NOTIZIARIO Neutroni e Luce di Sincrotrone - Issue 5 n.1, 2000

Cover photo:The lower thick polystyrene layer is tiledwith the two-dimensional neutron scatte-ring pattern exhibited by the thin fuilmof poly(methyl-methacrylate) lying ontop of it. The Bragg peaks, the result ofinterference between the front and backof the top film, are clearly visible. Thevan der Waals forces across the filmtends to destabilise the system, resultingin spinoidal dewetting which manifestsitself as a pattering of the film surface(data taken with the SURF Reflectometerat ISIS, courtesy of ISIS facility).

Il è pubblicato a

cura del C.N.R. in collaborazionecon il Dipartimento di Fisicadell’Università degli Studidi Roma “Tor Vergata”.

Vol. 5 n. 1 Giugno 2000Autorizzazione del Tribunale diRoma n. 124/96 del 22-03-96

DIRETTORE RESPONSABILE:

C. Andreani

COMITATO DI DIREZIONE:

M. Apice, P. Bosi

COMITATO DI REDAZIONE:

L. Avaldi, F. Boscherini, F. Carsughi, U. Wanderlingh

SEGRETERIA DI REDAZIONE:

D. Catena

HANNO COLLABORATO

A QUESTO NUMERO:

G. Chiarotti, A. Paoletti, E. Rimini, F. Sette, A. Stella

GRAFICA E STAMPA:

om graficavia Fabrizio Luscino 7300174 RomaFinito di stamparenel mese di Giugno 2000

PER NUMERI ARRETRATI:

Paola Bosi, Tel: +39 6 49932468Fax: +39 6 49932456E-mail: [email protected].

PER INFORMAZIONI EDITORIALI:

Desy Catena, Università degli Studidi Roma “Tor Vergata”, Dip. di Fisicavia della Ricerca Scientifica, 100133 RomaTel: +39 6 72594364Fax: +39 6 2023507E-mail: [email protected]

Vol. 5 n. 1 Giugno 2000

NOTIZIARIONeutroni e Luce di Sincrotrone

SOMMARIO

Rivista delConsiglio Nazionaledelle Ricerche

EDITORIALE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2C. Andreani

RASSEGNA SCIENTIFICA

Insight into Biosciences from Synchrotron Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3A. Congiu Castellano

Neutron Diffraction for Residual Stress Measurements: Applications to Materials andComponents for Automotive Technology . . . . . . . . . . . . . . . . . . . 10F. Fiori

Critical Behaviour of a Fluid Mixture Confinedin a Porous Glass Investigated Through SANS . . . . . . . . . . 16F. Formisano and J. Teixeira

Nano-Scale Spectroscopy and its Applications to Semiconductors . . . . . . . . . . . . . . . . . . . . . 23S. Heun and G. Salviati

Chain Deformation in Unfilled and FilledPolymer networks: a SAS Approach . . . . . . . . . . . . . . . . . . . . . . . . . 34W. Pyckhout-Hintzen et al.

Stress-Texture Studies in Thin Films and Coatings by Synchrotron Radiation XRDand Neutron Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41P. Scardi

VARIE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

SCUOLE E CONVEGNI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

CALENDARIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

SCADENZE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

NOTIZIARIONeutroni e Luce di Sincrotrone

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NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE • Vol. 5 n. 1 Giugno 2000

EDITORIALE

Ècon molta tristezza che mi accingo ascrivere questo primo editoriale, nellaveste di nuovo direttore del Notiziario, dalmomento che in questi primi mesi del 2000

tre gravi lutti hanno colpito la nostra comunitàscientifica. La scomparsa di Umberto Grassano, diVittorio Mazzacurati e di Francesco Paolo Ricci halasciato un grande vuoto in tutti noi e in questonumero alcuni colleghi che più da vicino li hannoconosciuti gli dedicano un breve ricordo. Come direttore del Notiziario voglio dedicarealcune parole, anche a nome del comitato diredazione, all’amico, prima ancora che ricercatoree maestro, Francesco Paolo Ricci, scomparso il 27Febbraio, che questa rivista ha fondato e diretto findalla sua nascita. Paolo ha vissuto gli ultimi annidella sua esitenza, affetto da una incurabile edolorosa malattia, con lo stesso spirito sereno,ironico, riservato e distaccato di sempre, quasi avolersi scusare con chi gli era più vicino per ildistrurbo che gli sembrava di arrecare. Chi halavorato insieme a lui ricorda una tensioneintensa, eccessiva forse per coloro che gli eranovicino e faticavano a tenere il passo, che scaturivadalla riflessione continua e da quel bisognoincessante di conoscenza che era al centro dellesua vita. Questa rivista rappresenta un esempioconcreto della miriade di atti, interventi, proposte,azioni che hanno caratterizzato il suo lavoro. Paoloera persona dalle forti convinzioni e dal caratteretestardo; questo suo modo di essere ha spessogenerato divergenze, a volte scontri con colleghi,amici e collaboratori, ma tutto questo non ha maiintaccato l’affetto profondo e la stima che sapevagenerare intorno a sé con il suo sorriso aperto,quasi uno specchio di un intimo candore chetroppo spesso mascherava con atteggiamentigigioneschi. Ci mancherà la sua scuola, il suoesempio, ci mancherà immensamente la suapresenza.

It is with great sadness that I am writing my first

editorial, as new director of Notiziario.

I would first of all like us all to remember the

three scientists of our community who have

recently passed away: Umberto Grassano, Vittorio

Mazzacurati and Francesco Paolo Ricci. In this issue,

three colleagues who knew them well describe their life

and work.

I would like to dedicate a few words, also on behalf of

all the editorial committee, to the friend Francesco

Paolo Ricci who passed away on February 27th and

was founder and director of this Journal from the very

beginning. Paolo lived the last years of his life, while he

suffered from a painful and incurable disease, with the

the same serene, ironical, detached and reserved

character so typical of him; it seemed he wanted to

excuse himself with those close to him for any

disturbance he might cause. Those who worked closely

with him know of his intense drive, which sometimes

appeared excessive to those close to him and who could

not keep pace; this drive originated in his continuous

need for understanding which was at the center of his

life. This Journal is a concrete example of the many

proposals and initiatives which characterized his work.

Paolo was a man with strong opinions who sometimes

appeared stubborn. This often gave rise to differences of

opinion with colleagues, friends and collaborators;

however, this never stopped the strong affection and

esteem which surrounded him due to his qualities and

his open smile, a mirror of his candour which he too

often masked with apparent lightheartedness. We will

miss his example and his teaching and we will

immensely miss his presence.

Carla Andreani


3

Vol. 5 n. 1 Giugno 2000 • NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

Articolo ricevuto in redazione nel mese di Luglio 1999

INSIGHT INTO BIOSCIENCESFROM SYNCHROTRON RADIATION

A. Congiu CastellanoDip. di Fisica and I.N.F.M., Università La SapienzaPiazzale A. Moro 00185 Roma

Recent advances in instrumentation and techniques, combinedwith high brightness X-ray sources, such as those provided bythird generation synchrotrons afford new opportunities forstudying biological systems.This paper describes some results obtained using Time-resolveddiffraction, X-ray absorption spectroscopy, Small anglescattering, and Microscopy.

The First International Conference on Biophysics andSynchrotron Radiation [1] was held in July 1986 atFrascati. Since that year, the usage of synchrotron radiation bybiologists has tripled, and the new strategies have beenimplemented to cope with the dramatic increase indemand. Although it is crystallographers who are mainlyresponsible for this increased use, biological research atthe synchrotron involves a wide variety of experimentalapproaches. This is a brief review of some important techniques suchas time-resolved crystallography, X-ray spectroscopy, noncrystalline diffraction, and imaging that play a key role inlife science research.Three third generation X-ray synchrotron radiationfacilities, characterized by high brilliance, have becomeavailable within the last few years: the EuropeanSynchrotron Radiation (ESRF) facility in Grenoble, France(a 6 GeV ring with a circumference of 850 m), theAdvanced Photon Source (APS) in Chicago ( at 7 GeV andring with a circumference of 1.1 Km) and the SuperPhoton ring (SPring-8) near Himeji in Japan (at 8 GeV and1.4 Km circumference). Approximately 30% of thebeamlines are devoted to structural biology research,including crystalline and non-crystalline diffraction,spectroscopy and imaging techniques.

Time-resolved crystallographyA number of technical advances have helped make SRwidely available as a standard technique for proteincrystallography. Currently the use of SR has moved awayfrom being a technique used only by a small number ofspecialists to one that is now routinely applied by the vastmajority of protein crystallography groups world-wide.There have been great advances in techniques forrecording multi-wavelength anomalous dispersion

(MAD) data on metalloproteins [2] and more importantlyon crystals of proteins or nucleic acids in which the sulfuratom of the methionine has been substituted by Se or Te. The use of area detectors, particularly imaging plates, andCharge Coupled Devices (CCDs), as well as thedevelopment of cryogenic freezing techniques, have beencritical to recent advances in structural biology.The SR source has allowed time-resolved crystallographicexperiments with nanosecond time resolution to beconducted on myoglobin and photoactive yellow protein.In both experiments, the molecules are first stimulatedand a structural change initiated by a brief laser flash - theso-called pump; after a suitably adjustable time delay inthe range from ns to ms, an X-ray pulse falls on the crystaland generates a diffraction pattern - the probe.Myoglobin, defined as the hydrogen atom of biology, is aheme protein found in muscle tissue. It acts as an oxygenstorage protein by reversibly binding oxygen moleculesthat have been transported to muscle by hemoglobin.Oxygen (or diatomic molecules such as carbon monoxide)binds to an iron ion located near the centre of the protein.The iron is part of an organic prosthetic group, the heme,the geometry of which changes with the ligand binding;this change is communicated to the protein throughproximal histidine and non-bonded contacts. Thesestructural variations can be triggered by a light flash thatbreaks the covalent bond between the carbon monoxideand the iron atom: the CO migrates away from the heme;the heme and the protein relax towards the stabledeoxyMb structure; if eventually the CO rebinds with theheme the MbCO structure occurs. At room temperaturein the crystal, the entire fully-reversible process (a proteinquake) is complete in a few hundred microseconds. InOctober 1994 two groups [3,4] published atomic-resolution structures of the photolysed state; the datawere collected at 40K at beamline X12-C and X26-C of theNational Synchrotron Light Source Brookhaven Nationallaboratory.Later, at ESRF nanosecond time-resolved crystallographicdata were collected [5], with 1.8 Å resolution, during theprocess of heme and protein relaxation, after carbonmonoxide photodissociation and during rebinding.Photolysis was initiated by 7.5 ns laser pulses.Similarly the structure of the light-activated, long-lived

4



intermediate in the photocycle of PYP (photoreceptorphotoactive yellow protein) was determined by time-resolved, multiwavelength Laue x-ray diffraction at aspatial resolution of 1.9 Å and a time resolution of 10 ms [6].The importance of this research is due to fact that so farthree-dimensional structures of photoactive proteinshave described proteins in their dark-state conformation.However , understanding the molecular mechanism forlight-induced signal transduction requires clarification ofthe conformational changes of proteins during thephotocycles. Time-resolved crystallography experimentswere performed at X26-C beamline of Nationalsynchrotron Light Source Brookhaven Nationallaboratory.

X-ray Absorption SpectroscopyEXAFS and XANES spectroscopy has become a structuraltool, experimentally accessible to the general scientificcommunity since the advent of XAS beamlines atSynchrotron radiation sources and the contemporaryunderstanding of the basic physics underlying thistechnique. XAS of dilute systems (such as biologicalmolecules) is only feasible with SRS and thesedevelopments have thus led to the application of XAS instructural molecular biology. Accurate bond lengths andactive site geometries, as determined by XAS, areparticularly important in deriving an understanding ofthe structure-function relationship in metalloproteins. The spectrum can be divided into two regions: the edgeregion (XANES) which contains transitions to boundstate orbitals including valence levels, and at higherenergies where the core electron is ejected as aphotoelectron, the extended X-ray absorption finestructure (EXAFS) region. When neighboring atoms arepresent these can backscatter some of the emittedphotoelectrons. Interference between outgoing andbackscattered waves causes the modulation of the X-rayabsorption. The EXAFS provides very accurate values forbond lengths, typically to better than 0.02 Å, which issuperior by approximately one order of magnitude toaccuracies available by protein crystallography. XAScontributes to structural biology in two major ways. Itcan provide information on species for whichcrystallography is not available and can also providecorrections and complementary information on systemsfor which a crystal structure is available. The question ofwhether there is a difference between an active site in aprotein solution and in the crystalline state can beaddressed by performing comparative measurements.XAS edge studies provide the means for determiningelectronic structure, including such properties asoxidation state, spin state and covalency for specificatomic sites in a macromolecule.Temperature dependent variations of the XANES of

alkaline metmyoglobin from sperm whale, clearly relatedto the iron spin state, have been reported by Oyanagy etal. [7] (fig 1). Magnetic susceptivity data showed thatFe(III) in this derivative is in a high spin state (S=5/2) atroom temperature and in a low spin state at 80 K (S=1/2). Recently a study of the spin-structure relationship inmetmyoglobin was published [8] describing the analysisof K-XANES spectra in the framework of the multiplescattering approach using spin resolved self consistentpotentials. XANES spectra of ferric myoglobin have beenacquired as a function of pH (between 5.3 and 11.3). AtpH=11.3 temperature-dependent spectra (between 20and 293 K) have been collected. The XANES spectra of metmyoglobin exhibit variousfeatures evolving with temperature and sensitive to bothFe spin state and Fe-heme structure. The method allowsspin effects and local structural effects to be computedseparately. It is possible to detect at least three structuralstates of the Fe-heme complex related to the multistateequilibrium: high-spin Mb+OH2 – high spinMb+ OH– – low spin Mb+ OH–.In fig. 2 from up to bottom: A) the temperaturedependence of the XANES derivative spectrum ofalkaline Mb+ OH- ( pH 11.3, T= 293, 220, 150 and 100 K);B) pH dependence of XANES derivative spectra of Mb+;C) XANES spectra of Mb+OH2 (pH 5.3,T= 293 K topcurve) and Mb+ OH- (pH 11.3, T= 293 K, middle curve;pH 11.3, T=100 K bottom curve)

Bond specific geometric information due to theapproximately cos2 α dependence of the EXAFS resultingfrom the plane-polarized nature of SR, can be obtainedfrom analysis data. Geometrical information is usuallynot available from non-polarized single-scatteringEXAFS. However, in some special cases such information

Fig. 1. XANES spectra of MbOH at 80K (low spin) and 300K (high spin)and their derivative spectra are compared (Oyanagy et al. 1987)

5



can be obtained via the multiple scattering approach.Single scattering EXAFS refers to the case when theoutgoing photoelectron is scattered only once beforereturning to the absorber. Multiple scattering (MS) occurswhen multiple atoms backscatter the photoelectron; inthis case the EXAFS is sensitive to the relativearrangement of atoms. Information on the number, thetype and the geometrical arrangement around theabsorber of nearby and more distant scattering centers[9,10,11,12] can be obtained by fits to experimental datathat also include MS contributions. Usingcrystallographic data of similar compounds and

structural indications from other techniques, the atomicgroup coordinated to the metal in the active site ofmetalloproteins may be identified. Recently [13] a detailed study of EXAFS spectrum oftetanus neurotoxin (TeNT) at Zn K-edge was performedwhich allows the complete identification of the aminoacid residues coordinated to the zinc active site.In this case the XAS study is the only structural probebecause there are no crystallographic data available forTeNT. Understanding the structure-function relationshipand therefore the biological mechanism responsible for adevastating disease such as tetanus can help to devise

new therapeutic strategies. Comparing the absorptionspectrum of tetanus neurotoxin to that of two otherstructurally similar zinc-endopeptidases - thermolysinand astacin - the authors inferred that in tetanusneurotoxin, zinc is coordinated to two histidines and atyrosine. The EXAFS data were analysed using thetheoretical approach developed by Benfatto et al. (1986)and Filipponi et al. (1995a) and the GNXAS package. Theusual MS expansion is replaced by an equivalentexpansion in terms of irreducible n-body signals, γ(n)..Fig. 3 shows the results of best fits on thermolysin,astacin and TeNT: (Panel a) n-body independentcontributions considered in the fit are reported; (Panel b)the total simulated signals (dotted line) aresuperimposed on the experimental points. At the bottomof panels b, the residual functions are plotted. Thehypothesized structure of Zn site in TeNT is comparedwith those in thermolysin and astacin in fig. 4.

Non-crystalline diffractionMany biological macromolecules, such as enzymes andcomplexes, viruses and photosynthetic reaction centers,may be investigated by crystallographic analysis. Overthe last decade a large number of new structures has been

Fig. 2. Up to bottom: A) the temperature dependence of the XANESderivative spectrum of alkaline Mb+ OH- ( pH 11.3, T=293,220,150 and 100K); B) pH dependence of XANES derivative spectra of Mb+ ; C) XANESspectra of Mb+OH2 (pH 5.3, T= 293K top curve) and Mb+ OH- (pH 11.3, T=293 K, middle curve; pH 11.3, T=100 K bottom curve) (Della Longa etal.1998)

Fig. 3. The results of the best fits on thermolysin, astacin and TeNT arereported : (Panel a) n-body independent contributions considered in thefit are reported; (Panel b) the total simulated signals, dotted line, aresuperimposed on the experimental points. At the bottom of panels b, theresidual functions are plotted ( Meneghini et al. 1998)

6



solved and the increasing availability of SR has been akey element in this spectacular success. Diffractionmethods have several limitations that are important forbiological systems.Despite the utility of determining static crystal structures,many biological systems are non-crystalline in vivo or aresimply not amenable to crystallographic study eitherbecause they cannot be crystallized, or their structures ordynamic behaviours change upon crystallization. Aneven more important consideration is that time resolvedinformation concerning changes in structure, such asbiological macromolecules perform their functions, isexperimentally inaccessible by the techniques ofmacromolecular crystallography.All biological structures have some degree of spatial or

dynamic order which can potentially be probed by noncrystalline diffraction and small angle X-ray scatteringtechniques.In recent years many experiments have been performedon muscle fibre and connective tissues by means ofdiffraction at Synchrotron radiation facilities.X-ray diffraction is currently the only technique whichprovides direct structural information at molecular level

on the mechanism of the conversion of chemical energyinto the production of strength and movement in muscletissues. The high resolution of diffraction patternsallowed by the use of Synchrotron radiation sourcessuggests that a revision of some hitherto acceptedmodels of contraction is necessary.Time resolved X-ray diffraction has also been used tostudy the physical properties of synthetic modelmembrane systems in order to understand suchprocesses as membrane fusion using various kinetictechniques such as T-jumps induced with lasers or rapidpressure changes.Another experimental approach uses oriented lipidbilayer systems to obtain structural information fromintegral membrane proteins.In the experiment performed at ELETTRA (Trieste) aninfrared laser that emitted 1-2 kJ pulses for duration ofabout 1 ms was used. Using suitable crystal optics thelaser pulse can be deposited onto a capillary sampleholder for SAXS such that temperature jumps of 10-20 0Care made in 1ms time, which corresponds to heating rateof 104 K/sec. For the investigation of liquid crystallinephase transitions which frequently span a transitionrange of 0.1 0C or less, this means that transition can betriggered within tens of microseconds.Solution scattering can be used to measure a smallnumber of important, molecular parameters: radius ofgyration, molecular weight, molecular volume anddistance distribution function P(r).An emerging application is that of stopped flow andother kinetic techniques for studying protein folding.The third generation sources combine high flux(1013 ph s-1) with small source sizes (100 micron) and very

Fig. 4. The structure of Zn site in TeNT (deduced from EXAFS analysis) iscompared with those in thermolysin and astacin (Meneghini et al. 1998)

Fig. 6. An image of EGF labeled with a fluorescein derivative, BODIPY inA431 cells. Bar=5 µm. (With permission of authors) ( Tobin et al. 1998)

7



low angular divergences (50 microradians). The smallintense beams from undulator sources could also makemore effective use of continuous flow devices for timeresolved solution scattering and deliver more flux to verysmall specimens. For further progress to be made noveltechnologies such as advanced charged coupled device(CCD) based detectors will be required.Another obstacle is that most small angle scattering andnon-crystalline diffraction experiments cannot make useof cryogenic techniques since freezing is incompatiblewith the physiological phenomenon.The compactness of a protein structure is an importantparameter that characterizes its degree of folding.Although the information about the secondary andtertiary structure is important, changes in the size andshape of a protein are crucial to an understanding of themechanism of protein folding.As protein unfolding often involves the exposure ofhydrophobic groups, protein aggregation can be a factorlimiting the utility of scattering techniques for probingcompactness in unfolded structures; hence the utilizationof Synchrotron Radiation sources can be a greatadvantage as it facilitates working at the lowest proteinconcentration.The SAXS intensity distribution of a protein in solutioncan be approximated by the Guinier relation:I(q)= I0 exp (-Rg 2q 2/3)where I0 denotes the intensity at zero scattering angle,q=2πS (named momentum transfer) and Rg is the radiusof gyration. The Kratky plot, I(q)q2 versus q, is a usefultool of the scattering profile for characterizing thestructure of an unfolded or folded chain: a peak in theKratky plot (panel b and c) indicates a compact globularstructure, and the absence of a peak is an indication of aloss of globularity. In fig. 5 Guinier plots (panel a) andKratky plots of ovalbumin, studied at LURE beamline, in

the native and in some thermal and chemical denaturedstates, are reported [14]. The refolding and unfolding ofthe apomyoglobin were studied at the Stanfordsynchrotron radiation laboratory [15] by time resolvedsmall angle x-ray scattering. Refolding was triggered byrapid dilution of 10 mg/ml protein in 5.6 M urea to 1.4mg/ml in 0.8 M urea. Time resolved stopped flow X-ray scatteringmeasurements using the integral intensity of scatteringallowed the kinetic refolding of β-lactoglobulin [16] to be

Fig. 7. Fluorescence lifetime of the region outlined in fig 6 is reported. Agood fit was obtained for a two exponential decay profile. (Withpermission of authors) (Tobin et al. 1998)

Fig. 8. A sample of a living, dividing cell, whose optical image is shownat the top, was mapped and the distributions of protein and lipid areshown. (With permission of authors) (Bantignies et al. 1998).

1540 cm-1 (amide II)

2925 cm-1 (lipids)

Position [µm]

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studied. The experiment performed on SAXS beamline ofthe Photon Factory (Tsukuba, Japan) showed that bothcompaction and secondary structure formation in proteinfolding are rapid processes, taking place on a millisecondtime-scale.

ImagingOne of the major advances at the high brightness thirdgeneration synchrotron is the dramatic improvement ofimaging capability. Considerable efforts have been madeto develop imaging X-ray, UV and infrared spectroscopicanalysis on a spatial scale ranging from a few microns to10 nm. These developments make use of infrared light,ultraviolet light and X-rays from 100 eV to 10 keV.

X-ray microscopy Below 10 keV, X-ray photons are primarily absorbed orphase shifted as they pass through matter. This meansthat X-ray microscopes offer unique opportunities forquantitative imaging without inelastic or multiple elasticscattering effects. Furthemore the penetration of X-raysin hydrated biological materials can be large: at energiesbetween the carbon and oxygen absorption edges at 284and 534 eV, respectively (the so-called water window),water layers of up to 10 microns thick are easily penetra-ted, while thin cellular structures provide sufficient con-trast. In spite of this high contrast, the specimen must beilluminated with sufficient X-rays per pixel and therefo-re the dose (energy deposited per unit mass) can produ-ce radiation damage. The introduction of cryogenicmethods for studying frozen hydrated specimens miti-gates (primarily by the immobilization of radiolyticalproducts in the ice matrix) many of the problems of ra-diation damage. A number of approaches have beenused to construct successful Synchrotron X-ray micro-scopes. In particular two use zone plates as focusing op-tics to obtain magnification images in transmission X-raymicroscopes (TXMs) or to produce finely focused spotsthrough which the specimens are rastered in ScanningTransmission X-ray Microscopes (STXMs). The spatialresolution of these microscopes can be 30-50 nm withsoft X-rays (< 1 keV).Whereas TXMs tend to use condenser zone plates asmonochromators with an energy resolving power E/∆Eof ~300, STXMs tend to use reflective grating monochro-mators with a resolving power of 3,000 or more. The hi-gher energy resolution makes STXMs especially well sui-ted to map the distribution of the chemical bonding sta-tes of the major constituents of a sample.One advantage of X-ray microscopy is its ability to studysingle cells in their entirety, rather than be limited to athickness of 400 nm, as is the case in electron tomo-graphy of frozen hydrated specimens.Magowan et al. [17] used X-ray microscopy to investiga-

te the structural development of Plasmodium falcipa-rum malaria parasites in normal and genetically abnor-mal erythrocytes treated with cysteine protease inhibi-tors. X-ray microscopy revealed the relationship betweenthe host erythrocyte membrane and the intraerythrocyticmalaria parasite by demonstrating for the first time thatconstituents of the erythrocyte membrane play a role innormal parasite structural development.

UV microscopyAt the Daresbury Laboratory Synchrotron RadiationSource (SRS) a confocal microscope provides a powerfulnew tool for studying biological systems (18). Mostcommercial instruments operate with fixed wavelengthlasers, because confocal microscopy requires a small,high intensity light source. The synchrotron radiation

Fig. 5. Guinier plots (panel a) and Kratky plots (panel b and c) ofovalbumin, in the native and some thermal and chemical denatured statesare reported (Congiu Castellano et al. 1996)

9



source provides easily tunable continuous UV-visibleradiation which, with the storage ring operating in singlebunch mode, has a pulsed time structure ideally suitedfor fluorescence lifetime spectroscopy. The collection of fluorescence lifetime data frommicroscopically small samples and regions withinsamples is allowed by the combination of single photoncounting and confocal microscopy. A resolution of 99 nm(lateral) and 483 nm (axial) at wavelength 290 nm hasbeen obtained.Time resolved microvolume fluorescence measurementshave been employed in the study of steroid hormoneinteraction in Leydig cells as the lifetime of a fluorophoreis sensitive to its environment and can therefore be usedto investigate the binding of signalling molecules inmicroscopic regions of individual cells. This method isalso being used in the study of growth factor binding andinternationalization in mammalian cells. Fig. 6 is an image of EGF labeled with a fluoresceinderivative, BODIPY, in A431 cells. Fig. 7 shows a fluorescence lifetime of the region outlinedin fig. 6. A good fit was obtained for a two exponentialdecay profile.

Infrared microscopyThe middle infrared spectral range, which coverswavelengths from 3-15 microns, is known as the"fingerprint region". It is here that the intramolecularvibrational modes exist and these play an important rolein analytical work. Infrared Synchrotron radiation is anideal source for microspectroscopy for two reasons:-high spatial resolution-the ability to work with samples of higher opticaldensity due to the superior signal levels availablethrough the small apertures. Biological materials, such ascells, hair and bone, all contain molecules with a richselection of intramolecular vibrational modes due toproteins, lipids and nucleic acids.The dominant features in the spectra are: the broad bandsfrom 2500-3500 cm-1 due to the NH and OH groups foundin water, proteins and polysaccharides (3063-3290 cm-1)and both the symmetric and asymmetric stretching modesof methylene (CH2) and methyl (CH3) groups (2850-2960cm-1) in lipids and proteins. The other main modes arisefrom CO-NH vibrations which are called amide1 (1650cm-1) and amide 2 (1540 cm-1). Sharper modes occurbelow these bands due to d-CH vibrations (1450 and 1390cm-1) and there is an amide 3 band at 1238 cm-1.These modes could be used to make chemical images ofproteins, lipids and nucleic acids in living biological cellswithout the use of stains and fixatives. The functionalgroups could be identified and their concentrationprofiles mapped with a spatial resolution of a fewmicrons. While the identification and mapping of such

functional groups in living cells is technically verychallenging, it may offer substantial fresh insight into thecell's chemical kinetics. A sample of a living, dividingcell, whose optical image is shown at the top of fig. 8 wasmapped and the distributions of protein and lipid havebeen shown [19]. Infrared spectroscopy is an analyticaltechnique that is sensitive to the mineral as well as to thebiological components in bone. The technique can beused to determine the chemical composition ofsubchondral bone as a function of subchondral bonethickness and severity of osteoarthritis.

ConclusionsGreat potential is offered to the biosciences by the use ofSynchrotron radiation.Structural determination of biological systems at high re-solution, time-resolved spectroscopies and spectromicro-scopies applied to proteins and living cells have allowedthe acquisition of very important results concerning fun-damental problems in the life sciences, such as the struc-ture-function relationship, the folding process of pro-teins and the cell's chemical kinetics.

References1. Biophysics and Synchrotron Radiation (1987) Ed. A. Bianconi and A.

Congiu Castellano Springer Verlag Berlin Heidelberg New YorkLondon Paris Tokyo

2. Zanotti G. Notiziario neutroni e Luce di sincrotrone Vol.3 n.2 (1998)3. Schlichting I., Berendzen J., Phillips G.N. Jr and Sweet R.M. Nature,

371, 808-812 (1994)4. Teng T.Y., Srajer V. and Moffat K. Structural Biology 1, 701-705 (1994)5. Srajer V., Teng T.Y., Ursby T., Pradervand C., Ren Z., Adachi S.,

Schildkamp W., Bourgeois D., Wulff M., Moffat K.Science 274,1726-1729 (1996)

6. Genick U.K., Borgstahl G.E.O., Kingman N., Ren Z., Pradervard C.,Burke P.M., Srajer V., Teng T.Y.,Schildkamp W., McRee D.E., Moffat K.,Getzoff E.D. Science 275,1471-1475 (1997)

7. Oyanagy H., Iizuka T., Matsushita T., Saigo S., Makino R., Ishimura Y.,and Ishiguro T. J. Phys. Soc. Jpn 56, 3381-3388 (1987)

8. Della Longa S., Pin S., Cortes R., Soldatov A.V., and Alpert B.Biophysical J. 75,3154-3162 (1998)

9. Strange R.W., Blackburn N.J., Knowles P.F., and Hasnain S.S. J.Am.Chem. Soc. 109, 7157-7162 (1987)

10. Benfatto M., Natoli C.R., Bianconi A., Garcia J., Marcelli A., FanfoniM., and Davoli I. Phys. Rev. B 34, 6426-6433 (1986)

11. Filipponi A., Di Cicco A., and Natoli C. R. Phys. Rev. B 52, 15122-15134(1995)

12. Filipponi A., Di Cicco A., M.J. Scott, Holm R.H., Hedman B., andHodgson K.O. J. Am. Chem. Soc. 119, 2470-2478 (1997)

13. Meneghini C. and Morante S. Biophysical J. 75, 1953-1963 (1998)14. Congiu Castellano A., Barteri M., Bianconi M., Bruni F., Della Longa

S., and Paolinelli C, Z. Naturforsch. 51c,379-385 (1996)15. Eliezer D., Jennings P. A. and Wright P. E. Science 270,487-488 (1995 )16. Arai M., Ikura T., Seminosotnov G.V., Kihara H., Amemya Y., and

Kuwajima K. J.Mol. Biol 275:149-162 (1998)17. Magowan C., Brown .T., Liang J., Heck J., Coppel R. L., Mohandas N.,

and Meyer-Ilse W. Proc.Natl.Acad.Sci. 94, 6222-6227 (1997)18. Tobin M.J., Martin-Fernandez M., and Jones G.R. Synchrotron

radiation News 11, 24-30 (1998)19. Bantignies J.L., Carr L., Dumas P., Miller L., and Williams G.P.

Synchrotron radiation News 11, 31-37 (1998)

10



The application of neutron diffraction technique for thedetermination of residual stresses in some materials andcomponents for automotive technology is presented. Afterintroducing the basic principles of the method, experimentalresults on the following samples are reported: AA6082cylinders submitted to different quenching and ageingtreatments, and a crown gear submitted to an innovativemulti-frequency induction surface treatment. In the latter casecomparisons with complementary measurements by X-raydiffraction are also presented.

1. IntroductionSeveral manufacturing industrial processes and thermalor mechanical treatments leave residual stresses (RS)within materials and components. RS can be beneficialor detrimental, depending if they counteract or not ex-ternal loads: tensile RS, when added to external loads(e.g. in welded samples), can accelerate the fatigue pro-cess and induce earlier failure of the component. On theother hand, surface treatments (e.g. shot-peening) arefrequently used to improve hardness properties and toinduce compressive RS, thus enhancing the surface tou-ghness and wear resistance under operating conditions.Therefore, the importance of a detailed knowledge of thespatial and directional distribution of RS in the compo-nent is evident, as it can permit to get a feeling of the li-fetime of the component with respect to the environmentit has to be used in. Furthermore, in many cases a precisemeasurement of RS can be used to validate mathematicaland numerical models of technological processes, lea-ding to more efficient and saving-cost manufacturingprocedures.To this end, several experimental methods exist, bothdestructive (e.g. hole drilling [1]) and non-destructive,such as acoustic-elastic methods by ultrasounds [2,3,4],micromagnetic methods (e.g. Barkhausen noise) [2,4],and diffraction techniques by X-rays or neutrons[4,5,6,7].In particular, diffraction techniques are nowadays proba-bly the most important and reliable ones. X-ray diffracto-meters dedicated to RS measurements are available in

many research and industrial laboratories, and high-energy X-rays (synchrotron radiation) are gaining moreand more importance for this purpose. Furthermore,spectrometers dedicated to RS determination are presentin all of the European Large Scale Facilities at neutronsources, like ILL and LLB (F), ISIS (UK), HMI-BENSC(D) and Risø National Laboratory (DK).

The main difference between “traditional” X-rays andneutrons (and synchrotron radiation as well) is that onlystress states in surface layers (≈10 µm) can be investigatedby X-rays, as they are strongly absorbed in metals, whileneutrons can penetrate down to few centimetres insidethe bulk material. Therefore, in principle, the completedetermination of the stress field can be obtained by acombined use of the two techniques.The principles of neutron diffraction for RSdetermination, together with some relevant experimentalaspects, are briefly described below. Then two typicalapplications to materials and components for automotivetechnology are presented, namely an investigation of RSinduced by quenching in AA6082 alloy and by aparticular surface thermal treatment (multi-frequency

NEUTRON DIFFRACTION FOR RESIDUAL STRESSMEASUREMENTS: APPLICATIONS TO MATERIALS ANDCOMPONENTS FOR AUTOMOTIVE TECHNOLOGYF. FioriIstituto Nazionale per la Fisica della Materia, Unità di Ricerca di Ancona and Università di Ancona, Istituto di Scienze FisicheVia Ranieri 65, I-60131 Ancona (Italy)

Articolo ricevuto in redazione nel mese di Aprile 2000

Fig. 1. Schematics of a neutron diffraction experiment for residual stressmeasurements.

11



induction tempering) in a steel crown gear. In the secondcase comparisons with complementary measurements byX-ray diffraction are also presented.

2. Neutron diffraction for residual stress measurements2.1. Theoretical principlesThe interplanar distance of a particular set of latticeplanes (dhkl) is determined by means of the Bragg’s law:

(1)

where 2θhkl is the diffraction angle with respect to theincident beam direction and λ is the neutron wavelength(fig.1). The lattice strain, whose direction is parallel to theexchanged wave vector Q, is calculated as

(2)

where d0,hkl is the unstrained interplanar distance. Finallythe stress components can be calculated according to theHooke’s law:

σij = Cijmnεmn or εij = Sijmnσmn (3)

The C and S 4th-rank tensors are called stiffness andcompliance, respectively. In principle they have 34=81components, but this number is reduced by theirsymmetry, and also by symmetry properties of thecrystals. For isotropic crystals, such as Aluminium, thereare only 2 independent components, which can beexpressed in terms of the Young’s (E) and Poisson’s (ν)moduli. Ehkl and νhkl, referred to the investigated latticeplanes, can be calculated according to existing models(Voigt, Reuss, Kröner) [4,7]. For isotropic crystals theelastic constants do not differ sensibly from a plane toanother and in such cases their macroscopic values canbe used as a good approximation. Strain and stress are 2nd rank symmetric tensors, thushaving 6 independent components. Therefore, inprinciple, measurements should be carried out in at least6 different spatial directions of the Q vector. Anyway, inmost cases, the principal strain/stress directions can beassumed to coincide with the sample principal axes.Measurements in these three directions are thus sufficientfor the complete determination of ε and σ and.Including eq.2 in the first of eqs.3, principal stresses canbe directly written as functions of the interplanardistances measured along the principal directions (i, j, k):

(4)

σν

ν ν

νii j kE d d d

d=

−

−( ) + +( )+( ) −

1 2

1

11

0 εhkl

hkl hkl

hkl

d d

d=

− 0

0

,

,

λ θ= 2d sinhkl hkl

Fig. 2. The DIANE diffractometer at LLB, Saclay, France.

Fig. 3. The ENGIN diffractometer at ISIS, Rutherford Appleton Laboratory, UK.

Incident beam

Sampletable

Radial collimator

Detector Gauge volume

Radial collimator

Slits

Sample

Detector

Beam stop

12



2.2. Experimental aspectsAs already remarked above, diffractometers dedicated toRS measurements are available at the main Europeanneutron sources. The DIANE spectrometer is shown infig.2. It was built at the Laboratoire Léon Brillouin (LLB),Saclay, France in the framework of a project carried out incollaboration between LLB and INFM [8]. The ENGINdiffractometer at the ISIS pulsed spallation source, builtin the framework of a Brite/Euram project which theResearch Unit of Ancona of INFM took part in [9], isshown in fig.3.In a neutron diffraction experiment the incidentmonochromatic neutron beam (wavelength λ) isdiffracted by the polycrystalline sample, and thescattered intensity is recorded in a Position-SensitiveDetector (PSD), at an angle 2θ with the incoming beamdirection (fig.1). Two collimators placed before and afterthe sample define the cross-sections of the incident andthe diffracted beams, so that the best geometricaldefinition of the gauge volume inside the sample isobtained with 2θ≈90°. Its size is usually in the range fromabout 1 mm3 up to few cm3, and the measured value ofRS must be intended as an average over the samplingvolume itself.The interplanar distance dhkl of the investigated (hkl)lattice planes is obtained from the Bragg's law (eq.1). Inmonochromatic neutron beams coming from steadynuclear reactors, dhkl is determined by preciselymeasuring the diffraction angle 2θ, corresponding to theintensity maximum of the Bragg peak. In the case ofspallation sources, such as ISIS, where neutrons in a widewavelength range are produced in the collision of highenergy protons with a heavy target, 2θ is fixed at 90°. Inthis case dhkl is determined by measuring the Time-Of-Flight (TOF) of neutrons between a fixed “start” pointand the detector. In fact, according to the De Broglierelation,TOF is given by

(5)

where m is the neutron mass, L the flight path length andh the Planck’s constant. By the TOF technique the wholediffraction pattern is recorded, and the lattice parameter(a) is obtained by Rietveld refinement algorithms [10].The determination of the unstrained interplanar distanced0 (or lattice parameter a0) is a crucial point of the experi-mental technique, as the definition of a true stress-freesample is not always trivial. Strains to be measured areusually of the order of 10-4 so that, from eqs. 2 and 4, it isobvious that a not precise determination of d0 can lead tobig errors and even to unreliable RS values. In most ca-ses, the following methods are commonly considered tobe sufficiently “safe” from this point of view:

1. measurements in powders of the same material ofthe investigated sample (often ground from thesample itself): the powder, even if submitted toplastic deformations, can be considered as stress-free, especially if submitted to stress-relieving heattreatments;

2. measurements in small coupons, completelyimmersed in the neutron beam, so that theequilibrium condition

(6)

can be applied. From eqs.6 and 4 it isstraightforwardly shown that, in the case of cubiccoupons, d0 can be calculated as the mean valueamong the interplanar distances measured in thethree principal directions;

3. measurements in regions of the sample which can beassumed not to be influenced by localised stress-inducing treatments (for instance, regions far fromwelds);

4. when allowed by the sample geometry, applicationof mathematical conditions to the sample itself(equilibrium, plane stress).

In any case, the validity of all of these methods should bechecked at least a posteriori, as some problems can raiseand make them unuseful. Among them, for methods 1and 2 we mention the presence of II ordermicrostresesses, at the distance scale of a few grains,which otherwise should be assumed to be vanishing, andthe presence of RS pre-existing to the investigatedtreatments for method 3. Furthermore, when usingpowders or coupons, systematic experimental errors canbe very difficult to be foreseen and eliminated. Finally,microstructural changes (e.g. precipitation) induced bythermal treatments, leading to different unstrained latticeparameter from one point to another in the sample,should be taken into account. Typical cases of this arewelded components. In principle, in such cases, adifferent d0 should be used for each of the investigatedgauge points [11,12].

3. Measurements3.1. Quenched AA6082 Al alloyFast quenching of metals from high temperatures causeshigh thermal gradients moving from surface zones to thebulk, with subsequent inhomogeneous cooling. Differentcooling rates generate plastically deformed zones and thesurface layers, more deformed than the inner ones, willresult in a compressive stress state.AA6082, a well known Al-Mg-Si alloy, widely used in

σ σ= ⋅ =∫10

VdV

V

TOF

mLh

= λ

13



automotive technology, exhibits mechanical propertiesthat are highly sensitive to thermal treatments. In fact,starting from the solubilised state, too slow cooling ratescan lead to the reduction of several important properties(strength, formability, toughness, etc.), while too rapidcooling can generate undesired macroscopicdeformations. From the microscopic point of view, thealloy elements are usually solubilised by hightemperature (520°C) annealing. In the subsequentcooling procedure, rapid quenching is needed to createthe Guinier-Preston zones, whose size increases as aconsequence of the subsequent ageing, leading to animprovement of the mechanical behaviour. However atoo rapid quench can enhance RS. On the other hand, tooslow quenching generates coarse incoherent precipitatesleading to a reduction of the mechanical performances.In order to optimise the quenching rate and thesubsequent thermal treatment, a research project aimingto determine the correlation between RS field andmicrostructure changes induced by different quenchingrates were undertaken. In this framework, combinedstudies of RS by neutron diffraction [13] andmicrostructure evolution by Small Angle NeutronScattering (SANS) [14], together with the use ofmechanical tests and electron microscopy observations,were carried out.Four cylindrical samples (10 cm high, radius 5 cm) wereinvestigated in neutron diffraction experiments. Theywere submitted to two different quenching rates, and totwo subsequent ageing treatments, as reported in tab.I.

Sample n. Quenching Ageing

2 In water @ 20°C (30°C/s) T6 (16h @ 165°C)

3 In water @ 20°C (30°C/s) Natural (72h @ 40°C)

8 In boiling water (1°C/s) T6 (16h @ 165°C)

9 In boiling water (1°C/s) Natural (72h @ 40°C)

Tab. I. Investigated samples and thermal treatments.

The AA6082 macroscopic elastic constants have beentaken for stress evaluation: E=69 GPa, ν=0.383.Samples n. 2, 3 and 8 (tab.I) were investigated at theENGIN diffractometer of the ISIS spallation source at theRutherford Appleton Laboratory (UK). Two differentdetector banks, at ±90° with respect to the incident beamdirection, allowed the simultaneous measurement in twomutually perpendicular Q directions. The samplingvolume was 2x2x10 mm3.Sample 9 was investigated at the D1A diffractometer ofthe ILL, Grenoble (F). In this case the Al (200) peak wasconsidered (d200≈2.024 Å). The used wavelength wasλ=2.99 Å, thus giving a scattering angle 2θ≈95°. Thesampling volume was 4x4x1 mm3.In both experiments measurements were carried out with

the Q vector parallel to the three principal strain/stressdirections, assumed to be coincident with the radial,hoop and axial ones.In all samples different points lying along a cylinderradius were considered, at two different depths: 3 mmunder one of the bases and 25 mm (middle of thespecimen). The unstrained lattice parameter (interplanardistance in the ILL measurements) was calculated byimposing the equilibrium condition

(7)

where A is the surface area of a whole section of thesample and is the RS component normal to it. Foreach sample, the condition (7) was applied to both theradial scans performed, giving coincident values withinexperimental errors. The residual stresses measured

σ ⊥

σ σ π⊥∫ ∫= ⋅ ⋅ =

A

axial

R

dA r r dr( )

0

2 0

Fig. 4. Residual stresses in AA6082 quenched cylinders; Z=25 mm (middleof the specimen).

Fig. 5. Residual stresses in AA6082 quenched cylinders; Z=3 mm underthe specimen surface

14



along the radial direction at 25 mm from the cylinderbases (middle of the sample) are shown in fig.4. Theeffect of the quenching rate is evident comparingsample #2 to #8 and #3 to #9: independently on thesubsequent ageing treatments, the cylinders appear tobe free of RS when submitted to slow quenching.Samples submitted to fast quenching show compressiveRS in the outer zones, and tensile ones in the bulk, asexpected according to above consideration. The effect ofageing on fast-quenched samples is a reduction of theRS values by a factor ≈2 in the sample submitted to T6treatment (#2), with respect to the one submitted tonatural ageing (#3).Concerning measurements along the radial direction at 3mm under one of the cylinder bases (fig.5), again samples

submitted to slow quenching are essentially stress-free.As expected, in the fast-quenched samples compressiveRS are found, higher by a factor ≈2 in sample #3 (naturalageing) with respect to #2 (T6 ageing).Also as expected, in all cases the radial componentapproaches zero near the side cylinder surface, thusfulfilling boundary conditions (the RS componentperpendicular to the sample surface should be zero onthe surface itself).

3.2. Steel crown gearThermal austenitising and tempering treatments arebeing developed in automotive industry to preventcrack initiation and propagation, especially incomponents where stress intensity factors influence thestress field and ultimately the fatigue life of thecomponent. This is the case of crown gears, where thetooth root typically undergoes impulsive and very highloads which frequently cause cracking if tensile RS arepresent at the surface. The sign reversal of these stresses

is the aim of austenitising and tempering treatments.In the case of automotive crown gears, failure can occurmainly due to fatigue under bending (tooth breaking),tooth side surface degradation (pitting) and collapse ofsub-surface layers (spalling). According to finite-elementcalculations, the applied loads during operation aremaximum at the surface or just below it. The most criticalregion is the tooth root, where fatigue cracks are initiatedand act as stress concentrators. The generation of acompressive RS is then fundamental to prevent theinitiation of fatigue cracks. To this end the Multi-Frequency Induction Tempering (MFIT) technique wasdeveloped [15], whose effectiveness was checked byneutron and X-ray diffraction [16].The investigated sample is a UNI55Cr3 steel crown gear.The material composition is the following (wt%, Fe bal.):C=0.52-0.59, Si=0.1-0.4, Mn=0.7-1, Cr=0.6-0.9, P=S=0.035.The gear has a tooth height of 9.25 mm and an axialthickness of 25 mm; the tooth helix inclination is 30°.From the microstrucural point of view, the final result ofMFIT is the generation of a martensitic structure(hardness > 750 HV) up to a depth of about 1/2 of thetooth height, and 0.4 mm under the root, and to a sorbitic(fine globular pearlitic phase) inner structure (hardness370÷420 HV) up to 0.8 mm under the tooth root.According to numerical simulations [15], MFIT cangenerate comparable or lower compressive RS valueswith respect to other conventional techniques (e.g.thermochemical treatments, shot-peening), but for adepth about twice as big.X-ray diffraction measurements were carried out withCo-Kα radiation, applying the "sin2ψ" technique [4,7].The investigated Bragg peak was α-Fe (310). Neutron diffraction measurements were carried out atthe E3 diffractometer of the HMI-BENSC, Berlin (D). Theused neutron wavelength was 1.370 Å, and the

Fig. 6. Residual stresses in steel crown gear submitted to MFIT surfacetreatment; neutron diffraction measurements.

Fig. 7. Residual stresses in steel crown gear submitted to MFIT surfacetreatment; X-ray diffraction measurements.

15



investigated peak was α-Fe (211). In this casemeasurements on UNI55Cr3 powders were performedfor the evaluation of the unstrained interplanar distance.The powders were ground from the martensitic layer andthe parent material of the investigated specimen.Both in neutron and X-ray experiments gauge points atdifferent depths under the tooth root were considered.The results for the hoop RS component measured byneutron and X-ray diffraction are shown in fig.6 and 7,respectively. The agreement between the two techniquesis very good, taking into account that neutrons results areaveraged on a wide gauge volume (2x2x2 mm3).According to X-ray measurements, the maximum RSlevel introduced by MFIT is about -700 MPa. Far from thesurface the RS are tensile (+200 MPa), as expectedaccording to equilibrium conditions. The compressivezone extends up to 500 µm from the surface. This is dueto the martensitic layer at the tooth root surface whichresults in compression after quenching, as its expansionis not allowed by the tough sorbitic substrate.In neutron measurements the gauge point nearest to thesurface actually includes the whole range investigated byX-rays, thus explaining the lower level detected (-400MPa). The +200 MPa level far from the surface isconfirmed. X-ray measurements have been also carriedout on a sample submitted to a conventional shot-peening treatment. In this case a higher peak RS isreached (-1000 MPa), but the resulting compressive zoneis about twice as narrow (fig.8).

4. ConclusionsThe neutron diffraction technique for residual stressdetermination has been presented, and its maintheoretical and experimental features have been brieflydiscussed.

Some results concerning its applications to materials andcomponents for automotive technology have beenshown. The influence of quenching rate and subsequentageing treatments in AA6082 alloy has been investigated,showing that the slow quenching rate leads to vanishingstresses. Fast quenching gives rise to residual stresses,compressive at the surface and tensile in the bulk, asexpected. A reduction of these stresses by a factor ≈2 wasfound in samples aged according to the T6 process.The effectiveness of Multi-Frequency Induction Tempe-ring technique to induce compressive residual stresses atthe surface of a steel crown gear was demonstrated byneutron and X-ray diffraction. The stress level found iscompatible with expectations, and its comparison withthe one induced by a conventional technique (shot-pee-ning) shows a twice as narrow compressive zone, thou-gh the peak stress is slightly lower.

References

1. A.M. Jones, AERE Rep. R13005, Materials Department Division,Harwell Lab., Oxfordshire, 1989.

2. M.R. James, O. Buck, CRC Crit. Rev. in Solid State and MaterialsScience, 9 (1981) 61.

3. E. Schneider, K. Goebbels, Non-Destructive Detection and Analysis ofResidual Stress States using Ultrasonic Techniques, in Residual Stress,ed. V.Hauk, E.Macherauch, DGM Verlag, 1983.

4. V. Hauk, Structural and Residual Stress Analysis by NondestructiveMethods, Elsevier Publ., 1997.

5. A.J. Allen, MT. Hutchings, C.G. Windsor, C. Andreani, Adv. in Phys.34 (1985) 445.

6. Proc. of the NATO Adv. Res. Workshop on Measurement of ResidualStress Using Neutron Diffraction (Oxford, March 1991), Kluwer Acad.Publ., 1992.

7. I.C. Noyan, J.B. Cohen, Residual Stress - Measurement by Diffractionand Intrerpretation, Springer-Verlag, New York, 1987.

8. M. Ceretti, R. Coppola, A. Lodini, M. Perrin, F. Rustichelli, Physica B,213-214 (1995) 803.

9. I. Harris, P.J. Withers, M.W. Johnson, L. Edwards, H.G. Priesmeyer, F.Rustichelli, J.S. Wright, Proc. of the 4th Eur. Conf. on Adv. Materialsand Processes – Symposium F (Materials and Processing Control),Padova, Italy, 25-28/9/1995, Associazione Italiana di Metallurgia,p.107.

10. R.A. Young (ed.), The Rietveld Method, International Union ofCrystallography, Oxford University Press (1993).

11. G. Albertini, G. Bruno, B.D. Dunn, F. Fiori, W. Reimers, J.S. Wright,Mat. Sci. Eng. A 224 (1997) 157.

12. A.D. Krawitz, R.A. Winholtz, Mat. Sci. Eng. A 185 (1994) 123.13. G. Albertini, G. Caglioti, F. Fiori, T. Pirling, V. Stanic, J. Wright,

Materials Science Forum, in print (2000).14. G. Albertini, G. Caglioti, F. Fiori, R. Pastorelli, Physica B, 276-278

(2000) 921.15. F. Romani, Graduation Thesis, Faculty of Engineering, University of

Ancona, Italy, 1998.16. G. Albertini, G. Bruno, F. Fiori, E. Girardin, A. Giuliani, E. Quadrini, F.

Romani, Physica B, 276-278 (2000) 925.

Fig. 8. Residual stresses in steel crown gear submitted to shot-peening; X-ray diffraction measurements

16



AbstractCollective phenomena occurring in fluids such as phasetransitions are completely modified when they are confined ina porous matrix, and many aspects related to the criticalbehaviour are actually unsolved. We show here how small angleneutron scattering (SANS) experiments can represent a veryeffective experimental probe to investigate this class ofproblems, by describing some of the results obtained through aSANS experiment on a binary fluid mixture confined in porousVycor glass.

IntroductionPhase transitions occurring in fluids close to the criticalpoint (CP) such as the liquid-gas transition in a simplefluid, or the liquid-liquid one in a binary fluid mixture,are transitions of second order, thus described in terms ofthe 3-D Ising model, similarly to the case of magnetictransitions. At high temperatures, a binary mixture AB atthe critical concentration xc is in the homogeneous phase(we consider in the following a normal mixture: attemperatures higher than the critical temperature Tc, themixture is homogeneous). Then, approaching Tc,fluctuations of concentration begin to appear, and theformation of domains richer in one of the twocomponents occurs [1], the extension of which ismeasured by the correlation length ξ. This quantity isstrongly dependent on how close the temperature is tothe CP where it diverges according to scaling laws:ξ=ξ(T)=ξ0 t-ν, where ξ0 is a constant depending on thesystem (typically few Å), t=(T-Tc)/Tc is the reducedtemperature, and ν≈0.64 is a critical index [2]; finally, atT<Tc, the system separates into two phases.The static structure factor S(q) that is measured through aradiation scattering experiment (q being the wavevectorexchanged from the radiation) on a system close to aphase transition follows the Ornstein-Zernike law (OZ),i.e. a Lorentzian given by

(1)

with IOZ scaling like ξ2 apart from small corrections notrelevant in this context. A similar scenario characterises

the liquid-gas transition in a fluid, the main differencesbeing that the order parameter is here the density insteadof the concentration, and that are density fluctuationswhich take place.In the last years many theoretical and experimentalstudies have been devoted to a better understanding ofthe confined fluid behaviour, either for fundamental andfor technological reasons (catalysis, properties of fluidsconfined in rocks or clays, simulation of complexsystems). Despite of these efforts, many questions are stillopen specially in the case of critical phenomena, such asthe existence of a macroscopic phase separation, or theuniversality class of this (eventual) transition [3]. Theconfinement of the fluid in a porous system leads in factto a drastic alteration of the bulk static and dynamicproperties; a first obvious effect lies in the highlydiminished role of gravity, which ultimately drives thetransition in a pure fluid. Also, the properties of theparticular porous system, fluid, and of their coupling,cause additional strong complications on both theoreticaland experimental side. A simple classification of porous material is based ontheir porosity. Well known examples of high-porositymaterials are aerogels and xerogels (porosity up to98%), which are not rigid systems displaying volumefractal character over distances typically rangingfrom 10 to few thousands of Å (i.e., the pores size mayvary continuously over few orders of magnitude). Inhighly porosity silica aerogels, confinements isexpected to be not very important; indeed a liquidgas-transition has been observed in confined N2 and4He: a critical point at a temperature below that of thebulk case has been measured, as well as a narrowercoexistence curve [4]. Differently, rigid low-porosity systems such as Vycorsilica glasses present the relevant feature of having a porediameter almost constant, φv≈75 Å, and therefore areference length in the system. This has been one of thereasons which induced us to study the critical behaviourof a binary fluid in this porous matrix through a SANSexperiment [5]. Before going in some of the experimentaldetails, a resume of the theoretical and experimental stateof art will be given, followed by a short description of theSANS technique.

221)(

ξq

IqI OZ

+=

CRITICAL BEHAVIOUR OF A FLUID MIXTURE CONFINEDIN A POROUS GLASS INVESTIGATED THROUGH SANSF. FormisanoI.N.F.M., Largo Enrico Fermi, 2 Arcetri, I-50125 Firenze, Italy.

J. TeixeiraLaboratoire Léon Brillouin, C.E.A./C.N.R.S., F-91191- Gif-sur-Yvette CEDEX, France.

17



Binary fluid mixtures confined in VycorVycor glass [6] is a low porous (28%) silica glass obtainedby quenching a borosilicate glass forming a melt belowits Tc. The mixture is thus forced to undergo spinodaldecomposition which induces the formation of twophases, one richer in SiO2 and the second one richer inB2O3; the latter is then leached out and the final result isa highly interconnected random 3D porous network,with a pore size distribution sharply peaked at a meandiameter value of φv≈75 Å [7]; a 2D reconstruction isreported in Fig. 1. Among the various effects whichinfluence the critical behaviour of the confined fluid, thefollowing processes play a major role:

• finite-size effects due to the confinement, i.e. the spatialconstraint of the mixture to the tortuous interconnectedpore network;• the quenched random disorder introduced by the hostmatrix, which represents a random source of interactionbetween fluid and glass;• the different interaction between the two componentsof the mixture and the silica walls, which may induce agradient of the fluid composition inside the pores;• metastability, hysteresis, strong history-dependenteffects induce a strong increase of the times the systemneeds to reach equilibrium [8], which may add to thecritical slowing down occurring in proximity of the CP.All these effects are, with a different weight, sample-

dependent, thus giving rise to the real difficulties whichhave to be faced, both theoretically and experimentally.On the theoretical side, two main models have beenproposed in order to describe such phenomena. TheRandom Field Ising Model (RFIM) [9] is based on theimportance of the preferential attraction between thesilica walls and one of the fluid components, whereasconfinement is neglected. Preferential adsorption may beseen as a random field acting on the fluid, because of the

randomness of the pore network. Therefore, the presenceof quenched, i.e., spatially fixed, impurities can bedescribed by using the RFIM formalism, in analogy withthe case of magnetic materials affected by structuraldisorder (impurities, dirty). A RFIM transition ispredicted to occur, characterised by a static structurefactor S(q) simply given from the OZ term of Eq.(1)superposed to a Lorentzian squared term (LSQ):

(2)

with ξOZ≡ξLSQ. Phase separation would occur at atemperature much lower than the pure case, similarly towhat is found for a single fluid in gel [4].On the contrary, the single pore model was successivelyintroduced [10] as finite size effects are predicted todictate the confined fluid behaviour, specially in the caseof narrow pores such as those occurring in Vycor.Randomness is not here taken into account, and the glassis considered as an assembly of cylindrical independentpores. According to this model, when ξ becomescomparable to φv, phase separation may occur only at amicroscopic level, because of the extremely long times(even not experimentally accessible) that fluctuationsneed for taking place throughout the complex porenetwork. Various configurations inside the pore mayexist which depend on the temperature and on the lengthscales involved: bubbles richer in one liquid occupyingthe tube, layer richer in one liquid and core richer in theother, and so on. This dualism has been not clarified by means of twoSANS experiments on water+lutidine imbibed insideVycor [11, 12], both performed close to bulk criticalconditions. The measured S(q), even though very similar[13], were interpreted according to the two models byusing the same Eq.(2) to describe the experimental resultsbut (i) in [12] ξOZ≠ξLSQ, and (ii) a very different modelwas used to describe an unexpected peak in the data (thispoint will be discussed in more detail later).. A commonfinding was that no true critical behaviour was observed,and only fluctuations up to few tens of Å were detected

Some SANS principlesBasically two reasons make the SANS technique a wellsuited experimental approach to this kind ofinvestigation:• SANS probes lengths in the 10-1000 Å range, thereforedistances over which critical fluctuations occur; • the large strength variation of the neutron-nucleusinteraction as a function of the atomic number allows tovary the scattered intensity without changing thephysical properties of the sample (contrast matching

S qI

q

I

q

OZ

OZ

LSQ

LSQ

( ) =+

++( )1 1

2 2 2 2 2ξ ξ

Fig.1. Digital reconstruction of a transmission electron micrograph of aVycor thin section which shows the random nature of the pore network(in black) immersed in the silica matrix (in white) (from [7]).

18



technique); this effect is particularly important in the caseof hydrogen and deuterium nuclei, making deuteration afrequent tool in neutron scattering.This section is dedicated to a short resume of the SANSprinciples, in order to give the basic ideas of thistechnique; the relations between the intensity I(q)measured at small values of q, and the quantity ofinterest, the static structure factor S(q), can be found inmany text books [14]. By SANS, it is generally meant the neutron diffraction atscattering angles θ<5°. In fact, in a neutron reactor,neutrons with the longest available wavelengths λ haveto be used for reaching low values of the exchangedmomentum q=4π/λ sin(θ/2)~2πθ/λ, thus giving access tolength scales of the order of r~q-1. To keep the flux at agood level, the beam is monochromatised through amechanical velocity selector at values of λ in the 4-20Årange (cold neutrons) and then collimated. Finally, theintensity scattered from the sample is collected by a two-dimensional circular detector placed at distances from 1to 10 m; the position sensitive detector consists of around4000 (or 16000) cells, 1×1cm2 (0.5×0.5cm2) each. Theoverall resolution is usually ∆q/q≈10%, mainly due to thebeam monochromatisation; despite of this large value, itis worth reminding that, apart from special cases, thelow-q signal displays a smooth behaviour, thereforeresolution is not crucial.Once obtained the intensity at constant θ, it isimmediately converted in I(q) at constant q, apart fromeventual corrections due to multiple and inelasticscattering. From I(q), the determination of the differentialcross-section dσ/dΩ is then straightforward, as these twoquantities are proportional; the coefficient ofproportionality depends on the experimental geometry(both sample and instrument), detection efficiency,incoming flux, sample transmission, and can beevaluated separately. In such way it is possible todetermine I(q) approximately in the 10-1-10-3 Å-1 q-range.For deriving the relation between S(q) and I(q), it isnecessary to remind that dσ/dΩ is the results of all thepossible interferences of the neutron waves scattered bythe nuclei, weighted by the amplitude of the nuclei-neutron interaction, that is

(3)

where the summation extends over all the N nuclei of thesample, rij is the distance between ith and jth atoms, <…>indicates an averaging over all the possibleconfigurations, and bi is the coherent scattering length ofnucleus i, which is of the order of 10-12 cm, reflecting theshort range of the nuclear forces; the reason why isotopic

substitution is very common in neutron diffraction is thatbi may vary strongly with the atomic number, the morestriking case being H and D nuclei where bH=-0.37 10-12

cm and bD=0.67 10-12 cm. The exact relation (3) needs to be worked in order toconnect it to S(q) at small q; without entering into thedetails of the complicated formalism which is needed tofulfil this task, it is more useful to describe its relevantphysical aspects: • in Eq.(3), mainly the components with q⋅r~1 give asignificant contribution to the sum;• the SANS technique probes distances much larger thanthe typical atomic size, therefore it is useless to look at theindividual atom positions, but it makes sense to averageover spatial regions containing large number of atoms.As a consequence, the notion of scattering length densityρ is naturally introduced, ρ=n⋅b, where n is numberdensity;• the static structure factor is defined as

(4)

that is a quantity reflecting the spatial distribution of thecentres of mass, as can be understood because the Fouriertransforms of the atom individual positions δ(r-ri) are theexponential term exp(-iq⋅ri) appearing in Eq.(4). It is alsoworth noticing that Eq.(3) can be seen as the Fouriertransform of the spatial fluctuations of the scatteringlength density b. Through these hypotheses, the simpleformula which relates the scattered intensity IAB(q) to S(q)via the scattering lengths densities ρA and ρB of the two-components system A+B is derived:

(5)

The structure, i.e. S(q), is therefore uncoupled from theneutron interaction properties of the sample, representedfrom the contrast KAB=ρA-ρB. As, by isotopic substitution,it is possible to largely modify the contrast of the system,the scattered intensity can be thus modulated, withoutaffecting the structure.

Experimental resultsIn order to elucidate some of the open questionspreviously mentioned, we have performed a new SANSexperiment on a binary mixture fluid confined in Vycorglass [5], with the intention of determining S(q) in athermodynamic region close to the bulk critical one.Among the effects which may lead to complications in

( ) ( ) ( )qSKqSqI ABBAA B22 )( =−= ρρ

S i iji j

Nq q r( ) = ⋅( )∑ exp

,

d

db b ii j ij

i

NσΩ

= ⋅∑ exp( )q r

19



the data interpretation, particularly severe is the roleplayed by the different wetting properties of the mixture;this effect could induce a strong (and uncontrolled) shiftof the fluid composition inside the pores and, possibly,also a true phase separation, not of thermodynamicorigin, but driven by wetting forces. We chose to performthe experiment on the mixture n-C6H14+n-C8F18(hexane+perfluorooctane, in the following namedhex/PFO), because: • the two fluids have a similar affinity to the silica, andpreferential adsorption is expected to be minimised;• fluorine compounds has high values of b, thus a goodcounting rate is allowed;• the bulk critical temperature is experimentally easilyaccessible;• by partially deuterating with C6D14, it is possible tovary the scattering length density of the fluid, and matchthe contrast with Vycor (ρv≈3.5 1010 cm-2).We have measured (PAXE small angle diffractometer,Laboratoire Léon Brillouin, CEA/CNRS, Saclay) S(q) of

the hex/PFO mixture imbibed inside Vycor at differentvalues of C6D14 concentration, but all of them with thesame bulk critical concentration of PFO. We could thenstudy three bulk critical mixtures with different contrastwith the Vycor. Deuteration induces a slight decrease ofthe bulk critical temperatures, which is Tc=38°C for thesample completely hydrogenated (#H), Tc=29°C for thesample completely deuterated (#D); the third sample(#HD, Tc=33°C) had an intermediate degree ofdeuteration, in order to match the contrast with the glass. The samples were imbibed inside the porous glass at

T=60°C, therefore deeply inside the single phase region;the quartz cells containing the slabs of Vycor were thensealed, in order to work at fixed concentration. Anotherdifficulty in such investigations results from the very lar-ge relaxation times which may occur in the evolutiontowards equilibrium. We decided to store #HD verylong times at low temperature before the experiment(two months at T=0°C). The presence of long times cha-racterising the relaxation of concentration fluctuationswas confirmed by the first set of measurements at T=55and 50°C: for #H and #D an exponential decrease of thesignal of the order of several tens of hours was observed,while #HD reached quickly equilibrium. Therefore, as inneutron scattering experiments the beam time is rare, wecould not wait until the system reached equilibrium atthese temperatures. At T=44.5°C, equilibrium was rea-ched within few hours, and we can consider these liketrue experimental stable measurements, in the sense thatrepeated runs showed a constant signal; it is worth spe-cifying that for such systems the concept of equilibriumis different from the classical one, as there is no a definitetransition from metastability to stability, but a slow con-tinuous time evolution of metastable states which can beassumed to be quasiequilibrium states [15]. Data have been collected at five temperatures fromT=44.5°C to T=15.5°C, therefore up to temperatureswhere the pure mixture would be phase separated. Theintensity I(q) corresponding to the highest and lowesttemperature are shown in absolute units in Fig. 2,together with the signal coming from the dry Vycor. Wemay note the following:• Dry Vycor. This signal is dominated by the huge broadpeak (Imax≈200 cm-1) centred at qv=0.023 Å-1, andinterpreted in terms of Eq.(5): Iv=K2

v Sv(q)=ρ2v Sv(q), as the

pores are empty. The presence of such peak reflects theexistence of a characteristic length, given by the almostconstant diameter of the quasiperiodic pore networkimmersed in the silica glass.• #H and #D. The amplitude of the dry Vycor peak isnow decreased because of the lower contrast due to thepresence of the fluid (see Eq.(5)). A strong increase of thesignal at low q is detected, when temperature isdecreased, in a similar way to what occurs in presence of

Fig.2. Logarithmic plot of the intensity (in absolute units) scattered fromthe dry Vycor (stars) and from the samples at the lowest (open symbols)and highest (full symbols) temperature. From the bottom: #HD (circles),#H (diamond), and #D (squares); the line represent the result of the fittingprocedure according to Eq.(8). In the inset at the bottom a pore sectionwith a layer richer in fluid B and a core part richer in fluid A is depicted;V stands for the Vycor. Such structure would give rise to a double peaksimilar to the one observed in the experimental data.

20



critical fluctuations. A small bump in the intensity atqsv=0.05 Å-1 is noted, and later commented.• #HD. Because of the contrast matching, in this sample alarge reduction of the signal level (of a factor ~200) hasbeen found. No particular features at low q are present,leading us to conclude that, unlike the other two samples,a thermodynamic phase separation took place during thetime it was kept at low temperature. The increase oftemperature from 0°C to 60°C (thus again in the singlephase of the pure mixture) at the moment of theexperiment, did not allow the remixing of the confinedmixture; this irreversible phenomenon can be understoodreminding that hysteresis effects appear also in the bulkcase, and the mixing of a mixture can be a very longprocess (differently from the separation) without hardlystirring the sample. The second peak, here largelyenhanced with respect to the other two samples, wasalready observed in [11, 12], and can be interpreted ascoming from a wetting layer, richer in one of the twofluids (fluid A for instance, as shown in the inset of Fig.2)which coats the pores walls, leaving a core part richer inthe other fluid [12]. As a consequence, the appearance ofa new characteristic length shorter than φv, and thereforeof a new peak at qsv>qv in S(q), are induced. The variationof temperature causes simply a remixing of the twophases, i.e. a modification of their contrasts, andtherefore of the peaks amplitudes. On the basis of the latter considerations, we haveanalysed the results of #H and #D trying to write downa model which takes in account the presence of thisdouble-layer structure. Such configuration can be seen asthe one coming from two interpenetrating quasiperiodicnetworks, analogously to the bicontinous phase. It isclear that this is an ideal representation, as it is realistic toassume the presence of a single phase (A or B) in some ofthe necks, corners, and narrower pores which are presentin this glass. But it is important to remark that it is thisdouble-layer configuration that is responsible for the twopeaks, while a pore occupied by a single fluid would givea contribution proportional to the dry Vycor peak. Thiscan be better understood when considering that thedouble-layers configuration can be represented by [16]

(6)

where Kbv (Kba) is the contrast between fluid B and Vycor(fluid B and A), and Fv (Fsv) is the corresponding formfactor. It is immediate to conclude that F2

v is exactly thedry Vycor structure factor Sv, as obtained in the case B=A(eventually the vacuum), and Eq.(6) reduces to (KbvFv)2,that is the dry Vycor structure factor modulated with adifferent contrast due to the presence of B. More care hasto be paid as far as the second term is concerned. The

starting point is that Vycor is obtained by spinodaldecomposition, for which the more general dynamicalscaling law is given from [17] :

(7)

where C is a constant, f(q/qmax) is an universal function ofthe ratio q/qmax, with qmax corresponding to the maximumof the structure factor (qv in case of Sv), and d=3 is thedimension of the system. This relation is a dynamical lawin the sense that describes the later stages of spinodaldecomposition of quenched unmixing mixtures, wherethe slow formation of pores of increasing size, andtherefore of time-dependent decreasing values of qmax(t),occurs; this time dependence is not explicitly indicated inEq.(7) as it refers to the static situation. As mentioned above, it is possible to represent the newdouble-layer structure as a new quasiperiodic structurehomotetic of the dry Vycor one, therefore as a previousstage of the spinodal decomposition which forms theglass: similarly to what we said about Sv, Ssv≡Fsv

2 repre-sents a new dry Vycor with narrower pores (as it can be

I q Cfq

qq d( ) =

−

maxmax

K F q K F qbv v ba sv( ) − ( )[ ]2

Fig.3. Experimental intensity scattered from dry Vycor Iv(q) (stars)compared with the calculated value Isv(q) (circles) as obtained fromIv(q) byapplying the scaling law (7).

21



seen equating B=V in Eq.(6) and in the inset of Fig.2),with Kba being the corresponding contrast. On the basisof these ideas, Ssv was calculated by (i) scaling the experi-mental values of Sv, in order to obtain f(q/qmax), and (ii)applying Eq.(7) with qmax≡qsv; the result is shown in Fig.3. Once defined a model to describe the structure, the data of#H and #D were fitted by adding to Eq.(6) the OZ term (1)in order to take into account the low-q behaviour, that is:

(8)

where Ioz, ξ, and the two contrasts are parameters of thefit; the good agreement with the experimental data (seeFig.2) suggests the validity of the model we adopted.Before looking at some of the results of the fit, it isinstructive to see the relative importance of the singleterms of Eq.(8) as obtained from the fit, which areshown in Fig.4 for #D at the lowest temperature; weobserve that:• as expected, the OZ term dominates at low q; theabsolute value of intensity is large, therefore criticalfluctuations extend over long distances.

• In these two samples, the contrast of the mixture withthe Vycor was rather large, and consequently also theterm K2

bvSv(q).• The term K2

baSsv(q) is very low (almost zero in thisscale), meaning that the contrast between B and A issmall, that is the composition of the two phases is verysimilar.• The cross term which describes the coupling betweenthe Vycor and the two phases is negative, and itscontribution extend over a wide q-range.These considerations apply for both samples at all theinvestigated temperatures, as shown in Fig.5, where thevalues of ξ and of the two contrasts are reported.Globally, we may note that the temperature influencesslightly the fluids behaviour, at least in this range oftemperatures, while in the pure case a phase transition isobserved. As far as the contrasts are concerned, the maindifference lies in their opposite signs, a fact which madeus to conclude [5] that is the hexane rich phase whichwets the silica walls (phase A in our representation),confirming previous observations on a similarperfluoroalkane+alkane mixture imbibed in silicaglasses. Quantitatively, the evaluation of the ratiobetween Kba=ρb-ρa and the ρ value of the imbibed criticalconcentration, gives the concentration composition shift

I qI

qK S q K S qOZ

bv v ba sv( ) =+

+ ( ) − ( )[ ]1 2 2

2

ξ

Fig. 4. Intensity scattered from #D at the lowest temperature (full squares),compared with the result of the fit to the data through Eq.(8). The symbolsindicating the different components of the fit are shown in the legend.

Fig. 5. F Fit parameters relative to #H (full symbols) and #D (opensymbols) as function of the temperature. In (a) the contrasts Kbv (square)and Kba (circles) are shown, while the dashed line indicates the zero level.ξ data are reported in (b), and compared with the mean pore diameter φv

(dashed line); two arrows mark the two bulk critical temperatures.

22



in the pore induced by the preferential adsorption. Wethus found a variation of ~10% for #H and of ~2% for #D,meaning that the confined fluid were still close tocriticality.The large values of the correlation length confirm that thetwo samples, mainly #D, were close to critical conditions,but the qualitative behaviour is very different than thebulk mixture where, close to CP, ξ varies rapidly. ξincreases slowly when lowering the temperature, evenwell below the bulk critical point, therefore the system isnot yet separated, unlike #HD where a thermodynamicphase separation had taken place. The critical point, ifany, is placed at lower temperatures than the pure case,as predicted. An important difference with the previousresults lies in the detection of ξ>φv, meaning thatfluctuations may extend along several pores, and that φvdoes not represent a length cut-off. It seems significantand realistic, even though based only on few points, thatwhen ξ is of the order of φv, the temperature dependenceξ=ξ(T) is rounded off, as if the effect of finite poredimension consisted in a smearing of the correlationlength distribution.

Conclusions and perspectivesWe believe that the class of mixtures we haveinvestigated are very suited for these studies as thewetting effect results of minor importance, and criticalfluctuations are enhanced. It is reasonable in fact toconclude that the adsorbed layer consists of a thin filmblocked on the pore while, in the free core part, criticalfluctuations of rather extended lengths can take place asthe concentration is still close to the critical one. Thissuggests that the RFIM is the proper model at least for thesystem here studied. We did not observe any presence ofa LSQ term, but a huge precision would be needed todistinguish such contribution from the remainingcomponents; also, the presence of a LSQ term,manifestation of a RFIM transition, could occur at lowertemperatures. It is clear that such subject deserves furtherinvestigation for a deeper understanding of thesephenomena. It would be interesting to study the liquid-gas transition in a simple fluid, but more complicatewould be the choice of the system, because the densityfluctuations scatter much less than concentrationfluctuations. In order to discriminate the OZ contributionfrom the other ones, a very good contrast should beachieved, but this is not feasible with the majority offluids. We are going to carry out new SANS experimentson perfluoroalkane+alkane mixtures with Tc higher thanthe one of the investigated mixture; in this way it will bepossible to study the critical phenomena on a moreextended temperature range, that represents a conditionnecessary for a better comprehension of this subject. As amatter of fact, SANS represents the good technique for

this purpose, but the real experimental difficulty which isemerged lies in the long relaxation times needed toperform equilibrium measurements. To partially bypassthis problem, which is in conflict with the low availabilityof neutron beam time, we believe that a contemporarystatic and dynamic study by light scattering isfundamental.

References1. It is worth to remind that the transition into the two-phase region does

not imply that fluid A is completely separated from the fluid B;2. For an introduction to this subject see Stanley H E 1971, Introduction

to phase transitions and critical phenomena (Clarendon Press,Oxford);

3. A resume of the experimental and theoretical state of art as well as acomplete list of the relevant literature can be found in Pitard E,Rosinberg M L and Tarjus G 1996, Mol. Sim. 17, 399;

4. Wong A P Y and Chan M H W 1990, Phys. Rev. Lett. 65, 2567;5. Formisano F and Teixeira J 1999, to be published in Europ. Phys. J. E;

Formisano F and Teixeira J 1999, to be published in J. Phys.: Condens.Matt.;

6. Vycor Glass No. 7930, Corning Glass Works, Corning, NY 14830;7. Levitz P, Ehret G, Sinha S K and Drake J M 1991, J. Chem. Phys. 95,

6151;8. Fisher D S 1986, Phys. Rev. Lett. 56, 416;9. Brochard F and de Gennes P G 1983, J. Phys. Lett. (Paris) 44, 785; de

Gennes P G 1984, J. Phys. Chem. 88, 6469; Andelmann D and Joanny J-F 1985, Scaling Phenomena in Disordered Systems, ed Pynn R andSkjeltorp A (New York: Plenum), p. 163;

10. Liu A J, Durian D J, Herbolzheimer E and Safran S A 1990, Phys. Rev.Lett. 65, 1897; Liu A J and Grest G 1991, Phys. Rev. A 44, R7894; Page JH, Liu J, Abeles B, Deckman H W and Wez D A 1993, Phys. Rev. Lett.71, 1216;

11. Dierker S B and Wiltzius P 1991, Phys. Rev. Lett. 66, 1185;12. Lin M Y, Sinha S K, Drake J M, WU X -l, Thiyagarajan P and Stanley H

B 1994, Phys. Rev. Lett. 72, 2207;13. A detailed analysis of these two experiments in terms of the two

models can be found in Monette L, Liu A J, and Grest G 1992, Phys.Rev. A 46, 7664;

14. See for instance Guinier A and Fournet G 1955, Small Angle Scatteringof X-Rays (Wiley, New York), and Glatter O and Kratky O 1982, SmallAngle X-Ray Scattering (Academic, London);

15. Fisher D S, Grinstein G M, and Khurana A 1988, Physics Today 41, 5616. See for instance Ottewill R H 1991, J. Appl. Cryst. 24, 436;17. Furukawa H 1984, Physica 123A, 497.

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Nano-structured semiconductor materials with a lateraldimension less than the de Broglie wavelength of electrons areexpected to exhibit quite different electronic properties fromthose of common devices. Fabrication technologies for nano-structured devices have been developed recently, and theelectrical and optical properties of such nanostructures are asubject of advanced research. However, classical spectroscopictechniques can not be applied to these structures because theirlateral resolution is not sufficient to resolve them. In order tounderstand and to control their physical properties, it isindispensable to evaluate the nanostructures by usingnanospectroscopic techniques. In this review article, thedifferent approaches to nanospectroscopy will be discussed, thatis, photon and electron probe nanospectroscopy and proximalprobe techniques. Particular emphasis will be put on thesynchrotron radiation photoelectron nanospectroscopy.

1. IntroductionThe semiconductor industry has grown rapidly in recentdecades. The main reasons for such phenomenal marketgrowth are the continued technological breakthroughs inintegrated circuits (ICs). The metal-oxide-semiconductorfield effect transistor (MOSFET) is by far the mostcommon type of transistor in IC technology [1]. In the1960s, Gordon Moore observed that the feature size inMOSFETs was decreasing by a factor 2 roughly every 18month [2]. This empirical trend has continued untiltoday, where structure sizes below 0.35 µm are used [3].Device miniaturization results in reduced unit cost and inimproved performance. This is illustrated with theperformance of a typical personal computer over theyears. Another benefit of miniaturization is the reductionof power consumption.However, researchers have projected that below 100 nm insize, the laws of physics will prevent further reduction inthe minimum size of today's MOSFETs, and new deviceconcepts will have to be found which take advantage ofthe quantum mechanical effects that dominate on such asmall scale [3,4]. A number of nanometer-scale deviceshave already been realized: Resonant-tunneling devices[5], single-electron transistors [6], and quantum dot arrays[7]. These devices have minimal structure sizes oftypically 50 nm [8-11]. All these designs have in commonthat the active region of the device is in the surface regionof the wafer (topmost µm).

The fabrication techniques at least for prototypenanoscale devices have already been developed. Whilethe traditional UV lithography, which is used for today'sdevices, probably will not go below 200 nm [3], x-raylithography allows feature sizes from 500 nm to 30 nm[12]. Electron-beam lithography can even do better withminimal structure sizes of a few tens of nanometers [13].There is also a strong effort to use proximal probetechniques for nanomanipulation. With the scanningtunneling microscope (STM) it is now possible to movesingle atoms in a controlled way on a surface [14]. STMsand atomic force microscopes (AFMs) have been used tobuild working nanodevices [15,16]. These scanningmethods are still too slow for real production, but thereare efforts to put several hundred tips or evenmicroscopes on one chip to speed things up [17,18].All practical semiconductor elemental analysis employsspectroscopy. A probe in a well defined quantum-mechanical state (usually a monochromatic photon orelectron beam) is interacting with the sample. Anychanges in the state of the probe beam are then measured,or other particles excited by the probe are detected. Inbrief, the main advantage of an electron probe is therelative ease of beam handling, especially also in focusingthe beam on a small spot on the surface [19]. On the otherhand, the use of a photon probe strongly reduces beamdamage on the sample [20]. The surface sensitivity of themethod is mainly determined by the choice of thedetected particles. Electrons with typical energies of 10 to2000 eV have a very small escape depth (less than 5 nm)[21]. Methods detecting low energy electrons aretherefore very surface sensitive. The attenuation length ofphotons in semiconductors is much larger, these methodstherefore are more bulk-sensitive [22].Among the classical spectroscopies, x-ray photoelectronspectroscopy (XPS) and Auger electron spectroscopy(AES) are by far the most common ones in surface science[21,23]. In AES, Auger electrons are excited by a photonor electron beam. Since Auger electrons have discretekinetic energies that are characteristic of the emittingatom, AES is particularly useful for an elemental analysisof the sample surface. In XPS, the sample is excited by amonochromatic x-ray beam, and the photoemittedelectrons are energy selected. The energy distributioncurve of the photoelectrons is, again, characteristic of the

NANO-SCALE SPECTROSCOPY AND ITS APPLICATIONSTO SEMICONDUCTORSS. HeunSincrotrone Trieste, S.S.14, km 163.5, Basovizza, 34012Trieste, Italy.

G. SalviatiIstituto MASPEC, CNR, Parco Area delle Scienze 37A,43010 Loc. Fontanini, Parma, Italy.

Articolo ricevuto in redazione nel mese di Marzo 2000

24



emitting atoms and, more importantly, of their chemicalenvironment. Therefore, XPS goes beyond elementalanalysis to provide chemical information. It should bestressed here that also with AES a chemical analysis ofthe sample is possible in selected cases. However, theanalysis of such results is more complicated than in thecase of XPS. The reader will find a detailed discussion ofthis topic in Ref. [23]. A typical probe spot size in XPS andAES is of the order of 300 µm [24-26]. Another methodvery commonly used in semiconductor science isphotoluminescence (PL) spectroscopy [27]. Light isdirected on a sample, where it is absorbed and can excitecharge carriers. When these carriers relax to theirequilibrium state, the excess energy can be emitted in theform of light. The energy of the light is related to theenergetic levels within the semiconductor. PL is thereforeuseful to determine the band gap of a semiconductor,impurity levels, and recombination mechanisms.However, all these classical spectroscopic techniques areof limited use in the study of semiconductornanostructures, because their lateral resolution is notsufficient. Therefore the use of spatially resolvedspectroscopic probes is required. In this review article,the different approaches to nanospectroscopy will bediscussed. We will restrict ourself to photons andelectrons as sample probes, their main advantages beinga limited modification of the sample surface and theircompatibility with ultra high vacuum [28]. Other kinds of

probes are less commonly used and are discussed indetail in Ref. [28]. After two sections dealing with photonand electron probe nanospectroscopy, we will dedicate athird section to proximal probe techniques.

2. Photon Probe Nanospectroscopy2.1. General ConsiderationsSince the spatial resolution of normal optical microsco-pes is diffraction-limited to approximately half the lightwavelength [29,30], nanometer resolution requires theuse of ultraviolet light or x-rays. Laboratory sources donot provide enough intensity for high resolution studies[28]. X-ray lasers are being considered as light sourcesfor nanospectroscopy [31], but so far no working instru-ment has been demonstrated. Therefore the only lightsource available at this moment for photon probe nano-spectroscopy are synchrotrons. Detection of light is pos-sible [32], but due to the large x-ray attenuation length ofa solid this results in a rather bulk-sensitive measure-ment (100 nm sampling depth and more) [22]. Work intransmission requires thinned samples (thickness ≈ 100nm) which is not straightforward [19]. Therefore the de-tection of photoexcited electrons with an escape depth ofonly a few nanometers is preferible in most semiconduc-tor applications. Here, the detection of photoelectrons isadvantageous with repect to the detection of Auger elec-trons, because the photoelectron characteristic peaks aremuch narrower than Auger electron peaks [28]. Further-

Fig. 1. A sketch of the ESCA microscopy beamline at Elettra. X-rays from the undulator are monochromatized and focused by a zone plate (ZP) throughan order selecting aperture (OSA) on the sample, which is mounted on a scanning stage. A hemispherical (HS) analyzer is collecting the photoelectrons.

monochromator

undulator

focusing optics (ZP&0SA)

HS analyser

scanning stage

25



more, the signal-to-background ratio for Auger electronsis smaller than for photoelectrons [28].There are two basic ideas about how to realize photonprobe nanospectroscopy: scanning mode and imagingmode. In the scanning type design, the spatial resolutionis obtained by focusing the illuminating light on a smallspot on the sample. The signals of interest such as thephotoelectrons, the fluorescence, or the transmitted x-rays are integrally collected. Images are obtained byscanning the sample relative to the beam. In imaging mo-de, the sample is homogeneously illuminated with pho-tons, and an electron optics forms a magnified image ofthe sample surface on a screen. The spectroscopic infor-mation is obtained by either scanning the photon energyor by providing the microscope with an energy filter.

2.2. Photoelectron Microscopes2.2.1. Scanning Type Photoelectron MicroscopesIn a scanning microscope, the light is focused by a Fre-snel zone plate or a Schwarzschild objective on a smallspot (diameter ≈ 100 nm) on the sample [30]. Both need ahigh brilliance light source. The excited photoelectronsare collected by a commercial hemispherical analyzerwith a typical energy resolution of 200 meV [30]. This issufficient for the detection of chemical shifts in core levelpeaks [33] and for valence band spectroscopy [34]. Sam-ples do not need to be flat, so that, for example, measu-rements on cross-sectioned samples can be performed[35]. Drawbacks of this design are the bad time resolu-tion caused by the need to scan the sample relative to thelight spot, and the high photon flux in a small spot, whi-ch might locally charge or damage the sample [36].

A typical setup for a scanning photoelectron microscope(SPEM) employing a Fresnel zone plate is shown inFig. 1. It shows the ESCA microscope at the Elettrasynchrotron radiation source in Trieste, Italy [37]. Fresnelzone plates are circular diffraction gratings made of analternating sequence of absorbing and transparent rings.In certain distances from the zone plate, all transmitted

lightwaves will have a phase difference of 2πn (n integer),i.e. the condition of constructive interference is met.Therefore zone plates act as lenses with several foci. To block the higher order foci, an order selecting aperture(OSA) is used. The (unfocused) zero-order light isblocked by a central stop in the zone plate. The efficiencyof modern zone plates can reach 55 % for hard x-rays (7 keV). For soft x-rays (hv < 1 keV), an efficiency of 10%is routinely achieved. The minimum spot size that can beobtained is 1.22 times the width of the outermost ring[38]. Nanolithography is therefore required to producezone plates with nanometer spot size. A typical focallength of a zone plate lens for light with 500 eV is somemillimeters. Since the focal length is proportional to thephoton energy, work at much lower photon energieswould result in unpractically short working distances.Therefore, zone plates are not used in photoemission atphoton energies below ≈ 300 eV.A Schwarzschild objective is consisting of a concave anda convex mirror. Fig. 2 shows as an example thespectromicroscopy beamline at Elettra [39]. The radiationimpinges nearly orthogonal on the Schwarzschild mirrorsurfaces. Since the reflectivity of metals for normalincidence in the VUV and for x-rays is very small (< 1 %[22]), multilayer coatings have to be employed. Theyenhance the reflectivity by constructive interference ofthe wavefronts reflected at the single layer boundaries.This condition is met if the wavelength equals 2 times thelayer thickness. Modern multilayer coatings can reach ina small energy range reflectance values of the order of 50% [24]. This implies that for each photon energy adedicated Schwarzschild objective has to be build. Scans

of the photon energy are practically impossible [24]. Sinceeach layer of the coating has a thickness comparable tothe photon wavelength, surface and interface roughnessprevents the use of Schwarzschild objectives for shorterwavelength, i. e. higher energies (E > 300 eV) [40].This particular property of Fresnel zone plates andSchwarzschild objectives explains also why there are still

Fig. 2. Schematic optical layout of the Spectromicroscopy beamline at Elettra. X-rays from thesource are directed to a pinhole (P), from where they are focused by a Schwarzschild objective onthe sample which is mounted on a scanning stage (SS). Photoelectrons (e-) are collected by ahemispherical energy analyzer.

Microscope

FocusingMirrors

SwitchingMirror

SourceRefocusingMirrors

Monochromatore–

26



two different systems in use, why it is not possible to findthe best technical solution. The use of Fresnel zone platesfor photoelectron spectroscopy at photon energies belowabout 300 eV is unpractical due to their short focal length,and exactly in this low energy range, the Schwarzschildobjectives show their best performance.

2.2.2. Imaging Type Photoelectron MicroscopesThe virtually only imaging photoelectron microscope isthe photoemission electron microscope (PEEM). In thissetup, the light is illuminating a spot of severalmicrometer diameter on the sample. This spot size is stillsmall relative to what is used in classical (integral)setups, but it is large compared to what is required in thescanning type design. A PEEM employs electrostatic ormagnetic lenses to form a magnified image of the sampleon a screen. It allows continuous imaging with video rate[41]. A basic PEEM is shown in Fig. 3 [42]. Such modernsystems reach a lateral resolution of better than 50 nm[42-45]. The early PEEM work has been performed withdeuterium or mercury lamps [41]. In these experiments,lateral variations of the work function of the sample were

used as contrast mechanism. However, to do realelemental sensitive work, higher photon energies arenecessary to excite atomic core levels. But even withsufficiently high photon energies, a standard PEEM cannot be used for micro-XPS because it is not equipped witha photoelectron energy analyzer. However, it has been

shown that the total photoelectron yield is almostproportional to the photoabsorption coefficient [46]. So,by scanning the photon energy one can perform opticalabsorption edge spectroscopy with the lateral resolutionof the PEEM. This technique is called µ-XANES (x-rayabsorption near edge spectroscopy). It is very useful forthe study of organic and of magnetic materials. Arequirement for this kind of experiments is a tunable x-ray source. Therefore spectroscopic work with PEEMrequires the use of a synchrotron. In summary, the PEEMis a simple instrument with by far the best time resolutionof all nanospectroscopies. No complicated x-ray optics isneeded, no sample scanning necessary. One drawback isthe need for a flat sample.The lateral resolution of this instrument is not limited bydiffraction, but rather by lens aberrations. Therefore, thespatial resolution of a PEEM can be increased by reducingthe aberrations. One way to do this is to add an energyfilter to the PEEM [43,47,48]. This reduces chromaticaberrations and allows to collect photoemission spectra,which in the case of semiconductors provide moreinformation than XANES spectra. A lateral resolution of22 nm and an energy resolution of better than 0.5 eV havebeen achieved with such an instrument at Elettra. Aschematic drawing of it is shown in Fig. 4 [49]. It is calledspectroscopic photoelectron and low energy electronmicroscope (SPELEEM) because it is also equipped withan electron gun to perform low energy electronmicroscopy with a lateral resolution of 8 nm [50]. Theseparation between incoming and outgoing electrons isachieved by a magnetic prism (sector field). The electronsemitted or reflected from the surface are transferred intothe image plane of the microscope, where a magnifiedimage of the sample can be observed with a video cameraor a slow scan CCD camera. When used as an electronmicroscope, the SPELEEM can be used to obtain real

Fig. 3. A schematic drawing of the IS-PEEM. The sample is illuminated byx-rays of energy hv. The PEEM consists of three electrostatic lenses. Thelateral photoelectron distribution is detected by a multichannelplate, ascreen (YAG crystal), and a CCD camera.

Fig. 4. Schematics of the spectroscopic photoemission and low energyelectron microscope (SPELEEM). The sample can be illuminated by x-raysor with an electron gun. The sector field is used to seperate the incomingand outgoing electrons. The analyzer selects electrons with a certainkinetic energy. The projector is used to display the magnified image of thesample on the screen.

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space images of the sample (LEEM) or to measure theintensity distribution in reciprocal space (low energyelectron diffraction (LEED)). Furthermore, the use of theenergy analyzer allows measurement of the energydistribution of the electrons (electron energy lossspectroscopy (EELS)). Both LEED and EELS can bemeasured from a micrometer spot on the sample. Incomplete analogy to this, three modes of operation areavailable when working with photons: PEEM as well asphotoelectron diffraction (PED) and photoelectronspectroscopy (PES). Details on the use of this instrumentcan be found in Refs. [43,49].

2.3. ExamplesIn the following we will give two examples which willillustrate what photoelectron nanospectroscopy cancontribute to semiconductor industry. The experimentswere performed with the SPELEEM at Elettra. Fig. 5shows spectromicroscopic images of a field effecttransistor (FET) at three different photoelectron energies,corresponding to the Ga 3d, Ti 3p, and Al 2p core levels[49]. The black circle in the FET-sketch indicates the fieldof view (FoV) for the images. It has a size of 19 µm. Thephoton energy used for the measurements was 131.3 eV.In the FET-structure, the GaAs substrate is visiblebetween drain and source and the gate. These regions areclearly visible as bright lines in the images taken at the Ga3d and As 3d (not shown) core levels. Also the Al gate isidentified as a bright line at the energy of the Al 2p corelevel. Drain and source are highlighted at the electronenergy of the Ti 3p core level. Fig. 5 also illustrates thatdefect analysis on devices can be performed bySPELEEM. The defects seen in the images can beanalyzed with nanospectroscopy.As we have already pointed out in the introduction,proximal probes have attracted attention as potentialnew tools for nanofabrication because of theirdemonstrated ability to image and manipulate matter onthe atomic level [14]. One of the most promisingtechniques that uses AFM and STM to produce a patternon a semiconductor surface and to fabricate workingnanodevices is local anodic oxidation (LAO) [16]. In ahumid environment, the biased tip of a scanningmicroscope can write nanometer wide oxide lines on asemiconductor- or metal-surface. In spite of the ease andof the effectiveness of the LAO process, no chemicalinformation is yet available on the nature of the patternedoxide. In the following we will give an example that

Fig. 5. Layout of the field effect transistor used for the measurements, andPEEM images from it taken with Ga 3d, Ti 3p, and Al 2p photoelectrons.

Fig. 6. SPELEEM images of an AFM locally oxidized sample showing astrong contrast inversion. Field of view 12 µm. The intensity (gray scale)is proportional to the photoemitted electron intensity at given kineticenergy. (a) Kinetic energy = 26.8 eV, binding energy 104.7 eVcorresponding to the high binding energy side of the Si 2p oxidecomponent. (b) Kinetic energy = 29.2 eV, binding energy 102.3 eVcorresponding to the low binding energy side of the Si 2p oxidecomponent.

Fig. 7. Si 2p core level spectra from native oxide and AFM written oxide.They are composed of a bulk component and an oxide component, shiftedtowards higher binding energies. For details, see text.

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addressed this problem by spatially resolvedphotoemission spectroscopy.Fig. 6 shows two images of AFM oxide lines on Si(001) attwo different photoelectron kinetic energies [51]. Thefour rectangular patches appearing in both picturescorrespond to the LAO structures. The field of view is12µm. The image on the left was taken with an electronkinetic energy of 26.8 eV, corresponding to a bindingenergy of 104.7 eV on the high binding energy side of theoxide component of the Si 2p core level emission peak.The image on the right was taken with an electron kineticenergy of 29.2 eV, corresponding to a binding energy of102.3 eV, on the low binding energy side of the samepeak. A remarkable contrast inversion is visible.Fig. 7 shows spectra obtained by plotting the spatially re-solved photoelectron intensity versus the binding energyfor the LAO patches and for the region covered by nativeoxide. The Si 2p core level emission peak is composed oftwo main components. The weak component at 99.3 eVbinding energy is related to the emission of electronsfrom the Si 2p core level in bulk silicon. It is attributed toemission from silicon below the oxidized surface. Thestrong component at higher binding energy is related tothe emission of electrons from the Si 2p core level in thesilicon oxide on the surface. The component taken fromthe native oxide shows an energy shift of 3.9 eV relativeto the bulk peak, in perfect agreement with literature.This shift reflects the degree of oxidation of Si atoms, istherefore a chemical shift. The component from the AFMoxide appears at a binding energy higher than the nativeoxide component. This can be attributed to a charging ofthe thick AFM oxide due to the photoemission, in quanti-tative agreement with an integral photoemission studyon SiO2/Si structures [52]. The experiment also eviden-ced a high degree of homogeneity and the stoichiometryof the AFM oxide. Furthermore, the data indicate that thedensity of the AFM oxide is lower than that of the nativeoxide. These topics must be addressed to develop a relia-ble and reproducible lithographic process. The data showthe need for laterally resolved spectroscopic analysis ofsuch nanoscopic structures.

3. Electron Probe Nanospectroscopy3.1. Transmission Electron Microscope (TEM)In a conventional Transmission Electron Microscope(CTEM or TEM), a thin specimen (typically in the rangeof 5-500 nm for 100 keV electrons) is irradiated by anelectron beam with energies ranging from 60 keV to 3MeV. The choice of the accelerating voltage and specimenthickness depends on the sample density and elementalcomposition and on the resolution desired. The point-to-point resolution of a TEM rougly depends on the energyof the impinging electrons and on the sphericalaberration coefficient of the magnetic coils. Appropriate

preparation techniques (chemical polishing followed byion milling for semiconductors and metal foils,ultramicrotomy for biological specimens) are necessaryto thin down the samples to the desired thickness.Electrons are emitted by thermoionic emission by tung-sten airpin cathodes, LaB6 rods, or by a field emissiongun (FEG) by pointed tungsten filament. A two-stagecondenser lens system allows to change the illuminationaperture and the illuminated specimen area.The electron intensity distribution below the sample isimaged with a three-stage lens system onto afluorescence screen; the image can be recorded by aphotographic plate or by CCD cameras and YAGscintillators (see Fig. 8) [53].Bright field contrast is due either to scattering contrast(absorption of electrons scattered through angles largerthan the objective aperture) or by interference betweenthe scattered wave and the incident wave at the imagepoint (phase contrast). Atomic resolution is achievable ina TEM because elastic scattering is strongly localized tothe region occupied by the screened Coulomb potentialof nuclei: a very recent prototype of an high resolutionTEM (HREM) reached 0.1 nm point-to-point resolution.Commercial HREMs working at intermediate accelera-ting voltages normally provide resolutions in the rangeof 1.5-1.7 nm.

Fig. 8. Sketch of a transmission electron microscope (TEM). The Si(Li)detector is used for energy dispersive x-ray microanalysis (EDS).

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A special capability in the most recent TEMs equippedwith a field emission gun is the formation of electronprobes with diameters < 1 nm. The instruments operatein the Scanning Transmission (STEM) mode and it ispossible to image thick or crystalline specimens, to re-cord secondary and backscattered electrons, cathodolu-minescence and electron beam induced currents etc. Themain advantage of the STEM mode is that it is possibleto perform microdiffraction and elemental analysis (X-ray microanalysis, electron energy loss spectroscopy)from very small specimen areas. The strenght of theTEM is that it is possible to provide atomic resolutionimages (containing information down to 0.1-0.2 nm) andto operate in various microanalytical modes (by usingelectron probes in the STEM in the range 1-5 nm). Thisresults in an high resolution analytical instrument whichis nowaday essential for high level advanced research inmaterial science. In the following, some of the most inte-resting capabilities of an analytical TEM will be brieflydiscussed [54].

3.1.1. Energy Dispersive X-ray microanalysis (EDS)The EDS is commonly used to determine the elementalcomposition of the specimens investigated both qualita-tively and quantitatively. X-ray spectrometers can becoupled to a (S)TEM to acquire X-ray quanta emitted bythe specimen under electron irradiation. In the imagingmode elemental mapping is also possible. An energy di-spersive detector (Si-Li or Ge) with an energy resolution∆Ex≈120-130 eV allows the simultaneous recording of allthe characteristic lines with X-ray quantum energyEx=hv greater than 1 keV. A disadvantage of the EDS isthat neighbouring characteristic lines are not well sepa-rated and the analytical sensitivity is not very high(about 5x10-5). However, since the X-ray quanta are ge-nerated by thin foils, only small corrections are neededfor a reliable quantitative elemental determination.

3.1.2. Electron Energy Loss Spectroscopy (EELS)Electrons that have been inelastically scattered in ioni-zation processes contain the fine structure of the inner-shell ionization steps. In the energy-loss spectrum, steepsteps are seen at energy losses, ∆E, above the ionizationenergy of a K, L, or M shell from which atomic electronsare excited to an unoccupied energy state above the Fer-mi level. Electron spectrometers incorporated in theTEM column or placed below the fluorecent screen canbe employed to record electron energy-loss spectra. Inaddition to the elemental composition, EELS spectra al-so contain information about the electronic structure ofthe specimens (Z>4). A study of the extended fine struc-ture allows to measure the nearest-neighbour distances.The EELS technique is therefore an optimum method toanalyze elements of low atomic number in thin film

with thicknesses smaller than or comparable to themean free path for inelastic scattering. Further, it is mo-re efficient than the EDS because the spectrometer col-lects a large fraction of inelastically scattered electronsthat are concentrated within small scattering angles (theX-ray quanta are isotropically emitted and only a smallsolid angle, ~10-2 rad, is collected by an EDS detector).Also for EELS the elemental mapping in the electronspectroscopic imaging mode is possible when an elec-tron energy filter is used.

3.1.3. Cathodoluminescence Spectroscopy and Imaging (SRCL)Cathodoluminescence is the physical process duringwhich a system (in this case a semiconductor) which isin an excited state because of the irradiation fromenergetic electrons (possibly in an STEM or in a SEM),emits photons during the relaxation to a lower energystate. The light emitted by the sample (that can becooled from room temperature to liquid heliumtemperature) is collected by a mirror (normallyparabolic in shape) and then sent to a monochromatorequipped with different gratings and detectors; finallythe signal is sent to a computer.If the temperature is sufficiently low (for instance 20 Kfor GaAs) excitons (electron-hole-pairs that form abound state) both free or bound to impurities can be ea-sily studied. In addition to band-to-band transitions,electrons from the conduction band can recombine withneutral acceptors, neutral donors can recombine withholes in the valence band, electrons bound to donorsmay directly recombine with holes bound to acceptors(at higher impurity concentration) giving rise to donor-acceptor pair (DAP) recombinations. In an STEM theelectron beam is well defined in energy and can be focu-sed to a very small spot (1-10 nm) with the possibility toscan the sample surface. This results in a map on a sub-micrometer scale of the intensity variations of the opticaltransitions on the growth plane and in the possibility ofmonochromatic imaging of selected emissions with highspatial resolution. When the electron beam is blanked, ti-me resolved cathodoluminescence spectroscopy can alsobe carried out. In contrast to PL, a disadvantage of thistechnique is that it is not straighforward to selectivelyexcite the specimens by electrons of such high energy.

3.1.4. Selected Area Electron Diffraction (SAD)In a TEM, on the exit side of a specimen, severaldiffracted beams are present in addition to thetransmitted beam. These are focussed by the objectivelens to form a spot pattern in its back focal plane. Electrondiffraction methods are used to identify different phasesby measuring the lattice plane spacing and to determinecrystal orientations in polycrystalline films or singlecrystal foils. Normally quantitative information can be

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obtained on the identity of phases and their orientationrelationship to the matrix, on the habit planes ofprecipitates, slip planes in materials, on the exactcrystallographic descriptions of crystal defects inducedby deformation, irradiation etc. and on order/disorder,spinodal decomposition, magnetic domains etc. Extraspots and strikes due to superstructures, antiphasestructures, plate-like precipitates etc. can also be studiedif a selected area is imaged by inserting a diaphragm inthe first intermediate image.

3.1.5. Convergent Beam Electron Diffraction (CBED)Convergent beam diffraction gives two dimensional ma-ps of the diffraction intensity as a function of the inclina-tion between incident electrons and a particular crystaldirection. They are normally composed of a series of di-scs each one corresponding to a different Bragg reflec-tion. The intensity variation inside the discs carries infor-mation about specimen orientation, thickness, localstrain etc. One of the most interesting fields, CBED canbe employed in, concernes the chemical composition andlocal strain determination in semiconducting hetero-structures and devices made by lattice mismatchedlayers. This is normally done by studying the shifts inthe High Order Laue Zone (HOLZ) line positions. Thespatial resolution depends on the specimen thicknessand probe size. With the modern FEG-TEMs, resolutionsof about 1-2 nm can be achieved in the CBED mode.

3.2. Scanning Electron Microscope (SEM)In a SEM (Fig. 9), electrons emitted by a thermoionic orfield emission cathode are accelerated from 1 to 40 keVbetween cathode and anode [55]. The smallest beamcross-section at the gun (crossover) is demagnified by athree-stage electron lens system so that the electron beamdiameter at the specimen surface can be of the order of 1-10 nm with probe currents of 10-10 to 10-12 A. A deflectioncoil system scans the electron probe in a raster across thespecimen in synchronism with the electron beam of aseparate TV monitor. The intensity on the monitor ismodulated by one of the signals coming from the electronprobe-specimen interaction to form the image.Some of the advantages of the SEM are the large depth offocus (some mm), the excellent image contrast, the veryeasy preparation of solid specimens (for semiconductingor conducting samples no preparation is necessary) andthe wide variety of products due to the electron beam-specimen interaction (Fig. 10) that can be employed forelemental and spectroscopic analyses of the specimensinvestigated. The most commonly employed signals areSecondary Electrons (SE), Backscattered Electrons (BSE),Auger Electrons (AE), X-ray quanta (XR), Cathodolumi-nescence (CL), and Electron Beam Induced Current(EBIC). When SRCL is performed in an SEM, depth resol-ved and excitation dependent spectra from the specimencan be easily achieved due to the possibility of varyingthe energy of the electron beam. Linearly polarizedcathodoluminescence can also be used to examine for in-stance the presence of strain and to probe the character ofthe hole states in the optical transitions by using a rotablevacuum linear polarizer inside the SEM chamber.The EBIC technique consists of measuring the currentflowing through the contacts of a semiconductor junc-tion after it has been excited by an electron beam. Typi-cally a p-n junction or a Schottky barrier arrangementare used. A sensitive current meter, coupled with a cur-rent amplifier is connected across the contacts and isused to measure the current produced in the junction.As a final remark it must be stressed that, unlike for theTEM where thin foils are investigated, in the SEM modethe lateral resolution achieved on the specimen surfacedoes not necessarily correspond to the analytical resolu-tion. This is due to the different interaction volumes insi-de the specimen where the various signals come from(Fig. 10). However, when the above mentioned techni-ques are attached to an SEM, a higher signal-to-noise ra-tio is achieved with respect to the TEM mode, due to thelarger thickness of the SEM specimens. However, there isa new technique, not commercially available yet, that canoffer unique advantages inside an SEM. This new techni-que is the ensamble of the SRCL and the Scanning NearField Optical Microscopy (SNOM), namely CL-SNOM.Using this technique it is possible to perform CL-measu-

Fig. 9. Schematics of a scanning electron microscope (SEM). For details,see text.

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rements in a SEM with the lateral resolution of a SNOM,which can be as good as 50 nm [56-58].

3.3. ExampleTo conclude this part, an example concerning a study bySEM-SRCL of excitonic transitions in GaN epilayers willbe presented. We have performed CL studies ofnominally hexagonal GaN grown on different substrates.We find an additional CL emission at about 362 nm onlywhen a very high density of planar defects is present inthe epilayers. We determine the nature of the structuraldefects and we ascribe the additional CL line to excitonsbound to stacking faults (SFE) [59].In Fig. 11 a comparison between 20 K CL spectra of theemissions of two GaN samples (#105 and #84) grown bygas source molecular beam epitaxy (GSMBE) underdifferent conditions on sapphire is reported [59]. The twospectra present a strong emission line at about 357 nmand the usual DAP band around 386 nm. Thetemperature dependence of this line in the two samplesand the comparison of our data with those reported inthe literature for hexagonal GaN, suggest they are nearband edge (NBE) radiative transitions (e.g. free andbound excitons).In the following we will focus on the CL additional emis-sion found in sample #105 at 362 nm. Plan view 77 Kmonochromatic CL imaging at 357 nm and 362 nm re-vealed a different intensity distribution across the speci-men surface. In particular, a close correspondencebetween the sample surface as imaged by atomic forcemicroscopy (Fig. 12 a) and the monochromatic CL distri-

bution of the 362 nm line was found (Fig. 12 b) [59].Depth resolved CL investigations on the samples (Fig. 13)evidenced an increase of the 362 nm line with respect tothe NBE only in sample #105 [59]. Further, CL spectra ob-tained in different areas of the two specimens showed theonset of an anticorrelation between the 362 nm and theNBE bands. This is in agreement with the inhomogeneousdistribution of the 362 nm line as shown in Fig. 12 b [59].Due to the different growth conditions, the role of structu-ral defects inhomogeneously distributed across the layersis taken into account. Cross sectional TEM micrographs(not shown here) revealed the presence of stacking faults(SF) only in sample #105. Due to the increase of the 362nm CL peak intensity by increasing the accelerating volta-ge, the SF density depth distribution has been studied bycross sectional TEM investigations. It has been found that

in sample #105, it decreased from 6x1013 cm-3 in a 150 nmtall region near the interface to 1.5x1013 cm-3 in the 700 nmthick top portion of the sample.On the basis of the previous results, as a preliminaryconclusion, we may state that the line at 362 nm is corre-lated with (and thus caused by) the presence of stackingfaults irrespectively of the growth mode. The role of in-version domain boundaries on the onset of extra lines inaddition to the free exciton one has been considered andthen ruled out on the basis of literature data. Further, al-so misfit dislocations in the (0001) plane, that are highlycharged due to the strong ionic character of the bond arenot expected to induce excitonic transitions usually re-sponsible for the dislocation luminescence.The high concentration of SFs revealed by detailed TEMinvestigations of samples #105 the anticorrelation of theadditional line with respect to the NBE emission and itsincrease in intensity near the buffer/layer interface, sug-

Fig. 10. Origin and information depth of secondary electrons (SE),backscattered electrons (BSE), Auger electrons (AE), and x-ray quanta (X)in the diffusion cloud of electron range R for normal incidence of theprimary electrons (PE)

Fig. 11. Low temperature CL spectra of samples grown by gas sourcemolecular beam epitaxy on Al2O3.

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gest the emissions at 362 nm are strictly related to exci-tons bound to SFs within the epilayer.

4. Proximal Probe TechniquesAfter the nobel-prize winning invention of STM in the80s, the field has seen a rapid development. New surfaceprobes were proposed and implemented. It is common toall these scanning probe microscopes that a surface probeis held in close proximity or in contact to the samplesurface, which is then scanned relative to the probe.Having established itself as a leading-edge microscopy,there is now a tremendous effort to utilize the high lateralresolution obtained by scanning probe microscopes forspectroscopy with high spatial resolution. Electrons andphotons are used for excitation and detection. Scanningtunneling spectroscopy is a local measure of the densityof states (occupied and unoccupied) close to the Fermilevel [60]. However, the tunneling electrons can also beused as a source of cathodoluminescence, which is thencollected by a lens or optical fiber and analyzed by amonochromator [61,62]. With scanning near-field opticalmicroscopy (SNOM), even the diffraction limit of far-field optics can be avoided, resulting in a lateralresolution of these microscopes of 50 nm and better forlight in the visible range [63,64]. Using this principle, it ispossible to perform photoluminescence [65] orcathodoluminescence [56-58] mesurements or to detectan optical beam induced current (OBIC) [66], all withbetter than 100 nm lateral resolution. These methodshave the potential to clarify the relationship betweenatomic-scale structures and optical properties.

5. ConclusionsEach of the instruments that we have discussed has itsspecial features and technical limitations that make itappropriate for certain experiments but not for others.

Most of the reviewed instruments are of the scanningtype, which is more flexible because it allows to usedifferent detector systems, but is inherently slow.Depending on the signal level, it typically takes secondsto minutes to acquire an image. Imaging techniques arefaster by construction; with PEEM and TEM, video ratecan be achieved, making it a very valuable tool for thestudy of the temporal evolution of a system. Work intransmission requires extensive sample preparation, butin the case of electron microscopy the reward is asuperior lateral resolution. Detecting low energyelectrons increases the surface sensitivity of a method(typical sampling depth some nanometers), while thedetection of photons increases the sampling depth tosome 100 nm. Elemental analysis can be performed byseveral methods, but real chemical analysis requires theuse of photoelectron spectroscopy. Electron microscopyoffers the better lateral resolution (1 nm and better) butsuffers from sample damage due to the high energyelectron beam. The use of a photon probe reduces beamdamage on the sample, but the lateral resolution issomewhat worse (10 nm at best).However, there are efforts to push the lateral resolutionof photon probe nanospectroscopies. The art of makingFresnel zone plates has seen tremendous progress in thelast years, and a best resolution of 10 nm seems possible.Furthermore, a new generation of PEEMs is underconstruction in different laboratories: the SMARTproject at BESSY [67], the PEEM-III project at the ALS

[68], and the XPLEEM project from Delong Instrumentsat Elettra [69]. These instruments will be similar to theSPELEEM (Fig. 4), but they will use an electron mirrorin the electron-optical path for aberration correction[70]. Their lateral resolution is calculated to be a fewnanometers [71].

Fig. 12. Comparison between AFM imaging (a) of the #105 samplesurface and monochromatic CL micrographs obtained at (b) 362 nm and(c) 357 nm.

Fig. 13. Low temperature CL spectra of the sample #105 at differentbeam energies.

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AcknowledgementsHelpful discussions with L. Sorba, M. Sancrotti, M.Bertolo, E. Di Fabrizio, M. Lazzarino, P. Pingue, F.Beltram, R. Vasina, and J. Westermann are greatfullyacknowledged

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34



Small Angle Neutron Scattering investigations into themicroscopic deformation of chains in uniaxially strainedpolymer networks are presented. The experimental data aresuccesfully interpreted in terms of a mean-field tube model ofHeinrich and Straube which describes the confinement ofchains due to the chemical crosslinking and chainentanglements by an effective tube which is anisotropic anddepends on strain non-affinely as d(λ)=d0√λ. Different lengthscales in the rubber are studied and a transition from affine tophantom-like behaviour of chain deformation is found fordecreasing lengths of the investigated part of the chain. A model system for the reinforcement phenomenon in filledelastomers, induced by microphase separation is studied byboth SANS and SAXS. The strain amplification concept couldbe proved unambigously for the first time.

IntroductionThe chain dynamics in entangled polymer melts has beentackled succesfully using the well known reptationmodel [1,2]. Here, entanglement constraints are modeledby a tube and the fluctuation of segments is restricted toits interior. Applied to rubbers, the neglect of chaininteractions which is the basic deficit of the phantomtheory of rubberelasticity can be relieved hereby [3,4].When real networks are strained, the polymer chains aredeformed and entanglements also become active. In thetube model, the latter chain interactions are simulated bya harmonic potential and their deformation behaviour isderived [5-7]. The tube diameters dµ are defined as theroot-mean-square segmental fluctuations in thedirections of the principal axes and follow a non-affinedeformation law as

(1)

with ν = 1/2. λµ is the strain ratio along the principal axesµ = x,y,z. The size and shape of the deformed polymer chains andtheir fluctuation width can be conveniently measured bySANS, thereby taking profit of the difference in thescattering length between hydrogen and deuterium [8].The chains can be made visible in a dense system just byimplanting deuterated chain sections along the path orreplace part of the normal chains by their deuteratedanalog. It is clear that it is a powerful tool to selectively

obtain information like deformation on several lengthscales covering the level of one elastic chain, the tube aswell as global information at tens or hundreds of elasticchain lengths.For micro-heterogeneous systems the contrast matchingtechnique must be applied. The contrast matchingtechnique bases on the fact that scattering lengths varyfrom one monomer to the other and enables one to matchcertain components. To analyze the structure of chains inthe rubbery phase in a microphase- separated crosslinkedblend or two-phase material in general, the solid phasecan be made invisible and especially information aboutthe matrix that cannot be obtained separately from othermethods, is extracted and allows the testing of theoreticalmodels [9,10]. This contribution will deal therefore withthe microscopic deformation at the chain level to testfundamental models of rubberelasticity and apply theconcept in the field of filled elastomers on a model-filler.

ExperimentalNarrow molecular weight distributed Polyisoprenes withhigh 1,4 microstructures are obtained by anionicpolymerization using sec-BuLi as the initiator in apolarsolvents. Isotopic triblock structures of the HDH-typewere obtained from sequential addition of carefullyweighed amounts of the respective monomers and underthe necessary precautions to limit chain degradation dueto impurities and to preserve symmetry in the wings. Thelabelled center fraction was varied between 3 and 35% byvolume. A block-copolymer PI-PS-PI with χ ⋅ ≈ 80 wasprepared by coupling a monodisperse diblock PI-PS withdimethylchlorosilane. The styrene content of 18.0 vol.%was confirmed by fluorescence spectroscopy. Molecularweights of homopolymers and total block copolymerswere determined by GPC to be 200000 g/mol and135000 g/mol respectively. The overall-polydispersitiesare less than 1.05. They were further confirmed by low-angle laser-light-scattering experiments and membraneosmometry.Randomly crosslinked networks were prepared usingdicumylperoxide (DCP) as the crosslinker. Samples andDCP were mixed in THF and evaporated over about 1week under high vacuum to assure solvent-free polymer.The crosslinking was performed under Argonatmosphere at a temperature T = 160° for 2-3 hours to

d dµ µνλ= ⋅0

CHAIN DEFORMATION IN UNFILLED AND FILLED POLYMER NETWORKS: A SAS APPROACHW.Pyckhout-Hintzen, S.Westermann, A.Botti, D.RichterForschungszentrum Jülich, IFF, D-52425 Jülich, Germany

E. StraubeUniversität Halle, FB Physik, D-06099 Halle, Germany

Articolo ricevuto in redazione nel mese di Maggio 2000

35



ensure complete decomposition of the DCP. Elastic chainlenghts, MC, were estimated from the swelling degree incyclohexane. In the case of the microphase-separatedpolymer, the block copolymer was 100000 g/mol and thehomopolymers about 90000 g/mol. Blends from a purehomopolymer mixture and PIPSPI were made to give90% and 50% of the triblock-copolymer, yielding PS-fillerdegrees of Φ1 = 0.16 and Φ2 = 0.09, respectively. MC, themass of the elastic chains, was estimated from swelling incyclohexane and yields for the unfilled sample(8.880±350) g/mol, identical to (8.530±340) g/mol for theΦ1 = 0.16 and (8.490±340) g/mol for the Φ2 = 0.09 sample.The average gel fraction was wgel=(0.962±0.004). Theswelling method yields directly real elastic masses sincethe PS-domains are equally dissolved in the goodsolvent. No corrections for insoluble filler materials arenecessary. Networks were strained in a calibratedstraining device and extension ratios were determinedfrom reference marks on the sample.SANS experiments were recorded in 2D-detection atPAXY (LLB, Saclay), NG-7 (NIST, Washington), D22 (ILL,Grenoble) and KWS1 (FZ, Jülich) using wavelengths λ ofrespectively 8, 7, 10 and 7 Å and ∆λ/λ ~ 0.1-0.15. SAXSdata were obtained at the synchroton beamline JUSIFA(DESY, Hamburg) using a wavelenght of 1.54Å.Scattering intensities were corrected for empty beam, celland detector efficiency and absolutely calibrated againstwater, silica or lupolen depending on the instrumentused. Cross-checks yielded a good agreement in theabsolute level of intensities. Incoherent backgroundsmeasured from fully protonated samples weresubtracted, weighed with their volume fraction present.Data reduction was carried out pixel-wise prior to radial-average isotropic data. Cross sections δΣ/δΩ weretransformed to the structure factors S(q ) of the system[11] according to

(2)

a is the total scattering length for deuterated andprotonated monomers, summed over the atoms of oneunit. Nchains is the number density of labeled chains ofpolymerization degree Z. (see later) Anisotropic dataalong principal axes were obtained from Zimm-likeextrapolations [12] following

(3)

e.g. for the parallel direction. The method proved to dobetter than sector-binned data and is physically correct. Ifnecessary 2D-data were fitted immediately. Dynamic mechanical experiments in oscillatory shear

mode were performed using an ARES-Rheometricsinstrument in the frequency range 0.1 to 100 rad/s in theparallel plate-plate geometry in an in situ investigation ofthe crosslinking reaction under a nitrogen blanket. Thestrain amplitude γ was 1%. The distance between theplates was adjusted to allow for thermal expansion ofplates and sample. The temperature program wasidentical to the temperature profile of a parallel SANSstudy. Details of this experiment will be publishedseparately [13].

SANS Structure factorThe normalized structure factor for a single, labeledchain, crosslinked into a network in the Warner-Edwardsapproach [4] can be simply recasted in terms of the

(4)

Here, Q is defined as Q = q ⋅ Rg and λµ is λ andrespectively following incompressibility. is

defined as the mean-square tube dimension in thedirection of observation f relative to the parallel axis ofstraining as

(5)

Eq. 1 is retrieved along parallel (φ = 0°) andperpendicular (φ = 90°). As a consequence, does not separate into the two principal axes. x, x' arereduced chain length coordinates over which isintegrated. The structure factor can be understood as theproduct of an affinely deformed random path with thecontributions from the restricted fluctuations around it.The parameters of the model are the tube diameter d0 andthe microscopic deformation λ.

S qlabr,λ( )

λ φ λ φ2 2 21⋅ ( ) + ⋅ ( )cos / sind dφ2

02= ⋅

dφ2

1 λ

− −( ) − ( − −( ) )) ]Qd

R

x x

d

Rg

g

µ µφ

φλ2 2

2

2 2

2

12 6

1

2 6

( exp'

S q dx dx Q x xlab

xr, ' exp 'λ λµ µ

µ( ) = −( ) −( )

∫ ∫ ∏20

1

0

2

S q q S q q Rg app, , ,⊥

− −

⊥( ) = ( ) ⋅ + ⋅( )1 12 20 1 3

d d a a N S qD H chainsΣ Ω = −( ) ⋅ ⋅ ( )2 r

Fig. 1. Left: 2D-representation of strained homopolymers. The straindirections is vertical. Right: Evaluation of the isotropy angle for theestimate of the deformation.

→

→

→

→

36



HomopolymersThe model perfectly describes two-dimensional SANSpatterns on networks made from long primary chains[12,14,15]. The typical appearance of lozenges as in Fig. 1is fully explained by the introduction of the f-dependentfluctuations in the off-axis directions and provides uswith the only possible model to date which fits at the sa-me time also both principal axes correctly. It has beenclearly shown in the appropriate references how a chan-ge in the deformation exponent of the tube induces sub-tle but consistent different shapes. A special angle forwhich the effective deformation is isotropic for bothchain and tube part can be identified from inspection ofEq. 5 and is experimentally easily accessible. From this, adirect and almost model-independent estimate for themicroscopic chain deformation is rendered possible. Ty-pical scattering pattern with theoretical fits to the struc-ture factor are shown below for good and virtually de-fectless networks. Here, the deformation that the chainexperiences, λ is affine and for the segment fluctuationparameter, which follows the direction cosines as intro-duced before, a size d0 = 42Å is obtained. We remark thatan alternative model in which the tube is not allowed todeform but restrictions are varied over the length of thechain can indeed yield a comparable quality of fitting[16]. However, the outcome is consistently wrong andeven contradictory to the own-made assumption of non-deformability for this tube diameter which effectivelybecomes a function of λ in order to fit the shape [17].

Triblock HDH copolymersIn contrast to the common homopolymer systems,triblock-copolymers of the HDH-type enable one tochange the length of the labeled path without affecting

the network properties. Then, the parameter d0/Rg as itoccurs in the structure factor becomes a static tool for thestudy of segmental dynamics in networks. Thecorrelation hole under deformation is well described byan RPA approach which is modified for the presence ofthe tube-like constraints. It is assumed that the inter-chain correlations can be decoupled from short-rangefluctuations as e.g. on the length scale of the tube. Afactorization of both effects was suggested. The structurefactor for the mean configuration of a block copolymer isthen proposed as

(6)

for both isotropic and deformed system. The deformationis included as before by rescaling Q ⋅ Rg with λ. The barepartial structure factors SDD, SHH and SHD comprise thearchitecture of the copolymer. We have introduced hereC(λ) as

(7)

which can be interpreted as the inter-chain structurefactor of the system. With the assumptions above thestructure factor for a system of constrained chains canthen easily be obtained from

(8)

Peak positions as well as relative heights are in perfectagreement with experiment [12]. Due to the peak shape,effects like thermal chain degradation and ageing uponcrosslinking can be quantified directly from the non-zerointensities at Q = 0. A kinetic degradation scheme basingon random scissioning of chains was developed ,solvednumerically and included in the data description,yielding an multi-component RPA treatment. As mainresult, DCP seemed to leave only between 40 and 80% ofthe triblock chains intact. Fig.2 presents a deformedcorrelation peak and fit for a HDH-polyisoprene networkwith a labelled section φD = 0.35, d0/Rg = 0.6 and strain1.8. The tube diameter is consistent with d0 = (42±1) Å.Experiments were performed on copolymers withφD = 0.35, 0.12 and 0.02, thereby varying d0/Rg from 0.6 to2.2. The affine deformation of the labeled path should bemaintained as long as it is well embedded andconstrained in the network. However, if the length scaleof interest is reduced, this inevitably necessitates theintroduction of reduced chain deformations for the casethat the elastic chain lengths now exceed the length of thelabeled segment fraction. This local non-affinity of theprimitive labeled path is then derived from

SDD,λ = C(λ) • Slab,λ

C(λ) = SDD,RPA,λ/SDD,λ

Fig. 2. Isotropic (open symbols) and deformed correlation hole (closed symbols) for the triblock HDH network with φD = 0.35 in parallel andperpendicular direction.

Stot,RPA =SDDSHH – S2

DH= SDD –

(SDD + SDH)2

SDD + SHH + 2SDH SDD + SHH + 2SDH

37



(9)

(0 < α < 1). N is the number of monomers per elasticchain, MC, and (j-i) becomes the length of thedeuterated part. This correction factor to λ depends onthe length scale with . Theagreement of the experimentally fitted values for fc withestimates from the crosslink density from swelling i.e.0.45 and 0.55 respectively for the samples with φD =0.12and 0.02 is excellent. In the case that constraints are not felt anymore, i.e. thelabeled segment is shorter than the tube dimensions, adescription of the scattering behaviour can only beachieved by the phantom model i.e. vanishing con-straint terms, and chain ends which are displaced asabove. It is the first proof of the existence of the tube-constraining potential and the phantom limit at the sa-me time in a well entangled network with minor de-grees of defect structures.

Defect NetworksThe existence of non-affine deformations in rubbers is notnew and is believed to be correlated to the presence ofdefect structures [18]. An initial characterization ofdefects or the effect on the microscopic deformation canbe achieved by the introduction of a non-affinity index βas λi = λb, introduced first to describe the fast decrease ofthe C2-constraint term upon swelling. It comprises bothlimiting cases of affine and no deformation at all. Anempirical relationship was set up by us by fitting througha set of data, obtained from a variation in primarymolecular weights and crosslinking density, in terms of

the number of chemical knots per chain, nC = MW/MC - 1to give β = tanh(0.065 nC). More elaborate theories involvea detailed knowledge of the crosslinking and scissioningchemistry of rubbers which is lacking. Fig.4 present thedependence. In 2D, less anisotropic patterns areobserved. It is of particular interest to note that theaffinity of deformation is reached at crosslink numbersper primary chain of ≈15-20 as are used in typical highperformance rubbers.

In situ experimentsFor the study of latter effects, the HDH copolymer withφD=0.35 was selected in view of its physical andscattering advantages over the shorter-labeled triblocks.In order to get more insight in the simultaneouscrosslinking and scissioning kinetics upon crosslinkingwith DCP radically, in situ SANS and parallel dynamicmechanical experiments were undertaken to study thelow frequency, i.e large scale structure, and highfrequency behaviour, i.e. local length scale structure atT = 140°C. The kinetic degradation scheme, derived forthe networks before, is in agreement with the newfindings and proves following: no degradation is foundfor the pure triblock and two steps in the degradation inthe presence of DCP can be recognized from SANS.Rheology is insensitive to these changes. Both steps arecorrelated to DCP by 1: its decomposition temperatureand 2: the gelpoint of the system. The rise in intensity atQ = 0 is due only to this mechanism of scission and nocrosslink influence can be derived from the early stages.Since the scission process is an activated process, the rateof scission will be larger at T = 160°C at which thesamples in the previous section were crosslinked. Thefraction of intact chains vs. temperature is shown in Fig.5for a reference melt and an in situ forming network.Thermal and crosslinking degradation can be clearlydistinguished.

j i N f M Mc lab C− = =/ /

rj i N

r rij ij ij, , ,

/λ

λ

λλ αλ2

2

22

12 2

12

1 1=

− −( )⋅ −( )=

Fig. 3. Strain relaxation factor α for three different situations fc = 0.3, fc =0.5 and the affine case of fc =1.

Fig. 4. Comparison of the experimentally obtained non-affinity exponentsβ with an empirical approach.

38



Filled ElastomersThe basic theories of rubberelasticity should still applyfor real, filled compounds. In filled elastomers, however,several new aspects enter and the total response is thesum of several mechanisms [19-21]. To unravel themicroscopic origin of the reinforcement process it is aprerequisite to isolate the effects through an adequatemodelling. Strain amplification due to the hydrodynamiceffect [22] is one of these and is described as

(10)

The overstrain factor, f, can be understood to parallel theincrease of the modulus E of the filled system comparedto the modulus E0 of the pure matrix,

E = f ⋅ E0 (11)

In a Padé approximation of the expansion of f up tosecond order in the volume fraction Φ for a system ofpolydisperse undeformable spheres derivedtheoretically [23,24],

(12)

a strong dependence on the volume fraction is expected.To simulate model filler properties, a triblock copolymerof the type PI-PS-PI ΦPS = 0.18 was selected. This blockcopolymer undergoes a thermodynamically drivenmicrophase separation, which favours spherical PSdomains. The degree of the in situ filling is adjusted byblending the PI-PS-PI starlike micelles with a PI

homopolymer matrix as the soft, rubbery phase. EffectivePS volume fractions of Φ1 = 0.16 and Φ2 = 0.09 were soprepared. Unlike the usual inverse block copolymer PS-PI-PS, our system has to be crosslinked to obtain apermanent network structure since the elastic, soft chainsare only connected to one single domain. The advantage,however, is a direct analogy with the pure matrixnetwork. These systems are believed to closely resemblethe structure of a carbon-black or silica reinforcednetwork whereas the typical fractal character of bothlatter industrial fillers can be avoided. Two contrast conditions, termed composition matchingand achieved by means of 2 homopolymers to match thescattering length of the PS-phase , and phase matchingto eliminate the scattering due to intra-block correlationsin the block copolymer must be considered. Ideally ablend of equally sized labeled and unlabeledhomopolymers is diluted with a phase-matchedcopolymer. The scattering intensity for this phase-matched copolymer with a blend of homopolymers,compositionally matched to this is [9,10]

(13)

Here, Ni (i = H, D) is the number density of ahomopolymer component, ZD the polymerization degreeof the D-homopolymers, ∆i = (bi - bPS) (i = H, D) is thescattering length contrast between the homopolymersand both blocks of the copolymer. bi is the scatteringlength density. Λ now represents the microscopicdeformation tensor acting on the chain level with thecomponents Λµ (µ - x,y,z).The phase matching condition applies for a triblock co-polymer with polyisoprene arms statistically built upfrom 16 vol-% deuterated and 84 vol-% protonated mo-nomers. The composition-matching is achieved bymixing 16 vol-% deuterated with 84 vol-% protonatedhomopolymers. The superstructure of the PS domainsallows the easy identification of additional scatteringcontributions at non-ideal contrast conditions. The mi-croscopic matrix chain deformation in the reinforcednetwork is evaluated using the tube model of rubber ela-sticity [5] which successfully describes the chain defor-mations of unfilled networks in SANS [12,15]. SAXS ena-bles us to determine the geometrical properties of oursystems, the scattering contrast now due to differencesin the electron densities of polystyrene and polyisopre-ne. The structure of PS domains in comparable block-co-polymer systems can be modeled by a liquid-like Percus-Yevick structure factor [25] or a BCC lattice-like structurefactor [26-28]. However, it is beyond the scope of this pa-per to discriminate between different structural models.In the case of a liquid-like structure of spheres, the

d

dq N N Z S qH H D D D D

ΣΩ

Λ ∆ ∆ Λr r, ,( ) = +( ) ⋅ ⋅ ( )2 2 2

f ≈ + ⋅− ⋅

12 5

1 2

. ΦΦ

λ λ− = ⋅ −1 1 f ( )

Fig. 5. Fraction of intact triblock chains versus reaction time. Upper curvecorresponds to the melt sample without DCP addition, lower curve to thenetwork with DCP. The decomposition and gelpoint temperatures aresituated around rt = 30 and 40.

39



scattering intensity is written as the product of theaverage formfactor of polydisperse spheres withsmeared boundary, σ, and the hard sphere structurefactor in the Percus-Yevick approximation SPY(Q). Thediffuse boundary, σ, represents the width of a boundarylayer, whose electron density profile is the convolution ofthe density profile for a sharp interface with a Gaussiansmearing function.For the isotropic network, the average radius of the

spheres of Rm = (83.0±1.2)Å with gaussian polydispersityof σR = (12.0±0.6)Å. The hard sphere radius wasRHS=(120.0±0.6)Å corresponding to a hard sphere volumefraction ηHS = (0.49±0.01). For σ we have used a Porodanalysis to obtain 4Å.An affine correlation of the filler displacement withmacroscopic strain as well as a deformation of the PS-domains are observed. The PS volume fraction can againbe calculated to φPS = η(Rm/RHS)3 = (0.16±0.20) inexcellent agreement with the chemical characterization.Further insight into details of order or disorder of themicrophase domains are unimportant for the purpose ofthis investigation of matrix properties. The SANS data on the block copolymer showed that thematching condition was chemically not perfect. Theexcess intensity, however, is isolated in a peak at QRgabout 2. A biased subtraction of this intensity from theblends to obtain Debye curve scattering yields correctedscattering intensities [29]. For the representative case ofΦ1 = 0.16 and a macroscopic deformation of λ = 1.65 thetheoretical curve calculated from the tube model (eq.5)based on the parameters of the unfilled reference sample

without an overstrain factor considerably disagrees as isshown in Fig. 6. Introducing the microscopic overstrainfactor f, given in eq.10, into eq.5, using thetransformation of λ to λ , the average microscopicoverstrain factor f becomes the only relevant parameterto be optimized further. Since the network parameters aresimilar, besides the strain amplification all chainparameters can be estimated from the unfilled case. Anextra confinement effect is not present. In therepresentative example a value of f = 1.9 was determined,which gives an excellent fit for the whole q-range studied.The model as such therefore represents the first directmicroscopic proof of a matrix chain overstrain in filledelastomers. To determine whether f also depends onstrain - unlike eq.12 - all anisotropic spectra wereevaluated in the same way. A fitting of the tube diameteragain proved to be unnecessary. The reinforcement factor in Fig. 7 seems to followperfectly the known relationship f (Φeff) as in Eq.12 withΦeff =Φ (1+δ) as a correction for the strongly bound phaseon the surface of the microphase separation [23].

SummaryWe have studied the microscopic deformation and tubeconfinement in peroxide-crosslinked networks by meansof the Small Angle Neutron Scattering technique. Wehave shown that the level of deformation dependsstrongly on the length scale of investigation. For well-crosslinked networks with typically 15-20 knots perprimary chain, affinity is found down to the elastic chain.Latter length scale was thoroughly investigated bymeans of selectively labeled HDH block copolymers withvarying deuterated fraction. It is observed that forlabeled parts that are shorter than the typical tube

P q Rm,( )

Fig. 6. Upper: 2D and axis description of blend with ΦPS = 0.16. Solidcurves are best fit to the theory without hydrodynamic correction f.Lower: 2D and axis description taking into account the strainamplification factor f=1.9.

Fig. 7. Dependence of strain amplification f (right) and radius of gyration(left) on the volume fraction of PS-filler. The agreement of f is perfect withthe suggested Pade-approach and an effective filler volume fraction.

40



diameter the tube constraints vanish and the phantommodel re-appears. Also the effect of reduced deformationin the case that the labeled part is shorter than theshortest elastic chain is included in the investigation. Basing on the information from the unfilled rubbers, wehave studied the phenomenon of rubber reinforcementon a model system by simulating the filler bymicrophase-separated spherical PS-domains. All lengthscales of interest as well as sizes of the domainsthemselves are available. This tailor-made blockcopolymer provides a one-to-one correspondence to realfilled elastomers. By judiciously matching the scatteringproperties of the filler component by that of the matrix,the effect of the reinforcement on the matrix chains wasstudied by SANS, whereas the response of the filler couldbe studied by SAXS.The SAXS experiment yielded a filler radius of about84Å, which compares well to typical sizes of carbon blackor silica fillers, and an affine correlation of the fillerdisplacement with macroscopic sample strain was found.The variation of the domain radius with the strainindicated that the PS spheres are softer than expected,which may be attributed to the presence of somepolyisoprene chains within the PS domains reducing thedensity of the micelle-like core.The SANS experiments were evaluated using anextension of the tube model for randomly cross-linkednetworks and the molecular parameters derived were ingood agreement with the expected ones for the unfilledcase. The reinforcement factor f depended on the fillerconcentration according to the overstrain picture andvaried slightly with strain. The data were fitted to a veryhigh degree of accuracy with the assumption of anhomogenous over-strain in the matrix but first signs of abreak-down of this crude treatment have shown up.This work reports for the first time a direct experimentaldetermination of the overstrain factor which has to beconsidered in reviewing semi-microscopic theories of therubber reinforcement with real filler materials. This workencourages the analysis of silica-filled systems which iscurrently still under progress.

AcknowledgementsThe authors thank Dr. G. Heinrich, Continental AG, forvaluable discussions during the progress of the work andMrs. M. Hintzen for the kind preparation of the networksamples.

References

1. S.F. Edwards and T.A. Vilgis, Rep. Prog. Phys. 1988, 51, 243-297.2. M. Doi and S.F. Edwards, The Theory of Polymer Dynamics,

Clarendon Oxford, 1986.3. R.T. Deam and S.F. Edwards, Philos. Trans. R. Soc. London, Ser. A

1976, 280, 317.

4. M. Warner and S.F. Edwards, J. Phys. A. 1978, 11, 1649.5. G. Heinrich, E. Straube, and G. Helmis, Advances in Polymer

Sciences 1988, 85, 33-87.6. G. Heinrich and E. Straube, Acta Polymerica 1983, 34, 589-594.7. G. Heinrich and E. Straube, Acta Polymerica 1984, 35, 115-119.8. A. Kloczkowski, J.E. Mark and B. Erman, Comp. Polym. Sci. 1992, 2,

8.9. X. Quan, I. Gancarz, and J.T. Koberstein, J. of polymer Science Part B:

Polymer Physics 1987, 25, 641.10. X. Quan and J.T. Koberstein, J. of Polymer Science Part B: Polymer

Physics 1987, 25, 138111. J.S. Higgins and H.C. Benoit, Polymers and Neutron Scattering,

Clarenden Oxford1994.12. S. Westermann, V. Urban, W. Pyckhout-Hintzen, D. Richter, and E.

Straube, Macromolecules 1996, 29, 6165-6174.13. A. Botti, W. Pyckhout-Hintzen, and D. Richter and E. Straube, in

preparation 1999.14. E. Straube, V. Urban, W. Pyckhout-Hintzen, and D. Richter,

Macromolecules 1994, 27, 7681.15. E. Straube, V. Urban, W. Pyckhout-Hintzen, D. Richter and C.J.

Glinka, Phys. Rev. Lett. 1995, 74, 4464.16. D. Read, Phys. Rev. Lett. 1997, 79, 87.17. D. Read, Phys. Rev. Lett. 1998, 80, 5449.18. J. Bastide, J. Herz, and F. Boue, J. Phys. (Paris) 1985, 46, 1967.19. J.-B. Donnet, Carbon Black, M. Dekker New York, Basel, Hong Kong

1993.20. D.C. Edwards, J. of Material Science 1990, 25, 4175-4185.21. J. Donnet, A. Vidal, Prog. Coll. Polym. Sci. 1987, 75, 201-212.22. E. Guth and O. Gold, Phys. Rev. 1938, 53, 322.23. R.M. Christensen, Mechanics of Composite Materials, Wiley New

York, Chichester, Brisbane, Toronto 1979.24. H.-S. Chen and A. Acrivos, Int. J. Solids Structures 1978, 14, 349.25. D.J. Kinning and E.L. Thomas, Macromolecules 1984, 17, 1712.26. L. Leibler, Macromolecules 1980, 13, 1602.27. M. Schwab and B. Stuehn, Phys. Rev. Lett. 1996, 76, 924.28. M. Schwab and B. Stuehn, J. Mol. Str. 1996, 383, 57.29. S. Westermann, M. Kreitschmann, W. Pyckhout-Hintzen, D. Richter

and E. Straube, Macromolecules 1999, 32, 5793.

41



Solo dopo aver conosciuto la superficie delle cose ci si puòspingere a cercare quel che c’è sotto. Ma la superficie delle coseè inesauribile.

(I. Calvino, Palomar, Einaudi, 1983)

Only after knowing the surface of things can one explore whatis underneath. But the surface of things is endless.

(free translation)

IntroductionIn the last decade non-conventional radiation sources,like Synchrotron Radiation (SD) storage rings and reac-tors or spallation neutron sources, have been increasin-gly used in structural and materials science studies.Many of these researches were based or Neutron Dif-fraction (ND) and X-ray Diffraction (XRD) techniques,whose potentiality is greatly enhanced by SR. Despitethe large number of scientific activities that are beingconducted, and new Large Scale Facilities (LSF) thatare planned for the near future (e.g., Diamond in UK),relatively few applications directly concerned techno-logical issues [1].A deeper discussion on this point would be far beyondthe scope of the present paper, but two factors at leastshould be considered: the access to LSF is notstraightforward, and costs and time length or researchescan be incompatible with industrial R&D and diagnosticrequirements. In addition, most companies are probablynot aware of the great potentiality of SR XRD and ND; onthe other hand, it is also possible that many scientistsengaged in SR XRD and ND studies are not completelyaware of the industrial needs and of the many possibleapplications of technological interest. Therefore, the roleof popularisation and information within the scientific aswell as industrial community cannot be overemphasised.It is the main purpose of this work to review some recentapplications of SR XRD and ND to typical examples ofMaterials Science & Engineering studies concerning thinfilms and coatings for metallurgical and thermal engineapplications of direct technological interest. SR XRD has several advantages over to correspondinglaboratory XRD: the most obvious is the high brilliance

that can reduce greatly measurement times, and allowmeasurements that would be unrealistically long on alab-scale equipment. More specifically, thin films andcoating studies can benefit of the following uniqueexperimental conditions: • Highly parallel (line or point) beam: ideal for texture

and strain studies.• Variable wavelength: necessary to measure gradients

of properties in coatings and surface layers.• Monochromatic, narrow instrumental profile: best

conditions for powder (θ-2θ) measurements, and LineProfile Analysis (LPA) studies in particular.

Beam penetration is probably the main limit of SR XRD;even if a transmission geometry can permit a through-thickness scansion of properties (e.g., residual strain[2,3]), thickness up to a few mm or cm can be reached forlow-absorption materials only (e.g., Al), and very highenergy. X-rays are intrinsically not suitable to producediffraction phenomena of practical interest for stress-texture measurements with very high energies (above≈20 keV). Therefore, apart from particular cases, typicalmeasurement depths range from fractions of microns to50÷100 µm.Much higher penetrations can be achieved by ND; metaland ceramic components of the order of several cm ormore can be easily crossed by a neutron beam [2,3]. Thelimit, in this case, is on the opposite side, i.e., the smallestdepth difference that can be distinguished, and theaverage over a relatively large sampling volume.In ordinary conditions (ENGIN, ISIS), strain depth-profiling cannot be measured with steps smaller than~0.25 mm. Therefore problems can arise when studyingcoatings of “intermediate” thickness, of the order of100÷200 µm, which can be viewed as too thick for SRXRD and too thin for ND.SR XRD and ND can be especially useful in problems ofresidual stresses, texture and phase compositions(including also the determination of nature and amountof lattice defects) of thin films and coatings; technologicalproperties (mechanical, thermal, electrical etc., but alsostability and service life) are closely related to thesefactors. In the following I will describe variable-

STRESS-TEXTURE STUDIES IN THIN FILMS AND COATINGS BY SYNCHROTRON RADIATION XRDAND NEUTRON DIFFRACTION Paolo ScardiDipartimento di Ingegneria dei Materiali, Università di Trento38050 Mesiano (TN), Italy

Articolo ricevuto in redazione nel mese di Aprile 2000

42



wavelength techniques to study through-thicknessvariation of the residual stress field in thinpolycrystalline diamond coatings for cutting toolapplications, and analogous topics in thick ceramics forThermal Barrier Coatings (TBCs) on engine components.Ample bibliography is reported for details on thesestudies.

Polycrystalline diamond coatingsPolycrystalline diamond coatings (PDCs) produced byChemical Vapour Deposition (CVD) techniques find anumber of applications as hard layers to improve wearresistance of cutting tools and metal components [4].Practical uses, however, can be limited by adhesion andcoating stability in service conditions, and both featuresare strongly connected with the stress field producedduring deposition or in service. Residual stress can be ofthermal or intrinsic nature: the former is due to the highdeposition temperature and differences in thermalexpansion coefficient (TEC) of substrates and PDC,whereas the latter is typically due to grain growth orphase transformations [5,6]. PDCs have a peculiar microstructure, with single-crystalgrains whose shape and orientation is closely related tothe CVD process conditions [7]. Surface pretreatmentsaffect nucleation and final microstructure, therebyadhesion and wear resistance change considerably [8,9].Typical pictures at the early stages of diamond growthand at the surface of a thick (5µm) PDC produced byHFCVD (Hot Filament CVD, [8]) are shown in Figure 1.In the following case of study, substrates were made ofTi-6Al-4V alloy; preliminary XRD lab measurementsrevealed the presence of a TiC layer between diamondand α-Ti substrate matrix, whereas the residual stressfield in the PDC proved to be planar and rotationallysymmetric (i.e., the only non-zero stress component is inthe surface plane, with σ11 = σ22) [10,11]. SR XRD data

were collected at British facility of Daresbury, station 2.3,using a 4-circle goniometer: measurement geometry isshown in Figure 2.Texture and residual strain in diamond coating andphases underneath were studied by selecting the mostappropriate wavelengths. Diamond (111) and (220) polefigures are shown in Figure 3, together with an analogouspicture for (024) α-Ti. PDC exhibits a broad (hh0) fibretexture (i.e., grains with [h00] growth direction and lackof any order in the growth plane), whereas no texture isobserved in TiC and α-Ti matrix.Based on the above information, residual strain wasmeasured on the three phases, stacked in the sequence α-Ti/TiC/PDC, using different wavelengths (two differentvalues for α-Ti matrix). Figure 4 shows the results in theform of sin2ψ plot (interplanar distance or strain as afunction of the sin2 of the ψ-tilting angle) [12]: trends arelinear, as expected from the planar stress hypothesis, butslopes are markedly different in the three phases.Average residual stresses, calculated by usingappropriate X-ray Elastic constants (Table 1), aredisplayed in Figure 3.

Phase: diamond TiC α-Ti(C) WC

wavelength (Å) 2.15 1.66 1.68 1.4 2.2 0.9 0.65

(hkl) 220 024

S1 (GPa)-1 9.2 x10-4 2.73 x10-3 1.13 x10-2 (°) 1.94 x10-3 (°)

_ S2 (GPa)-1 -5.5 x10-5 -4.50 x10-4 -2.7 x10-3 (°) -3.49 x10-4

(°)

ξ (at ψ=45°) (µm) 72.2 4.8 2.8 8.6 0.54 1.25 2.96

(°) calculated as (1+ν)/E and –ν/E, respectively (E=106 GPa; ν=0.31);

(°°) (E=640 GPa; ν=0.26).

Table 1. Wavelengths, information depth (ξ), XECs and Miller indices of

studied reflections.

The strong compressive stress in the PDC turns to weaklytensile in the substrate. This study was particularlyuseful to understand the role played by the TiC reactionlayer in adapting the strongly compressed PDC to themetal substrate. All the present phases could be accessedwithin the same measurement, profiting from thepossibility of tuning appropriately wavelengths. The thermal component of PDC residual stress can beestimated as σT ≈ ∆α ⋅ ∆T ⋅ E/(1-ν) (∆α is the differencebetween TEC of coating and substrate, E and ν are Youngmodulus and Poisson ration of PDC, respectively), whichgives σT = -6 GPa (for a PDC deposited on a Ti-alloy atTdep=650°C), very close to the measured value. This resultstrongly suggests that thermal stresses are dominant inthese systems. The same was also observed for PDCs on WC-Co cuttingtools [9,13]. In this case, SR XRD measurements onsamples produced at different Tdep gave interesting

Fig. 1. Early stages of polycrystalline diamond on a WC-Co component(Courtesy of R. Polini) (a); surface of a 5 micron PDC on WC-Co (b).

43



information on coating adhesion and stability. Given thethermal nature, compressive stress increases with thedeposition temperature; this is frequently observed inPDCs because diamond TEC is usually much lower thanthat of metals and many ceramics.Even if compressive stresses in coatings and surfacelayers can be beneficial, for they can improve theprotective action against wear, very high values can leadto coating detachment. It is therefore necessary to find anoptimal balance between the two needs: high surfacecompression and good adhesion. Figure 5 shows planarresidual stresses measured by SR XRD in PDCs on WC-Co components as a function of Tdep; experimental valuesare close to the calculated thermal stress up to a criticalvalue beyond which measured residual stress reduces,due to a progressive coating failure. XRD patterns are

collected on a relatively large surface area (≈1 cm2), solocalised failures can reduce without eliminating themeasured residual strain; Figure 4 can then be used toestablish the optimal (maximum) Tdep. Coatingsdeposited above Tdep>750°C are likely to be damaged: infact, above this temperature PDCs frequently spalledsoon after deposition, or did not resist the SR XRDmeasurements. Some of them were partially lifted fromthe substrate, without apparent damages, and onlyresidual strain measurements could disclose conclusiveevidence on their adhesion. Therefore, an important process parameter could betuned by means of SR XRD, and coating quality (andadhesion in particular) could be tested in a non-destructive way. Interestingly, analogous considerationscould also be done on the basis of a LPA study (detailsin ref. 13,14).Given the marked thermal nature of residual stress,numerical FEM models (based on the TEC differencesand other properties of coating and substrate) can beused to predict the stress field through the thickness ofcoated components. Results of these modelling usuallyshow a sharp stress change from compressive to tensileat the PDC-substrate interface [15]. However, directexperimental evidence of this important feature ismissing, even if, as we have already underlined, PDC-substrate interface stresses are determinant incontrolling adhesion and durability of coatedcomponents. A deeper insight on this important pointwas made possible by SR XRD [16].Sample was a WC-6%Co (K10 alloy) component coatedby PDC. The 5µm diamond coating was deposited at750°C (further details in references 13,14) and did not

Fig. 2. Schematic of the instrumental set-up, with definition of 2θ, ψ-tilting and azimuth (φ) angles.

Fig. 3. Pole figures ((220) diamond, (111) diamond, (220) TiC) and average residual stress in a Ti6Al4V component with PDC and TiC interface [11].

44



show significant texture. SR XRD revealed a compressivestress of about –1.7 GPa, comparable to the thermal stress(see Figure 5); the same value was obtained by using twodifferent wavelengths (Figure 6a), both with positive andnegative ψ-tilting, as well as at different azimuth (φ),confirming the planar, rotationally symmetric nature ofthe residual stress field [10].To investigate the residual stress in the interface region ofthe substrate, we selected three different wavelengths, inorder to collect residual strain data at different averagedepths in the substrate (Table I). The results are markedlydifferent, and clearly indicate the presence of a stressgradient that was studied as follows. The basic equationin X-ray residual stress analysis (XRSA) is [17]:

(1)

where the strain is measured in the laboratory system (L)along the scattering vector direction (ε33 component), andis averaged ( ) over all the crystalline domains whosehkl planes are in Bragg condition.On the other hand, the quantity of interest is themacroscopic residual strain, or the correspondingresidual stress, in the sample system (S). Fij are stressfactors, calculated from elastic constants accounting fortexture effects [18,19]. Unlike elastic constants, stressfactors are not tensor properties; their calculation can bequite complex and depends on the mechanism ofmechanical grain coupling in the material, which inprinciple is not known [17-19].In our case texture is absent, and the material can beconsidered as quasi-isotropic (texture-free, macro-scopically isotropic) and homogeneous. Therefore Fij canbe replaced by XECs that can be calculated from elastic

constants data with reasonable reliability [17]. In additionwe can assume a rotationally symmetric planar stress, sothat a gradient can be described simply as:

(2)

where z is the position below the surface. The averagesample stress in Eq. 1 is averaged over the X-rayabsorption low, and can be written as:

(3)

where t is thin film thickness, and ξ = (sinθ cosψ)/2µ isthe information depth, which depends on θ, ψ (Figure 2)and µ, the linear absorption coefficient. Introducing XECs(ξ=(sinθ cosψ)/2µ) we can write the sin2ψ equation in thepresence of a stress gradient [16,18]:

(4)

The biaxial stress hypothesis also allows the use of the

condition to calculate the strainfrom interplanar distance [17,18]. Eq. (4) can be used tosimultaneously fit strain data obtained from differentwavelength measurements, in order to refine thecoefficients (a,b,c..) of the stress gradient (Eq. 2). Theresult of this procedure in shown in Figure 6b, whereasthe stress distribution in the surface and interface regionof the coated component is reported in the drawing ofFigure 6c. No sharp change from compression to tensionis observed, and the neutral axis lays below the interface,inside the substrate. This clearly demonstrate that amodelling simply based on TEC differences is an

sin20 1 22ψε = = − ⋅S Shkl hkl½

ε ψ ξ ξ ξξ ξ

ξ ξ3312

2 22 11

2 11 2

11 2

L hkl hklt t

S S a bt

ec

t t

e= +[ ] ⋅ + −

−

+ −+( )

−

+

sin ...

σσ ξ

ξ

S

S zt

zt

z e dz

e dz

=( ) ⋅ −

−

∫

∫

0

0

σ σ σ11 222S S S z a b z c z= = ( ) = + + +.....

⟨ ⟩ =ε σ33L

ij ijSF

Fig. 5. Planar residual stress measured by SR XRD in PDCs deposited onWC-Co at different deposition temperatures.

Fig. 4. sin2ψ plot for diamond, TiC and α-Ti phases in the sample ofFigure 3 [11].

45



oversimplification that doesn’t reproduce the actualfeatures of the coating-substrate interface in realcomponents. These results find a direct correlation withthe wear behaviour, that was tested against severalmetallic and ceramic counterface materials. Details onthese studies can be found in reference 9.

Ceramic Thermal Barrier Coatings (TBCs)Thick layers of zirconia-based materials find importantapplications as TBCs on gas turbine hot components likecombustor cans, transition ducts and 1st stage vanes andairfoils, but also in Diesel engines parts, like piston headsand valves [20-22]. Thermal insulation of TBCs can

reduce the temperature of the underlying metalcomponent by 100°C or more, with a remarkable increasein durability and a reduction in fuel consumption;estimated fuel economy for a 250-aircraft fleet usingTBCs on turbine blades is of the order of 10 milliongallons per year [21]; conversely, an increase of 110°C inthe inlet gas temperature may allow a 20% increase inthrust of jumbo-jet gas turbines [23]. Therefore, the greattechnological and economical impact has fostered manyresearches in this field, for the production of better TBCsand cost reduction. Plasma Spray and EB-PVD are themost used (and suitable) techniques to produce ceramic

coatings in the thickness range from 0.1 to ca 2 mm (ormore). One of the main issues in the design of longdurability coatings is improving adhesion; coatingdebonding (spalling), in fact, is a primary failuremechanism. In turn, adhesion is directly connected withthe thermal stress developed during deposition and,especially, in service conditions [24].Modelling the behaviour of typical ceramic TBCs is aformidably difficult task [25]. The main reason lays in thecomplex microstructure (Figure 7), and plasticity andcreep phenomena at the metal interface that can bedifficult to model; in addition, corrosion (and oxidationin particular), phase transformations, action ofcontaminants in the fuel, stability of metal and oxidephases, ceramic sintering, are all important factors thatmake modelling and life prediction a complex issue. Adirect measurement of residual stresses is thereforerequired. SR XRD and ND are the only viable non destructive te-chniques to investigate the through-thickness stress di-stribution in coated components. The first example con-cerns a 300 µm TBC of Y-PSZ (Yttria Partially Stabilised

Fig. 6. sin2ψ plot for a PDC on WC-Co, as obtained by SR XRD by usingtwo different wavelengths (a); experimental data and modelling bymeans of Eq. (4) for the WC phase interface (b); trend of residual stress incoating and WC interface layer (c) [16].

Fig. 7. Microstructure of a typical Air Plasma Spray coating of Y-PSZ(fracture surface).

46



Zirconia) deposited on Al-alloy bars (9mm x 6mm x130mm) by Plasma Spray under controlled conditions oftemperature and atmosphere. After low temperatureageing, phase transformations taking place in the cera-mic led to a single-phase tetragonal material, seeminglyin a compressive in-plane stress state [26]. Even if thick-ness exceeds the depth accessible by X-rays, a measure-ment of gradient in the outer ≈50 _m layer can be carriedout by SR XRD, and the result can be integrated by infor-mation on the average stress in the coated componentobtained by measuring coating length and curvaturechange after debonding by chemical attack [26].The approach proposed by Eq.(5) was used again,considering that the thickness t tends to infinity (valuesabove ca 100 µm can be considered as infinity for theabsorption of X-ray wavelengths of the present study),and using two sets of data collected at differentwavelengths. The results of the least square fitting areshown in Figure 8a, and the corresponding residualstrain trend in Figure 8b. This result, which confirmed the

compression in the coating and revealed the presence ofa steep gradient, can be used together with values oflength and curvature changes after debonding as aninput of a suitable mechanical model, based onequilibrium conditions of forces and bending moments[27]. In this way it was possible to calculate the stresstrend inside the component, which is reported in Fig. 9.This result was of great interest from the methodologicalpoint of view, as it gave a through-thickness residualstress trend in a coated component, and demonstratedthe importance of phase transformations on residualstress evolution in TBCs. However, a direct analysis ofthe stress at the interface was out of reach. To thispurpose we can resort to ND. The following exampleconcerns a thick (1.6 mm) Y-PSZ TBC deposited by AirPlasma Spray (APS) on an Al-alloy piston head semi-component (diameter 87 mm, height 10 mm) [28-30]. A0.2mm bonding layer of Ni-CrAlY was deposited on themetal before APS. The component underwent a severethermal cycling, reproducing service conditions, in orderto study the failure mechanism. Thermally cycledcomponents started to develop a crack at the edge of thedisk (along the rim), near the ceramic side of theinterface region; the central area of the studied disk,instead, was still perfectly adherent and NDmeasurements were then conducted in that area.ND was done at the British facility of ISIS, using ENGINon the PEARL beamline. The instrument was specificallydesigned to make strain measurements, and in particularthrough-thickness scansions. The set-up used in ourstudy is reported in Figure 10: Time of Flight (TOF)patterns were collected at different z position, in order toplace the sampling volume at increasing depth inside thecomponent. Figure 11a shows some selected patterns,where we can see the various phases appearing atdifferent depth. The information on the strain is obtainedfrom peak position shifts that, under the adoptedgeometry, give an ε33 component.Data processing is not straightforward, and requiressome additional work. Besides the problem ofdetermining the interplanar distance for strain-stress freesamples [30], several corrections for aberrations arerequired; in addition, the trend of Figure 11b, obtainedfrom peak position shifts, is an average strain over thesampling volume (strictly, that part of sampling volumethat is actually intersecting the material for any given zposition). A suitable model is then necessary to obtain the residualstrain trend as a function of depth [30]; however, mostvaluable conclusions can be drawn on the basis of Figure11b without further processing. In fact, if we assume thatthe main stress component is a rotationally symmetricplane stress (only non-zero component σ11 = σ22), thenmeasured strain along the 33 direction can be interpreted

Fig. 8. Least squares fitting of residual strain data collected by SR XRD ona Y-PSZ TBC deposited on an Al-alloy component. Data were collected byusing two different wavelengths (a); residual strain gradient resultingfrom the analysis of (a) (b) [16,27].

47



as an in-plane compression or tension for positive andnegative strain values, respectively (simply a Poissoneffect). From Figure 11b we can then conclude that:• TBC surface is in compression, in agreement with

preliminary XRD observations; a compressive surfacestress is attributed, among other mechanisms, toceramic sintering and filling of porosity with corrosionproducts (also observed by XRD).

• in-plane compression decreases toward the inside,and turns to tension around the mid of the coatingthickness;

• compression increases again near the Y-PSZ/Ni-CrAlY interface. A steep strain gradient is presentwithin the ceramic, near the interface;

• the Ni-CrAlY bonding layer is in compression(experimental resolution didn’t allow the collection ofmore than one point for that phase);

• Al-alloy substrate is in tension at the interface; totalstresses and bending moments tend to equilibrate(even if, strictly, stress and moments shouldequilibrate over the entire component, and notnecessarily locally).

These observations are compatible with a model of

thermal cycling where substrate creep takes place in theinterface region. In fact, we can assume that thermalexpansion during the heating stage of each thermal cycleputs the Al-alloy in a compression, because TEC is almostdouble than that of TBC and bonding layer. During thehigh temperature part of the cycle, compression tend tobe released by substrate creep in the interface region. Oncooling the situation reverses, and when temperature issufficiently low to arrest creep, the coating tend to be incompression while the substrate is in tension. Theresulting stress tends to develop shear components alongthe edge of the coated disk, and cracks are most likely tonucleate and propagate in the interface area, inside theceramic (which is brittle), in the region where a steepstrain gradient was observed.This interpretation is well supported by otherexperimental observations, and suggested an interestingfailure model in thermally cycled TBCs [30]. Phase stability, besides adhesion, is an importantproblem in TBCs technology. Zirconia has severalpolymorphs: at room pressure we can find monoclinic(m), tetragonal (t) or cubic (c) zirconia (in order ofstability from low to high temperature). Hightemperature phases can be retained at RT for kineticreasons, but also by adding suitable stabilising oxides(like Yttria and /or Scandia in our TBCs). The aim isobtaining a single-phase material, stable in a widetemperature range, in order to prevent the catastrophiceffects of volume expansion associated with polymorphicphase transformations (especially the 4% volume changeof t-m transformation). Considerable efforts are thusaddressed to the development of new zirconia materials,and stabilising oxides in particular. Measuring phasecontent is an important issue: XRD is typically used, alsoas a routine-basis technique, even if overlapping amongpeaks of zirconia polymorphs can hinder the analysisand make results unclear. In a recent study on a new stabilising oxide mixture

Fig. 9. Residual stress trend across the coated component of Figure 8; theresult was obtained by using SR XRD data and coating length andcurvature change after debonding [27] (a). Detail of the stress trend in theTBC, with stress gradient obtained by SR XRD, with indication of theinformation depths for the two wavelengths used (b).

Fig. 10. Instrumental geometry of TOF data collection on ENGIN at ISIS(Didcot, UK). Schematic cross section of the studied coated component.

48



based on the Scandia-Yttria system [31], SR XRD wasused to disclose the complex phase equilibriumdetermined by a high temperature ageing of zirconiapowders and TBCs. The purpose of the study was toverify the stability of phase composition after anaccelerated high temperature ageing. Verifying the

formation of m-phase does not need, usually, verysophisticated instruments: two m-phase peaks at lowangle are easily distinguished from the t or c reflections.Understanding the composition of t and c phases is morecomplex. SR XRD patterns collected on TBCs heat treatedat 1400°C [31] are shown in Figure 12, together with theresult of the modelling by means of a program based onthe Rietveld method [32], which permits structurerefinement as well as quantitative phase analysis [33].The intense SR beam allowed the collection of highsignal-to-noise patterns: narrow, monochromatic profileswere the best conditions for clearly identifying thepresent phases. Analogous data collected on lab XRD

instruments led to no conclusion. The problem was in theidentification of three different t-phases, recognised onthe basis of the c/a ratio and considerations based on theZirconia-Scandia and Zirconia-Yttria phase diagrams[31,34]. In particular, after thermal cycling, the TBCmade of the new Scandia-Yttria stabilised Zirconia(SYSZ) showed an almost negligible m-phase content(Figure 12a), and was made mostly of a t’ (so-called non-transformable) tetragonal phase composing as-sprayedcoatings; very little t1 phase was found (zircon waspresent as a contaminant due to the preparation inquartz crucibles of the new SYSZ powder used forPlasma Spray). The state-of-art YSZ coating, inanalogous heat-treatment conditions developed a muchbigger amount of m-phase (Figure 12b); in addition, thet’ phase completely demixed in two t-phases, t1 and t2,leading to a complete destabilisation of the material,and progressive m-phase formation. The conclusiveevidence for the presence of the two t-phases, neverobserved clearly before, was given by long wavelengthmeasurements, like that shown in Figure 12c, thatallowed a better separation between peaks of thepresent polymorphs.

Highly textured thin filmsSR XRD and ND applications discussed so far concernedweakly textured or random coatings. However, a verylarge number of thin film systems of technological interestare strongly textured (typical pole figures of differentlytextured thin films are reported in Figure 13): epitaxial oretheroepitaxial thin films, frequently used for electronicapplications, tend to develop a single-crystal like texture,with order both along growth direction and in the growthplane; concerning strain-stress relationships they can bedescribed as single crystals, even if grain boundariescertainly play an important role [6].The case of fibre textured (FT) thin films in more com-plex. Most PVD thin films for metallurgical applications(e.g., hard nitride coatings, TiN, CrN etc.) belong to thiscategory. Fibre texture can be more or less sharp, and fi-bre components can be one or more; in addition this typeof PVD thin films are known to develop intense residualstresses (frequently the order of 5-10 GPa or more, mo-stly of intrinsic nature [35,36]), which area key-factor indetermining adhesion and stability.In this case stress-texture interaction is very strong andcannot be overlooked. In addition to the effect of textureon the stress-strain mechanical model (see the discussionabove on stress factors), texture measurements byconventional pole figures can be difficult to carry out;peak positions (fixed during pole figure measurements)change dramatically with ψ-tilting, due to the strongresidual stresses.

Fig. 11. Selected TOF patterns collected at different z values (a). Residualstrain (ε33 component) in the coated component. Data are averaged overthe sampling volume (curves reported just to drive the eye) (b). [29,30].

49



Texture and stress must be considered simultaneously.Recently we proposed a data collection strategy to studyFT thin films, based on the measurement of several θ-2θpatterns at increasing ψ-tilting values [36,18]. Due to theaxial symmetry, these θ−2θ/ψ maps can be collected forany arbitrary value of azimuth angle (φ). Figure 14 shows

a map for the (200) reflection of a TiN thin film onaustenitic steel; besides nitride, signal from the substrateis also visible, consisting of the (111) reflection ofaustenite and a weaker reflection from martensite (110)[10,18,36]. Schematically, intensity distribution as afunction of ψ gives an indication on texture, whereaspeak shift (in 2θ) is related to strain; further informationon lattice defects and domain size can be obtained fromprofile width and shape. From these data it is possible, bysuitable least squares fitting and assuming anappropriate model of mechanical grain-coupling, to havea valuable description of growth mechanisms andgrowth stresses, that frequently involve gradients [37,18].SR XRD can be very important, especially in connection

with the last point, i.e., the presence of gradients: presentday investigations [37,18,19], in fact, usually considerthin films as homogeneous. This may be true ofcomposition (although compositional gradients are alsoobserved, for instance in TiN coatings, but they can betaken into account, at least in principle), but is not easilyverified a priori for texture.FT thin film microstructure, including grain shape andorientation, usually changes in the initial growth stages:interfacial layers of different orientation are frequentlyobserved [6], and texture may change dramatically withthickness [18]. It is therefore important to collect data byusing different wavelengths, as shown in Figure 15 for aCoNiCrAlY superalloy thin film, in order to access diffe-rent depths in the thin film. This type of investigationscould hardly be done on a lab XRD system, and SR XRDis again a unique tool in the hands of materials scientistsand engineers. Promising developments are expected inthe future, to develop 3D texture descriptions.

LPA studiesA final word concerns the use of SR XRD in LPA studies.X-ray Powder Diffraction (XRPD) is probably one of thefirst and most successful applications of SR to structuralstudies. Station 2.3, used for many of the measurementsdescribed in this work, was specifically designed forpowder diffraction [38], and most LSF around the worldhave at least one XRPD station or more. It is not thepurpose of this work to review SR applications to XRPD,but it should be underlined that besides structuralstudies, materials science can greatly benefit of SR XRPD. So far we have described an application of XRPD to adelicate problem of quantitative phase analysis, which iscertainly a valuable application of SR. LPA can begreatly improved by using SR XRPD, because of themonochromatic beam conditions that can be obtainedtogether with narrow instrumental profiles and highbrilliancy. These features can be extremely importantwhen studying problems of anisotropic line broadening(dependence of profile width and shape on hkl [39,40])like in the case shown in Figure 16 [40]. A new approachto model the whole XRPD pattern on the basis of lineand plane lattice defects and domain size has beenrecently proposed, and could be tested in a complex caseinvolving 33 profiles of a spinel phase, including also 9peaks of a position standard (Si) [40]. The uniquefeatures of SR XRPD where fully exploited to reach therequired data quality to effectively test the procedure. Inthe detail of Figure 17a, we can appreciate the effect ofline broadening anisotropy, that in the spinel case wasmostly due to the anisotropic effects of dislocations.Such an effect can be described by the average contrastfactor [40.41], whose trend as a function of the

Fig. 12. SR XRD data collected at Daresbury, UK (station 2.3) in θ−2θconfiguration (λ=1.5406Å) on Yttria-Scandia-Zirconia (a) and Yttria-Zirconia (b) TBCs heat treated for 100h at 1400°C plus 24h at 1480°C.Detail of the pattern of (b), collected with λ=2.2 Å (c) [31]

50



orientational parameter (H = (h2k2+h2l2+k2l2)/(h2+k2+l2)2 )is also shown in Figure 17b. More details on thisinteresting and promising application can be found inreferences 39,40.

AcknowledgementsSR XRD and ND applications reviewed in this paperwere the result of the work of several people, amongwhich I wish to thank S. Setti, M. Leoni, S. Veneri, M.D’Incau (Univ. of Trento), R. Polini (Univ. Roma II), G.Cappuccio (CNR-INFN, Frascati (Rome)), L. Bertini(Univ. Pisa), J. Wright (ISIS, Didcot UK), C. Tang, R.Cernik and A. Neild (Daresbury SRS, UK).

References

1. See e.g.: Synchrotron Radiation Department, Scientific Report 1995-96(Daresbury Laboratory, UK), 1996; ibidem, Scientific Report 1996-97,1997-98, 1998-99; The Rutherford Appleton Laboratory, ISIS facilityannual report, 1996-97 (Didcot, UK); ibidem, ISIS facility annualreport, 1997-98, 1998-99.

2. P.J. Webster, G.B.M. Vaughan, G. Mills and W.P. Wang, Mat. Sci.Forum, 278-281 (1998) 323; Å. Kvick (ed), Local characterisation ofmaterials, Internal ESRF Publ. N°ESRF97KV10T, (ESRF, Grenoble),1997.

3. P.J. Webster and X. Wang, Surf. Eng., 10 (1994) 287; P.J. Webster, G.Mills, X.D. Wang, W.P. Wang and T.M. Holden, J. Neutron Res., 3(1996) 223.

4. J. Wilks, E. Wilks, Properties and applications of diamond,(Butterworth, Oxford), 1991. J.R. Davis (ed.), Tool Materials, (ASMInternational, Materials Park, USA), 1995.

5. I.C. Noyan, C.C. Goldsmith, Adv. X-ray Anal., 34 (1991) 587.6. P. Scardi, in Science and Technology of Thin Films, edited by F.C.

Matacotta and G. Ottaviani, (World Scientific Publisher Co.,Singapore), 1995. p. 241.

7. Ch. Wild, N. Herres, P. Koidl, J. Appl. Phys, 68 (1990) 973.8. R. Polini, G. Marcheselli, and E. Traversa, J. Am. Ceram. Soc., 77 (1994)

2043; R. Polini, G. Marcheselli, G. Mattei and E. Traversa, J. Am.Ceram. Soc., 78 (1995) 2431.

9. G. Straffelini, P. Scardi, A. Molinari, J. Mater. Res. (2000). Submitted; C.Carlando, Comportamento tribologico di rivestimenti di diamante po-licristallino su WC-Co, Thesis, Università di Trento, 1997. (In Italian).

Fig. 13. (h00) pole figures of polycrystalline thin films with differenttexture. Fibre-axis is [hhh] in the FT thin film. Growth normal is [hhh] forthe single-crystal like thin film.

Fig. 14. θ−2θ/ψ map for the (200) reflection of a fibre-textured TiN thinfilm on AISI 304 steel. Features attributed to the coating and substratephases are indicated (A: austenite, M: martensite).

Fig. 15. θ−2θ/ψmaps collected on a Co-Ni-base superalloy thin film by SRXRD at different wavelengths. Pictures refer to the high ψ-tilting range(44-80°) for the (111) (left, lower 2θ) and (200) (right, higher 2θ) fccreflections.

Polycrystalline thin films

Random Fibre-textured ‘Single-crystal’

70

50

30

10

-10

-30

-50

-70

Ψ

TiN A

M

40.5 42.5 44.5 46.52θ

0.4 Å

0.8 Å

51



10. M. Leoni, Residual Stress Gradients in Polycrystalline Coatings, PhDThesis. Università di Roma ‘Tor Vergata’, 1999.

11. P. Scardi, M. Leoni, G. Cappuccio, V. Sessa, M.L. Terranova, Diamondand Related Mat., 6 (1997) 807.

12. I.C. Noyan and J.B. Cohen, Residual Stresses, (Springer-Verlag, NewYork), 1987.

13. S. Veneri, Influenza dei parametri di deposizione sulle caratteristichemicrostrutturali di rivestimenti di diamante policristallino,Università di Trento, 1998. (In Italian).

14. P. Scardi, S. Veneri, M. Leoni, R. Polini and E. Traversa, Thin SolidFims, 290-291 (1996) 136.

15. J.K. Wright, R.L. Williamson, K.J. Maggs, Mat. Sci. Eng., A187 (1994) 87.16. P. Scardi, M. Leoni, S. Veneri, Advances in X-Ray Analysis, 40 (1997)

(on CD-ROM).17. V. Hauk, Structural and Residual Stress Analysis by Nondestructive

Methods, (Elsevier Amsterdam), 1997.18. P. Scardi, Y.H. Dong, Mat. Sci. Forum (2000). In press. P. Scardi, Y.H.

Dong, J. Mater. Res. (2000). Submitted.19. J,-D Kamminga, Origin and measurement of stresses in thin layers,

Delft University of Technology, 1999.20. R.A. Miller, Surf. Coat. Technol., 30 (1987) 1; K. Ebert, C. Verpoort,

Ch. Karsten, Mat. Sci. Forum, 163-165 (1994) 587; T.E. Strangman,Thin Solid Films, 127 (1985) 93; S.M. Meier, D.M. Nissley and K.D.Sheffler, NASA Contractor Report 18911, (NASA Lewis ResearchCenter, Cleveland, OH), 1991.

21. S.M. Meier, D.K. Gupta and K.D. Sheffler, J. Of Minerals (JOM), 43(1991) 50.

22. I. Kvernes, J.K. Solberg and K.P. Lillerud, in Proc. 2nd Conf.Advanced Materials for Alternative Fuel Capable Directly Fired HeatEngines, ed. J. W. Fairbanks and J. Stringer, (RD-2369-SR, EPRI, PaloAlto, CA), 1982. p. 6-8; Ibidem, p. 6-117.

23. W.P. Danesi and M. Semchyshen, in The Superalloys, ed. C.T. Simsand W.C. Hagel, (J. Wiley and Sons, New York), 1972, p. 565.

24. Kuroda and T.W. Clyne, Thin Solid Films, 200 (1995) 49; S.C. Gill andT.W. Clyne, Metall. Trans., B21 (1990) 377.

25. BRITE/EURAM Project BE-4212-90, Modelling and Characterisationof the manufacturing process of ceramic thermal barrier coatings, Fi-nal Report, Commission of the European Communities, 1995; BRI-TE/EURAM Project BE-4272-90, Finite Elements Modelling of Cera-mic TBCs to Extend the Operating Range of Heat Engine Compo-nents, Final Report, Commission of the European Communities, 1995.

26. P. Scardi, E. Galvanetto, A. Tomasi, L. Bertamini, Surf. & Coat. Techn.,68/69 (1994) 106; P. Scardi, M. Leoni, L. Bertamini, Surf. & Coat.Techn., 76-77 (1995) 106.

27. P. Scardi, M. Leoni, L. Bertamini, L. Bertini, Surf. and Coat. Technol.,94-95 (1997) 82

28. P. Scardi, M. Leoni, L. Bertamini, M. Marchese, Surf. and Coat.Technol., 86/87 (1996) 109

29. P. Scardi, A. Gualtieri, M. Bellotto, ”Industrial Applications ofPowder Diffraction”, CPD Newsletter, 19 (1997) 1(http://www.iucr.org/iucr-top/comm/cpd/).

30. P. Scardi, M. Leoni, F. Cernuschi and L. Bertini, J. Am. Ceram. Soc.,(2000). Submitted.

31. M. Leoni, R.L. Jones and P. Scardi, Surf. Coat. Technol., 108-109 (1998)107.

32. R.A. Young (ed.), The Rietveld Method, (Oxford Univ. Press, Oxford),1993.

33. M. Leoni, P. Scardi, Mat. Sci. Forum, 278-281 (1998) 177; Y.H. Dong &P. Scardi, J. Appl. Cryst., 33 (2000). In press.

34. R.L. Jones, Experiences in Seeking Stabilizers for Zirconia HavingHot Corrosion-Resistance and High Temperature Tetragonal (t’)stability, NRL/MR/6170—96—7841 (Naval Research Laboratory,Washington, DC), 1996.

35. L. Chollet, A.J. Perry, Thin Solid Films, 123 (1985) 223; R.Y. Fillit, A.J.Perry, Surf, Coat. Technol., 36 (1988) 647.

36. P. Scardi, M. Leoni, Y.H. Dong, Adv. X-ray Anal., 42 (1999) (On CD-ROM).

37. M. Leoni, U. Welzel, P. Scardi, (2000). In preparation.38. W. Parrish, M. Hart, Adv. X-ray Anal., 32 (1989) 481; R.J. Cernik, P.K.

Murray, P. Pattison and A.N. Fitch, J. Appl. Cryst., 23 (1990) 292.39. P. Scardi, in X-ray Powder Diffraction Analysis of Real Structure of

Matter, eds. H,-J Bunge, J. Fiala, R. L. Snyder (IUCr series, OxfordUniv. Press), 1999. p. 570.

40. P. Scardi and M. Leoni, J. Appl. Cryst., 32 (1999) 671.41. M. Wilkens, Phys. Stat. Sol., (a) 2 (1970) 359.

Fig. 16. Result of Rietveld refinement of a Li,Mn spinel sample with linebroadening anisotropy (SR XRD data, λ=1.2 Å) [40].

Fig. 17. Average contrast factor of dislocations as a function of theorientational parameter, H (a); detail of the pattern of Figure 16, withMiller indices of present reflections of spinel phase and Si internalstandard [40].

VARIE

IntroductionAccelerator based neutron scatteringsources are being recognised world-wide as the most feasible route forthe next generation high-flux neu-tron sources.1 The premier spallationsources exhibit neutron fluxes andbrilliances which are of the orderfrom ten to several hundred timesgreater than existing steady stateneutron sources. As a result, severalpulsed spallation sources are cur-rently under development aroundthe world (i.e., the second target sta-tion at ISIS, AUSTRON, JapaneseHadron Project and the EuropeanSpallation Source (ESS)). In the US,construction of the new 2 MW Spal-lation Neutron Source (SNS) com-menced last year at Oak Ridge Na-tional Laboratory (ORNL) and isscheduled for completion in 2005.With an average proton beam powerof 5 MW and a 50 Hz repetition rate,ESS was designed as the most pow-erful neutron source. With the pro-posed ESS design and appropriateinstrumentation experiments wereexpected to gain up to three ordersof magnitude in data collectionrates. A suite of 44 instruments andtwo target stations has been dis-cussed.3

With this in mind along with the vi-sion outlined in the ESS feasibilitystudy an ESS R&D Council was es-tablished in 1997 and an ESS R&Dproject phase was initiated. At theR&D phase, a unique possibility isoffered to connect the design of spe-cific neutron instruments directlywith the design of the target station,moderators and delivered protonbeam. Thus, even at the earlieststages of the future neutron sourcescientific interest and demand inneutron instrument usage can becombined with the technical layoutand construction of the future facility.

Potential instrument set-ups can beoptimised by simulation techniquesand the best possible moderator andneutron beam pulse structure can bedefined which will lead to an itera-tive optimisation process betweenthe accelerator design and the pro-posed spectrometers.At several European laboratories abroad range of ESS R&D efforts areorganised currently to achieve theexpected aim of a new and powerfulneutron source. The efforts with re-gards to instrumentation are concen-trated on a detailed concept for thecritical re-evaluation and optimisa-tion of all aspects of a particular in-struments. Main topics, at present,are instrument simulation packages,detector development, new instru-ment concepts and prototyping.Presently, these efforts involve nineEuropean laboratories and institu-tions, all of which are members of

the ESS R&D Council. Several ofthese activities are actively support-ed by projects within the EU-RTD.Results from these efforts were pre-sented recently at the 6th ESS Gener-al Meeting [Sept. 20.-22. 1999 inPortonovo ANC (Italy)]4.

Instrument SimulationThe development of sophisticatedand appropriate simulation pro-grams is an important effort. Newsimulation packages for the refine-ment of neutron instruments havebeen developed at Risø NationalLaboratory (Denmark) and theHahn-Meitner-Institute (HMI,Berlin, Germany). Additional workis being carried-out at the Ciemat re-search centre in Spain. In part, theseactivities are supported by the EUproject SCANS. Based on Monte Carlo simulationprocedures the Risø program McStascurrently supports simulation ofboth triple-axis and time-of-flight in-struments, and has preliminary sup-port for polarised neutrons (neu-tron.risoe.dk/ mcstas/). The virtual instrumentation toolVITESS, developed at HMI(dsora.hmi.de: 8888/projects/ess/vitess/), simulates the performanceof instruments at continuous andpulsed neutron sources. Recently theperformance of a high resolutionTime-Of-Flight (TOF) powderdiffractometer on a long pulsed spal-lation source has been simulated inconnection with experiments at Bu-dapest Neutron Center (BNC, Hun-gary) (see below). Calculations on acrystal analyser spectrometer, a re-flectometer and several SANS in-struments are available, some resultsare shown in Fig. 1. An importantnext step in the use of these simula-tion efforts will be the incorporationof the moderator design which willbe used at the ESS target station.

Detector DevelopmentsThe pulsed high-flux neutron beamsat the ESS require novel imaging de-

ESS R&D Activitieson Neutron Instrumentation

52


Fig. 1. Three simulated spectra from an en-semble of monodispers hard spheres for SANSinstruments housed at a continuous source(ILL) and on the planned second target stationof ESS operating either in the LPSS or SPSSmode shown.

VARIE

tector systems with improved reso-lution and faster response times,necessary for exploiting the im-proved beam intensity, flux densityand time structure. At HMI a newneutron detection system is underconstruction based on developmentsof highly efficient large-area multi-layer micro-strip gas chamber (MS-GC) detectors optimised for low-pressure, two-stage amplification(www.fz-juelich.de/ess/CUR/De-tectors. html). Such detectors willachieve a count rate capacity whichis intrinsically >106 mm-2s-1, howev-er, with economical readout modeslimited to >106 cps local rate and 107

cps per detector segment. At Interfaculty Reactor Institute (IRI,Delft, Netherlands) new gas electronmultiplier systems for similar countrates and resolution are being inves-tigated and improved (wwwiso.iri.tudelft.nl). Further studies are underway on solid state detectors andlarge crystal monochromators at theUniversity of Perugia in Italy, and ondeposition techniques of Gd for neu-tron converters and scintillators atCiemat. Fundamental support onmost of these R&D efforts is ob-tained by the EU project TECHNI,which is dedicated to the develop-ment of new neutron detectors.

New Instrument Concepts andPrototypingA major area of R&D activities is thedevelopment of new instrumentconcepts and prototyping. The re-search centres involved cover a widerange of applications and instrumen-tation. In collaboration betweenHMI and the Central Research Insti-tute for Physics (KFKI, Budapest,Hungary) a chopper test facility hasbeen built at BNC to explore new in-strument configurations and tobenchmark simulation calculations.Recent calculations for a high resolu-tion TOF powder diffractometer on along pulse spallation source wereverified (see above). An example ofhigh resolution powder data mea-

sured is shown in Fig. 2. The chop-per system developed can be used asa dedicated TOF monochromator infuture spallation source based in-struments. A project at HMI is dedicated to em-ploying the Laue technique at an ad-vanced spallation source. This tech-nique will have a major impact onneutron crystallography expandingthe scope of accessible experimentsto atomic resolutions of biologicalmacromolecules (www.kfa-juelich.de/ess/CUR/Single_ Cryst.html).Methodological improvements insingle crystal TOF diffraction atpulsed spallation neutron sourcesare required. This aspect will betackled by developing an analyticalcorrection for the effect of thermaldiffuse scattering around Bragg re-flection measurements.In collaboration with FZ Jülich andHMI the feasibility for neutron spin-echo spectroscopy at a pulsed spalla-tion source is being examined( w w w. k f a - j u e l i c h . d e / e s s /CUR/NSE. html). A pulsed TOF op-tion consisting of a set of choppersis being developed in hopes that itwill replace the standard velocity se-lector presently being used to pro-duce a broadband pulsed neutron

beam. Recently, implemented andsuccessfully tested at the IN15 spec-trometer at ILL (Grenoble, France), itserves as a test facility to performspin-echo spectroscopy under condi-tions of a pulsed neutron source. Theresults will be used to design a newspin-echo spectrometer at a pulsedspallation source for which fundinghas been applied for.The idea to combine TOF and Lar-mor precession for measuring theinitial as well as the final neutronwavelength in a 2D experiment isbeing studied at IRI. This conceptmay be used for the development ofa new flexible range quasi-/inelasticspectrometer or a resolution en-hanced TOF powder diffractometer.For the latter, repeat spacings be-yond the limit of the initial neutronpulse width maybe resolved using aLarmor frequency of up to 104 pre-cessions and enhanced collimation.Labelling the wavelength as well asthe scattered angle by Larmor pre-cession opens the possibility to de-velop a spin-echo small angle neu-tron scattering instrument (www.iri.tudelft.nl/~sfwww/ sesans/),which would enable measurementswith high intensity in the correlationrange of 5-1000 nm. A novel instrument for spectroscopicstudies in condensed matter with eVneutrons is being developed by theUniversity of Rome and INFM(Italy) in collaboration with the Uni-versity of Liverpool (England) andCLRC-RAL (England). The VESU-VIO project aims to provide proto-type instrumentation at the ISISpulsed neutron source in order to es-tablish a routine experimental andtheoretical program in neutron scat-tering spectroscopy at eV energies(www.roma2. infn.it/infm/vesu-vio/). A workshop to outline thenew developments under the VESU-VIO project was held recently [Nov.26.-27. 1999 in Abingdon (England)].R&D efforts for prototyping inelasticspectrometers at pulsed spallationsources are done within the TOSCA

53


Fig. 2. High resolution (?d/d ca. 2*10^-3) pow-der data measured with the TOF powderdiffractometer at the Budapest Neutron Centre.

VARIE

project by CNR (Italy) and ISIS.Their aim is to improve crystal ana-lyzer inverse geometry inelasticspectrometers for vibrational spec-troscopy (laser.ieq.fi.cnr.it/projects/tosca/main.htm). Test experimentscarried-out in order to optimize thegeometry and the performances ofthe TOSCA spectrometer will openthe way to new instrument geome-tries relevant to ESS.

Additional R&D EffortsAdditional R&D efforts with respectto ESS instrumentation are estab-lished at the Atominstitut Vienna(Austria), with research related tonew optical components for neutronbeam focussing and the develop-ment of moderators done at FZJülich, Paul Scherrer Institute (PSI,Switzerland) and Risø National Lab-oratory. 3He neutron spin filter cellsactive over a broad range of neutronwavelengths, to be used particularly

in white beams of pulsed spallationsources, are another R&D effort atHMI (www.kfa-juelich.de/ess/CUR/Spin_ Filter.html). Prototypefilter cells are already being usedand a special coil/shielding devicecapable of keeping the filter cells in ahomogeneous magnetic guide fieldwhen under transport or during thecourse of the experiment, have beentested. These efforts are supportedalso by the EU project ENPI.Further R&D efforts are continuous-ly occurring through research in alllaboratories and institutions en-gaged in neutron research through-out Europe. Workshops and meet-ings are organised on specific R&Dinstrumentation topics and progressreports are presented. Thus, sup-ported by the TMR neutron roundtable a workshop on "Protein Crys-tallography with Neutrons" washeld [Feb. 25.-26. 2000 in Berlin (Ger-many)] and a workshop on neutron

spin-echo spectroscopy and on mod-erator concepts is being announced.Information on these meetings andadditional news on the on-goingR&D efforts regarding instrumenta-tion and the ESS project as a wholeare available through the web atwww.kfa-juelich.de/ess/ess.html.

References1. D. Richter, T. Springer; A twenty years for-

ward look at neutron scattering facilities inthe OECD countries and Russia, TechnicalReport, ESF/OECD, Jülich, 1998

2. ESS – A Next Generation Neutron Sourcefor Europe, Volume I-III, 1997

3. J. Carlile; A Reference Instrument Suite forthe European Spallation Source and the Re-ports from the Instrument Working Groups,Jülich, 1998

4. F. Carsughi; Notiziario, 4(2), 38-39, 1999

T. Gutberlet, F. Mezei, M. SteinerHahn-Meitner-Institut Berlin,

Germany

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Il Comitato, nel suo primo anno diattività, ha fatto un attento esamedelle azioni fin qui intraprese dalCNR nel settore, in particolare lerealizzazioni strumentali presso iSincrotroni ESRF di Grenoble edELETTRA di Trieste. Con una pano-ramica sintetica delle possibilità diutilizzo della strumentazione sinorarealizzata e di quella futura che sipropone di realizzare, ha voluto da-re indicazioni per sviluppare e ge-stire questa attività strategica inter-disciplinare per il CNR. Su questabase ha preparato un piano trien-nale 2001-2003 sulla attività con lu-ce di Sincrotrone, da inserire nelpiano triennale dell’Ente.Alla fine del 1999 è scaduto il con-tratto stipulato da CNR, INFM eINFN, per la parte italiana, con l’Eu-ropean Synchrotron Radiation Faci-

lity (ESRF) per la gestione della lineaitaliana GILDA a Grenoble.Il Comitato ha esaminato la propostadi proroga, con piccoli emendamen-ti, del contratto dal 1/1/2000 al31/12/2004 presentata da ESRF,esprimendo parere positivo ed av-viando così l’iter formale che ha por-tato alla firma del medesimo. Comeavvenuto per il primo contratto, i treEnti italiani hanno concordato tra lo-ro una “Dichiarazione congiunta”, incui si sono impegnati a garantire ilfunzionamento di GILDA, sostenen-done gli oneri finanziari.Il 31 dicembre 1999 sono scaduti gliaccordi biennali stipulati tra il CNRe la Società Sincrotrone Trieste ( ST )relativi alle prime due linee speri-mentali realizzate in compartecipa-zione tra i due Organismi:• Fotoemissione ad Alta Risoluzione

Energetica (VUV), progettata e co-struita in compartecipazione tral’Istituto di Struttura della Materiadell’Area di Ricerca di Tor Vergata(CNR) e la ST. La linea è stata fi-nanziata al 50% dal CNR e dallaST e la gestione è interamente a ca-rico del CNR.

• Cristallografia Diffrattometrica daCristallo Singolo (XRD1), progetta-ta e costruita in compartecipazionetra il Dipartimento di Chimica del-l’Università “La Sapienza” di Ro-ma, l’Istituto di Strutturistica Chi-mica di Montelibretti (CNR) e laST. La linea è stata aperta all’uten-za nel febbraio ’96. La costruzioneè stata finanziata al 50% dal CNR edalla ST e la gestione è ripartita inugual misura tra i due Enti.

Sono stati pertanto predisposti, d’in-tesa con la ST, due schemi di accor-do, che il Comitato ha esaminato at-tentamente, già approvati dal Consi-glio Direttivo e prossimi alla firma.

ATTIVITA’ DEL COMITATO CNR DI COORDINAMENTOLUCE DI SINCROTRONE

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La Commissione ha proseguito la sua attività con regola-rità, dedicandosi prevalentemente al coordinamento congli Organi di gestione del CNR. Come noto, è in corsouna riorganizzazione di grandi proporzioni del Consi-glio Nazionale delle Ricerche, basata su due punti so-stanziali: decentramento delle attività scientifiche sugliOrgani di ricerca e snellimento degli Organi di controlloe gestione, con la creazione di due Consigli formati daesperti in vari settori, che affiancano la Presidenza del-l’Ente. La ristrutturazione è tuttora in corso e solo recen-temente si è avuta l’approvazione del nuovo regolamen-to. La Commissione ha cercato, quindi, di far sì che le at-tività di spettroscopia neutronica in corso potessero tro-vare spazio nella nuova struttura del CNR.Il risultato di maggior rilievo da menzionare è il comple-tamento della seconda fase del progetto TOSCA, che ve-de l’installazione della seconda fase dello spettrometroormai prossima. Più importante ancora, se possibile, è ladisponibilità di un sito per la futura stazione Italiana.Detta stazione, fortemente voluta dalla nostra comunità,permetterà la gestione di uno strumento adatto all’adde-stramento del personale ed alla preparazione delle espe-rienze, oltre che di ricerche scientifiche.È stata già fatta richiesta di un adeguato finanziamentoper detta stazione. Tale richiesta è stata fatta direttamen-te da Marco Zoppi dell’Istituto di Elettronica Quantistica

di Firenze, cioè direttamente da un Organo di ricerca for-temente impegnato nel campo della Spettroscopia Neu-tronica. In ogni caso un piccolo diffrattometro sarà in-stallato sul sito quanto prima, facendo uso di componen-ti già disponibili e dismessi da altri progetti. Appena di-sponibili i finanziamenti si procederà al disegno e svi-luppo di uno strumento multi-uso più sofisticato. Unadiscussione sull’impiego della stazione Italiana sarà sti-molata durante il prossimo congresso della SISN.È utile ricordare infine che la Commissione ha provve-duto a presentare al CNR un piano triennale (2001-2003)per la Spettroscopia Neutronica. È questo il primo pianodi questo tipo, in quanto il CNR si dota per la prima vol-ta di un suo piano triennale. Il prossimo triennio è moltoimportante poiché nella primavera del 2002 scade l’at-tuale accordo con ISIS. Un suo rinnovo necessiterà di unconsiderevole impegno da parte della Comunità per farsì che il CNR continui in questa collaborazione. Nel pia-no triennale si è anche presa in considerazione la possi-bilità di partecipare in modo adeguato allo sviluppo delprogetto della nuova sorgente Europea ESS. Tale proget-to, sebbene sia ancora in una fase di valutazione tecnicae scientifica, sarà sicuramente di grande importanza nelprossimo decennio e la Comunità Neutronica Italianadovrà confrontarsi con esso con grande attenzione.

Prof. Sacchetti

Attività della Commissione per la SpettroscopiaNeutronica del CNR

PremessaLe ricerche con le tecniche di spettroscopia neutronicaeffettuate dai ricercatori italiani presso la sorgente pulsatadi neutroni ISIS operante al Rutherford-AppletonLaboratory, (Oxford, U.K.) sono state sostenute dal CNRnel decennio 1985-1995, grazie ad un accordo stipulato tral’Ente e il SERC (Science and Engineering ResearchCouncil). Vista la notevole ricaduta scientifica, taleaccordo è stato successivamente rinnovato, nel marzo1996, (con il CLRC - Council for the Central Laboratory ofthe Research Councils, Ente che ha preso in carico leattivita’ del SERC) fino a marzo dell’anno 2002.Attraversoquesto accordo internazionale l’Ente:

• garantisce l’accesso alla strumentazione di ISIS a tuttala comunità italiana, con una percentuale di utilizzopari al 5% del tempo totale disponibile. La Tabella 1riporta la percentuale di utilizzo di tempo assegnataper l’attività di ricerca dei gruppi italiani nel corsodegli anni.

• finanzia direttamente lo sviluppo di strumentazione,progettata e costruita presso i propri organi di ricerca,anche in collaborazioni con gruppi universitari. In par-ticolare si ricordano il Progetto PRISMA realizzatopresso l’ISM (Istituto di Struttura della Materia, Fra-scati) nel periodo dal 1984 al 1991 ed il Progetto TO-SCA, realizzato presso l’IEQ (Istituto di Elettronica

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Situazione delle ricerche sostenute dal CNR e propostaper un piano triennale. Attività di spettroscopia NeutroniPiano triennale proposto dalla Commissione Neutroni del CNR

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Quantistica, Firenze), avviato nel 1996 e la cui conclu-sione è prevista contestualmente alla conclusione del-l'accordo in atto.

Questi accordi internazionali, insieme ad analoghi ac-cordi stipulati più recentemente dall’INFM, hanno avu-to un ruolo decisivo nello sviluppo della comunitàscientifica italiana che impiega le tecniche di diffusionedei neutroni.Tale comunità è cresciuta da un numero molto ridotto diricercatori nella prima metà degli anni ’80, fino a circa200 ricercatori oggi operanti presso le Università e gliEnti di Ricerca (CNR ed INFM). Detta comunità, sebbenesia ancora relativamente ridotta rispetto alle comunitàanaloghe che sono presenti in tutti i paesi avanzati, assu-me oggi una dimensione più appropriata in confrontocon le principali nazioni dell’Unione Europea. In partico-lare, i vari gruppi di ricerca conducono attività speri-mentali, sia presso i principali reattori che presso sorgen-ti pulsate di neutroni, su un ampio spettro di tematichescientifiche e sono anche attivamente impegnati nellosviluppo e realizzazione di nuova strumentazione perl’impiego dei neutroni.Il CNR inoltre ha aderito nel 1998, assieme all’INFM, alESS R&D Council, un consorzio di Enti e Istituzioni Euro-pee, che ha l’obiettivo di predisporre il progetto per la co-struzione di una nuova sorgente pulsata di neutroni, Eu-ropean Spallation Source (ESS), da sottoporre ai Governidell'Unione Europea.Detto progetto è molto importante nel panorama mon-diale di queste attività e rappresenta il mezzo che puòconsentire all’Europa di mantenere la sua posizione di ri-lievo nei confronti di Stati Uniti e Giappone. È opportunoosservare che, mentre l’INFM è un Istituto che sostiene ri-cerche tematiche di Fisica della Materia, il CNR ha l’im-portante ruolo di sostenere anche ricerche multidiscipli-nari. Le attività di ricerca e di sviluppo di strumentazionead ISIS ed in ambito ESS, per quello che concerne il CNR,sono coordinate da una apposita Commissione per laSpettroscopia Neutronica.Nel decennio 1985-1995 l’impegno diretto del CNR, pertramite dei suoi organi, nelle attività di ricerca e svilupponel campo della strumentazione per spettroscopianeutronica è quantificabile, in media, in 4 ricercatoridedicati per tutto il periodo, con un investimento per lastrumentazione pari a 3000 ML (Progetto PRISMA esviluppo di cristalli monocromatori). In aggiunta, nellostesso periodo, l’accesso alla sorgente ISIS ha comportatoun investimento oneroso pari a 20.000 ML. Nel periodo 1996-2001 l’impegno complessivo del CNR èquantificabile in media in 4.5 ricercatori, con uninvestimento per strumentazione pari a 3200 ML(Progetto TOSCA e sviluppo di cristalli monocromatori) eun investimento oneroso per l’accesso alla sorgente ISISpari a 12300 ML.

Attività di ricerca e sviluppo di strumentazione per l’anno 2000Per l’anno corrente è già previsto: a) l’impegno per l’accordo in atto con il CLRC Inglese

per l’accesso ad ISIS.b) il completamento del progetto TOSCA, per il quale è

opportuno prevedere un assegno di ricerca per ungiovane ricercatore da affiancare, in una fasesuccessiva, al ricercatore attualmente distaccato adISIS (assunto ex. Art. 36) già in servizio.

c) l’avvio effettivo delle attività previste dall’accordo ESSil quale prevede una quota onerosa relativamentemodesta e l’impegno di due unità di personale. Perquesti ricercatori vanno previste le spese di missionenecessarie per operare nell’ambito di questacollaborazione.

Previsione di spesa per l’esercizio 2000

Denominazione Tipologia dell’attività Personale Investimento(anni/uomo) (ML)

ISIS Acc. Internaz.Attivo 2050*

TOSCA Costruzione shutter

intermedio TOSCA/

stazione italiana 1 Ass. di ricerca 400#

ESS Acc. Internaz.Attivo 60@

ESS Missioni di 2 un.

di personale CNR 30

Totale 2540

* Quota onerosa prevista dall’accordo(Bilancio Uff. Relazioni Internazionali)# Richiesta imputabile a IEQ-CNR (Firenze)@ Quota prevista dall’accordo in via di stipula(Bilancio Uff. Relazioni Internazionali)

Attività di ricerca e sviluppo per il periodo di validità del piano triennale 2000-2001Nel corso del triennio 2001-2003 giungerà a scadenzal’accordo CNR-CLRC per l’accesso italiano ad ISISQuesta possibilità deve essere mantenuta per il futuroalmeno al livello attuale. Occorre quindi prevederenell’ambito del piano triennale il rinnovo dell’accordocon ISIS, essenzialmente alle stesse condizioni di quelloattualmente in atto. Dato che nel decennio 1988-1998 lapercentuale di utilizzo del tempo macchina ad ISIS si èmantenuta al di sopra del livello del 5% (il valore medionel decennio risulta pari al 6%, vedi Tabella 1) appareragionevole prevedere un rinnovo dall’accordo con ilCLRC almeno per le stesse percentuali di utilizzodell’accordo precedente, pari cioè al 5%. In analogia conl’accordo attualmente in essere si può prevedere unaquota onerosa pari al 4% (stimabile in 2250 ML/anno),mentre l’ulteriore quota dell’1% potrebbe essere coperta

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dalla realizzazione di un nuovo strumento italiano dainstallare ad ISIS. Questo nuovo progetto dovrà essereiniziato contemporaneamente all’avvio del nuovoaccordo, cioè all’inizio del 2002. Il suo costo(prevedibilmente dell’ordine di 3500 ML) dovrebbeessere ripartito su un arco di 3-4 anni, investendo quindicompetenze relative al piano triennale 2004-2007.

Progetto TOSCACon l’installazione del secondo banco di analizzatoriprevisto per la primavera del 2000 si concluderà la fase dicostruzione dello spettrometro e, a partire dall’esercizio2001, è necessario prevedere quindi solo le spese dimanutenzione ordinaria e di personale (un ricercatore atempo determinato - attualmente ex. Art. 36 - ed unAssegno di ricerca che dovrebbe essere distaccato ad ISISe potrebbe investire la stessa persona che copriràl'assegno di ricerca in Italia nel corso dell'anno 2000).Il progetto TOSCA, secondo gli accordi siglati a suo tem-po con il CLRC, prevede la realizzazione, a valle dellastazione sperimentale principale di TOSCA, una stazio-ne di test e sviluppo, sulla quale i ricercatori italiani di-sporranno del 50% del tempo. La realizzazione di una ta-le facility è di estrema importanza per la comunità na-zionale. Va infatti ricordato che l’Italia non dispone almomento di alcuna sorgente neutronica nazionale, anchedi bassa intensità. La disponibilità di una stazione conaccesso facilitato è di grande importanza per lo sviluppodi esperimenti preliminari, per test di nuova strumenta-zione, e per attività di formazione di giovani ricercatori.La stazione sperimentale a valle dello di TOSCA potreb-be essere efficacemente impiegata anche nelle attività diRicerca e Sviluppo previste dall’accordo ESS. Detta atti-vità non potrebbe essere condotta sulle linee “pubbli-che” di ISIS, le quali sono completamente dedicate allaricerca scientifica. Per la realizzazione di tale stazione ènecessario un investimento di 600 ML, distribuito suidue esercizi 2001 e 2002, oltre ad un’unità di personalericercatore. Vengono riportate di seguito le tabelle chedescrivono la previsione di spesa sulla base delle propo-ste presentate in precedenza. Dette previsioni non consi-derano il personale ricercatore in servizio con contratto atempo indeterminato o determinato. Sulla base di quan-to descritto in precedenza, oltre al personale con contrat-to a tempo indeterminato, in servizio presso organiCNR, si prevede la stipula o il mantenimento di due con-tratti per ricercatore a tempo determinato presso ISIS.

Considerazioni sul personale Oltre agli assegni di ricerca, i cui oneri sono statispecificati nelle tabelle precedenti, si consideranecessario che vengano mantenute ad ISIS due unità dipersonale ricercatore, con contratto a tempo determinato,con il compito di gestire la strumentazione (TOSCA + il

nuovo strumento) e di fornire supporto agli utentiitaliani. Non si ritiene di poter quantificare la spesa inoggetto, anche se questa è dell’ordine di 160 ML per annoper le due unità.

Previsione di spesa per l’esercizio 2001


ISIS Acc. Internaz. Attivo 2050*TOSCA 1 Ass. di Ricerca

(Estero) 40Manutenz. TOSCA 300Staz. Italiana ad ISIS 1 Ass. di Ricerca

(Estero) 400+40ESS Acc. Internaz.Attivo 130@

Missioni 2 Unità personale CNR 60

Totale 3020

Previsione di spesa per l’anno 2002


ISIS Acc. Internaz. Rinnovo 03/2000 2250*

TOSCA 1 Ass. di Ricerca (Estero) 40

Staz. Italiana ad ISIS 1 Ass. di Ricerca (Estero) 200+40

Nuovo Strumentoad ISIS 800#



Totale 3540

* Quota onerosa prevista dall’accordo(Bilancio Uff. Relazioni Internazionali).@ Quota onerosa prevista dall’accordo(Bilancio Uff. Relazioni Internazionali)# Lo strumento è valutato complessivamente 3500 ML da distribuirenegli anni di durata dell’accordo con ISIS (2002-2007)

Previsione di spesa per l’anno 2003


ISIS Acc. Internaz. 2250*TOSCA 1 Ass. di Ricerca

(Estero) 40Nuovo Strumento Nuovo Strumento

ad ISIS 1200#



Totale 3600

* Quota onerosa prevista dall’accordo (Bilancio Uff. Relazioni Internazionali)@ Quota onerosa prevista dall’accordo(Bilancio Uff. Relazioni Internazionali)#Lo strumento è valutato complessivamente 3500 ML da distribuirenegli anni di durata dell’accordo con ISIS (2002-2007)

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ITALIA ITALIA

Isis Giorni Percentuale Giorni Percentuale

Ciclo richiesti % assegnati %

88/1 222.3 11.8 100.1 10.5

89/1 203.0 10.3 55.1 6.0

89/2 198.3 11.4 64.8 9.8

90/1 198.8 10.7 33.0 5.5

90/2 170.3 8.8 53.5 7.6

91/1 176.0 7.9 61.8 7.9

91/2 169.3 8.1 57.4 5.8

92/1 135.3 4.7 49.8 4.6

92/2 167.4 7.3 61.3 7.5

93/1 172.0 6.1 45.9 4.9

93/2 158.6 6.7 51.9 5.1

94/1 112.3 4.6 39.4 4.2

94/2 123.6 5.0 51.1 4.9

95/1 190.4 8.2 72.4 6.5

95/2 141.8 5.7 56.5 4.7

96/1 119.7 5.3 53.3 4.6

96/2 143.7 5.9 57.7 4.7

97/1 102.0 4.6 56.3 4.5

97/2 164.0 7.5 71.0 6.0

98/1 123.0 5.7 52.0 4.1

98/2 189.0 8.8 92.0 6.6

99/1 127.0 6.6 68.0 5.6

99/2 205.0 10.6 105.0 7.3

TOTALE 3712.8 1409.3

14

12

10

8

6

4

2

0

88/1

89/2

90/2

91/2

92/2

93/2

94/2

95/2

96/2

97/2

98/2

99/2

RichiestiAssegnati

Italia % tempo

Utilizzo del tempo macchina presso ISIS da parte di gruppi di ricerca italiani

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There is little doubt that neutronscattering plays a major infrastruc-tural role in underpinning much ofcondensed matter science and tech-nology within the disciplines ofphysics, materials science, chemistry,the life sciences, the earth sciencesand engineering. Consequently thereis also little doubt that Europe canlegitimately claim a significantstrategic advantage in these fields ofresearch, not only because Europeboasts the world's premier neutronscattering sources but also becauseEurope hosts the largest, most expe-rienced and broadest-based commu-nity of neutron beam users. Indeedover 4,500 neutron scatterers, almosttwo thirds of the world's total num-ber, reside in Europe and exploit Eu-ropean neutron facilities. It is therefore tempting to concludethat European neutron scattering sci-ence is currently enjoying a "goldenage". From a short-term perspectivesuch a view is well justified: the Eu-ropean neutron scattering communi-ty can be proud of its achievements,and confident in its world lead.However a medium- to long-termperspective reveals that this lead isnot unassailable. On the one handEurope in particular faces the im-pending reality of the much dis-cussed "neutron drought". Thedrought, originally forecast by thelate Tormod Riste in a 1994 Analyti-cal Report commissioned by theOECD Megascience Forum, is a con-sequence of the continuing expan-sion of a multidisciplinary neutronscattering community and the immi-nent closure of many ageing re-search reactors. On the other hand avery serious challenge to European

supremacy in the field of neutronscience has been mounted by theUSA and Japan, both of whom arewell advanced with their plans to al-leviate their local "neutron droughts"through major financial, scientificand technological investments inthird generation advanced neutronsources. With these concerns in mind, dele-gates from the neutron scatteringcommunities and societies of severalEuropean nations met in Grenoble inSeptember 1994 to propose the foun-dation of a European Neutron Scat-tering Association, ENSA. From thestart it was clear that ENSA had a vi-tal role to play in providing a plat-form for discussion and a focus foraction in neutron scattering scienceand technology in Europe and, at theinaugural ENSA meeting in Decem-ber 1994 in Madrid, the delegatesidentified several specific aimswhich are now enshrined in the EN-SA Articles of Association. Specifi-cally ENSA seeks to • Identify the needs of the neutronscattering community in Europe. • Optimise the use of present Euro-pean neutron sources • Support long-term planning of fu-ture European neutron sources • Assist with the co-ordination of thedevelopment and construction of in-struments for neutron scattering• Stimulate and promote neutronscattering activities and training inEurope, and in particular to supportthe opportunities for young scientists • Promote channels of communica-tions with industry • Disseminate to the wider commu-nity information which demon-strates the powerful capabilities of

neutron scattering techniques andother neutron methods• Assist, if appropriate, national affil-iated bodies in the pursuit of theirown goalsEach of these aims is actively pur-sued with dedication and vigour byENSA, which has now grown into athriving affiliation of seventeen na-tional neutron scattering societiesand organisations that directly rep-resent neutron beam users. Dele-gates from Austria, Belgium, theCzech Republic and Slovakia, Den-mark, France, Germany, Hungary,Italy, the Netherlands, Norway,Poland, Portugal, Russia, Spain,Sweden, Switzerland and the UnitedKingdom, meet together twice year-ly. Recently Romania and Greecehave also sought membership ofENSA. Representatives of the majorEuropean neutron facilities and pro-jects, the Neutron Round Table andthe European Science Foundation allattend ENSA meetings with the sta-tus of observers and, corresponding-ly, the Chairman of ENSA has a seatat the Neutron Round Table and onthe European Spallation Source(ESS) Research and DevelopmentCouncil. Over the last five years ENSA hassucceeded in establishing an entirelyunique forum in which neutronbeam users and providers can meettogether to co-ordinate research anddevelopment programmes and opti-mise and promote neutron beamutilisation at facilities across Europe.Indeed, ENSA initiatives in the de-velopment of neutron instrumenta-tion and the creation of a neutronsoftware database, are ongoing ac-tivities, carried out in collaborationwith the neutron sources and theRound Table, and are well docu-mented on the ENSA web pages(http://www1.psi.ch/www_ensa_hn/welcome_ensa.html).Throughout its existence ENSA hasalso worked in close collaborationwith the European Science Founda-tion. As part of this collaboration

ENSA – The European NeutronScattering AssociationProf. Bob CywinskiChairman of the European Neutron Scattering AssociationUniversity of St Andrews, Scotland

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ENSA organised the "ESF Workshopon Scientific Prospects of NeutronScattering with Today's and FutureNeutron Sources", held at Autrans,near Grenoble, in January 1996 andmore recently conducted a compre-hensive "Survey of the Neutron Scat-tering Community and Facilities inEurope". Both activities have result-ed in extremely informative andwidely quoted ESF publicationswhich not only place European neu-tron scattering in perspective but al-so provide a framework upon whichfuture strategic decisions can bebased. Both reports can be down-loaded in full directly from either theESF or ENSA websites. The ENSA survey of the neutroncommunity has, in particular, pro-vided a remarkable and self-consis-tent insight into the nature and ex-tent of neutron science within Eu-rope. The survey dispels once andfor all the widely held myth thatneutron scattering is a specialisttechnique employed principally byphysicists. Instead it emerges as awidely applicable tool exploited by a

broad and vibrant condensed mattercommunity (figure 1a). Moreover,whilst the survey highlights the vitalrole of the pre-eminent high fluxneutron sources, ILL and ISIS (figure1b), it also provides a clear indica-tion that the future health of neutronscattering science within Europe isintimately linked to the develop-ment and construction of a majorthird generation high flux facility,such as the ESS, and that such a pro-ject must be considered as a matterof great urgency. Perhaps the best-known ENSA ac-tivity has been the inaugurationand organisation of the innovativeEuropean Conferences on NeutronScattering. The first ECNS confer-ence, held in Interlaken in 1996 inco-operation with the Paul ScherrerInstitute (Villigen), proved to be thelargest neutron scattering confer-ence ever held with almost 700 del-egates from 40 countries presentingover 650 published papers. The sec-ond conference in the series (EC-NS'99) held in Budapest in co-oper-ation with the Budapest Neutron

Centre, was equally successful.There is every reason to believe thatECNS'03 in Montpelier will contin-ue the tradition.ENSA has an extremely strong com-mitment to nurturing and promotingthe younger members of the Euro-pean neutron scattering community.Consequently an emerging hallmarkof the ECNS conference series is thehigh profile afforded to young scien-tists. Both ECNS’96 and ECNS'99were preceded by a Training Course,in each case attended by well over ahundred young scientists, many ofwhom received generous bursaries.At each meeting ten ENSA YoungScientist Awards were presented foroutstanding scientific contributions.Also, as part of a new initiative to se-cure the active involvement ofyoung scientists in the future devel-opment of neutron scattering sci-ence, techniques and facilities withinEurope, ENSA convened, prior toECNS'99, four Young Scientist Pan-els. The Panels, with a combinedmembership of 31 young expertsfrom 14 European countries elected

Figure 1 (a) European exploitation of neutron scattering techniques across the major scientific and technological disciplines (b) European neutronbeam usage by source type. (From the ENSA Survey of the Neutron Scattering Community and Facilities in Europe – an ESF/ENSA publication ISBN2-912049-00-8, 1998)

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AMaterials Science

19.4%

Engineering Science2.9%

Earth Science0.9%

Physics46.3%

Chemistry26.9%

Life Sciences3.6%

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from over a hundred nominations,have considered issues as wide-ranging as neutron sources, instru-mentation, sample environment anddata analysis software, all viewedfrom a largely new perspective. It ishoped and intended that the YoungScientists Panels will continue to op-erate in conjunction with ENSA wellbeyond ECNS'99.It is also important that the commu-nity should celebrate and publicisethe tremendous achievements of themore experienced neutron scien-tists. In this context ENSA has es-tablished the Walter Hälg Prize forEuropean Neutron Scattering, withthe help from a generous donationby Professor Hälg, the founder ofneutron scattering in Switzerland.The prize of 10,000 CHF is awardedbiannually to a European scientistfor "outstanding, coherent work inneutron scattering with long-termimpact on scientific and/or techni-cal neutron scattering applications".A particular highlight of ECNS'99 inBudapest was the ceremony andplenary associated with the presen-

tation of the first ENSA Hälg Prize.Ferenc Mezei (HMI Berlin) was thevery worthy recipient of this presti-gious award and it was quite fittingthat he should receive it in the verycity where he carried out his pio-neering work on the neutron spinecho technique. The second ENSAHälg Prize is to be awarded nextyear at ICNS'2001 in Munich, and acall for nominations will be an-nounced shortly. Although the twelfth committeemeeting is about to be held in May2000 in Munich, it is clear that thework of ENSA has only just begun.From the perspective of ENSA thefuture of European neutron scatter-ing science and research infrastruc-ture is both exciting and challenging.The excitement stems from the won-derful opportunities that are provid-ed by the continuing optimisation ofexisting neutron sources alongsidethe developing scientific and techni-cal case for the European SpallationSource which promises a strategicfacility that will keep Europe aheadof the field for at least the next half

century. The challenge is to secureappropriate funding mechanisms tomaintain our major facilities at thecutting edge of neutron science andto allow the ESS project to moverapidly ahead to realisation. My own personal challenge as EN-SA Chairman is to prove a worthysuccessor to Dieter Richter and Al-bert Furrer who, as first and secondChairmen respectively, have dy-namically and skilfully steered theAssociation through its formativeyears to establish ENSA as a majorscientific and political force in Euro-pean neutron scattering. This chal-lenge, however, is made consider-ably easier by the strong supportand expert advice offered by theprevious chairmen and the currentmembers of the ENSA executive,Lars Borjesson (Swedish delegateand ENSA Secretary) and FabrizioBarrocchi, the Italian delegate andENSA Vice-chairman.

B Low flux sources21.3%

Mediumflux sources

40.2%

InstitutLaue Langevin

21.2%

ISIS17.4%

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Nel panorama attuale della neutro-nica uno degli sviluppi più attesi eimportanti è il Millennium Program-me dell'Institut Laue-Langevin diGrenoble. La sua formulazione e de-finizione finale hanno preso un con-siderevole periodo di tempo, colcoinvolgimento di tutte le comunitàdi utilizzatori. E' un programma am-bizioso di costruzione di nuovi stru-menti, di upgrading di altri, e di mi-glioramenti importanti nelle infra-strutture. Coinvolgendo poi lo svi-luppo per i prossimi cinque anni del-la facility migliore nel mondo, que-sto programma ha importanti valen-ze di innovazione e progresso scien-tifico.Un altro punto di interesse èl'inquadramento di questo program-ma nel dibattito sulle future sorgen-ti. Chiaramente l'attuazione dei mi-glioramenti proposti per ILL daràun'idea più precisa della scienza chesi potrà fare con le sorgenti future indiscussione, e dunque anche del tipodi scelte che la comunità internazio-nale sarà chiamata a fare.Per tutti questi motivi è bene che lanostra comunità sia presente in que-sti dibattiti, questi sviluppi, e nel la-voro che sta già cominciando perrealizzare i progetti proposti.L'ultima riunione del ConsiglioScientifico dell'ILL è stata fortementecaratterizzata dalla discussione sulMillennium Programme. Le decisio-ni prese sono importanti e avrannouna certa rilevanza anche per la no-stra comunità, in quanto configura-no gli sviluppi della migliore sorgen-te neutronica per i prossimi tre-quattro anni. In particolare:1. Partono quest'anno i due progettiSuper D2B e nuovo D7;2. Per il prossimo anno verrannomessi in cantiere: a. Studio di Fatti-bilità della sorgente ultrafredda ba-sata su nanoparticelle di carbonionell'elio liquido raffreddato. b. Up-grade di IN3 per farne un ResonanceSpin Echo spectrometer.

c. Laboratorio deuterazione molecolebiologiche (in coll. con EMBL).d. Upgrade di IN14.Il resto dei progetti proposti per ilMillennium Programme verranno ri-discussi nel CS di autunno. Riassu-mo qui brevemente i Progetti: SuperD2B: upgrade di D2B mediante in-stallazione di un nuovo stack di 128rivelatori a filo e collimatori di my-lar, per avere un angolo solido dicollezione molto più grande, ma allostesso tempo altissima risoluzionenel piano orizzontale. Si prevede unaumento del counting rate di un fat-tore 6. D7: Viene previsto un au-mento di un fattore 30-40 del coun-ting rate installando analizzatori su-permirror in uno dei quattro stacksdi rivelatori Laboratorio Deuterazione:si prevede di creare una vera e pro-pria facility per permettere a usersesterni e locali di deuterare campionibiologici. Verrà fatto in collaborazio-ne con EMBL; non si sa ancora dove.Sorgente Ultrafredda: è stato solo ap-provato lo studio di fattibilità, cheprevede lo studio delle caratteristi-che fisiche di sospensioni di nano-particelle di carbonio in elio liquidoin funzione della dimensione, polidi-spersità, concentrazione. In caso dirisultati positivi, anche se non for-malmente deciso, è molto probabileche si proceda col progetto principa-le. IN3: si prevede di sviluppare latecnica di neutron spin eco risonantesu IN13, per aumentare la risoluzio-ne in energia a meglio di 10 meV, os-sia un ordine di grandezza superiorea quella di un tre assi standard. L'ap-plicazione principale prevista è allostudio dei rilassamenti delle eccita-zioni magnetiche o reticolari. IN14:Verrano installate ottiche supermir-ror su IN14 (triplo assi con sorgentefredda); si prevede un guadagno di3-6 nel flusso. Questi i progetti chesicuramente partiranno questo o ilprossimo anno.Altro argomento discusso è stato ilruolo dei CRG (Collaborating Re-search Groups), e la politica di ILLper il loro futuro. Si è deciso di avere

una discussione approfondita allaprossima riunione del CS. Anche perquesto aspetto siamo fortemente in-teressati, in quanto la nostra comu-nità è impegnata in due CRG, unogià operativo (IN13), e l'altro (BRISP)negli stadi finali della definizionedel progetto operativo (il contratto ègià stato firmato dai due Presidenti).Per quanto riguarda IN13, sono statedate garanzie di interesse per il suoupgrading. Il problema però rientrain quello più generale dell'upgra-ding di tutte le guide originali (ecioè vecchie di più di venti anni), ilcui costo previsto è di 64 Megafran-chi, che non ci sono. Il CS all'unani-mità ha chiesto allo Steering Com-mittee dell'ILL di trovare questo fi-nanziamento aggiuntivo, per ripor-tare il potenziale scientifico dell'ILLal meglio delle possibilità permessedalle attuali tecnologie. Chiaramente l'upgrading di IN13,che prevede appunto a sostituzionedella guida con supermirrors, è di-rettamente coinvolto in questo pro-getto generale. In ogni caso il Mana-gement si è espresso molto favore-volmente sulla prosecuzione e sul-

S.I.S.N.

Al XI Convegno Nazionale della Società Italiana di SpettroscopiaNeutronica (SISN) farà seguito, ilgiorno 20 Ottobre, un ConvegnoInternazionale di una giornatain memoria di Francesco PaoloRicci -recentemente scomparso-dal titolo "Francesco Paolo Riccimemorial: his legacy and futureperspectives of neutron spectro-scopy", per ricordare il suo con-tributo allo sviluppo della spet-troscopia neutronica in Italia e ilsuo impegno per l'accesso deglistudiosi Italiani alle facilities in-ternazionali e per la formazionedei giovani ricercatori.Ulteriori informazioni possonoessere richieste alla Sig.ra GraziaIanni ([email protected]) e allaProf.ssa Maria Antonietta Ricci([email protected]).

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The backscattering spectrometer IN13 atthe ILL became a CRG (CollaborativeResearch Group) instrument in July1998 under a contract between the Uni-versité J. Fourier and the ILL. It is nowoperated in the frame of a French-Italiancollaboration between the Université J.Fourier, the Institut de Biologie Structu-rale (CEA-CNRS, Grenoble), the Labo-ratoire Léon Brillouin (CEA-CNRS, Sa-clay) and the Istituto Nazionale per laFisica della Materia (INFM, Italy). A major upgrade of the electronics andinstrument control programs has beenperformed in August 1999 retaining theprevious instrument characteristics:energy resolution of about 10 meV, Q-range 0.3 to 5.5 Å-1, energy transfer upto ca. 250 meV. These characteristics areextremely well suited for the study oflarge molecular assemblies held togetherby weak interactions. Main purpose ofthe CRG is to investigate the low energydynamics of biological macromoleculesand the relationship between functionand microscopic dynamics. Some exam-ples of experiments recently performedon the instruments will be described.

Lo spettrometro in backscatteringIN13 all’ILL è stato rimesso in fun-zione nel Luglio del 1998 grazie adun accordo tra enti di ricerca Italianie Francesi: l’Istituto Nazionale per laFisica della Materia, l’Istituto di Bio-logia Strutturale (CEA-CNRS, Gre-noble), il Laboratorio Léon Brillouin(CEA-CNRS, Saclay) e l’Università J.Fourier di Grenoble. E’ stato cosìrealizzato un CRG (CollaborativeResearch Group) per la gestione del-lo spettrometro con l’obiettivo di im-piegarlo principalmente per lo stu-dio della dinamica a bassa energia dimacromolecole biologiche e della re-lazione tra funzione biologica e di-namica microscopica. Un ulterioreimportante obiettivo di questo pro-getto, soprattutto per la comunitàitaliana, è stato quello di favorirel’interazione di ricercatori con espe-rienza nel campo dei neutroni, ope-ranti per lo più nel campo della Fisi-ca dei solidi e dei liquidi, con gruppiattivi nel campo della Biofisica equindi di espandere e consolidare lacomunità degli utilizzatori delle tec-

niche neutroniche soprattutto neisettori della “soft matter” e dei siste-mi molecolari complessi. Tra gli strumenti ad alta risoluzionedell’ILL, IN13 è il solo in geometriadi backscattering che utilizza un fa-scio di neutroni termici; in tal modopuò accoppiare una elevata risolu-zione in energia (∆E ~ 10 µeV) con lapossibilità di accedere ad elevati mo-menti trasferiti, Q (l’intervallo di Qaccessibili va da 0.3 a 5.5 Å-1) Uno schema dello strumento è mo-strato in Fig. 1. Il fascio di neutronitermici (E=16.45 meV) viene diffrattoalla Bragg da un monocromatore diCaF2 posto in una criofornace la cuitemperatura può essere variata tra80 K e 350 K; in tal modo il passo re-ticolare del monocromatore vienemodificato e conseguentemente sipuò variare l’energia dei neutroni inun intervallo compreso tra –120 µeVe 230 µeV attorno all’energia inci-dente. I neutroni vengono quindi de-flessi sul campione e, dopo lo scatte-ring da quest’ultimo, vengono ana-lizzati in energia da un sistema dicristalli analizzatori, anch’essi diCaF2, che sono mantenuti a tempera-tura ambiente ed operano in geome-tria di backscattering. La scansionein energia si ottiene quindi variando

LO SPETTROMETRO IN13ALL’ISTITUTO LAUE-LANGEVIN

l'upgrading di IN13; un pò più fred-dino è stato il CS. In ogni caso il pro-getto dovrebbe proseguire, e questovuol dire che la nostra comunità saràchiamata ad una condivisione dellespese dell'upgrading: ILL curerà leguide (se otterrà i soldi), e i membridel CRG avranno la responsabilità difinanziare e costruire i previsti nuovimonocromatori e analizzatori.Dato che ci sarà la discussione suiCRG nel prossimo Consiglio Scientifi-co dell'ILL, sarebbe opportuno che lanostra comunità esprimesse forte-mente (se così valuta) l'interesse perIN13 e il suo upgrading. Da questopunto di vista sarebbe particolarmen-te importante il contributo di colleghibiologi, chimici etc, dato che IN13 è

risultato essere particolarmente inte-ressante per la sua valenza interdisci-plinare, e questa è una delle prioritàche la Direzione dell'ILL ha indicatoper gli sviluppi futuri.Concludo ricordando che sia i CRGche i progetti del Millennium Pro-gramme costituiscono un'importanteoccasione di cimentarsi nella proget-tazione, costruzione o miglioramen-to di spettrometri e strutture connes-se. Considerando che la nostra co-munità è ancora sottodimensionatafortemente nel campo della strumen-tistica, sarebbe oltremodo auspicabi-le che venissero dedicate risorse siafinanziarie che umane per partecipa-re a queste attività. Particolarmenteimportante ritengo sia la formazione

di giovani ricercatori in questo cam-po, e dunque l'accensione di borse didottorato, e di contratti di ricerca po-st doc sarebbe particolarmente op-portuna. Naturalmente dovrebbe es-serci una precisa finalizzazione, edunque scelte scientifiche e strategi-che sui progetti su cui intervenire.Non dimentichamo inoltre che ilprogetto Millennium è solo nella suaprima fase, e altre proposte e proget-ti verranno valutati nel prossimohanno. Dunque un momento digrandi opportunità, ma anche di va-lutazioni e di scelte, cui sarà chiama-ta la nostra comunità.

Marco FontanaPresidente della SISN

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la temperatura del monocromatorerispetto a quella degli analizzatori.La possibilità di accedere a valorielevati del momento trasferito, man-tenendo al contempo una elevata ri-soluzione in energia, è una caratteri-stica peculiare di IN13 che risultaparticolarmente utile per mettere inevidenza le anarmonicità nella dina-mica vibrazionale del campione edanche per studiare i moti diffusivi inun ampio intervallo di momenti tra-sferiti potendo così analizzare in det-taglio le caratteristiche geometrichedi questi processi. Questo tipo diinformazioni è particolarmente inte-ressante per lo studio della dinamicadei sistemi disordinati: transizionivetrose negli amorfi, dinamica ato-mica nei fluidi semplici e associati,

transizioni conformazionali nei poli-meri, dinamica delle biomolecole, in-terazioni molecola-solvente nei flui-di complessi.Nel corso del primo anno del proget-to si è provveduto ad un sostanzialeammodernamento degli apparati dicontrollo ed acquisizione dati dellospettrometro. L’elettronica di tipoCAMAC è stata sostituita da un si-stema VME controllato da un PC, edil nuovo software che è stato svilup-pato permette un controllo moltopiù semplice ed accurato di tutti iparametri sperimentali durante lamisura. Inoltre, grazie alla aumenta-ta velocità dei controlli, è stato possi-bile ottenere una migliore accuratez-za nella definizione della temperatu-ra del monocromatore e quindi della

energia dei neutroni incidenti sulcampione. La maggiore limitazionedello strumento è tuttora il suo bassoflusso, infatti IN13 è collocato lungouna guida di neutroni termici e distaoltre 70 m dal reattore. Per otteneredati con una buona statistica sononecessari tempi di acquisizione piut-tosto lunghi: circa 2 ore per una mi-sura elastica (hω =0) e da 3 a 4 giorniper ottenere lo spettro quasielasticocompleto. Un obiettivo importantenell’ambito di un possibile rinnovodel progetto, che nella forma attualescade nel Giugno 2001, dovrebbequindi essere un sostanziale aumen-to del flusso di neutroni sul campio-

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Fig. 3. Incoherent scattering from entire cells,and comparison with myoglobin as hydratedpowder (Doster et al. Nature 1999), and insolution. [G. Zaccai, M. Tehei, B. Franzetti, C.Pfister, IBS-Grenoble and B-Z. Ginzburg,Jerusalem, Israel].

Fig. 2. Elastically scattered intensity by ice Ih at20, 100, 180 and 260 K (from top to bottom.Lines are fits by a model in which protons areable to jump between two sites of differentenergies [L. Bove, F. Sacchetti and A. Paciaroni,INFM-Perugia, Italy and INFM-OGG-Grenoble,France].

Fig. 1. Schematic view of the IN13 backscattering spectrometer at the ILL

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ne; a questo scopo verranno condottisullo strumento attuale dei test nelcorso del 2000, una stima realisticasembrerebbe indicare come tecnica-mente realizzabile un aumento delflusso di un fattore 8 – 10.Grazie al CRG-IN13 diversi ricerca-tori INFM dell’area biofisica (Sezio-ne B) e dei sistemi disordinati (Se-zione C) hanno proposto ed avviatodei progetti di ricerca che prevedo-no l’utilizzo dello scattering deineutroni ad alta risoluzione; nel se-guito illustreremo alcuni esempi distudi condotti da ricercatori Italianie Francesi.Il primo (L. Bove et al. INFM-Peru-gia) riguarda lo studio della dinami-ca dell’idrogeno nel ghiaccio Ih a dif-ferenti temperature. Questo rappre-senta un sistema modello di parten-za relativamente semplice per ana-lizzare la dinamica dei protoni in si-stemi più complessi di reti di legameidrogeno, come ad esempio le protei-ne idratate. Lo scattering dal cam-pione è risultato totalmente elasticoanche alle temperature più elevateimpiegate (260 K). La dipendenza daQ dell’intensità di scattering (nell’in-tervallo di energia da –20 a +20 µeV)riportata in Fig.2, appare non armo-nica anche alle temperature più bas-se misurate (20 K). I dati sono statianalizzati con un modello in cui iprotoni possono saltare tra due siticon energie differenti verosimilmen-te lungo le direzioni dei legami ossi-geno-ossigeno nei “loop” esagonali

presenti nella struttura disordinatadel ghiaccio.Alcuni esperimenti condotti da ricer-catori dell’IBS di Grenoble si sonoposti l’obiettivo di studiare l’effettodell’influenza dell’ambiente intracel-lulare sulla dinamica delle proteine.Le misure sono state condotte su cel-lule di E. coli, di H. marismortui e glo-buli rossi del sangue a temperaturecomprese tra 280 e 320 K per evitareuna denaturazione da eccessivo raf-freddamento. Dopo aver sottratto ilcontributo allo scattering dovuto aimoti diffusivi del solvente, dalla di-pendenza da Q dell’intensità elasticaè stato dedotto, in approssimazioneGaussiana, uno spostamento qua-dratico medio in funzione della tem-peratura che è stato interpretato intermini di “rigidità” dell’ambienteintracellulare. I dati riportati in Fig. 3mostrano il confronto con gli sposta-menti quadratici medi misurati inpolveri idratate di mioglobina (datida Doster et al. Nature 337, 754,1989) e in soluzioni di mioglobina(media tra due misure con concen-trazioni di 100 e 200 mg/ml in D2O).Appare evidente che la dinamicamacromolecolare nelle cellule dipen-de dal tipo di cellula: infatti una “ri-gidità” via via maggiore si osservanei globuli rossi, nell’E. coli e nel-l’H.marismortui. Questo tipo di misu-re apre delle interessanti prospettiveper una migliore comprensione del-

l’effetto degli ambienti intracellulariin vivo e gli autori intendono esten-dere queste misure ad altri tipi dicelle di organismi termofili ed iper-termofili.Misure interessanti sono anche statecondotte su ribosomi, aggregati ma-cromolecolari di proteine ed acidinucleici. I campioni utilizzati per gliesperimenti sono stati ottenuti da E.coli (un organismo che ha raggiungela funzionalità ottimale a 35 C) eThermus thermophilus (un batteriotermofilo che vive a temperature di70-80 C). I risultati degli spostamentiquadratici medi in approssimazioneGaussiana (Fig. 4) indicano che men-tre i valori assoluti di ⟨u2⟩ sono, a 280K, leggermente superiori per il Ther-mus thermophilus rispetto al E. coli(ciò potrebbe essere dovuto ad unaleggera differenza di idratazione trai due campioni), la variazione di ⟨u2⟩con la temperatura è leggermentema significativamente inferiore per ilbatterio termofilo. Ciò indica che unorganismo termofilo deve raggiun-gere una temperatura più elevataperchè le biomolecole raggiungano ilgrado di “flessibilità” strutturale ne-cessario alla ottimizzazione della lo-ro funzione biologica.L’ultimo esempio qui riportato ri-guarda la dinamica di alcuni polisac-caridi: amilosio ed amilopectina chesono i due principali componentidell’amido. Nella Fig. 5 è mostrata

Fig. 6. Temperature dependence of the protonmean square displacement ⟨u2⟩ (normalised at20 K) for amylose (top) and amylopectine(bottom). The hydration is expressed as g.D2O/g. dry saccharide. The continuous line is afit of the low temperature data to an Einsteinmodel of independent harmonic oscillators [M.Di Bari, G. Albanese, F. Cavatorta, A. Deriu,INFM-Parma, Italy].

Fig. 5. Elastic scattered intensity vs Q2 atdifferent temperatures for an amylose samplehydrated at 0.47 (g. D2O/g. dry saccharide).The solid lines are fits to an asymmetric double-well potential. [M. Di Bari, G. Albanese, F.Cavatorta, A. Deriu, INFM-Parma, Italy].

Fig. 4. Energy resolved incoherent scatteringfrom ribosomes (70S) purified from E. coli andT. thermophilus. [C. Pfister, G. Zaccai, IBS-grenoble, I. Serdyuk and I. Scherbakova,Puschino, Russia].

Francesco Paolo Ricci, the Founder andEditor of this Journal died in Rome on27 February. He was professor of Phy-sics at "Università di Roma Tre" whichhe joined a few years ago at its start tohelp the new Physics Department to at-tain the high standard of the old PhysicsDepartment of "Università Roma - LaSapienza" where he had been Professorfor about 30 years, serving as Chairmanduring "the difficult seventies".With Paolo Ricci disappears an excep-tionally good man beloved by his fa-mily and friends and a distinguishedscientist who gave a remarkable contri-bution to neutron research.He is survived by the wife Silvana Pier-mattei a well known Medical Physicistand his former University mate, threesons and one daughter.The last son of a large family and grand-son of a painter who was very famous atthe turn of the century, Paolo Riccialways had a particular taste for beauty,

under every form it was appearing andin every field. His roots belonged toAbruzzo, a region east of Rome of greatnatural beauty which includes the hi-ghest mountains of peninsular Italy, oldvillages, green pastures and wide whitebeaches along the Adriatic sea.After fullfilling the requirements forgraduating in Physics he joined for histhesis and then postgraduate work theLow Temperature Laboratory at Roma -La Sapienza performing ion diffusionand mobility experiments in liquid He-lium until 1957 when E. Amaldi askedhim to start in Italy research in neutrondiffraction together with G. Caglioti andA. Paoletti.At that time neutron diffraction was stillat its childhood and work was beingperformed by about half a dozen grou-ps around the world where researchreactors were available: Argonne,Brookhaven, Chalk River, Harwell, OakRidge and Saclay. In Rome a small reac-tor was under construction at Casacciamostly for training, with few experi-mental beam-holes for neutron work.The first task of the group was obviou-sly to design a spectrometer. That ledimmediately into the problem of optimi-zing the physical parameters of the ap-

paratus to be built. Such a problem hadbeen faced already by all other groupsperforming neutron work, but the crite-ria and results were mostly dispersed inlocal reports if not in hand written notesand were barely mentioned in the "ex-perimental" sections of the existing lite-rature reporting the new exciting resultsobtained in crystal and magnetic struc-tures or were just orally transmittedfrom scientist to scientist.The Rome group took the occasion towork out, starting from simple models,closed formulas for powder and singlecrystal diffraction taking into proper ac-count the characteristics of monochro-mators, samples, collimators, detectors.That was the first work of the group, theonly one which could have been possi-bly performed on paper, without a reac-tor available. After that the three friendswent across the Ocean to learn the neu-tron diffraction technique: G. Caglioti toChalk River with B.N. Brookhouse, A.Paoletti to Brookhaven with R. Nathansand F.P. Ricci to MIT with C.G. Shull.Paolo was considered the luckiest as hewas the only one living in a beautifultown and working with the father ofneutron diffraction. But it turned outthat the MIT reactor was behind sche-

Early Neutron Diffraction in Italy: F.P. Ricci

l’intensità elastica ottenuta da misu-re su amilosio per differenti idrata-zioni. I dati, che per T>200 K mostra-no un andamento chiaramente anar-monico, sono stati analizzati utiliz-zando un modello di transizioniconformazionali delle catene polisac-caridiche descritte da un potenzialea doppia buca per la dinamica deiprotoni. Gli spostamenti quadraticimedi così ottenuti (Fig. 6) mostranoun comportamento armonico fino a320 K nel campione secco. Viceversanei campioni idratati si osserva unatransizione cinetica, simile alle tran-

sizioni vetrose nei sistemi amorfi, acirca 230 K. Le temperature di transi-zione dipendono marcatamente dal-l’umidità e, a parità di idratazione,sono molto più alte di quelle osser-vate nelle proteine globulari (tipica-mente 150-180 K). Questi studi pos-sono avere anche un interesse appli-cativo nel settore della “food scien-ce”: infatti in questo campo di ricer-ca oggi si applicano sempre piùspesso concetti e modelli derivatidalla fisica e chimica dei polimeri(processi cinetici metastabili, stati“vetrosi” dinamicamente confinati)

in luogo di modelli termodinamiciall’equilibrio. Da questo punto di vi-sta la temperatura di transizione ve-trosa, TG, può costituisce un parame-tro di interesse significativo in rela-zione alle proprietà fisiche ed allastabilità e dei prodotti alimentari.

A. DeriuUniversità di Parma e INFM, Parma

A. PaciaroniINFM Operative Group Grenoble

C. Pfister, IBS e Università J. FourierGrenoble

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dule at such an extent that after oneyear Paolo came back to Rome withouthaving "seen" a single neutron. Hoveverhe had plenty of opportunities for pre-paring and discussing forthcoming neu-tron work with Cliff Shull. That meantthat after all he gained the best trainingsince he could join in setting up the refi-ned experiments planned "Cliff's style",without even bothering collecting datawhich of course is a most important bu-siness but may also turn in a tediousone if it leads only to expected results.To that time dates the deep friendshipand esteem Cliff Shull always had forPaolo Ricci that means that Cliff evalua-ted at a good rate the cooperation ofPaolo who for a while was the only per-son working with him. Of course in away neutron work was more simplethan now, but it was absolutely newand someone doing research wasalways on his own, in "no man's land". In meantime Caglioti was learning latti-ce dynamics by inelastic neutron scatte-ring from its pioneer B.N. Brookhouseand Paoletti was looking at departuresfrom spherical symmetry of 3d electrondistribution with polarized neutrons,under the guide of Bob Nathans.At the end of '59 all members of thegroup were back in Italy and at that timethey separated. Caglioti went to theCP5Mw reactor in Ispra center which ju-st at that time was becoming an Euro-pean Establishment and took there thenew built spectrometer. Paoletti and Ric-ci preferred to stay in Rome at the Casac-cia TRIGA reactor of which in the mean-time had been decided the upgrading to1Mw, which meant a full year shutdown.However, before it, there was the possi-bility to test and perform the first measu-rements with a polarized neutron spec-trometer, the second coming to operationafter the one in Brookhaven. It had beenquickly built from a standard Xray dif-fractometer taking advantage for thespin flipping equipment of the laborato-ries in Frascati where it had been recen-tly built the R.F. system for a new 1 GevElectrosynchrotron.For about 10 years I had then the chanceand the honour of working with Paolo

Ricci. It was a great experience as hehad a deep vision of the problems andwithout underestimating difficulties hefound always a good reason for a joyfulapproach to work.In those years neutron work in Italywent along predictable paths withmajor emphasis on lattice dynamics andmechanical properties in Ispra and ma-gnetic properties in Rome where also athree axis spectrometer for the study ofmagnetic excitation had been set up.The results were not exceptional but ofgood quality and on line with the pro-blems being investigated through theworld at that time. But it was becomingincreasingly evident that the neutronstudy of condensed matter was lookingfor new fields.In September 1968 a Symposium on"Current Problems in Neutron Scatte-ring" was held in Rome at Casaccia withthe participation of practically all thescientists working with neutron scatte-ring in Europe and U.S.A. It appearedclear that Liquids and Phase Transitionswere catching more attention as a newgeneration of high flux reactors was co-ming into operation, at Brookhaven firstand later in Grenoble. A new class of experiments was madepossible, paving the way to the presentinvestigations in Complex Molecules,Multilayers and Biological Systems. Thegroups operating at small reactors wererather discouraged and the groups ofCasaccia and Ispra made no exception.At that time travelling was more diffi-cult and work at the neutron sourceswas not possible if one did not take careof the equipment which belonged to theoperating research group rather than tothe neutron source. That practically ex-cluded from regular work the groups ofthe countries which did not own theneutron source.Italy did not enter the ILL consortiumeither at its foundation or later at the ti-me when UK joined in. After losing thisopportunity Caglioti and Paoletti deci-ded to quit neutron work believing thatit would have been impossible toperform good work without a goodsource. But Paolo Ricci decided to go on,

gathering the few people left and star-ting at the 1 Mw reactor of Casaccia a li-ne of ingenious experiments whicheventually led to a renewed interest inItaly for the subject and to a new genera-tion of Italian neutron investigators wholater were able to take advantage of theresearch opportunities provided by theEuropean cooperation in the construc-tion and operations of intense sources.Paolo acted with humility and vision atthe same time, suggesting problems,teaching young students, encouragingthose who were dubious. He had a wideand solid culture and not only in Phy-sics. Until now, at 70 he was really theyeast of a wide scientific communitywhich grew under his continous careand gradually was accepted as a signifi-cant component of the internationalneutron community, as he was able toextract the best from his coworkers.Still he did not like the limelights: heenjoyed the back stage better as he wasan exceptional Director rather than anActor, discovering, discussing, testing,rehearsing that permanent, brilliant of-ten unexpected show which is Researchin Physics.Because of his ancestry he was alwayslooking for beauty and not only in Arttoward which he felt a strong attractionbut in Science as well. In a way helooked for an aesthetic dimension ofScience. Maybe he thought that beautywas a common component of humanactivity which indicated the presence ofat least some hint of the Truth mankindis always pursuing and never reaching.His comment after a good seminar th-rowing a new light on some difficultproblem invariably was "E' proprio bel-lo!" and saying that, he looked absolu-tely happy and indeed he was.Paolo Ricci was one of the very few per-sons to work with was fullfillment, joy,even pleasure. We are going to miss himgreatly, but we consider as a great gift oflife to have been for a long time his col-leagues, his coworkers, his friends.

Antonio PaolettiUniversità degli Studi di Tor Vergata

Facoltà di Ingegneria

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Umberto Maria Grassano ci ha lasciatinella notte tra il 3 e il 4 Maggio 2000.Aveva 61 anni e da qualche tempo eraaffetto da un male incurabile. Lascia ungrande vuoto specie in coloro, e sonotanti, che ne hanno apprezzato le elevatequalità morali, la dedizione alla ricerca eall'Università, l'impegno organizzativo alivello nazionale, la disponibilità a farsicarico dei problemi degli altri, l'assolutodisinteresse personale. Si era laureato inFisica all'Università di Pavia, alunno delCollegio Ghislieri, nel 1961. Nel 1963 siera trasferito all'Università di Messina epoi, nel 1965, all'Università di Roma "La Sapienza". Nel 1980 era tornato aMessina come professore straordinariodi Fisica Molecolare e dal 1981 era di-ventato professore straordinario e poiordinario di Fisica dello Stato Solido al-l'Università di Roma "Tor Vergata".Aveva trascorso vari periodi di studioall'estero: all’Imperial College di Londranel 1962, alla Cornell University nel1975, all’Università di Nimega nel 1981 e

82. Condirettore del corso “Excited statespectroscopy in solids” della Scuola “E.Fermi” di Varenna nel 1985, Direttoredel GNSM dal 1996 al 1998, membro delConsiglio direttivo e della Giunta esecu-tiva dell‘INFM dal 1987 al 1997, Diretto-re del Dipartimento di Fisica dell’Uni-versità di Roma “Tor Vergata” dal 1991al 1993, Presidente del Consiglio di Cor-so di Laurea in Fisica nella stessa Uni-versità dal 1983 al 1986 e dal 1999 allasua morte.L’attività scientifica di Umberto Grassa-no ha riguardato principalmente le pro-prietà ottiche dei cristalli ionici e si èsviluppata in modo coerente nell’arco diun quarantennio: dai centri di colore, ailaser per infrarosso, all’ottica non linea-re, ai nuovi materiali (per laser). Que-st’ultima attività lo aveva portato ad or-ganizzare, con i colleghi chimici, il corsodi diploma in Scienza dei materiali chein futuro si trasformerà in una laurea diprimo livello.Numerosi sono stati i suoi contributi

scientifici di grande rilievo. Senza prete-sa di completezza, desidero elencare iseguenti:Nel 1966 ha introdotto (in collaborazio-ne con lo scrivente) il metodo che oggiviene chiamato “pump and probe oPAP”, applicandolo, con sorgenti ottichetradizionali, allo studio degli stati ecci-tati del centro F(PRL 16,124 (1966)).Nel 1966 ha pubblicato (con lo scriventee con Renzo Rosei) la prima osservazio-ne dell’effetto Stark del centro F (PRL17, 1043 (1966)). Ha esteso in seguitoquesta tecnica a molti altri centri facen-done uno strumento per lo studio deglistati eccitati non raggiungibili da transi-zioni a un fotone (lavori in collaborazio-ne con G. Margaritondo, R. Rosei, M. Bonciani, A. Scacco, A. Tanga).Nel 1974 ha pubblicato la prima osser-vazione dell‘emissione stimolata da cen-tri F eccitati (Optics Comm. 11, 8(1974)in collaborazione con F. De Martini e F. Simoni). L’articolo contiene la propo-sta di costruire un laser a centri di colo-re. Ha in seguito collaborato alla realiz-zazione dei primi laser italiani a centridi colore (Revue Phys Appl. 18, 301(1983), in collaborazione con G. Baldac-chini, P. Violino e altri).

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In memoria diUmberto Maria Grassano

Vogliamo qui brevemente ricordare aicolleghi ed ai giovani ricercatori dellaFisica della Materia Francesco PaoloRicci (che si è spento dopo una lungamalattia lo scorso febbraio a Roma) contutto l’affetto, la profonda amicizia estima che sono frutto di tanti anni di la-voro in comune. Francesco Paolo è statoper lungo tempo elemento di stimolo edi discussione critica e vivace all’inter-no della nostra comunità scientifica inanni particolarmente critici (tra gli anniottanta e l’inizio degli anni novanta) neiquali si assisteva ad una notevole cre-scita culturale e scientifica ma alla qua-le non corrispondeva né una adeguatastruttura organizzativa né i mezzi fi-nanziari erano sufficienti a garantirne ilnaturale sviluppo. Come Segretario

scientifico e, successivamente, come Di-rettore del gruppo Nazionale di Strut-tura della Materia ha avuto un ruolo in-cisivo e determinante nell’evoluzionestrategica della organizzazione della ri-cerca in struttura della materia (poi di-venuta Fisica della Materia con l’appor-to di Elettronica Quantistica, Plasmi,Cibernetica e Biofisica) verso gli assettiche si sono più recentemente consolida-ti, avendo ben chiari alcuni riferimenti,ed in particolare:- La struttura del GNSM in settori Na-zionali Tematici (che furono il primomodello delle attuali sezioni INFM) connotevole autonomia gestionale e con lapartecipazione anche della componenteindustriale interessata alla ricerca.- Una forte interazione tra Unità di Ri-

cerca Universitarie ed Istituti e Centri diRicerca CNR, con l’intento di arrivaread una struttura complessiva con unaevidente composizione organica ed ilpiù possibile efficiente. Si deve alla suaazione la realizzazione dei progetticoordinati con la valutazione di refereeinternazionali.- Il potenziamento di progetti ed ini-ziative internazionali che facessero ri-ferimento alla grandi facilities europee(riguardanti in particolare l’utilizzo difasci di neutroni e la radiazione di sin-crotrone).Non dimenticheremo mai il vigore e lapassione con cui ha vissuto le vicendescientifiche ed organizzative più impor-tanti degli ultimi 30 anni, l’apertura aigiovani, la lealtà e la sincerità con cui siè battuto per affermare le proprie idee etrasmetterle agli altri.

Angiolino StellaEmanuele Rimini

In ricordo di Francesco Paolo Ricci

A seguito della sua lunga attività nelcampo dell’ottica non lineare, nel 1986ha esteso il range dell’assorbimento adue fotoni al campo spettrale della ra-diazione di sincrotrone, osservando glieccitoni 2p e 3p nel KCl a 8.5 eV (Eu-rophysics Lett. 2, 571 (1986), in collabo-razione con F. Bassani, M. Casalboni,M. Piacentini ed altri) che non sono ac-cessibili con le normali sorgenti ottiche.Ha sviluppato negli anni una pregevoleattività di ricerca sul dicroismo circolaremagnetico dei centri di colore (SolidState Comm. 21, 225 (1977); Phys. Rev.B16, 5570 (1977); Phys. Rev. B20, 4357(1979), in collaborazione con G. Baldac-chini e A. Tanga).Non ha avuto la soddisfazione di vederpubblicato il libro di Fisica dello statosolido (Bollati-Boringhieri in corso distampa) che ha scritto con Franco Bassa-ni. Resterà una delle testimonianze checi ha lasciato, a compimento della sualunga attività di studio e di ricerca.Vorrei ricordare ancora un aspetto dellasua attività di ricercatore: l'estremo ‘un-derstatement’ con cui parlava dei suoirisultati scientifici e il suo rifiuto di ogniabbellimento, enfatizzazione, richiesta

di priorità. Se dovessimo accettare l'in-giusta etichetta che ci è stata appiccicataanni or sono, quella di "baroni dellascienza", dovremmo dire che Umbertoera l'anti-barone per vocazione e perconvincimento. Aveva sviluppato moltecollaborazioni con sedi e gruppi diversisenza mai attribuirsi né richiedere ilruolo del ‘principal investigator ’ népreoccuparsi se altri se lo attribuissero.Umberto era un uomo buono, dotato diintime convinzioni religiose, che maiostentava e che lo hanno molto aiutatonegli ultimi mesi di sofferenza. Erasempre disponibile a farsi carico deiproblemi di tutti, sia a livello individua-le che delle istituzioni. Nell'ultimo anno,già provato da un male inesorabile, incondizioni difficili per la nostra Univer-sità a causa del passaggio al nuovo ordi-namento didattico, aveva accettato, congiovanile determinazione, l'incarico dipresidente del Consiglio di corso di lau-rea in Fisica. Esempio per tutti noi dispirito di servizio e anche velato rimpro-vero per coloro che preferiscono rinchiu-dersi nei loro studi o laboratori, senzarendersi conto che l'interesse generale èalla base degli interessi particolari.

Ha trascorso l'ultimo mese della sua vi-ta sereno e distaccato, quasi scusandosiper il disturbo che arrecava agli amici. Atratti era ironico, con l'ironia sfumata dichi ormai sta sopra alle vicende delmondo. Anche se l'ironia ha fatto partedel suo modo di vivere da sempre. Atratti, tuttavia, partecipava ai nostri pic-coli problemi, discuteva degli sviluppifuturi, dava consigli, si preoccupavadelle ricerche in corso. Insomma ha vis-suto compiutamente fino alla fine.Ricordo che l'ultima volta che l'ho visto,pochi giorni prima della morte, un suocollaboratore gli portò il testo dattilo-scritto di un suo lavoro. Egli lo prese eassicurò che lo avrebbe letto e commen-tato! E ancora: la lettera di dimissioni daPresidente di CCL fu firmata il giornoprima della morte "perché le mie attualicondizioni di salute mi impediscono diesplicare l'incarico in modo adeguato".Questo era Umberto! Addio, continue-rai a vivere nel ricordo di tutti noi! Po-tremo dire di te con il poeta: non omnismoriar multaque pars mei vitabit Libitinam.

Gianfranco ChiarottiMaggio 2000

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Il Foundation Phase Report (FPR) dellaEuropean Synchrotron Radiation Facility(ESRF), pubblicato nel 1987, prevedevala costruzione di una linea di luce dedi-cata alla spettroscopia Mössbauer e alloscattering anelastico dei raggi X (IXS). La parte dedicata allo IXS evidenziaval’interesse di poter studiare eccitazionidi tipo fononico ed elettronico con i rag-gi X come un complemento ed una al-ternativa a metodi esistenti quali lespettroscopie neutroniche e di fotoemis-sione. Questo progetto trovava la prin-cipale motivazione nelle applicazioni ditipo fononico, i.e. nella parte a piú altarisoluzione. Infatti, in questa direzione,c’erano giá stati dei tentativi fatti da unGruppo operante al Sincrotrone di Am-burgo, HASY-Lab, il quale aveva realiz-zato uno spettrometro per IXS. Questo

strumento aveva come scopo il raggiun-gimento di una risoluzione totale inenergia di 7 meV, e aveva dimostratosperimentalmente la possibilitá di potermisurare eccitazioni fononiche con unarisoluzione di circa 20 meV – il progettoauspicato nel FPR era quello di ottenerei 7 meV di risoluzione all’ESRF, grazieall’attesa maggiore collimazione dellanuova sorgente, e grazie ad un pro-gramma da lanciare per la costruzionedi analizzatori dell’energia dei fotonicon altissima risoluzione (ottenere 5meV a 14 KeV, i.e. ∆E/E~10-7).Accettai nel 1990 di venire all’ESRF,rientrando da una esperienza di otto an-ni in America, per occuparmi dello svi-luppo di questa linea di ricerca – lo svi-luppo dell’IXS all’ESRF. Grazie al miorientro, mi potei riavvicinare ad alcune

persone con le quali avevo studiato du-rante il periodo univerisitario, e in parti-colare con Giancarlo Ruocco e VittorioMazzacurati. In questo ritrovarsi, laconversazione si focalizzó subito sulmio nuovo progetto, e in particolare sul-le sue potenziali applicazioni nella fisicadei sistemi disordinati e sulla sua com-plementarietá ai neutroni e alle tecnichedi simulazione numerica. L’importanza di questo scambio di idee,iniziato nel 1990 e protrattosi fino ametá 1992, é stato di fondamentale im-portanza: risultó infatti chiaro che 7meV di risoluzione erano assolutamenteinsufficienti per sperare di poter accede-re con impatto e rilevanza a problemiaperti e di notevole interesse – 3 meVerano assolutamente necessari e possi-bilmente si doveva scendere a 1-2 meV.Convincersi di questo punto e’stato dicruciale importanza per tutta una seriedi motivi logistici: Tornare in America?Era fisicamente possibile spingere le tec-

Ricordando Vittorio Mazzacurati

niche di diffrazione da cristalli perfettial punto di poter ottenere ∆E/E~10-8?“I Tedeschi” non erano riusciti a costrui-re analizzatori con risoluzione in ener-gia meglio di 20 meV – potevamo noiarrivare a 1 meV?Utilizzando tecniche di diffrazione conangoli di Bragg vicini a 90o, per ottenerefino a 1 meV di risoluzione, si deve po-ter cambiare l’energia dei raggi X peraccedere a differenti riflessioni del cri-stallo – Questo implica che la coesisten-za dell’esperimento di IXS e di Mös-sbauer sulla stessa linea diventa impos-sibile. Quale sarebbe stato l’atteggia-mento dei direttori ESRF dinanzi alladomanda di dedicare una intera lineaallo scattering anelastico? Grazie a infinite discussioni, calcoli (cal-coletti e calcoloni), innumeri bottiglie divino (del migliore) ed anche un intossi-camento da nicotina (passivo e attivo)non indifferente, si venne a costituire franoi tre un enorme entusiasmo basatosul convincimento che, non solo si pote-va arrivare a spingere la risoluzione fi-no a 1 meV, ma anche che rimanevanoabbastanza fotoni per poter fare degliesperimenti. A capo delle discussioni sulla realizzabi-litá tecnica di un tale strumento, la con-vinzione dell’importanza di dover scen-dere ad almeno 3 meV veniva dal fattoche usando l’IXS si poteva accedere allaregione di momento (Q) ed energia (E)scambiate caratteristiche delle zona incui, in sistemi disordinati come vetri, li-quidi e fluidi densi, ci si aspetta la tran-sizione della dinamica collettiva da unasituazione descrivibile in termini idrodi-namici a quella caratteristica di particel-le quasi-libere fra collisioni successive.Questa transizione comporta cambia-menti qualitativi nel fattore di strutturadinamico, S(Q,E), che é la quantitá di-rettamente misurabile in una esperienzadi scattering anelastico coerente qualequello dei raggi X. Il grande entusiasmo nel progetto pro-veniva dal fatto che, per motivi cinema-tici, questa zona della S(Q,E) é pratica-mente inaccessibile alle spetroscopieneutroniche ed era nota principalmentegrazie alla simulazione numerica – con-seguentemente ci stavamo convincendoche forse saremmo arrivati a mettere a

punto un nuovo metodo sperimentaleper accedere a una regione molto pococonosciuta ma di fondamentale interesseper capire la dinamica microscopica deisistemi disordinati. La convinzione pro-veniva dal fatto che, facendo una stimasull’acqua, dove si tenne conto con at-tenzione ed in modo conservativo di tut-ti gli effetti strumentali e fisici, ottenem-mo – in modo ineluttabile – un countrateintegrato in energia di 1 conteggio/s conlo spettrometro operante a una risolu-zione di 1 meV. Un tale segnale, confron-tato con quello caratteristico di esperien-ze neutroniche, non é enorme ma équanto basta per cominciare a lavorare!Ed infatti segnó l’inizio dell’avventura:Ottenemmo il “divorzio” dal Mössbauer.In parallelo a uno spettrometro simile aquello realizzato ad HASY-Lab, otte-nemmo i fondi per costruire, come pro-getto ad alto rischio, uno spettrometroper spingere la risolzione fino a 1.5 meV– questo progetto venne catalogato co-me “in-House Research” e non comeuno strumento per “Routine User ’sOperation”. La sua principale caratteri-stica é la lunghezza di 7 m del bracciorotante che contiene l’analizzatore sferi-co a cristallo di silicio. Nonostante le di-mensioni, questo braccio deve avere ri-producibilitá e precisione meccanichenel range di 10-6 m e 10-6 rad.Lanciammo un programma completa-mente nuovo per la costruzione di ana-lizzatori a cristallo con grande accettan-za angolare (quattro volte superiore allatipica risoluzione in momento) e altissi-ma risoluzione. Questo perché ci ren-demmo conto che le soluzioni adottateprecedentemente dai “Tedeschi” soffri-vano di alcuni problemi di fondo checompromettevano in modo insolubile larisoluzione e l’accettanza angolare.Il periodo 1992-95 fú tutto un fervore didisegni, preparativi, test e pesanti co-struzioni con poli a Grenoble e L’Aqui-la. In questo periodo l’impegno di Vitto-rio su questo progetto fu quasi totale,ed, in particolare, con Giancarlo si presela responsabilitá della costruzione delbraccio. Nel Giugno 1994, un TIR targa-to L’Aquila approdava a Grenoble conl’intero sistema meccanico. Il seguitodell’avventura costituisce ormai domi-nio della letteratura scientifica ed é

esemplificato da: i) Una lista di publica-zioni tra il 1995 e il 2000 comprendentecirca 25 lettere a Physical Review Let-ters, Nature and Science, ii) Lo spettro-metro dell’Aquila é dall’inizio del suofunzionamento lo strumento piú richie-sto dagli Users della linea ESRF di IXS –ID16 …. anche dai “Tedeschi”, iii) Unanuova linea é stata costruita all’ESRFcon un braccio di 12 m, con il quale sivorrebbe arrivare a 0.8 meV di risolu-zione in un prossimo futuro, ed infineiv) Spettrometri praticamente identici aquello di ID16 sono in costruzione al-l’Advanced Photon Source (Argonne)ed a SPRING-8 in Giappone. Tutto que-sto é stato possibile anche grazie all’im-pegno, all’interesse sia nella parte scien-tifica che strumentale, ed all’entusiasmodi Vittorio. Tutto questa confidenza éstata ampiamente ripagata: basti direche oggi l’IXS viene considerato comeuno dei grandi successi delle sorgenti diluce di sincrotrone di terza generazione,e come una nuova tecnica spettroscopi-ca con vaste aree di applicazione.Caro Vittorio, per fortuna abbiamo avu-to il tempo di fare alcuni esperimenti in-sieme che ripagano il tuo lavoro, ma che,inoltre, segnano la storia scientifica deisistemi disordinati! In particolare: Ab-biamo svelato il mistero del suono velo-ce nell’acqua e abbiamo fatto vedere cheesso corrisponde al limite elastico dovela dinamica collettiva microscopica delliquido e del cristallo diventano equiva-lenti. Abbiamo fatto vedere che nei vetriesistono modi collettivi propaganti adalto Q. Questo, oltre a permettere di de-scrivere in modo completo la dinamicadei sistemi vetrosi, ha messo nel giustocontesto gli aspetti microscopici che in-fluenzano le anomalie termodinamichedei vetri rispetto ai cristalli corrispon-denti – In particolare abbiamo messo laparola fine a tante teorie e idee, spessoideate grazie alla mancanza del datosperimentale, sulle proprietá dei sistemidisordinati. Questo lavoro continua econtinuerá, purtroppo senza il tuo con-tributo, ma sicuramente nel tuo ricordo.

Francesco SetteESRF – BP220

F-38043 Grenoble Cedex – FranceTel: +33.4.7688.2224, e-mail: [email protected]

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Support for activitiesin the field of neutron scattering is availablefrom the neutron round-table.

The neutron round-table is funded by the EC (DGXII)with approximately 100.000 Euro per year. The mission of the round-table is:

1. To actively

encourage

co-ordination and collaboration

between user facilities - such

that the European users will

benefit through a better quality

and an increased quantity of

access to the European neutron

scattering facilities.

2. To spread the

knowledge about the

potential of neutron scattering,

and support studies on future

prospects with neutron

scattering.

3. To support training

of young scientists

and other scientists, new to the

field of neutron scattering about

the potential of the method.

4. The round-table

supports non-

national access to summer

schools, workshops, training

courses, co-ordination activities

etc. Detailed information on

how and when to apply for

support can be found on the

round-table web page:

http://www.risoe.dk/fys/TMR.htm

5. The round-table

consist of

representatives from all major

European neutron user facilities,

from EC supported networks

developing novel

instrumentation and techniques

for neutron scattering plus 5

user representatives appointed

by ENSA (European Neutron

Scattering Association). The

name of all contact persons can

be found on the web page

mentioned above. The present

chairman/co-ordinator of the

round-table is Kurt Nørgaard

Clausen, and can be contacted

as [email protected]

TMRTMRTraining and Mobility of Researchers

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SCUOLE E CONVEGNI

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Si è svolto nei giorni 10-12 febbraio2000 il decimo Users’ Metting di ESRF.Come ormai consueto la riunione si èarticolata in una giornata di relazioniplenarie e in tre workshop tematici.Quest’anno i titoli dei workshop sonostati "Fast structural changes", "SurfaceScience 2000" e "Challenging problemsin structural biology".Durante la giornata comune vi sonostate quattro relazioni scientifiche suinvito che hanno avuto come tema re-centi risultati ottenuti ad ESRF. E.Dooryhee (ESRF) ha spiegato come ladiffrazione da polveri ha contribuitoalla caratterizzazione dei cosmetici uti-lizzati dagli antichi egizi; questa rela-zione è un interessante esempio dellenuove e crescenti applicazioni della lu-ce di sincrotrone alla archeometria. Laseconda relazione su invito, di A. Liljas(Lund), ha avuto come tema la cristal-lografia macromolecolare, un settore incui l’uso della luce di sincrotrone è tut-tora in fortissima espansione; l’oratoreha parlato dei suoi recenti studi dellafunzione ribosomica. Il campo della al-ta pressione è stato oggetto della rela-zione di R. Luebbers (Paderborn) il

quale ha applicato la diffusione anela-stica nucleare per studiare il ferro adalta pressione ed ha illustrato le riper-cussioni geologiche dei risultati; questarelazione è un ulteriore esempio di co-me nuove tecniche con luce di sincro-trone vengono applicate a problemi diinteresse per le Scienze della Terra.Nell’ultima relazione, C. Meneghini(INFM – Grenoble) ha riportato i risul-tati di misure XAFS su manganiti pe-rovskitiche, spiegando come essi met-tono in luce la relazione fra strutturalocale, magnetismo e magnetoresisten-za colossale; questo lavoro illustra co-me la spettroscopia con luce di sincro-trone continui ad avere un ruolo di pri-mo piano nella indagine dei sistemielettronici correlati.Oltre alle relazioni su invito vi sonostate altre due comunicazioni a caratte-re scientifico. La prima è stata tenutadal vincitore dello "Young ScientistAward" del 2000, R. Neutze (Uppsala);egli ha presentato una stimolante rela-zione riguardante lo sviluppo di tecni-che con risoluzione temporale dal fem-to- al pico- secondo e la loro applica-zione a problemi di interesse chimico e

biologico. La seconda è stata tenuta daW. Thomlinson (ESRF) ed ha descrittole prime angiografie eseguite a Greno-ble su pazienti umani; questi esperi-menti sono stati effettuati nell’ambitodi una studio condotto in collaborazio-ne con l’ospedale di Grenoble, ed han-no suscitato grande interesse per le po-tenziali ricadute di notevole interessemedico e sociale.Le tecniche con luce di sincrotronehanno sempre maggiore interesse nelcampo industriale. Per illustrare alcu-ne di queste applicazioni tre ditte so-no state invitate a spiegare in qualemodo utilizzano la luce di sincrotro-ne: Unilever (detergenti), Aventis(biotecnologie) e L’Oreal (cosmetici).Questa sessione è stata organizzatadall’apposito ufficio per le relazioniindustriali di ESRF.Infine, lo Users Meeting è stato l’occa-sione per la presentazione del CD-ROM divulgativo "Synchrotron Light"prodotto da ESRF. Si tratta di uno sti-molante e divertente CD interattivo ilcui scopo è di illustrare le proprietà ele applicazioni della luce di sincrotro-ne; il CD sarà distribuito tra breve epuò essere utilizzato a vari livelli diapprofondimento.

F. Boscherini

ESRF Users Meeting 2000

Circa 170 ricercatori hanno partecipatoal settimo Users’ Meeting di Elettrache si è tenuto nel Main Building del-l’ICTP (Trieste) nei giorni 29 e 30 No-vemnbre scorsi. L’idea di estendere loUsers’ meeting con un workshop sa-tellite da tenersi nei giorni immediata-mente precedenti o seguenti si è rive-lata molto buona e circa 70 personehanno partecipato al meeting satellite,quest’anno dedicato a "Reactions atSurfaces". Nei due interventi di aper-tura M. Altarelli e R. Walker hanno il-lustrato lo stato ed i progetti a medio elungo termine sia della facility chedella macchina. Nove beam-line sonocompletate, una è in stadio avanzatodi commissioning ed altre nove sonoin costruzione. Le prospettive a mediotermine includono la costruzione di al-tre tre beam-line, il completamento

della fase di studio e l’implementazio-ne di insertion device nelle sezionidritte piu’ corte, la sostituzione dell’at-tuale Linac con un Linac più breve edun anello di booster. Quest’ultimo do-vrebbe garantire iniezioni più rapide ela possibilità di iniezioni con una pro-cedura "top-up", in cui il fascio nonviene mai completamente azzerato.Le relazioni seguenti hanno illustrato irisultati delle varie ricerche svolte adElettra, che si estendono dagli studi susingoli atomi e molecole in fase gasso-sa alla ricostruzione della struttura diproteine ed alla microfabbricazione. W.Gudat , guest speaker per il 1999, hapoi illustrato lo stato di avanzamentodella nuova sorgente di radiazione disincrotrone tedesca Bessy II.Durante il meeting è stato assegnato ilpremio Fonda-Fasella a A. Riboldi-

Tunniclife per il suo lavoro sulla strut-tura cristallina della proteina portatri-ce dell’infezione della "Legionellapneumophila". Questo premio stabili-to quest’anno per la prima volta, inmemoria di L. Fonda e P.M: Fasella,che hanno dato un fondametale contri-buto alla costruzione e sviluppo diElettra, verrà attribuito ogni anno adun giovane ricercatore per i risultatiottenuti ad Elettra.L’assemblea degli utenti di Elettra haeletto tre nuovi membri per il Comita-to degli Utenti. M. Sancrotti, N. Zema eH. Hamenitsch sostituiranno G. Stefa-ni, P. Carra e T. Prosperi. Mentre rin-graziamo i membri precedenti del Co-mitato per il lavoro svolto, facciamo inostri migliori auguri ai nuovi membriper il loro non facile ruolo di inerfacciatra un’"effervescente" comunità diutenti e la facilty.

L. Avaldi

ELETTRA Users Meeting

OTTAVO CONVEGNO SILS29 Giugno-1 Luglio 2000

Università di Palermo – Palermo

Caro collega,

ti ricordo la scadenza del 15/4/2000 per l’invio degli abstract all’indirizzo e-mail:

[email protected].

Le sedi del convegno saranno due: la seduta inaugurale del 29/6/2000 si terrà presso la Saladelle Capriate, a Palazzo Steri, sede dell’Università di Palermo, piazza Marina 61.

Le sedute del 30/6 e 1/7/2000 avranno luogo presso la Sala Consiliare della Provinciadi Palermo, Palazzo Comitini, via Maqueda 100.

Accludo un elenco di alberghi che offrono un prezzo scontato per i partecipanti al convegno

e che sono abbastanza vicini alle due sedi (il più lontano è il Politeama, a circa 20 minuti a

piedi). Ulteriori informazioni su alberghi, mappa della città, ecc. si possono trovare al sito:

www.comune.palermo.it

NB: ti consiglio di prenotare l’albergo con ampio anticipo, perché nel periodo del convegno

l’afflusso turistico sarà notevole.

Antonino Martorana

Hotel singola doppia Tel /Fax (prefisso 091)

Politeama Palace Hotel **** 180.000 250.000 322777 / 6111589

Grand Hotel des Palmes **** 180.000 250.000 540350 / 540330

Crystal Palace Hotel *** 140.000 198.000 6112580 / 112589

Hotel Tonic *** 100.000 130.000 581754 / 581754

Hotel Europa *** 115.000 170.000 6256323 / 256323

Albergo Mediterraneo *** 110.000 160.000 5811337 / 586974

Massimo Plaza Hotel *** 180.000 240.000 325657 / 325711

Grande Albergo Sole *** 150.000 200.000 6041510 / 110182

I prezzi includono la prima colazione. Alla prenotazione, le offerte sono valide entro il 15/5/2000, fareriferimento al congresso SILS e/o convenzione CNR.

73


SCUOLE E CONVEGNI

V Scuola di Spettroscopia Neutronica“Francesco Paolo Ricci”

Diffusione Anelastica dei Neutroni

Hotel Capo d’Orso - Località Cala Capra - Palau (SS)23 settembre - 3 ottobre 2000

Generalità sullo scattering dei Neutroni A. Albinati, Università di MilanoSorgenti e strumentazione C. Andreani, Università di Roma “Tor Vergata”

Diffusione anelastica coerente: eccitazioni collettive U. Bafile, Istituto di Elettronica Quantistica, CNR, FirenzeDiffusione anelastica incoerente: spettroscopia vibrazionale U. Balucani, Istituto di Elettronica Quantistica, CNR, Firenze

Diffusione quasielastica: moti diffusivi M. Bée, Università “J. Fourier”, GrenobleDistribuzione di impulso nei sistemi classici e quantistici R. Caciuffo, Università di Ancona

Dinamica microscopica dei liquidi C.J. Carlile, ILL, GrenobleDinamica dei sistemi macromolecolari D. Colognesi, CNR-ISIS, Chilton, U.K.

Spettroscopia di tunneling M.T. Di Bari, UdR-INFM, ParmaApplicazioni a: biologia, chimica, materiali B. Dorner, ILL, Grenoble

J. Eckert, Los Alamos, USAA. Paciaroni, OGG-INFM, GrenobleC. Petrillo, Politecnico di MilanoF. Sacchetti, Università di PerugiaU. Wanderlingh, Università di Messina

Il costo di partecipazione di Lit. 1.300.000 dà diritto alla frequenza delle lezioni, delle esercitazioni pratiche ed alla pensione completa presso l’HotelCapo d’Orso (www.delphina.it/orso.htm) per tutta la durata della Scuola.

SCADENZA ISCRIZIONI: 30 GIUGNO 2000

DirettoriA. Deriu, Dip. di Fisica, Università di Parma – M. Zoppi, Consiglio Nazionale delle Ricerche, IEQ, Firenze

Segreteria OrganizzativaG. Ianni, Gruppo Nazionale Struttura della Materia del CNR, Roma

Informazioni generali e Modulo per l’iscrizionea. A partire da questa edizione la Scuola viene intitolata alla

memoria del Prof. Francesco Paolo Ricci che ne era stato ilpromotore ed aveva sostenuto questa iniziativa fin dalla suaprima edizione nel 1981.

b. La domanda di iscrizione deve essere fatta compilando il modulodi partecipazione reperibile presso il sito Web della Scuola.

c. Oltre alle lezioni ufficiali la Scuola prevede seminari edesercitazioni pratiche che completeranno il programmadidattico.

d. Il numero degli studenti è limitato a 30. Persone con provataesperienza nel campo potranno essere ammesse comeosservatori. Dietro loro richiesta la segreteria potrà occuparsidella loro sistemazione alberghiera.

e. L’accettazione delle iscrizioni e l’eventuale contributo verrannocomunicati via e-mail entro il 31.07.2000.

f. È disponibile un certo numero di borse per coprire il costo dellapartecipazione.

Per informazioni rivolgersi alla Segreteria della Scuola:Grazia Ianni - GNSM, Viale dell’Università 11, 00185 RomaTel.: 06 4452258 - Fax: 06 4941159 - e-mail: [email protected] Web: http://SISN.unime.it/scuola_neutroni.html

SCUOLE E CONVEGNI

74


Spettroscopia Neutronica “F.P. Ricci”Diffusione Anelastica dei Neutroni

Hotel Capo d’Orso - Località Cala Capra - Palau (SS)

23 settembre - 3 ottobre 2000MODULO D’ISCRIZIONE

Nome …………………… Cognome ………………………

Posizione attualmente ricoperta (laureando, dottorando,

borsista,…) …………………………………………………

Affiliazione …………………………………………………

………………………………………………………………

Indirizzo ……………………………………………………

………………………………………………………………

Telefono …………………… Fax ……………………………

E-Mail …………………………………………………………

Campo di attività ……………………………………………

…………………………………………………………………

La scheda va inviata entro il 30 giugno 2000 a:Grazia Ianni, GNSM, Viale dell’Università 11, 00185 Romae-mail: [email protected] • fax 06 4941159

CALENDARIO

75


10-12 luglio 2000 OXFORD, U.K.

The Sixth International Conference on ResidualStresses.P. Farrelly, IoM Conferences & Events.Tel: 44 171 4517391; Fax: 44 171 8392289E-mail: [email protected]

26-29 luglio 2000 HALLE/SAALE, GERMANY

Many Particle Spectroscopy of Atoms, Molecules andSurfacese-mail: [email protected]

6-11 agosto 2000 ABERYSTWYTH, WALES, U.K.

NCM8, 8th International Conference on the Structureof Non-Crystalline Materialse-mail: [email protected]://www.sgt.org

21-25 agosto 2000 BERLIN, GERMANY

7th International Conference on SynchrotronRadiation Instrumentationhttp://sri2000.tu-berlin.de

31 agosto 1 settembre 2000 EDIMBURG, UK

5th International Conference on Quasi-Elastic NeutronScattering

4-9 settembre 2000 MURCIA, SPAIN

European Conference on Iteration TheoryFaculdad de Matematica, Campus de EspinardoTel: 34 968 364176; Fax: 34 968 364182

4-16 settembre 2000 ROMA, ITALY

II Scuola Sperimentale di Diffrazione di raggi X aDispersione di Energia (EDXD) ed Angolare (ADXD)Dipartimento di Chimica, Università “La Sapienza”

23 settembre - 3 ottobre 2000 PALAU (SS), ITALY

V Scuola di Spettroscopia Neutronica “F.P. Ricci” -Diffusione Anelastica di neutroni

2-6 ottobre 2000 CRIMEA, UKRAINE

NOLPC 2000 - 8th International Conference onNonlinear Optics of Liquid and Photo RefractiveCrystalshttp://www.isp.kiev.ua

31 ottobre - 2 novembre 2000 IBARAKI, JAPAN

ASR 2000: 1st International Symposium on AdvancedScience Research

1-4 novembre 2000 DENTON, USA

CAARI 2000: XVIth International Conference on theApplication of Acceleratoes in Research and Industryhttp://www.phys.unt.edu/accelcon/

6-9 novembre 2000 TSUKUBA, JAPAN

ICANS-XV: 15th Meeting of the InternationalCollaboration on Advanced Neutron Sources

27 novembre-1dicembre 2000 BOSTON, MA, USA

MRS Fall Meetinghttp://dns.mrs.org

9-13 settembre 2001 MUNCHEN, GERMANY

International Conference on Neutron Scattering 2001(ICNS 2001)Physik Dept. E13, Technische Univ. München , D-85747Garching, GermanyTel: +49 89 28912452; Fax: +49 89 289 12473e-mail: [email protected]://www.icns2001.de

maggio 2002 NIST, USA

American Conference on neutron Scattering

76


Scadenze per richieste di tempo macchina presso alcuni laboratori di Neutroni

ISISLa scadenza per il prossimo call for proposalsè il 16 aprile 2000 e il 16 ottobre 2000

ILLLa scadenza per il prossimo call for proposalsè il 15 febbraio 2000 e il 15 agosto 2000

LLB-ORPHEE-SACLAYLa scadenza per il prossimo call for proposalsè il 1 ottobre 2000per informazioni: Secrétariat Scientifique du LaboratoireLéon 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: [email protected]://www-llb.cea.fr

BENSCLa scadenza è il 15 marzo 2000 e il 15 settembre 2000

RISØ E NFLLa scadenza per il prossimo call for proposalsè il 1 aprile 2000

Scadenze per richieste di tempo macchinapresso alcuni laboratori di Luce di Sincrotrone

ALSLe prossime scadenzesono il 15 marzo 2000 (cristallografia macromolecolare)e il 1 giugno 2000 (fisica)

BESSYLe prossime scadenzesono il 15 febbraio 2000 e il 4 agosto 2000

DARESBURYLa prossima scadenzaè il 30 aprile 2000 e il 31 ottobre 2000

ELETTRALe prossime scadenzesono il 28 febbraio 2000 e il 31 agosto 2000

ESRFLe prossime scadenzesono il 1 marzo 2000 e il 1 settembre 2000

GILDA(quota italiana) Le prossime scadenzesono il 1 maggio 2000 e il 1 novembre 2000

HASYLAB(nuovi progetti) Le prossime scadenzesono il 1 marzo 2000, il 1 settembre 2000e il 1 dicembre 2000

LURELa prossima scadenza è il 30 ottobre 2000

MAX-LABLa scadenza è approssimativamente febbraio 2000

NSLSLe prossime scadenzesono il 31 gennaio 2000, il 31 maggio 2000e il 30 settembre 2000

SCADENZE

ALS Advanced Light SourceMS46-161, 1 Cyclotron Rd Berkeley, CA 94720, USAtel:+1 510 486 4257 fax:+1 510 486 4873http://www-als.lbl.gov/Tipo: D Status: O

AmPS Amsterdam Pulse StretcherNIKEF-K, P.O. Box 41882, 1009 DB Amsterdam, NLtel: +31 20 5925000 fax: +31 20 5922165Tipo: P Status: C

APS Advanced Photon SourceBldg 360, Argonne Nat. Lab. 9700 S. Cass Avenue,Argonne, Il 60439, USAtel:+1 708 252 5089 fax: +1 708 252 3222http://epics.aps.anl.gov/welcome.htmlTipo: D Status: C

ASTRIDISA, Univ. of Aarhus, Ny Munkegade, DK-8000 Aarhus, Denmarktel: +45 61 28899 fax: +45 61 20740Tipo: PD Status: O

BESSY Berliner Elektronen-speicherring Gessell.fürSynchrotron-strahlung mbHLentzealle 100, D-1000 Berlin 33, Germanytel: +49 30 820040 fax: +49 30 82004103http://www.bessy.deTipo: D Status: O

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

CAMD Center Advanced Microstructures & DevicesLousiana State Univ., 3990 W Lakeshore, Baton Rouge,LA 70803, USAtel:+1 504 3888887 fax: +1 504 3888887http://www.camd/lsu.edu/Tipo: D Status: O

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

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

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

ELETTRASincrotrone Trieste, Padriciano 99, 34012 Trieste, Italytel: +39 40 37581 fax: +39 40 226338http://www.elettra.trieste.itTipo: D Status: O

ELSA Electron Stretcher and AcceleratorNußalle 12, D-5300 Bonn-1, Germanytel:+49 288 732796 fax: +49 288 737869http://elsar1.physik.uni-bonn.de/elsahome.htmlTipo: PD Status: O

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

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

HASYLABNotkestrasse 85, D-2000, Hamburg 52, Germanytel: +49 40 89982304 fax: +49 40 89982787http://www.desy.de/pub/hasylab/hasylab.htmlTipo: D Status: O

INDUS Center for Advanced Technology, Rajendra Nagar,Indore 452012, Indiatel: +91 731 64626Tipo: D Status: C

L U C E D I S I N C R OT R O N ESYNCHROTRON SOURCES WWW SERVERS IN THE WORLD(http://www.esrf.fr/navigate/synchrotrons.html)

77


FACILITIES

FACILITIES

78


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

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

LNLS Laboratorio Nacional Luz SincrotronCP 6192, 13081 Campinas, SP Braziltel: +55 192 542624 fax: +55 192 360202Tipo: D Status: C

LUREBât 209-D, 91405 Orsay ,Francetel: +33 1 64468014; fax: +33 1 64464148E-mail: [email protected]://www.lure.u-psud.frTipo: D Status: O

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

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

NSRL National Synchrotron Radiation Lab.USTC, Hefei, Anhui 230029, PR Chinatel:+86 551 3601989 fax:+86 551 5561078Tipo: D Status: O

PohangPohang Inst. for Science & Technol., P.O. Box 125Pohang, Korea 790600tel: +82 562 792696 f +82 562 794499Tipo: D Status: C

Siberian SR CenterLavrentyev Ave 11, 630090 Novosibirsk, Russiatel: +7 383 2 356031 fax: +7 383 2 352163Tipo: D Status: O

SPring-82-28-8 Hon-komagome, Bunkyo-ku ,Tokyo 113, Japantel: +81 03 9411140 fax: +81 03 9413169Tipo: D Status: C

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

SRC Synchrotron Rad. CenterUniv.of Wisconsin at Madison, 3731 SchneiderDriveStoughton, WI 53589-3097 USAtel: +1 608 8737722 fax: +1 608 8737192http://www.src.wisc.eduTipo: D Status: O

SRRC SR Research Center1, R&D Road VI, Hsinchu Science, Industrial Parc,Hsinchu 30077 Taiwan, Republic of Chinatel: +886 35 780281 fax: +886 35 781881http://www.srrc.gov.tw/Tipo: D Status: O

SSRL Stanford SR LaboratoryMS 69, PO Box 4349 Stanford, CA 94309-0210, USAtel: +1 415 926 4000 fax: +1 415 926 4100http://www-ssrl.slac.stanford.edu/welcome.htmlTipo: D Status: O

SRS Daresbury SR SourceSERC, Daresbury Lab, Warrington WA4 4AD, U.K.tel: +44 925 603000 fax: +44 925 603174E-mail: [email protected]://www.dl.ac.uk/home.htmlTipo: D Status: O

SURFB119, NIST, Gaithersburg, MD 20859, USAtel: +1 301 9753726 fax: +1 301 8697628http://physics.nist.gov/MajResFac/surf/surf.htmlTipo: D Status: O

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

UVSORInst. for Molecular ScienceMyodaiji, Okazaki 444, Japantel: +81 564 526101 fax: +81 564 547079Tipo: D Status: O

D = macchina dedicata; PD = parzialmente dedicata; P = in parassitaggio.

O= macchina funzionante; C=macchina in costruzione.

D = dedicated machine; PD = partially dedicated; P = parassitic.

O= operating machine; C= machine under construction.

FACILITIES

79


BENSCBerlin Neutron Scattering Center, Hahn-Meitner-Institut,Glienicker Str. 100, D- 14109 Berlin-Wannsee, GermanyRainer Michaelsen;tel: +49 30 8062 3043 fax: +49 30 8062 2523E - Mail: [email protected]://www.hmi.de

BNLBrookhaven National Laboratory, Biology Department,Upton, NY 11973, USADieter Schneider;General Information: Rae Greenberg;tel: +1 516 282 5564 fax: +1 516 282 5888http://neutron.chm.bnl.gov/HFBR/

GKSSForschungszentrum Geesthacht, P.O.1160, W-2054Geesthacht, GermanyReinhard Kampmann; tel: +49 4152 87 1316 fax: +49 4152 87 1338E-mail: PWKAMPM@DGHGKSS4Heinrich B. Stuhrmann;tel: +49 4152 87 1290 fax: +49 4152 87 2534E-mail: WSSTUHR@DGHGKSS4

IFEInstitut for Energiteknikk, P.O. Box40, N-2007 Kjeller,NorwayJon Samseth; tel: +47 6 806080 fax: +47 6 810920 telex: 74 573 energ n E-mail: Internet [email protected]

ILLInstitute Laue Langevin, BP 156, F-38042, GrenobleCedex 9,FranceHerma Büttner; tel: +33 76207179 E-mail: [email protected]: +33 76 48 39 06 http://www.ill.fr

IPNSArgonne National Laboratory, 9700 South Cass Avenue,Argonne, IL 60439-4814, USAP.Thiyagarajan,Bldg.200,RM. D125;tel :+1 708 9723593 E-mail: THIYAGA@ANLPNSErnest Epperson, Bldg. 212;tel: +1 708 972 5701

fax: +1 708 972 4163 or + 1 708 972 4470 (Chemistry Div.)http://pnsjph.pns.anl.gov/ipns.html

ISISThe ISIS Facility, Rutherford Appleton Laboratory,Chilton, Didcot Oxfordshire OX11 0QX, UKRichard Heenan; tel +44 235 446744 E-mail: [email protected] King; tel: +44 235 446437 fax: +44 235 445720; Telex: 83 159 ruthlb gE-mail: [email protected]://www.isis.rl.ac.uk

JAERIJapan 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: JAERIJ24596http:// neutron-www.kekjpl

JINRJoint Institute for Nuclear Research, Laboratory forNeutron Physics, Head P.O.Box 79 Moscow, 141 980Dubna, USSRA.M. Balagurov;E-mail: [email protected] M. Ostaneivich;E-mail: [email protected]: +7 095 200 22 83 telex: 911 621 DUBNA SUhttp://www.jinr.dubna.su

KFAForschungszentrum Jülich, Institut fürFestkörperforschung, Postfach 1913, W-517 Jülich,GermanyDietmar Schwahn; tel: +49 2461 61 6661; E-mail: [email protected] Maier; tel: +49 2461 61 3567;E-mail: [email protected]: +49 2461 61 2610 telex: 833556-0 kf d

N E U T R O N INEUTRON SCATTERING WWW SERVERS IN THE WORLD(http://www.isis.rl.ac.uk)

FACILITIES

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LLBLaboratoire Léon Brillouin, Centre d’Etudes Nucleairesde Saclay, 91191 Gif-sur-Yvette Cédex FranceJ.P Cotton (LLB); tel: +33 1 69086460 fax: +33 1 69088261 telex: energ 690641 F LBS+E-mail: [email protected]://bali.saclay.cea.fr/bali.html

NISTNational Institute of Standards and Technology-Gaithersburg, Maryland 20899 USAC.J. Glinka; tel: + 301 975 6242 fax: +1 301 921 9847E-mail: Bitnet: GLINKA@NBSENTHInternet: [email protected]://rrdjazz.nist.gov

ORNLOak Ridge National Laboratory Neutron ScatteringFacilities, P.O. Box 2008, Oak Ridge TN 37831-6393 USAGeorge D. Wignall, Small Angle Scattering GroupLeader; tel: +1 423 574 5237 fax: +1 423 574 6268E-mail: [email protected]://neutrons.ornl.gov

PSIPaul Scherrer InstitutWurenlingen und VillingenCH-5232 Villingen PSItel: +41 56 992111 fax: +41 56 982327

RISØEC-Large Facility Programme, Physics Department, RisøNational Lab.P.O. Box 49, DK-4000 Roskilde, DenmarkK. Mortenses; tel: +45 4237 1212 fax: +45 42370115E-mail: [email protected] or [email protected] in SwedenE-mail: [email protected]

NOTIZIARIO Neutroni e Luce di Sincrotrone - Issue 5 n.1, 2000

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Transcript of NOTIZIARIO Neutroni e Luce di Sincrotrone - Issue 5 n.1, 2000