Applied Bias Voltage Research Articles

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.

Graphene‐Based Flexible Optically Transparent Dual‐Tunable Metasurface

AbstractDynamically tunable flexible metasurfaces with optical transparency are essentially useful in stealth, electromagnetic sensing, and camouflage while keeping continuous optical observation and communication. In this paper, a dual‐tunable graphene‐based metasurface is designed based on patterned graphene sandwich structures, showing independent dynamic control of reflection amplitude and resonance frequency, excellent optical transparency, and outstanding flexibility. Both the simulated and measured results demonstrate that the transition from dual band absorption at 12 and 24.8 GHz to broad band absorption from 10 to 25.7 GHz, and the absorption amplitude can be tuned between −5 and −15 dB on average in each case dynamically and independently by applying bias voltage to graphene layers. Lastly, the distributions of the induced electric field and surface currents, as well as an equivalent circuit model, are provided to illustrate the tunable electromagnetic absorption mechanism. The designed metasurface has potential applications that are speculated in the fields of electromagnetic tune and electromagnetic stealth.

Electrochemical migration behavior between Cu and Ag under a thin electrolyte layer containing chloride

PurposeThe purpose of this paper is to investigate the effects of chloride ion concentration and applied bias voltage on the electrochemical migration (ECM) behavior between Cu and Ag under an NaCl thin electrolyte layer (TEL).Design/methodology/approachA self-made experimental setup for the ECM behavior between Cu and Ag was designed. An HD video measurement microscopy was used to observe the typical dendrite/corrosion morphology and pH distribution. Short-circuit time (SCT), short-circuit current density and the influence of the galvanic effect between Cu and Ag on their ECM behavior were studied by electrochemical tests. The surface morphology and composition of dendrite were characterized by FESEM/EDS.FindingsThe SCT increased with increasing NaCl concentration but decreased with increasing applied bias voltage, and the SCT between Cu and Ag was less than that between Cu and Cu because their galvanic effect accelerated the dissolution and migration of Cu. When NaCl concentration was less than or equal to 6 mmol/L, cedar-like dendrite was formed, whereas no dendrite formed and only precipitation occurred at high chloride ion concentration (100 mmol/L). The composition of the dendrite between Cu and Ag was copper.Research limitations/implicationsThe significance of this study is to clarify the ECM failure mechanism of printed circuit board (PCB) with an immersion silver surface finish (PCB-ImAg).Practical implicationsThis study provides a basic theoretical basis for the selection of protective measures and metal coatings for PCB.Social implicationsThe social implication of this study is to predict the service life of PCB.Originality/valueThe ECM behavior of dissimilar metals under a TEL was investigated, the influence of the galvanic effect between them on their ECM was discussed, and the SCT increased with increasing NaCl concentration.

Effects of Soliton Creation on Transient Transport through a Polymer Chain.

By using a nonadiabatic molecular dynamics method combined with the hierarchical equations of motion, we have investigated the nonequilibrium transient transport through a conjugated polymer chain. The polymer chain is described by the Su-Schrieffer-Heeger model, and its two ends are coupled with metal electrodes of different chemical potentials. In order to present the evolutions of the electronic injection and transport in the real-time domain, we have mainly discussed the dynamic relaxation processes of the excited states and transient transport currents. It is found that due to the existence of electron-phonon couplings in the conjugated polymers, creation of solitons not only affects the time of the system achieving the steady state but also leads to periodical oscillations of the steady-state transport currents with time in our simulations. Furthermore, with increasing applied bias voltage, the steady-state transport electronic current increases, which proved that the creation of the solitons can assist the electronic transport. These results have shown that the creation of the excited states is important in understanding the transport properties in organic nanostructures.

Spectrally Stable Deep-Blue Light-Emitting Diodes Based on Layer-Transferred Single-Crystalline Ruddlesden-Popper Halide Perovskites.

A novel approach to producing high-color-purity blue-light-emitting diodes based on single-crystalline Ruddlesden-Popper perovskites (RPPs) is reported. The utilization of a pure bromide composition eliminates any possibility of halide segregation, which can otherwise lead to undesired shifts in the emission wavelength or irreversible degradation of the spectral line width. Phase-pure PEA2MAPb2Br7 single crystals with a lateral size exceeding 1 cm2 can be synthesized using the inverse temperature crystallization method. To prepare RPP layers with a thickness of less than 50 nm, we employ a thinning process of the initially thick bulk crystals, followed by a dry-transfer process to place them onto a hole transport layer and an indium-tin-oxide-coated glass substrate. By utilizing polydimethylsiloxane as a handling layer, deformations of the bulk RPP crystal and exfoliated RPP layer, as well as the formation of defects such as pinholes, can be effectively suppressed. Subsequent depositions of an electron transport layer and a metal contact complete the fabrication of electroluminescence (EL) devices. The EL devices utilizing the single-crystalline RPP demonstrate excellent spectral stability across a broad range of the applied bias voltage spanning from 4.5 to 10 V, exhibiting a significantly narrow line width of 14 nm at an emission wavelength of 440 nm that can potentially cover 99.3% of the Rec. 2020 color gamut. The sharp EL emission spectrum can be effectively preserved, avoiding any broadening of the line width, by suppressing Joule heating throughout the device operation, in addition to the intrinsic stability of single-crystalline RPPs.

Efficiently unbiased solar-to-ammonia conversion by photoelectrochemical Cu/C/Si-TiO2 tandems

Photoelectrochemical nitrate reduction reaction (PEC NO3RR) is of interest as a promising route to directly realizing the solar-to-ammonia (NH3) conversion but the limited efficiency and high applied bias voltage hamper its commercial prospects. Here, we report a bias-free photoelectrochemical cell for PEC NO3RR in aqueous conditions, achieving a substantial NH3 yield rate of 13.1 μmol·h−1·cm−2, high faradaic efficiency of 93.8%, and recorded solar-to-NH3 conversion of ∼1.5% under 1 sun illumination. A hierarchical-structured Si-based photocathode with Cu+/Cu2+-containing Cu nanoparticles cocatalysts achieves a highly efficient PEC NO3RR with NH3 yield rate of 115.3 μmol·h−1·cm−2 in a three-electrode system. Integrating operando characterizations and systematic PEC measurements, the formation of Lewis acid sites on Cu nanoparticles by accepting the photoinduced electrons is the dominant factor for facilitating the absorption and hydrogenation of nitrate. This work will guide the development of a robust, high-performance, and unbiased PEC device for sustainable solar-to-NH3/other fuels conversion.