Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 15: Postersitzung (Adsorption an Oberfl
ächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Rastersondentechniken, Zeitaufgelöste Spektroskopie, Methoden)
O 15.40: Poster
Freitag, 4. März 2005, 17:00–20:00, Poster TU D
A multi-parameter Ising model for the adsorption of molecules on structured surfaces — •Carsten Olbrich1, Klaus Morawetz1, Sibylle Gemming1,2, Reinhard Scholz1, Michael Schreiber1, Regina Ermrich2, and Gotthard Seifert2 — 1Institut für Physik, Technische Universität, D-09107 Chemnitz — 2Institut für Physikalische Chemie, Technische Universität, D-01062 Dresden
Several modifications of the standard two-parameter Ising model are necessary for the mesoscopic modelling of a realistic adsorbate ensemble on a non-ideal substrate. Depending on the shape of the molecule, the nearest-neighbour coupling exhibits a directionality, and also additional coupling terms with next nearest neighbours are taken into account. Structured or defective surfaces are modelled by local modifications of the magnetisation term. Several sets of coupling parameters were derived from first-principles calculations on PTCDA monomer, dimer, and adsorbate systems. The adsorbate distribution on the surface was investigated by Metropolis-Monte-Carlo simulations and cluster statistics employing the Hoshen-Kopelman cluster recognition algorithm. It was observed that surfacedefects like steps influence the pattern formation mainly close to the critical temperature of the order-disorder transition. It could be shown that all adsorbate-adsorbate interactions are connected by a straightforward scaling in the critical temperature, whereas the adsorbate-substrate interaction is of a more complicated nature, especially in the presence of surface defects.