Orbital identification in the INS and UPS spectra of chalcogens adsorbed on Ni(100)

Abstract

Orbital energy spectra of the c (2×2)Te structure on Ni(100) obtained by both UPS and INS show two Te-derived orbital peaks which we interpret as arising from the nonbonding and bonding orbitals of the surface Ni2Te molecular complex. These conclusions are suggested by the comparison of orbital peak shapes with those of the nonbonding 5d orbitals of Hg adsorbed on Ni(100) and by the energy positions relative to the p4 orbital energy level in free Te. Previously unpublished data on c (2×2)Se as well as considerations of relaxation energy indicate that this interpretation should also be carried over to the INS spectra for c (2×2)Se and c (2×2)S reported previously. Relative orbital intensity in the INS and UPS spectra support this interpretation if the chalcogen atom in the c (2×2) structure is bridge-bonded across the diagonal of the basic surface Ni square as previously proposed. INS and UPS spectra for c (2×4)Te show a single broad orbital peak requiring a different bonding configuration, probably of C4v symmetry involving four Ni atoms.