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HighlightsHighly ordered aluminum dimple arrays are fabricated via etidronic acid anodizing.The ordered dimple arrays display structural coloration with a rainbow distribution.Aluminum nanostructures can be transferred to polymers via nanoimprinting.The nanostructured polymer surfaces also exhibit structural coloration.
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AbstractPolymer nanoimprinting of submicrometer-scale dimple arrays with structural coloration was demonstrated. Highly ordered aluminum dimple arrays measuring 530 to 670 nm in diameter were formed on an aluminum substrate via etidronic acid anodizing at 210 to 270 V and subsequent anodic oxide dissolution. The nanostructured aluminum surface led to bright structural coloration with a rainbow spectrum, and the reflected wavelength strongly depends on the angle of the specimen and the period of the dimple array. The reflection peak shifts gradually with the dimple diameter toward longer wavelength, reaching 800 nm in wavelength at 670 nm in diameter. The shape of the aluminum dimple arrays were successfully transferred to a mercapto-ester ultra-violet curable polymer via self-assembled monolayer coating and polymer replications using a nanoimprinting technique. The nanostructured polymer surfaces with positively and negatively shaped dimple arrays also exhibited structural coloration based on the periodic nanostructure, and reflected light mostly in the visible region, 400-800 nm. This nanostructuring with structural coloration can be easily realized by simple techniques such as anodizing, SAM coating, and nanoimprinting.Keywords: Anodizing; Anodic Porous Alumina; Etidronic Acid; Structural Coloration; Nanoimprinting 4
IntroductionAnodic porous alumina possesses characteristic nanofeatures, including highly ordered porous structures with high-aspect ratio nanopores measuring several tens or hundreds of nm in diameter, and can easily be fabricated via aluminum anodizing in several appropriate acidic electrolyte solutions [1][2][3][4]. Because it is difficult to obtain such similar high-aspect ratio porous materials by other techniques, anodic porous alumina has been widely investigated by researchers in nano-science and engineering applications, such as fundamentals [5][6][7] [41]. In particular, anodizing in sulfuric, selenic, oxalic, malonic, tartaric, and phosphoric acid solutions under the appropriate electrochemical conditions causes self-ordering growth of the porous alumina [1,2,42]. Accordingly, highly ordered anodic porous alumina with a high aspect ratio has been successfully obtained on aluminum substrates. However, the cell diameter (interpore distance) of the porous alumina formed in these electrolyte solutions is limited to up to approximately 500 nm in diameter at the corresponding anodizing voltage of 200 V [1]. Therefore, a novel high-voltage electrolyte is required for the self-ordering of porous alumina with large-scale cell diameters.Recently, we reported a new self-ordering electrolyte for anodic porous alumina fabrication, etidronic acid (1-hydroxyethane-1,1-diphosphonic ...