Preparation of coating films doped with gold metal particles from methyltriethoxysilane-tetraethoxysilane solutions

Silica coating films of 0.5–0.7 m in thickness doped with gold metal particles were prepared by heating gel coating films obtained from solutions of acid-catalyzed methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) mixture containing chlorauric acid tetrahydrate. Transparent coating films with deep blue, red, and purple colors were obtained. Changes in size and shape of the gold particles with the MTES content were observed. Lower MTES contents gave bigger and non-spherical particles, while higher MTES contents produced smaller and more spherical particles with a more uniform size distribution. The effect of heat-treatment temeprature on the shape, size, and size distribution of the metallic gold particles was also studied.On leave from Dipartimento di Ingegneria Meccanica, Sezione Materiali, Universita di Padova, Via Marzolo, 9-35131 Padova, Italy.