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Volume 20 Issue 5
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Original Articles
New Types of the Lie Symmetries and Conserved Quantities for a Relativistic Hamiltonian System
LUO Shao-Kai
Chin. Phys. Lett. 2003, 20 (5): 597-599 .  
Abstract   PDF(pc) (181KB) ( 426 )
For a relativistic Hamiltonian system, two new types of the Lie symmetries and conservation laws are given under infinitesimal transformations of groups. On the basis of the theory of invariance of the relativistic Hamiltonian equations under infinitesimal transformations and introducing infinitesimal transformations for time t, generalized coordinates qs and generalized momentums ps, we obtain the determining equations, the structure equations and the conserved quantities of the Lie symmetries. Introducing infinitesimal transformation for generalized coordinates qs and generalized momentums ps, we construct the Lie symmetrical transformations of the system, which only depend on the canonical variables. A set of conserved quantities are directly obtained from the Lie symmetries of the system. An example is given to illustrate the application of the results.
Wave Function of Coupled Quantum-Classical Oscillator
HE Wei-Zhong, XU Liu-Su, ZOU Feng-Wu
Chin. Phys. Lett. 2003, 20 (5): 600-601 .  
Abstract   PDF(pc) (166KB) ( 424 )
Considering classical environment to be a classical oscillator, we describe the dynamics of a system consisting of a quantum oscillator coupled to classical oscillator. Using the Born-Oppenheimer approximation and the method of adiabatic invariants, we derive the classically effective Hamiltonian describing the complete dynamics of the system and the wave function of quantum part of the system. We also present a new method for investigating the dynamics of the quantum system in classical environment.
Solution of the Dirac Equation with Special Hulthén Potentials
GUO Jian-You, , MENG Jie, , XU Fu-Xin
Chin. Phys. Lett. 2003, 20 (5): 602-604 .  
Abstract   PDF(pc) (194KB) ( 655 )
The Dirac equation for the special case of a spinor in the relativistic potential with the even and odd components related by a constraint is solved exactly when the even component is chosen to be the Hulthén potential. The corresponding radial wavefunctions for two-component spinor are obtained in terms of the hypergeometric function, and the energy spectrum of the bound states is obtained as a solution to a given equation by boundary constraints, in which the nonrelativistic limit reproduces the usual Hulthén potential.
Berry’s Phase in Noncommutative Spaces
S. A. Alavi
Chin. Phys. Lett. 2003, 20 (5): 605-607 .  
Abstract   PDF(pc) (193KB) ( 340 )
We discuss the perturbative aspects of noncommutative quantum mechanics. Then we study Berry's phase in the framework of noncommutative quantum mechanics. The results show deviations from the usual quantum mechanics, which depend on the parameter of space/space noncommutativity.

Experimental Quantum Key Distribution over 14.8 km in a Special Optical Fibre
GUI You-Zhen, HAN Zheng-Fu, MO Xiao-Fan, GUO Guang-Can
Chin. Phys. Lett. 2003, 20 (5): 608-610 .  
Abstract   PDF(pc) (267KB) ( 640 )
We present an experimental setup for quantum key distribution in a special optical fibre at the wavelength of 850 nm. The system employs the BB84 protocol to establish a secret key between Alice and Bob over 14.8 km. The key is encoded in the phase of very weak laser of average photon number 0.11 per pulse. The measured error rate is lower than 10%.
Density Distribution of Bose-Condensed Gas in a Three-Dimensiuonal Optical Lattice
XU Zhi-Jun, CHENG Cheng, XIONG Hong-Wei
Chin. Phys. Lett. 2003, 20 (5): 611-614 .  
Abstract   PDF(pc) (294KB) ( 366 )
For the Bose-condensed gas in a magnetic trap and three-dimensional optical lattice, the non-uniform distribution of the atoms in different lattice sites is investigated and a propagator method is used to study the evolution of the interference pattern after the combined potentials are switched off. The analytical result of the wave function at any time t is given and especially the motion of the side peaks is described by a simple analytical expression.
Exact Solutions for String Cosmology
WANG Xing-Xiang
Chin. Phys. Lett. 2003, 20 (5): 615-617 .  
Abstract   PDF(pc) (161KB) ( 688 )
Some more general cosmological solutions of Bianchi types II, VIII, and IX for a cloud string are presented. The physical implications of the solutions are briefly discussed. Our solutions include some of the results previously given in the literature as special cases.

Entropy of Neutrino Field in Kerr-Newman-de Sitter Space-time
GAO Chang-Jun, , SHEN You-Gen, ,
Chin. Phys. Lett. 2003, 20 (5): 618-621 .  
Abstract   PDF(pc) (217KB) ( 426 )
By using the improved brick wall model, we regard the two null horizons in Kerr-Newman-de Sitter space-time as two independent thermal equilibrium systems and we calculate the entropies of both horizons due to neutrino field. We propose that the so-called “ superradiant” modes cannot be considered because fermion fields does not display supperradiance. In fact, the nonsuperradiant part does exactly show the expected area-law entropy. Moreover, our cut-off ε, which does not require an angular cut-off, is independent of angle θ.

Dynamic Scaling Behaviour in (2+1)-Dimensional Kuramoto-Sivashinsky Model
QI Hong-Ji, JIN Yong-Hao, CHENG Chuan-Fu, HUANG Li-Hua, YI Kui, SHAO Jian-Da
Chin. Phys. Lett. 2003, 20 (5): 622-625 .  
Abstract   PDF(pc) (490KB) ( 599 )
We study the evolution of (2+1)-dimensional surface morphology in the Kuramoto-Sivashinsky (K-S) model by using the numerical simulation approach. The results show that the surface morphology has the self-affine fractal properties and exhibits cellular structure after long time growth. With numerical correlation analysis, we explicitly observe the dynamic scaling characteristics and obtain the roughness exponent to be 0.77±0.07, the growth exponent to be 0.28 and 0.43, and the dynamic exponents 0.31 and 0.46, for the early times and later times. The simulating results are consistent with the theoretical values in the K-S model.

Empirical Baye’s Method and Roper Resonance State in Very Light Quark Region
DONG Shao-Jing, ZHANG Jian-Bo, YING He-Ping
Chin. Phys. Lett. 2003, 20 (5): 626-628 .  
Abstract   PDF(pc) (322KB) ( 647 )
Based on the Bayesian theorem, an empirical Baye method is discussed. A programming chart for mass spectrum fitting is suggested. Using this method to extract the spectrum, we observe the puzzled Roper resonance state on a 163 x 28 lattice with overlap fermions at very light quark region.

Calculation of Total Reaction Cross Sections Induced by Intermediate Energy α-Particles with the Boltzmann-Uehling-Uhlenbeck Model
ZHONG Chen, CAI Xiang-Zhou, SHEN Wen-Qing, , ZHANG Hu-Yong, WEI Yi-Bin, CHEN Jin-Gen, MA Yu-Gang, GUO Wei, FANG De-Qing
Chin. Phys. Lett. 2003, 20 (5): 629-631 .  
Abstract   PDF(pc) (335KB) ( 405 )
The Boltzmann-Uehling-Uhlenbeck (BUU) model, which includes the Fermi motion, the mean field, individual nucleon-nucleon (N-N) interactions and the Pauli blocking effect, etc., is used to calculate the total reaction cross section σR induced by α-particles on different targets in the incident energy range from 17.4 to 48.1 MeV/u. The calculation result can well reproduce the experimental data. The nucleus-nucleus interaction radius parameter r0 was extracted from experimental σR. It is found that r0 becomes constant with the increasing mass number of target.
Excited States in 207Rn
LUO Wan-Ju, GUO Ying-Xiang, ZHOU Xiao-Hong, ZHANG Yu-Hu, LEI Xiang-Guo, LIU Zhong, ZHENG Yong, LIU Min-Liang, HE Jian-Jun, ZHU Li-Hua, WEN Shu-Xian
Chin. Phys. Lett. 2003, 20 (5): 632-634 .  
Abstract   PDF(pc) (420KB) ( 725 )
Excited states in 207Rn are investigated via the 196Pt(16O,Sn)207Rn reaction at beam energies from 85 to 95 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-ray excitation function, x-γ and γ-γ-t coincidences are performed with ten BGO(AC)HPGe detectors. Based on these measurements, a level scheme of 207Rn, including 17 γ-rays and 18 levles, is established. Spins for most of the levels are proposed according to the measured DCO ratios. The level structure is compared with a weak-coupling calculation using the interaction energies extracted from neighbouring nuclei.

Influence of Nuclear Deformation on the Potential Energy Surface in Di-Nuclear Model
WANG Nan, ZHAO En-Guang, LI Jian-Feng, LI Wen-Fei, XU Hu-Shan, ZUO Wei, LI Jun-Qing,
Chin. Phys. Lett. 2003, 20 (5): 635-638 .  
Abstract   PDF(pc) (432KB) ( 358 )
Influence of the nuclear deformation on the potential energy surface (PES) in a di-nuclear system is studied in details. It is found that the PES shape changes greatly due to the deformation effect. The top point of the PES could be reduced significantly, which implies that the optimum excitation energy could also be reduced greatly and may enhance the formation probability of the compound nucleus. The dynamical deformation as a function of the reaction time in the reaction process is dramatic. The Z/N ratios of fragments tend to follow that of the compound nucleus during the nucleon exchange process, but to fluctuate.

Photon Radiation Induced by Multiple Parton Rescattering in Deeply Inelastic Scattering
ZHANG Ben-Wei, WANG En-Ke
Chin. Phys. Lett. 2003, 20 (5): 639-642 .  
Abstract   PDF(pc) (322KB) ( 329 )
Photon radiation induced by multiple parton rescattering and corresponding parton energy loss in eA deeply inelastic scattering are investigated by using the generalized factorization of higher twist parton distributions beyond the helicity amplitude approximation. It turns out that the behaviour of the nuclear size dependence of the parton energy loss is different in the photon and gluon radiation cases. The parton energy loss due to photon radiation depends linearly, instead of quadratically, on nuclear size due to gluon radiation.
Probing of the Isospin-Dependent Mean Field and Nucleon-Nucleon Cross Section in a Medium by Nucleon Emissions
LIU Jian-Ye, , XING Yong-Zhong, GUO Wen-Jun
Chin. Phys. Lett. 2003, 20 (5): 643-646 .  
Abstract   PDF(pc) (456KB) ( 371 )
We study the isospin effects of the mean field and two-body collision on the nucleon emissions at the intermediate energy heavy ion collisions by using an isospin-dependent transport theory. The calculated results show that the nucleon emission number Nn depends sensitively on the isospin effect of nucleon nucleon cross section and weakly on the isospin-dependent mean field for neutron-poor system in higher beam energy region. In particular, the correlation between the medium correction of two-body collision and the momentum-dependent interaction enhances the dependence of nucleon emission number Nn on the isospin effect of nucleon nucleon cross section. On the contrary, the ratio of the neutron proton ratio of the gas phase to the neutron proton ratio of the liquid phase, i.e., the degree of isospin fractionation <(N/Z)gasb/<(N/Z)liq>b depends sensitively on the isospin-dependent mean field and weakly on the isospin effect of two-body collision for neutron-rich system in the lower beam energy region. In this case, Nn and <(N/Z)gasb/<(N/Z)liq>b are the probes for extracting the information about the isospin-dependent nucleon nucleon cross section in the medium and the isospin-dependent mean field, respectively.
Effects of Electron Screening on Electron Capture Rates in High Density Presupernova Core
JIANG Guang-Fei, PENG Qiu-He, , CHOU Chih-Kang
Chin. Phys. Lett. 2003, 20 (5): 647-649 .  
Abstract   PDF(pc) (268KB) ( 415 )
Considering that the electron capture rate can be greatly reduced by the electron screening effect in the regime of high temperature and high density, we calculate the effect of electron screening on the electron capture rate for two important elements 56Ni and 55Co in the high density condition of a pre-supernova star. The effect of electron screening is so effective that the electron capture rate may be reduced to about 20%.

Neutron Star Properties in the Relativistic Mean Field Theory
SHEN Hong, , ZHANG Ze-Lin
Chin. Phys. Lett. 2003, 20 (5): 650-653 .  
Abstract   PDF(pc) (396KB) ( 349 )
We study the properties of neutron stars using the complete relativistic equation of state based on the relativistic mean field theory. The complete relativistic equation of state covers a wide density range from 10-7 to 1.2fm-3 for the use of describing both the interior region and the crusts of neutron stars. We include the Λ, Σ, and Ξ hyperons which may appear as new degrees of freedom at high densities. We also examine the sensibility of the results to the choice of hyperon couplings.
Radiative Transition Probability of the Eu3+ Ion in Polymer Optical Fibre
ZHENG Zhi-Qiang, LIANG Hao, MING Hai, ZHANG Qi-Jin, CHEN Biao, SUN Xiao-Hong, XIE Jian-Ping
Chin. Phys. Lett. 2003, 20 (5): 654-656 .  
Abstract   PDF(pc) (274KB) ( 621 )
An Eu-chelate-doped step-index polymer optical fiber (POF) is fabricated. Based on Judd-Ofelt (J-O) theory, the J-O parameters are calculated to be Ω2 = 16.93 x 10-20cm2, Ω4 = 1.36 x 10-20cm2, Ω6 = 6.75 x 10-20cm2 from the emission spectrum of Eu(DBM)3Phen-doped polymethyl methacrylate (PMMA). The J-O parameters have been used to calculate the total radiative transition rate (555.78 s-1) and radiative lifetime (1799μs) of the 5D0 exciting state. The stimulated emission cross-sections σij and the fluorescence branch ratios β for the 5D07FJ’ transitions are also evaluated. Analysis reveals that Eu(DBM)3Phen-doped PMMA is promising for use in rare-earth-doped polymer optical fiber devices.
Preliminary Experimental Results of Deep Levels for Dielectronic Recombination in He-Like High-Z Ions at Heidelberg Electron Beam Ion Trap
ZHANG Xue-Mei, GUO Pan-Lin, A. Gonzalez, J. CRESPO
Chin. Phys. Lett. 2003, 20 (5): 657-659 .  
Abstract   PDF(pc) (402KB) ( 425 )
An experimental system for dielectronic recombination was set-up on H-EBIT in order to carry out dielectronic recombination study. Some preliminary results of He-like Ge32+ and Cu27+ are obtained. Space charge shift on determination of the resonance position for Ge32+ at 100 mA is around 18% and that for Cu27+ is around 38%. Further analysis of experimental data is in progress.
Time-Frequency Analysis of Electromagnetic Pulse Response from a Spherical Target
CHEN Dong, JIN Ya-Qiu
Chin. Phys. Lett. 2003, 20 (5): 660-663 .  
Abstract   PDF(pc) (271KB) ( 572 )
Transient backscattering from a spherical target under incidence of an electromagnetic short pulse is studied. The target can be a perfectly conducting sphere, a dielectric sphere or a dielectric spherical shell. To understand the scattering mechanism from transient impulse echoes for target detection, both the short-time Fourier transform (STFT) and the wavelet transform (WT) are applied to retrieval of scattering information from the backscattering data. Analysis in both the time and frequency domains demonstrates that the WT is more feasible than the STFT to clarifying scattering process of the scatterer because of its excellent multi-resolution characteristic. This technique shall be helpful for scattering analysis and detection of more complex single or multi-targets.
Experimental Characterization of Correlation-Functions of Random Surfaces by Speckle Measurement and Complementary Algorithm
CHENG Chuan-Fu, LIU Man, TENG Shu-Yun, SONG Hong-Sheng, CHEN Jian-Ping, XU Zhi-Zhan
Chin. Phys. Lett. 2003, 20 (5): 664-667 .  
Abstract   PDF(pc) (383KB) ( 354 )
A method for the extracting the correlation functions of random surfaces is proposed by using the image speckle intensity. Theoretically we analyse the integral expression of average intensity of the image speckles, and compare it with the pair of Fourier-Bessel-transform-and-the-inversion of the exponential function of the height-height correlation function of the random surfaces. Then the algorithm is proposed numerically to complement the lacking Bessel function factor in the expression of the average speckle intensity, which changes the intensity data into the pair of the Fourier-Bessel-transform. Experimentally we measure the average image speckle intensities versus the radius of the filtering aperture in the 4f system and extract the height-height correlation function by using the proposed algorithm. The results of the practical measurements for three surface samples and the comparison with those by atomic force microscopy validate the feasibility of this method.

Scaled Fractional Fourier Transform for Partially Coherent Beams
CAI Yang-Jian, LIN Qiang
Chin. Phys. Lett. 2003, 20 (5): 668-670 .  
Abstract   PDF(pc) (271KB) ( 455 )
The definition of scaled fractional Fourier transform (SFRT) is extended to partially coherent beams based directly on the cross-spectral density. Based on this formula, an equivalent tensor ABCD law for the SFRT of partially coherent twisted anisotropic Gaussian-Schell model beams is derived. The derived formulae provide a powerful tool for analysing and calculating the SFRT of partially coherent beams. An application example is provided.
Holographic Properties of BR-D96N Film and Its Application in Hologram Aberration Correction
ZHENG Yuan, YAO Bao-Li, WANG Ying-Li, MENKE Neimule, LEI Ming, CHEN Guo-Fu, Norbert HAMPP
Chin. Phys. Lett. 2003, 20 (5): 671-673 .  
Abstract   PDF(pc) (335KB) ( 532 )
A biophotochromic material, i.e., genetic mutant bacteriorhodopsin (BR-D96N), was experimentally studied on its holographic recording properties. The saturation absorption curve and the diffraction efficiency curve were measured respectively. As holographic storage application, reflection type polarization holograms were recorded on the BR-D96N film. The 173°configuration between the object and reference beams proves that the spatial resolution of the film is over 6000 lines/mm. By using phase conjugate wave of reference beam as reconstruction beam, the distorted object image introduced by the optical components and the defects in the recording medium can be well corrected.

An Atomic Lens Using a Focusing Hollow Beam
XIA Yong, YIN Jian-Ping, WANG Yu-Zhu
Chin. Phys. Lett. 2003, 20 (5): 674-677 .  
Abstract   PDF(pc) (507KB) ( 480 )
We propose a new method to generate a focused hollow laser beam by using an azimuthally-distributed 2π-phase plate and a convergent thin lens, and calculate the intensity distribution of the focused hollow beam in free propagation space. The relationship between the waist w0 of the incident collimated Gaussian beam and the dark spot size of the focused hollow beam at the focal point, and the relationship between the focal length f of the thin lens and the dark spot size are studied respectively. The optical potential of the blue-detuned focused hollow beam for 185Rb atoms is calculated. Our study shows that when the larger waist w of the incident Gaussian beam and the shorter focal length f of the lens are chosen, we can obtain an extremely-small dark spot size of the focused hollow beam, which can be used to form an atomic lens with a resolution of several angstoms.
Transient Thermal Analysis of InAlAs/InGaAs/InP Mid-Infrared Quantum Cascade Lasers
ZHANG Yong-Gang, HE You-Jun, LI Ai-Zhen
Chin. Phys. Lett. 2003, 20 (5): 678-681 .  
Abstract   PDF(pc) (362KB) ( 1247 )
The transient thermal characteristics of InAlAs/InGaAs/InP mid-infrared quantum cascade lasers in pulse driving conditions have been simulated by using the finite-element method, and evaluated experimentally. The results show that specific heat of the materials and heat capacity of the device should be take into account to simulate the thermal performance of the devices in pulse driving conditions. In this case, good coincidence of the simulation with the measured results has been reached and the much higher apparent thermal resistance of the quantum cascade lasers under pulse driving conditions could be explained.
Micrograting Polymerization Fabrication with a Single Femtosecond Laser Pulse at 400 nm Wavelength
GUO Hong-Cang, GUO Heng-Chang, JIANG Hong-Bing, YANG Hong, GONG Qi-Huang, WANG Tao, SHI Meng-Quan, WU Fei-Peng
Chin. Phys. Lett. 2003, 20 (5): 682-684 .  
Abstract   PDF(pc) (288KB) ( 335 )
High diffraction efficiency refractive index-modulated holographic micrograting on a polymer thin film was obtained with a single femtosecond laser pulse interference and photo-polymerization. The diffractive efficiency of the micrograting with an He-Ne laser is up to 78% when the thickness of the film is 90μm, which corresponds to the refractive index-modulation as large as 2.4 x 10-3. The compared experiment with a femtosecond oscillator laser indicated that a single femtosecond laser pulse has the advantages in laser machining over the cw holography method such as high fabrication speed, good surface structure and high diffractive efficiency.


Heat Transfer from a dc Laminar Plasma-Jet Flow to Different Solid Surfaces
MENG Xian, PAN Wen-Xia, WU Cheng-Kang
Chin. Phys. Lett. 2003, 20 (5): 685-687 .  
Abstract   PDF(pc) (401KB) ( 760 )
The heat flux distributions were measured by using transient method for an argon dc laminar plasma-jet flow impinging normally on a plate surface embedded with copper probes. Different powders were coated on the probe surfaces and the effect of powder coatings on the heat transfer from jet flow to the probe surface was examined. Experimental results show that the maximum values of the heat flux to the probe increase with the coating of fine metal powders, while for the surfaces coated with fine ceramic powders, the maximum values of heat flux decrease, compared with that to the bare copper probe surface.
Electron Injection by E-Field Drift and its Application in Starting-up Tokamaks at Low Loop Voltage
PAN Yuan, YAN Xiao-Lin, LIU Bao-Hua
Chin. Phys. Lett. 2003, 20 (5): 688-691 .  
Abstract   PDF(pc) (525KB) ( 508 )
We propose an innovative method of electron injection by E-filed drift into a plasma device and discuss its application in starting-up tokamak plasmas at low loop voltage. The experimental results obtained from HT-6M Tokamak are also presented. The breakdown loop voltage is obviously reduced and the discharge performance is improved by using the electron injection method. It could be applied to some other types of plasma device.

Preparation of Diamond-Like Carbon Films in Methane by Electron Cyclotron Resonance Microwave Plasma Source Ion Implantation
LI Xin, TANG Zhen-An, MA Guo-Ja, WU Zhi-Meng, Deng Xin-Lu
Chin. Phys. Lett. 2003, 20 (5): 692-695 .  
Abstract   PDF(pc) (450KB) ( 517 )
Diamond-like carbon (DLC) films were prepared on Si (100) substrates by ion implantation from an electron cyclotron resonance microwave plasma source. During the implantation, 650 W microwave power was used to produce discharge plasma with methane as working gas, and -20 kV voltage pulses were applied to the substrate holder to accelerate ions in the plasma. Confocal Raman spectra confirmed the DLC characteristics of the films. Fourier-transform infrared characterization indicates that the DLC films were composed of sp3 and sp2 carbon-bonded hydrogen. The hardness of the films was evaluated with a Nano Indenter-XP System. The result shows that the highest hardness value was 14.6 GPa. The surface rms roughness of the films was as low as 0.104 nm measured with an atomic force microscope. The friction coefficient of the films was checked using a ball-on-disk microtribometer. The average friction coefficient is approximately 0.122.

Room-Temperature Dual Excitonic Emission from Amorphous ZnO
WANG Zhi-Jian, WANG Zhi-Jun, ZHANG Li-Gong, YUAN Jin-Shan, YAN Sheng-Gang, WANG Chun-Yan
Chin. Phys. Lett. 2003, 20 (5): 696-699 .  
Abstract   PDF(pc) (430KB) ( 611 )
Optical properties of amorphous ZnO have been investigated at room temperature. It is demonstrated that the ultraviolet emission components due to the recombination of two different excitons were verified by examining their relative energy positions and ultraviolet integrated photoluminescence intensity dependence on reaction time. The dual excitonic emissions are derived from amorphous ZnO and crystallized ZnO nanocrystallite, respectively. On the optimized condition, the photoluminescence spectrum of amorphous ZnO shows a strong ultraviolet emission while the visible emission is almost fully quenched. The enhanced ultraviolet emission is attributed to quantum confinement effect.



Diameter Modification of Si Nanowires via Catalyst Size
XING Ying-Jie, XI Zhong-He, XUE Zeng-Quan, YU Da-Peng
Chin. Phys. Lett. 2003, 20 (5): 700-702 .  
Abstract   PDF(pc) (292KB) ( 965 )
Si nanowires with different diameters are grown on catalyst coated Si substrates via a solid-liquid-solid mechanism. It is found that the thickness and type of catalyst film can modify the average diameter of Si nanowires obviously. The nanowires prepared on substrates deposited with Ni film of 40, 10, and 4 nm thick have a mean diameter around 41, 36, and 24 nm, respectively. Si nanowires with the smallest average diameter (~ 16 nm) are grown with a gold catalyst. Studies of diameter distributions show that the minimum diameter of nanowires does not shift with the average diameters spontaneously and has the same size of 10 nm.
Ordered Structures of a Binary Mixture with Mobile Particles System
ZHU Yue-Jin, MA Yu-Qiang
Chin. Phys. Lett. 2003, 20 (5): 703-705 .  
Abstract   PDF(pc) (327KB) ( 477 )
We study the ordered structures of a binary mixture through the introduction of mobile particles under periodically oscillating driving fields, and find that the particle motion can break up the isotropy of the system, so that the continuous structure along the oscillation forcing direction is observed for properly chosen oscillating field. Furthermore, the dependences of the morphology and domain size on the mixture-particle coupling interaction, the diffusion coefficient, and the quench depth are examined in details.

Many-Body Contributions to Cohesive Energy of Highly Compressed Solid 4He
TIAN Chun-Ling, LIU Fu-Sheng, CAI Ling-Cang, JING Fu-Qian,
Chin. Phys. Lett. 2003, 20 (5): 706-708 .  
Abstract   PDF(pc) (384KB) ( 359 )
A many-body expansion of cohesive energy of solid 4He is made up to five-body term, and short-range two-, three-, four- and five-body contributions have been computed by using the Hartree-Fock self-consistent-field technique and the same atomic basis set (6311G). At high densities the Hartree-Fock part of two- and four-body contributions are repulsive, whereas the three- and five-body ones are attractive. The four-body term increases as much as 15% repulsion of two-body term, and at the same time the five-body term reduces 4% of two-body repulsion at 2.5cm3/mol. The four- and five-body terms are found to be important to describe short-range inter-atomic interaction correctly and to compute the cohesive energy accurately in a wide compression range from 2.5 to 7.5cm3/mol.



Dynamic Scaling in Growth of ZrO2 Thin Films Prepared by Electronic Beam Evaporation
QI Hong-Ji, HUANG Li-Hua, YUAN Jing-Mei, CHENG Chuan-Fu, SHAO Jian-Da, FAN Zheng-Xiu
Chin. Phys. Lett. 2003, 20 (5): 709-712 .  
Abstract   PDF(pc) (537KB) ( 682 )
The growth front evolution of ZrO2 thin films deposited by electronic beam evaporation has been studied with atomic force microscopy. The dynamic scaling characteristics are observed during the deposition process. After numerical correlation analysis, the roughness exponent α = 0.80±0.005 and the growth exponent β = 0.141 are all obtained. Based on these results, we suggest that the growth of ZrO2 thin films can be described by the combination of the Edwards-Wilkinson equation, the Mullins diffusion equation and the shadowing effect.


Origin of the Blue Luminescence in Porous Anodic Alumina Films Formed in Oxalic Acid Solutions
GAO Tao, MENG Guo-Wen, ZHANG Li-De
Chin. Phys. Lett. 2003, 20 (5): 713-716 .  
Abstract   PDF(pc) (488KB) ( 847 )
Photoluminescence spectra of porous anodic alumina (PAA) films formed in oxalic acid solutions show a blue emission band peaked around 470 nm, in which the corresponding excitation bands locate at 248 nm, 304 nm, and 360 nm, respectively. With the help of ascertaining the mechanism of this blue luminescence, the roles of the oxalic ions on the optical properties of the PAA films was discussed by using optical absorption spectra. It is suggested that the oxalic impurities with different existing or distributing forms would play important roles on the optical properties of PAA films. The 470-nm blue luminescence band could be attributed to the incorporated oxalic impurities rather than the F+ centers existed in the PAA films formed in oxalic acid solutions.

Effects of Conduction Electron Band Structure on Transport of Quantum Dot Systems
YANG Kai-Hua, SONG Bo, , TIAN Guang-Shan, WANG Yu-Peng, HAN Ru-Shan, HAN Ru-Qi
Chin. Phys. Lett. 2003, 20 (5): 717-720 .  
Abstract   PDF(pc) (295KB) ( 469 )
We study the effects of the energy band structure of conduction-electron on the transport properties of an interacting quantum dot system. By applying the nonequilibrium Keldysh Green function technique, we show that the finite width of electron band in leads causes the negative differential conductance in some regions of the applied voltage. We also show that the van Hove singularities in the density of states of conduction-electron do not qualitatively change the differential conductance of the system, and hence can be safely ignored. Therefore, the wide band approximation used in the previous investigations is partially justified.
Hopping and Non-universal Conductivity in Half-Metallic CrO2 Composites
CHEN Ya-Jie, ZHANG Xiao-Yu, CAI Tian-Yi, LI Zhen-Ya,
Chin. Phys. Lett. 2003, 20 (5): 721-724 .  
Abstract   PDF(pc) (320KB) ( 698 )
We study the dependence of resistivity ρ on conducting volume fraction p in CrO2/TiO2 magnetic composite that is composed of acicular half-metallic particles and spherical insulating particles. The measured percolation threshold was determined to be pc = 0.192. It is found that the conductivity exhibits a non-universal critical exponent t = 2.52±0.08, which may be dominantly attributed to microstructure and higher-order hopping in this composite.


Superconductivity at 31 K in Alkaline Metal-Doped Cobalt Oxides
WEN Hai-Hu, YANG Hai-Peng, LU Xi-Feng, YAN Jing
Chin. Phys. Lett. 2003, 20 (5): 725-728 .  
Abstract   PDF(pc) (556KB) ( 967 )
By using a simple solid reaction method, we have fabricated alkaline metal doped cobalt oxides AnxCoO2+δ (An = Na, K). The magnetic measurement shows a superconducting-like diamagnetic signal at 31 K based on a strong superparamagnetic signal. Below 31 K, the magnetization hysteresis loops contain a strong rough linear superparamagnetic background and a superconducting hysteresis. The typical magnetization hysteresis loops for a type-II superconductor are found. Preliminary resistive data also show a fast dropping of resistance below Tc. These give indication of superconductivity below 31 K in AnxCoO2+δ (An = Na, K).

Novel Transitions in Doped Mott-Insulator KxCoO2
YANG Hai-Peng, LU Xi-Feng, WEN Hai-Hu
Chin. Phys. Lett. 2003, 20 (5): 729-730 .  
Abstract   PDF(pc) (323KB) ( 494 )
By measuring the temperature dependence of the magnetic susceptibility, two distinct transitions have been observed in potassium doped cobalt oxide KxCoO2 (x = 0.2-1.0). The transition around 125 K corresponds to a phase transition between a weak ferromagnetic plus a strong superparamagnetic phase (below 125 K) and a superparamagnetic phase (above 125 K). The susceptibility above the Curie point Tc cannot be described by the Curie-Weise law, being consistent with the superparamagnetism. Magnetization-hysteresis-loops have been measured in different temperature regions to uncover the underlying physics. The second transition near 30.8 K shows a strong novelty.

Level Statistics and Specific Heat of Metallic Nano-Particles
CHENG Nan-Pu, CHEN Zhi-Qian, CHEN-Hong
Chin. Phys. Lett. 2003, 20 (5): 731-734 .  
Abstract   PDF(pc) (443KB) ( 288 )
The thermodynamic properties of an ensemble of metallic nano-particles are affected by the level distribution and the level correlation between the discrete electronic energy levels. We numerically calculate the specific heat of metallic nano-particles in the canonical ensemble with an odd or even number of electrons by considering the effects of the level distribution and the level correlation. The behaviour of the specific heat at low and high temperatures, compared with the average nearest-neighbor level spacing, is also investigated.
A Modified Mean Field Theory for Spin Systems with Orbital Degeneracy
SHI Da-Ning
Chin. Phys. Lett. 2003, 20 (5): 735-737 .  
Abstract   PDF(pc) (226KB) ( 443 )
In order to understand the ground state of spin systems with orbital degeneracy, we present a modified mean-field theory that includes four order parameters. Our mean-field results suggest that for a small Hund interaction, the flavor liquid state is still stable against the solid state, but long-range orders may be attained in the system with sufficient deviation from the SU(4) limit. Finally, the implications for the experimental observations on the system LaMnO3 are discussed.
Effects of Magnetic Field on Charge-Ordering Transitions in La2CuO4.08 and Pr0.5Sr0.5MnO3
LI Jian-Qi, CHEN Ling, YU Hong-Chun, Y. Matsui, ZHAO Zhong-Xian
Chin. Phys. Lett. 2003, 20 (5): 738-741 .  
Abstract   PDF(pc) (375KB) ( 475 )
The applied magnetic field can result in evident changes on the charge-ordering transitions in both Cu-based high Tc superconductors and Mn-based colossal magnetioresistance materials. Alternations of charge modulation and melting of well-defined charge stripes can be commonly observed when the magnetic field is over 2T. We herein present the experimental data obtained in La2CuO4.08 and Pr0.5Sr0.5MnO3 materials, illustrating this kind of interesting phenomena at low temperatures. In particular, some essential structural features alternating along with charge-ordering transition have been discussed.


Magnetic and Transport Properties of Oxygen-Deficient Perovskite Manganites
ZHONG Wei, JIANG Hong-Ying, WU Xiao-Ling, TANG Nu-Jiang, CHEN Wei, DU You-Wei
Chin. Phys. Lett. 2003, 20 (5): 742-745 .  
Abstract   PDF(pc) (635KB) ( 609 )
Effects of oxygen deficiency on the magnetic and transport properties of La2/3Ba1/3MnO3-δ polycrystalline perovskites have been investigated. As the nonstoichiometry parameter δ increases from 0.00 to 0.10, the lattice parameters at room temperature increase from 3.892(3)Å to 3.909(3)Å, the resistivity increases and the ferromagnetic ordering transition temperature shifts from 337 K to 268 K. A large magnetoresistance effect with -Δρ/ρ0 of about 30% (955 kA/m, δ = 0.10) and a large magnetic entropy change of about 2.7 J/kg.K (796kA/m, δ = 0.00) is obtained in polycrystalline La2/3Ba1/3MnO3-δ. The enhanced magnetoresistance effect at low temperature would be related to the grain boundaries of the polycrystalline samples.

Annealing Effects on Properties of Bi-Substituted Garnet Films with Perpendicular Anisotropy Prepared by a Sol-Gel Method
ZHANG Yue-Pin, WANG Xian-Ying, Ruan Hao, SHEN De-Fang, GAN Fu-Xi
Chin. Phys. Lett. 2003, 20 (5): 746-748 .  
Abstract   PDF(pc) (491KB) ( 527 )
Bi-substituted garnet films with perpendicular anisotropy have been prepared by a sol-gel method. Annealing effects on magneto-optical properties and structures of the films are studied. The results indicate that the Kerr hysteresis loops of garnet films have good squareness at annealing temperatures above 650°C, the coercive force Hc of these films increases from 1070 to 1570 Oe with the increasing temperature from 650°C to 700°C. The Kerr rotation of the films was changed with the increasing annealing temperature, and there is a maximum value (0.82°C) at 675°C. It was found that the structure of the films is a single phase of garnet without preferring orientation when the annealing temperature is about 650°C, but a new phase (Bi2Al4O9) can be formed when the annealing temperature reaches 675°C, another new phase (Bi2Fe4O9) appears when the annealing temperature is about 700°C.

Dynamics of Below-Band-Gap Carrier in Highly Excited GaN
GUO Bing, WONG Kam-Sing, YE Zhi-Zhen, JIANG Hong-Xing, LIN Jing-Yu
Chin. Phys. Lett. 2003, 20 (5): 749-752 .  
Abstract   PDF(pc) (381KB) ( 496 )
Femtosecond time-resolved reflectivity was used to investigate below-band-gap (3.1 eV) carrier dynamics in a nominally undoped GaN epilayer under high excitation. A 2.5-ps rising process can be observed in the transient trace. This shot rising time results from the hot phonon effects which can cause a delayed energy relaxation of the initial photocarriers toward the band edge. From the density dependence of the carrier dynamics, the Mott density was estimated to be 1.51-1.56 x 1019cm-3. Below the Mott density, the initial probed carrier dynamics was explained to the effect of acoustic phonon-assisted tunneling for localized states, where a significant excitation density dependence of the tunneling probability was observed due to the optically-induced bandtail extension to lower energies. Above the Mott density, the measured carrier dynamics reflected the relaxation of an electron-hole plasma, in which a distinct fast decay component of 2.3 ps was observed due to the onset of nonlinear relaxation processes such Auger recombination.

Water-Soluble Multi-Walled Nanotube and its Film Characteristics
FENG Wei, ZHOU Feng, WANG Xiao-Gong, WAN Mei-Xiang, FUJII Akihiko, YOSHINO Katsumi
Chin. Phys. Lett. 2003, 20 (5): 753-755 .  
Abstract   PDF(pc) (325KB) ( 781 )
Covalent modification of multi-walled-nanotube (MWNT) surface enhanced solubility in water yields a thin transparent shining dark-colored film of soluble MWNT (s-MWNT) with a conductivity of 1.25 S/cm. Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV-vis absorption spectroscopy were used for the film characterization. The result shows that enhanced interactions between s-MWNT and water and between s-MWNTs play an important role in the increase of the solubility of the nanotubes in water and in the formation of uniform thin films.

Preparation and Structural Characterization of Superionic Conductor RbAg4I5 Crystalline Grain Film
CAO Yang, SUN Hong-San, SUN Jia-Lin, TIAN Guang-Yan, XING Zhi, GUO Ji-Hua
Chin. Phys. Lett. 2003, 20 (5): 756-758 .  
Abstract   PDF(pc) (390KB) ( 1000 )
Superionic conductor RbAg4I5 crystalline grain films were prepared by vacuum thermal evaporation on NaCl crystalline substrates. The surface morphology, microstructure and the electronic energy states of the films were examined by atomic force microscopy, transmission electron microscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The results show that the obtained RbAg4I5 layer has an epitaxial film of perfect crystalline structure, and the unit cell of crystalline grain RbAg4I5 films belongs to cubic crystal system. The principal x-ray diffraction peaks at d = 3.7447 and 1.8733Å are related to the structure of ternary compound RbAg4I5 films.
Effect of Metallic Film in Diamond Growth from an Fe-Ni-C System at High Temperature and High Pressure
XU Bin, LI Mu-Sen, YIN Long-Wei, CUI Jian-Jun, GONG Jian-Hong
Chin. Phys. Lett. 2003, 20 (5): 759-762 .  
Abstract   PDF(pc) (459KB) ( 656 )
The metallic film surrounding a diamond single crystal, which plays an important role in the diamond growth from an Fe-Ni-C system, has been successfully investigated by using transmission electron microscopy (TEM), Raman spectroscopy and x-ray photo-electron spectroscopy (XPS). Diamond and graphite were not found in surface layer (near diamond) of the film by TEM and Raman spectroscopy, but a parallel relationship exists between the (1ī ī) plane of γ-(Fe,Ni) and the (100) plane of (Fe,Ni)3C in this region. Compared to that of solvent metal (catalyst) near diamond, the binding energy in the valence bands of iron, nickel and carbon atoms of the film has an increase of 0.9 eV. According to the microstructures on the film obtained by the TEM, Raman spectra, and XPS, the catalytic mechanism of the film may be assumed as follows. In the surface layer of the film, iron and nickel atoms in the γ-(Fe,Ni) lattice can absorb carbon atoms in the (Fe,Ni)3C lattice and make them transform to an sp3-like state. Then carbon atoms with the sp3-like structure are separated from the (Fe,Ni)3C and stack on the growing diamond crystal. This study provides a direct evidence for the diamond growth from a metallic catalyst-graphite system under high temperature and high pressure.


Morphology of Platinum Nanowire Array Electrodeposited Within Anodic Aluminum Oxide Template Characterized by Atomic Force Microscopy
KONG Ling-Bin, LU Mei, LI Meng-Ke, GUO Xin-Yong, LI Hu-Lin
Chin. Phys. Lett. 2003, 20 (5): 763-766 .  
Abstract   PDF(pc) (260KB) ( 918 )
Uniform platinum nanowires were synthesized by electrodepositing the platinum under a very low altering current frequency (20 Hz) and increasing voltage (5-15 V) in the pores of anodic aluminum oxide (AAO) template. Atomic force microscopy observation indicates that the template membranes we obtained have hexagonally close-packed nanochannels. The platinum nanowires have highly ordered arrays after partially dissolving the aluminum oxide membrane. With the increasing dissolving time, the platinum nanowire array collapsed. A concave topography of the aluminum substrate was observed after the aluminum oxide membrane was dissolved completely and the platinum nanowires were released from the template. Platinum nanowires were also characterized by transmission electron microscopy and the phase structure of the Al/AAO/Pt composite was proven by x-ray diffraction.


A New Structure of Silicon-on-Insulator Metal-Oxide-Semiconductor Filed Effect Transistor to Suppress the Floating Body Effect
ZHU Ming, LIN Qing, ZHANG Zheng-Xuan, LIN Cheng-Lu
Chin. Phys. Lett. 2003, 20 (5): 767-769 .  
Abstract   PDF(pc) (350KB) ( 524 )
Considering that the silicon-on-insulator (SOI) devices have an inherent floating body effect, which may cause substantial influences in the performance of SOI device and circuit, we propose a novel device structure to suppress the floating body effect. In the new structure there is a buried p+ region under the n+ source and that region is extended to outside of the source, and this additional p+ region provides a path for accumulated holes to flow out of the body. Numerical simulations were carried out with Medici, and the output characteristics and gate characteristics were compared with those of conventional SOI counterparts. The simulated results show the suppression of floating body effect in the novel SOI device as expected.
Characterization of Uncooled Poly SiGe Microbolometer for Infrared Detection
DONG Liang, YUE Rui-Feng, LIU Li-Tian
Chin. Phys. Lett. 2003, 20 (5): 770-773 .  
Abstract   PDF(pc) (477KB) ( 427 )
An uncooled poly SiGe microbolometer for infrared detection has been fabricated and characterized. The poly SiGe thin film is deposited by ultrahigh vacuum chemical vapor deposition (UHVCVD) system and its structural properties are characterized by Rutherford backscattering spectrometry (RBS) and Raman. The dependences of the temperature coefficient of resistance on operation temperature and on annealing temperature have been investigated. A leg-supported microbridge is used to decrease the thermal conductance of microbolometer with the silicon micromachining technique. The results show that at a chopping frequency of 15 Hz and a bias voltage of 5 V, the maximum detectivity of 8.3 x 108cmHz1/2/W is achieved with a thermal response time of 16.6 ms.

Data Preprocessing in Cluster Analysis of Gene Expression
YANG Chun-Mei, WAN Bai-Kun, GAO Xiao-Feng
Chin. Phys. Lett. 2003, 20 (5): 774-777 .  
Abstract   PDF(pc) (465KB) ( 402 )
Considering that the DNA microarray technology has generated explosive gene expression data and that it is urgent to analyse and to visualize such massive datasets with efficient methods, we investigate the data preprocessing methods used in cluster analysis, normalization or logarithm of the matrix, by using hierarchical clustering, principle component analysis (PCA) and self-organizing maps (SOMs). The results illustrate that when using the Euclidean distance as measuring metrices, logarithm of relative expression level is the best preprocessing method, while data preprocessed by normalization cannot attain the expected results because the data structure is ruined. If there are only a few principle components, the PCA is an effective method to extract the frame structure, while SOMs are more suitable for a specific structure.


The First Observation of Circumstellar Nebula of VI Cyg 12
WANG Jun-Jie, ZHU Zhen-Xi,
Chin. Phys. Lett. 2003, 20 (5): 778-779 .  
Abstract   PDF(pc) (312KB) ( 455 )
An optical spectroscopic observation was made towards the circumstellar nebula of the supergiant VI Cyg 12, for the first time to our knowledge. Several emission lines appear in the spectrum. Based on the spectra of the star and its circumstellar matter, as well as the IRAS and NVSS data, we conclude that VI Cyg 12 has an expanding shell with an expansion velocity 3100 km s-1 due to strong stellar wind. It is an older star that possibly evolved from a very massive O-type star. The stellar wind and mass loss may take an important part in the evolution of this star.
Can Higgs Field Have a Cosmological Origin?
LIU Liao, PEI Shou-Yong
Chin. Phys. Lett. 2003, 20 (5): 780-782 .  
Abstract   PDF(pc) (205KB) ( 478 )
A proposal of the cosmological origin of Higgs particles is given. We show that the Higgs field could be created from the vacuum quantum conformal fluctuation (VQCF) of Anti-de Sitter space-time, the spontaneous breaking of vacuum symmetry and the mass of a Higgs particle are related to the cosmological constant of our universe, especially the theoretical estimated mass mФ of Higgs particles is mФ = √-2μ2 = √|Λ|/π. It seems that the Higgs particles with masses in GeV range may be the relics of the VQCF of Anti-de sitter space in inflational phase of our very early universe.

54 articles