Regensburg 2016 – scientific programme
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O: Fachverband Oberflächenphysik
O 77: Gerhard Ertl Young Investigator Award
O 77.2: Invited Talk
Thursday, March 10, 2016, 11:00–11:30, S051
When Electron Acceptors Donate Charge: Molecular Orbitals vs Hybrid Bands at Inorganic/Organic Interfaces — •Oliver T. Hofmann1, Patrick Rinke2, Matthias Scheffler3, and Georg Heimel4 — 1TU Graz, Graz, Austria — 2Aalto University, Helsinki, Finland — 3Fritz-Haber-Insitut der MPG, Berlin, Germany — 4Humboldt University of Berlin, Germany
At inorganic/organic interfaces, the concept of electrons moving in extended bands collides with the notion of localized molecular orbitals. For the adsorption of most electron accepting molecules, theory and experiment concordantly report an average charge-transfer smaller than one electron per molecule, raising the question how such an (indivisible) object can be divided between the subsystems. Using hybrid density functional theory (DFT) we prepare and contrast both situations for TCNE molecules on clean and NaCl-passivated Cu substrates. Hybrid DFT functionals localize electrons on a subset of individual molecules, who become charged and whose signatures and associated observables differ markedly from the delocalized band states of fractionally charged molecules obtained with semi-local DFT. We then apply our computational framework to F4TCNQ on ZnO(1010), which exhibits two different charge transfer types. Charge donation again leads to integer charging of individual molecules, whereas charge back-donation proceeds via covalent bonds and thus delocalized hybrid bands. Since back-donation also occurs for the uncharged F4TCNQ molecules in the organic film, we end up with the counterintuitive situation of positively charged electron acceptors on the ZnO surface.