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- 2018
- computer statistical experiment
- statistical optimization
- resonant-tunneling diode
- negative voltage current differential resistance
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- Electronic Science and Technology
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- Bauman Moscow State Technical University
- V.N. Karazin Kharkiv National University
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Asymptotics of resonant tunneling in a two-dimensional quantum waveguide with several equal resonators
摘要： The domain occupied by the waveguide is a strip with n+1 equal narrows of diameter ε. The wave function of a free electron satisfies the Dirichlet boundary value problem for the Helmholtz equation. Any part of the waveguide between two neighboring narrows plays the role of a resonator. Near a simple eigenvalue of the closed resonator, there are n resonant peaks of height close to 1. We let ε → 0 and obtain asymptotic formulas for the resonant values of the spectral parameter and for the widths of the resonant peaks at their half-height. The behavior of the transmission coefficient in a neighborhood of a resonance is described.
关键词： variable cross-section,Quantum waveguide,resonant tunneling,the Helmholtz equation,asymptotic description
更新于2025-09-12 10:27:22
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Online Monitoring of Aluminum Electrolytic Capacitors in Photovoltaic Systems by Magnetoresistive Sensors
摘要： Due to the environmental concerns and new energy policies, worldwide expectations for energy production utilizing photovoltaic (PV) systems are increasing significantly. The aluminum electrolytic capacitor (AEC) is extensively used in filtering application for power electronic converters in PV systems since they can achieve the highest energy density with the lowest cost. However, the lifetime of an AEC is limited due to the electrolyte vaporization. The degradation of AECs challenges the efficiency and reliability of a PV system. Therefore, the health-monitoring of AECs is indispensable for the PV systems to operate reliably. In this paper, an online AEC-monitoring scheme based on magnetic-field sensing is proposed for PV systems under various working conditions. The AEC-monitoring technique using the equivalent series resistance (ESR) and capacitance (C) as the health indicators were developed for the power electronic converters in PV systems. The proposed methodology considering the voltage drops on C can improve the accuracy in ESR-estimation and achieve the estimation of C. The simulation results with Simulink verified that the proposed method was capable of estimating the health indicators accurately over various levels of solar irradiance and ambient temperature. The tunneling magnetoresistive (TMR) sensors were pre-calibrated from -25 to 100 oC for implementation in PV systems. The experimental results proved that TMR sensors could measure the current of AECs effectively to achieve the precise estimations of the health indicators using the proposed technique. This technique is non-invasive, compact, and cost-effective since it can be realized with the TMR sensors or other MR sensors.
关键词： Aluminum electrolytic capacitor,tunneling magnetoresistive sensor,PV system,condition monitoring
更新于2025-09-12 10:27:22
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Ferromagnetism in quantum dot plaquettes
摘要： Following recent experimental progress concerning Nagaoka ferromagnetism in finite-size quantum dot plaquettes, a general theoretical analysis is warranted in order to ascertain in rather generic terms which arrangements of a small number of quantum dots can produce saturated ferromagnetic ground states and under which constraints on interaction and interdot tunneling in the plaquette. This is particularly necessary since Nagaoka ferromagnetism is fragile and arises only under rather special conditions. We test the robustness of ground state ferromagnetism in the presence of a long-range Coulomb interaction and long-range as well as short-range interdot hopping by modeling a wide range of different plaquette geometries accessible by arranging a few (～4) quantum dots in a controlled manner. We find that ferromagnetism is robust to the presence of long-range Coulomb interactions, and we develop conditions constraining the tunneling strength such that the ground state is ferromagnetic. Additionally, we predict the presence of a partially spin-polarized ferromagnetic state for 4 electrons in a Y-shaped 4-quantum-dot plaquette. Finally, we consider 4 electrons in a ring of 5 dots. This does not satisfy the Nagaoka condition; however, we show that the ground state is spin 1 for strong, but not infinite, on-site interaction. Thus, even though Nagaoka’s theorem does not apply, the ground state for the finite system with one hole in a ring of 5 dots is partially ferromagnetic. We provide detailed fully analytical results for the existence or not of ferromagnetic ground states in several quantum dot geometries which can be studied in currently available coupled quantum dot systems.
关键词： long-range Coulomb interactions,Nagaoka ferromagnetism,interdot tunneling,ferromagnetic ground states,quantum dot plaquettes
更新于2025-09-12 10:27:22
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A new ultra-scaled graphene nanoribbon junctionless tunneling field-effect transistor: proposal, quantum simulation, and analysis
摘要： In this paper, a new ultrascaled junctionless graphene nanoribbon tunnel field-effect transistor (JL GNRTFET) is proposed through a computational study. The quantum simulation approach is based on the resolution of the Schr?dinger equation using the mode space non-equilibrium Green’s function formalism coupled self-consistently with a Poisson equation in the ballistic limit. The proposed nanodevice is endowed with ungated region between the auxiliary and control gates as well as with a laterally graded channel doping in order to improve the switching performance of the ultrascaled junctionless GNRTFET. The performance assessment has included the IDS–VGS transfer characteristics, subthreshold swing, current ratio, intrinsic delay, and power-delay product. It has been found that the proposed ultrascaled junctionless GNR tunneling FET can provide improved switching performance than its conventional counterpart. The proposed strategy can be applied to improve similar ultrascaled junctionless tunneling field-effect transistors for the future digital electronics, where the high-performance and the aggressive downscaling should be in agreement.
关键词： Junctionless,Graphene nanoribbon (GNR),Tunneling field-effect transistor (TFET),Switching,Quantum simulation,Tunneling
更新于2025-09-11 14:15:04
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Resonant Tunneling Diode (RTD) Terahertz Active Transmission Line Oscillator with Graphene-Plasma Wave and Two Graphene Antennas
摘要： This study describes the design of a resonant tunneling diode (RTD) oscillator (RTD oscillator) with a RTD-gated-graphene-2DEF (two dimensional electron fluid) and demonstrates the functioning of this RTD oscillator through a transmission line simulation model. Impedance of the RTD oscillator changes periodically when physical dimension of the device is of considerable fraction of the electrical wavelength. As long as impedance matching is achieved, the oscillation frequency is not limited by the size of the device. An RTD oscillator with a graphene film and negative differential resistance (NDR) will produce power amplification. The positive electrode of the DC power supply is modified and designed as an antenna. So, the reflected power can also be radiated to increase RTD oscillator output power. The output analysis shows that through the optimization of the antenna structure, it is possible to increase the RTD oscillator output to 22 mW at 1.9 THz and 20 mW at 6.1 THz respectively. Furthermore, the RTD oscillator has the potential to oscillate at 50 THz with a matching antenna.
关键词： transmission line model,RTD-gated-graphene-2DEF,resonant tunneling diode (RTD),graphene-plasma,two-dimensional electron fluid (2DEF),resonant tunneling diode oscillator (RTD oscillator),terahertz
更新于2025-09-11 14:15:04
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Experimental Realization of a Quantum Dot Energy Harvester
摘要： We demonstrate experimentally an autonomous nanoscale energy harvester that utilizes the physics of resonant tunneling quantum dots. Gate-defined quantum dots on GaAs=AlGaAs high-electron-mobility transistors are placed on either side of a hot-electron reservoir. The discrete energy levels of the quantum dots are tuned to be aligned with low energy electrons on one side and high energy electrons on the other side of the hot reservoir. The quantum dots thus act as energy filters and allow for the conversion of heat from the cavity into electrical power. Our energy harvester, measured at an estimated base temperature of 75 mK in a He3=He4 dilution refrigerator, can generate a thermal power of 0.13 fW for a temperature difference across each dot of about 67 mK.
关键词： resonant tunneling,quantum dots,thermoelectric,energy harvester,nanoscale
更新于2025-09-11 14:15:04
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Supramolecular structures of terbium( <scp>iii</scp> ) porphyrin double-decker complexes on a single-walled carbon nanotube surface
摘要： This work mainly reports the observation of novel supramolecular structures of TbIII-5,15-bisdodecylporphyrin (BDP, C12P) double-decker complexes on the surfaces of single-walled carbon nanotubes (SWNTs) performed by scanning tunneling microscopy under an ultra-high vacuum and low temperature, atomic force microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, and ultraviolet-visible spectroscopy. The molecules formed a well-ordered self-assembled helix-shaped array with regular periodicity on the tube surface. Additionally, some magnetic properties of the BDP-molecule as well as the resulting BDP-SWNT composites were investigated by superconducting quantum interference measurements. The molecule exhibits single-molecule magnetic (SMM) properties and the composite's magnetization increases almost linearly with decreasing temperature which is possibly due to the coupling between porphyrin molecules and SWNTs. Consequently, this may enable the development of more advanced spintronic devices based on porphyrin-nanocarbon composites.
关键词： Scanning tunneling microscopy,Magnetic properties,Supramolecular structures,Single-walled carbon nanotube,Atomic force microscopy,Terbium(III) porphyrin
更新于2025-09-11 14:15:04
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revealed by resonant photoelectron spectroscopy
摘要： Resonant photoelectron spectroscopy at the Co and Mn 2p core absorption edges of half-metallic Co2MnGe has been performed to determine the element-speci?c density of states (DOS). A signi?cant contribution of the Mn 3d partial DOS near the Fermi level (EF) was clari?ed by measurement at the Mn 2p absorption edge. Further analysis by ?rst-principles calculation revealed that it has t2g symmetry, which must be responsible for the electrical conductivity along the line perpendicular to the ?lm plane. The dominant normal Auger contribution observed at the Co 2p absorption edge indicates delocalization of photoexcited Co 3d electrons. The difference in the degrees of localization of the Mn 3d and Co 3d electrons in Co2MnGe is explained by the ?rst-principles calculation. Our ?ndings of the element-/orbital-speci?c electronic states near EF will pave the way for future interface design of magnetic tunneling junctions to overcome the temperature-induced reduction of the magnetoresistance.
关键词： first-principles calculation,magnetic tunneling junctions,normal Auger contribution,half-metallic Co2MnGe,magnetoresistance,Resonant photoelectron spectroscopy,Mn 3d partial DOS,element-speci?c density of states,electrical conductivity
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE 5th International Workshop on Metrology for AeroSpace (MetroAeroSpace) - Torino, Italy (2019.6.19-2019.6.21)] 2019 IEEE 5th International Workshop on Metrology for AeroSpace (MetroAeroSpace) - Low temperature point contact spectroscopy and transport measurements on filled skutterudite compounds
摘要： Several members of the RPt4Ge12 skutterudites class (R = Sr, Ba, Th, La, Pr) show at low temperature the phenomenon of superconductivity, with R = Pr exhibiting the highest transition temperature of about 8 K. PrPt4Ge12 shows as well a wide variety of strongly correlated electron behavior, including metal-insulator transitions, spin fluctuations, and various magnetically ordered states. In this work, we have applied the point contact spectroscopy to investigate the superconducting order parameter of the PrPt4Ge12 compound. Superconductivity in PrPt4Ge12 is progressively suppressed by partially substituting the Pr ions with Ce ions. For this reason, electrical resistance measurements as a function of the temperature (R-T), in different applied magnetic fields have also been performed and analysed on Pr1-xCexPt4Ge12 samples for x = 0, 0.07, 0.10.
关键词： Electrical Resistance Measurements,Superconducting Materials,Tunneling
更新于2025-09-11 14:15:04
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In-situ Process to Form Passivated Tunneling Oxides for Front-surface Field in Rear-emitter Silicon Heterojunction Solar Cells
摘要： A novel approach involving CO2 plasma treatment of intrinsic hydrogenated amorphous silicon was developed to form ultra-thin silicon oxide (SiOx) layers, that is, passivated tunneling layers (PTLs), for the fabrication of passivated tunneling contacts. These contacts were formed by depositing the PTL/n-type hydrogenated nano-crystalline layer (nc-Si:H(n))/c-Si(n) stacks. The results indicated that a higher CO2 plasma treatment pressure was preferred for the formation of oxygen-richer components in the silicon oxide films, with Si2+, Si3+, and Si4+ peaks, and a smoother PTL/c-Si heterointerface. The PTLs with higher oxidation states and lower surface roughness exhibited advantages for the c-Si surface passivation, with a maximum implied open-circuit voltage of approximately 743 mV. The lowest contact resistivity of approximately 60 mΩcm2 was obtained using nc-Si:H(n)/PTL/c-Si(n) as the passivated tunneling contact. Most importantly, the in-situ process can help prevent the contamination of the heterointerface during device fabrication processes.
关键词： Passivated tunneling layer (PTL),Silicon oxide (SiOx),CO2 plasma treatment,Silicon surface passivation
更新于2025-09-11 14:15:04