Perturbations on surface electronic structure induced by trace impurities: K on Cu(111).

High resolution angle resolved photoemission experiments are reported which describe changes in the surface electronic structure of a Cu(111) crystal induced by the adsorption of trace quantities of potassium. The primary focus is on the zone-center sp intrinsic surface state. In accord with previous studies, a small shift to larger binding energy is observed as the work function decreases. This effect is explained semiquantitatively using a simple phase analysis model. Changing the binding energy of the surface state is equivalent to moving it up and down in its projected bulk band gap. We have observed and quantified the expected changes in bulk penetration length accompanying this movement.