Range Of Electric Fields Research Articles

Large-Area Au-Nanoparticle-Functionalized Si Nanorod Arrays for Spatially Uniform Surface-Enhanced Raman Spectroscopy.

In this study, large-area hexagonal-packed Si nanorod (SiNR) arrays in conjunction with Au nanoparticles (AuNPs) were fabricated for surface-enhanced Raman spectroscopy (SERS). We have achieved ultrasensitive molecular detection with high reproducibility and spatial uniformity. A finite-difference time-domain simulation suggests that a wide range of three-dimensional electric fields are generated along the surfaces of the SiNR array. With the tuning of the gap and diameter of the SiNRs, the produced long decay length (>130 nm) of the enhanced electric field makes the SERS substrate a zero-gap system for ultrasensitive detection of large biomolecules. In the detection of R6G molecules, our SERS system achieved an enhancement factor of >107 with a relative standard deviation as small as 3.9-7.2% over 30 points across the substrate. More significantly, the SERS substrate yielded ultrasensitive Raman signals on long amyloid-β fibrils at the single-fibril level, which provides promising potentials for ultrasensitive detection of amyloid aggregates that are related to Alzheimer's disease. Our study demonstrates that the SiNRs functionalized with AuNPs may serve as excellent SERS substrates in chemical and biomedical detection.

A computational framework for incompressible electromechanics based on convex multi-variable strain energies for geometrically exact shell theory

In this paper, a new computational framework for the analysis of incompressible Electro Active Polymer (EAP) shells subjected to large strains and large electric fields is presented. Two novelties are incorporated in this work. First, the variational and constitutive frameworks developed by the authors in recent publications (Gil and Ortigosa, 2016; Ortigosa and Gil, 2016; Ortigosa et al., 2016) in the context of three-dimensional electromechanics are particularised/degenerated to the case of geometrically exact shell theory. This formulation is computationally very convenient as EAPs are typically used as thin shell-like components in a vast range of applications. The proposed formulation follows a rotationless description of the kinematics of the shell, enhanced with extra degrees of freedom corresponding to the thickness stretch and the hydrostatic pressure, critical for the consideration of incompressibility. Different approaches are investigated for the interpolation of these extra fields and that of the electric potential across the thickness of the shell. Crucially, this allows for the simulation of multilayer and composite materials, which can display a discontinuous strain distribution across their thickness. As a second novelty, a continuum degenerate approach allows for the consideration of complex three-dimensional electromechanical constitutive models, as opposed to those defined in terms of the main strain measures of the shell. More specifically, convex multi-variable (three-dimensional) constitutive models, complying with the ellipticity condition and hence, satisfying material stability for the entire range of deformations and electric fields, are used for the first time in the context of shell theory.

Critical scaling analysis for displacive-type organic ferroelectrics around ferroelectric transition

The critical scaling properties of displacive-type organic ferroelectrics, in which the ferroelectric–paraelectric transition is induced by spin-Peierls instability, are investigated by Green’s function theory through the modified Arrott plot, critical isothermal and electrocaloric effect (ECE) analysis around the transition temperature TC. It is shown that the electric entropy change −ΔS follows a power-law dependence of electric field E:−ΔS∼En with n satisfying the Franco equation n(TC)=1+(β−1)/(β+γ)=0.618, wherein the obtained critical exponents β=0.440 and γ=1.030 are not only corroborated by Kouvel–Fisher method, but also confirm the Widom critical relation δ=1+γ/β. The self-consistency and reliability of the obtained critical exponents are further verified by the scaling equations. Additionally, a universal curve of −ΔS is constructed with rescaling temperature and electric field, so that one can extrapolate the ECE in a certain temperature and electric field range, which would be helpful in designing controlled electric refrigeration devices.

Isomerisation of an intramolecular hydrogen-bonded photoswitch: protonated azobis(2-imidazole).

Photoisomerisation of protonated azobis(2-imidazole), an intramolecular hydrogen-bonded azoheteroarene photoswitch molecule, is investigated in the gas phase using tandem ion mobility mass spectrometry. The E and Z isomers exhibit distinct spectral responses, with E-Z photoisomerisation occurring over the 360-520 nm range (peak at 460 nm), and Z-E photoisomerisation taking place over the 320-420 nm range (peak at 390 nm). A minor photodissociation channel involving loss of N2 is observed for the E-isomer with a maximum efficiency at 390 nm, blue-shifted by ≈70 nm relative to the wavelength for maximum photoisomerisation response. Loss of N2 is also the predominant collision-induced dissociation channel. Electronic structure calculations suggest that E-isomer photoisomerisation involves S1(ππ*) excitation, whereas the Z-isomer photoisomerisation involves S2(ππ*) excitation. Conversion between the E and Z isomers through collisional excitation, which is calculated to occur through both inversion and torsion pathways, is investigated experimentally by colliding the molecular ions with nitrogen buffer gas over a range of electric fields. This study demonstrates the versatility of tandem ion mobility mass spectrometry for exploring the isomerisation of molecular photoswitches initiated by either light or collisions.

Use of High-Voltage Cyclic Voltammetry to Characterize Bulk and Interfacial Conduction Processes in Anodic Alumina Films

A high-voltage cyclic voltammetry method is introduced that enables separate determination both the bulk conduction kinetics of anodic films and kinetics associated with interface processes. The results confirm that ionic conduction in the oxide follows a high-field exponential dependence on the electric field with a field coefficient of approximately 33nm/V, consistent with reported values for barrier-type films formed in neutral solutions. The correlation of the pre-exponential current density with the incorporation level of different acid anions from the anodizing bath suggests that conduction is enhanced by anionic contaminants. Current densities associated with self-ordered pore formation in different solutions seem to be associated with a common narrow range of electric fields. The large size of the interface potential drop suggests that it derives from the elevated conduction resistance of an anion-contaminated oxide layer close to the solution interface. Such resistive surface layers are thought to be the source of compressive stress that drives oxide flow during self-organized pore formation.

Temperature behavior of Franz-Keldysh oscillation and evaluation of interface electric fields attributed to strain effect of InAs/GaAs quantum dot

In this work, the electric field-induced Franz-Keldysh effect was used to investigate the localized electric fields in GaAs interfaces attributed to strain effect of InAs/GaAs quantum dots (QD). The electric fields were investigated by photoreflectance spectroscopy (PR). PR spectra of the InAs/GaAs QDs showed complex Franz-Keldysh oscillations (FKOs) with various temperatures. It is suggested that the FKOs originated from the interface electric fields predominately caused by the strain-induced polarization at GaAs interface near the InAs QDs. The InAs/GaAs QDs have a broad range of interface electric fields from ∼104 V/cm to ∼2х105 V/cm. Temperature behavior of FKO amplitude distribution is explained by temperature dependent carrier confinement effect.

High Power Density Pyroelectric Energy Conversion in Nanometer-Thick BaTiO3 Films

ABSTRACTSolid-state pyroelectric nanomaterials can be used for thermal-to-electrical energy conversion in the presence of temperature fluctuations. This article reports investigation of energy conversion in a 200 nm thick BaTiO3 film using the pyroelectric Ericsson cycle at cycle frequencies up to 3 kHz. The high cycle frequencies were achieved due to the low thermal mass of the nanometer-scale film, unlike previous studies in which the electrical power output was limited by the rate of heat transfer through the pyroelectric material. A microfabricated platform that allowed precise thermal and electrical cycling enabled us to study the effect of electric field range, temperature oscillation amplitude, and cycle frequency on the electrical power output from pyroelectric Ericsson cycles. We measured a maximum power density of 30 W/cm3 for a temperature range 20–120°C and electric field range 100–125 kV/cm, which represents a significant improvement over past work on pyroelectric cycles. The approach presented in this article could lead to high-power waste heat harvesting in systems with high-frequency temperature oscillations.

Near-membrane electric field calcium ion dehydration

The dehydration of ion-water complexes prior to ion channel transit has focused on channel protein-mediated dissociation of water. Ion dehydration by the membrane electric field has not previously been considered. Near membrane electric fields have previously been shown to cause the disassociation of non-covalently bound small molecule-small molecule, small molecule-protein, and protein–protein complexes. It is well known that cosmotropic, structure making ions such as calcium and sodium significantly bind multiple water ions in solution. It is also known that these ions are often not hydrated as they pass through membrane ion channels. Using capillary electrophoresis, the range of electric fields needed to strip water molecules from calcium ions has been measured. Ion migration velocity is a linear function of the electric field. At low electric fields, the migration rate of calcium ion was shown to be linearly related to the applied electric field. Using a form of the Stoke's equation applicable to ion migration, the hydrated calcium radius was found to be 0.334nm, corresponding to a water hydration shell of 5.09 water molecules. At higher electric fields, the slope of the calcium migration velocity as a function of the electric field increased, which was modeled as a decrease in the radius of the migrating ion as the water was removed. Using a tanh function to model the transition of the ion from a hydrated to a stripped state, the transition had a midpoint at 446V/cm, and was 88% complete at 587V/cm with a correlation coefficient of 0.9996. The migration velocity of the stripped calcium ion was found to be a function of both the decrease in radius and an increase in the effective, electronic viscosity of the dipole medium through which the dehydrated ion moved. The size of the electric field needed to dehydrate calcium occurs 6–7nm from the cell membrane. Calcium ions within this distance from the membrane will be devoid of water molecules when they reach the calcium selective channel pore entrances, all known to be approximately 1–2nm from the membrane. No matter what the calcium pore structure, calcium ions reaching the channel entrance will be devoid of a water shell.

Criticality: Concept to Enhance the Piezoelectric and Electrocaloric Properties of Ferroelectrics

Compositional engineering with a focus on structural phase transitions has been considered as the most important approach for enhancement of the functional properties of ferroelectric materials due to the critical fluctuation of physical properties. Of special interest are electric‐field‐induced phase transitions, which can terminate in a liquid–vapor‐type critical point with a strong enhancement of functional properties. Whereas the critical point in liquid–vapor space considers changes in temperature and pressure, the critical point in this study is placed in electric field–temperature diagrams. In single crystals, temperature and electric field of a critical point are sharply defined and therefore not appealing for practical applications. However, in ceramics, it is demonstrated that the orientational dependence of the critical point leads to a broadened temperature and electric field range. The presence of a diffuse critical point in ceramics provides a conceptually novel approach for the enhancement of functional properties, such as piezoelectric and electrocaloric (EC) responses, as validated here on the example of the 0.75Bi1/2Na1/2TiO3‐0.25SrTiO3 lead‐free relaxor ferroelectric ceramics. The realization of a broad criticality range will further facilitate the development of the piezoelectric and EC materials and provide an alternative concept to manipulate the functional properties by application of an electric field.

Axon Outgrowth of Rat Embryonic Hippocampal Neurons in the Presence of an Electric Field

Application of an electric field (EF) has long been used to induce axon outgrowth following nerve injuries. The response of mammalian neurons (e.g., axon length, axon guidance) from the central nervous system (CNS) to an EF, however, remains unclear, whereas those from amphibian or avian neuron models have been well characterized. Thus, to determine an optimal EF for axon outgrowth of mammalian CNS neurons, we applied a wide range of EF to rat hippocampal neurons. Our results showed that EF with either a high magnitude (100 mV/mm or higher) or long exposure time (10 h or longer) with low magnitude (10-30 mV/mm) caused a neurite collapse and cell death. We also investigated whether neuronal response to an EF is altered depending on the growth stage of neuron cultures by applying 30 mV/mm to cells from 1 to 11 days in vitro (DIV). Neurons showed the turnover of axon outgrowth pattern when electrically stimulated between 4-5 DIV at which point neurons have both axonal and dendritic formation. The findings of this study suggest that the developmental stage of neurons is an important factor to consider when using EF as a potential method for axon regeneration in mammalian CNS neurons.

Range, Magnitude, and Ultrafast Dynamics of Electric Fields at the Hydrated DNA Surface.

Range and magnitude of electric fields at biomolecular interfaces and their fluctuations in a time window down to the subpicosecond regime have remained controversial, calling for electric-field mapping in space and time. Here, we trace fluctuating electric fields at the surface of native salmon DNA via their interactions with backbone vibrations in a wide range of hydration levels by building the water shell layer by layer. Femtosecond two-dimensional infrared spectroscopy and ab initio based theory establish water molecules in the first two layers as the predominant source of interfacial electric fields, which fluctuate on a 300 fs time scale with an amplitude of 25 MV/cm due to thermally excited water motions. The observed subnanometer range of these electric interactions is decisive for biochemical structure and function.

Modeling of Forward Gate Leakage Current in MOSHEMT Using Trap-Assisted Tunneling and Poole–Frenkel Emission

Investigation of various forward gate leakage current mechanisms in an AlGaN/GaN metal–oxide–semiconductor high-electron-mobility transistor is done in this paper. During high temperature ( $T>388$ K), the trap-assisted tunneling (TAT) mechanism dominates the gate leakage current at low electric field for a range of gate biases from 0 to 0.2 V, whereas the Poole–Frenkel emission is the major component during medium and high electric field. During low temperature ( $T K), TAT alone is dominant and consistent throughout the whole range of electric field. A formulation of vertical electric field, across the oxide and barrier, is framed by incorporating oxide/barrier interface density of states. Then a physics-based compact analytical model for the TAT mechanism is developed and along with the existing PFE model, the forward gate leakage current is calculated. The results of the developed model in different regions of forward gate characteristics are in good agreement with the experimental results available in the literature.

Flexible bent rod model with a saturating induced dipole moment to study the electric linear dichroism of DNA fragments

In the present work we make a theoretical study of the steady state electric linear dichroism of DNA fragments in aqueous solution. The here developed theoretical approach considers a flexible bent rod model with a saturating induced dipole moment. The electric polarizability tensor of bent DNA fragments is calculated considering a phenomenological model which theoretical and experimental backgroung is presented here. The model has into account the electric polarizability longitudinal and transversal to the macroion. Molecular flexibility is described using an elastic potential. We consider DNA fragments originally bent with bending fluctuations around an average bending angle. The induced dipole moment is supposed constant once the electric field strength grows up at critical value. To calculate the reduced electric linear dichroism we determine the optical factor considering the basis of the bent DNA perpendicular to the molecular axis. The orientational distribution function has into account the anisotropic electric properties and the molecule flexibility. We applied the present theoretical background to fit electric dichroism experimental data of DNA fragments reported in the bibliography in a wide range of molecular weight and electric field. From these fits, values of DNA physical properties are estimated. We compare and discuss the results here obtained with the theoretical and experimental data presented by other authors. The original contributions of this work are: the inclusion of the transversal electric polarizability saturating with the electric field, the description of the electric properties with an electric polarizability tensor dependant on the bending angle and the use of an arc model originally bent.

Inter-particle interactions of weak homeotropic anchoring with electric field in a homogeneous nematic cell

ABSTRACTWe investigate the inter-particle interactions of weak homeotropic anchoring when electric field is applied parallel to far-field director in a homogeneous nematic cell. Two particles interact with the dipole–dipole and quadrupole–quadrupole interactions in the cell. A model of far-field solution dependent on the cell gap and the electric field with weak anchoring is considered to explain the experimental results. The effective radius is introduced to adapt the anchoring strength effect using the radius (R) and a coefficient . The model was experimentally proved with varying electric field and cell gap and it was reasonable for weak electric field. The coefficient was measured to be and for the dipole–dipole and quadrupole–quadrupole interactions, respectively, within the experimental range of the weak electric field. The anchoring strength was calculated as ~

Determination of 4H-SiC Ionization Rates Using OBIC Based on Two-Photon Absorption <sup></sup>

Optical Beam Induced Current (OBIC) measurements are performed on 4H-SiC avalanche diodes with a very thin and a highly doped active region. A pulsed green laser, with a wavelength of 532 nm, illuminates a reverse biased diode leading to generate electron-hole pairs in the space charge region. Comparison between the 4H-SiC bandgap and the incident photon energy shows that single photon absorption process can be neglected and two-photon absorption process dominates in this case. Ionization rates are then extracted from multiplication curve in a high electric field range (3 to 5 MV.cm–1). Results are in good agreement with previous ones obtained on the same diodes using single photon absorption process.

Highly tunable exchange in donor qubits in silicon

AbstractIn this article we have investigated the electrical control of the exchange coupling (J) between donor-bound electrons in silicon with a detuning gate bias, crucial for the implementation of the two-qubit gate in a silicon quantum computer. We found that the asymmetric 2P–1P system provides a highly tunable exchange curve with mitigated J-oscillation, in which 5 orders of magnitude change in the exchange coupling can be achieved using a modest range of electric field (3 MV/m) for ~15-nm qubit separation. Compared with the barrier gate control of exchange in the Kane qubit, the detuning gate design reduces the gate density by a factor of ~2. By combining large-scale atomistic tight-binding method with a full configuration interaction technique, we captured the full two-electron spectrum of gated donors, providing state-of-the-art calculations of exchange energy in 1P–1P and 2P–1P qubits.

Field Assisted Sintering of Nanostructured Zirconia-Alumina Ceramics for Demanding Applications

ABSTRACTFlash and field assisted sintering techniques (FAST) have been demonstrated in many singular ceramic systems. However, little has been done to thoroughly investigate this phenomenon in binary systems. Zirconia-alumina composites are of interest because of their widespread use in demanding situations for health care, petrochemical and energy applications. The prospect of minimizing grain growth associated with FAST whilst achieving maximum densification is vital for the above applications to improve performance. Flash sintering behaviour of several zirconia-alumina formulations was investigated under a range of DC electric fields up to 700V.cm–1. At low alumina contents (<10 wt%) the flash behaviour was controlled by the zirconia phase; intermediate compositions (10-70 wt%) show a composite effect; and at high alumina contents (>75 wt%) the effectiveness of field assisted sintering drops off. These pointers allowed to gain further insight into the mechanisms of flash sintering and will help to develop pathways for the adaptation of the technique to process complex ceramic systems.

A study of the avalanche-to-streamer transition in arbitrary gases by particle simulation

We systematically investigate the avalanche-to-streamer transition (AST) over a wide range of pressures and homogenous background electric fields and for a comprehensive list of gases, namely pure nitrogen, carbon dioxide, oxygen, argon, sulfur hexafluoride and synthetic air. The discharge starts from an initial seed electron and is temporally followed from the avalanche regime, through the first significant distortion of the background field and the subsequent increasing deviation from the Gaussian electron density profile, up to the occurrence of runaway electrons accompanied by the sudden and dramatic increase of electron energy and electron number multiplication. We detect weak influence of the background electric field value and the gas composition, but strong influence of the gas density on the electron number at which the transition occurs. The simulations are performed by means of a fully-interacting particle simulation program that combines a particle-in-cell/Monte Carlo collision model (PIC/MCC) with a three-dimensional Poisson solver in order to account for the space charge generated by the electrons and ions. The freely-available program is based on the METHES code and is universally applicable to arbitrary gas mixtures with complete cross section sets.

Columnar recombination for X-ray generated electron-holes in amorphous selenium and its significance in a-Se x-ray detectors

Although amorphous selenium (a-Se) has a long and successful history of application in optical and X-ray imaging, some of its fundamental properties are still puzzling. In particularly, the mechanism of carrier recombination following x-ray excitation and electric field and temperature dependences of the electron-hole pair creation energy (Wehp) remain unclear. Using the combination of X-ray photocurrent and pulse height spectroscopy measurements, we measure Wehp in a wide range of temperatures (218–320 K) and electric fields (10–100 V/µm) and show that the conventional columnar recombination model which assumes Langevin recombination within a column (a primary electron track) fails to explain experimental results in a wide range of electric fields and temperatures. The reason for the failure of the conventional model is revealed in this work, and the theory of the columnar recombination is modified to include the saturation of the recombination rate at high electric field in order to account for the experimental results in the entire range of fields and temperatures.

Universality of charge-carrier transport in molecularly doped polymers

The charge-carrier transport model based on the multiple-trapping quasi-band theory with the Gaussian or exponential energy distributions of traps for the two-layer structure of the molecularly doped polymer sample is used to explain the experimentally observed constancy of the flat plateau on time-of-flight curves in a wide electric-field range. The constant shape of the time-of-flight curve under the condition of nonequilibrium transport is observed for the exponential, rather than Gaussian, energy trap distribution. This observation may be used to distinguish between these trap distributions. Finding the true Poole–Frenkel constant requires that the nonequilibrium transport in molecularly doped polymers be taken into account during treatment of the data on the field dependence of mobility.