Achieving atomically ordered GaN/AlN quantum heterostructures: The role of surface polarity.

Interface engineering in heterostructures at the atomic scale has been a central research focus of nanoscale and quantum material science. Despite its paramount importance, the achievement of atomically ordered heterointerfaces has been severely limited by the strong diffusive feature of interfacial atoms in heterostructures. In this work, we first report a strong dependence of interfacial diffusion on the surface polarity. Near-perfect quantum interfaces can be readily synthesized on the semipolar plane instead of the conventional c-plane of GaN/AlN heterostructures. The chemical bonding configurations on the semipolar plane can significantly suppress the cation substitution process as evidenced by first-principles calculations, which leads to an atomically sharp interface. Moreover, the surface polarity of GaN/AlN can be readily controlled by varying the strain relaxation process in core-shell nanostructures. The obtained extremely confined, interdiffusion-free ultrathin GaN quantum wells exhibit a high internal quantum efficiency of ~75%. Deep ultraviolet light-emitting diodes are fabricated utilizing a scalable and robust method and the electroluminescence emission is nearly free of the quantum-confined Stark effect, which is significant for ultrastable device operation. The presented work shows a vital path for achieving atomically ordered quantum heterostructures for III-nitrides as well as other polar materials such as III-arsenides, perovskites, etc.

Super-Flexible Water-Proof Actuators.

Humidity-responsive materials hold broad application prospects in sensing, energy production, and other fields. Particularly, humidity-sensitive, flexibility, and water resistance are pivotal factors in the development of optimized humidity-responsive materials. In this study, hydrophobic linear polyurethane and hydrophilic 4-vinylphenylboronic acid (4-VPBA) form a semi-intercross cross-linking network. This copolymer of polyurethane exhibits excellent humidity-sensitive, mechanical properties, and water resistance. Its maximum tensile strength and maximum elongation can reach 40.56 MPa and 543.47%, respectively. After being immersed in water at various temperatures for 15 days, it exhibited a swelling ratio of only 3.28% in water at 5 °C and 9.58% in water at 70 °C. While the presence of 4-VPBA network imparts humidity-sensitive, reversible, and multidirectional bending abilities, under the stimulus of water vapor, it can bend 43° within 1.4 s. The demonstrated material surpasses current bidirectional humidity actuators in actuating ability. Based on these characteristics, automatically opening waterproof umbrellas and windows, as well as bionic-arms, crawling robots, and self-propelled boats, are successfully developed.

Alkane-Strengthened Viscoelasticity in Micellar Solutions of Surface-Active Ionic Liquids and Their Potential Application in Enhanced Oil Recovery.

Wormlike micelles (WLMs) are highly sensitive to alkanes, resulting in structural destruction and loss of viscosity. Therefore, the study of WLMs against alkanes holds great significant importance. Surface-active ionic liquids have shown increasing promise for different situations for customizing molecular structures with the specialty of flexible functional assembly. In this paper, we found that WLMs constructed from the long-chain fatty acid surface-active ionic liquid (N,N-dimethylbenzylamine-oleic acid, abbreviated as BD-OA) exhibit strengthened viscoelasticity with the introduction of alkanes, expanding the resistance range to alkane damage. Here, the rheological behavior, microstructure, and dissipative particle dynamics (DPD) simulations of BD-OA WLMs were investigated at macro-, micro-, and mesoscopic scales, before (and after) the introduction of alkane. Our findings confirm the structural transformation of the micellar system from WLMs to lamellar micelles with higher viscoelasticity after alkane induction. The rearrangement of the micelle configuration may be attributed to the infiltration of alkane molecules into the fence layer formed by the BD-OA WLMs, leading to an increase in the boundary accumulation parameter and ultimately resulting in the formation of lower curvature lamellar micelles. More importantly, the against alkanes BD-OA WLMs have exhibited excellent in enhanced oil recovery, which has a promise for substituting common oil-displacing agents in tertiary oil recovery processes.

Lens height paraments comparison according to ciliary sulcus width (CSW): a pilot study of the predictive role of CLR and STSL for vault after ICL implantation.

BACKGROUND: To assess the relationship between postoperative implantable collamer lens (ICL) vault and lens height obtained from two different measurements. METHODS: A retrospective case series study enrolled eyes with horizontally implanted ICL. Crystal lens rise (CLR) and the distance between STS plane and anterior crystalline lens surface (STSL) were measured in the horizontal and vertical directions using ultrasound biomicroscopy (UBM). We compared the differences in the parameters measured in both horizontal and vertical directions. The participants were categorized into three groups according to ciliary sulcus width (CSW) which is defined as the distance between the posterior angle of the iris and the anterior angle of the ciliary process: narrow CSW group (NSG); medium CSW group (MSG); and wide CSW group (WSG). The correlations between CLR/STSL and vault were examined in each of the three groups. Biased correlation analysis was used further to contrast the correlation between CLR/STSL and vault. RESULTS: This retrospective study included 223 myopic eyes. Vertical STSL (VSTSL) and vertical CLR (VCLR) exhibited significantly greater values compared to their horizontal counterparts (both P < 0.05). None of the indicators were statistically different between the three groups. In both NSG and MSG, STSL/CLR correlated with vault, while in WSG, only STSL correlated with vault (r=-0.316, P = 0.013). In contrast to HCLR, the correlation between HSTSL and vault remained after controlling for HCLR (r=-0.162, P = 0.015). CONCLUSIONS: STSL should deserve more attention in the preoperative evaluation of ICL compared to CLR especially when CSW is large.

Survey on pattern of myopia in school children in Hangzhou after the COVID-19 pandemic: a school-based vision screening study.

BACKGROUND: Myopia is a major health issue around the world. Myopia in children has increased significantly during the COVID-19 pandemic in China, but reports are scarce on the prevalence of myopia following the pandemic. This study collected vision screening data of school children in China for five consecutive years to observe the changes in myopia after the pandemic and compare the observed prevalence of myopia before and after the pandemic. METHODS: A school-based vision screening study used stratified samplings to collect the vision screening data in school children aged 6-13 from 45 primary schools in Hangzhou. Vision screening data including uncorrected visual acuity(UCVA) and spherical equivalent refraction(SER). Calculating the mean of SER and the prevalence of myopia and hyperopia from 2019 to 2023. RESULTS: A total of 79,068 screening results (158,136 eyes) were included in the analysis. A substantial myopic shift (approximately -0.30 diopters [D] on average) was found in 2020 and 2021 compared with 2019 in all age groups and a substantial myopic shift (approximately 0.4 D on average) was found in 2022 compared with 2021. A slight myopic shift (approximately -0.14 D on average) was found in 2023 compared with 2022. The prevalence of myopia in all age groups was the highest for five years in 2020 or 2021, which was 31.3% for 6-year-olds, 43.0% for 7-year-olds, and 53.7% for 8-year-olds. A positive change in the prevalence rate of myopia was found at 6 years old (0.59%, 0.12%, 0.36%, 0.25%, p < 0.001). The change in prevalence rate in myopia was shifted slightly in children aged 10-13 years. Children aged 8 to 13 years had a slight increase in myopia prevalence from 2022 to 2023. The prevalence of hyperopia was low and stable in all grade groups, ranging from 0.7% to 2.2% over five years. CONCLUSION: Myopia in children has increased rapidly during the COVID-19 pandemic. After the pandemic, the prevalence of myopia in children gradually decreased temporarily and then rebounded. Myopic shift was more apparent in younger children. Myopic shift in children may be related to the reduction of outdoor time, less light, and near work habits, and further research is needed.

An Ultrahigh Efficiency Excitonic Micro-LED.

High efficiency micro-LEDs, with lateral dimensions as small as one micrometer, are desired for next-generation displays, virtual/augmented reality, and ultrahigh-speed optical interconnects. The efficiency of quantum well LEDs, however, is reduced to negligibly small values when scaled to such small dimensions. Here, we show such a fundamental challenge can be overcome by developing nanowire excitonic LEDs. Harnessing the large exciton oscillator strength of quantum-confined nanostructures, we demonstrate a submicron scale green-emitting LED having an external quantum efficiency and wall-plug efficiency of 25.2% and 20.7%, respectively, the highest values reported for any LEDs of this size to our knowledge. We established critical factors for achieving excitonic micro-LEDs, including the epitaxy of nanostructures to achieve strain relaxation, the utilization of semipolar planes to minimize polarization effects, and the formation of nanoscale quantum-confinement to enhance electron-hole wave function overlap. This work provides a viable path to break the efficiency bottleneck of nanoscale optoelectronics.

Multi-Unit Needleless Electrospinning for One-Step Construction of 3D Waterproof MF-PVA Nanofibrous Membranes as High-Performance Air Filters.

The airborne particulate matter (PM) seriously threatens people's health. Personal protective equipment with electrospun nanofibers is an effective method to make people away from air pollutants. Herein, 3D waterproof melamine-formaldehyde polyvinyl alcohol (MF-PVA) nanofibrous membranes are fabricated by a one-step method combining multi-unit needleless electrospinning and a thermal treatment device in a line. 3D nanofibrous structures can be controlled by adjusting the solution concentration of each unit. The PVA nanofibrous membranes become waterproof after cross-linking with MF resin in the following thermal treatment device. The optimized MF-PVA nanofibrous membrane shows excellent air filtration performance (97.3% for PM0.3 , 100% for PM1.0 , and 100% for PM2.5 ) and low air resistance (76 Pa). These 3D waterproof MF-PVA nanofibrous membranes exhibit ultra-stable performance in various practical environments.

pH-Switchable W/O Polymer Emulsion: A Promising Strategy for Rapid Dissolution of Drag Reducers.

Additional hydrophilic surfactants are generally introduced into W/O emulsion drag reducer systems to enhance the dissolution capacity of polymers. The hydrophilic surfactants may decrease the stability of W/O emulsion, which leads to deterioration of polymer emulsions in the storage and transport process instead. Herein, a pH-switchable surfactant, N-(2-morpholinoethyl) oleamide (NMEO) was designed for stabilizing a W/O emulsion drag reducer. The surface activity and solubility changes occurring at pH < 6 of NMEO guaranteed the phase inversion from W/O to O/W of emulsions upon pH stimulation. Based on optimal conditions (oil-water ratio of 0.429, NMEO concentration of 3 wt%, and pH of 6.5), the inverse emulsion polymerization of poly(acrylamide-co-acrylic acid-co-2-acrylamide-2-methylpropane sulfonic acid) was proceeded to obtain a W/O polymer emulsion with the pH-switchable behavior. It was demonstrated that the polymer emulsions were provided with prolonged storage stability by NMEO and could be stored for at least 30 days due to the absence of hydrophilic surfactants. The polymers were released and completely dissolved within 2.5 min by pH stimulation, compared with traditional emulsion polymers and powder polymers that require 4 and 17 min, respectively. In addition, the emulsion drag reducer prepared by NMEO provided drag-reduction performance of 64.67% at 0.021 wt% concentration. The pH-switchable behavior of NMEO promotes the validity of W/O polymer emulsions along with the capacity of rapid release and solubilization, which eliminates the imbalance between the long-term storage stability and rapid solubility of traditional drag reducers. Thus, NMEO-stabilized emulsion drag reducers are expected to be a promising alternative for traditional products.

Stretchable Semi-Interpenetrating Carboxymethyl Guar Gum-Based Composite Hydrogel for Moisture-Proof Wearable Strain Sensor.

Wearable strain sensors of conductive hydrogels have very broad application prospects in electronic skins and human-machine interfaces. However, conductive hydrogels suffer from unstable signal transmission due to environmental humidity and inherent shortcomings of their materials. Herein, we introduce a novel moisture-proof conductive hydrogel with high toughness (2.89 MJ m-3), mechanical strength (1.00 MPa), and high moisture-proof sensing performance by using dopamine-functionalized gold nanoparticles as conductive fillers into carboxymethyl guar gum and acrylamide. Moreover, the hydrogel can realize real-time monitoring of major and subtle human movements with good sensitivity and repeatability. In addition, the hydrogel-assembled strain sensor exhibits stable sensing signals after being left for 1 h, and the relative resistance change rate under different strains (25-300%) shows no obvious noise signal up to 99% relative humidity. Notably, the wearable strain sensing is suitable for wearable sensor devices with high relative humidity.

Corneal remodeling after SMILE for moderate and high myopia: short-term assessment of spatial changes in corneal volume and thickness.

PURPOSE: To evaluate the early corneal remodeling and its influencing factors after Small incision lenticule extraction (SMILE) for moderate and high myopia. METHODS: This was a retrospective study. Pre- and post-operative (1 week and 1, 3, 6 months) corneal volume (CV), mean keratometry (Km), and corneal thickness (CT) were measured by Scheimpflug tomography. CT at the central, thinnest point, and on concentric circles of 2, 4, and 6 mm diameter was recorded to assess corneal thickness spatial profile (CTSP) and percentage of thickness increase (PTI) in the moderate and high myopia groups, and to explore possible influencing factors. RESULTS: After SMILE, the peripheral CT decreased in the moderate myopia group and central corneal thickness (CCT) increased in the high myopia group at 1 month compared to 1 week (all P < 0.05). The CV, Km and CT were significantly increased at 3 months compared to 1 month (all P < 0.05), but there was no significant change at 6 months compared to 3 months for both groups (all P > 0.05). Patients with high myopia showed greater corneal thickness changes (△CT) and higher PTI than moderate myopia (all P < 0.05). Regression analysis revealed that in addition to refraction, peripheral PTI was negatively correlated with CCT in the moderate myopia group (4 mm: ß = -0.023, P = 0.001; 6 mm: ß = -0.050, P < 0.001), as well as in the high myopia group (4 mm: ß = -0.038, P < 0.001; 6 mm: ß = -0.094, P < 0.001). Moreover, peripheral PTI in the moderate myopia group was negatively correlated with age (4 mm: ß = -0.071, P = 0.003; 6 mm: ß = -0.162, P < 0.001). CONCLUSIONS: After SMILE, the CV, Km, and CTSP showed dynamic changes in the early stage, which stabilized after 3 months. Compared to the moderate myopia group, the high myopia group experienced slower corneal stabilization. The change in PTI at 6 months after SMILE may be related to higher preoperative refraction, thinner CCT and younger age.

Phosphorus-Containing Polybenzoxazine Aerogels with Efficient Flame Retardation and Thermal Insulation.

Bisphenol A type benzoxazine (Ba) monomers and 10-(2, 5-dihydroxyphenyl)-10- hydrogen-9- oxygen-10- phosphine-10- oxide (DOPO-HQ) were employed to prepare flame retardant and heat insulated polybenzoxazine (PBa) composite aerogels. The successful preparation of PBa composite aerogels was confirmed by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The thermal degradation behavior and flame-retardant properties of the pristine PBa and PBa composite aerogels were investigated with thermogravimetric analysis (TGA) and cone calorimeter. The initial decomposition temperature of PBa decreased slightly after incorporating DOPO-HQ, increasing the char residue amount. The incorporation of 5% DOPO-HQ into PBa led to a decrease of 33.1% at the peak of the heat-release rate and a decrease of 58.7% in the TSP. The flame-retardant mechanism of PBa composite aerogels was investigated by SEM, Raman spectroscopy, and TGA coupled with infrared spectrometry (TG-FTIR). The aerogel has advantages such as a simple synthesis procedure, easy amplification, lightweight, low thermal conductivity, and good flame retardancy.

pH-Responsive Regulation of a Surfactant-Free Microemulsion Based on Hydrophobic Deep Eutectic Solvents.

Microemulsions containing a responsive hydrophobic deep eutectic solvent (HDES) as the oil phase that can replace conventional organic solvents are considered to be a green strategy. It is anticipated that a pH-responsive HDES is synthesized to prepare rapid responsive surfactant-free microemulsions (SFMEs), which enable the transition from SFMEs to nanoemulsions. Menthol and n-octanoic acid (OA) were assembled into HDES by hydrogen bonding at a molar ratio of 1:2. The pH-responsive HDES as the oil phase and isopropyl alcohol (IPA) as the double solvent could form HDES/IPA/water SFMEs, which have unique responsiveness. Specifically, from the nuclear magnetic resonance hydrogen spectrum, pH, thermogravimetry, and Fourier transform infrared spectroscopy investigations, the excellent switchability and stability of menthol-OA were demonstrated. On the basis of these complexes, microemulsions were successfully prepared. Electrical conductivity and pH measurements were used to determine the structures of microemulsions and the phase inversion process. The effects of the contents of water and HDES, NaCl concentration, and pH of the system were investigated. Nanoemulsions were successfully prepared on the basis of the pH response of the microemulsions. In addition, the prepared nanoemulsion has a unique pH-responsive behavior that can be controllably regulated among nanoemulsions, microemulsions, and phase separation systems.

pH-Induced reversible conversion between non-Pickering and Pickering high internal phase emulsion.

Solid-stabilized high internal phase emulsions have received extensive attention. Many previous studies have confirmed that solid emulsifiers in high internal phase Pickering emulsions (HIPPEs) provide a great interface mechanical barrier. With the development of research, novel solid-stabilized emulsions have emerged. These emulsions are stabilized by the electrostatic repulsion between the surfactants and hydrophilic solid particles. They are distinct from Pickering emulsions in that the solid particles do not exist at the oil-water interface, but are dispersed in the continuous phase, so it is called a non-Pickering emulsion. However, high internal phase non-Pickering emulsions (HIPNPEs) are rarely reported. Herein, HIPNPEs that are synergistically stabilized by anionic surfactants with dynamic covalent bonds and negatively charged nano-SiO2 particles were prepared. In the presence of dodecylamine, the acidity causes the dynamic covalent bonds to break and the surfactant to be inactivated. Additionally, the long-chain amine is protonated and adsorbed on nano-SiO2 particles to form a new surfactant for stabilizing HIPPEs. However, alkalinity causes the HIPNPEs to form again. In addition, rheological tests confirmed that the HIPNPEs and HIPPEs had similar rheological behaviors, which were typical gel-like fluids. The emulsion can quickly respond to realize the conversion between the different types of high internal phase emulsion by simple stimulation, which provides a new direction for stimulus-responsive high internal phase emulsions.

Preparation, Properties, and Mechanism of Flame-Retardant Poly(vinyl alcohol) Aerogels Based on the Multi-Directional Freezing Method.

In this work, exfoliated α-zirconium phosphate (α-ZrP) and phosphated cellulose (PCF) were employed to synthesize poly(vinyl alcohol) composite aerogels (PVA/PCF/α-ZrP) with excellent flame retardancy through the multi-directional freezing method. The peak heat release rate (PHRR), total smoke release (TSR), and CO production (COP) of the (PVA/PCF10/α-ZrP10-3) composite aerogel were considerably decreased by 42.3%, 41.4%, and 34.7%, as compared to the pure PVA aerogel, respectively. Simultaneously, the limiting oxygen index (LOI) value was improved from 18.1% to 28.4%. The mechanistic study of flame retardancy showed evidence that PCF and α-ZrP promoted the crosslinking and carbonization of PVA chains to form a barrier, which not only served as insulation between the material and the air, but also significantly reduced the emissions of combustible toxic gases (CO2, CO). In addition, the multi-directional freezing method further improved the catalytic carbonization process. This mutually advantageous strategy offers a new strategy for the preparation of composite aerogels with enhanced fire resistance.

Monolithic integration of multicolor InGaN LEDs with uniform luminescence emission.

We report the demonstration of monolithic integration of multicolor LEDs with highly spatially uniform emission wavelength. LEDs with colors ranging from green to orange are realized in a single selective area epitaxy process, and pronounced emission peak with very narrow spectral linewidth from photonic crystal effect is also achieved simultaneously. The In contents and emission colors are tuned by precisely controlling the nanowire emitter diameter and spacing. The emission wavelengths exhibit small variations of only a few nanometers among countless individual nanowire emitters over a sub-mm2 area region.

Deep Ultraviolet Luminescence Due to Extreme Confinement in Monolayer GaN/Al(Ga)N Nanowire and Planar Heterostructures.

We present experimental results confirming extreme quantum confinement in GaN/AlxGa1-xN (x = 0.65 and 1.0) nanowire and planar heterostructures, where the GaN layer thickness is of the order of a monolayer. The results were obtained from temperature- and excitation-dependent and time-resolved photoluminescence measurements. In the GaN/AlN nanowire heterostructure array sample, the measured emission peak at 300 K is ∼5.18-5.28 eV. This is in excellent agreement with the calculated optical gap of 5.23 eV and 160-260 meV below the calculated electronic gap of 5.44 eV, suggesting that the observed emission is excitonic in nature with an exciton binding energy of ∼160-260 meV. Similarly, in the monolayer GaN/Al0.65Ga0.35N planar heterostructure, the measured emission peak at 300 K is 4.785 eV and in good agreement with the calculated optical gap of 4.68 eV and 95 meV below the calculated electronic gap of 4.88 eV. The estimated exciton binding energy is 95 meV and in close agreement with our theoretical calculations. Excitation-dependent and time-resolved photoluminescence data support the presence of excitonic transitions. Our results indicate that deep-ultraviolet excitonic light sources and microcavity devices can be realized with heterostructures incorporating monolayer-thick GaN.

Ultrahigh Q microring resonators using a single-crystal aluminum-nitride-on-sapphire platform.

Aluminum-nitride-on-sapphire has recently emerged as a novel low-loss photonics platform for a variety of on-chip electro-optics as well as linear and nonlinear optics applications. In this Letter, we demonstrate ultrahigh quality factor (Qint) microring resonators using single-crystal aluminum nitride grown on a sapphire substrate with an optimized design and fabrication process. A record high intrinsic Qint up to 2.8×106 at the wavelength of 1550 nm is achieved with a fully etched structure, indicating a low propagation loss less than 0.13 dB/cm. Such high Qint aluminum-nitride-on-sapphire resonators with their wide bandgap and electro-optical and nonlinear optical properties is promising for a wide range of low-power and high-power compact on-chip applications over a broad spectral range.

Self-healable poly(acrylic acid-co-maleic acid)/glycerol/boron nitride nanosheet composite hydrogels at low temperature with enhanced mechanical properties and water retention.

Many living tissues possess excellent mechanical properties and water retention which enable them to self-heal at room temperature even below the freezing temperature of water. To mimic the unique features of living tissue, a poly(acrylic acid-co-maleic acid) composite hydrogel with enhanced mechanical properties and remarkable water retention was fabricated under accessible conditions. The hydrogel is functionalized by amino group modified boron nitride nanosheets (BNNS-NH2)/glycerol and exhibits self-healing abilities at low temperature. The self-healing process occurs through the re-establishing of hydrogen bonds and metal coordination interactions at the damaged surfaces. Its anti-freezing abilities enable the hydrogel to self-heal at -15 °C, and the self-healing efficiency based on tensile strength reaches up to ∼70%. Moreover, glycerol also endows the hydrogel with long-lasting water retention, which remains a water content of ∼99 wt% for more than 30 days. Meanwhile, the simultaneous introduction of BNNS-NH2 and glycerol significantly improved the mechanical properties of the hydrogel, which displays great stretchability (∼474%), tensile strength (∼151.3 kPa), stiffness (Young's modulus of ∼62.75 kPa) and toughness (∼355.13 kJ m-3). It is anticipated that these novel hydrogels will develop many fields and be exploited for new applications in extensive external environments.

Features of the piezo-phototronic effect on optoelectronic devices based on wurtzite semiconductor nanowires.

The piezo-phototronic effect, a three way coupling effect of piezoelectric, semiconductor and photonic properties in non-central symmetric semiconductor materials, utilizing the piezo-potential as a "gate" voltage to tune the charge transport/generation/recombination and modulate the performance of optoelectronic devices, has formed a new field and attracted lots of interest recently. The mechanism was verified in various optoelectronic devices such as light emitting diodes (LEDs), photodetectors and solar cells etc. The fast development and dramatic increasing interest in the piezo-phototronic field not only demonstrate the way the piezo-phototronic effects work, but also indicate the strong need for further research in the physical mechanism and potential applications. Furthermore, it is important to distinguish the contribution of the piezo-phototronic effect from other factors induced by external strain such as piezoresistance, band shifting or contact area change, which also affect the carrier behaviour and device performance. In this perspective, we review our recent progress on piezo-phototronics and especially focus on pointing out the features of piezo-phototronic effect in four aspects: I-V characteristics; c-axis orientation; influence of illumination; and modulation of carrier behaviour. Finally we proposed several criteria for describing the contribution made by the piezo-phototronic effect to the performance of optoelectronic devices. This systematic analysis and comparison will not only help give an in-depth understanding of the piezo-phototronic effect, but also work as guide for the design of devices in related areas.