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Regensburg 2013 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 32: Poster: Organic Semiconductors

CPP 32.8: Poster

Wednesday, March 13, 2013, 16:30–18:30, Poster C

Molecular orientation and growth mode of organic molecular beam deposited ultrathin HBC films on SiO2 — •Paul Beyer1,2, Tobias Breuer3, Saliou Ndiaye3, Gregor Witte3, and Stefan Kowarik21Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany — 2Institut für Physik, Humboldt-Universität zu Berlin, 12489 Berlin, Germany — 3Fachbereich Physik, Philipps-Universität Marburg, 35032 Marburg, Germany

Hexa-peri-hexabenzocoronene (HBC) is a polycyclic aromatic hydrocarbon that is investigated in supramolecular electronics due to its high electron mobility of up to 1 cm2/Vs. We examine the real-time growth kinetics of organic molecular beam deposited ultrathin HBC films on silicon dioxide using x-ray diffraction and x-ray spectroscopy.

With grazing incidence x-ray diffraction (GIXD) we observe a larger cristallinity at higher substrate temperatures of 150C but rough films. We observe smooth films as indicated by growth oscillations of specular x-ray reflectivity (XRR) during growth of HBC at lower temperatures of 25C. The growth oscillations show changes in the molecular arrangement during the first monolayers. To test whether the molecular orientation changes we use near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the BESSY II synchrotron. NEXAFS is used to determine the orientation of the π orbitals and therefore the orientation of the HBC molecules in (sub)mono- and multilayer films. We find that the molecules on average are tilted by an angle of 74 relative to the surface plane.

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