Berlin 2018 – scientific programme

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O: Fachverband Oberflächenphysik

O 14: Organic-inorganic hybrid systems and organic films II

O 14.1: Invited Talk

Monday, March 12, 2018, 15:00–15:30, MA 042

Non-commensurate epitaxy with and without coincidences — •Roman Forker — Friedrich-Schiller-Universität Jena, Institut für Festkörperphysik, Helmholtzweg 5, 07743 Jena, Germany

The self assembly of atoms or molecules at surfaces is governed by the balance between adsorbate–adsorbate and adsorbate–substrate interactions. Energetic minimization may be achieved through different types of epitaxy. Besides the well-known commensurate registries there are also the less familiar “on-line coincidences”, where the surface unit cells of the adsorbate and of the substrate have a common periodicity in one direction only [1]. Recently, highly ordered molecular monolayers were found to be room-temperature-stable even in the absence of any coincidence with the substrate Hence, the concept of lattice epitaxy fails to explain the evident energy minimum in such a case. Instead, we found that stabilization occurs through so-called static distortion waves that manifest in measurable sub-Ångström lateral shifts away from the positions of a translationally symmetric lattice (which itself is incommensurate) [2]. In the talk I will classify epitaxy using an easy-to-grasp scheme applicable both in reciprocal space and in real space. Several instructive literature examples of experimental structural characterization using scaning tunneling microscopy (STM) and low-energy electron diffraction (LEED) will be elaborated. The ultimate goal is to emphasize the importance of non-commensurate overlayer structures for the systematic understanding of epitaxy.

[1] R. Forker et al., Soft Matter 13, 1748 (2017).

[2] M. Meissner et al., ACS Nano 10, 6474 (2016).