Photocatalytic properties of TiO2 films prepared by O2 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.