Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B44: X-ray and Neutron Scattering |
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Sponsoring Units: GIMS Chair: Bennett Larson, Oak Ridge National Lab Room: LACC 518 |
Monday, March 21, 2005 11:15AM - 11:27AM |
B44.00001: Crystal-field splitting in UO$_2$ Heinz Nakotte, R. Rajaram, S. Kern, R. McQueeney, G.H. Lander Uranium Dioxide (UO$_{2})$ is an important nuclear fuel material. We performed high-resolution inelastic neutron scattering using PHAROS at the Los Alamos spallation source LANSCE in order to re-investigate the crystal field splitting in UO$_{2}$, determined with the knowledge of the dipole-allowed transitions. We obtained the crystal field parameters and the 5$f$ electron eigen functions for UO$_{2}$. The fourth- and sixth-degree crystal field parameters were found to be V$_{4}$= -116.24 and V$_{6}$=25.78, in good agreement with previously published results by Amoretti et al. [1]. On the other hand, these previous studies did reveal four crystal-field excitations in the 150-180 meV range, only three of which can be explained by the crystal-field model. Our experiments on a different UO$_{2}$ sample show that the previously observed peak at about 180 meV is a spurious one, thus it is not intrinsic to UO$_{2}$. [1] G. Amoretti et al., Phys. Rev. B 15 (1989) 1856 [Preview Abstract] |
Monday, March 21, 2005 11:27AM - 11:39AM |
B44.00002: Efficient Single Crystal Diffuse Neutron Scattering with Elastic Discrimination S. Rosenkranz, R. Osborn Many new phenomena of technological importance are governed by complex disorder and nanoscale self-organization such as stripe formation, phase separation, dimerization. Coherent diffuse scattering from single crystals is the most powerful probe of such complex disorder as it probes both the local distortions around a point defect as well as the length scale and morphology of defect-defect correlations. There are however formidable technical difficulties both in obtaining reliable diffuse scattering data and in using it to construct models of defect structures. White-beam pulsed neutron instruments provide efficient access to the large volumes of reciprocal space that are required to model disorder accurately, but accomplish this without energy analysis so that static diffuse scattering is contaminated by vibrational and other dynamic processes in the sample. At present, there is no way to eliminate this inelastic signal without monochromating the incident or scattered beams, which results in a substantial loss of intensity. A proposed instrument, named Corelli, solves this problem by combining the high-efficiency of white-beam Laue diffraction with energy discrimination produced by the use of a statistical chopper. The limitations of this cross–correlation method and the reasons for its effectiveness for energy discrimination will be discussed. \\ \\ This work is supported by US DOE BES-DMS W-31-109-ENG-38. [Preview Abstract] |
Monday, March 21, 2005 11:39AM - 11:51AM |
B44.00003: Placzek correction for neutron scattering from condensed matter Valentin Levashov, Maxim Lobanov, Takeshi Egami In neutron diffraction experiments with condensed matter the energy of the neutrons is comparable to the energy of phonons in the solid. Thus, in the two-axis diffraction measurement of powder, glasses or liquids the structure function determined from scattering intensity, in assumption of completely elastic scattering, can be distorted by inelasticity effects. Correction for inelasticity effects was first proposed by Placzek, by assuming ballistic collision of neutrons with the matter. However, such an assumption is valid only at high momentum transfer and high neutron energies, and in reality the approach developed by Placzek is not accurate enough for solid materials. Here we report on the development of an accurate method, based on multiphonon expansion, for inelasticity correction in solid materials. Then we discuss distortions introduced by inelasticity into pair distribution function. [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:03PM |
B44.00004: In-situ Neutron Diffraction Studies of the Reduction of a Model of an Oxidations Catalyst (ferric molybdate and bismuth molybdate) Ashfia Huq, R.G. Teller, J.W. Richardson, E.R. Maxey Three elements commonly found in metal oxide alkene oxidation catalysts are molybdenum, bismuth and iron. In the case of ammoxidation of propylene to acrylonitrile many catalyst have ferric molybdate and a mixture of bismuth molybdates present in the as-prepared formulations. It is generally recognized that during catalyst activation ferric molybdate is reduced to Fe$^{+2}$ phases, freeing molybdenum oxide for the formation of other phases. It is suspected, but has never been demonstrated, that this excess MoO$_{3}$ then reacts with the bismuth containing phase(s) to form the active catalyst phase. Although this reaction is generally believed to occur in a number of catalytic processes the mechanism of the reaction has never been extensively studied. Due to the ease of in-situ measurements and the sensitivity to oxygen in the presence of heavy metals neutron diffraction is an ideal probe to study this reaction mechanism. We have developed a reaction cell that can be used in the General Purpose Powder Diffractometer at IPNS, ANL for time resolved \textit{in situ} study. Recent upgrades to GPPD, which have increased data rates by a factor of 6, now make these measurements possible. Preliminary findings about the evolution of a model oxidation catalyst under reaction conditions will be presented in this talk. [Preview Abstract] |
Monday, March 21, 2005 12:03PM - 12:15PM |
B44.00005: A New Approach for Extracting the Pair Distribution Function of Liquds from X-Ray Scattering Experiments David Vaknin, Yaroslav Chushak, Alex Travesset A new approach for determining the pair distribution function (PDF, g(r)) from X-ray liquid structure factor in a reflection mode is described and applied to those of pure water and dilute water-salt solutions. The approach involves the construction of a model PDF function using parameterized generating functions that is refined by least square fitting procedure to the measured liquid S(Q). First, a histogram of the PDF is constructed using step-like functions that are convolved with width-varying gaussians for each interfacial step of the PDF to produce a smooth g(r). The structure factor S(Q) is then calculated from g(r) which is given by a linear combination of Error Functions. The fitted parameters are the positions and widths of the peaks of the g (r). The advantages of this procedure is that no absolute scaling of the intensity is necessary and it provides the uncertainties in calculated g(r). Measuring the S(Q) in reflection mode at grazing-angles of incidence (in particular below the critical angle for total reflectivity - GIXD mode) enables to obtain the liquid-gas interfacial S(Q) for which the new approach can be readily extended. [Preview Abstract] |
Monday, March 21, 2005 12:15PM - 12:27PM |
B44.00006: Multipole X-ray Spectroscopy Using Non-resonant X-ray Raman Scattering Tim Fister, Gerald Seidler, Adrienne Battle, Julie Cross, Albert Macrander, Qing Qian, Trevor Tyson The information obtained by non-resonant inelastic x-ray scattering, commonly known as non-resonant x-ray Raman scattering (XRS), has both similarities and key differences when compared with that obtained by traditional x-ray spectroscopies such as from XAFS measurements . In the dipole limit (\textit{qa $<<$ }1), the matrix elements for XRS is proportional to that for x-ray absorption spectroscopy but with the direction of the momentum transfer playing the role of the polarization vector. However, XRS measurements at high $q$ can often go beyond the dipole limit--- leading to ``forbidden'' multipole excitations. This $q$-dependence can help separate various contributions to the local density of states, providing new information on the symmetries of a material. A primary drawback to XRS is its low cross-section, which is compounded measurements at multiple values of $q$ are needed. In response, we have built a multi-element apparatus to measure up to 10 values of $q$ simultaneously. We apply this instrument to a range of problems, including the valence-band exciton in LiF and the $L$- and $M$-edges of transition metals, transition metal oxides, and several minerals for the purpose of prototyping future measurements under high pressure. [Preview Abstract] |
Monday, March 21, 2005 12:27PM - 12:39PM |
B44.00007: Direct Observation of X-ray Resonance Effects in Crystal Cavity Using Sub-meV Resolution Synchrotron Radiation Shih-Lin Chang, Yuriy P. Stetsko, Mau-Tsu Tang, Yen-Ru Lee, Wen-Hsien Sun, Hsueh-Hung Wu, Makina Yabashi, Tetsuya Ishikawa X-ray resonator, or cavity, has long been proposed and considered as a first step in realizing an X-ray laser for more than three decades. Attempt to realize the resonance in a crystal cavity has been pursued from time to time but with limited success. The difficulty arises mainly from lack of a sufficient energy resolution of X-rays and of a small-gap crystal cavity. That is, the required temporal coherence is not retained. With a high energy resolution of $\Delta $E=0.36 meV at 14.438 keV of X-ray synchrotron radiation and crystal plates with 100$\sim $150 $\mu $m gaps prepared by the microelectronic lithography technique, here we report the realization of a Fabry-Perot resonator for hard X-rays. Interference fringes inside the total reflection range in angle scans and inside the energy gap in energy scans near and at the (12 4 0) reflection position for two- and eight-plate silicon crystal cavities are clearly observed. This finding suggests many fundamental investigations and applications in high-resolution X-ray optics. [Preview Abstract] |
Monday, March 21, 2005 12:39PM - 12:51PM |
B44.00008: Sapphire Analyzers for Resonant Inelastic X-ray Scattering (RIXS) Hasan Yavas, Ercan Alp, Harald Sinn, Ruben Khachatryan, Yuri Shvyd’ko, Ahmet Alatas, Ayman Said, Simon Billinge Back-scattering analyzers for inelastic x-ray scattering experiments are under development for over two decades. Large angular acceptance, good reflectivity makes this geometry attractive. So far Si and Ge have been successfully used, due to availability of good crystals. However, there is a need to find other crystals, as IXS experiments at specific energies near the atomic absorption edge may provide element specific electronic state information. Hence crystals of lower symmetry containing more than one element are of great interest. In this study, we have developed new manufacturing techniques to build spherically bent, diced sapphire analyzers. Procedures regarding dicing, etching and bonding will be discussed, and initial test results for Al2O3 (0 4 14) at 8.9 keV will be presented. [Preview Abstract] |
Monday, March 21, 2005 12:51PM - 1:03PM |
B44.00009: High-Efficiency High Energy Resolution Detecting System for X-Ray Absorption Spectroscopy Qing Qian, Trevor Tyson A high-efficiency high energy resolution wave dispersing detecting system was developed. One extra short 182mm radius spherical bent analyzer with 100mm diameter is employed in Rowland circle geometry. All motions of the analyzer and detector are driven by step motors. The system is quite suitable for absorption spectroscopy in fluorescence mode. X-ray absorption spectroscopy measurements were carried out on powders and thin films. The total energy resolution is $\sim $4eV for Si(440) crystal analyzer at 6493 eV, with 2{\%} of the full solid angle collected. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:15PM |
B44.00010: Synchrotron X-ray Microdiffraction Study of Whisker Growth in Sn Films Wenjun Liu, Gene Ice, Bennett Larson, Wenge Yang, Jonathan Tischler A prototype three-dimensional x-ray crystal microscope is installed on beamline 34-ID at the Advanced Photon Source, Argonne National Lab, and has begun operation. The microscope has a routine spatial resolution of approximately 0.5 x 0.5 x 1.0 um$^{3}$. With scanning technique, spatially resolved microdiffraction measurements can be made in two or three dimensions. Properties that can be measured include the local crystalline phase, local texture (orientation), and the local strain tensors. One of its applications is to study the whiskers in Sn films, which is an example of anomalous grain growth and an area of long-standing interest to the application of Pb-free solder in electronic manufacturing. Recent measurements illustrated the ability of this newly developed crystal microscope to characterize the local orientation and strain of whiskers and near whisker regions. Research supported by the DOE, Division of Materials Sciences under contract with ORNL, operated by UT-Battelle, LLC. UNICAT is supported by ORNL, UIUC-MRL, NIST, and UOP Inc. [Preview Abstract] |
Monday, March 21, 2005 1:15PM - 1:27PM |
B44.00011: Relationship between pair and higher order correlations in solid solutions Don Nicholson, Rozaliya Barabash, Gene Ice, Cullie Sparks, Lee Robertson, Christopher Wolverton Diffusely scattered x-rays (neutrons) are sensitive to the correlations among atomic positions. However, only pair correlations in occupation and displacement can be recovered from diffuse scattering measurements in the kinetic approximation, where as a complete description of the structure requires knowledge of higher order correlation. It has been suggested that pair correlation functions either uniquely determine the higher order correlations or that they restrict the value of higher order correlations. These issues are clarified by the presentation of simulation results and proofs that for pair potential Hamiltonians the pair correlations determine all higher order correlations and that for many body Hamiltonians they do not. [Preview Abstract] |
Monday, March 21, 2005 1:27PM - 1:39PM |
B44.00012: Single crystal diamond study with rotating anode x-ray topography Yuncheng Zhong, Albert Macrander, Felix Krasnicki, Yong Chu, Joe Maj Synthetic high-temperature-high-pressure diamond crystals of type Ib having (100) and (111) surface orientations were studied using x-ray topography method. An asymmetrically cut monochromator was applied to expand the x-ray beam from a rotating anode source up to 70mm. Double crystal rocking curve measurements were performed on each crystal and the topography images were taken at each position on rocking curve. The detector is a CCD camera with pixel size of 60 micro meters. The method of comparing rocking curves obtained after azimuthal rotation of the crystal around the reciprocal vector provides the possibility to separate locally the lattice spacing variation (strain) and misorientation (tilt) on the sample. The results show the features on each crystal such as growth sector boundaries and saw scratches. The strain and tilt maps of the growth boundaries can be interpreted as nitrogen aggregation maps. The comparisons of the results from the crystals before and after surface etching show different effects on (111) crystals and (100) crystals. (The type IB crystals in this study were procured from Drukker/Element Six. This work supported by the U.S. DOE, Basic Energy Sciences, under Contract No. W-31-109-ENG-38. ) [Preview Abstract] |
Monday, March 21, 2005 1:39PM - 1:51PM |
B44.00013: Multi-Layer Laue Lenses for Nanfocusing of Hard X-rays H-C Kang, G.B. Stephenson, C. Liu, R. Conley, A.T. Macrander, J. Maser Multilayers consisting of tungsten-silicide on silicon bilayers that were grown with a graded thickness recipe to produce a linear zone plate structure have been tested. The results to date have produced a focus of 72 nm for 19.5 keV x-rays on a bending magnet beamline at the Advanced Photon Source. The multilayer stack consisted of more than 10 microns of sputtered material, and the optical devices were made by dicing and polishing to produce wedges having an optical depth between 5 and 15 microns. In addition to the focusing behavior, Laue case diffraction was studied. The structures have diffraction properties intermediate between Fresnel diffraction and volume diffraction. [Preview Abstract] |
Monday, March 21, 2005 1:51PM - 2:03PM |
B44.00014: X-ray optical limits of microdiffraction at arc second angular resolution and application to optoelectronic waveguides Alexander Kazimirov, Andrei Sirenko, Don Bilderback, Zhonghou Cai, Barry Lai, Rong Huang, A. Ougazzaden Synchrotron microbeam high-angular resolution diffraction setup is introduced based on a phase zone plate generating a microbeam with the size of 0.35 $\mu $m (vertical) and 0.24 $\mu $m (horizontal) and a perfect Si(004) analyzer crystal providing high angular resolution of about 2 arc sec. The broadening of the ``diffraction'' spot to 2.5 $\mu $m by perfect crystal has been experimentally observed in the diffraction (vertical) plane. This broadening is a consequence of the phase space conservation principle and unavoidable when high angular resolution in microbeam diffraction experiment is required. The use of perfect crystals in a non-dispersive arrangement offers flexibility in trading beam size/flux for resolution by choosing proper crystal or controlling the angular acceptance by changing asymmetry factor. The setup was applied to study strain and thickness variation in selectively grown InGaAlAs-based optoelectronic waveguide arrays with a minimum lateral size of 1.6 $\mu $m. [Preview Abstract] |
Monday, March 21, 2005 2:03PM - 2:15PM |
B44.00015: Convergent beam powder x-ray diffraction Wei Zhou, Carolyn MacDonald Polycapillary x-ray optics, arrays of hollow glass tubes, were used to collimate and focus x rays onto powder samples for diffraction measurements.\footnote{ C.A. MacDonald and W.M. Gibson, ``Applications and Advances In Polycapillary Optics'', X-ray Spectrometry, \textbf{32 (}3), 2003, pp 258-268.} Comparisons were made of system resolution and diffracted beam intensity for with and without focusing and collimating optics using a standard small spot rotating anode system in point source geometry. The results for simple inorganic standards and a variety of macromolecules were compared to those obtained with a very low power, 20 W, microfocus source which allowed smaller source-to-optic distances and therefore collection over larger solid angles.\footnote{ N. Mail, W. M. Gibson, and, C.A. MacDonald, ``Molybdenum Microfocus Source Coupling to Polycapillary Optics for Powder Diffraction,'' in Ali M. Khounsary , C.A. MacDonald, eds., \textbf{Advances in Laboratory-Based X-Ray Sources and Optics III}, SPIE vol. 4781, pp. 87-95, 2002.} In order to compare with theoretical calculations, detailed source and optic characterization were performed. Resolution and intensity were in good agreement with those obtained from simple geometrical calculations, which allows for system design and optimization for the desired sample characteristics. [Preview Abstract] |
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B44.00016: Observation of defects in single crystal diamond with high resolution x-ray topography Yuncheng Zhong, Albert Macrander, Felix Kasnicki, Yong Chu, Joe Maj Single crystal diamond is an important optical component at synchrotron facilities, and is one of the best candidates for the optics for the next generation X-ray light source. The imperfections and surface conditions of the synthetic diamond crystals affect their applications. It has been shown that surface etching can improve the FWHM of type IB synthetic diamond crystals having (100) surface orientation to a certain extent. We studied the remaining defects in the crystals after surface etching of high-pressure-high-temperature type IB crystals using a high resolution X-ray topography method at APS beamline 2BM. The results are interpreted as various types of imperfections such as growth boundaries, dislocation lines, stacking faults and dislocation networks. These defects have been analyzed to explain their contributions to the FWHM. These results will be compared to very recent measurements on type IIA crystals. (The type IB crystals were procured from Drukker/Element Six, and type IIA crystal was on loan from Sumitomo. This work supported by the U.S. DOE, Basic Energy Sciences, under Contract No. W-31-109-ENG-38. ) [Preview Abstract] |
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