Anodic Aluminum Oxide Process Research Articles

Rapidly fabrication of plasmonic structural color thin films through AAO process in an alkaline solution

Metallic nanostructures can be designed using reflective color filters, also known as plasmonic structural color (PSC) material. Compared with nanoparticles, self-ordered nanoscale pores, and subwavelength gratings, plain metal–dielectric–metal (MDM) structures are inexpensive, simple to manufacture, and treated within a short period of time. In this study, a new silicate- and phosphate-containing alkaline electrolyte was used for the fast fabrication of PSC thin films using an anodic aluminum oxide (AAO) process. The full treatment time, including AAO treatment and deposition of the outer metal layer, was only a few minutes. The structural color in the visible region was simply controlled by adjusting the applied current density during anodization. The surface and cross-sectional morphologies of the formed AAO coatings were then examined through field emission scanning electron microscopy, while the element compositions were determined through energy-dispersive X-ray spectroscopy. The electrochemical impedance spectroscopy method was also employed to further clarify the coating characteristics. Next, the color performance was studied using a colorimeter and ultraviolet–visible spectrophotometer; the effects of outer-metallic-layer thickness and roughness on color shift and saturation were also investigated. The results contribute to our understanding of how inner dielectric-metal structures form, as well as how the corresponding surface plasmon resonance was influenced when current density was applied to an alkaline electrolyte. Notably, plain MDM structures appear to be suitable for reflective color filtering applications with low cost and fast fabrication.

Effects of anodization parameters on the corrosion resistance of 6061 Al alloy using the Taguchi method

Anodizing 6061 aluminum alloy (AA6061) in a H2SO4 electrolyte solution is a crucial process in the formation of anodic aluminum oxide (AAO) film for enhancing the material’s corrosion resistance. In this work, the effects of electrolyte concentration, current density, and anodization time parameters on the evolution of corrosion resistance in AA6061 alloy were investigated using the Taguchi method. Each anodization parameter had three levels using an experimental set of L9 orthogonal arrays. Variation in the bias voltage was recorded during the AAO process, and an energy-dispersive spectrometer was used to analyze the variations in the composition of the oxidized films. Variations in surface morphology and cross-sections of the AAO were examined using a scanning electron microscope. Finally, the potentiostatic polarization method was used to judge the relative corrosion resistance of the oxidized films. The oxidized film with the best corrosion resistance (Icorr = 8.516 × 10−11 A/cm2) was obtained by anodizing at a current density of 1 A/dm2 in 1 M sulfuric acid for 20 min.

Continuous Fabrication of Multiscale Compound Eyes Arrays With Antireflection and Hydrophobic Properties

The multiscale hierarchical structures inspired by moth's compound eyes offer multifunctional properties in optoelectronic devices. However, it is still a major challenge to fabricate these hierarchical structures on large-area substrates using a simple and cost-effective technique. The roll-to-roll ultraviolet nanoimprint lithography (R2R UV-NIL) technique provides a solution for the continuous fabrication of multiscale compound eyes arrays due to its high-speed, large-area, high-resolution, and high-throughput. In this paper, the R2R UV-NIL technique was used to fabricate the multiscale compound eyes arrays on the PET substrate. The mold used in the R2R UV-NIL process was acquired by anodic aluminum oxide process and then the multiscale compound eyes arrays were directly obtained via one-step R2R imprinting. The obtained multiscale compound eyes arrays exhibit excellent antireflective performance within the wavelength 400-800 nm. Besides, the compound eyes arrays also equip the surface of the microlens with excellent hydrophobic characteristics. These multifunctional properties enable the multiscale compound eyes arrays to retain their superior optical properties in real-time environmental conditions. This report can provide a beneficial direction for the continuous production and widespread applications of the multiscale compound eyes arrays.

Heterogeneous Integrated MEMS Enabled by AAO Process Technologies

An alternative approach to fabricate specialty MEMS devices by heterogeneous integration of dissimilar materials such as PCB substrates and neodymium magnets with anodic aluminum oxide (AAO) templates was demonstrated. The importance of the use of copper metal as an intermediate layer for wet chemical etching of AAO templates in order to release MEMS devices was presented. The assembling of dissimilar materials before the final wet chemical etch and release was introduced which is not possible with standard MEMS micromachining processes. The unique anisotropic etching feature, excellent dielectric with good mechanical properties, low cost, and compatibility with other materials and processes make AAO an attractive candidate material and process for manufacturing microdevices for many MEMS applications.

Hot-rolled embossing of microlens arrays with antireflective nanostructures on optical glass

sGlass is an excellent material for optical devices requiring optical and mechanical properties better than those of a polymer. Because traditional micro- or nano-fabrication on glass substrates is typically slow and costly, the fabrication of micron- or nanometer-scale structures on glass has been a challenge. For a novel continuous fabrication of glass microlens arrays with antireflective nanostructures (AR-MLA), we have designed and implemented a hot-rolled embossing facility with synergetic heating. The mold of a hybrid micro/nanostructure was fabricated in two steps. First, a micron-scale lens cavity was embossed on a nearly pure aluminum sheet with an electroplated nickel mold; an anodic aluminum-oxide process was used to create a nanostructure on the microlens array cavity. The mold was then mounted on a roller and used in a hot embossing machine to fabricate AR-MLA on optical glass. The optical properties of the fabricated microlens with nanostructures have been verified. The image of focused spots of fabricated AR-MLA shows an effective converging ability, and the reflectance at 550 nm was decreased from 7.63 % to 0.53 % with the fabricated nanostructures. This proposed technique has proven its potential for hot-rolled embossing of glass components with micro/nanostructures.

Fast anodization fabrication of AAO and barrier perforation process on ITO glass

Thin films of porous anodic aluminum oxide (AAO) on tin-doped indium oxide (ITO) substrates were fabricated through evaporation of a 1,000- to 2,000-nm-thick Al, followed by anodization with different durations, electrolytes, and pore widening. A faster method to obtain AAO on ITO substrates has been developed, which with 2.5 vol.% phosphoric acid at a voltage of 195 V at 269 K. It was found that the height of AAO films increased initially and then decreased with the increase of the anodizing time. Especially, the barrier layers can be removed by extending the anodizing duration, which is very useful for obtaining perforation AAO and will broaden the application of AAO on ITO substrates.

Fabrication of various nano-structured nickel stamps using anodic aluminum oxide

This paper presents a fabrication method of various nickel stamps based on anodic aluminum oxide (AAO) and nickel electroforming (NE) processes. By AAO process, master templates which have closely-packed nano dimple or pore structure array are fabricated. Then nickel stamps having negative surface topology of the master templates are fabricated by NE process. Also positive nickel stamps are fabricated from the negative stamps by NE process with the help of nickel passivation technique. So achieved nickel stamps are employed in injection molding and hot embossing processes for replication of nano-structured surfaces.

Fabrication of Orderly Copper Particle Arrays on a Multi-Electrolyte-Step Anodic Aluminum Oxide Template

A multi-electrolyte-step (MES) anodic aluminum oxide (AAO) method was used to achieve nanochannel arrays with good circularity and periodic structure. The nano-channel array fabrication process included immersion in a phosphoric acid solution with a 120–150 bias voltage. Bowl-shaped structures were then formed by removing the walls of the nano-channel arrays. The nano-channel arrays were grown from the bottom of the bowl structure in an oxalic solution using a 50 V bias voltage. A comparison of this new MES process with the one-step and five-step AAO process showed a 50% improvement in the circularity over the one-step process. The standard deviation of the average period in the MES array was 25 nm which is less than that of one-step process. This MES method also took 1/4 of the growing time of the five-step process. The orderliness of the nano-channel arrays for the five-step and MES process was similar. Finally, Cu nanoparticle arrays with a 200 nm period were grown using an electroplating process inside the MES nano-channel arrays on fluorine doped tin oxide glass. Stronger surface plasmon resonance absorption from 550 nm to 750 nm was achieved with the MES process than was possible with the one-step process.