2D and 3D X-Ray Structural Microscopy Using Submicron-Resolution Laue Microdiffraction
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2D and 3D X-Ray Structural Microscopy Using Submicron-Resolution Laue Microdiffraction John D. Budai1, Wenge Yang1, Bennett C. Larson1, Jonathan Z. Tischler1, Wenjun Liu2, and Gene E. Ice2 1 Condensed Matter Sciences Division, Oak Ridge National Laboratory 2 Metals & Ceramics Division, Oak Ridge National Laboratory Oak Ridge, TN 37831-6030, U.S.A. ABSTRACT We have developed a scanning, polychromatic x-ray microscopy technique with submicron spatial resolution at the Advanced Photon Source. In this technique, white undulator radiation is focused to submicron diameter using elliptical mirrors. Laue diffraction patterns scattered from the sample are collected with an area detector and then analyzed to obtain the local crystal structure, lattice orientation, and strain tensor. These new microdiffraction capabilities have enabled both 2D and 3D structural studies of materials on mesoscopic length-scales of tenths-tohundreds of microns. For thin samples such as deposited films, 2D structural maps are obtained by step-scanning the area of interest. For example, 2D x-ray microscopy has been applied in studies of the epitaxial growth of oxide films. For bulk samples, a 3D differential-aperture x-ray microscopy technique has been developed that yields the full diffraction information from each submicron volume element. The capabilities of 3D x-ray microscopy are demonstrated here with measurements of grain orientations and grain boundary motion in polycrystalline aluminum during 3D thermal grain growth. X-ray microscopy provides the needed, direct link between the experimentally measured 3D microstructural evolution and the results of theory and modeling of materials processes on mesoscopic length scales.
INTRODUCTION The availability of intense, highly-collimated x-ray beams at synchrotron facilities is enabling the ongoing development of a broad range of high-resolution x-ray structural microscopy techniques worldwide [1-3]. Various approaches are progressing rapidly, including x-ray techniques based on fluorescence, absorption, phase contrast or diffraction contrast. In general, hard x-rays (> 5 keV) are more penetrating than electron probes and hence can provide complementary nondestructive information from thicker samples or microstructures in the interior of bulk materials. In the approach described here, achromatic Kirkpatrick-Baez (KB) mirrors are used to focus white (polychromatic) radiation to submicron diameter, and x-ray Laue diffraction patterns are used to determine the local lattice structure, orientation and strain [4-8]. White-beam diffraction differs from more-conventional monochromatic scattering in several ways. First, many reflections comprising a full Laue diffraction pattern at a particular spatial position are collected simultaneously by an area detector in one image rather than during diffractometer step-scans. Second, no sample rotations are required to obtain diffraction information, eliminating “sphere of confusion” errors inherent when rotating individual grains in a polycrystalline mater
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