Single-crystalline MgAl₂O₄ spinel nanotubes using a reactive and removable MgO nanowire template

Using MgO nanowires as a reactive template, we fabricated for the first time single-crystal MgAl₂O₄ spinel nanotubes through an interfacial solid-state reaction of MgO-Al₂O₃ core-shell nanowires. Single-crystal MgO nanowires are coated with a conformal thin layer of amorphous Al₂O₃ via atomic layer deposition. Subsequent annealing at 700 °C activates the interfacial reaction between MgO and Al₂O₃, transforming the alumina shell into a spinel shell. Finally, after etching away the remaining MgO core in ammonia sulfuric solution, MgAl₂O₄ spinel nanotubes are obtained. As a transition from conventional planar spinel layers via thin-film interface reactions, our result might open a window for the fabrication of a wide variety of MgO-based spinel one-dimensional nanostructures.