Nanoporous Alumina Templates Research Articles

Non-lithographic Nanofabrication Using Porous Alumina Membranes

ABSTRACTWe describe a fabrication method to prepare highly ordered Si nanopore arrays. A nanoporous alumina template of thickness ∼1μm is prepared by means of anodization of an aluminum film. The template has a highly ordered hexagonal array of pores of diameter ∼50nm. The template is detached from the aluminum layer and placed on a Si substrate. The nanoporous pattern is transferred onto silicon substrate by means of a dry plasma etch process. This produces an array of nanopores in silicon with a diameter of ∼50nm and depth of ∼300nm. We have used such an array to prepare Fe nanopillars inside the pores by means of thermal evaporation. Magnetization versus applied magnetic field measurements for the Fe nanoarrays, demonstrate large perpendicular anisotropy typical of high aspect ratio magnetic nanopillars. The value of coercivity is about 500Oe in the perpendicular direction and 40Oe in the parallel direction.

Synthesis and Characterization of Extremely Uniform Fe-Co-Ni Ternary Alloy Nanowire Arrays

We have fabricated extremely uniform arrays of polycrystalline Fe-Co-Ni ternary alloy nanowires having composition Fe 12.3 wt.%, Co 43.9 wt.% and Ni 43.8 wt.%. The wires are made by electrodeposition into nanoporous alumina templates, using an electrodeposition voltage of 15 V at 1000 Hz. Nanowires have been fabricated having diameters ranging from 43 nm to 120 nm, and lengths of 3 microm to 7 microm, as dependent upon template topology. The magnetization easy axis lies along the nanowire length, with an easy axis coercivity of 72 kA/m.

EDLC characteristics of CNTs grown on nanoporous alumina templates

Carbon nanotubes (CNTs) with uniform diameter were grown on the porous alumina templates. Well ordered nanoporous alumina templates for the growth of CNTs were fabricated by two-step anodization method in oxalic acid electrolyte. The diameter and length of pores of the porous alumina templates were ca. 90 nm and 2 μm, respectively, and the pore density was about ~10 10 pores/cm 2. The barrier layer at the bottom of the cylindrical pore was thinned and dissolved away by the voltage drop treatment and the pore widening processes, sequentially. For EDLC applications, aluminium metal substrate below the porous alumina layer can work directly as the conductive electrode. The EDLC characteristics were examined by measuring the capacitances from both the charge–discharge curves and cyclic voltammograms. The specific capacitance of CNT electrodes was 49 ± 3 F/g. The CNTs grown uniformly on the well ordered nanoporous templates resulted in the enhanced specific capacitances.

Plasma Etching Transfer of a Nanoporous Pattern on a Generic Substrate

We describe a nonlithographic nanofabrication method for creating a nanoporous pattern on any substrate. The approach utilizes plasma etching through a nanoporous template to transfer the pore pattern onto the substrate. We demonstrate this method to transfer a porous alumina pattern consisting of a hexagonal array of 50 nm diam pores onto an aluminum layer. A nanoporous alumina template (0.6 μm) is initially created by electrochemical anodization of an aluminum film (1 μm) deposited on a substrate. Controlled plasma etching is then used to etch through the pores onto the aluminum layer below the pores. In this manner, we demonstrate the hexagonal array of 50 nm diam pores in the aluminum film. © 2004 The Electrochemical Society. All rights reserved.

Anodization Behavior of Al Film on Si Substrate With Different Interlayers for Preparing Si-Based Nanoporous Alumina Template

Anodization Behavior of Al Film on Si Substrate With Different Interlayers for Preparing Si-Based Nanoporous Alumina Template

Anodization Behavior of Al Film on Si Substrate With Different Interlayers for Preparing Si-Based Nanoporous Alumina Template

The fabrication and applications of porous anodic alumina (PAA) have been studied for decades. Recently, preparation of PAA template directly formed on Si has been developed to enhance the performance of the fabricated nanostructures. However, less attention is paid to the anodization mechanism of the Al film on the Si substrate. In the current study, the PAA template was fabricated on Si of which an interlayer was sandwiched between the Al film and the Si substrate. The anodization behavior of the Al film, especially at the alumina–substrate interface, was investigated through the observation of the variation of oxidation current and the structural change of alumina. Different degree of dissolution at the pore base of alumina was revealed when a different interlayer was introduced, leading to the formation of the arched pore bottom. At the same time, difference in the variation of current was also observed as the pore base reached the alumina–Si interface. These features were different from those observed in conventional anodization of Al foils. The findings in this study are of scientific and technological importance for the template-mediated growth of nanostructures, especially for those to be integrated into Si devices.

Magnetic Manipulation of Copper−Tin Nanowires Capped with Nickel Ends

CuSn alloy nanowires capped with Ni were prepared using sequential electrodeposition of nickel and a copper/tin bronze alloy into nanoporous alumina templates. The liberated nanowires were suspended in solvents and their behavior monitored using optical microscopy. The nanowires were oriented and spun in circles as “nano stirbars” using applied magnetic fields. These segmented nanowires were also trapped between magnetized Ni stripes, demonstrating that nonmagnetic metallic nanowires can be manipulated and positioned by capping them with magnetic ends.

Improved EDLC Characteristics of the CNTs Grown on the Nanoporous Alumina Templates

AbstractThe specific capacitance of the carbon nanotube (CNT) electrode can be increased by using nanoporous alumina templates with the high pore density and the small and uniform pore diameter. The surface area of the CNTs was controlled and increased by preparing them with uniform diameters. The well-ordered nanoporous alumina templates were fabricated by a two-step anodization method. The cylindrical pore diameter, length, and density of the template utilized for the CNT growth was 53 ± 1 nm, 2 μm, and 3.1×1010 cm−2, respectively. The CNTs with uniform diameter of 44 ± 2 nm were grown on the porous alumina template as electrode materials for the electric double-layer capacitor (EDLC). The EDLC characteristic of the CNT electrodes was examined by measuring the capacitances from the cyclic voltammograms. The specific capacitance of the CNT electrodes can be increased to the value of 121 ± 5 F/g.

Electrodeposition of Cu[sub 2]O Nanowires Using Nanoporous Alumina Template

We first electrodeposited highly ordered Cu 2 O nanowires using a home-made alumina template. Home-made nanoporous alumina templates were prepared by a two-step anodization method and selective removal of aluminum substrate by bromine solution. Chronopotentiometry (i.e., constant current method) of -0.5 mA/cm 2 was applied to deposit compact Cu 2 O nanowires without disconnection into the honeycomb shaped pores of a home-made nanoporous alumina membrane. Analyzing morphological observations by scanning electron microscopy and transmission electron microscopy, we observed that the diameter of Cu 2 O nanowire was ca. 57 nm and the length was 4 μm demonstrating an aspect ratio of 70. X-ray diffraction structural analysis indicated that Cu 2 O(200) was preferentially formed compared with other Cu 2 O crystalline phases which may be due to an adjusted solution pH 9.

Novel magnetic materials prepared by electrodeposition techniques: arrays of nanowires and multi-layered microwires

The fabrication process by electrodeposition routes and the study of general magnetic properties is reported for two types of nanostructured magnetic materials: (a) nickel-filled highly-ordered nanoporous alumina templates, and (b) electrodeposited Ni layers onto glass coated amorphous microwires. Arrays of Ni nanowires, about 30 nm in diameter and separated by about 100 nm, are obtained by electrodeposition into the pores of alumina membranes prepared by two-steps anodization process from highly pure aluminum substrates. Morphological studies have been performed by high resolution scanning electron microscopy (HRSEM). The study includes the optimization of preparation parameters and the magnetic characterization of the hexagonally arranged nanowire arrays, i.e. the influence of the pore diameter and the interwire distance on the coercivity of the whole nanowire array. On the other hand, multi-layered magnetic microwires have been prepared in the following sequence: a nanometric Au coat is first sputtered onto Pyrex coated FeSiB amorphous microwires followed by electrodeposition of a 500 nm thick Ni external cover. While in as-cast microwires the hysteresis loop is squared shaped (magnetic bistability), in the case of the multilayer microwire, a transverse magnetic anisotropy is induced when reducing the measuring temperature as a consequence of the stresses induced by the different thermal expansion coefficients of the various layers.

Magnetotransport properties of bent ferromagnetic nanowires

Magnetotransport measurements were performed on individual multisegmented Pt–Ni–Pt nanowires fabricated by electrochemical deposition in nanoporous alumina templates. The nanowires were removed from the template, and precipitated onto substrates from liquid suspension. The Pt end segments provide an oxide-free interface to the magnetic central segment of interest. Centrifugation prior to precipitation induces sharp bends in the nanowires. The angular dependence of the magnetoresistance of both straight and bent nanowires was used to observe domain switching. The magnetic response of straight nanowires is well described by the curling model of domain reversal. In the case of the bent nanowires, the general behavior of each individual straight segment is also consistent with this model, but evidence for interactions between the segments is also observed.

Magnetization reversal of individual Fe nanowires in alumites studied by magnetic force microscopy

We have studied the magnetization reversal of two-dimensional (2D) arrays of parallel ferromagnetic Fe nanowires in nanoporous alumina templates. Combining bulk magnetization measurements using a superconducting quantum interference device with field-dependent magnetic force microscopy (MFM), we decomposed the macroscopic hysteresis loop in terms of irreversible magnetic responses of individual nanowires. The field-dependent MFM provides a microscopic method by which to obtain the hysteresis curve by registering the fraction of upward and downward magnetized wires for each field. The nanowire system proves to be an excellent example of the 2D classical Preisach model, well-known from the field of hysteresis modeling and micromagnetism.

Magnetization reversal of ferromagnetic nanowires studied by magnetic force microscopy

The magnetization reversal of two-dimensional arrays of parallel ferromagnetic Fe nanowires embedded in nanoporous alumina templates has been studied. By combining bulk magnetization measurements (superconducting quantum interference device magnetometry) with field-dependent magnetic force microscopy (MFM), we have been able to decompose the macroscopic hysteresis loop in terms of the irreversible magnetic responses of individual nanowires. The latter are found to behave as monodomain ferromagnetic needles, with hysteresis loops displaced (asymmetric) as a consequence of the strong dipolar interactions between them. The application of field-dependent MFM provides a microscopic method to obtain the hysteresis curve of the array, by simply registering the fraction of up and down magnetized wires as a function of applied field. The observed deviations from the rectangular shape of the macroscopic hysteresis loop of the array can be ascribed to the spatial variation of the dipolar field through the inhomogeneously filled membrane. The system studied proves to be an excellent example of the two-dimensional classical Preisach model, well known from the field of hysteresis modeling and micromagnetism.

WS-04 Nanotechnology Advances & Applications in Information Storage

A brief review of some applications of nanotechnology to information storage is given with the focus on self-assembled nanoporous alumina templates for patterned media. Ordered nanoporous alumina templates were fabricated by self-assembly technology. A two-step anodization process was also carried out to obtain templates with straight pores without removing the aluminum and barrier layer. Polycrystalline structure was observed with a grain size of about two micrometers in which the pores were almost perfect hexagonally ordered. The pore arrays exhibit different orientation along the boundaries of neighboring grains. Nanopatterning implemented by electron-beam lithography demonstrates a potential for writing concentric circular patterns with linewidths as small as 30nm.

Formation of organometallic polymer nanorods using a nanoporous alumina template and the conversion to magnetic ceramic nanorods.

Polyferrocenylsilane nanorods were prepared using a porous anodic aluminium oxide template followed by chemical etching; pyrolysis was used to obtain magnetic iron oxide-containing ceramic nanorods.

Synthesis and characterization of CdS particles within a nanoporous aluminum oxide template

Anodically grown porous aluminum oxide was used as a template in which to study the growth of CdS. The pores in this template are cylinders 50 nm in diameter by 30 μm in length. CdS was grown from aqueous solutions by a U-tube method were reagents entered the pores from opposite ends. The resulting semiconductor particles' size, shape, crystallinity, composition, and optical properties were characterized by transmission electron microscopy (TEM), electron diffraction, energy dispersive X-ray microanalysis (EDX), and UV-visible spectroscopy. Polycrystalline oval particles with sizes on the order of tens of nanometers formed within the pores of the template. These particles did not extend throughout the entire pore but grew in only one area of the pore. The structures, size distributions, and possible mechanisms for the formation of these nanoclusters is discussed.