Nanochannel Alumina Templates Research Articles

Structure and Electronic Properties of InSb Nanowires Grown in Flexible Polycarbonate Membranes.

A dense array of vertically aligned indium antimonide (InSb) nanowires with high aspect ratio (diameter 150 nm, length 20 m) were grown in the pores of a track-etched polycarbonate membrane via a one-step electrochemical method. There are several reports on InSb nanowire growth in the pores of a mechanically rigid, nano-channel alumina template (NCA), where nanowire growth occurs in the pores of the NCA. This work on InSb nanowire growth in pores of track-etched polycarbonate (PC) membrane sheds light on the various factors that affect nucleation and nanowire growth. The average length and diameter of the as-grown nanowires was about 10 m and 150 nm, respectively. Two possible mechanisms accounting for two different morphologies of the as-grown nanowires are proposed. The polycrystallinity observed in some of the nanowires is explained using the 3D ‘nucleation-coalescence’ mechanism. On the other hand, single crystal nanowires with a high density of twin defects and stacking faults grow epitaxially by a two-dimensional (2D) nucleation/growth mechanism. To assess the electrical quality of the nanowires, two- and four-terminal devices were fabricated using a single InSb nanowire contacted by two Ni electrodes. It was found that, at low bias, the ohmic current is controlled by charge diffusion from the bulk contacts. On the other hand, at high bias, the effects of space charge limited current (SCLC) are evident in the current–voltage behavior, characteristic of transport through structures with reduced electrostatic screening. A cross-over from ohmic to SCLC occurs at about 0.14 V, yielding a free carrier concentration of the order of cm.

Thermal conductivities of sub-micron Bi2Te3 films sputtered on anisotropic substrates

Approximately 450 nm thick Bi2Te3 films were deposited on flat Al2O3 substrate and nanochannel alumina (NCA) templates with different pore diameters through radio-frequency magnetron sputtering. The structure and morphology of Bi2Te3 films were investigated by x-ray diffraction and field-emission scanning electron microscopy. Moreover, the thermal conductivities of the films deposited on anisotropic substrates were evaluated by micro-Raman method combined with numerical simulation and optimization conducted by COMSOL Multiphysics. The thermal conductivities of Bi2Te3 films deposited on NCA templates with discontinuous Φ20 and Φ100 nm pores and flat Al2O3 substrate were 0.80, 0.99 and 1.54 Wm−1 K−1, respectively. The lower thermal conductivities of Bi2Te3 films deposited on NCA templates are attributed to much smaller grain size, bottom porous layers, and rougher surfaces through analysis.

One-step fabrication of ordered Pt–Cu alloy nanotube arrays for ethanol electrooxidation

Novel one dimensional (1D) nanostructured metallic electrodes have received much attention in the area of the fuel cell because of their extremely high surface-to-volume ratios and excellent activities. Here, we report the one-step fabrication of Pt–Cu alloy nanotube arrays. As determined by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, ordered Pt–Cu alloy nanotubes have been successfully fabricated utilizing a nanochannel alumina template. The electrocatalytic activities of the Pt–Cu alloy nanotubes for the oxidation of ethanol in acidic medium were investigated by cyclic voltammetry. The results show that the Pt–Cu alloy nanotubes can be used as effective electrocatalysts for ethanol oxidation in direct alcohol fuel cells.

Direct Electrodeposition of Porous Gold Nanowire Arrays for Biosensing Applications

Nanochannel alumina templates are used as templates for fabrication of porous gold nanowire arrays by a direct electrodeposition method. After modification with glucose oxidase, a porous gold nanowire-array electrode is shown to be an excellent electrochemical biosensor for the detection of glucose. The picture shows an SEM image of a nanowire array after removal of the alumina template by acid dissolution. We report the fabrication of porous gold nanowire arrays by means of a one-step electrodeposition method utilizing nanochannel alumina templates. The microstructure of gold nanowires depends strongly on the current density. The formation of porous gold nanowires is attributed to disperse crystallization under conditions of low nucleation rate. Interfacial electron transport through the porous gold nanowires is studied by electrochemical impedance spectroscopy. Cyclic voltammetric studies on the porous gold nanowire arrays reveal a low-potential electrocatalytic response towards hydrogen peroxide. The properties of the glucose oxidase modified porous gold nanowire array electrode are elucidated and compared with those of nonporous enzyme electrodes. The glucose oxidase modified porous gold nanowire-array electrode is shown to be an excellent electrochemical biosensor for the detection of glucose.

Direct electrodeposition of Pt nanotube arrays and their enhanced electrocatalytic activities

Ordered Pt nanotube arrays have been fabricated by one-step electrodeposition utilizing nanochannel alumina templates. The electro-oxidation of ethanol on Pt nanotube arrays in acidic medium has been investigated by cyclic voltammetry. The oxidation peak currents on the Pt nanotube array electrode for ethanol oxidation are about 1.7 times those on the commercial PtRu/C electrode. The high electrocatalytic activities of the Pt nanotube array towards the oxidation of ethanol made it an excellent platform for direct ethanol fuel cell applications.

Direct electrodeposition of gold nanotube arrays for sensing applications

We report the fabrication of gold nanotube arrays by means of a direct electrodeposition method utilizing nanochannel alumina templates. The observations by SEM and TEM show that gold nanotubes were obtained within the alumina template with different pore diameters. The mechanism related to the morphology formation is discussed. The sensing applications of the gold nanotube arrays have been investigated by using square-wave voltammetry and cyclic voltammetry. The gold nanotube arrays exhibit low-potential electrocatalytic detection of hydrogen peroxide with high sensitivity and show promise for biosensing applications.

Surface spin glass behavior in sol–gel derived La0.7Ca0.3MnO3 nanotubes

We report the fabrication of La(0.7)Ca(0.3)MnO(3) nanotubes (LCMONTs) with a diameter of about 200 nm, by a modified sol-gel method utilizing nanochannel alumina templates. High resolution transmission electron microscopy confirmed that the obtained LCMONTs are made up of nanoparticles (8-12 nm), which are randomly aligned in the wall of the nanotubes. The strong irreversibility between zero field cooling (ZFC) and field cooling (FC) magnetization curves as well as a cusplike peak in the ZFC curve gives strong support for surface spin glass behavior.

Patterning lyotropic liquid crystals as precursors for carbon nanotube arrays

We report on a simple patterning technique using lyotropic liquid-crystal solutions to fabricate organized arrays of high aspect ratio carbon nanostructures. An automated pen writing system is used in conjunction with nanochannel alumina templates to produce ordered arrays of nanotubes and nanofibers in a variety of shapes, widths, and carbon crystal structures set by surface anchoring phenomena. The nanostructure arrays are characterized with optical and electron microscopy and Raman spectroscopy to establish the morphology and crystal structures of the carbon nanoform arrays.

Synthesis and ferroelectric properties of multiferroic BiFeO3 nanotube arrays

We report the synthesis and characterization of ordered multiferroic BiFeO3 (BFO) nanotube arrays. BFO nanotubes with diameters of about 250nm and lengths of about 6μm were fabricated by means of a sol-gel method utilizing nanochannel alumina templates. After postannealing at 700°C, the BFO nanotubes exhibited a polycrystalline microstructure, and x-ray diffraction and transmission electron microscopy study revealed that they are of a perovskite crystal structure. Significant ferroelectric and piezoelectric characteristics of BFO nanotubes have been demonstrated by means of piezoresponse force microscopy measurement.

Site-controlled InAs quantum dots on GaAs patterned using self-organized nano-channel alumina template

Nano-pore arrays on GaAs by templated anodization of GaAs through a nano-channel alumina (NCA) membrane are reported for the first time. The NCA is formed by anodization of single-crystal aluminum grown epitaxially on a GaAs substrate. The anodization is continued into the GaAs underneath the NCA, which is anodized only at the pore bottoms of the NCA. After removal of the NCA, the nanostructured GaAs obtained is studied using scanning electron microscopy. The obtained nano-pores are 30–50 nm deep and spaced ∼100nm apart. Site-controlled InAs self-assembled quantum dots are demonstrated by regrowth on this nanostructured GaAs.

Synthesis and characterization of highly ordered BiFeO3 multiferroic nanowire arrays

Abstract We report the synthesis and characterization of multiferroic BiFeO 3 (BFO) nanowires. The perovskite BFO nanowires with diameters about 60 nm and lengths about 10 μm were fabricated by means of the sol-gel method utilizing nanochannel alumina templates with post annealing at 700 °C. The microstructure of the BFO nanowires was investigated by means of x-ray diffraction and transmission electron microscopy, and the ferroelectric characteristic of BFO nanowires were demonstrated.

Analysis of magnetic interaction in Ni nanowire array grown using electrodeposition process

Simulation and comparison of magnetic properties were performed on three types of Ni nanowire arrays grown by electrodeposition using commercial nano channel alumina (NCA) templates with nominal pore sizes of 200, 100 and 20nm. Experimental observations on the structural behaviour of the nanowires grown inside the pores of NCA templates show that the magnetic interaction depends on the effective pore diameter and the interpore distance. A numerical simulation model based on micromagnetic calculations using object-oriented micromagnetic computing framework (OOMMF) has been developed and reported experimental results on coercivity of Ni nanowires generally agreed with the simulated ones.

Fabrication and magnetic behavior of Co–Ni nanowire arrays with small diameters

Ultra small Co–Ni nanowires with 8 nm diameters have been successfully fabricated within nanochannel alumina templates. The nanowires possess an FCC structure, and the axes of the nanowires are orientated along the [1 1 0] direction. The nanowires show strong temperature-dependent magnetic behavior. The coercivity in these nanowires increases greatly with decrease in temperature, and has T 1/2 dependence. A coercivity as high as 2529 Oe has been obtained at 5 K.

Synthesis and piezoresponse of highly ordered Pb(Zr0.53Ti0.47)O3 nanowire arrays

We report the synthesis and characterization of ferroelectric lead zirconate titanate Pb(Zr0.53Ti0.47)O3 (PZT) nanowires. The PZT nanowires, with diameters of about 45nm and lengths of about 6μm, were fabricated by means of a sol-gel method utilizing nanochannel alumina templates. After postannealing at 700°C, the PZT nanowires exhibit a polycrystalline microstructure, and x-ray diffraction and transmission electron microscopy study revealed their perovskite crystal structure. The piezoelectric characteristics of individual PZT nanowires were demonstrated by piezoresponse force microscopy.

Growth of Au-catalyzed ordered GaAs nanowire arrays by molecular-beam epitaxy

Ordered gallium arsenide (GaAs) nanowires are grown by molecular-beam epitaxy on GaAs (111)B substrates using Au-catalyzed vapor–liquid–solid growth defined by nanochannel alumina (NCA) templates. Field-emission scanning electron microscope images show highly ordered nanowires with a growth direction perpendicular to the substrate. The size (i.e., diameter) distribution of the wires is drastically narrowed by depositing the gold catalyst through an NCA template mask; this narrows the size distribution of the gold dots and arranges them in a well-ordered array, as defined by the NCA template. The nanowire diameter distribution full width at half maximum on the masked substrate is 5.1 nm, compared with 15.7 nm on an unmasked substrate.

Thickness and pore size dependence of coercivity for nanonetwork of iron produced by template synthesis

In this article we have studied thickness and pore size dependence of coercivity in iron films over the thickness range 1.875–45 nm at which Néel-type domain wall dominates. Nanonetwork of iron films were sputter deposited on commercial nanochannel alumina templates with nominal pore diameters of 20, 100, and 200 nm. Continuous films deposited on conventional glass substrates have also been studied in order to understand the effect of porosity on an otherwise nonporous film. While nanonetworks showed expected higher coercivity values than their continuous counterpart, it was found that the coercivity for nanonetworks was influenced by the thickness and the effective pore diameter of the deposited iron layer. Coercivity for conventional films on glass followed an inverse power law. For nanonetworks, thickness dependence of coercivity was complex and showed convolutions. An empirical thickness dependence of coercivity is proposed to explain the behavior of the thickness-varying coercivity for the nanonetworks.

Template synthesis of well-graphitized carbon nanotube arrays

Highly ordered freestanding multiwalled carbon nanotube arrays on gold substrate have been fabricated by using hexagonal close-packed nanochannel alumina templates with a cobalt–nickel catalyst. High-resolution transmission electron microscopy images and electron diffraction pattern show that the carbon nanotubes are well graphitized. Raman spectrum shows its weak peak at 1354 cm −1 (D band) and strong peak at 1578 cm −1 (G band). The well-graphitized freestanding carbon nanotubes arrays will have potential applications in lithium-ion battery and other fields.

Highly-ordered carbon nanotube arrays for electronics applications

Highly-ordered arrays of parallel carbon nanotubes were grown by pyrolysis of acetylene on cobalt within a hexagonal close-packed nanochannel alumina template at 650 °C. The nanotubes are characterized by a narrow size distribution, large scale periodicity, and high densities. Using this method ordered nanotubes with diameters from 10 nm to several hundred nm and lengths up to 100 μm can be produced. The high level of ordering and uniformity in these arrays is useful for applications in data storage, field emission displays and sensors, and offers the prospect of deriving computational functions from the collective behavior of symmetrically coupled nanotubes. The fabrication method used is compatible with standard lithographic processes and thus enables future integration of such periodic carbon nanotube arrays with silicon microelectronics.