SEXITHIOPHENE THIN-FILMS EPITAXIALLY ORIENTED ON POLYTETRAFLUOROETHYLENE SUBSTRATES - STRUCTURE AND MORPHOLOGY

The structure and morphology of sexithiophene thin films vacuum-deposi ted on friction-transferred polytetrafluoroethylene (PTFE) substrates was investigated by optical and electron microscopy and electron diffr action. Highly birefringent 6T films are formed at high or low deposit ion rates. Electron diffraction indicates the presence of three differ ent crystal populations differing by the orientation of the 6T molecul ar axis and/or the molecular plane. First, the strongest substrate/dep osit interactions are based on epitaxy and lead to a well-defined, sym metric molecular arrangement (Type I) with the 6T molecular and the PT FE chain axes parallel and the 6T molecular planes tilted at +/-33 deg rees to the substrate. Second, more ''defective'' orientations result from interactions with the bare glass surface (Type II) and with the P TFE film edges or ridges (Type III), respectively. As shown in a paral lel study using spectroscopic techniques, these defective orientations have a definite impact on the overall optical properties of the sexit hiophene thin films. (C) 1997 Elsevier Science S.A.