Effect of H2 on the Microstructure and Properties of TiO2 Films Grown by Atmospheric Pressure MOCVD on Steel Substrates

TiO2 thin films were deposited under atmospheric pressure by MOCVD in the range 400-600 °C on various steel substrates under hydrogen ambiance. It is unusual to study the growth of functional oxide layers under H2 partial pressure, i.e. a reactive gas generally used as reductive atmosphere in CVD. Titanium tetra-isopropoxide was used as single source precursor of Ti and O. The growth rate of TiO2 layers grown under nitrogen increases with the temperature and reaches a maximum in the range 500-550 °C. At these temperatures the diffusion of substrate ions enhances the formation of rutile leading to a lower UV photocatalytic activity. Addition of H2 in the input gas phase during the deposition (i) reduces the formation of interface oxide layer, (ii) prevents the diffusion of cations from the steel substrate toward the TiO2 layer and (iii) favors the growth of anatase. This leads to an increase of photocatalytic efficiency under UV irradiation