Applied Bias Voltage Research Articles

Theoretical Study for Spin Transport properties of FM-(G/C)10- FM

In the present study, we propose a physical model to study spin transport through DNA system and provide apparent physical mechanism for spin dependent phenomenon. The system considered in our work is DNA bases guanine-cytosine coupled to two ferromagnetic leads (FM-(G/C)10-FM) in parallel and anti-parallel configuration case, throughout magnetic quantum contacts. Our treatment is based on the tight binding model to derive obvious formula for the transmission spectrum which is employed to investigate the spin dependent current-bias voltage characteristics and the temperature - Conductance dependence. Our calculations of for strong, weak and without backbone regimes. Various factors are involved in our -study. These are the electrical contacts between DNA molecules and electrodes, the structure of DNA molecule and the environment around DNA molecule. The system spin dependent factors, that are investigated extensively in our study include the spin dependent coupling between subsystems, the quantum contacts between active region and electrodes, majority and minority electrons spin in the ferromagnetic leads as well as externally applied bias voltage. Variation of these factors can enhanced or suppressed spin transport through (G/C)10 molecule. The transmission spectrum calculations conform that the spin transport throughout (G/C)10 originates by a coherent tunneling process between neighboring bases through the overlapping of the LUMO orbitals of the bases. Our results showed that the spin-polarized transport that can be effectively regulated by the type of regime as well as the spin configuration in the leads which can exhibit efficient spin filtering and spin switching by employing the spin blockade phenomenon

Unlocking and optimizing the thermodynamic potential of tetragonal Si and Ge: Strategies and insights from a tight-binding simulation framework for material engineering

This study theoretically explores the effects of external fields and doping on the electronic and thermoelectric properties of tetragonal silicon (T-Si) and tetragonal germanium (T-Ge) structures using a tight-binding model, Green’s function formalism, and the Kubo formula. External parameters modify the positions and intensities of the density of states (DOS) peaks, influencing charge carrier excitation and conductivity trends. Applying bias voltage introduces zero-intensity regions in thermal conductivity due to band gap opening, reducing thermal properties. In contrast, chemical potential and magnetic field significantly enhance thermal properties by increasing intensity and shifting the peak position. T-Ge exhibits higher thermal properties than T-Si across the selected parameter ranges. The findings highlight the potential for optimizing and enhancing the thermoelectric properties of tetragonal structures through external controllable parameters.

Electromagnetically induced transparent bimodal to unimodal conversion realized by the nematic liquid crystal

In this paper, under the action of a gigahertz (GHz) band circularly polarized (CP) wave, a kind of CP metastructure (MS) is proposed. Recently, the nematic liquid crystal (NLC) has received great attention, but it is still difficult to realize the electromagnetically induced transparency (EIT) bimodal to unimodal under the control of NLC. Through the direct mutual coupling of the metal cross resonator, metal ring resonator, and dielectric cross resonator, modes coupling can be formed and generate transparent windows. Two different EIT states (unimodal and bimodal EIT) accompanied by slow light effects can be observed by regulating the NLC with the applied bias voltage (V bias). When the V bias is 0 V, two transparent windows can be achieved in the 6.595–8.443 GHz and 8.443–10.161 GHz bands. When V bias is 20 V, only one transparent window can be achieved in the 6.891–8.682 GHz band. Due to the high symmetry, the MS has the polarization insensitivity to CP waves. These extremely excellent properties make this MS have a wide application prospect. Noteworthy, the theoretical calculation result of EIT is verified by the two-oscillator theory model and circuit model, the results obtained are basically consistent with the simulation results.

Voltage manipulation of magnetic rogue waves for controllable electromagnetic interference

In this paper, we investigated the excitation of magnetic rogue waves and their voltage control in ferromagnetic nanowires. Starting from the Maxwell equations coupled with the Landau–Lifshitz–Gilbert equation, we derived the generalized derivative nonlinear Schrödinger equation under the long-wave approximation, which describes the nonlinear wave evolution in anisotropic ferromagnetic nanowires. By constructing the corresponding Lax pair, we obtained the exact solutions of first-order and second-order magnetic rogue waves via a generalized Darboux transformation. After spectral analysis and modulation instability analysis, we present the excitation regions of magnetic rogue waves. Furthermore, we tested and achieved precise control over the occurrence positions of first-order and second-order magnetic rogue waves by applying bias voltage. We further discussed the physical implications of these results, highlighting their potential applications in controlled electromagnetic interference for data destruction.

Sludge reduction and hydrogen production in a microbial photoelectrochemical cell with a g-C3N4/CQDs/BiOBr composite photocathode

ABSTRACT Hydrogen (H2) remains a pivotal clean energy source, and the emergence of Solar-powered Microbial Photoelectrochemical Cells (MPECs) presents promising avenues for H2 production while concurrently aiding organic matter degradation. This study introduces an MPEC system employing a g-C3N4/CQDs/BiOBr photocathode and a bioanode, successfully achieving simultaneous H2 production and sludge reduction. The research highlights the effective formation of a Z-type heterojunction in the g-C3N4/CQDs/BiOBr photocathode, substantially enhancing the photocurrent response under light conditions. Operating at – 0.4 V versus RHE, it demonstrated a current density of – 3.25 mA·cm−2, surpassing that of g-C3N4/BiOBr (−2.25 mA·cm−2) by 1.4 times and g-C3N4 (−2.04 mA·cm−2) by 1.6 times. When subjected to visible light irradiation and a 0.8 V applied bias voltage, the MPEC system achieved a current density of 1.0 mA·cm−2. The cumulative H2 production of the MPEC system reached 8.9 mL, averaging a production rate of 0.13 mL·h−1. In the anode chamber, the degradation rates of total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), total suspended solids (TSS), volatile suspended solids (VSS), proteins, polysaccharides, and volatile fatty acids (VFA) in the sludge were recorded at 57.18%, 82.64%, 64.98%, 86.39%, 42.81%, 67.34%, and 29.01%, respectively.

High rectification effects of heterojunctions based on C3N4 nanoribbons

Two heterojunctions based on zigzag graphitic carbon nitride nanoribbons (ZCNNRs), namely, BnAn and CnAn, are considered and their electronic transport properties are studied using the nonequilibrium Green's function (NEGF) in combination with the density functional theory (DFT). The BnAn is formed by the joining of bare and partially hydrogenated ZCNNRs. The CnAn is created by the attachment of bare and fully hydrogenated ZCNNRs which leads to a Schottky barrier. The results show that current–voltage characteristics (I–V) can be significantly tuned by the length variation of heterojunctions. Furthermore, it is found that both heterojunctions have a remarkable nonlinear behavior in the whole bias range. The B4A4, B3A4, and B4A3 have forward rectifier performance whereas B2A2, B3A3, C2A2, C3A3, C4A4, C3A4, C4A3, C5A3, and C6A3 show the reverse rectification behavior. In the case of BnAn, the maximum rectification ratio (RR) of B4A4 is boosted up to 3.97 × 107 at 0.4 V. Additionally, for CnAn, the maximum RR of C4A3 can reach 1.37 × 105 at 1.0 V. Our investigation reveals that the BnAn heterojunction has negative differential resistance (NDR) under positive bias.The peculiar transport behaviors of B4A4 and C4A3 are explained due to the energy level shifts of electrodes with applied bias voltage and great alterations in the transmission spectrum. Furthermore, the Molecular projected self-consistent Hamiltonian (MPSH) and projected local density of states (PLDOS) are analyzed for these devices. The findings of this work reveal unique opportunities to design the ZCNNRs nanoelectronic devices.

Recent Advances in Ferroelectret Fabrication, Performance Optimization, and Applications.

The growing demand for wearable devices has sparked a significant interest in ferroelectret films. They possess flexibility and exceptional piezoelectric properties due to strong macroscopic dipoles formed by charges trapped at the interface of their internal cavities. This review of ferroelectrets focuses on the latest progress in fabrication techniques for high temperature resistant ferroelectrets with regular and engineered cavities, strategies for optimizing their piezoelectric performance, and novel applications. The charging mechanisms of bipolar and unipolar ferroelectrets with closed and open-cavity structures are explained first. Next, the preparation and piezoelectric behavior of ferroelectret films with closed, open, and regular cavity structures using various materials are discussed. Three widely used models for predicting the piezoelectric coefficients (d33) are outlined. Methods for enhancing the piezoelectric performance such as optimized cavity design, utilization of fabric electrodes, injection of additional ions, application of DC bias voltage, and synergy of foam structure and ferroelectric effect are illustrated. A variety of applications of ferroelectret films in acoustic devices, wearable monitors, pressure sensors, and energy harvesters are presented. Finally, the future development trends of ferroelectrets toward fabrication and performance optimization are summarized along with its potential for integration with intelligent systems and large-scale preparation.

Comprehensive dosimetric characterization of novel silicon carbide detectors with UHDR electron beams for FLASH radiotherapy.

The extremely fast delivery of doses with ultra high dose rate (UHDR) beams necessitates the investigation of novel approaches for real-time dosimetry and beam monitoring. This aspect is fundamental in the perspective of the clinical application of FLASH radiotherapy (FLASH-RT), as conventional dosimeters tend to saturate at such extreme dose rates. This study aims to experimentally characterize newly developed silicon carbide (SiC) detectors of various active volumes at UHDRs and systematically assesses their response to establish their suitability for dosimetry in FLASH-RT. SiC PiN junction detectors, recently realized and provided by STLab company, with different active areas (ranging from 4.5 to 10mm2) and thicknesses (10-20µm), were irradiated using 9MeV UHDR pulsed electron beams accelerated by the ElectronFLASH linac at the Centro Pisano for FLASH Radiotherapy (CPFR). The linearity of the SiC response as a function of the delivered dose per pulse (DPP), which in turn corresponds to a specific instantaneous dose rate, was studied under various experimental conditions by measuring the produced charge within the SiC active layer with an electrometer. Due to the extremely high peak currents, an external customized electronic RC circuit was built and used in conjunction with the electrometer to avoid saturation. The study revealed a linear response for the different SiC detectors employed up to 21Gy/pulse for SiC detectors with 4.5 mm2/10µm active area and thickness. These values correspond to a maximum instantaneous dose rate of 5.5 MGy/s and are indicative of the maximum achievable monitored DPP and instantaneous dose rate of the linac used during the measurements. The results clearly demonstrate that the developed devices exhibit a dose-rate independent response even under extreme instantaneous dose rates and dose per pulse values. A systematic study of the SiC response was also performed as a function of the applied voltage bias, demonstrating the reliability of these dosimeters with UHDR also without any applied voltage. This demonstrates the great potential of SiC detectors for accurate dosimetry in the context of FLASH-RT.

The Role of Spin – Orbit Coupling in the Spin Transport FM-(G/C)N-FM

The spin transport through DNA system formed by a guanine-cytosine is studied extendedly in our work. Hence, theoretical treatment is accomplished for one magnetized active region (includes base pairs and backbone) coupled to ferromagnetic leads in parallel configuration case, throughout magnetic quantum contacts (FM-(G/C)N-FM). Our treatment is based on the tight binding model to derive obvious formula for the spin dependent transmission spectrum which is employed to investigate the spin transport through DNA junction. Our calculations are accomplished in the presence of spin-orbit coupling for strong, weak and "without backbone" regimes. The role the system spin dependent factors of the transport of (G/C)N molecule are investigated in our study. These factors include the molecular length, as well as externally applied bias voltage. Variation of these factors can enhance or suppress spin transport through (G/C)N molecule (with N=10,15,20,25. The transmission spectrum results confirm that the spin transport throughout (G/C)N is originated by a coherent tunneling process between neighboring bases through the overlapping of the LUMO orbitals of the bases. The physical mechanism is raise from quantum interference combination with molecular length and the presence of spin-orbit coupling. The best functional feature for environmental effect, which may induce dephasing such as leads temperature, is investigated. The results showed that the spin-polarized transport can be effectively regulated by the molecular length of (G/C) which can exhibit efficient spin filtering and spin switching

Theory of electron spin resonance in scanning tunneling microscopy

Electron spin resonance (ESR) spectroscopy in scanning tunneling microscopy (STM) has enabled probing the electronic structure of single magnetic atoms and molecules on surfaces with unprecedented energy resolution, as well as demonstrating coherent manipulation of single spins. Despite this remarkable success, the field could still be greatly advanced by a more quantitative understanding of the ESR-STM physical mechanisms. Here, we present a theory of ESR-STM that quantitatively models not only the ESR signal itself, but also the full background tunneling current, from which the ESR signal is derived. Our theory is based on a combination of Green's function techniques to describe the electron tunneling and a quantum master equation for the dynamics of the spin system along with microwave radiation interacting with both the tunneling current and the magnetic system. We show that this theory is able to quantitatively reproduce the experimental results for a spin-1/2 system (TiH molecules on MgO) across many orders of magnitude in tunneling current, providing access to the relaxation and decoherence rates that govern the spin dynamics due to intrinsic mechanisms and to the applied bias voltage. More importantly, our work establishes that (i) sizable ESR signals, which are a measure of microwave-induced changes in the junction magnetoresistance, require surprisingly high tip spin polarizations, and (ii) the coupling of the magnetization dynamics to the microwave field gives rise to the asymmetric ESR spectra often observed in this spectroscopy. Additionally, our theory provides very specific predictions for the dependence of the relaxation and decoherence times on the bias voltage and the tip-sample distance. Finally, with the help of electromagnetic simulations, we find that the transitions in our ESR-STM experiments, in which the tunnel junction is irradiated by a nearby microwave antenna, can be driven by the ac magnetic field at the junction. Published by the American Physical Society 2024

Magnetoelectric coupling in Ba:Pb(Zr,Ti)O3/Co40Fe40B20 nanoscale waveguides studied by propagating spin-wave spectroscopy

In this study, we report on the characterization of the magnetoelectric coupling coefficient in Ba-substituted Pb(Zr, Ti)O3/Co40Fe40B20 (BPZT/CoFeB) nanoscaled waveguides with lateral dimensions of 700 nm using propagating spin-wave spectroscopy. The characterization was conducted in a Damon–Eshbach configuration to maximize the magnetoelastic coupling strength, as predicted by strain distribution calculations using finite element simulations. The spin-wave resonance frequency is controlled by applying bias voltages on the magnetoelectric waveguide. The magnitude of the frequency shift was correlated with the strength of the magnetoelastic field, which reached a maximum value of 5.71 mT in our experiments. In addition, the results demonstrated that the coupling coefficient behavior is associated with the hysteretic ferroelectric nature of BPZT, reaching a maximum value of 1.69 mT/V.

Multifunctional carbon nanotubes coated stainless steel mesh for electrowetting, hydrophobic, and dye absorption behavior

Electrowetting behaviour for carbon nanotubes (CNT) grown on stainless steel mesh was investigated. The effect of temperature, time, and applied bias voltage on the contact angle of water droplets was studied. The impact of temperature variation on contact angle was also performed for the temperature ranging from 25 to 70 °C. A decrement of contact angle by 68% was observed for the mentioned range indicating a transition from a hydrophobic to hydrophilic nature. A similar trend was observed on the application of electric potential to the CNT-modified stainless-steel mesh ranging from 0 to 8 V with a transition of contact angle from 146 to 30 deg respectively. A comparative analysis for the contact angle variation with time for CNT-coated mesh and uncoated mesh was performed for 180 min. It is observed that uncoated mesh shows a reduction in contact angle to 0 deg with time while the CNT coated mesh shows surplus hydrophobicity with a 2 deg decrement in the extent of time. CNT-modified mesh successfully absorbs 95% of rhodamine B (RB) dye and detergent from water in 10 cycles.

A behavioral nonlinear modeling implementation for MEMS capacitive microphones

We are highlighting the behavioral nonlinear system-level modeling approach for MEMS capacitive microphones. The combination of finite element modeling and large signal nonlinear circuit modeling provides a strong capability to predict electroacoustical performance for capacitive transductions. Circuit simulation tools such as Cadence Virtuoso have emerged as powerful aids in designing behavioral models in both linear and nonlinear regimes. Typical small signal lumped element models fail to capture the MEMS behavior which changes over pressure and electrical bias conditions. The models described herein capture diaphragm displacement and capacitance change over large pressure ranges for a simply supported circular plate. This can be coupled with the electrostatic force, due to the applied bias voltage, and converted back to pressure, thereby realizing a feedback loop in the circuit model. The nonlinear model capability is extended to predict capacitance-bias behavior and estimate pull-in of the MEMS device. The microphone sensitivity, signal-to-noise ratio, and harmonic distortions are accurately predicted using the nonlinear large signal model when compared to measured microphone data.

Design, simulation, and testing of a tunable MEMS multi-threshold inertial switch

This paper presents a tunable multi-threshold micro-electromechanical inertial switch with adjustable threshold capability. The demonstrated device combines the advantages of accelerometers in providing quantitative acceleration measurements and g-threshold switches in saving power when in the inactive state upon experiencing acceleration below the thresholds. The designed proof-of-concept device with two thresholds consists of a cantilever microbeam and two stationary electrodes placed at different positions in the sensing direction. The adjustable threshold capability and the effect of the shock duration on the threshold acceleration are analytically investigated using a nonlinear beam model. Results are shown for the relationships among the applied bias voltage, the duration of shock impact, and the tunable threshold. The fabricated prototypes are tested using a shock-table system. The analytical results agree with the experimental results. The designed device concept is very promising for the classification of the shock and impact loads in transportation and healthcare applications.

Non-KAM classical chaos topology for electrons in superlattice minibands determines the inter-well quantum transition rates

We investigate the quantum-classical correspondence for a particle tunnelling through a periodic superlattice structure with an applied bias voltage and an additional tilted harmonic oscillator potential. We show that the quantum mechanical tunnelling rate between neighbouring quantum wells of the superlattice is determined by the topology of the phase trajectories of the analogous classical system. This result also enables us to estimate, with high accuracy, the tunnelling rate between two spatially displaced simple harmonic oscillator states using a classical model, and thus gain new insight into this generic quantum phenomenon. This finding opens new directions for exploring and understanding the quantum-classical correspondence principle and quantum jumps between displaced harmonic oscillators, which are important in many branches of natural science.

High-performance, ultra-broadband Sb2Te3 photodetector assisted by multimechanism

Ultra-broadband spectral detection is critical for the application of several technologies, such as imaging, sensing, spectroscopy, and communication. However, the development of high-performance photodetectors with a wide spectral response remains a significant challenge. In this study, we present an ultra-broadband, responsive, dual-mechanism fusion photodetector based on the topological insulator Sb2Te3. By employing methods such as applying bias voltages, energy band structures, and photocurrent imaging, we have confirmed that the operating mechanism in the visible to the infrared light region is the photoconductive effect, exhibiting a room-temperature responsivity of 114.6 mA/W and a specific detectivity of 1.78 × 108 cm2 Hz1/2 W−1, especially under the working condition of 520 nm. Moreover, extending the spectral detection capability from infrared to terahertz is critically important. In the terahertz range, where photon energies are significantly lower than those in the visible to infrared spectrum, the detector achieves a room-temperature responsivity of 38.5 mA/W at 0.12 THz and a specific detectivity of 3.44 × 1010 cm2 Hz1/2 W−1, with a response time of 20 µs, primarily attributed to the asymmetric scattering behavior of the topological surface states. Notably, we have successfully demonstrated high-resolution imaging in the visible to infrared and terahertz spectral ranges at room temperature, providing strong evidence of practical applications for our photodetector. In conclusion, Sb2Te3, as an emerging broadband photodetection material, exhibits significant potential and lays a robust foundation for further research in the field of ultra-broadband photodetectors.

Anomalies-Rich Floquet superconductivities induced by joint modulation of dynamic driving and static parameters

Current theoretical and experimental endeavors to realize an anomalous Floquet chiral topological superconductor (TSC), which is characterized by chiral Majorana edge modes independent of the Chern number, remain insufficient. Herein, we propose a new scheme that involves jointly tuning dynamic driving and static parameters within a magnetic topological insulator-superconductor sandwich structure to achieve this goal. The Josephson phase modulation induced by an applied bias voltage across the structure is utilized as a Floquet periodic drive. It is found that the interplay between the two kinds of tunings can bring about a lot more exotic Floquet TSC phases than those caused by only tuning the dynamic driving parameter (frequency ω or period τ). More importantly, just tuning static parameters (the chemical potential µ, Zeeman field gz , and proximity-induced superconducting energy gap Δb ) also can induce a series of novel topological phase transitions. Particularly, the features in the context of the three tunings are different from each other, originating from the combination of intrinsic and different extrinsic mechanisms. In addition, jointly tuning τ and µ (gz ) can have its own unique TSC phases. The proposed scheme should be readily accessible in experiments, and thus the family of anomalous Floquet TSC phases may be considerably enriched.

Experimental analysis of the electric field distribution in semi-insulating GaAs detectors via alpha particles

Semi-insulating gallium arsenide (SI GaAs) detectors offer a promising alternative to commercially available silicon detectors. They demonstrate superior radiation hardness and provide improved efficiency for gamma and X-ray detection, primarily attributed to their higher density. In this study, we examined 350 μm thick SI GaAs detectors featuring front-side Ti/Pt/Au Schottky contacts with varying contact areas, complemented by back-side Ni/AuGe/Au ohmic contacts spanning the entire area. First, the reverse current-voltage characteristics of the prepared detectors were measured. The dependence of the reverse current and the breakdown voltage on the Schottky contact area was revealed. As the contact area decreases, the reverse current decreases and the breakdown voltage increases. The detection performance of the detectors was evaluated by alpha spectrometry using an 241Am source. After irradiation of the detectors from the Schottky electrode, the measured alpha spectra show an increasing CCE with decreasing Schottky contact area. Finally, the correlation between the applied bias voltage and the extent of the active detector area from the edge of the detector contact was investigated.

Bias voltage influence on the a-SiCx:H interlayer deposition using tetramethylsilane: Decorative applications of a-C:H thin films on steel

Hydrogenated amorphous carbon (a-C:H) is a type of coating vastly applied on steel alloys due to its low friction coefficient, high hardness, and chemical inertness. Also, its characteristic brilliant black color like onyx stone is desirable for decorative applications. Despite the beneficial properties conferred to ferrous substrates, the adhesion of a-C:H films is weakened by its residual stress. In order to improve the adhesion of a-C:H films/steel alloy structures, one adopted strategy is the addition of an interlayer. This research investigated the influence of the bias voltage applied on the deposition of hydrogenated amorphous silicon carbide (a-SiCx:H) interlayers, with tetramethylsilane (TMS) as the precursor, to promote adhesion in a-C:H/a-SiCx:H/ferrous alloy structures for decorative applications. The thicker interlayer was achieved at −600 V. Two regimes were proposed to explain this behavior considering ionization rates and resputtering rates and chemical reactions in plasma. The chemical structure in different regions of the a-SiCx:H interlayer was analyzed in detail. An increase in the applied bias voltage leads to oxygen incorporation at the a-C:H/a-SiCx:H interface. Higher bias voltages result in lower silicon content at the a-SiCx:H/steel interface, which is correlated to the −800 V sample’s poor adhesion. Finally, we have included a discussion about a new range of loads when a decorative piece is held by the hand where the critical loads for delamination of a-C:H coatings measured here are good enough for decorative applications.

Heterostructure of Reduced Titanium Dioxide Nanorods and Small Molecules Leads to Photo‐Induced Negative Differential Resistance Behaviors

AbstractNegative differential resistance (NDR) is of considerable interest due to the uncommon characteristic of having a region where the current decreases as the applied voltage bias increases. However, it is difficult to reproduce NDR devices and evaluate their reliability and stability because of the unstable NDR behaviors. In this paper, a highly stable photo‐induced hybrid photonic (HP)‐NDR device is presented for practical applications, which has heterostructure between TiO2‐x nanorods formed by oblique angle deposition and dinaphtho[2,3‐b:2′,3′‐f]‐thieno[3,2‐b]thiophene. The mechanism of NDR behaviors is investigated through morphological analysis, energy band structure, and electrical characteristics. In addition, diverse bias stress and endurance measurements are performed to demonstrate the reliability of the HP‐NDR device. As a result, the NDR behavior lasts up to 1,000 s in each bias stress and 38,850 cycles in the repeated current–voltage (I–V) characteristics Thus, the study has successfully achieved robust HP‐NDR devices with potential for practical applications.