Imaging Ultraviolet Light-Induced Oxygen Vacancy Diffusion on TiO₂(110) Surface

We report here scanning tunneling microscopy (STM) observations of bridge-bonded oxygen vacancies (OVs) on the TiO₂(110) surface diffusing under the influence of 266 nm ultraviolet (UV) laser irradiation. OV pairs, and even OV trimers, were formed as a result of UV light-induced OV diffusion. There are two stable STM representations of the OV-pair defects, which are interchangeable during scanning. An extended irradiation time (68 min) can lead to the formation of a TiO₂(110) surface with predominant OV-pair point defects. Our results enrich the understanding of OV behavior upon UV irradiation, and future photocatalytic studies on reduced rutile TiO₂(110) surfaces involving 266 nm UV light can benefit from the knowledge of the observed diffusion of OVs and the formation of OV oligomers. We also provide a plausible way to prepare an OV-pair abundant TiO₂(110) surface, a requisite for further investigations of the otherwise unapproachable defects.