Study On The Photocatalytic And Gas-sensitive Properties Of TiO₂ Semiconducting Thin Films

TiO₂ has been known as an n-type metal oxide semiconductor and an important inorganic function material.It can be used in fabricating medium material, photocatalytic films, reducing reflect coat, gas sensor, etc.TiO₂ films had excellent performance with photocatalysis, resisting photo erode, difficult dissolution in acidity condition, innocuity and stabilization in light and soon on. It can be regard as an excellent material with good prospect in wastewater treatment, sterilizing and air purification. TiO₂ can use a very small portion of solar energy because it only can be excitated only by ultraviolet radiation. In order to implement photo-catalysis in common condition, the band gap must be decrease. Doping is a good measure.In addition, with the industrialization development, the environments have been polluted more and more. TiO₂ have been known as a sensor material, exerting important function. But sensitivity and selectivity is seemed as the most important factor of restricting sensor development. Scientists have adopted different ways to change the microstructure of TiO₂ and electrical property in order to control the environment effectively.In this paper, photocatalytic property and gas-sensitive characterization has been studied, the principle of photocatalysis and preparation has been investigated and the approach of improving the photocatalytic efficiency has been put forward. TiO₂ films have been prepared by sol-gel method. It was found that the decompose efficiency to solution associated with the number of films layer; calcine temperature and PH value. Some analyses have been performed.TiO₂ films were also synthesized by reactive sputtering and chemical vapor deposition. Some gas-sensitive test to deoxidizing gas have carried out based on TiO₂ films by sputtering and doped some impurity. The experimental results showed that TiO₂ films have different electron injecting principle and reactive mechanism, the behaviors of gas-sensor for hydrogen and ethanol manifest dissimilitude. This is due to that the oxygen vacancies were compensated by the impurity. The sensitivity of TiO₂ films has been decreased as a result of the impurity doping. This is one of the innovations in this paper.In this paper, the TiO₂ gas-sensitive films produced by CVD were analyzed by XPS and SEM. The analysis data indicated that the TiO₂ films with excellent structuresof granule uniformity, few impurity, and large surface area could be obtained by CVD. It is very available to the gas-sensitive responses. It was also found that Nb-doped TiO₂ films were obstructed the formation of TiO₂ rutile structures over 1000℃ and led to improve sensitivity and decreasing work temperature. In this paper, K-V symbol and point defects have been used to discuss the mechanism of gas-sensor of metal-oxide. With this theory, the common rule of the change in conductance with the oxygen concentration has been summarized. The surface response has been studied. TiO₂ adsorbing O2 H2 and H2O has been analyzed. The ways of improving sensitivity and selectivity of TiO₂ have been brought forward.