Tuning the oxidation state of titanium dioxide mesoporous film by 1000 eV argon ion beam irradiation

This work proposes the creation of oxygen vacancies on the surface of TiO₂ mesoporous film using a 1000 eV argon ion (Ar⁺) beam. After X-ray photoelectron spectroscopic characterization, the survey spectra of TiO₂ nano-particles reveal the presence of oxygen (with chemical state O 1s), titanium (with chemical state Ti 2p), carbon (with chemical state C 1s) and argon (with chemical state Ar 2p) while the concentrations of each chemical states vary with an irradiation time of the Ar⁺ beam. The acquired Ti 2p spectra show five peaks at high resolution which correspond to Ti⁴⁺ 2p_3/2, Ti⁴⁺ 2p_1/2, Ti³⁺ 2p_3/2, Ti³⁺ 2p_1/2, and Ti²⁺ 2p_1/2. The concentrations of Ti²⁺ and Ti³⁺ increase with irradiation time while the concentrations of Ti⁴⁺ decrease as the irradiation time increases. Three peaks characterize high-resolution spectra of O 1s which correspond to lattice oxygen, oxygen vacancy, and adsorbed oxygen. The peak area of lattice oxygen decreases with irradiation time while that of oxygen vacancies increases with irradiation time which shows the creation of oxygen vacancies at the expense of contaminant removal due to Ar⁺ exposure. Valence spectra analysis shows an insignificant effect on the valance band as the sample exposure to Ar⁺ increases. This proposed method of oxygen vacancy creation would facilitate the effective utilization of TiO₂-based semiconductors in addressing many photo-catalytic challenges and widening the sunlight absorption capacity of the semiconductor.