On the Crystal Structural Control of Sputtered TiO₂ Thin Films

In this study, we focused on the origin on the selective deposition of rutile and anatase TiO₂ thin films during the sputtering process. The observation on microstructural evolution of the TiO₂ films by transmission electron microscopy revealed the coexistence of rutile and anatase TiO₂ phases in the initial stage under the preferential growth conditions for the anatase TiO₂; the observations further revealed that the anatase phase gradually dominated the crystal structure with increasing film thickness. These results suggest that the bombardment during the sputtering deposition did not obviously affect the TiO₂ crystal structure, and this was also confirmed by off-axis magnetron sputtering experiments. We also investigated the mechanism of the effect of Sn impurity doping on the crystal structure using first-principles calculations. It is found that the formation energy of Sn-doped rutile TiO₂ is lower than that of Sn-doped anatase TiO₂; this suggests that the Sn-doped TiO₂ favours the rutile phase. These results offer a guideline for the utilization of selective deposition of rutile and anatase TiO₂ thin films in various industrial applications.