UC Irvine

X-ray photoemission results for single crystals of M2CuO4 (M=Pr,Eu,Gd), MBa2Cu3Ox (M=Nd,Gd), and CuO are sintered La1.85Sr0.15CuO4 and YBa2Cu3O6.9 show valence-band spectra within 10 eV of the Fermi energy that are remarkably similar in appearance, with contributions that reflect Cu-O hybrid states and the rare-earth 4f states. For Pr2CuO4 and NdBa2Cu3Ox, there are two distinct 4f features due to ligand screening in the photoemission final state. The rare-earth 5p core-level emission overlaps the O 2s emission and reveals complex 5p-4f multiplet interactions. All O 1s spectra show a dominant peak at ∼528 eV that can be resolved into features separated by ∼0.7 eV. These reflect inequivalent oxygen bonding configurations in the lattice and are associated with the planes and chains for the 1:2:3 compounds and the planes and off-planes for the 2:1:4 compounds. The lower-binding-energy feature is associated with the Cu-O chains of the 1:2:3 compounds and the Cu-O planes of the 2:1:4 compounds. In addition to the O 1s main line for the Cu-O planes there is also a weak satellite. Time dependent studies of the Cu 2p and O 1s emission indicate surface modification, dependent upon the quality of the cleave. The effects of surface changes and the presence of imperfections are discussed in the context of surface studies and surface superconductivity. © 1988 The American Physical Society.