Studies on the Preparation of Polymeric Monolayer Thin Films by Vapor Deposition Polymerization

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Vapor deposition polymerization (VDP) is one of the most useful methods for producing high performance polymer thin films. This method also gives molecular orientation in the polymer film. For example, we have reported that nylon1010, alkyl-aromatic polyamide and polyamide films with molecular chain perpendicular to the substrates can be formed on the substrates. We have proposed that the formation of highly oriented polymer thin films by VDP is associated with alternating reaction-deposition process, which is similar to the molecular layer epitaxy for a GaAs thin film. In this study, the film formation process during alternating VDP was studied by a quartz film thickness monitor. Moreover, the dipole orientation of an odd-nylon (nylon 79) was measured by analyzing the second harmonic generation (SHG) in the thin films prepared by VDP in the presence of an electric field during the deposition.The change in the thickness during the alternating deposition suggests that the mechanism involves adsorption and descrption behavior indicating two types of adsorption, i.e., chemisorption and physisorption. This result suggests that the alternating VDP can produce a polyamide thin film with a layered structure like an LB film.The SH intensity profiles confirmed that the dipoles in the molecular chains aligned preferentially parallel to the electric field applied during the VDP process.These results lead to the conclusion that the two monomers can be deposited alternately to form a layer-by-layer structure with a molecular orientation perpendicular to the substrate. In addition, the electric field applied during the deposition can give rise to the spontaneous polarization in the film, where the dipoles align parallel to he applied electric field.