Amorphous-to-crystalline phase transformation of thin film rubrene

We report on the amorphous-to-crystalline phase transformation of rubrene thin films. The crystallization of the organic thin films displays disk-like domains whose nucleation and growth follow phase transformation kinetics well-established for inorganic materials under certain time and temperature conditions. We understood that the crystallization of amorphous rubrene thin film shows site-saturated nucleation behavior while the crystalline growth involves both diffusion and interface-controlled kinetics displaying spherulitic disk growth behavior. The activation energy of the transformation kinetics was about 0.78 eV on hexamethyldisilazane-functionalized SiO₂ substrate as mostly consumed at the growth process. The crystallization kinetics changes with the film substrate; more hydrophobic substrate induces a lesser number of crystalline nuclei while causing faster growth of those nuclei.