Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 18: Poster Session I - MA 141/144 (Atomic Wires; Size-Selected Clusters; Nanostructures; Metal Substrates: Clean Surfaces+Adsorption of Organic / Bio Molecules+Solid-Liquid Interfaces+Adsorption of O and/or H; Surface or Interface Magnetism; Oxides and Insulators: Clean Surfaces)
O 18.30: Poster
Montag, 25. Februar 2008, 18:30–19:30, Poster F
Methanethiolate diffusion on Au(100) and Au(111) — •Andreas Franke and Eckhard Pehlke — Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel
Alkanethioles on unreconstructed Au(111) and Au(100) surfaces are studied as model systems for the bonding and diffusion of organic molecules on metal surfaces. Unreconstructed (111) and (100) surfaces of Au exist under certain electrochemical conditions [1]. We have extend our work on CH3S/Au(111) in a twofold way: In accordance with other studies [2] at low coverages we found CH3S–radicals to bind as Au(SCH3)2 complexes to the Au(111) surface with a binding energy of 2.38 eV per CH3S. We here present an ab initio study of the diffusion barriers for these complexes and bare CH3S. To this purpose, we employ the nudged elastic band method (NEB) as implemented in the VASP code. Furthermore, we compare the diffusion of the bare CH3S–radical on the (100) and (111) surface. On Au(100) the adatom formation and subsequent adsorption of two CH3S–radicals at the adatom is slightly less favorable than chemisorption of individual radicals on the defect free surface. The most stable adsorption position for CH3S is a tilted hollow-bridge geometry (for one radical per (4×4) surface unit cell) with a binding energy of 2.27 eV. The radical is tilted to the surface normal by 54∘. Transition states along the minimum energy path with barrier heights of 620 meV and 640 meV have been calculated.
[1] M. A. Schneeweiss, et al., Appl. Phys. A 69, 537 (1999).
[2] P. Maksymovych, et al., Phys. Rev. Lett. 97, 146103 (2006).