Porous Anodic Aluminum Oxide Template Research Articles

Growth of Zr–BiFeO3 nanostructures on two step anodized porous alumina for estimation of optical and dielectric response

Abstract Nanostructures decorated with perfectly ordered porous anodic aluminum oxide templates have attained recent research interest for the production of highly efficient energy storage devices. Anodic aluminum oxide porous templates were synthesized using a two-step anodization technique in this work. Pure BiFeO3 and Zr–BiFeO3 nanostructures were grown on these ordered templates by well-controlled fluoride ions assisted autoclave enclosed hydrothermal method. Crystallographic information discloses the presence of rhombohedral crystal structure with geometric space group R3c belongs to BiFeO3. The morphological analysis depicts the formation of an average pore size of approximately 75 nm in anodic aluminum oxide templates. BiFeO3 contains fibrous nanoflakes like morphology with minute content of the monoclinic zirconia phase in Zr–BiFeO3. Optical measurements demonstrate a considerable variation in absorption and bandgap of anodic aluminum oxide with the growth of nanostructures. A significant increase in dielectric permittivity from 17.17 for anodic aluminum oxide to 187.19 for Zr incorporated compositions with a relatively low tangent loss of 0.66.

Magnetodynamic Properties of Rare-Earth-Doped Permalloy Nanowires

We investigated the effect of rare-earth (RE) element doping on magnetodynamic properties of 1D Ni80Fe20 (Py) nanowires. 5% of doping of RE element (La, Nd, and Sm) in Py nanowires was successfully done by electrodeposition technique in porous anodic alumina template. It is observed by the X-ray diffraction (XRD) measurements that the crystal structure of Py nanowires decreases from polycrystalline to amorphous phase with doping of RE element. The magnetic properties demonstrated that the saturation magnetization decreases upto 98% with the higher atomic number RE dopant. The ferromagnetic resonance measurements in field-sweep mode were done to analyze the magnetization dynamics of RE-doped nanowires. The fitting of resonance field and field linewidth was done by using the Landau–Lifshitz–Gilbert equation. It is observed that the resonance field increases with Sm doping as compared to La doping. The damping constants have been achieved by decocting the extrinsic linewidth and found to increase by ~12 times with RE doping. The increase of Gilbert damping emanates from the enhancement of L–S coupling in Py nanowires.

Magnetic properties and FORC analysis of iron nanowire arrays

Arrays of ferromagnetic nanowires are promising for diverse areas of practical application ranging from data storage to drug delivery. This makes it essential to study their magnetic behavior and magnetization reversal mechanisms. Here, we report on the fabrication of ordered hexagonal arrays of iron nanowires by templated electrodeposition with the use of porous anodic alumina templates. This technique made it possible to obtain nanocomposites with aligned nanowires of pure α-Fe that are stable against oxidation. The arrangement of the nanowires is revealed by small-angle X-ray scattering and scanning electron microscopy. Magnetic properties of the nanowire arrays are studied using first-order reversal curves (FORC) analysis supported by micromagnetic calculations and analytical models. Differences in the magnetic behavior of the arrays of nanowires, whose length varies by two orders of magnitude, are discussed. Experimental evidence of the antiparallel magnetization of the long nanowires in the array in low fields is demonstrated.

Fast growth of highly ordered porous alumina films based on closed bipolar electrochemistry

Highly ordered porous anodic alumina (PAA) is widely used as a template for preparing one-dimensional nanostructured materials. At present, research efforts to prepare PAA templates with straight channels mainly focus on improving their regularity or increasing the efficiency of the preparation methods. Herein, we introduce a novel anodization method to fabricate highly ordered PAA films based on closed bipolar electrochemistry. To the best of our knowledge, there have been no reports of the use of closed bipolar electrochemistry in PAA film fabrication. Compared to traditional anodization, a faster PAA film growth rate of 1.67 μm min−1 was obtained in 0.75 M oxalic acid when a voltage of 62 V was applied to the driving electrodes. Furthermore, different electrolyte solutions can be employed in the anodic and cathodic cells in the closed bipolar electrochemical system. In addition, no direct electrical connection to the aluminum sheets is required in this approach.

Facile synthesis of size- and shape-controlled freestanding Au nanohole arrays by sputter deposition using anodic porous alumina templates

To fabricate a freestanding through-hole Au membrane using an anodic porous alumina template, Au was deposited on the outermost surface of an anodic film followed by the removal of the template. Alumina templates with different dimensions (e.g. diameters and number of pores) were prepared by two-step anodization in the range of 40–80 V and pore-widening. The Au thin films were deposited onto alumina templates with well-controlled surface morphologies by sputter deposition using a commercially available ion sputter coater. After the removal of the alumina template, a variety of Au membranes with nanoholes, nanotubes, or branched pores were obtained, which reflect the morphology of the alumina template. When the sputtered Au penetrates the pores of the alumina film, Au nanotube arrays with an aspect ratio of ∼3 can be fabricated. The present method is much simpler than the traditional template process involving multi-step replication because there is no need to separate the alumina template from the aluminum substrate before Au deposition.

Co–Ni nanowires supported on porous alumina as an electrocatalyst for the hydrogen evolution reaction

Water electrolysis is a promising way to produce hydrogen fuel, but many electrocatalytic systems require electrodes made of noble metals such as platinum. There is a demand for high-efficiency, low-cost materials to replace these noble metals. Herein, porous anodic alumina (AAO) templates are prepared by direct current (DC) constant voltage anodization and the step-down method. Cobalt, nickel and Co–Ni alloy nanowires are then prepared by alternating current (AC) electrodeposition. This nanoarray system can be employed in fuel cells to minimize the use of precious metals and reduce the cost of the cathodes. The pores of the AAO template are uniform with a size range from 35 to 75 nm. Using cyclic voltammetry (CV) and linear sweep voltammetry (LSV), the Co–Ni nanowire array prepared on AAO by this method is shown to have a low overpotential for hydrogen evolution and excellent stability.

Synthesis of Sn nanowire by template electrodeposition and its conversion into Sn nanosolder

Electrodeposition of Sn within porous anodic aluminum oxide (AAO) template was used to synthesize Sn nanowires. Ag seed layer was sputtered upon AAO template firstly, then the Sn nanowires were electroplated upon the seed layer. After electrodeposition the Ag seed layer was removed and the AAO template was dissolved in order to obtain Sn nanowires finally. The diameter of Sn nanowires was about 200 nm, being consistent with the template pore size, while the length of nanowires had a linear growth rate of approximately 2.49 μm/min. X-ray diffraction (XRD) and electron diffraction revealed that individual Sn nanowire was single crystal without preferential growth direction. The surface of the nanowire was wrapped by a thin SnO film (~5 nm thick), as verified by transmission electron microscopy (TEM) observation and X-ray photoelectron spectrometer (XPS) analyses. The synthesized Sn nanowire powders had a dark brown color, which comes from the surface SnO layer. Through the differential scanning calorimetry (DSC) analysis, the melting point of Sn nanowires was determined as 231.73 °C, which is about 2.7% lower than the pure Sn particles. Fabrication of Sn nanosolders from Sn nanowires was tried using liquid bath melting method. It was found that Sn nanowires could convert into spheroidal nanosolder in liquid paraffin, which demonstrated a novel technology to fabricate nanosolders used for nanoscale interconnections.

Magneto-optical properties of plasmonic hyperbolic metamaterials

The results of the experimental studies and numerical simulation of optical and magneto-optical properties of composite structures containing gold nanorods in porous anodic alumina templates and coated by a continuous nickel film are presented. We reveal two features in the Faraday rotation spectra of the structures in the vicinity of the wavelengths of 540 nm and 810 nm, which correspond to the epsilon-near-pole and epsilon-near-zero regions, respectively. Experimentally observed distinct enhancement of magneto-optical effects in the structures in the spectral vicinity of these points are consistent with the simulation results and open up novel opportunities for magnetic-field-assisted light manipulation.

Fabrication of Micro-/Submicro-/Nanostructured Polypropylene/Graphene Superhydrophobic Surfaces with Extreme Dynamic Pressure Resistance Assisted by Single Hierarchically Porous Anodic Aluminum Oxide Template

By applying a three-step anodic oxidation method followed by etching and pore widening treatment, etched micro-/submicroscale pits of ∼2 μm and ∼230 nm as well as anodized nanopores of ∼70 nm are c...

Microstructural and optical properties of Sn4Sb6S13 nanocrystals deposited on PAA templates

In this study, the Sn4Sb6S13 (TAS) nanocrystals were grown on the porous anodic alumina (PAA) templates through the vacuum thermal evaporation process at different deposition temperatures. The influence of deposition temperature on the microstructural and optical properties of TAS/PAA was investigated systematically. As the substrate temperature is increased, crystallite size increases while the strain and the dislocation density decrease. An improvement of the crystallinity is deduced from Raman spectra and X-Ray diffraction (XRD) patterns. The homogeneous distribution of TAS nanocrystals on PAA substrates was observed from surface morphology by using atomic force microscopy (AFM) and scanning electron microscope (SEM). The average reflectance of TAS/PAA films decreased significantly from 77 % to 60 % in the visible and near-infrared spectral regions, indicating the large absorbance of the deposited thin film. The optical parameters and thickness of TAS/PAA layers were estimated on the basis of spectroscopic ellipsometry measurements.

Electrochemical Behaviour of Ti/Al2O3/Ni Nanocomposite Material in Artificial Physiological Solution: Prospects for Biomedical Application.

Inorganic-based nanoelements such as nanoparticles (nanodots), nanopillars and nanowires, which have at least one dimension of 100 nm or less, have been extensively developed for biomedical applications. Furthermore, their properties can be varied by controlling such parameters as element shape, size, surface functionalization, and mutual interactions. In this study, Ni-alumina nanocomposite material was synthesized by the dc-Ni electrodeposition into a porous anodic alumina template (PAAT). The structural, morphological, and corrosion properties were studied using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrochemical techniques (linear sweep voltammetry). Template technology was used to obtain Ni nanopillars (NiNPs) in the PAAT nanocomposite. Low corrosion current densities (order of 0.5 µA/cm2) were indicators of this nanocomposite adequate corrosion resistance in artificial physiological solution (0.9% NaCl). A porous anodic alumina template is barely exposed to corrosion and performs protective functions in the composite. The results may be useful for the development of new nanocomposite materials technologies for a variety of biomedical applications including catalysis and nanoelectrodes for sensing and fuel cells. They are also applicable for various therapeutic purposes including targeting, diagnosis, magnetic hyperthermia, and drug delivery. Therefore, it is an ambitious task to research the corrosion resistance of these magnetic nanostructures in simulated body fluid.

Tailoring Controllable Nanowire Morphologies Using a Multi-layer Porous Anodic Alumina Template for Technological Applications

Straight nanowires fabricated from single-layer porous anodic alumina (PAA) templates are known to be mechanically weak. To provide additional support, nanowires can be fabricated on multilayered PAA templates. In this work, Cu and Ni nanowires were fabricated using single-, double-, and three-layer PAA templates by pulse electrochemical deposition (PECD). The templates were made by anodizing Al-1 wt% Si and Al-0.5 wt% Cu thin films under different conditions. The morphologies of the PAA templates and fabricated nanowires were examined with scanning electron microscopy. The length of the nanowires was 3 μm, while the diameters ranged from 50 to 70 nm. The nanowires fabricated from a double-layered template (Al-0.5 wt% Cu/Al-1 wt% Si) were mechanically stronger with larger surface areas than those fabricated from an anodized Al-1 wt% Si template. The nanowires formed within the anodized Al-1 wt% Si layer had tree-like branches, while vertical nanowires with horizontal anchors were formed in the anodized Al-0.5 wt% Cu layer. The results also indicated that the volume expansion of the PAA template was controlled by depositing a Al-0.5 wt% Cu layer below the Al-1 wt% Si film. The Ni nanowires can be used as a platform for hydrogen production and in other technological applications.

Self-assembly plasmonic metamaterials based on templated annealing for advanced biosensing.

In this paper, we introduce a novel method for the fabrication of self-assembly plasmonic metamaterials by exploiting fluid instabilities of optical thin films. Due to interplay between template reflow and spinodal dewetting, two metal nanoparticles of different sizes are generated on the top mesas of free-standing porous anodic aluminum oxide (AAO) template, which results in the apprearance of double resonant peaks in the extinction spectrum. These two resonant peaks possess refractive index resolution 3.27 × 10-4 and 2.53 × 10-4 RIU, respectively. This optical intensity modulation based plasmonic nanoplatform shows a dramatically surface sensing performance with outstanding detection capacity of biomolecules, because of the very small decay length of electric field at dual-modes. The detection ability for concanavalin A (Con A) demonstrats that the limit of detection of dual-modes reaches as small as 68 and 79 nM, respectively.

Yttrium incorporated BiFeO3 nanostructures growth on two step anodized Al2O3 porous template for energy storage applications

Porous anodic aluminum oxide templates with average pore size of approximately 100 nm were synthesized by two step anodization processes. Pure and Yttrium substituted BiFeO3 nano-structures with different concentrations were hydrothermally grown on anodic aluminum oxide templates to explore its various physical properties. X-ray diffraction was employed to extract the crystallographic information revealed the formation of rhombohedral geometry with R-3c space group. Field emission scanning electron microscopy displayed the filling up of pores with growth of distorted diamond and flakes like BiFeO3 and Yttria enriched nanostructures, respectively. Energy dispersive X-ray spectroscopy was confirmed the presence of expected elemental contents in each template. UV–Vis spectrophotometry recorded a significant increment in optical absorption of AAO template with growth of nanostructures. The value of optical band gap was found to decrease from 2.49 eV to 2.02 eV with incorporation of metallic yttrium content. Dielectric permittivity was found to increase substantially from 19 to 159 in Yttria containing nano-flakes with comparatively low loss factor of 0.84 disclosed these templates as prominent candidate for energy storage applications.

Zinc aluminate nanotubes fabrication based on heating-induced volatilization and Kirkendall effect in nanopores of anodic aluminum oxide template

The fabrication of zinc aluminate nanotubes attracted considerable attention due to their potential application as catalysts, catalyst supports, and electronics. In this paper, it is presented the influence of heating temperature and time on the Kirkendall effect-related evolution of Zn nanowires embedded in nanopores of anodic aluminum oxide (AAO) template. With increasing of the reaction temperature and heating time, zinc aluminate nanotubes can be gradually achieved from Zn nanowires embedded in AAO template under the air environment. In particular, ZnO was formed in the pores of AAO template by the volatilization and oxidation of Zn nanowires. And then through the solid-solid interfacial reaction of ZnO and AAO template, the nanostructures were transformed to zinc aluminate nanotubes conserving the shape of the corresponding ZnO nanostructures, which was induced by the nanoscale Kirkendall effect. Combined with the volatilization and oxidation time of Zn nanowires, the wall thickness of the formed nanotubes can be further precisely controlled. Our finding provides a simple and efficient pathway to fabricate the complex hollow zinc aluminate nanostructures, which are expected to have potential applications in catalytic related fields.

Wide spectral photoresponse of template assisted out of plane grown ZnO/NiO composite nanowire photodetector

Zinc oxide (ZnO) one-dimensional nanostructures are extensively used in ultra-violet (UV) detection. To improve the optical sensing capability of ZnO, various nickel oxide (NiO) based p–n junctions have been employed. ZnO/NiO heterojunction based sensing has been limited to UV detection and not been extended to the visible region. In the present work, p-NiO/n-ZnO composite nanowire (NW) heterojunction based UV-visible photodetector is fabricated. A porous anodic aluminum oxide template based electrochemical deposition method is adopted for well separated and vertically aligned growth of composite NWs. The photoresponse is studied in an out of plane contact configuration. The fabricated photodetector shows fast response under UV-visible light with a rise and decay time of tens of ms. The wide spectral photoresponse is analyzed in terms of conduction from defect states of ZnO and interfacial defects during p–n junction formation. Light interaction with heterojunction along the length of the composite NW results in enhanced visible photoresponse of the detector and is further supported by simulation.

Platinum-Nickel Nanotubes Array as Cathode for PEMFC

Keywords: Electrocatalyst, PEMFC, PtNi alloy, Oxygen Reduction Reaction, Electrode The technology of polymer electrolyte membrane fuel cells (PEMFCs) have recently attracted much attention from both fundamental and applied point of views for their future potential as clean and mobile power sources. One of the barriers of their commercialization is the high cost of the catalyst [1]. In order to enhance their achievement on the market, it is mandatory to optimize the high costly catalyst and improve its durability and stability or to innovate a new structure of electrodes. Platinum nanoparticles supported on carbon is used due to its high surface area but has some limitations, namely insufficient activity and durability particularly at the cathode where the oxygen reduction reaction (ORR) occurs. The latter is limited by corrosion of the C and Pt dissolution/agglomeration through Electrochemical Ostwald ripening mechanism which is reflected by a fast and significant loss of electrochemical surface area (ECSA) over time during fuel cell operation [2]. This architecture can hardly be more optimized, it is for this reason that many researches have been lead to design new architectures of electrodes. Previous studies have demonstrated the benefits of Pt nanostructured electrodes showing high performances for low Pt loadings and stability such as NanoStructured Thin Film (NSTF) by 3M [3], Pt nanowires [4], unsupported Pt Aerogels [5], PtCu nanotubes [6].These architectures are highly desired to meet desirable performance to substitute the state-of-the-art Pt/C electrocatalysts architecture. The aim of this work is to develop and control a Pt-Based tubular nanostructure made only with catalyst without a carbon support. The vertically aligned tubes exibits less O2 loss because they are oriented parallel to the reactants flux [7]. Stamenkovic and co-workers reported that alloying Pt with Ni exhibits a higher ORR activity than with other transition metals [8]. Accordingly, combining the tubular structure and the higher activity of PtNi catalyst has the potential for overcoming the limitations of conventional Pt/C electrodes. In order to elaborate the PtNi nanotubes, porous anodic alumina template (PAAT) is used as a sacrificial mold in which Ni nanowires were electrodeposited. The PAAT allows the control of the geometry of the desired nanotubes. In terms of comparison, the theoretical Pt loading is fixed at 0,15 mg/cm² assuming that the tubes are made with Pt nanoparticles of 5 nm in diameter. Afterwards, Pt is deposited through spontaneous galvanic displacement process. The latter involves the control of a large set of parameters (Cation (K2PtCl6 and H2PtCl6), pH, annealing at different temperatures, concentrations, HCl addition at different concentrations, time, temperature) in order to transform NiNWs to PtNiNTs. Later, using the hot pressing process of Nafion® membrane on the synthetized nanotubes lead to their integration in a complete Membrane Electrode Assembly (MEA) in order to characterize their electrochemical and transport limitations in real operating conditions. Also, to the extent of optimizing the activity of the PtNiNTs, further studies to be done regarding the entire structure of nanotubes including their diameter, length, density and the introduction of Nafion® ionomer.

Fabrication of Silica Nanoparticle Monolayer Arrays Using an Anodic Aluminum Oxide Template.

Non-close-packed (NCP) silica nanoparticle monolayer arrays (SNMA) on ordered porous anodic aluminum oxide (AAO) templates were fabricated for the first time by a novel two-step spin-coating technique. The obtained NCP-SNMA-AAO was composed of silica nanoparticles (average primary particle size of 440 nm) and well-organized nanopores on the AAO substrates. NCP-SNMA-AAO with a supporting ratio of 87% silica nanoparticles showed a hydrophilic surface (water contact angle of 51.0°), while the original AAO substrate shows a hydrophobic surface (water contact angle of 107.9°). The maximum coefficient of static friction was decreased by 29% (0.327 → 0.233). The coefficient of dynamic friction was also decreased by 20% (0.281 → 0.226). We found that controlling the silica supporting ratio using the two-step spin-coating technique is an effective approach for surface modification of an AAO substrate.

Hierarchical and Spiral Polymer Structures: Direct Electrospinning on Porous Anodic Aluminum Oxide Templates

AbstractElectrospun fibers with hierarchical structures have attracted a great deal of attention because they have distinct properties, such as large specific surface areas and high surface area‐to‐volume ratios, and can be applied to various fields. Here, a simple and versatile method is demonstrated to prepare electrospun fibers with hierarchical structures by directly electrospinning poly(methyl methacrylate) (PMMA) solutions on porous anodic aluminum oxide (AAO) templates. Hierarchical PMMA structures with micro‐ and nanometer scales can be generated. The two length scales of the hierarchical structures can be independently controlled; the first length scale is controlled by the electrospinning conditions, and the second length scale is controlled by the pore sizes of the AAO templates. By adding water in the polymer solutions, the evaporation of the solvents and the whipping instability of the solution jets can be manipulated. Consequently, spiral and hierarchical structures can be obtained. This study opens a promising avenue in fabricating electrospun polymer fibers with hierarchical structures, which should have great potential in a variety of applications, such as filtration, diagnosis, and tissue regeneration.

Influence of anodizing voltage and electrolyte concentration on Al-1 wt% Si thin films anodized in H2SO4

Porous anodic alumina (PAA) templates have been extensively studied due to their unique morphology and extensive applications. The fabrication of PAA can be modulated to achieve a self-ordered pore structure with desired pore size and interpore separation. PAA thin film templates were fabricated from silicon doped aluminum film, Al-1 wt% Si, based on one-step anodization method at 22 °C. Effects of anodizing potential (10–20 V) as well as sulfuric acid concentrations (0.6–1.8 M) on current density, interpore distance, anodization rate, and volume expansion were evaluated. The results indicated that current density increased largely exponentially with a concentration of the electrolyte at a given anodizing voltage. In addition, distinct and well-ordered pores were obtained for anodization conducted at 15 V and 20 V. The volume expansion factor is proportional to the applied voltage. At 1.8 M sulfuric acid, the expansion factor increases with pore regularity with 1.4 considered as the transition point. The minimum current density (2.1 ± 0.15 mA cm−2) was observed at the minimum anodizing condition (0.6 M, 10 V). Also, maximum anodizing condition (1.8 M, 20 V) resulted in the highest current density of 34 ± 4 mA cm−2. As expected, anodization time decreases with an increase in both anodization voltage and electrolyte concentration.