Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 52: Time-Resolved Spectroscopy III

O 52.9: Vortrag

Mittwoch, 27. Februar 2008, 17:15–17:30, MA 042

Image-potential states and resonances on the clean and Argon covered (111)-surfaces of Copper and Silver — •Andreas Damm, Kai Schubert, Jens Güdde, and Ulrich Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg, Germany

We report on a comparative 2PPE study of the influence of Ar adlayers on the properties of image-potential states of Ag(111) and Cu(111). On both surfaces only the n=1 state is non resonant with bulk states. As a result of Ar adsorption a drop of the workfunction and a systematic lowering of the binding energies of the image-potential electrons is observed. On Cu(111) however the first image state is bound close to the conduction band minimum. Thus this state becomes a resonance for Ar coverages Θ≥2 ML, whereas it remains in the band gap of the bulk states on Ag(111) for coverages up to Θ=4 ML. This leads to a strikingly different dependence of the first image state’s lifetime on layer thickness for the two surfaces. On Ag(111) the lifetime of the first image state depends exponentially on the number of adsorbed Ar layers, and rises from 32 fs on the clean surface to about 6 ps for Ar coverages of 4 ML. On Cu(111) the initial lifetime increase with layer thickness is essentially the same, but at an Ar coverage of Θ=2 ML a kink occurs in correlation with that state becoming resonant with the conduction band of bulk Copper. For higher coverages the increase of lifetime shows again an exponential behavior, but surprisingly with a reduced thickness dependence compared to the non resonant case.