HREM study of epitaxial core-shell metal-oxide structure in passivated nanoparticles of iron and nickel

摘要

Metallic nanoparticles which are intrinsically reactive oxidize readily in air. They are usually passivated by slow oxidation in an atmosphere low in oxygen content. Passivated nanoparticles have a core-shell morphology in which the metal core is protected by an enclosing polycrystalline oxide shell from further oxidation. In the case of iron, the oxide shell has been found to be composed of fine grains of polycrystalline mixture of gamma - Fe_2O_3 and Fe_3O_4. Passivated metallic nanoparticles are therefore susceptible to further oxidation because of the limited protection provided by a polycrystalline shell consisting of a high density of grain boundaries. Consequently, they are stored in an inert gas atmosphere.