Investigation on thermal stability of TiO 2 films for application at high temperature

The thermal stability of electron beam deposited TiO₂ monolayers and TiO₂/SiO₂ high reflectors (HR) during 300 to 1100°C annealing is studied. It is found that the optical loss of film increases with the increase in annealing temperature, due to the phase change, crystallisation and deoxidising of film. Scattering loss dominates the optical property degradation of film below 900°C, while the absorption is another factor at 1100°C. The increase in refractive index and decrease in physical thickness of TiO₂ layer shift the spectra of HR above 900°C. The possible crack mechanism on the surface of HR during annealing is discussed. Guidance for application on high temperature stable optical coatings is given.