Monocrystalline spinel nanotube fabrication based on the Kirkendall effect

The fabrication of ultra-long single crystal ZnAl₂O₄ monocrystalline spinel nanotubes, was investigated. The fabrication was done through a spinel-forming interfacial solid-state reaction of core-shell ZnO-Al₂O₃ nanowires using the Kirkendall effect. The spline formation occurred at planar interfaces or in a powder form at high temperatures and the normal substrate was replaced by unidirectional or branched single-crystal ZnO nanowires. A nanotube with a hollow core and a single spline wall was obtained by keeping a suitable thickness relationship between the core and the shell. The composition and structure of the nanotube by atomic-resolution transmission electron microscopy (TEM) analysis showed that the Zn-O species diffuse into alumina during crystallization process, consistent with the solid-state mechanism of spline ZnAl₂O₄. Kirkendall effect is also used to obtain vertically aligned ordered spline nanotubes.