Structure and apparent topography of TiO2 (110) surfaces

TL;DR

This study uses ab-initio calculations and STM simulations to analyze TiO2 (110) surfaces, revealing how electronic effects influence observed topography and favoring an added-row surface structure in oxygen-deficient conditions.

Contribution

It provides a detailed theoretical analysis of TiO2 (110) surface structures and their STM imaging characteristics, clarifying the apparent topographic contrast and surface stability.

Findings

STM images are dominated by undercoordinated Ti atoms.

Apparent topography can reverse due to electronic effects.

Added-row structure is energetically favored for oxygen-deficient surfaces.

Abstract

We present self-consistent ab-initio total-energy and electronic-structure calculations on stoichiometric and non-stoichiometric TiO2 (110) surfaces. Scanning tunneling microscopy (STM) topographs are simulated by calculating the local electronic density of states over an energy window appropriate for the experimental positive-bias conditions. We find that under these conditions the STM tends to image the undercoordinated Ti atoms, in spite of the physical protrusion of the O atoms, giving an apparent reversal of topographic contrast on the stoichiometric 1x1 or missing-row 2x1 surface. We also show that both the interpretation of STM images and the direct comparison of surface energies favor an added-row structure over the missing-row structure for the oxygen-deficient 2x1 surface.