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O: Fachverband Oberflächenphysik

O 12: Organic Molecules at Surfaces 2: Characterization of Organic Monolayers

O 12.9: Talk

Monday, September 5, 2022, 17:00–17:15, S051

Van der Waals Heteroepitaxy: Intrinsic Epitaxial Alignment of Perfluoropentacene Films on Transition Metal Dichalcogenides — •Maximilian Dreher, Darius Günder, and Gregor Witte — Philipps-University Marburg, Germany

In this work, we have studied the formation and azimuthal alignment of crystalline adlayers of the organic semiconductor (OSC) perfluoropentacene (PFP) on the basal plane of several transition metal dichalcogenides (TMDC) single crystals, which are further compared to graphite and hBN. The quite inert basal planes of TMDCs enable an unrestricted growth of OSCs without the requirement of relaxation in terms of commensurability at the interface, since molecules exhibit a stronger interaction among each other than with the substrate. Nevertheless, the crystalline PFP multilayers exhibit distinct azimuthal twist angles relative to the substrate surface, which we could rationalize by so called 'on-line coincidences' introduced by Forker et al. recently. [1] Here, the molecules do not favor a specific adsorption site at the interface as it is often described by commensurate superstructures. Instead the bulk crystal structure remains unperturbed down to the interface, but a specific twist angle is adopted, where molecules avoid unfavored adsorption sites. The extreme sensitivity of the resulting twist angles by small deviations in the crystal structure enabled us further to use the large thermal expansion of the OSC to control the twist angles by changing the substrate temperature during deposition. [1] Forker et al., Soft Matter 13, 1748-1758 (2017) [2] Dreher et al., Chem. Mater. 32, 20, 9034-9043 (2020)