Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D10: Scattering and Diffraction |
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Sponsoring Units: GIMS Chair: Zahir Islam, Argonne National Lab Room: 108 |
Monday, March 2, 2020 2:30PM - 2:42PM |
D10.00001: Developing Wide Angle Spherical Neutron Polarimetry at Oak Ridge National Laboratory Nicolas Silva, Chenyang Jiang, Tianhao Wang, Jillian Ruff, Masaaki Matsuda, Fankang Li, Barry Winn, Lisa DeBeer-Schmitt, Roger Pynn Spherical Neutron Polarimetry (SNP) analyzes complex magnetic structures through distinguishing contributions from nuclear-magnetic interference and chiral structure in addition to nuclear magnetic scattering separation. This analysis is achieved through determining all components in the polarization transfer process. Wide-angle SNP is being realized at Oak Ridge National Laboratory (ORNL) for multiple beamlines including: the polarized triple-axis spectrometer (HB-1) and general-purpose small angle neutron scattering instrument (CG-2) at the High Flux Isotope Reactor (HFIR), as well as the hybrid spectrometer (HYSPEC) at the Spallation Neutron Source (SNS). The SNP device consists of three units: incoming/outgoing neutron polarization regions, sample environment and a zero-field chamber. The neutron polarization regions use high- superconducting YBCO films, magnetic guide fields, and mu-metal to achieve full control of neutron polarization. The sample environment is an orange cryostat with a customized tail piece placed into the zero-field chamber. The device has been fabricated and demonstration experiments were run at the University of Missouri Research Reactor (MURR) and at HYSPEC. |
Monday, March 2, 2020 2:42PM - 2:54PM |
D10.00002: Kilohertz-Rate MeV Ultrafast Electron Diffraction for Time-resolved Materials Studies Khalid M Siddiqui, Daniel B Durham, Fuhao Ji, Andrew M Minor, Robert A Kaindl, Daniele Filippetto Ultrafast electron diffraction (UED) enables direct insight into structural dynamics of solids. Relativistic MeV-scale electron beams yield access to high-momentum scattering and preserve beam coherence, yet their application at high repetition rates for high-sensitivity UED has been limited. We discuss the High Repetition-rate Electron Scattering (HiRES) instrument at Berkeley Lab and its first applications to UED of metallic films and quantum materials. HiRES employs a state-of-the-art photoinjector with RF bunch compression to generate high-brightness, relativistic 0.75 MeV electron pulses with up to 105-106 el./pulse and with highest achievable coherence length of 10 nm. The resulting high momentum range (±10 Å-1) yields access over multiple Brillouin zones. The sub-500 fs electron pulses are provided at 0.1-250 kHz repetition rate, and combined with optical pumping via a 1.03 µm fiber amplifier enable UED of cryogenically cooled materials. We will show examples of first experiments including transient Debye-Waller dynamics in ultrathin metals at kHz repetition rate as well as studies of charge density waves in 2D materials. |
Monday, March 2, 2020 2:54PM - 3:06PM |
D10.00003: Directive steerable emission from an opened chaotic cavity controlled through a reconfigurable metasurface Samuel Metais, Jean-Baptiste Gros, Geoffroy Lerosey Chaotic reverberating cavities have been demonstrated to have a large number of exploitable degrees of freedom[1] that can be controlled with a reconfigurable metasurface [2]. Following previous work on the emission of opened electromagnetic cavity in the GHz regime[3], we demonstrate here that a reconfigurable metasurface in a small volume cavity, 4*6*0.5 λ^3, allows us to control the emission through a large opening (3.5*5.5λ^2). Measuring the transmission between a single source inside the cavity and an outside antenna, we show that a simple partitioning algorithm allows us to reach very high directivity, as well as a steering capacity over 120°. We compare those results with known limitations on the performances of antenna [4] and conclude on the performances of our device. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D10.00004: Spatially-Resolved Layer, Interface and Dopant Profiling Using Tabletop Coherent EUV Beams Yuka Esashi, Michael Tanksalvala, Christina L. Porter, Bin Wang, Nicholas W. Jenkins, Zhe Zhang, Matthew N. Jacobs, Galen P. Miley, Naoto Horiguchi, Jihan Zhou, Robert M Karl, Charles Bevis, Peter Johnsen, Joshua Knobloch, Seth L. Cousin, Emma Cating, Michaël Hemmer, Chen-Ting Liao, Michael Gerrity, Henry Kapteyn, Margaret Murnane Next-generation devices, nanomaterials, quantum and magnetic materials necessarily have increasingly complex layers, dopants and 3D structures. As a result, non-destructive techniques that can image through visibly opaque layers with sensitivity to layer and interfacial composition are critical for synthesizing and optimizing these systems. We present a tabletop complex-imaging reflectometer illuminated by coherent high harmonic extreme ultraviolet (EUV) beams. Unlike most reflectometers that transversely average quantities such as film thicknesses over the sample, our reflectometer can attain diffraction-limited spatial resolution with high sensitivity to material composition by using coherent diffractive imaging (CDI). Our complex imaging reflectometer uses grazing-incidence CDI to generate high-resolution, high-fidelity phase and amplitude images of a sample at many incidence angles. The phase images are extremely sensitive to composition, allowing us to extract a 3D map of the sample. We demonstrate the ability to very sensitively probe diffusion at buried interfaces, layer thickness and dopant profiles in a non-destructive and spatially resolved manner, distinguishing our technique from others such as SIMS, Auger sputtering, or electron imaging. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D10.00005: 3D-ΔPDF Investigations of Structural Phase Transitions Raymond Osborn, Matthew Krogstad, Stephan Rosenkranz By exploiting a new generation of fast area detectors with wide dynamic range optimized for high-energy x-rays, it is possible to measure single crystal total scattering, S(Q), over large volumes of reciprocal space encompassing thousands of Brillouin zones in under 20 minutes. This allows detailed investigations of the temperature evolution of both weak Bragg peaks from modulations in the long-range crystal structure and diffuse scattering from short-range fluctuations in the atomic order. S(Q) can be transformed into real space to generate “difference” pair-distribution-functions (3D-ΔPDF), a powerful way of eliminating the average crystal structure to reveal subtle structural modifications and determine the correlation length of atomic fluctuations above and below Tc, all without detailed simulations.1 I will show examples of 3D-ΔPDF applied to both long-range and frustrated short-range structural transitions in correlated electron systems and intercalation compounds. |
Monday, March 2, 2020 3:30PM - 3:42PM |
D10.00006: Interferometric tracking of nanoparticle orientation with quantitative optical anisotropy imaging Zhixing He, Chengshuai Li, Yizheng Zhu, Hans Robinson We introduce Quantitative Optical Anisotropy Imaging (QOAI), an interferometric spectral multiplexing technique that allows imaging and tracking of the orientation of individual nanoparticles at the microsecond timescale. In QOAI, incident light whose polarization is modulated in the spectral domain is scattered off particles and structures, interfered with a reference beam, and detected spectroscopically. The signal is directly proportional to anisotropies in the particle polarizability, and can therefore be used to extract both orientation and shape information about each individual particle, even at sizes well below the diffraction limit of conventional microscopy. We use this technique to categorize the aspect ratio of gold nanorods and to characterize their rotational diffusion near a solid interface. QOAI can be straightforwardly combined with existing particle tracking techniques so that position and orientation can be tracked simultaneously and can also be modified to provide quantitative measurements of the chirality of individual particles. |
Monday, March 2, 2020 3:42PM - 3:54PM |
D10.00007: Measuring Dominant Local Structures in Amorphous Materials Using Nanobeam Electron Diffraction Makoto Schreiber, Matthias Wolf The atomic structure of amorphous materials has long been a mystery. Due to the lack of long-range periodical order, traditional techniques such as X-ray diffraction cannot be used to directly measure atomic coordinates. Through the analysis of pair-distribution functions, measurements of averaged structural features such as average bond lengths can be determined. By combining experimental data with simulations such as in reverse Monte-Carlo simulations, some models of 3D atomic structures can be determined. However it has not yet been possible to determine any local structure directly from experiment. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D10.00008: THz-driven Electron Bunch Compression and Timing Jitter Reduction for Relativistic Ultrafast Electron Diffraction Measurements Emma Snively, Mohamed A. K. Othman, Michael E. Kozina, Benjamin K Ofori-Okai, Stephen P. Weathersby, Suji Park, Xiaozhe Shen, Xijie Wang, Matthias C. Hoffmann, Renkai Li, Emilio Nanni We discuss the results of a THz-driven electron bunch compression experiment in which interaction between a quasi-single-cycle THz pulse and a relativistic electron beam in a parallel plate waveguide produced a beam energy chirp for velocity bunching. Measurements at the SLAC MEV-UED facility show a simultaneous reduction in the bunch length and timing jitter by up to a factor of 3, improving the overall timing resolution for applications like ultrafast electron diffraction and other beam-based ultrafast measurements. This technique employs unique advantages of all-optical beam manipulation, including the inherent synchronization which allows the compensation of electron beam timing jitter and the high field gradient which enables efficient chirping of the electron beam in a sub-millimeter interaction region. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D10.00009: Laboratory Based Hard X-ray Photoelectron Spectroscopy Susanna Eriksson, Brandon Giles Hard X-ray photoelectron spectroscopy (HAXPES) is generally used to study core topics in condensed matter physics. However with a worldwide increase in the number of HAXPES focused endstations, many other interest groups now recognize its broad appeal. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D10.00010: Probing bulk electronic structure with a laboratory-based hard x-ray angle-resolved photoemission spectrometer Joseph D Grassi, Arian Arab, Jay Paudel, Raj K Sah, Weibing Yang, Ravini U Chandrasena, Keisuke Kobayashi, Alexander Gray Hard x-ray angle-resolved photoemission (HARPES) employing multi-keV x-rays as the excitation source has recently emerged as a powerful tool for the direct measurement of momentum-resolved bulk electronic structure [1-3]. To date, comprehensive HARPES spectroscopic studies have only been feasible at large-scale national synchrotron facilities. Here, we describe a newly completed laboratory-based hard x-ray photoemission spectrometer system with HARPES capabilities. The system utilizes a high-flux (3E9 ph/s) high-resolution (<0.45 eV) monochromated Cr Kα x-ray source tuned to the intermediate hard/tender energy regime (5.4 keV), which enables bulk- and buried-layer/interface sensitivity (up to 10 nm deep) while still being sensitive to the valence-band states due to appreciable photo-ionization cross sections. We present a wide range of examples of angle-resolved investigations of solids, including core-level and valence-band spectroscopy, momentum-resolved band structure mapping, and element-sensitive x-ray photoelectron diffraction. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D10.00011: Development of in-situ differential thermal analysis for crystal growth experiments Yuri Janssen, Jose Nicasio, Kemar Dudley, Bingying Xia, Jack Simonson Differential thermal analysis (DTA) can give valuable information on melting and freezing of mixtures that are used for flux or solution growth of single crystals for materials research, and increasing the success rate of crystal growth attempts. DTA is especially valuable as a tool for undergraduate research involving crystal growth, as it can quickly give a realistic and easy-to-understand picture at what is happening inside a growth crucible as it is hiding the cooling crystal-growth mixture from view. In the past, we have performed DTA in a dedicated instrument, with small crucibles containing exactly the same composition as the larger growth crucible in the larger growth furnace. Now we are performing in-situ DTA inside the growth furnace and on as-prepared growth samples, for different type growths and furnaces, quickly improving crystal growth performed by undergraduate students with limited time dedicated to lab, and, moreover, on very inexpensive equipment. Here, we will present results of these developments. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D10.00012: Early stage of iron anodic oxidation measured by 25ms-resolution X-ray reflectometry Hiromasa Fujii, Takashi Doi, Yusuke Wakabayashi Anodic oxidation at metal/water interface is a general phenomenon that commonly takes place on many metals. Time evolution of the oxide thickness is proportional to log(t)[1]. However, early stage clearly deviates from log(t) and the mechanism has not been understood yet in spite of its fundamental importance[2]. To reveal the early-stage mechanism, precise structural basis is needed. Here we report 25ms-resolution X-ray reflectivity experiments[3] to investigate the early stage of anodic oxidation at Fe (100), (110) and (111) in pH 8.4 borate buffer solution as model materials. Experiments were performed at the BL13XU of SPring-8, Japan with a 25keV monochromatic X-ray. The film density in the early stage is lower than in the later stage by 13 %, which suggests that the film structure is a highly defective spinel oxide. Moreover, the growth rate in the early stage is found to be proportional to about t-1.5 but in later stage is t-1. The presumed mechanism based on the Point Defect Model[1] will be discussed in the presentation. |
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