Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 37: Metal substrates: Adsorption of organic / bio molecules V

O 37.3: Talk

Wednesday, March 25, 2009, 15:30–15:45, SCH A118

Di-4-mercaptopyridine on Au(111): A Tunneling Microscopy and Spectroscopy Study — •Berndt Koslowski, Anna Tschetschetkin, and Paul Ziemann — Universität Ulm, Institut für Festkörperphysik, Albert-Einstein-Allee 11, D-89069 Ulm

We report on STM and STS measurements at low temperature of di-4-mercaptopyridine (di-4MPy) molecules adsorbed on Au(111). The di-4MPy is typically used as precursor for SAM deposition of 4MPy in an electrochemical cell. Here, the molecules were sublimated from a crucible onto the Au sample held at a temperature slightly below 0 ^∘C. By STM, we find two distinct kinds of molecules at the Au surface: the first is small and similar to the appearance of 4MPy monomers, and the second appears much larger in topography and is attributed to di-4MPy. At step edges we find exclusively 4MPy which points to a catalytic activity of steps dissociating dimers. Within terraces, the di-4MPy form islands expelling the herringbone reconstruction of the Au substrate. The structure within islands is complicated and is most probably a c(12×8√3) built from two enantiomeric unit meshes having a windmill structure composed of 5 or sometimes 6 molecules. We analyze the LUMO of di-4MPy by z-V spectroscopy, and we discuss the absorption geometry of the molecules.