Abstract
The absence of two-dimensional (2D) van der Waals (vdW) ferromagnetic crystals with both above-room-temperature strong intrinsic ferromagnetism and large perpendicular magnetic anisotropy ...(PMA) severely hinders practical applications of 2D vdW crystals in next-generation low-power magnetoelectronic and spintronic devices. Here, we report a vdW intrinsic ferromagnetic crystal Fe
3
GaTe
2
that exhibits record-high above-room-temperature Curie temperature (
Tc
, ~350-380 K) for known 2D vdW intrinsic ferromagnets, high saturation magnetic moment (40.11 emu/g), large PMA energy density (~4.79 × 10
5
J/m
3
), and large anomalous Hall angle (3%) at room temperature. Such large room-temperature PMA is better than conventional widely-used ferromagnetic films like CoFeB, and one order of magnitude larger than known 2D vdW intrinsic ferromagnets. Room-temperature thickness and angle-dependent anomalous Hall devices and direct magnetic domains imaging based on Fe
3
GaTe
2
nanosheet have been realized. This work provides an avenue for room-temperature 2D ferromagnetism, electrical control of 2D ferromagnetism and promote the practical applications of 2D-vdW-integrated spintronic devices.
Two-dimensional (2D) materials have attracted much attention due to their unique properties and great potential in various applications. Controllable synthesis of 2D materials with high quality and ...high efficiency is essential for their large scale applications. Chemical vapor deposition (CVD) has been one of the most important and reliable techniques for the synthesis of 2D materials. In this perspective, the recent advances in the CVD growth of three typical types of two-dimensional materials, graphene, boron nitride and transition metal dichalcogenides (TMDs), are briefly introduced. Large area preparation, single crystal growth and some mechanistic insight are discussed with details. Finally we give a brief comment on the challenges of CVD growth of 2D materials.
The synthesis of high quality two-dimensional materials such as graphene, BN, and transition metal dichalcogenides by CVD provides a new opportunity for large scale applications.
Nitrogen-containing carbon sphere with hierarchical porous structure is obtained through a facile thermostabilization and carbonization method of biomass-derivative sodium lignosulfonate. The ...synthesis route we proposed is cost-effective and environment-friendly without additional nitrogen precursor, activation or templating agent. The as-prepared carbon spheres exhibit high specific surface area of 1255–1939 m2 g−1 and moderate surface nitrogen content of 1.14–1.66 at.%. When assembling into supercapacitors with 7 M KOH aqueous solution as electrolyte, the carbon sphere shows superior gravimetric specific capacitance up to 276 F g−1 at 0.1 A g−1, high gravimetric energy density of 7.8 Wh kg−1 and power density of 6.2 kW kg−1, together with unprecedented cycling stability (99.5% capacitance retention after 10000 cycles). Notably, in 1 M SBPBF4/PC organic electrolyte, the carbon sphere based supercapacitor presents impressive gravimetric energy density of 34.3 Wh kg−1 and power density of 9.4 kW kg−1. These outstanding electrochemical performances suggest that the as-prepared porous carbon spheres should be a promising candidate for the field of energy storage.
Display omitted
The long-standing issue of lithium dendrite growth during repeated deposition or dissolution processes hinders the practical use of lithium-metal anodes for high-energy density batteries. Here, we ...demonstrate a promising lithiophilic-lithiophobic gradient interfacial layer strategy in which the bottom lithiophilic zinc oxide/carbon nanotube sublayer tightly anchors the whole layer onto the lithium foil, facilitating the formation of a stable solid electrolyte interphase, and prevents the formation of an intermediate mossy lithium corrosion layer. Together with the top lithiophobic carbon nanotube sublayer, this gradient interfacial layer can effectively suppress dendrite growth and ensure ultralong-term stable lithium stripping/plating. This strategy is further demonstrated to provide substantially improved cycle performance in copper current collector, 10 cm
pouch cell and lithium-sulfur batteries, which, coupled with a simple fabrication process and wide applicability in various materials for lithium-metal protection, makes the lithiophilic-lithiophobic gradient interfacial layer a favored strategy for next-generation lithium-metal batteries.
Sodium ion batteries (SIBs) have attracted soaring attention lately as a promising alternative to lithium ion batteries (LIBs), because of the vast availability of sodium, its low price and similar ...physicochemical properties to lithium. In recent years, significant progress of sodium ion battery anodes, which restricted the development of SIBs in the past decades, has been achieved. Extensive investigations have demonstrated that carbonaceous materials can become the most promising anode candidates for SIBs due to their low cost, high stability and electronic conductivity. In this article, a variety of carbon nanomaterials, including carbon quantum dots (CQDs), carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon nanosheets, and graphene as well as graphite and amorphous carbon anodes for SIBs, are briefly reviewed in view of their different dimensions and graphitization degrees. It also elaborates on research on carbonaceous material modification by doping with heteroatoms, designing various porous morphologies or compositing with organic or inorganic species. Finally, some perspectives and directions on carbon design for SIBs are also proposed. These comprehensive and in-depth discussions will provide an insight into the optimization of carbonaceous materials in SIB anodes.
The review elaborates on diversified nanostructured carbon materials and their modifications from two different perspectives of dimensions and graphitization degree.
Exosomes (EXs) are emerging as novel players in the beneficial effects induced by exercise on vascular diseases. We have recently revealed that moderate exercise enhances the function of circulating ...endothelial progenitor cell-derived EXs (cEPC-EXs) on protecting endothelial cells against hypoxia injury. However, the relationship between the changes of cEPC-EXs and the effects of exercise on ischemic stroke (IS) is unknown. Here, we investigated whether exercise-regulated EPC-EXs contribute to the beneficial effects of exercise on IS. C57BL/6 mice received moderate treadmill exercise (10 m/min) for 4-wks and then were subjected to middle cerebral artery occlusion (MCAO) stroke. The neurologic deficit score (NDS), infarct volume, microvessel density, cell apoptosis, angiogenesis/neurogenesis, sensorimotor functions were determined on day 2 (acute stage) and/or day 28 (chronic stage) post-stroke. The miR-126 and EPC-EX levels were analyzed by RT-PCR or nanoparticle tracking analysis combined with microbeads and used for correlation analyses. The function of EPC-EXs from exercised mice was detected in a hypoxia neuron model. Cell apoptosis, axon growth ability and gene expressions (cas-3 and Akt) were measured. Our data showed that: i) On day 2, exercised mice had decreased NDS and infarct volume, reduced cell apoptosis rate and cleaved cas-3 level, and a higher microvessel density than those in control (no-exercise) mice. The levels of EPC-EXs in plasma and brain tissue were raised and positively correlated in exercised mice. Meanwhile, the miR-126 level in cEPC-EXs and in ischemic tissue were upregulated in exercised mice. The EPC-EXs and their carried miR-126 levels negatively correlated with the infarct volume and cell apoptosis, whereas positively correlated with microvessel density. In addition, cEPC-EXs from exercised mice elicited protective effects on neurons against hypoxia-induced apoptosis and compromised axon growth ability which were blocked by miR-126 and PI3k inhibitors in vitro. ii) On day 28, exercised mice had less infarct volume, higher microvessel density, angiogenesis/neurogenesis and better sensorimotor functions. The levels of BDNF, p-TrkB/TrkB and p-Akt/Akt were upregulated in the brain of exercised mice. These recovery indexes correlated with the levels of cEPC-EXs and their miR-126. In conclusion, our data suggest that moderate exercise intervention has protective effects on the brain against MCAO-induced ischemic injury in both acute and chronic stages which might via the release of miR-126 enriched EPC-EXs.
•Moderate treadmill exercise alleviated acute injury in IS.•Moderate treadmill exercise promoted chronic functional recovery in IS.•Moderate treadmill exercise enhanced the function of cEPC-EXs.•The levels of cEPC-EXs and miR-126 correlated with the acute injury index of IS.•The levels of cEPC-EXs and miR-126 correlated with the chronic recovery index of IS.
•Actual DHF experiments with sandstone were conducted for the first time.•The crack propagation law of DHF was compared by CT scans.•Sample failure characteristic was described and explained.•The ...crack control mechanism of DHF was analyzed in detail.
Hydraulic fracturing is mainly used for increasing large-scale coal seam permeability in coal mines to exploit coalbed methane and prevent coal and gas outbursts. However, conventional hydraulic fracturing cracks tend to propagate along the direction of maximum principal stress, which is inconsistent with reinforcement direction engineering and/or project area needs and makes identification of the orientation or specified location of increased coal seam permeability difficult. To address these problems, we have conducted physical similarity simulation experiments and numerical analysis of directional hydraulic fracturing (DHF) and obtained the crack propagation law of DHF technology. By analyzing the variation law of the maximum principal stress inside the rock mass, the crack propagation control mechanism of DHF technique is revealed. The influence of horizontal stress difference coefficients and angles between the hydraulic slotting direction and maximum principal stress direction (i.e., the hydraulic slotting deviation angle) on the crack propagation deflection is investigated. The results show that the DHF technique can achieve crack-oriented propagation along the desired direction. The maximum principal stress range in the rock mass is redistributed after slotting. A directional fracturing induction region is formed between the slots. In addition, DHF hydraulic pressure curves show a secondary fracturing stage when cracks connect the hydraulic fracturing and hydraulic slotting boreholes. Initiation pressures and values of maximum principle stress in the directional fracturing zone increase with increasing horizontal stress difference coefficients and slotting deviation angles. However, increasing the horizontal stress difference coefficient does not significantly influence the directional fracturing zone range. The results provide a reliable basis for subsequent theoretical research and engineering applications.
Phase engineering of two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoTe2 offers tremendous opportunities in various device applications. However, most of the existing methods ...so far only address the small-area local phase change or the growth of certain kinds of phases of MoTe2 film by laser irradiation, mechanical strain, or procursor type. Obtaining facile, tunable, reversible, and continuous-phase transition and evolution between different phases in direct growth of large-area, few-layer MoTe2 still remains challenging. Here, we develop a facile method to achieve phase control and transition and report a highly tunable, tellurization velocity-dependent metallic–semiconducting–metallic phase evolution in chemical vapor deposition (CVD) growth of large-area, few-layer MoTe2. We found four different phase stages, including two different types of coexistence phases of both 2H and 1 T′ phases, 100% 2H phase, and 100% 1T′ phase, would emerge, relying on the adopted tellurization velocity. Importantly, the tellurization velocity should be extremely controlled to obtain 100% 2H phase MoTe2, while 100% 1T′ phase requires a fast tellurization velocity. We further found that such metallic–semiconducting–metallic phase evolution took place with a homogeneous spatial distribution and differs from previous reports in which obvious phase separations are usually found during the phase transition. The resulting MoTe2 shows high quality with room-temperature mobility comparable with mechanically exfoliated materials. The results might impact large-scale phase engineering of TMDs and other 2D materials for Weyl semimetal topological physics and potential 2D semiconductor device applications.
► A micro supercapacitor with high-aspect-ratio interdigital electrodes is presented. ► Self-supporting nano porous composites are developed for micro electrodes. ► The prototype presents large ...capacitance and power per unit area. ► The combination of structure and material achieves a high overall performance.
This paper introduces a silicon three-dimensional (3D) micro supercapacitor, featured by using self-supporting nano porous composite materials and interdigital electrodes with high-aspect-ratio. A way to prepare self-supporting materials has been developed, and composites that contain an activated carbon as the active component have been studied and designed to meet the requirements for adequate specific capacitance, good conductivity and strong structure. By combining the designed composite with microfabrication techniques, a micro supercapacitor with high-aspect-ratio interdigital electrodes has been achieved. Electrochemical characterization results of the prototype with NaNO
3 electrolyte demonstrate that the 3D supercapacitor exhibits an outstanding overall performance. A large capacitance of 90.7
mF
cm
−2 and a fast power of 51.5
mW
cm
−2 are calculated. Robust stability and high charge/discharge efficiency are also observed. Moreover, this study provides a scalable device built by compatible fabrication method, which is applicable to the integration of high-performance supercapacitors on chip.
Abstract
Control of ferromagnetism is of critical importance for a variety of proposed spintronic and topological quantum technologies. Inducing long-range ferromagnetic order in ultrathin 2D ...crystals will provide more functional possibility to combine their unique electronic, optical and mechanical properties to develop new multifunctional coupled applications. Recently discovered intrinsic 2D ferromagnetic crystals such as Cr
2
Ge
2
Te
6
, CrI
3
and Fe
3
GeTe
2
are intrinsically ferromagnetic only below room temperature, mostly far below room temperature (Curie temperature, ~20–207 K). Here we develop a scalable method to prepare freestanding non-van der Waals ultrathin 2D crystals down to mono- and few unit cells (UC) and report unexpected strong, intrinsic, ambient-air-robust, room-temperature ferromagnetism with
T
C
up to ~367 K in freestanding non-van der Waals 2D CrTe crystals. Freestanding 2D CrTe crystals show comparable or better ferromagnetic properties to widely-used Fe, Co, Ni and BaFe
12
O
19
, promising as new platforms for room-temperature intrinsically-ferromagnetic 2D crystals and integrated 2D devices.
PDF
