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Volume 21 Issue 1
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Original Articles
Production of Squeezed State of Single Mode Cavity Field by the Coupling of Squeezed Vacuum Field Reservoir in Nonautonomous Case
AN Jun-Hong, WANG Shun-Jin, LUO Hong-Gang, JIA Cheng-Long
Chin. Phys. Lett. 2004, 21 (1): 1-4 .  
Abstract   PDF(pc) (224KB) ( 1213 )
The dissipative and decoherence properties as well as the asymptotic behaviour of the single mode electromagnetic field interacting with the time-dependent squeezed vacuum field reservoir are investigated in detail by using the algebraic dynamical method. With the help of the left and right representations of the relevant hw(4) algebra, the dynamical symmetry of the nonautonomous master equation of the system is found to be su(1,1). The unique equilibrium steady solution is found to be the squeezed state and any initial state of the system is proven to approach the unique squeezed state asymptotically. Thus the squeezed vacuum field reservoir is found to play the role of a squeezing mold of the cavity field.

Measuring the Wigner Functions of Two-Mode Cavity Fields and Testing the Bell’s Inequalities
ZHANG Zhi-Ming
Chin. Phys. Lett. 2004, 21 (1): 5-8 .  
Abstract   PDF(pc) (329KB) ( 1000 )
We propose a scheme for measuring the Wigner function of a two mode cavity field. The scheme bases on the interaction between the two-mode cavity field and three-level atoms. We find a simple relation between the Wigner function and the atomic population. One can obtain the Wigner function by measuring the atomic population with a micromaser-like experiment and doing a numerical integral. By using the two-mode Wigner function one can obtain the Clauser--Horne combination and test the Bell's inequalities. We test our equations with a two-mode entanglement state and the results are rather good.

Probabilistic Implementation of Non-Local CNOT Operation and Entanglement Purification
ZHENG Yi-Zhuang, YE Peng, GUO Guang-Can
Chin. Phys. Lett. 2004, 21 (1): 9-11 .  
Abstract   PDF(pc) (180KB) ( 656 )
We propose a protocol for implementation of nonlocal CNOT operation using a partially entangled channel and show that when partially entangled pairs are taken as quantum channels, the nonlocal CNOT operation can be implemented probabilistically by introducing a collective unitary transformation. The required resources for implementation of the nonlocal CNOT operation in this case are discussed. We also point out that the nonlocal CNOT operation can be used as a purification protocol to concentrate entanglement from an ensemble of partially entangled particles into a subensemble of maximally entanglement ones.
Quantum Dense Coding in Multiparticle Entangled States via Local Measurements
CHEN Jian-Lan, KUANG Le-Man
Chin. Phys. Lett. 2004, 21 (1): 12-14 .  
Abstract   PDF(pc) (178KB) ( 509 )
We study quantum dense coding between two arbitrarily fixed particles in a (N+2)-particle maximally-entangled states through introducing an auxiliary qubit and carrying out local measurements. It is shown that the transmitted classical information amount through such an entangled quantum channel is usually less than two classical bits. However, the information amount may reach two classical bits of information, and the classical information capacity is independent of the number of the entangled particles under certain conditions. The results offer deeper insight into quantum dense coding via quantum channels of multi-particle entangled states.

Multi-Mode Excited Logic Gates on Trapped Ions
ZENG Hao-Sheng, CHEN Dao-Jia, KUANG Le-Man, GAO Ke-Lin
Chin. Phys. Lett. 2004, 21 (1): 15-17 .  
Abstract   PDF(pc) (221KB) ( 362 )
Based on the scheme of “hot”trapped-ion quantum computation proposed by SФrensen and MФlmer, we construct a set of multi-mode excited logic gates on trapped ions, which may be operated on arbitrary even number of ions selected randomly from a string of ions trapped in a linear trap. The gate speed may be made faster than that of the corresponding one-mode excited logic gate by adjusting appropriately the detunings of driving lasers with respect to the sidebands of vibrational modes and can be demonstrated in current experimental techniques.
Tunnelling of Two-Level Atoms in Two-Photon Mazer: Atomic Coherence Effect and Statistics of Cavity Fields
HE Xiao-Ling, DU Si-De, ZHOU Lu-Wei, WANG Qi-Sheng, CHEN Hao
Chin. Phys. Lett. 2004, 21 (1): 18-21 .  
Abstract   PDF(pc) (503KB) ( 478 )
Tunnelling of a two-level atom is investigated in the two photon mazer when the atom is initially prepared in a coherent superposition state and the cavity in various quantum states. For a strong coherent field, the tunnelling exhibits more regular oscillations but less remarkable switch effect than that in the one-photon mazer. It is discovered that in the presence of atomic coherence, the transmission probabilities in the ultracold regime are significantly different when the cavity field is initially in coherent, squeezed vacuum, even cat and odd cat states, respectively.

Representation and Dimensional Reduction of the Universe
WU Zhong-Chao
Chin. Phys. Lett. 2004, 21 (1): 22-24 .  
Abstract   PDF(pc) (183KB) ( 667 )
The external space we live in or the apparent dimension in the Kaluza--Klein model can be identified by using the right representation in quantum cosmology. The external dimension of the Freund--Rubin model is min(s, n-s), where s is the rank of the antisymmetric field strength in the model.

Screw Instability in Black Hole Magnetosphere and kHz QPOs in X-Ray Binaries
YAO Guo-Zheng, , WANG Ding-Xiong, MA Ren-Yi
Chin. Phys. Lett. 2004, 21 (1): 25-28 .  
Abstract   PDF(pc) (341KB) ( 388 )
Screw instability of the magnetic field connecting a rotating black hole (BH) with its surrounding disc is discussed in coexistence with the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process. A scenario for kilohertz quasi-periodic oscillations (kHz QPOs) in x-ray binaries is proposed by introducing inductance components in the equivalent circuit for BH magnetosphere. It turns out that the period related to the screw instability is consistent with the observations of kHz QPO x-ray binaries.
Phase Transition of Hot Nuclear Matter
LI Zeng-Hua, ZUO Wei, LU Guang-Cheng
Chin. Phys. Lett. 2004, 21 (1): 29-32 .  
Abstract   PDF(pc) (416KB) ( 488 )
Based on the difference between the Fermi distributions at zero temperature and at the finite temperature, we introduce the temperature-dependent three-body force (TBF) into the microscopic finite-temperature Brueckner-Hartree-Fock theory (FTBHF). In terms of the meson-exchange current approach, i.e. the one boson exchange (OBE) approximation, the exchange of four important mesons π, ρ, σ and ω are considered. Using the FTBHF theory including TBF, we describe the critical temperature of the liquid-gas phase transition for symmetric nuclear matter and discuss its change trend with the increasing asymmetry parameter. Compared to the result excluding TBF, the value of the critical temperature turns out to be smaller.
Precise Measurement of Separation Between Two Spherical Source Masses
CHEN De-Cai, LUO Jun, HU Zhong-Kun, ZHAO Liang
Chin. Phys. Lett. 2004, 21 (1): 33-36 .  
Abstract   PDF(pc) (411KB) ( 467 )
A driving gauge method is performed to determine the separation between two spherical source masses in the measurement of Newtonian gravitational constant G. The experimental result shows that the uncertainty of determining the separation is about 0.35 μm, which would contribute an uncertainty of 7.3 ppm to the value of G.

Multisymplectic Hamiltonian Formulation for a One-Way Seismic Wave Equation of High-order Approximation
CHEN Jing-Bo
Chin. Phys. Lett. 2004, 21 (1): 37-39 .  
Abstract   PDF(pc) (172KB) ( 628 )
Based on the Lagrangian density and covariant Legendre transform, we obtain the multisymplectic Hamiltonian formulation for a one-way seismic wave equation of high-order approximation. This formulation provides a new perspective for studying the one-way seismic wave equation. A multisymplectic integrator is also derived.

Halo Effect on Direct Neutron Capture Process
LIU Zu-Hua, ZHOU Hong-Yu
Chin. Phys. Lett. 2004, 21 (1): 40-42 .  
Abstract   PDF(pc) (342KB) ( 382 )
We calculate the capture cross sections of the 10Be(n,γ) 11Be reaction by means of the asymptotic normalization coefficient method and demonstrate the halo effects on the capture cross sections for the direct radiative neutron capture where a p-, s- or d-wave neutron is captured into an s-orbit or p-orbit in 11Be by emitting an E1 γ-ray, respectively. The result shows that the enormous enhancement of the capture cross section is just due to the large overlap of the incident neutron wave with the extended tail of the halo, which is clearly illustrated by the reduced transition amplitude function.

Explicit and Dynamical Chiral Symmetry Breaking in an Effective Quark-Quark Interaction Model
ZONG Hong-Shi, WU Xiao-Hua, HOU Feng-Yao, ZHAO En-Guang,
Chin. Phys. Lett. 2004, 21 (1): 43-46 .  
Abstract   PDF(pc) (297KB) ( 415 )
A method for obtaining the small current quark mass effect on the dressed quark propagator from an effective quark-quark interaction model is developed. Within this approach both the explicit and dynamical chiral symmetry breakings are analysed. A comparison with the previous results is given.

Chemical Equilibration and Dilepton Production of Quark-Gluon Plasma at RHIC Energies
LONG Jia-Li, HE Ze-Jun, MA Guo-Liang, MA Yu-Gang, LIU Bo
Chin. Phys. Lett. 2004, 21 (1): 47-50 .  
Abstract   PDF(pc) (383KB) ( 538 )
An evolution model of the chemically equilibrating quark-gluon plasma system has been established based on the Jüttner distribution function of partons. By studying the dilepton production of the system, we find that due to high initial temperature, a dominant contribution to dileptons with intermediate masses is provided by gluon density of the system as well as large gluon fusion gg → cc cross section in the intermediate mass region, quark--antiquark annihilation qq → ll and, especially, thermal charmed quarks from the gluon fusion gg → cc and quark--antiquark annihilation qq → cc.
Application of 41Ca Tracer and Its AMS Measurement in CIAE
DONG Ke-Jun, HE Ming, WU Shao-Yong, YUE Dong-Fang, YOU Qu-Bo, BAO Yi-Wen, GUAN Yong-Jing, ZHENG Yuan-Feng, YIN Xin-Yi, WANG Hui-Juan, LI Guo-Qiang, YANG Yao-Yun, XU Guo-Ji, HU Yue-Ming, JIANG Shan
Chin. Phys. Lett. 2004, 21 (1): 51-53 .  
Abstract   PDF(pc) (480KB) ( 394 )
The man-made calcium isotope 41Ca is an ideal tracer for the study of calcium metabolism. We represent the first application of accelerator mass spectrometry (AMS) measurement of 41Ca tracer in China. The technique is being applied to the research field of cell messenger at the China Institute of Atomic Energy (CIAE). The sample preparation methods and the AMS measurements are discussed and some interesting results are presented.
Theoretical Analysis of Generalized Oscillator Strengths for Helium by R-Matrix Method
HAN Xiao-Ying, VoKy Lan, LI Jia-Ming,
Chin. Phys. Lett. 2004, 21 (1): 54-56 .  
Abstract   PDF(pc) (446KB) ( 522 )
The high-energy electronic-impact excitation cross section is directly proportional to the generalized oscillator strength (GOS) of the target atom. The generalized oscillator strengths of helium atom from the ground state to the excited states (21S, 21P and 31D) are calculated using the updated R-matrix codes within the first Born approximation. Our calculation results are in good agreement with the previous theoretical and experimental results at high incident energies. In order to treat the bound-bound and bound-continuum transitions in a unified manner, the GOS density is defined based on the quantum defect theory. We calculate the GOS densities of 1S, 1P and 1D channels, namely the complete high-energy collision cross sections of electronic-impact excitations into all the n1S, n1P and n1D excited states. In addition to high-energy excitation cross sections, a scheme to calculate the excitation cross sections for entire incident energy range is discussed.

Proposal of a Novel Compact Cold Atomic Fountain Clock
WEI Rong, QIAN Yong, ZHANG Yu, WANG Yu-Zhu
Chin. Phys. Lett. 2004, 21 (1): 57-60 .  
Abstract   PDF(pc) (351KB) ( 565 )
We propose a novel atomic fountain clock which is compact and transportable. The clock is 60-cm in height. Its linewidth is expected to be 1.75 Hz, with accuracy 10-14, stability 10-14 and signal-noise ratio 103. A hollow beam is applied as atomic wave-guide, which can increase the stability and the signal-noise ratio by one order. The hollow beam will not affect the accuracy of the clock, if the frequency shift due to the hollow beam is amended and the fluctuation of the hollow beam intensity is controlled to be smaller than 0.6%.
X-Ray Photoelectron Spectroscopy Analysis of the Electron Beam Treated SiC Films Before and After Hydrogen Ion Irradiation
Chin. Phys. Lett. 2004, 21 (1): 61-64 .  
Abstract   PDF(pc) (512KB) ( 531 )
SiC films deposited with rf magnetron sputtering followed by electron beam alloying were irradiated by hydrogen ion with an energy of 5 keV and a dose of 1 x 1018 ions/cm2. The x-ray photoelectron spectroscopy analysis was used to investigate the irradiation effects of hydrogen ion on SiC. The results show that hydrogen ion irradiation can cause preferential sputtering of component of SiC, and activated carbon can react chemically with hydrogen to form hydrocarbon species such as methane. The related mechanism is discussed.
Absolute Generalized Oscillator Strength Profiles of Rydberg Transitions in C2F6
FAN Xiao-Wei, LU Shan, ZHANG Xian-Zhou, K. T. Leung
Chin. Phys. Lett. 2004, 21 (1): 65-66 .  
Abstract   PDF(pc) (299KB) ( 477 )
Absolute generalized oscillator strengths (GOSs) for the two Rydberg excitations at 12.1 eV and 13.5 eV in C2F6 have been determined as functions of energy loss and momentum transfer (K) at impact energy of 2.5 keV. The GOS profiles for these two Rydberg transitions to 3 p Rydberg orbital have the characteristic dipole-dominated shapes with a strong maximum at K = 0.

Structural Phase Transformations of ZnS Nanocrystalline Under High Pressure
PAN Yue-Wu, QU Sheng-Chun, GAO Chun-Xiao, HAN Yong-Hao, LUO Ji-Feng, CUI Qi-Liang, LIU Jing, ZOU Guang-Tian
Chin. Phys. Lett. 2004, 21 (1): 67-69 .  
Abstract   PDF(pc) (456KB) ( 814 )
In-situ energy dispersive x-ray diffraction on ZnS nanocrystalline was carried out under high pressure by using a diamond anvil cell. Phase transition of wurtzite of 10 nm ZnS to rocksalt occurred at 16.0 GPa, which was higher than that of the bulk materials. The structures of ZnS nanocrystalline at different pressures were built by using materials studio and the bulk modulus, and the pressure derivative of ZnS nanocrystalline were derived by fitting the equation of Birch-Murnaghan. The resulting modulus was higher than that of the corresponding bulk material, which indicates that the nanomaterial has higher hardness than its bulk materials.

Factors in Design of Optical Super-Resolving Filters
XIAO Fan-Rong, YUAN Jing-He, WANG Gui-Ying, XU Zhi-Zhan
Chin. Phys. Lett. 2004, 21 (1): 70-72 .  
Abstract   PDF(pc) (274KB) ( 526 )
Three key factors in design of optical pupil filters with super-resolving are studied. For the same normalized spot size, the factor of sidelobe intensity is more important for designing filters in applications. Thus the phase-only filters do not always perform better than the transmittance filters which always have lower Strehl ratio. The drawback of lower central core intensity can be compensated for by the high power laser. The argument has been justified in our numerical experimental results with the simplest filter patterns.
New Vacuum State of the Electromagnetic Field-Matter Coupling System and the Physical Interpretation of Casimir Effect
LI Tong-Zhong
Chin. Phys. Lett. 2004, 21 (1): 73-75 .  
Abstract   PDF(pc) (186KB) ( 485 )
A new concise method is presented for the calculation of the ground-state energy of the electromagnetic field and matter field interacting system. With the assumption of squeezed-like state, a new vacuum state is obtained for the interacting system. The energy of the new vacuum state is lower than that given by the second-order perturbation theory in existing theories. In our theory, the Casimir effect is attributed neither to the quantum fluctuation in the zero-point energy of the genuine electromagnetic field nor to that in the zero-point energy of the genuine matter field, but to that in the vacuum state of the interacting system. Both electromagnetic field and matter field are responsible for the Casimir effect.
Electromagnetically Induced Absorption and Transparency Spectra of Degenerate Two-Level Systems with a Strong Coupling Field in Cs Vapour
ZHAO Yan-Ting, ZHAO Jian-Ming, XIAO Lian-Tuan, YIN Wang-Bao, JIA Suo-Tang
Chin. Phys. Lett. 2004, 21 (1): 76-78 .  
Abstract   PDF(pc) (348KB) ( 643 )
The electromagnetically induced absorption and electromagnetically induced transparency spectra of degenerate two-level systems with a strong coupling laser were observed. The frequency detuning and intensity effect of the coupling laser were demonstrated simultaneously. A dispersion-like spectrum can be obtained when the coupling laser is situated at blue-side detuning. The absorption inversion was realized when the coupling laser intensity is small. The coherent resonance has a linewidth much narrower than the natural linewidth of the optical transitions.

Comparison of Free Spectral Range and Quality Factor for Two-Dimensional Square and Circular Microcavities
GUO Wei-Hua, HUANG Yong-Zhen, LU Qiao-Yin, YU Li-Juan
Chin. Phys. Lett. 2004, 21 (1): 79-80 .  
Abstract   PDF(pc) (305KB) ( 466 )
Free spectral range of whispering-gallery (WG)-like modes in a two-dimensional (2D) square microcavity is found to be twice that in a 2D circular microcavity. The quality factor of the WG-like mode with the low mode number in a 2D square microcavity, calculated by the finite-difference time-domain (FDTD) technique and the Padé approximation method, is found to exceed that of the WG mode in 2D circular microcavity with the same cavity dimension and close mode wavelength.
Improvement of 1.3-μm GaInNAs Vertical Cavity Surface Emitting Lasers Grown by MOVPE
YUE Ai-Wen, SHEN Kun, SHI Jing, WANG Ren-Fan
Chin. Phys. Lett. 2004, 21 (1): 81-83 .  
Abstract   PDF(pc) (406KB) ( 461 )
We report the improved performance of the conventional contact 1.3 μm GaInNAs vertical cavity surface emitting lasers (VCSELs) grown by metal-organic vapour-phase epitaxy (MOVPE). A new wet etching approach was applied in the fabrication of 1.3 μm GaInNAs oxide-confined VCSELs. The threshold current of single mode device is 1.0 mA. The multiple mode devices show very low threshold currents below 2 mA at 5-85°C, which were the best results for 1.3 μm GaInNAs VCSELs reported. Maximum single mode output power of 0.256 mW and the maximum multiple mode power of 0.883 mW were obtained at room temperature.

Optimal Bandwidth for Distributed Multi-Pump Raman Amplifier Based on Hybrid Genetic Algorithm
LIU Xue-Ming, LI Yan-He
Chin. Phys. Lett. 2004, 21 (1): 84-86 .  
Abstract   PDF(pc) (454KB) ( 489 )
Based on a hybrid genetic algorithm, the bandwidth for distributed multi-pump Raman amplifier (DMRA) is optimized. Optimal results show that signal bandwidth Δλ can be evidently broadened by means of increasing the number of pumps, Δλ decreases with the increase of Raman gain and with the improvement of flatness property, and the hybrid erbium-doped fibre amplifier and DMRA can availably overcome the weakness of pure DMRA.
Reduction of Light Group Velocity by Coherent Population Oscillation in a Ruby Crystal
ZHANG Yun-Dong, FAN Bao-Hua, YUAN Ping, MA Zu-Guang
Chin. Phys. Lett. 2004, 21 (1): 87-89 .  
Abstract   PDF(pc) (332KB) ( 1011 )
We report the investigation of the reduction of the group velocity propagation resulting from the steep change of the refractive index by the coherent population oscillation in a ruby crystal at room temperature. Slow light propagation is observed in a solid-state material at room temperature. The measured delay is about 2.314±0.005 ms, corresponding to a group velocity as slow as 43.215±0.094 m/s in a non-sinusoid modulated waveform. The influences of pulse duration on the delay and the reduction of light propagation are given.

Finesse-Enhanced Ring Resonator Coupled Mach-Zehnder Interferometer All-Optical Switches
LI Chun-Fei, BANANEJ Alireza
Chin. Phys. Lett. 2004, 21 (1): 90-93 .  
Abstract   PDF(pc) (387KB) ( 495 )
In the all-optical switches using Mach-Zehnder interferometer side-coupled with a ring resonator, the switching power is quadratically reversely proportional to the resonator finesse in the high-finesse case. In order to enhance the resonator finesse, the loss rate a and the coupler reflectivity r should approach 1. Therefore, we propose a new configuration by inserting an amplifier into the ring to compensate for the losses in the ring and using a pumped nonlinear coupler instead of the ordinary coupler. The resonator finesse can be enhanced dramatically and the minimum switching power can be obtained.

Experimental and Theoretical Analysis of Nondegenerate Ultrabroadband Chirped Pulse Optical Parametric Amplification
LIU Hong-Jun, ZHAO Wei, CHEN Guo-Fu, WANG Yi-Shan, YU Lian-Jun, RUAN Chi, LU Ke-Qing
Chin. Phys. Lett. 2004, 21 (1): 94-97 .  
Abstract   PDF(pc) (543KB) ( 565 )
Experimental investigations of nondegenerate ultrabroadband chirped pulse optical parametric amplification have been carried out. The general mathematical expressions for evaluating parametric bandwidth, gain and gain bandwidth for arbitrary three-wave mixing parametric amplifiers are presented. In our experiments, a type-I noncollinear phase-matched optical parametric amplifier based on lithium triborate, which was pumped by a 5-ns second harmonic pulses from a Q-switched Nd:YAG operating at 10 Hz, seeded by a 14-fs Ti:sapphire laser at 800 nm, was presented. The 0.85 nJ energy of input chirped signal pulse with 57-FWHM has been amplified to 3.1 μJ at pump intensity 3 GW/cm2, the corresponding parametric gain reached 3.6 x 103, the 53 nm-FWHM gain spectrum bandwidth of output signal has been obtained. The large gain and broad gain bandwidth, which have been confirmed experimentally, provide great potentials to amplify efficiently the broad bandwidth femtosecond light pulses to generate new extremes in power, intensity, and pulse duration using optical parametric chirped pulse amplifiers pumped by powerful nanosecond systems.

Low-Threshold Mid-Infrared Optical Parametric Oscillator Using Periodically Poled LiNbO3
LIN Xue-Chun, ZHANG Ying, KONG Yu-Peng, ZHANG Jie, YAO Ai-Yun, HOU Wei, CUI Da-Fu, LI Rui-Ning, XU Zu-Yan, LI Jian
Chin. Phys. Lett. 2004, 21 (1): 98-100 .  
Abstract   PDF(pc) (314KB) ( 488 )
We report the generation of tunable mid-infrared optical pulses using all-solid-state pumped optical parametric oscillator in a periodically poled lithium niobate. Several ways were used to lower the threshold, resulting in a mean threshold as low as 6.5 mW and an achievement of wavelength conversion in the 2.77-4.04 μm spectral range. Continuous tuning range from 2.97 to 3.25 μm was achieved. The maximum idler output power of 466 mW at the wavelength of 3.41 μm was obtained, which represents an optical-to-optical conversion efficiency of 19% from incident pump power to the idler output.

Engineering Photonic Crystal Impurity Bands for Multiple Channelled Optical Switches
JIANG Hai-Tao, CHEN Hong, LIU Nian-Hua, ZHU Shi-Yao
Chin. Phys. Lett. 2004, 21 (1): 101-103 .  
Abstract   PDF(pc) (346KB) ( 430 )
We report theoretically on the engineering of photonic crystal impurity bands to realize multiple channelled optical switches. The mechanism is based on the confinement of the impurity band in a photonic quantum-well structure, leading to N-quantized confined states coming from N-coupled defects. Due to the strong localization of electromagnetic wave at defect regions, the transmission of confined states are greatly dependent on the defects and then multiple channelled optical switches can be realized by slightly changing the defects by a control light. The dependence of the threshold of such a switch on the layer number of photonic barriers is also given.

Multimode Interference 3-dB Coupler in Silicon-on-Insulator Based on Silicon Rib Waveguides with Trapezoidal Cross Section
XIA Jin-Song, YU Jin-Zhong, FANZhong-Chao, WANG Zhang-Tao, CHEN Shao-Wu
Chin. Phys. Lett. 2004, 21 (1): 104-106 .  
Abstract   PDF(pc) (303KB) ( 1072 )
A 3-dB multimode interference optical coupler based on rib waveguides with trapezoidal cross section was designed and fabricated on silicon-on-insulator wafer. Potassium hydroxide (KOH) anisotropic chemical etching of silicon was used to fabricate the waveguides to obtain smooth interface. A modified finite-difference beam propagation method was used to simulate the multimode rib waveguide with slope interfaces. The rms roughness of etching interface is as small as 1.49 nm. The propagation loss of the waveguide is 1.3 dB/cm at wavelength of 1.55 μm. The fabricated 3-dB coupler has a good uniformity of 0.2 dB.

Analysis and Correction of Diffraction Effect on the B/A Measurement at High Frequencies
ZHANG Dong, GONG Xiu-Fen, LIU Xiao-Zhou, KUSHIBIKI Jun-ichi, NISHINO Hideo
Chin. Phys. Lett. 2004, 21 (1): 107-109 .  
Abstract   PDF(pc) (374KB) ( 471 )
A numerical method is developed to analyse and to correct the diffraction effect in the measurement of acoustic nonlinearity parameter B/A at high frequencies. By using the KZK nonlinear equation and the superposition approach of Gaussian beams, an analytical model is derived to describe the second harmonic generation through multi-layer medium SiO2/liquid specimen/SiO2. Frequency dependence of the nonlinear characterization curve for water in 110-155 MHz is numerically and experimentally investigated. With the measured dip position and the new model, values of B/A for water are evaluated. The results show that the present method can effectively correct the diffraction effect in the measurement.

A Fast Field Scheme for the Parametric Sound Radiation from Rectangular Aperture Source
YANG Jun, SHA Kan, GAN Woon-Seng, TIAN Jing
Chin. Phys. Lett. 2004, 21 (1): 110-113 .  
Abstract   PDF(pc) (371KB) ( 437 )
A virtual complex source approach has been developed to calculate numerically the ultrasound field generated by a rectangular planar source with high efficiency. The sound field can be treated as the resultant sound pressure from a set of complex virtual sources located at a complex distance, and then by exploiting the integrability of Gaussian function, a substantial analytical reduction to single integral is derived for the second-order field of the sum-, difference-frequency and second harmonic components. The validity of this fast field scheme is confirmed by comparison of numerical results and the experimental data published previously.

Dual Role of Viscosity During Start-Up of a Maxwell Fluid in a Pipe
REN Ling, ZHU Ke-Qin
Chin. Phys. Lett. 2004, 21 (1): 114-116 .  
Abstract   PDF(pc) (370KB) ( 433 )
Based on the exact solution of start-up flow of Maxwell fluids in a long circular straight pipe, the effect of viscosity on the time of flow establishment is analysed. It is found that the viscosity of Maxwell fluids plays a dual role. A key parameter is the dimensionless relaxation time λ. For 0 < λ < 0.0432, the viscosity mainly plays the same role as in Newtonian fluids, and the time of flow establishment decreases with the increasing viscosity; for λ > 0.0432, the viscosity mainly plays a role of strengthening the oscillation, and the time of flow establishment increases with the incremental viscosity.

A Fractal Model for the Transverse Thermal Dispersion Conductivity in Porous Media
YU Bo-Ming, LI Jian-Hua
Chin. Phys. Lett. 2004, 21 (1): 117-120 .  
Abstract   PDF(pc) (320KB) ( 501 )
A quasi-analytical model, i.e. the fractal model, for the transverse thermal dispersion conductivity in porous media is presented based on the fractal characteristics of tortuous flow paths/streamlines in porous media. The fractal dimension of tortuous flow paths, the spatial deviation velocity and the transverse thermal dispersion conductivity are derived. The proposed model is expressed as functions of the fractal dimension of tortuous flow paths/streamlines, Peclet number, porosity and structural parameters. The present results are compared with those from the existing correlation, and good agreement is found between the present model predictions and those from the existing correlation.

Voids in an Experimental Dusty Plasma System
HUANG Feng, YE Mao-Fu, WANG Long, JIANG Nan
Chin. Phys. Lett. 2004, 21 (1): 121-124 .  
Abstract   PDF(pc) (353KB) ( 732 )
Various dusty voids are observed in a gas discharge dusty plasma system. They appear at the earlier stage of particle growth. Both the regular and irregular voids are observed in two and three dimensions. Regular voids observed in two dimensions include circular shapes and thin ring shapes. Regular voids in three dimensions appear dome-shaped and shell-shaped.

Acoustic Rotation Modes in Complex Plasmas
BAI Dong-Xue, WANG Zheng-Xiong, WANG Xiao-Gang
Chin. Phys. Lett. 2004, 21 (1): 125-128 .  
Abstract   PDF(pc) (315KB) ( 598 )
Acoustic rotation modes in complex plasmas are investigated in a cylindrical system with an axial symmetry. The linear mode solution is derived. The mode in an infinite area is reduced to a classical dust acoustic wave in the region away from the centre. When the dusty plasma is confined in a finite region, the breathing and rotating-void behaviour are observed. Vivid structures of different mode number solutions are illustrated.

Electromagnetic Instabilities Excited by Electron Temperature Anisotropy
LU Quan-Ming, WANG Lian-Qi, ZHOU Yan, WANG Shui
Chin. Phys. Lett. 2004, 21 (1): 129-132 .  
Abstract   PDF(pc) (476KB) ( 535 )
One-dimensional particle-in-cell simulations are performed to investigate the nonlinear evolution of electromagnetic instabilities excited by the electron temperature anisotropy in homogeneous plasmas with different parameters. The results show that the electron temperature anisotropy can excite the two right-hand electromagnetic instabilities, one has the frequency higher than Ωe, the other is the whistler instability with larger amplitude, and its frequency is below Ωe. Their dispersion relations are consistent with the prediction from the cold plasma theory. In the initial growth stage (prediction from linear theory), the frequency of the dominant mode (the mode whose amplitude is large enough) of the whistler wave almost does not change, but in the saturation stage the situation is different. In the case that the ratio of electron plasma frequency to cyclotron frequency is larger than 1, the frequency of the dominant mode of the whistler wave drifts from high to low continuously. However, for the case of the ratio smaller than 1, besides the original dominant mode of the whistler wave whose frequency is about 2.6 ωe, another dominant mode whose frequency is about 1.55 ωe also begins to be excited at definite time, and its amplitude increases with time until it exceeds the original dominant mode.

Properties and Structure of a Plasma Non-Neutral Shock
HU Ye-Min, HU Xi-Wei
Chin. Phys. Lett. 2004, 21 (1): 133-136 .  
Abstract   PDF(pc) (621KB) ( 370 )
The shock is described by the Navier-Stokes equations of the electron and ion fluids, and coupled with Poisson's equation for the self-induced electric field. Profiles of the flow and electric variables in the weak or moderate shock front with or without current for different Debye lengths are presented. Comparison of profiles of flow and electric variables in the front for different heat flow modes is given.

Naturally Occurring Velocity Shear Layer at the Plasma Edge of HT-7 Tokamak
XU Guo-Sheng, WAN Bao-Nian, SONG-Mei
Chin. Phys. Lett. 2004, 21 (1): 137-139 .  
Abstract   PDF(pc) (434KB) ( 394 )
A naturally occurring velocity shear layer was observed at the plasma edge of HT-7 tokamak in regular ohmic heated discharges. One fast reciprocating Langmuir probe was used to measure all quantities in the radial force balance equation for main ion, which enables us to present the first report about the radial force balance in the boundary region of the HT-7 tokamak. The sharp gradient of radial electric field and the reduced fluctuation correlation and turbulent particle flux characterized the edge velocity shear layer. It was found that the shear of turbulence poloidal velocity was dominated by the E x B flow shear and the poloidal rotation determined the structure of radial electric field profile and as a result the E x B flows.

Linear and Nonlinear Optical Properties of Quasicrystals
ZHOU Xiang, HU Cheng-Zheng, GONG Ping, ZHU Jia-Kun
Chin. Phys. Lett. 2004, 21 (1): 140-142 .  
Abstract   PDF(pc) (215KB) ( 528 )
An investigation is carried out on the linear and nonlinear optical properties of quasicrystals. The linear and nonlinear susceptibilities are determined for two- and three-dimensional quasicrystals. The results show that for optical linearity, two-dimensional quasicrystals are uniaxial, while icosahedral quasicrystals are optically isotropic. Meanwhile all quasicrystals, except those with 5, 5 m, N, Nmm (N = 8, 10, 12) symmetries, have no the first-order optical nonlinearity. The tensor scheme of the first-order nonlinear susceptibility is the same for these eight exceptional kinds of quasicrystals.

Continuous Method for Describing Dendrite Evolution During Solidification
LI Qiang, GUO Qiao-Yi, LI Dian-Zhong, QIAN Bai-Nian, LI Da-Ming, LI Ruo, ZHANG Ping-Wen
Chin. Phys. Lett. 2004, 21 (1): 143-145 .  
Abstract   PDF(pc) (270KB) ( 422 )
A continuous method is presented to deal with the discontinuous
physical properties on both sides of solid/liquid interface during the solidification process. Then single dendrite evolution in two and three dimensions is simulated by using this method. Multi-grain evolution is also simulated during solidification by the method. The method is easy to be understood and does not need all details of dendrite. The simulated results can reflect the random characteristic of dendrite evolution and the micro-segregation of solute.

Active Loss of Light Yield of PbWO4:Y Scintillation Crystals After Irradiation
REN Guo-Hao, WANG Shao-Hua, SHEN Ding-Zhong, YIN Zhi-Wen
Chin. Phys. Lett. 2004, 21 (1): 146-148 .  
Abstract   PDF(pc) (364KB) ( 620 )
PWO crystals doped with yttrium were grown with the Bridgman method in platinum crucible and by using an indigenously developed resistive heating furnace. After an exposure of γ-ray from a 60Co source, with the dose rate of 15 rad/h for 20 h, the light output increases for about 15%, accompanied with vanishing of an optical absorption band at 420 nm. The excitation and emission spectra of PWO crystals were measured before and after irradiation with different dose rates. The optical absorption band at 420 nm was also found in the PWO sample annealed in oxygen-rich atmosphere. It is suggested that the absorption band at 420 nm is related to Pb3+ point defects existing in the PWO crystal. The unusual change of light output after irradiation probably results from the transformation of lead ions from Pb3+ to Pb2+.

Effect of Hydrogen Implantation on SIMOX SOI Materials
YI Wan-Bing, CHEN Jing, CHEN Meng, WANG Xi, ZOU Shi-Chang
Chin. Phys. Lett. 2004, 21 (1): 149-152 .  
Abstract   PDF(pc) (380KB) ( 897 )
Hydrogen ions were implanted into separation by implantation of oxygen (SIMOX) silicon-on-insulator (SOI) wafers near the oxygen-implantation-induced damage peak under different conditions of energy and dose. It was found that the implanted hydrogen ions not only accelerate the diffusion of oxygen atoms from the annealing ambience into the wafer but also cause an outward diffusion of oxygen atoms in the buried oxide (BOX) layer. Thus, greatly broadened buried oxygen-rich (BOR) layers were formed in our experiments, which are 18%-79% broader than the BOX layer of standard SIMOX SOI wafers under the same conditions of oxygen implantation. The mechanism was discussed. A potential low cost method to fabricate SIMOX SOI wafers is proposed.

Analysis of Second-Harmonic Generation from CuttbPc LB Film/Metal Interface
CHENG Xiao-Man, YAO Su-Wei, LI Cheng-Quan, MANAKA Takaaki, IWAMOTO Mitsumasa
Chin. Phys. Lett. 2004, 21 (1): 153-155 .  
Abstract   PDF(pc) (349KB) ( 525 )
Second-harmonic generation signals from a CuttbPc LB film deposited on metal (Al or Au)--glass substrates were investigated. It was observed that there were two second-harmonic peaks at the wavelength of 1060 and 1250 nm in the CuttbPc/Al film, but only one peak at 1050 nm in the CuttbPc/Au film. Meanwhile the surface electric potentials (SEP) at the interfaces of LB film/metals were also measured using a Kelvin probe. The SEP in the CuttbPc/Al decreases and eventually approaches a saturated value of -1.0 V as the film thickness increases, while the SEP in the uttbPc/Au is nearly zero. Based on the experimental results and theoretical analysis, it was considered that the space-charge-induced electric field makes a main contribution to the second-harmonic generation at 1250 nm in the CuttbPc/Al film.

Low-Frequency and Abnormal Raman Spectrum in SnO2 Nanorods
LIU Ying-Kai, , DONG Yi, WANG Guang-Hou
Chin. Phys. Lett. 2004, 21 (1): 156-159 .  
Abstract   PDF(pc) (469KB) ( 1127 )
Raman-scattering spectra in SnO2 nanorods with different diameters were obtained at room temperature and the low-frequency Raman peaks have been observed for the first time. It was found that the low-frequency peaks shifted to high frequencies as the nanorod diameter decreased. The size dependence of the low-frequency peaks in SnO2 nanorods can be identified by the surface modes among the confined acoustic modes of SnO2 nanorods, given by solving Lamb theory. In addition, the Raman peaks of SnO2 nanorods not only vary with the excitation wavelength (514.5 nm and 785 nm), but have their line-width broadening and the line shapes asymmetric as well. Moreover, some IR active modes became Raman-active induced by disorders such as local lattice imperfections and oxygen deficiencies in the thinner nanorods when the diameter of the nanorod decreased down to 15 nm or smaller.

Quantum-Confinement Effects on Binding Energies and Optical Properties of Excitons in Quantum Dots
Chin. Phys. Lett. 2004, 21 (1): 160-163 .  
Abstract   PDF(pc) (382KB) ( 781 )
Quantum-confinement effects on the binding energy and the linear optical susceptibility of excitons in quantum dots are studied. It is found that the binding energy and the linear optical susceptibility are sensitive to the barrier height and the dot size. For an infinite barrier, the binding energy of excitons decreases monotonically with the increasing dot radius, and the absorption intensity has almost the same amplitude with the increasing photon energy. For a finite barrier, the binding energy has a maximum value with the increasing dot radius, and the absorption intensity damps rapidly with the increasing photon energy. The effective mass ratio is also found to have an influence on the binding energy. The results could be confirmed by future experiments on excitons in quantum dots.

Pentacene Organic-Thin-Film Field-Effect Transistors
ZHANG Su-Mei, SHI Jia-Wei, LIU Ming-Da, LI Jing, GUO Shu-Xu, WANG Wei
Chin. Phys. Lett. 2004, 21 (1): 164-165 .  
Abstract   PDF(pc) (359KB) ( 557 )
We have fabricated organic thin-film transistors using the small-molecule polycyclic aromatic hydrocarbon pentacene as an active material. Devices were fabricated on glass substrates by using rf-magnetron sputtered amorphous aluminium as the gate electrode, and gelatinized polyimide as the gate dielectric with physical vapour grown pentacene thin films pasted on it as the active layer, then using rf-magnetron sputtered amorphous aluminium as the source and drain contacts. Field effect mobility and threshold voltage is 0.092 cm2/Vs and 14.5 V, respectively. On-off current ratio is nearly 103.

Binding Energies of Excitons in Square Quantum-Well Wires in the Presence of a Magnetic Field
ZHANG Ying-Tao, DI Bing, XIE Zun, LI You-Cheng,
Chin. Phys. Lett. 2004, 21 (1): 166-169 .  
Abstract   PDF(pc) (424KB) ( 412 )
The binding energies of the ground state of excitons in the GaAs/Ga1-xAlxAs square quantum-well wire in the presence of a magnetic field are investigated by using the variational method. It is assumed that the magnetic field is applied parallel to the axis of the wire. The calculations of the binding energy as a function of the wire size have been performed for infinite and finite confinement potentials. The contribution of the magnetic field makes the binding energy larger obviously, particularly for the wide wire, and the magnetic field is much more pronounced for the binding energy in a square quantum wire than that in a cylindrical quantum wire. The mismatch of effective masses between the well and the barrier is also considered in the calculation.

Surface States in the AlxGa1-xN Barrier in AlxGa1-xN/GaN Heterostructures
LIU Jie, SHEN Bo, WANG Mao-Jun, ZHOU Yu-Gang, CHEN Dun-Jun, ZHANG Rong, SHI Yi, ZHENG You-Dou
Chin. Phys. Lett. 2004, 21 (1): 170-172 .  
Abstract   PDF(pc) (334KB) ( 464 )
Frequency-dependent capacitance-voltage (C-V) measurements have been performed on modulation-doped Al0.22Ga0.78N/GaN heterostructures to investigate the characteristics of the surface states in the AlxGa1-xN barrier. Numerical fittings based on the experimental data indicate that there are surface states with high density locating on the AlxGa1-xN barrier. The density of the surface states is about 1012cm-2eV-1, and the time constant is about 1 μs. It is found that an insulating layer (Si3N4) between the metal contact and the surface of AlxGa1-xN can passivate the surface states effectively.

Thermal Stability and Spectroscopic Properties of Yb:Zinc-Tungsten-Tellurite Glass
WANG Guo-Nian, XU Shi-Qing, YANG Jian-Hu, DAI Shi-Xun, ZHANG Jun-Jie, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2004, 21 (1): 173-175 .  
Abstract   PDF(pc) (264KB) ( 519 )
New multi-component Yb:zinc--tungsten--tellurite glasses (70TeO2-(20-x) ZnO-xWO3-5La2O3-2.5 K2O-2.5Na2O-1.0 Yb2O3 (x = 0, 15 mol%) have been presented. Thermal stability and spectroscopic properties of Yb3+ ions have been measured. The results show that TZW2 glass (x = 15 mol%) has thermal stability (Tx - Tg > 160°C with Tx being the onset crystallization temperature and Tg the glass transition temperature) better than TZN glass and that the stimulated emission cross-section of 1.32 pm2 for the 2F5/22F7/2 transition is higher than other laser glasses (QX, ADY, LY and FP), with the measured fluorescence lifetime of 0.93 ms and the broad fluorescence effective linewidth of 74.5 nm. Evaluated from the good potential laser parameters, TZW2 glass with both the minimum pump intensity (0.92 kW/cm2) and gain parameter (1.23 pm2ms) is promising for miniature solid fibre lasers or high-peak power lasers, as well as tunable lasers.

Composition Dependence of Spectroscopic Properties of Er3+ Doped TeO2-WO3-ZnO Glasses
LI Jia-Cheng, LI Shun-Guang, HU He-Fang, GAN Fu-Xi
Chin. Phys. Lett. 2004, 21 (1): 176-178 .  
Abstract   PDF(pc) (366KB) ( 494 )
Er3+-doped TeO2-WO3-ZnO glasses were prepared and the absorption spectra, emission spectra and fluorescence lifetimes were measured. With more TeO2 content in the glasses, the emission full width at half maximum (FWHM) increases while the lifetime of the 4I13/2level of Er3+ decreases. The stimulated emission cross-section of Er3+ calculated by the McCumber theory is as large as 0.86 pm2. The product of the FWHM and the emission cross-section σe of Er3+ in TeO2-WO3-ZnO glass is larger than those in other glasses, which indicates that the glasses are promising candidates for Er3+-doped broadband amplifiers. The Judd-Offelt parameter Ω6 shows close composition dependence of the 1.5 μm emission bandwidth. The more the TeO2 content is, the larger the values of Ω6 and FWHM.

Insulator--Metal Transition due to La Doping in Double Perovskite Sr2MnMoO6
LIU Xiao-Jun, HUANG Qiao-Jian, XU Sheng, ZHANG Shu-Yi, LUO Ai-Hua
Chin. Phys. Lett. 2004, 21 (1): 179-182 .  
Abstract   PDF(pc) (441KB) ( 661 )
Resistivity, thermal diffusivity, lattice and magnetic properties of double perovskite Sr2-xLaxMnMoO6 are investigated with systematic change of La doping concentration x from 0.0 to 0.4. The insulator to metal phase transition is observed with increasing x above 0.3, suggesting that the extra electrons via substitution of La3+ for Sr2+ ions occupy mainly the conduction Mo-4d band. According to the insulator to metal phase transition, the thermal diffusivity of Sr2-xLaxMnMoO6 enhances from 0.33 cm2/s at x = 0.0 to 0.49 cm2/s at x = 0.4. We further investigate the La doping effects on the lattice and magnetic properties.

Electronic Phase Diagram of Mixed-Valence Gold Chloride
LIU Xiao-Jun, MORITOMO Yutaka, KOJIMA Norimichi
Chin. Phys. Lett. 2004, 21 (1): 183-186 .  
Abstract   PDF(pc) (429KB) ( 379 )
A comprehensive electronic phase diagram is derived for mixed- valence gold chloride Cs2Au2Cl6 by means of high-pressure Raman spectroscopy. At all the temperatures investigated (100 K ≤ T ≤ 300 K), applications of pressure induce a phase transition from the mixed-valence (MV) state to a single-valence (SV) state. In the SV state, a broad Au-Cl stretching band appears at ~ 400cm-1 below ~ 200 K. We have interpreted the appearance of the band in terms of formation of the AuX-2-like local lattice distortion, or the bipolarons.

Structure and Physical Properties and Charge Ordering in La2-xSrxMnO4 (1.125 ≤ x ≤ 2.0)
FENG Zhen-Jie, DONG Cheng, LI Zhi-Chao, LI Jian-Qi
Chin. Phys. Lett. 2004, 21 (1): 187-190 .  
Abstract   PDF(pc) (531KB) ( 447 )
Structural measurements have revealed nonlinear changes of lattice parameters in the layered-perovskite manganites La2-xSrxMnO4 with increasing Sr content; these changes can be well understood by means of interactions among the charge, crystal lattice and the orbital degree of freedom in this strongly correlated system. A probably spin-glass transition was detected for the first time in the x = 1.75 sample at the temperature of around 44 K. Fundamental properties of charge ordering appearing in the range of 1.5 ≤ x ≤ 1.75 have been observed at low-temperatures and are interpreted in terms of the Mn3+-dz2 orbital ordering.

Magnetic Agglomeration Among Nd-Fe-B Particles and Its Influence on Field Aligning
HE Ye-Qing, WANG Zhen-Xi, ZHOU Shou-Zeng, ZHANG Zhen-Rong, HAN Bao-Shan
Chin. Phys. Lett. 2004, 21 (1): 191-193 .  
Abstract   PDF(pc) (327KB) ( 590 )
There exists strong magnetic agglomeration among Nd-Fe-B particles. Due to this effect, an applied field even up to 1350 kAm-1 still can not make the loose Nd-Fe-B powders to reach saturated magnetization. SEM images of a little amount of Nd-Fe-B powders were used to illustrate the agglomeration phenomenon. We believe that the general existence of misalignment grains in the magnetic force images of the sintered Nd-Fe-B magnet fabricated by die pressing with 1500 kAm-1 aligning field is a confirmation of the magnetic agglomeration.

Fronts of Stress Waves in Anisotropic Piezoelectric Media
LIU Ying, LIU Kai-Xin, GAO Ling-Tian
Chin. Phys. Lett. 2004, 21 (1): 194-196 .  
Abstract   PDF(pc) (249KB) ( 390 )
The characteristic of wave fronts in anisotropic piezoelectric media is analysed by adopting the generalized characteristic theory. Analytical expressions for wave velocities and wave fronts are formulated. Apart from the ordinary characteristics, a new phenomenon, energy velocity funnel, is formed on the wave fronts of quasi-transverse waves in anisotropic piezoelectric materials. A three-dimensional representation of wave fronts in anisotropic piezoelectric materials is given for a better understanding of the new phenomena.
Coherent Excitonic Wavepackets in Two-Dimensional Square Dot Arrays Driven by an In-Plane Uniform Electric Field
LI Xiu-Ping, YAN Wei-Xian,
Chin. Phys. Lett. 2004, 21 (1): 197-200 .  
Abstract   PDF(pc) (619KB) ( 593 )
We investigate the evolution behaviour of electron-hole pair wavepacket in optically excited square quantum-dot arrays driven by in-plane (x-y plane) uniform electric field E (viz, E = Exex + Eyey, ex, ey are unit vectors along x and y directions respectively), in the time domain. It is found that if the ratio of the x-component electric field Ex to the y-component electric field Ey is a rational p/q (p and q being coprime integer numbers), the wavepackets undergo a time-periodic breathing mode, with the period 2πp/ωBx, where ωBx = eExa/ħ, with a being the lattice constant of square dot arrays, ħ being Planck's constant, e being the electron charge. This finding provides a time-domain demonstration of the recent spectral result [Phys. Rev. Lett. {86} (2001) 3116].
Influence of Inert Gas Pressure on Growing Rate of Nanocrystalline Silicon Film Prepared by Pulsed Laser Deposition
WANG Ying-Long, FU Guang-Sheng, PENG Ying-Cai, ZHOU Yang, CHU Li-Zhi, ZHANG Rong-Mei
Chin. Phys. Lett. 2004, 21 (1): 201-202 .  
Abstract   PDF(pc) (292KB) ( 638 )
Nanocrystalline silicon film (nc-Si) was prepared by pulsed laser deposition in different inert gas atmospheres such as He, Ne and Ar. The influence of inert gas pressure on growing rate of the film was investigated. The results show that with increasing gas pressure, growing rate first increases and reaches its maximum and then decreases; the gas pressure at the maximum of growing rate is proportional to the reciprocal of atomic mass of gas. The rate maximum is 0.315 Å/pulse when He gas pressure is 8.3 Pa. The dynamic process is analysed theoretically by means of resputtering from the film surface and scattering of ablated particles. Furthermore, our results are compared with those in the case of Ag target.
Field Emission from Silicon Nanocrystallite Films with Compact Alignment and Uniform Orientation
YU Ke, WANG Wei-Ming, ZHU Zi-Qiang, ZHANG Yong-Sheng, YU Xian-Wen, CHEN Shao-Qiang, LI Qiong, YANG Guang-Da, ZHU Jian-Zhong, CHEN Qun, LU Wei, ZI Jian
Chin. Phys. Lett. 2004, 21 (1): 203-206 .  
Abstract   PDF(pc) (533KB) ( 480 )
Patterned silicon nanocrystallite (SiNC) films were fabricated on (100) orientation p-type boron-doped silicon wafer by the hydrogen ion implantation technique and the anodic etching method. The efficient field emission with low turn-on field of about 3.5 V/μm at current density of 0.1 μA/cm2 was obtained. The emission current density from the SiNC films reached 1 mA/cm2 under a bias field of about 9.1 V/μm. The experimental results demonstrate that there are great potential applications of the SiNC films for flat panel displays. A surface treatment with hydrogen plasma was performed on the SiNC films and a significant improvement of emission properties was achieved.

Heterogeneous Nucleation and Solidification Prediction of Sn-5wt.%Pb Droplets
TIAN Ya-Li, WU Ping, JIANG En-Yong, ANDO Teiichi
Chin. Phys. Lett. 2004, 21 (1): 207-210 .  
Abstract   PDF(pc) (448KB) ( 657 )
We develop a model for heterogeneous nucleation catalyzed by oxidation on the droplet surface and the internal nucleation similar to surface oxidation. The fraction covered by oxide on the surface of the droplet is calculated as a function of time and temperature based on the chemical reaction dynamic and transition state theory, which is a reasonable expression for the oxidation behaviour of Sn-5wt.%Pb droplets. The continuous-cooling-transformation curves were computed using the above experimental results under the heterogeneous surface nucleation and the internal nucleation of droplets. Also, we predict the solidification behaviour of the droplet in gas-atomized spraying process using this model. The same model can be applied to predict the nucleation behaviour for any type of cooling schedule.
Growth and Form in Biology: Generation of the Plant Morphology by Spontaneous Symmetry Breaking Based on a Pressure Field
WENG Yu-Xiang
Chin. Phys. Lett. 2004, 21 (1): 211-214 .  
Abstract   PDF(pc) (366KB) ( 466 )
Considering the role of mechanical forces playing in the morphogenetic pattern formation, we propose a second-order differential equation for the growth and form of plants based on the turgor pressure field at the organ and cellular level. The solutions can well describe various kinds of morphological features of flowers under certain hypotheses. The plant morphology is considered as the spontaneous symmetry breaking of a circular growing boundary, while the employed hypotheses are subjected to further experimental confirmation.
Stability of the Distribution in a Money Exchange Model
YANG Chun-Bin
Chin. Phys. Lett. 2004, 21 (1): 215-218 .  
Abstract   PDF(pc) (307KB) ( 441 )
A nonlinear money exchange model is revised and a correct master equation is derived. The evolution of the distribution is studied from direct numerical and analytical calculations. The stability of the final steady state of the system is investigated. It is argued that the final distribution is valid for a group of conservative money exchange models.

64 articles