XAS Structural Investigation of Amorphous TiO2:SiO2 and TiO2:GeO2 Thin Films for Mirrors of Gravitational-Wave Detectors

Thin films of amorphous TiO2:SiO2 and TiO2:GeO2 mixed oxides are of significant interest for coatings of the mirrors in gravitational waves (GW) interferometric detectors. The addition of TiO2 to amorphous silica or germania enables tailoring the optical properties of the mixture and its internal friction, which contributes to the total Brownian noise of the coating multilayer, one of the main limiting factors in GW detectors’ sensitivity. In this project, we propose a study of the structure of these amorphous mixed oxides using x-ray absorption spectroscopy. Specifically, we will study the local structure around each cationic species for different cationic ratios in thin films, both as-deposited and after the thermal treatments typically used to further reduce their mechanical losses. Additionally, we will investigate structural differences between coatings deposited by different methods which may lead to different atomic mixing and arrangement of the amorphous network.