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Volume 24 Issue 6
Online Date:
Original Articles
 Select Periodic Bifurcation and Soliton Deflexion for Kadomtsev--Petviashvili Equation DAI Zheng-De, , LI Shao-Lin, LI Dong-Long, ZHU Ai-Jun Chin. Phys. Lett. 2007, 24 (6): 1429-1432 .   Abstract   PDF(pc) (1416KB) ( 612 ) The spatial--temporal bifurcation for Kadomtsev--Petviashvili (KP) equations is considered. Exact two-soliton solution and doubly periodic solution to the KP-I equation, and two classes of periodic soliton solutions in different directions to KP-II are obtained using the bilinear form, homoclinic test technique and temporal and spatial transformation method, respectively. The equilibrium solution u0=-1/6, a unique spatial--temporal bifurcation which is periodic bifurcation for KP-I and deflexion of soliton for KP-II, is investigated.
 Select Initial-value Problems for Extended KdV--Burgers Equations via Generalized Conditional Symmetries ZHANG Shun-Li, LI Ji-Na Chin. Phys. Lett. 2007, 24 (6): 1433-1436 .   Abstract   PDF(pc) (230KB) ( 429 ) We classify initial-value problems for extended KdV--Burgers equations via generalized conditional symmetries. These equations can be reduced to Cauchy problems for some systems of first-order ordinary differential equations. The obtained reductions cannot bederived within the framework of the standard Lie approach.
 Select Transient and Stationary Simulations for a Quantum Hydrodynamic Model HU Xin, TANG Shao-Qiang Chin. Phys. Lett. 2007, 24 (6): 1437-1440 .   Abstract   PDF(pc) (275KB) ( 327 ) The transient and stationary characteristics of a one-dimensional quantum hydrodynamic model are comparatively studied for semiconductor charge transport in a resonant tunnelling diode. When the bias is not small, our numerical results show a deviation of the asymptotic transient solutions from the stationary ones. A dynamic instability accounts for such deviation. The stationary quantum hydrodynamic model is therefore unsuitable in general for simulating quantum devices.
 Select Angular Distributions for Heavy Quarkonium Decays into Baryon--Antibaryon Pairs PANG Cai-Ying, PING Rong-Gang Chin. Phys. Lett. 2007, 24 (6): 1441-1443 .   Abstract   PDF(pc) (292KB) ( 362 ) Based on the naive quark model, we calculate angular distributions for heavy quarkonium decays into pN*(1440), decuplet baryon pairs, and octet--decuplet baryon pairs. The general formulae of angular distributions are given explicitly. Quark mass effects on the violation of the helicity conservation and the prospect to look for them in J/ψ hadronic decays are discussed.
 Select A Hierarchy of Differential-Difference Equations and Their Integrable Couplings LUO Lin, FAN En-Gui Chin. Phys. Lett. 2007, 24 (6): 1444-1447 .   Abstract   PDF(pc) (203KB) ( 426 ) Starting from a discrete spectral problem, the corresponding hierarchy of nonlinear differential-difference equation is proposed. It is shown that the hierarchy possesses the bi-Hamiltionian structures. Further, two integrable coupling systems for the hierarchy are constructed through enlarged Lax pair method.
 Select Effects of Inhomogeneous Spin Coupling and Anisotropy on Thermal Entanglement GUO Jin-Liang, HUANG Xiao-Li, SONG He-Shan Chin. Phys. Lett. 2007, 24 (6): 1448-1451 .   Abstract   PDF(pc) (323KB) ( 457 ) We study the thermal entanglement properties of a simple system that includes three spins inhomogeneously coupled between them with additional anisotropy in their couplings. The main result is the systematic analysis of the concurrence evolution as functions of inhomogeneity, anisotropy and temperature. By adjusting proportional factor of the interaction J and anisotropy parameter △, the comparison between concurrences C12 andC13 is also presented.
 Select Influences of Temperature on Proton Conductivity in the Hydrogen-Bond Molecular Systems with Damping PANG Xiao-Feng, YU Jia-Feng Chin. Phys. Lett. 2007, 24 (6): 1452-1455 .   Abstract   PDF(pc) (309KB) ( 352 ) Influences of temperature of medium on proton conductivity in hydrogen-bonded systems exposed in an electric-field are numerically studied by the fourth-order Runge--Kutta method with our model. The results obtained show that the proton soliton is very robust against thermal perturbation and damping of medium, and is thermally stable in the temperature range T≤ 273K. From the simulation we find out that the mobility (or velocity) of proton conduction in ice crystal is a nonmonotonic function of temperature in the temperature range 170--273K: i.e., it increases initially, reaches a maximum at about 191K, subsequently decreases to a minimum at about 211K, and then increases again. This changed rule of mobility is qualitatively consistent with its experimental data in ice in the same temperature range. This result provides an evidence for existence of solitons in the hydrogen-bonded systems.
 Select Information-Disturbance Tradeoff in Estimating the Unknown Three-Qubit GHZ State ZHANG Sheng-Li, ZOU Xu-Bo, LI Ke, JIN Chen-Hui, GUO Guang-Can Chin. Phys. Lett. 2007, 24 (6): 1456-1459 .   Abstract   PDF(pc) (244KB) ( 457 ) In a recent paper, Sacchi (Phys. Rev. Lett. 96(2006)220502) studied the information-disturbance tradeoff in estimating an unknown two-qubit maximally entangled state. In this study, we explore thetradeoff in estimating an unknown three-qubit GHZ state. The optimalestimation process supplies a fidelity of 13/54 and the tradeoff interpolates smoothly between non-informative measurement and optimal estimation process.
 Select Intrinsic Decoherence of Two Atoms System With Kerr Medium ZHANG Xiao-Ting, ZHU Ai-Dong, ZHANG Shou, Chin. Phys. Lett. 2007, 24 (6): 1460-1462 .   Abstract   PDF(pc) (328KB) ( 544 ) We study the effect of Kerr medium on the intrinsic decoherence of a system which consists of two two-level atoms and a optical cavity. The entanglement of the system is calculated by making use of concurrence. Our results show that the intrinsic decoherence is very sensitive to the nonlinear coupling constant of Kerr medium. Both the oscillation period and the amplitude of the concurrence increase with the increasing nonlinear coupling constant.
 Select Quantum Key Distribution Network Based on Differential Phase Shift WANG Wan-Ying, WANG Chuan, WEN Kai, LONG Gui-Lu, Chin. Phys. Lett. 2007, 24 (6): 1463-1466 .   Abstract   PDF(pc) (280KB) ( 492 ) Using a series of quantum correlated photon pairs, we propose a theoretical scheme for any-to-any multi-user quantum key distribution network based on differential phase shift. The differential phase shift and the different detection time slots ensure the security of our scheme against eavesdropping. We discuss the security under the intercept--resend attack and the sourcereplacement attack.
 Select A Cavity-QED Scheme for Generating Long-Lived Maximally Entangled States XIANG Shao-Hua, , SHAO Bin, SONG Ke-Hui, ZOU Jian Chin. Phys. Lett. 2007, 24 (6): 1467-1470 .   Abstract   PDF(pc) (300KB) ( 598 ) We propose a potentially practical scheme to generate two-atom maximally entangled states by the large-detuning interaction between two three-level ∧-type atoms and coherent optical fields. Conditioned on the results of detecting cavity field, four pairs of atomic maximally entangled states with unity fidelity and high successful probability can be prepared. We also investigate the influence of the cavity dissipation on the generated entangledstates and discuss the experimental feasibility of our scheme.
 Select Modulational Instability of (1+1)-Dimensional Bose--Einstein Condensate with Three-Body Interatomic Interaction WU Lei, ZHANG Jie-Fang Chin. Phys. Lett. 2007, 24 (6): 1471-1474 .   Abstract   PDF(pc) (1172KB) ( 417 ) The modulational instability of Bose--Einstein condensate with three-body interatomic interaction and external harmonic trapping potential is investigated. Both of our analytical and numerical results show that the external potential will either cause the excitation of modulationally unstable modes or restrain the modulationally unstable modes from growing.
 Select Approach to a Cauchy Problem in Stability Study of the Schwarzschild Black Hole TIAN Gui-Hua, WANG Shi-Kun, ZHONG Shu-Quan Chin. Phys. Lett. 2007, 24 (6): 1475-1478 .   Abstract   PDF(pc) (220KB) ( 332 ) Generally, the Schwarzschild black hole is proven to be stable by two different methods: the mode-decomposition method and the integral method. We show that the integral method can only apply to the initial data vanishing at both the horizon and the spatial infinity. It can not treat the initial data only vanishing at the spatial infinity. We give an example to show the misleading information caused by the use of tortoise coordinates in the perturbation equations. Subsequently, the perturbation equations in the Schwarzschild coordinates are shown to be insufficient for the stability study.
 Select Charged Particle Tunnels from the Slowly Varying Reissner--Nordstrom Black Hole YANG Shu-Zheng, CHEN De-You Chin. Phys. Lett. 2007, 24 (6): 1479-1481 .   Abstract   PDF(pc) (198KB) ( 444 ) Extending Parikh and Wilczek's work to the non-stationary black hole, wediscuss the Hawking radiation of the slowly varying Reissner--Nordstromblack hole by considering the unfixed background spacetime and the self-gravitation interaction. The result shows that the tunnelling rate is related to both the variation of Bekenstein--Hawking entropy and the radiation spectrum deviating from the purely thermal one. This is in agreement with Parikh and Wilczek's result. Then a new method to study Hawking radiation of the non-stationary black holes is presented.
 Select Charged Particle Tunnels from the Slowly Varying Reissner--Nordstrom Black Hole YANG Shu-Zheng, CHEN De-You Chin. Phys. Lett. 2007, 24 (6): 1479-1481 .   Abstract   PDF(pc) (198KB) ( 574 ) Extending Parikh and Wilczek's work to the non-stationary black hole, wediscuss the Hawking radiation of the slowly varying Reissner--Nordstromblack hole by considering the unfixed background spacetime and the self-gravitation interaction. The result shows that the tunnelling rate is related to both the variation of Bekenstein--Hawking entropy and the radiation spectrum deviating from the purely thermal one. This is in agreement with Parikh and Wilczek's result. Then a new method to study Hawking radiation of the non-stationary black holes is presented.
 Select Effects of Continuous Size Distributions on Pressures of Granular Gases LI Rui, ZHANG Duan-Ming, CHEN Zhi-Yuan, SU Xiang-Ying, ZHU Hong-Ying, ZHANG Ling, HUANG Ming-Tao Chin. Phys. Lett. 2007, 24 (6): 1482-1485 .   Abstract   PDF(pc) (269KB) ( 443 ) Direct Monte Carlo simulations are employed to investigate the granular pressures in granular materials with a power-law particle size distribution. Specifically, smooth circular discs of uniform material density are engaged in a two-dimensional rectangular box, colliding inelastically with each other and driven by a homogeneous heat bath at zero gravity. The resulting pressures are found to decrease as the widths of particle size distribution are increased. Moreover, the granular pressures in power-law systems are found to be unequally distributed among the various sizes of particles, with large particlespossessing more pressure than their smaller counterparts. The width-dependent nature of the total pressures is induced by the more dispersion of smaller particles in the system as the particle size distribution is widened.
 Select Stretched Exponential Relaxation in Disordered Complex Systems: Fractal Time Random Walk Model Ekrem Aydiner Chin. Phys. Lett. 2007, 24 (6): 1486-1490 .   Abstract   PDF(pc) (206KB) ( 472 ) We have analytically derived the relaxation function for one-dimensionaldisordered complex systems in terms of autocorrelation function of fractal time random walk by using operator formalism. We have shown that the relaxation function has stretched exponential, i.e. the Kohlrausch--Williams--Watts character for a fractal time random walk process.
 Select Multiscale Entropy under the Inverse Gaussian Distribution: Analytical Results TANG Ying, PEI Wen-Jiang, XIA Hai-Shan, HE Zhen-Ya Chin. Phys. Lett. 2007, 24 (6): 1490-1493 .   Abstract   PDF(pc) (277KB) ( 349 ) The multiscale entropy (MSE) reveals the intrinsic multiple scales in the complexity of physical and physiological signals, which are usually featured by heavy-tailed distributions. However, most research results are pure experimental search. Recently, Costa et al. have made the first attempt to present the theoretical basis of MSE, but it only supports the Gaussian distribution [Phys Rev. E 71 (2005) 021906]. We present the theoretical basis of MSE under the inverse Gaussian distribution, a typical model for physiological, physical and financial data sets. The analysis allows for ncorrelated inverse Gaussian process and 1/f noise with the multivariateinverse Gaussian distribution, and then provides a reliable foundation for the potential applications of MSE to explore complex physical and physical time series.
 Select An Approach to Analyse Phase Synchronization in Oscillator Networks with Weak Coupling ZHANG Jian-Bao, LIU Zeng-Rong, LI Ying Chin. Phys. Lett. 2007, 24 (6): 1494-1497 .   Abstract   PDF(pc) (275KB) ( 450 ) We study phase synchronization in oscillator networks through phase reduced method. The dynamics of networks is reduced to phase equationsby this method. Analysing the phase equations through the master stability function method, one obtains that the oscillators with identical frequency can be in-phase synchronized by weak balanced coupling. Similarly, the problem of frequency synchronization of oscillators with different frequencies is transformed to the existence of a locally asymptotically stable equilibrium of the phase error system.
 Select Microlaser with Ramsey Separated Fields Cavity YU De-Shui, ZHUANG Wei, CHEN Jing-Biao Chin. Phys. Lett. 2007, 24 (6): 1498-1501 .   Abstract   PDF(pc) (327KB) ( 312 ) In a novel microlaser configuration with Ramsey separated-field cavity, we investigate a two-level atomic beam interacting with a single-mode high-Q Ramsey cavity, which is composed by two separated resonators. By using the well-known Ramsey cavity, one can recover the characters of microlaser even with a high flux atomic beam.
 Select Conformational Transition of Poly (Acrylic Acid) Detected by Microcantilever Sensing LI Kai, LIU Hong, ZHANG Qing-Chuan, XUE Chang-Guo, WU Xiao-Ping Chin. Phys. Lett. 2007, 24 (6): 1502-1504 .   Abstract   PDF(pc) (379KB) ( 500 ) Poly (acrylic acid) (PAA) chains are grafted on one side of a microcantilever by the self-assembled method and the deflections of the microcantilever are detected as a function of medium pH from 3 to 11. It is found that when the pH varies, the microcantilever deflects because of the changing surface stress. By analysing the electrostatic repulsive effect, the surface stress change is related to the conformation transition of PAA from a collapse state to a swelling state. This method offers the interaction information among the polymer chains during the conformational transition and affords an alternativeway to study conformational change of polymers.
 Select A Spectroscopic Ellipsometry Study of TiO2 Thin Films Prepared by dc Reactive Magnetron Sputtering: Annealing Temperature Effect Mati Horprathum, Pongpan Chindaudom, Pichet Limsuwan Chin. Phys. Lett. 2007, 24 (6): 1505-1508 .   Abstract   PDF(pc) (427KB) ( 3345 ) TiO2 thin films are obtained by dc reactive magnetron sputtering. A target of titanium (99.995%) and a mixture of argon and oxygen gases are used to deposit TiO2 films on to silicon wafers (100). The crystalline structure of deposited and annealed film are deduced by variable-angle spectroscopic ellipsometry (VASE) and supported by x-ray diffractometry. The optical properties of the films are examined by VASE. Measurements of ellipsometry are performed in the spectral range 0.72--3.55eV at incident angle 75°. Several SE models, categorized by physical and optical models, are proposed based on the simpler better' rule and curve-fits, which are generated andcompared to the experimental data using the regression analysis. It has been found that the triple-layer physical model together with the Cody--Lorentz dispersion model offer the most convincing result. The as-deposited films are found to be inhomogeneous and amorphous, whereas the annealed films present the phase transition to anatase and rutile structures. The refractive index of TiO2 thin films increases with annealing temperature. A more detailed analysis further reveals that thickness of the top sub-layer increases, whereas the region of the bottom amorphous sub-layer shrinks when the films are annealed at 300°C.
 Select Remarks on Exactly Solvable Noncommutative Quantum Field WANG Ning Chin. Phys. Lett. 2007, 24 (6): 1509-1512 .   Abstract   PDF(pc) (221KB) ( 634 ) We study exactly the solvable noncommutative scalar quantum field models of (2n) or (2n+1) dimensions. By writing out an equivalent action of the noncommutative field, it is shown that the special condition B.θ=±I in field theoretic context means the full restoration of the maximal U (∞) gauge symmetries broken due to kinetic term. It is further shown that the model can be obtained by dimensional reduction of a 2n-dimensional exactly solvablenoncommutative Ф4 quantum field model closely related to the 1+1-dimensional Moyal/matrix-valued nonlinear Schrodinger (MNLS) equation. The corresponding quantum fundamental commutation relation of the MNLS model is also given explicitly.
 Select Probing the TC2 model via Production of Top Quark Pairs at Tevatron and LHC GU Qin-Zhong, YANG Hua, WANG Xue-Lei Chin. Phys. Lett. 2007, 24 (6): 1513-1516 .   Abstract   PDF(pc) (257KB) ( 440 ) The topcolour-assisted technicolour (TC2) model is an interesting dynamical theory among the various new physics models. We calculate the total tt cross section and the relative correction of the TC2 model to the cross section atTevatron Run II and LHC. At the Tevatron Run II, the cross section predicted by the standard model (SM) is consistent with the experimental data, and in most parameter spaces of the TC2 model, the relative correction of the TC2 model to the cross section is too small to be detectable. We find that the tt cross section is more sensitive to the parameters of the TC2 model at the LHCand the relative correction of the TC2 model to the cross section is over 10% in general. Such a value of the relative correction should be large enough to be detectable at the LHC. Therefore, it is promising to find the clue of the TC2 model via the tt production at the LHC.
 Select Collective Band Structures in Neutron-Rich 108Mo Nucleus DING Huai-Bo, ZHU Sheng-Jiang, J. H. Hamilton, A. V. Ramayya, J. K. Hwang, Y. X. Luo, J. O. Rasmussen, I. Y. Lee, CHE Xing-Lai, WANG Jian-Guo, XU Qiang Chin. Phys. Lett. 2007, 24 (6): 1517-1520 .   Abstract   PDF(pc) (377KB) ( 450 ) High spin states in the neutron-rich 108Mo nucleus are studied by measuring prompt γ-rays following the spontaneous fission of 252Cf with a Gammasphere detector array. The ground-state band is confirmed, and the one-phonon γ-vibrational band is updated with spin up to 12ħ. A new collective band with the band head level at 1422.4keV is suggested as a two-phonon γ-vibrational band. Another new band is proposed as a two-quasi-proton excitation band. Systematic characteristics of the collective bands are discussed.
 Select Reduced Shell Model Calculations of 111Sb and 112Sb E. Dikmen, T. Akyuürek Chin. Phys. Lett. 2007, 24 (6): 1521-1524 .   Abstract   PDF(pc) (216KB) ( 657 ) The low-lying states of the mid-heavy odd--even 111Sb and odd--odd 112Sb isotopes are calculated for the first time within the shell model framework. The shell model calculations have been carried out within the reduced model space including the single particle orbits 1d 5/2, 0g 7/2, 1d 3/2, 2s 1/2. We obtain the energy spectra for the 111Sb and 112Sb isotopes in the reduced model space by using CD-Bonn two-body effective nucleon-nucleon interaction. The energy spectra are compared to the experimental results to give some discussion about the low-lying states of 111Sb and 112Sb.
 Select Energy and Mass Distributions of Induced-Fission of 197Au Nucleus by 29MeV Protons S. Soheyli Chin. Phys. Lett. 2007, 24 (6): 1525-1528 .   Abstract   PDF(pc) (228KB) ( 528 ) A thin target of 197Au is bombarded with 29MeV protons from the cyclotron at Department of Nuclear Research Centre for Agriculture and Medicine. Correlated energies of fission-fragment pairs are measured with silicon surface-barrier detectors and their time of flights is made using a spectrometry pair. The fission cross section, fragment mass distribution, and total kinetic energy distribution of the fission fragments are measured in ourexperiment. The results are also compared with the previous works and good agreements are found.
 Select Isospin Effects of Threshold Energy of Radial Flow in Heavy Ion Collisions BIAN Bao-An, ZHANG Feng-Shou, , ZHOU Hong-Yu, Chin. Phys. Lett. 2007, 24 (6): 1529-1532 .   Abstract   PDF(pc) (239KB) ( 333 ) The threshold energies of radial flow in reactions of 40Ca+40Ca and 48Ca+48Ca in central collisions are investigated within an isospin dependent quantum molecular dynamics model by using three different forms of symmetry energy. It is found that the neutron-rich system has smaller threshold energy of radial flow and this quantity depends on the form of symmetry potential. It is indicated that the threshold energy of radial flow canprovide a new method to determine the symmetry energy of asymmetric nuclear matter.
 Select Mass Resolution versus Chamber Resolution in ALICE Dimuon Forward Spectrometer WU Tao Chin. Phys. Lett. 2007, 24 (6): 1533-1536 .   Abstract   PDF(pc) (297KB) ( 436 ) The precisions and its sources of spatial resolutions of tracking chambers and mass resolutions of dimuon signals in ALICE Dimuon Forward Spectrometer are explored by tracking and reconstruction of AliRoot software. The dependences of γ mass resolution on spatial resolution of tracking chambers are presented with and without background events through simulations.
 Select Ultrahigh Harmonic Generation from an Atom with Superposition of Ground State and Highly Excited States YANG Yu-Jun, CHEN Ji-Gen, CHI Fang-Ping, ZHU Qi-Ren, ZHANG Hong-Xing, SUN Jia-Zhong Chin. Phys. Lett. 2007, 24 (6): 1537-1540 .   Abstract   PDF(pc) (315KB) ( 352 ) We investigate the high-order harmonic generation from an atom prepared in a superposition of ground state and highly excited state. When the atom is irradiated by an ultrashort pulse, the cutoff position of the plateau in the harmonic spectrum is largely extended compared with the case that the atom is initially in the ground state. The physics of the extension of the high-order harmonic plateau can be interpreted by the spatial structure of the atomic initial wave packet. We can optimize the generation of high-order harmonics by substituting the excited state for a particular coherent superposition of some highly excited states to form a spatially localized excited wave packet.
 Select Simultaneous Magneto-Optical Trapping of Fermionic 40K and Bosonic 87Rb Atoms WEI Dong, XIONG De-Zhi, CHEN Hai-Xia, WANG Peng-Jun, GUO Lu, ZHANG Jing Chin. Phys. Lett. 2007, 24 (6): 1541-1544 .   Abstract   PDF(pc) (641KB) ( 490 ) We report on simultaneous magneto-optical trapping of fermionic 40K andbosonic 87Rb atoms. This trap is the first step towards quantum degenerate fermi gas 40K. Laser lights for the two-species magneto-optical trap (MOT) are generated from diode lasers and tapered amplifier. The enriched 40K dispenser is utilized in the experimental setup. We obtain up to 107～108 40K and 108～109 87Rb atoms respectively in the steady-state single-species MOT.
 Select A Single-Layer Magnetic Atom Chip for Trapping an Array of Bose--Einstein Condensate LI Xiao-Lin, KE Min, YAN Bo, WANG Yu-Zhu, Chin. Phys. Lett. 2007, 24 (6): 1545-1548 .   Abstract   PDF(pc) (483KB) ( 363 ) We propose a simple single-layer magnetic microtrap configuration which can trap an array of magnetically-trapped Bose--Einstein condensate. The configuration consists of two series of parallel wires perpendicular to each other and all of the crossing points are cut off for maintaining the uniformity of the current. We analyse the trapping potential, the position of trapping centres and the uniformity of the array of the traps. The trapping depth and trapping frequency with different parameters are also calculated. Lastly, the effect of the cut-off crossing points, dissipate power, chip production are introduced concisely.
 Select Entanglement Dynamics in Typical Local- and Normal-Mode Molecules HOU Xi-Wen, WAN Ming-Fang, MA Zhong-Qi Chin. Phys. Lett. 2007, 24 (6): 1549-1552 .   Abstract   PDF(pc) (269KB) ( 374 ) The entanglement dynamics of two stretching vibrations in theoretically typical local- and normal-mode molecules and realistic molecules H2O and SO2 in an algebraic model is studied in terms of the reduced-density linear entropy withinitial entangled states taken to be two-mode squeezed vacuum states. It is shown that the behaviour of the entropy in theoretically typical molecules appears to be more regular than that in realistic ones, and that the entropy becomes irregular as the amplitude of two-mode squeezed vacuum states increases. For initial states with a small amplitude, it is demonstrated that theperiodicity and the classical'' beat phenomenon of the entropy occur with the beat in theoretically typical molecules being more regular than that in realistic molecules H2O and SO2.
 Select High Performance Small Optically Pumped Caesium Beam Frequency Standard ZHANG Jian-Wei, YANG Dong-Hai Chin. Phys. Lett. 2007, 24 (6): 1553-1555 .   Abstract   PDF(pc) (336KB) ( 542 ) An experiment of a high performance small optically pumped caesium (Cs)beam frequency standard is reported. An extended cavity diode laser works as the probing laser, of which the frequency is stabilized by the Zeeman modulation method. The running parameters of the frequency standard are dynamically optimized via digital servo electronics. The experimental setup improves the frequency stability up to 1.8×10-12 at τ=1s and about 1.0×10-13 at τ=105s (Allan deviation).
 Select Autler--Townes Splitting in Photoelectron Spectrum of Three-Level Li2 Molecule in Ultrashort Pulse Laser Fields HU Wen-Hui, YUAN Kai-Jun, HAN Yong-Chang, SHU Chuan-Cun, CONG Shu-Lin Chin. Phys. Lett. 2007, 24 (6): 1556-1559 .   Abstract   PDF(pc) (360KB) ( 591 ) The Autler--Townes (AT) splitting in femtosecond photoelectron spectrumof three-level Li2 molecules is theoretically investigated using time-dependent quantum wave packet method. With proper femtosecond laser pulses, three peaks of the AT splitting can be observed in the photoelectron spectrum. The AT splitting stems from rapid Rabi oscillation caused by intense ultrashort laser pluses. The effects of laser parameters on the molecular ionization dynamics are also discussed.
 Select Polarization of Radiation Emitted after Electron Impact Excitation WU Ze-Qing, LI Yue-Ming, DUAN Bin, YAN Jun, ZHANG Hong Chin. Phys. Lett. 2007, 24 (6): 1560-1562 .   Abstract   PDF(pc) (224KB) ( 730 ) A programme is developed to calculate the polarizations of the radiation emitted after electron impact excitation. The fully relativistic distorted-wave method is used in cross-section calculations. The programme is applied to He- and Li-like ions. The calculated values of line polarization are compared with other theoretical results and experimental values. For He-like U, at lowerincident energy, the present polarization agrees with the other theoretical ones within 1%, while at higher energy, the differences increase up to about 10%. For He-like Fe and Ti, the present results of polarization degree for most of the lines agree with the experimental data within the experimental error bars. For the Li-like Ti line q (1s2s2p2P 3/2 to 1s22s), the present value ofthe polarization agree excellently with another theoretical one, and both the values are consistent with the measured data within the experimental error bar.
 Select Time-Domain Scattering Modelling of Two-Dimensional Cylinder Located on a Rough Surface ZHANG Min, LI Le-Wei, LI Ling-Xia, WU Zhen-Sen Chin. Phys. Lett. 2007, 24 (6): 1563-1566 .   Abstract   PDF(pc) (278KB) ( 374 ) Numerical modelling on the transient electromagnetic scattering by a two-dimensional (2D) cylinder located on a time-evolving rough surface is presented by using time-domain integral equations. The proposed special choice of a tapered Gauss pulse incident wave removes the truncation error from the rough surface. Additionally, a two-level averaging technique is utilized to overcome the instability from the time marching procedure of solving integral equations. Excellent correspondences between the surface current distributions, as well as the far-zone fields, computed by the proposed method and that obtained by the traditional method of moments associated with the inverse discrete Fourier transformation scheme demonstrate the accuracy of the modelling.
 Select Scheme for Realizing Kerr Nonlinearity in Cavity QED LU Dao-Ming, ZHENG Shi-Biao Chin. Phys. Lett. 2007, 24 (6): 1567-1569 .   Abstract   PDF(pc) (201KB) ( 667 ) We propose a scheme for realizing the Kerr-type nonlinearity for a cavity mode. In the scheme the cavity mode interacts with a single three-level atom dispersively. Under certain conditions, the evolution of the cavity field, decoupled from the atomic degree of freedom, corresponds to the Kerr effect. The scheme can be generalized to implement cross-Kerr effect and two-qubit phase gates for two cavity modes.
 Select Trapping State in a System of Single Three-level Trapped Ion Driven by External Fields WANG Zhong-Jie, CHEN Feng Chin. Phys. Lett. 2007, 24 (6): 1570-1572 .   Abstract   PDF(pc) (186KB) ( 703 ) We investigate the interaction of a single three-level trapped ion with two laser beams. By applying a unitary transformation and a small rotating transformation, an exact solution to this quantum system is obtained without performing the Lamb--Dicke approximation, and the trapping state is observed.
 Select Low Timing Jitter and Tunable Dual-Wavelength Picosecond Pulse Generation from a Fabry--Pérot Laser Diode with External Injection YANG Yi-Biao, WANG Yun-Cai, ZHANG Ming-Jiang, LIANG Wei Chin. Phys. Lett. 2007, 24 (6): 1573-1576 .   Abstract   PDF(pc) (239KB) ( 382 ) A novel scheme to generate tunable dual-wavelength optical pulses with low timing jitter at arbitrary repetition rates is proposed and demonstrated experimentally. The pulses are generated from a gain-switched Fabry--Pérot laser diode with two external cw beams for injection seeding simultaneously. The cw light is generated by two independent distributed feedback laser diodes, and their wavelengths can be tuned independently by two temperature controllers. The dual-wavelength pulses with the pulse width of 57ps, the timing jitter of 340fs, are obtained. The sidemode-suppression ratio of the output pulses is better than 23dB over a 10-nm wavelength tuning range.
 Select Low-Threshold High-Temperature Operation of ～7.4μm Quantum Cascade Lasers LI Lu, LIU Feng-Qi, SHAO Ye, LIU Jun-Qi, WANG Zhan-Guo Chin. Phys. Lett. 2007, 24 (6): 1577-1579 .   Abstract   PDF(pc) (418KB) ( 418 ) We report low-threshold high-temperature operation of 7.4μm strain-compensated InGaAs/InAlAs quantum cascade lasers (QCLs). For anuncoated 22-μm-wide and 2-mm-long laser, the low-threshold currentdensities, i.e. 0.33kA/cm2 at 81K in pulsed mode and 0.64kA/cm2 at 84K in cw mode, are realized. High-temperature operation of uncoated devices, with a high value of 223K, is achieved in cw mode.
 Select A New Discharge Scheme of a Prepulse Plus Two Main Pulses for Capillary-Discharge Soft-X-Ray Laser LUAN Bo-Han, ZHAO Yong-Peng, WANG Qi, CHENG Yuan-Li, XIE Yao Chin. Phys. Lett. 2007, 24 (6): 1580-1582 .   Abstract   PDF(pc) (205KB) ( 348 ) Reducing the capillary-discharge current is one way of possibly decreasing the pumping power requirement. We examine the influence of various discharge currents on laser intensity and determine the suitable pre-discharge condition for a 46.9-nm discharge-pumped Ne-like Ar soft-x-ray amplifier. The experimental results show that a high additional pre-pulse current at amplitude of several kA and with a very short duration of several tens of nanosecond can effectively decrease the amplitude of the main discharge current at the lasing time. We propose a new discharge scheme of a pre-pulse plus two main pulses which appears to significantly decrease the requirement for discharge current. This in turn may decrease the pumping power requirement for the capillary discharge laser and can greatly increase laser efficiency.
 Select Passively Q-Switched Nd:KLuW Laser with Semiconductor Saturable Absorber GUO Lin, WANG Gui-Ling, ZHANG Hong-Bo, GENG Ai-Cong, CHEN Ya-Hui, LU Yuan-Fu, CUI Qian-Jin, ZHOU Yong, CUI Da-Fu, ZHANG Jian-Xiu, ZHANG Huai-Jin, WANG Ji-Yang, XU Zu-Yan Chin. Phys. Lett. 2007, 24 (6): 1583-1585 .   Abstract   PDF(pc) (262KB) ( 508 ) We demonstrate a passively Q-switched Nd:KLuW laser with a semiconductor saturable absorber mirror (SESAM) at wavelength 1070nm. At a pump power of 1.3W, the pulse width is measured to be about 17ns with repetition rate of 10kHz and with the average output power of 260mW. To our knowledge, this is the first demonstration of Nd:KLuW used for passively Q-switched laser with an SESAM.
 Select Long Optical Delay Lines Enhanced by Ring Configuration in Optical Fibres DONG Yong-Kang, LU Zhi-Wei, LI Qiang, GAO Wei Chin. Phys. Lett. 2007, 24 (6): 1586-1588 .   Abstract   PDF(pc) (218KB) ( 510 ) A long optically controlled delay line enhanced by ring configuration is demonstrated by using the group-velocity control of signal pulses based on stimulated Brillouin scattering. In experiment, two optical fibre ring cavities are used: one is used as the Brillouin laser, providing single-mode Stokes wave as probe wave; the other is used as the Brillouin amplifier, working as slow light medium. We achieve a maximum time delay of 215ns using the ring Brillouin amplifier, five times larger than the input probe pulse width of 40ns. In the meantime, a considerable pulse broadening is observed, which agreeswell with the theoretical prediction based on linear theory.
 Select Non-Degenerate Four-Wave Mixing in Microstructure Fibres ZHANG Xia, REN Xiao-Min, WANG Zi-Nan, XU Yong-Zhao, ZHANG Rui-Rui, HUANG Yong-Qing, CHEN Xue Chin. Phys. Lett. 2007, 24 (6): 1589-1591 .   Abstract   PDF(pc) (507KB) ( 456 ) Non-degenerate four wave mixing based on third-order susceptibility X3 in high nonlinearity microstructure fibres is experimentally demonstrated. The Stokes and anti-Stokes peaks are observed simultaneously by launching 10-fs pulses from an 800nm Ti:sapphire laser into the fibre.
 Select Coherent Phase Control of Ultrafast Polarization Beats in Reverse V-Type Three-Level System LI Ling, NIE Zhi-Qiang, JIANG Tong, ZHANG Yan-Peng, LI Pei-Zhe, GAN Chen-Li, SONG Jian-Ping, LI Yuan-Yuan Chin. Phys. Lett. 2007, 24 (6): 1592-1599 .   Abstract   PDF(pc) (269KB) ( 348 ) We investigate the third-order nonlinear absorption and dispersion of femto- and atto-second polarization beats between the one-photon degenerate four-wave mixing process and the two-photon nondegenerate four-wave mixing process in the pure homogeneously-broadened reverse V-three-level using twin noisy fields. The third-order nonlinear response can be controlled and modified by the colour-locked correlation of twin noisy fields. Most importantly, the coherent phase control in optical heterodyne detection for studying the phase dispersion of the third-order susceptibility is demonstrated. The radiation-matter detuning oscillation is also considered in the frequency domain.
 Select White-Light Nonlinear Photonic Lattices in Self-Defocusing Media GAO Yuan-Mei, LIU Si-Min Chin. Phys. Lett. 2007, 24 (6): 1596-1599 .   Abstract   PDF(pc) (887KB) ( 353 ) Using fully incoherent white light emitted from an incandescent lamp and amplitude mask, we experimentally investigate the influence of several factors on the fabrication of the lattice in photovoltaic self-defocusing LiNbO3:Fe crystal, the factors include the orientation of the crystalline c axis relative to the principal axis of the photonic lattice and the filament, the diameter of input dark spot and the separation of the adjacent input dark spots. Experimental results reveal that the best fabricating condition of photonic lattices is that the principal axis of lattice is tilted for 45° relative to the crystalline c axis which is parallel to the filament of the lamp. In addition, it is necessary that the diameter of the input dark spot is larger than the half of their separation.
 Select Extraordinary Transmission through Metallic Grating with Subwavelength Slits for S-Polarization Illumination YUAN Guang-Hui, WANG Pei, ZHANG Dou-Guo, JIAO Xiao-Jin, MIN Chang-Jun, MING Hai Chin. Phys. Lett. 2007, 24 (6): 1600-1602 .   Abstract   PDF(pc) (351KB) ( 521 ) Based on the rigorous coupled-wave analysis algorithm, we have systematically analysed the effect of the geometrical parameters of a dielectric film coated metallic grating with subwavelength slits on extraordinary optical transmission for s-polarization illumination. Results show that the dielectric film which sustains a waveguide electromagnetic mode on the top of the metallic lamellar grating can strongly enhance the transmittance, the positions of the transmission peaks are mainly determined by the period of the metallic grating, the thickness and refractive index of the dielectric film. This structure shows potential applications in excellent polarizers or polarization-isotropic devices at infrared spectral range byappropriately choosing the geometrical parameters.
 Select Fibre Bragg Gratings Inscribed in Homemade Microstructured Fibres JIN Long, KAI Gui-Yun, LI Jin-Yan, CHEN Wei, LIU Jian-Guo, LIU Yan-Ge, WANG Zhi, ZHANG Jian, LIU Bo, YUAN Shu-Zhong, DONG Xiao-Yi Chin. Phys. Lett. 2007, 24 (6): 1603-1606 .   Abstract   PDF(pc) (323KB) ( 472 ) Fibre Bragg gratings (FBGs) are inscribed in homemade microstructured fibres by the standard phase mask method. Enhanced couplings between the forward fundamental mode and backward cladding modes are obtained.The mode coupling and spectral characteristics are investigated experimentally. The cladding mode resonances can be affected by fillingactive materials into the air holes, which will be useful for the implementation of tunable photonic devices in optical fibre communication and sensing systems.
 Select Optimal Acoustic Attenuation of Weakly Compressible Media Permeated with Air Bubbles LIANG Bin, CHENG Jian-Chun Chin. Phys. Lett. 2007, 24 (6): 1607-1610 .   Abstract   PDF(pc) (233KB) ( 620 ) Based on fuzzy logic (FL) and genetic algorithm (GA), we present an optimization method to obtain the optimal acoustic attenuation of a longitudinal acoustic wave propagating in a weakly compressible mediumpermeated with air bubbles. In the optimization, the parameters of the size distribution of bubbles in the medium are optimized for providing uniformly high acoustic attenuation in the frequency band of interest. Compared with other traditional optimization methods, the unique advantage of the present method is that it can locate the global optimum quickly and effectively in need of knowing the mathematical model precisely. As illustrated by a numerical simulation, the method is effective and essential in enhancing the acoustic attenuation of such a medium in an optimal manner. The bubbly medium with optimized structural parameters can effectively attenuate longitudinal waves at intermediate frequencies with an acoustic attenuation approximating a constant value of 10(dB/cm). Such bubbly media with optimal acoustic attenuations may be applied to design acoustic absorbent by controlling broader attenuation band and higher efficiency.
 Select Young's Modulus Anisotropy and Magnetomechanical Damping of [110]Oriented Tb0.3 Dy0.7 Fe1.95 Alloy PEI Yong-Mao, FANG Dai-Ning Chin. Phys. Lett. 2007, 24 (6): 1611-1613 .   Abstract   PDF(pc) (218KB) ( 419 ) The △E effect and the magnetoelastic or magnetomechanical damping of vibrations in [110] oriented Tb0.3Dy0.7Fe1.95 alloy are experimentally studied by quasi-static stress--strain measurements under various constant magnetic fields between 0 and 3000Oe, where stress ranges are taken from about 0 to -25, -50, -75MPa. The linear stress--strain behaviour is obtained when the magnetic field is high enough (9000Oe). However, the modulus E varies with the angle θ between the compressive stress and magnetic field(9000Oe), which shows that the anisotropy of the modulus E is related to the magnetic domain distribution.
 Select Phase Space Compression in One-Dimensional Complex Ginzburg--Landau Equation GAO Ji-Hua, PENG Jian-Hua Chin. Phys. Lett. 2007, 24 (6): 1614-1617 .   Abstract   PDF(pc) (476KB) ( 431 ) The transition from stationary to oscillatory states in dynamical systems under phase space compression is investigated. By considering the model for the spatially one-dimensional complex Ginzburg--Landau equation, we find that defect turbulence can be substituted with stationary and oscillatory signals by applying system perturbation and confining variable into various ranges. The transition procedure described by the oscillatory frequency is studied via numerical simulations in detail.
 Select Topological Constraints on Scroll and Spiral Waves in Excitable Mediac ZHANG Hong, , HU Bambi, LI Bing-Wei, DUAN Yi-Shi Chin. Phys. Lett. 2007, 24 (6): 1618-1621 .   Abstract   PDF(pc) (412KB) ( 385 ) A conservation equation for topological charges of phase singularities (scroll and spiral waves) in excitable media is given. It provides some topological properties of scroll (spiral) waves: for example, the topological charge of the generated or annihilated spiral pair must be opposite. Additionally, we obtain another equation on scroll waves, which shows that singular filaments of scroll waves occur on a set of one-dimensional curves which may be either closed loops or infinite lines.
 Select Orientational Distribution of Fibres in Sheared Fibre Suspensions KU Xiao-Ke, LIN Jian-Zhong, Chin. Phys. Lett. 2007, 24 (6): 1622-1625 .   Abstract   PDF(pc) (256KB) ( 403 ) Motion of fibres in sheared fibre suspensions is simulated numerically by using the lattice Boltzmann method. The orientational distributions of the fibres are presented for different Reynolds numbers, Stokes numbers, shear rate and fibre aspect ratio. Some computational results are compared with the experimental data of pipe flow, and the qualitative agreement is achieved. The results show that the orientational distributions are greatly affected by the Reynolds numbers, while relatively insensitive to the fibre aspect ratio. The Stokes number and shear rate have obvious influence on the orientationdistribution.
 Select Long-Range Surface Plasmon Polaritons Guided by a Thin Metal Stripe RAO Yi, LIU Fang, HUANG Yi-Dong, DAI Ohnishi, ZHANG Wei, PENG Jiang-De Chin. Phys. Lett. 2007, 24 (6): 1626-1628 .   Abstract   PDF(pc) (322KB) ( 647 ) A long-range surface plasmon polariton (LRSPP) waveguide consisting of a15nm thick gold stripe embedded in a homogeneous polymer BCB is reported. LRSPPs are excited by TM-mode input light successfully using an end-fire method. By scanning the output coupling fibre, the near field of the LRSPP is measured. The propagation loss of as low as 2.34dB/mm is demonstrated.
 Select A New Doppler Shift Spectroscopy for Measurement of Neutral Beam Profile SHI Yue-Jiang, WANG Guang-Qi, FU Jia, WU Zhen-Wei, CHANG Jia-Feng, SUN Dan-Peng, GAO Wei, HUANG Juan, ZHOU Qian, GAO Xiang, WAN Bao-Nian Chin. Phys. Lett. 2007, 24 (6): 1629-1632 .   Abstract   PDF(pc) (1183KB) ( 550 ) A new diagnostic based on Doppler shift is designed to measure the power profile of a hydrogen or deuterium neutral beam on the magnetic confined fusion machines. The interference filters and multi-channel photon detector array (PDA) are the main components of this diagnosis. The multi-channel PDA measures the line integrated Doppler Hα signal emitted by the neutral beam at one section in two directions. The local intensity of neutral beam can be obtained with the tomography technique. Compared to the conventional calorimeter diagnoses, this diagnosis can provide the beam profile without blocking the injection of neutral beam.
 Select Effect of Substrate Bias on Microstructures of Zirconia Thin Films Deposited by Cathodic Vacuum Arc LI Xiang-Zhou, ZHANG Xian-Hui, HE Ping, NIU Er-Wu, XIA Yuan-Yu, HUANG Jun, FENG Ke-Cheng, YANG Si-Ze Chin. Phys. Lett. 2007, 24 (6): 1633-1636 .   Abstract   PDF(pc) (491KB) ( 465 ) Zirconium oxide (ZrO2) thin films are deposited at room temperature by cathodic arc at substrate biases of 0V, -60V and -120V, respectively. The crystal structure, composition, morphology, and deposition rate of the as-deposited thin films are systematically investigated by x-ray diffraction, x-ray photoelectron spectroscopy (XPS) as well as scanning electron microscopy. The results show that the crystal structure, morphology and deposition rate of the films all are dependant on substrate bias. With the increase of bias voltage from 0V to -120V, the zirconium oxide thin film grown on silicon wafer first exhibits monoclinic lattice and tetragonal lattice, further evolves monoclinic phase with the preferred orientation along the (-111) and (-222) directions at -60V and finally along nearly one observed preferred (002) direction under -120V. In addition, the variations of morphology with bias voltage are correlated to changes of the film structure. The results of XPS demonstrate that Zr elements are almost oxidized completely in the films achieved under -120V bias.
 Select Power Consideration for Pulsed Discharges in Potassium Seeded Argon XIA Sheng-Guo, HE Jun-Jia, LIU Ke-Fu Chin. Phys. Lett. 2007, 24 (6): 1637-1640 .   Abstract   PDF(pc) (296KB) ( 310 ) Minimization of energy consumed in plasma generation is critical for applications, in which a large volume of plasmas is needed. We suggestthat a high electron density atmospheric pressure plasmas can be generated by pulsed discharges in potassium seeded argon at an elevated temperature with a very small power input. The ionization efficiency and power budget of pulsed discharges in such plasmas are analytically studied. The results show that ionization efficiency of argon, especially at small reduced electric field E/N (the ratio of the electric field to the gas number density), is improved ffectively in the presence of small amount of potassium additives. Power input of pulsed discharge to sustain a prescribed average level of ionization in potassium seeded argon is three orders of magnitude lower than that in pure argon. Further, unlike in pure argon, it is found that very short high-voltage pulses with very high repetition rates are unnecessary in potassium seeded argon. A pulse with 100ns of pulse duration, 5kHz of repetition rate, and 2Td (1Td=1×10-21Vm2) of E/N is enough to sustain an electron density of 1019m-3 in 1 atm 1500K Ar+0.1% K mixture, with a very small power input of about0.08×104W/m3.
 Select Growth of Semi-Insulating GaN by Using Two-Step AlN Buffer Layer ZHOU Zhong-Tang, GUO Li-Wei, XING Zhi-Gang, DING Guo-Jian, ZHANG Jie, PENG Ming-Zeng, JIA Hai-Qiang, CHEN Hong, ZHOU Jun-Ming Chin. Phys. Lett. 2007, 24 (6): 1641-1644 .   Abstract   PDF(pc) (432KB) ( 957 ) Semi-insulating GaN is grown by using a two-step AlN buffer layer by metalorganic chemical vapour deposition. The sheet resistance of as-grown semi-insulating GaN is dramatically increased to 1013Ω/sq by using two-step AlN buffer instead of the traditional low-temperature GaN buffer. The high sheet resistance of as-grown GaN over 1013Ω/sq is due to inserting an insulating buffer layer (two-step AlN buffer) between the high-temperature GaN layer and a sapphire substrate which blocks diffusion of oxygen and overcomes the weakness of generating high density carrier near interface of GaN and sapphire when a low-temperature GaN buffer is used. The result suggests that the high conductive feature of unintentionally doped GaN ismainly contributed from the highly conductive channel near interface between GaN and the sapphire substrate, which is indirectly manifested by room-temperature photoluminescence excited by an incident laser beam radiating on growth surface and on the substrate. The functions of the two-step AlN buffer layer in reducing screw dislocation and improving crystal quality of GaN are also discussed.
 Select Growth of Semi-Insulating GaN Using N2 as Nucleation Layer Carrier Gas Combining with an Optimized Annealing Time ZHOU Zhong-Tang, XING Zhi-Gang, GUO Li-Wei, CHEN Hong, ZHOU Jun-Ming Chin. Phys. Lett. 2007, 24 (6): 1645-1648 .   Abstract   PDF(pc) (620KB) ( 528 ) Semi-insulating (SI) GaN is grown using N2 as the nucleation layer (NL) carrier gas combined with an optimized annealing time by metalorganic chemical vapour deposition. Influence of using H2 and N2 as the NL carrier gas is investigated in our experiment. It is found that the sheet resistance of unintentionally doped GaN can be increased from 104Ω/sq to 1010Ω/sq by changing the NL carrier gas from H2 to N2 while keeping the other growthparameters to be constant, however crystal quality and roughness of thefilm are degraded unambiguously. This situation can be improved by optimizing the NL annealing time. The high resistance of GaN grown onNL using N2 as the carrier gas is due to higher density of threading dislocations caused by the higher density of nucleation islands and small statistic diameter grain compared to the one using H2 as carrier gas. Annealing the NL for an optimized annealing time can decrease the density of threading dislocation and improve the film roughness and interface of AlGaN/GaN without degrading the sheet resistance of as-grown GaN significantly. High-quality SI GaN is grown after optimizing the annealing time, and AlGaN/GaN high electron mobility transistors are also prepared.
 Select Microstructure of Epitaxial Er2O3 Thin Film on Oxidized Si (111) Substrate XUE Xian-Ying, WANG Yu-Zhu, JIA Quan-Jie, WANG Yong, CHEN Yu, JIANG Xiao-Ming, ZHU Yan-Yan, JIANG Zui-Min Chin. Phys. Lett. 2007, 24 (6): 1649-2652 .   Abstract   PDF(pc) (382KB) ( 750 ) Er2O3 thin films are grown on oxidized Si (111) substrates by molecular beam epitaxy. The sample grown under optimized condition is characterized in its microstructure, surface morphology and thickness using grazing incidence x-ray diffraction (GIXRD), atomic force morphology and x-ray reflectivity. GIXRD measurements reveal that the Er2O3 thin film is a mosaic of single-crystaldomains. The interplanar spacing d in-plane residual strain tensor ε| and the strain relaxation degree ξ are calculated. The Poisson ratio μ obtained by conventional x-ray diffraction is in good agreement with that of the bulkEr2O3. In-plane strains in three sets of planes, i.e. (440), (404), and (044), are isotropic.
 Select Formation of Pd--Ni Based Bulk Metallic Glasses WANG Yao-Cen, CHEN Na, YAO Ke-Fu Chin. Phys. Lett. 2007, 24 (6): 1653-1655 .   Abstract   PDF(pc) (224KB) ( 454 ) Bulk metallic glasses are prepared in Pd40.5Ni40.5SixP19-x (x=0\$--14 at.%)alloys by a combination of flux treatment and water quenching technique. It is found that the thermal stability of the Pd40.5Ni40.5SixP19-x glassy alloys depends on the addition of Si content. Among the Pd40.5Ni40.5SixP19-x glassy alloys studied, the Pd40.5Ni40.5Si5P15 bulk metallic glass exhibits the largest supercooled liquid region (△T=119,K) and the highest activation energy of crystallization (283.3kJ/mol), showing enhanced glass formation ability and extraordinary glassy thermal stability.
 Select Melting Behaviour of Core-Shell Structured Ag--Rh Bimetallic Clusters PAN Yang, CHENG Dao-Jian, HUANG Shi-Ping, WANG Wen-Chuan Chin. Phys. Lett. 2007, 24 (6): 1656-1659 .   Abstract   PDF(pc) (437KB) ( 557 ) The melting behaviour of four typical core-shell structured 309-atom Ag--Rh bimetallic clusters, with decahedral and icosahedral geometric configurations, is investigated by using molecular dynamics simulation, based on the Sutton--Chen potential. The initial atomic configurations are obtained from semi-grand canonical ensemble Monte Carlo simulations. It is found that the melting point temperature Tm increases with the mole fraction of Rh in the bimetallic clusters, and Tm of Ag--Rh icosahedral clusters is higher than those of Ag--Rh decahedral clusters with the same Rh mole fraction. It is also found that the Ag atoms lie on the surface of Ag--Rh bimetallic clusters even after melting.
 Select Electronic Structures of PbMoO4 Crystals with F-Type Colour Centres CHEN Jian-Yu, ZHANG Qi-Ren, LIU Ting-Yu, SHAO Ze-Xu, PU Chun-Ying Chin. Phys. Lett. 2007, 24 (6): 1660-1663 .   Abstract   PDF(pc) (247KB) ( 632 ) Electronic structures of PbMoO4 crystals containing F-type colour centres with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Dirac--Slater theory, using a numerically discrete variational (DV-Xα) method. The calculated results show that F and F+ centres have donor energy levels in the forbidden band. The optical transition energies are 2.166eV and 2.197eV, respectively, corresponding to the 580nmabsorption bands in PbMoO4 crystal. The 580nm absorption band in PbMoO4 is originated from the F-type colour centres.
 Select Improved Performance of Organic Thin Film Transistor with an Inorganic Oxide/Polymer Double-Layer Insulator ZHAO Yi-Hua, DONG Gui-Fang, WANG Li-Duo, QIU Yong Chin. Phys. Lett. 2007, 24 (6): 1664-1667 .   Abstract   PDF(pc) (405KB) ( 632 ) We employ the Ta2O5/PVP (poly-4-vinylphenol) double-layer gate insulator to improve the performance of pentacene thin-film transistors. It is found that the double-layer insulator has low leakage current, smooth surface and considerably high capacitance. Compared to Ta2O5 insulator layers, the device with the Ta2O5/PVP double-layer insulator exhibits an enhancementof the field-effect mobility from 0.21 to 0.54cm2/Vs, and the decreasing threshold voltage from 4.38V to -2.5V. The results suggest that the Ta2O5/PVP double-layer insulator is a potential gate insulator for fabricating OTFTs with good electrical performance.
 Select First-Principles Prediction of High-Pressure Phase of CaC6 LI Yan, ZHANG Li-Jun, CUI Tian, LIU Yan-Hui, MA Yan-Ming, ZOU Guang-Tian Chin. Phys. Lett. 2007, 24 (6): 1668-1670 .   Abstract   PDF(pc) (295KB) ( 587 ) The lattice dynamics of rhombohedral CaC6 is studied as a function of pressure to probe its high pressure phase with low superconducting transition temperature using the density functional liner-response theory. The pressure-induced phase transition in CaC6 is attributable to the softening transverse acoustic (TA) phonon mode at the zone boundary X (0.5, 0.0, 0.5) point. The high pressure phase is then explored by performing fully structuraloptimization in the supercell which accommodates the atomic displacements corresponding to the eigenvectors of the unstable mode of TA(X). The high-pressure phase is predicted to be a monoclinic unit cell with space group P21/m.
 Select Compressibility of Nickel Nanoparticle Chain LI Xiao-Dong, TANG Ling-Yun, LI Yan-Chun, LIU Jing Chin. Phys. Lett. 2007, 24 (6): 1671-1673 .   Abstract   PDF(pc) (235KB) ( 393 ) We perform the high-pressure energy dispersive x-ray diffraction experiments of nickel nanoparticle chain using a synchrotron source under quasi-hydrostatic compression up to 44.7GPa. There is no phase transition over the pressure range. The bulk modulus K0, the first pressure derivative of bulk modulus K0' and the volume V0 are calculated from the pressure--volume datausing the Birch--Murnaghan equation of state. A decrease of compressibility is observed, in agreement with the Hall--Petch effect.
 Select Chemical Oxidation of La2CuO4 Epitaxial Thin Films Grown by Pulsed Laser Deposition WANG Chun-Chang, YAN Yun-Jie, ZHU Jing Chin. Phys. Lett. 2007, 24 (6): 1674-1677 .   Abstract   PDF(pc) (668KB) ( 550 ) Chemical oxidation is used to induce superconductivity in La2CuO4 expitaxial thin films fabricated by pulsed laser deposition technique. Details about the influence of oxidation time on structural, surface morphology, Raman spectra, and electrical properties have been investigated. The results convince that successful uptake of oxygen occurs in the oxidized films, and the content of the inserted oxygen increases with increasing oxidation interval. The possible mechanism for the excess oxygen insertion into the film is also discussed.
 Select Magnetic and Microstructure of Triple C/Co73Cr22Ta5/Ti for Perpendicular Media ZHEN Cong-Mian, HOU Deng-Lu, GUO Ge-Xin, YAN Zhen-Zhuang, NIE Xiang-Fu Chin. Phys. Lett. 2007, 24 (6): 1678-1681 .   Abstract   PDF(pc) (445KB) ( 385 ) The magnetic properties and microstructure of triple C/CoCrTa/Ti perpendicular recording films have been studied. Magnetic measurementsshow that the optimal thickness of Ti underlayer is 40nm and that of CoCrTa is 35nm. The optimal value of substrate temperature is found to be 400°C. A suitable Ti underlayer causes a magnetic layer to have a near-perfect hcp texture, with Co grains in the (002) preferred orientation. The film with needle-like grains is more suitable for perpendicular recording films.
 Select Effects of Dislocation on High Temperature Transport Characteristics of Unintentionally Doped GaN WANG Mao-Jun, SHEN Bo, XU Fu-Jun, WANG Yan, XU Jian, HUANG Sen, YANG Zhi-Jian, QIN Zhi-Xin, ZHANG Guo-Yi Chin. Phys. Lett. 2007, 24 (6): 1682-1685 .   Abstract   PDF(pc) (548KB) ( 1523 ) High temperature transport characteristics of unintentionally doped GaN have been investigated by means of high temperature Hall measurements from room temperature to 500°C. The increment of electron concentration from room temperature to 500°C is found to vary largely for different samples. The dispersion of temperature dependence of electron concentration is found to be directly proportional to the density of dislocations in GaN layers calculated by fitting the FWHM of the rocking curves in x-ray diffraction measurements (XRD). The buildup levels in persistent photoconductivity (PPC) are also shown to be directly proportional to the density of dislocations. The correlation of XRD, Hall and PPC results indicate that the high temperature dependence of electron density in unintentional doped GaN is directly dislocation related.
 Select Effect of Heavily Doped Boron on Bandgap Narrowing of Strained SiGe Layers YAO Fei, XUE Chun-Lai, CHENG Bu-Wen, WANG Qi-Ming Chin. Phys. Lett. 2007, 24 (6): 1686-1689 .   Abstract   PDF(pc) (237KB) ( 374 ) Taking into account the compensation effect of B to Ge in strained SiGe layers for the first time, the effect of heavily doped boron on the bandgap narrowing of strained SiGe layers is calculated, and the classical Jain--Roulston (J-R) model is modified. The results show that our modified J-R model well fits the experimental values. Based on the modified J-R model, the real bandgap narrowing distribution between the conduction and valence bands is further calculated, which has great influence on modelling the electrical characteristics of SiGe heterojunction bipolar transistors.
 Select Spin-Flip of Polaron in Polymers with a Magnetic Impurity CHEN Mei-Juan, YAN Yong-Hong, WU Chang-Qin Chin. Phys. Lett. 2007, 24 (6): 1690-1692 .   Abstract   PDF(pc) (224KB) ( 360 ) Using a nonadiabatic evolution method, we investigate the spin-flip process of polaron in polymers with a magnetic impurity. Our results show that when the spin orientation of this impurity is fixed to be perpendicular to the spin of polaron (θ=π/2), the magnetic impurity causes a spin-flip process. The probability of the spin-flip increases with the increase of exchange integralJ up to about 0.35eV and then decreases with the increase of J. In the case J is fixed while the spin orientation is adjustable, we find the probability of the spin-flip varies with the impurity orientation and reaches a maximum value at θ=π/2.
 Select Electronic Transport through a Waveguide in the Presence of a Magnetic Obstacle GAO Wen-Zhu, SUN Lang, ZHENG Yi-Song Chin. Phys. Lett. 2007, 24 (6): 1693-1696 .   Abstract   PDF(pc) (244KB) ( 398 ) By means of the transfer matrix technique, the electronic transport through a quantum waveguide in the presence of a magnetic obstacle is investigated theoretically. By comparing the calculated conductance spectra of the opposite spin electrons, we find that there exists a notable spin filtering window in the low energy region. Dependences of such a spin filtering window on the size, position and potential strength of the magnetic obstacle are studied in detail.
 Select Effect of Electric Field on Spin Polarized Current in Ferromagnetic/Organic Semiconductor Systems MA Yan-Ni, REN Jun-Feng, ZHANG Yu-Bin, LIU De-Sheng, XIE Shi-Jie Chin. Phys. Lett. 2007, 24 (6): 1697-1700 .   Abstract   PDF(pc) (238KB) ( 563 ) Considering the special carriers in organic semiconductors, the spin polarized current under electric field in a ferromagnetic/organic semiconductor system is theoretically studied. Based on the spin-diffusion theory, the current spin polarization under the electric field is obtained. It is found that electric field can enhance the current spin polarization.
 Select Helical Shell Structures of Ni--Al Alloy Nanowires and Their Electronic Transport Properties ZHANG Xue-Qing, LI Hui, LIEW Kim-Meow, LI Yun-Fang, SUN Feng-Wei Chin. Phys. Lett. 2007, 24 (6): 1701-1704 .   Abstract   PDF(pc) (375KB) ( 447 ) Six kinds of Ni--Al alloy nanowires are optimized by means of simulated annealing. The optimized structures show that the Ni--Al alloy nanowires are helical shell structures that are wound by three atomic strands, which is very similar to the case with pure metallic nanowires. The densities of states (DOS), transmission function T(E), current--voltage (I-V) curves, and the conductance spectra of these alloy nanowires are also investigated. Our results indicate that the conductance spectra depend on the geometric structure properties and the ingredients of the alloy nanowires. We observe and study the nonlinear contribution to the I--V characteristics that are due to the quantum size effect and the impurity effect. The addition of Ni atoms decreases the conductance of the Ni--Al alloy nanowire because the doping atom Ni change the electronic band structures and the charge density distribution. The interesting statistical results shed light on the physics of quantum transport at the nano-scale.
 Select Growth and Characterization of AlGaN/AlN/GaN HEMT Structures with a Compositionally Step-Graded AlGaN Barrier Layer MA Zhi-Yong, WANG Xiao-Liang, HU Guo-Xin, RAN Jun-Xue, XIAO Hong-Ling, LUO Wei-Jun, TANG Jian, LI Jian-Ping, LI Jin-Min Chin. Phys. Lett. 2007, 24 (6): 1705-1708 .   Abstract   PDF(pc) (548KB) ( 705 ) A new AlGaN/AlN/GaN high electron mobility transistor (HEMT) structure using a compositionally step-graded AlGaN barrier layer is grown on sapphire by metalorganic chemical vapour deposition (MOCVD). The structure demonstrates significant enhancement of two-dimensional electron gas (2DEG) mobility and smooth surface morphology compared with the conventional HEMT structure with high Al composition AlGaN barrier. The high 2DEG mobility of 1806cm2/Vs at room temperature and low rms surface roughness of 0.220nm for a scan area of 5μm×5μm are attributed to the improvement of interfacial and crystal quality by employing the step-graded barrier to accommodate the large lattice mismatch stress. The 2DEG sheet density is independent of the measurement temperature, showing the excellent 2DEG confinement of the step-graded structure. A low average sheet resistance of 314.5Ω/square, with a good resistance uniformity of 0.68%, is also obtained across the 50mm epilayer wafer. HEMT devices aresuccessfully fabricated using this material structure, which exhibits a maximum extrinsic transconductance of 218mS/mm and a maximum drain current density of 800mA/mm.
 Select Microwave Response of Bi2Sr2CaCu2O8+δ Surface Intrinsic Josephson Junctions with Bending Pancake Vortices WEI Yan-Feng, ZHAO Shi-Ping, ZHU Xiao-Bo, CHEN Geng-Hua, REN Yu-Feng, YU Hong-Wei, YANG Qian-Sheng Chin. Phys. Lett. 2007, 24 (6): 1709-1712 .   Abstract   PDF(pc) (265KB) ( 836 ) We study the microwave response of surface intrinsic Josephson junctions on Bi2Sr2CaCu2O8+δ, in which bending pancake vortex lines are introduced in a controllable way. It is found that the bending vortices can greatly influence the response. In some cases, typical Shapiro steps that lie far above the quasiparticle branch are observed, with the step interval satisfying the Josephson relation and their amplitude versus the square root of microwave power following the Bessel function behaviour. In the other cases, current steps that lie on the quasiparticle branch are observed, but only one or two steps appear at the same time under the variation of the microwave power.
 Select Microwave Response of MgB2/Al2O3 Superconducting Thin Films by Microstrip Resonator Technique SHI Li-Bin, ZHENG Yan, REN Jun-Yuan, LI Ming-Biao, ZHANG Feng-Yun, LI Bo-Xin, DONG Hai-Kuan Chin. Phys. Lett. 2007, 24 (6): 1713-1716 .   Abstract   PDF(pc) (525KB) ( 553 ) Double-sided superconducting MgB2 thin films are deposited onto c-Al2O3 substrates by the hybrid physical chemical vapour deposition method. The microwave response of MgB2/Al2O3 is investigated by microstrip resonatortechnique. A grain-size model is introduced to the theory of microstrip resonators to analyse microwave properties of the films. We obtain effective penetration depth of the films at 0K (λe0=463nm) and surface resistance (Rs=1.52mΩ at 11K and 8.73GHz) by analysing the resonant frequency and unload quality factor of the microstrip resonator, which suggests that the impurities and disorders of grain boundaries of MgB2/Al2O3 result in increasing penetration depth and surface resistance of the films.
 Select Magnetic Behaviour of Tb/Si Nanoscale Multilayers with Small Thickness of Rare Earth Layers A.V. Svalov, V.O. Vas'kovskiy, G.V.Kurlyandskaya, J.M. Barandiaran, N.N. Schegoleva, A.N. Sorokin Chin. Phys. Lett. 2007, 24 (6): 1717-1719 .   Abstract   PDF(pc) (250KB) ( 406 ) We report the magnetic properties of Tb/Si multilayers obtained by rf-sputtering at the Tb layer thickness LTb = 3nm. Analysis of the magnetization processes indicates more complex behaviour than canonical spin-glass transition. It is more probable that these multilayers contain both Tb superparamagnetic particles and Tb--Si spin-glass alloys.
 Select Light-Induced Domain Inversion in Mg-Doped near Stoichiometric Lithium Niobate Crystals LIU Hong-De, KONG Yong-Fa, HU Qian, WU Ri-Wen, WANG Wen-Jie, LI Xiao-Chun, CHEN Shao-Lin, LIU Shi-Guo, XU Jing-Jun Chin. Phys. Lett. 2007, 24 (6): 1720-1723 .   Abstract   PDF(pc) (403KB) ( 541 ) We investigate the influence of visible light on domain inversion in Mg-doped near stoichiometric lithium niobate crystals and find that the switching electric field decreases about 70% above a threshold light intensity. This effect helps us optically control domain switching and produce bulk domain structures on the micrometre scale. Finally, we introduce a model of photo-induced carriers to explain the origin of the reduction of switching electric field.
 Select Effective Dielectric Response of Nonlinear Composites of Coated Metal Inclusions CHEN Guo-Qing, WU Ya-Min Chin. Phys. Lett. 2007, 24 (6): 1724-1727 .   Abstract   PDF(pc) (388KB) ( 395 ) The effective dielectric response of the composites in which nondilute coated metal particles are randomly embedded in a linear host is investigated. Two types of coated particles are considered, one is that the core is nonlinear, the other is that the shell is nonlinear. We derive general expressions for the effective linear dielectric function and the effective third-order nonlinear susceptibility, and take one step forward to perform numerical calculations on the coated metal/dielectric composites. Numerical results show that the effective linear and nonlinear dielectric responses can be greatly enhanced near the surface plasmon resonant frequency. Moreover, the resonant peaksare found within a range from 0.46ωp to 0.57ωp for spherical particles and from 0.59ωp to 0.70ωp for cylindrical inclusions. In the frequency region, the resonant peak can achieve the maximum, according to an optimal structural parameter and volume fraction. The resonant frequency exhibits a redshift with the increasing structural parameter k or volume fraction f or dimensionality factor D.
 Select An Easily Operating Polymer 1×4 Optical Waveguide Switch Matrix Based on Vertical Couplers Kaixin Chen, Pak L Chu, Hau Ping Chan, Kin S. Chiang Chin. Phys. Lett. 2007, 24 (6): 1728-1730 .   Abstract   PDF(pc) (279KB) ( 452 ) A three-dimensional (3D) polymer thermo-optic (TO) 1×4 waveguide switchmatrix based on vertical couplers is demonstrated. It consists of four basic 3D switch units and because of its 3D structure, its construction is compact, only 9mm in length; moreover, the control logic of the entire switch is very simple, the light signal can be easily switched to any output port by operating only a single switch unit. The finished devices exhibit a switching extinction ratio greater than 21dB for all of four output ports and the crosstalk between twoadjacent output ports is lower than -19dB. The rise time and the fall time of the switch matrix are 0.8ms and 1.4ms, respectively. The required electrical power to initiate the switching function for all switching units is about 50mW.
 Select Evolution of Photocurrent during Coadsorption of Cs and O on GaAs (100) ZOU Ji-Jun, CHANG Ben-Kang, YANG Zhi, DU Xiao-Qing, GAO Pin, QIAO Jian-Liang Chin. Phys. Lett. 2007, 24 (6): 1731-1734 .   Abstract   PDF(pc) (340KB) ( 487 ) The photocurrent and spectral response characteristics of gallium arsenide (GaAs) are obtained by a multi-information measurement system, and the evolution of the photocurrent versus the Cs:O flux ratio is investigated. The experimental results show that the photocurrent increases approximately exponentially after the first exposure to Cs until a maximum sensitivity is reached, the detailed evolution process and the ultimate photocurrent are different for different samples. These differences are analysed, and according to the process of coadsorption of Cs and oxygen on GaAs, an equation is presented to explain the increase of photocurrent.
 Select High-Reflectivity AlGaN/AlN Distributed Bragg Reflector in Ultraviolet Region JI Xiao-Li, JIANG Ruo-Lian, XIE Zi-Li, LIU Bin, ZHOU Jian-Jun, LI Liang, HAN Ping, ZHANG Rong, ZHENG You-Dou, GONG Hai-Mei Chin. Phys. Lett. 2007, 24 (6): 1735-1737 .   Abstract   PDF(pc) (485KB) ( 543 ) Thirty-pair Al0.3 Ga 0.7 N/AlN distributed Bragg reflectors centred at 320nm are designed and grown on sapphire substrates by metalorganic chemical vapour deposition. No cracks are observed in the main area of the 2-inch wafer except for about 4mm margin under an optical microscope. Regular stack of alternating layers is shown by scanning electron microscopy. Clear two-dimensional growth steps and very low surface roughness are shown by atomic force microscopy (AFM). Well-defined periodicity is shown by high resolution x-ray diffraction. High reflectivity of 93% at 313nm with a bandwidth of 13nm is obtained.
 Select ZnO Nanostructures Grown on AlN/Sapphire Substrates by MOCVD WEI Hong-Yuan, HU Wei-Guo, ZHANG Pan-Feng, LIU Xiang-Lin, ZHU Qin-Sheng, WANG Zhan-Guo Chin. Phys. Lett. 2007, 24 (6): 1738-1740 .   Abstract   PDF(pc) (517KB) ( 562 ) ZnO nanorods and nanotubes are successful synthesized on AlN/sapphire substrates by metal-organic chemical vapour deposition (MOCVD). The different morphology and structure properties of ZnO nanorods and nanotubes are found to be affected by the AlN under-layer. The photoluminescence spectra show the optical properties of the ZnO nanorods and nanotubes, in which a blueshift of UV emission is observed and is attributed to the surface effect.
 Select Effects of Ag on Electrical Properties of Ag/Ni/p-GaN Ohmic Contact ZHAO De-Sheng, ZHANG Shu-Ming, DUAN Li-Hong, WANG Yu-Tian, JIANG De-Sheng, LIU Wen-Bao, ZHANG Bao-Shun, YANG Hui Chin. Phys. Lett. 2007, 24 (6): 1741-1744 .   Abstract   PDF(pc) (736KB) ( 1723 ) Properties of the Ag/Ni/p-GaN structure at different temperatures are studied by Auger electron spectroscopy, scanning electron microscopy and high resolution x-ray diffraction. The effect of Ag in ohmic contact on the crystalline quality is investigated and the optimized value of annealing temperature is reported. The lowest specific contact resistance of 2.5×10-4Ωcm2 is obtained at annealing temperature of 550°C.
 Select Performance Improvement of GaN Based Schottky Barrier Ultraviolet Photodetector by Adding a Thin AlGaN Window Layer ZHOU Mei, ZHAO De-Gang Chin. Phys. Lett. 2007, 24 (6): 1745-1748 .   Abstract   PDF(pc) (225KB) ( 690 ) We propose a new structure of GaN based Schottky barrier ultraviolet photodetector, in which a thin n-type AlGaN window layer is added on the conventional n--GaN/n+-GaN device structure. The performance of the Schottky barrier ultraviolet photodetector is found to be improved by the new structure. The simulation result shows that the new structure can reduce the negative effect of surface states on the performance of Schottky barrier GaN photodetectors, improving the quantum efficiency and decreasing the dark current. The investigations suggest that the new photodetector can exhibit a better responsivity by choosing a suitably high carrier concentration and thin thickness for the AlGaN window layer.
 Select Effect of Carbon Source with Different Graphitization Degrees on the Synthesis of Diamond LIU Wan-Qiang, MA Hong-An, LI Xiao-Lei, LIANG Zhong-Zhu, LIUMi-Lan, LI Rui, JIA Xiao-Peng, Chin. Phys. Lett. 2007, 24 (6): 1749-1752 .   Abstract   PDF(pc) (493KB) ( 723 ) Using three kinds of graphites with different graphitization degrees as carbon source and Fe--Ni alloy powder as catalyst, the synthesis of diamond crystals is performed in a cubic anvil high-pressure and high-temperature apparatus (SPD-6×1200). Diamond crystals with perfect hexoctahedron shape are successfully synthesized at pressure from 5.0 to 5.5GPa and at temperature from 1570 to 1770K. The synthetic conditions, nucleation, morphology, inclusion and granularity of diamond crystals are studied. The temperature and pressure increase with the increase of the graphitization degree of graphite. The quantity of nucleation and granularity of diamonds decreases with the increase of graphitization degree of graphite under the same synthesis conditions. Moreover, according to the results of the Mossbauerspectrum, the composition of inclusions is mainly Fe3C and Fe-Ni alloy phases in diamond crystals synthesized with three kinds of graphites.
 Select Growth of a Novel Periodic Structure of SiC/AlN Multilayers by Low Pressure Chemical Vapour Deposition ZHAO Yong-Mei, SUN Guo-Sheng, LI Jia-Ye, LIU Xing-Fang, WANG Lei ZHAOWan-Shun, LI Jin-Min Chin. Phys. Lett. 2007, 24 (6): 1753-1755 .   Abstract   PDF(pc) (303KB) ( 381 ) A novel 10-period SiC/AlN multilayered structure with a SiC cap layer is prepared by low pressure chemical vapour deposition (LPCVD). The structure with total film thickness of about 1.45μm is deposited on a Si (111) substrate and shows good surface morphology with a smaller rms surface roughness of 5.3nm. According to the secondary ion mass spectroscopy results, good interface of the 10 period SiC/AlN structure and periodic changes of depth profiles of C, Si, Al, N components are obtained by controlling the growth procedure. The structure exhibits the peak reflectivity close to 30% near the wavelength of 322nm. To the best of our knowledge, this is the first report of growth of the SiC/AlN periodic structure using the home-made LPCVD system.
 Select Photoluminescence Property of Co3O4 Nanowires XUE De-Sheng, GONG Yu, LIU Wen-Jing, SI Ming-Su, LIU Zai-Wen Chin. Phys. Lett. 2007, 24 (6): 1756-1758 .   Abstract   PDF(pc) (324KB) ( 670 ) Co3O4 nanowire arrays are fabricated by electrodeposition with following heat-treatment in atmosphere ambient. Photoluminescence is investigated at 295K. In the experiment, when increasing the excitation light wavelength from 260nm to 360nm, two kinds of emissions corresponding to the increasing excitation light wavelength are observed. One of them alters the excited emission position, another keeps its emission position. The distinct behaviour of excited emissions related to the increasing excitation wavelength indicatesthat the mechanism of them must be different. According to the experimental comparison and first-principle calculation, the two kinds of emissions are discussed.
 Select Electron Backscattered Diffraction of Transgranular Crack Propagation in Soft Steel A. Boumaiza, T. Baudin, N. Rouag, R. Penelle Chin. Phys. Lett. 2007, 24 (6): 1759-1762 .   Abstract   PDF(pc) (899KB) ( 612 ) We consider the crack propagation in a soft steel sheet during the formation. The drawability is considered in relation with the structural anisotropy, the mechanical behaviour is related to both the grain morphology and the texture. The structure heterogeneity could lead to the apparition of micro-cracks. The results show the texture effect on the crack propagation and on the crack arrest in soft steel during the formation. The EBSD technique allows to show that the adjustment of the grain orientation from the initial main component {111}<112> towards the deformation orientation {111}<110> incites a trans-granular crack through a grain with initial {111}<112> orientation in a globally ductile material. It is the presence of grains with{111}1<110> orientation which permits the closing of micro-cracks.
 Select Evaluation of Influence of Multiple Scattering Effect in Light-Scattering-Based Applications XU Sheng-Hua, SUN Zhi-Wei Chin. Phys. Lett. 2007, 24 (6): 1763-1766 .   Abstract   PDF(pc) (242KB) ( 432 ) The extinction cross sections of a system containing two particles are calculated by the T-matrix method, and the results are compared with those of two single particles with single-scattering approximation. The necessity of the correction of the refractive indices of water and polystyrene for different incident wavelengths is particularly addressed in the calculation. By this means, the volume fractions allowed for certain accuracy requirements of single-scattering approximation in the light scattering experiment can be evaluated. The volume fractions calculated with corrected refractive indices are compared with those obtained with fixed refractive indices which have been rather commonly used, showing that fixed refractive indices may cause significant error in evaluating multiple scattering effect. The results also give a simple criterion for selecting the incident wavelength and particle size to avoid the blind zone' in the turbidity measurement, where the turbidity change is insensitive to aggregation of two particles.
 Select Three-Dimensional Reconstruction of Icosahedral Virus by Symmetry-Adapted Functions LIU Hong-Rong, YANG Qi-Bin, CHENG Ling-Peng, ZENG Song-Jun, CAI Can-Ying Chin. Phys. Lett. 2007, 24 (6): 1767-1770 .   Abstract   PDF(pc) (876KB) ( 375 ) A three-dimensional (3D) reconstruction of icosahedral virus is carried out by the icosahedral symmetry-adapted function (ISAF) method in spherical coordinates. In order to reduce the influence of noise, it is better to use the basis functions that have identical symmetry with the object reconstructed. It is verified that the ISAF method has stronger ability to reduce the influence of noise to grain the resolution better than that of the conventional method by the simulation of 3D reconstruction.
 Select Oscillatory Activities in Regulatory Biological Networks and Hopf Bifurcation YAN Shi-Wei, , WANG Qi, XIE Bai-Song, ZHANG Feng-Shou, Chin. Phys. Lett. 2007, 24 (6): 1771-1774 .   Abstract   PDF(pc) (235KB) ( 382 ) Exploiting the nonlinear dynamics in the negative feedback loop, we propose a statistical signal-response model to describe the different oscillatory behaviour in a biological network motif. By choosing the delay as a bifurcation parameter, we discuss the existence of Hopf bifurcation and the stability of the periodic solutions of model equations with the centre manifold theorem and the normal form theory. It is shown that a periodic solution is born in a Hopf bifurcation beyond a critical time delay, and thus the bifurcation phenomenon may be important to elucidate the mechanism of oscillatory activities in regulatory biological networks.
 Select Ionizing Dose Effect of Thermal Oxides Implanted with Si+ Ions CHEN Ming, LUO Hong-Wei, ZHANG Zheng-Xuan, ZHANG En-Xia, YANG Hui, TIAN Hao, WANG Ru, YU Wen-Jie, Chin. Phys. Lett. 2007, 24 (6): 1775-1777 .   Abstract   PDF(pc) (252KB) ( 358 ) Total ionizing dose effects of Si+ ion implanted thermal oxides are studied by 10keV x-ray irradiation. Photoluminescence (PL) method is engaged to investigate nanostructures of samples. Ar+ implanted samples are also studied by the same way to provide a comparison. The results show that Si+ implantation following with high temperature annealing can significantly reduce the radiation induced flatband shift, which is caused by net positive charge accumulation in oxides. This reduction is attributed to the formation of Si nanoscale structures. Ar+ implantation is also found to reduce the radiation induced flatband shift, while it is different that the reduction with Si+ implantation shows little dependence on implant dose of Ar+ ions. This is explained by possible increase of recombination centres.
 Select Noise Behaviour of a THz Superconducting Hot-Electron Bolometer Mixer ZHANG Wen, LI Ning, JIANG Ling, MIAO Wei, LIN Zhen-Hui, YAOQi-Jun, SHI Sheng-Cai, CHEN Jian, WU Pei-Heng, S. I. Svechnikov, Yu. B. Vachtomin, S. V. Antipov, B. M. Voronov, G. N. Gol'tsman Chin. Phys. Lett. 2007, 24 (6): 1778-1781 .   Abstract   PDF(pc) (452KB) ( 579 ) A quasi-optical superconducting NbN hot-electron bolometer (HEB) mixer is measured in the frequency range of 0.5--2.5THz for understanding of the frequency dependence of noise temperature of THz coherent detectors. It has been found that noise temperature increasing with frequency is mainly due to the coupling loss between the quasi-optical planar antenna and the superconducting HEB bridge when taking account of non-uniform distribution of high-frequency current. With the coupling loss corrected, the superconducting HEB mixer demonstrates a noise temperature nearly independent of frequency.
 Select Observation Constraints on the Simplified GCG Model DONG Su-Mei, WU Pu-Xun Chin. Phys. Lett. 2007, 24 (6): 1782-1785 .   Abstract   PDF(pc) (281KB) ( 689 ) A simplified version of generalized Chaplygin gas (GCG) as a dark energy model is studied. By using the latest 162 ESSENCE type Ia supernovae (Sne Ia) data, 30 high redshift Sne Ia data, the baryonic acoustic oscillation peak from SDSS and the CMB data from WMAP3, a strong constraint on this simplified GCG model is obtained. At the 95.4% confidence level we obtain 0.21≤Ωm≤0.31 and 0.994≤α≤1.0 with the best fit Ωm=0.25 and α=1. This best fit scenario corresponds to an accelerating universe with q0≌-0.65 and z≌0.81 (a redshift of cosmic phase transition from deceleration to acceleration).
 Select Comment on `Electronic Properties of Red P-Type Tl2S5 Single Crystals' M. Cankurtaran, H. Celik Chin. Phys. Lett. 2007, 24 (6): 1786-1786 .   Abstract   PDF(pc) (148KB) ( 423 ) Recently, Gamal et al. [Chin. Phys. Lett. 22 (2005) 1530] reported the results of electrical conductivity, Hall effect and thermoelectric measurements on p-type Tl2S5 single crystals. From the experimental data for the temperature dependence of differential thermoelectric power, Gamal et al. determined thevalues of 2.66×10-41kg and 2.50×10-41kg, respectively, for the effective masses of electrons and holes in p-type Tl2S5, which are about ten orders of magnitude smaller than the free electron mass (9.11×10-31kg). We argue that the anomalously small values obtained for the effective mass of chargecarriers in Tl2S5 have no physical significance.
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