Preparation of a precursor solution for SiO2 film formation and its application to the formation of Au cluster-dispersed SiO2 films

A stable precursor solution for SiO2 film formation was prepared from the reaction of tetraethoxysilane with glucose in ethanol, by the regulation of the hydrolysis of the alkoxide through the complex formation of the sugar toward Si. The resulting solution involving diethylamine could be spin-coated on a quartz glass with excellent coatability. By firing the precursor film at above 600 degreesC, transparent and crack-free film with ca. 500 nm thickness was obtained. The precursor solution has a long-term stability. By the XPS spectra of the films formed at 600 and 1000 degreesC, it was elucidated that the nitrogen atoms were completely removed from the precursor films. Thermal properties of the precursor powders obtained from the solution were also examined by TG-DTA. Au-dispersed SiO2 films with several An content ratios of Au/Si in the range from 0.01 to 0.1 were also prepared by the application of the precursor solution. Graft-polymer stabilized Au clusters in ethanol were well dispersed into the SiO2 precursor solution. The SiO2 precursor solution added with An clusters, could be spin-coated on a quartz glass with excellent coatability. Blue shifts of the maximal positions of the absorption band due to the surface plasmon resonance of Au clusters were observed, in the absorption spectra of the Au-dispersed SiO2 films. By the XRD spectra of the SiO2 film with dispersed An clusters, it was elucidated that the crystallite size of the Au clusters does not depend on the contents.