Cathodoluminescence microscopy and spectroscopy of superconducting Bi_2Sr_2CaCu_2O_(8+x) single crystals

Cathodoluminescence (CL) microscopy and spectroscopy in the scanning electron microscope have been applied to the microcharacterization of superconducting Bi2Sr2CaCu2O8+x single crystals. CL spectra representative of the samples at macroscopic level, exhibit at low temperature two well resolved emission bands, centered at about 2.90 and 2.35 eV respectively, related to electronic processes in the oxygen sublattice. Panchromatic CL images reveal that regions with enhanced intensity usually correspond with growth layers or other topographic features of the crystals. CL spectra from the mentioned regions show a relative increase of the local oxygen deficiency related 2.3-2.4 eV emission band. The complex character of this band is revealed by CL spectroscopy, and by CL monochromatic images that relate certain peaks observed in the spectra to specific luminescent areas. Comparison of the present observations with previous luminescence studies of other high temperature superconductors, indicates that a possible origin of the 2.3-2.4 eV CL emission band lies in the Cu-O planes, common to these materials