Aerosol-gel deposition and low temperature heat-treatment of SiO2 layers

Aerosol-gel deposited SiO2 layers were obtained after heat-treatment in air at 80 degrees C. The layers were produced from reactive solutions specially designed for Aerosol-gel process implementation. A two-step solution preparation procedure was used, in order to control separately hydrolysis and condensation reactions. An effective reactivity control was achieved by adjusting the pH value from two during the first preparation step to four during the second step. The solutions appeared very stable in the diluted state, and very reactive during the post-deposition drying stage, producing a well developed and densified SiO2 network at low temperature. A competition mechanism between condensation and reesterification was put in evidence during aging of the solution at room temperature or at 60 degrees C. Layers were characterized by FTIR spectroscopy, (SI)-S-29-NMR, ellipsometry and by using simple mechanical quality evaluation tests. The results show that a good film mechanical resistance is the consequence of a suitable adjustment of the solution reactivity. Depending on the reactivity, mechanically resistant layers can be produced after a heat-treatment at only 80 degrees C. (C) 1999 Elsevier Science S.A. All rights reserved.