Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W24: Scattering and Diffraction |
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Sponsoring Units: GIMS Chair: Yaohua Liu, Argonne National Laboratory Room: 504 |
Thursday, March 6, 2014 2:30PM - 2:42PM |
W24.00001: A Novel X-ray Diffractometer for the Florida Split Coil 25 Tesla Magnet Shengyu Wang, Alexey Kovalev, Alexey Suslov, Theo Siegrist At National High Magnetic Field Laboratory (NHMFL), we are developing a unique X-ray diffractometer for the 25 Tesla Florida Split Coil Magnet for scattering experiments under extremely high static magnetic fields. The X-ray source is a sealed tube (copper or molybdenum anode), connected to the magnet by an evacuated beam tunnel. The detectors are either an image plate or a silicon drift detector, with the data acquisition system based on LabVIEW. Our preliminary experimental results showed that the performance of the detector electronics and the X-ray generator is reliable in the fringe magnetic fields produced at the highest field of 25 T. Using this diffractometer, we will make measurements on standard samples, such as LaB$_{\mathrm{6}}$, Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ and Si, to calibrate the diffraction system. Magnetic samples, such as single crystal HoMnO$_{\mathrm{3}}$ and stainless steel 301 alloys will be measured subsequently. The addition of X-ray diffraction to the unique split coil magnet will significantly expand the NHMFL experimental capabilities. Therefore, external users will be able to probe spin -- lattice interactions at static magnetic fields up to 25T. [Preview Abstract] |
Thursday, March 6, 2014 2:42PM - 2:54PM |
W24.00002: Ion-Irradiation Induced Vacancy and Interstitial Clusters in Fe Investigated by X-Ray Diffuse Scattering and Molecular Dynamics Simulations Bennett Larson, Jon Tischler, Yury Osetskiy, Roger Stoller, Yanfei Gao, Yanwen Zhang The size and nature of vacancy and interstitial clusters in 15 MeV Ni-ion irradiated Fe have been investigated using x-ray diffuse scattering combined with scattering cross-sections based on continuum elasticity and molecular dynamics (MD) simulations. X-ray diffuse scattering measurements performed at the Advanced Photon Source within the so-called asymptotic regime near the (002) reflection of \textless 001\textgreater oriented single crystal Fe have been analyzed using diffuse scattering cross-sections based on continuum elasticity and MD simulated lattice displacements around \textless 111\textgreater and \textless 100\textgreater surface-normal interstitial and vacancy loops. To assess the sensitivity of diffuse scattering measurements to loose vacancy clusters or voids, molecular dynamics based cross-sections were calculated for 3D vacancy structures as well as for planar vacancy loops. The diffuse scattering measurements for ambient temperature Ni-ion irradiations of Fe corresponding to 1 displacement per atom (DPA) will be presented, and the results of the analysis of the diffuse scattering measurements in terms of vacancy and interstitial cluster type, surface-normal orientation, and size distributions will be discussed. [Preview Abstract] |
Thursday, March 6, 2014 2:54PM - 3:06PM |
W24.00003: Correlated x-ray scattering, from nanoparticle solutions to proteins Derek Mendez, Thomas Joseph Lane, Jongmin Sung, Herschel Watkins, Daniel Ratner, Sebastian Doniach Recent developments in x-ray source technology have shed new light on the Kam correlated x-ray scattering (CXS) theory, first proposed in 1977 [1]. The goal of CXS is to obtain high resolution structural information for the individual particle in a solution of disoriented, identical particles. This is achieved by exposing the solution to bright, short (shorter than the particle diffusion time) pulses of x-rays and then calculating angular intensity correlations in the plane of an area detector. The resulting correlations contain more information than standard small and wide angle x-ray scattering (SAXS and WAXS) measurements. This information can be used to place constraints on low-resolution particle models. We have demonstrated the feasibility of CXS at atomic length scales for solutions of nanoparticles (in review), where recovery of the signal involved non-linear filtering of the intensities. This eliminated dominant systematic noises in the data, which was recorded at the Stanford Synchrotron Radiation Lightsource (SSRL). We are refining analysis techniques which will be applied to CXS measurement of biomolecules at the SPring-8 angstrom compact free electron laser (SACLA) facility. \\[4pt] [1] Kam, Zvi 1977 Macromolecules 10, 927-934. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:18PM |
W24.00004: Fourier-transform inelastic x-ray scattering from time- and momentum- dependent phonon-phonon correlations Mariano Trigo, David Reis In a solid, the elementary excitations of the crystalline lattice (phonons) determine the macroscopic properties such as thermal transport and structural stability. The spectrum of these elementary excitations is normally obtained from inelastic neutron and x-ray scattering near equilibrium conditions, which is a Fourier transform of the spatial and temporal correlations of the system. Recent advances in Free Electron Laser sources provide sufficient flux and time-resolution to explore the dynamics of solids at the fundamental time- and length-scales of the atomic motions. In this talk I will show that by probing phonon correlations by femtosecond diffuse scattering in photoexcited germanium, we were able to obtain the phonon dispersion with extreme frequency and momentum resolution without analyzing the energy of the outgoing photon. I will show that time-dependent coherences are generated when an ultrafast laser pulse slightly quenches the phonon frequencies, generating pairs of correlated phonons at equal and opposite momenta. Using this approach we obtain an extremely high-resolution probe of the excited-state phonon dispersion over large sections of momentum space by a simple Fourier transform. [Preview Abstract] |
Thursday, March 6, 2014 3:18PM - 3:30PM |
W24.00005: Magnetostriction in Ni Nanowires: Coherent X-ray Diffraction and Density Functional Analysis Erandi Wijerathna, Jong Woo Kim, San Wen Chen, Ross Harder, Sohini Manna, Boris Kiefer, Eric Fullerton, Edwin Fohtung, Jose De la Venta, Oleg Shpyrko Three-dimensional magnetostriction is mapped in Ni nanowires with the aid of Bragg coherent X-ray diffraction (BCXDI). By inverting the measured BCXDI patterns using iterative phase retrieval algorithms giant magnetostrictive strain are observed due to a differential anisotropy of the lattice displacements along the [111] and (001) directions. Density functional calculations performed is consistent with the experimental observation. Our finding paves the way for the fabrication and development of novel magnetostrictive sensor elements. [Preview Abstract] |
Thursday, March 6, 2014 3:30PM - 3:42PM |
W24.00006: Acoustic Pulses in Iron Observed by Femtosecond X-ray Diffraction Tom Henighan, Stefano Bonetti, Patrick Granitzka, Diling Zhu, Stuart Parkin, Mariano Trigo, David Reis, Herman Durr Interest in improving the performance of memory storage devices has fueled recent discoveries in novel mechanisms for manipulating magnetic spins on ultrafast timescales, including magnetoacoustics. Direct measurement of ionic motion could allow one to observe the coupling between the magnetic spins and lattice dynamics in a crystal. In this talk, I will discuss recent results on time-resolved acoustics observed by time-resolved diffuse X-ray scattering in a 25 nm thick alpha-iron crystal of high quality. Acoustic pulses are generated using a femtosecond optical laser which provides an impulsive strain in the crystal. The ensuing phonon dynamics are resolved by scattering of femtosecond X-ray pulses provided by the Linac Coherent Light Source. In particular, we observe terahertz oscillations in the Fourier components of the acoustic pulses imaged by the detector. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 3:54PM |
W24.00007: Near-Equilibrium Structural Dynamics on the 20ps Time Scale Michael Kozina, Te Hu, Apurva Mehta, David Reis, Aaron Lindenberg We observed near-equilibrium optically-induced structural dynamics at the Stanford Synchrotron Radiation Lightsource (SSRL). Hard x-ray diffraction experiments were performed in a typically unavailable regime: low optical pump fluence (20-250 $\mu$J/cm$^{2})$ and short x ray pulses (15-60ps). We studied several different thin films (BiFeO$_{3}$ (BFO), Pb(Zr)TiO$_{3}$ (PZT), and Bi), pumping above bandgap using 343nm (BFO, PZT) or 1030nm (Bi) laser light at a 1.28MHz repetition rate in a special low alpha (short pulse) mode of the synchrotron. The corresponding small diffraction pattern changes (including fractional changes in lattice constant on order 10$^{-6}$ were made much more apparent because of the ability of the experimental apparatus to make use of the high repetition rate of the x rays; it is precisely this rapid data acquisition process that allows such small changes to be measured. [Preview Abstract] |
Thursday, March 6, 2014 3:54PM - 4:06PM |
W24.00008: Measurement of the background in Auger-Photoemission Spectra (APECS) associated with multi-electron and inelastic valence band photoemission processes Prasad Joglekar, Karthik Shastry, Steven Hulbert, Alex Weiss Auger Photoelectron Coincidence Spectroscopy (APECS), in which the Auger spectra is measured in coincidence with the core level photoelectron, is capable of pulling difficult to observe low energy Auger peaks out of a large background due mostly to inelastically scattered valence band photoelectrons. However the APECS method alone cannot eliminate the background due to valence band VB photoemission processes in which the initial photon energy is shared by 2 or more electrons and one of the electrons is in the energy range of the core level photoemission peak. Here we describe an experimental method for estimating the contributions from these background processes in the case of an Ag N23VV Auger spectra obtained in coincidence with the 4p photoemission peak. A beam of 180eV photons was incident on a Ag sample and a series of coincidence measurements were made with one cylindrical mirror analyzer (CMA) set at a fixed energies between the core and the valence band and the other CMA scanned over a range corresponding to electrons leaving the surface between 0eV and the 70eV. The spectra obtained were then used to obtain an estimate of the background in the APECS spectra due to multi-electron and inelastic VB photoemission processes. [Preview Abstract] |
Thursday, March 6, 2014 4:06PM - 4:18PM |
W24.00009: A new TOF-SANS instrument at the Helmholtz-Zentrum Berlin Karsten Vogtt, Miriam Siebenbuerger, Daniel Clemens, Christian Rabe, Peter Lindner, Margarita Russina, Ferenc Mezei, Matthias Ballauff The V16/VSANS is a new small angle neutron scattering (SANS) instrument at the Helmholtz-Zentrum Berlin in Germany. It employs the time-of-flight (TOF) technique, i.e. the sample is irradiated with a broad band of neutron wavelengths rather than operating under monochromatic conditions. Thus a broader and dynamic range in momentum transfer $q$ can be accessed. Four choppers allow tailoring the wavelength band to individual requirements in terms of resolution in $q$ and neutron flux. Long pulse lengths lead to a broad wavelength band and a concomitant broad range in $q$ as well as high neutron flux, while short pulse lengths have the opposite effect. The TOF-mode permits free selection of time intervals from a sample file and thus allows tracing the chronological development of a sample run. Moreover the wavelength range of the experiment can be freely narrowed down for the data reduction process, providing a tool for further data optimization after the finish of the experiment. Special software and hardware is required to deal with the large volumes of data generated and to perform data correction and normalization. The talk addresses the instrumental setup as well as data processing procedures and discusses the challenges and opportunities of the method. [Preview Abstract] |
Thursday, March 6, 2014 4:18PM - 4:30PM |
W24.00010: Novel Multidimensional Cross-Correlation Data Comparison Techniques for Spectroscopic Discernment in a Volumetrically Sensitive, Moderating Type Neutron Spectrometer Cory Hoshor, Stephan Young, Brent Rogers, James Currie, Thomas Oakes, Paul Scott, William Miller, Anthony Caruso A novel application of the Pearson Cross-Correlation to neutron spectral discernment in a moderating type neutron spectrometer is introduced. This cross-correlation analysis will be applied to spectral response data collected through both MCNP simulation and empirical measurement by the volumetrically sensitive spectrometer for comparison in 1, 2, and 3 spatial dimensions. The spectroscopic analysis methods discussed will be demonstrated to discern various common spectral and monoenergetic neutron sources. [Preview Abstract] |
Thursday, March 6, 2014 4:30PM - 4:42PM |
W24.00011: Neutron Scattering Dependence on Proximate Human Tissue from Fast Neutrons Brent Rogers, Cory Hoshor, Paul Scott, Joseph Crow, Noah Kramer, Anthony Caruso Neutrons incident on a human may undergo scattering, altering their energy. It is necessary to acknowledge that a proximate human moderator may non-trivially alter the neutron flux and source spectrum for a given neutron detection/spectroscopic device. Using primarily the Monte Carlo N-Particle (MCNP) transport code, the neutron-human moderator dependence will be discussed with respect to the rigorous quantification of human tissue composition and proximity/geometry on neutron moderation. MCNP simulated results will then be discussed in view of empirical results. [Preview Abstract] |
Thursday, March 6, 2014 4:42PM - 4:54PM |
W24.00012: Digital holographic microscopy for imaging and characterization of micron-sized particles. Nava Subedi, Matthew Berg We use the digital holographic microcopy (DHM) technique for particle imaging and characterization. In this work, the interference pattern produced by superposition of unscattered reference light and the scattered light is recorded by a digital camera. This pattern constitutes a hologram from which an image of the particle is computationally reconstructed. This technique has the potential to provide \textit{in situ }particle information up to the sub-micron resolution level and helps in the development of instrumentation capable to characterize respirable-sized (1-10 $\mu $m) aerosol particles. [Preview Abstract] |
Thursday, March 6, 2014 4:54PM - 5:06PM |
W24.00013: Operando characterization of nanocatalysts via spectroscopy, scattering and imaging techniques in the same micro-reactor Yuanyuan Li, Anatoly Frenkel, Philipp Baumann, Ryan Tappero, Dmitri Zakharov, Eric Stach, Annika Elsen, Ulrich Jung, Ralph Nuzzo The increasing demand to rationally design new catalysts for energy generation/conversion calls for improvements in research methodology which enables multi-technique investigations of working catalysts in reaction conditions. Using the operando approach is necessary to establish structure activity/selectivity relationship. However, this approach is hindered by many challenges, e.g., the incompatibility of different characterization methods with respect to the sample concentration and environment, and, hence, the need to use multiple in situ reactor designs. We report on the development and tests of the single, portable reactor compatible with most useful techniques for operando studies of nanocatalysts: X-ray absorption, transmission electron microscopy, infrared and Raman spectroscopies. The test system was Pt/SiO2 nanocatalyst and the reaction was the ethylene hydrogenation. The reactor was a closed cell with SiN windows enabled catalytic reactions under atmospheric pressure. Both XAFS and TEM experiments were conducted in identical conditions, while monitoring the product formation using mass spectrometry. Comparison of TEM and XAFS results provided new information on the structure-activity relationship of these catalysts. [Preview Abstract] |
Thursday, March 6, 2014 5:06PM - 5:18PM |
W24.00014: Tin particle size measurements in high explosively driven shockwave experiments using Mie scattering method Shabnam Monfared, William Buttler, Martin Schauer, Brandon LaLone, Cora Pack, Gerald Stevens, Joseph Stone Los Alamos National Laboratory is actively engaged in the study of material failure physics to support the hydrodynamic models development, where an important failure mechanism of explosively shocked metals causes mass ejection from the backside of a shocked surface with surface perturbations. Ejecta models are in development for this situation. Our past work has clearly shown that the total ejected mass and mass-velocity distribution sensitively link to the wavelength and amplitude of these perturbations. While we have had success developing ejecta mass and mass-velocity models, we need to better understand the size and size-velocity distributions of the ejected mass. To support size measurements we have developed a dynamic Mie scattering diagnostic based on a CW laser that permits measurement of the forward attenuation cross-section combined with a dynamic mass-density and mass-velocity distribution, as well as a measurement of the forward scattering cross-section at 12 angles (5- 32.5 degrees) in increments of 2.5 degrees. We compare size distribution followed from Beers law with attenuation cross-section and mass measurement to the dynamic size distribution determined from scattering cross-section alone. We report results from our first quality experiments. [Preview Abstract] |
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