Angle-resolved photoemission studies of the nickel (111) surface and its interaction with carbon monoxide

Abstract

Angle-resolved photoelectron energy distributions have been recorded for the Ni(111) surface, both clean and following CO adsorption, using HeI and HeII photons. The results for the clean surface exhibit many features characteristic of an initial-state dependence, but indicate a narrower bandwidth than that inferred from calculated electronic energy band schemes. Qualitatively, the form of the energy-band dispersion predicted from the angular measurements on a simple free-electron-like assumption for the final state, is consistent with the form of the calculated bands and appropriate behavior in the measured dispersion for wave vectors in the vicinity of the Brillouin-zone boundary is observed. However, uncertainties in the component of electron momentum perpendicular to the surface preclude too close a comparison. For the CO-covered surface, comparison of the angular symmetries of the extra structure introduced following adsorption provides a basis for a new assignment in terms of $1\ensuremath{\pi}$, $5\ensuremath{\sigma}$, and $4\ensuremath{\sigma}$ molecular orbitals of CO.