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Volume 25 Issue 11
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Original Articles
large Last Multiplier of Generalized Hamilton System
MEI Feng-Xiang, SHANG Mei
Chin. Phys. Lett. 2008, 25 (11): 3837-3839 .  
Abstract   PDF(pc) (264KB) ( 532 )
We study an application of the Jacobi last multiplier to a generalized Hamilton system. A partial differential equation on the last multiplier of the system is established. The last multiplier can be found by the equation. If the quantity of integrals of the system is sufficient, the solution of the system can be found by the last multiplier.
Binary Darboux Transformation for the Modified Kadomtsev--Petviashvili Equation
HU Xiao-Rui, CHEN Yong,
Chin. Phys. Lett. 2008, 25 (11): 3840-3843 .  
Abstract   PDF(pc) (195KB) ( 475 )
Via the elementary Darboux transformation (DT) of the modified Kadomtsev--Petviashvili (mKP) equation, a binary Darboux transformation (BDT) of the mKP equation is constructed.
Periodic Wave Solutions of Generalized Derivative Nonlinear Schrödinger Equation
ZHA Qi-Lao, LI Zhi-Bin
Chin. Phys. Lett. 2008, 25 (11): 3844-3847 .  
Abstract   PDF(pc) (604KB) ( 737 )
A Darboux transformation of the generalized derivative nonlinear Schrödinger equation is derived. As an application, some new periodic wave solutions of the generalized derivative nonlinear Schrödinger equation are explicitly given.
Exact Solutions of the Dirac Equation for an Electron in a Magnetic Field with Shape Invariant Method
M. R. Setare, O. Hatami
Chin. Phys. Lett. 2008, 25 (11): 3848-3851 .  
Abstract   PDF(pc) (169KB) ( 2042 )
Based on the shape invariance property we obtain exact solutions of the Dirac equation for an electron moving in the presence of a certain varying magnetic field, then we also show its non-relativistic limit.
Nonadiabatic Geometric Phase in Composite Systems and Its Subsystem
LI Xin
Chin. Phys. Lett. 2008, 25 (11): 3852-3855 .  
Abstract   PDF(pc) (226KB) ( 449 )

We point out that the time-dependent gauge transformation technique may be effective in investigating the nonadiabatic geometric phase of a subsystem in a composite system. As an example, we consider two uniaxially coupled spin -1/2 particles with one of particles driven by rotating magnetic field. The influences of coupling and precession frequency of the magnetic field on geometric phase are also discussed in detail.

Quantum Key Distribution System with Six Polarization States Encoded by Phase Modulation
LIU Xiao-Bao, LIAO Chang-Jun, TANG Zhi-Lie, WANG Jin-Dong, LIU Song-Hao
Chin. Phys. Lett. 2008, 25 (11): 3856-3859 .  
Abstract   PDF(pc) (282KB) ( 576 )
An intrinsically stable quantum key distribution system (QKD) with six polarization states encoded by phase modulation is introduced. The encoder and decoder are in the same structures that consist of two polarizing Sagnac interferometers connected in tandem. The six polarization states are determined and distinguished by different sets of phase shifts induced by two respective electrically-driven integrated phase modulators. A mean visibility of interference fringes is kept stable at 97.58% for an hour's performance. Theoretical and experimental analyses show that the proposed QKD system features intrinsically stability immune from environment fluctuation.
Quantum Secure Direct Communication Based on Authentication
WANG Min-Jie, PAN Wei
Chin. Phys. Lett. 2008, 25 (11): 3860-3863 .  
Abstract   PDF(pc) (208KB) ( 740 )
We propose two schemes of quantum secure direct communication (QSDC) combined ideas of user authentication [Phys. Rev. A 73(2006)042305] and direct communication with dense coding [Phys. Rev. A. 68(2003)042317]. In these protocols, the privacy of authentication keys and the properties of the EPR pairs not only ensure the realization of identity authentication but also further improve the security of communication, and no secret messages are leaked even if the messages were broken.
Dark Soliton of a Growing Bose--Einstein Condensate in an External Trap
LI Hong, WANG D. N.
Chin. Phys. Lett. 2008, 25 (11): 3864-3866 .  
Abstract   PDF(pc) (599KB) ( 466 )
The dynamics of dark soliton in a growing Bose--Einstein condensate with an external magnetic trap are investigated by the variational approach based on the renormalized integrals of motion. The stationary states as physical solutions to the describing equation are obtained, and the evolution of the dark soliton is numerically simulated. The numerical results confirm the theoretical analysis and show that the dynamics depend strictly on the initial condition, the gain coefficient and the external potential.
Thermo-Hydrodynamic Lattice BGK Schemes with Lie Symmetry Preservation
RAN Zheng
Chin. Phys. Lett. 2008, 25 (11): 3867-3870 .  
Abstract   PDF(pc) (236KB) ( 438 )
A new class of lattice Bhatnagar--Gross--Krook (BGK) models is proposed, based on the Lie symmetry preservation ansatz for the local equilibria. This class extends the range of stability of previous models, especially for thermo-hydrodynamic lattice BGK schemes.
Two-Layer Feedback Neural Networks with Associative Memories
WU Gui-Kun, ZHAO Hong
Chin. Phys. Lett. 2008, 25 (11): 3871-3874 .  
Abstract   PDF(pc) (1194KB) ( 631 )
We construct a two-layer feedback neural network by a Monte Carlo based algorithm to store memories as fixed-point attractors or as limit-cycle attractors. Special attention is focused on comparing the dynamics of the network with limit-cycle attractors and with fixed-point attractors. It is found that the former has better retrieval property than the latter. Particularly, spurious memories may be suppressed completely when the memories are stored as a long-limit cycle. Potential application of limit-cycle-attractor networks is discussed briefly.
Synchronization and Pattern Dynamics of Coupled Chaotic Maps on Complex Networks
SHEN Yu, HOU Zhong-Huai, XIN Hou-Wen
Chin. Phys. Lett. 2008, 25 (11): 3875-3878 .  
Abstract   PDF(pc) (584KB) ( 537 )

The synchronization and pattern dynamics of coupled logistic maps on a certain type of complex network, constructed by adding random shortcuts to a regular ring, is investigated. For parameters where an isolated map is fully chaotic, the defect turbulence, which is dominant in the regular network, can be tamed into ordered periodic patterns or synchronized chaotic states when random shortcuts are added, and the patterns formed on the complex network can be grouped into two or three branches depending on the coupling strength.

Bursting Ca2+ Oscillations and Synchronization in Coupled Cells
JI Quan-Bao, LU Qi-Shao, Yang Zhuo-Qin, Duan Li-Xia
Chin. Phys. Lett. 2008, 25 (11): 3879-3882 .  
Abstract   PDF(pc) (443KB) ( 591 )
A mathematical model proposed by Grubelnk et al. [ Biophys. Chem. 94 (2001) 59] is employed to study the physiological role of mitochondria and the cytosolic proteins in generating complex Ca2+ oscillations. Intracellular bursting calcium oscillations of point--point, point--cycle and two-folded limit cycle types are observed and explanations are given based on the fast/slow dynamical analysis, especially for point--cycle and two-folded limit cycle types, which have not been reported before. Furthermore, synchronization of coupled bursters of Ca2+ oscillations via gap junctions and the effect of bursting types on synchronization of coupled cells are studied. It is argued that bursting oscillations of point--point type may be superior to achieve synchronization than that of point--cycle type.
Experimental Investigation of Chaos Synchronization in DFB Diode Lasers with Unsymmetrical Scheme
YANG Ling-Zhen, ZHANG Xiu-Juan, WANG An-Bang, GUO Dong-Ming, WANG Yun-Cai
Chin. Phys. Lett. 2008, 25 (11): 3883-3885 .  
Abstract   PDF(pc) (477KB) ( 641 )

We experimentally generate high dimension chaotic waveforms with smooth spectrum using a distributed feedback (DFB) semiconductor laser with unidirectional fibre ring long-cavity feedback, and implement the stable chaos synchronization when the chaotic light is injected into a solitary DFB laser diode. The synchronization quality is investigated by time-domain and frequency-domain analysis separately. The frequency-domain analysis indicates that the synchronization has higher quality in the high frequency band. The influences of the injection strength and the frequency detuning on the synchronization are measured. Our experimental results show that the robust synchronization can be maintained with the optical frequency detuning from -11GHz to 40 GHz.

Poincaré Map Based on Splitting Methods
GANG Tie-Qiang, CHEN Li-Jie, MEI Feng-Xiang
Chin. Phys. Lett. 2008, 25 (11): 3886-3889 .  
Abstract   PDF(pc) (373KB) ( 427 )
Firstly, by using the Liouville formula, we prove that the Jacobian matrix determinants of splitting methods are equal to that of the exact flow. However, for the explicit Runge--Kutta methods, there is an error term of order p+1 for the Jacobian matrix determinants. Then, the volume evolution law of a given region in phase space is discussed for different algorithms. It is proved that splitting methods can exactly preserve the sum of Lyapunov exponents invariable. Finally, a Poincaré map and its energy distribution of the Duffing equation are computed by using the second-order splitting method and the Heun method (a second-order Runge--Kutta method). Computation illustrates that the results by splitting methods can properly represent systems' chaotic phenomena.
N-Soliton Solution in Wronskian Form for a Generalized Variable-Coefficient Korteweg--de Vries Equation
XU Xiao-Ge, , MENG Xiang-Hua, GAO Yi-Tian
Chin. Phys. Lett. 2008, 25 (11): 3890-3893 .  
Abstract   PDF(pc) (235KB) ( 678 )

We concentrate on finding exact solutions for a generalized variable-coefficient Korteweg--de Vries equation of physically significance. The analytic N-soliton solution in Wronskian form for such a model is postulated and verified by direct substituting the solution into the bilinear form by virtue of the Wronskian technique. Additionally, the bilinear auto-Bäcklund transformation between the (N-1)- and N-soliton solutions is verified.

Improved Conditions for Global Asymptotic Stability of Cohen--Grossberg Neural Networks with Time-Varying Delays
CHEN Jun, CUI Bao-Tong, GAO Ming
Chin. Phys. Lett. 2008, 25 (11): 3894-3897 .  
Abstract   PDF(pc) (232KB) ( 413 )
The global asymptotic stability of delayed Cohen--Grossberg neural networks with impulses is investigated. Based on the new suitable Lyapunov functions and the Jacobsthal inequality, a set of novel sufficient criteria are derived for the global asymptotic stability of Cohen--Grossberg neural networks with time-varying delays and impulses. An illustrative example with its numerical simulations is given to demonstrate the effectiveness of the obtained results.
Magnetically Tunable Terahertz Switch and Band-Pass Filter
ZHANG Hui, GUO Peng, CHANG Sheng-Jiang, YUAN Jing-He
Chin. Phys. Lett. 2008, 25 (11): 3898-3900 .  
Abstract   PDF(pc) (741KB) ( 508 )

A novel design of a tunable terahertz switch and band-pass filter using liquid-crystal-filled photonic crystal waveguide is demonstrated. The effects of magnetic field on the photonic bandgaps and transmitting properties of a THz wave are investigated by using the plane wave expansion method and finite difference time domain method. The efficient photonic bandgap tuning is predicted such that the two-dimensional liquid-crystal-filled photonic crystal waveguide can serve as a switch and continuously tunable band-pass filter with controlling of the magnetic field.

All-Optical AND Logic Gate without Additional Input Beam by Utilizing Cross Polarization Modulation Effect
HAN Liu-Yan, WEN He, JIANG Huan, GUO Yi-Li, ZHANG Han-Yi
Chin. Phys. Lett. 2008, 25 (11): 3901-3904 .  
Abstract   PDF(pc) (425KB) ( 464 )

A novel design of all-optical AND gate is proposed by using cross polarization modulation effect in a semiconductor optical amplifier. In this scheme, an additional continuous-wave beam is not required as that in traditional scheme. AND output is obtained on either of two input signal wavelengths. The AND scheme is numerically simulated and experimentally demonstrated at a bit rate of 10Gb/s successfully.

Off-Shell Effect of Quarks in Bs→γe+e-
LI Nan, LU Yuan-Long, XIONG Zhao-Hua, YANG Min
Chin. Phys. Lett. 2008, 25 (11): 3905-3907 .  
Abstract   PDF(pc) (349KB) ( 398 )
We evaluate the rare decays Bs→γe+e- in the standard model, considering the off-shell effect of quarks in Bs meson as well as some contributions neglected in previous works. It is found that the quarks off-shell are large. With the predicted branching ratios at order of 10-8, it is expected that the radiative dileptonic decays will be detected in the LHC-b experiments.
Reanalysis of the (0+,1+) States Bs0 and Bs1 with QCD Sum Rules
WANG Zhi-Gang
Chin. Phys. Lett. 2008, 25 (11): 3908-3911 .  
Abstract   PDF(pc) (306KB) ( 362 )

We calculate the masses and decay constants of the P-wave strange-bottomed mesons Bs0 and Bs1 with the QCD sum rules, and observe that the central values of the masses Bs0 and Bs1 are smaller than the corresponding BK and B*K thresholds respectively, the strong decays Bs0→BK and Bs1B*K are kinematically forbidden. They can decay through the isospin violation processes Bs0→Bsη→wBsπ0 and Bs1→ Bsη→ Bs0. The bottomed mesons Bs0 and Bs1, just like their charmed cousins Ds0(2317) and Ds1(2460), may be very narrow.

Surface Emission of Quark Gluon Plasma at RHIC and LHC
XIANG Wen-Chang, WAN Ren-Zhuo, ZHOU Dai-Cui
Chin. Phys. Lett. 2008, 25 (11): 3912-3915 .  
Abstract   PDF(pc) (265KB) ( 378 )
Within the framework of a factorization model, we study the behaviour of nuclear modification factor in Au--Au collisions at RHIC and Pb--Pb collisions at LHC. We find that the nuclear modification factor is inversely proportional to the radius of the quark--gluon plasma and is dominated by the surface emission of hard jets. We predict the nuclear modification factor R AALHC~0.15 in central Pb--Pb collisions at LHC. The study shows that the factorization model can be used to describe the centrality dependence of nuclear modification factor of the high transverse momentum particles produced in heavy ion collisions at both RHIC and LHC.
Dileptons from a Chemically Equilibrating Quark--Gluon Plasma at Finite Baryon Density
GUAN Na-Na, HE Ze-Jun, LONG Jia-Li, CAI Xiang-Zhou
Chin. Phys. Lett. 2008, 25 (11): 3916-3919 .  
Abstract   PDF(pc) (347KB) ( 396 )

We perform a complete calculation for the dilepton production from the processes qq-→ll-, Compton-like (qg→qll-, q-g→q-ll-),qq-→gll-, gluon fusion gg-→cc-, annihilation qq-→cc- as well as multiple scattering of quarks in a chemically equilibrating quark--gluon plasma system at finite baryon density. It is found that quark-antiquark annihilation, Compton-like, gluon fusion and multiple scattering of quarks give important contribution. Moreover, the increase of the quark phase life-time with increasing initial quark chemical potential makes the dilepton yield as an increasing function of the initial quark chemical potential.

Simple Classification of Light Baryons
CHEN Yan, MA Bo-Qiang
Chin. Phys. Lett. 2008, 25 (11): 3920-3923 .  
Abstract   PDF(pc) (213KB) ( 417 )
We introduce a classification number n which describes the baryon mass information in a fuzzy manner. According to n and Jp of baryons, we put all known light baryons in a simple table in which some baryons with same (n,Jp) are classified as members of known octets or decuplets. Meanwhile, we predict two new possible octets.
A Chiral Macroscopic Force between Liquid of Butyl Alcohol and Copper Block
HU Yong-Hong, LIU Zhong-Zhu
Chin. Phys. Lett. 2008, 25 (11): 3924-3927 .  
Abstract   PDF(pc) (245KB) ( 392 )
A non-zero macroscopic chirality-dependent force between a copper block and a vessel of homochiral molecules (butyl alcohol) is calculated quantitatively with the central field approximation. The magnitude of the force is estimated with the published limits of the scalar and pseudo-scalar coupling constants.
Ultrahigh Spin Structures in 157,158,159Er
MA Hai-Liang, DONG Bao-Guo, YAN Yu-Liang
Chin. Phys. Lett. 2008, 25 (11): 3928-3931 .  
Abstract   PDF(pc) (424KB) ( 398 )
Rotational structures at ultrahigh spin in 157,158,159Er have been investigated with the configuration-dependent cranked Nilsson--Strutinsky approach. Configurations of observed bands are assigned and the corresponding deformations are given theoretically. The calculations suggest that one of ultrahigh spin bands in 158Er is triaxial highly deformed and the other is normal-deformed, while both ultrahigh spin bands in 157Er are suggested to be triaxial highly deformed. The possible ultrahigh spin bands in 159Er are predicted to be triaxial highly deformed and have shape coexistence in the same configuration. The configurations with two neutron holes in the Nosc=4 orbitals and two neutron holes in the h11/2 orbitals in 159Er are favoured for ultrahigh spin states but unfavoured for band termination, which is similar to ultrahigh spin bands in 157,158Er.
Equation of State for Isospin Asymmetric Matter of Nucleons and Deltas
LU Xiao-Hua, ZHANG Ying-Xun, LI Zhu-Xia, ZHAO Zhi-Xiang
Chin. Phys. Lett. 2008, 25 (11): 3932-3935 .  
Abstract   PDF(pc) (498KB) ( 488 )

An investigation on the equation of state of the isospin asymmetric, hot, dense matter of nucleons and deltas is performed based on the relativistic mean field theory. The QHD-II-type effective Lagrangian extending to the delta degree of freedom is adopted. Our results show that the equation of state is softened due to the inclusion of the delta degree of freedom. The baryon resonance isomer may occur depending on the delta-meson coupling. The results show that the densities for appearing the baryon resonance isomer, the densities for starting softening the equation of state and the extent of the softening depend not only on the temperature, the coupling strengths but also the isospin asymmetry of the baryon matter.

Parton Momentum Distribution at the Moment of Jet-Parton Collisions
WONG Cheuk-Yin
Chin. Phys. Lett. 2008, 25 (11): 3936-3939 .  
Abstract   PDF(pc) (275KB) ( 424 )
The early parton momentum distribution is extracted by using the STAR collaboration data of ridge particles associated with a near-side jet in central AuAu collisions at √sNN=200GeV. The ridge particles are identified as medium partons kicked by the jet near the surface and they carry direct information on the parton momentum distribution at the moment of jet-parton collisions. The extracted parton momentum distribution has a thermal-like transverse momentum distribution but a rapidity plateau structure with a relatively flat rapidity distribution at mid-rapidities with sharp kinematic boundaries at large rapidities that depend on the transverse momentum
The First Nine-Cell TESLA Cavity Made in China
LU Xiang-Yang, QUAN Sheng-Wen, ZHANG Bao-Cheng, HAO Jian-Kui, ZHU Feng, LIN Lin, XU Wen-Can, WANG Er-Dong, WANG Fang, JIN Song, XIN Tian-Mu, YAO Zhong-Yuan, CHEN Jia-Er, ZHAO Kui
Chin. Phys. Lett. 2008, 25 (11): 3940-3941 .  
Abstract   PDF(pc) (452KB) ( 445 )
A totally home-made 9-cell TESLA type superconducting cavity is made at Peking University. The cavity fabrication is according to DESY specification. The cavity is made of high purity niobium from OTIC, Ningxia. The electron beam welding is carried out at Harbin Institute of Technology, Harbin. By the cooperation, the cavity is tested at Thomas Jefferson National Accelerator Facility, USA. The preliminary result shows the acceleration gradient Eacc is 23MV/m without quench and has potential for improvement.
Automatic Estimation of Peak Regions in Gamma-Ray Spectra Measured by NaI Detector
ZHU Meng-Hua, LIU Liang-Gang, XU Ao-Ao, Ma Tao
Chin. Phys. Lett. 2008, 25 (11): 3942-3945 .  
Abstract   PDF(pc) (655KB) ( 990 )
We present an approach to estimate the width of peak regions for the background elimination of gamma ray spectrum. The synthetic and experimental data are used to test this method. With the estimated peak regions using the proposed method in the whole spectra, we find that the approach is simple and effective enough for the background elimination cooperating with the statistics-sensitive nonlinear iterative peak-clipping method.
Accurate One-Centre Method for Hydrogen Molecule Ions in Strong Magnetic Field
ZHANG Yue-Xia, KANG Shuai, SHI Ting-Yun
Chin. Phys. Lett. 2008, 25 (11): 3946-3949 .  
Abstract   PDF(pc) (264KB) ( 610 )
An accurate one-centre method for the hydrogen molecule ion is tested. The slow convergence and singularities at the nuclear positions that are problems in the general one-centre method are solved well by employing the optimal radial and angular B-spline basis. Therefore, the accuracy of the one-centre method is improved observably. For the ground state of the H2+ in the free field, 7×10-8 accuracy is obtained, which rivals the best one-centre calculation before. As a test, the nuclear distances and the total energies of the 1σg,u, 1πu, 1δg,u and 2σg states of the H2+ for the magnetic field strength B=1a.u. are also obtained. Compared to other results, five-digit accuracy at least can be arrived even for the antibonding states 1σu and 1δu, whose equilibrium distances R is very large
Classical Effects of Carrier--Envelope Phase on Nonsequential Double Ionization
ZHOU Yue-Ming, LIAO Qing, LAN Peng-Fei, LU Pei-Xiang
Chin. Phys. Lett. 2008, 25 (11): 3950-3953 .  
Abstract   PDF(pc) (365KB) ( 437 )
A classical microcanonical 1+1-dimensional model is used to investigate the ion momentum distributions in nonsequential double ionization with linearly
polarized few-cycle pulses. We find that the ion momentum distribution has a strong dependence on the carrier--envelope phase of the few-cycle pulse, which is consistent with the experimental results qualitatively. Back analysis shows that the ionization probability of the first electron at different phases and its returning kinetic energy play the main role on the ion momentum distributions.
Improvement of Atomic-Layer-Deposited Al2O3/GaAs Interface Property by Sulfuration and NH3 Thermal Nitridation
SHI Yu, SUN Qing-Qing, DONG Lin, LIU Han, DING Shi-Jin, ZHANG Wei
Chin. Phys. Lett. 2008, 25 (11): 3954-3956 .  
Abstract   PDF(pc) (484KB) ( 479 )
Fermi level pinning at the interface between high-k gate dielectric and GaAs induced by unstable native oxides is a major obstacle for high performance GaAs-based metal-oxide-semiconductor (MOS) devices. We demonstrate the improved Al2O3/GaAs interfacial characteristics by (NH4)2S immersion and NH3 thermal pretreatment prior to Al2O3 deposition. X-ray photoelectron spectroscopy (XPS) analysis confirms that sulfuration of GaAs surface by (NH4)2S solution can effectively reduce As-O bonds while Ga-O bonds and elemental As still exist at Al2O3/GaAs interface. However, it is found that N incorporation during the further thermal nitridation on sulfurated GaAs can effectively suppress the native oxides and elemental As in the sequent deposition of Al2O3. Atomic force microscopy (AFM) shows that the further thermal nitridation on sulfurated GaAs surface can also improve the surface roughness.
An Artificially Garnet Crystal Materials Using In Terahertz Waveguide
YANG Qing-Hui, ZHANG Huai-Wu, LIU Ying-Li, WEN Qi-Ye, ZHA Jie
Chin. Phys. Lett. 2008, 25 (11): 3957-3960 .  
Abstract   PDF(pc) (795KB) ( 792 )

A hypothesis is brought forward that the materials with low propagation loss in both optical and microwave band may exhibit good performance in terahertz (THz) band because THz wave band interspaces those two wave bands. For the purpose of exploring a kind of low-loss material for THz waveguide, Lu2.1Bi0.9Fe5O12(LuBiIG) garnet films are prepared by liquid phase epitaxy (LPE) method on a gadolinium~gallium~garnet (GGG) substrate from lead-free flux because of the good properties in both optical and microwave bands. In microwave band, the ferromagnetic resonance (FMR) linewidth of the film 2∆H=2.8-5.1Oe; in optical band, the optical absorption coefficient is 600cm-1 at visible range and about 100-170cm-1 when the wavelength is longer than 800nm. In THz range, our hypothesis is well confirmed by a THz-TDS measurement which shows that the absorbance of the film for THz wave is 0.05-0.3cm-1 and the minimum value appears at 2.3THz. This artificial ferromagnetic material holds a great promise for magnetic field tunable THz devices such as waveguide, modulator or switch.

Low Loss Plastic Terahertz Photonic Band-Gap Fibres
GENG You-Fu, TAN Xiao-Ling, ZHONG Kai, WANG Peng, YAO Jian-Quan
Chin. Phys. Lett. 2008, 25 (11): 3961-3963 .  
Abstract   PDF(pc) (369KB) ( 550 )

We report a numerical investigation on terahertz wave propagation in plastic photonic band-gap fibres which are characterized by a 19-unit-cell air core and hexagonal air holes with rounded corners in cladding. Using the finite element method, the leakage loss and absorption loss are calculated and the transmission properties are analysed. The lowest loss of 0.268dB/m is obtained. Numerical results show that the fibres could liberate the constraints of background materials beyond the transparency region in terahertz wave band, and efficiently minimize the effect of absorption by background materials, which present great advantage of plastic photonic band-gap fibres in long distance terahertz delivery.

Matrix-Based Polarization Analysis and Application of Semiconductor Optical Amplifiers
LI Zheng-Yong, WU Chong-Qing, SHUM Ping, DONG Hui
Chin. Phys. Lett. 2008, 25 (11): 3964-3967 .  
Abstract   PDF(pc) (270KB) ( 505 )

Employing the Mueller matrix method with polar decomposition, we analyse the polarization rotation (PR) effects in semiconductor optical amplifiers (SOAs) and demonstrate that the PR angle is linear to the birefringence dependent gain while the average PR coefficient is about 0.625 for the employed SOA. It is further evident that the current and optical intensity dependent PRs rotate reversely around the same axis. Thus we propose an optical-electric synchronous control scheme to obtain orthogonal polarization states with power-equalization, and implement it by a polarization-sensitive SOA. The polarization duration time is about 10 ns which is applicable to high-speed polarization state generation.

Experimental Investigation of Quality of Lensless Ghost Imaging with Pseudo-Thermal Light
SHEN Xia, BAI Yan-Feng, QIN Tao, HAN Shen-Sheng
Chin. Phys. Lett. 2008, 25 (11): 3968-3971 .  
Abstract   PDF(pc) (366KB) ( 558 )
Factors influencing the quality of lensless ghost imaging are investigated. According to the experimental results, we find that the imaging quality is determined by the number of independent sub light sources on the imaging plane of the reference arm. A qualitative picture based on advanced wave
optics is presented to explain the physics behind the experimental phenomena. The present results will be helpful to provide a basis for improving the quality of ghost imaging systems in future works.
Left-Handed Properties in Two-Dimensional Photonic Crystals Formed by Holographic Lithography
SHEN Xiao-Xia, YANG Xiu-Lun, CAI Lv-Zhong, WANG Yu-Rong, DONG Guo-Yan, MENG Xiang-Feng, XU Xian-Feng
Chin. Phys. Lett. 2008, 25 (11): 3972-3975 .  
Abstract   PDF(pc) (1112KB) ( 385 )
We give an analysis of the frequency distribution trends in the four lowest bands of two-dimensional square lattices formed by holographic lithography (HL) and in the lattices of the same kind but with regular dielectric columns with increasing filling ratios, and then present a comparative study on the left-handed properties in these two kinds of structures using plane wave expansion method and finite-difference time-domain (FDTD) simulations. The results show that the left-handed properties are more likely to exist in structures with large high-epsilon filling ratios or in a connected lattice.
Characterization of Photon Statistical Properties with Normalized Mandel Parameter
ZHANG Xin-Zheng, WANG Zhen-Hua, LI Hui, WU Qiang, TANG Bai-Quan, GAO Feng, XU Jing-Jun
Chin. Phys. Lett. 2008, 25 (11): 3976-3979 .  
Abstract   PDF(pc) (394KB) ( 670 )

Normalized Mandel Parameter <Q> is introduced as a new measurement of photon statistics. Dependences of Mandel parameter Q and corresponding normalized Mandel parameter <Q> on photon-counting time interval are experimentally investigated for pseudo-thermal light. We demonstrate that <Q> is more appropriate than Q to measure the statistical deviation from Poisson distribution, because <Q> presents clearly both the intrinsic statistical properties and measuring effects. The advantages of <Q> in charactering nonclassical emissions are also discussed.

Phase Noise of Optically Generated Microwave Using Sideband Injection Locking
HUANG Jin, SUN Chang-Zheng, SONG Yu, XIONG Bing, LUO Yi
Chin. Phys. Lett. 2008, 25 (11): 3980-3983 .  
Abstract   PDF(pc) (548KB) ( 404 )

Optically generated 20-GHz microwave carriers with phase noise lower than -75dBc/Hz at 10kHz offset and lower than -90dBc/Hz at 100kHz offset are
obtained using single- and double-sideband injection locking. Within the locking range, the effect of sideband injection locking can be regarded as narrow-band amplification of the modulation sidebands. Increasing the current of slave laser will increase the power of beat signal and reduce the phase noise to a certain extent. Double-sideband injection locking can increase the power of the generated microwave carrier while keeping the phase noise at a low level. It is also revealed that partially destruction of coherence between the two beating lights in the course of sideband injection locking would impair the phase noise performance.

Simultaneous Generation of Multi-Wavelength Laser from Nd:YAG Crystals in a Cruciform Cavity
CHEN Xiu-Yan, REN Zhao-Yu, ZHANG Hao-Lei, LI Xiu, ZHENG Xin-Liang, CHEN Hao-Wei, BAI Jin-Tao,
Chin. Phys. Lett. 2008, 25 (11): 3984-3987 .  
Abstract   PDF(pc) (297KB) ( 576 )
A cruciform cavity is presented for multi-wavelength laser generation. On the basis of considering the optimal power ratio and good spatial overlap of the two fundamental beams, the maximum output power of 589nm laser reaches 3.5W when the pumping power of Nd:YAG A and Nd:YAG B are 311.5W and 261.8W, respectively. At the same time, the other wavelength lasers are also obtained with the output power distribution of 2.5W at 660nm, 15W at 532nm, 100mW at 1319nm and 240mW at 1064nm. The corresponding beam quality factors are Mx2=4.93, My2=5.01 at 589nm, Mx2=4.51, My2=4.85 at 660nm, and Mx2=4.12, My2=3.96 at 532nm, respectively. The instabilities of the three visible lights are measured, which are also less than 2% within three hours.
Characteristics of Nd:YGG Laser Operating at 4F3/2-4I9/2
ZHANG Ling, ZHANG Chun-Yu, LI De-Hua, WEI Zhi-Yi, ZHANG Zhi-Guo, Hans J. Eichler, Stephan Strohmaier
Chin. Phys. Lett. 2008, 25 (11): 3988-3990 .  
Abstract   PDF(pc) (334KB) ( 437 )
The laser properties of the Nd:YGG crystal are investigated. The absorption spectrum from 500 to 900nm and emission spectrum from 850 to 1400nm of Nd:YGG are measured. As much as 1.35W output power of fundamental laser
operating at 935 and 938nm with a slope efficiency of 15.7% and 105mW output power of frequency doubled blue laser are successfully obtained.
Highly Efficient Diode-Side-Pumped Six-Rod Nd:YAG Laser
CUI Qian-Jin, PENG Qin-Jun, ZHANG Hong-Bo, YANG Xiao-Dong, BO Yong, GUO Xin-Jun, ZHOU Yong, LU Yuan-Fu, CUI Da-Fu, XU Zu-Yan
Chin. Phys. Lett. 2008, 25 (11): 3991-3994 .  
Abstract   PDF(pc) (620KB) ( 530 )

We have demonstrated a highly efficient, high average output power laser based on the optimized resonator made up of multiple Nd:YAG rods. The laser consists of three groups, each of which contains two rods with one quartz 90° rotator between them. By a desirable design of the resonator, the average output power of 1906W at 1064nm is reached with repetition rate of 1.1kHz. The optical to optical conversion efficiency is up to 50.8% with the pulse width 224μs and it is the highest conversion efficiency of six rods resonator.

Microchip Laser Feedback Interferometer with an Optical Path Multiplier
REN Zhou, TAN Yi-Dong, WAN Xin-Jun, LI Duo, ZHANG Shu-Lian
Chin. Phys. Lett. 2008, 25 (11): 3995-3998 .  
Abstract   PDF(pc) (367KB) ( 726 )
We present a microchip laser feedback interferometer with an optical path multiplier to enhance the resolution of traditional laser feedback interferometers (LFI). The optical path multiplier has a unique device, i.e. diffusive reflector. As class B microchip lasers have extremely high sensitivity to laser feedback, the diffusive reflector can easily reflect or diffuse back the laser beam without much manual adjustment to the optical system, which ensures the system's easy-adjustment and practical feature. The optical path multiplier is a two-mirror system which enables the laser beam to reflect between the two mirrors by N times. When the target shifts a distance of &#8710;d, the variation of the optical path will be about (4N×&#8710;d). Thus the system's resolution is about 4N times as high as the traditional LFI. Under typical room
conditions, the optical path multiplier can effectively enhance the system's resolution by more than 26 times as high as a traditional LFI system and even to the level of 0.1nm.
Influence of Temperature on Stimulated Raman Scattering in Single-Mode Silica Fibre
MEN Zhi-Wei, FANG Wen-Hui, SUN Xiu-Ping, LI Zuo-Wei, YI Han-Wei, WANG Zhao-Min, GAO Shu-Qin, LU Guo-Hui
Chin. Phys. Lett. 2008, 25 (11): 3999-4002 .  
Abstract   PDF(pc) (392KB) ( 558 )
One piece of single-mode silica fibre is used to study of temperature characteristics of stimulated Raman scattering (SRS), additional peaks (double-humped) are observed at both sides of pump light and 1st-order Stokes light in the experiment. The frequency shift of the double-humped is calculated by stimulated Four--Photon mixing (SFPM) phase matching theory, the result is consistent with the frequency shift of this experiment. Simultaneously, the experimental conditions accord with the theoretical calculation of effective coherence length. We indicate that the double-humped phenomenon is caused by SFPM. The intensity of double-humped is first increased, then decreased and finally disappeared as the temperature increases. This phenomenon has been explained theoretically.
Broadband Third-Harmonic Generation with a Composite KD*P Crystal
HAN Wei, ZHENG Wan-Guo, YUAN Peng, QIAN Lie-Jia, WANG Fang, YANG Yi-Sheng, FENG Bin, XIANG Yong, LI Ke-Yu, LI Fu-Quan
Chin. Phys. Lett. 2008, 25 (11): 4003-4005 .  
Abstract   PDF(pc) (371KB) ( 707 )
We predict that broadband efficient third-harmonic generation (THG) can be achieved with a frequency-doubling crystal and a novel composite KD*P tripler. The composite KD*P tripler is made of two partially deuterated KDP crystals with different deuteration levels by using the thermal bonding technique. The deuteration level of a partially deuterated KDP crystal is used as a degree of freedom to alter the phase-matching (PM) wavelength. Simulations show that the composite KD*P tripler can improve third-harmonic conversion efficiencies over a very wide band of input fundamental frequencies. In terms of robustness, alignment and stability, this THG scheme should be more promising than other broadband THG approaches because the composite KD*P tripler is a monolithic device.
Magnetostatic-Wave-Based Magneto-Optic Pulse Compression by Control of Phase Mismatching
WU Bao-Jian, GAO Xiang
Chin. Phys. Lett. 2008, 25 (11): 4006-4008 .  
Abstract   PDF(pc) (214KB) ( 422 )
Microwave magnetostatic waves (MSWs) as moving gratings in magneto-optic (MO) film can lead to the Bragg diffraction of guided optical waves (GOWs). The MO coupling characteristics are responsible for the amplitude and phase frequency spectra of diffracted pulses and even result in the compression of chirped optical pulses in time domain. We theoretically investigate the noncollinear diffraction of linearly chirped Gaussian optical pulses by continuous magnetostatic forward volume waves in detail. For a given chirped optical pulse, with the increase of phase-mismatching slopes, the compression efficiency (CE) is gradually improved up to the maximum followed by the transition of diffracted pulses from single peak to multi peaks. The larger the chirp parameter is, the smaller the required phase-mismatching slope to achieve the maximal CE is. However, the rise of the chirp parameter or phase-mismatching slope reduces the relative peak intensity of the diffracted pulse. Lastly, it is pointed out that the phase-mismatching slope can be greatly increased by using the high-order modes of MSWs and GOWs.
Passively Q-Switched Quasi-Continuous-Wave Diode-Pumped Intracavity Optical Parametric Oscillator at 1.57
WANG Yu-Ye, XU De-Gang, WEN Wu-Qi, WANG Peng, YAO Jian-Quan,
Chin. Phys. Lett. 2008, 25 (11): 4009-4012 .  
Abstract   PDF(pc) (664KB) ( 581 )

We report on a passively Q-switched quasi-cw diode-pumped Nd:YAG including an intracavity optical parametric oscillator. The dynamics of this system is described by solving the coupled equations. The effect of the initial transmission of Cr4+:YAG saturable absorber on the signal wave operation is studied. Under optimum conditions, we achieve 2.3mJ energy at 1.57μm wavelength for 40Hz repetition rate. The peak power of the pulses amounts to 0.88MW with the pulse width of 2.6ns. When the Fresnel reflection losses of the filters are taken into account, the pulse energy would be higher than 2.3mJ. To the best of our knowledge, this is the highest pulse energy and peak power for such a type of single resonant quasi-cw diode pumped Nd:YAG/Cr4+:YAG IOPO laser.

Distinguishing Structure Change of Cells Based on Analysis of Light Scattering Patterns
JIN Yong-Long, YANG Fang, WANG Meng, ZHANG Yu, GU Ning
Chin. Phys. Lett. 2008, 25 (11): 4013-4015 .  
Abstract   PDF(pc) (586KB) ( 372 )
We develop a new method to distinguish structural change of cells based on light scattering and Fourier spectra analysis. The light scattering detection system is composed of a laser source, an optical microscope, a CCD with high resolution and low distortion. After the scattering patterns of cells are recorded by the CCD, the Fourier spectra are obtained by the intensity distribution of scattered light. In the experiment, the change of cell structure is designed by sonication treatment. It is found that different typical peaks can be shown in the Fourier spectra of MCF7 cells with and without sonication treatment, which indicates that this method can be used to distinguish the structural change of cells.
Efficient Pumping Scheme by Direct Excitation of Upper Laser Level in Nd:CNGG
CAO Ning, LI Qi-Nan, ZHAO Yan-Ying, XU Chang-Wen, WEI Zhi-Yi, FENG Bao-Hua, ZHANG Zhi-Guo, ZHANG Huai-Jin, WANG Ji-Yang, HE Kun-Na, GAO Chun-Qing
Chin. Phys. Lett. 2008, 25 (11): 4016-4018 .  
Abstract   PDF(pc) (544KB) ( 443 )

We report an efficient pumping scheme which involves a direct excitation of the upper lasing level of a four-level laser in a Nd-doped Ca3(NbGa)2-xGa3O12 (Nd:CNGG) by using a tunable Ti:sapphire, 700-920nm, cw pump source. The slope efficiency is improved from 10.5% of the traditional band pumping at 808nm to 21.8% of the direct pumping at 882nm. The influence of pumping wavelength on lasing is discussed. We present a scheme of double pumping for lasing.

Synthesis and Band Gap Control in Three-Dimensional Polystyrene Opal Photonic Crystals
LIU Ye, ZHENG Zhong-Yu, QIN Fei, ZHOU Fei, ZHOU Chang-Zhu, ZHANG Dao-Zhong, MENG Qing-Bo, LI Zhi-Yuan
Chin. Phys. Lett. 2008, 25 (11): 4019-4022 .  
Abstract   PDF(pc) (512KB) ( 537 )
High-quality three-dimensional polystyrene opal photonic crystals are fabricated by vertical deposition method. The transmission properties with different incident angles and different composite refractive index contrasts are experimentally and theoretically studied. Good agreement between the experiment and theory is achieved. We find that with the increasing incident angle, the gap position shifts to the short wavelength (blue shift) and the gap becomes shallower; and with the increase of refractive index of the opal void materials and decrease the contrast of refractive index, the gap position shifts to the long wavelength (red shift). At the same time, we observe the swelling effects when the sample is immerged in the solutions with different refractive indices, which make the microsphere diameter in solution become larger than that in air. The understanding of band gap shift behaviour may be helpful in designing optical sensors and tunable photonic crystal ultrafast optical switches.
Flexible Control of Light Propagation Using a Novel Photonic Crystal Hetero-Waveguide Based on Silicon-on-Insulator Slab
WANG Yue, WU Yuan-Da, ZHANG Jia-Shun, HU Xiong-Wei
Chin. Phys. Lett. 2008, 25 (11): 4023-4025 .  
Abstract   PDF(pc) (440KB) ( 421 )

We demonstrate a photonic crystal hetero-waveguide based on silicon-on-insulator (SOI) slab, consisting of two serially connected width-reduced photonic crystal waveguides with different radii of the air holes adjacent to the waveguide. We show theoretically that the transmission window of the structure corresponds to the transmission range common to both waveguides and it is in inverse proportion to the discrepancy between the two waveguides. Also the group velocity of guided mode can be changed from low to high or high to low, depending on which port of the structure the signal is input from just in the same device, and the variation is proportional to the discrepancy between the two waveguides. Using this novel structure, we realize flexible control of transmission window and group velocity of guided mode simultaneously.

Cascaded Optical Buffer Based on Nonlinear Polarization Rotation in Semiconductor Optical Amplifiers
CHENG Mu, WU Chong-Qing, LIU Hua
Chin. Phys. Lett. 2008, 25 (11): 4026-4029 .  
Abstract   PDF(pc) (558KB) ( 504 )

A cascaded buffer based on nonlinear polarization rotation in semiconductor optical amplifiers is proposed, which is suitable for fast reconfiguration of buffering time at picoseconds. With the proposed buffer, sixty different buffer times are demonstrated at 2.5Gb/s.

Thermal Diffusion Process Estimation for Fabrication of Graded Plastic Optical Fibre
M. S. Kovacevic, A. Djordjevich
Chin. Phys. Lett. 2008, 25 (11): 4030-4033 .  
Abstract   PDF(pc) (458KB) ( 485 )

Thermal diffusion of dopants is investigated in the process of generating the graded-index profile of plastic optical fibres. Because the diffusion coefficient in high polymers has been shown to depend strongly on dopant concentration, it is allowed in this work to vary with the radial coordinate of the multistep-core fibre. A novel multi-layer model is presented for solving the diffusion equation with the variable diffusion coefficient. It is solved by the finite difference method. The solution determines the dopant diffusion profile in the fibre. It is verified against a solution from the literature and two cases of fibres with diffused profiles. The application is demonstrated on two examples of graded-index plastic optical fibres, one originally with a two-step and the other with four-step core. The results indicate that closer to the core-cladding interface, the computed diffused profile with variable diffusion coefficient D is closer to target profile than the profile obtained with constant D for the same time of thermal process.

Numerical Simulation of Random Close Packings in Particle Deformation from Spheres to Cubes
ZHAO Jian, LI Shui-Xiang
Chin. Phys. Lett. 2008, 25 (11): 4034-4037 .  
Abstract   PDF(pc) (801KB) ( 949 )
Variation of packing density in particle deforming from spheres to cubes is studied. A new model is presented to describe particle deformation between different particle shapes. Deformation is simulated by relative motion of component spheres in the sphere assembly model of a particle. Random close packings of particles in deformation form spheres to cubes are simulated with an improved relaxation algorithm. Packings in both 2D and 3D cases are simulated. With the simulations, we find that the packing density increases while the particle sphericity decreases in the deformation. Spheres and cubes give the minimum (0.6404) and maximum (0.7755) of packing density in the deformation respectively. In each deforming step, packings starting from a random configuration and from the final packing of last deforming step are both simulated. The packing density in the latter case is larger than the former in two dimensions, but is smaller in three dimensions. The deformation model can be applied to other particle shapes as well.
Multi-Bifurcation Effect of Blood Flow by Lattice Boltzmann Method
RAO Yong, NI Yu-Shan, LIU Chao-Feng
Chin. Phys. Lett. 2008, 25 (11): 4038-4041 .  
Abstract   PDF(pc) (314KB) ( 467 )

The multi-bifurcation effect of blood flow is investigated by lattice Boltzmann method at Re=200 with six different bifurcation angles α, which are 22.5°, 25°, 28°, 30°, 33°, 35°, respectively. The velocities and ratios of average velocity at various bifurcations are discussed. It is indicated that the maximum velocity at the section near the first divider increases and shifts towards the walls of branch with the increase of α. At the first bifurcation, the average horizontal velocities increase with the increase of α. The average horizontal velocities of outer branches at the secondary bifurcation decrease at 22.5°≤ α≤30° and increase at 30°≤α≤ 35°, whereas those of inner branches at the secondary bifurcation have the opposite variation, as the same as the above variations of the ratios of average horizontal velocities at various bifurcations. The ratios of average vertical velocities of branch at first bifurcation to that of outer branches at the secondary bifurcation increase at 22.5°≤α≤30° and decrease at 30°≤ α ≤ 35°, whereas the ratios of average vertical velocities of branch at first bifurcation to that of inner branches at the secondary bifurcation always decrease.

Deformation of Two-Dimensional Nonuniform-Membrane Red Blood Cells Simulated by a Lattice
LI Hua-Bing, JIN Li, QIU Bing
Chin. Phys. Lett. 2008, 25 (11): 4042-4045 .  
Abstract   PDF(pc) (265KB) ( 611 )
To study two-dimensional red blood cells deforming in a shear flow with the membrane nonuniform on the rigidity and mass, the membrane is discretized into equilength segments. The fluid inside and outside the red blood cell is simulated by the D2Q9 lattice Boltzmann model and the hydrodynamic forces exerted on the membrane from the inner and outer of the red blood cell are calculated by a stress-integration method. Through the global deviation from the curvature of uniform-membrane, we find that when the membrane is nonuniform on the rigidity, the deviation first decreases with the time increases and implies that the terminal profile of the red blood cell is static. To a red blood cell with the mass nonuniform on the membrane, the deviation becomes more large, and the mass distribution affects the profile of the two sides of the flattened red blood cell in a shear flow.
Experimental Investigation of Thermocapillary Convection in a Liquid Layer with Evaporating Interface
ZHU Zhi-Qiang, LIU Qiu-Sheng
Chin. Phys. Lett. 2008, 25 (11): 4046-4049 .  
Abstract   PDF(pc) (448KB) ( 559 )

Thermocapillary convection coupling with the evaporation effect of evaporating liquids is studied experimentally. This study focused on an evaporation liquid layer in a rectangular cavity subjected to a horizontal temperature gradient when the top evaporating surface is open to air, while most previous works only studied pure thermocapillary convection without evaporation. Two liquids with different evaporating rates are used to study the coupling of evaporation and thermocapillary convection, and the interfacial temperature profiles for different temperature gradients are measured. The experimental results indicate evidently the influence of evaporation effect on the thermocapillary convection and interfacial temperature profiles. The steady multicellular flow and the oscillatory multicellular flow in the evaporation liquid layer are observed by using the particle-image-velocimetry method.

Hard Sphere Diffusion Behaviour of Polymer Translocating through Interacting Pores
SUN Li-Zhen, LUO Meng-Bo
Chin. Phys. Lett. 2008, 25 (11): 4050-4053 .  
Abstract   PDF(pc) (317KB) ( 420 )

The translocation of polymer chain through a small pore from a high concentration side (cis side) to a low concentration side (trans side) is simulated by using Monte Carlo technique. The effect of the polymer--pore interaction on the translocation is studied. We find a special interaction at which the decay of the number of polymer chain, N, at the cis side obeys Fick's law, i.e. N decreases exponentially with time. The behaviour is analogous to the diffusion of hard sphere.

Self-Consistent Model for Atmospheric Pressure Dielectric Barrier Discharges in Helium
SUN Ji-Zhong, WANG Qi, ZHANG Jian-Hong, WANG Yan-Hui, WANG De-Zhen
Chin. Phys. Lett. 2008, 25 (11): 4054-4057 .  
Abstract   PDF(pc) (420KB) ( 429 )

We show the necessity of leaving out the approximation of constant average electron energy in many fluid models. For this purpose a one-dimensional self-consistent model for He atmospheric barrier discharges is developed. With this model, the electron energy distribution function in the atmospheric pressure glow discharge is obtained without introducing much difficulty, and the new model is readily implemented for investigating discharges in complicated gases.

Arc Root Motions in an Argon--Hydrogen Direct-Current Plasma Torch at Reduced Pressure
HUANG He-Ji, PAN Wen-Xia, WU Cheng-Kang
Chin. Phys. Lett. 2008, 25 (11): 4058-4060 .  
Abstract   PDF(pc) (422KB) ( 523 )
Arc root motions in generating dc argon--hydrogen plasma at reduced pressure are optically observed using a high-speed video camera. The time resolved angular position of the arc root attachment point is measured and analysed. The arc root movement is characterized as a chaotic and jumping motion along the circular direction on the anode surface.
Propagation and Interaction of Ion-Acoustic Solitary Waves in a Two-Dimensional Plasma Consisting of Isothermal Electrons and Hot Ions
HAN Jiu-Ning, DUAN Wen-Shan, TIAN Duo-Xiang, LIANG Gui-Zhen, LI Xiao-Li, YANG Xiao-Xia
Chin. Phys. Lett. 2008, 25 (11): 4061-4064 .  
Abstract   PDF(pc) (866KB) ( 498 )

We study the propagation and interaction of ion-acoustic solitary waves in a simple two-dimensional plasma by using the extended Poincaré-Lighthill--Kuo perturbation method. We consider the interaction between two ion-acoustic solitary waves with different propagation directions in such a system, and obtain two Korteweg-de Vries equations for small but finite amplitude solitary waves along both ξ and η trajectories. The effects of the ratio of ion temperature σ, the ratio of heat capacity γ and the colliding angle α on the amplitude, the width of the new nonlinear wave created by the collision between two solitary waves are studied. The effects of these parameters on both the colliding solitary waves are examined as well. It is found that all the above-mentioned parameters have significant effects on the properties of these nonlinear waves.

Effect of Elongation on Critical Gradient for Toroidal Electron Temperature Gradient Modes
PENG Li-Li, GAO Zhe
Chin. Phys. Lett. 2008, 25 (11): 4065-4067 .  
Abstract   PDF(pc) (271KB) ( 397 )
The electron temperature gradient mode is investigated in elongated toroidal plasmas with a gyrokinetic integral eigenmode equation code. Dependence of the critical electron temperature gradient on the elongation is calculated. It is found that when the elongation increases, the growth rate spectrum is greatly shifted towards shorter poloidal wavelength, and then the poloidal wavenumber at which the mode is destabilizing critically in elongated plasmas will be larger than that in circular plasmas.
Optical Emission Spectroscopy Investigation of a Surface Dielectric Barrier Discharge Plasma Aerodynamic Actuator
LI Ying-Hong, WU Yun, JIA Min, ZHOU Zhang-Wen, GUO Zhi-Gang, Yi-Kang
Chin. Phys. Lett. 2008, 25 (11): 4068-4071 .  
Abstract   PDF(pc) (446KB) ( 667 )
The optical emission spectroscopy of a surface dielectric barrier discharge plasma aerodynamic actuator is investigated with different electrode configurations, applied voltages and driving frequencies. The rotational temperature of N2 (C3IIu) molecule is calculated according to its rotational emission band near 380.5nm. The average electron energy of the discharge is evaluated by emission intensity ratio of first negative system to second positive system of N2. The rotational temperature is sensitive to the inner space of an electrode pair. The average electron energy shows insensitivity to the applied voltage, the driving frequency and the electrode configuration.
Effect of Silane Flow Rate on Structure and Corrosion Resistance of Ti-Si-N Thin Films Deposited by a Hybrid Cathodic Arc and Chemical Vapour Process
YIN Long-Cheng, LUAN Sen, LV Guo-Hua, WANG Xing-Quan, HUANG Jun, JIN Hui, FENG Ke-Cheng, YANG Si-Ze
Chin. Phys. Lett. 2008, 25 (11): 4072-4075 .  
Abstract   PDF(pc) (1210KB) ( 433 )

Ti--Si--N thin films with different silicon contents are deposited by a cathodic arc technique in an Ar+N2+SiH4 mixture atmosphere. With the increase of silane flow rate, the content of silicon in the Ti--Si--N films varies from 2.0at.% to 12.2at.%. Meanwhile, the cross-sectional morphology of these films changes from an apparent columnar microstructure to a dense fine-grained structure. The x-ray diffractometer (XRD) and x-ray photoelectron spectroscopy (XPS) results show that the Ti--Si--N film consists of TiN crystallites and SiNx amorphous phase. The corrosion resistance is improved with the increase of silane flow rate. Growth defects in the films produced play a key role in the corrosion process, especially for the local corrosion. The porosity of the films decreases from 0.13% to 0.00032% by introducing silane at the flow rate of 14sccm.

Growth and Characterization of a Kind of Nitrogen-Rich Niobium Nitride for Bolometer Applications at Terahertz Frequencies
LU Xue-Hui, KANG Lin, ZHOU Lei, CHEN Jian, JI Zheng-Ming, CAO Chun-Hai, JIN Biao-Bing, XU Wei-Wei, WU Pei-Heng, WANG Xiao-Shu
Chin. Phys. Lett. 2008, 25 (11): 4076-4078 .  
Abstract   PDF(pc) (475KB) ( 508 )
Niobium is sputtered onto a single crystalline silicon substrate in N2:Ar=4:1 gas mixture at the total pressure of 2Pa. The temperature coefficient of resistance of the sample is about 0.5% at 300K, and up to 7% at 77K, indicating the possibility of using it to make room-temperature bolometers with performances better than those based on Pt, Bi, or Nb. For a 60-nm-thick sample, the rms surface roughness is 0.45nm over an area of 2μm×2μm. Analyses based on x-ray diffraction and x-ray photoelectronic spectroscopy indicate that the samples are Nb5N6 thin films in which there is a combination of Nb3+ and Nb5+, or Nb4+.
Thermally Activated Photoconduction and Alternating-Current Conduction in Se75Ge20Ag5 Chalcogenide Glass: Investigation of Meyer--Neldel Rule
R. S. Sharma, N. Mehta, A. Kumar
Chin. Phys. Lett. 2008, 25 (11): 4079-4082 .  
Abstract   PDF(pc) (338KB) ( 443 )
We report on the observation of Meyer--Neldel rule in glassy Se75Ge20Ag5 alloy where &#8710;E is varied by two different methods. In the first approach, the intensity of light varies while measuring the photoconductivity in amorphous thin films of Se75Ge20Ag5 instead of changing composition of the glassy system. In the second approach, the variation of ac conductivity with temperature is found to be exponential and the activation energy is found to vary with frequency.
High-Temperature Characteristics of Ti/Al/Ni/Au Ohmic Contacts to n-GaN
ZHANG Yue-Zong, FENG Shi-Wei, GUO Chun-Sheng, ZHANG Guang-Chen, ZHUANG Si-Xiang, SU Rong, BAI Yun-Xia, LU Chang-Zhi
Chin. Phys. Lett. 2008, 25 (11): 4083-4085 .  
Abstract   PDF(pc) (441KB) ( 883 )

We present the high-temperature characteristics of Ti/Al/Ni/Au(15nm/220nm/40nm/50nm) multiplayer contacts to n-type GaN (Nd=3.7×1017cm-3, Nd=3.0×1018cm-3). The contact resistivity increases with the measurement temperature. Furthermore, the increasing tendency is related to doping concentration. The higher the doped, the slower the contact resistivity with decreasing measurement temperature. Ti/Al/Ni/Au ohmic contact to heavy doping n-GaN takes on better high temperature reliability. According to the analyses of XRD and AES for the n-GaN/Ti/Al/Ni/Au, the Au atoms permeate through the Ni layer which is not thick enough into the Al layer even the Ti layer.

Structural, Elastic and Electronic Properties of ReO2
LI Yan-Ling, , ZENG Zhi
Chin. Phys. Lett. 2008, 25 (11): 4086-4089 .  
Abstract   PDF(pc) (302KB) ( 913 )

Structural, elastic and electronic properties of ReO2 are investigated by first-principles calculations based on density functional theory. The ground state
of ReO2 has an orthorhombic symmetry which belongs to space group Pbcn with a=4.7868Å
b=5.5736Å, and c=4.5322Å. The calculated bulk moduli are 322GPa, 353GPa, and 345GPa for orthorhombic, tetragonal, and monoclinic ReO2, respectively, indicating that ReO2 has a strong incompressibility. ReO2 is a metal ductile solid and presents large elastic anisotropy. The obtained Debye temperatures are 850K for orthorhombic, 785K for tetragonal, and 791K for monoclinic ReO2.

Influence of Grain Size on Electrical and Optical Properties of InP Films
Mustafa Ö, ztas
Chin. Phys. Lett. 2008, 25 (11): 4090-4092 .  
Abstract   PDF(pc) (217KB) ( 2104 )

InP film samples were prepared by spray pyrolysis technique using aqueous solutions of InCl3 and Na2HPO4, which were atomized with compressed air as carrier gas onto glass substrates at 500°C with different thicknesses of the films. It is found that the resistivity of the polycrystalline films strongly depends on the grain size. It is observed that the grain size of the films increase with the decrease of the energy band gap and strain of the film. The changes observed in the energy band gap and strain related to the film grain size of the films are discussed in detail.

Noise Characteristics of Optocouplers on Neutron Radiation
LI Ying-Hui, CHEN Chun-Xia, LIU Yong-Zhi, JIANG Cheng, ZOU Ze-Ya, OU Yi, LI Zu-An
Chin. Phys. Lett. 2008, 25 (11): 4093-4096 .  
Abstract   PDF(pc) (1061KB) ( 486 )
Neutron dose radiation experiment is designed to study the optocoupler's displacement effects and the noise characteristics. The burst noise is introduced in optocouplers on neutron radiation, which is indicated from experiments. With the increasing neutron radiation the displacement defects in space-charge region increase, the scattering enhances and the noise signal mutations increase. All these represent the noise time series mutations, the random pulses and the increasing noise complexity. The burst noise becomes evident, and the power spectrum density, the characteristic frequency and the fractal dimension of time series of noise greatly increase.
Influence of AlN Buffer Thickness on GaN Grown on Si(111) by Gas Source Molecular Beam Epitaxy with Ammonia
LIN Guo-Qiang, ZENG Yi-Ping, WANG Xiao-Liang, LIU Hong-Xin
Chin. Phys. Lett. 2008, 25 (11): 4097-4100 .  
Abstract   PDF(pc) (643KB) ( 1044 )
Hexagonal GaN is grown on a Si(111) substrate with AlN as a buffer layer by gas source molecular beam epitaxy (GSMBE) with ammonia. The thickness of AlN buffer is changed from 9 to 72nm. When the thickness of AlN buffer is 36nm, the surface morphology and crystal quality of GaN is optimal. The in-situ reflection high energy electron diffraction (RHEED) reveals that the transition to a two-dimensional growth mode of AlN is the key to the quality of GaN. However, the thickness of AlN buffer is not so critical to the residual in-plane tensile stress in GaN grown on Si(111) by GSMBE for AlN thickness between 9 to 72nm.
Electronic States of Elliptical Quantum Rings Subjected to a Magnetic Field
LI Hai-Tao, , LIU Li-Zhe, LIU Jian-Jun,
Chin. Phys. Lett. 2008, 25 (11): 4101-4104 .  
Abstract   PDF(pc) (212KB) ( 596 )
We calculate the energy states and Aharonov--Bohm oscillations of an electron in elliptical quantum rings in the presence of a uniform magnetic field by using an exact numerical diagonalization. The calculated results show that the elliptical quantum rings are flatter, larger amplitudes and periods of the Aharonov--Bohm oscillations are observed. In addition, in the limits of a circular quantum ring, the results of our approach are in good agreement with those of earlier theories.
Quantum Waveguide Properties of Bethe Lattices with a Ring
LIN Zhi-Ping, HOU Zhi-Lin, LIU You-Yan
Chin. Phys. Lett. 2008, 25 (11): 4105-4108 .  
Abstract   PDF(pc) (3889KB) ( 420 )
Based on waveguide theory we investigate electronic transport properties of Bethe lattices with a mesoscopic ring threaded by a magnetic flux. The generalized eigen-function method (GEM) is used to calculate the transmission and reflection coefficients up to the fifth generation of Bethe lattices. The relationships among the transmission coefficient T, magnetic flux Φ and wave vector kl are investigated in detail. The numerical results are shown by the three-dimensional plots and contour maps. Some resonant-transmission features and the symmetry of the transmission coefficient T to flux Φ are observed and discussed.
Degradation of Ultra-Thin Gate Oxide NMOSFETs under CVDT and SHE Stresses
HU Shi-Gang, CAO Yan-Rong, HAO Yue, MA Xiao-Hua, CHEN Chi, WU Xiao-Feng, ZHOU Qing-Jun
Chin. Phys. Lett. 2008, 25 (11): 4109-4112 .  
Abstract   PDF(pc) (640KB) ( 573 )

Degradation of device under substrate hot-electron (SHE) and constant voltage direct-tunnelling (CVDT)stresses are studied using NMOSFET with 1.4- nm gate oxides. The degradation of device parameters and the degradation of the stress induced leakage current (SILC) under these two stresses are reported. The emphasis of this paper is on SILC and breakdown of ultra-thin-gate-oxide under these two stresses. SILC increases with stress time and several soft breakdown events occur during direct-tunnelling (DT) stress. During SHE stress, SILC firstly decreases with stress time and suddenly jumps to a high level, and no soft breakdown event is observed. For DT injection, the positive hole trapped in the oxide and hole direct-tunnelling play important roles in the breakdown. For SHE injection, it is because injected hot electrons accelerate the formation of defects and these defects formed by hot electrons induce breakdown.

Electrical and Magnetic Properties of FeSi2 Nanowires
PENG Zu-Lin, S. Liang
Chin. Phys. Lett. 2008, 25 (11): 4113-4116 .  
Abstract   PDF(pc) (326KB) ( 782 )

We report the characterization of self-assembled epitaxially grown FeSi2 nanowires (NWs) in terms of electrical and magnetic properties. NWs grown by reactive deposition epitaxy (RDE) on silicon (110) show dimensions of 10nm×5nm, and several micrometres in length. By using conductive-AFM (c-AFM), electron transport properties of one single NW is measured, resistivity of a single crystalline FeSi2 NW is estimated to be 225μ\Ω &#12539;cm. Using superconducting quantum interference device (SQUID), we measure a magnetic moment of 0.3±0.1 Bohr magneton per iron atom for these FeSi2 NWs.

Effect of Co-Substitution on Magnetic Properties in Spinels GeNi2O4 Systems
R. Masrour, M. Hamedoun, A. Benyoussef, A. Hourmatallah, K. Bouslykhane, N. Benzakour
Chin. Phys. Lett. 2008, 25 (11): 4117-4119 .  
Abstract   PDF(pc) (183KB) ( 761 )
The magnetic properties of spinel GeNi2-2xCo2xO4 systems in the range 0≤x≤1 are studied by mean field theory and high-temperature series expansions. The nearest neighbouring and the next-neighbouring super-exchange interactions J1 (x) and J2(x) are evaluated for these systems in the range 0≤x≤1, by using the first theory. The intra-planar and the inter-planar interactions and the exchange energy are deduced. The second theory is applied in the spinel GeNi2-2xCo2xO4 systems, combined with the Padé approximants method, to determine the magnetic phase diagrams (TN versus dilution x) in the range 0≤x≤1. The obtained theoretical results are in agreement with experimental data obtained by magnetic measurements. The critical exponents associated with the magnetic susceptibility γ and the correlation lengths ν are deduced.
Bianisotropy Picture of Higher Permeability at Higher Frequencies
XUE De-Sheng, LI Fa-Shen, FAN Xiao-Long, WEN Fu-Sheng
Chin. Phys. Lett. 2008, 25 (11): 4120-4123 .  
Abstract   PDF(pc) (484KB) ( 657 )
With an effective bianisotropy picture, high-frequency behaviours of different magnetic materials can be reconciled, and the higher permeability and higher resonance frequencies are achieved even in the GHz range. The validity of the bianisotropy picture is quantitatively verified by the in-plane anisotropic Fe34Co55Zr11 thin films. A prolate elliptical precession of the magnetization about its equilibrium direction is the key point, which can be induced by an artificial or an intrinsic bianisotropy system.
Quasi-Random Resistor Network Model for Linear Magnetoresistance of Metal--Semiconductor Composite
XU Jie, ZHANG Duan-Ming, DENG Zong-Wei, YANG Feng-Xia, LI Zhi-Hua, PAN Yuan
Chin. Phys. Lett. 2008, 25 (11): 4124-4127 .  
Abstract   PDF(pc) (431KB) ( 370 )

A new model for the linear magentoresistance (MR) of the Ag2+δSe and Ag2+δ Te thin films is proposed. The thin film is considered as a metal--semiconductor composite and dispersed into an N×N quasi-random resistor network. The network is constructed from four-terminal resistors and the mobility of carries μ within the network has a quasi-random distribution, i.e. a Gaussian distribution with two constraint conditions. The model predicts that the MR increases with the increasing magnetic fields, and increases linearly at high field. Moreover, the MR decreases with the increasing temperatures. A good agreement between the theoretical MR and the available experimental data is found.

Electromechanical Properties of Microcantilever Actuated by Enhanced Piezoelectric PZT Thick Film
LIU Hong-Mei, ZHAO Quan-Liang, CAO Mao-Sheng, YUAN Jie, DUAN Zhong-Xia, QIU Cheng-Jun,
Chin. Phys. Lett. 2008, 25 (11): 4128-4130 .  
Abstract   PDF(pc) (443KB) ( 720 )
Pb(Zr0.53,Ti0.47)O3 (PZT) films with thicknesses of 0.8μm, 2μm and 4μm are prepared by a sol-gel method and their longitudinal piezoelectric coefficients are analysed. The results show that the PZT thick films, whose density is closer to bulk PZT, has the better crystallization, with d33 and density much larger than those of PZT thin films. A piezoelectric microcantilever actuated by a 4-μm-thick PZT film is fabricated and its displacement is measured in different frequencies and voltages. The displacement increases linearly with the increasing bias, and the maximum displacement of 0.544μm is observed at 30kHz for 5V bias. The resonant frequency obtained in the experiment matches quite well with the theoretical result, and it is shown that the resonant frequency of PZT microcantilever could be controlled and predicated.
Effects of LSMO Buffer Layer on Crystalline Orientation and Ferroelectric Properties of Bi2.9Pr0.9Ti3O12 Thin Films Prepared by Radio-Frequency Magnetron Sputtering
WU Yun-Yi, ZHANG Duan-Ming, YU Jun, ZHENG Chao-Dan, WANG Yun-Bo
Chin. Phys. Lett. 2008, 25 (11): 4131-4134 .  
Abstract   PDF(pc) (748KB) ( 521 )
Ferroelectric Bi2.9Pr0.9Ti3O12/La0.67Sr0.33MnO3 (BPT/LSMO) films are fabricated on Pt(111)/TiO2/SiO2/Si substrates by rf-magnetron sputtering method. The influences of the LSMO deposition conditions and LSMO layer thickness on properties of BPT thin films are studied. The LSMO layer deposited at 300°C and 450°C favours preferred (117) orientation of BPT films, while deposited at 600°C for LSMO layer leads to strong (111)-preferred orientation of BPT film. With the LSMO buffer layer, the films exhibit improved ferroelectric properties and Pt/BPT/LSMO(20nm)/Pt capacitor shows the largest remnant polarization Pr of 18.4μC/cm2 at 14V. A similar change in dielectric constant with the increase of LSMO layer thickness is also observed and the highest dielectric constant of 342.7 is obtained for the Pt/BPT/LSMO(20nm)/Pt film. Compared with the Pt/BPT/Pt film, the Pt/BPT/LSMO/Pt films exhibit better fatigue endurance after 5×109 switching cycles. Moreover, the LSMO layer has apparent effect on leakage current density and the Pt/BPT/LSMO(20nm)/Pt film exhibits the lowest leakage current density.
Multilayer Au/TiO2Composite Films with Ultrafast Third-Order Nonlinear Optical Properties
LONG Hua, YANG Guang, CHEN Ai-Ping, LI Yu-Hua, LU Pei-Xiang
Chin. Phys. Lett. 2008, 25 (11): 4135-4138 .  
Abstract   PDF(pc) (421KB) ( 546 )
We report on the ultrafast third-order optical nonlinearity in multilayer Au/TiO2 composite films fabricated on quartz substrates by pulsed laser deposition technique. The linear optical properties of the films are determined and optical absorption peaks due to surface plasmon resonance of Au particles are observed at about 590nm. The third-order optical nonlinearities of the films are investigated by z-scan method using a femtosecond laser (50fs) at the wavelength of 800nm. The sample showed fast nonlinear optical responses with nonlinear absorption coefficient and nonlinear refractive index being -3.66×10-10m/W and -2.95×10-17m2/W, respectively. The results also show that the nonlinear optical effects increase with the increasing Au concentration in the composite films.
Uniaxial Strain Effects on Optical Properties of c-plane Wurtzite GaN
HAO Guo-Dong, CHEN Yong-Hai
Chin. Phys. Lett. 2008, 25 (11): 4139-4142 .  
Abstract   PDF(pc) (338KB) ( 449 )
We investigate the uniaxial strain effect in the c-plane on optical properties of wurtzite GaN based on k&#12539;p theory, the spin-orbit interactions are also taken into account. The energy dispersions show that the uniaxial strain in the c-plane gives an anisotropic energy splitting in the kx-ky plane, which can reduce the density of states. The uniaxial strain also results in giant in-plane optical polarization anisotropy, hence causes the threshold carrier density reduced. We clarify the relations between the uniaxial strain and the optical polarization properties. As a result, it is suggested that the compressive uniaxial strain perpendicular to the laser cavity direction in the c-plane is one of the preferable approaches for the efficient improvement of GaN-based laser performance.
Effect of Interface Roughness and Dislocation Density on Electroluminescence Intensity of InGaN Multiple Quantum Wells
ZHAO De-Gang, JIANG De-Sheng, ZHU Jian-Jun, LIU Zong-Shun, ZHANG Shu-Ming, WANG Yu-Tian, YANG Hui,
Chin. Phys. Lett. 2008, 25 (11): 4143-4146 .  
Abstract   PDF(pc) (387KB) ( 765 )
Effects of interface roughness and dislocation density on the electroluminescence (EL) intensity of InGaN multiple quantum wells (MQWs) are investigated. It is found that the EL intensity increases with the number of satellite peaks in the x-ray diffraction experiments of InGaN MQW samples. It is indicated that the rough interface will lead the reduction of EL intensity of InGaN MQW samples. It is also found that the EL intensity increases with the decrease of dislocation density which is characterized by the x-ray diffraction measurements. It is suggested that the EL intensity of InGaN MQWs can be improved by decreasing the interface roughness and dislocation density.
Strong Green Light Emission from Low-Temperature Grown a-SiNx:H Film after Different Oxidation Routes
DONG Heng-Ping, HUANG Rui, WANG Dan-Qing, CHEN Kun-Ji, LI Wei, MAZhong-Yuan, XU Jun, HUANG Xin-Fan
Chin. Phys. Lett. 2008, 25 (11): 4147-4150 .  
Abstract   PDF(pc) (784KB) ( 1004 )
Room-temperature deposited amorphous silicon nitride (a-SiNx:H) films exhibit intense green light emission after post-treated by plasma oxidation, thermal oxidation and natural oxidation, respectively. All the photoluminescence (PL) spectra are peaked at around 500nm, independent of oxidation method and excitation wavelength. Compared with the PL results from oxidized a-Si:H and as-deposited a-SiNx:H samples, it is indicated that not only oxygen but also nitrogen is of an important role in enhancing light emission from the oxidized a-SiNx:H. Combining the PL results with the analyses of the bonding configurations as well as chemical compositions of the films, the strong green light emission is suggested to be from radiative recombination in luminescent centres related to N--Si--O bonds.
Parameter Study on Far-Field Sub-Diffraction-Limited Hyperlens
HU Ji-Gang, , CAO Yong, WANG Pei, LU Yong-Hua, MING Hai,
Chin. Phys. Lett. 2008, 25 (11): 4151-4153 .  
Abstract   PDF(pc) (508KB) ( 465 )
Influence of hyperlens structure parameters, such as curvature radius and layer number, and incident wavelength on the beam propagation is numerically investigated by FDTD. It is found that the intensity and the full width at half maximum (FWHM) of the output beam can be controlled by the structure parameters and operating wavelength. The optimized structure
parameters and operating wavelength are obtained, which will be of great significance in design and fabrication of optical hyperlens with high resolution.
Field Emission Properties of Ball-Like Nano-Carbon Thin Films Deposited on Mo Films with Accidented Topography
WANG Long-Yang, WANG Xiao-Ping, WANG Li-Jun, ZHANG Lei
Chin. Phys. Lett. 2008, 25 (11): 4154-4157 .  
Abstract   PDF(pc) (608KB) ( 398 )
Ball-like nano-carbon thin films (BNCTs) are grown on Mo layers by microwave plasma chemical vapour deposition (MPCVD) system. The Mo layers are deposited on ceramic substrates by electron beam deposition method and are pretreated by ultrasonically scratching. The optimization effects of ultrasonically scratching pretreatment on the surface micro-structures of carbon films are studied. It is found from field-emission scanning electron microscope (FE-SEM) images and Raman spectra that the surface structures of the carbon films deposited on Mo pretreated are improved, which are composed of highly uniform nano-structured carbon balls with considerable disorder structures. Field emission (FE) measurements are carried out using a diode structure. The experimental results indicate that the BNCTs exhibit good FE properties, which have the turn on field of 1.56V/μm, and the current density of 1.0mA/cm2 at electric field of 4.0V/μm, the uniformly distributed emission site density from a broad well-proportioned emission area of 4cm2 are also obtained. Linearity is observed in Fowler--Nordheim (F-N) plots in higher field region, and the possible emission mechanism of BNCTs is discussed.
Fabrication and Characterization of Mg-Doped GaN Nanowires
ZHANG Dong-Dong, XUE Cheng-Shan, ZHUANG Hui-Zhao, HUANG Ying-Long, WANG Zou-Ping, WANG Ying, GUO Yong-Fu
Chin. Phys. Lett. 2008, 25 (11): 4158-4161 .  
Abstract   PDF(pc) (1030KB) ( 864 )
Mg-doped GaN nanowires have been synthesized by ammoniating Ga2O3 films doped with Mg under flowing ammonia atmosphere at 850°C. The Mg-doped GaN nanowires are characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL). The results demonstrate that the nanowires are single crystalline with hexagonal wurzite structure. The diameters of the nanowires are 20-30nm and the lengths are 50-100μm. The GaN nanowires show three emission bands with well-defined PL peak at 3.45eV, 3.26eV, 2.95eV, respectively. The large distinct blueshift of the bandgap emission can be attributed to the Burstein--Moss effect. The peak at 3.26eV represents the transition from the conduction-band edge to the acceptor level AM (acceptor Mg). The growth mechanism of crystalline GaN nanowires is discussed briefly.
Distributed Feedback Laser with Sampled Grating
WANG Huan, ZHU Hong-Liang, JIA Ling-Hui, CHEN Xiang-Fei, LI Jing-Si, WANG Wei
Chin. Phys. Lett. 2008, 25 (11): 4162-4164 .  
Abstract   PDF(pc) (369KB) ( 579 )

A distributed feedback laser with the sampled grating has been designed and fabricated. The typical threshold current of the sampled grating based DFB laser is 32mA, and the output power is about 10mW at the injected current of 100mA. The lasing wavelength is 1.5564μm, which is the -1st order mode of the sampled grating.

Improvement of Plasticity of Ti-Based Bulk Metallic Glasses by Addition of Nb
SHAN Sheng-Feng, ZHAN Zai-Ji, FAN Chang-Zeng, JIA Yuan-Zhi, ZHANG Bao-Qing, LIU Ri-Ping, WANG Wen-Kui
Chin. Phys. Lett. 2008, 25 (11): 4165-4167 .  
Abstract   PDF(pc) (654KB) ( 595 )
Ti-based bulk metallic glasses (Ti40Zr25Cu9Ni8Be18)100-xNbx with x=0 to 5at.% are prepared by copper-mold casting. The glass formation ability is almost unchanged by addition of Nb. The compression plasticity is, however, apparently changed, from 3% at x=0 to 13% at x=3, about 330% increases at the strain rate of 1×10-4s-1. The increment of the plasticity can be attributed to the segregation of Nb in the area of shear bands during the compression processing. An effective way to increase the plasticity of Ti-based bulk metallic glasses is thus proposed.
Effect of Low Diffusion Coefficient on Eutectic Instability of Al-25wt%Sm Alloy
WANG Nan
Chin. Phys. Lett. 2008, 25 (11): 4168-4170 .  
Abstract   PDF(pc) (458KB) ( 451 )
Diffusion coefficient decides the solute diffusion length and is a critical parameter in the selection of microstructure scales and in governing microstructure transitions. Al-25wt%Sm alloy is selected to reveal the impact of low diffusion coefficient on the eutectic instability, and the results are compared with those of Al--Cu alloys. Laser remelting experiments are performed and the transition growth velocity from eutectic to α-Al dendrite is examined. Compared with Al--Cu alloys, the eutectic instability takes place at a velocity more than one order of magnitude smaller. The theoretical calculation by the Trivedi--Magnin--Kurz (TMK) model also predicts that the eutectic will become instable at smaller growth velocity for Al--Sm alloy than Al--Cu alloy, which is ascribed to the low diffusion coefficient.
Annealing Induced Aggregations and Sign Alterations of Nonlinear Absorption and Refraction of Dense Au Nanoparticles in TiO2 Films
PENG Xiao-Niu, LI Min, YU Liao, ZHANG Xian, ZHOU Li
Chin. Phys. Lett. 2008, 25 (11): 4171-4173 .  
Abstract   PDF(pc) (951KB) ( 421 )
Au-TiO2 dis-conductive composite films with Au atom concentrate as high as 82% are prepared by using reactive co-sputtering technique. The annealing effect on the nanostructures and optical nonlinearities of the composite films are investigated. Au nanoparticles aggregated to semi-continuum network structures during the annealing processes. As the annealing temperature increases from 25°C to 400°C, the surface plasmon absorption band is shifted and its strength is increased, consequently, the nonlinear absorption coefficient β decreases from 5.6×104cm/GW to -1.7×104cm/GW, while the nonlinear refractive index γ increases from -0.95cm2/GW to 1.3cm2/GW.
High Speed and Ultra-Low-Power Phase Change Line Cell Memory Based on SiSb Thin Films with Nanoscale Gap of Electrodes Less Than 100nm
LV Shi-Long, SONG Zhi-Tang, ZHANG Ting, FENG Song-Lin
Chin. Phys. Lett. 2008, 25 (11): 4174-4176 .  
Abstract   PDF(pc) (412KB) ( 421 )
Si16Sb84-based line cell phase change random access memory (PCRAM), in which the Si16Sb84 phase change line is contacted by TiN electrodes with a nanoscale gap, is fabricated by electron beam lithography. The lowest current and measured pulse width for RESET operation are 115μA and 18ns, respectively. The measured shortest pulse width for recrystallization is 110ns, with applied pulse amplitude of 1.5V. SET and RESET currents for line cells with different line lengths are determined. Endurance of 106 cycles with a resistance ratio of above 800 has been achieved.
Network Entropy Based on Topology Configuration and Its Computation to Random Networks
LI Ji, WANG Bing-Hong, WANG Wen-Xu, ZHOU Tao
Chin. Phys. Lett. 2008, 25 (11): 4177-4180 .  
Abstract   PDF(pc) (269KB) ( 1060 )

A definition of network entropy is presented, and as an example, the relationship between the value of network entropy of ER network model and the connect probability p as well as the total nodes N is discussed. The theoretical result and the simulation result based on the network entropy of the ER network are in agreement well with each other. The result indicated that different from the other network entropy reported before, the network entropy defined here has an obvious difference from different type of random networks or networks having different total nodes. Thus, this network entropy may portray the characters of complex networks better. It is also pointed out that, with the aid of network entropy defined, the concept of equilibrium networks and the concept of non-equilibrium networks may be introduced, and a quantitative measurement to describe the deviation to equilibrium state of a complex network is carried out.

Node Weight Distribution and Disparity of Some Collaboration--Competition Networks
FU Chun-Hua, XU Xiu-Lian, LIU Ai-Fen, WU Yong-Ping, SHEN Dan, LIU Shui-Jing, QIAN Xia, FENG Ya-Chao, WEI Cheng-Liang, HE Da-Ren
Chin. Phys. Lett. 2008, 25 (11): 4181-4184 .  
Abstract   PDF(pc) (424KB) ( 1147 )

We present an empirical investigation of 14 real world networks, which can be described by bipartite graphs. We show that the basic elements (the actor nodes) in all the networks cooperate and compete in some acts (activities, organizations, or events). Each node is assigned by a `node weight', which denotes the obtained competition result. We are interested in the distribution and disparity of the node weight and propose three parameters for the description. Firstly, empirically we observe that the total node weight distributions of all the systems may be fitted by the so-called `shifted power law' function form. The key parameters of the function, α and γ, can be used to describe the disparity. Secondly, a `node weight disparity', Y, is defined for the same purpose. The empirical relationships among the parameters Y, α and γ, are obtained. From the relationships between Y and α as well as Y and γ, one can deduce the relationship between α and γ, which is in a good agreement with the empirically obtained relationship. The results show that the node weight distribution is very uneven.

Non-Thermal Photon Emission from Shell-Type Supernova Remnants
DOU Ya-Nan, ZHANG Li
Chin. Phys. Lett. 2008, 25 (11): 4185-4188 .  
Abstract   PDF(pc) (324KB) ( 382 )
We study the non-thermal photon emission from shell-type supernova remnants (SNRs) in the frame of a two-zone model. In this model, the sites of acceleration, escape and subsequent radiation of particles (both electron and proton) are divided into acceleration and escape zones, respectively. The particle distributions consist of two components, one is produced inside the acceleration zone, the other in the escape zone. We apply this model to two young and one old shell-type SNRs and show that the observed multi-waveband photon spectra for the three SNRs can be explained well in this model and high-energy γ-rays from these SNRs may have hadronic origins.
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