Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session J27: Focus Session: X-ray and Neutron Instruments and Sciences I |
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Sponsoring Units: GIMS Chair: Albert Macrander, Argonne National Laboratory Room: 329 |
Tuesday, March 17, 2009 11:15AM - 11:51AM |
J27.00001: Synchrotron X-ray Ultrafast Phase-Contrast Imaging Study of Fluids Invited Speaker: Visible light imaging has been the traditionally dominant technique for study of fluid mechanical systems. However, it suffers from strong refraction, reflection and scattering effects under various occasions. X-ray phase-contrast imaging technique with its inherent penetrability and edge-enhancement capability can circumvent these difficulties naturally. Here, I report that these advantages when combined with the high flux x-ray photons offered at 3$^{rd}$ generation synchrotron can offer a great tool for studying fluid mechanical systems with microsecond temporal and micron spatial resolutions. Several examples on dynamic multiphase flows and fluid singularities will be demonstrated. Future applications for other soft-condensed matter systems will also be discussed. [Preview Abstract] |
Tuesday, March 17, 2009 11:51AM - 12:03PM |
J27.00002: Implicit spatial averaging in inversion of inelastic x-ray scattering data P. Abbamonte Inelastic x-ray scattering (IXS) is usually said to measure the imaginary part of the dynamical density response of a material. However this is not rigorously true. The density response $\chi$, which describes the response of the system to a point charge source, is a function of {\it two} spatial coordinates and the time, i.e. $\chi = \chi(x_1,x_2,t)$. Its Fourier transform $\chi(k_1,k_2,\omega)$ is therefore a function of two, rather than just one, momenta. IXS does not probe this full response, but only its longitudinal or ``diagonal" part $Im[\chi(k,k,\omega)]$. In this talk I will show that recently developed IXS inversion algorithms [2], which have shown promise for imaging attosecond dynamics in real space, yield a specific spatial average of the response, i.e. $\chi(x_1,t) = \int dx' \chi(x_1,x_1+x',t)$. This can be thought of as an average over all possible source locations, a real space projection, or a specific type of Fourier space filtering. I will show, within a simple model, that the salient real space dynamics nonetheless survive, and that IXS inversion is still a useful and well-posed technique for imaging attosecond dynamics. [Preview Abstract] |
Tuesday, March 17, 2009 12:03PM - 12:15PM |
J27.00003: Quasi-zero dimensional CuB$_{2}$O$_{4}$ as an archetype for resonant inelastic X-ray scattering Jason Hancock, Guillaume Chabot-Couture, Yuan Li, Guerman Petrakovskii, Kenji Ishii, Ignace Jarrige, Jun-ichiro Mizuki, Martin Greven, Tom Devereaux We explore the general phenomenology of resonant inelastic scattering (RIXS) using CuB$_{2}$O$_{4}$, a network of CuO$_{4}$ plaquettes electronically isolated by B$^{+3}$ ions. Spectra show a small number of well-separated features, and we exploit the simple electronic structure to explore RIXS phenomenology by developing a calculation allowing for intermediate-state effects ignored in standard approaches. These effects are found to be non-negligible and good correspondence between our model and experiment leads to a simple picture of such phenomenology as the genesis of d$\to $d excitations at the K edge and intermediate-state interference effects. [Preview Abstract] |
Tuesday, March 17, 2009 12:15PM - 12:27PM |
J27.00004: Inelastic Neutron Scattering Study of $Ce_3Sn$ and $Ce_3In$ C.H. Wang, J.M. Lawrence, A.D. Christianson, E.A. Goremychkin, E.D. Bauer, N.R. de Souza , A.I. Kolesnikov In $Ce_3Sn$ and $Ce_3In$, the linear coefficients of specific heat $\gamma$ are 260 $mJ/mol Ce-K^2$ and 700 $mJ/mol Ce-K^2$, respectively. The Wilson ratio is 7.0 for $Ce_3Sn$ and 11.5 for $Ce_3In$. Such large values suggest the presence of ferromagnetic correlations in the ground state. Hence, this system is a potential candidate for studying the magnetic instability at a quantum critical point (QCP). As an initial measurement, we have measured the magnetic inelastic neutron scattering line shape of polycrystalline samples to determine the crystal field (CF) excitations. The low temperature spectrum of both $Ce_3Sn$ and $Ce_3In$ consist of a quasi- elastic line and two obvious inelastic lines resulting from the two excited crystal field doublets of $Ce^{3+}$ in the tetragonal symmetry. The quasi-elastic linewidth,which is related to the Kondo scale, is 3.2meV for $Ce_3Sn$ and 1.5meV for $Ce_3In$, consistent with the linear coefficients of specific heat. For $Ce_3Sn$ the two CF excitations are at 20meV and 35meV while for $Ce_3In$, the splitting is much larger giving the two excitations at 15meV and 47meV. [Preview Abstract] |
Tuesday, March 17, 2009 12:27PM - 12:39PM |
J27.00005: Resonant Multi-Wave X-Ray Diffraction Study on Iron Oxides System Shih-Chang Weng, Yen-Ru Lee, Jheng-Gang Chen, Chia-Hung Chu, Shih-Lin Chang The resonant X-ray scattering occurs when the incident photon energy is close to an absorption edge of a constituent atom. Under such circumstances, the corresponding atomic scattering factor will be modified due to anomalous dispersion, which is directly related to unoccupied states, magnetic moment, charge distribution, and the types of near-neighbor atoms. Therefore, the resonant X-ray scattering is widely used to investigate crystal structure, electronic structure, magnetic property and charge distribution, etc. On the other hand, the multi-wave diffraction can provide more information about reflection phase than the normal (two-beam) Bragg diffraction. In this paper, we will show that resonant multi-wave diffraction profiles in the vicinity of iron k-edge give the information about charge-ordering/charge distribution of iron oxide systems, such as Fe3O4. [Preview Abstract] |
Tuesday, March 17, 2009 12:39PM - 12:51PM |
J27.00006: X-ray Diffuse Scattering from Ultrafast Laser Excited Solids Mariano Trigo, Yu-Miin Sheu, Jian Chen, David Reis, Stephen Fahy, Eamonn Murray, Timothy Graber, Robert Henning Intense, ultrashort laser pulses can be used to excite and detect coherent phonons in solids. However, optical experiments can only probe a reduced fraction of the Brillouin zone and hence most of the decay channels of such coherent phonons become invisible. In contrast, time-resolved x-ray diffuse scattering (TRXDS) has the potential to be the ultimate tool to study these phonon decay processes throughout the Brillouin-zone of the crystal.~ In our work, performed at the BioCARS beamline at the Advanced Photon Source, we use synchrotron time-resolved diffuse x-ray scattering to study Si and Bi under intense laser excitation with 100 ps resolution. We show that reasonable signal levels can be achieved with incident flux of 10$^{12}$ photons comparable to the flux that will be available at future 4th generation sources such as the LCLS in a single pulse.~ These sources will also provide three orders of magnitude shorter pulses; thus, this experiment serves as a test of the feasibility of time-resolved X-ray diffuse scattering as a tool for studying nonequilibrium phonon dynamics in solids. [Preview Abstract] |
Tuesday, March 17, 2009 12:51PM - 1:03PM |
J27.00007: Antiferromagnetism in a Fe50Pt40Rh10 thin film investigated using neutron diffraction Gary Mankey, Dieter Lott, Jochen Fenske, Andreas Schreyer, Prakash Mani, Frank Klose, Wolfgang Schmidt, Karin Schmalzl, Elena Tartakovskaya The temperature-dependent magnetic structure of a 200 nm thick single-crystalline film of Fe[50]Pt[40]Rh[10] was studied by unpolarized and polarized neutron diffractions. By applying structure factor calculations, a detailed model of the magnetic unit cell was developed. In contrast to former studies on bulk samples, our experimental results show that the film remains in an antiferromagnetic state throughout the temperature range of 10--450 K. Remarkably, it can be demonstrated that the antiferromagnetic structure undergoes a smooth transition from a dominant out-of-plane order with the magnetic moments orientated in-plane to an in-plane order with the magnetic moments orientated perpendicular to the film plane. Theoretically this can be explained by the existence of two competing anisotropy contributions with different temperature dependencies. [Preview Abstract] |
Tuesday, March 17, 2009 1:03PM - 1:15PM |
J27.00008: Following Transient Phases at the Air/Water Interface Mati Meron, Jeff Gebhardt, Harold Brewer, P. James Viccaro, Binhua Lin A fast pixel array detector, the Pilatus 100K, has been used in studies of organic monolayers at the air-water interface. The area sensitivity and large dynamic range of the detector, in combination with a ``one dimensional pinhole'' geometry, make it possible to observe surface processes which were inaccessible to the previous generation of experimental techniques. Especially, time dependent phenomena acting on time scales ranging from seconds to minutes can be observed and analyzed. [Preview Abstract] |
Tuesday, March 17, 2009 1:15PM - 1:27PM |
J27.00009: Detecting Hidden Symmetries with Coherent X-Ray Diffraction Thomas Demmer, Alejandro Diaz Ortiz, Peter Wochner, Helmut Dosch An approach to analyze x-ray coherent diffraction patterns of amorphous systems is presented. We have investigated archetype hard-sphere systems where the local environment is simulated using different hundreds of geometric structures (i.e., regular and irregular polyhedra). The effect of positional and orientation randomness on the coherent diffraction pattern is studied numerically for samples containing up to $10^7$ particles. A library of such simulated diffraction data is then used to retrieve the underlying symmetries in amorphous systems. A discussion of the relevant experimental work is also presented. [Preview Abstract] |
Tuesday, March 17, 2009 1:27PM - 1:39PM |
J27.00010: Measuring phonon dispersion relations with momentum- and energy-resolved x-ray calorimetry. Ruqing Xu, Hawoong Hong, T.-C. Chiang X-ray Thermal Diffuse Scattering (TDS) is a powerful method for determining phonon dispersion relations, as has been demonstrated in a number of experiments. However, most previous studies employed a fitting procedure based on presumed atomic force constant models, and the results could be susceptible to systematic errors. In view of this issue, we have developed a new method based on momentum-resolved x-ray calorimetry: the phonon frequencies at specific wavevectors are determined directly from the temperature dependence of the TDS intensities, with no force constant models needed. A test of this method on Cu has yielded excellent results. However, a limitation exists for this method, as it requires data taken over a wide temperature range, and the minimum temperature must be significantly lower than the Debye temperature. This can be a problem for materials with phonon frequencies that change significantly with temperature. To overcome this problem, we are experimenting with another method: the scattered x-rays are energy analyzed, and the TDS intensity is determined relative to the Compton scattering intensity. With this internal intensity calibration, phonon frequencies can now be determined from TDS data taken over a narrow temperature range. Results of a test study on chromium will be presented. [Preview Abstract] |
Tuesday, March 17, 2009 1:39PM - 1:51PM |
J27.00011: Infrared emission induced by x-rays Richard Rosenberg, Mohammad Abu Haija, Simon Watkins Two of the most powerful methods for studying the properties of matter are Fourier transform infrared (FTIR) spectroscopy and synchrotron radiation (SR) based x-ray techniques. Having the ability to perform both types of research on the same samples at the same time would be a significant synergism. Furthermore, the spatial resolution of conventional FTIR microscopes is limited by diffraction, which in the mid IR is 2-20 $\mu $m, while SR based x-ray microscopes are capable of $<$30 nm diameter resolution. Thus, by utilizing nanometer sized x-ray beams to produce IR emission it should be possible to extend the spatial resolution of IR microscopy by orders of magnitude and simultaneously perform x-ray studies. To test the feasibility of this approach we have incorporated a commercial FTIR instrument into an existing ultra-high vacuum end station on an insertion device beamline at the Advanced Photon Source and measured the bandgap, exciton luminescence (0.4 eV) from InAs thin films. Results using both high intensity, near zero-order and low intensity, monochromatic x-rays will be presented. [Preview Abstract] |
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