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

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Abstract
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.