Propriétés optiques linéaires et non-linéaires de nanocomposites métal-diélectrique anisotropes

摘要

Nanocomposite materials based on metal particles embedded in a dielectric matrix present, due to the nanometric size of the metal particles, unusual properties which cannot be found in bulk materials. Most notably, the conduction electron resonance in the presence of incident light excitation, so-called surface plasmon resonance (spr), gives rise to an absorption band in the visible which have a drastic impact on the optical properties of the nanocomposite. The position, the width and the amplitude of this absorption band are complex functions of the nanostructural characteristics of the nanocomposite such as: the kind and concentration of metal, the nanoparticles size and shape, the refractive index of the matrix, etc. Specifically, the presence of asymmetric particles, like nanoellipsoids for example, allows for the observation of multiple spr absorption bands resulting in a non-symmetric material with anisotropic properties. In this thesis, we will present the development and the analysis of advanced fabrication techniques allowing the precise control of the synthesis of nanocomposites formed of gold nanoparticles embedded in a silica matrix. We have developed a three-step technique allowing us to fabricate nanocomposite films with particles of controlled size and shape. These steps are the following: 1) hybrid deposition sputtering/ plasma-enhanced chemical vapor deposition, 2) thermal annealing, 3) high energy heavy ion irradiation. Subsequently, the optical performance of the fabricated materials was tested by different techniques to evaluate their linear and nonlinear properties. The former were studied using ellipsometry and spectrophotometry while the latter were evaluated by the P-Scan and Z-Scan techniques. More particularly, we devoted a lot of time to the metrology and control of the anisotropic properties of the nanocomposite system formed by ion irradiation. A new approach developed to measure anisotropic nonlinear optical properties will be presented. In this document, the lector will find an exhaustive theoretical description of the optical properties (linear and nonlinear) of metal/dielectric nanocomposites including detailed models for the description of the properties of each constituents of the nanocomposite: metal (Drude, Lorentz) and dielectric (Cauchy).