Search

The high-performance determination of heavy metal ions (Cd2+) in water sources is significant for the protection of public health and safety. We have developed a novel sensor of nanograss boron and nitrogen co-doped diamond (NGBND) to detect Cd2+ using a simple method without any masks or reactive ion etching. The NGBND electrode is constructed based on the co-doped diamond growth mode and the removal of the non-diamond carbon (NDC) from the NGBND/NDC composite. Both the enlarged surface area and enhanced electrochemical performance of the NGBND film are achievable. Scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse anodic stripping voltammetry (DPASV) were used to characterize the NGBND electrodes. Furthermore, we used a finite element numerical method to research the current density near the tip of NGBND. The NGBND sensor exhibits significant advantages for detecting trace Cd2+ via DPASV. A broad linear range of 1 to 100 μg L−1 with a low detection limit of 0.28 μg L−1 was achieved. The successful application of this Cd2+ sensor indicates considerable promise for the sensitive detection of heavy metal ions. [ABSTRACT FROM AUTHOR]

Nano-needle boron-doped diamond (NNBDD) films increase their performance when used as electrodes in the determination of Pb2+. We develop a simple and economical route to produce NNBDD based on the investigation of the diamond growth mode and the ratio of diamond to non-diamond carbon without involving any templates. An enhancement in surface area is achievable for NNBDD film. The NNBDD electrodes are characterized through scanning electron microscopy, Raman spectroscopy, X-ray diffraction, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse anodic stripping voltammetry (DPASV). Furthermore, we use a finite-element numerical method to research the prospects of tip-enhanced electric fields for sensitive detection at low Pb2+ concentrations. The NNBDD exhibits significant advantages and great electrical conductivity and is applied to detect trace Pb2+ through DPASV. Under pre-deposition accumulation conditions, a wide linear range from 1 to 80 µgL−1 is achieved. A superior detection limit of 0.32 µgL−1 is achieved for Pb2+, which indicates great potential for the sensitive detection of heavy metal ions. [ABSTRACT FROM AUTHOR]

Identifying unbalanced phase currents is crucial for control and fault alarm rates in power grids, especially in urban distribution networks. The zero-sequence current transformer, specifically designed for measuring unbalanced phase currents, offers advantages in measurement range, identity, and size, compared to using three separate current transformers. However, it cannot provide detailed information on the unbalance status beyond the total zero-sequence current. We present a novel method for identifying unbalanced phase currents based on phase difference detection using magnetic sensors. Our approach relies on analyzing phase difference data from two orthogonal magnetic field components generated by three-phase currents, as opposed to the amplitude data used in previous methods. This enables the differentiation of unbalance types (amplitude unbalance and phase unbalance) through specific criteria and allows for the simultaneous selection of an unbalanced phase current in the three-phase currents. In this method, the amplitude measurement range of magnetic sensors is no longer a critical factor, allowing for an easily attainable wide identification range for current line loads. This approach offers a new avenue for unbalanced phase current identification in power systems. [ABSTRACT FROM AUTHOR]

Excellent high-temperature performance (298–523 K) of the 4H-SiC n-p-n bipolar phototransistor detector (PTD) was explored. It was fabricated using the 4H-SiC epitaxial wafer grown by high-temperature chemical vapor deposition (HTCVD). The static and dynamic properties of the device were tested and analyzed. The results show that the device still has an optical gain of up to 103, a wide linear response range, and good repeatability at the high temperatures up to 523 K under a 3-V bias with a wavelength of 360 nm. The temperature coefficient of the optical gain is extracted, the value of which is 1.02/K. Although the response time of the device increases with the temperature, the increased percentage in responsivity is significantly greater than that of the response time. The results provide an important experimental reference for the application of high-temperature detection and suggest that the PTD has the potential to be used in ultraviolet (UV) detecting systems at high temperatures. [ABSTRACT FROM AUTHOR]

In this work, high-performance GaN vertical Schottky barrier diodes (SBDs) are successfully fabricated on the GaN-on-GaN substrate by using the self-alignment trench structure and argon (Ar) ion implantation. The fabricated diodes achieve a high current ON/ OFF ratio of 108 and high breakdown voltage (BV) of 656 V due to the reduced surface electric field effect. Besides, the temperature-dependent reverse leakage characteristics show that two Poole–Frenkel emission (PFE) processes dominate the carrier transport. This work shows great potential of the self-alignment trench structure in fabricating GaN vertical SBDs to improve the BV with simply fabrication process. [ABSTRACT FROM AUTHOR]

In this article, we report the first experimental results of a novel 4H-silicon carbide (SiC) p-i-n photodetector based on a vertical nanocone array (NCA). It is fabricated by electron beam lithography and inductively coupled plasma (ICP) etching technology. The performance of static and dynamic behavior was studied systematically. It shows the responsivity of ~41.9 mA/W under 360 nm at a bias voltage of −0.5 V and has a linear response to the ultraviolet (UV) light in a wide light intensity range of 0.1–104 mW/cm2. The response time decreased as the light intensity rose from 3 mW/cm2 to 5 W/cm2 and then leveled off at higher light intensity (>100 mW/cm2), which is about 0.25 ms. The photodetector −3-dB cutoff is ~3400 Hz at $\boldsymbol {\lambda } = 360$ nm and light intensity = 100 mW/cm2. Besides, the detector can respond to the UV light from 260 to 360 nm and the peak responsivity is ~78 mA/W at 320 nm. The analysis results have reference values for the development of an innovative 4H-SiC UV photodetector to some extent. [ABSTRACT FROM AUTHOR]

A two-terminal 4H-SiC n-p-n bipolar phototransistor detector (PTD) with high gain is demonstrated. It was fabricated using the 4H-SiC epitaxial wafer grown by high-temperature chemical vapor deposition. The PTD shows a large photocurrent and responsivity enhancement over the conventional 4H-SiC p-i-n photodetector (PD). These enhancement effects are owing to the internal gain of the bipolar transistor. The detector shows a high optical gain of ~ 1450 at 360 nm and has a linear response to the ultraviolet (UV) light in the wide light intensity range of 0.7– 700 μW/cm2 at a low operating voltage of 3 V. The PTD can respond to the UV light from 220 to 340 nm and the peak responsivity is ~ 125A/W at 275 nm. This work is significant for developing high-performance SiC-based bipolar phototransistors. [ABSTRACT FROM AUTHOR]

A novel post-oxidation annealing (POA) process with supercritical N2O (SCN2O) fluid is reported to be highly effective in improving the interface properties of the SiO2/4H–silicon carbide (SiC) (0001) systems. After SCN2O POA, the interface state density reduces to 2.8 × 1011 eV−1cm−2, which is about 3.5 times lower than that after a traditional high-temperature N2O POA process. Meanwhile, the highest oxide critical electric field shows an increase of 18.19% and the near-interfacial oxide traps is reduced by 69.90% compared with that after N2O POA process. The process temperature is as low as 120 °C. The significantly reduced processing temperature avoids additional defect generation while the supercritical state provides a stronger nitridation effect. SCN2O annealing is a promising candidate for POA process toward high-performance SiC power metal-oxide-semiconductor field effect transistors (MOSFETs). [ABSTRACT FROM AUTHOR]

Surface treatment is quite vital to reduce the reverse leakage current and improve the current On–Off ratio of gallium nitride (GaN) quasi-vertical Schottky barrier diode (SBD). In this work, we report a new nondestructive low temperature supercritical CO2 fluid (SCF) nitridation technology to treat the surface of GaN and substantially reduce the leakage current of GaN quasi-vertical SBD. The X-ray photoelectron spectroscopy (XPS) reveals the increased nitriding degree and oxygen doping degree in the form of GaOx after the SCF process results in the leakage performance improvement. As a result, the defects at metal/semiconductor interface are passivated. Also, because of NH-2 and OH− generated from the SCF process, the surface peak electric field of n−GaN decreases, and thus the breakdown voltage is enhanced. The reverse leakage current density is reduced by more than three orders of magnitude from 3.7 × 10−6 to 3.52 × 10−9 A/cm2 (at −3 V) and the ON-/ OFF-current ratio is improved by three orders from 8 × 107 to 5.74 × 1010. [ABSTRACT FROM AUTHOR]

Considering potential applications related to superconductivity and aerospace (typically less than 100 K), in this article, the temperature dependence of silicon carbide (SiC) power diodes is systematically characterized and analyzed over a wide temperature range of 90–478 K, especially focusing on cryogenic temperature. First, the static performance degradation mechanism of SiC diodes is established in an ultrawide temperature range, including forward/reverse I-V characteristics and junction capacitance (Cj) characteristics. Second, the reverse recovery characteristics are achieved, including peak reverse recovery current (Irm), reverse recovery charge (Qrr), and switching energy (Esw), clarifying a clearer internal relationship between reverse recovery and junction temperature. Meanwhile, the aforementioned critical parameters are further analyzed on an electrical scale with normal atmosphere temperature, including switching speed range of 62.3–2054.8 A/μs, load current range of 6–30 A, and dc voltage range of 400–1000 V. Third, based on newly proposed power loss analysis method, the continuous operation performance of SiC diodes is quantified and analyzed in actual cryogenic converters. The excellent temperature dependence indicates that SiC diodes have great superiority for extreme applications. Importantly, SiC mosfet's body diode shows the great potential to operate as a freewheeling diode in the compact converter, especially at cryogenic temperature. [ABSTRACT FROM AUTHOR]

Supercritical CO2 fluid is reported as an effective media in optimizing the SiO2/SiC interface in 4H-SiC(0001) MOS structures at a temperature as low as 150 °C. After SCCO2 treatment, the breakdown electric field is improved to 10.7 MV cm−1. The near-interfacial oxide traps is decreased from 1.62 × 1011 to 1.84 × 1010 cm−2. The interface state density at 0.2 eV below EC is reduced from 6 × 1012 to 2.5 × 1012 eV−1 cm−2. A dynamic reaction model is proposed to explain the defect passivation reaction. This technique can be effectively applied to interface semiconductor devices to enhance performance. [ABSTRACT FROM AUTHOR]

The acoustic non-linearity parameter of Rayleigh waves can be used to detect various defects (such as dislocation and micro-cracks) on material surfaces of thick-plate structures; however, it is generally low and likely to be masked by noise. Moreover, conventional methods used with non-linear Rayleigh waves exhibit a low detection efficiency. To tackle these problems, a method of exciting reversed-phase Rayleigh waves in opposite directions is proposed to measure the acoustic non-linearity parameter of materials. For that, two angle beam wedge transducers were placed at the two ends of the upper surface of a specimen to excite two Rayleigh waves of opposite phases, while a normal transducer was installed in the middle of the upper surface to receive them. By taking specimens of 0Cr17Ni4Cu4Nb martensitic stainless steel subjected to fatigue damage as an example, a finite element simulation model was established to test the proposed method of measuring the acoustic non-linearity parameter. The simulation results show that the amplitude of fundamentals is significantly reduced due to offset, while that of second harmonics greatly increases due to superposition because of the opposite phases of the excited signals, and the acoustic non-linearity parameter thus increases. The experimental research on fatigue damage specimens was carried out using this method. The test result was consistent with the simulation result. Thus, the method of exciting reversed-phase Rayleigh waves in opposite directions can remarkably increase the acoustic non-linearity parameter. Additionally, synchronous excitation with double-angle beam wedge transducers can double the detection efficiency. [ABSTRACT FROM AUTHOR]

Recent marked advances in diamond metal–oxide–semiconductor field‐effect transistors (MOSFETs) have raised the issue of gate reliability. Herein, the threshold voltage stability of MOSFETs based on hydrogen‐terminated diamond surface conductivity is examined. The electrical output characteristic curves are characterized by cyclic gate sweeping from reverse to forward gate bias (RF) and from forward to reverse gate bias (FR), respectively. The characteristics of drain current versus drain voltage are affected by the gate bias sweeping direction. Marked hysteresis is also observed in the transfer curves for the RF and FR gate sweeping. The different gate sweeping directions induce threshold voltage variation and hole mobility change. The facts that 1) no extra interface states are generated due to gate sweeping and 2) the trapped charge density depends on the gate oxide thickness, reveal that charge trapping occurs at the border of the gate oxide. [ABSTRACT FROM AUTHOR]

Abstract: The spectra of 6H–SiC crystals including micropipes have been examined for the Si face using Raman scattering. The first-order Raman features reveal that the intensity of the transverse optical phonon band centered at ∼796cm−1 is sensitive to the micropipes. And the second-order Raman features of the micropipes in bulk 6H–SiC are well-defined using the selection rules for second-order scattering in wurtzite structure. It is found that there are some second-order peaks missing for the micropipe-including sample, which may be induced by the reduction of the incident laser intensity at around the micropipe, especially the uneven surface in the inner wall of the micropipe. These features might also be employed to characterize other structural defects such as screw-dislocations and threading edge dislocations. [Copyright &y& Elsevier]

Superhydrophobic surfaces are of great interest because of their remarkable properties. Due to its maximal hardness and chemical inertness, diamond film has great potential in fabricating robust superhydrophobic surfaces. In the present study, an oxygen-terminated polycrystalline boron-doped diamond (O-PBDD) superhydrophobic surface with micro/nano-hierarchical porous structures is developed. The preparation method is very simple, requiring only sputtering and dewetting procedures. The former involves sputtering gold and copper particles onto the hydrogen-terminated polycrystalline boron-doped diamond (H-PBDD) to form gold/copper films, whereas the latter involves placing the samples in an atmospheric tube furnace to form hierarchical pores. By controlling the etching parameters, the wettability of the O-PBDD surface can be adjusted from hydrophilic to superhydrophobic, which is significantly different to the normal hydrophilicity feature of O-termination diamonds. The water contact angle of the obtained O-PBDD surface can reach 165 ± 5°, which is higher than the superhydrophobic diamond surfaces that are reported in the literature. In addition, the O-PBDD surface exhibits excellent durability; it can maintain satisfactory superhydrophobicity even after high-pressure, high-temperature, and sandpaper friction tests. This work provides a new research direction for fabricating robust superhydrophobic materials with diamond film., (© 2024 Wiley‐VCH GmbH.)

Plant diseases cause significant economic losses and food security in agriculture each year, with the critical path to reducing losses being accurate identification and timely diagnosis of plant diseases. Currently, deep neural networks have been extensively applied in plant disease identification, but such approaches still suffer from low identification accuracy and numerous parameters. Hence, this paper proposes a model combining channel attention and channel pruning called CACPNET, suitable for disease identification of common species. The channel attention mechanism adopts a local cross-channel strategy without dimensionality reduction, which is inserted into a ResNet-18-based model that combines global average pooling with global max pooling to effectively improve the features' extracting ability of plant leaf diseases. Based on the model's optimum feature extraction condition, unimportant channels are removed to reduce the model's parameters and complexity via the L1-norm channel weight and local compression ratio. The accuracy of CACPNET on the public dataset PlantVillage reaches 99.7% and achieves 97.7% on the local peanut leaf disease dataset. Compared with the base ResNet-18 model, the floating point operations (FLOPs) decreased by 30.35%, the parameters by 57.97%, the model size by 57.85%, and the GPU RAM requirements by 8.3%. Additionally, CACPNET outperforms current models considering inference time and throughput, reaching 22.8 ms/frame and 75.5 frames/s, respectively. The results outline that CACPNET is appealing for deployment on edge devices to improve the efficiency of precision agriculture in plant disease detection., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Chen, Qi, Liang and Yang.)

Boron (B) termination plays an important role in determining the surface properties of the diamond (100) surface. A recent study [J. Mater. Chem. C, 2019, 7, 9756] reported a stable surface structure with one B atom per carbon atom based on high-symmetry adsorption sites having a negative electron affinity (EA) property. In this work, using the global structure prediction method and first-principle calculations, four kinds of B-diamond (100) surfaces with 0.5 monolayers (0.5 ML, one B atom per two carbon atoms), and 1 ML-α, 1 ML-β, and 1 ML-γ (one B atom per carbon atom with three types of configurations known as α, β, and γ) coverages obtained are dynamically and thermally stable. The calculations reveal that B termination effectively modulates the EA of the diamond (100) surface. The 0.5 ML coverage has a small positive EA of 0.24 eV, while the latter three 1 ML coverages with different configurations possess the negative EA of -1.27, -1.25, and -0.76 eV, respectively, due to the difference in charge accumulation and surface dipole moment. Moreover, the B-related surface states are introduced into the bandgap of the bulk diamond, and the band dispersions of the surface states are small (large) in 0.5 ML and 1 ML-γ (1 ML-α and 1 ML-β) as a consequence of the different arrangements of B atoms and the bond lengths between B atoms on the surface. Our finding provides theoretical guidance for the design and fabrication of B-diamond-based electronic devices.

Energy transfer is known to have a significant influence on random lasers. However, the study about the effect of energy transfer between metallic salt and dye molecules on random lasers is still lacking at present. Here, we investigate random lasing actions in Pyrromethene-597 (PM597), PM597-doped MnCl₂ (manganese (II) chloride), PM597-doped polymer-dispersed liquid crystal (PDLC) and PM597-doped PDLC with MnCl₂ capillary systems. We find that random lasing of the systems with MnCl₂ exhibits lower threshold, higher intensity, sharper peak and variable resonance wavelength in comparison with the systems without MnCl₂. This behavior is closely related to the decrease of fluorescence quenching effect and the enhancement of local field induced by energy transfer between MnCl₂ and PM597. Red-shift of wavelength is observed with increasing dosage concentration of MnCl₂ in the PM597-doped PDLC with MnCl₂ system. Through the analysis of single-shot emission spectra of PM597-doped PDLC without and with MnCl₂ systems, the role of MnCl₂ in the coupling of lasing modes is confirmed. Lengths of laser oscillation cavities of the PM597-doped PDLC without and with MnCl₂ systems are calculated by a power Fourier transform (PFT) analysis of their emission spectra. It well accounts for the effect of MnCl₂ on the variation of the oscillation cavity.