An in situ study on the depth-resolved chemical states of undoped SrTiO3(001) surfaces during Ar+ sputtering and annealing processes with XPS

Abstract

With synchrotron-based depth-resolved XPS measurements, the modification of the surface chemical states and the behavior of various impurities on undoped SrTiO₃(001) surfaces are investigated. During the Ar⁺ sputtering process, both the formation of oxygen vacancies in the TiO₂ layer and the formation of the SrO layer are found. When the UHV annealing process starts, the oxygen vacancies in the TiO₂ layer start to decrease, indicating oxygen migration from the bulk to the surface region. In the annealing step at 873 K, the concentration of the oxygen vacancies starts to increase due to the lattice oxygen loss to a UHV atmosphere. Throughout the surface preparation process, the sample impurities always exist on the surface with a small variation in their chemical states. The variation of the chemical states of SrTiO₃ and its impurities is an indication of the oxygen exchange during the sample preparation process. Our results provide valuable insights on how the elements of SrTiO₃ behave during the surface preparation process and interact with surface impurities.