Multi-Level Switching of Spin-Torque Ferromagnetic Resonance in 2D Magnetite.

2D magnetic materials hold substantial promise in information storage and neuromorphic device applications. However, achieving a 2D material with high Curie temperature (TC), environmental stability, and multi-level magnetic states remains a challenge. This is particularly relevant for spintronic devices, which require multi-level resistance states to enhance memory density and fulfil low power consumption and multi-functionality. Here, the synthesis of 2D non-layered triangular and hexagonal magnetite (Fe3O4) nanosheets are proposed with high TC and environmental stability, and demonstrate that the ultrathin triangular nanosheets show broad antiphase boundaries (bAPBs) and sharp antiphase boundaries (sAPBs), which induce multiple spin precession modes and multi-level resistance. Conversely, the hexagonal nanosheets display slip bands with sAPBs associated with pinning effects, resulting in magnetic-field-driven spin texture reversal reminiscent of "0" and "1" switching signals. In support of the micromagnetic simulation, direct explanation is offer to the variation in multi-level resistance under a microwave field, which is ascribed to the multi-spin texture magnetization structure and the randomly distributed APBs within the material. These novel 2D magnetite nanosheets with unique spin textures and spin dynamics provide an exciting platform for constructing real multi-level storage devices catering to emerging information storage and neuromorphic computing requirements.

High-Performance Broadband Image Sensing Photodetector Based on MnTe/WS2 van der Waals Epitaxial Heterostructures.

Two-dimensional transition metal dichalcogenide (TMDC) heterostructure is receiving considerable attention due to its novel electronic, optoelectronic, and spintronic devices with design-oriented and functional features. However, direct design and synthesis of high-quality TMDC/MnTe heterostructures remain difficult, which severely impede further investigations of semiconductor/magnetic semiconductor devices. Herein, the synthesis of high-quality vertically stacked WS2/MnTe heterostructures is realized via a two-step chemical vapor deposition method. Raman, photoluminescence, and scanning transmission electron microscopy characterizations reveal the high-quality and atomically sharp interfaces of the WS2/MnTe heterostructure. WS2/MnTe-based van der Waals field effect transistors demonstrate high rectification behavior with rectification ratio up to 106, as well as a typical p-n electrical transport characteristic. Notably, the fabricated WS2/MnTe photodetector exhibits sensitive and broadband photoresponse ranging from UV to NIR with a maximum responsivity of 1.2 × 103 A/W, a high external quantum efficiency of 2.7 × 105%, and fast photoresponse time of ∼50 ms. Moreover, WS2/MnTe heterostructure photodetectors possess a broadband image sensing capability at room temperature, suggesting potential applications in next-generation high-performance and broadband image sensing photodetectors.

Room-temperature ferromagnetic CoSe2nanoplates synthesized by chemical vapor deposition.

Among novel two-dimensional materials, transition metal dichalcogenides (TMDs) with 3dmagnetic elements have been extensively researched owing to their unique magnetic, electric, and photoelectric properties. As an important member of TMDs, CoSe2is an interesting material with controversial magnetic properties, hitherto there are few reports related to the magnetism of CoSe2materials. Here, we report the synthesis of CoSe2nanoplates on Al2O3substrates by chemical vapor deposition (CVD). The CVD-grown CoSe2nanoplates exhibit three typical morphologies (regular hexagonal, hexagonal, and pentagonal shapes) and their lateral sizes and thickness of CoSe2nanoplates can reach up to hundreds of microns and several hundred nanometers, respectively. The electric-transport measurement shows a metallic feature of CoSe2nanoplates. Furthermore, the slanted hysteresis loop and nonzero remnant magnetization of the CoSe2nanoplates confirm the ferromagnetism in the temperature range of 5-400 K. This work provides a novel platform for designing CoSe2-based spintronic devices and studying related magnetic mechanisms.

Atomic structure and large magnetic anisotropy in air-sensitive layered ferromagnetic VI3.

We report the air-sensitivity, atomic structure, and magnetic anisotropy of VI3 single crystals. We find that VI3 nanocrystals exhibit a large MR/MS ratio of around 0.75 and a uniaxial anisotropic constant of an order of 105 erg cc-1 below the Curie temperature. Furthermore, density functional theory calculations reveal that both the monolayer and bulk VI3 are ferromagnetic insulators, and the magnetic moment of the system arises mainly from the d orbital of the V atom. These findings open a feasible avenue to fabricating TEM specimens of air-sensitive layered materials, providing an in-depth comprehensive understanding of a layered ferromagnetic VI3.

Medical expenditure for strabismus: a hospital-based retrospective survey.

BACKGROUND AND AIMS: The misconception of the purpose of strabismus treatment has, on the one hand, affected the motivation of strabismus patients to seek care and, on the other hand, has resulted in strabismus not being covered by health insurance, both of which interact to limit the motivation of strabismus patients and also impose a financial burden on strabismus patients. Previous studies on the cost of strabismus had only addressed the cost utility and functional and psychosocial benefits of strabismus surgery. The aim of this study was to estimate the direct medical expenditure incurred for strabismus surgery and analyze the trend for the period 2014-2019 using the data collected by local eye hospitals in northeast China. METHODS: This study was based on 6-year strabismus medical expenditure data collected from the eye hospital of the first affiliated hospital of Harbin medical university, covering 3596 strabismus patients who had strabismus surgery. All medical expenditure data were adjusted to 2014 using China's annual consumer price index to remove the effects of inflation. RESULTS: The average direct medical expenditure for strabismus cares (in 2014) was 5309.6 CNY (US$870.4), and the annual growth rates from 2015 to 2019 (compared with the previous year) were 9.3, 7.7, 21.7, 14.5, and 4.3%, respectively. Surgical expenses accounted for the highest proportion (33.1%) of the total medical expenses followed by examinations expenses (19.7%) and medical consumables expenses (18.7%). The regression coefficient for general anaesthesia was 1804.5 and age was less than 0. CONCLUSION: The average direct medical expenditure for strabismus increases year by year, and the growth rate is rapid. Anesthesia was the most important factor increasing medical cost, and age was negatively correlated with cost.

High-sensitivity and versatile plasmonic biosensor based on grain boundaries in polycrystalline 1L WS2 films.

Structural defects play an important role in exploitation of two-dimensional layered materials (2DLMs) for advanced biosensors with the increasingly high sensitivity and low detection limit. Grain boundaries (GBs), as an important type of structural defect in polycrystalline 2DLM films, potentially provide sufficient active defect sites for the immobilization of bioreceptor units via chemical functionalization. In this work, we report the selective functionalization of high-density GBs with complementary DNA receptors, via gold nanoparticle (AuNP) linkers, in wafer-scale polycrystalline monolayer (1L) W(Mo)S2 films as versatile plasmonic biosensing platforms. The large surface area and GB-rich nature of the polycrystalline 1L WS2 film enabled the immobilization of bioreceptors in high surface density with spatial uniformity, while the AuNPs perform not only as bioreceptor linkers, but also promote detection sensitivity through surface plasmon resonance enhancement effect. Therefore, the presented biosensor demonstrated highly sensitive and selective sub-femto-molar detection of representative RNA sequences from the novel coronavirus (RdRp, ORF1ad and E). This work demonstrates the immense potential of AuNP-decorated GB-rich 2DLMs in the design of ultra-sensitive biosensing platforms for the detection of biological targets beyond RNA, bringing new opportunities for novel healthcare technologies.

Grain-boundary-rich polycrystalline monolayer WS2 film for attomolar-level Hg2+ sensors.

Emerging two-dimensional (2D) layered materials have been attracting great attention as sensing materials for next-generation high-performance biological and chemical sensors. The sensor performance of 2D materials is strongly dependent on the structural defects as indispensable active sites for analyte adsorption. However, controllable defect engineering in 2D materials is still challenging. In the present work, we propose exploitation of controllably grown polycrystalline films of 2D layered materials with high-density grain boundaries (GBs) for design of ultra-sensitive ion sensors, where abundant structural defects on GBs act as favorable active sites for ion adsorption. As a proof-of-concept, our fabricated surface plasmon resonance sensors with GB-rich polycrystalline monolayer WS2 films have exhibited high selectivity and superior attomolar-level sensitivity in Hg2+ detection owing to high-density GBs. This work provides a promising avenue for design of ultra-sensitive sensors based on GB-rich 2D layered materials.

Morphology-Tunable Synthesis of Intrinsic Room-Temperature Ferromagnetic γ-Fe2O3 Nanoflakes.

Intrinsic two-dimensional (2D) magnetic materials with room-temperature ferromagnetism and air stability are highly desirable for spintronic applications. However, the experimental observations of such 2D or ultrathin ferromagnetic materials are rarely reported owing to the scarcity of these materials in nature and for the intricacy in their synthesis. Here, we report a successful controllable growth of ultrathin γ-Fe2O3 nanoflakes with a variety of morphologies tunable by the growth temperature alone using a facile chemical vapor deposition method and demonstrate that all ultrathin nanoflakes still show intrinsic room-temperature ferromagnetism and a semiconducting nature. The γ-Fe2O3 nanoflakes epitaxially grown on α-Al2O3 substrates take a triangular shape at low temperature and develop gradually in lateral size, forming eventually a large-scale γ-Fe2O3 thin film as the growth time increases due to a thermodynamic control process. The morphology of the nanoflakes could be tuned from triangular to stellated, petaloid, and dendritic crystalloids in sequence with the rise of precursor temperature, revealing a growth process from thermodynamically to kinetically dominated control. Moreover, the petaloid and dendritic nanoflakes exhibit enhanced coercivity compared with the triangular and stellated nanoflakes, and all the nanoflakes with diverse shapes possess differing electrical conductivity. The findings of such ultrathin, air-stable, and room-temperature ferromagnetic γ-Fe2O3 nanoflakes with tunable shape and multifunctionality may offer guidance in synthesizing other non-layered magnetic materials for next-generation electronic and spintronic devices.

Toward Efficient All-Polymer Solar Cells via Halogenation on Polymer Acceptors.

Although halogenation has been widely regarded as an effective approach to adjust the properties of organic semiconductors, systematic investigation on the comparison of nonhalogenated and halogenated polymer acceptors only received minor attention in all-polymer solar cell (all-PSC) community. Herein, we report three IDIC-based narrow band gap polymer acceptors, PIDIC2T, PIDIC2T2F, and PIDIC2T2Cl, which are composed of IDIC-C16 building blocks as acceptor units, linking pristine bithiophene, fluorinated bithiophene, or chlorinated bithiophene as donor units. Although these three polymer acceptors exhibit nearly identical lowest unoccupied molecular orbital (LUMO) levels of ca. -3.87 eV with a similar optical band gap of ca. 1.54 eV, we found that different halogen species significantly affect the electron mobility and thin-film morphology of the polymer acceptors. All-PSCs were fabricated by pairing three polymer acceptors with a PBDB-T polymer donor, while PIDIC2T2Cl delivered a highest power conversion efficiency (PCE) of 5.34% due to its favorable bulk morphology with smaller root-mean-square (rms) roughness values, which induce the relatively more balanced charge carrier mobilities. By blending the fluorinated analogue of PBDB-T, PM6, further improved VOC, JSC, and fill factor (FF) of devices were achieved (5.46% for PM6:PIDIC2T, 4.96% for PM6:PIDIC2T2F, 7.11% for PM6:PIDIC2T2Cl), which can be due to the synergistic effect of the deeper highest occupied molecular orbital (HOMO) energy level of PM6, enhanced crystallinity, and more matched charge transport. This systematic study provides an insight into the influence of halogenation (fluorination and chlorination) on the optoelectrical properties of n-type organic semiconductors and demonstrates an efficient strategy that the design guideline for polymer acceptors can be enriched by backbone halogenation to further develop high-performance all-PSCs.

Giant Valley Coherence at Room Temperature in 3R WS2 with Broken Inversion Symmetry.

Breaking the space-time symmetries in materials can markedly influence their electronic and optical properties. In 3R-stacked transition metal dichalcogenides, the explicitly broken inversion symmetry enables valley-contrasting Berry curvature and quantization of electronic angular momentum, providing an unprecedented platform for valleytronics. Here, we study the valley coherence of 3R WS2 large single-crystal with thicknesses ranging from monolayer to octalayer at room temperature. Our measurements demonstrate that both A and B excitons possess robust and thickness-independent valley coherence. The valley coherence of direct A (B) excitons can reach 0.742 (0.653) with excitation conditions on resonance with it. Such giant and thickness-independent valley coherence of large single-crystal 3R WS2 at room temperature would provide a firm foundation for quantum manipulation of the valley degree of freedom and practical application of valleytronics.

Grain wall boundaries in centimeter-scale continuous monolayer WS2 film grown by chemical vapor deposition.

Centimeter-scale continuous monolayer WS2 film with large tensile strain has been successfully grown on oxidized silicon substrate by chemical vapor deposition, in which monolayer grains can be more than 200 µm in size. Monolayer WS2 grains are observed to merge together via not only traditional grain boundaries but also non-traditional ones, which are named as grain walls (GWs) due to their nanometer-scale widths. The GWs are revealed to consist of two or three layers. Though not a monolayer, the GWs exhibit significantly enhanced fluorescence and photoluminescence. This enhancement may be attributed to abundant structural defects such as stacking faults and partial dislocations in the GWs, which are clearly observable in atomically resolved high resolution transmission electron microscopy and scanning transmission electron microscopy images. Moreover, GW-based phototransistor is found to deliver higher photocurrent than that based on monolayer film. These features of GWs provide a clue to microstructure engineering of monolayer WS2 for specific applications in (opto)electronics.

Electric-Field Control of Spin-Orbit Torques in WS2/Permalloy Bilayers.

Transition metal dichalcogenides (TMDs) have drawn great attention owing to their potential for electronic, optoelectronic, and spintronic applications. In TMDs/ferromagnetic bilayers, an efficient spin current can be generated by the TMDs to manipulate the magnetic moments in the ferromagnetic layer. In this work, we report on the electric-field modulation of spin-orbit torques (SOTs) in WS2/NiFe bilayers by the spin-torque ferromagnetic resonance technique. It is found that the radio frequency current can induce a spin accumulation at the WS2/NiFe interface because of the interfacial Rashba-Edelstein effect. As a consequence, the SOT ratio between the field-like and antidamping-like torques can be effectively controlled by applying the back-gate voltage in WS2/NiFe bilayers. These results provide a strategy for controlling the SOT by using semiconducting TMDs.

Ultrahigh-Gain and Fast Photodetectors Built on Atomically Thin Bilayer Tungsten Disulfide Grown by Chemical Vapor Deposition.

The low responsivity observed in photodetectors based on monolayer transition-metal dichalcogenides has encouraged the pursuit of approaches that can efficiently enhance the external quantum efficiency, which relies predominantly on the light absorption, the lifetime of the excess carriers, and the charge collection efficiency. Here, we demonstrate that phototransistors fabricated on large-area bilayer tungsten disulfide (WS2) grown by chemical vapor deposition exhibit remarkable performance with photoresponsivity, photogain, and detectivity of up to ∼3 × 103 A/W, 1.4 × 104, and ∼5 × 1012 Jones, respectively. These figures of merit of bilayer WS2 provide a significant advantage over monolayer WS2 due to the greatly improved carrier mobility and significantly reduced contact resistance. The photoresponsivity of bilayer WS2 phototransistor can be further improved to up to 1 × 104 A/W upon biasing a gate voltage of 60 V, without evident reduction in detectivity. Moreover, the bilayer WS2 phototransistor exhibits a high response speed of less than 100 µs, large bandwidth of 4 kHz, high cycling reliability of over 105 cycles, and spatially homogeneous photoresponse. These outstanding figures of merit make WS2 bilayer a highly promising candidate for the design of high-performance optoelectronics in the visible regime.

Strain Release Induced Novel Fluorescence Variation in CVD-Grown Monolayer WS2 Crystals.

Tensile strain is intrinsic to monolayer crystals of transition metal disulfides such as Mo(W)S2 grown on oxidized silicon substrates by chemical vapor deposition (CVD) owing to the much larger thermal expansion coefficient of Mo(W)S2 than that of silica. Here we report fascinating fluorescent variation in intensity with aging time in CVD-grown triangular monolayer WS2 crystals on SiO2 (300 nm)/Si substrates and formation of interesting concentric triangular fluorescence patterns in monolayer crystals of large size. The novel fluorescence aging behavior is recognized to be induced by the partial release of intrinsic tensile strain after CVD growth and the induced localized variations or gradients of strain in the monolayer crystals. The results demonstrate that strain has a dramatic impact on the fluorescence and photoluminescence of monolayer WS2 crystals and thus could potentially be utilized to tune electronic and optoelectronic properties of monolayer transition metal disulfides.

Highly sensitive and fast monolayer WS2 phototransistors realized by SnS nanosheet decoration.

Two-dimensional chalcogenide monolayers are strong candidates for next-generation flexible and transparent optoelectronics. Due to the intrinsic ultrathin thickness and limited optical absorption, however, their responsivity is normally low. Here we develop a simple and low-cost method to fabricate high-performance hybrid phototransistors of monolayer WS2 with significantly enhanced responsivity and an extended spectral response range, by virtue of surface decoration with liquid-phase exfoliated SnS nanosheets (NSs). The hybrid phototransistors show a much enhanced responsivity of ∼2 A W-1 and an ultrahigh light/dark signal-to-noise ratio of 106 under 457 nm excitation, exhibiting a significant increase of 3 orders of magnitude in responsivity and a 100 fold increase in signal-to-noise ratio, compared with pure WS2 devices. Our hybrid photodetectors also exhibit a respectable response speed, with a rise and decay time of 51 µs and 98 µs, respectively. After optimal surface decoration with narrow bandgap SnS NSs atop a monolayer WS2 channel, an emergent optical responsivity in the near infrared region (1064 nm) is also observed.

Enhanced Photoresponse of SnSe-Nanocrystals-Decorated WS2 Monolayer Phototransistor.

Single-layer WS2 has shown excellent photoresponse properties, but its promising applications in high-sensitivity photodetection suffer from the atomic-thickness-limited adsorption and band-gap-limited spectral selectivity. Here we have carried out investigations on WS2 monolayer based phototransistors with and without decoration of SnSe nanocrystals (NCs) for comparison. Compared to the solely WS2 monolayer, SnSe NCs decoration leads to not only huge enhancement of photoresponse in visible spectrum but also extension to near-infrared. Under excitation of visible light in a vacuum, the responsivity at zero gate bias can be enhanced by more than 45 times to ∼99 mA/W, and the response time is retained in millisecond level. Particularly, with extension of photoresponse to near-infrared (1064 nm), a responsivity of 6.6 mA/W can be still achieved. The excellent photoresponse from visible to near-infrared is considered to benefit from synergism of p-type SnSe NCs and n-type WS2 monolayer, or in other words, the formed p-n heterojunctions between p-type SnSe NCs and n-type WS2 monolayer.

Observation of Strong Interlayer Coupling in MoS2/WS2 Heterostructures.

Epitaxial growth of A-A and A-B stacking MoS2 on WS2 via a two-step chemical vapor deposition method is reported. These epitaxial heterostructures show an atomic clean interface and a strong interlayer coupling, as evidenced by systematic characterization. Low-frequency Raman breathing and shear modes are observed in commensurate stacking bilayers for the first time; these can serve as persuasive fingerprints for interfacial quality and stacking configurations.

Grape seed proanthocyanidin extract protects human lens epithelial cells from oxidative stress via reducing NF-кB and MAPK protein expression.

PURPOSE: Oxidative damage induced by H2O2 treatment can irreversibly damage the lens epithelium, resulting in cell death and cataract. Grape seed extract (GSE) is a widely consumed dietary supplement that has the capability to scavenge oxidants and free radicals. GSE contain 70%-95% standardized proanthocyanidins. The study described herein investigated the protective effect of Grape seed proanthocyanidin extract (GSPE) on H2O2-induced oxidative stress in human lens epithelial B-3 (HLEB-3) cells and the possible molecular mechanism involved. METHODS: HLE-B3 cells exposed to different doses of H2O2 were cultured with various concentrations of GSPE and subsequently monitored for cell viability by the 4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide (MTT) assay. The apoptosis rate and ROS generation were detected by flow cytometric analysis. Expression of NF-кB/P65 and mitogen activated protein kinase (MAPK) proteins were measured by western blot. RESULTS: GSPE clearly reduced H2O2 induced cell apoptosis and reactive oxygen species (ROS) generation and protected HLEB-3 cells from H2O2 induced oxidative damage. GSPE depressed H2O2-induced activation and translocation of NF-кB/p65. GSPE also depressed H2O2-induced phosphorylation of the p38 and c-Jun N-terminal kinase (JNK) proteins of the MAPK family at various time points studied. CONCLUSIONS: GSPE could be useful in attenuation of H2O2-induced oxidative stress and the activation of NF-кB and MAPK signaling in HLE-B3 cells, which suggests that GSPE has a potential protective effect against cataractogenesis.

[Study on chemical constituents in total saponin from Trigonella foenum-graecum].

OBJECTIVE: To study the chemical constituents in the total saponin from Trigonellf foenum-graecum. METHOD: The compounds were isolated by column chromatography on macroporous resin and silica gel and elucidated by physical and chemical evidences and spectroscopic analysis. RESULT: Two compounds were obtained and identifiedas methyl-protodioscin and methyl-protodeltonin. CONCLUSION: Methyl-protodioscin and methyl-protodeltonin were isolated from this plant for the first time.