SOL-GEL THIN-FILM FORMATION

Sol-gel thin film formation by dipping (or spinning) involves gravitational (or centrifugal) draining accompanied by vigorous solvent evaporation. During dipping a steady-state film thickness profile develops, the shape of which is established by the evaporation rates of the fluid components and possible surface tension gradient driven flows. The entrained inorganic species are concentrated by the accompanying evaporation of solvent and compacted by capillary pressure developed at the final stage of the deposition process as liquid-vapor menisci recede into the gel interior. The important microstructural properties of the deposited film (% porosity, surface area, and pore size) depend on the size and structure of the inorganic species, the relative rates of condensation and evaporation during deposition, the magnitude of the capillary pressure, and the accompanying shear stress.