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Volume 27 Issue 2
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GENERAL
 Select Exact Solutions for Two Equation Hierarchies ZHAO Song-Lin, ZHANG Da-Jun, JI Jie Chin. Phys. Lett. 2010, 27 (2): 020201 .   DOI: 10.1088/0256-307X/27/2/020201 Abstract   PDF(pc) (320KB) ( 856 ) Bilinear forms and double-Wronskian solutions are given for two hierarchies, the (2+1)-dimensional breaking Ablowitz-Kaup-Newell-Segur (AKNS) hierarchy and the negative order AKNS hierarchy. According to some choices of the coefficient matrix in the Wronskian condition equation set, we obtain some kinds of solutions for these two hierarchies, such as solitons, Jordan block solutions, rational solutions, complexitons and mixed solutions.
 Select Lie Point Symmetries and Exact Solutions of the Coupled Volterra System LIU Ping, LOU Sen-Yue, Chin. Phys. Lett. 2010, 27 (2): 020202 .   DOI: 10.1088/0256-307X/27/2/020202 Abstract   PDF(pc) (612KB) ( 648 ) The coupled Volterra system, an integrable discrete form of a coupled Korteweg-de Vries (KdV) system applied widely in fluids, Bose-Einstein condensation and atmospheric dynamics, is studied with the help of the Lie point symmetries. Two types of delayed differential reduction systems are derived from the coupled Volterra system by means of the symmetry reduction approach and symbolic computation. Cnoidal wave and solitary wave solutions for a delayed differential reduction system and the coupled Volterra system are proposed, respectively.
 Select Realizing the Underlying Quantum Dynamical Algebra SU(2) in Morse Potential WANG Xue-Hong, LIU Yu-Bin Chin. Phys. Lett. 2010, 27 (2): 020301 .   DOI: 10.1088/0256-307X/27/2/020301 Abstract   PDF(pc) (312KB) ( 508 ) We establish an underlying quantum dynamical algebra SU(2) for a one-dimensional Morse potential.
 Select Universal Quantum Cloning Machine in Circuit Quantum Electrodynamics LV Dan-Dan, LU Hong, YU Ya-Fei, FENG Xun-Li, ZHANG Zhi-Ming, Chin. Phys. Lett. 2010, 27 (2): 020302 .   DOI: 10.1088/0256-307X/27/2/020302 Abstract   PDF(pc) (356KB) ( 447 ) We propose a scheme for realizing the 1→2 universal quantum cloning machine (UQCM) with superconducting quantum interference device (SQUID) qubits in circuit quantum electrodynamics (circuit QED). In this scheme, in order to implement UQCM, we only need phase shift gate operation on SQUID qubits and the Raman transitions. The cavity number we need is only one. Thus our scheme is simple and has advantages in the experimental realization. Furthermore, both the cavity and the SQUID qubits are virtually excited, so the decoherence can be neglected.
 Select Statistical Mechanical Entropy of a (4+n)-Dimensional Static Spherically Symmetric Black Hole ZHAO Fan, HE Feng Chin. Phys. Lett. 2010, 27 (2): 020401 .   DOI: 10.1088/0256-307X/27/2/020401 Abstract   PDF(pc) (300KB) ( 434 ) Supported by the Graduate Student Creative Foundation of HunanUniversity of Science and Technology under Grant No S080111, ScientificResearch Foundation for the Returned Overseas Chinese Scholars from StateEducation Ministry of China under Grant No 527[2004]) and the HunanProvincial Natural Science Foundation under Grant No 06JJ2026.
 Select Cosmological Gravitational Wave in de Sitter Spacetime LIU Liao Chin. Phys. Lett. 2010, 27 (2): 020402 .   DOI: 10.1088/0256-307X/27/2/020402 Abstract   PDF(pc) (244KB) ( 456 ) Since there is always an incorrect sign in the mass of the graviton in the so-called perturbation expansion approximation of de Sitter spacetime, the existence of a gravitational wave from the metric perturbation of de Sitter spacetime is doubtful. We try to take another way to start from the assumption that the cosmological gravitation wave equation should be both general covariant and conformal invariant. It is found that the so-called conformal gravitation is no longer part of the metric field and it has an effective mass of mg =√R/6 =√2Λ/3 with the correct sign in de Sitter spacetime, though its intrinsic mass remains zero.
 Select Fuzzy Modeling and Impulsive Control of a Memristor-Based Chaotic System ZHONG Qi-Shui, YU Yong-Bin, YU Jue-Bang Chin. Phys. Lett. 2010, 27 (2): 020501 .   DOI: 10.1088/0256-307X/27/2/020501 Abstract   PDF(pc) (438KB) ( 886 ) We mainly investigate the issues of fuzzy modeling and impulsive control of a memristor-based chaotic system and present a memristor-based chaotic system as the Takagi-Sugeno model-based fuzzy system. Then, based on the impulsive control theory of dynamical systems, a criterion ensuring impulsive stabilization of the memristor-based chaotic system is derived for the first time. An illustrative example is given to verify the effectiveness of the control scheme.
 Select Synchronization Control of Two Different Chaotic Systems with Known and Unknown Parameters GUAN Jun-Biao Chin. Phys. Lett. 2010, 27 (2): 020502 .   DOI: 10.1088/0256-307X/27/2/020502 Abstract   PDF(pc) (507KB) ( 536 ) Chaos synchronization of two different chaotic systems with known and unknown parameters is studied. Based on the Lyapunov stability theory, two different chaotic systems with known parameters realize global synchronization via the successfully designed nonlinear controller. By employing an adaptive synchronization scheme, the synchronization of two different chaotic systems with unknown parameters is achieved. Numerical simulations validate the effectiveness of the theoretical analysis.
 Select Noise Effects on Temperature Encoding of Neuronal Spike Trains in a Cold Receptor DU Ying, LU Qi-Shao Chin. Phys. Lett. 2010, 27 (2): 020503 .   DOI: 10.1088/0256-307X/27/2/020503 Abstract   PDF(pc) (698KB) ( 414 ) We examine how noise interacts with encoding mechanisms of neuronal stimulus in a cold receptor. From ISI series and bifurcation diagrams it is shown that there are considerable differences in interval distributions and impulse patterns caused by purely deterministic simulations and noisy simulations. The ISI-distance can be used as an effective and powerful way to measure the noise effects on spike trains of the cold receptor quantitatively. It is also found that spike trains observed in cold receptors can be more strongly affected by noise for low temperatures than for high temperatures in some aspects; meanwhile, the spike train has greater variability with increasing noise intensity.
 Select Analysis of Chaotic Dynamics in a Two-Dimensional Sine Square Map XU Jie, LONG Ke-Ping, FOURNIER-PRUNARET Daniele, TAHA Abdel-Kaddous, CHARGE Pascal Chin. Phys. Lett. 2010, 27 (2): 020504 .   DOI: 10.1088/0256-307X/27/2/020504 Abstract   PDF(pc) (1553KB) ( 469 ) We study an N-dimensional system based upon a sine map, which is related to the simplified model of an opto-electronic system. The system behavior is analyzed with the tools of nonlinear dynamics (bifurcations in the parameter plane, critical manifolds, basins of attraction, chaotic attractors). Our study relies on a two-dimensional system (N=2). It is interesting that this system shows the existence of bounded chaotic orbits, which can be considered for secure transmissions.
 Select Periodic, Quasiperiodic and Chaotic q-Breathers in a Fermi-Pasta-Ulam Lattice XU Quan, TIAN Qiang Chin. Phys. Lett. 2010, 27 (2): 020505 .   DOI: 10.1088/0256-307X/27/2/020505 Abstract   PDF(pc) (457KB) ( 413 ) We study the features of a single q-breather (SQB) in a Fermi-Pasta-Ulam lattice by the numerical method, and obtain that the stability of SQB correlates to coupling constant K and nonlinear parameter β. No matter whether K or β increases, the periodic SQB can be transformed into a quasiperiodic SQB or a chaotic SQB. We also obtain the conditions of excitation of periodic, quasiperiodic and chaotic SQBs.
 Select Spinless Bosons in a 1D Harmonic Trap with Repulsive Delta Function Interparticle Interaction II: Numerical Solutions MA Zhong-Qi, C. N. Yang, Chin. Phys. Lett. 2010, 27 (2): 020506 .   DOI: 10.1088/0256-307X/27/2/020506 Abstract   PDF(pc) (424KB) ( 560 ) Following the general theory developed in paper I [Chin. Phys. Lett. 26 (2009) 120506] we present here the numerical results for an N spinless boson system in a 1D harmonic trap with repulsive delta function interparticle interaction as N→∞, with √N/g= fixed.
 Select Spectrum Analysis and Circuit Implementation of a New 3D Chaotic System with Novel Chaotic Attractors DONG Gao-Gao, ZHENG Song, TIAN Li-Xin, DU Rui-Jin, Chin. Phys. Lett. 2010, 27 (2): 020507 .   DOI: 10.1088/0256-307X/27/2/020507 Abstract   PDF(pc) (2078KB) ( 651 ) The new autonomous system with only three equilibrium points is introduced. This system does not belong to the generalized Lorenz systems. The novel attractors are observed over a large range of parameters, which have rarely been reported in previous work. As an important component in chaotic signal generators, a physical circuit has been designed. The experimental results are in agreement with numerical simulations. More significantly, spectral analysis shows that the system has an extremely broad frequency spectral bandwidth in 0-131.6 Hz, without investigating any possible electronic techniques, which is more desirable for secure communications.
 Select A Scheme for Information Erasure in a Double-Well Potential WANG Xin-Xin, BAO Jing-Dong Chin. Phys. Lett. 2010, 27 (2): 020508 .   DOI: 10.1088/0256-307X/27/2/020508 Abstract   PDF(pc) (535KB) ( 502 ) We design an experimental scheme to realize one-bit information erasure and restoring processes by considering an overdamped colloidal particle in a double-well optical trap, which is added by a controllable laser tweezer. Using the Monte Carlo method, we simulate numerically the Langevin equation to calculate the mean work spent during the entire process and validate the entropy production fluctuation theory. Our result shows that the distribution of entropy production becomes narrow with increasing temperature and becomes stationary, represents the diminishing extent of irreversibility.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
 Select Transition Temperature of Lattice Quantum Chromodynamics with Two Flavors with a Small Chemical Potential WU Liang-Kai Chin. Phys. Lett. 2010, 27 (2): 021101 .   DOI: 10.1088/0256-307X/27/2/021101 Abstract   PDF(pc) (519KB) ( 501 ) We present the results for the transition temperature of quantum chromodynamics with two degenerate flavors (Nf=2) of Wilson quarks as a function of a small baryon chemical potential μB from Monte Carlo simulations at κ=0.175, κ is the hopping parameter. By using the imaginary chemical potential for which the fermion determinant is positive and the Ferrenberg-Swendsen reweighting method, we perform simulations on lattice 83×4 with 4 being the temporal extent. By analytic continuation of the data to the real chemical potential μ, we obtain the transition temperature for the small chemical potential, and compare our results with others.
NUCLEAR PHYSICS
 Select Lifetimes of High Spin States in an Odd-Proton Nucleus 129Cs WANG Lie-Lin, ZHU Li-Hua, LU Jing-Bin, WU Xiao-Guang, LI Guang-Sheng, HAO Xin, ZHENG Yun, HE Chuang-Ye, WANG Lei, LI Xue-Qin, LIU Ying, PAN Bo, ZHAO Yan-Xin, LI Zhong-Yu, DING Huai-Bo Chin. Phys. Lett. 2010, 27 (2): 022101 .   DOI: 10.1088/0256-307X/27/2/022101 Abstract   PDF(pc) (466KB) ( 462 )
 Select Nuclear Structure and Magnetic Moment of the Unstable 12B-12N Mirror Pair ZHENG Yong-Nan, ZHOU Dong-Mei, YUAN Da-Qing, ZUO Yi, FAN Ping, M. Mihara, K. Matsuta, M. Fukuda, T. Minamisono, T. Suzuki, XU Yong-Jun, ZHU Jia-Zheng, WANG Zhi-Qiang, LUO Hai-Long, ZHANG Xi-Zhen, ZHU Sheng-Yun Chin. Phys. Lett. 2010, 27 (2): 022102 .   DOI: 10.1088/0256-307X/27/2/022102 Abstract   PDF(pc) (351KB) ( 492 ) Magnetic moments of the A=12 unstable mirror pair nuclides 12B and 12N have been measured by the β-NMR technique. The experimentally measured magnetic moments are μ(12B)=1.001(17)μN and μ(12N)=0.4571(1)μN. The improved shell model using an SFO Hamiltonian with enhanced spin-isospin monopole proton-neutron interaction and modified single-particle energies is employed to calculate the magnetic moments of 12B and 12N. The calculation yields μ (12B)=0.929μN and μ(12N)=0.452μN and has produced a new magic number 6 for the short-lived unstable mirror pair nuclides 12B and 12N.
 Select Clustering Structure of 10Be Studied with the Deformed RMF+BCS Method ZHONG Ming-Fei, LI Jia-Xing, ZHANG Deng-Gao, HAN Rui, JI Juan-Xia, CHEN Li-Xiang Chin. Phys. Lett. 2010, 27 (2): 022103 .   DOI: 10.1088/0256-307X/27/2/022103 Abstract   PDF(pc) (402KB) ( 514 ) We investigate the nucleus 10Be using the deformed relativistic mean field (RMF) model and BCS theory. The calculated density distribution suggests two α clusters in the nucleus 10Be. According to BCS theory, the two valence neutrons transit to the first excited state 02+ in a pair and form a 2-n cluster. By comparing the two neutron separation energy (S2n) with the single neutron separation energy (Sn), and analyzing the difference between the neutron and proton rms radii (Rn-Rp) calculated by the deformed RMF, we suggest that 10Be is the best candidate for a two-neutron skin. The two-neutron skin clings to the 2α clusters closely and makes the two α clusters have cross and chain distribution.
 Select Observation of a Possible New Isomer in 175Ir WANG Hua-Lei, SONG Li-Tao, ZHAO Wei-Juan, LIU Zhong-Xia, ZHANG Yu-Hu, ZHOU Xiao-Hong, GUO Ying-Xiang, LEI Xiang-Guo Chin. Phys. Lett. 2010, 27 (2): 022301 .   DOI: 10.1088/0256-307X/27/2/022301 Abstract   PDF(pc) (618KB) ( 491 ) The neutron deficient nuclide 175Ir was produced by irradiation of 146Nd with 210 MeV 35Cl via a fusion-evaporation reaction channel. The reaction products were transported to a low-background location using a helium-jet recoil fast-moving tape-transport system for measurement. The experimental devices and data analysis method are introduced. Based on the decay-curve fitting of the β-delayed γ ray from 175Ir, realized by the least-square method, a new long-lived isomeric state of 175Ir is proposed and briefly discussed.
 Select Interferometry Signatures for QCD First-Order Phase Transition in High Energy Heavy Ion Collisions YU Li-Li, M. J. Efaaf, ZHANG Wei-Ning, Chin. Phys. Lett. 2010, 27 (2): 022501 .   DOI: 10.1088/0256-307X/27/2/022501 Abstract   PDF(pc) (400KB) ( 448 ) Using the technique of quantum transport of the interfering pair we examine the Hanbury-Brown-Twiss (HBT) interferometry signatures for the particle-emitting sources of pions and kaons produced in heavy ion collisions at 10-30 AGeV. The evolution of the sources is described by relativistic hydrodynamics with the first-order phase transition from quark-gluon plasma (QGP) to hadronic matter. We use quantum probability amplitudes in a path-integral formalism to calculate the two-particle correlation functions, where the effects of particle decay and multiple scattering are taken into consideration. Our model-calculated results indicate that both the HBT radii of pions and kaons increase with the system initial energy density. The HBT lifetimes of the pion and kaon sources increase significantly when the initial energy density is tuned to the phase boundary between the QGP and mixed phase. This increase of HBT lifetimes will likely appear in heavy ion collisions with an incident energy between 10-30 AGeV.
ATOMIC AND MOLECULAR PHYSICS
 Select Dynamics of a Rydberg Hydrogen Atom in a Generalized van der Waals Potential and a Magnetic Field WANG De-Hua Chin. Phys. Lett. 2010, 27 (2): 023201 .   DOI: 10.1088/0256-307X/27/2/023201 Abstract   PDF(pc) (5386KB) ( 431 ) The classical dynamics of a Rydberg hydrogen atom in a generalized van der Waals potential plus a magnetic field is investigated by using the Poincaré surface of section and phase space trajectories method. The dynamical character of this system depends sensitively on the magnetic field strength. The numerical calculations show that for a certain van der Waals potential, its classical dynamics is regular without the external magnetic field. However, with the addition of the external magnetic field, the dynamical property of the Rydberg hydrogen atom begins to change. With the increase of the magnetic field strength, order-chaos-order-chaos types of transition regions are observed for the hydrogen atom. As the magnetic field strength is very large, nearly all the phase space trajectories are chaotic. Under this condition, only chaotic motion appears. This is caused by the diamagnetic Zeeman effect. Our study provides a different perspective on the dynamical behavior of the Rydberg atom in the van der Waals potential and magnetic field.
 Select Elastic Scattering of Ultracold 23Na and 39K Atoms in the Singlet State HU Qiu-Bo, ZHANG Yong-Sheng, SUN Jin-Feng Chin. Phys. Lett. 2010, 27 (2): 023202 .   DOI: 10.1088/0256-307X/27/2/023202 Abstract   PDF(pc) (386KB) ( 435 ) The elastic scattering properties for collisions between ultracold 23Na and 39K atoms in the singlet state are investigated. Based on the recent theoretical and experimental results, the improved hybrid potential is presented for the singlet X1Σg+ ground state of NaK. By means of the Numerov and semiclassical methods, the values of the s-wave scattering length a for the singlet state are calculated to be 33.3757a0 and 37.9399a0, respectively. Pronounced shape resonances appear for the l = 1 partial wave for the X1Σg+ state. In addition, the s-wave scattering cross section, total cross section and energy positions of shape resonances for the X1Σg+ state are discussed.
 Select Continuous Imaging of a Single Neutral Atom in a Variant Magneto-Optical Trap\hyperlinks* XIA Tian, ZHOU Shu-Yu, CHEN Peng, LI Lin, HONG Tao, WANG Yu-Zhu Chin. Phys. Lett. 2010, 27 (2): 023701 .   DOI: 10.1088/0256-307X/27/2/023701 Abstract   PDF(pc) (499KB) ( 414 ) We demonstrate continuous imaging of a single 87Rb atom confined in a steep magneto-optical trap with an electron-multiplying charge-coupled device (EMCCD) camera and realize a one-dimensional micro-optical trap array with a Dammann grating. We adopt several methods to reduce the noise in the fluorescence signal we obtain with the EMCCD. Step jumping characteristics of the fluorescence demonstrate capturing and losing of individual atoms.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
 Select High Efficiency Multi-kW Diode-Side-Pumped Nd:YAG Laser with Reduced Thermal Effect XU Yi-Ting, XU Jia-Lin, CUI Qian-Jin, XIE Shi-Yong, LU Yuan-Fu, BO Yong, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan Chin. Phys. Lett. 2010, 27 (2): 024201 .   DOI: 10.1088/0256-307X/27/2/024201 Abstract   PDF(pc) (477KB) ( 650 ) We demonstrate a high efficiency multi-kW diode-side-pumped Nd:YAG laser. High cooling efficiency of the diode-side-pumped module in the laser is achieved. The middle portion of the Nd:YAG rod in the module is cooled by a coolant jet with screwed side surface, and the end-caps of the rod without screwed side surface are cooled by Au coated on the surface. The thermal effect of the laser rod is reduced, which leads to high output power with high optical-optical conversion efficiency. By using three identical Nd:YAG laser modules, an output power of 4.2 kW and beam quality of 58 mm・mrad with an optical-optical efficiency of 35% at 1064 nm is obtained in a laser oscillator. By using four identical Nd:YAG laser modules, an output power of 3.1 kW and beam quality of 17 mm・mrad with an optical-optical efficiency of 25.8% is demonstrated in a master oscillator power-amplifier system.
 Select Characterizations of Stress and Strain Variation in Three-Dimensional Forming of Laser Micro-Manufacturing ZHOU Ming, ZHAO Guo-Huan, HUANG Tao, DING Hua, CAI Lan Chin. Phys. Lett. 2010, 27 (2): 024202 .   DOI: 10.1088/0256-307X/27/2/024202 Abstract   PDF(pc) (893KB) ( 450 ) A micro-manufacturing technology is presented to form three-dimensional metallic micro-structures directly. Micro grid array structures are replicated on a metallic foil surface, with high spatial resolution in micron levels. The numerical simulation results indicate that the material deformation process is characterized by an ultrahigh strain rate. With increasing pulse duration, the sample absorption strain energy increases, and the sample deformation degree enlarges. The stress state of the central point fluctuates between tensile stress and compression stress. The stress state of the angular point is altered from compressive stress to tensile stress due to geometry and loading conditions. The duration length of pulse stress has an effect on the stress state, as with the increase of pulse duration, fluctuation in the stress state decreases. Therefore, laser micro-manufacturing technology will be a potential laser micro forming method which is characterized by low cost and high efficiency.
 Select Self-Collimation in Planar Photonic Crystals Fabricated by CMOS Technology YANG Zhi-Feng, WU Ai-Min, FANG Na, JIANG Xun-Ya, LIN Xu-Lin, WANG Xi, ZOU Shi-Chang Chin. Phys. Lett. 2010, 27 (2): 024203 .   DOI: 10.1088/0256-307X/27/2/024203 Abstract   PDF(pc) (439KB) ( 438 ) We report a self-collimating demonstration in planar photonic crystals (PhCs) fabricated in silicon-on-insulator (SOI) wafers using 0.18 μm silicon complimentary metal oxide semiconductor (CMOS) techniques. The emphasis was on demonstrating the self-collimation effect by using the standard CMOS equipment and process development of an optical test chip using a high-volume manufacturing facility. The PhCs are designed on the 230-nm-top-Si layer using a square lattice of air holes 280 nm in diameter. The lattice constant of the PhCs is 380 nm. The experimentally obtained wavelengths for self-collimation are in excellent agreement with theory.
 Select Photoinduced Reorientation Process and Nonlinear Optical Properties of Ag Nanoparticle Doped Azo Polymer Films DENG Yan, SHEN Jing Chin. Phys. Lett. 2010, 27 (2): 024204 .   DOI: 10.1088/0256-307X/27/2/024204 Abstract   PDF(pc) (358KB) ( 549 ) Azobenzene polymer films doped with and without Ag nanoparticles are prepared. The photoinduced reorientation process is investigated by using an Nd:YVO4 pump beam at 532 nm and a low semiconductor laser beam at 650 nm. The reorientation rate of azo polymer films is enhanced in the presence of Ag nanoparticles, and the rate of the azo polymer film with Ag concentration of 2.2 μg/ml is larger than that of the azo polymer films with Ag concentrations of 1.1 μg/ml and 4.4 μg/ml. The third-order nonlinear optical properties of the Ag/azo composite film are obtained by the Z-scan technique at a wavelength of 532 nm, and the measured nonlinear refractive index is 9.258×10-9 esu. It is shown that the main mechanisms involved in the large nonlinear optical responses come from the local field enhancement of Ag nanoparticles and the nonlinear effect of the azo polymer matrix.
 Select A Transverse-Longitudinal Cross-Spectral Density Matrix of Partially Coherent Electromagnetic Beams LI Jian-Long, TANG Shi-Hong, LU Bai-Da Chin. Phys. Lett. 2010, 27 (2): 024205 .   DOI: 10.1088/0256-307X/27/2/024205 Abstract   PDF(pc) (365KB) ( 428 ) A transverse-longitudinal cross-spectral density matrix (TLCSDM) of partially coherent electromagnetic beams is proposed. It can extend the traditional Stokes parameters and polarization singularities from the paraxial field to the more general situation. The impact produced by the atmospheric turbulence on polarization singularities of the partially coherent electromagnetic vortex beams is analyzed with the TLCSDM.
 Select A Single-Fundamental-Mode Photonic Crystal Vertical Cavity Surface Emitting Laser XIE Yi-Yang, XU Chen, KAN Qiang, WANG Chun-Xia, LIU Ying-Ming, WANG Bao-Qiang, CHEN Hong-Da, SHEN Guang-Di Chin. Phys. Lett. 2010, 27 (2): 024206 .   DOI: 10.1088/0256-307X/27/2/024206 Abstract   PDF(pc) (562KB) ( 592 ) Single-fundamental-mode photonic crystal (PhC) vertical cavity surface emitting lasers (VCSEL) are produced and their single-fundamental-mode performances are investigated and demonstrated. A two-dimensional PhC with single-point-defect structure is fabricated using UV photolithography and inductive coupled plasma reactive ion etching on the surface of the VCSEL's top distributed Bragg-reflector. The PhC VCSEL maintains single-fundamental-mode operating with output power 1.7 mW and threshold current 2.5 mA. The full width half maximum of the lasing spectrum is less than 0.1 nm, the far field divergence angle is less than 10° and the side mode suppression ratio is over 35 dB. The device characteristics are analyzed based on the effective index model of the photonic crystal fiber. The experimental results agree well with the theoretical expectation.
 Select Theoretical Studies of Optical Properties of Silver Nanoparticles MA Ye-Wan, WU Zhao-Wang, ZHANG Li-Hua, ZHANG Jie Chin. Phys. Lett. 2010, 27 (2): 024207 .   DOI: 10.1088/0256-307X/27/2/024207 Abstract   PDF(pc) (338KB) ( 1708 ) Optical properties of silver nanoparticles such as extinction, absorption and scattering efficiencies are studied based on Green's function theory. The numerical simulation results show that optical properties of silver nanoparticles are mainly dependent on their sizes and geometries; the localized plasmon resonance peak is red shifted when the dielectric constant of the particle's surrounding medium increases or when a substrate is presented. The influences of wave polarizations, the incident angles of light, the composite silver and multiply-layers on the plasmon resonance are also reported. The numerical simulation of optical spectra is a very useful tool for nanoparticle growth and characterization.
 Select Micro Extrinsic Fiber-Optic Fabry-Perot Interferometric Sensor Based on Erbium- and Boron-Doped Fibers RAO Yun-Jiang, XU Bing, RAN Zeng-Ling, GONG Yuan Chin. Phys. Lett. 2010, 27 (2): 024208 .   DOI: 10.1088/0256-307X/27/2/024208 Abstract   PDF(pc) (392KB) ( 640 ) Micro extrinsic Fabry-Perot interferometers (MEFPIs), with cavity lengths of up to ~ 9 μm and maximum fringe contrast of ~19 dB, are fabricated by chemically etching Er- and B-doped optical fibers and then splicing the etched fiber to a single-mode fiber, for the first time to the best of our knowledge. The strain and temperature responses of the MEFPI sensors are investigated experimentally. Good linearity and high sensitivity are achieved. Such a type of MEFPI sensor is cost-effective and suitable for mass production, indicating its great potential for a wide range of applications.
 Select Double-Arched LD Array Stagger Pumped Electro-Optic Q-Switched Nd:YAG Laser without Water Cooling CHEN Xin-Yu, JIN Guang-Yong, YU Yong-Ji, WANG Chao, HAO Da-Wei, WANG Yi-Bo Chin. Phys. Lett. 2010, 27 (2): 024209 .   DOI: 10.1088/0256-307X/27/2/024209 Abstract   PDF(pc) (411KB) ( 741 ) We report an experimental study on a double-arched LD array stagger pumped electro-optic Q-switched Nd:YAG laser without water cooling by using a convex-concave compensate resonator. Perfect matching of the gain field inside the rod and the fundamental mode of the cavity is made by this structure. When the repetition rate is 20 Hz, A maximum output energy at 1064 nm wavelength of 176 mJ (M2=1.55) and 9.6 ns FWHM pulse width in fundamental mode Q-switch operation is obtained with LD injection current 120 A. The optical-optical conversion efficiency is 14.7%, the divergence angle of the output beam is about 1.8 mrad.
 Select Wavelet-Transform Spectrum for Quantum Optical States SONG Jun, FAN Hong-Yi Chin. Phys. Lett. 2010, 27 (2): 024210 .   DOI: 10.1088/0256-307X/27/2/024210 Abstract   PDF(pc) (1210KB) ( 519 ) In the context of quantum mechanics we employ the technique of integration within an ordered product of operators to recast the classical wavelet transform to a squeezing-displacing transform between the mother wavelet vector and the state vector to be transformed. In this way we propose the wavelet-transform spectrum for quantum optical states. For some typical states we obtain numerical results which imply that the spectrum can be used to recognize a variety of quantum optical states, and the inverse wavelet transform has the possibility to play a role in quantum state engineering.
 Select An Efficient Pulsed CH3OH Terahertz Laser Pumped by a TEA CO2 Laser JIU Zhi-Xian, ZUO Du-Luo, MIAO Liang, QI Chun-Chao, CHENG Zu-Hai Chin. Phys. Lett. 2010, 27 (2): 024211 .   DOI: 10.1088/0256-307X/27/2/024211 Abstract   PDF(pc) (401KB) ( 785 ) An efficient pulsed CH3OH terahertz (THz) laser pumped by a TEA CO2 laser is investigated experimentally. To improve photon conversion efficiency and THz laser energy, two cavity configurations of the TEA CO2 laser, which is external and semi-external, are evaluated. The pump intensities are about 4.7 MW/cm2 and 1.2 MW/cm2, respectively. Higher pump intensity and more stable single lines are obtained in the external cavity. For the 3.8 J pump energy of the 9P(16) transition in the external cavity, the maximum terahertz output energy with 570.5 μm wavelength at 160 Pa is 431 μJ. With a 6 J energy pulse in terms of a semi-external cavity, a 353 μJ terahertz emission (570.5 μm) is produced. The corresponding photon conversion efficiencies are 1.36% and 0.705%, increasing by a factor of about 2.
 Select High Current Operation of a Semi-insulating Gallium Arsenide Photoconductive Semiconductor Switch Triggering a Spark Gap XU Ming, SHI Wei, HOU Lei, XUE Hong, WU Shen-Jiang, DAI Hui-Ying Chin. Phys. Lett. 2010, 27 (2): 024212 .   DOI: 10.1088/0256-307X/27/2/024212 Abstract   PDF(pc) (340KB) ( 1278 ) A transient peak current as high as 5.6 kA is obtained by a GaAs photoconductive semiconductor switch (PCSS) in series with a spark gap. Based on the characteristics of the GaAs PCSS, mechanisms of discharge between the PCSS and the spark gap are discussed. It is implied that a hybrid operation mode of photo-activated charge domain occurs due to the superposition of the bias voltage and the instantaneous radio frequency voltage.
 Select Slow Light Effect and Multimode Lasing in a Photonic Crystal Waveguide Microlaser XING Ming-Xin, ZHENG Wan-Hua, ZHOU Wen-Jun, CHEN Wei, LIU An-Jin, WANG Hai-Ling Chin. Phys. Lett. 2010, 27 (2): 024213 .   DOI: 10.1088/0256-307X/27/2/024213 Abstract   PDF(pc) (777KB) ( 423 ) The slow light effect in a photonic crystal waveguide is investigated theoretically and experimentally. Theoretical calculation indicates that there is a slow light region for the even mode, from which the resonance and lasing in a microcavity would benefit. A photonic crystal waveguide microlaser is fabricated, which is related to the group velocity of c/120.6.
 Select Design of a Fused-Silica Subwavelength Polarizing Beam Splitter Grating Based on the Modal Method ZHAO Hua-Jun, YUAN Dai-Rong, WANG Pei, LU Yong-Hua, MING Hai Chin. Phys. Lett. 2010, 27 (2): 024214 .   DOI: 10.1088/0256-307X/27/2/024214 Abstract   PDF(pc) (384KB) ( 524 ) A polarizing beam splitter (PBS) design based on a fused-silica lamellar subwavelength transmission grating is demonstrated with the modal method, where TE- and TM-polarized waves are mainly diffracted in the -1st and 0th orders, respectively. The physical explanation of the grating diffraction is illustrated by the interference of the corresponding parts of the two propagating modes, which is very similar to a Mach-Zehnder interferometer. It is shown that diffraction efficients over 99% for a TM-polarized wave in the -1st order and 90% for a TE-polarized wave in the 0th order are obtained at the wavelength of 1.053 μm. The polarization transmission extinction ratios are better than 33 dB and 51 dB for the order 0th and the -1st order, respectively. The splitting properties of the PBS grating designed by the modal method are in good agreement with the results simulated by the rigorous coupled wave analysis method.
 Select Accurate Phase Shift Extraction for Generalized Phase-Shifting Interferometry XU Xian-Feng, CAI Lu-Zhong, WANG Yu-Rong, LI Dai-Lin Chin. Phys. Lett. 2010, 27 (2): 024215 .   DOI: 10.1088/0256-307X/27/2/024215 Abstract   PDF(pc) (2595KB) ( 658 ) An accurate phase shift extraction method for generalized phase-shifting interferometry is suggested. Based on the nearly random phase distribution of the diffraction field of the object, a singular formula is derived to calculate the unknown phase shift without the requirements of an iteration process or the selection of the correct value from two or more possible phase shift solutions as needed before. This method can be used in the cases of two or more frames with both smooth and diffusing object surfaces. Computer simulations and optical experiments have satisfactorily verified the efficiency and accuracy of this method.
 Select Effect of Air Gap on Dual-Tripler Broadband Third-Harmonic Generation HAN Wei, WANG Fang, WANG Li-Quan, JIA Huai-Ting, WANG Wei, LI Fu-Quan, FENG Bin, XIANG Yong, LI Ke-Yu, ZHONG Wei Chin. Phys. Lett. 2010, 27 (2): 024216 .   DOI: 10.1088/0256-307X/27/2/024216 Abstract   PDF(pc) (377KB) ( 439 ) We experimentally study the effect of the air gap on conversion efficiency and the spectrum of generated third-harmonic pulses in the dual-tripler broadband third-harmonic generation scheme. The experimental results are in good agreement with predictions that the 4-cm air gap is equivalent to a full cycle of phase mismatch among the three interacting pulses (i.e. the fundamental, second-harmonic and third-harmonic pulse). The experimental results also show that the spectrum of the third-harmonic pulse is sensitive to the air gap. We also point out that the air gap effect can be ignored when the dual-tripler system is located in 1000 Pa atmosphere. These results will guide the design of the broadband third-harmonic generation system in high power lasers.
 Select Flow Reversal of Fully-Developed Mixed MHD Convection in Vertical Channels H. Saleh, I. Hashim Chin. Phys. Lett. 2010, 27 (2): 024401 .   DOI: 10.1088/0256-307X/27/2/024401 Abstract   PDF(pc) (324KB) ( 635 ) The present analysis is concerned with flow reversal phenomena of the fully-developed laminar combined free and forced MHD convection in a vertical parallel-plate channel. The effect of viscous dissipation is taken into account. Flow reversal adjacent to the cold (or hot) wall is found to exist within the channel as Gr/Re is above (or below) a threshold value. Parameter zones for the occurrence of reversed flow are presented.
 Select Numerical Study on Critical Wedge Angle of Cellular Detonation Reflections WANG Gang, ZHANG De-Liang, LIU Kai-Xin, Chin. Phys. Lett. 2010, 27 (2): 024701 .   DOI: 10.1088/0256-307X/27/2/024701 Abstract   PDF(pc) (1895KB) ( 501 ) The critical wedge angle (CWA) for the transition from regular reflection (RR) to Mach reflection (MR) of a cellular detonation wave is studied numerically by an improved space-time conservation element and solution element method together with a two-step chemical reaction model. The accuracy of that numerical way is verified by simulating cellular detonation reflections at a 19.3° wedge. The planar and cellular detonation reflections over 45°-55° wedges are also simulated. When the cellular detonation wave is over a 50° wedge, numerical results show a new phenomenon that RR and MR occur alternately. The transition process between RR and MR is investigated with the local pressure contours. Numerical analysis shows that the cellular structure is the essential reason for the new phenomenon and the CWA of detonation reflection is not a certain angle but an angle range.
 Select Key Factors in Determining the Magnitude of Vorticity in Turbulent Plane Wakes MI Jian-Chun, R. A. Antonia Chin. Phys. Lett. 2010, 27 (2): 024702 .   DOI: 10.1088/0256-307X/27/2/024702 Abstract   PDF(pc) (383KB) ( 481 ) We examine the effects of local turbulence Reynolds number Rλ and inflow conditions on the magnitude of vorticity in plane turbulent wakes. Measurements of the spanwise component (ω3) of the fluctuating vorticity vector ω = ω1i + ω2j + ω3k (here the subscripts 1, 2 and 3 denote the streamwise, lateral and spanwise directions, respectively) are made in turbulent wakes of a screen and a circular cylinder. Lateral distributions of ω3* (normalized) in general depend on both Rλ and inflow conditions. In the developing region, as the downstream distance x1 increases, ω3* increases significantly in the screen wake but decreases slightly in the cylinder wake. Far downstream in the self-preserving region, ω3* increases linearly with Rλ while it no longer varies with x1 and depends weakly on the influence of inflow conditions. Our analysis suggests that these findings from the measurement of ω3* should apply for the magnitude of ω.
 Select Stretching a Curved Surface in a Viscous Fluid M. Sajid, N. Ali, T. Javed, Z. Abbas Chin. Phys. Lett. 2010, 27 (2): 024703 .   DOI: 10.1088/0256-307X/27/2/024703 Abstract   PDF(pc) (295KB) ( 822 ) This work is concerned with the viscous flow due to a curved stretching sheet. The similarity solution of the problem is obtained numerically by a shooting method using the Runge-Kutta algorithm. The physical quantities of interest like the fluid velocity and skin friction coefficient are obtained and discussed under the influence of dimensionless curvature. It is evident from the results that dimensionless curvature causes an increase in boundary layer thickness and a decrease in the skin friction coefficient.
 Select Static Threshold Pressure Gradient Characteristics of Liquid Influenced by Boundary Wettability SONG Fu-Quan, WANG Jian-Dong, LIU Hai-Li Chin. Phys. Lett. 2010, 27 (2): 024704 .   DOI: 10.1088/0256-307X/27/2/024704 Abstract   PDF(pc) (477KB) ( 995 ) We propose an experimental setup to measure the threshold pressure gradient (TPG) of microchannels with different wettability surfaces by the static method in microchannels with diameters from 20 μm to 320 μm, and compare the TPG of microchannels with adsorption of cetyl trimethyl ammonium bromide (CTAB) with that without CTAB adsorption. The results show the existence of TPG in microchannels. The TPG of microchannels increases with decreasing hydrodynamic diameter, and the relation between TPG and diameter is in agreement with the single-log normalization. The TPG of a microchannel with CTAB adsorption decreases obviously as compared with the microchannel without CTAB adsorption. The TPG of microchannels with different wettabilities of boundary surface are different, and the resistance of liquid flow can be reduced by changing the wettability of boundary surfaces.
 Select Fractal Analysis of Surface Roughness of Particles in Porous Media CAI Jian-Chao, YU Bo-Ming, ZOU Ming-Qing, MEI Mao-Fei Chin. Phys. Lett. 2010, 27 (2): 024705 .   DOI: 10.1088/0256-307X/27/2/024705 Abstract   PDF(pc) (406KB) ( 1066 ) A fractal dimension for roughness height (RH) is introduced to characterize the degree of roughness or disorder of particle surface characters which significantly influence physical-chimerical processes in porous media. An analytical expression for the fractal dimension of RH on statistically self-similar fractal surfaces is derived and is expressed as a function of roughness parameters. The specific surface area (SSA) of porous materials with spherical particles is also derived, and the proposed fractal model for the SSA of particles with rough surfaces is expressed as a function of fractal dimension for RH and fractal dimension for particle size distribution, relative roughness of particle surface, and ratio of the minimum to the maximum particle diameters of spherical particles.
 Select Late-Stage Vortical Structures and Eddy Motions in a Transitional Boundary Layer LIU Xiao-Bing, CHEN Zheng-Qing, LIU Chao-Qun Chin. Phys. Lett. 2010, 27 (2): 024706 .   DOI: 10.1088/0256-307X/27/2/024706 Abstract   PDF(pc) (809KB) ( 535 ) A high-order direct numerical simulation of flow transition over a flat-plate at a free stream Mach number 0.5 is carried out. Formation and development of three-dimensional vortical structures, typically shown as λ-vortices, hairpin vortices and ring-like vortices, are observed. Numerical results show that there is a strong downdraft motion of fluid excited by every ring-like vortex in the late-stage of the transition process. At two sides of the vortical structure centerline, the downdraft motions induced by the ring-like vortex and the rotating legs superimpose. This is responsible for the appearance of a high-speed streak associated with the positive spike observed in a previous investigation and the appearance of a high-shear layer in the near wall region.
 Select Three-Dimensional Linear Instability Analysis of Thermocapillary Return Flow on a Porous Plane ZHAO Si-Cheng, LIU Qiu-Sheng, NGUYEN-THI Henri, BILLIA Bernard Chin. Phys. Lett. 2010, 27 (2): 024707 .   DOI: 10.1088/0256-307X/27/2/024707 Abstract   PDF(pc) (377KB) ( 423 ) A three-dimensional linear instability analysis of thermocapillary convection in a fluid-porous double layer system, imposed by a horizontal temperature gradient, is performed. The basic motion of fluid is the surface-tension-driven return flow, and the movement of fluid in the porous layer is governed by Darcy's law. The slippery effect of velocity at the fluid-porous interface has been taken into account, and the influence of this velocity slippage on the instability characteristic of the system is emphasized. The new behavior of the thermocapillary convection instability has been found and discussed through the figures of the spectrum.
 Select Lagrangian Structure Function's Scaling Exponents in Turbulent Channel Flow LUO Jian-Ping, LU Zhi-Ming, USHIJIMA Tatsuo, KITOH Osami, LIU Yu-Lu, Chin. Phys. Lett. 2010, 27 (2): 024708 .   DOI: 10.1088/0256-307X/27/2/024708 Abstract   PDF(pc) (456KB) ( 786 ) The Lagrangian structure function's scaling exponents and intermittency of three-dimensional incompressible turbulent channel flow are investigated by using direct numerical simulation. The intermittency in streamwise velocity increments is found to increase in the near-wall region, which can be attributed to the presence of strong mean shear and organized motions in the near-wall region. It is found that the intermittency of transverse velocity increments is weaker than that of longitudinal ones. The present ESS evaluation of ζL(q) for the structure function of the streamwise velocity component in the channel centre is fairly close to experimental estimates of isotropic turbulence.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
 Select Particle Simulation of Electrostatic Waves Driven by an Electron Beam GUO Jun Chin. Phys. Lett. 2010, 27 (2): 025201 .   DOI: 10.1088/0256-307X/27/2/025201 Abstract   PDF(pc) (472KB) ( 411 ) A one-dimensional electrostatic particle-in-cell simulation is performed to study electrostatic wave excitation due to an electron beam in a plasma system. The excited fundamental and harmonic waves are analyzed with the fast Fourier transformation and the wavelet transformation. The second harmonic is suggested to be generated by wave-wave coupling during the nonlinear evolution, which involves forward propagating and backward propagating Langmuir waves. Furthermore, the background electrons may be heated and accelerated by the electrostatic waves.
 Select Numerical Simulation of Anisotropic Preheating Ablative Rayleigh-Taylor Instability WANG Li-Feng, YE Wen-Hua, , LI Ying-Jun Chin. Phys. Lett. 2010, 27 (2): 025202 .   DOI: 10.1088/0256-307X/27/2/025202 Abstract   PDF(pc) (509KB) ( 475 ) The linear growth rate of the anisotropic preheating ablative Rayleigh-Taylor instability (ARTI) is studied by numerical simulations. The preheating model κ (T)=κSH [1+f(T)] is applied, where f(T) is the preheating function interpreting the preheating tongue effect in the cold plasma ahead of the ablative front. An arbitrary coefficient D is introduced in the energy equation to study the influence of transverse thermal conductivity on the growth of the ARTI. We find that enhancing diffusion in a plane transverse to the mean longitudinal flow can strongly reduce the growth of the instability. Numerical simulations exhibit a significant stabilization of the ablation front by improving the transverse thermal conduction. Our results are in general agreement with the theory analysis and numerical simulations by Masse [Phys. Rev. Lett. 98 (2007) 245001].
 Select Two-Dimensional Rayleigh-Taylor Instability in Incompressible Fluids at Arbitrary Atwood Numbers WANG Li-Feng, YE Wen-Hua, , LI Ying-Jun Chin. Phys. Lett. 2010, 27 (2): 025203 .   DOI: 10.1088/0256-307X/27/2/025203 Abstract   PDF(pc) (544KB) ( 511 ) The Rayleigh-Taylor instability in two-dimensional incompressible fluids at arbitrary Atwood numbers is studied by expanding the perturbation velocity potential to third order. The second and third harmonic generation effects of single-mode perturbation are analyzed, as well as the nonlinear correction to the exponential growth of the fundamental modulation. The mode coupling coefficients are dependent on the Atwood numbers. Our simulations support the weakly nonlinear results. We find that the ratio of the nonlinear saturation amplitude ηs and the perturbation wavelength λ is dependent on the Atwood number AT and the relation is ηs/λ=(1/π)[√2/5/√(1+3AT2 )].
 Select Lattice Waves in Two-Dimensional Hexagonal Quantum Plasma Crystals SUN Xiao-Xia, WANG Chun-Hua, GAO Feng Chin. Phys. Lett. 2010, 27 (2): 025204 .   DOI: 10.1088/0256-307X/27/2/025204 Abstract   PDF(pc) (331KB) ( 641 ) Lattice waves including a longitudinal wave and a transverse wave in two-dimensional hexagonal quantum plasma crystals are investigated by using the modified Debye-Hückel screening potential. It is shown that there exists an unstable region of lattice parameters, where the system will melt. The general dispersion relations are derived, and the waves propagating parallel to a primitive translation vector are discussed. We find that both the longitudinal and transverse waves are acoustic-like, and the longitudinal wave has a greater sound speed than that of the transverse wave in the long wavelength limit region.
 Select Surface Wave Analysis of Planar-Type Overdense Plasma with Surface Plasmon Polariton Resonance CHEN Zhao-Quan, LIU Ming-Hai, TANG Liang, LV Jian-Hong, HU Xi-Wei Chin. Phys. Lett. 2010, 27 (2): 025205 .   DOI: 10.1088/0256-307X/27/2/025205 Abstract   PDF(pc) (470KB) ( 505 ) Surface waves (SWs) in planar-type overdense plasmas are analyzed and the invariable SW mode caused by the resonant excitation of surface plasmon polaritons (SPPs) is presented. It is found that the electric field peaks at the location where the plasma density equals the cut-off density while the plasma density gradient and the collision rate have different influences on the field amplitude and the peak's width. Moreover, the mode conversion between SW of SPPs and electron plasma waves play a significant role in production of overdense plasma.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
 Select Mechanical Properties and Anisotropy in PbWO4 Single Crystal WANG Hong, , ZHANG Zhi-Jun, ZHAO Jing-Tai, XU Jia-Yue, HU Guan-Qin, LI Pei-Jun Chin. Phys. Lett. 2010, 27 (2): 026101 .   DOI: 10.1088/0256-307X/27/2/026101 Abstract   PDF(pc) (680KB) ( 865 ) The mechanical properties of PbWO4 (PWO) crystals grown by the vertical Bridgman method are systematically investigated using the microindentation technique. In the present work, the Vickers microhardness Hν, fracture toughness Kc, yield strength σy and friability index Bi of PbWO4 crystals are measured. The Vickers microhardness Hν on the (100) wafer is about 140 MPa, which means that PWO is a little soft'' scintillator. The anisotropy of mechanical properties is also investigated under a steady load of 0.5 kg. The (100) wafer of the crystal exhibits combined mechanical properties more excellent than those of (111) and (001) wafers, and the values of Kc, σy, and Bi are 0.538 MPa・m1/2, 51.11 kg/mm2 and 284.96 νm-1/2, respectively.
 Select Superconducting State Parameters of NbxTayMoz Superconductors Aditya M. Vora Chin. Phys. Lett. 2010, 27 (2): 026102 .   DOI: 10.1088/0256-307X/27/2/026102 Abstract   PDF(pc) (304KB) ( 397 ) We present screening dependence theoretical investigations of the superconducting state parameters, i.e. electron-phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature TC, isotope effect exponent α, and effective interaction strength N0V, of some BMG superconductors, namely Nb0.45Ta0.45Mo0.10, Nb0.30Ta0.40Mo0.30, Nb0.40Ta0.30Mo0.30, Nb0.30Ta0.30Mo0.40 and Nb0.15Ta0.15Mo0.70 by employing the well-known empty core model potential of Ashcroft for the first time. Five local field correction functions proposed by Hartree, Taylor, Ichimaru-Utsumi, Farid et al. and Sarkar et al. are used in the present investigation to study the screening influence on the aforesaid superconducting properties. The transition temperature TC obtained from the H-local field correction function is found to be in an excellent agreement with the available theoretical data. Also, the present results are found to be in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the superconductors.
 Select Raman Investigation of Sodium Titanate Nanotubes under Hydrostatic Pressures up to 26.9GPa TIAN Bao-Li, DU Zu-Liang, MA Yan-Mei, LI Xue-Fei, CUI Qi-Liang, CUI Tian, LIU Bing-Bing, ZOU Guang-Tian Chin. Phys. Lett. 2010, 27 (2): 026103 .   DOI: 10.1088/0256-307X/27/2/026103 Abstract   PDF(pc) (485KB) ( 1044 ) High pressure behavior of sodium titanate nanotubes (Na2Ti2O5) is investigated by Raman spectroscopy in a diamond anvil cell (DAC) at room temperature. The two pressure-induced irreversible phase transitions are observed under the given pressure. One occurs at about 4.2 GPa accompanied with a new Raman peak emerging at 834 cm-1 which results from the lattice distortion of the Ti-O network in titanate nanotubes. It can be can be assigned to Ti-O lattice vibrations within lepidocrocite-type (H0.7Ti1.825V0.175O4・H2O)TiO6 octahedral host layers with V being vacancy. The structure of the nanotubes transforms to orthorhombic lepidocrocite structure. Another amorphous phase transition occurs at 16.7 GPa. This phase transition is induced by the collapse of titanate nanotubes. All the Raman bands shift toward higher wavenumbers with a pressure dependence ranging from 1.58-5.6 cm-1/GPa.
 Select Mechanical Behavior of Nanometer Ni by Simulating Nanoindentation TANG Qi-Heng, YANG Tian-Yong, DING Lan Chin. Phys. Lett. 2010, 27 (2): 026104 .   DOI: 10.1088/0256-307X/27/2/026104 Abstract   PDF(pc) (665KB) ( 464 ) An indentation simulation of the crystal Ni is carried out by a molecular dynamics technique (MD) to study the mechanical behavior at nanometer scales. Indenter tips with both sphere shape and conical shape with 60° cone angle are used, and simulation samples with different crystal orientations are adopted. Some defects such as dislocations and point defects are observed. It is found that nucleated defects (dislocations, amorphous atoms) are from the local region near the pin tip or the sample surface. The temperature distribution of the local region is analyzed and it can explain our MD simulation results.
 Select Formability and Thermal Stability of Ce62Al15Fe8Co15 Bulk Metallic Glass WANG Zhi-Xin, LU Jin-Bin, YANG Wei-Tie Chin. Phys. Lett. 2010, 27 (2): 026105 .   DOI: 10.1088/0256-307X/27/2/026105 Abstract   PDF(pc) (486KB) ( 526 ) The formability and thermal stability of Ce62Al15Fe8Co15 bulk metallic glass (BMG) are studied by x-ray diffraction (XRD) and differential scanning calorimetry. The critical diameter of Ce62Al15Fe8Co15 BMG predicted by the parameter γ is about 3.1 mm, which is roughly in agreement with the XRD results. Stability of the BMG is investigated by means of continuous crystallization diagrams obtained from the extension of the Kissinger and Vogel-Fulcher-Tammann (VFT) equations comparatively. It is found that the dependence of crystallization temperature of the BMG on heating rates follows a nonlinear relationship rather than Kissinger and Lasoka's linear fittings. The thermal stability of the BMG is investigated by the VFT equation.
 Select Comparison Study on Characteristic Regimes in Shocked Porous Materials XU Ai-Guo, ZHANG Guang-Cai, LI Hua, ZHU Jian-Shi Chin. Phys. Lett. 2010, 27 (2): 026201 .   DOI: 10.1088/0256-307X/27/2/026201 Abstract   PDF(pc) (1191KB) ( 606 ) We perform a comparison study on characteristic regimes in shocked porous materials whose mechanical properties cover a wide range. Via the Minkowski functional analysis, it is found that different materials may show the same fractional size of characteristic regimes in the shock-loading procedure, even if one uses the same threshold value to define those regimes. Characteristic regimes in the material with larger initial yield are more dispersed. For a fixed shock strength, there exists a material strength with which the shock wave reaction contributes the maximum plastic work. With the decreasing of shock strength, this material strength becomes smaller. These observations may present helpful indications for new material designs.
 Select Metastable Phase Separation and Concomitant Solute Redistribution of Liquid Fe-Cu-Sn Ternary Alloy ZHANG Xiao-Mei, WANG Wei-Li, RUAN Ying, WEI Bing-Bo Chin. Phys. Lett. 2010, 27 (2): 026401 .   DOI: 10.1088/0256-307X/27/2/026401 Abstract   PDF(pc) (656KB) ( 557 ) Liquid Fe-Cu-Sn ternary alloys with lower Sn contents are usually assumed to display a peritectic-type solidification process under equilibrium condition. Here we show that liquid Fe47.5Cu47.5Sn5 ternary alloy exhibits a metastable immiscibility gap in the undercooling range of 51-329 K (0.19TL). Macroscopic phase separation occurs once undercooling exceeds 196 K and causes the formation of a floating Fe-rich zone and a descending Cu-rich zone. Solute redistribution induces the depletion of Sn concentration in the Fe-rich zone and its enrichment in the Cu-rich zone. The primary Fe phase grows dendritically and its growth velocity increases with undercooling until the appearance of notable macrosegregation, but will decrease if undercooling further increases beyond 236 K. The microsegregation degrees of both solutes in Fe and Cu phases vary only slightly with undercooling.
 Select Molecular Dynamics Simulation of Strontium Titanate SEETAWAN Tosawat, WONG-UD-DEE Gjindara, THANACHAYANONT Chanchana, AMORNKITBUMRUNG Vittaya Chin. Phys. Lett. 2010, 27 (2): 026501 .   DOI: 10.1088/0256-307X/27/2/026501 Abstract   PDF(pc) (480KB) ( 700 ) The molecular dynamics method is used to simulate the thermophysical properties of SrTiO3 thermoelectric material in the temperature range 300-2200 K. The Morse-type potential functions added to the Busing-Ida type potential for interatomic interaction are used in the simulation. The interatomic potential parameters are determined by fitting to the experimental data of lattice parameters with temperature and the data reported in literature. The linear thermal expansion coefficient, heat capacity and lattice contributions to the thermal conductivity are analyzed. The results agree with the data reported in the literature.
 Select Molecular Dynamics Simulation of Strontium Titanate SEETAWAN Tosawat, WONG-UD-DEE Gjindara, THANACHAYANONT Chanchana, AMORNKITBUMRUNG Vittaya Chin. Phys. Lett. 2010, 27 (2): 026501 .   DOI: 10.1088/0256-307X/27/2/026501 Abstract   PDF(pc) (480KB) ( 532 ) The molecular dynamics method is used to simulate the thermophysical properties of SrTiO3 thermoelectric material in the temperature range 300-2200 K. The Morse-type potential functions added to the Busing-Ida type potential for interatomic interaction are used in the simulation. The interatomic potential parameters are determined by fitting to the experimental data of lattice parameters with temperature and the data reported in literature. The linear thermal expansion coefficient, heat capacity and lattice contributions to the thermal conductivity are analyzed. The results agree with the data reported in the literature.
 Select Thermal Depth Profiling Reconstruction by Multilayer Thermal Quadrupole Modeling and Particle Swarm Optimization CHEN Zhao-Jiang, ZHANG Shu-Yi Chin. Phys. Lett. 2010, 27 (2): 026502 .   DOI: 10.1088/0256-307X/27/2/026502 Abstract   PDF(pc) (407KB) ( 558 ) A new hybrid inversion method for depth profiling reconstruction of thermal conductivities of inhomogeneous solids is proposed based on multilayer quadrupole formalism of thermal waves, particle swarm optimization and sequential quadratic programming. The reconstruction simulations for several thermal conductivity profiles are performed to evaluate the applicability of the method. The numerical simulations demonstrate that the precision and insensitivity to noise of the inversion method are very satisfactory.
 Select Self-Assembly of TBrPP-Co Molecules on an Ag/Si(111) Surface Studied by Scanning Tunneling Microscopy LI Qing, Shiro Yamazaki, Toyoaki Eguchi, MA Xu-Cun, JIA Jin-Feng, XUE Qi-Kun, Yukio Hasegawa Chin. Phys. Lett. 2010, 27 (2): 026801 .   DOI: 10.1088/0256-307X/27/2/026801 Abstract   PDF(pc) (1340KB) ( 412 ) Self-assembly of TBrPP-Co molecules on a Si(111)-√3t×√3 Ag substrate is studied by low-temperature scanning tunneling microscopy. With the same adsorbed amount (0.07 ML), the molecules deposited by low-temperature evaporation show three kinds of ordered structures whereas those deposited by high-temperature evaporation have size-dependent ordered structures. The distinct differences in the self-assembly structures and in the electron density of states inside the molecule near the Fermi energy demonstrate that the Br atoms of the molecule desorb at the higher evaporation temperature.
 Select Atomic-Scale Study of Ge-Induced Incommensurate Phases on Si(111) WU Rui, WANG Li-Li, ZHANG Yi, MA Xu-Cun, JIA Jin-Feng, XUE Qi-Kun, Chin. Phys. Lett. 2010, 27 (2): 026802 .   DOI: 10.1088/0256-307X/27/2/026802 Abstract   PDF(pc) (1059KB) ( 399 ) Two Ge-induced incommensurate phases, γ and β, on Si(111) are observed and studied by {\it in situ} scanning tunneling microscopy. The γ phase consists of aligned triangular domains whose stacking sequence is faulted with respect to the Si(111)-1×1 surface. The β phase consists of two kinds of triangular domains whose stacking sequences are faulted and unfaulted with respect to the Si(111)-1×1 surface, respectively. In the β phase, two types of domain walls, zigzag'' and face-to-face'', form to release the strain. The triangular domains all exhibit a quasi-1×1 hexagonal close-packed structure. By studying the structural evolution from magic clusters to incommensurate structures, the structure models for γ and β phases are proposed.
 Select Aggregation Behavior of Metal-Ethylene Complexes and Its Effect on Hydrogen Storage Capacity WANG Xiao-Xiong, LI Hong-Nian, YAO Chang-Hong Chin. Phys. Lett. 2010, 27 (2): 026803 .   DOI: 10.1088/0256-307X/27/2/026803 Abstract   PDF(pc) (564KB) ( 465 ) The aggregation of Li, Ti decorated ethylene molecules and its effect on hydrogen storage capacity have been thoroughly studied using a first-principles calculation. The results indicate that the aggregation of C2H4-metal complexes substantially impacts on the hydrogen storage capacity. The aggregation of C2H4-Li reduces the hydrogen storage capacity greatly and makes the hydrogen storage capacity of C2H4-Li complexes hardly meet the demands of the U.S. DOE. The C2H4Ti2 dimers can uptake hydrogen as much as 10 wt%, which suggests that the C2H4Ti2 dimer can be a promising candidate for practical applications.
 Select Effects of Rapid Thermal Processing on Microstructure and Optical Properties of As-Deposited Ag2O Films by Direct-Current Reactive Magnetron Sputtering GAO Xiao-Yong, FENG Hong-Liang, ZHANG Zeng-Yuan, MA Jiao-Min, LU Jing-Xiao Chin. Phys. Lett. 2010, 27 (2): 026804 .   DOI: 10.1088/0256-307X/27/2/026804 Abstract   PDF(pc) (805KB) ( 522 ) (111) preferentially oriented Ag2O film deposited by direct current reactive magnetron sputtering is annealed by rapid thermal processing at different annealing temperatures for 5 min. The film microstructure and optical properties are then characterized by x-ray diffractometry, scanning electron microscopy, and spectrophotometry, respectively. The results indicate that no clear Ag diffraction peak is discernable in the Ag2O film annealed below 200°C. In comparison, the Ag2O film annealed at 200°C begins to exhibit characteristic Ag diffraction peaks, and in particular the Ag2O film annealed at 250°C can demonstrate enhanced Ag diffraction peaks. This implies that the threshold of the thermal decomposition reaction to produce Ag particles is approximately 200°C for the Ag2O film. In addition, an evolution of the film surface morphology from compact and pyramid-like to a rough and porous structure clearly occurred with increasing annealing temperature. The porous structure might be attributable to the escape of the oxygen produced during annealing, while the rough surface might originate from the reconstruction of the surface. The dispersion of interference peak intensity in the reflectance and transmission spectra could be attributed to the Ag particles produced. The lowered crystallinity and Ag particles produced induce a lattice defect, which results in an enhanced transmissivity in the violet region and a weakened transmissivity in the infrared region.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
 Select Mechanical and Magnetic Properties of Rh and RhH: First-Principles Calculations CUI Xin, WANG Jian-Tao, LIANG Xi-Xia, ZHAO Guo-Zhong Chin. Phys. Lett. 2010, 27 (2): 027101 .   DOI: 10.1088/0256-307X/27/2/027101 Abstract   PDF(pc) (509KB) ( 547 ) Mechanical and magnetic properties of Rh in bcc, fcc structures and RhH in cubic structure are investigated by using first-principles calculations. Theoretical strengths of these structures are given for the first time. The results show that the NaCl-type cubic RhH has a lower bulk modulus and a theoretical strength larger than those of Rh in bcc and fcc structures. A strong magneto-volume effect of a transition from low magnetic moment-low cell volume'' to high magnetic moment-large cell volume'' is also found for both the bcc and fcc Rh structures as well as RhH.
 Select Degradation of AlGaN/GaN High Electron Mobility Transistors with Different AlGaN Layer Thicknesses under Strong Electric Field YANG Ling, MA Jing-Jing, ZHU Cheng, HAO Yue, MA Xiao-Hua Chin. Phys. Lett. 2010, 27 (2): 027102 .   DOI: 10.1088/0256-307X/27/2/027102 Abstract   PDF(pc) (470KB) ( 597 ) The degradation of AlGaN/GaN high electron mobility transistors (HEMTs) has a close relationship with a model of traps in AlGaN barriers as a result of high electric field. We mainly discuss the impacts of strong electrical field on the AlGaN barrier thickness of AlGaN/GaN HEMTs. It is found that the device with a thin AlGaN barrier layer is more easily degraded. We study the degradation of four parameters, i.e. the gate series resistance RGate, channel resistance R channel, gate current IG,off at VGS=-5 and VDS=0.1 V, and drain current ID,max at VGS=2 and VDS=5 V. In addition, the degradation mechanisms of the device electrical parameters are also investigated in detail.
 Select Second Harmonic Detection of Spin-Dependent Transport in Magnetic Nanostructures YU Hai-Ming, S. Granville, YU Da-Peng, J-Ph. Ansermet Chin. Phys. Lett. 2010, 27 (2): 027201 .   DOI: 10.1088/0256-307X/27/2/027201 Abstract   PDF(pc) (489KB) ( 561 ) Detection of the second harmonic response of magnetic nanostructures to an ac current is shown to be a very sensitive probe of the magnetization reversal process. A temperature oscillation is obtained by Joule heating instead of using a laser as the heat source, as in thermo-galvanic voltage measurements (TGV). Joule heating is used to produce a large local temperature gradient in asymmetric Co/Cu/Co spin valves. Evidence is found for an effect of a heat current on magnetization.
 Select Ultraviolet Sensitive Ultrafast Photovoltaic Effect in Tilted KTaO3 Single Crystals XING Jie, GUO Er-Jia, JIN Kui-Juan, LU Hui-Bin, HE Meng, WEN Juan, YANG Fang Chin. Phys. Lett. 2010, 27 (2): 027202 .   DOI: 10.1088/0256-307X/27/2/027202 Abstract   PDF(pc) (352KB) ( 330 ) An ultraviolet sensitive ultrafast photovoltaic effect is observed in tilted 10° KTaO3 (KT) single crystals. The rise time of the transient photovoltaic pulse is 497.4 ps and the full width at half maximum is 974.6 ps under irradiation of a 266 nm laser pulse with 25 ps duration. An open-circuit photovoltage sensitivity of 328 mV/mJ and a photocurrent sensitivity of 460 mA/mJ are obtained. The experimental results demonstrate the potential applications of KT single crystals in ultraviolet detection.
 Select Competition between Radiative Power and Dissipation Power in the Refrigeration Process in Oxide Multifilms ZHANG Li-Li, HU Chun-Lian, WANG Can, LÜ, Hui-Bin, HAN Peng, YANG Guo-Zhen, JIN Kui-Juan Chin. Phys. Lett. 2010, 27 (2): 027203 .   DOI: 10.1088/0256-307X/27/2/027203 Abstract   PDF(pc) (469KB) ( 354 ) The maximum refrigeration power dependence on the doping density in the p-BaTiO3/BaTiO3/SrTiO3/BaTiO3/ n-BaTiO3 system and in the p-AlGaAs/AlGaAs/GaAs/AlGaAs/n-AlGaAs system is obtained respectively based on the opto-thermionic refrigeration model. The results show that the maximum refrigeration power in the p-BaTiO3/BaTiO3/SrTiO3/BaTiO3/n-BaTiO3 system increases dramatically with the increase of doping density from 1.0×1018 cm-3 to 5.0×1019 cm-3 while that in the p-AlGaAs/AlGaAs/GaAs/AlGaAs/n-AlGaAs system is nearly a constant. It is found that the different Auger coefficients and the competition between radiative power and dissipation power lead to the different behavior of the maximum refrigeration power dependence on the doping density of the two systems.
 Select Clockwise vs Counter-Clockwise I-V Hysteresis of Point-Contact Metal-Tip/Pr0.7 Ca0.3MnO3/Pt Devices GANG Jian-Lei, LI Song-Lin, LIAO Zhao-Liang, MENG Yang, LIANG Xue-Jin, CHEN Dong-Min Chin. Phys. Lett. 2010, 27 (2): 027301 .   DOI: 10.1088/0256-307X/27/2/027301 Abstract   PDF(pc) (863KB) ( 799 ) Metal-tip/Pr0.7Ca0.3MnO3/Pt devices possess two types of I-V hysteresis: clockwise vs counter clockwise depending on the tip materials. The criteria for categorization of these two types of devices can be simply based on whether the Gibbs free energy of oxidation for the metal tip is lower or higher than that of PCMO, respectively. While the clockwise hysteresis can be attributed to electric field induced oxidation/reduction, the counter clockwise hysteresis can be explained by oxygen vacancy migration in an electrical field. Alternating-current conductance spectra also reveal distinct hopping barriers between these two categories of devices at high resistive states.
 Select Low-Cost UV-IR Dual Band Detector Using Nonporous ZnO Film Sensitized by PbS Quantum Dots SHAO Jia-Feng, A. G. U. Perera, P. V. V. Jayaweera, HE De-Yan Chin. Phys. Lett. 2010, 27 (2): 027302 .   DOI: 10.1088/0256-307X/27/2/027302 Abstract   PDF(pc) (466KB) ( 505 ) A low-cost photoconductive dual-band detector was prepared using a nanoporous ZnO film sensitized by PbS quantum dots (QDs). At room temperature the device shows a UV response in the wavelength range of 200-400 nm with a 370 nm peak responsivity of 4.0×105 V/W and a vis-NIR response from 500 to 1400 nm with a 700 nm peak responsivity of 5.4×105 V/W. By increasing the size of the PbS QD, the response can be extended up to 2.9 μm. It is suggested that the UV response is a result of interband absorption of UV radiation by ZnO and the IR response comes from the absorption of PbS QDs.
 Select Bending Loss Calculation of a Dielectric-Loaded Surface Plasmon Polariton Waveguide Structure YUE Song, LI Zhi, CHEN Jian-Jun, GONG Qi-Huang Chin. Phys. Lett. 2010, 27 (2): 027303 .   DOI: 10.1088/0256-307X/27/2/027303 Abstract   PDF(pc) (1058KB) ( 744 ) Based on full 3D finite element method simulations, the transmission of a dielectric-loaded surface plasmon polariton waveguide (DLSPPW) based 1/4 circle is calculated for a 90° bend model and a 270° bend model, respectively. It is found that the 270° bend model gives almost pure bending loss while the 90° bend model contains additional coupling loss. The models are applied to deduce the loss and unloaded quality factor of DLSPPW based waveguide ring resonators (WRRs) and the results of the 270° bend model agree well with direct simulating results of the WRRs. Thus the 270° bend model gives a fast and simple way to calculate bending loss and it is helpful for WRR design because no wavelength scan is needed.
 Select Effects of End Termination on Electronic Transport in a Molecular Switch ZHAO Peng, ZHANG Zhong, WANG Pei-Ji, ZHANG Hai-Kui, REN Miao-Juan, LI Feng Chin. Phys. Lett. 2010, 27 (2): 027304 .   DOI: 10.1088/0256-307X/27/2/027304 Abstract   PDF(pc) (532KB) ( 580 ) Based on the non-equilibrium Green's function formalism and first-principles calculations, we investigate the electronic transport properties of an anthracene-based molecular switch with two carbon nanotube electrodes. Our results show that different terminations at the carbon nanotube end strongly affect the transport properties of the switch. In the case of H-termination the current at low biases is dominated by non-resonant tunneling. In the N-termination case the current at low biases is dominated by quasi-resonant tunneling and is increased by several orders of magnitude. The enhancement is discussed by the molecular projected self-consistent Hamiltonian level, transmission function, and local density of states.
 Select Preparation of Ultra Low- k Porous SiOCH Films from Ring-Type Siloxane with Unsaturated Hydrocarbon Side Chains by Spin-On Deposition YANG Chun-Xiao, ZHANG Chi, SUN Qing-Qing, XU Sai-Sheng, ZHANG Li-Feng, SHI Yu, DING Shi-Jin, ZHANG Wei Chin. Phys. Lett. 2010, 27 (2): 027701 .   DOI: 10.1088/0256-307X/27/2/027701 Abstract   PDF(pc) (523KB) ( 907 ) An ultra-low-dielectric-constant (ultra low-k, or ULK) porous SiOCH film is prepared using a single ring-type siloxane precursor of the 2,4,6,8-tetravinyl-2,4,6,8-tetramethylcyclotetrasiloxane by means of spin-on deposition, followed by crosslinking reactions between the precursor monomers under UV irradiation. The as-prepared film has an ultra low k of 2.41 at 1 MHz due to incorporation of pores and hydrocarbon crosslinkages, a leakage current density of 9.86×10-7 A/cm2 at 1 MV/cm, as well as a breakdown field strength of ~1.5 MV/cm. Further, annealing at 300°C results in lower k (i.e., 1.94 at 1 MHz), smaller leakage current density (2.96×10-7 A/cm2 at 1 MV/cm) and higher breakdown field strength (about 3.5 MV/cm), which are likely caused by the short-ranged structural rearrangement and reduction of defects in the film. Finally, the mechanical properties and surface morphology of films are also evaluated after different temperature annealing.
 Select Microwave Absorbing Materials: Solutions for Real Functions under Ideal Conditions of Microwave Absorption HUANG Yao-Qing, YUAN Jie, SONG Wei-Li, WEN Bo, FANG Xiao-Yong, CAO Mao-Sheng Chin. Phys. Lett. 2010, 27 (2): 027702 .   DOI: 10.1088/0256-307X/27/2/027702 Abstract   PDF(pc) (641KB) ( 729 ) We present general equations for metal-substrate single-layer microwave absorbing materials. The optimum electromagnetic parameters and matching thicknesses for electric-loss, magnetic-loss, and electromagnetic-loss materials are given, and possible solutions for the equations and the corresponding theoretic curves are discussed as well. The results may be helpful for designing high-performance microwave absorbing materials.
 Select Influence of Radio-Frequecy Power on Structural and Electrical Properties of Sputtered Hafnium Dioxide Thin Films LIU Wen-Ting, LIU Zheng-Tang, TAN Ting-Ting, YAN Feng Chin. Phys. Lett. 2010, 27 (2): 027703 .   DOI: 10.1088/0256-307X/27/2/027703 Abstract   PDF(pc) (552KB) ( 1034 ) Hafnium dioxide (HfO2) thin films are prepared by rf magnetron sputtering. The influences of rf power on the structure, chemical states and electrical properties of the thin films were investigated through x-ray diffraction, x-ray photoelectron spectroscopy, capacitance-voltage and leakage current density-voltage measurement and UV-VIS spectrophotometry. The results show that the HfO2 thin films have a mixed structure of amorphous and polycrystalline phases. With increasing rf power, the crystallinity is enhanced and the crystallite size of the thin films is increased. The oxidation of Hf atoms is improved with increasing rf power for the HfO2 thin films. The flat band shift, oxide charge density and leakage current density of the thin films all decrease as the rf power increases from 50 to 110 W, and then increase as the rf power is increased to 140 W. The band gap energy is smaller for the thin film deposited at 110 W.
 Select Effects of Substitution of Sm for Bi in BiFeO3 Thin Films Prepared by the Sol-Gel Method HUANG Ning-Xiang, ZHAO Li-Feng, XU Jia-Yang, CHEN Ji-Li, ZHAO Yong, Chin. Phys. Lett. 2010, 27 (2): 027704 .   DOI: 10.1088/0256-307X/27/2/027704 Abstract   PDF(pc) (5488KB) ( 678 ) Bi1-xSmxFeO3 films with x= 0, 0.03, 0.05, 0.07 and 0.10 are prepared on LaNiO3/Si(100) substrates by the sol-gel method. X-ray diffraction patterns reveal that pure phase films with random orientations are fabricated. The results of SEM indicate that films with denser surfaces are obtained by Sm substitution. At the doping level of x=0.05, remnant polarization Pr increases to 3.19 μC/cm2 from 1.12 μC/cm2 of the un-substituted BiFeO3 film and shows enhanced ferroelectricity at room temperature. Because of the low leakage current density in the high electric field region, a polarization hysteresis loop with remanent polarization of 5.15 μC/cm2 is observed in the 0.10 Sm-substituted BiFeO3 films at the applied electric field of 226 kV/cm. Through the substitution of Sm, the leakage current density is reduced for the films with x= 0.07-0.10.
 Select High Characteristic Temperature 1.3μm InAs/GaAs Quantum-Dot Lasers Grown by Molecular Beam Epitaxy JI Hai-Ming, YANG Tao, CAO Yu-Lian, XU Peng-Fei, GU Yong-Xian, MA Wen-Quan, WANG Zhan-Guo Chin. Phys. Lett. 2010, 27 (2): 027801 .   DOI: 10.1088/0256-307X/27/2/027801 Abstract   PDF(pc) (624KB) ( 824 ) We report the molecular beam epitaxy growth of 1.3 μm InAs/GaAs quantum-dot (QD) lasers with high characteristic temperature T0. The active region of the lasers consists of five-layer InAs QDs with p-type modulation doping. Devices with a stripe width of 4 μm and a cavity length of 1200 μm are fabricated and tested in the pulsed regime under different temperatures. It is found that T0 of the QD lasers is as high as 532 K in the temperature range from 10°C to 60°C. In addition, the aging test for the lasers under continuous wave operation at 100°C for 72 h shows almost no degradation, indicating the high crystal quality of the devices.
 Select Irradiation Effects of Femtosecond Pulses on Refractive Index of Ag-Embedded Nanocomposite Glasses DONG Zhi-Wei, QIAN Shi-Xiong, YANG Xiu-Chun, CHEN De-Ying Chin. Phys. Lett. 2010, 27 (2): 027802 .   DOI: 10.1088/0256-307X/27/2/027802 Abstract   PDF(pc) (542KB) ( 456 ) The irradiation effects of femtosecond pulses on Ag-embedded composite glasses fabricated by ion-exchange are investigated using z-scan measurement. Both changes of the refractive index caused by the laser irradiation effect and the third-order optical nonlinearity are observed in the experiment. Taking the change of the linear and nonlinear refractive index into consideration, the fitting results are in agreement with the experimental results.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
 Select CuInSe2 Films Prepared by a Plasma-Assisted Selenization Process in Different Working Pressures YU Tao, ZHANG Yi, LI Bao-Zhang, JIANG Wei-Long, WANG He, CAI Yong-An, LIU Wei, LI Feng-Yan, SUN Yun Chin. Phys. Lett. 2010, 27 (2): 028101 .   DOI: 10.1088/0256-307X/27/2/028101 Abstract   PDF(pc) (823KB) ( 745 ) The effects of working pressure on the composition, structure and surface morphology properties of CuInSe2 (CIS) films selenized with a plasma-assisted selenization process is investigated. Higher selenium content, better crystalline quality and much more regular surface particles compared to the others are found in the CIS film with 40 Pa working pressure. A Cu(In,Ga)Se2 device fabricated with the optimized plasma-assisted selenization process is demonstrated to be better than our previous result. After discussion, the reason for these phenomena is attributed to the compromise of electron temperature and plasma density.
 Select Nanoscale Tapered Pt Bottom Electrode Fabricated by FIB for Low Power and Highly Stable Operations of Phase Change Memory LV Shi-Long, SONG Zhi-Tang, LIU Yan, FENG Song-Lin Chin. Phys. Lett. 2010, 27 (2): 028401 .   DOI: 10.1088/0256-307X/27/2/028401 Abstract   PDF(pc) (585KB) ( 627 ) Phase change random access memory (PC-RAM) based on Si2Sb2Te5 with a Pt tapered heating electrode (Pt-THE), which is fabricated using a focus ion beam (FIB), is investigated. Compared with the tungsten electrode, the Pt-THE facilitates the temperature rise in phase change material, which causes the decrease of reset voltage from 3.6 to 2.7 V. The programming region of the cell with the Pt-THE is smaller than that of the cell with a cylindrical tungsten heating electrode. The improved performance of the PC-RAM with a Pt-THE is attributed to the higher resistivity and lower thermal conductivity of the Pt electrode, and the reduction of the programming region, which is also verified by thermal simulation.
 Select Design and Characterization of Evanescently Coupled Uni-Traveling Carrier Photodiodes with a Multimode Diluted Waveguide Structure ZHANG Yun-Xiao, PAN Jiao-Qing, ZHAO Ling-Juan, ZHU Hong-Liang, WANG Wei Chin. Phys. Lett. 2010, 27 (2): 028501 .   DOI: 10.1088/0256-307X/27/2/028501 Abstract   PDF(pc) (652KB) ( 418 ) A new evanescently coupled uni-traveling carrier photodiode (EC-UTC-PD) is designed, fabricated and characterized, which incorporates a multimode diluted waveguide structure and UTC active waveguide structure together. A high responsivity of 0.68 A/W at 1.55-μm without an anti-reflection coating, a linear photocurrent responsivity of more than 21 mA, and a large -1 dB vertical alignment tolerance of 2.5 μm are achieved.
 Select Electrical Response of Flexible Vanadyl-Phthalocyanine Thin-Film Transistors under Bending Conditions WANG He, LI Chun-Hong, WANG Li-Juan, WANG Hai-Bo, YAN Dong-Hang Chin. Phys. Lett. 2010, 27 (2): 028502 .   DOI: 10.1088/0256-307X/27/2/028502 Abstract   PDF(pc) (522KB) ( 659 ) Flexible vanadyl-phthalocyanine (VOPc) thin-film transistors are fabricated by the weak epitaxy growth (WEG) method. The devices show a mobility of 0.5 cm2/Vs, an on/off ratio of 105 and a low leakage current of 10-9 A. The performances exhibit strong dependence on bending conditions and reversible change can be found when the bending strain is less than 1.5%. This results from the change of the trap density calculated by subthreshold slopes. The results indicate that VOPc films fabricated by the WEG method have good durability to flexing and possess great potential in flexible electronics.
 Select Electromechanical Behavior of Interdigitated SiO2 Cantilever Arrays GUAN Zhi-Qiang, LUO Gang, MONTELIUS Lars, XU Hong-Xing, Chin. Phys. Lett. 2010, 27 (2): 028503 .   DOI: 10.1088/0256-307X/27/2/028503 Abstract   PDF(pc) (580KB) ( 380 ) Bending and first flexural mode vibration behavior of electrostatic actuated nanometer-sized interdigitated cantilever arrays are characterized under vacuum conditions. The pull-in'' effect in dc driving and the `hard spring effect'' in ac driving are observed. A mass sensitivity of 20 fg is expected for our devices due to the ultra-small mass of the arm and relative high Q factor. The mass-spring lump model combined with Green's function method is used to fit the dc driving behaviors including the pull-in voltage. For the ac driving case, the polynomial expansion of the capacitive force is used in the model. The successfully fittings of the pull-in voltage and the hard spring effect prove that our simulation method could be used for guiding the geometrical design of cantilever-based sensors.
 Select Effects of CRAC Channel on Spatiotemporal Ca2+ Patterns in T Cells LI Cong-Xin, CHEN Xiao-Fang, WANG Peng-Ye, WANG Wei-Chi Chin. Phys. Lett. 2010, 27 (2): 028701 .   DOI: 10.1088/0256-307X/27/2/028701 Abstract   PDF(pc) (714KB) ( 410 ) A reaction-diffusion model is built to investigate the temporal and spatial patterns of cytoplasmic Ca2+ dynamics under the effects of Ca2+-release activated Ca2+ (CRAC) channels in T cells. Simulation results show a strong dependence of the modulation mode of Ca2+ oscillation and dynamic patterns of Ca2+ wave on the influx rate through the CRAC channel (ksoc). When ksoc is small, cytoplasmic Ca2+ is modulated as a frequency-modulation (FM) signal, whereas it shows an amplitude modulation (AM) mode after ksoc passes through a critical value. The heterogeneity in spatial Ca2+ distribution is mostly arising from the influx through CRAC channels in both FM and AM modes. During each Ca2+ spike, a more sustained cytoplasmic Ca2+ gradient is maintained in the AM mode rather than in the FM mode.
 Select Emergent Travelling Pattern in a Spatial Predator-Prey System LIU Pan-Ping Chin. Phys. Lett. 2010, 27 (2): 028702 .   DOI: 10.1088/0256-307X/27/2/028702 Abstract   PDF(pc) (308KB) ( 410 ) A predator-prey model taking into account both diffusion and migration is considered and a mathematical analysis of the spatial pattern is presented. The numerical simulations show that the travelling pattern can emerge when migration is added. The obtained results may account for the complexity of ecosystems.
 Select Stability of Novel Time-Sharing Dual Optical Tweezers Using a Rotating Tilt Glass Plate REN Yu-Xuan, WU Jian-Guang, CHEN Man, LI Huang, LI Yin-Mei, Chin. Phys. Lett. 2010, 27 (2): 028703 .   DOI: 10.1088/0256-307X/27/2/028703 Abstract   PDF(pc) (367KB) ( 483 ) A novel realization of time-sharing optical tweezers (TSOT) is demonstrated using a tilt glass plate. Objects are trapped in the time-sharing dual traps; each of them acts like a single beam gradient trap with an effective stiffness. The effective stiffness of TSOT is experimentally measured through analysis of dynamical images. In comparison, it is numerically calculated by adopting the Monte Carlo technique. Both simulation and experimental results agree well with each other and show a good linear relationship between the effective stiffness and trap switching frequency in the range from 5 Hz to 70 Hz.
 Select Coarse-Grained Molecular Dynamics Simulation of a Red Blood Cell JIANG Li-Guo, WU Heng-An, ZHOU Xiao-Zhou, WANG Xiu-Xi Chin. Phys. Lett. 2010, 27 (2): 028704 .   DOI: 10.1088/0256-307X/27/2/028704 Abstract   PDF(pc) (704KB) ( 1416 ) A worm-like chain model based on a spectrin network is employed to study the biomechanics of red blood cells. Coarse-grained molecular dynamics simulations are performed to obtain a stable configuration free of external loadings. We also discuss the influence of two parameters: the average bending modulus and the persistence length. The change in shape of a malaria-infected red blood cell can contribute to the change in its molecular-based structure. As the persistence length of the membrane network in the infected red blood cell decreases, the deformability decreases and the biconcave shape is destroyed. The numerical results are comparable with previously reported experimental results. The coarse-grained model can be used to study the relationship between macro-mechanical properties and molecular-scale structures of cells.
 Select Condensation of Self-Driven Particles in Scale-Free Networks SHEN Jing Chin. Phys. Lett. 2010, 27 (2): 028901 .   DOI: 10.1088/0256-307X/27/2/028901 Abstract   PDF(pc) (549KB) ( 524 ) A new simple model of self-driven particles in scale-free networks is introduced to understand the emergence of condensation in the natural world. In the model, at each time step, particles are driven to choose their next habitats according to the particle numbers at both the present habitats and neighbors. It is found that the hub effect results in the condensation. The present numerical results as well as the theoretical analysis of condensation transition show the criterion of condensation. Both simulations and theoretical analysis display that there are three phases for different hopping probabilities δ: non-condensation (δ<δc), partial condensation (δc≤ δ<1), and complete condensation (δ≥δc'= 1), and the mean occupation particle number at the stationary state is also obtained. Moreover, the noise effect on self-driven particles is studied, and it makes particle numbers at nodes tend towards being identical.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
 Select Is the Near-Earth Current Sheet Prior to Reconnection Unstable to Tearing Mode? WEI Xin-Hua, CAO Jin-Bin, ZHOU Guo-Cheng, FU Hui-Shan, Chin. Phys. Lett. 2010, 27 (2): 029401 .   DOI: 10.1088/0256-307X/27/2/029401 Abstract   PDF(pc) (487KB) ( 532 ) The tearing mode instability plays a key role in the triggering process of reconnection. The triggering collisionless tearing mode instability has been theoretically and numerically analyzed by many researchers. However, due to the difficulty in obtaining the observational wave number, it is still unknown whether the tearing mode instability can be excited in an actual plasma sheet prior to reconnection onset. Using the data from four Cluster satellites prior to a magnetospheric reconnection event on 13 September 2002, we utilized the wave telescope technique to obtain the wave number which corresponds to the peak of power spectral density. The wavelength is about 18RE and is consistent with previous theoretic and numerical results. After substituting the wave vector and other necessary parameters of the observed current sheet into the triggering condition of tearing mode instability, we find that the near-Earth current sheet prior to reconnection is unstable to tearing mode.
 Select Timing and Spectral Studies of Pulsar EXO2030+375 Shubhra Tiwari, S. N. A. Jaaffrey, Rizwan S. Khan, Sushil K. Gandhi, Santvana Bapna Chin. Phys. Lett. 2010, 27 (2): 029701 .   DOI: 10.1088/0256-307X/27/2/029701 Abstract   PDF(pc) (665KB) ( 423 ) We report the results of timing and spectral analysis of the x-ray pulsar EXO2030+375. The observations were made using the Rossi x-ray timing explorer space satellite. The spectral analysis is carried out for the flux of x-ray energy range 3-30 keV. The x-ray continuum spectra of proportional counter array could be represented by a two-component model, a power law with an exponential cutoff at higher energies and a blackbody. An iron line at about 6.4-6.6 keV was also detected.
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