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O: Fachverband Oberflächenphysik
O 60: Time-Resolved Spectroscopies
O 60.1: Vortrag
Donnerstag, 29. März 2007, 15:45–16:00, H42
2PPE measurements of PTCDA on Ag(111) — •Christian Schwalb1, Sönke Sachs2, Achim Schöll2, Eberhard Umbach2, and Ulrich Höfer1 — 1Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität Marburg, D-35032 Marburg, Germany — 2Universität Würzburg, Experimentelle Physik II, D-97074 Würzburg, Germany
Electron transfer at a metal-molecule interface plays an important role in many chemical disciplines, ranging from molecular electronics to surface photochemistry. We present measurements using time-resolved two-photon photoemission (2PPE) to probe the energetics and dynamics of electronically excited states in epitaxial 3,4,9,10-perylenetetracarboxylic acid-dianhydride (PTCDA) thin films on a Ag(111) surface for a thicknessrange from one to ten monolayers. These measurements allow the identification and determination of the energetic positions for the lowest unoccupied molecular orbital (LUMO), and LUMO + 1. Angle-resolved 2PPE-measurements show a weak dispersion for the LUMO of ~150 meV. Our experiments indicate that the excitation process for the LUMO is mainly done by electrons from the Ag(111) substrate. Time-resolved measurements probing the dynamics of the system show an increasing of lifetime for the LUMO for increasing layer thickness from 40 to 80 fs.