NOTIZIARIO Neutroni e Luce di Sincrotrone - Issue 9 n.1, 2004

Rivista del Consiglio Nazionale delle Ricerche

NOTIZIARIO Neutroni e Luce di Sincrotrone

ISSN 1592-7822

Vol. 9 n. 1

Febbraio 2004 - Aut. Trib. Roma n. 124/96 del 22-03-96 - Sped. Abb. Post. 70% Filiale di Roma - C.N.R. p.le A. Moro 7, 00185 Roma

www.cnr.it/neutronielucedisincrotrone

NOTIZIARIO Neutroni e Luce di Sincrotrone

Rivista del Consiglio Nazionale delle Ricerche Cover photo: Isosurfaces of the gOOw(r) SDF. The hydroxide ion is oriented along the vertical axis, with the oxygen in the origin of the reference frame.

SOMMARIO EDITORIALE

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A. De Maio

RASSEGNA SCIENTIFICA Effectsof Magnetic Field on the Cuprate High-Tc Superconductor La2-xSrxCuO4............................................. 4 B. Lake et al.

Solvation Shell of OH– Ions in Water

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A. Botti et al.

Firsts ComIXS Results ........................................................................................ 14 Il

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cura del C.N R. in collaborazione con la Facoltà di Scienze M.F.N. e il Dipartimento di Fisica dell’Università degli Studi di Roma “Tor Vergata”.

Vol. 9 n. 1 Febbraio 2004 Autorizzazione del Tribunale di Roma n. 124/96 del 22-03-96 DIRETTORE RESPONSABILE:

C. Andreani COMITATO DI DIREZIONE:

M. Apice, P. Bosi COMITATO DI REDAZIONE:

L. Avaldi, F. Aliotta, F. Carsughi, G. Paolucci SEGRETERIA DI REDAZIONE:

D. Catena

K.C. Prince et al.

Aggregation Phenomena in Supercritical Carbon Dioxide ........................................................................................................... 20 F. Lo Celso et al.

SCUOLE E CONVEGNI....................................................................................................................

VARIE ..............................................................................................................................................................

CALENDARIO ........................................................................................................................................

SCADENZE ...............................................................................................................................................

FACILITIES ...............................................................................................................................................

HANNO COLLABORATO A QUESTO NUMERO:

A. Claver, G. Cicognani S. Mobilio, G. Vlaic GRAFICA E STAMPA:

om grafica via Fabrizio Luscino 73 00174 Roma Finito di stampare nel mese di Febbraio 2004 PER NUMERI ARRETRATI E INFORMAZIONI EDITORIALI:

Desy Catena Università degli Studi di Roma “Tor Vergata”, Presidenza Facoltà di Scienze M.F.N. via della Ricerca Scientifica, 1 00133 Roma Tel: +39 6 72594100 Fax: +39 6 72594497 E-mail: desy.catena@uniroma2 it

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EDITORIALE

a luce di sincrotrone e lo scattering di neutroni rappresentano metodologie qualificanti in quella che oggi viene definita Fine Analysis of Matter (FAM), un settore di ricerca essenziale anche per le attività indirizzate allo sviluppo tecnologico e all’innovazione, comprese le ricerche industriali ad alto contenuto innovativo. Le tecniche basate sull’impiego di luce di sincrotrone e neutroni hanno in comune due importanti aspetti: • l’intrinseca multidisciplinarità delle applicazioni, e quindi della ricerca. In linea con le priorità tematiche individuate in ambito EU, il più alto impatto scientifico e tecnologico derivante dall’impiego delle tecniche di neutroni è atteso nei settori della Scienza dei Materiali ed Ingegneria, Fisica dello Stato Solido, Chimica, Materia Soffice e Sistemi Biologici, Mineralogia e Scienze della Terra, Ambiente e Beni Culturali; • la necessità di grandi infrastrutture, e quindi la localizzazione presso aree di ricerca nazionali e laboratori internazionali.

La multidisciplinarità della ricerca è uno dei punti prioritari sui quali si basa la strategia di riforma del CNR. Se la ricerca oggi vuole rappresentare un fatto significativo e determinante per lo sviluppo ed essere competitiva a livello internazionale non può che rafforzare, senza ovviamente escludere la ricerca disciplinare, l’interdisciplinarità dei gruppi di ricerca e la possibilità di creare attorno a specifiche tematiche la massa critica in grado di raggiungere risultati qualificanti.

Il tema delle grandi infrastrutture si pone oggi sempre più, oltre che a livello dei singoli paesi, a livello comunitario ed internazionale ed impone non solo collaborazioni ma scelte che ne facilitino lo sviluppo selezionando le localizzazioni per rendere possibili gli investimenti elevati che simili infrastrutture richiedono.

Il CNR sostiene l’attività di ricerca che la comunità italiana, impegnata nei settori di luce di sincrotrone (LS), dei neutroni e dei muoni, svolge presso le grandi installazioni di ricerca, attraverso il finanziamento diretto (ricerca e personale) dei propri Istituti; la sottoscrizione di accordi di collaborazione - con finanziamento oneroso e/o di sviluppo di strumentazione-, quali ad esempio le collaborazioni con ELETTRA (I), ESRF (F) ed ISIS (UK); la formazione del personale.

Grazie a queste iniziative, la comunità italiana di ricercatori operanti in LS, neutroni e muoni, ha potuto e può svolgere attività di ricerca significativa e riconosciuta in campo internazionale, e giovani laureati, dottorati e ricercatori hanno potuto formarsi in questi settori.

L’efficace collaborazione inter e intra-nazionale tra ricercatori di enti di ricerca e universitari è una linea di tendenza che ha dato positivi risultati e che va rafforzata in questo come in tutti i settori, in modo da poter utilizzare al massimo l’approfondimento disciplinare da una parte, e la messa in relazione delle più varie competenze dall’altra.

Anche grazie alle iniziative del CNR nel nostro paese si è sviluppata una consistente comunità di ricercatori che utilizza queste tecniche di indagine e partecipa alla progettazione di strumentazione, e che vede la presenza di Chimici, Fisici, Geologi, Biologi, Biotecnologi, Farmacologi, Ingegneri, Esperti di Scienze dell’Alimentazione e studiosi di Storia dell’Arte e Conservazione dei Beni Culturali. Stiamo lavorando affinché, in un prossimo futuro, un numero sempre maggiore di ricercatori di area Biotecnologica, Scienza dell’Alimentazione, Farmacologia e

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conservazione dei Beni Culturali possa avvalersi di queste tecniche di ricerca.

In questo quadro, con il supporto di ELETTRA, dei gruppi CNR e Universitari, si è rafforzata la leadership italiana per quanto riguarda la progettazione e realizzazione di strumenti e sottosistemi speciali, fornendo opportunità per le Imprese italiane.

La fornitura di strumentazioni sia in LS che in spettroscopia di neutroni ha inoltre attivato e sostenuto una capacità di Imprese italiane nell’acquisire accesso a un mercato internazionale che in questo campo è in rapida espansione.

Il Regno Unito con il CCLRC è attualmente impegnato nella costruzione, presso il Rutherford, di una sorgente di luce di sincrotrone di caratteristiche simili a quella già funzionante a Trieste, dove operano molti gruppi CNR, e di una seconda stazione sperimentale di neutroni, ISIS II. Nell’anno 2002 il CNR ha rinnovato l’accordo con il CCLRC per ISIS II per il periodo 2002-2008.

A partire dal 2004, a questo accordo il CNR ha anche associato un finanziamento destinato alla progettazione e costruzione dello spettrometro NIMROD che, a costruzione completata, affiancherà la strumentazione italiana già operante presso ISIS, e cioè PRISMA, TOSCA, VESUVIO, SLOWMu e quella in itinere e.VERDI, INES. Nel Novembre 2003, è stato rinnovato l’accordo di partecipazione scientifica tra CNR/INFM e l’Institut Laue-Langevin (ILL) di Grenoble (FR), che è la maggior Facility Internazionale per la Neutronica attualmente in funzione.

L’accordo, che copre il quinquennio 2004-2008, prevede la partecipazione italiana alle attività di ricerca in spettroscopia neutronica condotte presso ILL, nella misura del 3.5%. L’accordo garantisce anche il proseguimento nella conduzione dei Progetti Strumentali italiani “BRISP” e “IN13”.

In questi ultimi mesi, la collaborazione CCLRC-CNR si sta allargando alla luce di sincrotrone e alla prospettiva di costruzione delle nuove sorgenti FEL, incluse attività di formazione avanzata in collaborazione tra il CCLRC e la Sincrotrone Trieste, con il coinvolgimento di CNR e varie Università italiane e inglesi. Appare concretamente possibile una collaborazione che vuole essere una catalisi sia per un ampliamento della collaborazione già in essere tra i ricercatori per le attività di R&D in questi settori, sia per estendere le possibilità e le competenze della nostra comunità per quanto riguarda le sorgenti esistenti e future di luce di sincrotrone, neutroni e muoni. È allo studio la possibilità di concretizzare questo progetto attraverso la costituzione di un consorzio tra istituzioni di Ricerca, quali ad esempio CNR, ELETTRA, CCLRC, e Università Europee. La capacità italiana di progettazione e costruzione di strumentazione è particolarmente apprezzata da parte inglese e si ritiene che, con il possibile avvio di una progettazione e realizzazione complementare tra il progetto FERMI@Elettra di Trieste e quello denominato 4GLS proposto dal Laboratorio di Daresbury, si possa ulteriormente rafforzare la collaborazione e l’acquisizione di contratti di fornitura per le ditte italiane.

Dalla collaborazione sta nascendo, ed i nostri sforzi sono tesi a che si affermi sempre più, una strategia a livello europeo che renda la nostra ricerca sempre più attrattiva e competitiva a livello internazionale.

Adriano De Maio Commissario straordinario CNR

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ynchrotron radiation (SR) and neutron scattering are unique and powerful tools for the study of the Fine Analysis of Matter (FAM), an area of interest to an everincreasing range of applications addressed to technological development and innovation, including high-tech industrial research. Techniques based on synchrotron radiation and neutron scattering have in common two important aspects: • research and applications which are intrinsically multidisciplinary. In both cases the highest scientific and technological impact is expected in multidisciplinary science and technology within Europe, in the areas of Material and Engineering Science, Solid State Physics, Chemists, Soft Matter and System Biology, Mineralogy and Earth Science, Environment and Cultural Heritage; • large Infrastructures are needed; thus both kind of facilities require to set-up national and international laboratories.

Multidisciplinary research is one of the priorities driving at present the reform strategy of CNR, in that it provides opportunities for experts in practically every scientific and technical field that contributes significantly to our economy. In order to increase the impact of multidisciplinary research on every day’s life, while keeping disciplinary research going, an important requirement is to strengthen the interdisciplinarity of research groups favouring the growth of a critical mass in specific themes. This will lead to scientific, technological and industrial breakthroughs that will ultimately favour not only the European scientific community but also the business and industrial communities. Given the high investment needs, policy for Large Infrastructures demands collaboration, support and decisions at European and international level.

CNR supports the research activities of the Italian community taking place at Large Infrastructures for synchrotron radiation, muon and neutron scattering. CNR provides support through: 1) the direct financing of its own Research Institutions (of both personnel and research); 2) the subscription of national and international agreements with ELETTRA (I), ESRF (F) and CCLRC (UK) for ISIS - for both access and instrumentation- and 3) personnel training.

Thanks to these initiatives the Italian community, operating in synchrotron radiation muons and neutron scattering, can carry out top quality research and training for young researchers and PhD’s. The effective inter- and intra-national collaboration among researchers belonging to research Institutions and universities has been very productive. It needs to be reinforced in order that scientific and technological achievements can be most effectively shared among researchers and enterprises. The CNR support has favoured the growth of a large research community in our country. This community makes use of the experimental techniques in SR, Muons and Neutron Scattering, taking part to the design and construction of novel instrumentation. This community is composed of Biologists, Chemists, Engineers, Pharmacologists, Physicists, and most recently of experts in Nutrition Science, History of Arts and Cultural Heritage. In the latter case actions are taken so that an increasing number of researchers can benefit of these research techniques.

In this framework, with the support of ELETTRA, CNR and University groups, the Italian leadership has reinforced with respect to the design and construction of instrumentations, providing opportunities for the Italian industries. The supply of in-

strumentation for both synchrotron radiation and neutrons spectroscopy has also activated and supported a capability of Italian industries in acquiring access to an international market which is in rapid expansion in these fields.

In UK the CCLRC is presently engaged in the construction of a new source of synchrotron radiation, DIAMOND, with comparable characteristics to that presently operating in Trieste, and of a second experimental station for neutron scattering, named ISIS-II. In the year 2002 CNR has renewed the agreement with CCLRC regulating the access of the Italian community to ISIS for the period 2002-2008. From the year 2004 the CNR will also provide an additional support devoted to the design and construction of the NIMROD spectrometer. The latter, once completed, will stand beside the other instrumentation operating at ISIS, resulting from former British-Italian collaborations, such as PRISMA, TOSCA, VESUVIO, SLOWMu and in near future such as e.VERDI and INES. In November 2003, the agreement between CNR/INFM and Institut Laue-Langevin (ILL)- Grenoble (FR) has also been renewed. ILL represents the most intense reactor based neutron source operating in the world. The agreement, covering the period 2004-2008, covers a 3.5% share for the access of the Italian community to the research activities at ILL. It also guarantees the continuations of the Italian instrumental projects “BRISP” e “IN13”.

In these last months the CCLRC-CNR collaboration is enlarging to include synchrotron radiation and the perspective of construction of new FEL sources. This collaboration will also envisage training activities between CCLRC and ELETTRA with the involvement of CNR and British and Italian Universities. It seems possible that a collaboration starts aiming to act as a catalysts for broadening the existing collaborations among researchers and for the extension of the know-how of our community regarding the future sources of Synchrotron radiation and neutrons. A project with these scopes, presently under study, foresees the constitution of a consortium among CNR, ELETTRA, CCLRC and some European Universities.

The Italian capability in design and construction of novel instrumentation is well appreciated by our British partners and it is to be hoped that, with launch of FERMI@Elettra and 4GLS projects collaboration between British and Italian might reinforce. From this collaboration a strategy at the European level is growing and our efforts are geared towards making our research more and more internationally attractive and competitive.

Adriano De Maio Commissario straordinario CNR

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RASSEGNA SCIENTIFICA Articolo ricevuto in redazione nel mese di Ottobre 2003

EFFECTS OF MAGNETIC FIELD ON THE CUPRATE HIGH-TC SUPERCONDUCTOR La2-XSrXCuO4 B. Lake1, G. Aeppli2,3, N.B. Christensen4, K. Lefmann4, D.F. McMorrow3,4, K.N. Clausen4, H.M. Rønnow2,5, P. Vordewisch6, P. Smeibidl6, M. Mankorntong7, T. Sasagawa7, M. Nohara7, H. Takagi7,N.E. Hussey7,8,9.

1 Clarendon Laboratory, University of Oxford, Oxford, U.K. 2 University College London, Department of Physics and Astronomy, London U.K. 3 N.E.C. Research Institute, Princeton, U.S.A.

4 Risø National Laboratory, Roskilde, Denmark.

5 C.E.A. Grenoble, France, and Institute Laue-Langevin, Grenoble, France.

6 Hahn-Meitner Institute, Berlin, Germany.

7 University of Tokyo, Tokyo, Japan.

8 University of Loughborough, Loughborough, U.K. 9 H. H. Wills Physics Laboratory, University of Bristol, Bristol, UK.

1. Introduction This article discusses a series of neutron scattering measurements on the cuprate, high transition temperature superconductor La2-xSrxCuO4 in an applied magnetic field. For temperatures below Tc and fields less than Hc2, magnetic flux penetrates the superconductor via vortices which are cylindrical inclusions of resistive material embedded in the superconductor. Phase coherent superconductivity characterized by zero resistance is suppressed to the lower field-dependent irreversibility temperature

(Tirr(H)) and occurs when the vortices freeze into a lattice. Because superconductivity is destroyed within the vortex cores, an investigation of the vortex state could provide information about the ground state that would have appeared had superconductivity not intervened.

Our measurements show that both optimally doped La2xSrxCuO4 (x=0.16, Tc=38.5K) and underdoped La2-xSrxCuO4(x=0.10, Tc= 29K) have an enhanced antiferromagnetic response in a field. Measurements of the optimally doped system for H=7.5T show that inelastic sub-gap spin fluctuations first disappear with the loss of finite resistivity at Tirr, but then reappear at a lower temperature with increased lifetime and correlation length compared to the normal state. In the underdoped system elastic antiferromagnetism develops below Tc in zero field, and is significantly enhanced by application of a magnetic field; phase coherent superconductivity is then established within the antiferromagnetic phase at Tirr.

Fig. 1. (a) shows the phase diagram of La2-xSrxCuO4 as a function of Sr doping x and temperature, the system passes through the phases of antiferromagnetism, spin-glass/stripe behaviour and superconductivity with increasing x. (b) shows the reciprocal space of the two-dimensional copper oxide planes, in the undoped material, the commensurate antiferromagnetism gives rise to a Bragg peak at the (1/2,1/2) position (blue dot). As doping is increased the strength of the magnetism is reduced and the original Bragg peak splits into four incommensurate peaks, the red dots in (c) show the positions of the magnetism typically found in the superconducting phase.

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La 2-x Sr x CuO 4 is derived from the parent compound La2CuO4 which is an insulating antiferromagnet. The Cu2+ ions possess spin-1/2 and give rise to long-range magnetic order below a Néel temperature of TN=325K [1]. The magnetism is essentially two-dimensional with strong antiferromagnetic exchange interactions between nearest neighbours within the CuO2 planes that form within the material and weak interactions between these planes. Introduction of Sr doping, where the Sr replaces the La and releases charge carriers, produces a rich phase diagram, (fig 1a). At 2% Sr doping (x=2) the longrange commensurate order gives way to incommensurate magnetism visible as four peaks surrounding the original Bragg peak position. These peaks lie on the diagonals of the crystallographic axes that span the CuO2 planes and are thought to arise from stripe ordering. For larger Sr dopings, 0.06<x<0.25, La2-xSrxCuO4 enters its superconducting phase, the four peaks split further apart and rotate by 45 degrees to lie along the crystallographic axes (fig 1c) [2,3]. There are in fact two regimes within the superconducting doping range. The under-

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doped regime, 0.06<x<0.125, where long-range order continues to exist at the peak positions, and the optimally doped and overdoped regime, 0.125<x<0.25 where long-range order is lost but magnetic fluctuations persist at the peak positions and are visible in inelastic neutron scattering.

When a magnetic field is applied to La2-xSrxCuO4 it behaves like a type-II superconductor and magnetic flux is able to penetrate the material due to the formation of vorticies. These are cylindrical regions of normal state material embedded within the bulk superconductor each carrying one fluxon and lying parallel to the field direction. In conventional superconductors the vortices form below the zero field superconducting transition temperature, initially they are mobile but as temperature is lowered they freeze into a lattice. The vortex freezing temperature is also the temperature below which phase coherent superconductivity characterised by zero resistance occurs for a given applied field, and in this article

this is called the irreversibility temperature, Tirr, (fig 2b).

The reciprocal vortex lattice for a field of H=7.5T applied perpendicular to the superconducting CuO2 planes is illustrated in figure 2a The vortex lattice is square in contrast to the hexagonal lattice of a conventional superconductor and this is thought to be related to the d-wave superconducting mechanism found in the cuprate high-Tcs [4]. The vortex density increases with applied field and for H=7.5T the separation between the vorticies is av(7.5T)=166Å. The size of the vortex cores is typically given by the superconducting pair coherence length ξ which for La2-xSrxCuO4 is ξ~20Å.

This article discusses the effects of applied magnetic field on two La2-xSrxCuO4 samples, first an optimally doped sample with x=0.16 and a superconducting transition temperature of T c=38.5K, and second an underdoped crystal with x=0.10 and Tc=29K. The experimental technique in both cases is neutron scattering which is able to track changes in the magnetism of these materials

Fig. 2. (a) shows the reciprocal vortex lattice (small blue dots) in the copper oxide plane for a magnetic field of 7.5T applied perpendicular to the CuO2 plane, the magnetic peak positions for optimally doped La2-xSrxCuO4, x=0.16, are also shown (red dots). (b) shows the irreversibility line for La2-xSrxCuO4, x=0.16, as a function of temperature and applied magnetic field; here the irreversibility temperature is defined as the temperature below which the state of zero electrical resistance is achieved and is also thought to be the temperature at which the vortices freeze to form a lattice. (c) gives the magnetic susceptibility as a function of energy at the magnetic peak position for different fields and temperatures; red triangles – normal state, T=29K, H=0T; red circles – superconducting state, T=5K, H=0T; blue circles – superconducting state with applied field, T=7K, H=7.5T. (d) shows the field-induced signal – low temperature signal measured for H=7.5T minus zero-field signal.

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with applied field and temperature. The x=0.10 sample has long-range magnetic order and elastic neutron scattering is used to probe it; the x=0.16 sample has no longrange order, however it does have magnetic fluctuations which show up in inelastic neutron scattering.

The experiments on optimally doped La 2-x Sr x CuO 4 , x=0.16, took place on the RITA-1 triple-axis spectrometer at Risø National Laboratory, Denmark, just before the

Fig. 3. The magnetic signal of La2-xSrxCuO4, x=0.16 measured in zero field in the normal and superconducting states. The data is displayed as a function of wavevector for the trajectory shown by the green line in figure 1c that passes through two of the magnetic peaks. This scan was repeated for various energy transfers and the colours give the intensity of the magnetic scattering with red as most intense and blue as background. (a) shows the data collected in the normal state at Tc=38.5K where the red streaks indicate the magnetic peak positions. (b) shows the data collected in the superconducting state at T=5K, where the spin-gap is revealed by the absence of scattering below 6.7meV.

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closure of the reactor in 2000. The experiment owes its success to the state-of-the-art design of this instrument whose neutron flux was enhanced due to the use of neutron guides, a large focusing monochromator and analyser and a broad band velocity selector; in addition a large position sensitive detector allowed the optimization of signal to noise and provided a detailed understanding of the signal [5]. In zero field the main feature of optimally doped La2-xSrxCuO4, is the spin gap that appears in the superconducting state [6-8]. Figure 3 compares the magnetic response of the material as a function of energy in the normal state at Tc=38.5K with the superconducting state at 5K. In the normal state magnetic signal is observed at the incommensurate peak positions down to the lowest energies. In contrast at 5K a gap appears in the magnetic excitation spectrum at ∆=6.7meV below which the magnetic signal drops to zero. The spin-gap has similar origins to the superconducting energy gap observed in the quasi-particle excitation spectrum measured by for example angle resolved photoemission [9]. The latter is the energy required to break up the charge pairing that occurs in the superconducting state while the spin gap refers to the pairing energy of the spins of these quasi-particles.

Figure 2c shows the magnetic susceptibility at the incommensurate peak position as a function of energy for various fields and temperatures [10] where the applied fields were supplied by an 8T vertical field magnet manufac-

Fig. 4. Temperature dependence of the magnetic signal in La2-xSrxCuO4, x=0.16 measured below the spin-gap at 2.5meV, the data was collected at the magnetic peak position. The red circles shows the data collected in zero field where the signal drops rapidly below the superconducting transition temperature due to the opening up of the spin-gap. The blue circles shows the same measurement in an applied field of H=7.5T, magnetic signal lingers below Tc(H=0T) and does not drop away until the irreversibility temperature Tirr(H=7.5T)=19K is reached. As the temperature is cooled further the magnetic susceptibility rises again for T<10K.

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tured by Oxford Instruments. The red circles give the magnetic signal at 5K in zero field and show that there is complete loss of signal below the spin gap energy in the superconducting state, compared to the normal state at these energies (red triangles). If the measurement is now repeated at T=5K in an applied field of 7.5T, where the field direction is perpendicular to the copper oxide planes, (blue circles) the data reveal magnetic signal induced below the spin-gap energy. This signal appears as a peak with a maximum at an energy of ~4.3meV (fig. 2d) and when fitted to a damped harmonic oscillator it has an inverse lifetime of Γ=4.3meV which interestingly is much less than the normal state value of 9meV suggesting slower magnetic fluctuations. Further measurements of the wavevector-dependence of the field-induced signal reveal a correlation length at low temperatures of 75Å which is considerably greater than the normal state value of 24Å. These two results - an enhanced lifetime and an enhanced correlation length - suggest a greater tendency towards long-range magnetic order for La2-xSrxCuO4 in an applied field compared to its normal state.

As a first guess one might assume that the field-induced magnetism originates from the vortex cores however the correlation length which gives the size of the magnetic regions in the material is considerably larger than the diameter of the vorticies (ξ~20Å), implying that the magnetic signal does not originate just from the cores. Furthermore the size of the ordered spin moment obtained by a phonon normalization is 0.22µB/Cu2+ in absolute units [10]; this value is averaged over the Cu 2+ ions throughout the material and is clearly too large to come from the vortex cores alone which make up less than 5% of the total sample for a field of 7.5T. A potential scenario is for vortices to nucleate magnetism but where these magnetic regions extend beyond the vortex cores and spill out into the surrounding superconducting regions.

Evidence for this comes from high-field nuclear magnetic resonance experiments which have detected an enhanced resonance rate both within and surrounding the vortices in optimally doped YBa2Cu3O7-δ; this has been attributed to field-induced magnetic excitations [11,12].

There is also a very interesting result from scanning tunnelling microscopy measurements of optimally doped Bi2Sr2CaCu2O8+δ in an applied magnetic field. These measurements reveal a field-induced checkerboard pattern around the vorticies, and while this modulation is clearly associated with the formation of vorticies it extends beyond the cores to cover a region of ~100Å [13].

The signal measured by scanning tunnelling microscopy is electronic in nature and as yet the relationship between this field-induced electronic modulation and the field-induced magnetic signal measured by neutrons has not been made. Nevertheless it is probably reasonable to connect these two phonomena in which case the field-in-

duced magnetism would also originate from a region around the vortex cores.

Other interesting aspects of the field-induced signal can be deduced from the temperature dependence of the subgap magnetic signal which is shown in fig. 4. In the absence of an applied field the signal drops away rapidly as the sample is cooled below the zero-field superconducting transition temperature T c(H=0T) due to the opening up of the spin gap in the superconducting state.

In an applied field however the signal lingers quite far

Fig. 5. A possible model for the field effect in (a) optimally doped La2xSrxCuO4, x=0.16, and (b) underdoped La2-xSrxCuO4, x=0.10. In the optimally doped sample the magnetic regions are about 75Å in size making them greater than the vortex cores but smaller than the separation of the vortices. The magnetic regions are assumed to be nucleated by the vortices but to extend beyond the vortex cores. In the figure blue represents the superconducting regions, the vortex cores are represented by the red circles and the magnetic areas include the vortex cores and the orange regions surrounding them. The rising magnetic susceptibility found in this sample at low temperatures could arise from the coupling of the isolated magnetic regions through superconducting medium. In the underdoped sample the magnetic regions are large and give rise to long-range magnetic order. In a phase separation model the superconducting regions would be confined to isolated pockets in between the magnetic regions, in this case phase coherent superconductivity could only occur via Josephson coupling through the magnetic regions.

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below Tc(H=0T) and does not drop away until T<19K, a temperature that coincides with the irreversibility temperature for the applied field. At lower temperatures still T<10K the magnetic signal starts to increase rapidly as a function of temperature suggesting an onset to longrange order. Unfortunately the available temperatures did not go low enough to fully explore this region, however it is clear that rising magnetic susceptibility occurs within the state of phase coherent superconductivity possibly via a mechanism where magnetism nucleated by the vorticies starts to extend outwards beyond the cores as temperature is lowered and different magnetic regions begin to couple to each other through the intervening superconducting medium (see fig. 5a).

Since an applied magnetic field has the effect of inducing magnetism in optimally doped La2-xSrxCuO4 in the form

Fig. 6. The elastic magnetic scattering in underdoped La2-xSr xCuO 4, x=0.10, measured in the normal and superconducting states for zero field and H=14.5T. The data is plotted as a function of wavevector through one of the magnetic peaks (see inset diagram). (a) shows the data collected in zero field, the signal appears in the superconducting state measured at T=2K (red circles) but is absent in the normal state at Tc=29K (blue circles). (b) shows the data collected in an applied field of 14.5T, the signal in the superconducting state has increased by a factor of three while there is still no signal at Tc=29K.

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of magnetic fluctuations without long-range order, the question then arises as to what would be the effect of field on an underdoped sample which has long-range magnetic order in zero field. In the next set of experiments elastic neutron scattering measurements were performed on underdoped La2-xSrxCuO4 x=0.10. These measurements took place on the V2/FLEX triple-axis spectrometer at the Hahn-Meitner Institute in Berlin. This institute specializes in sample environment and the experiments made use of the VM1 15T vertical field magnet, manufactured by Oxford instruments – the highest field magnet available at the time for neutron scattering. Figure 6 shows a scan through one of the incommensurate peaks in zero field for H=14.5T [14]. In the normal state at Tc =29K (blue circles) no signal is observed, but on cooling down below Tc in zero field (red circles), signal appears in the superconducting state - a phenomenon that has been well documented in a number of La2CuO4 based superconductors [3]. If a magnetic field is now applied perpendicular to the CuO2 planes at low temperatures, an enhancement of the elastic magnetic signal is observed. This enhancement is strong, a factor of three larger than the zero field signal for an applied field of H=14.5T that is much smaller than the upper critical field of Hc2~45T. The magnetic peaks are resolution limited in both zero and non-zero field and this puts a lower limit of 400Å on the magnetic correlation length. This large correlation length is interesting because it suggests that the magnetic regions are not only greater than the vortex cores (ξ~20Å) but are also, unlike the case of the optimally doped sample, greater than the separation of the vorticies (av(5T)=200Å for H=5T). The large correlation length coupled with the large value of the average ordered spin moment of 0.24µB/Cu2+ at H=5T, imply that as for the optimally doped sample many more sites are involved in the magnetic ordering than the 3% of Cu2+ ions that form the vortex cores for this field. Other experiments have subsequently taken place that confirm this picture of field-induced long-range magnetic order in oxygen-doped La2CuO4+y [15,16].

Figure 7 compares the resistivity and the ordered spin moment as a function of temperature and magnetic field.

The data show that irrespective of the size of the field that is applied the Néel temperature for the magnetic ordering lies close to the zero-field superconducting transition temperature Tc(H=0T)=29K. and not the irreversibility temperature at which phase coherent superconductivity occurs. It is also clear that the state of phase coherent superconductivity characterised by zero resistance that occurs below Tirr always forms within the magnetically ordered phase - i.e. as the sample is cooled first it becomes magnetically ordered and than at a lower temperature it becomes superconducting. In many ways then the results for the underdoped sample are opposite

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to those for the optimally doped sample where phase coherent superconductivity is achieved at a higher temperature than the field-induced magnetism. At this point it is not known whether there is coexistence between superconducivity and magnetism in the same regions of the material or whether they phase separate and exclude one another. However given the large size of the magnetic correlation length, a phase separation scenario would mean that the superconducting regions would be pushed into the pockets between the magnetic regions.

This could explain the strong suppression of the irreversibility temperature with field because only when the temperature is sufficiently low would the superconducting regions be able to connect to each other via a Josephson coupling mechanism through the intervening magnetic medium (fig. 5b). Again this picture is the dual of that for optimally doped La2-xSrxCuO4 where the superconducting region percolate and the isolated magnetic regions only start to communicate with each other at sufficiently low temperatures.

This duality between underdoped and optimally doped La2-xSrxCuO4 is extremely interesting and one can imagine a gradual evolution of the magnetic ordering temperature as a function of doping resulting in a crossover from above to below the irreversibility temperature at some doping intermediate between x=0.10 and x=0.16

[17]. Other doping dependent changes occur in the correlation length and energy of the field-induced magnetism. In the optimally doped sample the field-induced signal lies at a non-zero energy transfer and has a finite correlation length, whereas the field-induced signal in the underdoped sample is elastic and has a large resolution limited correlation length. One can therefore picture a phase diagram where the energy of the subgap fieldinduced signal decreases progressively as the doping decreases while at the same time the correlation length and hence the size of the magnetic regions increases.

These experiments reveal the highly complex interaction between superconductivity and magnetism. In a conventional superconductor, superconductivity and magnetism are incompatible but in La2-xSrxCuO4 the situation is not so simple. In underdoped La2-xSrxCuO4 although a magnetic field suppresses phase coherent superconductivity suggesting competition between these phases, field-induced magnetic order is turned on at the zerofield superconducting transition temperature suggesting co-operation. In optimally doped La2-xSrxCuO4 the fieldinduced magnetism occurs within the state of phase coherent superconductivity again suggesting that they are not entirely incomplatible. A number of questions remain to be answered in particular do superconductivity and magnetism co-exist or phase separate, and to what extent do they compete and/or co-operate? There is also clearly a very strong doping dependence which need to be explored which could help reveal the nature of the quasi-particle pairing and mechanism for superconductivity in the cuprate high-Tcâ&#x20AC;&#x2122;s.

References 1.

2.

3.

4.

5.

6.

7.

8.

Fig. 7. The resistivity and magnetic signal in underdoped La2-xSrxCuO4, x=0.10 are displayed as a function of temperature and magnetic field. (a) shows the transport data, the colours give the size of the resistivity with blue indicating zero resisivity. The white dots mark the irreversibility temperature T irr below which phase coherent superconductivity is achieved. (b) shows the ordered moment squared per Cu2+ ions obtained from neutron scattering, blue indicates zero magnetic moment and red indicates a large moment. The data shows that irrespective of the size of the field that is applied the field-induced magnetism always arises at the zero field superconducting transition temperature (first contour).

9.

10.

11.

12.

13.

14.

15.

16.

17.

D. Vaknin,. et al. Phys. Rev. Lett. 58, 2802 (1987).

Y.S. Lee, et al. Phys. Rev. B 60, 3643 (1999).

H. Kimura, et al. Phys. Rev. B 59, 6517 (1999).

R. Gilardi et al Phys. Rev. Lett. 88, 217003 (2002).

T.E. Mason, K.N. Clausen, G. Aeppli, D.F. McMorrow, and J.K. Kjems.

Can. J. Phys. 73, 697 (1995).

B. Lake et al., Nature 400, 43 (1999).

K. Yamada, et al. Phys. Rev. Lett. 75, 1626 (1995).

S. Petit, A.H. Moudden, B. Hennion, A. Vietkin, and A. Revcolevschi, Physica B 234-236, 800 (1997).

B. Lake, et al. Science 291, 1759 (2001).

T. Yoshida et al. LANL Preprint server cond-mat/0206469 (2003).

V.F. Mitrovic et al Nature 413 501 (2001).

V.F. Mitrovic et al Phys. Rev. B 67, 220503 (2003) J.E. Hoffman et al. Science 295 466 (2002).

B. Lake et al. Nature 415 299 (2002).

B. Khaykovich et al. Phys. Rev. B 66, 014528 (2002) B. Khaykovich et al. Phys. Rev. B 67, 054501 (2003) E. Demler, S. Sachdev, Y. Zhang, Phys. Rev. Lett. 87 067202 (2001)

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Articolo ricevuto in redazione nel mese di Novembre 2003

SOLVATION SHELL OF OH- IONS IN WATER A. Botti, F. Bruni, S. Imberti, and M.A. Ricci Dipartimento di Fisica "E. Amaldi", Università degli Studi Roma Tre, and INFM, Unità di Roma Tre. Via della Vasca Navale, 84 . 00146 Roma, Italy

Under normal conditions in pure water a small fraction (10-7) of water molecules dissociates spontaneously to form H+ and OH- ions. It is well established that such ions in water are strongly hydrated [1] and the hydrogen bonds in their solvation shell are continuously breaking and re-forming, during the proton transfer process [2] which is known to play a significant role in many processes, such as for instance signal transduction and catalytic activity. The high mobility of these ions in water can be rationalized via a sort of "structural diffusion", as it is the coordination and pattern of hydrogen bonds characterizing the hydrated ions that migrate, not their individual constituents [3]. Consequently knowledge of the structure of the solvation shell of H+ and OH- is of great relevance to the understanding of their transport dynamics.

The ion solvation and proton transport process in aqueous solutions have been studied by means of either abinitio [3,4,5,6,7,8] or classical [9] simulations and a lively discussion is going in the literature about the validity of the classical argument that the OH- can be regarded as a water molecule missing a proton and that the transport mechanism of such defect can be inferred from that of the H+ ion by symmetry [10].

Although neutron diffraction experiments can in principle provide a test of the simulation results, direct experimental evidence for the solvation shell of the OH- ion was until recently [11] missing, due to the low concentration of such ions in pure water and to the difficulty of extracting the desired information from the total measured signal. As a matter of fact the ion concentration can be tuned to the experimental sensitivity by using a hydroxide solution instead of pure water; nevertheless by exploiting the hydrogen/deuterium substitution technique [12] one can extract only three Composite Partial Structure Factors (CPSF), which are usually referred to as SXX, SXH and SHH, where H labels the H/D substituted sites, while X indicates all not-substituted ones. In the case of pure water the three CPSF’s are fully exhaustive, as X and H coincide with the water oxygens, Ow, and hydrogens Hw; for hydroxide aqueous solutions they are instead linear combinations of site-site Partial Structure Factors (PSF), weighted by the concentration, ci, and scattering length, bi,[14] of the individual species, giving:

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A.K. Soper* ISIS Facility, Rutherford Appleton Laboratory.

Chilton, Didcot, Oxon, OX11 0QX, UK

SHH (Q) =

∑

i, j = H w ,H

c ic jbib j Sij (Q)

(∑ c b )

2

k

SXH (Q) =

∑

i=Ow ,O,CI ; j = H w

H

c ic jbib j S ij (Q) 2

∑

i, j= Ow ,O ,CI

(2)

k k

c ic jbib j Sij (Q)

(∑ c b )

2

k

(1)

k

(∑ c b ) k

SXX (Q ) =

k

(3)

k k

where Q is the exchanged wavevector, O and H and CI are labels for the hydroxide atoms and counterion respectively, the index k runs over all the i,j species appearing in the sum at the numerator of each equation, and bHw=bH equals the average between the scattering length of hydrogen and deuterium, according to the hydrogen content of the mixture of protiated and deuteriated samples. Consequently structural information on the coordination of water molecules around a solvated ion, e. g. the OH-, is not readily available from the Fourier transforms of the CPSF’s.

In this respect the recent availability of a Monte Carlo simulation code, the Empirical Potential Structure Refinement (EPSR),[15,16,17] tailored for the reduction to real space function of neutron diffraction data from liquid and amorphous samples, has opened new perspectives for an in depth analysis of the microscopic structure of aqueous solutions. This code performs a standard Monte Carlo computer simulation of the system in question, starting from a reasonable guess about the interaction potential and structure of the system, and uses the diffraction data to generate an additional "empirical potential" so that the simulation reproduces the experimental data as close as possible. All measured data are fitted simultaneously and in this way molecular configurations consistent with the measured data can be recorded, giving access to the whole set of Site-Site Radial Distribution Functions, SSRDF, of the system, avoiding noise and truncation effects that typically affect traditional Fourier transforms. Moreover the Spatial Distribution Functions, SDF, and the Orientational Correlation Functions, OCF, around a complex or molecule sitting in the origin of a reference frame can be calculated, avoiding

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angular averaging [18]. These are evaluated through a spherical harmonic expansion of the pair correlation rr r function g(r,Ω1, Ω2 ) of a pair of molecules. The SDF allows us to visualize in three dimensions the probability of finding a second molecule, however oriented, at a por sition r relative to a specified molecule at the origin.

The OCF describes the distribution of orientations of the r r second molecule relative to the first, (Ω2 − Ω1 ) at some specified position. It has to be mentioned here that, although it cannot be demonstrated from first principles that the solution of the iterative fitting procedure is unique, nevertheless it has been experimentally proven

that the SSRDF extracted by this technique are not sensibly dependent on the initial guess, provided that the quality of the diffraction data is good [16].

To demonstrate the performances of this code, here we report the results of a neutron diffraction experiment performed at the SANDALS diffractometer [19], installed at ISIS (UK), on a solution of NaOH in water at concentration of 1 solute per 12 solvent molecules, at room temperature [11,12]. The sample container was a standard flat Ti-Zr cell, 1 mm thick. Isotopic Hydrogen/Deuterium substitution has been exploited on both water and solute and data have been collected for a fully

Fig. 1. Composite partial structure factors for the 1: 12 solution: comparison between data (squares) and fit (thick solid line). The thin solid line is the residual. The XX and HH partial structure factors have been arbitrarily shifted for clarity. The same quality has been obtained for the other data sets.

Fig. 3. Site-site radial distribution function for the oxygens: the relative weight of the gOwOw(r) and gOwO(r) into the total gXX(r) function are ~78% and ~12.7%.

Fig. 2. Site-site radial distribution function for the hydrogens: the relative weight of the gHwHw(r) and gHwH(r) into the total gHH(r) function are ~92.3% and ~7.5%. Notice that the intramolecular HwHw peak at about 1.55Å is not shown.

Fig. 4. Site-site radial distribution function for oxygens and hydrogens: the relative weight of the gOwHw(r), gwO(r) and gOwH(r) into the total gXH(r) function are ~84.9%, ~7.9% and ~3.5%. Notice that the intramolecular OwHw peak at about 0.97Å is not shown

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deuteriated, a fully protiated solution and for an equimolar mixture of the two solutions. As a matter of fact NaOH readily dissociates in water into Na+ and OHand the solution used here contains enough ions to be detected in a neutron diffraction experiment, as well as enough water molecules to completely hydrate both ions, each one requiring about 6 water molecules in its first hydration shell [3,20,21].

After standard analysis the CPSF have been obtained and the Monte Carlo simulation has been performed on 490 water molecules, 41 Na+ and 41 OH- in a cubic box of 25.14 Å lateral dimension. We have used the SPC/E model [22] as reference potential for the water-water interactions. The Lennard-Jones (LJ) parameters for the interactions between the individual solute sites, as well as the fractional charges on the ions that best fit the data are reported in Table I. These have been obtained after the initial guess that the fractional charge on the hydroxide hydrogen is the same as that on the water hydrogens: this choice, which may not be unique, then sets the charges on the oxygen and sodium sites. It has to be noted also that, while in the SPC/E model the LJ parameters for the water oxygen account for the non electrostatic interactions between the whole water molecules, the best fit of the data has required two LJ centres on the OH- ion: consequently the LJ diameter for the O site is smaller than that for the Ow site. The parameters for the interaction between different species have been calculated according to the Lorentz-Berthelot law. The bond length of the hydroxyl ion has been taken equal to 0.98 Å. Figure 1 shows the best fit obtained for the experimental PSF; the deviations from the experimental data do not show structures and are well within the statistical noise. After convergence of the fit procedure, the atomic configurations have been recorded for 2500 simulation steps and the SSRDF describing the water correlations around an OH- ion calculated (see Figs. 2 - 4).

ε/kB(kJ/mol)

σ(Å)

0.65 3.106 Owa 0 0 Hwa 2.75b O 0.251b 1.443b H 0.184 b 2.5 Na 0.125 b afrom Ref. [22] bfrom Ref. [23]

m(a.u.)

q/e

16 2 16 2 23

-0.8476 +0.4238 -1.1029 +0.4238 +0.6791

Table 1. Parameters of the reference potential used in the EPSR code.

The subscript w labels the water atoms as opposite to the hydroxyl ones.

First of all we note that the water-hydroxyl first neighbor distance is shorter than the water-water one in all three site-site radial distribution functions, in qualitative agreement with previous simulation works [9,3]. In de-

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tail the two main peaks of the gHwH(r) function (see Fig. 2) are at shorter distance compared to those of the water-water distribution function, and the relative intensity of the first peak to the second one is sensibly higher.

Moreover we find the first OwO peak at ~2.3 Å while the OwOw peak is at ~2.8 Å (see Fig. 3). Integration of the first peaks of the gOwO(r) and gHwO(r) functions gives 3.9± 0.3 first neighboring water molecules per hydroxyl oxygen. Hence there are about four water molecules pointing their hydrogens toward the hydroxyl oxygen, giving a first peak in the gHwO(r) function at ~1.4 Å (see Fig. 4): this sharp peak signals the formation of hydrogen bonds much shorter than those formed between wa-

Fig. 5. Isosurfaces of the gOOw(r) SDF. The hydroxide ion is oriented along the vertical axis, with the oxygen in the origin of the reference frame.

The regions where the probability of finding a water molecule, whatever oriented, in the range 2 Å≤ r≤6.45 Å exceeds the threshold value of 0.15 are shown in dark cyan.

ter molecules and hence very close to linearity. On the contrary hydroxyl hydrogens have their first neighbor water oxygens at ~2.5 Å, i.e. at about the same distance as the second neighbors of the water hydrogens (compare gOwH(r) and gHwO(r) functions in Fig. 4). This latter peak is quite broad, its minimum approach distance is ~1.78 Å and integration out to a distance of 3.5 Å yields 6.3±0.4 water molecules, as expected given the solute concentration. Since the signature of strong H-bonds (namely a well resolved peak between 1.5 Å and 1.9 Å) is missing in the gOwH(r) function, the hydroxyl hydrogen seems to form only very weak H-bonds, if any. We notice also that the second peak of the gOwO(r) function is double structured and integration of this function between 2.75 Å and 3.2 Å yields 1.0±0.2 water molecule, at

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a distance from the H site between 1.77 Å and 2.22 Å.

These findings can be better visualized looking at the SDF, which span both radial and angular coordinates of the intermolecular separation vector; the isosurfaces of the gΟOw(r,Ω) SDF are shown in Fig. 5. The dark cyan regions correspond to regions where the probalility of finding a water molecule, whatever oriented, at distance r from an hydroxyl ion (oriented along the z-axis with the oxygen in the origin of the reference frame) exceeds a treshold value (0.15 in the present instance). Integration of the "cup" around the central ion gives four first neighboring water molecules: these are hydrogen bonded to form the (H9O5)- complex. This characteristic shape of the spatial density identified here suggests that the four OwO directions are not coplanar. The "dish" shaped region at the bottom of the plot is due to the water molecules contributing to the very broad feature of the gOwO(r) function between 3.2 Å and 5.2 Å. The density region on the top of the "cup" is due to the molecule belonging to the first peak of the gOwH(r) function between 1.77 Å and 2.22 Å and to the structure of the second peak of the gOwO(r) function between 2.75 Å and 3.2 Å. The relative orientation of this molecule with respect to the hydroxyl ion can be clarified looking at the gµwO-H(r,Ω) OCF (Fig. 6), namely at the preferred orientations of its dipole moment, µw, with respect to the O-H direction in the same reference frame used for Fig. 5. Since this OCF is not isotropic, the orientations of the fifth water molecule are correlated with that of the hydroxyl: in this sense this molecule can be considered as bonded, although weakly, to the (H9O5)- complex.

The picture that emerges from the above analysis is in agreement with the structure of the (H9O5)- complex proposed by Car-Parrinello ab-initio simulations [3,5,6]. Significantly our data reveal the presence of a fifth weakly bonded molecule in the hydration shell of the hydroxyl.

Fig.6. The gµwOH(r,Ω) OCF; the preferred orientations of the dipole moment of the water molecule immediately above the O-H vector of the the hydroxide ion are highlighted in dark cyan.

This molecule can play an active role in the proton transfer phenomena, according to Fig. 1 of Ref. [4]: as it can readily participate to the four-bonded network of water molecules as soon as a proton transfer along one of the hydrogen bonds of the (H9O5)- complex takes place, and the hydroxyl "migrates". Moreover it is conceivable that the smaller complexes found by means of ab-initio simulations [3], such as (H7O4)-, are not visible in a neutron diffraction experiment, being only transient.

In conclusion we have shown that by combining neutron diffraction experiments and Monte Carlo simulations, it is possible to determine the solvation shell of the so-called "water ions". In particular present results conflict with the traditional view of the OH- ion as a proton hole, while supporting Car-Parrinello ab-initio simulations [3,5,6].

References 1. D. Eisenberg, and W. Kauzmann, in "The Structure and Properties of Water", (Oxford University Press, 1969), pag. 225.

2. P.L. Geissler, C. Dellago, D. Chandler, J. Hutter, and M. Parrinello, Science, 291, 2121 (2001).

3. M.E. Tuckermann, K. Laasonen, M. Sprik, and M. Parrinello, J. Chem.

Phys., 103, 150 (1995); J. Phys. Chem. 99, 5749 (1995).

4. M.E. Tuckermann, D. Marx, and M. Parrinello, Nature, 417, 925 (2002).

5. B. Chen, I. Ivanov, J.M. Park, M. Parrinello, and M.L. Klein, J. Phys.

Chem. 106, 12006 (2002).

6. B. Chen, J.M. Park, I. Ivanov, G. Tabacchi, M.L. Klein, and M. Parrinello, J. Am. Chem. Soc. 124, 8534 (2002).

7. Z. Zhu and M.E. Tuckermann, J. Phys. Chem. 106, 8009 (2002).

8. D. Asthagiri, L.R. Pratt, J.D. Kress, and M.A. Gomez, Proc. Natl.

Acad. Sci. USA, in press.

9. Y. Guissani, B. Guillot, and S. Bratos, J. Chem. Phys. 88, 5850 (1988).

10. E. Huckel, Z. Elektrochem., 34, 546-562 (1928).

11. A. Botti, S. Imberti, F. Bruni, M.A. Ricci, and A.K. Soper, J. Chem.

Phys., 119, 5001 (2003).

12. A. Botti, S. Imberti, F. Bruni, M.A. Ricci, and A.K. Soper, J. Chem.

Phys., submitted .

13. F. Bruni, M.A. Ricci, and A.K. Soper, J. Chem. Phys., 114, 8056 (2001).

14. V.F. Sears, Neutron News 3, 26 (1992).

15. A.K. Soper, Chem. Phys. 202, 295 (1996).

16. A.K. Soper, Mol. Phys. 99, 1503 (2001).

17. F. Bruni, M.A. Ricci, and A.K. Soper, in Francesco Paolo Ricci: His Legacy and Future Perspectives of Neutron Spectroscopy, edited by M. Nardone and M. A. Ricci, (Italian Physical Society Conference Proceedings, SIF, Bologna, 2001) vol. 76, p. 37.

18. I.M. Svishchev and P.G. Kusalik, J. Chem. Phys., 99, 3049 (1993).

19. A.K. Soper, in Proceedings of the Conference on Advanced Neutron Sources 1988, edited by D.K. Hyer, IOP Conf. Proc. no. 97 (Institute of Physics and Physical Society, London, 1989), p. 353. Detailed information on the SANDALS diffractometer can be also found at the web site: www.isis.rl.ac.uk.

20. L.M. Ramaniah, M. Bernasconi, and M. Parrinello, J. Chem. Phys., 109, 6839 (1998).

21. J.A. White, E. Schwegler, G. Galli, and F. Gygi, J. Chem. Phys., 113, 4668 (2000).

22. H.J.C. Berendsen, J.R. Grigera, and T.P. Straatsma, J. Phys. Chem. 91, 6269 (1987).

23. M. Zapalowski and W.M. Bartczak, Computers and Chemistry 24, 459 (2000).

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Articolo ricevuto in redazione nel mese di Novembre 2003

FIRSTS COMIXS RESULTS Kevin C. Prince*, Maurizio Matteucci*, Marco Zangrando†, Federica Bondino†, Michele Zacchigna†, Fulvio Parmigiani†# , Daniele Cocco* *Sincrotrone Trieste, S.S. 14 Km163.5 in Area Science Park,

34012 Basovizza-Trieste, Italy †INFM-TASC S.S. 14 Km163.5 in Area Science Park, 34012 Basovizza-Trieste, Italy #Università Cattolica di Brescia, Dipartimento di Matematica e Fisica, via Musei 41, 25121 Brescia Italy

A new spectrometer has been designed, constructed and commissioned at Elettra to perform soft x-ray inelastic scattering.

It is based on two interchangeable Variable Line Spacing (VLS) spherical gratings. The energy scan is performed by a linear translation of a back illuminated CCD which can also collect the zero order light. This is a great aid in the alignment and calibration of the instrument. The two gratings have the same radius of curvature while the groove densities and the groove density variations differ by a factor four. Thus the energies focused by the gratings at a particular position differ by a factor of four. The energy range covered is roughly 25-1000 eV and the expected resolving power ranges from 1000 to 5000.

The spectrometer, conceived as a portable instrument, is currently mounted on the beamline Bach. It takes advantage of the small size of the photon spot in the experimental chamber and of the possibility to control the polarization of the incoming radiation. The small spot constitutes the virtual entrance slit, and the spectrometer collects the photons emitted in a solid angle of about 30x10 mrad 2 . The instrument, named ComIXS (Compact Inelastic X-ray Spectrometer), has been routinely operating since October 2002. Several experiments have already been carried out and some illustrative results are shown.

constraint arose from the necessity to allow installation on different experimental chambers without exotic solutions, and to simplify alignment procedures and mechanical design.

Due to the low count-rate, an exit slit and single counting system is not advisable, so a multichannel detector based on a position sensitive detector was chosen. In fact, if the incoming radiation impinges on the grating perpendicularly to the grooves, the different energies are diffracted in a plane generated by the grating normal and the incoming radiation direction. Therefore it is possible to associate the energy of a photon with a position in space. The ideal detector is therefore one with good spatial resolution (smaller than the dimension of the diffracted image) and the highest possible efficiency together with very low noise. We decided to work with a spherical grating having variable line spacing (VLS), which has several advantages. With a VLS grating is possible to reduce, or even eliminate, the aberration induced by the grating (similar to satisfying the Rowland condition [4]and simultaneously it is possible to focus the different photon energies on a relatively small area (and therefore to have a compact instrument). The general layout of the instrument is shown in figure 1.

To keep the mechanics of the instrument as simple as possible, the grating is fixed while the detector moves to select the energy.

The radius of curvature R of the gratings was chosen to satisfy the first part of the Rowland condition4 for each energy i.e. R=r/cos(α) (r is the source-grating distance and is the angle of incidence). Making this choice, and using a grating with a groove density D(x) which varies along the grating as a polynomial function D(x) = D0 + D1x + D2x2 + … (the origin is the pole of the grating) the equation describing the focal property of the grating becomes:

Optical layout The most important requirement for an x-ray spectrometer, common to all of the existing instruments [1-3], is the necessity to collect as many photons as possible, since the fluorescence yield is intrinsically very low. Nevertheless, to extract useful information from the scattered photons, it is usually necessary to energetically analyze them so that a soft x-ray monochromator should be used. It is well known that increasing the resolving power of a monochromator reduces the output flux. Therefore a major design parameter was to maximize the transmission while attaining moderate to good resolving power.

The basic concept was therefore to have as few elements as possible (possibly one, a diffraction grating) with the maximum possible efficiency. Another constraint was the requirement to make the spectrometer as compact and simple as possible, but with the possibility to have a relatively high energy resolving power. The compactness

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F200 =

 cos 2 β cos β   1 −nλD1 +  −  R   2   r'

(1)

In this way the parameter r' (focal distance of the grating) at a particular wavelength λ assumes different values depending on the groove density variation parame-

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ter D1. We select D1 in such a way that the focal positions of the grating at different energies were as close as possible to a straight line. In this way there is a considerable simplification of the mechanics necessary to select the energy and all the photon energies collected by the detector are in focus.

In principle it is possible to cover the full energy range (≈25-1000 eV) with a single grating, but to reduce the

Fig. 1. Layout of ComIXS [5]. The two interchangeable gratings are fixed (with respect to the source) while the detector (a back illuminated CCD) moves along a straight line of roughly 6 cm to select the appropriate energy window.

overall displacement of the detector and to increase the efficiency, we used two blazed gratings. For the reason explained above, they have the same radius of curvature (1432.7 cm) the same sample-grating distance (63 cm) and grazing angle of incidence (2.52o). The groove densities and the groove density variations differ by a factor four. In this way, where the low energy grating focuses a particular energy, the other focuses an energy four time

larger. To fulfil the above-mentioned requirements, it is necessary that the two gratings have a very large groove density variation. The low energy grating (25-300 eV) has a groove density ranging from 4000 to 6000 l/cm while the high energy one (100-1000eV) from 16500 to 23000 l/cm (with D0=19200 l/cm and D1=800 l/cm2).

The required groove density variation for the high energy grating is very difficult to achieve with holographic techniques, and therefore mechanical ruling was used as the manufacturing process. A CARL ZEISS Grating Ruling Engine GTM6 was used, and operated under interferometric control.

With these two gratings, all the energies lie on a curve (figure 2) that is not exactly a straight line, but close to it.

The maximum difference along the photon path between the straight line and the real focal curve is of the order of 2 mm over the full energy range. The divergence of the radiation is small enough not to enlarge appreciably the spot collected out of its ideal focus.

The closeness of the detector to the grating and to the sample offers two important advantages: a large angular acceptance (26x6 mrad2 (limited by the CCD width in horizontal)) and a large energy range collected in a single image (of the order of ± 50% of the central selected energy). In figure 3 an example of the width of the energy window for the two gratings is shown.

The spectrometer is well matched to the beamline BACH [6] at Elettra which hosts it. The beamline delivers monochromatic photons (of the order of 10 11 -10 12 ph/sec) in a very small spot (about 12 µm in the vertical direction). In this way, the spot becomes the source of the spectrometer without the necessity to adopt an entrance slit. The incoming light can be polarized linearly (horizontal and vertical) or elliptically (including circularly), permitting the performance of inelastic dichroic

Fig. 2. Focal position of the spectrometer as a function of energy. The numbers on the curve indicate the energy focused by the Low Energy Grating (red) or the High Energy Grating (blue). The lower full black line indicates the direction of the zero order, which is accessible. The directions of two diffracted beams and the CCD plane are also displayed. The origins of X and Y are the pole of the grating.

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Fig. 3. Top: Low energy grating. Resonant emission series of S 2p of a FeS2 sample collected in first and second diffraction order. The series was collected changing the energy of the incoming radiation. The energy window collected in a single image is 70-300 eV. Bottom: High energy grating. One collected emission spectrum of CuSi0.1Ge0.9O3. The different diffraction orders are easily distinguishable. The energy window is 290-1370 eV.

Fig. 4. Left: Sketch of the geometry used to collect the diffused photons from the irradiated sample. Right: Measured scattered peak in first diffraction order at 120 eV on a FeS2 polished sample.

X-ray scattering experiments. The scattering angle between incoming and outgoing photons is 60°.

With such a small spot in the experimental chamber, and with the gratings used, in principle the energy resolution can be very high (up to 30,000 at the lower energies). In

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practice, the actual resolution is mainly limited by the detector used. The resolving power is tested by measuring the photons elastically scattered by the sample as they have the same energy distribution as the incoming radiation. Since the resolving power of the beamline is much higher then that of the spectrometer, the measured width of the scattered photons is a direct measure of the instrument’s resolution. Over most of the range, the resolution has been found to be 1 to 2 pixels, corresponding to a resolving power of about 1000 in most of the range (fig. 4).

As mentioned above, due to the low expected countrate, parallel detection such as a position sensitive detector must be chosen. The energy of a photon is associated with a position in space recorded by the detector. The ideal detector is one with good spatial resolution (much smaller than the dimension of the diffracted image) and the highest possible efficiency together with very low noise. We used a back illuminate CCD (Princeton Instruments) mounted almost perpendicularly to the incoming radiation (a configuration which maximizes the efficien-

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cy and permits us to have all of the active surface usable). The CCD has a pixel size of 20x20 µm2.

Some results In the first example, fig. 5, we show oxygen K emission spectra (measured in second diffraction order) recorded at different incidence photon energies, and at 60o angle of incidence. The selected incoming photon energies correspond to particular positions across the oxygen x-ray adsorption edge (right figure) of the Fe2O3 sample. The light was vertically polarized and only a selection of the measured spectra is shown. The dashed vertical lines on the left figure highlight the dispersion of the resonant emission peaks: note how the emission peak moves as a function of incident energy. This is the signature for the existence of resonant Raman scattering conditions – the opposite case, where the emission spectrum does not change energy with the incoming photon energy, is called incoherent scattering. The good transmission of the spectrometer allows us to measure the spectrum on the tail of the absorption curve where the resonant Raman spectrum is simpler than the incoherent spectrum.

The spectra can then be aligned on a “binding energy” scale, that is, with respect to the elastic peak, fig. 5, bottom. The intensities are normalised to the maximum.

Then the spectra are all similar with the main change being the ratio of inelastic to elastic intensity. The spectrum is then interpreted in terms of inelastic losses on scattering, in a way similar to Electron Energy Loss Spectroscopy.

Fig. 5. Top left: resonant X-ray emission spectra at the oxygen K edge of Fe2O3. Top right: corresponding NEXAFS spectrum showing the energies at which the emission spectra were taken. Bottom: all spectra aligned with respect to the elastic peak and normalised to maximum intensity.

In the next example, fig. 6, we show the resonant inelastic scattering spectrum of pyrite, FeS2, at the sulphur 2p edge. In the low energy of the sulphur resonance, the diffuse elastic peak is very strong, and in fact the maximum is well outside the range of the graph. The graph is scaled to show the inelastic structure better. Also in this case it is possible to achieve resonant Raman conditions.

The difficulty here is to find weak peaks at the foot of the elastic peak. This is possible and demonstrates the transmission function of the spectrometer is correct, that is Gaussian-like, and does not have long tails.

Lastly we show the spectrum of Ni at the 2p edge in the

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ferrite compound NiFe2O4. Ferrites are an interesting class of compounds in which there is often interplay between ferromagnetic iron and another 3d metal, in this case Ni. The Ni can be investigated by exciting it at the L2 edge and observing the Lα and Lβ emission due to transitions of 3d electrons to the core 2p holes. However the structure is complex as it consists of many multiplets, depending on how the angular momentum of the 2p hole and 3d electrons couple. A simpler alternative, in principle, is to observe the transitions of 3s electrons to the 2p holes. The 3s electrons have zero angular momentum and spin up or down only, greatly simplifying the multiplet structure. However there are a few drawbacks: firstly the peak is rather broad as the final state has a 3s hole which decays rapidly (large lifetime broadening); secondly the 3s->2p transition probability is much lower

than that of the 3d->2p transition, and therefore difficult to detect; and thirdly configuration interaction complicates the picture [7]. However the lack of intensity is not a problem, as can be seen from the spectra. Since the multiplet splitting results in only states with the 3s hole parallel or antiparallel to the Ni spin, and the splitting is large, the large lifetime width is not a problem.

The spectra show that there is an exchange splitting of these two lines, corresponding to final 3s holes whose spin is parallel or antiparallel to the majority spin of the Ni 3d electrons in the valence band. This exchange splitting is modified by configuration interaction with other excited states.

Conclusions The ComIXS spectrometer is now operating and providing good resolution and high efficiency. In combination with the variable polarization of the BACH beamline, it provides a powerful tool for investigating the electronic structure of solids and surfaces.

References

Fig. 6. Resonant emission spectra of FeS2. On the right the base of the elastic peaks are shown. On the left the Lα,β transition peaks (circa 145-150 eV) are visible. In the inset the absorption spectra at the S 2p edge is shown.

1. Nordgren J., Bray G., Cramm S., Nyholm R., Rubensson J.E., Wassdahl N., Rev. Sci. Instrum. 60, 1690 (1989) 2. Osborn K.D., Callcott T.A., Rev. Sci. Instrum. 66, 3131 (1995) 3. Callcott T.A., Tsang K.L., Zhang C.H., Ederer D.L., Arakawa E.T., Rev. Sci. Instrum. 57, 2680 (1986) 4. Rowland H.A., Philosophical Magazine 13, 469, (1882) 5. Mechanics made by "Strumenti Scientifici CINEL SrL", www.cinel.com 6. Zangrando M., Finazzi M., Paolucci G., Comelli G., Diviacco B., Walker R.P., Cocco D., Parmigiani F., Rev. Sci. Instrum. 72, 1313 (2001) 7. Taguchi M., Braicovich L., Borgatti F., Ghiringhelli G., Tagliaferri A., Brookes N.B., Uozumi T. and Kotani A., Phys. Rev. B 63, 245114 (2001)

Fig. 7. Upper panel: X-ray emission spectra from NiFe2O4 at incident energy 870 eV (Ni L2 edge). Lower panel: detail of the 3s->2p emission.

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Articolo ricevuto in redazione nel mese di Novembre 2003

AGGREGATION PHENOMENA IN SUPERCRITICAL CARBON DIOXIDE Fabrizio Lo Celsoa, Irene Ruffob and Roberto Trioloa* a Dip. di Chimica Fisica "F. Accascina", Università degli

studi di Palermo, Viale delle Scienze, 90128 Palermo (Italy) b Istituto Superiore "U. Mursia", Carini (Italy)

Small angle neutron and X-ray scattering (SANS and SAXS) are used to investigate the monomer–aggregate transition of fluorocarbon–hydrocarbon diblock copolymers in supercritical carbon dioxide. SANS data are analysed using a polydisperse sphere core–shell model. Synchrotron Time Resolved SAXS data have been collected by profiling the pressure at different temperatures, and critical micellization densities have been obtained for a series of diblock solutions. Finally pressure jump experiments, combined with synchrotron SAXS, have revealed two steps in the dynamics of the formation of the aggregates.

by changing temperature and pressure. Indeed the high compressibility of SCF allows large changes in density, in a continuous manner, with pressure and temperature, and therefore the solvent ability can be easily modulated. These characteristics have made SCF a valid and valuable alternative to classic solvents in many processes such as separation, extraction, purification, reaction and crystallisation. The supercritical state for carbon dioxide is easy to reach from the experimental point of view (P > 73 bar and T > 31 °C) and among all SCF, CO 2 has gained in recent years a very good reputation for the environment friendly character when compared to severely polluting organic solvents.

Carbon dioxide is already well known to be a good solvent in its supercritical state (scCO2) for high molecular weight (HMW) amorphous fluorinated polymers, silicones and, poly(ether-carbonate) copolymers [2], while being a marginal solvent for HMW hydrogenated poly-

Introduction Supercritical fluids (SCF) have been widely investigated and exploited, both in the industrial field and in pure academic research for their interesting physical and chemical properties [1].

The ability to penetrate and dissolve chemicals, typical of gas and liquid phases respectively, can be easily tuned

Fig. 1. Pressure dependence of the SANS pattern as obtained from selected runs of 6% w/V CO2 solution of 10.3 K PVAc -b- 60.4 PTAN at 40°C. Solid lines represent best fits according to eq.1.

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mers. Therefore the tailored synthesis of block copolymers formed by a CO2-phobic and a CO2-philic portions [3] may lead to systems that may give, in certain conditions (low pressure above the critical value), micelle-like aggregates in which a solvophobic core prevents contacts with the solvent, while the solvophilic shell allows interactions with scCO2 [4-8].

At relatively high pressures CO2 becomes a good solvent for both portions bringing to the destruction of such aggregates and giving fully solvated random coil chains.

The latter situation can be also obtained by reducing the temperature at constant pressure in a region where the density of scCO2 changes considerably. The monomeraggregate transition seems indeed to be driven mostly by the density of the solvent and not by temperature and pressure considered as independent variables. In this scenario [4-8] it appeared appropriate to introduce the so called “Critical Micellization Density” (CMD), the value of the solvent density at which a block copolymer undergoes trough a monomer-aggregation transition. The concentration of the whole copolymer in solution is also a variable that should be taken into account along with the chemical nature of the two blocks, especially that of the CO2-phobic portion.

There is another factor that has to be considered about the monomer-aggregate transition: generally a polymer could be polydispersed and the solvating power of

tially correlated in space, and influence the Gibbs free energy of the solution. Using a rather simple core(CO2phobic)-shell(CO2-philic) model for the aggregates [4-8] the amphipatic nature of several di-block copolymers constituted by an hydrogenated and a fluorinated portion has been investigated using the Small Angle Neutron Scattering technique (SANS), which has clearly revealed the monomer-aggregate transition, giving as well structural parameter, in various ranges of pressure and temperature.

High brilliance X-ray sources could give a very interesting insight on the aggregation phenomenon for such copolymers both from the static and the dynamic point of view. Time Resolved Small Angle X-rays Scattering (TR-SAXS) measurements give the possibility to test the reversibility and reproducibility of the monomer-aggregate transition in a wide range of thermodynamic conditions as well as the evaluation of the density of the solvent (CMD) at which the polymer undergoes a transition (from monomer to aggregate).

The dynamics of the aggregate formation can be assessed through pressure jump experiments across the CMD value in different block copolymer solutions to reveal relaxation effects. Therefore experiments of this kind, coupled with accurate SANS measurements, will help to characterise the kinetics of micelle formation/decomposition as a consequence of density jumps across the CMD.

Fig. 2. Fraction of aggregated polymer (same solution of figure 1) as function of pressure

Fig. 3. SANS patterns of a 7% (w/V) 10.3 K PVAc-b- 43.1 K PFOA in CO2 at 40°C.

scCO2 may vary depending on the molecular weight of the various fractions of the polymer; depending on the pressure scCO2 may be a good solvent for the majority of the polymer, while being a poor solvent for the high molecular weight fractions. Therefore, the HMW fractions may slightly affect the CMD because they could undergo concentration fluctuations which are exponen-

Scattering equations for SANS data analysis.

The coherent elastic scattering cross section dΣ(q)/dΩ is essentially the sum of two contributions arising from Nagg micelles in equilibrium with Np random coil (RC) chains and it can be calculated [5] according to: dΣ(q)/dΩ = Np [dΣ(q)/dΩ]RC +Nagg [dΣ(q)/dΩ]agg

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(1)

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As said earlier, below the CMD the block copolymer chains have a random coil configuration. The scattering equation is given by the Debye [9] equation modulated in amplitude by a term, I (0), function of the contrast and of the volume of the chain: [dΣ(q)/dΩ]RC= 2 I(0)[(q Rg)2+exp[(-q Rg)2]-1]/(q Rg)4 (2)

square of average scattering amplitude and is zero for monodisperse spherical particles. For slightly polydisperse spherical micelles it is roughly independent of q and it is a function of the same parameters used for the form factor, thus this term does not introduce additional fitting parameters. The polydispersity was described via a Shultz distribution of particles sizes [10].

where Rg is the radius of gyration of the polymer coils, 2θ (the scattering angle) and λ (wavelength of the radiation used) determine the momentum transfer q (=4πλ1sinθ), and [dΣ(q)/dΩ] RC is the differential elastic scattering cross section. When concentration fluctuations correlated exponentially in space are present [5] the scattering equation contains also a Lorentzian term. Above the CMD block copolymers showing amphiphilic behavior may aggregate forming core-shell spherical aggregates. In the case of polydisperse aggregates, the scattering equation per particle and per unit volume is given by equation (3) [10-12] [dΣ(q)/dΩ]agg = P(q) [S(q)PY + S(q)ECF] + ∆(q)

(3)

P(q) being the form factor for a polydisperse core-shell sphere, S(q)PY corresponds to the structure factor arising from hard-sphere model, modified for exponentially correlated fluctuations S(q)ECF ∝[1 +q2a2]-1, where a is the concentration fluctuation correlation length. The structure factor S(q), may be calculated in the framework of the Mean Spherical Approximation (MSA) [13] or of the Percus-Yevick Approximation (PY) [14]. For uncharged systems like those here presented the Percus-Yevick [19] structure function S(q)PY is a simple function [15] of the diameter σ and of volume fraction η of aggregate. ∆(q) is the difference between the average squared and the

Fig. 4. SANS curve of a 6% w/V solution of 7.6 K D3PVAc-b- 62.K PFOA at T = 40°C and P = 182 bar.

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Fig. 5. Pressure dependence of the SANS patterns for a 8% w/V solution of 10.3 K PVAc-b-43.1 K PFOA in liquid CO2 at 20°C. Runs are vertically shifted for clarity reasons.

Results and discussion In figure 1 it is reported the effect of the carbon dioxide density variation on a 6% w/V solution of PVAc-bPTAN (10.3 K polyvinyl acetate - b - 60.4 K 1,1,2,2tetrahydroperfluoro-octyl acrylate) at 40 °C (CO2 is in the supercritical region of the phase diagram).

It is clearly shown that, as the pressure (density) of sc CO2 decreases the scattering intensity curves show a peak characteristic of the formation of micellar-like aggregates. Best fits to experimental data were obtained by using equation 1 mentioned in the previous section; thus a polydisperse core-shell model was used to describe the structural parameters of the aggregates considering that a fraction a of non aggregate polymer was always present as random coil chains.

In table 1 results of the best fit are reported as function of carbon dioxide pressure (density). This model allows also the penetration of the solvent inside the core expressed by the fitting parameter CS. Indeed, at constant pressure and temperature, CS is given by the number of CO2 molecules penetrating in the micelle’s core normalized to its value at the lowest pressure at which the polymer is still dissolved in solution. The core solvation increases as the pressure increases reflecting also the change in the polydispersity parameter Z that indicates

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the increase of the stiffness of the core-shell interface due to the deep penetration of the solvent.

At higher pressures, approaching the CMD value, the aggregates start to break giving eventually a scattering curve (P = 358 bar, see fig. 1) typical of a random coil solution. From this scattering curve it is possible, by means of equation 2, to evaluate the radius of gyration (Rg) for

Fig. 6. TR-SAXS scattering intensity surface of a solution at 8 % w/V solution of 18K PtBMA-b- 65 K PFOMA (T = 45 °C) as function of pressure and momentum transfer.

the monomers (see table 1). To obtain the value of the CMD, related to the monomer-aggregate transition, a fit of the experimental fraction of aggregated polymer (1α) to a Boltzmann sigmoidal curve has been carried out.

In figure 2 such procedure is shown, the analytical expression for the solid line is

(Rg = 25Å while, by lowering the pressure (density), a quite strong peak appears in the scattering profile as a consequence of the aggregation of the isolated random coil chains (micelle’s radius is about 120 Å). In figure 4 it is reported the only SANS experiment for a sample in which the CO2-phobic block (PVAc) has been deuterated, using the method of internal contrast variation. The SANS curve refers to a 6% w/V solution of D3PVAc-bPFOA (7.6 K polyvinyl acetate - b – 62.2 K 1,1 dihydroperfluoro-octyl acrylate) at T = 40° C and P = 182 bar.

Keeping into account the different molecular weight of the two blocks the structural parameters obtained for the best fit (solid line) are in good agreement (within a 10% difference) with those found for the non deuterated sample. The aggregation phenomenon previously observed in supercritical CO2 has been observed as well in liquid CO2. Figure 5 shows unambiguously the transition from random coil to micelles for a series of pressures in the liquid region of the CO2 phase diagram (T = 20° C).

SANS experimental data as well as best fits, according to model expressed by eq.1, shown in figure 5 (data are vertically shifted for clarity), resemble those observed for the same and similar polymers previously reported.

Time resolved SAXS experiments, due to the high brilliance of synchrotron source, give the possibility to explore in more detail the aggregation process by profiling temperature and pressure in a continuous manner, and therefore changing the solvent density, to obtain reproducible results concerning the transition region.

In a typical TR-SAXS experiment frames were collected at the speed of 6 frames per minute while pressure was changing at the rate of 10 bar per minute. Figure 6 shows the TR-SAXS pattern as function of the momentum transfer q and of pressure P for a 8 % w/V solution of PtBMA-b-PFOMA (18 K poly(tert-butyl methacrylate) - b - 65 K poly(1,1-dihydroperfluorooctyl

Y(x) = A2 + (A1 – A2) / [1 + exp (x-x0)/dx], Where A1 and A2 are the upper and lower values of (1-α) respectively, x0 is the center of the transition (CMD) and dx is the width. The CMD concept rely upon the fact that the transition is mainly driven by the density of the solvent and, a clear indication of that can be seen in the aggregation number and polydispersity values away from the transition zone, which remain constants independently from the value of pressure. Figure 3 reports the SANS profiles for a 7 % w/v solution of PVAc-b-PFOA (10.3 K polyvinyl acetate - b – 43.1 K 1,1 dihydroperfluoro-octyl acrylate) obtained for two different values of pressure (density) at 40°C. Also in this case, in which the CO2-philic moiety is different from the previous polymer, there is a clear indication of a monomer-aggregate transition. At high solvent density the block copolymer is dissolved as random coil

Fig. 7. Scattering intensity profile of solution of fig. 6 at T= 45°C and q = 0:008 Å as function of pressure.

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Fig. 8. Pressure dependence of the SAXS pattern for polymer of fig. 6 at T= 40°C (c = 8% w/V). In the inset the pressure dependence of the SANS pattern (available in absolute units, although vertically shifted for clarity reasons) is reported at the analogous experimental conditions. Solid lines represent best fits according to eq.1.

methacrylate) at 45° C. At high pressures, in the range going from 852 to 725 bar, the scattering intensity does not show any significant variation especially at low q.

In this range of pressures the block copolymer is dissolved as random coils that give a small contribution to the scattering intensity.

As the pressure lowers (P < 700 bar), carbon dioxide becomes a poor solvent for the hydrocarbon part of the block copolymer, which therefore tends to promote the formation of micelles which will attractively interact.

Both P(q) and S(q) will give a strong contribution to the scattering intensity at low q.

Experimentally we notice that by lowering the pressure, the scattering intensity increases dramatically. It is therefore possible to evaluate the CMD by simply recording the value of the intensity (at the lowest Q accessible) as a function of the pressure P. Figure 7 reports the scattering intensity recorded at q = 0:008 Å as function of P. For this value of q the scattering intensity profile for pressure de-

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creasing from 850 to 535 bar, shows two different linear regimes with different slopes.

The breakpoint that indicates the onset of the aggregation process can be simply derived by the intersection of the lines that describe the two linear regimes. Therefore from the value of pressure at the breakpoint the CMD can be evaluated. In the inset of figure 8 we report SANS data for the same system in the same experimental conditions.

The above-mentioned model was able to fit data at 344 and 416 bar thus indicating the existence of a micellar morphology at the two thermodynamics states. In particular the aggregates are characterized by a core radius of 100 Å, while the overall micellar radius is 120 Å. A substantial degree of polydispersity has been observed in the micellar sizes. Moreover indications of CO2 intrusion inside the micellar core have been derived, in agreement with similar results obtained for the polymers previously described. Attempts to fit data at 691 bar failed.

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Fig. 9. Experimental CMD–temperature phase diagram for different PtBMA-b-PFOMA diblock copolymers with different molecular weight.

This is certainly due to the fact that the transition pressure aggregate-random coil is very close to this pressure; accordingly, at 691 bar a complex morphology can be expected, corresponding to a very polydisperse distribution of aggregation numbers for the incipient micellar aggregates and eventually to the existence of a variety of geometrically undefined aggregates.

In figure 8 SAXS data are also reported for PtBMA-bPFOMA at different pressures (we do not attempt to fit the present SAXS data as it was not possible to collect data in absolute units, which turns out to be crucial for a correct modeling of the experimental data). These data show that at pressures higher than 692 bar the blockcopolymers are in the random coil configuration.

At 692 bar, minor featureless deviations from the curve at 1028 bar indicate the presence of aggregates at this stage undefined. At lower pressures, however, a distinct increase of the intensity and the presence of relevant features in the SAXS patterns indicate the existence of well-

defined aggregates: this reflects and confirms the previous observation based on SANS data.

Figure 10 shows the CMD as function of the temperature for three PtBMA-b-PFOMA polymers having different molecular weights for the two blocks (7, 16, 18 K for the CO2-phobic block and 48, 52, 65 for the CO2-philic block respectively). These three systems were studied in order to rationalize their behaviour as function of the different solvophilic–solvophobic balance. Indeed there is a considerable change in the CMD value comparing the 7-b-48 and 16-b-52 systems, which are characterized by a very different molecular weight in the CO2-phobic block and a comparable molecular weight in the CO2-philic portion. The CMD is greater in the case of the 16-b-52 block copolymer where the molecular weight of the CO2-phobic block is over a factor two larger than the corresponding block in the 7-b-48 sample. This fact can be simply interpreted in terms of the higher CO2-phobic character of the 16-b-52 respect to the 7-b-48 polymer; since 16-b-

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Fig. 10. Time evolution of the integrated scattering intensity Qa after a pressure jump (from 948 to 308 bar) for pure CO2 (triangles) and for a solutionof 16 K PtBMA-b- 52 K PFOMA (circles) at T = 45°C. In the inset we report three scattering intensity curves taken during the P-jump experiment.

52 has a longer hydrocarbon chain, a higher pressure is needed, at constant temperature, to break the aggregates and dissolve the polymer as random coil.

The CMD value increases going from the 16-b-52 to the 18-b-65 system; in this case, although the CO2-philic portions of the two polymers have different weights, the 18b-65 system has a CO2-phobic part slightly larger than the 16-b-52 and that could justify in principle its slightly higher CMD. TR-SAXS measurements can be performed also to give a dynamical insight on the aggregation process through pressure jump experiments (P-jump).

In fact, if the pressure jumps across two states defined by the block copolymer as random coil and as aggregate, respectively, one may observe a relaxation effect due to the formation or the destruction of the aggregates. Figure 10. shows the results of a P-jump experiment where the initial pressure was such that the block copolymer (16-b-52

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at 45 °C) was dissolved as random coil, while the final pressure was set to a lower value where the polymer forms micelles. sampling frequency was 10 frames/s for the first 10 s and then 1 frame/s till the end (usually more than 60 s). The profile of the integrated intensity shows a first step characterized by a fast dynamics followed by a second slower process. For sake of clarity it is also reported the integrated intensity relative to a Pjump of pure CO2 to highlight the negligible effects of the solvent on the overall relaxation dynamics.

The integrated intensity profile was fitted with a linear combination of two exponential growth functions from which two characteristic relaxation times were derived.

Usually the fast process was characterized by a relaxation time close to one second (τ1) while for the slow process characteristic time constants (τ2) were almost one order of magnitude greater.

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These two step dynamics has been observed for the three block copolymers investigated in a wide range of experimental conditions and also as a function of the depth of the pressure jump and of the temperature. Also in the case of aqueous solutions two relaxation processes characterized by two well defined relaxation times have been reported [16].

More precisely the first time (of the order of microseconds) is related to the fast exchange of monomers between micelles and surrounding solution. The longer one (of the order of milliseconds or more) is related to the process of formation and breakdown of the aggregate. However, in the case of our block copolymers in scCO2, the origin of the first relaxation time is most likely different. A possible interpretation of our results can be given by assuming that the initial phase separation between the polymer and the solvent (fast process) is followed by a second slow reorientation process of the block copolymer in which micelles are formed. In other words, in the first stage the random coils loose part of their solvation creating a network of connected coils.

Only when the network has been formed, the chains may form the micellar aggregates. Evidently portions of this interconnected network reflect closely the structure of the aggregate which will be eventually formed. It has been observed that the deeper is the pressure jump, the faster is the aggregation process. Experimental results are in agreement with a model in which large zone of loosely bound aggregates are generated (first stage);

these zone will eventually lead to the formation of micelles (second stage) trough the orientation of the solvophilic segment of the block copolymer towards the solvent rich domains. Evidently the deeper is the penetration in the two phase zone, the faster is the formation of micelles. In the inset of figure 10 three scattering curves are reported referred to three different snapshots of the P-jump experiment in agreement with the previous interpretation. The curve characterized by the lowest intensity refers to the random coil solution at high pressure (948 bar) recorded before the P-jump. The second curve refers to the average scattering curve recorded in the first plateau of the integrated intensity right after the fast process (1.8 s < t < 3.8 s). The excess scattering is due to partial aggregation which originates the loose network already discussed. Therefore it is not surprising that this curve is also similar to the third scattering curve recorded in the second plateau after the second slow process (aggregation) has been completed (t > 20 s). Reverse P-jumps have been performed, starting from a low value of pressure and going towards the destruction of the aggregates at high pressure. In this case the relative dynamics is very fast, well below the resolution time of the experimental set up.

This results indicates that the solvation process which brings to the collapse of the aggregate does not go through the formation of a loose network, which is indeed essential in the case of the direct process already discussed.

P (bar)

(1-α)a

ρb

172 179 186 199 213 227 241 255 268 282 295 358

0.925 0.925 0.925 0.900 0.900 0.875 0.875 0.850 0.750 0.650

0.821 1.0 0.830 1.0(1) 0.838 1.1(1) 0.849 1.1(1) 0.858 1.1(1) 0.868 1.1(2) 0.879 1.1(3) 0.889 1.1(1) 0.900 1.6(2) 0.909 1.8(2) Transition zone ρ = 0.91 g/cm3 Random coil Rg = 43.5Å

a b c d e

0.917

CSc

Agg.d 29.5(1) 29.3(3) 29.2(5) 28.0(3) 24.8(5) 21.7(2) 19.4(2) 18.6(2) 14.8(3) 12.0(2)

Ze 17.0(1) 17.0(1) 17.4(1) 19.5(3) 18.4(5) 18.0(2) 17.0(2) 17.0(2) 17.0(2) 10.0(2)

fraction of aggregated polymer expressed as percent of the total polymer concentration (6% w/v) density of CO2 (g/cm3) core swelling ratio based on the number average molecular weight of the polymer; errors in parentheses aggregation numbers; errors in parentheses Schultz polydispersity parameter; errors in parentheses

Table 1. Structural parameters obtained from best fits according eq. 1. Results are referred to 6% w/V solution of 10.3 K PVAc -b- 60.4 PTAN at 40°C.

Vol. 9 n. 1 Febbraio 2004

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RASSEGNA SCIENTIFICA

Conclusions Structural and dynamic characterization of the aggregation process of diblock copolymers in scCO2 has been investigated by combining SANS and TR-SAXS measurements. Static results are in agreement with the presence, at low solvent density, of polydisperse spherical micelles with a CO2-phobic core formed by the hydrogenated moiety surrounded by a solvophilic shell constituted by the fluorinated part.

As the pressure increases micelles are destroyed and therefore the polymer is dissolved as a collection of random coils. The dynamics of the aggregation, investigated by means of P-jump experiments, has shown the presence of a two step process. Going from high to low pressures there is a fast process characterized by a phase separation between the solvent and the polymer followed by a second slower process where the reorientation of the solvophilic moiety toward the solvent rich domains leads to the formation of the micelles. The characteristic time of the slow process depends upon the depth of the pressure jump so that a faster dynamics is observed for deeper jumps.

References 1. See papers in December issue of Ind. Eng. Chem. Res, 39 (2000) 2. Sarbu T., Styranec T. and Beckman E.J., Nature 405, 165-168 (2000) 3. a) De Simone J.M., Guan Z. and Elsbernd C.S., Science 257, 945-947 (1992) b) J.M. DeSimone et al., Science, 265, 356-359 (1994) 4. J.B. McClain et. al, Science 274, 2049-2053 (1996) 5. Triolo F. et al., Langmuir 16, 416-421 (2000) 6. Triolo F. et al., J. Appl. Cryst. 33, 641- 644 (2000) 7. Triolo A. et al., Phys. Rev. E. 61, 4640-4643 (2000) 8. Triolo A. et al., Phys. Rev. E., 62, 5839-5842 (2000) 9. P. Debye, J. Appl. Phys., 15, 338 (1944) 10. R. Triolo and E. Caponetti, Adv. Coll. Inter. Sci., 32, 235 (1990) 11. W.L. Griffith, R. Triolo and A. Compere, Phys. Rev. A, 35, 2200-2206 (1987) 12. W.L. Griffith, R. Triolo and A. Compere, Phys. Rev. A, 33, 2197-2200 (1986) 13. J.A. Barker and D. Henderson, Rev. Mod. Phys., 48, 587 (1976) 14. N.W. Ashcroft and J. Leckner, Phys. Rev., 83, 145-151 (1966) 15. K. Percus and G. Yevick, Phys. Rev., 110, 1 (1958) 16. Patist A., Oh S.G., Leung R. & Shah D.O., Colloids and Surfaces A, 176, 3-16, (2001)

Acknowledgements We wish to thank the many colleagues and friends who helped us with the experiments reported here, particularly G.D. Wignall (ORNL, Oak Ridge, USA), P. Thyiagaraian (IPNS, Chicago, USA), R. K. Heenan and S. King (RAL, Chilton, UK), H. Amenitsch, M. Kriechbaum and M. Steinhart (Elettra Synchrotron, Trieste, Italy) and Prof. J. DeSimone and its group, for kindly providing the block copolymers. Financial support from CNR and from INFM is gratefully acknowledged.

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â&#x20AC;˘

Vol. 9 n. 1 Febbraio 2004

SCUOLE E CONVEGNI

REPORT ON THE AIC-SILS COMMON MEETING Trieste 21-25 July 2003 The annual meetings of the Italian

tural

to

could be fruitfully combined to un-

Crystallographic Association (AIC)

“Archeometry”. The parallel micro

derstand the complex harmonic and

and of the Italian Synchrotron Light

symposia were organized separately

non-harmonic vibrational aspects of

Society (SILS) have been jointly held

from the two societies. The AIC or-

atoms in cuprite-type structures. S.

21st

Investigations”

and

to July

ganized one micro symposium on

Zanardi (Univ. Ferrara) and G.D.

25th 2003, in the beautiful area of the

“Structural Crystallography” and

Gatta (Univ. Bayreuth) illustrated

International Center of Theoretical

one on “Experiments, Modeling and

the T- and P- properties of natural

Physics in Miramare, in the sur-

Theories on Crystal Growth Mecha-

zeolites. Several contributions em-

rounding of Trieste. More than 170

nisms at the Atomic- and Nano-

phasized the application of time-re-

people coming from different Italian

scale”; the SILS organized a micro

solved in situ diffraction methods to

universities and research centers at-

symposium on “Studies with Syn-

industrially important processes ac-

tended to the conference. The goal of

chrotron Radiation”.

tivated by temperature: the control

the joint meeting was to favor the in-

The microsymposium “Diffraction in

exerted by Pt metal in the perfor-

teraction between two communities

Material Sience”, chaired by G. Arti-

mance of TWC catalsts (A. Longo,

that have strong scientific common

oli, aimed to present recent and in-

Univ. Palermo), the combustion of

interests. The crystallographic com-

novative applications of synchrotron

methane on iron oxide-based cata-

munity, that usually uses laboratory

and laboratory based diffraction

lysts (M. Merlini, Univ. Milano), the

sources, had the possibility to be in-

techniques in the structural and

template burning within zeolite TS-1

formed on recent progresses of the

physical characterization of inorgan-

(M. Milanesio, Univ. del Piemonte

modern synchrotron radiation facili-

ic materials. The invited lecture of L.

Orientale). In situ synchrotron dif-

ties and instruments. On the other

Margulies (Risoe National Laborato-

fraction techniques, when combined

hand synchrotron radiation scien-

ry and ESRF) was particularly well

with simultaneous spectroscopic

tists had an overview of many scien-

suited, as it focused on state-of-the-

(XAS) or analytical (MS, DTA) tech-

tific problems today of interest in the

art of diffraction techniques for the

niques, are truly powerful tools and

structural characterization of differ-

study of the crystallite shape, tex-

allow time-resolved investigation of

ent class of materials, from amor-

ture, and structure in bulk polycrys-

complex processes involving fluid

phous material to proteins.

talline materials. Such experimental

and solid phases. They are expected

The conference was structured in

techniques promise to fill the exist-

to play major role in materials sci-

four common symposia, three paral-

ing gap between powders and single

ence in the near future.

lel micro symposia, and a common

crystals in the characterization of

The symposium “Progress of Struc-

poster section. In addition a com-

materials. C. Giannini (Univ. Bari)

tural Biology promoted by Synchro-

mon section was dedicated to the

presented novel algorithms being

tron Sources”, chaired by A. Zagari

presentation of the European Syn-

developed for the microstructural

was opened by Jens Nyborg whose

chrotron Radiation Facility ESRF by

characterization of powder crystal-

plenary lecture was focussed on the

F. Sette and of the ELETTRA Facility

lites from full-profile analysis. L.

knowledge gained by the Aarhus

by G. Paolucci. The common micro-

Paolasini (ESRF) presented recent

group on the various elongation fac-

symposia were dedicated to “Dif-

applications of resonant X-ray scat-

tors. He illustrated how their find-

fraction in Material Science”, to

tering in strongly correlated electron

ings are related to protein biosynthe-

“Progress of Structural Biology pro-

systems. A. Sanson (Univ. Trento)

sis that takes place on the ribosome.

moted by Synchrotron Sources”, to

showed how temperature-depen-

R. Berisio (Naples) presented recent

“Spectroscopic Methods for Struc-

dent XRD and EXAFS techniques

results, obtained in collaboration

in Trieste from July the

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

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Vol. 9 n. 1 Febbraio 2004

SCUOLE E CONVEGNI

with Ada Yonath, on the interactions

fraction is perfectly suited for the

diffraction technique, applied to sur-

between antibiotics and ribosome.

characterization of strain, size, shape

face science problems. The local

M. Reconditi (Firenze) and A. Bigi

and ordering of semiconductor

atomic structure of adsorbed species

(Bologna) elucidated the structural

nano-structures and how anomalous

or of thin layers grown on single

organization of other complex sys-

diffraction at grazing incidence can

crystal surfaces provide a better

tems, such as myosin analysed by X-

be applied to determine the physical

physical and chemical insight into

ray interference and collagen bun-

and chemical properties of nanos-

the basic mechanism of surface phe-

dles analysed by fiber diffraction re-

tructures. F. Boscherini, (Dep. of

nomena and can be used as a start-

spectively. Three young crystallogra-

Physics and INFM, University of

ing point for the calculation of the

phers, V. Calderone (Siena), S.

Bologna, ITALY) gave an overview

electronic properties. Photoelectron

Geremia (Trieste) and M. Degano

of the application of X-ray Absorp-

diffraction is an experimental tech-

(Milan) described the structure of

tion Spectroscopy (XAS) as a struc-

nique able to yield such information.

phosphatases, a mini-hemoprotein,

tural tool in material science. XAS

Its combination of chemical, struc-

and CD1d, respectively,the latter in

has considerably benefited from the

tural and surface sensitivity yields a

relation to the activation of im-

availability of third generation

quantitative description of the local

munoregulatory NKT cells. A com-

sources, which provide photon

atomic geometry of the first layers of

mon feature of all the experimental

beams of high brilliance over a wide

solids. The use of a high brilliance

works was the utilization of Euro-

energy range. Examples included

synchrotron radiation source makes

pean sources. These topics stress the

oxide surfaces, phase transitions,

it possible to study the local struc-

increasing complexity of the biologi-

strain, inter-diffusion and clustering

ture of atoms in different chemical

cal systems studied in Italy.

in semiconductor nano-structures,

environments and to make full use

The symposium “Spectroscopic

dilute nitride alloys, time-resolved

of the polarization properties of syn-

Methods for Structural Investiga-

and high pressure studies, boron de-

chrotron radiation. Examples of the

tions” organized by M. Pedio (TASC

fects in silicon oxide glasses, im-

strength of the method were given.

INFM Laboratory) and C.R. Natoli

planted atoms and clusters. M. Ben-

Prof. A. Morgante (Universita’ di Tri-

(Frascati laboratory) provided an

fatto, LNF - INFN Frascati, showed

este e TASC-INFM) gave the talk

overview of Synchrotron Radiation

the recent theoretical advances in

“Surface and interfaces systems

spectroscopic methods and their use

XAS interpretation. The physical

studied by grazing X-ray diffraction

in structural and morphological

process of the near edge structures

and Photoelectron diffraction tech-

studies of different systems, from bi-

(XANES) is today fully understood

niques”, explaining how the combi-

ology to semiconductor nanostruc-

in the framework of multiple scatter-

nation of the two techniques (Graz-

tures, focusing on the state of the art

ing theory and their analysis provide

ing Incidence X-ray Diffraction

achieved in the different cases. T.

a reliable structural technique. The

(GIXD), Photoelectron diffraction

Schulli (ESRF Grenoble) gave a talk

new MXAN code provides a quanti-

(PED)) allow the determination of

“Semiconductor nanostructures in

tative analysis of XANES spectra in

surface structural parameters paral-

the light of Synchrotron radiation”,

terms of structural parameters. A de-

lel and perpendicular to the inter-

focussed on the use of synchrotron

tailed discussion on the strength and

face. He gave examples of the

radiation on quantum dots, i.e.

limitations of the method applied to

growth of thin metal films on metal

nano-sized islands that show quan-

real systems has been provided. In

and semiconductor substrates and

tum confinement effects. Quantum

particular the interplay between

discussed the relation of the film

dots are systems far from thermody-

possible multi electronic configura-

crystalline structure to the electronic

namic equilibrium and their state is

tions composition of the ground

(Quantum Size Effect QSE) and

due to competing effects of growth

state with the local geometry of the

magnetic properties of systems built

kinetics and elastic energy mini-

absorbing site. G. Paolucci (ELET-

layer by layer. S. Di Matteo (INFN

mization. He showed how X-ray dif-

TRA) described the photoelectron

Frascati) showed how dichroic ef-

Vol. 9 n. 1 Febbraio 2004

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NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

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SCUOLE E CONVEGNI

fects in X-ray absorption spectra and

The symposium was also the occa-

synchrotron data have been de-

X-ray scattering in resonant condi-

sion for Italian scientist active in this

scribed. The following contributions

tions allows detecting magnetic

field to present their works. Prof. A.

have been devoted to new trends in

and/or structural phase transitions

Sgamellotti, University of Perugia,

chemistry (Use of crystal-state con-

involving symmetry changes. In the

talked about studies carried out on

formational analysis to define new

case of superconducting cuprates,

the structural characterization of me-

molecular tools for de novo design

Cr 2 O 3 , LaMnO 3 , and

V 2 O 5 he

diaeval pigments of ceramic lustre

of biological systems by M. Saviano),

showed how, depending on the ex-

and paintings by x-ray absorption

frontier researches on polymers

perimental setup, different physical

measurements. Prof. S. Quartieri,

(Crystal Structures From Fiber Dif-

quantities are involved in the

University of Messina, showed her

fraction Patterns by C. Tedesco) and

processes.

results on the understanding of the

on incommensurate crystals (Struc-

The microsymposium “Archeome-

technological processes used in a

ture analysis of incommensurate

try”, chaired by R. Felici (OGG-

mediaeval glass factory. Prof. U. Val-

modulated crystals: theory and ap-

INFM Grenoble) and M. Piacentini

busa gave a presentation on the fox-

plications by L. Righi). Two contri-

(University Roma La Sapienza) con-

ing of ancient paper by the use of x-

butions have been devoted to theo-

cerned with structural studies of ar-

ray imaging. Dr. Sanchez del Rio,

retical research: “Ab initio protein

chaeological materials by synchro-

ESRF-Grenoble, talked about the

phasing: the Patterson deconvolu-

tron radiation; it was shown how a

Maya blue a millenary organic clay

tion method in SIR2002” by R.

microscopic comprehension of the

whose structure and preparation

Caliandro and “The algebraic ap-

structure favors the understanding

procedures are still not fully under-

proach for neutron scattering” by S.

of the origin of objects, of the treat-

stood. Dr. F. D’Acapito presented

Ciccariello.

ment suffered during their produc-

some studies performed at the Ital-

The microsymposium “Experiments,

tions and of the transformation ex-

ian beamline GILDA of the Euro-

Modelling and Theories on Crystal

perienced during their ageing. For

pean Synchrotron, ESRF, in Greno-

Growth Mechanisms at the Atomic-

the first time in Italy, recent results

ble; Dr. F. Zanin showed case studies

and Nano-scale” was chaired by N.

obtained by x-ray methods in this

performed at the ELETTRA imaging

Lovergine.

field were illustrated in order to

beamline. The symposium was

The microsymposium “Studies with

stimulate the use of these probes by

closed by a round table chaired by

Synchrotron Radiation”, chaired by

archaeologists, cultural heritage re-

M. Piacentini, where the future de-

G. Stefani ( University Roma TRE),

sponsible and restorers. Two invited

velopment in this research area were

gathered eleven contributions that

speakers opened the micro sympo-

outlined.

outlined recent achievements in the

sium; E. Dooryhée, from the Labora-

The microsymposium “ Structural

characterization of ordered and dis-

toire de Cristallographie of CNRS in

Crystallography”, chaired by G. Cas-

ordered materials by highly energy

Grenoble gave a general talk entitled

carano ( CNR-Bari) was devoted to

and/or space resolved synchrotron

“Synchrotron x-ray analysis in Art

results and advances in structural

radiation experiments. Photoemis-

and Archaeology”, showing how x-

crystallography. It was opened by

sion with high energy and spatial

ray diffraction of cosmetic powders

the clear and exhaustive talk by

resolution was used by A. Goldoni

used by ancient Egyptians allows

Andy Fitch (ESRF Grenoble) on the

(Sincrotrone Trieste) to characterize

the understanding of the technologi-

“Use of synchrotron radiation in

carbon nanostructures whose size

cal processes used to prepare them.

crystal structure solution: state of the

ranges from pure and doped C60 to

T. Hansen, from the Institute Laue

art and perspectives”. During the

nanotubes, that are relevant for ap-

Langevin of Grenoble, showed how

talk the instrumentation available

plications and fundamental science

texture studies on ancient copper

for high-resolution powder diffrac-

as well. A novel photoelectron mi-

tools found in the Alps region allows

tion measurements and different ap-

croscope was used by A. Locatelli

the understanding of their origin.

proaches to solve structures from

(Sincrotrone Trieste) to investigate at

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

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Vol. 9 n. 1 Febbraio 2004

SCUOLE E CONVEGNI

the atomic scale the influence of

ing X-ray surface diffraction.

orations can be foreseen. This will

chemical reactions on the structure

R. Gotter (INFM-TASC) has dis-

increase the number of crystallogra-

of an Au submonolayer deposited

cussed recent achievements of a nov-

phers that use synchrotron radiation

on a Rh(110) clean surface. The high

el spectroscopic method aimed at in-

based experimental methods, mak-

spatial resolution achieved by X-ray

vestigating electron-electron correla-

ing full profit of the potentiality of

microdiffraction was applied by A.

tion in transition metals by correlat-

such source. The synchrotron radia-

Cedola (CNR-IFN) to study bone

ing in time, energy and momentum

tion community, is now much more

growth processes with unprecedent-

photo- and Auger-electrons originat-

aware of the scientific structural

ed details. Local order in nano-ag-

ing from the same core hole state.

problems today investigated in dif-

gregates was the common denomi-

Last but not least, R. Richter (ELET-

ferent fields by the crystallogra-

nator of three papers presented. F.

TRA) described a novel method use-

phers, of their needs and of the tools

d’Acapito (ESRF-Grenoble) reported

ful to investigte elusive radiative de-

they use.

on the use of X-ray absorption to

cay channels in light isolated atoms.

characterize the local order of Si ox-

58 poster different studies were pre-

ide in the vicinityof Er+3 ions in MBE

sented and discussed in a lively

grown structures. M. Carboni (INFM

Poster Section, mainly concerning

and Università Bologna) discussed

Structural Crystallography and Biol-

the coordination of B and P atoms

ogy, Crystal Growth, Synchrotron

embedded in borophosphosilicate. S.

Radiation Studies and Archeometry.

Bernstorff (Sincrotrone Trieste) re-

According to their tradition both the

ported on the growth mechanism of

Societies

CdS nanocrystals synthesized on a

searchers. AIC gave the award to

SiO2 surface as studied using Graz-

Marco Milanesio of the University of

ing Incidence X-ray diffraction.

Piemonte Orientale, who presented

Characterization of low dimension-

a review lecture on his scientific

ality structures of organic molecules

work on experimental and theoreti-

grown on inorganic substrates was a

cal structural chemistry. SILS award-

further topic of the session. G. Iucci (

ed four young scientists working in

INFM and Università Roma Tre) and

different fields. Namely R. Carboni

R. Carbone (INFM and Università

from Bologna working in the charac-

Tor Vergata) reported on recent

terization of semiconductor nanos-

spectroscopic investigations on mol-

tructures, A. Sanson from Trento

ecules deposited under vacuum: on

working on the dynamical proper-

experimental and theoretical studies

ties of oxides, M. Merlini from Mi-

of the adsorption of phenylacetylene

lano, working on heterogeneous cat-

on the Cu (100) surface the former

alytic systems for methane combus-

and on circular dichroism in core

tion and L. Di Costanzo from Tri-

level photoemission from mirror di-

este,working on protein crystallogra-

asteroisomers

phy.

adsorbed

on

awarded

young

re-

Si(100)2x1 the latter. The influence

The smooth and collaborative at-

of salt and anphilic molecules on the

mosphere present at the meeting fa-

alignment process of phospholipides

vored deep and extensive discus-

was investigated by H. Amentisch

sions between the two communities

(Austrian Academy of Sciences) us-

and the birth of new scientific collab-

Vol. 9 n. 1 Febbraio 2004

S. Mobilio

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SCUOLE E CONVEGNI

VII SCUOLA NAZIONALE DI LUCE DI SINCROTRONE Santa Margherita di Pula (Cagliari) 15 –26 settembre 2003 Nonostante le difficoltà finanziarie complessive della Ricerca nel nostro Paese in questo anno 2003, la SILS è riuscita ad organizzare la VII edizione della Scuola Nazionale di Luce di Sincrotrone, tenutasi nel periodo 1526 settembre. Come di consueto la Scuola si è tenuta presso l’Hotel Flamingo di Santa Margherita di Pula.

La Scuola ha ricevuto finanziamenti dall’Associazione Italiana di Cristallografia, dalla European Round Table for Synchrotron Radiation and FEL, dall’Istituto Nazionale di Fisica Nucleare, dal Magnifico Rettore dell’Università di Cagliari e dal Consorzio Interuniversitario per la Scienza e Tecnologia dei Materiali. La Scuola

ha inoltre avuto supporto dalla Sincrotrone Trieste SpA e dal Consiglio Nazionale delle Ricerche. È grazie a questi contributi che la Scuola ha avuto luogo; ed è stato anche possibile assegnare 15 borse di studio “Carla Cauletti” ad altrettanti studenti a copertura parziale delle spese di soggiorno. Inoltre 19 studenti sono stati esonerati dal pagamento della tassa di iscrizione.

Come per le edizioni precedenti (1990, 1992, 1995, 1997, 1999 e 2001) la Scuola ha offerto a persone già operanti nel campo della Luce di Sincrotrone o interessate ad entrarvi una panoramica attuale delle caratteristiche e potenzialità dell’uso del-

I partecipanti alla Scuola, assieme ai direttori e ad alcuni docenti.

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Vol. 9 n. 1 Febbraio 2004

la stessa. Le possibilità di ricerca con L.S. sono state affrontate sia da un punto di vista teorico che sperimentale e viste nella loro connessione a varie discipline (chimica, fisica, biologia, scienze della terra) e a diversi tipi di materiali. Hanno partecipato 34 studenti, per la maggior parte iscritti a cicli di dottorato. 20 studenti erano di area fisica, 10 di area chimica e 4 di area scienza della terra.

Come già nella precedente edizione, il periodo di due settimane complete ha permesso di svolgere complessivamente circa 70 ore di lezione con un programma che prevedeva anche alcune lezioni introduttive nelle quali sono stati forniti agli studenti gli

SCUOLE E CONVEGNI

elementi di base necessari per poter seguire al meglio le lezioni più specialistiche successive. La scuola ha coperto i seguenti argomenti: • introduzione alla LdS: sua generazione e proprietà (4 ore) • interazione radiazione-materia: 2.5 ore di introduzione seguite da 2 ore di approfondimento; • diffrazione di raggi X: aspetti generali; diffrazione da polveri; diffrazione a basso angolo; diffrazione da superfici; tecniche DAFS e MAD; onde stazionarie; biocristallografia con luce di sincrotrone (14.5 ore); • assorbimento di raggi X: introduzione generale alle spettroscopie EXAFS e XANES (XAS); lo scattering multiplo; applicazioni XAS alla scienza dei materiali e alla catalisi eterogenea; ReflEXAFS (13.5 ore); • spettroscopie di fotoemissione: introduzione generale; proprietà elettroniche e strutturali delle superfici; fotoemissione da livelli di core, da fase gassosa e in presenza di reazioni chimiche; fotoemissione risolta in spin; spettroscopie in coincidenza (11.5 ore); • dicroismo magnetico e naturale;

magnetismo e LdS (3.5 ore); di microscopia e di imaging (5.5 ore); • LdS e scienze della terra (2 ore); • proprietà vibrazionali con LdS: spettroscopia infrarossa e scattering di raggi X ad altissima risoluzione (3 ore); • spettroscopie di emissione nel campo dei raggi X molli (2 ore) ; • litografia (2 ore); • presentazione delle facilities ELETTRA e ESRF ed attività degli enti di ricerca italiani (5ore).

Le lezioni hanno visto alternarsi 32 differenti docenti, di cui uno straniero J. Baruchel di ESRF. Al termine della Scuola i partecipanti hanno compilato un questionario anonimo con domande sugli argomenti della Scuola, sulla struttura del programma, sulla validità delle lezioni e del materiale didattico distribuito. I questionari si sono già in passato rivelati prezioso strumento per calibrare sempre al meglio i contenuti delle lezioni e le loro propedeuticità. Agli studenti è stata distribuita una copia del volume dei proceedings della edizione del 2001, aggiornati per la presente edizione, vo• tecniche

lume che raccoglie la maggior parte delle lezioni. Per le lezioni non presenti sul volume, i docenti hannno distribuito le fotocopie dei lucidi mostrati. Il volume come è noto è stato pubblicato dalla SIF nella collana “Atti di Conferenze” volume n.82, con il titolo: “Synchrotron Radiation: fundamentals, methodologies and applications”.

Tra docenti e studenti si è creato ben presto un clima di cordialità e affiatamento, favorito dalle splendide spiagge e dall’ottimo clima; molto apprezata è stata la gita sociale, con la visita al nuraghe di Barumini ed alla Giara di Gesturi, seguita dalla cena sociale svoltasi in un agriturismo di Villanovafranca che ha permesso a molti di scoprire la cucina ed il folklore sardi. Infatti il gruppo folk di Tuili ha allietato i presenti con danze e canti popolari.

L’indubbio successo registrato anche da questa edizione della Scuola, suggerisce di organizzare senz’alro nel 2005 la VIII edizione.

Settimio Mobilio e Gilberto Vlaic Direttori della Scuola

3rd EUROPEAN CONFERENCE ON NEUTRON SCATTERING Montpellier (France) 3 - settembre 2003 The European Conference on Neutron Scattering – organized every two years – took place in Montpellier, France, from 3 to 6 September. It cov-

Italian scientists on the way to the conference

ered the broad field investigated by neutron scattering, which includes physics, chemistry, biology, materials sciences and applications. Progress in instrumentation was also an important aspect of the conference.

The Scientific Programme consisted of 82 oral papers including 9 invited plenary lectures and 16 invited speakers. More than 630 posters were also presented and discussed in devoted sessions with over 618 attendees. A special session during the Conference was devoted to the presentation of The Walter Hälg Prize – awarded every two years by the Eu-

Vol. 9 n. 1 Febbraio 2004

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ropean Neutron Scattering Association, ENSA. The 2002 prize was awarded to Professor Roger A. Cowley of the University of Oxford, U.K., in recognition of his seminal work in the application of neutron scattering techniques to the study of quantum excitations in a broad field of condensed matter physics. The meeting was an overall great success and was very well organised.

Giovanna Cicognani Institut Laue-Langevin Grenoble Cedex 9, France

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VARIE

COMMISSIONE NEUTRONI DELL’INFM PROMOZIONE E SVILUPPO DELLA SPETTROSCOPIA NEUTRONICA Iniziative 2004 rivolte a giovani ricercatori

Bando per stages presso Large Scale Facilities di Neutroni La Commissione Neutroni dell'INFM ha istituito un fondo dedicato agli studenti che intendono effettuare uno Stage presso una sorgente di neutroni europea, finalizzato alla conoscenza dello scattering di neutroni come tecnica per l'indagine fine della materia condensata. Il Bando è indirizzato a: - studenti dell'ultimo anno e laureandi dei corsi di laurea delle Facoltà di Scienze M.F.N e Ingegneria del vecchio ordinamento - studenti del terzo anno dei corsi di

studio del nuovo ordinamento che prevedano attività di tirocinio presso laboratori anche esterni alla struttura universitaria.

Allo studente verrà conferito un contributo per la copertura spese fino ad un massimo di 4.500 euro complessive o di 750 euro al mese fino ad un massimo di 6 mesi. Gli studenti che intendano partecipare al Bando per usufruire del contributo devono far pervenire la proposta di attività, firmata dal docente responsabile o dal presidente del Consiglio di Corso di Laurea o di Studi, a: Dr. Elisabetta Narducci, INFM, Corso Perrone, 24 - 16152 Genova, email narducci@infm.it.

In assenza di un piano di ricerca specifico, lo studente che intenda partecipare verrà inserito presso i gruppi INFM operanti sul sito di Grenoble, e in particolare presso i

CRG sviluppati dall'INFM all'Institut Laue Langevin. In questo caso, è comunque obbligatorio far pervenire, oltre alla domanda, l'autorizzazione firmata dal presidente del Consiglio di Corso di Laurea o di Studi dell'Università di appartenenza e l'elenco degli esami sostenuti con la votazione riportata. Al termine dello stage, lo studente dovrà far pervenire un resoconto dell'attività svolta alla Commissione Neutroni.

L'assegnazione del contributo verrà definita dalla Commissione Neutroni dell'INFM e sarà comunicata tempestivamente agli interessati. Il Bando rimane aperto fino al 31 dicembre 2004 e le domande possono essere inviate, secondo le modalità indicate, in qualunque momento.

A NEW HOME FOR THE ESS WEBSITE !

The ESS information - technical description, science case, reference updated documentation, history, last news... - is still available and easily accessible.

The European Spallation Source Website is now part of the "European portal for neutron scattering and muon spectroscopy" - a portal designed as an entry point to available resources for those working in neutrons and muons.

The "European portal for neutron scattering and muon spectroscopy is a common entry point to facilities

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and information. It is a joint initiative by all European organisations engaged in neutrons and muons, and supported by the European Commission through FP5 and FP6.

It is an ambitious project and we are continuously working on it to provide all the information. We invite

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you to visit the new pages and would encourage you to to send us your comments and suggestions. http://www.neutron-eu.net/

Kurt Clausen - Former ESS director Ana Claver - Webmaster

VARIE

www.cnr.it/neutronielucedisincrotrone Aims and Scope Neutron and synchrotron radiation sources and their associated technologies have expanded at an extremely rapid rate during the past 20-25 years. Many new neutrons and synchrotron radiation sources have been constructed and exploited worldwide.

Notiziario Neutroni e Luce di Sincrotrone, published bi-yearly since 1996, aims to addresses the needs of neutron and synchrotron users worldwide. The magazine highlights the most notable success in the field of neutron and synchrotron radiation research as well as provides information on the instrumentation developments taking place at the Large Scale Facilities. Since the year 2000 English has become the official language of the journal and the Italian language is kept only for a limited number of items mostly concerning the Italian community.

Articles and a format are modelled with a broad scope to ensure interest to neutron and synchrotron users.

Appointed correspondents from most facilities around the world report on the major activities and most recent developments at their centres.

The letter includes improvements to the machines and the rapidly increasing number of new applications. The magazine might include review articles on specific scientific and technical fields and reports on projected new sources with progress updates plus meeting reports, announcements. The growth of this field will require the magazine's continued evolution.

Notiziario Neutroni e Luce di Sincrotrone online is a free service, allowing access to navigable HTML and PDF versions of the full contents of present and past issues of the journal. Subscription is free but it is a prerequisite for receiving the printed version of the journal.

SUBSCRIBE NOW !!

S

T A

F

F

Editor in Chief

Editorial Office

C. Andreani carla.andreani@roma2.infn.it

D. Catena desy.catena@uniroma2.it

Consulting Editors

Editorial Production

L. Avaldi lorenzo.avaldi@mlib.cnr.it

OM Grafica omgrafica@omgrafica.it Via F. Luscino 73, Roma

F. Aliotta aliotta@adam1.its.me.cnr.it

On line Version at

F. Carsughi F.Carsughi@alisf1.univpm.it

www.cnr.it/neutronielucedisincrotrone

by V. Buttaro vincenzo.buttaro@roma2.infn.it

G. Paolucci giorgio.paolucci@elettra.trieste.it Executive Editors M. Apice, P. Bosi

Vol. 9 n. 1 Febbraio 2004

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CALENDARIO

Feb 22 - 27, 2004

HANOI, VIETNAM

International Conference on Dynamics of Disordered Materials on the Nanometer Scale Contact: David L. Price E-mail: price@cnrs-orleans.fr URL: http://www.engconfintl.org/4ah.html

Mar 30-Apr 1, 2004

Collective Action for Nomadic Small-Angle Scatterers (can SAS-IV) Contact: Steve King E-mail: S.M.King@rl.ac.uk URL: http://www.isis.rl.ac.uk/LargeScale/LOQ/ cansas/cansas4/cansas4.htm

Jun 1 - 4, 2004

GRENOBLE CEDEX, FRANCE

Workshop at ILL: “Precision Measurements with Slow Neutrons at NIST”

TENNESSEE, USA

11th Beam Instrumentation Workshop (BIW04) Contact: Myra J. Fultz E-mail: fultzmj@ornl.gov URL: http://www.sns.gov/biw/04/

WASHINGTON DC, USA

5th International Workshop on Polarized Neutrons in Condensed Matter Investigation (PNCMI 2004) Contact: Frank Klose E-mail: pncmi2004@ornl.gov URL: http://www.sns.gov/PNCMI2004/

Jun 2 - 4, 2004 May 3 - 6, 2004

OXON, UK

LONDON, UK

Material Congress 2004 (IOM3) URL: http://www.iom3.org/congress2004

Apr 5 - 7, 2004

May 12 - 14, 2004

GRENOBLE CEDEX, FRANCE

Workshop at ILL: “CCP13/Fibre Diffraction & Non Crystalline Diffraction Workshop”

Jun 5 - 12, 2004

GRENOBLE CEDEX, FRANCE

Workshop at ILL: “European Bombannes Summer School” May 6 - 7, 2004

GRENOBLE CEDEX, FRANCE

Workshop at ILL: “First joint workshop of the IN2P3 and the ILL on Nuclear and Particle Physics”

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CALENDARIO

Jun 6-10, 2004

MARYLAND, USA

American Conference on neutron Scattering Contact: James Jorgensen (ANL), General Chair and Jeffrey Lynn (NIST), Co-program Chair E-mail: jjorgensen@anl.gov jeffrey.lynn@nist.gov URL: http://www.ncnr.nist.gov/acns/index.html

Jun 28, 2004

DENVER, COLORADO, USA

Advances in Computational Methods for X-Ray and Neutron Optics Contact: Manuel Sanchez del Rio E-mail: srio@esrf.fr URL: http://spie.org/Conferences/Calls/04/am/ conferences/index.cfm?fuseaction=AM304

WARWICK, UK Sep 1 - 4, 2004

New Perspectives in Neutron Science 2004 (NPNS 2004)

Jun 29 - 30, 2004

Aug 2 - 6, 2004

ARCACHON, FRANCE

7th International Conference on Quasi-Elastic Neutron Scattering (QENS 2004) E-mail: info@qens2004.org URL: http://www.qens2004.org

WARWICK, UK

Neutron & Muon Users Meeting 2004 (NMUM 2004) Oct 20 - 23, 2004 Jul 11 - 17, 2004

METZ, FRANCE

GRENOBLE CEDEX, FRANCE

Workshop at ILL: “International Workshop on Medium Pressure Advanced for Neutron Scattering”

12th International Conference on Liquid and Amorphous Metals LAM12 Nov 28 - Dec 2, 2005 Jul 19 - 23, 2004

PRAGUE, CZECH REPUBLIC

20th General Conference of the Condensed Matter Division (EPS) URL: http://cmd.karlov.mff.cuni.cz/CMD/

SYDNEY, AUSTRALIA

International Conference on Neutron Scattering (ICNS 2005) URL: http://www.sct.gu.edu.au/icns2005/

Vol. 9 n. 1 Febbraio 2004

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SCADENZE

Scadenze per richieste di tempo macchina presso alcuni laboratori di Neutroni

Scadenze per richieste di tempo macchina presso alcuni laboratori di Luce di Sincrotrone

BENSC

ALS

Le scadenze per il prossimo call for proposals sono il 15 marzo e il 15 settembre 2004

Le prossime scadenze sono il 15 marzo 2004 (cristallografia macromolecolare) e il 1 giugno 2004 (fisica)

ILL BESSY

La scadenza per il prossimo call for proposals è il 26 febbraio 2004

Le prossime scadenze sono il 15 febbraio e il 4 agosto 2004

ISIS DARESBURY

Le scadenze per il prossimo call for proposals sonoil 16 aprile e il 16 ottobre 2004

Le prossime scadenze sono il 30 aprile e il 31 ottobre 2004

LLB-ORPHEE-SACLAY La scadenza per il prossimo call for proposals è il 1 ottobre 2004 per informazioni: Secrétariat Scientifique du Laboratoire Léon Brillouin, TMR programme, Attn. Mme C. Abraham, Laboratoire Léon Brillouin, CEA/SACLAY, F-91191 Gif-sur-Yvette, France.

Tel: 33(0)169086038; Fax: 33(0)169088261 e-mail: abraham@bali.saclay.cea.fr http://www-llb.cea.fr

ELETTRA Le prossime scadenze sono il 28 febbraio e il 31 agosto2004

ESRF Le prossime scadenze sono il 1 marzo e il 1 settembre 2004

GILDA (quota italiana) Le prossime scadenze sono il 1 maggio e il 1 novembre 2004

SINQ Le scadenze per il prossimo call for proposals sono il 15 Maggio ed il 15 Novembre 2004 To be addressed to Scientific Coordination Office WHGA/147 Paul Scherrer Institute CH-5232 Villigen PSI, Switzerland Phone: +41 56 310 2087 Fax: +41 56 310 2939 e-mail: sinq@psi.ch

HASYLAB (nuovi progetti) Le prossime scadenze sono il 1 marzo, il 1 settembre e il 1 dicembre 2004

LURE La prossima scadenza è il 30 ottobre 2004

MAX-LAB FZ Juelich

La scadenza è approssimativamente febbraio 2004

Round 1/2004 of "Juelich Neutrons for Europe" is open for proposals until February 1, 2004.

All neutron scattering instruments at FZ Juelich are open to proposals.

General information about the instruments can be obtained from http://www.neutronscattering.de

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NSLS Le prossime scadenze sono il 31 gennaio, il 31 maggio e il 30 settembre 2004

Vol. 9 n. 1 Febbraio 2004

FACILITIES

LUCE DI SINCROTRONE SYNCHROTRON SOURCES WWW SERVERS IN THE WORLD (http://www.esrf.fr/navigate/synchrotrons.html) CAMD Center Advanced Microstructures & Devices Louisiana State University, Center for Advanced Microstructures & Devices, 6980 Jefferson Hwy., Baton Rouge, LA 70806 tel: (225) 578-8887 fax. (225) 578-6954 Fax http://www.camd.lsu.edu/ Tipo: D Status: O

ALS Advanced Light Source Berkeley Lab, 1 Cyclotron Rd, MS6R2100, Berkeley, CA 94720 tel: +1 510.486.7745 fax: +1 510.486.4773 http://www-als.lbl.gov/ Tipo: D Status: O

ANKA Forschungszentrum Karlsruhe Institut für Synchrotronstrahlung Hermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen, Germany tel: +49 (0)7247 / 82-6071 fax: +49-(0)7247 / 82-6172 http://hikwww1.fzk.de/iss/

CHESS Cornell High Energy Synchr. Radiation Source Wilson Lab., Cornell University Ithaca, NY 14853, USA tel: +1 607 255 7163 fax: +1 607 255 9001 http://www.tn.cornell.edu/ Tipo: PD Status: O

CLS Canadian Light Source, University of Saskatchewan, 101 Perimeter Road, Saskatoon, SK., Canada. S7N 0X4 http://www.cls.usask.ca/ Tipo:D status:C

APS Advanced Photon Source Bldg 360, Argonne Nat. Lab. 9700 S. Cass Avenue, Argonne, Il 60439, USA tel:+1 708 252 5089 fax: +1 708 252 3222 http://epics.aps.anl.gov/welcome.html Tipo: D Status: C

ASTRID ISA, Univ. of Aarhus, Ny Munkegade, DK-8000 Aarhus, Denmark tel: +45 61 28899 fax: +45 61 20740 http://www.aau.dk/uk/nat/isa Tipo: PD Status: O

DAFNE INFN Laboratori Nazionali di Frascati, P.O. Box 13, I-00044 Frascati (Rome), Italy tel: +39 6 9403 1 fax: +39 6 9403304 http://www.lnf.infn.it/ Tipo:P Status: C

DELTA Universität Dortmund,Emil Figge Str 74b, 44221 Dortmund, Germany tel: +49 231 7555383 fax: +49 231 7555398 http://prian.physik.uni-dortmund.de/ Tipo: P Status: C

BESSY Berliner Elektronen-speicherring Gessell.für Synchrotron-strahlung mbH BESSY GmbH, Albert-Einstein-Str.15, 12489 Berlin, Germany, tel +49 (0)30 6392-2999 fax +49 (0)30 6392-2990 http://www.bessy.de Tipo: D Status: O

BSRL Beijing Synchrotron Radiation Lab. Inst. of High Energy Physics, 19 Yucuan Rd.PO Box 918, Beijing 100039, PR China tel: +86 1 8213344 fax: +86 1 8213374 http://solar.rtd.utk.edu/~china/ins/IHEP/bsrf/bsrf.html Tipo: PD Status: O

DIAMOND Diamond Light Source Ltd, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX http://www.diamond.ac.uk/ Tipo:D status:C

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FACILITIES

ELETTRA Sincrotrone Trieste, Padriciano 99, 34012 Trieste, Italy tel: +39 40 37581 fax: +39 40 226338 http://www.elettra.trieste.it Tipo: D Status: O

Kurchatov Kurchatov Inst. of Atomic Energy, SR Center, Kurchatov Square, Moscow 123182, Russia tel: +7 95 1964546 Tipo: D Status: O/C

ELSA Electron Stretcher and Accelerator Nußalle 12, D-5300 Bonn-1, Germany tel:+49 288 732796 fax: +49 288 737869 http://elsar1.physik.uni-bonn.de/elsahome.html Tipo: PD Status: O

LNLS Laboratorio Nacional Luz Sincrotron CP 6192, 13081 Campinas, SP Brazil tel.: (+55) 0xx19 3287.4520 fax: (+55) 0xx19 3287.4632 http://www.lnls.br/ Tipo: D Status: C

ESRF European Synchrotron Radiation Lab. BP 220, F-38043 Grenoble, France tel: +33 476 882000 fax: +33 476 882020 http://www.esrf.fr/ Tipo: D Status: O

LURE Bât 209-D, 91405 Orsay ,France tel: +33 1 64468014; fax: +33 1 64464148 http://www.lure.u-psud.fr Tipo: D Status: O

EUTERPE Cyclotron Lab.,Eindhoven Univ. of Technol, P.O.Box 513, 5600 MB Eindhoven, The Netherlands tel: +31 40 474048 fax: +31 40 438060 Tipo: PD Status: C

MAX-Lab Box 118, University of Lund, S-22100 Lund, Sweden tel: +46 46 109697 fax: +46 46 104710 http://www.maxlab.lu.se/ Tipo: D Status: O

HASYLAB Notkestrasse 85, D-2000, Hamburg 52, Germany tel: +49 40 89982304 fax: +49 40 89982787 http://www-hasylab.desy.de/ Tipo: D Status: O

NSLS National Synchrotron Light Source Bldg. 725, Brookhaven Nat. Lab., Upton, NY 11973, USA tel: +1 516 282 2297 fax: +1 516 282 4745 http://www.nsls.bnl.gov/ Tipo: D Status: O

INDUS Center for Advanced Technology, Rajendra Nagar, Indore 452012, India tel: +91 731 64626 http://www.ee.ualberta.ca/~naik/accind1.html Tipo: D Status: C

NSRL National Synchrotron Radiation Lab. USTC, Hefei, Anhui 230029, PR China tel +86-551-5132231,3602034 fax +86-551-5141078 http://www.nsrl.ustc.edu.cn/en/enhome.html Tipo: D Status: O

KEK Photon Factory Nat. Lab. for High Energy Physics, 1-1, Oho, Tsukuba-shi Ibaraki-ken, 305 Japan tel: +81 298 641171 fax: +81 298 642801 http://www.kek.jp/ Tipo: D Status: O

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Pohang Pohang Inst. for Science & Technol., P.O. Box 125 Pohang, Korea 790600 tel: +82 562 792696 fax: +82 562 794499 http://pal.postech.ac.kr/english.html Tipo: D Status: C

Vol. 9 n. 1 Febbraio 2004

FACILITIES

Siberian SR Center Lavrentyev Ave 11, 630090 Novosibirsk, Russia tel: +7 383 2 356031 fax: +7 383 2 352163 http://ssrc.inp.nsk.su/english/load.pl?right=general.ht ml Tipo: D Status: O

SRRC SR Research Center 1, R&D Road VI, Hsinchu Science, Industrial Parc, Hsinchu 30077 Taiwan, Republic of China tel: +886 35 780281 fax: +886 35 781881 http://www.srrc.gov.tw/ Tipo: D Status: O

SLS Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI http://sls.web.psi.ch/view.php/about/index.html Tipo: D Status: O

SSRL Stanford SR Laboratory 2575 Sand Hill Road, Menlo Park, California, 94025, USA tel: +1 650-926-4000 fax: +1 650-926-3600 http://www-ssrl.slac.stanford.edu/welcome.html Tipo: D Status: O

SPring-8 2-28-8 Hon-komagome, Bunkyo-ku ,Tokyo 113, Japan tel: +81 03 9411140 fax: +81 03 9413169 http://www.spring8.or.jp/top.html Tipo: D Status: C

SOLEIL Centre Universitaire - B.P. 34 - 91898 Orsay Cedex http://www.soleil.u-psud.fr/ Tipo: D Status:C

SOR-RING Inst. Solid State Physics S.R. Lab, Univ. of Tokyo, 3-2-1 Midori-cho Tanashi-shi, Tokyo 188, Japan tel: +81 424614131 ext 346 fax: +81 424615401 Tipo: D Status: O

SRC Synchrotron Rad. Center Univ.of Wisconsin at Madison, 3731 Schneider DriveStoughton, WI 53589-3097 USA tel: +1 608 8737722 fax: +1 608 8737192 http://www.src.wisc.edu Tipo: D Status: O

SRS Daresbury SR Source SERC, Daresbury Lab, Warrington WA4 4AD, U.K. tel: +44 925 603000 fax: +44 925 603174 E-mail: srs-ulo@dl.ac.uk http://www.dl.ac.uk/home.html Tipo: D Status: O

SURF III B119, NIST, Gaithersburg, MD 20859, USA tel: +1 301 9753726 fax: +1 301 8697628 http://physics.nist.gov/MajResFac/surf/surf.html Tipo: D Status: O

TERAS ElectroTechnical Lab. 1-1-4 Umezono, Tsukuba Ibaraki 305, Japan tel: 81 298 54 5541 fax: 81 298 55 6608 Tipo: D Status: O

UVSOR Inst. for Molecular ScienceMyodaiji, Okazaki 444, Japan tel: +81 564 526101 fax: +81 564 547079 Tipo: D Status: O

D = macchina dedicata

D = dedicated machine

PD = parzialmente dedicata

PD = partially dedicated

P = in parassitaggio

P = parassitic

O = macchina funzionante

O = operating machine

C = macchina in costruzione

C = machine under construction

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FACILITIES

NEUTRONI NEUTRON SCATTERING WWW SERVERS IN THE WORLD (http://www.isis.rl.ac.uk) FRG-1 Geesthacht (D) Type: Swimming Pool Cold Neutron Source.

Flux: 8.7 x 1013 n/cm2/s Address for application forms and informations: Reinhard Kampmann, Institute for Materials Science, Div. Wfn-Neutronscattering, GKSS, Research Centre, 21502 Geesthacht, Germany Tel: +49 (0)4152 87 1316/2503; Fax: +49 (0)4152 87 1338 E-mail: reinhard.kampmann@gkss.de http://www.gkss.de

Atominstitut Vienna (A) Facility: TRIGA MARK II Type: Reactor. Thermal power 250 kW. Flux: 1.0 x 1013 n/cm2/s (Thermal); 1.7 x 1013 n/cm2/s (Fast) Address for information: 1020 Wien, Stadionallee 2 Prof. H. Rauch Tel: +43 1 58801 14111; Fax: +43 1 58801 14199 E-mail: boeck@ati.ac.at http://www.ati.ac.at Wap: wap.ati.ac.at

HMI Berlin BER-II (D) Facility: BER II, BENSC Type: Swimming Pool Reactor. Flux: 2 x 1014 n/cm2/s Address for application forms: Dr. Rainer Michaelsen, BENSC, Scientific Secretary, Hahn-Meitner-Insitut, Glienicker Str 100, 14109 Berlin, Germany Tel: +49 30 8062 2304/3043; Fax: +49 30 8062 2523/2181 E-mail: michaelsen@hmi.de http://www.hmi.de/bensc

NRU Chalk River Laboratories The peak thermal flux 3x1014 cm-2 sec-1 Neutron Program for Materials Research National Research Council Canada Building 459, Station 18 Chalk River Laboratories Chalk River, Ontario Canada K0J 1J0 Phone: 1 - (888) 243-2634 (toll free) Phone: 1 - (613) 584-8811 ext. 3973 Fax: 1- (613) 584-4040 http://neutron.nrc-cnrc.gc.ca/home.html

IBR2 Fast Pulsed Reactor Dubna (RU) Type: Pulsed Reactor.

Flux: 3 x 1016 (thermal n in core) Address for application forms: Dr. Vadim Sikolenko, Frank Laboratory of Neutron Physics Joint Institute for Nuclear Research 141980 Dubna, Moscow Region, Russia.

Tel: +7 09621 65096; Fax: +7 09621 65882 E-mail: sikolen@nf.jinr.dubna.su http://nfdfn.jinr.ru/flnph/ibr2.html

Budapest Neutron Centre BRR (H) Type: Reactor. Flux: 2.0 x 1014 n/cm2/s Address for application forms: Dr. Borbely Sándor, KFKI Building 10, 1525 Budapest, Pf 49, Hungary E-mail: Borbely@power.szfki.kfki.hu http://www.iki.kfki.hu/nuclear

FRJ-2 Research Reactor in Jülich (D) Type: Dido reactor. Flux: 2 x 1014 n/cm2/s Prof. D. Richter, Forschungszentrums Jülich GmbH, Institut für Festkörperforschung, Postfach 19 13, 52425 Jülich, Germany Tel: +49 2461161 2499; Fax: +49 2461161 2610 E-mail: d.richter@kfa-juelich.de http://www.kfajuelich.de/iff/Institute/ins/Broschuere_NSE/

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ILL Grenoble (F) Type: 58MW High Flux Reactor.

Flux: 1.5 x 1015 n/cm2/s Scientific Coordinator Dr. G. Cicognani, ILL, BP 156, 38042 Grenoble Cedex 9, France Tel: +33 4 7620 7179; Fax: +33 4 76483906 E-mail: cico@ill.fr and sco@ill.fr http://www.ill.fr

Vol. 9 n. 1 Febbraio 2004

FACILITIES

IPNS Intense Pulsed Neutron at Argonne (USA) for proposal submission by e-mail send to cpeters@anl.gov or mail/FAX to: IPNS Scientific Secretary, Building 360 Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439-4814, USA Phone: 630/252-7820, FAX: 630/252-7722 http://www.pns.anl.gov/

IRI Interfaculty Reactor Institute in Delft (NL) Type: 2MW light water swimming pool.

Flux: 1.5 x 1013 n/cm2/s Address for application forms: Dr. A.A. van Well, Interfacultair Reactor Institut, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands Tel: +31 15 2784738; Fax: +31 15 2786422 E-mail: vanWell@iri.tudelft.nl http://www.iri.tudelft.nl

ISIS Didcot (UK) Type: Pulsed Spallation Source.

Flux: 2.5 x 1016 n fast/s Address for application forms: ISIS Users Liaison Office, Building R3, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX Tel: +44 (0) 1235 445592; Fax: +44 (0) 1235 445103 E-mail: uls@isis.rl.ac.uk http://www.isis.rl.ac.uk

JAERI (J) Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken 319-11, Japan.

Jun-ichi Suzuki (JAERI); Yuji Ito (ISSP, Univ. of Tokyo); Fax: +81 292 82 59227 telex: JAERIJ24596 http://www.ndc.tokai.jaeri.go.jp/

JEEP-II Kjeller (N) Type: D2O moderated 3.5% enriched UO2 fuel.

Flux: 2 x 1013 n/cm2/s Address for application forms: Institutt for Energiteknikk K.H. Bendiksen, Managing Director, Box 40, 2007 Kjeller, Norway Tel: +47 63 806000, 806275; Fax: +47 63 816356 E-mail: kjell.bendiksen@ife.no http://www.ife.no

LLB Orphée Saclay (F) Type: Reactor. Flux: 3.0 x 1014 n/cm2/s Laboratoire Léon Brillouin (CEA-CNRS) Submissio by email at the following address : experience@llb.saclay.cea.fr http://www-llb.cea.fr/index_e.html

NFL Studsvik (S) Type: 50 MW reactor. Flux: > 1014 n/cm2/s Address for application forms: Dr. A. Rennie, NFL Studsvik, S-611 82 Nyköping, Sweden Tel: +46 155 221000; Fax: +46 155 263070/263001 E-mail: user.admin@studsvik.uu.se http://www.studsvik.uu.se

NIST Research Reactor, Washington, USA National Institute of Standards and Technology-Gaithersburg, Maryland 20899 USA Center Office: J. Michael Rowe, 6210, Director NIST Center for Neutron Research mike.rowe@nist.gov http://www.ncnr.nist.gov/

Vol. 9 n. 1 Febbraio 2004

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FACILITIES

NEUTRONI

NEWS FROM “JUELICH NEUTRONS FOR EUROPE”

NEUTRON SCATTERING WWW SERVERS IN THE WORLD

NRI Rez (CZ) Type: 10 MW research reactor.

Address for informations: Zdenek Kriz, Scientif Secretary Nuclear Research Institute Rez plc, 250 68 Rez Czech Republic Tel: +420 2 20941177 / 66173428 Fax: +420 2 20941155 E-mail: krz@ujv.cz / brv@nri.cz http://www.nri.cz

PSI-SINQ Villigen (CH) Type: Steady spallation source.

Flux: 2.0 x 1014 n/cm2/s Contact address: Paul Scherrer Institut SINQ Scientific Coordination Office CH-5232 Villigen PSI Phone: +41 56 310 2087 Fax: +41 56 310 2939 E-mail: sinq@psi.ch http://sinq.web.psi.ch

SPALLATION NEUTRON SOURCE, ORNL (USA) http://www.sns.gov/

TU Munich FRM, FRM-2 (D) Type: Compact 20 MW reactor.

Flux: 8 x 1014 n/cm2/s Address for information: Prof. Winfried Petry, FRM-II Lichtenbergstrasse 1, 85747 Garching Tel: 089 289 14701 Fax: 089 289 14666 E-mail: wpetry@frm2.tum.de http://www.frm2.tu-muenchen.de

Featured Instruments

Reflectometer (HADAS) HADAS is at present the only reflectometer worldwide fully optimised to measure off-specular scattering with polarisation analysis for investigations of magnetic domains in thin film structures.

Special features include: - polarisation analysis covering the entire 2D-detector - new sample environment: cryostat 4 K - 325 K magnetic field 0 - 1.5 T (0 - 0.9 T with cryostat) More information: http://www.fz-juelich.de/iff/wns_hadas Diffuse Neutron Spectrometer (DNS) DNS is the cold time-of-flight instrument with the highest flux for diffuse scattering with polarization analysis worldwide.

Special features include: - a new method for complete vector polarisation analysis works simultaneously for a multi detector with time-of-flight analysis - a new commercial 3D graphical software (AVS) to view S(Q,E) data for time-of-flight single crystal spectroscopy More information: http://www.fz-juelich.de/iff/wns_dns Neutron spin-echo spectrometer (NSE) NSE is worldwide the only instrument making incoherent scattering experiments possible down to Q=0.1A^-1 .

Special features include: - scattering vector: Q=0.03A^-1 to 1A^-1, time range: 0.01ns..25ns - low background: difficult problems from glass physics and polymer dynamics at intermediate scale can be tackled More information: http://www.fz-juelich.de/iff/wns_nse e-mail from Reiner Zorn received on the 12th December 2003

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Vol. 9 n. 1 Febbraio 2004

FACILITIES

NEXT ILL PROPOSAL ROUND

Next deadline for proposal submission is 18 February 2004, midnight (European time).

Proposal submission is only possible electronically. Electronic Proposal Submission (EPS) is possible via our Visitors Club (http://www.ill.fr <http://www.ill.fr/> , Users & Science, Visitors’ Club, or directly at http://vitraill.ill.fr/cv/) <http://vitraill.ill.fr/cv/)> , once you have logged in with your personal username and password. The web will be open from 5 January 2004.

You will get full support in case of computing hitches. If you have any difficulties at all, please contact our websupport (club@ill.fr).

Please note that one cycle (50 days) will be available for allocation for the forthcoming round. The accepted proposals will be scheduled during the summer holidays 2004, from 22 June to 11 August 2004. Please note that it will not be possible to have schedule flexibility this time.

Those proposals accepted at the next round, will be scheduled during the LAST CYCLE (n. 136) in 2004 (see the schedule information below).

The detailed guide-lines for the submission of a proposal at the ILL can be found on the ILL web site: www.ill.fr <http://www.ill.fr/>, Users & Science, User Information, Proposal Submission, Standard Submission.

As usual, for a continuation proposal you must send an experimental report (before the proposal submission deadline). Now, if your experimental report already exists on the web, it will be automatically sent with your continuation proposal to the subcommittee members.

* Instruments marked with an asterisk are CRG instruments, where a smaller amount of beam time is available than on ILL-funded instruments, but we encourage such applications.

You will find details of the instruments on the web, http://www.ill.fr/index_sc.html.

Scheduling period You are probably already aware of the fact that - due to reinforcement work of the reactor structure - the ILL has reduced the number of reactor cycles from 4.5 down to 3 cycles per year during the 2003-2005 period. Nevertheless, the ILL will do its best to offer a larger fraction of the available beam time to users, compared to what was achieved before. In particular, we have suppressed Director’s Discretion Time (DTT) and FAST tracks, which amounted together for 10 to 15% of the total available beam time.

Reactor Cycles for 2004 Cycle

From

To

Cycle n° 137 Cycle n° 138 Cycle n° 139

23.02.2004 22.04.2004 22.06.2004

13.04.2004 11.06.2004 11.08.2004

Start-ups and shut downs are planned at 8:30 am.

Instruments available

Experimental Reports Submission

The following instruments will be available for the forthcoming round: - powder diffractometers: D1A , D1B*, D2B, D20 - liquids diffractometer: D4 - polarised neutron diffractometers: D3, D23* - single-crystal diffractometers: D9, D10, D15*, VIVALDI - large scale structure diffractometers: D19, DB21, LADI - small-angle scattering: D11, D22 - reflectometers: ADAM*, D17, EVA* - small momentum-transfer diffractometer: D16 - diffuse-scattering spectrometer: D7 - three-axis spectrometers: IN1, IN3 , IN8, IN12*, IN14, IN20, IN22* - time-of-flight spectrometers: IN4, IN5, IN6 - backscattering and spin-echo spectrometers: IN10, IN11, IN13*, IN15, IN16 - nuclear-physics instruments: PN1, PN3 - fundamental-physics instruments: PF1, PF1B, PF2

You may already be familiar with our experimental reports search and submission systems. They are available on the Visitors Club’s main page (http://vitraill.ill.fr/cv/) and will be soon fully integrated in the EPS system. The new system will offer the possibility not only of completing the experimental report directly on the web, as it was in the past, but also to view it immediately on your screen as a pdf file.

Please note that it will be mandatory to submit the report as a postscript file (*.doc files will not be acceptable anymore) and that you will be asked to log in the Visitors Club before submitting your report.

Vol. 9 n. 1 Febbraio 2004

From correspondent Giovanna Cicognani Institut Laue-Langevin Scientific Coordinator B.P.156, 38042 Grenoble - Cedex 9, France 10th December 2003

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FACILITIES

CALL FOR PROPOSALS

Studsvik Neutron Research Laboratory (NFL)

Five instruments are scheduled

EU funded Access to Research Infrastructures Programme

REST

NFL is the Swedish Centre for reactor based research using neutrons in physics, chemistry and materials science.

Under our Access to Research Infrastructures contract a total of 105 days of beam time is available per year for users from EU countries and associated states, supporting the cost of the beam time, travel and subsistence. We expect that the EU sponsored access will continue in 2004 under FP6 with broadly similar arrangement to the current scheme.

The deadlines for proposals are 15 September, 15 January and 15 May. Accepted proposals can usually be scheduled quickly. Proposals arriving after the deadline will still be processed but we can not guarantee quick access.

NPD SLAD

SXD Single crystal diffractometer OSIRIS Radioactive ion source and on-line isotope separator Proposal forms, contact information and instrument details are available via http://www.studsvik.uu.se <http://www.studsvik.uu.se/> .

PS! If you do not want to get this mail in the future please send an email to User.Admin@studsvik.uu.se and we will delete you from the list.

A panel of international experts referees proposals, mainly by E-mail/FAX. We recommend that you discuss your proposals with NFL instrument scientists before submission. You are also given the opportunity to make modifications, if necessary, on the basis of the comments of the referee panel. Depending on the final results of the refereeing process, and confirmation from Brussels that you are eligible for support under the programme, your experiment can then be scheduled. The time between proposal and experiment can be as short as a few weeks.

We hope that this will make it easier for you to carry out your research programs.

It is also possible to apply for training of new students, or training in new techniques. In this case the proposal does not have to be linked to a specific experiment - in some cases it is more effective to use a ‘model’ experiment for training purposes.

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Diffractometer for residual stress and texture measurements High resolution powder diffractometer Disordered materials diffractometer (liquids, glasses, crystals)

Vol. 9 n. 1 Febbraio 2004

Dr. Per Zetterstrom Studsvik Neutron Research Laboratory Uppsala University S-611 82 Nykoping - Sweden Tel: +46 155 221837 Fax: +46 155 263001 E-mail: User.Admin@studsvik.uu.se http://www.studsvik.uu.se Received 2nd December 2003