Fabrication Of Nanopores Research Articles

Direct Fabrication of Atomically Defined Pores in MXenes Using Feedback-Driven STEM.

Controlled fabrication of nanopores in 2D materials offer the means to create robust membranes needed for ion transport and nanofiltration. Techniques for creating nanopores have relied upon either plasma etching or direct irradiation; however, aberration-corrected scanning transmission electron microscopy (STEM) offers the advantage of combining a sub-Å sized electron beam for atomic manipulation along with atomic resolution imaging. Here, a method for automated nanopore fabrication is utilized with real-time atomic visualization to enhance the mechanistic understanding of beam-induced transformations. Additionally, an electron beam simulation technique, Electron-Beam Simulator (E-BeamSim) is developed to observe the atomic movements and interactions resulting from electron beam irradiation. Using the MXene Ti3C2Tx, the influence of temperature on nanopore fabrication is explored by tracking atomic transformations and find that at room temperature the electron beam irradiation induces random displacement and results in titanium pileups at the nanopore edge, which is confirmed by E-BeamSim. At elevated temperatures, after removal of the surface functional groups and with the increased mobility of atoms results in atomic transformations that lead to the selective removal of atoms layer by layer. This work can lead to the development of defect engineering techniques within functionalized MXene layers and other 2D materials.

Strain-induced fabrication of anisotropic nanopores by in-situ E-beam irradiation

Anisotropic nanopores are essential to regulate materials' anisotropic performance including thermal conductivity, ion blocking and so on. Nevertheless, fabricating anisotropic nanopores remains challenging because the formation mechanism is ambiguous, due to the lack of direct experimental evidence. Here, we reveal a unique strain-induced mechanism for the fabrication of anisotropic nanopores under electron beam irradiation. With the in-situ transmission electron microscopy (TEM) technique, an initial symmetric nanopore, with another nanopore nearby, is found to expand relatively uniformly in the first stage. When the spacing between two nanopores reaches to a critical point, however, the area near to the reference nanopore is stretched drastically by a strong driving force along the spacing direction, resulting in an obvious anisotropic morphology. The surrounding environment, spacing and relative position between two nanopores significantly influence the shape of eventually formed nanopores by controlling the strain's uniformity, action range and direction, respectively. Our work demonstrates a novel mechanism and visual evidence for the preparation of asymmetric nanopores in real time, with the hope of assisting in the controllable fabrication of desired nanostructures.

Controllable Fabrication of Sub-10 nm Graphene Nanopores via Helium Ion Microscopy and DNA Detection.

Solid-state nanopores have become a prominent tool in the field of single-molecule detection. Conventional solid-state nanopores are thick, which affects the spatial resolution of the detection results. Graphene is the thinnest 2D material and has the highest spatial detection resolution. In this study, a graphene membrane chip was fabricated by combining a MEMS process with a 2D material wet transfer process. Raman spectroscopy was used to assess the quality of graphene after the transfer. The mechanism behind the influence of the processing dose and residence time of the helium ion beam on the processed pore size was investigated. Subsequently, graphene nanopores with diameters less than 10 nm were fabricated via helium ion microscopy. DNA was detected using a 5.8 nm graphene nanopore chip, and the appearance of double-peak signals on the surface of 20 mer DNA was successfully detected. These results serve as a valuable reference for nanopore fabrication using 2D material for DNA analysis.

Fast Fabrication Nanopores on a PMMA Membrane by a Local High Electric Field Controlled Breakdown.

The sensitivity and accuracy of nanopore sensors are severely hindered by the high noise associated with solid-state nanopores. To mitigate this issue, the deposition of organic polymer materials onto silicon nitride (SiNx) membranes has been effective in obtaining low-noise measurements. Nonetheless, the fabrication of nanopores sub-10 nm on thin polymer membranes remains a significant challenge. This work proposes a method for fabricating nanopores on polymethyl methacrylate (PMMA) membrane by the local high electrical field controlled breakdown, exploring the impact of voltage and current on the breakdown of PMMA membranes and discussing the mechanism underlying the breakdown voltage and current during the formation of nanopores. By improving the electric field application method, transient high electric fields that are one-seven times higher than the breakdown electric field can be utilized to fabricate nanopores. A comparative analysis was performed on the current noise levels of nanopores in PMMA-SiNx composite membranes and SiNx nanopores with a 5 nm diameter. The results demonstrated that the fast fabrication of nanopores on PMMA-SiNx membranes exhibited reduced current noise compared to SiNx nanopores. This finding provides evidence supporting the feasibility of utilizing this technology for efficiently fabricating low-noise nanopores on polymer composite membranes.

Strong Carbon Layer-Encapsulated Cobalt Tin Sulfide-Based Nanoporous Material as a Bifunctional Electrocatalyst for Zinc-Air Batteries.

Global demands for cost-effective, durable, highly active, and bifunctional catalysts for metal-air batteries are tremendously increasing in scientific research fields. In this work, a strategy for the rational fabrication of carbon layer-encapsulated cobalt tin sulfide nanopores (CoSnOH/S@C NPs) material as a bifunctional electrocatalyst for rechargeable zinc (Zn)-air batteries by a cost-effective and facile two-step hydrothermal method is reported. Moreover, the effect of metal elements on the morphology of CoSnOH nanodisks material via the hydrothermal method is investigated. Owing to its excellent nanostructure, exclusive porous network, and high specific surface area, the optimized CoSnOH/S@C NPs material reveals superior catalytic properties. The as-prepared CoSnOH/S@C NPs electrocatalyst reveals better properties of oxygen reduction reaction (half-wave potential of -0.88 V vs reversible hydrogen electrode) and oxygen evolution reaction (overpotential of 137mV at 10mAcm-2) when compared with commercial Pt/C and IrO2 catalyst materials. Most significantly, the CoSnO/S@C NPs-based Zn-air battery exhibits more excellent cycling stability than the Pt/C+IrO2 catalyst-based one. Consequently, the proposed material provides a new route for fabricating more active and stable multifunctional catalyst materials for energy conversion and storage systems.

Differentiating Single Multiple Nanopore Through Conductance Distribution Analysis

AbstractSolid‐state nanopore sensors, a type of resistive pulse sensing, achieve optimal signal‐to‐noise performance with a single nanopore. However, the processes involved in solid‐state nanopore fabrication and subsequent measurements frequently lead to the formation of multiple nanopores, posing a challenge for precise detection. To address this issue, here, a novel and expedient technique to verify the presence of a single nanopore on a chip is developed. The methodology includes measuring the nanopore's conductance in solutions of various salt conditions, followed by a comparison of these results against a theoretical conductance model. This comparison is instrumental in distinguishing between single and multiple nanopores. Additionally, the study delves into various factors that influence the conductance curve, such as deviations in pore shape from the standard circle and inconsistencies in pore diameter. This approach significantly enhances the practical application of low‐cost nanopore preparation techniques, particularly in scenarios like controlled breakdown nanopore fabrication, where the formation of multiple nanopores is a common concern.

Nanopore Fabrication Made Easy: A Portable, Affordable Microcontroller-Assisted Approach for Tailored Pore Formation via Controlled Breakdown.

With growing interest in solid-state nanopore sensing─a single-molecule technique capable of profiling a host of analyte classes─establishing facile and scalable approaches for fabricating molecular-size pores is becoming increasingly important. The introduction of nanopore fabrication by controlled breakdown (CBD) has transformed the economics and accessibility of nanopore fabrication. Here, we introduce the design of an Arduino-based, portable USB-powered CBD device, with an estimated cost of <150 USD, which is ≈10-100× cheaper than most commercial solutions, capable of fabricating single nanopores conducive for single molecule sensing experiments. We demonstrate the facile fabrication of 60 tailored nanopores (∼2.6-12.6 nm) with ∼80% of the pores within 1 nm of the target diameter. Selected pores were then tested with double-stranded DNA, the canonical molecular ruler, demonstrating their performance for single-molecule sensing applications. The device is constructed with off-the-shelf readily available components and controlled using a highly customizable MATLAB application, which has capabilities encompassing pore fabrication, pore enlargement, and current-voltage acquisition for pore size estimation. When combined with a portable amplifier, this device also provides a fully portable sensing platform, an important step toward portable solid-state nanopore sensing applications.

Fabrication and high-resolution transmission electron microscopy characterization of nanopores in silicon nitride and 2D materials

Fabrication and high-resolution transmission electron microscopy characterization of nanopores in silicon nitride and 2D materials

Dual-Side Fabrication of Nanopores on Bilayer Graphene Membranes for Selective Ion Transport

Dual-Side Fabrication of Nanopores on Bilayer Graphene Membranes for Selective Ion Transport

Practical guide for in-house solid-state nanopore fabrication and characterization

Solid-state nanopores are considered a better alternative to biological nanopores for several sensing applications due to their better chemical, mechanical, and temperature stability. In addition to sequencing, nanopores currently also find applications in education, biomarker identification, quantification, single-molecule chemistry, and DNA computing. Nanopore technology’s simplicity and wide interdisciplinary applications have raised further interest among industry and scientific community worldwide. However, further development in solid-state nanopore technology and exploring its applications presents the need to have the capability to fabricate them in-house. This will be a more financially viable and flexible approach, especially in resource-limited situations. In order to do an in-house fabrication of solid-state nanopores, two key steps are involved. The first step is to fabricate suspended thin films, and the second one is the drilling of pores in these suspended thin membranes. Successful implementation of these two steps involves tedious optimization and characterization of the fabricated chips and nanopores. In this work, we describe the nanopore fabrication process in a ready-to-follow step-by-step guide and present solutions for several practical difficulties faced during the silicon nitride pore fabrication process. This work will help anyone new to this field and make the pore fabrication process more accessible.

Nano TiC electrocatalysts embedded graphite felt for high rate and stable vanadium redox flow batteries

Developing electrodes with high stability and activity is critical to promoting the application of redox flow batteries. In this work, a multiscale-pore-network structured graphite felt embedded nano-sized TiC electrocatalysts is fabricated by fully utilizing the Ti and O atoms of TiO2 nano seeds. For the present electrode, the micro pores shaped by the crossed carbon fibers serve as pathways for electrolyte convection. At the same time, the simultaneous formation of TiC during nanopore fabrication can catalyze the V3+/V2+ redox reaction. The electrode leads to the battery performance with an energy efficiency of 85.2% and an electrolyte utilization of 82.7% at a current density of 200 mA cm−2, respectively 23.3% and 48.6% higher than the battery with pristine electrodes. Also, even at 300 mA cm−2, the battery's energy efficiency and electrolyte utilization with this electrode can still be maintained at 80.8% and 72.6%, respectively 14.0% and 29.6% higher than the thermally treated electrode. Moreover, the present battery demonstrates a stable energy efficiency above 80% during cycle tests. The results indicate that engineering structures of electrocatalysts in nanopores may open new avenues for advancing flow battery electrode technology.

Study on the controllability of the fabrication of single-crystal silicon nanopores/nanoslits with a fast-stop ionic current-monitored TSWE method

The application of single-crystal silicon (SCS) nanopore structures in single-molecule-based analytical devices is an emerging approach for the separation and analysis of nanoparticles. The key challenge is to fabricate individual SCS nanopores with precise sizes in a controllable and reproducible way. This paper introduces a fast-stop ionic current-monitored three-step wet etching (TSWE) method for the controllable fabrication of SCS nanopores. Since the nanopore size has a quantitative relationship with the corresponding ionic current, it can be regulated by controlling the ionic current. Thanks to the precise current-monitored and self-stop system, an array of nanoslits with a feature size of only 3 nm was obtained, which is the smallest size ever reported using the TSWE method. Furthermore, by selecting different current jump ratios, individual nanopores of specific sizes were controllably prepared, and the smallest deviation from the theoretical value was 1.4 nm. DNA translocation measurement results revealed that the prepared SCS nanopores possessed the excellent potential to be applied in DNA sequencing.

Morphology around Nanopores Fabricated by Laser-Assisted Dielectric Breakdown and Its Impact on Ion and DNA Transport and Sensing

Laser-assisted controlled dielectric breakdown (LaCBD) has emerged as an alternative to conventional CBD-based nanopore fabrication due to its localization capability, facilitated by the photothermal-induced thinning down in the hot spot. Here, we reported the potential impact of the laser on forming debris around the nanopore region in LaCBD. The debris was clearly observable by scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. We found that debris formation is a unique phenomenon in LaCBD that is not observable in the conventional CBD approach. We also found that the LaCBD-induced debris is more evident when the laser power and voltage stress are higher. Moreover, the debris is asymmetrically distributed on the top and bottom sides of the membrane. We also found unexpected rectified ionic and molecular transport in those LaCBD nanopores with debris. Based on these observations, we developed and validated a model describing the debris formation kinetics in LaCBD by considering the generation, diffusion, drift, and gravity in viscous mediums. These findings indicate that while laser aids in nanopore localization, precautions should be taken due to the potential formation of debris and rectification of molecular transport. This study provides valuable insights into the kinetics of LaCBD and the characteristics of the LaCBD nanopore.

Fabrication of Au/AAO/Au nanopore arrays based on induced excitation SPPs for the fabrication of nanopores on silicon surfaces

In this paper, a new method for preparing a nanohole surface based on surface plasmon polaritons (SPPs) is proposed. In the proposed method, a layer of gold film is sputtered onto the upper and lower surfaces of porous anodic aluminum oxide (AAO) by ion sputtering to obtain the composite structure of Au/AAO/Au (Metal-Media-Metal, MIM) periodic hole array. The periodic plasma excitation conditions and coupling of the nanohole array are deduced using Maxwell's equations to obtain the locally enhanced surface plasma wave. Afterward, the composite structure is irradiated with a nanosecond laser with a working wavelength of 532 nm to excite the surface plasmon. Simulation results show that Au/AAO/Au (MIM) can excite the surface plasmon under laser induction, and the preparation of nanoholes is realized through experiments. The nanohole array produced by surface plasmon can be used to increase the specific surface area. For some biosensors with special properties, such as microcantilever, enzyme, and other biosensors, a large surface area is required without changing their chemical stability and mechanical strength to increase the detection sensitivity.

Role of Chemical Etching in the Nucleation of Nanopores in 2D MoS2: Insights from First-Principles Calculations

Nanoscale devices made using two-dimensional (2D) materials, including transition-metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2), are currently being explored for various applications, e.g., optoelectronic devices, water desalination membranes, and DNA sequencing. In such applications, defects and nanopores play a key role in modulating the 2D material’s physicochemical properties, e.g., the band gap, chemical reactivity, catalytic activity, and molecular/ionic permeation rate. However, there exists a lack of a fundamental understanding of nanopore formation in TMDs, especially MoS2. In this work, we elucidate the mechanism of nanopore formation in 2D MoS2 using an extensive set of first-principles density functional theory (DFT) calculations. We calculate the energies of etching of atoms using DFT and use Marcus theory for atom-transfer reactions to convert the energies to activation barriers. We postulate the role of silicon as an etchant and show that the MoS6 vacancy can be a potential nucleation site for the growth of nanopores in MoS2. By fitting our kinetic predictions to experimental microscopy data on the formation time of a MoS6 vacancy, we show that the intrinsic barrier for the etching of atoms in MoS2, as described by Marcus theory, is 0.228 eV in the presence of silicon atoms. We find that the slowest step in the formation of the MoS6 vacancy is the step leading from a S5 vacancy to a S6 vacancy, with an activation barrier of ∼0.85 eV. This allows atoms to be etched at close to room-temperature conditions (27 °C) under the action of an electron beam that can move around the silicon etchant atoms. Using this new understanding of the nanopore formation process, researchers will be able to accurately model the controlled fabrication of nanopores in 2D MoS2.

Solid-State Nanopores for Biomolecular Analysis and Detection.

Advances in nanopore technology and data processing have rendered DNA sequencing highly accessible, unlocking a new realm of biotechnological opportunities. Commercially available nanopores for DNA sequencing are of biological origin and have certain disadvantages such as having specific environmental requirements to retain functionality. Solid-state nanopores have received increased attention as modular systems with controllable characteristics that enable deployment in non-physiological milieu. Thus, we focus our review on summarizing recent innovations in the field of solid-state nanopores to envision the future of this technology for biomolecular analysis and detection. We begin by introducing the physical aspects of nanopore measurements ranging from interfacial interactions at pore and electrode surfaces to mass transport of analytes and data analysis of recorded signals. Then, developments in nanopore fabrication and post-processing techniques with the pros and cons of different methodologies are examined. Subsequently, progress to facilitate DNA sequencing using solid-state nanopores is described to assess how this platform is evolving to tackle the more complex challenge of protein sequencing. Beyond sequencing, we highlight the recent developments in biosensing of nucleic acids, proteins, and sugars and conclude with an outlook on the frontiers of nanopore technologies.

Analyses of Pore-Size-Dependent Ionic Transport in Nanopores in the Presence of Concentration and Temperature Gradients.

Mass transport through nanopores occurs in various natural systems, including the human body. For example, ion transport across nerve cell membranes plays a significant role in neural signal transmission, which can be significantly affected by the electrolyte and temperature conditions. To better understand and control the underlying nanoscopic transport, it is necessary to develop multiphysical transport models as well as validate them using enhanced experimental methods for facile nanopore fabrication and precise nanoscale transport characterization. Here, we report a nanopore-integrated microfluidic platform to characterize ion transport in the presence of electrolyte and temperature gradients; we employ our previous self-assembled particle membrane (SAPM)-integrated microfluidic platform to produce various nanopores with different pore sizes. Subsequently, we quantify pore-size-dependent ionic transport by measuring the short circuit current (SCC) and open circuit voltage (OCV) across various nanopores by manipulating the electrolyte and temperature gradients. We establish three simple theoretical models that heavily depend on pore size, electrolyte concentration, and temperature and subsequently validate them with the experimental results. Finally, we anticipate that the results of this study would help clarify ion transport phenomena at low-temperature conditions, not only providing a fundamental understanding but also enabling practical applications of cryo-anesthesia in the near future.

Development and Analysis of Electrochemical Reactor with Vibrating Functional Element for AAO Nanoporous Membranes Fabrication.

Nanoporous anodic aluminum oxide (AAO) is needed for a variety of purposes due to its unique properties, including high hardness, thermal stability, large surface area, and light weight. Nevertheless, the use of AAO in different applications is limited because of its brittleness. A new design of an electrochemical reactor with a vibrating element for AAO nanoporous membranes fabrication is proposed. The vibrating element in the form of a piezoceramic ring was installed inside the developed reactor, which allows to create a high-frequency excitation. Furthermore, mixing and vibration simulations in the novel reactor were carried out using ANSYS 17 and COMSOL Multiphysics 5.4 software, respectively. By theoretical calculations, the possibility to excite the vibrations of five resonant modes at different frequencies in the AAO membrane was shown. The theoretical results were experimentally confirmed. Five vibration modes at close to the theoretical frequencies were obtained in the novel reactor. Moreover, nanoporous AAO membranes were synthesized. The novel aluminum anodization technology results in AAO membranes with 82.6 ± 10 nm pore diameters and 43% porosity at 3.1 kHz frequency excitation and AAO membranes with 86.1 ± 10 nm pore diameters and 46% porosity at 4.1 kHz frequency excitation. Furthermore, the chemical composition of the membrane remained unchanged, and the hardness decreased. Nanoporous AAO has become less brittle but hard enough to be used for template synthesis.

Silicon Nitride Nanopores Formed by Simple Chemical Etching: DNA Translocations and TEM Imaging.

We demonstrate DNA translocations through silicon nitride pores formed by simple chemical etching on glass substrates using microscopic amounts of hydrofluoric acid. DNA translocations and transmission electron microscopy (TEM) prove the fabrication of nanopores and allow their characterization. From ionic measurements on 318 chips, we report the effective pore diameters ranging from zero (pristine membranes) and sub-nm to over 100 nm, within 50 μm diameter membranes. The combination of ionic conductance, DNA current blockades, TEM imaging, and electron energy loss spectroscopy (EELS) provides comprehensive information about the pore area and number, from single to few pores, and pore structure. We also show the formation of thinned membrane regions as precursors of pores. The average pore density, about 5 × 10-4 pores/μm2, allows pore number adjustment statistically (0, 1, or more). This simple and affordable chemical method for making solid-state nanopores accelerates their adoption for DNA sensing and characterization applications.

Gallium-doped dual micro-nano titanium dental implants towards soft-tissue integration and bactericidal functions

Alongside osseointegration, effective soft-tissue integration (STI) is crucial to the long-term success of dental implants by preventing the ingress of oral pathogens. Nanoscale surface modification of titanium dental implants has shown promise in achieving enhanced bioactivity and antibacterial efficacy. We propose the fabrication of dual micro-nano anisotropic titania nanopores (TNPs) via electrochemical anodization of Ti, followed by incorporating gallium (Ga) towards enhanced antibacterial efficacy. Optimization of Ga chemical functionalization on TNPs was followed by in-depth surface topographical/chemical characterizations and in vitro Ga release. This study revealed that the surface chemistry, hydrophilicity, and topography of the TNPs were altered upon Ga-doping, resulting in the formation of Ga-containing nanoscale particulates firmly bound to TNPs. Further, gingival fibroblast bioactivity was favorably maintained on TNPs and Ga-releasing TNPs. Finally, a human oral salivary biofilm model confirmed the significant antibacterial efficacy of Ga-doped TNPs. Ga-doped dual micro-nano Ti dental implants are suitable as the next generation of bioactive and bactericidal dental implants.