We describe a synthetic method for the formation of surfactant-templated periodic mesoporous silica thin films. The films, when deposited between 0.22 < t/t(gel) < 0.67, are crack-free, consist of aggregated submicrometer particles, each of which contains the familiar honeycomb arrangement of 30-44 Angstrom diameter channels, and have specific surface areas greater than 400 m(2)/g. The synthetic method, which we call gas-catalyzed thin film synthesis (GCTFS), involves diffusing ammonia into a homogeneous micellar coating solution on a nonporous substrate. This method ameliorates the problems associated with coating substrates from inhomogeneous solutions. We have studied and optimized GCTFS with light scattering, Si-29 NMR, XRD, optical microscopy, SEM, TEM, and isothermal N-2 sorption measurements.