Dresden 2006 – scientific programme
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O: Oberflächenphysik
O 41: Electronic structure III
O 41.6: Talk
Thursday, March 30, 2006, 16:15–16:30, WIL B321
Coverage-dependent evolution of plasmon modes in adsorbed Cs layers on Si(111) — •Volkmar Zielasek1,2, Neele Rönitz3, Eddy Patrick Rugeramigabo1, Martin Henzler1, and Herbert Pfnür1 — 1Universität Hannover, Institut für Festkörperphysik, Appelstr. 2, 30167 Hannover — 2Universität Bremen, Institut für Angewandte und Physikalische Chemie, Leobener Straße, NW II, 28359 Bremen — 3Philips Semiconductors, Stresemannallee 101, 22529 Hamburg
The transition between substrate and overlayer metalization with varying alkali metal coverage has been studied for Si(111) (7×7)-Cs by EELS with ultra-high momentum resolution and measurements of electrical conductance at low temperatures. As the Cs coverage is increased from 0.5 to 1.2 ML coverage, the predominant surface plasmon transforms from a monopole mode, representing metallicity in substrate surface states modified by Cs, to an overlayer multipole mode, which indicates metallicity within a Cs adlayer. The multipole mode continuously shifts in energy from 1.4 to 2.2 eV until a continuous Cs wetting layer is formed. In contrast to previous conventional EELS experiments, the multipole plasmon is clearly identified by an extremely narrow angular distribution of the inelastic electron scattering, unaccounted for by standard dipole scattering theory. Its observation provides evidence for luminescence from atomic Cs layers on Si(111) which can be tuned from infrared to the visible energy range by adjusting Cs coverage.