Synthesis of Ordered Nanoporous Silica Film With High Structural Stability

A mesoporous silica film was prepared on a silicon substrate using a spin-coating process followed by a tetraethyl orthosilicate (TEOS) vapor treatment. The stability of a formed silica network before TEOS treatment is thought to be insufficient because the rate of the condensation reaction is not high at temperatures below 453 K. The density of silica wall surrounding surfactant assembly could be low, resulting in the structural contraction with the formation of a silica network. On the other hand, the TEOS-treated mesoporous silica film did not contract during calcination, showing high structural stability. In the TEOS treatment, TEOS molecules penetrate into an originally deposited silicate film and react with silanol groups. The densified silica wall has high structural stability and hardly contracts under a calcination process. A flat mesoporous silica film about 250 nm thick was grown from the silicon substrate. A periodic hexagonal porous structure was observed in the FE-SEM image of the cross section of the TEOS-treated film. This indicates that the channels run predominantly parallel to the surface of the silicon substrate. The developed film is a promising material such as chemical sensors, low-k films and other optoelectronic devices.