Electronic properties of adsorbed layers of nitrogen, oxygen, and sulfur on silver (111)

Abstract

We have studied ordered layers of nitrogen, oxygen, and sulfur adsorbed on an Ag (111) surface. Ultraviolet photoemission spectra (UPS) imply that each of these adsorbates induces a set of virtual levels above the $d$ band of silver, at about 3.4-eV binding energy, and below the $d$ band at about 8-eV binding energy. X-ray photoemission spectra show that the $1s$ binding energies of the nitrogen and oxygen layers are 397.9 and 530.4 eV, respectively, and that the $2p$ binding energy in the sulfur layer is 161.8 eV. Auger spectra excited by each of these core holes may be interpreted as arising from transitions involving electronic states measured in the above 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. The results show that the difference between the hole-hole repulsion and excess relaxation energies in the Auger final state are small. This evidence points to the formation of a silver-adsorbate surface layer in which the UPS observed electronic states have a high local density of states at the adsorbate atom cores and in which the two-hole Auger final states considered are delocalized.