbon nanohorns [1] (CNHs) are horn-shaped tubular structures (similar in structure to singlewalled carbon nanotubes) capped with a conical tip. Individual nanohorns tend to cluster and form a globular structure between 80 and 100 nanometres in diameter with the tips of individual nanohorns projecting outward from the centre in all directions. The high purity and the lack of metal particles of produced CNHs is their major advantage compared to carbon nanotubes. These nanomaterials have interesting properties such as chemical and mechanical stability as well as an average size that allows their inclusion through endocytosis into the inner cell. These properties make them suitable for biomedical applications. [2] CNHs have already been used as carriers in nanomedicine but the main handicap of these systems is their lack of specificity.

CNHs have the ability to carry many molecules grafted on their sidewall due to their high surface area. This property fact makes possible the creation of new systems where an antineoplastic agent is linked to CNHs, acting as vectors, bearing at the same time a targeting antibody.

Antibodies, also known as immunoglobulines, are a family of large Y-shaped proteins produced by the immune system to identify and neutralize foreign objects in the body. They can target key regulators in the development of cancer. The antineoplastic agent used in this work has been a cisplatin derivative. Cisplatin is responsible for the cure of over 90% of testicular cancer cases and it plays a vital role in the treatment of cancers such as ovarian, head and neck cancer, bladder cancer, cervical cancer, melanoma, lymphomas, as well as several others.

Different conjugates have been synthesized such as an antibody-CNH derivative, a cisplatin CNH derivative and an antibody-cisplatin-CNH derivative. These systems have been characterized using various techniques, including UV-vis-spectroscopy (Kaiser test and Ellman test), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA).

The synthetic approach will permit new modifications on the carbon nanohorns and the introduction of different antibodies and different drugs, opening the door to new studies.

References [1] Iijima, S.; Yudasaka, M.; Yamada, R.; Bandow, S.; Suenega, K.; Kokai, F.; Takahashi, K., Chem. Phys. Lett., 309 (1999) 165.

[2] Zhu, S. and Xu, G. 2012. Carbon Nanohorns and Their Biomedical Applications. Nanotechnologies for the Life Sciences.

[3] Rubio, N.; Herrero, M. A.; Meneghetti, M.; Díaz-Ortiz, A. Schiavon, M.; Prato, M.; Vázquez, E., J. Mater. Chem., 19 (2009) 4407.

Microstructural and Magnetic Properties of Hematite Submicron Pseudo-Cubes Obtained by Nanocrystal Oriented Attachment

C. Luna

1,2

2,3

and R. Mendoza-Reséndez

1

Centro de Investigación en Ciencias Físico Matemáticas/Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, 66450, Mexico.

2

Centro de Innovación, Investigación y Desarrollo en Ingeniería y Tecnología, Universidad Autónoma de Nuevo León, Apodaca, Nuevo León, 6440, Mexico.

3

Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, 66450, México.

carlos.lunacd@uanl.edu.mx Abstract Crystal growth does not always occur by atom-by-atom or molecule-by-molecule addition.

Studies of nanoscopic and submicrometric materials have revealed that they frequently grow through the self-organization of nanoparticles. Indeed, when these nanoelements are faceted single-cystals, their spontaneous aggregation often results in the oriented attachment into complex structures with pseudo-monocrystalline features and unusual physical properties [1-6].

Although it has been shown that a large variety of nanostructured materials grow by oriented attachment mechanism, it seems that nanostructures of certain materials (such as TiO2 [1], CuO [2], αFe2O3 [3], ZnO [4], CdSe [5] and PbSe [6], among others) are more conducive to be formed in solution by this crystal growth mode. Therefore, these materials particularly represent excellent experimental models to investigate the oriented attachment growth phenomena and the correlation between microstructure and optical, mechanical, electrical and magnetic properties. In this matter, very recently works have shown that oriented attachment of hematite (α-Fe2O3) nanocrystals can lead to the formation of nanostructures with interesting properties and many morphologies, including cubes [7], spindles [3], hollow spindles [8], urchin-like structures [9], disks [10] and tetrahedrons [10].

In the present contribution, the formation of submicron α-Fe2O3 cubes through oriented attachment of nanocrystal building blocks in acid iron (III) solutions at 100°C has been investigated in detail. In concrete, the growth mechanism of these structures was studied analyzing samples collected at different stages of the particle formation by various analytic techniques, such as X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED). In addition, vibrating sample magnetometry measurements were employed to examine the magnetic behaviors of the samples. These studies disclosed that the formation mechanism of the α-Fe2O3 cubes consists of several proposed growth mechanisms. Firstly, ultra-fine akaganéite particles are formed.

Then, they grow to form akaganéite rod-shape particles that tend to aggregate into rather cubic structures. Finally, these rods experience a crystallo-chemical transformation to α-Fe2O3 and readjust their positions to form submicron polycrystalline cubes with pseudo-monocrystalline characteristics.

Figures 1a-c show TEM micrographs of samples obtained at different reaction times. Figure 1d is the SAED pattern of an isolated submicron α-Fe2O3 cube. In agreement with this particle formation mechanism and their grainy structure, the submicron cubes exhibit magnetic properties mainly governed by surface effects. Particularly, the spin frustration of the antiferromagnetic coupling at nanocrystal surface give rise to exchange bias phenomena, suppression of the Morin transition and large coercivities at low and room temperature.

References [1] C. A. Chen, Y.-M. Chen, Y.-S. Huang, D.-S. Tsai , K.-K. Tiong and P.-C. Liao, CrystEngComn 11 (2009) 2313.

[2] Z. Zhang, H. Sun, X. Shao, D. Li, H. Yu and M. Han, Adv. Mater. 17 (2005) 42.

[3] R. Mendoza-Reséndez, C. Luna, E. D. Barriga-Castro, P. Bombille and C. J. Serna, Nanotechnology 23 (2012) 225601 [4] P. D. Cozzoli, M. L. Curri, A. Agostiano, G. Leo and M. Lomascolo, J. Phys. Chem. B, 107 (2003) 4756.

[5] Z. Yu, M. A. Hahn, S. E. Maccagnano-Zacher, J. Calcines, T. D. Krauss, E. S. Alldredge and J. Silcox, ACS Nano 2 (2008) 1179.

[6] K.-S. Cho, D. V. Talapin, W. Gaschler and C. B. Murray, J. Am. Chem. Soc. 127 (2005) 7140.

[7] B. Jia and L. Gao, Crystal Growth & Design. 8 (2008) 1372.

[8] S. Zeng, K. Tang, T. Li, Z. Liang, D. Wang, Y. Wang and W. Zhou, J. Phys. Chem. C 111 (2007) 10217.

[9] S. Zeng, K. Tang,T. Li and Z. Liang J. Phys. Chem. C 114 (2010) 274.

[10] W. Wang, J. Y. Howe and B. Gu, J. Phys. Chem. C 112 (2008) 9203.

Figures

Figure 1. TEM images of the samples synthesized at a) 0, b) 4 and c) 24 hours. Part d) of the figure shows the SAED pattern of an isolated α-Fe2O3 cube.

Toxicity studies of polymer based superparamagnetic iron oxide nanoparticles 1, 2

2

3

3

3

Lamiaa M.A.Ali , Victor sorribas *, Martin Gutierrez *, Rosa Cornudella , José Antonio Moreno , 1 1 1 1 Rafael Piñol , Lierni Gabilondo , Angel Millan , Fernando Palacio * 1 Instituto de Ciencia de Materiales de Aragón. CSIC - Universidad de Zaragoza, Zaragoza, Spain 2 Laboratory of Molecular Toxicology and Institute of Materials Science-Universidad de Zaragoza, Zaragoza, Spain 3 Departamento de Hematología, Facultad de Medicina- Universidad de Zaragoza, Zaragoza, Spain Miss_limo@yahoo.com, sorribas@unizar.es, marting@unizar.es, palacio@unizar.es Abstract Superparamagnetic iron oxide nanoparticles (SPIONs) have been of great interest since the last decades due to their important contributions to nanomedicine [1, 2]. These inorganic nanomaterials can be useful as a diagnostic tool (e.g. magnetic resonance image contrast agent), a therapeutic tool (e.g. hyperthermia), or a theranostic tool. Stable biocompatible suspension of these nanoparticles is mandatory for efficient application, which is achieved by an adequate polymeric coating. Our model consists of iron oxide nanoparticles (ɣ-Fe2O3) embedded within a hydrophobic poly(vinylpyridine) (P4VP) polymer and coated with a hydrophilic polyethylene glycol (PEG). A fraction of coating PEG can also be functionalized for the conjugation of fluorescent dyes (dual reporter nanoparticles), antibodies and drugs Fig1. These nanoparticles are dispersed in phosphate buffer saline (PBS) at pH 7.4 to mimic physiological conditions. The resulting ferrofluids have core diameter (ferric oxide nanoparticles diameter) ranging between 4 to 15 nm, with 10% size dispersion, and hydrodynamic diameter ranging between 50 to 164 nm.

Since the in vivo delivery of these nanoparticles for biomedical applications ends at the cell, studies pertaining to the toxicological effect on the cell (cytotoxicity), and nanoparticles cellular uptake and uptake kinetics are of utmost importance.

Cytotoxicity studies of the ferrofluids have been carried out on two different cell lines, opossum kidney cells (OK) and vascular smooth muscle cells (VSMS). The activity of the lactate dehydrogenase in culture media was determined as a function of the dose. LC50 has been also calculated.

As the nanoparticles uptake by the cell is depending on several factors [3], this work focused on the effect of the nanoparticle size and cell type on the cellular uptake. Sub cellular tracking studies have been carried out using fluorescent nanoparticles. Results show the localization of the nanoparticles after 24h of incubation with the cells inside the lysosomes Fig 2. By using the pharmacological inhibitor we found that the nanoparticles uptake takes place by clathrin-dependent endocytosis.

These nanoparticles are developed for intravenous administration; therefore, studies pertaining to their haematological behaviour are of outmost importance and should be included in the toxicity and compatibility tests to be made in the development of these nanoparticles. We studied the effect of the nanoparticles and their polymers on the blood coagulation process. Results show that P4VPg-PEGcoated SPIONs in PBS act as non-specific circulating anticoagulant agents in vitro. While PEG component does not seem to have any effect on the coagulation process, the coating copolymer P4VPg-PEG shows strong anticoagulant behaviour indicating that P4VP is at the origin of the effect.

References [1] Duncan R, Gaspar R, Mol Pharm, 8(6) (2011) 2101.

[2] Akbarzadeh A, Samiei M, Davaran S, Nanoscale Res Lett, 7(1) (2012)144.

[3]Verma A, Stellacci F, Small, 6(1) (2010) 12.

Figures

Fig 1. Polymer based superparamagnetic iron oxide nanoparticle model.

Fig 2. Subcellular localization of nanoparticles using markers of the endoplasmic reticulum (Anti-Derlin Ab), mitochondria (Mitotracker), early endosomes ( Anti-EEA1), lysosomes(lysotracker) by fluorescence microscopy. Cells were treated with fluorescent nanoparticles (R8) at 0.007 g/L Fe2O3 for 24 h.

The preparation and investigation of properties of Er2O3 M.N.Abdusalyamova , Kh.Kabgov, F.Sharipov, Ju.M. Yu..M.Shulga* Institute of Chemistry of Tajik Academy of Science, Ajni Str.299/2,734063 Dushanbe, Tajikistan, amahsuda@mail.ru * Institute of Problems of Chemical Physics Russian Academy of Science, Academic N.N.Semenov pr.1, 142432 Chernogolovka of Moscow Region, Russia. shulga@icp.ac.ru Erbium nanooxide has been obtained two methods.

Imethod Erbium nanooxide preparation method with chlorides: the corresponding metal amount was dissolved in hydrochloric acid and chloride was obtained. Distilled water +NaOH+NaCl was added to obtained chloride. It was heated at рН=3.6-3.8 and evaporated. Hydrate ErCl3 + NaCl was prepared. This mixture was roasted at 440°С, washed and filtered using Bruchner filter, the sediment was dried. The second sample was roasted at 540°С, the third one at 640°С. Roasting time for all samples was similar- 1hour.

X-ray phase analysis shown that in the process of roasting the reflex intensity is growing corresponding to cubic Er2O3 structure. Size value of coherent-scattering region calculated using the Sherrer formula for the sample roasted at 440 С, is approximately 31 nm. For the sample roasted at 540 С, this value is 62 nm. For sample roasted at 640 С, this value is 65 nm. Thus, ОКР size for all the studied samples is growing when roasting temperature is increasing but for all studied temperatures it remains in nanometric range.It can be noted that in diffraction patterns 1, there are also peaks that couldn't be identified yet apart from the peaks related to cubic of erbium oxide lattice. In diffraction patterns 2, all the peaks are related to Er2O3, crystallized in cubic lattice.

2- method of preparation of Er2O3 with use organic compounds, which consisted of several steps: 1step: Synthesis of sodium oleinate.

2step: Synthesis of erbium chloride.

3step: Synthesis of erbium olenate.

4step: Er2O3 nanocrystal preparation.

X-ray phase analysis has shown single phase nanooxide have been obtained with 24nm size.

Magnetic, thermic, chemical properties have been investigated.

Acknowledgements This work was supported by International Science & technology Center(ISTC), #Project T-1597

Size-Controllable Calcium Carbonate Crystals by Homologous Series of Anionic Surfactants Atthaphon Maneedaeng, Adrian E. Flood, Suchitra Phithaksoemsak School of Chemical Engineering, Suranaree University of Technology, 111 University Ave, Muang District, Nakhon Ratchasima 30000 THAILAND atthaphon@sut.ac.th One of the challenges for materials scientists and engineers is to control and manipulate the shapes of materials on the nanometer scale, as different shapes of the nanostructures can exhibit novel electronic, optical, or magnetic properties (He et al., 2005). It is commonly known that different CaCO3 particles polymorphic forms and particle sizes can essentially affect their practical applications. Calcium carbonate (CaCO3) particles appear to be essential as an effective additive for pulp and paper industry with special and new characteristics (Wang et al., 2009). They are also employed as filler in plastics industry in order to investigate into polymer cleavage energy proven that the addition of nanometric fillers such as CaCO3 favors the increase of homopolymers and copolymers plastic rigidity and characteristics (Chen et al., 1989). Recently, CaCO 3 nanoparticles revealed the method to the controlled release of bioactive molecules, and constituted a hot topic of research receiving a considerable attention (Haruta et al., 2003). Consequently, the control of morphology and particle size is crucial in optimizing their efficiencies.

The templated reactive crystallization of inorganic nanoparticles in amphipathic systems is a third area where development has been made over the last few years. In order to control morphology of inorganic nanocrystals, organic additive such as surfactant, is typically introduced to the synthetic reaction to manipulate the nucleation and growth of the nuclei. There have been numerous researches on single surfactant-assisted synthesis of inorganic compounds but the effect of hydrocarbon chain length on the synthesized crystal morphology is still lacking. Thus, this work aims to investigate the effect of homologous surfactants in both single and binary mixed systems on the size and shape of CaCO3 particles.

In this work, CaCO3 was obtained by reactive crystallization of sodium carbonate (Na2CO3) and calcium chloride (CaCl2) with the presence of different molar Sodium Octylsulfate concentrations of homologous anionic surfactants in aqueous solution. Sodium octylsulfate (NaOS), sodium decylsulfate (NaDeS), and sodium dodecylsulfate (NaDS) of both single and binary mixed systems were used above their critical micelle Sodium Decylsulfate concentration as the templates at 30C. The reaction was carried out for 48 hours to allow the systems to reach the equilibrium. All the collected synthetic CaCO 3 particles were calcined at 400C for 2 hours to remove surfactant template and organic impurities. The white CaCO3 powder was collected Sodium Dodecylsulfate and characterized by XRD, SEM and Mastersizer to investigate the morphology changes.

The formed CaCO3 for all systems is identified as calcite by X-ray diffraction analysis as shown in Fig. 1 and the estimation of single nanocrystals of CaCO3 is done by Shcerrer equation. SEM image analysis and Mastersizer give the shape and particle size distribution as shown in Fig. 2. Square and rhombic CaCO3 crystals with equivalent diameter of 2.22 m are observed for a crystallization system without any surfactant assistance as shown. The different carbon atoms in each surfactant molecules reveal the change in shape and size of CaCO 3 particles for the surfactant-assisted crystallization systems. At specific concentrations of surfactants used, flower-like and hexagonal flat sheet CaCO3 crystals are observed in NaOS systems with equivalent diameter of 4.62 m, NaDeS systems generate the rugged spherical shape with equivalent diameter of 3.91 m and the perfect spherical crystals are observed in NaDS systems with the equivalent diameter of 2.00 m. It is suggested that longer hydrocarbon chain length in homologous series of anionic surfactants produces the smaller CaCO3

particles. Presumably, the formation of micellar phase appears to influent the morphology change of crystals in solution phase. Surfactant concentration variation results in insignificant change of crystal size in this work, however, it has an apparent effect on its shapes.

For equimolar binary surfactant-assisted crystallization systems: NaOS/NaDeS, NaOS/NaDS, and NaDeS/NaDS, the different carbon atoms of surfactant tails in the mixed micelles generate the smaller size of CaCO3 crystals comparing to their sizes in single surfactant systems. Additionally, surprising result shows that spherical and needle-like shapes of CaCO3 crystals are obtained in these mixed surfactant systems. More results and detailed discussion will be given in the oral presentation.

References [1] J.H. He, C.S. Lao, L.J. Chen, D. Davidovic, Z.L. Wang., Journal of the American Chemical Society, 127 (2005) 16376.

[2] S. Wang, X.P. Li, E.L. Mao, Z.Y. Cheng, Advanced Materials Research, 236-238 (2009) 1124.

[3] L.-S. Chen, Y.-W. Mai, B. Cotterell, Polymer Engineering & Science, 29 (1989) 505.

[4] S. Haruta, T. Hanafusa, H. Fukase, H. Miyajima, T. Oki, Diabetes Technology & Therapeutics, 5 (2004) 1.

Figures NaDeS/NaDS 40 mM

NaOS/NaDS 40 mM

(a) NaOS/NaDeS 60 mM

NaDS 40 mM

(b) NaDeS 40 mM

NaOS 150 mM

(c) No surfactant

(110) (113)

(012)

20

30

40

(202)

(211) (122)

(104)

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2ď ą Fig 1: The selected XRD patterns of calcite CaCO3 with homologous series of surfactants assisted synthesis.

(d) Fig 2: the selected SEM images of calcite CaCO3 with homologous surfactant assisted synthesis: (a) absence of surfactant (b) NaOS 300 mM (c) NaDeS 40 mM (d) NaDS 40 mM.

“Ligand-Free” Metal-Nanoparticles in Ionic Liquids.

R. Marcos Esteban, F.M. Alberti, D. Marquardt, H. Meyer, C. Rutz, K. Schütte, C. Vollmer, C. Janiak* Heinrich-Heine Universität Düsseldorf, Institut für Anorganische und Struktur Chemie, Universitätstraße 1, 40225 Düsseldorf, Germany Raquel.Marcos.Esteban@uni-duesseldorf.de

Metal-nanoparticles (M-NPs) are of significance due to their versatile applications in many different areas of medicine, science or industry [1] especially in catalysis due to their high surface area and activity [2] as well as excellent scaffolds for the fabrication of novel chemical and biological sensors. [3].

In this context, we have been interested during the last few years in the synthesis and stabilization of metal nanoparticles (M-NPs) in ionic liquids (ILs) [4]. Ionic liquids are defined as molten salts with melting points below 100°C. Their tunable physicochemical properties by selecting an appropriate combination of cation and anion together with their low vapor pressure offer many advantages over common solvents [2, 4] In the process of the generation and stabilization of M-NPs, ILs generate a protective layer which avoids the use of external stabilizing agent like coordinating ligands, encapsulating polymers or micelles (Fig.1) and prevents M-NPs from aggregation and agglomeration processes.

Fig.1. Ionic Liquids as a template for the Metal-nanoparticles synthesis without external stabilizations.

M-NPs can be easily synthesized in ionic liquid from different metal salts (for example MXn where M = –

–

Au, Cu X = Cl, BF4 , NO3 , KAuCl4) or metal carbonyl precursors ([Au(CO)Cl] or Mx(CO)y where M = Pd, Mn, Rh, Ru, Ir, W) by reduction photo-induced or microwave assisted, hydrogen atmosphere or thermal decomposition [5].

In terms of catalysis, the stabilization in IL of M-NPs from metal carbonyl compounds is very interesting as they avoid the presence of undesired co-ligands (CO is easily removed) which may interfere in the catalytic activity of the M-NPs.

We have recently described the successfully catalytic hydrogenation of cyclohexene and benzene Rh- , Ir- or Ru-NPs in ILs (Fig.2.) [6], as well as the deposition of Ru- and Rh-NPs on graphene sheets in IL for the same catalytic reactions [7].

[1] See, for example: a) Nanoparticles and Catalysis, Wiley-vch, 2007, Didier Astruc; b) H. Goesmann, C. Feldmann, Angew. Chem. Int. Ed., 2010, 49, 1362-1395; c) J. A. Dahl, B. L. S. Maddux, J. E. Hutchison, Chem. Rev. 2007, 107, 2228-2269.

[2] J. D.Scholten, B .C.Leal, J. Dupont, ACS Catal. 2012, 2, 184-200.

[3] See, for example: K. Saha, S. S. Agasti, C. Kim, X. Li, V. M. Rotello, Chem. Rev. 2012, 112, 27392779.

[4] a) C. Vollmer, C. Janiak, Coord. Chem. Rev. 2011, 255, 2039; b) J. Dupont, J. D. Scholten, Chem.

Soc. Rev., 2010, 39, 1780-1804; b) E. Redel, J. Kramer, R. Thomann, C. Janiak, J. Organomet. Chem.

2009, 694, 1069-1075.

[5] a) D. Marquardt, Z. Xie, A. Taubert, R. Thomann, C. Janiak, Dalton Trans. 2011, 40, 8290.; b) E. Redel, R. Thomann, C. Janiak, Chem. Commun. 2008, 1789; c) J. Krämer, E. Redel, R. Thomann, C. Janiak, Organometallics 2008, 27, 1976.

[6] C.Vollmer, E.Redel, K.Abu-Shandi, R. Thomann, H. Manyar, C. Hardacre, C. Janiak, Chem. Eur. J. 2010, 16, 3849.

[7] D. Marquardt, C. Vollmer, R. Thomann, P. Steurer, R. Mülhaupt, E. Redel, C. Janiak, Carbon 2011, 49, 1326.

[8] C. Vollmer, M. Schröder, Y. Thomann, R. Thomann, C. Janiak, Applied Catalysys A, 2012, 425-426, 178-183.

Nanostructured thermoelectric alloys obtained by mechanical alloying followed by hot extrusion or by microwave sintering Presenting author: Remo A. Masut

M.K. Keshavarz, J. Arreguin-Zavala, D. Vasilevskiy, S. Turenne and R.A. Masut Département de génie physique et Département de génie mécanique, École Polytechnique de Montréal, P.O. Box 6079, Station Centre-Ville, Montréal, Québec H3C 3A7 Canada remo.masut@polymtl.ca

Abstract The introduction of multiple interfaces in bulk materials is expected to enhance their thermoelectric (TE) properties by lowering their thermal conductivity [1]. Bismuth telluride and lead telluride based alloys and composites nanostructured powders can be obtained by mechanical alloying (see Fig. 1) [2-4].

They are then processed into polycrystalline solids by hot extrusion. We have determined ranges of processing parameters in order to obtain mechanically strong bulk alloys, adequate for module fabrication processes [5], and whose TE performance has been proven in high power density modules (see for example Fig. 2)[2,6]. We have also succeeded in compacting lead telluride powders and producing bulk alloys by microwave sintering (see Fig.3). We analyze the structural and TE properties of different p-type bismuth antimony telluride composites produced so as to maintain the same Bi/Sb ratio (0.2/0.8) which we compare with a conventional (Bi0.2 Sb0.8)2Te3 homogeneous alloy. The minimum grain size of these composites, estimated at 180 nm, show a 50 % reduction compared to the homogeneous alloy. Hall Effect measurements suggest that the hole mobility values are limited by two dominant scattering mechanisms: ionized impurity and acoustic phonon scattering. The TE properties were evaluated via the Harman method from 300K up to 440K. No degradation of the power factor of the composites has been observed and peak dimensionless figure of merit (ZT) values range from 0.86 to 1.04. The thermal conductivity of the composites show a slight increase instead of the reduction expected due to the smaller grains and thus enhanced phonon scattering. Two concurrent factors can explain this increase: i) composites may not yet contain a significant number of grains with size sufficiently small to increase phonon scattering, and ii) each of the combined components of the composites corresponds to a composition with thermal conductivity higher than the minimum value corresponding to the homogeneous alloy. The introduction of multiple interfaces has to be implemented so as to override such limitations.

Acknowledgements The authors acknowledge J.-P. Massé for assistance with transmission electron microscopy measurements, and Rene Ferro for X-ray diffraction simulations. This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT).

References [1] [2]

[3]

[4] [5]

[6]

A.J. Minnich, M.S. Dresselhaus, Z.F. Ren and G. Chen, Bulk nanostructured thermoelectric materials: current research and future prospects, Energy Environ.Sci. 2 (2009) 466-479.

D. Vasilevskiy, M.S. Dawood, J.-P. Masse, S. Turenne, and R.A. Masut, Generation of Nanosized Particles during Mechanical Alloying and their Evolution through the Hot Extrusion Process in Bismuth Telluride Based Alloys, J. Electron. Mat. 39 (2010) 1890-1896.

D. Vasilevskiy, O. Bourbia, S. Gosselin, S. Turenne, R.A. Masut, Nanostructure characterization of bismuth telluride based powders and extruded alloys by various experimental methods, J. Electron. Mat. 40 (2011) 1046-1051.

N. Bouad, M.-C. Record, J.C. Tédenac and R.M. Marin-Ayral, Mechanical alloying of a thermoelectric alloy: Pb0.65Sn0.35Te, J. Solid State Chem. 177 (2004) 221-226.

S. Kashi, M.K. Keshavarz, D. Vasilevskiy, R.A. Masut, and S. Turenne, Effect of surface preparation on mechanical properties of Ni contacts on polycrystalline (Bi1-xSbx)2(Te1-ySey)3 alloys, J. Electron. Mat. (2012), published on line: DOI: 10.1007/s11664-011-1895-3 D.Vasilevskiy, N. Kukhar, S. Turenne, R. A. Masut, Hot Extruded (Bi,Sb)2(Te,Se)3 Alloys for Advanced Thermoelectric Modules, Proc. 5th European Conference on Thermoelectrics , Odessa (Ukraine), Sep. 2007.

Fig. 1 (left) : High-resolution (HR) transmission electron microscope (TEM) images of n-type bismuth telluride based alloy powders after 2 hours of mechanical alloying in an attritor (from ref. 3).

Nanograins with similar sizes of about 2030 nm can be clearly identified on all images taken with different resolutions.

The inset shows a bright field medium resolution TEM image illustrating the location of the observed nanograins inside the mother agglomerate.

Fig. 2 (left): Variation of the maximum temperature difference generated by a thermocouple with p- and n- legs of dimensions: 1.8 x1.8 mm2 (section) and 2.4 mm (length), as a function of the hot side temperature. The experimental setup is presented in the inset. The room temperature point for the curve labelled POLY corresponds to a 23 legs (0.6 x 0.6 mm2 and 1 mm long) module produced by the Thermion Company from alloys extruded at the Ă&#x2030;cole Polytechnique de MontrĂŠal.

Fig. 3 (left) : Bulk PbTe produced by microwave sintering. The PbTe powder is homogenized by milling during 3 hours. It is then compacted for one minute under 1 metric ton pressure, and micro-wave sintered at 540 ď&#x201A;°C.

Effect of the deposition conditions on the properties of magnetic nanowires Ionut Enculescua, Elena Mateia, Camelia Floricaa, Monica Enculescua, Victor Kuncsera, Maria Eugenia Toimil Molaresb a

National Institute of Materials Physics, PO Box MG-7, 77125, Magurele-Bucharest, Romania b

GSI, Helmholtz Centre, Planckstr. 1, D-64291, Darmstadt, Germany elena.matei@infim.ro

Nanowires, quasi 1 dimensional nano-objects, with magnetic properties represent a very interesting topic, mainly due to the wide field of potential applications [1]. By employing the template method, which consists in filling the pores of a membrane with the desired material, one can easily fabricate such nanowires with controlled morphological, structural and compositional properties [2].

Anodic alumina and ion track nanoporous membranes are excellent templates for fabricating arrays of highly uniform cylindrical nanowires by a template approach. The most straightforward method for filling the pores with the desired material is electrochemical deposition, which allows a high control over the properties of the final object.

In the present paper we report our recent results regarding the influence of the deposition conditions on the magnetic characteristics of metallic nanowires with magnetic properties. Using appropriate electrochemical baths both nickel and cobalt nanowire arrays were fabricated. We found that the deposition overpotential influences the structural properties, i.e. texture, of the metallic nanowires and further their magnetic and galvonomagnetic properties. Thus, besides the huge shape anisotropy found in nanowires, as a consequence of their aspect ratio, one can also exploit the crystalline anisotropy in tailoring the properties of metallic nanowires with magnetic properties designed for particular applications.

Acknowledgements This work was supported by CNDI â&#x20AC;&#x201C; UEFISCDI, project number PN-II-PT-PCCA-2011-3.1-1510.

References

[1] C. R. Martin, Science 266 (1994) 1961-1966 [2] E. Matei, L. Antohe, S. Antohe, R. Neumann, I. Enculescu, Nanotechnology 10 (2010) 105202

Figures

Figure 1. Array of nickel nanowires deposited at -800 (left) and -1100 mV (right) vs.SCE.

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-2500

0

2500

-1.00 -5000

5000

Magnetic Field (Oe)

-2500

0

2500

5000

Magnetic Field (Oe)

Figure 2. Magnetic properties of nickel nanowire arrays deposited at -800 (left) and -1100 mV (right) vs.

SCE.

Optical transmission spectra in Fibonacci photonic multilayers with mirror symmetry 1

2

P.W. Mauriz , M.L. Vasconcelos and E.L. Albuquerque

3

1

Departamento de Física, IFMA, 65025-001, São Luís-MA, Brazil Escola de Ciências e Tecnologia, UFRN, 59072-970, Natal-RN, Brazil 3 Departamento de Biofísica e Farmacologia, UFRN, 59072-970 Natal-RN, Brazil contact e-mail: pwmauriz@yahoo.com.br 2

Abstract It is the aim of this work to study the transmission properties of a light beam normally incident from a transparent medium into a symmetric Fibonacci photonic multilayers, made up of both positive (SiO2) and negative refractive index materials with a mirror symmetry (see Fig. 1 for details). These spectra are calculated by using a theoretical model based on the transfer matrix approach, in which many perfect transmission peaks (the transmission coefficients are equal to the unity) are numerically obtained. Besides, the transmission coefficients exhibit a six-cycle self-similar behavior with respect to the generation number of the Fibonacci sequence.

The numerical simulations were done for the light transmission considering medium A as silicon dioxide (SiO2), whose refractive index is nA = 1.45, while medium B is a metamaterial with nB = −1. Also, we assume the individual layers to be quarter-wave layers, for which the quasiperiodicity is expected to be more effective [1], with the central wavelength λ0 = 32 mm. These conditions yield the physical thickness dJ = (8/nJ) mm, J = A or B, such that nAdA = nBdB, yielding a reversed phase shift in the two materials. Considering medium C as vacuum, the phase shifts are given by δA = (π/2)Ω cos(θA) and δB = (π/2)Ω cos(θB), where Ω is the reduced frequency Ω = ω/ω0 = λ0/λ. For normal incidence, θA = θB = 0, and δA = −δB. Here, the negative phase shift for medium B means that the light waves propagate in a direction opposite to the energy flux (+z-direction), i.e., one plane light wave, whose electromagnetic field is proportional to exp(−iδB), propagates in the −z-direction, while the Poynting vector propagates in the +z-direction. Therefore, inside medium B the effect of the negative refraction index is to change the forward waves exp(iδB) into backward waves exp(−iδB) and vice-versa. This effect keeps the same configuration for the incident and reflected electromagnetic wave at the interface AB, but the electromagnetic wave at layer B has now a sign change in the exponentials when compared to the electromagnetic wave at layer A. The optical transmission spectrum for the 16th-generation of the quasiperiodic Fibonacci sequence with mirror symmetry, as a function of the reduced frequency Ω, is depicted in Fig. 2(a). The transmission spectrum presents a unique mirror symmetrical profile around the central peak frequency Ω =1, which is of course the mid-gap frequency of a periodic quarter-wavelength multilayer, since in this case the phase-shift δA = δB = π/2. Besides, the structure is transparent (the transmission coefficient is closely equal to 1.0) in the central range of frequency 0.942< Ω <1.058, and at the reduced frequencies distributed symmetrically at Ω = 0, 0.330, 0.487, 0710, 1,290, 1.513, 1.670 and 2.0, respectively.

The condition of transparentness implies that the layers A and B$ are equivalent from a wave point of view. The photonic band gaps can be better characterized if one consider the narrow frequency range $0.977 \leq \Omega \leq 1.023$ for the optical transmission spectrum, as it is depicted in Fig. 2(b). It is important to mention that the symmetric internal structure of the one-dimensional quasiperiodic systems can greatly enhance the transmission intensity, with a striking self-similar behavior occurring every time the difference between two generation numbers of the Fibonacci sequence is equal to six [2]. The transmission spectrum has scaling property with respect to the generation number of the Fibonacci sequence, within a symmetrical interval around. Our results present some differences from those found for the case of symmetric Fibonacci multilayers with both positive refractive index materials [2–4], namely, the transmission peaks are different in the form and in the intensity, mainly for low values of the number of generation of the Fibonacci’s sequence.

Acknowledgements: Thanks are due to the Brazilian Research Agencies CAPES (Procad and Rede NanoBioTec), CNPq (INCT-Nano(Bio)Simes and Casadinho-Procad) and FAPERN/CNPq (Pronex).

References [1] M.S. Vasconcelos, E.L. Albuquerque and A.M. Mariz, J. Phys.: Condens. Matter 10, 5839 (1998).

[2] P.W. Mauriz, M.S. Vasconcelos and E.L. Albuquerque, Phys. Lett. A 373, 496 (2009).

[3] R.W. Peng, X.Q. Huang, M. Wang, A. Hu, S.S. Jiang, D. Feng, Phys. Rev. B 69 165109 (2004).

Figure 1: Geometrical arrangement of the symmetrical Fibonacci quasiperiodic multilayer system considered in this work.

Figure 2: Normal-incidence transmission spectra of a light beam into a Fibonacci multilayered photonic structure with mirror symmetry as a function of the reduced frequency Ω = ω/ω0 = λ0/λ for the 16th generation of the Fibonacci sequence: (a) the transmittance T for the range of frequency 0 < Ω < 2. (b) same as in (a), but for the range of frequency 0.977< Ω <1. 023.

Evaluation of carbon nanotubes - oil dispersion stability Wojciech Mazela, Wojciech Krasodomski, Michał Pajda, Kamil Pomykała, Leszek Ziemiański Oil and Gas Institute, ul. Lubicz 25a, Cracow, Poland mazela@inig.pl Abstract (Arial 10) According to literature, the introduction of nanotubes into liquid fuels can have a positive impact on: the processes of combustion, electrical conductivity, antiknock properties of gasoline [1], diesel fuel cetane number and octane number of gasoline [2]. However, the main problem is to obtain sufficiently stable dispersions of carbon nanotubes in fuels [3].

This paper presents results of research on obtaining a stable dispersion of diesel fuel with multiwall carbon nanotubes of different sizes, single-wall and modified multi-wall carbon nanotubes, which contain hydroxyl groups or carboxyl groups. The paper also evaluates the impact on the stability of dispersions of four selected surfactants: polyisobutylene succinimide (PIBSI), polyisobutylene succinimide anhydride (PIBSA), the amide derivative of polyisobutylene succinimide anhydride (APIBSA) and propoxylated dodecylphenol, containing about 30 propoxyl groups (DF-30).

Dispersions in the base diesel and commercial diesel fuel were produced with the help of an ultrasonic disintegrator. The resulting samples were analyzed for the nature of the nanotubes, the type of dispersant and oil. Both multi and single-walled carbon nanotubes are highly tangled and have very low solubility in any solvent. Given the practical applications, this fact constitutes a barrier, both in terms of scientific research and industrial applications. The difficulty of obtaining homogeneous and stable dispersion is associated with strong π-π interactions between the carbon nanotubes [4].

Besides the obvious difficulties in obtaining stable and homogeneous dispersion of nanotubes, the important issue is to apply a useful method to assess the state of oil dispersion. Nanotube or nanotube agglomerates can be characterized directly or indirectly based on mechanical or electrical dispersed system properties.

In this case the evaluation of the stability of the dispersion was performed by turbidimetry. This method is based on measuring the correlation between the amount of light emitted by the source and the amount of light reaching the detector after passing through the cell with the test sample. This correlationship depends mainly on the concentration of suspended particles, which cause light scattering. For this purpose, samples prepared by sonication were transferred to test tubes and subjected to scanning using the Turbiscan Lab Expert instrument. Scanning began immediately after sonification and was performed at defined periods of time. It was assumed that the stability criterion would not allow light transmission through the sample (transmission = 0%). At once after preparing nanotubes dispersion (concentration 100 mg/kg) zero transmission was recorded. This condition was taken as stable. The advent of transmission other than zero was interpreted as a loss of stability of the dispersion.

In the case of multi-wall nanotubes, depending on their sizes, there was some difference in the ability to create dispersion in diesel fuel, although in any case, these dispersions are not stable enough.

To obtain a dispersion, which stability exceeds 12 months it is necessary to use an appropriate dispersant. Stable dispersions with single wall nanotubes were not obtained. Both the base and commercial diesel fuel, regardless of dispersant used, the stability of the dispersion did not exceed several hours. Also modified multiwall nanotubes, containing hydroxyl groups or carboxyl groups, did not form stable dispersions in diesel oil. A little more stable dispersion of a few days old, was observed in the case of nanotubes dispersed in the commercial diesel fuel, which shows the stabilizing influence of various additives used during diesel production.

References [1] US patent no. 6 419 717. Moy D., Chunming Niu, Tennet H., Hoch R., (2002).

[2] Kish S. S., Rashidi A., Aghabozorg H.R., Moadi L., Appl. Surf. Sci., 256 (2010) 3472.

[3] Krasodomski M., Krasodomski W., Ziemiański L., Scientific work of the Oil and Gas Institute, no. 156 (2008).

[4] Vaisman L., Wagner H. Daniel, Marom G., Adv. Colloid Interface Sci., 128–130 (2006) 37–46

Green Synthesis of Silver Nanoparticles Mediated by Bee Products

1

2

R. Mendoza-Reséndez , N.O. Nuñez , C. Luna

3

1 Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, 66450, México 2 Instituto de Ciencia de Materiales de Sevilla, CSIC-ICS, Avda. Americo Vespuccio nº 49, Isla de la Cartuja, 41092, Sevilla, Spain.

3 Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, 66450, México raquel.mendozars@uanl.edu.mx Abstract Since ancient times, honey and other bee products have been widely used as functional food ingredients and therapeutic agents due to the unique health benefits they provide (which includes antibacterial, antioxidant, antitumor, anti-inflamatory and antiviral activities) [1].

Recently, several investigations have shown that the high antioxidant potential of honey can also be exploited to develop new approaches to the efficient production and processing of nanomaterials [2-4], which offer interesting advantages over the conventional routes: they are quite simple, economically competitive and reduce risks to human health and the environment [5]. In addition, these greenchemical procedures provide new methods for the functionalization of nanostructures, especially for applications in biomedicine including drug delivery and tissue imaging [2, 5].

The powerful antioxidant action of honey has been attributed to its high content of phenolic compounds [1], however the identification of this compounds remains a difficult task. In an interesting work, Perez et al. [6] studied the antioxidant activity and the total polyphenol content in different kinds of nectar honey and honeydew honey, and they found that honeydew honeys generally showed higher antioxidant capacities. Therefore, bee products exhibit astonishing properties that remain to be elucidated fully and whose practical use could result in novel promising applications.

In the present contribution, eco-friendly syntheses of silver nanoparticles mediated by various bee products (raw honey, royal jelly, honeydew honey and propolis) have been explored. Studies performed by analytic techniques, such as X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), Ultraviolet-Visible spectrophotometry (UV-Vis) and Infrared spectroscopy (IR), revealed that the obtained samples are consisted of colloidal silver nanoparticles with ultra-fine sizes and narrow size distributions. Such particles are embedded into organic matrices that stabilize them by inhibiting their great tendency to grow by coalescence processes. In addition, such matrices allow the colloidal dispersion of the silver nanoparticles into highstable concentrated aqueous colloids. Figure 1a shows a TEM micrograph of the particles obtained with raw nectar honey. These particles are embedded in an organic matrix and display a median diameter of 2.7 ± 0.5 nm (see the particle size distribution presented in Figure 1b). High-resolution TEM (HRTEM) and SAED studies corroborated that these particles are nanoscopic crystals of metallic silver.

References [1] M. Viuda-Martos, Y. Ruiz-Navajas, J. Fernández-López and Pérez-Álvarez, Journal of Food Science, 73 (2008) R117.

[2] R.Venu,T.S.Ramulu,S.Anandakumar,V.S.Rani,C.G.Kim, Colloids and Surfaces A: Physicochem.

Eng. Aspects 384 (2011) 733.

[3] Daizy Philip, Spectrochimica Acta Part A 73 (2009) 650.

[4] Daizy Philip, Spectrochimica Acta Part A 75 (2010) 1078.

[5] Valentinas Snitk, Denys O. Naumenko, Lina Ramanauskaite,Sergiy A. Kravchenko, Boris A. Snopok, Journal of Colloid and Interface Science, (2012) doi:10.1155/2012/730746.

[6] Lucia Vela, Cristina de Lorenzo and Rosa Ana Perez, J Sci Food Agric. 87 (2007) 1069.

Figures

Figure 1. a) Conventional TEM image of silver nanoparticles synthesized using nectar honey. b) Particle size distribution of the same sample. c) HRTEM image of a silver nanoparticle. d) SAED pattern obtained for the area observed in part (a).

The surface Plasmon's frequencies of two Metallic Nanospheres by Bloch-Jensen Hydrodynamical Model 2

1

3

M.Mirasmouri ,F.Ebrahimi ,V.Ebrahimi m.mirasmouri@uoz.ac.ir 1 Department of Physics, Faculty of Sciences, university of zabol,zabol,Iran 2 Department of Physics, Faculty of Sciences, Shahid Beheshti University, Evin, Tehran, Iran 3 Department of Physics, Faculty of Sciences, university of Tabriz,Tabriz,Iran The wave guides and optical fibers have long been known to transmit light and electromagnetic fields in large dimensions. Recently, surface plasmons, that are collective plasma oscillations of valence electrons at metal surfaces,have been introduced as an entity that are able to guide light on the surfaces of the metal and to concentrate light in subwavelength volumes.It has been found that periodic array of metallic nanospheres, could be able to enhanced the light transmission, and guiding light at nanoscale[1-2].The coupling between two nanoparticle in these devices is very important.

The Bloch-Gensen hydrodynamical method has been used for computing surface plasmons frequencies of a single metallic nanosphere[3]. In this research,we compute the surface plasmons frequencies of two nanospheres by bloch-gensen hydrodynamical model for the first time. The results show that the plasmons frequencies are depend explicitly on the nanoparticle radius. The hydrodynamical model contains the entire pole spectrum automatically, so it is more exactly than the other computational methods.

The surface Plasmon's frequencies of two nanospheres We consider two nanospheres that they closely spaced in vacuum and the space between them is b in the z direction. According to figure1The center of sphere 1 is in z=0 and sphere 2 is in z=b.

The electron density for sphere 1 and sphere 2 is[3], (2) −i ω t n1 ( r , θ , ϕ , t ) = ∑ A lm(1)i l ( kr ) y lm (θ , ϕ )e − i ωl t + H .C , r ≤ R n2 (ξ , Θ,ϕ,t ) = ∑ Alm i l (k ξ ) y lm (Θ,ϕ )e l + H .C , ξ ≤ R (1) lm

lm

Where ( r ,θ ,ϕ ) and (ξ,Θ,φ) are polar coordinates of sphere 1 and sphere2 respectively, il ( kr ) is modified Bessel function and yl ,m is spherical harmonics. In order to surface plasmon's frequencies computation the electric potentials are calculated and then the boundary condition is applied, that is the radial electric current density at the surface is zero ( jr |r = R = 0 ) It should be noted that the total potential inside of sphere1 is due to the electron densities of spheres1,2, so the electrical potential resulting of electron density of sphere1 inside of it is [9], φ 11 ( r ,θ ,ϕ , t ) =

∑

(1) A lm

lm

4π kR r l ( il ( k r ) − i l − 1 ( k R )( ) ) y lm ( θ ,ϕ ) e − iω l t + H .C (2) 2 k 2l + 1 R

and the electron density of sphere2 produce electrical potential inside of sphere1 that is [3], A l(m2 ) y l m ( Θ , ϕ ) R l + 2 φ 2 ( ξ , Θ ,ϕ , t ) = − 4 π i ( k R ) e − i ω t + H .C (3)

∑

1

lm

2l + 1

ξ

l+1

k

l

l+1

r

r

r

This two potential should be written in the same coordinate so we use ξ = r − b [4] and so the total potential inside of sphere 1 is, φ 1T = φ 11 + φ 12 = 4π kR r l il − 1 ( k R ) ( ) ) y lm ( θ ,ϕ ) ∑ A l(m1 ) 2 ( i l ( k r ) − k

lm

−

∑ lm

A l(m2

)

2l + 1

R

4π R l+1 ( − 1 ) l + m H ( l ′ , l , m ) l ′ + 1 y l ′ − l ,m ( θ , ϕ ) ( k R ) r 2 k b

l ′− l

il + 1 ( k R )

(4)

Where, H ( l ′ , l , m ) = (

2l + 1 l′! l′! )1 / 2 ( 2( l ′ − l ) + 1 ) ( l + m ) !( l ′ − l + m ) !( l − m ) !( l ′ − l − m )!

(5)

Now the boundary condition is applied and by using the equation (1), jr |r =R = 0 →

∂φ1T ( r ,θ ,ϕ ) β 2 ∂n1( r ,θ ,ϕ ) |r =R = |r =R ∂r n0 ∂r (6)

by inserting (1) and (4) in the equation (6) and some algebra the following relation is achieved A l( ,1m ) [ ( =

∑

ω

l′ l ′≥ l + |m |

k

2 p 2

− β

A l(′ −2 l), m

2

)

ω

2 p

k

k( l + 1 ) β 2kl il + 1 ( k R ) − il − 1 ( k R ) ] 2l + 1 2l + 1 ( − 1 ) l ′− l + m H ( l ′ , l , m ) (

R l′+ 1 ) l il ′− l + 1 ( k R ) b

(7)

In order to applying the boundary condition j ξ |ξ = R = 0 we need to write the potential of sphere1 with respect of sphere2 coordinates, The computations are like the sphere1 computations and by doing them the relation (8) is obtained for sphere2,   ω p2 A l(′′2,m) ′′   2 − β   k

2

  k( l + 1 ) β 2 kl il + 1 ( k R ) − il − 1 ( k R )  =  + + 2 l 1 2 l 1  

∑

l′ l ′≥ l + |m |

A l(′ 1− l) ,m

ω k

2 p

( − 1 )2 l ′− l + m H ( l ′ , l , m ) (

R l ′+ 1 ) li l ′ − l + 1 ( k R ) b

(8)

It is necessary to computed matrix density coefficients and find the roots of its determinant, that they are surface plasmons modes of these two metallic spheres. By assuming that the radiuses of nanospheres are 25 nm. And by computing the roots of matrix coefficients, it is observed that two roots exist for a given b, these roots are surface Plasmon’s modes for these two nanospheres, and the frequencies are plotted in below fig. The results are shown that if the space between this two sphere increased, the frequencies get close together and are equal to single sphere surface plasmon frequency in the state 20nm

and

l = 1 . It is observed that surface plasmon frequency of a sphere with radius

β = 1084435.337 m / s

and

ω p = 6.79 × 10 15 rad / s

is

equal

to

ω = 3.95827 × 10 15 rad / s .

References [1] M.Quinten, A. Leitner,J.R.krenn,F.R.Aussenegg, “Electromagnetic energy transport via linear chains of silver nanoparticles”, Opt. Lett. 23 (1998), 1331.

[2] S. A. Maier, P. G. Kik, and H. A. Atwater, “Observation of coupled plasmon-polariton modes in Au nanoparticle chain waveguides of different lengths: estimation of waveguide loss,” Appl. Phys. Lett.

81(9) (2002), 1714–1716.

[3] N.Barbean and Bausells, “Plasmon excitation in metallic spheres”, phys.Rev.B 13(1985) ,6354 [4] F.claro,phys.Rev.B25,2483(1282)

Electrodeposition of Polyaniline nanowires 1

S. Mohajeri, A. Dolati , E.Jabbari Department of Materials Science and Engineering, Sharif University of Technology, Tehran, P.O.BOX 11155-9466, I.R.Iran Email: soha_posh@yahoo.com

Abstract Electrochemical supercapacitors are the charge-storage devices having high power density. The nano scale materials with high surface area and high porosity, give the best performances as electrode materials for supercapacitors due to their distinctive characteristics of conducting pathways and nano scale dimensions. Therefore, the synthesis and capacitive characterization of the high surface area nanomaterials such as nanowires have been carried out extensively.

In this research, polyaniline nanowires were electrochemically deposited on stainless steel electrode with the technique of choronoamperometry and pulse voltammetry and characterized by cyclic voltammetry and charge-discharge cycling for supercapacitive properties. The mechanism of electrodeposition was analyzed by cyclic voltammetry and chronoamperometry techniques. The morphology of coatings was investigated by scanning electron microscopy (SEM).

It was determined that electrodeposition is controlled by diffusion with a limited and steady state current and the mechanism of nucleation is absolutely uniform. SEM images of the polyaniline nanowires show that the diameter of the nanowires is in the range of 40-70 nm. The PANI nanowire arrayed electrodes have excellent specific capacitanceand high efficiency of charge/discharge cycling which is very important for the electrode materials of a capacitor to provide high power density.

Keywords: polyaniline, nanowire, supercapacitors, electrodeposition References [1] L.Permann, M.Latt, J.Leis, M.Arulepp, Electrochimica Acta , 51 (2006) 1274–1281 [2] F.Liu , L.Huangb, T.Wen, A.Gopalan, Synthetic Metals, 157 (2007) 651–658 [3] X.Yua, Y.Li, K.Kalantar-zadeh,Sensors and Actuators B, 136 (2009) 1–7 [4] H.Nguyen, Thi Le, B.Garcia, Deslouis. Le Xuan b, Electrochimica Acta 46 (2001) 4259–4272 [5] I.L.Lehr, S.B.Saidman, Materials Chemistry and Physics 100 (2006) 262–267 [6] F.Beck, R.Michaelis, F.Schloten, B.Zinger, Electrochimica Acta, 39 (1994) 229 [7] D.E.Tallman, M.P.Dewald, C.K.Vang, G.G.Wallace, G.P.Bierwagen, Current Applied Physics, 4 (2004) 137–140 [8] J.D.Morenoa, M.L.Marcosb, F.Ruedac, R.Guerrero, R.J.Martýn, J.M.Duarta, J.Velascob, Thin Solid Films, 348 (1999) 152-156

1

Corresponding author.Tel:+98 21 6616 5201,Fax:+98 21 66005717 Email address: dolati@sharif.edu (A.Dolati).

Figures

Figure 1. Cyclic voltammetry curves for

Figure 2. Variation of |Ep-Ep/2| versus scan rate

polymerization of polyaniline in different scan rates

(a) 2 2

Figure 3. Variation of I /I

m

versus t/tm in

different potentials

Figure 5. Nyquist curgves for polyaniline nanowires achieved by pulse voltammetry and chronoamperometry techniques

(b)

Figure 4. Scanning electron microscopy (SEM) of polyaniline achieved by chronoamperometry techniques at a) 70mV b) 75mV in 15 minutes

Figure 6. Variation of specific capacitance versus specific current for polyaniline prepared by chronoamperometry technique

Chemical remediation: Squaramide Magnetic Iron Nanoparticles for Removal of Toxic Metals ions in Water Jeroni Morey, Maria de las Nieves Pi帽a and Kenia A. L贸pez Department of Chemistry, University of the Illes Balears, Palma de Mallorca, Spain jeroni.morey@uib.es 2+

2+

2+

3+

Elimination of toxic heavy and transition metal ions, such as: Hg , Pb , Cd , Cr and its compounds 2+ in the environment is of great interest because of their high toxicity. For example, Pb ion can affect almost every organ and system in the human body, particularly in children, causing various symptoms such as anemia, kidney damage, and a disorder of the blood, memory loss, muscle paralysis, and [1] 2+ mental retardation by lead poisoning.

Also, there are many reports on the toxicity of Cd to procreation, bones, kidneys, nerve system, and tissues, consequently resulting in renal dysfunction, [2] calcium metabolism disorders, and an increased incidence of certain forms of cancers. .

2+ Especially in this regard, the Hg ion is considered highly dangerous because both elemental and ionic mercury can be converted into methyl mercury by bacteria in the environment, which subsequently bio [3] accumulates through the food chain.

[4]

The iron nanoparticles were synthesized as described by Sun. Here we report a simple approach to conjugate monodisperse Fe3O4 nanoparticles with a squaramide-dopamine unit.

O

O +

O

O

O

O

O

N H

Et2O

H2N

+ NH3 Cl

HO HO CH3OH HO

O

O

HO

N H

N H

+

Fe3O4

EtOH

O

O

O

O

N H

N H

Fe3O4

Figure 1. Preparation of Squaramide Iron-Nanoparticles (NPSq)

Our results, see Figure 2, show that hybrid squaramide magnetic iron nanoparticles (NPSq) remove 2+ 2+ 3+ from a water solution of a heavy toxic metals ions, the 99% of Pb , 92% of Hg , 87% of Cr and 85% 2+ 2+ of Cd . However, the Fe3O4 nanoparticles (NP), without functionalization, only remove 28% of Pb , 2+ 3+ 2+ 31% of a Hg , 6% of a Cr and less than 1% of Cd .

Figure 2: Metals ions retention by Squaramide Iron-Nanoparticles (NPSq) and iron-nanoparticles (NP).

References [1] Rifai, N., Cohen, G., Wolf, M., Cohen, L., Faser, C., Savory, J., DePalma, L. Ther. Drug Monit. 15, (1993), 71 and reference therein.

[2] Dobson, S. Cadmium: Environmental Aspects; World Health Organization: Geneva, (1992).

[3] Boening, D. W., Chemosphere 40, (2000), 1335. (b) Benoit, J. M.; Fitzgerald, W. F.; Damman, A. W. Environ. Res. 78, 1998, 118.

[4] Xie, J., Xu, C., Xu, Z., Hou, Y., Young, K. L., Wang, S. X., Pourmond, N., Sun, S. Chem. Mater. 18 (2006), 5401.

Spin-dependent transport in graphene nanoribbons with a periodic array of ferromagnetic strips 1

1,2

1

3

4

1

J. Munárriz , C. Gaul , A. V. Malyshev , P. A. Orellana , C. A. Müller , and F. Domínguez-Adame 1

GISC, Departamento de Física de Materiales, Universidad Complutense, E-28040 Madrid, Spain 2 CEI Campus Moncloa, UCM-UPM, Madrid, Spain 3 Departamento de Física, Universidad Católica del Norte, Casilla 1280, Antofagasta, Chile 4 Centre for Quantum Technologies, National University of Singapore, Singapore 117543, Singapore j.munarriz@fis.ucm.es Abstract Since the pioneering work by Esaki in the late 1950s [1], negative differential resistance (NDR) has been the basis for the operation of many quantum devices. The underlying mechanism of NDR is related to the resonant tunneling of carriers through the device. When the chemical potentials of the leads match one of the resonant levels of the device, the current I increases dramatically. The resonant level depends on the applied source-drain voltage VSD, which finally drives it out of resonance, such that the current decreases with a further increase of voltage. The resulting I-V characteristic in the NDR regime is not monotonic but N-shaped instead.

The unique properties of graphene, like its truly two-dimensional geometry as well as high carrier mobility and large mean free path, have attracted much attention for the design of novel quantum devices. Besides its remarkable properties for charge transport in nanostructures, the long spincoherence length up to several microns makes graphene a material of choice for spintronic devices [2].

Ferromagnetic insulators deposited on graphene can induce ferromagnetic correlations of itinerant electrons. This opens the possibility of spin current generation.

In this work, we combine the aforementioned aspects, NDR and spin selectivity, in a graphene-based device. We consider a spin-dependent superlattice realized by ferromagnetic strips placed on top of an armchair GNR (see Fig. 1). Similar settings have been studied by Niu et al [3] – using bulk, gapless graphene instead of nanoribbons – and by Ferreira et al [4] – without taking into account spin dependence. We compute the spin-dependent transmissions, T±, and I-V curves using a full tight binding (TBA) calculation, as well as the graphene Dirac Hamiltonian. The latter allows us to provide simple analytical expressions to determine the position of the resonant levels at N = 2, as well as the band structure as N → ∞.

The energies of the transmission peaks and transmission bands strongly depend on the spin σ. First, we address the unbiased system, i.e., VSD = 0. For the range of parameters chosen (W = 9.84 nm, N = 5, da = 23.9 nm, db = 55.8 nm, exchange splitting h = 5 meV; see Fig. 1), the overlap between transmission bands corresponding to different spins is small (see upper panel of Fig. 2). This is also revealed by the transmission polarization PT = (T+ - T-)/(T+ + T-), plotted in the lower panel of the figure, which presents abrupt shifts from -1 to 1, and vice versa. Then, we address the calculation of the current response of the device to a potential difference VSD between source and drain, whose chemical potentials, µS = e·VSD+µ and µD = µ have the same offset µ from their corresponding band-gap centers. The well-known Landauer-Büttiker scattering formalism is used, setting the temperature T to 4 K, the results being plotted in Fig. 3. The spin-dependent shift of transmission bands permits the NDR to be found at different biases. For spin down σ = -1, the NDR slope can be quite steep. This is due to the fact that, at lower bias, the distortion of the transmission profiles with respect to the unbiased case VSD = 0 is smaller, keeping a well defined peak at the energies of interest, surrounded by regions with vanishing transmission. At higher bias, the profiles are smoothed.

References [1] L. Esaki, Physical Review, 109 (1958) 603 [2] A. V. Rozhkov, G. Giavaras, Y. P. Bliokh, V. Freilikher, and F. Nori, Physics Reports, 503 (2011) 77 [3] Z. P. Niu et al, European Physical Journal B, 66 (2008) 245 [4] G. J. Ferreira, M. N. Leuenberger, D. Loss, and J. C. Egues, Physical Review B, 84 (2011) 125453

Figures

Figure 1: schematic view of a GNR, with N = 5 strips of a ferromagnetic insulator placed on top of it (shown as green bars). Source and drain terminals are denoted as S and D respectively.

Figure 2: Upper panel shows the transmission coefficients as function of energy for VSD = 0, obtained from the Dirac theory (dotted red and dashed blue lines show T- and T+, respectively), and from the tight-binding calculation (solid lines). Lower panel shows the degree of the transmission polarization PT=(T+-T-)/(T++T-).

Figure 3: Currents I+ (dashed) and I- (solid) as function of VSD for different values of the chemical potential Âľ in the leads.

Nanoparticles and nanocomposites as VOC recognition materials Ghulam Mustafa, Munawar Hussain, Peter A Lieberzeit University of Vienna, Department of Analytical Chemistry, Waehringer Strasse 38, 1090-Vienna, Austria ghulam.mustafa@univie.ac.at Implementation of functionalities into man-made matrices on molecular level is of substantial interest in modern recognition materials science. For on-line monitoring, chemical sensors are among the most promising and suitable techniques [1]. Their sensitivity and selectivity can be improved by increasing the specific surface area of the recognition materials i.e. by using nanoparticles layers instead of thin films.

Preliminary studies [2,3] revealed that a “soft” metal sulfide has substantial affinity towards thiol vapors.

The development of direct and non-destructive method for thiol detection is of great interest, because to date only very few gas sensors for thiols have been reported [2,3,4,5,6,7].

MoS2 nanoparticles have proven to be a suitable recognition material for thiol vapors. To further elucidate the influence of Pearson hardness on the sensor effects, different metal sulfides, e.g. copper sulfide and silver sulfide, were assessed according to their properties as sensor layers: Figure 1 compares the sensor signals of MoS2, Cu2S and Ag2S nanoparticles towards 30 ppm of 1-octanethiol obtained with quartz crystal microbalance (QCM), respectively. As can be seen, molybdenum disulfide NPs yield a sensor response of only 10 Hz which is three times less than that of Cu2S NPs. Furthermore, Ag2S NPs show 10 folds better sensor signal as compared to copper sulfide nanoparticles.

The order of sensor effects exactly corresponds to the order of Pearson "softness" supporting affinity interactions between thiol and nanoparticles. Exposing the soft metal sulfide NPs based sensors to different concentrations of n-octane yield no significant response. Similarly, CuS nanoparticles - being a hard material – do not give rise to any sensor signals, which further corroborates and supports the fundamental strategic approach for thiol sensing, namely addressing the Pearson hardness.

Recently, substantial efforts have been undertaken to integrate inorganic nano-particles into the interior of polymer microspheres. The resulting inorganic-organic composite microspheres bear novel collective mechanical, thermal, optical, magnetic and electronic properties [8]. Therefore, it is of substantial interest to generate composites of metal sulfide nanoparticles with molecularly imprinted polymers (MIP) to make use of the best of two worlds, namely appreciable sensitivity provided by the former and selectivity/pre-concentration ability from the latter. Figure 2 summarizes the comparison of sensor responses of silver sulfide nanoparticles (NPs) and nanocomposite towards different concentrations of 1-butanol ranging from 100 ppm to 400 ppm. Obviously, combining the Ag2S NPs and MIP leads to further improvement, because their signals are two times higher than the response of the pure nanoparticles. This clearly indicates that despite the appreciable affinity between NPs and the analyte, sensitivity is increased by the MIP functioning as a “pre-concentrator” for the volatile organic around the Ag2S nanoparticles. To the best of our knowledge, this reports the first NP/MIP composite for sensing applications.

References [1] C.K. Ho, A. Robinson, D.R. Miller, M.J. Davis, Sensors 5 (2005) 4–37.

[2] Peter A. Lieberzeit, A. Afzal, A. Rehman, Franz L. Dickert, Sensors and Actuators B 127 (2007) 132– 136.

[3] G. Mustafa, M. Hussain, N. Iqbal, F.L. Dickert, P.A. Lieberzeit, Sensors and Actuators B 162 (2012) 63– 67.

[4] P.G. Datskos, I. Sauers, Sensors and Actuators B, Chem, 61 (1999) 75–82.

[5] S.M. Briglin, T. Gao, N.S. Lewis, Langmuir, 20 (2004) 299–305.

[6] M. Kikushi, S. Shiratori, Sensors and Actuators B, Chem, 108 (2005) 564–571.

[7] T. Minamide, K. Mitsubayashi, H. Saito, Sensors and Actuators B, Chem, 108 (2005) 639–645.

[8] Y. N. Chan, G. S. W. Craig, R. R. Schrock and R. E. Cohen, Chemistry of Materials,4 (1992) 885894.

Figures

350

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Fig 1: Sensor signals of MoS2, Cu2S and Ag2S nanoparticles toward 30ppm of 1-octanethiol

Sensor Response [Hz]

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Fig 2: Sensor signals comparison of composite and nanoparticles towards different concentrations of 1butanol

Copper (II) Tetrasulfonated Phthalocyanine Immobilized on Superparamagnetic Nanoparticles Catalyzed Highly selective and Economical Heterogeneous Oxidation of Hydrocarbons in Water Atena Naeimi, Abdolreza Rezaeifard, Maasoumeh Jafarpour 1 Department of Inorganic Chemistry, Universitat Autònoma de Barcelona, Barcelona, Spain 2 Catalysis Research Laboratory, Department of Chemistry, University of Birjan, Birjand, Iran.

3 Department of Chemistry, College of Science, Shiraz, 71454, Iran Atena.Bagheini@uab.cat, At_naimi@yahoo.com Abstract In the age of environmental amity chemistry, heterogeneous reactions have become an important objective as these processes are used in industry, helping to minimize the problems of industrial disposal and waste treatment [1]. For practical applications of heterogeneous systems, the life time of catalyst and its recovery and extension of reusability are very important factor. Many attempts have been devoted for hetrogenization of porphyrin complexes as often-used bio-relevant catalysts within different organic and inorganic supports to enhance their chemical stability and allow catalyst recovery by simple filtration [2].

However, due to the diffusion of substrates and products through the pores of the support materials, a substantial decrease in the reaction rate is frequently observed compared to the homogeneous system [3]. To overcome this limitation the size of the support particles should be kept as small as possible providing nanoparticles with high external surface area. Consequently, a high loading of catalytically active sites is obtained and diffusion will no longer limit the kinetics.

Nanoparticles have recently emerged as efficient alternatives for the immobilization of homogeneous catalysts. Nevertheless, difficulties in recovering the nanometer-sized particles from the reaction mixture resulting from effective dispersion in solution by forming stable suspensions, severely limited their wide applications. There is currently intense interest in the use of magnetic nanoparticles (such as Fe3O4) for a wide range of biomedical and technological applications. They have been coated with metal catalysts or conjugated with enzymes, to combine the separating power of the magnetic properties with the catalytic activity of the metal surface or enzyme conjugate [4]. Furthermore, a recoverable catalyst requires a sustainable reaction media for application in scale-up procedures in practical goals. Discarding of harmful organic solvents is the major problem in chemical industries which accounts around 80% of their wastes.

Thus, a new challenge is to make innovative, “clean” methods by using non-toxic solvents in particularly aqueous media. Moreover, it has been found that reactions in water can facilitate access to different reactivity and selectivity patterns compared with those observed in common organic solvents due to its unique physical and chemical properties. In this regard, the use of water as a reaction solvent has attracted great attention in the recent past and has become an active area of research in green chemistry [5].

In this work water soluble copper (II) tetrasulfonated phthalocyanine supported on nano-sized Fe3O4 coated with a silica layer (CuPcS@Fe3O4) has been used as a magnetically recoverable heterogeneous nanocatalyst for highly selective aqueous oxidation of hydrocarbons using tetra-n-butylammonium peroxomonosulfate (TBAOX). Organic co-solvents, surfactants, co-catalyst and hydrophilic auxiliaries were completely missed in this heterogeneous catalytic strategy. The catalyst could easily be recycled by an external magnetic field and reused without loss of activity and the oxidant’s by-product (n-Bu4NHSO4) could also be recycled.

References [1] J. L. Zhang, Y. L. Liuab, C. M. Che, Chem. Commun.(2002) 2906-2907.

[2] A. Corma, H. Garcia, Chem. Rev. 102 (2002) 3837-3892.

[3] G. A. Somorjai, A. M. Contreras, M. Montano, R. M. Rioux, Proc. Natl. Acad. Sci. USA 103 (2006) 10577-10583.

[4] P. D. Stevens, J. Fan, H. M. R. Gardimalla, M. Yen, Y. Gao, Org.Lett. 7 (2005) 2085–2088.

[5] C.-J. Li, L. Chen, Chem. Soc. Rev. 35 (2006) 68-82.

Figures

Fig. 1. The oxygenation of hydrocarbons using CuPcS@Fe3O4 by n-Bu4NHSO5 in neat water o

99.82%, 201 C

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Fig. 2. SEM image of CuPcS@Fe3O4

Fig. 3. TGA thermogram of CuPcS@Fe3O4

Fano and Andreev Reflection in Quantum dots Pedro A. Orellana, Ana María Calle, Mónica Pacheco Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile Universidad T. Federico Santa María, Valparaíso, Chile orellana@ucn.cl Abstract Quantum dots are nano-devices in which electrons are confined in all space dimensions [1]. As a consequence of this confinement energy and charge are quantized. Because of both features are present in real atomic systems, useful analogies between and atomic systems have been exploited recently. By enforcing this analogy, effects like Fano effect [2,3] have been also found to be present in quantum dot configurations. The Fano effect originally arises when quantum interference takes place between two competing optical pathways, a discrete auto-ionized state with a continuum, giving rise to characteristically asymmetric line-shapes [2]. Unlike the conventional Fano resonance, the Fano effect in the quantum dot system has its advantage in that its parameters can be tuned continuously [3].

Recently, it has been much interest in the normal metal-superconductor junctions. These hybrid systems are very interesting for the so-called Andreev reflection (AR). In AR process an incident electron from the normal metal is reflected as a hole while a Cooper pair is created in the superconductor [4]. In these systems the superconductor acts as a source of spin for spintronics.

In the present work, we investigate the transport properties of a T-shape double quantum dot coupling to a superconductor lead and two normal leads. (Fig. 1) We found Fano-line shapes in the normalnormal quantum mechanics transmission due to Andreev reflection in the superconductor lead. This effect is studied as a function of the parameters defining the system.

References [1] L.Jacak, P. Hawrylak and A.Wójs, Quantum Dots (Springer--Verlag, Berlin, 1998).

[2] U. Fano, Phys. Rev. 124, 1866 (1961) [3] K.Kobayashi, H.Aikawa, A.Sano, S.Katsumoto and Y. Iye, Phys.Rev.B 70, 035319 (2004).

[4] Long Bai, Yang-Jin Wu, and Baigeng Wang, Phys. Status Solidi B 247, 335 (2010).

[7] J. Baranski, T. Domanski, Phys. Rev. B 85, 205451 (2012) Figures

Fig 1. Schematic view of T-shape double QD system coupled to left (L) and right (R) normal leads and a superconductor lead (S) with an inter-dot coupling denoted by t.

1

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Fig 2. Transmission from left to right lead (left panel) and from left to superconductor lead (right panel) versus energy for a T-shape DQD with parameters: Δ=ΓL, ΓR=ΓL, ε1 = ε2 =0, t=0.2ΓL a) ΓS =ΓL, b) ΓS =2ΓL and c) ΓS = 4ΓL Dashed line in left panel correspond to transmission with Δ=0, i.e for a system with three normal leads. (Δ superconductor gap)

Shape and Size Controlled ZnO Particles and Their Cytotoxic Behaviour 1

2

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3

Ugur Can Ozogut , Banu Barutca , Kenan Isik , Ender Suvaci , A. Tansu Koparal , Yucel Sahin 1

Anadolu University Department of Materials Science and Engineering Iki Eylul Campus 26480, Eskisehir, Turkey 2 Anadolu University Department of Biology Yunus Emre Campus Eskisehir, Turkey 3 Anadolu University Department of Chemistry, Yunus Emre Campus Eskisehir, Turkey

ugurcanozogut@gmail.com

ZnO particles are used in the cosmetic industry especially for their absorption ability of UVA and UVB lights that are harmful for human skin [1]. Moreover the size of particles go down to nano size, they gain a transparent and aesthetic appearance. Due to these properties, ZnO nanoparticles are promising materials for the sunscreen applications [2]. However ZnO particles can penetrate from the human skin when they have a nano size. Therefore synthesized ZnO nanoparticles with shape and size controlled as reducing their nanotoxicological effect is prerequisite. The objective of this study is to produce nano primer micron plate like shaped ZnO particles by solvothermal route and also investigate the toxicological behaviour on the cell. ZnO was used as zinc source (ZnO, Merck) and glycerol as a solvent (C3H8O3, Detsan) were used for the synthesis. Calcined particles and Zn-Organic complex were characterized with scanning electron microscopy (SEM, Zeiss Evo) , x-ray diffractometer (XRD, Rigaku).

Phase transformation between ZnO and Zn-Organic complex were observed from the XRD patterns.

The nano primer hexagonal shaped micron plates of ZnO has a size ranging from 2 to 10 µm ,that was seen from the SEM images. As a result, Zn-Organic complex with nano primer hexagonal micron plate o shape can be synthesized at 260 C for an hour , and ZnO structure can be formed with calcination.

Finally, the toxicological behaviour of ZnO particles on TIG 114 (human skin fibroblast) cell was investigated with plate like and precurcor particles comparatively. Cytotoxicity was determinated by MTT (3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. TIG 114 cells were treated with 0, 1.25, 2.5, 5, 10, 20, 40, 50, 80, 100 and 200 µg/ml ZnO nanoparticles in media for 24 hours. The results showed that precursor ZnO nanoparticles exhibited a significant effect on the viability of TIG 114 cells depent on concentrations. ZnO plate did not induced cytotoxicity at lower concentrations (range of 1.25 - 40 µg/ml), cytotoxic effect was observed at higher concentrations (50, 80, 100 and 200 µg/ml).

Consequently the use of plate like shaped ZnO particles were thought that precaution for penetrating the human skin and also protection against the UV lights with aesthetic apperiance.

Acknowledgements The financial support for this study from The Scientific and Technological Research Council of Turkey (TUBITAK) (Project Number: 109M585) and Anadolu University Scientific Research Projects Commission (Project Number : 1101F020) was gratefully acknowledged.

References 1. Innes, B., Tsuziki, T., Dawkins, H., Dunlop, J., Trotter, G., Nearn, M. ve McCormick, P.G., Nanotechnology and the cosmetic chemist, (2002) 2. Faunce, T., Murray, K., Nasu, H. ve Bowman, D., Sunscreen safety: The precautionary principle, The Australian Therapeutic Goods Administration and Nanoparticles in sunscreens, Nanoethics, 2, (2008) 231-240.

Figure 1. SEM images of nano primer hexagonal micron plate shaped ZnO a) before calcination (ZnOrganic Complex), b) after calcination.

o

Figure 2. XRD patterns of a) Zn-Organic Complex and b) ZnO after calcination occurs at 350 C

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Figure 3. Dose depent Cytotoxic behavior of precursor ZnO and synthesized ZnO plate on TIG-114 cells.

Cell Viability by MTT (% Control )

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Theoretical study of band alignment in nano-porous ZnO interacting with substituted Phthalocyanines P. Palacios a,b, P. Wahnón b,c, B. Mari d a) Dpt. Física y Química Aplicadas a la Técnica Aeronáutica, EUIT Aeronáutica, Universidad Politécnica de Madrid, Pz. Cardenal Cisneros 3, 28040, Madrid, Spain. b) Instituto de Energía Solar. Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040, Madrid, Spain. c) Dpt. Tecnologías Especiales Aplicadas a la Telecomunicación, ETSI Telecomunicación, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040, Madrid, Spain. d) Departament de Física Aplicada- IDF. Universitat Politècnica de València, Camí de Vera s/n, 46022 València, Spain. pablo.palacios@upm.es Abstract The aim of this work is the theoretical study of the band alignment between the two components of a hybrid organic-inorganic solar-cell. The working organic molecules are metal tetrasulphonated phthalocyanines (TsPcMe) and the inorganic material is nano-porous ZnO growth in the 001 direction.

The theoretical calculations are being made using the density functional theory (DFT) using a GGA functional with the SIESTA code, which projects electron wave functions and density onto a real space grid and uses as basis set a linear combination of numerical, finite-range localized atomic orbitals. We also used the DFT+U method included in the code that allows a semi-empirical inclusion of electronic correlations in the description of electronic spectra for systems such as zinc oxide.

Basis set were optimized in order to obtain good ground state energies, cell parameters and bond lengths in bulk ZnO. Furthermore C and N basis set were optimized to minimize the energy in the Pc. First the ZnO and the M-Pc’s have been studied individually.

For the TsPcMe’s we study the more stable geometry and the HOMO and LUMO for different metals (Zn and Cu) finding the most reacting part. The molecule is flat except the sulphonic groups which can freely rotate. The effect of these groups on the interaction with the nanostructure appeared to be very important for the bonding and not only for the molecule solubility.

Different ZnO surfaces have been modeled to find the optimal configuration, in their most stable wurtzite phase, and relaxed to find the minimum energy positions. The (001) growth direction was studied, so the available faces to the dyes will be a perpendicular one as the (100).

After that we study the interaction between the two systems and compared the different electronic energy levels. Different parallel and perpendicular orientations have been tested. We have obtained the total and projected density of states of the system and observed the level alignment. The aim was to determine which metal would be theoretically more efficient in the charge transfer between the dye and the nanostructure. A good estimation of band alignments between the adsorbate and the substrate was achieved with DFT+U, using the correlation corrections that gave good spectra for both systems separately. This theoretical study can be seen as a first step to show how charge transfer would be.

Experimental hybrid films were also prepared by cathodic electro-deposition The TsPcMe, Me=Cu content of the films can be varied in a wide range by variation of dye concentration in the electrodeposition bath. Photo electro-chemical characteristics of the electrodes were studied by photo current spectra and by time-resolved photocurrent measurements. We compare theoretical and experimental results References [1] B. Marí, M. M. Moya, K. C. Singh, M. Mollar, P. Palacios, E. Artacho, P. Wahnón , J. Electroanal.

Chem. 653 (2011) 86

Figures 4x(SO3Na) groups

TsPc

Fig.1) Free Metal Tetrasulphonated Phthalocyanine (TsPcMe) and TsPcMe bonded to a ZnO surface

Fig. 2) DFT Projected Density of states for the ZnO/Ts-CuPc hybrid system. The Fermi level is aligned with ZnO valence band.

Fig 3) Photocurrent action spectra of ZnO/Ts-CuPc films electrodeposited with 30 µM, 40 µM, 70 µM and µ100M concentrations of dye.

Synthesis of nano-sized SiC and Si/SiC from silicon and carbon powders by non-transferred arc thermal plasma 1

Kyoung-Geun Park1, Kyoung-Jun Ko1, Jin-Wo Kim1, Jae-Kang Kim2, Sang-Ki Kang2, Yeon-Tae Yu * 1

Division of Advanced Materials Engineering and Research Center for Advanced Materials Development, College of Engineering, Chonbuk National University, Jeonju 561-756, South Korea 2 Neoplant Co. LTD, Oho-ri, Heungdeok-Myeon, Gochang-gun, jeonrabuk-do, 585-821, South Korea yeontae@jbnu.ac.kr Abstract SiC is widely used as refractory materials, disc brakes, filter materials, cutting tools, catalyst support, and heater materials because of its superior properties, which include high fracture strength, excellent creep and wear resistances, high hardness, heat resistance at high temperatures, corrosion resistance at high temperatures, and abrasion resistance. Recently, SiC has been used both in hightemperature heating and in the fabrication process of silicon wafers, which are critical to the semiconductor industry, and is being actively studied with the aim of achieving high-purity and largescale production [1-3].

However, the problems being difficult to sinter and the poor fracture toughness can restrict the effective use of SiC in engineering. It is highly required for SiC-based materials to enhance the fracture toughness, high temperature creep strengths, and swelling resistance, especially for fusion applications.

To improve the mechanical properties of SiC, high quality nanopowders have been used. Many methods could be used to produce SiC powders, such as sol–gel methods, gas-phase reaction method, solid state synthesis of silicon with carbon and so on. Among these methods, solid state synthesis of silicon with carbon was considered to be an attractive method due to its proven advantages: lower energy requirement, simpler and cheaper equipment, higher product purity, and finer and well-sintered starting powders [4]. Thermal arc plasma has a high temperature and is rapidly cooled in the tail flame region. The high temperature region can provide enough energy for the melting and evaporation of the sintered SiC powder and the rapidly cooled tail can aids a rapid solidification produced nano-sized sic.

In the present work, nano-sized sic powder was synthesized by solid state reaction and thermal arc plasma process from silicon powder with particle size of 6 μm and carbon black with particle size of 60 μm. In addition, for preparing nano-sized Si/SiC composite powder, the composition of silicon and carbon black powders was changed from Si:C = 1:1 to Si:C= 1:2 in mole ratio. The silicon and carbon o black was mixed together by ball mill for 15h. The mixture was calcined in an electric furnace at 1200 C for 6h. The calcined SiC or Si/SiC powder was nano-sized by non-transferred arc thermal plasma at pressure of 220 Torr. The Phase and crystalline structural analysis were carried out by X-ray diffraction (XRD).The crystalline structure of nano-sized SiC powder was ß-phase (Fig.1). The morphology was observed by transmission electron microscopy (TEM) & Scanning electron microscopy (SEM). The particle size of synthesized Si and Si/SiC nano-powder was in the range of 40 ~ 100nm as shown in Fig.2.

References [1] H.S. Tanaka, J. Ceram. Soc. Jpn. 119 (2011) 218 [2] H. Tanaka, N. Hirosaki, N. Nishimura, J. Ceram. Soc. Jpn. 111 (2003) 878.

[3] B. Ghosh, S.K. Pradhan, J. Alloys Compd. 486 (2009) 480 [4] S. Prochazka, R.M. Scanlan, J. Am. Ceram. Soc. 58 (1975) 72.

Corresp. Author: yeontae@jbnu.ac.kr, Phone: +82-63-270-2288, Fax: +82-63-270-2305

Fig. 1. X-ray diffraction patterns of nano-sized (a) SiC powder and (b) Si/SiC composite powder.

Fig. 2. TEM image of nano-sized SiC powder (mixture composition, Si:C=1:2).

Corresp. Author: yeontae@jbnu.ac.kr, Phone: +82-63-270-2288, Fax: +82-63-270-2305

Novel method in synthesis of YSZ microtubes and their application as ALD substrates 1

1

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Marko Part, Keijo Riikj채rv, Kelli Hanschmidt, Aile Tamm, Hugo M채ndar, Gunnar Nurk, Kaupo 1 Kukli, Tanel T채tte 1

Institute of Physics, University of Tartu, Riia 142, 51014, Tartu, Estonia Institute of Chemistry, University of Tartu, Ravila 14a, 50411, Tartu, Estonia

2

markopa@ut.ee

Materials with microtubular geometry have attracted considerable attention during the past few decades due to their broad range of applications. One interesting field of these applications are microfluidic devices used for energy storage and production, like SOFC, where microtubular geometry could possess better thermo-mechanical properties and sealing simplicity compared to other geometries [1].

Another possible application of microtubes is to use these as miniature plasma chambers. There exists many different methods for preparation of ceramic microtubes applied for these purposes, including chemical vapor deposition (CVD), electrophoretic deposition, extrusion of slurries, different template methods etc. However, all the known methods have significant disadvantages, which set restrictions to use of the materials. In most of cases obtained tubes have lack in their mechanical properties, materials are highly porous also and cannot be applied to seal the gasses into tubes. Moreover, there seems to be no methods, suggested for preparation of gas-tight ceramic microtubes with diameter in the range from 10-100 microns. Therefore, it is important to elaborate the methods for preparation of microtubes in the mentioned range range.

In the present work we introduce a method for preparation of metal oxide microtubes in mentioned range. Obtained materials have superior physical and chemical properties due to their nanohomogeneous structure based on crystallites with size up to some tens of nanometers [Fig. 1, 2].

The method is based on sol-gel technology, known as a versatile preparation route to ceramics from corresponding metal alkoxides. Its main advantages are generally related to relatively low processing temperatures, flexibility of method in order to prepare materials in desired geometries etc [2]. In order to obtain the materials in desired shape, the processing should be combined with some kind of mechanical manipulations like use of templates or molds and their subsequent removal, dip coating procedure, extrusion etc. Our studies focus on yttria stabilized zirconia (YSZ), that is widely used as solid electrolyte and material in engineering of SOFC and for other technical solutions [3].

The proposed method is based on direct drawing of microtubes from metal alkoxide-based precursors.

The hollowing is achieved as a result of rearrangement of jet material during the solidification, which for the content is saturated on the outer surface of the jet, while released alcohol remains into tube [2].

Obtained gel structures are post-treated by aging and thermal annealing to achieve removal of alcohol and to achieve dense nanocrystalline structure. Doping of the materials with yttria results in 100% transition of tube material into tetragonal structure. Obtained tubes exhibit tensile strength around 1 GPa, the value that is close to same of stainless steel, while Young modulus remains into very high 100-200 GPa range at the same. Ionic conductivity of tubes remain into 0,002-0,05 S/cm range that that is comparable to YSZ materials obtained by conventional methods [Fig. 3]. Pressurizing of the tubes by applying gasses or oil inside enabled to show resistance up to 1000 atm pressure. The tubes are thermally stable at least up to 1000 C.

With these properties, the tubes we have synthesized met all requirements for SOFC and plasma chamber applications. For use in these applications the tubes should be functionalized by different coatings. We have demonstrated that LaSrMnO2 films as cathode of SOFC can be deposited on the inner side of the tubes by using sol-gel dip coating process [Fig. 4]. For real testing, the tubes can be sealed by using commercial high temperatural ceramic pastes. To favor emission of electrons form the inner surface of the tubes, required for plasma chamber applications, atomic layer deposition (ALD) of

MgO [Fig. 5] has been carried out on tubes. The films were deposited from magnesium beta-diketonate by using ozone as oxygen precursor [4]. Controlled growth of films enable to achieve ultrathin and dense films both on the inner and outer surface. Due to homogeneity of nanocrystalline structure, the tubes could also be applied as optical waveguides or miniature light sources in photonics [Fig 6].

References [1] R. Campana, A. Larrea, J.I. Pena, V.M. Orera, Ni.YSZ cermet micro-tubes with textured surface, Journal of the European Ceramic Society 29 (2009) 85-90.

[2] Tanel Tätte, Medhat Hussainov, Madis Paalo, Marko Part, Rasmus Talviste, Valter Kiisk, Hugo Mändar, Kaija Põhako, Tõnis Pehk, Kaido Reivelt, Marco Natali, Jonas Gurauskis, Ants Lõhmus and Uno Mäeorg, Science and Technology of Advanced Materials, 12 (2011) 034412.

[3] Kenji Shida, Yoko Suyama, Formation of Unstabilized and Yttria Stabilized ZrO 2 Fibers from a Suspension of Monodispersed ZrO2, Journal of the Ceramic Society of Japan, 114 [7] (2006) 590-593.

[4] Matti Putkonen, Leena Sisko Johansson, Eero Rauhala and Lauri Niinistö, Surface-controlled growth of magnesium oxide thin films by atomic layer epitaxy, Journal of Materials Chemistry, 9 (1999) 2449.

[5] Marko Part, Tanel Tätte, Uno Mäeorg, Valter Kiisk, Gunnar Nurk, Aleksei Vorobjov, Kelli Hanschmidt, Method for microtube fabrication, Invention, University of Tartu, P201000097, 31.12.2010.

Figures

Figure 1: YSZ microtubes appeared to be transparent. Optical microscope was used to evaluate the productivity of tubes and their primary parameters.

Figure 2: SEM was used to mesure diameters and wall thickness of microtubes.

Figure 3: Ion conductance of YSZ microtube as a function of temperature.

Figure 4: SEM image of LaSrMnO2 layer on inner surface of YSZ microtube.

Figure 5: Deposited MgO film on the inner surface of YSZ microtube.

Figure 6: Very good light emittance of YSZ microtubes indicates to their good nanocrystalline properties.

Synthesis & Functionalization of Fe3O4 Nanoparticles for Magnetic Particle Imaging 1

1,2

3

3

2

J. Pellico , J. Ruiz-Cabello , S. Veintemillas-Verdaguer , M. Puerto Morales , I. Rodríguez , 1 F. Herranz 1

Advance Imaging Unit, CNIC (Spanish National Cardiovascular Research Centre), C/ Melchor Fernández Almagro nº3.

28029 Madrid (Spain) 2 Dpto Químico-Física II, Facultad de Farmacia, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid (Spain) 3 Department of Biomaterials and Bioinsperired Materials, Instituto de Ciencia de Materiales de Madrid, ICMM- CSIC, c/ Sor- Juana Inés de la Cruz 3, 28049 Madrid, Spain juan.pellico@cnic.es

Magnetic Particle Imaging is a novel imaging technique recently developed by Philips to perform background-free detection of the spatial distribution of magnetic nanoparticles (MNPs) in biological tissue. Magnetic Particle Imaging (MPI) exploits the non-linear re-magnetization behavior of the particles and has the potential to surpass current methods for the detection of iron oxide in sensitivity and spatiotemporal resolution [1].

Despite much exciting progress in MPI scanner design and related image processing, relatively little effort has been devoted developing suitable MNPs. In fact, for the technique to successfully move beyond proof-of-principle experiments into the clinic or preclinical research laboratory, it will be critical to engineer MNP tracers that are optimized for MPI. Resovist® (Bayer Schering Pharma, Berlin), is, so far, the most used compound in MPI studies. However is far from being optimized for that purpose, with only 3% of the sample contributing to the signal [2]. Therefore, special interest is being placed on developing efficient tracers that depend on active targeting where each unit of tracer must generate the maximum achievable MPI signal voltage.

As well as being optimized in size, with an ideal core size about 30 nm, nanoparticles for MPI should have minimal variability in volume distribution, as well as a magnetic relaxation time that is fast enough to respond to the excitation field [3].

In CNIC, where the first MPI scanner for small animals in Europe it is being installed, we have started a program for the synthesis and biofunctionalization of MPI-suited tracers.

We will show our results using two new methods of synthesis, designed to obtain MNPs about 30 nm in core size and their biofunctionalization. The first approach is based on an aqueous route whereas the second one is based on the use of organic media.

Aqueous route We present an aqueous route for the synthesis of uniform magnetite nanoparticles with sizes around the monodomain diameter (20-100 nm). The method is based on the precipitation of a Fe (II) salt in a mild oxidant in hydroalcoholic solutions, producing highly uniform and crystalline magnetic nanoparticles in a single step. Colloidal suspensions of these particles were directly obtained by simple ultrasonic treatment of the powders thanks to the presence of sulphate anions at the particle surface.

All magnetization curves saturate at much lower magnetic fields and show larger saturation magnetization than samples prepared by coprecipitation. Saturation magnetization values vary between 83 and 92 emu g−1, close to the theoretical values reported for bulk magnetite at room temperature [4].

Pyrolysis of Iron (III) oleate route Magnetite nanoparticles were synthesized by the pyrolysis of iron (III) oleate in 1-octadecene. Iron (III) oleate was formed following the methodology described by Ferguson et al. [5]. To obtain magnetite nanoparticles a mixture of iron (III) oleate, 1-octadecene and oleic acid was heated, under argon atmosphere, and refluxed. The synthesis was performed twice with different times of reaction, obtaining different core sizes.

24h

6h

Functionalization Once obtained the nanoparticles with suitable features, we made a first functionalization to build interesting precursors.

OH -

SO 42-

OH- OH

H 2O ref lux

OH -

SO 42SO42- OH -

BTACl CHCl3

SO42-

O O

7

7

OH OH-

OH OH-

OH -

KMnO4

O

BTACl pH= 2.9

O

7

O

HO

After this, MNPs were functionalized with different biomolecules to obtain water stable and long circulating times after i,v, injection. These particles were fully characterized (TEM, DLS, VSM, FTIR and MS) and their capabilities as MPI tracers were measured.

OH -

OH OH -

OH OH-

Polymers

OH OH-

Proteins

Aqueous route O

O

Oligosaccharides

7 O

Water stable MNPs

OH

Organic route

References [1]. Thorsten M.Buzug, Jörn Borget. Magnetic Particle Imaging: A novel SPIO Nanoparticle Imaging Technique. Springer Proceeding in Physics 140.

[2]. B. Gleich and J. Weizenecker. “Tomographic imaging using the nonlinear response of magnetic particles,” Nature (London) 435, 1214–1217 (2005).

[3]. Timo F Sattel, Tobias Knopp, Sven Biederer, Bernhard Gleich, Juergen Weizenecker, Joern Borgert and Thorsten M Buzug. Single-sided device for magnetic particle imaging, J.Phys.D: Appl.Phys.42 (2009).

[4]. M Andrés Vergés, R Costo, A G Roca, J F Marco, G F Goya, C J Serna and M P Morales. Uniform and water stable magnetite nanoparticles with diameters around the monodomain-multidomain limit, J.Phys.D: Appl.Phys. 41 (2008) [5]. R. Matthew Ferguson, Kevin R. Minard, Amit P. Khandhar and Kannan M. Krishnan. Optimizing magnetite nanoparticles for mass sensitivity in magnetic particle imaging, Med. Phys. 38(3), March 2011

A Three dimensional e-beam lithography technique for the construction of high density micro and nanocoils 2 ¨ M. Peralta1 , J.-L. Costa-Kramer , E. Medina1 , A. Donoso1 1

Centro de F´ısica, Instituto Venezolano de Investigaciones Cient´ıficas (IVIC), Caracas, Venezuela.

2

´ Instituto de Microelectronica de Madrid, CSIC, Tres Cantos, 28760 Madrid, Spain. mayrafisucv@gmail.com

Abstract

With the of reduction of the size in electromechanical systems in order to access particular frequencies or noise limits, the needs for new efficient methods for miniaturization of circuit electronic components is of critical importance. Researchers have invested much effort in the development of micro and nanocoils [1, 2]. In the literature there are basically two kinds of micro coils: 3D solenoidal coils with rectangular and circular cross section, and planar spiral coils. The former is the easiest way to build an inductor at the macroscopic scale and is also the more efficient configuration because of the uniformity of the magnetic field inside the coil and the high inductance.

However when the scale is reduced, to the order of micro and nanometers, the difficulty for rolling a very thin wire around an axis increases considerably [3]. On the other hand, the planar geometry represents a very attractive way to construct micro and nanocoils because of the high compatibility with microfabrication techniques, although a cost is paid in the low uniformity of the inner magnetic field, and low inductance [3, 4].

In this work we present a procedure compatible with MEMS techniques for the fabrication of three dimensional micro and nanocoils. The technique used is based on the dependence, with dose, of the quantity of resist irradiated by the electron beam in the lithography (see Fig. 1), (3D lithography [5]). With this technique, we developed pyramidal structures with of 10 and 40 turns with a wire thickness from 5 to 1µm, and a distance between turns of approximately 100nm (See Fig. 2). The chosen shape of the coils increases the uniformity of the magnetic field within them as compared to the planar geometry, and also allows a greater density of turns, yielding an increased in the inductance. We will describe measurements of the coils inductance for several sizes of the wire, spacing between turns and minimum and maximum radii, comparing the experimental results with numerical simulations. These coils can be applied as magnetic field sensors [6] and in the development of electromagnetic actuators for energy harvesting applications [7].

References [1] G. Boero, C. de Raad Iseli, P. A. Besse and R. S. Popovicw, Sensors Actuators A 67 (1998) 18.

[2] M. Ohnmacht, V. Seidemann and S. Buttgenbach, Sensors Actuators A 83 (2000)124.

[3] K. Kratt, J. G. Korvink and U. Wallrabe, Actuator, 11th International Conference on New Actuators, Bremen, Germany 9 (2008) 311.

[4] K. Kratt, V. Badilita, T. Burger, J. G. Korvink and U. Wallrabe, J. Micromech. Microeng. 20 (2010) 015021.

[5] G. Piaszenski, U. Barth, A. Rudzinski, A. Rampe, A. Fuchs, M. Bender and U. Plachetka, Microelectronic Engineering 84 (2007) 945.

[6] H. Takahashi, T. Dohi, K. Matsumoto and I. Shimoyama, Proc. IEEE MEMS Kobe (2007) 549.

[7] L.-D. Liao, P. C.-P. Chao, J.-T. Chen, W.-D. Chen, W.-H. Hsu, C.-W. Chiu and C.-T. Lin, IEEE Transactions on Magnetics 45 (2009) 4621.

Figures

Figure 1: Diagram of the procedure followed to build 3D pyramidal coils. a) The first step consists of a dose varying electron beam lithography strategy. The gray scale in the arrows indicates different doses (from the smallest dose in gray until the highest in black). b) After developing, the resist will be removed in different amounts depending of the dose employed. c) Finally the conducting material (gold in our case) is deposited by thermal evaporation.

Figure 2: SEM images of the pyramidal structures fabricated with the technique described in this work. a) A ten turn pyramidal structure, with a wire thickness of 5Âľm and a separation between turns of approximately 100nm. b) A 40 turns pyramidal structure with a wire thickness of 1Âľm and a separation between turns of approximately 100nm. c) And d) close up images of the 40 turns structures and the external contact respectively.

Properties of Vanadium Dioxide Coatings for Smart Window Applications 1*

1

2

G.Philander , M. Maaza , and E. Iwuoha 1

Nanosciences African Network (NanoAfNet) - iThemba LABS, South Africa 2

University of the Western Cape, South Africa

*

corresponding author: ghouwaa@tlabs.ac.za

Abstract

Vanadium Dioxide (VO2) is a smart material which exhibits a phase transition at a temperature of 68 ̊C in its pure and single crystalline form. The phase transition from the monoclinic semi-conducting form to the tetragonal metallic (rutile) form is also accompanied by a change in the optical properties of VO2.

This simultaneous optical shift goes from an optically transparent to an optically opaque material where a change in solar radiation transmittance is observed. Although the introduction of a dopant into the lattice structure of VO2 has proven to decrease the transition temperature to near room temperature, the optical transmittance capability as well as the nature of the transition remains a challenge (1).

This research involves the development of a doped VO2 coating for smart window applications with enhanced properties. Apart from producing thermochromic VO2 with a reduced transition temperature, the focus is also largely placed on improving the optical properties of this material in the visible range of the electromagnetic spectrum.

The nanophotonic and thermochromic properties of the developed

material are studied using various physical and electrochemical analytical techniques.

Due to this thermochromic property, VO2 has received worldwide attention as a prospective material for energy saving technologies (2). As a direct result of the thermochromic property of this material, this technology will play a significant role in energy saving due to its ability to maintain temperature within a building or vehicle. The ultimate aim of this research is therefore; to develop a simple and cost effective chemical process for producing VO2 coatings with overall enhanced properties which will ultimately aid in the commercialization of this material.

References

1. Azens, F. M. and Granqvist, C. G., “Electrochromic smart windows: energy efficiency and device aspects” Journal of Solid State Electrochemistry, Vol. 7, No. 2, 64-68, 2003.

2. Parkin, I. P. and Manning, T. D., “Intelligent Thermochromic Windows” Journal of Chemical Education, Vol. 83, No. 3, 393–400, 2006.

A nanoplatform based on self-assembled plant-made nanoparticles with multiple applications Fernando Ponz, Flora Sánchez, Carmen Mansilla, Pablo Ibort, Sol Cuenca, Marta Aguado, César F. Cruz, Ivonne González Center for Biotechnology and Genomics of Plants, CBGP (UPM-INIA), Autopista M40, km 38, Campus Montegancedo, Pozuelo de Alarcón, 28223 Madrid. Spain fponz@inia.es Abstract Protein nanoparticles with self-assembly capabilities are of utmost relevance in ‘bottom-up’ nanobiotechnological approaches. Several examples are available which exemplify this concept for instances derived from the plant world. Most of them derive from plant viruses, natural nanoparticles self-assembling with a high efficiency [1]. These viral nanoparticles (VNPs) can take several forms, which mainly fall into two biological categories. Either the particles enclose and pack a nucleic acid (virions) or they do not (virus-like particles, VLPs). For some ‘in vitro’ applications, the presence of the nucleic acid does not involve any added inconvenience. However, when the application involves exposure of living entities to the VNP, or the modification imposed is incompatible with a normal viral life cycle, it is normally preferable to deal with VLPs. We have been developing a VNP platform based on Turnip mosaic virus (TuMV), a plant virus belonging to the genus Potyvirus. VNPs derived from viruses in this genus are elongated flexuous rods, approximately 750-850 nm long and approx. 15 nm wide [2]. Initial VNPs were generated in plants exposed to an infectious TuMV clone, developed by us years ago [3]. To deal with virions, these were purified from plants infected with natural or genetically modified TuMV. Extracts of the infected plants were subjected to standard protocols of virion purification. For VLPs, plants were infiltrated with genetic constructs coding exclusively for one single protein, the viral protein CP which is the only building block to make VLPs. These were also purified following similar procedures.

Both types of VNPs can be genetically or chemically modified for nanobiotechnological exploitation with several purposes. In the genetic manipulation, viral genes (normally the gene encoding the CP) are modified to confer the sought properties to their derived proteins. For instance we have made this protein longer so that the derived VNP can expose hundreds or thousands of copies of peptides or proteins on its external surface. The corresponding derived VNPs have been used to increase peptide antigenicity by orders of magnitude. They have also been deployed to increase substantially our ability to detect the presence of antibodies in biological fluids, the basis for new simple and ultrasensitive approaches for the diagnosis of diseased conditions. The CP gene can also be made shorter, still preserving the self-assembling capability of the CP. By doing so, we have made substantial progress in defining the size limit of the protein which retains self-assembly. This basic study of the properties of this system will now allow us to try to express much larger peptides and proteins in our VNPs. The chemical modification approach involves fusing peptides or proteins ‘in vitro’ to the previously purified VNP. Other macromolecules can be fused, too. Usual procedures for this involve the use of biheaded chemical reagents mediating the fusion. We have used this experimental approach for enzyme immobilization onto TuMV VNPs. The characterization of the resulting structures has revealed that the initial VNPs participate in the formation of higher ordered macromolecular assemblies involving both the exogenously added enzyme and the VNPs. The enzymatic activity associated to the new structures was several times higher than that of the non-immobilized enzyme indicating the applicability of this approach in nanobiocatalysis.

Current achievements in all these directions will be presented and discussed in the general context of the progress in developing this nanoplatform further. New possibilities in other areas, such as nanomaterials or nanodevices with new properties will also be explored.

References [1] J. Rong, Z. Niu, L. A. Lee and Q. Wang, Current Opinion in Colloid & Interface Science, 16 (2011) 441.

[2] F. Sánchez, D. Martínez-Herrera, I. Aguilar and F. Ponz, Virus Research, 55 (1998) 207.

[3] Hollings, M. and A. A. Brunt, CMI/AAB Descriptions of Plant Viruses, 245 (1981).

Crossover between magnetic reversal modes in ordered arrays of electrodeposited nanotubes 1,2

1

3

1

2

Mariana P. Proença , C. T. Sousa , J. Escrig , J. Ventura , M. Vázquez , J. P. Araújo

1

1

IFIMUP and IN – Institute of Nanoscience and Nanotechnology and Dep. Física e Astronomia, Univ.

Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal 2 Instituto de Ciencia de Materiales de Madrid, CSIC, 28049 Madrid, Spain 3 Dep. Física, Univ. Santiago de Chile, and Center for the Development of Nanoscience and Nanotechnology, Avda. Ecuador 3493, Santiago, Chile mpproenca@fc.up.pt

Abstract One of the most important properties of magnetic nanomaterials is its coercivity. The major part of the magnetic nanomaterials’ applications (permanent magnets, magnetic recording and spin electronics) requires a thorough understanding of the magnetization reversal mechanisms, which are directly related to coercivity. These are known to depend on geometric parameters (shape, length, diameter, wall thickness, spatial ordering, etc). The accurate control of such parameters combined with a detail study of the nanomaterial’s magnetic properties provides new information on the correct application of each nanomagnet array. Additionally, it eases the tuning of the magnetization reversal mode by modifying external parameters, such as the direction of the applied field.

A few studies have been reported on the angular dependent magnetic properties of nanowires (NWs) and nanotubes (NTs) fabricated inside nanopore arrays (polycarbonate track etched membranes [1], inclined Si columns [2]). However, only a small number of experimental results can be found on the angular dependence of the coercivity in highly ordered NW/NT arrays [3-5].

In the present work we optimized the fabrication of Ni and Co NW and NT arrays by controlled potentiostatic electrodeposition into suitably modified nanoporous alumina templates (NpATs) after its opening from both upper and bottom sides [6,7]. Long range ordering of hexagonal symmetry of precursor alumina membranes with 105 nm interpore distance and 50 nm pore diameter were achieved by a two-step anodization process combined with controlled pore opening. The fabricated NWs/NTs had a final diameter equal to that of the pores of the template, a length of ~10 μm, and NTs wall thickness of ~10 nm. Morphological characterization was performed using a scanning electron microscope (SEM; FEI Quanta 400FEG). Figure 1 shows SEM top and cross-sectional images of the obtained NWs and NTs inside NpATs. To investigate the angular dependent magnetization reversal processes of the Ni and Co NW and NT arrays, magnetization hysteretic loops were measured at different angles of applied external magnetic field, using a vibrating sample magnetometer (VSM; LOT-Oriel EV7). Three main modes of magnetization reversal can been identified depending on the geometry of the nanostructure: coherent mode, where all magnetic moments rotate simultaneously; transverse mode, where spins rotate progressively by the nucleation and propagation of a transverse domain wall; and vortex mode, where a vortex wall is nucleated and propagates [5,8]. In this work we used an adapted Stoner-Wohlfarth model [5,8,9] to estimate the angular dependence of the coercive field (H c) for each magnetization reversal process. Figure 2 shows the angular dependence of Hc measured experimentally and calculated analytically. The magnetization in Ni and Co NW arrays was found to reverse by means of the nucleation and propagation of a transverse domain wall. While for NT arrays a non-monotonic angular dependent Hc was observed, evidencing a transition between the vortex and the transverse reversal mode [10]. The critical angle at which this transition occurs was found to change with the size of the NTs, in good agreement with theoretical predictions. An accurate tuning of the NT parameters would allow an enhancement of the coercive field for a given angle.

References [1] A. Ghaddar, F. Gloaguen, J. Gieraltowski and C. Tannous, Physica B, 406 (2011) 2046.

[2] O. Albrecht, R. Zierold, S. Allende, J. Escrig, C. Patzig, B. Rauschenbach, K. Nielsch and D. Gorlitz, Journal of Applied Physics, 109 (2011) 093910A. [3] J. Escrig, J. Bachmann, J. Jing, M. Daub, D. Altbir and K. Nielsch, Physical Review B, 77 (2008) 214421.

[4] J. Escrig, R. Lavin, J. L. Palma, J. C. Denardin, D. Altbir, A. Cortes and H. Gomez, Nanotechnology, 19 (2008) 075713.

[5] R. Lavin, J. C. Denardin, J. Escrig, D. Altbir, A. Cortes and H. Gomez, Journal of Applied Physics, 106 (2009) 103903.

[6] M. P. Proenca, C. T. Sousa, J. Ventura, M. Vazquez and J. P. Araujo, Electrochimica Acta, 72 (2012) 215.

[7] M. P. Proenca, C. T. Sousa, J. Ventura, M. Vazquez and J. P. Araujo, Nanoscale Research Letters, 7 (2012) 280.

[8] P. Landeros, S. Allende, J. Escrig, E. Salcedo and D. Altbir, Applied Physics Letters, 90 (2007) 102501.

[9] S. Allende, J. Escrig, D. Altbir, E. Salcedo and M. Bahiana, The European Physical Journal B, 66 (2008) 37.

[10] M. P. Proenca, C. T. Sousa, J. Escrig, J. Ventura, M. Vazquez and J. P. Araujo, submitted.

Figures

Fig. 1: SEM cross-sectional and bottom views of Ni nanowire (a,b) and nanotube (c,d) arrays in nanoporous alumina templates.

Fig. 2: Angular dependence of the coercive field measured experimentally (squares) and calculated analytically (C mode: blue solid; T mode: red dashed; and V mode: green dotted) for Co (a,c) and Ni (b,d) NW (a,b) and NT (c,b) arrays in nanoporous alumina templates.

Systematic circular dichroism study of systems containing cysteine and silver nanoparticles Pavel Řezanka, Jakub Koktan, and Vladimír Král Department of Analytical Chemistry, Institute of Chemical Technology Prague, Technická 5, 166 28 Prague 6, Czech Republic pavel.rezanka@vscht.cz Abstract Mixtures containing silver nanoparticles (~45 nm) prepared by citrate reduction of AgNO3 and cysteine were prepared. Influences of cysteine concentration, mixture pH, and time on the circular dichroism spectra were studied. The mixtures were also analyzed by absorption spectroscopy in UV–Vis range and by surface-enhanced Raman scattering. The results showed interesting behavior of circular dichroism spectra and surface-enhanced Raman scattering spectra.

Introduction The behavior of nanoparticles in the presence of chiral compounds is in the field of interest of several scientists due to possible application in heterogeneous catalysis [1], material science [2], development of chemical sensors [3], and nanocatalysis [4]. The first such chiral system was described

by Shaaf et al. in 1998 for glutathione modified gold nanoparticles [5]. Several years later Choi et al. described electronic circular dichroism (ECD) of silver nanoparticles (AgNPs) 6.4 nm in diameter in the presence of L-cysteine and D-cysteine [6].

Here we report a systematic circular dichroism study of systems containing cysteine and silver nanoparticles. This work is a detailed study of our previous preliminary results [7].

Results and discussion Characterization of prepared AgNPs showed that nanoparticles have different shape and size (Fig. 1A) with average size of 45 nm. The wavelength of surface plasmon absorbance (415 nm, Fig. 1B) corresponds to the average diameter estimated by TEM [8].

The immobilization of cysteine on the AgNPs was proved by surface-enhanced Raman scattering (SERS) spectra of systems containing AgNPs and cysteine. Bands in Raman spectrum of pure cysteine (Fig. 2A) corresponds to SERS spectrum of AgNPs in the presence of cysteine (Fig. 2B). Control experiment with only AgNPs (Fig. 2C) showed different bands in SERS spectrum.

Moreover, we were able to detect the presence of cysteine even in a concentration of 5.10–9 mol L–1 (Fig. 2D), although in this spectrum are also bands corresponding to citrate that stabilize surface of AgNPs. For a concentration study AgNPs were diluted eight times in order to obtain values of absorbance at the wavelength of surface plasmon absorbance (415 nm) where Lambert-Beer law still holds true, i.e. values around 1 (for 1-cm cuvette).

To the diluted AgNPs solutions concentrated aqueous solutions of L- and D-cysteine were added resulting in mixtures with different concentrations of L- and D-cysteine (10-6, 5. 10-5, 10-5, 5. 10-5, 10-4, 5. 10-4, 10-3, 5. 10-3, and 10-2 mol L–1). After incubation overnight UV-Vis and ECD (Fig. 3 and 4) spectra were measured.

With increasing concentration of cysteine in the solution the absorbances of surface plasmon band slightly decrease and aggregation occurred in the presence of high concentrations of cysteine, as can be seen from the presence of a new band at 700 nm. This observation is similar to the results published before for gold nanoparticles [9].

In the case of ECD spectra the situation is more complicated due to several contributions that form the resulting spectrum. The spectral region below 250 nm corresponds to dissolved cysteine only (i.e. not bonded to AgNPs surface) [10] and the signal in this region increases with increasing cysteine concentration (Fig. 3 and 4). In the region above 250 nm the signal comes from chemisorption of cysteine on AgNPs [10] and this signal has a maximum for 10–4 mol L–1 cysteine concentration for both enantiomers (Fig. 3 and 4).

Acknowledgment The financial support from the Czech Science Foundation, project no. P206/12/P026, is gratefully acknowledged.

References [1] K.D.M.Harris and S.J.M.Thomas, ChemCatChem 1 (2009) 223-231.

[2] T.Verbiest, S.V.Elshocht, M.Kauranen, L.Hellemans, J.Snauwaert, and C.Nuckolls, Science 282 (1998) 913-915.

[3] A.N.Shipway, E.Katz, and I.Willner, Chem.Phys.Chem. 1 (2000) 18-52.

[4] P.Chen, W.Xu, X.Zhou, D.Panda, and A.Kalininskiy, Chem.Phys.Lett. 470 (2009) 151-157.

[5] T.G.Schaaff, G.Knight, M.N.Shafigullin, R.F.Borkman, and R.L.Whetten, J.Phys.Chem.B 102 (1998) 10643-10646.

[6] S.-H.Choi, H.-S.Lee, Y.-M.Hwang, K.-P.Lee, and H.-D.Kang, Rad.Phys.Chem. 67 (2003) 517-521.

[7] P.Řezanka, K.Záruba, and V.Král, Colloid.Surf.A 374 (2011) 77-83.

[8] R.F.Fakhrullin, A.I.Zamaleeva, M.V.Morozov, D.I.Tazetdinova, F.K.Alimova, A.K.Hilmutdinov, R.I.Zhdanov, M.Kahraman, and M.Culha, Langmuir 25 (2009) 4628-4634.

[9] P.Řezanka, H.Řezanková, P.Matějka, and V.Král, Colloid.Surf.A 364 (2010) 94-98.

[10] T.Li, H.G.Park, H.-S.Lee, and S.-H.Choi, Nanotechnology 15 (2004) S660-S663.

Figures Absorbance (A)

1.0 0.8 0.6 0.4 0.2 0.0 350

500

650

800

100 nm

Wavelength λ / nm) A B Fig. 1 TEM image (A) and UV-Vis spectrum (B) of AgNPs.

Raman Intensity / a.u.

2.0E+05 1.5E+05 d 1.0E+05

c

a

5.0E+04 b a 0.0E+00 1500

1300

1100

900

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Wavenumber / cm–1 Fig. 2 Raman spectrum of L-cysteine (a), SERS spectrum of silver nanoparticles in the presence of Lcysteine (c = 1.10–4 mol L–1) (b), SERS spectrum of silver nanoparticles (c), SERS spectrum of silver nanoparticles in the presence of L-cysteine (c = 5.10–9 mol L–1) (d).

20 10 0

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-30 220

Ellipticity (Φ / mdeg)

Ellipticity (Φ / mdeg)

30

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Wavelength λ / nm) Fig. 3 ECD spectra of AgNPs with various concentrations (mol L–1; a: 5.10–5; b: 10–4; c: 5.10–4; d: 10–3; e: 5.10–3; f: 10–2) of L-cysteine.

20

a

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0 -10 -20 -30 220

c 240

260

280

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320

Wavelength λ / nm) Fig. 4 ECD spectra of AgNPs with various concentrations (mol L–1; a: 5.10–5; b: 10–4; c: 5.10–4; d: 10–3; e: 5.10–3; f: 10–2) of D-cysteine.

Heterogeneous catalysis inside a microreactor containing acid-functionalized polymer brushes Roberto Ricciardi, Jurriaan Huskens, Willem Verboom Molecular Nanofabrication group, Mesa+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands r.ricciardi@utwente.nl Microreactor technology represents a new and promising approach to carry out analytical and organic 1 chemistry. This is mainly due to the numerous advantages, especially in terms of increased surfaceto-volume ratio as a result of the downsizing of the dimensions (order of microns). This allows a better and faster mixing between the components of a reaction. The small dimensions created within the channeling system increase the heat and mass transfer and facilitate the handling of exothermic and 2 runaway reactions. The large surface available within a microreactor can be exploited in catalysis, offering the possibility to increase the rate and the yield of a reaction. The use of polymer brushes anchored on the inner walls of glass microreactors offers the possibility to perform heterogeneous catalysis inside the chip (Figure 1).

Figure 1. Glass microreactor functionalized with polymer brushes.

3

Polymer brushes are polymer coatings consisting of polymer chains which are tethered to a surface.

The growth of such polymers via Surface Initiated-Atom Transfer Radical Polymerization (SI-ATRP) enables the control over the thickness and the type of monomer incorporated (homo-, copolymers).

Many functionalities can be incorporated in the polymeric structure either in terms of functional monomers or after-polymerization modification. The number and the density of these functionalities 4 can be tuned which is of use for heterogeneous catalysis. Here we present the fabrication and application of acid-functionalized polymer brushes grown at the inner walls of a glass microreactor (Scheme 1).

Scheme 1. General scheme for the growth of poly(3-sulfopropyl methacrylate) polymer brushes.

The acid-functionalized microreactor was then used for a test reaction, i.e. the acid-catalyzed hydrolysis of benzaldehyde dimethyl acetal (Scheme 2).

Scheme 2. Hydrolysis of benzaldehyde dimethyl acetal.

Preliminary results showed a good activity of the polymeric structure. The reaction reaches high conversions within 10 minutes when 0.1M solutions of both reactants in acetonitrile were flowed through the microreactor at room temperature (Figure 1). The expected thickness of the brushes is around 150 nm (as measured on a flat silicon oxide surface functionalized in the same way with poly(3-sulfopropyl methacrylate).

Studies were carried out to prove whether the catalytic activity is due to the sulfonic acid groups at the + polymer brushes. When the protons were replaced by Na flowing an aqueous solution of NaCl through the microreactor, the activity disappeared. Upon reactivation with a 3M HCl solution the pristine activity was resumed (Figure 2). The same reaction carried out in a bare microreactor did not show any conversion.

Figure 2. Conversion versus residence time for the acid-catalyzed hydrolysis of benzaldehyde dimethyl acetal.

Different types of acid-catalyzed reactions are being investigated using the sulfonic acid-functionalized microreactor.

References [1] C. Wiles and P. Watts, Chem. Commun., 47, 2011, 6512-6535.

[2] M. Brivio, W. Verboom and D. N. Reinhoudt, Lab. Chip, 6, 2006, 329-344.

[3] R. Barbery, L. Lavanant, D. Paripovic, N. Schuwer, C. Sugnaux, S. Tugulu and H.-A. Klok, Chem.

Rev., 109, 2009, 5437-5527.

[4] F. Costantini, W. P. Bula, R. Salvio, J. Huskens, H. J. G. E. Gardeniers, D. N Reinhoudt and W. Verboom, J. Am. Chem. Soc., 131, 2009, 1650-1651.

Effect of short-range order vs. long-range disorder on the effective properties of a 1D "metamaterial" chain of resonant particles José María Rico-García1, 2, José Manuel López-Alonso3 , Ashod Aradian2 1

Sección Departamental de Matemática Aplicada, Escuela Universitaria de Óptica, Universidad Complutense de Madrid. Av. Arcos de Jalón 118, Madrid, (Spain) 2

Centre de Recherche Paul Pascal, CNRS-Université Bordeaux 1 Avenue Schweitzer, 33600 Pessac, (France) 3

Departamento de Óptica I, Escuela Universitaria de Óptica, Universidad Complutense de Madrid, Av. Arcos de Jalón 118, Madrid, (Spain) jmrico@fis.ucm.es

Abstract The role of disorder in artificially-engineered materials poses important questions in regard to their interaction with light [1-4]. Such kind of queries comes into play most overtly in chemical selfassembled metamaterials [5], where short-range, positional order is kept but long-range disorder pervade the whole crystalline structure, mainly due to grain boundaries, stacking faults, and so on. As a result, effective parameters describing the composite in the long-wavelength limit suffer from unexpected changes due to these features. Because of that, assessing the actual ability of the formers to show an exotic response to radiation (negative refraction, near-zero behavior, artificial magnetism, etc ) is a must.

To account for that, and as a starting point of analysis, we propose a 1D toy model in the quasi-static regime to study the effect of correlated spatial disorder on the effective parameters of these composites [6]. Although this approach is rather limited, and does not provide with a bulk effective response, it gives indeed a meaningful quantity describing the averaged response of the 1D model, the external susceptibility. Moreover, we have modeled the deviations of periodicity as a block-like disorder which imposes crystalline short order but gives long range fluctuations (Figure 1), hence mimicking what happens in real 3D structures. In fact, we believe there is room to refine this approach, allowing both multipolar and spatial dispersion effects in modelling 3D composites [7]..

Thus, we will study the dependence on both filling fraction and correlation length in the response of one-dimensional chains of high-permittivity particles at Thz frequencies. These particles show a strong Mie magnetic resonance at these frequencies, opening the venue to get artificial magnetism if they are used as subwavelength resonators in 3D composites. Besides, we will analyze modifications in key features of the resonant response (amplitude, width, etc.). As main results of this investigation, we have found a regime transition in the electromagnetic response for a filling fraction around 50% (Figure 1).

Last, but not least, we have identified a boundary in the k-space of those modes living in the chain, which splits them into bright (coupled) modes to the impinging field and dark ones. We believe it entails a mobility edge, which can be significant to ascertain whether the composite can be described as an homogenized media.

References [1] K. Aydin, K. Guven, N. Katsarakis, C. M. Soukoulis, and E. Ozbay, “Effect of disorder on magnetic resonance band gap of split-ring resonator structures,” Opt. Express 12, 5896–5901 (2004).

[2] A. A. Zharov, I. V. Shadrivov, and Y. S. Kivshar, “Suppression of left-handed properties in disordered metamaterials,” J. Appl. Phys. 97, 113906 (2005).

[3] X. P. Zhao, Q. Zhao, L. Kang, J. Song, and Q. H. Fu, “Defect effect of split ring resonators in lefthanded metamaterials,” Phys. Lett. A 346, 87–91 (2005).

[4] M. V. Gorkunov, S. A. Gredeskul, I. V. Shadrivov, and Y. S. Kivshar, “Effect of microscopic disorder on magnetic properties of metamaterials,” Phys. Rev. E 73, 056605 (2006) [5] V. Ponsinet, A. Aradian, P. Barois, and S. Ravaine,“Self-assembly and nanochemistry techniques for the fabrication of meta materials” in Metamaterials Handbook: Applications of Metamaterials , F. Capolino, ed. (CRC Press, 2009), Vol.2 [6] J.M.Rico-García, J.M.López-Alonso, A.Aradian ,”Toy model to describe the effect of positional blocklike disorder in metamaterials composites” JOSA B, Vol. 29, Issue 1, 53-57 (2012) [7]C. Noguez and R. Barrera, “Multipolar and disorder effects in the optical properties of granular composites,” Phys. Rev. B 57, 302–313 (1998).

Figures

Figure 1: Imaginary part of the external susceptibility[6,7] as the filling fraction increases in the 1D chain. Inset: 1D blocklike disorder model. Particles are arranged in blocks where both the interparticle distance and the number of particles per block is fixed. In contrast, the interblock distance is a random variable Continous curves refers to disordered chains made of blocks of two particles (dimers), whereas dotted lines regards chains made of blocks of ten particles (decamers) [6]

Polymeric Cap psules as m multifuncctional too ol for intraacellular ion concen ntration Pilar R Rivera_Gil, Moritz Nazzarenus, Sum maira Ashra af, Wolfgang J. Parak Faachbereich Physik and WZMW, Ph hilipps Univversität Marrburg, 35037, Marrburg, Germ many Renthof 7, 3 Abstracct The con ncept of a long‐term ssensor for io on changes in the lyso osome is preesented. Th he sensor iss made by b layer‐by‐‐layer assem mbly of oppositely charged polyelectrolytess around io on sensitivee fluorophores, in th his case forr protons. The T sensor is spontaneously inco orporated by b cells and d resides over days in the lysossome. Intraacellular chaanges of th he concentration of protons upon n cellular stimulation n with pH active agentts are monittored by reaad‐out of th he sensor fluorescencee at real time. With help of this sensor co oncept we ccould demo onstrate thaat the different agentss used (M different kinetics and Monensin, Chloroquin ne, Bafilomycin A1, Amiloride) A p possessed d mechan nisms of acttion in affeccting the inttracellular p pH values.

References: 1.

P, Nazarenuss M, Ashraf S, Parak WJ: pH Sensitive Capsuless as Intracelllular Optical Rivera_Gil P Reporters for f Monitoring Lysoso omal pH Ch hanges upo on Stimulattion. Small 2012, DOI: 10.1002/sm mll.((smll.201 1101780)).

2.

Rivera Gil P, P del Mercaato LL, del‐P Pino P, Mun noz‐Javier A, A Parak WJ:: Nanoparticcle‐modified d polyelectrollyte capsuless. Nano Toda ay 2008, 3:12 2‐21.

3.

del Mercato o LL, Abbasi A AZ, Ochs M, P Parak WJ: M Multiplexed SSensing of Ions with Barccoded Polyelectrollyte Capsules. ACS Nano 2011, 5:966 68‐9674.

Disentangling the magnetoresistance response through the magnetization reversal in magnetic multilayers 1,2

1

3,4

4

1

2

4

C. Rodrigo , P. Perna , M. Muñoz , J. L. Prieto , A. Bollero , J. L. F. Cuñado , M. Romera , 4 2 1,2 5 1,2 1,2 J. Akermann , E. Jiménez , N. Mikuszeit , V. Cros , J. Camarero and R. Miranda 1

Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia, Campus Universidad Autónoma de Madrid, 28049 Madrid, Spain 2 Departamento de Física de la Materia Condensada and Instituto ”Nicolás Cabrera”, Universidad Autónoma de Madrid, 28049 Madrid, Spain 3 Instituto de Física Aplicada, CSIC, 28006 Madrid, Spain 4 Instituto de Sistemas Optoelectrónicos y Microtecnología (ISOM), Universidad Politécnica de Madrid, 28040 Madrid, Spain 5 Unité Mixte de Physique CNRS/Thales and Université Paris Sud 11, 91767 Palaiseau, France cecilia.rodrigo@uam.es

Artificial magnetic nanostructures have aroused great interest in the last years. Advances in fabrication of nanostructures and new experimental techniques have led to the discovery of new materials and new properties which take place only in systems with dimensions at the nanoscale [1]. Electronic phenomena governed by spin have given place to the birth of a new branch of electronics called Spintronics or Magnetoelectronics [2]. For instance, magnetoresistive effects and related phenomena in magnetic nanostructures have found widespread applications in magnetic sensing and recording technologies.

Large magnetoresistance (MR) effects observed in ferromagnetic (FM) layers separated by nonmagnetic (NM) spacers have attracted sustained interest over the past decades for both fundamental and technological reasons [3]. The effect could originate from several contributions of spin-dependent scattering processes of the electrons travelling across a multilayered structure with different relative magnetization orientation between adjacent FM layers [4]. In order to observe large MR responses one has to reorient the magnetization of the FM layers relative to one another, either by applying external magnetic fields (i.e., direct magnetic torque on the local magnetization) [3, 4], or by injecting spin polarized currents (i.e., via transfer of angular momentum between the spin polarized conduction electrons and the local magnetization) [5]. The maximum MR value is expected when the magnetic configuration of the FM layers reorients from a fully parallel (P) to a fully antiparallel (AP) configuration.

Even though it is commonly assumed that the MR depends on the magnetic anisotropy of multilayer structures, a comprehensive description of the magnetoresistive behavior related to the magnetization reversal is still lacking. In this work, we show that both amplitudes and shapes of the MR curves of a spin-valve structure depend on the orientation of the applied magnetic field and are directly related to the magnetization reversal processes. In particular, we advance towards a microscopic understanding of the MR properties by showing that their angular dependence leaves distinct fingerprints, which are directly related to their magnetization reversal processes.

We have employed a new MagnetoResistance-Optical Kerr Effect [M(R)-OKE] setup that allows us to determine simultaneously magnetoresistive responses and magnetization reversal processes. The M(R)-OKE set-up and the spin-valve structure used in this study are schematically shown in Figure 1.

The layer sequence Ni80Fe20(9nm)/Cu(2nm)/Ni80Fe20(9nm)/FeMn(15nm) was grown at room temperature (RT) by sputtering on an oxidized Si substrate pre-covered with a 2 nm thick Ta buffer layer [6]. Magnetization reversal processes and magnetoresistive properties were studied at RT by measuring simultaneously in-plane vectorial-resolved magnetization hysteresis loops and the corresponding resistance changes by employing a four probe ac technique with the applied current flowing parallel to the easy axis of the system. The magnetization loops were measured by high resolution vectorial-Kerr magnetometry by using p-polarized light focussed between the inner electric probes and analyzing the two orthogonal components of the reflected light. This provides the (additional) simultaneous determination of the hysteresis loops of both in-plane parallel, M||, and transverse, M^, magnetization components as a function of the applied magnetic field [7]. The angular-dependent study has been performed as a function of the sample in-plane angular rotation angle αH , keeping fixed the external magnetic field direction. The whole angular range was probed every 1.8, with 0.5 angular resolution.

The capability of the M(R)-OKE setup is shown in Figure 2. Both magnetization M||, M^ and MR are acquired simultaneously at the easy-axis (e.a.) and hard-axis (h.a.) direction. At a first glance, different magnetization reversal and MR responses are clearly distinguished when the angle of the applied field

is changed from the e.a. to h.a. direction. The correlation between both magnetization reversal and MR responses has been observed in the whole angular range, which indicates their direct relationship. For instance, reversible and irreversible transitions are similar in both MR and vectorial-resolved magnetization curves. Well-defined MR-plateaus are observed around the e.a. direction whereas just reversible MR transitions are found around the h.a. direction. The MR plateau value decreases as the magnetic field is misaligned with respect to the e.a. and the maximum of MR decreases approaching the h.a., where it presents the lowest resistivity changes, one order of magnitude lower than those at the e.a. direction. Our results directly show that the different magnetoresistive behaviors originate from the magnetic anisotropy of the structure and ultimately depend on the relative magnetization orientation of the FM layers.

References [1] [2] [3] [4] [5] [6] [7]

S. D. Bader, Rev. Mod. Phys. 78 (2006), 1.

G. Prinz, Science, 282 (1998), 1660.

M. N. Baibich, Phys. Rev. Lett. 61 (1988), 2472 A. Fert, Angew. Chem. Int. Ed. 47 (2008), 5956 J. Grollier, Appl. Phys. Lett. 78 (2001), 3663.

M. Romera, J. Appl. Phys. 106 (2009), 023922.

J. Camarero, Phys. Rev. Lett. 95 (2005), 057204.

Figures

Figure 1: Scheme of the experimental M(R)-OKE setup combining simultaneous vectorial-Kerr and magnetoresistance capabilities and the spin-valve structure investigated.

Figure 2: Characteristic in-plane hysteresis and MR curves of the spin-valve structure, at e.a. (left graph) and h.a. (right) directions. The experimental M||(H; ÎąH), M^(H; ÎąH) and MR(H; ÎąH) loops are represented by circles, squares and triangles, respectively. The corresponding ascending (descending) branches are displayed with filled (open) symbols.

Phonons Contribution to the Infrared and Visible Spectra of II-VI Semiconductor Nanoshells P. Rodríguez, C. Kanyinda-Malu and R.M. de la Cruz Departamento de Física, Universidad Carlos III de Madrid, EPS Av. de la Universidad 30, 28911 Leganés (Madrid), Spain E-mail: rmc@fis.uc3m.es Abstract We have investigated the phonons contribution in the infrared (IR) and visible (VIS) optical properties in II-VI semiconductor nanoshells of type I. For this, we use Mie scattering theory by defining appropriate dielectric functions for the constitutive materials of the nanoshells. Indeed, for the core we have considered dielectric function taking into account the spatial confinement of the charge carriers [1] along with the phonons contribution [2, 3]. In fact, to evaluate the exciton energy, we have considered the same treatment used previously in Ref. [4]; i.e., the Coulomb interaction is considered as a perturbative term in the Schrödinger equation in the framework of “Effective Mass Approximation with Finite Barrier Potential” for electrons and holes. For the shell, we have taken dielectric function similar to that used in bulk semiconductor [2, 3]. Independently of the core and shell sizes and the embedding medium, we obtain in the IR spectra, three resonant peaks ascribed to the Cd-S stretching vibration, the longitudinal optical (LO)-CdS and surface optical (SO)-ZnS phonon modes, respectively. The increase of core and shell sizes induces a red shift of the Cd-S stretching vibration and the SO ZnS branches, while a blueshift is obtained for the LO CdS branch. In fact, figure 1 shows this behavior; i.e., we plot the wavenumber versus the geometrical parameter Rs / Rc; being Rc the core radius, while Rs is the total nanoshell size. If the phonons contribution is not considered in the IR spectrum, the Cd-S stretching vibration is dissapeared.

On the other hand, in the VIS spectra, we obtain one sharp resonant peak related to the 1se 1sh optical transition, whose localization is characterized by the core size, essential parameter to evaluate the exciton energy. Phonons contribution in the VIS range yields information about the exciton-phonon coupling in II-VI semiconductor nanoshells. Indeed, we show in figures 2 and 3, the extinction versus the wavelength with and without phonons contribution for different nanoshell sizes. From the shifting of these two peaks (with and without phonons contribution), we estimate coupling energies of excitonphonon in the range of 36 meV - 21 meV. This feature is in good agreement with the size-dependence of exciton-phonon coupling energy previously reported in the literature [5].

When the embedding medium is glass, where the dielectric constants at high frequency of core, shell and islanding materials are similar, we obtain two effects on the IR as well as the VIS optical properties: (i) the phonon peaks (IR range) or the exciton peak (VIS range) are red-shifted, and (ii) the peaks intensities are greater. Therefore, in the light of these results, it can be concluded that the phonons contribution is primordial if the optical properties are investigated in the low-dimensional systems.

References [1] K.J. Webb and A. Ludwig, Phys. Rev. B 78 (2008) 153303.

[2] F. Demangeot, J. Frandon, M.A. Renucci, C. Meny, O. Briot and R.L. Aulombard, J. Appl. Phys. 82 (1997) 1305.

[3] R.M. de la Cruz, C. Kanyinda-Malu and P. Rodríguez, Physica E: Low Dimensional Systems http://dx.doi.org/10.1016/j.physe.2012.05.018 (2012).

[4] R.M. de la Cruz and C. Kanyinda-Malu, Physica E: Low Dimensional Systems 44 (2012) 1250.

[5] S. Nomura and T. Kobayashi, Phys. Rev. B 45 (1992) 1305.

Figures

Phosphonium-based ionic liquids for the formation of nanoparticles Borja Rodríguez-Cabo, Iago Rodríguez-Palmeiro, Adrián Sánchez, Eva Rodil, Ana Soto, Alberto Arce

Department of Chemical Engineering, University of Santiago de Compostela, E-15782, Santiago de Compostela, SPAIN alberto.arce@usc.es Abstract Ionic liquids (ILs) are very good solvents for many applications. They have been also studied for the synthesis of nanomaterials, having different roles in the obtaining of the nanostructures. Many times ILs are used as mere stabilizing agents, acting as surfactants or co-surfactants in the formation of micelles or microemulsions, as well as in the dispersion medium [1,2]. The nanomaterials can be directly dispersed in the chosen solvent or they can be synthesized by chemical methods: carrying out reactions between two precursors at high temperatures and or pressures is the most common technique. The use of reducing agents to obtain noble-metal structures in the nanometric scale is also frequently used.

Some works present the preparation of nanomaterials with the ionic liquid as only medium of synthesis, in the absence of other solvents, [3,4]. Once more, several techniques can be used to form nanobjects inside the ionic liquid, such as thermolysis, reduction/oxidation (reactive techniques in general), ultrasounds, UV radiation... Recently, a new method based on the dissolution/reprecipitation of nanoparticles in ionic liquids was reported [5]. This technique avoids chemical reactions between precursors (the only solid used is the bulk product), high pressure or extreme temperatures Despite inherent impurities of the ILs can alter and reduce the stability of nanoparticles, the metal nanoparticles dispersions are more stable in ionic liquids due to their microstructure and to possible interactions of the nanoparticles surface with the cation and/or anion of the molten salt [6]. Solvation and stabilization mechanisms allow the nanostructures to be stable without additional surface-active agents [7]. ILs act as supramolecular solvents, and spontaneous, well-defined, and extended ordering of nanoscale structures can take place within them [8]. Most studied ionic liquids for the preparation of nanomaterials are those based on an imidazolium ring cation. Their capability to control the size of nanoparticles depending on the length of the hydrocarbon chains was reported [9]. The influence of the cation was also studied [10]. Moreover, it was shown that tetralkylphosphonium ILs can act as both solving and stabilizing agents due to their long alkyl chains and obvious points of coordination with the particles [11,12].

In this work, several phosphonium-based ionic liquids were tested for the synthesis of different types of nanoparticles, (sulfides, metal oxides, silver derivatives) using the previously published method [5], see Figure 1. The nanoparticles were characterized by means of UV-vis absorption spectroscopy, X-ray powder diffraction, transmission electron microscopy and/or dynamic light scattering. The obtained nanoparticles are spherical, well-defined and with narrow size distributions. Depending on the ionic liquid and on the solid, different concentrations can be achieved.

References [1] M. Behboudnia, A. Habibi-Yangjeh, Y. Jafari-Tarzanag, A. Khodayari, Bull. Korean Chem. Soc., 29 (2008) 53.

[2] E. Rodil, L. Aldous, C. Hardacre, M. C. Lagunas, Nanotechnology, 19 (2008) 105603.

[3] V. Taghvaei, A. Habibi-Yangjeh, M. Behboudnia, Powder Technol., 195 (2009) 63.

[4] K. Okazaki, T. Kiyama, K. Hirahara, N. Tanaka, S. Kuwabata, T. Torimoto, Chem. Commun., 6 (2008) 691.

[5] B. Rodríguez-Cabo, E. Rodil, A. Soto, A. Arce, Angew. Chem. Int. Ed., 51 (2012) 1424.

[6] A. Banerjee, R. Theron, R. W. J. Scott, Chem. Sus. Chem., 5 (2012) 109.

[7] A. S. Pensado, A. A. H. Pádua, Angew. Chem. Int. Ed., 50 (2011) 8683.

[8] M. Antonietti, D. Kuang, B. Smarsly, Y.Zhou, Angew. Chem. Int. Ed., 38 (2004) 4988.

[9] T. Gutel, C. C. Santini, K. Philippot, A. Padua, K. Pelzer, B. Chaudret, Y. Chauvin, J.-M. Basset, J. Mater. Chem., 19 (2009) 3624.

[10] E. Redel, R. Thomann, C. Janiak, Inorg. Chem., 47 (2008) 14.

[11] M. Green, P.rahman, D. Smyth-Boyle, Chem. Commun. 6 (2007) 574.

[12] H. A. Kalviri, F. M. Kerton, Green Chem., 13 (2011) 681.

Figures

A

B

C

D

Figure 1. Nanoparticles of a) TiO2, b) MnS, c) Fe2O3, d) CdS prepared in the ionic liquid trihexyl(tetradecyl)phosphonium chloride.

Genetic Algorithms in the control and design of charge one qubit quantum gates in circular graphene quantum dots

Gibrán Amparán(1)(2) F. Rojas(1)(2) and Antonio Pérez-Garrido(1) (1)

Departamento de Física Aplicada, Antiguo Hospital de la Marina, Campo Muralla del Mar, UPCT, Cartagena 30202, Murcia Spain (2) Departamento de Física Teórica, Centro de Nanociencias y Nanotecnologías, Universidad Nacional Autónoma de México, UNAM. Apdo. Postal 356, Ensenada Baja California 22830 México frojas@cnyn.unam.mx

Abstract The design of quantum logic gates have been implemented in several physical systems, where the qubit is represented as charge states using trapped ions, nuclear magnetic resonance using the magnetic spin of ions and with light using light polarization or spin in solid state nanostructures. In graphene spin-qubits in graphene nano-ribbons has been also proposed.

In this work we propose the control and design for the one charge qubit quantum logic gates using the bound states of circular graphene quantum dots [1]. The nanostructure studied consists of graphene circular quantum dot (QD) grown over a semiconductor material which introduces a constant mass term which allow us to make a confinement that is made with a circular electric potential with constant radio (R) where homogeneous magnetic field (B) is applied in order to break the degeneracy between Dirac's points K and K’. We consider two independent Hilbert spaces where the orthonormal states have spinor form and are described by the Kummer functions identified by the half-odd integer j, this integer is eigenvalue of the total angular momentum operator.

The control for the three quantum gate implementation is made with an oscillating electric field [2] and a onsite (inside the quantum dot) pulse with amplitude and time width modulation which introduce relative phase and transitions between states respectively. This introduce a dipolar matrix between the states and the onsite energy in the dot. We solve and control the evolution of the time dependent Schrodinger equation to describe the evolution of the expansion coefficients, i.e. of being in the bound states in the dot Two bound states in QD are chosen to be the computational basis for the qubit subspace[3]: and states with j=1/2,-1/2 of the quantum dot . We study the general n states problem with all dipolar and onsite interactions included so that, our objective is optimize the time dependent physical interactions as control parameters in order to minimize the probability leaking out of the qubit subspace and achieve the desired one qubit gates successfully.

The control parameters optimization is solved as a maximization problem using a genetic algorithm [4] which find efficiently the optimal parameters for the gate implementation where the genes are: magnitude ( ) and direction ( ) of electric field, magnitude of gate voltage ( ) and pulse width ( ).

The fitness F is defined as the gate fidelity an one desire to obtain the best fitness (F=1) that allows us to produce the desired quantum logic gate and obtain the best combination of parameters[5] The results for example for the gate are shown in Fig. 1, for a QD of radius where the probability of the state and one achieve a fitness of F=.977, in our calculation n=7 states where considered, the optimal parameter obtained with the Genetic algorithm are shown in the figure caption. In Fig 2, we show how the control is achieved the time density probability in the QD, leading to the transformation of the wave function from to . So we were able to implement the three gates, and for the z gate we only use the pulse control.

Thanks to DGAPA an project PAPPIT IN112012 for financial support and sabbatical scholarship for F. Rojas and G.Amparan to Conacyt, Mexico for graduate scholarship.

References 1. Patrik Recher, Johan Nilsson, Guido Burkard, Björn Trauzettel, Phys. Rev. B 79, Issue 8, Bound states and magnetic field induced valley splitting in gate-tunable graphene quantum (2009) 085407.

2. Mark Fox, Optical Properties of Solids, Oxford University Press (2001), Quantum Theory of radiative absorption and emission.

3. Charles H. Bennett & David P. DiVincenzo, Nature Vol. 404, Quantum Information and Quantum Computation (2000) 247-255 4. Shuford, Kevin L, Krause, Jeffrey L, International Journal of Quantum Chemistry vol. 77, Issue 1 (200) 393-200

5.

nd

Edwin K. P. Chong and Stanislaw H. Zak, An introduction to optimization 2 Edition Editorial WILEY (2001), Chapter 14: Genetic Algorithms.

Figures Fig. 1. Optimal time Evolution of probabilities made from the initial state

to

under

quantum gate for each QD state. It shows the transition and a small leakage to the state

. The quantum dot

has a radius R=25nm and the perpendicular magnetic field is B=3.043 Teslas. The quantum gate with the following control parameters: =. , =. , and =

is obtained .

Fig. 2: Evolution under quantum gate of the probability density in the quantum dot and pseudospinâ&#x20AC;&#x2122;s direction. At t=0 the wave function is in the initial state and it evolves until at it reaches the state .

Insight into molecular dynamics properties of gemcitabine anticancer drugs loaded inside an open-ended single-walled carbon nanotube 1

2

3

Chompoonut Rungnim , Uthumporn Arsawang , Thanyada Rungrotmongkol and 2,4 Supot Hannongbua 1

Nanoscience and Technology Program, Graduate School, Chulalongkorn University, Bangkok 10330, Thailand 2 Computational Chemistry Unit Cell, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand 3 Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand 4 The Center of Excellence for Petroleum, Petrochemicals and Advanced Materials, Chulalongkorn University, Bangkok 10330, Thailand T.rungrotmongkol@gmail.com and Supot.h@chula.ac.th

Abstract Single-walled carbon nanotube (SWCNT) is a successful candidate of a transporter in drug delivery system applications due to the unique characteristics such as high surface area and long cylindrical cavity. To investigate the behavior of loading multiple drug molecules encapsulated inside SWCNT, an anticancer drug gemcitabine varying in number from one to six molecules encapsulated inside a (18,0) open-ended SWCNT with 14 Å diameter and 34 Å length were investigated using classical molecular dynamics (MD) simulations. Throughout the simulation times of all systems, gemcitabine molecules always located inside the SWCNT due to the partial π-π stacking interaction between the aromatic cytosine ring of gemcitabine and the inner surface of the SWCNT, as well as the interaction among gemcitabine molecules themselves through the π-π stacking and hydrogen bond formation. At a low loading level (less than 21% w/v), the cytosine rings of adjacent drugs were likely to be orientated in a parallel-displaced conformation with a probable π-π interaction. In contrast, at high drug concentrations, the drug molecules are closer to each other inside the SWCNT and this apparently promotes their electrostatic interaction between gemcitabine molecules with multiple hydrogen bond formations, but they totally lose the π-π interaction between each other. These results suggest that the design of drug loading and releasing process for DDSs should take into account these types of intermolecular interactions in order to obtain a SWCNT-based DDS with a high capacity of drug loading and release processes.

References [1] T. Rungrotmongkol, T. Udommaneethanakit, M. Malaisree, N. Nunthaboot, P. Intharathep, P. Sompornpisut, S. Hannongbua, Biophys. Chem. 145 (2009) 29.

[2] T. Rungrotmongkol, U. Arsawang, C. Iamsamai, A. Vongachariya, S.T. Dubas, U. Ruktanonchai, A. Soottitantawat, S. Hannongbua, Chem. Phys. Lett. 507 (2011) 134.

[3] U. Arsawang, O. Saengsawang, T. Rungrotmongkol, P. Sornmee, K. Wittayanarakul, T. Remsungnen, S. Hannongbua, J. Mol. Graph. Model. 29 (2011) 591.

[4] C. Rungnim, U. Arsawang, T. Rungrotmongkol, S. Hannongbua. Chem. Phys. Lett. (Submitted)

Figure 1 The representative structures taken from the last snapshot of six studied systems with different drug loadings contained inside the SWCNT cavity (1-6 gemcitabine molecules per SWCNT) are shown schematically.

Colloidal stability of Graphene Oxide and derivatives in water.

Sainz R a, Rodríguez-Tapiador M.I a, Alcázar C b, Moreno R b, Ferritto R a. a) Nanoinnova Technologies, C/Faraday 7, 28049 Madrid, Spain b) Instituto de Cerámica y Vidrio CSIC, C/Kelsen 5, 28049 Madrid, Spain rsainz@nanoinnova.com Abstract Graphene has attracted tremendous attention in recent years due to its extraordinary electronic, thermal and mechanical properties. Various techniques have been used for producing graphene including micromechanical cleavage, chemical vapor deposition, liquid-phase exfoliation of graphite, and reduction of graphene oxide by chemical reducing agents or thermal treatment [1]. Among these, chemical reduction of graphene oxide is an attractive method for the large-scale production of graphene. Though hydrophilic graphene oxide can be easily water-dispersed into homogeneous colloidal suspensions, chemical reduction of graphene oxide using agents such as hydrazine hydrate [2] yields a material that readily precipitates in water.

We present zeta-potential and turbiscan studies for graphene oxide and reduced graphene oxide synthesized by different methods. Reducing agents like N-methyl pyrrolidone, hydrazine hydrate or amines have been used and the resulting graphene derivatives were characterized.

References [1] Park, S.; Ruoff, R.S. Nat. Nanotechnol., 4 (2009) 217.

[2] Stankovich, S.; Dikin, D.A.; Piner R.D.; Kohlhaas, K.A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen S.T. and Ruoff, R.S. Carbon, 45 (2007) 1558.

Figures 20 10

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Fig. 3 Dispersion stability test by Turbiscan for 1 hr for a) GO, b) rGOB, c) rGON. Calculated sedimentation rates are 0.035, 0.76 and 0.092 mm/min respectively.

GO

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Fig.3 Scanning Electron Microscopy of GO, rGOB, rGON, GO-NH and GO-NH2.

Development of high performance electro-optical films by sol-gel method A. Salundi, M. Timusk, M. Järvekülg, R. Lõhmus, I. Kink and K. Saal Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia aigi.salundi@ut.ee GDLC (Gel-Glass Dispersed Liquid Crystal) materials were first reported in 1991 [1]. GDLCs are, in their nature sol-gel analogs to polymer dispersed liquid crystal materials (PDLCs) composing of organically modified silica [1-3] or mixed oxide [4] dispersed liquid crystal. GDLC material strongly scatters light in its normal state and changes its optical transmittance when electric field is applied, becoming more transparent. In order to achieve high performance, refractive index of the matrix must match the ordinary refractive index of the liquid crystal and the film thickness must be in order of 10μm. Achieving these conditions has been very difficult until now.

GDLC has several potential advantages over PDLC: smaller solubility of LC inside the matrix (smaller amount of LC needed in preparation of unit volume of the film material), better resistance to ultraviolet radiation, easier to control LC director field configuration through droplet shape and surface anchoring forces, determined by the chemical composition. Also, refractive index of the matrix is more easily tunable due to the availability of large amount of suitable precursors. The main potential applications of GDLC materials is “smart glass” (window with variable transmittance).

In this work we report the significant improvement compared to our previously reported results [3]. GDLC film preparation process was elaborated to incorporate titanium alkoxides in synthesis process. This enabled the adjustment of the refractive index of silica glass matrix without having destructive influence on macroscopic liquid crystal phase separation at the same time. A highperformance xerogel-liquid crystal composite electro-optical film that exhibits a 75.9 % change in its transmittance as an electric field is applied was prepared. Field-dependent scattering behaviour of a refractive index matched GDLC film over a broad spectral (from visible to near-IR) and temperature range was investigated. Transmittance vs. applied voltage measurements at different temperatures demonstrate electro-optical effects at least down to -13 °C which means that liquid crystal must be in molten (liquid crystal) state at these temperatures in the microscopic volume confined in xerogel matrix. That is remarkable since it is known that the used liquid crystal 4-cyano-4'-pentylbiphenyl crystallizes in macroscopic volume at 24.5 °C. The largest electro-optical effect was observed at 25.2 °C.

References [1] D. Levy, C. J. Serna, J. M. Otόn, Mat. Lett. 10 (1991), 470-476.

[2] M. Zayat, D. Levy, Chem. Mater., 15 (2003), 2122-2128.

[3] M. Timusk, M. Järvekülg, R. Lõhmus, I. Kink, K. Saal, Mater. Sci. Eng. B., 172 (2010), 1-5.

[4] M. Timusk, M. Järvekülg, A. Salundi, R. Lõhmus, S. Leinberg, I. Kink, K Saal, J. Mater. Res., 27 (2012), accepted

Figure

Fig. Cross-section of GDLC material.

IMPROVED MECHANICAL AND BARRIER PROPERTIES OF AMORPHOUS POLYAMIDE FILMS BY THE ADDITION OF A HIGHLY EXFOLIATED NANOCLAY Pablo Santamaría and Jose Ignacio Eguiazábal Department of Polymer Science and Technology and POLYMAT Faculty of Chemistry UPV/EHU Pº Manuel de Lardizabal 3, 20018 San Sebastián (SPAIN) pablo.santamaria@ehu.es Abstract It is known that many of the most relevant polymers have been successfully used to produce nanoclay-based polymer nanocomposites (NCs) with improved properties by melt blending. Among them, NCs based on polyamides (PAs) have received the greatest industrial and scientific attention, as they have shown the highest levels of exfoliation of the nanoclay.[1] Among the application fields of PAs, packaging is probably one of the most important, as it comprises an important part of the total PA production. In this field, the incorporation of highly exfoliated nanoclays is very attractive, as the nanoclay could offer an improved performance (mainly mechanical and barrier) to the base film. This has triggered the development of PA based NC films, and the aim of the present work has been to examine the structure, and the mechanical and barrier properties of uniaxially drawn films of amorphous PA (aPA) based NCs with Nanomer I30 nanoclay, which is modified with a one-tailed surfactant and is one of the most performing commercially available nanoclays.

The NC films were obtained by melt extrusion-kneading followed by flat film extrusion. The draw ratio (DR), which varied from a minimum of 5 to the maximum allowed for the polymer, and the nanoclay content, which ranged from 0 to 6 wt.%, were the studied variables. The effects of both variables on the nanostructure (X-ray diffraction (XRD) and transmission electron microscopy (TEM)) as well as on the mechanical properties (measured both in the machine (MD) and the transverse (TD) directions) and the barrier behaviour (water sorption, acetone vapor transmission rate and permeability to O2 and CO2) were determined.

In Figure 1, a micrograph of the 4% NC film obtained at the lowest DR is shown. The presence of uniformly dispersed individual nanoclay platelets indicates a high degree of exfoliation of the nanoclay. As also seen in Figure 1, the nanoclay platelets appear preferentially oriented along the drawing direction due to the fact that the molten and oriented polymeric chains orientate the nanoclay sheets in their own direction. Regarding the mechanical properties, Figure 2 shows the tensile modulus of the films both in the MD (a) and the TD (b) directions as a function of the DR and the nanoclay content. As can be seen, the important increases in the MD resulting from the presence of nanoclay are additional to those produced by drawing. This means that the two independent increases contribute to a combined modulus increase, which goes from 2700 MPa in the aPA to 4450 in the drawn 6% NC films (65%). Along the TD the moduli appear always lower than those in the MD, and they decrease with DR, as a consequence of the orientation in the draw (MD) direction. However, the nanoclay presence leads to an important modulus increase also in the TD. These unusual increases in the two directions of the film, which are not common in films filled with fibrilar reinforcements, are attributed to the planar geometry of the nanoclay which, upon drawing, is oriented on the plane of the film and reinforces the film in both directions. With respect to the transport properties, representative water sorption plots of aPA and the 6% NC films are collected in Figure 3. The diffusion coefficients (D) can be calculated from the plots, and the obtained values indicate that the presence of nanoclay leads to a reduction of the D of aPA which is attributed to the fact that it creates obstacles in the solvent pathway, and hinders the transport through the polymer.[2] As also seen in Figure 3, the height of the plateau, i.e., the maximum water uptake (solubility) decreases in the presence of nanoclay. Both observations indicate a clear reduction in the water uptake of the aPA. As one of the most characteristic properties of aPA is its very low O2 permeability, it was also studied as a function of the nanoclay content and the DR. As expected, O2 permeability of the pure aPA decreases gradually upon the addition of nanoclay from 0.024 barrers in the aPA to 0.013 barrers in the 6%NC. This is almost a 50% improvement in the barrier capacity of aPA that i) is attributed to the tortuous path created by the nanoclay,[2] ii) is of particular interest taking into account the initial very low permeability of the aPA, and iii) shows the adequacy of this laminar nanoclay for improving transport properties. The nanoclay addition also produces a decrease in the CO2 permeability and in the acetone vapor transmission rate of aPA films.

As a conclusion, the results show that the nanoclay, which is highly exfoliated and oriented along the drawing direction, produces an important tensile modulus increase both in MD and TD, and also leads to reduced water transport, permeability to O2 and CO2 as well as to lower acetone vapor transmission rate. Both properties improvements are attributed to the planar geometry of the oriented and exfoliated nanoclay.

Acknowledgements: The financial support of the Spanish “Ministerio de Economía y Competitividad” (Project MAT2010-16171), the Basque Government (IT-234-07) and the University of the Basque Country (UFI 11/56) is gratefully acknowledged. P. Santamaría also acknowledges the grant awarded by the Basque Government.

References [1] F. Chavarria, D.R. Paul, Polymer, 45 (2004) 8501-8515.

[2] G. Choudalakis, A.D. Gotsis, European Polymer Journal, 45 (2009) 967-984 Figures

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First Principles calculations of SnS2 layered semiconductor, taking into account the Van der Waals interactions.

Yohanna Seminovski1,2,3, Pablo Palacios1,4, Perla Wahnón1,2, and Ricardo Grau-Crespo3 1

Instituto de Energía Solar, Universidad Politécnica de Madrid UPM, Ciudad Universitaria, 28040 Madrid, Spain 2 Department of TEAT, ETSI Telecomunicación, UPM, Ciudad Universitaria, 28040 Madrid, Spain 3 Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom 4 Department of FyQATA, EIAE, UPM, Pz. Cardenal Cisneros 3, 28040 Madrid, Spain seminovski@etsit.upm.es Abstract Layered semiconductors of the type MX, (X =chalcogen) are considered promising alternative materials for solar energy conversion. The Van der Waals cleavage plane (0001) of layered semiconductors as SnS2 is characterized by hexagonal arrays of close packed chalcogenide ions which are covalently bound within X-M-X sandwiches. This is an ideal substrate to study fundamental aspects of the metal/semiconductor interaction as the perfect (0001) plane is considered to be free of surface states and intercalation of adsorbed metals may occur in stoichiometric amounts. In photovoltaic application the doped semiconductors plays a major roll, and one of the layered semiconductors studied is SnS2 which have been considered as a precursor of intermediate band materials (IBM) doped with vanadium [1].

SnS2 structure consists of sheets of tin atoms in the basal plane octahedrally coordinated between close packed sheets of sulphur atoms. The three-atomic-layer sandwich is repeated in the c direction.

SnS2 can exist in a number of different polytypes where the stacking sequences of these sandwiches vary. The simplest structure 2H (Ramsdall notation) has a stacking sequence, AB-AB where the Greek letter represents the metal atom. There is one layer, and one molecular unit per unit cell. The 4H structure has a stacking sequence AB-CD It has two layers and two molecular units per unit cell. The a lattice parameter is the same and the c lattice parameter approximately doubled with respect to the 2H structure. [2] In this work we study the structural disposition of the most important polytypes of this layered material, the named 2H and 4H using the interatomic Van der Waals interactions in our theoretical calculations.

We study the use of two theories in SnS2 layered material, the Grimme [3] dispersion correction that is applied after each autoconsistent PBE electronic calculation and the self-consistent Dion functional optimized for solids by Michaelides et al. [4] The Grimme approach, intrinsically possesses a semiempirical implementation which take into account the Van der Waals radius and the electrostatic interaction between the layers. The self-consistent functional, on the other hand, uses a complete theoretical approach. In this work the results demonstrates the enhancement of the geometric parameters by the use of the Van der Waals interactions in agreement with the experimental values when either Grimme or the new functionals are used.

References

[1] – P Wahnón, J C. Conesa, P Palacios, R Lucena, I Aguilera, Y Seminovski, F Fresno, Phys.

Chem. Chem. Phys. 13 (2011) 20401.

[2] - Mitchell R, Fujiki Y and Ishizawa Y, Nature 247 (1974) 537 [3]S. Grimme, J. Comp. Chem. 27 (2006)1787.

[4] M. Dion, H. Rydberg, E. Schröder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92 (2004) , 246401 ; J. Klimeš, D. R. Bowler, and A. Michaelides, Phys. Rev. B 83 (2011), 195131.

Figures

a)

b)

Fig 1 â&#x20AC;&#x201C; SnS2 polytypes supercells of b) 2H and b) 4H, where the differences on the pile stacking of the layers can be observed.

Towards a molecular dynamics description of the mechanical properties of antibodies as measured with a force microscope J.G. Vilhena1, Pedro Serena2, Ricardo García3, Rubén Pérez1 1-SPM-TH, Dep. de Física Teórica de la Materia Condensada, Universidad Autonoma de Madrid, Spain 2-Theory and Simulation of Materials, Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid, Spain 3-Force Tool, Instituto de Microelectrónica de Madrid, CSIC, Madrid, Spain pedro.serena@icmm.csic.es Abstract The antibodies are key elements of the immunological system. A better understanding of their nanomechanical properties could enable to exploit all of their targeting properties. Recent developments in force microscopy such as multi-frequency atomic force microscopy (AFM) provide information about the nanomechanics of proteins [1, 2]. The AFM has several features that are attractive to the biologists.

First, it is a tool with molecular resolution that enables imaging in physiologic-like environments [3] and secondly it also provides nanomechanical and chemical information at time scales relevant for biomolecular interactions [3].

Dynamic AFM images [1] of biological molecules on ambient conditions (liquid) are controlled by nonlinear tip-sample interaction, the cantilever dynamics and the feedback control. In order to extract accurate information about topography and materials properties, these effects have to be taken into account simultaneously. So far, these experiments have been analyzed using simple models based on continuum mechanics [1]. In order to address the ultimate spatial resolution and force sensitivity of the AFM on biological molecules we model an AFM experiment on the human immunoglobulin G (IgG) by performing classical atomistic molecular dynamics simulations. The tip and the supporting substrate for the IgG adsorption are modeled as a capped carbon nanotube and as a slab of graphite, respectively.

The inter- and intra-molecular forces used throughout all our simulations are the ones presented in well tested AMBER[4] (Assisted Model Building with Energy Refinement) force field suite. The tip and substrate force-fields are built using the antechamber tool (present in AMBER) and then these parameters are fine tuned to reproduce the correct[5] crystallographic and mechanical properties of the tip and the substrate.

These simulations provide an insight into the atomistic mechanisms controlling the local deformation (induced by an AFM tip) of the protein and also allow us to map the mechanical response of a protein on to its structure (amino-acid sequence).

References [1] D. Martinez-Martin, E.T. Herruzo, C. Dietz, J. Gomez-Herrero, and R. García, Phys. Rev. Lett., 106 (2011) 198101.

[2] R. Garcia, and E.T. Herruzo, Nat. Nanotechnol., 7 (2012) 217.

[3] R. Garcia , R. Pérez, Surf. Sci. Rep., 47 (2002) 197.

[4] D.A. Case, et al, AMBER 12, University of California, San Francisco (2012).

[5] S.-H. Tzeng, and J.-L. Tsai, Journal of Mechanics, 27 (2011) 461.

Figures:

Figure 1. Figure from Ref.[1]. Topography and flexibility map of a single IgM antibody. (a) Bimodal FM AFM image . (b) Flexibility map obtained simultaneously with the topography image. (c) Pentamer structure of the IgM antibody. The locations of the lowest (L) and highest elastic moduli (H) are marked. (d) Topography (grey) and flexibility (black) profiles along the lines marked, respectively, in (a) and (b).

Figure 2. Schematic representation of Human immunoglobulin G over a graphite slab. It is also represented the capped carbon nanotube that will serve as our AFM tip.

A novel nanovesicular carrier system for ocular delivery of clotrimazole Rehab Nabil Shamma*1, Mona Basha Ahmed2, and Sameh Hossam Eldin2.

1

Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, Cairo

University, Cairo, Egypt.

2

Department of Pharmaceutical Technology, National Research Center, Cairo, Egypt

Fungal Keratitis is a devastating disease that is responsible for corneal blindness. The limitations of the current therapeutic treatment of ophthalmic fungal infections are often due to poor bioavailability of antifungal agents in addition to the inability to provide long-term precorneal residence time.

The objective of the present investigation: was to explore the potential of novel vesicular nanocarriers for effective and sustained ocular delivery of Clotrimazole (CMZ). Vesicular nanocarriers were prepared using Span 60 and three types of edge activators. A 32 full factorial design was adopted to study the influence of the type of edge activator as well as the ratio of Span 60 to edge activator as independent variables. The particle size, entrapment efficacy and zeta potential of the developed nine formulations were selected as dependent variables.

Results: Results revealed that both the type of edge activator and ratio of Span 60 to edge activator had significant effects on the various physicochemical characteristics of the produced spanlastics (p < 0.05).

The analysis of variance was used to optimize the properties of the prepared formulation. The prepared optimized formulation was spherical in shape, with average particle size of 500 nm, and of negatively charged surface (-32 mV) and high entrapment efficiency (89%). In vivo Draize test showed no signs of ocular toxicity.

Characterization and in vitro evaluation of microleakage and antibacterial properties of prepared ZnO and ZnO:Ag nano sealers Maryam Shayani Rada, Ahamd Kompanya, Ali Khorsand Zaka, Majid Abrishamia, Maryam Javidib, Majed Mortazavib a

Materials and Electroceramics Laboratory, Department of Physics, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran b Department of Endodontics, Faculty of Dentistry, Mashhad University of medical Sciences, Mashhad, Iran mashayani@yahoo.com

Abstract Undoped and Ag doped Zinc Oxide (ZnO, ZnO:Ag) nanopowders were prepared and compared to ZOE (Zinc Oxide Eugenol) and AH26 (Epoxy resin sealer) which are commonly used in dentistry as sealer.

These nano sealers prepared via a modified sol- gel method using gelatin as polymerization agent. The undoped and Ag doped ZnO nanopowders prepared at calcination temperatures of 500, 600, 700째C for 8 hours. Also the microleakage and antibacterial property of the prepared samples were investigated. The prepared undoped and Ag doped ZnO nanopowders were characterized by a number of techniques, including x-ray diffraction (XRD) and transition electron microscopy (TEM) that results show their particle size and hexagonal (wurtzite) structure with presence of Ag metallic phase for Ag doped prepared samples. Results show that our prepared undoped and Ag doped ZnO nanopowders for using as sealer exhibit better microleakage and antibacterial properties comparing to ZOE and AH26 (common sealer).

Therefore these prepared nanopowders are significant filling material to be used as sealer in root canal treatment.

References: [1] Nomura K, Ohta H, Ueda K, Kamiya T, Hirano M, Hosono H, Science, 300 (2003), 1269-72.

[2] Look DC, Claflin B, Alivov YI, Park SJ, physica status solidi (a), 201 (2004), 2203-12.

[3] Xiang HJ, Yang J, Hou JG, Zhu Q, Applied Physics Letters, 89 (2006), 223111-3.

[4] Xu J, Pan Q, Shun Ya, Tian Z, Sensors and Actuators B: Chemical, 66 (2000), 277-9.

[5] Cory H, Janet L, Alex P, Reddy KM, Isaac C, Andrew C, et al, Nanotechnology, 19 (2008), 295103.

[6] Nair S, Sasidharan A, Divya Rani V, Menon D, Nair S, Manzoor K, et al, Journal of Materials Science: Materials in Medicine, 20 (2009), 235-41.

[7] Nitin K, Adam D, Jong-in H, Nanotechnology, 17 (2006), 2875.

[8] Chen C, Liu P, Lu C, Chemical Engineering Journal, 144 (2008), 509-13.

[9] Gui Y, Xie C, Zhang Q, Hu M, Yu J, Weng Z, Journal of Crystal Growth, 289 (2006), 663-9.

[10] Khorsand Zak A, Razali R, Abd. Majid WH, Darroudi M, International Journal of Nanomedicine, 6 (2011), 1399-403.

[11] Razali R, Zak AK, Majid WHA, Darroudi M, Ceramics International, 37 (2011) 3657-63.

[12] Yousefi R, Muhamad MR, Zak AK, Thin Solid Films, 518 (2010), 5971-7.

Figures:

Figure1. XRD patterns of ZnO and ZnO:Ag nanoparticles prepared at different calcination tempratures of 500, 600, and 700째C.

Figure 2. TEM graph of ZnO nanoparticles at 500, 600 and 700째C.

(a) (b) Figure3. (a) Microleakage and (b) Post-hoc analysis of the ZnO and ZnO:Ag nanoparticles comparing to AH26 and ZOE.

Figure4. Antibacterial properties of the undoped and Ag doped ZnO nanoparticles comparing to ZOE (ZnO micro powder).

Nanocomposite carbon material – silver nanoparticles: Preparation and antibacterial activity Slovak Petr, Dr. Kvitek Libor Palacky University, Krizkovskeho 8, Olomouc, Czech Republic Petslo@seznam.cz Abstract Silver nanoparticles (AgNPs) are suitable component for preparation of nanocomposite materials with an antibacterial activity. The preparation of such materials was realized by the adsorption of AgNPs from the aqueous dispersion. Carbon based materials, namely active carbon, carbon nanotubes and carbon aerogels, were used as adsorbents. Firstly were these carbon adsorbents used in pure form, secondly were used in oxidized state and thirdly in form modified by polyethylenimine. Oxidation was -3 handled by boiling in 5 mol∙dm HNO3, addition of polyethylenimine was done through the adsorption from the solution. These steps should lead to the better adsorption of AgNPs because of their higher affinity to the oxygen and especially to the nitrogen. There was also studied an antibacterial activity of nanocomposites that was created by adsorption high amount of AgNPs and which did not cause the aggregation of AgNPs. Key words:

Silver nanoparticles; Adsorption; Carbon materials; Oxidation; Antimicrobial activity

Introduction Carbon materials have important and irreplaceable position among all adsorbents.

Firstly, the most of carbon materials provides high specific surface area volume and good porosity. Secondly, they are often very cheap and available for many laboratories. Thirdly, every organic substance is made of carbon, so that the danger which could cause these adsorbents to the environment is minimal.

Carbon adsorbents are already used for 1 adsorption of heavy metals or for purification of 2 waste waters . These materials can be doped or impregnated with substances to improve their current properties or even to develop a new one. For example silver impregnated materials are used for removal of cyanide from 3 4 aqueous solution or for capturing the mercury .

Very interesting could be the modification of these carbon adsorbents with AgNPs providing antibacterial activity especially against 5 Staphylococcus aureus , Escherichia coli and 6 Pseudomonas aeruginosa . This combination can lead to the very promising materials with antibacterial activity which could be used for water purification and disinfection or for medical purposes.

Experimental The preparation of AgNPs was based on 7 modified Tollens method where the complex + cation [Ag(NH3)2] was reduced by maltose.

Such prepared nanoparticles had size range 24 – 33 nm and were used for adsorption after a day in order to avoid the creation of new nanoparticles during the adsorption.

Used carbon materials can be divided into two groups: to the first group belong active carbon (CXV) and multi-walled carbon nanotubes (MWCNT) which were bought as commercial adsorbents. To the second group belong three

types of carbon aerogels: RFA, RFA X and RFB which were prepared in the laboratory. The preparation of RFA and RFA X was based on 8 article by M. Reuß and L. Ratke . The ratio of resorcinol to formaldehyde was 1:1 and the -3 reaction was catalyzed with 0.23 mol∙dm HCl. The difference between RFA and RFA X is in the drying part of the preparation. While the RFA was after the addition of the catalyst 24 hours at room temperature, the RFA X was put for 1 hour into the autoclave at 110°C. Then were both materials for 24 hours in oven at 70°C and after that they were pyrolyzed. The preparation of RFB aerogel was based on 9 article by M. Wiener . The ratio of resorcinol to formaldehyde was 1:2 and the reaction was catalyzed with 0.035% solution of NaHCO3.

Then it was dried in the oven at 70°C for 48 hours and after that was that material pyrolyzed.

The oxidation of all adsorbents was done by boiling 4.5 g of chosen adsorbent in 100 ml -3 5 mol∙dm HNO3 for three hours. After boiling, the materials were washed in water to the neutral pH. These materials were characterized with IR spectrometry. The polyethylenimine was added through the adsorption from the solution.

0.5 g of oxidized material was shaken with 150 ml of 0.01% polyethylenimine for 2 hours and then for 1 hour in distilled water.

The adsorption of AgNPs from aqueous dispersion proceeded as follows: the 0.25 g of carbon adsorbent was shaken in the 75 ml of solution of AgNPs of six different concentrations for three hours and then was the solution filtered and an adsorbent dried at the room temperature. The amount of adsorbed nanoparticles was determined through the UV/Vis spectrometry from Lambert-Beer law.

Results and discussions Adsorption isotherms obtained from pure materials are showed at figure nr.1. The materials can be again divided into two groups – commercial available adsorbents which have adsorption limited by the maximum amount of AgNPs in the solutions (they adsorb 90-100%) and carbon aerogels which had quiet low adsorption ability. The low adsorption of carbon aerogels is probably caused by the size of their pores, which were measured to be around 2 – 10 nm where obviously AgNPs with size range 24 – 33 nm cannot fit. On the other hand, CXV and MWCNT created nanocomposites Ag@(carbon material) and their pictures from transmission electron microscopy (TEM) are showed at figures nr.2 and nr.3. Ag@CXV and Ag@MWCNT also exhibited good antimicrobial activity comparable with ionic silver or AgNPs. The oxidation had bad influence on adsorption abilities. All oxidized materials had worse results than pure ones and some of them did not adsorb at all. The modification with polyethylenimine again increased the adsorption of the materials, nevertheless there were observed some issues with desorption of polyethylenimine back to the solution which caused the adsorption of AgNPs also on the laboratory glass.

[6] Guzman M., Dille J., Godet S., Nanomedicine: Nanotechnology, Biology, and Medicine, 8 (2012) 37.

[7] Panacek A., Kvitek L., Prucek R., Kolar M., Vecerova R., Pizurova N., Sharma V. K., Nevecná T., Zboril R., Journal of Physical Chemistry B, 110 (2006) 16248.

[8] Reuß M., Ratke L., Journal of sol-gel science and technology, 47 (2008) 74.

[9] Wiener M., Reichenauer G., Scherb T., Fricke J., 350 (2004) 126.

Figures

Figure nr.1: The comparism of adsorption abilities of pure materials.

Conclusions From the five used carbon materials as adsorbents two were able to create nanocomposite with AgNPs. Ag@MWCNT and Ag@CXV had good antibacterial activity comparable with ionic silver or AgNPs. On the other hand, carbon aerogels are not suitable for this type of nanocomposite. At this stage of research, oxidation or any other modification did not improve the adsorption of AgNPs. Acknowledgements This work was financed by project nr.

CZ.1.07/2.2.00/28.0084.

I would also like to thank to the Mr. Ales Panacek and Dr. Vaclav Slovak for their help and cooperation.

References [1] Grazhulene S.S., Redkin A.N., Telegin G.F., Bazhenov A.V., Fursova T.N., Journal of Analytical Chemistry, 65 (2010) 682.

[2] Guo M.X., Qiu G.N., Song W.P., Waste Management, 30 (2010) 308.

[3] Adhoum N., Monser L., Chemical engeneering and processing, 41 (2002) 17.

[4] Luo G.Q., Yao H., Xu M.H., Cui X.W., Chen W.X., Gupta R., Xu Z.H., Energy Fuels, 24 (2010) 419.

[5] Mirzajani F., Ghassempour A., Aliahmadi A., Esmaeili M. A., Research in Microbiology, 162 (2011) 542.

Figure nr.2: The TEM image of Ag@MWCNT.

Figure nr.3: The TEM image of Ag@CXV.

Immunoglobulin G sensor by means of lossy mode resonances induced by a nanostructured polymeric thin-film deposited on a tapered optical fiber Abian B. Socorro, Jesus M. Corres, Ignacio Del Villar, Francisco J. Arregui, Ignacio R. Matias Nanostructured Optical Sensors Group (GSON), Electrical and Electronic Engineering Department at Edificio de los Tejos, Public University of Navarra, Campus de Arrosadia s/n, Pamplona, Spain ab.socorro@unavarra.es Abstract A novel approach to detect type G immunoglobulins (IgGs) has been developed, based on the combination of two ways of improving sensitivity applied to a simple optical structure. The first one is the fact of tapering the optical fiber, which permits to access the evanescent field of the light propagating through the waveguide and increases the detection surface. The second one is the use of a novel technology known as lossy mode resonances (LMRs) [1,2], which have proved to present higher versatility in some characteristics than surface plasmon resonances (SPRs) [3]. Due to this, although SPRs are normally used to detect biological reactions, LMRs can also address this topic.

To this purpose, a 30 mm uncladded segment of a 200/225 m core/cladding diameter optical fiber (FT200EMT, Thorlabs Inc.) was tapered by a system designed by Nadetech Innovations S.L. until a waist diameter of 100 m and a waist length of 10 mm were reached. This tapered uncladded multimode fiber (T-UMF) was subjected to a sputtering process (Quorum Technologies Inc.), in order to deposit a silver mirror on its tip, so that a simple reflective set-up could be prepared. The materials used for the thin-film fabrication were poly(allylamine hydrochloride) (PAH) and the polyanions poly(acrylic acid) (PAA) and poly(styrene sulfonate) (PSS), all from Sigma-Aldrich. These three substances were chosen since they have reported to generate LMRs by using the layer-by-layer electrostatic selfassembly technique (LbL-ESA), which is described elsewhere [4]. Apart from that, both anti-IgGs and IgGs, extracted from goat serum, were also obtained from Sigma-Aldrich.

Fig. 1 shows the equipment used to follow both construction and detection processes. First of all, an AQ4303-B (ANDO Inc.) white light source launched the optical power to an optical 2x1 bifurcator.

The light was introduced in the T-UMF and then reflected by the metallic mirror, at the same time it was modulated by the chemical substances being adsorbed during the process. Finally, the different spectra were captured by a spectrometer from 400 to 1000 nm (Ocean Optics Inc.) and then processed.

As it can be observed in Fig. 2 a and b, a [PAH/PAA]20 matrix was needed to locate the LMR at 600 nm. Here, a typical behavior of a LMR is observed. Low losses are registered until the LMR starts to be visible at bilayer 15. From then on, the resonance presents a red-shift to higher wavelengths as the nanocoating thickness increases. Then, a [PAH / PSS]5 polymeric matrix was deposited by LbL onto the previous one, in order to create an adequate environment for the deposition of the anti-IgGs, according to [5]. The end of the construction finished when the LMR reached the middle of the monitoring window, this means 700 nm (bilayer 25). The goal for doing this was to center the LMR in a position where the further displacements could be better monitorized wherever the resonance shifted.

The next step was to register the LMR displacement when adsorbing the anti-IgGs layer and the further shifts when detecting the different IgG concentrations. In this sense, Fig. 3 is provided, where the mentioned biological processes are presented, as a wavelength displacement while time passes. First, the substrate deposited by the previous paragraph was subjected to a 6 g/ml solution of anti-goat IgG in PBS during 4 hours, so that the anti-IgGs were deposited onto the substrate at room temperature. As it is presented in Fig. 3, the LMR shifted around 14 nm to the right, from 735 to 749nm. Then, 3 different IgG concentrations were detected by immersing the resulting biosensor in 1.4, 4.2 and 12.5 g/ml PBSIgGs solutions, obtaining shifts to 747, 752 and 757 nm respectively. The reason for this behaviour is a change of the effective refractive index due to the adsorption of the biological compounds, which makes the LMR shift from one position to other.

All things considered, a simple fiber-optic IgG biosensor has been developed by studying the behavior of a LMR induced by a polymeric thin-film deposited onto a tapered optical fiber. The effect of tapering the optical structure leads to a higher detection surface and it gives also an easy access to the evanescent field of the light propagating through it. This results in an improvement of the sensor properties when detecting IgGs concentrations.

References [1] A.B. Socorro, I. Del Villar, J.M. Corres, F.J. Arregui, I.R. Matias, Sens. Act. A, 180 (2012), 25-31.

[2] A.B. Socorro, I. Del Villar, J.M. Corres, F.J. Arregui, I.R. Matias, IEEE Sens. Jour. (2012), doi: 10.1109/JSEN.2012.2198464 (in press).

[3] I.Del Villar, C.R Zamarreño, M. Hernaez, F.J Arregui, I.R Matias, J.Light.Tech, 28(1) (2010),111-117.

[4] Decher G., Science 277 (1997), 1232–1237.

[5] Z. Feldötö, M. Lundin, S. Braesch-Andersen, E. Blomberg, J. Colloid and Interface Science 354 (2011), 31-37.

Figures

Fig. 1. Set-up prepared to monitorize both the construction and the detection processes.

Fig. 2. (a) LMR evolution as the thin-film thickness increases. (b) LMR profile at different bilayers.

Fig. 3. Tracking of the minimum of the LMR during the anti-IgGs deposition and the IgGs detection. The vertical dashed lines indicate when the sensor is immersed into the next IgGs solution.

Nanostructured tungsten trioxide thin films by aqueous chemical growth for applications in gas sensing and electrochromism 1,2,

3

4

2

1

B.T. Sone, T. Malwela, L. Vayssieres, E. Iwuoha and M. Maaza

1

NANOAFNET-Materials Research Department, iThemba LABS, P.O.B.722, Somerset West, South Africa 2 Chemistry Department, University of the Western Cape, P.B. X17, Bellville, South Africa 3 National Centre for Nanostructured Materials, CSIR, Meiring Naude, Pretoria, South Africa 4 National Institute for Materials Science (NIMS), Namili 1-1,Tsukuba, Ibaraki 305-0044, Japan Abstract Aqueous Chemical Growth (ACG) [1-3] is a low cost, low temperature and environmentally benign wet-chemistry technique that has been used to synthesize thin films and coatings of multifunctional Semiconductor Metal Oxides (SMO) that often find applications in gas sensing, smart windows, batteries, supercapacitors, etc.

We report here the use of the ACG technique to produce on bare Corning glass and F-doped Tin Oxide-on-glass (FTO) thin films of WO3, a SMO, which finds applications in gas sensing and electrochromic devices. SEM showed that nanoplatelet-containing structures were generally produced on the Corning glass substrates while urchin-like microspheres were produced on the FTO substrates. TEM, HRTEM, were used confirm the morphology of the structures observed in SEM while XRD alongside Raman spectroscopy were used to show that WO 3 in the thin films existed in the monoclinic, cubic and hexagonal phases.

While the WO3 thin films prepared on Corning glass substrates were evaluated for their gas sensing behaviour with respect to hydrogen, CO, and CO2 (flammable and poisonous gases common in mining and industrial environments), those that were prepared on FTO where evaluated for their electrochromic behaviour using Cyclic Voltammetry and UV-Vis-NIR spectrophotometry.

Results obtained on gas sensing showed that WO3 thin films on Corning glass are suitable for ˚ hydrogen sensing in the 200-350 C temperature window (Fig.1). Doping these thin films with ˚ graphene resulted in reduction of sensing temperatures to 100 C. Gas sensing of CO and CO2 ˚ was also observed to take place for the undoped WO 3 thin films at temperatures of 200 C and above.

For electrochromism (Fig. 2), the WO3 thin films on FTO demonstrated fairly fast optical switching + rates from blue to colourless, of less than 30 seconds upon H intercalation in 0.1 M H2SO4 electrolytic medium. This makes them potentially applicable for use as electrochromic materials in electronic displays, smart windows and other devices were optical switching is needed.

References [1] Lionel Vayssieres, Anders Hagfeldt, and Sten Eric Lindquist, Pure Applied Chemistry, 72 (2000) 47-52.

[2] Lionel Vayssieres and Arumugam Manthiram, J. Phys. Chem. B, 107 (2003) 2623-2625.

[3] Lionel Vayssieres, Lew Rabenbeg, and A. Manthiram, Nano Lett. , 2 (2002) 1393-1395.

Figures

(b)

50000000

WO3ACG, pH=0.91 o

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Fig.1. (a) SEM micrograph of WO3 nanoplatelet-containing desert-rose like structures; (b) Ë&#x161; Hydrogen sensing of WO3 thin film by Aqueous Chemical Growth at 250 C. Inset in Fig.1a shows WO3 thin film on Corning glass.

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Fig.2. (a) SEM micrograph of WO3 urchin-like microspheres produced by ACG; (b) Cyclic + voltamogramme of H intercalation in WO3 thin films on FTO carried out in 0.1M H2SO4 medium.

Inset in Fig. 2b shows electrochromic effect in WO 3 thin film on FTO.

Magnetic properties of nanostructured Ca1-xGdxMnO3 obtained by glycine-nitrate procedure V. Spasojevic, V. Kusigerski, M. Rosic, J. Blanusa, M. Perovic, A. Mrakovic, B. Antic, and B. Matovic

The Vinca Institute, University of Belgrade, P.O. Box 522, Belgrade, Serbia vojas@vinca.rs Ca1-xGdxMnO3 nanopowders (x=0.05, 0.10, 0.15, 0.20) with perovskite type crystal structure were synthesized by the glycine nitrate procedure [1]. Starting powders were prepared by combustion of solutions containing mixture of glycine with metal nitrates in their appropriate stoichiometric ratios. The so-obtained powders were annealed at the temperature of 850 oC for 10 minutes to produce final nanostructured samples with the average nanoparticle size of about 20 nm. Magnetic measurements show that electron doping by Gd3+ ions substantially changes CaMnO3 antiferromagnetic (AFM) behaviour. After introduction of Gd3+ ions, significant ferromagnetic (FM) component appears due to an emergence of double exchange interaction between Mn3+-Mn4+ ions. This resulted in appearance of a low temperature plateau in field cooled (FC) magnetization as well as in emergence of hysteresis loop with the relatively high coercivity up to 2300 Oe. Presence of competing long-range AFM and shortrange FM interactions and their randomness lead to a frustration of manganese magnetic moments, and appearance of the spin-glass state at low temperature of about TSG≈65 K (Fig.1, Inset). Concentration dependence of effective magnetic moments µeff(x) is linear, while Curie-Weiss temperature θ(x) changes its sign from negative to positive for concentrations above x=0.05 (Fig. 2) which points to the formation of FM clusters in AFM matrix [2]. The same picture is supported by low temperature M(H) measurements were maximums in Hc(x) and M(x) curves at certain concentration x is a consequence of the balance between FM-cluster/AF-matrix interactions (Fig. 3). Recorded large field-cooled hysteresis shift Hshift (Fig.4.) can be also considered as a consequence of exchange bias that emerges at the borderline of FM-AFM regions. We assume that these interactions are also responsible for the unusual Hc(T) plateau at the temperatures below spin-glass transitions (Fig. 4).

References [1] D. Markovic, V. Kusigerski, M. Tadic, J. Blanusa, V. Antisari, V. Spasojevic, Scr. Mater. 59 (2008) 35.

[2] I. Sudheendra, A. R. Raju and C. N. Rao, J. Phys.: Condens. Matter 15 (2003) 895.

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Nanocrystalline magnetic shape memory alloys: Ni-Mn-(In,Sn) J.J. Suñol, L. Escoda, J. Saurina, A. Carrillo, E. Bosch, B. Hernando* University of Girona, Campus Montilivi s/n, Girona, Spain joanjosep.sunyol@udg.edu *University of Oviedo, Calvo Sotelo s/n, Oviedo, Spain

Abstract Since martensitic transformation from cubic L21-type crystal structure to orthorhombic four-layered martensite (4O) was observed in Heusler alloys of the ternary system Ni 50Mn50-xSnx [1], important attention has been devoted to investigate structural transformations, magneto-elastic and magnetocaloric properties in these Ga-free ferromagnetic shape memory alloys (FSMA) [2-3]. The studies concluded that these materials are prospective for the development of magnetically driven actuators and working substances for magnetic refrigeration. One option is to produce nanostructured composites with polymer matrices containing FSMA particles. FSMA powders have been developed by crushing of bulk, by spark erosion of bulk or by mechanical alloying from elemental powders, flakes or fibres. In this work, we produce nanocrystalline alloys of the Ni-Mn-(In,Sn) quaternary system by crushing the arc-melted bulk material and by mechanical alloying of ribbon flakes previously obtained by melt-spinning. These procedures offer the possibility to obtain nanocrystalline powdered shape memory alloys that can be the metallic reinforcement of a nanostructured composite with polymer matrix.

Structural characterization was performed by X-ray diffraction. Morphology was followed by scanning electron microscopy coupled with EDX microanalysis. As an example, the figure shows the SEM micrograph of one powdered-like sample. Thermal analysis was performed by means of differential scanning calorimetry.

At room temperature, all X-Ray diffraction patterns showsthe austenite structure. Shape memory alloys exhibit a reversible austenite-martensite phase transition. This transformation is a first order phase transition which takes place by the difussionless shearing of the parent austenitic phase. By lowering the temperature the austenite phase transforms into a tetragonal orthorhombic or monoclinic martensite ordered by domains [2,3]. Crushed and milled materials shows lower enthalpy and entropy changes during the structural austenite-martensite transformation. Furthermore, it is known that annealing can increase both thermodynamic parameters in magnetic shape memory alloys [4]. Nevertheless, thermal treatment favors the crystalline growth and the loss of the nanocrystalline behavior.

References [1] Y. Sutuo, Y. Imano, N. Koeda, T. Omori, R. Kainuma, K. Ishida, K. Oikawa, Appl. Phys. Lett. 85 (2004) 4358.

[2] J.L. Sánchez-Llamazares, T. Sánchez, J.D. Santos, M.J. Pérez, M.L. Sánchez, B. Hernando, J.J. Suñol, L. Escoda, R. Varga, Appl. Phys. Lett. 92, (2008) 012513.

[3] B. Hernando, J.L. Sánchez-Llamazares, J.D. Santos, M.J. Pérez, J.J. Suñol, L. Escoda, R. Varga, Appl. Phys. Lett. 92, (2008) 042504.

[4] L. González-Legarreta, T. Sánchez, W.O. Rosa, J. García, D. Serantes, R. Caballero-Flores, V.M. Prida, L. Escoda, J.J. Suñol, V. Koledov, B. Hernando, J. Supercond. No. Magn. Doi: 10.1007/s10948012-1632-z

Figure

20 Âľm

Influence of Electron Correlations on Quasiparticle Energies and Lifetimes in an Atomic Nanowire Coupled to Electrodes Mark Szepieniec, Irene Yeriskin, Jim Greer Tyndall National Institute, University College Cork, Lee Maltings, Dyke Parade, Cork, Ireland mark.szepieniec@tyndall.ie Abstract As electronics devices scale to sub 10 nanometer lengths, the distinction between “device” and “electrodes” becomes blurred. A common approach to the modeling of molecular-scale electronics has relied on a combination of a density functional treatment for electronic structure and the non-equilibrium Green’s function formalism for transport, optionally with use of the GW approximation to correct the single-particle energy levels to account more accurately for screening effects. Recently, the effects of allowing lead excitations couple to molecular device states [1] has been explored and the inclusion of electron-electron interactions on electrodes coupled to a ‘device region’ has been formulated for the NEGF approach to transport [2].

In this work, the interaction between device and leads is studied in a simple model of a molecular tunnel junction. Using a complex absorbing potential [3], we are able to reproduce the single-particle energies of a device region including a description of the effects of the “semi-infinite” electrodes. With this approach, we are able to model the effect of coupling of a quantum device to electrodes while systematically studying the effect of many-electron interactions between the device and lead regions.

Varying the device-lead coupling strength, the effect of electron correlation on energy shifts and lifetimes of electronic states on the device region is studied by permitting the electron correlation or “many-electron interactions” to be more accurately treated through the inclusion of an increasing number of many-particle states in a configuration interaction expansion [4]. We find that the prediction of the electronic states of a device region is sensitive to both the amount of device-lead coupling and to the amount of electron correlation that is included in a calculation. The two effects mix in a complicated way, implying that detailed treatments of the electronic structure of nanoscale devices are required to predict electronic behaviour such as charge transport and photoexcitations in a molecular junction.

References [1] M. Galperin, A.Nitzan and M. A. Ratner, Physical Review Letters, 96 166803 (2006) [2] H. Ness and L.K. Dash, Physical Review B, 84, 235428 (2011) [3] T. Henderson, G. Fagas, E. Hyde, and J.C Greer, Journal of Chemical Physics, 125, 244104 (2006) [4] J. C. Greer, Journal of Computational Physics, 146, 181–202 (1998) Figures

Effect of Silver Nanoparticles on Rice Oryza Sativa L. KDML 105 seedlings

a

b

c

d

Thuesombat Pakvirun , Chadchawan Supachitra , Hannongbua Supot and Akasit Sanong .

a Nanoscience and Technology Program, Graduate School, Chulalongkorn University, Bangkok 10330, Thailand b Environment and Plant Physiology Research Unit, Department of Botany, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand c Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand d Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Contact@ panpak_2@hotmail.com Abstract With the advancement in nanotechnology, silver nanoparticles (AgNPs) have been applied in many industries. Possible effects of silvernanoparticles (AgNPs) on rice Oryza sativa L. cv. KDML 105 were investigated. The concentrations; 0.1, 1, 10, 100 and 1000 mg/L

-1

of AgNPs were used to

determine the effect of AgNPs on seedling growth. The results were showed that rice seedlings growth decreased when increased concentrations. Indicating that AgNPs were showed negative effect on seedling growth by inhibited seedling growth. The obtained results will lead to the understanding in nanomaterial safety information.

References [1] Mueller, N.C. and B. Nowack, Exposure Modeling of Engineered Nanoparticles in the Environment.

Environmental Science & Technology, 2008. 42(12): p. 4447-4453.

[2] Navarro, E., et al., Environmental behavior and ecotoxicity of engineered nanoparticles to algae, plants, and fungi. Ecotoxicology, 2008. 17(5): p. 372-86.

[3] Lin, S.J., et al., Uptake, Translocation, and Transmission of Carbon Nanomaterials in Rice Plants.

Small, 2009. 5(10): p. 1128-1132.

[4] Seeger, E., et al., Insignificant acute toxicity of TiO2 nanoparticles to willow trees. Journal of Soils and Sediments, 2009. 9(1): p. 46-53.

Figures

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Figure 1. 14 day of rice seedling (a) and 21 day (b) with control, 0.1, 1, 10, 100 and 1000 mg/L from the left.

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Synthesis of ZrC-TiC nanostructures Madis Umalas1,2, Valter Reedo1, Ants Lõhmus1,2 and Irina Hussainova3.

1

Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia Estonian Nanotechnology Competence Centre, Riia 142, 51014 Tartu, Estonia 3 Department of Materials Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia 2

e-mail: madis.umalas@gmail.com, Materials science and engineering has experienced a tremendous growth in the field of development of nanostructured materials with enhanced chemical, mechanical, and physical properties.

The binary solid carbide mixtures of (ZrC–TiC) are of special interest for ultrahigh temperature applications due to their refractoriness, high hardness, low thermal expansion, good thermal shock resistance and chemical stability at high temperatures. Formation of the heterogeneous finely dispersed structures in ZrC–TiC mixtures also are of a great interest because their possible contribution into development of superplastic ceramic-based composites [1-5]. Conventionally, the binary solid carbide compounds are synthesized by carbothermal reduction of metal oxides (ZrO2 and TiO2) and amorphous carbon mixture in controlled atmospheres at a temperature between (1700 – 2100 oC). The conventional method is energy and time consuming (10 – 24h) and a final product suffers from impurities and is inhomogeneous because the powders are mixed on a relatively coarse scale (e.g., micrometer-scale) [5-7].

In our work we use combination of sol-gel method and conventional carbothermal reduction to synthesize nanopowders for preparation of binary carbides material. Combination of these offers some advantages compared to conventional powder processing, such as the lower reaction temperatures/ shorter reaction times due to the intimate contact of the reactants.

The present study is novel way for synthesis of the mixed ZrC–TiC powders precursor from corresponding metal alkoxides by using of sol-gel method. The main advantage of the used sol-gel process is the reduction of the kinetic barriers between the formed metal oxide and the carbon particles created in pyrolysis of metal alkoxide polymer due to the homogeneous dispersion of reactants in the precursor material. The increased contact area of the nanograins results in carbothermal reduction between the metal oxide and carbon particles at lower temperature and shorter time as compared to conventional carbide synthesis methods. Moreover, the use of molecular precursors and the control of the synthesis conditions make possible to prepare homogeneous and pure multicomponent systems.

Also, we clarify the mechanism of carbothermal reduction of the binary solid carbides precursors in argon and vacuum environments. Titanium and zirconium carbides blend were synthesized by carbothermal reduction from polymer precursor of ZrC–TiC at 1500 oC in an argon atmosphere and vacuum. The resulting products had small crystallite size (~40 nm Fig.1.). However, these products contained little ZrO2.

The structural transformation of the polymeric materials into the carbides was characterized by sacning electron microscope (SEM), X – ray diffraction analysis and Raman spectroscopy.

Characterizations of heat treated samples at 800 oC to 1500 oC in argon and vacuum has showed that the carbothermal reduction of the binary solid carbide mixture (ZrC–TiC) polymeric precursor began in vacuum at lower temperature (1100 oC Fig. 2.) than in argon environment.

References [1] Morz, C. Advanced Refractory Technologies, Inc. Processing microcomposite TiZrC and TiZrB2 materials. (1993) 725-735.

and

properties

of

[2] Ivashchenko, V. I. Turchi, P.E.A. Shevchenko, V. I. Journal of Physics: Condense Matter. Firstprinciples study of elastic and stability properties of ZrC–ZrN and ZrC–TiC alloys.

(2009) 395-503.

[3] Sacks, D. M. Wang, C. Yang, Z. Jain, A. Journal of Materials Science. Carbothermal reduction synthesis of nanocrystalline zirconium carbide and hafnium carbide powders using solution-derived precursors. (2004) 6057-6066.

[4] Yung, D-L.; Kollo, L.; Hussainova, I.; Zikin, A. Proceedings of the 8th International Conference of DAAAM Baltic INDUSTRIAL ENGINEERING Reactive sintering of zirconium carbide based systems. (2012) 783-788.

[5] Umalas, M.; Reedo, V.; Lohmus, A.; Hussainova, I. Proceedings of the International Conference of DAAAM Baltic Industrial Engineering, Sol – gel solution based processing for nanocarbides. (2012) 753-758.

[6] Zhang, H. Li, F. Jia, Q. Ye, G. Sol-Gel Sci Technol. Preparation of titanium carbide powders by sol–gel and microwave carbothermal reduction methods at low temperature. (2008) 217–222.

[7] Doll´e, M. Gosset, D. Bogicevic, C. Karolak, F. Simeone, D. Baldinozzi, G. European Ceramic Society. Synthesis of nanosized zirconium carbide by a sol–gel route. (2007) 2061–2067.

o

Figure.1. . SEM images of synthesized typical ZrC – TiC powders at 1500 C at various

Figure. 2. X-ray diffraction patterns of a) ZrC-TiC polymeric precursor annealed in argon; b) ZrCTiC polymeric precursor annealed in vacuum.

Preparation of R-methyl Imidazolium-Sodium Hexaflorosilicate Complex Crystals 1

1

2

3

Raul Välbe , Valter Reedo , Uno Mäeorg , Andres Hoop , Ants Lõhmus

1

1

2

Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia.

Institute of Chemistry, University of Tartu, Ravila 14A, 50411 Tartu, Estonia.

3 Haine Paelavabrik OÜ, Tehase 21, Tartu, Estonia e-mail: raul005@ut.ee

Room temperature ionic liquids (IL) are by definition ionic compounds - salts, which are liquid below o

100 C. Most applicable ionic liquids are based on imidazolium or quaternary ammonium cations with -

the BF4 anion. Properties such as inertness to moisture and oxygen, poor coordination ability and a -

weak ligation makes BF4 a superior anion for ionic liquids. During recent years investigations on stability of ionic liquids in combination with different solvents have been increased and this may lead to inappropriate experimental design and utilization of these chemicals.

Sodium hexafluorosilicate is an odorless, white crystalline powder of hexagonal structure which has widespread use in water fluoridation. The interest on pure Na2SiF6 has been increased from this decade due to the similar refractive index with the natural ice crystals in visible light. Crystallization behaviour of sodium hexafluorosilicate is not well described and by our knowledge the crystallization in presence of ionic liquids is not mentioned at all.

The regular complex crystals of Na2SiF6 have been obtained in the aqueous solutions of different methylalkylimidazolium (ethyl-, butyl- and decyl-) tetrafluoroborate ionic liquids. (Fig.1.) It is demonstrated that sodium hexafluorosilicate crystalline compounds with good regularity and narrow size distribution containing dialkyl imidazolium ions between the nano hexagonal crystalline clusters interconnected to each other to a whole hexagonal aggregate can be obtained in large quantities.

-

This characteristic phenomenon of crystallization of ionic liquids containing BF 4 ions is reported for the first time. The mechanism of formation of various [RMIm]BF4-Na2SiF6 microcrystalline morphologies and the influence of temperature on growth kinetics are discussed. Crystallographic studies of the product were carried out by X-ray diffractometer (XRD), characterization by scanning electron microscopy (SEM) and optical microscopy; also infrared spectra (IR) were recorded. Thermal analyses were performed by differential scanning calorimetry-thermogravimetric analyser (TGA-DSC). Presence of ionic liquid cations was confirmed by high resolution mass spectrometry (HRMS).

Fig. 1: Optical and SEM images of different shape and size crystal structures: a), b), c) - [EMIm]BF4Na2SiF6 microcrystals; d) [BMIm]BF4-Na2SiF6 microcrystal - synthesized at room temperature in low concentrated ionic liquid aqueous solutions; e) optical image of [EMIm]BF 4-Na2SiF6 macrocrystal, o synthesized at 50 C in concentrated ionic liquid aqueous solution.

Described cluster structures can have several potential applications in different fields due to their nano comb-clustered complex structure. The developed, method allows easy production of Na2SiF6 structures with a narrow size distribution. There is a hypothetical possibility that these two-component systems have variable refractive index. The presence of conductive ionic liquid between the crystalline layers makes them attractive in fields like optics where they may be applicable as conductive sensors.

Electrical conductivity and relative permittivity of 15 nm Al2O3-water nanofluids. ab

a

a

ab

G. VilĂŁo , R. Iglesias , M.A. Rivas , F Coelho , T.P. Iglesias

a

a

Dpto. de FĂ­sica Aplicada, Facultad de Ciencias. Universidad de Vigo, 36310 Vigo, Spain

b

Department of Physics, School of Engineering - Polytechnic of Porto, 4200-072 Porto, Portugal tpigles@uvigo.es.

Abstract In recent years were conducted numerous theoretical and experimental studies since Choi [1]

established the new concept of nanofluid in 1993 , since then, great progress has been made in the study of thermal properties and their applications

[2-3]

.The presente work involves a study on the

electrical conductivity and relative permittivity of aluminiun oxide nanoparticles with milli-Ro and mili-Q water as base fluids. The effective electrical conductivity and permittivity have been measured as function of temperature, between 298.15 K and 328.15 K, for different volume fractions of aluminiun oxide nanoparticles, Al2O3, of 15 nm. The experiment was performed at atmospheric pressure. The experimental results show the importance of volume fraction of the Al2O3 nanoparticles in the relative permittivity and effective electrical conductivity of these [4-6]

nanofluids with the temperature.

. It is also shown as the purity of the base fluid (milli-Ro or mili-

Q water) used influences on the effective electrical conductivity values.

Keywords: permittivity, electrical conductivity, aluminiun oxide, nanofluids, nanoparticles

References [1] [2] [3] [4] [5] [6]

S. K. Das,S. U. S. Choi, W. Yu, T. Pradeed, Nanofluids, Science and Technology, (2008) Wiley.

D. Wen, Y. Ding, International Journal of Heat and Mass Transfer, 47 (2004) 5181.

Z. Heris, M. N. Esfahany, S. G. Etemad, International Journal of Heat and Fluid Flow, 28 (2007) 210.

M. A. Rivas, S. M. Pereira, T. P. Iglesias, J. Chem Thermodyn, 34 (2002) 1897.

S. M. Pereira, T. P. Iglesias, J. L. Legido, M. A. Rivas, J. N. Real, J. Chem Thermodyn, 33 (2001) 433.

T. P. Iglesias, J. L. Legido, S. M. Pereira, B. Cominges, M. I. Paz Andrade, J. Chem Thermodyn, 32 (2000) 923.

Detecting oil seeps in seawater, sensing bacteria in milk, and identifying disease states from a patient’s urine: New applications for gold nanoparticle chemiresistors Melissa S. Webster, Burkhard Raguse, Lech Wieczorek, Edith Chow, James S. Cooper, Lee J. Hubble CSIRO Materials Science and Engineering, Bradfield Road, West Lindfield, NSW 2070, Australia burkhard.raguse@csiro.au Abstract Thiol-functionalised gold nanoparticle (AuNP) chemiresistors have been shown to respond to lowmolecular weight chemicals through changes in electrical resistance. They can be fabricated by depositing gold nanoparticles onto microelectrodes, as illustrated in Figure 1. AuNP chemiresistors have mainly been used to detect chemicals in the gas phase but we have shown that they can also be used to detect low-molecular weight molecules in liquids [1] and we have characterised some of the properties relating to this new area of testing [2].

Building on this advancement, we have investigated several applications for the chemiresistor technology in liquid environments. An array of different thiol-functionalised AuNP chemiresistors has successfully detected and discriminated hydrocarbon fuels, such as crude oil, diesel and gasoline, in artificial seawater [3]. Such an application could generate millions of dollars by improving the prospecting process for oil in seawater. We have also demonstrated that AuNP chemiresistor devices will operate in biological fluids in combination with ultrafiltration membranes [4]. This work showed that an array of AuNP chemiresistors could detect the spoilage of milk in accordance with industry standard methods. A quick and easy screening method in the food and drink industry could help prevent the spread of food borne illnesses. We are now investigating chemiresistor sensor arrays for the diagnosis of disease. In this work our chemiresistors have detected known tuberculosis biomarkers in the low parts per billion range in synthetic urine. Chemiresistors have the potential to be developed into an inexpensive, easy to use and portable diagnostic device which could be utilized in developing countries to diagnose diseases such as tuberculosis and malaria and as such could have a dramatic impact on saving lives.

AuNP chemiresistors are emerging as potential technologies for applications in environmental monitoring, food quality control and medical device diagnostics and are continuing to advance into new areas. The performance of chemiresistors combined with their simplicity and low costs make the technology an appealing and exciting alternative to existing methods for small molecule detection in solution.

References [1] B. Raguse, E. Chow, C. S. Barton, L. Wieczorek, Analytical Chemistry, 79 (2007) 7333-7339.

[2] E. Chow, K-H Müller, E. Davies, B. Raguse, L. Wieczorek, J. S. Cooper, L. J. Hubble, Journal of Physical Chemistry C, 114 (2010) 17529-17534.

[3] J. S. Cooper, B. Raguse, E. Chow, L. Hubble, K.-H. Müller. L. Wieczorek, Analytical Chemistry, 82 (2010) 3788-3795.

[4] L. J. Hubble, E. Chow, J. S. Cooper, M. S. Webster, K.-H. Müller, L. Wieczorek, B. Raguse, Lab on a Chip, (2012) DOI:10.1039/C2LC40575J.

Figures

Figure 1. Illustration of a gold nanoparticle chemiresistor consisting of gold nanoparticles deposited onto electrodes.

Solutions containing analytes of interest can be exposed to the chemiresistor for testing.

Thermal Conductance Calculations of Silicon Nanowires 1 1 1 2 Kohei Yamamoto , Hiroyuki Ishii , Nobuhiko Kobayashi , and Kenji Hirose 1

Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, 305-8573, Japan Green Innovation Research Laboratory, NEC Corporation, Tsukuba, Ibaraki, 305-8501, Japan

2

bk201130108@s.bk.tsukuba.ac.jp Abstract Phonon thermal transport properties of silicon nanowires (SiNWs) have attracted much attention recently. As silicon electron devices with nanowire structures become small to nanometer-scale, we need to reduce the thermal heating problem. Also, SiNWs are good candidates for efficient thermoelectric devices. Here, we present the phonon thermal conductance calculations for SiNWs with diameters ranging from 1 to 5 nm by using the nonequilibrium Green’s function (NEGF) technique.

Experimentally, the thermal conductivities of SiNWs with diameters ranging from 15 to 115 nm have recently been measured and showed unusually low thermal transport properties. To understand the thermal transport properties of SiNWs less than 100 nm in diameter, we need to consider the phonon problems from an atomistic point of view. Thermal conductance calculations with the Boltzmann transport formula or molecular dynamics calculations are effective at high temperature in diffusive regime. Recent calculations with transmission model using the phonon dispersion relation with the data from “bulk” silicon showed good agreement with experiments for SiNWs which have diameters larger than 35 nm. However, for phonon transport at low temperature or with diameters less than 30 nm, the effects of nanometer-scale structures such as confinement and low speed modes on the phonon transport become significant. For such regimes, we need the computational approach taking the quantum effects explicitly into account. Here we use the NEGF technique with empirical Tersoff interatomic potential for the atomistic calculation of thermal conductance of SiNWs. We present thermal conductance calculations of SiNWs with diameters from 1 to 5 nm with vacancy defects based on the NEGF approach, focusing especially on the difference of the position of the vacancies. We introduce two types of vacancies in the SiNWs, “surface-defect” with atoms at the surface missing and “center-defect” with atoms at the center of cross section of wires missing, for both of which we consider single and double vacancies. Then we compute how the thermal conductance of SiNW changes its behavior as the temperature decreases, changing the thickness of wires.

Fig. 1 shows the thermal conductance of SiNWs as a function of the diameter D at various temperatures from 5 to 300 K. Overall, it looks that thermal conductance shows the quadratic behavior for the diameter D. To see the diameter dependence on the conductance G more precisely, we n extrapolate the curves of G to the power law of G=AD where A is the constant. The obtained exponent n is shown in the inset. At high temperature above 100 K, we see n = 2, which shows that the thermal conductance increases in proportion to its cross-sectional area S, proportional to the square of diameter D as a usual Ohmic-type behavior. However, as the temperature decreases below 100 K, the diameter dependence on the conductance is seen to change. At low temperature below 5 K, we see n = 0 which shows that the thermal conductance does not depend on the thickness of the nanowire structure at all.

This means that the thermal conductance changes its behavior from the usual Ohmic-type at room temperature, proportional to its cross-sectional area, to the unusual quantum-type at low temperature, not dependent on the cross-sectional area [1]. In the presentation, we show how we can understand these exponents behaviors. Also we found that introduction of the defects reduces the thermal conductance significantly and that “center-defect” reduces thermal conductance much more than “surface-defect”. We also show the comparison of the results using the empirical interatomic potentials with those from the ab-initio calculations.

References [1] K. Yamamoto, H. Ishii, N. Kobayashi, and K. Hirose, App. Phys. Express, 4 (2011) 085001.

Figures

Fig. 1. Thermal conductance as a function of the diameter of SiNW without vacancy defects for several temperatures. (Inset) Exponent n for several temperatures extrapolated for the thermal conductance as n G = AD where D is a diameter of SiNW.

Influence of ZnO surface polarity on the electrophoretic deposition of metal nanoparticles.

Roman Yatskiv, Jan Grym Institute of Photonics and Electronics, Chaberska 57, Prague, Czech Republic yatskiv@ufe.cz Abstract Zinc oxide (ZnO) is a wide band-gap (3.37 eV at room temperature) semiconductor with many advantageous properties such as large exciton binding energy of about 60 meV, high optical gain (about three times higher than in GaN), radiation hardness, or the possibility of wet-chemical processing. ZnO is a promising material for ultraviolet light emitting devices, laser diodes, solar cells, and gas sensors [1]. However the use of its potential requires the solution of several critical issues such as (a) preparation of p-type material, (b) understanding and control of electrical contact properties, (c) obtaining highly efficient ultraviolet emission from the near band edge. In the past few years, a number of studies have been conducted to improve the band-edge emission from ZnO films and nanostructures by metal capping; different metals (Ag, Au, Al and Pt in the form thin layer or small islands) have been used as capping layers [2,3]. A similar effect can be achieved by coverage of ZnO substrate by metal nanoparticles (NPs).

In this work we report the influence of ZnO spontaneous polarization [4] on the quality of the electrophoretically prepared metal nanolayer. Pt NPs were deposited on O-polar and Zn-polar n-type ZnO substrates growth by hydrothermal method (produced by MTI Company) by pulsed electrophoretic deposition (EPD) [5]. Pt NPs were prepared in isooctane by the reverse micelle technique reducing H2PtCl6 by hydrazine and were characterized by transmission electron microscopy (showing an average size of 10 nm) and by optical absorption spectra (two peaks at 260 nm and 236 nm due to surface plasmons of Pt nanoparticles, and a peak associated with AOT absorption were observed) [6]. As shown in Figure 1,significant face effect with higher coverage achieved on O- face compared to Zn- face was observed. This significant variation can be explained by the existence of nonzero net dipole moment perpendicular to Zn-polar and O-polar face. Free electrons move in an attempt to compensate the bound spontaneous polarization charge ( ) and reduce the internal electric field. Electrons accumulate near the O-polar face and depletion region forms adjacent to Zn-polar face (Figure 2). As a result, positively charged Pt NPsare attracted by the negative charge to the O-face. This effect allows the self-deposition of nanoparticles on the O-face of ZnO without attached electric field (Figure 3).

This work has been supported by the projectâ&#x20AC;&#x2122;s COST OC10021 and LD12014 of the Ministry of Education CR. References [1] U. Ozgur, et al., J. of Appl. Phys., 98 (2005) 041301.

[2] K. W. Liu et al., Appl. Phys. Lett., 94 (2009) 151102.

[3] C. W. Lai et al., Appl. Phys. Lett., 86 (2005) 251105.

[4] M. W. Allen et al., Appl. Phys. Lett.,90 (2007) 062104.

[5] J. Grym et al., Nanoscale Res. Lett., 6 (2011) 392.

[6] R. Yatskiv et al., Carbon, 50 (2012) 3928.

Figure 1 SEM images of Pt NPs deposited on the (a) Zn-face (b) O-face ZnO substrate by EPD (deposition time and applied bias were 1 h and 106 V, respectively).

Figure 2 Schematics of the free carrier distribution in n-type ZnO in response to the presence of a spontaneous polarization field.

Figure 3 SEM image of Pt NPs self-deposition (without electric field) on O-face ZnO substrate (deposition time was 1 h).

Electronegativity and Electron Currents in Molecular Tunnel Junctions I. Yeriskin1, S. McDermott1, R. J. Bartlett2, G. Fagas1, and J.C. Greer1 1Tyndall National Institute, University College Cork, Ireland 2Quantum Theory Project, University of Florida at Gainesville, FL, USA 32611

Tyndall National Institute, Lee Maltings, Dyke Parade, Cork, Ireland irene.yeriskin@tyndall.ie

Abstract: Electronegativity directly regulates charge transfer and energy level alignments, and hence electron currents in single molecule tunnel junctions.

We discuss the impact of improving ionization Potentials (IPs) and electron affinities (EAs), and hence the electro-negativity, on prediction of currents across single molecules and relate these approximations to transport methods that rely on a direct determination of the reduced density matrix [1]. Correcting the Green's function through second order in the self-energy leads to improved prediction of iP's and EA's Currents across molecules bonded between two metal electrodes are commonly treated as single electrons tunnelling through an effective potential barrier; this independent particle picture is well-known to describe many aspects of tunnelling. Examining quantum transport with explicit many-body treatments of the molecular region, we examine criteria for establishing effective single particle models to study tunnelling in metal-molecule-metal junctions. We find maximizing the overlap of the reduced density matrix derived from a single Slater determinant to the exact reduced density matrix defines the best single particle picture for transport [2].

Currents calculated from the one-electron reduced density matrix correct to second order in electron-electron correlation are identical to currents obtained from the one-electron Greenďž fs function corrected to second order in electron self-energy.

A tight binding model of hexa-1,3,5-triene-1,6-dithiol (Figure below) bonded between metal electrodes is introduced, and the effect of analytically varying electron-electron correlation on electron currents and electronegativity is examined. The model analysis is compared to electronic structure descriptions of a goldhexatriene (approximated by different exchange-correlation functionals) and Hartree-Fock states as zerothorder approximations to the one-electron Greenâ&#x20AC;&#x2122;s function.

Comparison between the model calculations and the electronic structure treatment allows us to relate the ability to describe electronegativity within a single particle approximation to predictions of current-voltage characteristics for molecular tunnel junctions. [3]

FIGURE: HEXA-1,3,5-TRIENE-1,6-DITHIOL BETWEEN TWO METAL CONTACTS

Bibliography: [1] P. Delaney and J.C. Greer, Phys. Rev. Lett. 93, 036805 (2004) [2] G. Fagas, P. Delaney, and J.C. Greer, Phys. Rev. B 73, 241314(R) (2006) [3] I. Yeriskin, S. McDermott, R. J. Bartlett, G. Fagas, and J.C. Greer, J. Phys. Chem. C, 114, 20564 (2010)

Morphology study of the electrodeposited platinum nanotube

E. Yousefi, A. Dolati, I. Imanieh Materials Science and Engineering Department, Sharif University of Technology, Azadi St., Tehran, I.R.Iran, P.O. Box 11365-9466 Corresponding Author: A.Dolati, Tell: 00982166165259, fax: 0098 66165717, dolati@sharif.edu Abstract Nanostructures applicability in different fields such as catalytic activities or sensor applications can be affected by their morphology and structure. Deposition potential as a driving force in electrochemical process can seriously influence the deposition mechanisms and consequently the morphology and the structure of the ultimate nanostructures. Hence, among various parameters which can affect the final morphology of the nanostructures, studying the deposition potential effect on the morphology and final application of the synthesized nanostructures can be a valuable exploit.

In this study, electrochemical methods were used in order to deposit platinum nanotubes inside the pores of the polycarbonate template (with the pore size of 200 nm). First of all, the templates were sputtered with a thin layer of gold and then soaked in anchor solution containing of 3aminopropyltrimethoxysilane. Then, electrodeposition was carried out in a solution containing of 5 mM H2PtCl6 and 0.1 M H2SO4 solved in doubly distilled water. The process was controlled by the electrochemical techniques such as voltammetry (Fig. 1-a) and chronoamperometry (Fig. 1-b) and all the measurements were recorded with respect to the Saturated Calomel Electrode (SCE). Subsequently the templates were solved in a chloroform (CH2Cl2) solution and the synthesized nanotubes were characterized with Scanning Electron Microscopy (SEM), Tunneling Electron Microscopy (TEM), X-ray diffraction patterns and EDX analysis. Observations indicate that the potential can seriously affect the final morphology (Fig 2) due to its effect on the kinetic behavior of the platinum reduction reactions.

Potential -0.35 V was found as an appropriate potential in order to obtain reasonable electro catalytic properties.

Keywords: Platinum, Nanotubes, Electrodeposition, Morphology References [1] B. I. Seo et al., Physica E: Low-dimensional Systems and Nanostructures, 37 (2007) 279.

[2] X. Zhang et al., Electrochemistry Communications ,11(2009)190.

[3] E. Bertin, S. b. Garbarino, A. Ponrouch, D. Guay, Journal of Power Sources, 206 (2012) 20.

[4] S. S. Mahshid et al., Electrochimica Acta, 58 (2011)551.

[5] M. Cortes, A. Serra , E. Gomez, E. Valless, Electrochimica Acta, 56(2011)8232.

[6] L. Soleimany, A. Dolati, M. Ghorbani, Journal of Electroanalytical Chemistry, 645 (2010)28.

[7] Y. Bi, G. Lu ,Electrochemistry Communications, 11(2009)45.

[8] H. Xu et al., Electrochemistry Communications, 10(2008)1893.

[9] S. M. Choi, J. H. Kim, J. Y. Jung, E. Y. Yoon, W. B. Kim, Electrochimica Acta, 53 (2008)5804.

[10] G.-Y. Zhao, H.-L. Li, Applied Surface Science, 254(2008)3232.

[11] X. Kang, Z. Mai, X. Zou, P. Cai, J. Mo, Talanta, 74(2008) 879.

[12] S. Kim, Y. Jung, S.-J. Park, Colloids and Surfaces A: Physicochemical and Engineering Aspects,314(2008) 189.

[13] F. Ye, L. Chen, J. Li, J. Li, X. Wang ,Electrochemistry Communications, 10(2008) 476.

[14] F. Qu, M. Yang, G. Shen, R. Yu, Biosensors and Bioelectronics, 22(2007) 1749.

[15] A. n. TrojĂ&#x192;ÂĄnek, J. Langmaier, Z. k. Samec, Journal of Electroanalytical Chemistry ,599(2007) 160.

[16] C.-H. Han et al., Sensors and Actuators B: Chemical, 128(2007) 320.

[17] L. Xiao, L. Wang, Chemical Physics Letters, 430 (2006) 319.

[18] Jinhua Yuan, Kang Wang, X. Xia, Advanced functional materials, 15(2005) 803.

[19] M. Platt, R. A. W. Dryfe, E. P. L. Roberts, Electrochimica Acta, 49(2004) 3937.

[20] C. Hippe, M. Wark, E. Lork, G. n. Schulz-Ekloff, Microporous and Mesoporous Materials, 31(1999) 235.

Figures

(a)

(b)

Fig. 1: (a) Linear voltammograms of the platinum nanotubes in various scan rates, (b) Chronoamperometry analysis for platinum reduction, potential from -0.2 to -0.4 V vs. SCE.

Fig. 2: FESEM results of the synthesized platinum nanotubes in various potentials vs. SCE, (a) -0.2 V, (b) -0.25 V, (c) -0.3 V, (d) -0.35 V.

Light scattering effect of nano-sized hollow TiO2 layer on conversion efficiency of DSSC Yeontae Yu, Kyeongjun Ko, Kyeonggeun Park Division of Advanced Materials Engineering and Research Center for Advanced Materials Development, College of Engineering, Chonbuk National University, Jeonju, South Korea yeontae@jbnu.ac.kr Abstract In the past two decades, the dye-sensitized solar cell (DSSC) has drawn much interest owing to its low cost and thereby its capability to replace conventional solar cells. DSSCs consist of a sensitizing dye, a transparent conducting substrate (F-doped tin oxide), a nanometer sized TiO 2 film, iodide electrolyte and a counter electrode (Pt or carbon).

Generally, semiconductor metal oxide materials have an effect on increase of the conversion efficiency in DSSC. To increase the conversion efficiency semiconductor metal oxide materials must have properties of high surface area, high electron mobility and good reactivity with sunlight. Especially, TiO2 is one of the most promising materials for semiconductor electrode in DSSC. Usually, UV-vis spectra of nano-sized TiO2 showed light absorption band in the range of 200-400 nm. However, hollow TiO2 synthesized by microwave-assisted hydrothermal method, using TiF4 as starting material, showed light absorption band in the range of 400-460 nm as well as 200-400 nm [1]. This nano-sized hollow TiO2 (150-200 nm) synthesized by microwave-assisted hydrothermal method, printed under the TiO2 nanoparticles (10-20 nm) layer as a semiconductor electrode, can have better light-scattering effect than conventional micro-sized TiO2 spheres.

In this study, the light scattering effect of nano-sized hollow TiO2 layer on conversion efficiency of DSSC was investigated. Furthermore, the effect of optical property and crystallinity of hollow TiO 2 spheres on conversion efficiency of DSSC were discussed in detail. To change optical property and crystallinity of hollow TiO2, microwave-assisted hydrothermal method reaction temperature and time was controlled. Fig. 1 shows TEM images of nano-sized hollow TiO2 synthesized with different temperatures and reaction times.

TEM and FE-SEM were used to observe the morphology of the hollow TiO 2 spheres. The diameter of hollow TiO2 and the size of each primary TiO2 particle are about 150-200 nm and 20-30nm respectively. The phase and structural analysis were carried out by X-ray diffraction. The optical properties of the hollow TiO2 and nano-sized TiO2 were detected by a UV-vis spectrometer. The poresize and surface area distribution of the hollow TiO 2 structure was obtained by BET measurement. I-V 2 curves of the prepared DSSCs were measured under AM 1.5G illumination (100mW/cm ). Fig. 2 shows the conversion efficiency of unit cell having light scattering layer prepared with nano-sized hollow TiO2 spheres. The efficiency was increased upto 7.4% from 6.2% due to the light scattering layer.

References [1] Y. Lee, M. Kang, Materials Chemistry and Physics., 122 (2010) 284.

[2] X. F. Wu, H. Y. Song, J. M. Yoon, Y. T. Yu, Y. F. Chen, Langmuir., 25 (2009) 6438.

[3] J. Yu, J. Fan, L. Zhao, Electrochimica Acta., 55 (2010) 597.

Figures

(a)

(b)

(c)

Fig. 1. TEM images of nano-sized hollow TiO2 synthesized with different temperatures and o o o reaction times. (a) 100 C / 1 hr, (b) 180 C / 15 hr, (c) 180 C / 48 hr

Fig 2. Conversion efficiency of DSSC with and without nano-sized hollow TiO2 layer for light scattering.

Structural and magnetic properties of nanocrystalline La1-xSrxMnO3+ 1

2

2

2

2

2

Pavel Žvátora , Miroslav Veverka , Pavel Veverka , Karel Knížek , Karel Závěta , Ondřej Kaman , 1 3 3 2 Vladimír Král , Etienne Duguet , Graziella Goglio and Emil Pollert 1

Department of Analytical Chemistry, Institute of Chemical Technology Prague, Technická 5, 166 28, Prague 6, Czech Republic.

2 Department of Magnetist and Superconductors, Institute of Physics AS CR, Cukrovarnická 10/112, Prague, 162 00, Prague 6, Czech Republic.

3 CNRS, Université de Bordeaux, ICMCB, 87 avenue du Dr Albert Schweitzer, F-33608 Pessac, France. pavel.zvatora@vscht.cz The mixed oxides of the general formula La1-xRxMnO3, where R denotes bivalent alkaline-earth constitute a large family of the manganese perovskites interesting from the fundamental as well as applications aspects, e.g. in the field of the colossal magnetoresistance [1], magnetic resonance imaging contrast agent and more recently in magnetic fluid hyperthermia [2-4]. They exhibit a large variety of properties mainly influenced by the structural distortions and manganese valency.

Recently, the influence of the oxygen stoichiometry on the structural and magnetic properties of La1-xSrxMnO3 nanoparticles in the composition range of 0  x  0.45 and size of 17-30 nm was observed [5, 6]. The present work is a continuation of this investigation in the way of a better understanding of the interplay between the composition, structure and size of the particles.

Syntheses of nanocrystalline particles of the general formula La1-xSrxMnO3+ were carried out employing sol-gel technique followed by thermal treatment at 700 °C, 800 °C and 900 °C, under flowing oxygen atmosphere. All the prepared nanocrystals were found to be rhombohedral with space group R-3c as expected.

The temperature and oxygen partial pressure applied during the synthesis of the studied materials induce deviations of the oxygen stoichiometry from the ideal one. Manganite perovskites La1-xSrxMnO3+ are known to present either an “oxygen excess” expected for lowest temperatures and characterized by the parameter δ > 0. With respect to the electroneutral condition, the actual state requires presence of cationic vacancies. Because their distribution between A and B sites is uniform as 2+ 3+ 4+ 3+ confirmed by our X-ray analysis, the original formula can be rewritten as: La aSr be Mn cMn df O3 where  and  denote vacancies on A and B sites, respectively, and, a = 3(1 - x)/(3 + δ), b = 3x/(3 + δ), c + d = a + b = 3/(3 + δ), e = f =1-(a + b). Condition of the electroneutrality gives 3a + 2b + 3c + 4d = 6.

Therefore it is possible replace in the following part of study the term “oxygen stoichiometry” given as 2+ 4+ 4+ 3+ (3 + δ) either by the corrected stoichiometric coefficient b of Sr ions or by the ratio Mn /(Mn + Mn ).

4+ The applied heating procedure led to an “oxygen excess” and thus to an increase of the Mn content in comparison to the ideal stoichiometry. This deviation, associated with vacancies on A- and B-sites, is all the more pronounced since materials are lanthanum-rich, as was mentioned previously [6]. At the same time the crystallite sizes increase with heating temperature in the range of 15 nm - 100 nm.

The X-ray analysis evidences a gradual contraction of the Mn-O bond distance and consequently a decrease of the elementary cell volume when b increases or heating temperature decreases. The effect is consistent with the decrease of the mean radii r(Mn)B induced by an increase of the content of tetravalent manganese ions on manganese sites. Moreover, the evolution of Mn-O-Mn angle and rhombohedral angle that the distortion decreases when b increases or heating temperature decreases.

The magnetic behaviour of the synthesized nanoparticles depends on the compositional effects 4+ 3+ 4+ influencing magnetic interactions via Mn /(Mn +Mn ) ratio and steric distortion. The determined 4+ 3+ 4+ dependences of the magnetization and Curie temperature on the Mn /(Mn +Mn ) ratio (see Figs. 1a, 1b and 1c) thus consist of two branches separated by the maxima lying at ~ 0.4  0.5, depending on the crystallite sizes.

Let us note that the described effects usually act simultaneously and it is difficult to separate their individual contributions. Nevertheless in spite of the encountered difficulties we attempted to show their significant influence on the evolution of the structural distortion and magnetic properties, namely magnetization and Curie temperature.

Author and coworkers believe better understanding of the interplay between the composition, structure, and size of the nanocrystalline particles of La1-xSrxMnO3+ help their application in the field of magnetic resonance imaging and magnetic fluid hyperthermia for treatment of oncological diseases.

Acknowledgements The authors thank the Ministry of Industry and Trade of the Czech Republic for the support under the grant FR-TI3/521, the grant A1 FCHI 2012 003 and our colleague Zdeněk Jirák for helpful discussions.

References [1] Colossal magnetoresistive oxides , ed. Y. Tokura, Gordon and Breach, New York, 2000.

[2] A. A. Kuznetsov, O. A. Shlyakhtin, N. A. Brusentsov, O. A. Kuznetsov. Eur Cells Mater, 3 (2002) 75.

[3] O. Kaman, E. Pollert, P. Veverka, M. Veverka, E. Hadová, V. Grünwaldová, S. Vasseur, R. Epherre, S. Mornet, G. Goglio, E. Duguet, Nanotechnology, (2009) 275610.

[4] K. Zhang, T. Holloway, J. Pradhan, M. Bahoura, R. Bah, R. P. Rakhimov, A. K. Pradhan, R. Prabakaran, G. T. Ramesh. J. Nano. Sci. Nanotechnol,, 10 (2010) 5520.

[5] R. Epherre, E. Duguet, S. Mornet, E. Pollert, S. Louguet, S. Lecommadoux, C. Schatz, G. Goglio. J. Mater. Chem., 21 (2011) 4393.

[6] J. Van Roosmalen, E. Cordfunke, J. Huijsmans. Solid State Ionics, 6 (1993) 285.

35

330

30

320

25

310

0.37 0.38 0.39 0.40 0.41 0.42 0.43 4+ 3+ 4+ Mn /(Mn + Mn )

20

0.38 0.40 0.42 0.44 0.46 0.48 0.50 4+ 3+ 4+ Mn /(Mn + Mn )

0.40

0.45

346

26

344

24

342

22

340 20 338 18

336 334 0.44

16 0.46 0.48 0.50 4+ 3+ 4+ Mn /(Mn + Mn )

] at 300 K

b [Sr ] 0.30 0.35

-1

0.25

2

] at 300 K

2+

0.20

750 kAm -1 [Am kg

340

c)

Tc [K]

40

2

Tc [K]

350

Tc [K]

-1

45

b [Sr ] 0.15 0.20 0.25 0.30 0.35 0.40 0.45 360 55 50 350 45 340 40 330 35 30 320 25 310 20 300 15

2 -1

360

b)

750 kAm-1 [Am kg

50

750 kAm-1 [Am kg

370

2+

2+

b [Sr ] 0.25 0.30 0.35 0.40 0.45

] at 300 K

Figures a) 0.15 0.20

0.52

Fig. 1: Dependence of the magnetization and the Curie temperature on the relative contents of 4+ 3+ 4+ tetravalent manganese ions Mn /(Mn + Mn ) determined by chemical analysis. a) 900 °C, () Tc, (□) magnetization, 66  15 nm; b) 800 °C, (×) Tc, (×) magnetization, 30  8 nm; c) 700 °C, (▲) Tc, (∆) magnetization, 19  3 nm. The connecting dashed lines are only guides for the eye.