Search

Abstract: Polychromatic microdiffraction uses small X-ray beams to characterize the local crystallographic structure of materials. When combined with a depth resolving technique called differential aperture microscopy, the phase and local orientation of femto-liter volumes (0.5×0.5×0.7μm3) can be resolved beneath the surface of a sample. In addition, the local elastic strain and dislocation tensors can also be determined and the local dislocation type can be modeled. Here we present recent technical developments, including example applications and emerging research directions. [Copyright &y& Elsevier]

Abstract: Variations in the local crystallographic orientation due to the presence of geometrically necessary dislocations and dislocation boundaries smear the distribution of intensity near Laue reflections. Here, some simple model distributions of geometrically necessary dislocations, GNDs, are used to estimate the dislocation tensor field from the intensity distribution of Laue peaks. Streaking of the Laue spots is found to be quantitatively and qualitatively distinct depending on the ratio between the absorption coefficient and the GND density gradient. In addition, different slip systems cause distinctly different Laue-pattern streaking. Experimental Laue patterns are therefore sensitive to stored dislocations and GNDs. As an example, white beam microdiffraction was applied to characterize the dislocation arrangement in a deformed polycrystalline Ni grain during in situ uniaxial tension. [Copyright &y& Elsevier]

Abstract: X-ray microdiffraction is a non-destructive technique that allows for depth-resolved, strain measurements with submicron spatial resolution. These capabilities make this technique promising for understanding the mechanical properties of MicroElectroMechancial Systems (MEMS). This investigation examined the local strain induced by irradiating a polycrystalline diamond thin film with a dose of 2×1017 H+/cm2 protons. Preliminary results indicate that a measurable strain, on the order of 10−3, was introduced into the film near the End of Range (EOR) region of the protons. [Copyright &y& Elsevier]

Abstract: The availability of intense, focused synchrotron X-ray microbeams has enabled new techniques for materials investigations with sub-micron spatial resolution. The scanning microbeam setup we have developed at the XOR-UNI beamline at the Advanced Photon Source (APS) is versatile in that it provides 1D, 2D or 3D scans (including depth resolution), and can alternate between polychromatic- and monochromatic-beam modes. Focusing in both modes uses elliptical Kirkpatrick–Baez (K–B) reflecting mirrors. Beam diameters of ~500 nm FWHM are now routine, and 90 nm focus has been demonstrated. In white-beam mode, a CCD detector records a complete Laue diffraction pattern, which is analyzed with an automated indexing program. These X-ray diffraction patterns provide real-space maps of the local lattice structure, crystal orientation, grain morphology, and strain tensor. Spatially-resolved X-ray microdiffraction studies are now providing previously unavailable measurements of local microstructures. These measurements, in turn, yield new insights in several classic fields of materials science. This paper will illustrate the application of polychromatic scanning X-ray microscopy with examples from 1D, 2D and 3D materials systems. In 1D systems, we have mapped the structure and orientation of an individual ZnO nanorod along with the associated Ge catalyst particle used to control the nanocrystal growth. In 2D systems, X-ray microdiffraction studies have revealed the mechanisms for local crystallographic tilting in epitaxial oxide films grown on textured Ni substrates for superconducting applications. In 3D systems, X-ray microscopy investigations have included in-situ studies of microstructural evolution during thermal grain growth in polycrystalline aluminum. In general, these spatially-resolved measurements provide important new insights and are valuable as input for theoretical and computer modeling studies of a wide range of material processes. [Copyright &y& Elsevier]