Nanoporous Alumina Templates Research Articles

A Study of Anodization Process during Pore Formation in Nanoporous Alumina Templates

We have carried out a systematic investigation of the anodization procedure in order to determine the exact chemical mechanism of the dissolution process responsible for pore formation in nanoporous alumina templates. We measured the anodization current as a function of time and compared it with the thickness of porous aluminum oxide layer obtained from cross-section scanning electron microscopy images. From this, we calculated the number of moles of electrons generated per mole of porous alumina grown. This analysis is consistent with a reaction mechanism in which aluminum is converted to aluminum oxide in addition with the direct transfer of aluminum ions across the thin barrier aluminum oxide into the electrolyte. Hence, experimental evidence is reported that indicate that the dissolution process observed is that of ions migrating across the barrier layer and dissolving into the solution. Contrary to the suggestion of some authors, these experiments indicate that at most a negligible amount of oxide dissolves during the anodization of aluminum.

Fabrication of Large‐Scale Patterned Gold‐Nanopillar Arrays on a Silicon Substrate Using Imprinted Porous Alumina Templates

Gold-nanopillar arrays are patterned at predefined positions on a silicon substrate (see figure; scale bar=600 nm). The technique is based on the electrodeposition of gold into nanoporous alumina templates. Prior to anodization the thin aluminum film is indented via an imprinting procedure to define the spots for nanopillar growth. This technique facilitates versatile patterning of metal-nanopillar arrays below the resolution limit of conventional photolithography.

Vortex pinning in superconducting Nb thin films deposited on nanoporous alumina templates

We present a study of magnetization and transport properties of superconducting Nb thin films deposited on nanoporous aluminium oxide templates. Periodic oscillations in the critical temperature vs. field, matching effects in fields up to 700 mT and strongly enhanced critical currents were observed. These fields are considerably higher than those typical for periodic pinning arrays made by lithographic techniques, which reflects the benefits of nanostructuring superconductors by using self-organized growth. This method provides a periodic pinning potential with sub-100 nm spacing between the pinning centers, which enhances vortex pinning in broad field and temperature ranges.

FABRICATION OF SELF-ORGANIZED METAL NANOWIRE ARRAY USING POROUS ALUMINA TEMPLATE FOR OFF-CHIP INTERCONNECTS

Porous anodic alumina formation on silicon substrate is an example of a nanostructured porous array that is well-suited as a template for growing metallic nanowires. Commercial silicon wafer deposited with aluminum is used as substrate. Prior to anodization, the aluminum film is cleaned with mixture of acids solution to remove its native oxide growth. Anodization of aluminum film on silicon wafer is performed in oxalic acid solution to generate uniform and self-organized nanoporous alumina film. The pores are in the range of 60 nm diameter and pore density is about 9 × 109/ cm 2. The nanoporous alumina template is filled with nickel nanowires by wet electrodeposition process. After nanowire is grown on silicon wafer, the alumina template is etched and the as grown nickel nanowire forest is patterned using laser pruning method. The crystallinity pattern of the as grown nickel naowire forest is characterized using X-ray diffraction technique.

Variable-size Ni magnetic nanowires as observed by magnetization and ferromagnetic resonance

We present magnetization and ferromagnetic resonance (FMR) measurements on arrays of Ni nanowires grown by electrodeposition on self-organized nanoporous alumina templates. The study focuses on the measurement by FMR of the anisotropy of these systems and its correlation with the magnetization loops as the wire diameter ( d) is changed in a series of three samples. The magnetization data indicates an easy axis along the wire for the d=35 and 55 nm, changing into an easy plane for d=65 nm (all samples have an average inter-wire separation D∼110 nm). FMR resonance allows observing the anisotropy effects in detail and is consistent with magnetization measurements. Yet FMR shows a complex behavior in the large- d sample that can be interpreted as resulting from a prevailing easy-plane anisotropy with some portions of the sample with easy axis along the wires, thus unveiling an inhomogeneous character.

Synthesis of Magnetic Molecularly Imprinted Polymer Nanowires Using a Nanoporous Alumina Template

A convenient imprinting method for the preparation of magnetic molecularly imprinted nanowires within the pores of nanoporous alumina membrane is described. The template molecule (theophylline in this paper) was immobilized on the pore walls of a nanoporous alumina membrane. The nanopores were then filled with a prepolymerization mixture containing the superparamagnetic MnFe2O4 nanocrystallites. After polymerization, the alumina membrane was subsequently removed by chemical dissolution, leaving behind magnetic polymer nanowires that contain theophylline binding sites uniquely residing at the surface and have a saturated magnetization (MS) of 1.97 emu/g. The resulting magnetic imprinted polymer nanowires were capable of binding theophylline more strongly than the nonimprinted nanowires.

Tungsten trioxide sensing layers on highly ordered nanoporous alumina template

The gas sensing properties of WO 3 thin films deposited on highly ordered nanoporous alumina templates were studied. WO 3 films were prepared by rf sputtering of a tungsten target in a mixture of Ar and O 2. The WO 3-based sensors were selective to NO 2, NH 3 and ethanol at the temperature range from 150 to 300 °C. A mechanism of the influence of the nanoporous template on the response of the sensing film is discussed.

Synthesis of carbon nanotubes within Pt nanoparticles-decorated AAO template

Template-based synthesis of Pt-doped carbon nanotubes has been conducted with a corona discharge enhanced chemical vapor deposition. In this paper, nanoporous anodic alumina template was firstly decorated with Pt nanoparticles upon its interior walls. As the fabrication of carbon nanotubes within the nanopores, Pt nanoparticles were simultaneously embedded into the carbon nanotubes. HRTEM indicated that the grain size of these Pt nanoparticles is 5 nm and they are homogeneously exposed on the outer surface of carbon nanotubes.

Improved electrochemical capacitive characteristics of the carbon nanotubes grown on the alumina templates with high pore density

Specific capacitances of the carbon nanotube (CNT) electrodes are significantly enhanced by using the nanoporous alumina templates with high pore density and uniform pore diameter. Well-ordered nanoporous alumina templates were fabricated by a two-step anodization method by applying a constant voltage of 25.0 V or 20.0 V in sulfuric acid solution. The cylindrical pore diameter and pore density of the templates prepared at the anodizing voltage of 25.0 V or 20.0 V were 53 ± 1 nm and 3.1 × 10 10 cm −2 or 38 ± 2 nm and 3.8 × 10 10 cm −2, respectively. The CNTs with uniform diameters of 44 ± 2 nm in the 53 nm pores and of 32 ± 5 nm in the 38 nm pores, respectively, were grown on the porous alumina template. For the electrochemical double layer capacitors (EDLCs), the aluminum metal below the porous alumina layer was used as a current collector for the CNT electrode without any binding material. The EDLC characteristics were analyzed by measuring the capacitances from cyclic voltammograms and the charge–discharge curves. A maximum value of 175 F g −1 was achieved for the specific capacitances of the CNT electrodes prepared on the alumina templates with high pore density.

Direct electrodeposition of highly ordered magnetic nickel nanowires on silicon wafer

Highly ordered nickel nanowire (50 and 12 nm in diameter) arrays were successfully deposited into the nanoporous alumina template film on a gold-coated silicon wafer. The electrodeposited nickel nanowires have a preferred (220) fibre texture, that is the [110] direction parallel to the wire axis. With electropolishing, nanoporous alumina template with ordered and uniform pores was prepared by anodisation. By complete removal of the barrier layer and careful control of electrodeposition procedures, nearly 100% pore filling of uniform nanowires can be directly deposited onto the Au-coated silicon substrate, therefore no pattern transfer is necessary and incorporation of these nanowires into silicon-based devices is readily possible

Fabrication and Characterization of Nickel Nanowire Polymer Composites

ABSTRACTMagnetic polymers are multi-functional composites emerging as a new category of smart materials. This work focuses on fabrication and characterization of magnetic polymer nanocomposites based on polydimethylsiloxane (PDMS) elastomer matrix. The magnetic fillers are commercially available Ni nanoparticles and respectively in-house fabricated Ni nanowires. Synthesis of Ni nanowires is achieved by electroless deposition inside nanoporous anodic alumina templates. After template removal, the nanowires are coated with 1-Octodecanethiol surfactant and mixed with PDMS using a FlackTek SpeedMixer™. In parallel, nanoparticles are mixed with PDMS, without undergoing surfactant coating. Both composites are evaluated by scanning electron microscope (SEM) to determine dispersion uniformity. Mechanical properties are resolved by tensile tests performed by an instron. Preliminary results suggest that surfactant addition enhances dispersion, while mechanical properties of the composites for up to 5 vol. % of added nickel remain close to that of the polymer matrix without filler.

Uniform gold nanorod arrays from polyethylenimine-coated alumina templates.

Monolithic Au nanorod arrays can be grown by electrodeposition in Au-backed nanoporous alumina templates using polyethylenimine (PEI) as an adhesion layer, with excellent height control between 300 nm and 1.4 microm. The local height distribution can be extremely narrow with relative standard deviations well below 2%. The uniform growth rate appears to be determined by the adsorbed PEI matrix, which controls the growth kinetics of the grains comprising the nanorods. The nanorods can be retained as free-standing 2D arrays after careful removal of the AAO template. Reflectance spectroscopy reveals a collective plasmon mode with a maximum near 1.2 microm, in accord with recent calculations for 2D arrays of closely spaced cylindrical nanoparticles.

Attenuation of Protein Adsorption on Static and Oscillating Magnetostrictive Nanowires

The research described here investigates the hypothesis that nanoarchitecture contained in a nanowire array is capable of attenuating the adverse host response generated when medical devices are implanted in the body. This adverse host response, or biofouling, generates an avascular fibrous mass transfer barrier between the device and the analyte of interest, disabling the implant if it is a sensor. Numerous studies have indicated that surface chemistry and architecture modulate the host response. These findings led us to hypothesize that nanostructured surfaces will inhibit the formation of an avascular fibrous capsule significantly. We are investigating whether arrays of oscillating magnetostrictive nanowires can prevent protein adsorption. Magnetostrictive nanowires were fabricated by electroplating a ferromagnetic metal alloy into the pores of a nanoporous alumina template. The ferromagnetic nanowires are made to oscillate by oscillating the magnetic field surrounding the wires. Radiolabeled bovine serum albumin, enzyme-linked immunosorbent assay (ELISA), and other protein assays were used to study protein adhesion on the nanowire arrays. These results display a reduced protein adsorption per surface area of static nanowires. Comparing the surfaces, 14-30% of the protein that absorbed on the flat surface adsorbed on the nanowires. Our contact angle measurements indicate that the attenuation of protein on the nanowire surface might be due to the increased hydrophilicity of the nanostructured surface compared to a flat surface of the same material. We oscillated the magnetostrictive wires by placing them in a 38 G 10 Hz oscillating magnetic field. The oscillating nanowires show a further reduction in protein adhesion where only 7-67% of the protein on the static wires was measured on the oscillating nanowires. By varying the viscosity of the fluid the nanowires are oscillated in, we determined that protein detachment is shear-stress modulated. We created a high shearing fluid with dextran, which reduced protein adsorption on the oscillating nanowires by 70% over nanowires oscillating in baseline viscosity fluid. Our preliminary studies strongly suggest that the architecture in the static nanowire arrays and the shear created by oscillating the nanowire arrays would attenuate the biofouling response in vivo.

Nanoporous Alumina Template with In Situ Barrier Oxide Removal, Synthesized from a Multilayer Thin Film Precursor

A nanoporous alumina template made from a multilayer metal film structure has been developed that allows for the in situ removal of the electrically insulating alumina barrier layer, exposing a Pt electrode at the pore bases. This barrier-free nanoporous system is of great use for dc electrodeposition of a wide variety of materials in the alumina pores. This work in particular describes the development of a multilayer thin film precursor consisting of a Si substrate with thin Pt and Ti and a thicker Al layer in that order. After the Al is anodized, producing the porous alumina, the resulting is selectively removed at the base of the alumina pores exposing the Pt electrode. The metals in the precursor perform different roles in the fabrication and allow the alumina template to be fabricated directly on the final substrate with no film transfer technique involved. This allows Si to be used as the substrate, which could then include electronic circuitry. Several techniques are used to analyze the resulting template.

EDLC characteristics with high specific capacitance of the CNT electrodes grown on nanoporous alumina templates

Abstract Well-ordered nanoporous alumina templates were fabricated by two-step anodization method by applying a constant voltage of 40 V in oxalic acid solution or of 25 V in sulfuric acid solution. The cylindrical pore diameter and pore density of the templates utilized for the carbon nanotube (CNT) growth were 86 ± 5 nm and 1.2 × 1010 cm−2 in oxalic acid solution and 53 ± 1 nm and 3.1 × 1010 cm−2 in sulfuric acid solution, respectively. The CNTs with uniform diameter of 50 ± 10 nm (oxalic acid) and 44 ± 2 nm (sulfuric acid) were grown on the porous alumina template as electrode materials for the electrochemical double layer capacitor (EDLC). The EDLC characteristics were examined by measuring the capacitances from cyclic voltammograms and the charge–discharge curves. The specific capacitances of the CNT electrodes are 30 ± 1 F/g (Φ = 50 ± 10 nm) and 121 ± 5 F/g (Φ = 44 ± 2 nm). The high specific capacitance of the CNT electrode was achieved by using nanoporous alumina templates with the high pore density and the small and uniform pore diameter.

Crystallographically-oriented single-crystalline copper nanowire arrays electrochemically grown into nanoporous anodic alumina templates

Highly crystallographically-oriented single-crystalline copper nanowire arrays were electrochemically deposited into nanoporous commercial alumina templates. A gold/copper backward contact was needed in the template, while the nanowires were grown from a 0.5 M CuSO4·5H2O solution adjusted to pH=1. The kinetics of the growing process is studied by means of current vs. time curves. The pore filling is between 80 to 90%. The structure and morphology of the wires are studied by XRD, SEM and TEM. The wires have an average diameter of 150 nm corresponding to the pore diameter of the template, with the cubic face-centered copper structure. This structure is highly oriented along the [100] direction parallel to the wire axis. The preferential growing along this direction was not previously found in the literature, which may have interesting applications when such direction is required.

Nanotechnology advances and applications in information storage

A brief review of some applications of nanotechnology to information storage is given with the focus on self-assembled nanoporous alumina templates for patterned media.Ordered nanoporous alumina templates were fabricated by self-assembly technology. A two-step anodization process was also carried out to obtain templates with pores perpendicular to the substrate without removing the aluminum and barrier layer. Polycrystalline structure was observed with a grain size of about 2 μm in which the pores were almost perfect hexagonally ordered. The pore arrays exhibit different orientation along the boundaries of neighboring grains. Nanopatterning implemented by electron-beam lithography demonstrates the ability to write pores forming concentric circles with pore diameter as small as 50 nm.

Fabrication and Magnetic Properties of Ternary Alloy Co–Ni–Pb Nanowire Arrays

Abstract Ferromagnetic–nonmagnetic heterogeneous ternary alloy Co–Ni–Pb nanowire arrays having composition, Co, 15 atom%; Ni, 45 atom%; Pb, 40 atom%, were successfully fabricated by alternating current (AC) electrodeposition into nanoporous alumina templates. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) observations revealed that the Co–Ni–Pb nanowries were polycrystalline with uniform diameters of around 20 nm and lengths up to several micrometers. Magnetic measurements showed that the coercivity of the samples increased with the annealing temperature up to 550 °C and reached a maximum (1020 Oe).

Controlled Growth of Gold Nanorod Arrays from Polyethylenimine-coated Alumina Templates.

Au nanorod arrays were grown by electrodeposition in Au-backed nanoporous alumina templates modified with polyethylenimine (PEI) as an adhesion layer. By varying the concentration and molecular weight of PEI, the length of nanorod arrays could be finely controlled. The local length distribution was extremely narrow with relative standard deviations on the order of 2% for rod lengths from 700 nm to 17 microns. The uniform growth rate appears to be determined by the adsorbed PEI matrix, which controls the growth kinetics of the grains comprising the nanorods. Templates coated with poly(acrylic acid) did not impart fine control in nanorod growth. The nanorods could also be thermally annealed within the template and released as monodisperse particles of uniform size.

Attenuation of Protein Adsorption on Static and Vibrating Magnetic Nanowires

AbstractThe research described here investigates the hypothesis that nanoarchitecture contained in a nanowire array is capable of attenuating the adverse host response, biofouling, generated when medical devices, such as sensors, are implanted in the body. This adverse host response generates an avascular fibrous mass transfer barrier between the device and the analyte of interest, disabling the sensor. Numerous studies have indicated that surface chemistry and architecture modulated the host response. These findings lead us to hypothesize that nanostructured surfaces will significantly inhibit the formation of an avascular fibrous capsule. We are investigating whether vibrating magnetostrictive nanowires, formed in nanowire arrays, can prevent protein and cell adhesion. Magnetostrictive nanowires are fabricated by electroplating a ferromagnetic metal alloy into the pores of a nanoporous alumina template. The ferromagnetic nanowires are made to vibrate by altering the magnetic field surrounding the wires. Enzyme-linked immunosorbent assay (ELISA) and other protein assays were used to study protein adhesion on the nanowire arrays. These results display a reduced protein adhesion per surface area of static nanowires. The vibrating nanowires show a further reduction in protein adhesion, compared to static wires. Studies were also preformed to investigate the effects of nanoarchitecture have on cell adhesion. These studies were performed with both static and vibrating nanowires. Preliminary protein adhesion studies have shown that a nanowire arrays modulate protein adhesion in vitro.