Chin. Phys. Lett.

Volume 25 Issue 3

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Nonsingular Travelling Complexiton Solutions to a Coupled Korteweg--de Vries Equation

YANG Xu-Dong, RUAN Hang-Yu, LOU Sen-Yue,

Chin. Phys. Lett. 2008, 25 (3): 805-808 .

Abstract

PDF(pc) (192KB) ( 1246 )

A class of novel nonsingular travelling complexiton solutions to a coupled Korteweg--de Vries (KdV) equation is presented via the first step Darboux transformation of the complex KdV equation with nonzero seed solution. Furthermore, the properties of the nonsingular solutions are discussed.

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A New Conserved Quantity Corresponding to Mei Symmetry of Tzenoff Equations for Nonholonomic Systems

ZHENG Shi-Wang, XIE Jia-Fang, CHEN Wen-Cong

Chin. Phys. Lett. 2008, 25 (3): 809-812 .

Abstract

PDF(pc) (153KB) ( 807 )

A new conserved quantity is investigated by utilizing the definition and
discriminant equation of Mei symmetry of Tzenoff equations for
nonholonomic systems. In addition, the expression of this conserved
quantity, and the determining condition induced new conserved quantity
are also presented.

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Physical Realization of Quantum C-Not Gate

HUO Jian-Li, WANG Shun-Jin, TAO Jun

Chin. Phys. Lett. 2008, 25 (3): 813-816 .

Abstract

PDF(pc) (146KB) ( 1117 )

We investigate a Heisenberg spin cluster with two particles controlled by a time-dependent magnetic field. The system is controlled by tuning the amplitude, frequency, and interaction time of the three-step time-dependent magnetic field. Then we solve the time-dependent Schrodinger equation of the two-particle system, and obtain the time evolution operator. By the
three-timestep interaction, the wavefunction evolves from the initial state to the final state, and the total evolution operator can be expressed as a product of the three evolution operators. By adjusting the physical parameters, the key two-qubit logic gate, the C-Not gate, can be realized physically.

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Entanglement in One-Dimensional Random XY Spin Chain with Dzyaloshinskii--Moriya Interaction

SHAN Chuan-Jia, CHENG Wei-Wen, LIU Tang-Kun, HUANG Yan-Xia, LI Hong

Chin. Phys. Lett. 2008, 25 (3): 817-820 .

Abstract

PDF(pc) (162KB) ( 1014 )

The impurities of exchange couplings, external magnetic fields and Dzyaloshinskii--Moriya (DM) interaction considered as Gaussian distribution, and the entanglement in one-dimensional random XY spin systems is investigated by the method of solving the different spin--spin correlation functions and the average magnetization per spin. The entanglement dynamics at central locations of ferromagnetic and antiferromagnetic chains have been studied by varying the three impurities and the strength of DM
interaction. (i) For the ferromagnetic spin chain, the weak DM interaction can improve the amount of entanglement to a large value, and the impurities have the opposite effect on the entanglement below and above critical DM interaction. (ii) For the antiferromagnetic spin chain, DM interaction can enhance the entanglement to a steady value. Our results imply that DM interaction strength, the impurity and exchange couplings (or magnetic field) play competing roles in enhancing quantum entanglement.

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Evolution of Coherent Light in a Simple Polariton Model

WANG Fa-Qiang, ZHANG Zhi-Ming

Chin. Phys. Lett. 2008, 25 (3): 821-824 .

Abstract

PDF(pc) (200KB) ( 692 )

We study the phase evolution behaviour of coherent light interacting with phonons initially in thermal equilibrium at temperature T in terms of phase distribution probability. It is shown that the phase not only shifts but also diffuses. The phase distribution broadens and narrows periodically with time. There is a threshold in the variation of the width of phase distribution as a function of coupling coefficient in the detuning case for fixed temperature. The phase diffusion changes rapidly with temperature for coupling coefficient
above the threshold while it changes little with temperature for coupling coefficient below the threshold.

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Sudden Death of Entanglement between Two Atoms with Initial Tripartite Entangled State in the Tavis--Cummings Model

YANG Qing, YANG Ming, CAO Zhuo-Liang,

Chin. Phys. Lett. 2008, 25 (3): 825-827 .

Abstract

PDF(pc) (157KB) ( 1221 )

We study the entanglement dynamics of two atoms with initial tripartite entangled W-like state in the Tavis--Cummings model. We find that the entanglement evolvement is sensitive not only to the entanglement degree of the initial state but also to the concrete form of the initial state. The so-called
sudden death effect occurs only for some initial states.

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Multiparty Quantum Chatting Scheme

SUN Ying, WEN Qiao-Yan, ZHU Fu-Chen

Chin. Phys. Lett. 2008, 25 (3): 828-831 .

Abstract

PDF(pc) (170KB) ( 711 )

We propose a new multiparty simultaneous quantum direct communication scheme based on Green--Horne--Zeilinger (GHZ) states and dense coding. For achieving high efficiency without leaking any information, four encoding
schemes are prepared in advance. The present scheme has the capacity
of transmitting (M+1) M classical bits per group of M-particle GHZ states when there exist M parties. The technique of rearranging particles makes the legal users coequally exchange their messages in the same length. Both high efficiency and excellent security against the common attacks are virtues of this new scheme.

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Maximizing Thermal Entanglement of XY Model Using Site-Dependent Magnetic Fields in Specific Directions

CHAN Wen-Ling, YANG Dong, GU Shi-Jian

Chin. Phys. Lett. 2008, 25 (3): 832-835 .

Abstract

PDF(pc) (943KB) ( 778 )

We study the thermal entanglement by means of concurrence in a two-qubit isotropic XY model in the presence of site-dependent external magnetic fields in arbitrary directions. We find that at a given temperature and magnetic field
strength, the mirror symmetry of the two fields about the x--y plane is a necessary condition for maximum entanglement. However, if there is no constraint on the field strengths, then the necessary condition for maximum entanglement reduces to the configuration that the two fields are vertical, anti-parallel and with the same strength. We also investigate the anisotropic XY model and find that the above conclusion more or less holds.

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Generation of Multi-Photon Cluster States through the Cavity Input--Output Process

ZHENG Hai-Yu, ZHANG Xiao-Ting, SHAO Xiao-Qiang, WEN Jing-Ji, ZHANG Shou

Chin. Phys. Lett. 2008, 25 (3): 836-838 .

Abstract

PDF(pc) (156KB) ( 970 )

We propose a scheme to generate the multi-photon cluster states via the cavity input--output process and the single-bit rotations. The method can be generalized to construct a series of multi-photon graph states, and the successful probability is close to unity in the ideal condition.

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Generation of Cluster-Type Entangled Coherent States via Cross-Kerr Nonlinearity

WANG Wen-Feng, SUN Xin-Yuan, LUO Xiao-Bing

Chin. Phys. Lett. 2008, 25 (3): 839-842 .

Abstract

PDF(pc) (172KB) ( 783 )

We propose an optical scheme for the generation of the cluster-type entangled coherent states in free travelling optical fields via cross-Kerr nonlinearity. The required resources for the generation are coherent state source, beam splitters, photodetectors, and Kerr media. We also discuss the
implementation of the Hadamard gate operation for coherent states and
the homodyne detection.

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Quantum Degenerate Fermi--Bose Mixtures of ⁴⁰K and ⁸⁷Rb Atoms in a Quadrupole-Ioffe Configuration Trap

XIONG De-Zhi, CHEN Hai-Xia, WANG Peng-Jun, YU Xu-Dong, GAO Feng, ZHANG Jing

Chin. Phys. Lett. 2008, 25 (3): 843-846 .

Abstract

PDF(pc) (827KB) ( 1000 )

We report on the attainment of quantum degeneracy of ⁴⁰K by means of efficient thermal collisions with the evaporatively cooled ⁸⁷Rb atoms. In a quadrupole-Ioffe configuration trap, potassium atoms are cooled to 0.5 times the Fermi temperature. We obtain up to 7.59i×10⁵ degenerate fermions ⁴⁰K.

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Generation of Coherent Trimers from Bose-Condensed Atoms via a Generalized Stimulated Raman Adiabatic Passage

JING Hui

Chin. Phys. Lett. 2008, 25 (3): 847-849 .

Abstract

PDF(pc) (105KB) ( 788 )

We propose to use a generalized technique of stimulated Raman adiabatic passage to create an atom--molecule dark state that permits the enhanced coherent creation of triatomic molecules in a repulsive atomic Bose--Einstein
condensate. As an interesting comparison, the similar cases of creating heteronuclear (bosonic or fermionic) trimers are also briefly discussed.

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Efimov Superchemistry: Quantum Dynamical Theory for Coherent Atom--Trimer Conversion in a Repulsive Atomic Bose--Einstein Condensate

JING Hui, GENG Zhen-Duo

Chin. Phys. Lett. 2008, 25 (3): 850-853 .

Abstract

PDF(pc) (845KB) ( 894 )

We show that by making a generalized atom--molecule dark state, coherent creation of triatomic molecules can be enhanced in a repulsive atomic Bose--Einstein condensate. The dynamics of heteronuclear trimer creation is significantly different from the homonuclear case and further enhancement can be realized by controlling its chemical reaction channels. The possibility of
manipulating atom--trimer conversion provides an appealing research area for current coherent matter--wave optics.

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Gravitational Collapse of Radiating Dyon Solution and Cosmic Censorship Hypothesis

K. D. Patil, S. S. Zade, A. N. Mohod

Chin. Phys. Lett. 2008, 25 (3): 854-857 .

Abstract

PDF(pc) (181KB) ( 896 )

We investigate the possibility of cosmic censorship violation in the gravitational collapse of radiating dyon solution. It is shown that the final outcome of the collapse depends sensitively on the electric and magnetic charge parameters. The graphs of the outer apparent horizon, inner Cauchy
horizon for different values of parameters are drawn. It is found that the electric and magnetic components push the apparent horizon towards the retarded time-coordinate axis, which in turn reduces the radius of the apparent horizon in Vaidya spacetime. Also, we extend the earlier work of Chamorro and Virbhadra [Pramana, J. Phys. 45(1995)181].

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Quasinormal Spectrum and Quantization of the Kerr--Newman Black Hole

JING Ji-Liang, DING Chi-Kun

Chin. Phys. Lett. 2008, 25 (3): 858-861 .

Abstract

PDF(pc) (176KB) ( 834 )

The intermediate asymptotic quasinormal mode spectrum of the charged scalar and Dirac fields in the near extremal Kerr--Newman black hole is studied analytically. It is found that the quasinormal mode spectrum can be expressed in terms of the Hawking temperature T_hb, the electric potential Φ₊ and the horizon's angular velocity Ω_H for the case of (eΦ_-+mΩ_H)> (1-4π T_hb)ReΩ (where e is the charge and m is the azimuthal projection number), whereas it is only relevant to the charge and the mass parameter for another case. It is also shown that by using the Bohr's correspondence principle, the fundamental change in the black-hole surface area induced by the emission of a rotating charged quantum from the Kerr--Newman black hole is in accord with the Bekenstein--Mukhanov general prediction.

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Control of Beam Halo-Chaos Based on Self-Field-Intensity of Particle Beam

YU Hai-Jun, BAI Long, WENG Jia-Qiang, LUO Xiao-Shu

Chin. Phys. Lett. 2008, 25 (3): 862-865 .

Abstract

PDF(pc) (426KB) ( 722 )

The KV beam through an axisymmetric periodic-focusing magnetic field is studied using the particle-core model. A new variable of the self-field-intensity of particle beam is selected, and an idea of self-field feedback controller is proposed based on the variable for controlling the halo-chaos. We perform
multiparticle simulation to control the halo by using the self-field feedback controller. The numerical results show that the halo-chaos and its regeneration can be eliminated effectively, and that the density uniformity can be found at the centre of beam as long as an appropriate control method is chosen. The control method may be operated in the experiment, because field intensity measurement is easy.

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Structure-Preserving Algorithms for the Lorenz System

GANG Tie-Qiang, MEI Feng-Xiang, CHEN Li-Jie

Chin. Phys. Lett. 2008, 25 (3): 866-869 .

Abstract

PDF(pc) (724KB) ( 1108 )

Based on a splitting method and a composition method, we construct some structure-preserving algorithms with first-order, second-order and fourth-order accuracy for a Lorenz system. By using the Liouville's formula, it is proven that the structure-preserving algorithms exactly preserve the volume of infinitesimal cube for the Lorenz system. Numerical experimental results illustrate that for the conservative Lorenz system, the qualitative behaviour of the trajectories described by the classical explicit fourth-order Runge--Kutta (RK4) method and the fifth-order Runge--Kutta--Fehlberg (RKF45) method is wrong, while the qualitative behaviour derived from the structure-preserving algorithms with different orders of accuracy is correct. Moreover, for the small
dissipative Lorenz system, the norm errors of the structure-preserving algorithms in phase space are less than those of the Runge--Kutta methods.

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Synchronized Anti-Phase and In-Phase Oscillations of Intracellular Calcium Ions in Two Coupled Hepatocytes System

SHEN Chuan-Sheng, CHEN Han-Shuang, ZHANG Ji-Qian

Chin. Phys. Lett. 2008, 25 (3): 870-873 .

Abstract

PDF(pc) (187KB) ( 840 )

We study the dynamic behaviour of two intracellular calcium oscillators that are coupled through gap junctions both to Ca²⁺ and inositol(1,4,5)-trisphosphate (IP₃). It is found that synchronized anti-phase and in-phase
oscillations of cytoplasmic calcium coexist in parameters space. Especially, synchronized anti-phase oscillations only occur near the onset of a Hopf bifurcation point when the velocity of IP₃synthesis is increased. In addition, two kinds of coupling effects, i.e., the diffusions of Ca²⁺ and IP₃ among cells on synchronous behaviour, are considered. We find that small coupling of
Ca²⁺ and large coupling of IP₃ facilitate the emergence of synchronized anti-phase oscillations. However, the result is contrary for the synchronized in-phase case. Our findings may provide a qualitative understanding about the mechanism of synchronous behaviour of intercellular calcium signalling.

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Synchronization between Different Networks

LI Ying, LIU Zeng-Rong, ZHANG Jian-Bao

Chin. Phys. Lett. 2008, 25 (3): 874-877 .

Abstract

PDF(pc) (118KB) ( 1053 )

Synchronization between two networks with different topology structures and different dynamical behaviours is studied. These two different networks are
driving and responding networks, respectively. Under the preconditions that the driving network gets synchronization, we give the conditions for the responding network to be synchronized to the same dynamics as the driving network with the help of the open-plus-closed-loop method. Then a example is given to verify the validity of the theoretical results.

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Existence of Formal Conservation Laws of a Variable-Coefficient Korteweg--de Vries Equation from Fluid Dynamics and Plasma Physics via Symbolic Computation

ZHANG Chun-Yi, LI Juan, MENG Xiang-Hua, XU Tao, GAO Yi-Tian,

Chin. Phys. Lett. 2008, 25 (3): 878-880 .

Abstract

PDF(pc) (100KB) ( 1098 )

Employing the method which can be used to demonstrate the infinite conservation laws for the standard Korteweg--de Vries (KdV) equation, we prove that the variable-coefficient KdV equation under the Painleve test
condition also possesses the formal conservation laws.

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Geometric Property of the Faddeev Model

SHI Chang-Guang

Chin. Phys. Lett. 2008, 25 (3): 881-883 .

Abstract

PDF(pc) (335KB) ( 636 )

Two functions u and v are used in expressing the solutions of the Faddeev model. The geometric property of the surface S determined by u and v is discussed and the shape of the surface is demonstrated as an example. The Gaussian curvature of the surface S is negative.

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Effects of Velocity-Dependent Force on the Magnetic Form Factors of Odd-Z Nuclei

DONG Tie-Kuang, REN Zhong-Zhou,

Chin. Phys. Lett. 2008, 25 (3): 884-887 .

Abstract

PDF(pc) (183KB) ( 732 )

We investigate the effects of the velocity-dependent force on the magnetic form factors and magnetic moments of odd-Z nuclei. The form factors are calculated with the harmonic-oscillator wavefunctions. It is found that the contributions of the velocity-dependent force manifest themselves in the very large momentum transfer region (q≥4fm^-1). In the low and medium q region the contributions of the velocity-dependent force are very small compared with those without this force. However, in the high-q region the contributions of the velocity-dependent force are larger than the normal form factors. The diffraction structures beyond the existing experimental data are found after the contributions of the velocity-dependent force are included. The formula of the correction to the single particle magnetic moment due to the velocity-dependent force is reproduced exactly in the long-wavelength limit (q=0) of the M1 form factor.

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Strangeness Production Process pp→nK⁺ Σ^ within Resonance Model

CAO Xu, LEE Xi-Guo, WANG Qing-Wu,

Chin. Phys. Lett. 2008, 25 (3): 888-891 .

Abstract

PDF(pc) (212KB) ( 619 )

We explore production mechanism and final state interaction in the pp→nK^⁺Σ⁺channel based on the inconsistent experimental data published
respectively by COSY-11 and COSY-ANKE. The scattering parameter a>0 for nΣ⁺ interaction is favoured by large near-threshold cross section within a nonrelativistic parametrization investigation, and a strong n∑⁺ interaction comparable to pp interaction is also indicated. Based on this analysis we calculate the contribution from resonance ∆* (1920) through π⁺exchange within resonance model, and the numerical result suggests a rather small near-threshold total cross section, which is consistent with the COSY-ANKE data. With an additional sub-threshold resonance Δ*(1620), the model gives a much better description to the rather large near-threshold total cross section published by COSY-11.

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Effects of Surface Emitting and Cumulative Collisions on Elliptic Flow

LIU Jian-Li, WU Feng-Juan, ZHANG Jing-Bo, TANG Gui-Xin, HUO Lei

Chin. Phys. Lett. 2008, 25 (3): 892-895 .

Abstract

PDF(pc) (193KB) ( 945 )

The integral and differential elliptic flow of partons is calculated using the multiphase transport model for Au+Au collisions at centre-of-mass energy
√s_NN=200GeV. It is shown that elliptic flow of partons freezing out at early time, which is affected mainly by surface emittance, decreases with time and elliptic flow of partons freezing out at late time, which is dominated by cumulative collisions, increases with time. The elliptic flow of partons freezing out early has a large contribution to the flatting of curve of final differential elliptic flow at large transverse momentum. It is argued that the effect of surface emittance is not neglectable.

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Ground State Energy Calculations of Isoelectronic Series of He in Double-Zeta Approximation Using Coulomb Potential with Noninteger Indices

GUSEINOV I. Israfil, AKSU Hüseyin

Chin. Phys. Lett. 2008, 25 (3): 896-898 .

Abstract

PDF(pc) (173KB) ( 865 )

Using formulae for one- and two-electron integrals of Coulomb interaction potential f_k(r)=r^-k with non-integer indices k established by one of the authors with the help of complete orthonormal sets of ψ^α-exponential-type
orbitals (α=1,0,-1,-2...), we perform the calculations for isoelectronic series of the He atom containing nuclear charges from 2 to 10, where k=1-μ (-1<μ<0). For this purpose we have used the double-zeta approximation, the configuration interaction and coupled-cluster methods employing the integer-n Slater-type orbitals as basis sets. It is demonstrated that the results of
calculations obtained are better than the numerical Hartree--Fock values.

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High-Pressure Behaviour of β-HMX Crystal Studied by DFT-LDA

LIAN Dan, LU Lai-Yu, WEI Dong-Qing, ZHANG Qing-Ming, GONGZi-Zheng, GUO Yong-Xin

Chin. Phys. Lett. 2008, 25 (3): 899-902 .

Abstract

PDF(pc) (542KB) ( 1004 )

Density functional theory (DFT) with local density approximation (LDA) is employed to study the structural and electronic properties of the high explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under high pressure compression up to 40GPa. Pressure dependences of the cell volume, lattice constants, and molecular geometry of solid β-HMX are presented and discussed. It is found that N--N and N--C bonds are subject to significant change. This may implies that these bonds may be related to the sensitivity. The band gap is calculated and plotted as a function of pressure. Compared the experimental results with other theoretical works we find that LDA gives good results.

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Fine-Structure Splittings of Nitrogen Isoelectronic Sequence: Competitions among Spin--Orbit Interactions, Breit Interactions and Electron Correlations

WANG Xiao-Lu, CHEN Shao-Hao, HAN Xiao-Ying, LI Jia-Ming,

Chin. Phys. Lett. 2008, 25 (3): 903-906 .

Abstract

PDF(pc) (103KB) ( 1213 )

Using the multi-configuration Dirac--Fock self-consistent field method and the relativistic configuration interaction method with quantum-electrodynamics
corrections performed by the GRASP code, we calculate the fine-structure energy levels of the ground-state configuration (1s²²s²²p³) of the nitrogen isoelectronic sequence, according to the L-S coupling scheme with atomic number Z up to 22. Based on the calculated results, we elucidate the mechanism of the orderings of fine-structure energy levels of ²D_3/2,5/2 and
²P_1/2,3/2 respectively, i.e. for ²D_3/2,5/2 orderings, the competition between the spin--orbit interactions and the Breit interactions; for ²P_1/2,3/2 orderings, the electron correlations, especially the electron correlations owing to the
2p⁵ configuration interactions.

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Guiding Neutral Atoms with Two Current-Carrying Wires and a Vertical Bias Field on the Atom Chip

KE Min, YAN Bo, LI Xiao-Lin, WANG Yu-Zhu

Chin. Phys. Lett. 2008, 25 (3): 907-910 .

Abstract

PDF(pc) (666KB) ( 901 )

We demonstrate the guiding of neutral atoms with two parallel microfabricated current-carrying wires on the atom chip and a vertical magnetic bias field. The atoms are guided along a magnetic field minimum parallel to the current-carrying wires and confined in the other two directions. We describe in detail how the precooled atoms are efficiently loaded into the two-wire guide. We present a detailed experimental study of the motional properties of the atoms in the guide and the relationship between the location of the guide and the vertical bias field. This two-wire guide with vertical bias field can be used to realize large area atom interferometer.

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High-Order Ultrawideband Pulse Generation from NRZ-DPSK Signals

DONG Jian-Ji, ZHANG Xin-Liang, YU Yu, XU Jing, HUANG De-Xiu

Chin. Phys. Lett. 2008, 25 (3): 911-914 .

Abstract

PDF(pc) (262KB) ( 939 )

A simple method to generate ultrawideband (UWB) doublet and triplet from nonreturn-to-zero (NRZ) differential phase shift keying (DPSK) signals is proposed and experimentally demonstrated. The proposed configuration consists of a Mach--Zehnder modulator (MZM) to generate NRZ-DPSK signals, a section of single-mode fibre to form a microwave bandpass filter, which is used to generate doublet pulses, and a Gaussian optical bandpass filter (OBF), which serves as a frequency discriminator to generate higher-order UWB pulses. A pair of polarity-reversed triplet pulses is achieved by locating the optical carrier at the positive and negative linear slopes of the OBF, where the OBF detuning is 0.12nm and -0.2nm, respectively. The spectra of the pair of UWB triplets have a central frequency of 5GHz and 5.6GHz, and have a -10dB bandwidth of 6.9GHz and 8.1GHz, respectively. The UWB pulses remain doublet shape when the light wavelength is located at the peak of the OBF. The spectrum of the doublet has a central frequency of 5.6GHz and a -10dB
bandwidth of 6.9GHz.

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Probing Wave Packet Dynamics of I₂^- Anions with Pump--Probe Femtosecond Spectroscopy

MIAO Xiang-Yang, LI Xin, SONG He-Shan

Chin. Phys. Lett. 2008, 25 (3): 915-918 .

Abstract

PDF(pc) (178KB) ( 612 )

The wave packet dynamics of I₂^- anions is studied by using the time-dependent wave packet method. Two conclusions can be drawn from the calculations. First, the period of the total photoelectron signal oscillating with the propagation of delay time is about 750fs. Second, the photoionization of I₂^- anions begin at the time 600fs, and the time needed for the population of the electronic state of I₂ neutral molecule to reach the maximum becomes shorter with the increasing delay time.

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Photodetachment of HF^- in an Electric Field

WANG De-Hua

Chin. Phys. Lett. 2008, 25 (3): 919-922 .

Abstract

PDF(pc) (195KB) ( 732 )

Photdetachment of a negative HF^- ion in an electric field is studied by using the two-centre model and the closed orbit theory. An analytic formula is presented for the electron flux of HF^- in the presence of an electric field. The results show that the oscillation in the electron flux distribution is caused by the rescattering effect of the molecular ion core and the interference between the two nuclei. In addition, the interference between the orbits passing through the given spatial point also plays an important role in the electron flux distribution. This study provides a new understanding of the photodetachment of polar molecules in the presence of external field.

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A New Desirable Molecular Species for Stark Deceleration

FU Guang-Bin, DENG Lian-Zhong, YIN Jian-Ping

Chin. Phys. Lett. 2008, 25 (3): 923-926 .

Abstract

PDF(pc) (243KB) ( 824 )

We demonstrate a new molecular sample (CH radical) for Stark deceleration by Monte Carlo simulation, study the dependences of the decelerating effect on the different phase angles, stage number and decelerating voltages, and obtain some new optimized conditions and parameters. We also calculate the Stark energy shift of different quantum states of CH radical in the Stark
decelerator electrostatic field and their populations in a supersonic CH molecular beam. Our study shows that the mean velocity of the supersonic CH molecular beam in the ²π_1/2 state can be decelerated from 380m/s to 24m/s, and the corresponding translation temperature is lowered from 2.8K to 27mK. It is thus clear that the CH radical is a new and desirable candidate for Stark
deceleration.

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Dielectronic Recombination of Sn¹⁰⁺ Ions and Related Satellite Spectra

FU Yan-Biao, DONG Chen-Zhong, SU Mao-Gen, Gerry O' Sullivan

Chin. Phys. Lett. 2008, 25 (3): 927-929 .

Abstract

PDF(pc) (188KB) ( 659 )

Based on the multi-configuration Dirac--Fock method, theoretical calculations are carried out for the dielectronic recombination (DR) rate coefficients and the collision excitation rate coefficients of Sn¹⁰⁺ ions. It is found that the total DR rate coefficient has its maximum value between 10eV and 100eV and is greater than either the radiative recombination or three-body recombination rate coefficients (the number of free electrons per unit is 10²¹cm³) for the case of T_e>1eV. Therefore, DR can strongly influence the ionization balance of laser produced multi-charged tin ions. The related dielectronic satellite cannot be ignored at low temperature T_e <5eV.

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KLn Dielectronic Recombination Process of B- Through He-like Cu Ions

GAO Ying-Hui, ZHANG Xue-Mei, NG Fan-Chang, CHEN Wen-Dong, CHEN Chong-Yang, ZOU Ya-Ming

Chin. Phys. Lett. 2008, 25 (3): 930-933 .

Abstract

PDF(pc) (207KB) ( 1028 )

The KLn dielectronic recombination processes of trapped highly charged B-like through He-like Cu ions are studied theoretically, and the theoretical results are used to analyse our previous experimental data at Heidelberg electron beam ion trap (EBIT). The theoretical resonant positions agree with the experimental resonant positions to a precision of 0.4%, in comparison with the resonant positions of those highest peaks between theory and experiment. The experimental spectra are then fitted using a formula with the theoretical resonant energies and strengths, the result shows good overall agreement between theory and experiment over a wide electron energy range. The distribution of highly charged states is obtained from the fitting parameters.

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Optimization Design of Helix Pitch for Efficiency Enhancement in the Helix Travelling Wave Tubes

DUAN Zhao-Yun, GONG Yu-Bin, LU Ming-Yi, WEI Yan-Yu, WANG Wen-Xiang

Chin. Phys. Lett. 2008, 25 (3): 934-937 .

Abstract

PDF(pc) (283KB) ( 1169 )

The output section of a helix travelling wave tube usually contains a helix pitch taper for high rf electron efficiency. By keeping the rf field as synchronous as possible with the decelerating electron beam bunches, the rf field can extract much more energy from the beam, and thus the maximum
electron efficiency can be realized. Recently, a global simulated annealing algorithm has been employed to design the helix pitch profile so as to improve the electron efficiency as much as possible. From the numerical results, it is concluded that the electron efficiency can be enhanced by about 4%--8%.

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Design of Super-resolution Filters with a Gaussian Beam in Optical Data Storage Systems

WANG Sha-Sha, ZHAO Xiao-Feng, LI Cheng-Fang, RUAN Hao

Chin. Phys. Lett. 2008, 25 (3): 938-941 .

Abstract

PDF(pc) (407KB) ( 975 )

Super-resolution filters based on a Gaussian beam are proposed to reduce the focusing spot in optical data storage systems. Both of amplitude filters and pure-phase filters are designed respectively to gain the desired intensity
distributions. Their performances are analysed and compared with those based on plane wave in detail. The energy utilizations are presented. The simulation results show that our designed super-resolution filters are favourable for use in optical data storage systems in terms of performance and energy utilization.

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Engineering of Two Quantum States via Conditional Measurement on Two-Mode Squeezed State

LIAN Yi-Min, ZHANG Jun-Xiang, XIE Chang-De, PENG Kun-Chi

Chin. Phys. Lett. 2008, 25 (3): 942-944 .

Abstract

PDF(pc) (105KB) ( 668 )

We propose a scheme for the simultaneously preparation radiation-field modes of a single photon and a superposition of zero- and one-photon states, based on the coherent quantum state displacement and photon subtraction from two-mode squeezed state. It is shown that the single-photon and the superposition states can be obtained by only choosing the suitable parameter of displacements. The experimental feasibility to
accomplish this scheme is also discussed.

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Engineering Two-Mode Squeezed Vacuum Motional State of a Single Intracavity Trapped Ion

TAN Hua-Tang, TAN Rong, LI Gao-Xiang

Chin. Phys. Lett. 2008, 25 (3): 945-948 .

Abstract

PDF(pc) (164KB) ( 885 )

We propose to generate two-mode squeezed vacuum motional state of an
intracavity trapped ion by taking the advantage of the dissipation of the cavity mode. At the first step, the steady and pure two-mode motional entanglement between two motional degrees of the cold ion is obtained by engineering the couplings of both the motional modes of the ion to the cavity field. Based on the first step, a two-mode squeezed vacuum motional state is then generated by manipulating the phases of the external laser pulses incident on the ion.

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Combined Effect of Dissipation and Thermal Mixed State on Entanglement in the Dispersive Limit

OBADA A. -S. F., HESSIAN H. A., MOHAMED A. -B. A.

Chin. Phys. Lett. 2008, 25 (3): 949-952 .

Abstract

PDF(pc) (141KB) ( 743 )

We investigate the entanglement in the interacting system of a single mode thermal field and a single qubit with dissipation in the dispersive limit. The influence of initial temperature of thermal field and atoms on the entanglement is then examined.

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Terahertz Quantum Cascade Laser at 3.39THz

CAO Jun-Cheng, LI Hua, HAN Ying-Jun, TAN Zhi-Yong, LU Jing-Tao, LUO Hui, LAFRAMBOISE Sylvain, LIU Hui-Chun

Chin. Phys. Lett. 2008, 25 (3): 953-956 .

Abstract

PDF(pc) (2644KB) ( 975 )

We demonstrate the growth of terahertz quantum cascade laser (THz QCL) by gas source molecular beam epitaxy. X-ray diffraction and cross-sectional transmission electron microscopic measurements show the high crystalline quality of the THz QCL active region. From the cross-sectional transmission electron microscopy image, sharp interfaces are observed and the deduced
cascade period thickness is consistent with the result of x-raydiffraction. The test device is lasing at 3.39THz and operating up to 100K in pulsed mode. At 10K, the maximum output power is greater than 1mW with a threshold current density of 738A/cm².

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LD-pumped 6W cw Tm³⁺-Doped Silica Double-Cladding Fibre Laser

DU Ge-Guo, LI Da-Jun, ZHANG Min, YAN Pei-Guang, CHEN Li-Cheng, ZHOU Yao-Hua, RUAN Shuang-Chen

Chin. Phys. Lett. 2008, 25 (3): 957-959 .

Abstract

PDF(pc) (159KB) ( 896 )

We report a thulium-doped silica fibre laser that generates a maximum cw output power of 6W in a 2μm wavelength range when cladding-pumped by a laser diode (LD) operating at approximately 791nm at room temperature. The
slope efficiency with respect to the launched pump power is 50% and 38.4%, with and without an output coupler mirror, respectively. The corresponding thresholds are 2.8W and 4.8W, respectively. The beam qualities M_x² and M_y² are 1.26 and 1.32, respectively. The experimental results are also analysed.

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All-Fibre Ytterbium-Doped Photonic Crystal Fibre Laser with High Efficiency

CHEN Wei, LI Jin-Yan, LU Pei-Xiang, LI Shi-Yu_, JI Ling-Ling, JIANG Zuo-Wen, ZHANG Ji-Huang, PENG Jing-Gang

Chin. Phys. Lett. 2008, 25 (3): 960-962 .

Abstract

PDF(pc) (921KB) ( 1142 )

A double-cladding ytterbium-doped photonic crystal fibre (PCF) with a 350-μm² effective area is fabricated. The measurement results show that the PCF has high absorption peak at 915nm. Its fluorescence lifetime is 840μs. Laser experiments with all-fibre configurations are carried out with this fibre. A continuous-wave output power of 3.96W is achieved with a 5.2W launched pump power. The central wavelength of the output spectrum is 1080.22nm. The results show that the PCF laser has a high slope efficiency of 79.6% and light conversion efficiency of 76.2%.

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Sixth Harmonic of A Nd:YVO₄ Laser Generation In KBBF for ARPES

ZHOU Yong, WANG Gui-Ling, LI Cheng-Ming, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan, WANG Xiao-Yang, ZHU Yong, CHEN Chuang-Tian, LIU Guo-Dong, DONG Xiao-Li, ZHOU Xing-Jiang

Chin. Phys. Lett. 2008, 25 (3): 963-965 .

Abstract

PDF(pc) (230KB) ( 819 )

We report that a deep ultraviolet (DUV) laser from the sixth harmonic of a 1064nm laser has been firstly used as light source in an ultrahigh energy-resolution angle-resolved photoemission spectroscopy (ARPES). The wavelength is 177.3nm obtained by using the second harmonic KBe₂BO₃F₂
crystal with a frequency tripled 1064nm Nd:YVO₄ laser. The large flux (10¹⁴-10¹⁵photons/s) and narrow line width (0.26meV) are suitable for the ultrahigh-energy resolution ARPES. The laser-ARPES can be a powerful tool to study the electronic structure at and near the Fermi level of the superconductor and correlated materials. The laser-ARPES has worked more than 500h already.

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Optical Rectification in Isotropic Thin Film Composed of Chiral Molecules with a Tripod-Like Structure

WANG Xiao-Ou, GONG Li-Jing, LI Chun-Fei

Chin. Phys. Lett. 2008, 25 (3): 966-969 .

Abstract

PDF(pc) (275KB) ( 975 )

Optical rectification (OR) effect in the isotropic thin film consisting of chiral molecules with a tripod-like structure is investigated. The expressions of static-electric polarization in the isotropic chiral thin films and the relations between the OR and microscopic parameters of chiral medium are obtained by theoretical derivation. Furthermore, the relations of static electric polarization with the wavelength of incident light and parameters of chiral molecules are simulated numerically.

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Ported from Self-Similar Analytic Solutions of Ginzburg--Landau Equation with Varying Coefficients

FENG Jie, XU Wen-Cheng, LI Shu-Xian, LIU Wei-Ci, LIU Song-Hao

Chin. Phys. Lett. 2008, 25 (3): 970-973 .

Abstract

PDF(pc) (481KB) ( 824 )

Employing the technique of symmetry reduction of analytic method, we solve the Ginzburg--Landau equation with varying nonlinear, dispersion, gain coefficients, and gain dispersion which originates from the limiting effect of transition bandwidth in the realistic doped fibres. The parabolic asymptotic
self-similar analytical solutions in gain medium of the normal GVD is found for the first time to our best knowledge. The evolution of pulse amplitude, strict linear phase chirp and effective temporal width are given with self-similarity results in longitudinal nonlinearity distribution and longitudinal gain fibre. These analytical solutions are in good agreement with the numerical simulations. Furthermore, we theoretically prove that pulse evolution has the characteristics of parabolic asymptotic self-similarity in doped ions dipole gain fibres.

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Three-Photon Absorption and Upconversion Fluorescence Properties of Series 1,3,4-Oxadiazole Derivatives

HUANG Wei, LU Chang-Gui, QIAN Ying, LIU Chang, WANG Zhu-Yuan, CUI Yi-Ping

Chin. Phys. Lett. 2008, 25 (3): 974-977 .

Abstract

PDF(pc) (198KB) ( 844 )

A newly synthesized 1,3,4-oxadiazole derivatives have been studied using a femtosecond Ti:sapphire laser system. The series molecules present strong three-photon absorption and frequency upconversion fluorescence at wavelengths from 1205nm to 1575nm. Furthermore, there is no proportional relationship between three-photon absorption cross sections and the chemical structure transformation from monomer, dimer to trimer. Effective
charge-transfer distance by π-conjugation bonds may be the contributing factor. In the experimental design, the far-field intensity distribution of femtosecond laser beam has been taken into account. We give the optimized analytical solution of nonlinear transmission in a three-photon absorption (3PA) process when the incident beam has a Gaussian transverse spatial profile.

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Design, Fabrication, and Measurement of Two-Dimensional Photonic Crystal Slab Waveguides

ZHANG Chao, TANG Xuan, MAO Xiao-Yu, CUI Kai-Yu, CAO Lei, HUANG Yi-Dong, ZHANG Wei, PENG Jiang-De

Chin. Phys. Lett. 2008, 25 (3): 978-980 .

Abstract

PDF(pc) (1437KB) ( 700 )

Two-dimensional photonic crystal slab waveguides on SOI wafer are designed and fabricated. Photonic band gap, band gap guided mode, and index guided mode are observed by measuring the transmission spectra. The experimental results are in good agreement with the theoretical ones.

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Room-Temperature Photonic Crystal Laser in H3 Cavity on InGaAsP/InP Slab

REN Gang, ZHENG Wan-Hua, ZHANG Ye-Jin, XING Ming-Xin, WANG Ke, DU Xiao-Yu, CHEN Liang-Hui

Chin. Phys. Lett. 2008, 25 (3): 981-984 .

Abstract

PDF(pc) (2391KB) ( 871 )

We fabricate and investigate two-dimensional photonic crystal H3 microcavities in an InGaAsP slab. The lasing action at room temperature is observed. The lasering threshold is 7mW under the pulsed pump of 0.75% duty cycle. The Q factor and the lasing mode characteristics are simulated by three-dimensional finite difference time domain method. The simulation result matches well with the experiment.

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High Efficient Tunable Fractal Axicon Based on LCoS

WANG Xin, DAI Hai-Tao, Xu Ke-Shu

Chin. Phys. Lett. 2008, 25 (3): 985-988 .

Abstract

PDF(pc) (1186KB) ( 678 )

Based on the Cantor function and phase modulation, a tunable fractal axicon is formed on a liquid crystal on silicon (LCoS) with an improved generating method. It has higher focusing efficiency in higher fractal stage and approaches to 100% theoretically. The on-axis intensity keeps its fractal structure unchanged in operation of fractal stages. The tunability of the
axicon is demonstrated by tune fractal stage from 1 to 3 and focal length from 0.8m to 1m. We also provide details of theoretical analyses and experimental results.

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High Closed Loop Correction Accuracy with a Liquid Crystal Wavefront Corrector

CAO Zhao-Liang, MU Quan-Quan, HU Li-Fa, LIU Yong-Gang, PENG Zeng-Hui, XUAN Li

Chin. Phys. Lett. 2008, 25 (3): 989-992 .

Abstract

PDF(pc) (595KB) ( 872 )

We investigate the accurate control of a liquid crystal wavefront corrector. First, the Gamma correction technique is adopted to amend the nonlinear phase modulation. Then, the control method and wavefront reconstruction are considered. Lastly, a closed loop correction experiment is carried out and a high correction accuracy is obtained with peak to valley (PV) of 0.08λ (λ=632.8nm), the wavefront phase rms 0.015λ, as well as the Strehl ratio of 0.99. The diffraction-limited resolution is achieved.

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Properties of Zero Dispersion Wavelengths in Silica Strands and Photonic Crystal Fibres

ZHANG De-Sheng, SHENG Qiu-Qin, DONG Xiao-Yi

Chin. Phys. Lett. 2008, 25 (3): 993-995 .

Abstract

PDF(pc) (442KB) ( 965 )

To design and calculate the zero-dispersion wavelength is one of the important aspects for highly nonlinear photonic crystal fibres. By using the air filling fraction f defined as f= (6d)/(2πΛ) here for the cladding effective index, and the step effective index model, the relationship between the properties of chromatic dispersion and the two different structures has been analysed. It is pointed that the variation of the zero dispersion wavelength is insensitive to the core diameter change in one range of core diameter D, while keeping the air filling fraction f constant. In the other range of core diameter D, the
photonic crystal fibres have the best nearly-zero ultra-flattened dispersion. These properties are significant to the design of chromatic dispersion and zero dispersion wavelength in photonic crystal fibres.

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Multiple Wavelength-Channels in SPP Waveguides for Optical Communication

ZHANG Zhi-You, HUANG Peng, GUO Xiao-Wei, WANG Jing-Quan, FANG Lang, DU Jing-Lei, LUO Xian-Gang, DU Chun-Lei

Chin. Phys. Lett. 2008, 25 (3): 996-999 .

Abstract

PDF(pc) (1022KB) ( 822 )

Surface plasmon polaritons (SPPs) can be excited, meanwhile some peculiar optical phenomena will appear when light irradiates metal structures under some conditions. Based on photonic band gap theory, in this Letter we present a kind of SPP waveguide with multiple wavelength-channels. By using the Bragg effect and introducing some geometric defect layers into a
quasi-periodic metal heterowaveguide, the multiple SPP forbidden bands (SPFBs) in a given waveband can be generated, and the multiple SPP pass bands (SPPBs) with narrow bandwidth in each SPFB can be realized. The SPP propagation in metal heterowaveguide is calculated by FDTD and transfer matrix methods. By selecting appropriate thickness, position and the number of defect layers, two SPPBs can be achieved in the SPFBs around 1.31 and 1.55μm simultaneously.

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Hybrid Lifting Wavelet-Like Transform for Solution of Electromagnetic Integral Equation

CHEN Ming-Sheng, WU Xian-Liang, SHA Wei, HUANG Zhi-Xiang

Chin. Phys. Lett. 2008, 25 (3): 1000-1003 .

Abstract

PDF(pc) (126KB) ( 920 )

A hybrid lifting wavelet-like transform scheme is successfully applied to the solution of electric field integral equation using Rao--Wilton--Glisson basis functions. To speed up the matrix transform process, the lifting scheme is
adopted. Numerical examples of different three-dimensional perfectly electric conducting objects are considered. Compared with the method of moments, the proposed matrix transform scheme can save considerable CPU time and memory.

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Fourier and Wavelet Transform Analysis of Pressure Signals during Explosive Boiling

YIN Tie-Nan, HUAI Xiu-Lan

Chin. Phys. Lett. 2008, 25 (3): 1004-1007 .

Abstract

PDF(pc) (1923KB) ( 813 )

The transient pressure in a liquid-pool during explosive boiling of acetone is measured by a micro-pressure-measuring system. The Fast Fourier transform and continuous wavelet transform methods are applied to investigate the
frequency characteristics. The results show that the dominant frequency of the explosive boiling is 0--2MHz, and the bubble cluster formed by numerous tiny bubbles departs twice. Analysis and discussions are also conducted to explain the bubble evolution during the explosive boiling.

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Effect of Surface Roughness and Reynolds Number on Self-Similarity of Velocity Profile in the Atmospheric Boundary Layer

LIN Jian-Zhong, LI Hui-Jun, ZHANG Kai

Chin. Phys. Lett. 2008, 25 (3): 1008-1010 .

Abstract

PDF(pc) (0KB) ( 447 )

Self-similarity of power law velocity profile of a simulated atmospheric boundary layer is studied experimentally. The results demonstrate that the self-similarity maintains very well along the streamwise direction for the same rough surface but changes significantly with the surface roughness at the
same position. The self-similarity of the vertical velocity profiles is affected by enhancement of the free stream velocity when the roughness concentration is relatively denser.

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Effect of Discharge Voltage on an Ion Sheath Formed at a Grid in a Multi-Dipole Discharge Plasma

M. K. Mishra, A. Phukan

Chin. Phys. Lett. 2008, 25 (3): 1011-1014 .

Abstract

PDF(pc) (163KB) ( 864 )

It is experimentally demonstrated that a relatively strong ion-rich sheath formed at a fixed negative bias of the grid can be changed to a rather weak ion sheath (sheath potential weakly retards electrons) only by increasing the discharge voltage in the system. At sufficiently high negative grid bias, an
increase of discharge voltage enhances the ion collection current at the grid. An explanation is put forward in support of this experimental observation. A slight density enhancement with a fall in plasma electron temperature is also observed with the increasing negative grid bias.

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Compressibility Effects on the Rayleigh--Taylor Instability Growth Rates

HE Yong, HU Xi-Wei, JIANG Zhong-He

Chin. Phys. Lett. 2008, 25 (3): 1015-1018 .

Abstract

PDF(pc) (131KB) ( 892 )

Effects of two compressibility parameters, i.e. the ratio of specific heats and the equilibrium pressure at the interface, on the Rayleigh--Taylor instability (RTI) growth rates are studied under the same initial conditions, which include the mass, pressure profile, and density profile of the two superposed fluids. The results obtained reconcile the stabilizing and destabilizing effects of compressibility reported in the literature. The influences of the ratio of specific heats on the RTI growth rates are not only stabilized but also destabilized. The effects of the equilibrium pressure at the interface on the growth rates are destabilized.

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A Microwave Air Plasma Source under Atmospheric Pressure

LIU Liang, ZHANG Gui-Xin, FENG Jian, WANG Xin-Xin, LUO Cheng-Mu

Chin. Phys. Lett. 2008, 25 (3): 1019-1021 .

Abstract

PDF(pc) (1475KB) ( 1880 )

We develop a new cavity with a mode similar to TE13 to produce microwave plasma, named APMPS II, which is able to produce a mass of air plasma with diameter of around 6cm, equipped with about 3kW input power under one atmosphere. The plasma seems to be homogeneous without significant filamentous discharge as observed by common camera device. We present the theory of this cavity, show the distribution of electric field of several
planes inside the cavity and give some experimental results.

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Avalanche Phenomenon of Superthermal Electrons Measured by SDD with New SPHA during ECRH

YANG Jin-Wei, ZHANG Yi-Po, LIAO Min, HU Li-Qun, LI Xu, SONG Xian-Ying, LIN Shi-Yao, LI Yong-Ge, LUO Cui-Wen, CHEN Liao-Yuan, RAO Jun, YANG Qing-Wei

Chin. Phys. Lett. 2008, 25 (3): 1022-1025 .

Abstract

PDF(pc) (2535KB) ( 980 )

Two high performance silicon drift detectors (SDD) are installed at the equatorial port with z=0 and z= -16.4cm on HL-2A tokamak, respectively. These SDDs combine with the new and non-conventional software pulse height analyser (SPHA) successfully developed more recently by us to measure the time evolution of soft x-rays spectra, the thermal and superthermal electron temperatures. The high-quality three-dimensional figure of time evolution for soft x-rays energy spectra is easily obtained by
combination of a new SPHA and computer. Therefore, the measurement
accuracies and the time resolutions of thermal and superthermal electron temperatures are also improved. The enhancement phenomenon of superthermal electron during electron cyclotron resonance heating (ECRH) can be explained by the combination of superthermal electron avalanche theory and experimental parameters.

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Algorithm Study on Reconstruction of Refractive Angles in Fan Beam Diffraction Enhanced Computed Tomography

WANG Min, CEN Yu-Wan, ZHU Pei-Ping, HU Xiao-Fang, YU Xiao-Liu

Chin. Phys. Lett. 2008, 25 (3): 1026-1029 .

Abstract

PDF(pc) (122KB) ( 773 )

Based on the 360°computing method of refractive angle for parallel beam diffraction enhanced imaging computed tomography (DE-CT) technique, a new algorithm used to calculate the refractive angle for fan-beam DE-CT technique is developed. The refractive index gradient can be obtained by using the new algorithm with projection data of an object in the range of 0-360°, and the new algorithm only needs to set the analyser at half slope position of the rocking curve.

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Theoretical Study on Structural and Elastic Properties of ZnO Nanotubes

YUAN Peng-Fei, DING Ze-Jun, JU Xin

Chin. Phys. Lett. 2008, 25 (3): 1030-1033 .

Abstract

PDF(pc) (579KB) ( 1020 )

A theoretical investigation on the structural and elastic properties of ZnO nanotubes is carried out by using atomistic calculations based on an inter-atomic pair potential within the shell-model approach. The calculation results are presented for the bond length, bond angle, radius dilation, strain energy, Young modulus and Poisson ratio as a function of tube radius. For small tube radius these properties depend on the helicity of the tube, while for the tube radius larger than 6.0AA, they are independent of the tube radius and helicity except for the strain energy which decreases with increasing tube radius.

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Evolution of Structural Defects in SiO_x Films Fabricated by Electron Cyclotron Resonance Plasma Chemical Vapour Deposition upon Annealing Treatment

HAO Xiao-Peng, WANG Bao-Yi, YU Run-Sheng, WEI Long, WANG Hui, ZHAO De-Gang, HAO Wei-Chang

Chin. Phys. Lett. 2008, 25 (3): 1034-1037 .

Abstract

PDF(pc) (294KB) ( 918 )

We study the structural defects in the SiO_x film prepared by electron cyclotron resonance plasma chemical vapour deposition and annealing recovery evolution. The photoluminescence property is observed in the as-deposited and annealed samples. [-SiO₃]^2- defects are the luminescence centres of the ultraviolet photoluminescence (PL) from the Fourier transform infrared spectroscopy and PL measurements. [-SiO₃]^2- is observed by positron annihilation spectroscopy, and this defect can make the S parameters increase. After 1000°C annealing, [-SiO₃]^2- defects still exist in the films.

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Transformation from β-Ga₂O₃ to GaN Nanowires via Nitridation

WANG Peng-Wei, SONG Yi-Pu, ZHANG Xin-Zheng, XU Jun, YU Da-Peng

Chin. Phys. Lett. 2008, 25 (3): 1038-1041 .

Abstract

PDF(pc) (5878KB) ( 971 )

Element doping is an important way to modify the properties of semiconductor materials. In our previous work, it was found that nitrogen-doping in β-Ga₂O₃ nanowires can induce a novel luminescence emission (around 740nm) caused by generation of acceptor levels at the middle of the band gap of the β-Ga₂O₃
nanowires. Here we report that further heavy doping of nitrogen can transform the β-Ga₂O₃ nanowires completely into wurtzite structured GaN nanowires. Transmission electron microscopy (TEM), x-ray diffraction (XRD) and Raman spectrum are used to evaluate the transition process. Both XRD and Raman analysis reveal that the monoclinic β-Ga₂O₃ nanowires start phase transformation at a temperature around 850°C towards wurtzite structured GaN. Our results will be very helpful to profound our understanding of the doping induced effects and phase transformation in semiconductor compounds.

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First Principles Study on Electronic Structures of Mn²⁺:CdMoO₄ Crystals

WANG Xi-En, LIU Ting-Yu, ZHANG Qi-Ren, ZHANG Hai-Yan, SONG Min, GUOXiao-Feng, YIN Ji-Gang

Chin. Phys. Lett. 2008, 25 (3): 1042-1044 .

Abstract

PDF(pc) (165KB) ( 851 )

Electronic structures of the Mn²⁺:CdMoO₄ crystal are studied within the framework of the fully relativistic self-consistent Dirac--Slater theory, using a
numerically discrete variation (DV-Xα) method. The calculated results indicate that the 3d states of Mn have donor energy level in the forbidden band of CdMoO₄ crystal. The transition energy of O 2p→Mn 3d is 3.12eV under excitation corresponding electronic transition being O^2-+Mn²⁺(hv_ex=3.12eV)→O^-+Mn⁺(hv_em)→O^2-+Mn²⁺. It is predicted that the wavelength of emission should be located in the range of the 500--600nm. Thus the 500--600nm emission bands peaking at 550nm (2.25eV) of CdMoO₄ crystal under excitation
may be related to the Mn-like dopant ion in CdMoO₄ crystal.

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Neutron Irradiation Effect in Two-Dimensional Electron Gas of AlGaN/GaN Heterostructures

ZHANG Ming-Lan, WANG Xiao-Liang, XIAO Hong-Ling, WANG Cui-Mei, RAN Jun-Xue, HU Guo-Xin

Chin. Phys. Lett. 2008, 25 (3): 1045-1048 .

Abstract

PDF(pc) (146KB) ( 1034 )

AlGaN/GaN heterostructures have been irradiated by neutrons with different fluences and characterized by means of temperature-dependent Hall measurements and Micro-Raman scattering techniques. It is found that the carrier mobility of two-dimensional electron gas (2DEG) is very sensitive to neutrons. At a low fluence of 6.13×10¹⁵cm^-2, the carrier mobility drops sharply, while the sheet carrier density remains the same as that of an unirradiated sample. Moreover, even for a fluence of up to 3.66×10¹⁶cm^-2, the sheet carrier density shows only a slight drop. We attribute the degradation of the figure-of-merit (product of n_s×μ ) of 2DEG to the defects
induced by neutron irradiation. Raman measurements show that neutron
irradiation does not yield obvious change to the strain state of AlGaN/GaN heterostructures, which proves that degradation of sheet carrier density has no relation to strain relaxation in the present study. The increase of the product of n_s×μ of 2DEG during rapid thermal annealing processes at relatively high temperature has been attributed to the activation of Ge_Ga transmuted from Ga and the recovery of displaced defects.

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Measurement of Critical Impact Velocity of Copper in Tension

HU Jin-Wei, JIN Yang-Hui, CHEN Da-Nian, WU Shan-Xing, WANG Huan-Ran, MA Dong-Fang

Chin. Phys. Lett. 2008, 25 (3): 1049-1051 .

Abstract

PDF(pc) (662KB) ( 1091 )

Critical impact velocity (CIV) of oxygen-free high-conductivity (OFHC) copper is experimentally measured with a novel facility in a gas gun system. The results are compared with the theoretical predictions using the typical constitutive relations, and the measured CIV value is much lower than the predictions. The difference of physical mechanisms in experiment and in theoretical calculation is discussed. It is suggested that the reduction of CIV in experiment would be related with the damage evolution in tensile copper that needs to be considered in the computation model.

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A Modified Free Volume Model for Characterizing of Rate Effect in Bulk Metallic Glasses

LIU Long-Fei, DAI Lan-Hong, BAI Yi-Long

Chin. Phys. Lett. 2008, 25 (3): 1052-1055 .

Abstract

PDF(pc) (138KB) ( 655 )

We investigate the plastic deformation and constitutive behaviour of bulk metallic glasses (BMGs). A dimensionless Deborah number De_ID=t_r/t_i is
proposed to characterize the rate effect in BMGs, where t_r is the structural relaxing characteristic time of BMGs under shear load, t_i is the macroscopic imposed characteristic time of applied stress or the characteristic time of macroscopic deformation. The results demonstrate that the modified free volume model can characterize the strain rate effect in BMGs effectively.

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Reversible Vertical Manipulations of Single Pt Adatom on Pt(111) Surface with a Triple-Apex Tip

XIE Yi-Qun, LIU Qing-Wei, ZHANG Peng, LI Yu-Fen, GAN Fu-Xi, ZHUANG Jun

Chin. Phys. Lett. 2008, 25 (3): 1056-1059 .

Abstract

PDF(pc) (564KB) ( 533 )

With a triple-apex tip, we investigate theoretically the vertical manipulation of single Pt adatom on the Pt(111) surface. The adatom adsorbed on the fcc site of the flat Pt(111) surface can be transferred vertically to the tip by adjusting the tip height properly. Moreover, based on the strong vertical trapping ability and the relatively weak lateral trapping ability of the tip, we propose a simple
method to realize a reversible vertical manipulation of the Pt adatom from the highly coordinated sites, the kink and the step sites, of the stepped Pt(111) surface. All the vertical manipulations are completed using only the atomic force between the tip and the adatom, without the electric field.

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First Principles Calculation of Universal Conductance Fluctuation in Monatomic Metal Chains

CHEN Jing-Zhe, ZHANG Jin, HAN Ru-Shan

Chin. Phys. Lett. 2008, 25 (3): 1060-1063 .

Abstract

PDF(pc) (355KB) ( 965 )

Combining the non-equilibrium Green's function method and density functional theory, we provide a first-principle scheme to calculate the universal conductance fluctuation (UCF) in quasi one-dimensional monatomic chains subject to a magnetic field. Our results show that for these monatomic chains, the amplitude of the UCF is much smaller than the previous theoretical prediction for mesoscopic conductors by Lee et al. [Phys. Rev. Lett. 55 (1985) 1622; Phys. Rev. B 35 (1987) 1039] The reason is that the ergodic hypothesis fails in these nanowires due to the confinement of geometry. We ascribe the phenomenon to the flux-dependent density of states fluctuation.

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First-Principles Calculations for Elastic Properties of ZnS under Pressure

CHEN Xiang-Rong, HU Cui-E, ZENG Zhao-Yi, CAI Ling-Cang

Chin. Phys. Lett. 2008, 25 (3): 1064-1067 .

Abstract

PDF(pc) (148KB) ( 1178 )

The pressure dependence of elastic properties of ZnS in zinc-blende (ZB) and wurtzite (WZ) structures are investigated by the generalized gradient approximation (GGA) within the plane-wave pseudopotential density functional theory (DFT). Our results are in good agreement with the available
experimental data and other theoretical results. From the high-pressure elastic constants obtained, we find that the ZB and WZ structures of ZnS are unstable when the applied pressures are larger than 15.8GPa and 21.3GPa, respectively. The sound velocities along different directions for the two structures are also obtained. It is shown that as pressure increases, the sound velocities of the shear wave decrease, and those of all the longitudinal waves increase. An analysis has been made to reveal the anisotropy and
highly noncentral forces in ZnS.

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Microwave Magnetic Properties of Nd₂Fe₁₇N_3-δwith Planar Anisotropy

LI Fa-Shen, WEN Fu-Sheng, ZHOU Dong, QIAO Liang, ZUO Wen-Liang

Chin. Phys. Lett. 2008, 25 (3): 1068-1070 .

Abstract

PDF(pc) (1359KB) ( 849 )

Microwave magnetic properties are studied for rhombohedral structure
NdNd₂Fe₁₇N_3-δ with planar magnetic anisotropy. Its resin composites show the permeability μ₀'=4.15 at low frequency, the natural resonance frequency f_r=1.71GHz and the resonance bandwidth 6.66GHz. The calculated static permeability of Nd₂Fe₁₇N_3-δ reaches 133. The microwave magnetic properties are determined by the c-axis anisotropy field, basal plane anisotropy field and high saturation magnetization. Based on microwave measurement and theoretical fitting on complex permeability spectra, Nd₂Fe₁₇N_3-δ may be a
promising microwave absorber with bandwidth wider than traditional hexaferrites materials in GHz ranges.

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Structural, Optical and Electrical Properties of Hydrogen-Doped Amorphous GaAs Thin Films

YAO Yan-Ping, LIU Chun-Ling, QIAO Zhong-Liang, LI Mei, GAO Xin, BO Bao-Xue

Chin. Phys. Lett. 2008, 25 (3): 1071-1074 .

Abstract

PDF(pc) (223KB) ( 869 )

Amorphous GaAs films are deposited on substrates of quartz glass and silicon by rf magnetron sputtering technique in different gas ambient. First, the amorphous structure of the prepared samples is identified by x-ray diffraction. Second, analysis by radial distribution function and pair correlation function method is established to characterize the microstructure of the samples. Then, the content and bond type of hydrogen are analysed using Fourier transform infrared absorption spectroscopy. It is found that the bonded hydrogen content increases with increasing partial pressure P_H of H₂. However, the hydrogen content saturates at P_H> 1×10^-1Pa. Hydrogen addition shifts the optical absorption edge to higher energy, decreases the dark conductivity and improves the photo-sensitivity. The optical gap, dark conductivity and photo-sensitivity of the films are dependent on the bonded hydrogen content. These results demonstrate that hydrogen has obvious passivation effects on rf sputtered amorphous GaAs thin films.

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Jahn--Teller Distortion of the Zinc Vacancy in ZnGeP₂

JIANG Xiao-Shu, Walter R. L. Lambrecht

Chin. Phys. Lett. 2008, 25 (3): 1075-1078 .

Abstract

PDF(pc) (166KB) ( 773 )

A symmetry analysis and a simple dangling bond model are presented for
the V^-_Zn in ZnGeP₂, identifying a possible Jahn--Teller distortion mechanism which could naturally explain the localization of the defect wavefunction on two of the nearest-neighbouring P atoms, as deduced for the electron nuclear double resonance experiments.

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Entanglement in One-Dimensional Anderson Model with Long-Range Correlated Disorder

GUO Zi-Zheng

Chin. Phys. Lett. 2008, 25 (3): 1079-1082 .

Abstract

PDF(pc) (143KB) ( 831 )

By using the measure of concurrence, the entanglement of the ground state in the one-dimensional Anderson model is studied with consideration of the long-range correlations. Three kinds of correlations are discussed. We compare the effects of the long-rang Gaussian and power-law correlations between the site energies on the concurrence, and demonstrate the existence of the band structure of the concurrence in the power-law case. The
emergence of the sharp kink on the concurrence curve shown in the intraband or in the interband indicates the position at which the localization extent of the state may have the severe variation. We use the Rudin--Shapiro model to describe the site energy distribution of the nucleotides of the DNA chain: guanine (G), adenine (A), cytosine(C), thymine (T). This model is a tetradic quasiperiodic sequence and is shown to be long-range correlated. Our results show that correlations between the site energies increase the concurrences.

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Localization Exponent for the Second Landau Level in the Quantum Hall Effect

TU Tao, ZHAO Yong-Jie, HAO Xiao-Jie, WANG Cheng-You, GUO Guang-Can, GUO Guo-Ping

Chin. Phys. Lett. 2008, 25 (3): 1083-1086 .

Abstract

PDF(pc) (150KB) ( 681 )

At temperature above 1K, we measured the temperature dependence of the longitudinal and Hall resistivity ρ_xx,ρ_xy in the regime of the quantum Hall
plateau-to-plateau transitions. The localization exponent v is extracted with an approach based on the variable range hopping theory. We find the quantity v≈2.3 at the second Landau level, which is proven to be accurately universal.

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Polarity-Free Resistive Switching Characteristics of Cu_xO Films for Non-volatile Memory Applications

LV Hang-Bing, ZHOU Peng, FU Xiu-Feng, YIN Ming, SONG Ya-Li, TANG Li, TANG Ting-Ao, LIN Yin-Yin

Chin. Phys. Lett. 2008, 25 (3): 1087-1090 .

Abstract

PDF(pc) (182KB) ( 1190 )

Resistive switching characteristics of Cu_xO films grown by plasma oxidation process at room temperature are investigated. Both bipolar and unipolar stable resistive switching behaviours are observed and confirmed by repeated current--voltage measurements. It is found that the RESET current is dependent on SET compliance current. The mechanism behind this new
phenomenon can be understood in terms of conductive filaments formation/rupture with the contribution of Joule heating.

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Performance Improvement of Bulk Heterojunction Organic Photovoltaic Cellby Addition of a Hole Transport Material

ZHANG Nan, LIU Qian, MAO Jie, LIU Zun-Feng, YANG Li-Ying, YINShou-Gen, CHEN Yong-Sheng

Chin. Phys. Lett. 2008, 25 (3): 1091-1093 .

Abstract

PDF(pc) (455KB) ( 626 )

A novel photovoltaic cell with an active layer of poly(phenyleneethynylene)
(PPE)/C₆₀/N,N'-diphenyl-N,N'-di-(m-tolyl)-p-benzidine (TPD) is designed. In the active layer, PPE is the major component; C₆₀ and TPD are the minor ones. Compared with a control BHJ device based on PPE/C₆₀, the short circuit
current density J_sc is increased by 1 order of magnitude, and the whole device performance is increased greatly, however the open circuit voltage V_oc is largely decreased. The possible mechanism of the improved performance may be as follows: In the PPE/C₆₀/TPD device, PPE, C₆₀, and TPD serve as the energy harvesting material, the electron transport material, and the hole
transport material, respectively. As the TPD and C₆₀ are spatially separated by PPE, the charge recombination is effectively retarded.

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Resonant Tunnelling and Storage of Electrons in Si Nanocrystals within a-SiN_x/nc-Si/a-SiN_x Structures

WANG Xiang, HUANG Jian, ZHANG Xian-Gao, DING Hong-Lin, YU Lin-Wei, HUANG Xin-Fan, LI Wei, XU Jun, CHEN Kun-Ji

Chin. Phys. Lett. 2008, 25 (3): 1094-1097 .

Abstract

PDF(pc) (959KB) ( 975 )

The a-SiN_x/nanocrystalline silicon (nc-Si)/a-SiN_x sandwiched structures with asymmetric double-barrier are fabricated in a plasma enhanced chemical vapour deposition (PECVD) system on p-type Si substrates. The nc-Si layer in
thickness 5nm is fabricated from a hydrogen-diluted silane gas by the layer-by-layer deposition technique. The thicknesses of tunnel and control SiN_x layers are 3nm and 20nm, respectively. Frequency-dependent capacitance spectroscopy is used to study the electron tunnelling and the storage in the sandwiched structures. Distinct frequency-dependent capacitance peaks due to electrons tunnelling into the nc-Si dots and capacitance-voltage (C-V)
hysteresis characteristic due to electrons storage in the nc-Si dots are observed with the same sample. Moreover, conductance peaks have also been observed at the same voltage region by conductance-voltage (G-V) measurements. The experimental results demonstrate that electrons can be loaded onto nc-Si dots via resonant tunnelling and can be stored in our a-SiN_x/nc-Si/a-SiN_x structures.

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Continuous-Variable Entanglement Transfer from Cavity Field to Two Mesoscopic Josephson Junctions

CHANG Ping, SHAO Bin, WANG Zhao-Ming, ZOU Jian

Chin. Phys. Lett. 2008, 25 (3): 1098-1101 .

Abstract

PDF(pc) (1384KB) ( 842 )

We consider a composite system of two remote mesoscopic Josephson
junctions interacting locally with a two-mode non-classical cavity field and investigate entanglement transfer from a bipartite continuous-variable (CV) system to a pair of localized mesoscopic Josephson junctions. We obtain analytically the time-dependent characteristic functions in the Wigner representation for the two CV subsystems, where two cases are considered for the zero and finite temperatures. Furthermore, we analyse the influences of the temperature on the period recovery of the entanglement.

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Influence of Randomness and Localization on RKKY Interactions in Diluted Magnetic Semiconductors

WANG Dan, XIONG Shi-Jie

Chin. Phys. Lett. 2008, 25 (3): 1102-1105 .

Abstract

PDF(pc) (334KB) ( 850 )

We show that the spatially random distribution of magnetic moments of
dopants in diluted magnetic semiconductors can partially localize the itinerant carriers and change the carrier-mediated indirect RKKY interaction. From numerical calculations of the electron states taking into account the interaction with magnetic impurities which are random both in spatial positions and in orientations of magnetic moments, we obtain the electron states and the RKKY interaction as a function of the distance between magnetic dopants L and of the sp-d exchange integral J. With the increase of disorder, the localization of itinerant electrons become stronger and the long-range regular oscillatory behaviour of the RKKY interaction gradually disappears and is replaced by severe fluctuations. The randomness and localization may enhance the RKKY interaction between dopants with short and middle distances and in favour of the ferromagnetism.

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Additional Y³⁺ Doping Effect on Ferromagnetism of Ce_0.97Co_0.03O_2-δ Compounds

SONG Yuan-Qiang, ZHANG Huai-Wu, WEN Qi-Ye, ZHU Hao, John Q. Xiao

Chin. Phys. Lett. 2008, 25 (3): 1106-1109 .

Abstract

PDF(pc) (5761KB) ( 707 )

Y³⁺ doping effect on magnetic roperties of Ce_0.97Co_0.03O_2-δ are examined.
Vibrating sample magnetometer (VSM) measurements indicate that e_0.97Co_0.03O_2-δ is ferromagnetic at room temperature. The saturated magnetization M_S is altered by additional Y³⁺ doping, i.e., with the increase of the amount of Y³⁺ doping concentration in Ce_0.97-yY_yCo_0.03O_2-δ (y=0.01, 0.05 and 0.10), M_S increases persistently. Raman spectra measurements
indicate that additional oxygen vacancies are introduced with the amount of Y³⁺ doping content. The results can be well elucidated by the F-centre exchange coupling (FCE) mechanism proposed recently, thus they are important for understanding the ferromagnetism origination in transitional metal-doped insulating oxides.

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Soft X-Ray Magneto-optical Faraday Effect around Ni M_2,3 Edges

CHEN Kai, CUI Ming-Qi, YAN Fen, ZHAO Jia, SUN Li-Juan, ZHENG Lei, MA Chen-Yan, XI Shi-Bo, ZHAO Yi-Dong

Chin. Phys. Lett. 2008, 25 (3): 1110-1112 .

Abstract

PDF(pc) (325KB) ( 773 )

We present magneto-optical (MO) Faraday spectra measured around the M_2,3 edges (60--70eV) of Ni films at the Beijing Synchrotron Radiation Facility (BSRF). A polarization analysis of the final state of the transmitted radiation from the Ni film is employed to determine the Faraday rotation at the edges. The MO effect becomes resonantly enhanced at the M_2,3 edges, and
accordingly large values for the rotation angle β of 1.85±0.19°for this ferromagnetic Ni film with thickness of 31nm are measured. Without the magnetic field, the azimuthal angles do not shift; with parallel and antiparallel magnetic field the rotation angles shift in the opposite way and they are symmetrical. The uncertainty of Faraday rotation angles mainly comes from the data fitting and the state change of the beamline when the angles are
measured.

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Strain and Size Effects on Ferroelectric Properties of BaTiO₃ Nanofilms

SANG Yong-Liang, LIU Bin, FANG Dai-Ning

Chin. Phys. Lett. 2008, 25 (3): 1113-1116 .

Abstract

PDF(pc) (447KB) ( 1096 )

The strain and size effects on the ferroelectric properties of BaTiO₃ films are studied using the molecular dynamics method based on a shell model. It is found that from microscopic view, these two effects share the same physical
nature, i.e., the resulting crystal cell distortions lead to the separation of negative and positive charge centres. The strain and size effects are therefore coupled, and the critical thicknesses of films would depend on the in-plane strains, which provides a possible interpretation on the discrepancies among the experimental measurements of the critical thicknesses. A polarization map is given to clearly reflect the relations among the size, strain and polarization of the nano films.

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Detection Limit of Glucose Concentration with Near-InfraredAbsorption and Scattering Spectroscopy

LUO Yun-Han, HUANG Fu-Rong, LI Shi-Ping, CHEN Zhe

Chin. Phys. Lett. 2008, 25 (3): 1117-1119 .

Abstract

PDF(pc) (170KB) ( 1329 )

Theoretical analyses and Monte Carlo simulation are performed to investigate the detection limit of glucose concentration with near-infrared spectroscopy. The relation between detection limitation of glucose concentration and
source--detector separation is derived. Monte Carlo simulation performed with a skin-layered model shows that the ratio of effective photons from the target layer could excess 50% by selecting proper source--detector separation, and that the detection limit of glucose concentration approaches to 0.28mM, which satisfies the requirement of food and drug administration for noninvasive glucose sensing.

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Tuning Photoluminescence Energy and Fine Structure Splitting in Single Quantum Dots by Uniaxial Stress

DOU Xiu-Ming, SUN Bao-Quan, WANG Bao-Rui, MA Shan-Shan, ZHOU Rong, HUANG She-Song, NI Hai-Qiao, NIU Zhi-Chuan

Chin. Phys. Lett. 2008, 25 (3): 1120-1123 .

Abstract

PDF(pc) (302KB) ( 893 )

We report a photoluminescence (PL) energy red-shift of single quantum dots (QDs) by applying an in-plane compressive uniaxial stress along the [110] direction at a liquid nitrogen temperature. Uniaxial stress has an effect not only on the confinement potential in the growth direction which results in the PL shift, but also on the cylindrical symmetry of QDs which can be reflected by the change of the full width at half maximum of PL peak. This implies that uniaxial stress has an important role in tuning PL energy and fine structure splitting of QDs.

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Ferromagnetic Antiresonance and Giant Microwave Magneto-Impedance in Polycrystalline La_0.49Sr_0.51MnO₃

LIU Wen-Jun, SHU Qi-Qing, S. M. BHAGAT, I. O. TROYANCHUK

Chin. Phys. Lett. 2008, 25 (3): 1124-1127 .

Abstract

PDF(pc) (170KB) ( 875 )

The ferromagnetic antiresonance (FMAR) phenomenon, i.e., the minimum of the microwave absorption, in polycrystalline La_0.49Sr_0.51MnO₃ is observed near Curie temperature T_C = 282K. Temperature-dependences of magnetization μ₀M are obtained from the FMAR. The results show that as
μ₀H =0, by fitting the scaling law M∝(T_C-T)^β to temperature-dependences of μ₀M at the different microwave frequencies, it yields T_C = 281.2K and β= 0.47. However, temperature-dependences of β₀M under different β₀H are not
in agreement with the scaling law. Due to FMAR, about 40% giant microwave magneto-impedance at 11.9GHz can occur under a low field μ₀H=0.03T.

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Effect of Post-Annealing on Microstructural and Electrical Properties of N⁺ Ion-Implanted into ZnO:In Films

KONG Chun-Yang, QIN Guo-Ping, RUAN Hai-Bo, NAN Mao, ZHU Ren-Jiang, DAI Te-Li

Chin. Phys. Lett. 2008, 25 (3): 1128-1130 .

Abstract

PDF(pc) (182KB) ( 996 )

We fabricate p-type conductive ZnO thin films on quartz glass substrates by codoping of In--N using radio frequency magnetron sputtering technique together with the direct implantation of acceptor dopants (nitrogen). The effects of thermal annealing on the structure and electrical properties of the ZnO films are investigated by an x-ray diffractometer (XRD) and a Hall
measurement system. It is found that the best p-type ZnO film subjected to annealed exhibits excellent electrical properties with a hole concentration of 1.22×10¹⁸cm^-3, a Hall mobility of 2.19²V^-1s^-1, and a low resistivity of about
2.33Ωcm, indicating that the presence of In may facilitates the incorporation of N into ZnO thin films.

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A Comparison of GaN Epilayers with Multiple Buffer Layers and with a Single Buffer Layer Grown on Si(111) Studied by HRXRD and RBS/Channeling

DING Zhi-Bo, WANG Kun, YAO Shu-De

Chin. Phys. Lett. 2008, 25 (3): 1131-1134 .

Abstract

PDF(pc) (1867KB) ( 796 )

Two hexagonal GaN epilayers (samples A and B) with multiple buffer layers and single buffer layer are grown on Si (111) by metal-organic vapour phase epitaxy (MOVPE). From the results of Rutherford backscattering (RBS)/channeling and high resolution x-ray diffraction (HRXRD), we obtain the lattice constant (a and c) of two GaN epilayers (a_A=0.3190nm, c_A=0.5184nm and a_B=0.3192nm, c_B=0.5179nm), the crystal quality of two GaN epilayers ( X_{min A}}=4.87%, X_{min B}=7.35% along <1213> axis) and the tetragonal
distortion e_T of the two samples along depth (sample A is nearly fully relaxed, sample B is not relaxed enough). Comparing the results with the two samples, it is indicated that sample A with multiple buffer layers have better crystal quality than sample B with a single buffer layer, and it is a good way to grow GaN epilayer on Si (111) substrates using multiple buffer layers to improve crystal quality and to reduce lattice mismatch.

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Effect of Density and Surface Roughness on Optical Properties of Silicon Carbide Optical Components

LIU Gui-Ling, HUANG Zheng-Ren, LIU Xue-Jian, JIANG Dong-Liang

Chin. Phys. Lett. 2008, 25 (3): 1135-1137 .

Abstract

PDF(pc) (1169KB) ( 2007 )

The effect of density and surface roughness on the optical properties of silicon carbide optical components is investigated. The density is the major factor of the total reflectance while the surface roughness is the major factor of the diffuse reflectance. The specular reflectance of silicon carbide optical components can be improved by increasing the density and decreasing the surface roughness, in the form of reducing bulk absorption and surface-related scattering, respectively. The contribution of the surface roughness to the specular reflectance is much greater than that of the density. When the rms surface roughness decreases to 2.228nm, the specular reflectance decreases to less than 0.7% accordingly.

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Spectral Study of Effects of Aluminium Nanoparticles on Fast Reaction of Nitromethane

WU Jing-He, YE Song, HU Dong, YANG Xiang-Dong

Chin. Phys. Lett. 2008, 25 (3): 1138-1141 .

Abstract

PDF(pc) (1236KB) ( 15087 )

Fast reactions between nitromethane and aluminium nanoparticles are studied using transient spectral methods. In comparison with species produced by pure nitromethane, the emergence time for species produced by nitromethane after addition of 1g of aluminium nanoparticles decreases by 46-58% and the emission intensity increases by 13-100%. The results demonstrate that aluminium nanoparticles have positive effect on accelerating the decomposition rate of nitromethane and that the explosion efficiency of nitromethane is greatly improved. Fast reactions carried out between nitromethane and aluminium nanoparticles in different environments (CO₂, H₂O and O₂) reveal that O₂ and an appropriate amount of H₂O improve the explosion efficiency of nitromethane, whereas CO₂ has the weakest effect on improving this parameter. The investigations provide insights into the process
occurring in actual systems involving propellants and fuel--air explosives.

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Chaotic Oscillator in Frequency by Using Tunable Laser with Fibre Bragg Grating

LV Guo-Hui, WANG Hui-Ying, JIANG Xu, DING Qun, ZHUANG Pei-Dong

Chin. Phys. Lett. 2008, 25 (3): 1142-1144 .

Abstract

PDF(pc) (142KB) ( 734 )

A novel chaotic oscillator in wavelength domain by using a tunable fibre laser is proposed. The generator of chaos in wavelength is composed of fibre Bragg grating (FBG) with hybrid delayed feedback loop which induces wavelength
nonlinearity. The dynamical regime of wavelength is ruled by a differential difference equation. We give the numerical simulation of the experimental setup and discuss its application in an optical encryption system.

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Effect of Vibration on Water Transport through Carbon Nanotubes

LU Hang-Jun, , GONG Xiao-Jing, WANG Chun-Lei, FANG Hai-Ping, WAN Rong-Zheng,

Chin. Phys. Lett. 2008, 25 (3): 1145-1148 .

Abstract

PDF(pc) (222KB) ( 889 )

We study the response of water permeation properties through a carbon nanotube on the time-dependent mechanical signals. It is found that there is a critical frequency of vibrating f_c (about 1333GHz) which plays a significant role in the water permeation properties. The total water flow, the net flux,
the number of hydrogen bonds and the dipole flipping frequency of the
single-file water chain inside the nanotube are almost unchanged for the frequency of vibrating f<f_c. Simulation results show that the nanotube can be effectively resistant to the mechanical noise. Such excellent effect of noise screening is attributed to the exceptional property of water molecules connected by strong hydrogen bonds with each other and forming a one-dimensional water chain inside the nanotube. Our findings are important for the understanding of why biological systems can achieve accurate information transfer in an environment full of fluctuations.

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Coupling Effect of Ion Channel Clusters on Calcium Signalling

TANG Jun, JIA Ya, YI Ming, MA Jun, YU Guang

Chin. Phys. Lett. 2008, 25 (3): 1149-1152 .

Abstract

PDF(pc) (165KB) ( 991 )

Based on a modified intracellular Ca²⁺ model involving diffusive coupling of two calcium ion channel clusters, the effects of coupling on calcium signalling are numerically investigated. The simulation results indicate that the diffusive coupling of clusters together with internal noise determine the calcium dynamics of single cluster, and for either homogeneous or heterogeneous coupled clusters, the synchronization of clusters, which is important to calcium signalling, is enhanced by the coupling effect.

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Topological Self-Similar Networks Introduced by Diffusion-Limited Aggregation Mechanism

YANG Lei, PEI Wen-Jiang, LI Tao, CHEUNG Yiu-Ming, HE Zhen-Ya

Chin. Phys. Lett. 2008, 25 (3): 1153-1156 .

Abstract

PDF(pc) (214KB) ( 958 )

We propose a model for growing fractal networks based on the mechanisms learned from the diffusion-limited aggregation (DLA) model in fractal geometries in the viewpoint of network. By studying the DLA network, our model introduces multiplicative growth, aging and geographical preferential attachment mechanisms, whereby featuring topological self-similar property and hierarchical modularity. According to the results of theoretical analysis and simulation, the degree distribution of the proposed model shows a mixed degree distribution (i.e., exponential and algebraic degree distribution) and the fractal dimension and clustering coefficient can be tuned by changing the values of parameters.

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An Explicit Fractal Interpolation Algorithm for Reconstruction of Seismic Data

LI Xin-Fu, LI Xiao-Fan

Chin. Phys. Lett. 2008, 25 (3): 1157-1159 .

Abstract

PDF(pc) (142KB) ( 1806 )

Based on our previous investigation and the pioneering work of other researchers, a novel explicit fractal interpolation method based on affine transform is proposed, in which we approximate the vertical scaling factors by the locally explicit expression. Numerical experiments indicate that the explicit fractal interpolation method shows great accuracy of reconstruction of the
seismic profile and yields significant improvement over wave-equation based trace interpolation methods (unified approach).

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Circular Loop Equation of a Cosmic String in Gauss--Bonnet--de

CHENG Hong-Bo, LIU Yun-Qi

Chin. Phys. Lett. 2008, 25 (3): 1160-1163 .

Abstract

PDF(pc) (154KB) ( 692 )

We perform the analysis of evolution of cosmic string loops in the background of Gauss--Bonnet--de Sitter. The equation of motion of cosmic string loops in this spacetime is derived. Having solved the equation numerically, we investigate the dependence of the loop evolution on the values of α, related
to the Gauss--Bonnet coupling. In the Gauss--Bonnet--de Sitter spacetimes with different dimensionality there exists a special parameter α_m. In the environment with α>α_m, all the cosmic string loops will collapse to form black holes. Within the region 0<α<α_m, the stronger Gauss--Bonnet effect will lead more cosmic string loops, including smaller ones, to form black holes. The larger the value of α is, the smaller the special values that exist, and only the cosmic string loops with initial radius larger than the special values can expand and evolve instead of becoming black holes.

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In Memoriam Yifan Gu (1933--2007)

Chin. Phys. Lett. 2008, 25 (3): 1164-1164 .

Abstract

PDF(pc) (39KB) ( 657 )

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