Reaction control of tetraethyl orthosilicate (TEOS)/O3 and tetramethyl orthosilicate (TMOS)/O3 counter diffusion chemical vapour deposition for preparation of molecular-sieve membranes

Counter diffusion chemical vapour deposition (CVD) is an excellent way to prepare inorganic thin films or membranes on the surface of porous or non-porous supports. Modification of the pore size of porous supports by this method to prepare molecular-sieve membranes is another interesting opportunity. However, control of the deposition profile is very difficult because of the complex reaction kinetics. In this study, counter diffusion CVD of tetraethyl orthosilicate (TEOS)/O-3 or tetramethyl orthosilicate (TMOS)/O-3 systems was investigated. To control the deposition layer profile in a thin porous ceramic substrate, numerical simulations of the reaction sequences were performed. The reactant concentration and temperature were varied to control the deposition profile, and the simulation results were compared with experimental results. It is shown that high quality membranes can be processed under the optimised reaction conditions. In addition, the effect of step-coverage of the CVD reaction on final membrane performance was also investigated by comparison of the TEOS/O-3 and TMOS/O-3 reactions.