日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Mesoporous silica films have conventionally been prepared by liquid deposition methods such as epitaxial growth, spin-coating, and dip-coating. On the contrary, we have demonstrated a vapor phase synthesis to prepare ordered mesoporous silica films. In this method, the surfactant films were exposed to tetraethoxysilane (TEOS) vapor. We have found nano-phase transition of surfactant-silicate composites under vapor infiltration of TEOS. The phase transition of the nanocomposites under vapor infiltration implies their high mobility in the absence of solvent. The swelling of film thickness and d spacing was observed under vapor infiltration. In the vapor phase synthesis, selection of surfactant is the most important factor to determine the porous structure similarly to the sol-gel method. Mesoporous silica films with a channel structure were formed when quaternary ammonium brimide (C_nTAB) was used as a surfactant. The pore channels run parallel to the substrate surface. When triblock copolymer was used as a surfactant, the silica thin films with two-dimensionally connected cage-like mesopores were formed. The mesostructured silica thin films have silicate layers with ordered pillars. The structure of pores of the films is of advantage for next-generation low-k films because the porous structure of the films is isotropic parallel to the film surface. The films show lower concentration of residual Si–OH group compared to the film prepared by a conventional sol-gel method. The films show high thermal stability up to 1200 K and high hydrothermal stability. The vapor-phase synthesis can be applied for organic-inorganic nanocomposites and mesoporous metal oxides other than silica and provides opportunities for the creation of new materials technologies.