Growth process and post-growth evolution of tetraphenylporphyrin thin films

The control of the growth of organic semiconductor thin films is one of the most intriguing challenges within the framework of organic electronics, in view of improving thin-film properties and device performances, and many efforts have been devoted to the understanding and modelling of film evolution and growth mechanisms. Here, the growth of Nickeltetraphenylporphyrin (NiTPP) thin films deposited by organic molecular beam epitaxy on two substrates, an organic crystal and graphite (KAP and HOPG), is studied by monitoring their morphology ex situ by Atomic Force Microscopy (AFM). On KAP, post-growth evolution is observed, leading to the formation of peculiar triangular-shaped NiTPP nanoaggregates, possibly originating from organic epitaxy with the substrate; however, by tuning the growth parameters, one single stable phase can be selected, driven by the intermolecular interactions among NiTPP molecules. On HOPG, post growth evolution is detected by AFM as well, and the analysis of images of NiTPP films with different thickness by heightheight correlation function leads to model the growth as a complex process in which surface diffusion and step-edge barriers are involved.