Multilayer thin films of colloidal gold and silica nanoparticles: Effect of polyelectrolyte coating.

The use of oppositely charged colloidal nanoparticles to build multilayered structures is an approach in thin film science. In this work, uniform spherical nano-dispersions of gold (ca. 20 nm) and silica (ca. 30 nm) were synthesised with specific volume concentration to achieve colloidal stability. Exploiting the use of self-assembly, multilayers of these oppositely charged nanoparticles were built using alternate coating with chitosan. Gold nanoparticles have strong optical absorption in visible region of electromagnetic spectrum resulting from its surface plasmon resonance. Silica nanoparticles have low refractive index and absorb light mostly in the ultraviolet (UV) region. The optical absorption band of the fabricated thin films extends from UV to visible region of the electromagnetic spectrum. The spectral characteristics of these thin-film assemblies are a combination of thickness and the order of the layers in a stack. These films have potential applications as optical elements and in optoelectronics. © 2011 Canadian Society for Chemical Engineering [ABSTRACT FROM AUTHOR]