Dresden 2014 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 79: Plasmonics and Nanooptics IV

O 79.8: Vortrag

Donnerstag, 3. April 2014, 17:45–18:00, TRE Ma

Plasmoelectrons: Electron emission by decay of confined bulk plasmons in epitaxial ultrathin Mg films — •Ulrich Hagemann and Hermann Nienhaus — Faculty of Physics and Center for Nanointegration (CeNIDE), University of Duisburg-Essen, D-47048 Duisburg, Germany

A novel electron emission process is observed for epitaxially grown Mg layers on Si(111)-7x7 surfaces. The metal film thickness ranges between 5 and 50 monolayers and the surface (SS) as well as quantum well states (QWS) are well resolved by ultraviolet photoelectron spectroscopy (UPS). Intensive replica peaks of the SS and QWS structures are detected in the UPS spectra on the secondary electron background at a constant kinetic energy independent of the energy of the incident photons (HeI, NeI, ArI, ArII). The emission structures are up to two orders of magnitude more intense than the photoelectron peaks. Since they appear for an excitation energy of 10.3 eV, i.e., the Mg bulk plasmon energy, the emission is explained by the decay of optically excited bulk plasmon modes confined in the ultrathin metal film. Such modes couple effectively to the QWS and SS of the Mg film. This plasmoelectron emission is only present for well-ordered and ultrathin Mg films. At 300 ML Mg films, the effect vanishes. A threshold photon energy for the plasmoelectron excitation is found between 12 and 13eV. First experiments with Mg and Al thin films demonstrate that a similar but weaker effect is found for surface plasmons as well.