Effect of High-Temperature Storage on Electrical Characteristics of Hydrogen-Treated AlGaN/GaN High-Electron-Mobility Transistors.

In this paper, high-temperature storage of hydrogen-treated AlGaN/GaN HEMTs is conducted for the first time to study the effect of high temperature on the electrical characteristics of the devices after hydrogen treatment, and it is found that high-temperature storage can effectively reduce the impact of hydrogen on the devices. After hydrogen treatment, the output current and the maximum transconductance of the device increase, and the threshold voltage drifts negatively. However, after high-temperature treatment at 200 °C for 24 h, the output current, threshold voltage, and the maximum transconductance of the device all approach their initial values before hydrogen treatment. By using low-frequency noise analysis technology, the trap density of the hydrogen-treated AlGaN/GaN HEMT is determined to be 8.9 × 1023 cm-3·eV-1, while it changes to 4.46 × 1022 cm-3·eV-1 after high-temperature storage. We believe that the change in the electrical characteristics of the device in hydrogen is due to the passivation of hydrogen on the inherent trap of the device, and the variation in the electrical properties of the device in the process of high-temperature storage involves the influence of two effects, namely the dehydrogenation effect and the improvement of the metal-semiconductor interface caused by high temperatures.

Enhanced Energy Storage Performance in Na0.5Bi0.5TiO3-Based Relaxor Ferroelectric Ceramics via Compositional Tailoring.

Owing to the high power density, excellent operational stability and fast charge/discharge rate, and environmental friendliness, the lead-free Na0.5Bi0.5TiO3 (NBT)-based relaxor ferroelectrics exhibit great potential in pulsed power capacitors. Herein, novel lead-free (1-x)(0.7Na0.5Bi0.5TiO3-0.3Sr0.7Bi0.2TiO3)-xBi(Mg0.5Zr0.5)O3 (NBT-SBT-xBMZ) relaxor ferroelectric ceramics were successfully fabricated using a solid-state reaction method and designed via compositional tailoring. The microstructure, dielectric properties, ferroelectric properties, and energy storage performance were investigated. The results indicate that appropriate Bi(Mg0.5Zr0.5)O3 content can effectively enhance the relaxor ferroelectric characteristics and improve the dielectric breakdown strength by forming fine grain sizes and diminishing oxygen vacancy concentrations. Therefore, the optimal Wrec of 6.75 J/cm3 and a η of 79.44% were simultaneously obtained in NBT-SBT-0.15BMZ at 20 °C and 385 kV/cm. Meanwhile, thermal stability (20-180 °C) and frequency stability (1-200 Hz) associated with the ultrafast discharge time of ~49.1 ns were also procured in the same composition, providing a promising material system for applications in power pulse devices.

Ferromagnetism and intrinsic half-metallicity of two-dimensional MnN monolayer with square-octagonal structure.

The MnN monolayer with square-octagonal structure (so-MnN) is explored using density functional calculations. The results show that theso-MnN monolayer is energetically, dynamically, thermally and mechanically stable, and exhibits the ferromagnetism and intrinsic half-metallicity. The total magnetic moment is 16 µBin unit cell (Mn4N4). The energy band of spin-up crosses the Fermi energy level (EF), while the spin-down channel has semiconductor characteristic with a direct band gap of 3.0 eV at Γ-point. By applying the biaxial strain, the band gap in spin-down channel can be tuned, and theso-MnN monolayer still possesses the characteristic of ferromagnetism and intrinsic half-metallicity. Finally, the Curie temperatureTCincreases gradually under biaxial strains from 0 to +3%, while theTChas a decreasing trend under the biaxial strains from 0 to -3%.

Inorganic gas sensing of green phosphorene nanosheet: insights from density functional theory.

Our work highlights the functionality of a novel two-dimensional phosphorene allotrope entitled green phosphorene for inorganic gas detection for the first time. Four inorganic molecules, NH3, SO2, HCN and O3, are considered as adsorbates and the adsorption conformation, adsorption energy, charge transfer, density of states, and electronic band structure are systematically scrutinized based on density functional theory. Our calculations show that the adsorption energy of O3 on pristine green phosphorene is the lowest among the four considered gas molecules, suggesting that the substrate is more sensitive to O3. Significant changes in electronic structures confirm the possibility of green phosphorene for O3 detection. Biaxial strains and electric fields were applied to investigate the changes in adsorption behavior. The presence of compressive strain could enhance adsorption sensitivity between O3 and green phosphorene, while the tensile strain induces the dissociative adsorption that not suitable for reversible sensor. Furthermore, by controlling the orientation of external electric field, it is possible to achieve O3 adsorption-desorption cycle, which is of great significance for green phosphorene in the application of reversible gas sensor.

Enhanced Electrocaloric Effect in Sr2+-Modified Lead-Free BaZr xTi1- xO3 Ceramics.

Barium strontium zirconate titanate ceramics ((BaSr)(ZrTi)O3-BSZT) with Zr4+ ionic contents of 15 and 20 mol % and Sr2+ ionic contents of 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. X-ray diffraction and scanning electron microscopy were used to characterize the lattice structure and morphologies of the ceramics. Permittivity and polarization as a function of temperature were characterized using an impedance analyzer and a Tower-Sawyer circuit. The electrocaloric effect was measured directly and calculated using the Maxwell relation (indirectly). The results indicated that the BSZT ceramics change from a normal ferroelectric to a relaxor ferroelectric with increasing Zr4+ ionic content, which can be further modified by the addition of Sr2+ ionic content. The optimized adiabatic temperature change Δ T obtained is 2.43 K in (Ba0.85Sr0.15)(Zr0.15Ti0.75)O3 ceramics, and Δ T >1.6 K over a wide temperature span of 120 °C was obtained.

Direct Measurement of Large Electrocaloric Effect in Ba(ZrxTi1-x)O3 Ceramics.

Barium zirconate titanate (BZT) (Ba(ZrxTi1-x)O3) ceramics with Zr4+ contents of x = 5, 10, 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. The microstructures, morphologies, and electric properties were characterized using X-ray diffraction, scanning electron microscopy, and impedance analysis methods, respectively. The dielectric analyses indicate that the BZT bulk ceramics show characteristics of phase transition from a normal ferroelectric to a relaxor ferroelectric with the increasing Zr4+ ionic content. The electrocaloric effect adiabatic temperature change decreases with the increasing Zr4+ content. The highest adiabatic temperature change obtained is 2.4 K for BZT ceramics with a 5 mol % of Zr4+ ionic content.

Mechanistic Study of Human Glucose Transport Mediated by GLUT1.

The glucose transporter 1 (GLUT1) belongs to the major facilitator superfamily (MFS) and is responsible for the constant uptake of glucose. However, the molecular mechanism of sugar transport remains obscure. In this study, homology modeling and molecular dynamics (MD) simulations in lipid bilayers were performed to investigate the combination of the alternate and multisite transport mechanism of glucose with GLUT1 in atomic detail. To explore the substrate recognition mechanism, the outward-open state human GLUT1 homology model was generated based on the template of xylose transporter XylE (PDB ID: 4GBZ), which shares up to 29% sequence identity and 49% similarity with GLUT1. Through the MD simulation study of glucose across lipid bilayer with both the outward-open GLUT1 and the GLUT1 inward-open crystal structure, we investigated six different conformational states and identified four key binding sites in both exofacial and endofacial loops that are essential for glucose recognition and transport. The study further revealed that four flexible gates consisting of W65/Y292/Y293-M420/TM10b-W388 might play important roles in the transport cycle. The study showed that some side chains close to the central ligand binding site underwent larger position changes. These conformational interchanges formed gated networks within an S-shaped central channel that permitted staged ligand diffusion across the transporter. This study provides new inroads for the understanding of GLUT1 ligand recognition paradigm and configurational features which are important for molecular, structural, and physiological research of the MFS members, especially for GLUT1-targeted drug design and discovery.