Dresden 2009 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 24: Organic Thin Films IV

DS 24.5: Vortrag

Mittwoch, 25. März 2009, 17:30–17:45, GER 38

Long-range ordered PTCDA layers on epitaxially grown NaCl films on Ag(100) — •Eric Le Moal, Oliver Bauer, Mathias Müller, and Moritz Sokolowski — Institut f. Physikalische u. Theoretische Chemie, Universität Bonn, Wegelerstr. 12, 53115 Bonn

Organic thin films on insulators attract increasing attention for both fundamental properties and promising applications in optoelectronics. Structural or chemical characterization on a long-range scale generally requires measurements by electron diffraction or spectroscopy, which cannot be conducted on insulators due to charge accumulation. This can be avoided by growing the organic films on thin insulating films on metallic substrates. Here we report the ordering of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) molecules on thin NaCl films grown on Ag(100), studied by spot-profile-analysis low energy electron diffraction (SPA-LEED). We show that high structural order can be achieved at the metal/insulator and insulator/organic interfaces and that LEED is operable on NaCl films about ten atomic layers in thickness. In agreement with Burke et al. [PRL 100, 186104 (2008)], the first monolayer (ML) of PTCDA forms a commensurate (3√2 × 3√2)R45^∘ superstructure with a quadratic unit cell (a=16.95 Å) and a T-shape in-plane molecular arrangement. This commensurate structure is metastable and can evolve to bulk-like nanocrystallites upon annealing above 273 K or exceeding 1 ML in coverage. However, growth at low temperature (223 K) yields PTCDA multilayers which are aligned with the first monolayer and exhibit an incommensurate structure. This project is financed by the A. v. Humboldt Foundation.