Characterisation and optimisation of sol-gel-derived thin films for use in optical sensing

Both tetraethylorthosilicate (TEOS) and Liquicoat-derived sol-gel films were fabricated by dip-coating onto silicon and glass substrates. For TEOS-derived films, film thickness and temporal stability were monitored as a function of dip-speed, watenprecursor ratio, sol aging time and time after dipping. Refractive indices of films were also studied. Film thickness was found to increase with sol aging time and with watenprecursor ratio. The time to achieve thickness stability was decreased at higher watenprecursor ratios. Film behaviour was interpreted in terms of the dependence of hydrolysis and condensation rates on the interplay between sol pH and water : precursor ratio. For Liquicoat films, refractive index and thickness as a function of time were investigated and compared with TEOS films. Refractive index tailoring was demonstrated using silica / titania Liquicoat mixtures. All films were doped with the oxygen-sensitive ruthenium complex, [Ru(II) - tris(4,7 - diphenyl - 1,10 - phenanthroline)], and optical quenching behaviour was investigated. Surface quality of all films was correlated with processing conditions. The study was motivated by the need to optimise methods and fabrication conditions for optical oxygen sensing