Magnetron Sputtering Of Nitrogen-doped Tio <sub> 2 </ Sub> Thin Films And Their Optical Properties

In recent years, it was discovered that TiO2 photocatalytic materials also have air purification, sterilization, deodorization, super-hydrophilic and other functions. It has been widely used in anti-bacterial ceramic, air purifier, the car rear view mirror and other fields. Nano-TiO2 semiconductor for their chemical stability, non-toxic and effectively removing pollutants from the atmosphere and water, is an ideal material for solving energy and environmental issues and caused widespread interest of national researchers. However, TiO2 is a wide band gap (Eg=3.2ev) semiconductor compounds, only the shorter wavelengths of solar light (<387nm) can be absorbed, which the UV (300～400nm) only reach 4%～6% of the sun light on the ground, solar energy utilization is very low. The visible solar energy accounts for 45% of the total combined amount. To improve the utilization of solar energy, it is a key technology to shorten the catalyst band gap so that the absorption spectrum could extend to the visible spectra. Its corresponding non-metallic element doping is expected to achieve energy band engineering and other beneficial features which has aroused wide spread concern and research. This preparation of nitrogen-doped TiO2 nanometer thin films is the more typical one. It does not reduce the basis of UV photocatalytic activity, but also can enhance the TiO2 nanometer thin films in the visible range of the expansion and intensity of absorption.There have been some reports on the property of TiO2-xNx thin films. TiO2-xNx thin films have different properties by different methods. In this dissertation, the TiO2-xNx thin films have been prepared by RF magnetron sputtering method on glass substrates. The structural and optical properties of TiO2-xNx thin films have been systemically investigated.The influence of conditions, such as the nitrogen argon flow ratio, working pressure, substrate temperature, sputtering power and annealing temperature on the characteristic of TiO2-xNx thin films have been studied.In the first chapter, the characteristic and applications of TiO2 materials have been introduced first.Then the progress of studies on the TiO2-xNx thin film materials have been mentioned and explained the reasons for the selected topic.In the second chapter, the preparation of thin films and their characterization test methods have been introduced. This chapter describes the thin-film preparation methods firstly, mainly for magnetron sputtering introduction. The TiO2-xNx thin films were deposited in a JGP-560-type multi-functional ultra-high vacuum magnetron sputtering system with a purity of 99.9%TiO2 ceramic target on glass substrates. A power supply operated at a crystal frequency of 13.56 MHz; the system background vacuum was 3×10-4Pa. The sputtering power was 50～250W. Argon gas was sputtering gas and reaction gas nitrogen.We use XRD to study the structure of the films, observe thin film surface morphology by AFM and study the optical properties of thin films from transmission spectra and PL spectra.In the third chapter, the structure and optical performance of TiO2-xNx thin films were discussed. X-ray diffraction (XRD) shows only A (101) a diffraction peak, indicating that TiO2-xNx thin films with preferred orientation of the growth trend. From the observation of surface morphology by AFM, the surface of nitrogen-doped films became smoother and N inhibited the formation of multi-crystalline structure. XPS patterns of the two samples show N elements into the film lattice indeed. The main form of nitrogen is substitute nitrogen and another is interval nitrogen. TiO2-xNx thin films are high transparent (大于80%) in the visible region, and has a steep absorption edge in the ultraviolet region. By calculating the optical band gap of films is about 2.44ev. Five emission peaks were observed in Room temperature photoluminescence emission spectra. They were respectively 340nm (A) as the center of the near ultraviolet light-emitting zone; 380nm (B),430nm (C) and 470nm (D) as the center of the three ultraviolet light-emitting zones; 535nm as the center of the blue luminescence band (E). A peak is derived from the direct exciton complex. B peak is the radiation compound luminescence between the bands. C peak is due to shallow defects captured exciton luminescence. D peak is a surface state and defect captured exciton luminescence. E peak is due to excessive oxygen vacancies caused by the formation of a spontaneous capture of electronic vacancy complex luminescence.The fourth chapter discussed the influence of preparation conditions on the structure and optical performance of the TiO2-xNx thin films. Using the control variable method, one by one to change the growth conditions of films, excellent preparation process parameters were found. The films are crystals of high crystalline, defects less uniform grain size and show excellent optical properties, deposited in these parameters. The luminescence mechanism of several light emitting peaks was analysed. We studied the films Luminescence Characteristics of various parameters and presented theoretical assumptions for red-shift of the absorption edge.The last chapter presented the main conclusions of papers and the developping prospect of nitrogen-doped TiO2 films.