Theoretical Analysis of STM Experiments at Rutile TiO_2 Surfaces

TL;DR

This paper uses a computationally efficient atomic orbital-based method to analyze the electronic structure and STM images of rutile TiO₂ surfaces, highlighting the relation between surface charge densities and experimental observations.

Contribution

It introduces a cost-effective first-principles approach to study oxide surfaces and their reconstructions, linking theoretical charge densities to STM imaging results.

Findings

Surface charge densities correlate with experimental STM images.

Positive bias images probe unoccupied Ti 3d states.

Oxygen atoms sit above Ti atoms, affecting image contrast.

Abstract

A first-principles atomic orbital-based electronic structure method is used to investigate the low index surfaces of rutile Titanium Dioxide. The method is relatively cheap in computational terms, making it attractive for the study of oxide surfaces, many of which undergo large reconstructions, and may be governed by the presence of Oxygen vacancy defects. Calculated surface charge densities are presented for low-index surfaces of TiO$_2$, and the relation of these results to experimental STM images is discussed. Atomic resolution images at these surfaces tend to be produced at positive bias, probing states which largely consist of unoccupied Ti 3$d$ bands, with a small contribution from O 2$p$. These experiments are particularly interesting since the O atoms tend to sit up to 1 angstrom above the Ti atoms, so providing a play-off between electronic and geometric structure in image formation.