Low-temperature elimination of organic components from mesostructured organic-inorganic composite films using vacuum ultraviolet light

A novel and simple procedure named photocalcination has been developed for removing organic components from mesostructured organic-inorganic composite films. This procedure employs an excimer lamp radiating vacuum ultraviolet (VUV) light of 172 nm in wavelength. Organic molecules are removed through two distinct photochemical reactions proceeding simultaneously at room temperature: the photocleavage of C-R and C-C bonds in the organic molecules by direct photoexcitation and their subsequent oxidation with activated oxygen species generated by the photoexcitation of atmospheric oxygen molecules. in this study, a composite of cetyltrimethylammonium chloride-silica (CTAC-silica) was used. Thin films of this organic-inorganic composite were prepared on Si substrates coated with a self-assembled monolayer of octadecyltrimethoxysilane. The films were irradiated with VUV light under pressures of 10, 10(2), 10(3), or 10(5) Pa. Although, in each case, the CTAC molecules in the composite films were completely oxidized and removed, the elimination rate increased with an increase in the photocalcination pressure. While 3 h of irradiation was necessary to completely remove the CTAC molecules at 10 Pa, only 0.5 h was required at 105,Pa. However, the periodic mesostructures of the film photocalcined at 10(5) Pa distorted significantly because of the rapid photooxidation. As a control experiment, identical CTAC-silica mesocomposite films-were calcined thermally. The films were heated in air at temperatures from 373 to 773 K. Although the CTAC molecules could be eliminated completely at temperatures higher than 573 K, the periodic mesostructures of the thermocalcined films were much more distorted than those of the photocalcined films.