Performance degradation mechanism of γ-ray irradiated sol-gel silica film

Abstract

γ-ray radiation effect on sol-gel silica films was investigated at different absorbed doses ranging from 10 kGy to 1000 kGy. The defect and microstructure evolutions of silica films were analyzed to understand the performance degradation behavior and mechanism of the γ-ray irradiated silica films. The cracks appear on the silica film surface and further expand at larger γ-ray absorbed dose, while surface roughness slightly decreases. During γ-ray irradiation, the thermal effect and the increased rate of diffusion-controlled process lead to the condensation of Si-OH groups and the recombination of ODCs. However, the ionization of atoms leads to generation and accumulation of E′ centers and NBOHCs. γ-ray irradiation leads to the reductions of bond lengths and bond angles of Si-O-Si groups, thus causing the densification of films. The refractive index and mechanical property firstly enhance and then reduce with the increase of absorbed dose associated with the change of silica film density. After γ-ray irradiation, the decreased contact angle and increased surface free energy indicate the reduction of anti-pollution ability of silica films. The dose-dependent surface quality, defects and mechanical properties determine the variation in laser-induced damage threshold (LIDT) of silica film. The results provide a reference to control the structural damage and performance degradation of silica films, which is very important for the research of safe operation of high-power laser facilities for inertial confinement fusion (ICF).