Polymer nanoimprinting using an anodized aluminum mold for structural coloration

Polymer nanoimprinting of submicrometer-scale dimple arrays with structural coloration was demonstrated. Highly ordered aluminum dimple arrays measuring 530–670 nm in diameter were formed on an aluminum substrate via etidronic acid anodizing at 210–270 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

Self-Ordering Behavior of Anodic Porous Alumina via Selenic Acid Anodizing

The self-ordering behavior of anodic porous alumina that was formed by anodizing in selenic acid elec-trolyte (H2SeO4) at various concentrations and voltages was investigated with SEM and AFM imaging.A high purity aluminum foil was anodized in 0.1-3.0 M selenic acid solutions at 273 K and at constantcell voltages in the range of 37 to 51 V. The regularity of the cell arrangement increased with increas-ing anodizing voltage and selenic acid concentration under conditions of steady oxide growth withoutburning. Anodizing at 42-46 V in 3.0 M selenic acid produced highly ordered porous alumina. By selec-tive dissolution of the anodic porous alumina, highly ordered convex nanostructures of aluminum withdiameters of 20 nm and heights of 40 nm were exposed at the apexes of each hexagonal dimple array.Highly ordered anodic porous alumina with a cell size of 102 nm from top to bottom can be fabricatedby a two-step selenic acid anodizing process, that includes the first anodizing step, the selective oxidedissolution, and the second anodizing step

Fabrication of Anodic Nanoporous Alumina via Acetylenedicarboxylic Acid Anodizing

The nano-morphologies of anodic porous alumina formed via anodizing in a new electrolyte, acetylenedicarboxylic acid (ADCA), are described. Anodic oxides grew uniformly on the aluminum at voltage of 87.5-95.0 V, but a burned black oxide film was formed at higher voltage. The burning voltage and the current density under steady-state oxide growth decreased with solution temperature. An anodic porous alumina film with a cell size of 250 nm and nanopores measuring 100 nm could be successfully obtained by ADCA anodizing. The anodic porous alumina possessed numerous non-straight nanopores due to the branching and extinction of the nanopores during anodizing

Rapid fabrication of self-ordered porous alumina with 10-/sub-10-nm-scale nanostructures by selenic acid anodizing

Anodic porous alumina has been widely investigated and used as a nanostructure template in various nanoapplications. The porous structure consists of numerous hexagonal cells perpendicular to the aluminum substrate and each cell has several tens or hundreds of nanoscale pores at its center. Because the nanomorphology of anodic porous alumina is limited by the electrolyte during anodizing, the discovery of additional electrolytes would expand the applicability of porous alumina. In this study, we report a new self-ordered nanoporous alumina formed by selenic acid (H2SeO4) anodizing. By optimizing the anodizing conditions, anodic alumina possessing 10-nm-scale pores was rapidly assembled (within 1 h) during selenic acid anodizing without any special electrochemical equipment. Novel sub-10-nm-scale spacing can also be achieved by selenic acid anodizing and metal sputter deposition. Our new nanoporous alumina can be used as a nanotemplate for various nanostructures in 10-/sub-10-nm-scale manufacturing

Fabrication of Self-Ordered Porous Alumina via Etidronic Acid Anodizing and Structural Color Generation from Submicrometer-Scale Dimple Array

Highly ordered anodic porous alumina with a large-scale cell diameter was successfully fabricated via anodizing in a new electrolyte, etidronic acid (1-hydroxyethane-1,1-diphosphonic acid). High-purity aluminum specimens were anodized in a 0.3 M etidronic acid solution under constant current density and voltage conditions. Etidronic acid anodizing at 210 to 270 V at the appropriate temperature caused the anodic porous alumina to exhibit self-ordering behavior, and periodic nanostructures measuring 530 to 670 nm in cell diameter were fabricated on the aluminum substrate. The self-ordering voltage and the corresponding cell diameter could be increased without burning by systematically increasing the stepwise voltage. Two-step etidronic acid anodizing without nanoimprinting can easily yield the formation of highly ordered anodic porous alumina with a large-scale cell diameter. A submicrometer- scale dimple array fabricated via etidronic acid anodizing and subsequent selective oxide dissolution gave rise to bright structural color with a rainbow distribution

Porous Aluminum Oxide Formed by Anodizing in Various Electrolyte Species

Anodizing of aluminum and its alloys is widely investigated and used for corrosion protection, electronic devices, and micro-/nanostructure fabrication. Anodizing of aluminum in acidic solutions causes formation of porous aluminum oxide films, which consists of numerous hexagonal cells perpendicular to the aluminum substrate, and each cell has nanoscale pores at its center. Recently, highly ordered porous aluminum oxide has been widely investigated for various novel nanoapplications. In this review article, we introduce the fundamentals of anodic oxide films including barrier and porous oxides. Then, we summarize the electrolyte species used so far for porous oxide fabrication and describe the self-ordering conditions during anodizing in these electrolyte solutions. Fabrication of highly ordered porous oxides through the vertical section can be achieved by a two-step anodizing and nanoimprint technique. Various nanoapplications based on the ordered porous oxide are also introduced

Ultra-High Density Single Nanometer-Scale Anodic Alumina Nanofibers Fabricated by Pyrophosphoric Acid Anodizing

Anodic oxide fabricated by anodizing has been widely used for nanostructural engineering, but the nanomorphology is limited to only two oxides: anodic barrier and porous oxides. Therefore, the discovery of an additional anodic oxide with a unique nanofeature would expand the applicability of anodizing. Here we demonstrate the fabrication of a third-generation anodic oxide, specifically, anodic alumina nanofibers, by anodizing in a new electrolyte, pyrophosphoric acid. Ultra-high density single nanometer-scale anodic alumina nanofibers (1010 nanofibers/cm(2)) consisting of an amorphous, pure aluminum oxide were successfully fabricated via pyrophosphoric acid anodizing. The nanomorphologies of the anodic nanofibers can be controlled by the electrochemical conditions. Anodic tungsten oxide nanofibers can also be fabricated by pyrophosphoric acid anodizing. The aluminum surface covered by the anodic alumina nanofibers exhibited ultra-fast superhydrophilic behavior, with a contact angle of less than 16, within 1 second. Such ultra-narrow nanofibers can be used for various nanoapplications including catalysts, wettability control, and electronic devices