Time-spliced X-ray Diffraction Imaging

Diffraction imaging of non-equilibrium dynamics at atomic resolution is becoming possible with X-ray free-electron lasers. However, there are unresolved problems with applying this method to objects that are confined in only one dimension. Here I show that one-dimensional coherent diffraction imaging is possible by splicing together images recovered from different delays in a time-resolved experiment. This is used to image the time and space evolution of antiferromagnetic order in a complex oxide heterostructure from measurements of a resonant soft X-ray diffraction peak. Mid-infrared excitation of the substrate is shown to lead to a magnetic front that propagates at a velocity exceeding the speed of sound, a critical observation for the understanding of driven phase transitions in complex condensed matter

X-Ray Diffraction

A Parkland College A with Honors project, this paper reviews X-ray diffraction, identifying the process, its developers, and its uses

X-ray diffraction from shock-loaded polycrystals

X-ray diffraction was demonstrated from shock-compressed polycrystalline metal on nanosecond time scales. Laser ablation was used to induce shock waves in polycrystalline foils of Be, 25 to 125 microns thick. A second laser pulse was used to generate a plasma x-ray source by irradiation of a Ti foil. The x-ray source was collimated to produce a beam of controllable diameter, and the beam was directed at the Be sample. X-rays were diffracted from the sample, and detected using films and x-ray streak cameras. The diffraction angle was observed to change with shock pressure. The diffraction angles were consistent with the uniaxial (elastic) and isotropic (plastic) compressions expected for the loading conditions used. Polycrystalline diffraction will be used to measure the response of the crystal lattice to high shock pressures and through phase changes

X-ray Diffraction Tomographic Imaging and Reconstruction

Material discrimination based on conventional or dual energy X-ray computed tomography (CT) imaging can be ambiguous. X-ray diffraction imaging (XDI) can be used to construct diffraction profiles of objects, providing new molecular signature information that can be used to characterize the presence of specific materials. Combining X-ray CT and diffraction imaging can lead to enhanced detection and identification of explosives in luggage screening. In this work we are investigating techniques for joint reconstruction of CT absorption and X-ray diffraction profile images of objects to achieve improved image quality and enhanced material classification. The initial results have been validated via simulation of X-ray absorption and coherent scattering in 2 dimensions.U. S. Department of Homeland Security (2008-ST-061-ED0001

Twins and their boundaries during homoepitaxy on Ir(111)

The growth and annealing behavior of strongly twinned homoepitaxial films on Ir(111) has been investigated by scanning tunneling microscopy, low energy electron diffraction and surface X-ray diffraction. In situ surface X-ray diffraction during and after film growth turned out to be an efficient tool for the determination of twin fractions in multilayer films and to uncover the nature of side twin boundaries. The annealing of the twin structures is shown to take place in a two step process, reducing first the length of the boundaries between differently stacked areas and only then the twins themselves. A model for the structure of the side twin boundaries is proposed which is consistent with both the scanning tunneling microscopy and surface X-ray diffraction data.Comment: 13 pages, 11 figure

X-ray diffraction study of cadmium hydroxyapatite

Solid solutions of cadmium and calcium hydroxyapatite [Ca10−x Cdx (PO4)6 (OH)2 (0 ≤ x ≤ 10)] were synthesized by a wet process in a basic medium. The lattice dimensions of these compounds vary linearly with the atom percent cadmium. The distribution of the calcium and cadmium ions between two non- equivalent crystallographic sites, (1) and (2), were determined by the Rietveld method. The site-occupancy factors of atoms indicate a slight preference of cadmium for site (2) in the apatite structure