4,145 research outputs found
Fabrication of Atomically Precise Nanopores in Hexagonal Boron Nitride
We demonstrate the fabrication of individual nanopores in hexagonal boron
nitride (hBN) with atomically precise control of the pore size. Previous
methods of pore production in other 2D materials create pores of irregular
geometry with imprecise diameters. By taking advantage of the preferential
growth of boron vacancies in hBN under electron beam irradiation, we are able
to observe the pore growth via transmission electron microscopy, and terminate
the process when the pore has reached its desired size. Careful control of beam
conditions allows us to nucleate and grow individual triangular and hexagonal
pores with diameters ranging from subnanometer to 6nm over a large area of
suspended hBN using a conventional TEM. These nanopores could find application
in molecular sensing, DNA sequencing, water desalination, and molecular
separation. Furthermore, the chemical edge-groups along the hBN pores can be
made entirely nitrogen terminated or faceted with boron-terminated edges,
opening avenues for tailored functionalization and extending the applications
of these hBN nanopores.Comment: 5 pages, 6 figure
Controlling nanopore size, shape and stability
Solid-state nanopores are considered a promising tool for the study of biological polymers such as DNA and RNA, due largely to their flexibility in size, potential in device integration and robustness. Here, we show that the precise shape of small nanopores (~5 nm diameter in 20 nm SiN membranes) can be controlled by using transmission electron microscope (TEM) beams of different sizes. However, when some of these small nanopores are immersed in an aqueous solution, their resistance is observed to decrease over time. By comparing nanopores of different shapes using (scanning) TEM both before and after immersion in aqueous solution, we demonstrate that the stability of small nanopores is related to their three-dimensional geometry, which depends on the TEM beam size employed during pore fabrication. Optimal stability is obtained using a TEM beam size of approximately the same size as the intended nanopore diameter. In addition, we show that thermal oxidation can serve as a means to independently control nanopore size following TEM fabrication. These observations provide key guidelines for the fabrication of stable solid-state nanopores on the scale of nucleic acids and small proteins
Nanopore Fabrication by Controlled Dielectric Breakdown
Nanofabrication techniques for achieving dimensional control at the nanometer
scale are generally equipment-intensive and time-consuming. The use of
energetic beams of electrons or ions has placed the fabrication of nanopores in
thin solid-state membranes within reach of some academic laboratories, yet
these tools are not accessible to many researchers and are poorly suited for
mass-production. Here we describe a fast and simple approach for fabricating a
single nanopore down to 2-nm in size with sub-nm precision, directly in
solution, by controlling dielectric breakdown at the nanoscale. The method
relies on applying a voltage across an insulating membrane to generate a high
electric field, while monitoring the induced leakage current. We show that
nanopores fabricated by this method produce clear electrical signals from
translocating DNA molecules. Considering the tremendous reduction in complexity
and cost, we envision this fabrication strategy would not only benefit
researchers from the physical and life sciences interested in gaining reliable
access to solid-state nanopores, but may provide a path towards manufacturing
of nanopore-based biotechnologies.Comment: 19 pages, 4 figures. Supplementary information contains 22 pages, 11
figures and 2 tables - A version of this manuscript was first submitted for
publication on April 23rd, 2013. It is currently under review at another
journa
Through-membrane electron-beam lithography for ultrathin membrane applications
We present a technique to fabricate ultrathin (down to 20 nm) uniform
electron transparent windows at dedicated locations in a SiN membrane for in
situ transmission electron microscopy experiments. An electron-beam (e-beam)
resist is spray-coated on the backside of the membrane in a KOH- etched cavity
in silicon which is patterned using through-membrane electron-beam lithography.
This is a controlled way to make transparent windows in membranes, whilst the
topside of the membrane remains undamaged and retains its flatness. Our
approach was optimized for MEMS-based heating chips but can be applied to any
chip design. We show two different applications of this technique for (1)
fabrication of a nanogap electrode by means of electromigration in thin
free-standing metal films and (2) making low-noise graphene nanopore devices
DNA Translocation through Graphene Nanopores
Nanopores -- nanosized holes that can transport ions and molecules -- are
very promising devices for genomic screening, in particular DNA sequencing.
Both solid-state and biological pores suffer from the drawback, however, that
the channel constituting the pore is long, viz. 10-100 times the distance
between two bases in a DNA molecule (0.5 nm for single-stranded DNA). Here, we
demonstrate that it is possible to realize and use ultrathin nanopores
fabricated in graphene monolayers for single-molecule DNA translocation. The
pores are obtained by placing a graphene flake over a microsize hole in a
silicon nitride membrane and drilling a nanosize hole in the graphene using an
electron beam. As individual DNA molecules translocate through the pore,
characteristic temporary conductance changes are observed in the ionic current
through the nanopore, setting the stage for future genomic screening
Fabrication and Characterization of Thinner Solid-State Nanopores
Solid State nanopores that are fabricated by the ion beam sculpting process and electron beam drilling have shown great promise as a sensing device for DNA and protein molecules. Even though biological pores such as the alpha-Haemolysin have been in use for quite some time, the use of solid state Nanopores in single biomolecule detection has been on the rise since the mid 1990s. Solid State nanopores have an advantage over biological pores in that they are more robust, stable, and can be sculpted to any desired size for use in translocation experiments. One of the major challenges in Nanopore fabrication by ion beam sculpting has been limited by the user\u27s ability to control the closure rate of pores in the fabrication process. Another challenge in
nanopore sensing is the resolution limitation due to the thickness of the pore. This is because most of the nanopores fabricated by the ion beam sculpting method are often thicker than they should. This thesis will focus on the modification of nanopore fabrication using the ion beam
sculpting system at the University of Arkansas by first baking the samples in vacuum under specified temperature conditions. Baking the samples will give the user better control over pore closure. This Thesis will also focus on thinning the sculpted pores by Reactive Ion Etching in an attempt to increase its resolution for single biomecule translocation experiments
Using Focused Electron Beams to Drill Straight Nanopores on a Membrane
A high-resolution focused electron beam is used for the fabrication of metal nanostructures and devices with insulating membranes by nanosculpting metal films. This top-down focused electron beam drilling method uses the controlled ablation of materials to produce nanoscale devices with near-atomic precision of order. Using the proposed procedure, nano-drilling is not directly realized through the aperture, but by using a focused electron beam to burn away the solvent. Recent studies have investigated silicon nitride nanopores with an hourglass profile and silica nanopores with a pyramid-shaped cross-section, but electronic drilling in these approaches failed to produce straight nanopores. A method is proposed to improve the membranes’ thermal conductivity to rapidly produce straight nanopores, and is experimentally confirmed and has significant potential for use in nano-sensors or nano-devices.</p
A Two-Step Etching Method to Fabricate Nanopores in Silicon
A cost effectively method to fabricate nanopores in silicon by only using the
conventional wet-etching technique is developed in this research. The main
concept of the proposed method is a two-step etching process, including a
premier double-sided wet etching and a succeeding track-etching. A special
fixture is designed to hold the pre-etched silicon wafer inside it such that
the track-etching can be effectively carried out. An electrochemical system is
employed to detect and record the ion diffusion current once the pre-etched
cavities are etched into a through nanopore. Experimental results indicate that
the proposed method can cost effectively fabricate nanopores in silicon.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Boosting infrared energy transfer in 3D nanoporous gold antennas
The applications of plasmonics to energy transfer from free-space radiation to molecules are currently limited to the visible region of the electromagnetic spectrum due to the intrinsic optical properties of bulk noble metals that support strong electromagnetic field confinement only close to their plasma frequency in the visible/ultraviolet range. In this work, we show that nanoporous gold can be exploited as a plasmonic material for the mid-infrared region to obtain strong electromagnetic field confinement, co-localized with target molecules into the nanopores and resonant with their vibrational frequency. The effective optical response of the nanoporous metal enables the penetration of optical fields deep into the nanopores, where molecules can be loaded thus achieving a more efficient light–matter coupling if compared to bulk gold. In order to realize plasmonic resonators made of nanoporous gold, we develop a nanofabrication method based on polymeric templates for metal deposition and we obtain antenna arrays resonating at mid-infrared wavelengths selected by design. We then coat the antennas with a thin (3 nm) silica layer acting as the target dielectric layer for optical energy transfer. We study the strength of the light–matter coupling at the vibrational absorption frequency of silica at 1240 cm−1 through the analysis of the experimental Fano lineshape that is benchmarked against identical structures made of bulk gold. The boost in the optical energy transfer from free-space mid-infrared radiation to molecular vibrations in nanoporous 3D nanoantenna arrays can open new application routes for plasmon-enhanced physical–chemical reactions
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