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The effective permeability of flake-shaped FeCuNbSiB particles/nonmagnetic matrix composition in high frequency was measured and calculated. In contrast to the relatively larger size and irregular shape particles, the flake particles have higher permeability. The results are attributed to the different magnetic loss mechanisms. According to the skin-effect criterion, we find that the magnetic loss in flake particles is mainly caused by the natural resonance, compared with the eddy current effect in the larger size and irregular shape particles. Using the shape anisotropy, the flake soft magnetic particles overcome the difficulty of the relatively small intrinsic anisotropies and increase the natural resonant frequencies to the gigahertz range, leading to the higher real part and imaginary part of the permeability. The resonance peak of flake particles was simulated using the combination of the Landau–Lifshitz–Gilbert equation and Bruggeman’s effective medium theory considering a random spatial distribution of magnetic easy axes. Our theory simulation agrees well with the experimental data. [ABSTRACT FROM AUTHOR]

Micromagnetic simulation was performed to investigate the equilibrium state and dynamic susceptibility spectra of magnetic elliptical nanoring. There are two equilibrium states (onion and vortex) obtained in elliptical nanoring. The onion state can be used to record information in MRAM. And it is important to investigate the dynamic susceptibility spectra of onion state, which is closely related to writing and reading speed of magnetic memory devices. Those results show that two or three resonance peaks are found under different thickness of elliptical nanoring with onion state, respectively. The low resonance frequency of two resonance peaks is increasing with the arm width of the elliptical ring, but is decreasing with the thickness. However, the high frequency of two resonance peaks is decreasing with the arm width of the elliptical ring. [ABSTRACT FROM AUTHOR]

Pt fibers (15 μm) were coated with topological insulator Bi2Se3 nanoplates via a single mode microwave-assisted synthesis technique. With the Bi2Se3/Pt fibers, flexible memory devices were facilely assembled, and they were demonstrated to exhibit rewritable nonvolatile resistive switching characteristics of low switching voltage (-1.2V and +0.7 V), high ON/OFF current ratio (106), and good retention (4500 s), showing the potential application in data storage. The resistive switching mechanism was analyzed on the bases of formation and rupture of conductive filaments. [ABSTRACT FROM AUTHOR]

Reported here are observations of isolated orthorhombic (o) ZrO2 nanoparticles (NPs) in the Pbca space group under atmospheric conditions. These NPs are composed of o domains separated by internal semi-coherent boundaries. They are identified to transform from lamellar-twinned tetragonal (t) NPs. The constraining effect of the twin boundaries impedes a direct martensitic transformation to the monoclinic (m) phase but favours a transformation to the o phase. The internal boundaries are considered to evolve from the lamellar-twinning boundaries, playing an important role in the stabilization of the o structure under atmospheric conditions. The observed o structure should be an adaptive martensite transformed from the t phase, different from the general consideration of the o phase as an intermediate stage. A new lattice correspondence (LC) relationship of (011)o‖(100)t and [100]o‖[001]t is determined for the t-to-o transformation. A possible transformation path is proposed to be t (space group P42/nmc) to o (Pbcm or Pbc21, named oA) to o (Pbca, named oB), and the LC relationship is identified to be (100)t‖(100)oA‖(011)oB and [001]t‖[010]oA‖[100]oB. [ABSTRACT FROM AUTHOR]

Abstract  Magnetite (Fe3O4) nanoparticles were synthesized by chemical precipitation. To reduce the aggregation of Fe3O4 nanoparticles, an effective surface modification method was proposed by grafting polystyrene onto the Fe3O4 particles. The results of Fourier transform infrared spectra and elemental analysis showed that the polymer chains have been successfully grafted from the surface of the Fe3O4 nanoparticles and that the percentage of grafting can reach 73%. Transmission electron microscope showed that grafted polymer chains on nanoparticles could prevent the aggregation of Fe3O4 nanoparticles markedly in toluene and improve their compatibility with organic phase. Another finding was the grafting reaction did not alter the crystalline structure of the Fe3O4 nanoparticles according to the X-ray diffraction patterns, and the saturation magnetization of PS-Fe3O4 nanoparticles was found to be lower than bulk magnetite. [ABSTRACT FROM AUTHOR]

Room-temperature electric field control of magnetization is of interest for the potential application of low consumption nonvolatile memory. Here, we report the realization of electric field modulation of magnetization in a single phase multiferroic material Ba0.5Sr1.5Co2Fe11AlO22. In this work, we use static and dynamic measurements to reveal the magnetoelectric coupling between magnetization (M) and polarization (P). At the temperature of 10 K, the first order magnetoelectric (ME) term is dominated and the magnetization linearly changes with the electric field. While at room temperature, the quadratic term become apparent, leading to symmetric butterfly-like P–H and M–E curves. Our study reveals that an alternating longitudinal conical (ALC) phase induced exchange interaction may exist in Y type hexaferrite Ba0.5Sr1.5Co2Fe11AlO22 and contribute to the ME coupling mechanism. [ABSTRACT FROM AUTHOR]

In two-dimensional layered materials, layer number and stacking order have strong effects on the optical and electronic properties. Tungsten disulfide (WS2) crystal, as one important member among transition metal dichalcogenides, has been usually prepared in a layered 2H prototype structure with space group P63/mmc () in spite of many other expected ones such as 3R. Here, we report simultaneous growth of 2H and 3R stacked multilayer (ML) WS2 crystals in large scale by chemical vapor deposition and effects of layer number and stacking order on optical and electronic properties. As revealed in Raman and photoluminescence (PL) measurements, with an increase in layer number, 2H and 3R stacked ML WS2 crystals show similar variation of PL and Raman peaks in position and intensity. Compared to 2H stacked ML WS2, however, 3R stacked one always exhibits the larger red (blue) shift of Raman (A1g) peak and the appearance of PL A, B and I peaks at lower energies. Thereby, PL and Raman features depend on not only layer number but also stacking order. In addition, circularly polarized luminescence from two prototype WS2 crystals under circularly polarized excitation has also been investigated, showing obvious spin or valley polarization of these CVD-grown multilayer WS2 crystals. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP) has recently drawn great attention in the field of electrocatalysis due to its distinct electrocatalytic activity for the oxygen evolution reaction (OER). However, the slow OER kinetics and the poor environmental stability of BP seriously limits its overall OER performance and prevents its electrocatalysis application. Here, sulfur (S)-doped BP nanosheets, which are prepared using high-pressure synthesis followed by liquid exfoliation, have been demonstrated to have much better OER electrocatalytic activity and environmental stability compared to their undoped counterparts. The S-doped BP nanosheets display a Tafel slope of 75 mV dec−1, which is a favorable value refered to the kinetics of OER in electrochemical tests. Notably, there is no degradation of S-doped BP nanosheets after six days exposure to ambient, indicating an excellent environmental stability of the S-doped BP. The density functional theory calculations show that the OER activity of BP originate from its crystal defects and heteroatom S doping can effectively enhance its OER activity and stability. These results highlight the doping effect on electrocatalytic activities and stability of BP and provide a simple and effective method to design highly efficient OER catalysts based on the modification of BP. [ABSTRACT FROM AUTHOR]

Nanostructure composites of ferromagnetic materials embedded in nanoporous carbon (NC) derived from metal–organic frameworks (MOFs) have attracted enormous attention due to their potential application in many fields, such as microwave absorption, energy storage, and conversion. The rational design of nanocomposites holds a determinant factor for overcoming the challenges involving the microwave absorption performance. Herein, CoS2/NC, CoP/NC, and CoS2−xPx/NC with a rhombic dodecahedral structure have been successfully fabricated by using the template cobalt-based MOFs (ZIF-67). A morphology analysis indicates that ferromagnetic nanoparticles are embedded in NC matrix. It is obvious that the rhombic dodecahedron can be maintained after the phosphorization and sulfurization of Co/NC derived from the thermal decomposition of ZIF-67. The microwave absorption performance can obviously be improved by the phosphorization and sulfurization of Co/NC. CoS2−xPx/NC exhibits an excellent microwave absorption property and the minimum reflection loss (RL) of CoS2−xPx/NC can reach −68 dB at 14.6 GHz with a thickness of 1.5 mm. An RL value less than −10 dB can be achieved in the microwave frequency range of 12.7–17.3 GHz (4.6 GHz) with a thickness of 1.5 mm for CoS2−xPx/NC. This article offers a novel way to fabricate cobalt-based materials/carbon composites for an excellent microwave absorber. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Through a facile self-assembled process, an ultralight reduced graphene oxide/black phosphorus (rGO/BP) composite aerogel was successfully fabricated. The BP nanosheets were homogeneously distributed throughout the rGO 3D framework, and the interfaces between rGO and BP possessed four kinds of interconnections, such as wrapping, wearing, bridging and weak linking. As an ultralight composite, the rGO/BP aerogel could easily stand on the stamen of a flower. Compared with pure rGO aerogel, the rGO/BP composite aerogel exhibited enhanced microwave absorption ability. The minimum reflection loss value of −46.9 dB with a thickness of 2.53 mm was obtained, and a wide absorption band of 6.1 GHz (RL < −10 dB) was achieved. The superior microwave absorption property was demonstrated to stem from the interfacial polarization loss mechanism in which the multiform interface interactions between the rGO skeleton and BP nanosheets played critical roles. The rGO/BP aerogel has great potential to be used as an ultralight microwave absorber. [ABSTRACT FROM AUTHOR]

In this work, bismuth selenides (Bi2Se3 and Bi3Se4), both of which have a layered rhombohedral crystal structure, have been found to be useful as electrode materials for supercapacitor applications. In a liquid electrolyte system (6M KOH), Bi2Se3 nanoplates exhibit much better performance as an electrode material than Bi3Se4 nanoparticles do, delivering a higher specific capacitance (272.9 F g−1) than that of Bi3Se4 (193.6 F g−1) at 5 mV s−1. This result may be attributed to the fact that Bi2Se3 nanoplates possess more active electrochemical surfaces for the reversible surface redox reactions owing to their planar quintuple stacked layers (septuple layers for Bi3Se4). To meet the demands of electronic skin, we used a novel flexible annular interdigital structure electrode to support the all-solid-state micro-supercapacitors (AMSCs). The Bi2Se3 AMSC device delivers a much better supercapacitor performance, exhibits a large stack capacitance of 89.5 F cm−3 at 20 mV s−1 (Bi3Se4: 79.1 F cm−3), a high energy density of 17.9 mWh cm−3 and a high power density of 18.9 W cm−3. The bismuth selenides also exhibit good cycle stability, with 95.5% retention after 1000 c for Bi2Se3 (Bi3Se4:90.3%). Clearly, Bi2Se3 nanoplates can be promising electrode materials for flexible annular interdigital AMSCs. [ABSTRACT FROM AUTHOR]

In this work, hierarchical architecture MoS2/CNT nanohybrids synthesized by the hydrothermal method, with different CNT proportions are systematically investigated for their microwave absorption. MoS2 nanoflowers are anchored uniformly on the surface of a CNT when the proportion of the MoS2/CNT nanohybrids was 10:2, and the reflection loss can attain −20 dB in the range of 3.4–13.9 GHz with multiple thicknesses from 1.5–5.0 mm, while an optimal consequence of −46 dB can be reached at 6.6 GHz at 2.9 mm. The excellent performance indicates that the MoS2/CNT = 10:2 nanohybrids have the potential for use as microwave absorbing materials. [ABSTRACT FROM AUTHOR]