X-ray-photoemission-spectroscopy study of the surface deterioration of Bi2Sr2CaCu2O8 and Bi1.7Pb0.3Sr2CaCu2O8 single crystals at 26 K

We examine the time evolution of the O 1s core-level and valence-band spectra of high-quality Pb-free and -doped Bi2Sr2CaCu2O8(001) single crystals cleaved at 20 K in ultrahigh vacuum. A component line at 533.5 eV of the O 1s spectrum is unambiguously identified as extrinsic and separated by the doublet structure related to the normal-state electronic structure of this compound. Evidence is given of the surface physisorption of carbon monoxide at low temperature (<30 K) that is removed at room temperature without loss of stoichiometric oxygen. The effects of pollution on the valence-band features are monitored and correlated with those of the core spectra. Spectral changes due to electron etching are also addressed. © 1991 The American Physical Society.