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Volume 23 Issue 11
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Original Articles
Solution of Gauss--Codazzi Equation with Applications in the Tzitzeica Equation
ZHU Jun-Yi, GENG Xian-Guo
Chin. Phys. Lett. 2006, 23 (11): 2885-2887 .  
Abstract   PDF(pc) (200KB) ( 719 )
The surface in R3 associated with the Tzitzeica equation is considered. By curvature coordinate ransformation and surface imbedding, the Gauss--Codazzi equation is presented. Resorting to the solutions of the Gauss--Codazzi equation, the solution of the Tzitzeica equation is obtained under a restrictive condition.
Effects of Anisotropy on Pair-wise Entanglement of a Four-Qubit Heisenberg
CAO Min, ZHU Shi-Qun
Chin. Phys. Lett. 2006, 23 (11): 2888-2891 .  
Abstract   PDF(pc) (323KB) ( 532 )
The pair-wise thermal entanglement in a four-qubit Heisenberg XXZ chain is investigated to study the role of anisotropy when an external magnetic field is included. It is found that pair-wise entanglement is absent between nearest- and next-nearest neighbouring qubits with anisotropic parameter Δ ≤ -1. For two nearest-neighbouring qubits, increasing the parameter can not only induce the entanglement, but also extend the entanglement region in terms of magnetic field B and temperature T. For two next-nearest-neighbouring qubits, increasing anisotropic parameter can shift the location of the entanglement and control the extent of the entanglement in terms of magnetic field at a finite temperature.
Quantum Fluctuations of Current and Voltage for Mesoscopic Quartz Piezoelectric Crystal at Finite Temperature
LI Hong-Qi, XU Xing-Lei, WANG Ji-Suo
Chin. Phys. Lett. 2006, 23 (11): 2892-2895 .  
Abstract   PDF(pc) (202KB) ( 542 )
The mesoscopic quartz piezoelectric crystal equivalent circuit is quantized by the method of damped harmonic oscillator quantization. It is shown that the quantum fluctuations of voltage and current of each loop are related to not only the equivalent circuit inherent parameter and squeezing parameter, but also the temperature, and decay according to exponent along with time in the thermal vacuum state, the thermal coherent state and the thermal squeezed state.
Efficient Quantum Cryptography Network without Entanglement and Quantum Memory
LI Chun-Yan, LI Xi-Han, DENG Fu-Guo, , ZHOU Ping, LIANG Yu-Jie, ZHOU Hong-Yu,
Chin. Phys. Lett. 2006, 23 (11): 2897-2899 .  
Abstract   PDF(pc) (242KB) ( 533 )
An efficient quantum cryptography network protocol is proposed with $d$-dimensional polarized photons, without resorting to entanglement and quantum memory. A server on the network, say Alice, provides the service for preparing and measuring single photons whose initial state are |0>. The users code the information on the single photons with some unitary operations. To prevent the untrustworthy server Alice from eavesdropping the quantum lines, a nonorthogonal-coding technique is used in the process that the quantum signal is transmitted between the users. This protocol does not require the servers and the users to store the quantum states and almost all of the single photons can be used for carrying the information, which makes it more convenient for application than others with present technology. We also discuss the case with a faint laser pulse
Teleportation of Multi-qudit Entangled States
ZHAN Xiao-Gui, LI Hong-Mei, ZENG Hao-Sheng
Chin. Phys. Lett. 2006, 23 (11): 2900-2902 .  
Abstract   PDF(pc) (203KB) ( 591 )
We propose a method to realize the teleportation of an unknown entangled state that consists of many qudits through a partially entangled-qudit quantum channel with the help of 2\log2d-bit classical communication. The operations used in the teleportation process include a generalized Bell-state measurement and a series of single-qudit π-measurements performed by Alice, a series of generalized qudit-Pauli gates and two-level unitary gates, as well as a qubit measurement performed by Bob. For a maximally entangled quantum channel, the successful probability of the teleportation becomes unit.
Exploring Extra Dimensions in Spectroscopy Experiments
LUO Feng, LIU Hong-Ya
Chin. Phys. Lett. 2006, 23 (11): 2903-2905 .  
Abstract   PDF(pc) (210KB) ( 405 )
We propose an idea in spectroscopy to search for extra spatial dimensions as well as to detect the possible deviation from Newton’s inverse-square law at small scale, and we take high-Z hydrogenic systems and muonic atoms as illustrations. The relevant experiments might help to explore a more than two extra dimensions scenario in the brane world model proposed by Arkani-Hamed, Dimopoulos, Dvali (ADD) and to set constraints for fundamental parameters such as the size of extra dimensions.
Dynamical Properties of Potassium Ion Channels with a Hierarchical Model
ZHAN Yong, AN Hai-Long, YU Hui, ZHANG Su-Hua, HAN Ying-Rong
Chin. Phys. Lett. 2006, 23 (11): 2906-2908 .  
Abstract   PDF(pc) (215KB) ( 592 )
It is well known that potassium ion channels have higher permeability than K ions, and the permeable rate of a single K ion channel is about 108 ions per second. We develop a hierarchical model of potassium ion channel permeation involving ab initio quantum calculations and Brownian dynamics simulations, which can consistently explain a range of channel dynamics. The results show that the average velocity of K ions, the mean permeable time of K ions and the permeable rate of single channel are about 0.92nm/ns, 4.35ns and 2.30× 108ions/s, respectively.
Synchronizing Complex Networks by an Adaptive Adjustment Mechanism
BU Shou-Liang, ZHANG You-Wei, WANG Bing-Hong,
Chin. Phys. Lett. 2006, 23 (11): 2909-2912 .  
Abstract   PDF(pc) (276KB) ( 528 )
We propose an adaptive adjustment mechanism for synchronizing complex networks, in particular for sociological or/and biological systems. We do not take it for granted that a dynamical system is put on isolated nodes and they are coupled with each other by one (or more) variable(s), as employed in most previous models. As a replacement, we suppose that each node may have any finite number of possible states, and their evolutions with time are determined by their nearest-neighbouring (or even second-nearest-neighbouring, etc) nodes in an adaptive adjustment mechanism. It is found that synchronization can be achieved for almost all connected networks and that the scale-free property can evidently improve the synchronizing speed.
Calculation of Elastic Constants of Ag/Pd Superlattice Thin Films by Molecular Dynamics with Many-Body Potentials
GAO Ning, LAI Wen-Sheng
Chin. Phys. Lett. 2006, 23 (11): 2913-2916 .  
Abstract   PDF(pc) (259KB) ( 570 )
The calculation of elastic constants of Ag/Pd superlattice thin films by molecular dynamics simulations with many-body potentials is presented. It reveals that the elastic constants C11 and C55 increase with decreasing modulation wavelength Λ of the films, which is consistent with experiments. However, the change of C11 and C55 with Λ is found to be around the values determined by a rule of mixture using bulk elastic constants of metals. No supermodulus effect is observed and it is due to cancellation between enhanced and reduced contributions to elastic constants from Ag and Pd layers subjected to compressive and tensile strains, respectively.
In-Situ Conductivity Measurement of BaF2 under High Pressure and High Temperature
HAO Ai-Min, GAO Chun-Xiao, LI Ming, HE Chun-Yuan, HUANG Xiao-Wei, ZHANG Dong-Mei, YU Cui-Ling, ZOU Guang-Tian, LI Yan-Chun, LI Xiao-Dong, LIU Jing
Chin. Phys. Lett. 2006, 23 (11): 2917-2919 .  
Abstract   PDF(pc) (235KB) ( 459 )
We perform the in-situ conductivity measurement on BaF2 at high pressure using a microcircuit fabricated on a diamond anvil cell. The results show that BaF2 initially exhibits the electrical property of an insulator at pressure below 25GPa, it transforms to a wide energy gap semiconductor at pressure from 25 to 30GPa, and the conductivity increases gradually with increasing pressure from 30GPa. However, the metallization predicted by theoretical calculation at 30--33GPa cannot be observed. In addition, we measure the temperature dependence of the conductivity at several pressures and obtain the relationship between the energy gap and pressure. Based on the experimental data, it is predicted that BaF2 would transform to a metal at about 87GPa and ambient temperature. The conductivity of BaF2 reaches the order of 10-3\Omega-1cm-1 at 37GPa and 2400K, the superionic conduction is not observed during the experiments, indicating the application of pressure elevates greatly the transition temperature of the superionic conduction.
Stabilization and Consistency for Subtracted and Unsubtracted QCD Sum Rules for 0++ Scalar Glueball
ZHANG Zhen-Yu, LIU Jue-Ping
Chin. Phys. Lett. 2006, 23 (11): 2920-2923 .  
Abstract   PDF(pc) (251KB) ( 450 )
Based on a semi-classical expansion for quantum chromodynamics in the instanton liquid background, the correlation function of the 0++ scalar glueball current is calculated. Besides the pure classical and quantum contributions, the contributions arising from the interactions between the classical instanton fields and quantum gluon ones come into play. It turns out that the latter contributions have a great role not only in making the stabilization of the subtracted and unsubtracted Laplace-transformed QCD sum rules for 0++ scalar glueball, but also in bring back the consistency between the two related sum rules, or equivalently between the QCD asymptotic expression and low energy theorem. The result for the scalar glueball mass is predicted to be mG=1.35GeV.
Symmetry and Conserved Quantity of Tzénoff Equations for Holonomic Systems with Redundant Coordinates
ZHENG Shi-Wang, XIE Jia-Fang, JIA Li-Qun
Chin. Phys. Lett. 2006, 23 (11): 2924-2927 .  
Abstract   PDF(pc) (215KB) ( 331 )
A holonomic system with redundant coordinates can be expressed in Tzénoff equations. We concentrate on the symmetry for these Tzénoff equations under the infinitesimal transformations of groups. The notions are given for both Mei symmetry and Lie symmetry of the Tzénoff equations for holonomic system with redundant coordinates. The determination equations of symmetries for these systems have been obtained and the sufficient and necessary conditions for deriving Lie symmetries from Mei symmetries are proposed. It is shown that Hojman conserved quantities can be found from a special Lie symmetry or a Lie symmetry derived from Mei symmetry for the Tzénoff equations of holonomic systems with redundant coordinates.
Finite Temperature Casimir Effect for Corrugated Plates
ZHAO Yan, SHAO Cheng-Gang, LUO Jun
Chin. Phys. Lett. 2006, 23 (11): 2928-2931 .  
Abstract   PDF(pc) (259KB) ( 444 )
Using the path-integral method, the corrections to the Casimir energy due to the combined effect of surface roughness and the finite temperature are calculated. For the specific case of two sinusoidally corrugated plates, the lateral Casimir force at finite temperature is obtained. The amplitude of the lateral Casimir force has a maximum at an optimal wavelength of λ \ap 2H with the mean plate distance H. This optimal parameter relation is almost independent of temperature.
Regular Magnetic Monopole from Generalized ’t Hooft Tensor
DUAN Yi-Shi, WU Shao-Feng
Chin. Phys. Lett. 2006, 23 (11): 2932-2935 .  
Abstract   PDF(pc) (228KB) ( 412 )
It is well known that ’t Hooft--Polykov magnetic monopole regularly realizes the Dirac magnetic monopole in terms of a two-rank tensor, i.e. the so-called ’t Hooft tensor in three-dimensional space, which has been generalized to all even rank ones. We propose an arbitrary odd rank ’t Hooft tensor, which universally determines the quantized low-energy boundaries of the even dimensional Georgi--Glashow models under asymptotic conditions. Furthermore, the dual magnetic monopole theory is built up in terms of the Ф-mapping theory.
Effects of Distorted Wave on Proton Elastic Scattering from Light Nuclei at 200MeV
GU Bai-Ping, MAO Ying-Chen
Chin. Phys. Lett. 2006, 23 (11): 2936-2939 .  
Abstract   PDF(pc) (260KB) ( 718 )
The distorted wave is introduced into the relativistic impulse approximation to generate the Dirac optical potentials for proton elastic scattering. Those potentials, produced by folding the target ground state wavefunction with the free nucleon-nucleon interactions, are used to reevaluate scattering observables, such as differential cross section, analysing power and spin rotation function, for proton elastic scattering from 12C and 16O at Elab= 200MeV, respectively. The inclusion of the distorted wave in the original relativistic impulse approximation has brought out better results of the observables, especially at small scattering angles.
Fission Barrier for 240Pu in the Quadrupole Constrained Relativistic Mean Field Approach
Lü Hong-Feng, GENG Li-Sheng, MENG Jie
Chin. Phys. Lett. 2006, 23 (11): 2940-2943 .  
Abstract   PDF(pc) (623KB) ( 725 )
The fission barrier for 240Pu is investigated beyond the second saddle point in the potential energy surface by the constrained relativistic mean field method with the newly proposed parameter set PK1. The microscopic correction for the centre-of-mass motion is essential to provide the correct potential energy surface. The shell effects that stabilize the nuclei against the fission is also investigated by the Strutinsky method. The shapes for the ground state, fission isomer and saddle-points, etc, are studied in detail.
Strong Self-Similar Fluctuations of Target Fragments in Ring-like Events in Ultra-Relativistic Nuclear Collision
Dipak Ghosh, Argha Deb, Samabrata Sarkar, Prabir Kumar Haldar
Chin. Phys. Lett. 2006, 23 (11): 2944-2947 .  
Abstract   PDF(pc) (243KB) ( 494 )
The intermittent fluctuation of target evaporated particles is studied in both ring-like and jet-like events emitted in 32S--emulsion interactions at 200AGeV within the framework of multi-dimensional factorial moment methodology using the concept of the Hurst exponent. It is observed that the intermittent fluctuation in the ring-like event is self-similar, whereas in the jet-like event fluctuation is self-affine. However, study indicates that the strength of fluctuation in the ring-like events is much stronger than that in the jet-like events.
Autocorrelation Function of Hydrogen Atoms in Magnetic Fields
YU Yong-Li, ZHAO Xia, LI Hong-Yun, GUO Wen-Hao, LIN Sheng-Lu
Chin. Phys. Lett. 2006, 23 (11): 2948-2951 .  
Abstract   PDF(pc) (219KB) ( 528 )
The autocorrelation function is an important quantity that can reflect the dynamical properties of the Rydberg wave packet and can be measured in experiments. Applying time-dependent perturbation theory and rotating wave approximation, we derive the autocorrelation function of the double-pulse laser describing the evolution of a Rydberg wave packet of ydrogen atoms in magnetic fields. The resulting expression is written as a sum of the modified Gaussian terms. Each Gaussian term comes from a parent semiclassical closed orbit. It provides a direct explanation and experimentally controllable measurement scheme, which allows us therefore to recognize the closed orbit and to determine its returning time in high precision.
Atom Lithography with a Chromium Atomic Beam
ZHANG Wen-Tao, LI Tong-Bao
Chin. Phys. Lett. 2006, 23 (11): 2952-2955 .  
Abstract   PDF(pc) (532KB) ( 599 )
Direct write atom lithography is a new technique in which resonant light is used to pattern an atomic beam and the nanostructures are formed when the atoms deposit on the substrate. We design an experiment setup to fabricate chromium nanolines by depositing an atomic beam of 52Cr through an off-resonant laser standing wave with the wavelength of 425.55nm onto a silicon substrate. The resulting nanolines exhibit a period of 215±3nm with height of 1nm.
Energetic Protons Emitted from Coulomb Explosion Dynamics of Large-Sized Hydrogen Clusters Driven by an Ultrashort Intense Laser Pulse
LI Hong-Yu, LIU Jian-Sheng, WANG Cheng, NI Guo-Quan, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2006, 23 (11): 2956-2959 .  
Abstract   PDF(pc) (235KB) ( 470 )
Protons with very high kinetic energy of about 10keV and the saturation effect of proton energy for laser intensity have been observed in the interaction of an ultrashort intense laser pulse with large-sized hydrogen clusters. Including the cluster-size distribution as well as the laser-intensity distribution on the focus spot, the theoretical calculations based on a simplified Coulomb explosion model have been compared with our experimental measurements, which are in good agreement with each other.
Holographic Grating Formation in Cationic Photopolymers with Dark Reaction
WEI Hao-Yun, CAO Liang-Cai, GU Claire, XU Zhen-Feng, HE Ming-Zhao, HE Qing-Sheng, HE Shu-Rong, JIN Guo-Fan
Chin. Phys. Lett. 2006, 23 (11): 2960-2963 .  
Abstract   PDF(pc) (332KB) ( 436 )
We propose a new formula to describe the dynamics of holographic grating formation under low intensity pulse exposures in cationic photopolymers, in which the dark reaction contributes dominantly to the grating strength. The formula is based on the living polymerization mechanism and the diffusion-free approximation. The analytical solution indicates that the grating formation time depends on the termination rate constant, while the final grating strength depends linearly on the total exposure energy. These theoretical predictions are verified experimentally using the Aprilis HMC-400μm photopolymer. The results can provide guidelines for the control and optimization of the holographic recording conditions in practical applications.
Entangled States Based on Two Coherent States 3π/2 out of Phase
AHMAD Muhammad Ashfaq, LIU Shu-Tian
Chin. Phys. Lett. 2006, 23 (11): 2964-2967 .  
Abstract   PDF(pc) (215KB) ( 453 )
Entangled states based on two coherent states 3π/2 out of phase with each other, i.e. |α> and
e|-iα>, as well as on a special state with a relative phase Ф=|α|2, are constructed. By analysing the amount of entanglement it is evident that entangled states based on this special state can be used as an excellent resource for quantum teleportation. It is also revealed that these entangled states possess some nonclassical features.
High-Duty-Cycle Operation of GaAs/AlGaAs Quantum Cascade Laser above Liquid Nitrogen Temperature
LIU Jun-Qi, LIU Feng-Qi, SHAO Ye, LI Lu, GUO Yu, WANG Zhan-Guo, WANG Liang-Chen
Chin. Phys. Lett. 2006, 23 (11): 2968-2971 .  
Abstract   PDF(pc) (849KB) ( 595 )
We present a detailed study of λ ~ 9.75μm GaAs/AlGaAs quantum cascade lasers. For a coated 2-mm-long and 40-μm-wide laser, an optical power of 85μW is observed at 95% duty cycle at 80K. At a moderate driving pulse (1kHz and 1% duty cycle), the device presents a peak power more than 20mW even at 120K. At 80K, the fitted result of threshold current densities shows evidence of potential cw operation.
A Low-Pump-Threshold Photonic Crystal Fibre Raman Laser
YAN Pei-Guang, RUAN Shuang-Chen, GUO Chun-Yu, YU Yong-Qin, SU Hong, LIU Cheng-Xiang
Chin. Phys. Lett. 2006, 23 (11): 2972-2973 .  
Abstract   PDF(pc) (245KB) ( 589 )
We investigate a photonic crystal fibre Raman laser using fibre Bragg grating pairs as cavity mirrors. The threshold pump power is up to 0.65W by decreasing the cavity loss and using a photonic crystal fibre with high Raman gain coefficient. A maximum continuous-wave output power of 2.7W is obtained at the maximum incident pump power of 5.6W. The corresponding optical conversion efficiency and the slope efficiency are about 48% and 56%, respectively.
Laser Feedback Technique for Precise Retardation Measurements
FEI Li-Gang, ZHANG Shu-Lian
Chin. Phys. Lett. 2006, 23 (11): 2974-2977 .  
Abstract   PDF(pc) (219KB) ( 514 )
A simple and precise retardation measurement based on laser feedback is demonstrated. The measurement principle is based on polarization flipping induced by optical feedback from an external birefringence cavity. The measured wave plate is located in the external cavity. When the length of the external cavity is tuned, the polarization states of laser will flip between two eigenstates, and the position of polarization flipping in one period of intensity modulation will vary with retardation of the wave plate. The duty ratio of two eigenstates is used to determine the retardation. Main advantages of the technique are that it is compact, low cost, fast and flexible. Especially, it is insensitive to a fluctuation of laser intensity and is suitable for on-line measurement. The experimental results have shown that the measurement uncertainty is better than 0.03° in the range 30°--150°
Numerical Investigation of Thermal Effect in Plasma Electrode Pockels Cell for High Average Power
CAO Ding-Xiang, ZHANG Xiong-Jun, ZHENG Wan-Guo, HE Shao-Bo, SUI Zhan
Chin. Phys. Lett. 2006, 23 (11): 2978-2981 .  
Abstract   PDF(pc) (427KB) ( 438 )
The average power of a Pockels cell is limited by thermal effects arising from the optical absorption of the laser pulse. These thermal effects can be managed by configuring the switch as a plasma-electrode thin plate Pockels cell, which works under heat-capacity operation. Simulation results show that, based on KD*P (in thickness 0.5cm) at an average power loading of 1kW, the aperture integrated depolarization loss at 1.06um is less than 10% in 5min working time.
Simulation of Patterns and Qualitative Analysis of Pattern Rotation in an End-Pumped Nd:YVO4 Laser
HAN Ke-Zhen, PAN Shu-Di, FAN Xiu-Wei, HUANG Hai-Tao, HE Jing-Liang
Chin. Phys. Lett. 2006, 23 (11): 2982-2984 .  
Abstract   PDF(pc) (901KB) ( 470 )
We simulate some laser output patterns observed in our previous experiment employing superposition of Laguerre--Gaussian modes. The rotating pattern is qualitatively analysed from the point of contemporary spatial burning hole effect of the lasing crystal.
Stimulated Raman Scattering of a Modulated Laser Beam in Air: a Perturbation Approach
WEI Xiao-Hong, QIAN Lie-Jia, LI Ke-Yu, ZHU He-Yuan, FAN Dian-Yuan
Chin. Phys. Lett. 2006, 23 (11): 2985-2988 .  
Abstract   PDF(pc) (234KB) ( 665 )
Stimulated Raman scattering (SRS) of a third-harmonic beam of a high-power laser in air is analysed by using a perturbation approach. It is found that intensity modulations of the third-harmonic beam, resulting from the surface ripple of nonlinear crystal, can be significantly enhanced due to SRS, and the gain of instability increases with the spatial period of modulation. Numerical simulations based on the nonlinear coupled-wave equations verify the validity of the perturbation approach.

Nonlinear Optical Response of nc-Si-SiO2 Films Studied with Femtosecond Four-Wave Mixing Technique
GUO Heng-Qun, WANG Qi-Ming
Chin. Phys. Lett. 2006, 23 (11): 2989-2992 .  
Abstract   PDF(pc) (227KB) ( 623 )
Nonlinear optical properties of silicon nanocrystals (nc-Si) embedded in SiO2 films are investigated using time-resolved four-wave mixing technique with a femtosecond laser. The off-resonant third-order nonlinear susceptibility X(3) is observed to be 1.3×10-10esu at 800nm. The relaxation time of the film is fast as short as 50fs. The off-resonant nonlinearity is predominantly electronic in origin and enhanced due to quantum confinement.
Ultra-Broadened Supercontinuum Generation in a Novel Dispersion-Flattened and Decreasing Fibre
CHEN Yong-Zhu, LI Yu-Zhong, QU Gui, XU Wen-Cheng
Chin. Phys. Lett. 2006, 23 (11): 2993-2995 .  
Abstract   PDF(pc) (260KB) ( 523 )
A new approach is introduced to enhance supercontinuum (SC) spectrum in a dispersion-flattened/decreasing fibre with a convex dispersion profile. A flat SC spectrum nearly extending from 1200nm to 2100nm can be generated based on this scheme. It is found that group-velocity dispersions (GVD) and self-phase modulation (SPM) effects are the primary factors for pump pulse compression and SC spectrum generation, stimulated Raman scattering (SRS) effect plays an essential role on the final SC-spectrum bandwidth and flatness, but self-steepening effect can be ignored.

Broadband Near-Infrared Emission from Transparent Ni2+-Doped Sodium Aluminosilicate Glass Ceramics
ZHOU Shi-Feng, FENG Gao-Feng, XU Shi-Qing, WU Bo-Tao, QIU Jian-Rong
Chin. Phys. Lett. 2006, 23 (11): 2996-2998 .  
Abstract   PDF(pc) (234KB) ( 964 )
Broadband near-infrared emission from transparent Ni2+-doped sodium aluminosilicate glass-ceramics is observed. The broad emission is centred at 1290nm and covers the whole telecommunication wavelength region (1100--1700nm) with full width at half maximum of about 340nm. The observed infrared emission could be attributed to the 3T2(F) → 3A2(F) transition of octahedral Ni2+ ions that occupy high-field sites in nanocrystals. The product of the lifetime and the stimulated emission cross section is 2.15×10-24cm2s. It is suggested that Ni2+-doped sodium aluminosilicate glass ceramics have potential applications in tunable broadband light sources and broadband amplifiers.
Structure Dependence of Mode Edges in Photonic Crystal Waveguide with Silicon on Insulator
TANG Hai-Xia, ZUO Yu-Hua, YU Jin-Zhong, WANG Qi-Ming
Chin. Phys. Lett. 2006, 23 (11): 2999-3002 .  
Abstract   PDF(pc) (442KB) ( 490 )
The mode edges of photonic crystal waveguide with triangular lattice based on a silicon-on-insulator slab are investigated by combination of the effective index method and the two-dimensional plane wave expansion method. The variations of waveguide-mode edges with the structure parameters of photonic crystal are deduced. When the ratio of the radius of air holes to the lattice constant, r/Λ, is fixed and the lattice constant of photonic crystal, Λ, increases, the waveguide-mode edges shift to longer wavelengths. When Λ is fixed and r/Λ increases, the waveguide-mode edges shift to shorter wavelengths. Additionally, when r/Λ and Λ are both fixed, the radius of the two-row air holes adjacent to the waveguide increases, the waveguide-mode edges shift to shorter wavelengths.

Modified Richardson Number in Non-Uniform Saturated Moist Flow
YANG Shuai, GAO Shou-Ting
Chin. Phys. Lett. 2006, 23 (11): 3003-3006 .  
Abstract   PDF(pc) (677KB) ( 474 )
As a useful index, i.e. the Richardson number Ri, is modified in non-uniform saturated moist flow, based on the fact that liquid water is partially dropped out in parcel air. This is more realistic in real moist atmosphere, especially in the rainfall process. The modified Ri presents adequately the influence of numerator, i.e. Brunt--Vaisala frequency (BVF), on instability. Compared to several former formulae generalized by Durran and Klemp, the modified Ri evidently decreases the stability in rainy regions. In theory, the modified BVF and Ri fix the discontinuity of latent heat release in the transition areas between saturated and unsaturated air by introducing the condensation probability function. Furthermore, the diagnostic analysis of the modified Ri validates the rationality of its application in the non-uniform sturated moist process.

Nonlinear Interaction and Coherent Structure in Tokamak Plasma Turbulence
DONG Li-Fang, FAN Wei-Li, WANG Hui-Juan, ZHANG Qing-Li, WANG Long
Chin. Phys. Lett. 2006, 23 (11): 3007-3009 .  
Abstract   PDF(pc) (453KB) ( 507 )
The nonlinear interaction in the coherent structure in the CT-6B tokamak plasma turbulence is studied by using the wavelet bicoherence technique. The results show that the coherent structure mainly results from the nonlinear interaction between waves.
Resonant Acceleration of Electrons in Combined Self-Consistent Quasistatic Electromagnetic Fields and Intense Laser Fields
CHEN Fen-Ce, HE Xian-Tu, SHENG Zheng-Mao, QIAO Bin, ZHANG Hong
Chin. Phys. Lett. 2006, 23 (11): 3010-3013 .  
Abstract   PDF(pc) (287KB) ( 374 )
Using the single electron model, the acceleration of electrons in combined circularly polarized intense laser fields and the spontaneous quasistatic fields (including axial and azimuthal magnetic fields, the axial and transverse electric fields) produced in intense laser plasma interaction is investigated analytically and numerically by fitting the proper parameters of the quasistatic fields based on the data from the experiment and numerical calculation. A new resonant condition is given. It is found that the resonance acceleration of electron depends not only on laser field, but also on the bounce frequency oscillating in the quasistatic magnetic field and electric field. The net energy gained by electron does not increase monotonously with axial electric field, but there are some optimal axial electric fields.
Study of Thermal Desorption of Helium from Hydrogenated Zirconium
SUN Wei-Ming, WEI Yu-Cheng, SHI Li-Qun
Chin. Phys. Lett. 2006, 23 (11): 3014-3017 .  
Abstract   PDF(pc) (230KB) ( 835 )
A new method prepared for helium and hydrogen co-containing Zr films is presented to simulate aging metal tritides, in which direct current magnetron sputtering with a He/H/Ar mixture is used. The retained amount and depth profiles of helium and hydrogen are determined by elastic recoil detection analysis. Thermal desorption spectrometry is applied to investigate He thermal release and the effect of hydrogen. It is found that the high-temperature peaks with a large mount of helium release obviously shifted toward lower temperature at high hydrogen concentration, especially at the hydride transformation region, and that the shapes of the release peaks also changed due to the additional hydrogen. However, at the low-temperature releasing region the peak intense decreases when phase transformation takes place. The mechanism of helium thermal release and the effect of hydrogen are also discussed.
Preparation and Microstructure of Tantalum Nitride Thin Film by Cathodic Arc Deposition
LI Li, NIU Er-Wu, LV Guo-Hua, FENG Wen-Ran, GU Wei-Chao, CHEN Guang-Liang, ZHANG Gu-Ling, FAN Song-Hua, LIU Chi-Zi, YANG Si-Ze
Chin. Phys. Lett. 2006, 23 (11): 3018-3021 .  
Abstract   PDF(pc) (453KB) ( 872 )
Tantalum nitride (TaN) thin films are achieved on Si(111) and SS317L substrates by cathodic vacuum arc technique, which is rarely reported in the literature. The crystal structure, composition and surface morphology of the films are characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), auger electron spectroscopy, and atomic force microscopy, respectively. The influence of substrate negative bias on crystal structure, composition, surface morphology of the TaN films is systematically studied. At the substrate bias of 0V and -50V, the amorphous TaN film is obtained. As the bias increases to -100V, cubic TaN phase can be found. Stoichiometric TaN with hexagonal lattice preferred (300) orientation is prepared at a bias of -200V. Combine the XRD and XPS results, the binding energy value of 23.6eV of Ta 4f7/2 is contributed to hexagonal TaN. Compared to other techniques, TaN thin films fabricated by cathodic vacuum arc at various substrate biases show different microstructures.
Liquid Water Structure from Anomalous Density under Ambient Condition
SUN Qiang, ZHENG Hai-Fei
Chin. Phys. Lett. 2006, 23 (11): 3022-3024 .  
Abstract   PDF(pc) (178KB) ( 505 )
From discussion of the structure of liquid water, we deduce that water under ambient condition is mainly composed of ice Ih-like molecular clusters and clathrate-like molecular clusters. The water molecular clusters remain in a state of chemical equilibrium (reversible clustering reactions). This structural model can be demonstrated by quantitative study on anomalous density with increasing temperature at ambient pressure.
Two-Particle Cluster Theory for Biaxial Nematic Phase Based on a Recently Proposed Interaction Potential
ZHANG Zhi-Dong, ZHANG Yan-Jun, SUN Zong-Li
Chin. Phys. Lett. 2006, 23 (11): 3025-3028 .  
Abstract   PDF(pc) (232KB) ( 453 )
Two-particle cluster theory is applied to study the biaxial nematic phase formed by biaxial molecules interacting with a simplified model proposed by Sonnet et al. [Phys. Rev. E 67 (2003) 061701]. For the temperature dependences of the internal energy per particle and of the order parameters, the two-particle theory yields an improved result compared with mean field theory. Concerning the phase diagram, the two-particle theory gives the numerical result in qualitative agreement with the mean field theory.
Effect of Molecular Weight on Liquid Crystal Photoalignment by Photosensitive Polyester Containing Thrifluoromethyl Moieties
FEI Chun-Hong, PENG Zeng-Hui, LV Feng-Zhen, ZHANG Ling-Li, YAO Li-Shuang, XUAN Li
Chin. Phys. Lett. 2006, 23 (11): 3029-3032 .  
Abstract   PDF(pc) (744KB) ( 429 )
We investigate the liquid-crystal (LC) alignment direction on photoalignment films formed from photosensitive polyester containing thrifluoromethyl moieties (PPDA) with various molecular weights by crossed polarized optical microscopy. It is found that LC alignment behaviour changes with molecular weight of PPDA. The LC alignment on PPDA irradiated films with the highest molecular weight is homogeneous, while those with low and intermediate molecular weights are homeotropic. However, surface morphologies show weak dependence on molecular weight. The surfaces are smooth and there is no clear morphological anisotropy on these aligned films observed by an atomic force microscope. The surface energies of the irradiated films are also measured by using an indirect contact-angle method where both surface energy and its polar component increase with increasing molecular weight. Different polar surface energies can be considered as a main reason for different alignment characteristics.


Scaling Behaviour of Diffusion Limited Aggregation with Linear Seed
TANG Qiang, TIAN Ju-Ping, YAO Kai-Lun,
Chin. Phys. Lett. 2006, 23 (11): 3033-3036 .  
Abstract   PDF(pc) (284KB) ( 434 )
We present a computer model of diffusion limited aggregation with linear seed. The clusters with varying linear seed lengths are simulated, and their pattern structure, fractal dimension and multifractal spectrum are obtained. The simulation results show that the linear seed length has little effect on the pattern structure of the aggregation clusters if its length is comparatively shorter. With its increasing, the linear seed length has stronger effects on the pattern structure, while the dimension Df decreases. When the linear seed length is larger, the corresponding pattern structure is cross alike. The larger the linear seed length is, the more obvious the cross-like structure with more particles clustering at the two ends of the linear seed and along the vertical direction to the centre of the linear seed. Furthermore, the multifractal spectra curve becomes lower and the range of singularity narrower. The longer the length of a linear seed is, the less irregular and nonuniform the pattern becomes.


Creep Behaviour of Fe--Mn Binary Alloys
O. Sahin, N. Ucar
Chin. Phys. Lett. 2006, 23 (11): 3037-3040 .  
Abstract   PDF(pc) (403KB) ( 557 )
Tensile creep behaviour of fine-grained Fe--Mn binary alloys containing 0.42--1.21wt.% Mn has been investigated in the temperature range from room temperature to 475K under 10--50MPa. Tensile tests are carried out with a constant cross-head speed under uniaxial load at a strain rate 10-4s-1. Stress exponent and activation energy are determined to clarify deformation mechanism. The obtained variation of steady state creep rate with respect to the applied stress for Fe--Mn binary alloys exhibits two distinct regimes at about 20MPa, indicating a possible change in creep mechanism. The average stress exponent is approximately 2.2, which is a characteristic of grain boundary sliding in the alloys. The activation energy for plastic flow varies from 135 to 92kJ/mol, depending on the Mn content.
Crystal-Orientation Dependent Evolution of Edge Dislocations from a Void in Single Crystal Cu
SONG Zhen-Fei, ZHU Wen-Jun, DENG Xiao-Liang, HE Hong-Liang
Chin. Phys. Lett. 2006, 23 (11): 3041-3044 .  
Abstract   PDF(pc) (408KB) ( 382 )
The micro-void growth by dislocation emission under tensile loading is explored with focus on the influence of crystal orientations. Based on the elastic theory, a dislocation emission criterion is formulated. It is predicted that the preferential location of dislocation nucleation and its threshold stress are dependent on the crystal orientation. Large-scale molecular dynamics (MD) simulations are also performed for single crystal copper to illustrate the dislocation evolution pattern associated with a nano-void growth. The results are in line with those given by the theoretical prediction. As revealed by MD simulations, the characteristics of void growth at micro-scale depend greatly on the crystal-orientation.

A New Method for Separation of Waves in Improving the Conventional SHPB Technique
LIU Kai-Xin, LI Xu-Dong
Chin. Phys. Lett. 2006, 23 (11): 3045-3048 .  
Abstract   PDF(pc) (235KB) ( 683 )
We present a new wave separation method to enable the split Hopkinson pressure bar (SHPB) technique to break through the limitation of the length of the incident bar and greatly to increase its measurable maximum strain. At the same time the dispersion effect of the elastic wave is significantly reduced. The fundamental principle of the new method is proven rigorously. The feasibility and credibility of the new method are also verified by experiments.
Shock Compression and Phase Transitions of Magnesiowüstite (Mg,Fe)O up to Earth’s Lowermost Mantle Conditions
ZHANG Li, GONG Zi-Zheng,
Chin. Phys. Lett. 2006, 23 (11): 3049-3051 .  
Abstract   PDF(pc) (221KB) ( 811 )
We report new shock-compression data for polycrystalline (Mg,Fe)O up to 130GPa shock pressures corresponding to Earth’s lowermost mantle conditions. Our data together with the existing shock-wave data of (Mg,Fe)O and its end-members MgO and FeO reveal that the Hugoniot curves of (Mg,Fe)O does not change with varying FeO content for their B1 phase (NaCl-structure) in the pressure--relative-volume plane. The evidence of the volume change within 3% at around 120GPa along the Hugoniot of (Mg0.6, Fe0.4)O is consistent with a structural transition from B1 phase (NaCl cubic) to B8 phase (NiAs-type hexagonal). Such a structural transition of (Mg,Fe)O, if indeed occurs, may in part contribute to the scattering of seismic waves and change in velocity gradient found in the lowermost mantle.
Fabrication of GaN Nanorods in a Large Scale on Si(111) Substrate by Ammoniating Technique
AI Yu-Jie, XUE Cheng-Shan, SUN Li-Li, SUN Chuan-Wei, ZHUANG Hui-Zhao, WANG Fu-Xue, CHEN Jin-Hua, LI Hong
Chin. Phys. Lett. 2006, 23 (11): 3052-3054 .  
Abstract   PDF(pc) (795KB) ( 407 )
GaN nanorods in a large scale have been synthesized on Si (111) substrates by ammoniating Ga2O3/Mg films under flowing ammonia atmosphere at the temperature of 1000°C for 15min. The as-synthesized GaN nanorods are characterized by scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results demonstrate that these straight nanorods are hexagonal wurtzite GaN single crystals in diameters ranging from 200nm to 600nm.
Synthesis of GaN Nanorods by Ammoniating Ga2O3/ZnO Films
XUE Shou-Bin, ZHUANG Hui-Zhao, XUE Cheng-Shan, HU Li-Jun
Chin. Phys. Lett. 2006, 23 (11): 3055-3057 .  
Abstract   PDF(pc) (624KB) ( 439 )
Large quantities of GaN nanorods are successfully synthesized on Si(111) substrates by ammoniating the films of Ga2O3/ZnO at 950°C in a quartz tube. The structure, morphology and optical properties of the as-prepared GaN nanorods are studied by x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, and photoluminescence. The results show that the GaN nanorods have a hexagonal wurtzite structure with lengths of several micrometres and diameters from 80nm to 300nm, which could supply an attractive potential to harmonically incorporate future GaN optoelectronic devices into Si-based large-scale integrated circuits. The growth mechanism is also briefly discussed.
Modelling of Gettering by Mechanical Damage of Metallic Impurities in Silicon
F. Ayad, M. Remram
Chin. Phys. Lett. 2006, 23 (11): 3058-3060 .  
Abstract   PDF(pc) (192KB) ( 379 )
Reducing the concentration of the metallic impurities present in silicon-based electronic components plays a vital role in manufactures. Gettering by induced mechanical damage is one of the methods used in neutralizing these impurities. To simulate this type of gettering, we explicitly include the role of the traps due to mechanical damage, based on the mechanism of kick-out. In our model, we choose the essential parameters including concentration of impurities, thickness, temperature, time, etc. The diffusion coefficient and equilibrium concentration of the silicon interstitials estimated from the literature have been adjusted to be in good agreement with the experimental data.
Comparative Analysis of Photo-Crystallization in a-Se95Te5 and a-Se95In5 Alloys
N. Mehta, D. Kumar, A. Kumar
Chin. Phys. Lett. 2006, 23 (11): 3061-3064 .  
Abstract   PDF(pc) (212KB) ( 506 )
We report a comparative study on photo-crystallization in a-Se95Te5 and a-Se95In5 alloys. The photo-crystallization is achieved by a shining white line on the thin films of these alloys in vacuum for different exposure times. The results indicate that photo-crystallization is fast in a-Se95In5 alloy as compared to a-Se95Te5 alloy. This is explained in terms of lower thermal stability of a-Se95In5 alloy as compared to a-Se95Te5 alloy.
Persistent Spin Current in a Quantum Wire with Weak Rashba Spin--Orbit Coupling
WANG Yi, SHENG Wei, ZHOU Guang-Hui,
Chin. Phys. Lett. 2006, 23 (11): 3065-3068 .  
Abstract   PDF(pc) (0KB) ( 527 )
We theoretically investigate the spin current for a parabolically confined semiconductor heterojunction quantum wire with weak Rashba spin--orbit coupling by means of the perturbation method. By analytical calculation, it is found that only two components of spin current density is non-zero in the equilibrium case. Numerical examples have demonstrated that the spin current of electron transverse motion is 10-3 times that of electron longitudinal motion. However, the former one is much more sensitive to the strength of Rashba spin--orbit coupling. These results may suggest an approach to the spin storage device and to the measurement of spin current through its induced electric field.

Thermal Stability and Spectroscopic Properties of Yb3+-Doped New Gallium--Lead--Germanate Glass
XU Shi-Qing, FENG Ai-Ming, ZHANG Li-Yan, ZHAO Shi-Long, WANG Bao-Ling, ZHANG Jue, WANG Wei, BAO Ren-Qiang
Chin. Phys. Lett. 2006, 23 (11): 3069-3071 .  
Abstract   PDF(pc) (219KB) ( 541 )
Yb3+-doped new gallium--lead--germanate glass is presented. Thermal stability, spectroscopic and laser performance parameters of the Yb3+-doped new gallium--lead--germanate glass are calculated. The results show that the Yb3+-doped new gallium--lead--germanate glass has good thermal stability (ΔT=198°C), high stimulated emission cross section (0.79pm2), and long fluorescence lifetime (1.46ms). Compared with other Yb3+-doped glass hosts, the Yb3+-doped new gallium--lead--germanate glass has better laser performance parameters and laser properties, indicating that Yb3+-doped new gallium--lead--germanate glass is a promising laser material for short pulse generation in diode pumped lasers, short pulse generation tunable laser, high-peak power and high-average power lasers.
Photoinduced Spin Disorder in Half-Metal CrO2 films
WU Xue-Wei, NIU Dong-Lin, LIU Xiao-Jun
Chin. Phys. Lett. 2006, 23 (11): 3072-3075 .  
Abstract   PDF(pc) (259KB) ( 519 )
We investigate the photoinduced effects on the spin state for half-metallic ferromagnet CrO2 (TC~390K), in which the conducting electrons are totally polarized, by means of the time-resolved pump--probe method at the temperature range from 300K to 470K. A significant negative change ΔT/T for the transmittance spectrum at 1.55eV under photo-excitation is found. The ΔT/T value monotonically decreases on approaching to TC from the low temperature side, suggesting a photoinduced spin disorder state. Furthermore, we calculate the saturation magnetization MS of CrO2 in both the ground and photo-excited states by using the local-spin-density approximation plus U (LSDA+U) method, and find a decrease of the MS-value in the photo-excited state. The suppressed MS-value in the photo-excited state is consistent with the experimental data.
Influence of Gauge Fluctuation on Electron Pairing Order Parameter and Correlation Functions of a Two-Dimensional System
LIN Ming-Xi, QI Sheng-Wen, LIU Yu-Liang
Chin. Phys. Lett. 2006, 23 (11): 3076-3079 .  
Abstract   PDF(pc) (255KB) ( 441 )
Based on a two-dimensional electron system with pure gauge field, we demonstrate that the long range order of the electron pairing order parameter can be destroyed by the gauge fluctuation for both s-wave and d-wave symmetric Cooper pair parameters, even if the pure gauge field mediates attractive interaction between the spin-up and spin-down electrons, while the signal of the Meissner effect is observable. This model can be used to explain the recent experimental data of the high Tc cuprate superconductors observed.
Segregation in Vertically Vibrated Binary Granular Mixtures with Same Size
SHI Qing-Fan, SUN Gang, HOU Mei-Ying, LU Kun-Quan
Chin. Phys. Lett. 2006, 23 (11): 3080-3083 .  
Abstract   PDF(pc) (342KB) ( 411 )
Segregation in vertically vibrated binary granular mixtures with same size is studied experimentally. A new partial segregated state is found in this system. This state exists between the completely mixed state and the pure segregated state, and has the characteristic that the lighter particles tend to rise and form a pure layer on the top of the system while the heavier particles and some of the lighter ones stay at the bottom and form a mixed layer. The ratio of the thickness of the pure top layer and that of the whole system varies continuously with the vibration frequency or amplitude. It is suggested to consider the ratio as an order parameter for describing the degree of the segregation quantitatively. By use of the order parameter, a detailed phase diagram is obtained in Γ versus f space. Finally, the formation of the observed partial segregated state is illustrated by the competition between the impact of momentum of the heavier particles and the stiffness of the layer composed of the mixed particles.
Anomalous Propagation of Electromagnetic Waves in Anisotropic Media with a Unique Dispersion Relation
SHU Wei-Xing, LUO Hai-Lu, LI Fei, REN Zhong-Zhou
Chin. Phys. Lett. 2006, 23 (11): 3084-3087 .  
Abstract   PDF(pc) (377KB) ( 549 )
We investigate the propagation of electromagnetic waves at the interface between an isotropic material and the anisotropic medium with a unique dispersion relation. We show that the refraction behaviour of E-polarized waves is opposite to that of H-polarized waves, though the dispersion relations for E- and H-polarized waves are the same. It is found that waves exhibit different propagation properties in anisotropic media with different sign combinations of the permittivity and permeability tensors. Some interesting properties of propagation are also found in the special anisotropic media, leading to potential applications.
Intramolecular Charge Transfer in Arylpyrazolines
WANG Ming-Liang, LIU Ju-Zheng, XU Chun-Xiang
Chin. Phys. Lett. 2006, 23 (11): 3088-3090 .  
Abstract   PDF(pc) (368KB) ( 542 )
Arylpyrazoline microparticles dispersed in water are synthesized and their absorption spectra are compared with those in solution. It is found that the absorbance of pyrazoline group in solution of 5-aryl arylpyrazoline is far greater than that in solution of arylpyrazolines with no 5-aryl group. This hyperchromic effect is intensified in 5-aryl arylpyrazoline microparticles. It is indicated that ntramolecular charge transfer exists between pyrazoline group and 5-aryl group and this kind of interaction is increased in their microparticles.
Red Electrophosphorescence from Oxadiazoles-Functionalized Iridium Complexes in Polymer Light-Emitting Devices
WU Zhong-Lian, LUO Cui-Ping, HU Zheng-Yong, JIANG Chang-Yun, HUANG Feng-Liang, ZHU Ke-Ming, ZHU Mei-Xiang, ZHU Wei-Guo
Chin. Phys. Lett. 2006, 23 (11): 3091-3093 .  
Abstract   PDF(pc) (223KB) ( 614 )
A type of oxadiazole-functionalized iridium complex is newly employed as red phosphor emitter in polymer light-emitting devices (PLEDs) using a blend of poly (9,9-dioctylfluorene)(PFO) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) as a host matrix. The devices show bright red electrophosphorescence with dominant peaks at about 593nm and shoulders at about 642nm. The highest luminance efficiency of 3.3cd/A at 9.3V and maximum luminance of 2912cd/m2 at 14.0V are achieved in the devices. At current density of 100mA/cm2, the devices still exhibit luminance efficiency of 2.2cd/A and luminance of 2300cd/m2. This indicates that the oxadiazole-functionalized iridium complexes have improved optoelectronic properties in the devices at high current density.
Improved Performances for Organic Light-Emitting Diodes Based on Al2O3-Treated Indium--Tin Oxide Anode
WANG Jing, SONG Rui-Li, LIU Chun-Ling, JIANG Wen-Long, CHEN Shu-Fen, ZHAO Yi, HOU Jing-Ying, LIU Shi-Yong
Chin. Phys. Lett. 2006, 23 (11): 3094-3096 .  
Abstract   PDF(pc) (661KB) ( 1409 )
Improved performances are obtained in organic light-emitting diodes (OLEDs) based on the indium--tin oxide (ITO) anode processed with ultrasonic in AlAl2O3 polishing solution. By optimizing the AlAl2O3 granularity to 0.6μm and the ultrasonic time to 10min, smoother ITO surfaces are acquired, which lead to the enhanced hole injection, and furthermore, to improving the performance of OLEDs. Compared with the control device without any treatment, the drive voltage of treatment device falls from 9V to 6V at 100cd/m2, the luminance is over three times that of the control device, reaching 25880cd/m2 at 15V, and the luminous efficiency is 3.82cd/A.

Thermal Stability and Kinetics of Binary Cu65Hf35 Bulk Metallic Glass
SHAN Shao-Tai, XIA Lei, DING Ding, DONG Yuan-Da
Chin. Phys. Lett. 2006, 23 (11): 3097-3100 .  
Abstract   PDF(pc) (245KB) ( 1086 )
We investigate the thermal stability and kinetics of Cu65Hf35 bulk metallic glass (BMG). Cu65Hf35 glassy rods in diameter up to 2mm are prepared by a conventional copper mould suction casting. Kinetics of glass transition and crystallizations are investigated and the ideal glass transition temperature of the alloy is obtained. It is found that the dependence of crystallization temperature of the BMG on the heating rates follows the Vogel--Fulcher--Tammann (VFT) non-linear relationship rather than the Kissinger and Lasocka linear fittings. The long-term thermal stability of the BMG is investigated by means of continuous crystallization diagrams obtained from the extension of VFT analysis. It is suggested that ideal glass transition and crystallization temperatures can also be regarded as the long-term stability criteria of the BMG.
Two-Photon Absorption Properties of Mn-Doped ZnS Quantum Dots
ZHENG Jia-Jin, ZHANG Gui-Lan, GUO Yang-Xue, WANG Xiao-Yan, CHEN Wen-Ju, ZHANG Xiao-Song, HUA Yu-Lin
Chin. Phys. Lett. 2006, 23 (11): 3097-3100 .  
Abstract   PDF(pc) (255KB) ( 569 )
We investigate the two-photon absorption and nonlinear refractive index properties of a quantum dot material based on ZnS nanocrystals doped with Mn isoelectronic impurities, using the Z-scan technique with 532\,nm picosecond laser pulses. The Mn-doped ZnS quantum dots have an average two-photon absorption cross section as high as 13600 Goeppert--Mayer units, which turn it into a very promising material for fluorescent label and imaging in biological samples. In addition, we also found that the two-photon absorption coefficient initially increases and then decreases with increasing pulse irradiance, which demonstrates the presence of the higher-order nonlinearity under the strong excitation.
Abnormal Photoluminescence Properties of Polycrystalline ZnO Nanowire Arrays Synthesized by Electrodeposition
XUE De-Sheng, GONG Yu
Chin. Phys. Lett. 2006, 23 (11): 3105-3107 .  
Abstract   PDF(pc) (536KB) ( 589 )
Large-scale ZnO nanowire arrays are synthesized by electrodeposition with subsequent heat treatment in atmosphere ambient at 450--650°C. Photoluminescence (PL) is investigated at 295K. Abnormal PL properties of an unusual sharp emission at 485nm and a broad ultraviolet emission which are different from the other works of ZnO PL before are observed. Field emission scanning electronic microscopy and transmission electron microscopy results show that the length of ZnO nanowires is nearly 5μm and their diameter is about 70nm. X-ray diffraction and electron diffraction results reveal that the ZnO nanowires are a polycrystalline structure.
Improved Performance by a Double-Insulator Layer in Organic Thin-Film Transistors
WANG Wei, SHI Jia-Wei, GUO Shu-Xu, ZHANG Hong-Mei, QUAN Bao-Fu, MA Dong-Ge
Chin. Phys. Lett. 2006, 23 (11): 3108-3110 .  
Abstract   PDF(pc) (422KB) ( 1584 )
Organic thin film transistors based on pentacene are fabricated by the method of full evaporation. The thickness of insulator film can be controlled accurately, which influences the device operation voltage markedly. Compared to the devices with a single-insulator layer, the electric performance of devices by using a double-insulator as the gate dielectric has good improvement. It is found that the gate leakage current can be reduced over one order of magnitude, and the on-state current can be enhanced over one order of magnitude. The devices with double-insulator layer exhibit field-effect mobility as large as 0.14cm2/Vs and near the zero threshold voltage. The results demonstrate that using a proper double insulator as the gate dielectrics is an effective method to fabricate OTFTs with high electrical performance.
Fabrication and Characteristics of Thin Film Bulk Acoustic Resonators with Highly c-Axis Oriented AlN Films
GU Hao-Shuang, ZHANG Kai, HU Guang, LI Wei-Yong
Chin. Phys. Lett. 2006, 23 (11): 3111-3114 .  
Abstract   PDF(pc) (426KB) ( 836 )
Thin film bulk acoustic resonators are fabricated by using silicon bulk micromachining technology, which are constructed mainly from aluminium nitride (AlN) piezoelectric films. The results of x-ray diffraction, scanning electron microscopy and atomic force microscopy show that the AlN films exhibit highly c-axis orientation with good surface morphology. The resonators with the AlN films possessed a reflection coefficient -10.6dB at the resonant frequency 2.537GHz, an effective electromechanical coupling coefficient 3.75%, series quality 101.8, and parallel quality 79.7.
Excitation Properties of the Biological Neurons with Side-Inhibition Mechanism in Small-World Networks
YUAN Wu-Jie, LUO Xiao-Shu, WANG Bing-Hong, WANG Wen-Xu, FANG Jin-Qing, JIANG Pin-Qun
Chin. Phys. Lett. 2006, 23 (11): 3115-3118 .  
Abstract   PDF(pc) (276KB) ( 792 )
We have studied the excitation properties of biophysical Hodgkin--Huxley neurons with the side-inhibition mechanism in small-world networks. The result shows that the excitation properties in the networks are preferably consistent with the characteristic properties of a brain neural system under external constant stimuli, such as fatigue effect, extreme excitation principle, and the brain neural excitation response induced by different intensity of noise and coupling. The results of the study might shed some light on the study of the brain nerve electrophysiology and epistemological science.
Memory-Based Boolean Game and Self-Organized Phenomena on Networks
HUANG Zi-Gang, WU Zhi-Xi, GUAN Jian-Yue, WANG Ying-Hai
Chin. Phys. Lett. 2006, 23 (11): 3119-3122 .  
Abstract   PDF(pc) (234KB) ( 595 )
We study a memory-based Boolean game (MBBG) taking place on a regular ring, wherein each agent acts according to its local optimal states of the last M time steps recorded in memory, and the agents in the minority are rewarded. One free parameter p between 0 and 1 is introduced to denote the strength of the agent willing to make a decision according to its memory. It is found that giving proper willing strength p, the MBBG system can spontaneously evolve to a state of performance better than the random game; while for larger p, the herd behaviour emerges to reduce the system profit. By analysing the dependence of dynamics of the system on the memor capacity M, we find that a higher memory capacity favours the emergence of the better performance state, and effectively restrains the herd behaviour, thus increases the system profit. Considering the high cost of long-time memory, the enhancement of memory capacity for restraining the herd behaviour is also discussed, and M=5 is suggested to be a good choice.
Optimizing Synchronizability of Scale-Free Networks in Geographical Space
WANG Bing, TANG Huan-Wen, XIU Zhi-Long, GUO Chong-Hui
Chin. Phys. Lett. 2006, 23 (11): 3123-3126 .  
Abstract   PDF(pc) (298KB) ( 1093 )
We investigate the relationship between the structure and the synchronizability of scale-free networks in geographical space. With an optimization approach, the numerical results indicate that when the network synchronizability is improved, the geographical distance becomes larger while the maximal load decreases. Thus the maximal betweenness can be a candidate factor that affects the network synchronizability both in topological space and in geographical space.
66 articles