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HL: Fachverband Halbleiterphysik

HL 23: Charge transfer effects in molecular materials II (CPP, jointly with BP, DS, HL)

HL 23.3: Vortrag

Montag, 11. März 2013, 15:45–16:00, H40

Metal-Molecule Charge Transfer through Surface-Induced Conjugation — •Georg Heimel¹, Steffen Duhm², Ingo Salzmann¹, Alexander Gerlach³, Antje Vollmer⁴, Frank Schreiber³, and Norbert Koch¹ — ¹Institut für Physik, Humboldt-Universität zu Berlin, 12489 Berlin, Germany — ²Institute of Functional Nano & Soft Materials, Soochow University, Suzhou 215123, P. R. China — ³Institut für Angewandte Physik, Universität Tübingen, 72076 Tübingen, Germany — ⁴Helmholtz Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany

For the majority of large π-conjugated molecules, the Fermi level of supporting coinage-metal substrates is pinned to stay well within their electronic energy gap. In some cases, however, the Fermi level does cross into either of the frontier molecular orbitals. On the basis of a combined multi-technique experimental and theoretical study on a particularly clear-cut case – pentacenequinone and pentacenetetrone on the (111) surfaces of Au, Ag, and Cu – we present an attempt for a unifying explanation of such intriguing cases: The conjugation length of the organic semiconductor increases through interaction of specific chemical substituents with the metal surfaces. The ensuing reduction of the energy gap is found to be the crucial ingredient needed to overcome Fermi-level pinning. Our findings aid in the design of charged molecular monolayers, which are of interest both from the fundamental- and the applied-physics point of view.