PNNL

Abstract

The surface structure of anatase TiO2(001) was investigated using scanning tunneling mircroscopy (STM), x-ray photoelectron spectroscopy (XPS), reflection high energy electron diffraction (RHEED), and low energy electron diffraction (LEED). A two-domain (1x4)/(4x1) reconstruction, similar to those previously reported in LEED and ion scattering studies, was observed by STM and RHEED. This reconstruction was found to be stable not only from room temperature up to 850 degrees Celcius in ultra-high vacuum and oxygen rich environments, but also during the anatase film growth. High-resolutions STM images obtianed at positive sample biases revealed two types of atomic rows within each surface unit cell, indicating different Ti-derived states at the surface. In contrast, XPS of the reconstructed surfaces showed no evidence of Ti3+ states. Based on the STM, XPS, RHEED, and LEED results, an "added" -and-"missing" -row model is proposed to account for the (1x4) reconstruction. Atomic steps and their relationship to the population of (1x4) and (4x1) domains were also investigated. Results showed that for vicinal surfaces, the domain population depended strongly on the overall surface step orientation. While populations of the (1x4) and the (4x1) domains were nearly equal on the flat (001) surfaces, they became signigicantly lopsided on the surface 2 degrees away from the (001) direction, demonstrating a strong correlation between surface steps and domain population on vicinal surfaces.