Band offsets at the epitaxial anatase TiO2/n-SrTiO3(001) interface

We have used high-energy resolution X-ray photoelectron spectroscopy to measure valence band offsets at the epitaxial anatase TiO2(0 0 1)/n-SrTiO3(0 0 1) heterojunction prepared by molecular beam epitaxy. The valence band offsets range between -0.06 +/- 0.05 and +0.16 +/- 0.05eV for anatase thicknesses between 1 and 8 monolayers and three different methods of substrate surface preparation, with no systematic dependence on film thickness. The conduction band offset (CBO) varies over a comparable range by virtue of the fact that anatase and SrTiO3 exhibit the same bandgap (similar to 3.2 eV). In contrast, density functional theory predicts the VBO to be +0.55 eV. The lack of agreement between theory and experiment suggests that either some unknown factor in the interface structure or composition excluded from the modeling is influencing the band offset, or that density functional theory cannot accurately calculate band offsets in these oxide materials. The small experimental band offsets have important implications for the use of this interface for fundamental investigations of surface photocatalysis. Neither electrons nor holes are likely to become trapped in the substrate and thus be unable to participate in surface photocatalytic processes. (c) 2009 Elsevier B.V. All rights reserved.