Photocatalytic and photoelectrochemical properties of TiO2-based multiple layer thin film prepared by sol-gel and reactive-sputtering methods

The multiple layers of a TiO2 thin film, consisting of a TiO2 thin film, a platinum electrode and a porous alumina substrate, were prepared by the sol -gel method in a previous study. As a sputtering process has some advantage s over wet-chemical processes, especially for practical manufacturing, a th in film photocatalyst with the same layer structure was prepared by the rea ctive-sputtering method in this study. The TiO2 thin film of the photoactiv e anatase phase was formed by using an appropriate gas pressure and tempera ture, however, the crystallite size of anatase was almost twice as large an d the band gap energy was slightly smaller than those of the sol-gel-proces sed thin film. The sputtering-processed thin film showed a typical columnar structure with some voids. The lower band gap energy and the coarse struct ure probably promoted the recombination between photoexcited electrons and holes, and resulted in lower photocatalytic activity and photocurrent compa red with the sol-gel-processed thin film.