Investigation of the photoreactivity of nanocrystalline TiO2 thin film by ion-implantation technique

A RF sputtering technique was employed to prepare transparent, nanocrystalline and photocatalytic TiO2 thin film with complete anatase phase on a borosilicate glass substrate. During the determination of the optimal sputtering parameters, it was found that the photocatalytic activity decreased with an increase of Ar/O2 sputtering gas pressure from 2 to View the MathML source, whereas a blue-shift behavior was observed in the absorption spectra which implies that the particle size decreases slightly. On the other hand, an ion implantation technique was used to improve the photoreactivity of the TiO2 thin film through surface modification. With different doses of Sn ion implantation, the photoreactivity of the nanocrystalline TiO2 thin films is improved obviously, but there exists an optimal implanted dose for improving the photoreactivity. Sn, as Sn4+, is thought to be substitutional on the Ti lattice site. The red shift in the absorption spectra shows that, when the Sn ions are implanted into the lattice of TiO2, the electron (hole) trapping states are formed between the valence band top and the conduction band bottom of the TiO2 particles. This suppresses the recombination of the photogenerated electrons and holes and improves the photoreactivity. However, the excess Sn-implanted doses induce the formation of impurity-defect complexes, which become the recombination center of the photogenerated electron–hole pairs.