SYMPOSIUM J

9:00 AM *J4-S1.1 (invited)
Sub-Nanosecond X-Ray Absorption Spectroscopy: Structural Observations of the Optical Recording Process in Ge₂Sb₂Te₅. (#1269) Paul Fons, Center for Applied Near-Field Optics Research, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan.

Both optical and electrical phase change memory (PCM) face apparently contradictory need for fast switching speed and long term data retention. In optical memory data storage is achieved by storing "on" bits as amorphous spots on an crystalline background. Data is written, erased, and read with the same laser by variation of both pulse power and duration. The recording process utilizes a short, intensive pulse which serves to excite the irradiated material with a subsequent thermal quench giving rise to generation of the more highly reflecting amorphous phase. In contrast, the erasing processes uses a longer, lower power laser pulse to recrystallize the material to its lower reflectivity state. The resulting differences in optical reflectivity (on the order of 30%) are then read out using a laser power low enough to not induce any change in the PCM. The actual recording and erasure times vary according to disk rotation speed in practice, however, the limits of recording and erase speed are a consequence of the fundamental material properties of the PCM and device structure. The success of optical memory recording is now leading to the development of a new generation of non-volatile electrical memory based upon the same class of materials. The high-speed switching of PCM in these devices and the apparent scalablility In electrical form of PCM, data is again stored as local (electrically) switched regions of amorphous and crystalline material, but electrical resistance serves as the data readout; the wide dynamic range also offers the possibility of multilevel bit recording. As PCM materials undergo the crystalline to amorphous structural change utilized by the recording process on the order of nanoseconds, attempts to investigate the structural details of the switching process have mainly utilized static measurements; extensions of the of the results of these measurements thus require making assumptions of the scalablility of the results over many orders of magnitude. In the current paper, we report on the development of a new spectroscopic technique that allows the making of structural observations on the time scale of the switching process itself with sub-nanosecond resolution. Chalcogenide-based phase-change memory alloys are in widespread commercial use in the form of rewriteable optical disks. Among these alloys Ge2Sb2Te5 serves as a prototypical phase change memory alloy in that it is being used both for the current generation of optical and the next generation of electrical based data storage; data is encoded using reflectivity (resistivity) changes between the amorphous and crystalline phases for optical (electrical) storage. This dual role played by \gst has lead to intense efforts in recent years to understand the details, from multiple perspectives including structural and optical, and electronic changes undergone by \gst during the phase transition process. It is hoped that a more detailed understanding of the phase change process will allow for insightful development of yet further optimized materials. In the current study, we have focused our efforts on understanding the structural details of optically induced phase transitions from the crystalline to the amorphous phase. As the transition from the crystalline to amorphous phase takes place on the nanosecond time scale and one endpoint of the transition involves the amorphous phase, it has proven difficult to apply traditional (glass) analysis techniques due to the extremely short time scales of the recording process. We have taken advantage of the reversible nature of the recording process to develop a pump-probe technique in which a short pulsed laser is used to opticallyl pump a thin layer of \gst inducing a crystalline to amorphous phase transition representative of the recording process. A synchrotron generated x-ray pulse is then used to probe the center of the laser irradiated spot using x-ray absorption (XAFS). XAFS probes local order by means of the quantum mechanical self-interference of a photoelectron wavefunction due to the local atomic order. The short (femtosecond) lifetime of the core hole allows observation of atomic positions in a near instantaneous snapshot. At the same time, the short lifetime of the XAFS process gives rise to short (∼ Å} coherence lengths over which structural observations are made. This short coherence length allows for the observation of crystalline, liquid, and amorphous structures on an equal footing. By locking the phase of the laser to the synchrotron x-ray pulses, structural snapshots of the laser induced changes have been recorded. The extremely fast (femtosecond) nature of the XAFS absorption process as determined by the core hole lifetime, leads to the ability to time-resolve structural changes on the 100 picosecond time scale duration of the x-ray probe pulses. In the current experiment, a fast (500~ps) optical pump laser induced amorphization of a 50~nm layer of Ge2Sb2Te5 within a (12 μm) spot on a rotating sample disk, while a controllably delayed focused 2 μm x-ray pulse was used to probe structural changes in the same region as a function of time before and after the pump pulse. A second CW laser focused at a different position on the same rotation locus recrystallized the \gst sample before it rotated back to the probe position. The experiment thus reversibly changes the sample from the crystalline to amorphous states each rotation cycle. XAFS spectra were acquired by fixing the delay between the pump and probe pulses while scanning the incident x-ray energy. Structural changes were obtained in 200 ps steps before and after the optical pump. The implications of these changes will be discussed.

9:30 AM *J4-S1.2 (invited)
New Opportunities to Study Dopants and Defects by Soft X-Ray Absorption Fine Structure. (#414) Federico Boscherini, Department of Physics, University of Bologna, Italy.

X-ray absorption fine structure (XAFS) spectroscopy can determine the local structure of most atoms in the periodic table. The great recent improvements in the performance of synchrotron radiation sources and in data analysis tools for the near edge region has opened new opportunities, especially in the study of dilute systems in the soft X-ray range. In this contribution we will show some recent results that demonstrate how semiconductor physics may greatly benefit from such progress. In fact, doping or alloying of semiconductors with light elements, that have K absorption edges in the soft X-ray range, is widely employed to tune semiconductor properties. ZnO is a wide band-gap semiconductor which has attracted renewed interest for optoelectronic applications. Reliable p-type doping is one of the major hurdles to be overcome for widespread applications. N is considered to be the most promising p-type dopant, but reliable growth procedures and physical understanding of the incorporation mechanisms are yet to be attained. We have recently approached the issue by combining N K-edge XAFS, ab-initio structural simulations and simulations of the near - edge lineshape [1]. We have shown that, for plasma assisted MBE growth, N is substitutionally incorporated in the ZnO lattice (on an O site). However, upon annealing N gas bubbles are formed, suggesting that only low temperature growth and processing is possible. More recent results on N doping in ZnMgO ternary alloys will also be reported. Using the same approach, we have also studied the intriguing phenomenon of hydrogen passivation of N-induced effects in GaAsN dilute alloys [2]. A combination of experiment and simulation allowed us to propose that a H-N complex is formed which is composed by two hydrogen atoms bound to the same N with C2v symmetry. More recent studies, performed also using diffraction and nuclear scattering techniques [3], have refined the picture, disentangling the role of bound and unbound hydrogen in determining variations in lattice strain and optical properties. The realization of ultra-shallow junctions with a high dopant concentration and sharp doping profiles is of great current interest. A promising method for B doping in Si is solid phase epitaxy regrowth (SPER): implantation of the dopant in a preamorphized substrate and subsequent activation by recrystallization. An open question is the origin of the limited fraction of electrically active B and in particular the process stage in which inactive B atoms appear. By using B K-edge XAFS we have demonstrated [4] that inactive B-B clusters are formed during the very early stages of recrystallization, when the B atoms are still in the amorphous matrix; these clusters are transferred to the crystalline Si matrix. More recent data on samples co-implanted with F will also be presented. References: [1] P. Fons, H. Tampo, A.V. Kolobov, M. Ohkubo, S. Niki, J. Tominaga, R. Carboni, F. Boscherini and S. Friedrich, Phys. Rev. Lett. 96 (2006) 045504. [2] G. Ciatto, F. Boscherini, A. Amore Bonapasta, F. Filipone, A. Polimeni and M. Capizzi, Phys. Rev. B 71 (2005) 201301R. [3] M. Berti, G. Bisognin, D. De Salvador, E. Napolitani, S. Vangelista, A. Polimeni, M. Capizzi, F. Boscherini and G. Ciatto, Phys. Rev. B 76, 205323 (2007). [4] D. De Salvador, G. Bisognin, M. Di Marino, E. Napolitani, A. Carnera, H. Graoui, M.A. Foad, F. Boscherini, and S. Mirabella, Appl. Phys. Lett. 89 (2006) 241901.

10:00 AM J4-S1.3
Thermal and Electromigration-Induced Strains in Polycrystalline Conductor Lines. (#659) G. S. Cargill III, H. Zhang; Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, USA.

We have used x-ray diffraction with submicron beam size to measure and map grain orientations and thermal and electromigration-induced strains in polycrystalline aluminum and copper conductor lines. White-beam Laue microdiffraction has been used to determine grain orientations and deviatoric strain tensors. Monochromatic microdiffraction has been used to measure the full perpendicular strain for (111) fiber texture Al conductor lines. Grain-by-grain orientation and strain measurements will be discussed in terms of models and simulations for electromigration and for strain development and relaxation. Parts of this work have been carried out jointly with C.-K. Hu (IBM); W. Liu (Advanced Photon Source), and L. Ge and A. M. Maniatty (RPI).. This research has been supported by NSF and has been carried out using beamline 34ID-E at the Advanced Photon Source, Argonne National Laboratory, which is supported by U.S. Department of Energy.

10:15 AM J4-S1.4
Use of X-Ray Absorption and Emission Spectroscopy in the Study of Electronic Structure. (#771) Andrew Preston¹, Ben John Ruck¹, Joe Trodahl¹, Kevin Smith², Louis Piper², Yufeng Zhang¹, Alex DeMasi¹, James Downes¹, Walter Lambrecht³; ¹School of Chemical and Physical Sciences, Victoria University of Wellington, New Zealand ; ²Boston University, Massachusetts, USA ; ³Case Western Reserve University, Cleveland, Ohio, USA.

Determining the electronic structure of materials plays a central role in condensed matter physics, as this structure underpins among other things the electrical conduction, optical response and magnetic properties. In recent times great advances have been made in band-structure calculation techniques, particularly through the development of density functional theory and its modifications. However, there remain many challenges, especially the treatment of electron-electron interactions in materials like strongly correlated oxides or rare-earth compounds. Theoretical developments must be combined with extensive experimental testing across a range of materials. Here again there have been exciting developments in the field of spectroscopy. Angle-resolved photoemission can be used to probe directly the band structure, but it is highly surface sensitive and is restricted to the occupied states of conducting materials. Synchrotron-based x-ray absorption and emission spectroscopies provide alternatives that probe both the filled and empty states, yielding the atom-specific and angular momentum-resolved partial density of states. The techniques are suitable for insulators as well as conductors, and probe the bulk of the material rather than just the surface. The extension to resonant x-ray emission, where the emission spectrum is sensitive to the excitation energy, can even be used to probe the k-dependent band structure. Here, these x-ray absorption and emission techniques will be described, with reference to specific examples from zinc oxide and ferromagnetic rare-earth nitrides such as GdN and SmN.

MORNING BREAK 10:30 AM - 11:00 AM

11:00 AM *J4-S2.1 (invited)
Characterization of Ferromagnet/Semiconductor Heterostructures by Grazing Incidence Diffraction of X-Rays. (#29) Bernd Jenichen, Vladimir Kaganer, Roman Shayduk, Wolfgang Braun; Paul-Drude-Institut, Berlin, Germany.

The combination of ferromagnetic and semiconducting materials is a prerequisite for the development of devices utilizing the spin of the carriers. For these spintronic applications it is highly desirable to explore ferromagnetic semiconductor heterostructures, which show excellent interface quality. High thermal stability is required for device processing and operation. Ferromagnetic MnAs and Fe3Si films were grown on GaAs(001) in MBE systems built into the diffractometer at the wiggler beamline U125/2 KMC (PHARAO) at the storage ring BESSY at substrate temperatures near 250 degrees C and 200 degrees C, respectively [1,2]. The epitaxial growth was studied in situ and the heteroepitaxial interfaces were characterized in detail using grazing incidence diffraction of x-rays. MnAs on GaAs is an example for extreme heteroepitaxy with large and anisotropic misfit resulting in a high density of periodically arranged misfit dislocations at the interface. The periodicity of the dislocation array and the penetration depth of its inhomogeneous strain field can be obtained from the analysis of the corresponding superstructure reflections. The periodic arrangement of the dislocations reduces the lateral inhomogeneities of the strain field. The lattice relaxation of the film can be observed during MnAs deposition. Fe3Si films were grown fully lattice matched on GaAs resulting in an excellent quality of the interface and a high degree of long range order in the Fe3Si, probed by the measurement of many crystal truncation rods. Simulations reveal that the films are well ordered already during deposition and only the upper two monolayers of the films and the monolayers near the interface exhibit some disorder. The layer-by-layer growth mode of Fe3Si on GaAs was monitored by oscillations of the x-ray intensity. [1] D. K. Satapathy et al. Phys. Rev. B 72, 155303 (2005) [2] B. Jenichen et al. Thin Solid Films 515, 5611 (2007) and arXiv:0712.2180v3 [cond-mat.mtrl-sci]

11:30 AM *J4-S2.2 (invited)
Synchrotron Imaging for Non-Destructive Characterization of Materials, Components and Devices. (#1327) Tilo Baumbach, ANKA, Forschungszentrum Karlsruhe GmbH, Eggenstein-Leopoldshafen, Germany.

The development and production of highly perfect materials and their application in components and devices requires information on their structural perfection. Of crucial importance is the relationship between structural properties and technological processing steps, starting from the raw material right up to the completed device. The availability of reliable experimental facilities at synchrotron radiation sources, with unique properties such as high intensity, small focus, high brilliance, and good coherence at the sample opens up advanced possibilities for non-destructive testing characterization of devices and components from fundamental and applied research laboratories. A range of imaging techniques based on absorption-, phase-, diffraction- and spectroscopic contrast are employed. In the talk we report on recent developments of * Microdiffraction imaging based on high brilliant beams e.g. for the microstructural characterization of patterned substrates and epitaxial lateral overgrowth * Synchrotron laminography - white beam laminography for fast and in-situ 3D inspection of devices and holographic laminography for light weight components * Coherent scattering for non-destructive characterization of semiconductor nanostructures The talk summarizes methodical progress and illustrates the application potential focusing on examples of microelectronics and microsystem technology.

12:00 PM J4-S2.3
Local Strain in Ternary Compound Semiconductors. (#596) Zohair Hussain¹, Claudia S Schnohr¹, Garry J. Foran², Mark C Ridgway¹; ¹Electronic Materials Engineering Department, Research School of Physical Sciences and Engineering, The Australian National University, Australian Capital Territory, Australia ; ²Australian Nuclear Science and Technology Organisation, Australia.

We have previously investigated the anomalous amorphisation behaviour of In(sub)xGa(sub)1-xAs where, unlike other ternary alloys such as Al(sub)xGa(sub)1-xAs, In(sub)xGa(sub)1-xAs did not exhibit amorphisation kinetics intermediate between the two binary extremes. This behaviour was attributed to the presence of a microscopic strain (determined by Extended X-ray absorption fine structure) due to disorder at the second nearest neighbour in the form of increased distortion in the bond length and bond angle distributions. We now investigate the amorphisation kinetics of In(sub)xGa(sub)1-xP in comparison to InP and GaP and compare them with In(sub)xGa(sub)1-xAs. We have utilised EXAFS to determine the structural parameters of In(sub)0.50Ga(sub)0.50P for comparison with measurements on InP, GaP, In(sub)0.53Ga(sub)0.47As and Al(sub)0.50Ga(sub)0.50As. In(sub)xGa(sub)1-xP was found to exhibit a bimodal bond length distribution as in the case of In(sub)xGa(sub)1-xAs. We attribute the anomalous amorphisation behaviour in these ternary alloys to this local strain.

12:15 PM J4-S2.4
Synchrotron X-Ray Diffraction Line Profile Analysis of Copper Nanoclusters. (#226) Kevin John Stevens, Quest Reliability/Industrial Research Ltd, New Zealand.

K.J. Stevens 1,2*, B. Ingham 2,3, M.F. Toney 4, S.A. Brown 2,5, K.C. Tee 5, and P. Convers 5 1 Quest Reliability Ltd, P.O. Box 38-096, Lower Hutt, New Zealand 2 The MacDiarmid Institute for Advanced Materials and Nanotechnology, P.O. Box 600, Wellington, New Zealand 3 Industrial Research Ltd, P.O. Box 31-310, Lower Hutt, New Zealand 4 Stanford Synchrotron Radiation Laboratory (SSRL), 2575 Sand Hill Rd., MS69, Menlo Park, California, CA 94025, U.S.A. 5 Nano Cluster Devices Ltd, University of Canterbury, Private Bag 4800, Christchurch, New Zealand *Corresponding author Copper nanoclusters deposited into high-aspect ratio trenches can be used to fabricate high conductivity interconnects for nanoelectronic circuits [1]. Synchrotron X-Ray Diffraction (XRD) patterns have been collected from copper nanoclusters prepared in a sputter Inert Gas Aggregation source and deposited on silicon substrates. These formed a surface cuprous oxide upon air exposure. Warren-Averbach and Williamson-Hall [2, 3] analyses of the X-Ray diffraction peaks have been used to measure a mean crystal size in 10, 25 and 40 nm diameter clusters. We find that the crystallite size in the 40 nm clusters is smaller than the particle size, indicating a defected multi-grain copper core, which is,possibly due to the effect of oxidation and / or interaction with the substrate surface.. Scanning Electron Microscopy has been used to measure the particle diameters across a range of 10 to 40 nm and coverages of 0.1, 0.25, 0.5 and 1.0 monolayers of particles. Analysis of the lattice fringes in the clusters using High Resolution Transmission Electron Microscopy (HRTEM) and multislice image simulation [4] has been used to measure the oxide thickness, to detect structural defects, and to validate the XRD line profile analysis. The influence of the oxide on the (111) peak widths has been monitored by XRD during in-situ hydrogen reduction experiments up to 325 ?C. References: 1. K.C. Tee, A. Lassesson, J. van Lith, S.A. Brown, J.G. Partridge, M. Schulze, IEEE Transactions on Nanotechnology, Vol. 6, Issue 5, Sept 2007, p556-560. 2. M. Birkholz, "Thin Film Analysis by X-Ray Scattering", Wiley-VCH, 2006. 3. T. Ungar, S. Ott, P.G. Sanders, A. Borbely and J.R. Weertman, Acta Mater. Vol. 46, No.10, 1998, p3693-3699. 4. http://cimewww.epfl.ch/people/stadelmann/jemsWebSite/jems.html

LUNCH 12:30 PM - 2:00 PM

2:00 PM *J4-S3.1 (invited)
Surface Compositional Profiles of Self-Assembled InAs/GaAs Quantum Rings. (#69) Stefan Josef Heun¹, Lucia Sorba¹, Giorgio Biasiol², Tomaz Mlakar², Rita Magri³, Andrea Locatelli⁴, Tevfik Onur Mentes⁴; ¹NEST CNR-INFM and Scuola Normale Superiore, Pisa, Italy ; ²Laboratorio Nazionale TASC INFM-CNR, Italy ; ³S3 INFM-CNR and Università di Modena e Reggio Emilia, Italy ; ⁴Sincrotrone Trieste S.C.p.A., Italy.

The composition profile of self-assembled InAs/GaAs quantum rings (QR) is studied both experimentally and theoretically. 2D surface maps obtained by X-ray photoemission electron microscopy (XPEEM) reveal a non-uniform profile with an In-rich core, corresponding to the central hole of the QR, surrounded by a rim with stronger In-Ga intermixing. These results are substantiated by an atomistic Valence Force Field (VFF) model which, for a given shape, identifies the composition distribution that minimizes the elastic energy of the system. The VFF calculation predicts a preference for the In atoms to remain localized in the QR hole, in agreement with the experimental findings. Further insight into the properties of QR is obtained by conductive atomic force microscopy. 2D current maps and I-V curves show a lower conductivity of the central QR hole as compared to the rim and wetting layer. This result is quite surprising if we take into account the XPEEM data: since it has been previously established that In-rich regions are more conducting with respect to GaAs, one would expect in such a sample the central hole to be the region with highest conductivity. However, when comparing these data, the surface native oxide layer of the QRs has to be considered. Including the presence of a surface oxide into numerical simulations yields results which show the same qualitative behaviour as the measured conductivities. Therefore, finally a consistent picture of the In concentration profile in QRs is obtained, which is in agreement with the XPEEM and the C-AFM results.

2:30 PM *J4-S3.2 (invited)
Small and Wide Angle X-Ray Scattering - Adventures on the Nanoscale. (#1279) David J Cookson, Australian Synchrotron, Australia.

The evolution of electronics is the story of mankind's ability to understand and manipulate matter on a range of length scales, ranging from the atomic to the macroscopic. Elastic x-ray scattering has been a key tool in the characterization of materials on nanometer length scales yielding data that reflects true electronic density. While wide angle scattering gives us insights as to the inherent properties of a base material, small angle x-ray scattering (SAXS) can give us information on the nature of heterostructures, whether they are created by top-down or bottom-up fabrication processes. Synchrotron light sources can produce hard x-ray beams which have sufficient flux to study small regions of interest and provide excellent signal to noise data from even weakly-scattering samples. Examples of SAXS/WAXS studies of electronic materials will be presented, along with some discussion of the role that synchrotrons and elastic x-ray scattering might play in this rapidly evolving field.

AFTERNOON BREAK 3:30 PM - 4:00 PM

4:00 PM *J4-S4.1 (invited)
X-Ray Diffraction From Semiconductor Nanostructures: Beyond the Ensemble Average. (#1456) J Stangl, C Mocuta, K Mundboth, A Diaz, T H Metzger, G Bauer, A V Zozulya, O M Yefanov, I Vartanyants; Institute for Semiconductor Physics, Johannes Kepler University Linz, Austria.

Semiconductor nanostructures are the basis of many device concepts in research as well as industry, because exploitation of quantum effects considerably enhances the design possibilities. For the optimization of nanostructures such as quantum dots or quantum wires, a sound structural characterization is mandatory. X-ray diffraction has a prominent role here, especially for the determination of strain state and chemical composition. Many studies achieved a high spatial resolution down to the nm scale by performing model calculations and fitting simulated x-ray diffraction patterns to the measured ones. But also direct inversion techniques based on coherent scattering and phase retrieval have come to high spatial resolution [1,2]. However, this spatial resolution is indirect in one important aspect: the measurements are performed on rather large ensembles of nanostructures, with typically several thousand to several million objects scattering simultaneously. Hence the obtained structural information is that of an "average object", and is really meaningful only if the dispersion of properties in the ensemble is small. In many cases, however, the fluctuations in the properties are especially interesting, for instance in order to observe different growth stages and their evolution, or if bimodal distributions occur, or if nanostructures are present only in small parts of a sample. The latter is often the case if nanostructures are to be embedded into devices. As an example, field effect transistor concepts exist, where quantum dots are embedded into the channel region [3]. Then it is interesting to investigate only a very small area of the sample, which is not possible with ensemble-averaging techniques. To overcome this limitation, we use extremely focused x-ray beams at beamline ID01 at the ESRF in Grenoble, France, to illuminate sample areas as small as few um down to few 100 nm. This enables us to perform x-ray diffraction experiments on individual nanostructures, like SiGe islands grown on Si(001), or InAs nanowires grown on InP(111). We are able to align a specific island into the x-ray beam, so that the results can be correlated to those of other methods like scanning electron microscopy or u-photoluminescence on exactly the same island. Using this technique, we characterized different growth stages of SiGe islands in liquid phase epitaxy, which has not been possible using other methods [4]. The focused x-ray beam with diameters below the coherence length of the synchrotron source may also be used for coherent scattering experiments, opening up the possibility of model-independent x-ray investigations of nanostructures. [1] J. Stangl et al., Rev. Mod. Phys. 76, 725-783 (2004). [2] I. A. Vartanyants et al., Phys Rev. B 77, 115317 (2007). [3] O.G. Schmidt et al., Mat. Sci. Eng. B89, 101 (2002). [4] C. Mocuta et al., Phys. Rev. B 77, 245425 (2008).

4:30 PM J4-S4.2
3D X-Ray Diffraction Nanoscopy: In Situ Non-Destructive Imaging of Dispersed Nano-Particles, Cracks and Metal-Metal Interfaces. (#153) Andrei Nikulin¹, Aliaksandr Darahanau¹, Nadia Zatsepin¹, Ruben Dilanian¹, Barry Muddle¹, Alexei Souvorov², Osami Sakata²; ¹School of Physics, Monash University, Victoria, Australia ; ²SPring-8/Japan Synchrotron Radiation Research Institute (JASRI), Japan.

A novel approach to x-ray diffraction data analysis for non-destructive determination of the shape of nanoscale particles and clusters in three-dimensions is illustrated with representative examples of composite nanostructures. The technique is insensitive to x-ray coherence, which allows 3-D reconstruction of a modal image without tomographic synthesis [1], as well as in situ analysis of a large (over a several cubic millimeters) volume of material [2] with spatial resolution of a few nanometers [1], rendering the approach suitable for laboratory facilities. High-angular-resolution Fraunhofer diffraction data were collected from several samples with interfaces between dissimilar metals and artificial cracks in a metal foil using synchrotron x-radiation. The refractive index profile in the vicinity of the interface and crack of each sample was reconstructed with spatial resolution of about 10-50 nm by the Phase Retrieval X-Ray Diffractometry technique, using only limited a priori knowledge of the sample. These studies have demonstrated the viability of the technique as an in-situ non-destructive method of characterization of internal interfaces within multiphase materials [3] and a crack developing under external force. 1. A. Y. Nikulin, R. A. Dilanian, N. A. Zatsepin, B. M. Gable, B. C. Muddle, A. Y. Souvorov, Y. Nishino, and T. Ishikawa. 3-D X-Ray Diffraction Imaging with Nanoscale Resolution using Incoherent Radiation. Nano Lett. 7(5), 1246 (2007). 2. N. A. Zatsepin, R. A. Dilanian, A. Y. Nikulin, B. M. Gable, B. C. Muddle, and O. Sakata. Early detection of nanoparticle growth from x-ray reciprocal space mapping. Appl. Phys. Lett. 92(3), 034101 (2008). 3. A. V. Darahanau, A. Y. Nikulin, R. A. Dilanian, and B.C. Muddle, X-ray diffraction profiling of metal-metal interfaces at nanoscale, Phys. Rev. B 75, 075416 (2007).

4:45 PM J4-S4.3
EXAFS Study of Ni Surroundings in Metal Induced Crystallization of Thin Film Amorphous Silicon. (#173) Rolly Grisenti, Giuseppe Dalba, Paolo Fornasini, Francesco Rocca; Dipartimento di Fisica, Università degli Studi di Trento, Italy.

EXAFS investigation about Metal Induced Crystallization (MIC) of a-Si thin films doped with Ni, has been carried out at the K edge of Ni. Several a-Si films deposited on quartz and annealed at different temperatures and a sample not-submitted to isochronal annealing have been analyzed in order to study the variation of the nickel surroundings as a function of temperature. Nickel particles were co-sputtered together with silicon to obtain a metal percentage of about at. 0.5%. In all the annealed samples it was found that nickel, in its first shell, is 8-fold coordinated to silicon while a weak signal corresponding to the second shell appears in the Fourier transform of the spectra as in crystalline nickel di-silicide (c-NiSi2) used as reference compound. No presence of Ni clustering has been ascertained. In the not-annealed sample, where the NiSi2 formation has never been observed, EXAFS shows that the silicon atoms begin to arrange themselves as to set up Ni local coordination as in NiSi2.

J4-S5.1
Synchrotron Characterization of Size Effects on the Structural and Thermal Properties of Ge Nanocrystals. (#468) Leandro L. Araujo, Mark C. Ridgway; Electronic Materials Engineering Department, Research School of Physical Sciences and Engineering, The Australian National University, Australian Capital Territory, Australia.

Synchrotron-based techniques were combined with conventional analysis methods to probe in detail the structural and thermal properties of Ge nanocrystals (Ge NCs) grown in a silica matrix (a-SiO[sub 2]) by ion implantation and thermal annealing, as well as the evolution of such properties as a function of nanoparticle size. The thorough analysis of X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and Raman spectroscopy data for Ge nanoparticles with mean diameters between 4 and 9 nm revealed peculiar properties of embedded Ge nanocrystals that are strongly dependent on particle size and mainly governed by the variation in the surface area-to-volume ratio. The evolution of structural parameters involves a reduction in the number of neighbouring atoms and an increase in mean interatomic distances, total disorder and asymmetry of the distance distribution as the Ge NC size decreases. The thermal expansion of interatomic distances also decreases with Ge NC size and the mean vibrational frequency increases, indicating stiffening of interatomic bonds. Furthermore, clear evidence of the formation of an amorphous-like Ge layer separating the a-SiO[sub 2] matrix and the Ge crystalline core was found for our embedded Ge NCs. Such results aid in explaining previously reported observations and contribute to the more efficient and rapid integration of Ge NCs in modern technologies.

J4-S5.3
Nanoscale Profiling of Weakly Diffracting Structures: Non-Destructive Characterisation of Structure Variation on Interfaces between Dissimilar Materials. (#90) Alexander V Darahanau, Andrei Nikulin, Ruben A Dilanian, Barry Muddle; Monash University, Victoria, Australia.

A high resolution x-ray diffraction technique has been applied to the characterization of non-homogeneous samples, where diffraction effects caused by the variation of complex refractive index within the sample, rather than thickness variation. Two samples contained metal-metal interfaces were analyzed and variations of the refractive index along the interface have been reconstructed for both samples with spatial resolution of 40 nm [1]. Following the successful pilot experimental studies, a series of computer simulations has been performed with an aim of estimating the minimal size of features practically analysable within interfaces and on the surface of various specimens [1]. The results of these preliminary theoretical studies have recently been confirmed by experimental results. It has been shown that 30-40 nm thick wires of gold deposited on the surface of a polymer membrane produce detectable diffraction effects, which contains enough information for quantitative characterisation of the surface relief. These findings is a major step towards the development of the practical method of non-destructive detection and/or characterization of randomly oriented internal interfaces in bi-crystals, thin films deposited on a substrate and other samples. 1. A.V. Darahanau, A.Y. Nikulin, R.A. Dilanian, and B.C. Muddle, 'X-ray diffraction profiling of metal-metal interfaces at nanoscale,' Phys. Rev. B, 75, p. 075416(1-11) (2007).

J4-S5.4
Angle-Dependent SAXS Measurements of Elongated Pt Nanocrystals. (#469) Raquel Giulian¹, Patrick Kluth¹, David John Sprouster¹, Claudia Sarah Schnohr¹, Leandro Langie Araujo¹, Aidan Byrne², David J. Cookson³, Mark Cameron Ridgway¹; ¹Electronic Materials Engineering Department, Research School of Physical Sciences and Engineering, The Australian National University, Australian Capital Territory, Australia ; ²College of Science, The Australian National University, Australian Capital Territory, Australia ; ³Australian Synchrotron Research Program, Australia.

Pt nanocrystals (NCs) formed in 2 &mum SiO[sub 2] films by ion implantation (4.5 MeV Pt ions, 1x10[sup 17] cm[sup -2]) and thermal annealing (1100 - 1300 [sup o]C, 1 h, forming gas) were irradiated with 185, 89, 54 and 27 MeV Au ions at fluences ranging from 2x10[sup 12] to 2x10[sup 15] cm[sup -2]. The NCs, which prior to irradiation were spherical in shape with mean diameters ranging from 30 - 140 Å , elongate in the direction of the incident beam as a function of irradiation fluence, achieving a rod-like shape for the highest fluences. Elongation was observed only for NCs larger than a threshold diameter, being &sim65 Å (&sim35 Å) for 185 MeV (27 MeV). We correlate the energy-dependent minor dimension of the NCs to the molten track induced in the amorphous SiO[sub 2] matrix by the energetic ions. Small angle X-ray scattering (SAXS) measurements were performed in transmission geometry at different angles, from zero (beam normal to the SiO[sub 2] surface) to 45 degrees. By varying the orientation of the samples relative to the beam direction, the scattering intensity was no longer isotropic, with significant differences in the measured intensity along the horizontal and vertical axes due to the non-spherical nature of the elongated NCs. Considering that the particles were highly oriented in one direction (normal to the SiO[sub 2] surface), selected angular sectors of the detector were integrated and analyzed separately, resulting in the individual evaluation of both the minor and major axes of the rod-like shaped NCs. Using this approach enabled the analysis of the spectra by means of existing methods (like maximum entropy), assuming spherical particles whose diameters correspond to the minor and major axes of the elongated NCs. Moreover, the resulting dimension distributions of the Pt NCs are in very good agreement with transmission electron microscopy analysis of the same samples.

J4-S5.5
Measurement of a Fine Structure in Latent Ion Tracks in a-SiO₂ Using Small Angle X-Ray Scattering. (#466) Patrick Kluth, Claudia S. Schnohr, David J. Sprouster, Raquel Giulian, Douglas Da Silva, Aidan P. Byrne, Mark C. Ridgway, David J. Cookson, Marcel Toulemonde, Christina Trautmann; Electronic Materials Engineering Department, Research School of Physical Sciences and Engineering, The Australian National University, Australian Capital Territory, Australia.

Swift heavy ion irradiation of a solid can leave a narrow trail of permanent damage along the ion path, a so-called latent track. The formation of these tracks is governed by the intense electronic excitation when the projectile ion passes through the material and the subsequent dissipation of the energy into the atomic system. Tracks have been observed in various crystalline and amorphous materials including semiconductors, insulators and metals. Particular attention has been focused on tracks in amorphous SiO[sub 2] (a-SiO[sub 2]) due to its technological relevance and a number of interesting applications, for example in nanofabrication, have been demonstrated (for a review of tracks in SiO[sub 2], see [1]). The characterization of latent ion tracks in amorphous materials is extremely challenging due to the lack of sufficient contrast attainable with most techniques and no direct measurements of ion track dimensions in a-SiO[sub 2] have been reported to date. Here we present measurements of a fine structure in latent ion-tracks in a-SiO[sub 2] using synchrotron-based small-angle x-ray scattering (SAXS). The tracks were generated by irradiation of 2 um thick SiO[sub 2] layers on Si substrates using Au ions with energies between 27 and 185 MeV and Xe ions at 0.64 and 1.4 GeV. SAXS measurements were performed at the Advanced Photon Source, Chicago, USA. At irradiation fluences (< 1x10[sup 11] ions/cm[sup 2]) where the track overlap is negligible, a cylindrically symmetrical density distribution resembling a core-shell structure is apparent in the ion tracks. Assuming a net densification of the SiO[sub 2] under swift heavy ion irradiation [1], our scattering data are well described by model calculations where the track consists of a lower density core and higher density shell relative to the un-irradiated matrix material. The observations are consistent with a frozen-in pressure wave outgoing from the center of the ion track. Calculations of the molten track diameter in SiO[sub 2] using an inelastic thermal spike model [2] are in remarkable agreement with the measured total track dimensions. The dimensions of the track core coincide with the radial distance where the temperature in the track exceeds the evaporation temperature. At high ion fluences (>6x10[sup 12] ions/cm[sup 2]), where the material experienced multiple track overlaps, SAXS measurements are consistent with the evolution of a non-homogeneous steady state in the material. The observed fine structure in the ion track density distribution was previously unresolved and provides new insights into the fundamental processes involved in ion track formation. [1] S. Klaumuenzer, Nucl. Instr. and Meth. B225 (2004) 136 [2] M. Meftah et al., Phys. Rev. B 49 (1994) 12457; Nucl. Instr. and Meth.B237 (2005) 563

J4-S5.6
Mn K-Edge XANES Studies of Pb_1-xMn_xTe Systems. (#1428) Ivana Radisavljevic¹, Nenad Ivanovic¹, Nikola Novakovic¹, Nebojsa Romcevic¹, Heinz-Eberhard Mahnke²; ¹Vinca Institute of Nuclear Sciences, Belgrade, Serbia and Montenegro ; ²Hahn-Meitner-Institut, Germany.

X-ray Absorption Near Edge Structure (XANES) was employed for the determination of Mn valence state and its coordination environment in the series of lead-telluride based semimagnetic semiconductors. Mn K-edge absorption data, collected at HASYLAB (DESY) at several different temperatures in the range from 10 K to room temperature, were analyzed with the help of the Real Space Full Multiple Scattering FEFF8.2 code. Highly disordered local structure discovered around manganese impurity atoms supports our previous findings for the similar narrow bandgap semiconductor materials.

J4-S5.7
Vibrational Properties of Cobalt Nanoparticles. (#548) David John Sprouster, Electronic Materials Engineering Department, Research School of Physical Sciences and Engineering, The Australian National University, Australian Capital Territory, Australia.

The size and crystal structure-dependent vibrational properties for Cobalt nanoparticles embedded within a silica host matrix have been determined by extended x-ray absorption fine spectroscopy (EXAFS) and compared with bulk Cobalt standards. EXAFS measurements were performed at the Cobalt K edge in the temperature range from 8 to 300 K at beam line 20-B of the Photon Factory Japan. By applying a correlated anharmonic Einstein model and thermodynamic perturbation to the Debye-Waller factors, differences in the mean Einstein temperature for the Cobalt nanoparticles were found when compared to the bulk standards. The differences reflect looser bonding, on average, in the nanoparticles, the result of which is attributed to the under-coordinated, disordered surface atoms. As the nanoparticles grow in size, the influence of the surface atom distortions become negligible and exhibit bulk-like behavior. Differences in the Einstein temperature were also found for the bulk standards. For the bulk ambient stable hexagonally-close-packed structure the Cobalt-Cobalt bonds were found to be stiffer than the face-centered-cubic structure.

J4-S5.8
The Electronic Structure of Amino-Acids Determined by Synchrotron-Based Photoemission Spectroscopy. (#1077) Anton Patrick Joseph Stampfl¹, Nicola Asquith¹, Susan Montgomery Graham¹, Justin King-Lacroix¹, Feng Wang², Ivan Kempson³, Yaw-Wen Yang⁴, Yeukuang Hwu⁵; ¹Australian Nuclear Science and Technology Organisation, Australia ; ²Swinburne University of Technology, Hawthorn, Victoria, Australia ; ³Ian Wark Research Institute, The University of South Australia, Australia ; ⁴National Synchrotron Radiation and Research Center, Australia ; ⁵Institute of Physics, Academia Sinica, Taiwan.

The twenty naturally occurring amino-acids form the family of fundamental biomolecules which have a common functionality at one end of the molecule, and are coupled to a range of gradually differentiated functionalities at the other. These functional groups give each amino-acid their particular properties throughout all phases: for example, the form of the molecule in solution (whether each group is protonated/deprotonated or not) is highly sensitive to pH, as is solubility. Crystals are predominately hydrogen-bonded and are often hydrates. Many amino-acids exhibit polymorphism, that is there may be several coexisting metastable phases. Even though much is known about amino-acids, solution and surface complexation chemistry is not well understood from a molecular viewpoint as well as crystalline growth. The electronic valence structure of amino-acids has been partially determined experimentally for some simple gas phase molecules (glycine and alanine) as well as in solid forms (as powders and thin films). We present here the complete set of valence band regions measured using synchrotron-based photoemission spectroscopy for the twenty natural solid amino-acids, as powders as well as glycine and alanine single crystal surfaces. There are three polymorphic modifications of glycine that differ in molecular packing and the structure of the intermolecular hydrogen bond networks: the alpha-modification has a space group of P21/n and can be obtained from saturated water solutions, while the beta-modification has a space group of P21 and can be obtained by adding glacial acetic acid, but is metastable and may quickly change to the alpha-form when humidity is high. The gamma-modification, which is P31 or P32, may be obtained from water-ethanol solutions. While the polymorphs of glycine have quite rigid bonding geometries, the bonding geometry of alanine is flexible, torsional angles between the alpha -carbon and the carboxylic and amine groups can vary widely: Thus the crystalline environment will significantly affect the molecular geometry of alanine. L-alanine crystallises in the P212121 space group with pairs of layers antiparallel to one another. The surfaces of these crystals are not at all characterised, and we also present in addition to our photoemission results, optical microscopy, x-ray microscopy and AFM images of these surfaces. Our overarching goal is to build a library of spectra which can then be used as fingerprints for particular groups of amino-acids and thus be used in characterising more complicated bio-molecules such peptides, proteins, and macromolecules.

J4-S5.9
The Adsorption of Glycine on Alumina: Surface Complexation and Polymerisation. (#1082) Anton Patrick Joseph Stampfl¹, Julie Lynette Murison¹, Tun-Wen Pi², Yaw-Wen Yang², Yoa-Chang Lee², Hwu Yeukuang³; ¹Australian Nuclear Science and Technology Organisation, Australia ; ²National Synchrotron Radiation Center, Taiwan ; ³Institute of Physics, Academia Sinica, Taiwan.

The deposition of the amino-acid, glycine, on alumina powder from solution is investigated by photoemission. High resolution x-ray photoelectron spectroscopy performed at the Taiwan synchrotron is used to study the extent of adsorption at various pH's, the character of each adsorbate ( acidic, zwitterionic, basic) and the number of discrete surface sites of adsorption. Core-level shifts indicate that glycine is intact and strongly chemisorbed on the surface through ester-type bonding across the range of pH's used, while direct adsorption of the amine-group is only observed around pH 9. Valence band spectra taken in the VUV regime correspond remarkably well to gas phase results suggesting that little interaction occurs between adsorbate molecules on the surface. Whereas core-level spectra indicate that some longer range interactions occur, which may be due to the formation of multilayers or peptide bonds. A number of simple surface complexation models are presented to explain the observations. Additionally, preliminary solution-FTIR results suggest that adsorbate uptake may be quantitatively monitored in-situ and may provide a direct spectroscopic alternative to pH monitoring.

J4-S5.10
A Data-Constrained Computational Model for 3D Material Compositions. (#977) Sam Yang, Australian Commonwealth Scientific and Research Organization (CSIRO), Australia.

The microstructure is generally accepted as an important in dictating the bulk properties of materials. Recently, a Scripta Materialia Viewpoint Set has been published on 3D characterisation and analysis of materials which is composed of a number of articles describing the state-of-art techniques and methodologies in 3D microstructures characterisation of material systems [1]. Up to now, experimental characterisations of 3D compositional microstructures have tended to be costly and sample invasive. On the other hand, considerable efforts have been devoted to theoretical and numerical predictions of material microstructures [2-8]. However, there is still a lack of a generic set of modelling and computational tools for sample-specific, non-invasive, high-resolution and quantitative prediction of 3D compositional microstructures. A data-constrained model (DCM) and software implementation under MS-Windows have been developed for a sample-specific non-invasive prediction of compositional structures [9-10]. The software is capable of generating a sample-specific quantitative 3D high-resolution compositional image approximately by incorporating 3D high-resolution tomography data sets and appropriate beam-energy dependent material absorption properties. Under certain conditions, a small number of 2D sectional maps are required to improve prediction accuracy. A simulated structure has been generated. X-ray tomography data sets with selected beam energies have been calculated on these structures, using absorption properties of a number of common polymer materials. The model predicted structure is consistent with the simulated random structure. The DCM principle could be incorporated with other imaging techniques. The ability to predict the 3-D compositional microstructure in a non-destructive manner will be of great value. For example, it would helpful in developing process models of porous materials for a wide range of applications from membranes to corrosion resistance [11]. References [1] G. Spanos (Eds), Viewpoint set no. 41: 3D Characterization and Analysis of Materials, Scripta Materialia 55 (2006) pp. 1-114 [2] R. D. MacPherson and D. J. Srolovitz, Nature 466 (2007) pp. 1053-1055. [3] S. Mourachov, Computational Materials Science 7 (1997) pp. 384-388 [4] D. Raabe, Annu. Rev. Mater. Res. 32 (2002) pp. 53-76 [5] A. L. Rohl, Current Opinion in Solid State and Materials Science, 7 (2003) pp. 21-26 [6] T. Suzudo, Physica A 343 (2004) pp. 185-200 [7] Y. S. Yang, N. Blake, T. B. Abbott and J. F. McCarthey, Scripta Metallurgica et Materialia 29 (1993) pp. 1285-1290 [8] Y. S. Yang, N. Blake, T. B. Abbott and J. F. McCarthey, Communications in Numerical Methods in Engineering 11 (1995) pp. 805-812 [9] Y. S. Yang, A. Tulloh, I. Cole, S. Furman, A. Hughes, International Conference and Exhibition - Materials and Austceram (4-6 July 2007, Sydney Australia) [10] S. Yang, S. Furman and A. Tulloh, Frontiers in Materials Science & Technology (26 - 28 March 2008, Brisbane, Australia) [11] I. S. Cole, D. A. Paterson, W. D. Ganther, Corrosion Engineering Science and Technology 38 (2003) pp. 129-134

J4-S5.11
X-Ray Diffraction Studies of Nanostructures: Applications of a Novel Triple Axis Diffractometry Technique to Early Detection of Nanoparticle Growth, from Reciprocal Space Maps Using Synchrotron X-Rays. (#86) Nadia Zatsepin, Monash University, Victoria, Australia.

Nadia A. Zatsepin (a), Andrei Y. Nikulin (a), Ruben A. Dilanian (a), Brian M. Gable (b), Barry C. Muddle (b), Osami Sakata (c) and James R. Hester (d) (a) School of Physics, Monash University, Clayton, Vic. 3800, Australia. (b) Department of Materials Engineering, Monash University, Clayton, Vic. 3800, Australia. (c) Japan Synchrotron Radiation Research Institute/SPring-8, Kouto, Sayo-cho, Sayo-gun, 679-5198, Hyogo, Japan (d) Australian Nuclear Science and Technology Organization, PMB 1, Menai, NSW 2234, Australia We are working towards non-destructive bulk material characterization of samples that contain embedded nanoparticles. To this end, a novel x-ray diffraction technique is being developed at the ANBF and SPring-8, to image in three dimensions (3D) at the nanometer scale [1]. The technique is being developed centred on analysing a technologically important light metal alloy, Al-xCu (where x is 2.0-5.0 % wt). The samples contain a crystallographically oriented, randomly distributed dispersion of weakly diffracting Al2Cu nanoprecipitates in an Al matrix. In the early stages of development, it is necessary to determine the sensitivity of the technique to variables such as nanoprecipitate dimensions, density, distribution and orientation, and sample thickness, to name a few. We have experimented with mono- and polycrystalline Al-xCu samples, with [100]Al or [111]Al normal to the surface, differing sample thicknesses, different orientations of the crystal, and various hard x-ray energies and optical elements. We will present the results of experiments performed at an undulator source at SPring-8 (BL13XU) and a bending magnet source at the ANBF (BL20B). These involved the use of an analyser crystal to collect two dimensional (2D) reciprocal space maps (RSM) via a triple axis diffractometry-based experimental setup. Our 2D RSMs, with supporting simulations, show the threshold of sensitivity of the technique to the presence and crystallographic orientation of sparse, weakly diffraction nanoparticles [2]. These results are, incidentally, a fundamental step towards in situ characterization of samples containing nanoscale precipitates at early stages of nanoprecipitate growth. 1. A. Y. Nikulin, R. A. Dilanian, N. A. Zatsepin, B. M. Gable, B. C. Muddle, A. Y. Souvorov, Y. Nishino, and T. Ishikawa. 3-D X-Ray Diffraction Imaging with Nanoscale Resolution using Incoherent Radiation. Nano Lett., 7(5):1246-1250, 2007. 2. N. A. Zatsepin, R. A. Dilanian, A. Y. Nikulin, B. M. Gable, B. C. Muddle, and O. Sakata. Early detection of nanoparticle growth from x-ray reciprocal space mapping. Appl. Phys. Lett., 92(3) 134101, 2008.