2×2R45∘ reconstruction and electron doping at the SrO-terminated SrTiO3(001) surface
AbstractThe atomic and electronic structure of SrTiO3(001) surfaces is investigated by low-energy electron diffraction, Auger electron spectroscopy, atomic force microscopy, ultraviolet photoemission spectroscopy (UPS), and theoretical calculations. While the surface is TiO2-terminated after annealing at 1225∘C for 72 h, an SrO-terminated surface is realized along with a 2×2R45∘ reconstruction after annealing at 1275∘C for 72 h. The stability of the surface structure revealing a 2×2R45∘ is evaluated by first-principles calculations, which shows that the most stable surface is a periodically SrO-deficient surface. Furthermore, UPS measured on the SrO-terminated 2×2R45∘ surface shows an upward band bending as compared to the TiO2-terminated surface. Neither in-gap nor metallic states are formed by doping electrons to the 2×2R45∘ surface in contrast to the TiO2-terminated surface.