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Using Monte Carlo ray tracing simulations to model the quantum harmonic oscillator modes observed in uranium nitride

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Physical Review B 2014年第14期89卷 144302-144302页

作者： J. Y. Y. Lin A. A. Aczel D. L. Abernathy S. E. Nagler W. J. L. Buyers G. E. Granroth Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

Recently an extended series of equally spaced vibrational modes was observed in uranium nitride (UN) by performing neutron spectroscopy measurements using the ARCS and SEQUOIA time-of-flight chopper spectrometers [A. A. Aczel et al., Nat. Commun. 3, 1124 (2012)]. These modes are well described by three-dimensional isotropic quantum harmonic oscillator (QHO) behavior of the nitrogen atoms, but there are additional contributions to the scattering that complicate the measured response. In an effort to better characterize the observed neutron scattering spectrum of UN, we have performed Monte Carlo ray tracing simulations of the ARCS and SEQUOIA experiments with various sample kernels, accounting for nitrogen QHO scattering, contributions that arise from the acoustic portion of the partial phonon density of states, and multiple scattering. These simulations demonstrate that the U and N motions can be treated independently, and show that multiple scattering contributes an approximate Q-independent background to the spectrum at the oscillator mode positions. Temperature-dependent studies of the lowest few oscillator modes have also been made with SEQUOIA, and our simulations indicate that the T dependence of the scattering from these modes is strongly influenced by the uranium lattice.

关键词： URANIUM MONTE Carlo method NITRIDES RAY tracing algorithms HARMONIC oscillators

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Tracking the solid-electrolyte-interphase (SEI) formation on Amorphous Si and Sn anodes for li-ion batteries 11

Tracking the solid-electrolyte-interphase (SEI) formation on...

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11th Annual TechConnect World Innovation Conference and Expo, Held Jointly with the 20th Annual Nanotech Conference and Expo, and the 2017 National SBIR/STTR Conference

作者： Kim, J.R. Doucet, M. Browning, J.F. Veith, G.M. Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak RidgeTN United States Chemical and Engineering Materials Division Oak Ridge National Laboratory Oak RidgeTN United States Materials Science and Technology Division Oak Ridge National Laboratory Oak RidgeTN United States

ISBN: (纸本)9780997511796

neutron reflectometry provides a detailed method in which to investigate the solid-electrolyte interphase (SEI) throughout its initial formation and under dynamic cycling conditions in lithium-ion batteries. Amorphous silicon (a-Si) and tin are investigated to demonstrate both the thickness and scattering length density of the SEI layer considering a fluoroethylene carbonate (FEC) electrolyte additive. Distinct differences and similarities between the two systems have been identified;both a-Si and Sn observe a reversible contraction/growth of the SEI layer throughout charge/discharge cycles originating from the buildup and dissolution of organic components at the electrolyte surface. a-Si observes a clear tendancy to form an initial Li2O/Li2CO3 layer based on a chemical reaction that occurs between the native oxide and the electrolyte prior to electrochemical cycling. Whereas the native tin oxide appears to remain intact, forming an SEI of different composition as a result.

关键词： Amorphous silicon

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High-energy continuum of magnetic excitations in the two-dimensional quantum antiferromagnet Sr2CuO2Cl2

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Physical Review B 2014年第18期89卷 180410(R)-180410(R)页

作者： K. W. Plumb A. T. Savici G. E. Granroth F. C. Chou Young-June Kim Department of Physics University of Toronto Toronto Ontario Canada M5S 1A7 Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Center for Condensed Matter Sciences National Taiwan University Taipei 10617 Taiwan

We have measured the magnetic excitation spectrum of the model square-lattice spin-1/2 antiferromagnet Sr2CuO2Cl2 over a broad range of energies and momenta using high-resolution inelastic neutron scattering (INS). The magnon dispersion along the zone boundary was accurately measured to be a 43 meV between (1/2,0) and (3/4,1/4) indicating the importance of coupling beyond nearest neighbors in the spin Hamiltonian. We observe a strong momentum dependent damping of the zone-boundary magnons at (1/2,0) revealing a high-energy continuum of magnetic excitations. A direct comparison between our INS measurements and resonant inelastic x-ray scattering (RIXS) measurements shows that the RIXS spectrum contains significant contributions from higher energy excitations not previously considered. Our observations demonstrate that this high-energy continuum of magnetic fluctuations is an ubiquitous feature of insulating monolayer cuprates, apparent in both inelastic neutron and light scattering measurements.

关键词： ANTIFERROMAGNETIC materials QUANTUM theory neutron scattering X-ray scattering SPECTRUM analysis

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neutron scattering study of spin dynamics in superconducting (Tl,Rb)2Fe4Se5

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Physical Review B 2013年第10期87卷 100501(R)-100501(R)页

作者： Songxue Chi Feng Ye Wei Bao Minghu Fang H. D. Wang C. H. Dong A. T. Savici G. E. Granroth M. B. Stone R. S. Fishman Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Physics and Astronomy University of Kentucky Lexington Kentucky 40506 USA Department of Physics Renmin University of China Beijing 100872 China Department of Physics Zhejiang University Hangzhou 310027 China Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

We observed in superconducting (Tl,Rb)2Fe4Se5 spin-wave branches that span an energy range from 6.5 to 209 meV. Spin dynamics are successfully described by a Heisenberg localized spin model whose dominant in-plane interactions include only the nearest (J1 and J1′) and next nearest neighbor (J2 and J2′) exchange terms within and between the tetramer spin blocks, respectively. These experimentally determined exchange constants would crucially constrain the theoretical viewpoints on magnetism and superconductivity in the Fe-based materials.

关键词： neutron scattering SUPERCONDUCTORS HEISENBERG model MAGNETIC materials MAGNETISM

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Immersive visualization for materials science data analysis using the Oculus Rift

Immersive visualization for materials science data analysis ...

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IEEE International Conference on Big data

作者： Margaret Drouhard Chad A. Steed Steven Hahn Thomas Proffen Jamison Daniel Michael Matheson Computational Sciences and Engineering Division Oak Ridge National Laboratory Oak Ridge TN Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge TN National Center for Computational Sciences Oak Ridge National Laboratory Oak Ridge TN

In this paper, we propose strategies and objectives for immersive data visualization with applications in materials science using the Oculus Rift virtual reality headset. We provide background on currently available analysis tools for neutron scattering data and other large-scale materials science projects. In the context of the current challenges facing scientists, we discuss immersive virtual reality visualization as a potentially powerful solution. We introduce a prototype immersive visualization system, developed in conjunction with materials scientists at the Spallation neutron Source, which we have used to explore large crystal structures and neutron scattering data. Finally, we offer our perspective on the greatest challenges that must be addressed to build effective and intuitive virtual reality analysis tools that will be useful for scientists in a wide range of fields.

关键词： data visualization Three-dimensional displays neutrons Solid modeling Crystals Virtual reality Instruments

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neutron scattering study of spin ordering and stripe pinning in superconducting La1.93Sr0.07CuO4

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Physical Review B 2015年第17期92卷 174525-174525页

作者： H. Jacobsen I. A. Zaliznyak A. T. Savici B. L. Winn S. Chang M. Hücker G. D. Gu J. M. Tranquada Condensed Matter Physics & Materials Science Department Brookhaven National Laboratory Upton New York 11973-5000 USA Nano-Science Center Niels Bohr Institute University of Copenhagen DK-2100 Copenhagen Ø Denmark Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA NIST Center for Neutron Research National Institute of Standards and Technology Gaithersburg Maryland 20899 USA

The relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La1.93Sr0.07CuO4, a superconductor with a transition temperature of Tc=20 K. At T≪Tc we find incommensurate spin fluctuations with a quasielastic energy spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below ∼10 K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpectedly strong fluctuations of the CuO6 octahedra about Cu-O bonds, which are associated with inequivalent O sites within the CuO2 planes. Furthermore, we observed a weak elastic (33¯0) superlattice peak that implies a reduced lattice symmetry. The presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped La2−xSrxCuO4. The coexistence of superconductivity with quasistatic spin-stripe order suggests the presence of intertwined orders; however, the rotation of the stripe orientation away from the Cu-O bonds might be connected with evidence for a finite gap at the nodal points of the superconducting gap function.

关键词： neutron scattering COPPER oxide superconductors DOPED semiconductors SUPERCONDUCTING transition temperature LANTHANUM compounds

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Temperature-dependent phonon lifetimes and thermal conductivity of silicon by inelastic neutron scattering and ab initio calculations

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Physical Review B 2020年第17期102卷 174311-174311页

作者： D. S. Kim O. Hellman N. Shulumba C. N. Saunders J. Y. Y. Lin H. L. Smith J. E. Herriman J. L. Niedziela D. L. Abernathy C. W. Li B. Fultz Department of Applied Physics and Materials Science California Institute of Technology Pasadena California 91125 USA Department of Mechanical and Civil Engineering California Institute of Technology Pasadena California 91125 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Physics and Astronomy Department Swarthmore University Swarthmore Pennsylvania 19081 USA Division of Materials Science and Technology Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Division of Neutron Scattering Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Mechanical Engineering University of California Riverside California 92521 USA

Inelastic neutron scattering on a single crystal of silicon was performed at temperatures from 100 to 1500 K. These experimental data were reduced to obtain phonon spectral intensity at all wave vectors Q⃗ and frequencies ω in the first Brillouin zone. Thermal broadenings of the phonon peaks were obtained by fitting and by calculating with an iterative ab initio method that uses thermal atom displacements on an ensemble of superlattices. Agreement between the calculated and experimental broadenings was good, with possible discrepancies at the highest temperatures. Distributions of phonon widths versus phonon energy had similar shapes for computation and experiment. These distributions grew with temperature but maintained similar shapes. Parameters from the ab initio calculations were used to obtain the thermal conductivity from the Boltzmann transport equation, which was in good agreement with experimental data. Despite the high group velocities of longitudinal acoustic phonons, their shorter lifetimes reduced their contribution to the thermal conductivity, which was dominated by transverse acoustic modes.

关键词： Lattice thermal conductivity Semiconductors neutron scattering Time-of-flight neutron spectroscopy

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Light atom quantum oscillations in UC and US

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Physical Review B 2016年第1期93卷 014306-014306页

作者： Yuen Yiu A. A. Aczel G. E. Granroth D. L. Abernathy M. B. Stone W. J. L. Buyers J. Y. Y. Lin G. D. Samolyuk G. M. Stocks S. E. Nagler Department of Physics and Astronomy University of Tennessee Knoxville Tennessee 37996 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Canadian Neutron Beam Centre Canadian Nuclear Laboratories Chalk River Ontario Canada K0J 1J0 California Institute of Technology Pasadena California 91125 USA Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

High-energy vibrational scattering in the binary systems UC and US is measured using time-of-flight inelastic neutron scattering. A clear set of well-defined peaks equally separated in energy is observed in UC, corresponding to harmonic oscillations of the light C atoms in a cage of heavy U atoms. The scattering is much weaker in US and only a few oscillator peaks are visible. We show how the difference between the materials can be understood by considering the neutron scattering lengths and masses of the lighter atoms. Monte Carlo ray tracing is used to simulate the scattering, with near quantitative agreement with the data in UC, and some differences with US. The possibility of observing anharmonicity and anisotropy in the potentials of the light atoms is investigated in UC. Overall, the observed data is well accounted for by considering each light atom as a single atom isotropic quantum harmonic oscillator.

关键词： Phonons Inelastic neutron scattering Monte Carlo methods

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Magnons and a two-component spin gap in FeV2O4

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Physical Review B 2014年第22期89卷 224404-224404页

作者： G. J. MacDougall I. Brodsky A. A. Aczel V. O. Garlea G. E. Granroth A. D. Christianson T. Hong H. D. Zhou S. E. Nagler Department of Physics and the Seitz Materials Research Laboratory University of Illinois at Urbana-Champaign Urbana Illinois 61801 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Physics and Astronomy University of Tennessee Knoxville Tennessee 37996 USA CIRE University of Tennessee Knoxville Tennessee 37996 USA

The spinel vanadates have become a model family for exploring orbital order on the frustrated pyrochlore lattice, and recent debate has focused on the symmetry of local crystal fields at the cation sites. Here, we present neutron scattering measurements of the magnetic excitation spectrum in FeV2O4, a recent example of a ferrimagnetic spinel vanadate which is available in single-crystal form. We report the existence of two emergent magnon modes at low temperatures, which draw strong parallels with the closely related material, MnV2O4. We were able to reproduce the essential elements of both the magnetic ordering pattern and the dispersion of the inelastic modes with semiclassical spin-wave calculations, using a minimal model that implies a sizable single-ion anisotropy on the vanadium sublattice. Taking into account the direction of ordered spins, we associate this anisotropy with the large trigonal distortion of VO6 octahedra, previously observed via neutron powder diffraction measurements. We further report on the spin gap, which is an order of magnitude larger than that observed in MnV2O4. By looking at the overall temperature dependence, we were able to show that the gap magnitude is largely associated with the ferro-orbital order known to exist on the iron sublattice, but the contribution to the gap from the vanadium sublattice is in fact comparable to what is reported in the Mn compound. This reinforces the conclusion that the spin canting transition is associated with the ordering of vanadium orbitals in this system, and closer analysis indicates closely related physics underlying orbital transitions in FeV2O4 and MnV2O4.

关键词： MAGNONS PYROCHLORE CRYSTAL field theory VANADIUM compounds LOW temperatures

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Influence of interstitial Mn on magnetism in the room-temperature ferromagnet Mn1+δSb

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Physical Review B 2015年第22期91卷 224418-224418页

作者： A. E. Taylor T. Berlijn S. E. Hahn A. F. May T. J. Williams L. Poudel S. Calder R. S. Fishman M. B. Stone A. A. Aczel H. B. Cao M. D. Lumsden A. D. Christianson Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Center for Nanophase Materials Sciences and Computer Science and Mathematics Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831-6494 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Physics and Astronomy University of Tennessee Knoxville Tennessee 37996 USA

We report elastic and inelastic neutron-scattering measurements of the high-TC ferromagnet Mn1+δSb. Measurements were performed on a large, TC=434 K, single crystal with an interstitial Mn content of δ≈0.13. The neutron-diffraction results reveal that the interstitial Mn has a magnetic moment, and that it is aligned antiparallel to the main Mn moment. We perform density functional theory calculations including the interstitial Mn and find the interstitial to be magnetic, in agreement with the diffraction data. The inelastic neutron-scattering measurements reveal two features in the magnetic dynamics: (i) a spin-wave-like dispersion emanating from ferromagnetic Bragg positions (HK2n), and (ii) a broad, nondispersive signal centered at forbidden Bragg positions (HK2n+1). The inelastic spectrum cannot be modeled by simple linear spin-wave-theory calculations and appears to be significantly altered by the presence of the interstitial Mn ions. The results show that the influence of the interstitial Mn on the magnetic state in this system is more important than previously understood.

关键词： FERROMAGNETIC resonance MAGNETISM SINGLE crystals neutron measurement MAGNETIC moments

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