TiO2 nanorod films grown on Si wafers by a nanodot-assisted hydrothermal growth

Abstract We report the controlled hydrothermal growth of rutile TiO 2 nanorods on Si wafers by using an anatase TiO 2 nanodot film as an assisted growth layer. The anatase nanodot film was prepared on the wafer by phase-separation-induced self-assembly and subsequent heat-treatment at 500 °C. The nanodots on the wafer were then subjected to hydrothermal treatment to induce the growth of rutile TiO 2 nanorod films. The size and dispersion density of the resulting TiO 2 nanorods could be varied by adjusting the Ti ion concentration in the growth solution. The TiO 2 nanorods were of the rutile phase and grew in the [001] direction. The growth mechanism reveals that the growth of the rutile nanorods was wholly dependent on the existence of rutile TiO 2 seeds, which could be formed by the dissolution–reprecipitation of the anatase nanodots during hydrothermal treatment or under the high-temperature conditions of the subsequent heat-treatment of the as-prepared nanodots. In controlling the rutile nanorod growth, the anatase nanodots show more efficiency than a dense anatase film. Preliminary evaluations of the rutile nanorod films have demonstrated that the wettability changed from highly hydrophobic to superhydrophilic and that the photocatalytic activity was enhanced with increasing nanorod dispersion density.