Chin. Phys. Lett.

Volume 26 Issue 3

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GENERAL

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Geometric Description of Fibre Bundle Surface for Birkhoff System

CAO Li-Mei, SUN Hua-Fei, ZHANG Zhen-Ning

Chin. Phys. Lett. 2009, 26 (3): 030201 . DOI: 10.1088/0256-307X/26/3/030201

Abstract

PDF(pc) (195KB) ( 653 )

A fibre bundle surface for the Birkhoff system is constructed. The metric and the Riemannian connection of the surface are defined and the representation of the Gaussian curvature of this surface is presented. Finally, three examples for the Birkhoff system are given to illustrate our results.

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N-Soliton Solutions of Non-Isospectral Derivative Nonlinear Schrödinger Equation

ZHAO Song-Lin, ZHANG Da-Jun, CHEN Deng-Yuan

Chin. Phys. Lett. 2009, 26 (3): 030202 . DOI: 10.1088/0256-307X/26/3/030202

Abstract

PDF(pc) (386KB) ( 1392 )

Bilinear forms of the non-isospectral derivative nonlinear Schrödinger equation are derived. The N-soliton solutions of this equation are obtained by Hirota's method.

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Lie Symmetry and Nonlinear Instability in Computation of KdV Solitons

ZHANG Hua-Yan, RAN Zheng

Chin. Phys. Lett. 2009, 26 (3): 030203 . DOI: 10.1088/0256-307X/26/3/030203

Abstract

PDF(pc) (218KB) ( 774 )

The soliton calculation method put forward by Zabusky and Kruskal has played an important role in the development of soliton theory, however numerous numerical results show that even though the parameters satisfy the linear stability condition, nonlinear instability will also occur. We notice an exception in the numerical calculation of soliton, gain the linear stability condition of the second order Leap-frog scheme constructed by Zabusky and Kruskal, and then draw the perturbed equation with the finite difference method. Also, we solve the symmetry group of the KdV equation with the knowledge of the invariance of Lie symmetry group and then discuss whether the perturbed equation and the conservation law keep the corresponding symmetry. The conservation law of KdV equation satisfies the scaling transformation, while the perturbed equation does not satisfy the Galilean invariance condition and the scaling invariance condition. It is demonstrated that the numerical simulation destroy some physical characteristics of the original KdV equation. The nonlinear instability in the calculation of solitons is related to the breaking of symmetry

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A Scheme for Atomic Entangled States and Quantum Gate Operations in Cavity QED

LI Peng-Bo, GU Ying, GONG Qi-Huang, GUO Guang-Can,

Chin. Phys. Lett. 2009, 26 (3): 030301 . DOI: 10.1088/0256-307X/26/3/030301

Abstract

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We propose a scheme for controllably entangling the ground states of five-state W-type atoms confined in a cavity and realizing swap gate and phase gate operations. In this scheme the cavity is only virtually excited and the atomic excited states are almost not occupied, so the produced entangled states and quantum logic operations are very robust against the cavity decay and atomic spontaneous emission.

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A Solved Model to Show Insufficiency of Quantitative Adiabatic Condition

LIU Long-Jiang, LIU Yu-Zhen, TONG Dian-Min

Chin. Phys. Lett. 2009, 26 (3): 030302 . DOI: 10.1088/0256-307X/26/3/030302

Abstract

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The adiabatic theorem is a useful tool in processing quantum systems slowly evolving, but its practical application depends on the quantitative condition expressed by Hamiltonian's eigenvalues and eigenstates, which is usually taken as a sufficient condition. Recently, the sufficiency of the condition was questioned, and several counterexamples have been reported. Here we present a new solved model to show the insufficiency of the traditional quantitative adiabatic condition.

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Special Lie Symmetry and Hojman Conserved Quantity of Appell Equations for a Holonomic System

JIA Li-Qun, CUI Jin-Chao, LUO Shao-Kai, YANG Xin-Fang

Chin. Phys. Lett. 2009, 26 (3): 030303 . DOI: 10.1088/0256-307X/26/3/030303

Abstract

PDF(pc) (251KB) ( 894 )

Special Lie symmetry and Hojman conserved quantity of Appell equations for a holonomic system are studied. Appell equations and differential equations of motion for holonomic mechanic systems are established. Under special Lie nfinitesimal transformations in which the time is invariable, the determining equation of the special Lie symmetry and the expressions of Hojman conserved quantity for Appell equations of holonomic systems are presented. Finally, an example is given to illustrate the application of the results.

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Calculation of Covariance Matrix for Multi-mode Gaussian States in Decoherence Processes

XIANG Shao-Hua, SHAO Bin, SONG Ke-Hui

Chin. Phys. Lett. 2009, 26 (3): 030304 . DOI: 10.1088/0256-307X/26/3/030304

Abstract

PDF(pc) (240KB) ( 3040 )

We investigate the dynamics of n single-mode continuous variable systems in a generic Gaussian state under the influence of the independent and correlated noises making use of the characteristic function method. In two models the bath is assumed to be a squeezed thermal one. We derive an explicit input-output expression between the initial and final covariance matrices. As an example, we study the evolution of entanglement of three-mode Gaussian state embedded in two noisy models.

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Dirac Quasinormal Modes of a Schwarzschild Black Hole surrounded by Free Static Spherically Symmetric Quintessence

ZHANG Yu, , WANG Chun-Yan, GUI Yuan-Xing, WANG Fu-Jun, YU Fei

Chin. Phys. Lett. 2009, 26 (3): 030401 . DOI: 10.1088/0256-307X/26/3/030401

Abstract

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We evaluate the quasinormal modes of massless Dirac perturbation in a Schwarzschild black hole surrounded by the free static spherically symmetric quintessence using the third-order Wentzel-Kramers-Brillouin (WKB) approximation. The result shows that the massless Dirac field damps more slowly due to the presence of quintessence. The real part of the quasinormal modes increases and the absolute value of the imaginary part increases when the state parameter w_q increases. In other words, the massless Dirac field decays more rapidly for the larger w_q. The peak value of potential barrier becomes higher as |k| increases and the location of peak moves along the right for fixed w_q.

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Orbital Precession Effect in the Reissner-Nordström Field with a Global Monopole

GONG Tian-Xi, WANG Yong-Jiu

Chin. Phys. Lett. 2009, 26 (3): 030402 . DOI: 10.1088/0256-307X/26/3/030402

Abstract

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Using an elegant mathematical method advanced by us, we calculate the orbital precession effect in the gravitational field of the centre mass with electric charge and a global monopole. Analysing the results, we obtain that the orbital precession effect increases on account of the global symmetry breaking, but the orbital precession effect aroused by the electric charge of the field source reduces the orbital precession effect aroused by the mass of the field source. Generalizing the effect in the Schwarzschild field, we obtain interesting results by discussing the parameters of the celestial body, which provide a feasible experimental verification of the general relativity.

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An Adaptive Denoising Algorithm for Noisy Chaotic Signals Based on Local Sparse Representation

XIE Zong-Bo, FENG Jiu-Chao

Chin. Phys. Lett. 2009, 26 (3): 030501 . DOI: 10.1088/0256-307X/26/3/030501

Abstract

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An adaptive denoising algorithm based on local sparse representation (local SR) is proposed. The basic idea is applying SR locally to clusters of signals embedded in a high-dimensional space of delayed coordinates. The clusters of signals are represented by the sparse linear combinations of atoms depending on the nature of the signal. The algorithm is applied to noisy chaotic signals denoising for testing its performance. In comparison with recently reported leading alternative denoising algorithms such as kernel principle component analysis (Kernel PCA), local independent component analysis (local ICA), local PCA, and wavelet shrinkage (WS), the proposed algorithm is more efficient.

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Localized Waves in Nonlinear Systems with Spatially Inhomogeneous Nonlinearity

GAO Yuan, TANG Xiao-Yan, LOU Sen-Yue,

Chin. Phys. Lett. 2009, 26 (3): 030502 . DOI: 10.1088/0256-307X/26/3/030502

Abstract

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A type of (2+1)-dimensional nonlinear Schrödinger equation with spatially inhomogeneous nonlinearity and an external potential is studied. It is found that special external potentials and spatially nonlinearities can support nonlinear localized waves.

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Self-Stable Chaos Control of dc-dc Converter

LU Wei-Guo, ZHOU Luo-Wei, WU Jun-Ke

Chin. Phys. Lett. 2009, 26 (3): 030503 . DOI: 10.1088/0256-307X/26/3/030503

Abstract

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A new concept related to self-stable chaos control is first put forward, and its theoretical basis and realization are presented from the frequency-domain perspective. With a new analogous-circuit realization of this control its
applications in the voltage-mode Buck converter is discussed. The harmonic-balance method is applied to determine the control range of the control parameter. The experiment results given in the last part confirm the validity of the proposed control method.

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Stochastic Signal Induced Multiple Spatial Coherence Resonances and Spiral Waves in Excitable Media

LI Yu-Ye, ZHANG Hui-Min, WEI Chun-Ling, YANG Ming-Hao, GU Hua-Guang, REN Wei

Chin. Phys. Lett. 2009, 26 (3): 030504 . DOI: 10.1088/0256-307X/26/3/030504

Abstract

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Multiple spatial coherence resonances and spiral waves with various temporal-spatial structures are simulated in a two-dimensional network of excitable cells driven by a stochastic signal. The relationship between the multiple resonances and correspondingly different transitions of the spiral wave are elucidated. The results further provide a possible approach of applications of stochastic signal to evoke pattern transitions in excitable media.

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Reactive Coupling Effects on Amplitude Death of Coupled Limit-Cycle Systems

WANG Jin-Hua, LI Xiao-Wen

Chin. Phys. Lett. 2009, 26 (3): 030505 . DOI: 10.1088/0256-307X/26/3/030505

Abstract

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Amplitude death in coupled limit-cycle systems induced by the reactive coupling is studied. The presence of reactive coupling parameter changes the amplitude death process of the system, and increases the critical coupling strength for the emergence of amplitude death. When the systems are in the state of complete or partial amplitude death, increasing the reactive coupling will increase the number of partial synchronization groups, implying the increase of disorder of the system. Increasing the reactive coupling makes the elimination of the amplitude death of the systems harder.

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Initial-Value Problem of a Coupled Dispersionless System: Dynamical System Approach

Kuetche Kamgang Victor, Gambo Betchewe, Bouetou Bouetou Thomas, , Timoleon Crepin Kofane,

Chin. Phys. Lett. 2009, 26 (3): 030506 . DOI: 10.1088/0256-307X/26/3/030506

Abstract

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We investigate the dynamical behaviour of a coupled dispersionless system (CDS) by solving its initial-value problem following a dynamical system approach. As a result, we unearth a typical miscellaneous travelling waves including the localized and periodic ones. We also investigate the energy density of such waves and find that under some boundary conditions, the localized waves moving towards positive direction are more stable than the periodic waves which on contrary stand for the most stable travelling waves in another situation of boundary conditions.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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Precise Measurement of Solar Neutrino Oscillation Parameters from Recent Experiments

YANG Ping, LIU Qiu-Yu

Chin. Phys. Lett. 2009, 26 (3): 031401 . DOI: 10.1088/0256-307X/26/3/031401

Abstract

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We analyse the available data of solar neutrino experiments up to the date May 2008, including SK-I, SK-II, SNO phase-I, SNO phase-II and first-generation Ga and Cl experiments. They show great improvement in constraints on solar neutrino oscillation parameters. Together with the new results from long base line reactor experiment KamLAND, the parameters are precisely determined, with 1σ allowed region in Δm²₁₂=7.586^+0.212_-0.203×10^-5eV², tan²θ₁₂=0.457^+0.076_-0.067.

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Neutrino Oscillation Induced by Chiral Phase Transition

MU Cheng-Fu, SUN Gao-Feng, ZHUANG Peng-Fei

Chin. Phys. Lett. 2009, 26 (3): 031402 . DOI: 10.1088/0256-307X/26/3/031402

Abstract

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Electric charge neutrality provides a relationship between chiral dynamics and neutrino propagation in compact stars. Due to the sudden drop of the electron density at the first-order chiral phase transition, the oscillation for low energy neutrinos is significant and can be regarded as a signature of chiral symmetry restoration in the core of compact stars.

NUCLEAR PHYSICS

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Nuclear Current and Magnetic Rotation

PENG Jing, XING Li-Feng

Chin. Phys. Lett. 2009, 26 (3): 032101 . DOI: 10.1088/0256-307X/26/3/032101

Abstract

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The magnetic rotational bands based on the configuration πh²_11/2Äνh^-2_{11/2 in}¹⁴²Gd are investigated with the newly developed tilted axis cranking relativistic mean field (RMF) theory with and without nuclear current. The effect of the nuclear current is discussed by comparing the total Routhians, single particle levels, electromagnetic transition probabilities B(M1) and B(E2) in self-consistent tilted axis cranking RMF calculation with those obtained without the nuclear current. The nuclear currents are found to play an important role in the magnetic rotation of nuclei.

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Relativistic Mean Field Study on Halo Structures of Mirror Nuclei

LIANG Yu-Jie, LI Yan-Song, LIU Zu-Hua, ZHOU Hong-Yu

Chin. Phys. Lett. 2009, 26 (3): 032102 . DOI: 10.1088/0256-307X/26/3/032102

Abstract

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Halo structures of some light mirror nuclei are investigated with the relativistic mean field (RMF) theory. The calculations show that the dispersion of the valence proton is larger than that of the valence neutron in its mirror nucleus, the difference between the root-mean-square (rms) radius of the valence nucleon in each pair of mirror nuclei becomes smaller with the increase of the mass number A, and all the ratios of the rms radius of the valence nucleon to that of the matter in each pair of mirror nuclei decrease almost linearly with the increase of the mass number A.

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Stability of Strutinsky Shell Correction Energy in Relativistic Mean Field Theory

NIU Yi-Fei, LIANG Hao-Zhao, MENG Jie,

Chin. Phys. Lett. 2009, 26 (3): 032103 . DOI: 10.1088/0256-307X/26/3/032103

Abstract

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The single-particle spectrum obtained from the relativistic mean field (RMF) theory is used to extract the shell correction energy with the Strutinsky method. Considering the delicate balance between the plateau condition in the Strutinsky smoothing procedure and the convergence for the total binding energy, the proper space sizes used in solving the RMF equations are investigated in detail by taking ²⁰⁸Pb as an example. With the proper space sizes, almost the same shell correction energies are obtained by solving the RMF equations either on basis space or in coordinate space.

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Experimental Evidence of Two-Proton Emissions from ¹⁸Ne Excited State

JIA Fei, LIN Cheng-Jian, ZHANG Huan-Qiao, YANG Feng, JIA Hui-Ming, XU Xin-Xing, WU Zhen-Dong, LIU Zu-Hua, ZHANG Gao-Long, ZHANG Chun-Lei

Chin. Phys. Lett. 2009, 26 (3): 032301 . DOI: 10.1088/0256-307X/26/3/032301

Abstract

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Experiment ¹⁸Ne+¹⁹⁷Au was performed in Heavy Ion Research Facility Radioactive Ion Beam Line at Lanzhou (RIBLL). The nuclear energy levels of ¹⁸Ne were built by complete kinematical reconstruction of the decay products and diproton decay were observed from ¹⁸Ne excited states. At 6.15MeV, the experimental relative momentum and angular correlations of the emitted protons are given. The obvious enhancement at |q_rel|=23MeV/c and θ_c.m. =40° shows the experimental criterion of ²He cluster decay from ¹⁸Ne^q.

ATOMIC AND MOLECULAR PHYSICS

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Coherent Phase Control of Multiphoton Ionization in Three-Level Ladder-Type System

ZHANG Shi-An, CHEN Yu-Ting, WANG Zu-Geng, SUN Zhen-Rong

Chin. Phys. Lett. 2009, 26 (3): 033201 . DOI: 10.1088/0256-307X/26/3/033201

Abstract

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We present the theoretical investigation of photoelectron spectroscopy resulting from the strong field induced multiphoton ionization in a typical three-level ladder-style system. Our theoretical results show that the photoelectron spectral structure can be alternatively steered by spectral phase modulation. This physical mechanism for strong field quantum control is explicitly exploited by the time-dependent dressed state population. It is concluded that the phase-shaped laser pulses can be used to selectively manipulate the multiphoton ionization process in complicated quantum systems.

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Measurement of the KLL Dielectronic Recombination Resonances in He-like to C-like Kr Ions

HU Zhi-Min, YANG Jia-Min, ZHANG Ji-Yan, ZHU Tuo, ZHANG Bao-Han, DINGYao-Nan, ZHENG Zhi-Jian, DUAN Bin, LI Yue-Ming, YAN Jun

Chin. Phys. Lett. 2009, 26 (3): 033401 . DOI: 10.1088/0256-307X/26/3/033401

Abstract

PDF(pc) (799KB) ( 729 )

The KLL dielectronic recombination processes of highly charged He-like to C-like Kr ions have been studied experimentally. The measurement was performed on the newly developed Shanghai electron beam ion trap (Shanghai-EBIT) facility. Characteristic x-rays from both dielectronic recombination and radiative recombination are detected as the electron beam energy is scanned through the resonances. The KLL resonant strengths obtained are 5.41×10^-19, 4.33×10^-19,3.59×10^-19,2.05×10^-19 and 0.98×10^-19cm²eV for He-like to C-like Kr ions, respectively.

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A Parallel Study on (BN)_n and (HAlNH)_n (n=11-22) Clusters: Geometry and Stability

JIAN Guo-Qiang, CHEN Xin, HU Zheng

Chin. Phys. Lett. 2009, 26 (3): 033601 . DOI: 10.1088/0256-307X/26/3/033601

Abstract

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A parallel study on (BN)_n and (HAlNH)_n (n=11-22) clusters is presented herein with ab initio HF/6-31G* method. Two types of structures, i.e. cage-like and needle-shaped, are constructed. The calculated results indicate that the classical cage-like geometry is energetically more favourable for (BN)_n while the needle-shaped (HAlNH)_n structures are more stable than their cage-like counterparts. It is suggested that the nanostructures with higher structural similarity to the corresponding bulk phases possess greater stability. This idea leads to the viable way to intercept segment from bulk materials to construct models for theoretical study of complex nanostructures.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

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FDTD Investigation on Electromagnetic Scattering from Two-Layered Rough Surfaces under UPML Absorbing Condition

LI Juan, GUO Li-Xin, ZENG Hao

Chin. Phys. Lett. 2009, 26 (3): 034101 . DOI: 10.1088/0256-307X/26/3/034101

Abstract

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Electromagnetic scattering from one-dimensional two-layered rough surfaces is investigated by using finite-difference time-domain algorithm (FDTD). The uniaxial perfectly matched layer (UPML) medium is adopted for truncation of FDTD lattices, in which the finite-difference equations can be used for the total computation domain by properly choosing the uniaxial parameters. The rough surfaces are characterized with Gaussian statistics for the height and the autocorrelation function. The angular distribution of bistatic scattering coefficient from single-layered perfect electric conducting and dielectric rough surface is calculated and it is in good agreement with the numerical result with the conventional method of moments. The influence of the relative permittivity, the incident angle, and the correlative length of two-layered rough surfaces on the bistatic scattering coefficient with different

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Stable High Power and High Beam Quality Diode-Side-Pumped Continuous-Wave Intracavity Frequency-Doubled Nd:YAG Laser

CHENG Xian-Kun, ZHOU Yong, CUI Qian-Jin, YANG Feng, BO Yong, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan,

Chin. Phys. Lett. 2009, 26 (3): 034201 . DOI: 10.1088/0256-307X/26/3/034201

Abstract

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We report a stable high power and high beam quality diode-side-pumped cw green laser from intracavity frequency-doubled Nd:YAG laser with KTP. By using a L-shaped concave--convex resonator, designed with two Nd:YAG rods birefringence compensation, a large fundamental mode size in the laser crystal and a tight focus in the nonlinear crystal could be obtained simultaneously. The green laser delivers a maximum 532nm output power of 23.2W. Under 532nm output power of 20.9W, the beam quality factor is measured to be 4.1, and the fluctuation of the output power is less than 1.4% in an hour.

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Effect of Coma Aberration on Orbital Angular Momentum Spectrum of Vortex Beams

CHEN Zi-Yang, PU Ji-Xiong

Chin. Phys. Lett. 2009, 26 (3): 034202 . DOI: 10.1088/0256-307X/26/3/034202

Abstract

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Spiral spectra of vortex beams with coma aberration are studied. It is shown that the orbital angular momentum (OAM) states of vortex beams with coma aberration are different from those aberration-free vortex beams. Spiral spectra of beams with coma aberration are spreading. It is found that in the presence of coma aberration, the vortex beams contain not only the original OAM component but also other components. A larger coma aberration coefficient and/or a larger beam waist will lead to a wider spreading of the spiral spectrum. The results may have potential applications in information encoding and transmittance.

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Generation and Modulation of Phase Difference of Output Intensities in a Feedback Nd:YAG Laser with an Extracavity Waveplate Rotated

REN Cheng, TAN Yi-Dong, ZHANG Shu-Lian

Chin. Phys. Lett. 2009, 26 (3): 034203 . DOI: 10.1088/0256-307X/26/3/034203

Abstract

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External anisotropic feedback effects on the phase difference behaviour of output intensities in a microchip Nd:YAG laser are presented. By rotating a quarter wave plate placed in the external cavity, the angle between laser initial polarization direction and o-axis of the wave plate is tuned from -45° to 45°, which results in variable extra-cavity birefringence along two orthogonal detection directions. With only one optical path and one wave plate, laser intensities of the two orthogonal directions, both modulated by the external cavity length, are output with a tunable phase difference, which can be continuously changed from zero to twice as large as that of the waveplate. Experimental results as well as a theoretical analysis based on Fabry--Perot cavity equivalent model and the refractive index ellipsoid, are presented. The potential applications of this phenomenon are also discussed.

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High-Order Above-Threshold Ionization of H₂⁺ in Intense Laser Field

GUO Ying-Chun, FU Pan-Ming, WANG Bing-Bing

Chin. Phys. Lett. 2009, 26 (3): 034204 . DOI: 10.1088/0256-307X/26/3/034204

Abstract

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The nonperturbative quantum electrodynamics method proposed by Fu et al. [Phys. Rev. A 75 (2007) 063419] is employed to study the high-order above-threshold ionization (ATI) of a diatomic molecule. Based on this frequency-domain theory, the high-order ATI process can be regarded as ATI followed by laser-assisted collision, where the total transition amplitude is the coherent summation of the contributions from each ATI channel. The angular-resolved ATI spectrum, which agrees with the results by Becker et al. based on the time-domain method, is obtained by this frequency domain theory. Furthermore, it is demonstrated that the interference characteristics representing the molecular structure in the ATI spectrum originates from the recollision of the electron with two-centre ion in each ATI channel.

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A Strip-Loading Optical Waveguide Using Well Poled Stability Organic/Inorganic Hybrid Materials

GAO Wei-Nan, TIAN Mei-Qiang, SUN Xiao-Qiang, WANG Wei, DENG Ling, GAOLei, ZHANG Da-Ming

Chin. Phys. Lett. 2009, 26 (3): 034205 . DOI: 10.1088/0256-307X/26/3/034205

Abstract

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An optical waveguide for a polymer modulator based on organic/inorganic hybrid electro-optic (EO) materials is designed and fabricated by utilizing a strip-loading structure. This hybrid material has a controllable refractive index, high EO coefficient and good poled stability, which are suitable for the EO modulators and switches. The embedded waveguide made of the above EO material can reduce the coupling loss. The light is coupled into the guided-core layer and then undergoes a transition from the buried waveguide into the EO material. Obvious modulation is observed by application of ac voltage to the EO material. The measured V_π of co-planar waveguide (CPW) is 5V for the Mach-Zehnder (MZ) modulator in length of 3.5cm.

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Experimental Study on Preparation Efficiency of Microstructured-Fibre Based Heralded Single-Photon Source at 1.5μm

ZHANG Si-Tuo, ZHANG Wei, ZHOU Qiang, HUANG Yi-Dong, PENG Jiang-De

Chin. Phys. Lett. 2009, 26 (3): 034206 . DOI: 10.1088/0256-307X/26/3/034206

Abstract

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We present an experimental study on the microstructured-fibre (MSF) based heralded single photon source (HSPS) at 1.5μm. The preparation efficiency is measured to be 8.7% under room temperature. The analysis of the experimental results shows that the preparation efficiency can be improved up to 22.9% by the Raman noise suppression with fibre cooling under the experimental setup parameters. Further efficiency improvement could be achieved by improving the collection efficiency and reducing dark counts of single photon detectors (SPDs). The experimental results and analysis show great potential applications of the MSF in high efficient HSPSs.

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A Proposal and Demonstration for Photonic Generation of a Microwave Signal by Incorporating a Microring Resonator

CHEN Guo-Jie, HUANG De-Xiu, ZHANG Xin-Liang, CAO Hui, CHEN Wei-Cheng

Chin. Phys. Lett. 2009, 26 (3): 034207 . DOI: 10.1088/0256-307X/26/3/034207

Abstract

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A proposal for photonic generation of a microwave signal is presented by employing a dual wavelength erbium-doped fibre ring laser. In the laser, a microring resonator is cascaded with a tunable bandpass filter to serve as a dual-wavelength selector, an unpumped polarization maintaining erbium-doped fibre is used as a saturable absorber. By replacing the microring resonator with a delay interferometer to verify the proposal, a wavelength-tunable dual wavelength single longitudinal mode laser is demonstrated, and a microwave signal at 10.01GHz with a linewidth of less than 25kHz is obtained by beating the two wavelengths at a photodetector.

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A Mid-IR 14.1W ZnGeP₂ Optical Parametric Oscillator Pumped by a Tm,Ho:GdVO₄ Laser

ZHU Guo-Li, JU You-Lun, WANG Tian-Heng, WANG Yue-Zhu

Chin. Phys. Lett. 2009, 26 (3): 034208 . DOI: 10.1088/0256-307X/26/3/034208

Abstract

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We report a high power and high efficiency double resonant ZnGeP₂ (ZGP) optical parametric oscillator (OPO) pumped by a Tm,Ho:GdVO₄ laser. We employ a Tm,Ho:GdVO₄ laser as the pump source operated at 2.049μm with M²=1.1. The ZGP OPO can generate a total combined output power of 14.1W at 3.80μm signal and 4.45μm idler under pumping power of 28.7W. The slope efficiency reaches 61.8%, and M²=3.6 for OPO output is obtained.

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Extraction of Parameters of Random Self-Affine Fractal Surfaces from Light Scattered Intensity by Levenberg-Marquardt Algorithm

ZHANG Ning-Yu, TENG Shu-Yun, SONG Hong-Sheng, LIU Gui-Yuan, CHENG Chuan-Fu

Chin. Phys. Lett. 2009, 26 (3): 034209 . DOI: 10.1088/0256-307X/26/3/034209

Abstract

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A method for simultaneously extracting the parameters of self-affine fractal surfaces from a single experimental profile of scattered intensity data is proposed. The Levenberg-Marquardt algorithm is introduced to fit the theoretical equation for the scattering intensity profile to the experimental data. A precision system is designed for acquisition of scattering intensity data using the Boxcar integration technique. The surface parameters extracted (root-mean-square roughness w, lateral correlation length ξ, and roughness exponent α) are compared to those obtained using atomic force microscopy.

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Preparation and Characterization of Transparent Conductive Nb-Doped ZnO Films by Radio-Frequency Sputtering

CAO Feng, WANG Yi-Ding, LIU Da-Li, YIN Jing-Zhi, GUO Bao-Jia, LI Lei, AN Yu-Peng

Chin. Phys. Lett. 2009, 26 (3): 034210 . DOI: 10.1088/0256-307X/26/3/034210

Abstract

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Niobium-doped ZnO (NZO) transparent conductive films are deposited on glass substrates by rf sputtering at 300°C. Effects of sputtering power on the structural, morphologic, electrical, and optical properties of NZO films are investigated by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Hall measurement, and optical transmission spectroscopy. The obtained films are polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The minimum resistivity of 4.0×10^-4Ω・cm is obtained from the film grown at the sputtering power of 170W. The average optical transmittance of the films is over 90%.

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Investigation on Guided-Mode Characteristics of Hollow-Core Photonic Crystal Fibre at Near-Infrared Wavelengths

YUAN Jin-Hui, YU Chong-Xiu, SANG Xin-Zhu, LI Wen-Jing, ZHOU Gui-Yao, LI Shu-Guang, HOU Lan-Tian

Chin. Phys. Lett. 2009, 26 (3): 034211 . DOI: 10.1088/0256-307X/26/3/034211

Abstract

PDF(pc) (495KB) ( 968 )

Guided-mode characteristics of hollow-core photonic crystal fibre (HC-PCF) are experimentally and theoretically investigated. The transmission spectrum in the range from 755 to 845nm is observed and the loss is measured to be 0.12dB/m at 800nm by cut-back method. Based on the full-vector beam propagation method and the full-vector plane-wave method, the characteristics of mode field over propagation distance 1m are simulated, and the results show that the propagation efficiency can be above 80%. Compared with the fundamental guided mode well confined in air core within shorter propagation distance, the second-order guided mode leaks into the cladding region and gradually attenuates due to larger refractive index difference. The primary loss factors in HC-PCF and the corresponding solutions are elementarily discussed.

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Dynamics of Incoherent Photovoltaic Spatial Solitons

ZHANG Yi-Qi, LU Ke-Qing, ZHANG Mei-Zhi, LI Ke-Hao, LIU Shuang, ZHANG Yan-Peng

Chin. Phys. Lett. 2009, 26 (3): 034212 . DOI: 10.1088/0256-307X/26/3/034212

Abstract

PDF(pc) (405KB) ( 813 )

Propagation properties of bright and dark incoherent beams are numerically studied in photovoltaic-photorefractive crystal by using coherent density approach for the first time. Numerical simulations not only exhibit that bright incoherent photovoltaic quasi-soliton, grey-like incoherent photovoltaic soliton, incoherent soliton doublet and triplet can be established under proper conditions, but also display that the spatial coherence properties of these incoherent beams can be significantly affected during propagation by the photovoltaic field.

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Suppression of Nonlinear Patterning Effect in Wavelength Conversion Based on Transient Cross-Phase Modulation in Semiconductor Optical Amplifier Assisted with a Detuning Filter

ZHOU En-Bo, ZHANG Xin-Liang, YU Yu, HUANG De-Xiu

Chin. Phys. Lett. 2009, 26 (3): 034213 . DOI: 10.1088/0256-307X/26/3/034213

Abstract

PDF(pc) (316KB) ( 600 )

Nonlinear patterning (NLP) effect in wavelength conversion based on transient cross-phase modulation (XPM) in semiconductor optical amplifier (SOA) assisted with a detuning filter is theoretically investigated. A non-adiabatic model is used to estimate the ultrafast dynamics of gain, phase and electron temperature in the SOA. Simulation results show that the NLP can be greatly suppressed by introducing an assist light, especially for the probe wavelength distant from gain peak. Furthermore, the results also indicate that the improvement is more evident for long wavelength probe light and assist light in counter-propagating configuration.

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A Novel Method for Enhancing Goos-Hänchen Shift in Total Internal Reflection

ZHANG Zhi-Wei, WEN Ting-Dun, ZHANG Ji-Long,

Chin. Phys. Lett. 2009, 26 (3): 034214 . DOI: 10.1088/0256-307X/26/3/034214

Abstract

PDF(pc) (307KB) ( 666 )

Due to the tiny shift in order of optical wavelength for Goos-Hänchen (GH) shift, it is very difficult to directly measure and apply the GH shift. We develop a new method for enhancing GH shift of both TE and TM polarized waves. The method is based on a total reflection prism made of BK9 glass combined with a precise measurement of the resulting spatial displacement with a one-dimensional charge coupled device (CCD). Measurements are performed to examine the validity of the method. Experimental and theoretical results indicate the feasibility of the method with an enhancement in optical wavelenghth shift at millimetre scale. The method is advantageous to application the GH shift in the optical domain, and is also meaningful for measuring even smaller changes in the refractive index of a liquid.

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High Speed 2×2 Optical Switch Based on Carrier Injection Effect in GaAs/AlGaAs

QI Wei, YU Hui, JIANG Xiao-Qing, YANG Jian-Yi, HAO Yin-Lei, ZHOU Qiang, WANG Ming-Hua

Chin. Phys. Lett. 2009, 26 (3): 034215 . DOI: 10.1088/0256-307X/26/3/034215

Abstract

PDF(pc) (345KB) ( 571 )

A 2×2 optical switch based on the carrier injection effect is demonstrated on GaAs/AlGaAs epitaxial material. At an injection current of 80mA, the extinction ratio exceeds 25dB at 1.55μm. The polarization sensitivity of the crosstalk is within ± 0.5dB. The switching speed is below 10ns. The flat response spectrum throughout the 1542-1562nm wavelength range indicates that this device is insensitive to wavelength.

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Discussion on Perturbation to Weak Noether Symmetry and Adiabatic Invariants for Lagrange Systems

WANG Peng, FANG Jian-Hui, WANG Xian-Ming

Chin. Phys. Lett. 2009, 26 (3): 034501 . DOI: 10.1088/0256-307X/26/3/034501

Abstract

PDF(pc) (203KB) ( 779 )

We study a new symmetric perturbation, i.e. weakly Noether symmetric perturbation (WNSP). The criterion and definition of WNSP and Noether symmetric perturbation (NSP) are given. A theorem between WNSP and adiabatic invariants is established. It is concluded that WNSP is different from NSP, the sufficient condition when WNSP is NSP can be presented, and the
former is broader. We apply our results to the planar Kepler problem.

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Radiation Effects on the Flow and Heat Transfer over a Moving Plate in a Parallel Stream

Anuar Ishak

Chin. Phys. Lett. 2009, 26 (3): 034701 . DOI: 10.1088/0256-307X/26/3/034701

Abstract

PDF(pc) (194KB) ( 1477 )

Effects of thermal radiation on the steady laminar boundary layer flow over a moving plate in a moving fluid is investigated. Under certain conditions, the present problem reduces to the classical Blasius and Sakiadis problems. It is found that dual solutions exist when the plate and the fluid move in the opposite directions. Moreover, the existence of thermal radiation is to reduce the heat transfer rate at the surface.

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Lattice Boltzmann Simulation of the Cross Flow Over a Cantilevered and Longitudinally Vibrating Circular Cylinder

XIA Yong, LU De-Tang, LIU Yang, XU You-Sheng

Chin. Phys. Lett. 2009, 26 (3): 034702 . DOI: 10.1088/0256-307X/26/3/034702

Abstract

PDF(pc) (508KB) ( 906 )

The multiple-relaxation-time lattice Boltzmann method (MRT-LBM) is implemented to numerically simulate the cross flow over a longitudinal vibrating circular cylinder. This research is carried out on a three-dimensional (3D) finite cantilevered cylinder to investigate the effect of forced vibration on the wake characteristics and the 3D effect of a cantilevered cylinder. To meet the accuracy of this method, the present calculation is carried out at a low Reynolds number Re=100, as well as to make the vibration obvious, we make the vibration strong enough. The calculation results indicate that the vibration has significant influence on the wake characteristics. When the vibrating is big enough, our early works show that the 2D vortex shedding would be locked up by vibration. Contrarily, this phenomenon would not appear in the present 3D case because of the end effect of the cantilevered cylinder.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Observation of E×B Flow Velocity Profile Change Using Doppler Reflectometry in HL-2A

XIAO Wei-Wen, ZOU Xiao-Lan, DING Xuan-Tong, DONG Jia-Qi, LIU Ze-Tian, SONG Shao-Dong, GAO Ya-Dong, YAO Liang-Hua, FENG Bei-Bin, SONG Xian-Ming, CHEN Cheng-Yuan, SUN Hong-Juan, LI Yong-Gao, YANGQing-Wei, YAN Long-Wen, LIU Yi, DUAN Xu-Ru, PAN Chuan-Hong, LIU Yong

Chin. Phys. Lett. 2009, 26 (3): 035201 . DOI: 10.1088/0256-307X/26/3/035201

Abstract

PDF(pc) (701KB) ( 825 )

A broadband, O-mode sweeping Doppler reflectometry designed for measuring plasma E×B flow velocity profiles is operated in HL-2A. The main feature of the Doppler reflectometry is its capability to be tuned to any selected frequency in total waveband from 26-40GHz. This property enables us to probe several plasma layers within a short time interval during a discharge, permitting the characterization of the radial distribution of plasma fluctuations. The system allows us to extract important information about the velocity change layer, namely its spatial localization. In purely Ohmic discharge a change of the E×B flow velocity profiles has been observed in the region for 28<r<30cm if only the line average density exceeds 2.2×10¹⁹m^-3. The density gradient change is measured in the same region, too.

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Heat Transport of Non-Local Effect with Modulated SMBI on HL-2A

SUN Hong-Juan, DING Xuan-Tong, YAO Liang-Hua, FENG Bei-Bin, LIU Ze-Tian, GAO Ya-Dong, LI Wei, LI Xue-Hong, DUAN Xu-Ru, YANG Qing-Wei

Chin. Phys. Lett. 2009, 26 (3): 035202 . DOI: 10.1088/0256-307X/26/3/035202

Abstract

PDF(pc) (744KB) ( 666 )

Modulated supersonic molecular beam (SMB) injection is introduced to study transport features of non-local transport phenomenon on HL-2A. Repetitive non-local effect induced by modulated SMBI allows Fourier transformation of the temperature perturbation, yielding detailed investigation of the pulse propagation. Fourier analysis provides evidence for existence of internal transport barriers. Meanwhile, experimental progress of non-local effect was made in the HL-2A Tokamak in 2007. The core electron temperature T_e rise increases from 18% to more than 40% and the duration of the T_e rise could be prolonged by changing the conditions of SMB injection.

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Diagnosis of Methane Plasma Generated in an Atmospheric Pressure DBD Micro-Jet by Optical Emission Spectroscopy

ZHANG Jun-Feng, BIAN Xin-Chao, CHEN Qiang, LIU Fu-Ping, LIU Zhong-Wei

Chin. Phys. Lett. 2009, 26 (3): 035203 . DOI: 10.1088/0256-307X/26/3/035203

Abstract

PDF(pc) (467KB) ( 2917 )

Diagnosis of methane plasma, generated in an atmospheric pressure dielectric barrier discharge (DBD) micro-plasma jet with a quartz tube as dielectric material by a 25kHz sinusoidal ac power source, is conducted by optical emission spectroscopy (OES). The reactive radicals in methane plasma such as CH, C₂, and H_α are detected in-situ by OES. The possible dissociation mechanism of methane in diluted Ar plasma is deduced from spectra. In addition, the density of CH radical, which is considered as one of the precursors in diamond-like (DLC) film formation, affected by the parameters of input voltage and the feed gas flow rate, is emphasized. With the Boltzmann plots, four Ar atomic spectral lines (located at 675.28nm, 687.13nm, 738.40nm and 794.82nm, respectively) are chosen to calculate the electron temperature, and the dependence of electron temperature on discharge
parameters is also investigated.

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Numerical Study of Spontaneous Outspread of Large-Scale Surface-Wave Plasma Excited by Slot-Antenna Array

LAN Chao-Hui, HU Xi-Wei, LIU Ming-Hai

Chin. Phys. Lett. 2009, 26 (3): 035204 . DOI: 10.1088/0256-307X/26/3/035204

Abstract

PDF(pc) (491KB) ( 730 )

The spontaneous outspread of surface-wave plasma (SWP) towards the edge of large-scale quartz window is studied using a time-stepping self-consistent model. The performances of three different types of slot-antenna arrays are compared, and the electron density distributions for each array at different stages are presented. The results show that slotting along both x and y directions can be helpful to the outspread and can thus enhance the uniformity of SWP. Meanwhile, when we use such an array, the absorption rate of input microwave power can reach more than 83%.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

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Surface Disorder of GaN Irradiated by Highly Charged Ar^q+-Ions

ZHANG Li-Qing, ZHANG Chong-Hong, YANG Yi-Tao, YAO Cun-Feng, LI Bing-Sheng, SUN You-Mei, SONG Shu-Jian

Chin. Phys. Lett. 2009, 26 (3): 036101 . DOI: 10.1088/0256-307X/26/3/036101

Abstract

PDF(pc) (402KB) ( 892 )

The surface damage to gallium nitride films irradiated by Ar^q+ (6≤q≤16) ions at room temperature is studied by the atomic force microscopy. It is found
that when charge state exceeds a threshold value, significant swelling was turned into obvious erosion in the irradiated region. The surface change of the irradiated region strongly depends on the charge state and ion fluence. On the other hand, surface change is less dependent on the kinetic energy nearly in the present experimental range (120keV≤E_k≤220keV). For q≤14, surface of the irradiated region is covered with an amorphous layer, rough and bulgy. A step-up appears between the irradiated and un-irradiated region. Moreover, the step height and the surface roughness are functions of the ion dose and charge state, and increase with the increase of dose and charge state. Especially at and near boundary, a sharp bump like ridges in irradiated areas is observed, and there appear characteristic grooves in un-irradiated areas. For q=16, surface of the irradiated region was etched and erased.

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Curie Transition of NC Nickel by Mechanical Spectroscopy and Magnetization Study

LI Ping-Yun, CAO Zhen-Hua, ZHANG Xi-Yan, WU Xiao-Lei, HUANG Yi-Neng, MENG Xiang-Kang

Chin. Phys. Lett. 2009, 26 (3): 036102 . DOI: 10.1088/0256-307X/26/3/036102

Abstract

PDF(pc) (451KB) ( 589 )

Mechanical spectroscopy measurement is performed to study the internal friction of nanocrystalline (NC) nickel with an average grain size of 23nm from room temperature to 610K. An internal friction peak is observed at about 550K, which corresponds to the Curie transition process of the NC nickel according to the result of magnetization test. Moreover, the fact that the Curie temperature of NC nickel is lower than that of coarse-grained nickel is explained by an analytical model based on the weakening of cohesive energy.

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Mechanism of Strain Rate Effect Based on Dislocation Theory

QIN Kun, YANG Li-Ming, HU Shi-Sheng

Chin. Phys. Lett. 2009, 26 (3): 036103 . DOI: 10.1088/0256-307X/26/3/036103

Abstract

PDF(pc) (253KB) ( 5465 )

Based on dislocation theory, we investigate the mechanism of strain rate effect. Strain rate effect and dislocation motion are bridged by Orowan's relationship, and the stress dependence of dislocation velocity is considered as the dynamics relationship of dislocation motion. The mechanism of strain rate effect is then investigated qualitatively by using these two relationships although the kinematics relationship of dislocation motion is absent due to complicated styles of dislocation motion. The process of strain rate effect is interpreted and some details of strain rate effect are adequately discussed. The present analyses agree with the existing experimental results. Based on the analyses, we propose that strain rate criteria rather than stress criteria should be satisfied when a metal is fully yielded at a given strain rate.

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Molecular Dynamics Simulation of Icosahedral Transformations in Solid Cu-Co Clusters

LI Guo-Jian, WANG Qiang, LIU Tie, LI Dong-Gang, LU Xiao, HE Ji-Cheng

Chin. Phys. Lett. 2009, 26 (3): 036104 . DOI: 10.1088/0256-307X/26/3/036104

Abstract

PDF(pc) (724KB) ( 875 )

We study the icosahedral transformations of solid Cu-Co clusters with different initial configurations by using molecular dynamics with the embedded atom method. It is found that the formation of symmetric icosahedral cluster is strongly related to the atomic number and initial configuration. The transformation originates from the surface into the interior of the cluster and is a structural change which is rapid and diffusionless. The icosahedral clusters with any composition and configuration, such as core-shell or three-shell cluster, can be prepared by the means of solid-solid phase transition in bimetallic clusters.

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Co-Adsorption of CO in NO-CO Reaction on a Metal Catalytic Surface Studied by Computer Simulation

Waqar Ahmad

Chin. Phys. Lett. 2009, 26 (3): 036401 . DOI: 10.1088/0256-307X/26/3/036401

Abstract

PDF(pc) (298KB) ( 880 )

The effect of co-adsorption of CO molecules in the NO-CO reaction on a metal catalytic surface like Pt(001) is studied by applying the Langmuir-Hinshelwood mechanism using the Monte Carlo simulations. The system is investigated by two approaches of NO adsorption; dissociatively at two empty surface sites and molecularly at a single vacant site. The elementary steps are the same as those in the conventional Ziff-Gulari-Barshad model. With the additional reaction step of co-adsorption, the sustained production of CO₂ is obtained, which has never been seen on a square lattice without introducing additional parameters. The most interesting result is the elimination of continuous second order phase transition, i.e. the production of CO₂ starts as soon as the partial pressure of CO departs from zero, which is in accordance with the experimental observations. The effect of co-adsorption probability on the phase diagrams has also been studied.

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Physical and Chemical Properties of TiO_xN_yPrepared by Low-Temperature Oxidation of Ultrathin Metal Nitride Directly Deposited on SiO₂

HAN Yue-Ping, HAN Yan

Chin. Phys. Lett. 2009, 26 (3): 036402 . DOI: 10.1088/0256-307X/26/3/036402

Abstract

PDF(pc) (282KB) ( 992 )

Physical and chemical properties of titanium oxynitride (TiO_xN_y) formed by low-temperature oxidation of titanium nitride (TiN) layer are investigated for advanced metal-oxide-semiconductor (MOS) gate dielectric application. TiO_xN_y exhibits polycrystalline properties after the standard thermal process for MOS device fabrication, showing the preferred orientation at [200]. Superior electrical properties of TiO_xN_y can be maintained before and after the annealing, probably due to the nitrogen incorporation in the oxide bulk and at the interface. Naturally formed transition layer between TiO_xN_y and SiO₂ is also confirmed.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Effect of Temperature on Polaron Stability in a One-Dimensional Organic Lattice

LIU Wen, LI Yuan, QU Zhen, GAO Kun, YIN Sun, LIU De-Sheng,

Chin. Phys. Lett. 2009, 26 (3): 037101 . DOI: 10.1088/0256-307X/26/3/037101

Abstract

PDF(pc) (432KB) ( 1161 )

Effect of temperature on the polaron stability in a one-dimensional organic lattice is investigated within the Su-Schrieffer-Heeger model. The temperature effect is simulated by introducing random forces to the equation of the lattice motion. It is found that the localized polaron state becomes delocalized even at low temperatures. The time of polaron keeping localized depends on the magnitude of temperatures. By taking into account the thermal effect, we find that the dissociation field is weaker as compared with earlier works.

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Exciton States and Linear Optical Spectra of Semiconducting Carbon Nanotubes under Uniaxial Strain

YU Gui-Li, JIA Yong-Lei

Chin. Phys. Lett. 2009, 26 (3): 037102 . DOI: 10.1088/0256-307X/26/3/037102

Abstract

PDF(pc) (297KB) ( 719 )

Considering the exciton effect, the linear optical spectra of semiconducting single-walled carbon nanotubes (SWNTs) under uniaxial strain are theoretically studied by using the standard formulae of Orr and Ward [Mol. Phys. 20(1971)513]. It is found that due to the wrapping effect existing in the semiconducting zigzag tubes, the excitation energies of the linear optical spectra show two different kinds of variations with increasing uniaxial strain, among which one decreases such as tube (11,0), and the other increases firstly and then decreases such as tube (10,0). These variations of the linear optical spectra are consistent with the changes of the exciton binding energies or the (quasi)continuum edge of these SWNTs calculated in our previous work, which can be used as a supplemented tool to detect the deformation degree of an SWNT under uniaxial strain.

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Anisotropic Spin Splitting in Step Quantum Wells

HAO Ya-Fei, CHEN Yong-Hai, HAO Guo-Dong, WANG Zhan-Guo

Chin. Phys. Lett. 2009, 26 (3): 037103 . DOI: 10.1088/0256-307X/26/3/037103

Abstract

PDF(pc) (268KB) ( 822 )

By the method of finite difference, the anisotropic spin splitting of the Al_xGa_1-xAs/GaAs/Al_yGa_1-yAs/Al_xGa_1-xAs step quantum wells (QWs) are theoretically investigated considering the interplay of the bulk inversion asymmetry and structure inversion asymmetry induced by step quantum well structure and external electric field. We demonstrate that the anisotropy of the total spin splitting can be controlled by the shape of the QWs and the external electric field. The interface related Rashba effect plays an important effect on the anisotropic spin splitting by influencing the magnitude of the spin splitting and the direction of electron spin. The Rashba spin splitting presents in the step quantum wells due to the interface related Rashba effect even without external electric field or magnetic field.

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Modelling of Hot-Electron Energy in Short-Channel MOSFETs by Electrical Method

SU Xin-Yan, HAN Yan, WANG Jian, YAO Jin-Jie

Chin. Phys. Lett. 2009, 26 (3): 037104 . DOI: 10.1088/0256-307X/26/3/037104

Abstract

PDF(pc) (319KB) ( 884 )

Channel hot-electron (HE) energy in short-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) is estimated based on electrical characterization. The HE assisted gate leakage is monitored, and its energy dependent tunnelling probability is calculated, from which the excess energy of HE is estimated. The credibility of the proposed method is supported by the experimental and theoretical results, and its accuracy in ultra-small-feature-size device application is also discussed.

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First-Principles Studies on Properties of Boron-Related Impurities in c-BN

TIAN Fu-Bo, WANG Xiao-Li, MA Yan-Ming, CUI Tian, LIU Bing-Bing, ZOU Guang-Tian

Chin. Phys. Lett. 2009, 26 (3): 037105 . DOI: 10.1088/0256-307X/26/3/037105

Abstract

PDF(pc) (457KB) ( 743 )

We investigate, by first-principles calculations, the pressure dependence of formation enthalpies and defective geometry and bulk modulus of boron-related impurities (V_B, C_B, N_B, and O_B) with different charged states in cubic boron nitride (c-BN) using a supercell approach. It is found that the nitrogen atoms surrounding the defect relax inward in the case of C_B, while the nitrogen atoms relax outward in the other cases. These boron-related impurities become much more stable and have larger concentration with increasing pressure. The impurity C_B⁺¹ is found to have the lowest formation enthalpy, make the material exhibit semiconductor characters and have the bulk modulus higher than ideal c-BN and than those in the cases of other impurities. Our results suggest that the hardness of c-BN may be strengthened when a carbon atom substitutes at a B site.

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Resistance Switching Characteristic and Charge Carrier Self-Trapping in Epitaxial Pr_0.7(Ca_1-xSr_x)_0.3MnO₃ Thin Films

CHEN Yuan-Sha, CHEN Li-Ping, LIAN Gui-Jun, XIONG Guang-Cheng

Chin. Phys. Lett. 2009, 26 (3): 037201 . DOI: 10.1088/0256-307X/26/3/037201

Abstract

PDF(pc) (426KB) ( 860 )

Carrier injection performed in Pr_0.7Ca_0.3MnO₃ junctions demonstrate resistance switching (RS) characteristic with dramatic changes in both resistances and interface barriers, which suggests a charge carrier self-trapping model in strongly correlated electronic framework. Un-stable RS behaviour without electric fields in epitaxial Pr_0.7(Ca_1-xSr_x)_0.3MnO₃ (PCSMO) films shows dependences on insulator--metal transition temperature, which indicates that RS process is really related to the intrinsic property of carriers. The switched resistance of epitaxial PCSMO films also depends on the amount of current pulses, which should be another evidence of the carrier self-trapping model, similarly to the dependence on the amount of self-trapped charge carriers.

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Magnetoresistance of Electrons Channelled by Microscopic Magnetic Field Modulation

DAI Bo, LIU Xiao-Xia, LEI Yong, Alain Nogaret

Chin. Phys. Lett. 2009, 26 (3): 037202 . DOI: 10.1088/0256-307X/26/3/037202

Abstract

PDF(pc) (314KB) ( 687 )

We report the magnetoresistance of two-dimensional electron gas, which is made of GaAs based epitaxial multilayers and laterally subjected to a periodic magnetic field. The modulation field is produced by an array of submicrometre ferromagnets fabricated at the surface of the heterostructure. The magnetoresistance of about 20% is found at low temperature 80K. The measurement is in quantitative agreement with semiclassical simulations, which reveal that the magnetoresistance is due to electrons trapped in snake orbits along lines of zero magnetic field.

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Origin of Electron and Hole Charging Current Peaks in Nanocrystal-Si Quantum Dot Floating Gate MOS Structure

HUANG Jian, CHEN Kun-Ji, FANG Zhong-Hui, GUO Si-Hua, WANG Xiang, DINGHong-Lin, LI Wei, HUANG Xin-Fan

Chin. Phys. Lett. 2009, 26 (3): 037301 . DOI: 10.1088/0256-307X/26/3/037301

Abstract

PDF(pc) (587KB) ( 873 )

The nanocrystal-Si quantum dot (nc-Si QD) floating gate MOS structure is fabricated by using plasma-enhanced chemical vapour deposition (PECVD) and furnace oxidation technology. The capacitance hysteresis in capacitance-voltage (C-V) measurements confirm the charging effect of nc-Si QDs. Asymmetric charging current peaks both for electrons and holes have been observed in current-voltage (I-V) measurements at room temperature for the first time. The characteristic and the origin of these current peaks in this nc-Si QD MOS structure is investigated systematically. Moreover, the charge density (10^-7C/cm²) calculated from the charging current peaks in the I-V measurements at different sweep rates shows that each quantum dot is charged by one carrier. The difference of charging threshold voltages between the electrons and holes charging peaks, ΔV_G, can be explained by the quantum confinement effect of the nc-Si dots in size of about 3.5nm.

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Dependence of Interlayer AF Coupling on Ferromagnetic Layer Thickness in [Pt/Co]₅/Ru/[Co/Pt]₅ Multilayers

ZHAO Jing, WANG Yin-Jun, HAN Xiu-Feng

Chin. Phys. Lett. 2009, 26 (3): 037302 . DOI: 10.1088/0256-307X/26/3/037302

Abstract

PDF(pc) (374KB) ( 615 )

We study magnetization reversal in the interlayer coupled [Pt/Co]₅/Ru/[Co/Pt]₅ multilayers (MLs) by means of the measurement of extraordinary Hall effect (EHE). Fitting experimental data to a simple model, we determine the interlayer coupling strength for various thicknesses of the ferromagnetic layers at a fixed Ru spacer thickness. It is found that the dependence of interlayer coupling strength on the Pt layer thickness is much stronger than the previous report in the ferromagnetic/nonmagnetic/ferromagnetic multilayers.

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Time-Dependent Transport in Nanoscale Devices

CHEN Zhi-Dong, ZHANG Jin-Yu, YU Zhi-Ping

Chin. Phys. Lett. 2009, 26 (3): 037303 . DOI: 10.1088/0256-307X/26/3/037303

Abstract

PDF(pc) (306KB) ( 696 )

A method for simulating ballistic time-dependent device transport, which solves the time-dependent Schrödinger equation using the finite difference time domain (FDTD) method together with Poisson's equation, is described in detail. The effective mass Schrödinger equation is solved. The continuous energy spectrum of the system is discretized using adaptive mesh, resulting in energy levels that sample the density-of-states. By calculating time evolution of wavefunctions at sampled energies, time-dependent transport characteristics such as current and charge density distributions are obtained. Simulation results in a nanowire and a coaxially gated carbon nanotube field-effect transistor (CNTFET) are presented. Transient effects, e.g., finite rising time, are investigated in these devices.

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Maximal Heat Generation in Nanoscale Systems

ZHOU Li-Ling, LI Shu-Shen, ZENG Zhao-Yang

Chin. Phys. Lett. 2009, 26 (3): 037304 . DOI: 10.1088/0256-307X/26/3/037304

Abstract

PDF(pc) (222KB) ( 848 )

We investigate the heat generation in a nanoscale system coupled to normal leads and find that it is maximal when the average occupation of the electrons in the nanoscale system is 0.5, no matter what mechanism induces the heat generation.

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Performance of Organic Field Effect Transistors with Self-Improved Cu/Organic Interfaces

HU Zi-Yang, CHENG Xiao-Man, , WU Ren-Lei, WANG Zhong-Qiang, YIN Shou-Gen,

Chin. Phys. Lett. 2009, 26 (3): 037305 . DOI: 10.1088/0256-307X/26/3/037305

Abstract

PDF(pc) (368KB) ( 853 )

We fabricate pentacene-based organic field effect transistors (OFETs) with Cu as source and drain (S-D) electrodes. The fabricated devices stored for ten hours under ambient atmospheric conditions exhibit superior performance compared with the as-prepared devices. The field-effect mobility increases from 0.012 to 0.03cm²V^-1s^-1, and the threshold voltage downshifts from -14 to -9V. The on/off current ratios are close to the order of 10⁴. The improved performance of the stored devices is attributed to the formation of thin Cu oxide at the Cu electrodes/organic interfaces. These results suggest a simple and available way to optimize device properties and to reduce fabrication cost for OFETs.

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Fermi Level Unpinning and Schottky Barrier Modification by Ti, Sc and V Incorporation at NiSi₂/Si Interface

GENG Li, MAGYARI-KOPE Blanka, ZHANG Zhi-Yong, NISHI Yoshio

Chin. Phys. Lett. 2009, 26 (3): 037306 . DOI: 10.1088/0256-307X/26/3/037306

Abstract

PDF(pc) (524KB) ( 925 )

A new method is proposed to modify the Schottky barrier height (SBH) for nickel silicide/Si contact. Chemical and electrical properties for NiSi₂/Si interface with titanium, scandium and vanadium incorporation are investigated by first-principles calculations. The metal/semiconductor interface states within the gap region are greatly decreased, which is related to the diminutions of junction leakage when Ti-cap is experimentally used in nickel silicide/Si contact process. It leads to an unpinning metal/semiconductor interface. The SBH obeys the Schottky-Mott theory. Compared to Ti substitution, the SBH for electrons is reduced for scandium and increases for vanadium.

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Simple One-Step Synthesis and Superconducting Properties of SmFeAsO_1-xF_x

MA Yan-Wei, GAO Zhao-Shun, WANG Lei, QI Yan-Peng, WANG Dong-Liang, ZHANG Xian-Ping

Chin. Phys. Lett. 2009, 26 (3): 037401 . DOI: 10.1088/0256-307X/26/3/037401

Abstract

PDF(pc) (552KB) ( 828 )

The recent discovery of superconductivity in REFeAsO (RE, rare-earth metal) has generated enormous interest because these materials are the first non-copper oxide superconductors with critical temperatures T_c exceeding 50K as well as upper critical fields well above 100T. However, for these new superconductors, very complicated synthesis routes, such as the complex two-step synthesis or high-pressure sintering, are required. Furthermore, there is the toxicity and volatility of arsenic to consider, sometimes a sealed quartz tube of arsenic exploded during annealing. We present a new method for producing high-temperature SmFeAsO_1-xF_x superconductors by using a one-step sintering process. Superconducting transition with the onset temperature of 54.6K and high critical fields H_c2(0)≥200T were confirmed in SmFeAsO_0.7F_0.3. At 5K and at self field, critical current densities J_cestimated from the magnetization hysteresis using the whole sample size and the average particle size have reached 8.5×10³and 1.2×10⁶A/cm², respectively. Moreover, J_c exhibited a very weak dependence on magnetic field. This simple and safe one-step synthesis technique should be effective in other rare earth derivatives of iron-based superconductors.

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Extended Power Law and Hall Anomaly of High-Temperature Superconductors

HE Li, HU Xiang, YIN Lan, XU Xiao-Lin, GUO Jian-Dong, LI Chuan-Yi, YIN Dao-Le

Chin. Phys. Lett. 2009, 26 (3): 037402 . DOI: 10.1088/0256-307X/26/3/037402

Abstract

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Starting from the free energy of a moving vortex, we obtain the extended power law form of longitudinal resistivity ρ_xx and the analytical form of Hall resistivity ρ_xy. Based on them, we obtain a scaling relation which agrees well with the experimental data of different kinds of high-temperature superconductors. Furthermore, the theoretical results well fit the scaling results.

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Thermal Stability of CoFe/Cu/CoFe/IrMn Top Spin Valve

ZHOU Guang-Hong, WANG Yin-Gang, QI Xian-Jin

Chin. Phys. Lett. 2009, 26 (3): 037501 . DOI: 10.1088/0256-307X/26/3/037501

Abstract

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We present a study of thermal stability of the top spin valve with a structure of seed Ta (5nm)/Co₇₅Fe₂₅ (5nm)/Cu (2.5nm)/Co₇₅Fe₂₅(5nm)/Ir₂₀Mn₈₀ (12nm)/cap Ta (8nm) deposited at room temperature by magnetron sputtering. A vibrating sample magnetometer fixed with a heater was used to record the magnetic hysteresis loops at variational temperatures and x-ray diffraction was performed to characterize the structure of the multilayer. The exchange field H_ex and the coercivity of the pinned CoFe layer H_cpdecrease monotonically with increasing temperature. The coercivity of the free CoFe layer H_cf in the spin valve shows a maximum at 498K. The temperature dependences of H_ex, H_cp and H_cf have also been discussed.

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Magnetic Behaviour of Sm₂Co₇/Fe/Sm₂Co₇, Nanocomposite Trilayers with Cr and Ti Additions

F. Shahzad, S. A. Siddiqi, J. Zhou

Chin. Phys. Lett. 2009, 26 (3): 037701 . DOI: 10.1088/0256-307X/26/3/037701

Abstract

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Trilayered Sm₂Co₇/Fe/Sm₂Co₇ spring exchange magnets are fabricated by dc magnetron sputtering on MgO substrates. Very thin layers (0.3-0.7nm) of Cr and Ti are added at the interfaces of the two magnetic phases. The thickness of Sm₂Co₇ is kept at 20nm and Fe at 6nm while the thickness of Cr and Ti are
varied as 0.3, 0.5, and 0.7nm. The base pressure of sputtering chamber is kept below 10^-7Torr and Ar pressure at 3-8mTorr. The samples are haracterized by x-ray diffraction (XRD) and SQUID magnetometer. We report improvement in exchange coupling of nonacomposite magnets by addition of thin layers of Cr at interfaces.

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Effect of Pyrolysis Atmosphere on Ferroelectric Properties of Bi_3.25La_0.75Ti₃O₁₂ Films Prepared by Sol-Gel Method

LI Jian-Jun, YU Jun, WU Yun-Yi, LI Jia, WANG Yun-Bo, ZHOU Wen-Li

Chin. Phys. Lett. 2009, 26 (3): 037702 . DOI: 10.1088/0256-307X/26/3/037702

Abstract

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The effect of pyrolysis atmosphere is investigated for Bi_3.25La_0.75Ti₃O₁₂ (BLT) films prepared on Pt/TiO₂/SiO₂/p-Si(100) substrates by sol-gel processes. The pyrolysis is carried out at 400°C for 20min under air or O₂ atmosphere and the successive anneal is performed at 700°C for 30min under O₂ atmosphere. The pyrolysis under O₂ is enough for complete removal of organic species, however after pyrolysis under air, carbon and hydrogen atomic species as organic fragment are partly remained in the film. This incomplete removal of organic fragments affects the grain growth and cause more defects in the film or between interfaces during the annealing for the crystallization of BLT film. The growth direction and grain size of the BLT film is revealed to affect ferroelectric properties. The remanent polarization P_r for the BLT films of pyrolysis in O₂ and air are measured to be 18.85μC/cm² and 12.56μC/cm², respectively. The defects degrade the fatigue property dramatically for the film of pyrolysis in air. It can be concluded that the pyrolysis is an important procedure to control ferroelectric properties.

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Studies on 2,4-DNT Mixtures Using Reflection Terahertz Time Domain Spectroscopy for Explosives Detection

ZHOU Zhen, CHEN An-Tao, FENG Li-Shuang

Chin. Phys. Lett. 2009, 26 (3): 037801 . DOI: 10.1088/0256-307X/26/3/037801

Abstract

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Absorption spectra (0.2-1.8THz) of the mixtures of explosive 2,4-DNT and polyethylene(PE) at different ratios are obtained using reflection terahertz time domain spectroscopy (THz-TDS). The pronounced absorption peak of 2,4-DNT at 1.08THz is always observed for the mixtures with 2,4-DNT ratios above 20%. Experimental results demonstrate that more applicable and realistic THz-TDS in reflection geometry can be used to distinguish explosive mixed with other material having no THz fingerprints, and has a high potential in the detection of explosives.

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Sub-wavelength Ripple Formation on Silicon Induced by Femtosecond Laser Radiation

ZHOU Ming, YUAN Dong-Qing, ZHANG Wei, SHEN Jian, LI Bao-Jia, SONG Juan, CAI Lan

Chin. Phys. Lett. 2009, 26 (3): 037901 . DOI: 10.1088/0256-307X/26/3/037901

Abstract

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Periodic microstructures on silicon bulk are formed by the irradiation of the femtosecond laser with the laser wavelength of 800nm and the pulse length of 130fs. We investigate the surface periodic ripple structures produced by femtosecond laser treatment. The effects of feedrate of sample, v, on laser-induced surface topography are studied. We find that the femtosecond laser produce periodic ripples of the sub-micron level on silicon surface. At the same time, we realize the optimal conditions to produce these surface structures. When choosing NA=0.3, and v=2000μm/s or 3000μm/s, we find a series of periodic-structure ripples where the spacing is about 120nm and the width is about 450nm. The experimental results indicate that femtosecond laser treatment can produce line arrays on the sub-micron level, which is a positive factor for fabricating grating and other optical applications in nanoscales.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Enhanced Field Emission from Vertical ZnO Nanoneedles on Micropyramids

ZHANG Yang, DIAO Da-Sheng

Chin. Phys. Lett. 2009, 26 (3): 038101 . DOI: 10.1088/0256-307X/26/3/038101

Abstract

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Vertical ZnO nanoneedles with sharp tips are secondarily grown on tips of primarily grown ZnO micropyramids by a vapour transport process. The field emission (FE) properties exhibit a lower turn-on electric field and a higher field enhancement factor as compared with vertical ZnO microrods. This result indicates that ZnO nanoneedles have good optimum shapes for FE due to electron accumulation at sharp tips.

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HPHT Synthesis of High-Quality Diamond Single Crystals with Micron Grain Size

LIU Xiao-Bing, JIA Xiao-Peng, MA Hong-An, HAN Wei, GUO Xin-Kai, JIA Hong-Sheng

Chin. Phys. Lett. 2009, 26 (3): 038102 . DOI: 10.1088/0256-307X/26/3/038102

Abstract

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High-quality diamond single crystals with micron grain size are synthesized with a new high-pressure and high-temperature (HPHT) synthesis technique in a cubic anvil high pressure apparatus. Morphology of the synthesized diamonds is observed by a scanning electron microscope (SEM). The samples are characterized using laser Raman spectra. The results show that the new synthesis technique improves the nucleation of diamond greatly, and diamond single crystals with perfect morphology and micron grain size are successfully synthesized, with the average grain size of about 6μm. This work provides a new synthesis technique to implement industrialization of high-quality diamond single crystals with super-fine grain size, and paves the way for future development.

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Optical and Structural Properties of Mn-Doped GaN Grown by Metal Organic Chemical Vapour Deposition

CUI Xu-Gao, ZHANG Rong, TAO Zhi-Kuo, LI Xin, XIU Xiang-Qian, XIE Zi-Li, ZHENG You-Dou

Chin. Phys. Lett. 2009, 26 (3): 038103 . DOI: 10.1088/0256-307X/26/3/038103

Abstract

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Mn-doped GaN epitaxial films were grown by metal organic chemical vapour deposition (MOCVD). Micro-structural properties of films are investigated using Raman scattering. It is found that with increasing Mn-dopants levels, longitudinal optical phonon mode A₁(LO) of films is broadened and shifted towards lower frequency. This phenomenon possibly derives from the difference in bonding strength between Ga-N pairs and Mn-N pairs in host lattice. In addition, optical properties of films are investigated using cathodoluminescence and absorption spectroscopy. Mn-related both emission band around 3.0eV and absorption bands around 1.5 and 2.95eV are observed. By studies on structural and optical properties of Mn-doped GaN, we find that Mn ions substitute for Ga sites in host lattice. However, carrier-mediated ferromagnetic exchange seems unlikely due to deep levels of Mn acceptors.

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Effects of NaN₃ Added in Fe-C System on Inclusion and Impurity of Diamond Synthesized at High Pressure and High Temperature

LIANG Zhong-Zhu, LIANG Jing-Qiu, JIA Xiao-Peng

Chin. Phys. Lett. 2009, 26 (3): 038104 . DOI: 10.1088/0256-307X/26/3/038104

Abstract

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Effects of NaN₃ added in Fe-C system to synthesize nitric diamond at high pressure and high temperature are investigated. Diamond crystals with high nitrogen concentration are synthesized by the system of Fe-C and NaN₃additive at pressure 5.8GPa and at temperatures 1750-1780K for 15min. The synthetic diamond crystals have a cubo-octahedral or octahedral shape with yellowish green or green colour. Some disfigurements are observed on the surfaces of most diamond crystals. The composition and content of inclusions formed by iron in diamond are changed and iron nitride is detected in diamond crystals synthesized with Fe-C-NaN₃ additive. As the amount of NaN₃ additive increases, Fe₃C decreases and iron nitride increases with α-Fe being nearly constant. Moreover, the nitrogen concentrations in diamond crystals synthesized with 1.5wt% NaN₃ additive is up to 2250ppm in substitutional form.

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Preparation of ZnO Nanospheres and Their Applications in Dye-Sensitized Solar Cells

ZHANG Yong-Zhe, WU Li-Hui, LIU Yan-Ping, XIE Er-Qing, YAN De, CHEN Jiang-Tao

Chin. Phys. Lett. 2009, 26 (3): 038201 . DOI: 10.1088/0256-307X/26/3/038201

Abstract

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ZnO nanospheres are synthesized by a two-step self-assembly method. X-ray diffraction pattern and Raman scattering spectra measurements show that all the samples present a typical wurtzite structure. A regular sphere shape is inspected by field emission scanning electron microscope and transmission electron microscope for the samples. It is shown that the as-synthesized ZnO nanosphere is composed of numbers of primary particles with size of around 10nm. A possible growth mechanism for the two-step self-assembly ZnO nanosphere is proposed. After applying the ZnO nanospheres to dye-sensitized solar cells (DSSCs), a 117% increase of the overall light to electricity conversion efficiency η is observed compared with that of the ZnO nanoparticles based DSSCs. Associated with the UV-vis results, light scattering is assigned to the great improvement of η.

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Li- Site and Metal-Site Ion Doping in Phosphate-Olivine LiCoPO₄ by First-Principles Calculation

LIN Zhi-Ping, ZHAO Yu-Jun, ZHAO Yan-Ming

Chin. Phys. Lett. 2009, 26 (3): 038202 . DOI: 10.1088/0256-307X/26/3/038202

Abstract

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We present a first-principles investigation of the crystal and electronic structure as well as the average insertion voltage of the Li-site (by Na and Cr) and metal-site (by isovalent Ni, Zn, Ca, Mg and Mn and aliovalent Cu, Al, In, Mo and Zr) doped LiCoPO₄. The results show that both the Li-site doping and metal-site doping may reduce the volume change of the material during Li extraction/reinsertion process. The metal doped at Li-site will block the path of Li ion diffusion. The doping by aliovalent transition metals will introduce defect levels in the energy band. It could influence the conductivity insertion voltage.

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Measurement on Effective Shear Viscosity Coefficient of Iron under Shock Compression at 100GPa

LI Yi-Lei, LIU Fu-Sheng, ZHANG Ming-Jian, MA Xiao-Juan, LI Ying-Lei, ZHANG Ji-Chun

Chin. Phys. Lett. 2009, 26 (3): 038301 . DOI: 10.1088/0256-307X/26/3/038301

Abstract

PDF(pc) (530KB) ( 601 )

The oscillatory damping curve of a shock front propagating in iron shocked to 103GPa is measured by use of two-stage light-gas gun and electric pin techniques. The corresponding effective shear viscosity coefficient is deduced to be about 2000 Pa・s from Miller and Ahrens' formula. The result is consistent with that of Mineev's data at 31GPa, while it is higher by five orders than the predictions based on the static measurements at about 5GPa and 2000K and molecular dynamic simulation up to 135-375GPa and 4300-6000K, and the discussions are presented.

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Squeezing Effect of a Nanomechanical Resonator Coupled to a Two-Level System: an Equilibrium Approach

LI Jing, CHEN Zhi-De

Chin. Phys. Lett. 2009, 26 (3): 038501 . DOI: 10.1088/0256-307X/26/3/038501

Abstract

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The squeezing effect of a nanomechanical resonator coupled to a two-level system is studied by variational calculations based on both the displaced-squeezed-state (DSS) and the displaced-oscillator-state (DOS). The stable region of the DSS ground state at both T=0 and T≠0 and the corresponding squeezing factor are calculated. It is found that when the resonator frequency lies in (k_BT,Δ), where Δ is the tunnelling splitting of the two-level-system in the presence of dissipation, tunnelling splitting of a DSS ground state decreases with the temperature, while tunnelling splitting of a DOS ground state increases with the temperature in low temperature region. This opposite temperature dependence can help to distinguish between the DSS and DOS ground state in the experiment.

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Composite-Collector InGaAs/InP Double Heterostructure Bipolar Transistors with Current-Gain Cutoff Frequency of 242 GHz

CHENG Wei, JIN Zhi, SU Yong-Bo, LIU Xin-Yu, XU An-Huai, QI Ming

Chin. Phys. Lett. 2009, 26 (3): 038502 . DOI: 10.1088/0256-307X/26/3/038502

Abstract

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To eliminate the conduction band spike at the base-collector interface, an InP/InGaAs double heterostructure bipolar transistor (DHBT) with an InGaAsP composite collector is designed and fabricated using the conventional mesa structure. The DHBT with emitter area of 1.6×15μm²exhibits current-gain cutoff frequency f_t = 242GHz at the high collector current density J_C=2.1mA/μm², which is to our knowledge the highest f_t reported for the mesa InP DHBT in China. The breakdown voltage in common-emitter configuration is more than 5V. The high-speed InP/InGaAs DHBT with high current density is very suitable for the application in ultra high-speed digital circuits.

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Water Transport through Multinanopores Membranes

ZENG Li, GUO Hong-Kai, ZUO Guang-Hong, WAN Rong-Zheng, FANGHai-Ping,

Chin. Phys. Lett. 2009, 26 (3): 038701 . DOI: 10.1088/0256-307X/26/3/038701

Abstract

PDF(pc) (1479KB) ( 657 )

We investigate the influence of correlation between water molecules transport through the neighbouring nanopores, whose centres are at a distance of only 6.2Å, using the molecular dynamics simulations. Water molecule distribution in nanopore and average water flow are obtained. It is found that the average water molecule number and water flow are slightly different between a system made of the neighbouring nanopores and a system of a single pore. This indicates that transport of water chains in neighbouring pores do no show significant influence each other. These findings should be helpful in designing efficient artificial membrane made of nanopores and providing an insight into effects of the biological channel structure on the water permeation.

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Stability of the BA Network: a New Approach to Rigorous Proof

XU Hong, SHI Ding-Hua

Chin. Phys. Lett. 2009, 26 (3): 038901 . DOI: 10.1088/0256-307X/26/3/038901

Abstract

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We propose a new approach to rigorously prove the existence of the steady-state degree distribution for the BA network. The approach is based on a vector Markov chain of vertex numbers in the network evolving process. This framework provides a rigorous theoretical basis for the rate equation approach which has been widely applied to many problems in the field of complex networks, e.g., epidemic spreading and dynamic synchronization.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Nonlinear Shock and Kink Waves with Complete Coriolis Force in Earth's Atmosphere

YU Xin, ZHAO Qiang

Chin. Phys. Lett. 2009, 26 (3): 039201 . DOI: 10.1088/0256-307X/26/3/039201

Abstract

PDF(pc) (174KB) ( 883 )

Nonlinear waves in a Boussinesq fluid model which includes both the vertical and horizontal components of Coriolis force are studied by using the semi-geostrophic approximation and the method of travelling-wave solution. Taylor series expansion has been employed to isolate the characteristics of the linear Rossby waves and to identify the nonlinear shock and kink waves. The KdV-Burgers and the compound KdV-Burgers equations are derived, their shock wave and kink wave solution are also obtained.

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Dynamic Evolution of Outer Radiation Belt Electrons due to Whistler-Mode Chorus

SU Zhen-Peng, ZHENG Hui-Nan, XIONG Ming

Chin. Phys. Lett. 2009, 26 (3): 039401 . DOI: 10.1088/0256-307X/26/3/039401

Abstract

PDF(pc) (1331KB) ( 796 )

Following our preceding work, we perform a further study on dynamic evolution of energetic electrons in the outer radiation belt L=4.5 due to a band of whistler-mode chorus frequency distributed over a standard Gaussian spectrum. We solve the 2D bounce-averaged Fokker-Planck equation by allowing incorporation of cross diffusion rates. Numerical results show that whistler-mode chorus can be effective in acceleration of electrons at large pitch angles, and enhance the phase space density for energies of about 1MeV by a factor of 10² or above in about one day, consistent with observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm. Moreover, neglecting cross diffusion often leads to overestimates of the phase space density evolution at large pitch angle by a factor of 5-10 after one day, with larger errors at
smaller pitch angle, suggesting that cross diffusion also plays an important role in wave-particle interaction.

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Mass Fraction of ¹³C-Pocket in Metal-Poor AGB Stars and the Primary Nature of Neutron Source

CUI Dong-Nuan, GENG Yuan-Yuan, CUI Wen-Yuan, ZHANG Bo

Chin. Phys. Lett. 2009, 26 (3): 039701 . DOI: 10.1088/0256-307X/26/3/039701

Abstract

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Chemical abundances of very metal-poor s-rich stars contain excellent information to set new constraints on models of neutron-capture processes at low metallicity. Using the parametric approach based on the radiative s-process nucleosynthesis model, we obtain the mass fraction q of ¹³C-pocket, the overlap factor r, the neutron exposure per interpulse Δτ, and the component coefficients of the s-process and the r-process for 25 s-rich stars, respectively. We find that q deduced for the lead stars is comparable to the overlap factor r, which is larger than the standard case (hereafter ST case) of the AGB model (q~0.05) about 10 times, and Δτ are about 10 times smaller than the ST case (Δτ=7.0mbarn^-1). Although the two parameters obtained for the lead stars are very different from the ST case of the AGB stellar model, it is worth noting that the total amounts of ¹³C in metal-poor condition are close to the ST case. The above relation is a significant evidence for the primary nature of the neutron source and the lead stars could be polluted by low-mass AGB stars. Because interpulse period declines with increasing stellar mass, for high-mass AGB star, the neutron irradiation may be terminated due to their shorter interpulse period. Thus the neutron exposure per interpulse of the larger AGB stars should be about 10 times smaller than the ST case. In this case, the primary nature of the neutron source also exists.

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