Molecular orientation and morphology of contact printed α-quaterthiophene films on gold

We present contact printing as a technique to deposit α-quaterthiophene (α-4T) films from the solid phase onto gold. The molecular orientation and morphology of both the printed film and the original polycrystalline α-4T film on silica were investigated with low energy ion scattering (LEIS), atomic force microscopy (AFM), X-ray diffraction (XRD) and optical microscopy. We show that the strong interaction between clean gold and α-4T induces a drastic change in the molecular orientation and morphology of a 380 nm thick α-4T film. On gold the α-4T molecules are orientated with the thiophene rings parallel to the substrate and form rod-like crystallites (typically 13×1.3 μm²), whereas on silica α-4T molecules stand almost upright and form large cobblestone-like crystallites (typical diameter 10 μm). Exposure of α-4T to a low energy ion beam (dose <1×10¹⁴ 3 keV ³He⁺ ions/cm²) prior to printing causes polymerisation, which decreases the ability to print and alters the morphology of the printed film.