Dresden 2009 – scientific programme

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DS: Fachverband Dünne Schichten

DS 22: Organic Thin Films II

DS 22.2: Talk

Wednesday, March 25, 2009, 11:30–11:45, GER 38

In-situ optical spectroscopy of ultrathin quaterrylene films epitaxially grown on graphite and mica — •Roman Forker, Christian Golnik, Christian Wagner, Moritz Eßlinger, and Torsten Fritz — Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany

Profound knowledge of the growth behavior of aromatic molecules on insulating and conducting substrates is highly desired since an alignment of the planar π-electron cores in face-on or edge-on geometry, respectively, will have a direct impact on the performance of devices, such as solar cells or OFETs. Here we report the epitaxial growth of quaterrylene (QT, C₄₀H₂₀) deposited on single-crystalline graphite and mica, as examined in-situ by a variant of optical absorption spectroscopy, namely differential reflectance spectroscopy (DRS). We found substantial differences in the shape and in the film-thickness-dependent evolution of the spectra that can only be understood in terms of dissimilar growth modes on these substrates. While the optical behavior of QT films on graphite resembles that of QT reported for a face-on heteroepitaxial arrangement on Au(111) [1], the growth of QT films on mica can more likely be described by an edge-on assembly, as also observed on SiO₂ [2]. With the help of low-energy electron diffraction (LEED) measurements we can evidence the occurrence of flat-lying QT molecules on graphite. In turn, we can exclude such a growth mode on mica, due to the fundamentally different optical spectra in that case. [1] R. Forker et al., Adv. Mater. in press, 10.1002/adma.200801112. [2] R. Hayakawa et al., J. Phys. Chem. C 111 (2007), 18703.