Evolution récente d'un hydrosystème continental : le Delta intérieur du Niger au Mali

Journées du Programme Environnement, CNRS/ORSTOM, Lyon, 13-15 janvier 1993. Actes des Journées du Programme Environnemen

Two-Dimensional Dynamics of Metal Nanoparticles on the Surface of Thin Polymer Films Studied with Coherent X-Rays

International audienc

Strain distribution in nitride quantum dot multilayers

International audienceNitride quantum dots (QD’s) grown in the wurtzite phase present a strong vertical ordering along the (0001) direction when they are stacked in multilayers. This alignment results from a minimum of the elastic energy density at the surface of the AlN capping layer induced by the buried GaN dot underneath. The aim of this work is to investigate the strain distribution in a quantum dot multilayer using high-resolution transmission electron microscopy and anomalous grazing incidence x-ray diffraction. This x-ray method is based on the strong sensitivity of the elastic scattering cross section to the Ga compounds for energies in the vicinity of the Ga absorption edge. It is observed that uncapped GaN dots are almost completely relaxed, while embedded quantum dots are compressively strained. In addition, a modulation of the in-plane lattice parameter in the AlN spacer layer is clearly identified, induced by the QD’s on the surrounding matrix which causes the vertical alignment

Efficient modeling of Bragg coherent x-ray nanobeam diffraction

International audienceX-ray Bragg diffraction experiments that utilize tightly focused coherent beams produce complicated Bragg diffraction patterns that depend on scattering geometry, characteristics of the sample, and properties of the x-ray focusing optic. Here, we use a Fourier-transform-based method of modeling the 2D intensity distribution of a Bragg peak and apply it to the case of thin films illuminated with a Fresnel zone plate in three different Bragg scattering geometries. The calculations agree well with experimental coherent diffraction patterns, demonstrating that nanodiffraction patterns can be modeled at nonsymmetric Bragg conditions with this approach—a capability critical for advancing nanofocused x-ray diffraction microscopy