Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 17: Poster Session I (Nanostructures at Surfaces; Metal Substrates: Epitaxy and Growth; Methods: Scanning Probe Techniques; Phase Transitions)
O 17.35: Poster
Montag, 26. März 2007, 17:30–20:30, Poster C
Adsorption and diffusion of CH3S–Au(111) — •Andreas Franke and Eckhard Pehlke — Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel
Alkanethiols have adopted the role of model systems for the bonding of organic molecules on metal surfaces via sulfur anchors and the formation of self-assembled monolayers. So far, however, little is known about the detailed diffusion mechanism of such molecules on the surface. As a starting point, we present a DFT-study of the adsorption and diffusion of CH3S–radicals on the Au(111)(1×1) surface in the low coverage regime using ab initio methods as implemented in the VASP code [1]. Unreconstructed Au(111) surfaces can be prepared under certain conditions at electrochemical interfaces [2]. In accordance with other DFT-studies (see e.g. [3] and references therein) we find that the most stable adsorption position is a tilted fcc-bridge geometry for all analysed coverages (Θ=1, 1/3, 3/16 molecules per (√3×√3) Au(111) surface unit cell) with a S-Au bond strenght of 1.86 eV (Θ=1) to 1.99 eV (Θ=3/16) and a tilt angles of 51∘ and 50∘ to the surface normal. Using the nudged elastic band (NEB) and the dimer-method, local transition states along the minimum energy path with diffusion barriers of 130 meV, 240 meV and 270 meV are identified. Calculations for CH3S adsorbed ontop of Au adatoms are underway.
[1] G. Kresse, J. Hafner, Phys. Rev. B 47, 15 (1993).
[2] M.A. Schneeweiss, H. Hagneström, M.J. Esplandiu, D.M. Kolb, Appl. Phys. A 69, 537 (1999).
[3] C. Masens, M.J. Ford, M.B. Cortie, Surf. Sci. 580, 19 (2005).