Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 13: Polymeric biomolecular films

O 13.10: Vortrag

Montag, 26. März 2012, 18:15–18:30, MA 005

Reaction mechanism of debromination on coinage metals — •Jonas Björk¹, Felix Hanke², and Sven Stafström¹ — ¹Linköping University, Sweden — ²University of Liverpool, UK

Covalent bonded molecular networks can be formed through self-assembly on various surfaces. A successful approach has been to use molecular building blocks with specific hydrogen atoms replaced by bromine atoms. The bromine atoms can split-off, allowing covalent coupling between the un-saturated carbon atoms. However, despite the experimental success in the field, there is a lack of theoretical understanding of covalent self-assembly. In particular, a coherent picture is lacking for the temperature dependence of the debromination reaction and the adsorption properties of reactants and products.

Here, we present a theoretical study of the debromination on the close-packed (111)-facets of coinage metals, commonly used in covalent self-assembly. Within the framework of van der Waals density-functional theory, and using bromobenzene as model component for the debromination, the catalytic activities of the Au, Ag and Cu surfaces are compared. It is found that the reactions are described by similar mechanisms on all surfaces, in that the C-Br dissociation follows an almost identical path and that there are no radical products. The reaction proceeds easiest on the Cu(111) surface, while it is associated with the largest energy barrier on Au(111). Finally, the consequences of the energy barriers on the temperature dependence for each surface will be discussed.