Bias Voltage Research Articles

The Photothermal Synergistic Mechanism of Rock Varnish Photoconductance Under Laser Irradiation.

Rock varnishes, complex structures formed by long-term deposition on rocks, exhibit unique light absorption characteristics and are widely distributed across arid environments on Earth's surface. The varnishes possess the ability to absorb and convert photons from solar radiation into electrons, which represents a newly discovered fundamental energy form in nature, with further elucidation required regarding the underlying mechanism of how semiconductor minerals respond to light radiation. The regulations governing the photoconductive responses of samples from the Alashan region in Gobi, China, and the mechanisms exhibited by rock rock varnishes under various bias voltages and irradiation wavelengths (532 nm, 808 nm, and 1064 nm) were studied. The photoconductivity response is positively correlated with the applied external bias, and the response caused by shorter wavelengths is larger. The synergistic effect was quantitatively assessed by monitoring and fitting the correlation between photoconductivity, temperature, and time during laser irradiation. As an effective method to study the fundamental physical properties of semiconductor minerals, the photoconductivity testing will help to establish a fundamental framework for investigating the intrinsic physical characteristics of natural rock varnishes.

Characteristics of 1D CRL position sensitive SiPM and its performance in acquiring 2D radiation imaging

The characteristics of one-dimensional (1D) position sensitive SiPM with an intrinsic continuous cap resistive layer (CRL) and its performance in acquiring two-dimensional (2D) radiation imaging are reported in this paper. The device, with an active size of 6.14 mm × 6.14 mm, demonstrated the position measurement error of 32.0 ± 24.0 µm without correction, which accounted for 0.5% of the length of the SiPM at a mean response photoelectron number around 230 and the reverse bias voltage of 40 V. Under the same condition, it demonstrated a position resolution of 128.7 ± 20.1 µm and a time resolution of 96.0 ± 33.2 ps. A 3D scintillation detector for acquiring 2D radiation imaging with depth information of interaction (DOI) is proposed by implementing two 1D CRL SiPMs in a perpendicular orientation on the two ends of a scintillator. Using this configuration, the 2D imaging of a pixelated 10 × 10 lutetium yttrium orthosilicate (LYSO) array, with each element having a volume of 0.52 mm × 0.52 mm × 20 mm, was successfully resolved by utilizing the natural radioactive radiation of lutetium element in LYSO without distortions at the edges and corners.

Self‐Powered High‐Responsivity Self‐Supporting SiC/SnO2 Nanoarray Photoelectrochemical Ultraviolet Photodetector: Toward All‐Scenario Harsh Underwater Applications

AbstractBattery‐free photodetection is necessary for underwater optical communication, which poses extremely high requirements in terms of the self‐powering capability of photodetectors (PDs) and their ability to operate in harsh liquid environments. Emerging photoelectrochemical (PEC) PDs are appealing owing to their inherent aqueous operation behaviors with highly tunable photoresponses. Herein, a novel self‐powered PEC ultraviolet (UV) PD applicable to all‐scenario harsh underwater environments, including seawater at different latitudes and solutions with different pH values and temperatures, is demonstrated based on integrated self‐supporting SiC/SnO2 heterojunction nanoarrays. The SiC/SnO2 heterojunction nanoarrays are achieved by utilizing the anodic oxidation and chemical bath deposition. The SiC/SnO2 PEC PD demonstrates excellent photodetection performance with rapid rise/decay times (τr/τd, 30/120 ms), high responsivity (Rλ, 1.97 A W−1), remarkable detectivity (D*, 1.98 × 1011 Jones), and large external quantum efficiency (EQE, 65.5%) in seawater under 375 nm UV light illumination with zero bias voltage. Moreover, the PEC PD delivers a high photoresponse and excellent aging stability in different latitudes of the world's oceans. The photodetection capability is robust even under harsh conditions, such as strongly acidic and alkaline liquid conditions, and at high temperatures. The developed device is a new type of photodetection device for future all‐scenario underwater optical communication.

Full-space programmable circularly polarized metasurface for space-multiplexing wireless communications

The programmable metasurface has been proved to be an effective tool to dynamically tailor electromagnetic (EM) waves. However, how to achieve real-time and independent controls of circularly polarized (CP) waves in the transmission and reflection spaces is still a challenge. To address this problem, we propose a full-space programmable CP metasurface, which can independently manipulate the CP waves in transmission and reflection spaces in real time by controlling the bias voltage. The polarization states of reflected and transmitted CP waves can be independently customized through elaborate meta-atom design. As a proof of concept, we designed, fabricated, and measured a full-space programmable CP metasurface that can realize copolarized reflection for right-handed circularly polarized (RCP) waves and cross-polarized transmission for left-handed circularly polarized (LCP) waves. Simulated and measured results verify that the wavefronts of reflected and transmitted CP waves can be independently manipulated in real time by reprogramming the reflection and transmission phase coding sequences. Based on the full-space programmable CP metasurface, a space-multiplexing wireless communication scheme is established, successfully delivering two different images along preset reflection and transmission channels.

Dual-functional GaN photodiode for photodetection and neuromorphic computing with high specific detectivity.

The discrepancy in the photoresponse characteristics between photodetectors (PDs) and photosynapses is posing a challenge for integrating the two functions into a single device. In this work, a photodetector integrated with neuromorphic capabilities is demonstrated. Under the joint action of the photovoltaic effect and photoconductive effect, the proposed device can switch between the photodetector and photosynapse by simply altering the polarity of bias voltage. Under a reverse or zero bias voltage, the device operates as a photodetector with low dark current and high specific detectivity. On the other hand, when a positive bias voltage is applied, the device showcases synaptic functionalities such as excitatory postsynaptic current, paired-pulse facilitation, and transition from short-term memory to long-term memory. The dual-functional devices hold promise for weak light detection and neuromorphic computing in complex environments.

Bias voltage driven tunneling magnetoresistance polarity reversal in 2D stripy antiferromagnet CrOCl

Atomically thin materials with coupled magnetic and electric polarization are critical for developing energy-efficient and high-density spintronic devices, yet they remain scarce due to often conflicting requirements of stabilizing both magnetic and electric orders. The recent discovery of the magnetoelectric effect in the 2D stripy antiferromagnet CrOCl highlights this semiconductor as a promising platform to explore electric field effects on magnetoresistance. In this study, we systematically investigate the magnetoresistance in tunneling junctions of bilayer and monolayer CrOCl. We observe that the transition from antiferromagnetic to ferrimagnetic phases in both cases induces a positive magnetoresistance at low bias voltages, which reverses to a negative value at higher bias voltages. This polarity reversal is attributed to the additional electric dipoles present in the antiferromagnetic state, as supported by our theoretical calculations. These findings suggest a pathway for the electric control of spintronic devices and underscore the potential of 2D magnets like CrOCl in advancing energy-efficient spintronic applications.

Ultra-tunable dielectric capacitors enhanced by coupling ferroelectric field effect and semiconductor field effect

Tunable ferroelectric film capacitors play an important role in tunable microwave devices and filter systems due to their high dielectric constant, low loss, and high dielectric tunability. However, there is a trade-off between low loss and high tunability, which limits further enhancement of dielectric performance. Here, we propose an ultra-tunable capacitor by designing a Ba0.7Sr0.3TiO3 (BST)–semiconductor heterostructure. In the tunable capacitor, the BST film is fabricated directly on p-type silicon substrates by magnetron sputtering, and a heterostructure layer is constructed. The coupling effects between the semiconductor depletion layer capacitance and the BST capacitance produce higher capacitance tunability than a traditional sandwich BST capacitor. Based on the coupling effects, a metal–ferroelectric–semiconductor–ferroelectric–metal capacitor is developed, which enables the capacitor to operate under both negative and positive biases, which has an n value (n=Cmax/Cmin) of 90 with 40 V bias voltage and a maximum Q of 1000. The results offer a potential approach to designing high-performance tunable capacitors on silicon with BST film that could build tunable filters for information processing in communication systems.

Optical response of WSe2-based vertical tunneling junction

Layered materials have attracted significant interest because of their unique properties. Van der Waals heterostructures based on transition-metal dichalcogenides have been extensively studied because of potential optoelectronic applications. We investigate the optical response of a light-emitting tunneling structure based on a WSe2 monolayer as an active emission material using the photoluminescence (PL) and electroluminescence (EL) experiments performed at low temperature of 5 K. We found that the application of the bias voltage allows us to change both a sign and a value of free carriers concentrations. Consequently, we address the several excitonic complexes emerging in PL spectra under applied bias voltage. The EL signal was also detected and ascribed to the emission in a high-carrier-concentration regime. The results show that the excitation mechanisms in the PL and EL are different, resulting in various emissions in both types of experimental techniques.

Enhanced Surface Mechanical and Tribological Properties of H13 Die Steel with TiAlSiN Coating Deposited by HiPIMS

TiAlSiN is a potential protection coating for die steel to improve the surface hardness, anti-wear performance and suitability. In the present study, TiAlSiN is deposited on H13 die steel by high power impulse magnetron sputtering and the effects of bias voltage, deposition temperature, and film thickness on the performance of coatings are studied. The microstructure, mechanical and tribological properties of coatings are analyzed by energy dispersive spectrometer, X-ray diffraction, nanoindentation, friction and wear tests. The results show that with the changes of sputtering parameters, the content of Ti, Al, Si, and N fluctuates slightly. With the increase of bias voltage, deposition temperature and film thickness, the diffraction peaks of Ti3Al2N2 phase become wider. Higher bias voltage, deposition temperature, and film thickness are beneficial for obtaining coatings with high hardness, and strong wear resistance. By observing the surface morphology of coatings after grinding with Si3N4 balls, it was found that the wear mechanism of coatings contains abrasive wear, fatigue wear, and oxidative wear.

Ultra-weak photon emission from DNA

It is conventionally believed that macromolecules found in living cells, including DNA, RNA, and proteins, do not exhibit inherent light emission. However, recent studies have challenged this concept by demonstrating spontaneous light emission from nucleic acids under certain conditions and physiological temperatures. By noninvasive monitoring of barley genomic DNA and advanced statistical physics analyses, temperature-induced dynamic entropy fluctuations and fractal dimension oscillations were identified at a key organizational threshold. The study revealed evidence for non-equilibrium phase transitions, a noticeable photovoltaic current jump at zero bias voltage, and a proportional increase (scaling) of the photoinduced current corresponding to increasing amounts of DNA. In addition, we estimated DNA’s energy production rate at criticality and introduced an interferometer using coherent light emissions from the DNA-water interface. These findings suggest that DNA is a major source of ultraweak photon emission in biological systems.

Cost-effective self-powered heterostructure π-SnS/Si photodetector with superior sensitivity for near-infrared light

Photodetectors generally require external power supplies to facilitate the separation of charge carriers and the generation of photocurrents. This significantly enlarges the device's dimensions and weight, limiting its applicability in real-time medical therapy monitoring and wireless environmental sensing. To address this limitation, extensive research focuses on developing self-powered photodetectors that operate autonomously without external power sources. The heterojunction structure photodetector, characterized by a sufficient built-in potential, facilitates the separation of photo charge carriers and the generation of photocurrent, leading to self-powered photodetectors. In this study, a novel and straightforward heterostructure photodetector was developed using a tin monosulfide (π-SnS) film and silicon (Si). This device exhibited a barrier height of 0.82 eV, which effectively separates photogenerated carriers and results in a highly sensitive (5.7 × 104) self-powered photodiode for near-infrared light. The SnS film was deposited onto an n-type Si wafer substrate using a simple and cost-effective chemical bath deposition method. The photoresponse characteristics were controlled and tuned by adjusting the operating bias voltage and illumination power density. At a bias voltage of 5 V, the photodiode demonstrated high responsivity (3863 mA/W) and detectivity (7.2 × 1011 Jones). The π-SnS/Si self-powered heterojunction photodetector, with its superior sensitivity, holds promise for advancing the technological implementation of optoelectronic devices.

Residual Stress Analysis in High‐Speed Physical Vapor Deposition Coatings

Several studies focus on impact of residual stress in coatings, predominantly those synthesized by conventional physical vapor deposition (PVD) techniques like arc PVD and magnetron sputtering. High‐speed PVD (HS‐PVD) is based on hollow cathode gas flow sputtering, enabling the deposition of thick coatings s > 20 μm in contrast to the mentioned processes, where coating thickness is limited due to compressive residual stresses. Therefore, the effect of residual stresses on HS‐PVD coatings and adhesion was analyzed for the first time. The aim is to evaluate the influence of diverse substrate materials, different coating systems, and process parameters on the residual stress states in HS‐PVD coatings. Different coating systems like AlCrN and AlCrO are deposited at different reactive gas flows, coating times, and bias voltages. The residual stress of oxide coatings, deposited on cemented carbide and steel X40CrMoV5–1, is analyzed using X‐ray diffraction (XRD) and the sin2ψ method. For AlCrN coatings, in addition to the XRD method, the residual stresses are measured by focused ion‐beam‐digital image correlation ring‐core method to investigate different measuring methods. Both coating systems show higher adhesion strength with increasing thickness. Lower residual compressive stresses are unexpectedly observed at higher coating thickness using both analysis methods.

Characterisation of 3D trench silicon pixel sensors irradiated at 1⋅1017 1 MeV neqcm-2

The 3D trench silicon pixel sensors developed by the TimeSPOT collaboration have demonstrated exceptional performance, even after exposure to extreme radiation fluences up to 1⋅1017 1 MeV neq/cm2. This study assesses the radiation tolerance of these sensors using minimum ionizing particles during a beam test campaign. The results indicate that while radiation damage reduces charge collection efficiency and overall detection efficiency, these losses can be mitigated to levels comparable to non-irradiated sensors by increasing the reverse bias voltage. Charge multiplication was observed and characterised for the first time in 3D trench sensors, revealing a distinct operating regime post-irradiation achievable at bias voltages close to 300 V. Additionally, the timing performance of irradiated sensors remains comparable to their non-irradiated counterparts, underscoring their resilience to radiation damage. Currently, 3D trench silicon detectors are among the fastest and most radiation-hard pixel sensors available for vertex detectors in high-energy physics colliders. These findings highlight the potential of these sensors for new 4D tracking systems of future experiments at the Future Circular Hadron Collider (FCC-hh), advancing the capabilities of radiation-hard sensor technology.

Self-Powered Broadband Photodetection Ranging from X-ray to UV-Vis Light in a Polar Perovskite Induced by Bulk Photovoltaic Effect.

Self-powered broadband photodetection has evoked increased interest in next-generation photoelectronic devices. However, realizing self-powered broadband photodetection in a single material is still a challenge because of the harsh requirements, including powerful built-in field, excellent charge transport behaviors, as well as the broad absorption. Herein, we first realize broadband photodetection in the range from X-ray to UV-vis light in a polar two-dimensional perovskite (2-FBA)2MAPb2I7 (2-FBA = 2-fluorobenzylamine, MA = methylamine) by incorporating an aromatic spacer into a three-dimensional prototype. As a result, (2-FBA)2MAPb2I7 exhibited a superior response to UV-vis light (377 to 637 nm) without voltage bias. Specifically, a high switching ratio of 1.05 × 104, an outstanding responsivity (R) of 1420 mA W-1, and detectivity (D*) of 1.59 × 1013 Jones were achieved under light illumination at 520 nm. Moreover, (2-FBA)2MAPb2I7 achieved a high sensitivity of 46.4 μC Gy-1 cm-2 without voltage bias, two times higher than that of a commercial α-Se film detector (20 μC Gy-1 cm-2). The sensitivity can be further improved to 3316 μC Gy-1 cm-2 at a 50 V bias. These results give insight into the design of 2D perovskites for self-powered broadband photodetection.

Features of the Influence of the Arrangement of Parts in the Chamber of Installation During Vacuum Arc Deposition on the Properties of Coatings

The effect of the spatial arrangement in the physical vapor deposition (PVD) chamber on the composition and properties of coatings is considered using the example of the deposition of the (Ti,Al)N coating. The proposed method is one of the ways (along with varying the arc current of the cathodes and the bias voltage, as well as using alloy cathodes) to change the ratio of elements in the coating, and achieves this across a wide range of values. The three samples were located, respectively, opposite the evaporator with a titanium cathode, opposite the evaporator with an aluminum cathode and in an intermediate position between the two evaporators. The coating was deposited without rotating the turntable. The aluminum content in the coatings decreases from 94.2 at.% for the sample located directly opposite the evaporator with an Al cathode to 10.3 at.% for the sample located opposite the evaporator with a Ti cathode. In the coating deposited on the sample located opposite the aluminum cathode, the formation of a nitrided layer with a thickness of about 250 nm was observed in the substrate. The maximum hardness (32.3 ± 1.7 GPa) belongs to a coating on the sample occupying an intermediate position. The coating on the sample located opposite the aluminum cathode has a hardness of 16.7 ± 0.8 GPa. The coating hardness on the sample located opposite the titanium cathode is 28.5 ± 1.1 GPa. The best fracture strength in the scratch test was observed for the coating on the sample occupying an intermediate position. The nature of the coating fracture in the scratch test was studied. A sufficiently high-quality coating can be obtained without rotating the turntable, and the coating composition can be controlled by changing the position of the sample relative to the evaporators.

Thermoelectric cooling of a finite reservoir coupled to a quantum dot

We investigate nonequilibrium transport of charge and heat through an interacting quantum dot coupled to a finite electron reservoir. Both the quantum dot and the finite reservoir are coupled to conventional electric contacts, i.e., infinite electron reservoirs, between which a bias voltage can be applied. We develop a phenomenological description of the system, combining a rate equation for transport through the quantum dot with standard expressions for bulk transport between the finite and infinite reservoirs. The finite reservoir is assumed to be in a quasiequilibrium state with a time-dependent chemical potential and temperature which we solve for self-consistently. We show that the finite reservoir can have a large impact on the stationary state transport properties, including a shift and broadening of the Coulomb diamond edges. We also demonstrate that there is a region around the conductance lines where a heat current flows out of the finite reservoir. Our results reveal the dependence of the temperature that can be reached by this thermoelectric cooling on the system parameters, in particular the coupling between the finite and infinite reservoirs and additional heat currents induced by electron-phonon couplings, and can thus serve as a guide for experiments on quantum-dot-enabled thermoelectric cooling of finite electron reservoirs. Finally, we study the full dynamics of the system, with a particular focus on the timescales involved in the thermoelectric cooling. Published by the American Physical Society 2024

Bromine‐Substituted Cation Anchoring to Suppress Ion Migration in Alternating Cations Intercalation‐Type Perovskite for Stable X‐Ray Detection

Metal halide perovskites have emerged as excellent direct X‐ray detection materials owing to their large mobility‐lifetime product, strong radiation absorption, and low‐cost preparation. However, it is still a challenge to achieve stable X‐ray detection due to the limitations associated with severe ion migration under high voltage bias. Herein, based on a bromine substitution strategy to suppress ion migration, a 2D alternating cations intercalation‐type (ACI) perovskite, (R‐MPA)(BrEA)PbBr4 (1, R‐MPA = methylphenethylamm‐onium; BrEA = 2‐bromoethylamine) is reported to achieve X‐ray detection. Specifically, introducing Br atom forms additional intermolecular interactions (i.e., Br···π) and enhances hydrogen bonding interactions, greatly improving the structure stability. Based on this enhanced interaction, 1 presents a higher activation energy of ion migration (1.05 eV) than that of (R‐MPA)EAPbBr4 resulting in a lower dark current drift of 9.17 × 10−8 nA cm−1 s−1 V−1, revealing that suppression of ion migration. Consequently, the 1‐based detector shows a high sensitivity of 2653.7 μC Gy−1 cm−2 and, most importantly, outstanding operational and environmental stability, maintaining ≈91% of its initial sensitivity at 50 V bias after 90 days in the air. This work demonstrates an efficient strategy for introducing halogen interactions via ACI to suppress ion migration for stable X‐ray detection.

Dark Current Suppression in Two‐dimensional Histamine Lead Iodine Perovskite Single Crystal for X‐ray Detection and Imaging

AbstractLead halide perovskites have emerged as attractive X‐ray detector materials, owing to properties such as strong X‐ray stopping power, excellent carrier transport, and high sensitivity. Additionally, they can be easily prepared by using solution‐based synthesis approaches. However, traditional 3D (three‐dimensional) perovskites X‐ray detectors have shown limited application due to high dark currents generated under bias voltage as a result of strong ion migration. In this work, an X‐ray detector with a vertical structure device is demonstrated using 2D (two‐dimensional) histamine lead halide perovskite single crystal HAPbI4 (HPI, HA = histamine). Due to the dielectric screening effect of diamine and the vertical structure of the HPI device, the fabricated detector shows a sensitivity of 7737 µC Gyair−1 cm−2 under a bias voltage of 30 V. Furthermore, the detector shows a sensitivity of 293 µC Gyair−1 cm−2 and detection limit of 51.38 nGyair s−1 without bias voltage, wherein the dark current is almost completely suppressed. All of these properties indicate the X‐ray detection device is a promising candidate for next‐generation optoelectronic applications.

Performance and Characterization of Additively Manufactured BST Varactor Enhanced by Photonic Thermal Processing

The demand for reconfigurable devices for emerging RF and microwave applications has been growing in recent years, with additive manufacturing and photonic thermal treatment presenting new possibilities to supplement conventional fabrication processes to meet this demand. In this paper, we present the realization and analysis of barium–strontium–titanate-(Ba0.5Sr0.5TiO3)-based ferroelectric variable capacitors (varactors), which are additively deposited on top of conventionally fabricated interdigitated capacitors and enhanced by photonic thermal processing. The ferroelectric solution with suspended BST nanoparticles is deposited on the device using an ambient spray pyrolysis method and is sintered at low temperatures using photonic thermal processing by leveraging the high surface-to-volume ratio of the BST nanoparticles. The deposited film is qualitatively characterized using SEM imaging and XRD measurements, while the varactor devices are quantitatively characterized by using high-frequency RF measurements from 300 MHz to 10 GHz under an applied DC bias voltage ranging from 0 V to 50 V. We observe a maximum tunability of 60.6% at 1 GHz under an applied electric field of 25 kV/mm (25 V/μm). These results show promise for the implementation of photonic thermal processing and additive manufacturing as a means to integrate reconfigurable ferroelectric varactors in flexible electronics or tightly packaged on-chip applications, where a limited thermal budget hinders the conventional thermal processing.

High-performance single SiC nanocable-based plasmonic photodetectors for ultraviolet communication systems

Silicon carbide (SiC) nanowires are the most promising candidate for developing high-performance single-nanowire-based UV photodetector (PD) with outstanding photoelectronic properties and low power consumption. However, SiC single-nanowire-based UV PDs commonly suffer from very low light current on the order of pA or nA, requiring precision equipment or an extra current amplification circuit, which greatly limit their practical application. To overcome this bottleneck, novel SiC single nanocable-based plasmonic PDs with the light current on the order of mA were successfully developed with the features of improving light absorption and reducing the dark current. The SiC/SiO2@Ag nanocables consisting of SiC nanowire core and uniform SiO2 shell encrusted with scattered and isolated Ag nanoparticles (NPs) were fabricated by a simple, low-cost, and space-confined vacuum-heating strategy using ultralong SiC nanowires and silver nitrate precursor followed by the annealing process. In such architecture, the in situ resulting SiO2 shell can effectively passivate the surface defects of the SiC nanowire core, restrain the photo-excited carrier's losses, and effectively block the hot electron injection, leading to a great reduction in the dark current and enhancement in the light current. The encrusted Ag NPs on the nanocable surface exhibited a strong LSPR effect with significantly increased optical absorption. Benefiting from the synergistic effect of SiO2 passivation and Ag nanoparticle LSPR effect, the device current increased dramatically by several orders of magnitude to reach 0.37 mA at a bias voltage of 3 V. Moreover, the developed SiC/SiO2@Ag PDs had faster response speed (0.27 s), lower dark current at the nA level, and high stability, which can be competent for the development of real-time, accurate, and cost-effective communication systems and flame detection with impressive switching ratio as high as 66012.