Porous Alumina Templates Research Articles

Fabrication and magnetic characteristics of electrodeposited FeCr nanowire arrays

Fe-based nanowire (NW) arrays have long been investigated due their potential applications in future-generation magnetic nanodevices. However, very few research studies have considered FeCr NWs so far. Herein, FeCr NW arrays with different compositions are fabricated using a pulsed ac electrodeposition technique in porous anodic alumina templates. The Cr electrolyte concentration changed between 2 and 8 mM, influencing morphological, compositional, structural and magnetic properties. As an additive, the element Cr enhanced coercivity and squareness of Fe NWs, inducing the formation of Fe (200) peak in the crystal structure. As an alloying component, although the Cr element kept the structural and magnetic properties almost constant, it considerably affected the NW length compared to Fe NWs. First-order reversal curve analysis showed significant reductions in magnetostatic interactions when increasing the Cr concentration. In this case, local interactions between the FeCr NW arrays were expected to increase compared to pure Fe NWs.

Optimization of High-Density Fe-Au Nano-Arrays for Surface-Enhanced Raman Spectroscopy of Biological Samples.

The method of realizing nanostructures using porous alumina templates has attracted interest due to the precise geometry and cheap cost of nanofabrication. In this work, nanoporous alumina membranes were utilized to realize a forest of nanowires, providing a bottom-up nanofabrication method suitable for surface-enhanced Raman spectroscopy (SERS). Gold and iron were electroplated through the straight channels of the membrane. The resulting nanowires are, indeed, made of an active element for plasmonic resonance and SERS as the hexagonal distribution of the nanowires and the extreme high density of the nanowires allows to excite the plasmon and detect the Raman signal. The method to reduce the distance between pores and, consequently, the distance of the nanowires after electrodeposition is optimized here. Indeed, it has been predicted that the light intensity enhancement factor is up to 1012 when the gap is small than 10 nm. Measurements of Raman signal of thiol groups drying on the gold nanowires show that the performance of the device is improved. As the thiol group can be linked to proteins, the device has the potential of a biosensor for the detection of a few biomolecules. To assess the performance of the device and demonstrate its ability to analyze biological solutions, we used it as SERS substrates to examine solutions of IgG in low abundance ranges. The results of the test indicate that the sensor can convincingly detect biomolecules in physiologically relevant ranges.

Self-ordered Porous Anodic Alumina Templates by a Combinatory Anodization Technique in Oxalic and Selenic Acids

Self-ordered Porous Anodic Alumina Templates by a Combinatory Anodization Technique in Oxalic and Selenic Acids

Small-diameter magnetic and metallic nanowire arrays grown in anodic porous alumina templates anodized in selenic acid

Despite the introduction of selenic acid for anodic porous alumina (APA) preparation with small nanopore diameters (< 20 nm), no attempt has been made to use it in the fabrication of small-diameter magnetic and metallic nanowire arrays. In this paper, considering the high cost of selenic acid, it has been attempted to initially use oxalic acid in preparation of an ordered pattern in the first anodization step and then employ selenic acid for the second anodization step by matching the appropriate voltage. By investigating the nanopore formation pattern in both acids, it was shown that the nanopores formed in the selenic acid had considerably smaller diameter (13 nm) than that of oxalic acid (35 nm). Under optimized conditions of electrodeposition, various metals were then grown in the selenic APA templates in order to fabricate nanowires with small diameters. The pore-filling percentage and crystalline properties were also investigated.

Magneto-optical effects in hyperbolic metamaterials based on ordered arrays of bisegmented gold/nickel nanorods

Hyperbolic metamaterials (HMM) based on multilayered metal/dielectric films or ordered arrays of metal nanorods in a dielectric matrix are extremely attractive optical materials for manipulating over the parameters of the light flow. One of the most promising tools for tuning the optical properties of metamaterials in situ is the application of an external magnetic field. However, for the case of HMM based on the ordered arrays of magneto-plasmonic nanostructures, this effect has not been clearly demonstrated until now. In this paper, we present the results of synthesis of HMM based on the highly-ordered arrays of bisegmented Au/Ni nanorods in porous anodic alumina templates and a detailed study of their optical and magneto-optical properties. Distinct enhancement of the magneto-optical (MO) effects along with their sign reversal is observed in the spectral vicinity of epsilon-near-zero and epsilon-near-pole spectral regions. The underlying mechanism is the amplification of the MO polarization plane rotation initiated by Ni segments followed by the light propagation in a strongly birefringent HMM. This stays in agreement with the phenomenological description and relevant numerical calculations.

Multilayer regular hexagonal prism barium ferrite nanodot arrays on a substrate based on an AAO mask

Herein, the multilayer regular hexagonal barium ferrite nanodot arrays have been prepared by pulsed laser deposition through a porous anodic alumina template. The BaM nanodot arrays displayed a c-axis oriented crystal with a multilayer regular hexagonal structure, and the degree of orientation was improved by the post-annealing. Furthermore, the hysteresis loops showed the annealed nanodot arrays have a high squareness ratio of 0.65 along the easy magnetization direction. The first-order reversal curve diagram confirmed that the nanodots have a small interactive field between the particles. Consequently, this effective approach is potentially applied in self-biased microwave devices.

Cooling property and application of Au–Bi2Te3 heterojunction nanowire array based on AAO template

In this work, selective radiation material was used to change heat transport of hot side, a novel heterostructure cooler, constructed by gold (Au)—bismuth telluride (Bi2Te3) nanowires array was reported experimentally. The heterostructure was fabricated by electrochemical deposition based on porous anodic alumina template (AAO). The Au nanowire cluster array is used as an infrared selective radiation surface to optimize heat transport of the heat side. And the Bi2Te3 nanowires generate thermoelectromotive force between the two sides of the device due to thermoelectric effect. More interestingly, the Au nanowire ends produce an interface between the metal and semiconductor to enhance the temperature difference, as the interfacial phonon scattering suppresses thermal conductivity. The co-effects create a linear-like relationship between the temperature difference and the applied heating strength to make the heating source hide from infrared detection. At a heating temperature of 170 °C, the radiation temperature difference arrives 16 °C in the Au–Bi2Te3 heterojunction, (increased by 200% to that in Bi2Te3 single phase), given by an intriguing demonstration of infrared camouflage effect. The Au–Bi2Te3 nanowires heterojunction device can not only realize infrared camouflage, but also convert the heat into electrical energy, which provides a new idea for the development of materials.

Communication—Fabrication of Li Nanohole Array by Replication Process Using Anodic Porous Alumina Template

Geometrically controlled Li nanohole arrays with high aspect features were fabricated by a two-step replication process using ordered anodic porous alumina as a template. The use of an appropriate electrolyte for Li electrodeposition and organic solvent for the removal of the polymer (PMMA) template allowed the preparation of Li nanohole arrays with precisely replicated nanostructures. The application of a template with the structures for the electrodeposition of Li contributed to the suppression of the formation of Li dendrites, contributing to the precise replication.

Preparation of Ni micropillar arrays with high aspect ratios using anodic porous alumina template and their application to molds for imprinting.

Anodic porous alumina templates with controlled microscale geometrical structures were prepared by a process combining mask formation and subsequent selective etching of the alumina layer. In this process, the anisotropic etching of anodic porous alumina allows the preparation of anodic porous alumina with microhole array patterns having high aspect ratios. The electrodeposition of Ni using the obtained alumina templates generated an array of Ni micropillars with high aspect ratios. The height of Ni micropillars could also be controlled by adjusting the thickness of the anodic porous alumina. The obtained Ni micropillar array with a high aspect ratio was applied as a mold for imprinting. The ordered microstructures of TiO2 with high aspect ratios were prepared by imprinting using the Ni mold.

Inch-Scale Ball-in-Bowl Plasmonic Nanostructure Arrays for Polarization-Independent Second-Harmonic Generation.

Second-harmonic generation (SHG) in plasmonic nanostructures has been investigated for decades due to their wide applications in photonic circuit, quantum optics and biosensing. Development of large-scale, uniform, and efficient plasmonic nanostructure system with tunable modes is desirable for their feasible utilizations. Herein, we design an efficient inch-scale SHG source by a solution-processed method instead of traditional high-cost processes. By assembling the gold nanoparticles with the porous anodic alumina templates, multiresonance in both visible and near-infrared regions can be achieved in hexagonal plasmonic nanostructure arrays, which provide strong electric field enhancement at the gap region. Polarization-independence SHG radiation has been realized owing to the in-plane isotropic characteristic of assembled unit. The tilt-angle dependent and angle-resolved measurement showed that wide-angle nonlinear response is achieved in our device because of the gap geometry of ball-in-bowl nanostructure with nonlinear emission electric dipoles distributed on the concave surface, which makes it competitive in practical applications. Our progress not only makes it possible to produce uniform inch-scale nonlinear arrays through low-cost solution process; and also advances the understanding of the SHG radiation in plasmonic nanostructures.

Advanced VLS growth of gold encrusted silicon nanowires Mediated by porous Aluminium Oxide template

Abstract A highly efficient technique for the generation of dense and homogeneous Au-nanodroplets using Anodic Aluminium Oxide template (AAO) for the fabrication of single crystal gold encrusted array of silicon nanowires (SiNWs) was successfully developed. In interest of extending AAO's practical applicability, the Au-thin film sandwiched between Si-substrate and AAO was torn-up into small nanodroplets at annealing temperature followed by removal of AAO template before VLS growth instead of growing SiNWs directly in presence of AAO template. It's observed that smaller Au-nanodroplets are mandatory to yield dense array of SiNWs, further, size of formed Au-droplets is directly relied on AAO pore-size. Thus, construction of desired pore diameter on AAO was critically controlled by the application of voltage in presence of different etchants (sulfuric acid (SA), oxalic acid (OA) and phosphoric acid (PA)). Among the different etchants used SA demonstrated smaller AAO-pore size at a specific voltage and concentration. Further, obtained smaller Au-nanodroplets (from SA etched AAO) exhibited a denser array of SiNWs on VLS growth at particular set of experimental conditions. Characterization by advanced techniques such as UV–Vis spectroscopy, Micro-Raman spectroscopy, Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), High-Angle Angular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM) and Energy Dispersive X-ray Spectroscopy (EDX) revealed that the formed SiNWs were of 199 ± 43 nm diameter with well-decorated gold nano encrustations on the surface and at the tip. The formed SiNWs were in resemblance with SiNWs obtained from high precision e-beam Lithography, evidencing the superiority of the current method.

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.

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.

Fabrication of CoFe2O4 Nanowire Using a Double-Pass Porous Alumina Template with a Large Range of Pore Diameters

In this work, CoFe2O4 nanowire was fabricated by using a self-designed double-pass porous alumina template. The double-pass porous alumina template was prepared by a two-step oxidation method using a mixed acid (phosphoric acid and oxalic acid) electrolyte and polymethyl methacrylate (PMMA) filler. The combustion of aluminum foil at a high voltage has been effectively resolved by using this mixed acid electrolyte. Additionally, the range of pore diameters has been obviously increased to 230–400 nm by using PMMA as the filler, which can prevent contact between the pore and solution when removing the barrier layer. Subsequently, CoFe2O4 ferrite nanowire arrays were successfully fabricated into the double-pass porous alumina template by an electrochemical deposition method, and show an anisotropic feature of magnetic properties.

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.

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.

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.

Thermal Stability of Nano-Crystalline Nickel Electrodeposited into Porous Alumina

Through-pores alumina membranes of 50 μm thickness and 70 × 70 mm size have been fabricated to deposit Ni nanowires by electrochemical processing. Due to highly ordered microstructure of the membranes, the pores were filled by nanowires almost to 100%. The membrane nanowires composite morphology, structure and thermodynamic characteristics have been studied by scanning electron microscopy, atomic-force microscopy, X-ray diffraction and differential thermal analysis. The thermal stability of Ni nanowires into porous alumina template and whole composite was determined.