Ideally Ordered Anodic Porous Alumina on Si Substrate Prepared by Anodization of Sputtered Al–Mg Thin Film

Anodic porous alumina with an ideally ordered hole arrangement was formed on a Si substrate by nanoimprinting and subsequent anodization. In this process, the arrayed shallow dimples formed by nanoimprinting using a mold act as initiation sites of hole development during the anodization. To realize the precise transfer of the mold patterns to the Al surface during nanoimprinting, we used sputtered Al alloy film as a starting material. This is because the Al alloy with appropriate impurities as a sputtering target can suppress the crystal grain growth during sputtering and allow the formation of Al alloy films with smooth surfaces on the substrate. Dimple arrays with 100 nm intervals could be formed on the flat surface of the Al–Mg film on the Si substrate. Ideally ordered anodic porous alumina with an interpore distance of 100 nm was successfully obtained by subsequent anodization. A Co/alumina composite was also obtained by the electrodeposition of Co into the alumina holes. The obtained samples are expected to be applied to various functional devices requiring an ideally ordered structure on a substrate.