Spin coating can often be used to create highly uniform coating son flat substrates using sol-gels and other precursor solutions. Typically, fluid flow considerations dominate the early part of spinning while solvent evaporation controls the behavior at later stages. However, even though evaporation does not control the early stage, it is still occurring throughout the entire process and evaporation-related issues can arise during the flow- dominated stage that may ultimately become coating thickness non-uniformities in the final product. Striation defect formation is a good example of this. During the spin coating process the evaporation of solvent takes place at the top surface of the flowing fluid, thus a concentration profile for the solute specs will exist within the flowing solution. Since the solute species in sol-gel solutions are often prone to condensation or cross-linking reactions, it is possible for this top surface to experience a rapid increase in viscosity and potentially to act as a barrier to further evaporation. This top layer could be equivalent to the skin layer on drying paint.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.