Porous Anodic Aluminum Oxide Template Research Articles

Parallelly and Normally Surface-Aligned Organic Nanofiber Arrays

Results are presented from a direct comparison of 2,7-diphenylcarbazole (DPC) nanofibers fabricated in the form of parallel to the surface plane aligned arrays by means of organic molecular beam deposition (OMBD) and fabricated in the form of normal to the surface aligned arrays by solution-assisted wetting of porous anodic alumina (PAA) membranes. The former method leads to the formation of mutually aligned needlelike nanoaggregates on muscovite mica substrates, while the latter method allows fabrication of arrays of closely packed upright standing nanofibers. The dimensions of the DPC nanofibers obtained by the OMBD technique depend strongly on the nominal film thickness and on the substrate temperature during deposition. The DPC nanofibers obtained by template wetting possess the same shape and dimensions as those of the pores of the PAA template. All of the obtained nanofibers show strong polarization anisotropy, but the polarization dependent measurements indicate a higher degree of mutual alignment of the DPC molecules in the fibers obtained by OMBD as compared to those obtained by membrane wetting. Temperature dependent fluorescence spectra from the DPC nanoaggregates reveal blue shifts and narrowing of the spectral peaks with decreasing temperature as well as a redistribution of peak intensities.

Effect of High Magnetic Field Annealing on Magnetic Properties of CoFe$_{2}$O$_{4}$ Nanowire Arrays

Cobalt ferrite (CoFe2O4) nanowire arrays with different diameters were prepared in porous anodic aluminum oxide (AAO) template by a sol-gel template method. A magnetic field annealing procedure was performed in the direction along wire axis (out of sample planes) at 600°C under 10-T applied magnetic field to orient the spinel CoFe2O4 crystalline. The morphology was studied by scanning electron and transmission electron microscope. X-ray diffraction (XRD) patterns show that samples performed by the magnetic field annealing procedure have a 〈110〉 texture along the nanowire axis, while those annealed without applied magnetic field show a nonoriented polycrystalline phase of spinel type structure. Vibration sample magnetometer (VSM) test shows the difference between CoFe2O4 nanowire arrays samples annealed with or without applied magnetic field. This difference shows the magneto-crystalline anisotropy with the easy magnetization direction along the nanowire axis, and is caused by the resultant effect of the easy magnetization direction distribution of the crystalline.

Synthesis and magnetic characterization of Co-NiO-Ni core-shell nanotube arrays

Well-aligned Ni and Co-NiO-Ni core-shell nanotube arrays with an average outer diameter of about 200 nm have been synthesized in a porous anodic aluminum oxide (AAO) template by the direct electro-deposition method. The result shows that the nanotubes were polycrystalline phase. Angular dependent coercivity Hc(θ) indicates that the magnetization reversal mechanisms are mainly dominated by the “curling mode” for Ni nanotubes, while a transition from curling to transverse is observed in Co-NiO-Ni core-shell nanotubes at a large angle. A sharp increase in saturated magnetization (Ms) of Ni and Co-NiO-Ni core-shell nanotubes at 5 K was observed, due to dominance of the surface effect. Besides, the existed superparamagnetic nanoparticles also resulted in the increase of Ms for both cases. These structures have potential applications in the novel spintronics device, ultrasmall magnetic media, and other nanodevices.

Optical Properties of Cu Nanocrystalline-OPAA Composite Film

Optically transparent Cu nanocrystalline/OPAA composite film was successfully prepared by electrodepositing Cu into ordered porous anodic alumina (OPAA) template using constant voltage direct current technique. The morphology, structure, linear optical absorption, third-order optical nonlinearity and ultrafast dynamics of the Cu/OPAA composite were characterized by field emission scanning electron microscope (FESEM), transmission electron microscope (TEM). UV-Vis spectrophotometer, Z-scan technique and femtosecond pump-probe experiment. The results show that Cu nanoparicles have diameters of 40–50nm with face center cubic structure and disperse in the branched pores of the OPAA template, which induce a surface plasmon resonance (SPR) absorption at 584 nm. When the probe optical wavelength is far away from the SPR wavelength, Cu nanocrystalline/OPAA composite film possesses a character of light-induced absorption. When the probe optical wavelength is near the SPR wavelength, it possesses a photo-bleaching character. The composite film has a non-resonant third-order nonlinear susceptibility of 0.73×10 esu and a response time of 1.3 ps.

Nanostructure and Chemical Characterisation of Individual NiFe/Pt Multilayer Nanowires

NiFe/Pt multilayer nanowires have been successfully fabricated by pulse electrodeposition into the channels of porous anodic aluminum oxide (AAO) templates, and characterized at the nanoscale. Individual nanowires have uniform structure and regular periodicity. The NiFe and Pt layers are polycrystalline, with random orientation fcc lattice structure crystallites and grain sizes 3-10 nm, and the average layer growth rate is 30 nm/s for NiFe and 4 nm/s for Pt. Nanoscale chemical analysis of individual NiFe/Pt nanowires by EDX and EELS shows that they contain alternating NiFe and Pt layers, with a small approximately 1% inclusion of Pt in the NiFe layer due to electrochemical co-deposition.

Electrodepositing fabrication and microstructures of the Fe nanowires with a preferred orientation

Highly ordered Fe nanowire arrays with 〈 1 1 0 〉 preferred orientation were fabricated out successfully by direct current electrodepositing into the pores of a porous anodic aluminum oxide template. The formation mechanism of Fe nanowires was ascertained by X-ray diffraction and transmission electron microscopy. Low index surface energy of Fe nanowires was calculated by means of broken-bond model. For Fe nanowire arrays, its aspect ratio ( h/ d) of the “circular cylinder” is less than 0.75, the {1 1 0} planes have the lowest surface energy. And authors deal with a reasonable explanation for Fe nanowires growth along with 〈 1 1 0 〉 preferred orientation using the two-dimensional nucleation theory.

Monitoring the Thermal Elimination of Infiltrated Polymer from AAO Templates: An Exhaustive Characterization after Polymer Extraction

Porous anodic aluminum oxide (AAO) templates have been demonstrated to be an easy way to prepare one-dimensional polymeric nanostructures by polymer infiltration into the nanopores. The opportunity to reuse the AAO templates significantly reduces the cost and time of production. Through treatment of infiltrated polyethylene oxide (PEO) into AAO templates at 450 °C, we were able to remove the entire polymer from the pores of templates. The completely elimination of PEO is confirmed by confocal Raman spectroscopy, wide-angle X-ray diffractometry (WAXD), and thermogravimetric analysis (TGA). This methodology can have wider application, since the adhesion coefficient is not as an important issue as it was in mechanical methods reported in the literature, and, therefore, it reduces cost and time significantly.

Superparamagnetic behavior in cobalt iron oxide nanotube arrays by atomic layer deposition

Cobalt iron oxide nanotube arrays with various wall thicknesses were prepared by atomic layer deposition in porous anodic alumina template. Nanotubes uniform in thickness and homogeneous in composition can be obtained with aspect ratios on the order of 50. These nanotubes have a polycrystalline spinel structure. Both the mean grain size and the grain size distribution increase with the tube wall thickness. Correspondingly, their magnetic properties (remanence and coercive field) also have a strong dependence on the thickness for measurements carried out at 300 K. This dependence is attributed to the superparamagnetic behavior of the grains that constitute the nanotube.

GaN-based light-emitting diodes with photonic crystals structures fabricated by porous anodic alumina template

In this paper, we propose and demonstrate a convenient and flexible approach for preparation large-area of photonic crystals (PhCs) structures on the GaN-based LED chip. The highly-ordered porous anodic alumina (AAO) with pitch of wavelength scale was adopted as a selective dry etching mask for PhCs-pattern transfer. The PhCs with different pore depths were simultaneously formed on the entire surfaces of GaN-based LED chip including ITO, GaN surrounding contacts and the sidewall of the mesa by one-step reactive ion etching (RIE). The light output power improvement of PhCs-based GaN LED was achieved as high as 94% compared to that of the conventional GaN-based LED.

Over 95% of large-scale length uniformity in template-assisted electrodeposited nanowires by subzero-temperature electrodeposition

In this work, we report highly uniform growth of template-assisted electrodeposited copper nanowires on a large area by lowering the deposition temperature down to subzero centigrade. Even with highly disordered commercial porous anodic aluminum oxide template and conventional potentiostatic electrodeposition, length uniformity over 95% can be achieved when the deposition temperature is lowered down to -2.4°C. Decreased diffusion coefficient and ion concentration gradient due to the lowered deposition temperature effectively reduces ion diffusion rate, thereby favors uniform nanowire growth. Moreover, by varying the deposition temperature, we show that also the pore nucleation and the crystallinity can be controlled.

A comparative study on the hydrogen absorption of thin films at room temperature deposited on non-porous glass substrate and nano-porous anodic aluminum oxide (AAO) template

The influence of different morphology of the thin films deposited on the non-porous glass and nano-porous anodic aluminum oxide (AAO) substrates on the hydrogen absorption at room temperature was studied. A well-known sandwich-like Pd/Mg/Pd film was investigated. It is observed that the film deposited on the porous AAO template demonstrates a better hydrogen absorption in the H 2 pressure range 10–600 mbar with respect to the same film supported by the non-porous glass substrate. Moreover, the layer grown on the AAO, owing to its specific morphology inherited from the nano-porous substrate, has revealed its resistance toward stress accumulation caused by the lattice expansion, showing no buckle-to-crack network formation upon the hydrogen uptake. This interesting feature is expected to improve the cycling properties and structural stability of the system, and may help to investigate better the interaction of the H 2 with metal.

Tribological properties of nano-porous anodic aluminum oxide template

A highly ordered porous alumina template with pores of 45 nm in diameter was synthesized by a two-step electrochemical anodizing process. The influence of pore-enlargement treatment on the porous structure and tribological properties of the film was investigated, and ultrasonic impregnation technology was applied on it to form self-lubricating surface. The structure of the self-lubricating film and its tribological properties were investigated in detail. It can be concluded that the optimum time of pore-enlargement treatment is 20 min. The diameter of the pores and the surface porosity of the film are about 70 nm and 30%, respectively, while the film maintains the property of its high hardness. Under the same friction condition, the frictional coefficient of the self-lubricating film is 0.18, much lower than that of the anodic aluminum oxide template, which is 0.52. In comparison with the lubricating surface of non-porous dense anodic aluminum oxide template, the lubricating surface fabricated by the ultrasonic impregnation method on the porous anodic aluminum oxide template keeps longer period with low friction coefficient. SEM examination shows that some C60 particles have been embedded in the nanoholes of the anodic aluminum oxide template by the ultrasonic impregnation technology.

Room temperature device performance of electrodeposited InSb nanowire field effect transistors

InSb nanowires have been formed by electrodeposition in porous anodic alumina templates and employed as transistor channels. The 100 nm diameter nanowires had a zinc blende crystal structure. Single-nanowire field-effect transistors (NW-FETs) with a channel length of 500 nm exhibited on-currents of ∼40 μA, on/off ratios of ∼16–20, drain conductances of ∼71 μS and field-effect electron mobility of ∼1200 cm2 V−1 s−1. Compared with reported NW-FETs, the on-current is large and the current saturation occurs at low source-drain voltages. These characteristics can be understood in terms of velocity saturation effects with enhanced scattering.

Effect of aspect ratio on microstructure and magnetic properties of spinel CoFe2O4 nanowire arrays

Cobalt ferrite (CoFe2O4) nanowire arrays with different diameters were prepared in porous anodic aluminum oxide (AAO) template by a sol-gel template method with the assistance of organic solvent and surfactant. The morphology was studied by scanning electron and transmission electron microscopy. A polycrystalline phase of spinel type structure was ascertained by X-ray diffraction (XRD) patterns. A magnetic test was performed using a physical property measurement system (PPMS), showing the uniaxial anisotropy with easy axis along the nanowire with an aspect ratio larger than 1000. A coercivity reduction from about 1500 Oe to about 800 Oe has been observed, while the diameter increases from 20 nm to 50 nm in this experiment. The cause of this has been discussed.

Synthesis and characterization of high density and high aspect ratio Ag2S nanoparticle nanowires from a paired cell method

Ag2S nanoparticle nanowires were prepared in a porous anodic aluminum oxide template by a simple paired cell method, and were characterized by XRD, FESEM, HRTEM and EDS. The results showed that the as-prepared nanowires were composed of monoclinic Ag2S nanoparticles. The nanowire diameters ranged from 165 to 270 nm, and Ag2S nanoparticles were nearly spherical with diameters of 40 to 60 nm. The paired cell method is simple, low cost and easy to control for the fabrication of high density and high aspect ratio Ag2S nanoparticle nanowires. A formation mechanism for the nanoparticle nanowires was suggested.

Transforming the Fabrication and Biofunctionalization of Gold Nanoelectrode Arrays into Versatile Electrochemical Glucose Biosensors

High-density arrays of conducting nanoelectrodes (i.e., nanoelectrode arrays [NEAs]) have been developed on the surface of a single electrode for numerous electrochemical sensing paradigms. However, a scalable fabrication technique and robust biofunctionalization protocol are oftentimes lacking and thus many NEA designs have limited efficacy and overall commercial viability in biosensing applications. In this report, we develop a lithography-free nanofabrication protocol to create large arrays of Au nanoelectrodes on a silicon wafer via a porous anodic alumina template. To demonstrate their effectiveness as electrochemical glucose biosensors, alkanethiol self-assembled monolayers (SAMs) are used to covalently attach the enzyme glucose oxidase to the Au NEA surface for subsequent glucose sensing. The sensitivity and linear sensing range of the biosensor is controlled by introducing higher concentrations of long-chain SAMs (11-mercaptoundecanoic acid: MUA) with short-chain SAMs (3-mercaptopropionic acid: MPA) into the enzyme immobilization scheme. This facile NEA fabrication protocol (that is well-suited for integration into electronic devices) and biosensor performance controllability (via the mixed-length enzyme-conjugated SAMs) transforms the Au NEAs into versatile glucose biosensors. Thus these Au NEAs could potentially be used in important real-word applications such as in health-care and bioenergy where biosensors with very distinct sensing capabilities are needed.

Molecular composition distribution of polycarbonate/polystyrene blends in cylindrical nanopores

Polycarbonate/polystyrene (PC/PS) blend nanorods with various diameters were prepared by melt-wetting porous anodic aluminum oxide templates with partially miscible blend melts. The molecular composition distribution of PC/PS blend polymers inside nanoporous templates of varying diameters was investigated by scanning electron microscopy, Fourier transform infrared and differential scanning calorimetry. A gradient composition distribution of the polymer blends formed in the nanopores owing to the difference in viscosity between the two polymers during capillary flow. The PC content of the nanorods increased from top to bottom along the long axis of the rods but decreased with rod diameter owing to stronger confinement by the nanopores. Polycarbonate/polystyrene (PC/PS) blend nanorods with various diameters were prepared by melt-wetting porous anodic aluminum oxide templates with partially miscible blend melts and the molecular composition distribution of PC/PS blends in various diameter nanopores was investigated by scanning electron microscopy, Fourier transform infrared and differential scanning calorimetry. Owing to the difference in viscosity between the two polymers during the capillary flow, gradient composition distribution of polymer blends was formed in nanopores.

Nanocomposite carbon material with ordered structure synthesized using porous aluminum oxide

The synthesis of nanocomposite carbon material with an ordered structure in a porous anodic aluminum oxide template is considered. A template with a highly ordered structure provides the formation of an array of aligned carbon tubes with high aspect ratios (higher than 1000) in polycrystalline anodic aluminum oxide. The obtained material is studied using scanning and transmission electron microscopy, Raman scattering spectroscopy, Auger electron spectroscopy, and infrared and X-ray photoelectron spectroscopy.

Preparation and magnetic properties of hard-magnetic (CoPt)/soft-magnetic (FeCo) composite nanocable array

An array of hard-magnetic (CoPt)/soft-magnetic (FeCo) composite nanocable has been fabricated in the pores of porous anodic aluminum oxide templates: CoPt nanotubes were first prepared by high temperature chemical reduction method; FeCo alloy was then electrodeposited into the CoPt nanotubes. The morphology and structure of the nanocable array were characterized by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The magnetic measurements showed that two apparent kinks appear in the hysteresis loop after the FeCo alloy was deposited into the CoPt nanotubes, which may be attributed to the hard-magnetic phase being partly or even completely decoupled from the soft-magnetic phase.

Tribological effects of pores on an anodized Al alloy surface as lubricant reservoir

Porous anodic alumina (PAA) templates having three kinds of nanometer pores were manufactured to investigate the effects of pores on an anodized aluminum surface as lubricant reservoir. Ball-on-disk wear tests of the PAA templates were carried out in the three types of lubrication conditions. The PAA templates submerged under water for 30 min showed lower friction coefficient and longer transition time to steady state compared to those that were not submerged. Pores act as a lubricant reservoir because the water stored inside the pore is released to the surface due to elastic–plastic deformation. However, the effect of oxide layer developed by tribochemical reaction on the surface is greater than lubricant reservoir effect of the pore. In particular, the submerged PAA templates with 260 nm pores under dry lubricant condition formed more hydroxide layers than other cases, which resulted in the decrease in friction.