Silica-encapsulated magnetic nanoparticles formed by a combined arc evaporation/chemical vapor deposition technique

A multistep technique has been developed for the generation of metallic/alloy nanoparticles coated with amorphous silica. As a proof of concept, an inert-gas blown-arc geometry was used to create nanoparticles from a bulk nickel source, and silica coating formation was accomplished via tetraethyloxysilane (TEOS) decomposition over the nanoparticles in an adjacent chemical vapor deposition chamber. The composite particles exhibit resistance to hydrochloric acid attack over extended times, thereby confirming the protective nature of the silica coating, and magnetic measurements indicate a superparamagnetic transition temperature of 41 K. TEOS flow rate was found to have a profound effect on particle morphology, and individually coated dispersed particles were observed for the intermediate flow rate studied. These results, combined with the well-established field of silica functionalization, offer the possibility that a variety of industrially significant coated magnetic nanostructures may be synthesized with this versatile approach.