Nanoporous Anodic Aluminum Oxide: Fabrication, Characterization, and Applications

Abstract

Anodic aluminum oxide (AAO) consists of parallel pores arranged in a honeycomb-like array. Since a two-step self-organized approach in anodic alumina fabrication was invented, tremendous attention was paid to this material. Structural features of anodic alumina, like pore diameter, interpore distance, and nanoporous oxide thickness, can be fully controlled by operating conditions, including type, concentration and temperature of the electrolyte, applied voltage, and duration of the anodization process. Moreover, these operating conditions have also a major impact on the nanoporous array arrangement. Quantitative arrangement analysis methods employing fast Fourier transforms have been developed to assess the nanopores' arrangement. The most frequent application of the anodic aluminum oxide is a template-assisted fabrication of nanostructures. Templates made of the AAO are being successfully applied in fabrication of nanowires, nanotubes, and nanodots by using diversity of techniques, including electrochemical deposition, physical and chemical vapor deposition, sol-gel techniques, etc. Due to the size of obtained nanostructures, magnetic, electric, piezoelectric, luminescent, and catalytic properties of the deposited materials can be significantly improved. Thus, control of the nanopores' structural features and arrangement is crucial for AAO applications in nanotechnology.

Towards Self-Organized Anodization of Aluminum in Malic Acid Solutions—New Aspects of Anodization in the Organic Acid

“…[ 4 , 5 , 6 , 7 ]. The attractiveness of the AAO template for nanofabrication results from the ability to precisely control its thickness, pore diameter ( D p ) or interpore distance ( D c ) by simple changing electrochemical parameters, such as applied voltage, temperature, anodizing time, or the electrode distance [ 8 , 9 ]. While D p can be additionally regulated (increase) by post-processing pore broadening in acidic solutions, the D c is fixed when the anodization is completed and is mainly determined by the anodization voltage.…”

On the Prediction of Well-Ordered Porous Anodic Alumina Films

“…Since the discovery of anodic alumina synthesis by electrochemical anodization of aluminum metal and the structural features of PAOX, it has become a well-known material system in the scientific community for several decades. In the mid 90s, seminal discoveries by Masuda and co-workers reported that the regularity of the pore arrangement can be optimized to almost perfect hexagonal lattices by using appropriate electrolysis conditions, specific potentials, sufficiently long anodization times, and pretexturing of the Al substrate. − This has led to an enormous increase on the studies of the functional properties and applications − of such porous materials with controlled pore geometry.…”

Effect of pore widening time on the structural aspects of self-organized nanopore arrays formed by anodization of aluminum in chromic acid

“…These membranes can be prepared using two-step anodization of aluminum in acidic electrolytes [6]. Highly-ordered alumina have been used for the nano porous pattern production and is obtained using oxalic [12], phosphoric [13] and sulfuric [14] acids, however chromic acid is rarely used because the AAO membranes are less ordered compare to those prepared by other electrolytes. With the applications of AAO, significant advances in magnetism of nanomaterials [8], energy storage [9], sensor assembly [10] and biomaterial significance [11] have been attained.…”