X-ray free electron lasers (FEL) are now operational worldwide spanning wavelengths from 0.07-30 nm. This presentation will describe briefly self-amplified spontaneous emission (SASE), the principle underlying FELs and extensions to approach a fully coherent x-ray source at nm wavelengths. This discussion naturally leads to a description of the properties of the x-ray beams. Finally some details of existing and planned FELs worldwide will be discussed.

Nanofoams are considered an essential component for high energy density physics experiments because they provide a convenient method to independently vary density without changing atomic number. Since the dynamics of its collapse upon implosion plays an essential role in achieving inertial confinement fusion, characterizing the performance of low density materials under these extreme conditions provides crucial feedback in developing materials with optimal properties. In order to achieve this understanding, it is crucial to directly probe the controlling phenomena, in-situ and in real time. Recently, we have successfully developed the capability of measuring small angle x-ray scattering using a single x-ray pulse, thus enabling the use of pump-probe experiments to measure structural changes in-situ during a shock. Compression of under-dense materials under dynamic loading condition has been studied for some time using a variety of techniques. The significant momentum involved in these dynamic compaction events make it nearly impossible to study the evolution of such systems ex-situ. As a result, experimental information concerning the rate of collapse and morphological changes associated with void closure are lacking. Likewise, the early stages of void formation in dynamically driven spall are also difficult to observe experimentally. We have developed a system to investigate both void formation, during spall in metals, and void collapse, in under-dense carbon aerogel foams, using time resolved small angle x-ray scattering at the Advanced Photon Source. The system utilizes a laser to generate ablatively driven loading and use of a standard X-ray scattering camera along with a chopper based single bunch isolator. The carbon based foam materials begin with significant levels of scattering and dramatic changes are observed during loading and release of the compression wave. During compression a decrease in the total scattering intensity and the average pore diameter are observed consistent with a collapse of the pore structure in the nanoporous carbon. Evolution of the foam structure continues with during release of the compression wave where large structures are observed in the scattering potential due to the breakup of the nanoporous carbon. Effects of initial carbon microstructure and the compression wave condition on the time scale for the pore collapse are explored.

Nanocrystals provide ideal systems with which to study structural phase changes. By making use of the ultra-short pulsed nature of synchrotrons and free-electron lasers, one may visualize with atomic-resolution and in real time how nanosized systems rearrange and potentially resolve the transition state itself. Such information could lead to new material design opportunities in which the phase-change behavior is optimal for a given application. Here we present ultrafast studies of both temperature and pressure-driven phase changes in nanocrystalline materials, utilizing x-ray diffraction and x-ray spectroscopy to monitor the atomic rearrangement on femtosecond time-scales. For a thermally-driven phase change, we consider the onset of superionicity, a unique superposition of liquid-like cationic conductivity within a solid-phase anionic lattice. Using near-edge spectroscopy, we observe the superionic structural transformation to occur faster than twenty picoseconds in laser-excited copper (I) sulfide nanocrystals, and show that it is the ionic hopping time which determines this time-scale. For pressure-induced studies, we investigate the dynamics of the well-known change of cadmium selenide nanocrystals from a wurtzite to rock-salt unit cell under increasing pressure. We use laser-induced shock compression to initiate the phase transformation and hard x-ray scattering techniques as a probe. . By using oriented films, we consider the effect of crystallographic direction on the structural pathway during the phase change, as well as the effect of nanocrystal shape.

Investigation on phase transitions of materials under shock compression has bottlenecked due to the limitation of traditional experimental approaches that provide incomplete information on structural dynamics. Time-resolved x-ray diffraction enables to monitor time evolution of crystal structure under shock compression. We demonstrated direct observation of shock-induced phase transition of polycrystalline zirconia ceramics (3 mol % Y2O3 stabilized tetragonal zirconia: 3Y-TZP) and bismuth via nanosecond time-resolved x-ray diffraction with a single-shot laser pump and x-ray probe scheme. The experiment was performed using the beamline NW-14A at the Photon Factory Advanced Ring, KEK Japan. The x-ray pulse from an undulator with the period length of 20 mm (U20) has the pulse duration of approximately 100 ps, the energy of 15.6 KeV, the bandwidth of 4.4 % and the flux of 3x108 photons/pulse. The nanosecond laser pulse (1064 nm, 700 mJ) was focused on the target assembly with a plasma-confinement geometry in order to induce shock compression. The Debye-Scherrer diffraction pattern was recorded on an x-ray CCD. For 3Y-TZP, the martensitic phase transformation from the tetragonal structure to the monoclinic structure, which is the stable phase for pure zirconia at ambient pressure and temperature, has been observed during shock compression at 5 GPa within 20 ns without any intermediates. This monoclinic structure reverts back to the tetragonal structure during pressure release. The results imply that the stabilization effect due to the addition of Y2O3 is to some extent negated by the shear stress under compression. For polycrystalline bismuth, the nanosecond time-resolved x-ray diffraction showed new diffraction peaks during both shock compression and release at the shock pressure of 5 GPa. The results reveal that structural phase transitions from Bi-I to Bi-III during compression and from Bi-III to Bi-I via Bi-II during release occur.

Functionalized surfaces/interfaces are highly relevant both in present basic research and for numerous applications. Examples are the heat transfer through glass windows which can be lowered or the flow of liquids in pipelines which can be increased by appropriate coatings leading in the end to more energy-efficient systems. We have engaged in a broad study of the structures of triblock-copolymer solutions with particular emphasis on Pluronic P123 [PEO20PPO70PEO20] which shows a rich phase behavior depending on temperature and concentration. SAXS and SANS measurements show a transition from unimers in solution to the formation of spherical micelles followed at higher temperature by a morphological change to elongated micelles. We argue that this phase transition is driven by a limited stability of the aggregates if a size parameter exceeds a critical value of 190 Å. Grazing incidence neutron diffraction in higher concentrated solutions reveal a crystallization with a structural transition from cubic to hexagonal which seems to be related again to the morphological stability of the individual micelles. Surprisingly, we find a pronounced thermal hysteresis for this phase transition. The polymer is found to coat hydrophilic surfaces while no attachment is observed for hydrophobic surface terminations. The process of hydrophobic coating with self-assembled monolayers from trichlorosilanes followed by in-situ synchrotron reflectivity measurements will be presented. While the packing is dense for amorphous oxide surfaces, the data reveal reduced packing densities for single crystalline materials where the degree of dilution depends on the structure of the oxide. In addition, distinctly different growth modes are found for crystalline and amorphous SiO2, while the macroscopic contact angles for water are about 110° in both cases. For hydrophilic surface terminations we find a complex sequence for the adsorption of unimers and micelles depending on temperature and concentration. These dense surface coatings build up already under conditions where there are no micelles in the bulk liquid. Again, the surface coatings show a thermal hysteresis which show great resemblance to bulk the properties observed at much higher concentration and temperature. Further, the mechanical stability of the surface coating and its recovery after destruction by shear will be reported on.

Lithium borohydride is a remarkable material. It is not only a candidate in its own right as a high wt% hydrogen store but also exhibits superionic conductivity above 1080C which may be significant for lithium battery electrolytes. Moreover, lithium borohydride readily accommodates almost four times its own weight of ammonia and can intercalate other molecules such as methylamine. Combined with lithium amide, it forms mixed lithium borohydride amide compounds with low melting points and promising hydrogen desorption profiles. A similar eutectic behaviour is found when lithium borohydride is reacted with calcium and magnesium borohydride. All these properties are believed to result from the highly dynamic atomic behaviour of both Li+ and BH4- ions. This presentation will discuss recent in-situ studies of lithium borohydride involving combined ionic conductivity and neutron powder diffraction experiments that are discussed within the context of computational modelling using DFT non-equilibrium molecular dynamics. The in-situ conductivity measurements confirm that there is no intermediate phase in the vicinity of the orthorhombic-tetragonal phase transition and that the continuous change in conductivity may be explained by the co-existence of both high and low temperature phases. Computational modelling of the phase transition using non-equilibrium DFT molecular dynamics (NEMD) shows that the first-order phase transition is principally order-disorder in character although there is a significant displacive computation. Diffusion coefficients and conductivity values obtained from the NEMD-DFT calculations are in good agreement with the in-situ conductivity measurements.

Hydrogen has been identified as a fuel of choice for providing clean energy for transport and other applications, and the development of materials to store hydrogen efficiently is key to this endeavour. Lightweight hydride materials have been promoted as potential hydrogen storage materials due to their high gravimetric and volumetric hydrogen storage capacities. Neutron scattering is the ideal tool to study hydrogen storage materials as hydrogen has the largest scattering interaction with neutrons of all the elements in the periodic table. To investigate the synthesis, structure, composition and decomposition of lightweight hydride systems we have developed novel apparatus that allows us to perform time-resolved simultaneous neutron diffraction and thermogravimetric measurements on materials using the GEM and HRPD diffractometers at ISIS. This apparatus, termed the Intelligent Gravimetric Analysis for Neutrons (IGAn, Figure 1), permits us to dynamically investigate hydrogenation and dehydrogenation processes within hydrogen storage materials. This apparatus, in conjunction with other techniques that include time-resolved X-ray synchrotron diffraction, thermogravimetric analysis with simultaneous mass spectroscopy and inelastic neutron scattering, allows us to develop a complete understanding of lightweight hydrogen storage materials. Here, we report the results of our simultaneous neutron diffraction and thermogravimetric studies into a prototypical lightweight hydride family, group 1 alkali metal amides (MND2, where M = Li, Na, K), using the IGAn apparatus. Our studies focus on the formation of MND2 from the reaction of MH with ammonia and subsequent temperature resolved decomposition. The role of time-resolved, simultaneous, neutron scattering techniques in understanding the complex chemistry that occurs on formation, decomposition and cycling of this family of materials is discussed.

The excitation of ultrasonic waves in perfect crystals can lead to interesting phenomena in neutron and X-ray diffraction, such as peak broadening caused by the lattice strain gradient, satellite reflections due to the space and time modulated structure, inelastic scattering, and caustics of the beam paths. Furthermore, spatially resolved diffraction on ultrashort time scales leads to the characterization of standing waves and shock waves. White beam Laue section topography is very sensitive to spatial wave field arrangements and shows up the transition between the dynamical and the kinematic theory of diffraction. The presentation reviews the concepts on our older work, gives unpublished experimental results and an outlook to the state-of-the-art and future capabilities of technological development, and their applications in materials science and physics.

The ultrafast pulses from X-ray free-electron lasers have opened up a new form of nanocrystallography for structure determination of molecules. These pulses are of high enough intensity and of sufficiently short duration that individual single-shot diffraction patterns can be obtained from a sample before significant radiation damage occurs. This “diffraction before destruction” method may enable the determination of structures of proteins that cannot be grown into large enough crystals or are too radiation sensitive for high-resolution crystallography. Ultrafast pump-probe studies of photoinduced dynamics in proteins or other materials can also be studied. We have carried out experiments in coherent diffraction from protein nanocrystals, including membrane bound proteins, at the Linac Coherent Light Source (LCLS) at SLAC. The crystals are delivered to the pulsed X-ray beam in a continuously flowing liquid jet. Millions of diffraction patterns were recorded at the LCLS repetition rate of 120 Hz. These patterns are indexed and combined into a single crystal diffraction pattern, which can be phased for structure determination. Details of the methodology, new opportunities for phasing, and novel applications will be discussed

The functionality of shape memory alloys depends on the martensitic phase transition of the material, which involves the transformation from one crystalline phase to another. Despite the wide use of such materials, the rearrangement of atoms that facilitates their structural transformations is not well understood. We have developed an experimental technique that enables in-situ, real-time measurements of these structural transformations. This technique utilizes the high degree of coherence available from synchrotron x-rays to produce modulations, or ``speckle'', in the materials scattering pattern. Fluctuations in speckle patterns - which are directly related to the evolving structure of the material - reveal the activity caused by microstructural change. An ideal test material for developing our measurement technique is pure cobalt, which undergoes a martensitic phase transition between close-packed cubic and hexagonal crystal structures. Our measurements have revealed that during rearrangement between these structures, there is a series of fluctuations, or "microstructural avalanches", as cobalt heterogeneously transforms from the fcc to the hcp phase. These avalanches are caused by the sudden, collective relief of stresses on the lattice that have accumulated during the rearrangement of atoms. Using a wavelet-based detection scheme to analyze speckle patterns, the spatial and temporal characteristics of microstructural avalanches in cobalt were determined. These characteristics are analogous to those observed in a diverse collection of systems that exhibit heterogeneous dynamics, such as earthquakes.

Power densities generated by current generation synchrotron-based x-ray beamlines have attained sufficient levels to alter the microstructure within inorganic as well as organic materials, providing new opportunities to tailor their local properties. Within silicon-on-insulator (SOI) technology, submicron x-ray beams are capable of altering the crystallinity of the active silicon layer. The interaction region between the affected silicon and its surrounding environment extends to distances substantially larger than the incident beam footprint. Through in-situ and ex-situ investigations, we demonstrate that irreversible deformation generated in the underlying silicon oxide layer is responsible for modifying the local orientation of the SOI. A second example will be presented on the interaction of x-rays with dielectric / metallic nanocomposites, where alteration of the dielectric material can be used to impose stress within encapsulated copper structures. The time-resolved evolution of stress can be quantified in-situ using synchrotron-based x-ray diffraction techniques. We will discuss the interplay between the composite geometry and the amount of irradiation on the observed changes in stress of the copper features. These findings are compared to mechanical modeling to reveal two distinct modes of modification that the dielectric material undergoes: densification followed by an increase in elastic modulus.

New sources of X-rays are making ever more intense and coherent beams available to experimentalists. One important emerging area is known as coherent diffractive imaging (CDI) in which the diffraction from an object is used to form a high-resolution image of it without the need for additional X-ray optics. This method has been the subject of very significant development over the last decade or so and it has now been developed to the point where it can be applied to a number of important problems in materials science and a range of other areas. In this talk, I will review this method and some of its more important areas of application. An important motivation of CDI has also been its application to studies with the new X-ray free electron laser facilties. If time permits, I will describe some very recent experiments in which it is observed that materials diffract in rather different ways when subjected to extremely intense coherent ultrashort X-ray pulses.

The intense, highly collimated and spatially localized beams produced by an undulator on an Energy Recovery Linac (ERL) will approach the Fourier transform limit, ΔxΔk ge; 1/2, for localizing waves. To make contact between the wave description and the more familiar rays of geometrical optics, one makes the approximation Δkasymp;kΔtheta;. The uncertainty relation is then given by ΔxΔtheta; ge; lambda;/4π, which is known as the “diffraction limit” and places a fundamental constraint on how small the phase-space area (the product of the size and the angular divergence) of an x-ray beam can become. The ERL&’s x-ray beams are also almost fully coherent - that is, the contrast of fringes in interference experiments is approaching unity. The exquisite x-ray beams produced by an ERL source will enable experimenters to use the most highly collimated beam consistent with the small spot size they desire. The full spatial coherence will enable coherent imaging techniques to move beyond demonstration studies and become widely useful research tools. Thus, the ERL will open up new frontiers in materials research including: enabling coherent diffraction imaging of strain fields inside of nanoparticles; the determination of the atomic structure of buried volumes ranging in size from nanometers to microns; in operando studies of electrodes in working batteries, fuel cells, and electrophotocatalysts; and time-resolved studies with sub-picosecond resolution. In this talk, I will review the basic concept of an ERL and the anticipated properties of its x-ray beams. Then, I will give a few brief examples of frontier areas of materials research which will be opened up by an ERL.

In the frame of the upgrade of the European Synchrotron Radiation Facility the ID10 beamline went through a major reconfiguration in 2012. The old multi station based on the beam multiplexing via transparent diamond monochromators, previously known as Troika, has been replaced by a serial double-station setup operating in 50% time-sharing mode with independent fully optimized optics. The first station has a dedicated setup for liquid scattering experiments in various grazing incidence geometries while the downstream station has a longer hutch hosting experiments based on the scattering of coherent hard X-rays (8keV), with techniques such as X-ray Photon Correlation Spectroscopy for quantifying temporal fluctuations in slowly varying speckle patterns and Coherent X-ray Diffraction Imaging (CXDI) for retrieving the exact spatial arrangement of static disordered samples from coherent diffraction patterns. CXDI is a lens-less imaging technique based on the inversion of oversampled diffraction patterns via phase retrieval algorithms. The resolution is just determined by the highest scattering angle where the intensity can be measured and it is ultimately limited by the radiation damage. By using CXDI it is possible to image micrometric-sized bulk samples with nanometer resolution in their natural state, where electron microscopy cannot be applied without sectioning. In particular, there is a strong interest in the 3D imaging of frozen-hydrated biological objects. Here we present the tools available for 3D CXDI at ID10, the high precision sample stage and the MAXIPIX pixel detector with a new data collection strategy for increasing oversampling without compromising the resolution in real space. Finally we show the first successful 3D imaging at 50 nm resolution of a micrometric agglomerate obtained from the spontaneous self-assembly of Fe2P nanoparticles.

The long pulse spallation neutron sources call for new experimental approaches to utilize the high power of the flux in the most efficient way. Novel multiplexing techniques, such as Repetition Rate Multiplication [1] and Wavelength Frame Multiplication [2] help to solve the main challenge in the instrument design at the future European Spallation Source: how to take full advantage of the high neutron peak flux and at the same time provide high instrumental flexibility. The underlying principle of multiplexing techniques is to use a set of monochromatic wavelengths or a set of wavelength bands coming from the same source pulse by means of mechanical chopper system. In this case the instrumental parameters, such as wavelength resolution, wavelength band, repetition rate are not any more determined by the source pulse parameters, but can be flexibly defined by the chopper frequency, speed and chopper pulse. With other words, multiplexing techniques, allow us to create instead of one long pulse a number of mini-pulses with variable frequencies and pulse lengths but with the same peak flux as original pulse. Introduced first at Los Alamos National laboratory in IN500 project [2], the methods have been recently experimentally implemented with the help of unconventional use of existing time-of-flight instruments at continuous reactor sources [3], [4]. The experiments provide full proof of principle of these methods and show an enhancement of data collection rates by up to an order of magnitude. The application of the Wavelength Frame Multiplication (WFM) in diffraction was found to provide unrestricted capability for flexible pulse shaping for high and variable resolution at long pulse sources, overcoming the conventional wavelength band limitations due the source pulse parameters [4],[5]. The results show constant TOF resolution and unperturbed spectral distributions, fully comparable to the common single wavelength frame operation of pulsed source diffractometers, even for every single source pulse. Furthermore, we introduced and tested WFM application [5] using phase slewing, asynchronous pulse shaping chopper operation, which allows to avoid the problem of the frame "stitching" in the data treatment procedures. References: 1. F. Mezei, J. Neutron Res. 6 (1997) 3 2. F. Mezei, M. Russina, Advances in neutron scattering instrumentation, in: I.S. Anderson, B. Guerard (Eds.), Proceedings of SPIE, vol. 4785, 2002, p. 24. 3. M.Russina, F. Mezei, Nuclear Instr. and Methods, A604 (2009) 624 4. M. Russina, Gy. Kali, Zs. Santa, F. Mezei, Nuclear Instr. and Methods A654,(2011), 383 5. M. Russina, F. Mezei, Gy. Kali, Journal of Physics: Conference Series, 340(2012) 012018 DOI: 10.1088/1742-6596/340/1/012018

We discuss the prospects of performing equilibrium and nonequilibrium phonon spectroscopy by time and momentum-resolved x-ray diffuse scattering. In particular, we present recent results on photo-excited semiconductors and semimetals using the x-ray pump-probe end station of the Linac Coherent Light Source, free electron laser at SLAC. With this source we were able to achieve few hundred femtosecond resolution at hard x-ray wavelengths, sufficient to follow nonthermal phonon emission at the Brillouin zone-edge, as well as to measure dispersion of acoustic phonons through much of the zone. Recent advances in the source and detectors will allow with much greater resolution and range in the near future.

The development of new advanced materials and devices such as fuel cells, organic solar cells, rechargeable batteries, catalytic materials, etc. involves many challenges. For example, the complexity of these heterogeneous devices can only be studied adequately by a combination of experimental methods, in order to reveal the interplay between the microscopic material properties and the macroscopic device performances. As the need for combining techniques has been instrumental in the development of electron microscopy it is seen as equally important for the evolution of hard x-ray synchrotron methods applied in-situ for studying both real devices under operating conditions and idealized model systems under precisely controlled environments. The properties of the high energy x-rays, and their use in the studies of liquids, crystalline, nanocrystalline and amorphous materials using reflectivity, imaging, small angle x-ray scattering, diffraction and auxiliary techniques are discussed. Some examples of the applications using these techniques in the fields of metallurgy and materials research are given.

We present results from our investigations into the electronic structure of atomically precise ligand-stabilized Au₁₃[PPh₃]₄[S(CH₂)₁₁CH₃]₂Cl₂ (Au₁₃ for short) and Au₂₅(SCH₂CH₂Ph)₁₈ (Au₂₅ for short) catalysts for styrene oxidation. The synchrotron radiation X-ray absorption fine structure spectroscopy (XAFS) revealed low coordination, different geometric arrangement (Au-Au contraction) and d-band vacancies in the ligand-stabilized Au clusters in comparison to bulk Au. Au₁₃ has a higher first shell Au coordination number than Au₂₅, while the size (average coordination number) of Au₁₃ was found to be smaller than Au₂₅. The ultraviolet photoemission spectra (UPS) reveal a trend of narrower d-band width and d-band apparent spin-orbit splitting and higher binding energy of d-band center position with decreasing size of Au cluster. The d-band hole population of Au₁₃ was seen to be higher than Au₂₅. The ligands not only act as stabilizer but also play an important role as electron acceptor for Au atoms. We propose that these differences in their electronic structure could be responsible for variations in their activity and selectivity.

In the present work we report the formation of self-assembled structures of silver nanoparticles arising directly during thermal decomposition of silver carboxylates with the general formula [Ag(O2CnH2n-1)]2. The formation of ordered periodic assemblies of silver nanoparticles occurs from oxidation of the anion, with residual anion also acting as the capping agent. Monodisperse silver nanoparticles rapidly self organize into stable structures on the order of 0.5-1 mu;, and are characterized by TEM and in situ synchrotron x-ray SAXS and WAXS data. The in situ synchrotron x-ray investigation shows the changes in the diffraction patterns of a series of silver carboxylates, [Ag(O2CnH2n-1)]2 with n = 10, 12, 14, 16, 18, 22, directly during heating. As the sample of silver carboxylates reaches 180°C, the intensity of the small-angle scattering peak at 2theta;=1.1° increases, and continues to increase as the temperature rises to 200°C. The in situ X-ray investigation of the thermal decomposition of silver carboxylates at the diffraction angles 2theta;= 32-46°, showed that from 180°C and above reflections of metallic silver appear in the diffraction patterns. The electron microscopic investigation of silver carboxylates decomposed thermally at the small-angle scattering maximum showed that the product is composed of silver nanoparticles ordered in a regular periodic structure. This structure was observed for all the silver carboxylates investigated in the present work. The size of the nanoparticles is 5.2nm ±0.1nm. Unlike the previous reports of the self-assembly of silver nanoparticles occurring during drying colloid solutions on solid substrates, we find that self-assembled structures can formed directly during the thermal decomposition of metal carboxylates. In this case the formation of ordered periodic assemblies of silver nanoparticles during thermal decomposition of silver carboxylates allows these structures to be obtained in large amounts without any additional operations, that is, directly from the thermal decomposition of long-chain silver carboxylates without additional capping agents, reducing agents or structure directing components.

There is currently enormous interest in the study of magnetoelectric coupling in solid solutions of multiferroic BiFeO3 with other ABO3 perovskites with a view to break the spatially modulated incommensurate spiral spin structure of pure BiFeO3 by introducing disorder in the magnetic sublattice. Amongst the various solid solutions of BiFeO3, the multiferroic (1-x)BiFeO3-(x)PbTiO3 (BF-xPT) system shows a rich variety of magnetic and structural phase transitions. In this presentation, we concentrate on the results of the discovery of an unusual ferroelectric to ferroelectric isostructural phase transition and associated giant negative thermal expansion for the tetragonal compositions near the morphotropic phase boundary (MPB). We have recently shown that the room temperature ferroelectric tetragonal phase (T1) of BF-xPT for x=0.31 exhibits extremely large tetragonality (~18%) on account of a first order isostructural phase transition from a high temperature ferroelectric phase which is also tetragonal (T2) but with lower tetragonality and identical space group (P4mm) and the occupied Wyckoff positions. The T2 phase finally transforms into the paraelectric cubic phase at still higher temperatures. Using group theoretical considerations, we have shown that the observed atomic displacements associated with this isostructural phase transition correspond to specific irreducible representations of the P4mm space group at its Brillouin zone centre. Pronounced anomalies in the thermal displacement parameters at the T1 to T2 transition provide evidence for such a phonon mediated isostructural phase transition. The high tetragonality ferroelectric phase (T1) of BF-0.31PT shows the largest negative thermal expansion coefficient reported so far in the mixed BF-xPT system. The isostructural transition is found to persist for tetragonal compositions of BF-xPT upto x = 0.60. We have established the complete phase diagram of the BF-xPT system showing the existence of a rare critical point in any perovskite system at T ~ 677 K for x raquo; 0.63. We acknowledge collaborations with Professor Y Kuroiwa, Professor C Moriyoshi and Mr Kazuaki Taji in this work and financial support from DST. References: [1] S. Bhattacharjee, S. Tripathi, and D. Pandey, Appl. Phys. Lett. 91, 042903 (2007). [2] S. Bhattacharjee, V. Pandey, R. K. Kotnala, and D. Pandey, Appl. Phys. Lett. 94, 012906 (2009). [3] S. Bhattacharjee, A. Senyshyn, P. S. R. Krishna, H. Fuess, and D. Pandey, Appl. Phys. Lett. 97, 262506 (2010). [4] S. Bhattacharjee, K. Taji, C. Moriyoshi, Y. Kuroiwa and D. Pandey. Phys. Rev. B. 84, 104116(2011).

Laue x-ray microdiffraction at synchrotron facilities enables mapping of local microstructures and strain distributions with submicron spatial resolution and high angular resolution. In particular, we have developed focused, polychromatic/monochromatic scanning microbeam techniques for microdiffraction and microfluorescence measurements with spatial-resolution of ~400 nm at the APS beamline 34-ID-E. This facility has been used to investigate the 3D microstructure and mesoscale evolution in a wide range of materials ranging from individual nanostructures to bulk polycrystals. In this talk, we describe in-situ microdiffraction of internal microstructural and strain changes associated with the metal-insulator transition in individual vanadium dioxide (VO2) microcrystals. VO2 is a strongly-correlated electron material that exhibits a classic first-order phase transition from a high-temperature tetragonal (rutile) metal to a lower-symmetry monoclinic insulator near room temperature. Understanding how the structural and electronic transitions couple with each other has remained an active research topic for decades. Unstrained samples transform abruptly from the rutile metal to the monoclinic M1 insulating phase, while relatively small external stresses can stabilize related monoclinic M2 and triclinic T insulating phases. Recently-developed techniques for growing high-quality micro- and nano-crystals with well defined geometries has enabled direct studies of the connections between local strain, symmetry and phase behavior, including our in-situ x-ray microscopy studies. Using scanning x-ray Laue microdiffraction, we obtained spatially-resolved maps of the crystal structure (phase) and orientation as a function of temperature. In addition, by inserting a monochromator into the beam and measuring the energy for particular Bragg peaks, the lattice strain was mapped. We will describe how stresses induced either by the substrate or by electrical currents can affect the metal-insulator transition and lead to the formation of different self-organized patterns of coexisting phases. Research supported by the US Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (JDB, JZT) by the BES Scientific User Facilities Division (AT, SK) and by the NSF (AK). XOR-UNI at APS 34-ID supported by DOE BES Scientific User Facilities Division.

The use of amphiphilic block copolymers as agents to modify cell membrane structure and function has been an area of increasing research interest. Of particular interest has been the use of commercially available amphiphilic triblock copolymers of PEOn-PPOm-PEOn, so-called Pluronics or Poloxamers. Numerous investigations have explored their use in a wide range of biomedical applications, including modifiers in drug delivery, in-situ generated implants, synthetic chaperones, barriers against bacterial adsorption, neuroprotective and restorative agents, and soft tissue injury treatments (including stroke and electrical / thermal burns). In our prior work, we have identified specific polymer architectures among this family of triblock copolymers that seal defects or that form anti-microbial barriers on cell surfaces. Specifically, Small-angle X-ray scattering studies permitted determination of the 1D electron density maps of the polymer associated with a model biological membrane. More recently, we have chemically modified these polymers with quorum sensing regulating groups (e.g., phosphate) and examined how introduction of these groups alters the polymers interaction with the lipid bilayer. Insights on the mode of insertion of the chemically modified polymer and how they influence membrane structure is provided using X-ray and neutron scattering. This work provides a strong foundation for a significantly larger effort coupling basic research on the physical principles of polymer architecture and their relationship to the association and function of cell membranes.

Understanding and further modeling of microstructure formation, i.e. transformation sequences and kinetics need in situ characterization to quantify the transformation kinetics as well as to get additional characteristic for the multiphase polycrystalline component. In situ characterization using high energy X-ray diffraction (ID15 ESRF) were realized in parallel to more conventional techniques (electrical resistivity or dilatometry) to characterize transformations in metastable Ti alloys. High energy allowed to analyze a consequent volume of the specimen, avoiding surface effects, and to increase the sensitivity and acquisition frequency for the diffraction patterns. Our contribution aims to highlight results that could only be obtained using the in situ characterizations. For the set up used, specimens were in rotation to increase the number of analyzed parent grains. Heating was achieved by a radiant furnace and cooling by gas blowing. A specific sample holder was realized able to measure the temperature by a thermocouple spot-welded on the surface, even for the specimen under rotation. This allowed to apply controlled thermal variations. The beam was monochromatic and Debye Scherrer rings were recorded in transmission on a 2D detector. Time for acquisition and read out was 3.5s. After calibration, Debye Scherrer rings were integrated integration to obtain I-2theta; diagrams that were analyzed using Rietveld method (Fullprof program). Different results will be given. At first, the influence of the thermal path on the transformation sequences will be shown. Notably, we will illustrate the formation of different metastable states for precipitation during ageing. A complex sequence occurred depending on the heating conditions. For some lower heating rate, hexagonal isothermal omega; formed at first. Additional peaks were also observed that could be indexed as peaks of a CFC structure. Increasing the time or temperature, an orthorhombic phase (α”) appeared while peaks corresponding to omega; and β2 vanished. It is worth mentioning that HEXRD clearly demonstrated the formation of a metastable orthorhombic phase that is never mentioned in TEM observations. In addition, the evolutions of FWHM will be shown and compared for different transformation conditions. For the higher transformation temperatures, the diffusive character of the transformation could explain FWHM variations in the parent phase. The variations observed for the lower transformation temperatures need to consider additional factors that affect the ray profiles (stress state for example).

The SNAP instrument at the SNS is currently the most advanced neutron diffractometer dedicated to high pressure research. The operating power of the SNS, current at 1 MW - and projected to reach 1.4 MW in the medium term - allows not only a very fast data collection, but also the reduction of sample size, in some cases, to sub milligram amounts. The ability to place the detectors at variable 2-theta; scattering angle and to select the appropriate neutron wavelength bandwidth range allows for the fine tuning of the ideal resolution/intensity parameters for each experiment. Since this facility has been made available to the high pressure user community, a broad range of materials systems have been investigated, in the form of powders, glasses and single crystals. Here we will present some recent scientific results of research performed at SNAP, namely examples of compression mechanisms of amorphous solids, magnetic phase diagrams in lanthanides, phase competition in manganites and structural studies of clathrate hydrates. These examples will highlight how appropriate use of the SNAP capabilities can be used to optimize high pressure experiments. In addition, ongoing improvements and additions to the SNAP capabilities will be discussed, in particular the recent development through the Instrument Development Team of a new generation of Diamond Anvil pressure cells that allows data collected up to 50 GPa, a new frontier in high pressure neutron scattering.

The advent of extremely high neutron flux, unique time event data acquisition and novel instrumentation at SNS open up new possibilities, especially for in-situ dynamic and kinetic studies. With the-state-of-art instrumentation and advanced data processing, the engineering diffractometer, VULCAN at SNS provides an entirely new approach to study time-resolved phenomena such as in-situ phase transformation under temperatures, stresses, or electrical charges, et al. In this talk, we will present the advanced capabilities by several great phase transformation studies with time scales ranging from minutes to sub seconds, including a demonstration measurement of transient phenomena of microseconds time scale. Details of this measurement methodology as well as its potential application in various scientific cases will also be presented.

The method of atomic pair-density function (PDF) has long been used to characterize the structure of glasses and liquids, which do not have long-range order, through x-ray and neutron diffraction. It is usually assumed that the sample is isotropic, and atomic distribution depends only on radial distances between atoms. For this reason it is also called the radial distribution function (RDF). However, the sample is not necessarily isotropic. For instance when a stress is applied and the sample undergoes elastic or plastic deformation it no longer remains isotropic. In this talk we discuss advanced PDF techniques, the anisotropic PDF method to characterize anisotropic materials, and the dynamic PDF method to describe local atomic and spin dynamics. In the anisotropic PDF method the three-dimensional PDF, g(r), and the structure function, S(Q), are expanded by the spherical harmonics. The anisotropic PDF, gml(r), is related to the anisotropic structure function, Sml(Q), through the spherical Bessel transformation. We show how this approach elucidated the atomic processes for elastic and anelastic deformation of metallic glasses. The lattice and spin dynamics of a solid are usually described in terms of phonons and magnons, whose dispersion can be observed in the dynamic structure factor, S(Q,omega;), measured by inelastic scattering. In strongly disordered systems such as liquids, however, phonons and magnons are strongly damped, and their dispersion cannot be easily seen in S(Q,omega;). In solids the phonon dispersion is determined by diagonalizing the dynamical matrix. However, in liquids the dynamical matrix itself is time-dependent, so the diagonalization does not lead to phonon eigen-state and strong localization ensues. The dynamic PDF (DPDF), g(r,omega;), is a Fourier-transform of S(Q,omega;) over Q, and describes local dynamics well. We show an example of DPDF for liquids which demonstrates super-localization of atomic dynamics in liquids.

Silicon solar cells are generally limited by inhomogeneous nanoscale defects scattered throughout the bulk material, especially in low-cost multicrystalline devices. The interactions of metal impurities with structural defects, such as grain boundaries and dislocations, limit electronic transport and can also result in low breakdown voltages and shunts. Synchrotron-based X-ray microscopy has proven successful at determining the elemental distributions and chemical states of second-phase metal precipitates at grain boundaries. However, characterization of dislocation-impurity interactions has proven particularly challenging, as dislocations are often tens of microns apart across the 15.6 cm x 15.6 cm wafer and are decorated with nanoscale second-phase metal silicides or atomic point defects. Techniques capable of bridging the 7 orders of magnitude of this characterization problem are few. Recent advances in zone plate optics and nanopositioning now provide smaller X-ray beam spot sizes. A state-of-the-art hard X-ray nanoprobe beamline with x-ray fluorescence imaging capability at the Center for Nanoscale Materials at beamline 26-ID (APS) now can achieve beam spot sizes < 50 nm, providing unparalleled XRF resolution while maintaining reasonable acquisition times. Using this nanoprobe, we show that the recombination activity of dislocations in mc-Si is strongly correlated with the presence of precipitated metals [1]. Furthermore, we examine wafers in the as-grown state after crystallization and compare to fully processed sister wafers to evaluate when during device processing dislocations are decorated with metals. Our preliminary findings suggest more widespread dislocation decoration during solar cell processing rather than during crystallization. Overall, we demonstrate a non-destructive hierarchical approach that can map elemental composition with 25 nm steps at selected regions of interest on a centimeter-scale sample. The advances in X-ray spatial resolution and sensitivity make tractable a host of inquiries pertaining to defect engineering in energy science such as the metal-dislocation interactions in silicon. [1] M. I. Bertoni , D. P. Fenning , M. Rinio , V. Rose , M. Holt , J. Maser and T. Buonassisi, “Nanoprobe X-ray fluorescence characterization of defects in large-area solar cells” Energy Environ. Sci., 2011,4, 4252-4257

Neutron imaging has been increasingly used to study the behavior of liquid water in operating fuel cells [1-4]. In the last years, the necessary spatial resolution for cross sectional imaging was achieved, and several studies reported the observation of water in the different functional layers of the cell [5-7], including the porous media used for the fine distribution of gases. In particular, by using an anisotropic resolution enhancement approach, we demonstrated the possibility of imaging with an effective resolution of 20 mu;m and exposure times of 10 seconds [7], making the observation of transient processes possible. The single observation and quantification of liquid water is not sufficient to understand its impact on cell operation. For this purpose, advanced electrochemical characterization methods were developed and simultaneously applied to imaging. Recently, we reported the use of a novel method using short pulses of helox (21% O2 in He) and of pure oxygen for the direct measurement of mass transport losses [8]. Here, we will present the results of our latest work using the combination of steady state and time resolved neutron imaging with advanced electrochemical methods, including the previously mentioned helox pulse analysis. The relation between liquid water accumulation and the electrochemical characteristics were studied using either standard cell structures (which include lateral and perpendicular transport) or so called 1D cell structures, in which the lateral transport is minimized. The latter allows meaningful comparisons to simple transport models, as a first step in providing a reliable determination of the impact of liquid water on cell operation. 1. A. Geiger, A. Tsukada, E. Lehmann, P. Vontobel, A. Wokaun, and G. Scherer, Fuel Cells 2, 92 (2002). 2. R. Satija, D. Jacobson, M. Arif, and S. Werner, J. Power Sources 129, 238 (2004). 3. N. Pekula, K. Heller, P. Chuang, A. Turhan, M. Mench, J. Brenizer, and K. Ünlü, Nucl. Instr. Meth. A 542, 134 (2005). 4. D. Kramer, E. Lehmann, G. Frei, P. Vontobel, A. Wokaun, and G. Scherer, Nucl. Instr. Meth. A 542, 52 (2005). 5. M. A. Hickner, N. P. Siegel, K. S. Chen, D. S. Hussey, D. L. Jacobson, and M. Arif, J. Electrochem. Soc. 155, B427 (2008). 6. S. Kim and M. Mench, J. Electrochem. Soc. 156, B353 (2009). 7. P. Boillat, G. Frei, E. H. Lehmann, G. G. Scherer, and A. Wokaun, Electrochem. Solid-State Lett. 13, B25 (2010). 8. P. Boillat, P. Oberholzer, A. Kaestner, R. Siegrist, E. H. Lehmann, G. G. Scherer, and A. Wokaun, J. Electrochem. Soc. , Accepted manuscript (2012).

We show using synchrotron as well as in-house x-ray diffraction methods that gaseous CO2 intercalates into the interlayer space of the synthetic smectite clay fluorohectorite at conditions close to ambient. The rate of intercalation is found to be dependent on the interlayer cation (Li+ or Na+ in this case), with about one order of magnitude increased rate in Li-fluorohectorite compared to Na-fluorohectorite. We further show that Li fluorohectorite is able to retain CO2 in the interlayer space at room temperature, which could have applications related to CO2 capture, transport and storage. De-intercalation starts occurring at temperatures exceeding 30 °C.

CrB₂ possess the hexagonal AlB₂ structure which belongs to the spacegroup of P6/mmm. The compound exhibits para- to antiferro-magnetic transition at 88 K. By using a macroscopic measurement technique, that is, a conventional resonant ultrasound spectroscopy with a millimeter size mono-crystal, significant elastic anomalies have been observed just above the magnetic transition temperature. On the other hand, elastic constants determined by a microscopic measurement technique, that is, an inelastic X-ray scattering method (BL35XU, SPring-8, Japan) do not show any elastic anomalies at around the transition temperature. In order to explain the discrepancy, we have introduced a kind of so called ΔE effect resulting from a multidomain structure. If crystal lattice is slightly deformed by a spontaneous magnetostriction in the antiferromagnetic state, the symmetry of crystal lattice is lowered from hexagonal to monoclinic when the symmetry of magnetic structure is taken into account. By the lowering of the symmetry, six magnetic domains are generated in the antiferro magnetic state. When magnetic domain boundaries move to response to externally applied stresses, the mechanical deformation is absorbed by nonelastic deformations induced by the movement of magnetic domain boundaries. This multidomain model well explains all the experimental results obtained by both microscopic (X-ray) and macroscopic (ultrasound) measurements. The microscopic measurement is useful to obtain the true elastic properties of crystal lattice without effects coming from a multidomain structure.

The sharp Bragg reflections that occur in diffraction patterns of all real crystals are used by conventional crystallography to deduce the average repetitive arrangements of atoms or molecules. Diffuse scattering, on the other hand, contains information about the deviations from the average (i.e., different types of disorder) and gives structural information on a length scale (~1Å - 1000Å) that goes well beyond that of the average unit cell. In many important materials, it is this extended range of structural information that is crucial in determining their unique or novel properties, rather than the average unit cell structure. For crystalline powders or nanoparticles this information is spherically averaged so that interpretation and analysis is significantly impeded. However for single crystals the full three-dimensional information is preserved with both orientational and distance information unambiguously accessible, offering perhaps the most definitive means of elucidating the nanoscale structure. Despite the fact that diffuse scattering is a powerful probe of local and nanoscale structural information the development of methods to interpret and analyze it has lagged well behind the development of conventional average structure determination. The reasons for this are, first, that diffuse scattering intensities are very much weaker than Bragg peaks, making the experimental observation vastly more demanding and time consuming. However, the advent of intense synchrotron sources and various kinds of area detectors means that this aspect of the problem is largely solved and it is now possible to obtain high quality three-dimensional (3D) diffuse scattering data relatively routinely. The second reason for the lag in development is that the sheer diversity of different types of disorder that occur in nature has made it difficult to formulate a solution strategy that will work for all problems. Although interpretation and analysis of diffuse scattering from single crystals remains a challenging problem many advances have been made. In particular the use of Monte Carlo (MC) computer simulation of a model structure has become a powerful and well-accepted technique for this purpose. The method consists of comparing diffraction patterns calculated from a computer model of the disordered structure with measured X-ray or neutron diffuse intensities. The advantage of the method is that it can be applied generally to all systems regardless of their complexity or the magnitude of the atomic displacements that might be present. The only limitation is the extent to which the MC energy can be made to provide a realistic representation of the real system energy. At one extreme a very simplified model may be useful in providing a qualitative demonstration of particular effects while at the other a quantitative and very detailed description of a disordered structure can be obtained.

Photoelectron spectroscopy (PES) is an excellent tool for material research due to the possibility to probe both electronic and geometric structure. PES provides direct access to the properties of novel materials. In this contribution we discuss some recent trends in PES and present state-of-the-art work within the different applications. Photoelectron spectroscopy went through a revolution in the 1990&’s, with the development of parallel angular detection using 2D detectors, a development that VG Scienta is proud to have contributed to. The possibility of simultaneous recording of Angular resolved PES (ARPES) spectra enables not only band structure measurements, but also X-ray photoelectron diffraction (XPD), depth profiling and standing wave spectroscopy. Recent examples of ARPES results will be given, including studies of super conductors, graphene, and topological insulators. Experiments done under normal surface science conditions (Ultra High Vacuum) are of limited use in some applications, e.g catalysis, due to the pressure gap problem. This motivates the study of systems at ambient pressures. Here we present a High Pressure Photoemission (HiPP) instrument developed in collaboration with Advanced Light Source (ALS). This instrument allows standard PES measurements as well as spatial and angle resolved spectra at HiPP conditions. Some recent results include spatially resolved investigations of solid oxide electrochemical cells (SOC:s) and electrochemical properties of junctions. We will also report on recent advances in constructing a new generation of instrumentation combining HiPP and Hard X-ray Photoelectron Spectroscopy (HAXPES). A novel electron analyser, designed for optimal transmission in combination with very efficient differential pumping, will be presented together with preliminary results.

Water/methane aqueous mixtures are important in the study and processing of wet natural gas as well as for understanding homogenous catalytic conversion of methane to methanol. Methane shows considerable non-ideal thermodynamic mixing properties. Presumably this is due to the formation of nanoscale structures in solution as a consequence of its hydrophobic character. Various nanostructures have been proposed, for example water cage structures surrounding a single methane molecule. However, there is no direct experimental evidence in the literature for methane solution structure. We performed small-angle neutron scattering (SANS) measurements of protonated methane in heavy water at 298 C and at 0.7 and 1.5 MPa, for which we designed and build a specialized gas-mixing cell. The SANS data follows the Debye-Bueche model of a randomly distributed two-phase system with a correlation length of about 255 Å at both pressures. The Porod invariant, on the other hand, gives Phi;(1-Phi;)Δρ² of 0.38 and 2.6 10¹⁶ cm⁴ at 0.7 and 1.5 MPa, respectively. This result indicates that the volume fraction of the methane-rich phase, Phi;, and or the composition of the phase, determining the contrast, Δρ, is dependent on the pressure. These results show a previously undisclosed aqueous solution structure of methane on the nanoscale domain.

In the last decade, there have been extensive efforts to develop new complex semiconductors capable of absorbing visible light and using the absorbed energy to split water and renewably produce hydrogen fuel. While a great deal of effort has been devoted to characterizing the activity of these semiconductors, much less effort has been devoted to understanding their structures and elucidating structure-property relationships. A combination of neutron and synchrotron powder diffraction experiments have been used to correct the structure of some wolframite and pyrochlore materials important to this field, as well as to determine the structure of novel pyrochlore and closely related compounds that we have designed and synthesized for visible light (E_g < 3.0 eV) water splitting applications. Furthermore, neutron pair-distribution function experiments have been carried out to understand disorder, inhomogeneities, intergrowths, and stacking faults in some oxynitride perovskite and wurtzite phases in concert with DFT studies, including Monte Carlo and molecular dynamics simulations.

Ferromagnetic shape memory alloys (FSMA) are considered for next-generation sensors and actuators due to their large magnetic-field-induced strains (up to 10%) and stress induced changes in magnetization (up to 30%). So far, Ni-Mn-Ga alloys have shown the largest magnetic-shape-memory (MSM) effect at ambient temperatures. The MSM effect arises from a strong coupling between the order parameters that characterize the electron spins and the orientation of the crystal lattice. The coupling between the equilibrium crystallographic and magnetic structures of an off-stoichiometric Ni2Mn1.14Ga0.86 alloy were elucidated from the refinement of high-resolution single crystal neutron diffraction data, following a (3+1)-dimensional superspace formalism. Structural and magnetic changes under the application of mechanical stress and/or magnetic field were determined from in situ diffraction experiments with polarized and unpolarized neutron beams. Under a compressive stress, single crystalline Ni2Mn1.14Ga0.86 was shown to exhibit a maximum pseudoplastic strain of ~5.5% , which results from orthogonal reorientation of the crystallographic twins. A method to quantify the amount of twin reorientation from in situ neutron diffraction patterns is presented, which shows that a 5.5% macroscopic strain corresponds to a reorientation of ~85% of the twins. Reorientation of crystallographic twins in Ni-Mn-Ga can also occur by the application of a moderate magnetic field of 1 T. Using polarized neutron diffraction, we have studied the rotation of the electron spins which occurs simultaneously during the process of twin reorientation. Furthermore, the effects of mechanical constraint and temperature on magnetic-field-induced structural and magnetic changes are also discussed.

Spatially resolved diffraction of high energy (> 50 keV) monochromatic x-rays is used to non-destructively map microstructure inside of bulk polycrystalline materials. Tracking of structural responses to thermal and mechanical processes allows direct comparisons to computational models. Measurements spanning macroscopic volumes of the order of a cubic millimeter with micron scale resolution generate large, statistically significant data sets for such comparisons. Measurements are carried out at the 1-ID high energy beamline at the Advanced Photon Source. Near-field High Energy Diffraction Microscopy (nf-HEDM) uses a line focused beam to illuminate planar cross-sections of samples. A precision rotation stage in combination with a high resolution area detector placed 5 to 15 mm downstream of the sample allows imaging of diffracted beams. Large numbers of Bragg peaks from each sample volume element are imaged as the sample rotates through 180 degrees. Measurements at multiple sample-to-detector distances encodes the scattering angles and the position of origin within the sample of each observed peak. Volumetric measurements consist of 100 or more such layer measurements. Microstructures, in the form of a voxel based crystallographic orientation field, are reconstructed via high performance computing using a forward model simulation of the experiment and sample structure. Examples illustrating these measurements will include annealing studies of high purity aluminum and nickel and tensile deformation measurements of copper and zirconium. Computational feature extraction and tracking will be described. Far-field HEDM measurements will be briefly described. Far-field HEDM measurements will be briefly described. These use a large format area detector placed about a meter downstream of the sample. Elastic lattice strain tensors are determined for individual crystalline grains inside of polycrystalline samples. Current work aimed at integrating near- and far-field measurements will be described. Integrated reconstructions should yield maps containing both the orientation and strain fields at sub-grain length scales. Such microstructure descriptions spanning macroscopic volumes in successive sample states should aid in addressing problems such as fatigue and failure which are dominated by rare initiation events.

The depth-dependent, as-grown and deformation-induced strain and dislocations partitioned through the interfaces in a two-phase layered NiAl-Cr(Mo) structure are directly measured at the mesoscale using 3D X-ray microdiffraction. It is demonstrated that in the as-grown, undeformed state, neighboring submicron Cr solid solution and NiAl eutectic lamellae (doped with ~3% Mo) form a hetero-interface with 180 degree rotation around a <112> pole. It is shown that the mechanical response to the indentation of a layered composite with alternating Cr(Mo)-NiAl lamellae is distinct from the response of single-phase materials. In the center of the indent, after the load is released, the NiAl lamellae are under compressive forward stresses (with the same sign as the indentation-induced compression) while Cr solid solution lamellae are under tensile back stresses (with opposite sign from the indentation load). Supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division.

2D detectors, when used for stress, texture and grain size evaluation, have many advantages over the conventional 0D and 1D detectors. First, the measurement time is significantly reduced due to the large portion of the diffraction ring being measured at each exposure. 2D diffraction data has a large angular coverage in both 2theta and gamma directions. The algorithms to analyze 2D data must be able cover the diffraction intensity distribution in both the 2theta and gamma directions. The diffraction vector approach has been approved to be the genuine theory in 2D data analysis. The unit diffraction vector for all the pixels in the 2D pattern measured in the laboratory coordinates can be transformed to the sample coordinates. The vector components expressed in the sample coordinates can then be used to derive fundamental equations for many applications. The 2D fundamental equation for stress measurement governs the relationship between the stress tensor and the diffraction cone distortion. The fundamental equation for stress analysis with 0D and 1D detector is a special case of the more general 2D equation. The diffraction intensity variation along the gamma represents the texture of the sample. The unit diffraction vector in sample coordinates maps the intensity variation into the pole-figure. The diffraction vector distribution given by the incident beam and gamma range also defines an instrument window which determines number of diffraction spots on the diffraction ring corresponding to the grain size and size distribution. Experimental examples in the above applications are also given in this presentation. Reference: Bob He, Two-dimensional X-ray Diffraction, John Wiley & Sons, 2009

Low-alloyed TRIP-assisted steels belong to a new generation of advanced steels that combine high strength with good formability. At room temperature, the TRIP microstructure contains three phases: ferrite, bainite and retained austenite. The remarkable combination of high strength and ductility results mainly from the TRansformation Induced Plasticity (TRIP) effect, which involves the martensitic transformation of the metastable austenite. However, the relation between the stability of the retained austenite and the mechanical properties of TRIP steels is still not understood in detail. The martensitic transformation behaviour of the meta-stable austenite phase occurring in low-alloyed TRIP steels has been studied in-situ at different length scales during deformation at the beam line ID11 of the ESRF. We have correlated the macroscopic behavior of the material to the observed changes in the volume fraction and lattice parameter of the phases obtained from the powder analysis of the diffraction data. The load partitioning and the texture evolution during deformation have been investigated as a function of temperature and stress, together with their effect on the austenite transformation behavior. Moreover, the intense beam of high energy X-rays with micron size dimensions makes it possible to monitor individual grains in the bulk of the material, we have been able to monitor the transformation of individual austenite grains into the TRIP microstructure. The critical stress for the transformation is correlated to microstructural characteristics like the austenite grain size, carbon content and Schmid factor. Combining the experimental results of powder data and single grains makes it possible to understand the austenite stability under mechanical loading.

The hydrogen uptake during operation, design basis loss of coolant accidents (LOCAs) and severe accidents (accidents beyond LOCA) results in a degradation of the mechanical properties of the nuclear fuel cladding tubes. This hydrogen related reduction of strength and toughness has high safety relevance for the reactor under service and transient conditions. The neutron imaging investigations were performed at the ICON facility at the Swiss neutron source SINQ (Paul Scherrer Institute Villigen, Switzerland). The non-destructive character of neutron imaging allows in-situ investigations of hydrogen uptake and relocation process in zirconium alloys. The strong contrast between hydrogen (very high total neutron cross section) and zirconium (very low total neutron cross section) provides the possibility to detect even small changes in the hydrogen concentrations. The hydrogen uptake during operation can results in the so called delayed hydride cracking (DHC). In material with subcritical tensile loading hydrogen diffuses in the strained region of the stress field above the tip of a crack. It reduces the strength and toughness of this area significantly. The crack can grow in this area. The stress field shifts ahead the newly formed crack tip and the hydrogen follows. First time resolved neutron radiography investigations of the hydrogen distribution in a yielded specimen were performed. The inhomogeneous hydrogen distributions in cladding tubes after LOCA result in brittle regions and influence the material hardness and the fracture appearance in the tensile. These distributions were visualized by neutron radiography and quantitative determined by means of neutron tomography. In severe accidents were higher temperature can occur compared to LOCAs the hydrogen uptake results in a shift of the alpha to beta zirconium phase transition. A reduction of the melting point and local meting below the expected temperature is the consequence.

Neutrons and synchrotron X-rays are complementary tools for the characterisation of (engineering) materials. The versatility of both types of radiation is demonstrated and reviewed using key experiments covering a range of length scales, from nano meters precipitates to bulk residual stress, and using a variety of techniques such as diffraction and imaging. An important aspect of the applications has always been the commercial exploitation of large scale neutron & synchrotron X-ray facilities, and the state of the art, as well as future potential is discussed.

The most commonly used of the modern 3D imaging methods is probably X-Ray Computed Tomography (XRCT) because of its multimaterial, multiscale and non destructive character. Thanks to synchrotron sources, XRCT has recently seen important improvements in terms of temporal and spatial resolution that we have applied for understanding the evolution of the microstructure of materials under load. XRCT can indeed be coupled with in situ loading of the sample (in situ tension or compression, in situ heating, in situ freezing, etc...). The 3D image of the initial microstructure of the sample can, in a final analysis stage, be used as a direct input for a numerical simulation of the response of the material to the load, the results of which being directly comparable to the in situ experiments. This presentation will illustrate this combination of techniques and how we have used it in recent studies in order to understand the deformation of heterogeneous materials. On the one hand, we will focus on recent examples where we have used ultra fast imaging (one tomography scan every second with a voxel size of 1 µm) for analyzing the fracture of fragile materials. On the other hand, we will also show examples where a very high resolution (voxel size below 100 nm) has been used to observe very small details of the microstructure and its evolution during ex situ tensile tests.

Neutron Imaging development has skyrocketed in the past few years. Coming from simple transmission images through computed tomography and stroboscopic imaging, current imaging methods are now exploiting scattering effects to gather spatially resolved information that could so far only be achieved in a spatially integrating mode by dedicated scattering instruments. The new imaging methods will not replace but complement current scattering instruments by determining inhomogeneities in scattering samples and determining regions of interest for further examination. Energy-resolved Bragg-edge scanning can now identify areas of stress and strain, dark field imaging with linear phase grids or macroscopic scatter grids create emission images of small angle scattering, and magnetic depolarisation imaging visualizes quantum phase transitions between ferromagnetic and paramagnetic states as well as spatial inhomogeneities and differences in transition temperatures within samples. The talk will give an overview about current research in neutron imaging methods at several European institutes, illustrated with specific examples.

Developments of composites materials had begun in the 1970's. They aimed in improving mechanical properties due to the presence of reinforcement particles. The addition of particles in a matrix led to different modifications: considering the nature of the phases and the microstructure, we can mention interface reactivity between matrix and particles, changes in the chemical composition of the matrix and modified kinetics of microstructure evolution in the matrix (as compared to the matrix without particles); considering the mechanical aspects, thermal stresses may be generated due to the differences in expansion coefficients between the particles and the matrix, or any changes in the matrix leading to a phase transformation. In the present work, we studied the evolution of the phases and the behavior of a steel based MMC during thermal treatments, for which a phase transformation occurred on cooling. Experiments and numerical simulation are considered. In order to characterize the phase evolution and mechanical state in the composite during thermal treatment, in situ high energy diffraction was used to provide direct analysis of the transformation sequences in the steel-based matrix composite (MMC) reinforced with TiC particles. The MMC was elaborated by powder metallurgy. Evolution of the phase fractions of the matrix and TiC particles as well as the mean cell parameters of each phase were determined by Rietveld refinement from high energy X-ray diffraction made on beamline ID15B (ESRF, Grenoble, France). The experimental results show that the presence of TiC particles modified the kinetics of phase transformation of the matrix, as compared to a matrix with same composition, by favoring the transformation at higher temperature. Phase transformation of the matrix from austenite to ferrite and cementite is evidenced by following the mass fraction of each phase. Moreover, evolution of the cell parameters evidences a non-linear behavior clearly observed at the end of cooling and associated with thermal stresses. The difference in the coefficient of thermal expansion between matrix and TiC particle as well as the phase transformation during heat treatment induce a strong effect on the stress state of each phase. In order to analyze the evolution of stress in each phase during thermal treatment and principally the effect of the phase transformation of the matrix, micromechanical calculations were performed using finite element method. The calculations take into account the thermal stresses and the volume changes associated with the matrix transformation. After cooling, it was found to be in compression (negative mean stress) in the TiC particles and in tension in the matrix area around the TiC particles with low shear stresses in both phases. The tendencies measured from in situ synchrotron diffraction (mean cell parameters) matched well with the numerical estimates.

Nondestructively resolving structural subtleties in nanomaterials that come about due to intrinsic size effects and extrinsic boundary conditions is a challenge for which high-resolution x-ray microscopy is well suited. X-ray Bragg ptychographic imaging techniques have been under development that combine aspects of nanodiffraction and coherent imaging, yielding a robust imaging approach that is sensitive to lattice strain and is capable of sub-beam diameter resolutions. Here, we will discuss the details of coherent x-ray Bragg projection ptychography (BPP) - a structural imaging technique we developed for nondestructively studying nanoscale materials - and present results obtained by applying the technique to measure strain in Si-Ge prototype devices. We have reconstructed, with 16 nm resolution, profiles of lattice deformation in 65 nm thick Si0.8Ge0.2 epitaxial thin film structures grown on a patterned (001) silicon-on-insulator substrate. Two sources of lattice distortion were revealed in this nanoelectronic system acting at length scales from tens to hundreds of nanometers from feature edges. The x-ray results will also be compared to cross-sectional TEM measurements and elastic modeling predictions to confirm their consistency with BPP analysis.

Fundamental understanding of precipitate nucleation and growth is essential for controlling the microstructure induced by phase transformation. Quite often, phase transformations in complex materials, which are spatially heterogeneous and chemically multicomponent, occur concurrently at multiple length scale. Over the last decade, we have been focusing on developing a powerful combination of experimental methods, in-situ diffraction and small angle scattering and complementary real-space atom probe tomography, to probe and elucidate how nanoscale precipitates nucleate and grow. In this talk, we will discuss nucleation in two materials systems: bulk metallic glass and nanostructured steel. In the case of bulk metallic glasses, simultaneous diffraction and small angle scattering showed how short- and medium-range order parameters compete and synergize to form long-range order during nano crystallization [1-3]. In the case of nanostructured steel, sub-nanometer individual nucleation events were successfully imaged by atom probe tomography after small angle neutron scattering experiments provided initial clues of what to look for [4]. MKM, XLW and ZWZ were sponsored in part by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Atom Probe tomography research (MKM, ZWZ) at the Oak Ridge National Laboratory SHaRE User Facility and the scattering work at Advanced Photon Source, Los Alamos Neutron Science Center, and Spallation Neutron Source were sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. 1. X.-L. Wang et al., "In-situ Synchrotron Study of Phase Transformation Behaviors in Bulk Metallic Glass Using Simultaneous X-ray Diffraction and Small Angle Scattering," Phys. Rev. Lett., 91, 265501 (2003). 2. L. Yang et al., “Nano-scale solute partitioning in devitrified bulk metallic glass,” Adv. Mat., 21, 305-308 (2009) 3. D. Ma et al., “Power-law scaling and fractal nature of the medium range order in metallic glasses,” Nat. Mat., 8, 30-34 (2009) 4. Z. W. Zhang et al., “From embryos to precipitates: a study of nucleation and growth in a multicomponent ferritic steel,” Phys. Rev. B, 84, 174114 (2011)

The electronic structure and local structure of thiol ligand stabilized (AuAg)₁₄₄SR₆₀ nanoclusters was investigated by X-ray absorption fine structure (XAFS). By comparing the XAFS of (AuAg)₁₄₄SR₆₀ with bulk Au and Ag, a better understanding of the effect of ligand and Ag on the Au-Ag structure was obtained. The Au L₃ edge X-ray absorption near edge structure (XANES) was used to examine the d-band character of Au, which is highly related to the electronic, magnetic and catalytic activities of Au. It was observed that the d band hole population of Au in (AuAg)₁₄₄SR₆₀ is higher than that of bulk Au. The Fourier transforms of Au L₃ edge and Ag K edge extended X-ray absorption fine structure (EXAFS) provided the information of atomic structure of (AuAg)₁₄₄SR₆₀ cluster such as average coordination number and bonding lengths. The form of AuAg alloy core was confirmed by EXAFS. The S K-edge XANES revealed the (AuAg)-S interaction in the (AuAg)₁₄₄SR₆₀ cluster. The (AuAg)₁₄₄SR₆₀ catalysts were investigated in the catalysis of styrene oxidation.

Electrochemical energy storage devices are key components for innovative power train systems such as PHV, FCHV and EV. Especially for a long-range EV, the energy density of the battery system is very critical. The battery system for the EV requires significantly higher energy density than that of state-of-art Li-ion battery (LIB). Therefore, a post-LIB system is very important as a future energy source for the EV. We believe the multivalent Mg based battery system may achieve higher energy density than LIB because a Mg-ion transfers two electrons resulting in an improved capacity. Mg metal is an ideal anode active material for a rechargeable Mg battery system because it shows very good cycle performance without the formation of any metallic dendrites. Recently, we have isolated the active species for Mg deposition through crystallization, [Mg2(mu;-Cl)3omicron;6(OC4H8)]+, but little is known about the mechanism for Mg deposition from this electrolyte. The electrochemical deposition of magnesium from [Mg2(mu;-Cl)3omicron;6(OC4H8)]+ has been monitored in situ with X-ray absorption spectroscopy (XAS). The utility of the cell was confirmed by XANES through a shift in the Mg K-edge after reduction of the electrolyte. Furthermore, the XANES and EXAFS regions data have been analyzed to probe the interface between the electrolyte and platinum working electrode. In situ measurements showed the presence of an additional Mg species besides the Mg dimer at potentials below Mg plating. The electrochemical XAS experiments establish a method to directly observe the reduction process from complex Mg electrolytes.

We use new neutron scattering instrumentation to follow in a single quantitative time-resolving experiment, the three key scales of structural development which accompany the crystallisation of synthetic polymers. These length scales span 3 orders of magnitude of the scattering vector. The study of polymer crystallisation dates back to the pioneering experiments of Keller and others who discovered the chain-folded nature of the thin lamellae crystals which are normally found in synthetic polymers. The inherent connectivity of polymers makes their crystallisation a multiscale transformation. Much understanding has developed over the intervening fifty years but the process has remained something of a mystery. There are three key length scales. The chain folded lamellar thickness is ~ 10nm, the crystal unit cell is ~ 1nm and the detail of the chain conformation is ~ 0.1nm. In previous work these length scales have been addressed using different instrumention or where coupled using compromised geometries. More recently researchers have attempted to exploit coupled time-resolved small-angle and wide-angle x-ray experiments. These turned out to be challenging experiments much related to the challenge of placing the scattering intensity on an absolute scale. However, they did stimulate the possibility of new phenomena in the very early stages of crystallisation. Although there is now considerable doubt on such experiments, they drew attention to the basic question as to the process of crystallisation in long chain molecules. We have used NIMROD on the second target station at ISIS to follow all three length scales in a time-resolving manner for poly(e-caprolactone). The technique provides a single set of data from 0.01 to 100Å-1 on the same vertical scale. We present the results using a multiple scale model of the crystallisation process in polymers to analyse the results.

Chemical vapour deposition on transition metal catalysts is a highly promising method for producing high quality graphene across large areas to enable the widespread use of graphene in applications. The limited understanding of the growth mechanism(s) involved in chemical vapour deposition of graphene means that growth control remains rudimentary. This motivates our in-situ approach to develop an atomic scale understanding of graphene formation and thus enable rational optimisation of the growth process. We perform time- and depth- resolved high-pressure X-ray photoelectron spectroscopy (XPS) and in-situ time resolved X-ray diffraction (XRD) on polycrystalline transition metal catalysts films during hydrocarbon exposure at temperatures of ~300-700C, and during subsequent cooling.¹ The use of synchrotron radiation [BESSY (Berlin), ESRF (Grenoble)] is critical in obtaining high-intensity X-rays with selectable energy to give the necessary time- and depth-resolution. We focus on graphene nucleation and graphene domain size in relation to the catalyst grain size distribution and the C chemical potential.² Time-resolved XPS allows a detailed comparison of transient states prior to and during graphene formation and corresponding C/metal core level signatures. We thus reveal that graphene growth occurs isothermally on Ni, rather than just by precipitation on cooling and that dissolved C in to the catalyst subsurface plays an important role.³ Based on these in-situ measurements we present a coherent growth model for graphene formation on metal catalysts with finite C solubility and demonstrate that this is an effective tool in optimising larger-area graphene growth. (1) Hofmann et al. J Phys Chem C 2009, 113, 1648. (2) Weatherup et al. Nano Lett. 2011, 11, 4154-60. (3) Weatherup et al. ChemPhysChem 2012, (Early View).

Reaction pathways in solid state reactions are often not well investigated and thus rational synthesis planning of new compounds is hardly possible. Identifying and characterizing intermediate phases by in situ studies can be very useful in this regard. In order to investigate time-resolved solid-gas reactions, in particular the hydrogenation of intermetallic compounds, we have constructed a gas pressure cell for elastic in situ neutron powder diffraction. It is based on the design of a sample holder for inelastic scattering [1] and consists of a sapphire single crystal tube with stainless steel endcaps. Using a single crystal as container material has got the advantage that Bragg peaks from the cell material can be avoided given a proper orientation of the cell, resulting in a cleaner background than amorphous (e. g. silica) or polycrystalline cell materials (e. g. metals). Sapphire has got additional benefits, such as high yield strength withstanding high gas pressures, chemical inertness, especially no hydrogen embrittlement, and optical transparency. Heating is achieved contactless by two lasers allowing temperatures up to 1300 K, while hydrogen (deuterium) gas pressure up to 30 MPa can be applied, enabling studies under controlled gas pressure and temperature conditions. The reaction pathways of the hydrogenation of intermetallic compounds could be examined up to 16 MPa hydrogen (deuterium) pressure and 700 K. For test cases such as palladium and LaNi5 the α-β transition was followed, allowing the elucidation of structural details, including occupation and thermal displacement parameters, by Rietveld refinement at all T-p conditions examined. In palladium rich intermetallic compounds in situ studies provided a very detailed picture of hydrogen induced atomic rearrangements, yielding a model with gliding of MPd3 layers as a probable reaction mechanism [2]. This model was successfully applied for synthesis planning, yielding new metastable metal hydrides and intermetallic compounds [2, 3]. Further examples include the hydrogenation (deuteration) of Zintl phases and hydrogen (deuterium) induced decomposition of rare earth compounds [4]. These investigations demonstrate the potential of the single crystal sapphire based gas pressure cell for in situ elastic neutron powder diffraction and testifies the importance of in situ investigations of reaction pathways in solid state research. [1] B. C. Chakoumakos, C. J. Rawn, A. J. Rondinone, L. A. Stern, S. Circone, S. H. Kirby, Y. Ishii, C. Y. Jones, B. H. Toby, Can. J. Phys. 2003, 81, 183-189 [2] H. Kohlmann, N. Kurtzemann, R. Weihrich, T. Hansen, Z. Anorg. Allg. Chem. 2009, 635, 2399-2405 [3] N. Kunkel, J. Sander, N. Louis, Y. Pang, L. M. Dejon, F. Wagener, Y. N. Zang, A. Sayede, M. Bauer, M. Springborg, H. Kohlmann, Eur. Phys. J. B 2011, 82, 1-6 [4] H. Kohlmann, E. Talik, T. C. Hansen, J. Solid State Chem. 2012, 187, 244-248

To date, the development of inert anode materials for processes in high temperature molten salts has relied on the characterisation of samples removed from their operational environment at various pre-defined points of interest. This ex situ approach can be problematic, as conventional analysis techniques typically require some form of sample preparation, ranging from simply allowing the sample to cool, to more invasive procedures such as cutting and polishing. While any material examined outside of its operational environment will be altered to some extent, friable surface layers, crucial to the understanding of the failure mechanism, are at particular risk. Obtaining clear information about how these layers evolve during cell operation, without disrupting their structure, requires a quantitative in situ characterisation method. Due to the aggressive sample environment - molten calcium chloride at 950 °C - the in situ characterisation of inert anodes is difficult and requires a penetrating, high energy method. Consequently, synchrotron energy-dispersive X-ray diffraction (ED-XRD) techniques were used. The intensity of such advanced radiation sources allows data to be collected on the time scales necessary to observe reaction changes and investigate their kinetics. This paper describes (i) the results from studies of selected anode materials during an electrolysis reaction in molten salts at 950°C using ED-XRD data collected on the JEEP beamline at the Diamond Light Source synchrotron, and (ii) the purpose built sample cell required to achieve the measurements.

Layered oxides have been the workhorse for rechargeable lithium ion batteries for the last two decades. During the delithiation and lithiation processes, many complex phenomena including transition metal migration, phase transformations can happen and affect the electrochemical performance of the batteries. Combining neutron and synchrotron x-ray diffraction we can monitor the complex changes in layered oxides at different state of charge/discharge. In situ neutron diffraction patterns were collected on the time-of-flight diffractometer, VULCAN, at the Spallation Neutron Source (SNS) during electrochemical charge/discharge cycling of the lithium-excess layered compound Li[Li0.2Ni0.18Mn0.53Co0.1]O2 and stoichiometric layered compound Li[Ni1/3Mn1/3Co1/3]O2. In this work, single-layer pouch cells were built for in situ study, graphite was used as anode material. Dynamic changes in d-spacing help to explain the lithium de-intercalation mechanism in these two materials. Strong anisotropy shifting of the lattice parameters during the first cycle and following cycles is observed. The in situ experiment shows distinct lithium and transition metal (TM) migration mechanisms in these two sets of cathode materials.

Measuring surface/interface structure evolution on atomic length scales in real electrochemical systems remains a technical challenge. Developing techniques for this kind of characterization is crucial for understanding technologically important systems such as fuel cells, batteries and electrophotocatalysts where the surface layers of the electrodes -- which control the activity, performance and life of the final device -- evolve with time. Bismuth is a component of several intermetallic materials which oxidize small organic molecules [1] and it can be epitaxially electrodeposited on GaAs (110) [2,3]. Therefore, Bi/GaAs (110) is attractive as a model test system on which we can obtain critical experience with a well-posed physical system before we study more complex electrochemical systems. In this talk, we present the results from an in-situ (real-time) two-dimensional X-ray Diffraction (XRD) study of the electrodeposition of bismuth thin films onto GaAs (110). We carried out the experiments at the A2 line of the Cornell High Energy Synchrotron Source. Bismuth was deposited from an aqueous electrolyte containing 1mM of Bi2O3 and 0.25M of HClO4 at several potentials from -40mV to -200mV (versus Ag/AgCl) and the XRD patterns were collected on an area detector (incident beam of 30KeV). A detailed analysis of the nucleation process of the bismuth as a function of the potential will be discussed by means chronoamperometry (CA) and Atomic Force Microscopy (AFM). The CA curves show that at low potentials -- below -150mV--, the nucleation is progressive whereas beyond -150mV the nucleation is instantaneous. In both cases the mechanisms of nucleation is controlled by diffusion of the species towards the electrode. The crystal quality will be also discussed as a function of the applied potential with special attention to the evolution of the film orientation, strain and texture. [1] Y. Liu, M.A. Lowe, K.D. Finkelstein, D.S. Dale, F.J. DiSalvo, H. D. Abruña. “X-ray fluorescence investigation of ordered intermetallic phases as electrocatalysts towards the oxidation of small organic molecules.” Chemistry 16 (2010) Pages 13689-13697. [2] P. M. Vereecken, K. Rodbell, C. Ji and P. C. Searson, "Electrodeposited Bismuth Thin Films on n-GaAs (110)," Appl. Phys. Lett. 86, (2005) 121916 [3] M. Plaza, M. Abuin, A. Mascaraque, M.A. Gonzalez-Barrio and L. Perez, “Epitaxial growth of Bi ultra-thin films on GaAs by electrodeposition” Mat. Chem. Phys. 134 (2012) Pages 523-530.

High Energy Diffraction Microscopy (HEDM) is a relatively new experimental technique that can provide an unprecedented level of detail for grain-resolved studies of polycrystalline materials. When applied to in situ thermo-mechanical processing experiments, it is possible to determine the activities and associated thresholds for individual dissipative mechanisms at the crystal scale, including slip, twinning, and displacive phase transformations. Results from three studies are presented: determination of critical resolved shear stresses and slip system activites in a Ti-7%Al alloy; observations of variant selection for tensile twinning in AZ31 magnesium alloy; and determination of the transformation mechanisms as well as variant selection for the high pressure αharr;ε phase transition in iron and the α→omega; phase transition in zirconium. We conclude with a brief discussion of the current state of HEDM, both in terms of the development of dedicated instruments at synchrotron user facilities as well as open source analysis software. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 (LLNL-ABS-561863). Funding through the Laboratory Directed Research and Development program (10-ERD-053) is gratefully acknowledged.

X-ray absorption spectroscopy (XAS) is a powerful and versatile means to study structures of materials. When combined with other tools such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and density-functional (DFT) calculations, a nearly complete structural and morphological picture of a chemical trainsformation in nanoparticles can be assembled. Theses combined methods enable the determination of both amorphous and crystalline phases in nanoparticles during unique nanoscale chemical transformations. In this study we synthesized nickel and Ni-P nanoparticles using tri-n-octylphosphine (TOP) as a P source and examined the nanoparticle samples with x-ray absorption spectroscopy (XAS) to report on the differences between the phases. We use a combination of XAS, x-ray diffraction (XRD) to characterize long-range order, and ICP-OES to confirm stoichiometry to gain insight into the Ni-P nanoparticle structure. These structural characteristics are related to the corresponding nanoparticle properties using a combination of both theoretical DFT (density functional theory) calculations and SQUID. By probing the local atomic structure of nanoparticles, XAS reveal a significant P concentration in the Ni and Ni_xP_y nanoparticle samples while XRD results show contributions only from fcc Ni. We compare the long-range structural order of XRD and the short-range radial structure from EXAFS and determine that phases. The possibility of XRD amorphous phases should be considered when using XRD for nanoparticle characterization, particularly when highly reactive reagents such as TOP are used in synthesis. Undesired impurities may significantly affect nanoparticle structure, and, in turn, their functionality. Magnetic and catalytic properties are shown to be greatly affected by phosphorus contents : DFT calculations show magnetization losses in the Ni system, as well as in Fe and Co systems. The work was supported in part by the National Science Foundation under Award Number CHE-1152922 and by the DOE, Office of Basic Energy Science under Award Number DE-SC0001086.

Small-angle neutron scattering (SANS) measurements were carried out simultaneously with rheological measurements using the Los Alamos Neutron Science Center Neutron Rheometer with Couette geometry on melts of high molecular weight hydrogenated polystyrene mixed with deuterated polystyrene at different ratios. From the rheological data, it was found that the melts exhibited monotonic shear thinning with viscosity decreasing as the inverse of the shear rate, indicating that the shear rates were in the convective constraint release (CCR) non-linear domain. The SANS of the polystyrene melts showed increased anisotropy with increasing shear rate up to 10 Hz, indicative of chain extension along the shear direction. The anisotropy decreased at higher shear rates. These effects may be explained in part by the current tube theories and the role of CCR in non-linear rheological effects. However, it is not clear what, if any, the well-known wall slip phenomenon plays at higher shear rates.

Diffraction is a now centenary tool to study crystallographic structures, from macroscopic bulk polycrystalline to nano-structured material. It is well known that dislocations in crystals cause streaking and broadening of Laue peaks. However, the footprint of a dislocation in a diffraction pattern doesn&’t originate from the dislocation itself but rather from its long-range elastic strain field. In case of an ensemble of dislocations the diffraction signal reflects the complex interaction of such strain fields. Deriving dislocation structures from diffraction peak profile analysis is then very involved. To improve data analysis, we use some micro-mechanical simulations (from MD to crystal plasticity in FEM) as input data to a new Laue diffraction simulation model for studying directly the effect of particular and known dislocation ensembles on the diffraction pattern and peak profile. The Fourier Transform approach for diffraction modelling has been used in a new ray-tracing code, to take into account both size and shape effect. In this work we link this tool with a 3D Discrete Dislocation Dynamic simulations [1-2] to follow the evolution of Laue diffraction patterns compared with dislocation activities during the deformation of micro-pillars. Therefore any a priori hypothesis on the dislocation structure in our sample is eliminated. Different starting configurations (dislocation structures and boundary conditions) are investigated to explore the effect on the peak shape, during micro-pillar tensile/compression test. This method fills the missing link between a pure modelling approach [3] and a pure experimental one [4], and provides tools for a qualitative and quantitative analysis of white beam micro-Laue patterns in term of dislocation structures [5].

Neutron diffraction experiments were a key part of a two-phase project to measure stress corrosion cracking and other safety hazards in pressurized anhydrous ammonia tanks called nurse tanks. Over 200,000 nurse tanks are in use in the U.S., and several have exploded in recent years causing extensive property damage, injuries, and loss of life. In this project, neutron diffraction revealed the residual stress distributions around the welds used to assemble tanks at the manufacturing facility. These measurements (performed at the Los Alamos Neutron Science Center using the Spectrometer for MAterials Research at Temperature and Stress - LANSCE/SMARTS) showed that residual stresses are quite high in the heat-affected zone near the welds, nearing the yield point of the metal at the inner surface of the tank. Since tensile stress is a critical factor in predicting stress corrosion crack growth rates, these residual stress data allow prediction of tank lifetimes as a function of crack sizes and locations. Stress relief annealing of the entire tank after it has been welded during manufacture should increase tank safety and service life because residual stresses would be largely removed by annealing. Only two companies manufacture nurse tanks in the U.S. today, and both companies tentatively agreed during project meetings to anneal all tanks manufactured in the future if it could be demonstrated that annealing would substantially improve nurse tank safety. To this end a test tank was given a stress-relief anneal. Neutron diffraction demonstrated a dramatic decrease in the residual stress and thus an increase in the projected tank lifetime. The experiments used 41 in. diameter, 12 in. tall hoop sections taken from nurse tanks by cutting the tanks 6 in. on each side of the circumferential weld. The cutting process resulted in a maximum stress change (monitored with five 3-strain-gage rosettes on each tank) of 27 MPa at the weld surface. This is much smaller than the 350 MPa to -200 MPa residual stresses shown by neutron diffraction The hoop, radial, and axial strains were determined for 76 2mm x 2mm x 2mm regions across the circumferential weld in a 1966, 1986, and annealed 2012 nurse tank. Unstrained lattice parameter measurements (d-zero measurements) were taken by cutting a thin slice of the hoop that contained the scanned region and then cutting slots in this slice so that diffraction patterns could be taken from 4mm x 4mm x 6 mm unconstrained “teeth”. These d-zero measurements proved that the changes in lattice parameter were not due to chemistry variations near the weld. SMARTS was key to this research because the large count rates allowed 5- to 30-minute inspections per data point, neutrons could penetrate through the 2-20 mm of steel in the beam path, and the SMARTS sample stage has better than the necessary 0.5mm positioning accuracy.

Superior mechanical properties of single-crystal (SX) Ni-based superalloys at high temperatures are achieved due to the optimization of alloying composition and the γ/γ&’ microstructure, which consists of high volume fraction of cubic γ&’ precipitates coherently embedded in the γ matrix. The two phases exhibit a small lattice parameter misfit δ (around 10-3) due to differences in composition. During service of the turbine blade, the combined influence of stress and elevated temperature induces the directional coarsening of the precipitates in a preferred direction (rafting) which can alter the mechanical properties of the alloy. The misfit and the plastic deformation introduced in the material during loading have been identified as the main parameters driving the rafting of the precipitates. For the first time, rafting is reported in engine-ready blades. Residual strains in a blade cooled from the solution heat treatment (SHT) are investigated with neutron diffraction supported by surfrace metrology and neutron tomography to insure the correct positioning of the neutron gauge volumes in the hollow internal structure of the blade. The measurements reveal the presence of large residual strains in the γ matrix in the area of the blade which exhibits a rafted microstructure in the engine-ready blade and corresponds with large misfit. The introduction of plastic deformation at this position is confirmed by TEM investigations of the microstructure. Where no rafting is observed, dislocations are not observed and both the γ lattice strain and misfit are much lower. Therefore the introduction of plastic deformation during the cooling after the SHT is believed to cause rafting during subsequent heat treatments. In addtition, the evolution of the misfit is followed in-situ during creep at high temperature using neutrons and X-rays diffraction in two alloys: a Re-free and a 3wt% Re-containing SX alloy. Simultaneously, the evolution of the mosaicity is measured during creep using an innovative experimental set-up at the X-ray diffraction beamline. These experiments reveal differences in the evolution of the misfit parallel and perpendicular to the applied stress. It reflects the decrease/increase of the internal stresses in the different γ matrix channels surrounding the cubic precipitates leading to rafting. The initial mosaicity of both alloys is rather small with a few tenths of degrees and describes the misorientation between neighbouring dendrites. Upon loading at 180MPa above 1000°C, the mosaicity decreases until the intensity maxima corresponding with each dendrite merge to form a broad single orientation region. At 950°C, the mosaic structure retains upon loading and is stable during creep deformation. The difference in mosaicity evolution between the different creep conditions is believed to come from the easier dislocation propagation at high temperature which induces a rotation of neighboring dendrites.

While the basic mechanisms of the high temperature plasticity of superalloys are known, modelling is made difficult by lack of experimental knowledge of both the stress distribution between both phases, and their relative strain rates. The aim of the present paper is to describe the results obtained by combining high temperature (1050°C -1150°C) testing under variable stress/temperature and real time in situ high energy X-Ray diffraction measurements using synchrotron Three Crystal Diffractometry (TCD). The peak profiles recorded during testing at 300 seconds intervals allow measuring the distribution of lattice parameters within the bulk of the material with a nearly10-5 relative precision on lattice parameters. From this distribution, we can deduce the relative volumes of the gamma and gamma prime phases, and their average lattice parameters (and thus the lattice mismatch), as well as the width of the lattice parameter distributions. The variations of the average lattice parameters are related to the temperature and stresses within the material, and can be used to calculate these stresses and the high temperature elastic constants. In superalloys with a rafted microstructure, these stress variations can be related to the difference between the plastic strains of the gamma and gamma prime phase: if the specimen strain (strain rate) is known, the plastic strain (strain rates) of each phase can be calculated, and related to the other experimental parameters. Last, the peak shape can be related to dislocation densities and spatial stress fluctuations. The present paper describes the results obtained on AM1 specimens with a rafted microstructure tested at the ID15A (ESRF) and BW5 (DESY) high energy beamlines. A careful analysis of the data allows measuring the temperature (i.e. elastic constants and corridor width) dependence of the propagation stress of dislocations within the gamma corridors, the variations of their density, and the stress and temperature (activation energy) and dislocation density dependences of the plastic strain rate of the rafts.

Understanding initiation, detonation, and mechanical properties of highly insensitive explosives based on TATB (1,3,5-triamino-2,4,6-trinitrobenzene) requires a comprehensive knowledge of the voids and microstructure, spanning length scales from nanometers to centimeters. We use a combination of synchrotron-based ultra-small angle x-ray scattering (USAXS) and synchrotron-based computed microtomography. At smaller sizes, theory (hot-spot modeling) suggests that voids and pores with sizes between about 100 nm and few microns in these materials affect initiation and detonation properties. The void distributions are interrogated with USAXS. At larger sizes from microns to cm, synchrotron-based tomography allows quantitative determination of compositional variation. LX-17, a TATB-based polymer-bonded explosive (PBX), nominally is 7.5% binder and 92.5% TATB, however, LX-17 possesses a heterogeneous microstructure on sub-millimeter length scales, seen with the tomography, where binder rich boundaries (~8.3% binder, ~1% void) surround binder poor (~5.1%) and void rich (~2%) areas. We have also studied how two insults, temperature cycling and compressive creep, cause very different microstructural damage. Temperature cycling, between -50 and 70C, causes an irreversible 1-2% volume expansion. In-situ USAXS observes the creation of voids from hundreds of nm to microns in size. Temperature cycling also causes some damage at larger length scales in the binder-poor areas of the explosive. Conversely, putting the explosive under a compressive load causes crack initiation and propagation at the binder-rich prill interfaces. These combined data are important to understanding microstructural mechanisms that affect mechanical properties, improving future TATB-based PBX materials. The results provide complete a comprehensive characterization of the structure from nanometers to centimeters and are also used as empirical input to computational models to determine how voids and microstructure affect shock response, initiation, and detonation properties.

A novel approach to quantifying intragranular distributions of orientation density and lattice strains is presented. The approach captures both the distribution of lattice orientation within a grain and the orientation dependence of the lattice strain tensor. Employing a finite element discretization over a ball in Rodrigues space facilitates the efficient use of degrees of freedom in the numerical approach, and provides a convenient framework for gradient based regularization of the method. Two applications are presented to demonstrate the utility of the method: A high-resolution study of substructure evolution in an embedded grain from a Ti-7%Al specimen, and the effect of severe plastic deformation on the αharr;ε phase transition in iron. Quantitative determination of sub-grain distributions enables new insights regarding material behavior, including the ability to determine the relative activities of competing deformation mechanisms, particularly from experiments involving in situ loading. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 (LLNL-ABS-561864). Funding through the Laboratory Directed Research and Development program (10-ERD-053) is gratefully acknowledged.

The interplay between the iron carbide phase cementite and the ferritic matrix has frequently been studied in the past using both X-ray and neutron diffraction. These studies, however, have been limited to ambient temperatures, where cementite is known to be a hard and brittle phase. Under that condition, the plastifying ferritic matrix is shedding part of its load to the cementite, which hence might be regarded as reinforcing phase in steel. After removal of the applied load, matrix and cementite are both left in a residual stress state with opposing sign. Ferritic steels, however, are also used in high temperature applications and the cementite might eventually plastically deform, chamfer, coarsen or transform into other type of carbides during service. Here, we investigate the characteristics of a 1%CrMoV creep resistant steel, used as rotor in steam turbines at maximum operating temperature of 565°C. Neutron diffraction has first been performed ex-situ after deformation on samples with different deformation histories. Samples have been deformed under tensile load at room temperature and elevated temperature (565°C) and under creep conditions (565°C, until the tertiary creep regime, 3000h). It is demonstrated that the residual strains in the ferritic matrix are strongly reduced in the samples deformed at elevated temperatures and this in both loading conditions. In-situ neutron and x-ray diffraction experiments were carried out at multiple facilities to follow the behaviour of both phases during similar deformation conditions (tensile at RT and 565°C, but short-term creep with higher stresses). The results demonstrate a redistribution of load among the ferrite grain families and to the cementite at the early stages of micro-plasticity, well before the 0.2% yield stress at 565°C. Carbide powder was extracted from samples before and after deformation by electrolytically dissolving the ferrite matrix. Powder diffraction experiments indicate that the large peak broadening observed for the cementite phase during in-situ testing can be solely ascribed to elastic interactions with the ferrite matrix.

The crystal structure and texture development of ferroelastic LaCoO3 and La0.8Ca0.2CoO3 based perovskites have been investigated under uniaxial compression using VULCAN beam line at the Spallation Neutron Source, Oak Ridge National Laboratory. Texture development was directly observed during cyclic compression experiments. Both microscopic strain by extensometer and lattice strain in cobaltites were measured and compared during cyclic loading/unloading in-situ compression experiments. Both radial and lateral strains were measured during sample's compression thus allowing calculation of Poisson's ratio of the cobaltites. It was found that calculated Poisson's ration is not a constant for a given material under investigation but it exhibited strong stress dependence. In addition to the cyclic loading the room temperature creep of pure LaCoO3 was studied at the constant 70 MPa stress, which corresponds to the coercive stress of this ferroelastic material. The crystal structure development of LaCoO3 was studied during four hours of creep experiments.

Residual stresses are expected in monolithic, aluminum clad uranium 10wt% molybdenum (U-10Mo) nuclear fuel plates because of the large mismatch in thermal expansion between the two bonded materials. The full residual stress tensor of the U-10Mo foil in a fuel plate assembly was mapped with 0.1mm resolution using high-energy x-ray diffraction. The in-plane stresses are strongly compressive, approaching -275MPa in the longitudinal direction and -120MPa in the transverse direction near the center of the fuel foil. The normal component of the stress is weakly compressive near the center of the foil and tensile near the corner. The disparity in the residual stress between the two in-plane directions far from the edges and the tensile normal stress suggest that plastic deformation in the aluminum cladding during fabrication by hot isostatic pressing also contributes to the residual stress field. A tensile in-plane residual stress is presumed to be present in the cladding to balance the large in-plane compressive stresses in the U-10Mo fuel foil.

Recent advances in High Energy X-ray Diffraction Microscopy have led to the ability to image crystallographic orientations of metals deep inside millimeter-sized samples. The resulting time-resolved, 3D orientation maps reliably capture the evolution of grain boundaries, triple-junction (TJ), quadruple-node (QN) as grains coarsens within the sample. 3D TJ, QN, and boundary distributions can be directly extracted from these orientation maps without the use of stereological estimates, which are often sensitive a priori assumptions of grain shapes and topologies. Here, we focus our attention in the evolution of triple lines and quadruple nodes in copper and nickel samples with different processing history and geometry. The necessity and power of 3D microstructure mapping techniques will be demonstrated by comparing of 2D stereological estimates with direct 3D measurements. Finally, the evolution of TJ and QN distribution as a function of grain coarsening will also be discussed. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 SFL, BWR, JVB, and MK are supported by the U.S. DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering. LLNL-ABS-561872

During the last twenty years, intermetallic TiAl alloys have undergone a development process that led to the application of this material class in modern jet-engine concepts. Their excellent specific high-temperature strength and creep behavior as well as low density and high stiffness perfectly match engine manufacturers&’ demands on alloys used for the production of jet-engine low-pressure turbine blades. An additional field of application for such TiAl alloys is in turbine wheels for automotive exhaust turbo-chargers. As the properties of TiAl alloys during processing, e.g. hot-working, as well as in use are dependent on the occurring phases, detailed knowledge on their volume fraction and distribution is of particular importance. Furthermore, the behavior of the individual phases during hot-deformation and subsequent heat-treatments is of interest for defining reliable and cost-effective industrial production processes. In-situ high energy X-ray diffraction methods offer the opportunity to determine phase fractions over a large temperature range. For the investigation of order-disorder transformations, Neutron-diffraction experiments are employed which exhibit strong superstructure reflections due to the negative and positive scattering length for Ti and Al, respectively. By using a fast detector and a suitable beamline-setup, the behavior of phases during deformation can be investigated by means of X-ray diffraction. In this presentation, an overview of the different in-situ diffraction techniques utilized for investigating TiAl alloys will be given and the merits and limitations of the methods discussed.

Transformation Induced Plasticity (TRIP) is one of important effects of steel strengthening mechanism to improve strength, ductility and excellent high- speed deformation behavior. [1] To measure strengthening mechanism of TRIP steel during deformation, in situ neutron diffraction measurement during tensile deformation was performed. Two kinds of TRIP steels with different carbon content were prepared and specimens with the parallel part of 55 mm long, 6 mm wide and 1.5 mm thick were used for in situ neutron diffraction measurement during tensile deformation. Neutron diffraction measurements were performed using beamline 19 TAKUMI [2], a pulsed-neutron TOF diffractometer in J-PARC, dedicated for engineering issues such as strain analysis in bulk materials. Tensile tests were conducted step by step with load controlling during the elastic regions, and continuously with constant crosshead speed by initial strain rate of 1.8x10-5 s-1 during the plastic regions. Austenite bears higher lattice strains in both steels, showing that it is harder that ferrite. Martensite seems to appear when plastic deformation starts, and it grows with increasing the plastic deformation. Detail results will be shown and discussed during presentation. [1] I. Tamura, Met. Sci., 16 (1982), 245 [2] S. Harjo, T. Ito, K. Aizawa, H. Arima, J. Abe, A. Moriai, T. Iwahashi, T. Kamiyama, Mater. Sci. Forum, 681 (2011), p. 443

Cellular materials such as foams and periodic lattices are used for applications in which energy dissipation and weight are primary design constraints. Examples include packaging, helmet linings, and blast shields. We have developed a composite system in which the void space of a thiol-ene periodic lattice is filled with polyurethane foam. The energy absorption efficiency of the composite under compression is higher than the sum of the efficiencies of the lattice and the foam alone. The mechanisms responsible for this performance enhancement are of special interest, as they can provide insights to guide the development of new composite materials for energy absorption. In this work we use synchrotron x-ray computed microtomography to examine the deformation mechanisms at play. By comparing the deformation of the lattice alone to that of the composite system, we find that the two phases deform in a synergistic manner, with the foam supporting the lattice and delaying the onset of elastic buckling.

The presentation will be twofold: The first part will focus on the measurement of lattice strains under torsion (pure shear) and a combination of tension and torsion. In the second part, a methodology will be described how to make use of combined diffraction and imaging detectors for strain investigations, using a time sensitive Multichannel Plate (MCP) detector in transmission geometry. 1) Torsion provides the unique opportunity to study the mechanical behavior of materials subjected to a state of pure shear stress and is of significance as most engineering components fail under the influence of shear, or combination of shear and axial stress. Results will be presented, which were obtained using a recently reported experimental approach applying the concept of a “strain rosette” [Woracek et al., Appl. Phys. Lett. 100, 191904 (2012)] and strain tensor determination, for a ferritic steel cylinder under pure torsion and combination of tension and torsion. 2) Wavelength dependent neutron transmission imaging has gained attention for the potential to spatially resolve texture, crystallographic phase and lattice strain by analysis of Bragg Edges. Especially promising is the time-of-flight (TOF) approach that takes maximum advantage of the new generation of pulsed spallation neutron sources, such as the SNS, JSNS and ESS. Results will be presented where two detector banks were used at 2theta; of ±90° and a MCP detector in transmission geometry (2theta;=180°). A tensile test was performed while acquiring data with all three detector systems, providing measurement of three separate strain components simultaneously. A torsion test was carried out, where imaging and diffraction was carried out separately, due to the non-uniform strain field in a torsion sample. Example data, experimental details and associated challenges will be discussed, which will be of relevance for current and future coupled imaging/diffraction beamlines and experiments. The herein described measurements were carried out at the TOF engineering diffractometer (SMARTS) at Los Alamos Neutron Scattering Center (LANSCE) and at the 2nd Generation Neutron Residual Stress Mapping Facility (NRSF2) at the High Flux Isotope Reactor (ORNL).

Diffraction provides a sensitive probe of phase transformations under many environmental conditions. Moreover, neutron diffraction and more recently high-energy synchrotron x-ray diffraction penetrate into the bulk of many materials, providing phase information at depth in the sample. We have used neutron and high-energy x-ray diffraction to monitor the phase evolution of Zr which was previously shock-loaded into the high pressure w-phase. In contrast to iron, after the release of the shock, a significant fraction (up to 80%) of the Zr remains quenched in the metastable w-phase, providing the opportunity for post-mortem analysis of the resulting microstructure. We observe reversion of the shocked Zr to the stable a-phase during heating (expected) and compressive deformation (unexpected). The phase fractions, phase stresses and preferred orientation were monitored during the reversion in multiple samples shocked to different pressures and at different temperatures and will be related to the as-shocked microstructure of the individual samples.

In-situ X-ray and neutron scattering techniques have been employed for decades to investigate the evolution of new phase and to determine the pertaining phase fractions. However little consideration has been given to changes in intensity and the distribution of intensity on the diffraction rings due to other contributing effects. We report on synchrotron high-energy X-ray studies on metals in phases that are present only at high temperature, evaluating the morphology of the Debye Scherrer rings to follow single-grain behavior in a polycrystalline matrix, such as sub-grain formation under plastic deformation as well as annealing phenomena such as static and dynamic recovery, recrystallization and grain growth. Dynamic extinction of radiation upon neutron powder diffraction reveals annealing behavior, such as the annihilation of dislocations and nucleation and growth phenomena of a precipitating second phase . The presentation will introduce new techniques that have recently been developed and we will provide information of studies of titanium, zirconium alloys and steel.

In-situ neutron diffraction has been used to measure lattice strains for different grain orientations as a function of applied stress in a solid-solution-strengthened extruded binary Mg-9wt.%Al alloy. An elastic-viscoplastic self-consistent (EVPSC) model of polycrystal plasticity was used to simulate the macroscopic stress-strain curve and the neutron diffraction data, yielding the relative contributions, critical resolved shear stresses and hardening behavior of the available slip and twinning modes. Non-linear behavior was observed during unloading after deforming the material into the fully plastic regime in tension. The model suggests that this non-linear behavior is mainly due to basal slip.

Forging residual stresses are detrimental to the production and performance of derived machine parts due to machining distortions, corrosion drivers and fatigue crack drivers. Residual strains in a 21-6-9 stainless steel warm High Energy Rate Forging (HERF) were measured via neutron diffraction. The finite element (FE) method was used to predict the residual stresses which occur during water quenching. The residual strains measured were used to calibrate simulations of the three dimension residual stress state of the forging.

The thermal stability of nanocomposite metals (a nanostructured copper matrix embedding niobium nanotubes) is investigated via time-resolved in situ annealing under synchrotron high-energy x-rays. The diffraction peak profile analysis demonstrates that internal-stress relaxation begins in the Nb nanotubes at a temperature far below the bulk recrystallization temperature and follows size-specific regimes originating from a proximity effect with the nanostructured Cu matrix: the increased Cu-Nb interface surface disrupts internal-stress relaxation processes, leading to larger thermal resistance [Acta Mat., 58 (2010), p6504; Adv. Eng. Mat., in press (2012)].

To understand the nucleation and growth mechanism of metal nanocrystals is crucial to rational synthesis and controllable properties in their pratical applications. In-situ experimentation with a time-resolution represents the most likely approach to investigate the key stages of dynamic process in the nucleation of nanocrystals. More recently, based on the development of synchrotron techniques, the in-situ X-ray absorption fine structures (XAFS) spectroscopy has been demonstrated as a powerful tool to study the initial nucleation. In this report, we investigated the nucleation and growth mechanism of Pt nanocrystals in the aqueous solution based on a home-built reactor employed for in-situ XAFS measurement. We found that the nucleation and growth of Pt nanocrystals underwent the two different pathways depending on the adding procedure of the reducing agent (ascorbic acid) into the Pt precursor (HPtCl4) aqueous solution.

Biocompatible gold nanoparticles (GNP) are an important emerging field due to the large potentialities in biomedical applications. The synthesis of GNP obtained through the reduction of a gold salt by ascorbic acid in a surfactant free water solution was followed by X-ray Absorption at the LIII edge of gold (XANES) and Small Angle X-ray Scattering. On the chemical point of view, the important originality of this study was to control the size of the GNP (from 7 to 25nm) by a fine tuning of the initial pH of the reducing solution. The time-resolved studies were intended to develop a comprehensive understand of the mechanisms controlling the size. Because of the initial high concentration of gold (3mM), the reaction was very rapid (1s). Hence, a stopped flow apparatus was necessary to ensure a good mixing in 4ms The XANES spectra were recorded in situ on the dispersive beam line ODE of SOLEIL synchrotron, with a time resolution of 0.1millisecond. This set of absorption data was coupled with sub-second in situ SAXS measurements obtained on the line SWING of SOLEIL synchrotron. The results were analyzed within the framework of a recent numerical model of nucleation and growth recently developed. This unique time resolution unraveled that the kinetics of reduction of the Au(III) into Au(I) then Au(0) is the key feature depending on pH and that controls the further growth of the nanoparticles.

Palladium-based nanoparticles have proven to function as highly active catalysts for fuel cell and hydrogen storage reactions. Temperature-induced transformations in physical mixtures of two types of single-metal nanoparticles, such as Pd and Cu nanoparticle mixtures with different mixing ratios are investigated. The capped nanoparticles used in this study were prepared by a modified 2-phase protocol. The nanoparticles were dispersed on different kinds (hydrophilic/hydrophobic) of substrates to understand the substrate effect on sintering. The mechanisms of coalescence and grain growth in these nanoparticles supported on planar silica on silicon are explored using in-situ and real-time synchrotron based X-ray diffraction in the temperature range 200-700C. These nanoparticles are also characterized by transmission electron microscopy and x-ray photoelectron spectroscopy measurements. The structural parameters of the nanoparticles probed are size, phase, composition and morphology. These nanoparticle mixtures undergo coalescence and structural phase transformations at relatively low temperature, and sinter at higher temperature. The nanoparticles were found to form alloys with ordered bcc (B2) structure at low temperature. At higher temperature (450C) the particles transform into an fcc (alloy) structure with Pd-rich phase. Grain growth is modeled with growth laws proposed for nanocrystalline materials and activation energy corresponding to the diffusion mechanism driving sintering was estimated. To the best of our knowledge, the relationship between sintering and phase transformations such as melting and alloying has not been studied in detail to date for Pd-based nanoparticles.

As devices become smaller, an understanding of the properties of materials on a nanometer scale continues to grow in importance. The physics governing thin semiconductor films and their growth therefore remains an active area of investigation. This study has focused on the idealized case of the room-temperature growth kinetics of silicon thin films on silicon substrates via both on-axis and off-axis plasma sputter deposition. The evolution of surface morphology was measured in real time with grazing incidence small angle x-ray scattering (GISAXS) at Beamline X21 of the National Synchrotron Light Source. GISAXS is a surface-sensitive, non-destructive technique ideally suited to a study of growth morphology kinetics. In addition to investigating the effect of on-axis versus off-axis bombardment, the effect of sputter gas partial pressure was examined. Additionally, comparisons have been made between the observed surface evolution during the early stages of growth and the results of Monte Carlo simulations. Finally, post-facto, ex-situ atomic force microscopy (AFM) was used to measure the final surface morphology of the films, which is subsequently compared with the surface morphology determined by GISAXS. This work was supported by the Department of Energy, Office of Basic Energy Sciences.

The negative thermal expansion material cubic ZrW₂O₈ has been examined by other workers as a potential component in a variety of controlled thermal expansion composites. However, this material and its close relative HfW₂O₈ undergo order-disorder phase transitions associated with a reorientation of WO₄ pairs on heating. There is a substantial change in their coefficients of thermal expansion (CTEs) associated with this transition and the disordered high temperature phase (β) has a lower magnitude CTE than the ordered (α) phase. Cubic ZrMo₂O₈ has a similar structure to cubic ZrW₂O₈, but it appears to display MoO₄ orientational disorder at all temperatures. The effect of hydrostatic pressure on the CTEs of cubic ZrW₂O8, HfW₂O₈ and ZrMo₂O₈, was investigated using high energy synchrotron x-ray diffraction along with a recently designed cell suitable for the precise control of temperature and hydrostatic pressure. This novel cell design uses internal collimation to largely eliminate parasitic scattering from the titanium pressure vessel. In ZrW₂O₈ at pressures above 210 MPa and temperatures between 298K and 358K, a transformation to the well-known orthorhombic phase was observed; this structure only displays marginal negative thermal expansion. A corresponding transition was not observed for HfW₂O₈ in the pressure range explored in our study (up to 411 MPa), which is in line with prior low temperature/high pressure neutron diffraction studies of these materials. In both cubic ZrW₂O₈ and HfW₂O₈, for temperatures just below their α-β phase transitions, the application of pressure was found to promote the orientational disordering of WO₄ pairs in ZrW₂O₈ (388-433K) and HfW₂O₈ (410-470K). The volume reduction associated with this reversible disordering gives rise to a dramatic softening in this temperature range; ZrW₂O₈ displays a 35% reduction in bulk modulus (64.2 GPa to 41.9 GPa) between room temperature and 418K, and HfW₂O₈ displays a 31% reduction (69.7 GPa to 48.0 GPa) between room temperature and 433K. The compressibility of ZrMo₂O₈ displayed no noticeable temperature dependence. These results suggest that the effects of stress and temperature should be considered carefully when designing controlled thermal expansion composites incorporating ZrW₂O₈ or HfW₂O₈.

Despite the growing use of nanoparticles in various applications, little is known about the mechanisms of nanoparticle uptake into cells and their location following internalization. Several studies have shown that the surface functionalization is a crucial factor. We have investigated the uptake of silica nanoparticles with different surface functionalization, size, and shape in human skin cells (keratinocytes) by tomographic studies using cryo X-ray microscopy/tomography. This enables us to localize single nanoparticles in cells and to investigate the influence of their physico-chemical properties on cellular uptake processes. We could show that 161 nm diameter silica particles with a gold core (49 nm) can be localized in the cytoplasma but cannot cross the nuclear membranes. It turned out that the uptake through the cell membrane is strongly enhanced by a positive surface charge. In contrast, 60 nm gold particles with or without a 3 nm silica shell can cross the perinuclear membranes and are localized close to the nuclear membrane. However, no particles were found inside the cell nuclei. These results are well-supported by electron microscopy studies and are correlated with the stability and aggregation behavior of nanoparticles in physiological solutions.

Atomic Layer Deposition (ALD) allows the deposition of thin films onto flat as well as complex geometry surfaces with excellent conformality. Thicknesses of few atomic layers can be achieved. Moreover, low-temperature deposition is possible and this enables the change of surface properties of many kinds of materials. Good adhesion characteristics and also good mechanical performance of ALD deposited thin films make the technique extremely interesting for several applications, as for example micro-electronics. TiO2 is a well studied semiconductor material because of its multifunctional properties that open a wide range of applications for example in photocatalysis, optics and solar cells. ALD is extremely completive to other technique, to deposit titania thin films, employed even to improve the biocompatibility of many kind of materials. TiO2 thin films are deposited with ALD technique at low temperature (90 °C) onto Kapton substrate and then crystallized ex-situ after annealing at 300 °C. X-ray diffraction (XRD) techniques are very suitable for the analysis of structure and microstructure of films and surface layers. In this work, XRD in combination with in situ tensile testing has been applied for the first time to measure elastic properties (elastic modulus and Poisson ratio) of TiO2 anatase thin films obtained by ALD. For the experimental conditions, the tensile stage was installed in a Synchrotron laboratory of Soleil. The information extracted from diffraction patterns is presented.

X-ray reflectivity is a powerful tool for exploring interdiffusion and roughness of nanoscale multilayer materials. Traditional reflectivity techniques involving step-scanning of the sample (or source) and detector for point-by-point measurements. This requires scan times on the order of minutes, which is too slow to track many rapid processes of interest. We have developed a technique for in situ time-resolved x-ray reflectivity in which the entire reflectivity pattern (from q=0 to 0.35 1/Å using 12 keV x-rays) is measured simultaneously. A synchrotron beam is incident on a specimen that is dynamically bent to a controllable radius of curvature. The scattered beam is angle-dispersed by the curved surface onto a mixed-mode pixel array device (MMPAD) area detector. This detector offers a large dynamic range (~1e7), critical for reflectivity measurements, and is capable of framing continuously at 1e3 Hz (1 ms per frame) while maintaining single x-ray sensitivity. Using this detector both the specular and diffuse scattering are measured simultaneously. To demonstrate this technique, we report initial observations of structural evolution in Al/Ni multilayers (deposited on Si wafers) during heating at rates up to 60 K/s to maximum temperatures of ~900 K. Heating was accomplished by Joule heating of the Si substrate. We tracked the evolution of the reflectivity patterns with a typical frame time of 100 ms, and demonstrated excellent signal-to-noise ratio in the reflectivity patterns with frame times as short as 2 ms. The reflectivity data provide information about interdiffusion of Ni and Al during heating, evolution of the roughness of the multilayers, and formation of new intermetallic phases. Finally, we discuss the potential for application of this technique at much higher heating rates (>1000 K/s) and to other transformations of interest.

Freeze-casting is a novel fabrication method for the manufacture of highly porous hybrid materials with a hierarchical architecture based on the directional solidification of a polymeric solution or ceramic particle slurry. The process involves freezing of a water-based colloidal system under conditions that promote the formation of lamellar or columnar ice. It allows the fabrication of bulk materials (several cm3) or entire components, including those with a complex shape. Freeze casting is a two-step process. First, a water-based polymeric solution or ceramic particle slurry is directionally solidified and “ice-templated” when phases separate into ice and a vitrified polymer or ceramic composite. In the second step, the frozen material is lyophilized where the ice crystals are removed by sublimation, leaving the vitrified polymer or ceramic composites dried further through the removal of bound water. Both steps combined determine the structure and properties of the overall freeze-cast scaffold and its cell walls. After initial qualitative observations of component self-assembly in the cell walls of freeze-casted scaffolds though optical and scanning electron microscopy, we applied synchrotron X-ray techniques (small angle X-ray scattering, wide angle X-ray scattering and full-field transmission X-ray microscopy) to investigate this phenomenon systematically both in-situ during directional solidification and afterwards on freeze-cast and lyophilized scaffolds. In-situ freezing of polymer and ceramic particles was performed with a Hele-Shaw cell-like setup for directional solidification. The experiments described here could successfully be performed only at a synchrotron X-ray source, because of the requirement of high beam brilliance to obtain high spatial resolution in both real and reciprocal space as well as high temporal resolution. By combining diffraction data from SAXS and WAXS measurements and 3D morphology information from X-ray nano-tomography experiments, it was possible to obtain quantitative information about the materials crystal structure and crystallographic texture (WAXS) and size, shape and orientation of nanoparticles and nanofibers (SAXS) and their evolution under a relative time scale, plus morphology information of the nanoparticles and nanofibers in 3D at nanometer scale (TXM).

Nanoporous metals (Au, Ag, Fe, Co, Ni, Pd, Pt and Ti) have numerous potential applications as functional materials, including sensors, actuators, super-capacitors, catalytic substrates, enhanced Raman scattering, and anode substrate for Li-ion battery. Nanoporous Ti alloy specifically can be fabricated by a two-step dealloying method. Ti-Cr-Zr-Cu prealloy, (Ti0.847Zr0.056Cr0.098)20-Cu80, are soaked it into a Mg melt bath at 810 °C and only the Cu element is selectively dissolved into the bath. The remained Ti-Cr-Zr alloy self-organize into the sponge structure. A composite of Ti-Cr-Zr and Mg-Cu is then formed. The Mg-Cu phase is then removed from the composite in a nitric acid aqueous solution to form the nanoporous Ti-Cr-Zr. The size of the metallic ligaments and the pore size and therefore the mechanical properties of the foam can be tuned by changing the duration of the Mg bath soaking time. Therefore, the change in morphology due to the different duration of the soaking time is in the interest of study. We prepared the Ti-Cr-Zr-Cu prealloy samples which were soaked in Mg bath for 5, 10 or 30 min respectively, followed by the etching processed. Both the composite (Ti-Cr-Zr and Mg-Cu) and the end-product Ti alloy nanofoam were imaged in 3D using x-ray tomography techniques. With synchrotron source, micro-CT and high-resolution nano-tomography experiments were carried out to reveal the 3D morphology of the nanoporous titanium alloy at multiple length scales. The nano-tomography especially, was carried out at National Synchrotron Light Source where a newly equipped transmission x-ray microscope provides a unique markerless, automated tomography. This was an essential capability which enables local tomography and therefore a destructive sample preparation such as focus-ion-beam (FIB) milling can be avoided. We found that FIB milling would change the microstructure of the Ti nanofoam. The quantitative analysis of the 3D morphology of the nanoporous Ti alloy subjected to various soaking time, before and after etching will be presented.

Materials with broken inversion symmetry are of great interest for their exotic electronic properties, but are relatively rare. We show here that even if a material is inversion-symmetric in the bulk form, in epitaxial thin films of the same compound the crystallographic unit cell can be quite asymmetric. To demonstrate this, we have used atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) to synthesize La_2-xSr_xCuO₄ films with Sr dopant atoms deposited above, below, or on both sides of each CuO₂ layer. Surface X-ray diffraction experiments analyzed by the Coherent Bragg Rod Analysis (COBRA) method have been carried out in combination with energy-differential diffraction measurements to determine whether the actual Sr distribution coincided or not with the nominal one (that would be expected in absence of La-Sr interdiffusion). This new method is very sensitive in determining the concentration of atomic species on a mono-atomic layer-by-layer basis. The results show that the concentration of Sr in La/Sr layers just above the CuO₂ layers is much larger than in layers just below them, irrespective of the deposition sequence, and drastically breaking the inversion symmetry.

The last 15 years have seen a massive development of crystalline structures with sub-micrometer sizes, either with a simple miniaturization goal, or in order to exploit quantum confinement effects. The study of these objects is a challenge for crystallographers, as their size implies a weak, diffuse scattering rather than sharp Bragg peaks. Moreover, nano-structures, either due to the synthesis method or by design, are often heterogeneous and therefore present inhomogeneous strain and composition 3D fields. This presentation will be focused on epitaxial nanostructures (nanowires, silicon-on-insulator, ..), grown or deposited on a substrate. For these types of samples several methods have emerged during the last 10 years, allowing accurate structural information at the nanoscale: although grazing incidence X-ray diffraction will often yield quantitative structural information, it is practically limited to samples with a limited dispersion of the structural properties (size, shape, mosaicity) of the objects. It is now possible to measure the scattering from single objects using Coherent Diffraction Imaging (CDI). This can be done thanks to the availability of coherent and intense X-ray beams (up to ~10^5 ph/s/nm^2) on synchrotron beamlines: CDI is a method where the scattering of a single object is measured, and this 2D or 3D scattering pattern corresponds (in the small angle regime) to the Fourier transform of the object's electronic density. While CDI has considerable applications for single non-crystalline objects [1] such as large macromolecules, it can also be used around Bragg reflections [2]: in that case the 3D scattering pattern is the Fourier transform of a complex 3D field which includes information about both the object's density and its deformation from a perfect lattice, in the case of an inhomogeneous strain. We will illustrate the use of Bragg CDI on single homogeneous and heterogeneous nano-structures used for photonic (single photon emission) and electronic (strained silicon-on-insulator) applications, and discuss the current performance, limits and prospects of the method. [1] Miao J, Charalambous P, Kirz J & Sayre D, Nature, 1999, 400, 342 [2] Newton MC, Leake SC, Harder R & Robinson IK, Nat Mater, 2010, 9, 120 [3] Favre-Nicolin V, Eymery J, Koester R & Gentile P, Phys Rev B, 2009, 79, 195401 [4] Favre-Nicolin V, Mastropietro F, Eymery J, New J Phys, 2010, 12, 35013.

Synchrotron x-ray radiation was used for in situ strain measurements in gold films on polyimide substrate during uniaxial and biaxial deformation tests [1]. We have used an area detector that allows inspecting multiple directions in the polycrystalline thin film without serial sectioning during straining i.e. time-resolved x-ray strain measurements. The configuration used and the attainable orientations are placed on pole figures for which the x-ray strains are measured. For the two configurations (uniaxial and biaxial), so-called ε-sin2 psi; curves were extracted. These latter are shown to be affected by geometrical effect unless equibiaxial loading is employed. Moreover, non-linearity of these curves can occur, even in the case of equibiaxial loading, when the film is thin (below 120 nm). This last phenomenon is explained by surface anisotropy. When the onset on plasticity is reached, we show its effect on the x-ray strains, which was not detected by optical (macroscopic) strain measurement. An original experimental approach is then proposed to extend tests to film compression [2]. The sputtering chamber was modified to permit deposition of the film on an untreated polyimide substrate tensily stressed by a the tensile device. Exploration of the compression response was made with the film being loaded, when unloading the polyimide substrates. The compression response of an ultra-thin film of gold (18.5 nm) deposited onto the elastically loaded substrate could be explored up to minus;0.5% (minus;440 MPa) in contrast to tensile loading reported at only 290 MPa. [1] G. Geandier, D. Thiaudière, R. N. Randriamazaoro, R. Chiron, S. Djaziri, B. Lamongie, Y. Diot, E. Le Bourhis, P.O. Renault, P. Goudeau, A. Bouaffad, O. Castelnau, D. Faurie, F. Hild, Rev. Sci. Instrum. 81 (2010) 103903. [2] P.O. Renault, D. Faurie, E. Le Bourhis, G. Geandier, M. Drouet, D. Thiaudière, Ph. Goudeau, Materials Letters, 73, 99 (2012)

High-energy X-rays (>30 keV) have two potentially advantageous properties. First, they are highly penetrating, which allows us to probe deeply buried interfaces and structures. Second, the large value of k (small value of lambda;) “flattens” the Ewald sphere, enabling an area detector to capture large portions of reciprocal space without the necessity of rocking the sample. These advantages allow for rapid data collection for time-resolved experiments in investigating materials in real time in real conditions. Here, we present high-energy X-ray capabilities that are currently available, and that are being developed at CHESS. We purchased a 40 cm x 40 cm flat-panel area detector (GE Inspection Technologies), which has a 2048 x 2048 array of 200 mu;m x 200 mu;m pixels. The detector has excellent efficiency (> 65%) at high X-ray energies. A significant additional advantage of the detector is its rapid read-out capability (30 Hz). Examples of applications of the detector to various experiments will be presented, which include in situ X-ray characterization of battery materials, electrochemical growth of thin films, and mechanical loading. To take full advantage of the high energy spectrum available from the wigglers at CHESS and the capabilities of the detector, we are implementing a set of sagitally-bent, asymmetric, Laue crystals, which are used to focus high-energy X-rays efficiently in the out of scattering plane direction [1]. The main advantages of the Laue geometry over the Bragg geometry are the smaller beam footprint on the crystals (enabling the use of smaller crystals) and the larger bending radii for a given focal length (minimizing the bending stress). Moreover, one can utilize the anticlastic bending in the meridional plane of the crystals to eliminate the chromatic aberration of the diffracted beam (by working on the Rowland circle) [1]. We have designed, built, and commissioned a prototype double-crystal Laue monochromator optimized for high energy X-rays. We characterized performance parameters such as flux, focal size, and energy and angular resolutions. We report on the design and highlight results from the characterization experiments. The prototype monochromator focuses a 30 keV X-ray beam that is 25 mm-wide at the upstream monochromator crystal to a 0.6 mm beam waist in the hutch. The lessons learned from these commissioning experiments will guide the design of the planned upgrade of a high-energy X-ray beamline at CHESS. [1] Z. Zhong et al. J. Appl. Cryst. (2001) 34, 504-509

Colloidal nanocrystals are subject of intense research because of their high potential for applications in electronic, magnetic and optical devices. Furthermore they show a high tendency to form ordered two and three-dimensional superstructures (“supercrystals”). The precise ordering in those supercrystals affects the electronic coupling between the individual nanocrystals and it was shown to lead to new collective properties such as vibrational coherence [1], reversible metal-to-insulator transitions [2], spin dependent electron transport [3]. These properties are related to, and hence strongly affected by the degree of ordering obtained in the supercrystals, which in turn depends on nanocrystal size, the capping ligands and chemical species of chosen nanocrystals, as well as the monodispersity of the used nanocrystal batch. Thus, quantifying the degree of ordering and perfectness of supercrystals is of major interest, in order to enable a quantitative correlation between ordering and the ordering-dependent physical properties. To judge the quality of self-assembly obtained in 3D nanocrystal superlattices, we use X-ray diffraction, applied to individual supercrystallites made from different materials. The supercrystals have typical sizes of 10-50mu;m, whereas the nanocrystals are below 20nm in diameter. While for two-dimensional arrays of self-assembled nanocrystals, ordering can be quantified by inspecting electron microscope images [4], for faceted 3D nanocrystal supercrystals, much more efforts have to be undertaken to obtain characteristic numbers, which allow to asses the degree of ordering obtained by the self assembly process. 3D reciprocal space maps are recorded at a synchrotron source using a micrometer sized X-ray beam. Bragg diffraction from the artificial superlattice structure is observed, from which we find that the quality of ordering is strongly anisotropic. The nanocrystals order in hexagonal planes, however the stacking perpendicular to these planes fluctuates. For Bi supercrystals reciprocal space maps show signatures of stacking defects. We will present the comparison of supercrystals from different nanocrystal systems, and discuss their particular ordering properties. 1. A. Courty, A. Mermet, P.A. Albouy, E. Duval, M.P. Pileni, Nat. Mater. (2005) 4, 395-398 2. C.P. Collier, R.J. Saykally, J.J. Shiang, S.E. Henrichs, J.R. Heath, Science (1997) 277, 1978-1981 . 3. C.T. Black, C.B. Murray, R.L. Sandstrom, S.H. Sun, Science (2000) 290, 1131-1134 4. S. Pichler, M.I. Bodnarchuk, M.V. Kovalenko, M. Yarema, G. Springholz, D.V. Talapin, W. Heiss, ACS Nano (2011) 5, 1703-1712.

Low open circuit voltage is a critical challenge for practical solar applications of iron pyrite (FeS2), an earth-abundant material for thin film solar cells. Past studies suggest phase impurities, bulk and surface defects, or sulfur vacancies may cause the observed photovoltage reduction. Utilizing tunable-energy synchrotron X-ray photoemission and absorption spectroscopies, we explore the surface and electronic structures of pyrite thin films grown by metal organic chemical vapor deposition (MO-CVD) on various substrates and as a function of different chemical treatments. We identify three sulfur species as seen on pyrite single crystals, and an additional species associated with residual sulfur precursor on as-deposited pyrite films, and with a mixture of elemental sulfur and polysulfide on films after high temperature sulfur annealing. Our nondestructive depth profiles, (obtained by varying the photoelectron kinetic energy) of each sulfur species and sodium provide a relative depth distribution of surface defects and impurities. Additionally, our results of valence band and Fe and S L-edge absorption spectra, supported by density-functional theory calculations, imply a narrowing of the band gap caused by sulfur defects.

X-ray dark field microscopy is a new synchrotron based technique for non-destructive 3D mapping of crystallographic information at the nano-scale. The imaging principle involves the magnification of the diffracted signal from individual (sub)grains by a compound refractive lens positioned between the sample and the 2D detector. Orientations and strain are mapped with a resolution of 0.001 deg and 10^-4, respectively. The spatial resolution is limited by the quality of available lenses, which currently is of the order of 200 nm. In comparison to existing techniques such as 3DXRD and DAXM spot overlap issue is less of an issue, and thicker specimens can therefore be studied. We present ongoing work on a first application and discuss the limitations of the technique.

For safety reasons, it is crucial to anticipate the evolution of the microstructure of structural material of light water nuclear reactors. In particular, the main barrier between the core and the outside is the reactor pressure vessel (RPV). The RPV is made of low alloyed bainitic steel. It is known that neutron irradiation causes embritlement of RPV steel, due to the formation of nano-clusters of solutes (Mn, Ni, Si, Cu, P). In order to predict the evolution of the RPV steel properties, it is essential to understand the formation mechanisms of these clusters (are they precipitates of a new phase, segregation to small point defect clusters, aggregates of vacancies-solute complexeshellip;?). In order to get a full description of the irradiated microstructure, a set of complementary techniques are usually used: Atom Probe Tomography (APT), Positron Annihilation Spectroscopy (PAS) and Small Angle Neutron Scattering (SANS). However, APT tomography is not able to see point defects such as vacancies. In addition, SANS and PAS data analysis are affected by some rather strong hypotheses that could introduce some doubts about the final results. For example, clusters are assumed to be Fe free in SANS [1,2] and all Cu atoms are supposed to be gathered into clusters in PAS data treatment [2]. These hypotheses are commonly in contradiction with APT observations [1]. To overcome these limitations a new approach, based on a combination of APT and extended X-ray absorption fine structure (EXAFS) spectroscopy, is proposed. This method is based on the idea that EXAFS cannot recognize whether an absorber atom belongs to the matrix or to a cluster but it is a good experimental method to investigate the nature and the number of atoms in the first shells around the absorbers and eventually the vacancies (interpreted as dump of the main peak of the Fourier transform of the EXAFS signal [3,4]). Moreover it can provide information on variation Debye Waller factor, parameter related to the mean square displacement and sensitive to the matrix irradiation damage. APT is well suited to implement EXAFS analysis because it can provide a volumetric distribution and consequently the proportion between the atoms in the matrix and in the clusters. This approach was used to investigate the nature of the clusters formed on a model alloy (Fe-1.5Mn-0.8Ni-0.1Cu-0.02P) irradiated with Fe ions in Jannus facilities in CEA saclay. APT and EXAFS results will be described and compared in this talk. 1- Cumblidge, S.E., Motta, A.T., Catchen G.L., Buohmert G.B.J., J. of Nucl. Mater. 320 (2003) 245-257 2- M.E. Fine, J.Z. Liu, M.D. Astam Materi. Scien. and Engineering A 463 (2007) 271-274. 3- S. Cammelli, C. Degueldre, G. Kuri, J. Bertsch, D. Lützenkirchen-Hecht, R. Frahm; J. of Nuc. Mater. 385 (2009) 319-324 ; 4- S. Cammelli, C. Degueldre, G. Kuri, J. Bertsch, NIMB 266 (2008) 4775-4781

Ultrafast x-ray diffraction reveals that strains on the order of 0.5% can be induced by above-bandgap optical excitation of 35-nm multiferroic BiFeO3 thin films. We correlate the structural and electronic response in BiFeO3 thin film upon optical excitation in the time domain. The rise (<100 ps) and the relaxation (~2 ns) of the induced strain correlates with the excitation and decay of charge carrier density measured by transient optical absorption. This quantitative correlation reveals the electronic origin of the ultrafast photostriction effect as a result of piezoelectric distortion due to the screening of the depolarizing field and the excitation of anti-bonding states. We also observed the broadening and distortion of the Bragg diffraction peak which may arise from localization of carriers that induces localized, uncorrelated lattice distortion. The result shows that it is possible to directly modify the polarization state in a multiferroic material thus opening the door for studying the ultrafast dynamics of electromagnetic coupling. The large strain can also be used as an ultrafast transducer to drive physics processes such as pressure induced insulator-metal transition.