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  • Intramolecular vibrational dynamical barrier due to extremely irrational couplings

    Ou Shu-Ching, Wu Guo-Zhen
    Chin. Phys. B 2007, 16 (10): 2952-2956
    The intramolecular vibrational dynamics due to extremely irrational couplings is demonstrated by contrast to the resonance couplings, for the three-mode case of H$_2$O as an example. The extremely irrational couplings are shown to impose such strong hindrance to intramolecular vibrational relaxation...

     
Chin. Phys. B  
  Chin. Phys. B--2007, Vol.16, No.10
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GENERAL

The periodic solution to a delayed sea--air oscillator coupling model for the El Ni?o--Southern Oscillation (ENSO)

Li Xiao-Jing
Chin. Phys., 2007, 16 (10): 2837-2840 doi: 10.1088/1009-1963/16/10/001
Full Text: [PDF 99 KB] (Downloads:549)
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A time-delay sea--air oscillator coupling model is studied. Using Mawhin's continuation theorem, the result on the existence of periodic solutions for the sea--air oscillator model is obtained.

Unified symmetry of non-holonomic singular systems

Li Yuan-Cheng, Wang Jing, Xia Li-Li, Hou Qi-Bao, Jing Hong-Xing
Chin. Phys., 2007, 16 (10): 2841-2844 doi: 10.1088/1009-1963/16/10/002
Full Text: [PDF 96 KB] (Downloads:443)
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Analytical mechanics methods for solving Whittaker equations

Mei Feng-Xiang, Xie Jia-Fang, Gang Tie-Qiang
Chin. Phys., 2007, 16 (10): 2845-2847 doi: 10.1088/1009-1963/16/10/003
Full Text: [PDF 87 KB] (Downloads:507)
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The purpose of this paper is to study the solution of the celebrated Whittaker equations by using analytical mechanics methods, including the Lagrange--Noether method, Hamilton--Poisson method and potential integral method.

Anomalous scaling in a non-Gaussian random shell model for passive scalars

Zhao Ying-Kui, Chen Shi-Gang, Wang Guang-Rui
Chin. Phys., 2007, 16 (10): 2848-2854 doi: 10.1088/1009-1963/16/10/004
Full Text: [PDF 646 KB] (Downloads:386)
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In this paper, we have introduced a shell-model of Kraichnan's passive scalar problem. Different from the original problem, the prescribed random velocity field is non-Gaussian and $\delta$ correlated in time, and its introduction is inspired by She and L\'{e}v\^{e}que (Phys. Rev. Lett. {\bf 72}, 336 (1994)). For comparison, we also give the passive scalar advected by the Gaussian random velocity field. The anomalous scaling exponents $H(p)$ of passive scalar advected by these two kinds of random velocities above are determined for structure function with values of $p$ up to 15 by Monte Carlo simulations of the random shell model, with Gear methods used to solve the stochastic differential equations. We find that the $H(p)$ advected by the non-Gaussian random velocity is not more anomalous than that advected by the Gaussian random velocity. Whether the advecting velocity is non-Gaussian or Gaussian, similar scaling exponents of passive scalar are obtained with the same molecular diffusivity.

The geometric phase of the quantum systems with slow but finite rate of the external time-dependent field

Jia Xin-Yan, Li Wei-Dong, Liang Jiu-Qing
Chin. Phys., 2007, 16 (10): 2855-2861 doi: 10.1088/1009-1963/16/10/005
Full Text: [PDF 135 KB] (Downloads:377)
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With the help of the time-dependent gauge transformation technique, we have studied the geometric phase of a spin-half particle in a rotating magnetic field. We have found that the slow but finite frequency of the rotating magnetic field will make the difference between the adiabatic geometric phase and the exact geometric phase. When the frequency is much smaller than the energy space and the adiabatic condition is perfectly guaranteed, the adiabatic approximation geometric phase is exactly consistent with the adiabatic geometric phase. A simple relation for the accuracy of the adiabatic approximation is given in terms of the changing rate of the frequency of the rotating magnetic field and the energy level space.

Unconditional secure two-way quantum dense key distribution

Lü Hua, Chen Ai-Xi, Yan Xu-Dong
Chin. Phys., 2007, 16 (10): 2862-2866 doi: 10.1088/1009-1963/16/10/006
Full Text: [PDF 132 KB] (Downloads:497)
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In this paper, we present a two-way quantum dense key distribution protocol. With double check modes, our scheme is secure regardless of the presence of noises. And with a quantum teleportation process, secret message can be encoded deterministically even if the quantum channel is highly lossy. Therefore, our scheme can be used in a realistic quantum channel regardless of the presence of noises and channel losses.

Probabilistic teleportation of an arbitrary GHZ-class state with a pure entangled two-particle quantum channel and its application in quantum state sharing

Zhou Ping, Li Xi-Han, Deng Fu-Guo, Zhou Hong-Yu
Chin. Phys., 2007, 16 (10): 2867-2874 doi: 10.1088/1009-1963/16/10/007
Full Text: [PDF 160 KB] (Downloads:694)
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This paper presents a scheme for probabilistic teleportation of an arbitrary GHZ-class state with a pure entangled two-particle quantum channel. The sender Alice first teleports the coefficients of the unknown state to the receiver Bob, and then Bob reconstructs the state with an auxiliary particle and some unitary operations if the teleportation succeeds. This scheme has the advantage of transmitting much less particles for teleporting an arbitrary GHZ-class state than others. Moreover, it discusses the application of this scheme in quantum state sharing.

A (2, 3) quantum threshold scheme based on Greenberger--Horne--Zeilinger state

Li Yuan, Zeng Gui-Hua
Chin. Phys., 2007, 16 (10): 2875-2879 doi: 10.1088/1009-1963/16/10/008
Full Text: [PDF 107 KB] (Downloads:428)
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In this paper, by using properties of quantum controlled-not manipulation and entanglement states, we have designed a novel (2, 3) quantum threshold scheme based on the Greenberger- Horne -Zeilinger (GHZ) state. The proposed scheme involves two phases, i.e. a secret sharing phase and a secret phase. Detailed proofs show that the proposed scheme is of unconditional security. Since the secret is shared among three participants, the proposed scheme may be applied to quantum key distribution and secret sharing.

Controlled teleportation of multi-qudit quantum information

Zhan Xiao-Gui, Li Hong-Mei, Ji Hua, Zeng Hao-Sheng
Chin. Phys., 2007, 16 (10): 2880-2887 doi: 10.1088/1009-1963/16/10/009
Full Text: [PDF 209 KB] (Downloads:670)
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We propose a scheme for realizing a controlled teleportation of random $M$-qudit quantum information under the control of $N$ agents. The resource consumption includes a prearranged $(2M + N + 1)$-qudit entangled quantum channel and $(2M + N + 1)\log _2 d$-bit classical communication. And the quantum operations used in the teleportation process are a series of generalized Bell-state measurements, single-qudit measurements, qudit $H$-gates, qudit-Pauli gates and qudit phase gates. It is shown that the original state can be restored by the receiver only on condition that all the agents work in collaboration with each others. If one agent does not cooperate with the other, the original state cannot be fully recovered.

Entanglement swapping of continuous variable using squeezed vacuum states

Yan Wei, Zhang Wei-Jun
Chin. Phys., 2007, 16 (10): 2885-2888 doi: 10.1088/1009-1963/16/10/010
Full Text: [PDF 101 KB] (Downloads:503)
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We present a realistic scheme for the entanglement swapping of continuous variable, in which a two-mode squeezed vacuum state serves as a quantum channel. The position sum and momentum difference of two local modes are measured. By taking the input entangled state also as a two-mode squeezed vacuum state, we investigate the average fidelity and the von Neumann entropy of the output state. The results show that the perfect teleportation can be achieved by increasing the squeezing of the quantum channel and that any nonzero squeezing in both the quantum channel and the input entangled state is sufficient to swap the entanglement.

Stability problem in Rindler spacetime

Tian Gui-Hua, Wang Shi-Kun, Zhong Shu-Quan
Chin. Phys., 2007, 16 (10): 2889-2893 doi: 10.1088/1009-1963/16/10/011
Full Text: [PDF 116 KB] (Downloads:550)
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The stability problem of the Rindler spacetime is carefully studies by using the scalar wave perturbation. Using two different coordinate systems, the scalar wave equation is investigated. The results are different in the two cases. They are analysed and compared with each other in detail. The following conclusions are obtained: (a) the Rindler spacetime as a whole is not stable; (b) the Rindler spacetime can exist stably only as part of the Minkowski spacetime, and the Minkowski spacetime can be a real entity independently; (c) there are some defects for the scalar wave equation written by the Rindler coordinates, and it is unsuitable for the investigation of the stability properties of the Rindler spacetime. All these results may shed some light on the stability properties of the Schwarzschild black hole. It is natural and reasonable for one to infer that: (a) perhaps the Regge--Wheeler equation is not sufficient to determine the stable properties; (b) the Schwarzschild black hole as a whole might be really unstable; (c) the Kruskal spacetime is stable and can exist as a real physical entity; whereas the Schwarzschild black hole can occur only as part of the Kruskal spacetime.

Improved calculation of relic gravitational waves

Zhao Wen
Chin. Phys., 2007, 16 (10): 2894-2902 doi: 10.1088/1009-1963/16/10/012
Full Text: [PDF 178 KB] (Downloads:411)
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In this paper, we have improved the calculation of the relic gravitational waves (RGW) in two aspects. First, we investigate the transfer function by taking into consideration the redshift-suppression effect, the accelerating expansion effect, the damping effect of free-streaming relativistic particles, and the damping effect of cosmic phase transition, and give a simple approximate analytic expression, which clearly illustrates the dependence on the cosmological parameters. Second, we develop a numerical method to calculate the primordial power spectrum of RGW in a very wide frequency range, where the observed constraints on $n_{\rm s}$ (the scalar spectral index) and $P_{\rm S}(k_0)$ (the amplitude of primordial scalar spectrum) and the Hamilton--Jacobi equation are used. This method is applied to two kinds of inflationary models, which satisfy the current constraints on $n_{\rm s}$, $\alpha$ (the running of $n_{\rm s}$) and $r$ (the tensor--scalar ratio). We plot them in the $r-{\it\Omega}_{\rm g}$ diagram, where ${\it\Omega}_{\rm g}$ is the strength of RGW, and study their measurements from the cosmic microwave background (CMB) experiments and laser interferometers.

Realization of generalized synchronization between different chaotic systems via scalar controller

Zhou Ping, Cao Yu-Xia
Chin. Phys., 2007, 16 (10): 2903-2907 doi: 10.1088/1009-1963/16/10/013
Full Text: [PDF 394 KB] (Downloads:599)
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In this paper, a very simple generalized synchronization method between different chaotic systems is presented. Only a scalar controller is used in this method. The method of obtaining the scalar controller from chaotic systems is established. The sufficient and necessary condition of generalized synchronization is obtained from a rigorous theory, and the sufficient and necessary condition of generalized synchronization is irrelative to chaotic system itself. Theoretical analyses and simulation results show that the method established in this paper is effective.

Dynamics of erbium-doped fibre laser with optical delay feedback and chaotic synchronization

Fan Wen-Hua, Tian Xiao-Jian, Chen Ju-Fang, Zheng Fan, Yu Yong-Li, Gao Bo, Luo Hong-E
Chin. Phys., 2007, 16 (10): 2908-2912 doi: 10.1088/1009-1963/16/10/014
Full Text: [PDF 574 KB] (Downloads:861)
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The dynamical behaviour of the erbium-doped fibre single-ring laser with an optical delay feedback is discussed. Simulation shows that as the delay rate increases, the lasing light displays period-doubling which leads to chaos and via reverse period-doubling route returns from chaos to periodic. At a particular delay rate the intermittently chaotic route to chaos is also observed. The identical synchronization based on chaos in this ring laser is demonstrated by numerical simulation.

Singular value decomposition with normalized period for magnetocaridiography signal processing

Li Zhuo, Liu Dang-Ting, Tian Ye, Chen Geng-Hua, Zhang Li-Hua, Yang Qian-Sheng, Feng Ji
Chin. Phys., 2007, 16 (10): 2913-2917 doi: 10.1088/1009-1963/16/10/015
Full Text: [PDF 930 KB] (Downloads:453)
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In this paper, we have developed an algorithm based on singular value decomposition (SVD) for matrix. And the novel SVD algorithm with normalized period of cardiac cycles is presented. The results from real magnetocardiography (MCG) data processing show that the new algorithm is better than the standard one not only in suppressing noises, but also in providing high-fidelity MCG signals.
CLASSICAL AREAS OF PHENOMENOLOGY

Generation and concentration of atomic entangled state via adiabatic evolution

Ye Sai-Yun
Chin. Phys., 2007, 16 (10): 2968-2972 doi: 10.1088/1009-1963/16/10/025
Full Text: [PDF 184 KB] (Downloads:465)
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Based on the idea of adiabatic evolution, we propose two probabilistic but simple schemes for generating maximally entangled states for two distant atoms and concentrating unknown atomic entangled states. Taking advantage of adiabatic passage, the atoms have no probability of being excited and thus the atomic spontaneous emission is suppressed. Furthermore, in the two schemes accurate adjustment of the interaction time is not required.

Inversionless gain enhancing due to Doppler broadening in a closed lambda-type system

Ma Hui, Tian Shu-Fen, Tan Xia, Tong Dian-Min, Fan Xi-Jun
Chin. Phys., 2007, 16 (10): 2973-2979 doi: 10.1088/1009-1963/16/10/026
Full Text: [PDF 586 KB] (Downloads:419)
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An analysis is made of the effect of Doppler broadening on gain without inversion (GWI) from different aspects in a closed lambda-type three-level system with an incoherent pump. It is shown that, regardless of the driving field being on resonance or not, for the counter- or co-propagating of the probe and driving fields (PDF), GWI does not monotonically decrease or increase with increasing Doppler width. Except for the case of counter-propagating PDF with off-resonance driving field, at a suitable Doppler width one can obtain a gain maximum value much larger than that without Doppler broadening; especially in the situation of the resonant driving field, the co-propagating geometry leads to a larger GWI. In addition, for the counter-propagating geometry, when Doppler width is larger enough, GWI oscillation occurs, and the oscillation amplitude and region increase with increasing Doppler width. These conclusions are very different from that obtained in previous investigation (Lukin {\it et al}, {\it Laser Phys.} {\bf 6} 436 (1996)).

Preparation of W state in resonant bimodal cavity quantum electrodynamics

Jia Lian-Jun, Yang Zhen-Biao
Chin. Phys., 2007, 16 (10): 2980-2983 doi: 10.1088/1009-1963/16/10/027
Full Text: [PDF 97 KB] (Downloads:446)
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A scheme is proposed for generating entangled W states with four cavity modes. In this scheme, we send a V-type three-level atom through two identical two-mode cavities in succession. After the atom exits from the second cavity, the four cavity modes are prepared in the W state. On the other hand we can obtain three-atom W states by sending three V-type three-level atoms through a two-mode cavity in turn. The present scheme does not require conditional measurement, and it is easily generalized to preparing $2n$-mode W states and $n$-atom W states.

Dressed multi-wave mixing in a V-type four-level atomic system

Jiang Tong, Zhang Yan-Peng, Nie Zhi-Qiang, Li Ling, Li Pei-Zhe, Shen Lei-Jian, Fu Xin, Gan Chen-Li, Zhao Rong-Kuo, Song Jian-Ping, Lu Ke-Qing
Chin. Phys., 2007, 16 (10): 2984-2992 doi: 10.1088/1009-1963/16/10/028
Full Text: [PDF 728 KB] (Downloads:534)
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The dressed four- and six-wave mixings in a V-type four-level system are considered. Under two different dressed conditions, two- and three-photon resonant Autler--Townes splittings, accompanied by enhancement and suppression of wave mixing signal, are obtained analytically. Meanwhile, an electromagnetic induced transparency of multi-wave mixing is presented, which shows multiple peaks and asymmetric effects caused by one-photon, two-photon and three-photon resonances, separately. The slow light propagation multiple region of multi-wave mixing signal is also obtained.

Realization of an efficient coherent combination via Michelson cavity

Jia Xiu-Jie, Liu Feng-Nian, Fu Sheng-Gui, Liu Yan-Ge, Yuan Shu-Zhong, Dong Xiao-Yi
Chin. Phys., 2007, 16 (10): 2993-2997 doi: 10.1088/1009-1963/16/10/029
Full Text: [PDF 604 KB] (Downloads:485)
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An intracavity coherent coupling Michelson erbium-doped fibre (EDF) laser (MCEDFL) is proposed and demonstrated. By using this laser system, we find a means to obtain a maximum power output at the same pumping power level. From the experiment based on fibre Bragg gratings (FBGs) with different reflectivities from 6{\%} to 100{\%}, we find that the reflectivity of the FBG plays a vital role in improving the performance of the MCEDFL. At the same time, the MCEDFL with a polarizer can be coherently combined effectively. This type of system, in principle, is compatible with other more powerful pumping methods, such as cladding pumping, and brings some novel perspectives to the realization of high power lasers.

Analytic approach to the small-signal frequency response of saturated semiconductor optical amplifiers using multisection model

Zhou En-Bo, Zhang Xin-Liang, Huang De-Xiu
Chin. Phys., 2007, 16 (10): 2998-3003 doi: 10.1088/1009-1963/16/10/030
Full Text: [PDF 496 KB] (Downloads:496)
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An analytic solution derived by multisection model to the small-signal frequency response (SSFR) of wavelength conversion based on cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) is presented. The result contains details that can affect the characteristics of SSFR significantly more than previous ones.

Oscillation of spatial solitons in a waveguide with a symmetrical refractive index profile

Dong Liang-Wei, Jin Hong-Zhen, Wang Hui
Chin. Phys., 2007, 16 (10): 3004-3008 doi: 10.1088/1009-1963/16/10/031
Full Text: [PDF 676 KB] (Downloads:364)
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Dynamics of (1+1)D spatial solitons in a Kerr medium with a transversely symmetrical refractive index profile is investigated. Propagation of solitons is analysed theoretically by using an effective-particle approach. Analytical results show that the soliton oscillates periodically with a variable acceleration. The expression of oscillatory period is derived by introducing a concept of `average acceleration'. Both acceleration and oscillatory period are determined by the parameters of the input soliton and the waveguide. Propagations of solitons are simulated numerically and good agreement is obtained between the theoretical and numerical results.
ATOMIC AND MOLECULAR PHYSICS

Neutralization process of Xeq+ ion grazing on Al(111) surface

Hu Bi-Tao, Zhang Hong-Jun, Zhang Jian, Song Yu-Shou, Wang Li-Li, Chen Chun-Hua, Gu Jian-Gan
Chin. Phys., 2007, 16 (10): 2918-2923 doi: 10.1088/1009-1963/16/10/016
Full Text: [PDF 1969 KB] (Downloads:411)
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A code has been developed to simulate the neutralization and grazing process of slow highly charged ion Xeq+ on Al(111) surface under the classical-over-the-barrier model. The image energy gain of Xeq+ ions are calculated and compared with experiment data. The simulation results of image energy gain are in good agreement with the experiment data. Meanwhile, in the present work, the reflection coefficient of incident Xeq+ on Al(111) surface as a function of the incidence angle, energy and charge state is also studied.

Population transfer via adiabatic passage in the Rydberg potassium atom

Li Xiao-Hong, Zhang Xian-Zhou, Zhang Rui-Zhou, Yang Xiang-Dong
Chin. Phys., 2007, 16 (10): 2924-2929 doi: 10.1088/1009-1963/16/10/017
Full Text: [PDF 944 KB] (Downloads:536)
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Using the time-dependent multilevel approach, we have calculated the coherent population transfer between the quantum states of potassium atom by a single frequency-chirped laser pulse. The result shows that a pair of sequential `broadband' frequency-chirped laser pulses can efficiently transfer population from the initial state of the ladder system to the target state. It is also found that the population can be efficiently transferred to a target state and trapped there by using an `intuitive' or a `counterintuitive' frequency sweep laser pulse in the case of `narrowband' frequency-chirped laser pulse. Our research shows that the complete population transfer is related to the pulse duration, chirp rate, and amplitude of the laser pulse.

Dominant wing spectroscopy of energy pooling collisions near the boundary layer involving thermal caesium vapour

Wang Tie-Yun, Huang Tao, Dong Shuang-Li, Xiao Lan-Tuan, Jia Suo-Tang
Chin. Phys., 2007, 16 (10): 2930-2933 doi: 10.1088/1009-1963/16/10/018
Full Text: [PDF 551 KB] (Downloads:512)
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We have observed the dominant wing spectroscopy of energy pooling collision near the boundary layer involving Cs atoms under the condition of moderate-to-high optical depths at line-centre. It appears from our experimental investigations that the energy-pooling fluorescence presents about 16 spectral lines, and all the lines can be assigned to the Cs atomic transitions. We find that all lines of the energy-pooling retrofluorescence from the heated Cs atomic vapour cell show two-peak profiles. In addition, its pumping power linear dependence in the energy pooling process has been measured and analysed.

Transition probabilities for NII 2p4f--2p3d and 2s2p23d--2s2p23p obtained by a semiclassical method

Shen Xiao-Zhi, Yuan Ping, Zhang Hua-Ming, Wang Jie
Chin. Phys., 2007, 16 (10): 2934-2937 doi: 10.1088/1009-1963/16/10/019
Full Text: [PDF 408 KB] (Downloads:528)
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Based on NII spectra, some transition probabilities for 2p4f--2p3d and 2s2p$^2$3d--2s2p$^2$3p are obtained by a semiclassical method. The results are in good agreement with other measurements and the data reported by the National Institute of Standards and Technology. The transition probability for a line of 424.18nm is reported for the first time. Meanwhile, a feasible method of calculating transition parameters related to special excited configurations or highly excited states is provided.

Generalized oscillator strengths for some higher valence-shell excitations of krypton atom

Zhu Lin-Fan, Zhang Fang-Xin, Cheng Hua-Dong, Yuan Hui, Yuan Zhen-Sheng, Li Wen-Bin, Liu Xiao-Jing, Xu Ke-Zun
Chin. Phys., 2007, 16 (10): 2938-2945 doi: 10.1088/1009-1963/16/10/020
Full Text: [PDF 446 KB] (Downloads:430)
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The valence-shell excitations of krypton atom have been investigated by fast electron impact with an angle-resolved electron-energy-loss spectrometer. The generalized oscillator strengths for some higher mixed valence-shell excitations in 4d, 4f, 5p, 5d, 6s, 6p, 7s $\leftarrow$ 4p of krypton atom have been determined. Their profiles are discussed, and the generalized oscillator strengths for the electric monopole and quadrupole excitations in $5\p \leftarrow 4\p$ are compared with the calculations of Amusia \it et al. (\it Phys. Rev. A \textbf67 022703 (2003)). The differences between the experimental results and theoretical calculations show that more studies are needed.

Two-colour coherent control of multiphoton ionization: a comparison between long-range and short-range potential model atoms

Li Peng-Cheng, Zhou Xiao-Xin
Chin. Phys., 2007, 16 (10): 2946-2951 doi: 10.1088/1009-1963/16/10/021
Full Text: [PDF 645 KB] (Downloads:438)
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Using the numerical solution of the time-dependent Schr\"odinger equation of a one-dimensional model atom in a two-colour laser field, we have investigated the effects of the potential models on coherent control of atomic multiphoton ionization. It is found that the photoelectron spectra are obviously different for the long-range (Coulomb-like) and short-range (with no excited bound states) potential model atoms, which are produced by two-colour coherent control of atomic multiphoton ionization in a few laser cycles. Our results indicate that two-colour coherent control of atomic multiphoton ionization can be observed in simulations, depending on the choice of the model potentials.

Intramolecular vibrational dynamical barrier due to extremely irrational couplings Hot!

Ou Shu-Ching, Wu Guo-Zhen
Chin. Phys., 2007, 16 (10): 2952-2956 doi: 10.1088/1009-1963/16/10/022
Full Text: [PDF 701 KB] (Downloads:363)
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The intramolecular vibrational dynamics due to extremely irrational couplings is demonstrated by contrast to the resonance couplings, for the three-mode case of H$_2$O as an example. The extremely irrational couplings are shown to impose such strong hindrance to intramolecular vibrational relaxation (IVR) that they act as barriers. They restrict the direct action/energy transfer between the two stretching modes, though they allow the transfer between a stretching and a bending modes. In contrast, the resonance is more mediated by the bending mode and leads to chaotic IVR. It is also shown that there is a region in the dynamical space in which resonance and extremely irrational couplings coexist.

Control of photoassociation reaction F+H→HF with ultrashort laser pulse

Liu Li, Niu Ying-Yu, Yuan Kai-Jun, Cong Shu-Lin
Chin. Phys., 2007, 16 (10): 2957-2961 doi: 10.1088/1009-1963/16/10/023
Full Text: [PDF 594 KB] (Downloads:416)
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The laser-induced vibrational state-selectivity of product HF in photoassociation reaction H+F$\rightarrow$HF is theoretically investigated by using the time-dependent quantum wave packet method. The population transfer process from the continuum state down to the bound vibrational states can be controlled by the driving laser. The effects of laser pulse parameters and the initial momentum of the two collision atoms on the vibrational population of the product HF are discussed in detail. Photodissociation accompanied with the photoassociation process is also described.

Investigations on spectroscopic parameters, vibrational levels, classical turning points and inertial rotation and centrifugal distortion constants for the X1+g state of sodium dimer

Yu Ben-Hai, Dai Qi-Run, Shi De-Heng, Liu Yu-Fang
Chin. Phys., 2007, 16 (10): 2962-2967 doi: 10.1088/1009-1963/16/10/024
Full Text: [PDF 155 KB] (Downloads:434)
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The density functional theory (B3LYP, B3P86) and the quadratic configuration-interaction method including single and double substitutions (QCISD(T), QCISD) presented in Gaussian03 program package are employed to calculate the equilibrium internuclear distance $R_{\rm e}$, the dissociation energy $D_{\rm e }$ and the harmonic frequency $\omega _{\rm e}$ for the $X{}^{1}\Sigma^{ + }_{\rm g}$ state of sodium dimer in a number of basis sets. The conclusion is gained that the best $R_{\rm e}$, $D_{\rm e}$ and $\omega _{\rm e}$ results can be attained at the QCISD/6-311G(3df,3pd) level of theory. The potential energy curve at this level of theory for this state is obtained over a wide internuclear separation range from 0.16 to 2.0~nm and is fitted to the analytic Murrell--Sorbie function. The spectroscopic parameters $D_{\rm e}$, $D_{0}$, $R_{\rm e}$, $\omega _{\rm e}$, $\omega _{\rm e}\chi _{\rm e}$, $\alpha _{\rm e}$ and $B_{\rm e}$ are calculated to be 0.7219~eV, 0.7135~eV, 0.31813~nm, 151.63~cm$^{ - 1}$, 0.7288~cm$^{ - 1}$, 0.000729~cm$^{ - 1}$ and 0.1449~cm$^{ - 1}$, respectively, which are in good agreement with the measurements. With the potential obtained at the QCISD/6-311G(3df,3pd) level of theory, a total of 63 vibrational states is found when $J=0$ by solving the radial Schr\"{o}dinger equation of nuclear motion. The vibrational level, corresponding classical turning point and inertial rotation constant are computed for each vibrational state. The centrifugal distortion constants ($D_{\upsilon }\, H_{\upsilon }$, $L_{\upsilon }$, $M_{\upsilon }$, $N_{\upsilon }$ and $O_{\upsilon })$ are reported for the first time for the first 31 vibrational states when $J=0$.
CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Brownian dynamics simulation of two confined colloidal particles

He Dong-Hui, Yang Tao, Li Wei-Hua, Zhang Qing-Lan, Ma Hong-Ru
Chin. Phys., 2007, 16 (10): 3138-3145 doi: 10.1088/1009-1963/16/10/054
Full Text: [PDF 731 KB] (Downloads:376)
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The dynamics of two confined colloidal particles is studied by means of Brownian dynamics simulation. The autocorrelation function and cross-correlation function of the two colloidal spheres are computed by utilizing the formulae of hydrodynamic diffusion matrix expanded to different orders, as well as the accurate tensor through numerical algorithm. Furthermore, the numerical results are compared with the experimental results and the theoretical approximation. It is found that the relatively simple theoretical approximation gives good predictions when two spheres are far away from each other, but fails when the two spheres are very close.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Effect of sheath potential on electromagnetic radiation emitted from the rear surface of a metallic foil target

Zheng Jian, Li Zhi-Chao, Zhang Hui, Yu Chang-Xuan, Yabuuchi Toshinori, Tanaka Kazuo
Chin. Phys., 2007, 16 (10): 3009-3015 doi: 10.1088/1009-1963/16/10/032
Full Text: [PDF 266 KB] (Downloads:453)
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In ultra-intense laser--matter interactions, intense electric fields formed at the rear surface of a foil target may have strong influences on the motion of energetic electrons, and thereby affect the electromagnetic emissions from the rear surface, usually ascribed to transition radiation. Due to the electric fields, transition radiation occurs twice and bremsstrahlung radiation also happens because the electrons will cross the rear surface twice and have large accelerations. In the optic region, transition radiation is dominant. The radiation spectrum depends on the electric field only when the electrons are monochromatic, and becomes independent of the electric field when the electrons have a broadband momentum distribution. Therefore, in an actual experiment, the electric field at the rear surface of a foil could not be studied just with the measurement of optic emissions. In the terahertz region, both bremsstrahlung and transition radiations should be taken into account, and the radiation power could be enhanced in comparison with that without the inclusion of bremsstrahlung radiation. The frequency at which the maximum terahertz radiation appears depends on the electric field.

Study on the transition from filamentary discharge to diffuse discharge by using a dielectric barrier surface discharge device

Li Xue-Chen, Liu Zhi-Hui, Jia Peng-Ying, Li Li-Chun, Yin Zeng-Qian, Dong Li-Fang
Chin. Phys., 2007, 16 (10): 3016-3021 doi: 10.1088/1009-1963/16/10/033
Full Text: [PDF 1222 KB] (Downloads:625)
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Discharge characteristics have been investigated in different gases under different pressures using a dielectric barrier surface discharge device. Electrical measurements and optical emission spectroscopy are used to study the discharge, and the results obtained show that the discharges in atmospheric pressure helium and in low-pressure air are diffuse, while that in high-pressure air is filamentary. With decreasing pressure, the discharge in air can transit from filamentary to diffuse one. The results also indicate that corona discharge around the stripe electrode is important for the diffuse discharge. The spectral intensity of N$_2^+$ (391.4\,nm) relative to N$_{2}$ (337.1\,nm) is measured during the transition from diffuse to filamentary discharge. It is shown that relative spectral intensity increases during the discharge transition. This phenomenon implies that the averaged electron energy in diffuse discharge is higher than that in the filamentary discharge.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

SIR phasing by combination of SOLVE/RESOLVE and dual-space fragment extension involving OASIS

He Yao, Gu Yuan-Xin, Lin Zheng-Jiong, Zheng Chao-De, Fan Hai-Fu
Chin. Phys., 2007, 16 (10): 3022-3028 doi: 10.1088/1009-1963/16/10/034
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A new phasing procedure has been proposed for dealing with single isomorphous replacement (SIR) x-ray diffraction data. The procedure combines {SOLVE/RESOLVE} with the dual-space fragment extension involving {OASIS}. Two sets of SIR data at 0.28~nm resolution taken from the protein (R)-phycoerythrin (PDB code: 1LIA) were used in the test. For one of the two SIR data sets, a default run of {SOLVE/RESOLVE} based on the heavy-atom substructure found by {SHLEXD} led automatically to an interpretable electron density map. {OASIS} could not effectively improve the result. For the other set of SIR data, {SOLVE/RESOLVE} resulted in a fragmented model consisting of 454 of the total 668 residues, in which only 29 residues were docked into the sequence. Based on this model, 7 iteration cycles of {OASIS-DM-RESOLVE} (build only) yielded automatically a model of 547 residues with 133 residues docked into the sequence. The overall-averaged phase error decreased considerably and the quality of electron density map was improved significantly. Two more cycles of iterative {OASIS}-{DM}-{RESOLVE} were carried out, in which the output phases and figures of merit from {DM} were merged with that from the original run of {SOLVE/RESOLVE} before they were passed onto {RESOLVE} (build only). This led automatically to a model containing 452 residues with 173 docked into the sequence. The resultant electron density map is manually traceable. It is concluded that when results of {SOLVE/RESOLVE} are not sufficiently satisfactory, the combination of {SOLVE/RESOLVE} and {OASIS}-{DM}-{RESOLVE} (build only) may significantly improve them.

Simulation of multilayer Cu/Pd(100) heteroepitaxial growth by pulse laser deposition

Wu Feng-Min, Lu Hang-Jun, Fang Yun-Zhang, Huang Shi-Hua
Chin. Phys., 2007, 16 (10): 3029-3035 doi: 10.1088/1009-1963/16/10/035
Full Text: [PDF 3395 KB] (Downloads:1493)
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The heteroepitaxial growth of multilayer Cu/Pd(100) thin film via pulse laser deposition (PLD) at room temperature is simulated by using kinetic Monte Carlo (KMC) method with realistic physical parameters. The effects of mass transport between interlayers, edge diffusion of adatoms along the islands and instantaneous deposition are considered in the simulation model. Emphasis is placed on revealing the details of multilayer Cu/Pd(100) thin film growth and estimating the Ehrlich--Schwoebel (ES) barrier. It is shown that the instantaneous deposition in the PLD growth gives rise to the layer-by-layer growth mode, persisting up to about 9 monolayers (ML) of Cu/Pd(100). The ES barriers of $0.08\pm0.01$\,eV is estimated by comparing the KMC simulation results with the real scanning tunnelling microscopy (STM) measurements.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

A study on the microwave responses of YBCO and TBCCO thin films by coplanar resonator technique

Shi Li-Bin, Wang Yun-Fei, Ke Yu-Yang, Zhang Guo-Hua, Luo Sheng, Zhang Xue-Qiang, Li Chun-Guang, Li Hong, He Yu-Sheng
Chin. Phys., 2007, 16 (10): 3036-3041 doi: 10.1088/1009-1963/16/10/036
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YBa2Cu3O7(YBCO) thin films have been prepared by thermal coevaporation on LaAlO3(LAO) substrates, and Tl2Ba2CaCu2O8(TBCCO) thin films are synthesized by magnetron sputtering method on LAO substrates. The transition temperature Tc is 90\,K for YBCO/LAO and 104\,K for TBCCO/LAO. Microwave responses of the films are studied systematically by coplanar resonator technique. Energy gaps of the films obtained are {\it\Delta}0=1.04kBTc for YBCO films and ${\it\Delta}_0=0.84kBTc for TBCCO films by analysing the temperature dependence of resonant frequencies of coplanar resonator. Penetration depth at 0\,K \lambda 0=198nm for YBCO films and \lambda0 =200nm for TBCCO films could also be obtained by using the weak coupling theory and two fluid theory. Results of penetration depth and energy gap confirm the weak coupling properties of the films. In addition, microwave surface resistances Rs of YBCO/LAO and TBCCO/LAO are also investigated by analysing the quality factor and insert loss of the coplanar resonator. Surface resistance of TBCCO/LAO is less than that of YBCO/LAO, so that TBCCO/LAO films may have more potential applications.

First principles studies on the electronic structures of LiMxFe1-xPO4 (M=Co, Ni and Rh)

Ouyang Xiao-Fang, Shi Si-Qi, Ouyang Chu-Ying, Jiang Di-You, Liu De-Sheng, Ye Zhi-Qing, Lei Min-Sheng
Chin. Phys., 2007, 16 (10): 3042-3045 doi: 10.1088/1009-1963/16/10/037
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The local crystal structures and electronic structures of LiMxFe1-xPO4 $(M$ = Co, Ni, Rh) are studied through first-principles calculations. The lattice constants and unit cell volumes are smaller for the Co and Ni doped materials than for pure LiFePO$_{4}$, while larger than for the Rh doped material. The local structures around $M$ atoms in the doped materials are studied in details. The total density of states (DOS) and atomic projected DOS (PDOS) are all calculated and analysed in detail. The results give a reasonable prediction to the improvement of electronic conductivity through Fe-site doping in LiFePO4 material.

First-principles calculations of structural and thermodynamic properties of BeB2 compound

Wang Yan-Ju, Tan Jia-Jin, Wang Yong-Liang, Chen Xiang-Rong
Chin. Phys., 2007, 16 (10): 3046-3051 doi: 10.1088/1009-1963/16/10/038
Full Text: [PDF 596 KB] (Downloads:527)
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The lattice parameter, bulk modulus and pressure derivative of BeB2 are calculated by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density function theory. The calculated results agree well with the average experimental data and other theoretical results. Through the quasi-harmonic Debye model, the dependences of the normalized lattice parameters $a/a_{0, }c/c0 and the normalized primitive cell volume $V/V0 on pressure $P$, the variation of the thermal expansion coefficient $\alpha $ with pressure $P$ and temperature $T$, as well as the dependences of the heat capacity CV on pressure $P$ and temperature $T$ are obtained systematically.

Coherent excitons at different orientation arrangements of local transition dipole moments in circular light-harvesting complexes

Chu Qian-Jin, Yin Hua-Wei, Weng Yu-Xiang
Chin. Phys., 2007, 16 (10): 3052-3058 doi: 10.1088/1009-1963/16/10/039
Full Text: [PDF 271 KB] (Downloads:395)
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The coherent exciton plays an important role in the photosynthetic primary process, and its functions are deeply dependent on the orientation arrangements of local transition dipole moments (TDMs). We theoretically and systematically study the physical property of the coherent exciton at different orientation arrangements of the local TDMs in circular light-harvesting (LH) complexes. Especially, if the orientation arrangements are different, the delocalized TDMs of the coherent excitons and the energy locations of the optically active coherent excitons (OACEs) can be obviously different, and then there are more manners to capture, store and transfer light energy in and between LH complexes. Similarly, if the orientation arrangements are altered, light absorption and radiative intensities can be converted fully between the OACEs in the upper and lower coherent exciton bands, and then the blue and red shifts of the absorption and radiative bands of the pigment molecules can occur simultaneously at some orientation arrangements. If the systems are in the vicinities of the critical orientation arrangements, the weak static disorder or small thermal excitation can destroy the coherent electronic excitations, and then the coherent exciton cannot exist any more.

On the possibility of self-trapping transition of acoustic polarons in two dimensions

Hou Jun-Hua, Liang Xi-Xia
Chin. Phys., 2007, 16 (10): 3059-3066 doi: 10.1088/1009-1963/16/10/040
Full Text: [PDF 777 KB] (Downloads:446)
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A 2D electron-longitudinal-acoustic-phonon interaction Hamiltonian is derived and used to calculate the ground-state energy of the acoustic polarons in two dimensions. The numerical results for the ground-state energy of the acoustic polarons in two and three dimensions are obtained. The 3D results agree with those obtained by using the Feynman path-integral approach. It is found that the critical coupling constant of the transition from the quasifree state to the self-trapped state in the 2D case is much smaller than in the 3D case for a given cutoff wave-vector. The theory has been used to judge the possibility of the self-trapping for several real materials. The results indicate that the self-trappings of the electrons in AlN and the holes in AlN and GaN are expected to be observed in 2D systems.

The choosing of reproducing kernel particle shape function with mathematic proof

Xia Mao-Hui, Li Jin
Chin. Phys., 2007, 16 (10): 3067-3071 doi: 10.1088/1009-1963/16/10/041
Full Text: [PDF 116 KB] (Downloads:321)
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Many mechanical problems can be induced from differential equations with boundary conditions; there exist analytic and numerical methods for solving the differential equations. Usually it is not so easy to obtain analytic solutions. So it is necessary to give numerical solutions. The reproducing kernel particle (RKP) method is based on the Garlerkin Meshless method. According to the Sobolev space and Fourier transform, the RKP shape function is mathematically proved in this paper.

Proximity effects in normal mental/spin-splitting material/superconductor junctions

Yu Hua-Ling, Dong Zheng-Chao
Chin. Phys., 2007, 16 (10): 3072-3079 doi: 10.1088/1009-1963/16/10/042
Full Text: [PDF 454 KB] (Downloads:450)
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We extend the Blonder, Tinkham and Klapwijk (BTK) theory to the study of the coexistence between ferromagnetism and s-wave superconductivity in ferromagnet/superconductor (F/S) structures. It is found that the ferromagnetism and s-wave superconductivity can coexist near the F/S interface, which is induced by proximity effects. On the F side, the density of states (DOS) exhibits some superconducting-like properties, and it displays a damped oscillation from `0' to `$\pi$' states with increasing either the thickness of F film or the exchange energy. We also study the influences of the spin-polarized exchange splitting in the F and the spin-degeneracy by Rashba spin--orbit coupling (RSOC) in the two-dimensional electron gas (2DGE) on the proximity effects. It is shown that the case of Rashba spin-degeneracy is very different from that of the spin-polarized exchange splitting.

The electron transport characters in a nanostructure with the periodic magnetic-electric barriers

Lu Jian-Duo, Shao Liang, Hou Yang-Lai, Dai Hou-Mei
Chin. Phys., 2007, 16 (10): 3080-2086 doi: 10.1088/1009-1963/16/10/043
Full Text: [PDF 1297 KB] (Downloads:479)
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This paper detailedly studies the transmission probability, the spin polarization and the conductance of the ballistic electron in a nanostructure with the periodic magnetic-electric barriers. These observable quantities are found to be strongly dependent not only on the magnetic configuration, the incident electron energy and the incident wave vector, but also on the number of the periodic magnetic-electric barriers. The transmission coefficient and the spin polarization show a periodic pattern with the increase of the separation between two adjacent magnetic fields, and the resonance splitting increases as the number of periods increases. Surprisingly, it is found that a polarization can be achieved by spin-dependent resonant tunnelling in this structure, although the average magnetic field of the structure is zero.

Magnetotransport in a dual waveguide coupled by a finite barrier: Energy filter and directional coupler

Xie Yue-E, Chen Yuan-Ping, Yan Xiao-Hong
Chin. Phys., 2007, 16 (10): 3087-3092 doi: 10.1088/1009-1963/16/10/044
Full Text: [PDF 437 KB] (Downloads:415)
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We propose in this paper that a dual waveguide coupled by a finite barrier be able to serve as an energy filter under a perpendicular magnetic field. In the waveguide direction, the conductance exhibits a periodic square-wave pattern in which the miniband is controlled by the magnetic and potential modulation. The electrons with energies in the miniband can completely transfer along one waveguide while the other electrons undergo filtration. Compared with the coupled waveguide without magnetic modulation, the structure under magnetic field is found to be a good directional coupler. By adjusting the potential barrier and magnetic field, the electrons input from one port of waveguide can transfer to any other ports.

The quantum Kirchhoff equation and quantum current and energy spectrum of a homogeneous mesoscopic dissipation transmission line

Cui Yuan-Shun
Chin. Phys., 2007, 16 (10): 3093-3096 doi: 10.1088/1009-1963/16/10/045
Full Text: [PDF 105 KB] (Downloads:418)
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On the basis of quantization of charge, the loop equations of quantum circuits are investigated by using the Heisenberg motion equation for a mesoscopic dissipation transmission line. On the supposition that the system has a symmetry under translation in charge space, the quantum current and the quantum energy spectrum in the mesoscopic transmission line are given by solving their eigenvalue equations. Results show that the quantum current and the quantum energy spectrum are not only related to the parameters of the transmission line, but also dependent on the quantized character of the charge obviously.

Quantization of the double-qubit structure and quantum computation

Liang Bao-Long, Wang Ji-Suo
Chin. Phys., 2007, 16 (10): 3097-3103 doi: 10.1088/1009-1963/16/10/046
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The quantization scheme of a double-qubit structure with superconducting quantum interference devices (SQUIDs) is given. By introducing unitary matrices and using spectral decompositions, the Hamiltonian operator of the system is exactly formulated in compact forms in spin-1/2 notation. A scheme of designing controlled-phase-shift (CPS) gates is also proposed by using this circuit system.

Effect of STI-induced mechanical stress on leakage current in deep submicron CMOS devices

Li Rui, Yu Liu-Jiang, Dong Ye-Min, Wang Ching-Dong
Chin. Phys., 2007, 16 (10): 3104-3107 doi: 10.1088/1009-1963/16/10/047
Full Text: [PDF 514 KB] (Downloads:1696)
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The shallow trench isolation (STI) induced mechanical stress significantly affects the CMOS device off-state leakage behaviour. In this paper, we designed two types of devices to investigate this effect, and all leakage components, including sub-threshold leakage ($I_{\rm sub})$, gate-induced-drain-leakage ($I_{\rm GIDL})$, gate edge-direct-tunnelling leakage ($I_{\rm EDT})$ and band-to-band-tunnelling leakage ($I_{\rm BTBT})$ were analysed. For NMOS, $I_{\rm sub}$ can be reduced due to the mechanical stress induced higher boron concentration in well region. However, the GIDL component increases simultaneously as a result of the high well concentration induced drain-to-well depletion layer narrowing as well as the shrinkage of the energy gap. For PMOS, the only mechanical stress effect on leakage current is the energy gap narrowing induced GIDL increase.

Preparation, structural and electrical properties of zinc oxide grown on silicon nanoporous pillar array

Yao Zhi-Tao, Sun Xin-Rui, Xu Hai-Jun, Li Xin-Jian
Chin. Phys., 2007, 16 (10): 3108-3113 doi: 10.1088/1009-1963/16/10/048
Full Text: [PDF 944 KB] (Downloads:545)
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Polycrystalline thick film of zinc oxide (ZnO) is grown on a unique silicon substrate with a hierarchical structure, silicon nanoporous pillar array (Si-NPA), by using a vapour phase transport method. It is found that as-grown ZnO film is composed of closely packed ZnO crystallites with an average size of $\sim$$10\,\mu$m. The film resistivity of ZnO/Si-NPA is measured to be $\sim$$8.9\Omega\cdot$\,cm by the standard four probe method. The lengthwise $I$-$V$ curve of ZnO/Si-NPA heterostructure is measured. Theoretical analysis shows that the carrier transport across ZnO/Si-NPA heterojunction is dominated by two mechanisms, i.e. a thermionic process at high voltages and a quantum tunnelling process at low voltages.

Comparison of hot-hole injections in ultrashort channel LDD nMOSFETs with ultrathin oxide under an alternating stress

Chen Hai-Feng, Hao Yue, Ma Xiao-Hua, Cao Yan-Rong, Gao Zhi-Yuan, Gong Xin
Chin. Phys., 2007, 16 (10): 3114-3119 doi: 10.1088/1009-1963/16/10/049
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The behaviours of three types of hot-hole injections in ultrashort channel lightly doped drain (LDD) nMOSFETs with ultrathin oxide under an alternating stress have been compared. The three types of hot-hole injections, i.e. low gate voltage hot hole injection (LGVHHI), gate-induced drain leakage induced hot-hole injection (GIDLIHHI) and substrate hot-hole injection (SHHI), have different influences on the devices damaged already by the previous hot electron injection (HEI) because of the different locations of trapping holes and interface states induced by the three types of injections, i.e. three types of stresses. Experimental results show that GIDLIHHI and LGVHHI cannot recover the degradation of electron trapping, but SHHI can. Although SHHI can recover the device's performance, the recovery is slight and reaches saturation quickly, which is suggested here to be attributed to the fact that trapped holes are too few and the equilibrium is reached between the trapping and releasing of holes which can be set up quickly in the ultrathin oxide.

Rotation of ferromagnetic clusters induced magnetoresistance in the junction composed of La0.9Ca0.1MnO3 +δ and 1 wt.% Nb-doped SrTiO3

Xie Yan-Wu, Wang Deng-Jing, Shen Bao-Gen, Sun Ji-Rong
Chin. Phys., 2007, 16 (10): 3120-3124 doi: 10.1088/1009-1963/16/10/050
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A junction composed of ultrathin La0.9Ca0.1MnO3 + \delta (LCMO) film and 1 wt.{\%} Nb-doped SrTiO$_{3}$ was fabricated and its magnetoresistance (MR) was studied and compared with LCMO film. It was found that the resistance of the junction has a similar dependence on magnetic field as that of the LCMO film: the curvature of $R$--$H$ curves is upward above Curie temperature ($T_{\rm C}$) and downward below $T_{\rm C}$. These behaviours strongly suggest that the rotation of ferromagnetic clusters in manganite also causes MR in the corresponding junction. This MR can be qualitatively understood by the change of the width of the barrier induced by the rotation of ferromagnetic clusters. These results suggest a possibility to obtain junctions with large low-field MR.

Ferroelectric behaviour of 30nm BaTiO3 ceramics prepared by high pressure assisted sintering

Xiao Chang-Jiang, Chi Zhen-Hua, Li Feng-Ying, Feng Shao-Min, Jin Chang-Qing, Wang Xiao-Hui, Deng Xiang-Yun, Li Long-Tu
Chin. Phys., 2007, 16 (10): 3125-3128 doi: 10.1088/1009-1963/16/10/051
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Dense nanocrystalline BaTiO3 ceramics with a homogeneous grain size of 30\,nm was obtained by pressure assisted sintering. The ferroelectric behaviour of the ceramics was characterized by the dielectric peak at around 120\,\du, the $P$-$E$ hysteresis loop and some ferroelectric domains. These experimental results indicate that the critical grain size for the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30\,nm. The ferroelectric property decreasing with decreasing grain size can be explained by the lowered tetragonality and the `dilution' effect of grain boundaries.

Synthesis and characterization of Ca2Sn1-xCexO4 with blue luminescence originating from Ce4+ charge transfer transition

Fu Shi-Liu, Yin Tao, Chai Fei
Chin. Phys., 2007, 16 (10): 3129-3133 doi: 10.1088/1009-1963/16/10/052
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Ce4+-doped Ca2SnO$_{4}$ with a one-dimensional structure, which emits bright blue light, is prepared by using a solid-state reaction method. The x-ray diffraction results show that the Ce4+ ions doped in Ca$_{2}$SnO$_{4}$ occupy the Sn4+ sites. The excitation and emission spectra of Ca$_{2}$Sn$_{1-x}$Ce$_{x}$O$_{4}$ appear to have broad bands with peaks at $\sim$\,268\,nm and $\sim$\,442\,nm, respectively. A long excited-state lifetime ($\sim$\,83\,$\mu$s) for the emission from Ca$_{2}$Sn$_{1-x}$Ce$_{x}$O$_{4}$ suggests that the luminescence originates from a ligand-to-metal Ce4+ charge transfer (CT). The luminescent properties of Ca$_{2}$Sn$_{1 - x}$Ce$_{x}$O$_{4}$ have been compared with those of Sr$_{2}$CeO$_{4}$, which is the only material reported so far to show Ce$^{4 + }$ CT luminescence. More interestingly, it is observed that the emission intensity of Ca$_{2}$Sn$_{1 - x}$Ce$_{x}$O$_{4}$ with a small doping concentration (x $\sim$\,0.03) is comparable to that of Sr$_{2}$CeO$_{4}$ in which the concentration of active centre is 100{\%}.

Spectroscopic study of local thermal effect in transparent glass ceramics containing nanoparticles

Gao Dang-Li, Zhang Xiang-Yu, Zheng Hai-Rong
Chin. Phys., 2007, 16 (10): 3134-3137 doi: 10.1088/1009-1963/16/10/053
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Local thermal effect influencing the fluorescence of triply ionized rare earth ions doped in nanocrystals is studied with laser spectroscopy and theory of thermal transportation for transparent oxyfluoride glass ceramics containing nanocrystals. The result shows that the local temperature of the nanocrystals embedded in glass matrices is much higher than the environmental temperature of the sample. It is suggested that the temperature-dependent thermal energy induced by the light absorption must be considered when the theory of thermal transportation is applied to the study of local thermal effect.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Nuclear statistical equilibrium at core-collapse supernova

Liu Men-Quan, Zhang Jie, Luo Zhi-Quan
Chin. Phys., 2007, 16 (10): 3146-3149 doi: 10.1088/1009-1963/16/10/055
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A new improved nuclear partition function is employed to calculate the nuclear statistical equilibrium (NSE) in core-collapse supernova environment. The results show that the change of nucleus abundance is slight even though the temperature is higher than 10$^{11}$\,K when shock propagates, which indicates that the effect of the nuclear partition function is not so important as shown in the previous calculations, but it can also be considered in detailed simulation if it is sensitive to weak interaction rates in core-collapse supernova.
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