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Abstract: High-performance Kirkpatrick-Baez (KB) neutron supermirror optics can nondispersively image neutrons to small spots. Ray tracing finds that under many conditions, KB mirrors work near the theoretical limit set by source brilliance and can deliver orders of magnitude greater intensities than is possible with conventional (nonfocusing) neutron optics. In general, KB neutron supermirrors are preferred when the required beam size at the sample is small and when the distance between the optics and the sample is not small. Waveguides with beam definings slits are preferred for very short wavelengths, for big beams and when the slits can be placed very close to the sample. For example, for λ ∼0.1nm, if the distance from the last optical element to the sample is ∼100mm, almost two orders of magnitude greater intensity can be focused onto a 100μm spot with M =3KB supermirrors than with a beam guide and symmetric slits. This is independent of whether the beam guide collimates or condenses the beam so long as without slits the beam is larger than the acceptable beam size at the sample. We describe the ray tracing and phase space arguments that support the use of KB supermirrors for producing intense small beams and describe the performance of a prototype KB device which achieved a 89μm×90μm focus. We briefly describe even more advanced methods that can increase the beam divergence on the sample while maintaining a small beam. [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: Three-dimensional (3D) measurements of strain tensor distributions with subgrain resolution are now possible due to an emerging class of instrumentation: the 3D X-ray crystal microscopes. These instruments combine ultra-intense synchrotron X-ray sources and advanced X-ray optics to probe polycrystalline materials with submicron spatial resolution. By employing polychromatic X-ray beams and a virtual pinhole camera method, called differential aperture microscopy, 3D distributions of the local crystalline phase, orientation (local texture) and elastic and plastic strain tensor distributions can be measured with resolution below the grain size of most materials. The elastic strain tensor elements can typically be determined with uncertainties less than 100ppm in brittle materials. Orientations can be quantified to ∼0.01° and the local unpaired dislocation density can be measured in ductile materials. Efforts are underway to improve the spatial resolution and increase the depth probed. Because the 3D X-ray crystal microscope is a penetrating nondestructive tool, it is ideal for studies of mesoscale structural evolution in materials. The unprecedented information that can be obtained with this new class of instrumentation is certain to advance our understanding of the materials physics underpinning the behavior of polycrystalline materials. [Copyright &y& Elsevier]

Abstract: This research presents a combined experimental-modeling study of lattice rotations and deviatoric strain gradients induced by focused-ion beam (FIB) milling in nitride heterostructures. 3D X-ray polychromatic microdiffraction (PXM) is used to map the local lattice orientation distribution in FIB-structured areas. Results are discussed in connection with microphotoluminescence (μ-PL), fluorescent analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data. It is demonstrated that FIB-milling causes both direct and indirect damage to the InGaN/GaN layers. In films subjected to direct ion beam impact, a narrow amorphidized top layer is formed. Near the milling area, FIB-induced stress relaxation and formation of complicated 3D strain fields are observed. The resulting lattice orientation changes are found to correlate with a decrease and/or loss of PL intensity, and agree well with finite element simulations of the three-dimensional strain fields near the relaxed trenches. Experimentally, it is found that the lattice surface normal has an in-plane rotation, which only appears in simulations when the GaN-substrate lattice mismatch annihilates the InGaN-substrate mismatch. This behavior further supports the notion that the film/substrate interface is incoherent. [Copyright &y& Elsevier]