Surface composition of clean, epitaxial thin films of YBa2Cu3O7−x from quantitative x-ray photoemission spectroscopy analysis

Abstract

Angle-dependent x-ray photoemission spectra (XPS) of epitaxial thin-film ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ show characteristic reversible and distinct changes with different surface treatments. These changes are analyzed by applying a new model for the quantitative XPS analysis, which takes into consideration the anisotropic structure of c-axis-oriented ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$. The analysis makes it possible to differentiate between different elemental compositions of the outer layers in the surface unit cell. Evaluations of our experimental data indicate that only surfaces with a nominal BaO and CuO layer composition exist in the outermost atomic layer.