Regensburg 2019 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 54: Organic Molecules on Inorganic Substrates III: Magnetism, Doping and Interfaces

O 54.4: Vortrag

Mittwoch, 3. April 2019, 11:15–11:30, H24

The Mixed Localization of Doping-Induced Charge Transfer at Semiconductor/Organic Interfaces: F4TCNQ on ZnO(10-10) — •Simon Erker and Oliver T. Hofmann — Institute of Solid State Physics, NAWI Graz, Graz University of Technology, Austria

At inorganic/organic interfaces, charge transfer occurs in different types, usually depending on the nature of the substrate. On metals, where the adsorbate often hybridizes with the substrate, hybrid bands are formed. These leads to a uniform, fractional charging of the organic overlayer. In contrast, on insulating and inert substrates, charge is transferred as integer electrons, which leads to the coexistence of charged and neutral molecules on the surface. In this work, we use DFT to study the charge distribution in an F4TCNQ monolayer adsorbed on the mixed terminated ZnO surface. Interestingly, we find that both mechanisms appear simultaneously for this system. Upon adsorption, the cyano groups of the molecule bind covalently to surface Zn atoms. The involved molecular orbitals hybridize with the substrate, leading to a homogeneous fractional positive charging of the molecular layer. Introducing free charge carriers in the substrate (e.g. by doping) additionally results in charge transfer of integer electrons into the unhybridized LUMOs of individual molecules. The fraction of molecules with filled LUMOs thereby directly depends on the charge carrier concentration in the ZnO. We conclude that hybridization of the orbitals, and not the "metallicity" of the substrates, determines the charge transfer mechanism.