Nanopore Arrays Research Articles

A high density nanopore 3-triangulene kagome lattice.

Nanopore-containing two-dimensional materials have been explored for a wide range of applications including filtration, sensing, catalysis, energy storage and conversion. Triangulenes have recently been experimentally synthesized in a variety of sizes. In this regard, using these systems as building blocks, we theoretically examined 3-triangulene kagome crystals with inherent holes of ∼12 Å diameter and a greater density array of nanopores (≥1013 cm-2) compared to conventional 2D systems. The energetic, electronic, and transport properties of pristine and B/N-doped 3-triangulene kagome crystals were evaluated through a combination of density functional theory and non-equilibrium Green's function method. The simulated scanning tunneling microscopy images clearly capture electronic perturbation around the doped sites, which can be used to distinguish the pristine system from the doped systems. The viability of precisely controlling the band structure and transport properties by changing the type and concentration of doping atoms is demonstrated. The findings presented herein can potentially widen the applicability of these systems that combine unique electronic properties and intrinsically high-density pores, which can pave the way for the next generation of nanopore-based devices.

Dual-polarization strong nonreciprocal thermal radiation with silicon-based nanopore arrays

Dual-polarization strong nonreciprocal thermal radiation with silicon-based nanopore arrays

Ultrahigh sensitive SERS film of silver nanorods grown on nanohole array template by oblique angle deposition

To develop a highly sensitive silver nanorod (AgNR) array SERS film, anodic aluminum oxide (AAO) nanohole array templates were employed as seed substrates for oblique angle deposition (O.A.D.) by thermal evaporation. By pore broadening process, precise hole arrays of various diameters were fabricated from preliminarily prepared nanoholes of 30 nm diameter comprising equilateral triangle unit cells whose side length is 100 nm. Aligned silver nanorods of ∼1 μm length were fabricated on the several kinds of seed templates. The optical properties of the AgNR films were measured using thiophenol self-assembled monolayers on the film surfaces and a micro-Raman spectrometer employing a 785 nm pump laser. Out of the AgNR array samples, the AgNR array deposited on an 80-nm hole array substrate showed the highest SERS activity. The highest surface enhancement factor (E.F.) of Raman signal measured in this experiment was ∼7·107, which is ∼7 times higher than that of the AgNR array fabricated on a flat substrate. The main role of the nanopore array substrate was found to decrease the density of the grown nanorods, which is the key parameter determining the E.F. values of the AgNR arrays. From this and previous works, the optimum nanorod density is anticipated to be 8–9 rods/μm2, where E.F. of > 109 could be obtained. The nanorod density of the optimum AgNR array in this experiment was ∼10/μm2. The origin of the key role conducted by the nanorod density cannot be explained by hot spot effect and waits for understanding in the future studies. The ultrahigh sensitive AgNR array SERS film obtained in this work can be a very powerful medium for various chemical and biological sensors.

Biosensor based on multiple metal layer-hole array

We propose a biosensor which is sensitive to the refraction index (RI) of the tested liquid. The sensor is composed of a metal-insulator-metal structure based on periodic nanopore arrays, whose absorption spectrum exhibits a narrow peak at the resonant wavelength. The finite difference time domain method is used to simulate the proposed structure. The results show that there is a narrow resonant peak at the wavelength of 800 nm with RI of 1.33. By adding grooves on the lower metal layer, the maximum absorption rate increases to 99.7%. When RI varies in the range from 1.33 to 1.35, it can have a high sensitivity of 550 nm /RIU, a narrow half peak full width of 5.87 nm, and a figure of merit of 93.7. In addition, the absorption peak value also changes significantly with a sensitivity of 1845%/RIU, which can be used to measure the concentration of bovine serum albumin and other solutions to achieve biosensors.

Improving the rectification characteristics of GaN/Si heterojunction by constructing an interpenetrating two-phase interface layer

Heterojunctions with patterned or nanostructured interfaces usually show specific advantages in developing high-performance optoelectronic devices, especially for those composed of two kinds of semiconductors with large lattice and thermal mismatches. In this study, a heterojunction with complex interface structures is prepared by growing GaN on a patterned Si hierarchical structure, the Si nanoporous pillar array (Si-NPA). The most prominent feature of GaN/Si-NPA is its interpenetrated two-phase interface layer composed of massive Si and GaN nanocrystallites. Compared with GaN/Si heterojunction with planar interface, GaN/Si-NPA shows improved electrical properties such as increased breakdown voltage and lowered leakage current density. The property improvement is ascribed to the promotion of the junction quality and the lowering of the overall defect density, both of which are attributed to the reduction of the strain and stress through a three-dimensional release mode. The research provides a viable approach for constructing high-quality heterojunctions by using largely mismatched semiconductors, which might find extensive applications in designing and fabricating optoelectronic devices.

An amplification-free CRISPR-SERS biosensor for specific, sensitive and rapid detection of Salmonella Typhimurium in poultry

CRISPR (Clustered regularly interspaced short palindromic repeats) has been a cutting-edge biotechnology in both gene editing and biosensing due to its desirable features, such as high base resolution and set-and-forget operation. However, as a nucleic acid detection method, an DNA/RNA amplification procedure is still inevitable in CRISPR biosensors. In this study, a highly-ordered nanopore array SERS substrate, coated with silver nanoparticles, was fabricated and utilized as a platform for the specific detection of Salmonella Typhimurium (S. Typhimurium) without the time-consuming DNA amplification step. The smart sensing strategy was established by introducing an ssDNA labeled with a Raman active molecule as a signal report probe to show the changes during target identification and detection. The CRISPR-SERS biosensor was developed by combining the ultra-sensitive sensing mechanism of CRISPR technology with the SERS analytical method, aiming at detecting the invasin A gene (invA) of S. Typhimurium. The sensing materials and operation conditions were optimized to maximize the output signal and minimize the cost. The results showed that the proposed biosensor could specifically detect S. Typhimurium with a limit of detection (LOD) of 110 CFU/mL in poultry samples within 2 h. This CRISPR-SERS sensing strategy could provide an alternative way for pathogen detection in food safety monitoring.

Bio-inspired, biodegradable, and fluffy 3D PLA fibrous sponges with dynamic fractal nano-sweepers for on-demand oil/water separation

Frequent oil leakage results in a huge waste of fossil fuel resources and severely threatens the global water-waste-energy nexus. Membrane separation technology is a promising effective and energy-saving approach for recycling waste oil resources and oily-environment remediation. Despite many bioinspired materials with the mitigated selectivity/permeability trade-off having been developed, a significant issue has been ignored, that is, most of the membranes are non-biodegradable and could cause secondary environmental pollution. In this work, inspired by the natural 3D coral organisms with sustainable fiber tentacles; we propose a biomimetic crystal-engineering strategy of space-confined solvent-induced recrystallization to prepare a 3D biodegradable PLA fibrous sponge with coral-like nanoflower/honeycomb sweeper arrays. By virtue of the coral-like nanoporous fractal arrays with superhydrophobicity and proactive fouling resistance, the resulting PLA sponge exhibits excellent separation performance of immiscible oil–water mixtures (ultrahigh permeation flux of up to 27,908 L m-2h−1) and water-in-oil emulsions (high separation efficiency of up to 99.9 %). Significantly, with the advantage of biodegradability and recyclability of PLA, we envision such environmentally friendly PLA fibrous sponges would show promising potential in the fields of environmental remediation, oil recovery, self-cleaning, etc.

Enhanced electrocatalytic hydrogen evolution of phase-modulated TiO2@MoS2 nanoporous flims decorated by Ni nanoclusters

In this study, we present the fabrication and characterization of phase- and morphology-modulated TiO2 @MoS2 nanopore arrays with additional Ni decoration. The groundwork for these structures is established by the creation of highly ordered TiO2 nanoporous arrays through facile anodic oxidation, forming a background for the subsequent MoS2 nanosheet arrays. Enhanced conductivity within the heterostructure is achieved through a phase modulation of MoS2, transitioning from the 2 H phase to the 1 T phase via a hydrothermal exfoliation treatment. Notably, the introduction of Ni nanoclusters proves advantageous in preserving the 1 T phase during storage and cycling, thus enhancing stability during the performance of the hydrogen evolution reaction. Phase variation and different doping sites are proposed via theoretical calculation, where, smaller energy barriers are attained within the Ni-doped 1 T-MoS2 nanopores toward H+ to H2 transformation. Using the prepared TiO2 @MoS2-1 T + Ni electrode, an overpotential of 270 mV was achieved at a current density of 10 mA/cm², along with a Tafel slope of 63 mV dec⁻¹ .

Optimizing the Operational Parameters Used in Preparing Anodic Aluminum Oxide (AAO) Templates from Low-purity Aluminum

Anodized aluminum oxide (AAO) templates with well-defined geometric pore features and uniform nanoporous arrays were successfully obtained from recyclable low-cost, low-purity (99.16%) aluminum via a two-step anodizing process. The templates were characterized by scanning electron microscopy (SEM) and operating parameters were optimized using a Box-Behnken experimental design. The best conditions were found for an oxalic acid electrolyte concentration of 0.6 M, an anodizing potential of 46 V, and a bath temperature of 10 °C. This process resulted in an averaged regularity ratio (ravg) value of 2.66 which compares very favorably with previously reported values obtained from higher-purity aluminum (99.5%). Templates developed from low-purity aluminum are more suitable for high-volume industrial applications where there is a practical trade-off between cost and the quality of the geometric pores.

Ultra-narrowband circular dichroism in all-dielectric chiral nanohole arrays based on griddings and monolayer MoS2

The strong circular dichroism (CD) of metallic chiral nanostructures can be applied to polarization conversion, negative refraction materials, and chiral molecule detection. However, metallic chiral nanostructures with losses struggle to produce dynamically tunable ultra-narrow band circular dichroism signals, which greatly limits their applications in sensing. In this paper, the MoS2 and Sb2S3 with phase change characteristics are introduced into all-dielectric chiral nanopore arrays (ACNAs) based on gridding to generate dynamically tunable ultra-narrow band circular dichroism signals. Simulation results show that ACNAs/MoS2 produce two strong narrow-band CD signals in the visible range. The maximum CD intensity can reach 0.75, and the maximum half-width can reach 0.8 nm. The electric field distribution indicates that two CD signals are mainly caused by the guided mode resonance. The ultra-narrow band CD signals both lie on their geometric parameters and can realize the dynamic regulation by changing the incidence angle of lights and the crystalline state of Sb2S3. Furthermore, the sensing characteristics of this device were evaluated by analyzing the effects of different concentrations of SARS-CoV-2 solutions on the CD spectra. These findings will facilitate the design of all-dielectric chiral nanostructures with dynamically tunable ultra-narrow band CDs and facilitate their applications in biosensing.

Dual-polarization strong nonreciprocal thermal radiation under near-normal incidence

Performance of irreversible radiation is limited by the single polarization and large incident angles. Given potential applications of nonreciprocal thermal radiation, the implementation of irreversible radiation for both TE and TM polarizations at small angles is highly demanded. A solution that combines periodic silicon-based nanopore arrays with magneto-optical material (InAs) is proposed in this work. The results show that the absorptivity and emissivity of two polarizations are close to 98% with an incident angle of 1.5° and a high Q factor over 1680. By adjusting the applied magnetic field, the emissivity and transverse magneto-optical Kerr effect can be dynamically tuned. The validity of the calculation results is verified by the rigorous coupled-wave analysis and finite element method. Impedance matching theory and coupled mode theory are adopted to further analyze the physical origin. The proposed scheme and thermal radiator that allow nonreciprocal thermal radiation for both TE and TM polarizations at an extremely small incident angle offer valuable guidance to the development of dual-polarization nonreciprocal radiation devices.

Nanopore-Enabled Dark-Field Digital Sensing of Nanoparticles.

In this study, we use nanopore arrays as a platform for detecting and characterizing individual nanoparticles (NPs) in real time. Dark-field imaging of nanopores with dimensions smaller than the wavelength of light occurs under conditions where trans-illumination is blocked, while the scattered light propagates to the far-field, making it possible to identify nanopores. The intensity of scattering increases dramatically during insertion of AgNPs into empty nanopores, owing to their plasmonic properties. Thus, momentary occupation of a nanopore by a AgNP produces intensity transients that can be analyzed to reveal the following characteristics: (1) NP scattering intensity, which scales with the sixth power of the AgNP radius, shows a normal distribution arising from the heterogeneity in NP size, (2) the nanopore residence time of NPs, which was observed to be stochastic with no permselective effects, and (3) the frequency of AgNP capture events on a 21 × 21 nanopore array, which varies linearly with the concentration of the NPs, agreeing with the frequency calculated from theory. The lower limit of detection (LOD) for NPs was 130 fM, indicating that the measurement can be used in applications in which ultrasensitive detection is required. The results presented here provide valuable insights into the dynamics of NP transport into and out of nanopores and highlight the potential of nanopore arrays as powerful, massively parallel tools for nanoparticle characterization and detection.

High-Resolution Nanotransfer Printing of Porous Crossbar Array Using Patterned Metal Molds by Extreme-Pressure Imprint Lithography.

High-resolution nanotransfer printing (nTP) technologies have attracted a tremendous amount of attention due to their excellent patternability, high productivity, and cost-effectiveness. However, there is still a need to develop low-cost mold manufacturing methods, because most nTP techniques generally require the use of patterned molds fabricated by high-cost lithography technology. Here, we introduce a novel nTP strategy that uses imprinted metal molds to serve as an alternative to a Si stamp in the transfer printing process. We present a method by which to fabricate rigid surface-patterned metallic molds (Zn, Al, and Ni) based on the process of direct extreme-pressure imprint lithography (EPIL). We also demonstrate the nanoscale pattern formation of functional materials, in this case Au, TiO2, and GST, onto diverse surfaces of SiO2/Si, polished metal, and slippery glass by the versatile nTP method using the imprinted metallic molds with nanopatterns. Furthermore, we show the patterning results of nanoporous crossbar arrays on colorless polyimide (CPI) by a repeated nTP process. We expect that this combined nanopatterning method of EPIL and nTP processes will be extendable to the fabrication of various nanodevices with complex circuits based on micro/nanostructures.

Numerical design of surface magneto-plasmon sensors of Au/Co double-layer square arrayed nanopores on the continuous gold thin film

Surface magneto-plasmon (SMP) sensors have attracted continuous attention due to their field enhanced signal-to-noise ratios, sensitivities, and detection limits. Although many progresses have been achieved in the nanodots, nanorods, or nanodiscs, few studies have been conducted on films containing arrays of nanopores or nanoholes. SMP sensors based on arrays of nanopores could be much more promising for future ultrasensitive optical detectors since they can couple the SMP enhancement with Fabry–Pérot interference of nanopores for high-performance resonator sensors that can be further tuned under a magnetic field. We, thus, propose a high-performance SMP sensor based on the magneto-optical Kerr effect (MOKE) of films containing a square array of Au–Co double-layer nanopores on the Au film substrate or SMP-MOKE sensor. The local electric field around the magneto-plasmon arrays of nanopore photonic crystals can be greatly enhanced by applying an external magnetic field due to their magneto-optical activity and excitation of high-quality surface plasmon resonances. Multi-physics coupling simulations and validation by COMSOL on the structure-dependent optical properties suggest that the proposed SMP-MOKE sensor has a high sensitivity of 711 nm/Refractive Index Units (RIUs) and a figure of merit (FOM) of the order of 105 RIU−1, which is an order of magnitude greater than the best grating-type sensors, to the best of our knowledge. Our results shall facilitate the theoretical design for the future fabrication of ultra-sensitive sensors or resonators with excellent FOM and reliability for air-quality monitoring or chemical sensing, etc.

Recent Progress of Self-Supported Metal Oxide Nano-Porous Arrays in Energy Storage Applications.

The demand for high-performance and cost-effective energy storage solutions for mobile electronic devices and electric vehicles has been a driving force for technological advancements. Among the various options available, transitional metal oxides (TMOs) have emerged as a promising candidates due to their exceptional energy storage capabilities and affordability. In particular, TMO nanoporous arrays fabricated by electrochemical anodization technique demonstrate unrivaled advantages including large specific surface area, short ion transport paths, hollow structures that reduce bulk expansion of materials, and so on, which have garnered significant research attention in recent decades. However, there is a lack of comprehensive reviews that discuss the progress of anodized TMO nanoporous arrays and their applications in energy storage. Therefore, this review aims to provide a systematic detailed overview of recent advancements in understanding the ion storage mechanisms and behavior of self-organized anodic TMO nanoporous arrays in various energy storage devices, including alkali metal ion batteries, Mg/Al-ion batteries, Li/Na metal batteries, and supercapacitors. This review also explores modification strategies, redox mechanisms, and outlines future prospects for TMO nanoporous arrays in energy storage.

Controllable Fabrication and Rectification of Bipolar Nanofluid Diodes in Funnel-Shaped Si3 N4 Nanopores.

Solid-state nanopores attract widespread interest, owning to outstanding robustness, extensive material availability, as well as capability for flexible manufacturing. Bioinspired solid-state nanopores further emerge as potential nanofluidic diodes for mimicking the rectification progress of unidirectional ionic transport in biological K+ channels. However, challenges that remain in rectification are over-reliance on complicated surface modifications and limited control accuracy in size and morphology. In this study, suspended Si3 N4 films of only 100nm thickness are used as substrate and funnel-shaped nanopores are controllably etched on that with single-nanometer precision, by focused ion beam (FIB) equipped with a flexibly programmable ion dose at any position. A small diameter 7nm nanopore can be accurately and efficiently fabricated in only 20ms and verified by a self-designed mathematical model. Without additional modification, funnel-shaped Si3 N4 nanopores functioned as bipolar nanofluidic diodes achieve high rectification by simply filling each side with acidic and basic solution, respectively. Main factors are finely tuned experimentally and simulatively to enhance the controllability. Moreover, nanopore arrays are efficiently prepared to further improve rectification performance, which has great potential for high-throughput practical applications such as extended release of drugs, nanofluidic logic systems, and sensing for environmental monitoring and clinical diagnosis.

Tape of the truth: Ta2O5 nanopore array formed under broad potential range and SERS potential after silver sputtering

The deposition of a plasmonic metal layer on a nanostructured oxide surface is one of the important methods of preparing a platform for surface-enhanced Raman scattering (SERS) measurements. In this contribution, we describe the formation of SERS substrates by the deposition of a silver layer on ordered a Ta2O5 nanopore array. The influence of various experimental anodization process parameters on the morphology of a Ta2O5 nanopore array was carefully studied. It was found that the formation of a Ta2O5 nanopore array is possible under a broad potential range (15–50 V) in a highly acidic solution containing F− ions. In some cases, the nanopore array structures were covered by an outer layer rich in F− and SO42− ions, which could easily be removed using adhesive tape or by sonication. The deposition of an Ag layer led to SERS activity. The optimal Ag layer thickness was specified based on SEM and DRS measurements. The SERS substrates formed exhibited high point-to-point, sample-to-sample and time durability.

Efficient Suppression of Persistent Photoconductivity in β-Ga2O3-Based Photodetectors with Square Nanopore Arrays.

In this work, square nanopore arrays were developed on the surface of β-Ga2O3 microflakes using focused ion beam (FIB) etching, and solar-blind photodetectors (PDs) were fabricated based on the β-Ga2O3 microflakes with square nanopore arrays. The β-Ga2O3 microflake-based device was transformed from a gate voltage depletion mode to an oxygen depletion mode by FIB etching. The developed device exhibited excellent solar-blind PD performance with extremely high responsivity (1.8 × 105 at 10 V), detectivity (3.4 × 1018 Jones at 10 V), and light-to-dark ratio (9.3 × 108 at 5 V) as well as good repeatability and excellent stability. The intrinsic mechanism responsible for this performance was then systematically discussed. This work opens up a new avenue for the fabrication of high-performance β-Ga2O3-based low-dimensional PDs with high reproducibility by employing the FIB etching process.

Controllable Fabrication of Silicon Nanopore Arrays by Two-Step Inductively Coupled Plasma Etching Using Self-Assembled Anodic Aluminum Oxide Mask

Silicon nanopore arrays (SiNPs) were prepared by a two-step inductively coupled plasma (ICP) etching process using a self-assembled anodic aluminum oxide film mask. The influence of etching parameters (first-step etching time, Cl2 proportion in the etching gas, etching pressure, ICP power, and radio frequency (RF) power) on the morphology of the SiNPs were systematically investigated. The results revealed that the first step of ICP etching can effectively remove the barrier layer of the mask. Higher Cl2 proportion and lower etching pressure increase the chemical corrosion and physical bombardment of ICP etching, respectively, which may damage the porous morphology. ICP power affects both chemical reaction etching and physical bombardment, but the RF power mainly affects physical etching. The etching rate is positively correlated with Cl2 proportion and RF power, and negatively correlated with etching pressure. The optimized first-step etching time, Cl2/Ar ratio, etching pressure, ICP power and RF power for high-quality SiNPs are approximately 10 s, 60%, 7 mTorr, 900 W and 100 W, respectively. Precise control of the pore size and depth of the SiNPs can be achieved using this controllable growth process. These results demonstrate a simple and controllable way to achieve good quality SiNPs with desired sizes.

High-resolution discrimination of homologous and isomeric proteinogenic amino acids in nanopore sensors with ultrashort single-walled carbon nanotubes

The hollow and tubular structure of single-walled carbon nanotubes (SWCNTs) makes them ideal candidates for making nanopores. However, the heterogeneity of SWCNTs hinders the fabrication of robust and reproducible carbon-based nanopore sensors. Here we develop a modified density gradient ultracentrifugation approach to separate ultrashort (≈5-10 nm) SWCNTs with a narrow conductance range and construct high-resolution nanopore sensors with those tubes inserted in lipid bilayers. By conducting ionic current recordings and fluorescent imaging of Ca2+ flux through different nanopores, we prove that the ion mobilities in SWCNT nanopores are 3-5 times higher than the bulk mobility. Furthermore, we employ SWCNT nanopores to discriminate homologue or isomeric proteinogenic amino acids, which are challenging tasks for other nanopore sensors. These successes, coupled with the building of SWCNT nanopore arrays, may constitute a crucial part of the recently burgeoning protein sequencing technologies.