High resolution X-ray photoemission of SrCu2O2

Pure and K-doped SrCu 2O 2 have been studied by high resolution X-ray photoemission spectroscopy. Valence band photoemission spectra are shown to be in good agreement with the bandstructure calculations of Ohta et al. and are dominated by the Cu 3d partial density of states. Conductivity measurements reveal that the Fermi level in nominally undoped material is pinned by acceptor states 0.24 eV above the valence band edge but moves toward the valence band with increasing doping. Changes in core and valence level binding energies with doping mirror the changes in the transport activation energy. © 2004 Elsevier B.V. All rights reserved

Competition between initial- and final-state effects in valence- and core-level x-ray photoemission of Sb-doped SnO2

High resolution valence- and core-level photoemission spectra of undoped and 3% Sb-doped SnO2 are presented. Conduction-band occupation due to Sb doping in SnO2 leads to a shift of valence-band features to high binding energy. However, the shift is less than the width of the occupied part of the conduction band. This is attributed to a shrinkage of the bulk band gap with doping, arising from an attractive dopant electron interaction and screening of the Coulomb repulsion between valence and conduction electrons. Core-level spectra provide evidence for strong screening by the conduction electron gas in 3% Sb-doped SnO2, giving rise to "screened" and "unscreened" final-state peaks in photoemission. The dominant screening response involves excitation of conduction electron plasmons. ©1999 The American Physical Society

N-type doping in CdO ceramics: a study by EELS and photoemission spectroscopy

Ceramic samples of yttrium- and indium-doped CdO (Cd 1-xY xO with 0≤x≤0.035 and Cd 1-xIn xO with 0≤x≤0.023) have been studied by electron energy loss spectroscopy (EELS) and ultraviolet and X-ray photoemission spectroscopy (UPS and XPS). Both In and Y act as efficient n-type dopants, although the carrier concentration is higher in In-doped material. The maximum surface plasmon loss energy in EELS is 0.66 eV in Y-doped samples and 0.72 eV for In-doped samples. Effective masses (m*) increase with increasing carrier concentration N and obey an approximately linear variation of the form m* = m* + cN, where c is a constant. UPS shows a well-defined conduction band feature for doped samples. A shift of the valence band edge towards high binding energy due to chemical doping was observed in He(I) UPS, which is confirmed by shifts of O 2p valence band features and Cd 4d core level peaks in high resolution XPS. However, the shifts are less than expected from the increased widths of the occupied part of the conduction band. This is due to shrinkage of the bandgap with doping. XPS demonstrates that there is pronounced surface segregation of dopant atoms. However, the segregated dopant atoms do not act as donor centres. © 1998 Elsevier Science B.V

An experimental and theoretical investigation of the electronic structure of CdO

Photoemission spectra of polycrystalline CdO have been measured under excitation with monochromatic x-rays and with variable energy UV radiation from a synchrotron source. Experimental data are compared with density of states profiles calculated by periodic Hartree-Fock and density functional methods. Both calculations suggest that there is significant mixing between Cd 4d and O 2p states, but the Hartree-Fock calculations better reproduce the experimental O 2p to Cd 4d separation and the O 2p bandshape. Constant initial state profiles measured with variable photon energy in the range between 30 eV and 100 eV provide experimental evidence for O 2p-Cd 4d mixing