ABSTRACTSilica coatings with as-deposited densities ranging from approximately 50-100% were deposited on sapphire substrates by electron beam evaporation and sol-gel techniques. The shrinkage, hardness, and etch rates of the coatings were measured after various heat treatments. Differences in shrinkage indicated that hardness was not controlled by bulk porosity alone. Most films exhibited a surface “crust” that was significantly harder, and etched more slowly than the interior of the sample. We propose that the differences in mechanical and chemical behavior are caused by Si-O network reorganization starting at the film/air interface.
Mechanical Properties of Silica Coatings