Dresden 2017 – scientific programme
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O: Fachverband Oberflächenphysik
O 51: Nanostructures at Surfaces: 1D and 2D Structures and Networks
O 51.10: Poster
Tuesday, March 21, 2017, 18:30–20:30, P1C
Epitaxy of Flexible 2D Crystals — •Matthias Meissner1, Falko Sojka1, Lars Matthes1, Friedhelm Bechstedt1, Xinliang Feng2, Klaus Müllen2, Stefan C. B. Mannsfeld3, Roman Forker1, and Torsten Fritz1 — 1Uni Jena Germany — 2MPI für Polymerforschung Mainz, Germany — 3cfaed, TU Dresden, Germany
The epitaxy of many organic films on inorganic substrates can be classified within the framework of rigid lattices which helps to understand the reproducible film orientations. For incommensurate systems, however, this classification fails as an explanation for an epitaxial alignment. Tiny shifts in atomic positions away from ideal lattice points, so-called static distortion waves (SDWs), had been proposed to be responsible for the orientational epitaxy in such cases. Using low-energy electron diffraction and scanning tunneling microscopy, we provide direct evidence for SDWs in the incommensurate monolayer of the molecule hexa-peri-hexabenzocoronene on graphite. They manifest as sub-Ångström molecular displacements away from an ideal, yet incommensurate lattice. By means of a density-functional-theory based gradient approach, we show that flexibility in the adsorbate layer is crucial to provide a total energy minimum for the observed domain orientation, constituting orientational epitaxy. While structural relaxation at an interface is a common assumption, the combination of the precise determination of the incommensurate epitaxial relation, the direct observation of SDWs in real space, and their identification as the sole source of epitaxial energy gain constitutes a comprehensive proof of this effect. [M. Meissner et al.: ACS Nano 10, 6474-6483 (2016).]