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.

An experimental investigation of the surface modification of polytetrafluoroethylene (PTFE) by an Ar and Ar/O 2 plasma created with an atmospheric-pressure radio frequency (r.f.) torch is presented here. The surfaces were analyzed by atomic force microscopy (AFM), XPS and water contact angle (WCA) to get an insight of the surface morphology and chemistry. An increase of roughness is observed with the Ar/O 2 plasma treatment. The WCA analysis shows that these surfaces are more hydrophobic than pristine PTFE; a contact angle of 135• was measured. When a PTFE surface is treated by Ar plasma, no roughening or significant change of the surface morphology and chemistry of PTFE was observed. The effects of the Ar and O 2 fluxes on the PTFE surface treatment were analyzed, as well as the effect of the power and treatment time. The plasma phase was also analyzed by optical emission spectroscopy, and some correlations with the treatment efficiency of the plasma are made. The chemistry on the surface is finally discussed and the competition between etching and re-deposition chemical reactions on the surface is proposed as a possible explanation of the results.

Two approaches to transition‐temperature engineering in liquid crystalline oligothiophenes are described: (i) substitution at the aromatic core with two identical branched alkyl chains and (ii) desymmetrization of the molecule with two alkyl substituents of different length or structure. Key steps in the synthesis of symmetrical and nonsymmetrical terthiophenes and quaterthiophenes involve Suzuki coupling and carbanion alkylation. A well‐adjusted balance between the π–π stacking of the aromatic core and the disorder caused by the peripheral alkyl chains is demonstrated to be important for the control of the thermotropic behavior of oligothiophene mesogens. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

We present a joint experimental and theoretical study of the structural and charge-transport properties of a liquid-crystalline α,ω-disubstituted oligothiophene derivative for application in organic field-effect transistors. The structural properties of the crystalline and smectic phases are investigated by atomic force microscopy, X-ray reflectometry, and X-ray diffraction. To complement these data, molecular mechanics calculations together with the simulation of X-ray diffraction spectra were performed to determine the relative positions of the molecules in the unit cell. The electrical characteristics of field-effect transistors based on the oligothiophene derivative were measured and compared in the crystalline and smectic phases. Although the silanation of the SiO2 gate dielectric promoted a marked improvement in the charge-carrier mobilities in the crystalline phase, the expected suppression of grain boundaries in the liquid-crystalline phase was not unambiguously evidenced. The experimental results were further complemented by a detailed theoretical analysis of the electronic couplings governing the charge-transport properties on the molecular scale.

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