Fabrication and Characterization of Cross-Linked Organic Thin Films with Nonlinear Mass Densities
journal contributionposted on 2016-05-13, 00:00 authored by Md. A. Rashed, Salinthip Laokroekkiat, Mitsuo Hara, Shusaku Nagano, Yuki Nagao
The preparation of urea (bonded) cross-linked multilayer thin films by sequential deposition of bifunctional and tetrafunctional molecular building blocks is demonstrated. Multilayer growth as a function of deposition cycles was inspected using UV–vis absorption spectroscopy. From infrared results, three characteristic infrared bands of amide I, amide II, and asymmetric νa(N–C–N) stretching confirmed the formation of polyurea networks by alternate dipping into solutions of amine and isocyanate functionality monomers. The deconvoluted component of the C 1s and N 1s spectra obtained by X-ray photoelectron spectroscopy shows clear evidence of stable polyurea networks. The enhancement of structural periodicity with film growth was demonstrated by grazing-incidence small-angle X-ray scattering measurements. The thin film near the substrate surface seems to have an amorphous structure. However, molecular ordering improves in the surface normal direction of the substrate with a certain number of deposited layers. Constant mass density was not observed with deposition cycles. The mass density increased up to 16% within deposited layers from proximate layers to those extending away from the substrate surface. This difference in the packing density might derive from the different degrees of cross-linking among layers proximate to the substrate surface and extending away from the substrate surface.