Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session D15: Focus Session: X-ray and Neutron Instruments and Measurement Science I |
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Sponsoring Units: GIMS Chair: Susan Mini, Northern Illinois University Room: B114 |
Monday, March 15, 2010 2:30PM - 3:06PM |
D15.00001: The X-ray Pump-Probe Instrument at LCLS Invited Speaker: The Linac Coherent Light Source (LCLS) will provide transversely-coherent hard X-rays with unprecedented flux and time resolution. These attributes of the LCLS have the potential to revolutionize the experimental investigation of structural dynamics with X-ray techniques by directly following the time evolution of the electron density during the course of a photo-induced biological, chemical, or physical transformation. The X-ray Pump-Probe instrument (XPP) is designed specifically for this purpose. XPP will be the first hard X-ray experimental station to operate at the LCLS in the fall of 2010. The design and status of XPP will be presented. Femtosecond-level synchronization techniques between the optical laser and the LCLS X-ray pulse, which will allow sub-picosecond time resolution, will be discussed. [Preview Abstract] |
Monday, March 15, 2010 3:06PM - 3:18PM |
D15.00002: The X-ray Correlation Spectroscopy Instrument at the LCLS Aymeric Robert The X-ray Correlation Spectroscopy Instrument (XCS) is one of the four hard x-ray experimental station to be operated at the Linac Coherent Light Source, the world's first hard x-ray free electron laser. The XCS instrument is designed to take full advantage of the unique properties of the LCLS to probe dynamical phenomena in condensed matter systems down to nanometric lengthscales by means of X-ray Photon Correlation Spectroscopy. The XCS instrument will use the unprecedented coherence and flux properties of the LCLS. It will enable to probe both slow (i.e. with a characteristic time scales larger than 10ms) and ultrafast dynamics (i.e. ranging between hundreds of femtoseconds up to several nanoseconds) in various scattering geometries (SAXS, WAXS, Grazing Incidence). The ultrafast dynamics will use a novel Split and Delay technique. The design and status of XCS will be presented and the unique science enabling capabilities of XCS will be discussed. [Preview Abstract] |
Monday, March 15, 2010 3:18PM - 3:30PM |
D15.00003: Kinoform Optics Applied to X-ray Photon Correlation Spectroscopy A.R. Sandy, S. Narayanan, M. Sprung, J.-D. Su, K. Evans-Lutterodt, A. Isakovic, A. Stein Moderate de-magnification, higher order silicon kinoform focusing lenses have been fabricated via e-beam lithography and deep etching to facilitate small-angle hard-x-ray photon correlation spectroscopy (XPCS) experiments. Typical lenses have focal lengths of one meter, focus in the vertical direction to within 80{\%} of the diffraction limit and have vertical acceptance apertures of 400 microns. The acceptance in the orthogonal (etch) direction is 50 microns. The measured efficiency of the lenses is 35{\%} and the flux gain at the focal line is 50. We discuss the effect of focusing on the resulting x-ray speckles. We conclude that one-dimensional vertical x-ray focusing via present-generation silicon kinoform lenses increases the usable coherent flux from third-generation storage-ring light sources for small-angle XPCS experiments by a factor of 3. We also discuss the prospects for further improvements in efficiency via diamond or lower order silicon kinoform lenses. [Preview Abstract] |
Monday, March 15, 2010 3:30PM - 3:42PM |
D15.00004: Ultrasmall-angle X-ray scattering photon correlation spectroscopy over extended length and time scales Andrew Allen, Fan Zhang, Lyle Levine, Jan Ilavsky, Gabrielle Long X-ray Photon Correlation Spectroscopy (XPCS) is an emerging technique offering unprecedented sensitivity to dynamics of structural changes in materials. Existing XPCS facilities are limited to microstructure length scales less than 50 nm, eliminating large classes of important materials. Recently, the scale range has been extended dramatically by combining XPCS speckle measurements with ultrasmall-angle scattering (USAXS) studies at the Advanced Photon Source. While USAXS characterizes microstructures from nanometer to micrometer length scales, a small entrance slit allows the undulator X-ray beam coherence to be exploited to give synergistic XPCS measurements of microstructure dynamics. At the larger length scales, the correspondingly slower dynamics are well matched to USAXS scan times. Progress will be discussed for composites in biomedical applications. [Preview Abstract] |
Monday, March 15, 2010 3:42PM - 3:54PM |
D15.00005: Time-resolved X-ray diffuse scattering from non-equilibrium phonons in solids Mariano Trigo, Yu-Miin Sheu, Jian Chen, David Reis, Timothy Graber, Robert Henning Intense, ultra-short laser pulses are currently used to study a wide range of coherent as well as incoherent excitations in solids. However, visible and infrared radiation can only probe a reduced fraction of the Brillouin zone near the zone center and hence do not provide direct information on shorter range interactions. With the availability of ultra-intense and ultra-short x-ray pulses as 4$^{th}$ generation x-ray free-electron lasers come online, time-resolved x-ray diffuse scattering has the potential to be the ultimate tool to study excitations and their decay channels throughout the Brillouin zone. Here we will present measurements of the generation and decay of incoherent phonons throughout the Brillouin zone in bulk semiconductors as well as single-shot measurements of ultrafast melting and recrystallization in bimuth. Finally, I will discuss some of the unique challenges these experiments present and how this is shaping potential future scientific directions at 4$^{th}$ generation sources. [Preview Abstract] |
Monday, March 15, 2010 3:54PM - 4:06PM |
D15.00006: Improving Scintillation Performance of Ce-doped Garnet Crystals Denys Solodovnikov, Marc Weber, David Bahr, Grant Norton, Drew Haven, Jalal Nawash, Romit Dhar, Kelvin Lynn The Center for Materials Research has developed a new mixed garnet scintillator host material -- Yttrium Gadolinium Gallium Aluminum Garnet (YGGAG). In addition to high thermal and chemical stability and radiation hardness found in garnet crystals it offers high neutron sensitivity due to presence of Gd atoms, has about 100\r{ }C lower melting temperature than standard yttrium aluminum garnet host and similar crystallization behavior suitable for growth of large volume crystals. Crystals of YGGAG doped with Ce and Tb of 10x10x10 mm in size already demonstrated energy resolution of 10{\%} at 662keV. Our group demonstrated strong correlation between scintillation performance and deferent types of defects in Ce:Er:YAG scintillators. Work on further improving YGGAG performance by eliminating defects is currently in progress. [Preview Abstract] |
Monday, March 15, 2010 4:06PM - 4:18PM |
D15.00007: Virtual Young's Double Slit Experiment for Hard X-ray Photons Abdel Isakovic, K. Evans-Lutterodt, D.P. Siddons, A. Stein, J.B. Warren, A. Sandy, S. Narayanan, M. Metzler Coherent hard X-ray beams underlie many of the recent advances in X-ray imaging and characterization, and it is crucial to quantify the coherence properties of X-ray beams for further advances. The classic Young's double slit experiment is an accepted method from which one can deduce the transverse coherence length, but unfortunately the double slit experiment is difficult to implement at these wavelengths. Micro-fabricated prisms are used to implement a virtual Young's double slit experiment, and interference fringes are quantified by X-ray fluorescence from a 30 nm Cr film in addition to being recorded with YAG crystal and CCD. The maximum number of fringes in the classical overlap region is comparable to $\delta $/4$\pi \beta $, the ratio of real to imaginary parts of the X-ray refractive index of the prism material. We have measured the horizontal and vertical transverse coherence lengths at beamline APS 8-ID. We suggest this to be a flexible, easily applied method that can be implemented at X-ray laboratories for both, coherence measurements and interferometric imaging. http://arxiv.org/abs/0910.5524 [Preview Abstract] |
Monday, March 15, 2010 4:18PM - 4:30PM |
D15.00008: A high-field (30 Tesla) pulsed magnet instrument for single-crystal scattering studies Zahirul Islam, Hiroyuki Nojiri, Yasuo Narumi, Jonathan Lang Pulsed magnets have emerged as a viable approach at synchrotron x-ray facilities for studying materials in high magnetic fields. We are developing a new high-field (30 Tesla) pulsed magnet system for single-crystal x-ray diffraction studies. It consists of a single 18mm-bore solenoid, designed and built at Tohoku University using high-tensile-strength and high conductivity CuAg wires. A dual-cryostat scheme has been developed at Advanced Photon Source in order to cool the coil using liquid nitrogen and the sample using a closed-cycle cryostat independently. Liquid nitrogen cooling allows repetition rate of a few minutes for peak fields near 30 Tesla. This scheme is unique in that it allows the applied magnetic field to be parallel to the scattering plane. Time-resolved scattering data are typically collected using a fast one-dimensional strip detector. Opportunities and challenges for experiments and instrumentation will be discussed. [Preview Abstract] |
Monday, March 15, 2010 4:30PM - 4:42PM |
D15.00009: Bulk-Sensitive X-Ray Absorption Spectroscopy Free of Self-Absorption Andrew Achkar, Tom Regier, Hiroki Wadati, George Sawatzky, Young-June Kim, David Hawthorn We demonstrate a new method to measure x-ray absorption spectroscopy (XAS) in addition to traditional transmission, total-electron yield (TEY) and total-fluorescence yield (TFY) that is bulk sensitive, like TFY, and is not affected by self-absorption corrections that plague TFY measurements. This measure of XAS is accomplished by measuring the x-ray emission (partial fluorescence yield, PFY) from a different element or excitation than the one probed by the incident photon energy. It is found that the reciprocal of such a PFY spectrum is proportional to the linear attenuation coefficient, offset by an energy independent constant. We demonstrate this technique on Cu L, La M and Nd M edges of the high-$T_C$ cuprate ${La_{2-x-y}Nd_ySr_xCuO_4}$ by comparing its TEY, TFY and PFY spectra. [Preview Abstract] |
Monday, March 15, 2010 4:42PM - 4:54PM |
D15.00010: Kapitza conductance of Bi/Sapphire interface measured by time-resolved x-ray diffraction Yu-Miin Sheu, Yi-Jiunn Chien, Ctirad Uher, Mariano Trigo, Jian Chen, Shambhu Ghimire, Donald Walko, Emily Peterson, Dohn Arms, Eric Landahl, David Reis We measure the thermal boundary (Kapitza) conductance at the interface between single crystal thin films of bismuth and sapphire using time-resolved x-ray diffraction. Films of varying thickness (65-284 nm) are grown by molecular beam epitaxy with their c-axis perpendicular to the surface. In the measurements, an ultrafast laser pulse is used to rapidly heat the near-surface region of the film, and x-ray diffraction is used to measure the average lattice constant of the film along the c axis. By comparing the depth dependence of the temporal profile with model calculations of the thermal transport, we extract an average Kaptiza conductance of $\sim$2000$\pm$1000 W/cm$^2$/K. These results do not significantly vary with film thickness or excitation density below the damage threshold. [Preview Abstract] |
Monday, March 15, 2010 4:54PM - 5:06PM |
D15.00011: True real space imaging with multi-beam inelastic X-ray scattering Yu Gan, Peter Abbamonte Inelastic X-ray scattering (IXS) has recently been used to image electron dynamics at the attosecond scale, but it has been shown that these images are spatially averaged. The problem is that the existing technique can only access the ``diagonal'' ($k_1=-k_2$) elements of the electron density response $\chi(k_1,k_2,\omega)$. It was shown long ago, however, that inelastic X-ray scattering at the Bragg position is sensitive to the entire response $\chi(k_1,k_2,\omega)$. With this method, a standing wave field is established in the sample by exciting a Bragg condition, allowing access to all the off-diagonal ($k_1\ne- k_2$) elements of $\chi$. In this talk I will present a simple model demonstrating that, in principle, this approach can be used to map the entire density response. In particular, I show that a one-dimensional system is experimentally impossible to probe, a two-dimensional system is experimentally accessible but typically difficult to measure in practice, and a three-dimensional system is experimentally both plausible and practicable. [Preview Abstract] |
Monday, March 15, 2010 5:06PM - 5:18PM |
D15.00012: Polarization-dependent MAD holography: Nanoscale Magnetic Imaging of Nonperiodic Objects Tianhan Wang, Diling Zhu, Benny Wu, Olav Hellwig, Joachim Stohr , Andreas Scherz We present a novel approach to the nanoscale imaging of nonperiodic magnetic structures by introducing x-ray polarization dependence to the multiple wavelength anomalous diffraction (MAD) phasing technique. Essential phase information can be extracted from the differences between coherent scattering patterns recorded at different x-ray wavelengths (on- or off-resonance) and polarizations. Combined with an iterative phase retrieval algorithm, the magnetization distribution can be reconstructed. Using left and right circularly polarized x-rays near the Co L3 edge, we successfully imaged the perpendicular magnetic worm domains of a Co/Pd multilayer sample within a 3 micron circular aperture. The absence of reference apertures and a resolution that is, in principle, only limited by the wavelength render this method attractive for polarization-dependent and element-specific studies in magnetism, correlated materials and polymer research. This research is supported by the U.S. Department of Energy, Office of Basic Energy Science. [Preview Abstract] |
Monday, March 15, 2010 5:18PM - 5:30PM |
D15.00013: Spatial structure of a focused x-ray beam diffracted from perfect crystals - what a ``standard'' microbeam diffraction experiment cannot see Alexander Kazimirov, Victor Kohn, Anatoly Snigirev, Irina Snigireva An experimental setup with a high-resolution detector at the focus and a crystal between the focusing optics and the focus allows one to study the spatial structure of a focused beam diffracted from crystals [1]. Several interesting phenomenon are observed. First, the initially small focused beam is broadened inside the crystal due to extinction effect. Second, for a sufficiently thin crystal, in addition to the peak reflected from the front surface, a second peak is observed which corresponds to reflection from the back surface of the crystal. Third, the spatial structure changes remarkably as the crystal moves away from the Bragg condition and diffraction become kinematical [2]. The experiments were performed with refractive lenses and perfect thick and thin silicon crystals. The results help to understand the origin of the diffracted intensity in a ``standard'' microbeam diffraction experiment in which the detector is away from the focus and these features cannot be observed.\\[4pt] [1] Kohn{\&}Kazimirov, Phys. Rev. B, 75 (2007) 224119;\\[0pt] [2] Kazimirov, \textit{et al}, J. Synchrotron Radiation, 16 (2009) 666. [Preview Abstract] |
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