Regensburg 2007 – scientific programme
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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 17.34: Poster
Monday, March 26, 2007, 17:30–20:30, Poster C
Interface molecular dipoles on metal surfaces — •Fernández-Torrente Isabel1, Sergio Monturet2, Katharina Jennifer Franke1, Nils Henningsen1, Nicolás Lorente2, and José Pascual1 — 1Institut für Experimentalphysik, Freie Universität Berlin, Germany — 2Université Paul Sabatier, Toulouse, France
Association of molecules with donor and acceptor character forms the so called molecular charge transfer complexes. Tetrathiafulvalene 7,7,8,8-tetracyanoquinodimethane (TTF-TCNQ) is a well-known example of a compound with a metal conducting behaviour governed by charge transfer interactions between the TTF (donor) and the TCNQ (acceptor). Here we report on the submonolayer growth of TTF on a Au(111) surface studied by Low Temperature Scanning Tunneling Microscopy. We find that TTF lies tilted on the surface and two S atoms dominate the adsorption. As a function of coverage we resolve several phases of the growth with different dimensionalities. In combination with DFT calculations we show that the growth is mediated by the balance between a repulsive and an attractive interaction. The repulsive force is associated to the creation of a dipole between TTF and the metallic surface while the attractive interaction is related to the formation of intermolecular H-bonds. At low coverage, molecules show primarily repulsion and they adsorb as monomers. As the coverage increases the attractive interaction gains importance and the molecules self-assemble in one and two dimensional structures.