KAPPA-RESOLVED INVERSE-PHOTOEMISSION STUDY OF HALF-MONOLAYER STRUCTURES OF O, C AND N ON NI(100) - A FINGERPRINT OF ADSORBATE-INDUCED RESTRUCTURING

k-resolved inverse photoemission (KRIPES) spectra have been measured in the isochromat mode at fixed photon energies of 10.0 and 11.5 eV from the half-monolayer chemisorption phases formed by O, N and C on Ni(100). In all cases adsorbate-induced features in the energy range 1-4 eV above the Fermi level are observed which are assigned to adsorbate 2p-related anti-bonding states. In the case of the simple overlayer chemisorption phase of Ni(100)-c(2 x 2)-O the O 2p state has an energy very similar to the bulk s-p band transition seen in 9.7 eV isochromats, consistent with previous speculation concerning this state. The dispersion of the O-induced surface band in parallel momentum is typical of s-p bonding. By contrast, the C- and N-induced bands are essentially dispersionless, indicating that the Ni d-bands may contribute more strongly to the adsorbate bonding of these species. The possible relevance of this d-band interaction in producing, or being a consequence of, the adsorbate-induced reconstruction in the C and N phases, is discussed.