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CN 11-5639/O4
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  • Tunneling dynamics of Bose–Einstein condensates with higher-order interactions in optical lattice

    Tie Lu, Xue Ju-Kui
    Chin. Phys. B 2011, 20 (12): 120311
    The nonlinear Landau-Zener tunneling and nonlinear Rabi oscillations of Bose-Einstein condensate (BEC) with higher-order atomic interaction between the Bloch bands in an accelerating optical lattice are discussed. Within the two-level model, the tunneling probability of BEC with higher-order atomic ...

     
  • Cation mixing (Li0.5Fe0.5)2SO4F cathode material for lithium-ion batteries

    Sun Yang, Liu Lei, Dong Jin-Ping, Zhang Bin, Huang Xue-Jie
    Chin. Phys. B 2011, 20 (12): 126101
    We study the crystal structure of a triplite-structured (Li0.5Fe0.5)SO4F with full Li+/Fe2+ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li+/Li with a theoretical capacity of 151 mAh/g. Its unique cation mixing structure does not block the Li+ ...

     
  • Persistent current in a magnetized Rashba ring

    Zhang Lin, Wang Jun
    Chin. Phys. B 2011, 20 (12): 127203
    We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spin-orbit interaction. By introducing uniform or nonuniform magnetization into the ring, we find that a nonzero persistent charge current circulates in the ring, which stems from the original equ...

     
Chin. Phys. B  
  Chin. Phys. B--2011, Vol.20, No.12
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GENERAL

Perturbation of symmetries for super-long elastic slender rods

Ding Ning, Fang Jian-Hui
Chin. Phys. B, 2011, 20 (12): 120201 doi: 10.1088/1674-1056/20/12/120201
Full Text: [PDF 130 KB] (Downloads:667)
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This paper analyses perturbations of Noether symmetry, Lie symmetry, and form invariance for super-long elastic slender rod systems. Criterion and structure equations of the symmetries after disturbance are proposed. Considering perturbation of all infinitesimal generators, three types of adiabatic invariants induced by perturbation of symmetries for the system are obtained.

Traveling wave solutions for two nonlinear evolution equations with nonlinear terms of any order

Feng Qing-Hua, Meng Fan-Wei, Zhang Yao-Ming
Chin. Phys. B, 2011, 20 (12): 120201 doi: 10.1088/1674-1056/20/12/120202
Full Text: [PDF 125 KB] (Downloads:740)
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In this paper, based on the known first integral method and the Riccati sub-ordinary differential equation (ODE) method, we try to seek the exact solutions of the general Gardner equation and the general Benjamin-Bona-Mahoney equation. As a result, some traveling wave solutions for the two nonlinear equations are established successfully. Also we make a comparison between the two methods. It turns out that the Riccati sub-ODE method is more effective than the first integral method in handling the proposed problems, and more general solutions are constructed by the Riccati sub-ODE method.

Forced solitary Rossby waves under the influence of slowly varying topography with time

Yang Hong-Wei, Yin Bao-Shu, Yang De-Zhou, Xu Zhen-Hua
Chin. Phys. B, 2011, 20 (12): 120201 doi: 10.1088/1674-1056/20/12/120203
Full Text: [PDF 399 KB] (Downloads:589)
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By using a weakly nonlinear and perturbation method, the generalized inhomogeneous Korteweg-de Vries (KdV)-Burgers equation is derived, which governs the evolution of the amplitude of Rossby waves under the influence of dissipation and slowly varying topography with time. The analysis indicates that dissipation and slowly varying topography with time are important factors in causing variation in the mass and energy of solitary waves.

Dynamics of organizational rumor communication on connecting multi-small-world networks

Xing Qi-Bin, Zhang Yuan-Biao, Liang Zhi-Ning, Zhang Fan
Chin. Phys. B, 2011, 20 (12): 120201 doi: 10.1088/1674-1056/20/12/120204
Full Text: [PDF 618 KB] (Downloads:872)
Show Abstract
We study the dynamics of an epidemic-like model for the spread of a rumor on a connecting multi-small-world-network (CM-SWN) model, which represents organizational communication in the real world. It has been shown that this model exhibits a transition between regimes of localization and propagation at a finite value of network randomness. Here, by numerical means, we perform a quantitative characterization of the evolution in the three groups under two evolution rules, namely the conformity and obeying principles. The variant of a dynamic CM-SWN, where the quenched disorder of small-world networks is replaced by randomly changing connections between individuals in a single network and stable connection by star nodes between networks, is also analysed in detail and compared with a mean-field approximation.

Dissipation of a two-mode squeezed vacuum state in the single-mode amplitude damping channel

Zhou Nan-Run, Hu Li-Yun, Fan Hong-Yi
Chin. Phys. B, 2011, 20 (12): 120301 doi: 10.1088/1674-1056/20/12/120301
Full Text: [PDF 121 KB] (Downloads:620)
Show Abstract
We explore how a two-mode squeezed vacuum state sechθ ea+b+ tanh θ |00> evolves when it undergoes a singlemode amplitude dissipative channel with rate of decay κ. We find that in this process not only the squeezing parameter decreases, tanh θ → e-κt tanh θ, but also the second-mode vacuum state evolves into a chaotic state exp{b+bln[1 - e-2κt tanh2 θ]}. The outcome state is no more a pure state, but an entangled mixed state.

Evolution of a two-mode squeezed vacuum in the amplitude dissipative channel

Jiang Nian-Quan, Fan Hong-Yi, Xi Liu-Sheng, Tang Long-Ying, Yuan Xian-Zhang
Chin. Phys. B, 2011, 20 (12): 120302 doi: 10.1088/1674-1056/20/12/120302
Full Text: [PDF 104 KB] (Downloads:538)
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For the first time we derive the dissipating result of an initial two-mode squeezed pure vacuum state passing through a two-mode amplitude dissipative channel described by the direct product of two independent single-mode master equations. Although these two master equations do not mix the two modes (there is no coupling between them), since the two-mode squeezed state is simultaneously an entangled state, the final state which emerges from passing this channel is a two-mode mixed density operator. The compact expression of the outcoming state is obtained, which manifestly shows that as time evolves, the squeezing effect decreases.

Energy level of an electron in a saddle-potential quantum dot under a uniform magnetic field obtained by the invariant eigenoperator method

Xie Chuan-Mei, Fan Hong-Yi
Chin. Phys. B, 2011, 20 (12): 120303 doi: 10.1088/1674-1056/20/12/120303
Full Text: [PDF 181 KB] (Downloads:562)
Show Abstract
We show that the recently proposed invariant eigenoperator method can be successfully applied to solving the energy levels of an electron in a saddle-potential quantum dot under a uniform magnetic field. The Landau diamagnetism decreases with the value ωy2 - ωx2 due to the existence of the saddle potential.

Generation and classification of the translational shape-invariant potentials based on the analytical transfer matrix method

Sang Ming-Huang, Yu Zi-Xing, Li Cui-Cui, Tu Kai
Chin. Phys. B, 2011, 20 (12): 120304 doi: 10.1088/1674-1056/20/12/120304
Full Text: [PDF 108 KB] (Downloads:618)
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For the conventional translational shape-invariant potentials (TSIPs), it has demonstrated that the phase contribution devoted by the scattered subwaves in the analytical transfer matrix quantization condition is integrable and independent of n. Based on this fact we propose a novel strategy to generate the whole set of conventional TSIPs and classify them into three types. The generating functions are given explicitly and the Morse potential is taken as an example to illustrate this strategy.

Wavelet transform for Fresnel-transformed mother wavelets

Liu Shu-Guang, Chen Jun-Hua, Fan Hong-Yi
Chin. Phys. B, 2011, 20 (12): 120305 doi: 10.1088/1674-1056/20/12/120305
Full Text: [PDF 616 KB] (Downloads:573)
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In this paper, we propose the so-called continuous Fresnel-wavelet combinatorial transform which means that the mother wavelet undergoes the Fresnel transformation. This motivation can let the mother-wavelet-state itself vary from |ψ> to Fr,s+ |ψ> , except for variation within the family of dilations and translations. The Parseval's equality, admissibility condition and inverse transform of this continuous Fresnel-wavelet combinatorial transform are analysed. By taking certain parameters and using the admissibility condition of this continuous Fresnel-wavelet combinatorial transform, we obtain some mother wavelets. A comparison between the newly found mother wavelets is presented.

Classical behaviour of various variables in an open Bose–Hubbard system

Nikola Burić
Chin. Phys. B, 2011, 20 (12): 120306 doi: 10.1088/1674-1056/20/12/120306
Full Text: [PDF 881 KB] (Downloads:578)
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Quantum dispersions of various sets of dynamical variables of an open Bose-Hubbard system in a classical limit are studied. To this end, an open system is described in terms of stochastic evolution of its quantum pure states. It is shown that the class of variables that display classical behaviour crucially depends on the type of noise. This is relevant in the mean-field approximation of open Bose-Hubbard dynamics.

Implementation of nonlocal Bell-state measurement and quantum information transfer with weak Kerr nonlinearity

Bai Juan, Guo Qi, Cheng Liu-Yong, Shao Xiao-Qiang, Wang Hong-Fu, Zhang Shou, Yeon Kyu-Hwang
Chin. Phys. B, 2011, 20 (12): 120307 doi: 10.1088/1674-1056/20/12/120307
Full Text: [PDF 179 KB] (Downloads:605)
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We propose a protocol to implement the nonlocal Bell-state measurement, which is nearly determinate with the help of weak cross-Kerr nonlinearities and quantum non-destructive photon number resolving detection. Based on the nonlocal Bell-state measurement, we implement the quantum information transfer from one place to another. The process is different from conventional teleportation but can be regarded as a novel form of teleportation without entangled channel and classic communication.

One-step generation of qutrit entanglement via adiabatic passage in cavity quantum electrodynamics

Ma Song-She, Chen Mei-Feng, Jiang Xia-Ping
Chin. Phys. B, 2011, 20 (12): 120308 doi: 10.1088/1674-1056/20/12/120308
Full Text: [PDF 112 KB] (Downloads:710)
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A scheme is proposed for generating a three-dimensional entangled state for two atoms trapped in a cavity by one step via adiabatic passage. In the scheme, the two atoms are always in ground states and the field mode of the cavity excited is negligible under a certain condition. Therefore, the scheme is very robust against decoherence. Furthermore, it needs neither the exact control of all parameters nor the accurate control of the interaction time. It is shown that qutrit entanglement can be generated with a high fidelity.

Perfect quantum teleportation and dense coding protocols via the 2N-qubit W state

Wang Mei-Yu, Yan Feng-Li
Chin. Phys. B, 2011, 20 (12): 120309 doi: 10.1088/1674-1056/20/12/120309
Full Text: [PDF 115 KB] (Downloads:753)
Show Abstract
In this paper, we investigate perfect quantum teleportation and dense coding by using an 2N-qubit W state channel. In the quantum teleportation scheme, an unknown N-qubit entangled state can be perfectly teleported. One ebit of entanglement and two bits of classical communication are consumed in the teleportation process, just like when using the Bell state channel. While N+1 bits of classical information can be transmitted by only sending N particles in the dense coding protocol.

Quantum logic operations on two distant atoms trapped in two optical-fibre-connected cavities

Zhang Ying-Qiao, Zhang Shou, Yeon Kyu-Hwang, Yu Seong-Cho
Chin. Phys. B, 2011, 20 (12): 120310 doi: 10.1088/1674-1056/20/12/120310
Full Text: [PDF 325 KB] (Downloads:545)
Show Abstract
Based on the coupling of two distant three-level atoms in two separate optical cavities connected with two optical fibres, schemes on the generation of several two-qubit logic gates are discussed under the conditions of Δ = δ - 2ν cos πk/2 >> g/2 and ν ~ g. Discussion and analysis of the fidelity, gate time and experimental setups show that our schemes are feasible with current optical cavity, atomic trap and optical fibre techniques. Moreover, the atom-cavity- fibre coupling can be used to generate an N-qubit nonlocal entanglement and transfer quantum information among N distant atoms by arranging N atom-cavity assemblages in a line and connecting each two adjacent cavities with two optical fibres.

Tunneling dynamics of Bose–Einstein condensates with higher-order interactions in optical lattice Hot!

Tie Lu, Xue Ju-Kui
Chin. Phys. B, 2011, 20 (12): 120311 doi: 10.1088/1674-1056/20/12/120311
Full Text: [PDF 327 KB] (Downloads:684)
Show Abstract
The nonlinear Landau-Zener tunneling and nonlinear Rabi oscillations of Bose-Einstein condensate (BEC) with higher-order atomic interaction between the Bloch bands in an accelerating optical lattice are discussed. Within the two-level model, the tunneling probability of BEC with higher-order atomic interaction between Bloch bands is obtained. We finds that the tunneling rate is closely related to the higher-order atomic interaction. Furthermore, the nonlinear Rabi oscillations of BEC with higher-order atomic interaction between the bands are discussed by imposing a periodic modulation on the level bias. Analytical expressions of the critical higher-order atomic interaction for suppressing/enhancing the Rabi oscillations are obtained. It is shown that the critical value strongly depends on the modulation parameters (i.e., the modulation amplitude and frequency) and the strength of periodic potential.

Controlling chaos in power system based on finite-time stability theory

Zhao Hui, Ma Ya-Jun, Liu Si-Jia, Gao Shi-Gen, Zhong Dan
Chin. Phys. B, 2011, 20 (12): 120501 doi: 10.1088/1674-1056/20/12/120501
Full Text: [PDF 302 KB] (Downloads:1125)
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Recent investigations show that a power system is a highly nonlinear system and can exhibit chaotic behaviour leading to a voltage collapse, which severely threatens the secure and stable operation of the power system. Based on the finite-time stability theory, two control strategies are presented to achieve finite-time chaos control. In addition, the problem of how to stabilize an unstable nonzero equilibrium point in a finite time is solved by coordinate transformation for the first time. Numerical simulations are presented to demonstrate the effectiveness and the robustness of the proposed scheme. The research in this paper may help to maintain the secure operation of power systems.

Chaotic memristive circuit: equivalent circuit realization and dynamical analysis

Bao Bo-Cheng, Xu Jian-Ping, Zhou Guo-Hua, Ma Zheng-Hua, Zou Ling
Chin. Phys. B, 2011, 20 (12): 120502 doi: 10.1088/1674-1056/20/12/120502
Full Text: [PDF 8072 KB] (Downloads:1238)
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In this paper, a practical equivalent circuit of an active flux-controlled memristor characterized by smooth piecewise-quadratic nonlinearity is designed and an experimental chaotic memristive circuit is implemented. The chaotic memristive circuit has an equilibrium set and its stability is dependent on the initial state of the memristor. The initial state-dependent and the circuit parameter-dependent dynamics of the chaotic memristive circuit are investigated via phase portraits, bifurcation diagrams and Lyapunov exponents. Both experimental and simulation results validate the proposed equivalent circuit realization of the active flux-controlled memristor.

A novel robust proportional-integral (PI) adaptive observer design for chaos synchronization

Mahdi Pourgholi, Vahid Johari Majd
Chin. Phys. B, 2011, 20 (12): 120503 doi: 10.1088/1674-1056/20/12/120503
Full Text: [PDF 410 KB] (Downloads:1193)
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In this paper, chaos synchronization in the presence of parameter uncertainty, observer gain perturbation and exogenous input disturbance is considered. A nonlinear non-fragile proportional-integral (PI) adaptive observer is designed for the synchronization of chaotic systems; its stability conditions based on the Lyapunov technique are derived. The observer proportional and integral gains, by converting the conditions into linear matrix inequality (LMI), are optimally selected from solutions that satisfy the observer stability conditions such that the effect of disturbance on the synchronization error becomes minimized. To show the effectiveness of the proposed method, simulation results for the synchronization of a Lorenz chaotic system with unknown parameters in the presence of an exogenous input disturbance and abrupt gain perturbation are reported.

Hyperchaotic behaviours and controlling hyperchaos in an array of RCL-shunted Josephson junctions

Ri Ilmyong, Feng Yu-Ling, Yao Zhi-Hai, Fan Jian
Chin. Phys. B, 2011, 20 (12): 120504 doi: 10.1088/1674-1056/20/12/120504
Full Text: [PDF 4913 KB] (Downloads:745)
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This paper deals with dynamical behaviours in an array composed of two resistive-capacitive-inductive-shunted (RCL-shunted) Josephson junctions (RCLSJJs) and a shunted resistor. Numerical simulations show that periodic, chaotic and hyperchaotic states can coexist in this array. Moreover, a scheme for controlling hyperchaos in this array is presented by adjusting the external bias current. Numerical results confirm that this scheme can be effectively used to control hyperchaotic states in this array into stable periodic states, and different stable periodic states with different period numbers can be obtained by appropriately choosing the intensity of the external bias current.

Generalized spatiotemporal chaos synchronization of the Ginzburg–Landau equation

Jin Ying-Hua, Xu Zhen-Yuan
Chin. Phys. B, 2011, 20 (12): 120505 doi: 10.1088/1674-1056/20/12/120505
Full Text: [PDF 158 KB] (Downloads:607)
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In this paper, the generalized synchronization of two unidirectionally coupled Ginzburg-Landau equations is studied theoretically. It is demonstrated that the drive-response system has bounded attraction domain and compact attractors. It is derived that the correction equation has asymptotically stable zero solutions under certain conditions and that the sufficient conditions for smooth generalized synchronization and Hölder continuous generalized synchronization exist in the coupling system. Numerical result analysis shows the correctness of theory.

No-chattering sliding mode control in a class of fractional-order chaotic systems

Chen Di-Yi, Liu Yu-Xiao, Ma Xiao-Yi, Zhang Run-Fan
Chin. Phys. B, 2011, 20 (12): 120506 doi: 10.1088/1674-1056/20/12/120506
Full Text: [PDF 1206 KB] (Downloads:1584)
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A no-chattering sliding mode control strategy for a class of fractional-order chaotic systems is proposed in this paper. First, the sliding mode control law is derived to stabilize the states of the commensurate fractional-order chaotic system and the non-commensurate fractional-order chaotic system, respectively. The designed control scheme guarantees the asymptotical stability of an uncertain fractional-order chaotic system. Simulation results are given for several fractional-order chaotic examples to illustrate the effectiveness of the proposed scheme.

A method of recovering the initial vectors of globally coupled map lattices based on symbolic dynamics

Sun Li-Sha, Kang Xiao-Yun, Zhang Qiong, Lin Lan-Xin
Chin. Phys. B, 2011, 20 (12): 120507 doi: 10.1088/1674-1056/20/12/120507
Full Text: [PDF 834 KB] (Downloads:661)
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Based on symbolic dynamics, a novel computationally efficient algorithm is proposed to estimate the unknown initial vectors of globally coupled map lattices (CMLs). It is proved that not all inverse chaotic mapping functions are satisfied for contraction mapping. It is found that the values in phase space do not always converge on their initial values with respect to sufficient backward iteration of the symbolic vectors in terms of global convergence or divergence (CD). Both CD property and the coupling strength are directly related to the mapping function of the existing CML. Furthermore, the CD properties of Logistic, Bernoulli, and Tent chaotic mapping functions are investigated and compared. Various simulation results and the performances of the initial vector estimation with different signal-to-noise ratios (SNRs) are also provided to confirm the proposed algorithm. Finally, based on the spatiotemporal chaotic characteristics of the CML, the conditions of estimating the initial vectors using symbolic dynamics are discussed. The presented method provides both theoretical and experimental results for better understanding and characterizing the behaviours of spatiotemporal chaotic systems.

Modified impulsive synchronization of fractional order hyperchaotic systems

Fu Jie, Yu Miao, Ma Tie-Dong
Chin. Phys. B, 2011, 20 (12): 120508 doi: 10.1088/1674-1056/20/12/120508
Full Text: [PDF 965 KB] (Downloads:950)
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In this paper, a modified impulsive control scheme is proposed to realize the complete synchronization of fractional order hyperchaotic systems. By constructing a suitable response system, an integral order synchronization error system is obtained. Based on the theory of Lyapunov stability and the impulsive differential equations, some effective sufficient conditions are derived to guarantee the asymptotical stability of the synchronization error system. In particular, some simpler and more convenient conditions are derived by taking the fixed impulsive distances and control gains. Compared with the existing results, the main results in this paper are practical and rigorous. Simulation results show the effectiveness and the feasibility of the proposed impulsive control method.

Solitary excitations in one-dimensional ferromagnetic spin chains with biquadratic exchange interaction

Yu Xiao-Yan, Chen Hao
Chin. Phys. B, 2011, 20 (12): 120509 doi: 10.1088/1674-1056/20/12/120509
Full Text: [PDF 142 KB] (Downloads:583)
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By using the traveling wave method, the solutions of the elliptic function wave and the solitary wave are obtained in a ferromagnetic spin chain with a biquadratic exchange interaction, a single ion anisotropic interaction and an anisotropic nearest neighbour interaction. The effects of the biquadratic exchange interaction and the single ion anisotropic interaction on the properties (width, peak and stability) of the soliton are investigated. It is also found that the effects vary with the strengths of these interactions.

Novel delay-dependent stability criteria for neural networks with interval time-varying delay

Wang Jian-An
Chin. Phys. B, 2011, 20 (12): 120701 doi: 10.1088/1674-1056/20/12/120701
Full Text: [PDF 119 KB] (Downloads:602)
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The problem of delay-dependent asymptotic stability for neural networks with interval time-varying delay is investigated. Based on the idea of delay decomposition method, a new type of Lyapunov-Krasovskii functional is constructed. Several novel delay-dependent stability criteria are presented in terms of linear matrix inequality by using the Jensen integral inequality and a new convex combination technique. Numerical examples are given to demonstrate that the proposed method is effective and less conservative.

Impact of substrate bias on radiation-induced edge effects in MOSFETs

Hu Zhi-Yuan, Liu Zhang-Li, Shao-Hua, Zhang Zheng-Xuan, Ning Bing-Xu, Chen Ming, Bi Da-Wei, Zou Shi-Chang
Chin. Phys. B, 2011, 20 (12): 120702 doi: 10.1088/1674-1056/20/12/120702
Full Text: [PDF 584 KB] (Downloads:957)
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This paper investigates the effects of gamma-ray irradiation on the Shallow-Trench Isolation (STI) leakage currents in 180-nm complementary metal oxide semiconductor technology. No hump effect in the subthreshold region is observed after irradiation, which is considered to be due to the thin STI corner oxide thickness. A negative substrate bias could effectively suppress the STI leakage, but it also impairs the device characteristics. The three-dimensional simulation is introduced to understand the impact of substrate bias. Moreover, we propose a simple method for extracting the best substrate bias value, which not only eliminates the STI leakage but also has the least impact on the device characteristics.

Total ionizing dose effect in an input/output device for flash memory

Liu Zhang-Li, Hu Zhi-Yuan, Zhang Zheng-Xuan, Shao Hua, Chen Ming, Bi Da-Wei, Ning Bing-Xu, Zou Shi-Chang
Chin. Phys. B, 2011, 20 (12): 120703 doi: 10.1088/1674-1056/20/12/120703
Full Text: [PDF 303 KB] (Downloads:686)
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Input/output devices for flash memory are exposed to gamma ray irradiation. Total ionizing dose has been shown great influence on characteristic degradation of transistors with different sizes. In this paper, we observed a larger increase of off-state leakage in the short channel device than in long one. However, a larger threshold voltage shift is observed for the narrow width device than for the wide one, which is well known as the radiation induced narrow channel effect. The radiation induced charge in the shallow trench isolation oxide influences the electric field of the narrow channel device. Also, the drain bias dependence of the off-state leakage after irradiation is observed, which is called the radiation enhanced drain induced barrier lowing effect. Finally, we found that substrate bias voltage can suppress the off-state leakage, while leading to more obvious hump effect.
RAPID COMMUNICATION

Cation mixing (Li0.5Fe0.5)2SO4F cathode material for lithium-ion batteries Hot!

Sun Yang, Liu Lei, Dong Jin-Ping, Zhang Bin, Huang Xue-Jie
Chin. Phys. B, 2011, 20 (12): 126101 doi: 10.1088/1674-1056/20/12/126101
Full Text: [PDF 534 KB] (Downloads:1716)
Show Abstract
We study the crystal structure of a triplite-structured (Li0.5Fe0.5)SO4F with full Li+/Fe2+ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li+/Li with a theoretical capacity of 151 mAh/g. Its unique cation mixing structure does not block the Li+ diffusion and results in a small lattice volume change during the charge/discharge process. The calculations show that it has a three-dimensional network for Li-ion migration with an activation energy ranging from 0.53 eV to 0.68 eV, which is comparable with that in LiFePO4 with only one-dimensional channels. This work suggests that further exploring cathode materials with full cation mixing for Li-ion batteries will be valuable.
CLASSICAL AREAS OF PHENOMENOLOGY

Choice of optimal crystal-orientation for terahertz transceiver with zincblende crystal

Tian Xiao-Guang, Ling Fu-Ri, He Jian, Liu Jin-Song, Yao Jian-Quan
Chin. Phys. B, 2011, 20 (12): 124201 doi: 10.1088/1674-1056/20/12/124201
Full Text: [PDF 231 KB] (Downloads:1168)
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This paper presents a set of equations describing the terahertz generation and electro-optic detection based on optical rectification in zincblende crystals. The dependence of terahertz emission efficiency on the polarization of incident beam and crystal-orientation is discussed. For the experimental setup with a transceiver which transmits and detects terahertz radiation in the same crystal, we have demonstrated the optimal combination of both parameters above to optimize the working efficiency. Equations supplied in this paper are valid for zincblende crystals with arbitrary crystal-orientation and every possible polarization of an incident beam, which are of great significance for the optimization of a system.

Negative refractive index in a four-level atomic system

Zhang Zhen-Qing, Liu Zheng-Dong, Zhao Shun-Cai, Zheng Jun, Ji Yan-Fang, Liu Nian
Chin. Phys. B, 2011, 20 (12): 124202 doi: 10.1088/1674-1056/20/12/124202
Full Text: [PDF 145 KB] (Downloads:730)
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A closed four-level system in atomic vapour is proposed, which is made to possess left handedness by using the technique of quantum coherence. The density matrix method is utilized in view of the rotating-wave approximation and the effect of a local field in dense gas. The numerical simulation result shows that the negative permittivity and the negative permeability of the medium can be achieved simultaneously (i.e. the left handedness) in a wider frequency band under appropriate parameter conditions. Furthermore, when analysing the dispersion property of the left-handed material, we can find that the probe beam propagation can be controlled from superluminal to subluminal, or vice versa via changing the detuning of the probe field.

Normal mode splitting and ground state cooling in a Fabry–Perot optical cavity and transmission line resonator

Chen Hua-Jun, Mi Xian-Wu
Chin. Phys. B, 2011, 20 (12): 124203 doi: 10.1088/1674-1056/20/12/124203
Full Text: [PDF 712 KB] (Downloads:742)
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Optomechanical dynamics in two systems which are a transmission line resonator and Fabrya-Perot optical cavity via radiation-pressure are investigated by linearized quantum Langevin equation. We work in the resolved sideband regime where the oscillator resonance frequency exceeds the cavity linewidth. Normal mode splittings of the mechanical resonator as a pure result of the coupling interaction in the two optomechanical systems is studied, and we make a comparison of normal mode splitting of mechanical resonator between the two systems. In the optical cavity, the normal mode splitting of the movable mirror approaches the latest experiment very well. In addition, an approximation scheme is introduced to demonstrate the ground state cooling, and we make a comparison of cooling between the two systems dominated by two key factors, which are the initial bath temperature and the mechanical quality factor. Since both the normal mode splitting and cooling require working in the resolved sideband regime, whether the normal mode splitting influences the cooling of the mirror is considered. Considering the size of the mechanical resonator and precooling the system, the mechanical resonator in the transmission line resonator system is easier to achieve the ground state cooling than in optical cavity.

Lie symmetry and Hojman conserved quantity of a Nielsen equation in a dynamical system of relative motion with Chetaev-type nonholonomic constraint

Wang Xiao-Xiao, Sun Xian-Ting, Zhang Mei-Ling, Xie Yin-Li, Jia Li-Qun
Chin. Phys. B, 2011, 20 (12): 124501 doi: 10.1088/1674-1056/20/12/124501
Full Text: [PDF 103 KB] (Downloads:607)
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The Lie symmetry and Hojman conserved quantity of Nielsen equations in a dynamical system of relative motion with nonholonomic constraint of the Chetaev type are studied. The differential equations of motion of the Nielsen equation for the system, the definition and the criterion of Lie symmetry, and the expression of the Hojman conserved quantity deduced directly from the Lie symmetry for the system are obtained. An example is given to illustrate the application of the results.

Completeness of eigenfunction systems for the product of two symmetric operator matrices and its application in elasticity

Qi Gao-Wa, Hou Guo-Lin, Alatancang
Chin. Phys. B, 2011, 20 (12): 124601 doi: 10.1088/1674-1056/20/12/124601
Full Text: [PDF 151 KB] (Downloads:858)
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The completeness theorem of the eigenfunction systems for the product of two 2×2 symmetric operator matrices is proved. The result is applied to 4×4 infinite-dimensional Hamiltonian operators. A modified method of separation of variables is proposed for a separable Hamiltonian system. As an application of the theorem, the general solutions for the plate bending equation and the free vibration of rectangular thin plates are obtained. Finally, a numerical test is analysed to show the correctness of the results.

Influences of initial velocity, diameter and Reynolds number on a circular turbulent air/air jet

Mi Jian-Chun, Du Cheng
Chin. Phys. B, 2011, 20 (12): 124701 doi: 10.1088/1674-1056/20/12/124701
Full Text: [PDF 341 KB] (Downloads:1421)
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This paper assesses the suitability of the inflow Reynolds number defined by ReoUoD/ν (here Uo and D are respectively the initial jet velocity and diameter while ν is kinematic viscosity) for a round air/air jet. Specifically an experimental investigation is performed for the influences of Uo, D and Reo on the mean-velocity decay and spread coefficients (Ku, Kr) in the far field of a circular air jet into air from a smoothly contracting nozzle. Present measurements agree well with those previously obtained under similar inflow conditions. The relations KuUo and Kr ∝ 1/Uo for Uo < 5 m/s appear to work, while each coefficient approaches asymptotically to a constant for Uo > 6 m/s, regardless of the magnitudes of Reo and D. It is revealed that Reo may not be an appropriate dimensionless parameter to characterize the entire flow of a free air/air jet. This paper is the first paper that has challenged the suitability of Reo for turbulent free jets.

Direct numerical simulation study of the interaction between the polymer effect and velocity gradient tensor in decaying homogeneous isotropic turbulence

Cai Wei-Hua, Li Feng-Chen, Zhang Hong-Na
Chin. Phys. B, 2011, 20 (12): 124702 doi: 10.1088/1674-1056/20/12/124702
Full Text: [PDF 446 KB] (Downloads:825)
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Direct numerical simulation of decaying homogeneous isotropic turbulence (DHIT) of a polymer solution is performed. In order to understand the polymer effect on turbulence or additive-turbulence interaction, we directly investigate the influence of polymers on velocity gradient tensor including vorticity and strain. By visualizing vortex tubes and sheets, we observe a remarkable inhibition of vortex structures in an intermediate-scale field and a small-scale field but not for a large scale field in DHIT with polymers. The geometric study indicates a strong relevance among the vorticity vector, rate-of-strain tensor, and polymer conformation tensor. Joint probability density functions show that the polymer effect can increase "strain generation resistance" and "vorticity generation resistance", i.e., inhibit the generation of vortex sheets and tubes, ultimately leading to turbulence inhibition effects.
ATOMIC AND MOLECULAR PHYSICS

Density-functional study of CO adsorbed on RhN (N=2–19) clusters

Tian Fu-Yang, Shen Jiang
Chin. Phys. B, 2011, 20 (12): 123101 doi: 10.1088/1674-1056/20/12/123101
Full Text: [PDF 1205 KB] (Downloads:719)
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We investigate the structural, electronic and adsorption properties of one single CO molecule adsorbed on RhN (N = 2-19) clusters, using the density-functional theory in the spin-polarized generalized gradient approximation. It is found that the structural growth model of the RhN clusters transforms from double layers (N = 12-16) to three layers (N = 17-19). Three different adsorption types are the atop site adsorption for N = 6, 8, 9, 11, 12, the bridge site adsorption for N = 2-5, 7, 10, 13-15, 17 and the face adsorption for N = 16, 18, 19. The adsorption abilities of RhN clusters are related to C-O bond length, vibrational frequency, adsorption energy and the charge transfer between CO and Rh clusters as well as the electronic density of state. With the increase of Rh cluster size, the adsorption energy of CO adsorbed on RhN clusters tends to be 2.2 eV-2.3 eV, which is 0.2 eV-0.3 eV larger than the theoretical value (about 2.0 eV) of CO molecule adsorption on clean Rh (111) surface.

Low-frequency vibrational modes of glutamine

Wang Wei-Ning, Wang Guo, Zhang Yan
Chin. Phys. B, 2011, 20 (12): 123301 doi: 10.1088/1674-1056/20/12/123301
Full Text: [PDF 165 KB] (Downloads:923)
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High-resolution terahertz absorption and Raman spectra of glutamine in the frequency region 0.2 THz-2.8 THz are obtained by using THz time domain spectroscopy and low-frequency Raman spectroscopy. Based on the experimental and the computational results, the vibration modes corresponding to the terahertz absorption and Raman scatting peaks are assigned and further verified by the theoretical calculations. Spectral investigation of the periodic structure of glutamine based on the sophisticated hybrid density functional B3LYP indicates that the vibrational modes come mainly from the inter-molecular hydrogen bond in this frequency region.

Selective excitation of the molecular rotational wave packet by two time-delayed laser pulses

Xu Shu-Wu, Huang Yun-Xia, Ji Xian-Ming
Chin. Phys. B, 2011, 20 (12): 123302 doi: 10.1088/1674-1056/20/12/123302
Full Text: [PDF 151 KB] (Downloads:610)
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In this paper, we investigate the control of the molecular wave packet of a linear molecule by two femtosecond laser pulses. It is shown that the odd and the even rotational wave packets created by a single laser pulse can be selectively excited by accurately controlling the time delay of another laser pulse. By inserting the peak of the second laser pulse at the position of maximum or minimum value around quarter or three quarter rotational period of the slope curve with odd (or even) rotational wave packet contribution that is created by the first laser pulse, the odd rotational wave packet can be enhanced (or suppressed) while the even rotational wave packet is suppressed (or enhanced). As a result, the molecular alignments around quarter and three quarter rotational periods can be obtained. Moreover, it is also shown that by inserting the second laser pulse around the quarter or three quarter rotational periods, the changes in the maximum degree of the molecular alignment for the odd and the even rotational wave packet contributions are consistent with their corresponding slope curves at these positions.

Quasi-classical trajectory approach to the O(1D)+HBr→OH+Br reaction stereo-dynamics on X1A′ potential energy surface

Li Hong, Zheng Bin, Yin Ji-Qing, Meng Qing-Tian
Chin. Phys. B, 2011, 20 (12): 123401 doi: 10.1088/1674-1056/20/12/123401
Full Text: [PDF 235 KB] (Downloads:631)
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The vector properties of reaction O(1D)+HBr→ OH+Br on the potential energy surface (PES) of X1A′ ground singlet state are studied by using the quasi-classical trajectory (QCT) theory. The polarization-dependent differential cross sections (PDDCSs), the average rotational alignment factor 2(j′· k)>, as well as the distributions reflecting vector correlations are also computed. The analysis of the results shows that the alignment and the orientation distribution of the rotation angular momentum vector of product molecule OH is influenced by both the effect of heavy-light-heavy (HLH) type mass combination and the deep well of PES.

Influence of rotational excitation and collision energy on the stereo dynamics of the reaction: N(4S)+H2 (v = 0, j = 0, 2, 5, 10)→NH(X3Σ-)+H

Yu Yong-Jiang, Xu Qiang, Xu Xiu-Wei
Chin. Phys. B, 2011, 20 (12): 123402 doi: 10.1088/1674-1056/20/12/123402
Full Text: [PDF 1404 KB] (Downloads:859)
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The N+H2 reaction has attracted a great deal of attention from both the experimental and the theoretical community, and most of the attention has been paid to the first excited state N(2D) atoms in collisions with hydrogen molecules and the scalar properties of the reaction. In this paper, we study the stereo dynamical properties and calculate the reaction cross sections of the N(4S) + H2 (v=0, j=0, 2, 5, 10) → NH(X3Σ-) + H using the quasi-classical trajectory (QCT) method on an accurate NH2 potential energy surface (PES) reported by Poveda and Varandas [Poveda L A and Varandas A J C 2005 Phys. Chem. Chem. Phys. 7 2867], in a collision energy range of 25 kcal·mol-1-140 kcal·mol-1. Results indicate that the reactant rotational excitation and initial collision energy both have a considerable influence on the distributions of the k-j′ correlation, the k-k′-j′ correlation and k-k′ correlation. The differential cross section is found to be sensitive to collision energy.

Dependence of loading time on control parameters in a standard vapour–loaded magneto–optical trap

Zhang Yi-Chi, Wu Ji-Zhou, Li Yu-Qing, Ma Jie, Wang Li-Rong, Zhao Yan-Ting, Xiao Lian-Tuan, Jia Suo-Tang
Chin. Phys. B, 2011, 20 (12): 123701 doi: 10.1088/1674-1056/20/12/123701
Full Text: [PDF 261 KB] (Downloads:679)
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Loading time is one of the most important dynamic characteristics of a magneto-optical trap. In this paper, we primarily report on a detailed experimental study of the effects of some magneto-optical trap control parameters on loading time, including the background vacuum pressure, the magnetic field gradient, and the intensities of trapping and repumping lasers. We compare the results with previous theoretical and experimental results, and give qualitative analysis. These experimental investigations offer some useful guidelines to control the loading time of magneto-optical traps. The controllable loading time achieved is helpful to enhance the signal-to-noise ratio of photoassociation spectroscopy, which is remarkably improved from 7 to 28.6.

Cold cesium molecules produced directly in a magneto–optical trap

Zhang Hong-Shan, Ji Zhong-Hua, Yuan Jin-Peng, Zhao Yan-Ting, Ma Jie, Wang Li-Rong, Xiao Lian-Tuan, Jia Suo-Tang
Chin. Phys. B, 2011, 20 (12): 123702 doi: 10.1088/1674-1056/20/12/123702
Full Text: [PDF 319 KB] (Downloads:821)
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We report on the observation of ultracold ground electric-state cesium molecules produced directly in a magneto- optical trap with a good signal-to-noise ratio. These molecules arise from the photoassociation of magneto-optical trap lasers and they are detected by resonantly enhanced multiphoton ionization technology. The production rate of ultracold cesium molecules is up to 4×104 s-1. We measure the characteristic time of the ground electric-state cesium molecules generated in the experiment and investigate the Cs2+ molecular ion intensity as a function of the trapping laser intensity and the ionization pulse laser energy. We conclude that the production of cold cesium molecules may be enhanced by using appropriate experimental parameters, which is useful for future experiments involving the production and trapping of ultracold ground electric-state molecules.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Near-wall conductivity effect under a space–charge-saturated sheath in the Hall thruster

Zhang Feng-Kui, Ding Yong-Jie, Qing Shao-Wei, Wu Xian-De
Chin. Phys. B, 2011, 20 (12): 125201 doi: 10.1088/1674-1056/20/12/125201
Full Text: [PDF 216 KB] (Downloads:512)
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In this paper, we adopt the modified Morozov secondary electron emission model to investigate the influence of the characteristic of a space-charge-saturated sheath near the insulated wall of the Hall thruster on the near-wall conductivity, by the method of two-dimensional (2D) particle simulation (2D+3V). The results show that due to the sharp increase of collision frequency between the electrons and the wall under the space-charge-saturated sheath, the near-wall transport current under this sheath is remarkably higher than that under a classical sheath, and equals the near-wall transport current under a spatially oscillating sheath in order of magnitude. However, the transport currents under a space-charge-saturated sheath and a spatially oscillating sheath are different in mechanism, causing different current density distributions under the above two sheaths, and a great influence of channel width on the near-wall transport current under a space-charge-saturated sheath.

Investigation of lower hybrid current drive during H-mode in EAST tokamak

Li Miao-Hui, Ding Bo-Jiang, Kong Er-Hua, Zhang Lei, Zhang Xin-Jun, Qian Jin-Ping, Yan Ning, Han Xiao-Feng, Shan Jia-Fang, Liu Fu-Kun, Wang Mao, Xu Han-Dong, Wan Bao-Nian
Chin. Phys. B, 2011, 20 (12): 125202 doi: 10.1088/1674-1056/20/12/125202
Full Text: [PDF 500 KB] (Downloads:676)
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H-mode discharges with lower hybrid current drive (LHCD) alone are achieved in EAST divertor plasma over a wide parameter range. These H-mode discharges are characterized by a sudden drop in Dα emission and a spontaneous rise in main plasma density. Good lower hybrid (LH) coupling during H-mode is obtained by putting the plasma close to the antenna and by injecting D2 gas from a pipe near the grill mouse. The analysis of lower hybrid current drive properties shows that the LH deposition profile shifts off axis during H-mode, and current drive (CD) efficiency decreases due to the increase in density. Modeling results of H-mode discharges with a general ray tracing code GENRAY are reported.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Theoretical studies on the structural, electronic, and optical properties of Ag2HgSnSe4

Li Dan, Zhang Xing-Hong
Chin. Phys. B, 2011, 20 (12): 126102 doi: 10.1088/1674-1056/20/12/126102
Full Text: [PDF 281 KB] (Downloads:742)
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We investigate the electronic structure of Ag2HgSnSe4 in a wurtzite-stannite structure with the first principles method. This crystal is a direct band-gap compound. In addition the dielectric function, absorption coefficient, reflectivity, and energy-loss function are studied using the density functional theory in the generalized gradient approximation. We discuss the optical transitions between the valence bands and the conduction bands in the spectrum of the imaginary part of the dielectric function at length. We also find a very high absorption coefficient and a wide absorption band for this material. The prominent structures in the spectra of reflectivity and the energy-loss function are discussed in detail.

Ab initio study of the electronic structure and elastic properties of Al5C3N

Xu Xue-Wen, Hu Long, Yu Xiao, Lu Zun-Ming, Fan Ying, frameLi Yang-Xian, Tang Cheng-Chun
Chin. Phys. B, 2011, 20 (12): 126201 doi: 10.1088/1674-1056/20/12/126201
Full Text: [PDF 199 KB] (Downloads:933)
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We investigate the electronic structure, chemical bonding and elastic properties of the hexagonal aluminum carbonitride, Al5C3N, by ab initio calculations. Al5C3N is a semiconductor with a narrow indirect gap of 0.81 eV. The valence bands below the Fermi level (EF) originate from the hybridized Al p-C p and Al p-N p states. The calculated bulk and Young's moduli are 201 GPa and 292 GPa, which are slightly lower than those of Ti3SiC2. The values of the bulk-to-shear-modulus and bulk-modulus-to-c44 are 1.73 and 1.97, respectively, which are higher than those of Ti2AlC and Ti2AlN, indicating that Al5C3N is a ductile ceramic.

Theoretical and experimental investigations of coherent phonon dynamics in sapphire crystal using femto- second time-resolved coherent anti-Stokes Raman scattering

Du Xin, Zhang Ming-Fu, He Xing, Meng Qing-Kun, Song Yun-Fei, Yang Yan-Qiang, Han Jie-Cai
Chin. Phys. B, 2011, 20 (12): 126301 doi: 10.1088/1674-1056/20/12/126301
Full Text: [PDF 205 KB] (Downloads:742)
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We report on the theoretical and the experimental investigations of the coherent phonon dynamics in sapphire crystal using the femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) technique. The temporal chirped white-light continuum (WLC) is used for the Stokes pulse, therefore we can perform the selective excitation of the phonon modes without using a complicated laser system. The expected quantum beat phenomenon is clearly observed. The theoretical formulas consist very well with the experimental results. The dephasing times of the excited phonon modes, the wavenumber difference, and the phase shift between the simultaneously excited modes are obtained and discussed. This work opens up a way to study directly high-frequency coherent phonon dynamics in bulk crystals on a femtosecond time scale and is especially helpful for understanding the nature of coherent phonons.

A cold 87Rb atomic beam

Wang Xiao-Jia, Feng Yan-Ying, Xue Hong-Bo, Zhou Zhao-Ying, Zhang Wen-Dong
Chin. Phys. B, 2011, 20 (12): 126701 doi: 10.1088/1674-1056/20/12/126701
Full Text: [PDF 286 KB] (Downloads:676)
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We demonstrate an experimental setup for the production of a beam source of cold 87Rb atoms. The atoms are extracted from a trapped cold atomic cloud in an unbalanced three-dimensional magneto-optical trap. Via a radiation pressure difference generated by a specially designed leak tunnel along one trapping laser beam, the atoms are pushed out continuously with low velocities and a high flux. The most-probable velocity in the beam is varied from 9 m/s to 19 m/s by varying the detuning of the trapping laser beams in the magneto-optical trap and the flux can be tuned up to 4×109 s-1 by increasing the intensity of the trapping beams. We also present a simple model for describing the dependence of the beam performance on the magneto-optical trap trapping laser intensity and the detuning.

Formation of rippled surface morphology during Si/Si (100) epitaxy by ultrahigh vacuum chemical vapour deposition

Hu Wei-Xuan, Cheng Bu-Wen, Xue Chun-Lai, Su Shao-Jian, Wang Qi-Ming
Chin. Phys. B, 2011, 20 (12): 126801 doi: 10.1088/1674-1056/20/12/126801
Full Text: [PDF 241 KB] (Downloads:477)
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The Si epitaxial films are grown on Si (100) substrates using pure Si2H6 as a gas source using ultrahigh vacuum chemical vapour deposition technology. The values of growth temperature Tg are 650 ℃, 700 ℃, 730 ℃, 750 ℃, and 800 ℃. Growth mode changes from island mode to step-flow mode with Tg increasing from 650 ℃ to 700 ℃. Rippled surface morphologies are observed at Tg = 700 ℃, 730 ℃, and 800 ℃, but disappear when Tg = 750 ℃. A model is presented to explain the formation and the disappearance of the ripples by considering the stability of the step-flow growth.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Valence band structure and density of states effective mass model of biaxial tensile strained silicon based on k·p theory

Kuang Qian-Wei, Liu Hong-Xia, Wang Shu-Long, Qin Shan-Shan, Wang Zhi-Lin
Chin. Phys. B, 2011, 20 (12): 127101 doi: 10.1088/1674-1056/20/12/127101
Full Text: [PDF 585 KB] (Downloads:3921)
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After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k·p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states (DOS) effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal-oxide semiconductor field effect transistor (MOSFET). It also a provides valuable reference for biaxial tensile strained silicon MOSFET design.

White-light emission of ZnO nanoparticles prepared by sol–gel method

Li Shi-Shuai, Zhang Zhong, Hang Jin-Zhao, Feng Xiu-Peng, Liu Ru-Xi
Chin. Phys. B, 2011, 20 (12): 127102 doi: 10.1088/1674-1056/20/12/127102
Full Text: [PDF 993 KB] (Downloads:1475)
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In:ZnO nanoparticles are prepared by the sol-gel process. The ratios of In/(Zn+In) are 0%, 5%, 8%, 10%, and 15%, respectively. Crystal phase structures and optoelectronic properties of these samples are characterized and the chromaticity coordinates of different samples are also calculated in CIE-XYZ colour system. The results show that preferred growth direction of ZnO changes from (002) plane to (001) plane and interplanar distance becomes shorter. When the doping amount of In is 5%, Zn atoms are completely replaced by In atoms. The resistivities of the samples first decrease, then increase afterwards with the increase of the amount of In. With the increase of In, the ultraviolet emission is redshifted and new peaks occur at 465 nm, 535 nm, and 630 nm. The sample with 10% indium has white-light emission. The band structures of samples with 0% and 12.5% indium are investigated by the first principle method. The mechanism of white emission is discussed from the viewpoint of additional energy levels.

Antiresonance induced spin-polarized current generation

Yin Sun, Min Wen-Jing, Gao Kun, Xie Shi-Jie, Liu De-Sheng
Chin. Phys. B, 2011, 20 (12): 127201 doi: 10.1088/1674-1056/20/12/127201
Full Text: [PDF 133 KB] (Downloads:584)
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According to the one-dimensional antiresonance effect (Wang X R, Wang Y and Sun Z Z 2003 Phys. Rev. B 65 193402), we propose a possible spin-polarized current generation device. Our proposed model consists of one chain and an impurity coupling to the chain. The energy level of the impurity can be occupied by an electron with a specific spin, and the electron with such a spin is blocked because of the antiresonance effect. Based on this phenomenon our model can generate the spin-polarized current flowing through the chain due to different polarization rates. On the other hand, the device can also be used to measure the generated spin accumulation. Our model is feasible with today's technology.

A pure spin-current injector of semiconductor quantum dots with Andreev reflection and Rashba spin–orbit coupling

Ye Cheng-Zhi, Nie Yi-Hang, Liang Jiu-Qing
Chin. Phys. B, 2011, 20 (12): 127202 doi: 10.1088/1674-1056/20/12/127202
Full Text: [PDF 340 KB] (Downloads:854)
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We propose a four-terminal device consisting of two parallel quantum dots with Rashba spin-orbit interaction (RSOI), coupled to two side superconductor leads and two common ferromagnetic leads, respectively. The two ferromagnetic leads and two quantum dots form a ring threaded by Aharonov-Bohm (AB) flux. This device possesses normal quasiparticle transmission between the two ferromagnetic leads, and normal and crossed Andreev reflections providing conductive holes. For the appropriate spin polarization of the ferromagnetic leads, RSOI and AB flux, the pure spin-up (or spin-down) current without net charge current in the right lead, which is due to the equal numbers of electrons and holes with the same spin-polarization moving along the same direction, can be obtained by adjusting the gate voltage, which may be used in practice as a pure spin-current injector.

Persistent current in a magnetized Rashba ring Hot!

Zhang Lin, Wang Jun
Chin. Phys. B, 2011, 20 (12): 127203 doi: 10.1088/1674-1056/20/12/127203
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We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spin-orbit interaction. By introducing uniform or nonuniform magnetization into the ring, we find that a nonzero persistent charge current circulates in the ring, which stems from the original equilibrium spin current due to the Rashba spin-orbit interaction. Because of broken time reversal symmetry, the two oppositely flowing spin-up and spin-down charge currents of the equilibrium spin current are no longer equal, and so a net persistent charge current can flow in the system. It is also found that the persistent current can be modulated by the Fermi energy, the Rashba spin-orbit interaction strength and the magnetization in the ring. Moreover, the magnetization perpendicular to the ring plane can optimize the current. The persistent current flowing in the ring is a manifestation of the nonzero equilibrium spin current existing in the ring.

The electrical characteristics of a 4H–silicon carbide metal–insulator–semiconductor structure with Al2O3 as the gate dielectric

Liu Li, Yang Yin-Tang, Ma Xiao-Hua
Chin. Phys. B, 2011, 20 (12): 127204 doi: 10.1088/1674-1056/20/12/127204
Full Text: [PDF 359 KB] (Downloads:1107)
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A 4H-silicon carbide metal-insulator-semiconductor structure with ultra-thin Al2O3 as the gate dielectric, deposited by atomic layer deposition on the epitaxial layer of a 4H-SiC (0001) 80N-/N+ substrate, has been fabricated. The experimental results indicate that the prepared ultra-thin Al2O3 gate dielectric exhibits good physical and electrical characteristics, including a high breakdown electrical field of 25 MV/cm, excellent interface properties (1×1014 cm-2) and low gate-leakage current (IG = 1 × 10-3 A/cm-2@Eox = 8 MV/cm). Analysis of the current conduction mechanism on the deposited Al2O3 gate dielectric was also systematically performed. The confirmed conduction mechanisms consisted of Fowler-Nordheim (FN) tunneling, the Frenkel-Poole mechanism, direct tunneling and Schottky emission, and the dominant current conduction mechanism depends on the applied electrical field. When the gate leakage current mechanism is dominated by FN tunneling, the barrier height of SiC/Al2O3 is 1.4 eV, which can meet the requirements of silicon carbide metal-insulator-semiconductor transistor devices.

The binding energy of a hydrogenic impurity in self-assembled double quantum dots

Zhang Hong, Wang Xue, Zhao Jian-Feng, Liu Jian-Jun
Chin. Phys. B, 2011, 20 (12): 127301 doi: 10.1088/1674-1056/20/12/127301
Full Text: [PDF 238 KB] (Downloads:763)
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The binding energy of a hydrogenic impurity in self-assembled double quantum dots is calculated via the finite-difference method. The variation in binding energy with donor position, structure parameters and external magnetic field is studied in detail. The results found are: (i) the binding energy has a complex behaviour due to coupling between the two dots; (ii) the binding energy is much larger when the donor is placed in the centre of one dot than in other positions; and (iii) the external magnetic field has different effects on the binding energy for different quantum-dot sizes or lateral confinements.

A density functional theory study of the electronic structures and magnetic properties of Fe(1-x)Cox alloy nanowires encapsulated in (10,0) carbon nanotubes

Xie You, Zhang Jian-Min
Chin. Phys. B, 2011, 20 (12): 127302 doi: 10.1088/1674-1056/20/12/127302
Full Text: [PDF 2229 KB] (Downloads:673)
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Under the generalized gradient approximation, the electronic structures and magnetic properties of Fe(1-x)Cox alloy nanowires encapsulated inside zigzag (10,0) carbon nanotubes (CNTs) are investigated systematically using firstprinciple density functional theory calculations. For the fully relaxed Fe(1-x)Cox/CNT structures, all the C atoms relax outwards, and thus the diameters of the CNTs are slightly increased. Formation energy analysis shows that the combining processes of all Fe(1-x)Cox/CNT systems are exothermic, and therefore the Fe(1-x)Coxalloy nanowires can be encapsulated into semiconducting zigzag (10,0) CNTs and form stable hybrid structures. The charges are transferred from the Fe(1-x)Coxnanowires to the more electronegative CNTs, and the Fe-C/Co-C bonds formed have polar covalent bond characteristics. Both the spin polarization and total magnetic moment of the Fe(1-x)Cox/CNT system are smaller than those of the corresponding freestanding Fe(1-x)Coxnanowire, and the magnetic moment of the Fe(1-x)Cox/CNT system decreases monotonously with increasing Co concentration, but the Fe(1-x)Cox/CNT systems still have a large magnetic moment, implying that they can be utilized in high-density magnetic recording devices.

Research on the electrical characteristics of an organic thin-film field-effect transistor based on alternating-current resistance

Chen Yue-Ning, Xu Zheng, Zhao Su-Ling, Yin Fei-Fei, Zhang Cheng-Wen, Jiao Bi-Yuan, Dong Yu-Hang
Chin. Phys. B, 2011, 20 (12): 127303 doi: 10.1088/1674-1056/20/12/127303
Full Text: [PDF 430 KB] (Downloads:606)
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In this article, an organic thin-film field-effect transistor (OTFFET) with top-gate and bottom-contact geometry based on pentacene as the active layer is fabricated. The experimental data of the I-V are obtained from the OTFFET device. The alternating-current (AC) resistance value of the OTFFET device is calculated using the derivation method from the experimental data, and the AC resistance trend curves of the OTFFET device are obtained with the region fitting method. We analyse the characteristics of the OTFFET device with an AC resistance trend curve. To discover whether it has a high resistance, it is proposed to judge the region of the source/drain voltage (VDS) less than the transition voltage, thereby determining whether the contact between the metal electrode and the organic semiconductor layer of the OTFFET device is Ohmic or non-Ohmic. The theoretical analysis shows that the field-effect mobility and the AC resistance are in reverse proportion. Therefore, we point out that reducing AC resistance is necessary if field-effect mobility is to be improved.

The effects of contact configurations on the rectification of dipyrimidinyl–diphenyl diblock molecular junctions

Zhang Guang-Ping, Hu Gui-Chao, Li Zong-Liang, Wang Chuan-Kui
Chin. Phys. B, 2011, 20 (12): 127304 doi: 10.1088/1674-1056/20/12/127304
Full Text: [PDF 931 KB] (Downloads:865)
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The transport properties of a conjugated dipyrimidinyl-diphenyl diblock oligomer sandwiched between two gold electrodes, as recently reported by [Díez-Pérez et al. Nature Chem. 1 635 (2009)], are theoretically investigated using the fully self-consistent nonequilibrium Green's function method combined with density functional theory. Two kinds of symmetrical anchoring geometries are considered. Calculated current-voltage curves show that the contact structure has a strong effect on the rectification behaviour of the molecular diode. For the equilateral triangle configuration, pronounced rectification behaviour comparable to the experimental measurement is revealed, and the theoretical analysis indicates that the observed rectification characteristic results from the asymmetric shift of the perturbed molecular energy levels under bias voltage. While for the tetrahedron configuration, both rectification and negative differential conductivity behaviours are observed. The calculated results further prove the close dependence of the transporting characteristics of molecular junctions on contact configuration.

The reliability of AlGaN/GaN high electron mobility transistors under step-electrical stresses

Ma Xiao-Hua, Jiao Ying, Ma Ping, He Qiang, Ma Ji-Gang, Zhang Kai, Zhang Hui-Long, Zhang Jin-Cheng, Hao Yue
Chin. Phys. B, 2011, 20 (12): 127305 doi: 10.1088/1674-1056/20/12/127305
Full Text: [PDF 271 KB] (Downloads:1174)
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In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors (HEMTs) still lack solid reliability. Devices under accelerated DC stress tests (off-state, VDS =0 state, and on-state step-stress) are investigated to help us identify the degradation mechanisms of the AlGaN/GaN HEMTs. All our findings are consistent with the degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effects in Ref. [1] (Joh J and del Alamo J A 2006 IEEE IDEM Tech. Digest p. 415). However, under the on-state condition, the devices are suffering from both inverse piezoelectric effects and hot electron effects, and so to improve the reliability of the devices both effects should be taken into consideration.

The effects of sapphire nitridation on GaN growth by metalorganic chemical vapour deposition

Le Ling-Cong, Zhao De-Gang, Wu Liang-Liang, Deng Yi, Jiang De-Sheng, Zhu Jian-Jun, Liu Zong-Shun, Wang Hui, Zhang Shu-Ming, Zhang Bao-Shun, Yang Hui
Chin. Phys. B, 2011, 20 (12): 127306 doi: 10.1088/1674-1056/20/12/127306
Full Text: [PDF 149 KB] (Downloads:1386)
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In situ optical reflectivity measurements are employed to monitor the GaN epilayer growth process above a low-temperature GaN buffer layer on a c-plane sapphire substrate by metalorganic chemical vapour deposition. It is found that the lateral growth of the GaN islands and their coalescence are promoted in the initial growth stage if optimized nitridation time and temperature are selected when the substrate is pre-exposed to ammonia. As confirmed by atomic force microscopy observations, the quality of the GaN epilayers is closely dependent on the surface morphology of the nitridated buffer layer, especially grain size and nucleation density.

The Wiedemann–Franz law in a normal metal–superconductor junction

R Ghanbari, G Rashedi
Chin. Phys. B, 2011, 20 (12): 127401 doi: 10.1088/1674-1056/20/12/127401
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In this paper the influence of superconducting correlations on the thermal and charge conductances in a normal metal-superconductor (NS) junction in the clean limit is studied theoretically. First we solve the quasiclassical Eilenberger equations, and using the obtained density of states we can acquire the thermal and electrical conductances for the NS junction. Then we compare the conductance in a normal region of an NS junction with that in a single layer of normal metal (N). Moreover, we study the Wiedemann-Franz (WF) law for these two cases (N and NS). From our calculations we conclude that the behaviour of the NS junction does not conform to the WF law for all temperatures. The effect of the thickness of normal metal on the thermal conductivity is also theoretically investigated in the paper.

Synthesis of ZnFe2O4 nanomagnets by Fe-ion implantation into ZnO and post-annealing

Pan Feng, Guo Ying, Cheng Feng-Feng, Fa Tao, Yao Shu-De
Chin. Phys. B, 2011, 20 (12): 127501 doi: 10.1088/1674-1056/20/12/127501
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Fe ions of dose 8 × 1016 cm-2 are implanted into a ZnO single crystal at 180 keV. Annealing at 1073 K leads to the formation of zinc ferrite (ZnFe2O4), which is verified by synchrotron radiation X-ray diffraction (SR-XRD) and X-ray photoelectron spectroscopy (XPS). The crystallographically oriented ZnFe2O4 is formed inside the ZnO with the orientation relationship of ZnFe2O4 (111)//ZnO (0001). Superconducting quantum interference device (SQUID) measurements show that the as-implanted and post-annealing samples are both ferromagnetic at 5 K. The synthesized ZnFe2O4 is superparamagnetic, with a blocking temperature (TB = 25 K), indicated by zero field cooling and field cooling (ZFC/FC) measurements.

Relation between oxidation microstructure and the maximum energy product loss of a Sm2Co17 magnet oxidized at 500 ℃

Liu Li-Li, Jiang Cheng-Bao
Chin. Phys. B, 2011, 20 (12): 127502 doi: 10.1088/1674-1056/20/12/127502
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The oxidation microstructure and maximum energy product (BH)max loss of a Sm(Co0.76, Fe0.1, Cu0.1, Zr0.04)7 magnet oxidized at 500 ℃ were systematically investigated. Three different oxidation regions were formed in the oxidized magnet: a continuous external oxide scale, an internal reaction layer, and a diffusion zone. Both room-temperature and high-temperature (BH)max losses exhibited the same parabolic increase with oxidation time. An oxygen diffusion model was proposed to simulate the dependence of (BH)max loss on oxidation time. It is found that the external oxide scale has little effect on the (BH)max loss, and both the internal reaction layer and diffusion zone result in the (BH)max loss. Moreover, the diffusion zone leads to more (BH)max loss than the internal reaction layer. The values of the oxidation rate constant k for internal reaction layer and oxygen diffusion coefficient D for diffusion zone were obtained, which are about 1.91 × 10-10 cm2/s and 6.54 × 10-11 cm2/s, respectively.

Effects of notches on the order of flux-closure state formation in bi-rings by micromagnetic simulation

He Shu-Ting, Chang Shuang-Quan, Shi Hui-Gang
Chin. Phys. B, 2011, 20 (12): 127503 doi: 10.1088/1674-1056/20/12/127503
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The effects of the number and the location of notches on the formation of flux-closure states in bi-rings with fields applied in the x direction (i.e., along the short axis direction of bi-rings) and y direction (i.e., along the long axis direction of bi-rings) are investigated using micromagnetic simulation. For the bi-rings with one notch and the bi-rings with two notches symmetric about y axis, the order of flux-closure state formation in each ring can be controlled. But the flux-closure state forms simultaneously in each ring for the bi-rings with two notches symmetric about x axis. For the bi-rings with two notches that are symmetric neither about x axis nor about y axis, only one ring can form a flux-closure state in the y-direction field and no flux-closure state can be found in rings in the x-direction field. Therefore, logic states can be defined by controlling the order of flux-closure state formation, which can be utilized in future logic devices.

The coexistence of ferroelectricity and ferromagnetism in Mn-doped BaTiO3 thin films

Ding Bin-Feng, Zhou Sheng-Qiang
Chin. Phys. B, 2011, 20 (12): 127701 doi: 10.1088/1674-1056/20/12/127701
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Due to the fault of the first author of the article entitled “The coexistence of ferroelectricity and ferromagnetism in Mn-doped BaTiO3 thin films”, published in Chinese Physics B, 2011, Vol. 20, Issue 12, Article No. 127701, has been found to copy from the article entitled “Decisive role of oxygen vacancy in ferroelectric versus ferromagnetic Mn-doped BaTiO3 thin films”, published in Journal of Applied Physics, 2011, Vol.109, Issue 8, article No. 084105. So the above article in Chinese Physics B has been withdrawn from the publication. [5 December 2011]

5-at% Mn-doped and undoped BaTiO3 thin films have been grown under different oxygen partial pressures by Pulsed Laser Deposition (PLD) on platinum-coated sapphire substrates. X-ray diffraction (XRD) measurements for all the thin films reveal a similar polycrystalline single-phase perovskite structure. Ferroelectricity is observed in the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Ferromagnetic coupling of the Mn dopant ions, on the other hand, is only seen in Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure in a wide temperature range from 5 K to 300 K, and is attributed to the enhanced exchange coupling between Mn dopants and electrons at oxygen vacancies. Our results show that the leakage current is decreased with the doped Mn, but increases the dielectric loss and decreases the dielectric constant, and the ferroelectricity is impaired. To produce ferromagnetism, oxygen vacancies are necessary, which unfortunately increase the leakage current. This confirms that the mutual interplay between the ferroelectricity and ferromagnetism can be tuned by exchange coupling of the doped-Mn and oxygen vacancies in the BaTiO3 thin films.

Bright blue photoluminescence from a mixed tin and manganese oxide xerogel prepared via sol–hydrothermal–gel process

Xiang Xia, Cheng Xiao-Feng, He Shao-Bo, Yuan Xiao-Dong, Zheng Wan-Guo, Li Zhi-Jie, Liu Chun-Ming, Zhou Wei-Lie, Zu Xiao-Tao
Chin. Phys. B, 2011, 20 (12): 127801 doi: 10.1088/1674-1056/20/12/127801
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A new blue photoluminescent material, a mixed tin and manganese oxide xerogel, is prepared via sol-hydrothermal-gel process assisted by citric acid. The composition xerogel exhibits strong blue emission at room temperature, with an emission maximum at 434 nm under short (234 nm) or long-wavelength (343 nm) ultraviolet excitation. The photoluminescent excitation spectrum of the mixed tin and manganese oxide xerogel, monitored at an intensity maximum wavelength of 434 nm of the emission, consists of two excitation peaks at 234 nm and 343 nm. With heat treatment temperature increasing from 110 ℃ to 200 ℃, the blue emission intensity increases remarkably, whereas it is almost completely quenched after being treated at 300 ℃. The carbon impurities in the mixed tin and manganese oxide xerogel, confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, should be responsible for the bright blue photoluminescence.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Raman analysis of epitaxial graphene grown on 4H–SiC (0001) substrate under low pressure condition

Wang Dang-Chao, Zhang Yu-Ming, Zhang Yi-Men, Lei Tian-Min, Guo Hui, Wang Yue-Hu, Tang Xiao-Yan, Wang Hang
Chin. Phys. B, 2011, 20 (12): 128101 doi: 10.1088/1674-1056/20/12/128101
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In this paper, we report a feasible route of growing epitaxial graphene on 4H-SiC (0001) substrate in a low pressure of 4 mbar (1 bar=105 Pa) with an argon flux of 2 standard liters per minute at 1200, 1300, 1400, and 1500 ℃ in a commercial chemical vapour deposition SiC reactor. Using Raman spectroscopy and scanning electron microscopy, we confirm that epitaxial graphene evidently forms on SiC surface above 1300 ℃ with a size of several microns. By fitting the 2D band of Raman data with two-Lorentzian function, and comparing with the published reports, we conclude that epitaxial graphene grown at 1300 ℃ is four-layer graphene.

Shape-controlled synthesis of diamond crystal by epitaxial growth under high pressure and high temperature conditions

Liu Xiao-Bing, Jia Xiao-Peng, Zhang Zhuang-Fei, Huang Hai-Liang, Zhou Zhen-Xiang, Ma Hong-An
Chin. Phys. B, 2011, 20 (12): 128102 doi: 10.1088/1674-1056/20/12/128102
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In this paper, the diamond epitaxial growth mechanism has been studied in detail by employing several types of diamond as a seed in a catalyst-graphite system under high pressure and high temperature (HPHT) conditions. We find that the diamond nucleation, growth rate, crystal orientation, and morphology are significantly influenced by the original seeds. The smooth surfaces of seeds are beneficial for the fabrication of high-quality diamond. Our results reveal that the diamond morphology is mainly determined by the original shape of seeds in the early growth stage, but it has an adjustment process during the growth and leads to well symmetry. Additionally, we have also established the growth model for the twinned diamond grown on several seeds, and proposed the possible growth processes by tracking the particular shapes of seeds before and after treatment under HPHT conditions. These results suggest that the shape-controlled synthesis of diamond with well morphology can be realized by employing certain suitable diamond seeds. This work is expected to play an important role in the preparation of trustworthy diamond-based electronic and photonic devices.

A novel planar vertical double-diffused metal-oxide- semiconductor field-effect transistor with inhomogeneous floating islands

Ren Min, Li Ze-Hong, Liu Xiao-Long, Xie Jia-Xiong, Deng Guang-Min, Zhang Bo
Chin. Phys. B, 2011, 20 (12): 128501 doi: 10.1088/1674-1056/20/12/128501
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A novel planar vertical double-diffused metal-oxide-semiconductor (VDMOS) structure with an ultra-low specific on-resistance (Ron,sp), whose distinctive feature is the use of inhomogeneous floating p-islands in the n-drift region, is proposed. The theoretical limit of its Ron,sp is deduced, the influence of structure parameters on the breakdown voltage (BV) and Ron,sp are investigated, and the optimized results with BV of 83 V and Ron,sp of 54 mOmega cdotmm2 are obtained. Simulations show that the inhomogeneous-floating-islands metal-oxide-semiconductor field-effect transistor (MOSFET) has a superior “Ron,sp/BV” trade-off to the conventional VDMOS (a 38% reduction of Ron,sp with the same BV) and the homogeneous-floating-islands MOSFET (a 10% reduction of Ron,sp with the same BV). The inhomogeneous-floating-islands MOSFET also has a much better body-diode characteristic than the superjunction MOSFET. Its reverse recovery peak current, reverse recovery time and reverse recovery charge are about 50, 80 and 40% of those of the superjunction MOSFET, respectively.

Improving the field-emission properties of carbon nanotubes by magnetically controlled nickel-electroplating treatment

Zheng Long-Wu, Hu Li-Qin, Xiao Xiao-Jing, Yang Fan, Lin He, Guo Tai-Liang
Chin. Phys. B, 2011, 20 (12): 128502 doi: 10.1088/1674-1056/20/12/128502
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A novel magnetically controlled Ni-plating method has been developed to improve the field-emission properties of carbon nanotubes (CNTs). The effect of the magnetic field and Ni-electroplating on CNT field-emission properties was investigated, and the results are demonstrated using scanning electron microscopy, J-E and the duration test. After treatment, the turn-on electric field declines from 1.55 to 0.91 V/μm at an emission current density of 100 μA/cm2, and the emission current density increases from 0.011 to 0.34 mA/cm2 at an electric field of 1.0 V/μm. Both the brightness and uniformity of the CNT emission performance are improved after treatment.

Early-warning signals for an outbreak of the influenza pandemic

Ren Di, Gao Jie
Chin. Phys. B, 2011, 20 (12): 128701 doi: 10.1088/1674-1056/20/12/128701
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Over the course of human history, influenza pandemics have been seen as major disasters, so studies on the influenza virus have become an important issue for many experts and scholars. Comprehensive research has been performed over the years on the biological properties, chemical characteristics, external environmental factors and other aspects of the virus, and some results have been achieved. Based on the chaos game representation walk model, this paper uses the time series analysis method to study the DNA sequences of the influenza virus from 1913 to 2010, and works out the early-warning signals indicator value for the outbreak of an influenza pandemic. The variances in the CGR walk sequences for the pandemic years (or + -1 to 2 years) are significantly higher than those for the adjacent years, while those in the non-pandemic years are usually smaller. In this way we can provide an influenza early-warning mechanism so that people can take precautions and be well prepared prior to a pandemic.

Radiation-induced robust oscillation [2mm]and non-Gaussian fluctuation

Liu Bo, Yan Shi-Wei, Geng Yi-Zhao
Chin. Phys. B, 2011, 20 (12): 128702 doi: 10.1088/1674-1056/20/12/128702
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There have been many recent studies devoted to the consequences of stochasticity in protein circuitry. Stress conditions, including DNA damage, hypoxia, heat shock, nutrient deprivation, and oncogene activation, can result in the activation and accumulation of p53. Several experimental studies show that oscillations can be induced by DNA damage following nuclear irradiation. To explore the underlying dynamical features and the role of stochasticity, we discuss the oscillatory dynamics in the well-studied regulatory network motif. The fluctuations around the fixed point of a delayed system are Gaussian in the limit of sufficiently weak delayed feedback, and remain Gaussian along a limit cycle when viewed tangential to the trajectory. The experimental results are recapitulated in this study. We illustrate several features of the p53 activities, which are robust when the parameters change. Furthermore, the distribution in protein abundance can be characterized by its non-Gaussian nature.

Noise transmission and delay-induced stochastic oscillations in biochemical network motifs

Liu Sheng-Jun, Wang Qi, Liu Bo, Yan Shi-Wei, Fumihiko Sakata
Chin. Phys. B, 2011, 20 (12): 128703 doi: 10.1088/1674-1056/20/12/128703
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With the aid of stochastic delayed-feedback differential equations, we derive an analytic expression for the power spectra of reacting molecules included in a generic biological network motif that is incorporated with a feedback mechanism and time delays in gene regulation. We systematically analyse the effects of time delays, the feedback mechanism, and biological stochasticity on the power spectra. It has been clarified that the time delays together with the feedback mechanism can induce stochastic oscillations at the molecular level and invalidate the noise addition rule for a modular description of the noise propagator. Delay-induced stochastic resonance can be expected, which is related to the stability loss of the reaction systems and Hopf bifurcation occurring for solutions of the corresponding deterministic reaction equations. Through the analysis of the power spectrum, a new approach is proposed to estimate the oscillation period.

Spiking patterns of a hippocampus model in electric fields

Men Cong, Wang Jiang, Qin Ying-Mei, Wei Xi-Le, Che Yan-Qiu, Deng Bin
Chin. Phys. B, 2011, 20 (12): 128704 doi: 10.1088/1674-1056/20/12/128704
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We develop a model of CA3 neurons embedded in a resistive array to mimic the effects of electric fields from a new perspective. Effects of DC and sinusoidal electric fields on firing patterns in CA3 neurons are investigated in this study. The firing patterns can be switched from no firing pattern to burst or from burst to fast periodic firing pattern with the increase of DC electric field intensity. It is also found that the firing activities are sensitive to the frequency and amplitude of the sinusoidal electric field. Different phase-locking states and chaotic firing regions are observed in the parameter space of frequency and amplitude. These findings are qualitatively in accordance with the results of relevant experimental and numerical studies. It is implied that the external or endogenous electric field can modulate the neural code in the brain. Furthermore, it is helpful to develop control strategies based on electric fields to control neural diseases such as epilepsy.

Enhancing the synchronizability of networks by rewiring based on tabu search and a local greedy algorithm

Yang Cui-Li, Tang Kit-Sang
Chin. Phys. B, 2011, 20 (12): 128901 doi: 10.1088/1674-1056/20/12/128901
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By considering the eigenratio of the Laplacian matrix as the synchronizability measure, this paper presents an efficient method to enhance the synchronizability of undirected and unweighted networks via rewiring. The rewiring method combines the use of tabu search and a local greedy algorithm so that an effective search of solutions can be achieved. As demonstrated in the simulation results, the performance of the proposed approach outperforms the existing methods for a large variety of initial networks, both in terms of speed and quality of solutions.

Link prediction based on a semi-local similarity index

Bai Meng, Hu Ke, Tang Yi
Chin. Phys. B, 2011, 20 (12): 128902 doi: 10.1088/1674-1056/20/12/128902
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Missing link prediction provides significant instruction for both analysis of network structure and mining of unknown links in incomplete networks. Recently, many algorithms have been proposed based on various node-similarity measures. Among these measures, the common neighbour index, the resource allocation index, and the local path index, stemming from different source, have been proved to have relatively high accuracy and low computational effort. In this paper, we propose a similarity index by combining the resource allocation index and the local path index. Simulation results on six unweighted networks show that the accuracy of the proposed index is higher than that of the local path one. Based on the same idea of the present index, we develop its corresponding weighted version and test it on several weighted networks. It is found that, except for the USAir network, the weighted variant also performs better than both the weighted resource allocation index and the weighted local path index. Due to the improved accuracy and the still low computational complexity, the indices may be useful for link prediction.

Chaos in complex motor networks induced by Newman–Watts small-world connections

Wei Du-Qu, Luo Xiao-Shu, Zhang Bo
Chin. Phys. B, 2011, 20 (12): 128903 doi: 10.1088/1674-1056/20/12/128903
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We investigate how dynamical behaviours of complex motor networks depend on the Newman-Watts small-world (NWSW) connections. Network elements are described by the permanent magnet synchronous motor (PMSM) with the values of parameters at which each individual PMSM is stable. It is found that with the increase of connection probability p, the motor in networks becomes periodic and falls into chaotic motion as p further increases. These phenomena imply that NWSW connections can induce and enhance chaos in motor networks. The possible mechanism behind the action of NWSW connections is addressed based on stability theory.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Variational assimilation in combination with a regularization method for sea level pressure retrieval from QuikSCAT scatterometer data II: simulation experiment and actual case study

Zhang Liang, Huang Si-Xun, Shen Chun, Shi Wei-Lai
Chin. Phys. B, 2011, 20 (12): 129201 doi: 10.1088/1674-1056/20/12/129201
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The sea level pressure field can be computed from sea surface winds retrieved from satellite microwave scatterometer measurements, based on variational assimilation in combination with a regularization method given in part I of this paper. First, the validity of the new method is proved with a simulation experiment. Then, a new processing procedure for the sea level pressure retrieval is built by combining the geostrophic wind, which is computed from the scatterometer 10-meter wind using the University of Washington planetary boundary layer model using this method. Finally, the feasibility of the method is proved using an actual case study.

The modulation effect of substrate doping on multi-node charge collection and single-event transient propagation in 90-nm bulk complementary metal-oxide semiconductor technology

Qin Jun-Rui, Chen Shu-Ming, Liu Bi-Wei, Liu Zheng, Liang Bin, Du Yan-Kang
Chin. Phys. B, 2011, 20 (12): 129401 doi: 10.1088/1674-1056/20/12/129401
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Variation of substrate background doping will affect the charge collection of active and passive MOSFETs in complementary metal-oxide semiconductor (CMOS) technologies, which are significant for charge sharing, thus affecting the propagated single event transient pulsewidths in circuits. The trends of charge collected by the drain of a positive channel metal-oxide semiconductor (PMOS) and an N metal-oxide semiconductor (NMOS) are opposite as the substrate doping increases. The PMOS source will inject carriers after strike and the amount of charge injected will increase as the substrate doping increases, whereas the source of the NMOS will mainly collect carriers and the source of the NMOS can also inject electrons when the substrate doping is light enough. Additionally, it indicates that substrate doping mainly affects the bipolar amplification component of a single-event transient current, and has little effect on the drift and diffusion. The change in substrate doping has a much greater effect on PMOS than on NMOS.
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