Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session J38: Focus Session: X-ray and Neutron Instruments and Sciences II |
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Sponsoring Units: GIMS Chair: Carolyn MacDonald, State University of New York at Albany Room: Colorado Convention Center 501 |
Tuesday, March 6, 2007 11:15AM - 11:27AM |
J38.00001: Picosecond X-ray Pulse Generation at the Advanced Photon Source Dennis Mills Synchrotron radiation from storage ring-based facilities typically has a pulse length of many tens to many hundreds of picoseconds. In an effort to improve the temporal resolution of the study of dynamic and transient properties, the APS has been exploring the possibilities of producing short (a few picosecond) pulses though transverse deflection of the particle beam via radio frequency cavities installed in straight sections of the storage ring. These cavities produce a longitudinally coordinated vertical momentum to particle bunch that, when passed through an insertion device, then emits radiation with similar properties. Slits can then be used to time slice the beam or crystal optics can be employed to temporally compress the chirped radiation beam. Several approached for the implementation of this capability at the APS will be discussed along with the expected performance. [Preview Abstract] |
Tuesday, March 6, 2007 11:27AM - 11:39AM |
J38.00002: TEMPO Beamline at the Soleil Synchrotron Radiation Source Fausto Sirotti, Manuel Izquierdo, Mathieu Silly, Francois Polack, Christian Chauvet TEMPO is a soft X-rays beamline now opening to the user community at the French synchrotron radiation source Soleil.[1] The two experimental stations will be based on photoelectron spectroscopy and will be mainly devoted to kinetic and dynamic studies of the electronic and magnetic properties of surfaces and interfaces. The high flux coupled to the energy resolution of the electron energy analyzer equipped with a new time resolved detector will allow the user to perform the following kind of investigations using photoelectron spectroscopy: i) the evolution of the chemical environment (surface coordination, chemical bonding with different elements) of selected chemical species at the surface using spectroscopic signatures; ii) the dynamics of magnetization reversal in nanostructures, using the temporal characteristics of Soleil at the scale of tens of picoseconds; iii) excited states using synchrotron pulses in the temporal range of a picosecond with pump-probe experiments with two photons (laser + synchrotron radiation). The beamline design and the technical solutions adopted for time resolved experiments will be presented along with the first results. [1] http://www.synchrotron-soleil.fr/anglais/science-and-users/experiments/tempo/index.htm [Preview Abstract] |
Tuesday, March 6, 2007 11:39AM - 11:51AM |
J38.00003: Using crystal optics as a guard aperture in coherent diffraction imaging experiments Xianghui Xiao, Hanfei Yan, Martin de Jonge, Yuncheng Zhong, Yong Chu, Qun Shen A crucial issue in coherent x-ray diffraction imaging experiments is how to increase the signal-to-noise ratio when measuring relatively weak diffraction intensities from a nonperiodic object. To achieve such a goal, a guard aperture that can block the unwanted parasitic scattering from the beam-defining aperture is necessary. The conventional guard-edge-type aperture, however, is not easy to align and may produce secondary scattering from itself. In this presentation we present a novel crystal guard aperture concept, in which a pair of multiple-bounce crystal optics is employed [Xiao et al, Opt. Lett. 31, 3194(2006)]. Different from the guard-edge-type aperture, the crystal guard aperture does not produce secondary scattering and therefore guarantee super-clean incident beam. The effectiveness of the crystal guard aperture method has been verified by the theoretical analysis and simulations based on Fresnel propagations of a dynamically diffracted Bragg wave. Recent coherent diffraction experiment results also confirmed the validity of this new guarding scheme. [Preview Abstract] |
Tuesday, March 6, 2007 11:51AM - 12:03PM |
J38.00004: Phase retrieval from coherent x-ray diffraction data utilizing pre-determined partial information Sang Soo Kim, Hyon Chol Kang, Shashi Marathe, Su Nam Kim, Do Young Noh, Alec R. Sandy, Suresh Narayan We developed a phase retrieval algorithm that utilizes pre-determined partial phase information to overcome insufficient oversampling ratio in diffraction data. Implementing the Fourier modulus projection and the modified support projection manifesting the pre-determined information, a generalized difference map and HIO (Hybrid Input-Output) algorithms are developed. Optical laser diffraction data as well as simulated x-ray diffraction data are used to illustrate the validity of the proposed algorithm, which revealed the strength and the limitations of the algorithm. Finally, the proposed algorithm is applied to reconstruct images from coherent x-ray diffraction data of Au patterns. The proposed algorithm can expand the applicability of the diffraction based image reconstruction. [Preview Abstract] |
Tuesday, March 6, 2007 12:03PM - 12:15PM |
J38.00005: Nano-Scale Resolution Spectro-Microscopy by Coherent X-ray Diffraction. C. Song, D. Ramunno-Johnson, H. Jiang, A. Mancuso, J. Miao, M. de Jonge, C. Rau, D. Paterson, I. McNulty Coherent x-ray diffraction microscope, with its spatial resolution limited only by signal-to-noise ratio, has paved a route to a generic nano-scope relieved from crystalline specimens and destructive sample preparation. We advanced it further as a versatile spectro-microscopy. By using stark contrast in x-ray scattering lengths in the vicinity of atomic absorption edges, we could identify elements distribution at a nanometer scale. As the element specificity is acquired from direct x-ray absorption, it provides full flexibility for \textit{ab initio} imaging. Successful results on elemental mapping of nano-structures and single biological cells from 1-3 keV range coherent x-ray source will be presented. [Preview Abstract] |
Tuesday, March 6, 2007 12:15PM - 12:27PM |
J38.00006: Diffuse scattering due to nanoprecipitation in Ni-Al-Si alloys Rozaliya Barabash, G. Ice, E. Specht, P. Zshack Ni-Al-Si alloys demonstrate the tendency to the formation of L1$_{2}$ ordered coherent precipitates. Diffuse X-ray scattering around both the fundamental and superstructure reflections is analyzed both theoretically and experimentally for Ni-Al-Si single crystal alloys with coherent ordered precipitates after stress annealing. The shape function of the coherent precipitates is discussed. Diffuse scattering reveals precipitation induced strong lattice distortions in the matrix. Distortions of the lattice together with the changes of the scattering factor in the volume occupied by the precipitate cause asymmetry of the diffuse scattering distribution. Oscillations of the diffuse scattering intensity are observed. The shape of the coherent precipitates is asymmetric with a 15{\%} elongation along the stress annealing direction. Research at ORNL sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences U.S. Department of Energy, under Contract DE-AC05-00OR22725 with UT-Battelle and at APS under contract No. W-31-109-ENG-38. [Preview Abstract] |
Tuesday, March 6, 2007 12:27PM - 12:39PM |
J38.00007: Studies of stressor effects on silicon nanostructures using synchrotron X-ray nanodiffraction Zhonghou Cai, Ashesh Parikh, Paul Evans Scaling in the semiconductor industry has been accomplished by reduction in gate length and oxide thickness to enable large-scale decreases in device area and improved transistor performance. Strained silicon offers improved mobility at no significant additional costs. Fundamental understanding of the structural equilibrium between the silicon and the stressors at the device level is critical in manipulating properties for performance gains. The inhomogeneous strains in the silicon channel of nanotransistor devices due the epitaxy and lattice mismatch between Si and SiGe were individually studied using X-ray nanodiffraction at the Advanced Photon Source. Diffraction intensity from the strained silicon of less than 1x10$^{-4}$ $\mu $m$^{3 }$and the SiGe stressor were mapped in reciprocal space around the points of (004), (115), and (-115). Lattice bending up to a few degrees at both sides of the Si/SiGe interface were measured, and the associated strains were quantitatively extracted in functions of the lattice curvature. The effect of the size of stressors was also studied. [Preview Abstract] |
Tuesday, March 6, 2007 12:39PM - 12:51PM |
J38.00008: X-ray photon correlation spectroscopy in microfluidic ssytems Andrei Fluerasu We present a new experimental method that combines X-ray photon Correlation Spectroscopy (XPCS) and microfluidics and allows the direct measurement of the mesoscale dynamics of various soft matter systems (e.g. colloids, polymers, biological molecules like proteins, RNA, etc.) under flow conditions. Such a setup reduces the risk of beam damage and also allows time-resolved studies of various processes taking place in mixing flowcells. In the experiments reported here, we have used colloidal suspensions of hard-spehere systems, and studied their Brownian dynamics under laminar flow. Our experimental results and theoretical predictions show that the diffusive (Brownian) dynamics of the colloids can be decoupled from the flow-induced, convective dynamics. [Preview Abstract] |
Tuesday, March 6, 2007 12:51PM - 1:03PM |
J38.00009: Development of new x-ray absorption spectroscopy measurement Hoyoung Jang, Jun-Sik Lee, Kyung-Tae Ko, Hangil Lee, Jae-Young Kim, Ki Bong Lee, Jae-Hoon Park The x-ray absorption spectroscopy (XAS) is a powerful tool to probe electronic structure of valence states. However, its conventional measurements such as total electron yields or fluorescence yields often restrict sample conditions due to surface sensitivity and charging effects in an insulator or self- absorption effects, respectively. As an alternative, we found to extract XAS spectra from soft x-ray reflectivity measurements for transition metal compounds. We performed the soft x-ray reflectivity measurements on reference transition metal oxides, CoO and NiO, at Co and Ni $L_{2,3}$-edges, respectively, and successfully extracted the XAS spectrum using Kramers-Kronig relation from the reflectivity data. In the measurements, the scattering angle was set to be in specular conditions. Considering that the reflectivity is a photon-in and photon-out experiment, this result suggests an alternative to obtain XAS spectra for systems, in which the conventional XAS measurements are not applicable. [Preview Abstract] |
Tuesday, March 6, 2007 1:03PM - 1:15PM |
J38.00010: Overcoming Experimental and Intrinsic Broadening in Excited State Spectroscopies using Richardson-Lucy Deconvolution W.T. Elam, T.T. Fister, G.T. Seidler, K.P. Nagle, J.J. Kas, J.O. Cross The oscillatory signature of the photoelectron interference phenomenon central to core shell spectroscopies is frequently broadened by experimental or intrinsic (i.e., core-hole lifetime) energy resolutions, limiting the interpretation of the measurement.~ For example, this problem occurs in x-ray absorption fine structure (XAFS) measurements of heavy elements where the core-hole lifetime is very short ($\hbar /\tau _{core-hole} \ge 5\,\mbox{eV})$, and also in non-resonant x-ray Raman scattering measurements where the instrumental resolution (typically $\sim $1 eV) can be nearly an order of magnitude larger than the intrinsic energy resolution.~ Given the small statistical uncertainties in typical XAFS data and in recent XRS measurements using dedicated multielement spectrometers, the question naturally arises as to deconvolving the data with respect to the known instrumental or intrinsic resolutions.~ Here, we demonstrate that the Richardson-Lucy iterative algorithm provides a robust maximum likelihood method for addressing this issue in both XAFS and XRS. We demonstrate this method on core-hole broadened Ag XAFS data and experimentally broadened diamond and graphite XRS data. [Preview Abstract] |
Tuesday, March 6, 2007 1:15PM - 1:27PM |
J38.00011: Organic-modified and biological silica studied by synchrotron x-ray pair distribution function measurements Elaine DiMasi, Clayton Jeffryes, Gregory Rorrer, David Belton, Carole Perry Biomineralization is a process by which living organisms create composite organic/mineral tissues which have hierarchical structures on micron and submicron scales. Fine control over mineral phase and morphology make biomineralization an important inspiration for materials science. It is often not appreciated that even amorphous minerals such as silica can exhibit hierarchical structure and special properties. One difficulty is that the molecular structures of amorphous phases can be hard to elucidate. We are exploring the use of pair distribution function measurements from synchrotron x-ray scattering to study silica structures, comparing both synthetic organic-modifed silicas and germanium-containing biosilica from diatoms. The raw scattering patterns show clear differences. We will discuss how these data can be scrutinized to determine what differences may be created at the molecular level by different silicification processes. [Preview Abstract] |
Tuesday, March 6, 2007 1:27PM - 1:39PM |
J38.00012: Non-Resonant Inelastic X-Ray Scattering and Energy-Resolved Wannier Function Investigation of \textit{d-d} Excitations in NiO and CoO B.C. Larson, J.Z. Tischler, P. Zschack, Wei Ku, C.C. Lee We have investigated dipole-forbidden $d-d$ excitations in the non-resonant inelastic x-ray scattering (NIXS) spectra of NiO and CoO. The spectral weight of these Mott-gap excitations vanishes at small q, but dominates the large-q NIXS spectra and is highly anisotropic with well-defined nodal directions. Theoretical analyses based on energy-resolved Wannier functions within LDA+$U$ have shown the origin of the anisotropy to be selection-rules reflecting the underlying cubic point group symmetry. The measured and calculated orientation anisotropies of the NIXS spectra will be discussed and the anisotropies for NiO and CoO will be compared to demonstrate that such measurements represent sensitive probes of weak symmetry breaking in particle-hole wave functions. [Preview Abstract] |
Tuesday, March 6, 2007 1:39PM - 1:51PM |
J38.00013: Wave-optical simulation of hard X-ray nanofocusing by precisely figured elliptical mirrors Albert Macrander, Cameron Kewish, Lahsen Assoufid, Jun Qian Computer simulations of nanofocusing by elliptical mirrors are presented wherein the diffraction and propagation of coherent hard X-rays are predicted using wave-optical calculations. Surface height data acquired \textit{via} microstitching interferometry were used to calculate the complex pupil function of a mirror, taking into account the Fresnel reflectivity and treating the surface topography as an aberration to a perfect elliptical mirror. The reflected wavefield amplitude and phase downstream of the mirror were obtained by numerically evaluating the Fresnel-Kirchhoff diffraction integral. Simulated intensity profiles, and contours (isophotes) around the focal plane are presented for coherent illumination by a 15~keV point source, which indicate nearly diffraction-limited focusing at the 40~nm level. The effect of high spatial frequency microroughness on nanofocusing was investigated by low-pass filtering the Fourier spectrum of the residual height profile. Simulations using the filtered metrology data revealed that roughness length scales shorter than 0.1~mm have a minor effect on the focal spot size and intensity. [Preview Abstract] |
Tuesday, March 6, 2007 1:51PM - 2:03PM |
J38.00014: Producing small size parallel x-ray beam by multi-plate crystal cavity with compound refractive lenses S.-Y. Chen, Y.-Y. Chang, M.-T. Tang, Yu. Stetsko, M. Yabashi, H.-H. Wu, Y.-R. Lee, B.-Y. Shew, S.-L. Chang To produce a coherent and extremely parallel x-ray source for advanced experiments, multi-plate crystal cavities consisting of compound refractive lenses were prepared on silicon wafers by lithographic techniques. The crystallographic orientation of the crystal is the same as that reported for x-ray resonators (Phys. Rev. Lett. 94, 174801, 2005). X-ray (12 4 0) back diffraction from these monolithic silicon crystal devices clearly showed interference fringes due to cavity resonance through the compound refractive lenses (CRL). However, the expected focusing effect from the CRL was not observed, but rather beam compression was detected. That is, the incident x--ray beam size of about 90$\mu $m across the CRL was reduced to 20$\mu $m. The beam size remained the same at different positions along the transmitted beam direction. Namely, a small sized parallel x-ray beam was produced. The origin of this beam compression mechanism is believed to be due to the competition between the multiple back reflection of the crystal cavity and the focusing of the CRL, in addition to crystal absorption. [Preview Abstract] |
Tuesday, March 6, 2007 2:03PM - 2:15PM |
J38.00015: Alignment system for doubly curved crystal x-ray optics Ayhan Bingolbali, Carolyn MacDonald Doubly curved crystal (DCC) optics efficiently diffract a large area beam from a laboratory point source to produce a monochromatic focus. DCC optics have application in crystallography, x-ray fluorescence, and imaging. In order to obtain maximum intensity from doubly curved crystal (DCC) optics, accurate alignment of the optic is crucial. A simulation model and alignment system have been developed which allow rapid optimization of the six axis position and angle of the optic in an x-ray system. [Preview Abstract] |
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