#### Current Issue

Volume 22 Issue 3
Online Date:
Original Articles
 Select Squeezing in the Real and Imaginary Spin Coherent States YAN Dong, WANG Xiao-Guang, WU Ling-An Chin. Phys. Lett. 2005, 22 (3): 521-524 .   Abstract   PDF(pc) (284KB) ( 1012 ) We study spin squeezing properties in the real and imaginary spin coherent states. We obtain analytical expressions of two spin squeezing parameters via a novel ladder operator formalism of the spin coherent state and the generation function method. Numerical results of the spin squeezing properties are discussed in detail, and the real and imaginary spin coherent state can be spin squeezed over a large range of parameters.
 Select Balanced Single-Photon Detectors Using InGaAs/InP Avalanche Photodiodes with Transformer-Based Spike Cancellation WU Guang, ZHOU Chun-Yuan, LI He-Xiang, ZENG He-Ping Chin. Phys. Lett. 2005, 22 (3): 525-528 .   Abstract   PDF(pc) (245KB) ( 724 ) We demonstrate balanced single-photon detectors at 1550nm with InGaAs/InP avalanche photodiodes by using transformer-based spike cancellation. The spike cancellation makes it possible to shorten the gate pulse width and to decrease the threshold of the discriminator. With a 4-ns gate, we obtain a dark-count probability of 8.5×10-5 per pulse at the detection efficiency of 10%. An after-pulse probability of 8.9×10-5 is obtained after 1-μs interval. Owing to its low after-pulse probability, the ratio of the dark count probability to the detection efficiency per pulse is about 7.5×10-5 while the repetition frequency ranges from 100 to 800kHz.
 Select Entangled States with Positive Partial Transpose in Any-Dimensional Quantum System WU Yu-Chun, CHEN Ping-Xing, ZHOU Zheng-Wei, GUO Guang-Can Chin. Phys. Lett. 2005, 22 (3): 529-532 .   Abstract   PDF(pc) (206KB) ( 575 ) It is well known that the positive partial transpose (PPT) criterion for determining separability is an operational separability criterion. However, in a high-dimensional (>6) situation, this criterion is not sufficient. How can we judge whether an entangled state in any high-dimensional quantum system is PPT or not? Here we propose a linear algebra method for checking the positivity of the partial transpose of a state and present a set of entangled mixed states with non-positive partial transpose.
 Select Damping in Collapses and Revivals of Interacting Bose--Einstein Condensates LIU Shu-Juan, XU Zhi-Jun, XIONG Hong-Wei, Chin. Phys. Lett. 2005, 22 (3): 533-535 .   Abstract   PDF(pc) (216KB) ( 544 ) We investigate the collapses and revivals of the interacting Bose--Einstein condensate based on the coherent state description of the condensate. Our research shows that the revival time is larger than the previous predication [Phys.Rev.Lett.77(1996)2158] when the high-order expansion of the chemical potential is considered. In particular, we predict an obvious damping effect in the process of collapses and revivals of the condensate.
 Select Non-Abelian Topological Excitations in Spinor Condensates ZHANG Yun-Bo, Harri Mä, kelä, Kalle-Antti Suominen Chin. Phys. Lett. 2005, 22 (3): 536-538 .   Abstract   PDF(pc) (213KB) ( 720 ) We investigate the topological defects in atomic spin-1 and spin-2 Bose--Einstein condensates by applying the homotopy group theory. With this rigorous approach we clarify the previously controversial identification of symmetry groups and order parameter spaces for the spin-1 case, and show that the spin-2 case provides a rare example of a physical system with non-Abelian line defects, and the possibility to have winding numbers of 1/3 and its multiples.
 Select Motion of Spinning Particles in Kerr Space--Time WANG Jun, WANG Yong-Jiu Chin. Phys. Lett. 2005, 22 (3): 539-542 .   Abstract   PDF(pc) (208KB) ( 460 ) We study the geodesic motion of pseudo-classical spinning particles in the Kerr space--time and investigate the generalized Killing equations for spinning space. The constants of motion are derived from the solutions to these equations. We discuss the special cases of motion in a plane. Because of the angular momentum per unit mass, the spinning particles in Kerr space--time are different from those in Schwarzschild space--time.
 Select Time Delay-Enhanced Synchronization and Regularization in Two Coupled Chaotic Neurons WANG Qing-Yun, LU Qi-Shao Chin. Phys. Lett. 2005, 22 (3): 543-546 .   Abstract   PDF(pc) (345KB) ( 782 ) Complete synchronization of two identical chaotic Morris--Lecar (ML) neurons with time-delay coupling is investigated. It is found that the coupled ML neurons may achieve synchronization by an efficient time delay at a low coupling strength. At the same time, the chaotic motion of the coupled neurons may become a regular periodic one during synchronization by the time-delay coupling, that is, the delay time coupling is able to suppress chaos in the process of synchronization. However, the time delay has the effect on enhancement of synchronization and regularization of coupled neurons only in certain coupling strength ranges. Moreover, synchronization of coupled neurons is achieved by time delay after regularization.
 Select Phase Synchronization in Electrically Coupled Different Neuronal Pacemakers with the Chay Model SHI Xia, LU Qi-Shao Chin. Phys. Lett. 2005, 22 (3): 547-550 .   Abstract   PDF(pc) (236KB) ( 559 ) We study the phase synchronization in different electrically coupled neuronal pacemakers with the Chay model. The numerical simulation results and the definition of the mean frequency show that phase synchronization is equal to the mean frequency locking. Nearly complete synchronization of different two coupled neuronal pacemakers is also investigated. It is shown that the cross-correlation of the membrane potential variables is suitable to judge the nearly complete synchronization.
 Select Analysis of Crisis for Producing Supertransients SHEN Ying, JIANG Yu-Mei, HE Yue, DAI Jun, HE Da-Ren Chin. Phys. Lett. 2005, 22 (3): 551-553 .   Abstract   PDF(pc) (415KB) ( 377 ) We report a crisis that is induced by an escape from a fat strange set formed by the forward images of an oscillating discontinuity borderline. It is analytically and numerically shown that the iteration lifetime obeys the universal power-law dependence on the controlling parameter and the scaling exponent takes an exceptional large value, i.e. v=1.72±0.04. The strange repeller, which appears after the crisis, is also a fat fractal. To our knowledge, this is the first example for a new mechanism that produces supertransients.
 Select A Simple Method to Generate Lie Point Symmetry Groups of the (3+1)-Dimensional Jimbo--Miwa Equation MA Hong-Cai Chin. Phys. Lett. 2005, 22 (3): 554-557 .   Abstract   PDF(pc) (517KB) ( 887 ) Taking the (3+1)-dimensional Jimbo--Miwa equation as a simple example, we develop a modified direct method to find symmetry groups and symmetry algebras. Some exact solutions of the model are given by the simple method.
 Select Equations of Propagation of Uncertainty on the ITS-90 in the Sub-ranges from 13.8033K to 933.473K KANG Zhi-Ru, FU Guang-Sheng, K. D. Hill Chin. Phys. Lett. 2005, 22 (3): 558-560 .   Abstract   PDF(pc) (188KB) ( 466 ) Based on implicit differentiation, we present the total differential of linear interpolation and the equation of propagation of uncertainty on the ITS-90 in any of the sub-ranges from 13.8033K to 933.473K. It is proven that the sensitivity coefficients of the linear interpolation are still linear combinations of the basis functions comprising the interpolation equation, only with different constants that can be presented in the determinant form. This solves the question to express the equation of propagation of uncertainty of a complex interpolation comprised of many different basic functions.
 Select Noncommutative QED Threshold Energy versus Optimum Collision Energy SHENG Zheng-Mao, FU Yong-Ming, YU Hai-Bo Chin. Phys. Lett. 2005, 22 (3): 561-564 .   Abstract   PDF(pc) (236KB) ( 398 ) Möller scattering and Bhabha scattering on noncommutative (NC) space--time is restudied. It is shown that the NC correction of scattering sections is not monotonic enhancement with total energy of colliding electrons, that there is an optimum collision energy to perform the greatest NC correction. Surprisingly, there is a linear relation between NC quantum electrodynamics threshold energy and the optimum collision energy.
 Select Large Decay Rate Variation of 7Be in Pd and Au ZHOU Shu-Hua, LIU Zhi-Yi, ZHOU Jing, MENG Qiu-Ying, LI Cheng-Bo, LIAN Gang, WANG Bao-Xiang, BAI Xi-Xiang Chin. Phys. Lett. 2005, 22 (3): 565-567 .   Abstract   PDF(pc) (208KB) ( 484 ) Platinum and gold have the similar crystal structure but different electronic affinities, as well as different effective electron densities near the implanted ions. Both the differences favour larger decay rate of 7Be in Pd than that in Au. We measured the variation of the decay rate of 7Be implanted in Pd and Au host materials. We have found that the decay rate of 7Be in Pd is larger than that in Au by 0.8%.
 Select Triaxial Superdeformed Band and Its Formation Mechanism in Odd--Odd-Nucleus 168Lu Tu Ya, , YU Shao-Ying, , CHEN Yong-Shou, SHEN Cai-Wan, CHEN Yong-Jing Chin. Phys. Lett. 2005, 22 (3): 568-571 .   Abstract   PDF(pc) (311KB) ( 531 ) Three-dimensional total Routhian surface calculations are carried out to determine the triaxial superdeformation of odd--odd nucleus 168Lu. One of the new four rotational bands observed in the experiment is identified as a triaxial superdeformed band, in which the neutron shell correction energy plays a key role and the deformation-driving effect of high j intruder orbital plays an additional role in the formation of triaxial superdeformation shape. Its deformation parameters (ε2,ε4, γ) are derived from the analysis, which can reproduce the experimental assignment.
 Select One-Proton Halo Structure in 23Al FANG De-Qing, MA Chun-Wang, MA Yu-Gang, CAI Xiang-Zhou, CHEN Jin-Gen, CHEN Jin-Hui, GUO Wei, TIAN Wen-Dong, WANG Kun, WEI Yi-Bin, YAN Ting-Zhi, ZHONG Chen, ZUO Jia-Xu, SHEN Wen-Qing Chin. Phys. Lett. 2005, 22 (3): 572-575 .   Abstract   PDF(pc) (334KB) ( 505 ) The Glauber theory is used to investigate the reaction cross section of proton-rich nucleus 23Al. A core plus a proton structure is assumed for 23Al. HO-type density distribution is used for the core while the density distribution for the valence proton is calculated by solving the eigenvalue problem of Woods--Saxon potential. The transparency function in an analytical expression is obtained by adopting multi-Gaussian expansion for the density distribution. Coulomb correction and finite-range interaction are introduced. This modified Glauber model is suitable for halo nuclei. A dominate s-wave is suggested for the last proton in 23Al from our analysis which is possible in the calculation of relativistic mean-field theory.
 Select Field-Free Orientation of Molecules with Small Permanent Dipole Moments by Using a Train of Half-Cycle Pulses CHI Fang-Ping, CHEN Ji-Gen, CHEN Gao, YANG Yu-Jun, DU Wen-He, ZHU Hai-Yan, ZHU Qi-Ren Chin. Phys. Lett. 2005, 22 (3): 576-679 .   Abstract   PDF(pc) (229KB) ( 608 ) We present a scheme aiming at the field-free orientation of molecules with smaller permanent dipole moments under the framework of the half-cycle pulse (HCP) method. Taking the HCCCl molecule as an example, we show that a train of identical HCPs with special time intervals can considerably raise the level of the orientation. The scheme is analytically interpreted in terms of intermittent Rabi oscillations by referring to a simplified two-state model.
 Select Simultaneous Extension and Enhancement of the HHG Plateau by Using Combined Lasers Irradiating on a United Two-Atom System CHEN Ji-Gen, CHEN Gao, YANG Yu-Jun, CHI Fang-Ping, DU Wen-He, ZHU Hai-Yan, ZHU Qi-Ren Chin. Phys. Lett. 2005, 22 (3): 580-583 .   Abstract   PDF(pc) (247KB) ( 599 ) We present the high-order harmonic generation spectrum from a united two-atom system simultaneously exposed to a fundamental Ti:sapphire and its 33rd harmonic (H33) lasers by numerically solving a one-dimensional time-dependent Schrödinger equation. At a suitable inter-nuclear separation, the harmonic plateau is widened from Ip+3.2Up in the single-atom case up to Ip+5.6Up in the united-atom case. Furthermore, the plateau is heightened in excess of six orders of magnitude by using the combined lasers compared with the case of the fundamental laser alone. Such a scheme can step by step accomplish the following processes: through a single H33 photon resonance transition an appropriate amount of electrons are first populated to an excited state, in which the electrons are easily ionized and subsequently accelerated by the fundamental laser; then they can recombine with the neighbouring atom, so that high-efficiency emissions of the harmonics beyond Ip+3.2Up are successfully realized.
 Select Frequencies-Selected Enhancement of the Extended High-Order Harmonic Generation Plateau from a United Two-Atom System Irradiated by a Combined Pulse CHEN Gao, CHEN Ji-Gen, YANG Yu-Jun, ZHU Hai-Yan, DU Wen-He, CHI Fang-Ping, ZHU Qi-Ren Chin. Phys. Lett. 2005, 22 (3): 584-587 .   Abstract   PDF(pc) (239KB) ( 496 ) We present a high-order harmonic generation (HHG) spectrum from a united two-atom system exposed to a combined laser pulse, by numerically solving a one-dimensional time-dependent Schrödinger equation. The combined laser pulse is composed of a low-frequency femtosecond pulse and a high-frequency attosecond one with respective appropriate amplitudes. For a suitable inter-nuclear separation, the harmonic emission efficiencies near the second cutoff of the extended plateau can be effectively enhanced by more than four orders of magnitude compared with the case of the low-frequency pulse alone. Such a combined pulse irradiating on the united two-atom system ionizes each atom, in a large rate (but not to a too large ionization yield), mainly at a particular time-interval. When the ionized electron from an atom reaches at the vicinity of the other atom and recombines with it, significant HHG enhancement is achieved for particular harmonics. This result, to our knowledge, is one of the best up to now in the endeavor for dramatically extending the width and simultaneously enhancing the height of the plateau.
 Select Luminescent Enhancement in Mg- and Er-Codoped LiNbO3 Crystals TANG Li-Qin, ZHAO Li-Juan, ZHANG Xin-Zheng, YU Hua, MENG Jie, LIANG Qin, XU Jing-Jun, KONG Yong-Fa Chin. Phys. Lett. 2005, 22 (3): 588-590 .   Abstract   PDF(pc) (215KB) ( 893 ) We investigate the MgO codoping-induced effect on the luminescent properties of Er3+-doped and Er/Mg codoped LiNbO3 crystals. The emission and excitation spectra and the absorption spectra are measured. The results show that the luminescent behaviour of Er3+ ions is very sensitive to the codoping of Mg2+ ions. According to the photorefractive level theory, we propose a quench model for the Er/Mg codoped lithium niobate crystal. The quench centres are suggested to be the bipolaron (NbLi-NbNb), we attribute the luminescent enhancement to the decreasing concentration of these centres. The luminescent enhancement effect is successfully explained.
 Select Absolute Generalized Oscillator Strength Profile of Negative Ion Resonance at 8.9eV in C2F6 FAN Xiao-Wei, GENG Zhen-Duo, ZHANG Yan-Song, K. T. Leung Chin. Phys. Lett. 2005, 22 (3): 591-594 .   Abstract   PDF(pc) (244KB) ( 738 ) A temporary negative ion resonance at 8.9eV in C2F6 has been clearly identified using angle-resolved electron energy loss spectroscopy at 2.5keV impact energy, and can be attributed to electron capture into 12alu, 12a1g, 22a2g, and 12eg virtual molecular orbitals. The corresponding absolute generalized oscillator strength profile is found to have a shape characteristic of non-dipole interaction with the maximum K ～ 0.8a.u. of momentum transfer.
 Select Generation of High-Dimensional Photon Entangled Coherent States in Double Electromagnetically Induced Transparency System GUO Yu, KUANG Le-Man Chin. Phys. Lett. 2005, 22 (3): 595-598 .   Abstract   PDF(pc) (239KB) ( 474 ) We present an approach to generate high-dimensional entangled coherent states between photons by using a dense atomic system in a double electromagnetically induced transparency state. The system under our consideration involves an atomic configuration with six internal states, two weak quantized probe lasers, and two strong classical coupling lasers. We show how to generate high dimensional entangled coherent states between the two probe lasers.
 Select Gain Spectrum in an Asymmetric Double Quantum Well XU Wei-Hua, WU Jin-Hui, GAO Jin-Yue Chin. Phys. Lett. 2005, 22 (3): 599-602 .   Abstract   PDF(pc) (241KB) ( 844 ) We propose a scheme for light amplification in an asymmetric double quantum well, where two excited states are coupled by resonant tunnelling through a thin barrier in a three-level system of electronic subbands. By applying a single driving laser, the steady state gain can be obtained. The calculated gain spectrum for an asymmetric GaAs/AlGaAs double quantum well structure was presented.
 Select Grazing Incidence Pumping X-Ray Laser Scheme with Application of Paraboloid Mirrors DONG Quan-Li, YAN Fei, ZHANG Jie, ZHONG Jia-Yong, ZHAO Jing, SHENG Zheng-Ming, LI Han-Ming, LI Ying-Jun Chin. Phys. Lett. 2005, 22 (3): 603-606 .   Abstract   PDF(pc) (364KB) ( 1199 ) A grazing incidence pumping x-ray laser scheme using JIGUANG II is proposed. We investigate the characteristics of the focusing of parabolas, and obtain the optimal intensity distributions in the target surfaces with paraboloid mirrors of different parameters by the vectorial ray-tracing. Kinetic simulations are carried out. The results show that due to the enhancement of absorption by the selectable plasma region (gain region), saturated amplification of the x-ray laser can be achieved with 100mJ energy in pre and pumping pulses, respectively, on 3mm Ti targets.
 Select Reducing Thermal Effect in End-Diode-Pumped Laser Crystal by Using a Novel Resonator YAO Ai-Yun, HOU Wei, LI Hui-Qing, BI Yong, LIN Xue-Chun, GENG Ai-Cong, KONG Yu-Peng, CUI Da-Fu, XU Zu-Yan Chin. Phys. Lett. 2005, 22 (3): 607-610 .   Abstract   PDF(pc) (318KB) ( 928 ) We report a new way, i.e. double-end-pumping, to extend the stability range of a laser resonator, in advantage of making the thermal loading be effectively divided between the ends of the laser crystal to reduce the thermal effect, thus to extend the stability range. Using this new way, we experimentally obtained a 2.7-W cw laser source at 671nm by intracavity frequency doubling of 1342nm of a Nd:YVO4 laser based on the nonlinear crystal LiB3O5. The maximum pump power is 28W, which is higher than 13W of the single-end-pumping.
 Select Generation and Evaluation of Sub-15fs Laser Pulses ZHU Chang-Jun, WANG Yun-Cai, ZHOU Jian-Ying Chin. Phys. Lett. 2005, 22 (3): 611-614 .   Abstract   PDF(pc) (253KB) ( 675 ) Full width at half maximum (FWHM) and rms formalisms are employed to characterize temporal and spectral profiles of sub-15fs laser pulses. Furthermore, intracavity spectral and spatial control is applied to improving the laser pulse quality. As a result, high quality sub-15fs laser pulses have been generated, which possess a satellite-free temporal profile, a smooth spectrum and a nearly single transverse mode.
 Select Broadband Infrared Luminescence of Bismuth-Doped Borosilicate Glasses MENG Xian-Geng, PENG Ming-Ying, CHEN Dan-Ping, YANG Lv-Yun, JIANG Xiong-Wei, ZHU Cong-Shan, QIU Jian-Rong Chin. Phys. Lett. 2005, 22 (3): 615-617 .   Abstract   PDF(pc) (209KB) ( 698 ) We prepare bismuth-doped borosilicate glasses and the luminescence properties in infrared wavelength region are investigated. Transmission spectrum, fluorescence spectrum and fluorescence decay curve are measured. The glasses exhibit a broad infrared luminescence peaking at 1340nm with the full width at half maximum of about 205nm, and lifetime of 273μs when excited by an 808-nm laser diode. The glasses are promising materials for broadband optical amplifiers and tunable lasers.
 Select Amplified Spontaneous Emission of Rhodamine B-Doped Step-Index Polymer Optical Fibre LI Zeng-Chang, LIANG Hao, ZHENG Zhi-Qiang, ZHANG Qi-Jin, MING Hai Chin. Phys. Lett. 2005, 22 (3): 618-620 .   Abstract   PDF(pc) (198KB) ( 879 ) A step-index polymer optical fibre (SI POF) containing rhodamine B in poly (methyl methacrylate) (PMMA) has been fabricated by a perform technique. The rhodamine B content of the doped SI POF is 5ppm-wt. The spectra of the doped SI POF with different fibre lengths were measured. Amplified spontaneous emission (ASE) at 609nm of an SI POF in length 40cm has been observed at ambient temperature by end-pumping with a Nd:YAG laser operated at 532nm. The threshold of absorbed pump power for the onset of ASE is about 0.003mJ.
 Select Thermo-optical Switch Matrix Based on Silicon-on-Insulator Waveguides LI Yan-Ping, YANG Di, SUN Fei, CHEN Shao-Wu, YU Jin-Zhong Chin. Phys. Lett. 2005, 22 (3): 621-623 .   Abstract   PDF(pc) (264KB) ( 662 ) A thermo-optical waveguide switch matrix is designed and fabricated on silicon-on-insulator wafer. Multi-mode interferometers are used as power splitters and combiners in a Mach--Zehnder structure. Inductively coupled plasma reactive ion etching is used to fabricate the waveguides. The rise and fall times of the switch matrix are 13μs and 7μs, respectively. Switch cells have an average switching power consumption of 340mW.
 Select Stereoscopic Particle Image Velocimetry Investigation of Three-Dimensional Characteristics of Vortex Structure in a Turbulent Channel Flow Feng-Chen LI, Yasuo KAWAGUCHI, Takehiko SEGAWA, Koichi HISHIDA Chin. Phys. Lett. 2005, 22 (3): 624-627 .   Abstract   PDF(pc) (734KB) ( 576 ) We investigate the three-dimensional characteristics of turbulence structures in a turbulent channel flow by employing stereoscopic particle image velocimetry (SPIV). The SPIV measurement was performed for a water flow at the Reynolds number Re = 1.1×104 in both the streamwise--spanwise (x--z) and spanwise--wall-normal (z--y) planes, respectively. A three-dimensional image of the vortex tubes or the hairpin vortex leg(s) inclined toward the wall was obtained. A series of wall-normal vortex cores were found to align with the low-speed streaks with opposite vorticity signals at both sides of the streaks in the x-z plane, which were cross-section slices of the inclined hairpin vortex leg(s).
 Select Sedimentation of Rigid Cylindrical Particles with Mechanical Contacts LIN Jian-Zhong, WANG Ye-Long, James A. Olsen Chin. Phys. Lett. 2005, 22 (3): 628-631 .   Abstract   PDF(pc) (335KB) ( 800 ) A collision model of two cylindrical particles is put forward. Based on the model the sedimentation of rigid cylindrical particles with mechanical contacts is simulated numerically by using the lattice Boltzmann method. Some numerical results are compared with the experimental ones given by us and others, and good agreements are found. In the sedimentation process, particles will rotate and drift at any initial orientation and terminal Reynolds number. The orientation, lateral position, drifty and sedimenting velocity of particles change periodically at small terminal Reynolds number. With the increasing terminal Reynolds number, the periodicity disappears, and an inverted T-structure forms. This structure appears more quickly and lasts for a longer time at larger terminal Reynolds number.
 Select Low Frequency Solitary Waves in Magnetized Electron--Positron--Ion Plasmas M. Ansar Mahmood, S. Mahmood, Arshad M. Mirza, H. Saleem, Chin. Phys. Lett. 2005, 22 (3): 632-635 .   Abstract   PDF(pc) (241KB) ( 901 ) Nonlinear electrostatic and electromagnetic low frequency waves are studied in magnetized electron--positron--ion (EPI) plasmas. The effects of full nonlinearity and three dimensional ion motion have been taken into account. It is shown that both density dips and humps can coexist in EPI plasmas along with bell-shaped and kink-type solitons. The new results as well as several limiting cases for comparison with earlier work have been discussed, for the sake of completeness. Relevance of this work to space, astrophysical and laboratory plasmas is pointed out.
 Select Acoustic Diagnostics of Plasma Channels Induced by Intense Femtosecond Laser Pulses in Air HAO Zuo-Qiang, YU Jin, ZHANG Jie, LI Yu-Tong, YUAN Xiao-Hui, ZHENG Zhi-Yuan, WANG Peng, WANG Zhao-Hua, LING Wei-Jun, WEI Zhi-Yi Chin. Phys. Lett. 2005, 22 (3): 636-639 .   Abstract   PDF(pc) (275KB) ( 473 ) Long plasma channels induced by femtosecond laser pulses in air are diagnosed using the sonographic method. By detecting the sound signals along the channels, the length and the electron density of the channels are measured. Refocusing is also observed at different laser energies and different focal lengths. We find that the sonographic method has manifest advantages compared to other techniques.
 Select Influence of Wall Charges on Discharge Characteristics of Surface Discharge LI Xue-Chen, WANG Long, RAN Jun-Xia, DONG Li-Fang Chin. Phys. Lett. 2005, 22 (3): 640-643 .   Abstract   PDF(pc) (250KB) ( 435 ) The discharge current and the inception voltage in a surface discharge device have been measured to investigate the influence of wall charges on the discharge characteristics in argon. The results show that the inception voltage decreases as the amplitude of the applied voltage Up increases. However, the sum of the inception voltage and the applied voltage almost keeps constant when Up is changed, due to the fact that the wall charges are generated in the discharge process. This phenomenon suggests that net electric field between the electrodes almost keeps constant when the amplitude of the applied voltage is changed. The electron temperature calculated by the intensity ratio of emitted spectral lines has been estimated to be less than 0.3eV and almost keeps constant under different amplitudes of the applied voltage. The result is consistent with nearly constant net field. The duty ratio of the discharge current increases as the amplitude of the applied voltage increases.
 Select Viscosity Characteristic in Metallic Melts with Medium/Short-Range Order Structures BIAN Xiu-Fang, ZHANG Jing-Xiang, JIA Yu-Bo, SUN Min-Hua Chin. Phys. Lett. 2005, 22 (3): 644-647 .   Abstract   PDF(pc) (265KB) ( 524 ) Viscosities and liquid structure of alloys Cu75Al25, Cu87Sn13 and Al-12.5%Si and pure metals Cu and Sn are investigated by using torsional oscillation viscometry and high temperature x-ray diffractometry. The viscosities of pure metals and eutectic alloy melts along with the short-range order structure are found to follow the Arrhenius law in a wide range of temperature above the liquidus. The breakpoints in Arrhenius plots emerge when the structures of alloy melts are transformed from the medium-range order structure to the short-range order structure. It has been found that the change of the viscosity of the metallic alloys is a characteristic of microstructure transformation in the related melts.
 Select Simulation of Space Charge Effect in Field Emission from a Nanowire PEI Yi, ZHANG Geng-Min Chin. Phys. Lett. 2005, 22 (3): 648-650 .   Abstract   PDF(pc) (206KB) ( 667 ) At present, field emission from nanowires (NWs) is under intense investigation. In experiments, the dependence of field emission current from an NW on applied voltage (I--V behavior) often deviates from the Fowler--Nordheim (FN) theory. We simulate the role of the space charge effect in the I--V behaviour of an NW. We determine the threshold electric field, at which the space charge effect starts to manifest itself, under different NW work functions. Our simulation result has confirmed that space charge effect is one of the possible factors responsible for the nonlinearity of the FN plots of an NW at high fields. Furthermore, our calculation reveals that the threshold field is related to the NW work function in an almost linear manner.
 Select Fabrication and Characterization of YBa2Cu3Oy Superconducting Nanowires LI Pei-Gang, FU Xiu-Li, CHEN Lei-Ming, ZHANG Hai-Ying, LI Ling-Hong, TANG Wei-Hua Chin. Phys. Lett. 2005, 22 (3): 651-653 .   Abstract   PDF(pc) (641KB) ( 668 ) Ordered YBa2Cu3Oy nanowires have been fabricated by filling YBa2Cu3Oy melting liquid into the pores of the anodized alumina templates. X-ray powder diffraction proves that YBa2Cu3Oy nanowires crystallized in the Y-123 structure. The temperature dependence of ac susceptibility indicates a superconducting transition at 91K for the YBa2Cu3Oy nanowire array.
 Select Effects of Techniques of Implanting Nitrogen into Buried Oxide on the Characteristics of Partially Depleted SOI PMOSFET ZHENG Zhong-Shan, LIU Zhong-Li, ZHANG Guo-Qiang, LI Ning, FAN Kai, ZHANG En-Xia, YI Wan-Bing, CHEN Meng, WANG Xi Chin. Phys. Lett. 2005, 22 (3): 654-656 .   Abstract   PDF(pc) (237KB) ( 570 ) Effects of techniques of implanting nitrogen into buried oxide on the characteristics of the partially depleted silicon-on-insulator (SOI) p-channel metal-oxide-semiconductor field-effect transistors (PMOSFETs) have been studied with three different nitrogen implantation doses, 8×1015, 2×1016, and 1×1017cm-2. The experimental results show that this technology can affect the threshold voltage, channel hole mobility and output characteristics of the partially depleted SOI PMOSFETs fabricated with the given material and process. For each type of the partially depleted SOI PMOSFET with nitrided buried oxide, the absolute value of the average threshold voltage increases due to the nitrogen implantation. At the same time, the average channel hole mobility decreases because of the nitrogen implantation. In particular, with the high nitrogen implantation doses, the output characteristic curves of the tested transistors present a distinct kink effect, which normally exists in the characteristic output curves of only partially depleted SOI NMOSFETs.
 Select Nanocavity Shrinkage and Preferential Amorphization during Irradiation in Silicon ZHU Xian-Fang, , WANG Zhan-Guo Chin. Phys. Lett. 2005, 22 (3): 657-660 .   Abstract   PDF(pc) (439KB) ( 464 ) We model the recent experimental results and demonstrate that the internal shrinkage of nanocavities in silicon is intrinsically associated with preferential amorphization as induced by self-ion irradiation. The results reveal novel thermodynamic nonequilibrium properties of such an open-volume nanostructure in condensed matter and also of covalently bound amorphous materials both at nanosize scale and during ultrafast interaction with energetic beam.
 Select Effects of Temperature on D2O Water Structure Investigated by Raman Spectroscopy SUN Qiang, ZHENG Hai-Fei, DUAN Ti-Yu Chin. Phys. Lett. 2005, 22 (3): 661-663 .   Abstract   PDF(pc) (223KB) ( 730 ) In situ Raman spectroscopy is employed to study the effects of temperature on D2O water structure up to 573K at 10MPa. With increasing temperature, the O--D stretching band moves to the higher wavenumber, implying that higher temperature can result in the break of hydrogen bonding. According to the discussion on the liquid water structure and from the van ’t Hoff equation, the hydrogen bond energy of D2O is calculated to be 2.50±0.3kcal/mol.
 Select Nanoscale Inhomogeneities in the Glass Transition of Zr41.2Ti13.8Cu12.5Ni10Be22.5 Bulk Metallic Glass SUN Min-Hua, WU Zhong-Hua, LIU Guang-Rong, CHEN Xing, CHEN Zhong-Jun Chin. Phys. Lett. 2005, 22 (3): 664-666 .   Abstract   PDF(pc) (223KB) ( 526 ) By using small-angle x-ray scattering technique, correlation lengths of the density fluctuation are determined for the bulk metallic glass Zr41.2Ti13.8Cu12.5Ni10Be22.5 around the glass transition temperature Tg. Nanoscale inhomogeneities were found to exist in the supercooled liquid and glass state. The correlation length was found to vary with temperature T in an exponential law δ(T)= δ0+A1exp[-(T-T∞)/T1], where T∞ is the Vogel temperature, and parameters δ0, A1 and T1 were simulated to be 16.45nm, 1.88×1029nm, and 9.65K, respectively, in the temperature region from Tg to Tg+80K. The correlation length of the density fluctuation obtained by the small-angle x-ray scattering method can be considered as the characteristic length of glass transition.
 Select An Approach for Calculating Strain Distributions in Arbitrarily Shaped Quantum Dots CHU Hai-Jian, WANG Jian-Xiang Chin. Phys. Lett. 2005, 22 (3): 667-670 .   Abstract   PDF(pc) (258KB) ( 790 ) We study strain distribution inside and outside an arbitrarily-shaped quantum dot (QD) buried in an infinite isotropic medium. By defining a very simple vector, we derive a compact formula for stress fields expressed by an integral over the interface between the QD and its surrounding material. Using this method, the analytical solution for a cuboidal QD is obtained, which is different from the previous result. It is shown that our solution satisfies the traction continuity condition on the interface. Based on this solution, it is found that the strain field in the cuboidal QD in the semiconductor heterostructure is sensitive to its height. In addition, the strain distribution around a hemispherical QD is also calculated and demonstrated.
 Select Many-Body Effect in Spin Dephasing in n-Type GaAs Quantum Wells WENG Ming-Qi, WU Ming-Wei, Chin. Phys. Lett. 2005, 22 (3): 671-674 .   Abstract   PDF(pc) (231KB) ( 490 ) By constructing and numerically solving the kinetic Bloch equations we perform a many-body study of the spin dephasing due to the D'yakonov--Perel’ effect in n-type GaAs (100) quantum wells for high temperatures. In our study, we include the spin-conserving scattering such as the electron--phonon, the electron--nonmagnetic impurity as well as the electron--electron Coulomb scattering into consideration. The dephasing obtained from our theory contains both the single-particle and the many-body contributions with the latter originating from the inhomogeneous broadening introduced by the DP term [J. Supercond.: Incorp. Novel Magn. 14(2001)245; Eur. Phys. J. B 18(2000)373]. Our result agrees very well with the experimental data [Phys. Rev. B 62(2000)13034] of Malinowski et al. We further show that in the case we study, the spin dephasing is dominated by the many-body effect.
 Select Total Structural Energy of Top-Site-Adsorbed CO/Nix--Cu1-x Systems ZHANG Hui, ZHANG Guo-Ying, LI Xing Chin. Phys. Lett. 2005, 22 (3): 675-677 .   Abstract   PDF(pc) (214KB) ( 444 ) We construct an atomic group model of the disordered binary alloy Nix--Cu1-x for the cases that the surface composition segregation exists or not. According the model, we calculate the electronic structure in a top site of Nix--Cu1-x alloy surface by using the recursion method when CO absorbed on the Nix--Cu1-x surface under the condition of coverage 0.5. The calculation result indicates that chemical absorption of CO reduces the density of states of the disordered binary alloy Nix--Cu1-x, widens the energy band, and strengthens the covalent bonds between the d electron of Ni and s or p electron of CO. Chemisorption of CO inhibits the enrichment of atom Cu on the alloy surface especially when bulk Ni concentration x is less than 0.8.
 Select Properties of Excitons Bound to Neutral Donors in GaAs Quantum-Well Wires LIU Jian-Jun, WANG Xue-Feng Chin. Phys. Lett. 2005, 22 (3): 678-681 .   Abstract   PDF(pc) (265KB) ( 506 ) In the effective mass approximation, the binding energy of an exciton bound to a neutral donor (D0, X) is calculated variationally for rectangular GaAs quantum-well wires (QWWs) by using a three-parameter wavefunction. The Coulomb interaction terms are treated exactly in their full three-dimensional forms throughout the calculation, especially in the case of (D0, X), which is a more physically realistic procedure than those employed in previous calculations which used effective one-dimensional potential [Chin. Phys. Lett. 21 (2004) 919]. Our treatment is unique in the use of a two-dimensional Fourier expansion of the Coulomb potential, which removes the numerical difficulty with the 1/r singularity and considerably reduces the computational effort. In addition, we also calculate the binding energies of (D0, X) when the donor is in different positions (at the centre, boundary and corner). The average interparticle distances in the square QWWs are discussed.
 Select Reentrant Spin Glass Behaviour and CE-Type Antiferromagnetic Phase in Half Doping (La,Pr)1,2Ca1/2 MnO3 Manganites CAO Gui-Xin, ZHANG Jin-Cang, SHA Yan-Na, YAO Kai, CAO Shi-Xun, JING Chao, SHEN Xue-Chu Chin. Phys. Lett. 2005, 22 (3): 682-685 .   Abstract   PDF(pc) (341KB) ( 620 ) The reentrant spin glass behaviour was observed in half doping (La,Pr)1,2Ca1/2 MnO3 manganites with a CE-type antiferromagnetic structure. It shows sequential multiple magnetic transitions from the paramagnetic to the ferromagnetic, antiferromagnetic, spin glass (SG) transitions, which reflects the complex magnetic interaction in the ground state of manganites. This can be explained by the competition interaction between the ferromagnetic and the CE-type antiferromagnetic matrix, and the disorder due to the tolerance factor t and A-cation size variance σ2. The results reveals the coexistence of ferromagnetic clusters and SG clusters in the background of the antiferromagnetic matrix in the ground state of half doping (La,Pr)1,2Ca1/2 MnO3 systems.
 Select Spin Glass Behaviour and Spin-Dependent Scattering in La0.7Ca0.3Mn0.9Cr0.1Ox Perovskites WU Bai-Mei, M. Ausloos, DU Ying-Lei, ZHENG Wei-Hua, LI Bo, J. F. Fagnard, Ph. Vanderbemden Chin. Phys. Lett. 2005, 22 (3): 686-689 .   Abstract   PDF(pc) (279KB) ( 402 ) The magnetic, electrical and thermal transport properties of the perovskite La0.7Ca0.3Mn0.9Cr0.1Ox have been investigated by measuring dc magnetization, ac susceptibility, the magnetoresistance and thermal conductivity in the temperature range of 5--300K. The spin glass behaviour with a spin freezing temperature of 70K has been well confirmed for this compound, which demonstrates the coexistence and competition between ferromagnetic and antiferromagnetic clusters by the introduction of Cr. Colossal magnetoresistance has been observed over the temperature range investigated. The introduction of Cr causes the double-bump'' feature in electrical resistivity ρ(T). Anomalies on the susceptibility and the thermal conductivity associated with the double-bumps in ρ(T) are observed simultaneously. The imaginary part of ac susceptibility shows a sharp peak at the temperature of insulating--metallic transition where the first resistivity bump was observed, but it is a deep-set valley near the temperature where the second bump in ρ(T) emerges. The thermal conductivity shows an increase below the temperature of the insulating--metallic transition, but the phonon scattering is enhanced accompanying the appearance of the second peak of double-bumps in ρ(T). We relate those observed in magnetic and transport properties of La0.7Ca0.3Mn0.9Cr0.1Ox to the spin-dependent scattering. The results reveal that the spin--phonon interaction may be of more significance than the electron (charge)--phonon interaction in the mixed perovskite system.
 Select Effects of Layer Deposition Sequence on Microstructure and Magnetostatic Coupling of Spin-Valves with Amorphous CoNbZr Layer WEN Qi-Ye, ZHANG Huai-Wu, JIANG Xiang-Dong, TANG Xiao-Li, ZHONG Zhi-Yong, John Q. Xiao Chin. Phys. Lett. 2005, 22 (3): 690-693 .   Abstract   PDF(pc) (527KB) ( 784 ) We investigate spin-valve sandwiches with thin amorphous CoNbZr as soft layers. The magnetoresistance (MR), microstructure, and magnetostatic coupling are studied in these sandwiches with different layer deposition sequences. For the CoNbZr/Cu/Co sandwich, the CoNbZr underlayer provides a smoother surface on which smooth Cu and Co layers can subsequently grow. The Cu spacer is dense and pinholes-free, leading to a good spin valve'' effect with a larger MR ratio of 3.8%. For the Co/Cu/CoNbZr sandwich, however, the Cu spacer is rough and pinholes were observed, which could induce a direct ferromagnetic coupling. Correlated rougher surfaces on both the sides of the Cu spacer were also observed, giving rise to an orangepeel'' coupling of about 0.105erg/cm-2. This strong ferromagnetic coupling in Co/Cu/CoNbZr results in a lower MR ratio of 1.6%. Moreover, upon proper thermal annealing, the CoNbZr/Cu/Co has a larger MR enhancement and a superior thermal stability to 350°C due to the dense and homogenous structure in the spacer layer.
 Select Fabrication and Characterization of ZnO-Based Film Bulk Acoustic Resonator with a High Working Frequency ZHANG Ting, , WANG Yu, LIU Wei-Li, CHENG Jian-Gong, SONG Zhi-Tang, FENG Song-Lin, CHAN-WONG Lai-Wa Helen, CHOY Chung-Loong Chin. Phys. Lett. 2005, 22 (3): 694-696 .   Abstract   PDF(pc) (214KB) ( 592 ) We report on the fabrication and characterization of a ZnO-based film-bulk acoustic-resonance device utilized as biosensor. The device has a multilayer structure which consists of piezoelectric element (Au/ZnO/Pt) and a Bragg-reflection-layer acoustic isolation consisting of multilayers of ZnO/Pt. Dielectric measurements have revealed that the device has a very high working frequency (up to ～3.1GHz), meaning that the device may have a higher sensitivity than the devices reported in the literature.
 Select Structural and Electrical Characteristics of Pb(Zr0.53,Ti0.47)O3 Thin Films Deposited on Si (100) Substrates CHEN Bin, YANG Hao, MIAO Jun, ZHAO Li, XU Bo, DONG Xiao-Li, CAO Li-Xin, QIU Xiang-Gang, ZHAO Bai-Ru Chin. Phys. Lett. 2005, 22 (3): 697-700 .   Abstract   PDF(pc) (405KB) ( 672 ) Pb(Zr0.53,Ti0.47)O3 (PZT) films were directly deposited on Si substrates without a buffer layer by pulsed laser deposition. Only (110)-oriented PZT peaks (other than Si substrate peaks) were observed from the XRD data. The electrical properties of the PZT/Si capacitor were characterized in terms of both the capacitance versus voltage (C--V) and current versus voltage (I--V) measurements. The clockwise trace of the C--V curve shows ferroelectric polarization switching, as is expected. From the I--V curves, the Schottky emission and space-charge-limited-current behaviour are found to be the mainly leakage current mechanism in a certain electric field range in the negative and positive bias, respectively.
 Select Enhancement of the Magneto-Optical Kerr Rotation at Short Wavelength in Sputtered Ag/TbFeCo Bilayer Films GAO Xiao-Yong, ZHANG Jin-Min, WANG Song-You, CHEN Liang-Yao Chin. Phys. Lett. 2005, 22 (3): 701-704 .   Abstract   PDF(pc) (246KB) ( 693 ) The magneto-optical Kerr rotation is enhanced at short wavelengths in sputtered Ag/TbFeCo bilayer films in which Ag not only acts as a protecting layer against the oxidation of TbFeCo, but also induces the enhancement of the magneto-optical Kerr rotation at short wavelengths. The enhancement of the Kerr rotation of Ag/TbFeCo bilayer films is not mainly due to the low optical constant of Ag near its plasma absorption edge and the interference effect occurring at the interface between Ag and TbFeCo, but due to the polarization of Ag d electrons caused by the ferromagnetic TbFeCo layer, which causes the off-diagonal elements of dielectric constant tensor of Ag/TbFeCo to be greatly increased.
 Select Raman Shift of RMnO3 (R = La, Pr, Nd, Sm) Manganites WANG Wei-Ran, XU Da-Peng, SU Wen-Hui, Chin. Phys. Lett. 2005, 22 (3): 705-707 .   Abstract   PDF(pc) (295KB) ( 878 ) Raman-active phonons in orthorhombic perovskite-like RMnO3 were studied by measuring Raman spectra in various scattering configurations. The experimental Raman line wave numbers and the expected shapes for the phonon modes were compared to those reported for other perovskite-like compounds with the Pnma structure and to the results of lattice dynamical calculations. The observed Raman lines in the spectra of RMnO3 were assigned to definite atomic motions. The remaining spectral weight can be explained by the presence of dynamic John--Teller distortions that lower the symmetry of the cubic perovskite.
 Select Spectroscopy of the Forming Process of Quantum Dots Accompanied by the Thinning of Wetting Layer ZHANG Zhen-Zhong, SHEN De-Zhen, ZHANG Ji-Ying, SHAN Chong-Xin, LIU Yi-Chun, LU You-Ming, FAN Xi-Wu Chin. Phys. Lett. 2005, 22 (3): 708-710 .   Abstract   PDF(pc) (218KB) ( 498 ) A series of Cd0.44Zn0.56Se/ZnSe sandwich structures with different Cd0.44Zn0.56Se embedded layer thicknesses were fabricated by metal organic chemical vapor deposition. When the embedded layer thickness exceeded 3.0nm, the photoluminescence spectra of the sample changed into the two-band structure from the one-band structure, and atomic force microscopy images indicate that Cd0.44Zn0.56Se quantum dots were formed. In the two-band photoluminescence spectrum, the band at the low energy side was attributed to be from quantum dots, and the high-energy one arose from the wetting layer. Thinning of the wetting layer with quantum dots forming was confirmed indirectly by the significant blue shift of the wetting-layer photoluminescence band compared to the photoluminescence band of the samples for which the Cd0.44Zn0.56Se layer thickness was less than 3.0nm. This thinning arose from mass migration during the Stranski--Krastanow growth of Cd0.44Zn0.56Se quantum dots.
 Select Luminescence Properties of Ca4GdO(BO3)3:RE (RE=Eu3+,Tb3+) under VUV Excitation DUAN Cheng-Jun, LI Wei-Feng, CHEN Hao-Hong, YANG Xin-Xin, ZHAO Jing-Tai, FU Yi-Bing, ZHANG Guo-Bin, QI Ze-Ming, SHI Zhao-Shu Chin. Phys. Lett. 2005, 22 (3): 711-714 .   Abstract   PDF(pc) (243KB) ( 649 ) We experimentally investigated the VUV excitation luminescence properties of Ca4GdO(BO3)3:RE (RE=Eu3+,Tb3+). Ca4GdO(BO3)3:Eu3+ and Ca4GdO(BO3)3:Tb3+ emitted bright red and green colour light, respectively, under 172nm excitation, resulting from the favorable position of the host absorption band (186nm) and efficient energy transfer from Gd3+ to activators (e.g. Eu3+ or Tb3+) by means of secondary absorption in the Ca4GdO(BO3)3 matrix. The f--d transitions of Eu3+ and Tb3+ in the host lattice are depicted.
 Select UV-Blue Upconverted Emission from Nd3+-Doped InF3-Based Heavy-Metal Fluoride Glasses for Blue Upconversion Fibre Laser ZHANG Qin-Yuan, YANG Gang-Feng, S. Buddhudu, JIANG Zhong-Hong, Chin. Phys. Lett. 2005, 22 (3): 715-718 .   Abstract   PDF(pc) (275KB) ( 547 ) We report spectral properties and thermal stability of Nd3+-doped InF3-based heavy-metal fluoride glasses. Fluoroindate glasses in the chemical compositions (in mol%) of (38-x)InF3-16BaF2-20ZnF2-20SrF2-3GdF3-1GaF3-2NaF- xNdF3 (x= 0.1, 0.5, 1, 2, 3) have been prepared under a controlled atmosphere in a dry box. Strong UV--blue upconversion emission from a green excitation wavelength has been observed and the involved mechanisms have been explained. Near-infrared emission occurs simultaneously upon excitation of the UV--blue upconversion emissions with a cw Ar+ laser. The upconversion spectra have revealed four dominant emissions at 354, 380, 412 and 449nm, which belong to the transitions of 43/2 → 4I9/2, 4D3/2 → 4I11/2 and 2P3/2 → 4I9/2,4D3/2 → 4I13/2 and 2P3/2 → 4I11/2, 4D3/2 → 4I15/2 and 2P3/2 → 4I13/2, respectively.
 Select Recombination Efficiency in Double-Layer Organic Light-Emitting Devices XU Xue-Mei, PENG Jing-Cui, QU Shu, LI Hong-Jian, WU Jian-Hao, OU-Yang Yu Chin. Phys. Lett. 2005, 22 (3): 719-722 .   Abstract   PDF(pc) (275KB) ( 538 ) We analyse the influence of properties of organic/organic interface (OOI) on the characteristics of recombination efficiency of organic double-layer light-emitting diodes. Based on the disordered hopping theory model, spatial and energetic disorder of hopping states are also discussed for the case of space charge limited currents in hole transmitting layers but injection-limited currents in electron transporting layers. The results show that the recombination efficiency increases firstly and then decreases for different OOI parameters, and there is a maximum value changed with different spatial disorder parameters and energetic disorder scale. Different spatial disorder parameters make carrier mobilities change greatly, and the energetic disorder scale causes various localized state densities. Our calculated results are qualitatively in agreement with the experimental data.
 Select Green-Yellow Electrophosphorescence from di [2,5-diphenyl-1,3,4-oxadiazole C2, N3 Platinum(II) Doped PVK Devices LIU Jian, ZHU Mei-Xiang, JIANG Chang-Yun, LIU Yu, WU Zhong-Lian, LI Jian-Ren, XING Kong-Qiang, CAO Yong, ZHU Wei-Guo Chin. Phys. Lett. 2005, 22 (3): 723-726 .   Abstract   PDF(pc) (256KB) ( 666 ) Employing a blend of poly (N-vinylcarbazole) (PVK) and 5-biphenyl-2-(4-tert-butyl)phenyl-1,3,4-oxadiazole) (PBD) as host matrix and a novel bicyclometalated Pt-complex containing 1,3,4-oxadiazole moiety as guest matrix with 2wt.% doping concentration, we have demonstrated efficient phosphorescence-based polymer light-emitting devices (PLEDs). The devices emitted intense green--yellow electrophosphorescence. No emission from either PVK or PBD was observed for the devices. The electroluminescence spectrum exhibited three primary peaks at 525nm, 568nm and 608nm. A maximum external quantum efficiency of 2.3% ph/el and a luminous efficiency of 3.8cd/A were achieved at a current density of 3.4mA/cm2. The results demonstrate that highly efficient electrophosphorescence can be achieved from platinum complex-based polymer light-emitting devices.
 Select High-Efficient Organic Light-Emitting Diodes Using Indium Tin Oxide Treated by KMnO4 Solution as Anode WANG Jing, LU Lin, JIANG Wen-Long, ZHANG Ying-Fang, ZHAO Yi, HOU Jing-Ying, LIU Shi-Yong Chin. Phys. Lett. 2005, 22 (3): 727-729 .   Abstract   PDF(pc) (368KB) ( 734 ) High-efficient organic light-emitting diodes (OLEDs) with indium-tin-oxide (ITO) anode treated by KMnO4 solution are demonstrated. The performance of the OLEDs depends on the concentration of KMnO4 solution and time of ultrasonic treatment. The OLED whose ITO anode was treated by ultrasonic in KMnO4 solution with concentration of 50mg/L for 15min displays the best performance. It has higher electroluminescent brightness and lower turn-on voltage than those of traditional devices. In particular, its efficiency can be increased by approximately 40%. The surfaces of the ITO anode with and without treating are analysed by scanning electron microscopy.
 Select Microstructure of Au Film Prepared by Magnetron Sputtering Deposition JIANG Yong, GUAN Bo, XU Xiao-Liang, Chin. Phys. Lett. 2005, 22 (3): 730-732 .   Abstract   PDF(pc) (294KB) ( 664 ) We study the formation of microstructure of gold films that generally undergo three processes: nucleation and nuclear growth, normal grain growth, and abnormal grain growth. Here the grains grow as a column in the normal grain growth process. When the grain size becomes larger than and comparable to the film thickness, the grains with favourable orientation will grow at the expense of the grains with unfavourable orientation, leading to abnormal grain growth. The abnormal grains grow along the favoured orientation (111), which has been certified by x-ray diffraction spectroscopy. Finally, the processes of the normal and abnormal grain growth are fitted using the Lifshitz--Slyozov--Wanger theory.
 Select Electronic Properties of Nanocrystalline-Si Embedded in Asymmetric Ultrathin SiO2 by In-Situ Fabrication Technique WU Liang-Cai, CHEN Kun-Ji, YU Lin-Wei, DAI Min, MA Zhong-Yuan, HAN Pei-Gao, LI Wei, HUANG Xin-Fan Chin. Phys. Lett. 2005, 22 (3): 733-736 .   Abstract   PDF(pc) (314KB) ( 533 ) Structures of nanocrystalline-Si (nc-Si) sandwiched between two asymmetric ultrathin SiO2 layers were fabricated. The nc-Si (dot density of 1011cm-2) was formed by decomposition of hydrogen-diluted silane and the ultrathin SiO2 layers (about 2nm) were prepared by plasma oxidation at a lower temperature (250°C). The whole fabrication processes were completed in situ in a plasma-enhanced chemical vapour deposition system. By using the capacitance--voltage (C--V) and conductance--voltage (G--V) spectroscopy, we studied the electronic properties of the annealed samples. The experimental results show that there are distinct capacitance peaks and conductance plateau or peaks for annealed samples at room temperature, which can be explained by direct tunnelling of electrons into the nc-Si. At the same time, Coulomb blockade plays an important role in the electronic transport in the nc-Si. The effect of thermal annealing in N2 ambient on the electronic properties was studied and the results indicate that high temperature (1000°C) annealing can improve the size uniformity of the nc-Si prepared by decomposition of hydrogen-diluted silane.
 Select Evidence of Ultrafast Energy Exchange-Induced Soft Mode of Phonons and Lattice Instability: a Nanotime Effect ZHU Xian-Fang, , WANG Zhan-Guo Chin. Phys. Lett. 2005, 22 (3): 737-740 .   Abstract   PDF(pc) (205KB) ( 579 ) With a series of supportive experimental phenomena as induced by ion beam bombardment, energetic beam-induced athermal activation process in Si is demonstrated. This is correlated with phenomena induced by ultrafast energy exchange in condensed matter in general. A critical modelling is presented on the above process and a universal concept: the ultrafast energy exchange-induced soft mode of phonons and the lattice
 Select Fabrication of Alumina Films with Three-Dimensional Ordered Macropores by Self-Assembly of Binary Colloidal Spheres LIU Li-Xia, DONG Peng, WANG Da-Jun, ZHOU Qian, CHENG Bing-Ying Chin. Phys. Lett. 2005, 22 (3): 741-743 .   Abstract   PDF(pc) (535KB) ( 686 ) We present a new process to obtain a three-dimensional ordered macroporous structure (3DOM). The 3DOM films were fabricated using a coassembly of monodispersed polystyrene spheres and alumina hydroxide sols in aqueous suspensions on a vertical substrate followed by a calcination treatment. The 3DOM film structure, quality and morphology have been characterized by scanning electron microscopy and transmission spectra.
 Select Mechanism of Explosive Technique on Relieving Welding Residual Stresses LIU Kai-Xin, ZHANG Jin-Xiang, ZHAO Kai, LI Xiao-Jie, ZHANG Kai Chin. Phys. Lett. 2005, 22 (3): 744-746 .   Abstract   PDF(pc) (431KB) ( 777 ) The complex physical process of welding residual stress relieving by means of explosive technique is studied experimentally and numerically. The experiments are carried out in welded 16MnR steel plates. In the numerical simulations, the explicit dynamic finite element method is adopted. The results from experiments and computations are consistent with each other. The mechanism of this technique is explained by considering the effect of stress wave reflection and superposition on the redistribution of stresses in this process. Based on the above studies, some advises and parameters are provided to practical applications of this technique.
 Select Shear Viscosity of Aluminium under Shock Compression LIU Fu-Sheng, YANG Mei-Xia, LIU Qi-Wen, CHEN Jun-Xiang, JING Fu-Qian, Chin. Phys. Lett. 2005, 22 (3): 747-749 .   Abstract   PDF(pc) (218KB) ( 621 ) Based on the Newtonian viscous fluid model and the analytic perturbation theory of Miller and Ahrens for the oscillatory damping of a sinusoidal shock front, a flyer-impact technique is developed to investigate the effective viscosity of shocked aluminium. The shear viscosity coefficient is determined to be about 5000 poises at 42GPa with strain rate of 1.27×106s-1, which is a reasonable estimation compared with the results of other measurement methods.
 Select Nonlinear Electrical Behaviour of Composite SnO2--Zn2SnO4 System ZANG Guo-Zhong, WANG Jin-Feng, CHEN Hong-Cun, SU Wen-Bin, WANG Chun-Ming, QI Peng Chin. Phys. Lett. 2005, 22 (3): 750-753 .   Abstract   PDF(pc) (241KB) ( 643 ) We have found a new composite SnO2--Zn2SnO4 varistor material and the effect of different content ratios of SnO2 to Zn2SnO4 on this system is investigated. The lowest breakdown voltage (EB=6.4V/mm) and the highest relative dielectric constant (εr=1.54× 104) with higher nonlinear coefficient (α=4.5) is obtained when the ratio of SnO2 to ZnO equals 100/35. The disappear of the Zn2SnO4 peak in x-ray diffraction (XRD) spectra of the SnO2+2.5mol%ZnO sample and the electric insulation behaviour of the samples with 2.5mol% ZnO and 200mol% ZnO indicate that 2.5mol% ZnO can be dissolved into SnO2 lattices and some reaction contributing to nonlinear electrical behaviour should occur between SnO2 and Zn2SnO4. The role of oxygen on the grain boundary is confirmed by the degradation of nonlinear electrical properties and the increase of relative dielectric constant of the samples annealed in nitrogen-rich atmosphere.
 Select Radio-Frequency Characteristics of the Coaxial Step-Disk-Loaded Slow-Wave Structure for Relativistic Travelling Wave Tubes YUE Ling-Na, WANG Wen-Xiang, WEI Yan-Yu, GONG Yu-Bin Chin. Phys. Lett. 2005, 22 (3): 754-757 .   Abstract   PDF(pc) (278KB) ( 887 ) We present a new periodic all-metal slow wave structure, a coaxial step-disc-loaded system and the dispersion characteristics of the structure. By using the field-matching method, the dispersion equation and the coupling impedance of this structure are obtained. The coaxial structure makes the bandwidth broader than that of the non-coaxial one. Compared with the coaxial disc-loaded and ridged-disc-loaded structures, the pass-band of coaxial step-disc-loaded structure is the broadest. The calculation results show that increasing the step width and decreasing the step thickness can improve the bandwidth.
 Select Reversible Phase Change for C-RAM Nano-Cell-Element Fabricated by Focused Ion Beam Method LIU Bo, SONG Zhi-Tang, FENG Song-Lin, CHEN Bomy Chin. Phys. Lett. 2005, 22 (3): 758-761 .   Abstract   PDF(pc) (560KB) ( 628 ) A single nano-cell-element of chalcogenide-random access memory was fabricated by using the focused ion beam method. The minimum contact size between the Ge2Sb2Te5 phase change film and the top electrode film for the cell element is with diameter of 60nm. The reversible phase transition between the RESET state and the SET state was successively realized. The minimum SET current is obtained to be about 0.28mA.
 Select Distribution of Words on the World-Wide Web WEI Fang-Ping, LI Sheng, MA Hong-Ru Chin. Phys. Lett. 2005, 22 (3): 762-764 .   Abstract   PDF(pc) (207KB) ( 607 ) The diverse words of all kinds of language are added into the World-Wide Web in an extremely complex and arbitrary manner. Behind the apparent arbitrariness topology, as we show here, there is an order hidden in the word network. By making use of Google search engine, we find that the distributions of the basic English words and Chinese characters on the web follow a universal power law. The power law exponent of rank-ordered frequency distribution is α ～ 0.99 for basic English words and α ～ 0.98 for Chinese characters. The Zipf law and page size distribution on the Web are used to explain the phenomena.
 Select Random and Preferential Attachment Networks with Aging WU Jian-Jun, GAO Zi-You, SUN Hui-Jun, HUANG Hai-Jun Chin. Phys. Lett. 2005, 22 (3): 765-768 .   Abstract   PDF(pc) (231KB) ( 627 ) A new model for network generation is proposed by considering both the preferential and random attachments with aging. The connectivity distribution is obtained with the mean-field theory. The simulation results show that the model can be used to generate such networks with different topology structures as random and scale-free ones. The networks with different densities (i.e., the average connectivity degrees) can also be generated by the model.
 Select Comparison of Two Kinds of Atmospheric Vorticity Equations AN Jing-Hui, WU Guo-Xiong, CUI Xiao-Peng Chin. Phys. Lett. 2005, 22 (3): 769-772 .   Abstract   PDF(pc) (223KB) ( 470 ) Comparison of two kinds of atmospheric vorticity equations, i.e. the traditional vorticity equation and the complete-form vorticity equation, is performed. The result shows that the two kinds of the vorticity equations can transform from each other and they are consistent in physical essence, while the complete vorticity equation has more advantages in diagnosis. Finally, the application of the complete form vorticity equation is analysed briefly with real data.
 Select Rebound Effect in the Kerr--Newman--Kasuya Field HE Tang-Mei, WANG Yong-Jiu Chin. Phys. Lett. 2005, 22 (3): 773-775 .   Abstract   PDF(pc) (167KB) ( 555 ) It is shown that the repulsive gravitational action of electric charge and magnetic charge make it possible that the neutral particles moving in the Kerr--Newman--Kasuya field stop and rebound at the surface of r=r0 =(e2+q2)/(2m). The phenomenon of dragging of inertial frames is analysed.
 Select Stability and Structure of Spiral Galaxies with Finite Thickness LIN Yi-Hui, PENG Qiu-He, CHOU Chih-Kang, LUO Xin-Lian Chin. Phys. Lett. 2005, 22 (3): 776-779 .   Abstract   PDF(pc) (284KB) ( 585 ) We calculate the effect of finite disc thickness on the structure and stability of a differentially rotating three-dimensional spiral galaxy with stars and gases. The problem is solved exactly in terms of the rigorous mathematical method of Green function and Bessel--Fourier transform. By using the appropriate three dimensional self-gravitational potential due to the density perturbations of the spiral arms in the galactic disc, the dispersion relation for the quasi-stationary density waves are deduced for the composite disc model of stars and gases with finite thickness. The stability criterion depicted by the Toomre Q parameter for these spiral modes are investigated in detail. In contrast to the standard Q parameter for an infinitely thin two-dimensional disc, our generalized Toomre Q parameter depends explicitly on the disc thickness and the location. In the limit of an infinitely thin disc, our result naturally reduces to Toomre’s criterion for a stellar disc and to Kalnajs’s result for a gaseous disc. In addition, the significant role played by the finite thickness of the galactic disc on the spatial structure of the stellar arms and the gaseous arms in the galactic plane is also briefly discussed. Application of our theory to the disc models with two stellar arms and four gaseous arms, gas content 15% and the total surface density in the solar neighbourhood σ = 52M0pc-2 but with the thickness parameter α in the range of 3.0 < α < 4.0 (250pc < hz < 325pc) appropriate to our Galaxy yields good results in general agreement with recent observations.
 Select Discovery of the 26 OH Megamaser Spots in the Circumnuclear Torus of IRAS10173+0828 with MERLIN Observations YU Zhi-Yao Chin. Phys. Lett. 2005, 22 (3): 780-782 .   Abstract   PDF(pc) (174KB) ( 655 ) We present the discovery of 26 OH megamaser spots in circumnuclear torus of galaxy IRAS10173+0828 with MERLIN observations. The physical parameters of the 26 OH megamaser spots are obtained.
 Select A Conjecture on the Origin of Dark Energy GAO Shan Chin. Phys. Lett. 2005, 22 (3): 783-784 .   Abstract   PDF(pc) (173KB) ( 788 ) A conjecture on the origin of the dark energy in our universe is proposed. The analysis indicates that the dark energy may originate from the quantum fluctuations of space--time limited in our universe. Applying both the uncertainty principle and the holographic principle, the author finds that the density of such quantum fluctuation energy is ρ V = 3c4 /32GLH 2, where LH is the size of the event horizon of our universe and G is the gravitational constant. Using this dark energy model which contains no adjustable parameters, we obtain the current fraction ΩΛ≡ ρV/ρc π/4 and the corresponding equation of state w(z) approximate - 1 + (1 - π /4)z with ρc being the critical energy density. These theoretical results are perfectly consistent with the recent cosmological observations. The striking coincidence implies that the quantum fluctuation energy of space--time may be the only source of dark energy. In addition, the analysis shows that the vacuum fluctuation energy does exist, but it comes from space--time rather than matter. This may have some deep implications for discrete space--time and quantum gravity.
73 articles