Electronic structure of ceramics and thin-film samples of high T c Bi2Sr2CaCu2O8+δ superconductors: Effects of Ar+ sputtering, O2 exposure, and Rb deposition

Abstract

The electronic structure of bulk, and, for the first time, thin‐film samples of the new class of high T_c Bi₂Sr₂CaCu₂O_8+δ superconductors, is investigated by photoemission spectroscopy using synchrotron radiation. Ar⁺ sputtering and Rb deposition result in disrupted Bi O bonds and subsequent change in the valency of Bi, while oxygen adsorption or annealing in oxygen is found to restore the Bi O bonds. The results also show that adsorbates of O₂ and/or Rb readily give rise to a number of new oxygen states in the valence band of Bi₂Sr₂CaCu₂O_8+δ. The Ar⁺‐sputtered film is found to be more sensitive to adsorbates of O₂ and Rb than the scraped bulk sample, as monitored by the Bi 5d core shifts and the oxygen‐induced valence‐band states.