Nanoporous Anodic Aluminum Oxide Templates Research Articles

Fabrication and Magnetic Behavior of Jellyfish-Like Ni Nanowires Synthesized Using Bilayered Nanoporous Anodic Alumina Templates.

The potential to produce nanostructures with intricate shapes in large quantities holds promise for a range of applications in the fields of nanoelectronics and biomedicine. Here a method for fabricating jellyfish-like Ni nanowires (JFNWs) using bilayered nanoporous anodic alumina templates with through pores of varying diameters in each layer is presented. To assess the capabilities of this method,samples are created with different voltages during the second step of anodization, resulting in distinct geometrical characteristics of the second layer of the template,and subsequently synthesizeNiJFNWs. By employing magnetometry and first-order reversal curve (FORC)method, the magnetic properties are examined and a significant alteration in their magnetic behavior,attributed to the differing shapes of theJFNWsand the magnetostatic interactions within the array,is observed.The study utilizes magnetic force microscopy to evaluate the stray magnetic fields generated by the individualJFNWsand unveils their unusual and asymmetric distribution. Through simulations based on the experimental data, the study analyzes the field- andcurrent-induced domain wall movement in a singleJFNWand their array. The findings revealnon-trivial micromagnetic configurations in these structures, including a remarkable 'corkscrew' state, and allowfor an examination of the process of magnetization switching.

Mechanically Robust and Thermally Conductive Nano-Porous Anodic Aluminum Oxide Templates via Thermal Stress Minimization and Alpha Phase Transformation for Interposer

Mechanically Robust and Thermally Conductive Nano-Porous Anodic Aluminum Oxide Templates via Thermal Stress Minimization and Alpha Phase Transformation for Interposer

A green method to produce nanoporous aluminum oxide templates and the direct application in the synthesis of nanowires

As technology improves and the desire increases to produce smaller devices and manipulate smaller objects, the ability to synthesize nanoscopic materials reliably and reproducibly becomes increasingly important. Nanowires are likely to be used in these devices in the future, but production of these nanowires remains challenging. Currently, anodized aluminum oxide templates can be used to produce large amounts of high aspect ratio nanowires, but producing these templates in an environmentally-friendly manner has proved to be a challenge. In this research, the production of anodized aluminum oxide templates was sought to be improved for both ease of production and environmental friendliness. Using a DES for electropolishing, phosphoric acid for dissolution, as well as more concentrated oxalic acid for anodization, anodic aluminum oxide templates were synthesized in a simple, more environmentally-friendly way. These templates exhibit good ordering of 70 nm (with a standard deviation of 5 nm), diameter pores with 31% porosity, and were able to produce nickel nanowires using AC, pulse, and DC deposition (of diameters of 71 nm, 66 nm, and 65 nm, respectively) without any other metals deposited in the pores due to the barrier layer thinning and cathodic barrier removal steps used in the production. Most notably, the simple apparatus uses only a beaker with suspended electrodes, leading to a repeatable, inexpensive, and green route to producing immediately usable nanoporous anodized aluminum oxide templates.

Electrochemical Synthesis, Magnetic and Optical Characterisation of FePd Dense and Mesoporous Nanowires.

Dense and mesoporous FePd nanowires (NWs) with 45 to 60 at.% Pd content were successfully fabricated by template- and micelle-assisted pulsed potentiostatic electrodeposition using nanoporous anodic alumina and polycarbonate templates of varying pore sizes. An FePd electrolyte was utilized for obtaining dense NWs while a block copolymer, P-123, was added to this electrolyte as the micelle-forming surfactant to produce mesoporous NWs. The structural and magnetic properties of the NWs were investigated by electron microscopy, X-ray diffraction, and vibrating sample magnetometry. The as-prepared NWs were single phase with a face-centered cubic structure exhibiting 3.1 µm to 7.1 µm of length. Mesoporous NWs revealed a core-shell structure where the porosity was only witnessed in the internal volume of the NW while the outer surface remained non-porous. Magnetic measurements revealed that the samples displayed a soft ferromagnetic behavior that depended on the shape anisotropy and the interwire dipolar interactions. The mesoporous core and dense shell structure of the NWs were seen to be slightly affecting the magnetic properties. Moreover, mesoporous NWs performed excellently as SERS substrates for the detection of 4,4'-bipyridine, showing a low detection limit of 10-12 M. The signal enhancement can be attributed to the mesoporous morphology as well as the close proximity of the embedded NWs being conducive to localized surface plasmon resonance.

Strongly Quantum-Confined Perovskite Nanowire Arrays for Color Tunable Blue Light-Emitting Diodes

Color tunability of perovskite light emitting diodes (PeLEDs) by mixed halide compositional engineering is one of the primary intriguing characteristics of PeLEDs. However, mixed halide PeLEDs are often susceptible to color red-shifting caused by halide ion segregation. In this work, strongly quantum-confined perovskite nanowires (QPNWs) made of CsPbBr3 are grown in nanoporous anodic alumina templates using a closed space sublimation (CSS) process. By tuning the pore size with atomic layer deposition (ALD), QPNWs with diameter of 6.6 nm to 2.8 nm have been successfully obtained, with continuous tunable photoluminescence emission color from green (512 nm) to pure blue (467 nm). To better understand the photo-physics of QPNWs, carrier dynamics and the benefit of alumina passivation are studied and discussed in detail. Eventually, PeLEDs using various diameters of CsPbBr3 QPNWs are successfully fabricated with cyan color (492 nm) PeLEDs achieving a record high 7.1% EQE for all CsPbBr3 based cyan color PeLEDs. And sky-blue (481 nm) and pure blue (467 nm) PeLEDs have also been successfully demonstrated, respectively. The work here demonstrates a unique approach to achieve quantum confined one-dimensional perovskite structures and color tunable PeLEDs, particularly blue PeLEDs.

Strongly Quantum-Confined Perovskite Nanowire Arrays for Color-Tunable Blue-Light-Emitting Diodes.

Color tunability of perovskite light-emitting diodes (PeLEDs) by mixed halide compositional engineering is one of the primary intriguing characteristics of PeLEDs. However, mixed halide PeLEDs are often susceptible to color red-shifting caused by halide ion segregation. In this work, strongly quantum-confined perovskite nanowires (QPNWs) made of CsPbBr3 are grown in nanoporous anodic alumina templates using a closed space sublimation process. By tuning the pore size with atomic layer deposition, QPNWs with a diameter of 6.6 to 2.8 nm have been successfully obtained, with continuous tunable photoluminescence emission color from green (512 nm) to pure blue (467 nm). To better understand the photophysics of QPNWs, carrier dynamics and the benefit of alumina passivation are studied and discussed in detail. Eventually, PeLEDs using various diameters of CsPbBr3 QPNWs are successfully fabricated with cyan color (492 nm) PeLEDs, achieving a record high 7.1% external quantum efficiency (EQE) for all CsPbBr3-based cyan color PeLEDs. Sky blue (481 nm) and pure blue (467 nm) PeLEDs have also been successfully demonstrated, respectively. The work here demonstrates a different approach to achieve quantum-confined one-dimensional perovskite structures and color-tunable PeLEDs, particularly blue PeLEDs.

Photoswitchable Composite Polymer Electrolytes Using Spiropyran-Immobilized Nanoporous Templates.

Composite polymer electrolytes (CPEs) with smart, stimuli-responsive characteristics have gained considerable attention owing to their noninvasive manipulation and applications in future technologies. To address this potential, in this work, we demonstrate photoresponsive composite polymer electrolytes, consisting of gel polymer electrolyte (GPE) and spiropyran-immobilized nanoporous anodic aluminum oxide (SP-AAO) templates. Under UV irradiation, the close SP form isomerizes to the open merocyanine (MC) form, creating extremely polarized AAO surfaces; whereas, under visible light irradiation, the MC form reverts to the SP form, creating neutral surface conditions. The electrostatic interactions between ions and AAO surfaces are investigated by attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. Moreover, the behavior of ionic conductivity of the GPE@SP-AAO is found to be consistent with the kinetics of isomerization tracked by UV-Vis spectroscopy. This work provides a promising platform for developing next-generation photoelectronic smart devices.

Confined Crystallization of Polymers within Nanopores

Crystallization of polymeric materials under nanoscopic confinement is highly relevant for nanotechnology applications. When a polymer is confined within rigid nanoporous anodic aluminum oxide (AAO) templates, the crystallization behavior experiences dramatic changes as the pore size is reduced, including nucleation mechanism, crystal orientation, crystallization kinetics, and polymorphic transition, etc. As an experimental prerequisite, exhaustive cleaning procedures after infiltrations of polymers in AAO pores must be performed to ensure producing an ensemble of isolated polymer-filled nanopores. Layers of residual polymers on the AAO surface percolate nanopores and lead to the so-called "fractionated crystallization", i.e., multiple crystallization peaks during cooling.Because the density of isolated nanopores in a typical AAO template exceeds the density of heterogeneities in bulk polymers, the majority of nanopores will be heterogeneity-free. This means that the nucleation will proceed by surface or homogeneous nucleation. As a consequence, a very large supercooling is necessary for crystallization, and its kinetics is reduced to a first-order process that is dominated by nucleation. Self-nucleation is a powerful method to exponentially increase nucleation density. However, when the diameter of the nanopores is lower than a critical value, confinement prevents the possibility to self-nucleate the material.Because of the anisotropic nature of AAO pores, polymer crystals inside AAO also exhibit anisotropy, which is determined by thermodynamic stability and kinetic selection rules. For low molecular weight poly(ethylene oxide) (PEO) with extended chain crystals, the orientation of polymer crystals changes from the "chain perpendicular to" to the "chain parallel to" the AAO pore axis, when the diameter of AAO decreases to the contour length of the PEO, indicating the effect of thermodynamic stability. When the thermodynamic requirement is satisfied, the orientation is determined by kinetics including crystal growth direction, nucleation, and crystal growth rate. An orientation diagram has been established for the PEO/AAO system, considering the cooling condition and pore size.The interfacial polymer layer has different physical properties as compared to the bulk. In poly(l-lactic acid), the relationship between the segmental mobility of the interfacial layer and crystallization rate is established. For the investigation of polymorphic transition of poly(butane-1), the results indicate that a 12 nm interfacial layer hinders the transition of Form II to Form I. Block and random copolymers have also been infiltrated into AAO nanopores, and their crystallization behavior is analogously affected as pore size is reduced.

EFFECT OF EXTERNAL MAGNETIC FIELD ON STRUCTURAL AND MAGNETIC PROPERTIES OF ELECTRODEPOSITED Co–Fe NANOWIRES

CoFe nanowires were successfully synthesized in nanoporous anodized aluminum oxide (AAO) template by employing DC electrodeposition process. These nanowires have been electrodeposited in the presence of external magnetic field applied parallel ([Formula: see text] to the axis of nanowires. The effects of externally applied magnetic field on magnetic and structural properties of CoFe nanowires were investigated. X-ray diffraction (XRD) was used to identify crystal structure of the samples. The XRD pattern indicates polycrystalline nature of Cobalt iron nanowires with Body Centered Cubic (BCC) crystal structure. Scanning Electron Microscopy (SEM) images revealed the uniform growth of nanowires inside the template. To explore the magnetic properties of Cobalt iron nanowires, vibrating sample magnetometer (VSM) was employed. It was revealed that for nanowires electrodeposited with external magnetic field, easy axis of magnetization is found parallel ([Formula: see text] to the nanowire axis with large variation in anisotropic magnetization. Whereas for nanowires electrodeposited without external magnetic, easy axis of magnetization is perpendicular ([Formula: see text] to nanowires axis with small variation in anisotropic magnetization.

A facile method to synthesize Ag/CuO composite nanowire arrays for electrochemical detection

A novel method using a combination of anodic aluminium oxide (AAO) templates, AgCuO alloy capillary wetting and hydrothermal reaction is developed for preparing Ag/CuO composite nanowire arrays. The nanopores of AAO templates are used for the penetration of molten Ag to form Ag nanowire arrays. Meanwhile, the skeletons of AAO templates are used to react with CuO to produce CuO nanowire arrays via the hydrothermal process. The interfaces and reaction products between AAO templates and CuO are analyzed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The Ag/CuO composite nanowire arrays are obtained via the hydrothermal reaction which is introduced to release the Ag nanowire arrays and grow CuO nanowire arrays. The as-obtained composite nanowire arrays show good electrochemical performance for the detection of hydrogen peroxide (H2O2).

Fabrication of Br doped ZnO nanosheets piezoelectric nanogenerator for pressure and position sensing applications

In this research, a unique strategy was developed to enhance the output performance of 2D ZnO nanosheets based piezoelectric nanogenerator (PENG). The Br doped 2D ZnO nanosheets were fabricated by facile hydrothermal method on nanoporous anodic aluminum oxide (AAO) template. Along with structural and optical characterization of Br doped 2D ZnO nanosheets, the electrical output performance of Br doped 2D ZnO PENG was demonstrated under external mechanical force. The corresponding output voltage of Br doped 2D ZnO nanosheets PENG reached to 8.82 V at 6HZ, which is 3 times higher than undoped ZnO nanosheets PENG. The output power density of Br doped 2D ZnO nanosheets PENG reached to 38.8962μWcm−2 at an external load resistanec of about 2 MΩ. The Br doping in ZnO nanosheets significantly increased the sensitivity of PENG for pressure sensing and the flexibility of PENG contribute in the application of position sensing.

Effects of Microstructure of Ni Anode on Nanotemplate Based Low Temperature Solid Oxide Fuel Cells

For nano-porous anodized aluminum oxide (AAO) template based low temperature solid oxide fuel cells (LT-SOFCs), anode structure has crucial effects on electrochemical characteristics because of triple phase boundary densities and electrical connectivity of metal catalysts on porous AAO substrates. In this study, we investigated effects of fabrication processes of Ni anode for AAO template based LT-SOFCs. Ni anodes were prepared at various deposition pressure, i.e. low pressure, high pressure and low pressure–high pressure, on nano-porous AAO substrates by physical vapor deposition. Surface morphology and cross-sectional structure of various Ni anodes were systematically evaluated. Electrochemical characterizations of LT-SOFCs with various anode structures were successfully conducted at 500 °C. The Ni anode prepared at low pressure showed high electrical conductivity and low catalytic activity. However, Ni anode which was fabricated at high pressure exhibited poor electrical conductivity and good catalytic activity. Bilayer Ni anode which was deposited in sequence at low pressure and high pressure presented both good electrical conductivity and good catalytic activity. The LT-SOFC with the bilayer Ni anode cell achieved the best performance, 201 mW/cm2 at 500 °C. Electrochemical impedance spectroscopy analysis was conducted to reveal detailed behaviors of AAO based LT-SOFCs. Therefore, we successfully optimized the anode structure for high performance AAO template based LT-SOFCs.

The effect of sulphuric acid and oxalic acid on the formation of anodic aluminium oxide templates using two-step anodization method

The prevention of corrosion on the surface of aluminum by formation of a thin coating layer using anodization methods for enhanced applications is an active area of research. In this study, the fabrication of nanoporous anodic aluminum oxide (AAO) templates was performed by a two-step anodization process using aluminum with 99.98% purity in 0.3 M solution of oxalic acid or 0.1, 0.3, or 0.5 M solutions of sulfuric acid as electrolyte. Anodizing time, electrolyte solution and concentration, and current were found to be the main factors determining the pore diameter and interpore size. In addition, the voltage affected the number of pores on the AAO template. The structural features of the nanoporous templates were examined by scanning electron microscopy. The optimum conditions were determined to be 0.3 M sulfuric acid at 25 V.

Highly Morphology-Controllable and Highly Sensitive Capacitive Tactile Sensor Based on Epidermis-Dermis-Inspired Interlocked Asymmetric-Nanocone Arrays for Detection of Tiny Pressure.

The tactile sensor lies at the heart of electronic skin and is of great importance in the development of flexible electronic devices. To date, it still remains a critical challenge to develop a large-scale capacitive tactile sensor with high sensitivity and controllable morphology in an economical way. Inspired by the interlocked microridges between the epidermis and dermis, herein, a highly sensitive capacitive tactile sensor by creating interlocked asymmetric-nanocones in poly(vinylidenefluoride-co-trifluoroethylene) film is proposed. Particularly, a facile method based on cone-shaped nanoporous anodized aluminum oxide templates is proposed to cost-effectively fabricate the highly ordered nanocones in a controllable manner and on a large scale. Finite-element analysis reveals that under vertical forces, the strain/stress can be highly strengthened and localized at the contact apexes, resulting in an amplified variation of film permittivity and thickness. Benefiting from this, the developed tactile sensor presents several conspicuous features, including the maximum sensitivity (6.583 kPa-1 ) in the low pressure region (0-100 Pa), ultralow detection limit (≈3 Pa), rapid response/recovery time (48/36 ms), excellent stability and reproducibility (10 000 cycles). These salient merits enable the sensor to be successfully applied in a variety of applications including sign language gesture detection, spatial pressure mapping, Braille recognition, and physiological signal monitoring.

A pyroelectric thin film of oriented triglycine sulfate nano-crystals for thermal energy harvesting

This study introduces a method for the fabrication of transparent and flexible pyroelectric thin films containing oriented triglycine sulfate (TGS) nanorods for thermal energy conversion or thermal sensing. For the fabrication of such thin films a highly nanoporous anodic aluminum oxide (AAO) template is mounted on top of a b-cut TGS seed crystal before filling the template’s nanopores with TGS solution. Crystal growth in the filled pores is done via the so-called temperature-lowering technique. Two principles are applied to grow oriented nanocrystals in the AAO template: first, the effect of different crystal growth rates in different directions of a nanopore’s confined space is exploited. Second, crystal growth at the bottom of the pores is initiated in a preferential direction by the TGS seed crystal. As confirmed by x-ray diffraction the crystal nanorods obtained are oriented in the desired spontaneous polarization vector of TGS (b-direction). Optical transparency of the filled AAO thin film is good when compared to a pure AAO film which indicates a reasonably high homogeneity and a reasonably low defect density of the TGS nanocrystals. Dielectric characterization at 1 kHz shows a relative permittivity similar to a bulk TGS crystal and a high resistivity of about 199 MΩ m. At its phase transition temperature (44 °C), the dielectric loss factor of the thin film is about 0.3. An average pyroelectric coefficient of 133 μC m−2 K−1 and a relative permittivity of 15.6 are calculated from measurement results at room temperature, taking the effect of the AAO thin film into account. With that, the pyroelectric voltage figure of merit (FOM) (pc/εrε0) and the energy harvesting FOM (pc2/εrε0) and are about 820 kV m−1 K−1 and 72 J m−3 K−2, respectively. In comparison to other approaches for growing thin films of oriented TGS crystals, the described method exhibits advantages concerning the growth of oriented nanocrystals, simplicity, fast growth, and an access to both sides of the nanocrystals.

Structural and Uniaxial Magnetic Anisotropy of Co1-XMgX(X = 0.04–0.12) Nanowires in Alumina Templates

The nanoporous anodized aluminum oxide (AAO) templates were synthesized by two-step anodization in a solution of 0.5 M phosphoric acid at 60 V and temperature T ~ 0 °C. The CoMg nanowires were synthesized by template-based AC Electrodeposition technique at different voltages by AC source 13–17 V at room temperature. These CoMg nanowires were investigated via different characterization techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). The SEM result shows that nanowires have average diameter about 150 nm and length about 23 μm. The EDX reveals that nanowires only consisted of Mg and Co atoms, and atomic ratio of Mg/(Co + Mg) showed increasing tendency with deposition voltage which depicts that higher AC electrodeposition voltage is more suitable for Mg-rich deposition. The XRD results show that CoMg nanowires have hexagonal crystal structure with polycrystalline nature. The MH loops confirm that nanowires are soft ferromagnetic with uniaxial magnetic anisotropy. It is observed from angular dependence of coercivity that magnetization reversal mechanism occurs by a combination of curling and nucleation mode. The squareness (Mr/Ms) is found to be 0.24 along nanowires and 0.16 perpendicular to nanowire axis suggesting that easy magnetization direction lies along the nanowires. The effective anisotropy is observed along the nanowire axis due to dominance of shape anisotropy and suppression of dipole-dipole interactions among nanowires.

Single-Crystalline Silver Nanowire Arrays Directly Synthesized on Substrates by Template Chemical Wetting

Silver (Ag) nanowire arrays have attracted extensive research attention for its outstanding electrochemical detection sensitivity and optical properties. The most frequently used technology for fabricating Ag nanowire arrays is electrodeposition within the pores of anodic aluminum oxide (AAO) templates. In this paper, single-crystalline Ag nanowire arrays were grown by the capillary wetting of the molten Ag in the nanopores of AAO templates at the temperature of 970°C. In order to improve the infiltrating height of molten Ag in the capillaries of AAO templates, copper oxide (CuO) was added as a supplement because it can improve the wetting behavior between molten Ag and AAO templates. After Ag nanowire arrays were embedded within AAO pores, a novel hydrothermal etching method was proposed to remove AAO templates because AAO had phase transition and became difficult to be removed after heating process at 970°C. To test the properties of Ag nanowire arrays obtained, the surface-enhanced Raman scattering (SERS) performance was also studied.

Large-area cost-effective lithography-free infrared metasurface absorbers for molecular detection

The implementation of metasurface absorbers for advanced sensing applications in the infrared spectral range is gaining prominence. Nevertheless, scale-up is challenging because their subwavelength features require complex fabrication techniques. Here, we present centimeter-sized nanostructured metasurface absorbers, prepared using the nanoporous anodic aluminum oxide template method, which exhibit a high and polarization-insensitive absorptivity at near-infrared wavelengths. Their sensing potential as surface-enhanced Raman spectroscopy substrates is demonstrated by analyzing Raman spectra of methyl parathion pesticides at concentrations as low as 100 ppb. Our results offer a stable, cost-effective, scalable, and uniform solution for metasurface-based molecular detection applications with a high sensitivity.

Through-hole AAO-SA templates with a small pore diameter prepared by the voltage pulse detachment method

A voltage pulse detachment method is a fast and simple alternative for the preparation of nanoporous anodic aluminum oxide (AAO) templates. Free-standing through-hole porous anodic aluminum oxide membranes were fabricated by a two-step self-organized anodization of aluminum in a sulfuric acid (SA) solution followed by a voltage pulse detachment process in a mixture of HClO4 and C2H5OH (1:1 vol). In this work, the influence of height, time and number of the voltage pulses, time and conditions of sample storage, and the thickness of oxide layer on the measured current density, bottom-side morphology of the AAO-SA membrane, pore diameter, and overall detachment effect were examined in detail for the first time. The pore diameter of the AAO-SA membranes was estimated from FE-SEM images. It was found that the maximum current density, measured during the voltage detachment process, is the most strongly affected by the conditions and time of sample storage and the AAO thickness. The number of applied pulses and pulse duration influence the most significantly the pore diameter at the bottom side. The as detached AAO membranes with the pore diameter of ca. 20 nm were used as templates for electrodeposition of Au nanowire arrays.

Strain-Mediated Phase Stabilization: A New Strategy for Ultrastable α-CsPbI3 Perovskite by Nanoconfined Growth.

All-inorganic cesium lead triiodide (CsPbI3 ) perovskite is considered a promising solution-processable semiconductor for highly stable optoelectronic and photovoltaic applications. However, despite its excellent optoelectronic properties, the phase instability of CsPbI3 poses a critical hurdle for practical application. In this study, a novel stain-mediated phase stabilization strategy is demonstrated to significantly enhance the phase stability of cubic α-phase CsPbI3 . Careful control of the degree of spatial confinement induced by anodized aluminum oxide (AAO) templates with varying pore sizes leads to effective manipulation of the phase stability of α-CsPbI3 . The Williamson-Hall method in conjunction with density functional theory calculations clearly confirms that the strain imposed on the perovskite lattice when confined in vertically aligned nanopores can alter the formation energy of the system, stabilizing α-CsPbI3 at room temperature. Finally, the CsPbI3 grown inside nanoporous AAO templates exhibits exceptional phase stability over three months under ambient conditions, in which the resulting light-emitting diode reveals a natural red color emission with very narrow bandwidth (full width at half maximum of 33 nm) at 702 nm. The universally applicable template-based stabilization strategy can give in-depth insights on the strain-mediated phase transition mechanism in all-inorganic perovskites.