Direct measure of surface impurity scattering by angle-resolved photomission.

High resolution angle-resolved photoemission experiments are reported which investigate the perturbations of the surface electronic structures of Cu(111) by dilute potassium impurities. The dominant effects are an energy shift and a broadening of the zone-center surface state. The shift is attributed to softening of the surface barrier accompanying the work function decrease. The broadening is directly related to scattering of surface state electrons by potassium centers. This endows the electrons with a finite mean-free-path and thus a broadened momentum spectrum. The data are quantified by an effective scattering cross-section of 5.2 +-2.0angstrom. This value is discussed in terms of various surface processes and the future possibilities of such experiments is investigated.