NOTIZIARIO Vol 12n1 2007people.fisica.uniroma2.it/~notiziario/2007/pdf/vol12-n1... · 2007. 2. 28. · the Aghlabids Arabs from Sicily by the Duchy of Naples. It was finally abandoned

Cover photo:CAD drawing of BEARexperimental room

published by CNR in collaborationwith the Faculty of Sciences and thePhysics Department of the Universityof Rome “Tor Vergata”.

Vol. 12 n. 1 Gennaio 2007Autorizzazione del Tribunale diRoma n. 124/96 del 22-03-96

EDITOR:

C. Andreani

EXECUTIVE EDITORS:

M. Apice, P. Bosi, D. Catena,P. Giugni

EDITORIAL OFFICE:

L. Avaldi, F. Bruni, S. Imberti,G. Paolucci, R. Triolo, M. Zoppi

EDITORIAL SERVICE AND ADVERTISINGFOR EUROPE AND USA:

P. Casella

CORRESPONDENTS AND FACILITIES:

J. Bellingham (NMI3)M. Bertolo (I3-IA-SFS)A.E. Ekkebus (SNS)

ON LINE VERSION:

V. Buttaro

CONTRIBUTORS TO THIS ISSUE:

M. Capellas EspunyG. Cicognani

GRAPHIC AND PRINTING:

om graficavia Fabrizio Luscino 7300174 RomaFinito di stamparenel mese di Gennaio 2007

PREVIOUS ISSUES ANDEDITORIAL INFORMATION:

Pina CasellaUniversità degli Studidi Roma “Tor Vergata”Tel: +39 06 72594560E-mail: [email protected]

Vol. 12 n. 1 January 2007

NOTIZIARIONeutroni e Luce di Sincrotrone

S U M M A R Y

Rivista delConsiglio Nazionaledelle Ricerche

EDITORIAL NEWSWell Deserved Prize for Jack Carpenter............................ 2I. Anderson

SCIENTIFIC REVIEWSUsing Neutrons to Track Ancient PotteryFiring Technology...................................................................... 3A. Botti, A. Sodo, M.A. Ricci

BEAR: a Bending Magnet for Emission Absorptionand Reflectivity .......................................................................... 8S. Nannarone, A. Giglia, N. Mahne, A. De Luisa, B. Doyle,F. Borgatti, M. Pedio, L. Pasquali, G. Naletto, M.G. Pelizzo,G. Tondello

MUON & NEUTRON & SYNCHROTRON RADIATION NEWS

News from ESRF ..................................................................... 20

News from ILL ........................................................................ 20

News from LCLS..................................................................... 24

News from NCXT ................................................................... 25

News from NMI3 .................................................................... 25

News from SNS........................................................................ 32

SCHOOL AND MEETING REPORTS .................................................. 34

CALENDAR ............................................................................................. 40

CALL FOR PROPOSAL ........................................................................ 42

FACILITIES .............................................................................................. 43

NOTIZIARIONeutroni e Luce di Sincrotrone

www.cnr.it/neutronielucedisincrotrone

EDITORIAL

2

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE • Vol. 12 n. 1 January 2007

John Carpenter, better known as Jack to his friends and

colleagues, received the 2006 Clifford G. Shull Prize from

the Neutron Scattering Society of America for his

groundbreaking work developing neutron sources and

instrumentation. The award was presented during the

American Conference on Neutron Scattering, June 18-

22, held in St. Charles, Illinois.

Jack, technical director at Argonne National Laboratory’s

Intense Pulsed Neutron Source, is receiving the award

«for seminal contributions to the development of neu-

tron sources and instrumentation that have had world-

wide impact on neutron scattering across a broad range

of scientific disciplines, culminating in the optimized de-

sign of the Spallation Neutron Source (SNS) at Oak

Ridge». The Clifford G. Shull Prize in Neutron Science is

named in honor of Clifford G. Schull, who shared the

Nobel Prize in physics in 1994 with Bertram Brockhouse

for pioneering developments in neutron science.

Jack, fondly known as the father of the modern Spalla-

tion Neutron Source, played a pivotal role in developing

pulsed neutron sources across the globe, including the

founding of IPNS. He pioneered exploitation of the in-

herent efficiency of the spallation process for producing

neutrons, together with the advantages of pulsed opera-

tion and time-of-flight measurements to study structure

and dynamics of materials. His patented design for the

moderator-reflector combination is at the heart of mod-

ern pulsed neutron sources. Since the IPNS was complet-

ed in 1981, Jack’s competence and skills have been called

on by facilities all over the world for advice on the de-

velopment of spallation sources including the KEK in

Japan, ISIS in the United Kingdom, the Lujan Center at

Los Alamos National Laboratory, Austron in Austria,

J-PARC in Japan, and ESS in Europe.

He was heavily involved in the world’s brightest pulsed

neutron source, the Spallation Neutron Source at Oak

Ridge National Laboratory which produced first neu-

trons in April of this year. He is already working on the

design of the next target station for SNS! Jack’s contribu-

tions to developing pulsed-source instrumentation and

coupling neutron source performance and instrument

design have expanded the use of pulsed neutron sources

to a broad range of scientific endeavors.

Despite his formidable reputation, Jack is known to his

friends and colleagues as a gentleman and a modest,

unassuming man.

Congratulations Jack!

Ian Anderson

Spallation Neutron SourceOak Ridge National Laboratory

Well Deserved Prize for Jack Carpenter

Carla Andreani and John Carpenter, during the Progress in Electron VoltNeutron Spectroscopy Workshop, held at the SNS, ORNL, October 2006.

FOR INFORMATION ON:Conference Announcements and Advertisingfor Europe and US, rates and inserts can befound at:

www.cnr.it/neutronielucedisincrotrone

Pina CasellaTel. +39 06 72594117E-mail: [email protected]

SCIENTIFIC REVIEWS

3

Vol. 12 n. 1 January 2007 • NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

Pottery finds are challenging systems; because they com-bine the physical complexity which originates from thecoexistence of an amorphous phase and a crystallinephase in the same sample, with the charming richness ofthe historical information delivered if properly interro-gated. Recent [1] [2] [3] and less recent [4] probing meth-ods have enriched the classical approach of the archaeol-ogists. The archaeometric investigation of the finds cangive access to a quite diverse number of physical-chemi-cal information, including the composition in terms ofelements [5] and minerals [1] [6], the structural proper-ties on the mesoscopic scale [2] up to the macroscopic in-homogeneities [7] [8] [9].The mesoscopic structure investigated through small an-gle neutron scattering (SANS) gives information aboutthe size and surface characteristics of the aggregates ofminerals. These parameters are sensitive to the firingtechnology used in the production process. In the fol-lowing we will show the correlation of these parameterswith the archaeological age of the finds from the excava-tion sites of Miseno an Cuma, and suggest inferences onthe technological choices made over the centuries.The interpretation of the SANS data is also based the si-multaneous knowledge of the mineral phase content ofthe sherds, as probed by Time of Flight Neutron Diffrac-tion (TOF-ND) measurements. During the Roman Age,the harbour of Miseno was the biggest military harbour

of the Mediterranean. After its conversion into a com-mercial harbour, it kept its activity until it was ceded tothe Aghlabids Arabs from Sicily by the Duchy of Naples.It was finally abandoned in the second half of the 9thcentury AD. The early production of ceramics in Misenois characterized by a careful manufacture and a selectivechoice of the shape of the pottery mainly designed forcarriage of foodstuffs [10,11]. This typology tends to dis-appear during the 8th century AD, while other typolo-gies of products made in Miseno continue to exist withcontinuity until the 9th century AD and are known as“broad band ceramic”, after their decoration made byrags or paint brush.The stylistic evaluation suggests a new employment andownership of the facilities, possibly associated to a tech-nological evolution: this is one of the issues that we wantto tackle. It has to be stressed that the samples examinedhere have been found in the same site, called ‘‘LocalitàCudemo’’, where two kilns have been discovered. Thetwo kilns were never operative at the same time, never-theless, the finds belong to the same typology.The second kiln was indeed constructed on top of thefirst one after its voluntary burial. In the area, there is noevidence of other facilities after the 9th century AD. To-gether with Miseno there were other important centres inthe Phlegrean area: Cuma, Pozzuoli and Ischia. In theseplaces production indicators have been found, such as

Using Neutrons to Track Ancient PotteryFiring TechnologyA. Botti, A. Sodo, M.A. Ricci

Dipartimento di Fisica “E. Amaldi”, Università degli Studi di Roma TRE, Via della Vasca Navale 84, 00146 Roma, Italy

s.n. Century Type Technique d Rg s.n. Century Type Technique d RgCumaC1 8th-11th comm. SANS 3.28 281 C8 7th-8th comm. ND-SANS 3.46 435C2 7th-8th comm. ND C11 7th-8th comm. SANS 3.70 418C3 7th-8th comm. ND-SANS 3.53 441 C12 6th-8th amph. ND-SANS 3.43 418C4 8th-11th comm. SANS 3.34 551 C15 6th-8th amph. ND-SANS 3.55 370C5 7th-8th comm. ND-SANS 3.54 404 C17 6th-8th amph. ND-SANS 3.45 422MisenoM3 6th-8th amph. ND-SANS 3.75 405 M10 7th-8th comm. ND-SANS 3.34 515M4 6th-8th amph. ND-SANS 3.67 350 M11 11th-13th comm. SANS 3.25 289M6 6th-8th amph. ND-SANS 3.77 376 M12 11th-13th comm. ND-SANS 3.52 523M7 7th-8th comm ND-SANS 3.45 378 M8 7th-8th comm ND-SANS 3.58 481

Table 1: List of the samples from Cuma and Miseno. In the table are reported the dating given by the archaeologists, the typology of use and the diffrac-tion technique used. Rg [Å] and d are radius of gyration and the fractal dimension of aggregates/voids, respectively. Error bars on d and Rg values areof the order of 1% and 10%, respectively.

SCIENTIFIC REVIEWS

4


kiln rejects, although no kiln itself has ever been local-ized. We have focused our attention on the finds fromCuma which present similar artistic features to thosefrom Miseno. The underlying question is whether theyalso present comparable microscopic characteristics.The archaeological samples are listed in Table 1.They belong to the ceramic production developed in the

south of Italy during the 6th-12th centuries discovered inMiseno (Mn samples) and Cuma (Cn samples).Three different typologies may be distinguished: trans-port amphorae, common ‘‘broad band ceramic’’ and twofragments of common ceramic from the 12th century ADfrom the area of Miseno; the latter samples have indeedbeen dated by the archaeologists after local productionhad ceased [10,11].In the Miseno area there are no clay deposit. In the sametable are reported the diffraction techniques that havebeen used and the dating ranges given by the archaeolo-gists. Small angle neutron scattering measurements havebeen carried out on KWS1 diffractometer, which was op-erative till May 2006 at DIDO reactor of Forschungszen-trum Jülich. Time of flight neutron diffraction experi-ment were performed on ROTAX diffractometer, in-stalled at pulsed neutron source ISIS of Rutherford Ap-pleton Laboratories.The experimental procedure is absolutely non destruc-tive and the samples have been exposed to the beamwithout any specific preparation.A diffraction pattern in the complete Q range exploredby both instruments is shown in fig. 1 as an example.Its best fit according to the Beaucage model [12], con-cerning the SANS part, and by Rietveld analysis [13],for the TOF-ND range, is represented with a red line.

Analysis of the SANS dataThe radius of gyration Rg and the fractal dimension d, asobtained from the fitting procedure, are reported inTable 1.The experimental determination of Rg suffers the biasintroduced by possible multiple scattering effects. Onthe contrary, the most reliable parameter is the fractal di-

mension of the voids/clusters, or equivalently the sloped of the high Q tail. The behaviour of this parameterwith respect to the age of the samples is depicted in fig.2.The abscissas have been calculated as the average valueof the archaeological dating.The samples of Cuma and Miseno share a similar behav-iour: d decreases from higher values for the older sam-ples to lower values for the more recent ones.This can be considered as the history of d: In principle,this history could have no regularity, in the present caseon the contrary it tells us that the more recent ceramicproductions have mesoscopic structures with a roughersurface with respect to the older ones.Using the information coming from the study of refer-ence samples, prepared with different maximum firingtemperature, heating rate and composition, it is possi-ble to state that higher maximum firing temperaturescorresponds to higher values of d [3]: that the smooth-ness of the aggregates surface increases with the firingtemperature.Moreover the dependence of d from the temperature islinear, with a slope that is composition independent. [3]This implies that the maximum firing temperature of thepottery find of Cuma and Miseno has been lowered intime. SANS analysis cannot, however, quantify thechange in maximum firing temperature, when the mi-

Figure 1. Measured (black line) and fitted (red line) SANS and TOF-NDintensity (enlarged in the inset) for M6 sample.

Figure 2: History of the fractal exponent d for samples coming fromMiseno (blue symbols) and Cuma (red symbols). The data relative to the12th century have been reported with a different symbol (triangles), sincethey have been produced at a different kiln.

SCIENTIFIC REVIEWS

5


croscopic composition is unknown. The latter informa-tion can be obtained complementing SANS results withmineralogical analysis. [3]In order to justify the differences between the data forsamples M11 and M12, we remind that Miseno kilnceased to produce pottery in the 9th century.This means the 12th century pottery sherds from Misenoarea were likely fired in a different kiln (or kilns) thanthe earlier Miseno samples.

Analysis of the ROTAX dataThe Rietveld analysis included in the model the follow-ing phases: quartz [14], calcite [15], dolomite [16], or-thoclase [17], bytownite [18], muscovite [19], haematite[20] and spinel [21]. The fitted parameters are: phasefractions; d-spacing zero shift; one common Debye-Waller factor for all the minerals except for muscovitewhich was kept constant (u=0.8 Å2) and the lattice pa-rameters for quartz. Once the phase fraction of mus-covite has been removed from the composition, the re-maining phases, compiled in Table 2, have been nor-malized to one. A better comprehension of the clustering and groupingof the samples can be achieved calculating their distancewith respect to a ‘‘mean sample’’, where the weight frac-tion of a phase in the ‘‘mean sample’’ is equal to the av-erage of all the measured weight fractions of that phasein all the sample selected for comparison.In Appendix A the analytical definitions of distance and“mean sample” are described.

In fig. 3 we show the distance plot for Cuma andMiseno samples. They gather in two groups with a con-sistent overlapping and different spread. The samplesof Miseno have been found close to the kiln where theywere produced and this could explain why they grouptogether around -2. As already mentioned, in Misenothere is no clay deposit, so that raw materials must

s.n. Quartz Orthoclase Bytownite q/m Hematite Calcite Dolomite SpinelCumaC2 0.46 0.17 0.31 0.80 0.00 0.06 0.00 0.00C3 0.38 0.16 0.39 0.74 0.01 0.05 0.01 0.00C5 0.38 0.18 0.33 1.16 0.01 0.10 0.00 0.00C8 0.60 0.22 0.00 1.16 0.00 ,0.18 0.00 0.00C12 0.29 0.21 0.39 0.76 0.00 0.10 0.01 0.00C15 0.39 0.16 0.34 0.85 0.01 0.09 0.01 0.00C17 0.44 0.19 0.22 1.85 0.03 0.03 0.02 0.07MisenoM3 0.38 0.21 0.39 1.00 0.02 0.00 0.00 0.00M4 0.39 0.21 0.39 0.72 0.01 0.00 0.00 0.00M6 0.53 0.13 0.21 1.05 0.01 0.12 0.00 0.00M7 0.61 0.14 0.24 1.01 0.01 0.00 0.00 0.00M8 0.43 0.21 0.35 0.50 0.01 0.00 0.00 0.00M10 0.51 0.20 0.20 1.21 0.01 0.08 0.00 0.00M12 0.39 0.23 0.35 1.13 0.02 0.01 0.00 0.00

Table 2: Phase fractions relative abundance for the Cuma and Miseno samples, once the muscovite phase fraction has been removed. The q/m columnrepresents the ratio of the phase fraction of quartz over that one of muscovite.

Figure 3: Distance plot for samples from Miseno (blue bars) and Cuma(red bars).

SCIENTIFIC REVIEWS

6


have been transported from somewhere else. The dataindicate that the source of the raw clay was keptthroughout the years.The homogeneity of the material in Miseno is confirmedalso by mineralogical and petrographic analysis. On thecontrary, the finds from Cuma have a broader distribu-tion in terms of the distance parameter, i.e. the miner-alogical composition. This suggests that they were pro-duced elsewhere and brought to Cuma (where no kilnhas been found so far), or on the contrary, that the rawmaterials have been imported from more than one place. Following the same procedure of Appendix A, a similarcomparison can be done including samples with knowncomposition and firing conditions. If ancient and refer-ence sherds have close composition, then it is possible touse the d vs T plot of the reference samples as calibrationcurve for the medieval sherds. [3] When this procedure is applied to the finds of Misenoand Cuma, the results of fig. 1 suggests that the maxi-mum firing temperature has been reduced on averagefrom about 900-1000 °C to about 700-800 °C over the peri-od ranging from the 7th century to the 12th century AD.This inference is confirmed by the small amount of cal-cite in the composition of almost all the investigatedsamples [22].The proximity of the two communities of Cuma andMiseno could be the reason for a similar d history, eitherdue to an exchange of goods or due to a technologicalosmosis. Samples from the 12th century deserve a cau-tious consideration, since they cannot belong to the samekiln of Miseno as the others, and because of the smallnumber of experimental determinations; nevertheless,the results on these samples suggest that they have beenproduced in the same region, with similar technology.

Appendix AThe result of the Rietveld analysis is an array of val-ues Aj=[ph1,j;ph2,j;.;phm,j], where j=1...N labels the sam-ple and m=1...kj the mineral phases, which describesboth qualitatively and quantitatively the mineralphase content of each sample. It is then assumed thatsamples manufactured from the same clay, with thesame firing history have the same content in terms ofmineral phases, while different firing histories maydetermine the loss of a particular phase and/or theappearance of a new component.At this stage it may be useful to gather the samples ingroups according to their distance with respect to a‘‘mean sample’’. The latter is defined starting from thearrays of all the N measured samples and is defined tocontain n phases: the mean sample exhibits all the (n≥k)phases which appear at least in one of the real samples.The weight fraction of a phase in the ‘‘mean sample’’ is

equal to the average of all the measured weight fractionsof that phase:

Obviously, some of the n phases which are present in thefictitious ‘‘mean sample’’ may be absent in a real sample.In this case, the weight fraction for the absent n-k phasesin the real sample are set to zero:

The distance of the j-th sample from the ‘‘average’’ isthen defined as:

δ j assumes both positive and negative values, de-pending on the balance between the concentrationsof the different phases.Possible compensation effects arising from positive andnegative terms can be monitored looking at both the to-tal distance and the distance of the individual phases(these comparisons have been done but the correspond-ing plots are not shown in the paper).In the last equation each phase has almost the sameweight, so that a minority phase also contributes to theunambiguous cataloguing of the samples.

AcknowledgmentThe authors would like to acknowledge the ‘‘Soprainten-denza Archeologica di Napoli e Caserta’’, for kindly pro-viding the archaeological samples.These experiments on ROTAX have been performedwithin the Agreement No. 01/901 between CCLRC andCNR, concerning collaboration in scientific research atthe spallation neutron source ISIS and with partial finan-cial support of CNR.

References1. W. Kockelmann A. Kirfel E. Hähnel. Journal of Archaeological Science,

28 213 (2001).2. T. J. Wess, M. Drakopoulos, A. Snigirev, J. Wouters, O. Paris, P. Fratzl,

M. Collins, J. Hiller, K. Nilsen. Archaeometry, 43 117 (2001).

SCIENTIFIC REVIEWS

7


3. A. Botti, M. A. Ricci, G. De Rossi, W. Kockelmann, A. Sodo. Journal ofArchaeological Science 33 307 (2006).

4. A. Castellano, M. Martini, E. Sibilia, Elementi di archeometria, Egea,Milano 2002.

5. J. W. Cogswell, H. Neff, M. D. Glacock. Journal of Archaeological Sci-ence, 23 283 (1996); O. S. Rye et al. Archaeometry, 24 59 (1982); P. M.Day, E. Kiriatzi, A. Tsolakidou, V. Kilikoglou. Journal of ArchaeologicalScience, 26 1025 (1999).

6. S. R Simms, J. R. Bright, A. Ugan. Journal of Archaeological Science, 24779 (1997); I. Sondi, D. Slovenec. Archaeometry, 45 251 (2003).

7. S. C. Jordan, C. Schrire, D. Miller. Journal of Archaeological Science, 261327 (1999).

8. M. F. Ownby, C. L. Ownby, E. J. Miksa. Journal of ArchaeologicalScience, 31 31 (2004); R. B. Mason, L. Golombek. Journal of Archaeologi-cal Science, 30 251 (2004).

9. J. Buxeda I Garrigós, R. E. Jones, V. Kilikoglou, S. T. Levi, Y. Maniatis,J. Mitchell, L. Vagnetti, K. A. Wardle, S. Andreou. Archaeometry, 45263 (2003); J. Buxeda I Garrigós, M. A. Cau Ontiveros, V. Kilikoglou.Archaeometry 45 1 (2003); M. Bertelle, S. Calogero, G. Leotta, L.Stievano, R. Salerno, R. Segnan. Journal of Archaeological Science 28 197(2001); A. Pierret, C. J. Moran, L.-M. Bresson. Journal of ArchaeologicalScience 23 419 (1996).

10. G. De Rossi, L’Africa romana XIV, Sassari 2000, Carocci Ed., Roma,2002, pp. 835-846.

11. G. De Rossi, Proceedings of: La ceramica altomedievale in Italia. VCongresso di Archeologia Medievale (CNR, Roma 26-27 November2001), All‘Insegna del Giglio, Firenze, 2004.

12. G. Beaucage, Journal of Applied Crystallography 28 717 (1995).13. H.M. Rietveld, Journal of Applied Crystallography 2 65 (1969).14. J.D. Jorgensen, Journal of Applied Physiology 49 5473 (1978).15. H. Chessin, W.C. Hamilton, B. Post, Acta Crystallographica 18 689

(1965).16. P.L. Althoff, American Mineralogist 62 772 (1977).17. E. Prince, G. Donnay, R.F. Martin, American Mineralogist 58 500

(1973).18. G. Chiari, P. Benna, E. Bruno, Zeitschrift fuer Kristallographie 169

35(1984).19. M. Catti, G. Ferraris, S. Hull, A. Pavese, European Journal of Mineral-

ogy 6 171 (1994).20. R.L. Blake, R.E. Hessevick, T. Zoltai, L.W. Finger, American Mineralo-

gist 51 123 (1966).21. N.G. Zorina, S.S. Kvitka, Kristallografiya 13 703 (1968).22. J. Buxeda, I. Garrigós, H. Mommsen, A. Tsolakidou, Archaeometry 44

187 (2002).

SCIENTIFIC REVIEWS

8


AbstractThe BEAR (Bending Magnet for Absorption Emissionand Reflectivity) apparatus is presented. The main partsof the apparatus including the transport optics and theexperimental end stations are essentially described. Anumber of scientific results are presented dealing withon going activity at BEAR. They include optical proper-ties of materials, studies of buried interfaces, diffuse in-terface scattering of light and the determination of elec-tronic structure and local geometry of a chemisorbedmolecule on a metal surface.

IntroductionThe BEAR (Bending magnet for emission, absorptionand reflectivity) apparatus [1] is operative at the Elettrastorage ring [2] located in the Science park area of Tri-este, Italy. BEAR is positioned at the 8.1 bending magnetexit of Elettra. The apparatus is conceived to exploit theexperimental possibilities provided by a photon beamof tunable energy with variable ellipticity and selectablehelicity (right circular polarization - RCP, left circularpolarization - LCP) in the study of the interplay of elec-tronic (magnetic included) and local structural proper-ties of solid materials, surfaces and interfaces in the visi-ble-soft X ray range. In fact a number of relevant aspectsare offered by this photon energy range including acomplete insight into the electronic structure giving ac-cess both to full and empty states of bulk [3], surfacesand interfaces [4], collective effects [5] and magneticproperties [6], joint density of states, local- atom selected

– atomic geometry, morphology [7] on a scale rangingfrom Å [8] to tens of nm and surface or interface rough-ness [9]. The BEAR apparatus delivers photons in the 3eV–1600 eV photon energy range. The experimental endstation is based on an ultra high vacuum (UHV) cham-ber which makes possible linear and circular dichroicreflectivity and absorption measurements, diffuse lightscattering, energy resolved visible luminescence, energyintegrated fluorescence and angle resolved photoemis-sion for valence band, core level and local structurestudies. A preparation chamber is connected in UHV tothe experimental chamber featuring surface and thinfilms deposition and preparation equipment.This paper is devoted to the presentation of the func-tioning principles and features of BEAR and of its per-formances as illustrated through a number of scientificcases selected from the theme currently under study bythis apparatus. The paper is organized as follows. InSec.1 the transport and beam handling optics is present-ed. In Sec.2 the experimental end station includingpreparation chamber and measurement chamber arepresented. Sec.3 is divided into a number of subsectionsdealing with, in order, the determination of the opticalconstants of materials, the study of buried interfaces by

BEAR: a Bending Magnetfor Emission Absorption and ReflectivityS. Nannarone1, A. Giglia2, N. Mahne2, A. De Luisa2, B. Doyle2, F. Borgatti2, M. Pedio2, L. Pasquali3,G. Naletto4, M.G. Pelizzo4, G. Tondello4

1TASC INFM-CNR SS 14 km 163,5 Trieste - Italy and Dip.

di Ingegneria dei materiali ed amb., Università di Modena eReggio Emilia; 2TASC INFM-CNR; 3Dip. di Ingegneria deimateriali ed amb., Università di Modena e Reggio Emilia;4LUXOR INFM-CNR

Fig. 1. Optical source of BEAR: about 4 mρ of the 5500 mm circularradius of the 8.1 bending magnet of Elettra are collected (3.3 mρ × 3.6 mρ– vertical × horizontal) by the first optics. The intensity distribution as afunction of the angle Ψ with respect to the orbit plane is shown for threephoton energies. Light emitted with Ψ > 0 ( Ψ < 0) is right (left) circularlypolarized. The axes of the laboratory frame of reference are shown.

SCIENTIFIC REVIEWS

9


combining standing field created in periodic stratifiedstructures (multilayers) and photoemission, the study ofinterfaces by diffuse scattering and the determination ofelectronic structure and local geometry of chemisorbedmolecules on metals.

1. Transport and handling opticsThe optics of BEAR accepts, as shown in Fig. 1, 3.6 mradin horizontal and 3.3 mrad in vertical of the light emittedby the arc of electron trajectory of the 8.1 bending mag-net (radius 5.5 m) of Elettra. Assuming the laboratoryframe of reference as indicated in Fig.1 (x axis along thebeam direction, y axis horizontal and z vertical axis) theelectromagnetic field emitted by the arc of trajectory atfrequency w and along a direction forming an angle Ψwith the orbit plane can be written as

(1)

According with the expressions for the radiation emittedby an accelerated charged particle [10] the y and z com-ponents of the field are given by

(2)

where + → Ψ>0 and – → Ψ0 (Ψ0 and left circular polarized emis-sion for Ψ

SCIENTIFIC REVIEWS

10


produce a beam of positive or negative helicity; indeeda variable ellipticity is obtained – see below – bychanging the angular acceptance in Ψ, which affects theE0y component as shown by the first of eq.’s (2). Thecorresponding dependence of the total intensity isshown in Fig.1 for three photon energies [11].A schematic drawing of the beamline[12] is shown in Fig.2. The optics do not have an entrance slit. The beam po-sition is continuously monitored by a four quadrantdiode device (BPM), the output reading can be used tocorrect the eventual drifts in energy of delivered photons[13]. Downstream from the source the ellipticity/helicityselector follows, its functioning is based on a slit of vari-able aperture (∆Ψ) and of variable vertical position. Thefirst optical element is a parabolic mirror (P1) working at2.5° of grazing incidence defocusing the source into aparallel beam (source in the focal point at 12000 mm).The optics works in sagittal focusing to reduce the ef-fects of slope errors in the dispersing plane (by a factorequal to sin(2.5°) = 4.4x10-2 in this specific case). The dis-persing/mochromatising section works in parallel light.It features two plane gratings (1200 l/mm and 1800 l/mm)working in the plane-mirror-plane-grating configura-tion (Naletto-Tondello) [14] and a third grating (1200l/mm) working in a normal incidence configuration. Asecond parabolic mirror (P2) working at 2.5° of grazingangle focuses the dispersed light onto the exit slit(placed in the focal point at 2300 mm). The couple ofparabolic mirrors feature a 5.2 demagnification. Themonochromatic beam is eventually refocused at the tar-get position by an elliptical mirror working at 2.5° ofgrazing incidence.The refocusing optics feature 1:1 magnification. Themain characteristics of all the optical elements are listedin Table 1.A chamber containing selectable filters for high orderrejection and a gas cell for energy calibration and reso-lution measurement are placed in sequence between theexit slit and the refocusing mirror.The vertical and horizontal divergence selector (alterna-tively used as ellipticity/helicity selector when workingin the vertical plane) and the beam intensity monitor arelocated between the refocusing optics and the experi-mental chamber. The latter features W and Au meshes of90% and 65% transmission, respectively, working indrain current and LiF beam splitter working at 60° com-bined with a EUV photodiode.The electric field at the target E

→

T, in the laboratory framecan be written as

(3)

where ηT = ETz/ ETy (related to ellipticity, see for instanceref.[15]) and δT is the relative phase shift at the target.Both quantities depend on the setting of theellipticity/helicity selector as described above; small in-fluence on both ellipticity and phase shift can arise fromreflection on the optical elements, mainly in the region ofthe edges of major contaminants (e.g. C and O).Moreover the ellipticity results from an average of the zcomponent of the field on Ψ, depending on the settings

(slit opening and vertical position) of polarization selec-tor; the light dependence on Ψ of the incidence angle onthe optical elements, can introduce a weak Ψ depen-dence of δT which is averaged on the slit aperture.The photon flux at the target position is shown in Fig.3in the 3 eV – 1600 eV photon energy range with a spotwhose cross section is vertical slit (typically 30 µm) × 400µm (variable) and whose maximum divergence is 20 mρvertical × horizontal. The energy bandwidth as a function of photon energy isshown in Fig.4 at different vertical exit slit apertures forthe 1200 l/mm grating (slightly smaller bandwidths areobtained with the 1800 l/mm grating).Single element multilayer polarimetry [16] is used to de-termine and monitor the linear, PL, and circular, PC , po-larization ratios of the beam through the measurementof Stokes parameters (S0, S1, S2 and ⏐S3⏐) [17] accordingto the relations

; (4)

Typical values range in the 30 – 100 eV photon energyranges from 0.5 to 0.8 (0.8 to 0.5) for PL (C). A PC ≈ 0.7

Fig. 3. Photon flux at the sample position with: stored current 200 mA,beam energy 2.4 GeV, vertical slit aperture (dispersive plane) 50 µm,normal incidence grating (3-40 eV) and grazing incidence grating (40 –1600 eV).

SCIENTIFIC REVIEWS

11


was obtained from circular magnetic dichroism at the CoL23 edge (780 eV).

2. End stationThe experimental chamber [18] is shown in fig.5 andfig.6. The chamber is an UHV chamber (base pressure 1x 10-10 mbar). The apparatus features a high flexibility(together with high precision, repeatability and resolu-tion in positioning of sample and detectors) in the choiceof the scattering geometries both from the point of viewof incidence and detection geometries.The frames of reference of laboratory, ΩL, chamber, ΩC,manipulator, ΩM are indicated in fig.5 (b) (the sampleframe of reference, ΩS – not indicated - coincides with ΩMwhen the sample is aligned). The sample manipulatorfeatures six degrees of freedom resulting from the XYZtranslation stage, and the combination of the rotationΘM, the azimuthal rotation ΦM and the sample normalprecession correction.Once the sample is aligned (precession corrected and ΘMaxis intersecting the surface in the centre of rotation ofthe chamber) the ΘM rotation actuates the rotation matrix

(5)

while the ΨC rotation actuates the rotation matrix

(6)

The combination of the ΘM and ΨC settings permits thepositioning of the sample normal in any position in thelaboratory frame of reference; ΨC scans at fixed ΘM resultin sample normal to precess in the laboratory frame. Combining the two rotations the electric field E

→

T of eq.(3) appears in the sample frame of reference in the form

(7)

This expression shows that by a suitable choice of thecouple of angles ΘM and ΨC a given component of theimpinging electric field can be positioned in any direc-tion with respect to the sample normal.Signal detection includes, basically, light detection by

EUV-XUV photodiodes (typically IRD SXUV-100 siliconphotodiodes), emitted electrons by electron energy ana-lyzer [19] (hemispherical, mean radius 66 mm, angularacceptance ± 2°, energy resolution ~ 1% pass energy inthe range 1-50 eV, equipped with 16 anodes for parallelacquisition) and sample drain current (femto-ammeter,Keithley). Helmholtz coils for magnetic field compensa-tion are provided.

The electron analyzer and four diodes are installed, asshown in Fig.s 5 (a) and (b), on the joint arm of the ex-perimental chamber featuring two mutually orthogonaland independent rotations actuated by an in-air go-niometer, ΘA, and by an in-vacuo ball bearing, ΦA. Thetwo rotations are represented by

(8)

Their combination allows to positioning a detector inany position in the frame of reference of the sample in-dependently from the values of ΘM and ΨC.In Table 2 the angular accuracy range of different rota-tions are reported. The diameter of the confusion sphereof the axes at the chamber center does not exceed 50 µm . Angular detector scans make possible, among others, an-gle resolved photoemission and θ-2 θ reflectivity scans.Optical absorption experiments can be performed both

Fig. 4. Energy bandwidth (experimental – dots; calculated full lines) as afunction of photon energy of BEAR in the 40 – 1400 eV energy range atdifferent vertical aperture of the exit slit.

SCIENTIFIC REVIEWS

12


in transmission or by measuring sample drain current orAuger or fluorescence yield. Diffuse light scattering ex-periments are feasible as well; possible modes includerocking scans and offset detector scans with typical an-gular resolutions in the scattered wave vector of the or-der of 10-3 nm-1. Additional detectors include diodes infixed position and energy resolved visible luminescence.Test spectra are shown in Fig.7 where the X-ray excitedluminescence from a BaF2 sample; Fig.7 (a) shows an ex-citation spectrum through the Ba M4,5 edges; and Fig.7(b) the spectral response with a fixed incident photonenergy of 130 eV.For the possibilities offered by luminescence see, for

example, [29] and [30] and referenes therein.Sample temperature in the measurement position canrange from ≈100 K to ≈ 500 K.The preparation chamber is shown in Fig.6. The samplemanipulator is shown and the ports where differentitems are installed are indicated. They include a cylin-drical mirror analyzer (CMA), evaporation section(evaporation flange and thickness monitor), ion gun(IG), low energy electron diffraction (LEED), load lockand transfer arm.The experimental chamber is shown rotated by an angleΨC = 45° around the beam axis. Sample temperature inpreparation chamber can range between 100 K and 1500 K.

Table 2. Linear and angular movements.

Frame or Axis Range Resolution

Analyser arm goniometer, primary rotation ΘA 360° 0.001°Analyser arm goniometer, secondary rotation ΦA 220° (± 110°) 0.01°Chamber rotation ΨC 100° 0.1°Manipulator arm goniometer ΘM 360° 0.001°Manipulator xM translation ± 5 mm 1 µmManipulator yM translation ± 5 mm 1 µmManipulator zM translation 20 mm 10 µmManipulator azimuth rotation ΦM 200° 0.1°Manipulator precession correction ΨP 3° 0.01°

Fig. 5. Experimental chamber: (a) CAD image: manipulator shaft, ΘM axis, alignment XYZ stage and goniometer with differentially pumped joints; ΘAgoniometer with differentially pumped joints and in-vacuo ΦA rotation; detector arm with electron analyzer and photo diodes; ΨC axis for chamber rota-tion around beam axis and differentially pumped joints and goniometers. (b) Conceptual of the experimental station, (mainly from the point of view ofrotations and translations of sample and detectors). Different frames of reference, associated to the different moving parts, are indicated. The shaft sup-porting the hemispherical electron analyser is also supporting photodiodes for reflectivity measurements. Light beam is directed along the xL axis.

SCIENTIFIC REVIEWS

13


3. Experiments

3.1 Optical constantsThe wide optical range, the continuous spectrum due tothe bending magnet source and the end station in UHVwith surface science facilities make BEAR a powerful ap-paratus for the determination of optical constants of ma-terials. Results related with the determination of the op-tical constants of Ce and Sc films are shown in Fig.8.Both materials are of particular interest in the design andconstruction of multilayer mirrors. Ce and Sc films wereprepared by evaporation on a substrate consisting of C

films of ~ 10 nm thickness deposited onto an electro-formed hexagonal micro-grid of Nickel. The experimental transmittances of Ce films of differentthicknesses evaporated in UHV onto an electron micro-scope nickel grid in the 5 eV – 1000 eV are reported inFig.8 (a) [20]. Experimental values of the real and imaginary part ofthe index of refraction of Sc films are shown in Fig.8 (b)and (c) [21] corresponding to the region of Sc M23 and ScL23, respectively. The extinction coefficient k(ω) was ob-tained by the Lambert law from transmission data at dif-ferent thicknesses; δ(ω) was obtained from k(ω) through

Fig. 6. BEAR preparation chamber: sample manipulator, cylindrical mirror analyzer (CMA), evaporation section (evaporation flange and thickness mon-itor), ion gun (IG), low energy electron diffraction (LEED), load lock, transfer arm. Experimental chamber is shown when rotated of an angle of 45°around the beam axis.

SCIENTIFIC REVIEWS

14


Fig. 7. X-ray excited luminescence from a test BaF2 sample: (a) excitationspectrum around the Ba M4,5 edges; (b) Spectral response at incidentphoton energy of 130 eV.

a Kramers-Kronig transformation. The δ(ω) and k(ω) val-ues obtained from data base of atomic scattering factors[22] are shown for comparison.

3.2 Multilayers and buried interfacesMultilayers are periodic stacks of layered materials wide-ly used as band pass filters in optical technology [23].The mirror reflectivity (Fig. 9 (a) and (b)) shows apeaked dependence through a mechanism totally analo-gous to the Bragg diffraction from a crystal.At Bragg peak a significant standing field is establishedinside the material with the periodicity of multilayerwhose peaks and valleys move through the interfaceswhile scanning in angle or in wavelength through theBragg condition. This fact results in a modulation of thelocalization of maxima and minima of the excitingfield, in particular at the interfaces inside the multilay-er an aspect which can be exploited in interface spec-troscopy [24].In Fig.9 the result of a photoemission study of the Ru-Siinterface, at fixed photon energy while scanning throughthe Bragg peak of a [Si41.2Å/Mo39.6Å]x40 multilayercapped with 15 Å of Ru, is summarized [25]. A typicalphotoemission spectrum in the region of Ru 3d excita-tion is shown together with the deconvolution into theinterface and bulk Ru components with the addition of asmall feature due to the emission from C 1s. The behav-ior in angle of the two Ru components is shown.

3.3 Interface diffuse scatteringBeside specular reflection, there is a contribution of dif-fuse scattering related to the roughness and the mor-phology of the interfaces [9].These processes are of particular relevance in the per-formance of optical devices including mirrors and mul-tilayers.The process is an elastic process whose kinematics is giv-en by K

→

S = K→

i + q→

z + q→

// where K→

i is the wave-vector ofthe incidence field, K

→

S the wave-vector of the diffusedone and q→ z and q

→

// are the normal and parallel compo-nent of the exchanged vector respectively. In this kind ofprocesses the interface roughness is commonly de-scribed by an autocorrelation function of the formH(⏐x - x’⏐,⏐y - y’⏐) = H(⏐R

→

⏐) = 2σ2[1-e-(R/ξ)]where R

→

≡ (x,y), σ the average roughness and ζ the auto-correlation length. In this framework the elastic scatter-ing crossection is given by

and appears as the Fourier transform in q→ // of a potentialbuilt in term of the autocorrelation function and of itsparameters σ and ζ.

SCIENTIFIC REVIEWS

15


Fig. 8. Optical constants of materials: (a) transmittance of Ce samples atdifferent thicknesses as a function of photon energy in the 5 eV-1000 eVrange [20]; refraction index n~ (ω) = 1-δ(ω)+ik(ω) of Sc, experimental δ(ω)and k(ω) in: (b) 20-60 eV range and (c) 200-600 eV range [21]. The valuesobtained from the data base of atomic scattering factors [22] are shownfor comparison.

Fig. 9. Reflectivity study of [Si41.2Å/Mo39.6Å ]x 40 multilayer capped with 15Å of Ru. Specular reflectivity in normal incidence (10°) (a) as a functionof the photon energy and (b) as a function of the grazing incidence angleat photon energy =838 eV; (c): Standing field analysis of Ru/Si buried ontop of the Si-Mo multilayer with a photon energy of 838 eV. A typicalphotoemission signal from Ru 3d is shown (see also text). The behavior ofthe areas of the Ru 3d components in Ru and in ruthenium silicides as afunction of grazing angle are shown [25].

SCIENTIFIC REVIEWS

16


The optical performance (peak reflectivity) of Mo-Simultilayers was contrasted with the construction proce-dures including ion assistance during growth and the in-terposition of a B4C buffer layer between Si and Mo lay-ers [26]. Ion assistance produces in both cases an in-crease of peak reflectivity ~ 5%. Diffuse scattering resultsare summarized in Fig.10.The inspection to the figure shows that ion assistance re-sults in a narrower scattering distribution around the

specular peak indicating an improvement of planarity ofthe interfaces.

3.4 Molecular thin filmsIn Fig. 11 the experimental results of a combined opticalabsorption study in the near UV region in the HOMO-LUMO interband transitions range and at the C K edge,for local structural studies, are reported for polystyrenethin films [27]. The films were prepared by spin coatingon fused quartz plates, with thickness from 50 nm(~2Rg) to 180 nm (~9Rg), where Rg is the unperturbedgyration ratio of the polymer. The UV spectra show cleardifferences with thicknesses attributed to different recip-rocal orientation of benzene ring dimers. Pentacene (Pn, brute formula C22H14) is a π-conjugatedacene molecule formed by five π-conjugated C rings.When deposited on solid substrates Pn can form a“standing up” layer or a “lying down” configuration.This latter geometry can hinder the formation of orderedlayers, a fact that can have technological relevance in thefield of organic electronics. Photoemission valence bandmeasurements and XAS spectra at C K-edge were col-lected for Pn thickness ranging from submonolayer tomultilayer [28]. The evolution of the XAS and VB pho-toemission spectra as a function of the Pn coverage areshown in Fig. 12.The dominant features were assigned to π resonances re-lated to the various molecular occupied (3b2g, 2au and3b3g) and unoccupied (labeled LUMO and LUMO+1)states. The XAS spectra were measured as a function ofthe electric field at the surface.For all the coverages the intensity of the π resonancesshow a strong dichroism. The evolution of the XAS for 1ML when the sample normal is made to precess (scan inΨC at fixed incidence angle) is shown in Fig. 12. A quan-titative analysis (see Fig. 13), based on the assumptionthat the optical absorption is proportional to ⏐p→.E

→

⏐2 andby using the parameters of the impinging elliptical elec-tromagnetic field, provides the average tilt angle of themolecule with respect to surface of 10°± 5°.

ConclusionsThe BEAR (Bending Magnet for Absorption Emissionand Reflectivity) was presented.The main parts of the apparatus including the transportoptics and the experimental end stations were essentiallydescribed. A number of scientific results were presenteddealing with at present on going activity at BEAR. Theyincluded optical properties of materials, studies ofburied interfaces, diffuse interface scattering of light andthe determination of electronic structure and local geom-etry of polymers films and chemisorbed molecule on ametal surface.

Fig. 10. Diffuse scattering as a function of q// wave vector for[Mo28Å/Si12Å]x40 and [Mo/ B4C /Si/B4C/Mo] x40. Full dots ion assistedgrowth. Results were obtained in an ω−scan around the specular direction(q// = 0) at 30° with a photon energy 94.7 eV (13.1 nm). After ref. [26].

SCIENTIFIC REVIEWS

17


Fig. 11. Optical absorption of Polystyrine films: (A) optical absorption in the 4-9 eV photon energy range, upper panel film thickness of 180 nm ( ~9Rg),lower panel 50nm (~2Rg) (B) optical absorption at C K-edge of 2Rg thick polystyrene at grazing incidence 20° at different direction of the incident elec-tric field along a precession scan. From ref. [27].

SCIENTIFIC REVIEWS

18


Fig.13 X-ray absorption spectrum at the CK edge of 1 monolayer of pentacene on Ag(111): (a) absorption spectra versus sample normal precession, fordetails see inset and text; (b) area of the first feature of resonance as a function of the molecule tilt angle (see also text) [28].

Fig. 12 Pentacene on Ag(111) as a function of coverage (for details see also text): (a) X-ray absorption at the CK edge; (b) valence band photoemissionwith a photon energy of 60 eV [28]

SCIENTIFIC REVIEWS

19


AcknowledgmentsProject funded by INFM and operated by TASC INFM-CNR (http://www.tasc.infm.it/research/bear/ ) At theapparatus is operative as public facility at Elettra(http://www.elettra.trieste.it/UserOffice). Public accessstarted in January 2003,S. D’Addato, S. Valeri, M. Sacchi for their contribution inthe early conception of the project. P. Finetti, G. Selvaggi,G. Gazzadi for their help in different stages of construc-tion and commissioning of the apparatus.The collaboration with Sincrotrone Trieste spa is ac-knowledged.The technical and administrative services of TASC areacknowledged recalling the invaluable assistance of me-chanical service (P. Bertoch, A. Gruden, P.F. Salvador). G. Paolicelli and G. Stefani are acknowledged for theirassistance in design, construction and commissioning ofthe electron analyzer.

References1. http://www.tasc.infm.it/research/bear/;2. http:// www.elettra.trieste.it;3. See for example “Photoemission in Solids” Vol II Eds. L. Ley and M.

Cardona Springer Verlag Berlin (1979).4. N.V.Smith, F. J. Himpsel “Photoelectron Spectroscopy” in “Handbook

on Synchrotron Radiation” Vol. 1b eds. E.-E. Koch, North Holland,NewYork (1983);

5. M. Sunjic and D. Sokcevic, Solid State Commun. 15(1974)165;6. J. Stöhr Journal of Electron Spectroscopy and Related Phenomena 75 (1995)

253;W. L. O’Brien and B. P. Tonner, Phys. Rev. B 50, 12672-12681(1994); M. Altarelli Phys. Rev. B 47, 597-598 (1993) C. W. M. Castletonand M. Altarelli, Phys. Rev. B 62, 1033-1038 (2000)

7. B.L. Henke and J. W. DuMond, J.Appl.Physics 26 (1955) 903;8. For absorption see J. Stoehr “NEXAFS spectroscopy” Springer Verlag

Berlin (1992); for Photoelectron diffraction see D.P. Woodruff et al.,Rep. Prog. Phys. 57 1029-1080(1994); C.S. Fadley, The Study of Sur-face Structures by Photoelectron Diffraction and Auger Electron Dif-fraction Synchrotron Radiation Research: Advances in Surface andInterface Science, Vol. 1: Techniques, editor R. Z. Bachrach (Plenum,New York, 1992)

9. S. K. Sinha, E. B. Sirota, S. Garoff, H. B. Stanley, Phys. Rev. B, 2297-2312 (1988); D. G. Stearns, J. Appl. Phys. 65 (1989) 491;

10. J. Schwinger , Phys Rev 175 (1949) 1912; see for example A. Hofmann“Synchrotron Radiation” ed. By G. R. Greaves and I. H. Munro, Pro-ceedings of the thirtieth Scottish University Summer School inPhysics Aberdeen 1985;

11. The site http://www-cxro.lbl.gov/optical_constants/bend2.htmlprovides numerical values of distribution curves;

12. S. Nannarone et al. AIP Conference Proceedings 705 (2004) 450;13. A. Giglia et al. Rev. Sci Instr. 76 (2005) 063111;14. G. Naletto, G. Tondello Pure Applied Optics 1, (1992) 357;15. R. D. Guenther “Modern Optics” J. Wiley and Sons 1990, p. 38;16. W. B. Westerveld, K. Becker, P. W. Zetner, J. J. Corr, J. W. McConkey,

Appl Optics 24 (1985) 2256; M.-G. Pelizzo, F. Frassetto, P. Nicolosi, A.Giglia, N. Mahne, S. Nannarone, Applied Optics 45, (2006) 1985;

17. Stokes parameters are given by

18. L. Pasquali, A. De Luisa, S. Nannarone AIP Conference Proceedings705 (2004) 1142;

19. G.Paolicelli et al. to be published;20. M. Fernández-Perea, J. A. Aznárez, J. I. Larruquert, J.A. Méndez, L.

Poletto, D. Garoli, A. M. Malvezzi, A. Giglia and S. Nannarone, Proc.SPIE Vol. 6317, 63170V (2006)

21. M.Fernandez-Perea, J.Larruquert, J.A.Arnarez, J.A.Mendez, L.Poletto,A.M.Malvezzi, A.Giglia, S.Nannarone, J.Opt.Soc.Am. A 23(2006)2880;

22. B.L.Henke et al. available at http://www.cxro.lbl.gov/optical_con-stants/

23. E. Spiller, Soft X-Ray Optics, Ed. SPIE, Bellingham, WA (1994);24. S.-H. Yang, B. S. Mun, N. Mannella, S.-K. Kim, J. B. Kortright, J. Un-

derwood, F. Salmassi, E. Arenholz, A. Young, Z. Hussain, M. A VanHove and C. S Fadley, J. Phys.: Condens. Matter 14 (2002);

25. Mahne et al to be published.26. A. Patelli, V. Rigato, G. Salmaso, F. Borgatto, S. Nannarone, LNL An-

nual Report 2004;27. S.Chattopadhyay, A.Datta, A.Das, A.Giglia, N.Mahne, S.Nannarone,

to be published;28. M. Pedio et al., submitted to Applied Surface Science;29. T.K. Sham et al., Phys. Rev. B 70, 0405313 (2004);30. I. Salish et al., Phys. Rev. B 69, 245401 (2004).

[Note of the Authors] - The scientific community of the Italian Surface Physics lost during the year 2006 MassimoSancrotti a friend of many of us, an excellent physicist and an enthusiastic teacher and organiser. This paper is devotedto his memory.

20


The ESRF Long-Term Strategy up-grade is an ambitious renewal pro-gramme that aims to ensure theleading scientific position of the fa-cility over the next two decades.«The upgrade is a very real chal-lenge for us, but is essential if theESRF is to continue to provide theEuropean scientific community withthe very best experimental tools»,says Professor Bill Stirling, DirectorGeneral of the ESRF. New and refur-bished beamlines are proposed toanswer new scientific needs, under-pinned by a programme to maintainand refurbish the accelerator com-plex which is at the heart of the ES-RF’s activities. The project includeshighly specialised nano-focus beam-lines, with even brighter hard X-raybeams, and the renewal of beamlinecomponents such as detectors, op-tics, sample environment and sam-ple positioning.The upgrade will involve the recon-struction of about one third of thebeamlines for significantly improvedperformance. Some will be extendedto about 120 meters to providenanometer focus capabilities.

In addition, the accelerator complexwill be upgraded, and science-dri-ven partnerships with both industryand academia will be developed, allunderpinned by an ambitious instru-ment development programme.This project is the result of threeyears of consultation and work be-tween the ESRF and the scientificuser community. This renewal pro-gramme will be submitted to theCouncil in 2007 and, if approved,would start in 2008.The down time for the facility wouldbe as short as possible in order tominimise disruption of the users’scientific programmes. The ESRF´s

upgrade is present in the first Euro-pean Roadmap for Research infra-structures.The document presents 35 largescale research infrastructure projects,identified as being of key impor-tance for the development of Euro-pean science and innovation.The ESFRI roadmap will allow acommon European approach to thedevelopment of such facilities, sup-port the definition of priorities andaid the pooling of the significant fi-nancial resources required for theirrealisation.

M. Capellas EspunyESRF Press Officer

MUON & NEUTRON &SYNCHROTRON RADIATION NEWS

News from ESRFThe ESRF’s Upgrade Programme

Figure 1. Artist’s impression of a section of the future extended and upgraded ESRF ExperimentalHall. This upgrade will enable longer beamlines to take advantage of the ESRF’s fine X-ray sourceproperties and allow specialised centres to be built around beamline clusters sharing scientificand/or technological expertise. Credits: ASSA.

News from ILLA direct Test of E = mc2

One of the most striking predictions ofEinstein’s theory of special relativity isprobably the best known formula in sci-ence: E = mc2. This report describesthe most precise direct test of thismass/energy relationship to date.Com-bining ultra-precise atomic mass andgamma-ray wavelength measurementsinvolving isotopes of silicon and sul-phur, we obtain two tests that separate-

ly confirm Einstein’s relationship andyield a combined result of 1–∆mc2/ E= (–1.4 ± 4.4) × 10–7.

A straightforward verification ofEinstein’s mass/energy equivalenceprinciple E = mc2 would be possibleby measuring the energy of annihila-tion radiation of two particles. How-ever, measurement of the 511 keV

annihilation radiation of the electronand positron is complicated by ini-tial kinetic energy, while accuratemeasurement of annihilation radia-tion of heavier particles is even moredifficult. An elegant way out is toconsider the mass and energy bal-ance in a nuclear reaction, which isinitiated by particles with a mini-mum of kinetic energy. Such a reac-

21


tion is realised when a nucleus withmass number A captures a neutron.In this case the mass of the resultingisotope, with mass number A+1,ought to differ from that of the origi-nal nucleus (plus unbound neutron)by the neutron binding energyEn(A+1). In most reactions all of theEnergy is emitted as gamma rays,the wavelength λι of which can beprecisely measured via Bragg dif-fraction. In this case Einstein’s equa-tion can be rewritten as

(MR(A)+MR(n)–MR(A+1))c2 =

= 1/u En(A+1) = 103NA hc Σ

1ëι ,

(1)

where the Avogadro constant NA re-lates a relative atomic mass MR (inunified atomic mass units u) to itsmass in kilograms m, h is the Planckconstant and c the speed of light. The summation in the right part ofequation (1) runs over all gammarays of a cascade connecting captureand ground state. The mass of theneutron can be eliminated fromequation (1) by introducing themasses of Hydrogen 1H and Deuteri-um 2D combined with the wave-length λD corresponding to the deu-terium binding energy.

(MR(A)+MR(2D)–MR(

1H)–MR(A+1)) == 103 NAh/c (Σ

1ëι –

1ëD)

(2)

The molar Planck constant isNAh = 3.990 312 716(27)·10

-10 J s(u/Kg), and has been independentlyconfirmed at the 5·10-8 level by di-verse experiments through its rela-tionship with the fine structure con-stant [1].The gamma-ray wavelengths havebeen measured in a collaboration ofscientists from the ILL and the Na-tional Institute of Standards andTechnology using the GAMS4 crys-tal spectrometer, which is positionedat the H6/H7 tangential beam tube[2] of the ILL. Gamma rays from aninpile target are diffracted by twonearly perfect flat Si crystals whoselattice spacing d has been carefully

determined. The diffraction anglesare measured with angle interferom-eters. These interferometers can becalibrated with respect to an ab-solute angle of 2π using a precisionoptical polygon. As the calibrationangle is much larger than the mea-sured Bragg angles, a very goodnon-linearity of the angle interfer-ometer is required. The energies ofgamma rays to be measured rangedfrom 0.8 to 5.5 MeV. Because the dif-fraction angle of a 5 MeV gamma rayby a low order reflection is less than0.1 degrees, our binding energy de-terminations were limited by ourability to measure the diffraction an-gles of the high-energy gamma raysbetter than 10-8 degrees. From the ex-periments we report values of

En(29Si)=hc/(0.146 318 275 (86)·10-12 m),

En(33S)=hc/(0.143 472 991 (54)·10-12 m)

and En(2D)=hc/(0.557 341 007 (98)·

10-12 m) [3].These numbers combine to yield rel-ative uncertainties of 5.1 10-7 (33S)and 8.0 · 10-7 (29Si) for the right-handside of equation (2). The mass differ-ence was determined at the Massa-chusetts Institute of Technology us-ing a new technique to directly com-pare the cyclotron frequencies of twodifferent ions simultaneously con-fined in a Penning trap [4]. Thisgreatly reduces many systematic andstatistical errors, particularly thosedue to magnetic field fluctuations.Two independent experiments with28,29Si and 32,33S were carried out. Dur-ing the measurements, the two ions


Figure 1. Illustration of the experimental concept to compare the mass and energy balance in a ther-mal neutron capture reaction. The atomic masses are measured using precision Penning Trap mea-surements at MIT (USA), while the energy is extracted by means of a diffraction measurement atthe GAMS spectrometers of the ILL.


22


A variable-temperature single-crystalLaue diffraction study on VIVALDI haslocated the gas absorption sites within ahydrogen-loaded metal-organic frame-work. Neutron Laue diffraction offersunique advantages in the characterisa-tion of such materials, which are possi-ble candidates for fuel storage in the au-tomotive industry.

In the first experiment of its kind, avariable-temperature (5-300K) sin-gle-crystal Laue diffraction studyon VIVALDI has been used to lo-cate the gas absorption sites withina hydrogen-loaded metal-organicframework. Low-temperature neutron Laue dif-fraction offers unique advantages in

the characterisation of these materi-als, providing information essentialto the development of this novelclass of framework compounds.One use of these compounds as gasstorage media, in conjunction withfuel cells, would be in the automo-tive industry.The technology already exists in the

are placed on a common circular or-bit (magnetron mode), on oppositesides of the centre of the trap andseparated by a distance of about 1mm. Correcting for the polarisationinduced shifts of the cyclotron fre-quencies we obtain ion mass ratios.Correcting further for the masses ofthe missing electron and the chemi-cal binding energies of the atom weobtain neutral mass ratios ofMR(

32S)+MR(H)–MR(33S) =

= 0.00843729682(30) uand MR(

28Si)+MR(1H)–MR(

29Si) == 0.00825690198(24) u.By adding MR(

2D)-2MR(1H) = – 0.001

548 286 29 (40) u to each one, we ob-tain the mass differences of equation(2) with a relative uncertainty ofabout 7 · 10-8 for both.

The comparison of the measured en-ergies and masses leads to two inde-pendent tests of (1- E /mc2) of2.1(5.2)·10-7 and -9.7(8.0)·10-7 withsulphur and silicon isotopes respec-tively, and a combined value of-1.4(4.4)·10-7.This test is 55 times more accuratethan the previous best direct test of E= mc2, performed by comparing theelectron and positron masses to theannihilation energy. The error onthis comparison is currently domi-nated by the uncertainty on the gam-ma-ray measurements.The major problems within thesemeasurements are the insufficientnon-linearity and time stability ofthe angle interferometers.However, there are already projects

to improve these parameters further,which would eventually allow theresults to be improved by one orderof magnitude.

References1. P.J. Mohr and B.N. Taylor, Rev. Mod. Phys. 77,

(2005) 1-1072. E.G. Kessler et al., Nucl. Instr. Meth. A 457,

(2001) 187-2023. M.S. Dewey et al., http://arxiv.org/abs/nu-

cl-ex/0507011, submitted to Phys. Rev. C.4. S. Rainville, J.K. Thompson, and D.E.

Pritchard, Science 303, (2004) 334-338

S. Rainville*Harvard University and

MIT Cambridge, USA

J.K. Thompson*, D.E. PritchardMIT Cambridge, USA

E.G. MyersFlorida State University, Tallahassee

J.M. BrownOxford University

M.S. Dewey, E.G. Kessler Jr., R.D. Deslattes

NIST Gaithersburg

H.G. Börner, M. Jentschel, P. MuttiILL

* These authors contributed equally to thiswork.

Figure 2. View of the GAMS4 double flat crys-tal spectrometer. The orientation of two perfectSi crystals is controlled by optical angle inter-ferometers. The absolute calibration of the in-terferometers is carried out using an opticalpolygon.

Hydrogen Storage in a Metal-Organic Framework

23


form of fuel cells to convert storedchemical energy, in the form of hy-drogen gas, directly into electricalenergy with high efficiency [1].However, the crucial factor that ishindering progress towards the com-mercial exploitation of these devicesis the safe and efficient storage of thehydrogen fuel gas. The design and technological devel-opment of storage media to over-come this difficulty is at the forefrontof current research [2].Of the various materials under in-vestigation, ordered porous materi-als such as metal-organic frame-works, are favourably considered tobe capable of fulfilling this role [3].The ability to adapt the surfacechemistry of the framework cavitiesmakes metal-organic frameworksparticularly attractive contenders forhydrogen-storage applications.By optimising the chemical and elec-tronic nature of the framework ar-chitecture, the gas uptake, at a givenpressure and temperature, can bemaximised.In a systematic approach to the mod-ification of a particular framework,with the aim to improve its gas ab-sorption properties, it is imperativeto understand which sections of thestructure interact strongly with the

physisorbed hydrogen gas.Once they are identified, these ele-ments of the structure can be en-hanced to increase the absorptioncharacteristics of the frameworkmaterial.Although there have been examplesreported of the use of single crystaland powder x-ray diffraction for de-termining the location of absorptionsites for a variety of gases (CO2, Ar,and O2) within porous coordinationpolymer complexes [4], this informa-tion is of limited use in terms of theadvancement of these materials forhydrogen storage.It is of greater benefit to determinethe location of hydrogen gas mole-cules themselves included within aframework structure, as this knowl-edge is of direct relevance.However, here x-ray diffraction isless suitable than neutron diffrac-tion, since the accuracy of the resultsobtained is greatly limited by thelow x-ray scattering ability of hydro-gen, particularly when the hydrogenundergoes large thermal vibration.In a pioneering experiment of itskind, a variable temperature (5-300K) single-crystal Laue neutron-diffraction study was conducted onVIVALDI, to locate the gas absorp-tion sites in a 0.1 mm3 hydrogen-

loaded crystal of Zn4O(CO2)6[Zn4O(1,4-benzenedicarboxylate)](figure 1). The greater adsorptionvolume associated with a singlecrystal compared to a powder wasan essential reason for this study.Two sites were unambiguously iden-tified, and these both display thecharacteristics of physiabsorbed hy-drogen molecules [5]. The space-fill-ing diagram of one of the frameworkcavities at 5K (figure 2) shows thatthe hydrogen gas congregates in thevicinity of the framework nodes.The gas enters and leaves the frame-work reversibly on cooling and heat-ing, even in a sealed capillary, witheight H2 molecules absorbed perframework formula unit at 5K, fourH2 molecules at 50K, and none at 120K. At 120K, the evacuated frame-work retains its integrity eventhough it contains ~77% of voidspace that is accessible to the hydro-gen gas.At 5K the physisorbed hydrogen gasoccupies approximately just 12% ofthis volume at a loading pressure of1 atm. Higher pressures may resultin further absorption near the organ-ic linker molecules, as predicted bygrand canonical Monte-Carlo simu-lations [6], and we will pursue thisaspect in future neutron studies.


Figure 2. A) The location of the two hydrogen absorption sites at 5K relative to the Zn4O(CO2)6framework. The H1-H2 site is 100% occupied at 50K, 30K and 5K; H4 is 98% occupied only at 5K.B) Space-filling diagram of one of the framework cavities at 5K. Purple: zinc; red: oxygen; black:carbon; grey: framework hydrogen atoms; gold: absorbed hydrogen gas.

Figure 1. One unit cell of the Zn4O(CO2)6 struc-ture. After accounting for the van der Waalsradii of the framework atoms, a sphere with adiameter of ~8 Å could diffuse freely throughthe framework.


24


The success of the experimentdemonstrated the ability of Laueneutron diffraction to study verysmall single crystals by neutronstandards, often in compromised en-vironments such as gas-exchangecapillaries.This means that this technique can beexpected to play a key role in thestructural study of framework mate-rials in the immediate future.

References1. B.C.H. Steele and A. Heinzel, Nature 414

(2001) 3452. L. Schlapbach and A. Züttel, Nature 414

(2001) 3533. M.J. Rosseinsky, Micropor. Mesopor. Mater.,

73 (2004) 154. Y. Kubota, M. Takata, R. Matsuda, R. Kitaura, S.

Kitagawa, K. Kato, M. Sakata and T.C.Kobayashi, Angew. Chem. Int. Ed., 2005, 44, 920

5. E.C. Spencer, J.A.K. Howard, G.J. McIntyre,J.L.C. Rowsell and O.M. Yaghi, Chem.Comm. 2005, accepted

6. T. Sagara, J. Klassen and E. Ganz, J. Chem.Phys. 121 (2004) 12543

Elinor C. SpencerDurham University and ILL

Judith A.K. HowardDurham University

Garry J. McIntyreILL

Jesse L.C. Rowsell andOmar M. Yaghi

University of Michigan, Ann Arbor

On October 23, 2006, the groundbreaking ceremony was held forLinac Coherent Light Source(LCLS), the world’s first X-ray free-electron laser.Scheduled for completion in 2009 atthe U. S. Department of Energy’sStanford Linear Accelerator Center,the LCLS will produce ultra-fast, ul-tra-short pulses of X-rays a billiontimes brighter than any other sourceon earth. The LCLS represents the4th generation of machines designed

to produce synchrotron radiation forscientific studies, an idea originallypioneered at SLAC in the 1970s. Un-like a circular storage ring, the LCLSwill produce x-rays using the final1/3 of SLAC’s existing linear accel-erator, in conjunction with long ar-rays of undulator magnets.Nearly 1,000 attendees listened tothe keynote address of DOE UnderSecretary of Science Raymond L.Orbach.The LCLS project is a collaboration

among Department of Energy labo-ratories including Argonne NationalLaboratory, Brookhaven NationalLaboratory, Los Alamos NationalLaboratory, Lawrence LivermoreNational Laboratory, and the Uni-versity of California Los Angeles.

Allen E. EkkebusSpallation Neutron Source, Oak Ridge

National Laboratory

News from LCLSGround Breaking for Linac Coherent Light Source

A map of LCIS site


25


News from NMI3Development of Neutron Detectorsfor Very High Resolutions and Counting Rates

In the JRA DETNI (DETectors forNeutron Instrumentation) three nov-el modular thermal neutron area de-tector types, based on thin solid neu-tron converter layers, are being de-veloped for time- and wavelength-resolved neutron detection in single-neutron counting mode, with two-dimensional spatial resolutions ofup to 50-100 µm FWHM, sub-mi-crosecond time-of-flight resolutionand counting rates of up to 108 neu-trons/s per detector module, i.e. forcoping with the highest resolutionand rate requirements at next gener-ation pulsed spallation sources likeESS. Recording only signals abovenoise in single-event counting, the

image contrast is greatly improvedin comparison to integrating detec-tors, like CCD cameras or imageplates. In addition, by scanning in asingle measurement a full wave-length train, in time-of-flight radiog-raphy-tomography the contrast ofindividual elements in the sample isenhanced specifically in element-specific resonances of the total neu-tron scattering cross section. In addi-tion to imaging, applications e.g. intime-of-flight Laue diffraction, very-high resolution single crystal diffrac-tion and reflectometry are envis-aged, among others. The detectortypes are:• Four-fold segmented modules of

Silicon micro-strip detectors (Si-MSD), with each segment com-prising a 157Gd converter layer be-tween two double-sided Si sensorsof 51 · 51 mm2 sensitive size andwith 80 µm pitch in the X and Ymicro-strip readout planes.

• Hybrid low-pressure micro-stripgas chamber (MSGC) detectors of254 · 254 mm2 sensitive size withthree-stage gas amplification gapsand novel two-dimensional posi-tion-sensitive multilayer MSGCplates either side of a composite157Gd/CsI converter which is coat-ed with columnar CsI secondaryelectron emitter layers.

• CASCADE detectors with stacks

News from NCXTNational Center for X-ray Tomography

The National Center for X-ray To-mography (NCXT) was dedicated onOctober 23, 2006.

It is located at the Advanced LightSource (ALS) of the U.S. Departmentof Energy’s Lawrence Berkeley Na-tional Laboratory.This new center features a first-of-its-kind x-ray microscope.According to cell biologist and mi-croscopy expert Carolyn Larabell,who is the principal investigator forthe new center, «X-ray microscopy isan emerging new technology thatexpands the imaging toolbox for celland molecular biologists, and weare going to make this technologyavailable to the greater biologicalcommunity».The NCXT is being funded withgrants from the U.S. Department ofEnergy (DOE) and from the National

Institutes of Health (NIH).As an NIH technology resource cen-ter, the NCXT will be available toqualified biomedical researchersthroughout the nation.The centerpiece of the NCXT is thefirst soft x-ray transmission micro-scope to be designed specifically forbiological and biomedical applica-tions. It is capable of imagingwhole, hydrated cells at resolutionsof about 35 nanometers, and specif-ic structural elements within thecell at a resolution of at least 25nanometers.

Allen E. EkkebusSpallation Neutron Source, Oak Ridge

National LaboratoryThe new soft x-ray microscope at the NationalCenter for X-ray Tomography captured its firstx-rays on August 23, 2006


26


of cascaded GEM (Gas ElectronMultiplier) foils on either side of adouble-sided, two-dimensionalposition-sensitive readout elec-trode. The GEM foils are coated onboth sides with 10B converter lay-ers and drift the secondary elec-trons, released in the gas by thesecondary ions emitted form 10Bafter neutron capture, to a lastGEM foil where they are amplifiedfor two-dimensional detection.

For readout, in DETNI two novelself-triggered high-rate ASIC (Appli-cation Specific Integrated Circuit)chips [1], subsequent ADC-FPGAboards with Gigabit glass fiber read-out links and the required data ac-quisition firmware and software arebeing developed. The ASICs, a low-noise 128-channelchip optimized for the Si-MSD andstrip rates of 160 khits/s, and a32-channel chip optimized for theMSGC with variable amplificationand strip rates of 900 khits/s, deliverspatial, analogue amplitude and fasttime stamp information with 4 and 2

ns resolution, respectively, the latterbeing necessary for X-Y strip correla-tion with low chance coincidencerate. The amplitude readout is usedfor improving the spatial resolutionby center-of-gravity interpolationbetween the strips and for gating forbackground suppression. Prototypes of all three detector typesare being prepared presently togeth-er with the readout electronics fortesting in 2007.

References1. A.S. Brogna et al., N-XYTER, a CMOS read-

out ASIC for high resolution time and am-plitude measurements on high rate multi-channel counting mode neutron detectors,Nucl. Instr. and Meth. A 568 (2006) 301-308

S.S. Alimov1,2, A. Borga3,A. Brogna1,2, S. Buzzetti2,4,

F. Casinini5, W. Dabrowski6,T. Fiutowski6, B. Gebauer1,

G. Kemmerling3, M. Klein2,B. Mindur1,6, C. Petrillo5,

F. Sacchetti5, C.J. Schmidt7,H.K. Soltveit2, R. Szczygiel6,

Ch. Schulz1, C.Thielmann3,U. Trunk8, P. Wiacek6, Th. Wilpert1

1Hahn-Meitner-Institut Berlin, GlienickerStr. 100, D-14109 Berlin, Germany

2Physikalisches Institut der UniversitätHeidelberg, Philosophenweg 12,D-69120 Heidelberg, Germany

3Zentralinstitut für Elektronik, For-schungszentrum Jülich,52425 Jülich, Germany

4INFM & Dipartimento di Elettronica e

Informazione, Politecnico di Milano,Piazza Leonardo da Vinci 32,

Milano I-20133, Italy5INFN & Dipartimento di Fisica, Univer-

sita di Perugia, Via A. Pascoli,Perugia I-06123, Italy

6Faculty of Physics and Applied ComputerScience, AGH University of Science and

Technology, al0. Mickiewicza 30,30-059 Krakow, Poland

7Gesellschaft für Schwerionenforschung,Planckstr. 1, 64291 Darmstadt, Germany

8Max-Planck-Institut für Kernphysik,Saupfercheckweg,69117 Heidelberg,

Germany

Neutron Optics and Phase Space TransformersThe most efficient means for increas-ing the flux at beam lines for neu-trons is the use of advanced focusingtechniques based either on diffrac-tive optics or the reflection of neu-trons from surfaces that are coatedwith artificial multilayer structurestermed “supermirror”. In addition,the flux can be increased by activelychanging the phase space of the ra-diation, for example by cooling thespectrum of the neutrons and/or bymoving monochromators. Of course,the flux can also be increased by in-creasing the source strength as it isfor example done in the US andJapan, where new high-power spal-lation sources are being built andcommissioned. The goal of the JRA3-collaboration

is the development and explorationof new focusing techniques andphase space transformations that al-low for the investigation of smallsamples as they occur often in thefields of soft condensed matter andin materials research as well as ma-terials exposed to extreme condi-tions, for example high magneticfields and/or high pressure.In order to increase the neutron fluxfor small angle neutron scattering(SANS), a multi-beam collimator hasbeen developed, featuring 7 maskswith 51 pinholes each. First test ex-periments using a suspension of La-tex spheres with a diameter of 225nm prove that the principle is work-ing leading to the expected fluxgains while maintaining the resolu-

tion. For inelastic neutron scatteringexperiments, the Q-resolution canoften be significantly relaxed. There-fore, a concept of focusing devicesconcentrating the neutron beams byreflection from supermirror-coatedglass tubes that are ellipticallycurved has been developed. A fluxgain of approximately 25 has beenmeasured using neutrons with awavelength in the range 3 Å < λ


27


Muons provide a unique probe ofatomic level structure and dynamicsand the experimental technique isknown as Muon Spin Rotation, Re-laxation and Resonance (µSR).A wide variety of properties can beinvestigated across a broad rangeof systems, including magnetic ma-terials, superconductors, semicon-ductors and molecular/polymericsystems.A muon can be thought of as a mi-croscopic magnetometer, with spin-1/2 and a magnetic moment threetimes that of the proton, and can beused to inform on local magneticstructure and dynamics.The muon mass is approximatelyone-ninth that of a proton, and inmany experiments muons are usedas a mimic to determine proton orhydrogen sites and dynamics, for ex-ample in semiconductors, metal hy-drides and proton conductors.Muons provide a complementaryprobe of condensed matter to othertechniques such as neutron scatter-ing and magnetic resonance, and areused by many research groupsacross Europe. This JRA is aimed atadvancing technologies in a numberof areas relevant to the performanceof muon experiments. These advances will benefit thewhole European muon community,and are aimed at enhancing the ca-pabilities of the European muon fa-cilities to extend their potential forcondensed matter investigations.Specifically, this JRA is aimed at de-

velopments in three areas:1. Detectors for muon spectroscopy;

in particular, development of fast-timing detectors and those capableof providing position information.

2. Instrument simulation; in particu-lar, the development of code toenable full simulation of muonspectrometers.

3. Advanced experimental methods,in particular development of novelpulsed techniques.

State-of-the-artDetectorsPosition sensitive detectors: our recentstudies have shown that, in additionto silicon-based detectors, scintillat-ing fibres too are very promising asposition-sensitive detectors for µSR.A detailed work including both sim-ulation and testing, has shown theequivalence of signals generated bymuon-decay-positron with thosearising from common beta emitters:this will make future test proceduressimple. Fast and magnetic field insensitive de-tectors: the performance Avalange-Photo-Diods/SiPMs detectors at lowtemperatures is at present known ina cryogenic environment. Mechani-cal difficulties concerning the assem-bly of the AMPD array on printedcircuit boards, will be overcome byusing light guides for signal trans-mission. Detailed Monte Carlo simu-lations for an improved light outputand an increased efficiency are beingcarried out. The results will be used

in the design of a revised version ofthe detector layout. Beside beingvery fast (some tenths of ns), the re-sponse of the blue-sensitive AMPDs,is expected to be also magnetic fieldindependent, as already shown fortheir green sensitive counterparts,making them an ideal choice for thedetector system of a high-field spec-trometer.

Simulations of detectors andspectrometersEfforts were devoted to the inclusionof positron track simulations into theexisting simulation code, and in par-ticular in the test against real data.The magnetic field-dependent effectswere investigated by using a pur-posely built positron detector, whichincludes two mobile detecting ele-ments mounted inside a supercon-ducting solenoid. The observed ef-fects seem to depend not only on thecyclotron motion of the positrons,but also on the field induced motionof the muons in the incoming beam.

Advanced µSR techniquesThe development of µSR in pulsedenvironments, e.g. microwave andRF-µSR, has been the main focus.The technology associated withcrossed-coil RF excitation has nowdeveloped to the point where tech-niques dependent on this technolo-gy (e.g. g-value determination andRF nuclear decoupling) make a reg-ular contribution to the ISIS userprogramme. RF decoupling, in par-

MUONS – Instrumentation forSpin-Polarized Muon Spectroscopy

and to reflectivity (R ≅ 0.70). It be-came clear that the morphology ofthe substrate is of utmost impor-tance to obtain an excellent perfor-mance. Elliptic guides have been de-veloped for the transport of the neu-

trons from the moderator to thespectrometer. First prototypes showthat the expected flux gains of morethan a factor of five compared to reg-ular neutron guides can be realised.It is gratifying to see that the new

techniques are already being incor-porated at the new Target Station 2 atISIS that is presently in the construc-tion phase.

Peter BöniTUM, for the JRA3 – NO-PST Team


28


The DLAB JRA within NMI3 is fo-cused on the development of meth-ods for the efficient and cost-effec-tive deuteration of biological macro-molecules. The project is fully dedi-cated to biological neutron scatter-ing , but has an important link to so-lution and solid state NMR. Themethods that are being developedas part of the project are now start-ing to have an impact on biologicalneutron scattering experiments onsolutions, fibres, crystallographyand dynamics.Real results in these areas that havebenefited from these methodologicaldevelopments are now coming intothe scientific press. In very broadterms, DLAB work cover the follow-ing general areas:1. Methods aimed at driving downthe cost of deuterated biomole-cules, thereby enhancing access.This is being done through the de-velopment of new methods to opti-mise bacterial growth. Two ap-proaches are being deployed here(I) the development of bacterialstrains that are more tolerant ofD2O and deuterated carbonsources, (II) fundamental proteomicapproaches in which the molecularnetworks involved in adaptationare investigated. 2. Methods aimed at developing theuse of new organisms for deuteri-um labelling, thereby extending therange of systems that can be deuter-ated. Here techniques are being de-

veloped to label organisms such asRalstonia eutropha and the eucaryoticorganism Pichia pastoris. to providevehicles for the expression of hetrol-ogous proteins that can not be ex-pressed in E. coli.3. Optimisation of methods for theselective deuteration of biologicalmacromolecules so that the visibili-ty of particular regions of thesestructures is enhanced in model-ling. A variety of approaches are be-ing developed, ranging from meth-ods whereby particular residues aredeuterated to those that facilitatemacro-scale labelling of large multi-component systems.4. Methods aimed at optimising se-lective hydrogenation of complexbiological systems to enable hydro-gen incoherent scattering studies ofspecific components. Techniquesfor the hydrogen labelling of specificamino acids in deutrated membraneproteins are being extended to vari-ous prockaryotic and eukaryotic sys-tems of major biological interest. Over and above the specific techni-cal goals, the DLAB project aims toextend its activities and expertise aswidely as possible throughout theEuropean neutron scattering com-munity. Within the current frame-work this is gradually happeningvia the network of neutron scatter-ing partners and NMR observerswithin the DLAB project. It is alsohappening through the dissemina-tion of results from successful

deuteration/labelling projects thathave exploited the expertise devel-oped. Many of these have used neu-tron scattering facilities at the ILL,but experiments on labelled sys-tems have also been carried out atISIS (where reflectometry resultshave complemented ILL SANSmeasurements and ssNMR studies,both also exploiting the labelling)and at Juelich (where measure-ments from the BSS spectrometerhave complemented data from oth-er spectrometers with different en-ergy resolutions).Clearly the involvement of all Euro-pean neutron scattering facilitiesinvolved in biological work is es-sential and this is a primary con-cern for this JRA in the context ofFP7. One intriguing aspect emerg-ing from current activities is thefact that neutron/NMR comple-mentarity is not restricted to mutu-al benefit simply through labellingrequirements. New neutron pro-posals are indeed emerging as a re-sult of the NMR deuteration & la-belling work because NMR usersare discovering first hand the valueadded to their work through theuse of neutrons. There is l ittledoubt that the same could be saidof many other techniques.

Trevor ForsythJRA7 – D-LAB Coordinator

Institute Laue LangevinKeele University, UK

Development of Methods for Biological Deuteration

ticular, requires large RF fields forefficient decoupling, and this tech-nique has greatly benefited fromwork carried out to improve the ef-ficiency of power delivery to thesample. Significant effort has alsobeen devoted to the developmentand demonstration of a microwavespectrometer at ISIS. A signal gen-

erator, power amplifier and othermicrowave components were pur-chased, and these, together with anin-house designed and built cavity,formed the basis of the instrument.With the cavity optimised at a fre-quency ~3GHz test experimentswere carried out, observing clea

Documents

NOTIZIARIO Vol 12n1 2007people.fisica.uniroma2.it/~notiziario/2007/pdf/vol12-n1... · 2007. 2. 28. · the Aghlabids Arabs from Sicily by the Duchy of Naples. It was finally abandoned