Field-emission and photofield-emission measurements of the surface density of electronic states have been carried out for copper chemisorbed on the (100) and (111) facets of a thermally annealed tungsten field emitter, in the range of temperature, and coverage where the adsorbed atoms form spatially homogeneous overlayers. Such overlayers are found to modify the intrinsic surface states of the substrate, and to introduce, on the (100) facet, additional features in the surface density of states. The observation of a final-state effect in surface photofield emission is reported, demonstrating that this technique can provide useful information on the surface density of states of an adsorbed overlayer in the energy range between the Fermi level and the vacuum level. The present work offers insight into earlier conflicting results concerning the effect of adsorbed copper on the intrinsic surface states of tungsten surfaces.

• Received 10 November 1993

DOI:https://doi.org/10.1103/PhysRevB.49.5575