Preparation Of TiO₂ Films By Atmospheric Pressure Chemical Vapor Deposition & Study Of Doping Properties

In this paper a comprehensive introduction of titanium dioxide film, which was focused on photocatalysis and hydrophilicity, had been given. The research background, the self-clean characteristic and some kinds of preparation methods were discussed. A summary about the factors which affect the photocatalysed efficiency and hydrophilicity was made. The paper put forward an aim to deposit N-doped titanium dioxide film on glass substrate by the atmospheric pressure chemical vapor deposition (APCVD) method.Using TiCl4 and Oa as precursors, titanium dioxide thin films had been deposited by APCVD method. Nitrogen had also been doped in the film when N2O gas was added as the dopant. The hydropilicity and photocatalysis of the samples were studied.The effects of the substrate temperature, carrier gas flux, O2 flux and N doping level on the microstructure, composition and properties of the films have been studied synthetically. The film prepared at low temperature was amorphous TiO2 and it's photocatalysed efficiency was very low. With the subtrate temperature's increasing, the reaction rate increased, the crystal type was transfered from anatase to rutile, the roughness increased, causing the increase in hydropilicity. When substrates' temperature ranged from 450~550℃, The TiO2 films were composed with the mixture of rutile and anatase, and the photocatalysed efficiency was the best. With the carrier gas flux rising, the film's thickness and the degree of crystallization increase. The band gap decreased little, and the photocatalysed efficiency was enhanced. However the films' hydrophilicity was not dependent on the carrier gas flux. There is no direct relation between the O2 flux, crystal type and reaction rate. With the O2 flux rising, the photocatalysed efficiency decreases while the hydrophilicity increases. When the film is deposited at 450℃, a kind of square substance exists on the surface of it. It is identified as Na0.23 TiO2. Experiments has proved that it has a negative effect on the photocatalysed efficiency, but it has no influence on the hydrophilicity.The flux of N2O greatly affected the film's microstructure. As the N2O flux was increased, the content of anatase decreased and rutile increased gradually. The size of rutile became smaller with increase of the flux of N2O. When the flux was higher than 80 standard cubic centimeter per minute (sccm), the bedded growing substance appeared like the snowflake. It contained sodium. With the flux rising, the number of snowflakes was increased but the area which each snowflake occupied decreased. The absorption edge shifted to the longest wavelengh when N2O flux was 40sccm, then it shifted back to the shorter wavelengh with the N2O flux rising. Excessive or less N2O flux would lead the falling down of photocatalysed efficiency under the UV light irradiation. With the doping of N, the photocatalysed efficiency under visible light irradiation was improved obviously. Also the hydrophilicity of the film increased with the doping level's rising.