Correlation between surface morphology and hydrophilic/hydrophobic conversion of MOCVD-TiO2 films

The relationship between hydrophilicity and surface morphology of TiO2 film was investigated. TiO2 films were deposited by MOCVD, and anatase films were crystallized. The rougher the surface of anatase film, the slower the conversion from hydrophilic to hydrophobic state. Also in some films, even the sonication could not accelerate the kinetics. However, the recovery rate to hydrophilicity under UV illumination had a reverse dependency on the surface roughness. It was assumed that the rougher TiO2 films could have a large concentration of Ti3+ generated by UV illumination on the surface, which plays a major role as adsorption sites of -OH in the water as well as in the air. Therefore, the healing kinetics of Ti3+ by oxygen in the air of a dark room could have been different among films with various surface roughnesses. Conclusively, the sustaining tendency of hydrophilic or hydrophobic properties could mainly depend on the concentration of Ti3+ by UV light, and in turn on the processing conditions of film deposition.