Photoemission study of high Tc oxide superconductors

The discovery of superconductivity above 30 K in oxide systems has given rise to a large variety of studies aimed at fully understanding their electronic and geometric structure. Photoemission spectroscopy can be an excellent technique for probing bonding, composition and oxidation state in these materials. The surface sensitivity of the technique, requires that surface preparation procedures be carefully scrutinized so as to ensure that the photoemission spectra are truly representative of the bulk material. Ion bombardment sputter cleaning is often used as a technique to remove contamination prior to surface analysis. However, since these compounds contain oxidized Cu, sputter cleaning of the samples is not possible due to the likelihood of sputter induced decomposition. Thus, both fracturing and scraping were explored as methods for surface preparation of YBa/sub 2/Cu/sub 3/O/sub 7/ ceramic oxides. Significant amounts of impurity BaCO/sub 3/ are found on the fractured surfaces whereas less is observed on the scraped surfaces. The BaCO/sub 3/ appears to be segregated at the grain boundaries. The implications of this result to the valence band spectra as well as to the processing of these materials and their critical current characteristics is discussed. The authors have also used photoemission to study surface and interfacial properties of the YBa/sub 2/Cu/sub 3/O/sub 7/ ceramic and its interfacial reactions with various metals