SURFACE-PROPERTIES OF CLEANED CERAMIC AND THIN-FILM YBA2CU3O7-X SAMPLES HEATED IN VACUUM OR EXPOSED TO H OR CL2

Surfaces of scrape-cleaned ceramic and of Or-annealed thin film samples of YBa2Cu3O7-x (YBCO) were studied at RT by applying Auger electron (AES) and electron energy-loss spectroscopy (EELS). Even after heating in O2, the film surfaces were found (by using AES) to be still chlorine-covered with 0.5 - 1.5 monolayers, while in the YBCO layer underneath the expected stoichiometric ratios of Y, Ba, and Cu could be confirmed. Approx. 25 different energy-loss features were recorded on both types of samples. Eight loss structures (90 eV < ΔE < 98 eV) are caused by electronic excitations from Ba 4d states. The experimental value of the bulk plasmon energy (24.8 eV) indicates surface-induced oxygen deficiency. Due to vacuum-annealing or exposure to H or Ch2 additional oxygen depletion is formed, mainly limited to a few atomic layers near to the surface. It can be detected most clearly by the energy loss of 4.4 eV caused by electron transitions in defect-induced O-Cu-O complexes. After H or Cl2 exposure, the thickness of the saturation-like surface layer is estimated from AES data. © 1990.