Stoichiometry-driven switching between surface reconstructions on SrTiO 3 (001).

Controlling the surface structure on the atomic scale is a major difficulty for most transition metal oxides; this is especially true for the ternary perovskites. The influence of surface stoichiometry on the atomic structure of the SrTiO3(001) surface was examined with scanning tunneling microscopy, low-energy electron diffraction, low-energy He+ ion scattering (LEIS), and X-ray photoelectron spectroscopy (XPS). Vapor deposition of 0.8 monolayer (ML) strontium and 0.3ML titanium, with subsequent annealing to 850°C in 4×10−6mbar O2, reversibly switches the surface between c(4×2) and (2×2) reconstructions, respectively. The combination of LEIS and XPS shows a different stoichiometry that is confined to the top layer. Geometric models for these reconstructions need to take into account these different surface compositions.