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Chin. Phys. B  
  Chin. Phys. B--2006, Vol.15, No.6
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New insights to old problems

Lee T. D.
Chin. Phys. B 2006, 15 (6): 01125;  doi: 10.1088/1009-1963/15/6/001
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From the history of the theta--tau puzzle and the discovery of parity non-conservation in 1956, we review the current status of discrete symmetry violations in the weak interaction. Possible origin of these symmetry violations are discussed.

First integrals and stability of second-order differential equations

Xu Xue-Jun, Mei Feng-Xiang
Chin. Phys. B 2006, 15 (6): 01134;  doi: 10.1088/1009-1963/15/6/002
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The stability of second-order differential equations is studied by using their integrals. A system of second-order differential equations can be considered as a mechanical system with holonomic constraints. A conserved quantity of the mechanical system or a part of the system is obtained by using the Noether theory. It is possible that the conserved quantity becomes a Liapunov function and the stability of the system is proved by the Liapunov theorem.

Interaction of a submerged horseshoe vortex with a free surface

Wu Yun-Gang, Tao Ming-De
Chin. Phys. B 2006, 15 (6): 01137;  doi: 10.1088/1009-1963/15/6/003
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In this paper a submerged horseshoe vortex under a free surface is discussed and the algebraic expression of the wave elevation is obtained. From this expression, some characteristics of the ship wave are described. There exists a smooth region near $\theta = 0^\circ$, but when the uniform stream passes the other singularities (source, sink, doublet, etc.) there is no smooth region. The mechanism of synthetic aperture radar (SAR) images of the narrow ship wakes is also explained.

New exact solitary wave solutions to generalized mKdV equation and generalized Zakharov--Kuzentsov equation

Taogetusang, Sirendaoreji
Chin. Phys. B 2006, 15 (6): 01143;  doi: 10.1088/1009-1963/15/6/004
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In this paper, based on hyperbolic tanh-function method and homogeneous balance method, and auxiliary equation method, some new exact solitary solutions to the generalized mKdV equation and generalized Zakharov--Kuzentsov equation are constructed by the method of auxiliary equation with function transformation with aid of symbolic computation system Mathematica. The method is of important significance in seeking new exact solutions to the evolution equation with arbitrary nonlinear term.

Head-on collision of ring dark solitons in Bose--Einstein condensates

Xue Ju-Kui, Peng Ping
Chin. Phys. B 2006, 15 (6): 01149;  doi: 10.1088/1009-1963/15/6/005
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The ring dark solitons and their head-on collisions in a Bose--Einstein condensates with thin disc-shaped potential are studied. It is shown that the system admits a solution with two concentric ring solitons, one moving inwards and the other moving outwards, which in small-amplitude limit, are described by the two cylindrical KdV equations in the respective reference frames. By using the extended Poincar\'e--Lighthill--Kuo perturbation method, the analytical phase shifts following the head-on collisions between two ring dark solitary waves are derived. It is shown that the phase shifts decrease with the radial coordinate $r$ according to the $r^{-1/3}$ law and depend on the initial soliton amplitude and radius.

Subwavelength rectangular cavity partially filled with left-handed materials

Jiang Tian, Chen Yan, Feng Yi-Jun
Chin. Phys. B 2006, 15 (6): 01154;  doi: 10.1088/1009-1963/15/6/006
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In this paper, we present the electromagnetic analysis of a rectangular cavity partially filled with a left-handed material slab. Our theoretical investigation shows that there exist novel resonant modes in the cavity, and such a cavity becomes a subwavelength cavity. The eigenvalue equation of the cavity is derived and the resonant frequencies of the novel modes are calculated by using numerical simulation. We also discuss the stability of the novel resonant modes and show the best condition under which a useful rectangular cavity of subwavelength dimensions with tolerable stability is obtained.

Entanglement dynamics in two-component Bose--Einstein condensates

Hao Ya-Jiang, Liang Jiu-Qing
Chin. Phys. B 2006, 15 (6): 01161;  doi: 10.1088/1009-1963/15/6/007
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Based on the exact solution of the time-dependent Schr\"{o}dinger equation for two-species Bose--Einstein condensates (BECs) consisting of two hyperfine states of the atoms coupled by a tuned adiabatic and time-varying Raman coupling, we obtain analytically the entanglement dynamics of the system with various initial states, particularly the SU(2) coherent state, for both of cases with and without the nonlinear interactions. It is shown that the effect of nonlinear interaction on the entanglement appears only in a longer time period depending on the BEC parameters.

Critical radius and dipole polarizability for a confined system

Xu Tian, Cao Zhuang-Qi, Ou Yong-Cheng, Shen Qi-Shun, Zhu Guo-Long
Chin. Phys. B 2006, 15 (6): 01172;  doi: 10.1088/1009-1963/15/6/008
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The analytical transfer matrix method (ATMM) is applied to calculating the critical radius $r_{\rm c}$ and the dipole polarizability $\alpha_{\rm d}$ in two confined systems: the hydrogen atom and the Hulth\'{e}n potential. We find that there exists a linear relation between $r_{\rm c}^{1/2}$ and the quantum number $n_{r}$ for a fixed angular quantum number $l$, moreover, the three bounds of $\alpha_{\rm d}$ ($\alpha_{\rm d}^{K}$, $\alpha_{\rm d}^{B}$, $\alpha_{\rm d}^{U}$) satisfy an inequality: $\alpha_{\rm d}^{K}\leq\alpha_{\rm d}^{B}\leq\alpha_{\rm d}^{U}$. A comparison between the ATMM, the exact numerical analysis, and the variational wavefunctions shows that our method works very well in the systems.

Probabilistically implementing nonlocal operations between two distant qutrits

Shan Yong-Guang, Nie Jian-Jun, Zeng Hao-Sheng
Chin. Phys. B 2006, 15 (6): 01177;  doi: 10.1088/1009-1963/15/6/009
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We propose a method to probabilistically implement a nonlocal operation, $% \exp {[}\i\xi U_{A}U_{B}{]}$, between two distant qutrits $A$ and $B$, where $% \xi \in [0,2\pi ]$ and $U_{A}$, $U_{B}$ are local unitary and Hermitian operations for qutrits $A$ and $B$ respectively. The consumptions of resource for one performance of the method are a single non-maximally entangled qutrit state and 1-trit classical communication. For a given $\xi $% , the successful probability of the method depends on the forms of both entanglement resource and Bob's partial-measurement basis. We systematically discuss the optimal successful probabilities and their corresponding conditions for three cases: adjustable entanglement resource, adjustable partial-measurement basis, adjustable entanglement resource and partial-measurement basis. It is straightforward to generalize the method for producing nonlocal unitary operations between any two $N$-level systems.

Thermodynamical quantities around\\[1.8mm] a RNAdS black hole

Mi Li-Qin, Li Zhong-Heng
Chin. Phys. B 2006, 15 (6): 01184;  doi: 10.1088/1009-1963/15/6/010
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The entropy density, energy density, pressure and equation of state around the RNAdS black hole are calculated in the WKB approximation on the Teukolsky-type master equation. The appearance of spin-dependent terms is demonstrated. The existence of these terms shows that the black hole radiation is not exactly thermal radiation and the black hole entropy is not strictly proportional to the area of the event horizon.

Finite-time control of chaotic systems with nonlinear inputs

Gao Tie-Gang, Chen Zeng-Qiang, Chen Guan-Rong, Yuan Zhu-Zhi
Chin. Phys. B 2006, 15 (6): 01190;  doi: 10.1088/1009-1963/15/6/011
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A finite-time controller is designed for a class of nonlinear systems subject to sector nonlinear inputs. A novel and simple approach is suggested based on the finite-time control principle. The designed sliding-mode controller can drive a chaotic system to track a smooth target signal in a finite time. The chaotic Duffing--Holmes oscillator is used for verification and demonstration.

Chaotic time series prediction using fuzzy sigmoid kernel-based support vector machines

Liu Han, Liu Ding, Deng Ling-Feng
Chin. Phys. B 2006, 15 (6): 01196;  doi: 10.1088/1009-1963/15/6/012
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Support vector machines (SVM) have been widely used in chaotic time series predictions in recent years. In order to enhance the prediction efficiency of this method and implement it in hardware, the sigmoid kernel in SVM is drawn in a more natural way by using the fuzzy logic method proposed in this paper. This method provides easy hardware implementation and straightforward interpretability. Experiments on two typical chaotic time series predictions have been carried out and the obtained results show that the average CPU time can be reduced significantly at the cost of a small decrease in prediction accuracy, which is favourable for the hardware implementation for chaotic time series prediction.

Analysing chaos in fractional-order systems with the harmonic balance method

Wu Zheng-Mao, Lu Jun-Guo, Xie Jian-Ying
Chin. Phys. B 2006, 15 (6): 01201;  doi: 10.1088/1009-1963/15/6/013
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In this paper, the fractional-order Genesio--Tesi system showing chaotic behaviours is introduced, and the corresponding one in an integer-order form is studied intensively. Based on the harmonic balance principle, which is widely used in the frequency analysis of nonlinear control systems, a theoretical approach is used to investigate the conditions of system parameters under which this fractional-order system can give rise to a chaotic attractor. Finally, the numerical simulation is used to verify the validity of the theoretical results.

Prediction of chaotic systems with multidimensional recurrent least squares support vector machines

Sun Jian-Cheng, Zhou Ya-Tong, Luo Jian-Guo
Chin. Phys. B 2006, 15 (6): 01208;  doi: 10.1088/1009-1963/15/6/014
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In this paper, we propose a multidimensional version of recurrent least squares support vector machines (MDRLS-SVM) to solve the problem about the prediction of chaotic system. To acquire better prediction performance, the high-dimensional space, which provides more information on the system than the scalar time series, is first reconstructed utilizing Takens's embedding theorem. Then the MDRLS-SVM instead of traditional RLS-SVM is used in the high-dimensional space, and the prediction performance can be improved from the point of view of reconstructed embedding phase space. In addition, the MDRLS-SVM algorithm is analysed in the context of noise, and we also find that the MDRLS-SVM has lower sensitivity to noise than the RLS-SVM.

The generation of a hyperchaotic system based on a three-dimensional autonomous chaotic system

Wang Jie-Zhi, Chen Zeng-Qiang, Yuan Zhu-Zhi
Chin. Phys. B 2006, 15 (6): 01216;  doi: 10.1088/1009-1963/15/6/015
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This paper reports a new four-dimensional hyperchaotic system obtained by adding a controller to a three-dimensional autonomous chaotic system. The new system has two parameters, and each equation of the system has one quadratic cross-product term. Some basic properties of the new system are analysed. The different dynamic behaviours of the new system are studied when the system parameter $a$ or $b$ is varied. The system is hyperchaotic in several different regions of the parameter $b$. Especially, the two positive Lyapunov exponents are both larger, and the hyperchaotic region is also larger when this system is hyperchaotic in the case of varying $a$. The hyperchaotic system is analysed by Lyapunov-exponents spectrum, bifurcation diagrams and Poincar\'{e} sections.

Control of beam halo-chaos by sample function

Bai Long, Zhang Rong, Weng Jia-Qiang, Luo Xiao-Shu, Fang Jin-Qing
Chin. Phys. B 2006, 15 (6): 01226;  doi: 10.1088/1009-1963/15/6/016
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The K-V beam through an axisymmetric uniform-focusing channel is studied using the particle--core model. The beam halo-chaos is found, and a sample function controller is proposed based on mechanism of halo formation and strategy of controlling halo-chaos. We perform multiparticle simulation to control the halo by using the sample function controller. The numerical results show that our control method is effective. We also find that the radial ion density changes when the ion beam is in the channel: not only can the halo-chaos and its regeneration be eliminated by using the sample function control method, but also the density uniformity can be found at the beam's centre as long as an appropriate control method is chosen.

Analysis of stochastic bifurcation and chaos in stochastic Duffing--van der Pol system via Chebyshev polynomial approximation

Ma Shao-Juan, Xu Wei, Li Wei, Fang Tong
Chin. Phys. B 2006, 15 (6): 01231;  doi: 10.1088/1009-1963/15/6/017
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The Chebyshev polynomial approximation is applied to investigate the stochastic period-doubling bifurcation and chaos problems of a stochastic Duffing--van der Pol system with bounded random parameter of exponential probability density function subjected to a harmonic excitation. Firstly the stochastic system is reduced into its equivalent deterministic one, and then the responses of stochastic system can be obtained by numerical methods. Nonlinear dynamical behaviour related to stochastic period-doubling bifurcation and chaos in the stochastic system is explored. Numerical simulations show that similar to its counterpart in deterministic nonlinear system of stochastic period-doubling bifurcation and chaos may occur in the stochastic Duffing--van der Pol system even for weak intensity of random parameter. Simply increasing the intensity of the random parameter may result in the period-doubling bifurcation which is absent from the deterministic system.

Dynamic behaviours of mix-game model and its application

Gou Cheng-Ling
Chin. Phys. B 2006, 15 (6): 01239;  doi: 10.1088/1009-1963/15/6/018
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In this paper a minority game (MG) is modified by adding into it some agents who play a majority game. Such a game is referred to as a mix-game. The highlight of this model is that the two groups of agents in the mix-game have different bounded abilities to deal with historical information and to count their own performance. Through simulations, it is found that the local volatilities change a lot by adding some agents who play the majority game into the MG, and the change of local volatilities greatly depends on different combinations of historical memories of the two groups. Furthermore, the analyses of the underlying mechanisms for this finding are made. The applications of mix-game mode are also given as an example.

A cellular automata model of epidemics of a heterogeneous susceptibility

Jin Zhen, Liu Quan-Xing
Chin. Phys. B 2006, 15 (6): 01248;  doi: 10.1088/1009-1963/15/6/019
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In this paper we present a model with spatial heterogeneity based on cellular automata (CA). In the model we consider the relevant heterogeneity of host (susceptible) mixing and the natural birth rate. We divide the susceptible population into three groups according to the immunity of each individual based on the classical susceptible--infected--removed (SIR) epidemic models, and consider the spread of an infectious disease transmitted by direct contact among humans and vectors that have not an incubation period to become infectious. We test the local stability and instability of the disease-free equilibrium by the spectrum radii of Jacobian. The simulation shows that the structure of the nearest neighbour size of the cell (or the degree of the scale-free networks) plays a very important role in the spread properties of infectious disease. The positive equilibrium of the infections versus the neighbour size follows the third power law if an endemic equilibrium point exists. Finally, we analyse the feature of the infection waves for the homogeneity and heterogeneous cases respectively.

Structure and analytical potential energy function for the ground state of the BCx (x=0, -1)

Geng Zhen-Duo, Zhang Yan-Song, Fan Xiao-Wei, Lu Zhan-Sheng, Luo Gai-Xia
Chin. Phys. B 2006, 15 (6): 01257;  doi: 10.1088/1009-1963/15/6/020
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In this paper, the electronic states of the ground states and dissociation limits of BC and BC$^-$ are correctly determined based on group theory and atomic and molecular reaction statics. The equilibrium geometries, harmonic frequencies and dissociation energies of the ground state of BC and BC$^-$ are calculated by using density function theory and quadratic CI method including single and double substitutions. The analytical potential energy functions of these states have been fitted with Murrell--Sorbie potential energy function from our ab initio calculation results. The spectroscopic data ($\alpha _\e $, $\omega _\e $ and $\omega _\e \chi _\e )$ of each state is calculated via the relation between analytical potential energy function and spectroscopic data. All the calculations are in good agreement with the experimental data.

Quantum interference effects in a multidriven transition Fg = 3\leftrightarrow Fe = 2

Dong Ya-Bin, Zhang Jun-Xiang, Wang Hai-Hong, Gao Jiang-Rui
Chin. Phys. B 2006, 15 (6): 01262;  doi: 10.1088/1009-1963/15/6/021
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We have theoretically and experimentally studied the quantum coherence effects of a degenerate transition $F_g = 3 \leftrightarrow F_e = 2$ system interacting with a weak linearly polarized (with $\sigma _\pm $ components) probe light and a strong linearly polarized (with $\sigma _\pm $ components) coupling field. Due to the competition between the drive Rabi frequency and the Zeeman splitting, electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) are present at the different values of applied magnetic field in the case where the Zeeman splitting of excited state $\Delta e$ is larger than the Zeeman splitting of ground state ${\Delta} g$ (i.e. ${\Delta} e > {\Delta} g)$.

Observation of four-wave mixing in caesium atoms using a noncycling transition

Wang Li-Rong, Ma Jie, Zhao Jian-Ming, Xiao Lian-Tuan, Jia Suo-Tang
Chin. Phys. B 2006, 15 (6): 01268;  doi: 10.1088/1009-1963/15/6/022
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In this paper the generation of four-wave mixing (FWM) signal using a noncycling transition of caesium atoms is investigated when the pumping laser is locked to the transition $6{\rm S}_{1/2}F=4\to6{\rm P}_{3/2}F'=4$, and meanwhile the probe frequency is scanned across the $6{\rm S}_{1/2}F=4 \to6{\rm P}_{3/2}$ transition. The efficiency of the four-wave mixing signal as a function of the intensity of the pumping beams and the detuning of the pumping beams is also studied. In order to increase the detection efficiency, a repumping laser which is resonant with $6{\rm S}_{1/2} F=3\to 6{\rm P}_{3/2}F'=4$ transition is used. A theoretical model is also introduced, and the theoretical results are in qualitative agreement with experimental ones.

Ultraviolet and visible upconversion dynamics in Er3+:YAlO3 under 2H11/2 excitation

Yang Hai-Gui, Dai Zhen-Wen, Sun Zhi-Wei
Chin. Phys. B 2006, 15 (6): 01273;  doi: 10.1088/1009-1963/15/6/023
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The luminescence of Er$^{3+}$:YAlO$_{3}$ in ultraviolet, visible and infrared ranges under the 518\,nm excitation of the multiples $^{2}$H$_{11 / 2}$ have been investigated. Ultraviolet (275\,nm and 318\,nm), violet (405\,nm and 413\,nm) and blue (474\,nm) upconversion and infrared downconversion luminescence has been observed. By means of measuring the fluorescence decay curves and using the theory of rate equations, the luminescence kinetics was studied in detail and the processes of energy transfer upconversion (ETU) and excitation state absorption (ESA) were proposed to explain the upconversion phenomena.

A modification potential method of calculating total cross sections of electrons scattering from complex molecules C2H6, C2F6,C6H6 and C6F6 at 100eV--5000eV

Shi De-Heng, Sun Jin-Feng, Zhu Zun-Lue, Liu Yu-Fang, Yang Xiang-Dong
Chin. Phys. B 2006, 15 (6): 01278;  doi: 10.1088/1009-1963/15/6/024
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A complex optical model potential modified by incorporating the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds between two atoms in a molecule, is first employed to calculate the total cross sections for electrons scattering from such complex molecules as C$_{2}$H$_{6}$, C$_{2}$F$_{6}$, C$_{6}$H$_{6}$ and C$_{6}$F$_{6}$ using the additivity rule model at Hartree--Fock level over the energy range from 100~eV to 5000~eV. The total cross sections are quantitatively compared with those obtained by experiments wherever available, and they are in good agreement with each other over a wide energy range. It is shown that the modified potential together with the additivity rule model is completely suitable for the calculation of total cross sections of electrons scattering from such complex molecules as C$_{2}$H$_{6}$, C$_{2}$F$_{6}$, C$_{6}$H$_{6}$ and C$_{6}$F$_{6}$ above 200~eV--300~eV.

Deterministic quantum key distribution based on Gaussian-modulated EPR correlations

He Guang-Qiang, Zeng Gui-Hua
Chin. Phys. B 2006, 15 (6): 01284;  doi: 10.1088/1009-1963/15/6/025
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This paper proposes a deterministic quantum key distribution scheme based on Gaussian-modulated continuous variable EPR correlations. This scheme can implement fast and efficient key distribution. The security is guaranteed by continuous variable EPR entanglement correlations produced by nondegenerate optical parametric amplifier. For general beam splitter eavesdropping strategy, the secret information rate $\Delta I=I(\alpha,\beta)-I(\alpha,\epsilon)$ is calculated in view of Shannon information theory. Finally the security analysis is presented.

TEM study on hollow and porous Cu2O nanoparticles prepared from solution phase

Zhang Huai-Ruo, Yu Hong-Chun, Shen Cheng-Min, Yang Huai-Xin, Li Jian-Qi
Chin. Phys. B 2006, 15 (6): 01290;  doi: 10.1088/1009-1963/15/6/026
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In this paper, hollow and porous Cu$_{2}$O nanoparticles were prepared by adjusting the cationic surfactant cetyltrimethylammonium (CTAB) concentration in the solution-phase reaction. Structural investigations reveal that Cu$_{2}$O nanoparticles can be either well-defined hollow nanoboxes or porous nanocubes depending on the synthesis conditions. The transmission electron microscopy (TEM) observations demonstrated that the nanoparticles in general are composed of small grains coherently growing along certain preferred orientations.

Analysis of the injection layer of PTCDA in OLEDs using x-ray photoemission spectroscopy and atomic force microscopy

Ou Gu-Ping, Song Zhen, Wu You-Yu, Chen Xiao-Qiang, Zhang Fu-Jia
Chin. Phys. B 2006, 15 (6): 01296;  doi: 10.1088/1009-1963/15/6/027
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Through the investigation of the sample surface and interface of 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA)/indium-tin-oxide (ITO) thin films using atomic force microscopy, it has been found that the surface is complanate, the growth is uniform and the defects cover basically the surface of ITO. Furthermore, the number of pinholes is small. The analysis of the sample surface and interface further verifies this result by using x-ray photoemission spectroscopy . At the same time, PTCDA is found to have the ability of restraining the diffusion of chemical constituents from ITO to the hole transport layer, which is beneficial to the improvement of the performance and the useful lifetime of the organic light emitting diodes (OLEDs).

Dislocation energy and Peierls stress: a rigorous calculation from the lattice theory

Wang Shao-Feng
Chin. Phys. B 2006, 15 (6): 01301;  doi: 10.1088/1009-1963/15/6/028
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In the classical Peierls--Nabarro (P-N) theory of dislocation, there is a long-standing contradiction that the stable configuration of dislocation has maximum energy rather than minimum energy. In this paper, the dislocation energy is calculated rigorously in the context of the full lattice theory. It is found that besides the misfit energy considered in the classical P-N theory, there is an extra elastic strain energy that is also associated with the discreteness of lattice. The contradiction can be automatically removed provided that the elastic strain energy associated with the discreteness is taken into account. This elastic strain energy is very important because its magnitude is larger than the misfit energy, its sign is opposite to the misfit energy. Since the elastic strain energy and misfit energy associated with discreteness cancel each other, and the width of dislocation becomes wide in the lattice theory, the Peierls energy, which measures the height of the effective potential barrier, becomes much smaller than that given in the classical P-N theory. The results calculated here agree with experimental data. Furthermore, based on the results obtained, a useful formula of the Peierls stress is proposed to fully include the discreteness effects.

Nickel-disilicide-assisted excimer laser crystallization of amorphous silicon

Liao Yan-Ping, Shao Xi-Bin, Gao Feng-Li, Luo Wen-Sheng, Wu Yuan, Fu Guo-Zhu, Jing Hai, Ma Kai
Chin. Phys. B 2006, 15 (6): 01310;  doi: 10.1088/1009-1963/15/6/029
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Polycrystalline silicon (poly-Si) thin film has been prepared by means of nickel-disilicide (NiSi$_{2})$ assisted excimer laser crystallization (ELC). The process to prepare a sample includes two steps. One step consists of the formation of NiSi$_{2}$ precipitates by heat-treating the dehydrogenated amorphous silicon (a-Si) coated with a thin layer of Ni. And the other step consists of the formation of poly-Si grains by means of ELC. According to the test results of scanning electron microscopy (SEM), another grain growth model named two-interface grain growth has been proposed to contrast with the conventional Ni-metal-induced lateral crystallization (Ni-MILC) model and the ELC model. That is, an additional grain growth interface other than that in conventional ELC is formed, which consists of NiSi$_{2}$ precipitates and a-Si. The processes for grain growth according to various excimer laser energy densities delivered to the a-Si film have been discussed. It is discovered that grains with needle shape and most of a uniform orientation are formed which grow up with NiSi$_{2}$ precipitates as seeds. The reason for the formation of such grains which are different from that of Ni-MILC without migration of Ni atoms is not clear. Our model and analysis point out a method to prepare grains with needle shape and mostly of a uniform orientation. If such grains are utilized to make thin-film transistor, its characteristics may be improved.

Finite element analysis of stress and strain distributions in InAs/GaAs quantum dots

Zhou Wang-Min, Wang Chong-Yu, Chen Yong-Hai, Wang Zhan-Guo
Chin. Phys. B 2006, 15 (6): 01315;  doi: 10.1088/1009-1963/15/6/030
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In this paper, we perform systematic calculations of the stress and strain distributions in InAs/GaAs truncated pyramidal quantum dots (QDs) with different wetting layer (WL) thickness, using the finite element method (FEM). The stresses and strains are concentrated at the boundaries of the WL and QDs, are reduced gradually from the boundaries to the interior, and tend to a uniform state for the positions away from the boundaries. The maximal strain energy density occurs at the vicinity of the interface between the WL and the substrate. The stresses, strains and released strain energy are reduced gradually with increasing WL thickness. The above results show that a critical WL thickness may exist, and the stress and strain distributions can make the growth of QDs a growth of strained three-dimensional island when the WL thickness is above the critical value, and FEM can be applied to investigate such nanosystems, QDs, and the relevant results are supported by the experiments.

Effect of substrate temperature and pressure on properties of microcrystalline silicon films

Wu Zhi-Meng, Lei Qing-Song, Geng Xin-Hua, Zhao Ying, Sun Jian, Xi Jian-Ping
Chin. Phys. B 2006, 15 (6): 01320;  doi: 10.1088/1009-1963/15/6/031
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In this paper intrinsic microcrystalline silicon films have been prepared by very high frequency plasma enhanced chemical vapour deposition (VHF-PECVD) with different substrate temperature and pressure. The film properties were investigated by using Raman spectra, x-ray diffraction, scanning electron microscope (SEM), and optical transmittance measurements, as well as dark conductivity. Raman results indicate that increase of substrate temperature improves the microcrystallinity of the film. The crystallinity is improved when the pressure increases from 50Pa to 80Pa and the structure transits from microcrystalline to amorphous silicon for pressure higher than 80Pa. SEM reveals the effect of substrate temperature and pressure on surface morphology.

Study on the spectral response of the Schottky photodetector of GaN

He Zheng, Kang Yong, Tang Ying-Wen, Li Xue, Fang Jia-Xiong
Chin. Phys. B 2006, 15 (6): 01325;  doi: 10.1088/1009-1963/15/6/032
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The Schottky photodetector was fabricated on GaN epilayers grown by metalorganic chemical vapour deposition (MOCVD). The spectral response of the Schottky photodetector was characterized. A new model is proposed to interpret the characteristic of the spectral response curve of the Schottky photodetectors by introducing a penetrating distance of an incident light at a certain wavelength in the current continuity equation and the interface recombination at the metal--semiconductor rectifying contact. The expressions for the spectral response of the Schottky photodetector are deduced and used successfully to fit the experimental data.

The influence of SiNx substrate on crystallinity of μc-Si film used in thin film transistors

Li Juan, Wu Chun-Ya, Liu Jian-Ping, Zhao Shu-Yun, Meng Zhi-Guo, Xiong Shao-Zhen, Zhang Li-Zhu
Chin. Phys. B 2006, 15 (6): 01330;  doi: 10.1088/1009-1963/15/6/033
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This paper found that the crystalline volume ratio ($X_{\rm c}$) of $\mu$c-Si deposited on SiN$_x$ substrate is higher than that on 7059 glass. At the same silane concentration (SC) (for example, at SC=2{\%}), the $X_{\rm c}$ of $\mu$c-Si deposited on SiN$_x$ is more than 64{\%}, but just 44{\%} if deposited on Conning 7059. It considered that the `hills' on SiN$_x$ substrate would promote the crystalline growth of $\mu$c-Si thin film, which has been confirmed by atomic force microscope (AFM) observation. Comparing several thin film transistor (TFT) samples whose active-layer were deposited under various SC, this paper found that the appropriate SC for the $\mu$c-Si thin film used in TFT as active layer should be more than 2{\%}, and $X_{\rm c}$ should be around 50\%. Additionally, the stability comparison of $\mu$c-Si TFT and a-Si TFT is shown in this paper.

Nanoelectronic devices---resonant tunnelling diodes grown on InP substrates by molecular beam epitaxy with peak to valley current ratio of 17 at room temperature

Zhang Yang, Zeng Yi-Ping, Ma Long, Wang Bao-Qiang, Zhu Zhan-Ping, Wang Liang-Chen, Yang Fu-Hua
Chin. Phys. B 2006, 15 (6): 01335;  doi: 10.1088/1009-1963/15/6/034
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This paper reports that InAs/In$_{0.53}$Ga$_{0.47}$As/AlAs resonant tunnelling diodes have been grown on InP substrates by molecular beam epitaxy. Peak to valley current ratio of these devices is 17 at 300K. A peak current density of 3kA/cm$^{2}$ has been obtained for diodes with AlAs barriers of ten monolayers, and an In$_{0.53}$Ga$_{0.47}$As well of eight monolayers with four monolayers of InAs insert layer. The effects of growth interruption for smoothing potential barrier interfaces have been investigated by high resolution transmission electron microscope.

Novel vertical stack HCMOSFET with strained SiGe/Si quantum channel

Jiang Tao, Zhang He-Ming, Wang Wei, Hu Hui-Yong, Dai Xian-Ying
Chin. Phys. B 2006, 15 (6): 01339;  doi: 10.1088/1009-1963/15/6/035
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A novel vertical stack heterostructure CMOSFET is investigated, which is structured by strained SiGe/Si with a hole quantum well channel in the compressively strained Si$_{1 - x}$Ge$_{x}$ layer for p-MOSFET and an electron quantum well channel in the tensile strained Si layer for n-MOSFET. The device possesses several advantages including: 1) the integration of electron quantum well channel with hole quantum well channel into the same vertical layer structure; 2) the gate work function modifiability due to the introduction of poly-SiGe as a gate material; 3) better transistor matching; and 4) flexibility of layout design of CMOSFET by adopting exactly the same material lays for both n-channel and p-channel. The MEDICI simulation result shows that p-MOSFET and n-MOSFET have approximately the same matching threshold voltages. Nice performances are displayed in transfer characteristic, transconductance and cut-off frequency. In addition, its operation as an inverter confirms the CMOSFET structured device to be normal and effective in function.

Magnetic properties of a three layer superlattice with a crystal field

Jiang Wei, Li Xin, Wang Xi-Kun, Guo An-Bang
Chin. Phys. B 2006, 15 (6): 01346;  doi: 10.1088/1009-1963/15/6/036
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In this paper the magnetic properties of a three layer superlattice with the crystal field on the honeycomb and square lattice have been studied based on the effective-field theory with self-spin correlations and the differential operator technique. The effects of the crystal field and longitudinal magnetic field on the susceptibility are discussed in detail. A number of interesting phenomena, originating from the competition between the longitudinal magnetic field, crystal-field, and coordination number, have been found.

Studies on high-moment soft magnetic FeCo/Co thin films

Fu Yu, Yang Zheng, Mitsunori Matsumoto, Liu Xiao-Xi, Akimitsu Morisako
Chin. Phys. B 2006, 15 (6): 01351;  doi: 10.1088/1009-1963/15/6/037
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The dependences of soft magnetic properties and microstructures of the sputtered FeCo (=Fe$_{65}$Co$_{35}$) films on Co underlayer thickness $t_{\rm Co}$, FeCo thickness $t_{\rm FeCo}$, substrate temperature $T_{\rm s}$ and target-substrate spacing $d_{\rm T-S}$ are studied. FeCo single layer generally shows a high coercivity with no obvious magnetic anisotropy. Excellent soft magnetic properties with saturation magnetization $\mu_{0}M_{\rm s}$ of 2.35 T and hard axis coercivity $H_{\rm ch}$ of 0.25 kA/m in FeCo films can be achieved by introducing a Co underlayer. It is shown that sandwiching a Co underlayer causes a change in orientation and reduction in grain size from 70 nm to about 10 nm in the FeCo layer. The magnetic softness can be explained by the Hoffmann's ripple theory due to the effect of grain size. The magnetic anisotropy can be controlled by changing $d_{\rm T-S}$, and a maximum of 14.3 kA/m for anisotropic field $H_{\rm k}$ is obtained with $d_{\rm T-S}$=18.0 cm.

Equivalent circuit with complex physical constants and equivalent-parameters-expressed dissipation factors of piezoelectric materials

Chen Yu, Wen Yu-Mei, Li Ping
Chin. Phys. B 2006, 15 (6): 01356;  doi: 10.1088/1009-1963/15/6/038
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The equivalent circuit with complex physical constants for a piezoelectric ceramic in thickness mode is established. In the equivalent circuit, electric components (equivalent circuit parameters) are connected to real and imaginary parts of complex physical coefficients of piezoelectric materials. Based on definitions of dissipation factors, three of them (dielectric, elastic and piezoelectric dissipation factors) are represented by equivalent circuit parameters. Since the equivalent circuit parameters are detectable, the dissipation factors can be easily obtained. In the experiments, the temperature and the stress responses of the three dissipation factors are measured.

Paraelectric--ferroelectric interface dynamics induced by latent heat transfer and irreversibility of ferroelectric phase transitions

Ai Shu-Tao
Chin. Phys. B 2006, 15 (6): 01364;  doi: 10.1088/1009-1963/15/6/039
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The temperature gradients that arise in the paraelectric--ferroelectric interface dynamics induced by the latent heat transfer are studied from the point of view that a ferroelectric phase transition is a stationary, thermal-electric coupled transport process. The local entropy production is derived for a ferroelectric phase transition system from the Gibbs equation. Three types of regions in the system are described well by using the Onsager relations and the principle of minimum entropy production. The theoretical results coincides with the experimental ones.

n-type ZnS used as electron transport material in organic light-emitting diodes

Du Peng, Zhang Xi-Qing, Sun Xue-Bai, Yao Zhi-Gang, Wang Yong-Sheng
Chin. Phys. B 2006, 15 (6): 01370;  doi: 10.1088/1009-1963/15/6/040
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This paper reports on the n-type ZnS used as electron transport layer for the organic light-emitting diodes (OLEDs). The naphthyl-substituted benzidine derivative (NPB) and tris (8-hydroxyquinoline) aluminium (Alq$_{3})$ are used as the hole transport layer and the emitting layer respectively. The insertion of the n-type ZnS layer enhances the electron injection in the OLEDs. The study was carried out on OLEDs of structures: indium--tin-oxide (ITO)/NPB/Alq$_{3}$/ZnS/LiF/AL, ITO/NPB/Alq$_{3}$/LiF/AL and ITO/NPB/Alq$_{3}$/AL. The luminance and efficiency of the device containing this electron transport layer are increased significantly over those obtained from conventional devices due to better carrier balance.

The role of hydrogen in hydrogenated microcrystalline silicon film and in deposition process with VHF-PECVD technique

Yang Hui-Dong, Su Zhong-Yi
Chin. Phys. B 2006, 15 (6): 01374;  doi: 10.1088/1009-1963/15/6/041
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The role of hydrogen in hydrogenated microcrystalline silicon ($\mu $c-Si:H) thin films in deposition processes with very high frequency plasma-enhanced chemical vapour deposition (VHF-PECVD) technique have been investigated in this paper. With \textit{in situ} optical emission spectroscopy (OES) diagnosis during the fabrication of $\mu $c-Si:H thin films under different plasma excitation frequency $\nu _{\rm e }$ (60MHz--90MHz), the characteristic peak intensities ($I_{{\rm SiH}^*}$, $I_{{\rm H}\alpha^*}$ and $I_{{\rm H}\beta ^*}$) in SiH$_{4}$+H$_{2}$ plasma and the ratio of ($I_{{\rm H}\alpha^* }$ + $I_{{\rm H}\beta^*}$) to $I_{{\rm SiH}^*}$ were measured; all the characteristic peak intensities and the ratio ($I_{{\rm H}\alpha^* }$ + $I_{{\rm H}\beta^* }$)/$I_{{\rm SiH}^*}$ are increased with plasma excitation frequency. It is identified that high plasma excitation frequency is favourable to promote the decomposition of SiH$_{4}$+H$_{2 }$ to produce atomic hydrogen and SiH$_x$ radicals. The influences of atomic hydrogen on structural properties and that of SiH$_x$ radicals on deposition rate of $\mu $c-Si:H thin films have been studied through Raman spectra and thickness measurements, respectively. It can be concluded that both the crystalline volume fraction and deposition rate are enhanced with the increase of plasma excitation frequency, which is in good accord with the OES results. By means of FTIR measurements, hydrogen contents of $\mu $c-Si:H thin films deposited at different plasma excitation frequency have been evaluated from the integrated intensity of wagging mode near 640 cm$^{ - 1}$. The hydrogen contents vary from 4{\%} to 5{\%}, which are much lower than those of $\mu $c-Si:H films deposited with RF-PECVD technique. This implies that $\mu $c-Si:H thin films deposited with VHF-PECVD technique usually have good stability under light-soaking.

Sensitivity of intrinsic mode functions of Lorenz system to initial values based on EMD method

Zou Ming-Wei, Feng Guo-lin, Gao Xin-Quan
Chin. Phys. B 2006, 15 (6): 01384;  doi: 10.1088/1009-1963/15/6/043
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Extreme sensitivity to initial values is an intrinsic character of chaotic systems. The evolution of a chaotic system has a spatiotemporal structure containing quasi-periodic changes of different spatiotemporal scales. This paper uses an empirical mode decomposition (EMD) method to decompose and compare the evolution of the time-dependent evolutions of the $x$-component of the Lorenz system. The results indicate that the sensitivity of intrinsic mode function (IMF) component is dependent on initial values, which provides some scientific evidence for the possibility of long-range climatic prediction.

Systematical study of the trapping forces of optical tweezers formed by different types of optical ring beams

Xu Sheng-Hua, Li Yin-Mei, Lou Li-Ren
Chin. Phys. B 2006, 15 (6): 01391;  doi: 10.1088/1009-1963/15/6/044
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The technique of optical tweezers has been improved a lot since its invention, which extends the application fields of optical tweezers. Besides the conventionally used Gaussian beams, different types of ring beams have also been used to form optical tweezers for different purposes. The two typical kinds of ring beams used in optical tweezers are the hollow Gaussian beam and Laguerre--Gaussian (LG) beam. Both theoretical computation and experiments have shown that the axial trapping force is improved for the ring beams compared with the Gaussian beam, and hence the trapping stability is improved, although the transverse trapping forces of ring beams are smaller than that of Gaussian beam. However, no systematic study on the trapping forces of ring beam has ever been discussed. In this article, we will investigate the axial and transverse trapping forces of different types of ring beams with different parameters systematically, by numerical computation in which the ray optics model is adopted. The spherical aberration caused by the refractive index mismatch between oil and water is also considered in the article. The trapping forces for different objectives that obey the sine condition and tangent condition are also compared with each other. The result of systematical calculation will be useful for the applications of optical tweezers formed by different types of ring beams.
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