Regensburg 2013 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 32: Poster: Organic Semiconductors
CPP 32.8: Poster
Mittwoch, 13. März 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 Kowarik2 — 1Fachbereich 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 150∘C 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 25∘C. 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.