Interface induced crystal structures of dioctyl-terthiophene thin films |
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Authors: | Werzer Oliver Boucher Nicolas de Silva Johann P Gbabode Gabin Geerts Yves H Konovalov Oleg Moser Armin Novak Jiri Resel Roland Sferrazza Michele |
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Institution: | Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 810 Graz, Austria. |
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Abstract: | Temperature dependent structural and morphological investigations on semiconducting dioctyl-terthiophene (DOTT) thin films prepared on silica surfaces reveals the coexistence of surface induce order and distinct crystalline/liquid crystalline bulk polymorphs. X-ray diffraction and scanning force microscopy measurements indicate that at room temperature two polymorphs are present: the surface induced phase grows directly on the silica interface and the bulk phase on top. At elevated temperatures the long-range order gradually decreases, and the crystal G (340 K), smectic F (348 K), and smectic C (360 K) phases are observed. Indexation of diffraction peaks reveals that an up-right standing conformation of DOTT molecules is present within all phases. A temperature stable interfacial layer close to the silica-DOTT interface acts as template for the formation of the different phases. Rapid cooling of the DOTT sample from the smectic C phase to room temperature results in freezing into a metastable crystalline state with an intermediated unit cell between the room temperature crystalline phase and the smectic C phase. The understanding of such interfacial induced phases in thin semiconducting liquid crystal films allows tuning of crystallographic and therefore physical properties within organic thin films. |
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