Dresden 2006 – wissenschaftliches Programm
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O: Oberflächenphysik
O 43: Time-resolved spectroscopy I
O 43.2: Vortrag
Donnerstag, 30. März 2006, 17:45–18:00, WIL C207
Competing Processes at Ice-Metal Interfaces: Ultrafast Electron Transfer and Solvation Dynamics — •Julia Stähler, Cornelius Gahl, Uwe Bovensiepen, and Martin Wolf — Freie Universität Berlin, Fachbereich Physik, Arnimalle 14, 14195 Berlin, Germany
The ultrafast dynamics of excess electrons photo-injected into ultrathin amorphous D2O layers on Ru(001) and Cu(111) are investigated using time-resolved two-photon photoelectron spectroscopy. On both substrates we observe electron localization and solvation in the ice films, competing with back relaxation to the metal. We identify two regimes of back transfer: (i) For t < 300 fs the initial back transfer rate is four times higher on Ru(001) (τ1Ru = 34 fs) compared to Cu(111) (τ1Cu = 140 fs). (ii) At t > 300 fs we observe a slower back transfer, which is comparable for both systems (τ2Ru = 302 fs, τ2Cu = 316 fs). By an empirical model calculation based on rate equations, which nicely reproduces our data, we show that the back transfer is initially determined by the electronic surface band structures of the two substrates, whereas the population decay at later times is dominated by tunneling through a potential barrier at the interface, which arises from the rearrangement of the surrounding polar molecules during solvation.