Étude structurale de matériaux sous forme de couches minces par diffraction des rayons X en incidence rasante

International audienceLes matériaux sous forme de couches minces sont couramment analysés par diffraction des rayons X en incidence rasante. Cependant, afin d'extraire les informations caractéristiques de ces systèmes, il est nécessaire de prendre en compte les effets d’élargissement instrumental dans les programmes d'affinement par la méthode de Rietveld utilisés pour le traitement des données. Dans cet exposé, il sera montré que cela permet d'extraire des informations quantitatives pertinentes sur la structure (contrainte et positions atomiques) et sur la microstructure (taille des cristallites et micro-contraintes) qui seront mises en relation avec la chimie des films minces. Ces points seront illustrés en prenant quelques exemples aussi bien de couches minces d'oxydes que de chalcogénures

Étude structurale de matériaux sous forme de couches minces par diffraction des rayons X en incidence rasante

International audienceLes matériaux sous forme de couches minces sont couramment analysés par diffraction des rayons X en incidence rasante. Cependant, afin d'extraire les informations caractéristiques de ces systèmes, il est nécessaire de prendre en compte les effets d’élargissement instrumental dans les programmes d'affinement par la méthode de Rietveld utilisés pour le traitement des données. Dans cet exposé, il sera montré que cela permet d'extraire des informations quantitatives pertinentes sur la structure (contrainte et positions atomiques) et sur la microstructure (taille des cristallites et micro-contraintes) qui seront mises en relation avec la chimie des films minces. Ces points seront illustrés en prenant quelques exemples aussi bien de couches minces d'oxydes que de chalcogénures

Relationship between atomic structure and excellent glass forming ability in Pd42.5Ni7.5Cu30P20 metallic glass

International audienceTo understand the relation of the glass-forming ability (GFA) to the local atomic configurations of a PdNiCuP (PNCP) metallic glass having the best GFA at present, the local structures were investigated by combining data obtained from anomalous X-ray scattering, X-ray and neutron diffraction, and applying reverse Monte Carlo modeling. By comparing the results of PNCP with PdNiP (PNP) and PdCuP (PCP) having a slightly and much worse GFAs, respectively, characteristic features were observed in the hyper-ordered atomic structures. Firstly, the concentration inhomogeneity of Ni/Cu in PNCP is larger than that of Ni in PNP and Cu in PCP. Secondly, a Voronoi tessellation showed that the fraction of pure icosahedral arrangements around the Cu atoms increases significantly in PNCP by adding icosahedral-preferred Ni atoms in PCP. Finally, a persistent homology (PH) analysis reveals the largest intermediate-size Cu PH rings in PNCP among the PH rings in these Pd-based BMGs. The structural heterogeneity for the excellent GFA of PNCP would be considered by an incompatible mixture of specific Pd-P configurations and icosahedral clusters around the secondary Ni and Cu metals

Development of a PCI Express Based Readout Electronics for the XPAD3 X-Ray Photon Counting Image

International audienceXPAD3 is a large surface X-ray photon counting imager with high count rates, large counter dynamics and very fast data readout. Data are readout in parallel by a PCI Express interface using DMA transfer. The readout frame rate of the complete detector comprising 0.5 MPixels amounts to 500 images per second without dead-time

Partial structure investigation of the traditional bulk metallic glass Pd40Ni40 P20

Local structures of Pd 40 Ni 40 P 20 bulk metallic glass were investigated by combining anomalous x-ray scattering close to the Pd and Ni K absorption edges, x-ray diffraction, neutron diffraction, and reverse Monte Carlo modeling, from which partial structure factors S i j (Q) and partial pair distribution functions g i j (r) as well as threedimensional atomic configurations were carefully obtained around the constituent elements. A disagreement is found in the local structures with an ab initio molecular dynamics simulation by Guan et al., i.e., the existence of the P-P nearest-neighboring configurations is clarified in the present experimental result. From the Voronoi tessellation analysis, a preference of the pure icosahedral configurations is observed around the Ni atoms, whereas the local configurations around the Pd and P atoms are rather distorted icosahedra. A persistent homology analysis was carried out to identify meaningful shape characteristics of the intermediate-range atomic configuration of large rings

Glancing incidence X-ray diffraction as an efficient tool to probe the structure and the microstructure of polycrystalline thin layers

International audienceThe development of techniques like spin and dip coating, physical or chemical vapor deposition during the past decades offers now the opportunity for tuning the composition of polycrystalline layers and coating at the nanometric scale. The knowledge of the structure and the microstructure of different layers allow to predict their long term stability under harsh environments. Glancing Incidence X Ray Diffraction technique, based on the variation of the refractive index across the interface between material and air, provides an efficient tool to collect diffraction patterns as a function of the probed depth [1]. As the experimental setup in GIXRD exhibits peculiar features, many corrections need to be applied to extract information about the structure and the microstructure from Rietveld refinement [2]. In this talk, we will firstly discuss those corrections implemented in a Rietveld refinement code and illustrate by different examples[3]. References: [1] see for instance Brunel, De Bergevin, Acta Cryst A42, 299 (1986); [2] D. Simeone, G. Baldinozzi, D. Gosset, G. Zalczer, and J. F. Berar. J. Appl. Crystallography, 44 :1205–1210, 2011 [3] G. Baldinozzi, G. Muller, C. Laberty-Robert, D. Gosset, D. Simeone, and C. Sanchez. J. Phys. Chem.C, 116(14) :7658–7663, 2012

Probing Strain and Microstrain in Nanostructured Thin Layers

International audienceThe analysis of the structures and microstructures of nanostructured thin layers can be performed using laboratory grazing incidence diffraction, provided accurate corrections are performed to handle the instrumental broadening effects related to the experiment geometry for an impinging beam close to the critical angle. Implementing these corrections in a Rietveld refinement software allows the accurate extraction of quantitative relevant information about the structure (strain and atomic positions) and the microstructure (particle size and microstrain), selectively probing the material on a depth of few nanometers

Local- and intermediate-range structures of As–Se glasses from the stoichiometric to the stiffness transition region

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