Regensburg 2019 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 38: Organic Molecules on Inorganic Substrates II: Electronic Properties and Charge Transfer
O 38.9: Vortrag
Dienstag, 2. April 2019, 16:00–16:15, H24
Charge distribution within molecular dipoles and their influence on the local work function of the substrate — •Sergey Trishin1, Daniela Rolf1, Christian Lotze1, Philipp Rietsch2, Siegfried Eigler2, and Katharina J. Franke1 — 1Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany — 2Institut für Chemie und Biochemie, Freie Universität Berlin, 14195 Berlin, Germany
Donor-acceptor (DA) molecules exhibit two charge-separated moieties, which makes them interesting for application in molecular electronics. However, deposition on metal surfaces, which may be necessary for certain applications, can alter the charge distribution of DA molecules due to screening and hybridization effects.
We study Ethyl-Diaminodicyanoquinone molecules on a Au(111) surface with scanning tunnelling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). By mapping the local contact potential difference (LCPD) over the molecules we show that the intrinsic dipole moment of the molecules is partially preserved upon adsorption on the Au(111) surface. Moreover the molecular orbitals appear to be shifting across the molecule. This shift follows the variation of the LCPD signal. Both findings can be explained by vacuum-pinned energy levels and local changes in the work function due to the molecular charges. An overall reduction of the work function is related to a local scale push-back effect. There molecules push back substrate electrons, which are leaking out into the vacuum.