Improved structural ordering in sexithiophene thick films grown on single crystal oxide substrates

We report on sexithiophene films, about 150-nm thick, grown by thermal evaporation on single-crystal oxides and, as comparison, on Si/SiO₂. By heating the entire deposition chamber at 100°C we obtain standing-up oriented molecules all over the bulk thickness. Surface morphology shows step-like islands, each step being only one monolayer in height. The constant and uniform warming of the molecules obtained by heating the entire deposition chamber allows a stable diffusion-limited growth process. Therefore, the regular growth kinetics is preserved when increasing the thickness of the film. Electrical measurements on differently structured films evidence the impact of the inter-island separation region size on the main charge-transport parameters.