High-temperature annealing in air is used to produce SrTiO3 (111) surfaces with two types of atomically flat terraces: those that promote photoanodic reactions and those that promote photocathodic reactions. Surface potential measurements show that the photocathodic terraces have a relatively more positive surface potential than the photoanodic terraces. After depositing thin TiO2 films on the surface, from 1 to 13 nm thick, the surface of the film above the photocathodic terraces also has photocathodic properties, similar to those of the bare surface. While a more positive surface potential can be detected on the surface of the thinnest TiO2 films (1 nm thick), it is undetectable for thicker films. The persistence of the localized photocathodic properties on the film surface, even in the absence of a measurable difference in local potential, indicates that the charge associated with specific terraces on the bare SrTiO3 (111) surface remains localized at the TiO2/SrTiO3 interface and that the buried charge influences the motion of photogenerated carriers.
Keywords: SrTiO3; TiO2; atomic force microscopy; heterostructure; photochemical reactivity.