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The utilization of pristine graphene as an anode material in sodium-ion batteries (SIBs) is limited by its inherent chemical inertness toward Na-ions. To address this issue, we propose a two-dimensional carbon allotrope (named as TD-graphene) by assembling tricyclo[4.4.1.11,6]dodecane (C12H20) skeleton. The topological non-hexagonal feature of C12H20 increases the degree of local carbon-ring disorder and introduces additional electron-deficient regions on the surface, thus enhancing the adsorption capability of Na. TD-graphene demonstrates exceptional stability across the energetic, thermodynamic, dynamic, and mechanical aspects. As a promising anode for SIBs, it exhibits an intrinsic metallicity, an ultra-high storage capacity (1487.58 mA h g−1), a low diffusion barrier (0.20 eV), a low average open-circuit voltage (0.33 V), and a small lattice expansion (0.6%). The presence of solvents with high dielectric constants improves the adsorption and migration capability of Na. Furthermore, taking into account the limitation of single-layer materials in practical applications, we employ h-BN as a promising substrate for TD-graphene, which can boost the Na adsorption and diffusion performance. These results render TD-graphene as a promising high-performance anode material for SIBs. [ABSTRACT FROM AUTHOR]

Although graphene has excellent electrical and mechanical properties, the giant delocalized π-electron system makes it chemically inert. Here, we propose an idea to design two-dimensional (2D) carbon allotropes via incorporating multiple rings in sp2-hybridized carbon networks, which can break the π-bonding network and enhance the surface reactivity. By assembling molecule of cyclobut(a)acenaphthylene, we predict a monolayer 2D carbon material, named as R12-graphene, which is composed of quadrilateral, pentagonal, hexagonal, and dodecagonal carbon rings. It shows great stability in energetic, dynamic, thermodynamic, and mechanical aspects. It exhibits high-performance as an anode material for potassium-ion batteries (PIBs), including an intrinsic metallic behavior, a high theoretical capacity (632 mA h g−1), a low K diffusion barrier (0.33 eV), and a low average open-circuit voltage (0.5 V). The presence of electrolytes can provide better K ion adsorption and diffusion capability compared to that in vacuum. Furthermore, R12-graphene has excellent wettability toward some commonly used electrolytes, which is beneficial for improving the charge/discharge rate for PIBs. [ABSTRACT FROM AUTHOR]

We demonstrate the construction of heterojunction arrays for boosting solar water splitting by combining in situ guided growth of heterointerfaces and energy band tuning. By directly growing an ultrathin Fe2WO6 layer on a preformed WO3 nanosheet array in full coverage, a uniform and dense array of intimately contacted WO3/Fe2WO6 heterojunction was created. The heterojunction array shows not only a largely broadened visible light absorption range but also a built-in interface polarization to accelerate hole transfer from WO3 to Fe2WO6. Meanwhile, fine-tuning to match energy levels at the heterojunction was achieved by doping WO3 with Fe (Fe-WO3), leading to improved electrical conductivity and reduced charge recombination. Photoanodes based on such heterojunction arrays have shown significantly enhanced photoelectrochemical (PEC) water splitting performance, clearly arising from the above-mentioned efforts. Furthermore, by decorating FeOOH/NiOOH cocatalysts on the heterojunction arrays in tandem, the surface water oxidation kinetics was considerably accelerated, and the resulting Fe-WO3/Fe2WO6/FeOOH/NiOOH photoanode achieved a photocurrent density of 2.78 mA/cm2 at 1.23 V vs reversible hydrogen electrode. This work highlights the benefits of in situ construction of heterojunction arrays for enhancing the PEC performance. [ABSTRACT FROM AUTHOR]

The evolution of bubble structure and electron injection in laser wakefield acceleration with different optical cycles is investigated through three-dimensional particle-in-cell simulations. Under fixed transverse and longitudinal ponderomotive force, the effect of optical cycles on the evolution of bubble structure and electron injection is studied by changing the laser wavelength. For a multi-cycle laser, electron acceleration is dominated by the ponderomotive force that produces symmetrical bubble and continuous injection. As the optical cycles decrease, the dominant effect of the electron acceleration can transition from the ponderomotive force to the carrier wave, and the carrier envelope phase shift can cause transverse oscillation of the bubble and periodic electron injection in the direction of laser polarization. The criterion for the dominant acceleration mechanism and the dependence of transition distance on the optical cycles and pulse width are obtained. The results are beneficial for manipulating electron acceleration and betatron radiation generation. [ABSTRACT FROM AUTHOR]

Although lithium-sulfur (Li-S) batteries are widely regarded as one of the most promising next-generation high energy density storage systems, their large-scale applications are seriously impeded by rapid capacity fading and poor Coulombic efficiency owing to the shuttling of lithium polysulfides (LiPSs) and irreversible discharge product Li2S. Here, by means of first principles calculations, we studied defective black phosphorene (BP) as a host material to realize high-performance Li-S batteries, including Stone Wales [SW(55-77)], single, and double vacancy [SV(5-9) and DV(5-9-5)] defects. Our results demonstrate that while BP has moderate adsorption energies towards LiPSs, the presence of defects could enhance the adsorption strength between LiPSs and BP because of increased charge transfer. Particularly, defective BP could strike a good balance between adsorption energy and integrity of LiPSs, which is beneficial to prevent the shuttling of LiPSs. Moreover, during the lithiation process, defective BP not only has narrow bandgaps but also decreases the dissociation energy of Li2S, facilitating the catalytic oxidation of Li2S back to sulfur. Therefore, it is highly desirable to fabricate defective BP to improve the reversible capacity and cycle stability of Li-S batteries. [ABSTRACT FROM AUTHOR]

In our previous work, we proposed a new design method for an aberration-free x-ray refractive focusing lens based on an ideal Cartesian oval shape to solve the aberration problem in x-ray compound refractive focusing. In this paper, we propose an optimization method for this new lens. By reducing the aperture of each lens, we achieve the objective of increasing the effective aperture and improving the focusing performance of the lens. The simulation of the beam propagation method shows that the focusing performance of the optimized lenses is better in compound refractive lens shape but worse in the kinoform shape. This is different from the results obtained with the conventional kinoform lens. After further comparison, we found that this is because the step height of the kinoform lens is small when the lens aperture is very small, resulting in a strong diffraction effect that weakens the focusing performance of the lens. Further modifications to the structure of the kinoform lens are needed to improve this phenomenon. [ABSTRACT FROM AUTHOR]

We use in situ high-pressure neutron powder diffraction to study elastic properties of Fe3O4 magnetite nanoparticles of different sizes. It is found that nanoparticles are elastically softer than the bulk. Apart from the smallest nanoparticle of diameter 8 nm, the atomic and magnetic structures do not change significantly with nanoparticle size or pressure. The 8 nm sample appears to take a disordered spinel structure instead of the inverse spinel structure of the bulk and larger nanoparticles, as seen in bond lengths and magnetic structures. Synchrotron x-ray total scattering was used to support this interpretation. Furthermore, this study suggests that the influence of magnetic disorder at the nanoparticle surface is significant for the size of 8 nm. [ABSTRACT FROM AUTHOR]

Under shock pressures up to 210 GPa, we measured the refractive index of sapphire at a wavelength of 1550 nm by performing plate impact experiments in order to investigate its refractive-index change behaviors and phase transitions along the Hugoniot state. There were two discontinuities in the refractive index at ~65 to 92 GPa and ~144 to 163 GPa, respectively. Moreover, above the Hugoniot elastic limit, the pressure dependence of the refractive index was divided into three segments, and there were large differences in their pressure-change trends: the refractive index decreased evidently with pressure in the first segment (~20 to 65 GPa), remained nearly constant from ~92 to ~144 GPa in the second segment, and obviously increased with pressure in the last segment (~163 to 210 GPa). Our first-principles calculations suggest that the observed discontinuities were closely related to the corundum-Rh2O3(II) and Rh2O3(II)-CaIrO3 structural transitions, and the shock-induced vacancy point defects could be one factor causing these great discrepancies in pressure-change trends. This work provides sapphire refractive-index information in a megabar-pressure range and clear evidence of its shock structural transitions. This not only has a great significance for the velocity correction of laser interferometer experiments and the analysis of sapphire high-pressure properties but also indicates a possible approach to explore the shock transitions of transparent materials. [ABSTRACT FROM AUTHOR]

Polycrystalline Sn-added SmFeAsO1-xFx tapes were prepared by an ex-situ powder-in-tube method. It is found that the transport critical current density (Jc) of the SmFeAsO1-xFx tapes can be significantly improved with 10-30 wt. % Sn addition. A transport Jc of 2.11 × 104 A cm-2 at 4.2 K in self-field was obtained in SmFeAsO1-xFx + 30 wt. % Sn sample. Most interestingly, Sn-added SmFeAsO1-xFx tapes without any sintering also showed substantial transport Jc of 9.81 × 103 A cm-2, which is reported for the first time. X-ray diffraction and scanning electron microscopy characterization revealed that the elemental Sn dispersed in the sample transformed into FeSn2 during the post-rolling sintering (PRS). The reaction between Sn and FeAs helps to eliminate the detrimental FeAs wetting phase, which blocks the supercurrent path between SmFeAsO1-xFx grains. The combined impact of fluorine loss and Sn reaction was discussed in this work by varying the Sn addition quantity and PRS condition. [ABSTRACT FROM AUTHOR]

The system architecture and method for monitoring and statistical analysis of the line losses of the transformer region are introduced. The statistical method for the current system is adopted to determine the functional relationship between the statistical line loss, statistical line loss rate, and gateway power supply of the transformer region. Moreover, the trend of the parameters in a typical residential area is analyzed. Based on the analysis, the three reasons for the formation of transformer regions with a reasonable rate of line loss and the measures for the unreasonable rates are summarized. It is recommended that the line loss monitoring and analysis system should include the functions of approval, examination, and verification, as well as automatic identification. The transformer region without any abnormality in the line loss should be exempt from the review. For the transformer region with a residential elevator, however, the statistical rules should be modified to calculate the actual line loss rate. Finally, the challenges in the management of the transformer region with a negative line loss rate are presented. It is concluded that the application of transformer–customer relationship automatic identification technology and artificial intelligence abnormality diagnosis can significantly improve the efficiency of line loss management. [ABSTRACT FROM AUTHOR]

The electronic structure and lattice dynamical properties of solid methane under high pressure have been studied based on density functional theory. We identify a cubic structure with space group of I[formula]3m below 14 GPa, the Pmn21 structure in the range of 14-21 GPa, and the P21/c structure from 21 to 65 GPa. Our obtained Raman spectra of the P21/c structure agree well with the typical Raman active modes in the available experimental data. At 65 GPa, methane undergoes a phase transition from P21/c to Pnma. The structures with P21/c and Pnma symmetries are insulating, and under any pressure studied methane always remains in molecular form. For Pnma phase, the orientational ordering of CH4 molecules varies significantly at 79, 88, and 92 GPa, and by further increasing pressure the rotation of the molecules freezes and orientational ordering remains unchanged. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the deposition of thin films of lithium niobate on silicon with radio frequency magnetron sputtering. Variables thought to critically affect the properties of the resulting films; Use of x-ray diffractometry using a cooper tube; Results of the Rutherford backscattering spectra.

We study the magnetic properties of W/Co40Fe40B20 (CoFeB)/MgO films using the spin-torque ferromagnetic resonance (ST-FMR) technique. This study takes the advantage of the spin Hall magnetoresistance (SMR) for generating an oscillating resistance, which is one of the necessary requirements for obtaining mixing voltage in the ST-FMR technique. We have measured both the as-grown and the annealed samples with different CoFeB layer thicknesses, which include the in-plane and out-of-plane magnetic anisotropies. The spectra for these two types of anisotropies show distinct signatures. By analyzing the ST-FMR spectra, we extract the effective anisotropy field for both types of samples. In addition, we investigate the influence of CoFeB thickness and annealing on the Gilbert damping constant. Our experiments show that by taking advantage of SMR, the ST-FMR measurement acts as an effective tool with high sensitivity for studying the magnetic properties of ultrathin magnetic films. [ABSTRACT FROM AUTHOR]

CaS, with a direct bandgap of 5.38 eV, is expected to be a strong candidate as the active-layer of high performance solar-blind UV photodiodes that have important applications in both civilian and military sectors. Here, we report that a seed-layer-assisted growth approach via molecular beam epitaxy can result in high crystalline quality rocksalt CaS thin films on zincblende GaAs substrates. The Au/CaS/GaAs solar-blind photodiodes demonstrated, more than five orders in its visible rejection power, a photoresponse of 36.8mA/w at zero bias and a corresponding quantum efficiency as high as 19% at 235 nm. [ABSTRACT FROM AUTHOR]

Novel low dimensional quantum phenomena at (110) LaAlO3/SrTiO3 (LAO/STO) interfaces are expected after the quasi two dimensional electron gas similar to that of (001) LAO/STO interfaces was found at this (110) system. Here, we report the two dimensional superconductivity with a superconducting transition temperature of ffi 184 mK at (110) LAO/STO interfaces. The two dimensional characteristics of the superconductivity are consistent with our analysis based on a Berezinskii-Kosterlitz-Thouless transition. The estimated superconducting layer thickness is about 18 nm. This discovery may inspire new studies of LAO/STO interfaces and open additional opportunities for design of novel oxide electronic devices. [ABSTRACT FROM AUTHOR]

With the consideration of the superthermal electron distribution, we present a theoretical investigation about the nonlinear propagation of electron-acoustic solitary and shock waves in a dissipative, nonplanar non-Maxwellian plasma comprised of cold electrons, superthermal hot electrons, and stationary ions. The reductive perturbation technique is used to obtain a modified Korteweg-de Vries Burgers equation for nonlinear waves in this plasma. We discuss the effects of various plasma parameters on the time evolution of nonplanar solitary waves, the profile of shock waves, and the nonlinear structure induced by the collision between planar solitary waves. It is found that these parameters have significant effects on the properties of nonlinear waves and collisioninduced nonlinear structure. [ABSTRACT FROM AUTHOR]

Seven-core Ag/Fe sheathed Sr0.6K0.4Fe2As2 (Sr-122) superconducting wires were produced by the ex situ powder-in-tube method. The relationship between the cold-work deformation process and the superconducting properties of the wires was systematically studied. It was found that flat rolling can efficiently increase the mass density of the superconducting core, thus, significantly improving the transport critical current density (Jc) of the as-drawn wires. The transport Jc of the best sample achieved 21.1 kA/cm2 at 4.2 K in self field, and showed very weak magnetic field dependence at high fields. Our result suggested a promising future of multifilamentary iron-based superconductors in practical applications. [ABSTRACT FROM AUTHOR]

Mn1.85Co0.3Ni0.85O4 thin films with single cubic spinel phase and compact surface were prepared by chemical solution deposition method on Al2O3 substrates. Temperature dependent ac impedance spectroscopy was employed to analyze the contributions of grain boundary (GB) and grain to the conduction mechanism. The major characteristics (hopping type, resistance versus temperature behavior, and characteristic temperature T0) of the GB and grain were obtained. The hopping type of GB is nearest-neighbor-hopping (NNH), and that of grain might be a transition from variable-range-hopping to NNH. The GB shows dominating resistance while the grain shows stronger temperature dependence. [ABSTRACT FROM AUTHOR]

The electronic density of states of two-dimensional (2D) Au quantum dot superlattice are explored by using cryogenic scanning tunneling microscopy and scanning tunneling spectroscopy. The 2D Au superlattice opens up a gap in its electronic density of states. The single-electron transfer of a single Au quantum dot can be effectively inhibited by this “artificial” forbidden gap. This finding opens a route toward modulating electronic energy band of solid on the basis of 2D metal quantum dot superlattice, which may generate materials with electronic properties for possible future electronic devices. [ABSTRACT FROM AUTHOR]

The electronic local density of states of a single Co3O4 semiconductor nanowire with the diameter of 3 nm is explored using low-temperature scanning tunneling microscopy and spectroscopy. The energy gap between the conduction band and valence band of the nanowire is about 1.7 eV, which is slightly enhanced compared to the bulk value, ∼1.5 eV, due to the quantum confinement effect. Two surface states are observed locating near the Fermi level in the band gap. [ABSTRACT FROM AUTHOR]

An array of Nb strips was fabricated on a Bi2Te3 thin film. Transport measurements show that an upturn of the resistance occurs below the Nb superconducting transition temperature. Corresponding to this resistance upturn, a differential resistance peak around zero bias and a prominent negative magnetoresistance at low magnetic fields are observed. The resistance upturn, differential resistance peak, and negative magnetoresistance can be suppressed by increasing measurement current, temperature, and applied magnetic field. We explain these phenomena in terms of an energy barrier effect induced by the Nb superconducting gap and the suppression of Andreev reflection due to the low transparency at the Nb-Bi2Te3 interface. [ABSTRACT FROM AUTHOR]