Porous Anodic Aluminum Oxide Template Research Articles

Single-crystal silver nanowires: Preparation and Surface-enhanced Raman Scattering (SERS) property

Ordered Ag nanowire arrays with high aspect ratio and high density self-supporting Ag nanowire patterns were successfully prepared using potentiostatic electrodeposition within the confined nanochannels of a commercial porous anodic aluminium oxide (AAO) template. X-ray diffraction and selected area electron diffraction analysis show that the as-synthesized samples have preferred (220) orientation. Transmission electron microscopy and scanning electron microscopy investigation reveal that large-area and ordered Ag nanowire arrays with smooth surface and uniform diameter were synthesized. Surface-enhanced Raman Scattering (SERS) spectra show that the Ag nanowire arrays as substrates have high SERS activity.

Selective Wet-Chemical Etching of the Barrier Layer during Formation of Porous Anodic Aluminum Oxide Template

A porous anodic aluminum oxide (AAO) template with a TiN bottom electrode was fabricated on a substrate. The anodizing process ended up stably with the formation of pillars penetrating the barrier layer, and the pillars were selectively and uniformly removed using standard clean-1 solution . Ru nanowires were fabricated in the AAO nanochannels with an aspect ratio of 10:1 by an atomic layer deposition process using as a precursor and as a reducing agent. The contact between Ru nanowires and a TiN bottom electrode was confirmed by a transmission electron microscope. The current–voltage characteristic of each Ru nanowire through the TiN bottom electrode was resolved by a conductive atomic force microscope, which showed the uniform ohmic behavior of the contact with a resistance of as low as per single Ru nanowire. The stable wet-chemical route to the selective and uniform removal of the barrier layer of the AAO template was applied to devices that require a good electrical connection to nanowires with high aspect ratios, such as sensors, batteries, or optoelectronic devices.

Synthesis and characterization of highly-ordered barium-strontium titanate nanotube arrays fabricated by sol—gel method

Highly uniformed barium-strontium titanate nanotube arrays were fabricated using a porous anodic aluminum oxide template from a barium-strontium titanate sol—gel solution. Electron microscope results showed that nanotubes with uniform length and diameter were obtained. The diameters and lengths of these nanotubes were dependent on the pore diameter and the thickness of the applied anodic aluminum oxide template. High resolution transmission electron microscopy and the selected-area electron diffraction pattern investigations demonstrated the perovskite structure and the polycrystalline of the fabricated barium-strontium titanate nanotubes. The characterization of the electrical and dielectric properties had also been made. Compared to thin film material, the intrinsic leakage current density is almost the same. Besides, at 30 ?C, the dielectric constant and dielectric loss of the fabricated nanotube is 80 and 0.027 at 1 MHz respectively.

Growth of copper-indium nanorods on Si substrate using porous anodic alumina as template

Copper-indium nanorod arrays have been synthesized by electrodeposition using porous anodic alumina nano template supported on a silicon substrate. Porous anodic alumina template was fabricated by evaporating aluminium film onto silicon substrate and then anodizing the aluminium film in diluted phosphoric acid. The approach employs a plasma etching to penetrate the alumina pore barrier layer before electrodeposition, which enables direct electrical and chemical contact with the silicon substrate electrode. The resulting template and copper-indium nonorods obtained were characterized using scanning electron microscopy (SEM) and energy-dispersived X-ray spectroscopic analyzer (EDS), the pores of alumina are found to have dimensions of 150–250 nm pore diameters and 330–510 nm pore spacings, partial filling of the pores of the alumina template by Cu-In is achieved. The results of this work reveal that the alumina nano template is particularly well suited to the etching mask and template-assisted growth of nanostructures to be integrated into rigid substrate.

Preparation and Characterization of Ordered Pb(Zr<sub>0.53</sub>Ti<sub>0.47</sub>)O<sub>3</sub> Nanotube Arrays by Sol-Gel Template Method

Ferroelectric lead zirconate titanate Pb(Zr0.53Ti0.47)O3 (PZT) nanotubes were prepared using porous anodic aluminum oxide (AAO) template by means of a simple sol-gel method. Scanning electron microscope (SEM) showed that closely packed PZT nanotubes were synthesized with a high pore-filling rate and aspect ratio after annealing at 700 °C. The X-ray diffraction investigations revealed that the annealed PZT nanotubes exhibit a polycrystalline microstructure and were composed of perovskite crystal structure. The results of polarization hysteresis and piezoresponse force microscope (PFM) measurements showed typical piezoelectricity in PZT nanotubes as well as stable electrical properties revealed by leakage current measurement, indicating potential applications using ferroelectric one-dimension nanostructures.

PREPARATION AND PHOTOLUMINESCENCE PROPERTIES OFNdVO4NANOTUBES IN AAO TEMPLATE

Porous anodized aluminum oxide (AAO) template was combined with sol-gel method in this work for the fabrication of high-ordered NdVO4nanotube arrays. The diameter, length, and wall thickness of the nanotubes can be adjusted conveniently. The sample was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), absorption spectra, and photoluminescence spectra. The results show that these uniformly distributed, high-ordered, and parallel nanotubes have great light emission in both the visible region and near-infrared region due to their corresponding energy level transitions. With this method, future application of rare-earth hollow nanostructures will be widely extended.

Electrodeposition of tubular-rod structure gold nanowires using nanoporous anodic alumina oxide as template

One-dimensional tubular-rod structure gold nanowires have been prepared using electrodeposition method at constant current mode with confined nanochannels of porous anodic aluminum oxide template. The reduction mechanism of gold ions and formation process of tubular-rod structure gold nanowires are studied. Electron microscopy results show that the tubular-rod structure gold nanowires transform to solid nanorods when the electrodeposition time is long enough. The tubular-rod structure gold nanowires have an average diameter of 180 nm, which coincide with the diameter of the template used. X-ray diffraction results confirm that the tubular-rod structure gold nanowires are crystalline structure.

Synthesis and characterization of Bi 3.15Nd 0.85Ti 3O 12 nanotube arrays

Nd-substituted bismuth titanate (Bi 3.15Nd 0.85Ti 3O 12, BNT) nanotube arrays are fabricated by means of a sol–gel method utilizing porous anodic aluminum oxide (AAO) template. The morphologies and structures have been determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The diameter and length of these nanotubes are about 200 nm and 60 μm, respectively, and their wall thickness is about 30 nm. The average grain size is around 40 nm. XRD data show that the BNT nanotubes possess bismuth-layered perovskite structure. High-resolution electron microscopy (HRTEM) image demonstrates that the BNT nanotubes are polycrystalline. Polarization–electric field ( P– E) response curves of BNT nanotube arrays were measured, and a size induced polarization reduction phenomenon is observed.

Self-supporting nanowire arrays templated in sacrificial branched porous anodic alumina for thermoelectric devices

Templated synthesis of thermoelectric nanowires in porous anodic alumina (PAA) have potential for enhanced performance relative to bulk materials. A significant challenge is the template material, which can serve as a thermal shunt. In this work, an approach for creating a branched PAA template is described. The process utilizes localized self-heating to destabilize the planar anodization front, yielding branched and interconnected pores growing at a rate of 300 μm/h. The template is selectively etched after electrodeposition of desired materials, yielding self-supporting nanowire arrays with thicknesses up to about 300 μm, thereby eliminating the thermal shunt through the template.

CRYSTALLIZATION AND ORIENTATION OF POLYETHELENE IN ANODIC ALUMINUM OXIDE TEMPLATES

Recently structure and morphology of polymers under nanoscale confinements have attracted much attention.For semicrystalline polymer materials,the degree of crystallinity and the orientation of the crystalline domains are important factors in controlling their physical properties,and many efforts have been devoted to the understanding of crystallization and orientation of polymers in nano-cylindrical confinements.In this paper,polyethylene nanofibers of 200 nm diameter were prepared by infiltrating porous anodic aluminum oxide(AAO)templates with polymer melt,and the crystallinity and orientation of polyethylene crystals in the nanofibers were studied by FTIR spectroscopy,polarized light microscopy(PLM),and X-ray diffraction(XRD).FTIR results showed that the degree of crystallinity in the nanofibers was lower than that in the bulk due to the confinement of the nanopores,and the crystals formed in the nanofibers oriented preferentially with the b axis aligning parallel to the axial direction of the nanofibers,while the a axis was perpendicular to the nanofiber direction.XRD data further confirmed that the b axis of the crystals was parallel to the fiber direction.It was found that the nuclei located mainly at the interface between the nanotemplate and the polymer bulk and radially grew with the fastest crystallographic growth direction(b axis)toward the bulk and the nanofibers.The crystals formed in the bulk were typical banded spherulites,while in the nanofibers,only the crystals with the growth directions compatible with the cylindrical confinement imposed by the pore geometry can grow bigger,and other growth directions were suppressed,leading to the preferred orientation of the crystals with the b axis aligning along the nanofiber direction.

Vertical Carbon Nanotube Devices With Nanoscale Lengths Controlled Without Lithography

Vertical single-walled carbon nanotubes (v-SWCNTs) are synthesized within highly ordered porous anodic alumina (PAA) templates supported on Si substrates. A process for obtaining thin-film PAA with long-range ordered nanopores is presented in this paper. Each nanopore contains at most one v-SWCNT that is supported by a dielectric and addressed by electrochemically formed Pd nanowire source contacts and evaporated Pd drain contacts. Characteristics of these completely vertical, two-terminal nanotube devices are presented. Control of the v-SWCNT length is demonstrated using a straightforward etching process with lengths of less than 100 nm achieved without the need for complex/expensive lithography. This effective nanoscale length control of highly ordered v-SWCNTs provides a practical basis for the realization of CNT-based nanoelectronics.

Fabrication and magnetic properties of Ni–Zn nanowire arrays

Ni–Zn nanowire arrays, with diameters of approximately 60 nm and lengths of around 40 μm, were fabricated by electrodeposition in porous anodic aluminum oxide templates at different electric potentials. X-ray diffraction observations demonstrated that the isolated nanowires had polycrystalline structure and that their phases changed with the deposition potential. The amount of deposited zinc in the nanowires increased with the deposition potential, whereas the amount of nickel decreased. Magnetic measurements showed that there was a gradual change of magnetism from isotropic to anistropic with increasing potential amplitude and that the coercivity reached a maximum value in the nanowire deposited at −1.35 V.

Fabrication of Silver Decorated Anodic Aluminum Oxide Substrate and Its Optical Properties on Surface-Enhanced Raman Scattering and Thin Film Interference

In this paper, a simple method to fabricate a three-dimensional (3D) nanostructure decorated with Ag nanoparticles for surface-enhanced Raman scattering (SERS) is demonstrated. Highly ordered porous anodic aluminum oxide (AAO) templates were employed to construct these compound nanostructures. First, the AAO templates were fabricated using a two-step anodization approach. Second, an alternating current (AC) electrochemical deposition was used to fill AAO templates with Ag nanoparticles. Taking 4-mercaptopyridine (4-MPy) as the probing molecule, high-quality SERS spectra were observed. The UV-vis mirror reflection spectra were measured to investigate the surface plasma resonance (SPR) absorbance. An interesting phenomenon of SPR-affected thin film interference was observed. SERS mapping was performed to characterize the homogeneity of as-prepared substrates. Good homogeneity and stability make these substrates good candidates for SERS spectroscopy.

Thermal conductivity of bismuth telluride nanowire array-epoxy composite

Electrodeposition of nanowire array in porous anodic alumina (PAA) templates combine the performance benefits offered by crystallographic texture control, lattice thermal conductivity suppression through boundary scattering of phonons, elastic relaxation of misfit strain, and scalablity essential for high efficiency thermoelectric devices. The template material, however, can serve as a thermal shunt thereby reducing the effective thermoelectric performance. Here, we demonstrate a process of minimizing the parasitic thermal conduction by replacing the PAA matrix with SU-8 (κ∼0.2 W/m K). We report a reduction in the performance penalty from 27% for Bi2Te3/PAA to ∼5% for Bi2Te3/SU-8 nanocomposite by thermal conductivity measurements using a photoacoustic technique.

Hierarchically structured anatase nanotubes and membranes

Hierarchically structured anatase membranes containing both macro- and mesopores were synthesized by liquid phase deposition of porous anodic aluminum oxide (AAO) templates at 50 °C. It was observed that titania initially forms nanotubes held together by residual AAO, then takes on completely the shape of the AAO template by displacing alumina and finally forms ‘capped’ membranes in which a layer of mesoporous titania covers the ends of the template. Besides the sub-250 nm diameter tube holes, nitrogen physisorption also revealed that the tube walls were mesoporous with pore diameters centered around 4 nm with extremely high specific surface areas ranging from 179 to 552 m 2/g. Active photodegradation of aqueous solutions of methylene blue indicated that the membranes were photocatalytically active and the highest degradation constant was observed for AAO templates that had been treated for 5 h by liquid phase deposition.

Alumina-membrane-assisted fabrication of porous hybrid molybdic acid/rhodamine B aggregates

Porous hybrid molybdic acid/rhodamine B (RhB) aggregates with various morphologies were prepared on porous anodic alumina (PAA) templates via a self-aggregation reaction in a molybdic acid/RhB colloidal solution. The results indicate that our method can easily prepare porous hybrid molybdic acid/RhB aggregates under the influence of PAA templates at low temperature in mild reaction conditions. Using the porous properties of the molybdic acid/RhB aggregates, a porous “sandwich-like” gas-sensor prototype was fabricated, which shows gas-sensing properties to ethanol, ammonia and ozone by changing its electrical resistance at room temperature. The gas sensitivity of the molybdic acid/RhB aggregates based on the integration of the individual molybdic acid/RhB aggregate was discussed. Our method may be a strategy for fabricating porous organic/inorganic hybrid functional materials at low cost and constructing microdevices using the porosity of both the aggregates and the anodic alumina membrane.

Fabrication of Nanostructured Materials Using Porous Alumina Template and Their Applications for Sensing and Electrocatalysis

Ordered porous anodic aluminum oxide templates have been used extensively for the preparation of various functional nanostructures. Researches on these nanostructured materials for various purposes have received a tremendous attention during recent years. A review of the literature on the fabrication of nanostructured materials using ordered porous anodic aluminum oxide templates and their applications is presented. A survey of the preparation of anodic aluminum oxide films is given first, with an emphasis on highly ordered anodic aluminum oxide films, as the ordered structure is the key point to prepare nanomaterials with uniform morphology. Methods for the fabrication of nanostructured materials using ordered porous anodic aluminum oxide templates are presented next: including dip filling, ion-encountering reaction, electroplating, and chemical vapor deposition method. Several typical examples of each preparation method are given. Finally, overview of applications on these nanostructured materials is presented, particular emphasis is focused on the field of sensing and electrocatalysis.

Synthesis and Characterization of Carbon Nanotubes by Using Catalyst LiNi<sub>0.5</sub>Co<sub>0.5</sub>O<sub>2</sub> on Anodized Alumina Substrate

Carbon nanotubes (CNTs) have been synthesized by chemical decomposition of acetylene gas at 580°C and 650°C using catalyst of LiNi0.5Co0.5O2. The effect of decomposition temperature on structure of the CNTs is that, CNTs grown at 650°C have lower defects concentration and higher crystallinity as compared to that grown at 580°C. The porous anodized aluminum oxide (AAO) template (as substrate), catalyst particles and the CNTs grown were analyzed by FE-SEM. The pore diameter in the template lies in range of 30 - 80 nm. The CNTs have been analyzed by using Raman spectroscopy and X-ray diffraction techniques. The up-shift in G-band of graphitic sheet and larger full width at half maximum of the peak in the Raman spectra of the CNT in comparison to those observed for graphite are indicative of the structural modification. XRD results also indicate the structural modification in CNT based on the fact that d-value becomes 3.42 Å, which is larger than 3.35 Å for graphite. The tube diameters lie in the range of 12 - 50 nm.

A Generic Approach to Desired Metallic Nanowires Inside Native Porous Alumina Template via Redox Reaction

We report a facile, economic, and generic way to mono- and multisegment metallic nanowires (MNWs) of various pure metals (e.g., Au, Pt, Pd, Cu, Ni, and Co) and their alloys with both linear and branched topologies, by merely infiltrating aqueous solutions of metal chloride salts into Au-coated native porous anodic aluminum oxide template with Al foil on its outside edge. Redox reactions of two galvanic cells where the Al foil acts as the anode are responsible for the formation of the MNWs. Redox reaction of the top galvanic cells on the surrounding Al foil leads to the formation of metal atoms on the Al foil surface, which subsequently diffuse away from the Al foil and into the nanochannels. Simultaneously, redox reaction of the bottom galvanic cell where the Au layer serves as a cathode results in the formation of metal atoms on the top surface of the bottom Au layer, followed by crystal nucleus formation and growth upward the channels to form short MNWs. With the elongation of the infiltration duration,...

Structural and photovoltaic properties of highly ordered ZnFe 2O 4 nanotube arrays fabricated by a facile sol–gel template method

Highly ordered ZnFe 2O 4 nanotube arrays were successfully prepared using porous anodic aluminum oxide (AAO) template from sol–gel solution. The ZnFe 2O 4 nanotubes are orderly arranged in parallel and each nanotube is composed of many agglutinating nanoparticles. The UV–vis absorption and surface photovoltage spectra of the ZnFe 2O 4 nanotubes and gel powders have been compared. The photovoltaic response threshold of the ZnFe 2O 4 nanotubes exhibited a blue-shift of about 150 nm with respect to that of the ZnFe 2O 4 gel powder, which implies that the photogenerated charges in the nanotubes have a higher redox activity than that of the gel powder. Both materials behave like a p-type semiconductor with photogenerated electrons accumulated at their surface.