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Volume 22 Issue 4
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Original Articles
Conserved Densities of the Black-Scholes Equation
QIN Mao-Chang, MEI Feng-Xiang, SHANG Mei
Chin. Phys. Lett. 2005, 22 (4): 785-786 .  
Abstract   PDF(pc) (167KB) ( 682 )
A class of new conserved densities of the Black-Scholes equation are constructed by using the multiplier that is derived from the result of divergence expression annihilation under the full Euler operator. The method does not depend on the symmetries of the Black-Scholes equation. These conserved densities can be expressed by solutions of the classical heat equation.
Drop Size Dependence of the Contact Angle of Nanodroplets
GUO Hong-Kai, FANG Hai-Ping
Chin. Phys. Lett. 2005, 22 (4): 787-790 .  
Abstract   PDF(pc) (239KB) ( 778 )
The contact angle of nanosized non-polarized argon sessile droplets on a solid substrate is studied by using molecular dynamics simulations. It is found that the drop size dependence of the contact angle is sensitive to the interaction between the liquid molecules and solid molecules. The contact angle decreases with the decreasing drop size for larger interaction between the liquid molecules and the solid substrate, and vice versa. This observation is consistent with most of the previous theoretical and experimental results.
Absence of GZK Cutoff and Test of de Sitter Invariant Special Relativity
CHANG Zhe, CHEN Shao-Xia, HUANG Chao-Guang
Chin. Phys. Lett. 2005, 22 (4): 791-794 .  
Abstract   PDF(pc) (222KB) ( 448 )
The possibility that the absence of Greisen--Zatsepin--Kuz’min (GZK) cutoff is used to discriminate between de Sitter invariant special relativity (SRc,R) and general relativity (GR) is studied.
A careful investigation shows, unfortunately, that the phenomenon fails to distinguish SRc,R from GR, at least, at classical level.

Recursion Relations of Radial Wavefunctions of the Hartmann Potential
CHEN Zi-Dong, CHEN Gang,
Chin. Phys. Lett. 2005, 22 (4): 795-797 .  
Abstract   PDF(pc) (184KB) ( 498 )
We obtain exact bound state solutions of the radial Schrödinger equation with the Hartmann potential, as well as two kinds of recursion relations of radial wavefunctions by using Laplace transformation. Those results are expressed only in terms of the principal and angular-momentum quantum numbers.
Direct Measurement of Squeezing in the Motion of Trapped Ions
ZENG Hao-Sheng, HU Ai-Qin, LIU Qiong, KUANG Le-Man
Chin. Phys. Lett. 2005, 22 (4): 798-800 .  
Abstract   PDF(pc) (199KB) ( 477 )
We present a simple method that can be used to directly measure the squeezing of the quantum motional states of a trapped ion. Through the use of the interaction between the trapped ion and classical lasers, one can design a required coupling between the internal electronic and external vibrational degrees of freedom of the ion and can transfer information of the expectation value of a vibrational operator to the atomic internal populations. Thus measurement of squeezing on the quantum motional state can directly be realized. By adjusting the phases of the interacting lasers, one can measure the squeezing of both position and momentum quadratures.
Construction of Controlled-NOT Gate with Thermal Ions
CHEN Chang-Yong, , GAO Ke-Lin,
Chin. Phys. Lett. 2005, 22 (4): 801-803 .  
Abstract   PDF(pc) (184KB) ( 729 )
A scheme is proposed to construct the controlled-NOT gate in an ion-trap computer, based on the interaction of trapped-thermal ions with bi-chromatic laser fields. In this scheme, a specific laser pulse sequence for the implementation of this gate is given. Furthermore, it is pointed out that this laser pulse sequence is different from that of Ref.[3] [Phys. Rev. Lett. 82 (1999) 1971), which cannot result in a real controlled-NOT gate.
Fermionic Concurrence in the Extended Hubbard Model
DENG Shu-Sa, GU Shi-Jian
Chin. Phys. Lett. 2005, 22 (4): 804-807 .  
Abstract   PDF(pc) (521KB) ( 554 )
We study the fermionic concurrence in an extended Hubbard model. Its behaviour at the ground state and at finite temperatures for general U and V is obtained numerically and analytically for a dimer system. We also investigate the properties of the concurrence under a nonuniform field, and we find that it can be used to modulate and to increase the concurrence.
Stabilizations of Two-Dimensional Trapped and Untrapped Matter Waves via a Feshbach Resonance Technique
LUO Xiao-Bing, HAI Wen-Hua
Chin. Phys. Lett. 2005, 22 (4): 808-811 .  
Abstract   PDF(pc) (221KB) ( 693 )
We have studied the dynamics of two-dimensional (2D) trapped and untrapped Bose--Einstein condensates (BECs) with a rapid periodic modulation of the scattering length via a Feshbach resonance technique, a → a0+a1sin(Ωt) with an attractive (negative) mean value and the large constants a0, a1 and Ω. Applying a variation approximation (VA), the critical threshold for the collapse of the 2D trapped vortex BEC is predicted and the collapse is prevented by causing the scattering length oscillating rapidly. On the other hand, with analytical calculation, we prove that the stabilization of a bright soliton in a 2D untrapped BEC is impossible for enough large interaction intensity and the upper limit of the intensity for the soliton stabilization is derived.
Incomplete Erasure of Which-Way Information Encoded in Atomic Hyperfine States
WEN Ling-Hua, , LIU Min, , KONG Ling-Bo, , ZHAN Ming-Sheng,
Chin. Phys. Lett. 2005, 22 (4): 812-815 .  
Abstract   PDF(pc) (242KB) ( 591 )
We propose an experimental scheme to investigate incomplete erasure of which-way information encoded in atomic hyperfine states. Due to the incomplete erasure of the which-way information, it is shown that the interference patterns of the atomic wave packets initially confined in a spin-dependent optical lattice are destroyed to a certain extent, which provides a new straight way to test further the validity of the theoretical model developed in our recent work. The remarkable merit of the proposal is that it is simple and can be implemented easily.
Dark Energy Density in Brane World
WEN Hai-Bao, HUANG Xin-Bing
Chin. Phys. Lett. 2005, 22 (4): 816-819 .  
Abstract   PDF(pc) (234KB) ( 560 )
We present a possible explanation to the tiny positive cosmological constant under the frame of AdS5 spacetime embedded by a dS4 brane. We calculate the dark energy density by summing the zero point energy of massive scalar fields in AdS5 spacetime. Under the assumption that the radius of AdS5 spacetime is of the same magnitude as the radius of observable universe, the dark energy density in dS4 brane is obtained, which is smaller than the observational value. The reasons are also discussed.
Scalar Field at the Phase Transition Point of RNdS Space
GUO Guang-Hai, GUI Yuan-Xing, TIAN Jian-Xiang
Chin. Phys. Lett. 2005, 22 (4): 820-823 .  
Abstract   PDF(pc) (264KB) ( 401 )
The real scalar field equation between the outer black hole horizon and the cosmological horizon is solved in the Reissner--Nordström--de Sitter space when it is at the phase transition point. We use an accurate approximation, the polynomial approximation, to approximate the tortoise coordinate x(r) for obtaining the inverse function r=r(x) and then for solving the wave equation. The case where the two horizons are very close to each other is discussed in detail. It is found that the wave function is characteristically similar to the harmonic in the whole range with x as the independent coordinate, while the waves pile up near the horizons with r as the independent coordinate. Furthermore, we find that the height of the potential increases as the cosmological constant Λ decreases.
Exclusion Statistics: a Generalized Description
WANG Bao-Quan, WANG Yu-Peng
Chin. Phys. Lett. 2005, 22 (4): 824-826 .  
Abstract   PDF(pc) (202KB) ( 367 )
By constructing the fused-particle representation of the free boson gas, we propose a description of the exclusion statistics which allows us to connect the Bose--Einstein statistics and the Fermi-Dirac statistics smoothly. With an proper choice of the exclusion factors γl, Hadane--Wu’s fractional statistics is retrieved in this representation.
A Forbidden Web in a Quasi-Dissipative System
DAI Jun, WANG Wen-Xiu, JIANG Yu-Mei, HE Yue, CHEN Wen, HE Da-Ren
Chin. Phys. Lett. 2005, 22 (4): 827-829 .  
Abstract   PDF(pc) (390KB) ( 409 )
A simultaneous transition of the system nature from everywhere smooth and conservative to piecewise smooth and quasi-dissipative is observed in a kicked billiard when adjusting single controlling parameter. The transition induces the appearance of a special kind of fat fractal forbidden web, which grows up and cuts off more parts from the original conservative stochastic web so that the remnant transient web becomes increasingly thinner. We numerically show a power law σ∝βv, where σ is the fractal exponent of the forbidden web, β is the control parameter, and the scaling exponent v =0.288±0.007, which describes this process.
Conservation Laws for the Derivative Nonlinear Schrödinger Equation with Non-vanishing Boundary Conditions
CHEN Xiang-Jun, HOU Li-Jie, LAM Wa Kun
Chin. Phys. Lett. 2005, 22 (4): 830-832 .  
Abstract   PDF(pc) (208KB) ( 579 )
Conservation laws for the derivative nonlinear Schrödinger equation with non-vanishing boundary conditions are derived, based on the recently developed inverse scattering transform using the affine parameter technique.
Exact Solution for the Osp(1|2n) Vertex Model under Open Boundary Conditions
LI Guang-Liang
Chin. Phys. Lett. 2005, 22 (4): 833-835 .  
Abstract   PDF(pc) (201KB) ( 434 )
We exactly solve the Osp(1|2n) vertex model with two different diagonal reflecting matrices with the nested Bethe ansatz method. It is shown that our results agree with that obtained by analytical Bethe
ansatz method.
Grüneisen Parameter along Hugoniot and Melting Temperature of ε-Iron: a Result from Thermodynamic Calculations
HUANG Hai-Jun, JING Fu-Qian, CAI Ling-Cang, Bi Yan
Chin. Phys. Lett. 2005, 22 (4): 836-838 .  
Abstract   PDF(pc) (233KB) ( 542 )
Based on the available data of specific heat Cv at constant volume and the Grüneisen parameter γ of both lattice and electron contributions, we present a consistent method for simultaneously calculating the effective or synthesized Grüneisen parameter along Hugoniot, γeH, covering solid, mixed, and liquid states, and the melting temperature Tm for ε-iron. The rationality validation for this method is confirmed as compared with the experimental data, including the measured Tm and Hugoniot bulk sound velocities Cb. The calculated γeH and Tm for ε-iron at the Earth’s inner-core boundary (330GPa) are 1.58 and 5930K, respectively, which are close to the values of 1.53 and 6050K given by Anderson [J. Phys. Chem. Solids} 64 (2003) 2125]. This method for determination of γeH could be, in principle, also applicable to any thermodynamic state calculations, e.g., along isothermal and isentropic paths, other than the Hugoniot locus.

A Monte Carlo Study on Cone-Angle Property of the Quark- and Gluon-Jets Identified by b-Tag Method
CHEN Gang, LIU Lian-Shou
Chin. Phys. Lett. 2005, 22 (4): 839-842 .  
Abstract   PDF(pc) (253KB) ( 663 )
Quark and gluon jets are studied in three-jet events generated by Jetset 7.4 and Herwig 5.9 at √s = 91.2GeV. The quark jets are identified by b-tag tracing, and the remaining jet is then defined as the gluon jet. A new physical variable, i.e. the cone-angle, which is able to describe the geometrical characteristic of the jet, is defined. It turns out that the cone-angle distribution of the gluon jet is wider than its mother quark jet, i.e. the gluon jet is ``fatter''. As the multiplicity increases, the cone-angle distribution of the quark jet has an upward-going trend, i.e. a positive correlation is present. The cone-angle of the gluon and quark jet versus their transverse momentum develop a valley. The mean cone-angles of both the gluon jet and the quark jet are negatively correlated with the transverse momentum for pt < 3GeV/c, but are positively correlated for pt > 3GeV/c. The mean cone-angles of the gluon and quark jets are well separated, showing that they can be utilized in the identification of the two kinds of jets.

Ground State Properties of New Element Z=113 and Its Alpha Decay Chain
TAI Fei, CHEN Ding-Han, XU Chang, REN Zhong-Zhou,
Chin. Phys. Lett. 2005, 22 (4): 843-845 .  
Abstract   PDF(pc) (207KB) ( 469 )
We investigate the ground state properties of the new element 278113 and of the α-decay chain with different models, where the new element Z=113 has been produced at RIKEN in Japan by cold-fusion reaction [Morita et al. J. Phys. Soc. Jpn. 73(2004)2593]. The experimental decay energies are reproduced by the deformed relativistic mean-field model, by the Skyrme--Hartree--Fock (SHF) model, and by the macroscopic-microscopic model. Theoretical half-lives also reasonably agree with the data. Calculations further show that prolate deformation is important for the ground states of the nuclei in the α-decay chain of 278113. The common points and differences among different models are compared and discussed.
Entrance Channel Dependence of Production Cross Sections of Superheavy Nuclei in Cold Fusion Reactions
FENG Zhao-Qing, , JIN Gen-Ming, FU Fen, ZHANG Feng-Shou, , JIA Fei, HUANG Xi, , HU Rong-Jiang, LI Wen-Fei, LI Jun-Qing,
Chin. Phys. Lett. 2005, 22 (4): 846-849 .  
Abstract   PDF(pc) (267KB) ( 405 )
Production cross sections of superheavy nuclei Rf and Hs for asymmetric and nearly symmetric projectile-target combinations are systematically studied within the framework of the dinuclear system model. The calculated results show that the production cross sections are strongly dependent on the symmetry of reaction systems. The obtained results are in good agreement with the available experimental data for asymmetric reaction systems. For nearly symmetric systems, the model gives opposite results with coupled channel model in which surface vibration and nucleon transfer are included.
Optical and Acoustical Frequencies in a Nonlinear Helicoidal Model of DNA Molecules
Chin. Phys. Lett. 2005, 22 (4): 850-852 .  
Abstract   PDF(pc) (201KB) ( 405 )
We compare optical and acoustical frequencies in the Peyrard--Bishop--Dauxois model, i.e. an extended Peyrard--Bishop model, of DNA molecules. We discuss how ratio of those frequencies depends on a value of the harmonic constant of the helicoidal spring K. Also, we suggest that the most favourable mode could be a resonance mode.
A Scaling Law of Photoelectron Angular Distributions in One-Cycle Laser Pulses
BAI Li-Hua, ZHANG Jing-Tao, XU Zhi-Zhan
Chin. Phys. Lett. 2005, 22 (4): 853-856 .  
Abstract   PDF(pc) (280KB) ( 376 )
The photoelectron angular distributions (PADs) from above-threshold ionization of atoms irradiated by one-cycle laser pulses satisfy a scaling law. The scaling law denotes that the main features of the PADs are determined by four dimensionless parameters: (1) the ponderomotive number up =Up /ħω, the ponderomotive energy Up in units of laser photon energy; (2) the binding number εb =Eb /ħω, the atomic binding energy Eb in units of laser photon energy; (3) the number of absorbed photons q; (4) the carrier-envelope phase Ф0, the phase of the carrier wave with respect to the envelope. We verify the scaling law by theoretical analysis and numerical calculation, compared to that in long-pulse case. A possible experimental test to verify the scaling law is suggested.
High-Resolution Spectra of the 10B18O and 11B18O: Rotational Analysis of the B--X Bands
V. Bojovic, A. Antic-Jovanovic, M. Kuzmanovic
Chin. Phys. Lett. 2005, 22 (4): 857-860 .  
Abstract   PDF(pc) (287KB) ( 435 )
Emission spectra of 10B18O and 11B18O isotopomers in the 230--330nm region have been investigated by means of conventional high-resolution spectroscopy. The molecules were produced in a low-pressure arc by discharging 8 Torr of mixture containing argon and oxygen 18 in the ratio of 4:1 and the spectra have been recorded using Ebert-type spectrograph. The boron needed to produce BO has been present in the system as amorphous powder with natural abundance of 10B and 11B. Rotational analysis of the 0, 0 and 0, 1 bands has been performed and spectroscopic constants have been extracted. The results have allowed first determination of the equilibrium rotational constants Be and De for both isotope species 10B18O and 11B18O in their lower electronic state. Assuming a linear dependence of Be on (v +1/2), the value of equilibrium distance re in the lower state has been derived.
Calculation of Total Cross Sections for Positron Scattering by Lithium at Intermediate Energies
WU Yong, ZHOU Ya-Jun
Chin. Phys. Lett. 2005, 22 (4): 861-864 .  
Abstract   PDF(pc) (229KB) ( 554 )
The total cross sections for positron scattering by lithium at intermediate energies (10--200eV) are calculated by using the coupled-channel optical method with a complex equivalent-local polarization potential which incorporates ionization continuum and positronium (Ps) formation channels contributions into the coupled channels framework. The effects of the two-body Ps rearrangement and three-body ionization process on the total cross section are found to be significant at lower energies and this effect is not negligible up to 30eV. Compared to the available theoretical data, the predicted total cross sections agree quite well with the calculations of McAlinden et al. [ J. Phys. B: At. Mol. Opt. Phys. 30 (1997) 1543] and Campbell et al. [ Nucl. Instrum. Methods Phys. B 143(1998) 41]
Improved Zone Plate Coded Imaging Technique by Using Four Special Designed Gabor Zone Plates
CAO Lei-Feng, SHEN Yu-Ji, ZHENG Zhi-Jian, DING Yong-Kun
Chin. Phys. Lett. 2005, 22 (4): 865-868 .  
Abstract   PDF(pc) (1424KB) ( 491 )
Direct-current component, high-order artifacts, and side lobe distortion provide serious drawbacks in the application of Fresnel zone plate coded imaging (ZPCI). The presentation provided here proposes a novel way to resolve all the above-mentioned problems. Four different Gabor zone plates are suggested to substitute the one Fresnel zone plate used in the conventional ZPCI. Perfect reconstruction will be obtained when integrally analysing the four coded images. Primary numerical simulation provided here shows good result.

Destructive Interference in a v-Type Coherently Driven Mazer
Chin. Phys. Lett. 2005, 22 (4): 869-872 .  
Abstract   PDF(pc) (232KB) ( 409 )
We derive an expression of the interaction between a quantum cavity field and an ultracold Λ-type three-level atom in which two upper levels are coupled by a coherent driving field. The effects of the driving-induced atomic coherence on the atomic emission probability are investigated. It is found that, due to the driving-induced atomic coherence, there are two transition channels for the atom interacting with the cavity field. Between the two transition channels, there is a quantum interference, which is a destructive interference. This destructive quantum interference suppresses the emission of the atom. The atomic emission probability decreases with the increasing driving field.
Optimization of High-Order Harmonic by Genetic Algorithm for the Chirp and Phase of Few-Cycle Pulses
XIAO Jun, SUN Zhen-Rong, WANG Yu-Feng, DENG Li, ZHANG Xiang-Yun, CHEN Guo-Liang, ZHANG Wei-Ping, WANG Zu-Geng, XU Zhi-Zhan, LI Ru-Xin
Chin. Phys. Lett. 2005, 22 (4): 873-876 .  
Abstract   PDF(pc) (283KB) ( 357 )
The brightness of a particular harmonic order is optimized for the chirp and initial phase of the laser pulse by genetic algorithm. The influences of the chirp and initial phase of the excitation pulse on
the harmonic spectra are discussed in terms of the semi-classical model including the propagation effects. The results indicate that the harmonic intensity and cutoff have strong dependence on the chirp of the laser pulse, but slightly on its initial phase. The high-order harmonics can be enhanced by the optimal laser pulse and its cutoff can be tuned by optimization of the chirp and initial phase of the laser pulse.
Diode-Pumped Self-Q-Switched Cr,Nd:YAG Laser with High Average Output Power
WANG Su-Mei, FENG Bao-Hua, ZHANG Qiu-Lin, ZHANG Ling, ZHANG Dong-Xiang, ZHANG Zhi-Guo, ZHANG Shi-Wen
Chin. Phys. Lett. 2005, 22 (4): 877-879 .  
Abstract   PDF(pc) (229KB) ( 659 )
A diode end-pumped self-Q-switched Cr,Nd:YAG laser was established with pulse duration in the range of 8--10 ns. The maximum average output power was 4.4W and the slope efficiency was 27% using an output coupler of R=70%. At pumping power of 17.4W the laser produces high-quality pulses at 1064nm in a TEM00-mode.
Photonic Superfluidity in a Kerr Nonlinear Black Body
Chin. Phys. Lett. 2005, 22 (4): 880-883 .  
Abstract   PDF(pc) (236KB) ( 513 )
We study a photon blackbody field in Kerr nonlinear crystals in a superfluid state in which bare photons with opposite wave vectors and helicities are bound into pairs and unpaired photons are transformed into a new kind of quasiparticle, the nonpolariton. The photon-pair system is a superfluid and the nonpolariton system is a normal fluid. At zero temperature the superfluid possesses a large persistent energy density. It has been found that the spectral energy density and the radiation pressure of a Kerr nonlinear black body are larger than those of a normal black body.
Omnidirectional Gaps of One-Dimensional Photonic Crystals Containing Single-Negative Materials
JIANG Hai-Tao, CHEN Hong, LI Hong-Qiang, ZHANG Ye-Wen
Chin. Phys. Lett. 2005, 22 (4): 884-886 .  
Abstract   PDF(pc) (396KB) ( 613 )
We show that a one-dimensional photonic crystal containing two kinds of single-negative materials can possess an omnidirectional gap whose edges are insensitive to incident angle and polarization, owing to the unusual field configuration in the structure. In contrast to an omnidirectional gap based on a photonic gap that corresponds to zero averaged refractive index, it can be made very wide by varying the ratio of the thicknesses of two media. Moreover, it is independent of polarization under special parameters. These properties may provide a mechanism to design a broadband omnidirectional reflector with fixed bandwidth.

A Selective C and L-Band Amplified Spontaneous Emission Source Using a 1×2 Optical Switch
HUANG Wen-Cai, MING Hai, CAI Zhi-Ping, XU Hui-Ying, YE Chen-Chun
Chin. Phys. Lett. 2005, 22 (4): 887-888 .  
Abstract   PDF(pc) (168KB) ( 723 )
We report on a band selective amplified spontaneous emission (ASE) source of an erbium-doped fibre (EDF), which can operate in either the C- or L-band region. The band selective ASE source is realized using a pump conversion technique by a 1×2 optical switch, which makes the ASE source design convert between a backward and a forward pumped configuration alternately. A heavily doped erbium fibre and a 1480nm laser diode are adopted for this design synchronously to enhance the power of L-band ASE. A power of 16.2mW for C-band ASE and 11.8mW for L-band ASE are obtained with a total pump power of 100mW.
Elastic Wave Propagation in Two-Dimensional Ordered and Weakly Disordered Phononic Crystals
YUAN Zuo-Dong, CHENG Jian-Chun
Chin. Phys. Lett. 2005, 22 (4): 889-891 .  
Abstract   PDF(pc) (211KB) ( 573 )
Elastic wave propagation in two-dimensional solid-solid ordered and weakly disordered phononic crystals is studied by using finite-difference time-domain method. Theoretical results show that obvious band gaps in the ordered crystal could be found, while in the weakly disordered ones the band gaps could partially vanish. Furthermore, with increase of disorder, band gaps are destructed badly and prominently in the high frequency regime while slightly in the low regime. Comparing the energy transmission dependent on time, we find that the coda wave phenomenon is prominent in the ordered crystal while weakened in the weakly disordered ones, and the physical properties are discussed.
Frequency Dependences of Sound Attenuation and Phase Velocity in Suspensions Containing Encapsulated Microbubbles
YU Jin-Fei, ZHANG Dong, GONG Xiu-Fen, GONG Yan-Jun, ZHU Zhe-Min, LIU Xue-Ming
Chin. Phys. Lett. 2005, 22 (4): 892-895 .  
Abstract   PDF(pc) (257KB) ( 739 )
Frequency dependences of the sound attenuation and phase velocity in an encapsulated bubbly liquid, such as ultrasound contrast agent or LevovistR suspensions, at three different concentrations are studied over a bandwidth 1.5--4.5MHz by using an ultrasonic spectroscopy technique. Measurement of acoustic attenuation spectra demonstrates that the resonant frequency of the LevovistR suspension is nearly 2.3--2.5MHz, and the sound attenuation enhances with the increasing concentration. With the measured sound attenuation spectra, the shear modulus and the shear viscosity are estimated to be 80Mpa and 1.3Pas, respectively. The phase velocity exhibits a rapid rise with frequency smaller than 3.0MHz, then appears to approach a frequency-independent limit above 3.0MHz, and the change of the phase velocity over the measured frequency range is also proportional to the concentration.
Lattice Boltzmann Simulation of Sedimentation of a Single Charged Elastic Dumbbell in a Newtonian Fluid
ZHANG Chao-Ying, TAN Hui-Li, LIU Mu-Ren, KONG Ling-Jiang, SHI Juan
Chin. Phys. Lett. 2005, 22 (4): 896-899 .  
Abstract   PDF(pc) (257KB) ( 412 )
Based on the lattice Boltzmann method, the sedimentations of elastic dumbbells with different charges in a Newtonian fluid under the same and different initial conditions are simulated. Due to the polarizing effects, there are Coulomb forces exerted on the charged elastic dumbbells during their sedimentations, which change their original motions significantly. All of the numerical results show that, if the charged elastic dumbbells are released at offset-centreline positions with zero velocity and settle under gravity, they fall down vertically off the centreline and their orientations tend to be the horizontal finally, and the distances apart from the centreline increase with the increasing charges of the elastic dumbbells.
Lower Hybrid Wave Current Drive Efficiency on the HT-7 Tokamak
CHEN Zhong-Yong, WAN Bao-Nian, SHI Yue-Jiang, HU Li-Qun, XU Han-Dong, LI Guo-Chao
Chin. Phys. Lett. 2005, 22 (4): 900-903 .  
Abstract   PDF(pc) (257KB) ( 423 )
Lower hybrid (LH) wave current drive efficiency on our HT-7 tokamak has been investigated based on the hot electrical conductivity theory. The interaction of the residual toroidal electric field with fast electrons has been included in the determination of current drive efficiency. The LH wave power scan was performed in the plasma parameter ranges of Ip=50-156kA, ňe=0.5×101.6-1.6× 1019m-3, PLH=50-350kW. The current drive efficiency is derived to be about 0.1× 1019-0.4×1019Am-2W-1 on the HT-7 tokamak, which depends on the electron density and the LH wave phase velocity. At the electron density of about 1.5×1019m-3, with the LH wave parallel refraction index peaked at 1.8, the highest current drive efficiency was obtained. A more generally normalized method is introduced to analyse the experimental data, which combines all the data in one curve. The normalized parameters are independent of the plasma parameters.
A Movable Mass Spectroscopy Sampling Apparatus for Measuring Spatial Distribution of Neutral Radicals in Silane Plasma
WANG Zhao-Kui, LIN Kui-Xun, LIN Xuan-Ying, QIU Gui-Ming, ZHU Zu-Song
Chin. Phys. Lett. 2005, 22 (4): 904-906 .  
Abstract   PDF(pc) (270KB) ( 498 )
A movable mass spectroscopy gas sampling apparatus has been established and a straight-line fit of silane depletion fraction f is proposed. The spatial density distributions of SiHn (n=0-3) radicals in
silane radio frequency glow discharge have been measured by a mass spectrometer. The experimental results demonstrate that the densities of the neutral radicals have the peak value near the middle position of electrodes, and the densities of SiH2 and SiH3 are higher than those of Si and SiH in silane plasma. This reveals that SiH2 and SiH3 may be the primary precursors in forming the a-Si:H film.
Thermal Decomposition Behaviour of Zn3N2 Powder
ZONG Fu-Jian, MA Hong-Lei, LIANG Wei, DU Wei, ZHANG Xi-Jian, XIAO Hong-Di, MA Jin, JI Feng, XUE Cheng-Shan, ZHUANG Hui-Zhao
Chin. Phys. Lett. 2005, 22 (4): 907-910 .  
Abstract   PDF(pc) (259KB) ( 1028 )
Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) are employed to investigate the thermal decomposition behaviour of zinc nitride powder, which indicated that the thermal oxidation of zinc nitride powder in air follows the two-step reaction model. When the temperature is between 200 and 500°C, compact ZnO or ZnxOyNz layers in the surface of zinc nitride powder will begin to form, and prevent the interior of zinc nitride powder from the thermal oxidation. When the temperature is higher than 500°C, fast thermal oxidation occurs in the interior of zinc nitride powder. Over 750°C, all the zinc nitride will turn into zinc oxide. The x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) of the zinc nitride powder annealed at different temperature in air are consistent with the two-step reaction model.
Low-Field Emission from Iron Oxide-Filled Carbon Nanotube Arrays
CHAI Yang, YU Li-Gang, WANG Ming-Sheng, ZHANG Qi-Feng, WU Jin-Lei
Chin. Phys. Lett. 2005, 22 (4): 911-914 .  
Abstract   PDF(pc) (602KB) ( 513 )
Arrays of multi-walled carbon nanotubes (MWCNTs) filled with iron oxide have been fabricated by a one-step route based on the pyrolysis of ferrocene under a well-chosen synthesis condition. The MWCNT arrays were observed with a scanning electron microscope, with which an energy dispersive x-ray spectrum (EDXS) was also acquired, and they are analysed by x-ray diffraction. Furthermore, individual MWCNTs were studied by using selected area electron diffraction (SAED) and the EDXS in a transmission electron microscopy observation. All the observation and analysis confirmed that the MWCNTs were filled with iron oxide. Field emission from these arrays of iron oxide-filled MWCNTs was measured and the turn-on field was determined to range from 0.83--1.01V/μm, appearing to be much lower than those of arrays of pure MWCNTs and arrays of nitrogen-doped MWCNTs fabricated in similar ways. The possible reasons of the observed low-field emission are discussed.
Thermal Conductivity Anomalies Related to the Double-Bump of Resistivity in Nd0.7Sr0.3Mn1-xCrxO3
GAO Hui-Ping, WU Bai-Mei, LI Bo, WANG Ming, DU Kan
Chin. Phys. Lett. 2005, 22 (4): 915-918 .  
Abstract   PDF(pc) (231KB) ( 351 )
The temperature dependence of the thermal conductivity k(T) and electrical resistivity ρ(T) has been measured for perovskite Nd0.7Sr0.3Mn1-xCrxO3 (0.01≤x ≤0.15) in the temperature range of 10--300K. The double-bump feature in ρ(T) is observed for x=0.08 and 0.10 samples. Below the insulating-metallic transition temperature TIM, k(T) shows a sharp increase and such an increase is depressed gradually by the increasing Cr content. While k(T) displays an anomalous decrease around the temperature where the second bump of ρ(T) emerges. We suggest that the enhancement of k(T) below TIM is related to both phonons and magnons, the ferromagnetic interaction of Mn3+-O-Cr3+ should be super-exchange interaction rather than double-exchange interaction, and the Cr doping just weakens the DE interaction in this system.
Ion-Sputter-Induced Nanodots on Si(110): Ion Energy Dependence
LI Wei-Qing, LING Li, QI Le-Jun, YANG Xin-Ju, FAN Wen-Bin, GU Chang-Xin, LU Ming
Chin. Phys. Lett. 2005, 22 (4): 919-922 .  
Abstract   PDF(pc) (573KB) ( 409 )
Nanodot arrays were formed on Si(110) surface under normal-incident Ar+ ion sputtering at substrate temperature of 800°C. The ion flux was 20μA/cm2, and the ion energies were 1-5keV. The surface was imaged by an atomic force microscope (AFM). It was found that with the increasing ion energy, the average ellipticity of the dots changes in an oscillating manner; meanwhile the average dot size increases monotonously. Based on a dynamic continuum model, and taking into consideration the asymmetry of the Ehrlich-Schwoebel diffusions along the <100> and <110> crystallographic directions, we carry out the simulations, which reproduce the experimental results qualitatively.

Effects of Temperature and Pressure on a Novel 1,3,4-Oxadiazole Derivative
LUO Ji-Feng, HAN Yong-Hao, TANG Ben-Chen, GAO Chun-Xiao, LI Min, ZOU Guang-Tianv
Chin. Phys. Lett. 2005, 22 (4): 923-926 .  
Abstract   PDF(pc) (347KB) ( 393 )
The electrical resistivity variation of 1,4-bis[(4-methylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-1) microcrystal is studied under variable pressure and temperature conditions by a quasi four-probe method in a diamond anvil cell. The sample resistivity is calculated with a finite element analysis method. The temperature and pressure dependencies of resistivity of OXD-1 microcrystal are measured up to 150°C and 15GPa. The resistivity decrease with temperature increasing indicates that OXD-1 exhibits an organic-semiconductor transport property in the experimental pressure region. With pressure increasing, the resistivity of OXD-1 increases firstly and reaches the maximum at about 6.2GPa, and then begins to decrease as the pressure increases continuously. In situ x-ray diffraction data under pressure provide obvious prove that the anomaly of resistivity variation at 6.2GPa is caused by the pressure-induced amorphism of OXD-1.
In-Situ Resistivity Measurement of ZnS in Diamond Anvil Cell under High Pressure
HAN Yong-Hao, LUO Ji-Feng, HAO Ai-Min, GAO Chun-Xiao, XIE Hong-Sen, QU Sheng-Chun, LIU Hong-Wu, ZOU Guang-Tian
Chin. Phys. Lett. 2005, 22 (4): 927-930 .  
Abstract   PDF(pc) (383KB) ( 1160 )
An effective method is developed to fabricate metallic microcircuits in diamond anvil cell (DAC) for resistivity measurement under high pressure. The resistivity of nanocrystal ZnS is measured under high pressure up to 36.4GPa by using designed DAC. The reversibility and hysteresis of the phase transition are observed. The experimental data is confirmed by an electric current field analysis accurately. The method used here can also be used under both ultrahigh pressure and high temperature conditions.
Chiral Parameter of Transparent Films Containing Polymer Cholesteric Liquid Crystal-R
TAO Wei-Dong, PAN Xue-Feng, CHEN Jian, YAN Fei-Biao, BAI Gui-Ru, LU Zu-Kang
Chin. Phys. Lett. 2005, 22 (4): 931-933 .  
Abstract   PDF(pc) (213KB) ( 459 )
The transparent film containing a kind of polymer cholesteric liquid crystal-R was fabricated by the freezing method. The optical polarization response of the film was investigated by a self-manufactured apparatus and its optical rotatory dispersion was measured by a novel technique at the wavelength from 350nm to 660nm. At various wavelengths, the chiral parameter of the film has been obtained. The results show that the chiral parameter decreases as the wavelength increases. The maximum and minimum chiral parameters are 0.0343 at the wavelength of 350nm and 0.0058 at the wavelength of 660nm, respectively. The obtained data indicate that this kind of polymer cholesteric liquid crystal-R is a promising candidate host material for solid optical chiral waveguides.
Electrical Properties of Ag-Doped Ge2Sb2Te5 Films Used for Phase Change Random Access Memory
XIA Ji-Lin, LIU Bo, SONG Zhi-Tang, FENG Song-Lin, CHEN Bomy
Chin. Phys. Lett. 2005, 22 (4): 934-937 .  
Abstract   PDF(pc) (250KB) ( 590 )
Ag-doped Ge2Sb2Te5 films were deposited by rf magnetron sputtering on SiO2/Si substrates. The content of Ag ranging from 4.5 to 11.3 at.% is determined by inductively coupled plasma atomic emission spectrometry. The crystallization temperature of Ag-doped Ge2Sb2Te5 increases with the increasing Ag content and the stability of phase change film is improved greatly. Structures were measured by x-ray diffraction and the face-centered-cubic structure was more stable after Ag doping. Four-point probe was used to measure the sheet resistance of Ag-doped Ge2Sb2Te5 films annealed at different temperatures and it is indicated that Ag atoms increase the sheet resistance of Ge2Sb2Te5 thin film when the annealing temperature is higher than about 360°C, which is beneficial for reducing the reset current. Current-voltage curves were tested and it is demonstrated that 4.5 at.% Ag doping into the Ge2Sb2Te5 film can reduce the threshold current from 1.46mA to 0.25mA and can only increase the threshold voltage slightly, which is very useful for low energy consumption.
Doping-Induced Phase Transitions in Polycrystalline La0.49Sr0.51(Mn1-xNbx)O3
LIU Wen-Jun, SHU Qi-Qing, MA Xiao-Cui, S. M. Bhagat, S. E. Lofland, I. O. Troyanchuk
Chin. Phys. Lett. 2005, 22 (4): 938-941 .  
Abstract   PDF(pc) (260KB) ( 448 )
Observations of temperature dependences of ac susceptibility Xac, resistivity (ρ) and dc magnetization M for polycrystalline La0.49Sr0.51(Mn1-xNbx)O3 (x = 0, 0.05, 0.15, and 0.25) show that due to substitution of Mn4+ by diamagnetic Nb5+, there appear to be (i) the decrease of Xac as T> TN, (ii) the occurrence of a maximum (insulator-metal-like transition) for ρ near TC, (iii) the decline of M as x>0.05, and (iv) the lowering of TC. The results might be ascribed to: (i) the rearrangement of Mn3+ and Mn4+ ions, (ii) the decrease of the number of Mn3+ and Mn4+ pairs involved in double exchange interaction, (iii) the delocalization of the electrons and holes, (iv) the reduction of the randomness of the delocalized carrier scattering by thermal spin fluctuation due to magnetic ordering, and (v) the compensation effect of Nb5+ ions for Sr2+ ions.
Magnetic and Crystalline Microstructures of the Sr--La--Co M-type Ferrites by Magnetic Force Microscopy
FANG Yi-Kun, DING Bo-Ming, PANG Zhi-Yong, WANG Bao-Yan, BAO Da-Xin, HAN Sheng-Hao, HAN Bao-Shan
Chin. Phys. Lett. 2005, 22 (4): 942-945 .  
Abstract   PDF(pc) (722KB) ( 449 )
With proper erosion of sample surface and making a grid of crystal boundaries, the magnetic and crystalline microstructures of Sr--La--Co M-type ferrites of nominal composition of La0.2Sr08Fe11.8Co0.2O19 (at.%) have been investigated by using magnetic force microscopy. By calculating average diameter and thickness, and average alignment degree of the grains of the ferrites, recognizing their domain patterns and calculating the proportion of grains with single domain or multi-domains, the Sr--La--Co M-type ferrites with high magnetic performance have been characterized at microcrystalline and micromagnetic level. In addition, we has interpreted why the grains always present plate-like domains.
Preisach Modelling on the Magnetic Properties of Nano-Particle Fe3O4
HOU Deng-Lu, ZHAO Jing, XU Jing, DU Zi-Xia, TANG Gui-De
Chin. Phys. Lett. 2005, 22 (4): 946-949 .  
Abstract   PDF(pc) (695KB) ( 599 )
A sample of nano-particle Fe3O4 was synthesized using coprecipitation, and characterized by zero field cooling (ZFC) and field cooling (FC) magnetic moments and the major hysteresis loops. The data are analysed within the framework of a generalized Preisach model, which provides an excellent description of the experimental data. The simulated results are in good agreement with the experimental data. Using the model, we obtain that the blocking temperature of Fe3O4 nano-particles with diameter of 8.4nm is 105K, and the interaction field distribution between the particles is 550Oe.
Multi-Imaging by Photonic Crystal Slab Using Negative Refraction
FANG Yun-Tuan, SHEN Ting-Gen
Chin. Phys. Lett. 2005, 22 (4): 949-951 .  
Abstract   PDF(pc) (408KB) ( 539 )
Point imaging by a photonic crystal slab due to the negative refraction is studied by the finite-difference time-domain scheme. With proper surface termination of a photonic crystal (PC) slab, multi-reflection and refraction will occur in the imaging system, which results in multi-images. The result further verifies that the PC can act as a negative refraction material.
Frequency Upconversion Fluorescence Emission of Er3+-Doped Oxychloride Germanate Glass
SUN Hong-Tao, ZHANG Li-Yan, ZHANG Jun-Jie, DAI Shi-Xun, YU Chun-Lei, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2005, 22 (4): 952-955 .  
Abstract   PDF(pc) (245KB) ( 678 )
Frequency upconversion fluorescence property of Er3+-doped oxychloride germanate glass is investigated. Intense green and red emissions centred at 525, 546, and 657nm, corresponding to the transitions 2H11/24I15/2, 4S3/24I15/2, and 4F9/24I15/2, respectively, were simultaneously observed at room temperature. The quadratic dependence of the 525, 546, and 657nm emissions on excitation power indicates that a two-photon absorption process occurs under 975nm laser diode (LD) excitation. The Raman spectrum investigation indicates that oxychloride germanate glass has the maximum phonon energy at ~805cm°C. The thermal stability of this oxychloride germanate glass is evaluated by differential scanning calorimetry, and thermal stability factor ΔT(ΔT = Tx-Tg) is 187°C. Intense upconversion luminescence and good thermal stability indicate that Er3+-doped oxychloride germanate glass is a promising upconversion laser material.

A Novel Coupled Quantum Well Structure with Low-Driving Voltage, Low Absorption Loss and Large Field-Induced Refractive Index Change
XU Zhi-Xin, JIANG Xiao-Qing, XU Yi-Gang, YANG Ai-Ling, WANG Ming-Hua, ZHOU Qiang, LI Xi-Hua, YANG Jian-Yi
Chin. Phys. Lett. 2005, 22 (4): 956-959 .  
Abstract   PDF(pc) (232KB) ( 710 )
Based on a two-energy-level system, we analyse the changing ground eigenenergies of symmetric GaAs/AlxGa1-x As coupled quantum wells in the presence of an applied electric field. From the theoretical analysis for symmetric coupled quantum well, we find the advantages and disadvantages when it is applied to travelling wave modulator. Hence the conception of quasi-symmetric coupled quantum wells is put forward. Based on the demands of travelling wave modulator for quantum well materials, the configuration of quasi-symmetric coupled quantum well is further optimized. Consequently, in the case of low applied electric field (F=20kV/cm) and low absorption loss (α≤100cm-1), a large field-induced refractive change Δn (for TE mode, Δn=0.021; for TM mode, Δn=0.0121) is attained in the optimized coupled quantum well.
Incorporation Behaviour of Arsenic and Phosphorus in GaAsP/GaAs Grown by Solid Source Molecular Beam Epitaxy with a GaP Decomposition Source
WU Shu-Dong, GUO Li-Wei, WANG Wen-Xin, LI Zhi-Hua, NIU Ping-Juan, HUANG Qi, ZHOU Jun-Ming
Chin. Phys. Lett. 2005, 22 (4): 960-962 .  
Abstract   PDF(pc) (199KB) ( 553 )
The incorporation behaviour of arsenic and phosphorus in the GaAsP ternary alloy under phosphorus-rich conditions is studied based on the incorporation coefficient model and the growth diffusion model combined with the alloy composition data obtained by high resolution x-ray diffraction analysis. It is found that As adatoms have longer surface lifetime and longer migration length than those of P adatoms, which leads to an arsenic incorporation efficiency much higher than that of phosphorous. With the increase of arsenic flux, the surface lifetime of arsenic adatoms decreases due to the competition of As adatoms. The detailed analysis and discussion are given here.

Excited-State Upconversion of Pr(0.5)Yb(1.5):ZBLAN under Two-Colour Excitation
CHEN Xiao-Bo, SONG Zeng-Fu
Chin. Phys. Lett. 2005, 22 (4): 963-966 .  
Abstract   PDF(pc) (247KB) ( 533 )
We report the excited-state upconversion in Pr(0.5)Yb(1.5):ZBLAN under two-colour excitation of 960nm laser and xenon lamp light. Three obvious upconversion excitation peaks around 856.0, 804.2 and 787.1nm were observed and the involved mechanism has been explained. The measured upconversion excitation peak 856.0nm corresponds to the sum of theoretical values 852nm and 866nm owing to the 1G4(Pr3+)→ 1I6(Pr3+) and 1G4(Pr3+)→ 3 P1(Pr3+) excited state absorption transitions. The measured 804.2 and 787.1nm upconversion excitation peaks originate from the excited state absorption transitions 3+H6(Pr3+)→ 1D2(Pr3+) and 1G4(Pr3+)→ 3+P2(Pr3+), respectively. The excited state absorption upconversion 1G4(Pr3+)→ 1I6(Pr3+) is strong because of its large oscillator strength f=23.040×10-6.
Rapid Thermal Annealing Effects on Structural and Optical Properties of Self-Assembled InAs/GaAs Quantum Dots Capped by InAlAs/InGaAs Layers
LÜ, Wei, LI Da-Bing, ZHANG Zi-Yang, LI Chao-Rong, ZHANG Ze, XU Bo, WANG Zhan-Gum
Chin. Phys. Lett. 2005, 22 (4): 967-970 .  
Abstract   PDF(pc) (745KB) ( 780 )
Effects of rapid thermal annealing on the optical and structural properties of self-assembled InAs/GaAs quantum dots capped by the InAlAs/InGaAs combination layers are studied by photoluminescence and transmission electron microscopy. The photoluminescence measurement shows that the photoluminescence peak of the sample after 850°C rapid thermal annealing is blue shifted with 370meV and the excitation peak intensity increases by a factor of about 2.7 after the rapid thermal annealing, which indicates that the InAs quantum dots have experienced an abnormal transformation during the annealing. The transmission electron microscopy shows that the quantum dots disappear and a new InAlGaAs single quantum well structure forms after the rapid thermal annealing treatment. The transformation mechanism is discussed. These abnormal optical properties are attributed to the structural transformation of these quantum dots into a single quantum well.
Effect of Misfit Dislocation Originated from Strained Layer on Photoluminescence Properties of InxGa1-xN/GaN Multiple Quantum Wells
LÜ, Wei, LI Da-Bing, LI Chao-Rong, CHEN Gang, ZHANG Ze
Chin. Phys. Lett. 2005, 22 (4): 971-974 .  
Abstract   PDF(pc) (318KB) ( 435 )
InxGaxN/GaN multiple quantum well (MQW) samples with strain-layer thickness larger/less than the critical one are investigated by temperature-dependent photoluminescence and transmission electron microscopy, and double crystal x-ray diffraction. For the sample with the strained-layer thickness greater than the critical thickness, we observe a high density of threading dislocations generated at the MQW layers and extended to the cap layer. These dislocations result from relaxation of the strain layer when its thickness is beyond the critical thickness. For the sample with the strained-layer thickness greater than the critical thickness, temperature-dependent photoluminescence measurements give evidence that dislocations generated from the MQW layers due to strain relaxation are main reason of the poor photoluminescence property, and the dominating status change of the main peak with increasing temperature is attributed to the change of the radiative recombination from the areas including dislocations to the ones excluding dislocations.
A Facile Synthesis of Silver-Coated Composite Particles by Swelling Surface Method
LIU Jun-Bing, LI Neng, WANG Si-Zhen, ZHANG Jian-Hui, WANG Zhen-Lin
Chin. Phys. Lett. 2005, 22 (4): 975-977 .  
Abstract   PDF(pc) (447KB) ( 1290 )
We report a facile and rapid method for fabrication of composite particles consisting of a polystyrene (PS) core and a uniform silver shell. The process involves the PS colloid surface swelling, the anchoring of silver ions and nanoparticles onto the surfaces, and the subsequent growth of metal seeds in a short period. The present approach has the advantages of simplicity and high efficiency. The TEM images show the morphology of the obtained PS core-silver shell particles, and their chemical composition and crystallinity are analysed by x-ray diffraction. To our knowledge, this is the first study based on swelling PS surface for synthesis of silver-coated PS particles and may be implemented for preparing other metal-coated PS particles.
Optical Waveguide in Gd0.275Y0.725Ca4O(BO3)3 Crystals Formed by MeV He Ion Implantation
QIN Xi-Feng, WANG Xue-Lin, LI Shi-Ling, HU Hui, CHEN Feng, WANG Ke-Ming, SHEN Ding-Yu, LIU Yao-Gang
Chin. Phys. Lett. 2005, 22 (4): 978-980 .  
Abstract   PDF(pc) (225KB) ( 592 )
A GdxY1-xCa4O(BO3)3 (GdxY1-xCOB) crystal, which belongs to rare-earth calcium oxyborate family, is used for non-critical phase-matching of visible and ultraviolet (UV) light. We employ 2.8-MeV He+ ions to form optical waveguides in the Gd0.275Y0.725COB crystal at room temperature. The doses are varied from 1.5 × 1016ions/cm2 to 5 × 1016ions/cm2. A model 2010 prism coupler is used to measure the modes in Gd0.275Y0.725COB waveguides formed by MeV He+ ion implantation. The refractive index profile is fitted based on the reflectivity calculation method. The shape of refractive index profile is compared with one of nuclear energy loss obtained by TRIM’98 simulation.

Field Emission Characteristics of BN Films Treated with H2 and O2 Plasma
GU Guang-Rui, WU Bao-Jia, JIN Feng-Xi, LI Quan-Jun, LI Zhe-Kui, ZHENG Wei-Tao, ZHAO Yong-Nian, JIN Zeng-Sun
Chin. Phys. Lett. 2005, 22 (4): 981-983 .  
Abstract   PDF(pc) (396KB) ( 509 )
BN films were synthesized on the (100)-oriented surface of n-Si (0.008--0.02Ωm) by rf magnetron sputtering physical vapor deposition (PVD). A BN film was first treated with H2 plasma for 60min and then the H2 treated sample was treated with O2 plasma for 15min. The films were characterizes by using Fourier transform infrared spectra (FTIR) and atomic force microscopy (AFM). The field emission characteristics of BN films were measured in an ultrahigh vacuum system. A turn-on electric field of 8V/μm and a current of 400μA/cm2 were obtained for the BN film treated with H2 plasma. The results show that the surface plasma treatment makes no apparent influence on the surface morphology of the BN films. The transformations of the sample emission characteristics have to do with the surface negative electron affinity (NEA) of the films possibly. The turn-on electric field of the BN film treated with H2 plasma is lower than that without treatment, which possibly attributes to the surface NEA effect. The surface NEA of the H2 treated BN film is lost after O2 plasma treatment.
Residual Stress on Surface and Cross-section of Porous Silicon Studied by Micro-Raman Spectroscopy
LEI Zhen-Kun, KANG Yi-Lan, CEN Hao, HU Ming, QIU Yu
Chin. Phys. Lett. 2005, 22 (4): 984-986 .  
Abstract   PDF(pc) (189KB) ( 503 )
Surface and cross-sectional residual stresses of electrochemical etching porous silicon are investigated quantitatively by micro-Raman spectroscopy. The results reveal that a larger tensile residual stress exists on the surface and increase linearly with the porosity. On the other hand, across the depth direction perpendicular to the surface, the tensile residual stress decreases gradually from the surface to regions near the interface between the porous silicon layer and the Si substrate. However, a compressive stress appears at the interface near to the Si substrate for balancing with the tensile stress in the porous silicon layer. The cross-sectional residual stress profile is due to the porosity and lattice mismatch gradients existing in the cross-section and influencing each other. Furthermore, the presented residual stresses of the porous silicon have a close relation with its microstructure.
Bulk-Quantity Synthesis and Conductive Properties of Comb-Like Dendritic ZnO Nanostructures
LIAO Zhi-Min, ZHANG Hong-Zhou, XU Jun, YU Da-Peng
Chin. Phys. Lett. 2005, 22 (4): 987-990 .  
Abstract   PDF(pc) (714KB) ( 521 )
Adopting a simple low-temperature (~500°C) vapour process, we have synthesized bulk quantity comb-like dendritic ZnO nanostructures in large area. An atomic force microscope equipped with Au-coated probes was employed to elucidate the current-voltage characteristic of the individual ZnO nanocomb. The connection electrodes were defined by depositing Pt wires using focused ion beam (FIB). A rectification effect was observed, while it was slightly suppressed compared with that of the previous reports. The good conductive properties of the sample can be attributed to the Ga+ ions implantation through the FIB process of electrode definition. We suggest that the material and the FIB method can be developed to fabricate novel nanosized devices.
Magnetic Properties of Diluted Magnetic Semiconductor Zn1-xMnxO Nanowires
CHANG Yong-Qin, XU Xiang-Yu, LUO Xu-Hui, LONG Yi, YE Rong-Chang
Chin. Phys. Lett. 2005, 22 (4): 991-994 .  
Abstract   PDF(pc) (321KB) ( 618 )
Zn1-xMnxO nanowires (x = 0.035 and 0.13) have been synthesized by the vapour phase growth at 500°C. The compositional lines scanned in the energy dispersive x-ray spectroscopy (EDX) modes exhibit the homogeneous distribution of manganese in ZnO nanowires. The magnetic property measurement results show that the magnetization changes linearly with the field at high temperature, while it changes nonlinearly at low temperature, and all of the data can be well fitted by the modified Brillouin function. The magnetization of the Zn1-xMnxO nanowires show paramagnetic the behaviour for x = 0.035 while it exhibits the ferromagnetic behaviour for x = 0.13 at 5K, which indicate that the ferromagnetism might be related to the manganese content.
Structure Properties of MgxZn1-xO Films Deposited at Low Temperature
ZHANG Xi-Jian, MA Hong-Lei, WANG Qing-Pu, MA Jin, ZONG Fu-Jian, XIAO Hong-Di, JI Feng
Chin. Phys. Lett. 2005, 22 (4): 995-997 .  
Abstract   PDF(pc) (333KB) ( 569 )
MgxZn1-xO films (x=0.23) have been prepared on silicon substrates by radio-frequency magnetron sputtering at 80°C. The structure properties of MgxZn1-xO films are studied using x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy and Raman spectra. The analysis of XRD and HRTEM indicates that the MgxZn1-xO films have hexagonal wurtzite single-phase structures and a preferred orientation with the c axis perpendicular to the substrates. Raman spectra of ZnO and MgxZn1-xO films reveal that the MgxZn1-xO films have not only the hexagonal wurtzite structure but also higher crystalline quality than ZnO films.
Structure and Photoluminescence of Nano-ZnO Films Grown on a Si (100) Substrate by Oxygen- and Argon-Plasma-Assisted Thermal Evaporation of Metallic Zn
LU Li-Xia, TANG Qin-Xin, SHAO Chang-Lu, LIU Yi-Chun,
Chin. Phys. Lett. 2005, 22 (4): 998-1001 .  
Abstract   PDF(pc) (282KB) ( 503 )
Nano-ZnO thin films were prepared by oxygen- and argon-plasma-assisted thermal evaporation of metallic Zn at low temperature, followed by low-temperature annealing at 300°C to 500°C in oxygen ambient. X-ray diffraction patterns indicate that the nano-ZnO films have a polycrystalline hexagonal wurtzite structure. Raman scattering spectra demonstrate the existence of interface layers between Zn and ZnO. Upon annealing at 400°C for 1h, the interface mode disappears, and photoluminescence spectra show a very strong ultraviolet emission peak around 381nm. The temperature-dependent PL spectra indicate that the UV band is due to free-exciton emission.
Unit-Cell by Unit-Cell Homoepitaxial Growth Using Atomically Flat SrTiO3(001) Substrates and Pulsed Laser Deposition
FEI Yi-Yan, WANG Xu, LU Hui-Bin, YANG Guo-Zhen, ZHU Xiang-Dong,
Chin. Phys. Lett. 2005, 22 (4): 1002-1005 .  
Abstract   PDF(pc) (381KB) ( 457 )
Using a combination of chemical etching and thermal annealing methods, we have obtained atomically flat TiO2-terminated SrTiO3(001) with large terraces. The average width of the terrace is only determined by miscut angles. When we continuously grow tens of SrTiO3 monolayers on such a surface under pulsed laser ablation deposition condition at 621°C, the growth proceeds in a layer-by-layer mode characterized by un-damped oscillations of the specular RHEED intensity. After the growth of 180 monolayers, the surface morphology is restored to the pre-growth condition with similarly large terraces after annealing in vacuum for only 30min, indicating efficient mass transfer on TiO2-terminated terraces.
Nonlinear Correlations of Protein Sequences and Symmetries of Their Structures
LI Ming-Feng, HUANG Yan-Zhao, XIAO Yi
Chin. Phys. Lett. 2005, 22 (4): 1006-1009 .  
Abstract   PDF(pc) (441KB) ( 568 )
We investigate the nonlinear correlations of protein sequences by using the nonlinear prediction method developed in nonlinear dynamical theory. It is found that a lot of protein sequences show strong nonlinear correlations and have deterministic structures. Further investigations show that the strong nonlinear correlations of these protein sequences are due to the symmetries of their tertiary structures. Furthermore, the correlation lengths of the sequences are related to the degrees of the symmetries. These results support the duplication mechanism of protein evolution and also reveal one aspect how amino acid sequences encode their spatial structures.

Atomic Force Microscopy Measurement of DNA Fragment Induced by Heavy Ions
SUI Li, ZHAO Kui, NI Mei-Nan, GUO Ji-Yu, KONG Fu-Quan, CAI Ming-Hui, LU Xiu-Qin, ZHOU Ping
Chin. Phys. Lett. 2005, 22 (4): 1010-1013 .  
Abstract   PDF(pc) (447KB) ( 633 )
Choosing 7Li and 12C heavy ions respectively with different linear energy transfer (LET) values, purified plasmid DNA samples in aqueous solution are irradiated with various doses. The atomic force microscopy (AFM) is used for analysis of DNA fragments induced by both the kinds of heavy ions. There is a change of three forms of DNA, i.e. supercoiled, open circular and linear form, as the dose is observed. The distribution function of DNA fragment length is obtained for the first time and fitted with the Tsallis entropy statistical theory. The result indicates that AFM is a useful tool for analysis of the short fragment of DNA, high-LET heavy ion radiation induces DNA double strand breaks (DSBs) more effectively, and the distributions of the DSBs are more local and dense in comparison with low-LET radiation.

Evolvement Complexity in an Artificial Stock Market
YANG Chun-Xia, ZHOU Tao, ZHOU Pei-Ling, LIU Jun, TANG Zi-Nan
Chin. Phys. Lett. 2005, 22 (4): 1014-1017 .  
Abstract   PDF(pc) (247KB) ( 663 )
An artificial stock market is established based on the multi-agent model. Each agent has a limited memory of the history of stock price, and will choose an action according to its memory and trading strategy. The trading strategy of each agent evolves ceaselessly as a result of a self-teaching mechanism. The simulation results exhibit that large events are frequent in the fluctuation of the stock price generated by the present model when compared with a normal process, and the price returns distribution is a Lévy distribution in the central part followed by an approximately exponential truncation. In addition, by defining a variable to gauge the evolvement complexity of this system, we have found a phase cross-over from simple-phase to complex-phase along with the increase of the number of individuals, which may be a ubiquitous phenomenon in multifarious real-life systems.
Effect of the Initial Mass Function of Primaries on Binary Stellar Populations
ZHANG Feng-Hui, HAN Zhan-Wen, LI Li-Fang
Chin. Phys. Lett. 2005, 22 (4): 1018-1021 .  
Abstract   PDF(pc) (244KB) ( 406 )
Using evolutionary population synthesis technique, we explore the behaviour of the integrated U-B, B-V, V-R and R-I colours, the integrated spectral energy distributions (ISEDs) and Lick/IDS absorption-line indices of instantaneous burst solar-metallicity binary stellar populations, as a function of the initial mass function (IMF) of primaries. It is found that the variation of the IMF of primaries produces a small effect on the integrated colours and the Lick/IDS indices, while a significant difference in the absolute ISEDs.
X-Ray Emission from Rotation-Powered Pulsars
LIN Gui-Fang, ZHANG Li,
Chin. Phys. Lett. 2005, 22 (4): 1022-1024 .  
Abstract   PDF(pc) (223KB) ( 526 )
We study the properties of pulsed component of hard (2--10keV) x-ray emission from pulsars based on the new version of outer gap model we proposed previously [Astrophys. J. 604(2004)317]. On the frame of this outer gap model, we derive an expression of non-thermal pulsed x-ray luminosity of rotation-powered pulsars, and then apply it to the pulsars whose pulsed x-rays are detected by ASCA. Using the Kolmogorov--Smirnov test, we determine the model parameter. The present results indicate LX ∝ L1.15sd for these x-ray pulsars, which is consistent with the observed data.
Standing Shocks in Viscous Accretion Flows around Black Holes
GU Wei-Min, LU Ju-Fu
Chin. Phys. Lett. 2005, 22 (4): 1025-1028 .  
Abstract   PDF(pc) (217KB) ( 636 )
We study the problem of standing shocks in viscous accretion flows around black holes. We parameterize such a flow with two physical constants, namely the specific angular momentum accreted by the black hole j and the energy quantity K. By providing the global dependence of shock formation in the j-K parameter space, we show that a significant parameter region can ensure solutions with shocks of different types, namely Rankine-Hugoniot shocks, isothermal shocks, and more realistically, mixed shocks.
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