Tao Chunxian

Effect of Oxygen Vacancy on the Band Gap and Nanosecond Laser-Induced Damage Threshold of Ta2O5 Films

Ta2O5 films are deposited on fused silica substrates by electron beam evaporation method. The optical property, x-ray photoelectron spectroscopy, band gap and nanosecond laser-induced damage threshold (LIDT) of the films before and after annealing are studied. It is found that the existence of an oxygen vacancy results in the decrease of the transmittance, refractive index, both macroscopic band gap and microscopic band gap, and the LIDT of Ta2O5 films. If the oxygen vacancy forms, the macroscopic band gap decreases 2%. However, when the oxygen vacancy forms the microscopic band gap decreases 73% for crystalline Ta2O5 and 77% for amorphous Ta2O5. The serious decrease of microscopic band gap may significantly increase the absorbance of the micro-area in Ta2O5 films when irradiated by laser, thus the damage probability increases. It is consistent with our experimental results that the LIDT of the as-deposited Ta2O5 films is 7.3J/cm2, which increases 26% to 9.2J/cm2 when the oxygen vacancy is eliminated after annealing.

Superhydrophilic and Wetting Behavior of TiO2 Films and their Surface Morphologies

TiO2 films, showing superhydrophilic behavior, are prepared by electron beam evaporation. Atomic force microscopy and the contact angle measurement were performed to characterize the morphology and wetting behavior of the TiO2 films. Most studies attribute the wetting behavior of TiO2 surfaces to their physical characteristics rather than surface chemistry. These physical characteristics include surface morphology, roughness, and agglomerate size. We arrange these parameters in order of effectiveness. Surface morphologies are demonstrated to be the most important. TiO2 films with particular morphologies show superhydrophilic behavior without external stimuli, and these thin films also show stable anti-contamination properties during cyclical wetting and drying.

Preparation of Ta-Doped TiO2 Using Ta2O5 as the Doping Source

A novel method for preparing Ta-doped TiO2 via using Ta2O5 as the doping source is proposed. The preparation process combines the hydrothermal fluorination of Ta2O5 and the subsequent formation of Ta-doped TiO2 sol. The results show that the doped sample annealed at 393 K generates an unstable intermediate NH4TiOF3, which converts into anatase TiO2 with the increase of temperature. After annealing at ≥673 K, the Ta-doped TiO2 nanocrystals with the grain size <20 nm are obtained. Both the XRD and TG-DSC results confirm that Ta doping prevents the anatase-rutile crystal transition of TiO2. The band gap values of the doped samples, as obtained by UV-vis diffuse reflectance spectra, are smaller than that of pure anatase TiO2. The first-principle pseudopotential method calculations indicate that Ta5+ lies in the TiO2 lattice at the interstitial position.