Final-state scattering in angle-resolved ultraviolet photoemission from copper

The problem of direct transition intensities in angle-resolved UV photoelectron spectroscopy is addressed. We demonstrate that the angular distribution of intensities integrated over the full 3d band of copper is dominated by final-state scattering effects much like those observed in the diffraction of core level photoelectrons. These UV photoelectron diffraction effects are very sensitive to the angular momentum character of the valence orbitals that form the band states, and to the atomic structure of the surface layers. Specifically, we have performed measurements on Cu(lll) and Cu(001) surfaces where we find excellent agreement of experimental angular distributions of integrated d band emission excited by He I and He II radiation and single-scattering cluster calculations, involving emission from localized d states, and including proper photon polarizations. At the same time the angle-resolved energy spectra show strong dispersion effects, reflecting the delocalized character of these band states. This duality may be a further indication for the localization of the valence hole upon photoemission.