Paper SS-TuP9
Photocatalytic Properties of TiO₂/NiO/Cu₂O Thin Films Prepared by Reactive Magnetron Sputtering

Tuesday, October 20, 2015, 6:30 pm, Room Hall 3

In recent years, various characteristics of TiO₂ have attracted considerable attention. One of their characteristics is a photocatalytic effect. The photocatalytic effect of TiO₂ shows antifouling or antimicrobial activity, and has the ability to decompose environmental pollutants. Thus TiO₂ has superior characteristics in many metal oxides, because its photo-excited state is very stable and does not cause self-decomposition. Therefore, TiO₂ can perform the electrolysis of water by light, however, a light reaction region of TiO₂ is limited within the ultraviolet region corresponded with only about 3 % of sunlight.

In this study, to improve the photocatalytic property of TiO₂ the TiO₂/NiO/Cu₂O thin films were fabricated by laminating the TiO₂ layer with 3.0 - 3.2 eV and the Cu₂O layer with 2.2 eV in a band gap energy. In order to prevent the diffusion of Cu, the NiO layer was inserted between the TiO₂ layer and the Cu₂O layer. NiO has a high melting point, high hardness and has been used as a barrier layer. These three layers were prepared by reactive magnetron sputtering.

The film composition and microstructure were investigated by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. Chromatic changes of a methylene blue solution were applied to the measurement of a photocatalytic property. Light irradiation to the TiO₂/NiO/Cu₂O thin films in a methylene blue solution was carried out using a commercial sterilizing lamp as ultraviolet light and an artificial sun lamp as visible light. Transmittance of a methylene blue solution was measured by a spectrophotometer.

On the XRD measurement for the crystal structure of TiO₂/NiO/Cu₂O thin films, the strong peaks of the anatase-rutile mixture from TiO₂ of the upper layer and the weak peaks of Cu₂O or NiO from the lower layer appeared. It was estimated that the diffusion of Cu from the Cu₂O layer was prevented by inserting the NiO layer. The suitable photocatalytic effect was obtained by inserting the NiO layer of 20 nm in a thickness and then the decomposition activity of a methylene blue solution showed about 57 % under an artificial sun light and about 77 % under a sterilization light. In the case of TiO₂/NiO/Cu₂O thin films, it was considered that the role of the NiO layer was not only the protection of the diffusion but also the electric effect as a p-type semiconductor.