Double Barrier Research Articles

Non-monotonically changes in double Schottky barrier of MnCO3–doped ZnO varistors during DC aging

Abstract ZnO varistors play a crucial role as core component in metal oxide arresters due to their excellent nonlinear current density-electrical field (J–E) characteristics. After long-term operation under DC stress (DC aging), the J–E curves of ZnO varistors invented in the last decade cross with the original curve. Unexpectedly, the ‘crossover’ phenomenon cannot be explained by the vastly-accepted ion migration mechanism by which the barrier height monotonically declines after DC aging. In the present study, aging and recovery experiments were carried out on MnCO3-doped ZnO varistors. The symmetry of J–E characteristics in the same direction as and the opposite direction to the DC stress was compared, parameters of double Schottky barrier were analyzed, and evolution of point defects was deduced using dielectric spectra. It was found that, in addition to ion migrations, there are electrons ionized by zinc interstitials filling the interface states in the early stage of aging. Because these processes are dominant in different stages, the barrier height changes non-monotonically. MnCO3 can suppress the formation of zinc interstitials, so it simultaneously inhibits ion migrations and filling of the interface states by electrons. When 0.38 mol% MnCO3 is doped, J–E characteristics and the Schottky barrier of ZnO varistors show the smallest deviations during aging and recovery. The findings are helpful in updating criteria for the long-term stability of ZnO varistors and suggest that modifications to their formulae targeting the suppression of the filling the interface states by electrons are also expected to bolster the stability.

Influence of physical and material parameters on switching current density in perpendicular STT-MTJ: a micromagnetic study

Abstract Switching in magnetic tunnel junctions (MTJs) is considered to be coherent according to the macrospin model but above a critical characteristic length (Rc) this process becomes incoherent. As a result, switching becomes a complex process and affects the switching current density (Jc). We designed a spin transfer torque (STT) based single barrier perpendicular MTJ (SMTJ) and observed the influence of the junction size and exchange stiffness constant (Aex) on the switching process through micromagnetic simulations performed on Object Oriented Micromagnetic Framework (OOMMF). It was found that coherent switching occurred only for junction diameter ≤ 20nm and showed dependence on Aex as well. The influence of damping constant and anisotropy on Jc is studied and the mechanism of magnetic reversal through domain formation is revisited in this work. Furthermore, Double barrier MTJ (DBMTJ) stack was designed, which showed increased STT efficiency in switching time with a requirement of Jc lower by 42.86% compared to SMTJ.

Double-barrier magnetic tunnel junctions with enhanced tunnel magnetoresistance

Tunnel magnetoresistance (TMR) ratio is a key parameter characterizing the performance of a magnetic tunnel junction (MTJ), and a large TMR ratio is essential for the practical application of it. Generally, the traditional solutions to increasing the TMR ratio are to choose different material combinations as the ferromagnetic (FM) leads and nonmagnetic tunnel barrier. In this work, we study an architecture of MTJs of “FM/barrier/FM/barrier/FM” with double barriers, in contrast to the traditional single barrier structure “FM/barrier/FM.” We first analytically show that double barrier MTJ will generally have much higher TMR ratio than the single barrier MTJ and then substantiate it with the well-known example of “Fe/MgO/Fe” MTJ. Based on density functional calculations combined with nonequilibrium Green's function technique for quantum transport study, in the single barrier “Fe/MgO/Fe” MTJ, the TMR ratio is obtained as 122%, while in the double barrier “Fe/MgO/Fe/MgO/Fe” MTJ, it is greatly increased to 802%, suggesting that double barrier design can greatly enhance the TMR and can be taken into consideration in the design of MTJs.

Optimization Design and Performance Verification of the CeYSZ/Al2O3 Double Ceramic Layer Thermal Barrier Coatings Structure Parameters

Optimization Design and Performance Verification of the CeYSZ/Al2O3 Double Ceramic Layer Thermal Barrier Coatings Structure Parameters

“Sandwich Structured” Composite Film with Double Barrier Radiative Cooling, Adjustable Heating, and Multi-reflective Electromagnetic Interference Shielding for All-Weather Protection

“Sandwich Structured” Composite Film with Double Barrier Radiative Cooling, Adjustable Heating, and Multi-reflective Electromagnetic Interference Shielding for All-Weather Protection

Dynamics of spin oscillation in double barrier synthetic antiferromagnet based magnetic tunnel junction in presence of spin-transfer torque

In this work, we have studied the spin dynamics of a synthetic antiferromagnet (AFM)/heavy metal/ferromagnet double barrier magnetic tunnel junction in the presence of Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction, interfacial Dzyaloshinskii–Moriya (iDM) interaction, Néel field, and Spin–Orbit Coupling (SOC) with different Spin-Transfer Torque (STT). We employ the Landau–Lifshitz–Gilbert–Slonczewski equation to investigate the AFM dynamics of the proposed system. We found that the system exhibits a transition from regular to damped oscillations with the increase in strength of STT for systems with a weaker strength of iDM interaction than RKKY interaction while displaying sustained oscillations for systems having the same order of RKKY and iDM interactions. On the other hand, the systems with sufficiently strong iDM interaction strength exhibit self-similar but aperiodic patterns in the absence of the Néel field. In the presence of the Néel field, the RKKY interaction dominating systems exhibit chaotic oscillations for low STT but display sustained oscillations under moderate STT. Our results suggest that the decay time of oscillations can be controlled via SOC. The system can work as an oscillator for low SOC but displays non-linear characteristics with the rise in SOC for systems having weaker iDM interaction than RKKY interactions. In contrast, opposite characteristics are noticed for iDM interaction dominating systems. We found periodic oscillations under low external magnetic fields in RKKY interaction dominating systems. However, moderate fields are necessary for sustained oscillation in iDM interaction dominating systems. Moreover, the system exhibits saddle-node bifurcations and chaos under moderate Néel field and SOC with suitable RKKY and iDM interactions. In addition, our results indicate that the magnon lifetime can be enhanced by increasing the strength of iDM interaction for both optical and acoustic modes.

A Novel Fourth-Order Finite Difference Scheme for European Option Pricing in the Time-Fractional Black–Scholes Model

This paper addresses the valuation of European options, which involves the complex and unpredictable dynamics of fractal market fluctuations. These are modeled using the α-order time-fractional Black–Scholes equation, where the Caputo fractional derivative is applied with the parameter α ranging from 0 to 1. We introduce a novel, high-order numerical scheme specifically crafted to efficiently tackle the time-fractional Black–Scholes equation. The spatial discretization is handled by a tailored finite point scheme that leverages exponential basis functions, complemented by an L1-discretization technique for temporal progression. We have conducted a thorough investigation into the stability and convergence of our approach, confirming its unconditional stability and fourth-order spatial accuracy, along with (2−α)-order temporal accuracy. To substantiate our theoretical results and showcase the precision of our method, we present numerical examples that include solutions with known exact values. We then apply our methodology to price three types of European options within the framework of the time-fractional Black–Scholes model: (i) a European double barrier knock-out call option; (ii) a standard European call option; and (iii) a European put option. These case studies not only enhance our comprehension of the fractional derivative’s order on option pricing but also stimulate discussion on how different model parameters affect option values within the fractional framework.

Ultracold-atom quantum tunneling through single and double optical barriers

Ultracold-atom quantum tunneling through single and double optical barriers

Pricing of timer volatility-barrier options under Heston’s stochastic volatility model

Timer options are financial instruments that enable investors to exercise their rights on a random maturity date the realized variance reaches the level of variance budget. These options provide a stable investment opportunity for investors under the unpredictable and complex financial markets, such as global financial crisis or COVID-19 pandemic, which can induce the drastic changes of the volatility for the underlying asset. Meanwhile, in the financial markets, investors who invest in standard timer options may face the problems caused by the postponement of the exercising time for too low volatility, compared to standard vanilla options. In this regard, to overcome such disadvantages, we propose timer volatility-barrier options, which are activated and expired when the volatility arrives at a relatively low barrier level, with the original properties of the standard timer options. In this paper, by making use of the method of images, we derive an analytical formulas for the timer volatility-barrier options so that the volatility process can be driven by Heston stochastic volatility model, and verify the pricing accuracy of the timer options by comparing our solutions with those obtained from Monte Carlo simulations. Finally, we conduct numerical studies on the timer volatility-barrier options to examine the pricing sensitivities with respect to the various model parameters, and implement the discussion for pricing formula of double volatility barrier type of the timer options.

Resonant tunneling properties of laser dressed hyperbolic Pöschl-Teller double barrier potential

We examine the resonant tunneling properties of the laser-dressed hyperbolic Pöschl-Teller double quantum barrier structure. We use the non-equilibrium Green's function method to investigate structure parameters and electric field bias on the transmission properties of the system. The transmission probabilities and resonance energy levels are significantly influenced by the well widths and barrier heights. The barrier height increases, resonance energy levels shift toward higher values, and the resonance peak width narrows, leading to sharper and more selective tunneling behavior. Our results show that increasing the electric field bias leads to a decrease in the transmission probability at the first resonance peak, but this effect is not as strong for the subsequent peaks. Moreover, we find that changes in the laser field's parameter and structure parameters allow for fine control over the electronic spectra, allowing for modifications like red or blue shifts based on particular needs. The significance of comprehending the interaction among structural factors, external fields, and transmission qualities in quantum barrier structures is highlighted by our research, providing valuable information for the development and enhancement of electronic and optoelectronic systems with customized functionality. Our findings show the laser field has a considerable impact on resonant tunneling properties, opening the door to new device applications.

MHz sampling rate measurements of N2(A3Σu+) population in a Ns pulse discharge in a heated plasma flow reactor

Abstract Absolute, time-resolved population of a metastable electronic state of molecular nitrogen, N2( A 3 Σ u + , v = 0 ), is measured in a heated plasma flow reactor excited by a ns pulse discharge burst, by tunable diode laser absorption spectroscopy using a distributed feedback laser. Nitrogen or NO–N2 gas mixture in the reactor are heated by a tube furnace maintained at T = 800–1000 K, at pressures of P = 50–300 Torr. A diffuse plasma in the flow channel made of quartz is generated using a repetitively pulsed, double dielectric barrier, ns discharge in a plane-to-plane geometry. N2( A 3 Σ u + ) molecules in the plasma are generated by electron impact excitation of N2 ( B 3 Π g ) and N2 ( C 3 Π u ) states, followed by their cascade quenching. The laser is tuned across an absorption line near 1028 nm in a N2 B 3 Π g , v ′ = 0 ← A 3 Σ u + , v ′ ′ = 0 band at 100 kHz–1 MHz. The laser output wavelength and the absorption signal are measured by an etalon and two high bandwidth detectors. At all operating conditions, the absorption signal is fully resolved in time. The data points are taken every 500 ns–5 μs, with the temporal uncertainty of 50–500 ns, respectively. The data are used to infer the line pressure broadening coefficient and its temperature dependence. This study demonstrates the feasibility of this approach for the time-resolved N2( A 3 Σ u + ) measurements in pulsed hypersonic flow facilities, behind strong shock waves and in hypervelocity expansion flows.

Ultra-Low Gate Leakage Current and Enhanced Gate Reliability in p-GaN HEMT With AlN/GaN/AlN Double Barriers Cap Layer

Ultra-Low Gate Leakage Current and Enhanced Gate Reliability in p-GaN HEMT With AlN/GaN/AlN Double Barriers Cap Layer

When language becomes an obstacle: the challenges of teaching immunology in french for moroccan students

The teaching of sciences, and more specifically immunology, in a foreign language presents numerous challenges, particularly in terms of understanding and assimilating knowledge. In this context, teaching sciences in the native language would be more conducive to learning, as students have been familiarized with these linguistic structures from a young age. Nevertheless, since 2014, Morocco has decided to teach scientific subjects (mathematics, physics, and life and earth sciences) in French starting from middle school to help students in scientific fields, initially educated in Arabic, to better pursue their higher education in French. This approach creates a double barrier for students whose mother tongue is Amazigh or Arabic, they must both master complex scientific concepts and express them in a foreign language. This article aims to examine these challenges through two studies targeting a sample of 185 (n1+n2+n3) teachers, one quantitative based on a questionnaire, and the other qualitative using the focus group technique. Both studies focus on the opinions of life and earth sciences teachers regarding the teaching of immunology in French the high school, a discipline with particularly complex concepts, and whether teaching scientific subjects in French is hindered by difficulties, and finally to propose possible alternatives to improve the effectiveness of this teaching. The results obtained show a negative appreciation from the teachers in our sample regarding the teaching of immunology in French, as it poses problems for students' understanding of this discipline. In fact, the results suggest that the majority of students lack interest and motivation in immunology courses taught in French, with low engagement in classroom discussions.

Molecular insights into the synergistic inhibition mechanisms of antifreeze protein and methanol on carbon dioxide hydrate growth

The formation of CO2 hydrates during CO2 transportation and deep-sea injection poses a significant risk of pipeline blockage. Combining kinetic (KHIs) and thermodynamic hydrate inhibitors (THIs) serves as a promising efficient and economical strategy to mitigate this issue, whose performance and microscopic mechanisms yet are still poorly understood. This study employs molecular dynamics simulations to explore the effects of the combination of winter flounder antifreeze protein (wf-AFP) as a KHI and methanol as a THI on CO2 hydrate growth. We find that methanol and wf-AFP exhibit an intriguing synergistic inhibition performance on hydrate growth. In the AFP-only system, AFP serves as a spatial hindrance near the hydrate growth interface. However, in the AFP + methanol system, AFP changes its position due to the attractive force of methanol. Part of the AFP fragment remains on the hydrate interface, while the rest surrounds the CO2 droplet. Methanol, in addition to disrupting the water structure, combines with AFP to act as a double barrier to CO2 dissolution into the aqueous solution, thereby significantly reducing the gas source for hydrate growth. These findings provide molecular-level insights into hydrate inhibition mechanisms and guide the design of efficient inhibitors for safe CO2 transportation and injection.

Gallium nitride-based resonant tunneling diode oscillators

We demonstrated GaN-based resonant tunneling diode (RTD) oscillators employing monolithic microwave integrated circuits. The GaN-based RTDs with a GaN quantum well and AlN double barriers were grown on freestanding c-plane semi-insulating GaN substrates using metal–organic chemical vapor deposition. The circuit components, including an RTD, a coplanar waveguide, a metal–insulator–metal capacitor, and shunt resistors, were monolithically fabricated on the GaN substrate. The circuits oscillated at a fundamental frequency of 17 GHz, which closely matched an estimated frequency using a three-dimensional electromagnetic simulator and a circuit simulator. This study contributes to the advancement of semiconductor high-frequency devices for millimeter wave and terahertz applications.

Optimal dividends and capital injection: A general Lévy model with extensions to regime-switching models

This paper studies a general Lévy process model of the bail-out optimal dividend problem with an exponential time horizon, and further extends it to the regime-switching model. We first show the optimality of a double barrier strategy in the single-regime setting with a concave terminal payoff function. This is then applied to show the optimality of a Markov-modulated double barrier strategy in the regime-switching model via contraction mapping arguments. We solve these for a general Lévy model with both positive and negative jumps, greatly generalizing the existing results on spectrally one-sided models.

Probing the black holes in a dark matter halo of M87 using gravitational wave echoes

Variations at the event horizon structure of a black hole will emit the signals of the gravitational wave echoes associated with the ringdown of the binary black hole merger. In this work, combining mass model of M87 and Einasto profile for dark matter halo, we construct one formal solution of black holes in dark matter halo, and this solution includes the regular black hole for geometric parameter a<2M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$a < 2M$$\\end{document} and the wormhole for a≥2M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$a \\ge 2M$$\\end{document}. Then, we test this solution under axial gravitational perturbation and calculate their quasinormal modes (QNM). Our results show that when geometric parameter a>2M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$a>2M$$\\end{document}, a series of gravitational wave echoes appear after the QNM, and one distinctive feature of gravitational wave echoes is the double barrier. Besides, we also study the impacts of shape parameters α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document} of Einasto profile both on the QNM and gravitational wave echoes, and extract their frequencies using WKB method and Prony method. In principle, with the increasing of shape parameter α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document}, the frequencies of the QNM and gravitational wave echoes between the different shape parameters must be different. But now there is zero difference of the frequencies between shape parameter α=0.18\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha =0.18$$\\end{document} and α=0.20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha =0.20$$\\end{document}. Zero difference is not allowed, so we give an upper limit for shape parameter α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document}, which is approximately α<0.18\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha <0.18$$\\end{document}. These signals of gravitational wave echoes in a dark matter halo may be detected in the near future, and these characteristics of gravitational wave echoes may serve as local measurements of dark matter.

Investigation on double TiN/Al(Nb,Ta)2 protective layers of TiAl-Ta alloy after high-temperature oxidation

The formation process of the double continuous TiN/AlNb2 protective oxide layers of TiAl-Ta alloy after high-temperature oxidation is investigated by experiment and first-principle calculation in this study. It is found that Ta promotes the formation of a double continuous protective barrier consisting of 2.5 μm TiN/0.5–1 μm Al(Nb,Ta)2 layers during high temperature oxidation. And the lowest energy of twenty different AlNb2(1‾10)/TiN(110) terminations are identified by the first-principle calculation, which is significantly influenced by the distance of Nb-N bonding. Based on this, the location of Ta is studied which is preferred to be doped at Nb position of AlNb2 for the formation of Al(Nb,Ta)2 phase, thereby minimizing the total energy of the system. The formation of Al(Nb,Ta)2 phase can facilitate the precipitation of a continuous TiN layer to form a strong interface with low energy. Finally, the formation mechanism of Al(Nb,Ta)2(1‾10)/TiN(110) is discussed in detail. The results provide new insights into the development of oxidation-resistant TiAl alloys.

Transmission Coefficients of The Asymmetric Single and Double Barriers

Transmission Coefficients of The Asymmetric Single and Double Barriers

One-Step Spraying Strategy for Fabricating Bioinspired, Graphene-Based, and Multifunctional-Integrated Coatings on Structural Steel with Good Water Repellency, Fireproofing, Anticorrosion, and Durability.

Traditionally, many coatings were merely concentrated on settling the inherent fire protection problem of steel structures, while surface contamination and corrosion susceptibility should also be considered. Concurrently addressing these problems in fireproof efficiency and surface multifunctionality has become an issue of great significance in further expanding the application value in industrial and daily scenarios. Based on this condition, ecofriendly, graphene-based, and superhydrophobic coatings with multifunctional integration were constructed on steel via a one-step spraying method. The as-prepared coatings mainly consist of epoxy resin (EP), silicone resin (SR), a cyclodextrin-based flame retardant (MCDPM), expandable graphite (EG), and multilayered graphene (MG). The results demonstrate that the water contact angle (WCA) and water sliding angle (WSA) of as-prepared coatings can reach 156.8 ± 1.6 and 5.8 ± 0.7°, respectively, revealing good water repellency and self-cleaning properties. The coatings can also exhibit adequate adaptability for various substrates including wood, polyurethane foam, and cotton fabrics. Besides, good durability and robustness of coatings have been also verified via acid/alkali immersion, outdoor exposure, O2/plasma etching, and linear abrasion tests. Simultaneously, the coatings can exhibit excellent anticorrosion capacity for steel materials via a double barrier effect. Most importantly, the coatings have exhibited the lowest backside temperature (234.5 °C) during fire impact tests, suggesting excellent fireproof and heat insulation performance. This fact can be ascribed to the conjunct action between the physical/chemical charring process of flame retardants and the remarkable thermal stability of graphene. Consequently, this article can be expected to further promote the development and application of multifunctional-integrated coatings for steel structures in more fields.