Optical monitoring of the sol-to-gel transition in spinning silica films

Temporal evolution during spin coating is interferometrically monitored, with close regard to gelation at the final stages of the process. Uniform silica films on silicon were produced from an established sol composition, from which slight deviations were taken to produce nonuniform, cracked films. A distinct evolution of the sol to gel transition could then be detected, at speed of rotations of 1000 - 3000 rpm and data acquisition at 100 Hz. Interpretation of a set of experimental results is discussed in terms of a two-phase system, in the light of, and as a test of, current theoretical models.