Quantitative analysis of X-ray photo emission spectra, acquired on c-axis oriented high-T_c superconducting YBa₂Cu₃O_7-δ thin films

Angle-resolved X-ray photoemission spectroscopy (ARXPS) was performed on c-axis oriented high-Tc superconducting YBa2Cu3O7−δ thin films. The layered structure of the YBa2Cu3O7−δ films was used to develop a model for the quantitative analysis of the ARXPS experiments. Our XPS results may be compared to spectra taken on YBa2Cu3O7−δ single-crystal surfaces. On the spectra features are supposed that are assigned to a thin non-superconducting surface layer. For the first time, relative ARXPS measurements show that the interface between the superconducting YBa2Cu3O7−δ film and the surface layer is formed by the atomic Y layer. The surface layer consists mainly of BaCO3 and C, A small volume fraction (≈20%) contains Ba- and Cu-oxides, probably in the form of BaCuO2. From absolute ARXPS measurements, the thickness of the surface layer was calculated to be 0.93 ± 0.06 nm. It is shown that the surface roughness of our films is on the order of 0.6 nm. A good agreement between theory and experiment has been found in this report.