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  • Discrete element crowd model for pedestrian evacuation through an exit

    Peng Lin(林鹏), Jian Ma(马剑), Siuming Lo(卢兆明)
    Chin. Phys. B 2016, 25 (3): 034501
    A series of accidents caused by crowds within the last decades evoked a lot of scientific interest in modeling the movement of pedestrian crowds. Based on the discrete element method, a granular dynamic model, in which the human body is simplified as a self-driven sphere, is proposed to simulate the...

     
  • Band gap anomaly and topological properties in lead chalcogenides

    Simin Nie(聂思敏), Xiao Yan Xu(许霄琰), Gang Xu(徐刚), Zhong Fang(方忠)
    Chin. Phys. B 2016, 25 (3): 037311
    Band gap anomaly is a well-known issue in lead chalcogenides PbX (X=S, Se, Te, Po). Combining ab initio calculations and tight-binding (TB) method, we have studied the band evolution in PbX, and found that the band gap anomaly in PbTe is mainly related to the high on-site energy of Te 5s orbital and...

     
  • High-pressure Raman study of solid hydrogen up to 300 GPa

    Xiaoli Huang(黄晓丽), Fangfei Li(李芳菲), Yanping Huang(黄艳萍), Gang Wu(吴刚), Xin Li(李鑫), Qiang Zhou(周强), Bingbing Liu(刘冰冰), Tian Cui(崔田)
    Chin. Phys. B 2016, 25 (3): 037401
    The high-pressure behavior of solid hydrogen has been investigated by in situ Raman spectroscopy upon compression to 300 GPa at ambient temperature. The hydrogen vibron frequency begins to decrease after it initially increases with pressure up to 38 GPa. This softening behavior suggests the weakenin...

     
Chin. Phys. B  
  Chin. Phys. B--2016, Vol.25, No.3
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TOPICAL REVIEW—Magnetism, magnetic materials, and interdisciplinary research

Review of magnetic properties and magnetocaloric effect in the intermetallic compounds of rare earth with low boiling point metals

Ling-Wei Li(李领伟)
Chin. Phys. B, 2016, 25 (3): 037502 doi: 10.1088/1674-1056/25/3/037502
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The magnetocaloric effect (MCE) in many rare earth (RE) based intermetallic compounds has been extensively investigated during the last two decades, not only due to their potential applications for magnetic refrigeration but also for better understanding of the fundamental problems of the materials. This paper reviews our recent progress on studying the magnetic properties and MCE in some binary or ternary intermetallic compounds of RE with low boiling point metal(s) (Zn, Mg, and Cd). Some of them exhibit promising MCE properties, which make them attractive for low temperature magnetic refrigeration. Characteristics of the magnetic transition, origin of large MCE, as well as the potential application of these compounds are thoroughly discussed. Additionally, a brief review of the magnetic and magnetocaloric properties in the quaternary rare earth nickel boroncarbides RENi2B2C superconductors is also presented.

GENERAL

Application of asymptotic iteration method to a deformed well problem

Hakan Ciftci, H F Kisoglu
Chin. Phys. B, 2016, 25 (3): 030201 doi: 10.1088/1674-1056/25/3/030201
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The asymptotic iteration method (AIM) is used to obtain the quasi-exact solutions of the Schrödinger equation with a deformed well potential. For arbitrary potential parameters, a numerical aspect of AIM is also applied to obtain highly accurate energy eigenvalues. Additionally, the perturbation expansion, based on the AIM approach, is utilized to obtain simple analytic expressions for the energy eigenvalues.

New variable separation solutions for the generalized nonlinear diffusion equations

Fei-Yu Ji(吉飞宇), Shun-Li Zhang(张顺利)
Chin. Phys. B, 2016, 25 (3): 030202 doi: 10.1088/1674-1056/25/3/030202
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The functionally generalized variable separation of the generalized nonlinear diffusion equations ut=A(u,ux)uxx+ B(u,ux) is studied by using the conditional Lie-Bäcklund symmetry method. The variant forms of the considered equations, which admit the corresponding conditional Lie-Bäcklund symmetries, are characterized. To construct functionally generalized separable solutions, several concrete examples defined on the exponential and trigonometric invariant subspaces are provided.

Bright and dark soliton solutions for some nonlinear fractional differential equations

Ozkan Guner, Ahmet Bekir
Chin. Phys. B, 2016, 25 (3): 030203 doi: 10.1088/1674-1056/25/3/030203
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In this work, we propose a new approach, namely ansatz method, for solving fractional differential equations based on a fractional complex transform and apply it to the nonlinear partial space-time fractional modified Benjamin-Bona-Mahoney (mBBM) equation, the time fractional mKdV equation and the nonlinear fractional Zoomeron equation which gives rise to some new exact solutions. The physical parameters in the soliton solutions: amplitude, inverse width, free parameters and velocity are obtained as functions of the dependent model coefficients. This method is suitable and more powerful for solving other kinds of nonlinear fractional PDEs arising in mathematical physics. Since the fractional derivatives are described in the modified Riemann-Liouville sense.

Geometric global quantum discord of two-qubit states

Yunlong Xiao(肖运龙), Tao Li(李陶), Shao-Ming Fei(费少明), Naihuan Jing(景乃桓), Zhi-Xi Wang(王志玺), Xianqing Li-Jost(李先清)
Chin. Phys. B, 2016, 25 (3): 030301 doi: 10.1088/1674-1056/25/3/030301
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We consider the geometric global quantum discord (GGQD) of two-qubit systems. By analyzing the symmetry of geometric global quantum discord we give an approach for deriving analytical formulae of the extremum problem which lies at the core of computing the GGQD for arbitrary two-qubit states. Furthermore, formulae of GGQD of arbitrary two-qubit states and some concrete examples are presented.

Hybrid entanglement concentration assisted with single coherent state

Rui Guo(郭锐), Lan Zhou(周澜), Shi-Pu Gu(顾世浦),Xing-Fu Wang(王兴福), Yu-Bo Sheng(盛宇波)
Chin. Phys. B, 2016, 25 (3): 030302 doi: 10.1088/1674-1056/25/3/030302
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Hybrid entangled state (HES) is a new type of entanglement, which combines the advantages of an entangled polarization state and an entangled coherent state. HES is widely discussed in the applications of quantum communication and computation. In this paper, we propose three entanglement concentration protocols (ECPs) for Bell-type HES, W-type HES, and cluster-type HES, respectively. After performing these ECPs, we can obtain the maximally entangled HES with some success probability. All the ECPs exploit the single coherent state to complete the concentration. These protocols are based on the linear optics, which are feasible in future experiments.

Entanglement detection in the mixed-spin Ising-XY model

Hamid Arian Zad
Chin. Phys. B, 2016, 25 (3): 030303 doi: 10.1088/1674-1056/25/3/030303
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In the present work, we initially verify anisotropy effect on the heat capacity of a mixed-three-spin (1/2,1,1/2) system (where spins (1/2,1/2) have XY interaction and spins (1,1/2) have Ising interaction together) at finite temperatures, then, the pairwise entanglement for spins (1/2,1/2), by means of negativity (as a measure of entanglement) as a function of the temperature T, homogeneous magnetic field B, and anisotropy parameter γ is investigated. In addition, we show that one can find magnetic phase transition points for the spins (1/2,1/2) at finite temperatures and understand properly their behavior with respect to the magnetic field and the anisotropy parameter, via the negativity function. An interval of the magnetic field from the negativity diagram of the spins (1/2,1/2) is presented in which quantum phase transition occurs for the tripartite mixed-three-spin system. Finally, some new interesting entanglement witnesses are introduced by using non-degenerate perturbation theory for the mixed-three-spin system.

Fidelity spectrum: A tool to probe the property of a quantum phase

Wing Chi Yu, Shi-Jian Gu
Chin. Phys. B, 2016, 25 (3): 030501 doi: 10.1088/1674-1056/25/3/030501
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Fidelity measures the similarity between two states and is widely adapted by the condensed matter community as a probe of quantum phase transitions in many-body systems. Despite its success in witnessing quantum critical points, information about the fine structure of a quantum phase one can get from this approach is still limited. Here, we proposed a scheme called fidelity spectrum. By studying the fidelity spectrum, one can obtain information about the characteristics of a phase. In particular, we investigated the spectra in the one-dimensional transverse-field Ising model and the two-dimensional Kitaev model on a honeycomb lattice. It was found that the spectra have qualitative differences in the critical and non-critical regions of the two models. From the distributions of them, the dominating k modes in a particular phase could also be captured.

Multi-valued responses and dynamic stability of a nonlinear vibro-impact system with a unilateral non-zero offset barrier

Wei Xu(徐伟), Dong-Mei Huang(黄冬梅), Wen-Xian Xie(谢文贤)
Chin. Phys. B, 2016, 25 (3): 030502 doi: 10.1088/1674-1056/25/3/030502
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In this paper, multi-valued responses and dynamic properties of a nonlinear vibro-impact system with a unilateral nonzero offset barrier are studied. Based on the Krylov-Bogoliubov averaging method and Zhuravlev non-smooth transformation, the frequency response, stability conditions, and the equation of backbone curve are derived. Results show that in some conditions impact system may have two or four steady-state solutions, which are interesting and not mentioned for a vibro-impact system with the existence of frequency island phenomena. Then, the classification of the steady-state solutions is discussed, and it is shown that the nontrivial steady-state solutions may lose stability by saddle node bifurcation and Hopf bifurcation. Furthermore, a criterion for avoiding the jump phenomenon is derived and verified. Lastly, it is found that the distance between the system's static equilibrium position and the barrier can lead to jump phenomenon under hardening type of nonlinearity stiffness.

Hysteresis-induced bifurcation and chaos in a magneto-rheological suspension system under external excitation

Hailong Zhang(张海龙), Enrong Wang(王恩荣), Fuhong Min(闵富红), Ning Zhang(张宁)
Chin. Phys. B, 2016, 25 (3): 030503 doi: 10.1088/1674-1056/25/3/030503
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The magneto-rheological damper (MRD) is a promising device used in vehicle semi-active suspension systems, for its continuous adjustable damping output. However, the innate nonlinear hysteresis characteristic of MRD may cause the nonlinear behaviors. In this work, a two-degree-of-freedom (2-DOF) MR suspension system was established first, by employing the modified Bouc-Wen force-velocity (F-v) hysteretic model. The nonlinear dynamic response of the system was investigated under the external excitation of single-frequency harmonic and bandwidth-limited stochastic road surface. The largest Lyapunov exponent (LLE) was used to detect the chaotic area of the frequency and amplitude of harmonic excitation, and the bifurcation diagrams, time histories, phase portraits, and power spectrum density (PSD) diagrams were used to reveal the dynamic evolution process in detail. Moreover, the LLE and Kolmogorov entropy (K entropy) were used to identify whether the system response was random or chaotic under stochastic road surface. The results demonstrated that the complex dynamical behaviors occur under different external excitation conditions. The oscillating mechanism of alternating periodic oscillations, quasi-periodic oscillations, and chaotic oscillations was observed in detail. The chaotic regions revealed that chaotic motions may appear in conditions of mid-low frequency and large amplitude, as well as small amplitude and all frequency. The obtained parameter regions where the chaotic motions may appear are useful for design of structural parameters of the vibration isolation, and the optimization of control strategy for MR suspension system.

Empirical investigation of topological and weighted properties of a bus transport network from China

Shu-Min Feng(冯树民), Bao-Yu Hu(胡宝雨), Cen Nie(聂涔), Xiang-Hao Shen(申翔浩), Yu-Sheng Ci(慈玉生)
Chin. Phys. B, 2016, 25 (3): 030504 doi: 10.1088/1674-1056/25/3/030504
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Many bus transport networks (BTNs) have evolved into directed networks. A new representation model for BTNs is proposed, called directed-space P. The bus transport network of Harbin (BTN-H) is described as a directed and weighted complex network by the proposed representation model and by giving each node weights. The topological and weighted properties are revealed in detail. In-degree and out-degree distributions, in-weight and out-weight distributions are presented as an exponential law, respectively. There is a strong relation between in-weight and in-degree (also between out-weight and out-degree), which can be fitted by a power function. Degree-degree and weight-weight correlations are investigated to reveal that BTN-H has a disassortative behavior as the nodes have relatively high degree (or weight). The disparity distributions of out-degree and in-degree follow an approximate power-law. Besides, the node degree shows a near linear increase with the number of routes that connect to the corresponding station. These properties revealed in this paper can help public transport planners to analyze the status quo of the BTN in nature.

STED microscopy based on axially symmetric polarized vortex beams

Zhehai Zhou(周哲海), Lianqing Zhu(祝连庆)
Chin. Phys. B, 2016, 25 (3): 030701 doi: 10.1088/1674-1056/25/3/030701
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A stimulated emission depletion (STED) microscopy scheme using axially symmetric polarized vortex beams is proposed based on unique focusing properties of such kinds of beams. The concept of axially symmetric polarized vortex beams is first introduced, and the basic principle about the scheme is described. Simulation results for several typical beams are then shown, including radially polarized vortex beams, azimuthally polarized vortex beams, and high-order axially symmetric polarized vortex beams. The results indicate that sharper doughnut spots and thus higher resolutions can be achieved, showing more flexibility than previous schemes based on flexible modulation of both phase and polarization for incident beams.
RAPID COMMUNICATION

Doping-driven orbital-selective Mott transition in multi-band Hubbard models with crystal field splitting

Yilin Wang(王义林), Li Huang(黄理), Liang Du(杜亮), Xi Dai(戴希)
Chin. Phys. B, 2016, 25 (3): 037103 doi: 10.1088/1674-1056/25/3/037103
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We have studied the doping-driven orbital-selective Mott transition in multi-band Hubbard models with equal band width in the presence of crystal field splitting. Crystal field splitting lifts one of the bands while leaving the others degenerate. We use single-site dynamical mean-field theory combined with continuous time quantum Monte Carlo impurity solver to calculate a phase diagram as a function of total electron filling N and crystal field splitting Δ. We find a large region of orbital-selective Mott phase in the phase diagram when the doping is large enough. Further analysis indicates that the large region of orbital-selective Mott phase is driven and stabilized by doping. Such models may account for the orbital-selective Mott transition in some doped realistic strongly correlated materials.

Velocity modulation of electron transport through a ferromagnetic silicene junction

Huai-Hua Shao(邵怀华), Dan Guo(郭丹), Ben-Liang Zhou(周本良), Guang-Hui Zhou(周光辉)
Chin. Phys. B, 2016, 25 (3): 037309 doi: 10.1088/1674-1056/25/3/037309
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We address velocity-modulation control of electron wave propagation in a normal/ferromagnetic/normal silicene junction with local variation of Fermi velocity, where the properties of charge, valley, and spin transport through the junction are investigated. By matching the wavefunctions at the normal-ferromagnetic interfaces, it is demonstrated that the variation of Fermi velocity in a small range can largely enhance the total conductance while keeping the current nearly fully valley-and spin-polarized. Further, the variation of Fermi velocity in ferromagnetic silicene has significant influence on the valley and spin polarization, especially in the low-energy regime. It may drastically reduce the high polarizations, which can be realized by adjusting the local application of a gate voltage and exchange field on the junction.

Band gap anomaly and topological properties in lead chalcogenides Hot!

Simin Nie(聂思敏), Xiao Yan Xu(许霄琰), Gang Xu(徐刚), Zhong Fang(方忠)
Chin. Phys. B, 2016, 25 (3): 037311 doi: 10.1088/1674-1056/25/3/037311
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Band gap anomaly is a well-known issue in lead chalcogenides PbX (X=S, Se, Te, Po). Combining ab initio calculations and tight-binding (TB) method, we have studied the band evolution in PbX, and found that the band gap anomaly in PbTe is mainly related to the high on-site energy of Te 5s orbital and the large s-p hopping originated from the irregular extended distribution of Te 5s electrons. Furthermore, our calculations show that PbPo is an indirect band gap (6.5 meV) semiconductor with band inversion at L point, which clearly indicates that PbPo is a topological crystalline insulator (TCI). The calculated mirror Chern number and surface states double confirm this conclusion.

High-pressure Raman study of solid hydrogen up to 300 GPa Hot!

Xiaoli Huang(黄晓丽), Fangfei Li(李芳菲), Yanping Huang(黄艳萍), Gang Wu(吴刚), Xin Li(李鑫), Qiang Zhou(周强), Bingbing Liu(刘冰冰), Tian Cui(崔田)
Chin. Phys. B, 2016, 25 (3): 037401 doi: 10.1088/1674-1056/25/3/037401
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The high-pressure behavior of solid hydrogen has been investigated by in situ Raman spectroscopy upon compression to 300 GPa at ambient temperature. The hydrogen vibron frequency begins to decrease after it initially increases with pressure up to 38 GPa. This softening behavior suggests the weakening of the intramolecular bond and the increased intermolecular interactions. Above 237 GPa, the vibron frequency softens very rapidly with pressure at a much higher rate than that of phase III, corresponding to transformation from phase III into phase IV. The phase transition sequence has been confirmed from phase I to phase III and then to phase IV at 208 and 237 GPa, respectively. Previous theoretical calculations lead to the proposal of an energetically favorable monoclinic C2/c structure for phase III and orthorhombic Pbcn structure for phase IV. Up to 304 GPa, solid hydrogen is not yet an alkali metal since the sample is still transparent.

ATOMIC AND MOLECULAR PHYSICS

Ab initio investigation of sulfur monofluoride and its singly charged cation and anion in their ground electronic state

Song Li(李松), Shan-Jun Chen(陈善俊), Yan Chen(陈艳), Peng Chen(陈朋)
Chin. Phys. B, 2016, 25 (3): 033101 doi: 10.1088/1674-1056/25/3/033101
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The SF radical and its singly charged cation and anion, SF+ and SF-, have been investigated on the MRCI/aug-cc-pVXZ (X = Q, 5, 6) levels of theory with Davidson correction. Both the core-valence correlation and the relativistic effect are considered. The extrapolating to the complete basis set (CBS) limit is adopted to remove the basis set truncation error. Geometrical parameters, potential energy curves (PECs), vibrational energy levels, spectroscopic constants, ionization potentials, and electron affinities of the ground electronic state for all these species are obtained. The information with respect to molecular characteristics of the SFn (n=-1, 0, +1) systems derived in this work will help to extend our knowledge and to guide further experimental or theoretical researches.

γ-and α-Ce phase diagram: First-principle calculation

Lin Zhang(张林), Ying-Hua Li(李英华), Xue-Mei Li(李雪梅), Zu-Gen Zhang(张祖根), Xiang-Ping Ye(叶想平), Ling-Cang Cai(蔡灵仓)
Chin. Phys. B, 2016, 25 (3): 033102 doi: 10.1088/1674-1056/25/3/033102
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Controversies about the phase diagram for the isostructural γα phase transition of cerium have long been standing out for several decades. To seek insight into the problems, high-precision equations of state (EOS) for γ-and α-cerium are constructed based on first-principle calculation. Versus previous works, the strong anharmonic effects of ion vibration and the variation of magnetism of γ-cerium are stressed. The new EOS generally agrees well with experimental data regarding thermodynamics, phase diagrams, and phase transitions. However, new EOS predicts that another part of phase boundary in pressure-temperature space may exist except for the commonly known boundary. In addition, the well-known critical point seems to be a critical point for γ-cerium to translate from a stable state to an unstable state.

Extreme ultraviolet and soft x-ray spectral lines in Rb XXIX

Indu Khatri, Arun Goyal, Sunny Aggarwal, A K Singh, Man Mohan
Chin. Phys. B, 2016, 25 (3): 033201 doi: 10.1088/1674-1056/25/3/033201
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An extensive theoretical set of atomic data for Rb XXIX in a wide range with L-shell electron excitations to the M-shell has been reported. We have computed energy levels for the lowest 113 fine structure levels of Rb XXIX. The fully relativistic multiconfigurational Dirac-Fock method (MCDF) within the framework of Dirac-Coulomb Hamiltonian taking quantum electrodynamics (QED) and Breit corrections into account has been adopted for calculations. Radiative data are reported for electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions from the ground level, although calculations have been performed for a much larger number of levels. To assess the accuracy of results, we performed analogous calculations using flexible atomic code (FAC). Comparisons are made with existing available results and a good agreement has been achieved. Most of the wavelengths calculated lie in the soft x-ray (SXR) region. Lifetimes for all 113 levels have also been provided for the first time. Additionally, we have provided the spectra for allowed transitions from n=2 to n= 3 within the x-ray region and also compared our SXR photon wavelengths with experimentally recognized wavelengths. We hope that our results will be beneficial in fusion plasma research and astrophysical applications.

Influence of the interaction volume on the kinetic energy resolution of a velocity map imaging spectrometer

Peng Zhang(张鹏), Zheng-Peng Feng(冯正鹏), Si-Qiang Luo(罗四强), Zhe Wang(王哲)
Chin. Phys. B, 2016, 25 (3): 033202 doi: 10.1088/1674-1056/25/3/033202
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We investigate the influence of the interaction volume on the energy resolution of a velocity map imaging spectrometer. The simulation results show that the axial interaction size has a significant influence on the resolution. This influence is increased for a higher kinetic energy. We further show that the radial interaction size has a minor influence on the energy resolution for the electron or ion with medium energy, but it is crucial for the resolution of the electron or ion with low kinetic energy. By tracing the flight trajectories we show how the electron or ion energy resolution is influenced by the interaction size.

Quantum and semiclassical studies on photodetachment cross sections of H- in a harmonic potential

Hai-Jun Zhao(赵海军), Wei-Long Liu(刘伟龙), Meng-Li Du(杜孟利)
Chin. Phys. B, 2016, 25 (3): 033203 doi: 10.1088/1674-1056/25/3/033203
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The photodetachment cross section of H- in a linear harmonic oscillator potential is investigated. This system provides a rare example that can be studied analytically by both quantum and semiclassical methods with some approximations. The formulas of the cross section for different laser polarization directions are explicitly derived by both the traditional quantum approach and closed-orbit theory. In the traditional quantum approach, we calculate the cross sections in coordinate representation and momentum representation, and get the same formulas. We compare the quantum formulas with closed-orbit theory formulas, and find that when the detachment electron energy is larger than 3/2ħω, where ω is the frequency of the oscillator potential, the quantum results are shown to be in good agreement with the semiclassical results.

Electron excitation from ground state to first excited state: Bohmian mechanics method

Yang Song(宋阳), Shuang Zhao(赵双), Fu-Ming Guo(郭福明), Yu-Jun Yang(杨玉军), Su-Yu Li(李苏宇)
Chin. Phys. B, 2016, 25 (3): 033204 doi: 10.1088/1674-1056/25/3/033204
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The excitation process of electrons from the ground state to the first excited state via the resonant laser pulse is investigated by the Bohmian mechanics method. It is found that the Bohmian particles far away from the nucleus are easier to be excited and are excited firstly, while the Bohmian particles in the ground state is subject to a strong quantum force at a certain moment, being excited to the first excited state instantaneously. A detailed analysis for one of the trajectories is made, and finally we present the space and energy distribution of 2000 Bohmian particles at several typical instants and analyze their dynamical process at these moments.

Accurate prediction of interference minima in linear molecular harmonic spectra by a modified two-center model

Xin Cui(崔鑫), Di-Yu Zhang(张頔玉), Gao Chen(陈高), Ji-Gen Chen(陈基根), Si-Liang Zeng(曾思良), Fu-Ming Guo(郭福明), Yu-Jun Yang(杨玉军)
Chin. Phys. B, 2016, 25 (3): 033205 doi: 10.1088/1674-1056/25/3/033205
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We demonstrate that the interference minima in the linear molecular harmonic spectra can be accurately predicted by a modified two-center model. Based on systematically investigating the interference minima in the linear molecular harmonic spectra by the strong-field approximation (SFA), it is found that the locations of the harmonic minima are related not only to the nuclear distance between the two main atoms contributing to the harmonic generation, but also to the symmetry of the molecular orbital. Therefore, we modify the initial phase difference between the double wave sources in the two-center model, and predict the harmonic minimum positions consistent with those simulated by SFA.

Production of projectile and target K-vacancy in near-symmetric collisions of 60-100 MeV Cu9+ ions with thin Zn target

Yipan Guo(郭义盼), Zhihu Yang(杨治虎), Shubin Du(杜树斌), Hongwei Chang(常宏伟), Qingliang Xia(夏清良), Qiumei Xu(徐秋梅)
Chin. Phys. B, 2016, 25 (3): 033401 doi: 10.1088/1674-1056/25/3/033401
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We report studies on both target and projectile K-shell ionization by collisions of Cu9+ ions on the thin Zn target in the energy range of 60-100 MeV. In this work, the relative ratio for the production of the target to projectile K-vacancy is measured. The result shows that it almost remains stable over this energy range and has good consistency with the predictions by vacancy transfer via the 2pσ-1sσ rotational coupling, which gives experimental evidence for K-vacancy sharing between two partners. Furthermore, the discussion for comparisons between the experimental ionization cross sections and the possible theoretical estimations is presented. These comparisons suggest that the experimental data agree well with those predicted by the Binary-Encounter approximation (BEA) model but are not in good agreement with the modified BEA calculations. It allows us to infer that the direct ionization (and/or excitation) is of importance to initial K-vacancy production before 2pσ-1sσ transitions in the present collision condition.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Spoof surface plasmon-based bandpass filter with extremely wide upper stopband

Xiaoyong Liu(刘小勇), Lei Zhu(祝雷), Yijun Feng(冯一军)
Chin. Phys. B, 2016, 25 (3): 034101 doi: 10.1088/1674-1056/25/3/034101
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We investigate the guiding modes of spoof surface plasmon polaritons (SPPs) on a symmetric ultra-thin plasmonic structure. From the analysis, we deduce the operating frequency region of the single-mode propagation. Based on this property, a spoof SPPs lowpass filter is then constituted in the microwave frequency. By introducing a transmission zero at the lower frequency band using a pair of stepped-impedance stubs, a wide passband filter is further realized. The proposed filter is fed by a transducer composed of a microstrip line with a flaring ground. The simulated results show that the presented filter has an extremely wide upper stopband in addition to excellent passband filtering characteristics such as low loss, wide band, and high square ratio. A prototype passband filter is also fabricated to validate the predicted performances. The proposed spoof-SPPs filter is believed to be very promising for other surface waveguide components in microwave and terahertz bands.

Theoretical studies on particle shape classification based on simultaneous small forward angle light scattering and aerodynamic sizing

Jin-Bi Zhang(张金碧), Lei Ding(丁蕾), Ying-Ping Wang(王颖萍), Li Zhang(张莉), Jin-Lei Wu(吴金雷), Hai-Yang Zheng(郑海洋), Li Fang(方黎)
Chin. Phys. B, 2016, 25 (3): 034201 doi: 10.1088/1674-1056/25/3/034201
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Particle shape contributes to understanding the physical and chemical processes of the atmosphere and better ascertaining the origins and chemical compositions of the particles. The particle shape can be classified by the aspect ratio, which can be estimated through the asymmetry factor measured with angularly resolved light scattering. An experimental method of obtaining the asymmetry factor based on simultaneous small forward angle light scattering and aerodynamic size measurements is described briefly. The near forward scattering intensity signals of three detectors in the azimuthal angles at 120° offset are calculated using the methods of T-matrix and discrete dipole approximation. Prolate spheroid particles with different aspect ratios are used as the shape models with the assumption that the symmetry axis is parallel to the flow axis and perpendicular to the incident light. The relations between the asymmetry factor and the optical size and aerodynamic size at various equivalent sizes, refractive indices, and mass densities are discussed in this paper. The numerically calculated results indicate that an elongated particle may be classified at diameter larger than 1.0 μm, and may not be distinguished from a sphere at diameter less than 0.5 μm. It is estimated that the lowest detected aspect ratio is around 1.5:1 in consideration of the experimental errors.

High-power electro-optic switch technology based on novel transparent ceramic

Xue-Jiao Zhang(张学娇), Qing Ye(叶青), Rong-Hui Qu(瞿荣辉), Hai-wen Cai(蔡海文)
Chin. Phys. B, 2016, 25 (3): 034202 doi: 10.1088/1674-1056/25/3/034202
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A novel high-power polarization-independent electro-optic switch technology based on a reciprocal structure Sagnac interferometer and a transparent quadratic electro-optic ceramic is proposed and analyzed theoretically and experimentally. The electro-optic ceramic is used as a phase retarder for the clockwise and counter-clockwise polarized light, and their polarization directions are adjusted to their orthogonal positions by using two half-wave plates. The output light then becomes polarization-independent with respect to the polarization direction of the input light. The switch characteristics, including splitter ratios and polarization states, are theoretically analyzed and simulated in detail by the matrix multiplication method. An experimental setup is built to verify the analysis and experimental results. A new component ceramic is used and a non-polarizing cube beam splitter (NPBS) replaces the beam splitter (BS) to lower the ON/OFF voltage to 305 V and improve the extinction ratio by 2 dB. Finally, the laser-induced damage threshold for the proposed switch is measured and discussed. It is believed that potential applications of this novel polarization-independent electro-optic switch technology will be wide, especially for ultrafast high-power laser systems.

Second-order interference of two independent and tunable single-mode continuous-wave lasers

Jianbin Liu(刘建彬) Dong Wei(卫栋), Hui Chen(陈辉), Yu Zhou(周宇), Huaibin Zheng(郑淮斌), Hong Gao(高宏), Fu-Li Li(李福利), Zhuo Xu(徐卓)
Chin. Phys. B, 2016, 25 (3): 034203 doi: 10.1088/1674-1056/25/3/034203
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The second-order temporal interference of two independent single-mode continuous-wave lasers is discussed by employing two-photon interference in Feynman's path integral theory. It is concluded that whether the second-order temporal interference pattern can or cannot be retrieved via two-photon coincidence counting rate is dependent on the resolution time of the detection system and the frequency difference between these two lasers. Two identical and tunable single-mode continuous-wave diode lasers are employed to verify the predictions. These studies are helpful to understand the physics of two-photon interference with photons of different spectra.

Electromagnetically induced transparency in a Zeeman-sublevels Λ-system of cold 87Rb atoms in free space

Xiaojun Jiang(蒋小军), Haichao Zhang(张海潮), Yuzhu Wang(王育竹)
Chin. Phys. B, 2016, 25 (3): 034204 doi: 10.1088/1674-1056/25/3/034204
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We report the experimental investigation of electromagnetically induced transparency (EIT) in a Zeeman-sublevels Λ-type system of cold 87Rb atoms in free space. We use the Zeeman substates of the hyperfine energy states 52 S1/2, F=2 and 52 P3/2, F'=2 of 87Rb D2 line to form a Λ-type EIT scheme. The EIT signal is obtained by scanning the probe light over 1 MHz in 4 ms with an 80 MHz arbitrary waveform generator. More than 97% transparency and 100 kHz EIT window are observed. This EIT scheme is suited for an application of pulsed coherent storage atom clock (Yan B, et al. 2009 Phys. Rev. A 79 063820).

Influence of Fano interference and incoherent processes on optical bistability in a four-level quantum dot nanostructure

Seyyed Hossein Asadpour, G Solookinejad, M Panahi, E Ahmadi Sangachin
Chin. Phys. B, 2016, 25 (3): 034205 doi: 10.1088/1674-1056/25/3/034205
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Role of Fano interference and incoherent pumping field on optical bistability in a four-level designed InGaN/GaN quantum dot nanostructure embedded in a unidirectional ring cavity are analyzed. It is found that intensity threshold of optical bistability can be manipulated by Fano interference. It is shown that incoherent pumping fields make the threshold of optical bistability behave differently by Fano interference. Moreover, in the presence of Fano interference the medium becomes phase-dependent. Therefore, the relative phase of applied fields can affect the behaviors of optical bistability and intensity threshold can be controlled easily.

Experimental study of electro-optical Q-switched pulsed Nd:YAG laser

A Maleki, M Kavosh Tehrani, H Saghafifar, M H Moghtader Dindarlu
Chin. Phys. B, 2016, 25 (3): 034206 doi: 10.1088/1674-1056/25/3/034206
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We report the specification of a compact and stable side diode-pumped Q-switched pulsed Nd:YAG laser. We experimentally study and compare the performance of the pulsed Nd:YAG laser in the free-running and Q-switched modes at different pulse repetition rates from 1 Hz to 100 Hz. The laser output energy is stabilized by using a special configuration of the optical resonator. In this laser, an unsymmetrical concave-concave resonator is used and this structure helps the mode volume to be nearly fixed when the pulse repetition rate is increased. According to the experimental results in the Q-switched operation, the laser output energy is nearly constant around 70 mJ with an FWHM pulse width of 7 ns at 100 Hz. The optical-to-optical conversion efficiency in the Q-switched regime is 17.5%.

Passively Q-switched dual-wavelength Yb:LSO laser based on tungsten disulphide saturable absorber

Jing-Hui Liu(刘京徽), Jin-Rong Tian(田金荣), He-Yang Guoyu(郭于鹤洋), Run-Qin Xu(徐润亲), Ke-Xuan Li(李克轩), Yan-Rong Song(宋晏蓉), Xin-Ping Zhang(张新平), Liang-Bi Su(苏良碧), Jun Xu(徐军)
Chin. Phys. B, 2016, 25 (3): 034207 doi: 10.1088/1674-1056/25/3/034207
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We demonstrate a passively Q-switched Yb:LSO laser based on tungsten disulphide (WS2) saturable absorber operating at 1034 nm and 1056 nm simultaneously. The saturable absorbers were fabricated by spin coating method. With low speed, the WS2 nanoplatelets embedded in polyvinyl alcohol could be coated on a BK7 glass substrate coated with high-refractive-index thin polymer. The shortest pulse width of 1.6 μs with a repetition rate of 76.9 kHz is obtained. As the pump power increases to 9 W, the maximum output power is measured to be 250 mW, corresponding to a single pulse energy of 3.25 μJ. To the best of our knowledge, this is the first time to obtain dual-wavelength Q-switched solid-state laser using few-layer WS2 nanoplatelets.

Theoretical analysis of the electromagnetic field inside an anomalous-dispersion microresonator under synthetical pump

Xin Xu(徐昕), Xiaohong Hu(胡晓鸿), Ye Feng(冯野), Yuanshan Liu(刘元山), Wei Zhang(张伟), Zhi Yang(杨直), Wei Zhao(赵卫), Yishan Wang(王屹山)
Chin. Phys. B, 2016, 25 (3): 034208 doi: 10.1088/1674-1056/25/3/034208
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We study the spatiotemporal evolution of the electromagnetic field inside a microresonator showing an anomalous dispersion at the pump wavelength by using the normalized Lugiato-Lefever equation. Unlike the traditional single continuous wave (CW) pumping, an additional pump source consisting of periodical pulse train with variable repetition rate is adopted. The influences of the microresonator properties and the pump parameters on the field evolution and the electromagnetic field profile are analyzed. The simulation results indicate that, in the anomalous dispersion regime, both increases of the input pulse amplitude and the repetition frequency can result in the field profiles consisting of multiple peaks. A series of equidistant pulses can also be obtained by increasing the CW pump power. In addition, we find that a large physical detuning between the pump laser carrier and the cavity resonance frequency also causes the splitting of the inside field.

Theoretical simulation of a novel birefringent photonic crystal fiber with surface plasmon resonance around 1300 nm

Duanming Li(李端明), Guiyao Zhou(周桂耀)
Chin. Phys. B, 2016, 25 (3): 034209 doi: 10.1088/1674-1056/25/3/034209
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In this paper, a novel birefringent photonic crystal fiber (PCF) with the silver-coated and liquid-filled air-holes along the vertical plane is designed. Simulation results show that the thickness of silver layer, the sizes of holes, and the refractive index of liquid strongly strengthen the gaps between two polarized directions. The surface plasmon resonance peak along y axis can be up to 675.8 dB/cm at 1.33 μm. The proposed PCF has important application in polarization devices, such as filters and beam splitters.

Wave propagation in beams with anti-symmetric piezoelectric shunting arrays

Sheng-Bing Chen(陈圣兵), Gang Wang(王刚)
Chin. Phys. B, 2016, 25 (3): 034301 doi: 10.1088/1674-1056/25/3/034301
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Piezoelectric shunting arrays are employed to control the wave propagation in flexible beams. Contrary to conventional symmetric configuration, a substrate beam with anti-symmetric shunting arrays is investigated by adapted transfer matrix method. Compared with symmetric scheme, the anti-symmetric one demonstrates some distinctive characteristics. Primarily, the longitudinal and flexural waves are coupled, so they are correlated and must be considered simultaneously. Moreover, the attenuation of flexural wave is much stronger in anti-symmetric scenario, while the longitudinal wave demonstrates the converse side. As a result, the anti-symmetric scheme can be utilized to improve the vibration isolation capability of shunting arrays. Finally, the theoretical analyses are validated by finite element simulations.

Discrete element crowd model for pedestrian evacuation through an exit Hot!

Peng Lin(林鹏), Jian Ma(马剑), Siuming Lo(卢兆明)
Chin. Phys. B, 2016, 25 (3): 034501 doi: 10.1088/1674-1056/25/3/034501
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A series of accidents caused by crowds within the last decades evoked a lot of scientific interest in modeling the movement of pedestrian crowds. Based on the discrete element method, a granular dynamic model, in which the human body is simplified as a self-driven sphere, is proposed to simulate the characteristics of crowd flow through an exit. In this model, the repulsive force among people is considered to have an anisotropic feature, and the physical contact force due to body deformation is quantified by the Hertz contact model. The movement of the human body is simulated by applying the second Newton's law. The crowd flow through an exit at different desired velocities is studied and simulation results indicated that crowd flow exhibits three distinct states, i.e., smooth state, transition state and phase separation state. In the simulation, the clogging phenomenon occurs more easily when the desired velocity is high and the exit may as a result be totally blocked at a desired velocity of 1.6 m/s or above, leading to faster-to-frozen effect.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Single-pinhole diffraction of few-cycle isolated attosecond pulses with a two-color field

Shaoyi Wang(王少义), Dan Han(韩丹), Kegong Dong(董克攻), Yuchi Wu(吴玉迟), Fang Tan(谭放), Bin Zhu(朱斌), Quanping Fan(范全平), Leifeng Cao(曹磊峰), Yuqiu Gu(谷渝秋)
Chin. Phys. B, 2016, 25 (3): 035201 doi: 10.1088/1674-1056/25/3/035201
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The spatio-temporal characterization of an isolated attosecond pulse is investigated theoretically in a two-color field. Our results show that a few-cycle isolated attosecond pulse with the center wavelength of 16 nm can be generated effectively by adding a weak controlling field. Using the split and delay units, the isolated attosecond pulse can be split to the two same ones, and then single-pinhole diffractive patterns of the two pulses with different delays can be achieved. The diffractive patterns depend severely on the periods of the attosecond pulses, which can be helpful to obtain temporal information of the coherent sources.

Spectral and ion emission features of laser-produced Sn and SnO2 plasmas

Hui Lan(兰慧), Xin-Bing Wang(王新兵), Du-Luo Zuo(左都罗)
Chin. Phys. B, 2016, 25 (3): 035202 doi: 10.1088/1674-1056/25/3/035202
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We have made a detailed comparison of the atomic and ionic debris, as well as the emission features of Sn and SnO2 plasmas under identical experimental conditions. Planar slabs of pure metal Sn and ceramic SnO2 are irradiated with 1.06 μm, 8 ns Nd:YAG laser pulses. Fast photography employing an intensified charge coupled device (ICCD), optical emission spectroscopy (OES), and optical time of flight emission spectroscopy are used as diagnostic tools. Our results show that the Sn plasma provides a higher extreme ultraviolet (EUV) conversion efficiency (CE) than the SnO2 plasma. However, the kinetic energies of Sn ions are relatively low compared with those of SnO2. OES studies show that the Sn plasma parameters (electron temperature and density) are lower compared to those of the SnO2 plasma. Furthermore, we also give the effects of the vacuum degree and the laser pulse energy on the plasma parameters.

Enhanced laser-induced plasma channels in air

Yanlei Zuo(左言磊), Xiaofeng Wei(魏晓峰), Kainan Zhou(周凯南), Xiaoming Zeng(曾小明),Jingqin Su(粟敬钦), Zhihong Jiao(焦志宏), Na Xie(谢娜), Zhaohui Wu(吴朝辉)
Chin. Phys. B, 2016, 25 (3): 035203 doi: 10.1088/1674-1056/25/3/035203
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Plasma is a significant medium in high-energy density physics since it can hardly be damaged. For some applications such as plasma based backward Raman amplification (BRA), uniform high-density and large-scale plasma channels are required. In the previous experiment, the plasma transverse diameter and density are 50-200 μm and 1-2×1019 cm-3, here we enhance them to 0.8 mm and 8×1019 cm-3, respectively. Moreover, the gradient plasma is investigated in our experiment. A proper plasma gradient can be obtained with suitable pulse energy and delay. The experimental results are useful for plasma physics and nonlinear optics.

Electric and plasma characteristics of RF discharge plasma actuation under varying pressures

Huimin Song(宋慧敏), Min Jia(贾敏), Di Jin(金迪), Wei Cui(崔巍), Yun Wu(吴云)
Chin. Phys. B, 2016, 25 (3): 035204 doi: 10.1088/1674-1056/25/3/035204
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The electric and plasma characteristics of RF discharge plasma actuation under varying pressure have been investigated experimentally. As the pressure increases, the shapes of charge-voltage Lissajous curves vary, and the discharge energy increases. The emission spectra show significant difference as the pressure varies. When the pressure is 1000 Pa, the electron temperature is estimated to be 4.139 eV, the electron density and the vibrational temperature of plasma are 4.71× 1011 cm-3 and 1.27 eV, respectively. The ratio of spectral lines I391.4peak/I380.5peak which describes the electron temperature hardly changes when the pressure varies between 5000-30000 Pa, while it increases remarkably with the pressure below 5000 Pa, indicating a transition from filamentary discharge to glow discharge. The characteristics of emission spectrum are obviously influenced by the loading power. With more loading power, both of the illumination and emission spectrum intensity increase at 10000 Pa. The pin-pin electrode RF discharge is arc-like at power higher than 33 W, which results in a macroscopic air temperature increase.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Theoretical analysis of the influence of flexoelectric effect on the defect site in nematic inversion walls

Gui-Li Zheng(郑桂丽), Hui Zhang(张辉), Wen-Jiang Ye(叶文江),Zhi-Dong Zhang(张志东), Hong-Wei Song(宋宏伟), Li Xuan(宣丽)
Chin. Phys. B, 2016, 25 (3): 036101 doi: 10.1088/1674-1056/25/3/036101
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Based on the experimental phenomena of flexoelectric response at defect sites in nematic inversion walls conducted by Kumar et al., we gave the theoretical analysis using the Frank elastic theory. When a direct-current electric field normal to the plane of the substrate is applied to the parallel aligned nematic liquid crystal cell with weak anchoring, the rotation of ± 1 defects in the narrow inversion walls can be exhibited. The free energy of liquid crystal molecules around the +1 and-1 defect sites in the nematic inversion walls under the electric field was formulated and the electric-field-driven structural changes at the defect site characterized by polar and azimuthal angles of the local director were simulated. The results reveal that the deviation of azimuthal angle induced by flexoelectric effect are consistent with the switching of extinction brushes at the +1 and-1 defects obtained in the experiment conducted by Kumar et al.

Size effect in the melting and freezing behaviors of Al/Ti core-shell nanoparticles using molecular dynamics simulations

Jin-Ping Zhang(张金平), Yang-Yang Zhang(张洋洋), Er-Ping Wang(王二萍), Cui-Ming Tang (唐翠明), Xin-Lu Cheng(程新路), Qiu-Hui Zhang(张秋慧)
Chin. Phys. B, 2016, 25 (3): 036102 doi: 10.1088/1674-1056/25/3/036102
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The thermal stability of Ti@Al core/shell nanoparticles with different sizes and components during continuous heating and cooling processes is examined by a molecular dynamics simulation with embedded atom method. The thermodynamic properties and structure evolution during continuous heating and cooling processes are investigated through the characterization of the potential energy, specific heat distribution, and radial distribution function (RDF). Our study shows that, for fixed Ti core size, the melting temperature decreases with Al shell thickness, while the crystallizing temperature and glass formation temperature increase with Al shell thickness. Diverse melting mechanisms have been discovered for different Ti core sized with fixed Al shell thickness nanoparticles. The melting temperature increases with the Ti core radius. The trend agrees well with the theoretical phase diagram of bimetallic nanoparticles. In addition, the glass phase formation of Al-Ti nanoparticles for the fast cooling rate of 12 K/ps, and the crystal phase formation for the low cooling rate of 0.15 K/ps. The icosahedron structure is formed in the frozen 4366 Al-Ti atoms for the low cooling rate.

Mechanism of floating body effect mitigation via cutting off source injection in a fully-depleted silicon-on-insulator technology

Pengcheng Huang(黄鹏程), Shuming Chen(陈书明), Jianjun Chen(陈建军)
Chin. Phys. B, 2016, 25 (3): 036103 doi: 10.1088/1674-1056/25/3/036103
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In this paper, the effect of floating body effect (FBE) on a single event transient generation mechanism in fully depleted (FD) silicon-on-insulator (SOI) technology is investigated using three-dimensional technology computer-aided design (3D-TCAD) numerical simulation. The results indicate that the main SET generation mechanism is not carrier drift/diffusion but floating body effect (FBE) whether for positive or negative channel metal oxide semiconductor (PMOS or NMOS). Two stacking layout designs mitigating FBE are investigated as well, and the results indicate that the in-line stacking (IS) layout can mitigate FBE completely and is area penalty saving compared with the conventional stacking layout.

Energetics of carbon and nitrogen impurities and their interactions with vacancy in vanadium

Juan Hua(华娟), Yue-Lin Liu(刘悦林), Heng-Shuai Li(李恒帅),Ming-Wen Zhao(赵明文), Xiang-Dong Liu(刘向东)
Chin. Phys. B, 2016, 25 (3): 036104 doi: 10.1088/1674-1056/25/3/036104
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We studied the energetic behaviors of interstitial and substitution carbon (C)/nitrogen (N) impurities as well as their interactions with the vacancy in vanadium by first-principles simulations. Both C and N impurities prefer the octahedral site (O-site). N exhibits a lower formation energy than C. Due to the hybridization between vanadium-d and N/C-p, the N-p states are located at the energy from-6.00 eV to-5.00 eV, which is much deeper than that from-5.00 eV to-3.00 eV for the C-p states. Two impurities in bulk vanadium, C-C, C-N, and N-N can be paired up at the two neighboring O-sites along the <111> direction and the binding energies of the pairs are 0.227 eV, 0.162 eV, and 0.201 eV, respectively. Further, we find that both C and N do not prefer to stay at the vacancy center and its vicinity, but occupy the O-site off the vacancy in the interstitial lattice in vanadium. The possible physical mechanism is that C/N in the O-site tends to form a carbide/nitride-like structure with its neighboring vanadium atoms, leading to the formation of the strong C/N-vanadium bonding containing a covalent component.

Density functional theory study of structural, electronic, and thermal properties of Pt, Pd, Rh, Ir, Os and PtPdX (X = Ir, Os, and Rh) alloys

Shabbir Ahmed, Muhammad Zafar, M Shakil, M A Choudhary
Chin. Phys. B, 2016, 25 (3): 036501 doi: 10.1088/1674-1056/25/3/036501
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The structural, electronic, mechanical, and thermal properties of Pt, Pd, Rh, Ir, Os metals and their alloys PtPdX (X = Ir, Os and Rh) are studied systematically using ab initio density functional theory. The groundstate properties such as lattice constant and bulk modulus are calculated to find the equilibrium atomic position for stable alloys. The electronic band structure and density of states are calculated to study the electronic behavior of metals on making their alloys. The electronic properties substantiate the metallic behavior for all studied materials. The firstprinciples density functional perturbation theory as implemented in quasi-harmonic approximation is used for the calculations of thermal properties. We have calculated the thermal properties such as the Debye temperature, vibrational energy, entropy and constant-volume specific heat. The calculated properties are compared with the previously reported experimental and theoretical data for metals and are found to be in good agreement. Calculated results for alloys could not be compared because there is no data available in the literature with such alloy composition.

Boron diffusion in bcc-Fe studied by first-principles calculations

Xianglong Li(李向龙), Ping Wu(吴平), Ruijie Yang(杨锐杰), Dan Yan(闫丹), Sen Chen(陈森), Shiping Zhang(张师平), Ning Chen(陈宁)
Chin. Phys. B, 2016, 25 (3): 036601 doi: 10.1088/1674-1056/25/3/036601
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The diffusion mechanism of boron in bcc-Fe has been studied by first-principles calculations. The diffusion coefficients of the interstitial mechanism, the B-monovacancy complex mechanism, and the B-divacancy complex mechanism have been calculated. The calculated diffusion coefficient of the interstitial mechanism is D0 = 1.05× 10-7exp(-0.75 eV/kT)m2· s-1, while the diffusion coefficients of the B-monovacancy and the B-divacancy complex mechanisms are D1 = 1.22× 10-6f1 exp(-2.27 eV/kT) m2· s-1 and D2 ≈ 8.36× 10-6exp(-4.81 eV/kT)m2· s-1, respectively. The results indicate that the dominant diffusion mechanism in bcc-Fe is the interstitial mechanism through an octahedral interstitial site instead of the complex mechanism. The calculated diffusion coefficient is in accordance with the reported experiment results measured in Fe-3%Si-B alloy (bcc structure). Since the non-equilibrium segregation of boron is based on the diffusion of the complexes as suggested by the theory, our calculation reasonably explains why the non-equilibrium segregation of boron is not observed in bcc-Fe in experiments.

Image potential states mediated STM imaging of cobalt phthalocyanine on NaCl/Cu(100)

Qinmin Guo(郭秦敏), Zhihui Qin(秦志辉), Min Huang(黄敏), Vladimir N. Mantsevich , Gengyu Cao(曹更玉)
Chin. Phys. B, 2016, 25 (3): 036801 doi: 10.1088/1674-1056/25/3/036801
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The adsorption and electronic properties of isolated cobalt phthalocyanine (CoPc) molecule on an ultrathin layer of NaCl have been investigated. High-resolution STM images give a detailed picture of the lowest unoccupied molecular orbital (LUMO) of an isolated CoPc. It is shown that the NaCl ultrathin layer efficiently decouples the interaction of the molecules from the underneath metal substrate, which makes it an ideal substrate for studying the properties of single molecules. Moreover, strong dependence of the appearance of the molecules on the sample bias in the region of relatively high bias (>3.1 V) is ascribed to the image potential states (IPSs) of NaCl/Cu(100), which may provide us with a possible method to fabricate quantum storage devices.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Electronic properties and topological phases of ThXY (X=Pb, Au, Pt and Y= Sb, Bi, Sn) compounds

Zahra Nourbakhsh, Aminollah Vaez
Chin. Phys. B, 2016, 25 (3): 037101 doi: 10.1088/1674-1056/25/3/037101
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The electronic properties and topological phases of ThXY (X=Pb, Au, Pt, Pd and Y= Sb, Bi, Sn) compounds in the presence of spin-orbit coupling, using density functional theory are investigated. The ThPtSn compound is stable in the ferromagnetic phase and the other ThXY compounds are stable in nonmagnetic phases. Band structures of these compounds in topological phases (insulator or metal) and normal phases within generalized gradient approximation (GGA) and Engel-Vosko generalized gradient approximation (GGA_EV) are compared. The ThPtSn, ThPtBi, ThPtSb, ThPdBi, and ThAuBi compounds have topological phases and the other ThXY compounds have normal phases. Band inversion strengths and topological phases of these compounds at different pressure are studied. It is seen that the band inversion strengths of these compounds are sensitive to pressure and for each compound a second-order polynomial fitted on the band inversion strengths-pressure curves.

Electronic structures of efficient MBiO3 (M = Li, Na, K, Ag) photocatalyst

Wen-Liu Zhou(周文流), Zong-Yan Zhao(赵宗彦)
Chin. Phys. B, 2016, 25 (3): 037102 doi: 10.1088/1674-1056/25/3/037102
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In order to deepen the understanding of the relationship between fundamental properties (including: microstructure and composition) and photocatalytic performance, four bismuthate compounds, including: LiBiO3, NaBiO3, KBiO3, and AgBiO3, are regarded as research examples in the present work, because they have particular crystal structures and similar compositions. Using density functional theory calculations, their structural, electronic, and optical properties are investigated and compared systematically. First of all, the calculated results of crystal structures and optical properties are in agreement with available published experimental data. Based on the calculated results, it is found that the tunneled or layered micro-structural properties lead to the stronger interaction between bismuth and oxygen, and the weaker interaction between alkaline-earth metal and [BiO6] octahedron, resulting in the feature of multi-band gaps in the cases of LiBiO3, NaBiO3, and KBiO3. This conclusion is supported by the case of AgBiO3, in which the feature of multi-band gaps disappears, due to the stronger interaction between the noble metal and [BiO6] octahedron. These properties have significant advantages in the photocatalytic performance: absorbing low energy photons, rapidly transferring energy carriers. Furthermore, the features of electronic structures of bismuthate compounds are well reflected by the absorption spectra, which could be confirmed by experimental measurements in practice. Combined with the calculated results, it could be considered that the crystal structures and compositions of the photocatalyst determine the electronic structures and optical properties, and subsequently determine the corresponding photocatalytic performance. Thus, a novel Bi-based photocatalyst driven by visible-light could be designed by utilizing specific compositions to form favorable electronic structures or specific micro-structures to form a beneficial channel for energy carriers.

Tunable localized surface plasmon resonances in one-dimensional h-BN/graphene/h-BN quantum-well structure

Kaibiao Zhang(张开彪), Hong Zhang(张红), Xinlu Cheng(程新路)
Chin. Phys. B, 2016, 25 (3): 037104 doi: 10.1088/1674-1056/25/3/037104
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The graphene/hexagonal boron-nitride (h-BN) hybrid structure has emerged to extend the performance of graphene-based devices. Here, we investigate the tunable plasmon in one-dimensional h-BN/graphene/h-BN quantum-well structures. The analysis of optical response and field enhancement demonstrates that these systems exhibit a distinct quantum confinement effect for the collective oscillations. The intensity and frequency of the plasmon can be controlled by the barrier width and electrical doping. Moreover, the electron doping and the hole doping lead to very different results due to the asymmetric energy band. This graphene/h-BN hybrid structure may pave the way for future optoelectronic devices.

Suppression of Andreev conductance in a topological insulator-superconductor nanostep junction

Yi-Jie Zheng(郑翌洁), Jun-Tao Song(宋俊涛), Yu-Xian Li(李玉现)
Chin. Phys. B, 2016, 25 (3): 037301 doi: 10.1088/1674-1056/25/3/037301
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When two three-dimensional topological insulators (TIs) are brought close to each other with their surfaces aligned, the surfaces form a line junction. Similarly, three TI surfaces, not lying in a single plane, can form an atomic-scale nanostep junction. In this paper, Andreev reflection in a TI-TI-superconductor nanostep junction is investigated theoretically. Because of the existence of edge states along each line junction, the conductance for a nanostep junction is suppressed. When the incident energy (ε) of an electron is larger than the superconductor gap (Δ), the Andreev conductance in a step junction is less than unity while for a plane junction it is unity. The Andreev conductance is found to depend on the height of the step junction. The Andreev conductance exhibits oscillatory behavior as a function of the junction height with the amplitude of the oscillations remaining unchanged when ε=0, but decreasing for ε=Δ, which is different from the case of the plane junction. The height of the step is therefore an important parameter for Andreev reflection in nanostep junctions, and plays a role similar to that of the delta potential barrier in normal metal-superconductor plane junctions.

Van der Waals heterostructure of phosphorene and hexagonal boron nitride: First-principles modeling

Peng Zhang(张鹏), Jing Wang(王静), Xiang-Mei Duan(段香梅)
Chin. Phys. B, 2016, 25 (3): 037302 doi: 10.1088/1674-1056/25/3/037302
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We have studied the structural and electronic properties of a hybrid hexagonal boron nitride with phosphorene nanocomposite using ab initio density functional calculations. It is found that the interaction between the hexagonal boron nitride and phosphorene is dominated by the weak van der Waals interaction, with their own intrinsic electronic properties preserved. Furthermore, the band gap of the nanocomposite is dependent on the interfacial distance. Our results could shed light on the design of new devices based on van der Waals heterostructure.

A subwavelength metal-grating assisted sensor of Kretschmann style for investigating the sample with high refractive index

Xu-Feng Li(李旭峰), Wei Peng(彭伟), Ya-Li Zhao(赵亚丽), Qiao Wang(王乔), Ji-Lin Wei(魏计林)
Chin. Phys. B, 2016, 25 (3): 037303 doi: 10.1088/1674-1056/25/3/037303
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In this paper, a subwavelength metal-grating assisted sensor of Kretschmann style that is capable of detecting the sample with a refractive index higher than that of the substrate is proposed. The sensor configuration is similar to the traditional Kretschmann structure, but the metal film is pattered into a grating. As a TM-polarized laser beam impinges from the substrate, a resonant dip point in reflectance curve is produced at a certain incident angle. Our studies indicate that the sensing sensitivity and resolution are affected by the grating's gap and period, and after these parameters have been optimized, a sensing sensitivity of 51.484°/RIU is obtained with a slightly changing resolution.

Resonant Andreev reflection in a normal-metal/quantum-dot/superconductor system with coupled Majorana bound states

Su-Xin Wang(王素新), Yu-Xian Li(李玉现), Jian-Jun Liu(刘建军)
Chin. Phys. B, 2016, 25 (3): 037304 doi: 10.1088/1674-1056/25/3/037304
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Andreev reflection (AR) in a normal-metal/quantum-dot/superconductor (N-QD-S) system with coupled Majorana bound states (MBSs) is investigated theoretically. We find that in the N-QD-S system, the AR can be enhanced when coupling to the MBSs is incorporated. Fano line-shapes can be observed in the AR conductance spectrum when there is an appropriate QD-MBS coupling or MBS-MBS coupling. The AR conductance is always e2/2h at the zero Fermi energy point when only QD-MBSs coupling is considered. In addition, the resonant AR occurs when the MBS-MBS coupling roughly equals to the QD energy level. We also find that an AR antiresonance appears when the QD energy level approximately equals to the sum of the QD-MBS coupling and the MBS-MBS coupling. These features may serve as characteristic signatures for the probe of MBSs.

Theoretical investigation of structural and optical properties of semi-fluorinated bilayer graphene

Xiao-Jiao San(伞晓娇), Bai Han(韩柏), Jing-Geng Zhao(赵景庚)
Chin. Phys. B, 2016, 25 (3): 037305 doi: 10.1088/1674-1056/25/3/037305
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We have studied the structural and optical properties of semi-fluorinated bilayer graphene using density functional theory. When the interlayer distance is 1.62 Å, the two graphene layers in AA stacking can form strong chemical bonds. Under an in-plane stress of 6.8 GPa, this semi-fluorinated bilayer graphene becomes the energy minimum. Our calculations indicate that the semi-fluorinated bilayer graphene with the AA stacking sequence and rectangular fluorinated configuration is a nonmagnetic semiconductor (direct gap of 3.46 eV). The electronic behavior at the vicinity of the Fermi level is mainly contributed by the p electrons of carbon atoms forming C=C double bonds. We compare the optical properties of the semi-fluorinated bilayer graphene with those of bilayer graphene stacked in the AA sequence and find that the semi-fluorinated bilayer graphene is anisotropic for the polarization vector on the basal plane of graphene and a red shift occurs in the [010] polarization, which makes the peak at the low-frequency region located within visible light. This investigation is useful to design polarization-dependence optoelectronic devices.

Fabrication and characterization of the normally-off N-channel lateral 4H-SiC metal-oxide-semiconductor field-effect transistors

Qing-Wen Song(宋庆文), Xiao-Yan Tang(汤晓燕), Yan-Jing He(何艳静), Guan-Nan Tang(唐冠男),Yue-Hu Wang(王悦湖), Yi-Meng Zhang(张艺蒙), Hui Guo(郭辉), Ren-Xu Jia(贾仁需),Hong-Liang Lv(吕红亮), Yi-Men Zhang(张义门), Yu-Ming Zhang(张玉明)
Chin. Phys. B, 2016, 25 (3): 037306 doi: 10.1088/1674-1056/25/3/037306
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In this paper, the normally-off N-channel lateral 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFFETs) have been fabricated and characterized. A sandwich-(nitridation-oxidation-nitridation) type process was used to grow the gate dielectric film to obtain high channel mobility. The interface properties of 4H-SiC/SiO2 were examined by the measurement of HF I-V, G-V, and C-V over a range of frequencies. The ideal C-V curve with little hysteresis and the frequency dispersion were observed. As a result, the interface state density near the conduction band edge of 4H-SiC was reduced to 2×1011 eV-1·cm-2, the breakdown field of the grown oxides was about 9.8 MV/cm, the median peak field-effect mobility is about 32.5 cm2·V-1·s-1, and the maximum peak field-effect mobility of 38 cm2· V-1· s-1 was achieved in fabricated lateral 4H-SiC MOSFFETs.

Charge recombination mechanism to explain the negative capacitance in dye-sensitized solar cells

Lie-Feng Feng(冯列峰), Kun Zhao(赵昆), Hai-Tao Dai(戴海涛), Shu-Guo Wang(王树国), Xiao-Wei Sun(孙小卫)
Chin. Phys. B, 2016, 25 (3): 037307 doi: 10.1088/1674-1056/25/3/037307
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Negative capacitance (NC) in dye-sensitized solar cells (DSCs) has been confirmed experimentally. In this work, the recombination behavior of carriers in DSC with semiconductor interface as a carrier's transport layer is explored theoretically in detail. Analytical results indicate that the recombination behavior of carriers could contribute to the NC of DSCs under small signal perturbation. Using this recombination capacitance we propose a novel equivalent circuit to completely explain the negative terminal capacitance. Further analysis based on the recombination complex impedance show that the NC is inversely proportional to frequency. In addition, analytical recombination resistance is composed by the alternating current (AC) recombination resistance (Rrac) and the direct current (DC) recombination resistance (Rrdc), which are caused by small-signal perturbation and the DC bias voltage, respectively. Both of two parts will decrease with increasing bias voltage.

Growth mechanism of atomic-layer-deposited TiAlC metal gatebased on TiCl4 and TMA precursors

Jinjuan Xiang(项金娟), Yuqiang Ding(丁玉强), Liyong Du(杜立永), Junfeng Li(李俊峰),Wenwu Wang(王文武), Chao Zhao(赵超)
Chin. Phys. B, 2016, 25 (3): 037308 doi: 10.1088/1674-1056/25/3/037308
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TiAlC metal gate for the metal-oxide-semiconductor field-effect-transistor (MOSFET) is grown by the atomic layer deposition method using TiCl4 and Al(CH3)3(TMA) as precursors. It is found that the major product of the TiCl4 and TMA reaction is TiAlC, and the components of C and Al are found to increase with higher growth temperature. The reaction mechanism is investigated by using x-ray photoemission spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The reaction mechanism is as follows. Ti is generated through the reduction of TiCl4 by TMA. The reductive behavior of TMA involves the formation of ethane. The Ti from the reduction of TiCl4 by TMA reacts with ethane easily forming heterogenetic TiCH2, TiCH=CH2 and TiC fragments. In addition, TMA thermally decomposes, driving Al into the TiC film and leading to TiAlC formation. With the growth temperature increasing, TMA decomposes more severely, resulting in more C and Al in the TiAlC film. Thus, the film composition can be controlled by the growth temperature to a certain extent.

Fractional-dimensional approach for excitons in GaAsfilms on AlxGa1-xAs substrates

Zhen-Hua Wu(武振华), Lei Chen(陈蕾), Qiang Tian(田强)
Chin. Phys. B, 2016, 25 (3): 037310 doi: 10.1088/1674-1056/25/3/037310
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Binding energies of excitons in GaAs films on AlxGa1-xAs substrates are studied theoretically with the fractional-dimensional approach. In this approach, the real anisotropic “exciton+film” semiconductor system is mapped into an effective fractional-dimensional isotropic space. For different aluminum concentrations and substrate thicknesses, the exciton binding energies are obtained as a function of the film thickness. The numerical results show that, for different aluminum concentrations and substrate thicknesses, the exciton binding energies in GaAs films on AlxGa1-xAs substrates all exhibit their maxima with increasing film thickness. It is also shown that the binding energies of heavy-hole and light-hole excitons both have their maxima with increasing film thickness.

Effect of exchange coupling on magnetic property in Sm-Co/α-Fe layered system

C X Sang(桑成祥), G P Zhao(赵国平), W X Xia(夏卫星), X L Wan(万秀琳), F J Morvan, X C Zhang(张溪超), L H Xie(谢林华), J Zhang(张健), J Du(杜娟), A R Yan(闫阿儒), P Liu(刘平)
Chin. Phys. B, 2016, 25 (3): 037501 doi: 10.1088/1674-1056/25/3/037501
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The hysteresis loops as well as the spin distributions of Sm-Co/α-Fe bilayers have been investigated by both three-dimensional (3D) and one-dimensional (1D) micromagnetic calculations, focusing on the effect of the interface exchange coupling under various soft layer thicknesses ts. The exchange coupling coefficient Ahs between the hard and soft layers varies from 1.8× 10-6 erg/cm to 0.45× 10-6 erg/cm, while the soft layer thickness increases from 2 nm to 10 nm. As the exchange coupling decreases, the squareness of the loop gradually deteriorates, both pinning and coercive fields rise up monotonically, and the nucleation field goes down. On the other hand, an increment of the soft layer thickness leads to a significant drop of the nucleation field, the deterioration of the hysteresis loop squareness, and an increase of the remanence. The simulated loops based on the 3D and 1D methods are consistent with each other and in good agreement with the measured loops for Sm-Co/α-Fe multilayers.

Preparation and characterization of Sr0.5Ba0.5Nb2O6 glass-ceramic on piezoelectric properties

Shan Jiang(姜珊), Xuan-Ming Wang(王炫明), Jia-Yu Li(李佳宇),Yong Zhang(张勇), Tao Zheng(郑涛), Jing-Wen Lv(吕景文)
Chin. Phys. B, 2016, 25 (3): 037701 doi: 10.1088/1674-1056/25/3/037701
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We studied the influence of heat treatment time on the optical, thermal, electrical, and mechanical properties of strontium barium niobate (Sr1-xBaxNb2O6; hereafter SBN) piezoelectric glass-ceramics with tungsten bronze-type structure, which have good piezoelectric properties and are important lead-free piezoelectric materials. We found that the best heat treatment time is 4 h. The properties of the prepared materials are better than that of SBN ceramics and the glass-ceramic growth is faster than the SBN crystal when the heat treatment time of the SBN piezoelectric glass-ceramic is controlled, reducing the preparation costs greatly.

Design of a multiband terahertz perfect absorber

Dan Hu(胡丹), Hong-yan Wang(王红燕), Zhen-jie Tang(汤振杰),Xi-wei Zhang(张希威), Lin Ju(鞠琳), Hua-ying Wang(王华英)
Chin. Phys. B, 2016, 25 (3): 037801 doi: 10.1088/1674-1056/25/3/037801
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A thin-flexible multiband terahertz metamaterial absorber (MA) has been investigated. Each unit cell of the MA consists of a simple metal structure, which includes the top metal resonator ring and the bottom metallic ground plane, separated by a thin-flexible dielectric spacer. Finite-difference time domain simulation indicates that this MA can achieve over 99% absorption at frequencies of 1.50 THz, 3.33 THz, and 5.40 THz by properly assembling the sandwiched structure. However, because of its asymmetric structure, the MA is polarization-sensitive and can tune the absorptivity of the second absorption peak by changing the incident polarization angle. The effect of the error of the structural parameters on the absorption efficiency is also carefully analyzed in detail to guide the fabrication. Moreover, the proposed MA exhibits high refractive-index sensing sensitivity, which has potential applications in multi-wavelength sensing in the terahertz region.

High-temperature Raman spectroscopic study of vanadoborate Na3VO2B6O11

Ji Zhang(张季), De-Ming Zhang(张德明), Qing-Li Zhang(张庆礼), Shao-Tang Yin(殷绍唐)
Chin. Phys. B, 2016, 25 (3): 037802 doi: 10.1088/1674-1056/25/3/037802
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Raman spectra of a vanadoborate (Na3VO2B6O11) crystal from room temperature up to the melting point have been recorded. The main internal vibrational modes of the crystal have been assigned. It was found that all the Raman bands exhibit decreases in frequency and the widths of the Raman bands increase with the increase of temperature. However, no phase transition was observed under 525 ℃. The micro-structure of its melt was studied by quantum chemistry ab initio calculation. The continuous three-dimensional network of the crystal collapsed and transformed into VO4 and VBO6 clusters during the melting process with an isomerization reaction from four-coordinated boron to a three-coordinated species.

Second harmonic generation of metal nanoparticles under tightly focused illumination

Jing-Wei Sun(孙经纬), Xiang-Hui Wang(王湘晖), Sheng-Jiang Chang(常胜江),Ming Zeng(曾明), Na Zhang(张娜)
Chin. Phys. B, 2016, 25 (3): 037803 doi: 10.1088/1674-1056/25/3/037803
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The near-field and far-field second harmonic (SH) responses of a metal spherical nanoparticle placed in the focal region of a highly focused beam are investigated by using the calculation model based on three-dimensional finite-difference time-domain (FDTD) method. The results show that off-axis backward-propagating SH response can be reinforced by tightly focusing, due to the increase of the relative magnitude of the longitudinal field component and the phase shift along the propagation direction.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Control of symmetric properties of metamorphic In0.27Ga0.73As layers by substrate misorientation

Shu-Zhen Yu(于淑珍), Jian-Rong Dong(董建荣), Yu-Run Sun(孙玉润), Kui-Long Li(李奎龙),Xu-Lu Zeng(曾徐路), Yong-Ming Zhao(赵勇明), Hui Yang(杨辉)
Chin. Phys. B, 2016, 25 (3): 038101 doi: 10.1088/1674-1056/25/3/038101
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Asymmetry in dislocation density and strain relaxation has a significant impact on device performance since it leads to anisotropic electron transport in metamorphic materials. So it is preferred to obtain metamorphic materials with symmetric properties. In this paper, we grew metamorphic In0.27Ga0.73As epilayers with symmetric low threading dislocation density and symmetric strain relaxation in two <110> directions using InAlGaAs buffer layers on 7° misoriented GaAs (001) substrates. To understand the control mechanism of symmetric properties of In0.27Ga0.73As layers by the substrate miscut angles, In0.27Ga0.73As grown on 2° and 15° misoriented substrates were also characterized as reference by atomic force microscopy, transmission electron microscopy, and high resolution triple axis x-ray diffraction. The phase separation and interaction of 60° misfit dislocations were found to be the reasons for asymmetry properties of In0.27Ga0.73As grown on 2° and 15° substrates, respectively. Photoluminescence results proved that the In0.27Ga0.73As with symmetric properties has better optical properties than the In0.27Ga0.73As with asymmetric properties at room temperature. These results imply that high quality metamorphic In0.27Ga0.73As can be achieved with controllable isotropic electron transport property.

Reflection of thermoelastic wave on the interface of isotropic half-space and tetragonal syngony anisotropic medium of classes 4, 4/m with thermomechanical effect

Nurlybek A Ispulov, Abdul Qadir, M A Shah, Ainur K Seythanova, Tanat G Kissikov, Erkin Arinov
Chin. Phys. B, 2016, 25 (3): 038102 doi: 10.1088/1674-1056/25/3/038102
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The thermoelastic wave propagation in a tetragonal syngony anisotropic medium of classes 4, 4/m having heterogeneity along z axis has been investigated by employing matrizant method. This medium has an axis of second-order symmetry parallel to z axis. In the case of the fourth-order matrix coefficients, the problems of wave refraction and reflection on the interface of homogeneous anisotropic thermoelastic mediums are solved analytically.

Unifying the crystallization behavior of hexagonal and square crystals with the phase-field-crystal model

Tao Yang(杨 涛), Zheng Chen(陈铮), Jing Zhang(张静), Yongxin Wang(王永新), Yanli Lu(卢艳丽)
Chin. Phys. B, 2016, 25 (3): 038103 doi: 10.1088/1674-1056/25/3/038103
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By employing the phase-field-crystal models, the atomic crystallization process of hexagonal and square crystals is investigated with the emphasis on the growth mechanism and morphological change. A unified regime describing the crystallization behavior of both crystals is obtained with the thermodynamic driving force varying. By increasing the driving force, both crystals (in the steady-state) transform from a faceted polygon to an apex-bulged polygon, and then into a symmetric dendrite. For the faceted polygon, the interface advances by a layer-by-layer (LL) mode while for the apex-bulged polygonal and the dendritic crystals, it first adopts the LL mode and then transits into the multi-layer (ML) mode in the later stage. In particular, a shift of the nucleation sites from the face center to the area around the crystal tips is detected in the early growth stage of both crystals and is rationalized in terms of the relation between the crystal size and the driving force distribution. Finally, a parameter characterizing the complex shape change of square crystal is introduced.

Linear theory of beam-wave interaction in double-slot coupled cavity travelling wave tube

Fang-ming He(何昉明), Wen-qiu Xie(谢文球), Ji-run Luo(罗积润), Min Zhu(朱敏), Wei Guo(郭炜)
Chin. Phys. B, 2016, 25 (3): 038401 doi: 10.1088/1674-1056/25/3/038401
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A three-dimensional model of the double-slot coupled cavity slow-wave structure (CCSWS) with a solid round electron beam for the beam-wave interaction is presented. Based on the “cold” dispersion, the “hot” dispersion equation is derived with the Maxwell equations by using the variable separation method and the field-matching method. Through numerical calculations, the effects of the electron beam parameters and the staggered angle between adjacent walls on the linear gain are analyzed.

Improved performance of polymer solar cells by using inorganic, organic, and doped cathode buffer layers

Taohong Wang(王桃红), Changbo Chen(陈长博), Kunping Guo(郭坤平), Guo Chen(陈果), Tao Xu(徐韬), Bin Wei(魏斌)
Chin. Phys. B, 2016, 25 (3): 038402 doi: 10.1088/1674-1056/25/3/038402
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The interface between the active layer and the electrode is one of the most critical factors that could affect the device performance of polymer solar cells. In this work, based on the typical poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) polymer solar cell, we studied the effect of the cathode buffer layer (CBL) between the top metal electrode and the active layer on the device performance. Several inorganic and organic materials commonly used as the electron injection layer in an organic light-emitting diode (OLED) were employed as the CBL in the P3HT:PCBM polymer solar cells. Our results demonstrate that the inorganic and organic materials like Cs2CO3, bathophenanthroline (Bphen), and 8-hydroxyquinolatolithium (Liq) can be used as CBL to efficiently improve the device performance of the P3HT:PCBM polymer solar cells. The P3HT:PCBM devices employed various CBLs possess power conversion efficiencies (PCEs) of 3.0%-3.3%, which are ca. 50% improved compared to that of the device without CBL. Furthermore, by using the doped organic materials Bphen:Cs2CO3 and Bphen:Liq as the CBL, the PCE of the P3HT:PCBM device will be further improved to 3.5%, which is ca. 70% higher than that of the device without a CBL and ca. 10% increased compared with that of the devices with a neat inorganic or organic CBL.

Effect of lateral structure parameters of SiGe HBTs on synthesized active inductors

Yan-Xiao Zhao(赵彦晓), Wan-Rong Zhang(张万荣), Xin Huang(黄鑫), Hong-Yun Xie(谢红云), Dong-Yue Jin(金冬月), Qiang Fu(付强)
Chin. Phys. B, 2016, 25 (3): 038501 doi: 10.1088/1674-1056/25/3/038501
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The effect of lateral structure parameters of transistors including emitter width, emitter length, and emitter stripe number on the performance parameters of the active inductor (AI), such as the effective inductance Ls, quality factor Q, and self-resonant frequency ω 0 is analyzed based on 0.35-μm SiGe BiCMOS process. The simulation results show that for AI operated under fixed current density JC, the HBT lateral structure parameters have significant effect on Ls but little influence on Q and ω 0, and the larger Ls can be realized by the narrow, short emitter stripe and few emitter stripes of SiGe HBTs. On the other hand, for AI with fixed HBT size, smaller JC is beneficial for AI to obtain larger Ls, but with a cost of smaller Q and ω 0. In addition, under the fixed collector current IC, the larger the size of HBT is, the larger Ls becomes, but the smaller Q and ω 0 become. The obtained results provide a reference for selecting geometry of transistors and operational condition in the design of active inductors.

Two-dimensional models of threshold voltage andsubthreshold current for symmetrical double-material double-gate strained Si MOSFETs

Yan-hui Xin(辛艳辉), Sheng Yuan(袁胜), Ming-tang Liu(刘明堂),Hong-xia Liu(刘红侠), He-cai Yuan(袁合才)
Chin. Phys. B, 2016, 25 (3): 038502 doi: 10.1088/1674-1056/25/3/038502
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The two-dimensional models for symmetrical double-material double-gate (DM-DG) strained Si (s-Si) metal-oxide semiconductor field effect transistors (MOSFETs) are presented. The surface potential and the surface electric field expressions have been obtained by solving Poisson's equation. The models of threshold voltage and subthreshold current are obtained based on the surface potential expression. The surface potential and the surface electric field are compared with those of single-material double-gate (SM-DG) MOSFETs. The effects of different device parameters on the threshold voltage and the subthreshold current are demonstrated. The analytical models give deep insight into the device parameters design. The analytical results obtained from the proposed models show good matching with the simulation results using DESSIS.

Evaluation of a gate-first process for AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors with low ohmic annealing temperature

Liuan Li(李柳暗), Jiaqi Zhang(张家琦), Yang Liu(刘扬), Jin-Ping Ao(敖金平)
Chin. Phys. B, 2016, 25 (3): 038503 doi: 10.1088/1674-1056/25/3/038503
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In this paper, TiN/AlOx gated AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) were fabricated for gate-first process evaluation. By employing a low temperature ohmic process, ohmic contact can be obtained by annealing at 600 ℃ with the contact resistance approximately 1.6 Ω· mm. The ohmic annealing process also acts as a post-deposition annealing on the oxide film, resulting in good device performance. Those results demonstrated that the TiN/AlOx gated MOS-HFETs with low temperature ohmic process can be applied for self-aligned gate AlGaN/GaN MOS-HFETs.

Mobility enhancement of strained GaSb p-channel metal—oxide—semiconductor field-effect transistorswith biaxial compressive strain

Yan-Wen Chen(陈燕文), Zhen Tan(谭桢), Lian-Feng Zhao(赵连锋), Jing Wang(王敬), Yi-Zhou Liu(刘易周),Chen Si(司晨), Fang Yuan(袁方), Wen-Hui Duan(段文晖), Jun Xu(许军)
Chin. Phys. B, 2016, 25 (3): 038504 doi: 10.1088/1674-1056/25/3/038504
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Various biaxial compressive strained GaSb p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) are experimentally and theoretically investigated. The biaxial compressive strained GaSb MOSFETs show a high peak mobility of 638 cm2/V·s, which is 3.86 times of the extracted mobility of the fabricated GaSb MOSFETs without strain. Meanwhile, first principles calculations show that the hole effective mass of GaSb depends on the biaxial compressive strain. The biaxial compressive strain brings a remarkable enhancement of the hole mobility caused by a significant reduction in the hole effective mass due to the modulation of the valence bands.

Design and fabrication of multi-channel photodetector array monolithic with arrayed waveguide grating

Qian-Qian Lv(吕倩倩), Pan Pan(潘盼), Han Ye(叶焓), Dong-Dong Yin(尹冬冬),Yu-Bing Wang(王玉冰), Xiao-Hong Yang(杨晓红), Qin Han(韩勤)
Chin. Phys. B, 2016, 25 (3): 038505 doi: 10.1088/1674-1056/25/3/038505
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We have provided optical simulations of the evanescently coupled waveguide photodiodes integrated with a 13-channels AWGs. The photodiode could exhibit high internal efficiency by appropriate choice of layers geometry and refractive index. Aseamless joint structure has been designed and fabricated for integrating the output waveguides of AWGs with the evanescently coupled waveguide photodiode array. The highest simulation quantum efficiency could achieve 92% when the matching layer thickness of the PD is 120 nm and the insertion length is 2 μm. The fabricated PD with 320-nm-thick matching layer and 2-μm-length insertion matching layer present a responsivity of 0.87 A/W.

Novel Fourier-based iterative reconstruction for sparse fan projection using alternating direction total variation minimization

Zhao Jin(金朝), Han-Ming Zhang(张瀚铭), Bin Yan(闫镔), Lei Li(李磊), Lin-Yuan Wang(王林元), Ai-Long Cai(蔡爱龙)
Chin. Phys. B, 2016, 25 (3): 038701 doi: 10.1088/1674-1056/25/3/038701
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Sparse-view x-ray computed tomography (CT) imaging is an interesting topic in CT field and can efficiently decrease radiation dose. Compared with spatial reconstruction, a Fourier-based algorithm has advantages in reconstruction speed and memory usage. A novel Fourier-based iterative reconstruction technique that utilizes non-uniform fast Fourier transform (NUFFT) is presented in this work along with advanced total variation (TV) regularization for a fan sparse-view CT. The proposition of a selective matrix contributes to improve reconstruction quality. The new method employs the NUFFT and its adjoin to iterate back and forth between the Fourier and image space. The performance of the proposed algorithm is demonstrated through a series of digital simulations and experimental phantom studies. Results of the proposed algorithm are compared with those of existing TV-regularized techniques based on compressed sensing method, as well as basic algebraic reconstruction technique. Compared with the existing TV-regularized techniques, the proposed Fourier-based technique significantly improves convergence rate and reduces memory allocation, respectively.

Successive lag synchronization on dynamical networks with communication delay

Xin-Jian Zhang(张新建), Ai-Ju Wei(韦爱举), Ke-Zan Li(李科赞)
Chin. Phys. B, 2016, 25 (3): 038901 doi: 10.1088/1674-1056/25/3/038901
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In this paper, successive lag synchronization (SLS) on a dynamical network with communication delay is investigated. In order to achieve SLS on the dynamical network with communication delay, we design linear feedback control and adaptive control, respectively. By using the Lyapunov function method, we obtain some sufficient conditions for global stability of SLS. To verify these results, some numerical examples are further presented. This work may find potential applications in consensus of multi-agent systems.
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