Effect of capping layers on the near-surface region of SrVO₃ films

Surfaces of correlated electron oxides are of significant interest from both fundamental and applied perspectives. Many such oxides feature a near-surface region (NSR) that differs from the bulk’s properties. The NSR can significantly affect the interpretation of the material’s electronic structure, especially for those in thin film form, and have detrimental effects for applications such as field effect devices and catalysts. In this work, we study the changes in the composition and the electronic structure of the NSR of SrVO₃ (SVO) thin films. We employ x-ray photoelectron spectroscopy (XPS) and compare TiO_x-capped SVO films to identical uncapped films that were exposed to ambient conditions. The significant overoxidation of the SVO surface in the bare film, illustrated by a primary V⁵⁺ component, is prevented by the TiO_x layer in the capped film. The capped film further exhibits a decrease in Sr surface phases. These results demonstrate the importance and potential of such capping layers in preserving the bulk properties of correlated oxides in their NSR, enabling more accurate probes for their underlying physics and offering a route for their integration into devices.