DETERIORATED LAYER FORMED ON BI2SR2CACU2OY SINGLE-CRYSTAL SURFACES

Various deteriorated surfaces of Bi2Sr2CaCu2Oy single crystals are inv estigated by X-ray photoelectron spectroscopy (XPS). From the results, it is found that the Ca 2p, 3/2 XPS peak position shifts to the highe r-energy side and its half-width becomes broader by exposing the air-c leaved surface of the cry stal to an atmosphere of CO2. This indicates that CaCO3 is produced by CO2 gas exposure for 40 min. The valence st ate of Cu changes from 2+ to 1+ by air, O-2, and CO2 gas exposure. Two XPS peaks at about 532 and 531 eV, which are probably related to the impurity oxides and carbonates, respectively, are observed in the XPS spectra of O 1 s core levels.