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  • Magneto–optical trap for neutral mercury atoms

    Liu Hong-Li, Yin Shi-Qi, Liu Kang-Kang, Qian Jun, Xu Zhen, Hong Tao, Wang Yu-Zhu
    Chin. Phys. B 2013, 22 (4): 043701
    Due to the low sensitivity to the blackbody radiation, neutral mercury is a good candidate for the most accurate optical lattice clock. Here we report the observation of cold mercury atoms in a magneto–optical trap (MOT). Because of the high vapor pressure at room temperature, the mercury sour...

     
  • Determining resistance of X-pinch plasma

    Zhao Shen, Xue Chuang, Zhu Xin-Lei, Zhang Ran, Luo Hai-Yun, Zou Xiao-Bing, Wang Xin-Xin, Ning Cheng, Ding Ning, Shu Xiao-Jian
    Chin. Phys. B 2013, 22 (4): 045205
    The current and the voltage of an X-pinch were measured. The inductance of the X-pinch was assumed to be a constant and estimated by the calculation of the magnetic field based on the well-known Biot-Savart's Law. The voltage of the inductance was calculated with L·di /dt and subtracted from ...

     
  • Spin-polarized injection into p-type GaAs layer from a Co2MnAl injector

    Yuan Si-Peng, Shen Chao, Zheng Hou-Zhi, Liu Qi, Wang Li-Guo, Meng Kang-Kang, Zhao Jian-Hua
    Chin. Phys. B 2013, 22 (4): 047202
    Electric luminescence and its circular polarization in a Co2MnAl injector-based light emitting diode (LED) has been detected at the transition of e-AC0, where injected spin-polarized electrons recombine with bound holes at carbon acceptors. A spin polarization degree of 24.6% is obtained at 77 K aft...

     
Chin. Phys. B  
  Chin. Phys. B--2013, Vol.22, No.4
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GENERAL

N-soliton solutions of an integrable equation studied by Qiao

Zhaqilao
Chin. Phys. B, 2013, 22 (4): 040201 doi: 10.1088/1674-1056/22/4/040201
Full Text: [PDF 227 KB] (Downloads:516)
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In this paper, we studied N-soliton solutions of a new integrable equation studied by Qiao [J. Math. Phys. 48 082701 (2007)]. Firstly, we employed the Darboux matrix method to construct a Darboux transformation for the modified Korteweg-de Vries equation. Then we use the Darboux transformation and a transformation, introduced by Sakovich [J. Math. Phys. 52 023509 (2011)], to derive N-soliton solutions of the new integrable equation from the seed solution. In particular, the multiple soliton solutions are explicitly obtained and shown through some figures.

Finite symmetry transformation group and localized structures of (2+1)-dimensional coupled Burgers equation

Lei Ya, Yang Duo
Chin. Phys. B, 2013, 22 (4): 040202 doi: 10.1088/1674-1056/22/4/040202
Full Text: [PDF 562 KB] (Downloads:517)
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In this paper, the finite symmetry transformation group of the (2+1)-dimensional coupled Burgers equation is studied by the modified direct method, and with the help of the truncated Painlevé expansion approach, some special types of localized structure for the (2+1)-dimensional coupled Burgers equation are obtained, especially, the dromion-like and solitoff-like structures.

Consensus problems of first-order dynamic multi-agent systems with multiple time delays

Ji Liang-Hao, Liao Xiao-Feng
Chin. Phys. B, 2013, 22 (4): 040203 doi: 10.1088/1674-1056/22/4/040203
Full Text: [PDF 247 KB] (Downloads:1199)
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Consensus problems of first-order multi-agent systems with multiple time delays are investigated in this paper. We discuss three cases: 1) continuous, 2) discrete, and 3) a continuous system with a proportional plus derivative controller. In each case, the system contains communication and input time delays simultaneously. Supposing a dynamic multi-agent system with directed topology that contains a globally reachable node, the sufficient convergence condition of the system is discussed with respect to each of the three cases based on the generalized Nyquist criterion and the frequency-domain analysis approach, yielding conclusions that are either less conservative than or in agreement with previously published results. And we know that the convergence condition of the system depends mainly on each agent's input time delay and the adjacent weights but is independent of the communication delay between agents, whether the system is continuous or discrete. Finally, simulation examples are given to verify the theoretical analysis.

Global dynamics of a novel multi-group model for computer worms

Gong Yong-Wang, Song Yu-Rong, Jiang Guo-Ping
Chin. Phys. B, 2013, 22 (4): 040204 doi: 10.1088/1674-1056/22/4/040204
Full Text: [PDF 262 KB] (Downloads:563)
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In this paper, we study worm dynamics in computer networks composed of many autonomous systems. A novel multi-group SIQR (susceptible-infected-quarantined-removed) model is proposed for computer worms by explicitly considering anti-virus measures and the network infrastructure. Then, the basic reproduction number of worm R0 is derived and the global dynamics of the model is established. It is shown that if R0 is less than or equal to 1, the disease-free equilibrium is globally asymptotically stable and the worm dies out eventually, whereas, if R0 is greater than 1, there exists one unique endemic equilibrium and it is globally asymptotically stable, thus the worm persists in the network. Finally, numerical simulations are given to illustrate the theoretical results.

Epidemic propagation on adaptive coevolutionary networks with preferential local-world reconnecting strategy

Song Yu-Rong, Jiang Guo-Ping, Gong Yong-Wang
Chin. Phys. B, 2013, 22 (4): 040205 doi: 10.1088/1674-1056/22/4/040205
Full Text: [PDF 827 KB] (Downloads:571)
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In the propagation of epidemic in population, individuals adaptively adjust their behaviors to avoid the risk of epidemic. Different from the existing studies where new links are established randomly, a local link is established preferentially in this paper. We propose a new preferentially reconnecting edge strategy depending on spatial distance (PR-SD). For the PR-SD strategy, the new link is established at random with probability p and in a shortest distance with the probability 1-p. We establish the epidemic model on adaptive network using Cellular Automata, and demonstrate the effectiveness of the proposed model by numerical simulations. The results show that the smaller the value of parameter p, the more difficult the epidemic spread is. The PR-SD strategy breaks long-range links and establishes short-range links as many as possible, which causes the network efficiency to decrease quickly and the propagation of epidemic is restrained effectively.

Virus spreading in wireless sensor networks with a medium access control mechanism

Wang Ya-Qi, Yang Xiao-Yuan
Chin. Phys. B, 2013, 22 (4): 040206 doi: 10.1088/1674-1056/22/4/040206
Full Text: [PDF 301 KB] (Downloads:777)
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In this paper, an extended version of standard susceptible-infected model is proposed to consider the influence of medium access control mechanism on virus spreading in wireless sensor networks. Theoretical analysis shows that the medium access control mechanism obviously reduces the density of infected nodes in the networks, which has been ignored in previous studies. It is also found that the increasing of the network node density or node communication radius greatly increases the number of infected nodes. The theoretical results are confirmed by numerical simulations.

The extended cubic B-spline algorithm for a modified regularized long wave equation

İ. Dağ, D. Irk, M. Sarı
Chin. Phys. B, 2013, 22 (4): 040207 doi: 10.1088/1674-1056/22/4/040207
Full Text: [PDF 370 KB] (Downloads:1258)
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A collocation method based on an extended cubic B-spline functions is introduced for the numerical solution of the modified regularized long wave equation. Accuracy of the method is illustrated by studying the single solitary wave propogation and interaction of two solitary waves of the modified regularized long wave equation.

Spinless particles in the field of unequal scalar–vector Yukawa potentials

M. Hamzavi, S. M. Ikhdair, K. E. Thylwe
Chin. Phys. B, 2013, 22 (4): 040301 doi: 10.1088/1674-1056/22/4/040301
Full Text: [PDF 231 KB] (Downloads:446)
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We present analytical bound state solutions of the spin-zero Klein-Gordon (KG) particles in the field of unequal mixture of scalar and vector Yukawa potentials within the framework of the approximation scheme to the centrifugal potential term for any arbitrary l-state. The approximate energy eigenvalues and unnormalized wave functions are obtained in closed forms using a simple shortcut of Nikiforov-Uvarov (NU) method. Further, we solve the KG-Yukawa problem for its exact numerical energy eigenvalues via amplitude phase (AP) method to test the accuracy of the present solutions found by using the NU method. Our numerical tests using energy calculations demonstrate the existence of inter-dimensional degeneracy amongst the energy states of KG-Yukawa problem. The dependence of the energy on the dimension D is numerically discussed for spatial dimensions D=2-6.

Relativistic symmetries in Rosen–Morse potential and tensor interaction using the Nikiforov–Uvarov method

Sameer M Ikhdair, Majid Hamzavi
Chin. Phys. B, 2013, 22 (4): 040302 doi: 10.1088/1674-1056/22/4/040302
Full Text: [PDF 276 KB] (Downloads:587)
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Approximate analytical bound-state solutions of the Dirac particle in the fields of attractive and repulsive Rosen-Morse (RM) potentials including Coulomb-like tensor (CLT) potential are obtained for arbitrary spin-orbit quantum number κ. The Pekeris approximation is used to deal with the spin-orbit coupling terms κ (κ ± 1)r-2. In the presence of exact spin and pseudospin (p-spin) symmetries, the energy eigenvalues and the corresponding normalized two-component wave functions are found by using the parametric generalization of the Nikiforov–Uvarov (NU) method. The numerical results show that the CLT interaction removes degeneracies between spin and p-spin state doublets.

Symmetric geometric measure and dynamics of quantum discord

Jiang Feng-Jian, Lü Hai-Jiang, Yan Xin-Hu, Shi Ming-Jun
Chin. Phys. B, 2013, 22 (4): 040303 doi: 10.1088/1674-1056/22/4/040303
Full Text: [PDF 317 KB] (Downloads:500)
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A symmetric measure of quantum correlation based on the Hilbert-Schmidt distance is presented in this paper. For two-qubit states, we simplify considerably the optimization procedure so that numerical evaluation can be performed efficiently. Analytical expressions for the quantum correlation are attained for some special states. We further investigate the dynamics of quantum correlation of the system qubits in the presence of independent dissipative environments. Several nontrivial aspects are demonstrated. We find that the quantum correlation can increase even if the system state is suffering from dissipative noise. Sudden changes occur, even twice, in the time evolution of quantum correlation. There exists a certain correspondence between the evolution of quantum correlation in the systems and that in the environments, and the quantum correlation in the systems will be transferred into the environments completely and asymptotically.

Quantum discord dynamics of two qubits in the single-mode cavities

Wang Chen, Chen Qing-Hu
Chin. Phys. B, 2013, 22 (4): 040304 doi: 10.1088/1674-1056/22/4/040304
Full Text: [PDF 283 KB] (Downloads:491)
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The dynamics of the quantum discord for two identical qubits in both two independent single-mode cavities and a common single-mode cavity are discussed. For the initial Bell state with correlated spins, while the entanglement sudden death can occur, the quantum discord vanishes only at discrete moments in the independent cavities and never vanishes in the common cavity. Interestingly, quantum discord and entanglement show opposite behaviors in the common cavity, unlike in the independent cavities. For the initial Bell state with anti-correlated spins, quantum discord and entanglement behave in the same way for both independent cavities and a common cavity. It is found that the detunings always stabilize the quantum discord.

Large payload quantum steganography based on cavity quantum electrodynamics

Ye Tian-Yu, Jiang Li-Zhen
Chin. Phys. B, 2013, 22 (4): 040305 doi: 10.1088/1674-1056/22/4/040305
Full Text: [PDF 220 KB] (Downloads:409)
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A large payload quantum steganography protocol based on cavity quantum electrodynamics (QED) is presented in the paper, which effectively uses the evolution law of atom in cavity QED. The protocol builds up hidden channel to transmit secret messages using entanglement swapping between one GHZ state and one Bell state in cavity QED together with the Hadamard operation. The quantum steganography protocol is insensitive to cavity decay and thermal field. The capacity, imperceptibility and security against eavesdropping are analyzed in detail in the protocol. It turns out that the protocol not only has good imperceptibility but also possesses good security against eavesdropping. In addition, its capacity of hidden channel achieves five bits, larger than most of those previous quantum steganography protocols.

Controlled remote implementation of quantum operations with high-dimensional systems

Zhan You-Bang, Li Xiao-Wei, Ma Peng-Cheng, Shi Jin
Chin. Phys. B, 2013, 22 (4): 040306 doi: 10.1088/1674-1056/22/4/040306
Full Text: [PDF 234 KB] (Downloads:366)
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We present two protocols for controlled remote implementation of quantum operations between three-party high-dimensional systems. Firstly, the controlled teleportation of an arbitrary unitary operation by bidirectional quantum state teleportaion (BQST) with high-dimensional systems is considered. Then, instead of using the BQST method, a protocol for controlled remote implementation of partially unknown operations belonging to some restricted sets in high-dimensional systems is proposed. It is shown that, in these protocols, if and only if the controller would like to help the sender with the remote operations, the controlled remote implementation of quantum operations for high-dimensional systems can be completed.

Efficient generation of two-dimensional cluster states in cavity QED

Zhang Gang, Zhou Jian, Xue Zheng-Yuan
Chin. Phys. B, 2013, 22 (4): 040307 doi: 10.1088/1674-1056/22/4/040307
Full Text: [PDF 191 KB] (Downloads:479)
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We propose a scheme to achieve a kind of nontrivial multipartite pair-wise controlled phase operation in a cavity QED setup. The operation implemented is of geometrical nature and not sensitive to the thermal state of the cavity. In particular, we are manage to avoid the conventional dispersive coupling so that high speed gate operation is achieved which is very important in view of decoherence. We show that this multipartite pair-wise controlled phase operation makes the generation of two-dimensional cluster states very efficient.

Non-Markovian dynamics of two non-coupled qubits interacting with two separate reservoirs with different spectral densities

Wang Xiao-Yun, Ding Bang-Fu, Zhao He-Ping
Chin. Phys. B, 2013, 22 (4): 040308 doi: 10.1088/1674-1056/22/4/040308
Full Text: [PDF 620 KB] (Downloads:536)
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The dynamics of two non-coupled qubits independently interacting with their reservoirs is solved by the time convolutionless projection operator method. We study two-qubit quantum correlation dynamics for two different types of spectral densities, which are a Lorentzian distribution and an Ohmic spectral density with a Lorentzian-Drude cutoff function. For two qubits initially prepared in the initial Bell state, quantum discord can keep longer time and reach larger values in non-Markovian reservoirs for the first spectral distribution or by reducing the cutoff frequency for the second case. For the initial Bell-like state, the dynamic behaviors of quantum discord and entanglement are compared. The results show that a long time of quantum correlation can be obtained by adjusting some parameters in experiment and further confirm that the discord can capture quantum correlation in addition to entanglement.

Generation of multiparticle three-dimensional entanglement state via adiabatic passage

Wu Xi, Chen Zhi-Hua, Ye Ming-Yong, Chen Yue-Hua, Lin Xiu-Min
Chin. Phys. B, 2013, 22 (4): 040309 doi: 10.1088/1674-1056/22/4/040309
Full Text: [PDF 259 KB] (Downloads:465)
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A scheme is proposed for generating multiparticle three-dimensional entangled state by appropriately adiabatic evolutions, where atoms are respectively trapped in separated cavities so that individual addressing is needless. In the ideal case, losses due to the spontaneous transition of atom and the excitation of photon are efficiently suppressed since atoms are all in ground states and the fields remain in vacuum state. Compared with the previous proposals, the present scheme reduces its required operation time via simultaneously controlling four classical fields. This advantage would become even more obvious with the number of atoms increasing. The experimental feasibility is also discussed. The successful preparation of high-dimensional multiparticle entangled state among distant atoms provides better prospects for quantum communication and distributed quantum computation.

Nonautonomous solitary-wave solutions of the generalized nonautonomous cubic–quintic nonlinear Schrödinger equation with time- and space-modulated coefficients

He Jun-Rong, Li Hua-Mei
Chin. Phys. B, 2013, 22 (4): 040310 doi: 10.1088/1674-1056/22/4/040310
Full Text: [PDF 2123 KB] (Downloads:644)
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A class of analytical solitary-wave solutions to the generalized nonautonomous cubic–quintic nonlinear Schrödinger equation with time- and space-modulated coefficients and potentials are constructed by using the similarity transformation technique. Constraints for the dispersion coefficient, the cubic and quintic nonlinearities, the external potential, and the gain (loss) coefficient are presented at the same time. Various shapes of analytical solitary-wave solutions which have important applications of physical interest are studied in detail, such as the solutions in Feshbach resonance management with harmonic potentials, Faraday-type waves in the optical lattice potentials, localized solutions supported by the Gaussian-shaped nonlinearity. The stability analysis of the solutions is discussed numerically.

Incomplete nonextensive statistics and the zeroth law of thermodynamics

Huang Zhi-Fu, Ou Cong-Jie, Chen Jin-Can
Chin. Phys. B, 2013, 22 (4): 040501 doi: 10.1088/1674-1056/22/4/040501
Full Text: [PDF 217 KB] (Downloads:590)
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On the basis of the entropy of incomplete statistics (IS) and the joint probability factorization condition, two controversial problems existing in IS are investigated: one is what expression of the internal energy is reasonable for a composite system and the other is whether the traditional zeroth law of thermodynamics is suitable for IS. Some new equivalent expressions of the internal energy of a composite system are derived through accurate mathematical calculation. Moreover, a self-consistent calculation is used to expound that the zeroth law of thermodynamics is also suitable for IS, but it cannot be proven theoretically. Finally, it is pointed out that the generalized zeroth law of thermodynamics for incomplete nonextensive statistics is unnecessary and the nonextensive assumptions for the composite internal energy will lead to mathematical contradiction.

Memristor oscillator based on twin-T network

Li Zhi-Jun, Zeng Yi-Cheng
Chin. Phys. B, 2013, 22 (4): 040502 doi: 10.1088/1674-1056/22/4/040502
Full Text: [PDF 3852 KB] (Downloads:1334)
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A novel inductance-free nonlinear oscillator circuit with a single bifurcation parameter is presented in this paper. This circuit is composed of a twin-T oscillator, a passive RC network, and a flux-controlled memristor. With the increase of control parameter, the circuit exhibits complicated chaotic behaviors from double periodicity. The dynamic properties of the circuit are demonstrated by means of equilibrium stability, Lyapunov exponent spectrum, and bifurcation diagram. In order to confirm the occurrence of chaotic behavior in the circuit, an analog realization of the piecewise-linear flux controlled memristor is proposed and Pspice simulation is conducted on the resulting circuit.

Complex dynamical behavior and chaos control for fractional-order Lorenz-like system

Li Rui-Hong, Chen Wei-Sheng
Chin. Phys. B, 2013, 22 (4): 040503 doi: 10.1088/1674-1056/22/4/040503
Full Text: [PDF 791 KB] (Downloads:867)
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In this paper, the complex dynamical behavior for a fractional-order Lorenz-like system with two quadratic terms is investigated. The existence and uniqueness of solutions for this system are proved. The stabilities of equilibrium points are analyzed as one of system parameters changes. The pitchfork bifurcation is discussed for the first time. Then, the necessary conditions for the commensurate and incommensurate fractional-order systems to remain chaos are derived. The largest Lyapunov exponents and phase portraits are given to check the existence of chaos. Finally, the sliding mode control law is provided to make the states of the Lorenz-like system asymptotically stable. Numerical simulation results show that the presented approach can effectively guide the chaotic trajectories to the unstable equilibrium points.

Forced bursting and transition mechanism in CO oxidation with three time scales

Li Xiang-Hong, Bi Qin-Sheng
Chin. Phys. B, 2013, 22 (4): 040504 doi: 10.1088/1674-1056/22/4/040504
Full Text: [PDF 1267 KB] (Downloads:409)
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The mathematical model of CO oxidation with three time scales on platinum group metals is investigated, in which order gaps between the time scales related to external perturbation and the rates associated with different chemical reaction steps exist. Forced bursters, such as point-point type forced bursting and point-cycle type forced bursting, are presented. The bifurcation mechanism of forced bursting is novel, and the phenomenon where two different kinds of spiking states coexist in point-cycle type forced bursting has not been reported in previous work. A double-parameter bifurcation set of the fast subsystem is explored to reveal the transition mechanisms of different forced bursters with parameter variation.

Rhythm dynamics of complex neuronal networks with mixed bursting neurons

Lü Yong-Bing, Shi Xia, Zheng Yan-Hong
Chin. Phys. B, 2013, 22 (4): 040505 doi: 10.1088/1674-1056/22/4/040505
Full Text: [PDF 1293 KB] (Downloads:468)
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Spatiotemporal order and rhythm dynamics of a complex neuronal network with mixed bursting neurons are studied in this paper. A quantitative characteristic, the width factor, is introduced to describe the rhythm dynamics of an individual neuron, and the average width factor is used to characterize the rhythm dynamics of a neuronal network. A parameter r is introduced to denote the ratio of the short bursting neurons in the network. Then we investigate the effect of the ratio on the rhythm dynamics of the neuronal network. The critical value of r is derived, and the neurons in the network are always keeping short bursting when the ratio r is larger than the critical value.

Hash function construction using weighted complex dynamical networks

Song Yu-Rong, Jiang Guo-Ping
Chin. Phys. B, 2013, 22 (4): 040506 doi: 10.1088/1674-1056/22/4/040506
Full Text: [PDF 280 KB] (Downloads:801)
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A novel scheme to construct a hash function based on a weighted complex dynamical network (WCDN) generated from an original message is proposed in this paper. First, the original message is divided into blocks. Then, each block is divided into components, and the nodes and weighted edges are well defined from these components and their relations. Namely, the WCDN closely related to the original message is established. Furthermore, the node dynamics of the WCDN are chosen as a chaotic map. After chaotic iterations, quantization and exclusive-or operations, the fixed-length hash value is obtained. This scheme has the property that any tiny change in message can be diffused rapidly through the WCDN, leading to very different hash values. Analysis and simulation show that the scheme possesses good statistical properties, excellent confusion and diffusion, strong collision resistance and high efficiency.

Synchronization of uncertain fractional-order chaotic systems with disturbance based on fractional terminal sliding mode controller

Wang Dong-Feng, Zhang Jin-Ying, Wang Xiao-Yan
Chin. Phys. B, 2013, 22 (4): 040507 doi: 10.1088/1674-1056/22/4/040507
Full Text: [PDF 1147 KB] (Downloads:932)
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This paper provides a novel method to synchronize the uncertain fractional-order chaotic systems with external disturbance via fractional terminal sliding mode control. Based on the Lyapunov stability theory, a new fractional-order switching manifold is proposed and in order to ensure the occurrence of the sliding motion in finite time, the corresponding sliding mode control law is designed. The proposed control scheme is applied to synchronizing the fractional-order Lorenz chaotic system and fractional-order Chen's chaotic system with parameters uncertainty and external disturbance. Simulation results show the applicability and the efficiency of the proposed scheme.

General hybrid projective complete dislocated synchronization with non-derivative and derivative coupling based on parameters identification in several chaotic and hyperchaotic systems

Sun Jun-Wei, Shen Yi, Zhang Guo-Dong, Wang Yan-Feng, Cui Guang-Zhao
Chin. Phys. B, 2013, 22 (4): 040508 doi: 10.1088/1674-1056/22/4/040508
Full Text: [PDF 584 KB] (Downloads:795)
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According to the Lyapunov stability theorem, a new scheme of general hybrid projective complete dislocated synchronization with non-derivative and derivative coupling based on parameters identification is proposed under the framework of drive-response systems. Every state variable of the response system equals the summation of hybrid drive systems in the previous hybrid synchronization, however, every state variable of the drive system equals the summation of hybrid response systems while evolving with time in our method. Complete synchronization, hybrid dislocated synchronization, projective synchronization, non-derivative and derivative coupling, and parameters identification are included as its special item. Lorenz chaotic system, Rössler chaotic system, the memristor chaotic oscillator system, and hyperchaotic Lü system are discussed to show the effectiveness of the proposed methods.

Interactions among special embed-solitons for the (3+1)-dimensional Burgers equation

Zhang Wen-Ting, Dai Chao-Qing, Chen Wei-Lu
Chin. Phys. B, 2013, 22 (4): 040509 doi: 10.1088/1674-1056/22/4/040509
Full Text: [PDF 2702 KB] (Downloads:11563)
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With the help of a modified mapping method and a new mapping method, we re-study the (3+1)-dimensional Burgers equation, and derive two families of variable separation solutions. By selecting appropriate functions in the variable separation solution, we discuss interaction behaviors among taper-like, plateau-type ring, and rectangle-type embed-solitons in the periodic wave background. All interaction behaviors among them are completely elastic, and no phase shift appears after interaction.

Lie symmetries and exact solutions for a short-wave model

Chen Ai-Yong, Zhang Li-Na, Wen Shuang-Quan
Chin. Phys. B, 2013, 22 (4): 040510 doi: 10.1088/1674-1056/22/4/040510
Full Text: [PDF 261 KB] (Downloads:691)
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In this paper, the Lie symmetry analysis and the generalized symmetry method are performed for a short-wave model. The symmetries for this equation are given. The phase portraits of the traveling wave systems are analyzed by using the bifurcation theory of dynamical systems. The exact parametric representations of four types of traveling wave solutions are obtained.

Stress distribution and surface instability of an inclined granular layer

Zheng He-Peng, Jiang Yi-Min, Peng Zheng
Chin. Phys. B, 2013, 22 (4): 040511 doi: 10.1088/1674-1056/22/4/040511
Full Text: [PDF 541 KB] (Downloads:452)
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Static granular materials may avalanche suddenly under continuous quasi-static drives. The phenomenon, which is important for many engineering applications, can be explained by analyzing stability of elastic solutions. We show this for a granular layer driven by its inclination angle in gravity, of which elastic problem could be solved generally and analytically. It is found that a lost of stability may occur only at free surface of the layer. The result is considered to be relevant for understanding surface avalanches and flows observed by experiments.

Hysteresis behavior and nonequilibrium phase transition in a one-dimensional evolutionary game model

Hua Da-Yin
Chin. Phys. B, 2013, 22 (4): 040512 doi: 10.1088/1674-1056/22/4/040512
Full Text: [PDF 357 KB] (Downloads:455)
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We investigate a simply evolutionary game model in one dimension. It is found that the system exhibits a discontinuous phase transition from a defection state to a cooperation state when the payoff b of a defector exploiting a cooperator is small. Furthermore, if b is larger enough, the system exhibits two continuous phase transitions between two absorbing states and a coexistence state of cooperation and defection, respectively. The tri-critical point is estimated roughly. Moreover, it is found that the critical behavior of the continuous phase transition with an absorbing state is in the directed percolation universality class.

Nb5N6 microbolometer array for terahertz detection

Tu Xue-Cou, Kang Lin, Liu Xin-Hua, Mao Qing-Kai, Wan Chao, Chen Jian, Jin Biao-Bing, Ji Zheng-Ming, Xu Wei-Wei, Wu Pei-Heng
Chin. Phys. B, 2013, 22 (4): 040701 doi: 10.1088/1674-1056/22/4/040701
Full Text: [PDF 943 KB] (Downloads:701)
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A novel room-temperature microbolometer array chip consisting of an Nb5N6 thin film microbridge and a dipole planar antenna, which is used as a terahertz (THz) detector is described in this paper. Due to the high temperature coefficient of the resistance, which is as high as -0.7% K-1, of the Nb5N6 thin film, such an antenna-coupled microbolometer is ideal for detecting signals in a frequency range from 0.22 THz to 0.33 THz. The dc responsivity, calculated from the measured I-V curve of the Nb5N6 microbolometer, is about -760 V/W at a bias current of 0.19 mA. A typical noise voltage as low as 10 nV/Hz1/2 yields a low noise equivalent power (NEP) of 1.3×10-11 W/Hz1/2 at a modulation frequency above 4 kHz, and the best RF responsivity, characterized using infrared device measuring method, is about 580 V/W, with the corresponding NEP being 1.7× 10-11 W/Hz1/2. In order to further test the performance of Nb5N6 microbolometer, we construct a quasi-optical type receiver by attaching it to the hyperhemispherical silicon lens, and the result is that the best responsivity of the receiver is up to 320 V/W. This work could offer another way to develop a large scale focal plane array in silicon with simple technique and low cost.
RAPID COMMUNICATION

Magneto–optical trap for neutral mercury atoms Hot!

Liu Hong-Li, Yin Shi-Qi, Liu Kang-Kang, Qian Jun, Xu Zhen, Hong Tao, Wang Yu-Zhu
Chin. Phys. B, 2013, 22 (4): 043701 doi: 10.1088/1674-1056/22/4/043701
Full Text: [PDF 449 KB] (Downloads:711)
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Due to the low sensitivity to the blackbody radiation, neutral mercury is a good candidate for the most accurate optical lattice clock. Here we report the observation of cold mercury atoms in a magneto–optical trap (MOT). Because of the high vapor pressure at room temperature, the mercury source and the cold pump were cooled down to -40 ℃ and -70 ℃, respectively, to keep the science chamber in ultra-high vacuum of 6×10-9 Pa. Limited by the power of the UV cooling laser, the one beam folded MOT configuration was adopted, and 1.5×105 Hg-202 atoms were observed in the fluorescence detection.

Study on signal intensity of low field nuclear magnetic resonance via indirect coupling measurement

Jiang Feng-Ying, Wang Ning, Jin Yi-Rong, Deng Hui, Tian Ye, Lang Pei-Lin, Li Jie, Chen Ying-Fei, Zheng Dong-Ning
Chin. Phys. B, 2013, 22 (4): 047401 doi: 10.1088/1674-1056/22/4/047401
Full Text: [PDF 600 KB] (Downloads:458)
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We carry out an ultra-low-field nuclear magnetic resonance (NMR) experiment based on high-Tc superconducting quantum interference devices (SQUIDs). The measurement field is in a micro-tesla range (~ 10 μT-100 μT) and the experiment is conducted in a home-made magnetically-shielded-room (MSR). The measurements are performed by an indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using SQUID with that achieved by using the conventional low-noise-amplifier, we perform the measurements by using a commercial room temperature amplifier. The results show that in a wide frequency range (~ 1 kHz-10 kHz) the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity with measurement field increasing. This is verified by compensating the field gradient using three sets of gradient coils.
ATOMIC AND MOLECULAR PHYSICS

The collision energy effect on the stereodynamics of the Ca + HCl→CaCl +H reaction

Wang Li-Zhi, Yang Chuan-Lu, Liang Jing-Juan, Duan Li-Li, Zhang Qing-Gang
Chin. Phys. B, 2013, 22 (4): 043101 doi: 10.1088/1674-1056/22/4/043101
Full Text: [PDF 1793 KB] (Downloads:401)
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The stereodynamics of the reaction of Ca+HCl is calculated at three different collision energies based on the potential energy surface [Verbockhaven G et al. 2005 J. Chem. Phys. 122 204307] by using the quasi-classical trajectory theory. The polarization-dependent differential cross sections (PDDCSs) (2π/σ)(dσ 00/dω t), (2π/σ)(dσ 20/dω t), (2π/σ)(dσ 22+/dω t), (2π/σ)(dσ 21-/dω t) and the distributions of P(θr), P(φr), and P(θrr) are calculated. The results indicate that the rotational polarization of product CaCl presents different characteristics for the different collision energies and the effects of collision energy on the vector potential, including the alignment, orientation, and PDDCSs, are not obvious.

Multireference calculations on low-lying states and X3Πu-3Πg absorption spectra of indium dimer

Zhou Ling-Song, Yan Bing, Jin Ming-Xing
Chin. Phys. B, 2013, 22 (4): 043102 doi: 10.1088/1674-1056/22/4/043102
Full Text: [PDF 470 KB] (Downloads:477)
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Multireference configuration interaction calculations are carried out on eleven Λ-S low-lying electronic states of indium dimer. The Ω states are investigated with spin-orbit pseudopotentials via state-interacting method, and characterized with fitted spectroscopic constants based on computed potential energy curves. The vibrational structures of double-potential well 0g+(I) (3Σ g-) state are analyzed. The experimentally observed absorption spectrum centred at ~ 13000 cm-1 is simulated and assigned to X3Πu (v' =0)-3Π g transition according to the present ab initio calculations on transition energies and dipole moments functions.

Characterizing passive coherent population trapping resonance in cesium vapor cell filled with neon as buffer gas

Liu Zhi, Wang Jie-Ying, Diao Wen-Ting, He Jun, Wang Jun-Min
Chin. Phys. B, 2013, 22 (4): 043201 doi: 10.1088/1674-1056/22/4/043201
Full Text: [PDF 497 KB] (Downloads:788)
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We present a pair of phase-locked lasers with a 9.2-GHz frequency difference by injection locking of a master laser to an RF-modulation sideband of a slave diode laser. Using this laser system, the coherent population trapping (CPT) signal with a typical linewidth of ~ 182 Hz is obtained in a Cs vapor cell filled with 30 Torr (4 kPa) of neon (Ne) as buffer gas. We investigate the influence of the partial pressure of Ne buffer gas on the CPT linewidth, amplitude, and frequency shift. The results may offer some references for CPT atomic clock and CPT atomic magnetometer.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Enhanced absorption property of ordered mesoporous carbon/Co-doped ordered mesoporous carbon double-layer absorber

Guo Shao-Li, Wang Liu-Ding, Wang Yi-Ming, Wu Hong-Jing, Shen Zhong-Yuan
Chin. Phys. B, 2013, 22 (4): 044101 doi: 10.1088/1674-1056/22/4/044101
Full Text: [PDF 3157 KB] (Downloads:629)
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Ordered mesoporous carbon (OMC) and metal-doped (M-doped) OMC composites are prepared and their electromagnetic (EM) parameters are measured. Using the measured EM parameters we calculate the EM wave absorption properties of double-layer absorber which is composed of OMC as an absorbing layer and M-doped OMC for matching layer. The calculated results show that the EM wave absorption performance of OMC/OMC-Co (2.2 mm/2.1 mm) is improved remarkably. The obtained effective absorption bandwidth is up to 10.3 GHz and the minimum reflection loss reaches -47.6 dB at 14.3 GHz. The enhanced absorption property of OMC/OMC-Co can be attributed to the impedance match between air and absorber. Moreover, it can be found that for the absorber with given matching layer, larger value of Δ tanδε (=tan δε absorbing -tan δε matching) can induce better absorption performance, indicating the impedance difference between absorbing layer and matching layer plays an important role in improving the absorption property of double-layer absorber.

A low-frequency wideband metamaterial absorber based on a cave-disk resonator and resistive film

Nie Yan, Cheng Yong-Zhi, Gong Rong-Zhou
Chin. Phys. B, 2013, 22 (4): 044102 doi: 10.1088/1674-1056/22/4/044102
Full Text: [PDF 615 KB] (Downloads:460)
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A low-frequency wideband, polarization-insensitive and wide-angle metamaterial absorber (MA) is designed, simulated and analyzed. This MA consists of a periodic arrangement of cave-disk resonator (CDR), square resistive film (RF), and metal ground plane (GP) (a 0.8-mm-thick FR-4 dielectric spacer is sandwiched in between CDR and RF, and another 1.2-mm-thick FR-4 dielectric spacer is inserted in between RF and GP). The simulated results based on the finite integration technology (FIT) indicate that the absorption of the MA is greater than 90% and almost perfectly impedance-matched to the free space in the whole frequency range of 1 GHz-7 GHz. The simulated absorptions under the conditions of different polarization and incident angles indicate that this composite structure absorber is polarization-insensitive and wide-angle. Furthermore, the distribution of the power loss density indicates that the wideband absorptivity is mainly from the composite electromagnetic loss of the CDR and RF. This design provides an effective and feasible way to construct a low-frequency wideband absorber.

Polycapillary X-ray lens for secondary focusing Beijing synchrotron radiation source

Li Yu-De, Lin Xiao-Yan, Liu Shi-Gang, He Jin-Long, Guo Fei, Sun Tian-Xi, Liu Peng
Chin. Phys. B, 2013, 22 (4): 044103 doi: 10.1088/1674-1056/22/4/044103
Full Text: [PDF 7062 KB] (Downloads:559)
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According to the intensity distribution of synchrotron radiation source focused by toroidal mirror at the Beijing synchrotron radiation biological macromolecule station, the theoretical modeling of Beijing synchrotron radiation source is developed for capillary optics. With this theoretical modeling, the influences of configuration curve of polycapillary X-ray lens on transmission efficiency and working distance are analyzed. The experimental results of transmission efficiency and working distance at the biological macromolecule station are in good agreement with theoretical results.

Wide-angle and broadband graded-refractive-index antireflection coatings

Zhang Jun-Chao, Xiong Li-Min, Fang Ming, He Hong-Bo
Chin. Phys. B, 2013, 22 (4): 044201 doi: 10.1088/1674-1056/22/4/044201
Full Text: [PDF 647 KB] (Downloads:2051)
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Design and fabrication of graded-refractive-index (GRIN) antireflection (AR) coatings with wide-angle and broadband characteristics are demonstrated. The optimization of the graded-index profiles with a genetic algorithm is used in the design of GRIN AR coatings. The average reflectance over the wavelength range from 400 nm to 800 nm and angles of incidence from 0° to 80° could be reduced to only 0.1% by applying an optimized AR coating onto BK7 glass. The optimization of step-graded GRIN AR coating is further investigated in detail. A two-layer AR coating was deposited by electron beam evaporation with glancing angle deposition technology. The positional homogeneity was improved by depositing the film from two opposite directions. The microstructure of the AR coating was investigated by scanning electron microscopy. Residual reflectances of the coating sample are in agreement with theoretical calculations. The optimized GRIN AR coatings are beneficial to increase the efficiency of light utilization.

Experimental research on the longitudinal field generated by a tightly focused beam

Zhang Ming-Qian, Wang Jia, Tian Qian
Chin. Phys. B, 2013, 22 (4): 044202 doi: 10.1088/1674-1056/22/4/044202
Full Text: [PDF 867 KB] (Downloads:513)
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The longitudinal optical field is a peculiar physical phenomenon which is always involved with the domain of near-field optics. Due to its extraordinary properties, recently, it attracts increasing attention in research and application. In this work, the longitudinal fields generated by the evanescent illumination of tightly focused different polarized hollow beams are investigated. The focused light fields are numerically simulated according to the vector diffraction theory and their vector analysis is also carried out. And the longitudinal fields on the focal plane are demonstrated experimentally using a tip-enhanced scanning near-field microscopy. The simulation and experimental results show that the tightly focused radially polarized beam is suited to generate a stronger and purer longitudinal optical field at the focus.

High-precision two-dimensional atom localization via probe absorption in M-scheme atomic system

Wu Jian-Chun, Liu Zheng-Dong, Zheng Jun
Chin. Phys. B, 2013, 22 (4): 044203 doi: 10.1088/1674-1056/22/4/044203
Full Text: [PDF 383 KB] (Downloads:426)
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In the present paper, we investigate the behavior of two-dimensional atom localization in a five-level M-scheme atomic system driven by two orthogonal standing-wave fields. We find that the precision and resolution of the atom localization depends on the probe field detuning significantly. And because of the effect of the microwave field, an atom can be located at a particular position via adjusting the system parameters.

Theoretical and experimental study on all-normal-dispersion Yb-doped mode-locked fiber lasers

Chi Jun-Jie, Li Ping-Xue, Yang Chun, Zhao Zi-Qiang, Li Yao, Wang Xiong-Fei, Zhong Guo-Shun, Zhao Hong, Jiang Dong-Sheng
Chin. Phys. B, 2013, 22 (4): 044204 doi: 10.1088/1674-1056/22/4/044204
Full Text: [PDF 2165 KB] (Downloads:857)
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We report on a theoretical and experimental study of all-normal-dispersion (ANDi) Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation (NPR) is used to realize mode-locking without any dispersion compensation. Based on the coupled nonlinear Schrödinger (CNLS) equation, a model simulating mode-locked process of all-normal-dispersion ring fiber laser is developed, which shows that the achievement of stable mode-locking depends on the alignment of the polarization controller (PC) along the fast-polarization axis of the fiber, the birefringence intensity, and the net cavity dispersion. According to the theoretical analysis, stable mode-locked pulses with pulse duration 300 ps and average output power 33.9 mW at repetition rate 36 MHz are obtained.

330-W single-frequency retrievable multi-tone monolithic fiber amplifier

Wang Xiao-Lin, Zhou Pu, Leng Jin-Yong, Du Wen-Bo, Xu Xiao-Jun
Chin. Phys. B, 2013, 22 (4): 044205 doi: 10.1088/1674-1056/22/4/044205
Full Text: [PDF 466 KB] (Downloads:483)
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A single-frequency retrievable phase modulated multi-tone fiber amplifier is presented in theory and demonstrated in experiment. A multi-tone seed laser generated by a sine wave phase modulated single-frequency laser is employed for stimulated Brillouin scattering suppression in all-fiber amplifier. A demodulation signal which is π phase shifted with respect to the modulation signal is used to retrieve the single-frequency laser from the multi-tone laser. In experiment, we first optimize the all-fiber master-oscillator power-amplifier. With this amplifier, we demonstrate a single-frequency retrievable multi-tone laser with 330-W output when driven by the multi-tone seed, while the ultimate output power is only 130 W when driven by the single-frequency laser. Then, we carry out an experiment for retrieving single-frequency laser from the amplified multi-tone laser. Results indicate that the single-frequency laser can be retrieved with a sideband suppression of more than 20 dB. Retrieving an even higher power single-frequency laser is possible if a high power demodulator is available.

Polarization characteristics of single shot nanosecond laser induced breakdown spectroscopy of Al

Liu Jia, Tao Hai-Yan, Gao Xun, Hao Zuo-Qiang, Lin Jing-Quan
Chin. Phys. B, 2013, 22 (4): 044206 doi: 10.1088/1674-1056/22/4/044206
Full Text: [PDF 666 KB] (Downloads:987)
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Polarization-resolved laser-induced breakdown spectroscopy (PRLIBS) technique which can significantly reduce the polarized emission from laser plasma by placing a polarizer in front of the detector, is a powerful tool to improve line-to-continuum ratio in LIBS application. It is shown that the continuum emission from the plasma produced through ablating an Al sample by nanosecond laser pulses is much more polarized than the discrete line emission with single-pulse PRLIBS technique. The effects of laser fluence, and detection angle on the Al polarization spectrum are systematically explored experimentally. The calculated result of polarization spectrum as a function of laser fluence shows that it is in agreement with the experimental observations.

Vortex solitons in the semi-infinite gap of optically induced periodic lattices

Wang Jian-Dong, Ji Hong, Liu Pu-Sheng
Chin. Phys. B, 2013, 22 (4): 044207 doi: 10.1088/1674-1056/22/4/044207
Full Text: [PDF 893 KB] (Downloads:477)
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Vortex solitons with a ring vortex core residing in a single lattice site in the semi-infinite gap of square optical lattices are reported. These solitons are no longer bound states of the Bloch-wave unit (Bloch-wave distribution in one lattice site) at the band edge of the periodic lattice, and consequently they do not bifurcate from the corresponding band edge. For saturable nonlinearity, one family of such solitons is found, and its existing curve forms a closed loop, which is very surprising. For Kerr nonlinearity, two families of such vortex solitons are found.

On the investigation of nonlinear waves of the Hirota and the Maxwell–Bloch equation in nonlinear optics

Li Chuan-Zhong, He Jing-Song, K. Porsezian
Chin. Phys. B, 2013, 22 (4): 044208 doi: 10.1088/1674-1056/22/4/044208
Full Text: [PDF 2267 KB] (Downloads:580)
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In this paper, considering the Hirota and Maxwell–Bloch (H-MB) equations which is governed by femtosecond pulse propagation through two-level doped fibre system, we construct the Darboux transformation of this system through linear eigenvalue problem. Using this Daurboux transformation, we generate multi-soliton, positon, and breather solutions (both bright and dark breathers) of the H-MB equations. Finally, we also construct the rogue wave solutions of the above system.

Giant enhancement of a Fano-type resonance in a gain-assisted silicon slab array

Dong Zheng-Gao, Li Jia-Qi, Shao Jian, Yu Xiao-Qiang, Wang Yu-Kun, Zhai Ya
Chin. Phys. B, 2013, 22 (4): 044209 doi: 10.1088/1674-1056/22/4/044209
Full Text: [PDF 457 KB] (Downloads:562)
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Giant resonance enhancement is demonstrated to be due to the Fano interference in a grating waveguide composed of gain-assisted silicon slabs. The Fano mode is characterized by its ultra-narrow asymmetric spectrum, different from that of a pure electric or magnetic dipole. The simulation indicates that a sharp Fano-interfered lineshape is responsible for the giant resonance enhancement featuring the small-gain requirements.

The influence of defects on the effective Young’s modulus of a defective solid

Shen Wei, Fan Qun-Bo, Wang Fu-Chi, Ma Zhuang
Chin. Phys. B, 2013, 22 (4): 044601 doi: 10.1088/1674-1056/22/4/044601
Full Text: [PDF 349 KB] (Downloads:733)
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It is difficult to establish structure-property relationships in defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on Young's modulus of defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young's modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young's modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method (FEM) and strict analytical calculation show that the influence of pore radius and crack length on the effective Young's modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young's modulus in vertical direction of the crack.

Numerical and experimental study on shear coaxial injectors with hot hydrogen-rich gas/oxygen-rich gas and GH2/GO2

Jin Ping, Li Mao, Cai Guo-Biao
Chin. Phys. B, 2013, 22 (4): 044701 doi: 10.1088/1674-1056/22/4/044701
Full Text: [PDF 971 KB] (Downloads:892)
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The influences of the shear coaxial injector parameters on the combustion performance and the heat load of the combustor are studied numerically and experimentally. The injector parameters, including the ratio of the oxidizer pressure drop to the combustor pressure (DP), the velocity ratio of fuel to oxidizer (RV), the thickness (WO), and the recess (HO) of the oxidizer injector posttip, the temperature of the hydrogen-rich gas (TH) and the oxygen-rich gas (TO), are integrated by the orthogonal experimental design method to investigate the performance of the shear coaxial injector. The gaseous hydrogen/oxygen at ambient temperature (GH2/GO2), and the hot hydrogen-rich gas/oxygen-rich gas are used here. The length of the combustion (LC), the average temperatures of the combustor wall (TW), and the faceplate (TF) are selected as the indicators. The tendencies of the influences of injector parameters on the combustion performance and the heat load of the combustor for the GH2/GO2 case are similar to those in the hot propellants case. However, the combustion performance in the hot propellant case is better than that in the GH2/GO2 case, and the heat load of the combustor is also larger than that in the latter case.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Analysis of electron energy distribution function in a magnetically filtered complex plasma

M K Deka, H Bailung, N C Adhikary
Chin. Phys. B, 2013, 22 (4): 045201 doi: 10.1088/1674-1056/22/4/045201
Full Text: [PDF 409 KB] (Downloads:753)
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The electron energy distribution function (EEDF) for a magnetically filtered dusty plasma is studied in a dusty double plasma device where the electron energy can be varied from 0.15 eV to ~ 2.8 eV and plasma density from 106 cm-3 to 109 cm-3. The characteristics of EEDF for these ranges of plasma parameters are investigated in a pristine plasma as well as in a dusty plasma. The results show that in the presence of dust, there is a drastic modification in EEDF patterns in a plasma with higher electron temperature and density than those in a low temperature and low density plasma produced by the magnetic filter.

Enhanced optical absorption by Ag nanoparticles in thin film Si solar cell

Chen Feng-Xiang,Wang Li-Sheng, Xu Wen-Ying
Chin. Phys. B, 2013, 22 (4): 045202 doi: 10.1088/1674-1056/22/4/045202
Full Text: [PDF 244 KB] (Downloads:1043)
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Thin film solar cells have potentials to significantly reduce the cost of photovoltaics. Light trapping is crucial to such a thin film silicon solar cell because of a low absorption coefficient due to its indirect band gap. In this paper, we investigate the suitability of surface plasmon resonance Ag nanoparticles for enhancing optical absorption in the thin film solar cell. For evaluating the transmittance capability of Ag nanoparticles and the conventional antireflection film, an enhanced transmittance factor is introduced. We find that under the solar spectrum AM1.5, the transmittance of Ag nanoparticles with radius over 160 nm is equivalent to that of conventional textured antireflection film, and its effect is better than that of the planar antireflection film. The influence of the surrounding medium is also discussed.

Selective triggering of phase change in dielectric by femtosecond pulse trains based on electron dynamics control

Xu Chuan-Cai, Jiang Lan, Leng Ni, Liu Peng-Jun
Chin. Phys. B, 2013, 22 (4): 045203 doi: 10.1088/1674-1056/22/4/045203
Full Text: [PDF 921 KB] (Downloads:356)
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In this study we experimentally reveal that the phase change mechanism can be selectively triggered by shaping femtosecond pulse trains based on electron dynamics control (EDC), including manipulation of excitations, ionizations, densities, and temperatures of electrons. By designing the pulse energy distribution to adjust the absorptions, excitations, ionizations, and recombinations of electrons, the dominant phase change mechanism experiences transition from nonthermal to thermal process. This phenomenon is observed in quadruple, triple, and double pulses per train ablation of fused silica separately. This opens up possibilities for controlling phase change mechanisms by EDC, which is of great significance in laser processing of dielectric and fabrication of integrated nano- and micro-optical devices.

The effects of process conditions on the plasma characteristic in radio-frequency capacitively coupled SiH4/NH3/N2 plasmas: Two-dimensional simulations

Liu Xiang-Mei, Song Yuan-Hong, Jiang Wei, Yi Lin
Chin. Phys. B, 2013, 22 (4): 045204 doi: 10.1088/1674-1056/22/4/045204
Full Text: [PDF 935 KB] (Downloads:1186)
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A two-dimensional (2D) fluid model is presented to study the behavior of silicon plasma mixed with SiH4, N2, and NH3 in radio-frequency capacitively coupled plasma (CCP) reactor. The plasma-wall interaction (including the deposition) is modeled by using surface reaction coefficients. In the present paper we try to identify, by numerical simulations, the effect of variations of the process parameters on the plasma properties. It is found from our simulations that by increasing the gas pressure and the discharge gap, the electron density profile shape changes continuously from an edge-high to a center-high, thus the thin films become more uniform. Moreover, as the N2/NH3 ratio increases from 6/13 to 10/9, the hydrogen content can be significantly decreased, without decreasing significantly the electron density.

Determining resistance of X-pinch plasma Hot!

Zhao Shen, Xue Chuang, Zhu Xin-Lei, Zhang Ran, Luo Hai-Yun, Zou Xiao-Bing, Wang Xin-Xin, Ning Cheng, Ding Ning, Shu Xiao-Jian
Chin. Phys. B, 2013, 22 (4): 045205 doi: 10.1088/1674-1056/22/4/045205
Full Text: [PDF 957 KB] (Downloads:500)
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The current and the voltage of an X-pinch were measured. The inductance of the X-pinch was assumed to be a constant and estimated by the calculation of the magnetic field based on the well-known Biot-Savart's Law. The voltage of the inductance was calculated with L·di /dt and subtracted from the measured voltage of the X-pinch. Then, the resistance of the X-pinch was determined and the following results were obtained. At the start of the current flow the resistance of the exploding wires is several tens of Ohms, one order of magnitude higher than the metallic resistance of the wires at room temperature, and then it falls quickly to about 1 Ω , which reflects the physical processes occurring in the electrically exploding wires, i.e., a current transition from the highly resistive wire core to the highly conductive plasma. It was shown that the inductive contribution to the voltage of the X-pinch is less than the resistive contribution. For the wires we used, the wires' material and diameter have no strong influence on the resistance of the X-pinch, which may be explained by the fact that the current flows through the plasma rather than through the metallic wire itself. As a result, the current is almost equally divided between two parallel X-pinches even though the diameter and material of the wires used for these two X-pinches are significantly different.

Nanopowder production by gas-embeded electrical explosion of wire

Zou Xiao-Bing, Mao Zhi-Guo, Wang Xin-Xin, Jiang Wei-Hua
Chin. Phys. B, 2013, 22 (4): 045206 doi: 10.1088/1674-1056/22/4/045206
Full Text: [PDF 1820 KB] (Downloads:563)
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A small electrical explosion of wire (EEW) setup for nanopowder production is constructed. It consists of a low inductance capacitor bank of 2 μF-4 μF typically charged to 8 kV-30 kV, a triggered gas switch, and a production chamber housing the exploding wire load and ambient gas. With the EEW device, nanosize powders of titanium oxides, titanium nitrides, copper oxides, and zinc oxides are successfully synthesized. The average particle size of synthesized powders under different experimental conditions is in a range of 20 nm-80 nm. The pressure of ambient gas or wire vapor can strongly affect the average particle size. The lower the pressure, the smaller the particle size is. For wire material with relatively high resistivity, such as titanium, whose deposited energy Wd is often less than sublimation energy Ws due to the flashover breakdown along the wire prematurely ending the Joule heating process, the synthesized particle size of titanium oxides or titanium nitrides increases with overheat coefficient k (k =Wd/Ws ) increasing.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Quantitative evaluation of equatorial small-angle X-ray scattering for cylindrical fibers

Li Xiao-Yun, Li Xiu-Hong, Yang Chun-Ming, Hua Wen-Qiang, Zhao Nie, Miao Xia-Ran, Tian Feng, Wang Yu-Zhu, Bian Feng-Gang, Wang Jie
Chin. Phys. B, 2013, 22 (4): 046102 doi: 10.1088/1674-1056/22/4/046102
Full Text: [PDF 1552 KB] (Downloads:811)
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Elongated microvoids, internal fibrillar structure, and edge scattering from both surface refraction cause an equatorial streak in small angle X-ray scattering. A model for analyzing edge scattering of fibers is proposed. Simulation results indicate that the intensity of edge scattering from surface refraction of a cylindrical fiber is strong and makes an important contribution to the equatorial streak. Two factors influence edge scattering intensity. One is the sample-to-detector distance (D); edge scattering intensity increases with increasing D. The equatorial streak becomes weak when D is shortened. The other factor is the refraction index. Edge scattering intensity increases as the real component of the refraction index decreases. In experiment, weak or even no equatorial streaks were found for samples measured in a roughly index-matching fluid. Edge scattering can be eliminated or weakened, and it can be calculated by comparing the intensities of a cylindrical fiber when it is measured in air and in index-matching fluid. The simulation data are basically in agreement with the experimental data.

Dual role of multiple-transistor charge sharing collection in single-event transient

Guo Yang, Chen Jian-Jun, He Yi-Bai, Liang Bin, Liu Bi-Wei
Chin. Phys. B, 2013, 22 (4): 046103 doi: 10.1088/1674-1056/22/4/046103
Full Text: [PDF 594 KB] (Downloads:394)
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As technologies scale down in size, that multiple-transistors are affected by a single ion becomes a universal phenomenon, and some new effects are present in single event transients (SETs) due to the charge sharing collection of the adjacent multiple-transistors. In this paper, not only the off-state p-channel metal-oxide semiconductor field-effect transistor (PMOS FET), but also the on-state PMOS is struck by a heavy-ion in two-transistor inverter chain, due to the charge sharing collection and the electrical interaction, the SET induced by striking the off-state PMOS is efficiently mitigated by the pulse quenching effect, but the SET induced by striking the on-state PMOS becomes dominant. It is indicated in this study that in the advanced technologies, the SET will no longer just be induced by ion's striking the off-state transistor, and the SET sensitive region will no longer just surround the off-state transistor either, as it is in the older technologies. We also discuss this issue in three-transistor inverter in depth, and the study illustrates that three-transistor inverter is still the better replacer for spaceborne integrated circuits design in the advanced technologies.

Influence of strain and electric field on the properties of silicane

Cheng Gang, Liu Peng-Fei, Li Zi-Tao
Chin. Phys. B, 2013, 22 (4): 046201 doi: 10.1088/1674-1056/22/4/046201
Full Text: [PDF 288 KB] (Downloads:596)
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We investigate the influence of strain and electric field on the properties of silicane sheet. Some elastic parameters of silicane, such as an in-plane stiffness of 52.55 N/m and a Poisson's ratio of 0.24, are obtained by calculating the strain energy. Compared with silicene, silicane is softer because of its relatively weaker Si-Si bonds. The band structure of silicane is tunable by a uniform tensile strain, with the increase of which the band gap decreases monotonously. Moreover, silicane undergoes an indirect-direct gap transition under a small strain, and a semiconductor-metal transition under a large strain. The electric field can change the Si-H bond length of silicane significantly. When a strong field is applied, the H atom at the high potential side becomes desorbed, while the H atom at the low potential side keeps bonded. So an external electric field can help to produce single-side hydrogenated silicene from silicane. We believe this study will be helpful for the application of silicane in the future.

Structural and mechanical stability of rare-earth diborides

Haci Ozisik, Engin Deligoz, Kemal Colakoglu, Gokhan Surucu
Chin. Phys. B, 2013, 22 (4): 046202 doi: 10.1088/1674-1056/22/4/046202
Full Text: [PDF 207 KB] (Downloads:1005)
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Structural and mechanical properties of several rare-earth diborides were systematically investigated by first principles calculations. Specifically, we studied XB2, where X=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Lu in the hexagonal AlB2, ReB2, and orthorhombic OsB2-type structures. The lattice parameters, bulk modulus, bond distances, second order elastic constants, and related polycrystalline elastic moduli (e.g. shear modulus, Young's modulus, Poisson's ratio, Debye temperature, sound velocities) were calculated. Our results indicate that these compounds are mechanically stable in the considered structures, and according to the "Chen's method," the predicted Vickers hardness shows that they are hard materials in AlB2- and OsB2-type structures.

Effect of grain size and arrangement on dynamic damage evolution of ductile metal

Qi Mei-Lan, Zhong Sheng, He Hong-Liang, Fan Duan, Zhao Li
Chin. Phys. B, 2013, 22 (4): 046203 doi: 10.1088/1674-1056/22/4/046203
Full Text: [PDF 1240 KB] (Downloads:800)
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Plate-impact experiments have been carried out to examine the effect of grain size and grain arrangement on the damage evolution of ultrapure aluminum. Two groups of samples, "cross-cut" and "longitudinal-cut," are obtained from the rolled aluminum rod along different directions. The peak compressive stress is approximately 1.25 GPa-1.61 GPa, which can cause incipient spall damage that is correlated to the material microstructure. The metallographic analyses of all recovered samples show that nearly all damage nucleates at the grain boundaries, especially those with larger curvature. Moreover, under lower shock stress, the spall strength of the "longitudinal-cut" sample is smaller than that of the "cross-cut" sample, because the different grain sizes and arrangement of the two samples cause different nucleation, growth, and coalescence processes. In this study, the difference in the damage distribution between "longitudinal-cut" and "cross-cut" samples and the causes for this difference under lower shock-loading conditions are also analyzed by both qualitative and semi-quantitative methods. It is very important for these conclusions to establish reasonable and perfect equation of damage evolution for ductile metals.

Kinetic Monte Carlo simulations of optimization of self-assembly quantum rings growth strategy based on substrate engineering

Liu Jian-Tao, Feng Hao, Yu Zhong-Yuan, Liu Yu-Min, Shi Qiang, Song Xin, Zhang Wen, Peng Yi-Wei
Chin. Phys. B, 2013, 22 (4): 046801 doi: 10.1088/1674-1056/22/4/046801
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In this paper, the kinetic Monte Carlo simulations of the self-assembly quantum rings (QRs) based on the substrate engineering, which is related to the eventual shape of the formed quantum ring, are implemented. According to the simulation results, the availability of the QR with tunable size and the formation of smooth shape on the ideal flat substrate are checked. Through designing the substrate engineering, i.e., changing the depth, the separation and the ratio between the radius and the height of the embedded inclusions, the position and size of QR can be controlled and eventually the growth strategy of optimizing the self-assembly QRs is accomplished.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Symmetry and size effects on energy and entanglement of an exciton in coupled quantum dots

Shen Man, Bai Yan-Kui, An Xing-Tao, Liu Jian-Jun
Chin. Phys. B, 2013, 22 (4): 047101 doi: 10.1088/1674-1056/22/4/047101
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We study theoretically the essential properties of an exciton in vertically coupled Gaussian quantum dots in the presence of an external magnetic field. The ground state energy of a heavy-hole exciton is split into four energy levels due to the Zeeman effect. For the symmetrical system, the entanglement entropy of the exciton state can reach a value of 1. However, for a system with broken symmetry, it is close to zero. Our results are in good agreement with previous studies.

Influence of Schottky drain contacts on the strained AlGaN barrier layer of AlGaN/AlN/GaN heterostructure field-effect transistors

Cao Zhi-Fang, Lin Zhao-Jun, Lü Yuan-Jie, Luan Chong-Biao, Wang Zhan-Guo
Chin. Phys. B, 2013, 22 (4): 047102 doi: 10.1088/1674-1056/22/4/047102
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Rectangular Schottky drain AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with different gate contact areas and conventional AlGaN/AlN/GaN HFETs as control were both fabricated with same size. It was found there is a significant difference between Schottky drain AlGaN/AlN/GaN HFETs and the control group both in drain series resistance and in two-dimensional electron gas (2DEG) electron mobility in the gate-drain channel. We attribute this to the different influence of Ohmic drain contacts and Schottky drain contacts on the strained AlGaN barrier layer. For conventional AlGaN/AlN/GaN HFETs, annealing drain Ohmic contacts gives rise to a strain variation in the AlGaN barrier layer between the gate contacts and the drain contacts, and results in strong polarization Coulomb field scattering in this region. In Schottky drain AlGaN/AlN/GaN HFETs, the strain in the AlGaN barrier layer is distributed more regularly.

Spin-dependent negative differential conductance in transport through single-molecule magnets

Luo Wei, Wang Rui-Qiang, Hu Liang-Bin, Yang Mou
Chin. Phys. B, 2013, 22 (4): 047201 doi: 10.1088/1674-1056/22/4/047201
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Transport properties are theoretically studied through an anisotropy single-molecule magnet symmetrically connected to two identical ferromagnetic leads. It is found that even though in parallel configuration of leads' magnetizations, the total current still greatly depends on the spin polarization of leads at certain particular bias region, and thus for large polarization a prominent negative differential conductance (NDC) emerges. This originates from the joint effect of single-direction transitions and spin polarization, which removes the symmetry between spin-up and spin-down transitions. The present mechanism of NDC is remarkably different from the previously reported mechanisms. To clarify the physics of the NDC, we further monitored the shot noise spectroscopy and found that the appearance of the NDC is accompanied by the rapid decrease of Fano factor.

Spin-polarized injection into p-type GaAs layer from a Co2MnAl injector Hot!

Yuan Si-Peng, Shen Chao, Zheng Hou-Zhi, Liu Qi, Wang Li-Guo, Meng Kang-Kang, Zhao Jian-Hua
Chin. Phys. B, 2013, 22 (4): 047202 doi: 10.1088/1674-1056/22/4/047202
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Electric luminescence and its circular polarization in a Co2MnAl injector-based light emitting diode (LED) has been detected at the transition of e-AC0, where injected spin-polarized electrons recombine with bound holes at carbon acceptors. A spin polarization degree of 24.6% is obtained at 77 K after spin-polarized electrons traverse a distance of 300 nm before they recombine with holes bound at neutral carbon acceptors in a p+-GaAs layer. The large volume of the p+-GaAs layer can facilitate the detection of weak electric luminescence (EL) from e-AC0 emission without being quenched at higher bias as in quantum wells. Moreover, unlike the interband electric luminescence in the p+-GaAs layer, where the spin polarization of injected electrons is destroyed by very effective electron-hole exchange scattering (BAP mechanism), the spin polarization of injected electrons seems to survive during their recombination with holes bound at carbon acceptors.

Design of electron wave filters in monolayer graphene with velocity modulations

Sun Li-Feng, Dong Li-Min, Fang Chao
Chin. Phys. B, 2013, 22 (4): 047203 doi: 10.1088/1674-1056/22/4/047203
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We compare the transport properties of electrons in monolayer graphene by modulating the Fermi velocity inside the barrier. A critical transmission angle is found only when the Fermi velocity in the barriers is larger than the one outside the barriers. It is shown that the transmission exhibits periodicity with the incident angle below the critical transmission angle, and attenuates exponentially in the opposite situation. For both situations, peak splitting occurs in the transmission as the number of the velocity barriers increases, and the characteristics of the transmission suggest an interesting application of an excellent band-pass filter. The dependence of the conductance on the Fermi energy through identical velocity-modulation structure differs wildly with different Fermi velocities of the barrier. The counterpart of the peak splitting is the sharp oscillations in the conductance profile. Furthermore, some oscillations for the multiple barriers are so sharp that the structure may be used as an excellent sensor.

Perforated nanocap array: Facile fabrication process and efficient surface enhanced Raman scattering with fluorescence suppression

Wang Jun, Huang Li-Qing, Tong Hui-Min, Zhai Li-Peng, Yuan Lin, Zhao Li-Hua, Zhang Wei-Wei, Shan Dong-Zhi, Hao Ai-Wen, Feng Xue-Hong
Chin. Phys. B, 2013, 22 (4): 047301 doi: 10.1088/1674-1056/22/4/047301
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Recently, individual reduced-symmetry metal nanostructures and their plasmonic properties have been studied extensively. However, little attention has been paid to the approach to fabricating ordered reduced-symmetry metal nanostructure array. In this paper, a novel perforated silver nanocap array with high surface-enhanced Raman scattering (SERS) activity and fluorescence suppression is reported. The array is fabricated by electron beam evaporating Ag onto the perforated barrier layer side of hard anodization (HA) anodic aluminum oxide (AAO) template. The morphology and optical property of the perforated silver nanocap array are characterized by atomic force microscope (AFM), scanning electron microscope (SEM) and absorption spectra. The results of SERS measurements reveal that the perforated silver nanocap array offers high SERS activity and fluorescence suppression compared with imperforated silver nanocap array.

Pure spin polarized transport based on Rashba spin–orbit interaction through the Aharonov–Bohm interferometer embodied four-quantum-dot ring

Wu Li-Jun, Han Yu
Chin. Phys. B, 2013, 22 (4): 047302 doi: 10.1088/1674-1056/22/4/047302
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The spin-polarized linear conductance spectrum and current–voltage characteristics in a four-quantum-dot ring embodied into Aharonov–Bohm (AB) interferometer are investigated theoretically by considering a local Rashba spin–orbit interaction. It shows that the spin-polarized linear conductance and the corresponding spin polarization each are a function of magnetic flux phase at zero bias voltage with a period of 2π, and that Hubbard U cannot influence the electron transport properties in this case. When adjusting appropriately structural parameter of inter-dot coupling and dot-lead coupling strength, the electronic spin polarization can reach a maximum value. Furthermore, by adjusting the bias voltages applied to the leads, the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situation. Based on the numerical results, such a model can be applied to the design of spin filter device.

Determination of interface states and their time constant for Au/SnO2/n-Si (MOS) capacitors using admittance measurements

H. M. Baran, A. Tataroğlu
Chin. Phys. B, 2013, 22 (4): 047303 doi: 10.1088/1674-1056/22/4/047303
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The frequency dependence of admittance measurements (capacitance-voltage (C-V) and conductance-voltage (G/ω -V)) of Au/SnO2/n-Si (MOS) capacitors was investigated by taking into account the effects of the interface states (Nss) and series resistance (Rs) at room temperature. Admittance measurements were carried out in frequency and bias voltage ranges of 1 kHz-1 MHz and (-5 V)-(+9 V), respectively. The values of Nss and Rs were determined by using a conductance method and estimating from the admittance measurements of the MOS capacitors. At low frequencies, the interface states can follow the AC signal and yield excess capacitance and conductance. In addition, the parallel conductance (Gp/ω) versus log (f) curves at various voltages include a peak due to the presence of interface states. It is observed that the Nss and their time constant (τ) range from 1.23× 1012 eV-1·cm-2 to 1.47× 1012 eV-1·cm-2 and from 7.29× 10-5 s to 1.81× 10-5 s, respectively.

Hot carrier degradation and a new lifetime prediction model in ultra-deep sub-micron pMOSFET

Lei Xiao-Yi, Liu Hong-Xia, Zhang Kai, Zhang Yue, Zheng Xue-Feng, Ma Xiao-Hua, Hao Yue
Chin. Phys. B, 2013, 22 (4): 047304 doi: 10.1088/1674-1056/22/4/047304
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The hot carrier effect (HCE) of ultra-deep sub-micron p-channel metal-oxide semiconductor field-effect transistor (pMOSFET) is investigated in this paper. Experiments indicate that the generation of positively charged interface states is the predominant mechanism in the case of ultra-deep sub-micron pMOSFET. The relation of the pMOSFET hot carrier degradation to stress time (t), channel width (W), channel length (L), and stress voltage (Vd) is then discussed. Based on the relation, a lifetime prediction model is proposed, which can predict the lifetime of the ultra-deep sub-micron pMOSFET accurately and reflect the influence of the factors on hot carrier degradation directly.

Influence of nanomechanical force on the electronic structure of InAs/GaAs quantum dots

Song Xin, Feng Hao, Liu Yu-Min, Yu Zhong-Yuan
Chin. Phys. B, 2013, 22 (4): 047305 doi: 10.1088/1674-1056/22/4/047305
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We show nanomechanical force is useful to dynamically control the optical response of self-assembled quantum dots, giving a method to shift electron and heavy hole levels, interval of electron and heavy hole energy levels, and the emission wavelength of quantum dots (QDs). The strain, the electron energy levels, and heavy hole energy levels of InAs/GaAs(001) quantum dots with vertical nanomechanical force are investigated. Both of the lattice mismatch and nanomechanical force are considered at the same time. The results show that the hydrostatic and the biaxial strains inside the QDs subjected to nanomechanical force vary with nanomechanical force. That gives the control for tailoring band gaps and optical response. Moreover, due to strain-modified energy, the band edge is also influenced by nanomechanical force. The nanomechanical force is shown to influence the band edge. As is well known, the band offset affects the electronic structure, which shows that the nanomechanical force is proved to be useful to tailor the emission wavelength of QDs. Our research helps to better understand how the nanomechanical force can be used to dynamically control the optics of quantum dots.

Different effects of Ce-doping on orbital and spin ordering in perovskite vanadate Sm1-xCexVO3

Hu Xin-Bo, Hu Ling, Luo Xuan, Zhao Bang-Chuan, Sun Yu-Ping
Chin. Phys. B, 2013, 22 (4): 047501 doi: 10.1088/1674-1056/22/4/047501
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The effects of Ce-doping on the phase transition of the orbital/spin ordering (OO/SO) are studied through the structural, magnetic, and electrical transport measurements of perovskite vanadate Sm1-xCexVO3. The measurements of structure show that the cell volume decreases as x ≤ 0.05, and then increases as Ce-doping level increases further. The OO state exists but is suppressed progressively in the sample with x ≤ 0.2 and disappears as x>0.2. The temperature at which the C-type SO transition is present increases monotonically with Ce-doping level increasing. The temperature dependence of resistivity for each of all samples shows a semiconducting transport behavior and the transport can be well described by the thermal activation model. The activation energy first decreases as x ≤ 0.2, and then increases for further doping. The obtained results are discussed in terms of the mixed-valent state of the doped-Ce ions.

Flexible tuning microwave permeability spectrum in [ferromagnet/antiferromagnet]n exchange-biasedmultilayer stack structure

Jin Li-Chuan, Zhang Huai-Wu, Tang Xiao-Li, Bai Fei-Ming, Zhong Zhi-Yong
Chin. Phys. B, 2013, 22 (4): 047502 doi: 10.1088/1674-1056/22/4/047502
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NiFe/[IrMn/NiFe/IrMn]5/[NiFe/IrMn]4/NiFe structured exchange-biased multilayer films are designed and prepared by magnetron sputtering. The static and the microwave magnetic properties are systematically investigated. The results reveal that adding partially pinned ferromagnetic layer can effectively broaden the ferromagnetic resonance linewidth toward low frequency domain. Moreover, a wideband multi-peak permeability spectrum with a 3.1-GHz linewidth is obtained by overlapping the spectra of different partially pinned ferromagnetic layers and [antiferromagnet/ferromagnet/antiferromagnet]n stacks. Our results show that the linewidth of the sample can be feasibly tuned through controlling the proper exchange bias fields of different stacks. The designed multilayered thin films have potential application for a tunable wideband high frequency noise filter.

Composition influence on the microstructures and magnetic properties of FePt thin films

Liu Li-Wang, Dang Hong-Gang, Sheng Wei, Wang Ying, Cao Jiang-Wei, Bai Jian-Min, Wei FuLin
Chin. Phys. B, 2013, 22 (4): 047503 doi: 10.1088/1674-1056/22/4/047503
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The FexPt100-x (10 nm) (x = 31-51) thin films are fabricated on Si (100) substrates by using magnetron sputtering. The highly ordered L10 FePt phase is obtained after post-annealing at 700 ℃ in Fe47Pt53 thin film. The sample shows good perpendicular anisotropy with a square loop and a linear loop in the out-of-plane and the in-plane direction, respectively. The variations of the magnetic domains are investigated in the films when the content value of Fe changes from 31% to 51%.

Electronic structures and magnetic couplings of B-, C-, and N-doped BeO

Pang Hua, Zhang Sha, Li Fa-Shen
Chin. Phys. B, 2013, 22 (4): 047504 doi: 10.1088/1674-1056/22/4/047504
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The electronic structures and magnetic properties of B-, C-, and N-doped BeO supercells are investigated by means of ab initio calculations using density functional theory. The magnetic exchange constants of C-doped BeO at different doping levels are also calculated. A phenomenological band structure model based on p-d exchange-like p-p level repulsion between the dopants is raised forward to explain the magnetic ground states in B-, C-, and N-doped BeO systems. The evolution from antiferromagnetic phase to ferromagnetic phase of C-doped BeO supercell with C concentration decreasing can also be well explained using this model. The findings in this study provide a simple guide for the design of band structure for magnetic sp-electron semiconductor.

Electronic structure and magnetic and optical properties of double perovskite Bi2FeCrO6 from first-principles investigation

Song Zhe-Wen, Liu Bang-Gui
Chin. Phys. B, 2013, 22 (4): 047506 doi: 10.1088/1674-1056/22/4/047506
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Double perovskite Bi2FeCrO6, related with multiferroic BiFeO3, is very interesting because of its strong ferroelectricity and high magnetic Curie temperature beyond room temperature. We investigate its electronic structure and magnetic and optical properties by using a full-potential density-functional method. Our optimization shows that it is a robust ferrimagnetic semiconductor. This nonmetallic phase is formed due to crystal field splitting and spin exchange splitting, in contrast to previous studies. Spin exchange constants and optical properties are calculated. Our Monte Carlo magnetic Curie temperature is 450 K, much higher than previous calculated value and consistent with experimental results. Our study and analysis reveal that the main magnetic mechanism is an antiferromagnetic superexchange between Fe and Cr over the intermediate O atom. These result are useful to understanding such perovskite materials and exploring their potential applications.

Half-metallic ferromagnetism in C-doped zinc-blende ZnO: A first-principles study

Dan Xu, Yao Kai-Lun, Gao Guo-Ying, Ma Guo-Qiang
Chin. Phys. B, 2013, 22 (4): 047507 doi: 10.1088/1674-1056/22/4/047507
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We perform a first-principles study of electronic structure and magnetism of C-doped zinc-blende ZnO using the full-potential linearized augmented plane wave method. Results show that C-doped zinc-blende ZnO exhibits half-metallic ferromagnetism with a stable ferromagnetic ground state. The calculated magnetic moment of the 32-atom supercell containing one C dopant is 2.00 μ B, and the C dopant contributes most. The calculated low formation energy suggests that C-doped zinc-blende ZnO is energetically stable. The hole-mediated double exchange mechanism can be used to explain the ferromagnetism in C-doped zinc-blende ZnO.

Non-depletion floating layer in SOI LDMOS for enhancing breakdown voltage and eliminating back-gate bias effect

Zheng Zhi, Li Wei, Li Ping
Chin. Phys. B, 2013, 22 (4): 047701 doi: 10.1088/1674-1056/22/4/047701
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A non-depletion floating layer silicon-on-insulator (NFL SOI) lateral double-diffused metal-oxide-semiconductor (LDMOS) is proposed and the NFL-assisted modulated field (NFLAMF) principle is investigated in this paper. Based on this principle, the floating layer can pin the potential for modulating bulk field. In particular, the accumulated high concentration of holes at the bottom of the NFL can efficiently shield the electric field of the SOI layer and enhance the dielectric field in the buried oxide layer (BOX). At variation of back-gate bias, the shielding charges of NFL can also eliminate back-gate effects. The simulated results indicate that the breakdown voltage (BV) is increased from 315 V to 558 V compared to the conventional reduced surface field (RESURF) SOI (CSOI) LDMOS, yielding a 77% improvement. Furthermore, due to the field shielding effect of the NFL, the device can maintain the same breakdown voltage of 558 V with a thinner BOX to resolve the thermal problem in an SOI device.

Effects of mode coupling on the admittance of an AT-cut quartz thickness-shear resonator

He Hui-Jing, Yang Jia-Shi, Zhang Wei-Ping, Wang Ji
Chin. Phys. B, 2013, 22 (4): 047702 doi: 10.1088/1674-1056/22/4/047702
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We study the effects of couplings to flexure and face-shear modes on the admittance of an AT-cut quartz plate thickness-shear mode resonator. Mindlin's two-dimensional equations for piezoelectric plates are employed. Electrically forced vibration solutions are obtained for three cases: pure thickness-shear mode alone; two coupled modes of thickness shear and flexure; and three coupled modes of thickness shear, flexure, and face shear. Admittance is calculated and its dependence on the driving frequency and the length/thickness ratio of the resonator is examined. Results show that near the thickness-shear resonance, admittance assumes maxima, and that for certain values of the length/thickness ratio, the coupling to flexure causes severe admittance drops, while the coupling to the face-shear mode causes additional admittance changes that were previously unknown and hence are not considered in current resonator design practice.

Optical properties of ultra-thin InN layer embedded in InGaN matrix for light emitters

Yang Wei, Wu Yi-Yang, Liu Ning-Yang, Liu Lei, Chen Zhao, Hu Xiao-Dong
Chin. Phys. B, 2013, 22 (4): 047801 doi: 10.1088/1674-1056/22/4/047801
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We theoretically investigate the optical properties of ultra-thin InN layer embedded in InGaN matrix for light emitters. The peak emission wavelength extends from ultraviolet (374 nm) to green (536 nm) with InN quantum well thickness increasing from 1 monolayer to 2 monolayers, while the overlap of electron-hole wave function remains at a high level (larger than 90%). Increase of In content in InGaN matrix provides a better approach to longer wavelength emission, which only reduces the spontaneous emission rate slightly compared with the case of increasing In content of the conventional InGaN quantum well. Also, the transparency carrier density derived from gain spectrum is of the same order as that in the conventional blue laser diode. Our study provides skillful design on the development of novel structure InN-based light emitting diodes as well as laser diodes.

Analysis of frequency selective surface absorbers via a novel equivalent circuit method

Liu Li-Guo, Wu Wei-Wei, Mo Jin-Jun, Fu Yun-Qi, Yuan Nai-Chang
Chin. Phys. B, 2013, 22 (4): 047802 doi: 10.1088/1674-1056/22/4/047802
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An equivalent circuit (EC) method for absorbers design is proposed in this paper. Without using full-wave analysis, the EC method can predict the performance of the absorbers. This method is employed to synthesize broadband absorbers by inserting the resistors respectively into the single- and double-square loops structures, then two different prototypes with broadband absorbing frequency bands are manufactured and measured. By comparisons with the results both by using the full-wave analysis and by the measurements, the correctness of the new EC method is verified. Some factors which affect the absorbing bandwidth are also investigated. Due to its fast and accurate characteristics, the EC method which can be theoretically applied to arbitrary FSS is a good candidate for broadband design of the absorbers.

Engineering of electronic and optical properties of ZnO thin films via Cu doping

Zhang Guo-Heng, Deng Xiao-Yan, Xue Hua, Xiang Gang
Chin. Phys. B, 2013, 22 (4): 047803 doi: 10.1088/1674-1056/22/4/047803
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ZnO thin films doped with different Cu concentrations are fabricated by reactive magnetron sputtering technique. XRD analysis indicates that the crystal quality of the ZnO:Cu film can be enhanced by moderate level of Cu-doping in the sputtering process. The results of XPS spectra of zinc, oxygen, and copper elements show that Cu-doping has an evident and complicated effect on the chemical state of oxygen, but little effect on those of zinc and copper. Interestingly, further investigation of the optical properties of ZnO:Cu samples shows that the transmittance spectra exhibit both red shift and blue shift with the increase of Cu doping, in contrast to the simple monotonic behavior of Burstein-Moss effect. Analysis reveals that this is due to the competition between oxygen vacancies and intrinsic and surface states of oxygen in the sample. Our result may suggest an effective way of tuning the bandgap of ZnO samples.

Improving luminescent property of SrIn2O4:Eu3+ by codoped A+ (A = Li, Na, K) or Sm3+

Wang Zhi-Jun, Li Pan-Lai, Yang Zhi-Ping, Guo Qing-Lin
Chin. Phys. B, 2013, 22 (4): 047804 doi: 10.1088/1674-1056/22/4/047804
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A series of SrIn2O4:Eu3+ phosphors are synthesized by a high temperature solid-state method, and their luminescent properties are investigated. They can be excited by 395-nm radiation, and produce red emission (619 nm); however, they have a low absorption of near-ultraviolet light with the wavelength of 400 nm-405 nm. When co-doped with A+ (A=Li, Na, K), the emission intensity of SrIn2O4:Eu3+ is significantly enhanced, but its emission and excitation spectral profile is unchanged. With codoping Sm3+, not only is the emission intensity of SrIn2O4:Eu3+ enhanced, but also the absorption is broadened and strengthened in the range of 400 nm-405 nm. The effect of Sm3+-doped content on the emission intensity of SrIn2O4:Eu3+, Sm3+ is investigated, and the optimal Sm3+ content is 0.02 mol.

Temperature-dependent efficiency droop behaviors of GaN-based green light-emitting diodes

Jiang Rong, Lu Hai, Chen Dun-Jun, Ren Fang-Fang, Yan Da-Wei, Zhang Rong, Zheng You-Dou
Chin. Phys. B, 2013, 22 (4): 047805 doi: 10.1088/1674-1056/22/4/047805
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The efficiency droop behaviors of GaN-based green light emitting diodes (LEDs) are studied as a function of temperature from 300 K to 480 K. The overall quantum efficiency of the green LEDs is found to degrade as temperature increases, which is mainly caused by activation of new non-radiative recombination centers within the LED active layer. Meanwhile, the external quantum efficiency of the green LEDs starts to decrease at low injection current level (<1 A/cm2) with a temperature-insensitive peak-efficiency-current. In contrast, the peak-efficiency-current of a control GaN-based blue LED shows continuous up-shift at higher temperatures. Around the onset point of efficiency droop, the electroluminescence spectra of the green LEDs also exhibit a monotonic blue-shift of peak energy and a reduction of full width at half maximum as injection current increases. Carrier delocalization is believed to play an important role in causing the efficiency droop in GaN-based green LEDs.

Efficiency of blue organic light-emitting diode enhanced by inserting charge control layers into emission region

Bai Juan-Juan, Wu Xiao-Ming, Hua Yu-Lin, Mu Xue, Bi Wen-Tao, Su Yue-Ju, Jiao Zhi-Qiang, Shen Li-Ying, Yin Shou-Gen, Zheng Jia-Jin
Chin. Phys. B, 2013, 22 (4): 047806 doi: 10.1088/1674-1056/22/4/047806
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We demonstrate high current efficiency of blue fluorescent organic light-emitting diode (OLED) by using the charge control layers (CCLs) based on Alq3. The CCLs that are inserted into the emitting layers (EMLs) could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2, which is about 2.19 times higher than that of the control device (CD) without the CCL, and the maximal luminance is 19.660 cd/m2 at 12 V. The device shows a good color stability though the green light emitting material Alq3 is introduced as CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.

Small amplitude approximation and stabilities for dislocation motion in superlattice

Liu Hua-Zhu, Luo Shi-Yu, Shao Ming-Zhu
Chin. Phys. B, 2013, 22 (4): 047807 doi: 10.1088/1674-1056/22/4/047807
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Starting from the traveling wave solution, in small amplitude approximation, Sine-Gordon equation can be reduced to a generalized Duffing equation to describe the dislocation motion in superlattice, and the phase plane properties of system phase plane are described in the absence of applied field, the stabilities are also discussed in the presence of applied field. It is pointed out that the separatrix orbit describing the dislocation motion as the kink wave may transfer the energy along the dislocation line, keep its form unchanged, and reveal the soliton wave properties of the dislocation motion. It is stressed that the dislocation motion process is the energy transfer and release process, and the system is stable when its energy is minimum.

A compact frequency selective stop-band splitter by using Fabry–Perot nanocavity in a T-shape waveguide

M Afshari Bavil, Sun Xiu-Dong
Chin. Phys. B, 2013, 22 (4): 047808 doi: 10.1088/1674-1056/22/4/047808
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By utlizing Fabry-Perot (FP) nanocavity adjacent to T-shape gap waveguide ports, spectrally selective filtering is realized. When the wavelength of incident light corresponds to the resonance wavelength of the FP nanocavity, the surface plasmons are captured inside the nanocavity, and light is highly reflected from this port. The resonance wavelength is determined by using Fabry–Perot resonance condition for the nanocavity. For any desired filtering frequency the dimension of nanocavity can be tailored. The numerical results are based on the two-dimensional finite difference time domain simulation under a perfectly matched layer absorbing boundary condition. The analytical and simulation results indicate that the proposed structure can be utilized for filtering and splitting applications.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Tuning nano-pillar array for enhancing the photoluminescence extraction efficiency of GaN-based light-emitting diodes

Chen Xia, Liang Zhu-Hong, Chen Zhan-Xu, Yang Wei-Ming, Chen Tu-Fu, Jin Chong-Jun, Zhang Bai-Jun
Chin. Phys. B, 2013, 22 (4): 048101 doi: 10.1088/1674-1056/22/4/048101
Full Text: [PDF 427 KB] (Downloads:909)
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We demonstrate the fabrication of hexagonal nano-pillar arrays at the surface of GaN-based light-emitting diodes (LEDs) by nanosphere lithography. By varying the oxygen plasma etching time, we could tune the size and shape of the pillar. The nano-pillar has a truncated cone shape. The nano-pillar array serves as a gradual effective refractive index matcher, which reduces the reflection and increases light cone. It is found that the patterned surface absorbs more pumping light. To compare extraction efficiencies of LEDs, it is necessary to normalize the photoluminescence power spectrum with total absorption rate under fixed pumping power, then we could obtain the correct enhancement factor of the photoluminescence extraction efficiency and optimized structure. The highest enhancement factor of the extraction efficiency is 10.6.

InAs/GaAs submonolayer quantum-dot superluminescent diodes with active multimode interferometer configuration

Li Xin-Kun, Jin Peng, Liang De-Chun, Wu Ju, Wang Zhan-Guo
Chin. Phys. B, 2013, 22 (4): 048102 doi: 10.1088/1674-1056/22/4/048102
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With a chirped InAs/GaAs SML-QD (quantum dot) structure serving as the active region, the superluminescent diodes emitting at wavelength of around 970 nm are fabricated. By using an active multimode interferometer configuration, these devices exhibit high continue-wave output powers from the narrow ridge waveguides. At continue-wave injection current of 800 mA, an output power of 18.5 mW, and the single Gaussian-like emission spectrum centred at 972 nm with a full width at half maximum of 18 nm are obtained.

Wideband dipole antenna with inter-digital capacitor

Xiong Han, Hong Jin-Song, Jin Da-Lin
Chin. Phys. B, 2013, 22 (4): 048401 doi: 10.1088/1674-1056/22/4/048401
Full Text: [PDF 1379 KB] (Downloads:732)
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A dipole antenna with wideband characteristics is presented. The proposed antenna consists of a dipole with periodic capacitive loading and a pair of coplanar striplines (CPSs) as an impedance transformer. By adding interlaced coupling lines at each section, periodic capacitive loading is realized. The periodic interlaced coupling lines divide each arm of the dipole into five sections, and currents are distributed on different sections at different frequencies, which is useful to achieve a wide impedance bandwidth. By parametric study using HFSS, the optimized parameters of this dipole antenna are obtained. In order to validate the simulation results, a prototype of the proposed dipole antenna is fabricated and tested. The results show that the proposed antenna can achieve a gain of 3.1 dB-5.1 dB and bandwidth of 51% for |S11|< -10 dB over the band of 3.9 GHz-6.6 GHz, indicating its good radiation performance and radiation efficiency.

Dual-gate lateral double-diffused metal–oxide semiconductor with ultra-low specific on-resistance

Fan Jie, Wang Zhi-Gang, Zhang Bo, Luo Xiao-Rong
Chin. Phys. B, 2013, 22 (4): 048501 doi: 10.1088/1674-1056/22/4/048501
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A new high voltage trench lateral double-diffused metal-oxide semiconductor (LDMOS) with ultra-low specific on-resistance (Ron,sp) is proposed. The structure features dual gate (DG LDMOS): a planar gate and a trench gate inset in the oxide trench. Firstly, the dual gate can provide dual conduction channel and reduce Ron,sp dramatically. Secondly, the oxide trench in the drift region modulates the electric field distribution and reduces the cell pitch but still can maintain comparable breakdown voltage (BV). Simulation results show that the cell pitch of the DG LDMOS can be reduced by 50% in comparison with that of conventional LDMOS at the equivalent BV; Furthermore, Ron,sp of the DG LDMOS can be reduced by 67% due to the smaller cell pitch and the dual gate.

Avian magnetoreception model realized by coupling a magnetite-based mechanism with a radical-pair-based mechanism

Lü Yan, Song Tao
Chin. Phys. B, 2013, 22 (4): 048701 doi: 10.1088/1674-1056/22/4/048701
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Many animal species are verified to use geomagnetic field for their navigation, but the biophysical mechanism of magnetoreception has remained enigmatic. In this paper, we present a special biophysical model that consists of magnetite-based and radical-pair-based mechanisms for avian magnetoreception. The amplitude of the resultant magnetic field around the magnetic particles corresponds to the geomagnetic field direction and affects the yield of singlet/triplet state products in the radical-pair reactions. Therefore, in the proposed model, the singlet/triplet state product yields are related to the geomagnetic field information for orientational detection. The resultant magnetic fields corresponding to two materials with different magnetic properties are analyzed under different geomagnetic field directions. The results show that ferromagnetic particles in organisms can provide more significant changes in singlet state products than superparamagnetic particles, and the period of variation for the singlet state products with an included angle in the geomagnetic field is approximately 180° when the magnetic particles are ferromagnetic materials, consistent with the experimental results obtained from avian magnetic compass. Further, the calculated results of the singlet state products in a reception plane show that the proposed model can explain the avian magnetoreception mechanism with an inclination compass.

AJAC: Atomic data calculation tool in Python

Amani Tahat, Jordi Marti, Kaher Tahat, Ali Khwaldeh
Chin. Phys. B, 2013, 22 (4): 048901 doi: 10.1088/1674-1056/22/4/048901
Full Text: [PDF 1208 KB] (Downloads:1096)
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In this work, new features and extensions of a currently used online atomic database management system are reported. A multiplatform flexible computation package is added to the present system, to allow the calculation of various atomic radiative and collisional processes, based on simplifying the use of some existing atomic codes adopted from the literature. The interaction between users and data is facilitated by a rather extensive Python graphical user interface working online and could be installed in personal computers of different classes. In particular, this study gives an overview of the use of one model of the package models (i.e., electron impact collissional excitation model). The accuracy of computing capability of the electron impact colisional excitation in the adopted model, which follows the distorted wave approximation approach, is enhanced by implementing the Dirac R-matrix approximation approach. The validity and utility of this approach are presented through a comparison of the current computed results with earlier available theoretical and experimental results. Finally, the source code is made available under the general public license and being distributed freely in the hope that it will be useful to a wide community of laboratory and astrophysical plasma diagnostics.

Backstepping-based lag synchronization of complex permanent magnet synchronous motor system

Wang Xing-Yuan, Zhang hao
Chin. Phys. B, 2013, 22 (4): 048902 doi: 10.1088/1674-1056/22/4/048902
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Through introducing the concept of complex current and resetting cross-coupling term, this paper proposes a novel complex permanent magnet synchronous motor system and analyze its properties. Base on complex permanent magnet synchronous motor system, we design controllers and achieve lag synchronizations both in real part and imaginary part with backstepping method. In our study, we take complex current, time delay, and structure of complex system into consideration. Numerical simulation results demonstrate the validity of controllers.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Efficient and rapid accuracy estimation of the Earth's gravitational field from next-generation GOCE Follow-On by the analytical method

Zheng Wei, Hsu Hou-Tse, Zhong Min, Liu Cheng-Shu, Yun Mei-Juan
Chin. Phys. B, 2013, 22 (4): 049101 doi: 10.1088/1674-1056/22/4/049101
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Firstly, a new analytical error model of the cumulative geoid height using the three-dimensional diagonal tensors of satellite gravity gradiometry (SGG) is introduced based on the variance-covariance matrix principle. Secondly, a study for the requirements demonstration on the next-generation GOCE Follow-On satellite gravity gradiometry system is developed using different satellite orbital altitudes and measurement accuracies of satellite gravity gradiometer by the new analytical error model of SGG. The research results show that it is preferable to design satellite orbital altitudes of 300 km-400 km and choose the measurement accuracies of 10-13/s2-10-15/s2 from satellite gravity gradiometer. Finally, the complementarity of the four-stage satellite gravity missions, including past CHAMP, current GRACE, and GOCE, and next-generation GOCE Follow-On, is contrastively demonstrated for precisely recovering the Earth's full-frequency gravitational field with high spatial resolution.

Orbit optimization for ASTROD-GW and its time delay interferometry with two arms using CGC ephemeris

Wang Gang, Ni Wei-Tou
Chin. Phys. B, 2013, 22 (4): 049501 doi: 10.1088/1674-1056/22/4/049501
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Astrodynamical space test of relativity using optical devices optimized for gravitation wave detection (ASTROD-GW) is an optimization of ASTROD to focus on the goal of detection of gravitation waves. The detection sensitivity is shifted 52 times toward larger wavelength compared with that of laser interferometer space antenna (LISA). The mission orbits of the three spacecrafts forming a nearly equilateral triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4, and L5. The three spacecrafts range interferometrically with one another with an arm length of about 260 million kilometers. In order to attain the required sensitivity for ASTROD-GW, laser frequency noise must be suppressed to below the secondary noises such as the optical path noise, acceleration noise, etc. For suppressing laser frequency noise, we need to use time delay interferometry (TDI) to match the two different optical paths (times of travel). Since planets and other solar-system bodies perturb the orbits of ASTROD-GW spacecraft and affect the TDI, we simulate the time delay numerically using CGC 2.7 (here, CGC stands for centre for gravitation and cosmology) ephemeris framework. To conform to the ASTROD-GW planning, we work out a set of 20-year optimized mission orbits of ASTROD-GW spacecraft starting at June 21, 2028, and calculate the differences in optical path in the first and second generation TDIs separately for one-detector case. In our optimized mission orbits of 20 years, changes of arm lengths are less than 0.0003 AU; the relative Doppler velocities are all less than 3 m/s. All the second generation TDI for one-detector case satisfies the ASTROD-GW requirement.
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