MODIFICATIONS IN THE ELECTRONIC-STRUCTURE OF BI2212 SINGLE-CRYSTALS INDUCED BY OXYGEN DESORPTION

We report a LEED, UPS and EELS study of Bi2Sr2CaCu2O8+delta single cry stal. The oxygen stoichiometry of a few layers below the surface was m odified by annealing in UHV at 250, 350 and 460 degrees C, and restore d with subsequent annealing at 750 degrees C in an O-2 atmosphere. It has been shown that, at lower temperatures, the disordered extra-stoic hiometric oxygen atoms desorb from the surface Bi-O plane, then at hig her 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 EE LS features, reconciling most of the published EELS data, has been per formed, taking into account the dependence of the EELS spectra of Bi22 12 on the primary electron beam energy and on the annealing treatments .