Porous Anodic Aluminum Oxide Template Research Articles

Dielectric properties of sodium nitrite particles embedded into porous alumina

Porous anodic alumina templates were fabricated using a two-step anodization in oxalic and phosphoric acid solutions. Dielectric studies were carried out for ferroelectric sodium nitrite embedded into porous alumina. Phase transition temperature in sodium nitrite within porous alumina is shifted compared to the bulk ferroelectric Curie point. The sign of this shift depends on the experimental conditions of sample preparation.

Ordered silver nanoparticle arrays as surface-enhanced Raman spectroscopy substrates for label-free detection of vitamin C in serum

A porous anodic aluminum oxide (AAO) template is fabricated using two-step anodization technology. The Ag nanostructure arrays are realized by electron beam evaporating a thin layer of silver onto the porous side of the AAO template. The device as a robust and cost-efficient surface-enhanced Raman scattering (SERS) substrate is used for label-free detection of vitamin C in serum. This substrate produces a high Raman signal due to its periodic hexagonal arrangements. The nanostructures have sharp edges to bring about a further enhancement to the local electromagnetic field. The partial least squares (PLS) regression method is applied on measuring vitamin in serum within physiological levels. In comparison with other methods of measuring vitamin C, our method provides the advantages of high precision and simple way in physiological levels. The error of vitamin C concentration is less than 0.04μmol/L between measurement by Raman spectrum and by high performance liquid chromatography (HPLC).

Optical and magnetic properties of porous anodic alumina films embedded with Co nanowires

A simple method to tune the optical properties of porous anodic alumina (PAA) films embedded with Co nanowires (PAA@Co nanocomposite films) is reported in this paper. The films exhibit vivid structural colors and magnetic properties. The optical properties of the films can be effectively tuned by adjusting the thickness of the PAA template. The deposition of Co nanowires greatly increases the color saturation of the PAA films. The theoretical results of the changes in structural color according to the Bragg—Snell formula are consistent with the experimental results. PAA@Co films can be used in many areas, including decoration, display, and multifunctional anti-counterfeiting applications.

Boron-doping Ni@Au nanotubes: Facile synthesis, magnetic property, and in vitro cytotoxicity on Molt-4 cells

A facile approach was applied for the preparation of boron-doping Ni@Au hybrid magnetic nanotubes via a chemical reduction technique using Ni nanotubes as a precursor. The Ni nanotubes with outer diameter of ~320nm were rapidly pre-fabricated with a porous anodic aluminum oxide (AAO) template by electroless deposition, and the Au nanoparticles were subsequently loaded onto the surfaces of the Ni nanotubes. The morphology, structure, composition, magnetic property, and cytotoxicity assays of the as-prepared Ni and Ni@Au nanotubes were all studied. The results indicated that annealing treatment can improve the crystalline structure and magnetic property of the Ni nanotubes. The Ni@Au hybrid nanotubes presented lower cytotoxicity on Molt-4 cells than that of the Ni nanotubes, which makes the magnetic Ni@Au hybrid nanotubes potentially applicable for biomedicine.

Capacitive behavior of mesoporous Co(OH)2 nanowires

Dual-template synthesis, which includes porous anodic alumina and lyotropic liquid crystalline templates, has been carried out at various electrodeposition potentials, annealing and electrodeposition temperatures for mesoporous Co(OH)2 nanowires. The maximum capacitance of 1180 F g−1 has been achieved at 4 A g−1. The chemical state and detailed structure of Co(OH)2 are examined by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) respectively. It reveals that the capacitance behavior of mesoporous Co(OH)2 nanowires depends on not only the oxygen atomic ratio of Co(OH)2 to CoO chemical state, but also the packed density of the interlaced nanostructure.

Colour-Coded Photoluminescence and Chemiluminescence of Fluorene Polymer-Based Organic Nanowires in Random and Organised Arrangements

Organic nanowires based on a fluorene homopolymer and a copolymer, i.e., poly(9,9-dioctylfluorene), F8, and poly(9,9-dioctylfluorene-co-benzothiadiazole), F8BT, respectively, were synthesised by solution assisted wetting of porous anodic alumina templates. Nanowires ranged between 3 microm and 50 microm in length, and were ca. 200 nm in diameter. Absorption and photoluminescence studies of F8BT nanowires yielded spectra characteristic of the parent material. By contrast, the well resolved spectra obtained for F8 nanowires indicated that, during synthesis, a fraction of the molecules within the wires underwent intra-chain re-orientation from the more random molecular conformations of the glassy phase to the more planar extended molecular conformation of the beta-phase. Importantly, both F8 and F8BT nanowires exhibited a distinct emission anisotropy, consistent with internal alignment of the emissive polymer chains along the long axes of the wires. This property was exploited by forming nanowire crossbar structures in which, by selecting either luminescence wavelength or polarisation state, spatial confinement and colour tuning of polarised light emission could be readily achieved. Finally, nanowire chemiluminescence was demonstrated. Characteristic blue and green-yellow luminescence was observed for F8 and F8BT wires, respectively, confirming that these novel nanostructures may act as nanoscale chemiluminescent light sources.

Elaboration and characterization of Cu/Co multilayered nanowires

Multilayered Cu/Co nanowires were elaborated by a low cost electrochemical technique consisting in reducing alternatively the Cu2+ and Co2+ ions, through a porous commercial anodic aluminum oxide template, onto a conductive substrate. The deposition parameters were determined from current-potential curves. The structure of the nanowires was characterized down to the atomic scale by transmission electron microscopy and atom probe tomography. The results show that the multilayers are polycrystallized with a nanometric grain size. The Cu layers are almost pure, while the Co ones consist in a Co-rich alloy with about 12 to 15% Cu.

Surface and interference co-enhanced Raman scattering from indium tin oxide nanocap arrays

Large-area indium tin oxide (ITO) nanocap arrays are fabricated on porous anodic alumina (PAA) templates to produce robust and cost-effective surface-enhanced Raman scattering (SERS) substrates. The electromagnetic enhancement mechanism is believed to be the main reason for the enhancement. The topography of the ITO nanocap arrays can be adjusted to optimize the enhancement factor by varying the anode voltage applied to the PAA templates. The optical interference in enhanced Raman scattering from the ITO nanocap arrays with different thicknesses are systematically studied and optical self-interference from the incident, scattered, and emitted light is observed to modulate the intensity and shape of the Raman signals.

Development and Application of Porous Anodic Alumina Template

Various porous alumina structures are formed in different electrolyte systems. Adjusting the anodizing parameters can yield different apertures and regularities of the porous alumina template. Thus, porous alumina is widely applied in the preparation of ordered nanostructured materials. This study introduces the porous alumina structure, including its formation mechanism, manufacturing technology, and application in the manufacture of nanostructure materials.

Length and temperature dependent 1/f noise in vertical single-walled carbon nanotube arrays

We report measurements of temperature- and length-dependent 1/f noise in vertical single-walled carbon nanotube (SWCNT) arrays. Carbon nanotubes are synthesized in a porous anodic alumina template with sub-micrometer channel lengths ranging from 100 to 700 nm. A significant difference is observed in the 1/f noise magnitude of quasi-ballistic and diffusive SWCNT devices, with quasi-ballistic devices exhibiting 1/f noise levels that are one to two orders of magnitude less than diffusively conducting devices. Furthermore, 1/f noise was measured from 90 to 400 K, and the noise prefactor decreased significantly at temperatures below 250 K.

High-Density Germanium Nanowire Arrays via Supercritical Fluid-Liquid-Solid Growth in Porous Alumina Templates

High-density germanium (Ge) nanowire arrays grown from porous alumina templates via supercritical fluid-liquid-solid (SFLS) growth were successfully synthesized. Before the growth of Ge nanowire arrays, the gold metal nanoparticles as growth catalyst layer were synthesized at the bottoms of anodic porous alumina (AAO) templates by pulsed electro-deposition. Partial exposure of Ge NW arrays from AAO or free standing of Ge NW arrays was demonstrated by using different etching solutions. The growth of single crystalline Ge NW arrays from AAO significantly provides a low-cost with high yield approach to control the size of Ge NWs by the AAO template. © 2013 The Electrochemical Society. [DOI: 10.1149/2.010306ssl] All rights reserved.

Formation, morphology and internal structure of one-dimensional nanostructures of the ferroelectric polymer P(VDF-TrFE)

We present an investigation of the formation, morphology, thermodynamic properties and crystal texture of P(VDF-TrFE) nanostructures obtained by wetting of porous anodic aluminum oxide templates, using electron microscopy, DSC and X-ray scattering. Wetting occurs initially via precursor film formation producing thin walled nanotubes. Formation of nanorods happens by subsequent thickening of the tube walls with thickness undulations occurring as a transient state. While crystallization within the one-dimensional nanostructures during cooling leads to the formation of highly oriented crystals in the high temperature paraelectric phase, the subsequent transition to the ferroelectric phase goes along with partial loss of orientation. Nevertheless, at room temperature the samples show a dominant orientation of the chains perpendicular to the long axis of the nanostructures. For narrow pores the size of crystalline domains is restricted by the strong confinement.

Polymeric nanowires and nanopillars fabricated by template wetting

Template wetting constitutes a common technique for the fabrication of elongated polymeric nanostructures such as nanorods, nanotubes, and nanowires. It is based on the infiltration of polymeric solutions inside the nanopores of a template, followed by the chemical dissolution of the template. It is affected by several parameters such as dimension and surface properties of the nanopores; molecular weight, concentration, and viscosity of the polymer; duration of infiltration and drying; etc. This study focuses particularly on the effects of the technique of infiltration for two cases, for free-standing nanorods and for nanopillars attached on a substrate. Poly-l-lactid acid, poly(methyl methacrylate), and poly(3-hexylthiophene) were chosen as model polymers due to their wide range of applications in different fields. Three different ways were tested to fabricate nanopillars by infiltration of the polymer solutions inside anodic porous alumina templates with open-through pores: One way was to position the template above a thin film of the polymer solution, the second way was to spread the polymer solution on the top surface of the template, and the third way was to dip the template inside the polymer solution. Nanopillars and nanowires with diameters in the range from 110 to 190 nm and height from 880 nm to 15 μm depending on the experimental conditions were fabricated. Preliminary measurements of the drug-release behavior of drug-loaded matrix dissolution nanopillars fabricated with the proposed techniques are presented.

Comparative Study of Loading of Anodic Porous Alumina with Silver Nanoparticles Using Different Methods.

Three different routes were used to infiltrate the pores of anodic porous alumina templates with silver nanoparticles, selected as an example of a bioactive agent. The three methods present a continuous grading from more physical to more chemical character, starting from ex situ filling of the pores with pre-existing particles, moving on to in situ formation of particles in the pores by bare calcination and ending with in situ calcination following specific chemical reactions. The resulting presence of silver inside the pores was assessed by means of energy dispersive X-ray spectroscopy and X-ray diffraction. The number and the size of nanoparticles were evaluated by scanning electron microscopy of functionalized alumina cross-sections, followed by image analysis. It appears that the best functionalization results are obtained with the in situ chemical procedure, based on the prior formation of silver ion complex by means of ammonia, followed by reduction with an excess amount of acetaldehyde. Elution of the silver content from the chemically functionalized alumina into phosphate buffer saline has also been examined, demonstrating a sustained release of silver over time, up to 15 h.

Engineered fabrication of ordered arrays of Au–NiO–Au nanowires

In the present paper, a novel method to fabricate ordered arrays of Au/NiO/Au nanowires is described, with the aim of filling the gap between the fundamental study of the electrical properties of scattered single nanowires and the engineered fabrication of nanowire arrays. This approach mainly consists of the following steps: (a) electrodeposition of Au/Ni/Au nanowires into an ordered porous anodic aluminum oxide template; (b) mechanical polishing of the sample to expose the gold tips of Au/Ni/Au nanowires to the template surface; (c) in situ annealing of the Au/Ni/Au nanowires without removing the template. The resulting structure consists in an ordered array of Au/NiO/Au nanowires slightly protruding out of a flat aluminum oxide template. Unlike current approaches, with the described method it is not necessary to remove the template in order to oxidize the middle metal, thus allowing the availability of an entire set of metal/oxide/metal nanowires ordered in a two-dimensional matrix and where single heterojunctions can be accessed individually.

Preparation of AgBr Nanowire Arrays in Porous Anodic Aluminium Oxide Template by Paired Cell Deposition

Firstly, porous anodic aluminum oxide template was prepared by a two-step anodization process, then AgBr nanowire arrays were successfully synthesized by paired cell deposition. X-ray diffraction (XRD) indicates that the as-synthesized samples are composed of face-centered AgBr. Field-emission scanning electron microscopy (FESEM) shows that the average diameter of the nanowire arrays is about 70nm.

A facile low-temperature growth of large-scale uniform two-end-open Ge nanotubes with hierarchical branches

We present a facile approach for the controlled fabrication of well-aligned arrays of Ge nanotubes (GeNTs) with tunable sizes and hierarchical branches inside the pre-designed nanochannels of porous anodic aluminum oxide (AAO) templates. Metal salts, such as nickel nitrate, silver nitrate, cobalt nitrate and copper sulphate are pre-decorated on the inner wall of the AAO nanochannels as catalyst precursors, where they are reduced into nickel, silver, cobalt, and copper clusters, and provide nucleation sites for subsequent Ge growth. GeNTs are formed by confining the Ge growth on the inner walls of the porous AAO template in a low temperature (300–380 °C) chemical vapor deposition process. The as-grown GeNTs have open ends with tailored wall thickness (between 10 and 26 nm), diameter (between 80 and 248 nm), and geometrical configuration (e.g., linear, Y-branching, multi-branching, and various multiple-generation branching). The GeNT formation process is sensitive to the choice of the catalyst precursor. Nickel salts lead to a uniform wall thickness of GeNTs compared with copper, silver, and cobalt salts. And GeNTs grown with copper salts as catalysts are polycrystalline, while nickel, silver and cobalt salts assisted GeNTs are amorphous though they can crystallize via post-annealing at 400 °C in Ar/H2 atmosphere. These open-end hollow nanotubes with tunable sizes and hierarchical branches can serve as nanoscale containers or pipes to deliver fluids and molecular species, and are excellent building blocks for the construction of large-scale nanofluidic systems.

Synchrotron small angle X-ray scattering for the evaluation of the interaction of silica nanotubes with lipid membranes

Synchrotron X-ray scattering measurements were used to assess the interaction of silica nanotubes (SNTs) with membrane model systems in conditions that mimic the physiological pH of healthy (pH 7.4) and pathological (pH 5.0) cellular membranes. SNT arrays were synthesized combining the sol–gel method with a porous anodic alumina (PAA) template assisted approach. The inner surfaces of the SNTs were functionalized with aminopropylethoxysilane (APTES). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the nanocarriers. A therapeutic anti-inflammatory drug (naproxen) was loaded into the SNTs by electrostatic interactions between the negatively charged carboxyl group of the drug and the protonated inner surface of the nanotubes. Small angle X-ray scattering (SAXS) measurements indicate that the unloaded SNTs do not interact significantly with both membranes. The negligible membrane disordering effect demonstrated by the unloaded SNTs may correlate with a desirable lack of membrane toxicity of these nanocarriers. Furthermore, the biophysical effect on membrane structure presented a similar profile at pH 5.0 for the drug (non-encapsulated) and for SNTs loaded with the drug indicating that SNTs are able to release the drug content under pathological conditions.

Conversion of porous anodic Al2O3into freestanding, uniformly aligned, multi-wall TiO2nanotube arrays for electrode applications

A combined conformal coating and gas/solid reaction process has been used for the first time to convert porous anodic alumina templates into robust, freestanding, multi-wall titania nanotube (MWTNT) arrays that resist appreciable nanotube bundling upon drying. A sol–gel infiltration process was first used to apply a thin conformal titania coating to the alumina templates. After selective etching to generate a gap between the template and the titania coating, exposed alumina was converted into nanocrystalline titania via reaction with titanium tetrafluoride gas and then with humid oxygen. After selective dissolution of residual aluminum-bearing phases and drying, freestanding, non-agglomerated, well-aligned MWTNT arrays were generated (i.e., with coating-derived inner titania tubes resting inside reaction-derived outer titania tubes). When incorporated as aligned electrodes in dye-sensitized solar cells, the dye loading and power conversion efficiencies were higher by factors of 2.2 and 1.8, respectively, than for solar cells with single-wall titania nanotube array electrodes. By controlling the conditions used for alumina template formation, sol–gel coating, and gas/solid reaction, this hybrid process may be used to generate robust, uniformly aligned MWTNT arrays with dimensions and functional chemistries tailored for a variety of electrical, optical, chemical, or biochemical applications.

A gecko-inspired double-sided adhesive

Geckos' outstanding abilities to adhere to various surfaces are widely credited to the large actual contact areas of the fibrillar and hierarchical structures on their feet. These special features regulate the essential structural compliance for every attachment and thus provide robust yet reversible adhesions. Inspired by gecko's feet and our commonly used double-faced tape, we have successfully fabricated a gecko-inspired double-sided dry adhesive by using porous anodic alumina template assisted nano-wetting on a stiff polymer. It was determined that the obtained 2-sided structure showed largely decreased effective stiffness compared with its 1-sided counterpart, which favored better compliance and interfacial integrity. We also demonstrated that the repeatable double-sided adhesive improved the macroscopic normal and shear adhesion capacities over the widely-studied 1-side structure by ~50% and ~85%, respectively. By using the synthetic double-sided adhesive, the usage of traditional pressure-sensitive/chemical adhesives could be well avoided. Besides, the double-sided nanostructures showed great potential in finding new interesting properties and practical applications for the synthetic dry adhesives.