Relationship between the Photocatalytic Characteristics and the Oxygen Partial Pressure of TiO₂ Thin Films Prepared by a DC Reactive Sputtering Method

Abstract

It was confirmed that the oxygen partial pressure that is used during DC reactive sputtering can influence the generation of oxygen defects on TiO 2 thin films and/or the surface structure, which then affects the photocatalytic characteristics. TiO 2 films were deposited by DC reactive magnetron sputtering on a Si wafer at 250 C under oxygen partial pressures of 0.1 Pa, 0.5 Pa and 0.8 Pa. Structural analysis of the TiO 2 thin films was conducted using X-ray diffraction (XRD), field-effect scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), the photo luminescence method (PL). Characterization of the photocatalytic properties was performed by measuring the concentration change of methylene blue (wet methylene blue method) and the change of the contact angle with pure water. All films showed a polycrystalline anatase structure. TiO 2 thin films deposited under reducing conditions (an oxygen partial pressure of 0.1 Pa) exhibited peaks that are characteristic of Ti 3þ and can also contain a number of oxygen defects. The domain size was about 150-300 nm, and the domain boundaries were unclear. On the other hand, for TiO 2 thin films deposited in oxidizing mode (oxygen partial pressures of 0.5 Pa and 0.8 Pa), the peak corresponding to Ti 3þ was not observed. The domain size was between 300-1000 nm and the boundaries were clear. TiO 2 thin films exhibit better photocatalytic properties when the domain size is large and there are fewer oxygen defects in the film. It has been suggested that the decreasing proportion of domain boundaries, which act as trapping centers for electrons, and the lower concentration of oxygen defects, which act as recombination centers for electronhole pairs, improved the photocatalytic characteristics.

Deposition of Photocatalytic TiO2 Films by Planar Magnetron Sputtering System with Opposed Ti Targets

“…The values of decomposition performance index of 14.0 and 9.2 were obtained for the electron confined system. The value of 9.2 was the same as that reported for the films by conventional DC reactive sputtering by Noguchi et al [15]. The performance index increased to 14.0 at x = 40 mm.…”

High-rate deposition of photocatalytic TiO2 films by oxygen plasma assist reactive evaporation method

“…While on the other hand, the index for glass substrate was 1.6 [μmol l − 1 min − 1 ]. These results indicate that our films, deposited at such a high deposition rate, have similar MB decomposition performance to that of films obtained using reactive sputtering method [15][16][17].…”

Ion exchanged potassium titanoniobate as photocatalyst under visible light

“…Especially, the positions of the peaks on the high binding energy side were different. The same difference was observed on O-defected TiO 2 [22]. This suggests that the states of the adsorbed compounds are different due to the different condition of the sample.…”