Effect of surface oxygen vacancies on electronic states of reduced SrTiO3(110) surface

The electronic structure of reduced SrTiO₃(110) surface prepared by annealing in ultrahigh vacuum (UHV), has been studied using photoemission spectroscopy (PES) and scanning tunneling microscopy/spectroscopy (STM/STS). In the PES spectra of reduced SrTiO₃(110) surface after annealing in UHV at 800°C, a clear metallic state with a sharp Fermi cut-off and a broad state centered at ∼1.1eV below the Fermi level are observed in the band gap region. A Ti3p->3d resonance enhancement is occurred for the metallic state, but not for the ∼1.1eV state. On the other hand, after the sample was annealed in UHV at 1000°C, it has been shown that the metallic state becomes drastically weak, and that only the ∼1.1eV state is seen in the band gap region. Thereafter, the ∼1.1eV state exhibits a clear Ti3p->3d resonance enhancement. The difference in the spectral feature of these band gap states is directly related to the surface geometric structural change.