Orthorhombic YBa₂Cu₃O₇ Cleaved Single Crystal by XPS

X-ray photoemission spectra from the cleaved surface of a single crystal of the high temperature superconductor, YBa2Cu3O7, are presented. All spectra were taken with the sample at room temperature. The spectra of this material are dependent on which cleavage planes are exposed following crystal fracture. Extremes in the spectra are given from the continuum of observed surfaces. These extremes are obtained from cleaves leaving large macroscopic terrace planes (larger than probe size), and from cleaves leaving highly stepped surfaces with microscopic terraces (smaller than the probe size). A distinct Fermi edge is observed in the valence band. The freshly cleaved surface is free from contamination, but the spectral line shape of O 1s changes with time. This may be related to the formation of contamination compounds and/or a chemical bonding instability at the cleaved surface of the superconductor.