Berlin 2008 – scientific programme
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O: Fachverband Oberflächenphysik
O 8: Metal Substrates: Adsorption of Organic/Bio Molecules I
O 8.5: Talk
Monday, February 25, 2008, 13:00–13:15, MA 041
Investigation of unoccupied electronic states in PTCDA/Ag(111) — •Sönke Sachs1, Christian Schwalb2, Manuel Marks2, Stefan Krause1, Achim Schöll1, Eberhard Umbach1,3, and Ulrich Höfer2 — 1Universität Würzburg, Experimentelle Physik II, Am Hubland, 97074 Würzburg — 2Universität Marburg, Fachbereich Physik, Renthof 5, 35032 Marburg — 3Forschungszentrum Karlsruhe, 76021 Karlsruhe
Energetics, momentum and time evolution of electronic states in organic semiconductors and at their interfaces are fundamental properties that strongly determine the performance in electronic applications. All of these properties can be explored with two-photon photoelectron (2PPE) spectroscopy for occupied and in particular for unoccupied electronic states.
In the archetypal system perylene-tetracarboxylic-dianhydride (PTCDA) on single crystal Ag(111) surfaces considerable differences between the electronic states of chemisorbed monolayer films and multilayer films are eminent. These differences, which are due to the altered chemical environment of PTCDA- and as well Ag-derived states in the vicinity of the interface, can be tracked with 2PPE. A new unoccupied interface state at the Ag/PTCDA interface with a free-electron like dispersion and comparatively short lifetime is detected that influences the charge injection characteristics considerably. The results of the 2PPE spectroscopy are compared to the results of complementary spectroscopies like UPS, IPES, and STS.