Observation and destruction of an elusive adsorbate with STM: O$_2$/TiO$_2$

TL;DR

This study uses low-temperature STM to observe O$_2$ molecules on TiO$_2$(110), revealing their dissociation at defects and the formation of O adatoms, clarifying the adsorption process at low temperatures.

Contribution

First direct STM observation of molecular O$_2$ adsorption and dissociation on TiO$_2$(110) at low temperatures, resolving previous controversies.

Findings

O$_2$ dissociates at defects on TiO$_2$(110)

Molecular precursor observed at vacancies at low temperature

O adatoms form after dissociation during STM imaging

Abstract

When a slightly defective rutile TiO$_2$(110) surface is exposed to O$_2$ at elevated temperatures, the molecule dissociates at defects, filling O vacancies (\ov) and creating O adatoms (\oad) on {\tifc} rows. The adsorption of molecular O$_2$ at low temperatures has remained controversial. Low-Temperature Scanning Tunneling Microscopy (LT-STM) of O$_2$, dosed on TiO$_2$(110) at a sample temperature of $\approx$ 100 K and imaged at 17 K, shows a molecular precursor at \ov as a faint change in contrast. The adsorbed O$_2$ easily dissociates during the STM measurements, and formation of \oad's at both sides of the original \ov is observed.