Presence Of High Electric Field Research Articles

Rapid Free Electron Reduction in Plasma Irradiated Microscale Water Droplets

Many reaction studies show that microdroplets can provide a new avenue for green chemistry by enabling the electrochemical activity of water molecules. The observation of enhanced chemical reaction rates in gas-phase microdroplets compared to bulk liquids, often by orders of magnitude, has sparked considerable research interest. A number of factors may be involved, including evaporation enhanced reactant concentration, partial solvation at the surface, high surface to bulk number ratio, enhanced surface rate constants, pH gradients, gas-phase reactions and mass transfer, electric field enhancement and surface charging. Plasma interactions with liquids involve the mass transfer and accommodation of reactive radicals and other plasma chemical species, often occurs in the presence of high electric field and temperature gradients, UV flux and electric currents.We have investigated the use of low temperature atmospheric pressure plasma irradiated liquid microdroplets. [1] Picolitre microdroplets are totally surrounded by plasma and their high surface area relative to volume receives chemical, photon and charge flux during flight leading to chemical reactions in the liquid at low temperature. With the inclusion of precursors, the small volume provides an excellent basis for gas phase chemical microreactors that can deliver products continuously and almost instantaneously downstream for applications such as plasma medicine and specialist chemical or nanomaterial printing.In particular, low temperature plasmas are a copious source of free electrons, up to 106 times greater than corona discharges, which can interact with the liquid surface to promote rapid reduction reactions and possibly on-water catalysis. We have observed the reduction of metal salts in flight to produce nanoparticles at rates many orders of magnitude greater than standard solution chemistry or via radiolysis. [2] We have measured the plasma gas temperature in the presence of microdroplet streams with droplet rates up to 5 x 104 s-1 and observed no significant increase in gas temperature, which is typically ~300 K, thus keeping the evaporation limited. [3] Recently, we carried out plasma simulations, coupled with downstream chemical flux measurements, to determine the evolution of gas-phase chemistry in the plasma and effluent. [4] We have also performed the first measurements of plasma charging of particles, at atmospheric pressure for diameters > 1 um. The determined average droplet charge per droplet was 2.5 x 106 electrons (400 fC). Using a number of plasma particle charging models we estimate the electron flux ranged from 5 x 1022 m-2 s-1 to 4 x 1025 m-2 s-1.In [2], at least 50% Au3+ to Au0 reduction of the droplet precursor (HAuCl4) was observed over a ~120 µs plasma flight time and the equivalent Au0 generation rate is ~1013 atoms s-1. The ratio of electron flux per droplet to metal generation rate provides a dimensionless figure of merit, e-/Au0, of ~100 - 1000. Using plasma chemistry simulations along with estimates of electron flux to the droplet surface, we then simulated the subsequent water reactions using a 1-D radial reaction – diffusion scheme. For 15 µm diameter droplets without precursor, surface H2O2 concentrations ranged from 0.1 M to 100 µM whereas surface OH· concentrations were almost constant (~1 mM), as electron flux density (m-2 s-1) increased. However the OH· concentration decayed rapidly with depth, reaching 1 nM within 1 µm. As the droplet size increased, surface concentration and penetration depth both decreased. For electron flux densities up to ~5 x 1022 m-2 s-1, the solvated electron surface concentration was ~0.1 mM and the penetration depth was ~250 nm but at higher fluxes, the penetration depth increases significantly likely due to the reduced concentration of sub-surface H2O2 and OH·, which scavenge electrons. When 1 mM HAuCl4 precursor is added, the surface electron concentration and penetration depth is significantly reduced (< 50 nm), even at very high flux densities. We also observe the loss of surface Au3+ and the increase in Au0 concentration. However, the maximum overall conversion rate is 15%, compared to the experimental observation of >50%. Enhanced conversion would likely require greater precursor transport from droplet centre to surface, either by internal fields or convection. We carried out preliminary simulations of (Au0)N (N: 2 → 20) cluster growth via simple collisions in this environment and observed almost complete conversion of Au0 to cluster (Au0)N with the concentration of (Au0)20 >> (Au0)2.[1] PD Maguire et al., Appl. Phys. Lett. 106, 224101 (2015); doi: 10.1063/1.4922034[2] PD Maguire et al., Nano Lett., 17, 1336–1343 (2017) doi: 10.1021/acs.nanolett.6b03440[3] N Hendawy et al 2020 Plasma Sources Sci. Technol. 29 085010 doi: 10.1088/1361-6595/aba2aa[4] H McQuaid et al 2022, in-press. See preprint - doi: 10.48550/arXiv.2207.04518

High-yield spray drying assembly and reactive properties of nanoenergetic mesoparticle composites

Electrospray has been demonstrated to assemble fuel and oxidizer nanoparticles with a gas-generating binder into microscale particle composites. This approach results in reactivity enhancement of nanothermite systems by alleviating reactive sintering of the nanoparticle components due to rapid gasification. However, this method is not readily scalable and amenable to large-scale manufacturing due to its slow solution processing rates and the risks associated with the presence of high electric fields in the presence of electrostatic discharge-sensitive reactive materials. Here, we explore spray drying as an alternative approach to assemble Al/CuO nanoparticles into nitrocellulose (NC)-based mesoparticle composites and evaluate their energetic performance against physically mixed powders and electrosprayed mesoparticles. The spray dried mesoparticles show ∼2–7-fold higher pressurization rates and shorter burn times than their physically mixed counterparts and follow a similar trend with electrospray. The higher reactivity of the mesoparticles is attributed to rapid gas generation and reduced sintering from the decomposition of the NC binder. We further demonstrate that spray drying generates mesoparticles with size (∼1.5–4 μm), morphology, and reactivity enhancement similar to that from the electrospray method, while achieving remarkably high production rates (as high as ∼275 g h−1). Thus, this work presents spray drying as a highly scalable strategy to achieve reactivity enhancement and processability, thereby enabling high-yield manufacturing of energetic materials, which is a prelude to what might evolve into 3-D printing approaches for propellants.

Integrated sub-micron vacuum gaps in semiconductor devices

We present characterization results of integrated vacuum gaps in semiconductors and report the highest breakdown field of dielectric layers ever recorded within microfabricated semiconductor devices. Difficulties associated with the characterization of vacuum gaps in the presence of high electric fields could be overcome by using cylindrical capacitors with silicon electrodes that were manufactured with standard semiconductor technology. With this approach, breakdown fields of up to 6 × 109 V/m were achieved. The vacuum gaps of 175(5) nm were significantly smaller than the mean free path of electrons within the gap such that a breakdown due to avalanche discharge was avoided. As the voltage was increased, initially a field emission current was observed that followed a Fowler–Nordheim tunneling behavior. The tunneling current started to increase at voltages about four times greater as compared to equivalent dielectric layers of silicon oxide. At higher voltages, a mechanical breakdown occurred, where the pillars that formed the central electrode of the capacitor snapped due to electrostatic forces. We provide characteristics of thin vacuum layers, which could be useful for device design in micro- and nanoelectromechanical systems as well as semiconductor devices.

Studies on fluorine-based impurity production in Triple-GEM detectors operated with C[formula omitted]-based gas mixture

One of the primary elements influencing gaseous detector operation is the purity of the gas mixture. Its quality can be undermined by the presence of impurities, already present in the supply gas bottles or that could be created in the gas system or from the detector itself. Gaseous detectors operated with Freon-based gas mixtures are subject to the formation of the products of gas molecules break up, occurring when the gas is exposed to high-rate radiation, and enhanced by the presence of high electric field. The release of highly reactive products could be critical as they could either create polymerized deposits or cause material etching, that could compromise detector performance and accelerate aging processes. Moreover, the operation of gas systems with gas recirculation, nowadays common in many gas systems, could worsen the risk of damage due to possible impurities accumulation. This work focuses on the production of fluorine-based impurities in Triple-GEMs detectors operated with CF4-based gas mixture. Detectors are operated in a LHC-like gas system and exposed to high-rate gamma irradiation thanks to the intense 137Cs source provided by the CERN Gamma Irradiation Facility (GIF++). Impurity production is characterized for different detector operation conditions such as gas mixture, working voltage, input flow rate, and irradiation rates. Furthermore, purifier module operation is validated proving its efficiency in removing Fluoride impurities.

On-Wafer Fast Evaluation of Failure Mechanism of 0.25-μm AlGaN/GaN HEMTs: Evidence of Sidewall Indiffusion

In this article, we present the results of on-wafer short-term (24 h) stress tests carried out on 0.25-μm AlGaN/GaN HEMTs. Devices on-wafer were submitted to 24-h dc tests, at various gate and drain voltage values corresponding to dissipated power densities PD up to 40 W/mm, with estimated channel temperature ~=375 °C. GEN1 devices adopted a Ni/Pt/Au gate metallization and conventional plasma-enhanced chemical vapor deposition (PE-CVD) SiN passivation; in GEN2 devices, a modified gate metallization and a two-layer SiN passivation were adopted. When tested at P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> > 25 W/mm, a substantial decrease of drain current ID and transconductance gm was measured in GEN1 HEMTs, without any significant shift of threshold voltage. Failure analysis revealed that Au and O interdiffusion took place from the sidewalls; Au gradually substituted Ni as a Schottky contact, while O, in the presence of high electric field, high temperature, and high current, promoted (Al)GaN oxidation and pitting. On the contrary, negligible degradation was found after high temperature storage of GEN1 devices without applied bias, up to 450 °C. In GEN2, process modification was effective in reducing the impact of this failure mechanism, resulting in only 5% gm decrease after 24 h at a junction temperature of 375 °C with P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> = 38 W/mm. Results demonstrate the effectiveness of the adopted on-wafer screening methodology in identifying potentially dangerous failure mechanisms.

Computational Analysis of Ballistic Saturation Velocity in Low-Dimensional Nano-MOSFET

The computational analysis of ballistic saturation velocity for low-dimensional nano-devices was presented. The ballistic transport is predicted in the presence of high electric field for non-degenerate and degenerate regime. The saturation velocity is found to be ballistic regardless of the device dimensions. The intrinsic velocity limits this saturation velocity. It's does not sensitively depend on the ballistic or scattering-limited nature of the mobility. In the degenerate realm, the saturation velocity is shown to be the Fermi velocity that is independent of temperature but strongly dependent on carrier concentration. In the nondegenerate realm, the intrinsic velocity is the thermal velocity that depends only on the ambient temperature.

Evidence of High Energy Storage Density and Break Down Voltage in the Eco-Friendly Eu-Substituted K0.5Bi0.5TiO3 Dielectric Ceramics

The significance of the energy storage and transfer device in the modern and upcoming era is undeniable. To tackle the energy scarcity in the coming era, the research and development on the various renewable energy sources and the storage materials are extensively propelled. The device with good energy storage density is required for the perfect utilization of the electricity which is produced by renewable energy sources. The ferroelectric material can be an effective choice as an energy storage material, because of its high dielectric constant, high break down voltage, and more thermal & mechanical stability. Usually, it is observed that the lead based anti-ferroelectric materials have the better energy storage density than the lead free normal ferroelectric material. The global requirement and the banning of lead based material thrust the exploration of the lead free materials with higher energy storage density. Several lead-based and lead-free A and/or B–site substituted perovskite type (ABO3 type structure) ferroelectric materials are developed to gain high energy storage density. As far as the environment is concerned, in this work the energy storage property is investigated on the optimized eco-friendly 4 mol % Eu3+ substituted K0.5Bi0.5TiO3. At the room temperature the obtained recoverable energy storage density is 0.84J/cm3 which is comparable to some the lead based solid solutions. The room temperature polarization vs. electric field curve of this compound is shown in figure 1. Figure 1 . Room temperature polarization vs. electric filed curve of 4 mol % Eu3+ substituted K0.5Bi0.5TiO3. The discharge path of the hysteresis loop is shown in red color. The recoverable energy storage density is calculated from area under the discharge curve of the hysteresis loop (shown in red color) and the polarization axis in the first quadrant. From the figure, it can be observed that this material shows a high break down strength of 131kV/cm, which enhances the applicability of the material in the presence of high electric field. Apart from the ferroelectric study, the temperature dependent dielectric study of the material has been carried out. The recoverable energy storage density and high break down strength of this lead free material shows its suitability for fabricating energy storage material. Figure 1

Field-Induced Carrier Localization Transition in Dielectric Polymers.

Organic polymers offer many advantages as dielectric materials over their inorganic counterparts because of high flexibility and cost-effective processing, but their application is severely limited by breakdown in the presence of high electric fields. Dielectric breakdown is commonly understood as the result of avalanche processes such as carrier multiplication and defect generation that are triggered by field-accelerated hot carriers (electrons or holes). In stark contrast to inorganic dielectric materials, however, there remains no mechanistic understanding to enable quantitative prediction of the breakdown field in polymers. Here, we perform systematic study of different electric fields on hot carrier dynamics and resulting chemical damage in a slab of archetypal polymer, polyethylene, using nonadiabatic quantum molecular dynamics simulations. We found that high electric fields induce localized electronic states at the slab surface, with a critical transition occurring near the experimentally reported intrinsic breakdown field. This transition in turn facilitates strong polaronic coupling between charge carriers and atoms, which is manifested by severe damping of the time evolution of localized states and the presence of C-H vibrational resonance in the hot-carrier motion leading to rapid carbon-carbon bond breaking on the surface. Such polaronic localization transition may provide a critically missing prediction method for computationally screening dielectric polymers with high breakdown fields.

Cross-linking of DNA monolayers by cisplatin examined using electrostatic denaturation

This paper reports on the electrostatic denaturation of double-stranded DNA monolayers in the presence of anti-cancer drug cis-Diamminedichloroplatinum(II) (cisplatin). Cisplatin binds DNA at purine bases, effecting its thermal stability and melting temperature. Here we show for the first time how cisplatin effects the stability of DNA monolayers in the presence of high electric fields generated at the electrode/solution interface, and how this behavior is effected by the method of monolayer preparation. A slight decrease in melting rate and a large decrease in the extent of melting are observed for electrodes prepared with methods that produce homogeneous DNA surface coverage where interstrand distances are maximized. On the other hand, heterogeneous and densely-packed monolayers are found to melt much slower and to a slightly greater extent with bound cisplatin. Three procedures for preparation of the mercaptohexanol/DNA mixed monolayers are compared, demonstrating the potential application of cisplatin, along with electrostatic denaturation analysis, to interrogate surface density and surface heterogeneity in self-assembled DNA monolayers.

Simulations of surface stress effects in nanoscale single crystals

Onset of vacuum arcing near a metal surface is often associated with nanoscale asperities, which may dynamically appear due to different processes ongoing in the surface and subsurface layers in the presence of high electric fields. Thermally activated processes, as well as plastic deformation caused by tensile stress due to an applied electric field, are usually not accessible by atomistic simulations because of the long time needed for these processes to occur. On the other hand, finite element methods, able to describe the process of plastic deformations in materials at realistic stresses, do not include surface properties. The latter are particularly important for the problems where the surface plays crucial role in the studied process, as for instance, in the case of plastic deformations at a nanovoid. In the current study by means of molecular dynamics (MD) and finite element simulations we analyse the stress distribution in single crystal copper containing a nanovoid buried deep under the surface. We have developed a methodology to incorporate the surface effects into the solid mechanics framework by utilizing elastic properties of crystals, pre-calculated using MD simulations. The method leads to computationally efficient stress calculations and can be easily implemented in commercially available finite element software, making it an attractive analysis tool.

ESD Behavior of MWCNT Interconnects—Part II: Unique Current Conduction Mechanism

High-current carrying capacity and superior thermal conductivity have made multiwall carbon nanotubes (MWCNTs) a material for next-generation interconnects. Its distinct electrical and thermal properties result in various physical phenomenon, interaction among which give rise to unique electro-thermal transport. The interaction aggravates in presence of high-electric fields, which generally occur under ESD conditions. In this paper, we present detailed investigation of electro-thermal transport through MWCNTs under ESD conditions. The role of the substrate, MWCNT shells, and sub-bands in ESD current conduction is highlighted, while considering two device architectures—suspended and dielectric-supported MWCNTs. The quantum electron–phonon transport under non-equilibrium (ESD) conditions is explained using CNT band structure and interplay between electrical and thermal transport along the nanotube. The investigation highlights the role of the dielectric substrate in mitigating the detrimental effects of ESD stress. A strong dependence of failure current on metal-MWCNT contact resistance is revealed. The overall breakdown mechanism is found to follow Wunsch–Bell model, indicating a direct scaling between the rate of oxidation of MWCNT shells and injected power.

Atomistic simulations of field assisted evaporation in atom probe tomography

Atom probe tomography (APT) is an extremely powerful technique for determining the three-dimensional structure and chemical composition of a given sample. Although it is designed to provide images of material structure with atomic scale resolution, reconstruction artifacts, well-known to be present in reconstructed images, reduce their accuracy. No existing simulation technique has been able to describe the origin of these artifacts. Here we develop a simulation technique which allows for atomistic simulations of the atom emission process in the presence of high electric fields in APT experiments. Our code combines hybrid concurrent electrodynamics—molecular dynamics and a Monte Carlo approach. We use this technique to demonstrate the atom-level origin of artifacts in APT image reconstructions on examples of inclusions and voids in investigated samples. The results show that even small variations in the surface topology give rise to distortions in the local electric field, limiting the accuracy of conventional APT reconstruction algorithms.

A Complex Variable Solution Based Analysis of Electric Displacement Saturation for a Cracked Piezoelectric Material

This paper presents an analysis of the effect of electric displacement saturation for a failing piezoelectric ceramic material based on a complex variable solution of a Mode III and a Mode I crack. This particular electric nonlinearity is caused by a reduction of the ionic movement in the material in the presence of high electric fields. Total and strain energy release rates are computed for varying far field stresses, electric displacements, and electric fields and compared for cases without and with full electric displacement saturation to further advance the understanding of failure initiation in piezoelectric ceramics.

Molecular dynamics simulations of ion irradiation of a surface under an electric field

The presence of high electric fields may affect significantly the process of sputtering of metal surfaces by energetic ions, especially in the vicinity of rough surface features. The effect can be significant if the energy of ions is fairly low. Moreover, the nanosized rough surface features – invisible to a naked eye, both intrinsic ones due to technological processing of surfaces and those forming because of sputtering – may affect the topology of surface erosion under ion bombardment. In this work we study by means of concurrent electrodynamics–molecular dynamics the sputtering yield of Cu+ ions hitting a flat Cu surface or a nanosized Cu protrusion as a function of both ion energy and electric field strength. The results show that the sputtering yield is significantly enhanced in the presence of an electric field in both cases.

Local changes of work function near rough features on Cu surfaces operated under high external electric field

Metal surfaces operated under high electric fields produce sparks even if they are held in ultra high vacuum. In spite of extensive research on the topic of vacuum arcs, the mystery of vacuum arc origin still remains unresolved. The indications that the sparking rates depend on the material motivate the research on surface response to extremely high external electric fields. In this work by means of density-functional theory calculations we analyze the redistribution of electron density on {100} Cu surfaces due to self-adatoms and in presence of high electric fields from −1 V/nm up to −2 V/nm (−1 to −2 GV/m, respectively). We also calculate the partial charge induced by the external field on a single adatom and a cluster of two adatoms in order to obtain reliable information on charge redistribution on surface atoms, which can serve as a benchmarking quantity for the assessment of the electric field effects on metal surfaces by means of molecular dynamics simulations. Furthermore, we investigate the modifications of work function around rough surface features, such as step edges and self-adatoms.

ENERGY QUANTIZATION ON THE CURRENT-VOLTAGE CHARACTERISTIC OF NANOSCALE TWO-DIMENSIONAL MOSFET

The current-voltage characteristic for nanoscale MOSFET is presented based to the velocity saturation and quantum confinement. It has been clarified that the drain velocity which is saturated with an increased drain voltage limits the onset of the current saturation. In the presence of high electric field, the motion of the velocity saturation that is randomly oriented in the equilibrium becomes streamlined and unidirectional. The model presents the current-voltage characteristic from the drift-diffusion regime to the ballistic regime with the presence of the quantum confinement on the charge carrier distribution and the energy quantization. The obtained results are considered in the modeling of the current-voltage characteristics of nanoscale two-dimensional MOSFET and show good agreement with the experimental data without using any artificial parameters.

Non-ohmic behavior of carrier transport in highly disordered graphene

We report measurements of disordered graphene probed by both a high electric field and a high magnetic field. By applying a high source–drain voltage, Vsd, we are able to study the current–voltage relation I–Vsd of our device. With increasing Vsd, a crossover from the linear I–Vsd regime to the non-linear one, and eventually to activationless-hopping transport occurs. In the activationless-hopping regime, the importance of Coulomb interactions between charged carriers is demonstrated. Moreover, we show that delocalization of carriers which are strongly localized at low T and at small Vsd occurs in the presence of high electric field and perpendicular magnetic field.

Research on Charge Transport in One-Dimensional Organic Semiconductors Material

1D conjugated polymers belong to the family of organic semiconductor materials, in which the charge carriers are polarons or bipolarons. Charge transport in 1D organic semiconductors in the presence of high electric fields is studied within the SSH model. It is found that under a sufficiently high electric field, the polaron is dissociated into free-like electron. The electron performs Bloch oscillation (BO) in the organic semiconductors. By enhancing the electric field, BO will be destroyed and electrons can transit from the valence band to the conduction band, which is Zener tunneling in organic semiconductors. The results also indicate a field-induced insulator-metal transition.

Multivalley spin relaxation inn-type bulk GaAs in the presence of high electric fields

Multivalley spin relaxation in $n$-type bulk GaAs in the presence of high electric field is investigated from the microscopic kinetic spin Bloch equation approach with the $\ensuremath{\Gamma}$ and $L$ valleys included. We show that the spin relaxation time decreases monotonically with the electric field, which differs from the two-dimensional case and is recognized due to to the cubic form of the Dresselhaus spin-orbit coupling of the $\ensuremath{\Gamma}$ valley in bulk. In addition to the direct modulation of the spin relaxation time, the electric field also strongly influences the density and temperature dependences of the spin relaxation. In contrast to the monotonic decrease with increasing lattice temperature in the field-free condition, the spin relaxation time is shown to decrease more slowly under the influence of the electric field and even to increase monotonically in the case with small electron density and high electric field. We even predict a peak in weakly doped samples under moderate electric field due to the anomalous lattice-temperature dependence of the hot-electron temperature. As for the $L$ valleys, we show that instead of playing the role of a ``drain''of the total spin polarization as in quantum-well systems, in bulk they serve as a ``momentum damping area'' that prevents electrons from drifting to higher momentum states in the $\ensuremath{\Gamma}$ valley. This tends to suppress the inhomogeneous broadening and hence leads to an increase of the spin relaxation time.

An accurate MOSFET aging model for 28 nm integrated circuit simulation

MOSFET device aging represents a significant challenge for the IC industry, being increasingly more responsible for reliability failure in advanced process technology nodes. As the device electrical characteristics, such as threshold voltage and drain current, degrade with time, circuit performance also deteriorates, resulting in shorter lifetime and narrower safety margins between requirements and actual product reliability.Major device aging mechanisms include the hot-carrier injection (HCI), the negative bias-temperature instability (NBTI) for p-channel MOSFETs, and the positive bias-temperature instability (PBTI) for n-channel devices.HCI in NMOS and PMOS has been known for many years. In the presence of high electric fields, carriers are injected from the drain end of the channel into the gate dielectric, changing its electrical properties over time.PMOS NBTI has been studied in the past, and it continues to present a challenge for today’s technologies. NMOS PBTI is a phenomenon notably present in high-k metal-gate stacks. The partial recovery of degradation, an effect important for both phenomena, has been particularly challenging to model for circuit simulation, and not addressing it may result in overly pessimistic circuit lifetime predictions.In this paper we present an accurate, physics-based MOSFET aging model that encompasses degradation due to HCI, NBTI and PBTI. The model formulation on bias, geometry and temperature, and a unique methodology for modeling the AC partial-recovery effect of BTI are detailed and analyzed. The extraction methodology of the aging model parameters is further described. The model is implemented in an efficient MOSRA flow for SPICE and Fast SPICE circuit simulation, which has been successfully used to improve IC reliability-related yield in numerous 28nm tapeouts.