Effects of ITO thin films on microstructural and photocatalytic properties of layered TiO2/ITO films prepared via an extended deposition period

This study elucidates how indium tin oxide (ITO) thin film affects the microstructural and photocatalytic properties of layered TiO2/ITO films prepared by DC magnetron sputtering. Two ITO substrates, as-received ITO (aITO) and in situ sputtered ITO (sITO), are adopted herein. Photocatalytic measurements of methylene blue and dimethyl sulfoxide indicate that the layered TiO2/sITO film has greater photocatalytic oxidation than the TiO2/aITO catalyst. According to photoelectrochemical tests, the latter exhibits a completely opposite activity to that of the former. Secondary ion mass spectrometry elemental depth profiles reveal that tin atoms in the sITO film really permeate into the growing TiO2 film and promote the formation of the crystalline Ti1−xSnxO2 layer. Additionally, cross-sectional transmission electron microscopy images and the selective area diffraction patterns show the difference between the diffusion of tin in the two catalysts. The photocatalytic oxidation capability is further enhanced in the layered TiO2/sITO film because of an increase in the bandgap energy and a positive shift in the Fermi level energy of the Ti1−xSnxO2 layer. Conversely, tin diffusion is limited in the aITO substrate under controlled conditions, in such a manner that a Schottky barrier can form at the TiO2/aITO interface. Therefore, photogenerated electrons can be efficiently transferred from the overlaid TiO2 film to the aITO substrate, producing a remarkable photocurrent density under UV illumination. Microstructural measurements reveal that the growth of the reactive {0 0 1} facets and columnar porous structure are favored by the synergetic effect of ITO substrate and an extended period of deposition. Accordingly, the photocatalytic capabilities are further raised.