Bias Voltage Research Articles

Realizing one-dimensional moiré chains with strong electron localization in two-dimensional twisted bilayer WSe2

Two-dimensional (2D) moiré systems based on twisted bilayer graphene and transition metal dichalcogenides provide a promising platform to investigate emergent phenomena driven by strong electron-electron interactions in partially filled flat bands. A natural question arises: Is it possible to expand the 2D correlated moiré physics to one-dimensional (1D) that electron-electron correlation is expected to be further enhanced? This requires selectively doping of 1D moiré chain, which seems to be not within the grasp of today's technology. Therefore, an experimental demonstration of the 1D moiré chain with partially filled electronic states remains absent. Here, we show that we can introduce 1D boundaries, separating two regions with different twist angles, in twisted bilayer WSe2 (tWSe2) by using scanning tunneling microscopy (STM) and demonstrate that the electronic states of 1D moiré sites along the boundaries can be selectively filled. The strong localized charge states of correlated moiré electrons in the 1D moiré chain can be directly imaged and manipulated by combining a back-gate voltage with the STM bias voltage. Our results open the door for realizing new correlated electronic states of the 1D moiré chain in 2D systems.

Solution‐Processed Tin‐Antimony Quaternary Chalcohalides for Self‐Powered Broadband Photodetectors

The mixed‐metal quaternary chalcohalides of group IV and V elements are a promising class of low‐toxicity perovskite‐inspired materials with tunable bandgaps and desirable defect tolerance. Sn2SbS2I3 is known for its broadband absorption, low exciton binding energy, ambient stability, and solution processability in thin films. However, its use in optoelectronic devices has so far been only limited to solar cells. In this work, the first self‐powered photodetectors based on Sn2SbS2I3 thin films, sandwiched in an n–i–p device configuration are reported. The insertion of an interlayer at the hole‐transport layer/gold top‐electrode interface reduces the dark current and improves the device performance. The high external quantum efficiency of the devices in the range of 350−900 nm hints to a broadband spectral photoresponsivity. The devices indeed exhibit promising photodetection properties, namely a photoresponsivity of 0.33 A W−1, a specific detectivity of 1.55 × 1012 Jones, and photoresponse/decay times of 0.52 and 0.45 s at zero bias voltage. These results, combined with the excellent operational stability of the photodetectors, encourage the exploration of a wide range of practical light‐sensing applications for quaternary chalcohalides and stimulate device and material engineering to further enhance photodetection across the UV‐Visible‐NIR spectrum.

Tunable bandpass frequency selective surface with wideband tuning and low insertion loss based on tunneling waveguide array

AbstractIn this paper, we present a tunable bandpass frequency‐selective surface (FSS) with wide tuning range. The FSS consists of a metallic rectangular waveguide array integrated into the double‐sided printed circuit board (DSPCB) and an array of embedded varactors with a bias network on the backside of the DSPCB. The waveguide array exhibits a frequency‐selective transmission peak due to the tunneling effect, and the transmission frequency can be adjusted by modifying the capacitance of varactors using different bias voltages. One benefit of this setup is that the varactors, along with the bias network, are situated on the same layer, resulting in a significant reduction in overall thickness to just 0.006λc (where λc represents the free‐space wavelength at the highest transmission frequency). Additionally, the insertion loss related to the parasitic resistance of varactors is notably reduced due to the innovative integrated design of biasing lines with varactors and the nearly full‐metal waveguide array. A prototype has been manufactured and tested, demonstrating that by varying the varactor capacitance from 0.12 to 1 pF, the passband showcases a frequency tuning range of 2.32:1, spanning from 5.8 to 2.5 GHz with an insertion loss ranging from 0.2 to 2.6 dB.

Hydrogel interfaced glass nanopore for high-resolution sizing of short DNA fragments

Solid-state nanopores, known for their label-free detection and operational simplicity, face challenges in accurately sizing the short nucleic acids due to fast translocation and a lack of enzyme-based control mechanisms as compared to their biological counterparts with sizing resolutions still limited to ≥100 bp. Here, we present a facile polyethylene glycol-dimethacrylate (PEG-DMA) hydrogel interfaced glass nanopore (HIGN) system by inserting glass nanopore into the hydrogel to achieve sub-100 base pair (bp) resolution in short DNA sizing analysis. We systematically investigated the effects of hydrogel mesh size, spatial configurations of glass nanopores about the hydrogel, applied bias voltage, and analyte concentration on the transport dynamics of 200 bp double-stranded DNA (dsDNA). A 7.5 w/v% PEG-DMA hydrogel induced ∼11x increase in the mean dwell times compared with bare solution nanopore system. The insertion locations and depths of the glass nanopore into the hydrogel resulted in 7.16% and 5.28% coefficients of variation (CV) for mean normalized event frequencies. This enhancement of dwell times and invariability in translocation characteristics enables precise sizing of dsDNA fragments under 400 bp using HIGN, with an achieved size resolution of 50 bp with observable mean normalized peak amplitude (ΔI/Io) of ∼0.005. Furthermore, we have demonstrated the capability of HIGN to perform multiplex detection of influenza A virus (IAV) and severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) through reverse transcriptase-polymerase chain reaction (RT-PCR). These results demonstrated the potential of HIGN as a versatile tool in nucleic acid analysis and multiplexed label-free molecular diagnostics.

Anticathode effect on electron kinetics in electron beam generated E×B plasma

Abstract Electron beam (e-beam) generated plasmas with applied crossed electric and magnetic (E×B) fields are promising for low damage processing of materials with applications to microelectronics and quantum information systems. In cylindrical e-beam E×B plasmas, radial confinement of electrons and ions is achieved by an axial magnetic field and radial electric field, respectively. To control the axial confinement of electrons, such e-beam generated plasma sources may incorporate a conducting boundary known as an anticathode, which is placed on the axially opposite side of the plasma from the cathode. In this work, it is shown that varying the anticathode voltage bias can control the degree to which the anticathode collects or repels incident electrons, allowing control of warm electron (electron energies in 10-30 eV range) and beam electron population confinement. It is suggested that the effect of the anticathode bias on the formation of these distinct electron populations is also associated with the transition between weak turbulence and strong Langmuir turbulence.

Bioinspired Three-Mode Photosensitive Synaptic LED for Optical Information Processing.

Inspired by human sense organs, AI is advancing toward multimodal perception, with display technology evolving into intelligent human-computer interaction tools. However, hardware networks with multimodal responses connected by different devices bring problems such as delayed information transfer and inefficiency. Thus, an innovative three-mode photosensitive synaptic LED (PSSL) is first proposed by adding a photosensitive layer indacenodithiophene-benzothiadiazole (IDTBT) to the quantum-dot light-emitting diode (QLED), switched by changing the bias voltage. The self-powered PSSL has a photoresponse range from 310 nm to 808 nm (ultraviolet-near-infrared, UV-NIR). The device exhibits a bipolar response under red and UV light at 1 V. When the voltage reaches the turn-on voltage, the PSSL device turns into a neuromorphic LED, exhibiting conductivity enhancement under red-light irradiation and suppression under UV-light irradiation. As a result, the PSSLs are expected to be applied in the field of optical encryption communication and in neuromorphic display.

Self-Powered Infrared-Detectable BP/Ta2NiS5 Heterojunction and Its Application in Energy-Efficient Optoelectronic Synapses.

The development of energy-efficient and high-performance optoelectronic devices is crucial for the advancement of modern optoelectronic and microelectronic systems. Although the self-powered devices and optoelectronic synapses based on 2D heterojunction show great application prospects, the high energy consumption and infrared band detection of self-powered optoelectronic synapses are still an urgent problem to be solved. In this report, a BP/Ta2NiS5 heterojunction is constructed to achieve infrared detection by leveraging differences in Fermi energy levels. This heterojunction exhibits a high specific detectivity of 6.57×1010, 2.6×1010, and 1.12×1010 Jones and responsivity of 20, 10.6, and 5.9mAW-1 for 1064, 1550, and 2200nm infrared light at 0 bias voltage, respectively. In addition, under the 2200nm light, by applying an ultra-low bias voltage of 800µV, the heterojunction exhibits ultra-low power and energy consumption of 28.8pW and 0.64pJ, successfully simulates a variety of synaptic behaviors under infrared light, and demonstrates its image perception and image memory capabilities. These findings position the BP/Ta2NiS5 heterojunction as an ideal candidate for a multifunctional optoelectronic device crucial for advanced photodetection, neuromorphic computing, and artificial intelligence.

Mechanical and high-temperature steam oxidation properties of Cr coatings deposited via high-power impulse magnetron sputtering

Applying protective coatings to Zr alloy cladding surfaces is one of the better methods to design fuel tolerant materials. In this study, the surface of a Zr-4 alloy was coated with Cr using high-power impulse magnetron sputtering. Furthermore, the mechanisms by which bias voltages affect the mechanical characteristics, resistance to high-temperature steam oxidation, and coating structure were elucidated. The coating exhibits a strong (200) weave structure with coarse grains at a bias voltage of -100 V. With increasing bias, the energy of deposited particles increases, grains continue to grow, (200) preferential growth orientation disappears, and the coating exhibits a (110) crystal orientation. The growth structure of the coating first shows a tendency to be dense and then loose. For the Cr coating with a (200) crystal orientation, a dense oxide layer is preferentially formed after oxidation, which can effectively block the internal diffusion of O. With increasing oxidation time, coarse Cr grains can effectively block the external diffusion of Zr. Furthermore, the Cr coating exhibiting a (110) crystal orientation was severely oxidized after oxidation, resulting in the formation of cracks at the film base; this accelerated the outward diffusion of Zr.

Photocurrent in Silic in Silicon/Barium Titanate/Nikel Structures

Photosensitive silicon/barium titanate/nickel structures with undoped barium titanate and doped europium were synthesized using the sol-gel method. The current-voltage characteristics were studied under illumination with a xenon lamp, highlighting a monochromatic line in the range of 400–800 nm and in dark mode. The synthesized structures showed the presence of a photocurrent on the reverse branch of the current-voltage characteristics over the entire studied range of illumination wavelengths. The maximum reverse branch current for a structure with undoped barium titanate was achieved when exposed to radiation with a wavelength of 470 nm and was about 0.6 μA for a bias voltage ranging from 2 to 10 V. Doping barium titanate with europium leads to an increase in the photocurrent by 17–26 %.

Receiving Paths Improvement of Digital Phased Array Antennas Using Adaptive Dynamic Range

In contemporary radar technology, the observation and detection of objects with low radar cross-sections remains a significant challenge. A multi-functional radar model employing a digital phased array antenna system offers notable advantages over traditional radar in addressing this issue. Nonetheless, to fully capitalize on these benefits, improving the structure of the receiving path in digital transceiver modules is crucial. A method for improving the digital receiving path model by implementing a matched filter approach is introduced. Given that the return signals from objects are often lower than the internal noise, the analog part of the digital transceiver modules must ensure that its dynamic range aligns with the level of this noise and the weak signal. The output signal level of the analog part must correspond to the allowable input range of the analog-to-digital converter. Improvements in the receiving path to achieve a fully matched model can reduce errors in the phase parameters and amplitudes of the useful signal at the output. The simulation results presented in this paper demonstrate a reduction in amplitude error by approximately 1 dB and a phase error exceeding 1.5 degrees for the desired signal at the output of each receiving path. Consequently, these improvements are expected to enhance the overall quality and efficiency of the spatial and temporal accumulation processes in the digital phased array antenna system. Furthermore, to maintain the matched filter model, we also propose incorporating an adaptive “pseudo-expansion” of the linear gain range. This involves adding a feedback stage with an automatic and adaptive bias voltage adjustment for the intermediate-frequency preamplifier in the analog part of the receiving path. Simulations to qualitatively verify the validity of this proposal are conducted using data from practical operational radar system models.

I-V Characteristics of Polycrystalline CAZTSe Heterojunction Solar Cells at Different Ag Content and Annealing Temperatures

Since the polycrystalline (Cu1-xAgx)2ZnSnSe4 (CAZTSe) demonstrated good optical absorption performance in the visible region, the focus of the present study is to grow the polycrystalline (Cu1-xAgx)2ZnSnSe4 thin films deposited by thermal evaporation method on silicon substrates with 800 nm thickness and 0.53 nm/sec deposition rate as a function of Ag content (0.0,0.1,0.2) and annealing temperature at 373 K, 473 K. From I-V measurements of Al/n-CdS/p-CAZTSe/n-Si(111)/Al heterojunction solar cells under dark and illumination conditions, we observed that the forward bias current changes roughly exponentially with bias voltage and the ideality factor and saturation current dependence on both x content and different temperatures (Ta).

Tunable Ambipolar Transport in a 2D Kagome Semiconductor

AbstractThe interference of electronic wavefunctions within a Kagome lattice can result in a flat band structure, where low‐energy electrons exhibit highly correlated behavior, facilitating exploration of interactions among intriguing electronic states. However, the inherent high carrier density in most known Kagome materials often hampers the manipulation of these quantum phenomena through conventional means, such as gate voltage. In this work, a unique tunability in the electrical and optoelectronic properties of exfoliated Nb3I8, a 2D semiconductor featuring a “breathing” Kagome lattice is uncovered. Characterization via temperature‐dependent ARPES confirms its semiconducting nature with a flat band structure. Experimental results from bias and gate voltage dependent transport measurements on thin film Nb3I8 transistor devices demonstrate ambipolar conductance. Notably, these findings reveal a broadband photoresponse in the device, spanning from visible to near infrared wavelengths (532 −1100 nm), with the photocurrent showing gate‐dependent characteristics that mirror the dark current's ambipolar nature. This observation marks the first instance of ambipolar transport in a Kagome semiconductor, opening up exciting new avenues for electronic and optoelectronic device development.

Plasma Etch of IGZO Thin Film and IGZO/SiO2 Interface Diffusion in Inductively Coupled CH4/Ar Plasmas

ABSTRACTIn this work, the etching characteristics of InGaZnO4 (IGZO) thin films were systemically investigated in inductively coupled CH4/Ar plasmas with various gas ratios, bias voltages, and surface temperatures. The ion flux in the CH4/Ar plasmas was analyzed using bias power and voltage, whereas the relative densities of CH and H radicals were quantified through optical actinometry. The change in CH3 radical density was also estimated based on plasma kinetics analysis. The correlations between the plasma properties and IGZO etch rate were investigated. In CH4/Ar plasmas with CH4 ratios below 80%, the IGZO etch rate increases with a higher CH4 proportion, aligning with the ascending trend of CH3 radical density, which suggests that CH3 radical density acts as a limiting factor (radical‐limited regime). However, the IGZO etch rate decreases when the CH4 ratio exceeds 80%, corresponding to the reduction in ion flux, which indicates that ion flux becomes a limiting factor in this ion‐limited regime. The IGZO etch rate shows a linear relationship with bias voltage and follows the Arrhenius equation with varying surface temperature in plasmas without bias voltage. A spontaneous etch model was proposed based on these relationships. In this model, the IGZO etch rate depends on CH3 radical density and IGZO surface reactivity, where ion bombardment contributes more significantly to surface reactivity than high surface temperature. IGZO thin film was deposited on SiO2 during the fabrication of a 3D stacked ferroelectric field‐effect transistor (FeFET) memory device. The interaction between IGZO and SiO2 during CH4/Ar plasma processing was investigated using time‐of‐flight secondary ion mass spectrometry. The efficacy of removing IGZO atoms that had diffused into the SiO2 network was enhanced when subjected to plasma with a bias voltage, compared to the process without a bias voltage. However, exposure to CH4/Ar plasma resulted in a deeper diffusion of IGZO atoms into the SiO2 network, primarily attributed to ion bombardment rather than elevated surface temperature. A significant improvement in surface smoothness was achieved after IGZO and SiO2 etch by introducing BCl3 into the SiO2 etching chemistry.

A high-performance selenium nanoflake-based avalanche photodetector

Photodetectors are now indispensable in our daily lives, and there is a pressing need to explore new materials and mechanisms that can push the boundaries of device performance. Two-dimensional (2D) van der Waals (vdW) semiconductors have emerged recently as a promising material platform with exceptional optoelectronic properties, making them particularly suitable for high-performance photodetectors. However, photoinduced carrier generation in conventional 2D vdW photodetectors are usually limited, and new mechanisms need to be introduced to enhance device performance. Herein, we report a high-performance avalanche photodetector based on selenium (Se) nanoflakes. Our device achieves a high photoresponsivity (R) and specific detectivity (D*) of 361 A·W−1 and 2.4 × 1012 Jones, respectively. These figures of merit are two orders of magnitude higher than that in conventional Se photoconductive photodetectors. As a large bandgap vdW semiconductor, the Se channel allows the application of an extremely large bias voltage across it, and the resulting high electric field leads to the avalanche multiplication of carriers, which lays the groundwork for the improved device performance.

One-Step Magneton Sputtering of Crystalline Cu-Doped TiO2 Coatings: Characterization and Antibacterial Activity

Early biofilm formation could be inhibited by applying a thin biocompatible copper coating to reduce periprosthetic infections. In this study, we deposited crystalline Cu-doped TiO2 films using one-step DC magnetron sputtering in an oxygen atmosphere on a biased Ti6Al4V alloy without external heating. The bias voltage varied from −25 V to −100 V, and the resultant substrate temperature was measured. The deposited coatings were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness, scratch and hydrophilicity tests, potentiodynamic polarization measurements, and antibacterial assays against S. aureus and E. coli. The findings demonstrated that when a higher negative bias is applied, the substrate temperature drops, and the anatase to rutile transformation is initiated without indicating obvious Cu-containing phases. The SEM images of the films showed spherical agglomerates with homogeneously distributed Cu with decreasing Cu content as the bias value increased. Higher bias results in the grain refinement of the thinning coatings with more lattice microstrain and more defects, together with an increase in water contact angles and hardness values. Samples biased at −75 V exhibited the highest adhesive strength between coatings and substrate, whereas the specimen biased at −50 V demonstrated higher corrosion resistance. Cu-containing TiO2 coatings with pure anatase phase composition and Cu concentrations of 2.62 wt.% demonstrated excellent bactericidal activity against both S. aureus and E. coli. The layers containing 2.34 wt.% Cu exhibited very good antibacterial properties against S. aureus, only. According to these findings, the produced copper-doped TiO2 coatings have high bactericidal qualities in vitro and may be used to prepare orthopaedic and dental implants in the future.

Performance of 3D trench silicon pixel sensors irradiated up to [formula omitted]

Tracking particles at extreme fluences requires the accurate measurement of the charged particle timing at the pixel level in order to cope with the increased occupancy of HL-LHC experiments. Maintaining this precision throughout the operational life of the detector is crucial. This work demonstrates that the 55×55μm2 wide 150μm thick 3D trench-type pixels, developed by the TimeSPOT Collaboration, maintain the performance of non-irradiated sensors even after exposure to fluences as high as 1⋅10171MeVneqcm−2. The preliminary results of a beam test characterization using minimum ionizing particles at the SPS North area beam facility reveal that the charge collection and the time resolution of the irradiated sensors are comparable to those of non-irradiated ones, by increasing the operational bias voltage. A minor reduction in detection efficiency, approximately 4%, is observed post-irradiation. Currently, 3D trench-type pixels are among the fastest pixel detectors available for tracking charged particles and hold significant promise for future tracking system upgrades. This preliminary evaluation suggests their suitability for use in even harsher radiation environments than High Luminosity Large Hadron Collider (HL-LHC) such as future experiments at the Future Circular Hadron Collider (FCC-hh).

Multifunctional electrically switchable metalens

Here, we propose three all-solid-state, electrically switchable, transmissive, and multifunctional metalens arrays comprising tunable metal-oxide material BaTiO3 (BTO) nanopillars with different structural parameters. To produce the required phase profile for each metalens, the rectangular nanopillars, as the unit cell of the BTO structure, are developed to support arbitrary combinations of two independent phase shifts (0−2π) with bias voltage states of 0 V and 60 V, at first. Second, the structure parameters of different functional metalens arrays are generated efficiently and accurately based on the dual-phase modulation characteristics of a single structure. Finally, we use the finite-difference time-domain method to simulate the three kinds of switchable metalenses. The results show that the three metalenses can realize the function of adjustable focus position, switchable beam focusing and beam deflection, and switchable beam focusing and beam splitting.

Bias-controlled modulation for monolithic III-nitride optoelectronic integration.

III-nitride multi-quantum well (MQW) diodes can modulate the light emitted by another diode with the same MQW structure by varying the bias voltage owing to the spectral overlap between the electroluminescence spectrum and spectral responsivity curve of the MQW diodes. Here, we investigate bias-controlled modulation by monolithically integrating an optical transmitter, waveguide, electro-absorption modulator (EAM), and slot grating coupler on a silicon-based III-nitride platform using compatible fabrication processes. The modulated light is coupled into a fiber, which is direct to a photodiode for characterization. The bandwidths of forward-biased emission modulation and reverse-biased absorption modulation are of the same order of magnitude, with the latter exhibiting significant performance improvements. In addition, real-time video signal transmission was achieved using an EAM, which provides a meaningful reference for modulation applications of silicon-based GaN optoelectronic integrated systems.

High performance Au/mix-phase MgZnO/Ga-doped ZnO/In heterojunction solar-blind UV detector with small work voltage

High performance UVC (220 nm–280 nm) detectors with low work voltage is key problem in wide application of UVC optoelectronic device. Here, Au/MgZnO/Ga-doped ZnO/In heterojunction detector is made with both high UVC sensitivity mix-phase MgZnO and high carrier density Ga-doped ZnO conductive layers. The heterostructure detector possess relative high response(0.36A/W)at 254 nm deep UV light without bias voltage. The avalanche breakdown phenomenon within the heterojunction detector, introduced high deep UV response (1390.3 A/W at 3.3 μW/cm2 230 nm) of the Au/MgZnO/Ga-doped ZnO/In heterojunction detector under 5 V bias voltage. The high response of Au/MgZnO/Ga-doped ZnO/In heterojunction detector under low work voltage, is not only much higher than MSM structure MgZnO detector under bias voltage over 25 V, but also higher than reported deep UV detector under small bias voltage. In addition, because of different internal breakdown mechanism, the peak response position of the Au/MgZnO/Ga-doped ZnO/In heterojunction detector is located at shorter wavelength position compared with MSM structure MgZnO detector. Therefore, Au/MgZnO/Ga-doped ZnO/In heterojunction detector is an ideal device structure in low voltage driven detector with relative high response at short wavelength UV light.

Influence of bias voltage and oxygen addition on the discharge aspects of a diffuse argon plume in an atmospheric pressure plasma jet

A remote plasma, also referred to as a plasma plume (diffuse or filamentary), is normally formed downstream of an atmospheric pressure plasma jet. In this study, a diffuse plume is formed by increasing the bias voltage (U b) applied to the downstream electrode of an argon plasma jet excited by a negatively pulsed voltage. The results indicate that the plume is filamentary when U b is low, which transits to the diffuse plume with increasing U b. The discharge initiated at the rising edge of the pulsed voltage is attributed to the diffuse plume, while that at the falling edge contributes to the filament in the plume. For the diffuse plume, the discharge intensity decreases with the increasing oxygen content (C o). Fast photography reveals that the diffuse plume results from a negative streamer, which has a dark region near the nozzle with C o = 0%. However, the dark region is absent with C o = 0.5%. From the optical emission spectrum, the electron density, electron excitation temperature, gas temperature, and oxygen atom concentration are investigated.