Photolithographic processing of silver loaded dielectric coatings based on preformed colloidal TiO₂ nanoparticles dispersed in a mesoporous silica binder

Titanium dioxide is a well known photocatalyst for reactions involving surface trapped photogenerated carriers. Noble metal photo-reduction may be used for the processing of silver/TiO₂ nanocomposite coatings that may exhibit interesting optical and electrical properties. We present here results of our investigations performed on an original system consisting of preformed colloidal TiO₂ nanoparticles homogeneously dispersed within a mesoporous silica host matrix. Light irradiation of samples immerged in an aqueous silver salt solution leads to the homogeneous deposition of silver islands in the vicinity of the TiO₂ particles and throughout the film thickness. The silver volume fraction is directly controlled by the irradiation dose up to a value of about 16 vol.%. Films exhibit tunable plasmonic properties that correspond to silver nanoparticles in interaction, and a percolation threshold is observed at 8-10 vol.%, leading to films with a conductivity of about 40 S cm^-1. The major interest of this method lies in the high silver reduction quantum efficiency (about 50%) and the possibility to modulate optical and electronic properties by light irradiation while the low temperature of processing permits the photolithographic deposition of metallic patterns on organic flexible substrates.