Etudes des propriétés physico-chimiques de revêtements sol-gel par spectroscopie, optoacoustique et endommagement laser

Abstract : Within the framework of the simulation project, the Atomic Energy Commission (CEA) aims to reproduce the pressure and temperature conditions of a thermonuclear fusion with the Megajoule laser (LMJ). Some of the optical components of the LMJ, in particular some focusing lenses, are coated with an antireflective (AR) layer made by a sol-gel process. These films are composed of silica nanoparticles 10 nm in diameter with 55% porosity. To increase the mechanical strength of these layers, the films are exposed to water and ammonia vapors during a post-process. This post-treatment creates covalent bonds between the silica nanoparticles and thus strengthens the colloidal film. In order to give all the qualities of an optical coating,besides the key optical properties, we have set ourselves the objective of understanding the mechanical stability of these nanomaterials. In particular, we wanted, in the context of this thesis to have a better understanding of the ammonia hardening process and for that we undertook a complete study of the physical and chemical parameters that govern the elasticity of this assembly of nanoparticles. In a second step, we highlighted the appearance of surface cracking causing optical diffusion and a decrease in mechanical reinforcement during the postprocess. In order to minimize or even eliminate these surface cracks, we performed a parametric study to identify the elements responsible for this cracking.
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Jérémy Avice. Etudes des propriétés physico-chimiques de revêtements sol-gel par spectroscopie, optoacoustique et endommagement laser. Matériaux. Le Mans Université, 2018. Français. ⟨tel-02152341⟩

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