Buried Charge at the TiO₂/SrTiO₃ (111) Interface and Its Effect on Photochemical Reactivity

High-temperature annealing in air is used to produce SrTiO 3 (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 TiO 2 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 TiO 2 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 SrTiO 3 (111) surface remains localized at the TiO 2 /SrTiO 3 interface and that the buried charge influences the motion of photogenerated carriers.