Hot-wall epitaxy and molecular-beam epitaxy have been employed for growing quaterthiophene thin films on the (010) cleavage face of potassium hydrogen phthalate, and the results are compared in terms of film properties and growth mode. Even if there is no geometrical match between substrate and overlayer lattices, these films are epitaxially oriented. To investigate the physical rationale for this strong orientation effect, optical microscopy, atomic force microscopy, and X-ray diffraction are employed. A clear correlation between the morphology of the thin films and the crystallographic orientation is found. The results are also validated by surface potential calculations, which demonstrate the primary role played by the corrugation of the substrate surface.
International audienceThe optical response of rubrene crystals is described by providing the full UV-VIS dielectric tensor. Consistently with the molecular and crystal symmetries, the lowest crystal transition originates from an Au molecular transition, it is polarized along the c axis (normal to the larger crystal face), and it is the origin of the emission, which is self-guided towards the edge where the corresponding polarization and intensity angular distribution are detected. By contrast, the Bu molecular transitions give rise to Davydov states described by the other two components of the diagonal dielectric tens
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