2D van der Waals (vdW) magnets, which present intrinsic ferromagnetic/antiferromagnetic ground states at finite temperatures down to atomic‐layer thicknesses, open a new horizon in materials science ...and enable the potential development of new spin‐related applications. The layered structure of vdW magnets facilitates their atomic‐layer cleavability and magnetic anisotropy, which counteracts spin fluctuations, thereby providing an ideal platform for theoretically and experimentally exploring magnetic phase transitions in the 2D limit. With reduced dimensions, the susceptibility of 2D magnets to a large variety of external stimuli also makes them more promising than their bulk counterpart in various device applications. Here, the current status of characterization and tuning of the magnetic properties of 2D vdW magnets, particularly the atomic‐layer thickness, is presented. Various state‐of‐the‐art optical and electrical techniques have been applied to reveal the magnetic states of 2D vdW magnets. Other emerging 2D vdW magnets and future perspectives on the stacking strategy are also given; it is believed that they will excite more intensive research and provide unprecedented opportunities in the field of spintronics.
2D van der Waals (vdW) magnets, which present intrinsic ferromagnetic/antiferromagnetic ground states down to atomiclayer thicknesses, open a new horizon in materials science. Recent state‐of‐the‐art characterization and tuning of the magnetic properties of 2D vdW magnets are outlined. Future perspectives and emerging 2D vdW magnets are also discussed, to provide unprecedented opportunities in the fields of spintronics.
Although only a few 2D materials have been predicted to possess ferroelectricity, 2D ferroelectrics are expected to play a dominant role in the upcoming nano era as important functional materials. ...The ferroelectric properties of 2D ferroelectrics are significantly different than those of traditional bulk ferroelectrics owing to their intrinsic size and surface effects. To date, 2D ferroelectrics have been reported to exhibit diverse properties ranging from bulk photovoltaic and piezoelectric/pyroelectric effects to the spontaneous valley and spin polarization. These properties are either dependent on ferroelectric polarization or coupled with it for easy electric control, thus making 2D ferroelectrics applicable to multifunctional nanodevices. At present, cumulative efforts are being made to explore 2D ferroelectrics in theories, experiments, and applications. Herein, such theories and methods are briefly introduced. Subsequently, intrinsic and extrinsic origins of 2D ferroelectricity are separately summarized. In addition, invented or laboratory‐validated 2D ferroelectric‐based applications are listed. Finally, the existing challenges and prospects of 2D ferroelectrics are discussed.
2D ferroelectrics are expected to play a dominant role in the upcoming nano era as important functional materials. Relevant theories, as well as intrinsic and extrinsic 2D ferroelectrics, are outlined. Further, the existing challenges and prospects of the exploration in 2D ferroelectrics are also discussed, which should provide unprecedented opportunities in the fields of electronics, spintronics, optoelectronics, and valleytronics.
Metal-organic frameworks (MOFs) appear as promising candidates for microwave absorbing materials with a low density as well as tunable electromagnetic parameters. In this study, a facile strategy to ...fabricate microwave absorbing materials has been demonstrated by introducing metallic Ni nanoparticles into carbon matrix which takes advantage of extremely porous structure. The magnetic Ni composition in the final products can be controlled, which offers an effective way to tune electromagnetic properties. Interfacial polarization is considered to be one of the most important attenuation mechanisms, which can be changed by increasing the interface area and electrical conductivity. When the filler loading of Ni/NiO/Cu@C composite in paraffin matrix is only 10 wt%, a minimum reflection loss of −38.1 dB is achieved at a layer thickness of 3.2 mm. The low density of the filler loading can be guaranteed by enhancing the conduction loss and impedance matching.
Recently, an emergent layered material Td‐WTe2 was explored for its novel electron–hole overlapping band structure and anisotropic inplane crystal structure. Here, the photoresponse of mechanically ...exfoliated WTe2 flakes is investigated. A large anomalous current decrease for visible (514.5 nm), and mid‐ and far‐infrared (3.8 and 10.6 µm) laser irradiation is observed, which can be attributed to light‐induced surface bandgap opening from the first‐principles calculations. The photocurrent and responsivity can be as large as 40 µA and 250 A W−1 for a 3.8 µm laser at 77 K. Furthermore, the WTe2 anomalous photocurrent matches its in‐plane crystal structure and exhibits light polarization dependence, maximal for linear laser polarization along the W atom chain a direction and minimal for the perpendicular b direction, with the anisotropic ratio of 4.9. Consistently, first‐principles calculations confirm the angle‐dependent bandgap opening of WTe2 under polarized light irradiation. The anomalous and polarization‐sensitive photoresponses suggest that linearly polarized light can significantly tune the WTe2 surface electronic structure, providing a potential approach to detect polarized and broadband lights up to far infrared range.
Semimetal Td‐WTe2 demonstrates broadband anomalous and polarization‐sensitive photoresponse. The giant photocurrent and responsivity reach 40 µA and 250 A W−1 for a 3.8 µm laser at 77 K, and the photocurrent anisotropic ratio of 4.9 for a 514.5 nm laser. Consistently, first‐principles calculations confirm angle‐sensitive bandgap opening of WTe2 by polarized light, showing its photodetection potential.
Directional water collection has stimulated a great deal of interest because of its potential applications in the field of microfluidics, liquid transportation, fog harvesting, and so forth. There ...have been some bio or bioinspired structures for directional water collection, from one-dimensional spider silk to two-dimensional star-like patterns to three-dimensional Nepenthes alata. Here we present a simple way for the accurate design and highly controllable driving of tiny droplets: by laser direct writing of hierarchical patterns with modified wettability and desired geometry on a superhydrophobic film, the patterned film can precisely and directionally drive tiny water droplets and dramatically improve the efficiency of water collection with a factor of ∼36 compared with the original superhydrophobic film. Such a patterned film might be an ideal platform for water collection from humid air and for planar microfluidics without tunnels.
We first reported that the topological insulator (TI) nanosheets solution filled in photonic crystal fiber can operate as an effective saturable absorber (SA) with the merits of low-insertion loss ...(~0.42 dB), long interaction length (>10 cm), and high-power tolerance. This SA device exhibited a saturable intensity of 14.9 MW/cm 2 , modulation depth of 19.1%, and nonsaturable loss of 25% at 1060 nm. Upo employing, this device rendered us to establish an ytterbium-doped all-fiber laser oscillator, where stable evanescent wave mode-locking operation has been achieved. This letter provided a new way of utilizing the unique nonlinear optical property of TI.
A tunable broadband terahertz (THz) absorber is designed in this paper, which is composed of graphene, silica medium and phase change material Vanadium dioxide (VO2). By simultaneously changing the ...fermi level of graphene and conductivity of VO2, the dual-controlled absorber can be realized. The results show that the full width at half maximum of the absorption spectrum is 1.03 THz, the bandwidth with the absorptance above 90% is 0.65 THz, and the absorptance is close to 100% at 1.2 THz. Moreover, the absorptance, transmittance and reflectance of the absorber can be dynamically adjusted from 0 to 99%, 0–65%, and 0–74%, respectively. The large tunability allows the proposed absorber to be used as THz tunable filters, sensors, switches and modulators.
•A broadband metamaterial absorber has been proposed based on the patterned graphene resonators.•Dual control and tunability is realized based on graphene array and phase change material vanadium dioxide.•The proposed structure can be dynamically tuned to act as an absorber or reflector.•The structure can be made to work in transmission or absorption mode by changing the conductivity of vanadium dioxide.
ZnO/graphene (ZnO-G) hybrid composites are prepared via hydrothermal synthesis with graphite, N-methyl-pyrrolidone (NMP), and Zn(NO₃)₂·6H₂O as the precursors. The characterizations, including X-ray ...diffraction (XRD), thermogravimetric analyses (TGA), Raman spectroscopy, and transmission electron microscopy (TEM) indicate the formation of ZnO-G. Gas sensors were fabricated with ZnO-G composites and ZnO as sensing material, indicating that the response of the ZnO towards acetone was significantly enhanced by graphene doping. It was found that the ZnO-G sensor exhibits remarkably enhanced response of 13.3 at the optimal operating temperature of 280 °C to 100 ppm acetone, an improvement from 7.7 with pure ZnO.
A cell-type saturable absorber has been demonstrated by filling the single mode photonic crystal fiber (SMPCF) with tungsten disulfide (WS2) nanosheets. The modulation depth, saturable intensity, and ...non-saturable loss of this SA are measured to be 3.53%, 159 MW/cm(2) and 23.2%, respectively. Based on this SA, a passively mode-locked EDF laser has been achieved with pulse duration of 808 fs and repetition rate of 19.57 MHz, and signal-noise-ratio (SNR) of 60.5 dB. Our results demonstrate that the cell-type WS2 nanosheets SA can serve as a good candidate for short-pulse mode locker.
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