Photoresponse of surface oxygen defects on TiO2(1 1 0)

Using scanning tunneling microscopy (STM), the local photoresponse of a rutile TiO2(1 1 0) surface was investigated on the atomic scale. While the illumination of 325 nm ultraviolet (UV) light excited almost all the areas on the (1 1 0) surface, steps and (1 2) ridges that are associated with oxygen deficiencies and a ‘‘rosette’’ structure exhibited higher response intensities. Previously proposed photoexcitation mechanism involving oxygen defect states in the energy band gap is examined by exciting newly created defect sites. These sites did respond to the illumination, but interestingly, when the sites are being paired, only one of them were active for the visible light illumination