Modification in the electronic structure of Bi2212 single crystals induced by oxygen desorbtion

We report a LEED, UPS and EELS study of Bi2Sr2CaCu2O8+delta single crystal. The oxygen stoichiometry of a few layers below the surface was modified by annealing in UHV at 250, 350 and 460 degrees C, and restored with subsequent annealing at 750 degrees C in an O-2 atmosphere. It has been shown that, at lower temperatures, the disordered extra-stoichiometric oxygen atoms desorb from the surface Bi-O plane, then at higher temperature an oxygen diffusion takes place from the Sr-O and Cu-O layers toward the surface Bi-O layer. An assignment of some Bi2212 EELS features, reconciling most of the published EELS data, has been performed, taking into account the dependence of the EELS spectra of Bi2212 on the primary electron beam energy and on the annealing treatments.