We present a systematic study on the epitaxial growth of $\alpha$-sexithiophene (6T) on two different types of substrates, phlogopite and muscovite mica. The study is based on a structural and morphological analysis using specular x-ray diffraction, x-ray diffraction pole figure technique, transmission electron microscopy, atomic force microscopy, and optical microscopy. It is shown, that 6T molecules on mica substrates crystallize in two different configurations, characterized either by the ($\stackrel{̲}{4}$11) or (100) contact plane. Whereas the first orientation consists of needle-like structures, the latter one forms an island-like morphology, and both crystal orientations exhibit a well-defined relationship with respect to each other. We demonstrate that this finding can be explained by directed epitaxy of islands along the sidewalls of the needle-like structures.

• Received 1 December 2010

DOI:https://doi.org/10.1103/PhysRevB.83.115443