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O: Fachverband Oberflächenphysik

O 42: Poster: Organic-Inorganic Hybrid Systems and Organic Films

O 42.8: Poster

Dienstag, 13. März 2018, 18:15–20:30, Poster A

Towards Computational Structure Prediction of Organic Thin Films and Multilayers: TCNE on Cu(111) — •Alexander T. Egger, Lukas Hörmann, Andreas Jeindl, Michael Scherbela, and Oliver T. Hofmann — Institute of Solid State Physics, Graz University of Technology, Austria

Organic thin films often crystallize in peculiar, surface-induced phases, which exhibit physical properties that are superior to the bulk structures. However, resolving the surface-induced thin film phases remains a huge challenge, in particular for first-principle calculations. While efficient structure determination strategies exist for isolated molecules or bulk crystals - and to a limited extend also molecular monolayers - none of these are efficiently applicable to multilayer structures or organic thin films.

In this contribution, we demonstrate a strategy to fill this gap. Using the SAMPLE approach, which combines coarse-graining of the potential energy surface with machine learning, we start from an energetically optimized first layer. Subsequently, we predict energetically favorable positions for a single molecule in the second layer. Using these positions as "building blocks", we create a new discretized PES to predict structure of higher layers.

Here, we demonstrate the applicability of this approach on TCNE (tetracyanoethene) on Cu(111). Specifically, we investigate whether, at high coverage, the system will undergo a phase transition from a densely packed, face-on geometry to upright standing molecules, or whether - and in which structure - a TCNE bilayer forms.