Modeling of x-ray fluorescence full field imaging using planar square pore micro-channel plate optics.

X-ray fluorescence imaging using perfect planar square pore micro-channel plate x-ray optics (MPO) is investigated through the modeling of the MPO point spread function (PSF). A semi-continuous model based on the use of a simplified two parameters reflectivity curve is developed including, in particular, three kinds of contributions. A validation of this model is carried out by calculating variations of several PSF characteristics with the MPO and fluorescence imaging parameters and comparing the results with ray-tracing simulations.

Tailoring Strain and Morphology of Core-Shell SiGe Nanowires by Low-Temperature Ge Condensation.

Selective oxidation of the silicon element of silicon germanium (SiGe) alloys during thermal oxidation is a very important and technologically relevant mechanism used to fabricate a variety of microelectronic devices. We develop here a simple integrative approach involving vapor-liquid-solid (VLS) growth followed by selective oxidation steps to the construction of core-shell nanowires and higher-level ordered systems with scalable configurations. We examine the selective oxidation/condensation process under nonequilibrium conditions that gives rise to spontaneous formation of core-shell structures by germanium condensation.

Inversion Domain Boundaries in GaN Wires Revealed by Coherent Bragg Imaging.

Interfaces between polarity domains in nitride semiconductors, the so-called Inversion Domain Boundaries (IDB), have been widely described, both theoretically and experimentally, as perfect interfaces (without dislocations and vacancies). Although ideal planar IDBs are well documented, the understanding of their configurations and interactions inside crystals relies on perfect-interface assumptions. Here, we report on the microscopic configuration of IDBs inside n-doped gallium nitride wires revealed by coherent X-ray Bragg imaging.

Stability of a Screw Dislocation in a ⟨011⟩ Copper Nanowire.

The stability of a screw dislocation in a free ⟨011⟩ copper nanowire is investigated using atomistic calculations. This study reveals a strong anisotropy of the Eshelby potential well (EPW) that traps the dislocation. Moreover the depth of the EPW is found to vanish when the radius of the nanowire decreases.

The first X-ray diffraction measurements on Mars.

The Mars Science Laboratory landed in Gale crater on Mars in August 2012, and the Curiosity rover then began field studies on its drive toward Mount Sharp, a central peak made of ancient sediments. CheMin is one of ten instruments on or inside the rover, all designed to provide detailed information on the rocks, soils and atmosphere in this region. CheMin is a miniaturized X-ray diffraction/X-ray fluorescence (XRD/XRF) instrument that uses transmission geometry with an energy-discriminating CCD detector.