Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 25: Organic films II

O 25.7: Talk

Tuesday, March 28, 2006, 17:15–17:30, PHY C213

Molecular Lifetime Contrast in Thin Pentacene Layers — •F.-J. Meyer zu Heringdorf, D. Thien, P. Kury, L.I. Chelaru, and M. Horn-von Hoegen — Institut für Experimentelle Physik, Universität Duisburg-Essen, Lotharstrasse 1, 47057 Duisburg

Whenever excited electrons are required to tailor specific properties of a thin film, the decay of the initial excitation over time defines an intrinsic limit for the performance. To determine the lifetime of such an electronic excitation in a heterogeneous layer requires a combination of microscopic and spectroscopic methodologies. We used an ultrahigh vacuum spectroscopic photoemission microscope (SPE-PEEM) together with a fs Ti:Sapphire laser to study the decay of electronic excitations in thin films of the aromatic molecule pentacene. This molecule, deposited on a Si surface, initially forms a wetting layer of flat-lying molecules, while subsequent layers stand upright and develop a typical dendritic shape. The change in morphology is reflected in the decay channels for the electronic excitation: while we determine a time constant of less than 200fs for the wetting layer, the lifetime in the dendritic islands is more than twice as high as the wetting layer. Mapping of the lifetime reveals that the morphology of the layer is in fact different for islands of different heights.