Effects of fundamental processing parameters on the durability of sol–gel-derived silica thin films in water

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Silica gel films were prepared on Si(100) substrates from Si(OC2H5)4- and Si(OCH3)4-derived sols by dip-coating, and the gel films were heat-treated at 100–700°C. The durability of the films against water was evaluated by measuring the thickness before and after soaking them in 80°C water for 24 h. The durability increased with increasing heat-treatment temperature principally due to the progress of film densification. Higher amounts of water for hydrolyzing Si(OC2H5)4 were greatly effective in achieving higher durability at lower heat-treatment temperatures. Longer sol aging was also effective in improving the durability of the Si(OC2H5)4-derived films. Si(OCH3)4-derived films exhibited much higher durability than Si(OC2H5)4-derived ones. All of these factors, i.e. the larger amounts of water for hydrolysis, the longer sol aging time and the employment of Si(OCH3)4, may provide more dense film structure and more chance to undergo condensation during gel film heat-treatment, leading to the higher durability at lower heat-treatment temperatures.