Screw dislocations on polycenes: A requirement for crystallization

The morphology and growth behavior of naphthalene, anthracene, and tetracene is studied both experimentally and by computer simulations. We will show that the attachment energy morphology prediction for all compounds gives approximately the correct habit, but that this is merely coincidental. Our Monte Carlo simulations and vapor growth experiments show that the thickness growth of the crystals perpendicular to the {001} faces is due to spirals on that face. If these screw dislocations were not present, the basal faces would not grow and no crystal would be formed at moderate driving force. At very high driving forces, very thin plates without screw dislocations were observed, with a morphology that is in agreement with the results of our Monte Carlo simulations.