Intense Electric Field Research Articles

Gate induced modulation of electronic states in monolayer organic field-effect transistor

Organic field-effect transistors with ionic liquids have attracted much attention, since the ionic liquids induce an intense electric field at a semiconductor interface, resulting in a high concentration of charge carriers. It is expected that such strong electric fields and highly doped charges induce nontrivial effects on the electronic band structures. Recently, the blue shift of the peak wavelength in photo-absorption spectra for a DNBDT-monolayer transistor was experimentally observed by increasing an ionic-liquid gate voltage, although the origin of the shift is still under debate. Therefore, we investigate the hole-doping and external electric-field effects on the electronic states of the organic semiconducting monolayer within the framework of the density functional theory. The calculated results show that the photo-absorption energy is increased by hole doping while an external field decreases the photo-absorption energy. We demonstrated that the calculations give useful information to understand the origin of the experimentally observed wavelength shift of photo-absorption spectra.

Integrated Molecular Optomechanics with Hybrid Dielectric-Metallic Resonators.

Molecular optomechanics describes surface-enhanced Raman scattering using the formalism of cavity optomechanics as a parametric coupling of the molecule’s vibrational modes to the plasmonic resonance. Most of the predicted applications require intense electric field hotspots but spectrally narrow resonances, out of reach of standard plasmonic resonances. The Fano lineshapes resulting from the hybridization of dielectric–plasmonic resonators with a broad-band plasmon and narrow-band cavity mode allow reaching strong Raman enhancement with high-Q resonances, paving the way for sideband resolved molecular optomechanics. We extend the molecular optomechanics formalism to describe hybrid dielectric–plasmonic resonators with multiple optical resonances and with both free-space and waveguide addressing. We demonstrate how the Raman enhancement depends on the complex response functions of the hybrid system, and we retrieve the expression of Raman enhancement as a product of pump enhancement and the local density of states. The model allows prediction of the Raman emission ratio into different output ports and enables demonstrating a fully integrated high-Q Raman resonator exploiting multiple cavity modes coupled to the same waveguide.

Front Cover: Investigation of entrance effects on particle electrophoretic behavior near a nanopore for resistive pulse sensing

DOI: 10.1002/elps.202100162 The cover picture illustrates entrance effects of a solid-state nanopore immersed in an electrolyte solution on the electrophoretic behavior of a charged biomolecule. The intense electric field in the high electrical resistance nanopore generated by an external electric potential bias across the membrane gives rise to a significant electroosmotic flow opposing the molecule migration. Whether or not the molecule can translocate through the nanopore for resistive pulse sensing is subject to both the zeta potential difference between the molecule and nanopore and the variation of the local electric field strength from the nanopore-reservoir junction into the nanopore.

Treating Spinal-Cord Tumors with TTFields — A Simulation Study

<h3>Purpose/Objective(s)</h3> Tumor Treating Fields (TTFields) are an anti-mitotic non-invasive therapy approved for the treatment of certain solid tumors such as glioblastoma (GBM) and malignant pleural mesothelioma (MPM). TTFields are low intensity electrical fields in the medium frequency range (100-500 kHz). TTFields are applied to the patient using two pairs of transducer arrays (TAs) placed on the patient skin. The therapeutic threshold for treatment is considered to be 1 V/cm. The distribution of the electric field within the body is determined by the geometry of the arrays, the anatomical area being treated, and the electric parameters of the different tissues, specifically their electrical conductivity. Treatment planning is necessary to maximize the efficacy of the treatment. However, some regions of the body are more challenging to treat with TTFields due to their geometrical characteristics. One such example is the spinal cord. The spinal cord is an elongated structure with high electric conductivity encompassed within relatively electrically insulating bone structure of the spine. This results in a cable-like structure. The unique structure of the spine makes delivering TTFields to spinal tumors a non-trivial task. While the electric fields can propagate well along the spinal cord, they cannot easily penetrate the vertebrae to reach the spinal cord. In this study, we used simulations to establish ground rules for treating the spinal cord. Specifically, we tested the feasibility of using TTFields for treating leptomeningeal metastases of breast cancer. <h3>Materials/Methods</h3> A realistic computational full body model of a healthy female was used in the study. Virtual transducer arrays were placed on the model's back at different heights, to the left and right of the spine. Arrays were also placed on the head and hips of the model. To simulate the delivery of TTFields to the spinal cord and CSF, we used Sim4Life v6.0 (ZMT Zürich) Ohmic-quasi-static solver. We applied 1A current at 150 kHz to the virtual arrays. In each simulation, we paired one array on the left to one array on the right, with different heights. The resulting field distribution along the spinal cord, CSF and nerves was then extracted. <h3>Results</h3> The field distribution has been analyzed along the axial plane of the patient. The mean field value for every slice was calculated, and the resulting axial-distribution was compared to the location of the two arrays along the models back. The results show that the maximal slice-averaged field intensity in the spinal cord is obtained between the arrays and in most cases is above the required 1 V/cm. <h3>Conclusion</h3> This work demonstrates that by orthogonally positioning the two pairs of arrays on the patient back to surround the tumor area, it may be possible to provide sufficient field intensity to tumors within the CSF or of the spinal cord.

Design and Optimization of Interdigitated Microwave Sensor for Multidimensional Sensitive Characterization of Solid Materials

This paper presents an interdigital capacitor (IDC)-based high sensitivity microwave sensor for the multidimensional (complex permittivity and thickness) characterization of solid materials. The proposed sensor was implemented by etching a slot resonator with an IDC on the ground layer of 0.76 mm-thick RF-35 substrate with relative permittivity of 3.5 and loss tangent of 0.0018. The IDC fingers were configured as a spur-line structure to create an intense electric field zone that interacted significantly with the material under test (MUT), resulting in high sensitivity. A sensor prototype with optimized dimensions generated dual resonant frequencies of 2.35 GHz and 5.79 GHz and was used to measure the MUT’s complex permittivity and thickness, respectively. Experimental results revealed that the resonant frequencies of the developed sensor exhibited high sensitivities (276 MHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> for permittivity and 143 MHz/mm for thickness) and resolutions (0.27678 for permittivity and 0.1439 for thickness) of solid materials. Moreover, the sensing accuracies were 99.9% for real permittivity and 97.7% for imaginary permittivity. The demonstrated high performance of the developed sensor validates its applications in the multidimensional characterization of various solid materials.

Frequency-Domain Spectroscopy and Charge Trap Characteristics of Cellulose Based Pressboard Modified by Nano-TiO2 Particles

Dielectric response and charge decay test are widely used for evaluating the electric properties of the insulation pressboards in the converter transformer. In this paper, Frequency Domain Spectroscopy (FDS) test, breakdown test, and charge decay characteristics experiments are carried out on the cellulose pressboards modified by TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> with different mass fractions and diameters. The FDS of the modified cellulose pressboards at ambient temperature is measured from 0.0001 to 1000 Hz by IDAX 300. The process is conducted at the laboratory to study the characteristics parameters of the dielectric response behaviors, such as complex relative permittivity. The results show that the values of the relative permittivity for the insulation pressboards modified by TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (5 wt%, 10 nm) are reduced. To verify the accurate results, the microstructures of the pressboards modified by 5 wt% with 10 nm diameter are observed by a Scanning Electron Microscope (SEM). The breakdown strength tests are carried on the samples modified by 1 wt%, 3 wt%, 5 wt%, 7 wt% with 10 nm TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> under the intensity electric and high-temperature field, respectively. The values of the breakdown strength are increased by 38% and 11.5% for single layer samples and oil/pressboard composite insulation models modified by 5 wt% nano-TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> filler. In addition, the charge decay characteristics are tested on the samples. The proper proportion additions can reduce the trap density.

Insight into molecular rearrangement of a sessile ionic nanodroplet with applied electric field

This work deploys the molecular dynamics simulations to study the effect of an external electric field on the structural and dynamic properties of a sessile ionic nano-droplet. The results show that the presence of the ions at different concentrations causes significant deformations in the hydration shells. Such deformations resemble the effect of high pressure on water molecules. Due to the disintegration of the droplet under the influence of high intensity electric fields, the drift velocities and mobilities of the sodium and chlorine ions exhibit a decreasing trend in the presence of the solid substrate which is not observed in free droplets. The change in the ion-water interaction energy increases with the increasing electric field intensity. This implies an underlying reduction in the strength of ionic hydration. The presence of the Pt surface enhances the ion-water and water-water interactions.

Generation of electron – positron pairs by laser-ion implosion of a target with a spherical microbubble inside

Laser targets with microbubbless have recently been intensely studied, including with the aim of generating superintense electromagnetic fields. Under the action of laser radiation, ion beams are formed in the target, converging to the centre of the microbubbles. In the central region, the ion density can be several times higher than the target density, leading to the generation of an extremely intense electric field and high-energy ions. Using PIC simulation, the dynamics of target electrons is investigated taking into account the effects of quantum electrodynamics (QED) and the development of a QED cascade in the intense field region. It is shown that an increase in the electron temperature leads to a much more efficient formation of electron – positron pairs. The contribution of bremsstrahlung to the generation of photons in the central region of the microbubbles is analysed. It is found that the contribution of bremsstrahlung is insignificant in comparison with the synchrotron mechanism of electron emission in the collective field of ions.

Rod–sphere cluster irradiation with femtosecond laser pulses: cut and paste at the nanoscale

Abstract We report on the irradiation of gold rod–sphere assemblies with ultrashort laser pulses, producing structures that are very difficult to obtain by other methods. The optical response of these assemblies displays several peaks arising from the interaction of the plasmon modes of the individual particles, offering thus great flexibility to control the energy deposited on the individual particles. Judicious selection of the wavelength and fluence of the laser pulses allow fine control over the changes produced: the particles can be melted, welded and/or the organic links cleaved. In this way, it is possible to generate structures “à la carte” with a degree of control unmatched by other synthetic protocols. The method is exemplified with gold nanoparticles, but it can be easily implemented on particles composed of different metals, widening considerably the range of possibilities. The final structures are excellent candidates for surface-enhanced spectroscopies or plasmonic photothermal therapy as they have a very intense electric field located outside the structure, not in the gaps.

Integrating flexible electronics for pulsed electric field delivery in a vascularized 3D glioblastoma model

Glioblastoma is a highly aggressive brain tumor, very invasive and thus difficult to eradicate with standard oncology therapies. Bioelectric treatments based on pulsed electric fields have proven to be a successful method to treat cancerous tissues. However, they rely on stiff electrodes, which cause acute and chronic injuries, especially in soft tissues like the brain. Here we demonstrate the feasibility of delivering pulsed electric fields with flexible electronics using an in ovo vascularized tumor model. We show with fluorescence widefield and multiphoton microscopy that pulsed electric fields induce vasoconstriction of blood vessels and evoke calcium signals in vascularized glioblastoma spheroids stably expressing a genetically encoded fluorescence reporter. Simulations of the electric field delivery are compared with the measured influence of electric field effects on cell membrane integrity in exposed tumor cells. Our results confirm the feasibility of flexible electronics as a means of delivering intense pulsed electric fields to tumors in an intravital 3D vascularized model of human glioblastoma.

Temporal Klein Model for Particle-Pair Creation

This work considers the creation of electron-positron pairs from intense electric fields in vacuum, for arbitrary temporal field variations. These processes can be useful to study quantum vacuum effects with ultra-intense lasers. We use the quantized Dirac field to explore the temporal Klein model. This model is based on a vector potential discontinuity in time, in contrast with the traditional model based on a scalar potential discontinuity in space. We also extend the model by introducing a finite time-scale for potential variations. This allows us to study the transition from a singular electric field spike, with infinitesimal duration, to the opposite case of a static field where the Schwinger formula would apply. The present results are intrinsically non-perturbative. Explicit expressions for pair-creation as a function of the potential time-scales are derived. This work explores the spacetime symmetry associated with pair creation in vacuum: the space symmetry breaking of the old Klein paradox model, in contrast with the time symmetry breaking of the temporal Klein model.

Plasma-surface interaction: dynamic evolution of interfacial pattern modes during transformation process from dielectric to metallic substrate

Plasma–surface interaction is a complex system involving the codependency between the plasma and the substrate, especially for substrate’s with different permittivities. Therefore, a better understanding of the dynamic evolution of interactions with different substrates is essential for optimizing the required changes of specific substrates. In this work, we report two modes of interfacial pattern formation by a pulsed helium plasma jet interacting with indium tin oxide (ITO) glass and a metal substrate, and we mainly focus on the dynamic evolution process for interfacial pattern modes during a transformation process from ITO glass to metal substrate. Pattern morphology, current–voltage characteristics, intensified charge coupled device images, and reactive species distribution are used to examine the evolution mechanism of the plasma-jet–substrate interaction. Results show that, for the ITO glass substrate, a circular interfacial pattern with plenty of streamer channels is generated while, for the metal substrate, a constricted solid spot interfacial pattern is formed; these two pattern mode transformations are realized from the glass dielectric to the metal substrate. Furthermore, during the transformation process from the dielectric to metal substrate, the pattern area is gradually decreased, while the discharge intensity, emission intensity, and local electric field gradually become stronger. Importantly, by observing the dynamic behavior of the interfacial pattern, the ionization wave on the substrate surface is stopped from spreading toward the metal direction and a bright touch point appears at the interface between the dielectric and the metal, while the surface ionization wave still spreads and has no influence on the other direction besides the metal direction. Additionally, the evolution mechanism of pattern mode transformation is discussed, which may be attributed to the difference in the substrate conductivity leading to the different distribution of the local electric field. This study is beneficial to deep insights into the nature of the plasma–surface interaction.

Simultaneous measurement of thickness and permittivity using microwave resonator‐based planar sensor

This article presents a microwave sensor for dielectric characterization and thickness measurement of solid materials. The proposed sensor incorporates an interdigital capacitor (IDC) and a split-ring resonator to create an intense electric field, allowing it to efficiently interact with a sensing material. IDC parameters such as width and gap of the finger and length and gap of the electrode are optimized to enhance the material characterization sensitivity. The microwave resonant sensor structure is designed to operate at 1.8 GHz, making it applicable to measure permittivity and thickness of solid materials. The proximity of the material to be sensed influences the field distribution of the developed sensor, which, in turn, enables the simultaneous measurement of permittivity and thickness based on variations in a resonant frequency. Experimental results reveal that the highest sensitivity value reaches 113.4 MHz/mm and 47.6 MHz/∆εr for permittivity of the solids, when the thickness is between 0 and 1 mm. Furthermore, the developed sensor demonstrates a high accuracy (99.6%) and adequate accuracy (87.6%) for both real and imaginary permittivity, respectively. The developed microwave resonant sensor also shows excellent resolution for permittivity (0.04716) and thickness (0.1314), validating its high-performance for measuring permittivity and thickness for various solids.

Peculiarities of Neurostimulation by Intense Nanosecond Pulsed Electric Fields: How to Avoid Firing in Peripheral Nerve Fibers.

Intense pulsed electric fields (PEF) are a novel modality for the efficient and targeted ablation of tumors by electroporation. The major adverse side effects of PEF therapies are strong involuntary muscle contractions and pain. Nanosecond-range PEF (nsPEF) are less efficient at neurostimulation and can be employed to minimize such side effects. We quantified the impact of the electrode configuration, PEF strength (up to 20 kV/cm), repetition rate (up to 3 MHz), bi- and triphasic pulse shapes, and pulse duration (down to 10 ns) on eliciting compound action potentials (CAPs) in nerve fibers. The excitation thresholds for single unipolar but not bipolar stimuli followed the classic strength–duration dependence. The addition of the opposite polarity phase for nsPEF increased the excitation threshold, with symmetrical bipolar nsPEF being the least efficient. Stimulation by nsPEF bursts decreased the excitation threshold as a power function above a critical duty cycle of 0.1%. The threshold reduction was much weaker for symmetrical bipolar nsPEF. Supramaximal stimulation by high-rate nsPEF bursts elicited only a single CAP as long as the burst duration did not exceed the nerve refractory period. Such brief bursts of bipolar nsPEF could be the best choice to minimize neuromuscular stimulation in ablation therapies.

Dynamic Electroporation Model Evaluation on Rabbit Tissues.

Biological electroporation is a process of opening pores in the cell membrane when exposed to intense electric fields. This work provides results for validation of a dynamic model of electroporation on biological tissues. Computational simulations were carried out and results for the electrical current through the tissue and increase of the tissue temperature were compared to experimental results. Two calculation methods were used: Equivalent Circuit Method and Finite Element Method. With Equivalent Circuit Method the dielectric dispersion present in biological tissues was included. Liver, kidney and heart of rabbit were used in the experiments. Voltage pulse protocols and voltage ramps were applied using stainless steel needles electrodes. There is good agreement between the simulated and experimental results with mean errors below 15%, with the simulated results within the experimental standard deviation. Only for the protocol with fundamental frequency of 50 kHz, the simulation performed by the Finite Element Method using a commercial software did not correctly represent the current, with errors reaching 50%. The justification for the error found is due to the dielectric dispersion that was not included in this simulator.

Metal particle induced spacer surface charging phenomena in direct current gas-insulated transmission lines

The interpretation of the surface charge pattern of spacers in gas-insulated transmission lines (GIL) is a research topic with great importance, which requires a comprehensive understanding of charge behaviors at physical interfaces. Here, we report a surface charging phenomenon of spacers in the presence of metal particles inside the direct current (DC) GIL. The charging of spherical metal particles on the spacer surface appears as dotted discontinuously distributed charge spots, which are due to the charge injection from the induced charge of the metal particle and gas ionization over the metal particle surface. Concentrically distributed bipolar charge patterns are seen to build up, which are due to the surface trapping of charges from gas ionization at the end tip of the acicular metal particle. The lateral type of ionization obeys the law of dielectric barrier discharge of the needle-plate electrode in an intense DC electric field, which may bring significant influence on the safety of the spacer. The study in this letter provides direct evidence demonstrating the surface charge patterns of spacers in the presence of metal particles, which serves as an important basis for the design of DC GIL.

Fluorescence of CoTPP Mediated by the Plasmon–Exciton Coupling Effect in the Tunneling Junction

CoTPP, as a common hypsoporphyrin, is usually not a luminescent molecule because of the open-shell Co ion. In this paper, well-defined multilayer CoTPP molecules self-assembled on Au(111) surface are characterized layer by layer with scanning tunneling microscope (STM) induced luminescence. By using the highly localized STM tunneling current, we not only investigate the influence of bias polarity on the amplitude of distinct plasmonic emission resulted from the interaction between the metal substrate and the metal ions but also first obtain the light emission from the hypsoporphyrins in the tunneling junction. The density-matrix method and the combined approach of classical electrodynamics and first-principles calculation are used to explain the mechanism of the light emission. These findings may expand the underlying physics of plasmon-exciton coupling in STM nanocavity and reveal a new possible path to overcome the fluorescent potential of hypsoporphyrins by the intense localized electric fields.

Radiation electric field produced by the lightning leader formation in a thundercloud: Observations and modeling

Recently for a number of thunderstorm systems in different regions of the planet there have been reports of observations of high frequency radio emission with duration varying from several to more than one hundred of milliseconds which may both be isolated or precede the lightning initiation. There is a consensus that this radiation originates from continuous sequences of short-duration discharges that randomly fill the areas of strong electric field between the main negative and the upper positive charge regions. But the concrete physical mechanism of discharge activity evolution and its contribution to the lightning leader formation remain unclear. To answer these questions several hypotheses were proposed, among which the runaway breakdown and fast positive discharge can be accentuated. In this study, we present another explanation which is based on comparison of experimental data of thundercloud radio activity obtained in the Nizhny Novgorod region of the Russian Federation on May 15, 2019 with the use of a wide band radio interferometer with the results of our numerical simulation of the lightning leader formation in the active part of a thundercloud. It is shown that the observed intense electric field bursts can originate from mergers of two or more streamer systems or bipolar leaders with lengths ranging from several to several tens of meters. In the framework of our approach, the sequence of such mergers can, under certain conditions, result in the self-sustaining leader channel formation finishing the lightning initiation process.

Electro-optical measurement of intense electric field on a high energy pulsed power accelerator

We describe a direct electro-optical approach to measuring a strong 118 MV/m narrow pulse width (~ 33 ns) electric field in the magnetically insulated transmission line (MITL) of a pulsed power accelerator. To date, this is the highest direct external electric field measured electro-optically in a pulsed power accelerator, and it is between two to three orders of magnitude higher than values reported in comparable high energy scientific experiments. The MITL electric field is one of the most important operating parameters in an accelerator and is critical to understanding the properties of the radiation output. However, accurately measuring these high fields using conventional pulsed power diagnostics is difficult due to the strength of interfering particles and fields. Our approach uses a free-space laser beam with a dielectric crystal sensor that is highly immune to electromagnetic interference and does not require an external calibration. Here we focus on device theory, operating parameters, laboratory and pulsed power accelerator experiments as well as challenges that were overcome in the measurement environment.

Localized surface plasmon resonance coupling with piezophototronic effect for enhancing hydrogen evolution reaction with Au@MoS2 nanoflowers

The hydrogen evolution rate of Au nanoparticles encapsulated by MoS 2 nanoflowers (Au@MoS 2 NFs) was dramatically increased through localized surface plasmon resonance (LSPR) coupling with the piezophototronic effect. The heterostructured Au@MoS 2 NFs had highly active reaction sites for intense piezoelectric polarization that established an electric field and a surface plasmon effect to play a crucial role in regulating interfacial charge migration. Simultaneous light irradiation and mechanical vibration applied to the Au@MoS 2 NFs increased the hydrogen evolution from 2981 μmol g −1 h −1 for the solely piezocatalytic process to 4808 μmol g −1 h −1 . The hydrogen evolution rate of the Au@MoS 2 NFs was 161% that of pristine MoS 2 NFs. The considerable performance improvement was attributed to piezoelectric generation of hot electrons through LSPR. Density functional theory and the finite element method were employed to simulate the charge transfer of the Au@MoS 2 NFs under simultaneous light irradiation and mechanical vibration. Greater mechanical strain on the heterostructured catalysts yielded a greater electric field, demonstrating the piezophototronic effect had strong synergy with LSPR and thus increasing the hydrogen evolution rate. The hydrogen evolution rate of Au nanoparticles encapsulated by MoS 2 nanoflowers (Au@MoS 2 NFs) was dramatically increased through localized surface plasmon resonance (LSPR) coupling with the piezophototronic effect. Simultaneous light irradiation and mechanical vibration applied to the Au@MoS 2 NFs increased the hydrogen evolution from 2981 μmol g −1 h −1 for the solely piezocatalytic process to 4808 μmol g −1 h −1 . • Heterostructured Au@MoS 2 nanoflower catalysts have highly active reaction sites. • Intense piezoelectric polarization built-in electric field coupled with localized surface plasmon (LSPR) effect. • The synergistic combination of LSPR and the piezophototronic effect yielded a considerable internal electric field. • Electric field regulating the interfacial charge migration to trigger electrochemical reactions.