Fabrication of Porous Anodic Alumina with Ultrasmall Nanopores (original) (raw)
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Fabrication of hexagonally ordered nanopores in anodic alumina: An alternative pretreatment
Surface Science, 2011
Anodic aluminum oxide (AAO) or anodic alumina template containing hexagonally ordered nanopores has been widely used over the last decade for the development of numerous functional nanostructures such as nanoscale sensors, computing networks and memories. The long range pore order requires the starting aluminum surface to be extremely smooth. Electropolishing is the most commonly used method for surface planarization prior to anodization. While prevalent, this method has several limitations in terms of throughput, polishing area and requirement of special experimental setups, which introduce additional speed bottlenecks in the intrinsically slow AAO-based nanofabrication process. In this work we report a new generation of the so-called-chemical polishing‖ approach which circumvents these stumbling blocks in the pretreatment phase and offers a viable, simpler, safer and faster alternative to electropolishing. These benefits are obtained without sacrificing the quality of the final AAO template. In this work we have (a) identified the optimum parameter regime for chemical polishing and (b) determined process conditions for which a novel parallel nanoridge configuration self-assembles and extends over a distance of several microns. Such patterns can be used as a mask for fabricating nanocrossbars, which are the main structural components in myriad nanoscale memories and crosspoint architectures.
Electrochimica Acta, 2010
The nanopore arrays were fabricated by two-step self-organized anodization of aluminum carried out in 0.3 M oxalic acid at the temperature of 20 • C. This relatively high temperature shortens significantly the anodizing time and allows to fabricate quickly thick through-hole membranes without the additional operating cost of a cooling circuit. The structural features of anodic porous alumina such as pore diameter, interpore distance, porosity, pore density and pore circularity were investigated at various durations of pore opening/widening process carried out in 5% H 3 PO 4 . An excellent agreement of AAO structural features measured in FE-SEM images of the studied samples with results from software calculations was observed. The pore shape can be monitored qualitatively by fast Fourier transforms (FFTs) and quantitatively by calculation the percentage of pore circularity. Additionally, the regularity of the hexagonal arrangement of nanopores in through-hole AAO membranes was compared for various opening/widening time ranging from 40 to 100 min. It was shown that three-dimensional (3D) representations of FE-SEM images and their surface-height distribution diagrams provide interesting information about the surface roughness evolution during the pore opening/widening process. A template-assisted fabrication of Ag and Sn nanowire arrays by electrochemical deposition into the pores of the prepared AAO templates was also successfully demonstrated.
International Journal of Scientific and Engineering Research
Nanoporous anodic alumina (AAO) was fabricated using one-step anodizing at room temperature and low voltage. All specimens were potentiostaticaly anodized at 5 V for 20 minutes in phosphoric acid (H3PO4). Morphology of the AAO layers was characterized by scanning electron microscopy (SEM). By anodizing at 20% (by vol.) phosphoric acid, a uniform porous structure with nearly parallel cylindrical pores, ~200 nanometers wide, were detected. The thickness of the porous layer was higher than the barrier layer. The electrochemical impedance test (EIS), using 0.1 M Na2SO4 electrolyte, confirmed the presence of a multi layers structure of a barrier layer and a porous layer with the highest resistance value (365.1 kΩ). Using AC impedance technique (IS), samples anodized in 20% (by vol.) phosphoric acid, proved to have the highest electrical resistance (26 kΩ), reflecting a po-rous structure formation. The mechanism of pores formation as well as electrical conductivity is to be discussed.
Materials Letters, 2013
A simple method of fabrication of anodic aluminum oxide at low voltages (from 5 to 15 V) in 0.3 M oxalic acid is presented. To overcome the issues concerning the anode's burning, a high velocity stirring was applied. It allowed to achieve nanopores with ultra-small diameters (even 12 nm), interpore distance (even 31 nm) and tremendously high pore densities (up to 980 pores per 1 mm 2 ) with simultaneous high porosity (up to 38%). Moreover, the presented approach (no modifier added to the electrolyte) resulted in the AAO with relatively well arranged ultra-small nanopores.
Regularity of nanopores in anodic alumina formed on orientated aluminium single-crystals
Materials Chemistry and Physics, 2011
On aluminium single crystals with (1 1 1), (1 1 0) and (1 0 0) orientation, nanoporous alumina layers were formed in a two-step anodization process within sulphuric acid. The pore ordering within the hexagonal arrangement of the nanopores was documented by scanning electron microscopy (SEM), described on the basis of defect thermology and analyzed quantitatively by image evaluation. The best ordering was obtained in nanoporous alumina on (1 0 0) aluminium. We supposed that this is caused by the interface energy term within the driving force for the formation of the nanoporous alumina, since-in contrast to (1 1 1) and (1 1 0) aluminium as substrate-in the case of (1 0 0) aluminium the interface energy is minimised in the waved interface between aluminium and hexagonally arranged nanoporous alumina.
Fabrication of Nanomaterials on Porous Anodic Alumina Template Using Various Techniques
2015
Porous anodic aluminum oxide film is a versatile template for the fabrication of nanomaterials. Porous alumina can be fabricated electrochemically through anodic oxidation of aluminum by self-organization method yielding highly ordered arrays of nanoholes. Various techniques such as chemical vapor deposition, electrodeposition, spin coating, dip coating, physical vapor deposition are elaborated for the fabrication of nanomaterials using porous anodic alumina as template.
Effect of the anodization voltage on the pore-widening rate of nanoporous anodic alumina
Nanoscale research …, 2012
A detailed study of the pore-widening rate of nanoporous anodic alumina layers as a function of the anodization voltage was carried out. The study focuses on samples produced under the same electrolyte and concentration but different anodization voltages within the self-ordering regime. By means of ellipsometry-based optical characterization, it is shown that in the porewidening process, the porosity increases at a faster rate for lower anodization voltages. This opens the possibility of obtaining three-dimensional nanostructured nanoporous anodic alumina with controlled thickness and refractive index of each layer, and with a refractive index difference of up to 0.24 between layers, for samples produced with oxalic acid electrolytes.
Materials Chemistry and Physics, 2012
In aluminum anodization process the spontaneous current oscillation in certain electrolytes and anodization voltages can occur. The behavior of current in this process is called spontaneous oscillatory current otherwise we call the current behavior as non-oscillatory. The current difference between the spontaneous oscillatory and non-oscillatory conditions is appreciable (more than 50 mA/cm 2) whereas to switch from spontaneous oscillatory to non-oscillatory behavior we only need to change the anodization voltage less than 3 V. The pore structure of porous anodic alumina film can be modulated by this oscillatory behavior. This effect occurs due to the variation of the anodization current which causes the variation of pore diameter along the pores. But by this procedure it is hard to control the structure of the pore as it is required, because the modulated structure mainly depends on the spontaneous current oscillation. In this article, it is shown that this spontaneous oscillatory behavior can be switched to nonoscillatory condition by changing the anodization voltage. Therefore by switching the anodization voltage between the spontaneous oscillatory and non-oscillatory behaviors, in any time interval, the pore structure of nanopore alumina can be engineered.