Cu nanowires with widths ranging from 110 to 300 nm were fabricated on a c-plane sapphire substrate using E-beam lithography and lift-off processes. Thermal annealing of these polycrystalline metal nanowires at 700°C in an inert ͑nitrogen͒ atmosphere showed that for lines of width 160 nm or less, there was complete breakdown into widely spaced, individual beads in a short time ͑1 h͒. It was shown that the morphological changes were driven by reduction in the surface energy, with surface diffusion as the predominant transport mechanism. The spacing between the beads was approximately 1.8 times greater than the values predicted by Rayleigh instability theory for a free standing rod with equivalent radius. Based on thermodynamic and kinetic considerations, discrepancies between the experimental observations and the predictions of Rayleigh instability theory were attributed to the stabilization effect of the substrate.

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It has recently been demonstrated that it is possible to produce a pristine surface layer on a lapped sapphire substrate by depositing a thin film of aluminum and subjecting it to an appropriate thermal treatment. This process also shows promise for the fabrication of nanopatterned sapphire by pre-patterning the aluminum metal prior to thermal conversion to sapphire. We have explored two distinct patterning processes: a dual layer photoresist e-beam lithography technique for fabricating arbitrarily shaped aluminum structures, and a novel, non-conventional mask-liftoff method involving nanoporous anodized aluminum oxide, useful for patterning very large scale arrays of sub-micron aluminum dots or posts. Our work is focused on refining the fabrication process and investigating the morphological stability of such metal nanostructures during conversion to sapphire.