Magnetic and structural studies of sputtered metallic multilayers

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Nucleation and growth of platelets in hydrogen-ion-implanted silicon

H ion implantation into crystalline Si is known to result in the precipitation of planar defects in the form of platelets. Hydrogen-platelet formation is critical to the process that allows controlled cleavage of Si along the plane of the platelets and subsequent transfer and integration of thinly sliced Si with other substrates. Here we show that H-platelet formation is controlled by the depth of the radiation-induced damage and then develop a model that considers the influence of stress to correctly predict platelet orientation and the depth at which platelet nucleation density is a maximum.This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences

On the twinning impact on the grain structure formation of multi-crystalline silicon for photovoltaic applications during directional solidification

Grain orientation and competition during growth has been analyzed in directionally solidified multi-crystalline silicon samples. In situ and real-time characterization of the evolution of the grain structure during growth has been performed using synchrotron X-ray imaging techniques (radiography and topography). In addition, Electron Backscattered Diffraction has been used to reveal the crystalline orientations of the grains and the twin relationships. New grains formed during growth have two main origins: random nucleation and twinning. It is demonstrated that the solidified samples are dominated by P3 twin boundaries showing that twinning on {111} facets is the dominant phenomenon. Moreover, thanks to the in situ characterization of the growth, it is shown that twins nucleate on {111} facets located at the sides of the sample and at grain boundary grooves. The occurrence of multiple P3 twins during growth prevents the initial grains from developing all along the sample, and twin boundaries with higher order coincidence site lattices can form at the encounter of two grains in twin position. The grain competition phenomenon following nucleation and twinning acts as a grain selection mechanism leading to the final grain structure

On the Deformation of Dendrites During Directional Solidification of a Nickel-Based Superalloy

International audienc

Investigation of grain boundary grooves at the solid–liquid interface during directional solidification of multi-crystalline silicon: in situ characterization by X-ray imaging

International audienc

Czochralski and mono-like p-type and n-type silicon solar cells: Relationship between strain and stress induced by the back contact, and photovoltaic performance

International audienc

Multiscale 3D virtual dissections of 100-million-year-old flowers using X-Ray Synchrotron micro- and nanotomography

International audienceA multiscale approach combining phase-contrast X-ray micro- and nanotomography is applied for imaging a Cretaceous fossil inflorescence in the resolution range from 0.75 mm to 50 nm. The wide range of scale views provides three-dimensional reconstructions from the external gross morphology of the inflorescence fragment to the finest exine sculptures of in situ pollen. This approach enables most of the characteristics usually observed under light microscopy, or with low magnification under scanning and transmission electron microscopy, to be obtained nondestructively. In contrast to previous tomography studies of fossil and extant flowers that used resolutions down to the micron range, we used voxels with a 50 nm side in local tomography scans. This high level of resolution enables systematic affinities of fossil flowers to be established without breaking or slicing specimens

In situ experimental observation of the time evolution of a dendritic mushy zone in a fixed temperature gradient

10th International Meeting on Thermodiffusion (IMT), Univ Libre Bruxelles (ULB), Brussels, BELGIUM, JUN 04-08, 2012International audienceThis paper describes a series of experiments performed on BM05 at the European Synchrotron Radiation Facility (ESRF), dedicated to the analysis of a mushy zone evolution in a fixed temperature gradient. A mushy zone is the partially solid/partially liquid zone that is formed when solidification proceeds with the development of dendrites, and it has been recently shown that synchrotron X-ray radiography is a powerful technique, perfectly adapted for such a study. In situ and real-time characterisation clearly evidences the microstructural changes of the mushy zone during the holding stage, and measurements of the mushy zone boundary positions using image processing enable us to analyse the successive regimes. Each regime is directly related to solute diffusion mechanisms, namely temperature gradient zone melting, solute diffusion in the inter-dendritic liquid channels due to the solid-fraction gradient and solute diffusion in the melt