HREELS STUDY OF YBA2CU3O7-X SURFACES

The high-T(c) superconductor YBa2Cu3O7-x(100) surface was studied by high-resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). Both thin films and cleaved single crystals were investigated. The surfaces of the epitaxially grown thin films were contaminated with carbon which could be removed by sputtering with Ar+ ions. HREEL spectra of these sputtered surfaces exhibit losses at 440 and 630 cm-1. A high background was also found in the HREEL spectra. The background diminishes with decreasing temperature, which is typical of non-conducting materials. The surfaces of the cleaved single crystals were contamination-free. The LEED pattern corresponds to a (1 X 1) structure. In the HREEL spectra losses at 365, 453 and 630 cm-1 were found. These losses could also be observed far above T(c) and are due to different vibrations of the oxygen atoms. The appearance of the mode at around 630 cm-1 for both the thin films and cleaved single crystals shows that in both cases non-superconducting layers exist on the surface.