CHARACTERIZATION OF ARGON-ION-BOMBARDED AND CHEMICALLY ETCHED Y1BA2CU3O7-DELTA-SINGLE CRYSTAL-SURFACES

This XPS surface study shows that it is difficult to ''clean'' the a-b surfaces of large tetragonal and orthorhombic YBCO single crystals by either chemical etching or argon-ion-bombardment. For both treatments a carbon contamination peak was detected and found to arise from random patches on the large surfaces. However, both chemical etching and low angle ion-bombardment resulted in minimum disruption to the surface atom termination. For the chemically etched surfaces of the YBCO crystals the 0 1 s emission spectra have been analysed and the origin of the component peak discussed. The pairs of peaks centred at 527.5, 528.2 eV and 527.5, 528.8 eV are considered to be intrinsic to the o- and t-structures. For 45-degrees incidence ion-bombarded surfaces of o- and t-YBCO crystals, both show the O 1s spectrum and the Cu(L3VV)-Auger transition to be identical and consequently the surface structures formed are considered to be identical. In fact, these surfaces appear to have Cu2BaO2 formed in the surface region. Valence-band and low energy core level emissions are reported for the chemically etched surfaces of both types of crystals. In the case of the tetragonal crystals the valence-band spectrum is more intense and a significant difference is observed in the shape of the band at approximately 3 eV compared to that obtained from orthorhombic crystals. After ion-bombardment both spectra were very similar, the valence-bands having a maximum at 3.7 eV, increased intensity relative to the Ba 5p but were almost devoid of fine structure.