Nanopore architectures in anodic aluminum oxide: effects of anodization voltage and time on planar and non-planar aluminum substrates

In this paper, we report on the surface roughness evolution of highly ordered anodic aluminum oxide (AAO) films based on an atomic force microscopy (AFM) study. Root mean square of the surface roughness was measured on AFM images taken from highly ordered AAO films produced by two-step anodization under different conditions including electrolyte type, anodization voltage, and anodization time. Surface roughness of highly ordered AAO films increases step by step through the two-step anodizing process including electropolishing, first-step anodization, dissolution, and second-step anodization. However, increase of the surface roughness is proportional to the anodization voltage and time. The surface roughness of AAO films changes as a function of length scale until it finally approaches a maximum termed the saturation roughness. The variation of roughness of the growth of AAO could be scaled with an anomalous dynamic behavior as it saturates over a critical length scale while the saturation roughness is dependent on the anodizing time and voltage.

Aluminum foil was anodic oxidized by a two-step anodization process in oxalic acid solutions. While the influence of processing parameters, such as voltage, time and solution concentration, for the 1st and 2nd steps of anodization process on the characteristics of pores of the anodic aluminum oxides(AAO) films was investigated. Results show that for the 1st anodization, the pores spacing increases with the rising voltage, yet the anodization time and the concentration of oxalic acid solution have almost no influence; for the 2nd anodization process, the pores spacing doesn't change when varying the voltage, the anodization time and the concentration of solution, but the pore diameter rises greatly with the rise of the voltage. The pores of the AAOs films are well arranged in a form of hexagonal array. Furthermore, the shape of the pores changes slightly when increasing the voltage for the 2nd anodization. High concentration(up to 0.4 mol/L) oxalic acid solution for the 2nd anodization resulted in an oriented piercing of the pore's wall, even a dissolving of the AAO layer, but the pores arrangement was not affected.

Wet-chemical etching of the barrier oxide layer of anodic aluminum oxide (AAO) was systematically investigated by using scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), and a newly devised experimental setup that allows accurate in situ determination of the pore opening point during chemical etching of the barrier oxide layer. We found that opening of the barrier oxide layer by wet-chemical etching can be significantly influenced by anodization time (tanodi). According to secondary ion mass spectrometry (SIMS) analysis, porous anodic aluminum oxide (AAO) samples formed by long-term anodization contained a lower level of anionic impurity in the barrier oxide layer compared to the short-term anodized one and consequently exhibited retarded opening of the barrier oxide layer during the wet-chemical etching. The observed compositional dependence on the anodization time (tanodi) in the barrier oxide layer is attributed to the progressive decrease of the electrolyte concentration upon anodization. The etching rate of the outer pore wall at the bottom part is lower than that of the one at the top part due to the lower level of impurity content in that region. This indicates that a concentration gradient of anionic impurity in the outer pore wall oxide may be established along both the vertical and radial directions of cylindrical pores. Apart from the effect of electrolyte concentration on the chemical composition of the barrier oxide layer, significantly decreased current density arising from the lowered concentration of electrolyte during the long-term anodization (~120 h) was found to cause disordering of pores. The results of the present work are expected to provide viable information not only for practical applications of nanoporous AAO in nanotechnology but also for thorough understanding of the self-organized formation of oxide nanopores during anodization.

The nanoporous anodic alumina oxide formed by two-step anodization

Nanopore Architectures in Anodic Aluminum Oxide (Aao): Effects of Anodization Voltage and Time on Planar and Non-Planar Aluminum Substrates

Anodic alumina oxide surfaces prepared by dual hard and mild anodization at subzero temperature: Surface microscopic characterization and influence on wettability

A colorimetric sensor based on anodized aluminum oxide (AAO) substrate for the detection of nitroaromatics

Anodic aluminum oxide is a well-known template for nanofabrication. Structural features of anodic aluminum oxide, such as pore diameter, can be controlled by adjusting anodization operating conditions. In this paper we will describe how nanoporous alumina of different porosities was prepared using electrochemical anodization. The influence of anodization time, potential, and temperature on the formation of well-ordered porous anodic aluminum oxide was studied. Results from high-resolution field-emission scanning electron microscopy have shown that pore diameter increases with increasing potential, temperature, and anodization time. Optimal anodic aluminum oxide pore diameter and arrangement were obtained for samples anodized at 40 V, 30°C for 60 min.

Optical constants of anodic aluminum oxide films formed in oxalic acid solution

Anodic aluminum oxide (AAO) is well known for its nanoscopic structures and its applications in microfluidics, sensors and nanoelectronics. The pore density, the pore diameter, and the interpore distance of an AAO substrate can be controlled by varying anodization process conditions. In this research, the self-organized two-step anodization is carried out with a low-grade (Al6061) aluminium substrate using a 40V voltage at the temperature of 2 to 5 °C. Three experiments are done with the anodization time of 24 hours, 48 hours and 72 hours. The structural features of AAO are characterized by a field emission electron microscope (FE-SEM). The data from FE-SEM show that the average pore diameter increases with the anodization time, and that the Al6061 aluminium substrate can be used to fabricate a nanoporous AAO film with an average pore diameter smaller than 17 nanometers.

Effects of the voltage and time of anodization on modulation of the pore dimensions of AAO films for nanomaterials synthesis

Nanoporous anodic aluminum oxide (AAO) membranes formed by anodic oxidation of metallic Al have become one of the most popular templates for the fabrication of diverse range of nanostructured materials in the form of nanodots, nanowires, and nanotubes. A key advantage of using AAO instead of other templates is a highly ordered and close-packed distribution of pores within the template. In addition, the fabrication of porous AAO membrane via electrochemical anodization is relatively simple and inexpensive. All structural features of anodic oxide templates, such as pore diameter, pore-to-pore distance, thickness of the template, pore density, porosity, etc., can be easily controlled by anodizing conditions, especially type of electrolyte, potential applied, temperature and duration of the process. For the preparation of porous AAO templates, two different approaches can be distinguished: a pre-patterned guided anodization and a self-organized two-step anodization. In the first case, a pre-patterned (pre-textured) aluminum substrate is used for anodization, while the latter is based on a self-organized pre-patterning of Al during the first anodizing step and the removal of irregular oxide layer before the final (second) anodization. The pre-patterned guided anodization results in a perfectly arranged pore lattice formed over a surface area defined by the dimensions of the previously prepared stamp (mold) or indented Al surface. The pre-pattern guided anodization can result in pore shapes and cell configurations different from the pattern with circular and hexagonally arranged pores, which is typically observed for self-organized AAO templates. In particular, complex nontypical regular pore patterns on AAOs (e.g., square, triangle, diamond, triangle–diamond, checkerboard, etc.) can be formed. The self-organization process of AAO formation can occur over a macroscopic surface area, however it always results in a non-perfectly ordered hexagonal arrangement of pores. A typical self-organized anodization results in porous AAO layers with straight cylindrical nanochannels parallel to each other. However, a great variety of procedure modifications was recently proposed. They allow for the fabrication of anodic alumina films with a more complex internal architecture (e.g., Y-branched, multilevel Y-branched, and multi-branched nanochannels) and various nanochannel shapes (e.g., conical, step-shaped, serrated, periodically branched, and modulated nanochannels).

Special porous anodic aluminum oxide (AAO) membranes are created on Al in a phosphonic acid electrolyte solution through one-step anodic oxidation and modified with polydimethysiloxane using a vapor deposition technique. In this context, the anodic oxidation time is tuned during its process. As such, the Al surface's wettability, and self-cleaning property are controlled by the tunable anodic oxidation time, for the anodic oxidation, time can regulate the structure of the AAO and the proportion of the air-liquid interface.

A porous anodic aluminium oxide (AAO) templates were fabricated on aluminium by electrodeposition method using a two-step anodization process. The AAO templates were anodized in 0.3 M oxalic acid solution by applying a constant voltage of 40V, which was afterward treated with chemical etching process in a mixed solution of 6% phosphoric acid and 1.8% chromic acid, respectively. The temperature was kept constant in 15oC during the anodization process and the anodization time were done between 20 to 60 min. All the samples were characterized using by scanning electron microscopy (SEM) to study the surface morphology of AAO templates. It was found that the pore diameters of AAO templates can be controlled by changing the anodizing time. The influence of the electropolishing were also discussed. Highly uniform self-ordered AAO template were effectively formed from these polished foils via an anodizing process.

The anodic aluminum oxide (AAO) films were prepared by anodization method from the 15 vol. % sulphuric acid solution, and prepared AAO films were heat-treated in the ranges of 25~1000°C. AAO films were characterized by EDAX, SEM and XRD techniques, respectively. The crystal phases of prepared AAO film is amorphous. The apertures of AAO film are in 25~30 nm. AAO films are amorphous when heat treatment temperatures of AAO films are below 800 °C. After the AAO film being heat-treated in the ranges of 850°C~900 °C, the heat-treated AAO film are γ-Al2O3film. When the AAO film is heat-treated at 950 °C, the part of γ-Al2O3change into α-Al2O3, and the heat-treated AAO film are mixed film of γ-Al2O3and α-Al2O3. After the AAO film being heat-treated at 1000 °C, the heat-treated AAO film is α-Al2O3film.