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 inter-changeable during scanning. An extended irradiation time (68 min) can lead to the formation of a TiO2(110) surface with pre-dominant 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.