Dresden 2014 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 104: Organic electronics and photovoltaics II (organized by DS)

HL 104.6: Vortrag

Donnerstag, 3. April 2014, 19:00–19:15, CHE 91

Commensurability as the determining factor for molecular tilt and multilayer growth: In-situ and real-time growth study of the nanographene HBC on SiO2 and HOPG — •Paul Beyer1, Tobias Breuer2, Saliou Ndiaye2, Anton Zykov1, Andreas Viertel1, Manuel Gensler1, Jürgen P. Rabe1, Stefan Hecht1, Gregor Witte2, and Stefan Kowarik11HU Berlin, 12489 Berlin — 2Philipps-Universität Marburg, 35032 Marburg

We investigate the influence of symmetries and the substrate-molecule commensurability on the structure and growth kinetics of the nanographene hexa-peri-hexabenzocoronene (HBC). We study organic molecular beam deposited ultrathin HBC films on SiO2, pristine and sputtered HOPG because of the similar surface energies, singling out the influence of the lattice-matching between HBC and graphite. Using real-time and in situ x-ray growth oscillations we find the first ad-layer to grow lying down on both substrates. On pristine HOPG we find a superstructure of hexagonally arranged, recumbent molecules in a new polymorph using GIXD, XRR and NEXAFS. The loss of commensurability in the sputtered HOPG leads to mainly upright molecules. Equally, we find a transition to upright molecules on amorphous SiO2 surfaces. On SiO2 micro-crystallites in the bulk structure that completely cover the substrate are found, while the strong ordering on HOPG leads to island growth of the new polymorph as observed by AFM. Our results demonstrate that the (lack of) symmetry- and lattice-matching critically determines the molecular orientation and occurrence of surface induced polymorphs.

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