Long-range ordered aluminum oxide nanotubes by nanoimprint-assisted aluminum film surface engineering

Abstract

The authors present successful fabrications of hexagonally ordered and vertically aligned anodic aluminum oxide (AAO) nanotube array patterns over a large area (at least ∼6×6 mm2) by utilizing nanoimprint-guided anodization on sputter deposited Al thin films. Perfectly periodic nanotube arrays with no domain boundaries are obtained. Nanoindented patterns comprising hexagonal pillar arrays having a periodically absent pillar in the center of each hexagon were pattern transferred onto a poly(methyl methacrylate) coated Al film surface via reactive ion etch (RIE) followed by a subsequent guided anodization to produce long-range ordered vertical pore arrays. Upon further anodization, a self-assembled extra pore was formed in the center of each hexagon in addition to the regular pores formed at the impression location, thus leading to a pattern increase by 50%. Interestingly, it is seen that the resultant AAO structure can be altered via RIE process time duration, i.e., Al surface topographic modification prior to anodization. Similarly, a pattern-tripling phenomenon was observed when a triangular-patterned nanoimprint stamp was used by producing self-assembled central pores in the center of all triangles as well as guided pores at the impressed location, thus increasing the total number of pores by a factor of 3.