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

气相沉积聚合（VDP）是制备高性能聚合物薄膜最有用的方法之一。该方法还给出了聚合物薄膜中的分子取向。例如，我们已经报道了尼龙1010、烷基芳聚酰胺和分子链垂直于底物的聚酰胺薄膜可以在底物上形成。我们提出了VDP形成高取向聚合物薄膜与交替反应沉积过程有关，这类似于GaAs薄膜的分子层外延。本研究利用石英薄膜厚度监测仪研究了交替VDP过程中薄膜的形成过程。此外，通过分析VDP制备的薄膜在电场作用下的二次谐波产生（SHG），测量了奇数尼龙（尼龙79）的偶极子取向。交替沉积过程中厚度的变化表明其机制涉及吸附和描述行为，表明两种类型的吸附，即化学吸附和物理吸附。这一结果表明，交替VDP可以制备出具有类似LB膜的层状结构的聚酰胺薄膜。SH强度谱证实了分子链中的偶极子优先平行于VDP过程中施加的电场。这些结果表明，这两种单体可以交替沉积，形成分子取向垂直于衬底的层接层结构。此外，在沉积过程中施加的电场可以引起薄膜中的自发极化，其中偶极子排列平行于施加的电场。

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.