Nanoporous anodic aluminum oxide with a long-range order and tunable cell sizes by phosphoric acid anodization on pre-patterned substrates

Abstract

Nanoporous anodic aluminum oxide (AAO) has been explored for various applications due to its regular cell arrangement and relatively easy fabrication processes. However, conventional two-step anodization based on self-organization only allows the fabrication of a few discrete cell sizes and formation of small domains of hexagonally packed pores. Recent efforts to pre-pattern aluminum followed with anodization significantly improve the regularity and available pore geometries in AAO, while systematic study of the anodization condition, especially the impact of acid composition on pore formation guided by nanoindentation is still lacking. In this work, we pre-patterned aluminium thin films using ordered monolayers of silica beads and formed porous AAO in a single-step anodization in phosphoric acid. Controllable cell sizes ranging from 280 nm to 760 nm were obtained, matching the diameters of the silica nanobead molds used. This range of cell size is significantly greater than what has been reported for AAO formed in phosphoric acid in the literature. In addition, the relationships between the acid concentration, cell size, pore size, anodization voltage and film growth rate were studied quantitatively. The results are consistent with the theory of oxide formation through an electrochemical reaction. Not only does this study provide useful operational conditions of nanoindentation induced anodization in phosphoric acid, it also generates significant information for fundamental understanding of AAO formation.

Enhanced Absorption in Organic Thin-Films from Imprinted Concave Nanostructures

“…It can be easily observed that the structures in (a) have a more regular honeycomb like pattern as compared to (b). This is an effect of the longer anodization process of the thick Al foil [45] as well as the two step anodization process [46]. The size of the Al concaves for the semi periodic Al concave patterns fabricated after double and long anodization of Al foil is 368 nm, while the aperiodic concave patterns fabricated after anodization of a thin Al film supported on Si result in a size of 324 nm.…”

Microfluidic devices with templated regular macroporous structures for HIV viral capture

“…In these porous materials, the pore geometries are regular and pore sizes are tunable within a wide range by selecting appropriate templates. 26,28 These nanotemplated matrices have not yet been tested for viral separation.…”

Innovative Nanoimprint-Assisted Fabrication of Anodic Aluminum Oxide

“…Lee's group used a traditional photolithography fabrication to replicate a nickel imprint stamp with a defect-less hexagonal pattern in order to produce an ideal AAO nanoporous structure (Lee and Lee, 2010). Focus ion-beam lithography (Liu et al, 2001), scanning probe microscopic lithography (Masuda et al, 2002), optical diffraction grating (Mikulskas et al, 2001), and microbeads (Masuda et al, 2004;Surawathanawises and Cheng, 2014) have been investigated as pretreatments of aluminum. However, these fabrication processes are relatively slow and expensive.…”