XPS and XAES study of Ag-Pd and Cu-Ni alloys: spectra, shifts and electronic structure information

The problem of determining the electronic structure of random metallic alloys is of fundamental importance. Although it represents one of the simplest situations beyond that of perfect crystals, it presents difficult challenges for electronic structure theory. We report a study of Ag-Pd and Cu-Ni alloys employing X-ray photoemission spectroscopy (XPS) and X-ray excited auger spectroscopy (XAES) utilizing conventional radiation sources We compare experimentally measured XPS shifts in Ag-Pd with recently reported calculations and show that, although the Pd shift appears to be consistent with a complete screening picture, it is not possible to reach such an unambiguous conclusion for the Ag shift on the basis of such a comparison. By applying a previously derived technique to the XPS and XAES energy shifts, we demonstrate that charge transfer is essentially absent in these systems and we derive the changes in d and sp electronic occupations of the alloy components, in agreement with experimental Auger parameter shifts. We note that the Ag d-band loses electrons in dilute Ag alloys and gains electrons otherwise, in contrast with any other alloy system studied to date. (C) 2004 Elsevier B.V. All rights reserved.