Introductory guide to the application of XPS to epitaxial films and heterostructures

Abstract

XPS is an important characterization method for epitaxial films and heterostructures. Although standard approaches for XPS data collection and analysis provide useful information such as average composition and the presence of contaminants, more in-depth analyses provide information about the film structure, surface termination, built-in electric potentials, and band offsets. The high degree of structural order in these materials enables such information to be extracted from spectral data but also adds complications to the analysis. This guide highlights three topics of importance in this field: (i) the impacts of crystallinity on XPS signals and quantification, (ii) the unexpected spectral line shapes that can occur in unusual or novel materials, and (iii) the ability of XPS to yield information about built-in potentials and band offsets. Concepts are demonstrated using complex oxide heterostructures. Although these topics are highly relevant to epitaxial films and heterostructures, they also apply to single crystals of complex materials.