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Chin. Phys. B  
  Chin. Phys. B--2009, Vol.18, No.1
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On dynamics of elastic rod based on exact Cosserat model

Liu Yan-Zhu
Chin. Phys. B, 2009, 18 (1): 1-8 doi: 10.1088/1674-1056/18/1/001
Full Text: [PDF 243 KB] (Downloads:700)
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The analysis of kinematics and dynamics of an elastic rod with circular cross section is studied on the basis of exact Cosserat model under consideration of the tension and shear deformation of the rod. The dynamical equations of a rod with arbitrary initial shape are established in general form. The dynamics of a straight rod under axial tension and torsion is discussed as an example. In discussion of static stability in the space domain the Greenhill criteria of stability and the Euler load are corrected by the influence of tension and shear strain. In analysis of dynamical stability in the time domain it is shown that the Lyapunov and Euler stability conditions of the rod in space domain are the necessary conditions of Lyapunov's stability in the time domain. The longitudinal, torsional and lateral vibrations of a straight rod based on exact model are discussed, and an exact formula of free frequency of lateral vibration is obtained. The free frequency formulas of various simplified models, such as the Rayleigh beam, the Kirchhoff rod, and the Timoshenko beam, can be seen as special cases of the exact formula under different conditions of simplification.

Approximate calculation of electronic energy levels of axially symmetric quantum dot and quantum ring by using energy dependent effective mass

Liu Yu-Min, Yu Zhong-Yuan, Ren Xiao-Min
Chin. Phys. B, 2009, 18 (1): 9-15 doi: 10.1088/1674-1056/18/1/002
Full Text: [PDF 1023 KB] (Downloads:713)
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Calculations of electronic structures about the semiconductor quantum dot and the semiconductor quantum ring are presented in this paper. To reduce the calculation costs, for the quantum dot and the quantum ring, their simplified axially symmetric shapes are utilized in our analysis. The energy dependent effective mass is taken into account in solving the Schr?dinger equations in the single band effective mass approximation. The calculated results show that the energy dependent effective mass should be considered only for relatively small volume quantum dots or small quantum rings. For large size quantum materials, both the energy dependent effective mass and the parabolic effective mass can give the same results. The energy states and the effective masses of the quantum dot and the quantum ring as a function of geometric parameters are also discussed in detail.

The influences of thickness of spacing layer and the elastic anisotropy on the strain fields and band edges of InAs/GaAs conical shaped quantum dots

Liu Yu-Min, Yu Zhong-Yuan, Ren Xiao-Min
Chin. Phys. B, 2009, 18 (1): 16-22 doi: 10.1088/1674-1056/18/1/003
Full Text: [PDF 1212 KB] (Downloads:1288)
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Based on the continuum elastic theory, this paper presents a finite element analysis to investigate the influences of elastic anisotropy and thickness of spacing layer on the strain field distribution and band edges (both conduction band and valence band) of the InAs/GaAs conical shaped quantum dots. To illustrate these effects, we give detailed comparisons with the circumstances of isolated and stacking quantum dot for both anisotropic and isotropic elastic characteristics. The results show that, in realistic materials design and theoretical predication performances of the optoelectronic devices, both the elastic anisotropy and thickness of the spacing layer of stacked quantum dot should be taken into consideration.

Implementation of quantum search scheme by adiabatic passage in a cavity--laser--atom system

Liu Wen-Wu, Li Hong-Cai, Yang Rong-Can
Chin. Phys. B, 2009, 18 (1): 23-29 doi: 10.1088/1674-1056/18/1/004
Full Text: [PDF 498 KB] (Downloads:1162)
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This paper proposes a scheme for implementing the adiabatic quantum search algorithm of different marked items in an unsorted list of N items with atoms in a cavity driven by lasers. N identical three-level atoms are trapped in a single-mode cavity. Each atom is driven by a set of three pulsed laser fields. In each atom, the same level represents a database entry. Two of the atoms are marked differently. The marked atom has an energy gap between its two ground states. The two different marked states can be sought out respectively starting from an initial entangled state by controlling the ratio of three pulse amplitudes. Moreover, the mechanism, based on adiabatic passage, constitutes a decoherence-free method in the sense that spontaneous emission and cavity damping are avoided since the dynamics follows the dark state. Furthermore, this paper extends the algorithm with m (m>2) atoms marked in an ideal situation. Any different marked state can be sought out.

Teleporting a quantum controlled-Not with one target/two targets gate using two partially entangled states

Chen Li-Bing, Jin Rui-Bo, Lu Hong
Chin. Phys. B, 2009, 18 (1): 30-34 doi: 10.1088/1674-1056/18/1/005
Full Text: [PDF 154 KB] (Downloads:1181)
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This paper considers the teleportation of quantum controlled-Not (CNOT) gate by using partially entangled states. Different from the known probability schemes, it presents a method for teleporting a CNOT gate with unit fidelity and unit probability by using two partially entangled pairs as quantum channel. The method is applicable to any two partially entangled pairs satisfying the condition that their smaller Schmidt coefficients μ and ν are (2μ + 2ν - 2μν - 1)≥0. In this scheme, the sender's local generalized measurement described by a positive operator valued measurement (POVM) lies at the heart. It constructs the required POVM. It also puts forward a scheme for teleporting a CNOT with two targets gate with unit fidelity by using same quantum channel. With assistance of local operations and classical communications, three spatially separated users are able to complete the teleportation of a CNOT with two targets gate with probability of (2μ + 2ν- 1). With a proper value of μ and ν, the probability could reach nearly 1.

The quantum spectral analysis of the two-dimensional annular billiard system

Zhang Yan-Hui, Zhang Ji-Quan, Xu Xue-You, Lin Sheng-Lu
Chin. Phys. B, 2009, 18 (1): 35-39 doi: 10.1088/1674-1056/18/1/006
Full Text: [PDF 425 KB] (Downloads:825)
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Based on the extended closed-orbit theory together with spectral analysis, this paper studies the correspondence between quantum mechanics and the classical counterpart in a two-dimensional annular billiard. The results demonstrate that the Fourier-transformed quantum spectra are in very good accordance with the lengths of the classical ballistic trajectories, whereas spectral strength is intimately associated with the shapes of possible open orbits connecting arbitrary two points in the annular cavity. This approach facilitates an intuitive understanding of basic quantum features such as quantum interference, locations of the wavefunctions, and allows quantitative calculations in the range of high energies, where full quantum calculations may become impractical in general. This treatment provides a thread to explore the properties of microjunction transport and even quantum chaos under the much more general system.

Dynamical nonlocality of the entangled coherent state in the phase damping model

Lu Huai-Xin, Li Ying-De
Chin. Phys. B, 2009, 18 (1): 40-45 doi: 10.1088/1674-1056/18/1/007
Full Text: [PDF 235 KB] (Downloads:865)
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This paper studies the dynamics of nonlocality for a bosonic entangled coherent state in a phase damping model. The density operator of the system is solved by using a superoperator method. The dynamics of nonlocality for the bosonic entangled coherent state is uncovered by the Bell operator based on the pseudospin operator of a light field. The dynamics of the nonlocality for this state has also been studied by other Bell operators. The result of the numerical calculations of the Bell function shows that the quantum nonlocality heavily depends on the chosen Bell operator.

The queueing model for quantum key distribution network

Wen Hao, Han Zheng-Fu, Guo Guang-Can, Hong Pei-Lin
Chin. Phys. B, 2009, 18 (1): 46-50 doi: 10.1088/1674-1056/18/1/008
Full Text: [PDF 715 KB] (Downloads:1666)
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This paper develops a QKD (quantum key distribution)-based queueing model to investigate the data delay on QKD link and network, especially that based on trusted relays. It shows the mean packet delay performance of the QKD system. Furthermore, it proposes a key buffering policy which could effectively improve the delay performance in practice. The results will be helpful for quality of service in practical QKD systems.

Linear optical realization of unambiguous quantum state comparison

Lin Qing
Chin. Phys. B, 2009, 18 (1): 51-55 doi: 10.1088/1674-1056/18/1/009
Full Text: [PDF 273 KB] (Downloads:822)
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In this paper, we propose an experimental scheme for unambiguous quantum state comparison assisted by linear optical manipulations, twin-photons produced from parametric down-conversion, and postselection from the coincidence measurement. In this scheme the preparation of the general two mixed qubit states with arbitrary prior probabilities and the realization of the optimal POVMs for unambiguous quantum state comparison are presented. This proposal is feasible by current experimental technology, and may be used in single-qubit quantum fingerprinting.

Realization of Toffoli gate operation using four-level atoms in cavity QED system

Tang Shi-Qing, Zhang Deng-Yu, Xie Li-Jun, Zhan Xiao-Gui, Gao Feng
Chin. Phys. B, 2009, 18 (1): 56-61 doi: 10.1088/1674-1056/18/1/010
Full Text: [PDF 257 KB] (Downloads:1114)
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This paper proposes a scheme for realization of a three-qubit Toffoli gate operation using three four-level atoms by a selective atom--field interaction in a cavity quantum electrodynamics system. In the proposed protocol, the quantum information is encoded on the stable ground states of atoms, and atomic spontaneous emission is negligible as the large atom--cavity detuning effectively suppresses the spontaneous decay of the atoms. The influence of the dissipation on fidelity and success probability of the three-qubit Toffoli gate is also discussed. The scheme can also be applied to realize an N-qubit Toffoli gate and the interaction time required does not rise with increasing the number of qubits.

Hawking radiation from the dilaton--(anti) de Sitter black hole via covariant anomaly

Han Yi-Wen, Bao Zhi-Qing, Hong Yun
Chin. Phys. B, 2009, 18 (1): 62-65 doi: 10.1088/1674-1056/18/1/011
Full Text: [PDF 150 KB] (Downloads:1515)
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Adopting the anomaly cancellation method, initiated by Robinson and Wilczek recently, this paper discusses Hawking radiation from the dilaton--(anti) de Sitter black hole. To save the underlying gauge and general covariance, it introduces covariant fluxes of gauge and energy--momentum tensor to cancel the gauge and gravitational anomalies. The result shows that the introduced compensating fluxes are equivalent to those of a 2-dimensional blackbody radiation at Hawking temperature with appropriate chemical potential.

Subleading terms of thermodynamic quantities around static spherical black holes

Li Gu-Qiang
Chin. Phys. B, 2009, 18 (1): 66-69 doi: 10.1088/1674-1056/18/1/012
Full Text: [PDF 144 KB] (Downloads:771)
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The thermodynamic quantities for the gases of massless particles with spin s = 1 / 2, 1, 3 / 2, 2 around static spherical black holes are investigated by using the brick-wall method. The appearance of the spin-dependent subleading terms is demonstrated and the terms are shown to contain not only the linear and quadratic terms of the spins but also a zero-power term of the spins.

Stochastic resonance in a parallel array of linear elements

Dong Xiao-Juan
Chin. Phys. B, 2009, 18 (1): 70-75 doi: 10.1088/1674-1056/18/1/013
Full Text: [PDF 180 KB] (Downloads:938)
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This paper studies stochastic resonance (SR) phenomenon in a parallel array of linear elements with noise. Employing the signal-to-noise ratio (SNR) theory, it obtains the output SNR, and investigates the effects on the output SNR of the system with signal-independent noise and signal-dependent noise respectively. Numerical results show: the curve of the output SNR is monotone with signal-independent noise; whereas SR appears with signal-dependent noise. Moreover, the output SNR enhances rapidly with the increase of N which is the number of elements in this parallel array linear system. This result may provide smart array of simple linear sensors which are capable of acting as noise-aided amplifiers.

Adaptive synchronization in an array of asymmetric coupled neural networks

Gao Ming, Cui Bao-Tong
Chin. Phys. B, 2009, 18 (1): 76-83 doi: 10.1088/1674-1056/18/1/014
Full Text: [PDF 584 KB] (Downloads:1240)
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This paper investigates the global synchronization in an array of linearly coupled neural networks with constant and delayed coupling. By a simple combination of adaptive control and linear feedback with the updated laws, some sufficient conditions are derived for global synchronization of the coupled neural networks. The coupling configuration matrix is assumed to be asymmetric, which is more coincident with the realistic network. It is shown that the approaches developed here extend and improve the earlier works. Finally, numerical simulations are presented to demonstrate the effectiveness of the theoretical results.

Analysis of transition between chaos and hyper-chaos of an improved hyper-chaotic system

Gu Qiao-Lun, Gao Tie-Gang
Chin. Phys. B, 2009, 18 (1): 84-90 doi: 10.1088/1674-1056/18/1/015
Full Text: [PDF 3338 KB] (Downloads:1088)
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An improved hyper-chaotic system based on the hyper-chaos generated from Chen's system is presented, and some basic dynamical properties of the system are investigated by means of Lyapunov exponent spectrum, bifurcation diagrams and characteristic equation roots. Simulations show that the new improved system evolves into hyper-chaotic, chaotic, various quasi-periodic or periodic orbits when one parameter of the system is fixed to be a certain value while the other one is variable. Some computer simulations and bifurcation analyses are given to testify the findings.

Synchronization of noise-perturbed generalized Lorenz system by sliding mode control

Kong Cui-Cui, Chen Shi-Hua
Chin. Phys. B, 2009, 18 (1): 91-97 doi: 10.1088/1674-1056/18/1/016
Full Text: [PDF 343 KB] (Downloads:974)
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Synchronization of a noise-perturbed generalized Lorenz system by using sliding mode control method is investigated in this paper. Two sliding mode control methods are proposed to synchronize the noise-perturbed generalized Lorenz system. Numerical simulations are also provided for the illustration and verification of the methods.

Development and transition of spiral wave in the coupled Hindmarsh--Rose neurons in two-dimensional space

Ma Jun, Ying He-Ping, Liu Yong, Li Shi-Rong
Chin. Phys. B, 2009, 18 (1): 98-105 doi: 10.1088/1674-1056/18/1/017
Full Text: [PDF 2256 KB] (Downloads:1498)
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The dynamics and the transition of spiral waves in the coupled Hindmarsh--Rose (H--R) neurons in two-dimensional space are investigated in the paper. It is found that the spiral wave can be induced and developed in the coupled HR neurons in two-dimensional space, with appropriate initial values and a parameter region given. However, the spiral wave could encounter instability when the intensity of the external current reaches a threshold value of 1.945. The transition of spiral wave is found to be affected by coupling intensity D and bifurcation parameter r. The spiral wave becomes sparse as the coupling intensity increases, while the spiral wave is eliminated and the whole neuronal system becomes homogeneous as the bifurcation parameter increases to a certain threshold value. Then the coupling action of the four sub-adjacent neurons, which is described by coupling coefficient D’, is also considered, and it is found that the spiral wave begins to breakup due to the introduced coupling action from the sub-adjacent neurons (or sites) and together with the coupling action of the nearest-neighbour neurons, which is described by the coupling intensity D.

Cost and effect of pinning control for network synchronization

Li Rong, Duan Zhi-Sheng, Chen Guan-Rong
Chin. Phys. B, 2009, 18 (1): 106-118 doi: 10.1088/1674-1056/18/1/018
Full Text: [PDF 380 KB] (Downloads:967)
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The problem of pinning control for the synchronization of complex dynamical networks is discussed in this paper. A cost function of the controlled network is defined by the feedback gain and the coupling strength of the network. An interesting result is that a lower cost is achieved by using the control scheme of pinning nodes with smaller degrees. Some strict mathematical analyses are presented for achieving a lower cost in the synchronization of different star-shaped networks. Numerical simulations on some non-regular complex networks generated by the Barabási--Albert model and various star-shaped networks are performed for verification and illustration.

Design and implementation of a novel multi-scroll chaotic system

Zhang Chao-Xia, Yu Si-Min
Chin. Phys. B, 2009, 18 (1): 119-129 doi: 10.1088/1674-1056/18/1/019
Full Text: [PDF 3701 KB] (Downloads:1322)
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This paper proposes a novel approach for generating a multi-scroll chaotic system. Together with the theoretical design and numerical simulations, three different types of attractor are available, governed by constructing triangular wave, sawtooth wave and hysteresis sequence. The presented new multi-scroll chaotic system is different from the classical multi-scroll chaotic Chua system in dimensionless state equations, nonlinear functions and maximum Lyapunov exponents. In addition, the basic dynamical behaviours, including equilibrium points, eigenvalues, eigenvectors, eigenplanes, bifurcation diagrams and Lyapunov exponents, are further investigated. The success of the design is illustrated by both numerical simulations and circuit experiments.

Dynamical potential approach to dissociation of H--C bond in HCO highly excited vibration

Fang Chao, Wu Guo-Zhen
Chin. Phys. B, 2009, 18 (1): 130-135 doi: 10.1088/1674-1056/18/1/020
Full Text: [PDF 183 KB] (Downloads:733)
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The highly excited vibrational levels of HCO in the electronic ground state, \tilde {X}1A',are employed to determine the coefficients of an algebraic Hamiltonian, by which the dynamical potential is derived and shown to be very useful for interpreting the intramolecular vibrational relaxation (IVR) which operates via the HCO bending motion. The IVR inhibits the dissociation of H atom and enhances the stochastic degree of dynamical character. This approach is from a global viewpoint on a series of levels classified by the polyad number which is a constant of motion in a certain dynamical domain. In this way, the seemingly complicated level structure shows very regular picture, dynamically.

Nucleon--nucleon interactions in the double folding model for fusion reactions

Zhang Gao-Long, Liu Hao, Le Xiao-Yun
Chin. Phys. B, 2009, 18 (1): 136-141 doi: 10.1088/1674-1056/18/1/021
Full Text: [PDF 211 KB] (Downloads:1282)
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Nucleus--nucleus potentials are determined in the framework of double folding model for M3Y--Reid and M3Y--Paris effective nucleon--nucleon (NN) interactions. Both zero-range and finite-range exchange parts of NN interactions are considered in the folding procedure. In this paper the spherical projectile--spherical target system 16O+208Pb is selected for calculating the barrier energies, fusion cross sections and barrier distributions with the density-independent and density-dependent NN interactions on the basis of M3Y--Reid and M3Y--Paris NN interactions. The barrier energies become lower for Paris NN interactions in comparison with Reid NN interactions, and also for finite-range exchange part in comparison with zero-range exchange part. The density-dependent NN interactions give similar fusion cross sections and barrier distributions, and the density-independent NN interaction causes the barrier distribution moving to a higher position. However, the density-independent Reid NN interaction with zero-range exchange part gives the lowest fusion cross sections. We find that the calculated fusion cross sections and the barrier distributions are in agreement with the experimental data after renormalization of the nuclear potential due to coupled-channel effect.

The research of high-directive anisotropic magnetic metamaterial antenna loaded with frequency-selective surface

Sun Yong-Zhi, Ran Li-Xin, Peng Liang, Wang Wei-Guang, Li Ting, Zhao Xu, Chen Qiu-Lin
Chin. Phys. B, 2009, 18 (1): 174-178 doi: 10.1088/1674-1056/18/1/027
Full Text: [PDF 3606 KB] (Downloads:1632)
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This paper uses a Computer Simulation Technology microwave studio to simulate the performance of a new high-directivity anisotropic magnetic metamaterial antenna loaded with a frequency-selective surface. Frequency-selective surface with cross-dipole element has a great effect on the directivity, radiation pattern, and gain of such an antenna. The experimental results show that frequency-selective surface (FSS) significantly improve the radiation performance of anisotropic magnetic metamaterial antenna. For example, as a single anisotropic magnetic metamaterial antenna, half power beam width is 4 degrees in the H planes, and the gain of this antenna is 19.5 dBi at 10 GHz, achieving a 2.1 degree increment in half power beam width, and a 7.3 dB gain increment by loading with the FSS reflector. The simulating results are consistent with our experimental results.

Material parameter equation for rotating elliptical spherical cloaks

Ma Hua, Qu Shao-Bo, Xu Zhuo, Zhang Jie-Qiu, Wang Jia-Fu
Chin. Phys. B, 2009, 18 (1): 179-182 doi: 10.1088/1674-1056/18/1/028
Full Text: [PDF 1282 KB] (Downloads:1000)
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By using the coordinate transformation method, we have deduced the material parameter equation for rotating elliptical spherical cloaks and carried out simulation as well. The results indicate that the rotating elliptical spherical cloaking shell, which is made of meta-materials whose permittivity and permeability are governed by the equation deduced in this paper, can achieve perfect invisibility by excluding electromagnetic fields from the internal region without disturbing any external field.

Phase zone photon sieve

Jia Jia, Xie Chang-Qing
Chin. Phys. B, 2009, 18 (1): 183-188 doi: 10.1088/1674-1056/18/1/029
Full Text: [PDF 855 KB] (Downloads:898)
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A novel diffractive optical element, named phase zone photon sieve (PZPS), is presented. There are three kinds of phase plates in PZPSs: PZPS1, PZPS2, and PZPS3. Each of the PZPSs has its own structure and is made on quartz substrate by etching. The three PZPSs have stronger diffraction peak intensity than a photon sieve (PS) when the margin pinhole and zone line width are kept the same. The PZPS3 can produce a smaller central diffractive spot than the ordinary PS with the same number of zones on the Fresnel zone plate. We have given the design method for and the simulation of PZPS and PS. PZPS has potential applications in optical maskless lithography.

The recording of digital hologram at short distance and reconstruction using convolution approach

Chen Li-Ping, Lü Xiao-Xu
Chin. Phys. B, 2009, 18 (1): 189-194 doi: 10.1088/1674-1056/18/1/030
Full Text: [PDF 2842 KB] (Downloads:983)
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By adopting in-line lensless Fourier setup and phase-shifting technique, we recorded the phase-shifting digital hologram at short distance. As the Fresnel diffraction condition is no longer valid, the convolution approach is chosen for the reconstruction. However, the simulated reference wave for the reconstruction would suffer from severe under-sampling due to the comparatively large pixel size. To solve this problem, sinc-interpolation is introduced to get the pixel-size of the hologram reduced prior to the reconstruction. The experimental results show that an object image of high fidelity is obtained with this method.

Generation of superpositions of coherent states for an atomic sample in cavity QED

Zheng Shi-Biao
Chin. Phys. B, 2009, 18 (1): 195-198 doi: 10.1088/1674-1056/18/1/031
Full Text: [PDF 146 KB] (Downloads:798)
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This paper proposes a scheme for generation of superpositions of coherent states of the effective bosonic mode in a collection of atoms. In the scheme an atomic sample interacts with a slightly detuned cavity mode and a resonant strong classical field. Under certain conditions the atomic system evolves from a coherent state to a superposition of coherent states.

Ultranarrow absorptive spectral line induced by microwave field

Hu Zheng-Feng, Ma Yi-Sheng, Deng Jian-Liao, He Hui-Juan, Wang Yu-Zhu
Chin. Phys. B, 2009, 18 (1): 199-202 doi: 10.1088/1674-1056/18/1/032
Full Text: [PDF 167 KB] (Downloads:811)
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This paper investigates the absorptive spectral lines of four-level atomic system driven by a coupling, probe and microwave fields. Due to the perturbation of the microwave field, the original electromagnetically induced transparency is changed to electromagnetically induced absorption and the absorptive spectral line can be very narrow. This ultranarrow spectral line has potential applications to the microwave atomic frequency standard and the measurement of very weak magnetic field.

2D parameter optimization of Ne-like Cr x-ray laser on slab

Cheng Tao, Li Ying-Jun, Meng Li-Min, Yuan Su-Ying, Zhang Jie
Chin. Phys. B, 2009, 18 (1): 203-208 doi: 10.1088/1674-1056/18/1/033
Full Text: [PDF 1472 KB] (Downloads:754)
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A method of studying a non-equilibrium x-ray laser plasma is developed by extending the existing one-dimensional similarity equations to the case of two-dimensional plasma study in the directions perpendicular to the slab and along a focal line. With this method the characteristics of pre-plasma are optimized for transient neon-like Cr x-ray laser. It is found that when the duration and the intensity of 1.053μm pre-pulse are 1.2ns and 6.5 TW/cm2 respectively with a delay time of 1.5ns, the temperature and the temperature discrepancy each approach a proper state, which will provide a uniform distribution of properly ionized neon-like Cr ions before the arrival of pumping pulse.

Modulational instability of incoherently coupled beams in azobenzene-containing polymer with photoisomerization nonlinearity

Zhang Bing-Zhi, Cui Hu, She Wei-Long
Chin. Phys. B, 2009, 18 (1): 209-214 doi: 10.1088/1674-1056/18/1/034
Full Text: [PDF 424 KB] (Downloads:699)
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The modulational instability of two incoherently coupled beams in azobenzene-containing polymer with photoisomerization nonlinearity is investigated analytically and numerically. Our results show that as a precursor to spatial optical soliton formation, modulational instability can be adjusted and controlled by the wavelength combinations of the signal and background beams. We also discuss the dependences of strength of modulational instability on intensities of two signal beams and background beam. These findings make it possible to predict the formation of incoherently coupled soliton pairs in azobenzene-containing polymer.

Algorithm of far-field centre estimation based on phase-only matched filter

Gao Yan-Qi, Zhu Bao-Qiang, Liu Dai-Zhong, Liu Xiao-Feng, Lin Zun-Qi
Chin. Phys. B, 2009, 18 (1): 215-220 doi: 10.1088/1674-1056/18/1/035
Full Text: [PDF 3064 KB] (Downloads:857)
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Estimation of the far-field centre is carried out in beam auto-alignment. In this paper, the features of the far-field of a square beam are presented. Based on these features, a phase-only matched filter is designed, and the algorithm of centre estimation is developed. Using the simulated images with different kinds of noise and the 40 test images that are taken in sequence, the accuracy of this algorithm is estimated. Results show that the error is no more than one pixel for simulated noise images with a 99% probability, and the stability is restricted within one pixel for test images. Using the improved algorithm, the consumed time is reduced to 0.049s.

Optical soliton with group delay in microring coupled-resonator optical waveguides

Tian He, Zhang Yun-Dong, Wang Hao, Ouyang Qiu-Yun, Wang Nan, Yuan Ping
Chin. Phys. B, 2009, 18 (1): 221-224 doi: 10.1088/1674-1056/18/1/036
Full Text: [PDF 300 KB] (Downloads:922)
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This paper derives the dispersion relation of microring coupled-resonator optical waveguides (CROWs) without any approximation by using the transfer matrix method. Based on the established dispersion relation of CROWs it obtains the slow group velocity and dispersion coefficient. It finds that the effect of dispersion on optical pulses can be adjusted to balance the effect of nonlinearity by changing coupling coefficient or loss, so optical soliton with group delay can be obtained in microring CROWs. The optical soliton with group delay is of great significance for applications of microring CROWs in delay lines and optical buffers of future all-optical communication systems.

Optical matching layer structures in evanescent coupling photodiodes at a wavelength of 1.55μm: physics, design and simulation

Zhang Yun, Zuo Yu-Hua, Guo Jian-Chuan, Ding Wu-Chang, Cheng Bu-Wen, Yu Jin-Zhong, Wang Qi-Ming
Chin. Phys. B, 2009, 18 (1): 225-230 doi: 10.1088/1674-1056/18/1/037
Full Text: [PDF 1691 KB] (Downloads:941)
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We have studied the optical matching layers (OMLs) and external quantum efficiency in the evanescent coupling photodiodes (ECPDs) integrating a diluted waveguide as a fibre-to-waveguide coupler, by using the semi-vectorial beam propagation method (BPM). The physical basis of OML has been identified, thereby a general designing rule of OML is developed in such a kind of photodiode. In addition, the external quantum efficiency and the polarization sensitivity versus the absorption and coupling length are analysed. With an optical matching layer, the absorption medium with a length of 30μm could absorb 90% of the incident light at 1.55μm wavelength, thus the total absorption increases more than 7 times over that of the photodiode without any optical matching layer.

Effect of micro-dimple patterns on capillary pull-off force and friction force of silicon surface

Zhang Xiang-Jun, Dong Yun-Kai, Liu Yong-He, J. A. Schaefer
Chin. Phys. B, 2009, 18 (1): 231-237 doi: 10.1088/1674-1056/18/1/038
Full Text: [PDF 2087 KB] (Downloads:724)
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A microtribometer is used to measure and compare pull-off forces and friction forces exerted on (a) micro-dimpled silicon surfaces, (b) bare silicon surfaces, and (c) octadecyltrichlorosilane (OTS) treated silicon surfaces at different relative humidity (RH) levels separately. It is found that above a critical RH level, the capillary pull-off force increases abruptly and that the micro-dimple textured surface has a lower critical RH value as well as a higher pull-off force value than the other two surfaces. A micro topography parameter, namely sidewall area ratio, is found to play a major role in controlling the capillary pull-off force. Furthermore, micro-dimpled silicon surface is also proved to be not sensitive to variation in RH level, and can realize a stable and decreased friction coefficient compared with un-textured silicon surfaces. The reservoir-like function of micro dimples is considered to weaken or avoid the breakage effect of liquid bridges at different RH levels, thereby maintaining a stable frictional behaviour.

Rapid internal conversion in a symmetric molecule LD 700 studied by means of femtosecond fluorescence depletion

Guo Xun-Min, Wan Yan, Xia An-Dong, Wang Su-Fan, Liu Jian-Yong, Han Ke-Li
Chin. Phys. B, 2009, 18 (1): 142-148 doi: 10.1088/1674-1056/18/1/022
Full Text: [PDF 539 KB] (Downloads:792)
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The rapid internal conversion dynamics at room temperature is determined by using the femtosecond time-resolved fluorescence depletion measurements of a complex solvated molecule of LD 700 (rhodamine 700) combined with steady-state absorption and fluorescence spectroscopy, as well as quantum chemical calculation. The molecule is excited by a 50fs laser pulse at 400nm which directly populated the highly excited singlet state, the rapid internal conversions (ICs) are observed, which leads to the directional changes of the emission transition moment following photoexcitation to the highly excited singlet state S5 of LD 700.

Theoretical study of slowing supersonic CH3F molecular beams using electrostatic Stark decelerator

Deng Lian-Zhong, Fu Guang-Bin, Yin Jian-Ping
Chin. Phys. B, 2009, 18 (1): 149-156 doi: 10.1088/1674-1056/18/1/023
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We have calculated the Stark effect of CH3F molecules in external electrical fields, the rotational population of supersonic CH3F molecules in different quantum states, and analyse the motion of weak-field-seeking CH3F molecules in a state |J=1, KM= -1? inside the electrical field of a Stark decelerator by using a simple analytical model. Three-dimensional Monte Carlo simulation is performed to simulate the dynamical slowing process of molecules through the decelerator, and the results are compared with those obtained from the analytical model, including the phase stability, slowing efficiency as well as the translational temperature of the slowed molecular packet. Our study shows that with a modest dipole moment (~1.85 Debye) and a relatively slight molecular weight (~34.03), CH3F molecules in a state |J=1, KM= -1? are a good candidate for slowing with electrostatic field. With high voltages of ±10 kV applied on the decelerator, molecules of 370 m/s can be brought to a standstill within 200 slowing stages.

Spectra and oscillator strengths of 3p63d9--3p53d10 and 3p63d9--3p63d84p transitions for cobalt-like Sn23+ ion

Chen Ming-Lun, Yu Xiao-Guang
Chin. Phys. B, 2009, 18 (1): 157-160 doi: 10.1088/1674-1056/18/1/024
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This paper calculates the spectra and oscillator strengths for highly ionized cobalt-like Sn23+ ions 3p63d9--3p53d10, 3p63d9--3p63d84p transitions by using a multi-configuration self-consistent field method program together with the proposed fitting formula. The calculations have a good agreement with observations.

Density-dependent photoabsorption cross sections of atomic Xe

Ma Xiao-Guang
Chin. Phys. B, 2009, 18 (1): 161-166 doi: 10.1088/1674-1056/18/1/025
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The evolution of the photoabsorption cross sections of atomic xenon with number densities varying from ideal gas to condensed matter has been studied by an alternative view in the present work. The alternative expressions of the photoabsorption cross sections presented by Sun et al recently were used with the local field models that has proven to be generalized easily to multiatomic systems including molecules and condensed phase systems. The present results show that the variation of the photoabsorption cross sections of atomic xenon in the giant resonance region from the isolated to the condensed conditions is very small, which agrees well with the variation law of the solid and gas experiments.

The characteristics of O+HD (υ=0, j=0) reaction dynamics

Luo Wen-Lang, Ruan Wen, Zhang Li, Zhu Zheng-He, Fu Yi-Bei
Chin. Phys. B, 2009, 18 (1): 167-173 doi: 10.1088/1674-1056/18/1/026
Full Text: [PDF 477 KB] (Downloads:869)
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The analytical potential energy function of HDO is constructed at first using the many-body expansion method. The reaction dynamics of O+HD (υ=0, j=0) in five product channels are all studied by quasi-classical trajectory (QCT) method. The results show that the long-lived complex compound HDO is the dominant product at low collision energy. With increasing collision energy, O+HD → OH+D and O+HD → OD+H exchange reactions will occur with remarkable characteristics, such as near threshold energies, different reaction probabilities, and different reaction cross sections, implying the isotopic effect between H and D. With further increasing collision energy (e.g., up to 502.08 kJ/mol), O+HD → O+H+D will occur and induce the complete dissociation into single O, H, and D atoms.

Industrial diamonds grown in Ni70Mn25Co5--graphite--sulfur system under HPHT

Zhou Lin, Jia Xiao-Peng, Ma Hong-An, Zheng You-Jin, Li Yan-Tao
Chin. Phys. B, 2009, 18 (1): 333-338 doi: 10.1088/1674-1056/18/1/054
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This paper reports that diamond single crystals were synthesized from sulfur-added Ni70Mn25Co5+C system under high pressure and high temperature (HPHT). It was found that additive sulfur had inhibited the nucleation and growth of diamond to some extent. X-ray diffraction of the collected sample indicated that under the synthesis conditions, a new compound MnS had been formed through the reaction of additive sulfur with manganese in the catalyst. The MnS has a fcc structure, and its average crystal size was about 30 nm. By scanning electron microscope, the {111} surface of diamond was found to be flat, while there was usually a large depression on the central region of {100}. Further observation showed that there were many small upside-down pyramidal pits in the expression. The results of x-ray photoelectron spectroscopy shows that MnS can only be detected in the depression in the range of detection precision. It was inferred that MnS had been dissolved in the melted alloy during the growth experiment, and precipitated in the sequent quenching process.

Theoretical study of the stereodynamics of the He+HD+ reaction

Xu Wen-Wu, Liu Xin-Guo, Luan Shi-Xia, Sun Shan-Shu, Zhang Qing-Gang
Chin. Phys. B, 2009, 18 (1): 339-343 doi: 10.1088/1674-1056/18/1/055
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This paper investigates the stereodynamics of the reaction He+HD+ by the quasi-classical trajectory (QCT) method using the most accurate AQUILANTI surface [Aquilanti et al 2000 Mol. Phys. 98 1835]. The distribution Pr) of dihedral angle and the distribution P(θr) of angle between κ and j′ have been presented at three different collision energies. Four generalized polarization-dependent differential cross-sections (2π/σ)(dσ00/dωt), (2π/σ)(dσ20/ dωt), (2π/σ)(dσ22+/dωt),(2π/σ)(dσ22-/dωt) are also calculated. Some interesting results are obtained from the comparison of the stereodynamics of the title reaction at different collision energies.

Density functional theory calculations of tetracene on low index surfaces of copper crystal

Dou Wei-Dong, Zhang Han-Jie, Bao Shi-Ning
Chin. Phys. B, 2009, 18 (1): 344-348 doi: 10.1088/1674-1056/18/1/056
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This paper carries out the density functional theory calculations to study the adsorbate--substrate interaction between tetracene and Cu substrates (Cu (110) and Cu (100) surface). On each of the surfaces, two kinds of geometry are calculated, namely `flat-lying' mode and `upright standing' mode. For `flat-lying' geometry, the molecule is found to be aligned with its longer molecular axis along close-packed direction of the substrate surfaces. For `upright standing' geometry, the long axis of tetracene is found to be parallel to the surface normal of the substrate on Cu (110) surface. However, tetracene appears as `tilted' mode on Cu (100) surface. Structures with `flat-lying' mode have much larger adsorption energy and charge transfer upon adsorption than that with `upright standing' mode, indicating the preference of `flat-lying' geometry on both Cu (110) and Cu (100) surface.

Influence of optical interference and carrier lifetime on the short circuit current density of organic bulk heterojunction solar cells

You Hai-Long, Zhang Chun-Fu
Chin. Phys. B, 2009, 18 (1): 349-356 doi: 10.1088/1674-1056/18/1/057
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Based on simple analytical equations, short circuit current density (JSC) of the organic bulk heterojunction solar cells has been calculated. It is found that the optical interference effect plays a very important role in the determination of JSC; and obvious oscillatory behaviour of JSC was observed as a function of thickness. At the same time, the influence of the carrier lifetime on JSC also cannot be neglected. When the carrier lifetime is relatively short, JSC only increases at the initial stage and then decreases rapidly with the increase of active layer thickness. However, for a relatively long carrier lifetime, the exciton dissociation probability must be considered, and JSC behaves wave-like with the increase of active layer thickness. The validity of this model is confirmed by the experimental results.

Interaction of hydrogen molecules on Ni-doped single-walled carbon nanotube

Ni Mei-Yan, Wang Xian-Long, Zeng Zhi
Chin. Phys. B, 2009, 18 (1): 357-362 doi: 10.1088/1674-1056/18/1/058
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Adsorption of hydrogen molecules on an Ni-doped (8,0) single-walled carbon nanotube (SWNT) is investigated by using first-principles density functional calculations. The result shows that a single Ni atom adsorbed on the bridge site of the tube could cannot dissociate the H2, however it can chemisorb three H2 at most, with the average binding energy per H2 suitable for the hydrogen storage at the room temperature. More H2 would physisorb around an Ni atom weakly. As for the SWNT with an Ni dimer adsorbed, we find that when the H2 approaches the Ni--Ni bond, it dissociates without overcoming any barrier and makes bonds with Ni atom.

The structural analysis of protein sequences based on the quasi-amino acids code

Zhu Ping, Tang Xu-Qing, Xu Zhen-Yuan
Chin. Phys. B, 2009, 18 (1): 363-369 doi: 10.1088/1674-1056/18/1/059
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Proteomics is the study of proteins and their interactions in a cell. With the successful completion of the Human Genome Project, it comes the postgenome era when the proteomics technology is emerging. This paper studies protein molecule from the algebraic point of view. The algebraic system (,+,*) is introduced, where is the set of 64 codons. According to the characteristics of (,+,*), a novel quasi-amino acids code classification method is introduced and the corresponding algebraic operation table over the set ZU of the 16 kinds of quasi-amino acids is established. The internal relation is revealed about quasi-amino acids. The results show that there exist some very close correlations between the properties of the quasi-amino acids and the codon. All these correlation relationships may play an important part in establishing the logic relationship between codons and the quasi-amino acids during the course of life origination. According to Ma F et al (2003 J. Anhui Agricultural University 30 439), the corresponding relation and the excellent properties about amino acids code are very difficult to observe. The present paper shows that (ZU, ⊕,○x) is a field. Furthermore, the operational results display that the codon tga has different property from other stop codons. In fact, in the mitochondrion from human and ox genomic codon, tga is just tryptophane, is not the stop codon like in other genetic code, it is the case of the Chen W C et al (2002 Acta Biophysica Sinica 18(1) 87). The present theory avoids some inexplicable events of the 20 kinds of amino acids code, in other words it solves the problem of `the 64 codon assignments of mRNA to amino acids is probably completely wrong' proposed by Yang (2006 Progress in Modern Biomedicine 6 3).

Chaos game representation (CGR)-walk model for DNA sequences

Gao Jie, Xu Zhen-Yuan
Chin. Phys. B, 2009, 18 (1): 370-376 doi: 10.1088/1674-1056/18/1/060
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Chaos game representation (CGR) is an iterative mapping technique that processes sequences of units, such as nucleotides in a DNA sequence or amino acids in a protein, in order to determine the coordinates of their positions in a continuous space. This distribution of positions has two features: one is unique, and the other is source sequence that can be recovered from the coordinates so that the distance between positions may serve as a measure of similarity between the corresponding sequences. A CGR-walk model is proposed based on CGR coordinates for the DNA sequences. The CGR coordinates are converted into a time series, and a long-memory ARFIMA (p, d, q) model, where ARFIMA stands for autoregressive fractionally integrated moving average, is introduced into the DNA sequence analysis. This model is applied to simulating real CGR-walk sequence data of ten genomic sequences. Remarkably long-range correlations are uncovered in the data, and the results from these models are reasonably fitted with those from the ARFIMA (p, d, q) model.

Threshold property of a nematic liquid crystal cell with two grating surface substrates

Ye Wen-Jiang, Xing Hong-Yu, Yang Guo-Chen, Yuan Meng-Yao
Chin. Phys. B, 2009, 18 (1): 238-245 doi: 10.1088/1674-1056/18/1/039
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A grating surface can drive the liquid crystal molecules to orientate along the direction parallel or vertical to the projected plane of the grating surface. The nematic liquid crystal (NLC) cell manufactured with two pre-treated grating surface substrates may realize the vertical display, parallel display and twist display. In this paper, the threshold property of this NLC cell is investigated systematically. With the Frank elastic theory and the equivalent anchoring energy formula of grating surface substrate, the analytic expressions of the threshold voltage related to three displays are obtained, which are dependent on their geometrical parameters such as amplitude δ and pitch λ of the grating surface substrate. For a certain anchoring strength, the threshold voltage increases or decreases with the increase of the value δ/λ of the different displays.

Charge-sensitive deep level transient spectroscopy of helium-ion-irradiated silicon, as-irradiated and after thermal annealing

Li Bing-Sheng, Zhang Chong-Hong, Yang Yi-Tao, Zhou Li-Hong, Zhang Hong-Hua
Chin. Phys. B, 2009, 18 (1): 246-250 doi: 10.1088/1674-1056/18/1/040
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Electrically active defects in the phosphor-doped single-crystal silicon, induced by helium-ion irradiation under thermal annealing, have been investigated. Isothermal charge-sensitive deep-level transient spectroscopy was employed to study the activation energy and capture cross-section of helium-induced defects in silicon samples. It was shown that the activation energy levels produced by helium-ion irradiation first increased with increasing annealing temperature, with the maximum value of the activation energy occurring at 873K, and reduced with further increase of the annealing temperature. The energy levels of defects in the samples annealed at 873 and 1073K are found to be located near the mid-forbidden energy gap level so that they can act as thermally stable carrier recombination centres.

Dislocation formation and twinning from the crack tip in Ni3Al: molecular dynamics simulations

Xie Hong-Xian, Wang Chong-Yu, Yu Tao, Du Jun-Ping
Chin. Phys. B, 2009, 18 (1): 251-258 doi: 10.1088/1674-1056/18/1/041
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The mechanism of low-temperature deformation in a fracture process of L12 Ni3Al is studied by molecular dynamic simulations. Owing to the unstable stacking energy, the [ 0\bar {1}1] superdislocation is dissociated into partial dislocations separated by a stacking fault. The simulation results show that when the crack speed is larger than a critical speed, the Shockley partial dislocations will break forth from both the crack tip and the vicinity of the crack tip; subsequently the super intrinsic stacking faults are formed in adjacent {111} planes, meanwhile the super extrinsic stacking faults and twinning also occur. Our simulation results suggest that at low temperatures the ductile fracture in L12 Ni3Al is accompanied by twinning, which is produced by super-intrinsic stacking faults formed in adjacent {111} planes.

On some classes of two-dimensional local models in discrete two-dimensional monatomic FPU lattice with cubic and quartic potential

Xu Quan, Tian Qiang
Chin. Phys. B, 2009, 18 (1): 259-268 doi: 10.1088/1674-1056/18/1/042
Full Text: [PDF 5934 KB] (Downloads:771)
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This paper discusses the two-dimensional discrete monatomic Fermi--Pasta--Ulam lattice, by using the method of multiple-scale and the quasi-discreteness approach. By taking into account the interaction between the atoms in the lattice and their nearest neighbours, it obtains some classes of two-dimensional local models as follows: two-dimensional bright and dark discrete soliton trains, two-dimensional bright and dark line discrete breathers, and two-dimensional bright and dark discrete breather.

Phase transition and thermodynamic properties of TiO2 from first-principles calculations

Yu Jing-Xin, Fu Min, Ji Guang-Fu, Chen Xiang-Rong
Chin. Phys. B, 2009, 18 (1): 269-274 doi: 10.1088/1674-1056/18/1/043
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The pressure induced phase transitions of TiO2 from anatase to columbite structure and from rutile to columbite structure and the temperature induced phase transition from anatase to rutile structure and from columbite to rutile structure are investigated by ab initio plane-wave pseudopotential density functional theory method (DFT), together with quasi-harmonic Debye model. It is found that the zero-temperature transition pressures from anatase to columbite and from rutile to columbite are 4.55 GPa and 19.92GPa, respectively. The zero-pressure transition temperatures from anatase to rutile and from columbite to rutile are 950 K and 1500 K, respectively. Our results are consistent with the available experimental data and other theoretical results. Moreover, the dependence of the normalized primitive cell volume V/V0 on pressure and the dependences of thermal expansion coefficient ɑ on temperature and pressure are also obtained successfully.

First-principle study of Mg adsorption on Si(111) surfaces

Ying Min-Ju, Zhang Ping, Du Xiao-Long
Chin. Phys. B, 2009, 18 (1): 275-281 doi: 10.1088/1674-1056/18/1/044
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We have carried out first-principle calculations of Mg adsorption on Si(111) surfaces. Different adsorption sites and coverage effects have been considered. We found that the threefold hollow adsorption is energy-favoured in each coverage considered, while for the clean Si(111) surface of metallic feature, we found that 0.25 and 0.5 ML Mg adsorption leads to a semiconducting surface. The results for the electronic behaviour suggest a polarized covalent bonding between the Mg adatom and Si(111) surface.

Macroscopic spin and charge transport theory

Li Da-Fang, Shi Jun-Ren
Chin. Phys. B, 2009, 18 (1): 282-286 doi: 10.1088/1674-1056/18/1/045
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According to the general principle of non-equilibrium thermodynamics, we propose a set of macroscopic transport equations for the spin transport and the charge transport. In particular, the spin torque is introduced as a generalized `current density' to describe the phenomena associated with the spin non-conservation in a unified framework. The Einstein relations and the Onsager relations between different transport phenomena are established. Specifically, the spin transport properties of the isotropic non-magnetic and the isotropic magnetic two-dimensional electron gases are fully described by using this theory, in which only the macroscopic-spin-related transport phenomena allowed by the symmetry of the system are taken into account.

Quick preparation and thermal transport properties of nanostructured β-FeSi2 bulk material

Li Han, Tang Xin-Feng, Cao Wei-Qiang, Zhang Qing-Jie
Chin. Phys. B, 2009, 18 (1): 287-292 doi: 10.1088/1674-1056/18/1/046
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This paper reports that the nanostructured β-FeSi2 bulk materials are prepared by a new synthesis process by combining melt spinning (MS) and subsequent spark plasma sintering (SPS). It investigates the influence of linear speed of the rolling copper wheel, injection pressure and SPS regime on microstructure and phase composition of the rapidly solidified ribbons after MS and bulk production respectively, and discusses the effects of the microstructure on thermal transport properties. There are two crystalline phases (α-Fe2Si5 and ε-FeSi) in the rapidly solidified ribbons; the crystal grains become smaller when the cooling rate increases (the 20 nm minimum crystal of ε-FeSi is obtained). Having been sintered for 1 min above 1123K and annealed for 5min at 923 K, the single-phase nanostructured β-FeSi2 bulk materials with 200--500nm grain size and 98% relative density are obtained. The microstructure of β-FeSi2 has great effect on thermal transport properties. With decreasing sintering temperature, the grain size decreases, the thermal conductivity of β-FeSi2 is reduced remarkably. The thermal conductivity of β-FeSi2 decreases notably (reduced 72% at room temperature) in comparison with the β-FeSi2 prepared by traditional casting method.

The effects of fast neutron irradiation on oxygen in Czochralski silicon

Chen Gui-Feng, Yan Wen-Bo, Chen Hong-Jian, Li Xing-Hua, Li Yang-Xian
Chin. Phys. B, 2009, 18 (1): 293-297 doi: 10.1088/1674-1056/18/1/047
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The effects of fast neutron irradiation on oxygen atoms in Czochralski silicon (CZ-Si) are investigated systemically by using Fourier transform infrared (FTIR) spectrometer and positron annihilation technique (PAT). Through isochronal annealing, it is found that the trend of variation in interstitial oxygen concentration ([Oi]) in fast neutrons irradiated CZ-Si fluctuates largely with temperature increasing, especially between 500 and 700℃. After the CZ-Si is annealed at 600℃, the V4 appearing as three-dimensional vacancy clusters causes the formation of the molecule-like oxygen clusters, and more importantly these dimers with small binding energies (0.1--1.0eV) can diffuse into the Si lattices more easily than single oxygen atoms, thereby leading to the strong oxygen agglomerations. When the CZ-Si is annealed at temperature increasing up to 700℃, three-dimensional vacancy clusters disappear and the oxygen agglomerations decompose into single oxygen atoms (O) at interstitial sites. Results from FTIR spectrometer and PAT provide an insight into the nature of the [Oi] at temperatures between 500 and 700℃. It turns out that the large fluctuation of [Oi] after short-time annealing from 500 to 700℃ results from the transformation of fast neutron irradiation defects.

Rectifying effect of heterojunction fabricated in freestanding thin film of polyaniline containing azobenzene side-chain

Yin Zhi-Hua, Long Yun-Ze, Huang Kun, Wan Mei-Xiang, Chen Zhao-Jia
Chin. Phys. B, 2009, 18 (1): 298-302 doi: 10.1088/1674-1056/18/1/048
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An innovative heterojunction is fabricated between two sides of a freestanding thin film of HCl-doped polyaniline (PANI) derivative containing azobenzene side-chain, which is synthesized through an N-alkyl-substituted reaction. Of the film, the side with being irradiated by UV light during preparation is represented as `A side'; the other side without being irradiated is represented as `N side'. The electrical properties of the heterojunction are measured and the rectifying effect is observed in the {current--voltage} characteristic curves with the values of rectifying ratio (γ) being 20 at ±0.06 V at T= 77K and 4 at ±0.02V at T=300 K separately.

A super junction SiGe low-loss fast switching power diode

Ma Li, Gao Yong
Chin. Phys. B, 2009, 18 (1): 303-308 doi: 10.1088/1674-1056/18/1/049
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This paper proposes a novel super junction (SJ) SiGe switching power diode which has a columnar structure of alternating p- and n- doped pillar substituting conventional n- base region and has far thinner strained SiGe p+ layer to overcome the drawbacks of existing Si switching power diode. The SJ SiGe diode can achieve low specific on-resistance, high breakdown voltages and fast switching speed. The results indicate that the forward voltage drop of SJ SiGe diode is much lower than that of conventional Si power diode when the operating current densities do not exceed 1000 A/cm2, which is very good for getting lower operating loss. The forward voltage drop of the Si diode is 0.66V whereas that of the SJ SiGe diode is only 0.52 V at operating current density of 10 A/cm2. The breakdown voltages are 203 V for the former and 235 V for the latter. Compared with the conventional Si power diode, the reverse recovery time of SJ SiGe diode with 20 per cent Ge content is shortened by above a half and the peak reverse current is reduced by over 15{\%}. The SJ SiGe diode can remarkably improve the characteristics of power diode by combining the merits of both SJ structure and SiGe material.

Effect of substrate bias on negative bias temperature instability of ultra-deep sub-micro p-channel metal--oxide--semiconductor field-effect transistors

Cao Yan-Rong, Hao Yue, Ma Xiao-Hua, Hu Shi-Gang
Chin. Phys. B, 2009, 18 (1): 309-314 doi: 10.1088/1674-1056/18/1/050
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The effect of substrate bias on the degradation during applying a negative bias temperature (NBT) stress is studied in this paper. With a smaller gate voltage stress applied, the degradation of negative bias temperature instability (NBTI) is enhanced, and there comes forth an inflexion point. The degradation pace turns larger when the substrate bias is higher than the inflexion point. The substrate hot holes can be injected into oxide and generate additional oxide traps, inducing an inflexion phenomenon. When a constant substrate bias stress is applied, as the gate voltage stress increases, an inflexion comes into being also. The higher gate voltage causes the electrons to tunnel into the substrate from the poly, thereby generating the electron--hole pairs by impact ionization. The holes generated by impact ionization and the holes from the substrate all can be accelerated to high energies by the substrate bias. More additional oxide traps can be produced, and correspondingly, the degradation is strengthened by the substrate bias. The results of the alternate stress experiment show that the interface traps generated by the hot holes cannot be annealed, which is different from those generated by common holes.

A new analytical model of high voltage silicon on insulator (SOI) thin film devices

Hu Sheng-Dong, Zhang Bo, Li Zhao-Ji
Chin. Phys. B, 2009, 18 (1): 315-319 doi: 10.1088/1674-1056/18/1/051
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A new analytical model of high voltage silicon on insulator (SOI) thin film devices is proposed, and a formula of silicon critical electric field is derived as a function of silicon film thickness by solving a 2D Poisson equation from an effective ionization rate, with a threshold energy taken into account for electron multiplying. Unlike a conventional silicon critical electric field that is constant and independent of silicon film thickness, the proposed silicon critical electric field increases sharply with silicon film thickness decreasing especially in the case of thin films, and can come to 141V/μm at a film thickness of 0.1μm which is much larger than the normal value of about 30V/μm. From the proposed formula of silicon critical electric field, the expressions of dielectric layer electric field and vertical breakdown voltage (VB,V) are obtained. Based on the model, an ultra thin film can be used to enhance dielectric layer electric field and so increase vertical breakdown voltage for SOI devices because of its high silicon critical electric field, and with a dielectric layer thickness of 2μm the vertical breakdown voltages reach 852 and 300V for the silicon film thicknesses of 0.1 and 5μm, respectively. In addition, a relation between dielectric layer thickness and silicon film thickness is obtained, indicating a minimum vertical breakdown voltage that should be avoided when an SOI device is designed. 2D simulated results and some experimental results are in good agreement with analytical results.

Growth and characterization of InAsSb alloys by metalorganic chemical vapour deposition

Yan Jun-Feng, Wang Tao, Wang Jing-Wei, Zhang Zhi-Yong, Zhao Wu
Chin. Phys. B, 2009, 18 (1): 320-323 doi: 10.1088/1674-1056/18/1/052
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Low pressure metalorganic chemical vapour deposition (LP-MOCVD) growth and characteristics of InAsSb on (100) GaSb substrates are investigated. Mirror-like surfaces with a minimum lattice mismatch are obtained. The samples are studied by photoluminescence spectra, and the output is 3.17μm in wavelength. The surface of InAsSb epilayer shows that its morphological feature is dependent on buffer layer. With an InAs buffer layer used, the best surface is obtained. The InAsSb film shows to be of n-type conduction with an electron concentration of 8.52×1016cm-3.

Growth mechanism and photoluminescence of the SnO2 nanotwists on thin film and the SnO2 short nanowires on nanorods

Wang Bing, Xu Ping
Chin. Phys. B, 2009, 18 (1): 324-332 doi: 10.1088/1674-1056/18/1/053
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SnO2 nanotwists on thin film and SnO2 short nanowires on nanorods have been grown on single silicon substrates by using Au--Ag alloying catalyst assisted carbothermal evaporation of SnO2 and active carbon powders. The morphology and the structure of the prepared nanostructures are determined on the basis of field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electronic diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD), Raman and photoluminescence (PL) spectra analysis. The new peaks at 356, 450, and 489 nm in the measured PL spectra of two kinds of SnO2 nanostructures are observed, implying that more luminescence centres exist in these SnO2 nanostructures due to nanocrystals and defects. The growth mechanism of these nanostructures belongs to the vapour--liquid--solid (VLS) mechanism.

Nuclear energy generation rates on magnetar surfaces

Luo Zhi-Quan, Liu Hong-Lin, Liu Jing-Jing, Lai Xiang-Jun
Chin. Phys. B, 2009, 18 (1): 377-381 doi: 10.1088/1674-1056/18/1/061
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Based on the new screening model, this paper discusses the influence of superstrong magnetic fields on nuclear energy generation rates on the surface of magnetars. The obtained result shows that the superstrong magnetic fields can increase the nuclear energy generation rates by many orders of magnitude. The enhancement may have a significant influence for further study of the magnetars, especially for the cooling, the x-ray luminosity observation and the evolution of the magnetars.
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