Nanoporous Templates Research Articles

Electrochemical Manipulation of Aligned Block Copolymer Templates.

Block copolymers have a wide range of functions in advanced electrochemistry because of their ability to self-assemble into ordered nanometer-sized structures, resulting in their extensive usage as nanoporous templates that can be electrochemically manipulated. These highly ordered nanoporous templates are used as working electrodes for electrodeposition and electropolymerization to build nanoelectrode arrays and can serve as models to study the diffusion pathway of redox-active units with regard to chemical modification of pores. The block copolymer system allows different morphologies to be utilized, but the most exploited structures are standing cylinders of the minority block that are etched to expose highly aligned porous nanoelectrode array templates. This review starts with introducing alumina and track-etched membranes as pioneer porous templates transitioning to the production of block copolymer films as succeeding templates, with a particular focus on both poly(styrene)-block-poly(methylmethacrylate) (PS-b-PMMA) and poly(styrene)-block-poly(lactide) (PS-b-PLA). The aim is to give fundamental insights of electrochemistry where functionality extends beyond to applications in the nanoscience field of biosensors and plastic electronics.

Driving the polymerization of PEDOT:PSS by means of a nanoporous template: Effects on the structure

Poly(3,4-ethylenedioxythiophene) (PEDOT) polymerization has been carried out both in a template-free environment and inside the nanopores of SBA-15 mesoporous silica. Comparing the two methods and the secondary doping of commercial PEDOT:PSS, we were able to study the structural effect of the templated polymerization via a multi-technique approach. We found that the confined polymerization favours a more linear configuration of the polymer chains, in a similar way to the well-known secondary doping with organic solvents. Moreover, comparison of computational and experimental results suggests that the PEDOT mean chain length is greater when the polymerization occurs in the nanoporous template, promoting the formation of a polymer with larger molecular weight and crystallinity.

Synthesis of polypyrrole nanorods via sacrificial removal of aluminum oxide nanopore template: A study on cell viability, electrical stimulation and neuronal differentiation of PC12 cells.

Synthesis of nanomaterials having uniform shape and size is a challenging task. Properties exhibited by such substrates would be compatible and homogeneous compared to the average properties displayed by those substrates with heterogeneous size. Herein, we report the synthesis of polypyrrole nanorods (PPy-NRs) of almost uniform size via oxidative chemical polymerization of pyrrole within anodized aluminum oxide nanopores followed by sacrificial removal of the template. Field emission scanning electron microscopy (FE-SEM), fourier transformed infra-red (FT-IR) spectra, X-ray diffraction (XRD), and ultra-violet-visible-near infra-red (UV-Vis-NIR) spectra of the substrate were used to analyze the physicochemical properties of as-synthesized PPy-NRs. PPy-NRs treated MC3T3-E1 and PC12 cells exhibited good biocompatibility in CCK-8 and live/dead assays. The assay showed more cell viability on PC12 cell lines. Electrical stimulation through PPy-NRs treated PC12 cells accelerated neuronal differentiation compared to those without electrical stimulation during in vitro cell culture.

Electrodeposition of Porous Fe-Ni-Co Nanowires Using Hydrogen Gas Bubbles

The use of hydrogen gas bubbles as a dynamic template accompanied with metal species reduction has recently been used to create porous metal thin films, where the metal deposits within spaces between bubbles. Creating porous nanowires within a nanoporous template is a greater challenge, as the gas bubbles can block the pores of the template, preventing deposition. Thus, the competition between the rate of metal deposition and hydrogen evolution reaction needs to be balanced. While this talk will focus on the electrodeposition process in creating porous metal nanowires, the selected Fe-Ni-Co material serves as a model oxygen electrocatalyst. Conditions making it possible to potentiostatically electrodeposit porous Fe-Ni-Co nanowires using a polycarbonate (PC) nanotemplate are presented. Results show that the pH plays an important role not only in defining the rate of hydrogen evolution, but also the type of metal ion species that are reduced, leading to a change of composition. The porous structure, obtained from the solution having a pH less than 1.0, was confirmed by SEM and TEM. Such an observation is contradictory to the results from anodic alumina oxide (AAO) templates, where no nanowires or very short nanowires were found at the same conditions due to bubble coalescence. The changes in the ionic strength gradient at the electrode surface towards the bulk electrolyte, and the absorbed metal ion intermediates, are suggested to play an important role in deterring bubble coalescence making it possible to create porous nanowires.

(Invited) Electrodeposited Metallic Nanowires for Bioanalytic Nanofluidic Devices

Electrodeposited metallic nanowires have been demonstrated as electrode or sensing materials in many applications such as optoelectronic devices, energy devices, and biosensors due to their excellent electrical and optical properties. However, most of previous demonstrations utilized the metallic nanowires in the form of percolating networks. Individual nanowires also have potential as nanoscale electrodes or nanoscale sensing materials for the applications where electrical signals need to be extracted from nanoscale components of the device. In this sense, metallic nanowires are suitable electrode or sensing materials for bioanalytic nanofluidic devices where electrical signals from nanoscale single molecules need to be interrogated in a device with nanoscale components. This talk will present strategies and technical challenges to be resolved in applying individual metallic nanowires in bioanalytic nanofluidic devices. While high rate synthesis of metallic nanowires can be achieved via electrodeposition in a nanoporous template, the main challenges to produce nanofluidic devices with individual nanowire electrodes include position and aligning the nanowires at designated locations and cover-plate bonding in the presence of electrode structures. Also, the efforts on device fabrication need to be combined with the effort on engineering nanowires with both sufficient mechanical strength and improved electrical conductivity, so that the nanowires are compatible with both the fabrication and operational protocols. This work is a part of the effort from the NIH Center for BioModular Multiscale Systems for Precision Medicine (CBM2) where the center goal is to design, produce and deliver to the medical community mixed-scale tools for analyzing circulating biomarkers for disease management for precision medicine

Progress in Nanoporous Templates: Beyond Anodic Aluminum Oxide and Towards Functional Complex Materials.

Successful synthesis of ordered porous, multi-component complex materials requires a series of coordinated processes, typically including fabrication of a master template, deposition of materials within the pores to form a negative structure, and a third deposition or etching process to create the final, functional template. Translating the utility and the simplicity of the ordered nanoporous geometry of binary oxide templates to those comprising complex functional oxides used in energy, electronic, and biology applications has been met with numerous critical challenges. This review surveys the current state of commonly used complex material nanoporous template synthesis techniques derived from the base anodic aluminum oxide (AAO) geometry.

Directed Self-Assembly of Colloidal Quantum Dots Using Well-Ordered Nanoporous Templates for Three-Colored Nanopixel Light-Emitting Diodes

We demonstrate high-resolution light-emitting diodes based on well-defined nanoarrays of colloidal quantum dots (QDs) with different sizes in a large area using nanoporous templates. To fabricate t...

Use of pyrophosphate and boric acid additives in the copper-zinc alloy electrodeposition and chemical dealloying

Over the last decade, nanoporous metals have attracted a growing attention due to the combination of structural and functional properties, such as their very high surface to volume ratio and mechanical rigidity. A recent and versatile process producing nanoporous metals is the dealloying of an initial alloy, i.e. the selective dissolution of the more reactive element of the alloy. In this work, we report on a method of CuZn alloy formation, without the use of furnaces or expensive techniques, and its subsequent chemical dealloying leading to nanoporous copper. Co-electrodeposition of CuZn alloys on a copper substrate is performed using pyrophosphate as a complexing agent in presence of boric acid, copper sulfate and zinc sulfate. The electrochemical behavior of this system is characterized by cyclic voltammetry, showing that a copper-zinc alloy is formed at −1.5 V vs. SCE. Cauliflower-like Zn-rich γ-brass and ε-brass coatings are obtained by co-electrodeposition. The thickness, the structure and the composition of the electrodeposited alloy can be tuned by varying the electrodeposition conditions. Thicker and rougher coatings with a higher zinc content are formed at more cathodic conditions. The electrodeposited CuZn coatings were chemically dealloyed, and a two-step dealloying protocol leads to open-framework nanoporous copper templates, which are a material of interest for energy storage, biosensors, and catalysis applications.

Electrochemical synthesis of nanowire anodes from spent lithium ion batteries

A novel process is proposed to produce nanostructured batteries anodes from spent lithium-ion batteries. The electrodic powder recovered by the mechanical treatment of spent batteries was leached and the dissolved metals were precipitated as cobalt carbonates. Two different precipitation routes were separately tested producing cobalt carbonates with different Cu and Fe contents. Nanowire anodes were produced by electrodeposition into nanoporous alumina templates from the electrolytic baths prepared by dissolution of the precipitated carbonates. The electrochemical performances of the produced anodes were evaluated as compared to nanowire anodes produced with the same electrodeposition method but using a synthetic cobalt bath. The application of the carbonates produced by directly precipitating all the leached metals gave nanowires with capacity about halved as compared to the nanowires electrodeposited from the synthetic bath. Selectively removing Cu and Fe prior cobalt carbonate precipitation yielded, in contrast, nanowires with capacity initially larger and then gradually approaching that attained by the nanowire electrodeposited from the synthetic bath. A detailed analysis is presented describing the role of metallic impurities in determining the capacity of the produced nanowires. The impact of the illustrated results for the development of sustainable recycling processes of lithium-ion batteries is discussed.

Copper–zinc alloy electrodeposition mediated by triethanolamine as a complexing additive and chemical dealloying

Nanoporous metals offer an open nanostructured network with a very high specific area and nanoporous templates can be used in many applications from energy storage and catalysis to sensors. One way to produce nanoporous (noble) metal templates is the dealloying approach starting from an alloy based on elements of different reactivities. In this work, co-electrodeposition of CuZn alloys is performed with triethanolamine (TEA) as a complexing agent to produce CuZn precursor films for further dealloying. To investigate the phenomena of electrodeposition, the electrochemical behavior of a copper substrate is compared to an ITO substrate in different NaOH electrolytes, with and without metal salt or additive. Cyclic voltammetry shows that a passivating layer forms on a copper substrate but is of lower stability in the presence of TEA. Potentiostatic electrodeposition from copper sulfate and zinc sulfate with TEA leads to Zn-rich γ-brass coatings. Nanoporous structuration is obtained after chemical dealloying of the electrodeposited alloy coatings. The dealloying process induces an increase of the electrochemically active surface area by a factor 25. The nanoscale structuration is confirmed by FIB-SEM.

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.

Controlled Growth of Highly Aligned Cu Nanowires by Pulse Electrodeposition in Nanoporous Alumina.

Metallic nanowire networks are emerging as potential replacements for transparent conducting oxide coatings because of their high conductivity, flexibility and relative transparency. However, a cheap, reliable and controlled manufacturing process is required to exploit this and the surface of the copper nanowire needs to be protected if high conductivity is to be retained. In this study a fabrication method for highly aligned and densely packed copper nanowires with controlled length using pulse-electrodeposition and a nanoporous alumina template has been developed. Nanoporous alumina was obtained by anodisation of pure aluminum in oxalic acid using a two-step anodisation process. In order to provide the conductivity at the bottom of the pores, a dendritic structure at the interface was created through the stepwise voltage reduction method with a voltage reduction rate of 15 V/s followed by mild chemical etching. Highly repeatable near 100% filling of copper is achieved. Copper nanowire length was highly controllable from 100 nm to 2 μm with a fixed diameter of 60 ± 5 nm by monitoring current density during the deposition. Such controlled growth of Cu nanowires could lead towards transparent conducting layer applications but the protection of the material against oxidation remains an issue.

Hierarchical Nanoporous Carbon Templated and Catalyzed by the Bicontinuous Nanoporous Copper for High Performance Electrochemical Capacitors

AbstractTo enhance the performance of electrochemical capacitor, the nanostructured carbon materials with large surface area, appropriate pore distributions, suitable electronic conductivity and perfect chemical stability are pursued. Herein, the highly graphitized hierarchical porous carbon with well‐defined porosity are fabricated. For the first time, the novel bicontinuous nanoporous copper is used as both the template and the catalyst to synthesize the porous carbon materials. The as‐prepared porous carbon demonstrates a high specific surface area of 1826 m2 g−1 benefitting from the bicontinuous nanoporous copper template and KOH activation. By electrochemical test, the nanoporous carbon material displays a specific capacitance of 210 F g−1 at a current density of 0.2 A g−1 within 6 M KOH aqueous solution. The material demonstrates excellent cycling stability with a 95.4% capacity retention for 10 000 cycles with a current density of 1 A g−1. The present work provides a facile approach for fabrication of carbon‐based electrode materials for electrochemical capacitors.

Luminescent Organic Barcode Nanowires for Effective Chemical Sensors.

Chemical materials are sometimes harmful to the environment as well as humans, plants, and animals. Thus, high-performance sensor systems have become more important in the past few decades. To achieve pH scale sensing in nanosystems, we applied luminescence polymer nanowires with alumina oxide template method with electrochemical polymerization. We made polymer nanowire barcode by alternately stacking poly(3-methylthiophene) (P3MT) and poly(3,4-ethylenedioxythiophene) (PEDOT) in a nanoporous template. After polymerization, a hydrofluoric acid solvent was used to remove the template, and, for changing the pH scale, we used sodium hydroxide. We measured optical properties of each part of barcode using Raman scattering and photoluminescence and confirmed that only P3MT was changed by alkali treatment.

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.

Characterization of PDPPBTT:PC71BM bulk heterojunction nanostructures synthesized by a porous alumina template-assisted method

To enhance the charge transfer efficiency of bulk heterojunction materials, a nanostructure comprising blended PDPPBTT and PC71BM prepared via the porous alumina template-assisted method was proposed. Both materials were dissolved in chloroform in a 1:1 ratio at two different concentrations (5 and 10 mg mL−1) and infiltrated into the nanopore template using a centrifuge method. The characterization results showed that one-dimensional nanostructures were successfully prepared. The high concentration solution resulted in nanostructures with large diameters but short lengths, which could absorb light effectively. Moreover, the high concentration solution exhibited low photoluminescence intensity, thus indicating efficient charge transfer from PDPPBTT to PC71BM.

Fabrication of porous anodic alumina (PAA) templates with straight pores and with hierarchical structures through exponential voltage decrease technique

The present work aims to become a standard step for the fabrication of the next generation porous anodic alumina (PAA) templates based devices and to provide new insights on the mechanism involved in the porous anodic alumina formation. The oxide barrier layer at the bottom of the pores has been successfully thinned by applying an exponential voltage decrease process followed by a wet chemical etching. The impact of the potential drop on the PAA structure has been deeply investigated, as well as the electrolyte temperature, the number of potential steps and the exponential decay rate. The presented results underline that a smart adjustment between the anodization conditions and exponential voltage decay parameters can simultaneously give PAA structures with straight pores and remove the dielectric layer in spite of applying the exponential voltage decay step. Additionally, the PAA structure has been tuned to fabricate hierarchically nanoporous templates with secondary pores ranging from 2 up to 10 branches.

Impact of the Interfacial Energy and Density Fluctuations on the Shift of the Glass-Transition Temperature of Liquids Confined in Pores

The behavior of the low- and high-molecular weight glass formers confined in nanoporous templates remains an unsolved puzzle despite the intensive long-term studies in this matter. Special effort is taken to understand the enhancement of segmental or structural dynamics and the depression of the glass-transition temperatures, Tgs in materials infiltrated in pores of the nanometric size. In this paper, we have analyzed dielectric, calorimetric, and contact angle data collected for various systems to determine which factors are responsible for these effects. It turned out that with increasing interfacial energy, molecules attached to the pore walls (interfacial layer) vitrify at higher temperatures. Moreover, the dynamics of core molecules starts to deviate from bulk-like behavior. Therefore, a greater depression of the glass-transition temperature, Tg, of this fraction of molecules is noted. Also, it was found that the sensitivity of structural dynamics to the density fluctuations, quantified by the pressu...

Deep ultraviolet light-emitting diodes with improved performance via nanoporous AlGaN template.

We report the performance enhancement of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) using AlGaN nanoporous template (NPT). The NPT was fabricated by the electrochemical etching method and served as the dislocation filtering layer and strain relieving layer. The n-AlGaN laterally regrown on NPT showed reduced dislocation density and mitigated compressive strain comparing with that on the as-grown template (AGT). A 23% improvement of internal quantum efficiency was achieved for the multiple quantum wells thereon. Moreover, the nanopores in the NPT transformed into elongated air voids during high temperature growth process, which could facilitate the escaping of photons by scattering and thus improve the light extraction efficiency. As a consequence, the DUV LED based on NPT demonstrated an increase of the light outpower by 50% at 20 mA than that on AGT.

The Effect of Magnetic Field on Electro-deposition of Nickel and Cobalt Nanowires

Anodized Aluminum Oxide (AAO) nano-porous template is fabricated and nickel (Ni) nanowires are synthesized in the nano pores of AAO template by AC electro-deposition technique in the presence and absence of magnetic field applying only in a direction parallel to nanowire axis. Cobalt (Co) nanowires are fabricated by applying magnetic field externally both in perpendicular and parallel directions to the axis of nanowires. Magnetic field can bring change in the preferential grain growth of Ni and Co nanowires. Magnetic field applied parallel to nanowire axis increases deposition rate and current density due to magneto hydrodynamic effect, while magnetic field applied in perpendicular to the surface of electrode does not bring significant change in the chemical reaction. Magnetic properties are also affected by applying external magnetic field during deposition. These changes associated with grain growth in the preferred direction of Ni and Co nanowires are discussed in this article.