Klaus-Dieter Liss, Australian Nuclear Science and Technology Organisation
Rozaliya Barabash, University of Tennessee/Oak Ridge National Laboratory
Ulrich Lienert, Deutsches Elektronen-Synchrotron
Burkhard Schillinger, Technische Universitaet M#65533;nchen
VV2: Novel Techniques and Sources II
Monday PM, November 26, 2012
Sheraton, 2nd Floor, Independence W
2:30 AM - *VV2.01
X-Ray Free Electron Lasers: New X-Rays for New Science
Jerome Hastings 1
1SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
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.
3:00 AM - VV2.02
Time Resolved Small Angle X-Ray Scattering Measurements in Foams and Metals Loaded in High Rate Compression
Tony van Buuren 1 Jim McNaney 1 Bassem El-Dasher 1 Jim Hawreliak 1 Despina Milathianaki 3 Jan Ilavsky 2 Tim Graber 2 Robert Henning 2
1LLNL Livermore USA2Argonne National Laboratory Chicago USA3SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
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.
3:15 AM - VV2.03
Viewing Nanocrystal Structural Changes with Femtosecond Resolution
Timothy Alan Miller 1 Joshua S. Wittenberg 1 Aaron M. Lindenberg 1 2 3
1Stanford University Stanford USA2SLAC National Accelerator Laboratory Menlo Park USA3SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
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.
3:30 AM - *VV2.04
Structural Dynamics of Polycrystals under Shock Compression Observed via Nanosecond Time-resolved X-Ray Diffraction
Kazutaka G Nakamura 1 Jianbo Hu 1 Kouhei Ichiyanagi 2 Shin-ichi Adachi 3
1Tokyo Institute of Technology Yokohama Japan2University of Tokyo Tokyo Japan3High Energy Accelerator Research Organization Tsukuba JapanShow Abstract
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.
VV3: Functional Materials and Local Order I
Monday PM, November 26, 2012
Sheraton, 2nd Floor, Independence W
4:30 AM - *VV3.01
Polymer Micelles and Functionalized Interfaces
Andreas Magerl 1
1University of Erlangen-Namp;#252;rnberg Erlangen GermanyShow Abstract
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.
5:00 AM - VV3.02
Combined Computational and In-situ Neutron Scattering and Conductivity Studies of Superionic Lithium Borohydride
Bill David 1 2
1Rutherford Appleton Laboratory Chilton United Kingdom2University of Oxford Oxford United KingdomShow Abstract
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.
5:15 AM - VV3.03
Simultaneous Neutron Diffraction and Thermogravimetric Studies of Hydrogen Storage Materials
Martin Owen Jones 1 Bill David 1 2 Joshua Makepeace 2
1ISIS, STFC Didcot United Kingdom2University of Oxford Oxford United KingdomShow Abstract
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.
5:30 AM - VV3.04
Diffraction from Vibrating Crystals: From Ultrasound to Phonons
Klaus-Dieter Liss 1 Andreas Magerl 2
1Australian Nuclear Science and Technology Organisation Lucas Heights Australia2Friedrich-Alexander-Universitamp;#228;t Erlangen-Namp;#252;rnberg Erlangen GermanyShow Abstract
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.
VV1: Novel Techniques and Sources I
Monday AM, November 26, 2012
Sheraton, 2nd Floor, Independence W
9:30 AM - *VV1.01
Diffraction before Destruction: Imaging with an X-Ray Free-electron Laser
Henry N. Chapman 1 2 Anton Barty 1
1DESY Hamburg Germany2University of Hamburg Hamburg GermanyShow Abstract
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
10:00 AM - VV1.02
Direct Measurement of Microstructural Avalanches Using Coherent X-Ray Scattering
Michael C. Rogers 1 Mark Sutton 1 Karl F. Ludwig 2
1McGill University Montreal Canada2Boston University Boston USAShow Abstract
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.
10:15 AM - VV1.03
Microstructure Manipulation in Silicon-based Systems Using X-Rays
Conal E Murray 1 Sean M Polvino 2 I. C Noyan 2 E. Todd Ryan 3 Paul R Besser 4 Jean L Jordan-Sweet 1 Zhonghou Cai 5 Martin V Holt 5
1IBM T.J. Watson Research Center Yorktown Heights USA2Columbia University New York USA3GLOBALFOUNDRIES, Albany Nanotech Center Albany USA4GLOBALFOUNDRIES Sunnyvale USA5Argonne National Laboratories Argonne USAShow Abstract
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.
10:30 AM - *VV1.04
Coherent X-Ray Diffraction Imaging: New Approaches to High Resolution Imaging
Keith Alexander Nugent 1 Brian Abbey 1
1The University of Melbourne Parkville AustraliaShow Abstract
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.
11:30 AM - *VV1.05
Transformative Materials Science Enabled by an Energy Recovery Linac (ERL)
Joel D Brock 1 2
1Cornell University Ithaca USA2Cornell University Ithaca USAShow Abstract
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.
12:00 PM - VV1.06
Progress of 3D Coherent X-Ray Diffraction Imaging at the Refurbished ESRF Beamline ID10
Federico Zontone 1 Yuriy Chushkin 1 Oleg Konovalov 1
1ESRF Grenoble FranceShow Abstract
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.
12:15 PM - VV1.07
Novel Multiplexing Techniques for Advanced Instruments at Long Pulsed Spallation Source
Margarita Russina 1
1Helmholtz Zentrum Berlin Berlin GermanyShow Abstract
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  and Wavelength Frame Multiplication  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 , the methods have been recently experimentally implemented with the help of unconventional use of existing time-of-flight instruments at continuous reactor sources , . 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 ,. 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  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
12:30 PM - *VV1.08
Phonon Spectroscopy Using Time-resolved X-Ray Diffuse Scattering
David Reis 1
1Stanford PULSE Institute, SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
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.
Klaus-Dieter Liss, Australian Nuclear Science and Technology Organisation
Rozaliya Barabash, University of Tennessee/Oak Ridge National Laboratory
Ulrich Lienert, Deutsches Elektronen-Synchrotron
Burkhard Schillinger, Technische Universitaet M#65533;nchen
VV5: Phase Transformations and Chemical Processes I
Tuesday PM, November 27, 2012
Sheraton, 2nd Floor, Independence W
2:45 AM - *VV5.01
Advanced Materials Exploration Using Time-resolved High Energy X-Ray Diffraction and Imaging Techniques
Veijo Honkimaeki 1
1ESRF Grenoble FranceShow Abstract
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.
3:15 AM - VV5.02
Electronic Structure of Ligand-stabilized Atomically Precise Gold Nanocluster Catalysts
Jing Liu 1 2 Sai Krishna Katla 1 2 Yaroslov. B. Losovyj 1 2 Soma Chattopadhyaya 3 4 Jeffrey T. Miller 5 Challa S.S.R. Kumar 1 2
1Louisiana State University Baton Rouge USA2Louisiana State University Baton Rouge USA3Argonne National Laboratory Lemont USA4Illinois Institute of Technology Chicago USA5Argonne National Laboratory Lemont USAShow Abstract
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.
3:30 AM - VV5.03
In situ Synchrotron X-Ray Investigation of the Formation of Ordered Array of Silver Nanoparticles during Thermal Decomposition of Silver Carboxylates
Boris Bokhonov 1 Marat Sharafutdinov 1 Boris Tolochko 1
1Institute of Solid State Chemistry, Siberian Branch Novosibirsk Russian FederationShow Abstract
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.
3:45 AM - VV5.04
Isostructural Phase Transition between Two Ferroelectric Phases of (1-x)BiFeO3-(x)PbTiO3 and Its Consequences on the Phase Diagram
Shuvrajyoti Bhattacharjee 1 Dhananjai Pandey 1
1Indian Institute of Technology, Banaras Hindu University,Varanasi Varanasi IndiaShow Abstract
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:  S. Bhattacharjee, S. Tripathi, and D. Pandey, Appl. Phys. Lett. 91, 042903 (2007).  S. Bhattacharjee, V. Pandey, R. K. Kotnala, and D. Pandey, Appl. Phys. Lett. 94, 012906 (2009).  S. Bhattacharjee, A. Senyshyn, P. S. R. Krishna, H. Fuess, and D. Pandey, Appl. Phys. Lett. 97, 262506 (2010).  S. Bhattacharjee, K. Taji, C. Moriyoshi, Y. Kuroiwa and D. Pandey. Phys. Rev. B. 84, 104116(2011).
4:30 AM - *VV5.05
In-situ X-Ray Laue Microdiffraction Studies of Phase Transitions in Vanadium Dioxide Microcrystals
John D. Budai 1 Alexander Tselev 1 Jonathan Tischler 1 Sergei Kalinin 1 Andrei Kolmakov 2
1Oak Ridge National Laboratory Oak Ridge USA2Southern Illinois University Carbondale Carbondale USAShow Abstract
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.
5:00 AM - VV5.06
Small-angle X-Ray and Neutron Scattering Studies of Chemically-tailored Polymers for Regulating Biomembrane Function
Scott M. Brombosz 1 Soenke Seifert 1 Millicent Anne Firestone 1
1Argonne National Laboratory Lemont USAShow Abstract
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.
5:15 AM - VV5.07
HEXRD to Study Transformations Kinetics in Titanium Alloys
Moukrane Dehmas 1 Elisabeth Aeby-Gautier 1 Guillaume Geandier 1 Amico Settefrati 1 2 Benoit Appolaire 3
1Institut Jean Lamour Nancy France2Airbus Operations Toulouse France3ONERA Chatillon FranceShow Abstract
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).
5:30 AM - VV5.08
Recent Results at SNAP, the High Pressure Diffractometer at the SNS
Antonio M dos Santos 1 Christopher A. Tulk 1 Jamie J. Molaison 1 Neelam Pradhan 1
1Oak Ridge National Laboratory Oak Ridge USAShow Abstract
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.
5:45 AM - VV5.09
Visualize Phase Transformation of Materials by in-situ Time Event Neutron Diffraction
Ke An 1 Alexandru Stoica 1 Dong Ma 1 Harley Skorpenske 1
1Oak Ridge National Laboratory Oak Ridge USAShow Abstract
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.
VV4: Functional Materials and Local Order II
Tuesday AM, November 27, 2012
Sheraton, 2nd Floor, Independence W
9:30 AM - *VV4.01
Advanced PDF Methods for Complex Materials
Takeshi Egami 1 2
1University of Tennessee Knoxville USA2Oak Ridge National Laboratory Oak Ridge USAShow Abstract
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.
10:00 AM - VV4.02
Multiscale Synchrotron-based Study of the Physics and Device Impacts of Metal-dislocation Interactions in Silicon Solar Cell Materials
David P Fenning 1 Mariana I. Bertoni 1 2 Volker Rose 3 4 Joerg Maser 3 4 Tonio Buonassisi 1
1Massachusetts Institute of Technology Cambridge USA2Arizona State University Tempe USA3Argonne National Laboratory Argonne USA4Argonne National Laboratory Argonne USAShow Abstract
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 . 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.  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
10:15 AM - VV4.03
Determination of the Impact of Water in Fuel Cells Using Neutron Imaging and Advanced Electrochemical Methods
Pierre Boillat 1 Pierre Oberholzer 1 Eberhard H. Lehmann 2 Gamp;#252;nther G. Scherer 1 Alexander Wokaun 3
1Paul Scherrer Institut (PSI) Villigen Switzerland2Paul Scherrer Institut (PSI) Villigen Switzerland3Paul Scherrer Institut (PSI) Villigen SwitzerlandShow Abstract
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 , 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 . 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).
10:30 AM - VV4.04
Intercalation and Retention of Carbon Dioxide in Synthetic Fluorohectorite Clay at near-ambient Conditions
Henrik Hemmen 1 Karin Rustenberg 1 Jon Otto Fossum 1 Tomas Plivelic 2
1Norwegian University of Science and Technology (NTNU) Trondheim Norway2MaAXIV Laboratory at Lund University Lund SwedenShow Abstract
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.
10:45 AM - VV4.05
Difference in Elastic Properties of CrB2 Determined by Microscopic and Macroscopic Measurements
Katsushi Tanaka 1 Satoshi Tsutsui 2 Norihiko L Okamoto 3 Haruyuki Inui 3 Alfred QR Baron 2 4
1Kobe University Kobe Japan2SPring-8 Sayo-cho, Sayo-gun Japan3Kyoto University Kyoto Japan4SPring-8 Sayo-cho, Sayo-gun JapanShow Abstract
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.
11:30 AM - *VV4.06
The Interpretation and Analysis of Diffuse X-Ray Scattering
Richard Thomas Welberry 1
1Australian National University Canberra AustraliaShow Abstract
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.
12:00 PM - VV4.07
Recent Trends in Photoelectron Spectroscopy for Materials Research
Henrik Bergersen 1 John Ahlund 1 Robert Moberg 1
1VG Scienta AB Uppsala SwedenShow Abstract
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.
12:15 PM - VV4.08
Aqueous Solution Structure of Methane by Small-angle Neutron Scattering
Monika A. Hartl 1 Mark A. Taylor 1 John C. Gordon 2 Rex Paul Hjelm 1
1Los Alamos Natl Lab Los Alamos USA2Los Alamos Natl Lab Los Alamos USAShow Abstract
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 0.3