Properties Of Anodic Aluminum Oxide Research Articles

Stained Glass Effect in Anodic Aluminum Oxide Formed in Selenic Acid.

A combination of the unique porous structure and physical and chemical properties of anodic aluminum oxide (AAO) makes it widely used in cutting-edge areas of materials science and nanotechnology. Selenic acid electrolyte provides the ability to obtain AAO with low porosity and high optical transparency and thus is promising for the preparation of AAO photonic crystals (PhCs). Here, we show the influence of crystallographic orientation of Al on the electrochemical oxidation rate in 1 M H2SeO4 as well as on the growth rate, porosity, and the effective refractive index of AAO. The cyclic anodization regime is used to prepare AAO PhCs with photonic band gaps, their wavelength positions are used to measure the AAO growth rate. At an anodization voltage of 40-45 V, the growth rate varies by up to 22.6% with crystallographic orientation of Al grains, causing the stained glass effect, which can be seen with the naked eye.

Asymmetric Nanoporous Alumina Membranes for Nanofluidic Osmotic Energy Conversion.

The potential of harnessing osmotic energy from the interaction between seawater and river water has been recognized as a promising, eco-friendly, renewable, and sustainable source of power. The reverse electrodialysis (RED) technology has gained significant interest for its ability to generate electricity by combining concentrated and diluted streams with different levels of salinity. Nanofluidic membranes with tailored ion transport dynamics enable efficient harvesting of renewable osmotic energy. In this regard, anodic aluminum oxide (AAO) membranes with abundant nanochannels provide a cost-effective nanofluidic platform to obtain structures with a high density of ordered pores. AAO can be utilized in constructing asymmetric composite membranes with enhanced ion flux and selectivity to improve output power generation. In this review, we first present the fundamental structure and properties of AAO, followed by summarizing the fabrication techniques for asymmetric membranes using AAO and other nanostructured materials. Subsequently, we discuss the materials employed in constructing asymmetric structures incorporating AAO while emphasizing how material selection and design can resist and promote efficient energy conversion. Finally, we provide an outlook on future applications and address the challenges that need to be overcome for successful osmotic energy conversion.

Evaluation of the electrochemical corrosion behavior of anodic aluminum oxide produced by the two-step anodization process

Purpose This study aims to investigate the effect of different pore diameter and pore length on corrosion properties of anodic aluminum oxide (AAO) film. Design/methodology/approach AAO layer was produced by two-step anodization aluminum in oxalic acid. The surface morphology was investigated using field emission scanning electron microscopy. The pore diameters were ranging from 25 ± 5 to 65 ± 5 nm and the pore length ranging from 5 to 17 µm. The corrosion properties of the AAO films was analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy tests. Corrosion properties and morphology of the anodic films depending on anodization times and pore expansion times were evaluated. Findings All highlights of this work can be summarized with the following specified below: more treatment with the protective barrier layer of the solution as the pore diameter increases depends on the morphology of the nanotube structured AAO layer. The excellent corrosion resistance renders AAO films without pore expansion very promising. The oxide layer thickness does not affect the corrosion resistance. The better corrosion resistance of AAO films at low pore length can be ascribed to the barrier layer thickness and the more homogeneous structure. The presence of defects for the higher pore length decreases its corrosion resistance. Originality/value The AAO films were fabricated by a two-step anodization method in oxalic acid. The anodization times and pore expansion times affect the corrosion performance. The AAO film without pore expansion has good corrosion resistance. The corrosion resistance decreases as the pore length increases.

Effect of Conductive Layer Condition on the Morphology of Anodic Aluminum Oxide Template-Assisted Indium Antimonide Nanowires.

Indium antimonide nanowires were synthesized by electrochemical deposition using anodic aluminum oxide template in the presence of gold film as conductive layers. Field emission scanning electron microscopy and energy dispersive X-ray spectrometry measurements were carried out to investigate the effect of adhesive insulated tape covered below the conductive layer. Results showed that the anodic aluminum oxide template covered with insulating tapes had better morphology with less presence of overgrown rough film on the topside of the anodic aluminum oxide template and it exhibited a smoother nanowire sidewall as compared to the uncovered ones. Additionally, the unique properties of anodic aluminum oxide were controllable pore diameter with a narrow size distribution at some intervals. It was evident from the energy dispersive X-ray spectrum that the nanowires synthesized from the covered template condition exhibited better InSb composition and stoichiometric ratio compared to the uncovered template condition.

A technique for a nano-textured gapless microlens array using self-formation characteristics of anodic alumina.

This paper presents a method to utilize the growth properties of anodic alumina possessing self-formation characteristics to fabricate a nano-textured microstructure and also introduces an application technique of the proposed method. The growth rate of anodic alumina, fabricated on aluminum surfaces, has a strong dependence on the intensity of the applied current density or electric field. The uniformity of the thickness of anodic alumina is determined by its electrical distribution characteristics. Accordingly, microscale structures can be fabricated using the growth rate deviation of anodic alumina. A patterned insulative layer is an important factor that determines the current density distribution property of a local region. A computational analysis and a verification experiment can verify this characteristic through the correlation between structural dimensional conditions and a cross-section of the fabricated anodic alumina. The anodic alumina fabricated by the verification experiment in this study had a swollen shape and a nano & micro complex structure, in which a nanoscale base pattern was formed on all bottom surface due to the process characteristics. Based on the advantages of the proposed process, evidenced by the reliability evaluation results, gapless microlens array (MLA) replication molds with nanostructured surfaces were fabricated to verify the applicability of the proposed technique to other fields. A patterned insulative layer with a cylindrical cavity and dimensional conditions was designed to induce the fabrication of lens-shaped anodic alumina. The anodic alumina fabricated by the long process was selectively etched out, and an additional process was conducted to fabricate a nanoporous structure having controlled dimensional conditions on the engraved gapless MLA surface. The textured aluminum surface was used as a replication mold for the imprinting process. The analysis of the fabrication results showed that the gapless MLA surface had a nanopillar structure. In addition, we investigated the reflection characteristics of the fabricated gapless N-MLA structure according to the incident light and verified the low reflectance of the gapless microlens. The results of this study affirmed that the proposed technique is applicable to various fields including those concerning optical devices.

Composite model of the dependence of mechanical properties of anodic aluminum oxide on porosity

Results of the application of a theory concerning elasticity of composite materials to calculate the elastic modulus of anodic aluminum oxide (AAO) are presented. The basis of the proposed AAO elasticity model is the assumption that the space of the anodic aluminum oxide may be represented as a composite material in the form of a matrix—bulk amorphous oxide filling the space between the pores reinforced by a hollow fiber with zero wall thickness. The maximum error of this simplification in the range of the actually used porosity values is 5% for the Young’s modulus and 0.7% for the shear modulus. The results are in proper agreement with the experimental data of other authors. Proper agreement of the results holds out a hope that this approach may be applied when the AAO pores are filled with some material (adsorbent, liquid, etc.), as is possible, for example, in cases of AAO application as a material for cantilever sensors.

Photoluminescence properties of anodic aluminum oxide formed in a mixture of ammonium fluoride and oxalic acid

Photoluminescence properties of anodic aluminum oxide formed in a mixture of ammonium fluoride and oxalic acid

Effects of Process Parameters on the Passivation Properties of Anodic Aluminum Oxide/Silicon Interface

In this paper, surface passivation properties of anodic aluminum oxide (AAO) on silicon substrate has been investigated. Metal–insulator–semiconductor with AAO as a dielectric layer is fabricated, and AAO/Si interface charges are evaluated from the capacitance–voltage ( C–V ) and conductance–voltage ( G–V ) characteristics. It has been observed that the effective charge density ( $Q$ $_{\text{eff}}$ ) and interface defect density ( $D$ $_{\text{it}}$ ) varied from $-$ 3.0 $\times$ 10 $^{10}$ to 2.5 $\times$ 10 $^{11}$ cm $^{-2}$ and 2.5 $\times$ 10 $^{10}$ to 5.7 $\times$ 10 $^{11}$ eV $^{-1}$ $\cdot$ cm $^{-2}$ , respectively, depending on the process conditions such as molarity of the electrolyte, electrolyte temperature, applied dc-bias voltage, and the type of the electrolyte used for growth of AAO through the electrochemical anodization process. Further, capacitance transient (C-t) characteristics are used to evaluate the minority carrier lifetime, and it is found that the use of the AAO passivation layer increases minority carrier lifetime to 90 $\mu$ s from the initial value of 2 $\mu$ s.

Experimental study on physical properties of nanoporous anodic aluminum oxide by proton implantation

Implantation is a promising method to control the surface characteristics by changing surface energy of target materials. Previously, polymer surfaces have been investigated for the change of their morphology and the corresponding contact angle after implantation. Furthermore, oxide thin films have been studied for how their surface properties are changed by implantation. However, nanoporous oxide materials have rarely explored for the effect of implantation. Here, we investigated the effects of proton implantation on morphological, mechanical, electrical, and surface properties of anodic aluminum oxide (AAO). We prepared nanoporous amorphous AAO films with different thicknesses (5 and 10 μm). Atomic force microscopy (AFM), contact angle (CA) measurements, two-probe electrical measurements, and nanoindentation were used to analyze the physical properties. By increasing fluences from 1015 to 1016 ions/cm2, CA is significantly changed up to about 40°, but the other properties hardly changed.

Optical properties of anodic aluminum oxide produced in a complex electrolyte

Features of the absorption, transmission, photoluminescence, and infrared (IR) spectra of anodic aluminum oxide (AAO) formed in a complex electrolyte and annealed at 800, 900, 1000, and 1300°C are investigated. The variations in the phase composition changes of the anodic aluminum oxide are reflected in the respective features of its optical properties. A decrease in the transmission coefficient in the visible range of the spectrum is shown for the phase series: amorphous AOA → γ-Al2O3, γ-, θ-, δ-Al2O3 mixture → α-Al2O3. It is established that the highest absorption coefficient is characteristic of α-Al2O3, and the amorphous samples are the most transparent in the visible range. An intensive luminescence band in the red region of the spectrum with maxima at 678 and 694 nm is found for α-Al2O3. The emergence of this band is explained by the presence of octahedrally coordinated Mn+4 and Cr+3 impurity ions in the structure. A luminescence band at 700–800 nm is observed for the mixture of low-temperature phases. Intense luminescence in the region 350–500 nm is found for amorphous AAO and γ-Al2O3.

Effects of pore-channel ordering on the mechanical properties of anodic aluminum oxide nano-honeycombs

The mechanical properties of anodic aluminum oxide (AAO) nano-honeycombs with different spatial ordering of pore-channels are investigated by nanoindentation. The pore-channel ordering is systematically varied by carefully adjusting the orientation of the aluminum used for anodization. The results indicate that the strength of AAO structures increases significantly with the regularity of their pore-channel arrangement, whereas the elastic modulus is less sensitive to pore-channel regularity.

The effect of high temperature heat treatment on the structure and properties of anodic aluminum oxide

Nanoporous anodic aluminum oxide (AAO) membranes can be fabricated with highly controllable thickness and porosity, making them ideal for filtration applications. Use of these membranes is currently limited largely due to their size and overall fragility. The objective of this research was to improve mechanical properties of AAO membranes through use of high temperature heat treatment to induce phase transformations in the material. A repeatable two-step anodization process was developed for consistent sample fabrication and heat treatments were performed at 900 °C and 1200 °C in air. The pore morphology and phase composition of the as-anodized and heat-treated membranes were then observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Microhardness testing was utilized to evaluate the mechanical behavior of the membranes before and after heat treatment. As-anodized AAO membranes were determined to be amorphous, and membranes heat-treated to 900 °C and 1200 °C were transformed to crystalline phases while retaining their original porous structure. Heat treatment to 900 °C resulted in formation of the γ-alumina transition phase in the skeleton regions of the membrane and nanocrystalline regions of α-alumina throughout the structure, while heat treatment to 1200 °C completely transformed the material to the stable α-alumina structure. The microhardness testing showed an increase in hardness from 2.5 ± 0.4 GPa to 4.7 ± 1.0 GPa in the transformation from amorphous to α-alumina.

Strong Vertical Alignment of Liquid Crystal on Porous Anodic Aluminum Oxide Film

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Properties of anodic aluminum oxide (AAO) film as a liquid crystal (LC) alignment material is studied. We deposit the transparent porous AAO film on glass with the diameter of the pores controlled between 17–65 nm. The liquid crystal can be aligned vertically against the substrate with the AAO film. The measured polar anchoring strength is about 1.5<formula formulatype="inline"> <tex Notation="TeX">$\,\times 10 ^{-5} {\rm J/m} ^{2}$</tex></formula>, which is comparable to that of N,N-dimethyl-N-octadecyl-3-aminopropyl -trimethoxysilyl chloride (DMOAP) layer. AAO films with smaller pore diameters exhibit higher anchoring strengths. On the other hand, the uniformity of the pore array in the AAO films does not affect the alignment quality significantly. </para>

Pulse Electrodeposition of Iridium Oxide on Silicon Nanotips for Field Emission study

To improve electron field emission properties of anodic aluminum oxide (AAO) templated Si nanotips, IrO2 nanoparticles were deposited on the nanotips using bipolar pulse electrodeposition method. The IrO2 nanoparticles had a uniform size distribution with an average value of approximately 4 nm, and well dispersed on the ordered Si nanotips. Due to the small radius and a lower work function, the IrO2/Si nanotip exhibited field emission properties better than the bare Si nanotip with a field enhancement factor of approximately 128. The SEM and TEM were utilized to investigate the structure and morphology. The physical and chemical properties were evaluated XRD and X-ray photoelectron spectroscopy (XPS).

Mechanical properties of anodic aluminum oxide for microelectromechanical system applications

Aluminum oxide features good electrical properties such as high dielectric constant and high breakdown voltage. During these last years it has been introduced for the fabrication of metal oxide semiconductor and metal insulator metal capacitors. In the present paper, the mechanical properties of anodic Al2O3 are addressed as well as its interest for microelectromechanical system applications including membranes or cantilevers for humidity, flow, pressure, or biological sensors.

Influence of electrolyte composition on photoluminescent properties of anodic aluminum oxide

Luminescent properties of anodic alumina fabricated in anodizing solutions containing oxalic, sulfuric, and phosphoric acids in addition to those modified by thermal annealing are investigated. Comparison of the obtained data shows that F+-centers are responsible for the luminescence band at 390 nm. The intense photoluminescence band of porous anodic alumina substrates at 450–500 nm is associated with oxalate anions.

Mechanical Properties and Residual Stress Measurements in Anodic Aluminium Oxide Structures Using Nanoindentation

Anodic alumina has been used widely for corrosion protection of aluminum surfaces or as a dielectric material in microelectronics applications. It exhibits a homogeneous morphology of parallel pores that can easily be controlled between 10 and 400 nm. It has been applied as a template for fabrication of the nanometer-scale composite. In this study, the mechanical properties of anodic aluminum oxide (AAO) structures are measured by the nanoindentation method. The nanoindentation technique is one of the most effective methods to measure the mechanical properties of nanostructures. Using the nanoindentation method, we investigated the residual stress and mechanical properties such as the indentation modulus and hardness of the AAO structure with different-sized nanoholes. As a result, we find that the “hole effect” that changes the mechanical properties is the hole size.