MORPHOLOGY AND ROUGHNESS OF HIGH-VACUUM SUBLIMED OLIGOMER THIN-FILMS

We present an atomic force microscopy study on the morphology and roug hness of sexithienyl (T6) thin films evaporated on mica in high vacuum . The effects of two thermal processes are investigated: (i) temperatu re of the substrate during evaporation, and (ii) annealing temperature in high vacuum. The former yields a good control on the extension of grain boundaries and the aggregate ordering, but does not affect surfa ce roughness. The latter is characterized by a threshold temperature ( similar to 175 degrees C) above which a smooth continuous surface is f ormed, The roughness scaling behaviour is analysed by the power spectr um of the topographical profiles. T6 surface is self-affine over 1-2 o rders of magnitude of the spatial frequencies. However, films prepared at substrate temperatures above 200 degrees C or annealed above the c ritical temperature exhibit an extended self-affine behaviour. The rou ghness scaling factor suggests a growth process of the Kardar-Parisi-Z hang universality class.