Tip Electric Field Research Articles

Bio-inspired fabrication of chitosan/PEO/Ti3C2Tx 2D MXene nanosheets supported palladium composite nanofiber catalysts via electrospinning

In this study, novel chitosan/polyethylene oxide/Ti3C2Tx 2D MXene nanosheets (CS/PEO/Ti3C2Tx) nanofibers were successfully prepared by a continuous electrospinning process. During the electrospinning process, induced by the syringe tip capillary effects and electric field force, the Ti3C2Tx nanosheets were aligned along the direction of the nanofiber formation to occur a highly oriented structure. This well-ordered arrangement of the inorganic Ti3C2Tx nanosheets within the organic polymer matrix nanofiber was similar with nacre-like ‘brick-and-motar’ structure to some extent, resulting in a marked increase in thermal stability and mechanical properties of the resultant CS/PEO/Ti3C2Tx nanofiber. As 4 wt% of Ti3C2Tx nanosheets loaded, the highest tensile strength of the CS/PEO/Ti3C2Tx nanofiber mats was achieved as 31.7 MPa, about two times that of neat CS/PEO nanofibers. Uniformly dispersed Pd nanoparticles in size of about 1.6 nm have been successfully immobilized on the composite nanofiber with a solution impregnation process. With a loading as low as 0.2 mol% of Pd, the resultant Pd@CS/PEO/Ti3C2Tx composite nanofiber catalysts were highly active for both Heck and Sonogashira coupling reactions with broad reactants application scope, and could be recycled 15 runs without significant loss of activities.

High-output tuber crops-derived porous spherical carbons: Curved tip electric field-dependent activity for oxygen reduction catalysis

Metal-free nanocarbons with highly editable compositions and well-defined morphologies, and adjustable coordination environments have been considered as promising and inexpensive electrode materials that can be used in the fields of fuel cells and metal-air batteries. Herein, the typical micromorphology of high-output tuber crops potato was examined for the first time by cryo-electron microscopy, and nitrogen-doped spherical carbons with highly curved carbon layers were prepared from potato and sweet potato by hydrothermal and ammonia-activated treatments. The potato-derived carbon (PC) and sweet potato-derived carbon (SPC) with enriched nitrogen dopants on native curved carbon layers exhibit favorable oxygen reduction reaction (ORR) activities in both acidic and alkaline media. The half-wave potential of the curved PC is 60 mV higher than that of commercial Pt/C (20 wt% Pt) in 0.1 M KOH. Impressively, the zinc-air battery using the curved PC displays excellent stability and achieves a peak power density of 116 mW cm−2, surpassing the performance of Pt/C (108 mW m−2). Finite element method (FEM) simulations and molecular dynamics (MD) calculations reveal that the curved carbon surface-enhanced tip electric field on the spherical structure, could further induce charge transfer and accelerate the ORR process. This work elucidates the origin of the catalytic activity of spherically structured metal-free carbons with N-doping, providing meaningful insights into the development of low-cost and highly active catalysts and advancing the field of sustainable energy.

Research on Singularity in Calculation of Induced Electric Field in Pointed Conductors

In the electric field environment of thunderstorm, the tip of a grounded object at a high place is more likely to produce corona discharge and finally cause lightning flash. Therefore, the study of the surface electric field of the grounded object tip in the electric field environment has important theoretical value and practical significance for the analysis of the characteristics of the head-on discharge. Due to the strong singularity of the tip structure, the traditional numerical analysis method cannot accurately calculate its surface electric field. Therefore, the traditional literature usually chamfers the conductor tip, but in lightning physics, researchers are most concerned about the maximum field strength in the local area. In order to study the electric field distribution on the tip conductor surface, a semi-analytical boundary element method is proposed to calculate the tip structure directly. Firstly, the analytical formula of the electric field on the tip conductor surface and the boundary element semi-analytical common method are derived, and the tip conductor model is established to calculate the tip electric field excited by the external electric field using the analytical solution and the semi-analytical method. The correctness of the semi-analytical method is verified by calculating the L2 loss function of the two, and the influence of the tip angle on the semi-analytical calculation results is studied. The results show that for the three-dimensional cone model, the L2 loss function is 10-5, which meets the calculation accuracy. The special treatment of the semi-analytical method at the strong singular integral makes the calculation accuracy much higher than that of the Gaussian integral, where the L2 loss function is greatly reduced. Further, based on the change of tip angle, as the conductor tip becomes sharper, the greater the electric field distortion is, and the greater the L2 loss function is. The research results provide a method reference for the calculation of the electric field on the tip conductor surface.

Manipulating single excess electrons in monolayer transition metal dihalide

Polarons are entities of excess electrons dressed with local response of lattices, whose atomic-scale characterization is essential for understanding the many body physics arising from the electron-lattice entanglement, yet difficult to achieve. Here, using scanning tunneling microscopy and spectroscopy (STM/STS), we show the visualization and manipulation of single polarons in monolayer CoCl2, that are grown on HOPG substrate via molecular beam epitaxy. Two types of polarons are identified, both inducing upward local band bending, but exhibiting distinct appearances, lattice occupations and polaronic states. First principles calculations unveil origin of polarons that are stabilized by cooperative electron-electron and electron-phonon interactions. Both types of polarons can be created, moved, erased, and moreover interconverted individually by the STM tip, as driven by tip electric field and inelastic electron tunneling effect. This finding identifies the rich category of polarons in CoCl2 and their feasibility of precise control unprecedently, which can be generalized to other transition metal halides.

Highly sensitive and stable probe refractometer based on configurable plasmonic resonance with nano-modified fiber core

A dispersion model is developed to provide a generic tool for configuring plasmonic resonance spectral characteristics. The customized design of the resonance curve aiming at specific detection requirements can be achieved. According to the model, a probe-type nano-modified fiber optic configurable plasmonic resonance (NMF-CPR) sensor with tip hot spot enhancement is demonstrated for the measurement of the refractive index in the range of 1.3332–1.3432 corresponding to the low-concentration biomarker solution. The new-type sensing structure avoids excessive broadening and redshift of the resonance dip, which provides more possibilities for the surface modification of other functional nanomaterials. The tip hot spots in nanogaps between the Au layer and Au nanostars (AuNSs), the tip electric field enhancement of AuNSs, and the high carrier mobility of the WSe₂ layer synergistically and significantly enhance the sensitivity of the sensor. Experimental results show that the sensitivity and the figure of merit of the tip hot spot enhanced fiber NMF-CPR sensor can achieve up to 2995.70 nm/RIU and 25.04 RIU⁻¹, respectively, which are 1.68 times and 1.29 times higher than those of the conventional fiber plasmonic resonance sensor. The results achieve good agreements with numerical simulations, demonstrate a better level compared to similar reported studies, and verify the correctness of the dispersion model. The detection resolution of the sensor reaches up to 2.00×10⁻⁵ RIU, which is obviously higher than that of the conventional side-polished fiber plasmonic resonance sensor. This indicates a high detection accuracy of the sensor. The dense Au layer effectively prevents the intermediate nanomaterials from shedding and chemical degradation, which enables the sensor with high stability. Furthermore, the terminal reflective sensing structure can be used as a practical probe and can allow a more convenient operation.

Atomic View on the (111) Surface of a Cu2O Single Crystal: Reconstruction, Electronic Properties, and Band-Bending Effects

The nature of the (√3 × √3)R30° reconstruction of the Cu2O(111) surface has been heavily debated for almost 30 years. This work demonstrates that the nanopyramidal reconstruction model that was recently developed for Cu2O(111) thin films is valid also for bulk samples. For this purpose, the surface of a natural Cu2O(111) crystal was prepared by common surface science methods, yielding a robust and reproducible (√3 × √3)R30° superstructure pattern in electron diffraction. Atomically resolved STM images display a regular array of trifold symmetric protrusions, in perfect agreement with the nanopyramidal model in which Cu4O units attach to every third Cu–O six-membered ring of a Cu-depleted (111) surface. STM conductance spectra reveal the p-type character of the oxide with the valence-band top pinned to the Fermi level. From band-bending effects in the tip electric field, an induced carrier concentration of 6 × 1017 cm–3 is determined for the (√3 × √3)R30° phase. This value increases to 4 × 1018 cm–3 on the few (1 × 1) patches covered with a Cu-poor minority phase, indicating a close interplay between atomic structure and local screening response for a given surface termination. Our work clarifies the nature of the (√3 × √3)R30° reconstruction of bulk Cu2O(111) by connecting it to the recently proposed nanopyramidal reconstruction model.

Process investigation of nanofiber diameter based on linear needleless spinneret by response surface methodology

Needleless electrsopinning is of a great attention to researcher in industrial production of nanofibers for nearly ten years. Many innovative and different shapes needleless spinnerets are designed and then used to fabricate mass nanofibers. There are a lot of reports about spinning process parameters. In this study, we developed a novel linear flume needleless spinneret to fabricate nanofiber. The finite element analysis software was used to simulate electric field contour of different included angle spinneret. The curves of electric field intensity were drawn to evaluate the tip electric field intensity of spinneret. In addition, Response Surface Methodology (RSM) was adopted to investigate the effect of process parameters on nanofiber diameter. Two-dimensional and three-dimensional response surface contour were obtained to discuss the interaction of the different process parameters. This work provided a novel idea and approach for optimizing design of the needleless spinneret through numerical simulation method. Investigation of process parameter could guide the controllable production of desired nanofibers.

An inventive multi-scale, multiphysics modelling approach and comparative analysis of distinctive features of planar ionization waves in air: II. Positive streamers

A robust numerical framework for positive streamer modelling based on electro-hydrodynamic equations coupled with Poisson and Helmholtz differential equations for the photoionization process is presented. The proposed multi-layer meshing scheme in a 2D non-axisymmetric finite-element model along with a hybrid meshing technique presented in part I of this series paper for negative streamers provide high accuracy, spatial resolution, and capability to present the major features of both positive and negative streamers. In addition, the presented model is utilized to simulate multi positive and negative streamers propagation in a non-uniform electric field in the air. The main characteristics of the positive and negative streamers including the morphology, distribution pattern of space charges, local electric field, diameter, length, and velocity are presented, discussed, and compared with the experiment. Moreover, the impacts of initial seed density and voltage on the propagation of streamers are presented and explained. The branching mechanism arising from Laplacian instability and its impact on the streamer parameters such as tip electric field and dominant charge density is explained.

Long-life and dendrite-free zinc metal anode enabled by a flexible, green and self-assembled zincophilic biomass engineered MXene based interface

• Green zincophilic biomass engineered MXene based interface is designed for dendrite-free Zn anode. • The MX/CS layer enhances the hydrophilicity and promotes uniform Zn nucleation. • The MX/CS layer significantly suppress the Zn dendrites growth and side reactions. • The MX/CS layer buffers the volume change of Zn metal anode during cycling. • MX/CS@Zn anode exhibits extended cycling life and high reversibility. As a promising candidate of safety, low-cost and eco-friendliness, Zn metal batteries still suffer from poor stability and irreversibility, which attribute to dendrite growth and accompanied side reactions. To enable highly reversible Zn anode, a flexible and self-assembled biomass engineered MXene film, functioning as an artificial protective interface, is firmly adhered on the Zn foil surface by facile blade-casting. This amine-rich ultrathin protective film not only effectively protects fresh Zn against water corrosion, but also promotes Zn nucleation and triggers homogeneous Zn plating/stripping underneath the film attributing to its excellent adhesion, flexibility, hydrophilicity and strong coordination of amine groups to Zn 2+ . Meanwhile, the conductive MXene component can terminate the accidental Zn dendrites by ionizing the contacted Zn and dispersing the tip electric field. Consequently, the protected Zn electrode delivers prolonged cycling life and improved coulombic efficiency, which also conduces to improving the full cell performance when it is matched with MnO 2 cathodes. This work brings a new insight into the practical design of highly reversible Zn metal anodes.

Underlying mechanism of the stagnation of positive streamers

Several publications have shown that it is challenging to model the stagnation of positive streamers. They find that as the streamers propagate, the space charge region at the streamer tip reduces in size and that the associated electric field increases towards infinity. In a recent study on streamer propagation in unsteady airflow, we circumvented this problem by relaxing the local density and electric field approximation in the drift-diffusion model, commonly used in the past models. The results, recently published, show that the electric field remains bounded during the streamer propagation. In the present paper, we explore the process of stagnation further with a more rigorous approach. We confirm that the instability in the electric field is an immediate effect of the local density and field approximation and that an extended description of ionization stabilizes the electric field and leads to a decelerating streamer. Finally, we discuss the role of positive ions in the stagnation and we show that the stagnating streamer velocity decreases till it becomes comparable to the ion velocities in the streamer head. This causes a broadening of the streamer head which leads to a sharp decrease in the streamer tip electric field and the streamer stagnation.

Asymmetric Backward Peaking Radiation Pattern From a Relativistic Particle Accelerated by Lightning Leader Tip Electric Field

AbstractTerrestrial Gamma ray Flashes exhibit slopes of ionizing radiation associated with bremsstrahlung. Bremsstrahlung has a continuous spectrum of radiation from radio waves to ionizing radiation. The Poynting vector of the emitted radiation, that is, the radiation pattern around a single particle under the external lightning electric field during interaction with other particles or atoms, is not quite well known. The overall radiation pattern arises from the combination of radiation of parallel and perpendicular motions of a particle caused by the acceleration from the lightning electric field and the bremsstrahlung. The calculations and displays of radiation patterns are generally limited to a low‐frequency approximation for radio waves and separate parallel and perpendicular motions. Here, we report the radiation patterns of combined parallel and perpendicular motions from accelerated relativistic particles at low and high frequencies of the bremsstrahlung process with an external lightning electric field. The primary outcome is that radiation patterns have four relative maxima with two forward peaking and two backward peaking lobes. The asymmetry of the radiation pattern, that is, the different intensities of forward and backward peaking lobes, are caused by the Doppler effect. A novel outcome is that bremsstrahlung has an asymmetry of the four maxima around the velocity vector caused by the curvature of the particle's trajectory as it emits radiation. This mathematical modeling helps to better understand the physical processes of a single particle's radiation pattern, which might assist the interpretation of observations with networks of radio receivers and arrays of γ‐ray detectors.

Investigations of positive streamers as quasi-steady structures using reduced order models

Single streamers are currently well simulated using detailed computational models. Most of these models are inhibitively complex to use for modelling many-streamer interactions in a streamer corona. This work develops reduced order models of single positive streamers in atmospheric pressure air that replicate the core macroscopic behaviour of detailed models while using a simpler physics representation. Models are developed using the 1.5D framework, with emphasis placed on solving the equations of motion in the streamer reference frame. The solution in this quasi-steady frame is shown to be a good representation of the instantaneous state of the streamer. Finally, a method of uniquely characterizing the instantaneous state of a streamer using its macroscopic parameters (velocity, radius, tip electric field and channel electric field) is developed. This characterization is interpreted graphically, with streamers treated as quasi-steady structures which evolve in time at a rate much slower than the time scale of electron transport. Previous work in the literature is shown to be well captured by this interpretation.

Fluid-Structure Interaction Analysis of a Piezoelectric Cantilever for Energy Harvesting

A numerical investigation was conducted to study the impact of varying the velocity magnitude and the elasticity of the cantilever on the performance of the piezoelectric beam such as tip deflection and voltage, tip electric field and maximum electric field. COMSOL software was used to solve for the governing equations taking into account fluid-structure interaction. The results of this investigation were compared against analytical results found in the literature and the agreement was excellent. The results presented in this study demonstrated a substantial impact of the flow velocity magnitude and elasticity of the cantilever on the tip deflection and voltage as well as maximum electric field. As the velocity increased and the elasticity of the microcantilever decreased, the tip deflection increased and consequently increased voltage and electric field. This study suggests that high voltage and electricity can be generated from energy harvester if they are subjected to high fluctuations.

Single spin resonance driven by electric modulation of the g -factor anisotropy

We address the problem of electronic and nuclear spin resonance of an individual atom on a surface driven by a scanning tunnelling microscope. Several mechanisms have been proposed so far, some of them based on the modulation of exchange and crystal field associated to a piezoelectric displacement of the adatom driven by the RF tip electric field. Here we consider a new mechanism, where the piezoelectric displacement modulates the g factor anisotropy, leading both to electronic and nuclear spin flip transitions. We discuss thoroughly the cases of Ti-H (S = 1/2) and Fe (S = 2) on MgO, relevant for recent experiments. We model the system using two approaches. First, an analytical model that includes crystal field, spin orbit coupling and hyperfine interactions. Second, we carry out density functional based calculations. We find that the modulation of the anisotropy of the g tensor due to the piezoelectric displacement of the atom is an additional mechanism for STM based single spin resonance, that would be effective in S = 1/2 adatoms with large spin orbit coupling. In the case of Ti-H on MgO, we predict a modulation spin resonance frequency driven by the DC electric field of the tip.

Investigation of the Capacitance-Voltage Electrical Characteristics of Thin-Film Transistors Caused by Hydrogen Diffusion under Negative Bias Stress in a Moist Environment.

In this study, the impact of moisture on the electrical characteristics of an amorphous In-Ga-Zn-O thin-film transistor (a-IGZO TFT) was investigated. In commercial applications of such TFTs, high stability and quality performance in humid environments are essential. During TFT operation under ambient moisture, the electrolysis of water molecules occurs via the tip electric field effect. Hydrogen diffuses from the etch-stop layer or back-channel into the main channel under a negative electric field. The hydrogen atoms act as shallow donors (which causes the carrier concentration in the channel to rise), causing the threshold voltage (VTH) to shift in the negative direction. Hydrogen diffusion from the overlap of the source/drain and gate electrodes to the channel center caused by the tip electric field induces a significant barrier lowering and VTH shifts in a short-channel device. However, under negative bias stress (NBS) in ambient moisture, the negative VTH shift is more obvious in short- than in long-channel devices, indicating suppressed hydrogen diffusion in long-channel devices. This is attributed to the electrolysis of water by the tip electric field at the source, drain, and gate electrodes, which causes hydrogen to diffuse to the center of the channel. Here, a novel physical model of the capacitance-voltage (C-V) electrical property changes under ambient moisture is proposed, based on the early appearance of abnormalities in the C-V measurements. The electrolysis of water caused by the tip electric field and electrical abnormalities caused by hydrogen diffusion into the a-IGZO active layer are explained by this model. A secondary-ion mass spectrometry analysis shows that hydrogen content in the channel generally increases under NBS in ambient moisture. The degradation behavior due to moisture in a-IGZO is clarified. Thus, inhibiting the tip electric field may benefit future flexible-display and gas-sensing applications.

Optimization of electric field uniformity of multi-needle electrospinning nozzle

Multi-needle electrospinning technology is a method for mass production of nanofibers, which can improve the production efficiency of nanofibers by increasing the number and density of needles for multi-needle electrospinning. However, when the arrangement density of the needle is high, the electric field of the needle tip is not uniform, causing instability such as jet dripping and broken jet. In this paper, the electric field uniformity optimization problem of multi-needle electrospinning technology is used to simulate the needle tip electric field by using COMSOL finite element analysis software. The influence of the needle size and the dielectric material on the electric field of the tip was studied. Finally, the method of using dielectric material on the tip of the middle part of the needle is beneficial to the electric field uniformity. The uniformity of the needle tip electric field in the case of high-density arrangement of the needle is realized, and the nozzle is provided for mass production of nanofibers by multi-needle electrospinning.

Switching off the SERS signal for highly sensitive and homogeneous detection of glucose by attenuating the electric field of the tips

The advances in surface-enhanced Raman scattering (SERS) have resulted in significant improvements for sensing glucose, achieving a highly detecting sensitivity of the order of μM. Highly sensitive glucose detection, however, is still a challenge due to extremely small Raman scattering cross section of glucose molecules and weak interaction between the molecules and the metal nanoparticles. Here, we designed a novel homogeneous SERS-based nanoplatform composing of the SERS tags and glucose oxidase in aqueous solution for a highly sensitive glucose detection. Adding glucose caused enzymatic oxidation reaction to etch the tip electric field (E) of silver nanotriangle. Thus, the decreased intensity of E was greatly amplified by the change of SERS signal (E4 dependent), which resulted in an excellent glucose detection limit of 0.4 nM was firstly achieved. Furthermore, the nonlinear relationship between the decreased SERS intensity and the glucose concentrations was reasonably revealed based on theoretical calculations and deeply understanding of the enhancement mechanism, which is very useful in improving the sensitivity and accuracy of trace glucose detection. The as-prepared nanoplatform showed good sensitivity and high selectivity only through observing the SERS intensity change, which is potential for highly sensitive and practical glucose detection for clinical trace analyses.

The Similarity of the Action of Franklin and ESE Lightning Rods under Natural Conditions

In the lightning rods categorized as Early Streamer Emission (ESE) types, an intermittent voltage impulse is applied to the lightning rod to modulate the electric field at its tip in an attempt to speed up the initiation of a connecting leader from the lightning rod when it is under the influence of a stepped leader moving down from the cloud. In this paper, it is shown that, due to the stepping nature of the stepped leader, there is a natural modulation of the electric field at the tip of any lightning rod exposed to the lightning stepped leaders and this modulation is much more intense than any artificial modulation that is possible under practical conditions. Based on the results, it is concluded that artificial modulation of the electric field at the tip of lightning rods by applying voltage pulses is an unnecessary endeavor because the nature itself has endowed the tip of the lightning rod with a modulating electric field. Therefore, as far as the effectiveness of artificial modulation of the tip electric field is concerned, there could be no difference in the lightning attachment efficiency between ESE and Franklin lightning rods.

Field emission properties of SiO2-wrapped CNT field emitter

Carbon nanotubes (CNTs) exhibit unstable field emission (FE) behavior with low reliability due to uneven heights of as-grown CNTs. It has been reported that a mechanically polished SiO2-wrapped CNT field emitter gives consistent FE performance due to its uniform CNT heights. However, there are still a lack of studies on the comparison between the FE properties of freestanding and SiO2-wrapped CNTs. In this study, we have performed a comparative study on the FE properties of freestanding and SiO2-wrapped CNT field emitters. From the FE measurements, freestanding CNT field emitter requires lower applied voltage of 5.5 V μm−1 to achieve FE current density of 22 mA cm−2; whereas SiO2-wrapped field emitter requires 8.5 V μm−1 to achieve the same current density. This can be attributed to the lower CNT tip electric field of CNTs embedded in SiO2, as obtained from the electric field simulation. Nevertheless, SiO2-wrapped CNTs show higher consistency in FE current than freestanding CNTs. Under repeated FE measurement, SiO2-wrapped CNT field emitter achieves consistent FE behavior from the 1st voltage sweep, whereas freestanding field emitter only achieved consistent FE performance after 3rd voltage sweep. At the same time, SiO2-wrapped CNTs exhibit better emission stability than freestanding CNTs over 4000 s continuous emission.

Fabrication of nano ion–electron sources and nano-probes by local electron bombardment

A new method for fabricating nano ion–electron sources and nano probes with an apex in the range of 1nm is introduced. The method is based on bombarding a regular tip apex with electrons extracted and accelerated from a nearby source by the electric field. This can be achieved by placing a metal ring around a precursor metal tip at a level below the tip apex in a field ion microscope (FIM). The metal ring is then heated, by a grounded DC power source, to a temperature below the thermionic emission value. The electric field between the tip and the hot ring is high enough to cause electrons to be extracted from the metal ring, i.e. Schottky field emission, and then accelerated to the shank with energy sufficient to dislodge atoms from the shank. An atomic scale apex with a single atom end can be obtained by monitoring the evolution of the tip apex due to the movement of mobile atoms while adjusting the tip electric field and the temperature of the metal ring. As this method depends only on the electron bombardment mechanism, this makes it a clean process that can be applied to any metal or heavily doped semiconductor materials appropriate for generating a high electric field for FIM applications.