Depth Profiling of Strain in Textured Tungsten Thin Films

International audienceThe stability of heterophase interfaces between metal systems, their kinetic, structural, and thermomechanical properties are a matter of concern for high demanding applications involved in the development of technological coatings for the first wall materials in fusion reactors and their prototypes (ITER). We would like to discuss preliminary results of X-ray experiments on model coatings made of tungsten, in particular the problems related to strain inhomogeneity in metal films on heterophase substrates. These analyses of nanostructured thin layers can be performed using laboratory grazing incidence diffraction, 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. References Results The local strain in the three films is almost identical at a given depth. This suggests that the deposition method produce reliable microstructural characteristics for the three films. In the three films the maximum amplitude of the strain is close to the surface of the films and it decreases smoothly when the depth increases. It seems likely that the larger strain observed close to the surface could be partly related to the interaction of the films with the gases of the ambient atmosphere: nevertheless, these effects seems to remain small and do not seem to require a reassessment of the absorbance of the films. Grazing incidence X-ray diffraction can be a workhorse technique for deriving crystallite size in nanoscale systems due to its non-destructive character, the fast data collection and the relative simplicity of the experimental setup, This information is relevant for an accurate description of nanocrystalline systems prepared as thin films and it can significantly improve the knowledge of their structure-properties relationships. This work was partly supported by Laboratoire d'Excellence Physique Atomes Lumière Matière (LabEx PALM) through a French national grant of Agence Nationale de la Recherche within the "Programme Investissements d'Avenir" wit