Optical sol-gel coatings : ellipsometry of film formation

Alan J. Hurd , C. Jeffrey Brinker

A method was developed to image an area of a drying, steady-state film during dip-coating using ellipsometry, thereby obtaining the film's thickness and refractive index as a function of position. Measurements on TiO 2 and SiO2 alcohol-based sols indicate that the film approaches a volume fraction Φ ∼ 0.2 in the wet state and suggests that the film resists densifying further for kinetic reasons. In dense films, as the final drying front passes, the film undergoes a rapid collapse owing to capillary forces ; porous films formed from relatively large SiO2 aggregates appear to collapse more slowly in the final stage due to smaller capillary forces. The thickness profiles are consistent with thinning by a combination of evaporation and gravitational draining.

Keywords: capillarity; ellipsometry; gels; optical films; porous materials; refractive index; silicon compounds; sols; thickness measurement; titanium compounds

Domains: Physics archives

Alan J. Hurd, C. Jeffrey Brinker. Optical sol-gel coatings : ellipsometry of film formation. Journal de Physique, 1988, 49 (6), pp.1017-1025. ⟨10.1051/jphys:019880049060101700⟩. ⟨jpa-00210768⟩