Atomic-Scale Surface Structures of TiO2(110) Determined by Scanning Tunneling Microscopy: A New Surface-Limited Phase of Titanium Oxide

Abstract

The structure transformation of a TiO2(110) surface was observed at atomic-scale resolution by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Irregular corrugations on an argon-bombarded TiO2(110) surface crystallized to stacked (1 × 1) terraces by vacuum annealing at 600—800 K. The terraces grew in dimension to be as large as 30 × 30 nm2 at 900 K. The unoccupied surface states localized on individual Ti4+ ions were resolved on a (1 × 1) terrace. The position of the Ti4+ ions was probed by imaging adsorbed formate ions. Annealing at higher temperatures resulted in the formation of a wide row structure comprising double strands. Imaging of individual adsorbed formate ions was used to grade possible structure models by probing Ti ions exposed on the surface; thereby, an added Ti2O3 row model, which is a new surface-limited phase of titanium oxide consisting of Ti3+ ions of the optimum six-fold coordination, was concluded for the double-strand structure. These results demonstrate the ability of probing experiments with an adsorbed molecule to determine the chemical nature of imaged sites on multi-component materials by STM.