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O: Fachverband Oberflächenphysik

O 26: Organic-inorganic hybrid systems and organic films III

O 26.7: Vortrag

Dienstag, 13. März 2018, 12:00–12:15, MA 042

F4-TCNQ and F6-TCNNQ Adsorbed on H-Si(111): Structure and Work-Function Changes. — •Haiyuan Wang, Svenja Janke, Sergey Levchenko, Mariana Rossi, and Matthias Scheffler — Fritz Haber Insitute of the Max Planck Society, Berlin, Germany

The tunability of hybrid inorganic/organic materials makes them promising candidates for more efficient photovoltaic and electronic devices. Even though the electronic properties of these materials critically depend on the structure of the interface, the latter is often poorly understood or characterized. Here we address model hybrid systems composed by the efficient electron acceptor molecules F4-TCNQ and F6-TCNNQ adsorbed on hydrogenated Si(111) surfaces [H-Si(111)]. We demonstrate how structural variations can lead to different electronic properties through a characterisation of these systems with density-functional theory, employing the HSE06 functional augmented with many-body van-der-Waals corrections [1]. We present exhaustive structure searches that show that F4-TCNQ and F6-TCNNQ lie flat on H-Si(111) at low coverages and become negatively charged. Interestingly, increasing the coverage to around 25% leads to a more stable structural motif with molecules standing at an angle to the surface. This motif is necessary to explain the work-function increase observed in experiment for the same system, which are performed in collaboration with T. Shultz and N. Koch (HU Berlin). This work is supported by SFB-951 project (HIOS).
A. Ambrosetti et al., J. Chem. Phys. 140, 18 (2014).