Two-Step Growth of Large Pentacene Single Crystals Based on Crystallization of Pentacene Monolayer Film

A two-step growth method, namely, initial crystallization from pentacene,monolayer grains to nanosized single crystals (nanocrystals) and,. subsequent physical vapor transport (PVT) growth on the nanocrystals as seeds, is demonstrated to fabricate larger microsized pentacene single crystals. The pentacene monolayer film deposited on a bare SiO2 substrate was found to self assemble to nanoparticles during a post annealing process. Selected area electron diffraction demonstrates unambiguously the nanoparticles and the microsized particles grown by the following PVT are both. single crystals but with different crystal phases. Such a two-step growth technology maintains the intrinsic interface states between the SiO2 dielectric and the pentacene active layer and provides a more flexible way to in-situ prepare oraganic single crystals for device fabrication. The detailed investigation of morphology evolution and the discussion of formation mechanism of nanocrystal seeds indicate that the pentacene molecular transport during annealing is controlled by molecular surface diffusion. A crystal growth diagram based on thermodynamic analysis is proposed to qualitatively interpret the molecular transport from the monolayer film to the nanocrystals of pentacene.