Two-step Anodization Process Research Articles

Material characteristics and capacitive properties of aluminum anodic oxides formed in various electrolytes

The microstructure and composition of aluminum oxide films, formed by a two-step anodization process in various electrolytes at 100 V then subject to an intermediate heat treatment (500 °C, 2 min), were investigated. The anodization electrolytes used included ammonium adipate electrolyte, phosphoric acid electrolyte, ammonium dihydrogen phosphate electrolyte, and their mixtures. The cross-section morphologies, crystal structure, and chemical composition of aluminum anodic oxides were examined by transmission electron microscopy. X-ray photoelectron spectroscopy was carried out to study the surface chemical state of the anodic films. The corresponding capacitances and retention voltages of these oxide films were also explored. The results indicated that amorphous-to-crystalline transformation of the oxide, primarily in films formed in ammonium adipate electrolyte, was induced by the heat treatment. Electron diffraction analyses further revealed the oxide films consisted of two distinct zones, which included an inner amorphous layer and an outer layer containing crystalline γ′-Al2O3. This study found that the phosphorous species in either the primary or the re-anodization electrolytes had a potential to cause changes of Al and O distributions within the oxides. The oxide film primarily anodized in ammonium adipate and re-anodized in phosphoric acid had the highest capacitance due to its high degree of crystallinity and thinness compared to oxides formed in other electrolytes. The presence of phosphorus, from the primary anodization electrolytes, in the oxides could inhibit the formation of crystalline γ′-Al2O3 and, consequently, decrease the capacitances of the anodic films. At the same time, the retention voltage and hydration resistance of these oxide films were improved.

Fabrication of ordered array of tungsten nanoparticles on anodic porous alumina by electron-beam-induced selective deposition

Using an ordered nanopore array of anodic porous alumina membrane obtained by a two-step anodization process, ordered array of tungsten nanoparticles was fabricated using an electron-beam-induced selective deposition process. The nanoparticles were preferentially formed in the pores in the electron-beam irradiated area. The microstructure and composition of as-deposited nanoparticles were characterized. The as-deposited nanoparticles contain many nanocrystallites. The nanocrystallites were identified to be the equilibrium phase of bcc structure metal W at room temperature.

Effect of electrolyte composition on hydration resistance of anodized aluminum oxide

Abstract The hydration reactions (in boiling water) of aluminum oxide films, which are used in electrolytic capacitor applications, are investigated. The films formed by a two-step anodization process in various electrolytes at 100 V are investigated. The anodization solutions are ammonium adipate, phosphoric acid, ammonium dihydrogen phosphate, and their mixtures. The cross-section morphologies and crystal structure of the oxides are examined by transmission electron microscopy. The hydration resistance of the anodized film, judging by its variation in film capacitance and retention (tolerance) voltage after immersion in boiling water for 15 min, is explored. After the hydration test, an outer fibrous hydrated layer was observed for each film primarily anodized in ammonium adipate (regardless of the electrolyte used in the re-anodization process). The hydrated layer is a composite with many fine γ′-Al 2 O 3 grains dispersed in the pseudoboehmite matrix. Re-anodization in phosphorous-containing electrolytes can cause an increase in hydration resistance by retarding the formation of fibrous hydrated oxide. Phosphorus is found to be incorporated in the oxides for those formed in phosphorous-containing primary anodization electrolytes. The presence of phosphorus in the oxides can significantly improve their stability against hydration. The formation of fibrous hydrated layer results in an increase in capacitance and a decrease of retention voltage.

Synthesis of germanium nanodots on silicon using an anodic alumina membrane mask

We explore here the use of an anodic alumina membrane as a mask for the fabrication of highly ordered nanodots. The masks were synthesized using a two-step anodization process of aluminum foils in acid solutions. Masks that contain highly ordered pores with aspect ratios of 4:1 to 1:1 were obtained by controlling the duration of the second anodization and the time to remove the buried layer. The size of the pores can be varied from 10 to 200 nm depending on the anodization acid used or the anodization voltage. Germanium (Ge) nanodots on silicon (Si) were obtained by evaporating Ge onto the Si wafer through the mask. The height of the nanodots can be controlled via the deposition rate and duration of the Ge films. The spacing between nanodots can be varied by immersing the mask in phosphoric acid to enlarge the pores. We have fabricated a metal–insulator–semiconductor memory structure with Ge nanodots embedded in silicon oxide matrix as the insulator layer. The nanodots have a diameter of 80 nm and a density of ∼10 10 cm −2. The capacitance versus voltage characteristics of these devices exhibited a charge storage capacity of 9.0×10 11 Ccm −2.

A new method for fabrication nano-porous aluminum grating array

The fabrication technique of highly ordered anodic porous alumina membrane by anodization of Al and the obtained membrane as a mask to the fabrication of 100 nm period antireflection grating hole are described. The two-step anodizing process improves the quality of the nanohole because the periodic seeds are generated by the first anodization. Antireflection grating structures are fabricated by using ordered anodic porous alumina mask and etched by SF6 fast atom beam on silicon wafer. The reflectivity of the antireflection grating structures is measured and compared with that of the calculated value and the polished silicon surface.

Fabrication Parameters for Highly Ordered Nano-Pore Arrays in Alumina Template

The fabrication parameters for highly ordered nanopore arrays formed by self-organized anodization on aluminum have been investigated. To fabricate ordered nanopore arrays in alumina layer a two-step anodization process was used in oxalic acid solution. The regular nanopore arrangement, interpore distance and pore diameter in alumina surface were strongly dependent on the applied potential at anodization. The interpore distance and pore diameter increased with anodic applied potential, and hexagonally ordered pore arrangements in alumina were obtained by anodization at 40V. For the effects of the heat treatment of aluminum substrate on size of domains with same pore orientation, the domain size increased with increasing annealing time.

Growth of Patterned Nanopore Arrays of Anodic Aluminum Oxide

An inexpensive procedure to fabricate highly ordered, patterned through‐hole nanopore arrays of anodic aluminum oxide (AAO, see Figure) with intermittent aluminum supports has been developed. Silica was used as the anodization barrier. Using a two‐step anodization process, straight nanopores of AAO are formed in the unpatterned areas; no pores are found in the patterned areas.

WS-04 Nanotechnology Advances & Applications in Information Storage

A brief review of some applications of nanotechnology to information storage is given with the focus on self-assembled nanoporous alumina templates for patterned media. Ordered nanoporous alumina templates were fabricated by self-assembly technology. A two-step anodization process was also carried out to obtain templates with straight pores without removing the aluminum and barrier layer. Polycrystalline structure was observed with a grain size of about two micrometers in which the pores were almost perfect hexagonally ordered. The pore arrays exhibit different orientation along the boundaries of neighboring grains. Nanopatterning implemented by electron-beam lithography demonstrates a potential for writing concentric circular patterns with linewidths as small as 30nm.

Fabrication of Sequential Nanostripes by Controlled Electrodeposition

ABSTRACTAu nanowires and sequential metal nanostripes were prepared by AC pulse electrodeposition in anodic alumina membrane (AAM). Due to the high toxicity of cyanide-based electrolytes, which commonly used for electrodeposition of noble metals, new types of Au electroplating solution has been introduced. Electroplating solutions of noble metals Au, Ag and Pt were alternately used for nanostripes fabrication. The AAM was prepared by a two-step electrochemical anodization process in oxalic acid. The pore size was controlled by varying anodizing voltage and current density. The AAM was investigated by SEM and AFM. The results show hexagonally ordered channels with a pore diameter 50 nm. The morphology and composition of nanowires and nanostripes were examined by TEM and optical microscopes, which show uniformly, ordered Au nanowires with a length about 250 nm and a diameter about 50 nm. Au-Ag-Au-Pt-Au sequential nanostripes have a length about 3.5 μm and diameter 50 nm has been successfully prepared.

Er-doped oxidised porous silicon waveguides

The present work reports Er-doped channel oxidized porous silicon waveguides (OPSWG) formed from n +-type Si by the two-step anodisation process. Er has been introduced into porous silicon before oxidation by a cathodic treatment in 0.1 M Er (NO 3) 3 aqueous solution. A correlation between Er concentration and refractive index profiles has shown dominant core doping with Er relative to cladding regions. Reported Er concentration of 0.8 at.% in the OPSWG is large enough to attain the amplification effect.

Self-organized formation of hexagonal nanopore arrays in anodic alumina

Conditions for a self-organized formation of ordered hexagonal structure in anodic alumina were investigated, using oxalic or sulphuric acid as an electrolyte. Highly-ordered nanopore arrays with pore densities of 9×109-6.5×1010cm-2 and high aspect ratios over 3000 were fabricated by a two-step anodization process. The array exhibits characteristics analogous to a two-dimensional polycrystalline structure of a few micrometres in size. The interpore distance can be controlled by changing the electrolyte and/or the applied voltage. The formation mechanism of ordered arrays is consistent with a previously proposed mechanical stress model, i.e., the repulsive forces between neighbouring pores at the metal/oxide interface promote the formation of hexagonally ordered pores during the oxidation process.

Highly ordered two-dimensional carbon nanotube arrays

Highly ordered multiwalled carbon nanotube arrays have been fabricated by using porous anodic alumina templates prepared by a two-step anodization process. Nanotubes were very uniform in diameter. Two-dimensional tube arrays were highly ordered within domain boundaries, and their vertical alignment was nearly perfect. The density of nanotubes, 1.1×1010 tubes/cm2, was very high. Our fabrication technique enabled us to easily control the tube diameter, length, and density. There was no practical limitation to the size of the alumina template, so that very large panels of well-aligned carbon nanotubes could be made. Our results offer a potentially elegant technique for fabricating cold-cathode flat panel displays.

Polycrystalline nanopore arrays with hexagonal ordering on aluminum

Nanopore arrays with 6×108–5×1010 cm−2 pore densities were fabricated by self-organized anodization on aluminum. A two-step anodization process was used to oxidize aluminum in oxalic, sulfuric, and phosphoric acid solutions. Hexagonally ordered pore arrays were obtained within domains of a few micrometers, which are separated from neighboring domains with different orientation of the pore lattice by domain boundaries, i.e., the nanopore arrays show characteristics analogous to two-dimensional polycrystalline structure. The interpore distance can be controlled by changing the electrolyte and/or the applied voltage.

Porous GaAs formed by a two-step anodization process

Abstract In this letter, we proposed a method in which a n-type GaAs wafer was first anodized in HF for a short time to form a high density of etch pits on its surface and then anodized in KOH solution to form a high density of pores with uniform distribution in it. Scanning electron microscopy revealed feature sizes of the porous structure in the nanometer range. The porous GaAs has been investigated using double crystal X-ray diffraction technique. Crystal quality and crystallographic orientation of the porous layer were similar to those of the substrate. The lattice constant of porous layer is slightly larger than that of the substrate in the growth direction.

Microstructure, heat treatment, and oxidation study of porous silicon formed on moderately doped p-type silicon

A porous Si (PS) layer with a spongy microstructure on top of a dendritic microstructure was fabricated on a moderately doped p-type Si wafer using a two-step anodization process. This illustrates that in addition to substrate doping, anodization current density also has an effect on the porous Si microstructure. A preoxidation heat treatment of the spongy-type porous Si was found to change the porous structure significantly, making it more difficult to fully oxidize the layer at low temperatures. However, dendritic porous Si can better withstand the heat treatment without suffering noticeable changes in structure. X-ray photoelectron spectroscopy, infrared spectroscopy, and electrical breakdown tests were used to analyze the oxidized porous Si samples. The oxidation process and the resultant oxide were found to depend on several factors, including the porosity, the microstructure itself (e.g., spongy or dendritic-type), and the heat treatment history prior to oxidation. With similar porosity, dendritic PS is easier to oxidize compared to spongy PS.

モリブデンオキシ水酸化物皮膜を利用したアルミニウムアノード酸化皮膜の物性の向上

It was found that a two-step anodizing process to form porous oxide films on aluminum, consisting of cathodic deposition of Mo (V)-Mo (VI) mixed oxyhydroxide films on aluminum from an ammonium molybdate solution followed by anodizing of the aluminum in acid solutions, results in films having improved mechanical properties. Anodic oxide films formed in a sulfosuccinic acid solution by the present process showed an increase in Vickers hardness of about 20% and the best results were Hv50=690±23 (±1σ) for cross section. The process is being extended using chromate treatment in the first step, and further improvements in physicochemical properties are expected.

アルミニウムのアノード酸化によるコバルトブルー皮膜

Cobalt blue films were prepared on aluminum by a two-step anodic oxidation process. Aluminum plate was anodized in sulfuric acid by direct current and cobalt was deposited into the pores of the film by AC electrodeposition. The alumina film with deposited cobalt was then reanodized in a molten mixture of sodium bisulfate and ammonium bisulfate.The surfaces of cobalt blue films formed in the bisulfate melt were porous and their X-ray diffraction patterns indicated the crystalline structure of a defective spinel, CoO·3Al2O3, which constitutes cobalt blue pigment.

Inhibition of the Oxygen Reduction Reaction Using 8-Hydroxyquinoline

Abstract A corrosion-resistant surface is obtained on steel by a two-step anodization process in which 8-hydroxyquinoline (HQ) is added to the borate anodizing bath in the second step. Additional corrosion resistance is obtained in neutral halide media by a chromate post-treatment. It is conjectured that a multilayer structure impedes the flow of electrons necessary for the oxygen reduction reaction, and the surface is inhibited for the cathodic reaction. The high coverage of the iron surface by the organic complex leads to (1) insulation of the iron from the environment and (2) an inhibition of the anodic reaction.