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O: Fachverband Oberflächenphysik

O 40: Metal substrates: Adsorption of organic / bio molecules V

O 40.6: Vortrag

Mittwoch, 16. März 2011, 12:30–12:45, PHY C213

Interplay of acceptor and donor species in charge-transfer complexes — •Tobias R. Umbach¹, Isabel Fernández-Torrente¹, Janina Ladenthin¹, Michael Kleinert¹, Robert Drost¹, Riccardo Rurali², Jose I. Pascual¹, and Katharina J. Franke¹ — ¹Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany — ²Institut de Ciència de Materiales de Barcelona (ICMAB),Consejo Superior de Investigaciones Científicas (CSIC), Campus de Bellaterra, 08193 Bellaterra (Barcelona), Spain

The redistribution of charge between donor and acceptor species plays a key role for tuning the electronic functionality of organic compounds. By low temperature scanning tunneling microscopy and spectroscopy (LT-STM, LT-STS) we investigate molecular layers of the donor acceptor complexes Na-TCNQ, Na-TNAP, TTF-TNAP and TTF-TCNQ on a Au(111) surface. Due to the presence of the metallic surface the amount of charge transfer (CT) and its localization can differ from the bulk system. Both TTF-TCNQ and Na-TCNQ exhibit a CT of one electron, demonstrated by the presence of the Kondo resonance. In the case of Na-TCNQ the electron is localized at the Na-CN bond, whereas for TTF-TCNQ it lies in the conjugated lowest unoccupied molecular orbital. By changing the molecular acceptor the CT can be varied. TCNQ offers a lower electron affinity and higher symmetry compared to TNAP. In contrast to the first two systems, Na-TNAP as well as TTF-TNAP show no Kondo resonance, evidencing an even or non-integer CT.