Nanoparticles are increasingly being heralded as the next-generation building blocks for modern materials design. Coating of semiconductor, metal, or metal oxide nanoparticles with a thin layer of a compatible material makes possible the control of interparticle and particle-matrix interactions, thereby further improving functional properties of devices and expanding the range of potential applications . The core-shell geometry has previously allowed for the enhancement of luminescence of semiconductor nanoparticles, charging of metal cores, chemical and colloidal stability, and optimization of magnetic properties of nanoparticles.

The work reported here uses new approaches to synthesize metal-coated nanoparticles characterized with high-resolution electron microscopy (HRTEM), micro-diffraction, and electron energy dispersive X-ray (EDX). Colloidal uniform composite nanoparticles of SiO2/TiO2 were synthesized using the sol-gel process. Fig. l-(a) shows a TEM micrograph of a group of particles coated with an outer layer.