Switchable metal–insulator transition in core–shell cluster-assembled nanostructure films

Fe/Fe3O4 core-shell-cluster-assembled nanostructured films were prepared using the low-energy cluster beam deposition technique. The temperature-dependent resistivity behaviors were investigated for the films with changing core-occupation ratio of clusters. Much interestingly and surprisingly, a switchable metal-insulator transition can be observed, featuring the rapid switching from the metal state to the insulation state and then back to the metal state, for films within a specific range of core-occupation ratio. Further, the resistivity change rate used to characterize the metal-insulator transition can reach as high as two orders of magnitude over a very narrow temperature region. The design of Fe/Fe3O4 core-shell clusters plays a decisive role in the mechanism of the switchable metal-insulator transition in these films. The assembled core-shell clusters in the films form current conduction channels that are switchable between the cores and shells of clusters as the temperature changes. The switching of the current conduction channels can be regulated by controlling the core-occupation ratios of clusters, which induce a switchable metal-insulator transition and can be verified by the effective medium theory over a specific core-occupation ratio range.