Wafer-scale vertical injection III-nitride deep-ultraviolet light emitters.

A ground-breaking roadmap of III-nitride solid-state deep-ultraviolet light emitters is demonstrated to realize the wafer-scale fabrication of devices in vertical injection configuration, from 2 to 4 inches. The epitaxial device structure is stacked on a GaN template instead of conventionally adopted AlN, where the primary concern of the tensile strain for Al-rich AlGaN on GaN is addressed via an innovative decoupling strategy, making the device structure decoupled from the underlying GaN template. Moreover, the strategy provides a protection cushion against the stress mutation during the removal of substrates.

Gas Outburst Warning Method in Driving Faces: Enhanced Methodology through Optuna Optimization, Adaptive Normalization, and Transformer Framework.

Addressing common challenges such as limited indicators, poor adaptability, and imprecise modeling in gas pre-warning systems for driving faces, this study proposes a hybrid predictive and pre-warning model grounded in time-series analysis. The aim is to tackle the effects of broad application across diverse mines and insufficient data on warning accuracy. Firstly, we introduce an adaptive normalization (AN) model for standardizing gas sequence data, prioritizing recent information to better capture the time-series characteristics of gas readings.

Group-III nitride heteroepitaxial films approaching bulk-class quality.

III-nitride wide bandgap semiconductors are promising materials for modern optoelectronics and electronics. Their application has progressed greatly thanks to the continuous quality improvements of heteroepitaxial films grown on large-lattice-mismatched foreign substrates. But compared with bulk single crystals, there is still tremendous room for the further improvement of the material quality.

One-stage tracheostomy during surgery reduced early pulmonary infection and mechanical ventilation length in complete CSCI patients.

Objective: Complete cervical spinal cord injury (CSCI) is a devastating injury that usually requires surgical treatment. Tracheostomy is an important supportive therapy for these patients. To evaluate the effectiveness of early one-stage tracheostomy during surgery compared with necessary tracheostomy after surgery, and to identify clinical factors for one-stage tracheostomy during surgery in complete cervical spinal cord injury.

Inhibition of HMGB1 Attenuates Spinal Cord Edema by Reducing the Expression of Na-K-Cl Cotransporter-1 and Na/H Exchanger-1 in Both Astrocytes and Endothelial Cells After Spinal Cord Injury in Rats.

Sodium/water transport through Na-K-Cl cotransporter-1 (NKCC1) and sodium/hydrogen exchanger-1 (NHE1) in both astrocytes and endothelial cells is critical to cytotoxic and ionic edema following spinal cord injury (SCI). High-mobility group box-1 (HMGB1) promotes spinal cord edema after SCI. Accordingly, we sought to identify both the role of HMGB1 and the mechanism of its effect on NKCC1 and NHE1 expression in astrocytes and endothelial cells as well as the role of the regulation of spinal cord edema after SCI.

Quasiclassical Trajectory Simulation as a Protocol to Build Locally Accurate Machine Learning Potentials.

Direct trajectory calculations have become increasingly popular in recent computational chemistry investigations. However, the exorbitant computational cost of trajectory calculations usually limits its application in mechanistic explorations. Recently, machine learning-based potential energy surface (ML-PES) provides a powerful strategy to circumvent the heavy computational cost and meanwhile maintain the required accuracy.

Preparation and characterization of low oil absorption corn starch by ultrasonic combined with freeze-thaw treatment.

This study investigated the effects of ultrasonic, freeze-thaw, and combined pretreatments on corn starch oil absorption. Low-field nuclear magnetic resonance (LF NMR) was used to study the oil absorption changes after frying of corn starch (CS) subjected to different treatments. The structural characteristics of samples were evaluated using various techniques.

Sub-nanometer ultrathin epitaxy of AlGaN and its application in efficient doping.

Solving the doping asymmetry issue in wide-gap semiconductors is a key difficulty and long-standing challenge for device applications. Here, a desorption-tailoring strategy is proposed to juggle the carrier concentration and transport. Specific to the p-doping issue in Al-rich AlGaN, self-assembled p-AlGaN superlattices with an average Al composition of over 50% are prepared by adopting this approach.

Entropic Path Sampling: Computational Protocol to Evaluate Entropic Profile along a Reaction Path.

Fleeting intermediates constitute dynamically stepwise mechanisms. They have been characterized in molecular dynamics trajectories, but whether these intermediates form a free energy minimum to become entropic intermediates remains elusively defined. We developed a computational protocol known as entropic path sampling to evaluate the entropic variation of reacting species along a reaction path based on an ensemble of trajectories.

Hexagonal BN-Assisted Epitaxy of Strain Released GaN Films for True Green Light-Emitting Diodes.

Epitaxial growth of III-nitrides on 2D materials enables the realization of flexible optoelectronic devices for next-generation wearable applications. Unfortunately, it is difficult to obtain high-quality III-nitride epilayers on 2D materials such as hexagonal BN (h-BN) due to different atom hybridizations. Here, the epitaxy of single-crystalline GaN films on the chemically activated h-BN/AlO substrates is reported, paying attention to interface atomic configuration.

Migratory Aptitudes in Rearrangements of Destabilized Vinyl Cations.

The Lewis acid-promoted generation of destabilized vinyl cations from β-hydroxy diazo ketones leads to an energetically favorable 1,2-shift across the alkene followed by an irreversible C-H insertion to give cyclopentenone products. This reaction sequence overcomes typical challenges of counter-ion trapping and rearrangement reversibility of vinyl cations and has been used to study the migratory aptitudes of nonequivalent substituents in an uncommon C(sp) to C(sp) vinyl cation rearrangement. The migratory aptitude trends were consistent with those observed in other cationic rearrangements; the substituent that can best stabilize a cation more readily migrates.

Synthesis of Biaryls via Decarbonylative Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling of Carboxylic Acids.

The biaryl motif is a building block in many drugs, agrochemicals, and materials, and as such it is highly desirable as a synthesis target. The state-of-the-art process for biaryl synthesis from ubiquitous carboxylic acids is decarboxylative cross-coupling involving loss of carbon dioxide (CO). However, the scope of these methods is severely limited, mainly due to specific substitution required to promote decarboxylation.

Highly-chemoselective step-down reduction of carboxylic acids to aromatic hydrocarbons palladium catalysis.

Aryl carboxylic acids are among the most abundant substrates in chemical synthesis and represent a perfect example of a traceless directing group that is central to many processes in the preparation of pharmaceuticals, natural products and polymers. Herein, we describe a highly selective method for the direct step-down reduction of carboxylic acids to arenes, proceeding well-defined Pd(0)/(ii) catalytic cycle. The method shows a remarkably broad substrate scope, enabling to direct the classical acyl reduction towards selective decarbonylation by a redox-neutral mechanism.

Convenient and sensitive colorimetric detection of melamine in dairy products based on Cu(ii)-HO-3,3',5,5'-tetramethylbenzidine system.

The illegal adulteration of melamine in dairy products for false protein content increase is a strong hazard to human health. Herein, a simple and sensitive colorimetric method was developed for the quantification of melamine in dairy products based on a Cu-hydrogen peroxide (HO)-3,3',5,5'-tetramethylbenzidine (TMB) system. In this strategy, Cu exhibits peroxidase-like activity and can catalyze the oxidation of TMB to oxidized TMB (oxTMB) in the presence of HO with a blue colour change of the solution.

Exciton emission of quasi-2D InGaN in GaN matrix grown by molecular beam epitaxy.

We investigate the emission from confined excitons in the structure of a single-monolayer-thick quasi-two-dimensional (quasi-2D) InGaN layer inserted in GaN matrix. This quasi-2D InGaN layer was successfully achieved by molecular beam epitaxy (MBE), and an excellent in-plane uniformity in this layer was confirmed by cathodoluminescence mapping study. The carrier dynamics have also been investigated by time-resolved and excitation-power-dependent photoluminescence, proving that the recombination occurs via confined excitons within the ultrathin quasi-2D InGaN layer even at high temperature up to ~220 K due to the enhanced exciton binding energy.

High quality AlN epilayers grown on nitrided sapphire by metal organic chemical vapor deposition.

Influence of sapphire pretreatment conditions on crystalline quality of AlN epilayers has been investigated by metal organic chemical vapor deposition (MOCVD). Compared to alumination treatment, it is found that appropriate sapphire nitridation significantly straightens the surface atomic terraces and decreases the X-ray diffraction (0002) full width at half maximum (FWHM) to a minimum of 55 arcsec, indicating a great improvement of the tilting feature of the grain structures in the AlN epilayer. More importantly, there is no inversion domains (IDs) found in the AlN epilayers, which clarifies that optimal sapphire nitridation is promising in the growth of high quality AlN.

High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography.

We report epitaxial growth of AlN films with atomically flat surface on nano-patterned sapphire substrates (NPSS) prepared by nano-imprint lithography. The crystalline quality can be greatly improved by using the optimized 1-μm-period NPSS. The X-ray diffraction ω-scan full width at half maximum values for (0002) and (102) reflections are 171 and 205 arcsec, respectively.

High-Output-Power Ultraviolet Light Source from Quasi-2D GaN Quantum Structure.

Quasi-2D GaN layers inserted in an AlGaN matrix are proposed as a novel active region to develop a high-output-power UV light source. Such a structure is successfully achieved by precise control in molecular beam epitaxy and shows an amazing output power of ≈160 mW at 285 nm with a pulsed electron-beam excitation. This device is promising and competitive in non-line-of-sight communications or the sterilization field.

Mechanism of stress-driven composition evolution during hetero-epitaxy in a ternary AlGaN system.

Two AlGaN samples with different strain were designed to investigate mechanism of stress-driven composition evolution. It is discovered that AlGaN grown on AlN or (AlN/GaN superlattices (SLs))/GaN both consist of two distinct regions with different compositions: transition region and uniform region, which is attributed to the compositional pulling effect. The formation of the transition region is due to the partial stress release caused by the generation of misfit dislocations near the hetero-interface.

Growth of high quality and uniformity AlGaN/GaN heterostructures on Si substrates using a single AlGaN layer with low Al composition.

By employing a single AlGaN layer with low Al composition, high quality and uniformity AlGaN/GaN heterostructures have been successfully grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). The heterostructures exhibit a high electron mobility of 2150 cm(2)/Vs with an electron density of 9.3 × 10(12) cm(-2).

Lattice-Polarity-Driven Epitaxy of Hexagonal Semiconductor Nanowires.

Lattice-polarity-driven epitaxy of hexagonal semiconductor nanowires (NWs) is demonstrated on InN NWs. In-polarity InN NWs form typical hexagonal structure with pyramidal growth front, whereas N-polarity InN NWs slowly turn to the shape of hexagonal pyramid and then convert to an inverted pyramid growth, forming diagonal pyramids with flat surfaces and finally coalescence with each other. This contrary growth behavior driven by lattice-polarity is most likely due to the relatively lower growth rate of the (0001̅) plane, which results from the fact that the diffusion barriers of In and N adatoms on the (0001) plane (0.

Free and bound excitonic effects in Al0.5Ga0.5N/Al0.35Ga0.65N MQWs with different Si-doping levels in the well layers.

Free exciton (FX) and bound exciton (BX) in Al0.5Ga0.5N/Al0.

Effect of injection current on the optical polarization of AlGaN-based ultraviolet light-emitting diodes.

The injection current dependence of optical polarization of ultraviolet (UV) light-emitting diodes (LEDs) emitting at wavelength of 310 nm and 277 nm was investigated by electroluminescence (EL) measurements. For both diodes, it was found that the degree of polarization (DOP) decreased obviously as the injection current increased. We attribute the decrease in DOP to the different changing trend of the intensity of the light emission from transverse electric (TE) polarization (E⊥c) and transverse magnetic (TM) polarization (E∥c) as the injected carriers occupy higher states above k = 0 with increasing the injection current.

Strain effect on the optical polarization properties of c-plane Al₀.₂₆Ga₀.₇₄N/GaN superlattices.

A new approach to realize ultraviolet (UV) light emitting diodes (LEDs) is using AlN/GaN or AlxGa1-xN/GaN SL structure as active layers. Effect of a uniaxial strain on the degree of polarization (DOP) of Al0.26Ga0.

Optical investigation of strong exciton localization in high Al composition AlxGa₁-xN alloys.

The exciton localization in wurtzite AlxGa₁-xN alloys with x varying from 0.41 to 0.63 has been studied by deep-ultraviolet photoluminescence (PL) spectroscopy and picosecond time-resolved PL spectroscopy.