Electronic structure of atomic oxygen adsorbed on Ni(100) and Cu(100) studied by soft-x-ray emission and photoelectron spectroscopies

The electronic structure of c(2×{}2)-O/Ni(100) and p(2 {}2 ×{} {}2 )R45^∘{}-O/Cu(100) has been studied by soft-x-ray emission spectroscopy (SXES), ultraviolet, and x-ray photoemission spectroscopies (UPS and XPS). For O/Ni(100), the 2p-derived states are centered at 6 eV below the Fermi level. There is intensity from these states all the way up to the Fermi level, due to the 2p-3d hybridization. The sharp edge of the SXES intensity at the Fermi edge indicates that the antibonding 2p-3d states are partly occupied. This is also manifested in the asymmetric line shape of the O 1s XPS peak. In O/Cu(100), on the other hand, these states are close to fully occupied, and observed around 1--2 eV binding energy in the UP and SXE spectra. The higher energies of the excitations from the filled 2p-3d states result in a discrete satellite about 3 eV from the O 1s main line in the O/Cu(100) XPS spectrum. The main SXES intensity is positioned at about 4--5 eV, i.e., in the region of the Cu d band, indicating a larger O-Cu hybridization in this energy region than previously reported.