Massive, eco-friendly, and facile fabrication of multi-functional anodic aluminum oxides: application to nanoporous templates and sensing platforms

Abstract

In this paper, we report on an efficient and eco-friendly approach to fabricate AAOs in oxalic acid electrolyte, which exhibits a relatively wide range of electrolyte temperatures for stable anodization. Our strategy consists of simultaneous multi-surfaces anodization (SMSA) for fabricating plural AAOs and direct detachment of those AAOs from an aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs. A unit sequence including SMSA sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate for mass production of AAOs. Dimensional characteristics of AAOs were quantitatively controlled with respect to the electrolyte temperature as well as the number of applied sequences, and SRBs-based direct detaching characteristics depending on the AAO thickness were investigated as a function of the number of stairs in SRBs. The AAOs fabricated here were used as nanoporous templates for synthesizing pconjugated polymer nanomaterials with various diameters, and their structural and optical characteristics were studied with respect to their physical dimensions. We also fabricated capacitive humidity sensors designed on interdigitated electrode structures with nanoporous AAOs, and discussed their superior device performances.

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

“…AAO growth rate was estimated to be about 8.0 and 7.5 μm/h on the front and back surface of the Al substrate at the electrolyte temperature of 15 °C, respectively (Refer to reference 57 for more details). V with the increment of -1 V and without time interval between adjacent stairs.…”

“…However, SRBs, a key distinction of our methods, enable the detachment of those AAOs from the corresponding multi-surfaces of the Al substrate in the same acidic electrolyte used for the SMSAs indicating mass-production, simplicity, and green technological characteristics. We would like to point out that SRBsbased detachment is an optimal strategy for plural AAOs fabricated by SMSAs 56,57 and even valid for relatively thinner thicknesses of AAOs 57 when compared with cathodic delamination (i.e., constant reverse bias) on single-surface…”

“…All the experimental approaches listed above have been applied to a "single-surface" of the Al specimen, excluding surface protecting/ engineering purposes, and this feature of the conventional technologies exhibits critical limitations of the AAO fabrication in terms of yield as well as processibility, which also influences the potential applicability of the AAOs 56,57 .…”

“…To satisfy the increasing demands in the AAO-related fields in terms of facile, high yield, and green technological approaches, we previously reported on SMSA and direct detachment through SRBs under sulfuric 56 and oxalic 57 acid electrolyte, respectively. It is a well-known fact that plural AAOs can be formed on the multiple surfaces of the Al substrate immersed into acidic electrolytes.…”

The effect of ethylene glycol on pore arrangement of anodic aluminium oxide prepared by hard anodization

“…Meanwhile, as a nano-template or host material, AAO plays an essential role for various surface engineering applications, e.g. molecular separation, catalysis, energy storage, electronics, sensors, drug delivery and template synthesis [ 5 , 6 ], and is a component in a diverse range of nanostructured materials in the form of nanodots, nanowires and nanotubes [ 7 , 8 ].…”