Aluminum Oxide Template Research Articles

Effective anisotropy in Fe-Ni nanowire arrays with strong dipolar interaction

The effective magnetic anisotropy field Heff of Fex Ni(100-x) (x = 15, 25, 38) nanowires of 65 nm diameter forming ordered arrays within dense alumina templates of ∼35% porosity, was determined. Different values for Heff were obtained depending on the determination method, which were: magnetization evolution along major hysteresis loops; ferromagnetic resonance at 34 GHz; and magnetization switching by curling nucleation (through angular variation of the coercive field). Heff values determined from magnetization measurements differ from those arising from FMR measurements, being these latter quite smaller in every case. No evidence of an easy plane behavior was found, as theoretically predicted for high porosity arrays as ours.These results suggest that new internal degrees of freedom need to be considered for the effective anisotropy description in quasistatic hysteresis loops, during polarization reversal and in ferromagnetic resonance dynamic processes, to understand and model these experimental findings. We discuss possible causes.

Nanosized Proton Conductor Array with High Specific Surface Area Improves Fuel Cell Performance at Low Pt Loading.

The use of ordered catalyst layers, based on micro-/nanostructured arrays such as the ordered Nafion array, has demonstrated great potential in reducing catalyst loading and improving fuel cell performance. However, the size (diameter) of the basic unit of the most existing ordered Nafion arrays, such as Nafion pillar or cone, is typically limited to micron or submicron sizes. Such small sizes only provide a limited number of proton transfer channels and a small specific area for catalyst loading. In this work, the ordered Nafion array with a pillar diameter of only 40 nm (D40) was successfully prepared through optimization of the Nafion solvent, thermal annealing temperature, and stripping mode from the anode alumina oxide (AAO) template. The density of D40 is 2.7 × 1010 pillars/cm2, providing an abundance of proton transfer channels. Additionally, D40 has a specific area of up to 51.5 cm2/cm2, which offers a large area for catalyst loading. This, in turn, results in the interface between the catalyst layer and gas diffusion layer becoming closer. Consequently, the peak power densities of the fuel cells are 1.47 (array as anode) and 1.29 W/cm2 (array as cathode), which are 3.3 and 2.9 times of that without array, respectively. The catalyst loading is significantly reduced to 17.6 (array as anode) and 61.0 μg/cm2 (array as cathode). Thus, the nanosized Nafion array has been proven to have high fuel cell performance with low Pt catalyst loading. Moreover, this study also provides guidance for the design of a catalyst layer for water electrolysis and electrosynthesis.

Nanoporous anodic aluminum oxide-confined ZIF-67 for efficiently activating peroxymonosulfate to degrade organic pollutants

The limited mass transfer of short-lived radical species is an inherent drawback of heterogeneous oxidation processes. Herein, we fabricated zeolitic imidazolate framework (ZIF)-67 loaded nanoreactors with precise pore sizes based on anodic alumina oxide (AAO) templates to achieve nanoscale spatial confinement for enhanced radicals-mediated oxidation reactions. The prepared ZIF-67@AAO membrane/peroxymonosulfate (PMS) system exhibits perfect catalytic performance with a rhodamine B (RhB) removal of 100 % within 60 s under an AAO pore size of < 20 nm. The reaction rate constant of RhB degradation by the ZIF-67@AAO<20 nm/PMS system was 2.52 and 893 times that by the ZIF-67@AAO200–300 nm/PMS and ZIF-67/PMS system (no confinement), respectively. The ordered mesoporous structure of the ZIF-67@AAO nanoreactors provided many channels for PMS and RhB molecules to enter the confined inner space of the catalyst, leading to a significant improvement in catalytic performance under nanoconfinement. Radical quenching and electron paramagnetic resonance (EPR) results indicated that SO4−, ·OH, 1O2, and O2− were generated in the ZIF-67@AAO/PMS system, and their amounts were affected by spatial confinement and achieved the maximum at a pore size of < 20 nm. Furthermore, the ZIF-67@AAO catalytic membrane exhibited attractive long-term operation stability with perfect activity and neglectable Co leaching. The results of this study provide an important reference for designing novel catalytic membranes for water decontamination.

Conductive carbon paint: An efficient way to electrodeposit metallic nanowires by using porous membranes

The present work demonstrates that conductive carbon paint, used for sample preparation in electron microscopy, can be a more straightforward and as-effective substitute for the metallic layer deposition usually used for the electrodeposition of metallic nanowires within porous membranes. AFM images demonstrated the good surface quality of the carbon layer. Raman spectroscopy confirmed the high crystallinity of carbon and high density of π-electrons. The electrical conductivity of the carbon layer was estimated using the linear sweep voltammetry technique. This new cathode was employed to grow continuous (Ni) and composition-modulated (Ni/Cu) nanowires within alumina templates, starting from aqueous solutions of Ni2+ and Cu2+ mixed salts. The obtention of metallic copper and nickel, and their separation can be readily observed by scanning electron microscopy and elemental mapping by EDS.

The Renaissance and Golden Age of Epitaxial Dry Germanene

Germanene, as an artificial graphene-like near room temperature topological insulator, compatible with ubiquitous silicon technology, is potentially the most promising artificial Xene for ultra-scale nanoelectronics. Here, we follow its emergence and development when prepared in situ under ultra-high vacuum in clean and controlled conditions by dry epitaxy on prominent metal surfaces (e.g., aluminum, silver, gold). We describe its predicted electronic properties and its birth in 2014, even if it was just a renaissance, as it was only understood after 51 years after an undeciphered birth certificate lost in oblivion. We emphasize the lifting of germanene flakes from an aluminum template with the tip of a scanning tunneling microscope, and their repositioning to form bilayer germanene with Bernal stacking. Finally, we discuss the growth of monolayer germanene in a single phase harboring Dirac fermions, following a bottom-up synthesis strategy by segregation on a gold thin film in epitaxy on a germanium support.

All‐Dielectric Insulated 3D Plasmonic Nanoparticles for Enhanced Self‐Floating Solar Evaporation under One Sun

AbstractPlasmonic absorbers, featured by unique capability of broadband light absorption and nanoscale optical concentration, have long been regarded as ideal candidates for self‐floating interfacial solar evaporation yet suffering from low energy transfer efficiency because of poor thermal localization. In this work, by implanting an ion beam exfoliation of the continuous metallic film from the gold/nanoporous alumina template (Au/NPT), the all‐dielectric insulated plasmonic absorbers are demonstrated as efficient self‐floating interfacial solar evaporators with measured efficiency of ≈80% under one sun, which shows a ≈20% increment to conventional Au/NPT and is comparable to mainstream complicated carbon‐based evaporators with external thermal insulators. The enhanced energy transfer process can be ascribed to synergistic effect of plasmon‐enhanced solar absorption, broadband light induced thermal localization and/or insulation, as well as efficient mass transport channels. The results here would provide a new insight in underlying understanding and inspire further development of plasmonic solar thermal conversion.

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.

Polymerization within Nanoporous Anodized Alumina Oxide Templates (AAO): A Critical Survey.

In the last few years, the polymerization of monomers within the nanocavities of porous materials has been thoroughly studied and developed, allowing for the synthesis of polymers with tailored morphologies, chemical architectures and functionalities. This is thus a subject of paramount scientific and technological relevance, which, however, has not previously been analyzed from a general perspective. The present overview reports the state of the art on polymerization reactions in spatial confinement within porous materials, focusing on the use of anodized aluminum oxide (AAO) templates. It includes the description of the AAO templates used as nanoreactors. The polymerization reactions are categorized based on the polymerization mechanism. Amongst others, this includes electrochemical polymerization, free radical polymerization, step polymerization and atom transfer radical polymerization (ATRP). For each polymerization mechanism, a further subdivision is made based on the nature of the monomer used. Other aspects of "in situ" polymerization reactions in restricted AAO geometries include: conversion monitoring, kinetic studies, modeling and polymer characterization. In addition to the description of the polymerization process itself, the use of polymer materials derived from polymerization in AAO templates in nanotechnology applications, is also highlighted. Finally, the review is concluded with a general discussion outlining the challenges that remain in the field.

Overview of Engineering Carbon Nanomaterials Such As Carbon Nanotubes (CNTs), Carbon Nanofibers (CNFs), Graphene and Nanodiamonds and Other Carbon Allotropes inside Porous Anodic Alumina (PAA) Templates

The fabrication and design of carbon-based hierarchical structures with tailored nano-architectures have attracted the enormous attention of the materials science community due to their exceptional chemical and physical properties. The collective control of nano-objects, in terms of their dimensionality, orientation and size, is of paramount importance to expand the implementation of carbon nanomaterials across a large variety of applications. In this context, porous anodic alumina (PAA) has become an attractive template where the pore morphologies can be straightforwardly modulated. The synthesis of diverse carbon nanomaterials can be performed using PAA templates, such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and nanodiamonds, or can act as support for other carbon allotropes such as graphene and other carbon nanoforms. However, the successful growth of carbon nanomaterials within ordered PAA templates typically requires a series of stages involving the template fabrication, nanostructure growth and finally an etching or electrode metallization steps, which all encounter different challenges towards a nanodevice fabrication. The present review article describes the advantages and challenges associated with the fabrication of carbon materials in PAA based materials and aims to give a renewed momentum to this topic within the materials science community by providing an exhaustive overview of the current synthesis approaches and the most relevant applications based on PAA/Carbon nanostructures materials. Finally, the perspective and opportunities in the field are presented.

FABRICATION OF SEMICONDUCTOR NANO STRUCTURED POROUS ALUMINA TEMPLATES BY ANODIZATION

Photo voltaic Semiconductor nano structures are required to have high energy change efficiencies because of the expanded retention coefficients of semiconductor nano structures. Furthermore, the slender film permeable layout can be utilized for ideal surface finishing of sun powered cells prompting extra improvement in energy transformation effectiveness. A significant prerequisite for these applications is the capacity to blend nano structure varieties of various measurements with great size control. This task utilized nano permeable alumina layouts made by the anodization of aluminum slender moves stored on glass substrates for the creation of the nano structures and upgraded the interaction boundaries to acquire uniform pore distances across. An extra prerequisite is consistency or routineness of the nano structure exhibits. While consistent current anodization was seen to give controlled pore distances across, steady voltage anodization was required for commonality of the nanostructure clusters. Along these lines a two-venture anodization measure was researched and created in this task for improving the pore size circulation and pore periodicity of the nano porous alumina templates Key words: Nano Porous Alumina Templates, Anodization,

Superhydrophobic Mechano-Bactericidal Surface with Photodynamic Antibacterial Capability

Bacterial invasion and proliferation on various surfaces pose a serious threat to public health worldwide. Conventional antibacterial strategies that mainly rely on bactericides exhibit high bacteria-killing efficiency but might trigger the well-known risk of antibiotic resistance. Here, we report a superhydrophobic mechano-bactericidal surface with photodynamically enhanced antibacterial capability. First, bioinspired nanopillars with polycarbonate as the bulk material were replicated from anodized alumina oxide templates via a simple hot-pressing molding method. Subsequently, a facile bovine serum albumin phase-transition method was used to introduce chlorin e6 onto the nanopillar-patterned surface, which was then perfluorinated to render the surface superhydrophobic. Benefiting from its strong liquid super-repellency and photodynamically enhanced mechano-bactericidal properties, the superhydrophobic nanopillar-patterned surface exhibits 100% antibacterial efficiency after 30 min visible light irradiation (650 nm, 20 mW cm-2). More strikingly, the surface exhibited impressive long-lasting antimicrobial performance, maintaining a very high bactericidal efficiency (≥99%) even after 10 cycles of bacterial contamination tests. Also, the superhydrophobic nanopillar-patterned surface displays good hemocompatibility with a much lower than the 5% hemolysis rate. Overall, this work offers a new method for significantly enhancing the antibacterial efficiency of structural antimicrobial surfaces without involving any bactericidal agents, and this functional surface shows great potential in the field of advanced medical materials and hospital surfaces.

Manipulating Dual Bound States in the Continuum for Efficient Spatial Light Modulator

Spatial light modulators (SLMs) that could control diverse optical properties are highly demanded by many optoelectronic systems. Recently, the integration of nonlinear χ(2) materials and metasurfaces has been recognized as a promising strategy for next-generation SLMs. However, their modulation efficiency still encounters challenges due to low quality factor and weak light-matter interaction. Here, we demonstrate an efficient SLM by manipulating the dual bound state in continuum (BIC) with the assistance of a binary-pore anodic alumina oxide template technique. The coexistence of symmetry-protected BIC and Fabry-Pérot BIC is obtained by a desirable sandwich configuration with a BIC metasurface and EO polymer, which efficiently restrain radiative loss and generate a strong quasi-BIC resonance. The assembled SLM with large absorption and Q-factor delivers a modulation depth of 77% and an f3dB of nearly 100 MHz. This dual BIC metasurface provides potential for applications including switches, LIDAR, augmented and virtual reality, and so on.

Small-sized Ag nanoparticle stacked films promoted by sustainedly released surfactants for plasmonic broadband super absorption

Large-area, highly absorptive films stacked of uniform Ag nanoparticles (AgNPs) with sub-20 nm size were fabricated by magnetron sputtering at the presence of adhesive tape, during which O-containing compounds were sustainedly released from the adhesive glue that acted as gaseous surfactants to promote the nucleation and simultaneously suppress the coalescence of the AgNPs. Plasmonic absorbers of metal-insulator-metal (MIM) configuration with a gradient-thickness insulator layer were constructed by conformally depositing such small-sized AgNP stacked films (S-AgSFs) on alumina templates with V-shaped nanopores. The broadband optical impedance matching of this novel MIM structure enables broadband light absorption from ultraviolet to near-infrared region, by working together with the large absorption cross-section, strong interparticle plasmon coupling of closely stacking small-sized AgNPs, and the light-trapping effect of the porous template. The average absorbance reaches 96.8 % in the visible region and 86.7 % in the 200–1600 nm range, respectively, showing the great potential of this absorber for applications in antireflection, solar energy harvesting and utilizing, etc. This adhesive-tape-assisted physical vapor deposition approach is simple, cost-effective, and can be applied to various types of substrates, which will enrich the fabrication strategy of metal nanostructures with effectively controlled geometries and optical properties.

Synthesis and Characterization of Gold-Shell Magnetic Nanowires for Theranostic Applications

Increasing interest has been given in recent years to alternative physical therapies for cancer, with a special focus on magneto-mechanical actuation of magnetic nanoparticles. The reported findings underline the need for highly biocompatible nanostructures, along with suitable mechanical and magnetic properties for different configurations of alternating magnetic fields. Here, we show how the biocompatibility of magnetic nanowires (MNWs), especially CoFe, can be increased by gold coating, which can be used both in cancer therapy and magnetic resonance imaging (MRI). This study provides a new approach in the field of theranostic applications, demonstrating the capabilities of core–shell nanowires to be used both to increase the cancer detection limit (as T2 contrast agents) and for its treatment (through magneto-mechanical actuation). The MNWs were electrodeposited in alumina templates, whereas the gold layer was electroless-plated by galvanic replacement. The gold-coated CoFe nanowires were biocompatible until they induced high cellular death to human osteosarcoma cells via magneto-mechanical actuation. These same MNWs displayed increased relaxivities (r1, r2). Our results show that the gold-coated CoFe nanowires turned out to be highly efficient in tumor cell destruction, and, at the same time, suitable for MRI applications.

Freestanding μm-thin nanomesh electrodes exceeding 100x current density enhancement for high-throughput electrochemical applications

Nanomeshes (NMs), regularly interconnected 3D nanowire-networks, obtained from electroplating in rationally designed alumina templates, are attractive for numerous fields due to their extremely high surface area and porosity. Until now, non-porous support substrates were required to provide sufficient mechanical robustness to the highly porous NM. However, to exploit these compelling nano-architectures as freestanding electrodes in electrochemical flow cells, e.g. water electrolysis, it is essential that the nanowire-network is accessible from all sides requiring a porous support structure. To demonstrate the advantage of the high volumetric NM surface area of 26 m2/cm3 for water electrolysis up to 1 A/cm2, we monolithically integrated a nickel NM with an open support grid in a facile and up-scalable fabrication flow. The freestanding NM electrodes show beyond state-of-the-art performance for the alkaline hydrogen- and oxygen evolution reaction (HER and OER), with over 100x enhanced current densities in respect to planar nickel. Interestingly, the regular nano-architecture of the electrodes causes an intrinsic catalytic effect for the HER. The high potential of these novel 4 μm thin electrodes toward high-throughput electrochemical applications is shown by the significant 400 mV lower overpotential compared to commercial 1.6 mm thick nickel foams (<0.01 m2/cm3) in the alkaline anion-exchange membrane water electrolysis.

(Invited, Digital Presentation) High-Efficiency and Stable Perovskite LEDs and Displays with Nanophotonic Methods

Perovskite light-emitting diodes (PeLEDs) have experienced rapid development in the past 8 years. The external quantum efficiencies (EQEs) of red, green, and near-infrared (NIR) PeLEDs have all surpassed the 20% milestone. Meanwhile, the blue PeLEDs also achieved EQEs higher than 10% and are catching up quickly with PeLEDs of other colors.However, there are still two key problems remaining within the PeLEDs for their further development, namely the light extraction problem and the short lifetime problem. Therefore, in this report, we will discuss our recent work targeting addressing the above two critical problems.First, our work on improving the light extraction efficiency by deploying the nanophotonic substrates will be introduced. Second, the improvement of the device’s operational lifetime at high luminance conditions with perovskite nanowires embedded in a porous alumina template will be discussed. Third, a full evaporation method that is compatible with industrialization will be shown. Last but not least, our endeavors on the displays based on perovskite materials will be covered.

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.

Coupled electrodeposition and magnetic properties of ternary CoFeW alloys

The iron (Fe) cobalt (Co) tungsten (W) alloys exhibit unique combinations of mechanical and soft magnetic properties, good corrosion and wear resistance, and biocompatibility, which makes them desirable candidate for numerous practical applications. A nano-porous alumina template with electrodeposited FeCoW alloy nanowires (NWs) is a polycrystalline material with the grain size was about ~1 − 3 nm. Here, we first time report the composition dependent structural, and magnetic properties of FeCoW NWs embedded in ~25 nm anodic alumina (AAO) template by electrodeposition. By keeping the W concentration same, and decreasing the concentration of Co2+ and Fe2+ ions in the solution, 2–3% to 8–9% W content was increased. The EDX and XPS analysis confirms the co-deposition of W ions along with Fe and Co ions. The magnetization curves showed that 2–3% At. % of W in CoFe NWs significantly increases the saturation magnetization of NWs. Therefore, FeCoW alloy with low W content could be targeted for the design of recording components and shape memory devices in future. Deposition potential also has a notable effect on the final composition, structure and magnetic properties of NWs.

Integration of supercapacitor with solar cell based on NiO 2 and CdS nanopillars embedded in porous anodic alumina templates

Integration of supercapacitor with solar cell based on <scp> NiO ₂ </scp> and <scp>CdS</scp> nanopillars embedded in porous anodic alumina templates

A high-efficient and low-consumption nanoimprint method to prepare large-area and high-quality Nafion array for the ordered MEA of fuel cell

Recently, the third-generation-ordered membrane electrode assembly (MEA) is widely researched, because it can simultaneously provide abundant and continuous ordered charge, proton, and mass transfer channels. However, the development of the ordered MEA is restricted by the preparation of the ordered channels. In this work, we developed a high-efficient (<1 min), contamination-free and low-consumption nanoimprint method to prepare large area (up to 1800 cm2) composite proton exchange membrane (PEM) with ordered Nafion array by repeatedly using porous anodic alumina oxide (AAO) template. Firstly, prepare the ordered Nafion nano-arrays by filling AAO template with low Nafion solution loading (only 0.75 g/m2). Secondly, imprint the ordered Nafion nano-arrays onto the commercial PEM under 140 °C to prepare the composite PEM with Nafion array. Thirdly, demold the composite PEM from the AAO template by using water as clean release agent. Lastly, recycle the AAO template to repeatedly prepare the composite PEM with Nafion array (at least 50 times). This nanoimprint method can prepare abundant composite PEMs by imprinting diverse ordered Nafion array structures on different commercial PEMs. In PEMFC, the composite PEM above has 1.6 times higher performance and one tenth lower hydrogen crossover than the corresponding commercial PEM. This nanoimprint method can be expanded to prepare the arrays on alkaline electrolyte membrane (AEM), PBI membrane and other electrolyte membranes. Furthermore, the application of these membranes can greatly promote the ordered MEA in PEMFC, AEM fuel cell, water electrolysis, and electrochemical synthesis, etc.