Photocatalytic properties of TiO₂ films prepared by O ₂ cluster ion beam assisted deposition method

Titanium dioxide (TiO₂) films were prepared on Si(1 0 0) substrate by oxygen (O₂) cluster ion beam assisted deposition method. The TiO₂ films prepared at a substrate temperature of 200 °C or less were amorphous, whereas those at a substrate temperature of 300 °C contained both rutile and anatase. The refractive indexes of the TiO₂ films increased with increasing substrate temperature. The surface state of the TiO₂ film was smooth at an atomic level. The TiO₂ films prepared at a substrate temperature of 300 °C showed high photocatalytic decomposition of methylene blue by ultraviolet (UV) irradiation, similar to those of TiO₂(1 0 0) bulk state in a rutile structure. The contact angle of the TiO₂ film with an initial value of 75° decreased to 10° by UV irradiation for 30 min, although that for TiO₂(1 0 0) bulk state in rutile structure remained at the initial value even after the UV irradiation. It is considered that anatase in the TiO₂ films was contributed to both photocatalytic decomposition and photocatalytic hydrophilicity of the films.