Volume 117, 2000

Structure and dynamics of excited electronic states at the adsorbate/metal interface: C6F6/Cu(111)

Abstract

Excited state electron transfer at the adsorbate/metal interface represents a key step in molecular electronic devices. The dynamics of such processes are governed by ultrafast energy relaxation which can be probed directly by time-resolved two-photon photoemission (2PPE). Using 2PPE spectroscopy we investigate the energetics and lifetimes of the unoccupied electronic states of C6F6 adsorbed on Cu(111) as a model system for electron transfer at organic/metal interfaces. With increasing C6F6 layer thickness we find a pronounced decrease in the energetic position of the lowest unoccupied state, which is accompanied by a strong increase in its lifetime as well as a decrease in the effective electron mass. The frequently employed dielectric continuum model which describes delocalized (quantum well) states within adsorbate layers does not give a consistent explanation of these findings. By adsorption of Xe overlayers onto C6F6/Cu(111) we can show that, even for one monolayer of C6F6, the excited state must be localized predominantly inside the C6F6 layer and thus originates from a molecular state (presumably an antibonding σ* orbital). With increasing coverage this state becomes more delocalized within the adsorbate layer, which reduces the coupling to the metal substrate and thus enhances the excited state lifetime.

Article information

Article type
Paper
Submitted
16 May 2000
First published
17 Oct 2000

Faraday Discuss., 2000,117, 191-202

Structure and dynamics of excited electronic states at the adsorbate/metal interface: C6F6/Cu(111)

C. Gahl, K. Ishioka, Q. Zhong, A. Hotzel and M. Wolf, Faraday Discuss., 2000, 117, 191 DOI: 10.1039/B003308L

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