Surface and interface chemical composition of thin epitaxial SrTiO3 and BaTiO3 films: Photoemission investigation

Abstract

In this work, we use SrTiO3 and BaTiO3 films (thickness <10nm) epitaxially grown on Si(100) substrates, and x-ray and ultraviolet (UV) photoemission spectroscopy to investigate the effect of surface preparation on chemical and electronic film and interface properties. Depending on the surface treatment, e.g., ex situ UV generated ozone or annealing in oxygen or vacuum, the valence band maximum position shifts by more than 2eV, whereas the oxide core levels shift by less than 0.6eV. These findings indicate that extremely careful cleaning procedures must be applied, as surface composition and film morphology are of paramount importance in the determination of the electronic structure of the crystalline oxides. In addition, the interfaces between SrTiO3 and BaTiO3 and Si are shown to be unstable at annealing temperatures required to thoroughly clean and order the surface.