Silica-based hybrid films with double-charged diazoniabicyclo[2.2.2]octane chloride group: Preparation and optical properties related to transition layer structure

Transparent thin films of silica-based hybrid material containing the double-charged diazoniabicyclo[2.2.2]octane chloride group were prepared by optically monitored dip-coating with regard to optical properties, measured by complementary techniques. Double-optical monitoring in real time showed that film formation was basically dominated by solvent flow. After annealing, Ellipsometry and Spectrophotometry (Envelope Method) results generally presented good agreement for the isotropic films, except when slight physical thickness non-uniformity was present. However, refractive indices determined by polarimetry (Abeles Method) at the near-surface were significantly higher than those obtained from the previous methods. Detailed analysis, as discussed, indicates the existence of a very thin transition layer with graded refractive index, increasing towards the film-air interface. Optical applicability is also considered.