Preparation of silica microspheres containing Ag nanoparticles

Two sol-gel fabrication processes were investigated to make silica spheres containing Ag nanoparticles: (1) a modified Stober method for silica spheres below 1 mu m size, and (2) a SiO2-film formation method on spheres of 3-7 mu m size. The spheres were designed to incorporate silver nanoparticles of high chi((3)) in a spherical optical cavity structure for the resonance effect. For the incorporation, interaction between [AS(NH3)(2)](+) ion and Si-OH was important. In the Stober method, the size of the silica spheres was determined by a charge balance of plus and minus ions on the silica surface. In the film formation method, the capture of Ag complex ion on the silica surface depended on whether the surface was covered with OH groups or not. After doping [Ag(NH3)(2)](+) into silica particles or SiO2 films on the spheres, these ions were reduced by NaBH4 to form silver nanoparticles. From plasma absorption at around 420 nm wavelength and TEM photographs of nanometer-sized silver particles, their formation inside the spherical cavity structures was confirmed.