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Chin. Phys. B  
  Chin. Phys. B--2011, Vol.20, No.9
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GENERAL

Knotted pictures of the Bell bases on the surface of a trivial torus

Gu Zhi-Yu, Qian Shang-Wu
Chin. Phys. B 2011, 20 (9): 090201;  doi: 10.1088/1674-1056/20/9/090201
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By means of the method of torus knot theory, this paper gives the complete processes of obtaining the knotted pictures of four Bell bases from the knotted pictures of four basic two qubit states.

The construction of homoclinic and heteroclinic orbitals in asymmetric strongly nonlinear systems based on the Pad'e approximant

Feng Jing-Jing, Zhang Qi-Chang, Wang Wei
Chin. Phys. B 2011, 20 (9): 090202;  doi: 10.1088/1674-1056/20/9/090202
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In this paper, the extended Pad'e approximant is used to construct the homoclinic and the heteroclinic trajectories in nonlinear dynamical systems that are asymmetric at origin. Meanwhile, the conservative system, the autonomous system, and the nonautonomous system equations with quadratic and cubic nonlinearities are considered. The disturbance parameter varepsilon is not limited to being small. The ranges of the values of the linear and the nonlinear term parameters, which are variables, can be determined when the boundary values are satisfied. New conditions for the potentiality and the convergence are posed to make it possible to solve the boundary-value problems formulated for the orbitals and to evaluate the initial amplitude values.

Modified (2+1)-dimensional displacement shallow water wave system and its approximate similarity solutions

Liu Ping, Fu Pei-Kai
Chin. Phys. B 2011, 20 (9): 090203;  doi: 10.1088/1674-1056/20/9/090203
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Recently, a new (2+1)-dimensional shallow water wave system, the (2+1)-dimensional displacement shallow water wave system (2DDSWWS), was constructed by applying the variational principle of the analytic mechanics in the Lagrange coordinates. The disadvantage is that fluid viscidity is not considered in the 2DDSWWS, which is the same as the famous Kadomtsev—Petviashvili equation and Korteweg—de Vries equation. Applying dimensional analysis, we modify the 2DDSWWS and add the term related to the fluid viscidity to the 2DDSWWS. The approximate similarity solutions of the modified 2DDSWWS (M2DDSWWS) is studied and four similarity solutions are obtained. For the perfect fluids, the coefficient of kinematic viscosity is zero, then the M2DDSWWS will degenerate to the 2DDSWWS.

Maximal and total skew information for a two-qubit system using nonlinear interaction models

Sun Hong-Gui, Liu Wan-Fang, Li Chun-Jie
Chin. Phys. B 2011, 20 (9): 090301;  doi: 10.1088/1674-1056/20/9/090301
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Maximal and total skew information is studied. For symmetric pure states of two-qubit, they are closely related to the linear entropy, the concurrence, and the spin squeezing parameter. For a two-qubit system implemented in three nonlinear interaction models with an external field, we give the exact state vectors and the expectation value 〈Sz〉 at any time t. Based on 〈Sz2, we give the maximal and the total skew information and a condition in which the maximal and the total skew information can reach 1 and 2, respectively.

The effect of atomic spontaneous decay on the dynamics of the negativity of the Wigner function of radiation

Abdel-Baset A. Mohamed
Chin. Phys. B 2011, 20 (9): 090303;  doi: 10.1088/1674-1056/20/9/090303
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The exact solution of the master equation for the case of a high-Q cavity with atomic decay is found. We use the negativity of the Wigner function (WF) as an indicator of nonclassicality. It is found that the negative values of the field WF are very sensitive to any change in the damping parameter. The atomic spontaneous decay leads to the simultaneous disappearance of both entanglement and nonclassicality of quantum states. Moreover, the purity of the field states is completely lost.

Efficient scheme for entangled states and quantum information transfer with trapped atoms in a resonator

Li Peng-Bo, Li Fu-Li
Chin. Phys. B 2011, 20 (9): 090304;  doi: 10.1088/1674-1056/20/9/090304
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A protocol is proposed to generate atomic entangled states and implement quantum information transfer in a cavity quantum electrodynamics system. It utilizes Raman transitions or stimulated Raman adiabatic passages between two systems to entangle the ground states of two three-state Λ-type atoms trapped in a single mode cavity. It does not need the measurements on cavity field nor atomic detection and can be implemented in a deterministic fashion. Since the present protocol is insensitive to both cavity decay and atomic spontaneous emission, it may have some interesting applications in quantum information processing.

Controlled quantum state sharing of arbitrary two-qubit states with five-qubit cluster states

Wang Dong, Zha Xin-Wei, Lan Qian, Li Ning, Wei Jing
Chin. Phys. B 2011, 20 (9): 090305;  doi: 10.1088/1674-1056/20/9/090305
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In this paper, we propose a controlled quantum state sharing scheme to share an arbitrary two-qubit state using a five-qubit cluster state and the Bell state measurement. In this scheme, the five-qubit cluster state is shared by a sender (Alice), a controller (Charlie), and a receiver (Bob), and the sender only needs to perform the Bell-state measurements on her particles during the quantum state sharing process, the controller performs a single-qubit projective measurement on his particles, then the receiver can reconstruct the arbitrary two-qubit state by performing some appropriate unitary transformations on his particles after he has known the measured results of the sender and the controller.

Variational principles for two kinds of extended Korteweg–de Vries equations

Cao Xiao-Qun, Song Jun-Qiang, Zhang Wei-Min, Zhao Jun
Chin. Phys. B 2011, 20 (9): 090401;  doi: 10.1088/1674-1056/20/9/090401
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Variational principles are constructed using the semi-inverse method for two kinds of extended Korteweg—de Vries (KdV) equations, which can be regarded as simple models of the nonlinear oceanic internal waves and atmospheric long waves, respectively. The obtained variational principles have also been proved to be correct.

Yang–Yang thermodynamics of one-dimensional Bose gases with anisotropic transversal confinement

Hao Ya-Jiang, Yin Xiang-Guo
Chin. Phys. B 2011, 20 (9): 090501;  doi: 10.1088/1674-1056/20/9/090501
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By combining the thermodynamic Bethe ansatz and local density approximation, we investigate the Yang—Yang thermodynamics of interacting one-dimensional Bose gases with anisotropic transversal confinement. It is shown that with the increase of anisotropic parameter at low temperature, the Bose atoms are distributed over a wider region, while at high temperature the density distribution is not affected obviously. Both the temperature and transversal confinement can strengthen the local pressure of the Bose gases.

Modified coupled map car-following model and its delayed feedback control scheme

Ge Hong-Xia
Chin. Phys. B 2011, 20 (9): 090502;  doi: 10.1088/1674-1056/20/9/090502
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A modified coupled map car-following model is proposed, in which two successive vehicle headways in front of the considering vehicle is incorporated into the optimal velocity function. The steady state under certain conditions is obtained. An error system around the steady state is studied further. Moreover, the condition for the state having no traffic jam is derived. A new control scheme is presented to suppress the traffic jam in the modified coupled map car-following model under the open boundary. A control signal including the velocity differences between the following and the considering vehicles, and between the preceding and the considering vehicles is used. The condition under which the traffic jam can be well suppressed is analysed. The results are compared with that presented by Konishi et al. (the KKH model). The simulation results show that the temporal behaviour obtained in our model is better than that in the KKH model. The simulation results are in good agreement with the theoretical analysis.

Integrated systemic inflammatory response syndrome epidemic model in scale-free networks

Cai Shao-Hong, Zhang Da-Min, Gong Guang-Wu, Guo Chang-Rui
Chin. Phys. B 2011, 20 (9): 090503;  doi: 10.1088/1674-1056/20/9/090503
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Based on the scale-free network, an integrated systemic inflammatory response syndrome model with artificial immunity, a feedback mechanism, crowd density and the moving activities of an individual can be built. The effects of these factors on the spreading process are investigated through the model. The research results show that the artificial immunity can reduce the stable infection ratio and enhance the spreading threshold of the system. The feedback mechanism can only reduce the stable infection ratio of system, but cannot affect the spreading threshold of the system. The bigger the crowd density is, the higher the infection ratio of the system is and the smaller the spreading threshold is. In addition, the simulations show that the individual movement can enhance the stable infection ratio of the system only under the condition that the spreading rate is high, however, individual movement will reduce the stable infection ratio of the system.

Security analysis of a one-way hash function based on spatiotemporal chaos

Wang Shi-Hong, Shan Peng-Yang
Chin. Phys. B 2011, 20 (9): 090504;  doi: 10.1088/1674-1056/20/9/090504
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The collision and statistical properties of a one-way hash function based on spatiotemporal chaos are investigated. Analysis and simulation results indicate that collisions exist in the original algorithm and, therefore, the original algorithm is insecure and vulnerable. An improved algorithm is proposed to avoid the collisions.

A novel adaptive finite-time controller for synchronizing chaotic gyros with nonlinear inputs

Mohammad Pourmahmood Aghababa
Chin. Phys. B 2011, 20 (9): 090505;  doi: 10.1088/1674-1056/20/9/090505
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In this paper, the problem of the finite-time synchronization of two uncertain chaotic gyros is discussed. The parameters of both the master and the slave gyros are assumed to be unknown in advance. The effects of model uncertainties and input nonlinearities are also taken into account. An appropriate adaptation law is proposed to tackle the gyros' unknown parameters. Based on the adaptation law and the finite-time control technique, proper control laws are introduced to ensure that the trajectories of the slave gyro converge to the trajectories of the master gyro in a given finite time. Simulation results show the applicability and the efficiency of the proposed finite-time controller.

Hopf bifurcation and uncontrolled stochastic traffic- induced chaos in an RED-AQM congestion control system

Wang Jun-Song, Yuan Rui-Xi, Gao Zhi-Wei, Wang De-Jin
Chin. Phys. B 2011, 20 (9): 090506;  doi: 10.1088/1674-1056/20/9/090506
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We study the Hopf bifurcation and the chaos phenomena in a random early detection-based active queue management (RED-AQM) congestion control system with a communication delay. We prove that there is a critical value of the communication delay for the stability of the RED-AQM control system. Furthermore, we show that the system will lose its stability and Hopf bifurcations will occur when the delay exceeds the critical value. When the delay is close to its critical value, we demonstrate that typical chaos patterns may be induced by the uncontrolled stochastic traffic in the RED-AQM control system even if the system is still stable, which reveals a new route to the chaos besides the bifurcation in the network congestion control system. Numerical simulations are given to illustrate the theoretical results.

Relationships of exponents in multifractal detrended fluctuation analysis and conventional multifractal analysis

Zhou Yu, Leung Yee, Yu Zu-Guo
Chin. Phys. B 2011, 20 (9): 090507;  doi: 10.1088/1674-1056/20/9/090507
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Multifractal detrended fluctuation analysis (MF-DFA) is a relatively new method of multifractal analysis. It is extended from detrended fluctuation analysis (DFA), which was developed for detecting the long-range correlation and the fractal properties in stationary and non-stationary time series. Although MF-DFA has become a widely used method, some relationships among the exponents established in the original paper seem to be incorrect under the general situation. In this paper, we theoretically and experimentally demonstrate the invalidity of the expression τ(q)=qh(q)-1 stipulating the relationship between the multifractal exponent τ(q) and the generalized Hurst exponent h(q). As a replacement, a general relationship is established on the basis of the universal multifractal formalism for the stationary series as τ(q)=qh(q)-qH'-1, where H' is the nonconservation parameter in the universal multifractal formalism. The singular spectra, α and f(α), are also derived according to this new relationship.

Comments on “The feedback control of fractional order unified chaotic system”

Elham Amini Boroujeni, Hamid Reza Momeni
Chin. Phys. B 2011, 20 (9): 090508;  doi: 10.1088/1674-1056/20/9/090508
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Our comments point out some mistakes in the main theorem given by Yang and Qi in Ref. [1] concerning the equivalent passivity method to design a nonlinear controller for the stabilizing fractional order unified chaotic system. The proof of this theorem is not reliable, since the mathematical basis of the fractional order calculus is not considered. Moreover, there are some algebraic mistakes in the inequalities used, thus making the proof invalid. We propose a proper Lyapunov function and the stability of Yang and Qi's Controller is investigated based on the fractional order Lyapunov theorem.

Modified scaling function projective synchronization of chaotic systems

Xu Yu-Hua, Zhou Wu-Neng, Fang Jian-An
Chin. Phys. B 2011, 20 (9): 090509;  doi: 10.1088/1674-1056/20/9/090509
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This paper investigates a kind of modified scaling function projective synchronization of uncertain chaotic systems using an adaptive controller. The given scaling function in the new method can be an equilibrium point, a periodic orbit, or even a chaotic attractor in the phase space. Based on LaSalle's invariance set principle, the adaptive control law is derived to make the states of two chaotic systems function projective synchronized. Some numerical examples are also given to show the effectiveness of the proposed method.

Forming and implementing a hyperchaotic system with rich dynamics

Liu Wen-Bo, Wallace K. S. Tang, Chen Guan-Rong
Chin. Phys. B 2011, 20 (9): 090510;  doi: 10.1088/1674-1056/20/9/090510
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A simple three-dimensional (3D) autonomous chaotic system is extended to four-dimensions so as to generate richer nonlinear dynamics. The new system not only inherits the dynamical characteristics of its parental 3D system but also exhibits many new and complex dynamics, including assembled 1-scroll, 2-scroll and 4-scroll attractors, as well as hyperchaotic attractors, by simply tuning a single system parameter. Lyapunov exponents and bifurcation diagrams are obtained via numerical simulations to further justify the existences of chaos and hyperchaos. Finally, an electronic circuit is constructed to implement the system, with experimental and simulation results presented and compared for demonstration and verification.

Hölder continuity of generalized chaos synchronization in complex networks

Hu Ai-Hua, Xu Zhen-Yuan, Guo Liu-Xiao
Chin. Phys. B 2011, 20 (9): 090511;  doi: 10.1088/1674-1056/20/9/090511
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A complex network consisting of chaotic systems is considered and the existence of the Hölder continuous generalized synchronization in the network is studied. First, we divide nodes of the network into two parts according to their dynamical behaviour. Then, based on the Schauder fixed point theorem, sufficient conditions for the existence of the generalized synchronization between them are derived. Moreover, the results are theoretically proved. Numerical simulations validate the theory.

Adaptive lag synchronization and parameter identification of fractional order chaotic systems

Zhang Ruo-Xun, Yang Shi-Ping
Chin. Phys. B 2011, 20 (9): 090512;  doi: 10.1088/1674-1056/20/9/090512
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This paper proposes a simple scheme for the lag synchronization and the parameter identification of fractional order chaotic systems based on the new stability theory. The lag synchronization is achieved and the unknown parameters are identified by using the adaptive lag laws. Moreover, the scheme is analytical and is simple to implement in practice. The well-known fractional order chaotic Lü system is used to illustrate the validity of this theoretic method.

Impulsive synchronization of two coupled complex networks with time-delayed dynamical nodes

Wang Shu-Guo, Yao Hong-Xing
Chin. Phys. B 2011, 20 (9): 090513;  doi: 10.1088/1674-1056/20/9/090513
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In this paper, we investigate the impulsive synchronization between two coupled complex networks with time-delayed dynamical nodes. Based on the Lyapunov stability, the linear feedback control and the impulsive control theories, the linear feedback and the impulsive controllers are designed separately. By using the generalized Barbalat's lemma, the global asymptotic impulsive synchronization of the drive—response complex networks is derived and some corresponding sufficient conditions are also obtained. Numerical examples are presented to verify the effectiveness and the correctness of the synchronization criteria.

Elimination of spiral waves and spatiotemporal chaos by the synchronization transmission technology of network signals

Zhang Qing-Ling, Lü Ling, Zhang Yi
Chin. Phys. B 2011, 20 (9): 090514;  doi: 10.1088/1674-1056/20/9/090514
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A method to eliminate spiral waves and spatiotemporal chaos by using the synchronization transmission technology of network signals is proposed in this paper. The character of the spiral waves and the spatiotemporal chaos in the Fitzhugh—Nagumo model is presented. The network error evolution equation with spatiotemporal variables and the corresponding eigenvalue equation are determined based on the stability theory, and the global synchronization condition is obtained. Simulations are made in a complex network with Fitzhugh—Nagumo models as the nodes to verify the effectiveness of the synchronization transmission principle of the network signal.

Rotating consensus of multi-agent systems without relative velocity measurement

Chen Xiao-Ping, Xu Hong-Bing, Ban Yong-Xin
Chin. Phys. B 2011, 20 (9): 090515;  doi: 10.1088/1674-1056/20/9/090515
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We study the rotating consensus of multi-agent systems without the relative velocity measurement in this paper. A new protocol is proposed. Then we use the theory of the complex system combined with the function continuity to derive a condition, under which all agents finally reach the rotating consensus. Finally, a numerical example is provided to illustrate our theoretical results.

Uncertainty reevaluation in determining the volume of a silicon sphere by spherical harmonics in an Avogadro project

Zhang Ji-Tao, Wu Xue-Jian, Li Yan
Chin. Phys. B 2011, 20 (9): 090601;  doi: 10.1088/1674-1056/20/9/090601
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To determine the Avogadro constant with a target relative uncertainty of 2 × 10-8, the uncertainty component of the silicon sphere's volume introduced by the spherical harmonics method, which is usually used in determining the sphere's volume, is reevaluated. By means of representing the shape of the silicon sphere by an ellipsoid with Gaussian white noise in its diameters, the uncertainty of the current mapping methods based on the spherical harmonics theory can be estimated theoretically. It is evidenced that the uncertainty component attributed to the current mapping method is underestimated. To eliminate this effect as much as possible, the number of mapping points should be increased to more than before. Moreover, a new mapping method is proposed to accomplish the equal-area mapping with large number points on the silicon sphere.

High birefringence, low loss terahertz photonic crystal fibres with zero dispersion at 0.3 THz

Yin Guo-Bing, Li Shu-Guang, Wang Xiao-Yan, Liu Shuo
Chin. Phys. B 2011, 20 (9): 090701;  doi: 10.1088/1674-1056/20/9/090701
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A terahertz photonic crystal fibre (THz-PCF) is designed for terahertz wave propagation. The dispersion property and model birefringence are studied by employing the finite element method. The simulation result reveals the changing patten of dispersion parameter versus the geometry. The influence of the large frequency band of terahertz on birefringence is also discussed. The design of low loss, high birefringence THz-PCFs with zero dispersion frequency at 0.3 THz is presented.
RAPID COMMUNICATION

Coherent state evolution in a Raman dispersion process

Du Jian-Ming, Ren Gang, Fan Hong-Yi
Chin. Phys. B 2011, 20 (9): 090302;  doi: 10.1088/1674-1056/20/9/090302
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By using the technique of integration within an ordered product of operators, we derive the evolution of an initial coherent state in a Raman dispersion process.

boldmath In situ high temperature X-ray diffraction studies of ZnO thin film

Chen Xiang-Cun, Zhou Jie-Ping, Wang Hai-Yang, Xu Peng-Shou, Pan Guo-Qiang
Chin. Phys. B 2011, 20 (9): 096102;  doi: 10.1088/1674-1056/20/9/096102
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An epitaxial ZnO thin film was entirely fabricated by pulsed laser deposition. Both the orientation and the size of the crystallites were studied. The X-ray diffraction (XRD) patterns of the film show strong c-axis oriented crystal structure with preferred (002) orientation. The Phi-scan XRD pattern confirms that the epitaxial ZnO exhibits a single-domain wurtzite structure with hexagonal symmetry. In situ high-temperature XRD studies of ZnO thin film show that the crystallite size increases with increasing temperature, and (002) peaks shift systematically toward lower 2θ values due to the change of lattice parameters. The lattice parameters show linear increase in their values with increasing temperature.

Magnetic phase transitions and magnetocaloric effect in the Fe-doped MnNiGe alloys

Zhang Cheng-Liang, Wang Dun-Hui, Chen Jian, Wang Ting-Zhi, Xie Guang-Xi, Zhu Chun
Chin. Phys. B 2011, 20 (9): 097501;  doi: 10.1088/1674-1056/20/9/097501
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The magnetic phase transition and magnetocaloric effects in Fe-doped MnNiGe alloys are investigated. The substitution of Fe for Ni decreases the structural transition temperature remarkably, resulting in the magnetostructural transition occurring between antiferromagnetic and ferromagnetic states in MnNi1 - xFexGe alloy. Owing to the enhanced ferromagnetic coupling induced by the substitution of Fe, metamagnetic behaviour is also observed in TiNiSi-type phase of MnNi1 - xFexGe alloys at temperature below the structural transition temperature.
ATOMIC AND MOLECULAR PHYSICS

Physical properties of hexagonal WN2 under pressure

Li Xiao-Feng, Zhai Hong-Cun, Fu Hong-Zhi, Liu Zhong-Li, Ji Guang-Fu
Chin. Phys. B 2011, 20 (9): 093101;  doi: 10.1088/1674-1056/20/9/093101
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A first-principles study on the mechanical stability, elastic and thermodynamic properties of WN2 with P63/mmc and P-6m2 phases are reported using the pseudo potential plane wave method within the generalized gradient approximation. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible WN2 are determined in the wide pressure range. By the elastic stability criteria, it is predicted that P63/mmc and P-6m2 phases in WN2 are not stable above 175.1 GPa and 170.1 GPa, respectively. Finally, by using the quasiharmonic Debye model, the isothermal and adiabatic bulk modulus, and the heat capacity of WN2 are also successfully obtained.

Elastic scattering of sodium and cesium atoms at ultracold temperatures

Zhang Ji-Cai, Wang Ke-Dong, Liu Yu-Fang, Sun Jin-Feng
Chin. Phys. B 2011, 20 (9): 093401;  doi: 10.1088/1674-1056/20/9/093401
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The elastic scattering properties in a mixture of sodium and cesium atoms are investigated at cold and ultracold temperatures. Based on the accurate interatomic potential for the NaCs mixture, the interspecies s-wave scattering lengths, the effective ranges and the p-wave scattering lengths are calculated by the quantal method and the semiclassical method, respectively. The s-wave scattering lengths are 512.7a0 for the singlet state and 33.4a0 for the triplet state. In addition, the spin-change and elastic cross sections are also calculated, and the g-wave shape resonance is found in the total elastic cross sections.
CLASSICAL AREAS OF PHENOMENOLOGY

Independently tunable multichannel terahertz filters

Zhang Hui-Yun, Gao Ying, Zhang Yu-Ping, Wang Shi-Fan
Chin. Phys. B 2011, 20 (9): 094101;  doi: 10.1088/1674-1056/20/9/094101
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We numerically demonstrate terahertz multichannel filters with independently tunable defect modes based on fractal photonic crystals. Single defect and multiple defects models are proposed to fabricate the multichannel terahertz filters. The facts that the wave functions of the defect states do not overlap and their bases are orthogonal lead to the independency among the defect modes. The simulated results theoretically provide the principle for fabricating independently tunable multichannel terahertz filters by utilizing one-dimensional photonic crystals with defects.

Terahertz wave polarization rotation in bianisotropic metamaterials

Shi Yu-Lei, Zhou Qing-Li, Liu Wei, Zhao Dong-Mei, Li Lei, Zhang Cun-Lin
Chin. Phys. B 2011, 20 (9): 094102;  doi: 10.1088/1674-1056/20/9/094102
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Utilizing a polarization sensitive terahertz detection method where the detector is rotated by either 0° or 90° to measure the electric field Ep, s (t) of each polarization component, we have characterized the properties of split ring resonators. The strong polarization dependence of the bianisotropic-circular-current-driven and linear-polarization-induced resonances is in excellent agreement with the simulation when the p-polarized terahertz transmission is measured. However, these electromagnetic responses vanish when the s-polarized terahertz transmission is measured. There is only a transmission minimum at 1.64 THz and the terahertz polarization rotation angle of about 90° is observed. The polarized terahertz transmission amplitudes and spectra detected at orthogonal orientations show that these behaviours are probably attributed to the birefringent effect of the sample.

Gain calculation of a free-electron laser operating with a non-uniform ion-channel guide

A. Hasanbeigi, H. Mehdian, S. Jafari
Chin. Phys. B 2011, 20 (9): 094103;  doi: 10.1088/1674-1056/20/9/094103
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Amplification of an electromagnetic wave by a free electron laser (FEL) with a helical wiggler and an ion channel with a periodically varying ion density is examined. The relativistic equation of motion for a single electron in the combined wiggler and the periodic ion-channel fields is solved and the classes of possible trajectories in this configuration are discussed. The gain equation for the FEL in the low-gain-per-pass limit is obtained by adding the effect of the periodic ion channel. Numerical calculation is employed to analyse the gain induced by the effects of the non-uniform ion density. The variation of gain with ion-channel density is demonstrated. It is shown that there is a gain enhancement for group I orbits in the presence of a non-uniform ion-channel but not in a uniform one. It is also shown that periodic ion-channel guiding is used to reach the maximum peak gain in a low ion-channel frequency (low ion density).

Design of periodic metal-insulator-metal waveguide back structures for the enhancement of light absorption in thin-film solar cells

Zheng Gai-Ge, Jiang Jian-Li, Xian Feng-Lin, Qiang Hai-Xia, Wu Hong, Li Xiang-Yin
Chin. Phys. B 2011, 20 (9): 094201;  doi: 10.1088/1674-1056/20/9/094201
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To increase the absorption in a thin layer of absorbing material (amorphous silicon, a-Si), a light trapping design is presented. The designed structure incorporates periodic metal-insulator-metal waveguides to enhance the optical path length of light within the solar cells. The new design can result in broadband optical absorption enhancement not only for transverse magnetic (TM)-polarized light, but also for transverse electric (TE)-polarized light. No plasmonic modes can be excited in TE-polarization, but because of the coupling into the a-Si planar waveguide guiding modes and the diffraction of light by the bottom periodic structures into higher diffraction orders, the total absorption in the active region is also increased. The results from rigorous coupled wave analysis show that the overall optical absorption in the active layer can be greatly enhanced by up to 40%. The designed structures presented in this paper can be integrated with back contact technology to potentially produce high-efficiency thin-film solar cell devices.

Elegant Ince–Gaussian beams in a quadratic-index medium

Bai Zhi-Yong, Deng Dong-Mei, Guo Qi
Chin. Phys. B 2011, 20 (9): 094202;  doi: 10.1088/1674-1056/20/9/094202
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Elegant Ince—Gaussian beams, which are the exact solutions of the paraxial wave equation in a quadratic-index medium, are derived in elliptical coordinates. These kinds of beams are the alternative form of standard Ince—Gaussian beams and they display better symmetry between the Ince-polynomials and the Gaussian function in mathematics. The transverse intensity distribution and the phase of the elegant Ince—Gaussian beams are discussed.

Experimental investigation on partially coherent higher-order non-diffractive beams

Chen Guang-Ming, Hua Li-Min, Lin Hui-Chuan, Pu Ji-Xiong
Chin. Phys. B 2011, 20 (9): 094203;  doi: 10.1088/1674-1056/20/9/094203
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We experimentally study the generation of a partially coherent non-diffractive beam by focusing a partially coherent vortex beam with an axicon. The investigation results show that when the partially coherent vortex beam is focused by the axicon, the beam is transferred into a partially coherent higher-order non-diffractive beam. In the non-diffractive zone, the transverse intensity distribution of the partially coherent higher-order non-diffractive beam is invariant during propagation. In addition, the range of the non-diffractive zone is related to the coherence of the partially coherent vortex beam. The poorer the coherence of the partially coherent vortex beam, the shorter the range of the non-diffractive zone.

Periodic adjustment of the position of a laser beam spot on a semiconductor saturable absorber mirror in a passively mode-locked solid-state laser

Xia Pa-Keti, Yan Ping, Gong Ma-Li
Chin. Phys. B 2011, 20 (9): 094204;  doi: 10.1088/1674-1056/20/9/094204
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A laser diode end-pumped passively mode-locked Nd:YVO4 solid-state laser with a semiconductor saturable absorber mirror (SESAM), in which the intracavity laser beam spot on the SESAM can be adjusted periodically, is investigated. Inserting a rectangular prism (RP) into the laser cavity is a promising approach towards the goal of periodically moving the position of the focus spot of the intracavity pulse on the SESAM surface to avoid the long-time irradiation of the laser beam on the same position, thereby solving a series of problems caused by damage to the SESAM and greatly prolonging its usage life. The adjustment of the rectangular prism in the laser cavity does not break the stable continuous wave (CW) mode-locked condition. The laser generates a stable picosecond pulse sequence at 1064 nm with an output power of 3.6 W and a pulse width of 14 ps. The instabilities of the output power and the pulse width are 1.77% and 4.5%, respectively.

A method to control the polarization of random terahertz lasing in two-dimensional disordered ruby medium

Liu Yong, Liu Jin-Song, Wang Ke-Jia
Chin. Phys. B 2011, 20 (9): 094205;  doi: 10.1088/1674-1056/20/9/094205
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Terahertz (THz) random lasing is studied numerically for two-dimensional disordered media made of ruby grains with a three-level atomic system. A method via the adjustment of the pumping area to control the polarization of the THz wave is proposed. Computed results reveal that transverse electric THz lasing modes could occur if pumping is supplied on the whole medium, while transverse magnetic THz lasing modes could occur if pumping is appropriately supplied on a partial area of the medium.

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well vertical-cavity surface-emitting laser

Guan Bao-Lu, Ren Xiu-Juan, Li Chuan, Li Shuo, Shi Guo-Zhu, Guo Xia
Chin. Phys. B 2011, 20 (9): 094206;  doi: 10.1088/1674-1056/20/9/094206
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A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) based on an intra-cavity contacted structure is fabricated. A threshold current of 1.5 mA for a 22 μm oxide aperture device is achieved, which corresponds to a threshold current density of 0.395 kA/cm2. The peak output optical power reaches 17.5 mW at an injection current of 30 mA at room temperature under pulsed operation. While under continuous-wave (CW) operation, the maximum power attains 10.5 mW. Such a device demonstrates a high characteristic temperature of 327 K within a temperature range from -12℃ to 96℃ and good reliability under a lifetime test. There is almost no decrease of the optical power when the device operates at a current of 5 mA at room temperature under the CW injection current.

Intersubband transitions in Al0.82In0.18N/GaN single quantum well

Chin. Phys. B 2011, 20 (9): 094207;  doi: 10.1088/1674-1056/20/9/094207
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The influence of the width of a lattice-matched Al0.82In0.18N/GaN single quantum well (SQW) on the absorption coefficients and wavelength of the intersubband transition (ISBT) has been investigated by solving the Schrödinger and Poisson equations self-consistently. The wavelength of 1—2 ISBT increases with L, the thickness of the single quantum well, ranging from 2.88 μm to 3.59 μm. The absorption coefficients of 1—2 ISBT increase with L at first and then decrease with L, with a maximum when L is equal to 2.6 nm. The wavelength of 1—3 ISBT decreases with L at first and then increases with L, with a minimum when L is equal to 4 nm, ranging from approximately 2.03 μm to near 2.11 μm. The absorption coefficients of 1—3 ISBT decrease with L. The results indicate that mid-infrared can be realized by the Al0.82In0.18N/GaN SQW. In addition, the wavelength and absorption coefficients of ISBT can be adjusted by changing the width of the SQW.

Propagation of high-power partially coherent fibre laser beams in a real environment

Tao Ru-Mao, Si Lei, Ma Yan-Xing, Zou Yong-Chao, Zhou Pu
Chin. Phys. B 2011, 20 (9): 094208;  doi: 10.1088/1674-1056/20/9/094208
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The propagation performance of high-power partially coherent fibre laser beams in a real environment is investigated and the theoretical model of a high-power fibre laser propagating in a real environment is established. The influence of a collimating system and thermal blooming is considered together with atmospheric turbulence and mechanical jitter. The laser energy concentration of partially coherent beams in the far field is calculated and analysed based on the theoretical model. It is shown that the propagation performance of partially coherent beams depends on the collimating system, atmospheric turbulence, mechanical jitter and thermal blooming. The propagation performance of partially coherent beams and fully coherent beams is studied and the results show that partially coherent beams are less sensitive to the influence of thermal blooming, which results in that the energy degeneration for partially coherent beams is only 50% of that for fully coherent beams. Both partially coherent beams and fully coherent beams become less sensitive to thermal blooming when the average structural constant of the refraction index fluctuations increases to 1.7 × 10-14 m-2/3. The investigation presents a reference for applications of a high-power fibre laser system.

High-speed chaotic communication using an optical fibre ring as a key

Zou Lin, Feng Ye, Yang Yi-Biao, Wang An-Bang, Yang Ling-Zhen, Zhang Jian-Zhong
Chin. Phys. B 2011, 20 (9): 094209;  doi: 10.1088/1674-1056/20/9/094209
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A chaotic communication scheme with a fibre ring inserted in the optical feedback of the transmitter laser as an additional key is proposed under anticipating synchronization. The numerical results show that the key can enhance the communication security effectively. It is theoretically safe for the communication scheme to transmit messages with a frequency beyond the relaxation oscillation frequency.

Propagation properties of partially coherent Hermite–Gaussian beams through non-Kolmogorov turbulence

He Xue-Mei, Lü Bai-Da
Chin. Phys. B 2011, 20 (9): 094210;  doi: 10.1088/1674-1056/20/9/094210
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The propagation properties of partially coherent Hermite—Gaussian beams through non-Kolmogorov atmospheric turbulence are studied. The effects of non-Kolmogorov turbulence and beam nonparaxiality on the average intensity evolution and the beam-width spreading are stressed. It is found that the evolution of the average intensity distribution and the beam-width spreading depends on the generalized exponent factor, namely, on the non-Kolmogorov turbulence strength for the paraxial case. For the non-paraxial case the effect of the turbulence is negligible, while the beam-width spreading becomes very large. The analytical results are illustrated numerically and interpreted physically.

Photoluminescence and persistent luminescence properties of non-doped and Ti4+-doped Mg2SnO4 phosphors

Zhang Jia-Chi, Qin Qing-Song, Yu Ming-Hui, Zhou Hong-Liang, Zhou Mei-Jiao
Chin. Phys. B 2011, 20 (9): 094211;  doi: 10.1088/1674-1056/20/9/094211
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Mg2SnO4 exhibits green photoluminescence and persistent luminescence, which originate from oxygen vacancies. When Ti4+ ions were doped, an interesting Mg2SnO4:Ti4+ phosphor with bluish white photoluminescence under ultraviolet irradiation and with green persistent luminescence was first obtained. Our investigation reveals that two emission centres exist in Mg2SnO4:Ti4+. The centres responsible for the green emission are considered to be the F centres (oxygen vacancies) and the blue centres are the TiO6 complex. Trap clusters in the band gap with different depths, such as [SnMg—Oi], [SnMg—VO·], [SnMg—VO×] and MgSn, correspond to the components at 85 ℃, 146 ℃ and 213 ℃ of the thermoluminescence curve.

Rugate filters prepared by rapidly alternating deposition

Zhang Jun-Chao, Fang Ming, Shao Yu-Chuan, Jin Yun-Xia, He Hong-Bo
Chin. Phys. B 2011, 20 (9): 094212;  doi: 10.1088/1674-1056/20/9/094212
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A methodology for the fabrication of composite (Nb2O5)1-x(SiO2)x thin-film rugate filters by using pulsed direct current magnetron sputtering is presented. The two materials are mixed using rapidly alternating deposition technology. The optical properties of the composite films varying with the composition of the material are studied in detail. Refractive indices between 1.50 and 2.14 can be realized in our coating system. Two designed rugate filters with a reflection band at the wavelength of 532 nm are fabricated using an automatic deposition process. The microstructure of the rugate filter is investigated by using scanning electron microscopy. The calculated and the measured transmittance spectra are in good agreement with each other. The causes of the slight differences between them are also analysed.

Piezoelectric transducer parameter selection for exciting a single mode from multiple modes of Lamb waves

Zhang Hai-Yan, Yu Jian-Bo
Chin. Phys. B 2011, 20 (9): 094301;  doi: 10.1088/1674-1056/20/9/094301
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Excitation and propagation of Lamb waves by using rectangular and circular piezoelectric transducers surface-bonded to an isotropic plate are investigated in this work. Analytical stain wave solutions are derived for the two transducer shapes, giving the responses of these transducers in Lamb wave fields. The analytical study is supported by a numerical simulation using the finite element method. Symmetric and antisymmetric components in the wave propagation responses are inspected in detail with respect to test parameters such as the transducer geometry, the length and the excitation frequency. By placing only one piezoelectric transducer on the top or the bottom surface of the plate and weakening the strength of one mode while enhancing the strength of the other modes to find the centre frequency, with which the peak wave amplitude ratio between the S0 and A0 modes is maximum, a single mode excitation from the multiple modes of the Lamb waves can be achieved approximately. Experimental data are presented to show the validity of the analyses. The results are used to optimize the Lamb wave detection system.

Dynamic bifurcation of a modified Kuramoto–Sivashinsky equation with higher-order nonlinearity

Huang Qiong-Wei, Tang Jia-Shi
Chin. Phys. B 2011, 20 (9): 094701;  doi: 10.1088/1674-1056/20/9/094701
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Under the periodic boundary condition, dynamic bifurcation and stability in the modified Kuramoto—Sivashinsky equation with a higher-order nonlinearity μ(ux)puxx are investigated by using the centre manifold reduction procedure. The result shows that as the control parameter crosses a critical value, the system undergoes a bifurcation from the trivial solution to produce a cycle consisting of locally asymptotically stable equilibrium points. Furthermore, for cases in which the distances to the bifurcation points are small enough, one-order approximations to the bifurcation solutions are obtained.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Numerical analysis of high Mach flow and flow reversal in the experimental advanced superconducting tokamak divertor

Ou Jing, Yang Jin-Hong
Chin. Phys. B 2011, 20 (9): 095201;  doi: 10.1088/1674-1056/20/9/095201
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The B2-Eirene (SOLPS 4.0) code package is used to investigate the plasma parallel flow, i.e., the scrape-off layer (SOL) flow, in the experimental advanced superconducting tokamak (EAST) divertor. Simulation results show that the SOL flow in the divertor region can exhibit complex behaviour, such as a high Mach flow and flow reversal in different plasma regimes. When the divertor plasma is in the detachment state, the high Mach flow with approaching or exceeding sonic speed is observed away from the target plate in our simulation. When the divertor plasma is in the high recycling state, the flow reversal with a small Mach number (|M|< 0.2) is observed near the X-point along the separatrix region. The driving mechanisms for the high Mach flow and the reversed flow are analysed theoretically through momentum and continuity equations, respectively. The profile of the ionization sources is shown to be a possible formation condition causing the complex behaviour of the SOL flow. In addition, the effects of the high Mach flow and the flow reversal on the impurity transport are also discussed in this paper.

Relativistic correction of (v/c)2 to the collective Thomson scattering for high-temperature high-density plasma

Jiang Chen-Fan-Fu, Zheng Jian, Zhao Bin
Chin. Phys. B 2011, 20 (9): 095202;  doi: 10.1088/1674-1056/20/9/095202
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Collective Thomson scattering is theoretically investigated with the inclusion of the relativistic correction of (v/c)2. The correction is rather small for the plasma parameters inferred from the spectra of the thermal electron plasma waves in the plasma. Since the full formula of the corrected result is rather complicated, a simplified one is derived for practical use, which is shown to be in good agreement with the un-simplified one.

Emission spectrum from an Al/Mg tracer in the blow-off region of a radiatively ablated capsule

Pu Yu-Dong, Chen Bo-Lun, Zhang Lu, Yang Jia-Min, Huang Tian-Xuan, Ding Yong-Kun
Chin. Phys. B 2011, 20 (9): 095203;  doi: 10.1088/1674-1056/20/9/095203
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A study of X-ray emissions from Al/Mg tracers buried at two different depths in a plastic shell is presented. The X-rays originating from the K-shell transitions of the Al/Mg ions begin to irradiate after the ablative heating wave has passed through the trace layer and are recorded with a streaked crystal spectrometer. Only emissions from the capsule with the trace layer buried at a smaller depth are observed. Hydrodynamic simulations and a collisional—radiative model including detailed atomic physics are used to investigate the measured spectrum. It is found that the effects of the radiative heating play important roles in the formation of the K-shell emission. The time correlation between the simulations and the measurements is obtained by comparing the measured time profile of the He α emission with the calculated one. The line ratio of Ly α to He α is also calculated and is found to be in fairly good agreement with the experimental data. Finally, the relation between the time profile of the He α emission and the ablation velocity is also discussed.

Effects of electron temperature on dielectric function and localization of laser beams in underdense collisional plasma

Xia Xiong-Ping, Cai Ze-Bin, Yi Lin
Chin. Phys. B 2011, 20 (9): 095204;  doi: 10.1088/1674-1056/20/9/095204
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Effects of electron temperature on dielectric function and localization of laser beams in underdense collisional plasmas are investigated. Simulation results show that the electron temperature has a strong effect on the dielectric constant and the laser beam localization. It is observed that due to the influence of the electron temperature, the dielectric function presents some interesting and complicated nonlinear variations, and gives rise to the laser beam localization. Moreover, the amplitudes of the beam width and the beam intensity are subjected to continuously oscillatory variation in the region of localization. In addition, the effects of several parameters on the dielectric function and the beam localization are discussed.

Identification of the magnetic island structure in the HL-2A tokamak

Ji Xiao-Quan, Yang Qing-Wei, Feng Bei-Bin, Xu Yuan, Sun Teng-Fei, Yuan Bao-Shan
Chin. Phys. B 2011, 20 (9): 095205;  doi: 10.1088/1674-1056/20/9/095205
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The identification of the magnetic island structure in the HL-2A tokamak is presented. First, the perturbation current as a source for the perturbation flux can be determined by using Mirnov probe measurements. By superposing the perturbation flux and the equilibrium flux reconnected by equilibrium fitting, the structure and the width of the magnetic islands can be estimated. The method has been used in the HL-2A experiments.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Thermal properties of single-walled carbon nanotube crystal Hot!

Hu Li-Jun, Liu Ji, Liu Zheng, Qiu Cai-Yu, Zhou Hai-Qing, Sun Lian-Feng
Chin. Phys. B 2011, 20 (9): 096101;  doi: 10.1088/1674-1056/20/9/096101
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In this work, the thermal properties of a single-walled carbon nanotube (SWCNT) crystal are studied. The thermal conductivity of the SWCNT crystal is found to have a linear dependence on temperature in the temperature range from 1.9 K to 100.0 K. In addition, a peak (658 W/mK) is found at a temperature of about 100.0 K. The thermal conductivity decreases gradually to a value of 480 W/mK and keeps almost a constant in the temperature range from 100.0 K to 300.0 K. Meanwhile, the specific heat shows an obvious linear relationship with temperature in the temperature range from 1.9 K to 300.0 K. We discuss the possible mechanisms for these unique thermal properties of the single-walled carbon nanotube crystal.

Self-assembly and growth of manganese phthalocyanine on an Au(111) surface Hot!

Jiang Yu-Hang, Liu Li-Wei, Yang Kai, Xiao Wen-De, Gao Hong-Jun
Chin. Phys. B 2011, 20 (9): 096401;  doi: 10.1088/1674-1056/20/9/096401
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Self-assembly and growth of manganese phthalocyanine (MnPc) molecules on an Au(111) surface is investigated by means of low-temperature scanning tunneling microscopy. At the initial stage, MnPc molecules preferentially occupy the step edges and elbow sites on the Au(111) surface, then they are separately adsorbed on the face-centered cubic and hexagonal closely packed regions due to a long-range repulsive molecule—molecule interaction. After the formation of a closely packed monolayer, molecular islands with second and third layers are observed.

Influence of Boron doping on microcrystalline silicon growth

Li Xin-Li, Chen Yong-Sheng, Yang Shi-E, Gu Jin-Hua, Lu Jing-Xiao, Gao Xiao-Yong, Li Rui, Jiao Yue-Chao, Gao Hai-Bo, Wang Guo
Chin. Phys. B 2011, 20 (9): 096801;  doi: 10.1088/1674-1056/20/9/096801
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Microcrystalline silicon (μc-Si:H) thin films with and without boron doping are deposited using the radio-frequency plasma-enhanced chemical vapour deposition method. The surface roughness evolutions of the silicon thin films are investigated using ex situ spectroscopic ellipsometry and an atomic force microscope. It is shown that the growth exponent β and the roughness exponent α are about 0.369 and 0.95 for the undoped thin film, respectively. Whereas, for the boron-doped μc-Si:H thin film, β increases to 0.534 and α decreases to 0.46 due to the shadowing effect.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Detecting magnetic field direction by a micro beam operating in different vibration modes

Chen Jie, Qin Ming, Huang Qing-An
Chin. Phys. B 2011, 20 (9): 097101;  doi: 10.1088/1674-1056/20/9/097101
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A new method to detect the magnetic field direction by using a silicon structure is presented in this paper. The structure includes a micro beam and an in-plane coil electrode. When the electrode under a magnetic field is applied with an alternating current, the micro beam is actuated under the effect of the Lorentz forces. Magnetic fields of different directions cause different vibration profiles. The direction of the magnetic field is obtained by measuring the vibration amplitudes of the micro beam, which is driven to work at first- and second-order resonant modes. A micro structure has been fabricated using the bulk micromachined silicon process. A laser Doppler vibrometer system is implemented to measure the vibration amplitudes. The experimental results show that the amplitude of the structure, which depends on the different modes, is a sine or cosine function of the angle of the magnetic field. It agrees well with the simulation result. Currently a resolution of 10° for the magnetic field direction measurement can be obtained using the detecting principle.

Electron-correlation-induced band renormalization and Mott transition in Ca1-xSrxVO3

Wang Guang-Tao, Zhang Min-Ping, Zheng Li-Hua
Chin. Phys. B 2011, 20 (9): 097102;  doi: 10.1088/1674-1056/20/9/097102
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We present the local density approximate+Gutzwiller results for the electronic structure of Ca1-xSrxVO3. The substitution of Sr2+ by Ca2+ reduces the bandwidth, as the V—O—V bond angle decreases from 180° for SrVO3 to about 160° for CaVO3. However, we find that the bandwidth decrease induced by the V—O—V bond angle decrease is smaller as compared to that induced by electron correlation. In correlated electron systems, such as Ca1-xSrxVO3, the correlation effect of 3d electrons plays a leading role in determining the bandwidth. The electron correlation effect and crystal field splitting collaboratively determine whether the compounds will be in a metal state or in a Mott-insulator phase.

Detailed balance limit efficiency of silicon intermediate band solar cells

Cao Quan, Ma Zhi-Hua, Xue Chun-Lai, Zuo Yu-Hua, Wang Qi-Ming
Chin. Phys. B 2011, 20 (9): 097103;  doi: 10.1088/1674-1056/20/9/097103
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The detailed balance method is used to study the potential of the intermediate band solar cell (IBSC), which can improve the efficiency of the Si-based solar cell with a bandgap between 1.1 eV to 1.7 eV. It shows that a crystalline silicon solar cell with an intermediate band located at 0.36 eV below the conduction band or above the valence band can reach a limiting efficiency of 54% at the maximum light concentration, improving greatly than 40.7% of the Shockley—Queisser limit for the single junction Si solar cell. The simulation also shows that the limiting efficiency of the silicon-based solar cell increases as the bandgap increases from 1.1 eV to 1.7 eV, and the amorphous Si solar cell with a bandgap of 1.7 eV exhibits a radiative limiting efficiency of 62.47%, having a better potential.

Vibrational frequency of a strong-coupling polaron in a quantum rod at finite temperatures

Ding Zhao-Hua, Xiao Jing-Lin
Chin. Phys. B 2011, 20 (9): 097104;  doi: 10.1088/1674-1056/20/9/097104
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The Hamiltonian of a quantum rod with a boundary is presented after a coordinate transformation that changes the original ellipsoidal boundary into a spherical one. We then study the effect of temperature on the vibrational frequency and the ground state binding energy of the strong-coupling polaron in the rod. The two quantities are expressed as functions of the aspect ratio of the ellipsoid, the transverse and the longitudinal effective confinement lengths, the temperature and the electron—phonon coupling strength by linear combination operator and unitary transformation methods. It is found that the vibrational frequency and the ground state binding energy will increase rapidly with decreasing transverse and longitudinal effective confinement lengths. They are increasing functions of the electron—phonon coupling strength but become decreasing ones of the temperature and the aspect ratio.

A time-dependent density functional theory investigation of plasmon resonances of linear Au atomic chains

Liu Dan-Dan, Zhang Hong
Chin. Phys. B 2011, 20 (9): 097105;  doi: 10.1088/1674-1056/20/9/097105
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We report theoretical studies on the plasmon resonances in linear Au atomic chains by using ab initio time-dependent density functional theory. The dipole responses are investigated each as a function of chain length. They converge into a single resonance in the longitudinal mode but split into two transverse modes. As the chain length increases, the longitudinal plasmon mode is redshifted in energy while the transverse modes shift in the opposite direction (blueshifts). In addition, the energy gap between the two transverse modes reduces with chain length increasing. We find that there are unique characteristics, different from those of other metallic chains. These characteristics are crucial to atomic-scale engineering of single-molecule sensing, optical spectroscopy, and so on.

Influence of thermal stress on the relative permittivity of the AlGaN barrier layer in an AlGaN/GaN heterostructure Schottky contacts

Lü Yuan-Jie, Lin Zhao-Jun, Zhang Yu, Meng Ling-Guo, Cao Zhi-Fang, Luan Chong-Biao, Chen Hong, Wang Zhan-Guo
Chin. Phys. B 2011, 20 (9): 097106;  doi: 10.1088/1674-1056/20/9/097106
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Ni Schottky contacts on AlGaN/GaN heterostructures were fabricated. Some samples were thermally treated in a furnace with N2 ambience at 600 °C for different times (0.5 h, 4.5 h, 10.5 h, 18 h, 33 h, 48 h, and 72 h), the others were thermally treated for 0.5 h at different temperatures (500 °C, 600 °C, 700 °C, and 800 °C). With the measured current—voltage (IV) and capacitance—voltage (CV) curves and by self-consistently solving Schrodinger's and Poisson's equations, we found that the relative permittivity of the AlGaN barrier layer was related to the piezoelectric and the spontaneous polarization of the AlGaN barrier layer. The relative permittivity was in proportion to the strain of the AlGaN barrier layer. The relative permittivity and the strain reduced with the increased thermal stress time until the AlGaN barrier totally relaxed (after 18 h at 600 °C in the current study), and then the relative permittivity was almost a constant with the increased thermal stress time. When the sample was treated at 800 °C for 0.5 h, the relative permittivity was less than the constant due to the huge diffusion of the contact metal atoms. Considering the relation between the relative permittivity of the AlGaN barrier layer and the converse piezoelectric effect, the conclusion can be made that a moderate thermal stress can restrain the converse piezoelectric effect and can improve the stability of AlGaN/GaN heterostructure devices.

An easy and efficient way to treat Green's function for nano-devices with arbitrary shapes and multi-terminal configurations

Yang Mou, Ran Xian-Jin, Cui Yan, Wang Rui-Qiang
Chin. Phys. B 2011, 20 (9): 097201;  doi: 10.1088/1674-1056/20/9/097201
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The efficiency of the calculation of Green's function (GF) for nano-devices is very important because the calculation is often needed to be repeated countlessly. We present a set of efficient algorithms for the numerical calculation of GF for devices with arbitrary shapes and multi-terminal configurations. These algorithms can be used to calculate the specified blocks related to the transmission, the diagonals needed by the local density of states calculation, and the full matrix of GF, to meet different calculation levels. In addition, the algorithms for the non-equilibrium occupation and current flow are also given. All these algorithms are described using the basic theory of GF, based on a new partition strategy of the computational area. We apply these algorithms to the tight-binding graphene lattice to manifest their stability and efficiency. We also discuss the physics of the calculation results.

Transport properties and magnetoresistance in La0.8Te0.2MnO3/ZrO2 composites

Wang Jian-Yuan, Zhai Wei, Jin Ke-Xin, Chen Chang-Le
Chin. Phys. B 2011, 20 (9): 097202;  doi: 10.1088/1674-1056/20/9/097202
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The transport properties and magnetoresistance of electron-doped manganate / insulator composites (La0.8Te0.2MnO3)1 - x/(ZrO2)x (x=0, 0.3, and 0.5) are investigated. It is found that the metal-insulator transition temperature of this system shifts to a lower value as the ZrO2 content increases. The introduction of ZrO2 enhances both the domain scattering and electron relative scattering in the metal transport region. In the adiabatic small polaron hopping transport region, the thermal activation energy seems invariable regardless of the ZrO2 content. The application of a magnetic field promotes the charge transportation capabilities of the composites, and the magnetoresistance is enhanced with an increase of the ZrO2 content. This could be attributed to the more remarkable modification effect of magnetic field on ordering degree in the composites than in pure La0.8Te0.2MnO3.

The effect of a HfO2 insulator on the improvement of breakdown voltage in field-plated GaN-based HEMT

Mao Wei, Yang Cui, Hao Yue, Ma Xiao-Hua, Wang Chong, Zhang Jin-Cheng, Liu Hong-Xia, Bi Zhi-Wei, Xu Sheng-Rui, Yang Lin-An, Yang Ling, Zhang Kai, Zhang Nai-Qian, Pei Yi
Chin. Phys. B 2011, 20 (9): 097203;  doi: 10.1088/1674-1056/20/9/097203
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A GaN/Al0.3Ga0.7N/AlN/GaN high-electron mobility transistor utilizing a field plate (with a 0.3 μm overhang towards the drain and a 0.2 μm overhang towards the source) over a 165-nm sputtered HfO2 insulator (HfO2-FP-HEMT) is fabricated on a sapphire substrate. Compared with the conventional field-plated HEMT, which has the same geometric structure but uses a 60-nm SiN insulator beneath the field plate (SiN-FP-HEMT), the HfO2-FP-HEMT exhibits a significant improvement of the breakdown voltage (up to 181 V) as well as a record field-plate efficiency (up to 276 V/μm). This is because the HfO2 insulator can further improve the modulation of the field plate on the electric field distribution in the device channel, which is proved by the numerical simulation results. Based on the simulation results, a novel approach named the proportional design is proposed to predict the optimal dielectric thickness beneath the field plate. It can simplify the field-plated HEMT design significantly.

The edges and terrace effect of Ag particles on optical resonance absorption property

Zhao Ya-Li, Gui Ya-Qiang, Zhang Zhen-Lin, Ma Fu-Hua, Xu Xiao-Li, Xu Xiao-Liang
Chin. Phys. B 2011, 20 (9): 097301;  doi: 10.1088/1674-1056/20/9/097301
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Alternative Ag and SiO2 multilayers are prepared by using radio frequency magnetron sputtering. The Ag particles are found to diffuse toward and mostly accumulate near the surface of the Ag—SiO2 composite film via a rapid thermal treatment. Different shapes of the Ag particles are obtained by changing the thickness of each Ag and SiO2 layer. The response absorption property of the Ag composite film is also investigated. We relate the resonance absorption to the surface level and the Fermi level. To induce the obvious resonance absorption in an Ag composite film, it is necessary to maintain special shapes with sharp edges and wide terraces and to maintain the particle sizes ranging from 0 nm to 100 nm.

Magnetotransport properties of two-dimensional electron gas in AlGaN/AlN/GaN heterostructures

Ma Xiao-Hua, Ma Ping, Jiao Ying, Yang Li-Yuan, Ma Ji-Gang, He Qiang, Jiao Sha-Sha, Zhang Jin-Cheng, Hao Yue
Chin. Phys. B 2011, 20 (9): 097302;  doi: 10.1088/1674-1056/20/9/097302
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Magnetotransport measurements are carried out on the AlGaN/AlN/GaN in an SiC heterostructure, which demonstrates the existence of the high-quality two-dimensional electron gas (2DGE) at the AlN/GaN interface. While the carrier concentration reaches 1.32 × 1013 cm - 2 and stays relatively unchanged with the decreasing temperature, the mobility of the 2DEG increases to 1.21 × 104 cm2/(V·s) at 2 K. The Shubnikov—de Haas (SdH) oscillations are observed in a magnetic field as low as 2.5 T at 2 K. By the measurements and the analyses of the temperature-dependent SdH oscillations, the effective mass of the 2DEG is determined. The ratio of the transport lifetime to the quantum scattering time is 9 in our sample, indicating that small-angle scattering is predominant.

Flat-band voltage shift in metal-gate/high-k/Si stacks

Huang An-Ping, Zheng Xiao-Hu, Xiao Zhi-Song, Yang Zhi-Chao, Wang Mei, Paul K. Chu, Yang Xiao-Dong
Chin. Phys. B 2011, 20 (9): 097303;  doi: 10.1088/1674-1056/20/9/097303
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In metal-gate/high-k stacks adopted by the 45 nm technology node, the flat-band voltage (Vfb) shift remains one of the most critical challenges, particularly the flat-band voltage roll-off (Vfb roll-off) phenomenon in p-channel metal-oxide-semiconductor (pMOS) devices with an ultrathin oxide layer. In this paper, recent progress on the investigation of the Vfb shift and the origin of the Vfb roll-off in the metal-gate/high-k pMOS stacks are reviewed. Methods that can alleviate the Vfb shift phenomenon are summarized and the future research trend is described.

An improvement to computational efficiency of the drain current model for double-gate MOSFET

Zhou Xing-Ye, Zhang Jian, Zhou Zhi-Ze, Zhang Li-Ning, Ma Chen-Yue, Wu Wen, Zhao Wei, Zhang Xing
Chin. Phys. B 2011, 20 (9): 097304;  doi: 10.1088/1674-1056/20/9/097304
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As a connection between the process and the circuit design, the device model is greatly desired for emerging devices, such as the double-gate MOSFET. Time efficiency is one of the most important requirements for device modeling. In this paper, an improvement to the computational efficiency of the drain current model for double-gate MOSFETs is extended, and different calculation methods are compared and discussed. The results show that the calculation speed of the improved model is substantially enhanced. A two-dimensional device simulation is performed to verify the improved model. Furthermore, the model is implemented into the HSPICE circuit simulator in Verilog-A for practical application.

Dispersion effect on the current voltage characteristic of AlGaN/GaN high electron mobility transistors

Pu Yan, Pang Lei, Chen Xiao-Juan, Yuan Ting-Ting, Luo Wei-Jun, Liu Xin-Yu
Chin. Phys. B 2011, 20 (9): 097305;  doi: 10.1088/1674-1056/20/9/097305
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The current voltage (IV) characteristics are greatly influenced by the dispersion effects in AlGaN/GaN high electron mobility transistors. The direct current (DC) IV and pulsed IV measurements are performed to give a deep investigation into the dispersion effects, which are mainly related to the trap and self-heating mechanisms. The results show that traps play an important role in the kink effects, and high stress can introduce more traps and defects in the device. With the help of the pulsed IV measurements, the trapping effects and self-heating effects can be separated. The impact of time constants on the dispersion effects is also discussed. In order to achieve an accurate static DC IV measurement, the steady state of the bias points must be considered carefully to avoid the dispersion effects.

Dynamical localization effect in a coupled quantum dot array driven by an AC magnetic field

Xia Jun-Jie, Nie Yi-Hang
Chin. Phys. B 2011, 20 (9): 097306;  doi: 10.1088/1674-1056/20/9/097306
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We have studied the transport properties of a ring-coupled quantum dot array driven by an AC magnetic field, which is connected to two leads, and we give the response of the transport current to the dynamical localization. We found that when the ratio of the magnetic flux to the total quantum dots number is a root of the zeroth order Bessel function, dynamical localization and collapse of quasi-energy occurs and importantly, the transport current displays a dip which is the signal of dynamical localization. The dynamical localization effect is strengthened as a result of the increase of the quantum dot number, and it is weakened on account of the increase of the dots-lead hopping rate.

Ferrimagnetism induced by asymmetrical ferromagnetic next-nearest-neighbour exchange interactions in an antiferromagnetic spin-1/2 zigzag chain

Wang Zhong-Long, Fu Hua-Hua
Chin. Phys. B 2011, 20 (9): 097502;  doi: 10.1088/1674-1056/20/9/097502
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The magnetic properties of an antiferromagnetic bond alternating spin-1/2 zigzag chain with asymmetrical ferromagnetic next-nearest-neighbour exchange interactions at finite temperature are investigated by using the many-body Green's function theory. It is found that the ferrimagnetic ordering does not appear in the symmetrical next-nearest-neighbour coupling case, and takes place only for the asymmetrical next-nearest-neighbour case at finite temperature rather than the ground state. Furthermore, as the asymmetry degree of the next-nearest-neighbour exchange interactions increases, the ferrimagnetism becomes more and more dominant. It is shown that the elementary excitation spectra are responsible for the observed magnetic behaviour.

Effects of Fe2+ substitution on magnetic and dielectric properties of CdCr2S4

Yan Li-Qin, Sun Yang, He Lun-Hua, Wang Fang-Wei, Shen Jun
Chin. Phys. B 2011, 20 (9): 097503;  doi: 10.1088/1674-1056/20/9/097503
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The magnetic and dielectric properties of polycrystalline Cd1 - xFexCr2S4 (0 ≤ x ≤ 0.9) are investigated. Upon substitution of Cd by Fe, the Curie temperature (TC) is increased while the saturation magnetization is decreased. A low doping level of Fe increases the permittivity, while a high doping level decreases the permittivity, which is explained by the internal barrier layer capacitor model. Kinks are observed in the temperature-dependent permittivity and loss tangent near TC for the samples with x= 0.5, 0.7, 0.9, implying the existence of the magnetodielectric effect. Furthermore, with the increase of Fe content, a decrease of anomaly deviation rate induced by internal molecular field is revealed in the permittivity, while an increase is observed for the loss tangent.

Local structure distortion and spin Hamiltonian parameters for Cr3+–VZn tetragonal defect centre in Cr3+ doped KZnF3 crystal

Yang Zi-Yuan
Chin. Phys. B 2011, 20 (9): 097601;  doi: 10.1088/1674-1056/20/9/097601
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The quantitative relationship between the spin Hamiltonian parameters (D, g, Δg) and the crystal structure parameters for the Cr3+—VZn tetragonal defect centre in a Cr3+:KZnF3 crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr3+—VZn tetragonal defect centre in the KZnF_3 crystal are systematically investigated using the complete diagonalization method. It is found that the VZn vacancy and the differences in mass, radius and charge between the Cr3+ and the Zn2+ ions induce the local lattice distortion of the Cr3+ centre ions in the KZnF3 crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Δg. We find that the ligand F- ion along [001] and the other five F- ions move towards the central Cr3+ by distances of Δ1 = 0.0121 nm and Δ2 = 0.0026 nm, respectively. Our approach takes into account the spin—orbit interaction as well as the spin—spin, spin—other-orbit, and orbit—orbit interactions omitted in the previous studies. It is found that for the Cr3+ ions in the Cr3+:KZnF3 crystal, although the spin—orbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin—spin, spin—other-orbit, and orbit—orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting (ZFS) parameter D.

Effects of the strain relaxation of an AlGaN barrier layer induced by various cap layers on the transport properties in AlGaN/GaN heterostructures

Liu Zi-Yang, Zhang Jin-Cheng, Duan Huan-Tao, Xue Jun-Shuai, Lin Zhi-Yu, Ma Jun-Cai, Xue Xiao-Yong, Hao Yue
Chin. Phys. B 2011, 20 (9): 097701;  doi: 10.1088/1674-1056/20/9/097701
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The strain relaxation of an AlGaN barrier layer may be influenced by a thin cap layer above, and affects the transport properties of AlGaN/GaN heterostructures. Compared with the slight strain relaxation found in AlGaN barrier layer without cap layer, it is found that a thin cap layer can induce considerable changes of strain state in the AlGaN barrier layer. The degree of relaxation of the AlGaN layer significantly influences the transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures. It is observed that electron mobility decreases with the increasing degree of relaxation of the AlGaN barrier, which is believed to be the main cause of the deterioration of crystalline quality and morphology on the AlGaN/GaN interface. On the other hand, both GaN and AlN cap layers lead to a decrease in 2DEG density. The reduction of 2DEG caused by the GaN cap layer may be attributed to the additional negative polarization charges formed at the interface between GaN and AlGaN, while the reduction of the piezoelectric effect in the AlGaN layer results in the decrease of 2DEG density in the case of AlN cap layer.

Electromechanical-induced antiferroelectric–ferroelectric phase transition in PbLa(Zr,Sn,Ti)O3 ceramic

Zhang Chong-Hui, Xu Zhuo, Gao Jun-Jie, Zhu Chang-Jun, Yao Xi
Chin. Phys. B 2011, 20 (9): 097702;  doi: 10.1088/1674-1056/20/9/097702
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Antiferroelectric—ferroelectric (AFE—FE) phase transition in ceramic Pb0.97La0.02(Zr0.75Sn0.136Ti0.114)O3 (PLZST) was studied by dielectric spectroscopy as functions of frequency (102—105 Hz) and pressure (0—500 MPa) under a DC electric field. The hydrostatic pressure-dependent remnant polarization and dielectric constant were measured. The results show that remnant polarization of the metastable rhombohedral ferroelectric PLZST poled ceramic decreases sharply and depoles completely at phase transition under hydrostatic pressure. The dielectric constant undergoes an abrupt jump twice during a load and unload cycle under an electric field. The two abrupt jumps correspond to two phase transitions, FE—AFE and AFE—FE.

Bipolar resistive switching in Cr-doped TiOx thin films

Xing Zhong-Wen
Chin. Phys. B 2011, 20 (9): 097703;  doi: 10.1088/1674-1056/20/9/097703
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The electric-pulse-induced resistive switching effect is studied for Ti0.85Cr0.15Ox (TCO) films grown on Ir—Si substrates by pulsed laser deposition. Such a TCO device exhibits bipolar switching behaviour with an electric-pulse-induced resistance ratio as large as about 1000% and threshold voltages smaller than 2 V. The resistive switching characteristics may be understood by resistance changes of a Schottky junction composed of a metal and an n-type semiconductor, and its nonvolatility is attributed to the movement of oxygen vacancies near the interface.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Gradual variation method for thick GaN heteroepitaxy by hydride vapour phase epitaxy Hot!

Du Yan-Hao, Wu Jie-Jun, Luo Wei-Ke, John Goldsmith, Han Tong, Tao Yue-Bin, Yang Zhi-Jian, Yu Tong-Jun, Zhang Guo-Yi
Chin. Phys. B 2011, 20 (9): 098101;  doi: 10.1088/1674-1056/20/9/098101
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Two strain-state samples of GaN, labelled the strain-relief sample and the quality-improved sample, were grown by hydride vapour phase epitaxy (HVPE), and then characterized by high-resolution X-ray diffraction, photoluminescence and optical microscopy. Two strain states of GaN in HVPE, like 3D and 2D growth modes in metal-organic chemical vapour deposition (MOCVD), provide an effective way to solve the heteroepitaxial problems of both strain relief and quality improvement. The gradual variation method (GVM), developed based on the two strain states, is characterized by growth parameters' gradual variation alternating between the strain-relief growth conditions and the quality-improved growth conditions. In GVM, the introduction of the strain-relief amplitude, which is defined by the range from the quality-improved growth conditions to the strain-relief growth conditions, makes the strain-relief control concise and effective. The 300-μm thick bright and crack-free GaN film grown on a two-inch sapphire proves the effectiveness of GVM.

A device model for thin silicon-on-insulator SiGe heterojunction bipolar transistors with saturation effects

Xu Xiao-Bo, Xu Kai-Xuan, Zhang He-Ming, Qin Shan-Shan
Chin. Phys. B 2011, 20 (9): 098501;  doi: 10.1088/1674-1056/20/9/098501
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In this paper, we describe the saturation effect of a silicon germanium (SiGe) heterojunction bipolar transistor (HBT) fabricated on a thin silicon-on-insulator (SOI) with a step-by-step derivation of the model formulation. The collector injection width, the internal base—collector bias, and the hole density at the base—collector junction interface are analysed by considering the unique features of the internal and the external parts of the collector, as they are different from those of a bulk counterpart.

Size and temperature effects on electric properties of CdTe/ZnTe quantum rings

Woo-Pyo Hong, Seoung-Hwan Park
Chin. Phys. B 2011, 20 (9): 098502;  doi: 10.1088/1674-1056/20/9/098502
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The electronic properties of CdTe/ZnTe quantum rings (QRs) are investigated as functions of size and temperature using an eight-band strain-dependent k·p Hamiltonian. The size effects of diameter and height on the strain distributions around the QRs are studied. We find that the interband transition energy, defined as the energy difference between the ground electronic and the ground heavy-hole subbands, increases with the increasing QR inner diameter regardless of the temperature, while the interband energy decreases with the increasing QR height. This is attributed to the reduction of subband energies in both the conduction and the valence bands due to the strain effects. Our model, in the framework of the finite element method and the theory of elasticity of solids, shows a good agreement with the temperature-dependent photoluminescence measurement of the interband transition energies.

The advantage of blue InGaN multiple quantum wells light-emitting diodes with p-AlInN electron blocking layer

Lu Tai-Ping, Li Shu-Ti, Zhang Kang, Liu Chao, Xiao Guo-Wei, Zhou Yu-Gang, Zheng Shu-Wen, Yin Yi-An, Wu Le-Juan, Wang Hai-Long, Yang Xiao-Dong
Chin. Phys. B 2011, 20 (9): 098503;  doi: 10.1088/1674-1056/20/9/098503
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InGaN based light-emitting diodes (LEDs) with different electron blocking layers have been numerically investigated using the APSYS simulation software. It is found that the structure with a p-AlInN electron blocking layer showes improved light output power, lower current leakage, and smaller efficiency droop. Based on numerical simulation and analysis, these improvements of the electrical and optical characteristics are mainly attributed to the efficient electron blocking in the InGaN/GaN multiple quantum wells (MQWs).

Speeding up the MATLAB complex networks package using graphic processors

Zhang Bai-Da, Tang Yu-Hua, Wu Jun-Jie, Li Xin
Chin. Phys. B 2011, 20 (9): 098901;  doi: 10.1088/1674-1056/20/9/098901
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The availability of computers and communication networks allows us to gather and analyse data on a far larger scale than previously. At present, it is believed that statistics is a suitable method to analyse networks with millions, or more, of vertices. The MATLAB language, with its mass of statistical functions, is a good choice to rapidly realize an algorithm prototype of complex networks. The performance of the MATLAB codes can be further improved by using graphic processor units (GPU). This paper presents the strategies and performance of the GPU implementation of a complex networks package, and the Jacket toolbox of MATLAB is used. Compared with some commercially available CPU implementations, GPU can achieve a speedup of, on average, 11.3×. The experimental result proves that the GPU platform combined with the MATLAB language is a good combination for complex network research.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Remote sensing of atmospheric duct parameters using simulated annealing

Zhao Xiao-Feng, Huang Si-Xun, Xiang Jie, Shi Wei-Lai
Chin. Phys. B 2011, 20 (9): 099201;  doi: 10.1088/1674-1056/20/9/099201
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Simulated annealing is one of the robust optimization schemes. Simulated annealing mimics the annealing process of the slow cooling of a heated metal to reach a stable minimum energy state. In this paper, we adopt simulated annealing to study the problem of the remote sensing of atmospheric duct parameters for two different geometries of propagation measurement. One is from a single emitter to an array of radio receivers (vertical measurements), and the other is from the radar clutter returns (horizontal measurements). Basic principles of simulated annealing and its applications to refractivity estimation are introduced. The performance of this method is validated using numerical experiments and field measurements collected at the East China Sea. The retrieved results demonstrate the feasibility of simulated annealing for near real-time atmospheric refractivity estimation. For comparison, the retrievals of the genetic algorithm are also presented. The comparisons indicate that the convergence speed of simulated annealing is faster than that of the genetic algorithm, while the anti-noise ability of the genetic algorithm is better than that of simulated annealing.
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