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Volume 23 Issue 8
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Original Articles
Local Minority Game with Evolutionary Strategies
YANG Wei-Song, LI Ping, ZOU Shan-Shan, WANG Bing-Hong
Chin. Phys. Lett. 2006, 23 (8): 1961-1964 .  
Abstract   PDF(pc) (235KB) ( 445 )
We study a model of local minority game in the random Kauffman network with evolutionary strategies and propose three methods to update the strategy of poor agents, with lower points in a given generation: namely to update either the Boolean function of their strategies randomly, or their local information of randomly adjacent m agents, or the number m of randomly chosen adjacent agents. The results of extended numerical simulations show that the behaviour of strategies in the three methods may enhance significantly the entire coordination of agents in the system. It is also found that a poor agent tends to use both small m strategies and correlated strategies, and the strategies of agents will finally self-organize into a steady-state distribution for a long time playing of the game.

Time-Dependent Variational Approach to the Phonon Dispersion Relation of the Commensurate Quantum Frenkel--Kontorova Model
Chin. Phys. Lett. 2006, 23 (8): 1965-1968 .  
Abstract   PDF(pc) (217KB) ( 578 )
The phonon dispersion relation of the commensurate quantum Frenkel--Kontorova model is studied by means of the time-dependent variational approach combined with a Hartree-type many-body trial wavefunction for the particles. The single-particle state is taken to be a frozen Jackiw--Kerman wavefunction. Under the condition of minimum uncertainty, equations of motion for the particle expectation values are derived to obtain the phonon dispersion relation. It is shown that the strength of the substrate potential and the phonon excitation gap are reduced due to the quantum fluctuations in comparison with those of the classical model. We also compare our results with those previously obtained by using the path-integral molecular dynamics.
SUSY QM in a One-Dimensional Box and Local Observable Quantities
Salvatore De Vincenzo
Chin. Phys. Lett. 2006, 23 (8): 1969-1972 .  
Abstract   PDF(pc) (209KB) ( 446 )
We investigate several Hamiltonians for a free particle in a one-dimensional box, in the context of supersymmetric quantum mechanics. Specifically, we study this problem with the Neumann boundary condition, the periodic and antiperiodic boundary condition, and some mixed and complex boundary conditions. This is achieved by using an approach recently proposed which expresses the factorization of the partner Hamiltonians in terms of the probability density and current for the ground-state eigenfunction of one of them.
Efficient One-Sender Versus N-Receiver Quantum Secure Direct Communication
MAN Zhong-Xiao, XIA Yun-Jie
Chin. Phys. Lett. 2006, 23 (8): 1973-1975 .  
Abstract   PDF(pc) (195KB) ( 522 )
An efficient quantum secure direct communication protocol with one-sender versus N-receiver is proposed. The secret bits can be encoded in the N+1-particle GHZ states and can be decoded by the N receivers with a classical information of the sender plus their own measurement outcomes. Any attacks can be detected by comparing measurement results on the detecting states.
Quantum Key Distribution Using High-Dimensional Quantum Error-Avoiding Code
LIU Wen-Yu, LI Ning, LIU Yu
Chin. Phys. Lett. 2006, 23 (8): 1976-1979 .  
Abstract   PDF(pc) (215KB) ( 408 )
Using high-dimensional quantum error-avoiding code, we present two new quantum key distribution protocols over a collective noisy channel, i.e. six-photon and five-photon quantum error-avoiding codes. Compared with the previous protocols using four-photon and three-photon quantum error-avoiding code, the qubit efficiencies of the new protocols have increases of 16.67% and 5% respectively. In addition, the security of these protocols is analysed with a conclusion that the new protocols are much more secure than the four-photon and three-photon ones.
Teleportation for an Ionic Entangled Internal State by Entanglement Swapping
ZHENG Xiao-Juan, FANG Mao-Fa, LIAO Xiang-Ping, CAI Jian-Wu
Chin. Phys. Lett. 2006, 23 (8): 1980-1983 .  
Abstract   PDF(pc) (219KB) ( 464 )
We present an effective scheme to teleport an unknown ionic entangled internal state via trapped ions ithout joint Bell-state measurement. In the constructed quantum channel process, we adopt entanglement swapping to avoid decrease of entanglement during the distribution of particles. Thus our scheme provides new prospects for quantum teleportation over longer distance. The distinct advantages of our scheme are that our scheme is insensitive to heating of vibrational mode and can be generalized to teleport an N-ion electronic entangled GHZ class state. Furthermore, in our scheme the success probability can reach 1.
Efficient Scheme for Greenberger--Horne--Zeilinger State and Cluster State with Trapped Ions
ZHAN Zhi-Ming, YANG Wen-Xing, LI Wei-Bin, LI Jia-Hua
Chin. Phys. Lett. 2006, 23 (8): 1984-1987 .  
Abstract   PDF(pc) (214KB) ( 462 )
We propose a scheme to generate the Greenberger--Horne--Zeilinger (GHZ) states and the cluster states of many trapped ions. In the scheme, the ion is illuminated by a single laser tuned to the first lower vibrational sideband. The scheme only requires resonant interactions. Thus the scheme is very simple and the quantum dynamics operation can be realized at a high speed, which is important in view of decoherence.
Multiparty Quantum Secret Sharing of Classical Message using Cavity Quantum Electrodynamic System
HAN Lian-Fang, LIU Yi-Min, ZHANG Zhan-Jun,
Chin. Phys. Lett. 2006, 23 (8): 1988-1991 .  
Abstract   PDF(pc) (210KB) ( 426 )
An experimental feasible scheme of multiparty secret sharing of classical messages is proposed, based on a cavity quantum electrodynamic system. The secret messages are imposed on atomic Bell states initially in the sender's possession by local unitary operations. By swapping quantum entanglement of atomic Bell states, the secret messages are split into several parts and each part is distributed to a separate party. In this case, any subset of the entire party group can not read out the secret message but the entirety via mutual ooperations. In this scheme, to discriminate atomic Bell states, additional classical fields are employed besides the same highly-detuned single-mode cavities used to prepare atomic Bell states. This scheme is insensitive to the cavity decay and the thermal field, and usual joint Bell-state measurements are unnecessary.
A Scheme for Connecting Quantum Components
TAN Xiao-Hui, FANG Xi-Ming, WANG Guo-You
Chin. Phys. Lett. 2006, 23 (8): 1992-1995 .  
Abstract   PDF(pc) (273KB) ( 323 )
We propose an approach to connect components of a quantum computer by using a linear cluster state, with which an arbitrary N-particle state can be perfectly propagated between quantum components in two ways that are based on feedback measurements and local transformation.
Liquid Nuclear Magnetic Resonance Implementation of Quantum Computation in Subspace
YAO Xi-Wei, XUE Fei, PANG Wen-Min, DU Jiang-Feng, ZHOU Xian-Yi, HAN Rong-Dian,
Chin. Phys. Lett. 2006, 23 (8): 1996-1999 .  
Abstract   PDF(pc) (270KB) ( 343 )
Based on the logical labelling method, we prepare an effective pure state in a subsystem of a three spin system via liquid nuclear magnetic resonance technique. Then with this subspace effective pure state we implement the Deutsch--Jozsa algorithm. The tomography for the subspace effective pure state and the corresponding spectrum of the output for the Deutsch--Jozsa algorithm agree with theoretical predictions, which shows that we have successfully implemented the Deutsch--Jozsa algorithm in a subsystem of a nuclear spin system and demonstrated a subspace quantum computation.
Nonlinear Wave in a Disc-Shaped Bose--Einstein Condensate
DUAN Wen-Shan, CHEN Jian-Hong, YANG Hong-Juan, SHI Yu-Ren, WANG Hong-Yan
Chin. Phys. Lett. 2006, 23 (8): 2000-2003 .  
Abstract   PDF(pc) (367KB) ( 430 )
We discuss the possible nonlinear waves of atomic matter wave in a Bose--Einstein condensate. One and two of two-dimensional (2D) dark solitons in the Bose--Einstein condensed system are investigated. A rich dynamics is studied for the interactions between two solitons. The interaction profiles of two solitons are greatly different if the angle between them are different. If the angle is small enough, the maximum amplitude during the interaction between two solitons is even less than that of a single soliton. However, if the angle is large enough, the maximum amplitude of two solitons can gradually attend to the sum of two soliton amplitudes.
Quantum Effects of Many Atoms in Spinor Bose--Einstein Condensates
YU Zhao-Xian, LIANG Jiu-Qing, JIAO Zhi-Yong
Chin. Phys. Lett. 2006, 23 (8): 2004-2007 .  
Abstract   PDF(pc) (315KB) ( 326 )
We have studied the evolutions of the population transfer, tunnelling current and antibunching effects between spin-(+1) and spin-(-1) in the case of the strong laser pulses. It is found that the population transfer and tunnelling current exhibit periodical oscillation. For the same Rabi frequency, the larger the atom number, the longer the oscillation period is. For the spin-(-1) component, when the atomic numbers are N=4 and 10, the antibunching effect can appear. For different atomic numbers, the appearing regions are very different. For spin component +1, the antibunching effect can always appear for different atomic numbers.

Non-Equilibrium Quantum Transport of Bosons through a Quantum Dot
CHEN Zuo-Zi, Lü Rong, ZHAI Hui, CHANG Lee
Chin. Phys. Lett. 2006, 23 (8): 2008-2011 .  
Abstract   PDF(pc) (275KB) ( 411 )
The quantum dot coupled to reservoirs is known as a typical mesoscopic setup to manifest the quantum characteristics of particles in transport. In analogue to many efforts made on the study of electronic quantum dots in the past decades, we study the transport of bosons through such a device. We first generalize the formula which relates the current to the local properties of dot in the bosonic situation. Then, as an illustrative example, we calculate the local density of state and lesser Green function of the localized boson with a bosonic Fano--Anderson model. The current--voltage (I-V) behaviour at zero temperature is presented, and in the bosonic dot it is the I-V curve, in contrast to the differential conductance in the electronic dot, which is found to be proportional to the spectral function.
Spontaneous Emission of an Inertial Multi-Level Atom in a Spacetime with a Reflecting Plane Boundary
ZHU Zhi-Ying, YU Hong-Wei
Chin. Phys. Lett. 2006, 23 (8): 2012-2015 .  
Abstract   PDF(pc) (215KB) ( 340 )
We calculate the contributions of the vacuum fluctuations and radiation reaction to the rate of change of the mean atomic energy for a multi-level hydrogen atom in the multipolar coupling scheme in a spacetime with a reflecting boundary. Our results show that, due to the presence of the boundary, the polarizations of the atom in the parallel direction and in the normal direction are weighted differently in terms of their contributions to the spontaneous emission rate, which is an oscillating function of the atom distance from the boundary. The possible experimental implications of our result are briefly discussed.
Brick Wall Model and the Spectrum of a Schwarzschild Black Hole
LI Xiang, ZHAO Zheng
Chin. Phys. Lett. 2006, 23 (8): 2016-2018 .  
Abstract   PDF(pc) (197KB) ( 339 )
The quantum entropy of a scalar field near a Schwarzschild black hole is investigated by employing the brick-wall model in the grand canonical ensemble. A positive chemical potential is introduced if the cutoff is set to be of order of the Planck length. We also discuss the relation between the chemical potential and the mass quantum of the black hole.
Tunnelling Effect and Hawking Radiation from a Vaidya Black Hole
REN Jun, ZHANG Jing-Yi, ZHAO Zheng
Chin. Phys. Lett. 2006, 23 (8): 2019-2022 .  
Abstract   PDF(pc) (199KB) ( 591 )
We extend Parikh’s study to the non-stationary black hole. As an example of the non-stationary black hole, we investigate the tunnelling effect and Hawking radiation from a Vaidya black hole whose Bondi mass is identical to its mass parameter. The Hawking radiation is considered as a tunnelling process across the event horizon and we calculate the tunnelling probability. It is found that the result is different from Parikh’s study because drH/dv is the function of Bondi mass m(v).

Unpredictability of Iteration Destination in an Integrate-and-Fire Circuit
DAI Jun, HU Chin-Kun, CHU Xiang-Sheng, HE Da-Ren,
Chin. Phys. Lett. 2006, 23 (8): 2023-2026 .  
Abstract   PDF(pc) (362KB) ( 294 )
Based on our previous study that discovered a new mechanism of the riddled-like basin appearance in piecewise continuous and noninvertible links of two conservative mappings, and the mechanism being the mixing of different attraction basins on a fat-fractal set, which was addressed as the forbidden region net [Phys. Rev. E 72 (2005) 025201(R)], we show numerically that the riddled-like attraction basins and the new mechanism appear in an integrate-and-fire circuit that can be described by piecewise continuous and noninvertible links of two dissipative mappings. This leads to the fact that vast increase of the precision of the initial condition results in practically no improvement in predictability of the iteration destination. Predictability is usually characterized by examining how error probability in the prediction, f(ε), scales with the precision ε under the initial condition. Typically, f(ε) ~ εα with 0 ≤ α ≤ 1 being the uncertainty exponent. For riddled-like basins, α should be zero, which is in good agreement with the numerical simulation results.

A General Response System Control Method Based on Backstepping Design for Synchronization of Continuous Scalar Chaotic Signal
WANG Jing, GAO Jin-Feng, MA Xi-Kui, LIANG Zhan-Hong
Chin. Phys. Lett. 2006, 23 (8): 2027-2029 .  
Abstract   PDF(pc) (236KB) ( 356 )
A general response system control method for synchronization of continuous scalar chaotic signal is presented. The proposed canonical general response system can cover most of the well-known chaotic systems. Conversely, each of these chaotic systems can also be used to construct the general response system. Furthermore, a novel controller of the proposed response system is designed based on backstepping technique, with which the output of the general response system and the given continuous chaotic signal can synchronize perfectly. Two numerical examples are given to illustrate the effectiveness of the proposed control method.
Effects of Periodic Forcing Amplitude on the Spiral Wave Resonance Drift
WU Ning-Jie, LI Bing-Wei, YING He-Ping
Chin. Phys. Lett. 2006, 23 (8): 2030-2033 .  
Abstract   PDF(pc) (366KB) ( 378 )
We study dynamics of spiral waves under a uniform periodic temporal forcing in an excitable medium. With a specific combination of frequency and amplitude of the external periodic forcing, a resonance drift of a spiral wave occurs along a straight line, and it is accompanied by a complicated `flower-like’ motion on each side of this bifurcate boundary line. It is confirmed that the straight-line drift frequency of spiral waves is not locked to the nature rotation frequency as the forcing amplitude expends the range of the spiral wave frequency. These results are further verified numerically for a simplified kinematical model.
Effect of Nonlinearity on Scattering Dynamics of Solitary Waves
WEN Zhen-Ying, ZHAO Hong, WANG Shun-Jin, ZHANG Xiu-Ming
Chin. Phys. Lett. 2006, 23 (8): 2034-2037 .  
Abstract   PDF(pc) (254KB) ( 442 )
We discuss the effect of nonlinearity on the scattering dynamics of solitary waves. The pure nth power model with the interaction potential V(x)=xn/n is present, which is a paradigm model in the study of solitary waves. The dependence of the scattering property on nonlinearity is closely related to the topological structures of the solitary waves. Moreover, for one of the four collision types, the rates of energy loss increase with the strength of nonlinearity and would reach 1 at n≥10, which means that the two solitary waves would become of fragments completely after the collision.
Study of W-Exchange Mode D0 → ФK0
DU Dong-Sheng, LI Ying, Lü Cai-Dian
Chin. Phys. Lett. 2006, 23 (8): 2038-2041 .  
Abstract   PDF(pc) (243KB) ( 392 )
We calculate the branching ratio of rare decay D0 → ФK0 using the perturbative QCD factorization approach based on kT factorization. Our result shows this branching ratio is (8.7±1.4)× 10-3, which is consistent with experimental data. We hope that the CLEO-C and BES-III can measure it more accurately, which will help us to understand QCD dynamics and D meson weak decays.
Theoretical Study on Negative Parity States of 191,193,195,197Au in Particle Triaxial-Rotor Model
CHEN Guo-Jie, LIU Yu-Xin, , CAO Hui, SONG Hui-Chao
Chin. Phys. Lett. 2006, 23 (8): 2042-2045 .  
Abstract   PDF(pc) (254KB) ( 315 )
By taking the particle triaxial-rotor model with variable moment of inertia, we investigate the energy spectra, the deformation and the single particle configuration of the negative-parity states in nuclei 191,193,195,197Au systemically. The calculated energy spectra agree well with experimental data. The obtained results indicate that the negative-parity states in 191,193,195,197Au originate from the proton-hole h11/2 configuration coupled to a triaxial oblate Hg core. Meanwhile the main single particle configuration of the bands 1, 2 and 3 are identified to be |5h11/2 1/2 > (α= - 1/2), |5h11/2 > (α= 1/2) and |5h9/2 7/2>;, respectively.

Shell-Model Calculations of β Decays in 18N
ZHANG Yu-Mei, XU Fu-Rong,
Chin. Phys. Lett. 2006, 23 (8): 2046-2048 .  
Abstract   PDF(pc) (241KB) ( 396 )
We investigate β decays of the neutron-rich nucleus 18N and the structure of the daughter nucleus 18O using the shell model. The reduced transition strengths B(GT) and branching ratios of the β decays in 18N are calculated in the psd and spsdpf} shell spaces with the WBT interaction. The calculations in the two different spaces are compared. The psd calculations obtain a better agreement with the observation of the β-delayed neutron emission, which seems to show that the observed properties of 18N and 18O are mainly produced by one particle being excited from the p-shell to the sd-shell.
Resonance Conversion as the Effective Way of Triggering the 178m2Hf Isomer Energy
Chin. Phys. Lett. 2006, 23 (8): 2049-2051 .  
Abstract   PDF(pc) (218KB) ( 446 )
Experiments on photo-induced de-excitation triggering of 178m2Hf are revisited. We present an alternative and more effective way of triggering by exploiting the resonance internal conversion. Full theoretical description of a possible channel is presented. It is therefore revisited the impact itself produced by those experiments.
Improvement of Test of Solar Neutrino Coherent Scattering with Torsion Pendulum
FENG Guo-Qiang, YANG Shan-Qing, TU Liang-Cheng, LUO Jun
Chin. Phys. Lett. 2006, 23 (8): 2052-2055 .  
Abstract   PDF(pc) (299KB) ( 340 )
A torsion pendulum containing two sapphire crystals and two lead rings is used to test Weber’s theory of enhanced solar neutrino coherent scattering. Our experiment gives a null result for the diurnal force with a noise level of 3.8×10-14N, which is 526 times smaller than the predicted value of Weber’s theory, and directly rules out Weber’s theory and the experimental result. This experiment also reveals a test of the weak equivalence principle with η (Al2O3, Pb) = (0.8±3.1) × 10-10 for masses falling toward the Sun.
Tritium Burn-up Depth and Tritium Break-Even Time
LI Cheng-Yue, DENG Bai-Quan, HUANG Jin-Hua, YAN Jian-Cheng
Chin. Phys. Lett. 2006, 23 (8): 2056-2058 .  
Abstract   PDF(pc) (197KB) ( 360 )
Similarly to but quite different from the xenon poisoning effects resulting from fission-produced iodine during the restart-up process of a fission reactor, we introduce a completely new concept of the tritium burn-up depth and tritium break-even time in the fusion energy research area. To show what the least required amount of tritium storage is used to start up a fusion reactor and how long a time the fusion reactor needs to be operated for achieving the tritium break-even during the initial start-up phase due to the finite tritium breeding time that is dependent on the tritium breeder, specific structure of breeding zone, layout of coolant flow pipe, tritium recovery scheme, extraction process, the tritium retention of reactor components, unrecoverable tritium fraction in breeder, leakage to the inertial gas container, and the natural decay etc., we describe this new phenomenon and answer this problem by setting up and by solving a set of equations, which express a dynamic subsystem model of the tritium inventory evolution in a fusion experimental breeder (FEB). It is found that the tritium burn-up depth is 317g and the tritium break-even time is approximately 240 full power days for FEB designed detail configuration and it is also found that after one-year operation, the tritium storage reaches 1.18kg that is more than the least required amount of tritium storage to start up three of FEB-like fusion reactors.

Theoretical Investigation of Decay Process in a Doubly Excited 2s2 1S0 State of He-Like Ions
ZHANG Deng-Hong, DONG Chen-Zhong, Fumihiro Koike
Chin. Phys. Lett. 2006, 23 (8): 2059-2062 .  
Abstract   PDF(pc) (255KB) ( 354 )
In the framework of multi-configuration Dirac--Fock theory, a detailed calculation is performed for the decay rates and the energies of the doubly excited 2s2 1S0 state of He-like ions, of which atomic number Z ranges from 6 to 92. The 2s2 1S0-1s 2S1/2 Auger decay is predominant at low Z regime, whereas the 2s2 1S0-1s2p 1,3P1 two-electron one-photon transitions become quite important in moderate and high Z regimes. For heavy ions with Z≥72, the contribution of 2s2 1S0-1s2s 3S1 M1 transition is significant. The Breit interaction considerably enhances the 2s2 1S0-1s 22S1/2 Auger rate at high Z regime.
Effect of Al3+ on Photoluminescence Properties of Eu3+-Doped BaZr(BO3)2 Phosphors
LI Guang-Min, LI-Lan, WANG Da-Jian, ZHANG Xiao-Song, TAO Yi
Chin. Phys. Lett. 2006, 23 (8): 2063-2065 .  
Abstract   PDF(pc) (219KB) ( 523 )
We discuss the influence of Al3+ on the charge transfer state (CTS) and the photoluminescence roperties of BaZr(BO3)2:Eu. The results reveal that there is a red shift which is about 20nm for the charge transfer state when doping with Al3+ and indicate the formation of `free’ electrons due to the change of microstructures. In addition, the influence of Al3+ doping on the PPR is analysed and a new explanation is raised based on the photo luminescent mechanism. It is the CTS intensity rather than the CTS energy that influences the peak-peak ratio.
Simulation of the Propagation Property of Metal Wires Terahertz Waveguides
HE Xiao-Yong, CAO Jun-Cheng, FENG Song-Lin
Chin. Phys. Lett. 2006, 23 (8): 2066-2069 .  
Abstract   PDF(pc) (249KB) ( 689 )
The propagation property of metal wires terahertz waveguides is studied and simulated under the framework of the Sommerfeld model. The group velocity dispersion, attenuation amplitude, transverse magnetic mode and propagating energy have been obtained by numerically solving the complex eigenvalue equation for the propagation constant. It is found that the group velocity dispersion and attenuation amplitude decrease with the increasing radii of metal wires. The energy power within the dielectric layer increase with the increase of radiation frequency.
Vectorial Nonparaxial Four-Petal Gaussian Beams and Their Propagation in Free Space
GAO Zeng-Hui, Lü Bai-Da
Chin. Phys. Lett. 2006, 23 (8): 2070-2073 .  
Abstract   PDF(pc) (424KB) ( 463 )
The vectorial nonparaxial four-petal Gaussian beam (FPGB) is introduced. The closed-form propagation expressions for the free-space propagation of FPGBs are derived and their more general applicable advantages are illustrated analytically and numerically. Some special interesting cases, in particular the paraxial one, are discussed. It is found that the parameter f =1/kw0 with the k being the wave number and w0 being the waist width plays a crucial role in determining the nonparaxiallity of FPGBs. For small values of the f parameter the paraxial approximation is allowable. In the nonparaxial regime the beam order n additionally affects the vectorial and nonparaxial behaviour of FPGBs.
A Compact Nanosecond-Pulse Shaping System Based on Pulse Stacking in Fibres
SUI Zhan, LIN Hong-Huan, WANG Jian-Jun, ZHAO Hong-Ming, LI Ming-Zhong, QIAN Lie-Jia, ZHU He-Yuan, FAN Dian-Yuan
Chin. Phys. Lett. 2006, 23 (8): 2074-2076 .  
Abstract   PDF(pc) (327KB) ( 563 )
We demonstrate a compact pulse shaping system based on temporal stacking of pulses in fibres, by which synchronized pulses of ultrashort and nanosecond lasers can be obtained. The system may generate shape-controllable pulses with a fast rise time and high-resolution within a time window of ~2.2ns by adjusting variable optical attenuators in the 32 fibre channels independently. With the help of optical amplifiers, the system delivers mJ-level pulses with a signal-to-noise ratio of ~35dB.
Simultaneously Large and Opposite Lateral Beam Shifts for TE and TM Modes on a Double Metal-Cladding Slab
LIU Xuan-Bin, CAO Zhuang-Qi, ZHU Peng-Fei, SHEN Qi-Shun, LIU Xiang-Min
Chin. Phys. Lett. 2006, 23 (8): 2077-2079 .  
Abstract   PDF(pc) (241KB) ( 577 )
We report simultaneously large and opposite Goos--Hänchen shifts for TE and TM beams on a double metal-cladding slab. Theoretical examination shows that both positive and negative lateral shifts are in two orders of the wavelength. It is also found that the magnitude of the lateral beam shift strongly depends on the thickness of the upper metal layer. The optimal thickness of the upper metal layer for zero reflection is found to be the critical thickness above which a negative beam shift occurs. Numerical calculations are in good agreement with the theoretical results.
Phase-Space Analysis of Wavefront Coding Imaging Systems
YANG Qing-Guo, SUN Jian-Feng, LIU Li-Ren
Chin. Phys. Lett. 2006, 23 (8): 2080-2083 .  
Abstract   PDF(pc) (261KB) ( 560 )
We explore the use of the Radon--Wigner transform, which is associated with the fractional Fourier transform of the pupil function, for determining the point spread function (PSF) of an incoherent defocused optical system. Then we introduce these phase-space tools to analyse the wavefront coding imaging system. It is shown that the shape of the PSF for such a system is highly invariant to the defocus-related aberrations except for a lateral shift. The optical transfer function of this system is also investigated briefly from a new understanding of ambiguity function.

Sideband-Induced Two-Photon Transparency
CHENG Guang-Ling, HU Xiang-Ming
Chin. Phys. Lett. 2006, 23 (8): 2084-2087 .  
Abstract   PDF(pc) (230KB) ( 380 )
We show that it is possible to use a single sideband to induce two-photon transparency in a three-level cascade medium. The medium simultaneously absorbs two photons as a one-step process when the middle level is far off one-photon resonance. A resonant sideband coupling on the upper transition and the two-photon one-step process drive the medium into a trapped state, and the dominant component is the ground state. Thus almost all population is trapped in the ground state and the two-photon absorption is dramatically suppressed. We present a numerical calculation for arbitrary values of the atomic and field parameters and also provide an analytic description for the required conditions.
Characteristics of Nd:GdVO4 Laser with Different Nd-Doping Concentrations
ZHANG Ling, ZHANG Chun-Yu, WEI Zhi-Yi, ZHANG Zhi-Guo, Stephan Strohmaier, Hans J. Eichler
Chin. Phys. Lett. 2006, 23 (8): 2088-2091 .  
Abstract   PDF(pc) (223KB) ( 474 )
We report the properties of a compact diode-pumped continuous-wave Nd:GdVO4 laser with a linear cavity and different Nd-doped laser crystals. In a 0.2at.% Nd-doped Nd:GdVO4 laser, 1.54W output
laser power is achieved at 912nm wavelength with a slope efficiency of 24.8% at an absorbed pump power of 9.4W. With 0.3at.% Nd-doping concentration, we can obtain the either single-wavelength emission at 1064nm or 912nm or the dual-wavelength emission at 1064nm and 912nm by controlling the incident pump power. From an incident pump power of 11.6W, the 1064nm emission between 4F3/2 and 4I11/2 is suppressed completely by the 912nm emission between 4F3/2 and 4I9/2. We obtain 670mW output of the 912nm single-wavelength laser emission with a slope efficiency of 5.5% by taking an incident pump power of 18.4W. Using a Nd:GdVO4 laser with 0.4at.% Nd-doping concentration, we obtain either the single-wavelength emission at 1064nm or the dual-wavelength emission at both 1064nm and 912nm by increasing the incident pump power. We observe a strong competition process in the dual-wavelength laser.
Realization of Stable Narrow Linewidth Dual-Wavelength Lasing in an Erbium-Doped Fibre Laser by Cleaving the Wavelength-Selective Filter Spectrum
JIA Xiu-Jie, LIU Yan-Ge, SI Li-Bin, GUO Zhan-Cheng, FU Sheng-Gui, LIU Feng-Nian, YUAN Shu-Zhong, DONG Xiao-Yi
Chin. Phys. Lett. 2006, 23 (8): 2092-2094 .  
Abstract   PDF(pc) (238KB) ( 529 )
We propose and demonstrate a new concept of stable narrow-line-width and close wavelength spacing dual-wavelength lasing in an Er-doped fibre ring laser (EDFRL) by cleaving the spectrum with a wavelength-selective component in the EDFRL. A fibre loop mirror (FLM) combining with a polarization controller (PC) acts as the cleaver. The cleaver can produce a fine pectinate spectrum. By adjusting the PC, the fine pectinate spectrum can be so changeable that cleaving the spectrum of a fibre Bragg grating (FBG) into two parts. As a result, we obtain the dual-wavelength fibre lasering with a bandwidth of only 0.03nm and a wavelength spacing of only 0.07nm. Furthermore, the laser can also perform stable switchable single wavelength or stable different-bandwidth dual-wavelength by carefully adjusting the PC at room temperature.

Compact, Low Threshold Nd3+:YVO4 Self-Raman Laser at 1178nm
WANG Bao-Shan, TAN Hui-Ming, GAO Lan-Lan, PENG Ji-Ying, MIAO Jie-Guang,
Chin. Phys. Lett. 2006, 23 (8): 2095-2097 .  
Abstract   PDF(pc) (210KB) ( 521 )
A compact low-threshold Raman laser at 1178nm is experimentally realized by using a diode-end-pumped actively Q-switched Nd3+:YVO4 self-Raman laser. The threshold is 370mW at a pulse repetition frequency of 5kHz. The maximum Raman laser output is 182mW with the pulse duration smaller than 20ns at a pulse repetition frequency of 30kHz with 1.8W incident power. The optical efficiency from the incident power to the Raman laser is 10% and the slope efficiency is 13.5%.
Compact Single-Stage Femtosecond Multipass Ti:Sapphire Amplifier at 1kHz with High Beam Quality
ZHAO Wei, WANG Yi-Shan, CHENG Zhao, ZHU Shao-Lan, LIU Hong-Jun, LING Wei-Jun, CHEN Guo-Fu
Chin. Phys. Lett. 2006, 23 (8): 2098-2100 .  
Abstract   PDF(pc) (470KB) ( 575 )
A compact femtosecond Ti:sapphire amplifier system is reported using single-stage multipass configuration with high beam quality. A high dispersion glass stretcher and a pair of double prisms for compression are introduced based on broadband femtosecond seed pulses. The non-grating-based pulse stretcher and compressor are advantageous to increase high beam quality and to reduce the high-order dispersion. A Gaussian filter is used to reduce the gain narrowing effect in amplification. The compact femtosecond Ti:sapphire nine-pass amplifier delivers pulses with a duration of 26fs and an energy of 800μJ at 7mJ pumping pulses energy at 1kHz. The 1-kHz femtosecond amplifier with high beam quality and high stability is very suitable for ultrafast physics research applications, such as attosecond science, ultra-precision micromachining, and THz wave generation.
Transition from Backscattering Speckles to Phase Conjugation in LiNbO3:Fe
WU Qiang, XU Jing-Jun, RUPP Romano, ZHANG Xin-Zheng, LOU Ci-Bo, BUGAYCHUK Sveta
Chin. Phys. Lett. 2006, 23 (8): 2101-2104 .  
Abstract   PDF(pc) (395KB) ( 418 )
We investigate the backscattering for converging beams in iron-doped lithium niobate crystals. Due to the nonlinear properties of the crystal, backscattering exhibits temporally fluctuating speckles that make a transition to the phase conjugate of the incident beam under certain circumstances. Our observation seems to point to a new kind of self-pumped phase conjugation in photorefractive media.

Optical Performance and Nonlinear Scattering of Soluble Polystyrene Grafted Multi-Walled Carbon Nanotubes
TONG Rui, WU Hui-Xia, QIU Xue-Qiong, QIAN Shi-Xiong, LIN Yang-Hui, CAI Rui-Fang
Chin. Phys. Lett. 2006, 23 (8): 2105-2108 .  
Abstract   PDF(pc) (680KB) ( 537 )
Three soluble polystyrene grafted multi-walled carbon nanotube (MWNT) samples are synthesized, and their optical performance and nonlinear scattering properties are investigated by z-scan method using nanosecond pulses of 532nm from a frequency-doubled Q-switched Nd:YLF laser. Analysis of the experimental results shows that other than nonlinear scattering, nonlinear absorption plays a major role in optical limiting performance of these stable and well-dispersed suspensions. These new synthesized materials which can be better dispersed in common organic solvents than MWNT itself can be considered as potential sources for further optical applications.
Evolution and Stability of Dark Holographic Solitons in Photorefractive Dissipative Systems
ZHANG Hui-Lan, LIU Jin-Song
Chin. Phys. Lett. 2006, 23 (8): 2109-2112 .  
Abstract   PDF(pc) (737KB) ( 350 )
The dynamics evolution of dark holographic solutions in a dissipative system is investigated numerically provided that the double balance, i.e. diffraction is balanced by nonlinearity and loss is balanced by gain, is satisfied. The influence of the system parameters, such as the linear loss of the crystal, the external biased field and the angel between input beams, on the stable propagation of soliton beams is discussed numerically. Results show that such solitons can be easily amplified or absorbed by adjusting these system parameters. Furthermore, numerical simulations indicate that dissipative dark holographic solitons are stable for small perturbation on amplitude.
A Low-Pump-Threshold High-Repetition-Rate Intracavity Optical Parametric Generator Based on Periodically Poled Lithium Niobate
JI Feng, , ZHANG Bai-Gang, , LI En-Bang, ZHOU Rui, ZHANG Tie-Li, LU Yang, ZHAO Pu, WANG Peng, YAO Jian-Quan,
Chin. Phys. Lett. 2006, 23 (8): 2113-2116 .  
Abstract   PDF(pc) (229KB) ( 440 )
A low-pump-threshold high-repetition-rate intracavity optical parametric generator (IOPG) by using a periodically poled lithium niobate (PPLN) is reported. The PPLN, which is 18.7mm long and has a grating period of 28.93μm at room temperature, is inserted in a diode-end-pumped Nd:YVO4 laser with an acousto-optic Q switch. The parametric generation threshold is 1.3W (diode laser power) at a Q-switch repetition rate of 19kHz. At an incident diode pump power of 5W, an average signal output power of 280mW has been achieved. The signal pulse duration is approximately 85ns. By changing the crystal temperature from 120°C to 250°C, the signal wavelength can be tuned from 1.493μm to 1.538μm.
Spatially Inhomogeneous Gain Modification in Photonic Crystals
LI Fei, HUANG Yi-Dong, ZHANG Wei, PENG Jiang-De
Chin. Phys. Lett. 2006, 23 (8): 2117-2120 .  
Abstract   PDF(pc) (1183KB) ( 318 )
The electric and magnetic energy distributions in photonic crystals (PC) are calculated by using the plane wave expansion (PWE) method. Even though the total electric and magnetic energy in each unit cell of photonic crystals are equal to each other, the ratio of electric and magnetic energy densities varies depending on the local position. Based on Fermi’s golden rule, the optical gain is analysed in the full quantum framework that takes the nonuniform energy density ratio into account. This nonuniform energy density ratio in photonic crystals, defined in an equal form as gain modification factor, leads to spatially inhomogeneous modification of optical gain. Results reported in the paper provide a new perspective for analysing gain characteristics, as well as the lasing properties, in photonic crystals.
Design Guideline of Hollow-Core Fibres with Cobweb Cladding Structure
HUO Liang, YU Rong-Jin, ZHANG Bing, CHEN Ming-Yang, LI Bing-Xin
Chin. Phys. Lett. 2006, 23 (8): 2121-2124 .  
Abstract   PDF(pc) (251KB) ( 384 )
By using a plane wave expansion method, some important parameters of designing the hollow-core fibre with cobweb cladding structure are analysed. Taking a dielectric material PMMA, for example, the tolerance of the parameters is discussed. The results show that the parameters of the structure possess oneself of a egularity and limit, and have a larger tolerance for the structural parameters in fabrication.
Mode Exciting Properties of Photonic Crystal Fibres with the Optical Field Incident from a Single Mode Fibre
LIU Jian-Guo, XUE Li-Fang, KAI Gui-Yun, LIU Yan-Ge, ZHANG Wei-Gang, LI Yan, WANG Zhi, ZHANG Chun-Shu, DONG Xiao-Yi
Chin. Phys. Lett. 2006, 23 (8): 2125-2128 .  
Abstract   PDF(pc) (345KB) ( 426 )
We numerically investigate the mode exciting properties of photonic crystal fibres by using the beam propagation method when the optical field is input from a traditional single mode fibre. The results show that both the excited mode spectrum and the coupling-efficiency of each excited mode depend on the normalized pitch Λ/λ and the normalized hole-size Λ/λ. Furthermore, we obtain the boundary profile of the optimizing coupling-efficiency for the excited fundamental mode: the boundary (Λ/λ)* is linear to the boundary (d\λ)*. All of these will pave the way for smoothing applications of photonic-crystal fibres, such as splicing and designing photonic-crystal-fibre functional devices.

Quantum Statistical Theory of Polarization Mode Dispersion
ZHANG Yong-Sheng, GUO Guang-Can
Chin. Phys. Lett. 2006, 23 (8): 2129-2131 .  
Abstract   PDF(pc) (194KB) ( 361 )
Polarization mode dispersion is modelled as decoherence of polarization under the disturbance of environment and the coupling with frequency. This model is described by the quantum master equation and the Langevin equation. It can be predicted that the optical beam is depolarized exponentially in a fibre and the differential group delay (DGD) is proportional to the square root of the propagation distance. The distribution of the DGD can also be calculated.
Sound Absorption of Locally Resonant Sonic Materials
ZHAO Hong-Gang, LIU Yao-Zong, WEN Ji-Hong, YU Dian-Long, WANG Gang, WEN Xi-Sen
Chin. Phys. Lett. 2006, 23 (8): 2132-2134 .  
Abstract   PDF(pc) (226KB) ( 618 )
The acoustic properties of locally resonant sonic materials with viscosity are theoretically investigated by using the multiple-scattering approach. We find that the absorption of a two-layer slab dominates the wave attenuation in the resonant frequency region under the condition of moderate or high viscous level. The fundamental mechanism operating in local resonance for absorption is investigated for the viability by the mode translation in the scattering process of a single scatterer. Finally the absorption performance in a multi-layer system is discussed.
Linear Stability of Taylor-Couette Flows with Axial Heat Buoyancy
CHEN Jian-Guo, REN Ling, FU Song
Chin. Phys. Lett. 2006, 23 (8): 2135-2138 .  
Abstract   PDF(pc) (395KB) ( 398 )
The linear stability is studied of flows confined between two concentric cylinders, in which the radial temperature gradient and axial gravity are considered for an incompressible Newtonian fluid. Numerical method based on the Petrov--Galerkin scheme is developed to deal with the buoyancy term in momentum equations and an additional temperature perturbation equation. Computations of the neutral stability curves are performed for different rotation cases. It is found that the flow instability is influenced by both centrifugal and axial shear instabilities, and the two instability mechanisms interact with each other. The outer cylinder rotation plays dual roles of stabilizer and destabilizer under different rotating stages with the inner cylinder at rest. For the heat buoyancy-induced axial flow, spiral structures are found in the instability modes.
Intermittency Growth in Fluid Turbulence
ZHU Jian-Zhou
Chin. Phys. Lett. 2006, 23 (8): 2139-2142 .  
Abstract   PDF(pc) (238KB) ( 402 )
Measurement and phenomenological analyses of intermittency growth in an experimental turbulent pipe flow and numerical turbulence are performed, for which working definitions such as degree, increment, and growth rate of intermittency are introduced with the help of quasiscaling theory. The logarithmic--normal inertial scaling model is extended to quasiscaling as the second-order truncation of the Taylor expansion and is used for studying the intermittency growth problem. The extended self-similarity properties are shown to be not consistent with the monotonicity of the third order local quasiscaling exponent and the nonmonotonic behaviour of the intermittency growth rate as a result of bottleneck. Digestions of the results with scale-dependent multifractals are provided.
Investigation of Impurity Ion Transport with Laser Blow-off in HL-2A Tokamak
CUI Zheng-Ying, HUANG Yuan, SUN Ping, ZHENG Yong-Zhen, SHI Pei-Lan, LU Jie, FU Bing-Zhong, ZHANG Peng, PAN Yu-Dong, DONG Yun-Bo, DENG Wei, YANG Qing-Wei, DING Xuan-Tong
Chin. Phys. Lett. 2006, 23 (8): 2143-2146 .  
Abstract   PDF(pc) (658KB) ( 454 )
Non-recycling impurities are injected into ohmic HL-2A plasma for the first time. The impurities of titanium and aluminium are injected in the discharges with varying plasma density and current. The convection and diffusion process of the injected impurity ions during the inward phase are qualitatively investigated. The results show that the transport of impurities is much slower in the central region of the plasma than outside of it and that it is greatly enhanced during sawtooth crashes.
Theoretical and Experimental Study of Scattering of a Plane Wave by an Inhomogeneous Plasma Sphere
SONG Fa-Lun, CAO Jin-Xiang, WANG Ge, WANG Yan, ZHU Ying, ZHU Jian, WANG Liang, NIU Tian-Ye
Chin. Phys. Lett. 2006, 23 (8): 2147-2150 .  
Abstract   PDF(pc) (357KB) ( 385 )
Scattering of electromagnetic waves by an inhomogeneous plasma sphere has been studied theoretically and experimentally. The offset angles of electromagnetic waves caused by the plasma sphere have been observed experimentally. The effects of the electromagnetic wave frequency and plasma density on the offset angle are discussed. The plasma density is estimated with the offset angle.
Short Wavelength Ion Temperature Gradient Driven Instability in Noncircular Flux Surface Plasmas with Finite Aspect Ratio
WANG Ying, GAO Zhe
Chin. Phys. Lett. 2006, 23 (8): 2151-2154 .  
Abstract   PDF(pc) (303KB) ( 532 )
By employing the local equilibrium of shaped tokamak plasmas, a gyrokinetic model with integral eigenmode equations is developed to investigate effects of the finite aspect ratio and noncircular flux surface on short wavelength ion temperature gradient (SWITG) driven modes. It is found that when nonadiabatic electron and trapped particle effects are not considered, the SWITG mode can be stabilized by finite aspect ratio A, elongation k and triangularity δ, and can be destabilized by the Shafranov shift gradient ∂R0/∂r.
Effects of Charge in Heavy Ions on Solitary Kinetic Alfvén Waves in Double-Ion Plasmas
YANG Lei, WU De-Jin
Chin. Phys. Lett. 2006, 23 (8): 2155-2157 .  
Abstract   PDF(pc) (228KB) ( 400 )
After the charge of heavy ions is considered, a Sagdeev equation is obtained for the solitary kinetic lfvén waves (SKAWs) in a low-β (me/mp « β « or mp/me » α » 1), three-component (electrons, protons, and highly charged heavy ions) plasma. Numerical results show that the charge number q of heavy ions can cause the width of the solitary structure to decrease, but increase for the maximum of electron density nem≤ 1.2 and the initial abundance of heavy ions Cb0 ≤ 0.1. The parallel phase speed of the waves increases with larger q.
Deep InP Gratings for Opto-Electronic Devices Etched by Cl2/CH4/Ar Inductively Coupled Plasma
WANG Jian, TIAN Jian-Bai, XIONG Bing, SUN Chang-Zheng, HAO Zhi-Biao, LUO Yi
Chin. Phys. Lett. 2006, 23 (8): 2158-2160 .  
Abstract   PDF(pc) (629KB) ( 799 )
Deep InP gratings are etched by Cl2/CH4/Ar inductively coupled plasma (ICP) at room temperature. A comparison is made between SiNx mask patterns formed by wet and dry etching. SF6 reactive ion etching is adopted for smooth and vertical sidewall. The etching conditions of Cl2/CH4/Ar ICP are optimized for high anisotropy, and a 1.7-μm-deep InP grating with an aspect ratio of 10:1 is demonstrated. The technique is then used for the fabrication of 1.55-μm laterally coupled distributed feedback AlGaInAs-InP laser.
Preparation of Mg55Ni35Si10 Amorphous Powders by Mechanical Alloying and Consolidation by Vacuum Hot Pressing
YANG Deng-Ke, WEN Cui-E, HAN Fu-Sheng, WANG Qing-Zhou, LI Hai-Jin
Chin. Phys. Lett. 2006, 23 (8): 2161-2164 .  
Abstract   PDF(pc) (608KB) ( 303 )
Amorphous Mg55Ni35Si10 powders are fabricated by using a mechanical alloying technique. The amorphous powders are found to exhibit a relatively high crystallization temperature of 380°C. The as-milled amorphous Mg55Ni35Si10 powders are consolidated successfully into bulk body by vacuum hot pressing technique. Limited nanocrystallization is noticed. The Vickers microhardness range of the Mg55Ni35Si10 bulk sample is 7834 to 8048MPa. Its bending strength and compressive strength are 529MPa and 1466MPa, respectively.
ZnO Nanorods Produced by the Method of Arc Discharge
WU Xu-Feng, XU Chun-Xiang, ZHU Guang-Ping, LING Yi-Ming
Chin. Phys. Lett. 2006, 23 (8): 2165-2168 .  
Abstract   PDF(pc) (838KB) ( 594 )
ZnO nanorods are fabricated by arc discharge with ZnO powder as source materials. The sample is characterized by x-ray diffraction, Raman scattering spectra, scanning electron microscopy and high-resolution transmission electron microscopy. The ZnO nanorods exhibit single crystals with the hexagonal wurtzite structure. Many of them are tetrapod-like. The diameters range from several nanometres to about 100nm, and the main diameters of the nanorods is around 20nm. The length-to-diameter ratio is more than 5, and the grown directions are along the [001] axis. Photoluminescence spectra show a narrow ultraviolet emission at around 389nm and a broad green emission at around 520nm. The growth process can be interpreted by the vapour-solid mechanism.
Low Energy Ion Channelling in Single-Wall Nanotubes
ZHENG Li-Ping., XU Zi-Jian, WANG Cheng-Bin, ZHU Zhi-Yuan, ZHU De-Zhang, XIA Hui-Hao
Chin. Phys. Lett. 2006, 23 (8): 2169-2171 .  
Abstract   PDF(pc) (230KB) ( 423 )
Monte Carlo simulation is used to study the low energy He ion channelling in a (17, 0) single-wall nanotube and its rope. The simulation shows that the channelling critical angle Psic= 48E-1/2 (E is incident energy) for a 1.31-nm-diameter initial beam into the nanotube, while Psic= 45E-1/2 for the 1.31-nm-diameter initial beam into its rope.
Enhanced Field Emission from Well-Patterned Silicon Nanoporous Pillar Arrays
FU Xiao-Nan, LI Xin-Jian
Chin. Phys. Lett. 2006, 23 (8): 2172-2174 .  
Abstract   PDF(pc) (746KB) ( 491 )
The silicon nanoporous pillar array (Si-NPA) is synthesized by using hydrothermal etching method, and the electron field emission properties are studied. The results show that Si-NPA has a low turn-on field of 1.48μm at the emission current of 0.1μA and its field emission is relatively stable. The field emission enhancement of Si-NPA is believed to originate from its unique morphology and structure. Our finding demonstrates that the Si-NPA is a promising candidate material for field emission applications.
Ab Initio Study of Structural and Electronic Properties of Hexagonal BC2N
LUO Xiao-Guang, LIU Zhong-Yuan, GUO Xiao-Ju, HE Ju-Long, YU Dong-Li, TIAN Yong-Jun, SUN Jian, WANG Hui-Tian
Chin. Phys. Lett. 2006, 23 (8): 2175-2178 .  
Abstract   PDF(pc) (503KB) ( 458 )
We investigate hexagonal BC2N in graphite unit cells using the first-principles method and calculate the total energies, lattice parameters, and electronic band structures after full relaxation. It is shown that stable hexagonal BC2N should be stacked sequentially with one graphite layer and one h-BN layer. The density of states indicates that this structure should have metallicity.
Development in Laser Induced Extrinsic Absorption Damage Mechanism of Dielectric Films
XIA Zhi-Lin, DENG De-Gang, FAN Zheng-Xiu, SHAO Jian-Da
Chin. Phys. Lett. 2006, 23 (8): 2179-2182 .  
Abstract   PDF(pc) (239KB) ( 394 )
Absorption of host and the temperature-dependence of absorption coefficient have been considered in valuating temperature distribution in films, when laser pulse irradiates on films. Absorption of dielectric materials experience three stages with the increase of temperature: multi-photon absorption; single photon absorption; metallic absorption. These different absorption mechanisms correspond to different band gap energies of materials, which will decrease when the temperature of materials increases. Evaluating results indicate that absorption of host increases rapidly when the laser pulse will be over. If absorption of host and the temperature-dependence of absorption are considered, the maximal temperatures in films will be increased by a factor of four.
Near Infrared Photoluminescence from Yb,Al Co-implanted SiO2 Films on Silicon
ZHANG Jian-Guo, WANG Xiao-Xin, CHENG Bu-Wen, YU Jin-Zhong, WANG Qi-Ming
Chin. Phys. Lett. 2006, 23 (8): 2183-2186 .  
Abstract   PDF(pc) (242KB) ( 531 )
Intense room-temperature near infrared (NIR) photoluminescence (980nm and 1032nm) is observed from Yb,Al co-implanted SiO2 films on silicon. The optical transitions occur between the 2F5/2 and 2 F7/2 levels of Yb3+ in SiO2. The additional Al-implantation into SiO2 films can effectively improve the concentration quenching effect of Yb3+ in SiO2. Photoluminescence excitation spectroscopy shows that the NIR photoluminescence is due to the non-radiative energy transfer from Al-implantation-induced non-bridging oxygen hole defects in SiO2 to Yb3+ in the Yb-related luminescent complexes. It is believed that the defect-mediated luminescence of rare-earth ions in SiO2 is very effective.
Growth and Annealing Study of Mg-Doped AlGaN and GaN/AlGaN Superlattices
WANG Bao-Zhu, WANG Xiao-Liang, HU Guo-Xin, RAN Jun-Xue, WANG Xin-Hua, GUO Lun-Chun, XIAO Hong-Ling, LI Jian-Ping, ZENG Yi-Ping, LI Jin-Min, WANG Zhan-Guo
Chin. Phys. Lett. 2006, 23 (8): 2187-2189 .  
Abstract   PDF(pc) (237KB) ( 747 )
Mg-doped AlGaN and GaN/AlGaN superlattices are grown by metalorganic chemical vapour deposition (MOCVD). Rapid thermal annealing (RTA) treatments are carried out on the samples. Hall and high resolution x-ray diffraction measurements are used to characterize the electrical and structural prosperities of the as-grown and annealed samples, respectively. The results of hall measurements show that after annealing, the Mg-doped AlGaN sample can not obtain the distinct hole concentration and can acquire a resistivity of 1.4×103Ωcm. However, with the same annealing treatment, the GaN/AlGaN superlattice sample has a hole concentration of 1.7×1017cm-3 and a resistivity of 5.6Ωcm. The piezoelectric field in the GaN/AlGaN superlattices improves the activation efficiency of Mg acceptors, which leads to higher hole concentration and lower p-type resistivity.
Multi-Shock Compression of Dense Hydrogen--Helium Mixture Beyond 100GPa
ZHANG Ming-Jian, LIU Fu-Sheng, TIAN Chun-Ling, SUN Yan-Yun
Chin. Phys. Lett. 2006, 23 (8): 2190-2193 .  
Abstract   PDF(pc) (237KB) ( 558 )
A cryogenic target system for preparing the dense gaseous samples is established on a two-stage light-gas gun and is applied to study the equation of state of hydrogen--helium mixture at higher pressures and at high temperatures by means of the multi-shock technique. The recorded optical radiation signal clearly indicates the beginning moments of the third-, fourth-, sixth-, eighth-, and tenth-shock processes, which are in good agreement with the predictions of the Mansoori--Canfield--Ross variational perturbation theory up to the observed ultimate state of 104GPa.
Fe3O4 Segregation and Transport Properties of La0.67Ca0.33MnO3
ZHOU Qian-Xue, DAI Ming-Xing, WANG Ren-Hui, FENG Xin-Nan, WANG Yang, XIA Zheng-Cai
Chin. Phys. Lett. 2006, 23 (8): 2194-2197 .  
Abstract   PDF(pc) (1014KB) ( 369 )
Effect of Fe3O4 segregation at grain boundaries on the electrical transport and magnetic properties of La0.67Ca0.33MnO3 is investigated. The experimental results show that the Fe3O4 segregation not only shifts the paramagnetic--ferromagnetic transition temperature of La0.67Ca0.33MnO3 to a lower temperature region but also induces a new transition in a lower temperature region. Meanwhile, the transition processes observed in both the resistivity and magnetization curves are obviously widened. Compared to pure La0.67Ca0.33MnO3, we assume that the Fe3O4 segregation level at the grain boundaries can modify the electrical transport and magnetic properties of
Ground State of a Polaron in a Symmetric Triangular Quantum Well
Chin. Phys. Lett. 2006, 23 (8): 2198-2201 .  
Abstract   PDF(pc) (227KB) ( 503 )
We study the effects of electron--phonon interaction on the electron ground state in a symmetric triangular quantum well, and calculate the ground state energy of an electron in the GaAs/Al0.96Ga0.04As triangular quantum well including the effects of the interaction between electrons and confined LO phonons by using a modified Lee--Low--Pines variational method. The electron wavefunction in the triangular well is chosen as the Airy function. The numerical results are given and discussed.
Photoemission Spectroscopy and Electronic Structures of LiMn2O4
WU Qi-Hui, THISSEN Andreas, JAEGERMANN Wolfram
Chin. Phys. Lett. 2006, 23 (8): 2202-2205 .  
Abstract   PDF(pc) (231KB) ( 481 )
We study the electronic structures of LiMn2O4 by x-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) and resonant photoelectron spectroscopy (RPES). XPS data suggest that the average oxidation state of Mn ions is 3.55, probably due to the small amount of lithium oxides on the surface. UPS and RPES data imply that Mn ions are in a high spin state, and RPES results show strong Mn3d--O2p hybridization in the LiMn2O4 valence band.
Interband Optical Transitions due to Donor Bound Excitons in Wurtzite InGaN Strained Coupled Quantum Dots: Strong Built-in Electric Field Effects
CHI Yue-Meng, SHI Jun-Jie
Chin. Phys. Lett. 2006, 23 (8): 2206-2209 .  
Abstract   PDF(pc) (239KB) ( 426 )
Considering the three-dimensional confinement of the electrons and holes and the strong built-in electric field (BEF) in the wurtzite InGaN strained coupled quantum dots (QDs), the positively charged donor bound exciton states and interband optical transitions are investigated theoretically by means of a variational method. Our calculations indicate that the emission wavelengths sensitively depend on the donor position, the strong BEF, and the structure parameters of the QD system.
Ab Initio Calculation on Self-Assembled Base-Functionalized Single-Walled Carbon Nanotubes
SONG Chen, XIA Yue-Yuan, ZHAO Ming-Wen, LIU Xiang-Dong, LI Ji-Ling, LI Li-Juan, LI Feng, HUANG Bo-Da
Chin. Phys. Lett. 2006, 23 (8): 2210-2212 .  
Abstract   PDF(pc) (444KB) ( 620 )
We perform ab initio calculations on the self-assembled base-functionalized single-walled carbon nanotubes (SWNTs) which exhibit the quasi-1D `ladder’ structure. The optimized configuration in the ab initio calculation is very similar to that obtained from molecular dynamics simulation. We also calculate the electronic structures of the self-assembled base-functionalized SWNTs that exhibit distinct difference from the single-branch base-functionalized SWNT with a localized state lying just below the Fermi level, which may result from the coupling interaction between the bases accompanied by the self-assembly behaviour.
Multiterminal Conductance and Decoherence Effect of a Three-Terminal Kondo Dot
FANG Tie-Feng, WANG Shun-Jin,
Chin. Phys. Lett. 2006, 23 (8): 2213-2216 .  
Abstract   PDF(pc) (265KB) ( 441 )
A three-terminal Kondo dot modelled by the Anderson Hamiltonian is investigated. In the strong correlation limit, we calculate the multiterminal conductance and the voltage-induced characteristic splitting of the nonequilibrium Kondo resonance by using the equation of motion approach from viewpoint of the correlation dynamics. A qualitative and reasonable agreement with a recently reported experiment is obtained. We also simulate phenomenologically the decoherence of the Kondo-coherent state formed in the two-terminal setup in the framework of our three-terminal model.
Antiresonance Effect in Electronic Tunnelling through a One-Dimensional Quantum Dot Chain
SUN Pu-Nan
Chin. Phys. Lett. 2006, 23 (8): 2217-2220 .  
Abstract   PDF(pc) (262KB) ( 438 )
Electronic tunnelling through a one-dimensional quantum dot chain is theoretically studied, when two leads couple to the individual component quantum dots of the chain arbitrarily. If there are some dangling quantum dots in the chain outside the leads, the electron tunnelling through the quantum dot chain is wholly forbidden while the energy of the incident electron is just equal to the molecular energy levels of the dangling quantum dots, which is known as the antiresonance effect. In addition, the influence of electron interaction on the antiresonance effect is discussed within the Hartree--Fock approximation.
Relation of Structure and Superconductivity in Self-Compensating Y1-xCaxBa2-xLaxCu3Oy
SUN Xue-Feng, YU Jing, WANG Fa, ZHANG Han
Chin. Phys. Lett. 2006, 23 (8): 2221-2224 .  
Abstract   PDF(pc) (252KB) ( 405 )
The self-compensating compound of Y1-xCaxBa2-xLaxCu3Oyis synthesized through a solid-state reaction method with x from 0.25 to 0.55. Structural and superconducting properties have been
investigated by x-ray diffraction, Rietveld refinement, and dc magnetization measurement, respectively. The impure peaks appear when x is more than 0.5 in the diffraction pattern. Orthorhombic--tetragonal transition occurs at x=0.45. Some local structural parameters, such as Cu(1)--O(4), Cu(2)--O(4) bond lengths, change randomly in a narrow range. The relationship between the character of (Ba/La)--O plane and Tc is rather interesting. We attribute the behaviour of superconductivity to the joint effects of these local structural parameters. The results give the evidence that the influence of the structural change on superconductivity is essential and independent of carrier concentration.
Magnetic and Electrical Transport Properties of Sr1-xLaxRuO3 (0≤x≤0.10)
PI Li, FAN E-Hua, XIAO Ying, ZHANG Yu-Heng
Chin. Phys. Lett. 2006, 23 (8): 2225-2228 .  
Abstract   PDF(pc) (265KB) ( 478 )
We investigate the lightly doped polycrystalline Sr1-xLaxRuO3 (x =0, 0.02, 0.08 and 0.10). With La doping, the ferromagnetism in the system has been suppressed. The transition temperature is Tc’ at which the long-range ferromagnetism establishes and the magnetization under 3T at 5K decreases with increasing x. In contrast to Sr1-xCaxRuO3, the samples remain with the PM-FM transition at 162K, which might be attributed to the valency change of Ru.
Magnetic Properties of Melted ThMn12-Type Carbides and Their Nitrides
LIU Shun-Quan, HAN Jing-Zhi, DU Hong-Lin, WANG Chang-Sheng, YANG Ying-Chang
Chin. Phys. Lett. 2006, 23 (8): 2229-2231 .  
Abstract   PDF(pc) (216KB) ( 410 )
The carbides of NdDy0.2Fe12-yMoyC0.6 (y=1.5, 2) crystallized in the ThMn12-type structure have been successfully synthesized by arc melting method, followed by a heat treatment. The magnetic properties are strongly enhanced with the addition of carbon. Upon the carbonation the saturation magnetization Ms is increased by about 20emu/g and the Curie temperature Tc is enhanced by 40--70K. The spin reorientation (SR) temperature decreases from 125 K for NdDy0.2Fe10Mo2 to 55 K for NdDy0.2Fe10Mo2C0.6 indicating the change of magnetocrystalline anisotropy in the Nd sublattice. It is found that the intrinsic magnetic properties of the carbides can be improved by further nitrogenation. The composite carbon--nitrogen compounds show a Tc~560K, Ms~105emu/g and Ha (anisotropy field) ~86kOe for NdDy0.2Fe10Mo2C0.6Nz and a Tc~628K, Mx~119emu/g and Ha~115kOe for NdDy0.2Fe10.5Mo1.5C0.6Nz. These magnetic properties are even better than those of simple nitrides, suggesting that these compounds can be considered as a good candidate for permanent magnet applications.
Relaxor Behaviour and Ferroelectric Properties of (Li0.12Na0.88)(Nb0.9-xTa0.10Sbx)O3 Lead-Free Ceramics
WANG Ying, LI Yong-Xiang, YI Zhi-Guo, WANG Dong, YIN Qing-Rui
Chin. Phys. Lett. 2006, 23 (8): 2232-2235 .  
Abstract   PDF(pc) (382KB) ( 519 )
New lead-free ceramics (Li0.12Na0.88)(Nb0.9-xTa0.10Sbx)O3 (0.01×0.06) are synthesized by solid-state reaction method. The dielectric, piezoelectric and ferroelectric properties of the ceramics are studied. The dielectric constant dependence with temperature and frequency of the ceramic specimen with x=0.04 shows typical characteristics of relaxor ferroelectrics, and the Vogel--Fulcher relationship is fulfilled. The dielectric behaviour and its relation to the phase transition phenomena are discussed. The polarization hysteresis loops at room temperature are also measured.
Electrical Properties of La-Doped Al2O3 Films on Si (100) Substrates as a High-Dielectric-Constant Gate Material
LIU Yan-Ping, LAN Wei, HE Zhi-Wei, WANG Yin-Yue
Chin. Phys. Lett. 2006, 23 (8): 2236-2238 .  
Abstract   PDF(pc) (235KB) ( 583 )
Amorphous La-doped Al2O3 (La: Al2O3) thin films are deposited on n-type (100) Si substrates by rf magnetron co-sputtering. The composition of the deposited films is measured by energy dispersive x-ray spectroscopy. Capacitance--voltage measurement shows that the dielectric constant k of La-doped Al2O3 films ranges from 8.5 to 11.6 with the increasing La content, and the highest k value of 11.6 is obtained for the 20.14% La content film. In the structure of the Al/La:Al2O3/Si metal oxide semiconductor, the dominant conduction stems from the space-charge-limited current at different temperatures. In addition, the wavelength dependence of the transmittance is studied by ultraviolet spectroscopy and the band gap of all the deposited films is above 5.5eV. The results demonstrate that La-doped Al2O3 can meet the requirement of next-generation gate materials.
A Method for Quantitative Analysis of Chemical Mixtures with THz Time Domain Spectroscopy
ZHANG Zeng-Yan, JI Te, YU Xiao-Han, XIAO Ti-Qiao, XU Hong-Jie
Chin. Phys. Lett. 2006, 23 (8): 2239-2242 .  
Abstract   PDF(pc) (236KB) ( 567 )
A method for analysing chemical mixtures quantitatively with terahertz time domain spectroscopy is proposed. The experimental results demonstrate the feasibility of this technique. Transmission coefficient of THz wave at the sample surface is taken into account to improve the analytic precision. Isomer mixtures are chosen as the experimental samples. Compared to similar techniques, the analytic precision could be improved evidently in this method.
Luminescent Characteristics of Near Ultraviolet InGaN/GaN MQWs Grown on Grooved Sapphire Substrates Fabricated by Wet Chemical Etching
YU Nai-Sen, GUO Li-Wei, CHEN Hong, XING Zhi-Gang, WANG Jing, ZHU Xue-Liang, PENG Ming-Zeng, YAN Jian-Feng, JIA Hai-Qiang, ZHOU Jun-Ming
Chin. Phys. Lett. 2006, 23 (8): 2243-2246 .  
Abstract   PDF(pc) (347KB) ( 713 )
InGaN/GaN multiple quantum wells (MQWs) are grown on planar and maskless periodically grooved sapphires by metal organic vapour phase epitaxy (MOCVD). High-resolution x-ray rocking curves and transmission electron microscopy (TEM) are adopted to characterize the film quality. Compared with the MQWs grown on planar sapphire, the sample grown on grooved sapphire shows better crystalline quality: a remarkable reduction of dislocation densities is achieved. Meanwhile, the MQWs grown on grooved sapphire show two times larger PL intensity at room temperature. Temperature-dependent PL measurements are adopted to investigate the luminescence properties. The luminescence thermal quenching based on a fit to the Arrhenius plot of the normalized integrated PL intensity over the measured temperature range suggests that the nonradiative recombination centres (NRCs) are greatly reduced for the sample grown on grooved sapphire. We assume that the reduction of dislocations which act as NRCs is the main reason for the sample grown on pattern sapphire having higher PL intensity.
Colour Tuning of Single Host Phosphors for White Light by Al Addition
WANG Da-Jian, WANG Ji-Lei, LI Lan
Chin. Phys. Lett. 2006, 23 (8): 2247-2250 .  
Abstract   PDF(pc) (237KB) ( 534 )
We report a newly found strong disturbing effect of Al addition to the intensity ratios of blue and green emissions from single host full-colour phosphor of Ba-3MgSi2-xAlxO8:0.02Eu2+, 0.1Mn2+ for near-UV excited white light. The phase-pure silicate phosphor in the size of around 4μm is prepared by salt-assisted spray pyrolysis route, having three-colour emissions at the wavelength peak values of 437nm, 500nm and 608nm simultaneously under the excitation of 375nm. The amount variation of Al ion added to the phosphor host results in a drastic change of the intensity ratio between green and blue emissions, while the intensity of red light keeps unchanged. As a consequence, the combination of three colours lies in the white light region and can be tuned by precisely controlled addition of Al content. The Raman spectroscopy verifies the modifying effect of Al ion to the tetrahedral network in silicate hosts. We assume that by addition of Al ion, the amount of those two kinds of Eu2+ substituting for those two kinds of Ba2+ lattice sites with distinct energy levels of blue and green featured emissions can be adjusted to contribute to diversification of the ratios of blue and green emissions.
Instability Parameters of Optical Oscillation Frequency in Plasma Central Discharge and Periphery Region
ZHOU Zhu-Wen, M. A. LIEBERMAN, Sungjin KIM
Chin. Phys. Lett. 2006, 23 (8): 2251-2254 .  
Abstract   PDF(pc) (312KB) ( 440 )
We have observed relaxation oscillations in a capacitive discharge in Ar gas, connected to a peripheral ground chamber. The plasma oscillations observed from time-varying optical emission from the main discharge chamber show, for example, a high frequency (75.37kHz) relaxation oscillation, at 100mTorr and 8W absorbed power, and a low frequency (2.72Hz) relaxation oscillation, 100mTorr and 325W absorbed power. Time-varying optical emission intensity and plasma density are also detected with a Langmuir probe. The theoretical result agrees well with experiments.
Propagation of Plasma Generated by Intense Pulsed Ion Beam Irradiation
WU Di, GONG Ye, LIU Jin-Yuan, WANG Xiao-Gang, LIU Yue, MA Teng-Cai
Chin. Phys. Lett. 2006, 23 (8): 2255-2258 .  
Abstract   PDF(pc) (605KB) ( 673 )
Taking the calculation results based on the established two-dimensional ablation model of the intense-pulsed-ion-beam (IPIB) irradiation process as initial conditions, we build a two-dimensional hydrodynamic ejection model of plasma produced by an IPIB-irradiated metal titanium target into ambient gas. We obtain the conclusions that shock waves generate when the background pressure is around 133mTorr and also obtain the plume splitting phenomenon that has been observed in the experiments.

Preparation of Cu(In,Ga)Se2 Thin Film Solar Cells by Selenization of Metallic Precursors in an Ar Atmosphere
XU Chuan-Ming, SUN Yun, ZHOU Lin, LI Feng-Yan, ZHANG Li, XUE Yu-Ming, ZHOU Zhi-Qiang, HE Qing
Chin. Phys. Lett. 2006, 23 (8): 2259-2261 .  
Abstract   PDF(pc) (385KB) ( 1698 )
Cu(In,Ga)Se2 thin films are deposited on Mo-coated glass substrates by Se vapour selenization of sputtered metallic precursors in the atmosphere of Ar gas flow under a pressure of about 10Pa. The it in situ heat treatment of as-grown precursor leads to the formation of a better alloy. During selenization, the growth of CuInSe2 phase preferably proceeds through Se-poor phases as CuSe and InSe at relatively low substrate temperature of 250°C, due to the absence of In2Se3 at intermediate stage at low reactor pressure. Subsequently, the Cu(In,Ga)Se2 phase is produced by the reactive diffusion of CuInSe2 with a Se-poor GaSe phase at high temperature of up to 560°C. The final film exhibits smooth surface and large grain size. The absorber is used to fabricate a glass/Mo/Cu(In,Ga)Se2/CdS/ZnO cell with the total-area efficiency of about 7%. The low open-circuit voltage value of the cell fabricated should result from the nonuniform distribution of In and Ga in the absorber, due to the diffusion-controlled reaction during the phase formation. The films, as well as devices, are characterized.
Continuous Wave Performance and Tunability of MBE Grown 2.1μm InGaAsSb/AlGaAsSb MQW lasers
ZHANG Yong-Gang, ZHENG Yan-Lan, LIN Chun, LI Ai-Zhen, LIU Sheng
Chin. Phys. Lett. 2006, 23 (8): 2262-2265 .  
Abstract   PDF(pc) (258KB) ( 703 )
InGaAsSb/AlGaAsSb multi quantum well ridge waveguide lasers at 2.1μm wavelength are fabricated by using molecular beam epitaxy. Continuous wave performance and tunability of the lasers are evaluated in a wide temperature range extend to 80°C. Output power of the laser at 30°C exceeds 30mW/facet at driving current of 0.5A, the characteristic temperature T0 is 89K in 0--50°C range. No fast degradation is observed in accelerated aging test at 90°C for those lasers with lower Al content in cladding layers. Temperature tunability of the lasers is 1.36nm/K. Single-mode output with side mode suppression ratios greater than 20dB is achieved in a certain driving current region; current tunability is 8×10-3nm/mA regardless of mode hopping.
Behaviour of Self-Standing CVD Diamond Film with Different Dominant Crystalline Surfaces in Thermal-Iron Plate Polishing
CHEN Guang-Chao, ZHOU Zu-Yuan, LI Bin, ZHOU You-Liang, J. Askri, LI Cheng-Ming, TANG Wei-Zhong, TONG Yu-Mei, LU Fan-Xiu
Chin. Phys. Lett. 2006, 23 (8): 2266-2268 .  
Abstract   PDF(pc) (609KB) ( 383 )
Self-standing CVD diamond films with different dominant crystalline surfaces are polished by the thermal-iron plate polishing method. The influence of the dominant crystalline surfaces on polishing efficiency is investigated by measuring the removal rate and final roughness. The smallest rms roughness of 0.14μm is measured with smallest removal rate in the films with the initial (220) dominant crystalline surface. Activation energy for the polishing is analysed by the Arrhenius relation. It is found that the values are 170kJ/mol, 222kJ/mol and 214kJ/mol for the film with three different dominant crystalline surfaces. Based on these values, the polishing cause is regarded as the graphitization-controlling process. In the xperiment, we find that transformation of the dominant crystalline surfaces from (111) to (220) always appears in the polishing process when we polish the (111) dominant surface.
In Situ Observation of Skeletal Shape Transition during BaB2O4 Crystal Growth in High-Temperature Solution
PAN Xiu-Hong, JIN Wei-Qing, HONG Yong, AI Fei
Chin. Phys. Lett. 2006, 23 (8): 2269-2272 .  
Abstract   PDF(pc) (557KB) ( 463 )
The transition from a flat solid--liquid interface to a skeletal shape during BaB2O4 (BBO) single crystal growth in Li2B4O7 flux is observed in real time by an optical high-temperature in-situ observation system. The movement of crystal step is also investigated. The observation results demonstrate that the steps propagate along and parallel to the flat interface when the crystal size is small. Nevertheless, they will `bend’ close to the face centre if the crystal size becomes greater. Atomic force microscopy reveals that more deposition places near the face centre give rise to the bending of advancing steps and thus the formation of a vicinal interface structure. Measurements of step velocity show that the velocity keeps nearly constant at different moments for one specific step, whereas the step on a newly formed layer advanced faster than that on a previously formed one when the crystal size is larger than 210μm or so. Thus interfacial morphological instability occurs and a skeletal interface is obtained.
Effects of Post-Thermal Treatment on Quality of SiC Grown by PVT Method
ZHU Li-Na, CHEN Xiao-Long, YANG Hui, PENG Tong-Hua, NI Dai-Qin, HU Bo-Qing
Chin. Phys. Lett. 2006, 23 (8): 2273-2276 .  
Abstract   PDF(pc) (718KB) ( 730 )
We report the effects of post-thermal treatment on the quality of 2-inch 6H-SiC wafer cut from a crystal boule grown by physical vapour transportation method. The full widths at half maximum of x-ray diffraction rocking curves measured on sites across the 2-inch wafer become narrower, indicating the quality improvement after a three-step post-thermal treatment. It is found that the most common defects such as micropipes and inclusions can be significantly reduced after the treatment. Our results show that the post-thermal treatment is an effective route to improve the quality of SiC single crystals.
Effect of Incident Intensity on Films Growth in Pulsed Laser Deposition
GUAN Li, ZHANG Duan-Ming, LI Zhi-Hua, TAN Xin-Yu, LI Li, LIU Dan, FANG Ran-Ran, LIU Gao-Bin, HU De-Zhi
Chin. Phys. Lett. 2006, 23 (8): 2277-2280 .  
Abstract   PDF(pc) (304KB) ( 340 )
Incident intensity, defined by the amount of particles deposited per pulse, is an important parameter in the film growth process of pulsed laser deposition (PLD). Different from previous models, we investigate the irreversible and reversible growth processes by using a kinetic Monte Carlo method and find that island density and film morphology strongly depend on pulse intensity. At higher pulse intensities, lots of adatoms instantaneously diffuse on the substrate surface, and then nucleation easily occurs between the moving adatoms resulting in more smaller-size islands. In contrast, at the lower pulse intensities, nucleation event occurs preferentially between the single adatom and existing islands rather than forming new islands, and therefore the average island size becomes larger in this case. Additionally, our results show that substrate temperature plays an important role in film growth. In particular, it can determine the films shape and weaken the effect of pulse intensity on film growth at the lower temperatures by controlling the mobility rate of atoms. Our results can match the related theoretical and experimental results.

First-Principles Calculations for Structures and Melting Temperature of Si6 Clusters
BAI Yu-Lin, CHEN Xiang-Rong, ZHOU Xiao-Lin, CHENG Xiao-Hong, YANG Xiang-Dong,
Chin. Phys. Lett. 2006, 23 (8): 2281-2284 .  
Abstract   PDF(pc) (463KB) ( 475 )
We investigate the structures and the melting temperature of the Si6 cluster by using the first-principles pseudopotential method in real space and Langevin molecular dynamics. It is shown that the ground structure of the Si6 cluster is a square bipyramid, and the corresponding melting temperature is about 1923K. In the heating procedure, the structures of the Si6 cluster change from high symmetry structures containing 5--8 bonds, via prolate structures containing 3--4 bonds, to oblate structures containing 1--2 bonds.

Synthesis of Cubic Boron Nitride by the Reaction of Li3N and B2O3
SU Zuo-Peng, DU Yong-Hui, JI Xiao-Rui, YANG Da-Peng, YANG Xu-Xin, GONG Xi-Liang, ZHANG Tie-Chen
Chin. Phys. Lett. 2006, 23 (8): 2285-2287 .  
Abstract   PDF(pc) (491KB) ( 801 )
Cubic boron nitride is synthesized by the reaction of Li3N and B2O3 under high pressure and high temperature (4.0--5.0GPa, 1350--1500°C). The minimum pressure of cBN formation is 4.0GPa. The present condition of cBN formation is clearly lower than the eutectic temperature of Li3BN2 and BN in the Li3N-hBN system (5.5GPa, 1610°C). The content of $c$BN in the sample increases, while the content of hBN decreases with the temperature and pressure. The maximum conversion rate (5.0GPa, 1500°C) is about 34%, which is higher than that in the hBN-Li3N system. The cBN crystals are octahedral or tetrahedral in shape and approximately 20μm in diameter.
Influence of Yb-Doped Nanoporous TiO2 Films on Photovoltaic Performance of Dye-Sensitized Solar Cells
XU Wei-Wei, DAI Song-Yuan, HU Lin-Hua, LIANG Lin-Yun, WANG Kong-Jia
Chin. Phys. Lett. 2006, 23 (8): 2288-2291 .  
Abstract   PDF(pc) (771KB) ( 684 )
Yb-doped TiO2 pastes with different Yb/TiO2 weight ratios are prepared in the sol-gel process to obtain dye-sensitized solar cells (DSCs). The nanocrystalline size of Yb-TiO2 becomes smaller and the lattice parameters change. Lattice distortion is observed and dark current is detected. It is found that a part of Yb existing as insulating oxide Yb2O3 state acts as barrier layers at the electrode--electrolyte interface to suppress charge recombination. A Yb-doped TiO2 electrode applied in DSCs leads to a higher open-circuit voltage and a higher fill factor. How the Yb-doped TiO2 films affect the photovoltaic response of DSCs is discussed.
A Small Signal Equivalent Circuit Model for Resonant Tunnelling Diode
MA Long, HUANG Ying-Long, ZHANG Yang, WANG Liang-Chen, YANG Fu-Hua, ZENG Yi-Ping
Chin. Phys. Lett. 2006, 23 (8): 2292-2295 .  
Abstract   PDF(pc) (251KB) ( 651 )
We report a resonant tunnelling diode (RTD) small signal equivalent circuit model consisting of quantum capacitance and quantum inductance. The model is verified through the actual InAs/In0.53Ga0.47As/AlAs RTD fabricated on an InP substrate. Model parameters are extracted by fitting the equivalent circuit model with ac measurement data in three different regions of RTD current--voltage (I--V) characteristics. The electron lifetime, representing the average time that the carriers remain in the quasibound states during the tunnelling process, is also calculated to be 2.09ps.
Damascene Array Structure of Phase Change Memory Fabricated with Chemical Mechanical Polishing Method
LIU Qi-Bin, SONG Zhi-Tang, ZHANG Kai-Liang, WANG Liang-Yong, FENG Song-Lin, CHEN Bomy
Chin. Phys. Lett. 2006, 23 (8): 2296-2298 .  
Abstract   PDF(pc) (547KB) ( 543 )
A damascene structure of phase change memory (PCM) is fabricated successfully with the chemical mechanical polishing (CMP) method, and the CMP of Ge2Sb2Te5 (GST) and Ti films is investigated. The polished surface of wafer is analysed by scanning electron microscopy (SEM) and an energy dispersive spectrometer (EDS). The measurements show that the damascene device structure of phase change memory is achieved by the CMP process. After the top electrode is deposited, dc sweeping test on PCM reveals that the phase change can be observed. The threshold current of array cells varies between 0.90mA and 1.15mA.
A Novel Ni/Ag/Pt Ohmic Contact to P-Type GaN for Flip-Chip Light-Emitting Diodes
MA Hong-Xia, HAN Yan-Jun, SHENTU Wei-Jin, ZHANG Xian-Peng, LUO Yi,
Chin. Phys. Lett. 2006, 23 (8): 2299-2202 .  
Abstract   PDF(pc) (383KB) ( 1245 )
We present a high-quality Ni/Ag/Pt Ohmic contact to p-type GaN. After the sample is annealed at 500°C in O2 ambient for 3min, a specific contact resistance as low as 2.6×10-5Ω.cm2 and an optical reflectivity of 82% at 460nm are obtained. The Auger electron spectroscopy analysis shows that the Pt layer can improve the surface morphology and thermal reliability of the annealed Ag-based electrode, Ag plays a key role in achieving good ohmic contact due to the outdiffusion of Ga into Ag forming Ga vacancies which increase the hole concentration, while the surface contamination of p-type GaN is reduced by Ni.
Demonstration of Four Fundamental Operations of Liquid Droplets for Digital Microfluidic Systems Based on an Electrowetting-on-Dielectric Actuator
YUE Rui-Feng, WU Jian-Gang, ZENG Xue-Feng, KANG Ming, LIU Li-Tian
Chin. Phys. Lett. 2006, 23 (8): 2303-2306 .  
Abstract   PDF(pc) (783KB) ( 515 )
An electrowetting-on-dielectric actuator is developed, in which the liquid is sandwiched between top and bottom plates. For the bottom plate, silicon wafer is used as the substrate, the heavily phosphorus-doped polysilicon film is deposited by low pressure chemical vapour deposition as the microelectrode array, and thermally grown SiO2 film as the dielectric layer. The top plate is a glass plate covered with transparent and conductive indium tin oxide as the ground electrode. In addition, a TeflonR AF1600 film is spun on the surface of both the plates as the hydrophobic layer. The experimental results show that when the gap height between two plates is 133μm, a prototype of the device is capable of creating, transporting, merging and dividing droplets of deionized water in an
air environment with a 70V at 10Hz voltage pulse. This is also established by simulations using the computational fluidic software of CFD-ACE+.
Dynamical Analysis of Protein Regulatory Network in Budding Yeast Nucleus
LI Fang-Ting, JIA Xun
Chin. Phys. Lett. 2006, 23 (8): 2307-2310 .  
Abstract   PDF(pc) (645KB) ( 453 )
Recent progresses in the protein regulatory network of budding yeast Saccharomyces cerevisiae have provided a global picture of its protein network for further dynamical research. We simplify and modularize the protein regulatory networks in yeast nucleus, and study the dynamical properties of the core 37-node network by a Boolean network model, especially the evolution steps and final fixed points. Our simulation results show that the number of fixed points N(k) for a given size of the attraction basin k obeys a power-law distribution N(k) ∝ k-2.024. The yeast network is more similar to a scale-free network than a random network in the above dynamical properties.
Local Events and Dynamics on Weighted Complex Networks
ZHAO Hui, GAO Zi-You
Chin. Phys. Lett. 2006, 23 (8): 2311-2314 .  
Abstract   PDF(pc) (273KB) ( 472 )
We examine the weighted networks grown and evolved by local events, such as the addition of new vertices and links and we show that depending on frequency of the events, a generalized power-law distribution of strength can emerge. Continuum theory is used to predict the scaling function as well as the exponents, which is in good agreement with the numerical simulation results. Depending on event frequency, power-law distributions of degree and weight can also be expected. Probability saturation phenomena for small strength and degree in many real world networks can be reproduced. Particularly, the non-trivial clustering coefficient, assortativity coefficient and degree-strength correlation in our model are all consistent with empirical evidences.
Investigation of the Elasticity of Polymer Nanoparticle by Vibrating Scanning Polarization Force Microscopy
ZHANG Li-Juan, WANG Hua-Bin,
Chin. Phys. Lett. 2006, 23 (8): 2315-2318 .  
Abstract   PDF(pc) (519KB) ( 570 )
The elasticity of an individual polymer nanoparticle may be greatly different from that of the bulk one. Understanding the properties of individual particles such as elasticity and deformation under external forces is of great importance in controlling the final structures and functions of bulk materials. We study the compression properties of single polyethylenimine (PEI) particles using vibrating scanning polarization force microscopy. By controllably imaging PEI particles at different vibration amplitude set-point values, it is demonstrated that we can compress the single PEI nanoparticle with an atomic force microscopy tip in different loads. Based on the force--height and force-strain curves obtained, Young’s moduli of PEI (5--160MPa) in three force regions are estimated according to the Hertz model. The results indicate that PEI has excellent elasticity, which may contribute to its high efficiency as vectors in gene transfection.

An Economical Magnetocardiogram System Based on High-Tc SQUIDs
LI Zhuo, ZHU Xue-Min, ZHANG Li-Hua, HUANG Xu-Guang, REN Yu-Feng, CHEN Geng-Hua, YANG Qian-Sheng, FENG Ji
Chin. Phys. Lett. 2006, 23 (8): 2319-2322 .  
Abstract   PDF(pc) (298KB) ( 621 )
An economical magnetocardiogram (MCG) system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-Tc superconducting quantum interference device (SQUID) magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements.
Complex Behaviour for the Origin and Destination Matrix Estimation Problem
SUN Hui-Jun, WU Jian-Jun,
Chin. Phys. Lett. 2006, 23 (8): 2323-2326 .  
Abstract   PDF(pc) (230KB) ( 452 )
The origin and destination (O-D) matrix estimation is an important problem in traffic networks. We apply the gravitation model to express the preference attachment and to analyse the statistical characteristics of the traffic flow in each O-D pair in theory. It is found that the distribution of the future O-D matrix decays as a power law. Additionally, different exponents are obtained for both the constant and variable link cost.
Notes on the Algorithm for Calculating Betweenness
ZHOU Tao, LIU Jian-Guo, WANG Bing-Hong
Chin. Phys. Lett. 2006, 23 (8): 2327-2329 .  
Abstract   PDF(pc) (233KB) ( 480 )
We investigate a common used algorithm [Phys. Rev. E64(2001)016132] to calculate the betweenness centrality for all vertices. The inaccurateness of that algorithm is pointed out and a corrected algorithm, also with O(MN) time complexity, is given. In addition, the comparison of calculating results for these two algorithm aiming at the protein interaction network of yeast is shown.
Evolution of Weighted Networks by Duplication--Divergence Mechanism
ZHANG Jian-Guo, YAN Jia-Ren, LIU Zi-Ran, WANG Li
Chin. Phys. Lett. 2006, 23 (8): 2330-2333 .  
Abstract   PDF(pc) (284KB) ( 431 )
The duplication and divergence process is ubiquitous in nature and man-made networks. Motivated by the duplication--divergence mechanism which depicts the growth of protein networks, we propose a weighted network model in which topological evolution is coupled with weight dynamics. Large scale numerical results indicate that our model can naturally generate networks with power-law-like distributions of degree, strength and weight. The degree--strength correlation is illustrated as well. These properties are in agreement well with empirical data observed in real-world systems. Furthermore, by altering the retention probability σ, weighted, structured exponential networks are realized.
First-Principles Study of Orthorhombic Perovskites MgSiO3 up to 120GPa and Its Geophysical Implications
DENG Li-Wei, ZHAO Ji-Jun, JI Guang-Fu, GONG Zi-Zheng, WEI Dong-Qing,
Chin. Phys. Lett. 2006, 23 (8): 2334-2337 .  
Abstract   PDF(pc) (415KB) ( 643 )
High-pressure behaviour of orthorhombic MgSiO3 perovskite crystal is simulated by using the density functional theory and plane-wave pseudopotentials approach up to 120GPa pressure at zero temperature. The lattice constants and mass density of the MgSiO3 crystal as functions of pressure are computed, and the corresponding bulk modulus and bulk velocity are evaluated. Our theoretical results agree well with the high-pressure experimental data. A thermodynamic method is introduced to correct the temperature effect on the 0-K first-principles results of bulk wave velocity, bulk modulus and mass density in lower mantle P/T range. Taking into account the temperature corrections, the corrected mass density, bulk modulus and bulk wave velocity of MgSiO3-perovskite are estimated from the first-principles results to be 2%, 4%, and 1% lower than the preliminary reference Earth model (PREM) profile, respectively, supporting the possibility of a pure perovskite lower mantle model.
Hot Oxygen Corona at Mars and Its Effect on Solar Wind Deceleration
ZHANG Tie-Long, Lichtenegger Herbert, SHI Jian-Kui, WANG Xiao, Lammer Helmut
Chin. Phys. Lett. 2006, 23 (8): 2338-2340 .  
Abstract   PDF(pc) (193KB) ( 415 )
Phobos 2 plasma measurements have revealed solar wind deceleration of about 100km/s upstream of the Martian bow shock. It is suggested that the deceleration is due to the mass loading by the ions originating from the hot oxygen corona of Mars. In this study, we use a gas-dynamic model to estimate the solar wind deceleration caused by the mass loading effect and the result shows that the deceleration is only about 10--15km/s when we invoke the well established hot oxygen corona density profiles.
Sagnac Effect in the Kerr--Newman and Reissner--Nordström Fields
HU Ping-Hui, WANG Yong-Jiu
Chin. Phys. Lett. 2006, 23 (8): 2341-2343 .  
Abstract   PDF(pc) (187KB) ( 602 )
By means of a formal analogy with the Aharonov--Bohm effect, the Sagnac time delay and the corresponding Sagnac phase shift in the Kerr--Newman and Reissner--Nordström spacetimes are discussed. We find that the effect depends on the properties of the source of the gravitational field. The contributions made by the electric charge of the gravitational source can be employed to weaken it in the Kerr--Newman spacetime, even if a phase shift and a time delay still appear. This is due to the properties of the rotating source of the gravitational field.
Antigravitational Instability of Cosmic Substrate in the Newtonian Cosmology
Chin. Phys. Lett. 2006, 23 (8): 2344-2347 .  
Abstract   PDF(pc) (200KB) ( 418 )
A new version of the forming Universe large-scale structures is proposed, based on the refuse of analyses of only the gravitational instability of the cosmological substrate. Vacuum, i.e. the dominant nonbaryonic matter in the Universe, creates the antigravitational instability of the baryonic cosmic substrate itself and causes the formation of galaxies.
Erratum: Observation of Tri-photon K-Shell X Rays [Chin. Phys. Lett. 23 (2006) 826]
Chin. Phys. Lett. 2006, 23 (8): 2348-2348 .  
Abstract   PDF(pc) (99KB) ( 461 )
105 articles