Annealing Effects on Structures and Morphologies of Fe/Si Core–Shell Clusters

Abstract

Transmission electron microscopy, X-ray diffraction and electrical resistivity have been observed for annealed Fe/Si core–shell clusters and their assemblies in comparison with those for annealed Fe and Si clusters. Fe clusters are wholly oxidized, where voids are formed in the central regions. Si clusters are not wholly oxidized, keeping a diamond-like structure, where voids are scarcely formed in the central regions because the initially-oxidized surfaces play roles of passive layers and protect the cores from oxidations. In Fe–Si core/Si shell clusters, SiO_X thin layers are also formed on Si shell surfaces, protecting Si shells and Fe–Si cores from further oxidations. Fe–Si core regions maintain a bcc structure, where no ordered phase is detected probably due to the chemical heterogeneity among these clusters and the surface segregation of Si atoms. Excess vacancies are accumulated to become voids between Fe–Si cores and Si-shells.