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.

Energy of Step Defects on the TiO2 Rutile (110) Surface: An ab initio DFT Methodology

“…An island of unquestionable similarity on an annealed rutile (110) sample was also observed by Diebold et al 20 It is evident that the island shape predicted with a / morphology is inconsistent with the observed island shape for all values of . In contrast, the / morphology (or indeed / , which are not drawn but look very similar) produces an island shape which converges quite convincingly to that seen in experiments [19][20][21] by approximately 8 layers thickness and beyond. The predictions are clearly less reliable for slab thicknesses of less than about 7 layers.…”

“…Among these studies, Onishi et al 19 was the first to discover a new surface phase of highly organised "double-strand rows" after annealing at 1150 K, although we don't consider that phase…”

“…[10][11][12][13][14][15] The (110) surface of the rutile phase is particularly important because rutile is the most abundant macroscopic phase of TiO 2 and the (110) surface is the most stable surface of this phase, 16,17 comprising the majority of the total surface area in laboratory samples. Scanning tunnelling microscopy (STM) studies [18][19][20][21][22] have emerged since the early 1990's which invariably show that extended step defects comprise a very significant proportion of the overall surface area of rutile (110). Thus, a proper understanding of steps on the atomic level is crucial in moving towards a complete characterisation of this extremely important system, which has in many ways become the archetypal representative for transition metal oxide surfaces.…”

“…In published STM studies [18][19][20][21][22] of vacuum-annealed rutile (110) surfaces, terraces bound by extended step defects running almost exclusively along the and directions are observable, where the surface roughness is seen to decrease with higher annealing temperatures.…”

Measurement of the surface-growth kinetics of reducedTiO2(110)during reoxidation using time-resolved scanning tunneling microscopy

“…22,23 This shows that the species is diffusing along the troughs. The streaks result from the brief presence of the moving species underneath the tip for the time needed to scan one or two lines of the image.…”