Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 56: Metal substrates: Adsorption of organic / bio molecules III

O 56.6: Vortrag

Mittwoch, 28. März 2012, 18:00–18:15, A 053

Charge state of a donor-acceptor complex on the surface of a metal — •Isabel Fernandez-Torrente, Tobias R. Umbach, Adrian Olivera, Jose Ignacio Pascual, and Katharina J. Franke — Institut für Experimentalphysik, Freie Universität Berlin, Berlin, Germany

The charge state of a molecule has a strong impact on its reactivity and transport properties. We investigate by means of scanning tunneling microscopy (STM) and spectroscopy (STS) the electronic properties of the electron-acceptor 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) adsorbed on Au(111), and its mixture with the electron-donor tetrathiafulvalene (TTF). Highly ordered pure F4TCNQ islands leave the underlying herringbone reconstruction unaffected. The charge state of the molecule depends strongly on the adsorption site: only the molecules located on the hcp regions are single charged, as demonstrated by the presence of a Kondo resonance in STS experiments. Combined deposition of TTF and F4TCNQ results in the formation of two mixed, ordered phases with 1:1 and 5(F4TCNQ):4(TTF) stoichiometries that destroy the reconstruction of the surface. The F4TCNQ within each unit cell are not homogeneously coupled to the surface due to the lateral interaction with TTF and, consequently, they exhibit different charge states. Furthermore, STS displays extremely sharp features on the F4TCNQ molecules of this mixed phases that are associated to charging/discharging events in a double barrier tunnelling junction mediated by the electric field of the STM tip.