Controlled morphology of aluminum alloy nanopillar films: from nanohorns to nanoplates Short title: Aluminum alloy nanopillar films

Nanopillar films of Al-Nb alloys have been fabricated on substrates with a regular concave cell structure by oblique angle physical vapor deposition. The concave cell structure of substrate increases the shadow region for the flux of depositing atoms, assisting the formation of an isolated nanopillar on each cell. Depending upon the alloy composition and deposition angle, the pillar shape changes from horn-like nanopillars through triangle nanoprisms to nanoplates. The Al-Nb alloy nanoplate films with wide gaps between plates are of interest as an electrode for capacitor application. The dielectric oxide film formed on the nanoplate film showed the capacitance more than 10 times larger than that on the respective flat film, due to enlarged surface area. Keywords; nanopillar film, oblique angle deposition, Al-Nb alloys, anodic oxide,