Masayuki Kamei

Photocatalytic Property and Deep Levels of Nb-doped Anatase TiO2 Film Grown by Metalorganic Chemical Vapor Depostion

A Nb-doped anatase TiO2 (Nb: 5 at%) film was grown on a SrTiO3(001) substrate by metalorganic chemical vapor deposition. Deep level transient spectroscopy analysis revealed that this film possessed two kinds of deep levels due to the Nb ions, which were found to exist at 0.32 eV and 0.67 eV below the bottom of the conduction band. The photocatalytic activity of this film was low compared with that of the undoped anatase film, suggesting that the deep levels acted as recombination centers of photoexcited electron-hole pairs.

Pulse mode effects on crystallization temperature of titanium dioxide films in pulse magnetron sputtering

Pulse mode effects on the crystallization temperature and photocatalytic properties of TiO 2 films were investigated. TiO 2 films were deposited on silica glass substrates using a pulse magnetron sputtering apparatus in the unipolar and the bipolar pulse modes. X-Ray diffraction showed that in the bipolar pulse mode the rutile phase TiO 2 film grew at lower substrate temperature compared with the unipolar pulse mode. The photocatalytic activities obtained from the photoreduction of Ag ions at the surface of TiO 2 films indicated that the anatase phase TiO 2 films grown in the bipolar pulse mode had higher photocatalytic activity compared with those grown in the unipolar pulse mode. This suggests that the bipolar pulse mode is an effective technique to achieve higher nhotocatalytic activity of TiO 2 film.

Deep Level Transient Spectroscopy Analysis of an Anatase Epitaxial Film Grown by Metal Organic Chemical Vapor Deposition

The deep level transient spectroscopy (DLTS) study of anatase-type TiO2 material was performed for the first time. The anatase film was epitaxialy grown on a conductive Nb-doped single-crystalline SrTiO3 (100) substrate by metal organic chemical vapor deposition. The photoluminescence characteristics of this anatase film were identical to those in previous reports, where they were attributed to the radiative recombination of self-trapped excitons. According to the DLTS analysis, it was revealed that this anatase film had a characteristic deep level located at 0.96 eV below the bottom of the conduction band with large concentration (6.5×1016/cm3) and capture cross section (8.3×10-13 cm2). Since the capture cross section of this level appeared to be too large to be caused by point defects, the origin of this deep level was attributed to line defects such as dislocations.

Superior Schottky electrode of RuO2 for deep level transient spectroscopy on anatase TiO2

An anatase TiO2 film was epitaxially grown on a conductive Nb-doped single-crystalline SrTiO3 (100) substrate by metalorganic chemical vapor deposition. RuO2 Schottky electrode was fabricated on the epitaxial anatase film by reactive dc magnetron sputtering. The dark I–V and capacitance–voltage characteristics indicated the good rectification and thermal stability of the RuO2/anatase junction. This RuO2/anatase junction enables the stable measurements of deep level transient spectroscopy in the high-temperature region and is a promising Schottky electrode to examine the origins of deep levels in the band gap of anatase.

Comparative Study of TiO2 Anatase Epitaxial Thin Films Grown by Magnetron Sputtering and Metalorganic Chemical Vapor Deposition

Thin films of TiO2 anatase structure were heteroepitaxially grown on SrTiO3(001) single crystalline substrates by direct current magnetron sputtering (DCSP) and metalorganic chemical vapor deposition (MOCVD). The DCSP-grown films always showed larger lattice constants than those of the MOCVD-grown films. The RBS measurements revealed a difference in the depth profiles of the misfit dislocations in the films, which was considered to be the origin of the larger lattice constants in the DCSP-grown films. A striking difference was also present in the photoluminescence characteristics in MOCVD-grown films and DCSP-grown films; the photoluminescence peak originating from the self-trapping excitons observed in MOCVD-films disappeared in DCSP-films.

Discovery of the deep level related to hydrogen in anatase TiO2

Deep level transient spectroscopy was carried out to investigate the origin of the deep levels in the band gap of anatase TiO2. The epitaxial anatase-TiO2 film grown by metal-organic chemical vapor deposition possessed a deep level whose activation energy was 0.52eV. In contrast, this deep level at 0.5eV was not observed in the films grown by sputtering. However, by adding CH4 or H2 to the sputtering gas, the deep level at 0.5eV was observed in the sputter-grown films. Furthermore, the density of this deep level increased with increasing hydrogen gas, suggesting that this deep level originated from hydrogen doping.Deep level transient spectroscopy was carried out to investigate the origin of the deep levels in the band gap of anatase TiO2. The epitaxial anatase-TiO2 film grown by metal-organic chemical vapor deposition possessed a deep level whose activation energy was 0.52eV. In contrast, this deep level at 0.5eV was not observed in the films grown by sputtering. However, by adding CH4 or H2 to the sputtering gas, the deep level at 0.5eV was observed in the sputter-grown films. Furthermore, the density of this deep level increased with increasing hydrogen gas, suggesting that this deep level originated from hydrogen doping.