Figure 9

XPS spectra of Ti 2p states from the TiO ₂ films. Samples were annealed at 1,000°C after removing 3-nm surface layer by Ar⁺ ion sputtering (a); annealed at 1,000°C without Ar⁺ ion sputtering (b); and annealed at 800°C without Ar⁺ ion sputtering (c). The dashed curves are multiple-peak Gaussian fitting of the Ti 2p_3/2 peak with two components from the valence states of Ti⁴⁺ (blue) and Ti³⁺ (red).