Ion bombardment-induced retarded moisture adsorption in optical thin films

Abstract
Moisture adsorption and desorption in optical filters made of TiO2 and SiO2 can be retarded by bombarding the completed films with 3-keV oxygen ions. This effect is not seen in filters made of ZrO2 and SiO2 We propose that retardation is due primarily to a swelling of the TiO2 surface as material is converted from crystalline to amorphous. In ZrO2, bombardment induces a transition toward more crystalline order, and the effect is not observed. This paper describes our experiments and results and discusses alternate explanations of the retardation effect.