Effect of total and oxygen partial pressures on structure of photocatalytic TiO2 films sputtered on unheated substrate

Crystalline titanium dioxide, TiO2, photocatalytic films were deposited by reactive r.f. magnetron sputtering on glass substrates without additional external heating. A pure metallic titanium target was sputtered in a mixture of argon and oxygen. The effect of the total pressure and the oxygen partial pressure on the deposition rate, the phase composition, the crystallinity, the surface morphology and the resulting photocatalytic properties was investigated. The films were characterized by X-ray diffraction, scanning electron microscopy and scanning probe microscopy. The photocatalytic activity was evaluated by the measurement of the decomposition of methylene blue under UV irradiation. The results showed that the crystalline anatase, anatase/rutile or rutile films can be successfully deposited on unheated substrate and their formation is dependent on the total pressure and the oxygen partial pressure. A schematic phase diagram was constructed. The surface morphology is strongly influenced by the total pressure and the anatase TiO2 films with a more open surface, a higher surface roughness and a larger surface area are formed at higher total pressures. The anatase films with such surface morphology deposited in the reactive sputtering mode exhibit the best photocatalytic activity.