Nano-Structure Studies of Perhydropolysilazane - Derived Silica Thin Layers

Abstract

The structure of perhydropolysilazane (PHPS)-derived silica (PDS) thin layers which were synthesized on the surface of the Si-, Al 2 O 3 -, MgO-, and polyvinyl alcohol PVA-substrate have been studied by neutron reflectivity (NR) analyses. The results suggested that uniform PDS thin layers were synthesized on the surface of the substrates and the density of the layers varied depending on the type of substrate. Since the change in PDS density is correlated with the p K a value of the OH group on the substrate, it can be suggested that the acidity of the substrate would be one of the main factors determining the density of the coated PDS thin layers. On the other hand, the fine nanostructure of the PDS thin layer in the deep-buried condition have been poorly understood because a large background scattering originating from the sample matrix is a major obstacle for fine-structure analysis of a nanometric layer buried in a bulk material. As polarization analysis can decrease undesired scattering in a NR profile, we performed NR experiments with polarization analysis on a polypropylene (PP)/PDS/Si substrate sample, having a deep-buried layer of SiO 2 for increasing the amplitude of the Kiessig fringes in the higher scattering vector ( Q z ) region of the NR profiles in the sample by decreasing the undesired background scattering. Fitting and Fourier transform analysis results of the NR data indicated that the synthesized PDS layer remained between the PP plate and Si substrate with a thickness of approximately 109 Å. Furthermore, the scattering length density of the PDS layer, obtained from the background subtracted data appeared to be more accurate than that obtained from the raw data. Although the density of the PDS layer was lower than that of natural SiO 2 , the PDS thin layer had adequate mechanical strength to maintain a uniform PDS layer in the depth-direction under the deep-buried condition.