Thin Film Growth of Pentacene on Polymeric Dielectrics: Unexpected Changes in the Evolution of Surface Morphology with Substrate

We have examined the thin film growth of pentacene on SiO₂ and on three different polymeric dielectrics using in situ synchrotron X-ray scattering and ex situ atomic force microscopy (AFM). The polymeric dielectrics investigated spanned the range from a low surface energy hydrophobic surface (polystyrene, PS) to a high surface energy hydrophilic surface [poly­(ethylene imine), PEI]. On all surfaces, pentacene forms a polycrystalline thin film, whose structure is that of the previously identified “thin film” phase. From in situ real-time X-ray scattering, we find that pentacene exhibits layer-by-layer (LbL) growth on all surfaces investigated, but the extent of LbL growth is a strong function of the underlying substrate. In particular, LbL growth is significantly more prolonged on PEI and least extended on PS. The roughness and the in-plane feature sizes of thick, ∼10 monolayer, pentacene thin films also vary with the surface energy of the substrategrowth on the high surface energy polymer thin film, PEI, is the smoothest and is characterized by the largest features. It appears that interlayer transport is influenced by the underlying substrate, even for layers that are not in direct contact with the polymer dielectric