Collective excitations of thin films of disordered potassium adsorbed on Ag(110)

Abstract

Collective electronic excitations of disordered potassium adsorbed on Ag(110) have been studied by energy loss spectroscopy–low-energy electron diffraction (ELS–LEED) for overlayer thicknesses varying from 0.3 to 2.3 monolayers. We find that, in the long-wavelength limit, the argon surface plasmon energy shifts upwards with increasing potassium coverage, contrary to the expectation of classical dielectric theory, while its dispersion decreases. The potassium-induced loss, connected to the 3s to 3p interband transition, sets in above half a monolayer coverage, indicating a filling of the K(3s) state. Above one monolayer coverage collective potassium-induced modes are observed as well.