Crystal structure of polycrystalline films of quaterthiophene grown by organic molecular beam deposition

The growth of thin films of oligothiophenes by organic molecular beam deposition (OMBD) can produce highly ordered polycrystalline samples. Recently. quaterthiophene (4T) thin films were grown on different substrates (silica, graphite, potassium acid phthalate, silicon). In some cases. their optical behavior was found to resemble that of 4T single crystals, with a macroscopic anisotropy close to that of the bulk crystal. A careful structural characterization of these films was undertaken. A morphological and optical characterization was performed by atomic force microscopy (AFM) and optical absorption. Electron microscopic examination in both bright field and diffraction was carried out on 4T thin films deposited on two selected substrates: silica and single crystals of potassium phthalate acid salt. The crystal polymorph, contact plane, and coherent orientation obtained on these 4T microcrystalline films fully agree with the optical behavior of the samples. (C) 2003 Elsevier Science B.V. All rights reserved.