Surface hole–proton mixed conduction of Ti0.99Sc0.01O2−δ thin film with anatase structure

We have investigated the structural and electrical properties of the Sc3+-doped TiO2 (Ti0.99Sc0.01O2−δ) thin film with Anatase structure prepared by radio-frequency magnetron sputtering using a ceramic target. The thin film prepared at a substrate temperature of 300 °C was a single phase, which is closely matched to the X-ray diffraction peaks of the ceramic. The oxygen vacancy concentration was quantitatively evaluated through photoemission spectroscopy (PES) and defect chemical analysis. The electrical conductivity (σ) in the in-plane exhibited p-type semiconductor-like behavior with an activation energy of 0.56 eV and a positive Hall coefficient in the temperature range from 30 °C to 200 °C. The conducting carriers were estimated to be holes and protons from the Po2 dependence of σ, the increase in the energy gap, and the presence of OH- bond peaks in the O 1s-PES spectrum. These results indicate that the Ti0.99Sc0.01O2−δ thin film with Anatase structure has a hole–proton mixed conduction on the surface below 200 °C.