Nanohole Size Research Articles

A First Principles Study of Lithium Adsorption in Nanoporous Graphene

Recently, nanoporous graphene has attracted great interest in the scientific community. It possesses nano-sized holes; thus, it has a highly accessible surface area for lithium adsorption for energy storage applications. Defective graphene has been extensively studied. However, the lithium adsorption mechanism of nanoporous graphene is not clearly understood yet. Here, we present theoretical investigations on the lithium-ion adsorption mechanism in nanoporous graphene. We perform ab initio electronic structure calculations based on density functional theory. Lithium adsorption in a graphene nanopore is studied and adsorption sites are determined. We also study different lithium-ion distributions in graphene nanopores to determine the best lithium–nanoporous graphene structures for lithium-ion batteries. We show that lithium ions can be adsorbed in a graphene nanopore, even in a single layer of graphene. It is also shown that adding more nanopores to multilayer nanoporous graphene can result in higher Li storage capacity for new-generation lithium-ion batteries.

Understanding disorder in monolayer graphene devices with gate-defined superlattices

Engineering superlattices (SLs)-which are spatially periodic potential landscapes for electrons-is an emerging approach for the realization of exotic properties, including superconductivity and correlated insulators, in two-dimensional materials. While moiré SL engineering has been a popular approach, nanopatterning is an attractive alternative offering control over the pattern and wavelength of the SL. However, the disorder arising in the system due to imperfect nanopatterning is seldom studied. Here, by creating a square lattice of nanoholes in the SiO2dielectric layer using nanolithography, we study the SL potential and the disorder formed in hBN-graphene-hBN heterostructures. Specifically, we observe that while electrical transport shows distinct SL satellite peaks, the disorder of the device is significantly higher than graphene devices without any SL. We use finite-element simulations combined with a resistor network model to calculate the effects of this disorder on the transport properties of graphene. We consider three types of disorder: nanohole size variations, adjacent nanohole mergers, and nanohole vacancies. Comparing our experimental results with the model, we find that the disorder primarily originates from nanohole size variations rather than nanohole mergers in square SLs. We further confirm the validity of our model by comparing the results with quantum transport simulations. Our findings highlight the applicability of our simple framework to predict and engineer disorder in patterned SLs, specifically correlating variations in the resultant SL patterns to the observed disorder. Our combined experimental and theoretical results could serve as a valuable guide for optimizing nanofabrication processes to engineer disorder in nanopatterned SLs.

Positron annihilation spectroscopic investigation of pillared clay-based catalytic hybrid nanocomposites

Positron annihilation lifetime spectra for pillared montmorillonite clay (PILC), as encapsulated with chitosan (CS) chains, supported with Pd nanoparticles, fresh and recovered PILC-CS@Pd heterogeneous catalysts, along with the starting montmorillonite clay (MC) were measured. After pillaring modification, as the interlayer nano-space expanded, the sub nanometer level free-volume nanohole size increases obviously from 0.182 nm (MC) to 0.246 nm (PILC). Then, as the CS chains and active Pd species encapsulated within the interlayer nano-space, the o-Ps lifetime (τ3) and intensity (I) undergo a continuous decrease, indicating the decrease of the free-volume nanohole size and concentration. Meanwhile, in practical catalytic application scenarios, it is found that the variations of the free-volume parameters show close correlation with the recycling aging behavior and catalytic performance decline of the catalytic nanocomposites. The decrease in density of sub nanometer level molecular stacking due to the leaching of Pd species and degradation of CS chains in the interlayer galleries nano-space of the recovered PILC-CS@Pd hybrid nanocomposite has been sensitively detected by the o-Ps probe.

Capacitive Humidity Sensor with a Rapid Response Time on a GO-Doped P(VDF-TrFE)/LiCl Composite for Noncontact Sensing Applications

Humidity-sensing devices are widely utilized in various fields, including the environment, industries, food processing, agriculture, and medical processes. In the past few years, the development of noncontact sensors based on moisture detection has increased rapidly due to the COVID-19 pandemic. Moisture-detection, noncontact and breath-monitoring sensors have promising applications in various fields. In this study, we proposed a rapid-response graphene oxide (GO)-doped P(VDF-TrFE)/LiCl nanocomposite-based moisture sensor fabricated on an interdigitated electrode. The synthesis of GO/P(VDF-TrFE)/LiCl resulted in a porous structure with nano-sized holes due to the effect of LiCl. Moreover, doped GO improved the conductivity of the sensing film. The created nanoporous structure improved the recovery time better than the response time, with the times being 4.8 s and 7.8 s, respectively. Not only did our sensor exhibit rapid response and recovery times, it also exhibited a high sensitivity of 1708.8 pF/%RH at 25% to 93%RH. We also presented a real-time breath-monitoring system for noncontact sensing applications based on GO-doped P(VDF-TrFE)/LiCl composites. The results revealed that GO-doped P(VDF-TrFE)/LiCl is a good candidate for fabricating real-time moisture-detection noncontact sensing devices.

Femtosecond-laser-assisted high-aspect-ratio nanolithography in lithium niobate.

We report the successful fabrication of high-aspect-ratio lithium niobate (LN) nanostructures by using femtosecond-laser-assisted chemical etching. In this technique, a 1 kHz femtosecond laser is first used to induce local modifications inside the LN crystal. Then, selective chemical wet etching is conducted using a buffered oxide etch (BOE) solution. The etching rate in the laser-modified area reaches 2 μm h-1, which is enhanced by a factor of ∼660 in comparison to previous reports without laser irradiation. Such high selectivity in chemical etching helps realize high-performance maskless nanolithography in lithium niobate. In the experiment, we have fabricated high-quality LN nanohole arrays. The nanohole size reaches ∼100 nm and its aspect ratio is above 40 : 1. The minimal period of the LN hole array is 300 nm. Our work paves a way to fabricate LN nano-integrated devices for advanced optic and electronic applications.

Enhanced thermoelectric performance of holey silicon thin films using F4TCNQ surface doping

Silicon thin films have great potential as chip-integrated Peltier micro-coolers and thermoelectric power generators due to their industry compatibility and cost effectiveness. Improving the thermoelectric figure of merit, zT, and therefore the device efficiency can be achieved by increasing the power factor while decreasing the thermal conductivity. In this work, we study single crystalline silicon thin films with patterned nano-holes with sizes comparable to the phonon mean free path to suppress thermal conductivity. The holey silicon thin films are then surface doped with organic molecules F4TCNQ to create a three-dimensional modulation doping scheme. As the dopants are outside the host material, there is less impurity scattering, which improves carrier mobility and the overall power factor. We fabricate silicon thin films with periodic arrays of nano-sized holes, with a fixed pitch size of 300 nm. By changing the hole diameters, we vary the neck size from 169 nm to 22 nm. The in-plane thermal conductivity, measured using the heat diffusion imaging method, demonstrates an order of magnitude reduction compared to bulk silicon and a change from 26 Wm−1K−1 to 5 Wm−1K−1 at room temperature. The films with large hole diameters allow space for the relatively large F4TCNQ molecules and hence effective surface doping, which is evident by orders of magnitude improvement in the electrical conductivity and power factor.

Tailoring nanohole sizes through the deacetylation process in chitosan powders obtained from squid pens

An experimental study on the evolution of the physicochemical, thermal and nanostructural properties of chitosan samples obtained from squid pens as the deacetylation treatment proceeds is presented. To this aim, potentiometric titration, capillary viscosimetry, infrared spectroscopy, differential scanning calorimetry and positron annihilation lifetime spectroscopy were used. The results obtained are discussed in terms of the influence of the deacetylation time on the deacetylation degree, average molecular weight, thermal parameters and average free nanohole size of the different samples. A way of preparing chitosan matrices with tailored nanostructural characteristics for specific applications through the deacetylation process is explored.

Discussion on fabrication accuracy of infrared topological photonic structures using hyperspectral Fourier image spectroscopy

Compared to conventional periodic nanostructures such as photonic crystals, topological photonic systems require more precise fabrication techniques due to the need to place multiple dielectrics at appropriate positions within a unit cell, and this becomes particularly remarkable in the optical communication band. In this paper, observing photonic band structures by using hyperspectral Fourier image spectroscopy, we quantitatively discuss the fabrication accuracy of typical topological photonic systems in which triangle nanoholes were arranged in a deformed honeycomb lattice with C 6 v symmetry. Here the size and corner radius of triangle nanoholes were precisely controlled using shape correction electron beam lithography. The results showed that the fabrication error must be controlled to below ∼ 10 n m for the size and ∼ 30 n m for the corner radius, in order to achieve the desired topological edge state that occurs at the interface between two photonic structures different in topology.

Enhancement of Exchange Bias and Perpendicular Magnetic Anisotropy in CoO/Co Multilayer Thin Films by Tuning the Alumina Template Nanohole Size.

The interest in magnetic nanostructures exhibiting perpendicular magnetic anisotropy and exchange bias (EB) effect has increased in recent years owing to their applications in a new generation of spintronic devices that combine several functionalities. We present a nanofabrication process used to induce a significant out-of-plane component of the magnetic easy axis and EB. In this study, 30 nm thick CoO/Co multilayers were deposited on nanostructured alumina templates with a broad range of pore diameters, 34 nm ≤ Dp ≤ 96 nm, maintaining the hexagonal lattice parameter at 107 nm. Increase of the exchange bias field (HEB) and the coercivity (HC) (12 times and 27 times, respectively) was observed in the nanostructured films compared to the non-patterned film. The marked dependence of HEB and HC with antidot hole diameters pinpoints an in-plane to out-of-plane changeover of the magnetic anisotropy at a nanohole diameter of ∼75 nm. Micromagnetic simulation shows the existence of antiferromagnetic layers that generate an exceptional magnetic configuration around the holes, named as antivortex-state. This configuration induces extra high-energy superdomain walls for edge-to-edge distance >27 nm and high-energy stripe magnetic domains below 27 nm, which could play an important role in the change of the magnetic easy axis towards the perpendicular direction.

Rapid and sensitive magnetic field sensor based on photonic crystal fiber with magnetic fluid infiltrated nanoholes

A fast response time (0.1 s) magnetic field sensor has been demonstrated utilizing a photonic crystal fiber with nano-size air holes infiltrated with polyethylene glycol based magnetic fluid. The effect of magnetic nanoparticles concentration in the fluid on the magneto-optical sensor performance and its dependence under varying magnetic-field loads was investigated in detail. In particular, the sensor response was analytically modelled with a Langevin function with a good fit (Rge 0.996). A threshold sensing point as low as 20 gauss was recorded and a detection range of 0–350 gauss was demonstrated by means of optical transmission measurements. The experimental results were validated by theory using a waveguide light transmission model fed by finite-element method simulations of the principal guided modes in the infiltrated fiber sensor. The simple interrogation scheme, high sensitivity and quick response time makes the proposed hybrid fiber-optic magneto-fluidic probe a promising platform for novel biochemical sensing applications.

Metal‐Organic Frameworks: Synthesis, Structures, and Applications

Metal‐Organic Frameworks: Synthesis, Structures, and Applications

Theoretical Model of a Plasmonically Enhanced Tunable Spectrally Selective Infrared Photodetector Based on Intercalation-Doped Nanopatterned Multilayer Graphene.

We showed in past work that nanopatterned monolayer graphene (NPG) can be used for realizing an ultrafast (∼100 ns) and spectrally selective mid-infrared (mid-IR) photodetector based on the photothermoelectric effect and working in the 8-12 μm regime. In later work, we showed that the absorption wavelength of NPG can be extended to the 3-8 μm regime. Further extension to shorter wavelengths would require a smaller nanohole size that is not attainable with current technology. Here, we show by means of a theoretical model that nanopatterned multilayer graphene intercalated with FeCl3 (NPMLG-FeCl3) overcomes this problem by substantially extending the detection wavelength into the range from λ = 1.3 to 3 μm. We present a proof of concept for a spectrally selective infrared (IR) photodetector based on NPMLG-FeCl3 that can operate from λ = 1.3 to 12 μm and beyond. The localized surface plasmons (LSPs) on the graphene sheets in NPMLG-FeCl3 allow for electrostatic tuning of the photodetection wavelength. Most importantly, the LSPs along with an optical cavity increase the absorbance from about N × 2.6% for N-layer graphene-FeCl3 (without patterning) to nearly 100% for NPMLG-FeCl3, where the strong absorbance occurs locally inside the graphene sheets only. Our IR detection scheme relies on the photothermoelectric effect induced by asymmetric patterning of the multilayer graphene (MLG) sheets. The LSPs on the nanopatterned side create hot carriers that give rise to the Seebeck effect at room temperature, achieving a responsivity of V/W, a detectivity of D* = 2.3 × 109 Jones, and an ultrafast response time of the order of 100 ns. Our theoretical results can be used to develop graphene-based photodetection, optical IR communication, IR color displays, and IR spectroscopy over a wide IR range.

Conversion of a Helical Surface Plasmon Polariton into a Spiral Surface Plasmon Polariton at the Outlet of a Metallic Nanohole.

The conversion of a helical surface plasmon polariton (SPP) creeping out of a circular nanohole in a thick metal (Ag or Au) film into a spiral (Hankel type) SPP outward propagating at the film’s interface is studied theoretically. The dispersion relations of SPPs of various modes in a nanohole, calculated from a transcendental equation, show that the propagation length of an SPP of mode 1 is much larger than the other modes in a specific frequency band, which is dependent on the nanohole size. In this band, the streamlines of the Poynting vector (energy flux) of mode-1 SPP in nanohole exhibit helixes; the surface component of the energy flux is perpendicular to the phase front of the SPP. Numerical results show that, after a helical SPP tunnels through a nanohole, most of the energy flux fans out at the outlet as a dipole radiation. The spatial phase distribution of Ez above the interface indicates that the transmission light carries orbital angular momentum with a topological charge of 1. Additionally, a part of the helical SPP creeping along the edge of an outlet naturally converts into a spiral (Hankel type of order 1) SPP outward propagating at the film’s interface; both SPPs have the same handedness. Moreover, the interferences of multi SPPs generating from two nanoholes and even from a two-dimensional nanohole array are also related to the spiral SPP.

The Scattering of SH Wave in a Nano Hole Embedded the Infinite Inhomogeneous Medium

Scattering of the shear waves by a nano-sized cylindrical hole embedded the inhomogeneous is investigated in this study. The Helmholtz equation with a variable coefficient is transformed the standard Helmholtz equation by the complex function method and the conformal mapping method. By wave function expanding method, the analytical expressions of the displacement field and stress field in the inhomogeneous medium are obtained. Considering the surface effect and using the generalized Young-Laplace equation, we obtain the boundary conditions at nano arbitrary-shaped hole, then the field equations satisfying boundary conditions are attributed to solving a set of infinite algebraic equations. Numerical results show that when the radius of the cylindrical cavity shrinks to nanometers, surface energy becomes a dominant factor that affects the dynamic stress concentration factor (DSCF) around the cylindrical cavity. The influence the density variation of the inhomogeneity on the DSCF is discussed at the same time.

Nano-optical method for transforming a single yeast cell using exogenous genes.

We report a highly efficient nano-optical method for transforming a single yeast cell using exogenous genes. It used laser tweezers or micromanipulators to immobilize the cell immersed in a DNA solution and created a transient nano-sized hole on its cell wall concurrently with laser scissors to deliver nano moles of DNA into the cell. With this method, one can directly transfer the naked DNA of exogenous genes into yeast cells for transformation. We successfully transformed S. cerevisiae yeasts respectively with GFP (Green Fluorescent Protein) plasmid and the nucleic acid extraction of a bacteria GF1 from the gut of Coptotermes formosanus termites. The experimental results demonstrated that the recombinants had high survival rate and transformation efficiency (28%). The recombinant GFP-yeast system showed green fluorescence for generations. GF1 DNA sequences were incorporated into the yeast genome as a heritable component with stable expression for multi-generations so that the recombinant GF1-yeast had a strong capability of digesting biomass as GF1. Our method would apply to different cells with cell walls for various gene transformations.

Rational design of 3D N-doped graphene with a holey structure as a bifunctional electrode for sensitive methyl parathion detection and supercapacitors.

N-doped graphene with nano-sized holes possesses abundant electrochemically active sites at the exposed edge and an open porous structure, leading to a better electrochemical performance and faster electron and ion transport than the basal planes in graphene. In this study, three-dimensional graphene with a porous structure and abundant doped N (3d-NHG) were synthesized as bifunctional electrodes for methyl parathion (MP) detection and supercapacitors. The roles of N-doping and the holey construction in the electrochemical performance of the 3d-NHG were systematically investigated through a combined theory-experiment strategy. The 3d-NHG-based electrochemical sensor successfully detected methyl parathion in the range of 38 nm-380 μM with a low detection limit (2.27 nM) and superior sensitivity. Furthermore, the 3d-NHG also demonstrated potential for use in supercapacitors with a specific capacitance of 207 F g-1 at 1 A g-1 and excellent rate capability (76% capacitance retention at 10 A g-1). Density functional theory calculations revealed that the exposed carbon sites at the edge are the reactive sites for species adsorption. Moreover, the holey structure in 3d-NHG plays a dominating role in electrochemical processes and in the enhanced electrocatalysis. This work provides guidance for the rational design of high-performance bifunctional electrodes for MP detection and supercapacitors by defect engineering.

Thermoplasmonics of metal layers and nanoholes

Since the early 2000s, the experimental and theoretical studies of photothermal effects in plasmonics have been mainly oriented toward systems composed of nanoparticles, mostly motivated by applications in biomedecine, and have overlooked the case of plasmonic resonances of nanoholes in metal layers (also called nanopores or nano-apertures). Yet, more and more applications based on plasmonic nanoholes have been reported these last years (e.g., optical trapping, molecular sensing, and surface-enhanced Raman scattering), and photothermal effects can be unexpectedly high for this kind of systems, mainly because of the very large amount of metal under illumination, compared with nanoparticle systems. Nanoholes in metal layers involve a fully different photothermodynamical picture, and few of what is known about nanoparticles can be applied with nanoholes. A plasmonic nanohole mixes localized and surfaces plasmons, along with heat transport in a two-dimensional highly conductive layer, making the underlying photothermodynamical physics particularly complex. This Tutorial is aimed to provide a comprehensive description of the photothermal effects in plasmonics when metal layers are involved, based on experimental, theoretical, and numerical results. Photothermal effects in metal layers (embedded or suspended) are first described in detail, followed by the study of nanoholes, where we revisit the concept of absorption cross section and discuss the influences of parameters such as layer thickness, layer composition, nanohole size and geometry, adhesion layer, thermal radiation, and illumination wavelength.

Ultra-Compact Mode-Division Multiplexed Photonic Integrated Circuit for Dual Polarizations

Polarization and mode division multiplexing are powerful tools for large-capacity parallel optical communications. Dual-polarization and mode-division multiplexed silicon photonic integrated circuit with ultra-small footprint is proposed and experimentally demonstrated. The circuits consist of a mode multiplexer, 3-dB power splitter and two demultiplexers which can simultaneously handle TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> mode. Compared with conventional device structure, the device footprint is scaled down via pixelated waveguide meta-structure. The mode multiplexer and the splitter have a footprint of only 6.8 μm × 6 μm and 6 μm × 5.25 μm, respectively. The fabrication tolerance on the nanohole size variations are studied, and the fabricated devices are systematically characterized. The measured insertion losses of the multiplexer and 3-dB power splitter are below 1.4 dB and 4.5 dB for all four modes within the wavelength range from 1530 nm-1570 nm. In the meantime, the measured maximum inter-mode cross talk is below -15 dB over a 30 nm bandwidth. The experimental results also indicate the power imbalance of the splitter is within 0.4 dB from 1530 nm-1570 nm. Since the demonstrated polarization and mode handling devices via pixelated meta-structures occupy significantly smaller chip area than conventional wisdoms, this work shows the potential for large scale and dense integration of polarization and mode division multiplexing system on photonic chip.

Synthesis and characterization of Benzyl chloride-based hypercrosslinked polymers and its amine-modification as an adsorbent for CO2 capture

As one of the microporous polymers with nano-sized holes, HCPs have attracted much attention in CO 2 capture for a variety of reasons such as their low density, high chemical and physical stability and high specific surface area. On the other hand, amine-modification of the adsorbent is known to improve it. Therefore, research on amine-functionalization of adsorbent HCPs is on the rise. The aim of this study was to synthesize benzyl chloride-based hypercrosslinked adsorbent (B-Cl) using the Friedel–Crafts reaction for CO 2 adsorption. In addition, it was modified by post-synthesis modification using low-cost wet impregnation process with an amine to improve its adsorption capacity. Post-synthetically functionalized amination was performed using ethylenediamine (EDA) in the presence of water (B-Cl-1) and methanol (B-Cl-2). Structural properties of the adsorbent were depicted by various spectroscopic techniques. A higher specific surface area was reported for B-Cl (1248.87 m 2 .g −1 ) compared to the amine-modified samples (B-Cl-1 (1115.08 m 2 .g −1 ) and B-Cl-2 (409.49 m 2 .g −1 )). The CO 2 adsorption capacity of benzyl chloride-based hypercrosslinked (B-Cl) and amine-modified samples (B-Cl-1 and B-Cl-2) was evaluated in the different conditions. B-Cl adsorption capacity at (1 bar, 273 K) is 75.14 mg.g −1 , which is higher than the amine-modified samples B-Cl-1 (39.15 mg.g −1 ) and B-Cl-2 (19.10 mg.g −1 ). On the other hand, the adsorption capacity of amine-modified adsorbent in the presence of accessible and low-cost water solvent (B-Cl-1) at temperatures above 45 ºC increased compared to the unmodified adsorbent. In order to better understand the absorption process, experiments were conducted to investigate isotherm, kinetic, and thermodynamic of the process. • Benzyl chloride-based hypercrosslinked (B-Cl) was synthesized for CO 2 adsorption. • (B-Cl) was functionalized with ethylenediamine (EDA) to obtain (B-Cl-1) and (B-Cl-2). • CO 2 adsorption capacity of (B-Cl, B-Cl-1 and B-Cl-2) was evaluated. • CO 2 adsorption capacity of B-Cl-1 at temperature above 45 °C was higher than that of B Cl. • The kinetics, isotherms, and thermodynamics of the adsorption were investigated.

High-Q resonances governed by bound states in the continuum of a cross-shape nanohole array perforated on a photonic crystal slab

Optical BICs are investigated of a Si3N4 slab perforated with cross-shape nanohole array. BICs at normal incident angle and oblique incidence are both be found in this nanostructure by adjusting the nanohole shape and size and refractive index of the surrounding medium. Q-factor at at-Γ BIC and at off-Γ BIC can be more than 106, which indicates light is confined in this nanostructure perfectly. High Q-factor modes containing BIC of this structure is associated with structure parameters and they are sensitive to the environment. The results from both methods accord each other well, and they have a certain significance for the design of novel ultra-high sensitivity.