Enhanced photocatalytic activity of TiO₂-ZnO thin films deposited by dc reactive magnetron sputtering

The effect of deposition conditions on the photocatalytic activity of TiO₂-ZnO thin films was studied. By using a (Ti)₉₀-(Zn)₁₀ alloy target, the samples were deposited at room temperature on glass substrates by dc reactive magnetron sputtering and post-annealed in air at 500 °C. The dependence of the physical properties of the films on the O₂/Ar gas ratio and the deposition working pressure was investigated. XRD patterns showed mainly the formation of the anatase phase of TiO₂. Optical absorption measurements exhibited a blue shift of the band-gap energy with increasing working pressure. XPS spectra indicated the presence of the Ti⁴⁺ and Zn²⁺ oxidation states, which correspond to TiO₂ and ZnO, respectively. The chemical state of Ti was further analyzed by means of the modified Auger parameter, α’, which gave a value of ca. 873 eV. The photocatalytic property of the films was assessed by the degradation of a methylene blue aqueous solution. The maximum photocatalytic performance was observed for the samples deposited at 3.0 mTorr and O₂/Ar gas ratio of 10/90. These results are explained in terms of the structural, optical, and morphological properties of the films.