Coercivity mechanisms in nanostructured permanent magnets
Coercivity mechanism in permanent magnets has been debated for many years. In this paper, various models of the coercivity mechanism are classified and re-examined by the comparison and contrast. Coherent rotation and curling models can reveal the underlying reversal mechanism clearly based on isolated grains with elliptic shapes. By contrast, the numerical methods consider inter-grain interactions while simulating the evolution of the spins and hysteresis loops with complicated shapes. However, an exact simulation of magnetic reversal in permanent nanomagnets requires many meshes to mimic the thin domain wall well.
Nucleation and pinning are the two main coercivity mechanisms in permanent magnets. The former signifies the beginning of the magnetic reversal, whilst the latter completes it. Recently, it is proposed that the large difference between the intrinsic magnetic properties of the nucleation centers and those of the main phase can result in a large pinning field (self-pinning), which has the attributes of both traditional nucleation and pinning. Such a pinning explains the experimental data of permanent magnets very well, including the enhancement of the coercivity by the grain boundary pinning.
Progress in recycling of Nd-Fe-B sintered magnet wastes
Grain boundary restructuring and La/Ce/Y application in Nd-Fe-B magnets
Factors influencing electromagnetic scattering from the dielectric periodic surface
The scattering characteristics of the periodic surface of infinite and finite media are investigated in detail. The Fourier expression of the scattering field of the periodic surface is obtained in terms of Huygens's principle and Floquet's theorem. Using the extended boundary condition method (EBCM) and T-matrix method, the scattering amplitude factor is solved, and the correctness of the algorithm is verified by use of the law of conservation of energy. The scattering cross section of the periodic surface in the infinitely long region is derived by improving the scattering cross section of the finite period surface. Furthermore, the effects of the incident wave parameters and the geometric structure parameters on the scattering of the periodic surface are analyzed and discussed. By reasonable approximation, the scattering calculation methods of infinite and finite long surfaces are unified. Besides, numerical results show that the dielectric constant of the periodic dielectric surface has a significant effect on the scattering rate and transmittance. The period and amplitude of the surface determine the number of scattering intensity peaks, and, together with the incident angle, influence the scattering intensity distribution.
New hybrid FDTD algorithm for electromagnetic problem analysis
Since the time step of the traditional finite-difference time-domain (FDTD) method is limited by the small grid size, it is inefficient when dealing with the electromagnetic problems of multi-scale structures. Therefore, the explicit and unconditionally stable FDTD (US-FDTD) approach has been developed to break through the limitation of Courant-Friedrich-Levy (CFL) condition. However, the eigenvalues and eigenvectors of the system matrix must be calculated before the time iteration in the explicit US-FDTD. Moreover, the eigenvalue decomposition is also time consuming, especially for complex electromagnetic problems in practical application. In addition, compared with the traditional FDTD method, the explicit US-FDTD method is more difficult to introduce the absorbing boundary and plane wave. To solve the drawbacks of the traditional FDTD and the explicit US-FDTD, a new hybrid FDTD algorithm is proposed in this paper. This combines the explicit US-FDTD with the traditional FDTD, which not only overcomes the limitation of CFL condition but also reduces the system matrix dimension, and introduces the plane wave and the perfectly matched layer (PML) absorption boundary conveniently. With the hybrid algorithm, the calculation of the eigenvalues is only required in the fine mesh region and adjacent coarse mesh region. Therefore, the calculation efficiency is greatly enhanced. Furthermore, the plane wave and the absorption boundary introduction of the traditional FDTD method can be directly utilized. Numerical results demonstrate the effectiveness, accuracy, stability, and convenience of this hybrid algorithm.
Design of an augmented reality display based on polarization grating
A new optical system for an augmented reality (AR) display is proposed in this paper. The optical system mainly includes a ray deflector, coupling input grating, optical waveguide, and coupling output grating. Both the ray deflector and the coupling input grating are designed based on the diffraction characteristics of the polarization grating, and the coupling output grating is the Bragg reflection grating. Compared with other AR schemes, this AR optical system not only reduces the number of projections from two to one, but also improves the efficiency of light coupling into the optical waveguides. The energy loss is reduced by utilizing the single-order diffraction characteristics of the polarization grating in its coupling input structure. The light deflector uses the polarization selectivity of the polarization grating and the characteristics of the rotating light of the twisted nematic liquid crystal layer to realize beam deflection. The working principle of the optical system is experimentally and theoretically demonstrated.
Multi-functional optical fiber sensor system based ona dense wavelength division multiplexer
We propose a novel and efficient multi-functional optical fiber sensor system based on a dense wavelength division multiplexer (DWDM). This system consists of an optical fiber temperature sensor, an optical fiber strain sensor, and a 48-channel DWDM. This system can monitor temperature and strain changes at the same time. The ranges of these two sensors are from -20℃ to 100℃ and from -1000 με to 2000 με, respectively. The sensitivities of the temperature sensor and strain sensor are 0.03572 nm/℃ and 0.03808 nm/N, respectively. With the aid of a broadband source and spectrometer, different kinds and ranges of parameters in the environment can be monitored by using suitable sensors.
Light propagation characteristics of turbulent plasma sheath surrounding the hypersonic aerocraft
The characteristics of light propagation through turbulent plasma sheath surrounding the hypersonic aircraft have been studied. The turbulent flow fields around a hypersonic aircraft are given by using the Navier-Stokes (NS) equations and k-ε turbulence model. Based on the distribution of flow field, refractive index and density of the plasma sheath for a blunt cone are discussed with different flight velocities and altitudes. The refractive index is mainly influenced by the electrons in the turbulent plasma sheath. The influence of different velocities and altitudes on the features of light propagation in the turbulent plasma sheath is analyzed. The results show that as the flight speed increases or the flight altitude decreases, the refractive index fluctuation becomes larger. It is also found that the refractive index fluctuation varies with the incident wavelength. This study shows how the characteristics of an optical beam propagating through plasma sheath are affected by the incident wavelength, flight velocities, and altitudes.
Phase-dependent double optomechanically induced transparency in a hybrid optomechanical cavity system with coherently mechanical driving
We propose a scheme that can generate tunable double optomechanically induced transparency in a hybrid optomechanical cavity system. In this system, the mechanical resonator of the optomechanical cavity is coupled with an additional mechanical resonator and the additional mechanical resonator can be driven by a weak external coherently mechanical driving field. We show that both the intensity and the phase of the external mechanical driving field can control the propagation of the probe field, including changing the transmission spectrum from double windows to a single-window. Our study also provides an effective way to generate intensity-controllable, narrow-bandwidth transmission spectra, with the probe field modulated from excessive opacity to remarkable amplification.
Flexible broadband polarization converter based on metasurface at microwave band
A flexible broadband linear polarization converter is proposed based on the metasurface operating at microwave band. To achieve bandwidth extension property, long and short metallic arc wires, as well as the metallic disks placed over a ground plane, are combined into the polarizer, which can generate three neighboring resonances. Due to the combination of the first two resonances and the optimized size and thickness of the unit cell, the polarization converter can have a weak incident angle dependence. Both simulated and measured results confirm that the average polarization conversion ratio is over 85% from 11.3 GHz to 20.2 GHz within a broad range of incident angle from 0° to 45°. Moreover, the proposed polarization converter based on flexible substrates can be applied for conformal design. The simulation and experiment results demonstrate that our designed polarizer still keeps high polarization conversion efficiency, even when it adheres to convex cylindrical surfaces. The periodic metallic structure of the designed polarizer has great potential application values in the microwave, terahertz, and optic regimes.
Soliton guidance and nonlinear coupling for polarized vector spiraling elliptic Hermite-Gaussian beams in nonlocal nonlinear media
We investigate the incoherent beams with two orthogonal polarizations in nonlocal nonlinear media, one of which is a fundamental Gaussian beam and the other is spiraling elliptic Hermite-Gaussian beam carrying the orbital angular momentum (OAM). Using the variational approach, we obtain the critical power and the critical OAM required for the vector spiraling elliptic Hermite-Gaussian solitons. In the strong nonlocality region, two components of the vector beam contribute to the nonlinear refractive index in a linear manner by the sum of their respective power. The nonlinear refractive index exhibits a circularly symmetrical profile in despite of the elliptic shapes for spiraling Hermite-Gaussian beams. We find that in the strong nonlocality region, the critical power and the rotational velocity are the same regardless of the relative ratio of the constituent powers. The nonlinear refractive index loses its circular symmetry in weak nonlocality region, and the nonlinear coupling effect is observed. Due to the radiation of the OAM, the damping of the rotation is predicted, and can be suppressed by decreasing the proportion of the spiraling elliptic component of the vector beam.
Memory effect evaluation based on transmission matrix calculation
The memory effect is a type of auto correlation observed in linear systems, which is widely used to control scattered light through thin scattering layers. We show that there exists a strong correlation among the optimized phase distributions of adjacent focal points in focusing through scattering media. The numeric simulation and experiment indicate that within the memory effect, the phase difference between the two adjacent focal points shows an optical phase fringe pattern, and the closer the adjacent focal points are, the wider the fringe pattern will be, corresponding to the tilting of a plane wave phase added onto the acquired optical phase distribution at the focal point. This effect can be utilized for achieving optimal phase distributions of focal point scanning without optical phase evaluation via the experiment, which has great potential application in imaging through the scattering medium.
Unidirectional plasmonic Bragg reflector based on longitudinally asymmetric nanostructures
Plasmonic Bragg reflectors are essential components in plasmonic circuits. Here we propose a novel type of plasmonic Bragg reflector, which has very high reflectance for the right-side incidence and meanwhile has extremely large absorption for the left-side incidence. This device is composed of longitudinally asymmetric nanostructures in a metal-insulator-metal waveguide. In order to efficiently analyze, design, and optimize the reflection and transmission characteristics of the proposed device, we develop a semi-analytic coupled-mode model. Results show that the reflectance extinction ratio between plasmonic modes incident from the right-side and the left-side reaches 11 dB. We expect this device with such striking unidirectional reflection performance can be used as insulators in nanoplasmonic circuits.
Phase-related noise characteristics of 780 nm band single-frequency lasers used in the cold atomic clock
We propose a method to directly measure phase-related noise characteristics of single-frequency lasers in the 728-980 nm band based on a 120° phase difference interferometer. Differential phase information of the laser under test is demodulated via the interferometer. Other parameters related to the phase noise characteristics such as linewidth at different observation time, phase/frequency noise, power spectrum density of phase/frequency fluctuation, and Allan deviation are further obtained. Frequency noise as low as 1 Hz2/Hz can be measured using our system. Then the phase-related noise characteristics of two commercial lasers frequently used in cold atomic clocks are studied systematically by the method. Furthermore, several influencing factors and their relative evolution laws are also revealed, such as the pump current and frequency-locking control parameters. This would help to optimize the laser performance, select laser sources, and evaluate the system performance for cold atomic physics applications.
Hollow and filled fiber bragg gratings in nano-bore optical fibers
To combine the technical functions and advantages of solid-core fiber Bragg gratings (FBGs) and hollow-core optical fibers (HCFs), the hollow and filled FBGs in nano-bore optical fibers (NBFs) with nano-bore in the GeO2-doped core are proposed. The fundamental mode field, effective mode index, and confinement loss of NBF with 50 nm-7 μ-diameter hollow and filled nano-bore are numerically investigated by the finite element method. The reflected spectra of FBGs in NBFs are obtained by the transmission matrix method. The hollow FBGs in NBFs can be acheived with~5% power fraction in the bore and the~0.9 reflectivity when bore diameter is less than 3 μ. The filled FBGs can be realized with~1% power fraction and 0.98 reflectivity with different fillings including o-xylene, trichloroethylene, and chloroform for 800-nm bore diameter. The feasibility of the index sensing by our proposed NBF FBG is also analyzed and discussed. The experimental fabrication of hollow and filled FBGs are discussed and can be achieved by current techniques. The aim of this work is to establish a principle prototype for investigating the HCFs and solid-core FBGs-based fiber-optic platforms, which are useful for applications such as the simultaneous chemical and physical sensing at the same position.
Lamb waves topological imaging combining with Green's function retrieval theory to detect near filed defects in isotropic plates
A method of combining Green's function retrieval theory and ultrasonic array imaging using Lamb waves is presented to solve near filed defects in thin aluminum plates. The defects are close to the ultrasonic phased array and satisfy the near field calculation formula. Near field acoustic information of defects is obscured by the nonlinear effects of initial wave signal in a directly acquired response using the full matrix capture mode. A reconstructed full matrix of inter-element responses is produced from cross-correlation of directly received ultrasonic signals between sensor pairs. This new matrix eliminates the nonlinear interference and restores the near-field defect information. The topological imaging method that was developed in recent ultrasonic inspection is used for displaying the scatterers. The experiments are conducted on both thin aluminum plates containing two and four defects, respectively. The results show that these defects are clearly identified when using a reconstructed full matrix. The spatial resolution is equal to about one wavelength of the selectively excited mode and the identifiable defect is about one fifth of the wavelength. However, in a conventional directly captured image, the images of defects overlap together and cannot be distinguished. The proposed method reduces the background noise and allows for effective topological imaging of near field defects.
Dramatic change of the self-diffusions of colloidal ellipsoids by hydrodynamic interactions in narrow channels
The self-diffusion problem of Brownian particles under the constraint of quasi-one-dimensional (q1D) channel has raised wide concern. The hydrodynamic interaction (HI) plays an important role in many practical problems and two-body interactions remain dominant under q1D constraint. We measure the diffusion coefficient of individual ellipsoid when two ellipsoidal particles are close to each other by video-microscopy measurement. Meanwhile, we obtain the numerical simulation results of diffusion coefficient using finite element software. We find that the self-diffusion coefficient of the ellipsoid decreases exponentially with the decrease of their mutual distance X when X < X0, where X0 is the maximum distance of the ellipsoids to maintain their mutual influence, X0 and the variation rate are related to the aspect ratio p=a/b. The mean squared displacement (MSD) of the ellipsoids indicates that the self-diffusion appears as a crossover region, in which the diffusion coefficient increases as the time increases in the intermediate time regime, which is proven to be caused by the spatial variations affected by the hydrodynamic interactions. These findings indicate that hydrodynamic interaction can significantly affect the self-diffusion behavior of adjacent particles and has important implications to the research of microfluidic problems in blood vessels and bones, drug delivery, and lab-on-chip.
Direct simulation Monte Carlo study of metal evaporation with collimator in e-beam physical vapor deposition
The flow properties and substrate deposition rate profile, which are the important parameters in electron beam physical vapor deposition, are investigated computationally in this article. Collimators are used to achieve the desired vapor beam and deposition rate profile in some applications. This increases the difficulty measuring boundary conditions and the size of the liquid metal pool inside the collimators. It is accordingly hard to obtain accurate results from numerical calculations. In this article, two-dimensional direct simulation Monte Carlo (DSMC) codes are executed to quantify the influence of uncertainties of boundary conditions and pool sizes. Then, three-dimensional DSMC simulations are established to simulate cerium and neodymium evaporation with the collimator. Experimental and computational results of substrate deposition rate profile are in excellent agreement at various evaporation rates and substrate heights. The results show that the DSMC method can assist in metal evaporation with a collimator.
Measuring the flexibility matrix of an eagle's flight feather and a method to estimate the stiffness distribution
Flight feathers stand out with extraordinary mechanical properties for flight because they are lightweight but stiff enough. Their elasticity has great effects on the aerodynamics, resulting in aeroelasticity. Our primary task is to figure out the stiffness distribution of the feather to study the aeroelastic effects. The feather shaft is simplified as a beam, and the flexibility matrix of an eagle flight feather is tested. A numerical method is proposed to estimate the stiffness distributions along the shaft length based on an optimal Broyden-Fletcher-Goldfarb-Shanno (BFGS) method with global convergence. An analysis of the compressive behavior of the shaft based on the beam model shows a good fit with experimental results. The stiffness distribution of the shaft is finally presented using a 5th order polynomial.
Effects of heat loss and viscosity friction at walls on flame acceleration and deflagration to detonation transition
The coupled effect of wall heat loss and viscosity friction on flame propagation and deflagration to detonation transition (DDT) in micro-scale channel is investigated by high-resolution numerical simulations. The results show that when the heat loss at walls is considered, the oscillating flame presents a reciprocating motion of the flame front. The channel width and Boit number are varied to understand the effect of heat loss on the oscillating flame and DDT. It is found that the oscillating propagation is determined by the competition between wall heat loss and viscous friction. The flame retreat is led by the adverse pressure gradient caused by thermal contraction, while it is inhibited by the viscous effects of wall friction and flame boundary layer. The adverse pressure gradient formed in front of a flame, caused by the heat loss and thermal contraction, is the main reason for the flame retreat. Furthermore, the oscillating flame can develop to a detonation due to the pressure rise by thermal expansion and wall friction. The transition to detonation depends non-monotonically on the channel width.
Analysis of extreme ultraviolet spectral profiles of laser-produced Cr plasmas
Radiation from laser-produced plasmas was examined as a potential wavelength calibration source for spectrographs in the extreme ultraviolet (EUV) region. Specifically, the EUV emission of chromium (Cr) plasmas was acquired via spatio-temporally resolved emission spectroscopy. With the aid of Cowan and flexible atomic code (FAC) structure calculations, and a comparative analysis with the simulated spectra, emission peaks in the 6.5-15.0 nm range were identified as 3p-4d, 5d and 3p-4s transition lines from Cr5+-Cr10+ ions. A normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model were assumed for the spectral simulations, and used to estimate the electron temperature and density in the plasma. The results indicate that several relatively isolated emission lines of highly charged ions would be useful for EUV wavelength calibration.
Characteristics and underlying physics of ionic wind in dc corona discharge under different polarities
During a dc corona discharge, the ions' momentum will be transferred to the surrounding neutral molecules, inducing an ionic wind. The characteristics of corona discharge and the induced ionic wind are investigated experimentally and numerically under different polarities using a needle-to-ring electrode configuration. The morphology and mechanism of corona discharge, as well as the characteristics and mechanism of the ionic wind, are different when the needle serves as cathode or anode. Under the different polarities of the applied voltage, the ionic wind velocity has a linear relation with the overvoltage. The ionic wind is stronger but has a smaller active region for positive corona compared to that for negative corona under a similar condition. The involved physics are analyzed by theoretical deduction as well as simulation using a fluid model. The ionic wind of negative corona is mainly affected by negative ions. The discharge channel has a dispersed feature due to the dispersed field, and therefore the ionic wind has a larger active area. The ionic wind of positive corona is mainly affected by positive ions. The discharge develops in streamer mode, leading to a stronger ionic wind but a lower active area.
Formation of electron depletion layer and parallel electric field in the separatrix region of anti-parallel magnetic reconnection
It is generally accepted that during collisionless magnetic reconnection, electrons flow toward the X line in the separatrix region, and then an electron depletion layer is formed. In this paper, with two-dimensional (2D) particle-in-cell (PIC) simulation, we investigate the characteristics of the separatrix region during magnetic reconnection. In addition to the electron depletion layer, we find that there still exists an electric field parallel to the magnetic field in the separatrix region. Because a reduced ion-to-electron mass ratio and light speed are usually used in PIC simulation models, we also change these parameters to analyze the characteristics of the separatrix region. It is found that the increase in the ion-to-electron mass ratio makes the electron depletion layer and the parallel electric field more obvious, while the influence of light speed is less pronounced.
Influence of vibration on spatiotemporal structure of the pattern in dielectric barrier discharge
The influence of vibration on the spatiotemporal structure of the pattern in dielectric barrier discharge is studied for the first time. The spatiotemporal structure of the pattern investigated by an intensified charge-coupled device shows that it is an interleaving of three sublattices, whose discharge sequence is small rods-halos-large spots in each half-cycle of the applied voltage. The result of the photomultiplier indicates that the small rods are composed of moving filaments. The moving mode of the moving filaments is determined to be antisymmetric stretching vibration by analyzing a series of consecutive images taken by a high-speed video camera. The antisymmetric stretching vibration affects the distribution of wall charges and leads to the halos. Furthermore, large spots are discharged only at the centers of the squares consisting of vibrating filaments. The vibration mechanism of the vibrating filaments is dependent on the electric field of wall charges.
Control on β conformation of poly(9,9-di-n-octylfluorene) via solvent annealing
Films of poly(9,9-dioctylfluorene) (PFO) are of great importance in fabricating light emitting diodes. In practice, the β-phase of PFO is expected due to its high efficiency in the transport of charge carrier. To promote the formation of β-phase, PFO films are immersed and annealed in the mixture of solvent/nonsolvent. The effects of temperature, solvent/nonsolvent ratio, and annealing time are examined systematically. It is found that the fraction of β-phase can be highly improved by increasing the ratio of solvent/nonsolvent. The reconfiguration of PFO molecules for β-phase in annealing is generally finished in 10 min. The finding in this study demonstrates that solvent-assisted annealing offers a fast and economic approach for mass annealing.
Characterization of structural transitions and lattice dynamics of hybrid organic-inorganic perovskite CH3NH3PbI3
By combining temperature-dependent x-ray diffraction (XRD) with temperature-dependent Raman scattering, we have characterized the structural transitions and lattice dynamics of the hybrid organic-inorganic perovskite CH3NH3PbI3. The XRD measurements cover distinct phases between 15 K and 370 K and demonstrate a general positive thermal expansion. Clear anomalies are found around the transition temperatures. The temperature evolution of the lattice constants reveals that the transition at 160 K/330 K is of the first-/second-order type. Raman measurements uncover three strong low-frequency modes, which can be ascribed to the vibration of the Pb/I atoms. The temperature evolution of the modes clearly catches these transitions at 160 K and 330 K, and confirms the transition types, which are exactly consistent with the XRD results. The present study may set an experimental basis to understand the high conversion efficiency in methylammonium lead iodide.
Micron-sized diamond particles containing Ge-V and Si-V color centers
Micron-sized diamond particles containing germanium-vacancy (Ge-V) color centers with a zero-photon line (ZPL) around 602.3 nm are successfully grown using hot filament chemical vapor deposition. The crystal morphology changes from icosahedron to truncated octahedron and decahedron, finally becomes spherical with the growth pressure increase. Due to the chamber containing Si, all diamond particles contain silicon-vacancy (Si-V) color centers. High growth pressure contributes to the formation of Ge-V and Si-V in diamonds. With prolonging growth time, the change in the full width at half maximum (FWHM) of the diamond peak is small, which shows that the concentration of Ge-V and Si-V centers nearly maintains a constant. The FWHM of the Ge-V ZPL is around 4 nm, which is smaller than that reported, suggesting that the Ge-V center has a more perfect structure. Ge-V and Si-V photoluminescence (PL) intensities increase with the prolonging growth time due to the increased diamond content and reduced content of sp2-bonded carbon and trans-polyacetylene. In summary, increasing the growth pressure and prolonging the growth time are beneficial to enhance the Ge-V and Si-V PL intensities.
Effects of helium irradiation dose and temperature on the damage evolution of Ti3SiC2 ceramic
The effects of 400 keV helium ion irradiation dose and temperature on the microstructure of the Ti3SiC2 ceramic were systematically investigated by grazing incidence x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The helium irradiation experiments were performed at both room temperature (RT) and 500 °C with a fluence up to 2.0×1017 He+/cm2 that resulted in a maximum damage of 9.6 displacements per atom. Our results demonstrate that He irradiations produce a large number of nanometer defects in Ti3SiC2 lattice and then cause the dissociation of Ti3SiC2 to TiC nano-grains with the increasing He fluence. Irradiation induced cell volume swelling of Ti3SiC2 at RT is slightly higher than that at 500 °C, suggesting that Ti3SiC2 is more suitable for use in a high temperature environment. The temperature dependence of cell parameter evolution and the aggregation of He bubbles in Ti3SiC2 are different from those in Ti3AlC2. The formation of defects and He bubbles at the projected depth would induce the degradation of mechanical performance.
Realization of THz dualband absorber with periodic cross-shaped graphene metamaterials
A dualband terahertz (THz) absorber including periodically distributed cross-shaped graphene arrays and a gold layer spaced by a thin dielectric layer is investigated. Numerical results reveal that the THz absorber displays two perfect absorption peaks. To elucidate the resonant behavior, the LC model is introduced to fit the spectra. Moreover, the strength and linewidth of the absorption peak can be effectively tuned with structural parameters and the relaxation time of graphene. Owing to its rotational symmetry, this THz absorber exhibits polarization insensitivity. Our designed absorber is a promising candidate in applications of tunable optical sensors and optical filters.
Impact of proton-induced alteration of carrier lifetime on single-event transient in SiGe heterojunction bipolar transistor
This paper presents an investigation into the impact of proton-induced alteration of carrier lifetime on the single-event transient (SET) caused by heavy ions in silicon-germanium heterojunction bipolar transistor (SiGe HBT). The ion-induced current transients and integrated charge collections under different proton fluences are obtained based on technology computer-aided design (TCAD) simulation. The results indicate that the impact of carrier lifetime alteration is determined by the dominating charge collection mechanism at the ion incident position and only the long-time diffusion process is affected. With a proton fluence of 5×1013 cm-2, almost no change is found in the transient feature, and the charge collection of events happened in the region enclosed by deep trench isolation (DTI), where prompt funneling collection is the dominating mechanism. Meanwhile, for the events happening outside DTI where diffusion dominates the collection process, the peak value and the duration of the ion-induced current transient both decrease with increasing proton fluence, leading to a great decrease in charge collection.
Supercooled liquids analogous fractional Stokes-Einstein relation in NaCl solution above room temperature
The Stokes-Einstein relation D~T/η and its two variants D~τ-1 and D~T/τ follow a fractional form in supercooled liquids, where D is the diffusion constant, T the temperature, η the shear viscosity, and τ the structural relaxation time. The fractional Stokes-Einstein relation is proposed to result from the dynamic heterogeneity of supercooled liquids. In this work, by performing molecular dynamics simulations, we show that the analogous fractional form also exists in sodium chloride (NaCl) solutions above room temperature. D~τ-1 takes a fractional form within 300-800 K; a crossover is observed in both D~T/τ and D~T/η. Both D~T/τ and D~T/η are valid below the crossover temperature Tx, but take a fractional form for T>Tx. Our results indicate that the fractional Stokes-Einstein relation not only exists in supercooled liquids but also exists in NaCl solutions at high enough temperatures far away from the glass transition point. We propose that D~T/η and its two variants should be critically evaluated to test the validity of the Stokes-Einstein relation.
Enhancement of MAD/MIR phasing at low resolution and a new procedure for automatic phase extension
To achieve de novo protein structure determination of challenging cases, multi-wavelength anomalous diffraction (MAD) and multiple isomorphous replacement (MIR) phasing can be powerful tools to obtain low-resolution initial phases from heavy-atom derivative datasets, then phase extension is needed against high-resolution data to obtain accurate structures. In this context, we propose a direct-methods procedure here that could improve the initial low-resolution MAD/MIR phase quality. And accordingly, an automated process for extending initial phases to high resolution is also described. These two procedures are both implanted in the newly released IPCAS pipeline. Three cases are used to perform the test, including one set of 4.17 Å MAD data from a membrane protein and two sets of MAD/MIR data with derivatives truncated down to 6.80 Å and 6.90 Å, respectively. All the results have shown that the initial phases generated from the direct-methods procedure are better than that from the conventional MAD/MIR methods. The automated phase extensions for the latter two cases starting from 6.80 Å to 3.00 Å and 6.90 Å to 2.80 Å are proved to be successful, leading to complete models. This may provide convenient and reliable tools for phase improvement and phase extension in difficult low-resolution tasks.
Isostructural phase transition-induced bulk modulus multiplication in dopant-stabilized ZrO2 solid solution
The electrical transport properties and structures of Y2O3/ZrO2 solid solution have been studied under high pressure up to 23.2 GPa by means of in situ impedance spectroscopy and x-ray diffraction (XRD) measurements. In the impedance spectra, it can be found that the pressure-dependent resistance of Y2O3/ZrO2 presents two different change trends before and after 13.3 GPa, but the crystal symmetry still remains stable in the cubic structure revealed by the XRD measurement and Rietveld refinement. The pressure dependence of the lattice constant and unit cell volume shows that the Y2O3/ZrO2 solid solution undergoes an isostructural phase transition at 13.1 GPa, which is responsible for the abnormal change in resistance. By fitting the volume data with the Birch–Murnaghan equation of state, we found that the bulk modulus B0 of the Y2O3/ZrO2 solid solution increases by 131.9% from 125.2 GPa to 290.3 GPa due to the pressure-induced isostructural phase transition.
Semiconductor-metal transition in GaAs nanowires under high pressure
We investigate the structural phase transitions and electronic properties of GaAs nanowires under high pressure by using synchrotron x-ray diffraction and infrared reflectance spectroscopy methods up to 26.2 GPa at room temperature. The zinc-blende to orthorhombic phase transition was observed at around 20.0 GPa. In the same pressure range, pressure-induced metallization of GaAs nanowires was confirmed by infrared reflectance spectra. The metallization originates from the zinc-blende to orthorhombic phase transition. Decompression results demonstrated that the phase transition from zinc-blende to orthorhombic and the pressure-induced metallization are reversible. Compared to bulk materials, GaAs nanowires show larger bulk modulus and enhanced transition pressure due to the size effects and high surface energy.
Adsorption behavior of triphenylene on Ru(0001) investigated by scanning tunneling microscopy
As a representative of small aromatic molecules, triphenylene (TP) has markedly high carrier mobility and is an ideal precursor for building graphene nanostructures. We mainly investigated the adsorption behavior of TP molecules on Ru(0001) by using scanning tunneling microscopy (STM). In submonolayer regime, TP molecules are randomly dispersed on Ru(0001) and the TP overlayer can be thoroughly dehydrogenated and converted into graphene islands at 700 K. Due to weak interaction between TP molecules and graphene, the grooves formed among graphene islands have confinement effect on TP molecules. TP adopts a flat-lying adsorption mode and has two adsorption configurations with the 3-fold molecular axis aligned almost parallel or antiparallel to the direction of the substrate. At TP coverages of 0.6 monolayer (ML) and 0.8 ML, the orientational distributions of the two adsorption configurations are equal. At about 1.0 ML, we find the coexistence of locally ordered and disordered phases. The ordered phase includes two sets of different superstructures with the symmetries of (√19×√19)R23.41° and p(4×4), respectively. The adsorption behavior of TP on Ru(0001) can be attributed to the delicate balance between molecule-substrate and molecule-molecule interactions.
Global phase diagram of a spin-orbit-coupled Kondo lattice model on the honeycomb lattice Hot!
Motivated by the growing interest in the novel quantum phases in materials with strong electron correlations and spin-orbit coupling, we study the interplay among the spin-orbit coupling, Kondo interaction, and magnetic frustration of a Kondo lattice model on a two-dimensional honeycomb lattice. We calculate the renormalized electronic structure and correlation functions at the saddle point based on a fermionic representation of the spin operators. We find a global phase diagram of the model at half-filling, which contains a variety of phases due to the competing interactions. In addition to a Kondo insulator, there is a topological insulator with valence bond solid correlations in the spin sector, and two antiferromagnetic phases. Due to the competition between the spin-orbit coupling and Kondo interaction, the direction of the magnetic moments in the antiferromagnetic phases can be either within or perpendicular to the lattice plane. The latter antiferromagnetic state is topologically nontrivial for moderate and strong spin-orbit couplings.
Effects of layer stacking and strain on electronic transport in two-dimensional tin monoxide
Tin monoxide (SnO) is an interesting two-dimensional material because it is a rare oxide semiconductor with bipolar conductivity. However, the lower room temperature mobility limits the applications of SnO in the future. Thus, we systematically investigate the effects of different layer structures and strains on the electron-phonon coupling and phonon-limited mobility of SnO. The A2u phonon mode in the high-frequency region is the main contributor to the coupling with electrons for different layer structures. Moreover, the orbital hybridization of Sn atoms existing only in the bilayer structure changes the conduction band edge and conspicuously decreases the electron-phonon coupling, and thus the electronic transport performance of the bilayer is superior to that of other layers. In addition, the compressive strain of ε=-1.0% in the monolayer structure results in a conduction band minimum (CBM) consisting of two valleys at the Γ point and along the M-Γ line, and also leads to the intervalley electronic scattering assisted by the Eg(-1) mode. However, the electron-phonon coupling regionally transferring from high frequency A2u to low frequency Eg(-1) results in little change of mobility.
Electronic and magnetic properties of CrI3 nanoribbons and nanotubes
CrI3 in two-dimensional (2D) forms has been attracting much attention lately due to its novel magnetic properties at atomic large scale. The size and edge tuning of electronic and magnetic properties for 2D materials has been a promising way to broaden or even enhance their utility, as the case with nanoribbons/nanotubes in graphene, black phosphorus, and transition metal dichalcogenides. Here we studied the CrI3 nanoribbon (NR) and nanotube (NT) systematically to seek the possible size and edge control of the electronic and magnetic properties. We find that ferromagnetic ordering is stable in all the NR and NT structures of interest. An enhancement of the Curie temperature TC can be expected when the structure goes to NR or NT from its 2D counterpart. The energy difference between the FM and AFM states can be even improved by up to 3-4 times in a zigzag nanoribbon (ZZNR), largely because of the electronic instability arising from a large density of states of iodine-5p orbitals at EF. In NT structures, shrinking the tube size harvests an enhancement of spin moment by up to 4%, due to the reduced crystal-field gap and the re-balance between the spin majority and minority populations.
Quantum Monte Carlo study of the dominating pairing symmetry in doped honeycomb lattice
We perform a systematic determinant quantum Monte Carlo (DQMC) study of the dominating pairing symmetry in a doped honeycomb lattice. The Hubbard model is simulated over a full range of filling levels for both weak and strong interactions. For weak couplings, the d-wave state dominates. The effective susceptibility as a function of filling shows a peak, and its position moves toward half filling as the temperature is increased, from which the optimal filling of the superconducting ground state is estimated. Although the sign problem becomes severe for strong couplings, the simulations access the lowest temperature at which the DQMC method generates reliable results. As the coupling is strengthened, the d-wave state is enhanced in the high-filling region. Our systematic DQMC results provide new insights into the superconducting pairing symmetry in the doped honeycomb lattice.
High quality NbTiN films fabrication and rapid thermal annealing investigation
NbTiN thin films are good candidates for applications including single-photon detector, kinetic inductance detector, hot electron bolometer, and superconducting quantum computing circuits because of their favorable characteristics, such as good superconducting properties and easy fabrication. In this work, we systematically investigated the growth of high-quality NbTiN films with different thicknesses on Si substrates by reactive DC-magnetron sputtering method. After optimizing the growth conditions, such as the gas pressure, Ar/N2 mixture ratio, and sputtering power, we obtained films with excellent superconducting properties. A high superconducting transition temperature of 15.5 K with narrow transition width of 0.03 K was obtained in a film of 300 nm thickness with surface roughness of less than 0.2 nm. In an ultra-thin film of 5 nm thick, we still obtained a transition temperature of 7.6 K. In addition, rapid thermal annealing (RTA) in atmosphere of nitrogen or nitrogen and hydrogen mixture was studied to improve the film quality. The results showed that Tc and crystal size of the NbTiN films were remarkably increased by RTA. For ultrathin films, the annealing in N2/H2 mixture had better effect than that in pure N2. The Tc of 10 nm films improved from 9.6 K to 10.3 K after RTA in N2/H2 mixture at 450℃.
Direct observation of the f-c hybridization in the ordered uranium films on W(110)
A key issue in metallic uranium and its related actinide compounds is the character of the f electrons, whether it is localized or itinerant. Here we grew well ordered uranium films on a W(110) substrate. The surface topography was investigated by scanning tunneling microscopy. The Fermi surface and band structure of the grown films were studied by angle-resolved photoemission spectroscopy. Large spectral weight can be observed around the Fermi level, which mainly comes from the f states. Additionally, we provided direct evidence that the f bands hybridize with the conduction bands in the uranium ordered films, which is different from previously reported mechanism of the direct f-f interaction. We propose that the above two mechanisms both exist in this system by manifesting themselves in different momentum spaces. Our results give a comprehensive study of the ordered uranium films and may throw new light on the study of the 5f-electron character and physical properties of metallic uranium and other related actinide materials.
Discrete modulational instability and bright localized spin wave modes in easy-axis weak ferromagnetic spin chains involving the next-nearest-neighbor coupling
We report a theoretical work on the properties of modulational instability and bright type nonlinear localized modes in one-dimensional easy-axis weak ferromagnetic spin lattices involving next-nearest-neighbor couplings. With a linear stability analysis, we calculate the growth rates of the modulational instability, and plot the instability regions. When the strength of the next-nearest-neighbor coupling is large enough, two new asymmetric modulational instability regions appear near the boundary of the first Brillouin zone. Furthermore, analytical forms of the bright nonlinear localized modes are constructed by means of a quasi-discreteness approach. The influence of the next-nearest-neighbor coupling on the Brillouin zone center mode and boundary mode are discussed. In particular, we discover a reversal phenomenon of the propagation direction of the Brillouin zone boundary mode.
Thickness-dependent magnetic anisotropy in obliquely deposited Fe(001)/Pd thin film bilayers probed by VNA-FMR
The thickness-dependent magnetic anisotropy of obliquely deposited Fe(001)/Pd thin films on Mg(001) is investigated by fitting the field-dependent resonant field curve using the Kittel equation. In this study, three Fe film samples with thicknesses of 50 monolayers (ML), 45 ML, and 32 ML deposited at 0°, 45°, and 55°, respectively, are used. The magnetic anisotropy constant obtained from ferromagnetic resonance (FMR) spectra exhibits a dominant fourfold magnetocrystalline anisotropy (MCA) at the normal deposition angle with larger Fe thickness. However, the in-plane uniaxial magnetic anisotropy (UMA) is induced by a higher oblique deposition angle and a smaller thickness. Its hard axis lies between the and directions. The FMR data-fitting analysis yields a precise measurement of smaller contributions to the magnetic anisotropy, such as in-plane UMA. Due to MCA, when the magnetic field is weaker than the saturated field, the magnetization direction does not always align with the external field. The squared frequency-dependent resonant field measurement gives an isotropic Landé g-factor of 2.07. Our results are consistent with previous experiments conducted on the magneto-optical Kerr effect (MOKE) and anisotropic magnetoresistance (AMR) systems. Thus, a vector network analyzer ferromagnetic resonance (VNA-FMR) test-method for finding UMA in obliquely deposited Fe(001)/Pd bilayer ferromagnetic thin films, and determining the magnetic anisotropy constants with respect to the film normal deposition, is proposed.
Regulating element distribution to improve magnetic properties of sintered Nd-Fe-B/Tb-Fe-B composite magnets
Nd content was varied in Nd13.2-xFe80.8+xB6 (x=0, 0.5, 1, and 1.5) to optimize the magnetic properties of sintered Nd-Fe-B/Tb-Fe-B composite magnets, which were prepared by mixing 9 g of Nd-Fe-B with 1 g of Tb17Fe75B8 powder. In conventional magnets, by reducing Nd content, the coercivity of 10.4 kOe in Nd13.2Fe80.8B6 decreases to 7.2 kOe in Nd12.2Fe81.8B6; meanwhile, in Nd-Fe-B/Tb-Fe-B magnets the coercivity does not decrease when reducing Nd content. In the intergranular phase, the Tb content increases owing to the reducing Nd content of the Nd-Fe-B alloy in the sintered composite magnets. Therefore, the excess Tb in Tb17Fe75B8 enters the intergranular phase, and more Tb atoms can substitute for Nd at the grain boundary of the Nd-Fe-B phase, leading to a more significant increase in coercivity. The remanence increases with reducing Nd content, and the energy product of 39.1 MGOe with a high coercivity of 21.0 kOe is obtained in Nd12.2Fe81.8B6/Tb17Fe75B8 magnets. These investigations show that magnetic properties can be further improved by regulating the element distribution in sintered composite magnets.
Field-variable magnetic domain characterization of individual 10 nm Fe3O4 nanoparticles
The local detection of magnetic domains of isolated 10 nm Fe3O4 magnetic nanoparticles (MNPs) has been achieved by field-variable magnetic force microscopy (MFM) with high spatial resolution. The domain configuration of an individual MNP shows a typical dipolar response. The magnetization reversal of MNP domains is governed by a coherent rotation mechanism, which is consistent with the theoretical results given by micromagnetic calculations. Present results suggest that the field-variable MFM has great potential in providing nanoscale magnetic information on magnetic nanostructures, such as nanoparticles, nanodots, skyrmions, and vortices, with high spatial resolution. This is crucial for the development and application of magnetic nanostructures and devices.
Influence of annealing treatment on the luminescent properties of Ta:β-Ga2O3 single crystal
Ta5+ doped β-Ga2O3 single crystals were grown by using the optical floating zone method, and then annealed in the air and nitrogen gas at 1400℃ for 20 hours. The transmittance spectra, photoluminescence (PL), x-ray irradiation spectra, and PL decay profiles of the samples were measured at room temperature. The relevant results show that the optical transmittance of the samples annealed in the air or nitrogen gas was improved. By drawing the (ahv)2-hv graph, it can be seen that the band gap decreased after being annealed in the air, but increased in nitrogen gas. The PL spectra and x-ray irradiation spectra show that the luminescent intensity of the sample annealed in the air increased substantially, while decreased for the sample annealed in nitrogen. The PL decay time of the Ta:β-Ga2O3 annealed in the air increased significantly compared with that of the Ta:β-Ga2O3 sample without annealing, but the tendency after annealing in nitrogen gas was opposite.
Secondary electron yield suppression using millimeter-scale pillar array and explanation of the abnormal yield-energy curve
The phenomenon of secondary electron emission is of considerable interest in areas such as particle accelerators and on-board radio frequency (RF) components. Total secondary electron yield (TSEY) is a parameter that is frequently used to describe the secondary electron emission capability of a material. It has been widely recognized that the TSEY vs. primary electron energy curve has a single-hump shape. However, the TSEY-energy curve with a double-hump shape was also observed experimentally–this anomaly still lacks explanation. In this work, we explain this anomaly with the help of a millimetre-scale (mm-scale) silver pillar array fabricated by three-dimensional (3D) printing technology. The TSEY-energy curve of this pillar array as well as its flat counterpart is obtained using sample current method. The measurement results show that for the considered primary electron energy (40-1500 eV), the pillar array can obviously suppress TSEY, and its TSEY-energy curve has an obvious double-hump shape. Through Monte Carlo simulations and electron beam spot size measurements, we successfully attribute the double-hump effect to the dependence of electron beam spot size on the primary electron energy. The observations of this work may be of help in determining the TSEY of roughened surface with characteristic surface structures comparable to electron beam spot size. It also experimentally confirms the TSEY suppression effect of pillar arrays.
Annealing-enhanced interlayer coupling interaction inGaS/MoS2 heterojunctions
Fabrication of large-area atomically thin transition metal dichalcogenides is of critical importance for the preparation of new heterojunction-based devices. In this paper, we report the fabrication and optical investigation of large-scale chemical vapor deposition (CVD)-grown monolayer MoS2 and exfoliated few-layer GaS heterojunctions. As revealed by photoluminescence (PL) characterization, the as-fabricated heterojunctions demonstrated edge interaction between the two layers. The heterojunction was sensitive to annealing and showed increased interaction upon annealing at 300 °C under vacuum conditions, which led to changes in both the emission peak position and intensity resulting from the strong coupling interaction between the two layers. Low-temperature PL measurements further confirmed the strong coupling interaction. In addition, defect-related GaS luminescence was observed in our few-layer GaS, and the PL mapping provided evidence of edge interaction coupling between the two layers. These findings are interesting and provide the basis for creating new material systems with rich functionalities and novel physical effects.
Growth of high quality Sr2IrO4 epitaxial thin films onconductive substrates
Ruddlesden-Popper iridium oxides have attracted considerable interest because of the many proposed novel quantum states that arise from the large spin-orbit coupling of the heavy iridium atoms in them. A prominent example is the single layer Sr2IrO4, in which superconductivity has been proposed under electron doping. However, the synthesis of Sr2IrO4 high quality thin films has been a huge challenge due to the easy formation of impurities associated with different numbers of SrO layers. Thus techniques to optimize the growth of pure phase Sr2IrO4 are urgently required. Here we report the deposition of high quality Sr2IrO4 thin films on both insulating SrTiO3 and conducting SrTiO3:Nb substrates using pulsed laser deposition assisted with reflective high-energy electron diffraction. The optimal deposition temperature of Sr2IrO4 epitaxial films on SrTiO3:Nb substrates is about 90 °C lower than that on SrTiO3 substrates. The electrical transports of high quality Sr2IrO4 films are measured, which follow the three-dimensional Mott variable-range hopping model. The film magnetizations are measured, which show weak ferromagnetism below~240 K with a saturation magnetization of~0.2 μB/Ir at 5 K. This study provides applicable methods to prepare high quality 5d Sr2IrO4 epitaxial films, which could be extended to other Ruddlesden-Popper phases and potentially help the future study of exotic quantum phenomena in them.
Molecular beam epitaxial growth of high quality InAs/GaAs quantum dots for 1.3-μ quantum dot lasers
Systematic investigation of InAs quantum dot (QD) growth using molecular beam epitaxy has been carried out, focusing mainly on the InAs growth rate and its effects on the quality of the InAs/GaAs quantum dots. By optimizing the growth rate, high quality InAs/GaAs quantum dots have been achieved. The areal quantum dot density is 5.9×1010 cm-2, almost double the conventional density (3.0×1010 cm-2). Meanwhile, the linewidth is reduced to 29 meV at room temperature without changing the areal dot density. These improved QDs are of great significance for fabricating high performance quantum dot lasers on various substrates.
Thermal conductivity characterization of ultra-thin silicon film using the ultra-fast transient hot strip method
Thermal conductivity is an important material parameter of silicon when studying the performance and reliability of devices or for guiding circuit design when considering heat dissipation, especially when the self-heating effect becomes prominent in ultra-scaled MOSFETs. The cross-plane thermal conductivity of a thin silicon film is lacking due to the difficulty in sensing high thermal conductivity in the vertical direction. In this paper, a feasible method that utilizes an ultra-fast electrical pulse within 20 μs combined with the hot strip technique is adopted. To the best of our knowledge, this is the first work that shows how to extract the cross-plane thermal conductivity of sub-50 nm (30 nm, 17 nm, and 10 nm) silicon films on buried oxide. The ratio of the extracted cross-plane thermal conductivity of the silicon films over the bulk value is only about 6.9%, 4.3%, and 3.8% at 300 K, respectively. As the thickness of the films is smaller than the phonon mean free path, the classical heat transport theory fails to predict the heat dissipation in nanoscale transistors. Thus, in this study, a ballistic model, derived from the heat transport equation based on extended-irreversible-hydrodynamics (EIT), is used for further investigation, and the simulation results exhibit good consistence with the experimental data. The extracted effective thermal data could provide a good reference for precise device simulations and thermoelectric applications.
Modulation of magnetic and electrical properties of bilayer graphene quantum dots using rotational stacking faults
Bilayer graphene quantum dots with rotational stacking faults (RSFs) having different rotational angles were studied. Using the first-principles calculation, we determined that these stacking faults could quantitatively modulate the magnetism and the distribution of spin and energy levels in the electronic structures of the dots. In addition, by examining the spatial distribution of unpaired spins and Bader charge analysis, we found that the main source of magnetic moment originated from the edge atoms of the quantum dots. Our research results can potentially provide a new path for producing all-carbon nanodevices with different electrical and magnetic properties.
Effects of CeO2 and nano-ZrO2 agents on the crystallization behavior and mechanism of CaO-Al2O3-MgO-SiO2-based glass ceramics
The crystallization behavior and mechanism of CaO-Al2O3-MgO-SiO2 (CAMS)-based diopside glass ceramics with nano-ZrO2 nucleators and CeO2 agents have been investigated. The use of nanoscale ZrO2 as nucleators is favorable to the crystallization of glass ceramic at a relatively lower temperature due to the reduction of the activation energy, while the activation energy is increased after adding the CeO2 agent. The microstructure and orientation have been analyzed by scanning electron microscopy and electron backscatter diffraction. Two discernible layers are observed, featured in glass and crystalline phases, respectively. Remarkably textured polycrystalline diopsides are verified for the samples (A and B) free of CeO2 agents, with c-axes perpendicular to the interface of the two layers. Comparatively, the c-axes of diopside grains of the sample (C) with CeO2 agents are proved to be parallel to the interface. Nanocrystals are detected in the vicinity of the interface for sample C.
First-principles insight into Li and Na ion storage in graphene oxide
The structural, electronic, and adsorption properties of Li/Na ions on graphene decorated by epoxy groups are investigated by first-principles calculations based on density functional theory. Our results show that the concentration of epoxy groups remarkably affects the structural and electronic properties of graphene. The bandgaps change monotonically from 0.16 eV to 3.35 eV when the O coverage increases from 12.5% to 50% (O/C ratio). Furthermore, the highest lithiation potential of 2.714 V is obtained for the case of graphene oxide (GO) with 37.5% O coverage, while the highest sodiation potential is 1.503 V for GO with 12.5% O coverage. This clearly demonstrates that the concentration of epoxy groups has different effects on Li and Na storage in GO. Our results provide a new insight into enhancing the Li and Na storage by tuning the concentration of epoxy groups on GO.
Artificial solid electrolyte interphase based on polyacrylonitrile for homogenous and dendrite-free deposition of lithium metal
High chemical reactivity, large volume changes, and uncontrollable lithium dendrite growth have always been the key problems of lithium metal anodes. Coating has been demonstrated as an effective strategy to protect the lithium metal. In this work, the effects of polyacrylonitrile (PAN)-based coatings on electrodeposited lithium have been studied. Our results show that a PAN coating layer provides uniform and dendrite-free lithium deposition as well as better cycling performance with carbonate electrolyte. Notably, heat treatment of the PAN coating layer promotes the formation of larger deposit particle size and higher coulombic efficiency (85%). The compact coating layer of heat-treated PAN with a large Young modulus (82.7 GPa) may provide stable protection for the active lithium. Improved homogeneity of morphology and mechanical properties of heat-treated PAN contribute to the larger deposit particles. This work provides new feasibility to optimize the polymer coating through rational modification of polymers.
Effect of defects properties on InP-based high electron mobility transistors
The performance damage mechanism of InP-based high electron mobility transistors (HEMTs) after proton irradiation has been investigated comprehensively through induced defects. The effects of the defect type, defect energy level with respect to conduction band ET, and defect concentration on the transfer and output characteristics of the device are discussed based on hydrodynamic model and Shockley-Read-Hall recombination model. The results indicate that only acceptor-like defects have a significant influence on device operation. Meanwhile, as defect energy level ET shifts away from conduction band, the drain current decreases gradually and finally reaches a saturation value with ET above 0.5 eV. This can be attributed to the fact that at sufficient deep level, acceptor-type defects could not be ionized any more. Additionally, the drain current and transconductance degrade more severely with larger acceptor concentration. These changes of the electrical characteristics with proton radiation could be accounted for by the electron density reduction in the channel region from induced acceptor-like defects.
Wavelength dependence of intrinsic detection efficiency of NbN superconducting nanowire single-photon detector
Superconducting nanowire single-photon detectors (SNSPDs) have attracted considerable attention owing to their excellent detection performance; however, the underlying physics of the detection process is still unclear. In this study, we investigate the wavelength dependence of the intrinsic detection efficiency (IDE) for NbN SNSPDs. We fabricate various NbN SNSPDs with linewidths ranging from 30 nm to 140 nm. Then, for each detector, the IDE curves as a function of bias current for different incident photon wavelengths of 510-1700 nm are obtained. From the IDE curves, the relations between photon energy and bias current at a certain IDE are extracted. The results exhibit clear nonlinear energy-current relations for the NbN detectors, indicating that a detection model only considering quasiparticle diffusion is unsuitable for the meander-type NbN-based SNSPDs. Our work provides additional experimental data on SNSPD detection mechanism and may serve as an interesting reference for further investigation.
Topological magnon insulator with Dzyaloshinskii-Moriya interaction under the irradiation of light
The topological magnon insulator on a honeycomb lattice with Dzyaloshinskii-Moriya interaction (DMI) is studied under the application of a circularly polarized light. At the high-frequency regime, the effective tight-binding model is obtained based on Brillouin-Wigner theory. Then, we study the corresponding Berry curvature and Chern number. In the Dirac model, the interplay between a light-induced handedness-dependent effective DMI and intrinsic DMI is discussed.
Effects of Mg2+ on the binding of the CREB/CRE complex: Full-atom molecular dynamics simulations
Metal ions play critical roles in the interaction between deoxyribonucleic acid (DNA) and protein. The experimental research has demonstrated that the Mg2+ ion can affect the binding between transcription factor and DNA. In our work, by full-atom molecular dynamic simulation, the effects of the Mg2+ ion on the cyclic adenosine monophosphate (cAMP) response element binding protein (CREB)/cAMP response elements (CRE) complex are investigated. It is illustrated that the number of hydrogen bonds formed at the interface between protein and DNA is significantly increased when the Mg2+ ion is added. Hence, an obvious change in the structure of the DNA is observed. Then the DNA base groove and base pair parameters are analyzed. We find that, due to the introduction of the Mg2+ ion, the DNA base major groove becomes narrower. A potential mechanism for this observation is proposed. It is confirmed that the Mg2+ ion can enhance the stability of the DNA-protein complex.
Pyramid scheme model for consumption rebate frauds
There are various types of pyramid schemes that have inflicted or are inflicting losses on many people in the world. We propose a pyramid scheme model which has the principal characters of many pyramid schemes that have appeared in recent years:promising high returns, rewarding the participants for recruiting the next generation of participants, and the organizer takes all of the money away when they find that the money from the new participants is not enough to pay the previous participants interest and rewards. We assume that the pyramid scheme is carried out in the tree network, Erdös-Réney (ER) random network, Strogatz-Watts (SW) small-world network, or Barabasi-Albert (BA) scale-free network. We then give the analytical results of the generations that the pyramid scheme can last in these cases. We also use our model to analyze a pyramid scheme in the real world and we find that the connections between participants in the pyramid scheme may constitute a SW small-world network.