Diffusion centrale des rayons X en incidence rasante appliquée à l'étude in situ de la croissance de nanostructures

Ce manuscrit se concentre sur l'analyse du GISAXS d'îlots sur un substrat. Les données GISAXS doivent être analysées de façon quantitative afin d'obtenir des paramètres morphologiques précis (courbes de croissance, forme d'équilibre de l'îlot et énergie interfaciale) pour le processus d'élaboration. L'accent est mis sur le facteur de forme de l'îlot, c'est-à-dire la transformée de Fourier de la forme de l'îlot. On montre que la forme de l'îlot et la taille peuvent être obtenues à partir de la symétrie de l'îlot, la présence de facettes de l''îlot, le comportement asymptotique loin dans l'espace réciproque pour une grande polydispersité et les zéros ou les minima de l'intensité pour une faible polydispersité. Une comparaison approfondie entre l'approximation de Born et l'approximation plus précise de l'onde distordue (DWBA) met en évidence la spécificité apportée par la géométrie en incidence rasante. L'analyse quantitative est illustrée pour des images GISAXS acquises in situ pendant l'épitaxie par jet moléculaire de nano-îlots Ag ou Pd sur MgO(001) pour différentes épaisseurs et températures. Les paramètres morphologiques obtenus sont en très bon accord avec des résultats de microscopie électronique à transmission. Finalement, la diffusion incohérente a été mise en évidence en GISAXS et a pour origine des corrélations entre les îlots

Anomalous grazing-incidence small-angle X-ray scattering of Ga 2 O 3 -based nanoparticles

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Morphology of sol-gel porous In-Ga-Zn-O thin films as a function of annealing temperatures

International audienceThe physics of solution-processed thin films is studied with the example of In-Ga-Zn-O. After annealing at 450 degrees C, the films become fully inorganic and the pore distribution is modeled by a hexagonal close-packed based structure. The surface porosity is approximately 0.23 and the volume porosity deduced from small-angle X-ray scattering is approximately 0.26. The corresponding specific surface area is in the range of 65 m(2) g(-1). An instability model allows to successfully describe the film morphology. The solution diffusion coefficient, estimated from the rate of thinning as a function of temperature, follows an Arrhenius behavior with an activation energy of approximately 9.1 x 10(3) J mol(-1) and a pre-exponential coefficient Do of approximately 1.8 x 10(-8) m(2) S-1. Moreover, the surface tension-to-viscosity ratio of the solution is determined from the surface morphology. In addition, the observed phase separation between ZnO and Ga2O3 may come from the solubility difference of these oxides in the solvent. This separation has a major consequence on the electronic material properties. Finally, during cooling, the large tensile stress occurring between the film and the substrate is relaxed by the pores which adopt an oblate spheroid shape. The surface energy of In-Ga-Zn-O is then estimated to 1.5 J m(-2) from the pressure on the spheroidal pore. (C) 2016 Elsevier B.V. All rights reserved

Local structure around Zn and Ga in solution-processed In-Ga-Zn-O and implications for electronic properties

International audienceWe study by X-ray absorption spectroscopy the local structure around Zn and Ga in solution-processed In-Ga-Zn-O thin films as a function of thermal annealing. Zn and Ga environments are amorphous up to 450 degrees C. At 200 degrees C and 450 degrees C, the Ga atoms are in a beta-Ga2O3 like structure, mostly tetrahedral gallium oxide phase. Above 300 degrees C, the Zn atoms are in a tetrahedral ZnO phase for atoms inside the nanoclusters. The observed formation of the inorganic structure above 300 degrees C may be correlated to the rise of the mobility for IGZO TFTs. The Zn atoms localized at the nanocluster boundary are undercoordinated with O. Such ZnO cluster boundary could be responsible for electronic defect levels. Such defect levels were put in evidence in the upper half of the band gap. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Sol–gel derived barium strontium titanate thin films using a highly diluted precursor solution

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Effect of thermal annealing on the morphology of sol–gel processed barium strontium titanate thin films: Consequences on electrical properties

International audienceThe link between the morphology and the electrical properties of the sol–gel processed Ba0.7Sr0.3TiO3 thin films is investigated. Previous studies have not fully explained the differences in growth morphology as a function of the elaboration conditions. The thin films were investigated by Grazing Incidence Small-Angle X-ray Scattering (GISAXS), x-ray diffraction, and scanning electron microscopy. More precisely, prototype films were studied as a function of the annealing temperature: at low temperatures (140 °C–200 °C) by in situ GISAXS and at high temperatures (600 °C–800 °C) by ex situ GISAXS. At ∼150 °C, self-organized domains with a preferential distance of approximately 14 nm are formed. At high annealing temperatures, the growing domains become either nanoparticles or pores with a preferential distance of approximately 85 nm at 600 °C. This growth evolution is successfully explained by a general model based on convection and evaporation. With thermal annealing, the characteristic lengths parallel to the surface increase due to convection and the characteristic lengths perpendicular to the surface decrease due to evaporation. In addition, two types of annealing were investigated at 700 °C. For annealing after each other layer, a growth with vertically shifted particles occurs with no ferroelectric behavior. On the contrary, for annealing after each deposited layer, a columnar growth occurs and a ferroelectric hysteresis loop is obtained. The ferroelectricity of the sol–gel barium strontium titanate thin films is definitely linked to the complete removal of organic constituents leading to columnar growth

Phase transitions in flexible solution-processed ferroelectric P(VDF-TrFE) copolymer thin films

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Design Optimization of Printed Multi-layered Electroactive Actuators Used for Steerable Guidewire in Micro-Invasive Surgery

International audienceTo treat cardiovascular diseases (i.e., a major cause of mortality after cancers), endovascular-technique-based guidewire has been employed for intra-arterial navigation. To date, most commercially available guidewires (e.g., Terumo, Abbott, Cordis, etc.) are non-steerable, which is poorly suited to the human arterial system with numerous bifurcations and angulations. To reach a target artery, surgeons frequently opt for several tools (guidewires with different size integrated into angulated catheters) that might provoke arterial complications such as perforation or dissection. Steerable guidewires would, therefore, be of high interest to reduce surgical morbidity and mortality for patients as well as to simplify procedure for surgeons, thereby saving time and health costs. Regarding these reasons, our research involves the development of a smart steerable guidewire using electroactive polymer (EAP) capable of bending when subjected to an input voltage. The actuation performance of the developed device is assessed through the curvature behavior (i.e., the displacement and the angle of the bending) of a cantilever beam structure, consisting of single- or multi-stack EAP printed on a substrate. Compared to the single-stack architecture, the multi-stack gives rise to a significant increase in curvature, even when subjected to a moderate control voltage. As suggested by the design framework, the intrinsic physical properties (dielectric, electrical, and mechanical) of the EAP layer, together with the nature and thickness of all materials (EAP and substrate), do have strong effect on the bending response of the device. The analyses propose a comprehensive guideline to optimize the actuator performance based on an adequate selection of the relevant materials and geometric parameters. An analytical model together with a finite element model (FEM) are investigated to validate the experimental tests. Finally, the design guideline leads to an innovative structure (composed of a 10-stack active layer screen-printed on a thin substrate) capable of generating a large range of bending angle (up to 190°) under an acceptable input level of 550 V, which perfectly matches the standard of medical tools used for cardiovascular surgery