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  • Fabrication of Al/AlOx/Al Josephson junctions and superconducting quantum circuits by shadow evaporation and a dynamic oxidation process

    Wu Yu-Lin, Deng Hui, Yu Hai-Feng, Xue Guang-Ming, Tian Ye, Li Jie, Chen Ying-Fei, Zhao Shi-Ping, Zheng Dong-Ning
    Chin. Phys. B 2013, 22 (6): 060309
    Besides serving as promising candidates for realizing quantum computing, superconducting quantum circuits are one of a few macroscopic physical systems in which fundamental quantum phenomena can be directly demonstrated and tested, giving rise to a vast field of intensive research work both theoreti...

     
  • A picosecond widely tunable deep-ultraviolet laser for angle-resolved photoemission spectroscopy

    Zhang Feng-Feng, Yang Feng, Zhang Shen-Jin, Xu Zhi, Wang Zhi-Min, Xu Feng-Liang, Peng Qin-Jun, Zhang Jing-Yuan, Wang Xiao-Yang, Chen Chuang-Tian, Xu Zu-Yan
    Chin. Phys. B 2013, 22 (6): 064212
    We develop a picosecond widely tunable laser in a deep-ultraviolet region from 175 nm to 210 nm, generated by two stages of frequency doubling of a 80-MHz mode-locked picosecond Ti:sapphire laser. Aβ-BaB2O4 walk-off compensation configuration and a KBe2BO3F2 prism-coupled device are adopted for...

     
  • Tunable interface anisotropy in Pt/Co1-xFex/Pt multilayer

    Chen Yong-Yong, Shi Zhong, Zhou Shi-Ming, Rui Wen-Bin, Du Jun
    Chin. Phys. B 2013, 22 (6): 067504
    Interfacial magnetic anisotropy in Pt/Co1-xFex/Pt multilayer is tuned by doping iron atoms into cobalt layer. The perpendicular magnetic anisotropy and out-of-plane coercivity are found to decrease with x increasing. For a specific x, the out-of-plane coercivity acquires a maximal value as a functio...

     
Chin. Phys. B  
  Chin. Phys. B--2013, Vol.22, No.6
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TOPICAL REVIEW—Topological insulator

Spin Chern numbers and time-reversal-symmetry-broken quantum spin Hall effect

Sheng Li, Li Hui-Chao, Yang Yun-You, Sheng Dong-Ning, Xing Ding-Yu
Chin. Phys. B, 2013, 22 (6): 067201 doi: 10.1088/1674-1056/22/6/067201
Full Text: [PDF 5219 KB] (Downloads:2205)
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The quantum spin Hall (QSH) effect is considered to be unstable to perturbations violating the time-reversal (TR) symmetry. We review some recent developments in the search of the QSH effect in the absence of the TR symmetry. The possibility to realize a robust QSH effect by artificial removal of the TR symmetry of the edge states is explored. As a useful tool to characterize topological phases without the TR symmetry, the spin-Chern number theory is introduced.

Elastic scattering of surface states on three-dimensional topological insulators

Wang Jing, Zhu Bang-Fen
Chin. Phys. B, 2013, 22 (6): 067301 doi: 10.1088/1674-1056/22/6/067301
Full Text: [PDF 436 KB] (Downloads:617)
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Topological insulators as a new type of quantum matter materials are characterized by a full insulating gap in the bulk and gapless edge/surface states protected by the time-reversal symmetry. We propose that the interference patterns caused by the elastic scattering of defects or impurities are dominated by the surface states at the extremal points on the constant energy contour. Within such a formalism, we summarize our recent theoretical investigations on the elastic scattering of topological surface states by various imperfections, including non-magnetic impurities, magnetic impurities, step edges, and various other defects, in comparison with the recent related experiments in typical topological materials such as BiSb alloys, Bi2Te3, and Bi2Se3 crystals.

Transport properties of topological insulators films and nanowires

Liu Yi, Ma Zheng, Zhao Yan-Fei, Meenakshi Singh, Wang Jian
Chin. Phys. B, 2013, 22 (6): 067302 doi: 10.1088/1674-1056/22/6/067302
Full Text: [PDF 4401 KB] (Downloads:997)
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The last several years have witnessed the rapid developments in the study and understanding of topological insulators. In this review, after a brief summary of the history of topological insulators, we focus on the recent progress made in transport experiments on topological insulator films and nanowires. Some quantum phenomena, including the weak antilocalization, the Aharonov-Bohm effect, and the Shubnikov-de Haas oscillations, observed in these nanostructures are described. In addition, the electronic transport evidence of the superconducting proximity effect as well as an anomalous resistance enhancement in topological insulator/superconductor hybrid structures is included.

Topological edge states and electronic structures of a 2D topological insulator: Single-bilayer Bi (111)

Gao Chun-Lei, Qian Dong, Liu Can-Hua, Jia Jin-Feng, Liu Feng
Chin. Phys. B, 2013, 22 (6): 067304 doi: 10.1088/1674-1056/22/6/067304
Full Text: [PDF 1846 KB] (Downloads:1477)
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Providing the strong spin-orbital interaction, Bismuth is the key element in the family of three-dimensional topological insulators. At the same time, Bismuth itself also has very unusual behavior, existing from the thinnest unit to bulk crystals. Ultrathin Bi (111) bilayers have been theoretically proposed as a two-dimensional topological insulator. The related experimental realization achieved only recently, by growing Bi (111) ultrathin bilayers on topological insulator Bi2Te3 or Bi2Se3 substrates. In this review, we started from the growth mode of Bi (111) bilayers and reviewed our recent progress in the studies of the electronic structures and the one-dimensional topological edge states using scanning tunneling microscopy/spectroscopy (STM/STS), angle-resolved photoemission spectroscopy (ARPES), and first principles calculations.

From magnetically doped topological insulator to the quantum anomalous Hall effect

He Ke, Ma Xu-Cun, Chen Xi, Lü Li, Wang Ya-Yu, Xue Qi-Kun
Chin. Phys. B, 2013, 22 (6): 067305 doi: 10.1088/1674-1056/22/6/067305
Full Text: [PDF 2635 KB] (Downloads:720)
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Quantum Hall effect (QHE), as a class of quantum phenomena that occur in macroscopic scale, is one of the most important topics in condensed matter physics. It has long been expected that QHE may occur without Landau levels so that neither external magnetic field nor high sample mobility is required for its study and application. Such a QHE free of Landau levels, can appear in topological insulators (TIs) with ferromagnetism as the quantized version of the anomalous Hall effect, i.e., quantum anomalous Hall (QAH) effect. Here we review our recent work on experimental realization of the QAH effect in magnetically doped TIs. With molecular beam epitaxy, we prepare thin films of Cr-doped (Bi,Sb)2Te3 TIs with wellcontrolled chemical potential and long-range ferromagnetic order that can survive the insulating phase. In such thin films, we eventually observed the quantization of the Hall resistance at h/e2 at zero field, accompanied by a considerable drop in the longitudinal resistance. Under a strong magnetic field, the longitudinal resistance vanishes, whereas the Hall resistance remains at the quantized value. The realization of the QAH effect provides a foundation for many other novel quantum phenomena predicted in TIs, and opens a route to practical applications of quantum Hall physics in low-power-consumption electronics.

Molecular-beam epitaxy of topological insulator Bi2Se3 (111) and (221) thin films

Xie Mao-Hai, Guo Xin, Xu Zhong-Jie, Ho Wing-Kin
Chin. Phys. B, 2013, 22 (6): 068101 doi: 10.1088/1674-1056/22/6/068101
Full Text: [PDF 839 KB] (Downloads:1402)
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This paper presents an overview of growth of Bi2Se3, a prototypical three-dimensional topological insulator, by molecular-beam epitaxy on various substrates. Comparison is made between growth of Bi2Se3 (111) on van der Waals (vdW) and non-vdW substrates, with attention paid to twin suppression and strain. Growth along the [221] direction of Bi2Se3 on InP (001) and GaAs (001) substrates is also discussed.
GENERAL

A symmetry-preserving difference scheme for high dimensional nonlinear evolution equations

Xin Xiang-Peng, Chen Yong, Wang Yun-Hu
Chin. Phys. B, 2013, 22 (6): 060201 doi: 10.1088/1674-1056/22/6/060201
Full Text: [PDF 219 KB] (Downloads:318)
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In this paper, a procedure for constructing discrete models of the high dimensional nonlinear evolution equations is presented. In order to construct the difference model, with the aid of the potential system of the original equation and compatibility condition, the difference equations which preserve all Lie point symmetries can be obtained. As an example, invariant difference models of the (2+1)-dimensional Burgers equation are presented.

The nonrelativistic oscillator strength of a hyperbolic-type potential

H. Hassanabadi, S. Zarrinkamar, B. H. Yazarloo
Chin. Phys. B, 2013, 22 (6): 060202 doi: 10.1088/1674-1056/22/6/060202
Full Text: [PDF 476 KB] (Downloads:378)
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We consider the D-dimensional Schrödinger equation under the hyperbolic potential V0 (1-coth (αr)) +V1 (1-coth (αr))2. Using a Pekeris-type approximation, the approximate analytical solutions of the problem are obtained via the supersymmetric quantum mechanics. The behaviors of energy eigenvalues versus dimension are discussed for various quantum numbers. Useful expectation values as well as the oscillator strength are obtained.

Solve the spin-weighted spheroidal wave equation

Li Yu-Zhen, Tian Gui-Hua, Dong Kun
Chin. Phys. B, 2013, 22 (6): 060203 doi: 10.1088/1674-1056/22/6/060203
Full Text: [PDF 195 KB] (Downloads:318)
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In this paper we solve spin-weighted spheroidal wave equations through super-symmetric quantum mechanics with a different expression of the super-potential. We use the shape invariance property to compute the "excited" eigenvalues and eigenfunctions. The results are beneficial to researchers for understanding the properties of the spin-weighted spheroidal wave more deeply, especially its integrability.

Singular solitons and other solutions to a couple of nonlinear wave equations

Mustafa Inc, Esma Ulutaş, Anjan Biswas
Chin. Phys. B, 2013, 22 (6): 060204 doi: 10.1088/1674-1056/22/6/060204
Full Text: [PDF 210 KB] (Downloads:488)
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This paper addresses the extended (G'/G)-expansion method and applies it to a couple of nonlinear wave equations. These equations are modified Benjamin-Bona-Mahoney equation and the Boussinesq equation. This extended method reveals several solutions to these equations. Additionally, the singular soliton solutions are revealed, for these two equations, by the aid of ansatz method.

A double optical solitary wave in a nonlinear Schrödinger-type equation

Yin Jiu-Li, Ding Shan-Yu
Chin. Phys. B, 2013, 22 (6): 060205 doi: 10.1088/1674-1056/22/6/060205
Full Text: [PDF 230 KB] (Downloads:448)
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A qualitative analysis method to efficiently solve the shallow wave equations is improved, so that a more complicated nonlinear Schrödinger equation can be considered. By using the detailed study, some quite strange optical solitary waves are obtained in which the bright and dark optical solitary waves are allowed to coexist.

An improved local radial point interpolation method for transient heat conduction analysis

Wang Feng, Lin Gao, Zheng Bao-Jing, Hu Zhi-Qiang
Chin. Phys. B, 2013, 22 (6): 060206 doi: 10.1088/1674-1056/22/6/060206
Full Text: [PDF 984 KB] (Downloads:815)
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The smoothing thin plate spline (STPS) interpolation using the penalty function method according to the optimization theory is presented to deal with the transient heat conduction problems. The smooth conditions of the shape functions and derivatives can be satisfied so that the distortions could hardly occur. Local weak forms are developed using the weighted residual method locally from the partial differential equations of the transient heat conduction. Here the Heaviside step function is used as the test function in each sub-domain to avoid the need for domain integral. The essential boundary conditions can be implemented like the finite element method (FEM) as the shape functions possess the Kronecker delta property. The traditional two-point difference method is selected for the time discretization scheme. Three selected numerical examples are presented in this paper to demonstrate the availability and accuracy of the present approach comparing with the traditional thin plate spline (TPS) radial basis functions.

A conservative Fourier pseudospectral algorithm for a coupled nonlinear Schrödinger system

Cai Jia-Xiang, Wang Yu-Shun
Chin. Phys. B, 2013, 22 (6): 060207 doi: 10.1088/1674-1056/22/6/060207
Full Text: [PDF 632 KB] (Downloads:408)
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We derive a new method for coupled nonlinear Schrödinger system by using the square of first-order Fourier spectral differentiation matrix D1 instead of traditional second-order Fourier spectral differentiation matrix D2 to approximate second derivative. We prove the proposed method preserves the charge and energy conservation laws exactly. In numerical tests, we display the accuracy of numerical solution and the role of the nonlinear coupling parameter in cases of solitons collision. Numerical experiments also exhibit the excellent performance of the method in preserving the charge and energy conservation laws. These numerical results verify that the proposed method is both a charge-preserving and an energy-preserving algorithm.

A new coupled-map car-following model based on a transportation supernetwork framework

Yao Jing, Huang Jing-Yi, Chen Guan-Rong, Xu Wei-Sheng
Chin. Phys. B, 2013, 22 (6): 060208 doi: 10.1088/1674-1056/22/6/060208
Full Text: [PDF 1447 KB] (Downloads:365)
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A new car-following model is proposed by considering information from a number of preceding vehicles with inter-vehicle communication. A supernetwork architecture is first described, which has two layers: a traffic network and a communication network. The two networks interact with and depend on each other. The error dynamic system around the steady state of the model is theoretically analyzed and some nonjam criteria are derived. A simple control signal is added to the model to analyze the criteria of suppressing traffic jams. The corresponding numerical simulations confirm the correctness of the theoretical analysis. Compared with previous studies concerning coupled map models, the controlled model proposed in this paper is more reasonable and also more effective in the sense that it takes into account the formation of traffic congestion.

Analysis of the generalized Camassa and Holm equation with the improved element-free Galerkin method

Cheng Rong-Jun, Wei Qi
Chin. Phys. B, 2013, 22 (6): 060209 doi: 10.1088/1674-1056/22/6/060209
Full Text: [PDF 653 KB] (Downloads:420)
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In this paper, we analyze the generalized Camassa and Holm (CH) equation by the improved element-free Galerkin (IEFG) method. By employing the improved moving least-square (IMLS) approximation, we derive the formulas for the generalized CH equation with the IEFG method. A variational method is used to obtain the discrete equations, and the essential boundary conditions are enforced by the penalty method. Because there are less coefficients in the IMLS approximation than in the MLS approximation, and in the IEFG method, less nodes are selected in the entire domain than in the conventional EFG method, the IEFG method should result in a higher computing speed. The effectiveness of the IEFG method for the generalized CH equation is investigated by numerical examples in this paper.

An element-free Galerkin (EFG) method for generalized Fisher equations (GFE)

Shi Ting-Yu, Cheng Rong-Jun, Ge Hong-Xia
Chin. Phys. B, 2013, 22 (6): 060210 doi: 10.1088/1674-1056/22/6/060210
Full Text: [PDF 509 KB] (Downloads:487)
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A generalized Fisher equation (GFE) relates the time derivative of the average of the intrinsic rate of growth to its variance. The exact mathematical result of GFE has been widely used in population dynamics and genetics, where it originated. Many researchers have studied the numerical solutions of GFE, up to now. In this paper, we introduce an element-free Galerkin (EFG) method based on the moving least-square approximation to approximate positive solutions of the GFE from population dynamics. Compared with other numerical methods, the EFG method for GFE needs only scattered nodes instead of meshing the domain of the problem. The Galerkin weak form is used to obtain the discrete equations, and the essential boundary conditions are enforced by the penalty method. In comparison with the traditional method, numerical solutions show that the new method has higher accuracy and better convergence. Several numerical examples are presented to demonstrate the effectiveness of the method.

New operator identities regarding to two-variable Hermite polynomial by virtue of entangled state representation

Yuan Hong-Chun, Li Heng-Mei, Xu Xue-Fen
Chin. Phys. B, 2013, 22 (6): 060301 doi: 10.1088/1674-1056/22/6/060301
Full Text: [PDF 197 KB] (Downloads:274)
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By virtue of the entangled state representation we concisely derive some new operator identities regarding to two-variable Hermite polynomial (TVHP). By them and the technique of integration within an ordered product (IWOP) of operators we further derive new generating function formulas of TVHP. They are useful in quantum optical theoretical calculations. It is seen from this work that by combining the IWOP technique and quantum mechanical representations one can derive some new integration formulas even without really performing the integration.

New decomposition of the Fresnel operator corresponding to optical transformation in ABCD-systems

Du Jian-Ming, Fan Hong-Yi
Chin. Phys. B, 2013, 22 (6): 060302 doi: 10.1088/1674-1056/22/6/060302
Full Text: [PDF 192 KB] (Downloads:349)
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By virtue of the coherent state representation of the newly introduced Fresnel operator and its group product property, we obtain new decomposition of the Fresnel operator as the product of quadratic phase operator, squeezing operator, and fractional Fourier transformation operator, which in turn sheds light on the matrix optics design of ABCD-systems. The new decomposition for the two-mode Fresnel operator is also obtained by the use of entangled state representation.

The Yukawa potential in semirelativistic formulation via supersymmetry quantum mechanics

S. Hassanabadi, M. Ghominejad, S. Zarrinkamar, H. Hassanabadi
Chin. Phys. B, 2013, 22 (6): 060303 doi: 10.1088/1674-1056/22/6/060303
Full Text: [PDF 259 KB] (Downloads:471)
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We apply an approximation to the centrifugal term and solve the two-body spinless-Salpeter equation (SSE) with the Yukawa potential via the supersymmetric quantum mechanics (SUSYQM) for arbitrary quantum numbers. Useful figures and tables are also included.

Deformed oscillator algebra for quantum superintegrable systems in two-dimensional Euclidean space and on the complex two-sphere

H. Panahi, Z. Alizadeh
Chin. Phys. B, 2013, 22 (6): 060304 doi: 10.1088/1674-1056/22/6/060304
Full Text: [PDF 188 KB] (Downloads:409)
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In this work, we study the superintegrable quantum systems in two-dimensional Euclidean space and on the complex two-sphere with second-order constants of the motion. We show that these constants of motion satisfy the deformed oscillator algebra. Then, we easily calculate the energy eigenvalues in an algebraic way by solving of a system of two equations satisfied by its structure function. The results are in agreement to the ones obtained from the solution of the relevant Schrödinger equation.

Relativistic symmetries with the trigonometric Pöschl-Teller potential plus Coulomb-like tensor interaction

Babatunde J. Falaye, Sameer M. Ikhdair
Chin. Phys. B, 2013, 22 (6): 060305 doi: 10.1088/1674-1056/22/6/060305
Full Text: [PDF 300 KB] (Downloads:397)
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The Dirac equation is solved to obtain its approximate bound states for a spin-1/2 particle in the presence of trigonometric Pöschl-Teller (tPT) potential including a Coulomb-like tensor interaction with arbitrary spin-orbit quantum number κ using an approximation scheme to substitute the centrifugal terms κ(κ± 1)r-2. In view of spin and pseudo-spin (p-spin) symmetries, the relativistic energy eigenvalues and the corresponding two-component wave functions of a particle moving in the field of attractive and repulsive tPT potentials are obtained using the asymptotic iteration method (AIM). We present numerical results in the absence and presence of tensor coupling A and for various values of spin and p-spin constants and quantum numbers n and κ. The non-relativistic limit is also obtained.

Solutions of the Duffin Kemmer Petiau equation in the presence of Hulthén potential in (1+2) dimensions for unity spin particles using the asymptotic iteration method

Z. Molaee, M. K. Bahar, F. Yasuk, H. Hassanabadi
Chin. Phys. B, 2013, 22 (6): 060306 doi: 10.1088/1674-1056/22/6/060306
Full Text: [PDF 261 KB] (Downloads:479)
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The relativistic Duffin-Kemmer-Petiau equation in the presence of Hulthén potential in (1+2) dimensions for spin-one particles is studied. Hence, the asymptotic iteration method is used for obtaining energy eigenvalues and eigenfunctions.

Steganalysis and improvement of a quantum steganography protocol via GHZ4 state

Xu Shu-Jiang, Chen Xiu-Bo, Niu Xin-Xin, Yang Yi-Xian
Chin. Phys. B, 2013, 22 (6): 060307 doi: 10.1088/1674-1056/22/6/060307
Full Text: [PDF 197 KB] (Downloads:548)
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Quantum steganography that utilizes quantum mechanical effect to achieve the purpose of information hiding is a popular topic of quantum information. Recently, El Allati et al. proposed a new quantum steganography using GHZ4 state. Since all of the 8 groups of unitary transformations used in the secret message encoding rule change the GHZ4 state into 6 instead of 8 different quantum states when the global phase is not considered, we point out that a 2-bit instead of a 3-bit secret message can be encoded by one group of the given unitary transformations. To encode a 3-bit secret message by performing a group of unitary transformations on the GHZ4 state, we give another 8 groups of unitary transformations that can change the GHZ4 state into 8 different quantum states. Due to the symmetry of the GHZ4 state, all the possible 16 groups of unitary transformations change the GHZ4 state into 8 different quantum states, so the improved protocol achieves a high efficiency.

Cryptanalysis and improvement of the controlled secure direct communication

Kao Shih-Hung, Hwang Tzonelih
Chin. Phys. B, 2013, 22 (6): 060308 doi: 10.1088/1674-1056/22/6/060308
Full Text: [PDF 131 KB] (Downloads:343)
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This paper points out that, due to a flaw in the sender's encoding, the receiver in Gao et al.'s controlled quantum secret direct communication (CQSDC) protocol [Chin. Phys. 14 (2005), No. 5, p. 893] can reveal the whole secret message without the permission from the controller. An improvement is proposed to avoid this flaw.

Fabrication of Al/AlOx/Al Josephson junctions and superconducting quantum circuits by shadow evaporation and a dynamic oxidation process Hot!

Wu Yu-Lin, Deng Hui, Yu Hai-Feng, Xue Guang-Ming, Tian Ye, Li Jie, Chen Ying-Fei, Zhao Shi-Ping, Zheng Dong-Ning
Chin. Phys. B, 2013, 22 (6): 060309 doi: 10.1088/1674-1056/22/6/060309
Full Text: [PDF 1978 KB] (Downloads:1837)
Show Abstract
Besides serving as promising candidates for realizing quantum computing, superconducting quantum circuits are one of a few macroscopic physical systems in which fundamental quantum phenomena can be directly demonstrated and tested, giving rise to a vast field of intensive research work both theoretically and experimentally. In this paper we report our work on the fabrication of superconducting quantum circuits, starting from its building blocks, Al/AlOx/Al Josephson junctions. By using electron beam lithography patterning and shadow evaporation, we have fabricated aluminum Josephson junctions with a controllable critical current density (jc) and wide range of junction sizes from 0.01 μm2 up to 1 μm2. We have carried out systematical studies on the oxidation process in fabricating Al/AlOx/Al Josephson junctions suitable for superconducting flux qubits. Furthermore, we have also fabricated superconducting quantum circuits such as superconducting flux qubit and charge-flux qubit.

Phase-controlled atom-photon entanglement in a three-level Λ -type closed-loop atomic system

Ali Mortezapour, Zeinab Kordi, Mohammad Mahmoudi
Chin. Phys. B, 2013, 22 (6): 060310 doi: 10.1088/1674-1056/22/6/060310
Full Text: [PDF 788 KB] (Downloads:358)
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We study the entanglement of dressed atom and its spontaneous emission in a three-level Λ -type closed-loop atomic system in multi-photon resonance condition and beyond it. It is shown that the von Neumann entropy in such a system is phase-dependent, and it can be controlled by either intensity or relative phase of applied fields. It is demonstrated that for the special case of Rabi frequency of applied fields, the system is disentangled. In addition, we take into account the effect of Doppler broadening on the entanglement and it is found that a suitable choice of laser propagation direction allows us to obtain the steady state degree of entanglement (DEM) even in the presence of Doppler effect.

The vibron dressing in α-helicoidal macromolecular chains

D. Čevizović, S. Galović, A. Reshetnyak, Z. Ivić
Chin. Phys. B, 2013, 22 (6): 060501 doi: 10.1088/1674-1056/22/6/060501
Full Text: [PDF 309 KB] (Downloads:289)
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We present a study of the physical properties of the vibrational excitation in α-helicoidal macromolecular chains, caused by the interaction with acoustical and optical phonon modes. The influence of the temperature and the basic system parameters on the vibron dressing has been analyzed by employing the simple mean-field approach based on the variational extension of the Lang-Firsov unitary transformation. Applied approach predicts a region in system parameter space where one takes place an abrupt transition from partially dressed (light and mobile) to fully dressed (immobile) vibron states. We found that the boundary of this region depends on system temperature and type of bond among structural elements in the macromolecular chain.

Effects of non-Gaussian noise on the dynamical properties of a logistic system

Wang Can-Jun
Chin. Phys. B, 2013, 22 (6): 060502 doi: 10.1088/1674-1056/22/6/060502
Full Text: [PDF 269 KB] (Downloads:414)
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The dynamical properties of a tumor cell growth system described by the logistic system with coupling between non-Gaussian and Gaussian noise terms are investigated. The effects of the nonextensive index q on the stationary properties and the transient properties are discussed, respectively. The results show that the nonextensive index q can induce the tumor cell numbers decrease greatly in the case of q>1. Moreover, the switch from the steady stable state to the extinct state is speeded up as the increases of q, and the tumor cell numbers can be more obviously restrained for a large value of q. The numerical results are found to be in basic agreement with the theoretical predictions.

The mean first passage time of a three-level atomic optical bistable system subjected to noise

Wei Yong-Gang, Zeng Chun-Hua, Wang Hua, Li Kong-Zhai, Hu Jian-Hang
Chin. Phys. B, 2013, 22 (6): 060503 doi: 10.1088/1674-1056/22/6/060503
Full Text: [PDF 595 KB] (Downloads:393)
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The transient properties of a three-level atomic optical bistable system in the presence of multiplicative and additive noises are investigated. The explicit expressions of the mean first-passage time (MFPT) of the transition from the high intracavity intensity state to low one are obtained by numerical computations. The impacts of the intensities of the multiplicative noise DM and the additive noise DA, the intensity of correlation between two noises λ, and the intensity of the incident light y on the MFPT are discussed, respectively. Our results show: (i) For the case of no correlation between two noises (λ=0.0), the increase in DM and DA can lead to an increase in the probability of the transition to the low intracavity intensity state, while the increase in y can lead to a retardation of the transition; and (ii) for the case of correlation between two noises (λ≠0.0), the increase in λ can cause an increase in the probability of the transition, and the increase in DA can cause a retardation of the transition firstly and then an increase in the probability of the transition, i.e., the noise-enhanced stability is observed for the case of correlation between two noises.

Modeling and simulation of high-speed passenger train movements in the rail line

Cao Cheng-Xuan, Xu Yan, Li Ke-Ping
Chin. Phys. B, 2013, 22 (6): 060504 doi: 10.1088/1674-1056/22/6/060504
Full Text: [PDF 2341 KB] (Downloads:1931)
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In this paper, we propose a new formula of the real-time minimum safety headway based on the relative velocity of consecutive trains and present a dynamic model of high-speed passenger train movements in the rail line based on the proposed formula of the minimum safety headway. Moreover, we provide the control strategies of the high-speed passenger train operations based on the proposed formula of the real-time minimum safety headway and the dynamic model of high-speed passenger train movements. The simulation results demonstrate that the proposed control strategies of the passenger trains operations can greatly reduce the delay propagation in the high-speed rail line when the random delay occurs.

Analysis of random laser scattering pulse signals with lognormal distribution

Yan Zhen-Gang, Bian Bao-Min, Wang Shou-Yu, Lin Ying-Lu, Wang Chun-Yong, Li Zhen-Hua
Chin. Phys. B, 2013, 22 (6): 060505 doi: 10.1088/1674-1056/22/6/060505
Full Text: [PDF 977 KB] (Downloads:330)
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The statistical distribution of natural phenomena is of great significance in studying the laws of nature. In order to study the statistical characteristics of a random pulse signal, a random process model is proposed theoretically for better studying of the random law of measured results. Moreover, a simple random pulse signal generation and testing system is designed for studying the counting distributions of three typical objects including particles suspended in the air, standard particles, and background noise. Both normal and lognormal distribution fittings are used for analyzing the experimental results and testified by chi-square distribution fit test and correlation coefficient for comparison. In addition, the statistical laws of three typical objects and the relations between them are discussed in detail. The relation is also the non-integral dimension fractal relation of statistical distributions of different random laser scattering pulse signal groups.

Explosive synchronization of complex networks with different chaotic oscillators

Zhao Jun-Chan
Chin. Phys. B, 2013, 22 (6): 060506 doi: 10.1088/1674-1056/22/6/060506
Full Text: [PDF 1438 KB] (Downloads:761)
Show Abstract
Recent studies have shown that explosive synchronization transitions can be observed in networks of phase oscillators [Watts D J and Strogatz S H 1998 Nature 391 440] and chaotic oscillators [Newman M E J and Watts D J 1999 Phys. Lett. A 263 341]. Here, we study the effect of different chaotic dynamics on the synchronization transitions in small world networks and scale free networks. The continuous transition is discovered for Rössler systems in both of the above complex networks. However, explosive transitions take place for the coupled Lorenz systems, and the main reason is the abrupt change of dynamics before achieving complete synchronization. Our results show that the explosive synchronization transitions are accompanied by the change of system dynamics.

Network evolution driven by dynamics applied to graph coloring

Wu Jian-She, Li Li-Guang, Wang Xiao-Hua, Yu Xin, Jiao Li-Cheng
Chin. Phys. B, 2013, 22 (6): 060507 doi: 10.1088/1674-1056/22/6/060507
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An evolutionary network driven by dynamics is studied and applied to the graph coloring problem. From an initial structure, both the topology and the coupling weights evolve according to the dynamics. On the other hand, the dynamics of the network are determined by the topology and the coupling weights, so an interesting structure-dynamics coevolutionary scheme appears. By providing two evolutionary strategies, a network described by the complement of a graph will evolve into several clusters of nodes according to their dynamics. The nodes in each cluster can be assigned the same color and nodes in different clusters assigned different colors. In this way, a coevolution phenomenon is applied to the graph coloring problem. The proposed scheme is tested on several benchmark graphs for graph coloring.

Controlling hyperchaotic complex systems with unknown parameters based on adaptive passive method

Gamal M. Mahmoud, Emad E. Mahmoud, Ayman A. Arafa
Chin. Phys. B, 2013, 22 (6): 060508 doi: 10.1088/1674-1056/22/6/060508
Full Text: [PDF 481 KB] (Downloads:377)
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The aim of this paper is to study the control of hyperchaotic complex nonlinear systems with unknown parameters using passive control theory. An approach is stated to design the passive controller and estimate the unknown parameters based on the property of the passive system. The feasibility and effectiveness of the proposed approach is demonstrated through its application to the hyperchaotic complex Lü system, as an example. The estimated values of the unknown parameters are calculated. The analytical form of the complex controller is derived and used in the numerical simulation to control the hyperchaotic attractors of this example. Block diagrams of this example using Matlab/Simulink are constructed after and before the control to ensure the validity of the analytical results. Other examples of hyperchaotic complex nonlinear systems can be similarly treated.

Comparison of performance between bipolar and unipolar double-frequency sinusoidal pulse width modulation in a digitally controlled H-bridge inverter system

Lei Bo, Xiao Guo-Chun, Wu Xuan-Lü
Chin. Phys. B, 2013, 22 (6): 060509 doi: 10.1088/1674-1056/22/6/060509
Full Text: [PDF 1177 KB] (Downloads:11222)
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By deriving the discrete-time models of a digitally controlled H-bridge inverter system modulated by bipolar sinusoidal pulse width modulation (BSPWM) and unipolar double-frequency sinusoidal pulse width modulation (UDFSPWM) respectively, the performances of the two modulation strategies are analyzed in detail. The circuit parameters, used in this paper, are fixed. When the systems, modulated by BSPWM and UDFSPWM, have the same switching frequency, the stability boundaries of the two systems are the same. However, when the equivalent switching frequencies of the two systems are the same, the BSPWM modulated system is more stable than the UDFSPWM modulated system. In addition, a convenient method of establishing the discrete-time model of piecewise smooth system is presented. Finally, the analytical results are confirmed by circuit simulations and experimental measurements.

A novel study for impulsive synchronization of fractional-order chaotic systems

Liu Jin-Gui
Chin. Phys. B, 2013, 22 (6): 060510 doi: 10.1088/1674-1056/22/6/060510
Full Text: [PDF 305 KB] (Downloads:440)
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The stability of impulsive fractional-order systems is discussed. A new synchronization criterion of fractional-order chaotic systems is proposed based on the stability theory of impulsive fractional-order systems. The synchronization criterion is suitable for the case of the order 0 < q ≤ 1. It is more general than those of the known results. Simulation results are given to show the effectiveness of the proposed synchronization criterion.

The KdV-Burgers equation in modified speed gradient continuum model

Lai Ling-Ling, Cheng Rong-Jun, Li Zhi-Peng, Ge Hong-Xia
Chin. Phys. B, 2013, 22 (6): 060511 doi: 10.1088/1674-1056/22/6/060511
Full Text: [PDF 459 KB] (Downloads:873)
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Based on the full velocity difference model, Jiang et al. put forward the speed gradient model through the micro-macro linkage. In this paper, the Taylor expansion is adopted to modify the model. The backward travel problem is overcome by our model, which exists in many higher-order continuum models. The neutral stability condition of the model is obtained through the linear stability analysis. Nonlinear analysis shows clearly that the density fluctuation in traffic flow leads to a variety of density waves. Moreover, the Korteweg-de Vries-Burgers (KdV-Burgers) equation is derived to describe the traffic flow near the neutral stability line and the corresponding solution for traffic density wave is derived. The numerical simulation is carried out to investigate the local cluster effects. The results are consistent with the realistic traffic flow and also further verify the results of nonlinear analysis.

Totally asymmetric exclusion processes at constrained m-input n-output junction points

Li Shao-Da, Liu Ming-Zhe, Pei Xiang-Jun
Chin. Phys. B, 2013, 22 (6): 060512 doi: 10.1088/1674-1056/22/6/060512
Full Text: [PDF 476 KB] (Downloads:372)
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Totally asymmetric exclusion processes at constrained m-input n-output junction points under random update are studied by theoretical calculation and computer simulation in this paper. At the junction points, the hopping rate of particles from m-input parallel lattices to n-output parallel lattices is assumed to be equal to r/n (0 < r < 1). The mean-field approach and Monte Carlo simulations show that the phase diagram can be classified into three regions at any value of r. More interestingly, there is a threshold rc = n( 1-√1-m/n)/m. In the cases of r > rc and r < rc, qualitatively different phases exist in the system. With the increase of the value of m/n, the regions of (LD, LD) and (MC, LD) or (HD, LD) decrease, and the (HD, HD) is the only phase that increases in the region (LD stands for low density, HD stands for high density, and MC for maximal current). Stationary current and density profiles are calculated, showing that they are in good agreement with Monte Carlo simulations.

Brownian localization: A generalized coupling model yielding a nonergodic Langevin equation description

Lin Jian, Wang Hai-Yan, Bao Jing-Dong
Chin. Phys. B, 2013, 22 (6): 060513 doi: 10.1088/1674-1056/22/6/060513
Full Text: [PDF 283 KB] (Downloads:585)
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A minimal system-plus-reservoir model yielding a nonergodic Langevin equation is proposed, which origins from cubic-spectral density of environmental oscillators and momentum-dependent coupling. This model allows the ballistic diffusion and classical localization simultaneously, in which the fluctuation-dissipation relation is still satisfied but the Khinchin theorem is broken. The asymptotical equilibrium for nonergodic system requires the initial thermal equilibrium, however, when the system starts from nonthermal conditions, it does not approach the equilibration even a nonlinear potential is used to bound particle, this can be confirmed by the zeroth law of thermodynamics. In the dynamics of Brownian localization, due to the memory damping function inducing a constant term, our results show that the stationary distribution of the system depends on its initial preparation of coordinate rather than momentum. The coupled oscillator chain with a fixed end boundary acts as such heat bath, which has long been used in studies of collinear atom/solid-surface scattering and lattice vibration, we investigate this problem from the viewpoint of nonergodicity.
ATOMIC AND MOLECULAR PHYSICS

Differences in adsorption of FePc on coinage metal surfaces

R.A. Rehman, Cai Yi-Liang, Zhang Han-Jie, Wu Ke, Dou Wei-Dong, Li Hai-Yang, He Pi-Mo, Bao Shi-Ning
Chin. Phys. B, 2013, 22 (6): 063101 doi: 10.1088/1674-1056/22/6/063101
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A study of the electronic and structural properties of iron phthalocyanine (FePc) molecule adsorbed on coinage metal surfaces Cu (100) and Cu (110) has been conducted by means of density functional theory calculations. The strength of the molecule-substrate interactions is interpreted in terms of the lateral adsorption geometry and the site specific electronic structure of the molecule. In the case of FePc on (100)-oriented copper surface, the benzopyrrole leg is found to be oriented at an angle of 9° or 3° from the [01-1] substrate direction. Further, an upward bend in the molecular plane ranging from 7° to 10° is also observed; giving an almost buckled shape to the molecule. However, in the case of FePc on Cu (110), neither a bend nor a sizable rotation is observed. From general knowledge of the principals of structural and electronic properties, it is concluded that FePc-Cu (100) interaction is relatively stronger than FePc-Cu (110) interaction, which is further evidenced by the charge transfer, work function changes, changes in the shape of the adsorbed molecular orbitals, and the orbital shifts. Furthermore, a density of states analysis shows that valence band level shift is surface- and site-dependent.

A full-dimensional analytical potential energy surface for the F+CH4→HF+CH3 reaction

Yang Chuan-Lu, Wang Mei-Shan, Liu Wen-Wang, Zhang Zhi-Hong, Ma Xiao-Guang
Chin. Phys. B, 2013, 22 (6): 063102 doi: 10.1088/1674-1056/22/6/063102
Full Text: [PDF 372 KB] (Downloads:394)
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A full-dimensional analytical potential energy surface (APES) for the F+CH4→HF +CH3 reaction is developed based on 7127 ab initio energy points at the unrestricted coupled-cluster with single, double, and perturbative triple excitations. The correlation-consistent polarized triple-split valence basis set is used. The APES is represented with a many-body expansion containing 239 parameters determined by the least square fitting method. The two-body terms of the APES are fitted by potential energy curves with multi-reference configuration interaction, which can describe the diatomic molecules (CH, H2, HF, and CF) accurately. It is found that the APES can reproduce the geometry and vibrational frequencies of the saddle point better than those available in the literature. The rate constants based on the present APES support the experimental results of Moore et al. [Int. J. Chem. Kin. 26, 813 (1994)]. The analytical first-order derivation of energy is also provided, making the present APES convenient and efficient for investigating the title reaction with quasiclassical trajectory calculations.

X-ray-boosted photoionization for the measurement of an intense laser pulse

Ge Yu-Cheng, He Hai-Ping
Chin. Phys. B, 2013, 22 (6): 063201 doi: 10.1088/1674-1056/22/6/063201
Full Text: [PDF 991 KB] (Downloads:324)
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Investigations show that the X-ray-boosted photoionization (XBP) has the following advantages for in-situ measurements of ultrahigh laser intensity I and field envelope F(t) (time t, pulse duration τL, carrier-envelope-phase φ): accuracy, dynamic ranges, and rapidness. The calculated XBP spectra resemble inversely proportional functions of the photoelectron momentum shift. The maximum momentum p and the observable value Q (defined as a double integration of a normalized photoelectron energy spectrum, PES) linearly depend on I1/2 and τL, respectively. φ and F(t) can be determined from the PES cut-off energy and peak positions. The measurable laser intensity can be up to and over 1018 W/cm2 by using high energy X-rays and highly charged inert gases.

The stereodynamic properties of the F + HO (v, j)→HF + O reaction on the 1A' and 3A' potential energy surfaces by quasi-classical trajectory: Initial excitation effect (v =1-3, j = 0 and v = 0, j =1-3)

Zhao Dan, Chu Tian-Shu, Hao Ce
Chin. Phys. B, 2013, 22 (6): 063401 doi: 10.1088/1674-1056/22/6/063401
Full Text: [PDF 450 KB] (Downloads:292)
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The stereodynamic properties of the F + HO (v, j) reaction are explored by quasi-classical trajectory (QCT) calculations performed on the 1A' and 3A' potential energy surfaces (PESs). Based on the polarization-dependent differential cross sections (PDDCSs) and the angular distributions of the product angular momentum with the reactant at different values of initial v or j, the results show that the product scattering and product polarization have strong links with initial vibrational-rotational numbers of v and j. The significant manifestation of the normal DCSs is that the forward scattering gradually becomes predominant with the initial vibrational excitation increasing, and the scattering angle of the HF product taking place on the 3A' potential energy surface is found to be more sensitive to the initial value of v. The product orientation and alignment are strongly dependent on the initial rovibrational excitation effect. With enhancement in the initial rovibrational excitation effect, there is an overall decrease in the product orientation as well as in the product alignment either perpendicular to the reagent relative velocity vector k or along the direction of the y axis, for which the initial rotational excitation effect is much more noticeable than the vibrational excitation effect. Moreover, the initial rovibrational excitation effect on the product polarization is more pronounced for the 3A' potential energy surface than for the 1A' potential energy surface.

The effect of the rotational excitation of NO on the stereodynamics for the reaction C(3P) + NO (X2Π)→CN (X2+) +O (3P)

Ma Jian-Jun, Zou Yong, Liu Hou-Tong
Chin. Phys. B, 2013, 22 (6): 063402 doi: 10.1088/1674-1056/22/6/063402
Full Text: [PDF 359 KB] (Downloads:280)
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The stereodynamic properties of the reaction C(3P) + NO (X2Π)→CN (X2+) +O (3P) in different rotational states of reactant NO are studied theoretically by using quasiclassical trajectory method on 2A00 and 2A0 potential energy surfaces (PESs) at a collision energy of 0.06 eV. The vector properties in different rotational states on the two surfaces are discussed in detail. The results indicate that the rotational excitation of NO has considerable influence on the stereodynamic property of reaction occurring on the two surfaces. At the same time, the calculated polarization-dependent differential cross sections (PDDCSs) in different initial rotational states manifest that products are strongly polarized at three scattering angles.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Nonparaxial propagation of Hermite-Laguerre-Gaussian beams in uniaxial crystal orthogonal to the optical axis

Xu Yi-Qing, Zhou Guo-Quan, Wang Xiao-Gang
Chin. Phys. B, 2013, 22 (6): 064101 doi: 10.1088/1674-1056/22/6/064101
Full Text: [PDF 853 KB] (Downloads:375)
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Analytical expressions for the three components of the nonparaxial propagation of a Hermite-Laguerre-Gaussian (HLG) beam in uniaxial crystal orthogonal to the optical axis are derived. The intensity distribution of an HLG beam and its three components propagating in a uniaxial crystal orthogonal to the optical axis are demonstrated by numerical examples. Although the y and z components of an HLG beam in the incident plane are both equal to zero, they emerge upon propagation inside the uniaxial crystal. Moreover, the beam profile of the x component is relatively stable and the beam profiles of the y and z components have the same evolution law. If the ratio of the extraordinary refractive index to the ordinary refractive index is larger than unity, the beam profile of the HLG beam is elongated in the x direction and generally rotates clockwise. Otherwise, the beam profile of the HLG beam is elongated in the y direction and generally rotates anticlockwise. This research is beneficial to the optical trapping and nonlinear optics involved in the rotation of the beam profile.

Scattering by an array of parallel metallic carbon nanotubes

Afshin Moradi
Chin. Phys. B, 2013, 22 (6): 064201 doi: 10.1088/1674-1056/22/6/064201
Full Text: [PDF 279 KB] (Downloads:350)
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The scattering of electromagnetic wave by an array of parallel metallic single-walled carbon nanotubes is investigated based on the boundary-value method. Electronic excitations over each nanotube surface are modeled as an infinitesimally thin cylindrical layer of the free-electron gas. The scattering cross section of both transverse magnetic (TM) and transverse electric (TE) uniform plane waves by the system at normal incidences is obtained.

Experimental verification on tightly focused radially polarized vortex beams

Du Fu-Rong, Zhou Zhe-Hai, Tan Qiao-Feng, Yang Chang-Xi, Zhang Xiao-Qing, Zhu Lian-Qing
Chin. Phys. B, 2013, 22 (6): 064202 doi: 10.1088/1674-1056/22/6/064202
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The theoretical and experimental results of tightly focused radially polarized vortex beams are demonstrated. An auto-focus technology is introduced into the measurement system in order to enhance the measurement precision, and the radially polarized vortex beams are generated by a liquid-crystal polarization converter and a vortex phase plate. The focused fields of radially polarized vortex beams with different topological charges at numerical apertures (NAs) of 0.65 and 0.85 are measured respectively, and the results indicate that the total intensity distribution at focus is dependent not only on the NA of the focusing objective lens and polarization pattern of the beam but also on the topological charge l of the beam. Some unique focusing properties of radially polarized vortex beams with fractional topological charges are presented based on numerical calculations. The experimental verification paves the way for some practical applications of radially polarized vortex beams, such as in optical trapping, near-field microscopy, and material processing.

An image compression method for space multispectral time delay and integration charge coupled device camera

Jin Long-Xu, Zhang Ran-Feng
Chin. Phys. B, 2013, 22 (6): 064203 doi: 10.1088/1674-1056/22/6/064203
Full Text: [PDF 448 KB] (Downloads:589)
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Multispectral time delay and integration charge coupled device (TDICCD) image compression requires low-complexity encoder because it is usually completed on board where the energy and memory are limited. The Consultative Committee for Space Data Systems (CCSDS) has proposed an image data compression (CCSDS-IDC) algorithm which is so far most widely implemented in hardware. However, it cannot reduce spectral redundancy in multispectral images. In this paper, we propose a low-complexity improved CCSDS-IDC (ICCSDS-IDC)-based distributed source coding (DSC) scheme for multispectral TDICCD image consisting of a few bands. Our scheme is based on an ICCSDS-IDC approach that uses a bit plane extractor to parse the differences in original image and its wavelet transformed coefficient. The output of bit plane extractor will be encoded by a first order entropy coder. Low-density parity-check-based Slepian-Wolf (SW) coder is adopted to implement the DSC strategy. Experimental results on space multispectral TDICCD images show that the proposed scheme significantly outperforms the CCSDS-IDC-based coder in each band.

Atom dynamical dissipation in the laser cavity with quasimode

Jiang Wen-Ying, Zhao Zhi-Min, Tian Tian, Zheng Li, Zheng Tai-Yu
Chin. Phys. B, 2013, 22 (6): 064204 doi: 10.1088/1674-1056/22/6/064204
Full Text: [PDF 196 KB] (Downloads:319)
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In this paper we study the atom dissipation effect in a laser cavity. The cavity field mode is described by the Fox-Li quasimode due to the leaky of cavity. Our results show that the atom decay rate versus the decay rate of the quasimode is a Lorentz type. Effects of the atom-cavity detuning as well as cavity size are also discussed.

Unified analytical treatments to qubit-oscillator systems

He Shu, Zhang Yu-Yu, Chen Qing-Hu, Ren Xue-Zao, Liu Tao, Wang Ke-Lin
Chin. Phys. B, 2013, 22 (6): 064205 doi: 10.1088/1674-1056/22/6/064205
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An effective scheme within two displaced bosonic operators with equal positive and negative displacements is extended to study the qubit-oscillator systems analytically in a unified way. Many previous analytical treatments, such as generalized rotating-wave approximation (GRWA) [Phys. Rev. Lett. 99, 173601 (2007)] and an expansion in the qubit tunneling matrix element in the deep strong coupling regime [Phys. Rev. Lett. 105, 263603 (2010)] can be recovered straightforwardly within the present scheme. Moreover, further improving GRWA and the extension to the finite-bias case are implemented easily. The algebraic formulae for the eigensolutions are then derived explicitly and uniquely, which work well in a wide range of the coupling strengthes, detunings, and static bias including the recent experimentally accessible parameters. The dynamics of the qubit for an oscillator in ground-state is also studied. At the experimentally accessible coupling regime, GRWA can always work well. When the coupling is enhanced to the intermediate regime, only the improving GRWA can give the correct description, while the result of GRWA shows strong deviations. The previous Van Vleck perturbation theory is not valid to describe the dynamics in the present-day experimentally accessible regime, except for the strongly biased cases.

Enhancing stationary optomechanical entanglement with Kerr medium

Zhang Dan, Zhang Xiao-Ping, Zheng Qiang
Chin. Phys. B, 2013, 22 (6): 064206 doi: 10.1088/1674-1056/22/6/064206
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We theoretically investigate the stationary entanglement of a optomechanical system with additional Kerr medium in the cavity. There are two kinds of interactions in the system, photon-mirror interaction and photon-photon interaction. The optomechanical entanglement created by the former interaction can be effectively controlled by the latter one. We find that the optomechanical entanglement is suppressed by Kerr interaction due to photon blockage. We also find that the Kerr interaction can create the stationary entanglement and induce the resonance of entanglement in the small detuning regime. These results show that the Kerr interaction is an effective controlling knob to the optomechanical system.

Electronic states and shape of silicon quantum dots

Huang Wei-Qi, Miao Xing-Jian, Huang Zhong-Mei, Cheng Han-Qiong, Shu Qin
Chin. Phys. B, 2013, 22 (6): 064207 doi: 10.1088/1674-1056/22/6/064207
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A curviform surface breaks the symmetrical shape of silicon quantum dots on which some bonds can produce localized electronic states in the bandgap. The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces, for example, a Si-O-Si bridge bond on curved surface provides localized levels in bandgap and its bonding energy is shallower than that on the facet. The red-shifting ofthe photoluminescence spectrum on smaller silicon quantum dots can be explained by the curved surface effect. Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided by the curved surface effect.

A theoretical and experimental investigation of an in-band pumped gain-switched thulium-doped fiber laser

Zhou Ren-Lai, Ju You-Lun, Zhao Jie, Yang Chao,Wang Yue-Zhu
Chin. Phys. B, 2013, 22 (6): 064208 doi: 10.1088/1674-1056/22/6/064208
Full Text: [PDF 690 KB] (Downloads:1314)
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In this paper, the theoretical rate equation model of in-band pumped gain-switched thulium-doped fiber (TDF) laser is investigated. The analytical formulations of pump energy threshold, peak power extraction efficiency, and pulse extraction efficiency are derived through analyzing the interaction process between pump pulse and laser pulse. They are useful for understanding, designing, and optimizing the in-band pumped TDF lasers in a 1.9 μm-2.1 μm wavelength region. The experiment of all fiber gain-switched TDF laser pumped by 1.558-μ pulse amplifier is conducted, and our experimental results show good agreement with theoretical analysis.

The improved output performance of a broad-area vertical-cavity surface-emitting laser with an optimized electrode diameter

Zhang Xing, Ning Yong-Qiang, Qin Li, Tong Cun-Zhu, Liu Yun, Wang Li-Jun
Chin. Phys. B, 2013, 22 (6): 064209 doi: 10.1088/1674-1056/22/6/064209
Full Text: [PDF 646 KB] (Downloads:375)
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The output performance of 980-nm broad-area vertical-cavity surface-emitting laser (VCSEL) is improved by optimizing the p-electrode diameter in this study. Based on a three-dimensional finite-element method, the current density distribution within the active region of the VCSEL is optimized through the appropriate adjustment of p-electrode diameter, and the uniform current-density distribution is achieved. Then, the effects of this optimization are studied experimentally. The L-I-V characteristics under different temperatures of the VCSELs with different p-electrode diameters are investigated, and a better temperature stability is demonstrated in the VCSEL with optimized p-electrode diameter. The far-field measurements show that with an injected current of 2 A, the far-field divergence angle of the VCSEL with optimized p-electrode diameter is 9°, which is much lower than the far-field angle of the VCSEL without this optimization. Also the VCSEL with optimized p-electrode diameter shows a better near-field distribution.

Crystalline undulator radiation and sub-harmonic bifurcation of system

Luo Xiao-Hua, He Wei, Wu Mu-Ying, Shao Ming-Zhu, Luo Shi-Yu
Chin. Phys. B, 2013, 22 (6): 064210 doi: 10.1088/1674-1056/22/6/064210
Full Text: [PDF 426 KB] (Downloads:306)
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Looking for a new light source, especially short wavelength laser light source has attracted widespread attention. In the paper analytically described is the radiation of crystalline undulator field by the sine-squared potential. In the classical mechanics and the dipole approximation, the motion equation of particle is reduced to a generalized pendulum equation with damping term and forcing term. The bifurcation behavior of periodic orbits is analyzed by using the Melnikov method and numerical method, and the stability of the system is discussed. The results show that the stability of the system relates to its parameters, and only by adjusting appropriately these parameters, in principle can the occurrence of bifurcation be avoided or suppressed.

Generation of compact high-power high-efficiency normal-dispersion pumping supercontinuum in silica photonic crystal fiber pumped with 1064-nm picosecond pulse

Chen Hong-Wei, Jin Ai-Jun, Yang Wei-Qiang, Chen Sheng-Ping, Hou Jing, Lu Qi-Sheng
Chin. Phys. B, 2013, 22 (6): 064211 doi: 10.1088/1674-1056/22/6/064211
Full Text: [PDF 259 KB] (Downloads:382)
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Broadband normal dispersion pumping supercontinuum (SC) generation in silica photonic crystal fiber (PCF) is investigated in this paper. A 1064-nm picosecond fiber laser is used to pump silica PCF for the SC generation. The length of PCF is optimized for the most efficient stimulated Raman scattering process in the picosecond pump pulse region. The first stimulated Raman Stokes peak is located in the anomalous dispersion regime of the PCF and nearby the zero dispersion wavelength; thus the SC generation process can benefit from both normal dispersion pumping scheme and anomalous dispersion pumping scheme. The 51.7-W SC spanning from about 700 nm to beyond 1700 nm is generated with an all-fiber configuration, and the pump-to-SC conversion efficiency is up to 90%. In order to avoid the output fiber end face damage and increase the stability of the system, an improved output solution for the high power SC is proposed in our experiment. This high-efficiency near-infrared SC source is very suitable for the applications that the average output power and spectral power density are firstly desirable.

A picosecond widely tunable deep-ultraviolet laser for angle-resolved photoemission spectroscopy Hot!

Zhang Feng-Feng, Yang Feng, Zhang Shen-Jin, Xu Zhi, Wang Zhi-Min, Xu Feng-Liang, Peng Qin-Jun, Zhang Jing-Yuan, Wang Xiao-Yang, Chen Chuang-Tian, Xu Zu-Yan
Chin. Phys. B, 2013, 22 (6): 064212 doi: 10.1088/1674-1056/22/6/064212
Full Text: [PDF 324 KB] (Downloads:475)
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We develop a picosecond widely tunable laser in a deep-ultraviolet region from 175 nm to 210 nm, generated by two stages of frequency doubling of a 80-MHz mode-locked picosecond Ti:sapphire laser. Aβ-BaB2O4 walk-off compensation configuration and a KBe2BO3F2 prism-coupled device are adopted for the generation of second harmonic and fourth harmonics, respectively. The highest power is 3.72 mW at 193 nm, and the fluctuation at 2.85 mW in 130 min is less than ± 2%.

Characterization of spectral hole depth in Tm3+:YAG within cryogenic temperature range

Chen Lei, Ma Xiu-Rong, Wang Wei, Zhang Shuang-Gen, Mu Kuan-Lin, Wang Xia-Yang, Zhang Shi-Yu
Chin. Phys. B, 2013, 22 (6): 064213 doi: 10.1088/1674-1056/22/6/064213
Full Text: [PDF 497 KB] (Downloads:353)
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In this paper, spectral hole depth dependence on temperature below 10 K in Tm3+:YAG crystal is investigated in detail. A novel model is proposed to analyze the temperature dependence on spectral hole. By using the proposed model, we theoretically deduce the temperature dependence of spectral hole depth. The results are compared with experimental results and they are in good agreement. According to the theoretic results, the optimum temperature in experiment can be found.

Generation of self-oscillations from a singly resonant periodically poled potassium titanyl phosphate crystal frequency doubler

Li Yuan-Ji, Liu Qin, Feng Jin-Xia, Zhang Kuan-Shou
Chin. Phys. B, 2013, 22 (6): 064214 doi: 10.1088/1674-1056/22/6/064214
Full Text: [PDF 363 KB] (Downloads:264)
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We report on the generation of self-oscillations from a continuously pumped singly resonant frequency doubler based on a periodically poled potassium titanyl phosphate crystal (PPKTP). The sustained square-wave and staircase curve of self-oscillations are obtained when the incident pump powers are below and above the threshold of subharmonic-pumped parametric oscillation (SPO), respectively. The self-oscillations can be explained by the competition between the phase shifts induced by cascading nonlinearity and thermal effect, and the influence of fundamental nonlinear phase shift by the generation of SPO. The simulation results are in good agreement with the experiment data.

Extension of high-order harmonic cutoff frequency by synthesizing waveform of laser field via optimization of classical electron trajectory in laser field

Zhao Di, Li Fu-li
Chin. Phys. B, 2013, 22 (6): 064215 doi: 10.1088/1674-1056/22/6/064215
Full Text: [PDF 474 KB] (Downloads:318)
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We theoretically investigate the high-order harmonic generation by employing the strong-field approximation (SFA) and present a new approach to the extension of the high-order harmonic cutoff frequency via an exploration of the dependence of high-order harmonic generation on the waveform of laser fields. The dependence is investigated via a detailed analysis of the classical trajectories of the ionized electron moving in the continuum in the velocity-position plane. The classical trajectory consists of three sections (Acceleration Away, Deceleration Away, and Acceleration Back), and their relationship with the electron recollision energy is investigated. The analysis of classical trajectories indicates that, besides the final (Acceleration Back) section the electron recollision energy also relies on the previous two sections. We simultaneously optimize the waveform in all the three sections to increase the electron recollision energy, and an extension of the cutoff frequency up to Ip+20.26Up is presented with a theoretically synthesized waveform of the laser field.

A tunable comb filter using single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop

Ruan Juan, Zhang Wei-Gang, Zhang Hao, Geng Peng-Cheng, Bai Zhi-Yong
Chin. Phys. B, 2013, 22 (6): 064216 doi: 10.1088/1674-1056/22/6/064216
Full Text: [PDF 785 KB] (Downloads:620)
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A novel tunable comb filter composed of a single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop is proposed and experimentally demonstrated. The filter tunability is achieved by rotating the polarization controller. The spectral shift is dependent on rotation direction and the position of polarization controller. In addition, the adjustable range achieved by rotating the half-wave-plate polarization controller is twice higher than that of the quarter-wave-plate one.

Deposition of Cu seed layer film by supercritical fluid deposition for advanced interconnects

Zhao Bin, Zhao Ming-Tao, Zhang Yan-Fei, Yang Jun-He
Chin. Phys. B, 2013, 22 (6): 064217 doi: 10.1088/1674-1056/22/6/064217
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The deposition of a Cu seed layer film is investigated by supercritical fluid deposition (SCFD) using H2 as a reducing agent for Bis(2,2,6,6-tetramethyl-3,5- heptanedionato) copper in supercritical CO2 (scCO2). The effects of deposition temperature, precursor, and H2 concentration are investigated to optimize Cu deposition. Continuous metallic Cu films are deposited on Ru substrates at 190 ℃ when a 0.002 mol/L Cu precursor is introduced with 0.75 mol/L H2. A Cu precursor concentration higher than 0.002 mol/L is found to have negative effects on the surface qualities of Cu films. For a H2 concentration above 0.56 mol/L, the root-mean-square (RMS) roughness of a Cu film decreases as the H2 concentration increases. Finally, a 20-nm thick Cu film with a smooth surface, which is required as a seed layer in advanced interconnects, is successfully deposited at a high H2 concentration (0.75 mol/L).

Thermal conductivity of a kind of mesoporous silica SBA-15

Huang Cong-Liang, Feng Yan-Hui, Zhang Xin-Xin, Li Jing, Wang Ge
Chin. Phys. B, 2013, 22 (6): 064401 doi: 10.1088/1674-1056/22/6/064401
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Mesoporous silica SBA-15 consists of uniform hexagonal, unconnected cylindrical channels with diameters that can be tuned within a range of 1.5 nm-30 nm, and is thought to have a special thermal conductivity. The theoretical investigation of the shell thermal conductivity of the mesoporous silica is performed in the relaxation time approximation in this paper. And an available one-dimensional heat transfer model is used to predict the effective thermal conductivity (ETC) of the mesoporous silica. The experimental result of the ETC is also presented for comparison. The shell thermal conductivity of the mesoporous silica decreases with mesochannel radius increasing or wall thickness decreasing, but does not strictly decrease with porosity increasing. The thermal radiation possibly plays a primary role in heat transfer at the large porosity scale. The predicted ETC of SBA-15 with only conduction considered is quite low at the large porosity, even lower than the thermal conductivity of the silica aerogels. To realize it, doping carbon or other matters which can strongly absorb infrared light into SBA-15 is a possible way.

Volt-ampere characteristics of a nitrogen DC plasma arc with anode melting

Zhao Peng, Ni Guo-Hua, Meng Yue-Dng, Nagatsu Masaaki
Chin. Phys. B, 2013, 22 (6): 064701 doi: 10.1088/1674-1056/22/6/064701
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The characteristics of nitrogen arc using graphite cathode and melting anode in pilot-scale plasma furnace are investigated. The voltage is examined as a function of current and apparent plasma length. The voltage increases non-linearly with the increase of apparent plasma length, with the current fixed. The experimental data so obtained are compared with the predictions of the Bowman model for the electric arc, and with numerical simulations as well. The level of agreement between the experimental data at the melting anode and the numerical predictions confirms the suitability of the proposed the Bowman model. These characteristics are relevant to the engineering design and evaluation of DC plasma furnace and reactor for the treatment of hazardous fly ash waste.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Optimization of 4.7-keV X-ray titanium sources driven by 100-ps laser pulse

Xiong Jun, Dong Jia-Qin, Jia Guo, Wang Rui-Rong, Wang Wei, Fu Si-Zu, Zheng Wu-Di
Chin. Phys. B, 2013, 22 (6): 065201 doi: 10.1088/1674-1056/22/6/065201
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An experiment with thin titanium foils irradiated by two pulses delayed in time is conducted on the Shenguang-II laser facility. A prepulse induces an underdense plasma, 2-ns later a main pulse (λ L=0.35 μm, EL ≈ 120 J, τ L ≈ 100 ps) is injected into the underdense plasma and produces strong line emission from titanium K shell (i.e., Heα at 4.7 keV). Data show that the intensity of 4.7-keV X-ray emission with the prepulse is approximately twice more than without the prepulse, and can be used as a backlighting source satisfying the diagnostic requirements for dense plasma probing. High-quality plasma images are obtained with the backlighting 4.7-keV X-rays in a Rayleigh-Taylor hydrodynamic instability experiment.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Growth and characterization of GaAs/InxGa1-xAs/GaAs axial nanowire heterostructures with symmetrical heterointerfaces

Lü Xiao-Long, Zhang Xia, Liu Xiao-Long, Yan Xin, Cui Jian-Gong, Li Jun-Shuai, Huang Yong-Qing, Ren Xiao-Min
Chin. Phys. B, 2013, 22 (6): 066101 doi: 10.1088/1674-1056/22/6/066101
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We report on the Au-assisted vapour-liquid-solid (VLS) growth of GaAs/InxGa1-xAs/GaAs (0.2 ≤ x ≤ 1) axial double-heterostructure nanowires on GaAs (111) B substrates via metal-organic chemical vapor deposition (MOCVD) technique. The influence of indium content in Au particle on the morphology of nanowires is investigated systematically. A short period of pre-introduced indium precursor before the growth of InxGa1-xAs segment, coupled with a group III precursor interruption, is conducive to obtaining symmetrical heterointerfaces as well as the desired In/Ga ratio in the InxGa1-xAs section. The nanowire morphology, such as kinking and tapering, are thought to be related to the In composition in the catalyst alloy as well as the VLS growth mechanism.

A first-principles study of the structural and elastic properties of orthorhombic and tetragonal Ca3Mn2O7

Zhang Wei, Tong Pei-Qing
Chin. Phys. B, 2013, 22 (6): 066201 doi: 10.1088/1674-1056/22/6/066201
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The structural and elastic properties of multiferroic Ca3Mn2O7 with ferroelectric orthorhombic (O-phase) and paraelectric tetragonal structures (T-phase) have been studied by first-principles calculations within the generalized gradient approximation (GGA) and the GGA plus Hubbard U approaches (GGA+U). The calculated theoretical structures are in good agreement with the experimental values. The T-phase is found to be antiferromagnetic (AFM) and the AFM O-phase is more stable than the T-phase, which also agree with the experiments. On these basis, the single-crystal elastic constants (Cijs) and elastic properties of polycrystalline aggregates are investigated for the two phases. Our elasticity calculations indicate Ca3Mn2O7 is mechanically stable against volume expansions. The AFM O-phase is found to be a ductile material, while the AFM T-phase shows brittle nature and tends to be elastically isotropic. We also investigate the influence of strong correlation effects on the elastic properties, qualitatively consistent results are obtained in a reasonable range of values of U. Finally, the ionicity is discussed by Bader analysis. Our work provides useful guidance for the experimental elasticity measurements of Ca3Mn2O7, and makes the strain energy calculation in multiferroic Ca3Mn2O7 thin films possible.

High-pressure Raman study of MgV2O6 synthesized at high pressure and high temperature

Tang Rui-Lian, Li Yan, Tao Qiang, Li Na-Na, Li Hui, Han Dan-Dan, Zhu Pin-Wen, Wang Xin
Chin. Phys. B, 2013, 22 (6): 066202 doi: 10.1088/1674-1056/22/6/066202
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A new structural phase of MgV2O6 was obtained by a high-pressure, high-temperature (HPHT) synthesis method. The new phase was investigated by Rietveld analysis of X-ray powder diffraction data, showing space group Pbcn (No. 60) symmetry and a=13.6113(6) Å (1 Å=0.1 nm), b=5.5809(1) Å, c=4.8566(3) Å, V=368.93(2) Å3 (Z=4). High pressure behavior was studied by Raman spectroscopy at room temperature. Under 22.5 GPa, there was no sign of a structural phase transition in the spectra, demonstrating stability of the HPHT phase up to the highest pressure.

Complex force network in marginally and deeply jammed solids

Hu Mao-Bin, Jiang Rui, Wu Qing-Song
Chin. Phys. B, 2013, 22 (6): 066301 doi: 10.1088/1674-1056/22/6/066301
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This paper studies the force network properties of marginally and deeply jammed packings of frictionless soft particles from the perspective of complex network theory. We generate zero-temperature granular packings at different pressures by minimizing the inter-particle potential energy. The force networks are constructed as nodes representing particles and links representing normal forces between the particles. Deeply jammed solids show remarkably different behavior from marginally jammed solids in their degree distribution, strength distribution, degree correlation, and clustering coefficient. Bimodal and multi-modal distributions emerge when the system enters deep jamming region. The results also show that small and large particles can show different correlation behavior in this simple system.

One-dimensional diffusion of vacancies on Sr/Si(100)-c(2×4) surface

Yang Jing-Jing, Du Wen-Han
Chin. Phys. B, 2013, 22 (6): 066801 doi: 10.1088/1674-1056/22/6/066801
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An Sr/Si(100)-c(2×4) surface is investigated by high-resolution scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The semiconductor property of this surface is confirmed by STS. The STM images of this surface shows that it is bias-voltage dependent and an atomic resolution image can be obtained at an empty state under a bias voltage of 1.5 V. Furthermore, one-dimensional (1D) diffusion of vacancies can be found in the room-temperature STM images. Sr vacancies diffuse along the valley channels, which are constructed by silicon dimers in the surface. Weak interaction between Sr and silicon dimers, low metal coverage, surface vacancy, and energy of thermal fluctuation at room temperature all contribute to this 1D diffusion.

First-principles study of Ar adsorptions on the (111) surfaces of Pd, Pt, Cu, and Rh

Niu Wen-Xia, Zhang Hong, Gong Min, Cheng Xin-Lu
Chin. Phys. B, 2013, 22 (6): 066802 doi: 10.1088/1674-1056/22/6/066802
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In the present paper we give a detailed report on the results of our first-principles investigations of Ar adsorptions at the four high symmetry sites on M (111) (M = Pd, Pt, Cu, and Rh) surfaces. Our studies indicate that the most stable adsorption sites of Ar on Pd (111) and Pt (111) surfaces are found to be the fcc-hollow sites. However, for Ar adsorptions on Cu (111) and Rh (111) surfaces, the most favorable site is the on-top site. The density of states (DOS) is analyzed for Ar adsorption on M (111) surfaces, and it is concluded that the adsorption behavior is dominated by the interaction between 3s, 3p orbits of Ar atoms and the d orbit of the base metal atoms.

Structural and optical properties of tungsten-doped vanadium dioxide films

Wang Xue-Jin, Liu Yu-Ying, Li De-Hua, Feng Bao-Hua, He Zhi-Wei, Qi Zheng
Chin. Phys. B, 2013, 22 (6): 066803 doi: 10.1088/1674-1056/22/6/066803
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Thin films of tungsten (W)-doped thermochromic vanadium dioxide (VO2) were deposited onto the soda-lime glass and fused silica by radio frequency magnetron sputtering. The doped VO2 films were characterized by X-ray diffraction, optical transmittance measurement, and near field optical microscopy with Raman. X-ray diffraction patterns show that the (011) peak of W-doped thermochromic VO2 film shifts to a lower diffraction angle with the increase of W concentration. The optical measurements indicated that the transmittance change (ΔT) at wavelength of 2500 nm drops from 65% (ΔT at 35 ℃ and 80 ℃ for undoped VO2 film) to 38% (ΔT at 30 ℃ and 42 ℃ for the doped VO2 film). At the same time, phase transition temperature drops from 65 ℃ to room temperature or lower with the increase of W concentration. Near field optical microscopy image shows that the surface of W-doped VO2 film is smooth. Raman results show that the main Raman modes of W-doped VO2 are centered at 614 cm-1, the same as that of undoped VO2, suggesting no Raman mode changes for lightly W-doped VO2 at room temperature, due to no phase transition appearing under this condition.

Thermal stability and electrical properties of copper nitride with In or Ti

Du Yun, Gao Lei, Li Chao-Rong, Ji Ai-Ling
Chin. Phys. B, 2013, 22 (6): 066804 doi: 10.1088/1674-1056/22/6/066804
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Thin films of ternary compounds CuxInyN and CuxTiyN were grown by magnetron sputtering to improve the thermal stability of Cu3N, a material that decomposes below 300 ℃, and thus promises many interesting applications in directwriting. The effect of In or Ti incorporation in altering the structure and physical properties of copper nitride was evaluated by characterizing the film structure, surface morphology, and temperature dependence of electrical resistivity. More Ti than In can be accommodated by copper nitride without completely deteriorating the Cu3N lattice. A small amount of In or Ti can improve the crystallinity, and consequently the surface morphology. While the decomposition temperature is rarely influenced by In, the Ti-doped sample, Cu59.31Ti2.64N38.05, shows an X-ray diffraction pattern dominated by characteristic Cu3N peaks, even after annealing at 500 ℃. Both In and Ti reduce the bandgap of the original Cu3N phase, resulting in a smaller electrical resistivity at room temperature. The samples with more Ti content manifest metal-semiconductor transition when cooled from room temperature down to 50 K. These results can be useful in improving the applicability of copper-nitride-based thin films.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

First-principles study of hydrogen adsorption on titanium-decorated single-layer and bilayer graphenes

Pan Hong-Zhe, Wang Yong-Long, He Kai-Hua, Wei Ming-Zhen, Ouyang Yu, Chen Li
Chin. Phys. B, 2013, 22 (6): 067101 doi: 10.1088/1674-1056/22/6/067101
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The adsorption of hydrogen molecules on titanium-decorated (Ti-decorated) single-layer and bilayer graphenes is studied using density functional theory (DFT) with the relativistic effect. Both the local density approximation (LDA) and the generalized gradient approximation (GGA) are used for obtaining the region of the adsorption energy of H2 molecules on Ti-decorated graphene. We find that a graphene layer with titanium (Ti) atoms adsorbed on both sides can store hydrogen up to 9.51 wt% with average adsorption energy in a range from -0.170 eV to -0.518 eV. Based on the adsorption energy criterion, we find that chemisorption is predominant for H2 molecules when the concentration of H2 molecules absorbed is low while physisorption is predominant when the concentration is high. The computation results for the bilayer graphene decorated with Ti atoms show that the lower carbon layer has no contribution to hydrogen adsorption.

Density-functional theory investigation of electronic structure, elastic properties, optical properties, and lattice dynamics of Ba2ZnWO6

Guo San-Dong
Chin. Phys. B, 2013, 22 (6): 067102 doi: 10.1088/1674-1056/22/6/067102
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The electronic structures, optical dielectric functions, elastic properties, and lattice dynamics of Ba2ZnWO6 have been investigated by using the generalized gradient approximation. The density of states and distributions of charge density show that O and Ba tend toward ionic bond, but O and W or Zn display the covalent bond character. The calculated energy band structure shows that Ba2ZnWO6 is a wide indirect band gap semiconductor. The static value 2.28 of the refractive index is attained. The analysis of the elastic properties of Ba2ZnWO6 indicates a rather weak elastic anisotropy. The phonon dispersion is calculated, suggesting no structure instability, which is agreement with the recent low temperature neutron diffraction experiments. The mensurability Cv (phonon heat capacity) as the function of the temperature is also calculated to judge our results for future experiment.

The effect of interface hopping on inelastic scattering of oppositely charged polarons in polymers

Di Bing, Wang Ya-Dong, Zhang Ya-Lin, An Zhong
Chin. Phys. B, 2013, 22 (6): 067103 doi: 10.1088/1674-1056/22/6/067103
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The inelastic scattering of oppositely charge polarons in polymer heterojunctions is believed to be fundamental importance for the light-emitting and transport properties of conjugated polymers. Based on the tight-binding SSH model, and by using a nonadiabatic molecular dynamic method, we investigate the effects of interface hopping on inelastic scattering of oppositely charged polarons in a polymer heterojunction. It is found that the scattering processes of the charge and lattice defect depend sensitively on the hopping integrals at the polymer/polymer interface when the interface potential barrier and applied electric field strength are constant. In particular, at an intermediate electric field, when the interface hopping integral of the polymer/polymer heterojunction material is increased beyond a critical value, two polarons can combine to become a lattice deformation in one of the two polymer chains, with the electron and the hole bound together, i.e., a self-trapped polaron-exciton. The yield of excitons then increases to a peak value. These results show that interface hopping is of fundamental importance and facilitates the formation of polaron-excitons.

Influence of drain bias on the electron mobility in the AlGaN/AlN/GaN heterostructure field-effect transistors

Lü Yuan-Jie, Feng Zhi-Hong, Cai Shu-Jun, Dun Shao-Bo, Liu Bo, Yin Jia-Yun, Zhang Xiong-Wen, Fang Yu-Long, Lin Zhao-Jun, Meng Ling-Guo, Luan Chong-Biao
Chin. Phys. B, 2013, 22 (6): 067104 doi: 10.1088/1674-1056/22/6/067104
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Using measured capacitance-voltage curves and current-voltage characteristics for the AlGaN/AlN/GaN heterostructure field-effect transistors with different gate lengths and drain-to-source distances, the influence of drain bias on the electron mobility is investigated. It is found that below the knee voltage the longitudinal optical (LO) phonon scattering and interface roughness scattering are dominant for the sample with a large ratio of gate length to drain-to-source distance (here 4/5), and the polarization Coulomb field scattering is dominant for the sample with a small ratio (here 1/5). However, the above polarization Coulomb field scattering is weakened in the sample with a small drain-to-source distance (here 20 μm) compared with the one with a large distance (here 100 μm). This is due to the induced strain in the AlGaN layer caused by the drain bias.

Calculating Hamiltonian parameters for Yb3+ in a low-symmetry lattice site, and fitting the structure and levels of Yb3+:RETaO4 (RE=Gd, Y, and Sc)

Zhang Qing-Li, Ning Kai-Jie, Ding Li-Hua, Liu Wen-Peng, Sun Dun-Lu, Jiang Hai-He, Yin Shao-Tang
Chin. Phys. B, 2013, 22 (6): 067105 doi: 10.1088/1674-1056/22/6/067105
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An iterative method is used to find the values of the Hamiltonian parameters for Yb3+ in a given low-symmetry crystalline site. Samples of Yb3+:RETaO4 (RE=Gd, Y, and Sc) were prepared and their structures were determined. Based on the obtained structure data, their orbital-spin parameters and crystal field parameters were fitted by the superposition model (SM). Using the crystal field parameters obtained by the SM fitting as the initial parameters, the Hamiltonian parameters were fitted iteratively. The calculated and experimental energy levels for Yb3+:RETaO4 are consistent, and the maximal mean-root-square deviation is only 2.84 cm-1, indicating that the method is effective to determine the Hamiltonian parameters of Yb3+ in low-symmetry crystalline sites.

Electron mobility in the linear region of AlGaN/AlN/GaN heterostructure field-effect transistor

Yu Ying-Xia, Lin Zhao-Jun, Luan Chong-Biao, Wang Yu-Tang, Chen Hong, Wang Zhan-Guo
Chin. Phys. B, 2013, 22 (6): 067203 doi: 10.1088/1674-1056/22/6/067203
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We simulate the current-voltage (I-V) characteristics of the AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with different gate lengths using the quasi-two-dimensional (quasi-2D) model. The calculation results obtained using modified mobility model are found to accord well with the experimental data. By analyzing the variation of the electron mobility for the two-dimensional electron gas (2DEG) with the electric field in the linear region of the AlGaN/AlN/GaN HFET I-V output characteristics, it is found that the polarization Coulomb field scattering still plays an important role in the electron mobility of AlGaN/AlN/GaN HFET at the higher drain voltage and channel electric field. As drain voltage and channel electric field increase, the 2DEG density reduces and the polarization Coulomb field scattering increases, as a result, the 2DEG electron mobility decreases.

Coupled edge plasmon modes of metal/dielectric multi-wedges

Wang Xuan-Zhang
Chin. Phys. B, 2013, 22 (6): 067303 doi: 10.1088/1674-1056/22/6/067303
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We present a metallic/dielectric multi-wedge model to investigate the coupled edge plasmon modes (CEPMs), where all wedges have a common edge and the wave propagates along the edge direction. A general theoretical method valid to many practical structures is presented. The analytical dispersion relations of CEPMs in these structures are obtained and the CEPM properties are discussed with numerical results and the dispersion relations. For all structures mentioned in this paper, we find that the structures containing an even number of metallic wedges own four CEPMs and those with an odd-number of metallic wedges have two CEPMs. Further the periodic structures containing any odd number of periods and any even number of periods possess their common CEPMs, respectively.

A low on-resistance buried current path SOI p-channel LDMOS compatible with n-channel LDMOS

Zhou Kun, Luo Xiao-Rong, Fan Yuan-Hang, Luo Yin-Chun, Hu Xia-Rong, Zhang Bo
Chin. Phys. B, 2013, 22 (6): 067306 doi: 10.1088/1674-1056/22/6/067306
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A novel low specific on-resistance (Ron,sp) silicon-on-insulator (SOI) p-channel lateral double-diffused metal-oxide semiconductor (pLDMOS) compatible with high voltage (HV) n-channel LDMOS (nLDMOS) is proposed. The pLDMOS is built in the N-type SOI layer with a buried P-type layer acting as a current conduction path in the on-state (BP SOI pLDMOS). Its superior compatibility with the HV nLDMOS and low voltage (LV) complementary metal-oxide semiconductor (CMOS) circuitry which are formed on the N-SOI layer can be obtained. In the off-state the P-buried layer built in the N-SOI layer causes multiple depletion and electric field reshaping, leading to an enhanced (reduced surface field) (RESURF) effect. The proposed BP SOI pLDMOS achieves not only an improved breakdown voltage (BV) but also a significantly reduced Ron,sp. The BV of the BP SOI pLDMOS increases to 319 V from 215 V of the conventional SOI pLDMOS at the same half cell pitch of 25 μ, and Ron,sp decreases from 157 mΩ·cm2 to 55 mΩ·cm2. Compared with the PW SOI pLDMOS, the BP SOI pLDMOS also reduces the Ron,sp by 34% with almost the same BV.

Spin-correlation function of the fully frustrated Ising model and ± J Ising spin glass on the square lattice

M Y Ali, J Poulter
Chin. Phys. B, 2013, 22 (6): 067502 doi: 10.1088/1674-1056/22/6/067502
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In this work we study the correlation function of the ground state of two-dimensional fully frustrated Ising model as well as spin glass. The Pfaffian method is used to calculate free energy and entropy as well as correlation function. We estimate the exponent of spin correlation function for fully frustrated model and spin glass. In this paper an overview of the latest results on the spin correlation function is presented.

The effects of Zn vacancies on ferromagnetism in Cu-doped ZnO films controlled by oxygen pressure and Li doping

Ran Cong-Jun, Yang Hai-Ling, Wang Yan-Kai, Hassan Farooq M, Zhou Li-Gong, Xu Xiao-Guang, Jiang Yong
Chin. Phys. B, 2013, 22 (6): 067503 doi: 10.1088/1674-1056/22/6/067503
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Zn0.99Cu0.01O films were studied both experimentally and theoretically. The films were prepared by pulsed-laser deposition on Pt(111)/Ti/SiO2/Si substrates under various oxygen pressures to investigate the growth-dependence of ferromagnetic (FM) properties. The structural, magnetic, and optical properties were studied. It was found that all the samples possess a typical wurtzite structure, and the films exhibit room temperature ferromagnetism. The sample deposited at 600 ℃ and oxygen pressure of 10 Pa shows a large saturation magnetization of 0.83 μB/Cu. The enhanced FM in the (Cu, Li)-codoped ZnO is attributable to the existence of Zn vacancies (VZn), as shown by first-principles calculations. The photoluminescence analysis demonstrates the existence of VZn in both Zn0.99Cu0.01O and (Cu, Li)-codoped ZnO thin films, which plays an important role in the increase of ferromagnetism, according to the results of first-principles calculations.

Tunable interface anisotropy in Pt/Co1-xFex/Pt multilayer Hot!

Chen Yong-Yong, Shi Zhong, Zhou Shi-Ming, Rui Wen-Bin, Du Jun
Chin. Phys. B, 2013, 22 (6): 067504 doi: 10.1088/1674-1056/22/6/067504
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Interfacial magnetic anisotropy in Pt/Co1-xFex/Pt multilayer is tuned by doping iron atoms into cobalt layer. The perpendicular magnetic anisotropy and out-of-plane coercivity are found to decrease with x increasing. For a specific x, the out-of-plane coercivity acquires a maximal value as a function of the CoFe layer thickness. At low temperature, the coercivity is enhanced. Small coercivity but reasonably large perpendicular magnetic anisotropy can be obtained by controlling x and CoFe layer thickness.

Equivalent oxide thickness scaling of Al2O3/Ge metal-oxide-semiconductor capacitors with ozone post oxidation

Sun Jia-Bao, Yang Zhou-Wei, Geng Yang, Lu Hong-Liang, Wu Wang-Ran, Ye Xiang-Dong, David Zhang Wei, Shi Yi, Zhao Yi
Chin. Phys. B, 2013, 22 (6): 067701 doi: 10.1088/1674-1056/22/6/067701
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Aluminum-oxide films deposited as gate dielectrics on germanium (Ge) by atomic layer deposition (ALD) were post oxidized in an ozone atmosphere. No additional interfacial layer was detected by the high-resolution cross-sectional transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS) measurements made after the ozone post oxidation (OPO) treatment. Decreases in the equivalent oxide thickness of the OPO-treated Al2O3/Ge MOS capacitors were confirmed. Furthermore, a continuous decrease in the gate leakage current was achieved with increasing OPO treatment time. The results can be attributed to the film quality having been improved by the OPO treatment.

The charge storage characteristics of ZrO2 nanocrystallite-based charge trap nonvolatile memory

Tang Zhen-Jie, Li Rong, Yin Jiang
Chin. Phys. B, 2013, 22 (6): 067702 doi: 10.1088/1674-1056/22/6/067702
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ZrO2 nanocrystallite-based charge trap flash memory capacitors incorporating a (ZrO2)0.6(SiO2)0.4 pseudobinary high-k oxide film as the charge trapping layer were prepared and investigated. The precipitation reaction in the charge trapping layer, forming ZrO2 nanocrystallites during rapid thermal annealing, was investigated by transmission electron microscopy and X-ray diffraction. It was observed that a ZrO2 nanocrystallite-based memory capacitor after post-annealing at 850 ℃ for 60 s exhibits a maximum memory window of about 6.8 V, good endurance and a low charge loss of ~ 25% over a period of ten years (determined by extrapolating the charge loss curve measured experimentally), even at 85 ℃. Such 850 ℃-annealed memory capacitors appear to be candidates for future nonvolatile flash memory device applications.

An ultrathin wide-band planar metamaterial absorber based on fractal frequency selective surface and resistive film

Fan Yue-Nong, Cheng Yong-Zhi, Nie Yan, Wang Xian, Gong Rong-Zhou
Chin. Phys. B, 2013, 22 (6): 067801 doi: 10.1088/1674-1056/22/6/067801
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We propose an ultrathin wide-band metamaterial absorber (MA) based on Minkowski (MIK) fractal frequency selective surface (FSS) and resistive films. This absorber consists of a periodic arrangement of dielectric substrate sandwiched with MIK fractal loop structure electric resonator and resistive film. The finite element method (FEM) is used to simulate and analyze the absorption of MA. Compared with the MA backed copper film, the designed MA backed resistive film exhibits an absorption of 90% in a frequency region of 2 GHz-20 GHz. The power loss density distribution of MA is further illustrated to explain the mechanism of proposed MA. Simulated absorptions in different cases of incidence indicate that this absorber is polarization-insensitive and of wide-angle. Finally, the further simulated results indicate that surface resistance of resistive film and dielectric constant of substrate can affect the absorbing property of the MA. This absorber may be used in many military fields.

Planar terahertz metamaterial with three-resonant frequencies

Chen Zhi, Zhang Ya-Xin
Chin. Phys. B, 2013, 22 (6): 067802 doi: 10.1088/1674-1056/22/6/067802
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In this paper, we study a three-resonant metamaterial with the combination of dual-resonant and single-resonant metamaterials. It presents a new method to design multi-resonant metamaterial which has a smaller dimension than the general symmetric and asymmetric multi-resonant metamaterials. Theoretical and experimental results show that the structure has three distinct absorption frequencies centering around 0.29 THz, 0.46 THz, and 0.92 THz, and each of them corresponds to a different resonant mode. Due to the well-separation of different resonances, this design provides a unique and effective method to construct multiband terahertz devices.

Mode stability analysis in the beam-wave interaction process for a three-gap Hughes-type coupled cavity chain

Luo Ji-Run, Cui Jian, Zhu Min, Guo Wei
Chin. Phys. B, 2013, 22 (6): 067803 doi: 10.1088/1674-1056/22/6/067803
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Based on space-charge wave theory, the formulae of the beam-wave coupling coefficient and the beam-loaded conductance are given for the beam-wave interaction in an N-gap Hughes-type coupled cavity chain. The ratio of the nonbeam-loaded quality factor of the coupled cavity chain to the beam quality factor is used to determine the stability of the beam-wave interaction. As an example, the stabilities of the beam-wave interaction in a three-gap Hughes-type coupled cavity chain are discussed with the formulae and the CST code for the operations of the 2π, π, and π/2 modes, respectively. The results show that stable operation of the 2π, π, and π/2 modes may all be realized in an extended-interaction klystron with the three-gap Hughes-type coupled cavity chain.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

The investigation of ZnO:Al2O3/metal composite back reflectors in amorphous silicon germanium thin film solar cells

Wang Guang-Hong, Zhao Lei, Yan Bao-Jun, Chen Jing-Wei, Wang Ge, Diao Hong-Wei, Wang Wen-Jing
Chin. Phys. B, 2013, 22 (6): 068102 doi: 10.1088/1674-1056/22/6/068102
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Different aluminum-doped ZnO (AZO)/metal composite thin films, including AZO/Ag/Al, AZO/Ag/nickel-chromium alloy (NiCr), and AZO/Ag/NiCr/Al, are utilized as the back reflectors of p-i-n amorphous silicon germanium thin film solar cells. NiCr is used as diffusion barrier layer between Ag and Al to prevent mutual diffusion, which increases the short circuit current density of solar cell. NiCr and NiCr/Al layers are used as protective layers of Ag layer against oxidation and sulfurization, the higher efficiency of solar cell is achieved. The experimental results show that the performance of a-SiGe solar cell with AZO/Ag/NiCr/Al back reflector is best. The initial conversion efficiency is achieved to be 8.05%.

Effects of ramp vibrational states on flexural intrinsic vibrations in Besocke-style scanners

Zhang Hui, Jiang Guo-Zhu, Liu Zhao-Qun, Zhang Shu-Yi, Fan Li
Chin. Phys. B, 2013, 22 (6): 068103 doi: 10.1088/1674-1056/22/6/068103
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For both vibrating and steady supporting surfaces of a scanning disc in a Besocke-style piezoelectric scanner, a theoretical model is given by considering the nonlinear lateral friction at the micro-contact interface between the positioning legs and the supporting surface. Numerical simulations demonstrate that unexpected flexural vibrations can arise from a vibrating ramp, and their frequencies are lower than the eigenfrequencies of the scanner in the linearly elastic regime. The vibrations essentially depend on 1) the vibrational states of the supporting ramp and the steel ball tips on the three piezoelectric positioning legs and 2) the tribological characteristics of the contacts between the tips and the ramp. The results give insight into the intrinsic vibrations of the scanners, and are applicable in designing and optimizing piezoelectric scanning systems.

The effect of collision energy on the stereo-dynamics of the reaction H(2S)+NH(X3-, v=0, j=0)→N(4S)+H2

He Di, Wang Mei-Shan, Yang Chuan-Lu, Jiang Zhi-Jun
Chin. Phys. B, 2013, 22 (6): 068201 doi: 10.1088/1674-1056/22/6/068201
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The quasi-classical trajectory (QCT) is calculated to study the stereo-dynamics properties of the title reaction H(2S)+NH(X3-)→N(4S)+H2 on the ground state 4A" potential energy surface (PES) construced by Zhai and Han [2011 J. Chem. Phys. 135 104314]. The calculated QCT reaction probabilities and cross sections are in good agreement with the previous theoretical results. The effects of the collision energy on the k-k' distribution and product polarization of H2 are studied in detail. It is found that the scattering direction of the product is strongly dependent on the collision energy. With the increase of the collision energy, the scattering directions of products change from backward scattering to forward scattering. The distribution of P(θ r) is strongly dependent on collision energy below the lower collision energy (about 11.53 kcal/mol). In addition, the P(φr) distribution dramatically changes as the collision energy increases. The calculated QCT results indicate that the collision energy plays an important role in determining stereo-dynamics of the title reaction.

Stereodynamics study of the exchange reaction O(3P) + CH4→H + OCH3

Cheng Da-Hai, Yuan Jiu-Chuang, Yang Tian-Gang, Chen Mao-Du
Chin. Phys. B, 2013, 22 (6): 068202 doi: 10.1088/1674-1056/22/6/068202
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A new London-Eyring-Polanyi-Sato potential energy surface is employed in this work to study the stereo properties of the O(3P) + CH4 → H + CH3O reaction in its rovibrationally ground state using the quasiclassical trajectory method (QCT). Our calculations are performed at a range of collision energies, Ec = 1.5 eV~3.5 eV, and the excitation function obtained by the QCT method accords well with the experimental data. The product rotational polarization is calculated, and the product shows a strong rotational polarization in the centre-of-mass coordinate system. The orientation of the product rotational angular momenta is sensitive to the increase in collision energy, and the alignment of the product rotational angular momenta shows some of the properties of the heavy heavy-light mass combination reactions. In the isotopic substituted reaction study, when the H atoms in methane are replaced by D atoms, the rotational polarization is obviously reduced. The polarization-dependent differential cross section is also studied by this QCT calculation to provide detailed information about the rotational alignment and orientation of the product.

A theoretical study of the stereodynamics on the abstraction reactions H/D+HS/DS

Xu Guo-Liang, Liu Pei, Liu Yan-Lei, Liu Yu-Fang, Yuan Wei, Zhang Xian-Zhou
Chin. Phys. B, 2013, 22 (6): 068203 doi: 10.1088/1674-1056/22/6/068203
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The quasi-classical trajectory (QCT) method is employed to calculate the stereodynamics of the abstraction reactions H/D + HS/DS based on an accurate potential energy surface [Lü S J, Zhang P Y, Han K L and He G Z 2012 J. Chem. Phys. 136 094308]. The reaction cross sections of the title reaction are computed, and the vector correlations for different collision energies and different initial vibrational states are presented. The influences of the collision energy and reagent vibration on the product polarization are studied, and the product polarizations of the title reactions are found to be distinctly different, which arises from the different mass factors, collision energies, and reagent vibrational states.

Effects of rapid thermal annealing on room temperature NO2-sensing properties of WO3 thin film under LED radiation

Hu Ming, Jia Ding-Li, Liu Qing-Lin, Li Ming-Da, Sun Peng
Chin. Phys. B, 2013, 22 (6): 068204 doi: 10.1088/1674-1056/22/6/068204
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WO3 thin films were sputtered onto alumina substrates by DC facing-target magnetron sputtering. One sample was rapid-thermal-annealed (RTA) at 600 ℃ in a gas mixture of N2:O2=4:1, and as a comparison, another was conventionally thermal-annealed at 600 ℃ in air. The morphology of both was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the crystallization structure and phase identification were characterized by X-ray diffraction (XRD). The NO2-sensing measurements were taken under LED light at room temperature. Sensitivity of the RTA-treated sample is high, up to nearly 100, whereas sensitivity of the conventionally thermal-annealed sample is about 5 under the same conditions. From the much better selectivity and response-recovery characteristics, it can be concluded that, compared to conventional thermal annealing, RTA has a greater effect on the NO2-sensing properties of WO3 thin films.

The voltage current relationship and equivalent circuit implementation of parallel flux-controlled memristive circuits

Bao Bo-Cheng, Feng Fei, Dong Wei, Pan Sai-Hu
Chin. Phys. B, 2013, 22 (6): 068401 doi: 10.1088/1674-1056/22/6/068401
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A flux-controlled memristor characterized by smooth cubic nonlinearity is taken as an example, upon which the voltage-current relationships (VCRs) between two parallel memristive circuits, i.e., parallel memristor and capacitor circuit (called as parallel MC circuit), and parallel memristor and inductor circuit (called as parallel ML circuit), are investigated. The results indicate that the VCR between these two parallel memristive circuits is closely related to the circuit parameters, and the frequency and amplitude of the sinusoidal voltage stimulus. Equivalent circuit model of the memristor is built, upon which the circuit simulations and experimental measurements of both parallel MC circuit and parallel ML circuit are performed, of which the results verify the theoretical analysis results.

Comparative study of electrical properties of Au/n-Si (MS) and Au/Si3N4/n-Si (MIS) Schottky diodes

Adem Tataroğlu
Chin. Phys. B, 2013, 22 (6): 068402 doi: 10.1088/1674-1056/22/6/068402
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In this paper, the electrical parameters of Au/n-Si (MS) and Au/Si3N4/n-Si (MIS) Schottky diodes are obtained from the forward bias current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. Experimental results show that the rectifying ratios of MS and MIS diode at ± 5 V are found to be 1.25×103 and 1.27×104, respectively. The main electrical parameters of MS and MIS diode, such as the zero-bias barrier height (Φ Bo) and ideality factor (n) are calculated to be 0.51 eV (I-V), 0.53 eV (C-V), and 4.43, and 0.65 eV (I-V), 0.70 eV (C-V), and 3.44, respectively. Also, the energy density distribution profile of the interface states (Nss) is obtained from the forward bias I-V. In addition, the values of series resistance (Rs) for the two diodes are calculated from Cheung's method and Ohm's law.

High voltage super-junction lateral double diffused metal-oxide semiconductor with partial lightly doped pillar

Wu Wei, Zhang Bo, Fang Jian, Luo Xiao-Rong, Li Zhao-Ji
Chin. Phys. B, 2013, 22 (6): 068501 doi: 10.1088/1674-1056/22/6/068501
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A novel super-junction lateral double diffused metal-oxide semiconductor (SJ-LDMOS) with partial lightly doped P pillar (PD) is proposed. Firstly, the reduction of the charges in the partial P pillar ensures the charge balance and suppresses the substrate assisted depletion effect. Secondly, the new electric field peak produced by P/P- junction modulates the surface electric field distribution. Both of them result in a high breakdown voltage (BV). In addition, due to the same conduction paths, the specific on-resistance (Ron,sp) of the PD SJ-LDMOS is approximately identical to the conventional SJ-LDMOS. Simulation results indicate that the average value of the surface lateral electric field of the PD SJ-LDMOS reaches 20 V/μm at 15-μm drift length, resulting in a BV of 300 V.

Hardening measures for bipolar transistor against microwave-induced damage

Chai Chang-Chun, Ma Zhen-Yang, Ren Xing-Rong, Yang Yin-Tang, Zhao Ying-Bo, Xin Hai
Chin. Phys. B, 2013, 22 (6): 068502 doi: 10.1088/1674-1056/22/6/068502
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In the present paper we study the influences of the bias voltage and the external components on the damage progress of a bipolar transistor induced by high power microwave (HPM). The mechanism is presented by analyzing the variation of device internal distribution of the temperature. The findings show that the device becomes less vulnerable to damage with the increase of bias voltage. Both the series diode at the base and the relatively low series resistance at the emitter Re can make the burnout time of the device prolonged obviously. However, Re will aid the damage of the device when the value is sufficiently high due to the fact that the highest hot spot shifts from the base-emitter junction to the base region. Moreover, the series resistance at the base Rb will weaken the capability of the device to withstand microwave damage.

AlGaN/GaN high-electron-mobility transistor with transparent gate by Al-doped ZnO

Wang Chong, He Yun-Long, Zheng Xue-Feng, Ma Xiao-Hua, Zhang Jin-Cheng, Hao Yue
Chin. Phys. B, 2013, 22 (6): 068503 doi: 10.1088/1674-1056/22/6/068503
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AlGaN/GaN high electron mobility transistors (HEMTs) with Al-doped ZnO (AZO) transparent gate electrodes are fabricated, and the Ni/Au/Ni-gated HEMTs are produced in comparison. The AZO-gated HEMTs show good DC characteristics and Schottky rectifying characteristics, and the gate electrodes achieve excellent transparencies. Compared with Ni/Au/Ni-gated HEMTs, AZO-gated HEMTs show low saturation current, high threshold voltage, high Schottky barrier height, and low gate reverse leakage current. Due to the higher gate resistivity, AZO-gated HEMT exhibits current-gain cutoff frequency (fT) of 10 GHz and power gain cutoff frequency (fmax) of 5 GHz, and lower maximum oscillation frequency than Ni/Au/Ni-gated HEMTs. Moreover, the characteristics of C-V are measured, and the gate interface characteristics of the AZO-gated devices are investigated by C-V dual sweep.

Residual gas properties in field emission device with ZnO emitters

Wang Jin-Chan
Chin. Phys. B, 2013, 22 (6): 068504 doi: 10.1088/1674-1056/22/6/068504
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In this paper, a vacuum system is employed to compare the emission stabilities of the same ZnO cathode in a sealed field emission (FE) device and under ultrahigh vacuum (UHV) condition. It is observed that the emission current is more stable under the UHV level than that in the device. When all conditions except the ambient gases are kept unchanged, the emission current degradation is mainly caused by the residual gases in the sealed device. The quadrupole mass spectrometer (QMS) equipped on the vacuum system is used to investigate the residual gas components. Based on the QMS data obtained, the following conclusions can be drawn: the residual gases in ZnO-FE-devices are H2, CH4, CO, Ar, and CO2. These residual gases can change the work function at the surface through adsorption or ion bombardment, thereby degrading the emission current of the cathode.

Droop improvement in blue InGaN light emitting diode with GaN/InGaN superlattice barriers

Tong Jin-Hui, Zhao Bi-Jun, Wang Xing-Fu, Chen Xin, Ren Zhi-Wei, Li Dan-Wei, Zhuo Xiang-Jing, Zhang Jun, Yi Han-Xiang, Li Shu-Ti
Chin. Phys. B, 2013, 22 (6): 068505 doi: 10.1088/1674-1056/22/6/068505
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GaN/InGaN superlattice barriers are used in InGaN-based light-emitting diodes (LEDs). The electrostatic field in the quantum wells, electron hole wavefunction overlap, carrier concentration, spontaneous emission spectrum, light-current performance curve, and internal quantum efficiency are numerically investigated by using the APSYS simulation software. It is found that the structure with GaN/InGaN superlattice barriers shows the improved light output power, lower current leakage, and efficiency droop. According to our numerical simulation and analysis, these improvements in the electrical and optical characteristics are mainly attributed to alleviation of the electrostatic field in the active region.

Micromagnetic simulation with three models of FeCo/L10 FePt exchange-coupled particles for bit-patterned media

Wang Ying, Wang Rui, Xie Hai-Long, Bai Jian-Min, Wei Fu-Lin
Chin. Phys. B, 2013, 22 (6): 068506 doi: 10.1088/1674-1056/22/6/068506
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Compositing soft and hard materials is a promising method to decrease the coercivity of L10 FePt, which is considered to be a suitable material for bit patterned media. This paper reports the simulation of three models of FeCo/L10 FePt exchange-coupled composite particles for bit patterned media by micromagnetic simulation software OOMMF. The three models are: enclosed model, side-enclosed model, and top-covered model. All of them have the same volumes of soft and hard parts but different shapes. Simulation results show that the switching fields for the three models can be reduced to about 10 kOe (1 Oe = 79.5775 A/m) and the factor gain can be improved to 1.4 when the interface exchange coefficient has a proper value. Compared to the other models, the enclosed model has a wider range of interface exchange coefficient values in which low switching field and high gain can be obtained. The dependence of switching fields on the angle of the applied field shows that none of the three models are easily affected by the stray field of a magnetic head.

Non-isothermal kinetics of styrene-butadiene-styrene asphalt combustion

Wu Ke, Zhu Kai, Han Jun, Wang Jin-Chang, Huang Zhi-Yi, Liang Pei
Chin. Phys. B, 2013, 22 (6): 068801 doi: 10.1088/1674-1056/22/6/068801
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The combustion characteristics of styrene-butadiene-styrene (SBS) asphalt are studied by thermogravimetric analysis (TG/DTG) at four different heating rates. According to the saturates/aromatics/resins/asphaltenes (SARA) fractionation method, the combustion process of SBS asphalt can be divided by Gaussian peak fitting into three main stages: oil content release, resin pyrolysis, and asphaltene and char combustion. When the heating rate increases, the mass losses of the oil content and resin pyrolysis increase, and less asphaltenes are formed at a higher temperature. The activation energy values are calculated by the Coats-Redfern method to be in the range 61.6 kJ/mol-142.9 kJ/mol. The Popescu method is used for the kinetic analysis, and the result shows that the three stages of asphalt combustion can be explained by the sphere phase boundary reaction model, the second order chemical reaction model, nucleation, and its subsequent growth model, respectively.

The effects of InGaN layer thickness on the performance of InGaN/GaN p-i-n solar cells

Li Liang, Zhao De-Gang, Jiang De-Sheng, Liu Zong-Shun, Chen Ping, Wu Liang-Liang, Le Ling-Cong, Wang Hui, Yang Hui
Chin. Phys. B, 2013, 22 (6): 068802 doi: 10.1088/1674-1056/22/6/068802
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InGaN/GaN p–i–n solar cells, each with an undoped In0.12Ga0.88N absorption layer, are grown on c-plane sapphire substrates by metal–organic chemical vapor deposition. The effects of the thickness and dislocation density of the absorption layer on the collection efficiency of InGaN-based solar cells are analyzed, and the experimental results demonstrate that the thickness of the InGaN layer and the dislocation density significantly affect the performance. An optimized InGaNbased solar cell with a peak external quantum efficiency of 57% at a wavelength of 371 nm is reported. The full width at half maximum of the rocking curve of the (0002) InGaN layer is 180 arcsec.

Analysis of network traffic flow dynamics based on gravitational field theory

Liu Gang, Li Yong-Shu, Zhang Xi-Ping
Chin. Phys. B, 2013, 22 (6): 068901 doi: 10.1088/1674-1056/22/6/068901
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For further research on the gravity mechanism of routing protocol on complex networks, we introduce the concept of routing awareness depth, represented with ρ . On this basis, we define the calculating formula of the gravity of the transmission route for the packet, and propose a routing strategy based on gravitational field of node and routing awareness depth. In order to characterize the efficiency of the method, we introduce an order parameter η to measure the throughput of the network by the critical value of phase transition from free flow to congestion, and use the node betweenness centrality B to test the transmission efficiency of the network and congestion distribution. We simulate the network transmission performance under different values of routing awareness depth ρ . Simulation results show that if the value of routing awareness depth ρ is too small, the gravity of the route is composed of the attraction of very few nodes on the route, which cannot improve the capacity of the network effectively; if the value of routing awareness depth ρ is greater than the network's average distance <l>, the capacity of the network may be improved greatly and no longer change with the sustainable increment of routing awareness depth ρ , the performance of the routing strategy enters into a constant state; moreover, whatever the value of routing awareness depth ρ is, our algorithm always effectively balances the distribution of betweenness centrality and realizes the equal distribution of network load.
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