Fabrication Of Nanopores Research Articles

Nanopore Fabrication of Two-Dimensional Materials on SiO2 Membranes Using He Ion Microscopy

Structures with pores having diameters of several nanometers can be used for distinguishing nucleotides in DNA. A 2-D material such as a thin membrane is expected to enhance precise molecule recognition. Here, we present the nanopore fabrication to thin 2-D membranes using He ion microscopy (HIM). We transferred three 2-D materials, chemical vapor deposition (CVD) graphene, CVD boron nitride, and peel-off MoS2, to the submicrometer pore of freestanding SiO2 membranes on a silicon substrate. The number of atomic layers of the 2-D materials was confirmed via Raman spectroscopy and X-ray photoelectron spectroscopy. We examined the reproducibility and accuracy of nanopore fabrication as a function of the focal position and beam irradiation intensity of the HIM system. Reproducible nanopores having diameters of less than 10 nm were realized by optimizing the intensity and focal position. We achieved 1.5-nm-diameter nanopores in a single layer of graphene using this HIM technique.

Optically-Monitored Nanopore Fabrication Using a Focused Laser Beam

Solid-state nanopores (ssNPs) are extremely versatile single-molecule sensors and their potential have been established in numerous biomedical applications. However, the fabrication of ssNPs remains the main bottleneck to their widespread use. Herein, we introduce a rapid and localizable ssNPs fabrication method based on feedback-controlled optical etching. We show that a focused blue laser beam irreversibly etches silicon nitride (SiNx) membranes in solution. Furthermore, photoluminescence (PL) emitted from the SiNx is used to monitor the etching process in real-time, hence permitting rate adjustment. Transmission electron microscopy (TEM) images of the etched area reveal an inverted Gaussian thickness profile, corresponding to the intensity point spread function of the laser beam. Continued laser exposure leads to the opening of a nanopore, which can be controlled to reproducibly fabricate nanopores of different sizes. The optically-formed ssNPs exhibit electrical noise on par with TEM-drilled pores, and translocate DNA and proteins readily. Notably, due to the localized thinning, the laser-drilled ssNPs exhibit highly suppressed background PL and improved spatial resolution. Given the total control over the nanopore position, this easily implemented method is ideally suited for electro-optical sensing and opens up the possibility of fabricating large nanopore arrays in situ.

Solid-state nanopore fabrication in LiCl by controlled dielectric breakdown.

Nanopore fabrication via the controlled dielectric breakdown (CDB) method offers an opportunity to create solid-state nanopores directly in salt solution with sub-nanometer precision. Driven by trap assisted current tunneling, the method uses localized defects, or traps, in the dielectric material to isolate a breakdown point and fabricate a single pore in less than 10minutes. Here we present an approach to controlled dielectric breakdown of SiNx in which the nanopore is fabricated in LiCl buffer instead of the traditional KCl buffer. Direct fabrication in LiCl buffer promotes a uniform, symmetric, cylindrical nanopore structure that is fully wet and can be used for experiments in situ. We have shown that fabrication in LiCl reduces the necessity for overnight pore stabilization and allows for the desired analyte to be added in significantly less time than it would take if fabrication was performed in KCl. Pores created by this approach can be used for biosensing applications, including the detection of double-stranded DNA. DNA translocation experiments were conducted in both LiCl and KCl buffer. Experiments conducted in LiCl buffer resulted in about a 2-fold increase in dsDNA transport duration when compared to experiments conducted in KCl buffer of the same concentration. An increase in transport duration of over 10-fold in comparison to KCl was observed when the concentration of the LiCl buffer was increased by a factor of 3.

Plasmonic Nanopore Fabrication for Single Molecule Bio Sensor By Using Electron Beam Irradation

Recently the portable device called MINion for single molecule analysis was developed by Oxford Nanopore Technology. The electrical detection technique for the solid state device was utilized for single molecule detection . However, the large error rates were reported by several journals, even though the significant error reduction was developed after the invention of the portable nanopore device. In this report, we introduce the optical nanopore fabrication by using plasmonic optical enhancement effect. First, the Au thin films were vacuum-deposited on the nanometer thin SiN film, followed by removal of SiN film and by drilling Au apertures by using focused ion beam (FIB) technique. Then, electron beam irradiations on the specimens either by using low energy field emission electron beam microscopy (FESEM) or high energy Transmission electron beam microscopy (TEM). In addition, the periodic grooves, or the periodic Au aperture array were fabricated on the Au sample in order to provide strong plamonic optical enhancements. During the electron irradiation on the fabricated Au surface, we observed the diffused binary Au-C membrane due to Ostwald ripening and also the unstable Au-C mixed phase change via spinodal decomposition. We also found that the Au cluster diffusion would depend upon the electron beam fluence. However, the exact understanding of this phenomenon is still on-going investigation. Figure 1

Fabrication of Nanopores in an Ultra-Thin Polyimide Membrane for Biomolecule Sensing

Single molecule detection using nanopores has proven to be a powerful way of identifying biomolecules. Therefore, a variety of materials and methods have been developed by the nanopore community to generate credible outcomes. Here we report as the first time a novel polyimide nanopore platform for single DNA sensing. Novelty of the platform arises both from the ultra-thin structure of the polyimide membrane and also the technique used in the nanopore fabrication on a polymer membrane. Furthermore, the ultra-thin nature of the membrane eliminates the involvement of highly demanding fabrication steps often employed in the solid-state nanopore membrane production. Herein we present the fabrication of nanopores in such an ultra-thin polymer membrane and its successful application in sensing DNA molecules at single molecule level, holding a promise as a potential single-molecule analytical device unlike its common use in research.

Facile and fast electrospinning of crystalline ZnO 3D interconnected nanoporous nanofibers for ammonia sensing application

One-dimensional nanoporous metal oxide nanostructures have attracted great interest for their noticeable properties in gas sensor applications. In this paper, we report fabrication of crystalline sub 100 nm 3D interconnected nanoporous nanofibers with about 250 nm diameter. Theses nanostructures have high surface to volume ratio. Glycerol monostearate is used in precursor solution using electrospinning technique and then a subsequent heat treatment is performed on it by calcination process at high temperature. We achieve high crystalline structure of ZnO wurtzite phase. The fabricated crystalline ZnO interconnected nanoporous nanofiber (C–ZnO–INN) is characterized by scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, energy dispersive spectroscopy, and X-ray diffraction. In addition, gas sensitivity of C–ZnO–INN is studied at room temperature. Cobalt is doped in C–ZnO–INN as a gas catalyst to increase sensitivity of the sensor. The results of the tests indicate that the sensor sensitivity is high for ammonia in the range of 1–800 ppm at room temperature. Moreover, the results show that the gas responsivity is linear to methanol, 2-propanol, acetone, acetic acid, and ammonia gases for Co doped C–ZnO–INN comparing with bare ZnO nanofibers. The C–ZnO–INN can be a best candidate for applications in diverse fields including sensor sensing or catalytic fields due to high surface to volume ratio of fabricated nanoporous nanofibers. Furthermore, it has the potential to be used in various semiconductor nanosensor applications (biosensors, high performance chemoresistive gas sensors, and etc.) because of using the facile and fast electrospinning nanoporous nanofibers fabrication method.

Multi-purposed Ar gas cluster ion beam processing for graphene engineering

Graphene, with unique mechanical and electrical properties, offers diverse application opportunities from beyond Moore’s nano-electronics to water filtration. However, accomplishing these relies on cleaning and processing large areas of supported and suspended graphene sheets. Here, we demonstrate the use of an Ar cluster ion beam as a versatile tool for graphene cleaning, defect engineering, and nanopore fabrication. In-situ and ex-situ characterization techniques were utilized in combination with first principles molecular dynamics, to highlight the differences in processing of the supported and suspended graphene samples. In this work, we monitor interaction of the Ar cluster ion beam with graphene as a function of ion dose with in-situ secondary ion mass spectrometry (SIMS), as well as ex-situ Raman spectroscopy measurements. Scanning transmission electron microscopy (STEM) results confirm that the Ar cluster ion beam can form nanopores in the suspended graphene; while the basal plane of graphene remains intact maintaining the lattice structure. Finally, Scanning Electron Microscopy (SEM) image analysis of the irradiated samples allows quantitative tracking of pore areas and their distribution as a function of ion dose. This study highlights the flexibility of the Ar cluster ion beam in 2D material processing, and offers insights into Ar beam interaction with graphene.

Muitilpe Nanopores Fabrication in a SiNX Membrane via Controlled Breakdown

Solid-state nanopores are widely used in single-molecule detection and bio-molecule analysis, i.e. DNA sensing, DNA - protein and protein- protein interaction. Recently, the Tabard-Cossa group reported a low-cost and broadly accessible synthetic nanopore fabrication approach, controlled breakdown (CDB). Since CDB uses conductance feedback to monitor the nanopore fabrication, it cannot tell whether there is a large single nanopore or multiple small nanopores in the membrane. In this work, we found that despite the stochastic process during the breakdown, nanopores created via breakdown in a SiNx membrane tend to have the same scale. We proposed a resistance model to govern the multiple nanopores formation by the conductance feedback - the number of nanopores in the membrane was determined by the membrane resistance and the nanopore sizes were controlled by the enlargement electric field. We further characterized our multiple nanopores by transmission electron microscopy (TEM) imaging and the fluorescence of Ca2+-activated dyes. We anticipate that by combining with optical measurements, this fabrication approach could accelerate the process of nanopore sensing towards a high-throughput and multichannel technique.

Nanopore Fabrication in Ultrathin HFO2 Membranes for Nanopore-Based DNA Sequencing

Nanopore Fabrication in Ultrathin HFO2 Membranes for Nanopore-Based DNA Sequencing

Fabrication of nanopores and nanoslits with feature sizes down to 5 nm by wet etching method

This paper presents an improved three-step wet etching method for the fabrication of single-crystal silicon nanopores and nanoslists. A diffusion model was built to analyze the influence of the color-based feedback mechanism on the final pore size. Reference structures were added aside normal pore patterns, to obtain a more precise control of the pore size during the pore opening process. By using this method, square nanopores with the minimum size of 8 nm × 8 nm, rectangle nanopores and nanoslits with feature sizes down to 5 nm were successfully obtained. Focused ion beam cutting revealed that the nanopore profile keeps well the inverted-pyramid shape, with an included angle of 54.7°.

Fabrication of multiple nanopores in a SiNx membrane via controlled breakdown

This paper reports a controlled breakdown (CBD) method to fabricate multiple nanopores in a silicon nitride (SiNx) membrane with control over both nanopore count and nanopore diameter. Despite the stochastic process of the breakdown, we found that the nanopores created via CBD, tend to be of the same diameter. We propose a membrane resistance model to explain and control the multiple nanopores forming in the membrane. We prove that the membrane resistance can reflect the number of nanopores in the membrane and that the diameter of the nanopores is controlled by the exposure time and strength of the electric field. This controllable multiple nanopore formation via CBD avoids the utilization of complicated instruments and time-intensive manufacturing. We anticipate CBD has the potential to become a nanopore fabrication technique which, integrated into an optical setup, could be used as a high-throughput and multichannel characterization technique.

Nanopores creation in boron and nitrogen doped polycrystalline graphene: A molecular dynamics study

In the present paper, molecular dynamic simulations have been conducted to investigate the nanopores creation on 10% of boron and nitrogen doped polycrystalline graphene by silicon and diamond nanoclusters. Two types of nanoclusters based on silicon and diamond are used to investigate their effect for the fabrication of nanopores. Therefore, three different diameter sizes of the clusters with five kinetic energies of 10, 50, 100, 300 and 500 eV/atom at four different locations in boron or nitrogen doped polycrystalline graphene nanosheets have been perused. We also study the effect of 3% and 6% of boron doped polycrystalline graphene with the best outcome from 10% of doping. Our results reveal that the diamond cluster with diameter of 2 and 2.5 nm fabricates the largest nanopore areas on boron and nitrogen doped polycrystalline graphene, respectively. Furthermore, the kinetic energies of 10 and 50 eV/atom can not fabricate nanopores in some cases for silicon and diamond clusters on boron doped polycrystalline graphene nanosheets. On the other hand, silicon and diamond clusters fabricate nanopores for all locations and all tested energies on nitrogen doped polycrystalline graphene. The area sizes of nanopores fabricated by silicon and diamond clusters with diameter of 2 and 2.5 nm are close to the actual area size of the related clusters for the kinetic energy of 300 eV/atom in all locations on boron doped polycrystalline graphene. The maximum area and the average maximum area of nanopores are fabricated by the kinetic energy of 500 eV/atom inside the grain boundary at the center of the nanosheet and in the corner of nanosheet with diameters of 2 and 3 nm for silicon and diamond clusters on boron and nitrogen doped polycrystalline graphene.

Fabrication of nanopores in polycrystalline boron-nitride nanosheet by using Si, SiC and diamond clusters bombardment

In this paper, molecular dynamic simulations have been performed to fabricate nanopores in a polycrystalline boron-nitride nanosheet applied to DNA sequencer devices by using Si clusters bombardment. Three different sizes of Si clusters with ten different kinetic energies and impacts at five different locations of the polycrystalline boron-nitride nanosheet have been simulated. Our results show that desired nanopores with expected size and topography can be created by controlling the kinetic energy and size of the cluster. The area size of nanopores also increase by rising the kinetic energy of the cluster. We have also observed that the existing grain boundary in the incident location highly affects the shape and size of the nanopores. Therefore, we subsequently applied an external tensile strain on the boron-nitride nanosheet and determined the effect of straining nanosheet on the area, quality and the shape of fabricated nanopores. We find that increasing the external tensile strain leads to a large increase in the area of nanopores, but the shape and quality of fabricated nanopores remains nearly unaffected, particularly compared to drilling nanopores in the unstrained nanosheet. In order to investigate the effect of the cluster type, two new type of clusters (SiC and diamond) have been used to generate nanopores. Our results reveal that SiC and diamond clusters bombardment lead to fabricate almost the same shape and quality of nanopores as well as the Si cluster. On the other hand, increasing the kinetic energy of the SiC and diamond cluster barely influences the area size of the nanopores. Among all clusters, the diamond cluster bombardment leads to fabricate the largest average area size of the nanopores.

Rapid fabrication of solid-state nanopores with high reproducibility over a large area using a helium ion microscope.

The fabrication of solid-state nanopores in an insulating membrane has attracted much attention for biomolecule analysis such as DNA sequencing and detection in recent years. For practical applications and device integration, the challenges include precise size control for sub 10 nm nanopores, excellent repeatability and rapid fabrication over a large area to reduce the cost for mass production. A helium ion beam could provide an effective fabrication approach to produce such solid-state nanopores. It is easy to control the nanopore size and reach sub 10 nm pore size with a simple change in the milling time with an appropriate ion beam current. Here we report new results in a set of experiments demonstrating that with a small range of stage automatized motions and equal mill times one can obtain good fabrication reproducibility in nanopore sizes (<10% variation in size). The automation in the stage motion and milling time opens a door for the rapid mass production of nanopore chips over a wafer size of several inches.

Fabrication of 3D nanovolcano-shaped nanopores with helium ion microscopy

Both helium and gallium ion beams were employed to fabricate nanopores. Herein, three-dimensional nano-volcano-shaped nanopores (3D-NVNs) were directly formed using helium ion beam with no precursors required, while the gallium ion beam produced V-shaped nanopores. Hundreds of 3D-NVNs were fabricated with a mean diameter of 229 ± 7 nm, where the He ion beam milling rate for the 3D-NVNs was 3.6 ± 0.2 μm3/μC. The height of the 3D-NVNs was greater than their depth when the dose range was 0–10 nC/μm2, while the height remained constant for doses above 10 nC/μm2. Trajectory simulations of the ion bombardment into the gold film clarified that ion implantation could primarily account for the volcano-shaped nanopore formation.

Conductance-based profiling of nanopores: Accommodating fabrication irregularities.

Solid-state nanopores are nanoscale channels through otherwise impermeable membranes. Single molecules or particles can be passed through electrolyte-filled nanopores by, e.g. electrophoresis, and then detected through the resulting physical displacement of ions within the nanopore. Nanopore size, shape, and surface chemistry must be carefully controlled, and on extremely challenging <10nm-length scales. We previously developed a framework to characterize nanopores from the time-dependent changes in their conductance as they are being formed through solution-phase nanofabrication processes with the appeal of ease and accessibility. We revisited this simulation work, confirmed the suitability of the basic conductance equation using the results of time-dependent experimental conductance measurements during nanopore fabrication by Yanagi etal., and then deliberately relaxed the model constraints to allow for (i) the presence of defects; and (ii) the formation of two small pores instead of one larger one. Our simulations demonstrated that the time-dependent conductance formalism supports the detection and characterization of defects, as well as the determination of pore number, but with implementation performance depending on the measurement context and results. In some cases, the ability to discriminate numerically between the correct and incorrect nanopore profiles was slight, but with accompanying differences in candidate nanopore dimensions that could yield to post-fabrication conductance profiling, or be used as convenient uncertainty bounds. Time-dependent nanopore conductance thus offers insight into nanopore structure and function, even in the presence of fabrication defects.

Fabrication of Subnanometer-Precision Nanopores in Hexagonal Boron Nitride

We demonstrate the fabrication of individual nanopores in hexagonal boron nitride (h-BN) with atomically precise control of the pore shape and size. Previous methods of pore production in other 2D materials typically create pores with irregular geometry and imprecise diameters. In contrast, other studies have shown that with careful control of electron irradiation, defects in h-BN grow with pristine zig-zag edges at quantized triangular sizes, but they have failed to demonstrate production and control of isolated defects. In this work, we combine these techniques to yield a method in which we can create individual size-quantized triangular nanopores through an h-BN sheet. The pores are created using the electron beam of a conventional transmission electron microscope; which can strip away multiple layers of h-BN exposing single-layer regions, introduce single vacancies, and preferentially grow vacancies only in the single-layer region. We further demonstrate how the geometry of these pores can be altered beyond triangular by changing beam conditions. Precisely size- and geometry-tuned nanopores could find application in molecular sensing, DNA sequencing, water desalination, and molecular separation.

Microfluidic multiplexing of solid-state nanopores

Although solid-state nanopores enable electronic analysis of many clinically and biologically relevant molecular structures, there are few existing device architectures that enable high-throughput measurement of solid-state nanopores. Herein, we report a method for microfluidic integration of multiple solid-state nanopores at a high density of one nanopore per (35 µm2). By configuring microfluidic devices with microfluidic valves, the nanopores can be rinsed from a single fluid input while retaining compatibility for multichannel electrical measurements. The microfluidic valves serve the dual purpose of fluidic switching and electric switching, enabling serial multiplexing of the eight nanopores with a single pair of electrodes. Furthermore, the device architecture exhibits low noise and is compatible with electroporation-based in situ nanopore fabrication, providing a scalable platform for automated electronic measurement of a large number of integrated solid-state nanopores.

Solution self‐assembly behavior of A‐B‐C triblock polymers and the implications for nanoporous membrane fabrication

ABSTRACTSelf‐assembled block polymer membranes are rising to the fore of next‐generation separations technologies, and a particular fabrication process of significant interest is the self‐assembly and non‐solvent induced phase‐separation (SNIPS) method. This is because the SNIPS process allows for the facile manipulation of independent variables to produce simultaneously size‐ and chemically‐selective membranes in a scalable manner. Despite significant advances in the SNIPS membrane fabrication procedure, the early‐stage solution behavior of many of the polymer–solvent systems employed is still poorly understood. This work addresses the challenges posed by these systems and illuminates guiding relationships for the optimization of SNIPS membrane casting solutions. Specifically, polymer aggregate structures and critical micelle concentration (CMC) values are determined for an A‐B‐C triblock polymer dissolved in 1,4‐dioxane using a combination of scattering and atomic force microscopy techniques. The CMC of this system ranges from 20 to 80 μM and shows a strong dependence on the polymer composition and solution processing method. Additionally, the shape of the self‐assembled structures in solution can be altered by varying these parameters. These studies establish the relationships between polymer solution properties (i.e., the block polymer composition and the processing method) and assembly behavior as they impact membrane fabrication through SNIPS processing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45531.

Wireless Bipolar Nanopore Electrode for Single Small Molecule Detection.

Solid-state nanopore-based techniques have become a promising strategy for diverse single molecule detections. Owing to the challenge in well and rapid fabrication of solid-state nanopores with the diameter less than 2 nm, small molecule detection is hard to be addressed by existing label-free nanopore methods. In this work, we for the first time propose a metal-coated wireless nanopore electrode (WNE) which offers a novel and generally accessible detection method for analyzing small molecules and ions at the single molecule/ion level. Here, a silver-coated WNE is developed as a proof-of-principle model which achieves the detection the self-generated H2, the smallest known molecule, and Ag+ at single molecule/ion level by monitoring the enhanced ionic signatures. Under a bias potential of -800 mV, the WNE could accomplish the distinction of as low as 14 H2 molecules and 28 Ag+ from one spike signal. The finite element simulation is introduced to suggest that the generation of H2 at the orifice of the WNE results in the enhanced spike of ionic current. As a proof-of-concept experiment, the WNE is further utilized to directly detect Hg2+ from 100 pM to 100 nM by monitoring the frequency of the spike signals. This novel nanoelectrode provides a brand new label-free, ultrasensitive, and simple detection mechanism for various small molecules/ions detection, especially for redox analytes.