In situ formation and characterization of oxygen vacancies in SnO₂ and WO₃ in near-ambient pressure hard X-ray photoelectron spectroscopy

Abstract Detection of a small amount of oxygen vacancies is often difficult. In this study, using near-ambient pressure hard X-ray photoelectron spectroscopy, oxygen vacancies were formed in situ in SnO 2 − x and WO 3 − y under a reducing gas atmosphere. The number of oxygen vacancies was so small that they could not be detected in the core-level photoelectron spectra. However, the effects of the vacancies were observed in the valence band spectra. This is because under the measurement conditions, the relative sensitivity of the metal outer orbitals (Sn 5s and W 5d) occupied when the oxygen vacancies are formed is significantly higher than that of the O 2p orbital predominantly forming the valence band. The x and y values were estimated to be ∼0.007–0.01 and ∼0.008–0.02, respectively, which correspond to vacancy ratios of sub-percent.