In this paper, we propose a conformal momentum-preserving method to solve a damped nonlinear Schrödinger (DNLS) equation. Based on its damped multi-symplectic formulation, the DNLS system can be split into a Hamiltonian part and a dissipative part. For the Hamiltonian part, the average vector field (AVF) method and implicit midpoint method are employed in spatial and temporal discretizations, respectively. For the dissipative part, we can solve it exactly. The proposed method conserves the conformal momentum conservation law in any local time-space region. With periodic boundary conditions, this method also preserves the total conformal momentum and the dissipation rate of momentum exactly. Numerical experiments are presented to demonstrate the conservative properties of the proposed method.

We study the ionization of helium Rydberg atoms in an electric field above the classical ionization threshold within the semiclassical theory. By introducing a fractal approach to describe the chaotic dynamical behavior of the ionization, we identify the fractal self-similarity structure of the escape time versus the distribution of the initial launch angles of electrons, and find that the self-similarity region shifts toward larger initial launch angles with a decrease in the scaled energy. We connect the fractal structure of the escape time plot to the escape dynamics of ionized electrons. Of particular note is that the fractal dimensions are sensitively controlled by the scaled energy and magnetic field, and exhibit excellent agreement with the chaotic extent of the ionization systems for both helium and hydrogen Rydberg atoms. It is shown that, besides the electric and magnetic fields, core scattering is a primary factor in the fractal dynamics.

It has been found that for a fixed degree of fuzziness in the coarsened references of measurements, the quantum-to-classical transition can be observed independent of the macroscopicity of the quantum state. We explore a general situation that the degree of fuzziness can change with the rotation angle between two states (different rotation angles represent different references). The fuzziness of reference comes from two kinds of fuzziness:the Hamiltonian (rotation frequency) and the timing (rotation time). For the fuzziness of the Hamiltonian alone, the degree of fuzziness for the reference will change with the rotation angle between two states, and the quantum effects can still be observed with any degree of fuzziness of Hamiltonian. For the fuzziness of timing, the degree of the coarsening reference is unchanged with the rotation angle. During the rotation of the measurement axis, the decoherence environment can also help the classical-to-quantum transition due to changing the direction of the measurement axis.

We analyze universal conditions where the l_{1} norm and relative entropy of coherence are amplified and frozen under identical bit-flip channels; that is, using pre-measurements (quantum weak measurements or quantum measurement reversals) on the systems before undergoing local bit-flip channels. With the option of quantum weak measurements or quantum measurement reversals, the measurement strength and the success probability are all determined by the initial state of the quantum system.

The stopping time of a one-dimensional bounded classical random walk (RW) is defined as the number of steps taken by a random walker to arrive at a fixed boundary for the first time. A quantum walk (QW) is a non-trivial generalization of RW, and has attracted a great deal of interest from researchers working in quantum physics and quantum information. In this paper, we develop a method to calculate the stopping time for a one-dimensional QW. Using our method, we further compare the properties of stopping time for QW and RW. We find that the mean value of the stopping time is the same for both of these problems. However, for short times, the probability for a walker performing a QW to arrive at the boundary is larger than that for a RW. This means that, although the mean stopping time of a quantum and classical walker are the same, the quantum walker has a greater probability of arriving at the boundary earlier than the classical walker.

Chang et al. [Chin. Phys. B23 010305 (2014)] have proposed a quantum broadcast communication and authentication protocol. However, we find that an intercept-resend attack can be preformed successfully by a potential eavesdropper, who will be able to destroy the authentication function. Afterwards, he or she can acquire the secret transmitted message or even modify it while escaping detection, by implementing an efficient man-in-the-middle attack. Furthermore, we show a simple scheme to defend this attack, that is, applying non-reusable identity strings.

We use the path-integral formalism to investigate the vortex properties of a quasi-two dimensional (2D) Fermi superfluid system trapped in an optical lattice potential. Within the framework of mean-field theory, the cooper pair density, the atom number density, and the vortex core size are calculated from weakly interacting BCS regime to strongly coupled while weakly interacting BEC regime. Numerical results show that the atoms gradually penetrate into the vortex core as the system evolves from BEC to BCS regime. Meanwhile, the presence of the optical lattice allows us to analyze the vortex properties in the crossover from three-dimensional (3D) to 2D case. Furthermore, using a simple re-normalization procedure, we find that the two-body bound state exists only when the interaction is stronger than a critical one denoted by G_{c} which is obtained as a function of the lattice potential's parameter. Finally, we investigate the vortex core size and find that it grows with increasing interaction strength. In particular, by analyzing the behavior of the vortex core size in both BCS and BEC regimes, we find that the vortex core size behaves quite differently for positive and negative chemical potentials.

Cluster synchronization is an important dynamical behavior in community networks and deserves further investigations. A community network with distributed time delays is investigated in this paper. For achieving cluster synchronization, an impulsive control scheme is introduced to design proper controllers and an adaptive strategy is adopted to make the impulsive controllers unified for different networks. Through taking advantage of the linear matrix inequality technique and constructing Lyapunov functions, some synchronization criteria with respect to the impulsive gains, instants, and system parameters without adaptive strategy are obtained and generalized to the adaptive case. Finally, numerical examples are presented to demonstrate the effectiveness of the theoretical results.

The present work reports the development of nonlinear time series prediction method of genetic algorithm (GA) with singular spectrum analysis (SSA) for forecasting the surface wind of a point station in the South China Sea (SCS) with scatterometer observations. Before the nonlinear technique GA is used for forecasting the time series of surface wind, the SSA is applied to reduce the noise. The surface wind speed and surface wind components from scatterometer observations at three locations in the SCS have been used to develop and test the technique. The predictions have been compared with persistence forecasts in terms of root mean square error. The predicted surface wind with GA and SSA made up to four days (longer for some point station) in advance have been found to be significantly superior to those made by persistence model. This method can serve as a cost-effective alternate prediction technique for forecasting surface wind of a point station in the SCS basin.

In order to improve the transform efficiency of bi-stable energy harvester (BEH), this paper proposes an advanced bi-stable energy harvester (ABEH), which is composed of two bi-stable beams coupling through their magnets. Theoretical analyzes and simulations for the ABEH are carried out. First, the mathematical model is established and its dynamical equations are derived. The formulas of magnetic force in two directions are given. The potential energy barrier of ABEH is reduced and the snap-through is liable to occur between potential wells. To demonstrate the ABEH's advantage in harvesting energy, comparisons between the ABEH and the BEH are carried out for both harmonic and stochastic excitations. Our results reveal that the ABEH's inter-well response can be elicited by a low-frequency excitation and the harvester can attain frequent jumping between potential wells at fairly weak random excitations. Thus, it can generate a higher output power. The present findings prove that the ABEH is preferable in harvesting energy and can be optimally designed such that it attains the best harvesting performance.

Anomalous (or non-Fickian) transport behaviors of particles have been widely observed in complex porous media. To capture the energy-dependent characteristics of non-Fickian transport of a particle in flow fields, in the present paper a generalized continuous time random walk model whose waiting time probability distribution depends on the preceding jump length is introduced, and the corresponding master equation in Fourier-Laplace space for the distribution of particles is derived. As examples, two generalized advection-dispersion equations for Gaussian distribution and lévy flight with the probability density function of waiting time being quadratic dependent on the preceding jump length are obtained by applying the derived master equation.

First-principle simulations have been applied to investigate the effect of copper (Cu) or aluminum (Al) content on the ductility of Al_{3}Ti, AlTi, AlCu, and AlTiCu_{2} alloys. The mechanical stable and elastic properties of Al-based intermetallic compounds are researched by density functional theory with the generalized gradient approximation (DFT-GGA). The calculated lattice constants are in conformity with the previous experimental and theoretical data. The deduced elastic constants show that the investigated Al_{3}Ti, AlTi, AlCu, and AlTiCu_{2} structures are mechanically stable. Shear modulus, Young's modulus, Poisson's ratio, and the ratio B/G have also been figured out by using reckoned elastic constants. A further analysis of Young's modulus and Poisson's ratio reveals that the third added element copper content has significant effects on the Al-Ti-based ICs ductile character.

The isotope shifts (ISs) for the 2s^{2}S_{1/2} to 2p^{2}P_{J} (J=1/2, 3/2) transitions of the lithium nuclei including the stable and short-lived isotopes are calculated based on the multi-configuration Dirac-Hartree-Fock method and the relativistic configuration interaction approach. The results are in good agreement with the previous theoretical and experimental results within a deviation less than 0.05%. The methods used here could be applied to the IS calculations for other heavier Li-like ions and few-electron systems.

We apply the strong-field Lewenstein model to demonstrate the high-order harmonic generation of CO_{2} with three vibrational modes (balance vibration, bending vibration, and stretching vibration) driven by an intense laser field. The results show that the intensity of harmonic spectra is sensitive to molecular vibrational modes, and the high harmonic efficiency with stretching vibrational mode is the strongest. The underlying physical mechanism of the harmonic emission can be well explained by the corresponding ionization yield and the time-frequency analysis. Finally, we demonstrate the attosecond pulse generation with different vibrational modes and an isolated attosecond pulse with a duration of about 112 as is generated.

We report a pure ferromagnetic metallic magnetoplasmonic structure consisting of two-dimensional ordered Ni nanodisks array on Co film. With a sufficient height of the nanodisks, a steep and asymmetric Fano resonance can be excited in this structure. We attribute the fascinating spectral lineshape to the strong coupling between the excitation of surface plasmon polaritons at the interface and the localized surface plasmon resonance of nanodisks. The conclusion is fully confirmed by spectrum measurements in nanostructures with different heights. Furthermore, the enhancement and sign of the magneto-optical Kerr rotation in this structure are significantly modified by the Fano resonance.

There is no available theoretical description of electron transfer from negative projectiles at a velocity below 0.1 a.u. during grazing scattering on insulating surfaces. In this low-velocity range, electron-capture and electron-loss processes coexist. For electron capture, the Demkov model has been successfully used to explain the velocity dependence of the negative-ion fraction formed from fast atoms during grazing scattering on insulating surfaces. For electron loss, we consider that an electron may be transferred from the formed ionic diabatic quasi-molecular state to the formed covalent diabatic quasi-molecular state by the crossing of the potential curves of negative projectiles approaching the surface cations, which can be described by the Landau-Zener two-energy-level crossing model. Combining these two models, we obtain good agreement between the experimental and calculated data for the F^{-}-LiF(001) collision system, which is briefly discussed.

To realize scale quantum processors, the surface-electrode ion trap is an effective scaling approach, including single-layer, double-layer, and quasi-double-layer traps. To calculate critical trap parameters such as the trap center and trap depth, the finite element method (FEM) simulation was widely used, however, it is always time consuming. Moreover, the FEM simulation is also incapable of exhibiting the direct relationship between the geometry dimension and these parameters. To eliminate the problems above, House and Madsen et al. have respectively provided analytic models for single-layer traps and double-layer traps. In this paper, we propose a semi-analytical model for quasi-double-layer traps. This model can be applied to calculate the important parameters above of the ion trap in the trap design process. With this model, we can quickly and precisely find the optimum geometry design for trap electrodes in various cases.

We propose a versatile electrostatic trap scheme using several charged spherical electrodes and a bias electric field. We first give the two-ball scheme and derive the analytical solution of the electric field. In order to make a comparison, we also give the numerical solution calculated by the finite element software (Ansoft Maxwell). Considering the loading of cold polar molecules into the trap, we give the three-ball scheme. We first give the analytical and numerical solutions of the distribution of the electric field. Then we simulate the dynamic process of the loading and trapping cold molecules using the classical Monte Carlo method. We analyze the influence of the velocity of the incident molecular beam and the loading time on the loading efficiency. After that, we give the temperature of the trapped cold molecules. Our study shows that the loading efficiency can reach 82%, and the corresponding temperature of the trapped molecules is about 24.6 mK. At last, we show that the single well divides into two ones by increasing the bias electric field or decreasing the voltages applied to the spherical electrodes.

We propose a new ion-trap geometry to carry out accurate measurements of the quadrupole shifts in the ^{171}Yb ion. This trap will minimize the quadrupole shift due to the harmonic component of the confining potential by an order of magnitude. This will be useful to reduce the uncertainties in the clock frequency measurements of the 6s ^{2}S_{1/2}→4f^{13}6s^{2}^{2}F_{7/2} and 6s ^{2}S_{1/2}→5d ^{2}D_{3/2} transitions, from which we can deduce the precise values of the quadrupole moments (Θs) of the 4f^{13}6s^{2}^{2}F_{7/2} and 5d ^{2}D_{3/2} states. Moreover, it may be able to affirm the validity of the measured Θ value of the 4f^{13}6s^{2}^{2}F_{7/2} state, for which three independent theoretical studies defer almost by one order of magnitude from the measurement. We also calculate Θs using the relativistic coupled-cluster (RCC) method. We use these Θ values to estimate the quadrupole shift that can be measured in our proposed ion trap experiment.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Continuous phase plate (CPP), which has a function of beam shaping in laser systems, is one kind of important diffractive optics. Based on the Fourier transform of the Gerchberg-Saxton (G-S) algorithm for designing CPP, we proposed an optical diffraction method according to the real system conditions. A thin lens can complete the Fourier transform of the input signal and the inverse propagation of light can be implemented in a program. Using both of the two functions can realize the iteration process to calculate the near-field distribution of light and the far-field repeatedly, which is similar to the G-S algorithm. The results show that using the optical diffraction method can design a CPP for a complicated laser system, and make the CPP have abilities of beam shaping and phase compensation for the phase aberration of the system. The method can improve the adaptation of the phase plate in systems with phase aberrations.

The expressions of the second harmonic (2f) signal are derived on the basis of absorption spectral and lock-in theories. A parametric study indicates that the phase shift between the intensity and wavelength modulation makes a great contribution to the 2f signal. A self-calibration wavelength modulation spectroscopy (WMS) method based on tunable diode laser absorption spectroscopy (TDLAS) is applied, combining the advantages of ambient pressure, temperature suppression, and phase-shift influences elimination. Species concentration is retrieved simultaneously from selected 2f signal pairs of measured and reference WMS-2f spectra. The absorption line of acetylene (C_{2}H_{2}) at 1530.36 nm near-infrared is selected to detect C_{2}H_{2} concentrations in the range of 0-400 ppmv. System sensitivity, detection precision and limit are markedly improved, demonstrating that the self-calibration method has better detecting performance than the conventional WMS.

In this paper, we present a theoretical simulation of ^{87}Rb absorption spectrum in a thermal cm-cell which is adaptive to the experimental observation. In experiment, the coupling and probe beams are configured to copropagate but perpendicular polarized, making up to five velocity selective optical pumping (VSOP) absorption dips able to be identified. A Λ-type electromagnetically induced transparency (EIT) is also observed for each group of velocity-selected atoms. The spectrum by only sweeping the probe beam can be decomposed into a combination of Doppler-broadened background and three VSOP dips for each group of velocity-selected atoms, accompanied by an EIT peak. This proposed theoretical model can be used to simulate the spectrum adaptive to the experimental observation by the non-linear least-square fit method. The fit for the high quality of experimental observation can determine valuable transition parameters such as decaying rates and coupling beam power accurately.

We present an experimental study of multi-Raman gain resonances in a hot rubidium vapor. The experiment is performed based on a high-efficiency four-wave mixing process due to the Raman-driven coherence in a double-Λ configuration. The Raman gain resonance for ^{85}Rb atoms under a bias magnetic field is shown to be split into five or six peaks, depending on the orientation of the magnetic field. The formed multi-Raman gain resonances have potential applications in measurement of magnetic fields and generation of multi-frequency correlated twin beams.

Based on the spatial modulation of active Raman gain, a two-dimensional gain cross-grating is theoretically proposed. As the probe field propagates along the z direction and passes through the intersectant region of the two orthogonal standing-wave fields in the x-y plane, it can be effectively diffracted into the high-order directions, and the zero-order diffraction intensity is amplified at the same time. In comparison with the two-dimensional electromagnetically induced cross-grating based on electromagnetically induced transparency, the two-dimensional gain cross-grating has much higher diffraction intensities in the first-order and the high-order directions. Hence, it is more suitable to be utilized as all-optical switching and routing in optical networking and communication.

In this study, we show how a static magnetic field can control photon-induced electron transport through a quantum dot system coupled to a photon cavity. The quantum dot system is connected to two electron reservoirs and exposed to an external perpendicular static magnetic field. The propagation of electrons through the system is thus influenced by the static magnetic and the dynamic photon fields. It is observed that the photon cavity forms photon replica states controlling electron transport in the system. If the photon field has more energy than the cyclotron energy, then the photon field is dominant in the electron transport. Consequently, the electron transport is enhanced due to activation of photon replica states. By contrast, the electron transport is suppressed in the system when the photon energy is smaller than the cyclotron energy.

We report an efficient continuous-wave self-Raman laser at 1176 nm based on a 20-mm-long composite YVO_{4}/Nd:YVO_{4}/YVO_{4} crystal and pumped by a wavelength-locked 878.9 nm diode laser. A maximum output power of 5.3 W is achieved at a pump power of 26 W, corresponding to an optical conversion efficiency of 20% and a slope efficiency of 21%. The Raman threshold for the diode pump power was only 0.92 W. The results reveal that in-band pumping by a wavelength-locked diode laser significantly enhances output power and efficiency of self-Raman lasers by virtue of improved pump absorption and relieved thermal loading.

Silver nanowire (AgNW) film was proposed to apply on the surface of the vertical-cavity surface-emitting lasers (VCSELs) with large aperture in order to obtain a uniform current distribution in the active region and a better optical beam quality. Optimization of the AgNW film was carried out with the sheet resistance of 28.4 Ω/sq and the optical transmission of 94.8% at 850 nm. The performance of VCSELs with and without AgNW film was studied. When the AgNW film was applied to the surface of VCSELs, due to its better current spreading effect, the maximum output optical power increased from 23.4 mW to 24.4 mW, the lasing wavelength redshift decreased from 0.085 nm/mA to 0.077 nm/mA, the differential resistance decreased from 23.95 Ω to 21.13 Ω, and the far field pattern at 50 mA decreased from 21.6° to 19.2°. At the same time, the near field test results showed that the light in the aperture was more uniform, and the far field exhibited a better single peak characteristic. Various results showed that VCSELs with AgNW on the surface showed better beam quality.

We proposed a two-coupled microsphere resonator structure as the element of angular velocity sensing under the Sagnac effect. We analyzed the theoretical model of the two coupled microspheres, and derived the coupled-resonator-induced transparency (CRIT) transfer function, the effective phase shift, and the group delay. Experiments were also carried out to demonstrate the CRIT phenomenon in the two-coupled microsphere resonator structure. We calculated that the group index of the two-coupled sphere reaches n_{g}=180.46, while the input light at a wavelength of 1550 nm.

The structural deformation induced by intense laser field of liquid nitrobenzene (NB) molecule, a typical molecule with restricting internal rotation, is tracked by time- and frequency-resolved coherent anti-Stokes. Raman spectroscopy (CARS) technique with an intense pump laser. The CARS spectra of liquid NB show that the NO_{2} torsional mode couples with the NO_{2} symmetric stretching mode, and the NB molecule undergoes ultrafast structural deformation with a relaxation time of 265 fs. The frequency of NO_{2} torsional mode in liquid NB (42 cm^{-1}) at room temperature is found from the sum and difference combination bands involving the NO_{2} symmetric stretching mode and torsional mode in time- and frequency-resolved CARS spectra.

In this paper, we introduce a horizontal slot in the reversed-rib chalcogenide glass waveguide to tailor its dispersion characteristics. The waveguide exhibits a flat and low dispersion over a wavelength range of 1080 nm, in which the dispersion fluctuates between -10.6 ps·nm^{-1}·km^{-1} and+11.14 ps·nm^{-1}·km^{-1}. The dispersion tailoring effect is due to the mode field transfer from the reversed-rib waveguide to the slot with the increase of wavelength, which results in the extension of the low dispersion band. Moreover, the nonlinear coefficient and the phase-matching condition of the four-wave mixing process in this waveguide are studied, showing that the waveguide has great potential in nonlinear optical applications over a wide wavelength range.

When building an experimental platform for light propagation along an inhomogeneous turbulent path, it is very essential to set up the reasonable distribution of phase screen. Based on multi-layered model of phase screen, an iterative optimization algorithm of phase screen position is given in this paper. Thereafter, the optimal position of phase screens is calculated under the Hufnagel-Valley5/7 and Hefei-day turbulence profile. The results show that the positions of phase screen calculated by the iterative algorithm can fit well with the turbulence profile rather than mechanically placed phase screens at equal distance. Compared with the uniform distribution of phase screens position, the residual phase error of the iterative algorithm decreases very significantly. The similarity degree between them is minimal when number of layers is equal to two.

A high-contrast grating (HCG) focusing reflector providing phase front control of reflected light and high reflectivity is proposed and fabricated. Basic design rules to engineer this category of structures are given in detail. A 1550 nm TM polarized incident light of 11.86 mm in focal length and 0.8320 in reflectivity is obtained in experiment. The wavelength dependence of the fabricated HCGs from 1530 nm to 1580 nm is also tested. The test results show that the focal length is in the range of 11.81-12 mm, which is close to the designed focal length of 15 mm. The reflectivity is almost above 0.56 within a bandwidth of 50 nm. At a distance of 11.86 mm, the light is focused to a round spot with the highest concentration, which is much smaller than the size of the incident beam. The FWHM of the reflected light beam decreases to 120 nm, and the intensity increases to 1.18.

We numerically simulate the generation of an optical frequency comb (OFC) in a microring based on the traditional Si_{3}N_{4} strip waveguide and a temperature compensated slot waveguide. The results show that OFCs are susceptible to temperature with strip waveguide while they can keep stable when temperature changes 10 K in either low-Q (10^{5}) or high Q (10^{6}) microcavity with the well-designed slot waveguide, which has great superiority in practical applications where the temperature drift of the cavity due to the intense pump or surrounding change is unavoidable.

Atmospheric turbulence (AT) induced crosstalk can significantly impair the performance of a free-space optical (FSO) communication link using orbital angular momentum (OAM) multiplexing. In this paper, we propose a multiple-user detection (MUD) turbulence mitigation scheme in an OAM-multiplexed FSO communication link. First, we present a MUD equivalent communication model for an OAM-multiplexed FSO communication link under AT. In the equivalent model, each input bit stream represents one user's information. The deformed OAM spatial modes caused by AT, instead of the pure OAM spatial modes, are used as information carriers, and the overlapping between the deformed OAM spatial modes are computed as the correlation coefficients between the users. Then, we present a turbulence mitigation scheme based on MUD idea to enhance AT tolerance of the OAM-multiplexed FSO communication link. In the proposed scheme, the crosstalk caused by AT is used as a useful component to deduce users' information. The numerical results show that the performance of the OAM-multiplexed communication link has greatly improved by the proposed scheme. When the turbulence strength C_{3in}^{2} is 1×10^{-15} m^{-2/3}, the transmission distance is 1000 m and the channel signal-to-noise ratio (SNR) is 26 dB, the bit-error-rate (BER) performance of four spatial multiplexed OAM modes l_{m}=+1,+2,+3,+4 are all close to 10^{-5}, and there is a 2-3 fold increase in the BER performance in comparison with those results without the proposed scheme. In addition, the proposed scheme is more effective for an OAM-multiplexed FSO communication link with a larger OAM mode topological charge interval. The proposed scheme is a promising direction for compensating the interference caused by AT in the OAM-multiplexed FSO communication link.

Polar dielectrics are important optical materials enabling the subwavelength manipulation of light in infrared due to their capability to excite phonon polaritons. In practice, it is highly desired to actively modify these hyperbolic phonon polaritons (HPPs) to optimize or tune the response of the device. In this work, we investigate the plasmonic material, a monolayer graphene, and study its hybrid structure with three kinds of hyperbolic thin films grown on SiO_{2} substrate. The inter-mode hybridization and their tunability have been thoroughly clarified from both the band dispersions and the mode patterns numerically calculated through a transfer matrix method. Our results show that these hybrid multilayer structures are of strong potentials for applications in plasmonic waveguides, modulators and detectors in infrared.

This study reports on the propagation of elastic waves in 1D and 2D mass spring structures. An analytical and computation model is presented for the 1D and 2D mass spring systems with different examples. An enhancement in the band gap values was obtained by modeling the structures to obtain low frequency band gaps at small dimensions. Additionally, the evolution of the band gap as a function of mass value is discussed. Special attention is devoted to the local resonance property in frequency ranges within the gaps in the band structure for the corresponding infinite periodic lattice in the 1D and 2D mass spring system. A linear defect formed of a row of specific masses produces an elastic waveguide that transmits at the narrow pass band frequency. The frequency of the waveguides can be selected by adjusting the mass and stiffness coefficients of the materials constituting the waveguide. Moreover, we pay more attention to analyze the wave multiplexer and DE-multiplexer in the 2D mass spring system. We show that two of these tunable waveguides with alternating materials can be employed to filter and separate specific frequencies from a broad band input signal. The presented simulation data is validated through comparison with the published research, and can be extended in the development of resonators and MEMS verification.

Metallic nanofilms are important components of nanoscale electronic circuits and nanoscale sensors. The accurate characterization of the thermophysical properties of nanofilms is very important for nanoscience and nanotechnology. Currently, there is very little specific heat data for metallic nanofilms, and the existing measurements indicate distinct differences according to the nanofilm size. The present work reports the specific heats of 40-nm-thick suspended platinum nanofilms at 80-380 K and ~5×10^{-4} Pa using the 3ω method. Over 80-380 K, the specific heats of the Pt nanofilms range from 166-304 J/(kg·K), which are 1.65-2.60 times the bulk values, indicating significant size effects. These results are useful for both scientific research in nanoscale thermophysics and evaluating the transient thermal response of nanoscale devices.

By using the discrete variational method, we study the numerical method of the general nonholonomic system in the generalized Birkhoffian framework, and construct a numerical method of generalized Birkhoffian equations called a self-adjoint-preserving algorithm. Numerical results show that it is reasonable to study the nonholonomic system by the structure-preserving algorithm in the generalized Birkhoffian framework.

The structures of the Si/Cu heterogenous interface impacted by a nanoindenter with different incident angles and depths are investigated in detail using molecular dynamics simulation. The simulation results suggest that for certain incident angles, the nanoindenter with increasing depth can firstly increase the stress of each atom at the interface and it then introduces more serious structural deformation of the Si/Cu heterogenous interface. A nanoindenter with increasing incident angle (absolute value) can increase the length of the Si or Cu extended atom layer. It is worth mentioning that when the incident angle of the nanoindenter is between -45° and 45°, these Si or Cu atoms near the nanoindenter reach a stable state, which has a lower stress and a shorter length of the Si or Cu extended atom layer than those of the other incident angles. This may give a direction to the planarizing process of very large scale integration circuits manufacture.

This paper presents the buoyancy effects on the magneto-hydrodynamics stagnation point flow of an incompressible, viscous, and electrically conducting nanofluid over a vertically stretching sheet. The impacts of an induced magnetic field and viscous dissipation are taken into account. Both assisting and opposing flows are considered. The overseeing nonlinear partial differential equations with the associated boundary conditions are reduced to an arrangement of coupled nonlinear ordinary differential equations utilizing similarity transformations and are then illuminated analytically by using the optimal homotopy investigation strategy (OHAM). Graphs are introduced and examined for different parameters of the velocity, temperature, and concentration profile. Additionally, numerical estimations of the skin friction, local Nusselt number, and local Sherwood number are explored using numerical values.

The three-dimensional premixed H_{2}-O_{2} detonation propagation in rectangular ducts is simulated using an in-house parallel detonation code based on the second-order space-time conservation element and solution element (CE/SE) scheme. The simulation reproduces three typical cellular structures by setting appropriate cross-sectional size and initial perturbation in square tubes. As the cross-sectional size decreases, critical cellular structures transforming the rectangular or diagonal mode into the spinning mode are obtained and discussed in the perspective of phase variation as well as decreasing of triple point lines. Furthermore, multiple cellular structures are observed through examples with typical aspect ratios. Utilizing the visualization of detailed three-dimensional structures, their formation mechanism is further analyzed.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

The efficient and safe operation of large fusion devices strongly relies on the plasma configuration inside the vacuum chamber. It is important to construct the proper plasma equilibrium with a desired plasma configuration. In order to construct the target configuration, a shape constraint module has been developed in the tokamak simulation code (TSC), which controls the poloidal flux and the magnetic field at several defined control points. It is used to construct the double null, lower single null, and quasi-snowflake configurations for the required target shape and calculate the required PF coils current. The flexibility and practicability of this method have been verified by the simulated results.

A one-dimensional hybrid model was developed to study the electrical asymmetry effect (EAE) caused by the fourth-order harmonic in a dual-frequency capacitively coupled Ar plasma. The self-bias voltage caused by the fourth-order frequency changes periodically with the phase angle, and the cycle of self-bias with the phase angle is π/2, which is half of that in the second-order case. The influence of the phase angle between the fundamental and its fourth-order frequency on the ion density profiles and the ion energy distributions (IEDs) were studied. Both the ion density profile and the IEDs can be controlled by the phase angle, which provides a convenient way to adjust the sheath characters without changing the main discharge parameters.

We investigate the transport properties and mechanical response of glassy hard disks using nonlinear Langevin equation theory. We derive expressions for the elastic shear modulus and viscosity in two dimensions on the basis of thermal-activated barrier-hopping dynamics and mechanically accelerated motion. Dense hard disks exhibit phenomena such as softening elasticity, shear-thinning of viscosity, and yielding upon deformation, which are qualitatively similar to dense hard-sphere colloidal suspensions in three dimensions. These phenomena can be ascribed to stress-induced “landscape tilting”. Quantitative comparisons of these phenomena between hard disks and hard spheres are presented. Interestingly, we find that the density dependence of yield stress in hard disks is much more significant than in hard spheres. Our work provides a foundation for further generalizing the nonlinear Langevin equation theory to address slow dynamics and rheological behavior in binary or polydisperse mixtures of hard or soft disks.

A new mechanism of light-to-electricity conversion that uses InGaN/GaN QWs with a p-n junction is reported. According to the well established light-to-electricity conversion theory, quantum wells (QWs) cannot be used in solar cells and photodetectors because the photogenerated carriers in QWs usually relax to ground energy levels, owing to quantum confinement, and cannot form a photocurrent. We observe directly that more than 95% of the photoexcited carriers escape from InGaN/GaN QWs to generate a photocurrent, indicating that the thermionic emission and tunneling processes proposed previously cannot explain carriers escaping from QWs. We show that photoexcited carriers can escape directly from the QWs when the device is under working conditions. Our finding challenges the current theory and demonstrates a new prospect for developing highly efficient solar cells and photodetectors.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Anti-structured defects bridge atom migration among heterogeneous sublattices facilitating diffusion but could also result in the collapse of ordered structure. Component distribution Ni_{75} Al_{x}V_{25-x} alloys are investigated using a microscopic phase field model to illuminate relations between anti-structured defects and composition, precipitate order, precipitate type, and phase stability. The Ni_{75} Al_{x}V_{25-x} alloys undergo single Ni_{3} V (stage I), dual Ni_{3} Al and Ni_{3} V (stage Ⅱ with Ni_{3} V prior; and stage Ⅲ with Ni_{3} Al prior), and single Ni_{3} Al (stage IV) with enhanced aluminum level. For Ni_{3} V phase, anti-structured defects (V_{Ni1}, Ni_{V}, except V_{Ni2}) and substitution defects (Al_{Ni1}, Al_{Ni2}, Al_{V}) exhibit a positive correlation to aluminum in stage I, the positive trend becomes to negative correlation or smooth during stage Ⅱ. For Ni_{3} Al phase, anti-structured defects (Al_{Ni}, Ni_{Al}) and substitution defects (V_{Ni}, V_{Al}) have a positive correlation to aluminum in stage Ⅱ, but Ni_{Al} goes down since stage Ⅲ and lasts to stage IV. V_{Ni} and V_{Al} fluctuate when Ni_{3} Al precipitates prior, but go down drastically in stage IV. Precipitate type conversion of single Ni_{3} V/dual (Ni_{3} V+Ni_{3} Al) affects Ni_{3} V defects, while dual (Ni_{3} V+Ni_{3} Al)/single Ni_{3} Al has little effect on Ni_{3} Al defects. Precipitate order swap occurred in the dual phase region affects on Ni_{3} Al defects but not on Ni_{3} V.

Remarkable room-temperature ferromagnetism was observed both in undoped and Cu-doped rutile TiO_{2} single crystals (SCs). To tune their magnetism, Ar ion irradiation was quantitatively performed on the two crystals in which the saturation magnetizations for the samples were enhanced distinctively. The post-irradiation led to a spongelike layer in the near surface of the Cu-doped TiO_{2}. Meanwhile, a new CuO-like species present in the sample was found to be dissolved after the post-irradiation. Analyzing the magnetization data unambiguously reveals that the experimentally observed ferromagnetism is related to the intrinsic defects rather than the exotic Cu ions, while these ions are directly involved in boosting the absorption in the visible region.

The bulk properties of materials in an extreme environment such as high temperature and high pressure can be understood by studying anharmonic effects due to the vibration of lattice ions and thermally excited electrons. In this spirit, in the present paper, anharmonic effects are studied by using the recently proposed mean-field potential (MFP) approach and Mermin functional which arise due to the vibration of lattice ions and thermally excited electrons, respectively. The MFP experienced by a wanderer atom in the presence of surrounding atoms is constructed in terms of cold energy using the local form of the pseudopotential. We have calculated the temperature variation of several thermophysical properties in an extreme environment up to melting temperature. The results of our calculations are in excellent agreement with the experimental findings as well as the theoretical results obtained by using first principle methods. We conclude that presently used conjunction scheme (MFP+pseudopotential) is simple computationally, transparent physically, and accurate in the sense that the results generated are comparable and sometimes better than the results obtained by first principle methods. Local pseudopotential used is transferable to extreme environment without adjusting its parameters.

The distribution of He in η-Fe_{2}C has been studied by first-principles calculations. The formation energies of interstitial He and substitutional He (replacing Fe) are 3.76 eV and 3.49 eV, respectively, which are remarkably smaller than those in bcc Fe, indicating that He is more soluble in η-Fe_{2}C than in bcc Fe. The binding potencies of both a substitutional-interstitial He pair (1.28 eV) and a substitutional-substitutional He pair (0.76 eV) are significantly weaker than those in bcc Fe. The binding energy between the two He atoms in an interstitial-interstitial He pair (0.31 eV) is the same as that in bcc Fe, but the diffusion barrier of interstitial He (0.35 eV) is much larger than that in bcc Fe, suggesting that it is more difficult for the interstitial He atom to agglomerate in η-Fe_{2}C than in bcc Fe. Thus, self-trapping of He in η-Fe_{2}C is less powerful than that in bcc Fe. As a consequence, small and dense η-Fe_{2}C particles in ferritic steels might serve as scattered trapping centers for He, slow down He bubble growth at the initial stage, and make the steel more swelling resistant.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Inspired by the recently proposed Legendre orthogonal polynomial representation for imaginary-time Green's functions G(τ), we develop an alternate and superior representation for G(τ) and implement it in the hybridization expansion continuous-time quantum Monte Carlo impurity solver. This representation is based on the kernel polynomial method, which introduces some integral kernel functions to filter the numerical fluctuations caused by the explicit truncations of polynomial expansion series and can improve the computational precision significantly. As an illustration of the new representation, we re-examine the imaginary-time Green's functions of the single-band Hubbard model in the framework of dynamical mean-field theory. The calculated results suggest that with carefully chosen integral kernel functions, whether the system is metallic or insulating, the Gibbs oscillations found in the previous Legendre orthogonal polynomial representation have been vastly suppressed and remarkable corrections to the measured Green's functions have been obtained.

We have investigated the factors affecting the current spreading length (CSL) in GaN-based light-emitting diodes (LEDs) by deriving theoretical expressions and performing simulations with APSYS. For mesa-structure LEDs, the effects of both indium tin oxide (ITO) and n-GaN are taken into account for the first time, and a new Q factor is introduced to explain the effects of different current flow paths on the CSL. The calculations and simulations show that the CSL can be enhanced by increasing the thickness of the ITO layer and resistivity of the n-GaN layer, or by reducing the resistivity of the ITO layer and thickness of the n-GaN layer. The results provide theoretical support for calculating the CSL clearly and directly. For vertical-structure LEDs, the effects of resistivity and thickness of the CSL on the internal quantum efficiency (IQE) have been analyzed. The theoretical expression relating current density and the parameters (resistivity and thickness) of the CSL is obtained, and the results are then verified by simulation. The IQE under different current injection conditions is discussed. The effects of CSL resistivity play a key role at high current injection, and there is an optimal thickness for the largest IQE only at a low current injection.

We investigate the effects of strain on the electronic and magnetic properties of ReS_{2} monolayer with sulfur vacancies using density functional theory. Unstrained ReS_{2} monolayer with monosulfur vacancy (V_{S}) and disulfur vacancy (V_{2S}) both are nonmagnetic. However, as strain increases to 8%, V_{S}-doped ReS_{2} monolayer appears a magnetic half-metal behavior with zero total magnetic moment. In particular, for V_{2S}-doped ReS_{2} monolayer, the system becomes a magnetic semiconductor under 6% strain, in which Re atoms at vicinity of vacancy couple anti-ferromagnetically with each other, and continues to show a ferromagnetic metal characteristic with total magnetic moment of 1.60μ _{B} under 7% strain. Our results imply that the strain-manipulated ReS_{2} monolayer with V_{S} and V_{2S} can be a possible candidate for new spintronic applications.

The crossover of large to small radius polaron is studied in terms of the inverse-relaxation time and temperature. It is found that the small radius polaron exists at higher temperature than the large radius polaron. A formula which relates the inverse-relaxation time to the ratio of arbitrary temperature and Debye temperature of the crystal is derived. The polaron crossover temperatures in NaCl and KBr are found from plotted graphs. The straight line emerging at the Debye temperature T_{D} of a graph reflects the increase of the inverse relaxation time for increasing temperature up to the collapse of the small radius polaron. The relationship between the small and large radius polarons is found and known ratios of the effective and the bare masses of the electrons for the two substances are used to validate our results. The small radius polaron's mass is later compared with the mass obtained from the hopping formula and is found to be approximately equal. Finally, we point out that the crossover temperature is material-specific since it depends on the Debye and the effective dielectric function.

The spin fluctuation in rubidium atom gas is studied via all-optical spin noise spectroscopy (SNS). Experimental results show that the integrated SNS signal and its full width at half maximum (FWHM) strongly depend on the frequency detuning of the probe light under resonant and non-resonant conditions. The total integrated SNS signal can be well fitted with a single squared Faraday rotation spectrum and the FWHM dependence may be related to the absorption profile of the sample.

A novel and accurate method is proposed to extract the intrinsic elements of the GaN high-electron-mobility transistor (HEMT) switch. The new extraction method is verified by comparing the simulated S-parameters with the measured data over the 5-40 GHz frequency range. The percentage errors E_{ij} within 3.83% show the great agreement between the simulated S-parameters and the measured data.

The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs double quantum well wire is calculated, and expressions for the electronic states are presented. The system is modeled by considering T=0 K and also with a single parabolic conduction band, which is split into a subband system due to the confinement. The gain and differential cross-section for an electron Raman scattering process are obtained. In addition, the emission spectra for several scattering configurations are discussed, and interpretations of the singularities found in the spectra are given. The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers.

In this paper, we study the quantum properties of a bilayer graphene with (asymmetry) line defects. The localized states are found around the line defects. Thus, the line defects on one certain layer of the bilayer graphene can lead to an electric transport channel. By adding a bias potential along the direction of the line defects, we calculate the electric conductivity of bilayer graphene with line defects using the Landauer-Büttiker theory, and show that the channel affects the electric conductivity remarkably by comparing the results with those in a perfect bilayer graphene. This one-dimensional line electric channel has the potential to be applied in nanotechnology engineering.

Fluorine plasma treatment was used prior to the Schottky metal deposition on the undoped Al_{0.45}Ga_{0.55}N, which aimed at the solar-blind wavelength. After fluorine plasma treatment and before depositing the Ni/Au Schottky, the samples were thermal annealed in the N_{2} gas at 400℃. The reverse leakage current density of Al_{0.45}Ga_{0.55}N Schottky diode was reduced by 2 orders of magnitude at -10 V. The reverse leakage current density was reduced by 3 orders of magnitude after thermal annealing. Further capacitance-frequency analysis revealed that the fluorine-based plasma treatment reduces the surface states of AlGaN by one order of magnitude at different surface state energies. The capacitance-frequency analysis also proved that the concentration of carriers in AlGaN top is reduced through fluorine plasma treatment.

In this paper, the enhancement-mode AlGaN/GaN HEMT combined with the low damage recessed-gate etching and the optimized oxygen plasma treatment was fabricated. Scanning electron microscope/energy dispersive spectrometer (SEM/EDS) method and x-ray photoelectron spectroscopy (XPS) method were used to confirm the formation of oxides. Based on the experimental results, the obtained enhancement-mode HEMT exhibited a threshold voltage of 0.5 V, a high peak transconductance of 210 mS/mm, and a maximum drain current of 610 mA/mm at the gate bias of 4 V. Meanwhile, the on/off current ratio of enhancement-mode HEMT was as high as 10^{8}, drain induced barrier lowering (DIBL) was as low as 5 mV/V, and subthreshold swing (SS) of 80 mV/decade was obtained. Compared with the conventional HEMT, the Schottky reverse current of enhancement-mode HEMT was three orders of magnitude lower, and the off-state breakdown voltage of which was higher. In addition, a power gain cutoff frequency (f_{max}) of the enhancement-mode HEMT was larger than that of the conventional one.

Bipolar resistance switching characteristics are investigated in Cu/sputtered-HfO_{2}/Pt structure in the application of resistive random access memory (RRAM). The conduction mechanism of the structure is characterized to be SCLC conduction. The dependence of resistances in both high resistance state (HRS) and low resistance state (LRS) on the temperature and device area are studied. Then, the composition and chemical bonding state of Cu and Hf at Cu/HfO_{2} interface region are analyzed by x-ray photoelectron spectroscopy (XPS). Combining the electrical characteristics and the chemical structure at the interface, a model for the resistive switching effect in Cu/HfO_{2}/Pt stack is proposed. According to this model, the generation and recovery of oxygen vacancies in the HfO_{2} film are responsible for the resistance change.

We have studied spin-dependent thermoelectric transport through parallel triple quantum dots with Rashba spin-orbital interaction (RSOI) embedded in an Aharonov-Bohm interferometer connected symmetrically to leads using nonequilibrium Green's function method in the linear response regime. Under the appropriate configuration of magnetic flux phase and RSOI phase, the spin figure of merit can be enhanced and is even larger than the charge figure of merit. In particular, the charge and spin thermopowers as functions of both the magnetic flux phase and the RSOI phase present quadruple-peak structures in the contour graphs. For some specific configuration of the two phases, the device can provide a mechanism that converts heat into a spin voltage when the charge thermopower vanishes while the spin thermopower is not zero, which is useful in realizing the thermal spin battery and inducing a pure spin current in the device.

First-principles calculations by means of the full-potential linearized augmented plane wave method using the generalized gradient approximation with correlation effect correction (GGA+U) within the framework of spin polarized density functional theory (DFT+U) are used to study the structural, electronic, and magnetic properties of cubic perovskite compounds RbXF_{3} (X=Mn, V, Co, and Fe). It is found that the calculated structural parameters, i.e., lattice constant, bulk modulus, and its pressure derivative are in good agreement with the previous results. Our results reveal that the strong spin polarization of the 3d states of the X atoms is the origin of ferromagnetism in RbXF_{3}. Cohesive energies and the magnetic moments of RbXF_{3} have also been calculated. The calculated electronic properties show the half-metallic nature of RbCoF_{3} and RbFeF_{3}, making these materials suitable for spintronic applications.

Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators. Previously, we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi_{2}Te_{3} surface. In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi_{2}Te_{3} surface.

We study a mixed spin-( 3/2, 1) ladder system with antiferromagnetic rung coupling and next-nearest-neighbor interaction. The exactly solved Ising-chain model is employed to investigate the ground-state properties and thermodynamics of the low-dimensional ladder system. Our results show that the competition between different exchange couplings brings in a large variety of ground states characterized by various values of normalized magnetization equal to 0, 1/5, 2/5, 3/5, 1. Moreover, an interesting double-peak structure is also detected in the thermal dependence of magnetic susceptibility and specific heat when the frustration comes into play. It is shown that the double-peak phenomenon at zero-field for the case of AF_{2} ground-state arises from the very strong antiferromagnetic rung coupling, while other cases are attributed to the excitations induced by temperature and external field around the phase boundary.

Glassy magnetic behavior and exchange bias phenomena are observed in single phase Mn_{3}O_{4} nanoparticles. Dynamics scaling analysis of the ac susceptibility and the Henkel plot indicate that the observed glassy behavior at low temperature can be understood by taking into account the intrinsic behavior of the individual particles consisting of a ferrimagnetic (FIM) core and a spin-glass surface layer. Field-cooled magnetization hysteresis loops display both horizontal and vertical shifts. Dependence of the exchange bias field (H_{E}) on the cooling field shows an almost undamped feature up to 70 kOe, indicating the stable exchange bias state in Mn_{3}O_{4}.H_{E} increases as the particle size decreases due to the higher surface/volume ratio. The occurrence of the exchange bias can be attributed to the pinning effect of the frozen spin-glass surface layer upon the FIM core.

The temperature dependences of magnetostriction in Pr_{1-x}Dy_{x}Fe_{1.9} (0≤x≤1.0) alloys between 5 K and 300 K were investigated. An unusual decrease of magnetostriction with temperature decreasing was found in Pr-rich alloys (0≤x≤0.2), due to the change of the easy magnetization direction (EMD). Dy substitution reduces the magnetostriction in high-magnetic field (10 kOe≤H≤90 kOe) at 5 K, while a small amount of Dy substitution (x=0.05) is beneficial to increasing the magnetostriction in low-magnetic field between 10 K and 50 K. This makes the alloys a potential candidate for low temperature applications.

To investigate the coercivity, corrosion resistance, and thermal stability of Nd-Fe-B magnets, their properties were investigated at room and high temperature before and after doping with Dy_{80}Ga_{20} (at.%) powder. The coercivity of the magnets increased from the undoped value of 12.72 kOe to a doped value of 21.44 kOe. A micro-structural analysis indicates that a well-developed core-shell structure forms in the magnets doped with Dy_{80}Ga_{20} powder. The improvement in magnetic properties is believed to be related to the refined and uniform matrix grains, continuous grain boundaries, and a hardened (Nd, Dy)_{2}Fe_{14}B shell surrounding the matrix grains. Additionally, the doped magnets exhibit an obvious improvement in thermal stability. For the magnets with added Dy_{80}Ga_{20} powder, the temperature coefficients of remanence (α) and coercivity (β) increased to -0.106%℃^{-1} and -0.60%℃^{-1} over the range 20-100℃, compared to temperature coefficients of -0.117%℃^{-1} (α) and -0.74%℃^{-1} (β) in the regular magnets without Dy_{80}Ga_{20} powder. The irreversible loss of magnetic flux (Hirr) was investigated at different temperatures. After being exposed to 150℃ for 2 h, the Hirr of magnets with 4 wt.% Dy_{80}Ga_{20} decreased by ~95% compared to that of the undoped magnets. The enhanced temperature coefficients and Hirr indicate improved thermal stability in the doped Nd-Fe-B magnets. The intergranular addition of Dy_{80}Ga_{20} also improved the corrosion resistance of the magnets because of the enhanced intergranular phase. In a corrosive atmosphere for 96 h, the mass loss of the sintered magnets with 4 wt.% Dy_{80}Ga_{20} was 2.68 mg/cm^{2}, less than 10% of that suffered by the undoped magnets (28.1 mg/cm^{2}).

This paper presents a lumped equivalent circuit model of the nonreciprocal magnetoelectric tunable microwave band-pass filter. The reciprocal coupled-line circuit is based on the converse magnetoelectric effect of magnetoelectric composites, includes the electrical tunable equivalent factor of the piezoelectric layer, and is established by the introduced lumped elements, such as radiation capacitance, radiation inductance, and coupling inductance, according to the transmission characteristics of the electromagnetic wave and magnetostatic wave in an inverted-L-shaped microstrip line and ferrite slab. The nonreciprocal transmission property of the filter is described by the introduced T-shaped circuit containing controlled sources. Finally, the lumped equivalent circuit of a nonreciprocal magnetoelectric tunable microwave band-pass filter is given and the lumped parameters are also expressed. When the deviation angles of the ferrite slab are respectively 0° and 45°, the corresponding magnetoelectric devices are respectively a reciprocal device and a nonreciprocal device. The curves of S parameter obtained by the lumped equivalent circuit model and electromagnetic simulation are in good agreement with the experimental results. When the deviation angle is between 0° and 45°, the maximum value of the S parameter predicted by the lumped equivalent circuit model is in good agreement with the experimental result. The comparison results of the paper show that the lumped equivalent circuit model is valid. Further, the effect of some key material parameters on the performance of devices is predicted by the lumped equivalent circuit model. The research can provide the theoretical basis for the design and application of nonreciprocal magnetoelectric tunable devices.

Ta/Nd/NdFeB/Nd/Ta sandwiched films are deposited by magnetron sputtering on Si (100) substrates, and subsequently annealed in vacuum at different temperatures for different time. It is found that both the thickness of NdFeB and Nd layer and the annealing condition can affect the magnetic properties of Ta/Nd/NdFeB/Nd/Ta films. Interestingly, the thickness and annealing temperature show the relevant behaviors that can affect the magnetic properties of the film. The high coercivity of 24.1 kOe (1 Oe=79.5775 A/m) and remanence ratio (remanent magnetization/saturation magnetization) of 0.94 can be obtained in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed for 3 min at 1023 K. In addition, the thermal stability of the film is also linked to the thickness of NdFeB and Nd layer and the annealing temperature as well. The excellent thermal stability can be achieved in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed at 1023 K.

Si-rich SiO_{x} and amorphous Si clusters embedded in SiO_{x} films were prepared by the radio-frequency magnetron cosputtering method and high-temperature annealing treatment. The threshold resistance switching behavior was achieved from the memory mode by continuous bias sweeping in all films, which was caused by the formation of clusters due to the local overheating under a large electric field. Besides, the I-V characteristics of the threshold switching showed a dependence on the annealing temperature and the SiO_{x} thickness. In particular, formation and rupture of conduction paths is considered to be the switching mechanism for the 39 nm-SiO_{x} film, while for the 78 nm-SiO_{x} film, adjusting of the Schottky barrier height between insulator and semiconductor is more reasonable. This study demonstrates the importance of investigation of both switching modes in resistance random access memory.

The exchange effect and the magneto-plasmon mode dispersion are studied theoretically for an anisotropic two-dimensional electronic system in the presence of a uniform perpendicular magnetic field. Employing an effective low-energy model with anisotropic effective masses, which is relevant for a monolayer of phosphorus, the exchange effect due to the electron-electron interaction is treated within the self-consistent Hartree-Fock approximation. The magneto-plasmon mode dispersion is obtained by solving a Bethe-Salpeter equation for the electron density-density correlation function within the ladder diagram approximation. It is found that the exchange effect is reduced in the anisotropic system in comparison with the isotropic one. The magneto-plasmon mode dispersion shows a clear dependence on the direction of the wave vector.

The Judd-Ofelt theoretic transition intensity parameters A_{tp}^{k} of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence. It is very difficult to determine them with emission or absorption spectra for a long time. A “full profile fitting” method to obtain A_{tp}^{k} in solids with its emission spectrum is proposed, in which the contribution of a radiative transition to the emission spectrum is expressed as the product of transition probability, line profile function, instrument measurement constant and transition center frequency or wavelength, and the whole experimental emission spectrum is the sum of all transitions. In this way, the emission spectrum is expressed as a function with the independent variables intensity parameters A_{tp}^{k}, full width at half maximum (FWHM) of profile functions, instrument measurement constant, wavelength, and the Huang-Rhys factor S if the lattice vibronic peaks in the emission spectrum should be considered. The ratios of the experimental to the calculated energy lifetimes are incorporated into the fitting function to remove the arbitrariness during fitting A_{tp}^{k} and other parameters. Employing this method obviates measurement of the absolute emission spectrum intensity. It also eliminates dependence upon the number of emission transition peaks. Every experiment point in emission spectra, which usually have at least hundreds of data points, is the function with variables A_{tp}^{k} and other parameters, so it is usually viable to determine A_{tp}^{k} and other parameters using a large number of experimental values. We applied this method to determine twenty-five A_{tp}^{k} of Yb^{3+} in GdTaO_{4}. The calculated and experiment energy lifetimes, experimental and calculated emission spectrum are very consistent, indicating that it is viable to obtain the transition intensity parameters of rare-earth ions in solids by a full profile fitting to the ions' emission spectrum. The calculated emission cross sections of Yb^{3+}:GdTaO_{4} also indicate that the F-L formula gives larger values in the wavelength range with reabsorption.

We explore the dispersion properties and optical gradient forces from mutual coupling of surface plasmon polariton (SPP) modes at two interfaces of nanoscale plasmonic waveguides with hyperbolic metamaterial cladding. With Maxwell's equations and Maxwell stress tensor, we calculate and compare the dispersion relation and optical gradient force for symmetric and antisymmetric SPP modes in two kinds of nanoscale plasmonic waveguides. The numerical results show that the optical gradient force between two coupled hyperbolic metamaterial waveguides can be engineered flexibly by adjusting the waveguide structure parameters. Importantly, an alternative way to boost the optical gradient force is provided through engineering the hyperbolic metamaterial cladding of suitable orientation. These special optical properties will open the door for potential optomechanical applications, such as optical tweezers and actuators.

A detailed study of the magnetic characterizations of the top structure MgO/CoFeB/Mo is presented. The samples show strong perpendicular magnetic anisotropy (PMA) when the thickness of CoFeB is 0.9 nm and 1.1 nm. The saturation magnetic moment and interface anisotropy constant are 1566 emu/cm^{3} and 3.75 erg/cm^{2}, respectively. The magnetic dead layer (MDL) is about 0.23 nm in this system. Furthermore, strong capping layer thickness dependence is also observed. The strong PMA of 1.1 nm CoFeB only exists in a Mo cap layer thickness window of 1.2-2 nm. To maintain PMA, the metal layer could not be too thin or thick in these multilayers. The oxidation and diffusion of the metal capping layer should be respectively responsibility for the degradation of PMA in these thin or thick metal capping layer samples.

We have studied processes of interaction of pulsed laser radiation with resonant groups of plasmonic nanoparticles (resonant domains) in large colloidal nanoparticle aggregates having different interparticle gaps and particle size distributions. These processes are responsible for the origin of nonlinear optical effects and photochromic reactions in multiparticle aggregates. To describe photo-induced transformations in resonant domains and alterations in their absorption spectra remaining after the pulse action, we introduce the factor of spectral photomodification. Based on calculation of changes in thermodynamic, mechanical, and optical characteristics of the domains, the histograms of the spectrum photomodification factor have been obtained for various interparticle gaps, an average particle size, and the degree of polydispersity. Variations in spectra have been analyzed depending on the intensity of laser radiation and various combinations of size characteristics of domains. The obtained results can be used to predict manifestation of photochromic effects in composite materials containing different plasmonic nanoparticle aggregates in pulsed laser fields.

The discovery of the three-dimensional Dirac semimetals have expanded the family of topological materials, and attracted massive attentions in recent few years. In this short review, we briefly overview the quantum transport properties of a well-studied three-dimensional Dirac semimetal, Cd_{3}As_{2}. These unusual transport phenomena include the unexpected ultra-high charge mobility, large linear magnetoresistivity, remarkable Shubnikov-de Hass oscillations, and the evolution of the nontrivial Berry's phase. These quantum transport properties not only reflect the novel electronic structure of Dirac semimetals, but also give the possibilities for their future device applications.

We review the recent, mainly theoretical, progress in the study of topological nodal line semimetals in three dimensions. In these semimetals, the conduction and the valence bands cross each other along a one-dimensional curve in the three-dimensional Brillouin zone, and any perturbation that preserves a certain symmetry group (generated by either spatial symmetries or time-reversal symmetry) cannot remove this crossing line and open a full direct gap between the two bands. The nodal line(s) is hence topologically protected by the symmetry group, and can be associated with a topological invariant. In this review, (i) we enumerate the symmetry groups that may protect a topological nodal line; (ii) we write down the explicit form of the topological invariant for each of these symmetry groups in terms of the wave functions on the Fermi surface, establishing a topological classification; (iii) for certain classes, we review the proposals for the realization of these semimetals in real materials; (iv) we discuss different scenarios that when the protecting symmetry is broken, how a topological nodal line semimetal becomes Weyl semimetals, Dirac semimetals, and other topological phases; and (v) we discuss the possible physical effects accessible to experimental probes in these materials.

The recent discovery of three-dimensional (3D) topological insulators (TIs) has provided a fertile ground for obtaining further insights into electron localization in condensed matter systems. In the past few years, a tremendous amount of research effort has been devoted to investigate electron transport properties of 3D TIs and their low dimensional structures in a wide range of disorder strength, covering transport regimes from weak antilocalization to strong localization. The knowledge gained from these studies not only offers sensitive means to probe the surface states of 3D TIs but also forms a basis for exploring novel topological phases. In this article, we briefly review the main experimental progress in the study of the localization in 3D TIs, with a focus on the latest results on ultrathin TI films. Some new transport data will also be presented in order to complement those reported previously in the literature.

Weak localization and antilocalization are quantum transport phenomena that arise from the quantum interference in disordered metals. At low temperatures, they can give distinct temperature and magnetic field dependences in conductivity, allowing the symmetry of the system to be explored. In the past few years, they have also been observed in newly emergent topological materials, including topological insulators and topological semimetals. In contrast from the conventional electrons, in these new materials the quasiparticles are described as Dirac or Weyl fermions. In this article, we review our recent efforts on the theories of weak antilocalization and interaction-induced localization for Dirac and Weyl fermions in topological insulators and topological semimetals.

The discovery of Dirac semimetal and Weyl semimetal has motivated a growing passion for investigating the unique magneto-transport properties in the topological materials. A Weyl semimetal can host Weyl fermions as its low-energy quasi-particle excitations, and therefore perform exotic features analogous to those in high-energy physics, such as the violation of the chiral charge conservation known as the chiral anomaly. One of the electrical transport signatures of the chiral anomaly is the Adler-Bell-Jackiw (ABJ) anomaly which presents as a negative magnetoresistance when the magnetic field and the current are parallel. Very recently, numerous experiments reported negative longitudinal magnetoresistance (NLMR) in topological materials, but the details of the measurement results are various. Here the materials and the corresponding experiment results are briefly reviewed. Besides the plausible explanation of the ABJ anomaly, some other origins of the NLMR are also discussed.

Under a strong magnetic field, the quantum Hall (QH) effect can be observed in two-dimensional electronic gas systems. If the quantized Hall conductivity is acquired in a system without the need of an external magnetic field, then it will give rise to a new quantum state, the quantum anomalous Hall (QAH) state. The QAH state is a novel quantum state that is insulating in the bulk but exhibits unique conducting edge states topologically protected from backscattering and holds great potential for applications in low-power-consumption electronics. The realization of the QAH effect in real materials is of great significance. In this paper, we systematically review the theoretical proposals that have been brought forward to realize the QAH effect in various real material systems or structures, including magnetically doped topological insulators, graphene-based systems, silicene-based systems, two-dimensional organometallic frameworks, quantum wells, and functionalized Sb(111) monolayers, etc. Our paper can help our readers to quickly grasp the recent developments in this field.

The recent discovery of topological insulators (TIs) offers new opportunities for the development of thermoelectrics, because many TIs (like Bi_{2}Te_{3}) are excellent thermoelectric (TE) materials. In this review, we will first describe the general TE properties of TIs and show that the coexistence of the bulk and boundary states in TIs introduces unusual TE properties, including strong size effects and an anomalous Seebeck effect. Importantly, the TE figure of merit zT of TIs is no longer an intrinsic property, but depends strongly on the geometric size. The geometric parameters of two-dimensional TIs can be tuned to enhance zT to be significantly greater than 1. Then a few proof-of-principle experiments on three-dimensional TIs will be discussed, which observed unconventional TE phenomena that are closely related to the topological nature of the materials. However, current experiments indicate that the metallic surface states, if their advantage of high mobility is not fully utilized, would be detrimental to TE performance. Finally, we provide an outlook for future work on topological materials, which offers great possibilities to discover exotic TE effects and may lead to significant breakthroughs in improving zT.

Topological insulators/superconductors are new states of quantum matter with metallic edge/surface states. In this paper, we review the defects effect in these topological states and study new types of topological matters–topological hierarchy matters. We find that both topological defects (quantized vortices) and non topological defects (vacancies) can induce topological mid-gap states in the topological hierarchy matters after considering the superlattice of defects. These topological mid-gap states have nontrivial topological properties, including the nonzero Chern number and the gapless edge states. Effective tight-binding models are obtained to describe the topological mid-gap states in the topological hierarchy matters.

Disorder inevitably exists in realistic samples, manifesting itself in various exotic properties for the topological states. In this paper, we summarize and briefly review the work completed over the last few years, including our own, regarding recent developments in several topics about disorder effects in topological states. For weak disorder, the robustness of topological states is demonstrated, especially for both quantum spin Hall states with Z_{2}=1 and size induced nontrivial topological insulators with Z_{2}=0. For moderate disorder, by increasing the randomness of both the impurity distribution and the impurity induced potential, the topological insulator states can be created from normal metallic or insulating states. These phenomena and their mechanisms are summarized. For strong disorder, the disorder causes a metal-insulator transition. Due to their topological nature, the phase diagrams are much richer in topological state systems. Finally, the trends in these areas of disorder research are discussed.

Two-dimensional (2D) topological insulators (TIs, or quantum spin Hall insulators) are special insulators that possess bulk 2D electronic energy gap and time-reversal symmetry protected one-dimensional (1D) edge state. Carriers in the edge state have the property of spin-momentum locking, enabling dissipation-free conduction along the 1D edge. The existence of 2D TIs was confirmed by experiments in semiconductor quantum wells. However, the 2D bulk gaps in those quantum wells are extremely small, greatly limiting potential application in future electronics and spintronics. Despite this limitation, 2D TIs with a large bulk gap attracted plenty of interest. In this paper, recent progress in searching for TIs with a large bulk gap is reviewed briefly. We start by introducing some theoretical predictions of these new materials and then discuss some recent important achievements in crystal growth and characterization.

The rise of topological insulators in recent years has broken new ground both in the conceptual cognition of condensed matter physics and the promising revolution of the electronic devices. It also stimulates the explorations of more topological states of matter. Topological crystalline insulator is a new topological phase, which combines the electronic topology and crystal symmetry together. In this article, we review the recent progress in the studies of SnTe-class topological crystalline insulator materials. Starting from the topological identifications in the aspects of the bulk topology, surface states calculations, and experimental observations, we present the electronic properties of topological crystalline insulators under various perturbations, including native defect, chemical doping, strain, and thickness-dependent confinement effects, and then discuss their unique quantum transport properties, such as valley-selective filtering and helicity-resolved functionalities for Dirac fermions. The rich properties and high tunability make SnTe-class materials promising candidates for novel quantum devices.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Low metal-graphene contact resistance is important in making high-performance graphene devices. In this work, we demonstrate a lower specific contact resistivity of Au_{0.88} Ge_{0.12}/Ni/Au-graphene contact compared with Ti/Au and Ti/Pt/Au contacts. The rapid thermal annealing process was optimized to improve AuGe/Ni/Au contact resistance. Results reveal that both pre- and post-annealing processes are effective for reducing the contact resistance. The specific contact resistivity decreases from 2.5×10^{-4} to 7.8×10^{-5} Ω·cm^{2} by pre-annealing at 300℃ for one hour, and continues to decrease to 9.5×10^{-7} Ω·cm^{2} after post-annealing at 490℃ for 60 seconds. These approaches provide reliable means of lowering contact resistance.

Graphene oxide (GO) has a wide fluorescence bandwidth, which makes it a prospective candidate for numerous applications. For many of these applications, the fluorescence yield of GO should be further increased. The sp^{2}-hybridized carbons in GO confine the π-electrons. Radiative recombination of electron-hole pairs in such sp^{2} clusters is the source of fluorescence in this material. Palladium nanoparticles are good catalysts for sp^{2} bond formations. We report on the preparation of GO, palladium nanoparticles and their nanocomposites in two different solvents. It is shown that palladium nanoparticles can considerably enhance the intrinsic fluorescence of GO in the blue-green part of the visible light spectrum. Fluorescence enhancement has been attributed to the catalytic role of palladium nanoparticles in increasing the number of sp^{2} bonds of GO with the molecules of the surrounding media. It is shown that palladium nanoparticles could be the nanoparticle of choice for fluorescence enhancement of GO because of their catalytic role in sp^{2} bond formation.

Graphene is an alternative material for photodetectors owing to its unique properties. These include its uniform absorption of light from ultraviolet to infrared and its ultrahigh mobility for both electrons and holes. Unfortunately, due to the low absorption of light, the photoresponsivity of graphene-based photodetectors is usually low, only a few milliamps per watt. In this letter, we fabricate a waveguide-integrated graphene photodetector. A photoresponsivity exceeding 0.11 A·W^{-1} is obtained which enables most optoelectronic applications. The dominating mechanism of photoresponse is investigated and is attributed to the photo-induced bolometric effect. Theoretical calculation shows that the bolometric photoresponsivity is 4.6 A·W^{-1}. The absorption coefficient of the device is estimated to be 0.27 dB·μ^{-1}.

Large diamonds have successfully been synthesized from FeNiMnCo-S-C system at temperatures of 1255-1393 ° C and pressures of 5.3-5.5 GPa. Because of the presence of sulfur additive, the morphology and color of the large diamond crystals change obviously. The content and shape of inclusions change with increasing sulfur additive. It is found that the pressure and temperature conditions required for the synthesis decrease to some extent with the increase of S additive, which results in left down of the V-shape region. The Raman spectra show that the introduction of additive sulfur reduces the quality of the large diamond crystals. The x-ray photoelectron spectroscopy (XPS) spectra show the presence of S in the diamonds. Furthermore, the electrical properties of the large diamond crystals are tested by a four-point probe and the Hall effect method. When sulfur in the cell of diamond is up to 4.0 wt.%, the resistance of the diamond is 9.628×10^{5} Ω·cm. It is shown that the large single crystal samples are n type semiconductors. This work is helpful for the further research and application of sulfur-doped semiconductor large diamond.

Color centers in diamond are prominent candidates for generating and manipulating quantum states of light, even at room temperature. However, the photon collection efficiency of bulk diamond is greatly reduced by refraction at the diamond/air interface. To address this issue, we fabricated arrays of diamond nanostructures, differing in both diameter and top end shape, with HSQ, PMMA, and Cr as the etching mask materials, aiming toward large scale fabrication of single-photon sources with enhanced collection efficiency made of nitrogen vacancy (NV) embedded diamond. With a mixture of O_{2} and CHF_{3} gas plasma, diamond pillars with diameters down to 45 nm were obtained. The top end shape evolution has been represented with a simple model. The tests of size dependent single-photon properties confirmed an improved single-photon collection efficiency enhancement, larger than tenfold, and a mild decrease of decoherence time with decreasing pillar diameter was observed as expected. These results provide useful information for future applications of nanostructured diamond as a single-photon source.

In this paper, small diameter InP nanowires with high crystal quality were synthesized through a chemical vapor deposition method. Benefitting from the high crystallinity and large specific surface area of InP nanowires, the simply constructed photodetector demonstrates a high responsivity of up to 1170 A·W^{-1} and an external quantum efficiency of 2.8×10^{5}% with a fast rise time of 110 ms and a fall time of 130 ms, even at low bias of 0.1 V. The effect of back-gate voltage on photoresponse of the device was systematically investigated, confirming that the photocurrent dominates over thermionic and tunneling currents in the whole operation. A mechanism based on energy band theory at the junction between metal and semiconductor was proposed to explain the back-gate voltage dependent performance of the photodetectors. These convincing results indicate that fine InP nanowires will have a brilliant future in smart optoelectronics.

The self-assembly of diblock copolymers confined around one square-shaped particle is studied systematically within two-dimensional self-consistent field theory (SCFT). In this model, we assume that the thin block copolymer film is confined in the vicinity of a square-shaped particle by a homopolymer melt, which is equivalent to the poor solvents. Multiple sequences of square-shaped particle-induced copolymer aggregates with different shapes and self-assembled internal morphologies are predicted as functions of the particle size, the structural portion of the copolymer, and the volume fraction of the copolymer. A rich variety of aggregates are found with complex internal self-assembled morphologies including complex structures of the vesicle, with one or several inverted micelle surrounded by the outer monolayer with the particle confined in the core. These results demonstrate that the assemblies of diblock copolymers formed around the square-shaped particle in poor solvents are of immediate interest to the assembly of copolymer and the morphology of biomembrane in the confined environment, as well as to the transitions of vesicles to micelles.

A new industrial method has been developed to produce polydisperse spherical colloidal silica particles with a very broad particle size, ranging from 20-95 nm. The process uses a reactor in which the original seed solution is heated to 100 ° C, and then active silicic acid and the seed solution are titrated to the reactor continuously with a constant rate. The original seeds and the titrated seeds in the reactor will go through different particle growth cycles to form different particle sizes. Both the particles' size distribution and morphology have been characterized by dynamic light scattering (DLS) and the focus ion beam (FIB) system. In addition, the as-prepared polydisperse colloidal silica particle in the application of sapphire wafer's chemical mechanical polishing (CMP) process has been tested. The material removal rate (MRR) of this kind of abrasive has been tested and verified to be much faster than traditional monodisperse silica particles. Finally, the mechanism of sapphire CMP process by this kind of polydisperse silica particles has been investigated to explore the reasons for the high polishing rate.

In this paper, ground-signal-ground type through-silicon vias (TSVs) exploiting air gaps as insulation layers are designed, analyzed and simulated for applications in millimeter wave. The compact wideband equivalent-circuit model and passive elements (RLGC) parameters based on the physical parameters are presented with the frequency up to 100 GHz. The parasitic capacitance of TSVs can be approximated as the dielectric capacitance of air gaps when the thickness of air gaps is greater than 0.75 μm. Therefore, the applied voltage of TSVs only needs to achieve the flatband voltage, and there is no need to indicate the threshold voltage. This is due to the small permittivity of air gaps. The proposed model shows good agreement with the simulation results of ADS and Ansoft's HFSS over a wide frequency range.

An ultra-wideband pattern reconfigurable antenna is proposed. The antenna is a dielectric coaxial hollow monopole with a cylindrical graphene-based impedance surface coating. It consists of a graphene sheet coated onto the inner surface of a cylindrical substrate and a set of independent polysilicon DC gating pads mounted on the outside of the cylindrical substrate. By changing the DC bias voltages to the different gating pads, the surface impedance of the graphene coating can be freely controlled. Due to the tunability of graphene's surface impedance, the radiation pattern of the proposed antenna can be reconfigured. A transmission line method is used to illustrate the physical mechanism of the proposed antenna. The results show that the proposed antenna can reconfigure its radiation pattern in the omnidirectional mode with the relative bandwidth of 58.5% and the directional mode over the entire azimuth plane with the relative bandwidth of 67%.

The frequency characteristics of free oscillation magnetron (FOM) and injection-locked magnetron (ILM) are theoretically investigated. By using the equal power voltage obtained from the experiment data, expressions of the frequency and radio frequency (RF) voltage of FOM and ILM, as well as the locking bandwidth, on the anode voltage and magnetic field are derived. With the increase of the anode voltage and the decrease of the magnetic field, the power and its growth rate increase, while the frequency increases and its growth rate decreases. The theoretical frequency and power of FOM agree with the particle-in-cell (PIC) simulation results. Besides, the theoretical trends of the power and frequency with the anode voltage and magnetic field are consistent with the experimental results, which verifies the accuracy of the theory. The theory provides a novel calculation method of frequency characteristics. It can approximately analyze the power and frequency of both FOM and ILM, which promotes the industrial applications of magnetron and microwave energy.

Tunnel field effect transistors (TFETs) are promising devices for low power applications. An analytical threshold voltage model, based on the channel surface potential and electric field obtained by solving the 2D Poisson's equation, for strained silicon gate all around TFETs is proposed. The variation of the threshold voltage with device parameters, such as the strain (Ge mole fraction x), gate oxide thickness, gate oxide permittivity, and channel length has also been investigated. The threshold voltage model is extracted using the peak transconductance method and is verified by good agreement with the results obtained from the TCAD simulation.

An equivalent distributed capacitance model is established by considering only the gate oxide-trap capacitance to explain the frequency dispersion in the C-V curve of MOS capacitors measured for a frequency range from 1 kHz to 1 MHz. The proposed model is based on the Fermi-Dirac statistics and the charging/discharging effects of the oxide traps induced by a small ac signal. The validity of the proposed model is confirmed by the good agreement between the simulated results and experimental data. Simulations indicate that the capacitance dispersion of an MOS capacitor under accumulation and near flatband is mainly caused by traps adjacent to the oxide/semiconductor interface, with negligible effects from the traps far from the interface, and the relevant distance from the interface at which the traps can still contribute to the gate capacitance is also discussed. In addition, by excluding the negligible effect of oxide-trap conductance, the model avoids the use of imaginary numbers and complex calculations, and thus is simple and intuitive.

Radio-frequency (RF) characteristics under ultra-low temperature of multi-finger partially depleted silicon-on-insulator (PD SOI) n-type metal-oxide-semiconductor field-effect transistors (nMOSFETs) with tunnel diode body-contact (TDBC) structure and T-gate body-contact (TB) structure are investigated in this paper. When operating at 77 K, TDBC device suppresses floating-body effect (FBE) as well as the TB device. For TB device and TDBC device, cut-off frequency (f_{T}) improves as the temperature decreases to liquid-helium temperature (77 K) while that of the maximum oscillation frequency (f_{MAX}) is opposite due to the decrease of the unilateral power gain. While operating under 77 K, f_{T} and f_{MAX} of TDBC device reach to 125 GHz and 77 GHz, representing 8% and 15% improvements compared with those of TB device, respectively, which is mainly due to the lower parasitic resistances and capacitances. The results indicate that TDBC SOI MOSFETs could be considered as promising candidates for analog and RF applications over a wide range of temperatures and there is immense potential for the development of RF CMOS integrated circuits for cryogenic applications.

A simple process flow method for the fabrication of poly-Si nanowire thin film transistors (NW-TFTs) without advanced lithographic tools is introduced in this paper. The cross section of the nanowire channel was manipulated to have a parallelogram shape by combining a two-step etching process and a spacer formation technique. The electrical and temperature characteristics of the developed NW-TFTs are measured in detail and compared with those of conventional planar TFTs (used as a control). The as-demonstrated NW-TFT exhibits a small subthreshold swing (191 mV/dec), a high ON/OFF ratio (8.5×10^{7}), a low threshold voltage (1.12 V), a decreased OFF-state current, and a low drain-induced-barrier lowering value (70.11 mV/V). The effective trap densities both at the interface and grain boundaries are also significantly reduced in the NW-TFT. The results show that all improvements of the NW-TFT originate from the enhanced gate controllability of the multi-gate over the channel.

We characterized the dependence of the timing jitter of an InGaAs/InP single-photon avalanche diode on the excess bias voltage (V_{ex}) when operated in 1-GHz sinusoidally gated mode. The single-photon avalanche diode was cooled to -30 degrees Celsius. When the V_{ex} is too low (0.2 V-0.8 V) or too high (3 V-4.2 V), the timing jitter is increased with the V_{ex}, particularly at high V_{ex}. While at middle V_{ex} (1 V-2.8 V), the timing jitter is reduced. Measurements of the timing jitter of the same avalanche diode with pulsed gating show that this effect is likely related to the increase of both the amplitude of the V_{ex} and the width of the gate-on time. For the 1-GHz sinusoidally gated detector, the best jitter of 93 ps is achieved with a photon detection efficiency of 21.4% and a dark count rate of ~2.08×10^{-5} per gate at the V_{ex} of 2.8 V. To evaluate the whole performance of the detector, we calculated the noise equivalent power (NEP) and the afterpulse probability (P_{ap}). It is found that both NEP and P_{ap} increase quickly when the V_{ex} is above 2.8 V. At 2.8-V V_{ex}, the NEP and P_{ap} are ~2.06×10^{-16} W/Hz^{1/2} and 7.11%, respectively. Therefore, the detector should be operated with V_{ex} of 2.8 V to exploit the fast time response, low NEP and low P_{ap}.

In this study, the high performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs) with Al-doped ZnO (AZO) transparent conductive layers (TCLs) has been demonstrated. The AZO-TCLs were fabricated on the n^{+}-InGaN contact layer by metal organic chemical vapor deposition (MOCVD) using H_{2}O as an oxidizer at temperatures as low as 400℃ without any post-deposition annealing. It shows a high transparency (98%), low resistivity (510^{-4} Ω·cm), and an epitaxial-like excellent interface on p-GaN with an n^{+}-InGaN contact layer. A forward voltage of 2.82 V@20 mA was obtained. Most importantly, the power efficiencies can be markedly improved by 53.8%@20 mA current injection and 39.6%@350 mA current injection compared with conventional LEDs with indium tin oxide TCL (LED-Ⅲ), and by 28.8%@20 mA current injection and 4.92%@350 mA current injection compared with LEDs with AZO-TCL prepared by MOCVD using O_{2} as an oxidizer (LED-Ⅱ), respectively. The results indicate that the AZO-TCL grown by MOCVD using H_{2}O as an oxidizer is a promising TCL for a low-cost and high-efficiency GaN-based LED application.

Some kinds of muscles can oscillate spontaneously, which is related to the dynamic instability of the collective motors. Based on the two-state ratchet model and with consideration of the motor stiffness, the dynamics of collective myosin Ⅱ motors are studied. It is shown that when the motor stiffness is small, the velocity of the collective motors decreases monotonically with load increasing. When the motor stiffness becomes large, dynamic instability appears in the force-velocity relationship of the collective-motor transport. For a large enough motor stiffness, the zero-velocity point lies in the unstable range of the force-velocity curve, and the motor system becomes unstable before the motion is stopped, so spontaneous oscillations can be generated if the system is elastically coupled to its environment via a spring. The oscillation frequency is related to the motor stiffness, motor binding rate, spring stiffness, and the width of the ATP excitation interval. For a medium motor stiffness, the zero-velocity point lies outside the unstable range of the force-velocity curve, and the motion will be stopped before the instability occurs.

The epitaxial-Si (epi-Si) growth on the crystalline Si (c-Si) wafer could be tailored by the working pressure in plasma-enhanced chemical vapor deposition (PECVD). It has been systematically confirmed that the epitaxial growth at the hydrogenated amorphous silicon (a-Si:H)/c-Si interface is suppressed at high pressure (hp) and occurs at low pressure (lp). The hp a-Si:H, as a purely amorphous layer, is incorporated in the lp-epi-Si/c-Si interface. We find that:(i) the epitaxial growth can also occur at a-Si:H coated c-Si wafer as long as this amorphous layer is thin enough; (ii) with the increase of the inserted hp layer thickness, lp epi-Si at the interface is suppressed, and the fraction of a-Si:H in the thin films increases and that of c-Si decreases, corresponding to the increasing minority carrier lifetime of the sample. Not only the epitaxial results, but also the quality of the thin films at hp also surpasses that at lp, leading to the longer minority carrier lifetime of the hp sample than the lp one although they have the same amorphous phase.

The social force model has been widely used to simulate pedestrian evacuation by analyzing attractive, repulsive, driving, and fluctuating forces among pedestrians. Many researchers have improved its limitations in simulating behaviors of large-scale population. This study modifies the well-accepted social force model by considering the impacts of interaction among companions and further develops a comprehensive model by combining that with a multi-exit utility function. Then numerical simulations of evacuations based on the comprehensive model are implemented in the waiting hall of the Wulin Square Subway Station in Hangzhou, China. The results provide safety thresholds of pedestrian density and panic levels in different operation situations. In spite of the operation situation and the panic level, a larger friend-group size results in lower evacuation efficiency. Our study makes important contributions to building a comprehensive multi-exit social force model and to applying it to actual scenarios, which produces data to facilitate decision making in contingency plans and emergency treatment.

Enhancement of the electron fluxes in the inner radiation belt, which is induced by the powerful North West Cape (NWC) very-low-frequency (VLF) transmitter, have been observed and analyzed by several research groups. However, all of the previous publications have focused on NWC-induced >100-keV electrons only, based on observations from the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and the Geostationary Operational Environmental Satellite (GOES) satellites. Here, we present flux enhancements with 30-100-keV electrons related to NWC transmitter for the first time, which were observed by the GOES satellite at night. Similar to the 100-300-keV precipitated-electron behavior, the low energy 30-100-keV electron precipitation is primarily located east of the transmitter. However, the latter does not drift eastward to the same extent as the former, possibly because of the lower electron velocity. The 30-100-keV electrons are distributed in the L=1.8-2.1 L-shell range, in contrast to the 100-300-keV electrons which are at L=1.67-1.9. This is consistent with the perspective that the energy of the VLF-wave-induced electron flux enhancement decreases with higher L-shell values. We expand upon the rationality of the simultaneous enhancement of the 30-100- and 100-300-keV electron fluxes through comparison with the cyclotron resonance theory for the quasi-linear wave-particle interaction. In addition, we interpret the asymmetry characteristics of NWC electric power distribution in north and south hemisphere by ray tracing model. Finally, we present considerable discussion and show that good agreement exists between the observation of satellites and theory.

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