A LEED/UPS study on the interaction of oxygen with a Ni(111) surface

Exposure of a Ni(111) surface to oxygen leads at first to the formation of a chemisorbed overlayer which is characterized by a 2 × 2-superstructure and a maximum in the photoemission spectrum (hv = 40.8 eV) centered at 5.6 eV below the Fermi level E_F. The emission from the Ni d-states is nearly unaffected at this stage of interaction. After high oxygen exposures the epitaxial growth of NiO can be identified from the LEED pattern. The corresponding photoelectron spectrum is strongly altered and exhibits close agreement with the transition energies as calculated by Messmer et al. for a NiO₆^10- -cluster.