Dresden 2009 – scientific programme

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DS: Fachverband Dünne Schichten

DS 16: Poster I

DS 16.20: Poster

Tuesday, March 24, 2009, 09:30–12:30, P5

Optical observation of charged organic molecules on metal surfaces — •Christian Golnik, Roman Forker, and Torsten Fritz — Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany

We report on the in situ optical absorbance spectroscopy of ultrathin films of the organic semiconductor 3,4,9,10 perylene-tetracarboxylic-dianhydride (PTCDA) on the metal single crystals Au(111), Ag(111) and Al(111). As Differential Reflectance Spectroscopy (DRS) has a sensitivity in the range of submonolayers, we could extract the dielectric function from the DR-spectra in dependency of the film thickness in the monolayer regime. A broad absorption due to strong interaction with the metal surface in the first monolayer and a monomeric absorption in the second monolayer were observed in the є"-spectra. Different charged states of PTCDA related to the direction of the interface dipole [1] between the metal surface and the organic film were found, namely PTCDA-anions in the first monolayer on aluminium and PTCDA-cations in the second monolayer on gold. The absorption signatures of the charged states are in good agreement with PTCDA-anions obtained by potassium doping on mica [2] and absorption spectra of charged PTCDA-related molecules in solution [3].

[1] A. Kahn et al., J. of Polymer Science Part B 41 (2004), 2529-2548

[2] A. Krause et al., submitted

[3] T. Kircher et al., Phys. Chem. Chem. Phys. 1 (1999), 3987-3992