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

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 π-conjugated 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.