By using an alternative wet-etch procedure, high-quality atomically flat TiO2 terminated surfaces of SrTiO3 single crystals were obtained having a morphology which was equivalent to that of conventional wet-etching methods. By combining photoluminescence spectroscopy, reflection high-energy electron diffraction, atomic force microscopy imaging and soft X-ray absorption, it was possible to identify and monitor the complex evolution of O defect states and Ti valency at the surface and near-surface layers. The experiments revealed a high level of local defects, resulting in the presence of the Ti3+ states at the surface. A method was developed for controlling the defect states capable of a marked reduction in the defect concentration. It was demonstrated that photoluminescence and X-ray absorption were able to distinguish surface-related Ti3+ states from O vacancies trapping charge transfer vibronic excitons that defined the photoluminescence intensity.

Atomic Control and Characterization of Surface Defect States of TiO2 Terminated SrTiO3 Single Crystals. Kareev, M., Prosandeev, S., Liu, J., Gan, C., Kareev, A., Freeland, J.W., Xiao, M., Chakhalian, J.: Applied Physics Letters, 2008, 93[6],