Molecular origin of structural defects in the zinc phthalocyanine film

Abstract

Controlling the growth of thin phthalocyanine films is a long-term challenge for the science of applied nanomaterials. So, this contribution deals with films of unsubstituted zinc phthalocyanine (ZnPc) and seeks to acquire structural information that is unavailable via physical experiments, thus, finding out how the film morphology can be seriously improved. A model of the vapor-deposited film has been created using the molecular dynamics method. Specifically, the ZnPc molecules are dosed into the simulation box under normal conditions, reproducing key features of the real film, such as the trimolecular wetting layer and the island-like three-dimensional (3D) phase that is structured like the α-polymorph; then all film fragments are characterized via their radial distribution functions and mean-squared displacements. The simulation model indicates that the 3D phase starts to develop smoothly through multimolecular cofacial stacking but finally becomes fragmental because the wetting layer is too meager to be a good platform for regular film growth. Accordingly, the film morphology may be improved if the wetting layer is thickened via restraining the vertical development of the 3D phase. Following this idea, uniform ZnPc films impaired by neither grain boundaries nor coarser defects were deposited from solutions and visualized at the nanometer scale.