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Volume 20 Issue 9
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Original Articles
Darboux Transformation and Variable Separation Approach: the Nizhnik-Novikov-Veselov Equation
HU Heng-Chun, LOU Sen-Yue, LIU Qing-Ping
Chin. Phys. Lett. 2003, 20 (9): 1413-1415 .  
Abstract   PDF(pc) (190KB) ( 641 )
Darboux transformation (DT) is developed to systematically find variable separation solutions for the Nizhnik-Novikov-Veselov equation. Starting from a seed solution with some arbitrary functions, the one-step DT yields the variable separable solutions, which can be obtained from the truncated Painlevé analysis, and the two-step DT leads to some new variable separable solutions, which are the generalization of the known results obtained by using a guess ansatz to solve the generalized trilinear equation.
Molecular Dynamics Simulations of Helium Behaviour in Copper Crystals
WANG Ling, NING Xi-Jing
Chin. Phys. Lett. 2003, 20 (9): 1416-1419 .  
Abstract   PDF(pc) (352KB) ( 599 )
Molecular dynamics simulations are performed to investigate the behaviour of helium atoms generated from tritium decay in perfect Cu crystals at 300 K. At the early stage just after a 3He atom generation, the lattice structure is badly deformed and the local temperature rises considerably above 300 K. Single 3He atom diffuses by interstitial paths whereas two 3He atoms attract each other and can form a stable dimmer, which pushes a Cu atom out of its original lattice site and occupies the vacancy. This dimmer can catch another 3He atom and form a trimmer with an equilateral triangular structure.
Construction of the Einstein-Podolsky-Rosen Entangled States
RUAN Man-Qi, ZENG Jin-Yan,
Chin. Phys. Lett. 2003, 20 (9): 1420-1422 .  
Abstract   PDF(pc) (180KB) ( 364 )
As simultaneous eigenstates of a complete set of commuting observables, construction of the Einstein-Podolsky-Rosen entangled states for a two-particle system is investigated and a sufficient condition to ensure the entanglement between a pair of commuting observables is given. It is found that for a two-particle system, four types of entangled states concerning the usually interested observables may be constructed.
A Peculiar Tripartite Entangled State
HUANG Yan-Xia, YU Ya-Fei, ZHAN Ming-Sheng
Chin. Phys. Lett. 2003, 20 (9): 1423-1425 .  
Abstract   PDF(pc) (198KB) ( 391 )
We present a scheme to prepare two-atom Einstein-Podolsky-Rosen states and three-atom entangled states via cavity quantum electrodynamics, and it can be realized experimentally. Importantly, we find that in the set of tripartite entangled states prepared by our scheme there is a peculiar tripartite entangled state except the Greenberger-Horne-Zeilinger (GHZ) state. The peculiar tripartite entangled states have double feature of the GHZ state (i.e. τ123 > 0) and W state (i.e. the remaining reduce density matrices ρij retain entanglement according to the positive partial transformation (PPT) criterion) simultaneously. However, its entanglement properties are not completely identical either to the GHZ state or to the W state. It is interesting that for peculiar entanglement properties, the remaining reduced density matrices ρij can retain entaglement or disentanglement independently, which can be chosen freely according to our need.
Quantum Computations with Transverse Modes of An Optical Field Propagating in Waveguides
FU Jian, TANG Shao-Fang
Chin. Phys. Lett. 2003, 20 (9): 1426-1429 .  
Abstract   PDF(pc) (270KB) ( 396 )
A fully optical method to perform quantum computation with transverse modes of the optical field propagating in waveguide is proposed by supplying the prescriptions for a universal set of quantum gates. The proposal for quantum computation is based on implementing a quantum bit with two normal modes of multi-mode waveguides. The proposed C-NOT gate has the potential of being more compact and easily realized than some optical implementations, since it is based on planar lightwave circuit technology and can be constructed by using Mach-Zehnder interferometer having semiconductor optical amplifiers with very large refractive nonlinearity in its arms.
Control of the collapse of a Bose Condensate by Optical Dipole Force
FU Hai-Xiang, LUO You-Hua, LI Ming-Zhe, GAO Bo, WANG Yu-Zhu,
Chin. Phys. Lett. 2003, 20 (9): 1430-1433 .  
Abstract   PDF(pc) (313KB) ( 549 )
We propose an experimental scheme of using the far-off resonance optical dipole force to control tunable collapse of Bose-Einstein condensation with attractive interactions. This scheme can conveniently alter collapse phenomena while keeping interatomic processes unchanged. Effects on the critical interaction strength and time delay are studied with numerical simulation. We show that for the blue-detuning case those two quantities are increased while for the red-detuning case they are decreased.
Variational Calculations for the Spectrum of Finite Bosons in Harmonic Potentials
MA Yong-Li, CHEN Zhong-Zhou
Chin. Phys. Lett. 2003, 20 (9): 1434-1436 .  
Abstract   PDF(pc) (232KB) ( 364 )
Using both the Gaussian and Fetter's variational calculations for the N-body ground-state wave function of the trapped Bose-Einstein condensate, we give explicit analytic formulas for the spectrum of finite bosons in harmonic potentials based on the corrected sum rules and generalized virial identities. We compare the low-lying excitation spectra among the Gaussian and Fetter's variational calculations and the exact numerical results. The Gaussian approximation has the simplest reasonable results, validing for N → ∞ and high-lying excitations.
Proper Accelerations of Time-Like Curves near a Null Geodesic
TIAN Gui-Hua, ZHAO Zheng
Chin. Phys. Lett. 2003, 20 (9): 1437-1440 .  
Abstract   PDF(pc) (199KB) ( 474 )
It is well known that when given a null geodesic γ0(λ) with a point r in (p,q) conjugate to p along γ0(λ), there will be a variation of γ0(λ) which can give a time-like curve from p to q. Here we prove that the time-like curves coming from the above-mentioned variation (with the second derivative β2 ≠ 0) have a proper acceleration A = √AaAa which approaches infinity as the time-like curve approaches the null geodesic. Because the curve obtained from variation of the null geodesic must be everywhere time-like, we also discuss the constraint of the‘acceleration’βa0 of the variation vector field on the null geodesic γ0(λ). The acceleration βa0 of the variation vector field Za on the null geodesic γ0(λ) cannot be zero.

A Method of Controlling Synchronization in Different Systems
CHEN Jun, LIU Zeng-Rong
Chin. Phys. Lett. 2003, 20 (9): 1441-1443 .  
Abstract   PDF(pc) (244KB) ( 344 )
A new control method to synchronize between two different systems is proposed and the mathematical proof of this method is provided. Moreover, numerical simulation validates the efficiency of the proposed method.
Minimal Braid in Applied Symbolic Dynamics
ZHANG Cheng, ZHANG Ya-Gang, PENG Shou-Li
Chin. Phys. Lett. 2003, 20 (9): 1444-1447 .  
Abstract   PDF(pc) (325KB) ( 416 )
Based on the minimal braid assumption, three-dimensional periodic flows of a dynamical system are reconstructed in the case of unimodal map, and their topological structures are compared with those of the periodic orbits of the Rössler system in phase space through the numerical experiment. The numerical results justify the validity of the minimal braid assumption which provides a suspension from one-dimensional symbolic dynamics in the Poincaré section to the knots of three-dimensional periodic flows.
Multilinear Variable Separation Approach in (3+1)-Dimensions: the Burgers Equation
YING Jin-Ping, LOU Sen-Yue,
Chin. Phys. Lett. 2003, 20 (9): 1448-1451 .  
Abstract   PDF(pc) (216KB) ( 501 )
The multi-linear variable separation approach has been proven to be very useful in solving many (2+1)-dimensional integrable systems. Taking the (3+1)-dimensional Burgers equation as a simple example, here we extend the multi-linear variable separation approach to (3+1)-dimensions. The form of the universal formula obtained from many (2+1)-dimensional system is still valid. However, a more general arbitrary function (with three independent variables) has been included in the formula. Starting from the universal formula, one may obtain abundant (3+1)-dimensional localized excitations. In particular, we display a special paraboloid-type camber soliton solution and a dipole-type dromion solution which is localized in all directions.

Small Stress Change Triggering a Big Earthquake: A Test of the Critical Point Hypothesis for Earthquakes
WAN Yong-Ge, WU Zhong-Liang, , ZHOU Gong-Wei
Chin. Phys. Lett. 2003, 20 (9): 1452-1455 .  
Abstract   PDF(pc) (302KB) ( 348 )
Whether or not a small stress change can trigger a big earthquake is one of the most important problems related to the critical point hypothesis for earthquakes. We investigate global earthquakes with different focal mechanisms which have different levels of ambient shear stress. This ambient stress level is the stress level required by the earthquakes for their occurrence. Earthquake pairs are studied to see whether the occurrence of the preceding event encourages the occurrence of the succeeding one in terms of the Coulomb stress triggering. It is observed that the stress triggering effect produced by the change of Coulomb failure stress in the same order of magnitudes, about 10-2MPa, is distinctly different for different focal mechanisms, and thus for different ambient stress levels. For non-strike-slip earthquakes with a relatively low ambient stress level, the triggering effect is more evident, while for strike-slip earthquakes with a relatively high ambient stress level, there is no evident triggering effect. This water level test provides an observational support to the critical point hypothesis for earthquakes.
Optical Fibre Mode Structures Measured by Collection Mode Near-Field Scanning Optical Microscopy
TANG Lin, BAI Ming, MING Hai, XIE Jian-Ping
Chin. Phys. Lett. 2003, 20 (9): 1456-1458 .  
Abstract   PDF(pc) (286KB) ( 642 )
High order fibre mode structures are measured by a near-field scanning optical microscope (NSOM) and are determined to be consistent with the standard fibre LP patterns. The mode-field distortions of high-order mode LP11 and LP21 structures by far-field measurement are analysed based on scalar diffraction theory, and the max distortions may reach as high as 5.1% and 6.2%. This shows that the method of using the NSOM is more accuracy than the far-field measurement method, especially for high-order mode structures of optical fibres.
Isovector Giant Dipole Resonance of Stable Nuclei in a Consistent Relativistic Random-Phase Approximation
CAO Li-Gang, MA Zhong-Yu,
Chin. Phys. Lett. 2003, 20 (9): 1459-1461 .  
Abstract   PDF(pc) (247KB) ( 425 )
A fully consistent relativistic random phase approximation is applied to study the systematic behaviour of the isovector giant dipole resonance of nuclei along the β-stability line in order to test the effective Lagrangians recently developed. The centroid energies of response functions of the isovector giant dipole resonance for stable nuclei are compared with the corresponding experimental data and the good agreement is obtained. It is found that the effective Lagrangian with an appropriate nuclear symmetry energy, which can well describe the ground state properties of nuclei, could also reproduce the isovector giant dipole resonance of nuclei along the β-stability line.
Structures of 17F and 17O, 17Ne and 17N in the Ground State and the First Excited State
ZHANG Hu-Yong, SHEN Wen-Qing, REN Zhong-Zhou, MA Yu-Gang, CHEN Jin-Gen, CAI Xiang-Zhou, LU Zhao-Hui, ZHONG Chen, GUO Wei, WEI Yi-Bin, ZHOU Xing-Fei, MA Guo-Liang, WANG Kun
Chin. Phys. Lett. 2003, 20 (9): 1462-1465 .  
Abstract   PDF(pc) (370KB) ( 398 )
The structures of two couples of mirror nuclei 17F and 17O, 17Ne and 17N in the ground state and in the first excited state are investigated using the relativistic mean-field approach. Two-proton halo in 17Ne in the first excited state and in the ground state and two-neutron halo in 17N in the first excited state are suggested. Meanwhile, one-proton halo in 17F in the first excited state and one-neutron halo in 17O in the first excited state are also suggested. The skin structure appears in 17F and 17N in the ground state.
Development of the Neck in Fusion Reactions 40Ca+90,96Zr
WANG Ning, WU Xi-Zhen, LI Zhu-Xia,
Chin. Phys. Lett. 2003, 20 (9): 1466-1469 .  
Abstract   PDF(pc) (534KB) ( 485 )
The neck dynamics and nucleon transfer through the neck in fusion reactions 40Ca+90,96Zr are studied by applying the improved quantum molecular dynamics model. A special attention is paid to the dynamic behaviour of the neck development at touching point and to the contribution of excess neutrons in a neutron-rich target (or projectile) to neck formation and nucleon transfer.
New Astrophysical Reaction Rates for 18F(p, α)15O and 18F(p, γ)19Ne
SHU Neng-Chuan, D. W. Bardayan, J. C. Blackmon, CHEN Yong-Shou, R. L. Kozub, P. D. Parker, M. S. Smith
Chin. Phys. Lett. 2003, 20 (9): 1470-1473 .  
Abstract   PDF(pc) (290KB) ( 556 )
The rates of the thermonuclear 18F(p, α)15O and 18F(p, γ)19Ne reactions in hot astrophysical environments are needed to understand gamma-ray emission from nova explosions. The rates for these reactions have been uncertain due to discrepancies in recent measurements, as well as to a lack of a comprehensive examination of the available structure information in the compound nucleus 19Ne. We have examined the latest experimental measurements with radioactive and stable beams, and made estimates of the unmeasured 19Ne nuclear level parameters, to generate new rates with uncertainties for these reactions. The rates are expressed as numerical values over the temperature range relevant for stellar explosions, as well as analytical expressions as functions of temperature in a format suitable for use in astrophysical simulations. Comparisons with the previous rate calculations are carried out, and the astrophysical implications are briefly discussed.


Analysis of Charge State Distribution by Non-Local Thermodynamic-Equilibrium Spin-Orbit-Split-Array Collisional Radiative Model
ZHANG Hong, ZHANG Ji-Yan, YANG Xiang-Dong, YANG Guo-Hong, ZHENG Zhi-Jian
Chin. Phys. Lett. 2003, 20 (9): 1474-1477 .  
Abstract   PDF(pc) (290KB) ( 605 )
A collisional radiative model based on the spin-orbit-split-arrays is used to determine the charge state distribution of gold plasmas. The ab initio atomic structure code of Cowan and the spin-orbit-split-array model were used to calculate all the emission spectra of the different gold species, and a non-local thermodynamic-equilibrium model was coupled to calculate the ion populations at a given plasma density and electron temperature. The charge state distribution and other plasma parameters were determined by comparing the experimental spectra with the theoretical simulated spectra of gold plasmas.
Realization of Low Threshold of InGaAs/InAlAs Quantum Cascade Laser
LI Cheng-Ming, LIU Feng-Qi, JIN Peng, WANG Zhan-Guo
Chin. Phys. Lett. 2003, 20 (9): 1478-1481 .  
Abstract   PDF(pc) (346KB) ( 954 )
By optimizing the molecule beam epitaxy growth condition, the quality of quantum cascade (QC) material has greatly been improved. The spectrum of double x-ray diffraction indicates that the interface between the constituent layers is very smooth, the lattice mismatch between the epilayer and the substrate is less than 0.1%, and the periodicity fluctuation of the active region is not more than 4.2%. The QC laser with the emission wavelength of about 5.1μm is operated at the threshold of 0.73kA/cm2 at liquid nitrogen temperature with the repetition rate of 10 kHz and at a duty cycle of 1%. Meanwhile, the performance of the laser can be improved with suitable post process techniques such as the metallic ohmic contact technology.
Energy Quantization and Probability Density of Electron in Intense-Field-Atom Interactions
AO Shu-Yan, CHENG Tai-Wang, LI Xiao-Feng, WU Ling-An, FU Pan-Ming
Chin. Phys. Lett. 2003, 20 (9): 1482-1484 .  
Abstract   PDF(pc) (427KB) ( 321 )
We find that, due to the quantum correlation between the electron and the field, the electronic energy becomes quantized also, manifesting the particle aspect of light in the electron-light interaction. The probability amplitude of finding electron with a given energy is given by a generalized Bessel function, which can be represented as a coherent superposition of contributions from a few electronic quantum trajectories. This concept is illustrated by comparing the spectral density of the electron with the laser assisted recombination spectrum.
L-Shell X-Ray Production Cross Sections of Au and Ir Atoms by Electron Impact near the Threshold Region
WU Zhang-Wen, YANG Dai-Lun, LUO Xiao-Bin, HE Fu-Qing, PENG Xiu-Feng, LUO Zheng-Ming
Chin. Phys. Lett. 2003, 20 (9): 1485-1487 .  
Abstract   PDF(pc) (361KB) ( 718 )
L-shell production cross sections Lα, Lβ and Lγ for Au and Ir atoms have been measured by electron impact at incident electron energies of about one to three times of the threshold energy. The total production cross section and mean ionization cross section were obtained from the experimental results and by using mean fluorescence yield, respectively. The influence of electrons reflected from the substrate and multiple electron scattering inside the target have been corrected. The experimental results are compared with the existing measured results and the theoretical predictions.
Theoretical Analysis of Structures of Ga4N4 Clusters
SONG Bin, CAO Pei-Lin
Chin. Phys. Lett. 2003, 20 (9): 1488-1491 .  
Abstract   PDF(pc) (633KB) ( 697 )
The structures and energies of a Ga4N4 cluster have been calculated using a full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO MD) method. We obtained twenty-four structures for a Ga4N4 cluster. The most stable structure we obtained is a Cs three-dimensional structure, the energy of which is lower than that of the C2v symmetry structure proposed by Kandalam et al. [J. Phys. Chem. B 106(2002) 1945] The calculated results show that the isomer with an N3 subunit is preferred, supporting the previous result made by Kandalam et al. We found that the most stable structure of Ga4N4 clusters presented semiconductor-like properties through the calculation of the density of states.
Time-Resolved Investigation of Ionization of Clusters Irradiated by a Strong Laser
LIU Jian-Sheng, LI Ru-Xin, WANG Cheng, LI Shao-Hui, WANG Xiang-Xin, ZHU Pin-Pin, ZENG Zhi-Nan, NI Guo-Quan, XU Zhi-Zhan, LIU Jing-Ru
Chin. Phys. Lett. 2003, 20 (9): 1492-1495 .  
Abstract   PDF(pc) (456KB) ( 457 )
Ionization dynamics of clusters irradiated by chirped femtosecond lasers is investigated by using a linearly chirped pulse spectral interferometry with a time resolution of less than 100 fs. The production of an average charged ~Xe18+ and ~Kr9+ ions indicates a strong energy coupling between laser and cluster. Ultrafast depletion of the probing laser is observed to be strictly coincident with the ionization front as seen in other experiments. Moreover, a two-step ionization process for Xe and Kr clusters irradiated by high-intensity lasers has been observed, which implies the role of resonance enhancement during the cluster explosion.
Optical Properties and Structure Analyses of Zinc Sulfide Nanorods
ZHAO Qi-Tao, HOU Li-Song, HUANG Rui-An, GU Si-Peng
Chin. Phys. Lett. 2003, 20 (9): 1496-1497 .  
Abstract   PDF(pc) (210KB) ( 708 )
ZnS nanorods were synthesized using solvothermal process with ethylenediamine as a bidentate ligand to form Zn2+ complexes and dodecylthiol providing an effective control over the crystal growth of ZnS nanorod. The microstructure of the nanorods was characterized by x-ray diffraction and transmission electron microscopy. The optical properties of ZnS nanorods were examined by the photoluminescence spectrum.
Experimental Study on Mechanical Characteristics of Coupling Pulsed Laser to Solid Targets
LIN Li-Yun, WANG Sheng-Bo, WU Hong-Xing, GUO Da-Hao, DAI Yu-Sheng, XIA Xiao-Ping, GUO Lei, LUO Zhi-Cheng
Chin. Phys. Lett. 2003, 20 (9): 1498-1500 .  
Abstract   PDF(pc) (297KB) ( 472 )
A set of experiments were designed to research on the mechanical characteristics of laser driving lightcraft, and the minimum laser power density needed to drive the lightcraft (weight 1.010 kg) is measured to be 71.986 x 109W.cm-2 during the confined laser ablation of targets in vacuum. A set of parameters are discovered important to improve the propulsion efficiency, such as the restraint layers on the targets (the K9 glass is the optimal), and larger laser power density. In view of the impracticality of the confined ablation, we propose the applications of those target materials that can not only produce powerful plasma propulsion but also can be used in repetitively pulsed laser.
Terahertz Conductivity of Single Walled Nanotube Films
HAN Jia-Guang, ZHU Zhi-Yuan, HE Feng, LIAO Yi, WANG Zhen-Xia, ZHANG Wei, YU Li-Ping, SUN Li-Tao, WANG Ting-Tai
Chin. Phys. Lett. 2003, 20 (9): 1501-1503 .  
Abstract   PDF(pc) (297KB) ( 440 )
The conductivity of single walled nanotube films is investigated with a combination of the Maxwell-Garnett (MG) model and the Drude-Lorentzian (DL) model in the Terahertz region. A theoretical fit for Jeon's experiment is given and a decrease of the real conductivity with increasing frequency is predicted. Meanwhile, the MG and DL models are also discussed for different samples.
Measuring Transmittance in Rubidium Vapor Cells Using an Extremely Weak Coherent Field of Light
DENG Jian-Liao, LI Yong-Qing, WANG Yu-Zhu
Chin. Phys. Lett. 2003, 20 (9): 1504-1506 .  
Abstract   PDF(pc) (319KB) ( 612 )
The absorptive properties of the atomic transition in the Rb85D2 (A) line (5S1/2-5P3/2) at 780.0 nm are measured by using a continuous tunable diode laser and a CCD detector in Rb vapor cell under the condition of extremely weak incident intensity. When the intensity of incident light decreases from 420 pW/cm2 to 0.03 pW/cm2, the transmittance is found to be independent of the incident intensity within our experimental accuracy.
Dependence of Electromagnetically Induced Transparency on Laser Linewidth
GUO Rui-Min, XIAO Feng, LIU Cheng, ZHANG Yu, CHEN Xu-Zong
Chin. Phys. Lett. 2003, 20 (9): 1507-1510 .  
Abstract   PDF(pc) (407KB) ( 1032 )
The influence of the linewidth of coupling laser on the electromagnetically induced transparency (EIT) spectral width is theoretically investigated. The model to describe the EIT spectral width is based on the standard semi-classical theory. The result shows that the effect of the linewidth of coupling laser is equivalent to an additional relaxation between two ground states in the Λ-type configuration. A broadening linewidth of coupling laser implies the increasing relaxation between the two ground states, which will make the wider EIT spectral linewidth.
Interpretation of Plateau in High-Harmonic Generation
CHENG Tai-Wang, LI Xiao-Feng, AO Shu-Yan, FU Pan-Ming
Chin. Phys. Lett. 2003, 20 (9): 1511-1513 .  
Abstract   PDF(pc) (332KB) ( 400 )
The plateau in high-harmonic generation is investigated in the frequency domain. Probability density of an electron in an electromagnetic field is obtained through analysing the quantized-field Volkov state. The plateau of high-harmonic generation reflects the spectral density of the electron at the location of nucleus after above-threshold ionization.

Localization and Threshold of Bistable Switching by Gap-Edge Shifting
CHEN Li-Xue, KIM Dalwoo, SONG Ying-Lin, DING Wei-Qiang, LI Wen-Hui, LIU Shu-Tian
Chin. Phys. Lett. 2003, 20 (9): 1514-1516 .  
Abstract   PDF(pc) (469KB) ( 494 )
We numerically investigate the localization behaviour of light propagation in a one-dimensional nonlinear photonic crystal (1D-NPC). It is found that the localization of a high gap-edge mode is better than that of a low one, so that the switching threshold of the 1D-NPC with plus Kerr L-layers is much lower than that with minus Kerr H-layers. For a structure of 16 periods, the threshold of the structure with nonlinear L-layers is about 1/10 of that with nonlinear H-layers in the same level of nonlinear refractive coefficient.
Optical and Thermal Properties of Nickel-Azo Dyes for Digital Versatile Disc-Recordable
WEI Bin, WU Yi-Qun, GU Dong-Hong, GAN Fu-Xi
Chin. Phys. Lett. 2003, 20 (9): 1517-1519 .  
Abstract   PDF(pc) (405KB) ( 1125 )
We investigate the absorption spectra, optical constants and thermal decomposition as well as red-light (650 nm) static recording properties of three novel nickel-azo dye films based on 4-methylthiazole, benzothiazole and 6-methylbenzothiazole. Particularly, we obtain the nickel-azo complex film based on 4-methylthiazole, peaking at 562 nm and 613 nm, with higher refractive index (n = 2.46) and lower extinction coefficient (k = 0.18) at the wavelength 650 nm and a sharp threshold of thermal decomposition at 330°C. The results of the static optical recording test of this dye film indicate that high reflectivity contrast of 51% can be observed at a laser writing power of 5.9 mW and pulse width of 350 ns. These results imply that the nickel-azo complex based on 4-methylthiazole is a promising candidate for a recording medium of digital versatile disc-recordable.

Effect of Invariant Transformation in One-Dimensional Randomly-Perturbed Photonic Crystal
HAN Peng, WANG He-Zhou
Chin. Phys. Lett. 2003, 20 (9): 1520-1523 .  
Abstract   PDF(pc) (283KB) ( 718 )
An effect of invariant transformation in one-dimensional randomly-perturbed photonic crystals is presented analytically and numerically. According to this effect, localization length can be investigated in different identical intervals, and the relations among these zones are governed by a simple expression. A concept of effective randomness is introduced as a result, which denotes the disorder of phase shifts actually. The divergent behaviour of localization length in the limit of low frequency can be interpreted directly through this effect. Since the effect is obtained without any approximation, it is expected to be useful in understanding the general intrinsic nature of one-dimensional randomly-perturbed photonic crystals.
Experimental Observation of Traveling Hexagon Patterns in Dielectric Barrier Discharge
DONG Li-Fang, HE Ya-Feng, YIN Zeng-Qian, CHAI Zhi-Fang
Chin. Phys. Lett. 2003, 20 (9): 1524-1526 .  
Abstract   PDF(pc) (348KB) ( 567 )
Traveling hexagon patterns have been observed in dielectric barrier discharge in an air-argon mixture. The phase diagram of hexagon pattern appearance as functions of applied voltage and air concentration is given. The spatial frequency of hexagon pattern increases with increasing applied voltage and air concentration. The current waveforms of hexagon pattern also vary with the air concentration. The drift velocity of traveling hexagon pattern changes from 4 mm/s to 18 mm/s.
Tuning Effect on the Electron Energy Distribution Function of an Inert Gas Mixture in Nitrogen Inductively Coupled Plasma Discharges
MA Jie, PU Yi-Kang
Chin. Phys. Lett. 2003, 20 (9): 1527-1529 .  
Abstract   PDF(pc) (329KB) ( 660 )
By using a Langmuir probe, the electron energy distribution function (EEDF) is measured in inductively coupled plasma discharges in N2/Ar mixtures at 200 W rf powers. In pure N2 discharges a Maxwellian EEDF is observed. When the mixing ratio of Ar increases, the distribution of high energy electrons evolves with a different trend from that of low energy electrons, resulting in an apparent “two temperature structure”of the EEDF. We discuss this non-Maxwellian EEDF and its effect on the measurement and the interpretation of “electron temperature” by both the probe and line ratio technique.
Calculation of Internal Energy and Pressure of Dense Hydrogen Plasma by Direct Path Integral Monte Carlo Approach
LIU Song-Fen, HU Bei-Lai
Chin. Phys. Lett. 2003, 20 (9): 1530-1532 .  
Abstract   PDF(pc) (267KB) ( 588 )
The internal energy and pressure of dense hydrogen plasma are calculated by the direct path integral Monte Carlo approach. The Kelbg potential is used as interaction potentials both between electrons and between protons and electrons in the calculation. The complete formulae for internal energy and pressure in dense hydrogen plasma derived for the simulation are presented. The correctness of the derived formulae are validated by the obtained simulation results. The numerical results are discussed in details.
Research on Stimulated Raman Scattering Spectrum for Cavity Targets at the Shenguang-II Laser Facility
ZHANG Jia-Tai, LIU Zhan-Jun, ZHENG Chun-Yang, JIANG Xiao-Hua
Chin. Phys. Lett. 2003, 20 (9): 1533-1536 .  
Abstract   PDF(pc) (492KB) ( 594 )
The stimulated Raman scattering (SRS) experiments with half cavity targets have been carried out at the Shenguang-II laser facility. The imitative optic multiple-channel analyser (OMA) spectrograph is used to obtain the SRS experimental spectrum. We have developed a two-dimensional laser plasma interaction (LPI2D) code. The SRS spectrum for half-cavity targets is analysed theoretically and simulated numerically using the LPI2D code. These simulations quantitatively reproduce the experimental results firstly.
Sheath Structure of an Electronegative Plasma
WANG Zheng-Xiong, LIU Jin-Yuan, ZOU Xiu, LIU Yue, WANG Xiao-Gang
Chin. Phys. Lett. 2003, 20 (9): 1537-1539 .  
Abstract   PDF(pc) (320KB) ( 424 )
We investigate the sheath structure of an electronegative plasma at steady state with the assumptions of cold positive ions and hot negative ions. The modified Bohm criterion is obtained with the Sagdeev potential by introducing a modified ion sound velocity. At the same time the electric potential, net space charge and particles densities in the sheath are analysed in several cases of different temperature ratios of electrons to negative ions and different density ratios of negative ions to positive ions.
Carbon Nitride Compounds Synthesized by Thermal Annealing Amorphous Nanostructured Graphite under the Flow of NH3 Gas
GONG Zhi-Guang, LI Mu-Sen
Chin. Phys. Lett. 2003, 20 (9): 1540-1543 .  
Abstract   PDF(pc) (325KB) ( 1320 )
Graphitic-C3N4 (g-C3N4) and pseudocubic-C3N4 (p-C3N4) have been synthesized by thermally annealing high-energy ball milled amorphous nanostructured graphite powders under NH3 atmosphere. The experimental results by x-ray, transmission electron microscopy, selected electron area diffraction and parallel electron energy loss spectroscopy indicated that g-C3N4 grew from the milled graphite powders in the presence of NH3 gas at a temperature of 1050°C. After treatment at a temperature of 1350°C, the pseudocubic-C3N4 phase forms. It was believed that the high-energy ball milling generates nanosized amorphous graphite structures, under subsequent isothermal annealing in a flow of NH3 gas, the carbon nitride compound can easily form through reaction of nanostructured carbon with nitrogen of NH3.
Piezoresistive Effect of Doped Carbon Nanotube/Cellulose Films
WANG Wan-Lu, LIAO Ke-Jun, LI Yong, WANG Yong-Tian
Chin. Phys. Lett. 2003, 20 (9): 1544-1547 .  
Abstract   PDF(pc) (337KB) ( 503 )
The strain-induced resistance changes in iodine-doped and undoped carbon nanotube films were investigated by a three-point bending test. Carbon nanotubes were fabricated by hot filament chemical vapor deposition. The experimental results showed that there has a striking piezoresistive effect in carbon nanotube films. The gauge factor for I-doped and undoped carbon nanotube films under 500 microstrain was about 125 and 65 respectively at room temperature, exceeding that of polycrystalline silicon (30) at 35°C. The origin of the piezoresistivity in the films may be ascribed to a strain induced change in the band gap for the doped tubes and to the intertube contact resistance for the undoped tubes.
Nanostructure and Properties of Corrosion Resistance in C+Ti Multi-Ion-Implanted Steel
ZHANG Tong-He, WU Yu-Guang, LIU An-Dong, ZHANG Xu, WANG Xiao-Yan
Chin. Phys. Lett. 2003, 20 (9): 1548-1551 .  
Abstract   PDF(pc) (460KB) ( 1188 )
The corrosion and pitting corrosion resistance of C+Ti dual and C+Ti+C ternary implanted H13 steel were studied by using a multi-sweep cyclic voltammetry and a scanning electron microscope. The effects of phase formation on corrosion and pitting corrosion resistance were explored. The x-ray diffraction analysis shows that the nanometer-sized precipitate phases consist of compounds of Fe2Ti, TiC, Fe2C and Fe3C in dual implanted layer and even in ternary implanted layer. The passivation layer consists of these nanometer phases. It has been found that the corrosion and pitting corrosion resistance of dual and ternary implanted H13 steel are improved extremely. The corrosion resistance of ternary implanted layer is better than that of dual implantations and is enhanced with the increasing ion dose. When the ion dose of Ti is 6 x 1017/cm2 in the ternary implantation sample, the anodic peak current density is 95 times less than that of the H13 steel. The pitting corrosion potential of dual and ternary implantation samples is in the range from 55 mV to 160 mV which is much higher than that of the H13 steel. The phases against the corrosion and pitting corrosion are nanometer silkiness phases.
Dopant Effects on Defects in GaN Films Grown by Metal-Organic Chemical Vapor Deposition
LU Min, YANG Hua, LI Zi-Lan, YANG Zhi-Jian, LI Zhong-Hui, REN Qian, JIN Chun-Lai, LU Shu, ZHANG Bei, ZHANG Guo-Yi
Chin. Phys. Lett. 2003, 20 (9): 1552-1553 .  
Abstract   PDF(pc) (285KB) ( 483 )
The effects of dopants on the defects of GaN films were investigated by using different methods, such as wet etching of pits, x-ray diffraction and photoluminescence (PL). Three kinds of the samples were prepared with different dopants, that is, nominally undoped, Si-doped and Mg-doped GaN films. It was found that the lowest density of the etched pit was existed in the nominally undoped GaN, while the highest in the Mg-doped sample. The effects of the dopants on the etching pits were discussed.
Effective Route to Graphitic Carbon Nitride from Ball-Milled Amorphous Carbon in NH3 Atmosphere Under Annealing
FEI Zhen-Yi, LIU Yu-Xian
Chin. Phys. Lett. 2003, 20 (9): 1554-1557 .  
Abstract   PDF(pc) (344KB) ( 1525 )
Graphitic carbon nitride (g-C3N4) powders were successfully synthesized from ball-milled amorphous carbon under NH3 atmosphere at high temperature, for the first time to our knowledge. The combined characteristic data obtained by x-ray diffraction, high-resolution transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, energy dispersive spectroscopic analysis, and Fourier transformation infrared spectroscopy provide substantial evidence for the graphite-like sp2-bonded structure with C3N4 stoichiometry.
Shell Coupling Through a Single Multiwall Carbon Nanotube
LI Qiu-Hong, WANG Tai-Hong
Chin. Phys. Lett. 2003, 20 (9): 1558-1560 .  
Abstract   PDF(pc) (316KB) ( 466 )
Transport properties of single multiwall carbon nanotubes at high bias voltages have been investigated in vacuum by scanning the bias voltage at room temperature. The characteristics of current-voltage exhibit a rapid increase of current, which can be well understood in terms of the density of states and multi-shell coupling. The breakdown experiment shows that the inner shells also contribute to conductance and can break at the bias voltage higher than that of the outer shells. This demonstrates that multi shells participate the transport. It is also found that the breakdown occurs at the center of the MWNT, indicating that the transport is diffusive rather than ballistic.
Phonon Characteristics of Polycrystalline Cubic SrTiO3 Thin Films
DU Yu-Le, CHEN Guang, ZHANG Ming-Sheng, YANG Sen-Zu
Chin. Phys. Lett. 2003, 20 (9): 1561-1564 .  
Abstract   PDF(pc) (410KB) ( 719 )
Polycrystalline SrTiO3 thin films with the cubic perovskite structure were grown on quartz substrates by pulsed laser deposition. The first-order Raman scattering processes, which were forbidden in SrTiO3 single crystals, were observed in the films at 300 K and lower temperatures due to the structural distortion causing by strain effect and oxygen vacancies. The polar TO2 phonon showed a typical Fano asymmetry in the entire temperature region from 95 K to 300 K. In contrast, the nonpolar TO3 phonon and polar TO4 phonons were mostly symmetric.
Doping-Induced Spectral Weight Transfer with d-p Interaction
CAO Tian-De, LI Chuan-Qi, ZHAO De-Lin, CHENG Guo-Sheng, GUO Sheng-Li
Chin. Phys. Lett. 2003, 20 (9): 1565-1567 .  
Abstract   PDF(pc) (196KB) ( 1076 )
The doping-induced spectral weight transfer is studied by using the d-p model and considering spatial fluctuations in the high-Tc cuprates. The results leaded by the Cu-O interaction are found as follows: (i) the energy levels are grown inside the charge-transfer gap, (ii) the spectral weight is decreased below EF, and (iii) the d holes at Cu-sites in CuO2 planes are delocalized with hole doping. Both metal-insulator transition and electrons of two states are also discussed.
Rabi Oscillation of Exciton Dressed by Phonons In a Quantum Dot
LI Wai-Sang, ZHU Ka-Di,
Chin. Phys. Lett. 2003, 20 (9): 1568-1570 .  
Abstract   PDF(pc) (191KB) ( 431 )
The effect of strong exciton-phonon interacton on the excitonic Rabi oscillations in a coherently driven quantum dot in a high-Q single mode cavity is investigated theoretically. We show that the Rabi oscillation of exciton dressed by phonons can persists with the Rabi frequency ge-λ/2 at absolute zero temperature, where g is the single-photon Rabi frequency and λ is the Huang-Rhys factor. The results also present that such coherent oscillations can be modified by manipulating the Rabi frequency of the driving field.
Near Band-Edge and Mid-Gap Photoluminescence of a ZnO Thin Film Grown on a (001) Silicon Substrate
GUO Bing, YE Hui, QIU Zhi-Ren,
Chin. Phys. Lett. 2003, 20 (9): 1571-1573 .  
Abstract   PDF(pc) (386KB) ( 587 )
A nominally undoped wurtzite ZnO thin film of highly c-axis orientation was successfully grown on (001) silicon by metal-organic chemical vapor deposition, and its photoluminescence was measured as a function of excitation intensity at room temperature. The ZnO sample exhibited a strong near band-edge (NBE) line at 379.48 nm (3.267 eV) and a weak broad green band around ~ 510 nm (2.43 eV), showing a linear and sublinear excitation dependence of the luminescence intensity, respectively. No discernable intensity dependence of lineshape and emission peak was found for the NBE line. On the other hand, the peak energy of the green luminescence was found to increase nearly logarithmically with the increasing excitation intensity. The above results clearly indicate that in the ZnO epilayer, the NBE line was due to an excitonic spontaneous emission, while the mid-gap green luminescence can be assigned to the tunnel-assisted donor-acceptor pair (DAP) radiative recombination. Moreover, we obtained an energy depth β ~ 11.74 meV for the potential wells due to the fluctuating distribution of the unintentional impurities/defects responsible for the tunnel-assisted DAP emission.
Coherent Coupling of Double Quantum Dots Embedded in a Mesoscopic Ring
WU Shao-Quan, WANG Shun-Jin
Chin. Phys. Lett. 2003, 20 (9): 1574-1577 .  
Abstract   PDF(pc) (467KB) ( 562 )
We theoretically study the properties of the ground state of a series-coupled double quantum dot embedded in a mesoscopic ring in the Kondo regime by means of the two-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. It is shown that two dots can be coupled coherently, which is reflected in the appearance of parity effects and the complex current-phase relation in this system. This system might be a possible candidate for future device applications.
Enhancement of Magnetoresistance in Granular CrO2/Polystyrene Composites
CHEN Ya-Jie, ZHANG Xiao-Yu, LI Zhen-Ya,
Chin. Phys. Lett. 2003, 20 (9): 1578-1581 .  
Abstract   PDF(pc) (448KB) ( 346 )
We present a study of magnetotransport in CrO2/polystyrene (PS) composites over a range of polystyrene concentration (0-30 wt.%). In the experiment, an obvious enhancement in magnetoresistance (MR) is observed at 77 K and at room temperature as the half-metallic CrO2 particles are encapsulated with a thin layer of insulating polystyrene. The enhanced MR can be interpreted in terms of spin-dependent intergranular tunneling with 4-nm-thick PS barrier. Moreover, it is found that the novel PS barrier contributes to room-temperature MR more significantly than that at 77 K. Temperature dependence of resistance is good agreement with ~ T-1/4 in the temperature range from 77 to 298 K.
Fingerprints of Mott Superconductivity
WANG Qiang-Hua
Chin. Phys. Lett. 2003, 20 (9): 1582-1585 .  
Abstract   PDF(pc) (204KB) ( 364 )
We improve a previous theory of doped Mott insulators with duality between pairing and magnetism by a further duality transform. As the result we obtained a quantum Ginzburg-Landau theory describing the Cooper pair condensate and the dual of spin condensate. We address the superconductivity by doping a Mott insulator, which we call the Mott superconductivity. Some fingerprints of such novelty in cuprates are the scaling between neutron resonance energy and superfluid density, and the induced quantized spin moment by vortices or Zn impurity (together with circulating charge supper-current to be checked by experiments).
Preliminary Monte Carlo Results for the Three-Dimensional Holstein Model
WU Yan-Li, LIU Chuan, LUO Qiang,
Chin. Phys. Lett. 2003, 20 (9): 1586-1588 .  
Abstract   PDF(pc) (284KB) ( 402 )
Monte Carlo simulations are used to study the three-dimensional Holstein model. The relationship between the band filling and the chemical potential is obtained for various phonon frequencies and temperatures. The energy of a single electron or a hole is also calculated as a function of the lattice momenta.

Phase Separation and Magnetoresistance in Nd0.52Sr0.48MnO3
LI Zhi-Qing, JIANG En-Yong, LIU Hui, LI Yang-Xian, YU Ao, LIU Xin-Dian, WU Ping, BAI Hai-Li,
Chin. Phys. Lett. 2003, 20 (9): 1589-1592 .  
Abstract   PDF(pc) (545KB) ( 606 )
Polycrystalline Nd0.52Sr0.48MnO3 ceramic is prepared by a Pechini process. Its electron spin resonance spectra, magnetic and transport properties have been investigated experimentally. At temperature above 270 K, the compound is paramagnetic insulator, while in temperature between 160 K and 270 K, the compound is separated into a paramagnetic insulator and a ferromagnetic metal coexisting state. Below 160 K, theferromagnetic phase coexists with an antiferromagnetic state, but the ferromagnetic phase remains to be dominant. This makes the compound exhibiting a metallic character even at temperature far below TN.
Magnetic Behaviour of Antiferromagnetic Monolayer under an External Field
HUANG Chen, WANG Huai-Yu, WANG En-Ge
Chin. Phys. Lett. 2003, 20 (9): 1593-1595 .  
Abstract   PDF(pc) (336KB) ( 594 )
Magnetic behaviour of antiferromagnetic monolayer under external field is studied. This is the first time to calculate all components of spin statistical average of an antiferromagnetic system with the random phase approximation. To do so, a method is developed by many-body Green's function theory. Magnetization and susceptibility are investigated when external field is applied in either the x- or z-direction. The results are compared with the ferromagnetic monolayer.
Optical Parameters and Absorption of Azo Dye and Its Metal-Substituted Compound Thin Films
WEI Bin, WU Yi-Qun, GU Dong-Hong, GAN Fu-Xi
Chin. Phys. Lett. 2003, 20 (9): 1596-1599 .  
Abstract   PDF(pc) (479KB) ( 677 )
We determine the complex refractive indexes N(N = n-ik), dielectric constants ε(ε = ε1 - iε2), and absorption coefficients α of a new azo dye [2-(6-methyl-2-benzothiazolyazo)-5-diethylaminophenol(MBADP)]-doped polymer and its nickel- and zinc-substituted compounds(Ni-MBADP and Zn-MBADP) spin-coated thin films from an scanning ellipsometer in the wavelength 400-700 nm region. Metal chelation strongly (about one times) enhances the optical and dielectric parameters at the peaks and results in a large bathochromic shift (50-60 nm) of absorption band. Bathochromic shift of Ni-MBADP is about 10 nm larger than that of Zn-MBADP due to different spatial configurations formed in the metal-azo complexes.
Correlation Between the IR Transmission Spectra and the CdZnTe Qualities
LI Guo-Qiang, JIE Wan-Qi, GU Zhi, HUA Hui
Chin. Phys. Lett. 2003, 20 (9): 1600-1602 .  
Abstract   PDF(pc) (288KB) ( 934 )
Tens of Cd0.9Zn0.1Te wafers from three ingots grown by the vertical Bridgman method (VBM) are characterized by infrared (IR) transmission. Four types of distinct IR transmission spectra are found for these wafers. Each of them corresponds to one kind of wafers with specified qualities. At the same time, approximate mathematical relations exist between the wafer dislocation density and their IR transmissions at the wavenumber 4000 cm-1, as well as between the resistivity and the IR transmissions at the wavenumber 500 cm-1. The reasons of the above results are attempted to be given.
Jahn-Teller Distortions Cooperating with Magnetic Interaction in the Raman Spectra of La0.75Ca0.25MnO3 Thin Film
LIU Yong, LI Guang, FENG Shuang-Jiu, LI Xiao-Guang
Chin. Phys. Lett. 2003, 20 (9): 1603-1606 .  
Abstract   PDF(pc) (463KB) ( 883 )
Remarkable changes (additional peaks, frequency shift, and peak width) of Raman spectra of a La0.75Ca0.25MnO3 thin film have been observed during the paramagnetic insulator-ferromagnetic metal transition. The v1 band (230 cm-1) hardens by lattice contraction as a result of the rearrangement of MnO6 octahedra. The Jahn-Teller distortions seem to be responsible for the broadening of v2 band (485 cm-1) above the magnetic transition temperature TC. It is proposed that the 438 cm-1 vibration mode activated in the magnetic ordering state is associated with the rearrangement of MnO6 octahedra. The softening of v3 band (610 cm-1) below TC can be ascribed to the magnetic interaction that brings into spin-phonon coupling terms.




Effect of Phosphorescent Sensitizer on White Organic Light-Emitting Devices
CHENG Gang, QIU Song, ZHAO Yi, MA Yu-Guang, LIU Shi-Yong
Chin. Phys. Lett. 2003, 20 (9): 1607-1609 .  
Abstract   PDF(pc) (396KB) ( 826 )
We have fabricated high-efficiency white organic light-emitting devices by using the phosphorescent material fac tris (2-phenylpyridine) iridium [Ir(ppy3)] as a sensitizer. Ir(ppy)3 and the fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9 enyl) (DCJTB) are co-doped into 4,4'-N,N'-dicarbazole-biphenyl (CBP) host. N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) acts as a blue light-emitting as well as hole-transporting layer. The chromaticity of white emission can be tuned by adjusting the concentration of Ir(ppy)3 and DCJTB. The maximum efficiency and luminance of the device with 3-wt.% Ir(ppy)3 and 2-wt.% DCJTB are 7.5 cd A-1 and 12020 cd m-2, respectively, which produces fairly pure white emission with the commission international De L'Eclairage coordinates of (0.33, 0.32) at 10 V.
Dynamical Model in Low-Frequency-Pulsed Electron-Stimulated Desorption
ZHANG Tong, WU Xiao-Shan, HU An, MAO Fu-Ming, YANG Xue-Qian, CUI Yi-Ping
Chin. Phys. Lett. 2003, 20 (9): 1610-1612 .  
Abstract   PDF(pc) (231KB) ( 379 )
A dynamical model of low-frequency-pulsed electron-stimulated desorption is developed. The characteristic of desorbed gas flow is taken as an exponential function, and can be degenerated to a triangular and square wave. The transient pressure is given according to the gas flow of desorbing gas and vacuum system parameters, including the pumping speed and the system volume. Although the mathematical model is deduced from the electron-stimulated desorption, it can be applied to other similar processes of intermittent desorption.
Deposition of Er:Al2O3 Films and Photoluminescence Characteristics
LI Cheng-Ren, SONG Chang-Lie, LI Shu-Feng, RAO Wen-Xiong
Chin. Phys. Lett. 2003, 20 (9): 1613-1615 .  
Abstract   PDF(pc) (382KB) ( 402 )
Er3+-doped Al2O3 films were deposited on silicon substrates by reactive closed-field unbalanced magnetron sputtering. The process parameters, such as target bias voltage, substrate bias voltage, O2 gas flows, sputtering gas pressure, were studied. The 1.53μm photoluminescence characteristics from Er3+ were measured. The relations among the PL peak intensity, annealing temperatures, and pump power were experimentally investigated.
Properties of InGaP/GaAs Grown by Solid-Source Molecular Beam Epitaxy with a GaP Decomposition Source
SHANG Xun-Zhong, NIU Ping-Juan, WU Shu-Dong, WANG Wen-Xin, GUO Li-Wei, HUANG Qi, ZHOU Jun-Ming
Chin. Phys. Lett. 2003, 20 (9): 1616-1618 .  
Abstract   PDF(pc) (357KB) ( 1005 )
Lattice-matched InGaP on GaAs (001) was successfully grown by solid-source molecular beam epitaxy with a GaP decomposition source. A 0.5-μm-thick InGaP epilayer shows photoluminescence peak energy as large as 1.991 eV at 15 K, the full width at half maximum as small as 9.4 meV and x-ray diffraction rocking curve linewidth as narrow as 25 arcsec. The electron mobilities of undoped and Si-doped InGaP layers obtained by Hall measurements are comparable to similar InGaP/GaAs heterojunction grown by solid-source molecular beam epitaxy with other sources or other growth techniques. The results reveal that the InGaP/GaAs heterojunction grown by the present growth way have great potential applications for semiconductor devices.
Deposition of Diamond-Like Carbon Films by High-Intensity Pulsed Ion Beam Ablation at Various Substrate Temperatures
MEI Xian-Xiu, LIU Zhen-Min, MA Teng-Cai, DONG Chuang
Chin. Phys. Lett. 2003, 20 (9): 1619-1621 .  
Abstract   PDF(pc) (405KB) ( 540 )
Diamond-like carbon (DLC) films have been deposited onto Si substrates at substrate temperatures from 25°C to 400°C by a high-intensity pulsed-ion-beam (HIPIB) ablation deposition technique. The formation of DLC is confirmed by Raman spectroscopy. According to an x-ray photoelectron spectroscopy analysis, the concentration of sp3 carbon in the films is about 40% when the substrate temperature is below 300°C. With the increase of substrate temperature from 25°C to 400°C, the concentration of sp3 carbon decreases from 43% to 8%. In other words, sp3 carbon is graphitized into sp2 carbon when the substrate temperature is above 300°C. The results of x-ray diffraction and atomic force microscopy show that, with the increase of the substrate temperature, the surface roughness and the friction coefficient increase, and the microhardness and the residual stress of the films decrease.
Thermodynamic Analyses of the Solid-Liquid Interface and Growth Mode Transition in Undercooled Melts
LIU Ri-Ping
Chin. Phys. Lett. 2003, 20 (9): 1622-1625 .  
Abstract   PDF(pc) (303KB) ( 448 )
Free energy change for atoms transferred from liquid onto liquid-solid interface is calculated according to the structural model proposed by Jackson. Relationship among the change in free energy, the fraction of sites on the interface occupied by atoms and the interfacial undercooling is presented. This relationship can be used to judge the possible state that an interface may take, and to predict the corresponding crystal growth mode. For silicon and germanium, the experimentally observed growth mode transition from lateral growth at small undercooling to continuous growth at large undercooling is hardly to be explained by this thermodynamic calculation, which implies that the transition is possibly caused by some dynamic reasons. For nickel, crystallization is carried out only by the continuous mode, which is consistent with the experimental observations.
Effect of Size Polydispersity on Melting of Charged Colloidal Systems
CHEN Yong
Chin. Phys. Lett. 2003, 20 (9): 1626-1629 .  
Abstract   PDF(pc) (271KB) ( 464 )
We introduce simple prescriptions of the Yukawa potential to describe the effect of size polydispersity and macroion shielding effect in charged colloidal systems. The solid-liquid phase boundaries were presented with the Lindemann criterion based on molecular dynamics simulations. Compared with the Robbins-Kremer-Grest simulation results, a deviation of melting line is observed at small λ, which means large macroion screening length. This deviation of phase boundary is qualitatively consistent with the simulation result of the nonlinear Poisson-Boltzmann equation with full many-body interactions. It is found that this deviation of the solid-liquid phase behaviour is sensitive to the screening parameter.
Mössbauer Investigation of the Ferromagnetic Coupling in Copper-Iron Polycyanides
HE Yun, DAI Yao-Dong, HUANG Hong-Bo, A. M. Ali, LIN Jun, YU Zhi, XIA Yuan-Fu
Chin. Phys. Lett. 2003, 20 (9): 1630-1633 .  
Abstract   PDF(pc) (634KB) ( 401 )
One of the Prussian blue analogs, molecular magnet CuII3[FeIII(CN)6]2.11.6H2O, was investigated by Mössbauer spectroscopy. It was found that transition temperature was around TC = 18.5 K from paramagnetic phase to ferromagnetic phase. The β value of the critical exponent is around 0.338 at magnetic ordering temperature. Therefore, the ferromagnetic coupling interaction of Cu-Fe cyanide could be clearly explained by spin wave theory.

Computer Simulation of Influence of Sedimentation on Rapid Coagulation
SUN Zhi-Wei, CHEN Zhi-Ying
Chin. Phys. Lett. 2003, 20 (9): 1634-1636 .  
Abstract   PDF(pc) (316KB) ( 350 )
A computer simulation was performed to explore the features and effects of sedimentation on rapid coagulation. To estimate the accumulated influence of gravity on coagulation for dispersions, a sedimentation influence ratio is defined. Some factors possibly related to the influence of sedimentation were considered in the simulation and analysed by comparing the size distribution of aggregates, the change in collision number, and coagulation rates at different gravity levels (0 g, 1 g and more with g being the gravitational constant).
Chemical Sensors Based on Piezoresistive Cantilever Array
YU Xiao-Mei, ZHANG Da-Cheng, WANG Cong-Shun, DU Xian-Feng, WANG Xiao-Bao, RUAN Yong
Chin. Phys. Lett. 2003, 20 (9): 1637-1640 .  
Abstract   PDF(pc) (382KB) ( 550 )
U-shaped and rectangle piezoresistive cantilever arrays have been designed with the analysing results of stress, noise and sensitivity of the cantilevers. Based on silicon micromachining technology, the piezoresistive cantilevers were fabricated by using polysilicon as the piezoresistive materials. With the measurement results of noise and sensitivity, the Hooge factor is calculated to be 3 x 10-3, the gauge factor is 27, and the minimum detectable deflection of piezoresistive cantilevers are calculated to be 1.0 nm for rectangle cantilever and 0.5 nm for the U-shaped cantilever at a 6 V bias voltage and a 1000 Hz measurement bandwidth. Using polymer-coated cantilevers as individual sensors, their responses to water vapor and ammonia were tested by measuring their output voltage signals. The measured results show that the sensor sensitivity to ammonia can reach a few ppm and the sensor responses are quick.
Improvement of Axial Resolution in Confocal Microscopy by an Optical Pupil Filter with Two Zones Phase-Shifted by π
LIN Lie, WANG Xiang-Hui, WANG Zhao-Qi, MU Guo-Guang
Chin. Phys. Lett. 2003, 20 (9): 1641-1643 .  
Abstract   PDF(pc) (318KB) ( 519 )
A filter with two zones phase-shifted by π is proposed to improve the axial resolution of confocal microscopes with a finite-sized detector. The optimum axial resolution for a given size of the detector can be achieved by adjusting the zone boundary of the filter. The experimental results are well in agreement with the theoretical predictions.
Coexistence of Two Mechanisms for Extracting Energy from a Rotating Black Hole
MA Ren-Yi, WANG Ding-Xiong, LEI Wei-Hua
Chin. Phys. Lett. 2003, 20 (9): 1644-1647 .  
Abstract   PDF(pc) (475KB) ( 651 )
Evolution characteristics of a rotating black hole (BH) are discussed in coexistence of the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process in the parameter space consisting of the BH spin and the power law index of the magnetic field on the disc. The condition for the coexistence of the two energy mechanisms are derived by using the mapping relation between the angular coordinate on the BH horizon and the radial coordinate on the disc. It is shown that not only the two mechanisms can coexist, but also the power and the rate of change of BH entropy in the BZ process will dominate over those in the MC process, provided that the BH spin and the power-law index are great enough.
Dynamical Evolution of Globular Clusters in the Galaxy
WU Zhen-Yu, SHU Cheng-Gang, CHEN Wen-Ping
Chin. Phys. Lett. 2003, 20 (9): 1648-1651 .  
Abstract   PDF(pc) (281KB) ( 366 )
Given the initial conditions of spatial density distribution, velocity distribution and mass function, the dynamical evolution of globular clusters in the Milky Way is investigated in details by means of Monte Carlo simulations. Four dynamic mechanisms are considered: stellar evaporation, stellar evolution, tidal shocks due to both the disk and bulge, and dynamical friction. It is found that stellar evaporation dominates the evolution of low-mass clusters and all four are important for massive ones. For both the power-law and lognormal initial clusters mass functions, we can find the best-fit models which can match the present-day observations with their main features of the mass function almost unchanged after evolution of several Gyr. This implies that it is not possible to determine the initial mass function only based on the observed mass function today. The dispersion of the modeled mass functions mainly depends on the potential wells of host galaxies with the almost constant peaks, which is consistent with current observations.
A New 2MASS/2df Selected Sample of Pairs of Galaxies and Calibration of Merging Rate in the Local Universe
SUN Yan-Chun, C. K. XU, HE Xiang-Tao
Chin. Phys. Lett. 2003, 20 (9): 1652-1655 .  
Abstract   PDF(pc) (225KB) ( 393 )
We present a new sample of 37 close major-merger galaxy pairs, selected from the 2-degree field redshift survey of the two-micron all-sky survey (2MASS) galaxies. The selection criteria for our near-infrared pairs are more closely related to galaxy mass (a very important parameter in galaxy evolution models) than those for optical selected samples. Our sample benefits enormously from the high homogeneity and accuracy of the 2MASS database, and false matchings are minimized by the essentially three-dimensional selection procedure. Taking into account the biases, we find that 1.96 (±0.4)% of galaxies are in close major-merger pairs. This indicates a local merging rate of 1.0%, in good agreement with the results in recent studies of optical selected pairs in the local universe. The results derived with our sample have high confidence.
Toy Model for Eternal Expanding Universe Driven by Quintessence
GAO Chang-Jun, SHEN You-Gen, ,
Chin. Phys. Lett. 2003, 20 (9): 1656-1658 .  
Abstract   PDF(pc) (266KB) ( 553 )
Recent observations of microwave background and type Ia supernovae (SNe Ia) suggest a space-flat and accelerated expansion Universe. On the other hand, observations of supernovae 1997ff reveal that the Universe has undergone a decelerating-accelerating process. Combining these two classes of observations, we present an eternal expanding Universe toy model driven by quintessence. In this picture, the Universe undergoes an endless sequence of accelerating-decelerating cycles.
71 articles