Constructing drain surrounded double gate structure in AlGaN/GaN HEMT for boosting breakdown voltage.

AlGaN/GaN high electron mobility transistors (HEMTs) play an important role in the field of high-voltage and high-frequency power devices. However, the current collapse effect of the HEMTs under high voltage greatly limits the development of AlGaN/GaN HEMTs. In this work, a breakdown performance enhanced drain surrounded double gate (DSDG) AlGaN/GaN HEMT is investigated. This structure has two separate gates located on the right and the left of the drain. The optimized off-state characteristics are analyzed by the Sentaurus TCAD simulation tool. The additional gate contributes to restraining the movement of electrons injected by the source therefore reducing the source-to-drain punch-through current. Moreover, the energy band pulled up by the relatively low voltage of the right gate helps to alleviate the drain induced barrier lower (DIBL) effect. As a result, DSDG-HEMT could postpone the breakdown by approximately 100 V through suppressing buffer leakage.

Integrating ultraviolet sensing and memory functions in gallium nitride-based optoelectronic devices.

Optoelectronic devices present a promising avenue for emulating the human visual system. However, existing devices struggle to maintain optical image information after removing external stimuli, preventing the integration of image perception and memory. The development of optoelectronic memory devices offers a feasible solution to bridge this gap. Simultaneously, the artificial vision for perceiving and storing ultraviolet (UV) images is particularly important because UV light carries information imperceptible to the naked eye. This study introduces a multi-level UV optoelectronic memory based on gallium nitride (GaN), seamlessly integrating UV sensing and memory functions within a single device. The embedded SiO2 side-gates around source and drain regions effectively extend the lifetime of photo-generated carriers, enabling dual-mode storage of UV signals in terms of threshold voltage and ON-state current. The optoelectronic memory demonstrates excellent robustness with the retention time exceeding 4 × 104 s and programming/erasing cycles surpassing 1 × 105. Adjusting the gate voltage achieves five distinct storage states, each characterized by excellent retention, and efficiently modulates erasure times for rapid erasure. Furthermore, the integration of the GaN optoelectronic memory array successfully captures and stably stores specific UV images for over 7 days. The study marks a significant stride in optoelectronic memories, showcasing their potential in applications requiring prolonged retention.

Ultraflexible, High-Performance Transistors and Logic Circuits on Biocompatible Polylactic Acid (PLA) Substrate.

Wearable and implantable devices have gained significant popularity, playing a crucial role in smart healthcare and human-machine interfaces, which necessitates the development of more complex electronic devices and circuits on biocompatible flexible materials. Polylactic acid (PLA) stands out due to its biodegradability, cost-effectiveness, and low immunogenicity. In this study, we utilize a solution-based spin-coating method to produce high-quality PLA thin films, serving as substrates for the fabrication of thin-film transistors (TFTs) in which the dielectric layer material is silicon dioxide, the channel layer material is IGZO, and the gate, drain, and source material is ITO at low temperatures (<40 °C) through a shadow masking technique. The resulting PLA-TFT devices exhibited remarkable flexibility, biocompatibility, and impressive electrical characteristics, including a charge carrier mobility of 27.81 cm2/(V s), a subthreshold swing of 162.8 mV/decade, and an ON/OFF current ratio of up to 1 × 106, and maintained performance under various deformations. We successfully constructed fundamental logic gate circuits using PLA-TFTs, including AND, OR, and NOT gates, which effectively performed logical functions and demonstrated stability under diverse bending conditions. These research findings provide valuable support for future endeavors in fabricating intricate logic circuits and realizing advanced functionalities on biocompatible flexible materials.

Effect of Co Doping on Electrocatalytic Performance of Co-NiS2/CoS2 Heterostructures.

There are abundant water resources in nature, and hydrogen production from electrolyzed water can be one of the main ways to obtain green and sustainable energy. Traditional water electrolysis uses precious metals as catalysts, but it is difficult to apply in massive volumes due to low reserves and high prices. It is still a challenge to develop hydrogen electrocatalysts with excellent performance but low cost to further improve the efficiency of hydrogen production. This article reported a potential candidate, the Co-NiS2/CoS2 (material is based on NiS2, and after Co doping, The NiS2/CoS2 heterostructure is formed) heterostructures, prepared by hydrothermal method with carbon paper as the substrate. In a 0.5 M sulfuric acid solution, the hydrogen evolution reaction with Co-NiS2/CoS2 as the electrode showed excellent catalytic performance. When the Co (Cobalt) doping concentration is increased to 27%, the overpotential is -133.3 mV, which is a drop of 81 mV compared with -214.3 mV when it is not doped. The heterostructure formed after doping also has good stability. After 800 CV cycles, the difference in overpotential is only 3 mV. The significant improvement of the catalytic performance can be attributed to the significant changes in the crystal structure and properties of the doped heterostructures, which provide an effective method for efficient electrocatalytic hydrogen production.

Structural changes in the oral microbiome of the adolescent patients with moderate or severe dental fluorosis.

Dental fluorosis is a very prevalent endemic disease. Although oral microbiome has been reported to correlate with different oral diseases, there appears to be an absence of research recognizing any relationship between the severity of dental fluorosis and the oral microbiome. To this end, we investigated the changes in oral microbial community structure and identified bacterial species associated with moderate and severe dental fluorosis. Salivary samples of 42 individuals, assigned into Healthy (N = 9), Mild (N = 14) and Moderate/Severe (M&S, N = 19), were investigated using the V4 region of 16S rRNA gene. The oral microbial community structure based on Bray Curtis and Weighted Unifrac were significantly changed in the M&S group compared with both of Healthy and Mild. As the predominant phyla, Firmicutes and Bacteroidetes showed variation in the relative abundance among groups. The Firmicutes/Bacteroidetes (F/B) ratio was significantly higher in the M&S group. LEfSe analysis was used to identify differentially represented taxa at the species level. Several genera such as Streptococcus mitis, Gemella parahaemolysans, Lactococcus lactis, and Fusobacterium nucleatum, were significantly more abundant in patients with moderate/severe dental fluorosis, while Prevotella melaninogenica and Schaalia odontolytica were enriched in the Healthy group. In conclusion, our study indicates oral microbiome shift in patients with moderate/severe dental fluorosis. We identified several differentially represented bacterial species enriched in moderate and severe fluorosis. Findings from this study suggests that the roles of these bacteria in oral health and related diseases warrant more consideration in patients with moderate and severe fluorosis.

Fabrication of NiS2 Nanomaterials for Cd2+ Sensing.

Heavy metal Cadmium (Cd) will continuously pollute the atmosphere, soil and various water environments through material circulation, and even pose a threat to human safety. It has been designated as a first-class pollutant in sewage by China, therefore there is an urgent need to find new, more effective, and low-cost method to accurately detect Cadmium ion (Cd2+) concentration. We experimentally prepared a new Cd2+ sensor based on NiS2 nanomaterials capable of measuring Cd2+ concentration. The corresponding relationship between over potential of NiS2 nanomaterials in H2SO4 electrolyte solutions with different Cd2+ concentration and reduction peak with change of Cd2+ concentration was obtained by electrochemical method.

Co-FeS2/CoS2 Heterostructured Nanomaterials for pH Sensing.

Biosensors are widely used in production and life, and can be used in medicine, industrial production, and scientific research. Among them, the detection of pH has always received extensive attention. In this study, we demonstrate the use of a one-step hydrothermal method to prepare Co-FeS2/CoS2 nanomaterials as pH sensor (pH vs. overpotential) for the first time. The proposed pH sensor exhibits outstanding performance in KOH solutions via electrochemical methods with good stability. Overall, the results of this study not only add to the non-noble transition metal electrocatalysis research, but also identify important sensing characteristics for electrocatalysts.

Hydrothermal Synthesis of Polyhedral Nickel Sulfide by Dual Sulfur Source for Highly-Efficient Hydrogen Evolution Catalysis.

Transition metal sulfides are cheap and efficient catalysts for water splitting to produce hydrogen; these compounds have attracted wide attention. Nickel sulfide (NiS2) has been studied in depth because of its simple preparation process, excellent performance and good stability. Here, we propose a modification to the hydrothermal synthesis method for the fabrication of a highly efficient and stable NiS2 electrocatalyst prepared by two different sulfur sources, i.e., sulfur powder and C3H7NaO3S2 (MPS), for application in hydrogen evolution reactions. The obtained NiS2 demonstrated excellent HER performance with an overpotential of 131 mV to drive -10 mA cm-1 in 0.5 M H2SO4 solution with 5mV performance change after 1000 cycles of stability testing. We believe that this discovery will promote the industrial development of nonprecious metal catalysts.

A Robust and Low-Power Bismuth Doped Tin Oxide Memristor Derived from Coaxial Conductive Filaments.

Memristor, processing data storage and logic operation all-in-one, is an advanced configuration for next generation computer. In this work, a bismuth doped tin oxide (Bi:SnO2 ) memristor with ITO/Bi:SnO2 /TiN structure has been fabricated. Observing from transmission electron microscope (TEM) for the Bi:SnO2 device, it is found that the bismuth atoms surround the surface of SnO2 crystals to form the coaxial Bi conductive filament. The self-compliance current, switching voltage and operating current of Bi:SnO2 memristor are remarkably smaller than that of ITO/SnO2 /TiN device. With the content of 4.8% Bi doping, the SET operating power of doped device is 16 µW for ITO/Bi:SnO2 /TiN memory cell of 0.4 × 0.4 µm2 , which is cut down by two orders of magnitude. Hence, the findings in this study suggest that Bi:SnO2 memristors hold significant potential for application in low power memory and broadening the understanding of existing resistive switching (RS) mechanism.