Composition-dependent structural, optical, mechanical, and moisture resistant properties of CaF₂-TiO₂ composite films prepared by reactive ion-assisted codeposition

The influences of TiO₂ contents on the structural, optical, mechanical, and moisture resistant properties of CaF₂-TiO₂ composite films prepared by reactive ion-assisted codeposition are systematically investigated. The CaF₂ films deposited at an ambient substrate temperature are found to have superior optical, mechanical, and moisture resistant properties with the addition of 10 at. % TiO₂. The structure of this film changes from polycrystalline CaF₂ to a mixed phase of amorphous TiO₂ and polycrystalline CaF₂. The hardness of composite films containing 45 at. % TiO₂ is even higher than that of pure TiO₂ and glass, which is attributed to the isolation of the crystalline CaF₂ grains by the interconnection of the amorphous TiO₂ dispersoids.