Vapor-phase synthesis of mesoporous silica thin films

Nano-phase transition of an organic-inorganic nanocomposite under vapor infiltration of tetraethoxysilane (TEOS) or tetramethoxysilane (TMOS) was found in mesoporous thin film preparation. The rearrangement into a hexagonal periodic structure implies high mobility of the surfactant-silicate composites in solid phase. The swelling of film thickness and d spacing was observed under vapor infiltration. The nano-phase transition under vapor infiltration contains two competitive processes: (1) the penetration of TEOS or TMOS into the film and (2) the reaction of the silanol group. Film thickness and d spacing were controlled by changing synthetic temperature, silica sources (TEOS and TMOS), catalysts (HCl and NH3), and the thickness of surfactant films. The films prepared from vapor phase show superior characteristics, such as high structural stability and high resistance to water adsorption. The vapor infiltration method is a simpler process than conventional sol-gel techniques and attractive for mass production of a variety of organic-inorganic composite materials and inorganic porous films.