Investigation on the crystallization kinetics of amorphous Ta2O5 thin films for interferometric gravitational wave detectors

Current interferometric gravitational wave detectors (VIRGO, LIGO) rely critically on the use of ultra–stable Fabry–Perot cavities. In these systems, a fundamental limit to the inherent performance is set by the thermal noise associated with the dielectric coatings of the cavity Bragg mirrors. Very frequently the mirrors in such applications consist of multilayers of a low refractive index material, such as amorphous SiO2, alternating with a high refractive index material, which is often amorphous Ta2O5. Unfortunately the local structure of a-Ta2O5 has not yet been fully characterised. There is a growing interest to study partially crystallized a-Ta2O5 (where nanocrystallites are formed) as a material with improved mechanical performances. Our aim is thus to investigate the thermal evolution of the local structure of a-Ta2O5 thin films by time–resolved pair distribution function analysis and the crystallization kinetics as well.

干涉型引力波探测器（VIRGO、LIGO）严重依赖超稳定法布里-珀罗腔（Fabry–Perot cavity）的应用。在这类系统中，其固有性能的基本限制源自腔布拉格反射镜（Bragg mirror）的介质涂层所关联的热噪声。此类应用中的反射镜通常由低折射率材料（如非晶二氧化硅（amorphous SiO₂））与高折射率材料交替堆叠的多层膜构成，而高折射率材料多为非晶五氧化二钽（amorphous Ta₂O₅）。遗憾的是，非晶五氧化二钽的局域结构尚未得到完全表征。当前，人们对研究部分晶化（即形成纳米晶粒）的非晶五氧化二钽作为机械性能更优材料的兴趣与日俱增。因此，本研究旨在通过时间分辨对分布函数分析（time-resolved pair distribution function analysis），探究非晶五氧化二钽薄膜局域结构的热演化过程与结晶动力学。