ENERGY-LOSS AND CHARGE-EXCHANGE STUDIES OF CLEAVED YBA2CU3O7-DELTA SINGLE-CRYSTAL SURFACES

The results of reflection, electron energy loss spectroscopy studies of the a-b surfaces of orthorhombic single crystals of YBa2Cu3O7-delta have been reported. The surfaces studied were produced by either cleavage or argon ion-bombardment and the loss transitions are detailed for the energy range of 3 to 27 eV. In the case of the cleaved surfaces, the data is very similar to that previously reported for clean surfaces, but since different origins have been assigned to some of the same loss transitions, we present an attempt at a new and consistent interpretation for the data. Our interpretation for each transition is based on a comparison of peak positions from cleaved surfaces with those from ion-bombarded and therefore non-intrinsic surfaces. The observed shifts in the positional energies of the loss and XPS peaks for the ion-bombarded surfaces (compared with the cleaved surface data) are correlated. For a higher electron irradiation dose and a primary energy close to the O1s-O2p threshold, we observed the dipole forbidden O2p-O2p charge exchange excited transition. Its relative intensity increased with increase of the electron dose indicating electron irradiation induced oxygen diffusion to the surface. This resonance effect is strongly dependent on the oxygen content of the YBCO crystals and could be used as a sensitive technique to monitor the relative changes in the surface oxygen content of these crystals in UHV.