Communication: Polycrystalline zeolite films-of great importance in catalysis, separation, and sensing-can be grown on various substrates, but in most cases there are problems in detaching the films. It is shown that a mercury surface accelerates the nucleation and crystallization of MFI-type zeolites and that the surface of the film against the mercury (left in Figure) is smoother than that on the solution side (right in Figure).