Improvement of functionality of sol-gel-derived silica glass thin films by tailoring their nanostructure at low heat-treatment temperature.

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Establishment of technique to produce silica glass thin film coating on semiconductor, plastics and metal substrates at temperatures below 500ﾟC in low cost and without complicated processes is nowadays more and more strongly demanded.The sol-gel method has been developed for that purpose, but the heat-treatment at 600-800ﾟC is still required for transforming silica gel films to dense glass films, In the present study, we found through the examination of nano-structure change of the alkoxy-derived silica gels on heating by X-ray diffraction analysis method that 4-fold sioxane ring units are prevailing in the gels, and the heat-treatment at 600-800ﾟC is indispensable for changing gels to glasses. Then we invented the method by which silica gels consisting of 6-fold siloxane rings are obtainable. The glass coating films thus obtained, however, were still porous below 500ﾟC.Perhydropolysilazane (PHPS) gives dense silica glass coating film by the heat-treatment at 450ﾟC in the air. It was found in the present study that Si-H bonds remaining up to 450ﾟC make difficult the lowering of glassification temperature. Then novel PHPS from which Si-H bonds are easily removed on heating was synthesized to obtain silica glass films below 450ﾟC.However, the raw materials are still expensive.Finally we tried to combine above two methods. The combination, namely the preparation of silica glass coating by using the mixture of alkoxy-derived sioxane oligomers consisting of 6-fold rings and PHPS as raw materials in the ratio of 9 to 1 was found to be very prospective for making silica glass coatings below 450ﾟC in low cost and with ease.