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 °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.