Multiple Transmission-Reflection IR Spectroscopy Shows that Surface Hydroxyls Play Only a Minor Role in Alkylsilane Monolayer Formation on Silica

Multiple transmission-reflection (MTR) a recently developed infrared spectroscopy sampling method for surfaces has been applied to the study of silane monolayer formation on silicon oxide. Thanks to the excellent signal:noise ratio of data obtained by MTR, spectra of silane monolayers on a silica substrate could be readily obtained. This system has been previously difficult to investigate by standard sampling methods. The data is particularly important for gaining insights into the nature of the silica-silane interaction. The results support a model in which the inherent strain caused by the mismatch of alkyl-chain van der Waals radius and Si-O-Si bond distance is relieved in silane monolayers by the formation of a structure resembling snow moguls or closely packed umbrellas.