Regensburg 2010 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 46: Organic Thin Films III

DS 46.3: Vortrag

Freitag, 26. März 2010, 14:30–14:45, H8

Standing and lying α-6T molecules probed by PEEM spectroscopy — •Thorsten Wagner, Daniel Roman Fritz, Martin Oehzelt, and Peter Zeppenfeld — Johannes Kepler University Linz, Institute of Experimental Physics, Austria

The growth of α-sexithiophene (α-6T) depends strongly on the quality of the substrate surface: If the surface is clean and well ordered, the molecules are flat lying on the surface and form characteristic needles. If the surface is disordered, they grow in a upright standing manner forming platelet like crystallites [1]. We have applied photoelectron emission microscopy (PEEM) to study the growth of α-6T films on Ag(110) at different temperatures. By using a Hg-lamp with a photon energy of 4.9 eV it is not possible to overcome the ionization threshold of the molecule itself. Therefore, thick films of the molecules do not emit photoelectrons themselves but absorb these emitted from the metal substrate. Due to the coupling to the metallic substrate the first wetting layer shows an increased PEEM intensity. By applying high energy light sources available in the lab (D₂ with 6.4 eV and HeI with 21.2 eV) one can overcome the ionization potential and actually probe photoelectrons originating from the organic film. As the PEEM also allows energy filtering of the images, it is possible to probe the density of states on a 50 nm scale. The data reveal different emission spectra for the needles and the platelet like crystallites due to the orientation of the molecules in agreement with Duhn and Ivanco [1].

[1] S. Duhm et al., Nature Materials 7, 326 (2008) and J. Ivanco et al., Surf. Sci. 601, 178-187 (2007)