Optical and structural characterization of copper-based colloidal particles in SiO2 coatings

The optical properties and structural characteristics of copper doped SiO2 coatings, prepared using the sol-gel method, were determined from spectrosc opy ellipsometry, optical transmission and x-ray diffraction measurements. Coatings with 8 and 25 at. wt % of copper were analyzed. The samples were h eat treated in air and under a CO atmosphere at various temperatures. The x -ray data show that samples thermally treated, in air have an amorphous str ucture. In the coatings with 25 wt % of copper and annealed in the reducing atmosphere, there is precipitation of copper particles with nanometer size s. The effective complex index of refraction of the coatings is deduced fro m the ellipsometric data using the Forouhi-Bloomer and Maxwell-Garnett expr essions for samples with amorphous and composite structures, respectively. The optical transmission measurements indicate that Cu2+ ions are present i n oxidized samples. The optical density spectra from reduced samples were a nalyzed with the Mie theory. There is a good agreement between the results from the different measurements. (C) 1999 American Vacuum Society. [S0734-2 101(99)18904-8].