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 speciall y designed for Aerosol-gel process implementation. A two-step solution prep aration procedure was used, in order to control separately hydrolysis and c ondensation reactions. An effective reactivity control was achieved by adju sting the pH value from two during the first preparation step to four durin g the second step. The solutions appeared very stable in the diluted state, and very reactive during the post-deposition drying stage, producing a wel l developed and densified SiO2 network at low temperature. A competition me chanism between condensation and reesterification was put in evidence durin g 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 usi ng 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 resistan t layers can be produced after a heat-treatment at only 80 degrees C. (C) 1 999 Elsevier Science S.A. All rights reserved.