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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 13: Poster: Crystallization and Self Assembly

CPP 13.4: Poster

Montag, 22. März 2010, 16:30–18:00, Poster C

Substrate induced orientation in thin crystalline polythiophene fims — •Anas Mujtaba, Thomas Henze, Nitin Shigne, and Thomas Thurn-Albrecht — Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle (Saale)

We studied if and to what extent the crystal orientation of poly (3-hexyl thiophene) thin films can be controlled by substrate effects. Regioregular head-to-tail (HT)-coupled P3HT thin films were crystallized on silicon and HOPG (highly oriented pyrolytic graphite) substrates. Surface morphology and crystal orientation were probed by atomic force microscopy (AFM) and X-ray diffraction (XRD). For both substrates, AFM measurements showed edge-on crystalline lamellae separated by amorphous inter-lamellar zones. The surface topography showed characteristic differences for the two substrates. In some cases for graphite, the crystal orientation reflected the three fold rotational symmetry of the underlying substrate indicating epitaxial effects. XRD measurements revealed different crystal orientation for the two cases. On silicon the crystal a-axis stands perpendicular on the substrate, i.e. the layered structure consisting of separated main and side chains is lying parallel to the substrate, while on graphite the crystal b-axis i.e. the π-π stacking direction is oriented perpendicular to the substrate and consequently the main/side chain layered structure aligned perpendicular to the graphite substrate. The orientation on silicon can be attributed to the wetting effects active in high temperature layered phase, on contrary graphite acts as a nucleating surface inducing oriented epitaxial crystallization.