Surface characterization of fluorinated polyimide films grown by vapor deposition polymerization

Abstract

Vapor deposition polymerization (VDP) was used to prepare fluorinated polyimide films. The process utilizes the coevaporation of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) monomers. We characterized the surface by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy, atomic force microscopy (AFM), and scanning tunneling microscopy (STM). The XPS analysis showed that the film stoichiometry greatly depended on the ratio of source effusion rates, and that a 6FDA/TFDB pressure ratio of 1:10 was best for obtaining stoichiometric 6FDA/TFDB polyimide. The surface structure image obtained by AFM was clearly different from that of spin-cast films. The surface morphology of the VDP films was characterized by an accumulation of parallel rod shaped structures, whereas that of the spin-cast one was a rough structure. The surface morphology of the VDP grown films at the initial growth state was also found to be a vertical stripe structure according to STM results.