Engineering two-dimensional electron gases at the (001) and (101) surfaces of TiO2 anatase using light

TL;DR

This study demonstrates the formation of two-dimensional electron gases at TiO2 anatase surfaces, revealing their electronic structure, anisotropy, and how UV light can modify these properties for potential nano-engineering applications.

Contribution

It provides the first detailed characterization of 2DEGs at different TiO2 anatase surfaces and shows how UV radiation can control their electronic states.

Findings

2DEGs exist at (001) and (101) surfaces of TiO2 anatase.

The (001) 2DEG is isotropic, while the (101) 2DEG is anisotropic.

UV radiation can eliminate the 2DEG by altering surface stoichiometry.

Abstract

We report the existence of metallic two-dimensional electron gases (2DEGs) at the (001) and (101) surfaces of bulk-insulating TiO2 anatase due to local chemical doping by oxygen vacancies in the near-surface region. Using angle-resolved photoemission spectroscopy, we find that the electronic structure at both surfaces is composed of two occupied subbands of d_xy orbital character. While the Fermi surface observed at the (001) termination is isotropic, the 2DEG at the (101) termination is anisotropic and shows a charge carrier density three times larger than at the (001) surface. Moreover, we demonstrate that intense UV synchrotron radiation can alter the electronic structure and stoichiometry of the surface up to the complete disappearance of the 2DEG. These results open a route for the nano-engineering of confined electronic states, the control of their metallic or insulating nature, and the tailoring of their microscopic symmetry, using UV illumination at different surfaces of anatase.