| The environmental protection is the common problem which the mankind faces. The alarm system for gas detection or regulation be manufactured by gas sensors provides a kind of effective supervision method to protect environment. Metal-oxide semiconductor which is regard as a new-style materials is subjected to close concern. TiO2 has been known as an n-type metal oxide semiconductor and an important inorganic function material. In recent years, TiO2 solid thin film sensor combining micro-electronics technical adapt the development request of low energy consumption and miniaturization. A lot of effective ways proposed to optimize the microstructure and electrical property of TiO2 solid thin film sensor in order to control the environment effectively.In this paper, TiO2 solid thin film was fabricated by different ways and the character in different gas environment was studied systematically. The property and process of TiO2 solid thin film surface and the influence of impurity upon the material function was been analysed. Simultaneity, the character of point defects, impurity defects, crystal surface and adsorption process of TiO2 was investigated by first-principles pseudopotential calculations based on density-functional theory (DFT). The main content is as follows:1.W/TiO2 thin film, deposited by RF reactive sputtering from a composite target of W and Ti, was investigated through AFM for structural characterization and by volt-amperometric technique for electrical and gas-sensing properties. It was found that the film with Ti and W concentration ratio of 80%:20% has the lowest resistivity at the 600℃annealing temperature. P type doped had been implemented with the 700℃annealing temperature. The film, which has high sensitivity, short response time and recovery time, could detect the low concentration gas of to NO2 and SO2. A detection limit lower than 100 ppb of NO2 was expected.2.TiO2 thin film was prepared on substrate by ultrasonic spray pyrolysis (USP) method from dissolving titanium oxide acetylacetonate in pure methyl alcohol. Scanning electron microscopy (SEM) was employed to analyze the crystalline and microscopic structure of the film. Results showed that the films doped Ru, Rh, Ir be sensitive to oxygen. The effects of catalyst incorporation on semiconductor gas sensors described in terms of the operation temperature and the response magnitude. It was conclude that pure TiO2 thin film measured at 400℃displayed a low response of oxygen of 1500ppm and 15000ppm, whereas TiO2 thin film using impregnated catalysts proved to have the highest response to O2 at an optimal operating temperature of 250℃.3.Pure TiO2 and Nb-doped and Cu-doped TiO2 nanoparticles were produced by flame spray pyrolysis (FSP) and tested for sensing of CO and ethanol at 400℃in dry air. The powders were characterized by transmission electron microscopy and X-ray diffraction. Niobium stabilized the anatase phase and retarded anatase change toward rutile. Both dopants improved the sensitivity towards CO over that of pure TiO2. In contrast, for ethanol a high increase in sensitivity was observed only for Nb/TiO2.4.TiO2 compound films also were fabricated in this study. Bilayered and monolayered TiO2-KTaO3 films had been fabricated by sol-gel spin-coating method and heated at deferent temperature for an hour. The humidity-sensing characterizations of the films were investigated. Morphological characterization had been studied by SEM and XRD. It proved that the films possessed nanosized gains and capillary nanoporous structure. During the relative humidity variation from 12% to 97%, TiO2/KTaO3 films annealed at 500℃exhibited the highest humidity sensitivity. Compared to monolayered films, the bilayered films showed the large change in impedance. The reasons of humidity sensing properties of TiO2-KTaO3 films also had been discussed.5.TiO2-WO3 composite thin films had been synthesized by E-beam evaporation and heated at 500℃for two hours. Morphological characterization had been studied by SEM and XRD. It showed that the films have very high sensitivity to alcohol, acetone and SO2. The influence of temperature, composite concentration and gas concentration on the gas sensing capability of the films had also been studied.6.Surface property and surface reaction process of TiO2 had been investigated and the influence of impurities upon the TiO2 had been researched. TiO2 adsorbing O2 H2 and H2O have been analyzed. K-V symbol and point defects had been used to discuss the mechanism of gas-sensor of metal-oxide. It was concluded that the electric conductivity coefficient of TiO2 thin film is proportional to oxygen pressure ? 16 square in normal atmosphere pressure and is proportional to oxygen pressure ? 14 square in low pressure.7 . In this paper, first-principles calculations within the Local Density Approximation (LDA) was carried out on studying the character of the band structure, bond length, density of states and population of TiO2 with defect. By comparing with perfect crystal, it was found that in the case of oxygen vacancy Fermi energy goes up and no defect level appears in the gap and in the case of titanium vacancy Fermi energy goes down and a defect level appears in the gap, which is about 0.4eV above Fermi energy in rutile and about 0.25eV above Fermi energy in anatase.8.The electronic structure of N, S, C doping TiO2 would made band gap narrow in different extent, which is advantageous to decrease the gap width and improve the sensor activity of TiO2.9.The atomic and electronic structure of rutile TiO2 (110) surface was given using DFT. It was found that the relaxation and restructure occur on (110) surface, and the corresponding distance of the relaxation decreases with increasing in the atomic layer thickness. The width of forbidden band gap at the surface decreases so that it shows the quasi-metal property. The highest occupied and the lowest unoccupied molecular orbits are composed of the p orbit s and d orbit s of the Ti atoms. The active sites are localized at the surface Ti4+ sites.10.Rutile TiO2(110) surface with absorption H2 were studied by using DFT. It was discovered that H-H band and Ti-O band split and O-H band combined. By analyzing band structure and density of states, it was found that the gap decreased and the conductance increased because of adsorption of H2. s-p hybrid orbital and similar s-p band was formed in value band. It was evidenced that electron moved locally in rutile (110) surface.
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