Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 27: Time-Resolved Spectroscopy II
O 27.6: Vortrag
Dienstag, 26. Februar 2008, 12:30–12:45, MA 043
Electron Transfer & Solvation Dynamics at the NH3/Cu(111) Interface: Determination of Tunneling Barriers — •Julia Stähler, Michael Meyer, Uwe Bovensiepen, Daniela O. Kusmierek, and Martin Wolf — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin
Understanding the fundamental processes of heterogeneous electron transfer (ET) is highly important for a variety of different fields, as e.g. the development of nanoscale molecular electronic devices or photovoltaic cells. Here, we investigate ET and solvation dynamics at the interface of amorphous NH3 and Cu(111) using femtosecond time-resolved two-photon photoelectron spectroscopy. After photoexcitation with UV light, metal electrons are injected into the adsorbate layer. They localize at favorable sites and are stabilized by reorientations of the surrounding solvent molecules. Concurrently, they decay back to the metal substrate. Two different regimes are observed for both, electron solvation and electron back transfer: Initially, electron decay and stabilization occur on fs-timescales. The dynamics slow down abruptly after 250 fs leading to electron transfer and solvation on ps-timescales. The lifetime of this second species of solvated electrons depends exponentially on the ammonia layer thickness, showing that ET is mediated by distance-dependent tunneling through an interfacial barrier. The acquired data allows for an estimate of the temporal evolution of this transient potential barrier, yielding profound insight into the ET mechanisms at molecule-metal interfaces.