Growth of ultrathin pentacene films on polymeric substrates

Growth of vapor deposited submonolayer thick pentacene films on polystyrene, poly(α-methylstyrene), and poly(methyl methacrylate) was investigated using tapping-mode atomic force microscopy. For comparison we also studied pentacene thin-film growth on SiO₂. On polar surfaces pentacene nucleates in the form of two-dimensional islands, while on apolar surfaces at higher temperatures a noticeable fraction of three-dimensional island nucleation is also observed. By measuring the monolayer-island nucleation densities and coverages as a function of substrate temperature, we showed that a transition from complete to the initially incomplete condensation occurs in the temperature range from 45 to 55 ^∘C on all surfaces. We calculated the activation energies for surface diffusion of pentacene molecules on all substrates. From the temperature dependence of the first and subsequent pentacene layer coverages we deduced that the substrate-pentacene interaction is weaker in the case of apolar surfaces as compared to polar surfaces. Our findings suggest that it is possible to predict the submonolayer nucleation behavior of pentacene on inert substrates based on the polar component of the substrate surface energy.