Structure and electronic states on reduced SrTiO3(110) surface observed by scanning tunneling microscopy and spectroscopy

Abstract

The SrTiO3(110) surface, after annealing in ultrahigh vacuum (UHV) was observed by scanning tunneling microscopy/spectroscopy (STM/S). These observations were compared with the ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS) data previously reported. The surface, after annealing at 800 °C, is dominated by flat regions where tunneling spectra are of metallic character, in agreement with the UPS data that showed a clear cutoff at the Fermi energy, EF. After annealing above 1000 °C, step edges along [11̄0] and rowlike structures along [001] with spacing ∼2.2 nm, close to 4√2a, are observed. The tunneling spectra showed an energy gap and an in-gap state ∼1 eV below EF, both of which are similar to those reported on the SrTiO3(100) surface after annealing in UHV. After 20 cycles of annealing above 1000 °C, a new ordering with c(2×6) periodicity is observed on the terraces. The STM/S results are explained by formation of (100) and (010) microfacets in the course of annealing in vacuum.