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Volume 18 Issue 8
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Original Articles
Extracting Information from the Atom-Laser Wave Function Using Interferometric Measurement with a Laser Standing-Wave Grating
LIU Zheng-Dong, ZENG Liang, LIN Yu, WU Qiang, ZHU Shi-Yao
Chin. Phys. Lett. 2001, 18 (8): 1000-1003 .  
Abstract   PDF(pc) (213KB) ( 393 )
The reconstruction of the atom-laser wave function is performed using interferometric measurement with a standing-wave grating, and the results in this scheme are studied. The relation between the measurement data and the atomic wave function are also presented. This scheme is quite applicable and effectively avoids the initial random phase problem of the method that employs the laser running wave. The information which is encoded in the atom-laser wave is extracted.
Probabilistic Teleportation of the Three-Particle Entangled State via Entanglement Swapping
LU Hong
Chin. Phys. Lett. 2001, 18 (8): 1004-1006 .  
Abstract   PDF(pc) (212KB) ( 852 )
A scheme of teleportation of a three-particle entangled state via entanglement swapping is proposed. It is shown that if a two-particle entangled state and a three-particle entangled state (both are not maximum entangled states) are used as quantum channels, probabilistic teleportation of the three-particle entangled state can be realized.
Bubbles Created from Vacuum Fluctuation
LIU Liao, HE Feng,
Chin. Phys. Lett. 2001, 18 (8): 1007-1008 .  
Abstract   PDF(pc) (163KB) ( 449 )
The authors show that the bubbles S2 x S2 can be created from vacuum fluctuation in the background de Sitter universes of k = 0,1, so the space-time foam-like structure might really be constructed from bubbles of S2 x S2 in the very early inflating phase of our universe. Still, whether such foam-like structure persisted during the later evolution of the universe is a problem unsolved at present.
Gravitational Effects Near the Kerr-Newman Black Hole
WANG Yong-Jiu, TANG Zhi-Ming
Chin. Phys. Lett. 2001, 18 (8): 1009-1011 .  
Abstract   PDF(pc) (205KB) ( 364 )
We have reached a solution of Dirac equation and the energy spectrum of electron in the gravitational field of the Kerr-Newman black hole. The results are interesting in astrophysics for observation of the black hole.
Precise Determination of Separation Between Spherical Attracting Masses in Measuring the Gravitational Constant
LUO Jun, WANG Wen-Min, HU Zhong-Kun, WANG Xue-Li
Chin. Phys. Lett. 2001, 18 (8): 1012-1014 .  
Abstract   PDF(pc) (324KB) ( 370 )
A rotating gauge method is used to measure the span between two spheres with high precision in determination of the gravitational constant G. A rectangular gauge block slightly shorter than the span is located horizontally between two spheres, and the angle between two symmetric bounding points during rotation can be determined by measuring the shift of a laser beam passing through an optical plate fixed on the gauge block. Experimental results show that the uncertainty in the determination of the span between the two spheres is less than 0.5 μm.
Estimation of Local Energy Density in Relativistic Heavy-Ion Collisions
ZHANG Jing-Shan, MA Zhong-Biao, GAO Chong-Shou,
Chin. Phys. Lett. 2001, 18 (8): 1015-1017 .  
Abstract   PDF(pc) (209KB) ( 329 )
The energy density for the central region in relativistic heavy-ion collisions can be estimated via the pseudorapidity distribution of transverse energy. The way to estimate the local energy density for the central region in relativistic heavy-ion collisions is proposed, in which only final state particles emitted from the same source are included. The energy density arrived in the NA49 experiments is about 0.9 GeV/fm3.
Inclusive Glueball Production in High-Energy p+p(P) Collisions
PENG Hong-An, DUAN Chun-Gui, HE Zhen-Min
Chin. Phys. Lett. 2001, 18 (8): 1018-1020 .  
Abstract   PDF(pc) (348KB) ( 362 )
Using the factorizable character of amplitudes for the double diffractive process in the Landshoff-Nachtmann model, we have discussed the inclusive glueball production in high-energy pp collision via the fusion process of two non-perturbative gluons, and have compared it with double diffractive alike process. We found that, as the c.m. energy Ecms increases from 20 to 20000 GeV, the cross sections of the latter process are about one to two orders larger than the former. Such an outcome could be explained from the hypothesis of duality between glueballs and Promeron.
Contribution of Vector Meson Dominance to the Single-Spin Azimuthal Asymmetry in Semi-inclusive Pion Electro-Production
XU Qing-Hua, LIANG Zuo-Tang
Chin. Phys. Lett. 2001, 18 (8): 1021-1023 .  
Abstract   PDF(pc) (281KB) ( 427 )
We calculate the contribution of vector meson dominance to deeply inelastic lepton-nucleon scattering in the kinematic region of the HERMES experiment. The results obtained show that this contribution is quite significant. Together with the fact that there exist very striking left-right asymmetries for hadron produced in single-spin hadron-hadron collisions, these results imply that the single-spin azimuthal asymmetry observed by HERMES cannot be simply regarded as a pure fragmentation effect.
Halo-like Structures Observed in 209Pb
LIU Zu-Hua
Chin. Phys. Lett. 2001, 18 (8): 1024-1026 .  
Abstract   PDF(pc) (328KB) ( 390 )
The density distributions of the last neutron in 209Pb wereinvestigated by analysis of the 208Pb(d,p)209Pb transfer reactions at 8 MeV. The results show that the last neutron in the 2d5/2,3s1/2,1g7/2 and 2d3/2 states is present with appreciable probability at distances much larger than the core radius. Therefore, these states should be the neutron halo or skin states. Moreover, the density distributions extracted illustrate that there is intrinsic relationship between the node number of state and the halo formation.
The πh11/2 Band-Crossing and Possible Octupole Correlations in 122Ba
ZHU Sheng-Jiang, M. Sakhaee, YANG Li-Ming, GAN Cui-Yun, ZHU Ling-Yan, XU Rui-Qing, JIANG Zhuo, ZHANG Zheng, LONG Gui-Lu, WEN Shu-Xian, WU Xiao-Guang
Chin. Phys. Lett. 2001, 18 (8): 1027-1029 .  
Abstract   PDF(pc) (393KB) ( 759 )
High-spin states in 122Ba have been investigated in the 107Ag(19F, 4n) reaction by in-beam γ-ray spectroscopic methods. The ground-state band has been observed with spin up to 20ħ and a negative-parity band is identified with spin state up to 19ħ. A band-crossing in the yrast band is observed at a rotational frequency of ħω ≈ 0.36 MeV and, in accordance with cranked shell model calculations, is interpreted as arising from the alignment of two h11/2 protons. Strong E1 transitions between the negative-parity and the yrast bands have been observed, which are proposed as possible evidence for octupole correlations.
Static Properties of Λ-Hypernuclei
TAN Yu-Hong, LUO Yan-An, NING Ping-Zhi, MA Zhong-Yu
Chin. Phys. Lett. 2001, 18 (8): 1030-1032 .  
Abstract   PDF(pc) (246KB) ( 387 )
Static properties of Λ-hypernuclei are calculated self-consistently in the relativistic mean-field model. The effect of Λ on the core nucleons are investigated. It is found that the rms radii of neutron become smaller than those of ordinary nuclei, when a closed-shell nuclear core is embeded in a 1s1/2 Λ hyperon is added.
Measurements of Total Reaction Cross Sections for Exotic Nuclei Close to the Proton Drip-line at Intermediate Energies and Observation of a Proton Halo in 27P
FANG De-Qing, SHEN Wen-Qing, FENG Jun, CAI Xiang-Zhou, MA Yu-Gang, ZHANG Hu-Yong, ZHONG Chen, ZHAN Wen-Long, GUO Zhong-Yan, XIAO Guo-Qing, WANG Jian-Song, WANG Jin-Chuan, LI Jia-Xing, WANG Meng, WANG Jian-Feng, NING Zhen-Jiang, WANG Quan-Jin, CHEN Zhi-Qiang
Chin. Phys. Lett. 2001, 18 (8): 1033-1036 .  
Abstract   PDF(pc) (383KB) ( 507 )
Measurements of total reaction cross sections (σR) for some proton-rich nuclei (N = 11-15 isotones) on carbon target at intermediate energies have been performed on the Radioactive Ion Beam Line of the Heavy Ion Research Facility in Lanzhou. A large enhancement of σR for 27P has been observed than for its neighbors. Evidence for a proton halo in 27P has been revealed in the Glauber analysis of the total reaction cross sections in terms of the difference factor d.
Experimental Probe to the Isospin-Dependent Properties of Hot Nuclei in Reactions 40Ar+112,124Sn at 30 MeV/u
XIAO Zhi-Gang, JIN Gen-Ming, WU He-Yu, WEI Zhi-Yong, WANG Hong-Wei, DUAN Li-Min, LIU Yong-Ying, LI Zu-Yu, ZHANG Bao-Guo, ZHU Yong-Tai, WANG Su-Fang, LU Zhao-Hui, ZHU Hai-Dong, HU Rong-Jiang
Chin. Phys. Lett. 2001, 18 (8): 1037-1039 .  
Abstract   PDF(pc) (305KB) ( 387 )
Protons are emitted much more affluently in neutron-deficient system 40Ar+112Sn while triton emissions are greater in a neutron-rich system 40Ar+124Sn at incident energy of 30 MeV/u. Similar to neutron, proton emission provied a dominant contribution to neutralize the system N/Z in the decay process of the hot nuclei. The emission of hydrogen isotopes with high energies is much enhanced in the 112Sn system. The original temperature of the hot nuclei in the 40Ar+112Sn reaction is 5.8±0.3 MeV, about 0.7 MeV higher than 5.1±0.3 MeV as in the 40Ar+124Sn reaction.
Entrance Channel Dependence of the Isospin Effects of the Nuclear Stopping in Intermediate Energy Heavy-Ion Collisions
YANG Yan-Fang, LIU Jian-Ye, ZUO Wei, GUO Wen-Jun, ZHAO Qiang
Chin. Phys. Lett. 2001, 18 (8): 1040-1043 .  
Abstract   PDF(pc) (462KB) ( 488 )
The entrance channel dependence of the isospin effects of nuclear stopping in intermediate energy heavy-ion collisions has been studied by using an isospin-dependent quantum molecular dynamics with three different kinds of symmetry potentials. It is shown that nuclear stopping is sensitive to the beam energy, the impact parameter and the mass of the colliding system, specially very sensitive to the isospin dependence of in-medium nucleon-nucleon cross section, but insensitive to symmetry potential and the ratio of neutron to proton of colliding system. From this investigation. It is proposed that nuclear stopping can be used as a new probe to extract the information on the isospin dependence of in-medium nucleon-nucleon cross section in intermediate energy heavy-ion collisions.

Fluctuations of K/π Ratios in Pb-Pb Collisions at Super Proton Synchrotron Energies
ZHOU Dai-Mei, WANG Xiao-Rong, YANG Chun-Bin, CAI Xu
Chin. Phys. Lett. 2001, 18 (8): 1044-1046 .  
Abstract   PDF(pc) (230KB) ( 363 )
The Monte Carlo generator (LUCIAE) is used to investigate the
fluctuations of K/π ratios at super proton synchrotron energies. The distribution of K/π ratios seems to be Gaussian from the simulation and the distribution width, and the relative variance are larger than those from the Poissonian-type pure-statistical fluctuations. This discrepancy might be attributed to the dynamical fluctuations involved in the LUCIAE model.
Two-Colour Effect on the Ionization and Harmonic Generation of One-Dimensional He+
QU Wei-Xing, GAN Ming-Long, XIA Yu-Xing, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2001, 18 (8): 1047-1049 .  
Abstract   PDF(pc) (432KB) ( 409 )
Using the one-demensional ion mode, We theoretically investigate the dynamics ionization process and the high-order harmonic generation of the He+ subject to different kinds of two-colour laser pulse with the same fundamental frequency but various harmonic frequencies. It is found that from the results calculated by numerically solving the time-dependent Schrödinger equation, the two-colour laser pulse with the fundamental frequency and harmonic frequency enables the power spectrum of high-order harmonic generation to increase by a few orders of magnitude and the yield of He+ to enhance significantly when the harmonic frequency of laser pulse is close to the energy interval between the ground state and the first excited state of He+; even the harmonic field added into the pulse is much weaker than the fundamental one.
Temporal Behaviour of Harmonics from One-Dimensional H+2 in an Ultrashort Laser Pulse
QU Wei-Xing, XIA Yu-Xing, GAN Ming-Long, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2001, 18 (8): 1050-1052 .  
Abstract   PDF(pc) (642KB) ( 415 )
With the method of wavelet transform, we consider the temporal
behaviour of high-order harmonic generation from one-dimensional H+2 exposed to an ultrashort laser pulse with a duration of tens of femtoseconds. The results, which are calculated by numerically solving the corresponding time-dependent Schrödinger equation with the split-operator method in the non-Born-Oppenheimer approach, show that: (1) The high-order harmonics in the cut-off range emitted as a train of pulses have better coherence than those in the plateau. (2) The harmonics are emitted early in time when the intensity of laser pulse increases.
An Empirical Formula of Atomic K-Shell Ionization Cross Sections by Electron Impact
TANG Chang-Huan, AN Zhu, FAN Xiao-Qiang, LUO Zheng-Ming
Chin. Phys. Lett. 2001, 18 (8): 1053-1055 .  
Abstract   PDF(pc) (462KB) ( 406 )
An empirical formula is proposed to describe the K-shell
ionization cross sections by electron impact over a wide range of atomic numbers and overvoltages U (the ratio between the electron incident energy and the binding energy of the electrons in the K-shell). The study is based on the analysis of existing experimental data of K-shell ionization cross sections. The expression shows the results in good agreement with the data for Z < 6 atoms as well as for 6 ≤ Z ≤ 79.
Fragmentation Mechanism of Fullerenes in the Positive and Negative Ion Channels
KONG Qing-Yu, ZHAO Li, ZHUANG Jun, QIAN Shi-Xiong, LI Yu-Fen
Chin. Phys. Lett. 2001, 18 (8): 1056-1059 .  
Abstract   PDF(pc) (525KB) ( 400 )
The authors have performed the photofragmentation studies of pristine C60 and C60/C70 composites on the reflectron time-of-flight mass spectrometer (RTOF MS) in the positive and negative ion channels. The mechanism of the formation of daughter fullerenes in the negative ion channel and the enhancement of fullerene coalescence reactions have been discussed compared to our previous studies on the linear TOF. The 5 cm free expansion path in the RTOF experiments provides sufficient time and favorable environment for the electrons to attach to the neutral daughter species, so it is thought to play a key role for the appearance of strong mass peaks of anionic fragmentation and aggregation fullerene products. The appearance of odd-numbered “fullerene”fragments is briefly discussed.
Electronic Structure and Stability of C20 Isomers
CAO Ze-Xian
Chin. Phys. Lett. 2001, 18 (8): 1060-1063 .  
Abstract   PDF(pc) (256KB) ( 400 )
The electronic structure of C20 cluster in monocyclic ring, bowl and fullerene isomers has been calculated using the tight-binding scheme developed by Harrison, starting in particular from the sp2.803-hybrids for the fullerene structure. The study of energetics predicts the fullerene to be the ground state with the bowl and ring lying over 1.32 and 3.35 eV higher in energy. The total energies will be lowered by Peierls or Jahn-Teller distortion, but the energetic ordering remains unchanged. It is also shown that the range of valence electron, the level difference between the highest occupied molecular orbital and the lowest unoccapied molecular orbital as well as the σ - π gap, which are less sensitive to the exact geometry, vary in the ring, bowl and fullerene sequence.
Scattering-Suppression in Photochromic LiNbO3:Fe:Mn Non-volatile Holographic Recording
LIU De-An, LIU Li-Ren, LIU You-Wen, ZHOU Chang-He, XU Liang-Ying
Chin. Phys. Lett. 2001, 18 (8): 1064-1066 .  
Abstract   PDF(pc) (593KB) ( 470 )
We propose and experimentally investigate a new scheme capable of suppressing the light-induced scattering by periodical incoherent erasure during every non-volatile holographic recording cycle in photochromic LiNbO3:Fe:Mn crystals. The results demonstrate that the scattering noise is suppressed effectively, and the final diffraction efficiency of the fixed grating is significantly enhanced, rather than decrease, by about 30% compared with the conventional recording procedure. The period of the recording and incoherent erasure cycle is theoretically calculated and experimentally optimized.
Nonlinear Theory of Light Speed Reduction in a Three-Level Λ System
WANG De-Zhong, LI Dai-Jun, LIU Xia-J, LI Shi-Qun, , WANG Yu-Zhu
Chin. Phys. Lett. 2001, 18 (8): 1067-1068 .  
Abstract   PDF(pc) (194KB) ( 375 )
We present a nonlinear theory of light velocity reduction in a three-level Λ system based on electromagnetically induced transparency. Analysis shows that probe field propagates with a velocity that is quite strongly dependent on its intensity instead of being merely approximately dependent on the coupling intensity. Moreover, the minimum group velocity of the probe field is analytically given for a given input power.
Momentum Transfer of an Atom Moving in an Optical Cavity
ZHANG Jing-Tao, XU Zhi-Zhan
Chin. Phys. Lett. 2001, 18 (8): 1069-1071 .  
Abstract   PDF(pc) (332KB) ( 344 )
When an atom moves in an optical cavity, the total momentum of the atom does not keep constant. We study a two-level atom moving slowly in an optical cavity, and give the time dependence of its mean momentum. It is found that when the initial momentum of the atom is larger than that of the photon, the mean momentum oscillates around a value less than the initial value, But, if the initial momentum is less than the momentum of the photon, the mean momentum of the atom is greater than its initial value in most time.
Quantum State Engineering by Superpositions of Coherent States along a Straight Line in Cavity Quantum Electrodynamics
ZHENG Shi-Biao
Chin. Phys. Lett. 2001, 18 (8): 1072-1073 .  
Abstract   PDF(pc) (161KB) ( 351 )
A scheme is proposed for generating the superpositions of several coherent states in a cavity field with dispersive cavity quantum electrodynamics (QED). In the scheme, a sequence of atoms interact dispersively with the cavity field, connected with a microwave source, and is manipulated by classical fields, followed by state-selective measurements. In this way, the cavity field is collapsed onto a superposition of several coherent states along a straight line with controllable coefficients.This scheme provides the possibility for quantum state engineering via coherent-state superpositions in cavity QED for the first time.
High Power 1.5μm InGaAsP/InP Integrated Superluminescent Light Source
LIU Yang, SONG Jun-Feng, ZENG Yu-Ping, WU Bin, ZHANG Yuan-Tao, QIAN Ying, SUN Ying-Zhi, DU Guo-Tong
Chin. Phys. Lett. 2001, 18 (8): 1074-1077 .  
Abstract   PDF(pc) (599KB) ( 503 )
The axis of the integrated superluminescent light source was tilted with respect to the output facet normal for lasing suppression. A new phenomenon (lasing suppression) was observed in the tilted integrated device. Three new schemes were proposed and demonstrated further to suppress the lasing by analysing the reason of lasing in the tilted structure. The lasing was suppressed successfully at high pumping level, and high superluminescent power (more than 300 mW}) was obtained at a pulsed condition with the spectral full width at half maximum of 25-30 nm.
Optical Limiting Performance of a Crystal Violet Cation Fulleride Salt
LIU Chun-Ling, GONG Qi-Huang, CHEN Yi-Xian, CHEN Hui-Ying, IANG Di
Chin. Phys. Lett. 2001, 18 (8): 1078-1080 .  
Abstract   PDF(pc) (353KB) ( 893 )
Optical limiting properties of a crystal violet cation fulleride salt dissolved in tetrahydrofuran have been studied by using 10 ns, 532 nm laser pulses. The fluence-dependent transmissivity measurements were performed on the samples with the same concentration and different path lengths in a collimated optical set-up. For comparison, the fluence-dependent transmissivities of fullerene C60 and crystal violet solutions were also measured under the same linear transmissivity. The nonlinear optical limiting effect of the fulleride salt in tetrahydrofuran was even slightly stronger than that of C60 in toluene.
Deep Ultraviolet Harmonic Generation with KBe2BO3F2 Crystal
CHEN Chuang-Tian, LÜ, Jun-Hua, WANG Gui-Ling, XU Zu-Yan, WANG Ji-Yang, ZHANG Cheng-Qian, LIU Yao-Gang
Chin. Phys. Lett. 2001, 18 (8): 1081-1081 .  
Abstract   PDF(pc) (200KB) ( 550 )
A special prism coupling technique with the KBe2BO3F2 crystal is adopted to produce deep ultraviolet light including the fourth harmonic from an Nd:YAG laser, for which a conversion efficiency as high as 10% has been obtained.
A Novel Polarizer Made from Two-Dimensional Photonic Bandgap Materials
ZHANG Chun, QIAO Feng, WAN Jun, ZI Jian
Chin. Phys. Lett. 2001, 18 (8): 1082-1084 .  
Abstract   PDF(pc) (449KB) ( 432 )
We demonstrate theoretically that two-dimensional photonic bandgap materials are indeed perfect polarizers provided that they have a proper photonic band structure along the incident direction of light. This kind of polarizer is fundamentally different from the conventional ones. It can function in a wide frequency range with high performance and its size can be made very compact, which renders it useful as a micropolarizer in micro-optics.
Theoretical Description for the Focused Parametric Field After Inserting a Sample
ZHANG Dong, LU Rong-Rong, GONG Xiu-Fen
Chin. Phys. Lett. 2001, 18 (8): 1085-1087 .  
Abstract   PDF(pc) (287KB) ( 338 )
In the parabolic and quasi-linear approximations, a theoretical description for the acoustical parametric field from a focusing source after inserting a sample is derived by using superposition method of Gaussain beams. This model takes into consideration of attenuation, diffraction and nonlinear effects. The numerical computations of the axial sound pressure amplitude curves for the difference frequency sound after insertion of a sample are presented. The results indicate that this new model can be extended to measure or image the nonlinear parameter in the focused field.
Hot Dust Acoustic Solitary Waves in Dust Plasma with Variable Dust Charge
DUAN Wen-Shan, LÜ, Ke-Pu, ZHAO Jin-Bao
Chin. Phys. Lett. 2001, 18 (8): 1088-1089 .  
Abstract   PDF(pc) (172KB) ( 385 )
Considering the variation of dust charges, We have analytically studied the governing equation for the system with the same model as that for cold dust acoustic waves in a demagnetized plasma but the contribution of hot dust. The result indicates that the governing equation is also a Korteweg-de Vries equaiton, although its amplitude and width will be smaller compared with the cold dust case.
Electron Heat Diffusivity in the HT-7 Tokamak with Si-Coating Wall
ZHANG Xian-Mei, WAN Bao-Nian, RUAN Huai-Lin, WU Zhen-Wei
Chin. Phys. Lett. 2001, 18 (8): 1090-1091 .  
Abstract   PDF(pc) (341KB) ( 402 )
Electron heat diffusivity inferred from the electron power balance was studied in the ohmically heated plasma on an HT-7 tokamak. The results obtained before and after siliconization were compared and it is found that the diffusivity is reduced obviously in the half of the outer region (r/a > 0.5) after siliconization, which was the reason why energy confinement was improved after siliconization.
Fluctuation Phenomenon Analysis of an Arc Plasma Spraying Jet
ZHAO Wen-Hua, TIAN Kuo, LIU Di, ZHANG Guan-Zhong
Chin. Phys. Lett. 2001, 18 (8): 1092-1094 .  
Abstract   PDF(pc) (374KB) ( 793 )
The effects of three factors, including the power supply, the arc behaviour in the arc channel and the fluid dynamic process of the jet, on a plasma spraying jet have been experimentally detected by means of spectroscopic diagnostic techniques. The fast Fourier transform method has been applied to the analysis on the arc voltage and spectral line intensity of the jet. The three factors have been studied and distinguished from each other.
Some Nonlinear Phenomena in a Preformed Underdense Plasma
CAO Li-Hua, LIU Zhi-Yong, CHANG Wen-Wei, YUE Zong-Wu
Chin. Phys. Lett. 2001, 18 (8): 1095-1097 .  
Abstract   PDF(pc) (515KB) ( 360 )
The propagation of a laser pulse with a peak intensity 1019W/cm2 through the preformed underdense plasma with the density 0.014nc are studied by using two-dimensional particle-in-cell simulations. The longitudinal electron heating is identified and verified, and its major property agrees with the theoretical prediction. The electron distributions in phase space, patterns of the electric fields, profiles of the ion or electron density and other plasma nonlinear phenomena are presented and discussed.
Helicon Discharge Using a Nagoya Type III Antenna
FANG Tong-Zhen, WANG Long, JIANG Di-Ming, ZHANG Hou-Xian
Chin. Phys. Lett. 2001, 18 (8): 1098-1100 .  
Abstract   PDF(pc) (377KB) ( 586 )
A helicon mode discharge is realized in a newly erected set-up and two jumps are observed in the variation of plasma density with the controlled magnetic field, which is a typical characteristic of helicon mode discharge. A reasonable explanation is proposed for the appearance of the density jumps. The helicon wavelength is evaluated to be about 20 cm and it is nearly constant in the helicon mode discharge. The density obtained is nearly up to 3.5 x 1018m-3 with only 0.5Pa argon pressure and 300W radio frequency power supply, and it is more than one magnitude higher than that in other discharges at comparable pressures and input powers. The electron temperature is found to be increased as the pressure is decreased.
Optimization of Electron Density and Temperature Profiles in Tokamaks via Safety Factor Profile
QIU Xiao-Ming, PENG Xiao-Dong
Chin. Phys. Lett. 2001, 18 (8): 1101-1102 .  
Abstract   PDF(pc) (235KB) ( 445 )
The turbulent particle and thermal transport scaling laws are derived by means of Lagrangian invariant of trapped electron dynamics in tokamaks, which are in good agreement with experimental results. On the basis of the two scaling laws, it is proposed that the optimization of electron density and temperature profiles can be achieved by designing a desirable safety factor profile.
Assistant Anode in a Cathodic Arc Plasma Source
ZHANG Tao, ZHANG Hui-Xing, Ian. G. Brown, Paul K. Chu
Chin. Phys. Lett. 2001, 18 (8): 1103-1104 .  
Abstract   PDF(pc) (264KB) ( 571 )
The performance and characteristics of a cathodic arc plasma source, consisting of a titanium cathode, an anode with and without a tungsten mesh, and a coil producing a focusing magnetic field between the anode and cathode, are investigated. The high transparency and large area of the mesh allow a high plasma flux to penetrate the anode from the cathodic arc. The mesh helps to decrease the arc resistance and the ignition voltage of the cathodic arc in the focusing magnetic field, and increase the life of the source. which means that the source makes the cathodic arc easily and greatly stabilized during the operation when a focusing magnetic field exists in the source.
Electronic Localization Length of Carbon Nanotubes with Different Chiral Symmetries
YANG Hua-Tong, DONG Jin-Ming, XING Ding-Yu
Chin. Phys. Lett. 2001, 18 (8): 1105-1107 .  
Abstract   PDF(pc) (326KB) ( 510 )
The electronic localization lengths λ of metallic carbon nanotubes with different chiral symmetries have been calculated by one parameter scaling method. It is found that λ is independent of the nanotube chirality, but depends linearly on their diameters. The dependence of λ on the disorder strength W has also been studied, and a power-law relation between λ and W is also found to be independent of the tube chirality. Our numerical results are in good agreement with recent experimental observations and other theoretical result for only the “armchair” nanotubes.
Electrical Properties of ZnO/Si Heterostructure
LIU Ci-Hui, CHEN Yu-Lin, LIN Bi-Xia, ZHU Jun-Jie, FU Zhu-Xi, PENG Cong, YANG Zhen
Chin. Phys. Lett. 2001, 18 (8): 1108-1110 .  
Abstract   PDF(pc) (430KB) ( 560 )
The electrical Properties of a type of semiconductor heterostructure fabricated by depositing zinc oxide film on a silicon substrate are investigated. The I-V, I-T curves, and deep level transient spectra are measured. From these results, we acquire the information of the characteristics of the junction, and compute some energy levels of the samples.

Change of Work Function of Pd, Ag, K on Al(001) as a Function of External Electric Field
ZHU Zi-Zhong, HOU Zhu-Feng, HUANG Mei-Chun, HUANG Rong-Bin, ZHENG Lan-Sun
Chin. Phys. Lett. 2001, 18 (8): 1111-1113 .  
Abstract   PDF(pc) (385KB) ( 796 )
We present a local density functional calculation of the effect of an external electric field on the work function change of Pd and Ag adsorption on an Al(001) surface. The adsorption of K has also been considered for comparison. We found that the work functions for all the systems increased linearly when the strength of external electric field was increased. Since the polarized electrons at the interstitial regions between the adsorbate and substrate for Pd/Al(001) and Ag/Al(001) react to the external electric field differently, the subtle differences between Pd/Al(001) and Ag/Al(001) bondings has been characterized through the comparison of slopes of the work function change versus electric field.

Giant Magnetic Entropy Change in Manganese Perovskites near Room Temperature
ZHONG Wei, CHEN Wei, WANG Jin-Hui, DU You-Wei
Chin. Phys. Lett. 2001, 18 (8): 1114-1116 .  
Abstract   PDF(pc) (408KB) ( 480 )
A large magnetic entropy change about twice as high as that of pure gadolinium metal near room temperature has been discovered in manganese perovskites La0.837Ca0.098Na0.038Mn0.987O3.00(8.3 J.kg-1.K-1, at 256K) and La0.822Ca0.096K0.043Mn0.974O3.00 (6.8 J.kg-1.K-1, at 265 K) under a magnetic field of 1.5 T. This phenomenon indicates that manganese perovskites have potential applications for magnetic refrigerants in an extended temperature range even near room temperature.
Interface Effects on the Magneto-Optical Kerr Effect and Optical Properties in Co/Ni Multilayer
WANG Hai, ZHOU Yun-Song, CHEN Jin-Chang, LI Tong, ZHAO Hong-Wu, ZHAN Wen-Shan, WANG Song-You, CHEN Liang-Yao
Chin. Phys. Lett. 2001, 18 (8): 1117-1119 .  
Abstract   PDF(pc) (397KB) ( 506 )
The influence of interfaces on the magneto-optical Kerr effect in the Co/Ni multilayer has been investigated. It was found that the magnetic-optical Kerr rotation varies with the numbers of interfaces (x) in Co/Ni multilayer, which indicated that the interface states play an important role in the Kerr effect. Moreover, ellipticity and optical constants n and k are also found to vary with x. Some possible mechanisms have been discussed.
Two-Photon Absorption and Optical Power Limiting Based on New Organic Dyes
ZHOU Guang-Yong, WANG Chun, LEI Hong, WANG Dong, SHAO Zong-Shu, JIANG Min-Hua
Chin. Phys. Lett. 2001, 18 (8): 1120-1122 .  
Abstract   PDF(pc) (433KB) ( 609 )
Two new organic dye samples J and L with a large two-photon absorption (TPA) cross section have been reported. The linear absorption spectra show that there is no linear absorption at the wavelength from 650 to 1200 nm. The molecular TPA cross section was measured to be as high as 2.59 x 10-47cm4.s and 2.98 x 10-47cm4.s at 1064 nm for samples J and L, respectively. The input-output curves indicate that there is a clear optical power limiting behaviour when the input intensity is higher than 0.4 GW/cm2. Furthermore, basic theorety of TPA process has been discussed.
Raman Analysis of a Crystalline SiC Sample Prepared from Carbon-Saturated Melt of Silicon
MA Jian-Ping, CHEN Zhi-Ming, LU Gang, HANG Lian-Mao, FENG Xian-Feng, LEI Tian-Min
Chin. Phys. Lett. 2001, 18 (8): 1123-1125 .  
Abstract   PDF(pc) (383KB) ( 1142 )
Crystalline SiC samples were prepared in solidification of silicon melt saturated by carbon solved from the inner wall of a graphite crucible. The Crystalline structure of the samples was analysed in Raman spectroscopy and confirmed as 3C-SiC both in x-ray diffraction and x-ray photoelectron spectroscopy(XPS). The Raman spectra of the samples present a strong sharp peak located at 796.3 cm-1 with a full width at half maximum about 6 cm-1 and three weak peaks broadened around 1525.6, 1631.4 and 1719.1 cm-1, respectively. The former belongs to the transverse optical phonons of 3C-SiC, while the latter can be attributed to the second-order scattering. However, the longitudinal optical mode of 3C-SiC has not been found for our samples. An additional broadened peak at 532.2 cm-1 may imply the existence of some lattice defect in the samples, which is related to nitrogen introduced unintentionally into the lattice in the growth process and confirmed in XPS of N 1s binding energy centered at 400.9 eV.
Effects of Pulse Drive on Single Bubble Sonoluminescence
CHEN Wei-Zhong, CHEN Xi, LU Mei-Jun, MIAO Guo-Qing, WEI Rong-Jue
Chin. Phys. Lett. 2001, 18 (8): 1126-1128 .  
Abstract   PDF(pc) (375KB) ( 454 )
Single bubble sonoluminescence (SBSL) flashes have been steadily upscaled by a sinusoidal wave with a pulse at each cycle at some suitable phase positions, which proves the prediction of the spiking SBSL suggested by Moss et al. [Phys. Lett. A 211(1996)69]. Based on the Rayleigh-Plesset bubble dynamics, the numerical simulation shows a well qualitative agreement with those measured in experiment.

Effective Dielectric Properties of an Array of Multishell Carbon Nanotubes
LÜ, Wen-Gang, WANG Rong-Zhou, DONG Jin-Ming
Chin. Phys. Lett. 2001, 18 (8): 1129-1131 .  
Abstract   PDF(pc) (317KB) ( 523 )
Using a photonic band calculation method, we calculate the effective dielectric function of an array of carbon nanotubes which have a simple equivalent isotropic dielectric function. The results for the equivalent dielectric function and for the local graphite-like dielectric tensor are found to be almost the same. Taking a fixed outer diameter of the nanotubes to be 10 nm and a fixed distance between them to be 10.3 nm, we investigate the effect of the hollow core and found that the ratio of the inner to the outer radii is approximately larger than 0.3. By taking a large ratio of 0.58, the theoretical results are improved greatly and can describe the experimental data very well.
Field Emission from Nanostructured Carbon Films on Si Tips
WANG Wan-Lu, LIAO Ke-Jun, HU Cheng-Guo, FANG Liang
Chin. Phys. Lett. 2001, 18 (8): 1132-1134 .  
Abstract   PDF(pc) (464KB) ( 459 )
Nanostructured carbon thin films on Si tips were prepared by hot filament chemical vapour deposition at different substrate temperatures. The Si tips and films were obtained under various deposition conditions in the same reaction chamber. It was found that the field emission properties from graphite-like nanostructured carbon on Si tips were greatly improved as compared with those of nanodiamond films on Si tips. A turn-on field of 1.2 V.cm-1 was observed for high sp2 content thin films on Si tips. The analysis showed that the field emission enhancement effect was caused by the tip geometry, tunnel effect and sp2 content in the films. However, the geometrical enhancement was greater than that of the tunnel and sp2 content effects.


Initial Growth of Thin Films with Low Nucleus Density and Linear Lateral Growth Rate on a Substrate Surface
SHAO Qing-Yi, FANG Rong-Chuan, ZHU Kai-Gui, LIAO Yuan, XUE Zeng-Quan
Chin. Phys. Lett. 2001, 18 (8): 1135-1137 .  
Abstract   PDF(pc) (280KB) ( 365 )
Based on corrected rate equations, the kinetics is revealed for initial growth of thin films with low nucleus density and linear lateral growth rate on a substrate surface. In this case, the mobility and coalescence terms in rate equations are neglected, and the coverage term takes a dominant role. All the calculated results are in agreement with experimental data. These results introduce a new scaling in the case of dominant coverage, which is different from the those in the case of coalescence or mobility in a dominant role.
Monte Carlo Simulation of Diamond Deposition at Low Temperature
DONG Li-Fang, ZHANG Yu-Hong
Chin. Phys. Lett. 2001, 18 (8): 1138-1140 .  
Abstract   PDF(pc) (322KB) ( 416 )
Diamond deposition at low temperature is investigated and the relationship between substrate temperature for diamond growth and the energy of the carbonaceous species is given. The electron energy distribution and velocity distribution during the electron assisted chemical vapor deposition have been obtained by using Monte Carlo simulation. The main results obtained are as follows. (1) The substrate temperature for diamond growth will be lower than 800°C when the carbonaceous species on the substrate have mobility energy. For example, if the energy of the carbonaceous species is 0.75 eV, the substrate temperature will be 380°C - 600°C. (2) The great number of atomic H on the substrate is of importance to the growth of diamond films.

Characterization of Microarc Oxidation Discharge Process for Depositing Ceramic Coating
YANG Guang-Liang, LÜ, Xian-Yi, BAI Yi-Zhen, JIN Zeng-Sun
Chin. Phys. Lett. 2001, 18 (8): 1141-1143 .  
Abstract   PDF(pc) (92KB) ( 704 )
The specific features of current variation during different stages of the microarc oxidation process were studied on the timescale. The cathodic current was found to be closely related to the microarc discharge. The discharge was responsible for the formation of a dense coating with unique physical characteristics. A method for obtaining high-quality coating has been discussed.
Electrorheological Effects of Cerium-Doped TiO2
YIN Jian-Bo, ZHAO Xiao-Peng,
Chin. Phys. Lett. 2001, 18 (8): 1144-1146 .  
Abstract   PDF(pc) (449KB) ( 358 )
It is found that doping of cerium ion into anatase TiO2 can improve the electrorheological (ER) effects of TiO2 and broaden operational temperature range. Especially, substitution of 7-11mol% of the cerium dopant for Ti can obtain a relatively high shear stress, τ = 7.4kPa (at 4kV/mm), which is ten times larger than that of pure TiO2 ER fluid. Also, the typical Ce-doped TiO2 ER fluid shows the highest shear stress at 80°C, but 40°C for pure TiO2 ER fluid. The dielectric loss and dielectric constant at low frequency of TiO2 is improved by the doping of cerium, and the temperature dependence of the dielectric properties shows an obvious difference between pure and doped TiO2 ER fluid. These can well explain the ER behaviour of doped TiO2. Furthermore, the change of rheological and dielectric properties is discussed on the basis of the lattice distortion and defects in TiO2 arising from the doping of cerium.
Field Effect Transistor with Self-Organized In0.15Ga0.85As/GaAs Quantum Wires as a Channel Grown on (553)B GaAs Substrates
LI Xian-Jie, YAN Fa-Wang, ZHANG Wen-Jun, ZHANG Rong-Gui, LIU Wei-Ji, AO Jin-Ping, ZENG Qing-Ming, LIU Shi-Yong, LIANG Chun-Guang
Chin. Phys. Lett. 2001, 18 (8): 1147-1149 .  
Abstract   PDF(pc) (589KB) ( 456 )
A functional field effect transistor with self-organized In0.15Ga0.85As/GaAs quantum wires (QWRs) as a channel was achieved by molecular beam epitaxy on a (553)B GaAs substrate. Both the three-dimensional image of atom force microscopy and the polarization of the photoluminance peaks reveal that the channel of the device is a self-organized QWR structure. The device with a gate-length of 2 μm and a source-drain spacing of 5μm performed a good enhancement-mode characteristic and a maximum transconductance of 65 mS/mm was obtained at the gate voltage of 1.0 V by the geometric gate-width at room temperature. The saturated drain current is as high as 5.6 mA. The device exhibited a much larger current capacity due to the high density of the self-organized QWRs in its channel layer. In addition, the effective gate width was discussed in comparison with the geometric gate width of the device, from which a larger maximum transconductance of 130 mS/mm could be estimated.
Magnetic Coupling of a Rotating Black Hole with the Surrounding Accretion Disc
WANG Ding-Xiong, XIAO Kan, LEI Wei-Hua
Chin. Phys. Lett. 2001, 18 (8): 1150-1152 .  
Abstract   PDF(pc) (243KB) ( 625 )
The evolution characteristics and energy extraction of a rotating black hole are investigated by considering magnetic coupling with the surrounding accretion disc. It is found that both mass and spin of the black hole might be reduced by the joint effects of disc accretion and magnetic coupling, provided that the latter is stronger than the former. The efficiencies of the two energy mechanisms are calculated and compared to a variety of parameters. In addition, the validity of the laws of black hole thermodynamics is discussed.
Gamma-Ray Burst Afterglows with Energy Injection: Homogeneous Versus Wind External Media
WANG Wei, DAI Zi-Gao
Chin. Phys. Lett. 2001, 18 (8): 1153-1155 .  
Abstract   PDF(pc) (284KB) ( 412 )
Assuming an adiabatic evolution of a gamma-ray burst (GRB)
fireball interacting with an external medium, we calculate the hydrodynamics of the fireball with an energy injection from a strongly magnetic millisecond pulsar through magnetic dipole radiation, and obtain the light curve of the optical afterglow from the fireball by synchrotron radiation. The results are given both for a homogeneous external medium and for a wind ejected by GRB progenitor. Our calculations are also available in both ultra-relativistic and non-relativistic phases. Furthermore, the observed R-band light curve of GRB000301C can be well fitted in our model, which might provide a probe of the properties of GRB progenitors.
53 articles