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.

非晶态TiO₂:SiO₂与TiO₂:GeO₂混合氧化物薄膜，在引力波（GW）干涉探测器的反射镜涂层领域具有重要研究与应用价值。将TiO₂掺入非晶态二氧化硅或二氧化锗中，可调控混合体系的光学特性与内摩擦；而该内摩擦是涂层多层膜总布朗噪声的关键贡献来源，亦是制约引力波探测器灵敏度的核心限制因素之一。本项目拟采用X射线吸收光谱（X-ray Absorption Spectroscopy）对这类非晶混合氧化物的结构展开系统研究。具体而言，我们将针对不同阳离子配比的薄膜样品，分别探究沉积态与经典型热处理工艺（用于进一步降低机械损耗）处理后，各阳离子物种周围的局域原子结构。此外，我们还将调研不同沉积方法制备的涂层间的结构差异——此类差异可能导致原子混合方式与非晶网络排布的不同。