2×2R45∘ reconstruction and electron doping at the SrO-terminated SrTiO3 (001) surface

Abstract

The atomic and electronic structure of ${\mathrm{SrTiO}}_{3}$(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 ${\mathrm{TiO}}_{2}$-terminated after annealing at $1225{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ for 72 h, an SrO-terminated surface is realized along with a $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ reconstruction after annealing at $1275{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ for 72 h. The stability of the surface structure revealing a $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ 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 $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ surface shows an upward band bending as compared to the ${\mathrm{TiO}}_{2}$-terminated surface. Neither in-gap nor metallic states are formed by doping electrons to the $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ surface in contrast to the ${\mathrm{TiO}}_{2}$-terminated surface.