Nanoporous Anodic Aluminum Oxide Templates Research Articles

Stabilizing High-Energy Crystal Structure in Silver Nanowires with Underpotential Electrochemistry

We demonstrate that commonly face-centered cubic (fcc) metallic nanowires can be stabilized in hexagonal structures even when their surface energy contribution is relatively small. With a modified electrochemical growth process, we have grown purely single-crystalline 4H silver nanowires (AgNWs) of diameters as large as 100 nm within nanoporous anodic alumina and polycarbonate templates. The growth process is not limited by the/Ag Nernst equilibrium potential, and time-resolved imaging with high-resolution transmission electron microscopy (TEM) indicates a kinematically new mechanism of nanowire growth. Most importantly, our experiments aim to separate the effects of confinement and growth conditions on the crystal structure of nanoscale systems.

Preparation of acrylonitrile-butadiene-styrene terpolymer nanotubes with array structure in anodic aluminium oxide membrane using wetting techniques

Acrylonitrile-butadiene-styrene terpolymer (ABS) nanotubes and their arrays with different structures were prepared successfully using nanoporous Anodic Aluminium Oxide (AAO) template through polymer solution and melt wetting method, a simple physical technique. According to the results of Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), nanotubes can be obtained using either polymer solution or polymer melt. As for solution wetting method, the integrity of ABS nanotubes depends on the concentration of polymer solution. The wall of ABS nanotubes made from 2.5 wt% solution has pore defects, while intact nanotubes can be obtained using 5.0 wt% solution. As for melt wetting method, the structure of nanotubes depends on the temperature of the melt. ABS nanotubes can be prepared at both 240 and 270 °C but the thickness of tubular wall and the length of the nanotubes are different. TGA tests showed that the thermal decomposition temperature of ABS nanotubes is ca. 100 °C lower than that of bulk ABS polymer.

Photocatalytic properties of titanium dioxide sputtered on a nanostructured substrate

The effective one-step physical approach is demonstrated for the fabrication of anatase titanium dioxide nanotubes through r.f. magnetron sputtering of TiO 2 on a highly ordered nanoporous anodic alumina template. The nanostructured TiO 2 benefited from the combination of unique properties of both the sputtering technique that provided well-controlled environment for the fabrication of anatase phase TiO 2 and the porous anodic alumina (PAA) that provided uniform and ordered nanopores. The photocatalytic properties of TiO 2 films were characterized following the degradation of methylene blue molecules under UV light irradiation. The photocatalytic activity of the nanostructured TiO 2 films has been found to be approximately twice higher in comparison with the flat TiO 2 films fabricated at the same conditions.

Hopping conduction in disordered carbon nanotubes

We report electrical transport measurements on individual disordered multiwalled carbon nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template. In both as-grown and annealed types of nanotubes, the low-field conductance shows an exp [ − ( T 0 / T ) 1 / 2 ] dependence on temperature T , suggesting that hopping conduction is the dominant transport mechanism, albeit with different disorder-related coefficients T 0 . The electric field dependence of low-temperature conductance behaves as exp [ − ( ξ 0 / ξ ) 1 / 2 ] at high electric field ξ at sufficiently low T . Finally, both annealed and unannealed nanotubes exhibit weak positive magnetoresistance at T = 1.7 K . Comparison with theory indicates that our data are best explained by Coulomb-gap variable-range hopping conduction and permits the extraction of disorder-dependent localization length and dielectric constant.

Fabrication of Copper Indium Diselenide Nanowires

AbstractNanostructured semiconductors have received a great deal of attention due to their unusual physical properties. The possibility of controlling these properties by varying the particle size, shape and surface properties is of great interest for nanoscale device applications in microelectronics, non-linear optics and optoelectronics in particular. Copper Indium diselenide (CIS), a p-type semiconductor with a band gap of about 1.04 eV has shown promise as an absorber for photovoltaic cells. Polycrystalline CIS film has been fabricated by various physical and chemical techniques over the past couple of decades. However, the preparation of nanostructured CIS is still challenging due to the fact that CIS tends to agglomerate resulting in large grains. Furthermore, an annealing step is also required to improve the film properties, which results in increased grain size. Here we report a simple, low cost solution to this problem through electrochemical deposition of CIS into the confined nanopores of an anodic aluminum oxide (AAO) template. The nanoporous aluminum oxide template, a few microns thick was prepared by either a one step or a two anodization in oxalic acidic media. CIS was deposited into the nanoporous AAO template by pulsed cathodic electro-deposition from an aqueous mixture. The electrodeposited nanowires had diameter ranging up to 40 nm and length ranging from 600 nm to 5 μm depending on the length of the template. The hybrid nanostructured CIS/AAO was annealed in vacuum at 230ºC for several hours to achieve stoichiometric CuInSe2 phase. The embedded CIS nanowires were characterized by X-ray diffraction and scanning electron microscopy. The optical bandgap was deduced from UV-Vis absorption spectroscopy measurements.

Fabrication and magnetic properties of Fe∕Pt multilayered nanowires

Fe ∕ Pt multilayered nanowires with well-defined interfaces and layer thicknesses were fabricated by a pulse-plating technique in nanoporous anodic alumina templates. The structure, surface morphology, and magnetic properties of the multilayered nanowire arrays have been characterized by x-ray diffractometer, field emission scanning electron microscope, transmission electron microscopy, and superconducting quantum interference device magnetometer. It is found that after being annealed at temperatures of 300°C, FePt ordered phase with high magnetic anisotropy is formed. This can be explained by rapid diffusion at Fe∕Pt interface.

Research on fabrication and properties of nanoporous GaN epilayers

Gallium nitride (GaN) epilayers with nanopore arrays were fabricated by inductive coupled plasma (ICP) etching using anodic aluminum oxide (AAO) as mask. Nanoporous AAO templates were formed by anodizing the Al films deposited on GaN epilayers. The diameter of the perforations in the AAO masks could be easily controlled by tuning the technique parameters of AAO fabrication process. Cl 2/Ar and Cl 2/He were employed as etching gas. Scanning electron microscopy (SEM) analysis shows that vertical nanoporous arrays with uniform distribution can directly be transferred from AAO masks to GaN films in some proper conditions. Photoluminescence (PL) spectra, X-ray diffraction (XRD) and Raman spectroscopy were applied to assess properties of the nanoporous GaN films with different average pore diameters and interpore distances.

Large-Area Highly-Oriented SiC Nanowire Arrays: Synthesis, Raman, and Photoluminescence Properties

Large-area highly oriented SiC nanowire arrays have been fabricated by chemical vapor reaction using an ordered nanoporous anodic aluminum oxide (AAO) template and a graphite reaction cell. Their microstructures were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. The results show that the nanowires are single-crystalline beta-SiC's with diameters of about 30-60 nm and lengths of about 8 microm, which are parallel to each other, uniformly distributed, highly oriented, and in agreement with the nanopore diameter of the applied AAO template. The nanowire axes lie along the [111] direction and possess a high density of planar defects. Some unique optical properties are found in the Raman spectroscopy and photoluminescence emission from oriented SiC nanowire arrays, which are different from previous observations of SiC materials. The growth mechanism of oriented SiC nanowire arrays is also analyzed and discussed.

Non-Polar Polymer Nanotubes and Nanowires Fabricated by Wetting Anodic Aluminium Oxide Template

Non-polar polymer nanotubes and nanowires were fabricated using nanoporous Anodic Aluminium Oxide (AAO) template via a physical wetting of the polymer solution and melt. Testing results of field emission scanning electron microscopy (FESEM) demonstrate that non-polar polymer nanotubes can be prepared by polymer solution, while nanotubes and nanowires can be obtained by polymer melt at higher temperature and at lower temperature respectively. As for melt wetting method, there is a critical temperature for preparing nanotubes, and the structure of products depends on the viscosity and flowability of the polymer melt. The mechanism of melt wetting method is also 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.

Composition-dependent structural and magnetic properties of Co1−xPtx (0.09⩽x⩽0.86) nanowire arrays

Highly ordered 14nm diam cobalt platinum alloy nanowire arrays with Pt content ranging from 9to86at.% have been electrodeposited into nanoporous anodic aluminum oxide templates. The crystal structure of the as-deposited Co1−xPtx nanowire arrays changes progressively from hcp to a mixture of hcp and fcc phases and finally to pure fcc with increasing Pt content. The coercivity, squareness, and saturation magnetization of the as-deposited nanowire arrays have been investigated as a function of nanowire composition.

Magnetic nanowires for acoustic sensors (invited)

Tiny hairlike sensors or cilia play a very important role in detection for many biological species, including humans. This research took inspiration from the packaging and transduction processes of the inner ear’s cochlea and cilia to design acoustic sensors. Specifically, this work uses nanowires of magnetostrictive materials as artificial cilia to sense acoustic signals. Anodic aluminum oxide (AAO) templates with hexagonal spacings were fabricated using a two-step anodization process as well as nanoimprint assisted self-assembly and were characterized using atomic force microscopy. Patterned microelectrodes were also fabricated at the backside of several templates using photolithography. Ni, Co, and Galfenol (Fe1−xGax0.1⩽x⩽0.25at.%) nanowires were fabricated using electrochemical deposition into nanoporous AAO templates where the pores had various geometries and some had large-area ordering as dictated by nanoimprinting. High aspect ratio nanowires with diameters varying from 10 to 200 nm and lengths up to 60μm were fabricated in arrays and were collectively and individually characterized using scanning electron microscopy. Galfenol thin films, fabricated electrochemically using a Hull cell, were characterized using x-ray diffraction and energy dispersive x-ray spectroscopy to determine the optimum current density for deposition. The magnetic response of millimeter-scale cantilevered beams to dynamic bending loads was also measured and compared to constitutive and free-energy models. A giant magnetoresistive sensor behind the beam measured the magnetic response of mechanical excitation applied to the tip of each rod and validated the models. Potenial applications of these nanowire cilia include sonar arrays, underwater cameras, and medical devices.

Silver nanowire arrays electrochemically grown into nanoporous anodic aluminatemplates

Silver nanowire arrays with high aspect ratios have been prepared using potentiostaticelectrodeposition within the confined nanochannels of a commercial porous anodicaluminium oxide template. The nucleation and growth processes are intensively studied bycurrent versus time transients. Scanning electron microscopy results show that thenanowires have a highly anisotropic structure with diameters and lengths of 170 nm and58 µm, respectively, which coincide with the dimensions of the template used. Structuralcharacterization using x-ray diffraction shows that the Ag nanowires are highly crystalline,and those obtained at higher overpotentials present a very strong [220] preferredcrystallographic orientation. The optical properties of the silver nanowires embedded in thealumina template show a clear edge close to 320 nm, that is an expected value for asilver–alumina composite material.

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.

Control of magnetic behavior in Fe/sub 3/O/sub 4/ nanostructures

Hexagonally well-ordered nanoporous anodized aluminum oxide (AAO) templates were synthesized by electrochemical method. Then, magnetite (Fe/sub 3/O/sub 4/) nanoparticles of 8-15-nm diameter were filled in the pores of the AAO template, and then the morphology and magnetic properties were characterized. Vibrating sample magnetometer measurement indicated that the nanoparticles inside AAO showed superparamagnetic behavior at as-filled state. But after annealing at 600/spl deg/C for 2 hr, the nanostructure (i.e., an assembly of nanoparticles) exhibited coercivity of 80 Oe. Superconducting quantum interference measurement device data showed that after annealing the blocking temperature was above 300 K. Thus, the annealed magnetite nanostructures possessed ferrimagnetism.

Controlled large-scale synthesis and magnetic properties of single-crystal cobalt nanorods

We report detailed synthesis studies of large-scale fabrication of single-crystalline cobalt nanorods using thermally evaporated gold as a conducting electrode on a nanoporous anodized aluminum oxide (AAO) template. By varying the time (i.e., adjusting the current density), it is possible to control the length of the nanorods and these rods grow in highly anisotropic face-centered (L10) phase. The large-scale isolation of these nanorods was achieved using a mild HF solution to dissolve the AAO membranes, leaving behind large scale ensemble of the isolated Co nanorods. Scanning electron microscopy and transmission electron microscopy examinations show clear evidence for metallic Co nanorods (about 100 nm in diameter) formed inside an array of AAO nanopores. We observe more uniform length of nanorods when an external magnetic field is applied during synthesis. A preferred perpendicular (shape) anisotropy is observed in these nanorod arrays. Magnetic properties indicate both coercivity and thermal activation volume increase with increasing nanorod length.

Synthesis and Characterization of Polythiophene and Poly (3-methylthiophene) Nanotubes and Nanowires

We synthesized nanotubes and nanowires of π-conjugated polythiophene (PT) and poly (3-methylthiophene) (P3MT) by using nanoporous anodic aluminum oxide (A1 2O 3) template through electrochemical polymerization method From SEM and TEM photographs, we observed the formation of nanotubes with diameters of 100 ∼ 200 nm and wall thicknesses of 5 ∼ 10 nm. The length of PT and P3MT nanotubes and nanowires was up to ∼40 μm. To discern the structural and optical properties of the systems, we measured UV/Vis absorbance and FT-IR spectra. We observed that the doping level, the π-π * transition peak, and bipolaron peaks in P3MT nanotubes varied with synthetic temperature. Based on measured I-V characteristic curves with gate bias for a single strand of PT nanotube, the systems should be considered to exhibit p-type nature.

Field emission of carbon nanotubes on anodic aluminum oxide template with controlled tube density

The tube number density of aligned carbon nanotubes (CNTs) grown over the nanoporous anodic aluminum oxide (AAO) template can be directly controlled by adjusting the CH4∕H2 feed ratio during the CNT growth. We ascribe the variation of the tube density as a function of the CH4∕H2 feed ratio to the kinetic competition between outgrowth of cobalt-catalyzed CNTs from the AAO pore bottom and deposition of the amorphous carbon (a-C) overlayer on the AAO template. A pore-filling ratio of 18% to 82% for the nanotubes overgrown out of nanopores on the AAO template can be easily achieved by adjusting the CH4∕H2 feed ratio. Enhanced field emission properties of CNTs were obtained by lowering the tube density on AAO. However, at a high CH4 concentration, a-C by-product deposit on the CNT surface can degrade the field emission property due to a high energy barrier and significant potential drop at the emission site.

Characteristics and photoluminescence of nanotubes and nanowires of poly (3-methylthiophene)

We synthesized nanotubes and nanowires of π-conjugated poly (3-methylthiophene) (P3MT) by using nanoporous anodic aluminum oxide (Al2O3) template through electrochemical polymerization method. From scanning electron microscope and transmission electron microscope photographs, we observed the formation of nanotubes with diameters of 100–200 nm and wall thicknesses of 5–10 nm. Relatively long nanotubes and nanowires of P3MT (about 40μm in length) were obtained. To discern the structural and optical properties of the systems, we measured ultraviolet and visible absorbance and Fourier transform-infrared spectroscopy. We observed that the doping level, the π-π* transition peak, and bipolaron peaks in P3MT nanotubes varied with synthetic temperature. The photoluminescence (PL) spectra of the P3MT nanotubes solution were observed at ∼490nm. For the P3MT nanotubes synthesized at lower temperatures, the PL peaks became sharper and the resistance decreased.

Tube number density control of carbon nanotubes on anodic aluminum oxide template

We demonstrate that the tube number density of well-aligned carbon nanotubes (CNTs) grown over the nanoporous anodic aluminum oxide (AAO) template can be directly controlled by adjusting the CH 4/H 2 feed ratio during the CNT growth in a microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system. During the CNT growth, the nanotube growth and the amorphous carbon deposition on the AAO pore wall take place simultaneously. The amorphous carbon sediment will gradually cover up the AAO nanopores and prevent the nanotubes to grow out of the nanopores. By adjusting the CH 4/H 2 feed ratio, one can control the amount of the deposited amorphous carbon and thus the number of CNTs grown over the AAO nanopores. It was found that the CNT density decreases linearly with increasing the CH 4 concentration. The CNT density decreased by a factor of about 4.5 when the CH 4 concentration increased from 9% to 91%.