Photoelectric Properties Of Multilayered Molybdenum Doped TiO 2 Films Prepared By Magnetron Sputtering

TiO2films are transparent, stable materials that have considerate photocatalytic and hydrophilic property under the illumination of ultraviolet rays. However, a wide energy gap (Eg=3.20eV) restrains its utilization under visible light.Cationic doping is an effective approach to enhance photoelectric property of TiO2films. Due to a similar ions size, Mo could replace Ti4+in TiO2lattice effectively and thereby form typical n-type doping. Under a large doping concentration, however, excessive Mo may also squeeze into lattice and form interstitial defects, which will boost up lattice distortion and decrease the concentration of carriers. As a consequence, there is a best doping content for Mo in TiO2lattice, although the concrete value of this optimized content varies as doping methods change.In this study, based on radio frequency (RF) magnetron co-sputtering, we managed to take accurate control of doping content as well as the thickness of each layer, thereby implant several upward electric fields, which could speed up internal charge transfer, during a single sputtering process. The influence of Mo doping on surfaces, crystal structures, elements’valence states and absorption band of TiO2films were studied. To investigate the photoelectric characteristic of ITO (Indium Tin Oxide)/Mo-Ti02electrode, a series of cyclic voltammetry experiments were conducted. The results indicate1. An appropriate amount of Mo atoms, observed as Mo6+and Mo5+by XPS, could inhibit the crystal particles’growth, enhance the surface roughness of the film and bring about a remarkable red shift of the absorption spectra. As the concentration of Mo increased, the energy gap declined at first until the percent of doped Mo eventually reached3.6at.%, when a blue shift of spectra turned up and the energy gap grew wider. Irradiated by a xenon lamp, the sample doped with0.9at.%Mo showed the highest photocurrent which didn’t stop rising with the voltage exerted on the anode increasing. After that, with Mo concentration kept rising, photocurrent began to decrease. Compared to the pure TiO2film, the sample with3.6at.%Mo had a much lower photocurrent. Our experiments demonstrate that Mo doping, when the concentration was controlled under a relatively low limit, could bring about a significant promotion to the improvement of TiO2film’s photoelectric properties. The highest photocurrent observed is2.4times that of the sample with no Mo doped inside. 2. Double-layer structure covered by an undoped surface has a remarkable red-shifted absorption edge and much stronger photocurrent compared to uniform-doping sample, signifying that the electric field implanted at the interface between particles in different layers accelerated internal charge transfer effectively. However, a heavy-doped layer implanted at the bottom of the three-layer film merely brought about negative effects on the photoelectric property, mainly because of the Schottky junction existed above the substrate.3. By rising the Mo concentration to1020cm-3, where thickness of the depletion layer fell into the order of angstroms, the negative effects resulted from bottom Schottky barrier could be eliminated by a high tunneling coefficient. Under this circumstance, the Schottky junction disappeared and the strongest photocurrent was observed in the three-layer film.