Doping dependence of the O 1s core-level photoemission in Bi-Sr-Ca-Cu-O superconductors

The O 1s core level of three different Bi-Sr-Ca-Cu-O superconductors has been studied by means of high-resolution x-ray-photoelectron spectroscopy (XPS) and x-ray-absorption spectroscopy (XAS). The O 1s XPS spectra could be decomposed into three components that were unambiguously assigned to the emission from the three different oxide layers in the crystal structure. These are, in order of increasing binding energy, Cu-O2, Sr-O, and Bi-O. Furthermore, the component assigned to the Cu-O2 layers exhibits a shift which depends on the hole doping as monitored by the XAS spectra.