Nanoporous Anodic Alumina Membranes Research Articles

Two-Step Cycle for Producing Multiple Anodic Aluminum Oxide (AAO) Films with Increasing Long-Range Order.

Nanoporous anodic aluminum oxide (AAO) membranes are being used for an increasing number of applications. However, the original two-step anodization method in which the first anodization is sacrificial to pre-pattern the second is still widely used to produce them. This method provides relatively low throughput and material utilization as half of the films are discarded. An alternative scheme that relies on alternating anodization and cathodic delamination is demonstrated that allows for the fabrication of several AAO films with only one sacrificial layer thus greatly improving total aluminum to alumina yield. The thickness for which the cathodic delamination performs best to yield full, unbroken AAO sheets is around 85 μm. Additionally, an image analysis method is used to quantify the degree of long-range ordering of the unit cells in the AAO films which was found to increase with each successive iteration of the fabrication cycle.

Morphological and Optical Characterization of High Density Au/PAA Nanoarrays

Hexagonal nanoarrays of Au nanorods and nanopillar were deposited on nanoporous anodic alumina (PAA) membranes utilizing dc electrodeposition. The surface morphologies and optical properties were characterized by using field emission-scanning electron microscopy (FE-SEM) and UV-Vis spectrophotometer, respectively. The optical reflectance spectra of the as-prepared, pore widened, and 2D-Au nanorods-coated PAA membranes were studied in detail. The effects of the angle of incident, pore widening time, and electrodeposition time on the characteristic peaks positions and intensities of the fabricated nanoarrays were addressed. As the angle of incident increased, the interference peaks and transverse surface resonance are shifted to longer wavelengths, but the longitudinal surface plasmon resonance is shifted to shorter wavelengths. Also, the reflected intensities are decreased linearly for the as-prepared sample and decreased exponentially for Au/PAA samples. Using the modified Kubelka-Munk radiative transfer model, the energy gap is increased from 2.83 to 3.06 eV and the refractive index is decreased from 1.84 to 1.36 for the as-prepared and 70 min pore widened PAA membranes, respectively. Based on the advantages of the fabrication approach and the enhanced and controlled properties, this generation of Au/PAA arrays can be used as efficient building blocks for nanoelectronics and nanophotonic devices.

Nanoporous Aluminum Oxide Membranes Coated with Atomic Layer Deposition-Grown Titanium Dioxide for Biomedical Applications: An In Vitro Evaluation.

The surface topographies of nanoporous anodic aluminum oxide (AAO) and titanium dioxide (TiO2) membranes have been shown to modulate cell response in orthopedic and skin wound repair applications. In this study, we: (1) demonstrate an improved atomic layer deposition (ALD) method for coating the porous structures of 20, 100, and 200 nm pore diameter AAO with nanometer-thick layers of TiO2 and (2) evaluate the effects of uncoated AAO and TiO2-coated AAO on cellular responses. The TiO2 coatings were deposited on the AAO membranes without compromising the openings of the nanoscale pores. The 20 nm TiO2-coated membranes showed the highest amount of initial protein adsorption via the micro bicinchoninic acid (micro-BCA) assay; all of the TiO2-coated membranes showed slightly higher protein adsorption than the uncoated control materials. Cell viability, proliferation, and inflammatory responses on the TiO2-coated AAO membranes showed no adverse outcomes. For all of the tested surfaces, normal increases in proliferation (DNA content) of L929 fibroblasts were observed over from 4 hours to 72 hours. No increases in TNF-alpha production were seen in RAW 264.7 macrophages grown on TiO2-coated AAO membranes compared to uncoated AAO membranes and tissue culture polystyrene (TCPS) surfaces. Both uncoated AAO membranes and TiO2-coated AAO membranes showed no significant effects on cell growth and inflammatory responses. The results suggest that TiO2-coated AAO may serve as a reasonable prototype material for the development of nanostructured wound repair devices and orthopedic implants.

Carbon nanotube-nanoporous anodic alumina composite membranes with controllable inner diameters and surface chemistry: Influence on molecular transport and chemical selectivity

This work presents the fabrication of carbon nanotube composite membranes with controllable nanotube dimensions (inner diameters and lengths) and surface chemistry and explores their influence on the transport properties and chemical based transport selectivity. These membranes were prepared by growing of vertically aligned multiwalled carbon nanotubes (MWCNTs) inside nanoporous anodic alumina membranes (NAAMs) through a catalyst-free chemical vapour deposition (CVD) approach. The deposition time during CVD process and the length of NAAMs were used to control nanotube dimensions. The thermal annealing and wet and dry oxidation processes were used to control the surface chemistry of inner walls of nanotubes from highly graphitic-hydrophobic to oxygen rich and hydrophilic. The structural features and chemical composition of the prepared membranes are characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The influence of the nanotube dimensions and surface chemistry on molecular transport properties of prepared membranes are assessed by analysing the transport of two models molecules with different hydrophilic–hydrophobic and charge properties. The obtained results reveal that the diffusional flux of model molecules through CNTs-NAAMs can be controlled by nanotube dimensions and surface chemistry of graphitic surface and these parameters can be used to tailor their chemical based molecular separation for specific applications.

Photoswitchable membranes based on peptide-modified nanoporous anodic alumina: toward smart membranes for on-demand molecular transport.

A smart and reversibly photoswitchable membrane based on an azobenzene photo-switch containing peptides attached inside the pores of nanoporous anodic alumina membranes (NAAMs) is presented. The transport of molecules of interest across the photoswitchable peptide (PSP) functionalized NAAMs can be effectively controlled and manipulated as a function of the photostationary state of the azobenzene group in a PSP.

Synthesis and Characterization of Gold Nanoparticles Grafted on Nanoporous Anodic Aluminum Oxide (AAO) Membrane

Gold nanoparticles (Au NPs) supported on nanoporous anodic aluminium oxide (AAO) membrane has been successfully prepared by direct anionic exchange for further application in catalysis. The nanoporous AAO membrane is immersed in HAuCl4 solution at different pH to achieve gold nanoparticles grafted on AAO (Au-AAO). It was found that the pH of the HAuCl4 solution played an important role for controlling the size of Au NPs as well as the amount of Au depositing on the surface of AAO membrane. The prepared Au-AAO membranes were characterized by diffuse reflectance UV-Vis spectroscopy, high-resolution scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) spectroscopy.

Development of electrostatic supercapacitors by atomic layer deposition on nanoporous anodic aluminum oxides for energy harvesting applications

Nanomaterials can provide innovative solutions for solving the usual energy harvesting and storage drawbacks that take place in conventional energy storage devices based on batteries or electrolytic capacitors, because they are not fully capable for attending the fast energy demands and high power densities required in many of present applications. Here, we report on the development and characterization of novel electrostatic supercapacitors made by conformal Atomic Layer Deposition on the high open surface of nanoporous anodic alumina membranes employed as templates. The structure of the designed electrostatic supercapacitor prototype consists of successive layers of Aluminium doped Zinc Oxide, as the bottom and top electrodes, together Al2O3 as the intermediate dielectric layer. The conformality of the deposited conductive and dielectric layers, together with their composition and crystalline structure have been checked by XRD and electron microscopy techniques. Impedance measurements performed for the optimized electrostatic supercapacitor device give a high capacitance value of 200 µF/cm2 at the frequency of 40 Hz, which confirms the theoretical estimations for such kind of prototypes, and the leakage current reaches values around of 1.8 mA/cm2 at 1 V. The high capacitance value achieved by the supercapacitor prototype together its small size turns these devices in outstanding candidates for using in energy harvesting and storage applications.

Effect of Pore Thickness and the State of Polarization on the Optical Properties of Hexagonal Nanoarray of Au/Nanoporous Anodic Alumina Membrane

Hexagonal nanoarrays of Au particles were deposited on nanoporous anodic alumina membrane (NAAM) utilizing r.f. magnetron sputtering. The thickness of the NAAMs is adjusted by changing the second anodization time from 5 min to 20 min. The surface morphology, composition, and optical properties are characterized by using SEM, EDX, and spectrophotometer, respectively. The effects of the NAAM thickness and state of polarization on the morphological changes and on the optical properties of the fabricated nanoarrays were addressed. According to the measured optical spectra, the rate of decrease of NAAMs refractive index was found to be 3.825 × 10−4 nm−1. Using the modified Kubelka‐Munk radiative transfer model, the energy gap of NAAMs was calculated from diffused reflectance and was decreased from 1.682 to 1.376 as the anodization time increased from 5 to 20 min. Also, the saturation of interference fringes is substantially enhanced, and field enhancement can be achieved due to the excitation and constructive interference of surface plasmon waves by coating NAAMs with the hexagonal nanoarrays of Au. Based on the advantages of the fabrication approach and the enhanced and controlled properties, this new generation of samples can be used as promising building blocks for nanophotonic and nanoelectronics devices.

Magnetization reversal dependence on effective magnetic anisotropy in electroplated Co–Cu nanowire arrays

Arrays of Co(100−x)Cu(x) (0 ≤ x ≤ 27) nanowires with 45 nm of diameter and 18 μm in length, have been potentiostatically electrodeposited into the hexagonally self-assembled nanopores of anodic alumina membranes.

Enhancing the platinum atomic layer deposition infiltration depth inside anodic alumina nanoporous membrane

Nanoporous platinum membranes can be straightforwardly fabricated by forming a Pt coating inside the nanopores of anodic alumina membranes (AAO) using atomic layer deposition (ALD). However, the high-aspect-ratio of AAO makes Pt ALD very challenging. By tuning the process deposition temperature and precursor exposure time, enhanced infiltration depth along with conformal coating was achieved for Pt ALD inside the AAO templates. Cross-sectional scanning electron microscopy/energy dispersive x-ray spectroscopy and small angle neutron scattering were employed to analyze the Pt coverage and thickness inside the AAO nanopores. Additionally, one application of platinum-coated membrane was demonstrated by creating a high-density protein-functionalized interface.

Chemical solution growth of La0.7Sr0.3MnO3 nanotubes in confined geometries

Self-standing La0.7Sr0.3MnO3 nanotubes with outer diameter ranging from 100 to 200 nm have been successfully synthesized by template assisted chemical solution deposition using nanoporous anodized alumina membranes of varying pore size. This template synthetic strategy provides rather monodisperse size distributed nanotubes. A sol–gel based polymer precursor route was used to fill the porous membranes and a subsequent heat treatment (700–1,000 °C) enabled the phase formation and crystallization of the nanotubes. A good control over viscosity, stoichiometry and stability of the precursor solution were identified as crucial parameters for the template aided synthesis. The synthesized La0.7Sr0.3MnO3 nanotubes are polycrystalline and ferromagnetic with a Curie temperature of 350 K. Control over the nanowall thickness is attained by varying template filling time which is corroborated by magnetic moment results.

2D and 3D ordered arrays of Co magnetic nanowires

Cobalt nanowire arrays spatially distributed in 2D and 3D arrangements have been performed by pulsed electrodeposition into the pores of planar and cylindrical nanoporous anodic alumina membranes, respectively. Morphological characterization points out the good filling factor reached by electroplated Co nanowires in both kinds of alumina membranes exhibiting hexagonally self-ordered porous structures. Co nanowires grown in both kinds of alumina templates exhibit the same crystalline phases. DC magnetometry and First Order Reversal Curve (FORC) analysis were carried out in order to determine the overall magnetic behavior for both nanowire array geometries. It is found that when the Co nanowires of two kinds of arrays are perpendicularly magnetized, both hysteresis loops are identical, suggesting that neither the intrinsic magnetic behavior of the nanowires nor the collective one depend on the arrays geometry. FORC analysis performed along the radial direction of the Co nanowire arrays embedded in the cylindrical alumina template reveals that the contribution of each nanowire to the magnetization reversal process involves its specific orientation with respect to the applied field direction. Furthermore, the comparison between the magnetic properties for both kinds of Co nanowire arrays allows discussing about the effect of the cylindrical geometry of the template on the magnetostatic interaction among nanowires.

Study of magnetoelastic and magnetocrystalline anisotropies in Co Ni1− nanowire arrays

Abstract Highly ordered Co x Ni 1− x nanowire (NW) arrays were electrodeposited inside nanoporous anodic aluminum oxide membranes. The control of the applied potential during the electrodeposition process allowed us to easily tune the Co% in the alloy. Systematic studies on the morphological and crystallographic properties together with static and dynamic magnetic characterizations were performed. In this work we focus on the study of the dynamic magnetic properties of CoNi NW arrays using the ferromagnetic resonance method at both room (RT) and low (LT) temperatures. The careful comparison analysis performed between the magnetic anisotropy fields obtained at RT and LT, allowed us to extract for the first time the magnetocrystalline anisotropy effect of the Co component and, most importantly, the magnetoelastic anisotropy effect of Ni.

Free-standing alumina nanobottles and nanotubes pre-integrated into nanoporous alumina membranes

A novel interfacial structure consisting of long (up to 5 μm), thin (about 300 nm), highly-ordered, free-standing, highly-reproducible aluminum oxide nanobottles and long tubular nanocapsules attached to a rigid, thin (less than 1 μm) nanoporous anodic alumina membrane is fabricated by simple, fast, catalyst-free, environmentally friendly voltage-pulse anodization. A growth mechanism is proposed based on the formation of straight channels in alumina membrane by anodization, followed by neck formation due to a sophisticated voltage control during the process. This process can be used for the fabrication of alumina nanocontainers with highly controllable geometrical size and volume, vitally important for various applications such as material and energy storage, targeted drug and diagnostic agent delivery, controlled drug and active agent release, gene and biomolecule reservoirs, micro-biologically protected platforms, nano-bioreactors, tissue engineering and hydrogen storage.

Biocompatibility of composite membranes composed of anodic aluminium oxide (AAO) and Poly (2-hydroxyethylmethacrylate) for use as a cell culture substrate

In this study we investigate the biomedical potential of composite membranes composed of anodic aluminium oxide (AAO) and Poly (2-hydroxyethylmethacrylate) (pHEMA). The nano-porous AAO membranes were produced using a temperature controlled two-step electrochemical anodization technique. The AAO/pHEMA composite membranes were formed using the solution template wetting technique. The Cercopithecus aethiops (African green monkey) Kidney (Vero) epithelial cell line was used to demonstrate the applicability of the synthesised membranes and composites. Investigating cell adhesion, morphology and proliferation over a 72h period assessed cellular interactions and responses of this cell line to the various membranes types. The novelty of the results stems from the use of pHEMA as a constituent, a material which normally does not promote cell adhesion, hence its use in contact lens and catheters.

Template‐assisted Co–Ni alloys and multisegmented nanowires with tuned magnetic anisotropy (Phys. Status Solidi A 5∕2014)

Nanostructured magnetic materials synthesized through electrochemical methods by employing nanoporous anodic aluminum oxide membranes as patterned templates have recently attracted a huge attention. In their work reported on pp. 1041–1047, García et al. synthesized Co100-xNix (15 ≤ x ≤ 61) alloy nanowires of about 180 nm in diameter and 14 μm in length, as well as multisegmented Co54Ni46/Co85Ni15 nanowires with an approximate length of 300 nm per each segment, by means of electrochemical deposition into the pores of hard-anodic alumina membranes. The composition and crystalline structure of Co-Ni alloy segments and nanowires were properly adjusted by varying the electrodeposition potential. The magnetic properties of the alloyed nanowire arrays were correlated with their microstructural features. Co-richer nanowires show a hard magnetic phase due to the stronger influence of the high magnetocrystalline anisotropy of the majority hcp phase, whilst the Co-poorer ones exhibit a softer magnetic phase (fcc) and their magnetic behaviour is mainly determined by shape anisotropy. The comparison between the alloyed nanowires with different cobalt contents sheds light into the magnetization processes determining the overall magnetic behaviour of the multisegmented nanowire arrays.

Modified nanoporous membranes on centrifugal microfluidic platforms for detecting heavy metal ions

The modified nanoporous membranes on centrifugal microfluidic platforms are developed for detecting heavy metal ions with high selectivity. The nanomaterials of polyrhodanine, activated alumina and activated carbon are deposited on nanoporous anodic aluminium oxide (AAO) membranes for enhancing filtration to remove ions of lead (Pb(II)), arsenic (As(III)) and cadmium (Cd(II)) from aqueous solution. By detecting chemiluminescence (CL) reaction, the concentrations of heavy metal ions can be obtained. A pneumatic-and-centrifugal microfluidic detection system was used to perform microfluid separation and CL detection for measuring selected ions concentration. The removal efficiency of 92, 82 and 78% were observed for Pb(II), As(III) and Cd(II) ions, respectively. The removal rate is performed up to 70% for mixed ions filtration by a sequence of multi-modified AAO membranes. The modified nanofiltration films on microfluid platform have potential applications in removing heavy metal ions from water, soil, food and drug.

High-frequency ferromagnetic resonance of Co nanowire arrays

Highly ordered arrays of Co nanowires with different diameters have been fabricated by electrodeposition in nanoporous anodic aluminum oxide membranes. The prepared Co nanowires have hexagonal close-packed structure and are [002] preferred oriented crystalline with the c-axis parallel to the long axis of the nanowires. The high anisotropy of Co nanowires offers the possibility to control their magnetic properties and microwave properties, which are experimentally characterized by a vibrating sample magnetometer and frequency-swept ferromagnetic resonant flip-chip based techniques, respectively. The nanowire arrays exhibit strong magnetic anisotropies. As for the ferromagnetic resonance frequency, it increases with increasing value of the applied field, and zero-field ferromagnetic resonance frequencies up to 28–34 GHz. Also, the magnetic anisotropies and high ferromagnetic resonance frequency of Co nanowire arrays, are shown to be determined by the combined effect of shape anisotropy, crystalline anisotropy, and dipolar interactions between the nanowires.

Can Anodic Aluminium Oxide Nanomembranes Treated with Nanometre Scale Hydroxyapatite be Used as a Cell Culture Substrate

In this study we investigate the biomedical potential of composite membranes composed of anodic aluminium oxide (AAO) and nanometre scale hydroxyapatite (HAP). The nano-porous AAO membranes were produced using a temperature controlled two-step anodization technique. The AAO/HAP composite membranes were formed using the solution template wetting technique. The Cercopithecus aethiops (African green monkey) Kidney (Vero) epithelial cell line was used to demonstrate the biocompatibility of the synthesised membranes and composites. Investigating cell adhesion, morphology and proliferation over a 72 h period assessed cellular interactions and responses of the cell line to the various membranes types.

Morphological Studies of ZnO Nanostructures Deposited on Nanoporous Anodic Alumina Membrane by Rapid Dip Coating Technique

Inthiswork,differentmorphologiesofzincoxide(ZnO)nanostructureshavebeenfabricatedbya simpleandrapid dip coating method.Inthis method ZnO nanostructuresare deposited from sol-gel of zinc acetateusing dip coating onto Porous Anodic Alumina Membrane (PAAM).Afterthermalannealinginoxygenat600°Cfor30 min,the ZnO nanoparticles are uniformly agglomerated into, almost, 1D nanorods array. When the starting precursor is zinc nitrate and the annealing was carried out for 10 h at the same conditions, the ZnO nanoparticles are uniformly agglomerated into, almost, nanoseeds (nanocolloidal particles).