Vibrational Spectroscopy and Atomic Force Microscopy Studies of Silane Adsorption onto Silicon and Glass.

The adsorption of two surfactants, n-octadecyltrichlorosilane and perfluorodecyl(ethyl)trichlorosilane, onto silica surfaces, was investigated by Fourier transform infrared attenuated total reflection, (FTIR-ATR), spectroscopy and by atomic force microscopy, (AFM). The rate of formation of the monolayers and the effect of surface coverage on the packing of these long-chain molecules was studied by both methods and the results compared. The silica surface was provided by the native silicon oxide layer on the surface of the silicon ATR prism for FTIR-ATR spectroscopy and by float glass substrates for AFM. Polarized radiation was used in the FTIR-ATR experiments to determine the relative dichroic ratios of cast and self-assembled films on silicon, and these results were compared with a theoretical model. The conclusion was that the cast silane layers were orientationally disordered, whilst the self-assembled layers showed a greater orientational order. In situ FTIR-ATR spectroscopy was employed to study the adsorption of these long-chain silanes at a silica-deuterated toluene interface. The silica surface was provided by the native oxide layer on a silicon ATR prism. The experiment required careful calibration in order to determine the Gibbs surface excess of these silanes on this surface. The Gibbs surface excess was calculated over a variety of silane concentrations, enabling the area occupied by the silane molecules to be calculated. The rates of formation of the monolayers were also determined and compared to the results obtained from the AFM and FTIR-ATR experiments, (not in situ). FTIR-ATR and Raman spectroscopy and microscopy were employed to investigate the interactions in silicon (or quartz)/silane/poly(vinylchloride) laminates. Specifically, (3-aminopropyl)trimethoxysilane and (3-mercaptopropyl)triethoxysilane were the silanes studied. Confocal Raman microscopy was used to discover whether interdiffusion of the silanes into the polymer overlayers had occurred, and also to determine the distribution of the silane molecules over the polymer surface. This was successfully achieved with the laminate containing the mercaptosilane.