The Study Of Structure And Properties Of Gd Doped TiO₂ Thin Films

In this work, Ag thin films with different thickness on TiO₂ films prepared by sol-gel are deposited by RF magnetron sputtering, and their structure and properties are analyzed. TiO₂ films doped with 0.3?0.6 at% Gd are deposited by reactive DC magnetron co-sputtering of Ti-Gd metallic target and annealed at 1000 ?. Structural, surface morphological, optical and photocatalytic properties of Gd doped TiO₂ films relative to pure TiO₂ films are characterized by electron probe microscopy analysis ?EPMA?, X-ray diffraction ?XRD?, scanning electron microscope ?SEM?, atomic force microscope ?AFM?, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy ?XPS? and room temperature photoluminescence ?PL?, respectively. The results are as follows:1. Phase transformation of TiO₂ thin films prepared by sol-gel after annealing at different temperatures is from anatase ?400?? to mixture of anatase and rutile ?550?? and to rutile ?700??. Two kinds of growth behavior of Ag particle films on the TiO₂ thin films are observed, one is mainly the Ag islands growth with Ag depositon time of 20-55s and characteristic size increasing from 32 to 37 nm; the other is the Ag islands growth that focused on merging with others into big islands in which depositon time of Ag island is 90-200s, with characteristic size 37 nm and maximum size ranging from 72 to 170 nm. Photocatalytic efficiency of Ag/TiO₂ films in the decreasing order is Ag?200s?/TiO₂^ Ag?55s?/TiO₂?Ag?20s?/TiO₂?Ag?90s?/TiO₂ and TiO₂.2. Gd-doped TiO₂ films promote the anatase-to-rutile phase transformation ?ART?, and the phase transformation process in view of Gd doping is from pure anatase ?Gd:0 at%? to mixture of anatase and rutile?Gd:0.3 at%? to pure rutile?Gd:0.4?0.6 at%?. XPS analysis confirms that Gd ions are in the +3 oxidation state, Ti ions are in the +4 oxidation state, and Gd doping promotes the increasing of oxygen vacancy concentration. Optical band gap for annealed films with Gd content of 0,0.3,0.4 and 0.6 at.% is 3.32±0.03,3.25±0.03,2.94± 0.03, and 2.97±0.03 eV, respectively. Moreover, via PL measurement further exhibits their energy band structure, especially the indirect transition, which is dependent on the occurrence of anatase ?Gd:0 at%, at 3.26eV? or rutile phase ?Gd:0.4±0.6 at%, at 3.07-3.1 eV? in films due to Gd doping, while the intraband transition at 3.61 and 3.41 eV is also observed in both pure TiO₂ and 0.3 at.% Gd-doped TiO₂ films. PL peak at 2.71 eV is assigned to oxygen vacancy, indicating the increase in oxygen vacancy concentration in the Gd-doped TiO₂ films with Gd content increasing, in accordance with XPS analysis. As-deposited films with appropriate content of Gd doping ?0.3-0.4 at%? exhibit an improvement in photocatalytic activity, but photocatalytic activity of the annealed films decreases with increasing Gd content.