Self-Ordered Aluminum Anodizing in Phosphonoacetic Acid and Its Structural Coloration

Abstract

Ordered anodic porous alumina with large-scale periodicity was fabricated via phosphonoacetic acid anodizing. Aluminum specimens were anodized in a 0.1-0.9 M phosphonoacetic acid solution under various electrochemical operating conditions, and optimum anodizing at 205-225 V exhibited self-ordering growth of the porous alumina. These self-ordering voltages during phosphonoacetic acid anodizing filled an undiscovered vacant region in the linear relationship between the self-ordering voltage and the cell diameter. The nanostructured aluminum surface formed via self-ordering phosphonoacetic acid anodizing produced a bright structural coloration with a visible light wavelength of 500-700 nm, which is useful for optical nanoapplications. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0021508ssl] All rights reserved. Self-ordered anodic porous alumina possesses a well-defined periodic porous structure with numerous nanopores that have high aspect ratios. [1][2][3] This characteristic nanoporous material is widely used for various novel nanoapplications, including electronic, optical, and sensing devices. [4][5][6][7][8][9][10][11][12] Ordered porous alumina can be fabricated by electrochemical anodizing in several acidic electrolyte solutions under appropriate experimental conditions such as concentration and applied voltage. The periodical size of the obtained ordered porous alumina, defined as the "cell size" or "interpore distance", is typically determined by the electrolyte species used.2,3,13 In self-ordered anodizing, the regularity of the pore arrangement in the porous structure can be accurately determined by a quantitative analysis based on Fourier transformation.14-19 Sulfuric, oxalic, and phosphoric acids were found early and have been commonly used as the standard self-ordering electrolytes to date. 13,20,21 However, the cell size of these ordered porous alumina is limited to the following narrow nanometer-scale regions: 50-60 nm in sulfuric acid, 100 nm in oxalic acid, and 405-500 nm in phosphoric acid.13 Therefore, the identification of novel electrolytes for self-ordered porous alumina with different cell sizes has been a recent challenge to extensively expand the nano-periodicity. Additional dicarboxylic acids with a large molecular structure, malonic and tartaric acids, for the fabrication of anodic porous alumina were reported by Ono et al., and self-ordering was achieved by anodizing with these acids for 300 and 500 nm intervals, respectively. Particularly, etidronic acid anodizing exhibited large-scale self-ordering behavior measuring 530-670 nm in cell diameter. Eti...

Nanostructural characterization of large-scale porous alumina fabricated via anodizing in arsenic acid solution

“…Because the chemical and physical properties and the nanomorphology of porous alumina are still limited by a few typical electrolyte used during anodizing, the discovery of additional electrolytes would expand the applicability of porous alumina. For example, anodizing in etidronic and phosphonoacetic acid solutions can occur at high potential differences (voltage), i.e., >200 V [31][32][33][34], and produces a large-scale ordered porous alumina and generates a bright structural coloration from the nanostructured surface. Anodizing in pyrophosphoric acid (H 4 P 2 O 7 ) causes growth of single nanometer-scale alumina nanofibers, and the nanofiber-covered aluminum surface exhibits rapid superhydrophilicity [35][36][37][38].…”

Manufacturing of highly ordered porous anodic alumina with conical pore shape and tunable interpore distance in the range of 550 nm to 650 nm

“…Since the heights of pillars are very important at longer wavelength region, the larger area of the cone base makes it possible to obtain better graduation of refractive index along the pore walls for relatively high pores. Self-ordered PAA with D c > 500 nm and parallel pores (constant pore diameter throughout the PAA thickness) have previously been synthesized [27][28][29][30].…”

Superhydrophilicity of a nanofiber-covered aluminum surface fabricated via pyrophosphoric acid anodizing

“…Aluminum anodizing is a simple electrochemical technique that is used to form thick anodic oxide films on an aluminum surface and has been widely investigated in the fields of surface science and engineering for corrosion protection, electronic devices, and optical materials [1][2][3][4][5][6][7]. Anodic oxide films fabricated via aluminum anodizing can be typically classified into the following two groups: barrier type oxide films formed in neutral solutions and porous type oxide films (porous alumina) formed in acidic and alkaline solutions [1,2,[8][9][10][11][12][13][14][15][16][17][18]. Typically, anodizing in acidic solutions, such as sulfuric (H 2 SO 4 ), oxalic ((COOH) 2 ), and phosphoric acid (H 3 PO 4 ), causes the formation of porous alumina which consists of numerous nanoscale hexagonal cells measuring several tens or hundreds of nanometers in diameter with a nanopore at the center of each cell [19][20][21][22][23][24][25].…”