It was shown how the vacancy diffusion length scale should be considered in the context of the diameter of a nanowire when exploiting the Kirkendall phenomenon in the fabrication of metal oxide nanotubes starting from metal nanowires. It was found that the diameter of the nanowire relative to the diffusion length scale of the vacancy will affect greatly the type of voids that could be generated. By using a larger diameter nickel nanowire, it was shown that segmented heterojunction void formation could be avoided and that the resulting structure would serve as a precursory 'template' for subsequent oxidation processes at high temperatures. In doing so, the formation of bamboo-like structures could be prevented and uniform nickel oxide nanotubes could be obtained by direct oxidation; something which had previously proved to be difficult. This result was also significant because the interplay of vacancy diffusion length and nanostructure dimension was important in the oxidation of other types of metal nanostructures; especially when void formation and the Kirkendall effect were involved.

Diameter Dependence of the Void Formation in the Oxidation of Nickel Nanowires. Y.Ren, S.Y.Chiam, W.K.Chim: Nanotechnology, 2011, 22[23], 235606