Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 88: Metal substrates: Adsorption of organic / bio molecules IX

O 88.3: Talk

Thursday, March 17, 2011, 17:45–18:00, PHY C213

Self-Assembly of Melem on Ag(111) - emergence of porous structures based on amino-heptazine hydrogen bonds — •Johanna Eichhorn¹, Stefan Schlögl¹, Bettina V. Lotsch¹, Wolfgang M. Heckl², and Markus Lackinger¹ — ¹Ludwig-Maximilians-University and Center for Nanoscience (CeNS), Munich, Germany — ²Deutsches Museum, Munich, Germany

Supramolecular self-assembly has been proven to be a powerful bottom-up technique for surface functionalization. In particular, two-dimensional nanoporous networks have attracted broad interest. Depending on the molecular building blocks, size and shape of cavities can be tuned. Many porous structures are stabilized by intermolecular hydrogen bonds between carboxylic acids. Yet, on more reactive substrates, carboxylic acids often bind strongly to the surface which hampers network formation. Therefore, we investigate less reactive building blocks for nanoporous networks on more reactive surfaces. In this respect amino groups in combination with heterocycles offer a promising alternative.

We studied self-assembly of melem, a triply amine functionalized heptazine ring, on Ag(111) by means of UHV-STM. Three different polymorphs were observed, where two structures exhibit pores with a diameter of ~1.5 nm. Each of those pores is bordered by six melem molecules interconnected by hydrogen bonds between amino groups and nitrogen in the heptazine ring. One of the porous structure exhibits two molecules per unit cell with a dimer as basic structural motif, while the densely packed polymorph exhibits only one molecule per unit cell.