Berlin 2008 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 19: Organic Interfaces (SYSA 6)
DS 19.5: Vortrag
Mittwoch, 27. Februar 2008, 15:45–16:00, H 2013
A molecular gas in two dimensions: Substrate-mediated repulsive interaction in an organic sub-monolayer film — •Christian Kumpf1, Achim Schöll1, Christoph Stadler1, Ingo Kröger1, and Eberhard Umbach1,2 — 1Universität Würzburg, Experimentelle Physik II, 97074 Würzburg — 2Forschungszentrum Karlsruhe, 76133 Karlsruhe
The formation of the first molecular layer on a solid surface plays an important role for the growth behaviour of organic thin films. The first layer acts as a nucleus for further growth. It hence affects the structural properties of the entire film and consequently the electronic and optical properties. The development of the first layer depends strongly on the substrate bonding and the intermolecular interaction. Usually the latter is attractive due to van-der-Waals forces between the organic molecules thus resulting in island formation.
Here we report on an organic adsorbate system exhibiting repulsive intermolecular interaction mediated by the substrate. With increasing coverage Metal-Phthalocyanine (MePc) molecules continuously rearrange on a Ag(111) surface and -- at all coverages -- fill the entire surface homogenously. This is in contrast to discrete, well defined phase transitions which usually occur for such systems. Such unusual behaviour was found for Sn-, Cu- and TiOPc molecules. We report experimental results from spot-profile analysis-low energy electron diffraction, x-ray standing waves and photoelectron spectroscopy, and discuss an electronic donation/back-donation process as the fundamental origin of the intermolecular repulsion.