Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

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

O 56.7: Talk

Wednesday, March 28, 2012, 18:15–18:30, A 053

Site-specific adsorption and reversible switching of C60 on porphyrin double-decker complexes — •Saranyan Vijayaraghavan, David Écija, Sushobhan Joshi, Willi Auwärter, and Johannes Barth — Physik Department E20, Technische Universität München, D-85748 Garching, Germany

Organic solar cells based on donor-acceptor architectures are the next paradigm in photovoltaics taking into account that they are flexible, easier to process than the inorganic counterparts and environmental friendly. . Accordingly, a fundamental understanding of molecular donor-acceptor systems is of immense interest for related applications. Here, we report a scanning tunneling microscopy (STM) and spectroscopy (STS) study characterizing C60 molecules on CeTPP2 arrays on a Ag(111) substrate. At low coverage and temperature, the C60s adsorb on the center of the top porphyrin of the CeTPP2, thus forming non-covalent porphyrin-C60 dyads. The STS measurements indicate a weak coupling of the C60 to the Ag substrate, as evidenced by a large HOMO-LUMO gap and a negative differential resistance regime. High-resolution images resolve three distinct orientations of the C60 on CeTPP2. By applying a current pulse with the STM tip, it is possible to switch individual C60s between these three configurations without changing the lateral registry. A plot of tunneling current vs. time reveals three levels of conductance. Each level corresponds to one of the distinct C60 orientations and thus represents a specific intra-dyad coupling