Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 76: Organic, Polymeric, Biomolecular Films - also with Adsorbates

O 76.2: Vortrag

Donnerstag, 28. Februar 2008, 15:30–15:45, MA 043

Mercaptopyridine and 4-aminothiophenol self-assembled layers in metal-molecule-metal contacts: a computational DFT study — •Jan Kucera and Axel Groß — Institute für Theoretische Chemie, Universität Ulm, Germany

Recently it has become possible to deposit two-dimensional Pd layers on top of a 4-mercaptopyridine (Mpy) or a 4-aminothiophenol (4-ATP) self-assembled monolayer (SAM) on Au(111) leading to metal-molecule-metal contacts [1]. We performed periodic density functional theory (DFT) calculations in order to contribute to the interpretation of the experimentally observed geometric and electronic structures.

The calculations show that the adsorption structures of Mpy and 4-ATP on Au(111) are very similar. Both molecules prefer to bind to bridge-hollow sites at low as well as at high coverages. At low coverages, the molecules are significantly tilted from the Au(111) surface normal, whereas a denser packing leads to more upright configurations. The Pd/SAM interfaces correspond to metastable configurations in spite of the relatively strong Pd-Au interaction. The Pd-SAM contact is made through one-fold coordinated Pd-N bonds. In agreement with the experiment, the density of states (DOS) of Pd layer shows a significant reduction close to the Fermi level with respect to bulk Pd due to the Pd-N interaction. Also in agreement with experiment, the calculations confirm that 4-ATP is able to form bilayer structures connected through hydrogen bonds between the sulfur head group and up to to three hydrogen atoms of the amino group.

[1] H.-G. Boyen et al., Nature Materials 5, 394 (2006)