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Chin. Phys. B  
  Chin. Phys. B--2006, Vol.15, No.10
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Three-order pseudo-Hamilton canonical equations

Ma Shan-Jun, Huang Pei-Tian, Yan Rong, Zhao Hong-Xia
Chin. Phys., 2006, 15 (10): 2193-2196 doi: 10.1088/1009-1963/15/10/001
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Based on the three-order Lagrangian equations, Hamilton's function of acceleration H^\ast and generalized acceleration momentum P_\alpha ^\ast are defined, and pseudo-Hamilton canonical equations corresponding to three-order Lagrangian equations are obtained. The equations are similar to Hamilton's canonical equations of analytical mechanics in form.

New non-Noether conserved quantities of mechanical system in phase space

Yan Xiang-Hong, Fang Jian-Hui
Chin. Phys., 2006, 15 (10): 2197-2201 doi: 10.1088/1009-1963/15/10/002
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This paper focuses on studying non-Noether conserved quantities of Lie symmetry and of form invariance for a mechanical system in phase space under the general infinitesimal transformation of groups. We obtain a new non-Noether conserved quantity of Lie symmetry of the system, and Hojman and Mei's results are of special cases of our conclusion. We find a condition under which the form invariance of the system will lead to a Lie symmetry, and, further, obtain a new non-Noether conserved quantity of form invariance of the system. An example is given finally to illustrate these results.

Construction of doubly-periodic solutions to nonlinear partial differential equations using improved Jacobi elliptic function expansion method and symbolic computation

Zhao Xue-Qin, Zhi Hong-Yan, Zhang Hong-Qing
Chin. Phys., 2006, 15 (10): 2202-2209 doi: 10.1088/1009-1963/15/10/003
Full Text: [PDF 133 KB] (Downloads:768)
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Some doubly-periodic solutions of the Zakharov--Kuznetsov equation are presented. Our approach is to introduce an auxiliary ordinary differential equation and use its Jacobi elliptic function solutions to construct doubly-periodic solutions of the Zakharov--Kuznetsov equation, which has been derived by Gottwald as a two-dimensional model for nonlinear Rossby waves. When the modulus k \rightarrow 1, these solutions reduce to the solitary wave solutions of the equation.

New exact solutions to some difference differential equations

Wang Zhen, Zhang Hong-Qing
Chin. Phys., 2006, 15 (10): 2210-2215 doi: 10.1088/1009-1963/15/10/004
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In this paper, we use our method to solve the extended Lotka--Volterra equation and discrete KdV equation. With the help of Maple, we obtain a number of exact solutions to the two equations including soliton solutions presented by hyperbolic functions of \sinh and \cosh, periodic solutions presented by trigonometric functions of \sin and \cos, and rational solutions. This method can be used to solve some other nonlinear difference--differential equations.

Dynamics of solitons in Bose-Einstein condensate with time-dependent atomic scattering length

Li Hua-Mei
Chin. Phys., 2006, 15 (10): 2216-2222 doi: 10.1088/1009-1963/15/10/005
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The evolution of solitons in Bose--Einstein condensates (BECs) with time-dependent atomic scattering length in an expulsive parabolic potential is studied. Based on the extended hyperbolic function method, we successfully obtain the bright and dark soliton solutions. In addition, some new soliton solutions in this model are found. The results in this paper include some in the literature ({\em Phys. Rev. Lett.} {\bf 94} (2005) 050402 and {\em Chin. Phys. Lett.} {\bf 22} (2005) 1855).

On the generator of Lorentz boost

Wang Zhi-Yong, Xiong Cai-Dong
Chin. Phys., 2006, 15 (10): 2223-2227 doi: 10.1088/1009-1963/15/10/006
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Traditionally, the theory related to the spatial angular momentum has been studied completely, while the investigation in the generator of Lorentz boost is inadequate. This paper shows that the generator of Lorentz boost has a nontrivial physical significance: it endows a charged system with an electric moment, and has an important significance for the electrical manipulations of electron spin in spintronics. An alternative treatment and interpretation for the traditional Darwin term and spin--orbit coupling are given.

High-dimension multiparty quantum secret sharing scheme with Einstein-Podolsky-Rosen pairs

Chen Pan, Deng Fu-Guo, Long Gui-Lu
Chin. Phys., 2006, 15 (10): 2228-2235 doi: 10.1088/1009-1963/15/10/007
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In this paper a high-dimension multiparty quantum secret sharing scheme is proposed by using Einstein--Podolsky--Rosen pairs and local unitary operators. This scheme has the advantage of not only having higher capacity, but also saving storage space. The security analysis is also given.

Heisenberg algebra for noncommutative Landau problem

Li Kang, Cao Xiao-Hua, Wang Dong-Yan
Chin. Phys., 2006, 15 (10): 2236-2239 doi: 10.1088/1009-1963/15/10/008
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The Landau problem on non-commutative quantum mechanics is studied, where the Heisenberg algebra and the Landau energy levels as well as the non-commutative angular momentum are constructed in detail in non-commutative space and non-commutative phase space respectively.

Probabilistic teleportation of a non-symmetric three-particle state

Chen Xiu-Bo, Wen Qiao-Yan, Zhu Fu-Chen
Chin. Phys., 2006, 15 (10): 2240-2245 doi: 10.1088/1009-1963/15/10/009
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This paper proposes a scheme for teleporting a kind of essential three-particle non-symmetric entangled state, which is much more valuable than a GHZ and W state for some applications in quantum information processing. In comparison with previous proposal of teleportation, the resources of entangled states as quantum channel and the number of classical messages required by our scheme can be cut down. Moreover, it is shown that there exists a class of transformations which ensure the success of this scheme, because the two-particle transformation performed by the receiver in the course of teleportation may be a generic two-particle operation instead of a control-NOT (CNOT) operation. In addition, all kinds of transformations performed by sender and receiver are given in detail.

A new optical scheme for teleportation of entangled coherent state

Liao Jie-Qiao, Kuang Le-Man
Chin. Phys., 2006, 15 (10): 2246-2251 doi: 10.1088/1009-1963/15/10/010
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We propose a nearly perfect optical scheme for the quantum teleportation of entangled coherent states using optical devices such as nonlinear Kerr media, beam splitters, phase shifters, and photon detectors. Different from those previous schemes, our scheme needs only ``yes' or `no' measurements of the photon number of the related modes, i.e. nonzero- and zero-photon measurements, while in previous schemes one has to exactly identify the even or odd parity character of the photon numbers detected by detectors.

Secret sharing of quantum information via entanglement swapping

Zhang Ying-Qiao, Jin Xing-Ri, Zhang Shou
Chin. Phys., 2006, 15 (10): 2252-2255 doi: 10.1088/1009-1963/15/10/011
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Based on entanglement swapping, a scheme for the secret sharing of an arbitrary two-particle entangled state is proposed. If the controllers do not co-operate with the eavesdropper, the eavesdropper's successful probability decreases with the number of the controllers increasing. In addition, only the Bell-state measurements are required to realize the secret sharing scheme.

Hawking radiation of a uniformly accelerating black hole

Ren Jun, Cao Jiang-Ling, Zhao Zheng
Chin. Phys., 2006, 15 (10): 2256-2259 doi: 10.1088/1009-1963/15/10/012
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In this paper, we study the Hawking radiation via tunnelling from a uniformly accelerating black hole. Although the Bekenstein--Hawking entropy is proportional also to the area of the event horizon, the radius of it, r_{\rm H}, is a function of \theta, which leads to the difficulties in the calculation of the emission rate. In order to overcome the mathematical difficulties, we propose a new technique to calculate the emission rate and the result obtained is reasonable.

Experimental observation of partial amplitude death in coupled chaotic oscillators

Liu Wei-Qing, Yang Jun-Zhong, Xiao Jing-Hua
Chin. Phys., 2006, 15 (10): 2260-2265 doi: 10.1088/1009-1963/15/10/013
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The dynamics of coupled Lorenz circuits is investigated experimentally. The partial amplitude death reported in {\em Phys. Rev.} E {\bf 72}, 057201 (2005) is verified by physical experiments with electronic circuits. With the increase of coupling constant, the coupled circuits undergo the transition from the breakdown of both the reflection symmetry and the translational symmetry to the partial amplitude death. Its stability is also confirmed by analysing the effects of noise.

Passive control of chaotic system with multiple strange attractors

Song Yun-Zhong, Zhao Guang-Zhou, Qi Dong-Lian
Chin. Phys., 2006, 15 (10): 2266-2270 doi: 10.1088/1009-1963/15/10/014
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In this paper we present a new simple controller for a chaotic system, that is, the Newton--Leipnik equation with two strange attractors: the upper attractor (UA) and the lower attractor (LA). The controller design is based on the passive technique. The final structure of this controller for original stabilization has a simple nonlinear feedback form. Using a passive method, we prove the stability of a closed-loop system. Based on the controller derived from the passive principle, we investigate three different kinds of chaotic control of the system, separately: the original control forcing the chaotic motion to settle down to the origin from an arbitrary position of the phase space; the chaotic intra-attractor control for stabilizing the equilibrium points only belonging to the upper chaotic attractor or the lower chaotic one, and the inter-attractor control for compelling the chaotic oscillation from one basin to another one. Both theoretical analysis and simulation results verify the validity of the suggested method.

Time-resolved measurement of atomic emission enhancement by fs--ns dual-pulsed laser-induced breakdown spectroscopy

Yan Li-Xin, Zhang Yong-Sheng, Zheng Guo-Xin, Liu Jing-Ru, Cheng Jian-Ping, Lü Min
Chin. Phys., 2006, 15 (10): 2271-2274 doi: 10.1088/1009-1963/15/10/015
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Time-resolved measurement of atomic emission enhancement is performed by using a 500-fs KrF laser pulse incident upon a high density supersonic O_{2} gas jet, synchronized with an orthogonal ns frequency-doubled Nd:YAG laser pulse. The ultra-short pulse serves as an igniter of the gas jet, and the subsequent ns-laser pulse significantly enhances the atomic emission. Analysis shows that the contributions to the enhancement effect are made mainly by the bremsstrahlung radiation and cascade ionization.

Low-parasitic ESD protection strategy for RF ICs in 0.35μm CMOS process

Wang Yuan, Jia Song, Chen Zhong-Jian, Ji Li-Jiu
Chin. Phys., 2006, 15 (10): 2297-2305 doi: 10.1088/1009-1963/15/10/018
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A systemic and comprehensive ESD-induced parasitic model is presented in this paper, which is used to analyse the parasitic influences of electrostatic discharge (ESD) protection circuits on the performance of radio frequency applications. A novel low-parasitic ESD protection structure is made in a 0.35\mum 1P3M silicide CMOS process. The measured results show that this novel structure has a low parasitic capacitance about 310fF and a low leakage current about 12.2nA with a suitable ESD robustness target about 5kV human body model.

Soliton-like pulse timing jitter in dispersion-managed systems

Li Qi-Liang, Li Qing-Shan, Lin Li-Bin
Chin. Phys., 2006, 15 (10): 2306-2314 doi: 10.1088/1009-1963/15/10/019
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In this paper, the timing jitter in dispersion-managed soliton-like systems with the Gaussian pulse is studied by using two methods. Firstly, the derivation of the dynamic equations for the evolution of soliton-like parameters and the timing jitter expressions for the dispersion-managed soliton-like systems are carried out by the perturbed variational method. By analysing and simulating these timing jitter expressions, one can find that the timing jitter is induced by the amplified spontaneous emission noise and the frequency shift, etc. Nonlinear gain can suppress the timing jitter. The chirp sign and the filters action have also effects on the total timing jitter. Secondly, the timing jitter is calculated and analysed by using the moment method. The results of the two methods prove to be consistent with each other.

Generation of four-atom cluster states in thermal cavity and implementing remote controlled not gate

Yang Rong-Can, Li Hong-Cai, Chen Mei-Xiang, Lin Xiu
Chin. Phys., 2006, 15 (10): 2315-2319 doi: 10.1088/1009-1963/15/10/020
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We propose an experimentally feasible scheme for preparing a four-atom cluster state in a thermal cavity. In the scheme, the cavity field is only virtually excited and the photon-number-dependent part in the effective Hamiltonian is cancelled so that the system is insensitive to the cavity decay and the thermal field. At the same time, the scheme can be generalized to prepare n-atom cluster states with the success probability 100\%. In addition, using the four-atom cluster state, we also propose a simpler scheme for implementing a remote--controlled not gate (CNOT) without the Bell states measurement.

Implementing the Deutsch--Jozsa algorithm by using Schr?dinger cat states in cavity QED

Yang Rong-Can, Li Hong-Cai, Lin Xiu, Chen Mei-Xiang
Chin. Phys., 2006, 15 (10): 2320-2323 doi: 10.1088/1009-1963/15/10/021
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We propose a scheme to implement the Deutsch--Jozsa algorithm by using Schr\"{o}dinger cat states in cavity quantum electron-dynamics (QED). The scheme is based on the Raman interaction of a degenerate three-level \Lambda -type atom with a coherent state in a cavity. By using Schr\"{o}dinger cat states, the atomic spontaneous emission can be minimized and the Hadamard transformation in our scheme is not needed.

The statistical fluctuation of a single-mode laser system driven by coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts

Xu Dai-Hai, Cheng Qing-Hua, Cao Li, Wu Da-Jin
Chin. Phys., 2006, 15 (10): 2324-2331 doi: 10.1088/1009-1963/15/10/022
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Using the linear approximation method, this paper studies the statistical property of a single-mode laser driven by both coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts, and calculates the steady-state mean normalized intensity fluctuation and intensity correlation time. It analyses the influences of the modulation signal, the net gain coefficient, the noise and its correlation form on the statistical fluctuation of the laser system respectively. It is found that the coloured pump noise modulated by the signal has a great suppressing action on the statistical fluctuation of the laser system; the pump noise self-correlation time and the specific frequency of modulation signal have the result that the statistical fluctuation tends to zero. Furthermore, the `colour' correlation of pump noise has much influences on the statistical fluctuation of the laser system. Increasing the intensity of pump noise will augment the statistical fluctuation of the laser system, but the intensity of quantum noise and the coefficient of cross-correlation between its real and imaginary parts have less influence on the statistical fluctuation of the laser system. Therefore, from the conclusions of this paper the statistical property can be known and a theoretical basis for steady operation and output of the laser system can be provided.

Electron acceleration by two crossed Bessel--Gaussian beams in vacuum

Zhao Zhi-Guo, Lü Bai-Da
Chin. Phys., 2006, 15 (10): 2332-2337 doi: 10.1088/1009-1963/15/10/023
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The direct acceleration of electrons by using two linearly polarized crossed Bessel--Gaussian (BG) beams with equal frequency and amplitude in vacuum is proposed and studied. It is shown that two linearly polarized BG beams of the same order (0 or 1) with a \textit{\pi }-rad phase difference have a resultant non-zero longitudinal electric field on the z-axis and can be used, in principle, to accelerate electrons.

Carrier--envelope phase effects for a dipolar molecule interacting with ultrashort laser pulse

Zhao Ke, Li Hong-Yu, Liu Ji-Cai, Wang Chuan-Kui
Chin. Phys., 2006, 15 (10): 2338-2342 doi: 10.1088/1009-1963/15/10/024
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In this paper the phase-dependent features of ultrashort laser pulse resonant propagation in a two-level dipolar molecule are demonstrated by solving full Maxwell--Bloch equations. The electronic properties of dipolar molecule 4-trans-[p-(N, N-Di-n-butylamino)-p -stilbenylvinyl] pyridine (DBASVP) molecule, one-dimensional asymmetric organic molecule, is calculated by density functional theory at \textit{ab initio} level. The numerical results show that the carrier propagation and the spectrum evolution of the pulse are sensitive to its initial phase and the phase sensitivity is more obvious for larger area pulse. The phase-dependent feature is more evident in dipolar molecule because the permanent dipole moment makes the nonlinear effects stronger.

The damage of the optical components induced by the stimulated Brillouin scattering

Ge Zi-Ming, Lü Zhi-Wei, Cai Jun-Wei, Ao Shu-Yan, Luo You-Hua
Chin. Phys., 2006, 15 (10): 2343-2346 doi: 10.1088/1009-1963/15/10/025
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A theory of excitation of ultrasonic waves in the stimulated Brillouin scattering (SBS) process is presented in this paper. By using several reasonable approximations, a numerical calculation of the transient longitudinal SBS shows that large amplitude of acoustic waves can be built up by the nanosecond pulse of high-power laser, which may result in the damage of optical glasses. The maximal density change and the maximal acoustic wave intensity in optical glasses of 5\,cm in thickness are calculated by using different parameters of the high-energy laser, such as the intensity, the pulse width, and the wave length. The damage threshold of the optical glasses is about 80 GW/cm^{2} when using a 1064 nm laser. The dynamic mechanism of SBS is the electrostriction effect of the components coupling with the high-power laser.

The effect of intermolecular interactions on photoluminescence of a porphyrin side-chain polymer

Wang Hui, Zhang Wei, Yu Han-Cheng, Huang Jin-Wang, Lin Wei-Zhu, Ji Liang-Nian
Chin. Phys., 2006, 15 (10): 2347-2351 doi: 10.1088/1009-1963/15/10/026
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Photoluminescence properties and exciton decay dynamics in a porphyrin side-chain polymer, poly[porphyrin acrylate- acrylonitrile (abbreviated p[(por)A-AN]), have been investigated by femtosecond time-resolved photoluminescence spectroscopy. All the luminescences of p[(por)A-AN] films are due to the emissive decay of the photoexcited singlet excitons in the porphyrins. The luminescence efficiencies and lifetimes are increased for samples from pure films to dilute blend films. However, they are increased as the intrachain concentration of the porphyrin sidechain groups is decreased. The intrachain rotation motions of porphyrin sidechain groups result in the initial ultrafast luminescence decays, which are much faster than those due to the interchain interactions. All the samples show no significant red-shift and broadening of the transient luminescence spectra. The interchain and intrachain nonradiative exciton relaxation processes may play an important role in the luminescence dynamics in the p[(por)A-AN] films. The possible origin of different intrachain and interchain dynamic behaviours in p[(por)A-AN] films is discussed.

An analysis of the incompressible viscous flows problem by meshless method

Xiong Yuan-Bo, Wang Hao
Chin. Phys., 2006, 15 (10): 2352-2356 doi: 10.1088/1009-1963/15/10/027
Full Text: [PDF 215 KB] (Downloads:571)
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Generally the incompressible viscous flow problem is described by the Navier--Stokes equation. Based on the weighted residual method the discrete formulation of element-free Galerkin is inferred in this paper. By the step-by-step computation in the field of time, and adopting the least-square estimation of the-same-order shift, this paper has calculated both velocity and pressure from the decoupling independent equations. Each time fraction Newton--Raphson iterative method is applied for the velocity and pressure. Finally, this paper puts the method into practice of the shear-drive cavity flow, verifying the validity, high accuracy and stability.

Laser controlled quantum motion of two Paul trapped ions

Cai Li-Hua, Hai Wen-Hua, Lu Geng-Biao
Chin. Phys., 2006, 15 (10): 2275-2287 doi: 10.1088/1009-1963/15/10/016
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We investigate the quantum motion of two ions stored in a Paul trap and interacting with a time-periodic laser field. In the pseudopotential approximation and large detuning condition, we find that the relative motion is independent of the laser field, but the exact centre-of-mass motion is closely related to the laser field. By adjusting the laser intensity and frequency, we can well control the quantum motion of the centre-of-mass. We illustrate some physical properties described by the centre-of-mass states, such as the squeezed coherent property, the widths and heights of the wavepackets of probability density, the classical-quantum correspondence, the resonance ladders of expectation energy and the transition probabilities between time-dependent quantum levels.

The second dissociation threshold bound levels of hydrogen molecule

Zhang Yan-Peng, Song Jian-Ping, Gan Chen-Li, Yan Xiang-An, Nie Zhi-Qiang, Jiang Tong, Li Ling, Du Kai, Zhang Xiang-Chen, Lu Ke-Qing, Eyler E.E.
Chin. Phys., 2006, 15 (10): 2288-2296 doi: 10.1088/1009-1963/15/10/017
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The near-threshold highly bound states of all three stable isotopic variants of molecular hydrogen have been studied. Numerous perturbations and unexpected transitions are observed as far as 1cm\sj{-1} just below the second dissociation threshold. This complex structure may arise from a combination of nonadiabatic coupling between B, B', C electronic states, perturbations due to fine and hyperfine interactions, and strong shape resonances. The perturbed near-threshold states and vibrational continuum exhibit finegrained structure, differing greatly between isotopes because of varying nonadiabatic coupling.

The spike timing precision of FitzHugh--Nagumo neuron network coupled by gap junctions

Zhang Su-Hua, Zhan Yong, Yu Hui, An Hai-Long, Zhao Tong-Jun
Chin. Phys., 2006, 15 (10): 2450-2457 doi: 10.1088/1009-1963/15/10/044
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It has been proved recently that the spike timing can play an important role in information transmission, so in this paper we develop a network with N-unit FitzHugh--Nagumo neurons coupled by gap junctions and discuss the dependence of the spike timing precision on synaptic coupling strength, the noise intensity and the size of the neuron ensemble. The calculated results show that the spike timing precision decreases as the noise intensity increases; and the ensemble spike timing precision increases with coupling strength increasing. The electric synapse coupling has a more important effect on the spike timing precision than the chemical synapse coupling.

Modulation of ionization on laser frequency in ultra-short pulse intense laser--gas-target

Hu Qiang-Lin, Liu Shi-Bing
Chin. Phys., 2006, 15 (10): 2357-2362 doi: 10.1088/1009-1963/15/10/028
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Based on the dispersion relation of intense laser pulse propagating in gradually ionized plasma, this paper discusses the frequency modulation induced by ionization of an ultra-short intense laser pulse interacting with a gas target. The relationship between the frequency modulation and the ionization rate, the plasmas frequency variation, and the polarization of atoms (ions) is analysed. The numerical results indicate that, at high frequency, the polarization of atoms (ions) plays a more important role than plasma frequency variation in modulating the laser frequency, and the laser frequency variation is different at different positions of the laser pulse.

Effects of atomic number Z on the energy distribution of hot electrons generated by femtosecond laser interaction with metallic targets

Cai Da-Feng, Gu Yu-Qiu, Zheng Zhi-Jian, Zhou Wei-Min, Jiao Chun-Ye, Chen Hao, Wen Tian-Shu, Chunyu Shu-Tai
Chin. Phys., 2006, 15 (10): 2363-2367 doi: 10.1088/1009-1963/15/10/029
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The effects of atomic number Z on the energy distribution of hot electrons generated by the interaction of 60fs, 130mJ, 800nm, and 7\ti10\sj{17}W/cm\sj{2} laser pulses with metallic targets have been studied experimentally. The results show that the number and the effective temperature of hot electrons increase with the atomic number Z of metallic targets, and the temperature of hot electrons are in the range of 190--230keV, which is consistent with a scaling law of hot electrons temperature.

Observation of hydrogen pellet ablation material flow by tomography

Dong Jia-Fu, Wang Shi-Qing, Li Wen-Zhong
Chin. Phys., 2006, 15 (10): 2368-2373 doi: 10.1088/1009-1963/15/10/030
Full Text: [PDF 645 KB] (Downloads:417)
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An H\al emission measurement array with 25 detection channels has been built on HL-1M tokamak. Reconstruction maps of H\al emission distribution in plasma cross-section have been obtained by using tomography, with a hydrogen pellet injected into the plasma. The dimension, the shape and the rotation characteristic of the cross-section of the pellet ablation material flow tube have been observed. These results have been analysed and explained tentatively by using the `tail' model and the linear expansion model.

Spatial distribution of SiCln (n=0--2) in SiCl4 plasma measured by mass spectroscopy

Wang Zhao-Kui, Lin Kui-Xun, Lou Yan-Hui, Lin Xuan-Ying, Zhu Zu-Song
Chin. Phys., 2006, 15 (10): 2374-2377 doi: 10.1088/1009-1963/15/10/031
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For a better understanding of the deposition mechanism of thin films in SiCl4 source gas, we have measured the spatial distributions of SiCln (n=0--2) radicals in SiCl4 radio frequency glow discharge plasma utilizing a mass spectrometer equipped with a movable gas sampling apparatus. The experimental results demonstrate that the relative densities of SiCln (n=0--2) radicals have peak values at the position of 10mm above the powered electrode along the axial direction; the relative densities of the Si and SiCln (n=1, 2) radicals have peak values at the positions of 27mm and 7mm away from the axis along the radial direction, respectively. Generally speaking, in the whole SiCl4 plasma bulk region, the relative density of Si is one order of magnitude higher than that of SiCl, and the relative density of SiCl is several times higher than that of SiCl2/sub>. This reveals that Si and SiCl may be the primary growth precursors in forming thin films.

Deformation measurements of three types of Portevin--Le Chatelier bands

Xiang Guo-Fu, Zhang Qing-Chuan, Liu Hao-Wen, Jiang Hui-Feng, Wu Xiao-Ping
Chin. Phys., 2006, 15 (10): 2378-2384 doi: 10.1088/1009-1963/15/10/032
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In this paper a technique based on high-speed digital photography and the digital speckle correlation (DSC) method is used for the quantitative measurement of the displacement and strain fields of various Portevin--Le Chatelier (PLC) bands (types A, B, and C). The experimental results clearly show the nucleation process of a type-B band and the propagation of a type-A band. The results also reveal that there exists an elastic shrinkage deformation outside a PLC band during a large avalanche-like deformation inside the PLC band.

The optical properties of MgxZn1-xO thin films

Zhang Xi-Jian, Ma Hong-Lei, Li Yu-Xiang, Wang Qing-Pu, Ma Jin, Zong Fu-Jian, Xiao Hong-Di
Chin. Phys., 2006, 15 (10): 2385-2388 doi: 10.1088/1009-1963/15/10/033
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MgxZn1-xO thin films have been prepared on silicon substrates by radio frequency magnetron sputtering at 60℃. The thin films have hexagonal wurtzite single-phase structure and a preferred orientation with the c-axis perpendicular to the substrates. The refractive indices of MgxZn1-xO films are studied at room temperature by spectroscopic ellipsometry over the wavelength range of 400--760\,nm at the incident angle of 70℃. Both absorption coefficients and optical band gaps of MgxZn1-xO films are determined by the transmittance spectra. While Mg content is increasing, the absorption edges of MgxZn1-xO films shift to higher energies and band gaps linearly increase from 3.24.eV at x=0 to 3.90\,eV at x=0.30. These results provide important information for the design and modelling of ZnO/ MgxZn1-xO heterostructure optoelectronic devices.

Local field distribution and configuration of CO molecules adsorbed on the nanostructure platinum surface

Huang Xiao-Jing, He Su-Zhen, Wu Chen-Xu
Chin. Phys., 2006, 15 (10): 2389-2396 doi: 10.1088/1009-1963/15/10/034
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This paper shows that the local electric field distribution near the nanostructure metallic surface is obtained by solving the Laplace equation, and furthermore, the configuration of CO molecules adsorbed on a Pt nanoparticle surface is obtained by using Monte Carlo simulation. It is found that the uneven local electric field distribution induced by the nanostructure surface can influence the configuration of carbon monoxide (CO) molecules by a force, which drags the adsorbates to the poles of the nanoparticles. This result, together with our results obtained before, may explain the experimental results that the nanostructure metallic surface can lead to abnormal phenomena such as anti-absorption infrared effects.

Emitter of hetero-junction solar cells created using pulsed rapid thermal annealing

Xu Ying, Diao Hong-Wei, Hao Hui-Ying, Zeng Xiang-Bo, Liao Xian-Bo
Chin. Phys., 2006, 15 (10): 2397-2401 doi: 10.1088/1009-1963/15/10/035
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In this paper, we use a pulsed rapid thermal processing (RTP) approach to create an emitter layer of hetero-junction solar cell. The process parameters and crystallization behaviour are studied. The structural, optical and electric properties of the crystallized films are also investigated. Both the depth of PN junction and the conductivity of the emitter layer increase with the number of RTP pulses increasing. Simulation results show that efficiencies of such solar cells can exceed 15% with a lower interface recombination rate, but the highest efficiency is 11.65% in our experiments.

GaN-based heterostructures: electric--static equilibrium and boundary conditions

Zhang Jin-Feng, Hao Yue
Chin. Phys., 2006, 15 (10): 2402-2406 doi: 10.1088/1009-1963/15/10/036
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In the GaN-based heterostructures, this paper reports that the strong electric fields induced by polarization effects at the structure boundaries complicate the electric--static equilibrium and the boundary conditions. The basic requirements of electric--static equilibrium for the heterostructure systems are discussed first, and it is deduced that in the application of the coupled Schr\"{o}dinger--Poisson model to the heterostructures of electric--static equilibrium state, zero external electric field guarantees the overall electric neutrality, and there is no need to introduce the charge balance equation. Then the relation between the screening of the polar charges in GaN-based heterostructures and the possible boundary conditions of the Poisson equation is analysed, it is shown that the various boundary conditions are equivalent to each other, and the surface charge, which can be used in studying the screening of the polar charges, can be precisely solved even if only the conduction band energy is correctly known at the surface. Finally, through the calculations on an AlGaN/GaN heterostructure with typical structure parameters by the coupled Schr\"{o}dinger--Poisson model under the various boundary conditions, the correctness of the above analyses are validated.

The photoluminescence of ZnSe bulk single crystals excited by femtosecond pulse

Li Huan-Yong, Jie Wan-Qi, Zhang Shi-An, Sun Zhen-Rong, Xu Ke-Wei
Chin. Phys., 2006, 15 (10): 2407-2414 doi: 10.1088/1009-1963/15/10/037
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This paper reports on the photoluminescence spectra of ZnSe single crystal with trace chlorine excited by the femtosecond laser pulse. Three emission bands, including second-harmonic-generation, two-photon-excited peak and a broad band at 500--700nm, were detected. The thermal strain induced by femtosecond pulse strongly influences the photoluminescence of ZnSe crystal. The corresponding strain \va in ZnSe crystal is estimated to be about 8.8 \ti10-3 at room temperature. The zinc-vacancy, as the main point defect induced by femtosecond pulse, is successfully used to interpret the broad emission at 500--700nm. The research shows that self-activated luminescence possesses the recombination mechanism of donor--vacancy pair, and it is also influenced by a few selenium defects and the temperature. The rapid decrease in photoluminescence intensity of two-photon-excited fluorescence and second-harmonic generation emission at lower temperature is attributed to the fact that more point defects result in the thermal activation of the two-photo-absorption energy converting to the stronger recombination emission of chlorine--zinc vacancy in 500--700nm. The experimental results indicate that the femtosecond exciting photoluminescence shows a completely different emission mechanism to that of He--Cd exciting luminescence in ZnSe single crystal. The femtosecond laser exhibits a higher sensitive to the impurity in crystal materials, which can be recommended as an efficient way to estimate the trace impurity in high quality crystals.

Nonideal effects in quantum field-effect directional coupler

Xie Yue-E, Yan Xiao-Hong, Chen Yuan-Ping
Chin. Phys., 2006, 15 (10): 2415-2421 doi: 10.1088/1009-1963/15/10/038
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The nonideal effects in a quantum field-effect directional coupler where two quantum wires are coupled through a finite potential barrier are studied by adopting the lattice Green function method. The results show that the electron energy distribution, asymmetric geometry and finite temperature all have obvious influence on the electron transfer of the coupler. Only for the electrons with energies in a certain region, can the complete periodic transfer between two quantum wires take place. The conductance of these electrons as a function of the barrier length and potential height exhibits a fine periodic or quasi-periodic pattern. For the electrons with energies beyond the region, however, the complete periodic transfer does not hold any more since many irregular oscillations are superimposed on the conductance profile. In addition, the finite temperature and asymmetric geometry both can reduce the electron transfer efficiency.

A bistable, self-latching inverter by the monolithic integration of resonant tunnelling diode and high electron mobility transistor

Ma Long, Huang Ying-Long, Zhang Yang, Yang Fu-Hua, Wang Liang-Chen
Chin. Phys., 2006, 15 (10): 2422-2426 doi: 10.1088/1009-1963/15/10/039
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This paper reports that the structures of AlGaAs/InGaAs high electron mobility transistor (HEMT) and AlAs/GaAs resonant tunnelling diode (RTD) are epitaxially grown by molecular beam epitaxy (MBE) in turn on a GaAs substrate. An Al0.24Ga0.76As chair barrier layer, which is grown adjacent to the top AlAs barrier, helps to reduce the valley current of RTD. The peak-to-valley current ratio of fabricated RTD is 4.8 and the transconductance for the 1-μm gate HEMT is 125mS/mm. A static inverter which consists of two RTDs and a HEMT is designed and fabricated. Unlike a conventional CMOS inverter, the novel inverter exhibits self-latching property.

Resistivity and critical temperature of (La1-xPrx)0.7Ca0.3MnO3

Liu Zi-Xin, Bai Chun-Xu
Chin. Phys., 2006, 15 (10): 2427-2430 doi: 10.1088/1009-1963/15/10/040
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An empirical formula of the critical temperature that is concentration dependent for polycrystalline (La1-xPrx)0.7Ca0.3MnO3 is presented in this paper. With this formula, the temperature dependence of resistance is simulated for various values of x by using the random resistor network model and the Monte Carlo method. The hysteresis effect in \rho -- T curves is reasonably explained. The simulation results are in good agreement with the relevant experimental measurements.

Evaluation of negative bias temperature instability in ultra-thin gate oxide pMOSFETs using a new on-line PDO method

Ji Zhi-Gang, Xu Ming-Zhen, Tan Chang-Hua
Chin. Phys., 2006, 15 (10): 2431-2438 doi: 10.1088/1009-1963/15/10/041
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A new on-line methodology is used to characterize the negative bias temperature instability (NBTI) without inherent recovery. Saturation drain voltage shift and mobility shift are extracted by ID-VD characterizations, which were measured before stress, and after every certain stress phase, using the proportional differential operator (PDO) method. The new on-line methodology avoids the mobility linearity assumption as compared with the previous on-the-fly method. It is found that both reaction--diffusion and charge-injection processes are important in NBTI effect under either DC or AC stress. A similar activation energy, 0.15 eV, occurred in both DC and AC NBTI processes. Also degradation rate factor is independent of temperature below 90\du\ and sharply increases above it. The frequency dependence of NBTI degradation shows that NBTI degradation is independent of frequencies. The carrier tunnelling and reaction--diffusion mechanisms exist simultaneously in NBTI degradation of sub-micron pMOSFETs, and the carrier tunnelling dominates the earlier NBTI stage and the reaction--diffusion mechanism follows when the generation rate of traps caused by carrier tunnelling reaches its maximum.

Study on the thermo-optic properties of DR1/PMMA composite

Li Xiang, Cao Zhuang-Qi, Shen Qi-Shun, Yang Yan-Fang
Chin. Phys., 2006, 15 (10): 2439-2444 doi: 10.1088/1009-1963/15/10/042
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This paper reports that the thermo-optic coefficient (\dd n / \dd T) as well as thermal expansion coefficients (\beta) of DR1/PMMA polymer film are measured for both TE (transversal electric) and TM (transversal magnetic) polarizations by using an attenuated total reflection configuration at the wavelengths of 832nm. The thermo-optic coefficients of DR1/PMMA are negative and as high as the order of 10-4/℃. The influences of dopant concentration, poling process and photobleaching process on the thermo-optic properties of DR1/PMMA are also investigated.

Structure and visible photoluminescence of Sm3+, Dy3+ and Tm3+ doped c-axis oriented AlN films

Liu Fu-Sheng, Liu Quan-Lin, Liang Jing-Kui, Luo Jun, Su Jun, Zhang Yi, Sun Bao-Juan, Rao Guang-Hui
Chin. Phys., 2006, 15 (10): 2445-2449 doi: 10.1088/1009-1963/15/10/043
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Visible photoluminescence (PL) has been observed from rare earth (Tm, Sm and Dy)-doped AlN films grown by radio-frequency magnetron reactive sputtering. X-ray diffraction indicates that the films are c-axis-oriented hexagonal wurtzite type structure with an average crystal size of about 80--110nm. Room-temperature PL spectra indicate that the blue emission is due to the transition of 1D2 to 3F4 and 1G2 to 3H6 intra 4f electron of Tm3+, the yellow emissions of AlN:Sm are due to 4G5/2 to the 6HJ (J = 5/2, 7/2, 9/2, 11/2) and the reddish emissions of AlN:Dy correspond to the 4F9/2 to 6HJ (J = 15/2, 13/2, 11/2 and 9/2) and 6F11/2 transitions.

Effect of change in large and fast solar wind dynamic pressure on geosynchronous magnetic field

N L Borodkova, Liu Jing-Bo, Huang Zhao-Hui, G N Zastenker, Wang Chi, P E Eiges
Chin. Phys., 2006, 15 (10): 2458-2464 doi: 10.1088/1009-1963/15/10/045
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We present a comparison of changes in large and sharp solar wind dynamic pressure, observed by several spacecraft, with fast disturbances in the magnetospheric magnetic field, measured by the geosynchronous satellites. More than 260 changes in solar wind pressure during the period 1996--2003 are selected for this study. Large statistics show that an increase (a decrease) in dynamic pressure always results in an increase (a decrease) in the magnitude of geosynchronous magnetic field. The amplitude of response to the geomagnetic field strongly depends on the location of observer relative to the noon meridian, the value of pressure before disturbance, and the change in amplitude of pressure.

Dynamics of quintessential inflation

Zhai Xiang-Hua, Zhao Yi-Bin
Chin. Phys., 2006, 15 (10): 2465-2469 doi: 10.1088/1009-1963/15/10/046
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In this paper, we study a realistic model of quintessential inflation with radiation and matter. By the analysis of the dynamical system and numerical work about the evolution of the equation of state and cosmic density parameter, we show that this model is a good match for the current astronomical observation. The conclusion we obtain is in favour of the model where the modular part of the complex field plays the role of the inflaton whereas the argument part is the quintessence field. Numerical calculation shows that a heteroclinic orbit (solution of the dynamical system) is interpolated between early-time de Sitter phase (an unstable critical point) and a late-time de Sitter attractor.
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