A Facile Method for Controllable Fabrication of Porous Anodic Aluminum Oxide Templates with Multiple-Scale Structures

Abstract

Porous anodic aluminum oxide (AAO) templates with diverse nano/submicron/micron multiple-scale structures have been fabricated by a facile and controllable two-step anodization process. The first step anodization has been achieved by using a simple competitive growth process with high anodization voltage (U a ) in ethanol-oxalic acid mixture electrolytes. The effects of U a (300-600 V), anodization current density (J a , 100-200 A m −2 ), and the proportion of ethanol adding (0.3 M oxalic acid : ethanol = 1 : 1, 3 : 2, V/V) on the submicron/micron structures of AAO templates have been investigated in detail. The second step anodization has been conducted under relatively lower U a of 30 V and 40 V, respectively. The effects of U a , etching process, and anodization time on the nanostructures of as-fabricated porous AAO templates have been studied carefully. In addition, related intrinsic formation mechanisms have also been investigated. Based on these quantitative experimental results, the fabrication of multiple-scale porous AAO films with diverse nano/submicron/micron structures can be more controllable and designable, facilitating their practical applications in simple template synthesis of complex multiple-scale functional materials.Anodic aluminum oxide (AAO) films prepared by aluminum anodization have been investigated and used in numerous fields for more than 150 years. 1-24 In 1953, Keller et al. investigated the structural features of porous type AAO films in detail with the electron microscope and proposed a corresponding structural model. 5 Since then, porous AAO films which contain a large number of nanopores have attracted considerable attention. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] In 1995, Masuda et al. firstly proposed a pre-patterning fabrication process which contains the first anodization for forming highly ordered dimples on the aluminum surface, and the second anodization for obtaining ideally ordered porous AAO films. 12,13 At present, they have become one of the most commonly used nanoporous templates for the fabrication of diverse nanomaterials (e.g., nanowire, nanotube, and nanodot) because of their apparent advantages, such as good reproducibility, adjustable pore size, and controllable film thickness, etc. 25-35 Moreover, they can also be used as functional materials for many applications: e.g., biotechnology, photonics, sensors. [36][37][38][39][40] Nowadays, although porous AAO films can be applied in many practical fields, there are still some shortcomings which greatly limit their applications: most of the fabricated porous AAO films have a simple honeycomb-like microstructure, and their pore size is typically limited to nanoscale or submicron scale. Based on these structural features, it is difficult for their template synthesis of functional materials with micron scale or nano/submicron/micron multiple-scale structures. Over the last decade, tremendous research has been focused on the development of multiple-scale materials which have become a h...

Characteristic Resonance Reflection Spectra of Nanoporous Alumina Films and Its Application to Precise Thickness Measurement

“…Moreover, Li et al developed a new approach to fabricate porous AAO films with multi-scale nano-micro structures. 6 The numerous AAO growing processes were introduced for high-quality AAO but monitoring AAO processes was an accompanied crucial issue. Some AAO related reviews reported the fundamental aspects of film growth including ionic transport under intense electric fields, highly uniform thickness over a large area and anodic polarization developed in suitable electrolytes.…”

Controllable Fabrication and Microstructure Modulation of Unique AAO Structures Based on Patterned Aluminum Surface

“…[34][35][36] Accordingly, finding proper methods for the fabrication of AAO with various controllable microstructures has become a hot topic. 11,[34][35][36][37][38][39][40][41][42][43][44][45][46] Among these methods, conducting anodization processes on patterned aluminum surface instead of the smooth one, has been known as one of the most effective ways for obtaining unique AAO structures. [39][40][41][42][43] Therefore, finding facile, low-cost, controllable and repeatable methods for preparing patterned aluminum surface, thus obtaining diverse unique AAO structures, is significant from the viewpoint of both fundamental research and practical applications.…”

“…51,52 However, most of these porous AAO films were fabricated based on smooth aluminum surface. Considering that performing anodization processes on patterned aluz E-mail: msliyi@scut.edu.cn minum surface is one of the most effective ways for obtaining unique AAO structures, [39][40][41][42][43] comparative studies have been done based on smooth aluminum surface and patterned aluminum surface.…”

“…At present, there are plenty of methods that can form patterns on aluminum surface. [39][40][41][42][43] Among these methods, using anodization processes and a following AAO removing procedure has been proven to be effective, when considering the factors of cost, process flow, and the dependence on special equipment. In fact, the two-step anodization process firstly proposed by Masuda et al can also be classified as this kind of patterning methods.…”

“…38,[53][54][55] In addition, unique submicron/micron patterns can also be formed on aluminum surface based on competitive growth anodization processes. 43,44 These research work undoubtedly played an important role for the improvement of the anodization patterning method.…”