Observation of a two-dimensional electron gas at the surface of annealed   SrTiO3 single crystals by scanning tunneling spectroscopy
  Scanning tunneling spectroscopy suggests the formation of a two dimensional electron gas (2DEG) on the TiO2 terminated surface of undoped SrTiO3 single crystals annealed at temperature lower than 400 {\deg}C in ultra high vacuum conditions. Low energy electron diffraction indicates that the 2D metallic SrTiO3 surface is not structurally reconstructed, suggesting that non-ordered oxygen vacancies created in the annealing process introduce carriers leading to an electronic reconstruction. The experimental results are interpreted in a frame of competition between oxygen diffusion from the bulk to the surface and oxygen loss from the surface itself. 
R. Di Capua, M. Radovic, G. M. De Luca, I. Maggio-Aprile, F. Miletto   Granozio, N. C. Plumb, Z. Ristic, U. Scotti di Uccio,...
cond-mat.mtrl-sci cond-mat.other