Modification of para-sexiphenyl layer growth by UV induced polarity changes of polymeric substrates

We report on the deposition of para-sexiphenyl (PSP) on poly(diphenyl bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate) (PPNB) by hot wall epitaxy (HWE). The surface polarity of the substrate, PPNB, can be increased by UV-illumination via a photo-Fries rearrangement. The influence of the changed surface polarity on the surface morphology and the structure of the PSP layers were studied by atomic force microscopy (AFM), X-ray diffraction (XRD) and grazing incidence X-ray diffraction (GIXD). The observation of growth spirals and islands, providing mono-layer step heights of standing PSP molecules, underline a high crystallographic order of the films which is confirmed by XRD analysis. GIXD experiments show a strong preferential (0 0 1) orientation of the PSP layers with better alignment on substrates with smaller surface polarity. The γ- and Baker-crystal structures are present in the films grown at low substrate temperatures, but only Baker structure was found in the films deposited at high substrate temperatures. However the main influence on the growth of PSP, is caused by the polarity change induced by pre-treating the PPNB substrate by UV-illumination.