Fabrication Of Anodic Aluminum Oxide Research Articles

Direct Fabrication of High-Aspect Ratio Anodic Aluminum Oxide with Continuous Pores on Conductive Glass

The role of metal interlayers in maintaining adhesion during the direct fabrication of anodic aluminum oxide (AAO) with high-aspect ratio pores on tin-doped indium oxide (ITO) is studied. Chromium and titanium interlayers can maintain adhesion while anodization is conducted in either sulfuric, oxalic, or phosphoric acid solutions. However, the ability to form high-aspect ratio pores is dependent on the interlayer and aluminum thickness, the method of aluminum deposition, and possibly the cleaning/surface treatment of ITO prior to aluminum deposition. AAO films approximately thick were prepared in oxalic and phosphoric acids, yielding high-aspect ratio pores with length to diameter ratios of 47 and 14, respectively. The distinct stages of pore formation are also correlated with the time-resolved current response of the anodization cell, which provides in situ information about the anodization process so that adhesion can be maintained throughout pore formation. The direct fabrication of AAO on ITO/glass substrates from a single-step evaporation of thick aluminum films enables the formation of smooth and continuous gold nanowires, which have potential applications in photonics.

Superhydrophobic fabrication of anodic aluminum oxide with durable and pitch-controlled nanostructure

Durable and pitch-controlled nanostructures to have well-defined superhydrophobic functions were fabricated by post-etching of AAO with a self-assembled heptadecafluoro-1,1,2,2-tetrahydrodecyl-trichlorosilane monolayer coating. The inter-pore distance at the surface of anodic aluminum oxide (AAO) was found to be an important factor for controlling the superhydrophobic adhesiveness. The hysteresis of the contact angles and the adhesiveness to a water droplet were minimized in two-steps during post-etching in phosphoric AAO (PAAO). A more durable nanostructure was obtained with the superhydrophobic surface of PAAO than those of oxalic AAO and of sulfuric AAO because of the inherent hardness of PAAO and its long inter-pore distance (500 nm).

Effect of oxalic acid concentration on the formation of anodic aluminum oxide using pulse anodization at room temperature

Most anodic aluminum oxide (AAO) or porous anodic aluminum (PAA) films were fabricated using the potentiostatic method from high-purity (99.999%) aluminum films at low temperatures of 0–10°C to avoid dissolution effects at room temperature (RT). In this article, the fabrication of AAO or PAA film from commercial purity (99%) aluminum at RT has been investigated using hybrid pulse anodization under different oxalic acid concentration and process duration. The effect of acid concentration and anodization duration on the formation of AAO size and morphology has been studied. Both pore diameter and oxide layer thickness of AAO films were examined via SEM images and found that both increased with increasing oxalic concentration and anodization duration. In addition, the pore distribution was more concentrated at high electrolytic concentration and anodization duration.

Fabrication of Anodic Aluminum Oxide Film on Large-Area Glass Substrate

Fabrication of anodic aluminum oxide (AAO) on 4 in. glass substrate was demonstrated. Using unique structure with quadruple contacts as electrode support during anodization, we reported gradual transformation from opaque aluminum to transparent AAO over the entire substrate. In contrast, partial transformation was observed with typical single contact approach where growth of insulating AAO inhibited subsequent anodization by interrupting current flow from the contact point. Results from optical spectroscope revealed moderate reduction in transmittance after AAO formation. Successful development of large-area AAO on glass substrate opens up opportunities for AAO templated devices that require a large footprint.

Research on fabrication and properties of nanoporous GaN epilayers

Gallium nitride (GaN) epilayers with nanopore arrays were fabricated by inductive coupled plasma (ICP) etching using anodic aluminum oxide (AAO) as mask. Nanoporous AAO templates were formed by anodizing the Al films deposited on GaN epilayers. The diameter of the perforations in the AAO masks could be easily controlled by tuning the technique parameters of AAO fabrication process. Cl 2/Ar and Cl 2/He were employed as etching gas. Scanning electron microscopy (SEM) analysis shows that vertical nanoporous arrays with uniform distribution can directly be transferred from AAO masks to GaN films in some proper conditions. Photoluminescence (PL) spectra, X-ray diffraction (XRD) and Raman spectroscopy were applied to assess properties of the nanoporous GaN films with different average pore diameters and interpore distances.

Vertically Aligned Nanopillar Arrays with Hard Skins Using Anodic Aluminum Oxide for Nano Imprint Lithography

Master molds with nano-pillar structures were fabricated by using anodic aluminum oxide (AAO) for nano-imprint lithography (NIL). The proposed method consists of (1) AAO fabrication, (2) transfer of the thin AAO layer onto a substrate, (3) aluminum sputtering, (4) aluminum melting, and (5) removal of the thin AAO layer. Since the sputtered aluminum penetrated into the porous alumina walls of the AAO template during the melting step, the pillars had skin layers of aluminum/alumina composite which added additional mechanical strength and chemical resistance. The diameter of a pillar in the nano-pillar master mold was larger than that of the hole diameter of the original AAO template because of the hard skin of aluminum/alumina composite layer which covers the pillar surface. The pillar structure could be used as a mold for NIL, resulting in a regular pore array on a polymer film.

Fabrication of Anodic Aluminum Oxide on Si and Sapphire Substrate

We carried out anodic aluminum oxide (AAO) on a Si and a sapphire substrate. For anodic oxidation of Al two types of specimens prepared were Al(0.5 <TEX>$\mu\textrm{m}$</TEX>)!Si and Al(0.5 <TEX>$\mu\textrm{m}$</TEX>)/Ti(0.1 <TEX>$\mu\textrm{m}$</TEX>)<TEX>$SiO_2$</TEX>(0.1 <TEX>$\mu\textrm{m}$</TEX>)/GaN(2 <TEX>$\mu\textrm{m}$</TEX>)/Sapphire. Surface morphology of Al film was analyzed depending on the deposition methods such as sputtering, thermal evaporation, and electron beam evaporation. Without conventional electron lithography, we obtained ordered nano-pattern of porous alumina by in- situ process. Electropolishing of Al layer was carried out to improve the surface morphology and evaluated. Two step anodizing was adopted for ordered regular array of AAO formation. The applied electric voltage was 40 V and oxalic acid was used as an electrolyte. The reference electrode was graphite. Through the optimization of process parameters such as electrolyte concentration, temperature, and process time, a regular array of AAO was formed on Si and sapphire substrate. In case of Si substrate the diameter of pore and distance between pores was 50 and 100 nm, respectively. In case of sapphire substrate, the diameter of pore and distance between pores was 40 and 80 nm, respectively

Fabrication of Alumina Membrane Using Anodic Oxidation Process

Anodic aluminum oxide (AAO) membrane was made of aluminum sheet (99.6%, 0.2 mm thickness). The regular array of hexagonal nano pores or channels were prepared by two step anodization process. A detail description of the AAO fabrication is presented. After the 1st anodization in oxalic acid (0.3 M) at 45 V, The formed AAO was removed by etching in a solution of 6 wt% <TEX>$H_3$</TEX><TEX>$PO_4$</TEX>＋1.8 wt% <TEX>$H_2$</TEX><TEX>$CrO_4$</TEX>. The regular arrangement of the pores was obtained by the 2nd anodization, which was carried out in the same condition as the 1st anodization. Subsequently, the alumina barrier layer at the bottom of the channel layer was removed in phosphoric acid (1M) after removing of aluminum. Pore diameter, density, and thickness could be controlled by the anodization process parameters such as applied voltage, anodizing time, pore widening time, etc. The pore diameter is proportional to the applied voltage and pore widening time. The pore density and thickness can be controlled by anodization temperature and voltage.