AAO Membrane Research Articles

Copper-assisted, templated preparation of submicron-sized tubular CNT arrays by corona discharge enhanced CVD

The corona discharge enhanced CVD technique is used to synthesize copper nanoparticle-doped submicron carbon nanotubes. The average diameter of prepared copper nanoparticles is as small as 3 nm. Under the blank membrane condition (no metal loading), however, no nanotubes are formed. The existence of copper nanoparticles seems to facilitate the homogeneous deposition of carbon species onto the interior surface of an AAO membrane.

Vertically Well-Aligned C60 Microtube Crystal Array Prepared Using a Solution-Based, One-Step Process

A simple, one-step, solution-based process for preparing vertically aligned C60 microtube crystals was proposed. The whole surface of a 25 mm diameter AAO membrane can be covered by vertically aligned C60 microtube crystals with hexagonal cross-section and highly oriented crystallographic direction.

Synthesis and high gas sensitivity of tin oxide nanotubes

Abstract Semiconductor tin oxide (SnO 2 ) nanotubes have been synthesised in bulk quantities using a sol–gel template (AAO membrane) synthetic technique. The morphology and crystal structure of SnO 2 nanotubes were characterised by a field emission scanning electron microscope (FESEM) and a transmission electron microscope (TEM). The as-prepared SnO 2 nanotubes are polycrystalline with an outer diameter of 200 nm, an inner diameter of about 150 nm and a length extending to tens of micrometers. SnO 2 nanotube sensors exhibited high sensitivity towards ethanol gas.

Direct Fabrication of Well-Aligned Free-Standing Mesoporous Carbon Nanofiber Arrays on Silicon Substrates

Using nonionic triblock copolymer F127 as a soft template and AAO membranes as hard templates, well-aligned free-standing mesoporous carbon nanofiber arrays have been fabricated on silicon wafer through a confined self-assembly process. Hexagonally arranged circular mesochannels locate at the edge of the carbon nanofibers and some well-ordered columnar oriented mesochannels are wrapped by circular mesochannels at the center of the nanofibers. The surface interaction with the alumina pore walls is probably responsible for the formation of both circular and columnar oriented mesochannels.

Preparation of open-through anodized aluminium oxide films with a clean method

AAO membranes were detached from Al substrates via an anodic voltage pulse using aqueousHClO4 solution without any organic reagents. Previous studies used a mixture ofHClO4(aq) and 2,3-butanedione or methanol. However, 2,3-butanedione has a strong disagreeableodour, methanol is harmful, and the oxidized products of organic reagents contaminate theAAO template. Eliminating organic reagents makes the detachment process easy and clean,with great potential for the mass fabrication and application of AAO films. The voltageand acidity are critical factors in obtaining open-through AAO films. We propose amechanism for the detachment process, consistent with our experimental results.

Synthesis of Sulfide Nanowire Arrays through Template-Assisted Electrodeposition

Sulfide nanowire arrays have been synthesized by DC electrodeposition from an electrolyte containing S in DMSO. The AAO membrane with the barrier layer has been directly used as template in electrodeposition. The as-synthesized products are characterized by SEM, TEM and resonance Raman spectroscopy. CdS and ZnS nanowires have been obtained, respectively.

Fabrication of indium sulfide nanofibers via a hydrothermal method assisted by AAO template

β-In 2S 3 nanofibers were successfully synthesized via a hydrothermal method with AAO membrane as a template at 150 °C for 15 h. XRD patterns indicated the perfect crystallization of β-In 2S 3. SEM images showed that the β-In 2S 3 nanofibers grew up from the channel ends of the AAO template. TEM images confirmed that the nanofibers had a high aspect ratio of ca. 40–50 and diameters of about 10 nm. The room temperature photoluminescence (PL) spectrum of the β-In 2S 3 nanofibers indicated its potential applications in light-emission devices.

Pore-widening with the assistance of ultrasonic: A novel process for preparing porous anodic aluminum oxide membrane

The AAO membrane with nanopore arrays were fabricated by anodizing highly pure aluminum foils in oxalic acid, the pore-widening process of the membrane was carried out within ultrasonic bath. The quality of the fabricated AAO membrane has also been improved by using ultrasonic process. The microstructure of the AAO membrane obtained was characterized by field emission scanning electron microscopy (FE-SEM) indicating that the AAO membranes prepared with the ultrasonic wave assistance are more homogeneous than those in ordinary way related to the pore diameters as well as the quality of pore walls.

AAO Nanowells: Synthesis, in-situ Growth Study, and Applications in Ultra-sensitive Chemical Detection

ABSTRACTAnodized aluminum oxide (AAO) membranes consist of locally highly ordered nanopores. The pore diameter (20-200 nm) and pore-to-pore distance are controlled through the anodizing voltage and the choice of etching solution. High aspect ratio over 1,000 can easily be achieved which makes AAO membranes the ideal templates for making nanowires and nanotubes. In this work, the early stage of nanopore formation was studied in-situ with the use of small angle x-ray scattering (SAXS) and glazing incidence GISAXS techniques. The nanopores were found to grow as a function of the square root of growth time. The resulting short nanopores or nanowells with length below 200 nm were further characterized with use of SEM and AFM. These AAO nanowells showed interference color. Their reflectance UV-Vis spectra indicated strong angular dependence and can be understood with a simple single layer (nanoporous alumina over aluminum) model. These spectra are influenced by the nanowells thickness and diameter. Therefore, large array of interferometric AAO nanowells sensors are possible. When these nanowells are coated with Ag or Au thin films, in addition to enhanced interference color, highly sensitive surface enhanced Raman scattering (SERS) effect has been observed. These results will be presented.

Structure of assemblies of metal nanowires in mesoporous alumina membranes studied by EXAFS, XANES, X-ray diffraction and SAXS.

Mesoporous alumina membranes ("anodic aluminium oxide", or "AAO") are made by anodic oxidation of aluminium metal. These membranes contain hexagonal arrays of parallel non-intersecting cylindrical pores perpendicular to the membrane surface. By varying the anodisation voltage, the pore diameters are controllable within the range 5-250 nm. We have used AAO membranes as templates for the electrochemical deposition of metals within the pores to produce nanowires. These represent assemblies of one-dimensional quantum wires with prospective applications in electronic, optoelectronic and magnetic devices. Detailed characterisation of the structures of these nanowire assemblies on a variety of length scales is essential to understand their physical properties and evaluate their possible applications. We have used EXAFS, XANES, WAXS, high energy X-ray diffraction and SAXS to study their structure and bonding. In this paper we report the results of our studies of four different nanowire systems supported in AAO membranes. These are the ferromagnetic metals iron and cobalt, the superconducting metal tin, and the semiconductor gallium nitride. Iron nanowires in pores of diameter over the range 12 nm-72 nm are structurally very similar to bcc bulk iron. They have a strong preferred orientation within the alumina pores. Their XANES shows significant differences from that of bulk iron, showing that the electronic structure of the iron nanowires depends systematically on their diameter. Cobalt nanowires are composed of a mixture of hcp and fcc phases, but the ratio of the two phases does not depend in a simple way on the pore diameter or preparation conditions. In bulk cobalt, the fcc beta-phase is normally stable only at high temperatures. Strong preferred orientation of the c-axis in the pores was found. Tin nanowires in alumina membranes with pores diameters between 12 nm and 72 nm have a tetragonal beta-structure at ambient temperature and also at 80 K. Magnetic susceptibility measurements show that they are diamagnetic, and become superconducting at the same temperature as bulk tin (3.7 K). Gallium nitride nanowires have been prepared in alumina membranes with pore diameter 24 nm by a novel method. Gallium nitrate was deposited in the pores from aqueous solution and thermolysed at 1000 degrees C to form Ga2O3, which was reacted with ammonia at 1000 degrees C. The GaN nanowires have the wurtzite structure. Preparation at 1150 degrees C led to the incorporation of aluminium in the GaN. The mesoscopic ordering of the pores in the AAO membranes and their filling by metal nanowires has been studied by SAXS, which shows patterns of Bragg peaks arising from the pore arrays. Additionally, the cobalt nanowires have been the subject of an initial ASAXS study.

Preparation of Porous Anodic Aluminum Oxide in Water-Deficient Electrolytes

Well-ordered large-pore anodic aluminum oxide membranes were one-step prepared in water-deficient electrolytes using ethanol as main solvent. The effects of water content, electrolyte concentration and solvent types were studied with the help of SEM. The results showed that the involved electrochemical anodization and corrosion could be controlled by changing the amount of water added in the electrolyte, and the pores of the AAO membranes could be made in a controlled manner within a long reaction time. The pores were hexagonally ordered and narrowly diameter-distributed ((95 +/- 13) nm) in comparison with those produced with normal electrolytes using water as the sole solvent ((95 +/- 30) nm). With this method, the applied anodizing voltage spans a wider range, and so does the tuning of the pore diameters. This approach can broaden the application of the AAO templates in the fabrication and processing of nanoarrays and porous materials.

Fabrication and optical characterization of poly(2,5‐di‐n‐butoxyphenylene) nanofibril arrays

AbstractAnodic aluminum oxide (AAO) membrane can be used as template for the synthesized nanostructures. In this article, we have prepared the AAO membrane by using electrooxidation of aluminum substrate in phosphoric acid, and fabricated poly(2,5‐di‐n‐butoxyphenylene) (BuO–PPP) nanofibril arrays by oxidative coupling polymerization of 1,4‐di‐n‐butoxybenzene (DBB) within the pores of the AAO template membrane. The detailed molecular structure of the polymer nanofibrils was characterized by using infrared and 1H nuclear magnetic resonance spectra, and estimated to consist of almost equal fractions of 1,4‐ and 1,3‐ linkages. We have used transmission electron microscopy, scanning electron microscopy, and atom force microscopy to confirm the morphologies and images of the AAO template membrane and the fabricated nanometer scale of BuO–PPP nanofibril arrays. The experimental results demonstrated that the pores of the AAO membrane were regular and uniform, and parallel each other, and the BuO–PPP chains in the narrowest template‐synthesized nanofibrils were oriented parallel to the porous axes of the AAO membrane and perpendicular to the surface of the aluminum substrate. The polymer chain orientation was partially responsible for the enhanced conductivity. The ultraviolet absorption spectrum of the BuO–PPP nanofibril arrays shown that the polymer contains a better extended π‐conjugation system along poly‐(p‐phenylene) backbone, which resulted in longer wavelength shift of the absorption band, the absorption maxima were located at 258 nm (E1 absorption band) and 332 nm (E2 absorption band), respectively. Photoluminescence spectrum of the BuO–PPP nanofibril arrays exhibited a blue emission. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 425–430, 2004