Structural, electrical, optical, and photoelectrochemical properties of thin titanium oxinitride films (TiO2−2xNx with 0⩽x⩽1)

Abstract

Nanocrystalline titanium oxinitride (TiO2−2xNx) thin films (0⩽x⩽1) were prepared by reactive dc magnetron sputtering from a titanium target in an argon-oxygen-nitrogen atmosphere. By increasing the reactive gas component nitrogen the phases changed from TiO2 to TiO2−2xNx and finally to TiN. The reactively sputtered films were characterized by elastic recoil detection analysis, Raman spectroscopy, and resistivity measurements. The crystallographic structures of TiO2 were maintained up to a nitrogen concentration of about 20at.%; however, the crystallite size decreased significantly and a transition from the low-temperature anatase to the high-temperature rutile phase of TiO2 occurred. Optical transmission measurements revealed that the indirect energy band gap can be reduced from 3.2to2.6eV for nitrogen concentrations up to 20at.%. The film properties for photocatalytic water oxidation were investigated by differential electrochemical mass spectroscopy. While the photoactivity in the visible increases, the overall photoelectrochemical activity appears to be deteriorated significantly by nitrogen doping, most probably due to the formation of defect states near to the valence band of TiO2.

Recent advances in TiO2-based photocatalysis

“…However, doping can directly increase the carrier density and result in a narrower depletion region, which greatly hinders the electron-hole separation process. [71][72][73][74] In addition, surface dopants generally act as charge recombination centres. 75 These drawbacks greatly limit the practical use of doped TiO 2 .…”

Spectroscopic evidence of NOx formation and band-gap narrowing in N-doped TiO2 films grown by pulsed magnetron sputtering

“…Sputter deposition of titanium oxynitride (TiO x N y ) films has been widely used since it is capable of yielding TiNeTiO solid solutions with tunable composition from pure TiO 2 to TiN compounds by increasing the N 2 /O 2 ratio in the gas discharge. Most of the previous works on TiO x N y have been performed by DC [29,30] and RF [31,32] discharges with metallic and compound targets, respectively. The studies by RPMS are less scarce since it is a more recent configuration.…”

Selective local nitrogen doping in a TiO2 electrode for enhancing photoelectrochemical water splitting

“…8,9 However, for most of the doped semiconductors, while doping extended the light utilization region to visible light, the monochromatic incident photon-toelectron conversion efficiency (IPCE) in the intrinsic light absorption region was decreased meanwhile unfortunately. [10][11][12][13] Such deficiency of doping methods greatly restricts the promotion of the solar energy conversion efficiency. Therefore, to further improve the photocatalytic or PEC activities of the semiconductors by using the doping strategy, an important issue is to solve the diminution of IPCE in the intrinsic light absorption region.…”