Can photoemission accurately probe the bulk electronic structure of the complex oxides?

The surface of the complex oxides, in particular the manganese perovskites, is dominated by a different free enthalpy at the surface. This can be demonstrated by surface segregation after annealing the samples. By comparing relative x-ray photoelectron spectroscopy intensities of the manganese perovskite La1-xCaxMnO3 (x = 0.1, 0.35) for different emission angles, the profile of elemental concentration was determined. Analysis shows evidence for pronounced surface segregation of calcium. Our results suggest that there are strong differences between surface and bulk enthalpies without segregation or surface relaxation. This is consistent with the previously observed surface resonance in the electronic band structure. (C) 1998 American Vacuum Society. [S0734-2101(98)00505-3].