Dresden 2009 – scientific programme
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O: Fachverband Oberflächenphysik
O 44: Metal substrates: Adsorption of organic / bio molecules VI
O 44.2: Talk
Thursday, March 26, 2009, 10:45–11:00, SCH A118
SPA-LEED study on metal-free phthalocyanine sub-monolayers on Ag(111) — •Patrick Bayersdorfer1, Ingo Kröger1, Friedrich Reinert1,2, and Christian Kumpf1,3 — 1Universität Würzburg, Experimentelle Physik II, D-97074 Würzburg — 2FZ Karlsruhe, Gemeinschaftslabor für Nanoanalytik, D-76021 Karlsruhe — 3FZ Jülich GmbH, IBN-3, D-52425 Jülich
The geometrical alignment of organic molecules in the first adlayer on a surface strongly influences interface properties like surface dipoles or charge transfer, but it also plays an important role for the growth of further molecular layers. Phthalocyanines (Pcs) deposited on a silver surface play a prominent role in this context since they exhibit an unusual adsorption behaviour. We use high-resolution low energy electron diffraction (SPA-LEED) in order to investigate geometrical aspects of metal-free Pc (H2Pc) sub-monolayers on Ag(111). At room temperature (RT) and up to a coverage of 0.75 ML no long range ordered structures occur. The molecules arrange themselves randomly on the surface and maximize the distance to their neighbours. Between 0.75 ML and 0.91 ML a commensurate superstructure is formed followed by a series of continuously changing point-on-line structures above 0.91 ML. The latter superstructures were already observed for metal Pcs in our group (CuPc, SnPc, TiOPc, see contributions of I. Kröger, M. Häming and M. Kochler). They proof the existence of a dominant intermolecular repulsion between the molecules on Ag(111). However, in contrast to the metal Pcs, H2Pc exhibits a commensurate structure also at RT which indicates a reduced intermolecular repulsion.