Dresden 2014 – scientific programme

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O: Fachverband Oberflächenphysik

O 77: Focussed Session: Towards a Quantitative Understanding of Complex Adsorption Structures: Surface Science goes Organic III

O 77.2: Talk

Thursday, April 3, 2014, 16:30–16:45, TRE Phy

Diffusion and site selection of PTCDA on KCl(100) studied by fluorescence spectroscopy and STM — Alexander Paulheim, Christian Marquardt, Qinmin Guo, and •Moritz Sokolowski — Institut für Physikalische und Theoretische Chemie der Universität Bonn Wegelerstraße 12, 53115 Bonn, Germany

We report an investigation on the optical properties of the model molecule PTCDA at very low coverages (below 1% of a monolayer) on thin epitaxial KCl(100) films. From STM data we derive a statistical adsorption of isolated molecules at low temperature. Upon thermal activation, diffusion to steps edge sites occurs, comparable to that on other alkali halide surfaces [1]. This scenario was investigated also by fluorescence spectroscopy (FL) and FL excitation spectroscopy, exploiting its high sensitivity. Different adsorption sites lead to different optical transition energies due to differences in the molecule substrate interactions [2]. In addition, from the external vibronic modes we conclude that the PTCDA molecule is distorted from its planar geometry by the interaction with the KCl surface. [1] H. Karacuban et al., Nanotech., 2011, 22, 295305; [2] Paulheim et al., Phys. Chem. Chem. Phys., 2013, 15, 4906.