Observation of a two-dimensional electron gas at the surface of annealed SrTiO3 single crystals by scanning tunneling spectroscopy

TL;DR

This study demonstrates the formation of a two-dimensional electron gas on SrTiO3 surfaces through annealing, revealing how oxygen vacancies induce surface conductivity without structural reconstruction.

Contribution

It provides direct experimental evidence of 2DEG formation on SrTiO3 surfaces via scanning tunneling spectroscopy and analyzes the role of oxygen vacancies in this process.

Findings

2DEG observed on annealed SrTiO3 surface

Surface remains structurally unreconstructed

Oxygen vacancies induce surface metallicity

Abstract

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.