Regensburg 2010 – scientific programme
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O: Fachverband Oberflächenphysik
O 48: Surface dynamics I
O 48.3: Talk
Wednesday, March 24, 2010, 11:00–11:15, H40
Ultrafast electron transfer across polar molecule-metal interfaces: strong coupling vs. molecular screening — •Julia Stähler1,2, Michael Meyer1, Uwe Bovensiepen1,3, and Martin Wolf1,2 — 1Freie Universität Berlin, FB Physik, Berlin, Germany — 2Fritz-Haber-Institut der MPG, Abt. Phys. Chemie, Berlin, Germany — 3Universität Duisburg-Essen, FB Physik, Duisburg, Germany
Heterogeneous charge transfer plays a crucial role for the development of molecular electronics such as, for example, OLEDs. The screening properties of the involved molecules hereby play an important role as they determine the timescales on which electron transfer (ET) occurs. However, also the substrate’s electronic band structure significantly influences the ET dynamics. We use amorphous D2O and NH3 layers on Cu(111) and Ru(001) surfaces as model systems for systematic investigation of the ultrafast ET dynamics at polar molecule-metal interfaces by means of time-resolved two-photon photoelectron (2PPE) spectroscopy. With a 1st laser pulse, electrons are excited in the metal and injected into the adsorbate layer where they localize at favorable sites. The subsequent electron (back) transfer to the substrate is monitored with a 2nd, time-delayed laser pulse. The study unveils that (i) molecular screening is observed for t>200 fs after electron injection, (ii) before, ET is dominated by the strong coupling to the substrate states. Our results strongly suggest that this transition from the substrate-dominated to the barrier-determined regime of ET is a general characteristic of ET across (polar) molecule-metal interfaces.