Electronic properties of noble metal surfaces and ultrathin metal films on noble metal substrates.

摘要

Auger-Photoelectron Coincidence Spectroscopy (APECS) was used to examine the electronic structure of elemental Ag and the Ag/Cu(100) and Pd/Cu(100) surface alloys. Using APECS, the intrinsic shape of Auger lines can be determined. APECS data for the elemental Ag M 5VV and M4VV Auger lines were modeled using a many-body theory developed by Cini and Sawatzky, and the fit to the model indicates that the hole-hole correlation energy of the 1G4 Auger final state is 4.8 +/- 0.1 eV.; For the Ag/Cu(100) and Pd/Cu(100) surface alloys, we examined the M5VV Auger line as a proxy for directly measuring the valence d-bands of Ag and Pd. The valence d-bands of the Ag and Pd impurities are predicted to shift away from the Fermi level (EF) by 0.7 eV and 0.64 eV, respectively, for an impurity incorporated into the first layer of the Cu lattice. These d-band shifts should manifest themselves as a shift of Auger peaks to lower kinetic energy. We observe a small shift of 0.25 eV in the Ag M5VV Auger line. In contrast, Pd exhibits a much larger shift of ∼ 1 eV.; We also examined the inverse photoemission spectra of Cs/Cu(100) and Cs/Cu(111). For low coverages, a Cs-induced state appears at 0.29 eV above EF and this feature moves towards EF with increasing Cs coverage. The orbital character of the Cs-induced state is d-like when in a projected band gap of the substrate and s, p-like when degenerate with a projected bulk band of the Cu host. A novel aspect of orbital hybridization is proposed to explain these observations.; We also report on the first angle-resolved APECS (AR-APECS) measurements from a solid. The angular distribution of L3 VV Auger electrons from the Cu(111) surface was measured in time coincidence with emission from Cu 2p3/2 core level. Significant dissimilarities in the coincidence pattern are apparent when the 2 p3/2 level is at a photoelectron diffraction (PED) maximum vs. when the core level is off maximum. The AR-APECS technique may be sampling different scattering sites on and off the PED maxima, or the technique may be sensitive to differences between lattice-like and atomic-like effects.