Sol-gel replication of microoptical elements and arrays

Facile replication of microoptical elements and arrays was performed in sol−gel matrixes prepared by the fast sol−gel method. These sol−gel resins, made from mixtures of alkylalkoxysilane monomers, undergo hydrolysis and polymerization within 10−20 min and curing within a few days. Single-step reproducible fabrication of large crack-free elements of 1 cm thickness and up to 10 cm in diameter was demonstrated. High accuracy of replication was facilitated by maintaining a very small shrinkage of only a few percent during the curing stage. This was attained by removing most of the volatile products from the sol, without gelling, prior to casting it onto the template. Accurate replication depends on adequate control of two key parameters:  the replica-template adhesion-separation timing, by manipulating the template surface via oxidative etching, and the drying-cross-linking relative pace, by accurately tailoring the silanes mixture, the water-to-silane ratio, and their hydrolysis and polymerization.