Electronic properties of adsorbed layers of nitrogen, oxygen, and sulfur on copper (100)

Abstract

Adsorbed layers of nitrogen and oxygen in the $c(2\mathrm{}\times 2)$ structure and sulfur in the (2 × 2) structure on copper (100) have been studied. Ultraviolet photoemission spectroscopy (UPS) shows that each of these layers induces a resonance above the "$d$ band" of copper at about 1.3-eV binding energy with respect to the Fermi level and below the "$d$ band" at about 6-eV binding energy. X-ray photoemission spectroscopy has been used to determine that the $1s$ electronic binding energies of adsorbed atoms of $c(2\mathrm{}\times 2)$ nitrogen and oxygen are 396.3 and 529.8 eV, respectively, and that the $2p$ electronic binding energy of adsorbed 2 × 2 sulfur is 161.2 eV. The highest-energy Auger peaks excited by each of these core holes may be interpreted as arising from Auger transitions involving the surface electronic states measured in these UPS experiments. Good agreement with most features of the experimental Auger spectra has been obtained using measured and calculated data for the surface electronic binding energies under the assumption that Auger final-state effects are small. Therefore the evidence points to the formation of a copper-adsorbate surface complex in which these UPS-observed resonances have a high local density of states at the adsorbate atom cores and in which the final-state hole momenta are only loosely coupled.