title: Crossover between monopole and multipole plasmon of Cs monolayers on Si(111) individually resolved in energy and momentum.
abstract: The evolution of the plasmon spectrum of the Si(111) (7 x 7)-Cs surface has been studied by energy loss spectroscopy individually resolved in energy and momentum during the transition from substrate to Cs overlayer metallization. The multipole plasmon is identified by an extremely narrow angular distribution of the inelastic electron scattering, unaccounted for by standard dipole scattering theory. A crossover between multipole and monopole surface plasmon is observed at finite surface wave vectors , depending on Cs coverage, and reveals a high sensitivity of the short-wavelength multipole components on surface morphology.
authors.affiliation: Institut für Festkörperphysik, Universität Hannover, Germany.
authors.forename: Volkmar
authors.initials: V
authors.lastname: Zielasek
authors.forename: Neele
authors.initials: N
authors.lastname: Rönitz
authors.forename: Martin
authors.initials: M
authors.lastname: Henzler
authors.forename: Herbert
authors.initials: H
authors.lastname: Pfnür