Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 59: Molecular Nanostructures

O 59.5: Talk

Thursday, February 28, 2008, 10:30–10:45, MA 041

A scalable open-pore network: melamine and fatty acids on graphite — •Hermann Walch, Anne-Kathrin Maier, Wolfgang M. Heckl, and Markus Lackinger — LMU München, Sektion Kristallographie, Theresienstr. 41, 80333 München

Scanning tunneling microscopy (STM) at the liquid-solid interface was utilized to investigate bimolecular open pore networks comprised of melamine and the homologous series of fatty acids extending from pentanoic through dodecanoic acid. Since at room temperature longer fatty acids (from decanoic acid on) are solid a novel heatable sample holder for measuring at slightly elevated temperatures was designed. Structural properties of the self-assembled mononlayers (SAMs) were deduced from the STM data and modelled by force field calculations. Melamine is a heterocyclic aromatic molecule consisting of a triazine ring functionalized with three amine-groups at the 2-, 4-, and 6-positions. In this study, the fatty acids serve as a solvent for melamine but are also incorporated into the SAMs. For all solvents hexagonal honeycomb structures were observed, where the lattice parameter increases linearly from 2.8 nm to 3.8 nm with the chain length of the solvent. All networks exhibited a similar architecture: melamine molecules are located at the corner of hexagons and two adjacent melamins are interconnected by fatty acid molecules in head to tail configuration. Each of the connecting fatty acid molecules forms two H-bonds with one of the melamine molecules. Hence, melamine accounts for the symmetry of the structures, whereas the fatty acid molecules act as a spacer, thus giving rise to the remarkable scalability of these bimolecular networks.