High-resolution transmission electron microscopy study of epitaxial oxide shell on nanoparticles of iron

Remarkably oxidation-resistant nanoparticles of iron prepared at Tianjin University have been studied by electron diffraction and high-resolution transmission electron microscopy (HRTEM). HRTEM images clearly show the polyhedral epitaxy of γ-Fe2O3 layers on equivalent {100} facets of the {100} truncated {110} rhombic dodecahedral nanoparticles of iron. Oxide layers on {110} facets are formed by the lateral extension of the epitaxial {100} γ-Fe2O3 layers over adjacent {110} facets. The {110} oxide layers are bent and concave inward. The compressive γ-Fe2O3 layers which are about 4 nm thick give effective protection, according to the theory of Caberra–Mott, to the iron core from further oxidation.