Nucleation and Growth of Fe Nanoparticles in SiO2: A TEM, XPS, and Fe L-Edge XANES Investigation

Magnetic iron nanoparticles embedded in insulating oxides matrices are prized targets for on chip magnetic sensors, nano fluxgates and nano hard magnets. In this study, the nucleation and growth of iron nanoparticles in the near surface region of 400 nm silica thin films (on silicon substrates) during ion implantation and post- implantation electron beam annealing was systematically investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fe L-edge X-ray absorption near edge spectroscopy (XANES). Results show the presence of Fe oxides after low-fluence low-energy ion implantation in SiO2, suggesting that initially Fe substitutes for Si in the silica matrix. Larger Fe fluences lead to the formation of sub-2 nm metallic Fe nuclei. Postimplantation annealing transformed the dispersed cationic Fe species into metallic Fe nanoclusters (diameter 1-10 nm) that are stabilized by a thin passivating surface oxide film. The versatility of ion implantation and electron beam annealing for the synthesis iron nanoparticles in silica matrices is demonstrated.