Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 31: Organische Dünnschichten II
O 31.15: Vortrag
Donnerstag, 27. März 2003, 18:30–18:45, HSZ/02
Time-Resolved Two-Photon-Photo-Emission on Alkanethiol Monolayers on Gold Films — •Sandra Dantscher, Markus Kerpes, Sven Schramm, and Walter Pfeiffer — Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg
Alkanethiols form ordered self assembled monolayers (SAM) on gold surfaces. The strong covalent-ionic interaction between the gold and sulfur atoms leads to the binding of the molecules on the substrate. We investigate the influence of this surface modification on the relaxation of electronic states using femtosecond time-resolved two-photon-photo-emission. The substrates consist of 35nm thick polycristalline gold films on which a layer of hexadecanethiol molecules is adsorbed. The experiments reveal a reduced work function of a gold/SAM system with respect to a clean gold film. This reduction is attributed to a positively charged surface layer at the gold-sulfur-interface. The spectra exhibit no signatures of the LUMO state of the molecules. However, time-resolved two-photon-photoemission spectroscopy shows that the adsorption of alkanethiols leads to a decrease of the lifetime of the excited electronic states (EF+1.5eV, EF+2.7eV). The underlying increase of the electronic scattering rate can be explained by a modification of the gold d-bands by the chemisorption.