Fabrication and application of nanoporous anodic aluminum oxide: a review

Abstract

Due to the unique optical and electrochemical properties, large surface area, tunable properties, and high thermal stability, nanoporous anodic aluminum oxide (AAO) has become one of the most popular materials with a large potential to develop emerging applications in numerous areas, including biosensors, desalination, high-risk pollutants detection, capacitors, solar cell devices, photonic crystals, template-assisted fabrication of nanostructures, and so on. This review covers the mechanism of AAO formation, manufacturing technology, the relationship between the properties of AAO and fabrication conditions, and applications of AAO. Properties of AAO, like pore diameter, interpore distance, wall thickness, and anodized aluminum layer thickness, can be fully controlled by fabrication conditions, including electrolyte, applied voltage, anodizing and widening time. Generally speaking, the pore diameter of AAO will affect its specific application to a large extent. Moreover, manufacturing technology like one/two/multi step anodization, nanoimprint lithography anodization, and pulse/cyclic anodization also have a major impact on overall array arrangement. The review aims to provide a perspective overview of the relationship between applications and their corresponding AAO pore sizes, systematically. And the review also focuses on the strategies by which the structures and functions of AAO can be utilized.

Deuterated polyethylene nanowire arrays for high-energy density physics

“…The AAO templates are formed by electrochemical anodization of pure aluminum. They consist of parallel arrays of holes surrounded by hexagonal cells of aluminum oxide that grow perpendicular to the metallic surface as the anodization advances, forming a structure that resembles a honeycomb [35,36] . They are commercially available (e.g., SmartMembrane).…”

Evidence of oxygen bubbles forming nanotube embryos in porous anodic oxides

“…[1][2][3][4][5][6][7][8] Although porous anodic alumina and anodic TiO 2 nanotubes have been studied for decades, however, the formation mechanism of these porous nanoscale structures remains a lot of controversy. 1,[9][10][11][12][13][14][15] First of all, is there any connection or difference between the porous structure and the nanotube structure? There is a main difference in porous structure of porous anodic alumina and anodic TiO 2 nanotubes.…”

“…For example, the field-assisted reaction of porous anodic alumina is Al 2 O 3 + 6H + → 2Al 3+ + 3H 2 O. 9,10 The field-assisted reaction of TiO 2 nanotubes is TiO 2 + 6F − + 4H + → [TiF 6 ] 2− + 2H 2 O. 12,15,17 The field-assisted reaction of Ta 2 O 5 nanotubes is Ta 2 O 5 + 10H + + 14F -→ 2[TaF 7 ] 2-+ 5H 2 O.…”

“…19 Although these reactions have been repeatedly cited to explain the mechanism of nanopore formation, it has never been reported that any of these dissolution reactions actually exist. [9][10][11][12]20 On the contrary, in recent years there have been a number of articles denying the field-assisted dissolution reaction. [20][21][22][23] Skeldon et al 21 demonstrated that the acid dissolves alumina weakly, 21 which could not sustain the growth of the pores.…”

“…How the electric field acts on the above dissolution reaction to assist the growth of nanotubes is always vague. 1,[10][11][12][13][14][15][33][34][35] The third controversy is about the two modes in which nanotubes grow, whether they grow in the "top-down digging mode" on the surface of the oxide film or in the "bottom-up flow mode" around the oxygen bubble under the oxide film. 1,[10][11][12] It is well known that the traditional three theories of field-assisted dissolution, field-induced injection, oxide growth and dissolution equilibrium believe that the growth of nanopores is in accordance with the "top-down digging mode".…”