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Impact ionization, which supports carrier multiplication, is promising for applications in single photon detection1 and sharp threshold swing field effect devices2. However, initiating the impact ionization of avalanche breakdown requires a high applied electric field in a long active region, which hampers carrier multiplication with a high gain, low bias and superior noise performance3,4. Here we report the observation of ballistic avalanche phenomena in sub-mean free path (MFP) scaled vertical InSe/black phosphorus (BP)5–9 heterostructures10. We use these heterojunctions to fabricate avalanche photodetectors (APDs) with a sensitive mid-infrared light detection (4 μm wavelength) and impact ionization transistors with a steep subthreshold swing (<0.25 mV dec–1). The devices show a low avalanche threshold (<1 V), low noise figure and distinctive density spectral shape. Our transport measurements suggest that the breakdown originates from a ballistic avalanche phenomenon, where the sub-MFP BP channel support the lattice impact ionization by electrons and holes and the abrupt current amplification without scattering from the obstacles in a deterministic nature. Our results provide new strategies for the development of advanced photodetectors1,11,12 via efficient carrier manipulation at the nanoscale.Ballistic avalanche phenomena in vertical InSe/BP heterostructures enable the demonstration of high-performance avalanche photodetectors and impact ionization transistors.

The progress in exploiting new electronic materials has been a major driving force in solid-state physics. As a new state of matter, a Weyl semimetal (WSM), in particular a type-II WSM, hosts Weyl fermions as emergent quasiparticles and may harbour novel electrical transport properties. Nevertheless, such a type-II WSM material has not been experimentally observed. In this work, by performing systematic magneto-transport studies on thin films of a predicted material candidate WTe 2 , we observe notable negative longitudinal magnetoresistance, which can be attributed to the chiral anomaly in WSM. This phenomenon also exhibits strong planar orientation dependence with the absence along the tungsten chains, consistent with the distinctive feature of a type-II WSM. By applying a gate voltage, we demonstrate that the Fermi energy can be in-situ tuned through the Weyl points via the electric field effect. Our results may open opportunities for implementing new electronic applications, such as field-effect chiral devices. Controllable electric transport of topological particles in solid state systems hold the key towards novel electronic applications. Here, Wang et al . demonstrate gate-tunable negative longitudinal magnetoresistance in WTe 2 , featuring controllable transport of Type-II Weyl fermions.

Semiconducting two-dimensional transition metal dichalcogenides are emerging as top candidates for post-silicon electronics. While most of them exhibit isotropic behaviour, lowering the lattice symmetry could induce anisotropic properties, which are both scientifically interesting and potentially useful. Here we present atomically thin rhenium disulfide (ReS 2 ) flakes with unique distorted 1T structure, which exhibit in-plane anisotropic properties. We fabricated monolayer and few-layer ReS 2 field-effect transistors, which exhibit competitive performance with large current on/off ratios (∼10 7 ) and low subthreshold swings (100 mV per decade). The observed anisotropic ratio along two principle axes reaches 3.1, which is the highest among all known two-dimensional semiconducting materials. Furthermore, we successfully demonstrated an integrated digital inverter with good performance by utilizing two ReS 2 anisotropic field-effect transistors, suggesting the promising implementation of large-scale two-dimensional logic circuits. Our results underscore the unique properties of two-dimensional semiconducting materials with low crystal symmetry for future electronic applications. Many two-dimensional materials exhibit isotropic properties, but anisotropy can extend the functionality of future devices. Here, the authors fabricate field-effect transistors from single and few-layer rhenium disulfide and observe an anisotropic ratio of three to one along the two principle axes

Bright light conditions are supposed to curb eye growth in animals with experimental myopia. Here we investigated the effects of temporal bright light at very low frequencies exposures on lens-induced myopia (LIM) progression. Myopia was induced by application of -6.00 D lenses over the right eye of guinea pigs. They were randomly divided into four groups based on exposure to different lighting conditions: constant low illumination (CLI; 300 lux), constant high illumination (CHI; 8,000 lux), very low frequency light (vLFL; 300/8,000 lux, 10 min/c), and low frequency light (LFL; 300/8,000 lux, 20 s/c). Refraction and ocular dimensions were measured per week. Changes in ocular dimensions and refractions were analyzed by paired t-tests, and differences among the groups were analyzed by one-way ANOVA. Significant myopic shifts in refractive error were induced in lens-treated eyes compared with contralateral eyes in all groups after 3 weeks (all < 0.05). Both CHI and LFL conditions exhibited a significantly less refractive shift of LIM eyes than CLI and vLFL conditions ( < 0.05). However, only LFL conditions showed significantly less overall myopic shift and axial elongation than CLI and vLFL conditions (both < 0.05). The decrease in refractive error of both eyes correlated significantly with axial elongation in all groups ( < 0.001), except contralateral eyes in the CHI group ( = 0.231). LFL condition significantly slacked lens thickening in the contralateral eyes. Temporal bright light at low temporal frequency (0.05 Hz) appears to effectively inhibit LIM progression. Further research is needed to determine the safety and the potential mechanism of temporal bright light in myopic progression.

The development of myopia is associated with scleral remodeling, but it is unclear which factors regulate this process. This study investigated bone morphogenetic protein-2 (BMP-2) expression in the sclera of guinea pigs with lens-induced myopia (LIM) and after recovery from myopia and evaluated the effect of BMP-2 on extracellular matrix (ECM) synthesis in human scleral fibroblasts (HSFs) cultured in vitro. Lens-induced myopia was brought about in two groups of guinea pigs (the lens-induced myopia and myopia recovery groups) by placing -4.00 D lenses on the right eye for three weeks. The left eye served as a contralateral control. In the recovery group, the lenses were removed after one week. The refractive power and axial length of the eyes were measured, and the BMP-2 expression levels in the sclera were measured. After three weeks, the lens-induced eyes acquired relative myopia in both groups of guinea pigs. Immunostaining of the eyeballs revealed significantly decreased BMP-2 expression in the posterior sclera of the myopic eyes compared to the contralateral eyes. One week after lens removal, BMP-2 expression recovered, and no differences were observed between the experimental and contralateral eyes in the recovery group. HSFs were cultured with BMP-2 or transforming growth factor-β1 (TGF-β1). Type I and type III collagen synthesis was significantly up-regulated following BMP-2 treatment in culture after one and two weeks, but the ratio of type III to type I collagen mRNA was not increased. Biosynthesis of glycosaminoglycan (GAG) and aggrecan was increased in HSFs treated with BMP-2. Some chondrogenesis-associated genes expression increased in HSFs treated with BMP-2. From this study, we concluded that BMP-2 is involved in scleral remodeling in the development and recovery of lens-induced myopia.

To examine the prevalence of refractive errors in children aged 3-6 years in China. Children were recruited for a trial of a home-based amblyopia screening kit in Guangzhou preschools, during which cycloplegic refractions were measured in both eyes of 2480 children. Cycloplegic refraction (from 3 to 4 drops of 1% cyclopentolate to ensure abolition of the light reflex) was measured by both autorefraction and retinoscopy. Refractive errors were defined as followed: myopia (at least -0.50 D in the worse eye), hyperopia (at least +2.00 D in the worse eye) and astigmatism (at least 1.50 D in the worse eye). Different definitions, as specified in the text, were also used to facilitate comparison with other studies. The mean spherical equivalent refractive error was at least +1.22 D for all ages and both genders. The prevalence of myopia for any definition at any age was at most 2.5%, and lower in most cases. In contrast, the prevalence of hyperopia was generally over 20%, and declined slightly with age. The prevalence of astigmatism was between 6% and 11%. There was very little change in refractive error with age over this age range. Previous reports of less hyperopic mean spherical equivalent refractive error, and more myopia and less hyperopia in children of this age may be due to problems with achieving adequate cycloplegia in children with dark irises. Using up to 4 drops of 1% cyclopentolate may be necessary to accurately measure refractive error in paediatric studies of such children. Our results suggest that children from all ethnic groups may follow a similar pattern of early refractive development, with little myopia and a hyperopic mean spherical equivalent over +1.00 D up to the age of 5-6 years in most conditions.

The aim of this study was to investigate the time-course of changes in choroidal thickness (ChT) following complete mydriasis induced by compound tropicamide. ChT was measured by OCT with the enhanced-depth imaging technique (Spectralis HRA+OCT, Heidelberg Engineering, Germany) at nine locations of the fundus: subfoveal ChT (SFChT) and ChT at 1 mm and 3 mm from the fovea in four quadrants. Mydriasis was induced with compound tropicamide (0.5% tropicamide plus 0.5% phenylephrine hydrochloride, three doses at 5-minute intervals). Measurements were conducted prior to the instillation and at 0, 30, and 60 min following complete mydriasis. Results at different time-points were compared using repeated-measures ANOVA to investigate the time-course of the changes. Thirty-nine subjects (mean age 11.9±2 years; 16 males and 23 females) were enrolled in the study. Compound tropicamide resulted in a statistically significant decrease in SFChT at 0, 30, and 60 min after complete mydriasis, as compared to baseline (-5±4 μm, -12±4 μm, and -13±4 μm, respectively; all P<0.0001). No significant changes were detected in the parafoveal choroid except at 1 mm temporal (T1mm) and nasal (N1mm) to the fovea at 30 and 60 min (T1mm: -6±4 μm and -7±5 μm at 30 and 60 min; N1mm: -6±4 μm and -7±5 μm at 30 and 60 min, respectively; all P<0.0001). Repeated-measures ANOVA showed a significant interaction between the time after complete mydriasis and the effect of the mydriasis agent. Complete mydriasis induced by compound tropicamide led to choroidal thinning, and the magnitude varied over time.

All-trans retinoic acid (ATRA) plays an important role in ocular development. Previous studies found that retinoic acid could influence the metabolism of scleral remodeling by promoting retinal pigment epithelium (RPE) cells to secrete secondary signaling factors. The purpose of this study was to investigate whether retinoic acid affected secretion of bone morphogenetic protein 2 (BMP-2) and matrix metalloproteinase 2 (MMP-2) and to explore the signaling pathway of retinoic acid in cultured acute retinal pigment epithelial 19 (ARPE-19) cells. The effects of ATRA (concentrations from 10-9 to 10-5 mol/l) on the expression of retinoic acid receptors (RARs) in ARPE-19 cells were examined at the mRNA and protein levels using reverse transcription-polymerase chain reaction (RT-PCR) and western blot assay, respectively. The effects of treating ARPE-19 cells with ATRA concentrations ranging from 10-9 to 10-5 mol/l for 24 h and 48 h or with 10-6mol/l ATRA at different times ranging from 6h to 72h were assessed using real-time quantitative PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA). The contribution of RARβ-induced activation of ARPE-19 cells was confirmed using LE135, an antagonist of RARβ. RARβ mRNA levels significantly increased in the ARPE-19 cells treated with ATRA for 24h and 48h. These increases in RARβ mRNA levels were dose dependent (at concentrations of 10-9 to 10-5 mol/l) with a maximum effect observed at 10-6 mol/l. There were no significant changes in the mRNA levels of RARα and RARγ. Western blot assay revealed that RARβ protein levels were increased significantly in a time-dependent manner in ARPE-19 cells treated with 10-6 mol/l ATRA from 12 h to 72 h, with a marked increase observed at 24 h and 48 h. The upregulation of RARβ and the ATRA-induced secretion in ARPE-19 cells could be inhibited by the RARβ antagonist LE135. ATRA induced upregulation of RARβ in ARPE-19 cells and stimulated these cells to secrete BMP-2 and MMP-2.

Background Myopia presents a noteworthy global health concern, urging exploration of innovative treatments. The role of intraocular pressure (IOP) in regulating the progression of myopia has been controversial. Methods To investigate the impact of reducing IOP to varying extents on myopia progression, three groups receiving distinct IOP-lowering medications (Brinzolamide, Latanoprost, and a combination of Brinzolamide and Latanoprost) were designed in a form-deprived myopic guinea pig model. Additionally, proteomics analyses were conducted to identify differentially expressed proteins in the sclera. Results Based on 24-h and 4-week IOP monitoring, the group receiving both Brinzolamide and Latanoprost exhibited the greatest magnitude of IOP reduction and the most significant inhibition of axial length (AL) growth. Moreover, the administration of IOP-lowering medications increased choroidal thickness and induced alterations in the structure of scleral collagen fibrils. Notably, scleral proteomics revealed remodeling processes associated with key mechanisms, including proteolysis, fibrinolysis, and metal ion binding. Conclusions Our findings highlight that pressure-dependent scleral remodeling contributes to the deceleration of AL elongation. These results underscore the efficacy of IOP reduction in mitigating the progression of myopia, providing a promising alternative strategy for myopia management.

Purpose. To determine three-year change of the corneal biomechanical parameter stress-strain index (SSI) in schoolchildren aged 7– 9 years and their correlation with refractive error and axial length (AL). Methods. This is a prospective cohort study. Data of the AL, refractive error, and corneal biomechanical parameter SSI were collected at baseline and a 3-year follow-up for 217 schoolchildren. SSI, AL, and refractive error were measured via corneal visualization Scheimpflug technology (Corvis ST), IOLMaster biometry, and cycloplegic refraction. Three years of changes in SSI and its association with refractive error and AL were analyzed. Participants were divided into persistent nonmyopia (PNM), newly developed myopia (NDM), and persistent myopia (PM). The three-year difference in SSI among the three groups was analyzed. Results. After three years of follow-up, the corneal biomechanical parameter SSI decreased in all participants (P<0.01). There was a negative correlation between the change in SSI and the change in AL (r = −0.205, P=0.002) and a positive correlation between the change in refractive error (r = 0.183, P=0.007). After three years of follow-up, there was a decrease in the SSI for the NDM, PM, and PNM participants, with a median change of −0.05 for PNM and −0.13 and −0.09 for the NDM and PM, respectively. There was a significant decrease in corneal biomechanical properties for NDM patients compared with PNM patients (P<0.01). Conclusion. In 7- to 9-year-old schoolchildren, SSI decreased after three years of the longitudinal study, and the change in SSI was correlated with the change in AL and refractive error. There was a rapid decrease in corneal biomechanical properties among newly developed myopic patients.