Catalysts and the structure of SiO2 sol-gel films

In the fabrication of silica films by sol-gel synthesis, the role of various catalysts is systematically examined. The precursor solutions were made by mixing tetraethylorthosilicate (TEOS), ethanol and water in the molar ratio of 1 : 2 : 2. The spin coated films were thermally treated at various temperatures, and characterised using ellipsometry, molecular probe ellipsometry (MPE), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and optical scattering. By employing different catalysts with the same concentration (0.1 M in water), it was found that dramatic effects on the porosity, optical quality, shrinkage, thickness, structural evolution during thermal treatment, and film stress can be observed.