Kinetics of selecting polymorphism in organic molecular film growth

The kinetics of nucleation and growth of metal-phthalocyanine thin films on Ag(100) surface were studied as a model system to elucidate the mechanism of polymorphic selectivity in organic molecular films. Real-time low-energy electron microscopy combined with scanning tunneling microscopy and DFT calculations revealed that the intermolecular vibrational modes determining kinematic discrete paths are specific to a particular in-plane arrangement of molecules, which in turns, tunes the growth and decay of polymorphic embryos. Phonon-constrained kinematic paths for interface-mediated kinetic processes, therefore, determine the phase transition and polymorph selection, rather than classical kinetic equilibrium. This phonon-constrained kinetics allows for selecting the growth mode and phase transition spontaneously from among competitive polymorphs.