Imaging the displacement field within epitaxial nanostructures by coherent diffraction: a feasibility study

International audienceWe investigate the feasibility of applying coherent diffraction imaging to highly strained epitaxial nanocrystals using finite-element simulations of SiGe islands as input in standard phase retrieval algorithms. We discuss the specific problems arising from both epitaxial and highly strained systems and we propose different methods to overcome these difficulties. Finally, we describe a coherent microdiffraction experimental setup using extremely focused x-ray beams to perform experiments on individual nanostructures

Oxygen Absorption in Free-Standing Porous Silicon: A Structural, Optical and Kinetic Analysis

Porous silicon (PSi) is a nanostructured material possessing a huge surface area per unit volume. In consequence, the adsorption and diffusion of oxygen in PSi are particularly important phenomena and frequently cause significant changes in its properties. In this paper, we study the thermal oxidation of p+-type free-standing PSi fabricated by anodic electrochemical etching. These free-standing samples were characterized by nitrogen adsorption, thermogravimetry, atomic force microscopy and powder X-ray diffraction. The results show a structural phase transition from crystalline silicon to a combination of cristobalite and quartz, passing through amorphous silicon and amorphous silicon-oxide structures, when the thermal oxidation temperature increases from 400 to 900 °C. Moreover, we observe some evidence of a sinterization at 400 °C and an optimal oxygen-absorption temperature about 700 °C. Finally, the UV/Visible spectrophotometry reveals a red and a blue shift of the optical transmittance spectra for samples with oxidation temperatures lower and higher than 700 °C, respectively

La stratégie régionale de lutte contre la désertification : le défi des États sahéliens

1985 : fin de la sécheresse au Sahel ? L’année 1985 a été marquée par une nette rémission de la sécheresse sur la quasi totalité du Sahel. Les récoltes et la régénération des pâturages ont été satisfaisantes, notamment dans les sous-zones méridionale et centrale du domaine sahélien. Mais, car il y a un mais, rien dans l’état actuel de nos connaissances, ne permet d’affirmer que l’amélioration observée cette année-là sera durable. Ceci peut paraître paradoxal au moment où la communauté scienti..

Place hospitality : a way to inderstand and improve the place marketing approach

International audienc

Réflexion et Hypothèses sur le Fonctionnement Actuel, Passé et Future de la Rivière Kiriya (Xinjiang, Chine)

International audienceLa géomorphologie et l’archéologie révèlent que les cours d’eau nés dans les Kunlun ont, dans le passé, traversé ou pénétré profondément dans le désert sableux du Taklamakan. Le fonctionnement hydrologique de la Kiriya est-il, a-t-il été déterminé par le climat et/ou par le développement de l’irrigation? Peut-on à partir de la connaissance de l’actuel et du passé imaginer le futur ? Telles sont les questions auxquelles nous nous proposons de répondre

Formation of porous silicon: an in situ investigation with high-resolution X-ray diffraction

PACS. 61.10.Eq X-ray scattering (including small-angle scattering), 68.55.-a Thin film structure and morphology, 81.07.-b Nanoscale materials and structures: fabrication and characterization, 68.55.Ac Nucleation and growth: microscopic aspects,

Rinsing and drying studies of porous silicon by high resolution X-ray diffraction

International audienceThe remarkable single-crystal property of p+-type porous silicon (PS) is used to investigate, with high resolution X-ray diffraction, the effects of silicon crystal transfer from wet to dry state: these effects are emphasized by the porous silicon’s large specific area. The transfer of silicon from a hydrofluoric acid solution to air via a rinsing stage in water is of fundamental and technological interests as it occurs in most of chemical treatments of silicon. First, during drying, a contraction of the PS layer is observed, related to the change of surface chemistry, in addition with some reversible deformation. Second, the rinsing stage in water leads to different behavior depending on the rinsing duration: short rinsing stage reduces the strong elongation observed on unrinsed PS while long rinsing stage leads to non-homogeneous strains in the PS layer