中国物理B

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An application of a combined gradient system to stabilize a mechanical system

陈向炜, 张晔, 梅凤翔

2016 (10): 100201-100201. doi: 10.1088/1674-1056/25/10/100201

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A gradient system and a skew-gradient system can be merged into a combined gradient system. The differential equations of the combined gradient system are established and its property is studied. If a mechanical system can be represented as a combined gradient system, the stability of the mechanical system can be studied by using the property of the combined gradient system. Some examples are given to illustrate the applications of the results.

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Consensus for second-order multi-agent systems with position sampled data

王如生, 高利新, 陈文海, 戴大蒙

2016 (10): 100202-100202. doi: 10.1088/1674-1056/25/10/100202

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In this paper, the consensus problem with position sampled data for second-order multi-agent systems is investigated. The interaction topology among the agents is depicted by a directed graph. The full-order and reduced-order observers with position sampled data are proposed, by which two kinds of sampled data-based consensus protocols are constructed. With the provided sampled protocols, the consensus convergence analysis of a continuous-time multi-agent system is equivalently transformed into that of a discrete-time system. Then, by using matrix theory and a sampled control analysis method, some sufficient and necessary consensus conditions based on the coupling parameters, spectrum of the Laplacian matrix and sampling period are obtained. While the sampling period tends to zero, our established necessary and sufficient conditions are degenerated to the continuous-time protocol case, which are consistent with the existing result for the continuous-time case. Finally, the effectiveness of our established results is illustrated by a simple simulation example.

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Nonlinear radiation response of n-doped indium antimonide and indium arsenide in intense terahertz field

龚姣丽, 刘劲松, 褚政, 杨振刚, 王可嘉, 姚建铨

2016 (10): 100203-100203. doi: 10.1088/1674-1056/25/10/100203

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The nonlinear radiation responses of two different n-doped bulk semiconductors: indium antimonide (InSb) and indium arsenide (InAs) in an intense terahertz (THz) field are studied by using the method of ensemble Monte Carlo (EMC) at room temperature. The results show that the radiations of two materials generate about 2-THz periodic regular spectrum distributions under a high field of 100 kV/cm at 1-THz center frequency. The center frequencies are enhanced to about 7 THz in InSb, and only 5 THz in InAs, respectively. The electron valley occupancy and the percentage of new electrons excited by impact ionization are also calculated. We find that the band nonparabolicity and impact ionization promote the generation of nonlinear high frequency radiation, while intervalley scattering has the opposite effect. Moreover, the impact ionization dominates in InSb, while impact ionization and intervalley scattering work together in InAs. These characteristics have potential applications in up-convension of THz wave and THz nonlinear frequency multiplication field.

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Terahertz-dependent identification of simulated hole shapes in oil—gas reservoirs

宝日玛, 詹洪磊, 苗昕扬, 赵昆, 冯程静, 董晨, 李羿璋, 肖立志

2016 (10): 100204-100204. doi: 10.1088/1674-1056/25/10/100204

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Detecting holes in oil-gas reservoirs is vital to the evaluation of reservoir potential. The main objective of this study is to demonstrate the feasibility of identifying general micro-hole shapes, including triangular, circular, and square shapes, in oil-gas reservoirs by adopting terahertz time-domain spectroscopy (THz-TDS). We evaluate the THz absorption responses of punched silicon (Si) wafers having micro-holes with sizes of 20 μm-500 μm. Principal component analysis (PCA) is used to establish a model between THz absorbance and hole shapes. The positions of samples in three-dimensional spaces for three principal components are used to determine the differences among diverse hole shapes and the homogeneity of similar shapes. In addition, a new Si wafer with the unknown hole shapes, including triangular, circular, and square, can be qualitatively identified by combining THz-TDS and PCA. Therefore, the combination of THz-TDS with mathematical statistical methods can serve as an effective approach to the rapid identification of micro-hole shapes in oil-gas reservoirs.

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The bound state solution for the Morse potential with a localized mass profile

S Miraboutalebi

2016 (10): 100301-100301. doi: 10.1088/1674-1056/25/10/100301

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We investigate an analytical solution for the Schrödinger equation with a position-dependent mass distribution, with the Morse potential via Laplace transformations. We considered a mass function localized around the equilibrium position. The mass distribution depends on the energy spectrum of the state and the intrinsic parameters of the Morse potential. An exact bound state solution is obtained in the presence of this mass distribution.

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Binding energy of the donor impurities in GaAs-Ga_1-xAl_xAs quantum well wires with Morse potential in the presence of electric and magnetic fields

Esra Aciksoz, Orhan Bayrak, Asim Soylu

2016 (10): 100302-100302. doi: 10.1088/1674-1056/25/10/100302

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The behavior of a donor in the GaAs-Ga_1-xAl_xAs quantum well wire represented by the Morse potential is examined within the framework of the effective-mass approximation. The donor binding energies are numerically calculated for with and without the electric and magnetic fields in order to show their influence on the binding energies. Moreover, how the donor binding energies change for the constant potential parameters (D_e, r_e, and a) as well as with the different values of the electric and magnetic field strengths is determined. It is found that the donor binding energy is highly dependent on the external electric and magnetic fields as well as parameters of the Morse potential.

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A novel scheme of hybrid entanglement swapping and teleportation using cavity QED in the small and large detuning regimes and quasi-Bell state measurement method

R Pakniat, M K Tavassoly, M H Zandi

2016 (10): 100303-100303. doi: 10.1088/1674-1056/25/10/100303

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We outline a scheme for entanglement swapping based on cavity QED as well as quasi-Bell state measurement (quasi-BSM) methods. The atom-field interaction in the cavity QED method is performed in small and large detuning regimes. We assume two atoms are initially entangled together and, distinctly two cavities are prepared in an entangled coherent-coherent state. In this scheme, we want to transform entanglement to the atom-field system. It is observed that, the fidelities of the swapped entangled state in the quasi-BSM method can be compatible with those obtained in the small and large detuning regimes in the cavity QED method (the condition of this compatibility will be discussed). In addition, in the large detuning regime, the swapped entangled state is obtained by detecting and quasi-BSM approaches. In the continuation, by making use of the atom-field entangled state obtained in both approaches in a large detuning regime, we show that the atomic as well as field states teleportation with complete fidelity can be achieved.

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Controlled remote preparation of an arbitrary four-qubit cluster-type state

陈维林, 马松雅, 瞿治国

2016 (10): 100304-100304. doi: 10.1088/1674-1056/25/10/100304

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Two schemes are proposed to realize the controlled remote preparation of an arbitrary four-qubit cluster-type state via a partially entangled channel. We construct ingenious measurement bases at the sender's and the controller's locations, which play a decisive role in the proposed schemes. The success probabilities can reach 50% and 100%, respectively. Compared with the previous proposals, the success probabilities are independent of the coefficients of the entangled channel.

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Parameter allocation of parallel array bistable stochastic resonance and its application in communication systems

刘健, 王友国, 翟其清, 刘进

2016 (10): 100501-100501. doi: 10.1088/1674-1056/25/10/100501

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In this paper, we propose a parameter allocation scheme in a parallel array bistable stochastic resonance-based communication system (P-BSR-CS) to improve the performance of weak binary pulse amplitude modulated (BPAM) signal transmissions. The optimal parameter allocation policy of the P-BSR-CS is provided to minimize the bit error rate (BER) and maximize the channel capacity (CC) under the adiabatic approximation condition. On this basis, we further derive the best parameter selection theorem in realistic communication scenarios via variable transformation. Specifically, the P-BSR structure design not only brings the robustness of parameter selection optimization, where the optimal parameter pair is not fixed but variable in quite a wide range, but also produces outstanding system performance. Theoretical analysis and simulation results indicate that in the P-BSR-CS the proposed parameter allocation scheme yields considerable performance improvement, particularly in very low signal-to-noise ratio (SNR) environments.

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Demodulation of acoustic telemetry binary phase shift keying signal based on high-order Duffing system

燕并男, 刘崇新, 倪骏康, 赵亮

2016 (10): 100502-100502. doi: 10.1088/1674-1056/25/10/100502

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In order to grasp the downhole situation immediately, logging while drilling (LWD) technology is adopted. One of the LWD technologies, called acoustic telemetry, can be successfully applied to modern drilling. It is critical for acoustic telemetry technology that the signal is successfully transmitted to the ground. In this paper, binary phase shift keying (BPSK) is used to modulate carrier waves for the transmission and a new BPSK demodulation scheme based on Duffing chaos is investigated. Firstly, a high-order system is given in order to enhance the signal detection capability and it is realized through building a virtual circuit using an electronic workbench (EWB). Secondly, a new BPSK demodulation scheme is proposed based on the intermittent chaos phenomena of the new Duffing system. Finally, a system variable crossing zero-point equidistance method is proposed to obtain the phase difference between the system and the BPSK signal. Then it is determined that the digital signal transmitted from the bottom of the well is ‘0’ or ‘1’. The simulation results show that the demodulation method is feasible.

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A novel color image encryption algorithm based on genetic recombination and the four-dimensional memristive hyperchaotic system

柴秀丽, 甘志华, 路杨, 张苗辉, 陈怡然

2016 (10): 100503-100503. doi: 10.1088/1674-1056/25/10/100503

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Recently, many image encryption algorithms based on chaos have been proposed. Most of the previous algorithms encrypt components R, G, and B of color images independently and neglect the high correlation between them. In the paper, a novel color image encryption algorithm is introduced. The 24 bit planes of components R, G, and B of the color plain image are obtained and recombined into 4 compound bit planes, and this can make the three components affect each other. A four-dimensional (4D) memristive hyperchaotic system generates the pseudorandom key streams and its initial values come from the SHA 256 hash value of the color plain image. The compound bit planes and key streams are confused according to the principles of genetic recombination, then confusion and diffusion as a union are applied to the bit planes, and the color cipher image is obtained. Experimental results and security analyses demonstrate that the proposed algorithm is secure and effective so that it may be adopted for secure communication.

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Quantitative measurement of hydroxyl radical (OH) concentration in premixed flat flame by combining laser-induced fluorescence and direct absorption spectroscopy

陈爽, 苏铁, 李中山, 白菡尘, 闫博, 杨富荣

2016 (10): 100701-100701. doi: 10.1088/1674-1056/25/10/100701

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An accurate and reasonable technique combining direct absorption spectroscopy and laser-induced fluorescence (LIF) methods is developed to quantitatively measure the concentrations of hydroxyl in CH₄/air flat laminar flame. In our approach, particular attention is paid to the linear laser-induced fluorescence and absorption processes, and experimental details as well. Through measuring the temperature, LIF signal distribution and integrated absorption, spatially absolute OH concentrations profiles are successfully resolved. These experimental results are then compared with the numerical simulation. It is proved that the good quality of the results implies that this method is suitable for calibrating the OH-PLIF measurement in a practical combustor.

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Calculations of the dynamic dipole polarizabilities for the Li⁺ ion

张永慧, 唐丽艳, 张现周, 史庭云

2016 (10): 103101-103101. doi: 10.1088/1674-1056/25/10/103101

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The B-spline configuration-interaction method is applied into the investigations of dynamic dipole polarizabilities for the four lowest triplet states (²3S, ³3S, ²3P, and ³3P) of the Li⁺ ion. The accurate energies for the triplet states of n³S, n³P, and n³D, the dipole oscillator strengths for ²3S(³3S)→n³P, ²3P(³3P)→n³S, and ²3P(³3P)→n³D transitions, with the main quantum number n up to 10 are tabulated for references. The dynamic dipole polarizabilities for the four triplet states under a wide range of photon energy are also listed, which provide input data for analyzing the Stark shift of Li⁺ ion. Furthermore, the tune-out wavelengths in the range from 100 nm to 1.2 μm for the four triplet states, and the magic wavelengths in the range from 100 nm to 600 nm for the ²3S→³3S, ²3S→²3P, and ²3S→³3P transitions are determined accurately for the experimental design of the Li⁺ ion.

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An ab initio investigation of vibrational, thermodynamic, and optical properties of Sc₂AlC MAX compound

M A Ali, M T Nasir, M R Khatun, A K M A Islam, S H Naqib

2016 (10): 103102-103102. doi: 10.1088/1674-1056/25/10/103102

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The structural vibrational, thermodynamical, and optical properties of potentially technologically important, weakly coupled MAX compound, Sc₂AlC are calculated using density functional theory (DFT). The structural properties of Sc₂AlC are compared with the results reported earlier. The vibrational, thermodynamical, and optical properties are theoretically estimated for the first time. The phonon dispersion curve is calculated and the dynamical stability of this compound is investigated. The optical and acoustic modes are observed clearly. We calculate the Helmholtz free energy (F), internal energy (E), entropy (S), and specific heat capacity (C_v) from the phonon density of states. Various optical parameters are also calculated. The reflectance spectrum shows that this compound has the potential to be used as an efficient solar reflector.

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Low-lying electronic states of CuN calculated by MRCI method

张树东, 刘超

2016 (10): 103103-103103. doi: 10.1088/1674-1056/25/10/103103

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The high accuracy ab initio calculation method of multi-reference configuration interaction (MRCI) is used to compute the low-lying eight electronic states of CuN. The potential energy curves (PECs) of the X³Σ^-, 1³Π, 2³Σ^-, 1³Δ, 1¹Δ, 1¹Σ^-, 1¹Π, and ⁵Σ^- in a range of R=0.1 nm-0.5 nm are obtained and they are goodly asymptotes to the Cu(²S_g )+N(⁴S_u) and Cu(²S_g)+N(²D_u) dissociation limits. All the possible vibrational levels, rotational constants, and spectral constants for the six bound states of X³Σ^-, 1³Π, 2³Σ^-, 1¹Δ, 1¹Σ^-, and 1¹Π are obtained by solving the radial Schrödinger equation of nuclear motion with Le Roy provided Level8.0 program. Also the transition dipole moments from the ground state X³Σ^- to the excited states 1³Π and 2³Σ^- are calculated and the result indicates that the 2³Σ^--X³Σ ^- transition has much higher transition dipole moment than the 1³Π-X³Σ^- transition even though the 1³Π state is much lower in energy than the 2³Σ^- state.

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Effect of chloride introduction on the optical properties in Eu³⁺-doped fluorozirconate glasses

金含, 莫兆军, 张晓松, 苑琳琳, 晏明, 李岚

2016 (10): 103201-103201. doi: 10.1088/1674-1056/25/10/103201

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Fluorozirconate glass containing Eu³⁺ ions and chloride ions are prepared by a meltquenching method. The luminescence behavior of Eu³⁺ affected by Cl ions is investigated. With increasing Cl ion concentration, the luminous intensity of Eu³⁺ is significantly enhanced and the quantum efficiency of fluorozirconate glass is improved. Meanwhile, the intensity parameter Ω₂ increases according to the Judd-Ofelt calculation, which indicates the decrease of local symmetry. The average lifetime of Eu³⁺ increases by introducing the Cl ions. Moreover, we find two kinds of sites for Eu³⁺ ions in a glass network by analyzing the fluorescence decay. The distribution of Eu³⁺ ions changes with increasing Cl ion concentration. In addition, the excessive Cl ions lead to the separation of the glass phase and the formation of the crystal phase, thus reducing the transmittance dramatically.

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Analysis of the blackbody-radiation shift in an ytterbium optical lattice clock

徐艺琳, 徐信业

2016 (10): 103202-103202. doi: 10.1088/1674-1056/25/10/103202

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We accurately evaluate the blackbody-radiation shift in a ¹⁷¹Yb optical lattice clock by utilizing temperature measurement and numerical simulation. In this work. three main radiation sources are considered for the blackbody-radiation shift, including the heated atomic oven, the warm vacuum chamber, and the room-temperature vacuum windows. The temperatures on the outer surface of the vacuum chamber are measured during the clock operation period by utilizing seven calibrated temperature sensors. Then we infer the temperature distribution inside the vacuum chamber by numerical simulation according to the measured temperatures. Furthermore, we simulate the temperature variation around the cold atoms while the environmental temperature is fluctuating. Finally, we obtain that the total blackbody-radiation shift is -1.289(7) Hz with an uncertainty of 1.25×10^-17 for our ¹⁷¹Yb optical lattice clock. The presented method is quite suitable for accurately evaluating the blackbody-radiation shift of the optical lattice clock in the case of lacking the sensors inside the vacuum chamber.

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Absorption of laser radiation in ultracold plasma

N Y Shaparev

2016 (10): 103203-103203. doi: 10.1088/1674-1056/25/10/103203

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In this paper, we analyze the spectral behavior (optical thickness, shape and linewidth) of laser radiation absorption under the correlation heating of ions in an ultracold plasma. The Voigt formula is used to find the absorption coefficient. The spectral line width is shown to grow with time while the optical thickness reduces. Our modeling results are in good agreement with the experimental findings reported in the literature.

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Ultra-thin two-dimensional transmissive anisotropic metasurfaces for polarization filter and beam steering application

郭文龙, 王光明, 李海鹏, 张昆, 蔡通

2016 (10): 104101-104101. doi: 10.1088/1674-1056/25/10/104101

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We propose an anisotropic planar transmitting metasurface, which has the ability to manipulate orthogonally-polarized electromagnetic waves in the reflection and refraction modes respectively. The metasurface is composed of four layered rectangular patches spaced by three layered dielectric isolators each with a thickness of 0.15λ₀ at 15 GHz. By tailoring the sizes of the patches, the metasurface functions as a band-stop filter for the y-polarzied wave and a band-pass filter for the x-polarized wave operating from 14 GHz to 16 GHz. Moreover the phases of the transmitting x-polarized wave can be modulated at about 15 GHz, which contributes to beam steering according to the general refraction law. Experimental results are in good accordance with the simulated ones, in which the reflection efficiency is almost 100% while the transmission efficiency of the x-polarized wave reaches 80% at 15 GHz. Besides, the transmitted x-polarized wave is effectively manipulated from 14 GHz to 16 GHz.

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Two-dimensional atom localization induced by a squeezed vacuum

王飞, 徐俊

2016 (10): 104201-104201. doi: 10.1088/1674-1056/25/10/104201

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A scheme of two-dimensional (2D) atom localization induced by a squeezed vacuum is proposed, in which the three-level V-type atoms interact with two classical standing-wave fields. It is found that when the environment is changed from an ordinary vacuum to a squeezed vacuum, the 2D atom localization is realized by detecting the position-dependent resonance fluorescence spectrum. For comparison, we demonstrate that the atom localization originating from the quantum interference effect is distinct from that induced by a squeezed vacuum. Furthermore, the combined effects of the squeezed vacuum and quantum interference are also discussed under appropriate conditions. The internal physical mechanism is analyzed in terms of dressed-state representation.

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Photon bunching and anti-bunching with two dipole-coupled atoms in an optical cavity

郑雅梅, 胡长生, 杨贞标, 吴怀志

2016 (10): 104202-104202. doi: 10.1088/1674-1056/25/10/104202

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We investigate the effect of the dipole-dipole interaction (DDI) on the photon statistics with two atoms trapped in an optical cavity driven by a laser field and subjected to cooperative emission. By means of the quantum trajectory analysis and the second-order correlation functions, we show that the photon statistics of the cavity transmission can be flexibly modulated by the DDI while the incoming coherent laser selectively excites the atom-cavity system's nonlinear Jaynes-Cummings ladder of excited states. Finally, we find that the effect of the cooperatively atomic emission can also be revealed by the numerical simulations and can be explained with a simplified picture. The DDI induced nonlinearity gives rise to highly nonclassical photon emission from the cavity that is significant for quantum information processing and quantum communication.

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Quantum metrology with two-mode squeezed thermal state: Parity detection and phase sensitivity

李恒梅, 徐学翔, 袁洪春, 王震

2016 (10): 104203-104203. doi: 10.1088/1674-1056/25/10/104203

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Based on the Wigner-function method, we investigate the parity detection and phase sensitivity in a Mach-Zehnder interferometer (MZI) with two-mode squeezed thermal state (TMSTS). Using the classical transformation relation of the MZI, we derive the input-output Wigner functions and then obtain the explicit expressions of parity and phase sensitivity. The results from the numerical calculation show that supersensitivity can be reached only if the input TMSTS have a large number photons.

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Spontaneous emission from a microwave-driven four-level atom in an anisotropic photonic crystal

姜丽, 万仁刚, 姚治海

2016 (10): 104204-104204. doi: 10.1088/1674-1056/25/10/104204

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The spontaneous emission from a microwave-driven four-level atom embedded in an anisotropic photonic crystal is studied. Due to the modified density of state (DOS) in the anisotropic photonic band gap (PBG) and the coherent control induced by the coupling fields, spontaneous emission can be significantly enhanced when the position of the spontaneous emission peak gets close to the band gap edge. As a result of the closed-loop interaction between the fields and the atom, the spontaneous emission depends on the dynamically induced Autler-Townes splitting and its position relative to the PBG. Interesting phenomena, such as spectral-line suppression, enhancement and narrowing, and fluorescence quenching, appear in the spontaneous emission spectra, which are modulated by amplitudes and phases of the coherently driven fields and the effect of PBG. This theoretical study can provide us with more efficient methods to manipulate the atomic spontaneous emission.

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Effects of annealing time on the structure, morphology and stress of gold-chromium bilayer film

张洪, 晋云霞, 王虎, 孔钒宇, 黄昊鹏, 崔云

2016 (10): 104205-104205. doi: 10.1088/1674-1056/25/10/104205

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In this work, a 200-nm-thick gold film with a 10-nm-thick chromium layer used as an adhesive layer is fabricated on fused silica by the electron beam evaporation method. The effects of annealing time at 300 ℃ on the structure, morphology and stress of the film are studied. We find that chromium could diffuse to the surface of the film by formatting a solid solution with gold during annealing. Meanwhile, chromium is oxidized on the surface and diffused downward along the grain grooves in the gold film. The various operant mechanisms that change the residual stresses of gold films for different annealing times are discussed.

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An acoustic Maxwell's fish-eye lens based on gradient-index metamaterials

袁保国, 田野, 程营, 刘晓峻

2016 (10): 104301-104301. doi: 10.1088/1674-1056/25/10/104301

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We have proposed a two-dimensional acoustic Maxwell's fish-eye lens by using the gradient-index metamaterials with space-coiling units. By adjusting the structural parameters of the units, the refractive index can be gradually varied, which is key role to design the acoustic fish-eye lens. As predicted by ray trajectories on a virtual sphere, the proposed lens has the capability to focus the acoustic wave irradiated from a point source at the surface of the lens on the diametrically opposite side of the lens. The broadband and low loss performance is further demonstrated for the lens. The proposed acoustic fish-eye lens is expected to have the potential applications in directional acoustic coupler or coherent ultrasonic imaging.

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Acoustic focusing through two layer annuluses in air

管义钧, 孙宏祥, 刘树森, 袁寿其, 夏建平, 葛勇

2016 (10): 104302-104302. doi: 10.1088/1674-1056/25/10/104302

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We report an acoustic focusing lens composed of two-layer annuluses made of metal cylinders in air. We find that the cylindrical waves can be focused into a perfect point without diffraction in the centre of the annuluses, which arises from the Mie-resonance modes in the annuluses. The focusing frequencies are related to the size of the inner annulus, and the focusing effect can be applied to the annuluses with different shapes and incident positions. Interesting applications of the focusing lens in the acoustic beam splitter and directional transmitter with energy enhancement are further discussed.

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Pseudopotential multi-relaxation-time lattice Boltzmann model for cavitation bubble collapse with high density ratio

单鸣雷, 朱昌平, 姚澄, 殷澄, 蒋小燕

2016 (10): 104701-104701. doi: 10.1088/1674-1056/25/10/104701

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The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In the present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q et al. [ Li Q, Luo K H and Li X J 2013 Phys. Rev. E 87 053301] is adopted to develop a cavitation bubble collapse model. In the respects of coexistence curves and Laplace law verification, the improved pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. It is found that the thermodynamic consistency and surface tension are independent of kinematic viscosity. By homogeneous and heterogeneous cavitation simulation, the ability of the present model to describe the cavitation bubble development as well as the cavitation inception is verified. The bubble collapse between two parallel walls is simulated. The dynamic process of a collapsing bubble is consistent with the results from experiments and simulations by other numerical methods. It is demonstrated that the present pseudopotential multi-relaxation-time lattice Boltzmann model is applicable and efficient, and the lattice Boltzmann method is an alternative tool for collapsing bubble modeling.

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Pattern formation in superdiffusion Oregonator model

冯帆, 闫佳, 刘富成, 贺亚峰

2016 (10): 104702-104702. doi: 10.1088/1674-1056/25/10/104702

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Pattern formations in an Oregonator model with superdiffusion are studied in two-dimensional (2D) numerical simulations. Stability analyses are performed by applying Fourier and Laplace transforms to the space fractional reaction-diffusion systems. Antispiral, stable turing patterns, and travelling patterns are observed by changing the diffusion index of the activator. Analyses of Floquet multipliers show that the limit cycle solution loses stability at the wave number of the primitive vector of the travelling hexagonal pattern. We also observed a transition between antispiral and spiral by changing the diffusion index of the inhibitor.

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Bio-inspired optimization algorithms for optical parameter extraction of dielectric materials: A comparative study

Md Ghulam Saber, Kh Arif Shahriar, Ashik Ahmed, Rakibul Hasan Sagor

2016 (10): 105101-105101. doi: 10.1088/1674-1056/25/10/105101

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Particle swarm optimization (PSO) and invasive weed optimization (IWO) algorithms are used for extracting the modeling parameters of materials useful for optics and photonics research community. These two bio-inspired algorithms are used here for the first time in this particular field to the best of our knowledge. The algorithms are used for modeling graphene oxide and the performances of the two are compared. Two objective functions are used for different boundary values. Root mean square (RMS) deviation is determined and compared.

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Electronic transport of Lorentz plasma with collision and magnetic field effects

吕冲, 弯峰, 贾默然, 李子良, 桑海波, 谢柏松

2016 (10): 105201-105201. doi: 10.1088/1674-1056/25/10/105201

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The electronic transverse transport of Lorentz plasma with collision and magnetic field effects is studied by solving the Boltzmann equation for different electron density distributions. For the Maxwellian distribution, it is shown that transport coefficients decrease as Ω increases, Ω is the ratio of an electron's magneto-cyclotron frequency to plasma collision frequency. It means that the electrons are possible to be highly collimated by a strong magnetic field. For the quasi-monoenergetic distribution with different widths, it is found that the transport coefficients decrease greatly as ε decreases. In particular when the width approaches to zero the transverse transport coefficients are hardly affected by the magnetic field and the minimal one is obtained. Results imply that the strong magnetic field and quasi-monoenergetic distribution are both beneficial to reduce the electronic transverse transport. This study is also helpful to understand the relevant problems of plasma transport in the background of the inertial confinement fusion.

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K—P—Burgers equation in negative ion-rich relativistic dusty plasma including the effect of kinematic viscosity

A N Dev, M K Deka, J Sarma, D Saikia, N C Adhikary

2016 (10): 105202-105202. doi: 10.1088/1674-1056/25/10/105202

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The stationary solution is obtained for the K-P-Burgers equation that describes the nonlinear propagations of dust ion acoustic waves in a multi-component, collisionless, un-magnetized relativistic dusty plasma consisting of electrons, positive and negative ions in the presence of charged massive dust grains. Here, the Kadomtsev-Petviashvili (K-P) equation, three-dimensional (3D) Burgers equation, and K-P-Burgers equations are derived by using the reductive perturbation method including the effects of viscosity of plasma fluid, thermal energy, ion density, and ion temperature on the structure of a dust ion acoustic shock wave (DIASW). The K-P equation predictes the existences of stationary small amplitude solitary wave, whereas the K-P-Burgers equation in the weakly relativistic regime describes the evolution of shock-like structures in such a multi-ion dusty plasma.

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Effect of Bohm quantum potential in the propagation of ion-acoustic waves in degenerate plasmas

M M Hasan, M A Hossen, A Rafat, A A Mamun

2016 (10): 105203-105203. doi: 10.1088/1674-1056/25/10/105203

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A theoretical investigation has been carried out on the propagation of the ion-acoustic (IA) waves in a relativistic degenerate plasma containing relativistic degenerate electron and positron fluids in the presence of inertial non-relativistic light ion fluid. The Korteweg-de Vries (K-dV), modified K-dV (mK-dV), and mixed mK-dV (mmK-dV) equations are derived by adopting the reductive perturbation method. In order to analyze the basic features (phase speed, amplitude, width, etc.) of the IA solitary waves (SWs), the SWs solutions of the K-dV, mK-dV, and mmK-dV are numerically analyzed. It is found that the degenerate pressure, inclusion of the new phenomena like the Fermi temperatures and quantum mechanical effects (arising due to the quantum diffraction) of both electrons and positrons, number densities, etc., of the plasma species remarkably change the basic characteristics of the IA SWs which are found to be formed either with positive or negative potential. The implication of our results in explaining different nonlinear phenomena in astrophysical compact objects, e.g., white dwarfs, neutron stars, etc., and laboratory plasmas like intense laser-solid matter interaction experiments, etc., are mentioned.

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Influence of number and depth of magnetic mirror on Alfvénic gap eigenmode

苌磊, 胡宁, 姚建尧

2016 (10): 105204-105204. doi: 10.1088/1674-1056/25/10/105204

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Alfvénic gap eigenmode (AGE) can eject energetic particles from confinement and thereby threaten the success of magnetically controlled fusion. A low-temperature plasma cylinder is a promising candidate to study this eigenmode, due to easy diagnostic access and simple geometry, and the idea is to arrange a periodic array of magnetic mirrors along the plasma cylinder and introduce a local defect to break the field periodicity. The present work validates this idea by reproducing a clear AGE inside a spectral gap, and more importantly details the influence of the number and depth (or modulation factor) of magnetic mirror on the characteristics of AGE. Results show that AGE is suppressed by other modes inside the spectral gap when the number of magnetic mirrors is below a certain value, which leads to a weakened Bragg's effect. The structure and frequency of AGE remain unchanged for a decreased number of magnetic mirrors, as long as this number is enough for the AGE formation. The width of spectral gap and decay constant (inverse of decay length) of AGE are linearly proportional to the depth of magnetic mirror, implying easier observation of AGE through a bigger mirror depth. The frequency of AGE shifts to a lower range with the depth increased, possibly due to the unfrozen plasma with field line and the invalidity of small-perturbation analysis. Nevertheless, it is exciting to find that the depth of field modulation can be increased to form AGE for a very limited number of magnetic mirrors. This is of particular interest for the experimental implementation of AGE on a low-temperature plasma cylinder with limited length.

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LIF diagnostics of hydroxyl radical in a methanol containing atmospheric-pressure plasma jet

钱沐杨, 刘三秋, 裴学凯, 卢新培, 张家良, 王德真

2016 (10): 105205-105205. doi: 10.1088/1674-1056/25/10/105205

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In this paper, a pulsed-dc CH₃OH/Ar plasma jet generated at atmospheric pressure is studied by laser-induced fluorescence (LIF) and optical emission spectroscopy (OES). A gas-liquid bubbler system is proposed to introduce the methanol vapor into the argon gas, and the CH₃OH/Ar volume ratio is kept constant at about 0.1%. Discharge occurs in a 6-mm needle-to-ring gap in an atmospheric-pressure CH₃OH/Ar mixture. The space-resolved distributions of OH LIF inside and outside the nozzle exhibit distinctly different behaviors. And, different production mechanisms of OH radicals in the needle-to-ring discharge gap and afterglow of plasma jet are discussed. Besides, the optical emission lines of carbonaceous species, such as CH, CN, and C₂ radicals, are identified in the CH₃OH/Ar plasma jet. Finally, the influences of operating parameters (applied voltage magnitude, pulse frequency, pulsewidth) on the OH radical density are also presented and analyzed.

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Influence of dielectric materials on uniformity of large-area capacitively coupled plasmas for N₂/Ar discharges

梁英爽, 张钰如, 王友年

2016 (10): 105206-105206. doi: 10.1088/1674-1056/25/10/105206

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The effect of the dielectric ring on the plasma radial uniformity is numerically investigated in the practical 450-mm capacitively coupled plasma reactor by a two-dimensional self-consistent fluid model. The simulations were performed for N₂/Ar discharges at the pressure of 300 Pa, and the frequency of 13.56 MHz. In the practical plasma treatment process, the wafer is always surrounded by a dielectric ring, which is less studied. In this paper, the plasma characteristics are systematically investigated by changing the properties of the dielectric ring, i.e., the relative permittivity, the thickness and the length. The results indicate that the plasma parameters strongly depend on the properties of the dielectric ring. As the ratio of the thickness to the relative permittivity of the dielectric ring increases, the electric field at the wafer edge becomes weaker due to the stronger surface charging effect. This gives rise to the lower N₂⁺ ion density, flux and N atom density at the wafer edge. Thus the homogeneous plasma density is obtained by selecting optimal dielectric ring relative permittivity and thickness. In addition, we also find that the length of the dielectric ring should be as short as possible to avoid the discontinuity of the dielectric materials, and thus obtain the large area uniform plasma.

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Static and dynamic properties of polymer brush with topological ring structures: Molecular dynamic simulation

万吴兵, 吕红红, 候格, 吴晨旭

2016 (10): 106101-106101. doi: 10.1088/1674-1056/25/10/106101

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By defining a topological constraint value (rn), the static and dynamic properties of a polymer brush composed of moderate or short chains with different topological ring structures are studied using molecular dynamics simulation, and a comparison with those of linear polymer brush is also made. For the center-of-mass height of the ring polymer brush scaled by chain length h～N^ν, there is no significant difference of exponent from that of a linear brush in the small topological constraint regime. However, as the topological constraint becomes stronger, one obtains a smaller exponent. It is found that there exists a master scaling power law of the total stretching energy scaled by chain length N for moderate chain length regime, F_ene～Nρ^ν, for ring polymer brushes, but with a larger exponent ν than 5/6, indicating an influence of topological constraint to the dynamic properties of the system. A topological invariant of free energy scaled by <c>^5/4 is found.

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Self-compliance multilevel storage characteristic in HfO₂-based device

高晓平, 傅丽萍, 陈传兵, 袁鹏, 李颖弢

2016 (10): 106102-106102. doi: 10.1088/1674-1056/25/10/106102

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In this paper, the self-compliance bipolar resistive switching characteristic of an HfO₂-based memory device with Ag/HfO₂/Au structure for multilevel storage is investigated. By applying a positive voltage, the dual-step set processes corresponding to three stable resistance states are observed in the device. The multilevel switching characteristics can still be observed after 48 hours. In addition, the resistance values of all the three states show negligible degradation over 10⁴ s, which may be useful for the applications in nonvolatile multilevel storage.

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Tensile properties and microstructure of 2024 aluminum alloy subjected to the high magnetic field and external stress

李桂荣, 薛飞, 王宏明, 郑瑞, 朱弋, 储强泽, 程江峰

2016 (10): 106201-106201. doi: 10.1088/1674-1056/25/10/106201

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In order to explore the dependence of plasticity of metallic material on a high magnetic field, the effects of the different magnetic induction intensities (H= 0 T, 0.5 T, 1 T, 3 T, and 5 T) and pulses number (N = 0, 10, 20, 30, 40, and 50) on tensile strength (σ_b) and elongation (δ) of 2024 aluminum alloy are investigated in the synchronous presences of a high magnetic field and external stress. The results show that the magnetic field exerts apparent and positive effects on the tensile properties of the alloy. Especially under the optimized condition of H^*=1 T and N^*=30, the σ_b and δ are 410 MPa and 17% that are enhanced by 9.3% and 30.8% respectively in comparison to those of the untreated sample. The synchronous increases of tensile properties are attributed to the magneto-plasticity effect on a quantum scale. That is, the magnetic field will accelerate the state conversion of radical pair generated between the dislocation and obstacles from singlet to the triplet state. The bonding energy between them is meanwhile lowered and the moving flexibility of dislocations will be enhanced. At H^*=1 T and N^*=30, the dislocation density is enhanced by 1.28 times. The relevant minimum grain size is 266.1 nm, which is reduced by 35.2%. The grain refining is attributed to the dislocation accumulation and subsequent dynamic recrystallization. The (211) and (220) peak intensities are weakened. It is deduced that together with the recrystallization, the fine grains will transfer towards the slip plane and contribute to the slipping deformation.

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Dynamic behaviors of water contained in calcium—silicate—hydrate gel at different temperatures studied by quasi-elastic neutron scattering spectroscopy

易洲, 邓沛娜, 张丽丽, 李华

2016 (10): 106401-106401. doi: 10.1088/1674-1056/25/10/106401

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The dynamic behaviors of water contained in calcium-silicate-hydrate (C-S-H) gel with different water content values from 10% to 30% (by weight), are studied by using an empirical diffusion model (EDM) to analyze the experimental data of quasi-elastic neutron scattering (QENS) spectra at measured temperatures ranging from 230 K to 280 K. In the study, the experimental QENS spectra with the whole Q-range are considered. Several important parameters including the bound/immobile water elastic coefficient A, the bound water index BWI, the Lorentzian with a half-width at half-maximum (HWHM) Γ₁(Q) and Γ₂(Q), the self-diffusion coefficients D_t1 and D_t2 of water molecules, the average residence times τ₀₁ and τ₀₂, and the proton mean squared displacement (MSD) <u²> are obtained. The results show that the QENS spectra can be fitted very well not only for small Q ( ≤ 1 Å^-1) but also for large Q. The bound/immobile water fraction in a C-S-H gel sample can be shown by the fitted BWI. The distinction between bound/immobile and mobile water, which includes confined water and ultra-confined water, can be seen by the fitted MSD. All the MSD tend to be the smallest value below 0.25 Å² (the MSD of bound/immobile water) as the Q increases to 1.9 Å^-1, no matter what the temperature and water content are. Furthermore, by the abrupt changes of the fitted values of D_t1, τ₀₁, and Γ₁(Q), a crossover temperature at 250 K, namely the liquid-to-crystal-like transition temperature, can be identified for confined water in large gel pores (LGPs) and/or small gel pores (SGPs) contained in the C-S-H gel sample with 30% water content.

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Radial transport dynamics studies of SMBI with a newly developed TPSMBI code

王亚辉, 郭文峰, 王占辉, 任启龙, 孙爱萍, 许敏, 王爱科, 项农

2016 (10): 106601-106601. doi: 10.1088/1674-1056/25/10/106601

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In tokamak plasma fueling, supersonic molecule beam injection (SMBI) with a higher fueling efficiency and a deeper penetration depth than the traditional gas puffing method has been developed and widely applied to many tokamak devices. It is crucial to study the transport dynamics of SMBI to improve its fueling efficiency, especially in the high confinement regime. A new one-dimensional (1D) code of TPSMBI has also been developed recently based on a six-field SMBI model in cylindrical coordinate. It couples plasma density and heat radial transport equations together with neutral density transport equations for both molecules and atoms and momentum radial transport equations for molecules. The dominant particle collisional interactions between plasmas and neutrals, such as molecule dissociation, atom ionization and charge-exchange effects, are included in the model. The code is verified to be correct with analytical solutions and also benchmarked well with the trans-neut module of BOUT++ code. Time-dependent radial transport dynamics and mean profile evolution are studied during SMBI with the TPSMBI code in both slab and cylindrical coordinates. Along the SMBI path, plasma density increases due to particle fuelling, while plasma temperature decreases due to heat cooling. Being different from slab coordinate, the curvature effect leads to larger front densities of molecule and atom during SMBI in cylindrical coordinate simulation.

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Effects of Si surficial structure on transport properties of La_2/3Sr_1/3MnO₃ films

顾晓敏, 王伟, 周国泰, 高凯歌, 蔡宏灵, 张凤鸣, 吴小山

2016 (10): 106701-106701. doi: 10.1088/1674-1056/25/10/106701

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La_2/3Sr_1/3MnO₃ films are deposited on (001) silicon substrates, in which the silicon surfaces have artificially been treated into the scallops-like, pyramid-like, and smooth polishing structure, by pulsed laser deposition. The magnetoresistances of the films on etched substrates under low applied field are very sensitive to the applied field, and much larger (14.3% for acid-etched, and 42.9% for alkali-etched) than that on the polished Si at 5 K. Zero-field-cooled and field-cooled magnetization behaviors are measured and analyzed. Remarkable upturn behaviors in temperature-dependent resistivity for all samples are observed at low temperature, which follows the Efros-Shkloskii variable range hopping law and the Arrhenius law. We believe that the rough surface may be useful in device design.

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Thick c-BN films deposited by radio frequency magnetron sputtering in argon/nitrogen gas mixture with additional hydrogen gas

赵艳, 高伟, 徐博, 李英爱, 李红东, 顾广瑞, 殷红

2016 (10): 106801-106801. doi: 10.1088/1674-1056/25/10/106801

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The excellent physical and chemical properties of cubic boron nitride (c-BN) film make it a promising candidate for various industry applications. However, the c-BN film thickness restricts its practical applications in many cases. Thus, it is indispensable to develop an economic, simple and environment-friend way to synthesize high-quality thick, stable c-BN films. High-cubic-content BN films are prepared on silicon (100) substrates by radio frequency (RF) magnetron sputtering from an h-BN target at low substrate temperature. Adhesions of the c-BN films are greatly improved by adding hydrogen to the argon/nitrogen gas mixture, allowing the deposition of a film up to 5-μm thick. The compositions and the microstructure morphologies of the c-BN films grown at different substrate temperatures are systematically investigated with respect to the ratio of H₂ gas content to total working gas. In addition, a primary mechanism for the deposition of thick c-BN film is proposed.

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Optical absorption enhancement in slanted silicon nanocone hole arrays for solar photovoltaics

张淑媛, 刘雯, 李兆峰, 刘敏, 刘雨生, 王晓东, 杨富华

2016 (10): 106802-106802. doi: 10.1088/1674-1056/25/10/106802

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We investigate slanted silicon nanocone hole arrays as light absorbing structures for solar photovoltaics via simulation. With only 1-μm equivalent thickness, a maximum short-circuit current density of 34.9 mA/cm² is obtained. Moreover, by adding an Ag mirror under the whole structure, a short-circuit current density of 37.9 mA/cm² is attained. It is understood that the optical absorption enhancement mainly results from three aspects. First, the silicon nanocone holes provide a highly efficient antireflection effect. Second, after breaking the geometric symmetry, the slanted silicon nanocone hole supports more resonant absorption modes than vertical structures. Third, the Fabry-Perot resonance enhances the light absorption after adding an Ag mirror.

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HfO₂-based ferroelectric modulator of terahertz waves with graphene metamaterial

蒋然, 吴正冉, 韩祖银, Hyung-Suk Jung

2016 (10): 106803-106803. doi: 10.1088/1674-1056/25/10/106803

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Tunable modulations of terahertz waves in a graphene/ferroelectric-layer/silicon hybrid structure are demonstrated at low bias voltages. The modulation is due to the creation/elimination of an extra barrier in Si layer in response to the polarization in the ferroelectric Si:HfO₂ layer. Considering the good compatibility of HfO₂ with the Si-based semiconductor process, the highly tunable characteristics of the graphene metamaterial device under ferroelectric effect open up new avenues for graphene-based high performance integrated active photonic devices compatible with the silicon technology.

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Electronic structures and edge effects of Ga₂S₂ nanoribbons

王宝基, 李晓华, 张利伟, 王国东, 柯三黄

2016 (10): 107101-107101. doi: 10.1088/1674-1056/25/10/107101

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Ab initio density functional theory calculations are carried out to predict the electronic properties and relative stability of gallium sulfide nanoribbons (Ga₂S₂-NRs) with either zigzag- or armchair-terminated edges. It is found that the electronic properties of the nanoribbons are very sensitive to the edge structure. The zigzag nanoribbons (Ga₂S₂-ZNRs) are ferromagnetic (FM) metallic with spin-polarized edge states regardless of the H-passivation, whereas the bare armchair ones (Ga₂S₂-ANRs) are semiconducting with an indirect band gap. This band gap exhibits an oscillation behavior as the width increases and finally converges to a constant value. Similar behavior is also found in H-saturated Ga₂S₂-ANRs, although the band gap converges to a larger value. The relative stabilities of the bare ANRs and ZNRs are investigated by calculating their binding energies. It is found that for a similar width the ANRs are more stable than the ZNRs, and both are more stable than some Ga₂S₂ nanoclusters with stable configurations.

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Observation of trapped light induced by Dwarf Dirac-cone in out-of-plane condition for photonic crystals

Subir Majumder, Tushar Biswas, Shaymal K Bhadra

2016 (10): 107102-107102. doi: 10.1088/1674-1056/25/10/107102

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Existence of out-of-plane conical dispersion for a triangular photonic crystal lattice is reported. It is observed that conical dispersion is maintained for a number of out-of-plane wave vectors (k_z). We study a case where Dirac like linear dispersion exists but the photonic density of states is not vanishing, called Dwarf Dirac cone (DDC) which does not support localized modes. We demonstrate the trapping of such modes by introducing defects in the crystal. Interestingly, we find by k-point sampling as well as by tuning trapped frequency that such a conical dispersion has an inherent light confining property and it is governed by neither of the known wave confining mechanisms like total internal reflection, band gap guidance. Our study reveals that such a conical dispersion in a non-vanishing photonic density of states induces unexpected intense trapping of light compared with those at other points in the continuum. Such studies provoke fabrication of new devices with exciting properties and new functionalities.

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New ordered MAX phase Mo₂TiAlC₂: Elastic and electronic properties from first-principles

M A Hadi, M S Ali

2016 (10): 107103-107103. doi: 10.1088/1674-1056/25/10/107103

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First-principles computation on the basis of density functional theory (DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical Vickers' hardness of newly discovered ordered MAX phase carbide Mo₂TiAlC₂. The computed structural parameters are very reasonable compared with the experimental results. The mechanical stability is verified by using the computed elastic constants. The brittleness of the compound is indicated by both the Poisson's and Pugh's ratios. The new MAX phase is capable of resisting the pressure and tension and also has the clear directional bonding between atoms. The compound shows significant elastic anisotropy. The Debye temperature estimated from elastic moduli (B, G) is found to be 413.6 K. The electronic structure indicates that the bonding nature of Mo₂TiAlC₂ is a mixture of covalent and metallic with few ionic characters. The electron charge density map shows a strong directional Mo-C-Mo covalent bonding associated with a relatively weak Ti-C bond. The calculated Fermi surface is due to the low-dispersive Mo 4d-like bands, which makes the compound a conductive one. The hardness of the compound is also evaluated and a high value of 9.01 GPa is an indication of its strong covalent bonding.

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First-principles studies of effects of interstitial boron and carbon on the structural, elastic, and electronic properties of Ni solution and Ni₃Al intermetallics

黄梦礼, 王崇愚

2016 (10): 107104-107104. doi: 10.1088/1674-1056/25/10/107104

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The effects of boron and carbon on the structural, elastic, and electronic properties of both Ni solution and Ni₃Al intermetallics are investigated using first-principles calculations. The results agree well with theoretical and experimental data from previous studies and are analyzed based on the density of states and charge density. It is found that both boron and carbon are inclined to occupy the Ni-rich interstices in Ni₃Al, which gives rise to a cubic interstitial phase. In addition, the interstitial boron and carbon have different effects on the elastic moduli of Ni and Ni₃Al. The calculation results for the G/B and Poisson's ratios further demonstrate that interstitial boron and carbon can both reduce the brittleness of Ni, thereby increasing its ductility. Meanwhile, boron can also enhance the ductility of the Ni₃Al while carbon hardly has an effect on its brittleness or ductility.

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Time-dependent evolution process of Sb₂Te₃ from nanoplates to nanorods and their Raman scattering properties

孟秀清, 汤宁, 钟绵增, 叶慧群, 方允樟

2016 (10): 107105-107105. doi: 10.1088/1674-1056/25/10/107105

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High-quality Sb₂Te₃ nanostructures are synthesized by a simple hydrothermal method. The morphologies of the nanostructures change from hexagonal nanoplates to nanorods with the extension of growth time. Secondary nucleation is the dominant factor responsible for the change of the morphologies. Structural analyses indicate that all the obtained nanostructures are well crystallized. IR-active phonons are mainly observed in the Raman spectra of the nanoplates and nanorods. The slight deviations are observed in the Raman modes between the nanoplates and nanorods, which could originate from confinement effect in the nanostructures.

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Modified model of gate leakage currents in AlGaN/GaN HEMTs

王元刚, 冯志红, 吕元杰, 谭鑫, 敦少博, 房玉龙, 蔡树军

2016 (10): 107106-107106. doi: 10.1088/1674-1056/25/10/107106

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It has been reported that the gate leakage currents are described by Frenkel-Poole emission (FPE) model, at the temperatures higher than 250 K. However, the gate leakage currents of our passivated devices do not accord with the FPE model. Therefore, a modified FPE model is developed in which an additional leakage current, besides the gate (I_II), is added. Based on the samples with different passivations, the I_II caused by a large number of surface traps is separated from total gate currents, and is found to be linear with respect to (φ_B-V_g)^0.5. Compared with these from the FPE model, the calculated results from the modified model agree well with the I_g-V_g measurements at temperatures ranging from 295 K to 475 K.

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The spin Hall effect in single-crystalline gold thin films

田岱, 陈才干, 王华, 金晓峰

2016 (10): 107201-107201. doi: 10.1088/1674-1056/25/10/107201

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The spin Hall effect has been investigated in 10-nm-thick epitaxial Au (001) single crystal films via H-pattern devices, whose minimum characteristic dimension is about 40 nm. By improving the film quality and optimizing the in-plane geometry parameters of the devices, we explicitly extract the spin Hall effect contribution from the ballistic and bypass contribution which were previously reported to be dominating the non-local voltage. Furthermore, we calculate a lower limit of the spin Hall angle of 0.08 at room temperature. Our results indicate that the giant spin Hall effect in Au thin films is dominated not by the interior defects scattering, but by the surface scattering. Besides, our results also provide an additional experimental method to determine the magnitude of spin Hall angle unambiguously.

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First-principles hybrid functional study of the electronic structure and charge carrier mobility in perovskite CH₃NH₃SnI₃

伍丽娟, 赵宇清, 陈畅文, 王琳芝, 刘标, 蔡孟秋

2016 (10): 107202-107202. doi: 10.1088/1674-1056/25/10/107202

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We calculate the electronic properties and carrier mobility of perovskite CH₃NH₃SnI₃ as a solar cell absorber by using the hybrid functional method. The calculated result shows that the electron and hole mobilities have anisotropies with a large magnitude of 1.4×10⁴ cm²·V^-1·s^-1 along the y direction. In view of the huge difference between hole and electron mobilities, the perovskite CH₃NH₃SnI₃ can be considered as a p-type semiconductor. We also discover a relationship between the effective mass anisotropy and electronic occupation anisotropy. The above results can provide reliable guidance for its experimental applications in electronics and optoelectronics.

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Design and experimental verification of a dual-band metamaterial filter

朱洪杨, 姚爱琴, 钟敏

2016 (10): 107301-107301. doi: 10.1088/1674-1056/25/10/107301

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In this paper, we present the design, simulation, and experimental verification of a dual-band free-standing metamaterial filter operating in a frequency range of 1 THz-30 THz. The proposed structure consists of periodically arranged composite air holes, and exhibits two broad and flat transmission bands. To clarify the effects of the structural parameters on both resonant transmission bands, three sets of experiments are performed. The first resonant transmission band shows a shift towards higher frequency when the side width w₁ of the main air hole is increased. In contrast, the second resonant transmission band displays a shift towards lower frequency when the side width w₂ of the sub-holes is increased, while the first resonant transmission band is unchanged. The measured results indicate that these resonant bands can be modulated individually by simply optimizing the relevant structural parameters (w₁ or w₂) for the required band. In addition, these resonant bands merge into a single resonant band with a bandwidth of 7.7 THz when w₁ and w₂ are optimized simultaneously. The structure proposed in this paper adopts different resonant mechanisms for transmission at different frequencies and thus offers a method to achieve a dual-band and low-loss filter.

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Resistive switching characteristic and uniformity of low-power HfO_x-based resistive random access memory with the BN insertion layer

苏帅, 鉴肖川, 王芳, 韩叶梅, 田雨仙, 王晓旸, 张宏智, 张楷亮

2016 (10): 107302-107302. doi: 10.1088/1674-1056/25/10/107302

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In this letter, the Ta/HfO_x/BN/TiN resistive switching devices are fabricated and they exhibit low power consumption and high uniformity each. The reset current is reduced for the HfO_x/BN bilayer device compared with that for the Ta/HfO_x/TiN structure. Furthermore, the reset current decreases with increasing BN thickness. The HfO_x layer is a dominating switching layer, while the low-permittivity and high-resistivity BN layer acts as a barrier of electrons injection into TiN electrode. The current conduction mechanism of low resistance state in the HfO_x/BN bilayer device is space-charge-limited current (SCLC), while it is Ohmic conduction in the HfO_x device.

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Transport properties of the topological Kondo insulator SmB₆ under the irradiation of light

朱国宝, 杨慧敏

2016 (10): 107303-107303. doi: 10.1088/1674-1056/25/10/107303

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In this paper, we study transport properties of the X point in the Brillouin zone of the topological Kondo insulator SmB₆ under the application of a circularly polarized light. The transport properties at high-frequency regime and low-frequency regime as a function of the ratio (κ) of the Dresselhaus-like and Rashba-like spin-orbit parameter are studied based on the Floquet theory and Boltzmann equation respectively. The sign of Hall conductivity at high-frequency regime can be reversed by the ratio κ and the amplitude of the light. The amplitude of the current can be enhanced by the ratio κ. Our findings provide a way to control the transport properties of the Dirac materials at low-frequency regime.

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Topological phase transition in a ladder of the dimerized Kitaev superconductor chains

周博臻, 周斌

2016 (10): 107401-107401. doi: 10.1088/1674-1056/25/10/107401

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We investigate the topological properties of a ladder model of the dimerized Kitaev superconductor chains. The topological class of the system is determined by the relative phase θ between the inter- and intra-chain superconducting pairing. One topological class is the class BDI characterized by the Z index, and the other is the class D characterized by the Z₂ index. For the two different topological classes, the topological phase diagrams of the system are presented by calculating two different topological numbers, i.e., the Z index winding number W and the Z₂ index Majorana number M, respectively. In the case of θ =0, the topological class belongs to the class BDI, multiple topological phase transitions accompanying the variation of the number of Majorana zero modes are observed. In the case of θ =π/2 it belongs to the class D. Our results show that for the given value of dimerization, the topologically nontrivial and trivial phases alternate with the variation of chemical potential.

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Theoretical investigations of half-metallic ferromagnetism in new Half—Heusler YCrSb and YMnSb alloys using first-principle calculations

M Atif Sattar, Muhammad Rashid, M Raza Hashmi, S A Ahmad, Muhammad Imran, Fayyaz Hussain

2016 (10): 107402-107402. doi: 10.1088/1674-1056/25/10/107402

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Structural, electronic, and magnetic properties of new predicted half-Heusler YCrSb and YMnSb compounds within the ordered MgAgAs C1_b-type structure are investigated by employing first-principal calculations based on density functional theory. Through the calculated total energies of three possible atomic placements, we find the most stable structures regarding YCrSb and YMnSb materials, where Y, Cr(Mn), and Sb atoms occupy the (0.5, 0.5, 0.5), (0.25, 0.25, 0.25), and (0, 0, 0) positions, respectively. Furthermore, structural properties are explored for the non-magnetic and ferromagnetic and anti-ferromagnetic states and it is found that both materials prefer ferromagnetic states. The electronic band structure shows that YCrSb has a direct band gap of 0.78 eV while YMnSb has an indirect band gap of 0.40 eV in the majority spin channel. Our findings show that YCrSb and YMnSb materials exhibit half-metallic characteristics at their optimized lattice constants of 6.67 Å and 6.56 Å, respectively. The half-metallicities associated with YCrSb and YMnSb are found to be robust under large in-plane strains which make them potential contenders for spintronic applications.

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Quantitative analysis of ammonium salts in coking industrial liquid waste treatment process based on Raman spectroscopy

曹亚南, 王贵师, 谈图, 蔡廷栋, 刘锟, 汪磊, 朱公栋, 梅教旭

2016 (10): 107403-107403. doi: 10.1088/1674-1056/25/10/107403

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Quantitative analysis of ammonium salts in the process of coking industrial liquid waste treatment is successfully performed based on a compact Raman spectrometer combined with partial least square (PLS) method. Two main components (NH₄SCN and (NH₄)₂S₂O₃) of the industrial mixture are investigated. During the data preprocessing, wavelet denoising and an internal standard normalization method are employed to improve the predicting ability of PLS models. Moreover, the PLS models with different characteristic bands for each component are studied to choose a best resolution. The internal and external calibration results of the validated model show a mass percentage error below 1% for both components. Finally, the repeatabilities and reproducibilities of Raman and reference titration measurements are also discussed.

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Theory of specific heat of vortex liquid of high T_c superconductors

白晨, 迟诚, 王江帆

2016 (10): 107404-107404. doi: 10.1088/1674-1056/25/10/107404

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Superconducting thermal fluctuation (STF) plays an important role in both thermodynamic and transport properties in the vortex liquid phase of high T_c superconductors. It was widely observed in the vicinity of the critical transition temperature. In the framework of Ginzburg-Landau-Lawrence-Doniach theory in magnetic field, a self-consistent analysis of STF including all Landau levels is given. Besides that, we calculate the contribution of STF to specific heat in vortex liquid phase for high T_c cuprate superconductors, and the fitting results are in good agreement with experimental data.

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Controlled synthesis of ferromagnetic MnSe_x particles

孙俊杰, 李超, 陈铎, 康仕寿, 刘国磊, 于淑云, 韩广兵, 梅良模

2016 (10): 107405-107405. doi: 10.1088/1674-1056/25/10/107405

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The MnSe_x (x=1,2) nanoparticles were synthesized under hydrothermal condition, by reaction of the reduced selenium and Mn²⁺ ion in the presence of hydrazine and acetic acid. By precisely controlling the pH value of the solution, a series of MnSe_x particles were synthesized. The structure and morphology of as-prepared particles were examined with x-ray diffractometer (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The average sizes of as-prepared particles varied from nanoscale to microscale with pH value increase. Furthermore, the nucleation and growth mechanism associated with pH values were discussed, which can be applied to the hydrothermal synthesis of metal chalcogenide in general. Finally, the optical and magnetic properties of as-prepared particles were measured. All as-made particles exhibit a ferromagnetic behavior with low coercivity and remanence at room temperature.

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Negative dependence of surface magnetocrystalline anisotropy energy on film thickness in Co₃₃Fe₆₇ alloy

王得来, 崔明启, 杨栋亮, 董俊才, 徐伟

2016 (10): 107501-107501. doi: 10.1088/1674-1056/25/10/107501

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In this work, the magnetocrystalline anisotropy energy (MAE) on the surface of Fe₃₃Co₆₇ alloy film is extracted from x-ray magnetic linear dichroism (XMLD) experiments. The result indicates that the surface MAE value is negatively correlated with thickness. Through spectrum calculations and analysis, we find that besides the thickness effect, another principal possible cause may be the shape anisotropy resulting from the presence of interface roughness. These two factors lead to different electron structures on the fermi surface with different exchange fields, which produces different spin-orbit interaction anisotropies.

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Effect of exchange interaction in ferromagnetic superlattices: A Monte Carlo study

R Masrour, A Jabar

2016 (10): 107502-107502. doi: 10.1088/1674-1056/25/10/107502

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The Monte Carlo simulation is used to investigate the magnetic properties of ferromagnetic superlattices through the Ising model. The reduced critical temperatures of the ferromagnetic superlattices are studied each as a function of layer thickness for different values of exchange interaction. The exchange interaction in each layer within the interface and the crystal field in the unit cell are studied. The magnetic coercive fields and magnetization remnants are obtained for different values of exchange interaction, different values of temperature and crystal field with fixed values of physical parameters.

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Large linear magnetoresistance in a new Dirac material BaMnBi₂

王义炎, 郁巧鹤, 夏天龙

2016 (10): 107503-107503. doi: 10.1088/1674-1056/25/10/107503

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Dirac semimetal is a class of materials that host Dirac fermions as emergent quasi-particles. Dirac cone-type band structure can bring interesting properties such as quantum linear magnetoresistance and large mobility in the materials. In this paper, we report the synthesis of high quality single crystals of BaMnBi₂ and investigate the transport properties of the samples. BaMnBi₂ is a metal with an antiferromagnetic transition at T_N=288 K. The temperature dependence of magnetization displays different behavior from CaMnBi₂ and SrMnBi₂, which suggests the possible different magnetic structure of BaMnBi₂. The Hall data reveals electron-type carriers and a mobility μ(5 K)=1500 cm²/V·s. Angle-dependent magnetoresistance reveals the quasi-two-dimensional (2D) Fermi surface in BaMnBi₂. A crossover from semiclassical MR～H² dependence in low field to MR～H dependence in high field, which is attributed to the quantum limit of Dirac fermions, has been observed in magnetoresistance. Our results indicate the existence of Dirac fermions in BaMnBi₂.

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Structural and magnetic properties of turmeric functionalized CoFe₂O₄ nanocomposite powder

E Mehran, S Farjami Shayesteh, M Sheykhan

2016 (10): 107504-107504. doi: 10.1088/1674-1056/25/10/107504

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The structural and magnetic properties of the synthesized pure and functionalized CoFe₂O₄ magnetic nanoparticles (NPs) are studied by analyzing the results from the x-ray diffraction (XRD), transmission electron microscopy (TEM), FT-IR spectroscopy, thermogravimetry (TG), and vibrating sample magnetometer (VSM). To extract the structure and lattice parameters from the XRD analysis results, we first apply the pseudo-Voigt model function to the experimental data obtained from XRD analysis and then the Rietveld algorithm is used in order to optimize the model function to estimate the true intensity values. Our simulated intensities are in good agreement with the experimental peaks, therefore, all structural parameters such as crystallite size and lattice constant are achieved through this simulation. Magnetic analysis reveals that the synthesized functionalized NPs have a saturation magnetization almost equal to that of pure nanoparticles (PNPs). It is also found that the presence of the turmeric causes a small reduction in coercivity of the functionalized NPs in comparison with PNP. Our TGA and FTIR results show that the turmeric is bonded very well to the surface of the NPs. So it can be inferred that a nancomposite (NC) powder of turmeric and nanoparticles is produced. As an application, the anti-arsenic characteristic of turmeric makes the synthesized functionalized NPs or NC powder a good candidate for arsenic removal from polluted industrial waste water.

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Emergent ferroelectricity in disordered tri-color multilayer structure comprised of ferromagnetic manganites

牛利伟, 陈长乐, 董祥雷, 邢辉, 罗炳成, 金克新

2016 (10): 107701-107701. doi: 10.1088/1674-1056/25/10/107701

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Multiferroic materials, showing the coexistence and coupling of ferroelectric and magnetic orders, are of great technological and fundamental importance. However, the limitation of single phase multiferroics with robust magnetization and polarization hinders the magnetoelectric effect from being applied practically. Magnetic frustration, which can induce ferroelectricity, gives rise to multiferroic behavior. In this paper, we attempt to construct an artificial magnetically frustrated structure comprised of manganites to induce ferroelectricity. A disordered stacking of manganites is expected to result in frustration at interfaces. We report here that a tri-color multilayer structure comprised of non-ferroelectric La_0.9Ca_0.1MnO₃(A)/Pr_0.85Ca_0.15MnO₃(B)/Pr_0.85Sr_0.15MnO₃(C) layers with the disordered arrangement of ABC-ACB-CAB-CBA-BAC-BCA is prepared to form magnetoelectric multiferroics. The multilayer film exhibits evidence of ferroelectricity at room temperature, thus presenting a candidate for multiferroics.

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Optoelectronic and thermoelectric properties of Zintl YLi₃X₂(X=Sb, Bi) compounds through modified Becke—Johnson potential

T Seddik, G Uğur, R Khenata, Ş Uğur, F Soyalp, G Murtaza, D P Rai, A Bouhemadou, S Bin Omran

2016 (10): 107801-107801. doi: 10.1088/1674-1056/25/10/107801

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In the present work, we investigate the structural, optoelectronic and thermoelectric properties of the YLi₃X₂(X=Sb, Bi) compounds using the full potential augmented plane wave plus local orbital (FP-APW+lo) method. The exchange-correlation potential is treated with the generalized gradient approximation/local density approximation (GGA/LDA) and with the modified Becke-Johnson potential (TB-mBJ) in order to improve the electronic band structure calculations. In addition, the estimated ground state properties such as the lattice constants, external parameters, and bulk moduli agree well with the available experimental data. Our band structure calculations with GGA and LDA predict that both compounds have semimetallic behaviors. However, the band structure calculations with the GGA/TB-mBJ approximation indicate that the ground state of the YLi₃Sb₂ compound is semiconducting and has an estimated indirect band gap (Γ-L) of about 0.036 eV while the ground state of YLi₃Bi₂ compound is semimetallic. Conversely the LDA/TB-mBJ calculations indicate that both compounds exhibit semiconducting characters and have an indirect band gap (Γ-L) of about 0.15 eV and 0.081 eV for YLi₃Sb and YLi₃Bi₂ respectively. Additionally, the optical properties reveal strong responses of the herein materials in the energy range between the IR and extreme UV regions. Thermoelectric properties such as thermal conductivity, electrical conductivity, Seebeck coefficient, and thermo power factors are also calculated.

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Transient grating study of the intermolecular dynamics of liquid nitrobenzene

吴红琳, 宋云飞, 于国洋, 杨延强

2016 (10): 107802-107802. doi: 10.1088/1674-1056/25/10/107802

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Femtosecond time-resolved transient grating (TG) technique is used to study the intermolecular dynamics in liquid phase. Non-resonant excitation of the sample by two crossing laser pulses results in a transient Kerr grating, and the molecular motion of liquid can be detected by monitoring the diffraction of a third time-delayed probe pulse. In liquid nitrobenzene (NB), three intermolecular processes are observed with lifetimes of 37.9±1.4 ps, 3.28±0.11 ps, and 0.44±0.03 ps, respectively. These relaxations are assigned to molecular orientational diffusion, dipole/induced dipole interaction, and libration in liquid cage, respectively. Such a result is slightly different from that obtained from OKE experiment in which the lifetime of the intermediate process is measured to be 1.9 ps. The effects of electric field on matter are different in TG and optical Kerr effect (OKE) experiments, which should be responsible for the difference between the results of these two types of experiments. The present work demonstrates that TG technique is a useful alternative in the study of intermolecular dynamics.

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Effects of multiple interruptions with trimethylindium-treatment in the InGaN/GaN quantum well on green light emitting diodes

乔良, 马紫光, 陈弘, 吴海燕, 陈雪芳, 杨浩军, 赵斌, 何苗, 郑树文, 李述体

2016 (10): 107803-107803. doi: 10.1088/1674-1056/25/10/107803

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In this study, the influence of multiple interruptions with trimethylindium (TMIn)-treatment in InGaN/GaN multiple quantum wells (MQWs) on green light-emitting diode (LED) is investigated. A comparison of conventional LEDs with the one fabricated with our method shows that the latter has better optical properties. Photoluminescence (PL) full-width at half maximum (FWHM) is reduced, light output power is much higher and the blue shift of electroluminescence (EL) dominant wavelength becomes smaller with current increasing. These improvements should be attributed to the reduced interface roughness of MQW and more uniformity of indium distribution in MQWs by the interruptions with TMIn-treatment.

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Polaron effect on the optical rectification in spherical quantum dots with electric field

冯振宇, 闫祖威

2016 (10): 107804-107804. doi: 10.1088/1674-1056/25/10/107804

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The polaron effect on the optical rectification in spherical quantum dots with a shallow hydrogenic impurity in the presence of electric field is theoretically investigated by taking into account the interactions of the electrons with both confined and surface optical phonons. Besides, the interaction between impurity and phonons is also considered. Numerical calculations are presented for typical Zn_1-xCd_xSe/ZnSe material. It is found that the polaronic effect or electric field leads to the redshifted resonant peaks of the optical rectification coefficients. It is also found that the peak values of the optical rectification coefficients with the polaronic effect are larger than without the polaronic effect, especially for smaller Cd concentrations or stronger electric field.

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Proper In deposition amount for on-demand epitaxy of InAs/GaAs single quantum dots

尚向军, 徐建星, 马奔, 陈泽升, 魏思航, 李密峰, 查国伟, 张立春, 喻颖, 倪海桥, 牛智川

2016 (10): 107805-107805. doi: 10.1088/1674-1056/25/10/107805

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The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots (SQDs) to raise the growth repeatability. Here, through many growth tests on rotating substrates, we develop a proper In deposition amount (θ) for SQD growth, according to the measured critical θ for test QD nucleation (θ_c). The proper ratio θ/θ_c, with a large tolerance of the variation of the real substrate temperature (T_sub), is 0.964-0.971 at the edge and >0.989 but <0.996 in the center of a 1/4-piece semi-insulating wafer, and around 0.9709 but <0.9714 in the center of a 1/4-piece N⁺ wafer as shown in the evolution of QD size and density as θ/θ_c varies. Bright SQDs with spectral lines at 905 nm-935 nm nucleate at the edge and correlate with individual 7 nm-8 nm-height QDs in atomic force microscopy, among dense 1 nm-5 nm-height small QDs with a strong spectral profile around 860 nm-880 nm. The higher T_sub in the center forms diluter, taller and uniform QDs, and very dilute SQDs for a proper θ/θ_c: only one 7-nm-hight SQD in 25 μm². On a 2-inch (1 inch=2.54 cm) semi-insulating wafer, by using θ/θ_c = 0.961, SQDs nucleate in a circle in 22% of the whole area. More SQDs will form in the broad high-T_sub region in the center by using a proper θ/θ_c.

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Atomic-layer-deposited Al₂O₃ and HfO₂ on InAlAs: A comparative study of interfacial and electrical characteristics

武利翻, 张玉明, 吕红亮, 张义门

2016 (10): 108101-108101. doi: 10.1088/1674-1056/25/10/108101

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Al₂O₃ and HfO₂ thin films are separately deposited on n-type InAlAs epitaxial layers by using atomic layer deposition (ALD). The interfacial properties are revealed by angle-resolved x-ray photoelectron spectroscopy (AR-XPS). It is demonstrated that the Al₂O₃ layer can reduce interfacial oxidation and trap charge formation. The gate leakage current densities are 1.37×10^-6 A/cm² and 3.22×10^-6A/cm² at +1 V for the Al₂O₃/InAlAs and HfO₂/InAlAs MOS capacitors respectively. Compared with the HfO₂/InAlAs metal-oxide-semiconductor (MOS) capacitor, the Al₂O₃/InAlAs MOS capacitor exhibits good electrical properties in reducing gate leakage current, narrowing down the hysteresis loop, shrinking stretch-out of the C-V characteristics, and significantly reducing the oxide trapped charge (Q_ot) value and the interface state density (D_it).

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Electric-field-dependent charge delocalization from dopant atoms in silicon junctionless nanowire transistor

王昊, 韩伟华, 赵晓松, 张望, 吕奇峰, 马刘红, 杨富华

2016 (10): 108102-108102. doi: 10.1088/1674-1056/25/10/108102

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We study electric-field-dependent charge delocalization from dopant atoms in a silicon junctionless nanowire transistor by low-temperature electron transport measurement. The Arrhenius plot of the temperature-dependent conductance demonstrates the transport behaviors of variable-range hopping (below 30 K) and nearest-neighbor hopping (above 30 K). The activation energy for the charge delocalization gradually decreases due to the confinement potential of the conduction channel decreasing from the threshold voltage to the flatband voltage. With the increase of the source-drain bias, the activation energy increases in a temperature range from 30 K to 100 K at a fixed gate voltage, but decreases above the temperature of 100 K.

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Phase transition of solid bismuth under high pressure

陈海燕, 向士凯, 颜小珍, 郑黎荣, 张毅, 刘盛刚, 毕延

2016 (10): 108103-108103. doi: 10.1088/1674-1056/25/10/108103

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As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III, and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction (XRD) technology. Using x-ray absorption fine structure (XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation.

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Influence of secondary treatment with CO₂ laser irradiation for mitigation site on fused silica surface

蒋勇, 周强, 邱荣, 高翔, 王慧丽, 姚彩珍, 王俊波, 赵鑫, 刘春明, 向霞, 祖小涛, 袁晓东, 苗心向

2016 (10): 108104-108104. doi: 10.1088/1674-1056/25/10/108104

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The ablation debris and raised rim, as well as residual stress and deep crater will be formed during the mitigation of damage site with a CO₂ laser irradiation on fused silica surface, which greatly affects the laser damage resistance of optics. In this study, the experimental study combined with numerical simulation is utilized to investigate the effect of the secondary treatment on a mitigated site by CO₂ laser irradiation. The results indicate that the ablation debris and the raised rim can be completely eliminated and the depth of crater can be reduced. Notable results show that the residual stress of the mitigation site after treatment will reduce two-thirds of the original stress. Finally, the elimination and the controlling mechanism of secondary treatment on the debris and raised rim, as well as the reasons for changing the profile and stress are analyzed. The results can provide a reference for the optimization treatment of mitigation sites by CO₂ laser secondary treatment.

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Particles inside electrolytes with ion-specific interactions, their effective charge distributions and effective interactions

丁茗楠, 梁逸浩, 邢向军

2016 (10): 108201-108201. doi: 10.1088/1674-1056/25/10/108201

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In this work, we explore the statistical physics of colloidal particles that interact with electrolytes via ion-specific interactions. Firstly we study particles interacting weakly with electrolyte using linear response theory. We find that the mean potential around a particle is linearly determined by the effective charge distribution of the particle, which depends both on the bare charge distribution and on ion-specific interactions. We also discuss the effective interaction between two such particles and show that, in the far field regime, it is bilinear in the effective charge distributions of two particles. We subsequently generalize the above results to the more complicated case where particles interact strongly with the electrolyte. Our results indicate that in order to understand the statistical physics of non-dilute electrolytes, both ion-specific interactions and ionic correlations have to be addressed in a single unified and consistent framework.

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Hydrodynamics of passing-over motion during binary droplet collision in shear flow

王程遥, 张程宾, 黄庠永, 刘向东, 陈永平

2016 (10): 108202-108202. doi: 10.1088/1674-1056/25/10/108202

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A combined experimental and numerical study is undertaken to investigate the hydrodynamic characteristics of single-phase droplet collision in a shear flow. The passing-over motion of interactive droplets is observed, and the underlying hydrodynamic mechanisms are elucidated by the analysis of the motion trajectory, transient droplet deformation and detailed hydrodynamic information (e.g., pressure and flow fields). The results indicate that the hydrodynamic interaction process under shear could be divided into three stages: approaching, colliding, and separating. With the increasing confinement, the interaction time for the passing-over process is shorter and the droplet processes one higher curvature tip and more stretched profile. Furthermore, the lateral separation Δy/R₁ exhibits larger decrease in the approaching stage and the thickness of the lubrication film is decreased during the interaction. As the initial lateral separation increases, the maximum trajectory shift by the collision interaction is getting smaller. During the collision between two droplets with different sizes, the amplitude of the deformation oscillation of the larger droplet is decreased by reducing the size ratio of the smaller droplet to the bigger one.

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Mode analysis and design of 0.3-THz Clinotron

李爽, 王建国, 王光强, 曾鹏, 王东阳

2016 (10): 108401-108401. doi: 10.1088/1674-1056/25/10/108401

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To develop a high-power continuous-wave terahertz source, a Clinotron operating at 0.3 THz is investigated. Based on the analyses of field distribution and coupling impedance, the dispersion characteristic of a rectangular resonator is preliminarily studied. The effective way to select fundamental mode to interact with the electron beam is especially studied. Finally, the structure is optimized by particle-in-cell simulation, and the problems of manufacture tolerance, current density threshold, and heat dissipation during Clinotron's operation are also discussed. The optimum device can work with a good performance under the conditions of 8 kV and 60 mA. With the generation of signal frequency at 315.89 GHz and output power at 12 W on average, this device shows great prospects in the application of terahertz waves.

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Physical modeling of direct current and radio frequency characteristics for InP-based InAlAs/InGaAs HEMTs

孙树祥, 吉慧芳, 姚会娟, 李胜, 金智, 丁芃, 钟英辉

2016 (10): 108501-108501. doi: 10.1088/1674-1056/25/10/108501

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Direct current (DC) and radio frequency (RF) performances of InP-based high electron mobility transistors (HEMTs) are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shockley-Read-Hall recombination, Auger recombination, radiative recombination, density gradient model and high field-dependent mobility are used to characterize the devices. The simulated results and measured results about DC and RF performances are compared, showing that they are well matched. However, the slight differences in channel current and pinch-off voltage may be accounted for by the surface defects resulting from oxidized InAlAs material in the gate-recess region. Moreover, the simulated frequency characteristics can be extrapolated beyond the test equipment limitation of 40 GHz, which gives a more accurate maximum oscillation frequency (f_max) of 385 GHz.

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Characteristics of cylindrical surrounding-gate GaAs_xSb_1-x/In_yGa_1-yAs heterojunction tunneling field-effect transistors

关云鹤, 李尊朝, 骆东旭, 孟庆之, 张也非

2016 (10): 108502-108502. doi: 10.1088/1674-1056/25/10/108502

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A III-V heterojunction tunneling field-effect transistor (TFET) can enhance the on-state current effectively, and GaAs_xSb_1-x/In_yGa_1-yAs heterojunction exhibits better performance with the adjustable band alignment by modulating the alloy composition. In this paper, the performance of the cylindrical surrounding-gate GaAs_xSb_1-x/In_yGa_1-yAs heterojunction TFET with gate-drain underlap is investigated by numerical simulation. We validate that reducing drain doping concentration and increasing gate-drain underlap could be effective ways to reduce the off-state current and subthreshold swing (SS), while increasing source doping concentration and adjusting the composition of GaAs_xSb_1-x/In_yGa_1-yAs can improve the on-state current. In addition, the resonant TFET based on GaAs_xSb_1-x/In_yGa_1-yAs is also studied, and the result shows that the minimum and average of SS reach 11 mV/decade and 20 mV/decade for five decades of drain current, respectively, and is much superior to the conventional TFET.

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A two-dimensional analytical modeling for channel potential and threshold voltage of short channel triple material symmetrical gate Stack (TMGS) DG-MOSFET

Shweta Tripathi

2016 (10): 108503-108503. doi: 10.1088/1674-1056/25/10/108503

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In the present work, a two-dimensional(2D) analytical framework of triple material symmetrical gate stack (TMGS) DG-MOSFET is presented in order to subdue the short channel effects. A lightly doped channel along with triple material gate having different work functions and symmetrical gate stack structure, showcases substantial betterment in quashing short channel effects to a good extent. The device functioning amends in terms of improved exemption to threshold voltage roll-off, thereby suppressing the short channel effects. The encroachments of respective device arguments on the threshold voltage of the proposed structure are examined in detail. The significant outcomes are compared with the numerical simulation data obtained by using two-dimensional (2D) ATLAS^TM device simulator to affirm and formalize the proposed device structure.

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Photoresponse and trap characteristics of transparent AZO-gated AlGaN/GaN HEMT

王冲, 赵梦荻, 何云龙, 郑雪峰, 张坤, 魏晓晓, 毛维, 马晓华, 张进成, 郝跃

2016 (10): 108504-108504. doi: 10.1088/1674-1056/25/10/108504

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AZO-gated and Ni/Au-gated AlGaN/GaN HEMTs are fabricated successfully, and an excellent transparency of AZO-gated electrode is achieved. After a negative gate bias stress acts on two kinds of the devices, their photoresponse characteristics are investigated by using laser sources with different wavelengths. The effect of photoresponse on AZO-gated electrode device is more obvious than on Ni/Au-gated electrodes device. The electrons are trapped in the AlGaN barrier of AZO-gated HEMT after it has experienced negative gate bias stress, and then the electrons can be excited effectively after it has been illuminated by the light with certain wavelengths. Furthermore, the trap state density D_T and the time constant τ_T of the AZO-gated Schottky contact are extracted by fitting the measured parallel conductance in a frequency range from 10 kHz to 10 MHz. The constants of the trap range from about 0.35 μs to 20.35 μs, and the trap state density increased from 1.93×10¹³ eV^-1·cm^-2 at an energy of 0.33 eV to 3.07×10¹¹ eV^-1·cm^-2 at an energy of 0.40 eV. Moreover, the capacitance and conductance measurements are used to characterize the trapping effects under different illumination conditions in AZO-gated HEMTs. Reduced deep trap states' density is confirmed under the illumination of short wavelength light.

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Surface treatment on polyethylenimine interlayer to improve inverted OLED performance

魏昌庭, 庄锦勇, 陈雅丽, 张东煜, 苏文明, 崔铮

2016 (10): 108505-108505. doi: 10.1088/1674-1056/25/10/108505

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Polyethylenimine (PEI) interlayer rinsing with different solvents for inverted organic light emitting diodes (OLEDs) is systematically studied in this paper. In comparison with the pristine one, the maximum current efficiency (CE_max) and power efficiency (PE_max) are enhanced by 21% and 22% for the device rinsing by ethylene glycol monomethyl ether (EEA). Little effect is found on the work function of the PEI interlayer rinsed by deionized water (DI), ethanol (EtOH), and EEA. On the other hand, the surface morphologies of PEI through different solvent treatments are quite different. Our results indicates that the surface morphology is the key to improving the device performance for IOLED as the work function of PEI keeps stable.

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Optical nuclear spin polarization in quantum dots

李爱仙, 段素青, 张伟

2016 (10): 108506-108506. doi: 10.1088/1674-1056/25/10/108506

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Hyperfine interaction between electron spin and randomly oriented nuclear spins is a key issue of electron coherence for quantum information/computation. We propose an efficient way to establish high polarization of nuclear spins and reduce the intrinsic nuclear spin fluctuations. Here, we polarize the nuclear spins in semiconductor quantum dot (QD) by the coherent population trapping (CPT) and the electric dipole spin resonance (EDSR) induced by optical fields and ac electric fields. By tuning the optical fields, we can obtain a powerful cooling background based on CPT for nuclear spin polarization. The EDSR can enhance the spin flip-flop rate which may increase the cooling efficiency. With the help of CPT and EDSR, an enhancement of 1300 times of the electron coherence time can be obtained after a 10-ns preparation time.

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Ultra-compact terahertz switch with graphene ring resonators

孙建忠, 章乐, 高飞

2016 (10): 108701-108701. doi: 10.1088/1674-1056/25/10/108701

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We propose and numerically demonstrate a compact terahertz wave switch which is composed of two graphene waveguides and three graphene ring resonators. Changing the bias voltage of the Fermi level in the center graphene ring, the resonant mode can be tuned when the plasmon waves in the waveguides and rings are coupled. We theoretically explain their mechanisms as being due to bias voltage change induced carrier density of graphene modification and the coupling coefficients of graphene plasmon effect after carrier density change, respectively. The mechanism of such a terahertz wave switch is further theoretically analyzed and numerically investigated with the aid of the finite element method. With an appropriate design, the proposed device offers the opportunity to ‘tune’ the terahertz wave ON-OFF with an ultra-fast, high extinction ratio and compact size. This structure has the potential applications in terahertz wave integrated circuits.

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Elemental x-ray imaging using Zernike phase contrast

邵其刚, 陈健, Faiz Wali, 鲍园, 王志立, 朱佩平, 田扬超, 高昆

2016 (10): 108702-108702. doi: 10.1088/1674-1056/25/10/108702

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We develop an element-specific x-ray microscopy method by using Zernike phase contrast imaging near absorption edges, where a real part of refractive index changes abruptly. In this method two phase contrast images are subtracted to obtain the target element: one is at the absorption edge of the target element and the other is near the absorption edge. The x-ray exposure required by this method is expected to be significantly lower than that of conventional absorption-based x-ray elemental imaging methods. Numerical calculations confirm the advantages of this highly efficient imaging method.

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Comparision between Ga- and N-polarity InGaN solar cells with gradient-In-composition intrinsic layers

鲁麟, 李明潮, 吕琛, 高文根, 江明, 许福军, 陈其工

2016 (10): 108801-108801. doi: 10.1088/1674-1056/25/10/108801

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Performances of Ga- and N-polarity solar cells (SCs) adopting gradient-In-composition intrinsic layer (IL) are compared. It is found the gradient ILs can greatly weaken the negative influence from the polarization effects for the Ga- polarity case, and the highest conversion efficiency (η) of 2.18% can be obtained in the structure with a linear increase of In composition in the IL from bottom to top. This is mainly attributed to the adsorptions of more photons caused by the higher In composition in the IL closer to the p-GaN window layer. In contrast, for the N-polarity case, the SC structure with an InGaN IL adopting fixed In composition prevails over the ones adopting the gradient-In-composition IL, where the highest η of 9.28% can be obtained at x of 0.62. N-polarity SC structures are proven to have greater potential preparations in high-efficient InGaN SCs.

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Device simulation of lead-free CH₃NH₃SnI₃ perovskite solar cells with high efficiency

杜会静, 王韦超, 朱键卓

2016 (10): 108802-108802. doi: 10.1088/1674-1056/25/10/108802

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The lead-free perovskite solar cells (PSCs) have drawn a great deal of research interest due to the Pb toxicity of the lead halide perovskite. CH₃NH₃SnI₃ is a viable alternative to CH₃NH₃PbX₃, because it has a narrower band gap of 1.3 eV and a wider visible absorption spectrum than the lead halide perovskite. The progress of fabricating tin iodide PSCs with good stability has stimulated the studies of these CH₃NH₃SnI₃ based cells greatly. In the paper, we study the influences of various parameters on the solar cell performance through theoretical analysis and device simulation. It is found in the simulation that the solar cell performance can be improved to some extent by adjusting the doping concentration of the perovskite absorption layer and the electron affinity of the buffer and HTM, while the reduction of the defect density of the perovskite absorption layer significantly improves the cell performance. By further optimizing the parameters of the doping concentration (1.3×10¹⁶ cm^-3) and the defect density (1×10¹⁵ cm^-3) of perovskite absorption layer, and the electron affinity of buffer (4.0 eV) and HTM (2.6 eV), we finally obtain some encouraging results of the J_sc of 31.59 mA/cm², V_oc of 0.92 V, FF of 79.99%, and PCE of 23.36%. The results show that the lead-free CH₃NH₃SnI₃ PSC is a potential environmentally friendly solar cell with high efficiency. Improving the Sn²⁺ stability and reducing the defect density of CH₃NH₃SnI₃ are key issues for the future research, which can be solved by improving the fabrication and encapsulation process of the cell.

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Pedestrian choice behavior analysis and simulation of vertical walking facilities in transfer station

李永行, 贾洪飞, 李军, 周亚楠, 原志路, 李延忠

2016 (10): 108901-108901. doi: 10.1088/1674-1056/25/10/108901

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Considering the interlayer height, luggage, the difference between queuing pedestrians, and walking speed, the pedestrian choice model of vertical walking facilities is established based on a support vector machine. This model is verified with the pedestrian flow data of Changchun light-rail transfer station and Beijing Xizhimen transfer station. Adding the pedestrian choice model of vertical walking facilities into the pedestrian simulation model which is based on cellular automata, the pedestrian choice behavior is simulated. In the simulation, the effects of the dynamic influence factors are analyzed. To reduce the conflicts between pedestrians in opposite directions, the layout of vertical walking facilities is improved. The simulations indicate that the improved layout of vertical walking facilities can improve the efficiency of pedestrians passing.

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A new cellular automata model of traffic flow with negative exponential weighted look-ahead potential

马骁, 郑伟范, 江宝山, 张继业

2016 (10): 108902-108902. doi: 10.1088/1674-1056/25/10/108902

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With the development of traffic systems, some issues such as traffic jams become more and more serious. Efficient traffic flow theory is needed to guide the overall controlling, organizing and management of traffic systems. On the basis of the cellular automata model and the traffic flow model with look-ahead potential, a new cellular automata traffic flow model with negative exponential weighted look-ahead potential is presented in this paper. By introducing the negative exponential weighting coefficient into the look-ahead potential and endowing the potential of vehicles closer to the driver with a greater coefficient, the modeling process is more suitable for the driver's random decision-making process which is based on the traffic environment that the driver is facing. The fundamental diagrams for different weighting parameters are obtained by using numerical simulations which show that the negative exponential weighting coefficient has an obvious effect on high density traffic flux. The complex high density non-linear traffic behavior is also reproduced by numerical simulations.

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Asymmetric and symmetric meta-correlations in financial markets

李晓辉, 沈翔瀛, 黄吉平

2016 (10): 108903-108903. doi: 10.1088/1674-1056/25/10/108903

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In financial markets, the relation between fluctuations of stock prices and trading behaviors is complex. It is intriguing to quantify this kind of meta-correlation between market fluctuations and the synchronous behaviors. We refine the theoretical index leverage model proposed by Reigneron et al., to exactly quantify the meta-correlation under various levels of price fluctuations [Reigneron P A, Allez R and Bouchaud J P 2011 Physica A 390 3026]. The characteristics of meta-correlations in times of market losses, are found to be significantly different in Chinese and American financial markets. In addition, unlike the asymmetric results at the daily scale, the correlation behaviors are found to be symmetric at the high-frequency scale.

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Subtle role of latency for information diffusion in online social networks

熊菲, 王夕萌, 程军军

2016 (10): 108904-108904. doi: 10.1088/1674-1056/25/10/108904

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Information diffusion in online social networks is induced by the event of forwarding information for users, and latency exists widely in user spreading behaviors. Little work has been done to reveal the effect of latency on the diffusion process. In this paper, we propose a propagation model in which nodes may suspend their spreading actions for a waiting period of stochastic length. These latent nodes may recover their activity again. Meanwhile, the mechanism of forwarding information is also introduced into the diffusion model. Mean-field analysis and numerical simulations indicate that our model has three nontrivial results. First, the spreading threshold does not correlate with latency in neither homogeneous nor heterogeneous networks, but depends on the spreading and refractory parameter. Furthermore, latency affects the diffusion process and changes the infection scale. A large or small latency parameter leads to a larger final diffusion extent, but the intrinsic dynamics is different. Large latency implies forwarding information rapidly, while small latency prevents nodes from dropping out of interactions. In addition, the betweenness is a better descriptor to identify influential nodes in the model with latency, compared with the coreness and degree. These results are helpful in understanding some collective phenomena of the diffusion process and taking measures to restrain a rumor in social networks.

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