Double crystal x-ray diffraction simulations of diffusion in semiconductor microstructures

Diffusion in group IV, III-V and II-VI semiconductors is an interesting problem not only from a fundamental physics viewpoint but also in practical terms, since it could determine the useful lifetime of a device. Any attempt to control the amount of diffusion in a semiconductor device, whether it be a quantum well structure or not, requires an accurate determination of the diffusion coefficient. The present theoretical study shows that this could be achieved via x-ray diffraction studies in quantum well structures. It is demonstrated that the rocking curves of single quantum wells are not sensitive to diffusion. However the intensity of the first order satellite, which is characteristic of superlattice rocking curves, is strongly dependent upon diffusion and it is proposed that this technique could be used to measure the diffusion coefficient D. © 1998 American Institute of Physics

Estimation de la recharge de la nappe phréatique du Continental Terminal (Niamey, Niger) à partir des teneurs en tritium

Dans l'environnement typiquement sahélien de la région de Niamey, la réalimentation de la nappe phréatique du Continental Terminal est essentiellement due à l'infiltration de la pluie concentrée dans les mares endoréiques temporaires. Les teneurs en tritium sont un bon indicateur de l'intensité de la recharge. Un modèle simple utilise une chronique reconstituée des teneurs de la pluie à Niamey depuis 40 ans et fournit les taux de renouvellement correspondant aux valeurs mesurées dans la nappe (25 mm/an). Ces résultats sont cohérents avec ceux de l'approche hydrodynamique. (Résumé d'auteur

Advanced characterization techniques for high-angular and high-spatial resolutions in the scanning electron microscope

High-angular resolution electron diffraction-based techniques aim at measuring relative lattice rotations and elastic strains with an accuracy about 1.10-4 (<0.01°) in the scanning electron microscope (SEM). These metrics are essential for the fine characterization of deformation structures in terms of grain internal disorientations and geometrically necessary dislocation densities. To this purpose, relative deformations between electron diffraction patterns are retrieved with subpixel accuracy using digital image correlation (DIC) techniques. Here, a novel DIC approach is proposed. It relies on a linear homography [1], i.e., a geometric transformation often met in photogrammetry to model projections. The method is implemented in ATEX-software [2], developed at the University of Lorraine. Its performances are illustrated from both a semi-conductor and a metal. First, lattice rotation and elastic strain fields are investigated in the vicinity of a giant screw dislocation in GaN single crystal using the electron backscattered diffraction technique (Fig. 1). Second, the proposed method is coupled with the on-axis Transmission Kikuchi Diffraction (TKD) configuration to characterize a nanocrystalline aluminium obtained by severe plastic deformation. On-axis TKD consists in observing a thin foil in transmission in the SEM, using a scintillator is placed beneath the specimen, perpendicularly to the electron beam. Thanks to this coupling, high-spatial (3-6 nm) and high-angular (~0.01°) resolutions are simultaneously achieved in SEM. [3]

Dislocation transport and intermittency in the plasticity of crystalline solids

International audienceWhen envisioned at the relevant length scale, plasticity of crystalline solids consists in the transport of dislocations through the lattice. In this paper, transport of dislocations is evidenced by experimental data gathered from high-resolution extensometry carried out on copper single crystals in tension. Spatiotemporal kinematic fields display spatial correlation through characteristic lines intermittently covered by plastic activity. Intermittency shows temporal correlation and power-law distribution of avalanche size. Interpretation of this phenomenon is proposed within the framework of a field dislocation theory attacking the combined problem of dislocation transport and long-range internal stress field development. Intermittency and transport properties show remarkable independence from sample size, aspect ratio, loading rate, and strain-rate sensitivity of the flow stress

Sequential localization of a complex electron fluid

Complex and correlated quantum systems with promise for new functionality often involve entwined electronic degrees of freedom. In such materials, highly unusual properties emerge and could be the result of electron localization. Here, a cubic heavy fermion metal governed by spins and orbitals is chosen as a model system for this physics. Its properties are found to originate from surprisingly simple low-energy behavior, with two distinct localization transitions driven by a single degree of freedom at a time. This result is unexpected, but we are able to understand it by advancing the notion of sequential destruction of an SU(4) spin-orbital-coupled Kondo entanglement. Our results implicate electron localization as a unified framework for strongly correlated materials and suggest ways to exploit multiple degrees of freedom for quantum engineering.Comment: 21 pages, 4 figures (preprint format

Probing impulsive strain propagation with x-ray pulses

Pump-probe time-resolved x-ray diffraction of allowed and nearly forbidden reflections in InSb is used to follow the propagation of a coherent acoustic pulse generated by ultrafast laser-excitation. The surface and bulk components of the strain could be simultaneously measured due to the large x-ray penetration depth. Comparison of the experimental data with dynamical diffraction simulations suggests that the conventional model for impulsively generated strain underestimates the partitioning of energy into coherent modes.Comment: 4 pages, 2 figures, LaTeX, eps. Accepted for publication in Phys. Rev. Lett. http://prl.aps.or