Probing strain and microstrain in nanostructured thin layers.
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Probing strain and microstrain in nanostructured thin layers. Gianguido Baldinozzi1,2, David Simeone2,1, Dominique Gosset2,1 and Jean-Francois Bérar3 1 SPMS, Equipe Matériaux Fonctionnels pour l’Energie, CNRS, Ecole Centrale Paris, ChâtenayMalabry, France; 2 DEN, DMN, CEA, CE Saclay, Gif-sur-Yvette, France; 3 Institut Neel, CNRS, Grenoble, France. ABSTRACT The 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 Rietveld refinement software allows the accurate extraction of quantitative relevant information about the structure (strain and atomic positions) and the microstructure (crystallite size and microstrain), selectively probing the material on a depth of few nanometers. INTRODUCTION There is a steadily growing interest in nanostructured thin films consisting of increasingly complex compounds for their unique structural and functional properties. The characterization of thin films of metal oxides, possessing various types of nanoscale or mesoscale organization1, is a subject needing attention, especially because these systems are the result of rather simple and straightforward coating preparation methods, adapted to diverse potential applications including sensing, ionic conduction, catalytic and optical applications. To obtain a sound understanding of these systems, it is then necessary to determine their structures, their microstructures and to relate these features to the properties that are technologically relevant. Indeed, nano-sized materials have thermal, electrical, magnetic and optical properties that are significantly different from the corresponding bulk solid material. As the crystallite size is scaled down to a few nanometers, the bulk properties of the material are modified by the presence of an increasing density of interfaces and by competing interactions in the materials at the same length scale. When the ratio of surface to volume increases, the significant fraction of surface atoms compared to the bulk atoms yields new properties 2 , often related to changes of the Gibbs energies associated with the formation of nanocrystalline phases3. Besides the per se understanding of these systems, the knowledge of the structures and the microstructural features is a key element to control and to tailor the technological properties. The interest in such studies, aimed at characterizing these nanostructured materials and their evolution as a function of the temperature and eventually as a function of an applied field, is rapidly increasing, but standards for characterization of these types of materials are not well established yet. It is important to distinguish between particle size and crystallite size because they do not have the same meaning and equal consequences on the physical properties of these systems
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