Preparation of Ordered Nanohole Arrays by Anodization of Textured Metal Substrates

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The anodization of metals can form nanohole array structures composed of various metal oxides. The resulting anodic oxide film is expected to be used in various applications, such as catalysts, electrodes, and sensors, because of the material's properties and unique geometric structure. When applying nanohole arrays obtained by anodization of metal substrates to various functional devices, it is important to control geometrical structures such as pore size and pore depth, which affect device performance. We previously reported that forming a pattern of depressions on substrate surfaces prior to anodization allows the formation of ordered nanohole arrays by subsequent anodization [1–3]. In previous studies, the depression pattern was formed by dry etching with a mask, which made it impossible to increase the area of the pattern. In this study, we investigated the formation of depression patterns using a template process and the control of the starting point of pore generation by anodic oxidation to form large-area ordered nanohole arrays. Herein, we present the results of our study using Sn as the model material. Anodized porous alumina, which can self-assemble large-area ordered structures, was used as a template to form ordered depression patterns on the Sn substrates. An ordered anodic porous alumina membrane, used as a template, was obtained by selectively dissolving the Al substrate from the anodized sample. The Sn thin film was formed on the back side of the obtained template by thermal evaporation and electrodeposition, and the alumina membrane was peeled off to obtain a Sn thin film with an ordered depression pattern on the surface. The resulting Sn thin film was anodized to generate holes from each depression, resulting in an ordered nanohole array. SEM observations confirmed that the ordered pattern on the anodic porous alumina backside was successfully transferred to the Sn surface by this process. Anodization of the obtained Sn thin films induced pore generation from each depression, resulting in ordered nanohole arrays. This process is expected to produce large-area ordered nanohole arrays because the anodic porous alumina used as a template can be fabricated in large areas. The Sn oxide nanohole arrays obtained by this method are expected to have various applications.