Chin. Phys. Lett.

Volume 25 Issue 1

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A Darboux Transformation for the Coupled Kadomtsev--Petviashvili Equation

YANG Guang-You, LIU Qing-Ping

Chin. Phys. Lett. 2008, 25 (1): 1-3 .

Abstract

PDF(pc) (144KB) ( 2447 )

The coupled Kadomtsev--Petviashvili equation is considered. It is shown that a Darboux transformation can be constructed by means of an elementary approach.

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Small Amplitude Solitons in Bose--Einstein Condensates with External Perturbation

WANG Feng-Jiao, YAN Xiao-Hong, WANG Deng-Long,

Chin. Phys. Lett. 2008, 25 (1): 4-7 .

Abstract

PDF(pc) (146KB) ( 1220 )

By developing a small amplitude soliton approximation method, we study analytically weak nonlinear excitations in cigar-shaped condensates with repulsive interatomic interaction under consideration of external perturbation potential. It is shown that matter wave solitons may exist and travel over a
long distance without attenuation and change in shape by properly adjusting the strength of interatomic interaction to compensate for the effect of external perturbation potential.

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Darboux Transformation and Multi-Solitons for Complex mKdV Equation

ZHA Qi-Lao, LI Zhi-Bin

Chin. Phys. Lett. 2008, 25 (1): 8-11 .

Abstract

PDF(pc) (1072KB) ( 1762 )

An explicit N-fold Darboux transformation with multi-parameters for coupled mKdV equation is constructed with the help of a gauge transformation of the
Ablowitz--Kaup--Newell--Segur (AKNS) system spectral problem. By using the Darboux transformation and the reduction technique, some multi-soliton solutions for the complex mKdV equation are obtained.

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A Four-Dimensional Measurement Scheme for Single Photon Time-Polarization

REN Xi-Jun, ZHOU Zheng-Wei, SUN Fang-Wen, GUO Guang-Can

Chin. Phys. Lett. 2008, 25 (1): 12-15 .

Abstract

PDF(pc) (176KB) ( 700 )

We propose an experimental scheme to realize the four-dimensional projective measurements for a single photon. The photon polarization and time--energy provide the four-dimensional Hilbert space. Based on this scheme, we suggest an experiment to test the violation of Bell inequalities of
four-dimensional systems. In addition, by virtue of a maximally entangled biphoton state, we also show that it is possible to construct a quantum key distribution channel that can provide two-bit key with one pair of entangled photons.

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Multiparty Quantum Secret Sharing of Quantum States Using Entanglement States

GUO Ying, HUANG Da-Zu, ZENG Gui-Hua, LEE Moon Ho

Chin. Phys. Lett. 2008, 25 (1): 16-19 .

Abstract

PDF(pc) (310KB) ( 1334 )

A multi-partite-controlled quantum secret sharing scheme using several non-orthogonal entanglement states is presented with unconditional security. In this scheme, the participants share the secret quantum state by exchanging the secret polarization angles of the disordered travel particles. The security
of the secret quantum state is also guaranteed by the non-orthogonal multi-partite-controlled entanglement states, the participants' secret polarizations, and the disorder of the travelling particles. Moreover, the present scheme is secure against the particle-number splitting attack and the intercept-and-resend attack. It may be still secure even if the distributed quantum state is embedded in a not-so-weak coherent-state pulse.

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Remote Preparation of Photon Polarization States within a Network

FAN Qiu-Bo

Chin. Phys. Lett. 2008, 25 (1): 20-23 .

Abstract

PDF(pc) (240KB) ( 772 )

We propose a new linear optical protocol for remote state preparation (RSP) between two parties under control of a number of controllers in terms of optical elements. The realization of this protocol is appealing due to the fact that the quantum state of light is robust against the decoherence, and photons are ideal carriers for transmitting quantum information over long
distances.

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One Atom in an Optical Cavity: Entanglement and Applications to Quantum Computation

ZHANG Jian-Song, XU Jing-Bo

Chin. Phys. Lett. 2008, 25 (1): 24-26 .

Abstract

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We propose a scheme to implement two-bit quantum phase gates and one-bit unitary gates by using the two-mode two-photon Jaynes--Cummings model. The entanglement between the atom and cavity is also investigated in the presence of phase decoherence. It is found that there is stationary entanglement that is sensitive with the detuning.

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Scheme for Implementing an N-Qubit Phase Gate via Selective Atom--Field Interaction with Cavity Quantum Electrodynamics

SHAO Xiao-Qiang, JIN Xing-Ri, ZHU Ai-Dong, ZHANG Shou, YEONKyu-Hwang

Chin. Phys. Lett. 2008, 25 (1): 27-30 .

Abstract

PDF(pc) (177KB) ( 942 )

A scheme for implementing a two-qubit phase gate with atoms sent through a high-Q optical cavity is proposed by choosing nonidentical coupling constants between the atoms and cavity. The atomic spontaneous emission can be suppressed due to the large atom--field detuning. Moreover, the scheme can be generalized to implement an N-qubit phase gate and the gating time
does not change with an increase of the number of qubits.

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Negativity in the Extended Hubbard Model under External Magnetic Field

YANG Zhen, NING Wen-Qiang

Chin. Phys. Lett. 2008, 25 (1): 31-34 .

Abstract

PDF(pc) (1406KB) ( 751 )

We exactly calculate the negativity, a measurement of entanglement, in the two-site extended Hubbard model with external magnetic field. Its behaviour at different temperatures is presented. The negativity reduces with the increasing temperature or with the increasing uniform external magnetic field. It is also found that a non-uniform external magnetic field can be used to
modulate or to increase the negativity.

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Partial Transposition on Bipartite System

REN Xi-Jun, HAN Yong-Jian, WU Yu-Chun, GUO Guang-Can

Chin. Phys. Lett. 2008, 25 (1): 35-38 .

Abstract

PDF(pc) (111KB) ( 954 )

Many properties of partial transposition are unclear as yet. Here we carefully consider the number of the negative eigenvalues of ρ^T (ρ's partial transposition) when ρ is a two-partite state. There is strong evidence to show that the number of negative eigenvalues of ρT is N(N-1)/2 at most when ρ is a state in Hilbert space C^N×C^N. For the special case, the 2×2 system,
we use this result to give a partial proof of the conjecture |ρ^T|^T≥0. We find that this conjecture is strongly connected with the entanglement of the state corresponding to the negative eigenvalue of ρ^^T or the negative entropy of ρ.

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Dynamics of Bright/Dark Solitons in Bose--Einstein Condensates with Time-Dependent Scattering Length and External Potential

ZHANG Ai-Xia, XUE Ju-Kui

Chin. Phys. Lett. 2008, 25 (1): 39-41 .

Abstract

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We present an analytical study on the dynamics of bright and dark solitons in Bose--Einstein condensates with time-varying atomic scattering length in a time-varying external parabolic potential. A set of exact soliton solutions of
the one-dimensional Gross--Pitaevskii equation are obtained, including fundamental bright solitons, higher-order bright solitons, and dark solitons. The results show that the soliton's parameters (amplitude, width, and period) can be changed in a controllable manner by changing the scattering length and external potential. This may be helpful to design experiments.

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Asymmetric Superradiant Scattering Patterns from Bose--Einstein Condensates

CHEN Yuan-Kai, ZHOU Xiao-Ji, YANG Fan, CHEN Xu-Zong

Chin. Phys. Lett. 2008, 25 (1): 42-45 .

Abstract

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The asymmetric patterns of superradiance from Bose--Einstein condensates
are studied for the spatially inhomogeneous pump pulse with the semiclassical Maxwell--Schrodinger equations. The coupling dynamics between the optical field and condensate in the strong pulse and a faded wing in the weak coupling regime are discussed, which not only explain the spatial effects in the process of superradiance, but also supply a new method to control its patterns.

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Entanglement of Area Quantums in Quantized Space

SHAO Dan, SHAO Liang, SHAO Chang-Gui, NODA Huzio

Chin. Phys. Lett. 2008, 25 (1): 46-47 .

Abstract

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Employing the area qantum 1/2 excited by the Wilson loop, a possible origin of qubit is argued. At the same time, the existences of possible entanglement of area quantums, and non-local property of the entangled states are
demonstrated in quantized space.

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Quantum Fluids of Self-Assembled Chains of Polar Molecules at Finite Temperature

ZHU Kun-Yan, TAN Lei, GAO Xiang, WANG Daw-Wei

Chin. Phys. Lett. 2008, 25 (1): 48-51 .

Abstract

PDF(pc) (389KB) ( 769 )

The finite temperature properties of self-assembled dipole chains of polar molecules in strongly confined pancake traps are investigated. The single-chain vibrations at finite temperature, which become important for long chains in a strongly interacting regime, are found to lower the transition temperature and to shift the chain distribution by less than 10%. We also propose
experimental parameters to observe such quantum phase transition.

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On Kaup and Newell's Method for Solving DNLS Equation

YAN Tian, YU Jia-Lu, HUANG Nian-Ning

Chin. Phys. Lett. 2008, 25 (1): 52-54 .

Abstract

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Kaup and Newell's revised inverse scattering transform for the derivative nonlinear Schrodinger (DNLS) equation is investigated. We compared it with a more reasonable approach proposed recently, which is rigorously proven by
the Liouville theorem. It is concluded that Kaup and Newell's revision is only suitable for giving single-soliton solution and can not be generalized to multi-soliton case.

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Nucleon Mass Splitting at Finite Isospin Chemical Potential

CHANG Sheng, LIU Ji-Feng, ZHUANG Peng-Fei

Chin. Phys. Lett. 2008, 25 (1): 55-57 .

Abstract

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We investigate nucleon mass splitting at finite isospin chemical potential in the frame of the two-flavour Nambu--Jona-Lasinio model. It is analytically proven that in the phase with explicit isospin symmetry breaking, the proton mass decreases and the neutron mass increases linearly in the isospin
chemical potential.

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Revisiting the QCD Corrections to the R-Parity Violating Processes pp/pp →eμ+X

WANG Shao-Ming, HAN Liang, MA Wen-Gan, ZHANG Ren-You, JIANG Yi

Chin. Phys. Lett. 2008, 25 (1): 58-61 .

Abstract

PDF(pc) (237KB) ( 650 )

We present the theoretical predictions up to QCD next-to-leading order for the cross section of high-mass electron--muon pair production at the Tevatron and at the Large Hadron Collider (LHC), considering only the dominant contributions from the third-generation sneutrino. The dependence of the
renormalization and factorization scales on the total cross section, and the effects on the K-factor due to the uncertainty of parton distribution function are carefully investigated. By considering soft-gluon resummation effects to all orders in α_s of leading logarithm, we present the transverse momentum distributions of the final eμ pair.

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Derivation of the Ward--Takahashi Identity in GWS Gauge Theory

BAO Ai-Dong, WU Shi-Shu

Chin. Phys. Lett. 2008, 25 (1): 62-65 .

Abstract

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With the help of a postulate of gauge group parameter involved with ghost fields, the infinitesimal gauge transformation laws preserving the gauge-invariance of the quantum Lagrangian itself of the quantized Glashow--Weinberg--Salam model are established precisely. The corresponding Ward--Takahashi identity for the model is derived exactly.

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Associated Production of Scalars and New Gauge Bosons from a Little Higgs Model at the LHC

YUE Chong-Xing, ZHANG Nan, DING Li, ZHU Shi-Hai, WANG Li-Hong

Chin. Phys. Lett. 2008, 25 (1): 66-69 .

Abstract

PDF(pc) (138KB) ( 596 )

The littlest Higgs model with T-parity (LHT model) predicts the existence of the T-odd scalars (Ф^±, Ф⁰, and Ф^p). We consider the production of these new particles associated with T-odd gauge bosons at the Large Hadron Collider (LHC). It is found that the partonic process qq'→Ф⁺B_H can generate a number of the characteristic signal events with a charged lepton and large missing energy at the LHC.

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Enhancement of β⁺-Decay Rate of ²²Na in Metal Pd at Low Temperature

LIAN Gang, SU Jun, WANG Bao-Xiang, JIANG Chao, BAI Xi-Xiang, ZENGSheng, ZHENG Yong-Nan, ZHU Sheng-Yun, ZHU Li-Hua, LIU Wei-Ping, LI Zhi-Hong, WANG You-Bao, GUO Bing, LI Yun-Ju, QIN Xing

Chin. Phys. Lett. 2008, 25 (1): 70-72 .

Abstract

PDF(pc) (240KB) ( 739 )

Temperature dependence of nuclear decays in metallic environments is a controversial issue. We measured the temperature dependence of the β⁺-decay half-life of ²²Na implanted into the metal host of palladium. It is found that the β⁺-decay half-life of ²²Na in the metal Pd cooled to T=15K is shorter by 0.46(14)% than that at room temperature. The result is consistent in sign with, but clearly smaller than, the estimated one by the Debye model.

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Boundary Conditions of Wigner-Seitz Cell in Inner Crust of Neutron Stars with Relativistic Mean Field Approach

CAO Ji-Guang, YANG Ding, MA Zhong-Yu, Nguyen Van Giai

Chin. Phys. Lett. 2008, 25 (1): 73-76 .

Abstract

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The microscopic structure of the Wigner--Seitz (W-S) cell in the inner crust of neutron stars is investigated with the relativistic mean field (RMF) approach. The W-S cell is composed of a cluster of neutrons and protons localized in a
region around the centre and surrounded by a neutron gas of approximately uniform density. In order to generate the density of the W-S cell, appropriate boundary conditions in the calculation of the single-particle wavefunctions are necessary. We emphasize on the choice of the boundary conditions in the RMF approach. Three kinds of boundary conditions are suggested. The properties of the W-S cell with the three kinds of boundary conditions are investigated. The neutron density distributions in the RMF and Hartree--Fock--Bogoliubov (HFB) models are compared. It is found that the neutron gas densities of the W-S cell in the RMF model is higher than those obtained in the HFB model.

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Shell Correction and Pairing Energies in the Dinuclear System Model

WANG Nan, LI Jun-Qing, ZHAO En-Guang,

Chin. Phys. Lett. 2008, 25 (1): 77-80 .

Abstract

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We investigate the dependences of the potential energy surfaces (PES) and the fusion probabilities for some cold fusion reactions leading to super-heavy elements on the nuclear shell effect and pairing energy. It is found that the shell effect plays an important role in the fusion of the super-heavy element while pairing energy's contribution is insignificant. The fusion probabilities and evaporation residue cross sections as functions of the Ge-isotope projectile bombarding ²⁰⁸Pb are also investigated. It is found that evaporation residue cross sections do not always increase with the increasing neutron number of Ge-isotope.

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A New Numerical Approach to Evaluate Variation of Electric Field Strength at the End of Particle Trajectory in Nuclear Track Detectors

SUN Xiu-Dong, Ali Mostofizadeh, HOU Chun-Feng, M. Reza Kardan

Chin. Phys. Lett. 2008, 25 (1): 81-84 .

Abstract

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A geometrical model for an electrochemical etching (ECE) track in a dielectric detector is defined and a primary programme is written to generate the track. The generated track is transformed to an M × N matrix of primary voltages. Using a numerical method, the matrix of final voltages is computed, and using another numerical approach, the electric field strengths in the elements of detector volume are computed. The final field strength at the end of particle trajectory is obtained. The results of our numerical computation show that there are exact correlations between the field strength at the end of particle
trajectory and the parameters of track under ECE. It is found that although two traditional models of Mason and Smythe in dielectrics can be partly applied for short and long tracks, none of them areable to explain the behaviour of field strength in a `general case'.

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Research on Intracavity Laser Cooling of Solid

JIA You-Hua, ZHONG Biao, JI Xian-Ming, YIN Jian-Ping

Chin. Phys. Lett. 2008, 25 (1): 85-88 .

Abstract

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A theoretical study of intra-cavity laser cooling by anti-Stokes luminescence in a rare-earth doped glass is performed. Compared with cooling in an external cavity by multipassing the radiation, intra-cavity cooling has the advantage of
high pumping power and high-absorbed power. However, one must ensure
that the cavity can still form a laser by locating the material in the cavity. A model is developed to evaluate the enhancement factor and the absorbed power. The results show that for a low optical density, especially when the sample length is less than 2mm, the intracavity configuration is a very efficient method for laser cooling. The diode laser, which may become the best candidate for our model, is briefly discussed.

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Monte Carlo Simulation of Cooling Induced by Parametric Resonance

ZHANG Peng-Fei, ZHANG Hai-Chao, XU Xin-Ping, WANG Yu-Zhu

Chin. Phys. Lett. 2008, 25 (1): 89-92 .

Abstract

PDF(pc) (178KB) ( 750 )

We demonstrate that the parametric resonance in a magnetic quadrupole
trap can be exploited to cool atoms by using Bird's method. In our programme the parametric resonance was realized by anisotropically modulating the trap potential. The modulation frequency dependences of temperature and fraction of the trapped atoms are explored. Furthermore, the temperature after the modulation as functions of the modulation amplitude and the mean elastic collision time are also studied. These results are valuable for the experiment of parametric resonance in a quadrupole trap.

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Controllable Photonic Band Gap and Defect Mode in a 1D CO₂-Laser Optical Lattice

ZHOU Qi, YIN Jian-Ping

Chin. Phys. Lett. 2008, 25 (1): 93-96 .

Abstract

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We propose a new method to form a novel controllable photonic crystal with cold atoms and study the photonic band gap (PBG) of an infinite 1D CO₂-laser optical lattice of ⁸⁵Rb atoms under the condition of quantum coherence. A significant gap generated near the resonant frequency of the atom is founded and its dependence on physical parameters is also discussed. Using the eigenquation of defect mode, we calculate the defect mode when a defect is introduced into such a lattice. Our study shows that the proposed new method can be used to optically probe optical lattice in situ and to design some novel and controllable photonic crystals.

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Electron Scattering by C₄H₁₀ and C₆H₆ in the Energy Range 100--1000eV

MA Er-Jun, , MA Yu-Gang, CAI Xiang-Zhou, FANG De-Qing, SHEN Wen-Qing, TIAN Wen-Dong

Chin. Phys. Lett. 2008, 25 (1): 97-100 .

Abstract

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We investigate the applicability of the independent atom model (IAM) to elastic electron scattering from complex polyatomic molecules, namely C₄H₁₀ and C₆H₆, in the energy range 100--1000eV. The cross sections of the elastic
electron scattering are calculated by employing the IAM together with the relativistic partial waves. The incorporation of both the modified absorption potential and the extended structural factor in the IAM makes the elastic differential cross sections and momentum transfer cross sections have a good agreement with the available experimental data. The present simple model seems to be insensitive to the complexity of the target molecules so that the proposed procedure can be quite useful for calculation of electron scattering from bio-molecules.

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Electromagnetic Wave Transmission from Slightly Gaussian Rough Surface of Layered Medium

REN Xin-Cheng, GUO Li-Xin

Chin. Phys. Lett. 2008, 25 (1): 101-104 .

Abstract

PDF(pc) (214KB) ( 910 )

The electromagnetic wave transmission from the slightly rough surface of three-layered medium is studied, and formulae of the transmission coefficients for different polarizations are derived using the small perturbation method. A Gaussian rough surface is presented for describing rough surface of the layered medium, the influence of permittivity of the layered medium, the mean layer thickness of the intermediate medium, the roughness surface parameters and the incident frequency on the transmission coefficient of HH polarization are obtained and discussed with numerical implementation.

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Hybrid Deconvolution of Adaptive Optics Retinal Images from Wavefront Sensing

TIAN Yu, RAO Chang-Hui, RAO Xue-Jun, WANG Cheng, YU Xiang, LIUQian, XUE Li-Xia, LING Ning, JIANG Wen-Han

Chin. Phys. Lett. 2008, 25 (1): 105-107 .

Abstract

PDF(pc) (1694KB) ( 1000 )

Adaptive optics can be used to compensate for the wave aberration of the human eyes to achieve high-resolution imaging in real time. However the correction is partial due to the limitation of hardware. We propose a kind of hybrid image post-processing method, which uses the blind deconvolution combined with the residual data in wavefront sensor to restore the partially adaptive optics corrected retinal image. This method is applied in the image restoration of the vivid human retinal images. The results show that it is effective to improve the retinal image quality.

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Phase Controlled Laser Interference for Tunable Phase Gratings in Dye-Doped Nematic Liquid Crystals

LI Ming, ZHANG Pei-Qing, GUO Jing, XIE Xiang-Sheng, LIU Yi-Kun, LIANG-Bing, ZHOU Jian-Ying, XIANG Ying

Chin. Phys. Lett. 2008, 25 (1): 108-111 .

Abstract

PDF(pc) (1584KB) ( 775 )

A phase controlled multi-beam interference is applied to excite the doped liquid crystals. Control of the phase difference between the exciting beams allows the external control of the interference pattern inside the liquid
crystal. The dynamic variation of the grating is made possible with a time-dependent phase change to derive the nonlinear refractive index as well as the responding speed of the material. The induced grating structure is numerically modelled with reorientational phase gratings in the liquid crystal, and the diffraction dynamics is found to be in good agreement between theoretical and experimental results.

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Effect of Time-Dependent Ionization on Propagation of a Few-Cycle Circularly Polarized Laser Pulse in Two-Level Medium

ZHANG Xiang-Yun, SUN Zhen-Rong, CHEN Guo-Liang, WANG Zu-Geng

Chin. Phys. Lett. 2008, 25 (1): 112-115 .

Abstract

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Influence of multiphoton ionization on the propagation and spectrum of few-cycle circularly (elliptically) polarized laser pulses in an open two-level medium
(two-level plus continuum model) is investigated based on the conventional two-level model proposed by Slavcheva and Hess (Phys. Rev. A 72 (2005) 053804), and the propagation dynamics of an arbitrary elliptically polarized laser pulse is reduced into that of right and left circularly polarized laser pulses. When the laser intensity is high enough to cause ionization, there are significant impacts of ionization on the pulse reshaping and on the higher order spectral components, and the impacts for the open two-level model
are different from those for the closed two-level model.

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Tm-Doped Fibre Laser Pumped Cr²⁺:ZnSe Poly-Crystal Laser

YANG Yong, TANG Yu-Long, XU Jian-Qiu, HANG Yin

Chin. Phys. Lett. 2008, 25 (1): 116-118 .

Abstract

PDF(pc) (182KB) ( 865 )

Demonstrations of cw lasing in Cr²⁺:ZnSe poly-crystal are reported. The laser consists of a 1.7-mm-thick Cr²⁺:ZnSe poly-crystal disc pumped by a Tm-silica
double-clad fibre laser at 2050nm. Using a concave high-reflection mirror with a radius of curvature of 500mm as the rear mirror, the laser delivers up to 1030mW of radiation around 2.367μm.

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High Power Continuous-Wave and Acousto-Optic Q-Switched Nd:GdVO₄ Laser Operated at 912nm

GAO Jing, YU Xin, CHEN Fei, LI Xu-Dong, ZHANG Zhen, YU Jun-Hua, WANG Yue-Zhu

Chin. Phys. Lett. 2008, 25 (1): 119-121 .

Abstract

PDF(pc) (167KB) ( 771 )

We present a high power and efficient operation of the ⁴F_3/2to⁴I_9/2 ransition in Nd:GdVO₄ at 912nm. In the cw mode, the maximum output power of 8.6W is achieved when the incident pump power is 40.3W, leading to a slope efficiency of 33.3% and an optical-optical efficiency of 21.3%. To the best of our knowledge, this is the highest cw laser power at 912,nm obtained with the conventional Nd:GdVO₄ crystal. Pulsed operation of 912nm laser has also been realized by inserting a small acousto-optic (A-O) Q-Switch inside the
resonator. As a result, the minimal pulse width of 20ns and the average laser power 1.43W at the repetition rate of 10kHz are obtained, corresponding to 7.1kW peak power. We believe that this is the highest laser peak power at 912nm. Furthermore, duration of 65ns has also been acquired when the repetition rate is 100kHz.

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Eye-Safe Raman Laser at μm Based on BaWO₄Crystal

WANG Zheng-Ping, HU Da-Wei, FANG Xin, ZHANG Huai-Jin, XU Xin-Guang, WANG Ji-Yang, SHAO Zong-Shu

Chin. Phys. Lett. 2008, 25 (1): 122-124 .

Abstract

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Using an external couple cavity and a pump beam compression system, efficient 1.5μm eye-safe Raman laser is obtained based on BaWO₄ crystal. The largest output energy is 8.5mJ, corresponding to an electric-optical conversion efficiency of 47%.

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Physical mechanism of two-photon response in semi-insulating GaAs

LIU Xiu-Huan, CHEN Zhan-Guo, JIA Gang, SHI Bao

Chin. Phys. Lett. 2008, 25 (1): 125-128 .

Abstract

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The physical mechanism of two-photon response (TPR) in semi-insulating GaAs is studied. The measured photocurrent generated from the fabricated hemispherical GaAs sample responding to 1.3μm continuous wave laser shows a quadratic dependence on the coupled optical power and no saturation with the bias. The angular dependence of the photocurrent on the azimuth is in agreement with the anisotropy of double-frequency absorption
(DFA) in GaAs single crystals. These results demonstrate DFA is the dominant mechanism of TPR in GaAs.

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Simulation of Femtosecond Pulse Propagation through Hollow Fibre Filled with Noble Gases of Gradient Temperature

SONG Zhen-Ming, ZHANG Guang-Xiao, CAO Shi-Ying, PANG Dong-Qing, CHAI Lu, WANG Qing-Yue, ZHANG Zhi-Gang,

Chin. Phys. Lett. 2008, 25 (1): 129-132 .

Abstract

PDF(pc) (1242KB) ( 809 )

We propose a novel technique for generating intense few to mono-cycle
femtosecond pulses. The simulation demonstrate that for the temperature
difference of 300K, the spectrum of the output pulses is increased by 67% and the transform limited pulse width is reduced almost by half, compared with those obtained with hollow fibres in uniform temperature.

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Space-Selective Precipitation of Ba₂TiSi₂O₈Crystals in Sm³⁺-Doped BaO--TiO₂--SiO₂ Glass by Femtosecond Laser Irradiation

ZHU Bin, DAI Ye, MA Hong-Liang, LIN Geng, QIU Jian-Rong

Chin. Phys. Lett. 2008, 25 (1): 133-136 .

Abstract

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The ferroelectric crystal Ba₂TiSi₂O₈ with high second-order optical nonlinearity
is precipitated in Sm³⁺-doped BaO--TiO₂--SiO₂ glass by a focused 800nm, 250kHz and 150fs femtosecond laser irradiation. No apparent blue and red emissions are observed at the beginning, while strong blue emission due to second harmonic generation and red emission due to the f--f transitions of
Sm³⁺ are observed near the focal point of the laser beam after irradiation for 25s. Micro-Raman spectra confirm that Ba₂TiSi₂O₈ crystalline dots and lines are formed after laser irradiation. The mechanism of the phenomenon is discussed.

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Nonlinear Localization due to a Double Negative Defect Layer in a One-Dimensional Photonic Crystal Containing Single Negative Material Layers

Munazza Zulfiqar Ali, Tariq Abdullah

Chin. Phys. Lett. 2008, 25 (1): 137-140 .

Abstract

PDF(pc) (167KB) ( 611 )

We investigate the effects of introducing a defect layer in a one-dimensional photonic crystal containing single negative material layers on the transmission
properties. The width of the defect layer is taken to be the same or smaller than the period of the structure. Different cases of the defect layer being linear or nonlinear and double positive or double negative are discussed. It is found that only a nonlinear double negative layer gives rises to a localized mode within the zero-Ф_eff gap in this kind of structure. It is also shown that the important characteristics of the nonlinear defect mode such as its frequency, its FWHM and the threshold of the associated bistability can be controlled by changing the widths of the defect layer and the host layers.

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An Integrative Biosensor Based on Contra-Directional Coupling Two-dimensional Photonic Crystal Waveguides

MAO Xiao-Yu, YAO Di-Bi, ZHAO Ling-Yun, HUANG Yi-Dong, ZHANG Wei, PENG Jiang-De

Chin. Phys. Lett. 2008, 25 (1): 141-143 .

Abstract

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We propose an integrative biochemical sensor utilizing the dip in the transmission spectrum of a normal single-line defect photonic crystal (PC) waveguide, which has a contra-directional coupling with another PC waveguide. When the air holes in the PC slab are filled with a liquid analyte with different refractive indices, the dip has a wavelength shift. By detecting the output power variation at a certain fixed wavelength, a sensitivity of 1.2×10^-4 is feasible. This structure is easy for integration due to its plane waveguide structure and omissible pump source. In addition, high signal to noise ratio can be expected because signal transmits via a normal single-line defect PC waveguide instead of the PC hole area or analyte.

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Effect of a Two-Dimensional Periodic Dielectric Background on Complete Photonic Band Gap in Complex Square Lattices

ZHANG Yan, SHI Jun-Jie

Chin. Phys. Lett. 2008, 25 (1): 144-147 .

Abstract

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A two-dimensional photonic crystal model with a periodic square dielectric background is proposed. The photonic band modulation effects due to the two-dimensional periodic background are investigated in detail. It is found that periodic modulation of the dielectric background greatly alters photonic band structures, especially for the E-polarization modes. The number, width and position of the photonic band gaps sensitively depend on the dielectric constants of the two-dimensional periodic background. Complete band gaps are found, and the dependence of the widths of these gaps on the structural and material parameters of the two alternating rods/holes is studied.

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Design of Highly Sensitive Surface Plasmon Resonance Sensors Using Planar Metallic Films Closely Coupled to Nanogratings

YANG Xiao-Yan, XIE Wen-Chong, LIU De-Ming

Chin. Phys. Lett. 2008, 25 (1): 148-151 .

Abstract

PDF(pc) (222KB) ( 855 )

We investigate the sensitivity enhancement of surface plasmon resonance
(SPR) sensors using planar metallic films closely coupled to nanogratings. The strong coupling between localized surface plasmon resonances (LSPRs) presenting in metallic nanostructures and surface plasmon polaritons (SPPs) propagating at the metallic film surface leads to changes of resonance reflection properties, resulting in enhanced sensitivity of SPR sensors. The effects of thickness of the metallic films, grating period and metal materials on the refractive index sensitivity of the device are investigated. The refractive index sensitivity of nanograting-based SPR sensors is predicted to be about
543nm/RIU (refractive index unit) using optimized structure parameters. Our study on SPR sensors using planar metallic films closely coupled to nanogratings demonstrates the potential for significant improvement in refractive index sensitivity.

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A Theoretical and Experimental Research on Terahertz Electro-Optic Sampling at Near-Zero Optical Transmission Point

XU Shi-Xiang, CAI Hua

Chin. Phys. Lett. 2008, 25 (1): 152-155 .

Abstract

PDF(pc) (174KB) ( 970 )

We report an improved theoretical model to characterize terahertz electro-optic (EO) sampling detection operating at near crossed-polarizer design by considering the nonzero minimal transmission of polarizers and the polarization purity of laser beam. The proof-of-concept experiments show that the model can give quiet reasonable explanations on many experimental phenomena in THz EO detection, e.g. the modulation depth vs the different optical biases, the noise level from the balance detector vs the input probe beam power, the main origin of the background light and the incomplete
cancellation of noise from the laser intensity fluctuation in balanced detection. The terahertz signals and the noises are also measured based on two different EO sampling schemes for comparison. The measured results support our model very well.

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Analysis and Determination of Refractive Index Profiles of O²⁺ Ion-Implanted LiNbO₃ Planar Waveguide Using Etching and Ellipsometry Techniques

LIU Han-Ping, LU Fei, WANG Xue-Lin, YANG Tian-Lin, LV Ying-Bo, LI Yan-Hui, LIU Xiang-Zhi, ZHANG Rui-Feng, SONG Qiang, MA Xue-Jian

Chin. Phys. Lett. 2008, 25 (1): 156-159 .

Abstract

PDF(pc) (174KB) ( 603 )

The refractive index profiles of 3MeV O²⁺ ion-implanted planar waveguides in lithium niobate are reconstructed based on etching and ellipsometry techniques. SRIM2003 code is used to simulate the damage distribution in waveguide. It is demonstrated that the index profile of this kind of waveguide, extending to several micrometres in depth, can be determined by
etching in combination with following ellipsometric measurements. A good agreement is found between the simulated damage distributions in waveguide and the index profiles based on experimental data, and the
width of refractive index barrier is wider than the result of SRIM2003.

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Bragg Gratings Written in Photonic Crystal Fibres with a High-Index Germanosilicate Core

JIN Long, GUAN Bai-Ou, FANG Qiang, WANG Zhi, LIU Bo, LIU Jian-Guo, YUE Yang, KAI Gui-Yun, DONG Xiao-Yi

Chin. Phys. Lett. 2008, 25 (1): 160-163 .

Abstract

PDF(pc) (423KB) ( 617 )

Bragg gratings are straightforwardly written into a 10-ring photonic crystal fibre (PCF) with a highly Ge³⁺-doped core by means of a 193nm ArF excimer laser. The grating inscription efficiency is improved, due to enhanced
photosensitivity and the large overlap between the fundamental mode and the photosensitive core. The exposure duration only lasts less than 180s. In addition, the high-index core changes the modal properties of the PCF and two groups of higher order mode resonance dips are therefore obtained. A strong cladding mode resonance is observed, because the LP₀₂-like mode has a large overlap integral with the fundamental mode.

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Characteristics of Photonic Bandgap Fibres with Hollow Core's Inner Surface Coated by a Layer Material

DU Jiang-Bing, LIU Yan-Ge, WANG Zhi, LIU Zhan-Yuan, KAI Gui-Yun, DONGXiao-Yi

Chin. Phys. Lett. 2008, 25 (1): 164-167 .

Abstract

PDF(pc) (1010KB) ( 826 )

Hollow core's inner surface coating in a photonic bandgap fibre (PBGF) is investigated by means of finite element method. The coat material and thickness-dependence dispersion curve and group velocity dispersion are numerically studied. The coating with materials of low index or small thickness
will rise up the dispersion curve but will not induce surface modes. However, coating with materials of high index or big coat thickness will induce surface modes and avoided-crossings. By varying coat material's refractive index and thickness, the appearances of surface modes and avoided-crossings can be changed. It is found that the avoided-crossing can enormously enlarge the negative dispersion which can find applications in dispersion compensation. We numerically achieve a negative dispersion as large as - 1416.15ps/nm/km. The results give a physical insight into the propagation properties of PBGFs with the hollow core coated by a layer of material and are of crucial significance in the applications of PBGF coating.

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Directional Nanoslit-Bump Coupler for Surface Plasmon Polaritons

ZHANG Yong-Liang, ZHAO De-Yin, ZHOU Chuan-Hong, JIANG Xun-Ya

Chin. Phys. Lett. 2008, 25 (1): 168-171 .

Abstract

PDF(pc) (1859KB) ( 684 )

We investigate a p-polarized plane wave transmitted through a metallic slit--bump nanostructure using the finite difference time domain simulation. It is found that narrow bumps with suitable separation can diffract surface plasmons into highly directional collimating beams. The number and directionality of the beams can be controlled by adjusting the geometry parameters of the nanostructure. The structure with optimized parameters may be interesting for practical applications as directional nanoslit SPP-light coupler in integrated photonic devices.

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Real-Time Measurements and Modelling on Dynamic Behaviour of SonoVue Bubbles Based on Light Scattering Technology

TU Juan, GUAN J. F., MATULA T. J., Crum L. A., WEI Rongjue

Chin. Phys. Lett. 2008, 25 (1): 172-175 .

Abstract

PDF(pc) (358KB) ( 650 )

The dynamic behaviour of SonoVue microbubbles, a new generation ultrasound contrast agent, is investigated in real time with light scattering method. Highly diluted SonoVue microbubbles are injected into a diluted gel made of xanthan gum and water. The responses of individual SonoVue bubbles to driven ultrasound pulses are measured. Both linear and nonlinear
bubble oscillations are observed and the results suggest that SonoVue microbubbles can generate strong nonlinear responses. By fitting the experimental data of individual bubble responses with Sarkar's model, the shell coating parameter of the bubbles and dilatational viscosity is estimated to be 7.0 nm·s·Pa.

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Thermal Diffusivity of Film/Substrate Structures Characterized by Transient Thermal Grating Method

XU Xiao-Dong, MA Di, ZHANG Shu-Yi, LUO Ai-Hua, KIYOTAKA Wasa,

Chin. Phys. Lett. 2008, 25 (1): 176-179 .

Abstract

PDF(pc) (711KB) ( 767 )

Transient thermal grating method is used to measure the thermal diffusivity of absorbing films deposited on transparent substrates. According to periodically modulated dielectric constant variations and thermoelastic deformations of the thin films caused by the transient thermal gratings, an improved optical diffraction theory is presented. In the experiment, the probing laser beam reflectively diffracted by the thermal grating is measured by a photomultiplier at different grating fringe spaces. The thermal diffusivity of the film can be
evaluated by fitting the theoretical calculations of diffraction signals to the experimental measured data. The validity of the method is tested by measuring the thermal diffusivities of absorbing ZnO films deposited on glass substrates.

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Analytic Solution for Steady Slip Flow between Parallel Plates with Micro-Scale Spacing

ZHANG Tian-Tian, JIA Li, WANG Zhi-Cheng

Chin. Phys. Lett. 2008, 25 (1): 180-183 .

Abstract

PDF(pc) (177KB) ( 988 )

The Navier--Stokes equations for slip flow between two very closely spaced parallel plates are transformed to an ordinary differential equation based on the pressure gradient along the flow direction using a new similarity transformation. A powerful easy-to-use homotopy analysis method was used to obtain an analytical solution. The convergence theorem for the homotopy analysis method is presented. The solutions show that the second-order homotopy analysis method solution is accurate enough for the current problem.

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Boundary Slip and Surface Interaction: A Lattice Boltzmann Simulation

CHEN Yan-Yan, , YI Hou-Hui, LI Hua-Bing,

Chin. Phys. Lett. 2008, 25 (1): 184-187 .

Abstract

PDF(pc) (206KB) ( 742 )

The factors affecting slip length in Couette geometry flows are analysed by means of a two-phase mesoscopic lattice Boltzmann model including non-ideal fluid-fluid and fluid-wall interactions. The main factors influencing the boundary slip are the strength of interactions between fluid-fluid and fluid-wall particles. Other factors, such as fluid viscosity, bulk pressure may also change the slip length. We find that boundary slip only occurs under a certain density (bulk pressure). If the density is large enough, the slip length will tend to zero. In our simulations, a low density layer near the wall does not need to be postulated a priori but emerges naturally from the underlying non-ideal mesoscopic dynamics. It is the low density layer that induces the boundary slip. The results may be helpful to understand recent experimental observations on the slippage of micro flows.

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Direct Numerical Simulation of Three-Dimensional Richtmyer--Meshkov Instability

FU De-Xun, MA Yan-Wen, LI Xin-Liang

Chin. Phys. Lett. 2008, 25 (1): 188-190 .

Abstract

PDF(pc) (2143KB) ( 672 )

Direct numerical simulation (DNS) is used to study flow characteristics after interaction of a planar shock with a spherical media interface in each side of which the density is different. This interfacial instability is known as the
Richtmyer--Meshkov (R-M) instability. The compressible Navier--Stoke equations are discretized with group velocity control (GVC) modified fourth order accurate compact difference scheme. Three-dimensional numerical simulations are performed for R-M instability installed passing a shock through a spherical interface. Based on numerical results the characteristics of 3D R-M
instability are analysed. The evaluation for distortion of the interface, the deformation of the incident shock wave and effects of refraction, reflection and diffraction are presented. The effects of the interfacial instability on produced vorticity and mixing is discussed.

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Large Eddy Simulation of Turbulent Channel Flow with 3D Roughness Using a Roughness Element Model

YANG Fan, ZHANG Hui-Qiang, CHAN Cheong-Ki, WANG Xi-Lin

Chin. Phys. Lett. 2008, 25 (1): 191-194 .

Abstract

PDF(pc) (1046KB) ( 828 )

Large eddy simulation of turbulent channel flow with dense and small 3D roughness elements is carried out using a roughness element model. Profiles of mean Reynolds stress, mean velocity and rms velocity as well as turbulent structures near the wall are obtained. The shear stress in the rough wall is larger than that in the smooth wall side and the rough wall has a larger influence on the channel flow. Profiles of mean streamwise velocity near the wall have logarithmic velocity distributions for both smooth and roughness walls, while there is a velocity decrease for the rough wall due to larger fractional drag. All the three components of rms velocities in the rough wall region are larger than that in the smooth wall region, and the roughness elements on the wall increase turbulent intensity in all directions. The streak
spacing and average diameter of near wall quasi-streamwise vortices increase with the presence of roughness elements on the wall and it is
shown that the rough wall induces complex and strong streamwise vortices. Results of dense and small 3D roughness elements in both turbulent statistics and structure, obtained with a relatively simple method, are found to be comparable to related experiments.

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Fully Developed Convective Heat Transfer of Power Law Fluids in a Circular Tube

ZHENG Lian-Cun, ZHANG Xin-Xin, MA Lian-Xi

Chin. Phys. Lett. 2008, 25 (1): 195-197 .

Abstract

PDF(pc) (160KB) ( 1911 )

We present a theoretical analysis for fully developed convective heat transfer in a circular tube for power law fluids by assuming that the thermal diffusivity is a function of temperature gradient. The analytical solution is obtained and the heat transfer behaviour is investigated under a constant heat flux boundary condition. It is shown that the Nusselt number strongly depends on the value of power law index n. The Nusselt number sharply decreases in the range of 0<n<0.1. However, for n>0.5, the Nusselt number decreases monotonically with the increasing n, and for n>20, the values of Nusselt number approach a constant.

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A New Dynamics Expansion Mechanism for Plasma during Pulsed Laser Deposition

TAN Xin-Yu, ZHANG Duan-Ming, FENG Sheng-Qin, LI Zhi-Hua, LIU Gao-Bin, FANG Ran-Ran, SUN Min

Chin. Phys. Lett. 2008, 25 (1): 198-201 .

Abstract

PDF(pc) (245KB) ( 676 )

The dynamics expansion mechanisms for plasma plume generated by pulsed laser radiation are studied in detail, taking account of plasma ionization effect. Based on the consideration of local conservations of mass, momentum, collected as the assumption that plasma can be viewed as compressible ideal fluid and high temperature-high pressure ideal gas, we develop a new dynamics expansion mechanism for plasma produced by pulsed laser radiation. Using the analytical method, the space number density and pressure evolvement of plasma in cylindrical coordinate are obtained, the dynamics evolvement equations are also derived. The results from the present model indicate that the plasma dynamic expansion behaviour can be evidently influenced by the ionization fraction η. Its effect is similar to a new dynamic source for plasma expansion and increases the expansion acceleration in all directions. The predictions of the expansion of the plasma is
affected by the temperature, the average atoms mass and the ionization degree of the plasma are consistent with the experimental results.

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A Microfabricated Inductively Coupled Plasma Excitation Source

WANG Yong-Qing, PU Yong-Ni, SUN Rong-Xia, TANG Yu-Jun, CHEN Wen-Jun, LOU Jian-Zhong, MA Wen

Chin. Phys. Lett. 2008, 25 (1): 202-204 .

Abstract

PDF(pc) (2389KB) ( 1159 )

A novel miniaturization of inductively coupled plasma (ICP) source based on printed circuit produced using micro-fabrication techniques is presented. The basic parameters of the novel ICP, including its radio frequency, power loss, size, and argon consumption are less than 1% of that for the case of atmospheric pressure ICP source. For example, at 100Pa of argon gas pressure, the present ICP source can be ignited by using the rf power less than 3.5W. Potential applications of the ICP is discussed.

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Elastic Analysis of Physisorption-Induced Substrate Deformation

ZHANG Ji-Qiao, PAN Xia-Hui, YU Shou-Wen, FENG Xi-Qiao

Chin. Phys. Lett. 2008, 25 (1): 205-208 .

Abstract

PDF(pc) (255KB) ( 752 )

Physisorption may cause a dimple on a deformable solid surface due to adsorbate--substrate interaction. The interactive force between the adsorbate and the crystal atoms depends on their distances, which may change with substrate deformation. This feature of displacement-dependence indicates that the equilibrium problem is a force-deformation coupled nonlinear procedure. In the present study, a continuum mechanics model, in which the force is considered as a function of the displacement field of the medium, is presented to calculate the physisorption-induced deformation in a
semi-infinite elastic medium. It is found that the nonlinear effect due to force-deformation coupling should be taken in consideration in the adsorbate--substrate interaction analysis.

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Si Underlayer Induced Nano-Ablation in AgInSbTe Thin Films

JIAO Xin-Bing, WEI Jing-Song, GAN Fu-Xi

Chin. Phys. Lett. 2008, 25 (1): 209-211 .

Abstract

PDF(pc) (2599KB) ( 630 )

AgInSbTe/Si thin films on glass substrates are prepared by dc magnetron sputtering at room temperature. Using Si underlayer as the thermal diffusion layer, the super-resolution nano-ablation holes with a size of 70nm in the
AgInSbTe phase change films are obtained by a far-field focused laser experimental setup, with laser wavelength 405nm and objective-lens numerical aperture 0.90. The nano-ablation formation mechanism is analysed and discussed via the thermal diffusion of sample structures.

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Carbon Nanoparticles in Nematic Liquid Crystals

S. Eren San, Mustafa Okutan, Oguz Koysal, Yusuf Yerli

Chin. Phys. Lett. 2008, 25 (1): 212-215 .

Abstract

PDF(pc) (779KB) ( 1199 )

Fullerene C₆₀, C₇₀, single-walled and multi-walled carbon nanotubes and graphene sheets are doped to nematic liquid crystal (LC) host in the same percentage. Planar samples of these mixtures are prepared and our measurements constitute an optimization basis for possible applications. Fullerene balls are found to be the best compatible material for optical aims
and reorientation of LC molecules, while the carbon nanotubes experience some reorientation possibility in LC media and graphene layers are good barriers to preserve reorientation.

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Ab Initio Study of Structural and Electronic Properties of Sodium Bromide

REN Ping, DENG Hui-Yong, ZHANG Jun-Xi, DAI Ning

Chin. Phys. Lett. 2008, 25 (1): 216-218 .

Abstract

PDF(pc) (123KB) ( 886 )

The structural and electronic properties of sodium bromide (NaBr) are investigated by the density functional theory (DFT) within the generalized gradient approximation (GGA) for the exchange and correlation energy. The
equilibrium lattice constant, bulk modulus and its pressure derivative are obtained by fitting the calculated total energy to the third-order Birch--Murnaghan equation of state. The band structure along the higher symmetry axes in the Brillouin zone, the density of states (DOS) and the partial density of states (PDOS) are presented. The results have been discussed and compared with the available experimental and theoretical data.

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P-BN/n-Si Heterojunction Prepared by Beryllium ion Implantation

HE Bin, CHEN Guang-Hua, LI Zhi-Zhong, DENG Jin-Xiang, ZHANG Wun-Jun

Chin. Phys. Lett. 2008, 25 (1): 219-222 .

Abstract

PDF(pc) (840KB) ( 863 )

A boron nitride (BN)/silicon p-n heterojunction is fabricated by implanting beryllium (Be) ions into the BN films deposited by rf sputtering on n-type Si (111) substrates. The FTIR observations indicate that the films deposited have a mixed phase composition of sp²- and sp³-hybridized BN. Considering the thickness of the BN layer, the ion implantation is conducted at an ion
energy of 100keV with the dose of 5×10¹⁵cm^-2. After annealing at a high temperature, the surface resistance of the BN film decreases significantly by 6 orders down to 1.2×10⁵Ω. Space-charge-limited current characteristic, which indicates the existence of shallow traps in the film, is observed. Current-voltage measurements across the BN film and the Si substrate reveal a clear
rectification feature, demonstrating the achievement of p-type doping of BN films by Be ion implantation.

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Effects of Vacuum on Fused Silica UV Damage

XU Shi-Zhen, LV Hai-Bing, YUAN Xiao-Dong, HUANG Jin, JIANG Xiao-Dong, WANG Hai-Jun, ZU Xiao-Tao, ZHENG Wan-Guo

Chin. Phys. Lett. 2008, 25 (1): 223-226 .

Abstract

PDF(pc) (296KB) ( 1081 )

Damage points induced by 355nm laser irradiation increase more quickly on the surface of fused silica in vacuum of about 10^-3Pa than in atmospheric air at the same fluence. The larger concentration of point defects in vacuum is confirmed by photoluminescence intensity. X-ray photoelectron spectroscopy and infrared absorption indicate the formation of sub-stoichiometric silica on the surface. The degradation mechanism of fused silica in vacuum is discussed.

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Investigation of SOI Substrates Incorporated with Buried MoSi₂ for High Frequency SiGe HBTs

CHEN Chao, LIU Wei-Li, MA Xiao-Bo, SHEN Qin-Wo, SONG Zhi-Tang, LIN Cheng-Lu

Chin. Phys. Lett. 2008, 25 (1): 227-229 .

Abstract

PDF(pc) (1203KB) ( 865 )

Highly arsenic-doped Si-on-insulator (SOI) substrate incorporated with buried MoSi₂ layers is fabricated aiming at decreasing the collector series resistance of SiGe heterojunction bipolar transistors (HBTs) on SOI, thereby enhancing cutoff frequency (f_T) performance and increasing the maximum value of f_T (f_TMAX). The f_T performance at medium current is enhanced and current required for f_T=15GHz is reduced by half. The value of f_TMAX is improved by 30%.

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Phase Transition and Melting Curves of Calcium Fluoride via Molecular Dynamics Simulations

ZENG Zhao-Yi, CHEN Xiang-Rong, , ZHU Jun, HU Cui-E,

Chin. Phys. Lett. 2008, 25 (1): 230-233 .

Abstract

PDF(pc) (229KB) ( 2400 )

The phase transition and melting curves of CaF₂ are investigated by using the general utility lattice programme (GULP) via the shell model with molecular dynamics method. By calculating the entropy H (at 0K) and Gibbs free energy G* (at 300K), we find that the phase transition pressure from the face-centred cubic (fcc) structure to the orthorhombic structure is 11.40GPa and 9.33GPa at 0K and 300K, respectively. The modified melting point of the fcc CaF₂ is in the range of 1650--1733K at 0GPa. All these results are well consistent with the available experimental data and other theoretical results. We also obtain that the melting temperature of high pressure phase is 990--1073K at 10GPa. Moreover, the temperature dependences of the elastic constants C_ij, bulk module B and shear module G are also predicted.

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Strong Surface Diffusion Mediated Glancing-Angle Deposition: Growth, Recrystallization and Reorientation of Tin Nanorods

WANG Huan-Hua, SHI Yi-Jian, William CHU, Yigal BLUM

Chin. Phys. Lett. 2008, 25 (1): 234-237 .

Abstract

PDF(pc) (6170KB) ( 824 )

Different from usual glancing-angle deposition where low surface diffusion is necessary to form nanorods, strong surface diffusion mediated glancing-angle deposition is exemplified by growing tin nanorod films on both silicon and glass substrates simultaneously via thermal evaporation. During growth, the
nanorods were simultaneously baked by the high-temperature evaporator, and therefore re-crystallized into single crystals in consequence of strong surface diffusion. The monocrystalline tin nanorods have a preferred orientation perpendicular to the substrate surface, which is quite different from the usual uniformly oblique nanorods without recrystallization.

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Influence of Different Interlayers on Growth Mode and Properties of InN by MOVPE

ZHANG Ri-Qing, LIU Xiang-Lin, KANG Ting-Ting, HU Wei-Guo, YANG Shao-Yan, JIAO Chun-Mei, ZHU Qing-Sheng

Chin. Phys. Lett. 2008, 25 (1): 238-241 .

Abstract

PDF(pc) (3864KB) ( 898 )

We grow InN epilayers on different interlayers by metal organic vapour phase epitaxy (MOVPE) method, and investigate the effect of interlayer on the properties and growth mode of InN films. Three InN samples were deposited on nitrided sapphire, low-temperature InN (LT-InN) and high-temperature GaN (HT-GaN), respectively. The InN layer grown directly on nitrided sapphire owns the narrowest x-ray diffraction rocking curve (XRC) width of 300 arcsec among the three samples, and demonstrates a two-dimensional (2D) step-flow-like lateral growth mode, which is much different from the three-dimensional (3D) pillar-like growth mode of LT-InN and HT-GaN buffered samples. It seems that mismatch tensile strain is helpful for the lateral epitaxy of InN film, whereas compressive strain promotes the vertical growth of InN films.

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Evolution of Ge and SiGe Quantum Dots under Excimer Laser Annealing

HAN Gen-Quan, ZENG Yu-Gang, YU Jin-Zhong, CHENG Bu-Wen, YANG Hai-Tao

Chin. Phys. Lett. 2008, 25 (1): 242-245 .

Abstract

PDF(pc) (1650KB) ( 806 )

We present different relaxation mechanisms of Ge and SiGe quantum dots
under excimer laser annealing. Investigation of the coarsening and relaxation of the dots shows that the strain in Ge dots on Ge films is relaxed by dislocation since there is no interface between the Ge dots and the Ge layer, while the SiGe dots on Si_0.77Ge_0.23film relax by lattice distortion to coherent dots, which results from the obvious interface between the SiGe dots and the
Si_0.77Ge_0.23 film. The results are suggested and sustained by Vanderbilt and Wickham's theory, and also demonstrate that no bulk diffusion occurs during the excimer laser annealing.

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Polymerization of Silicon-Doped Heterofullerenes: an Ab Initio Study

LI Ji-Ling, XIA Yue-Yuan, ZHAO Ming-Wen, LIU Xiang-Dong, SONG Chen, LI Li-Juan, LI Feng, HUANG Bo-Da

Chin. Phys. Lett. 2008, 25 (1): 246-249 .

Abstract

PDF(pc) (1019KB) ( 637 )

We perform the calculations on geometric and electronic structures of Si-doped heterofullerene C₅₀Si₁₀ and its derivatives, a C₄₀Si₂₀-C₄₀Si₂₀ dimer and a C₄₀Si₂₀-based nanowire by using density-functional theory. The optimized configuration of the C₄₀Si₂₀-based nanowire exhibits a regular dumbbell-shaped chain nanostructure. The electronic structure calculations indicate that the HOMO--LUMO gaps of the heterofullerene-based materials can be greatly modified by substitutionally doping with Si atoms and show a decreasing trend with increase cluster size. Unlike the band structures of the
conventional wide band gap silicon carbide nanomaterials, the C₄₀Si₂₀-based nanowire has a very narrow direct band gap of 0.087eV.

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Transport Characteristics of Mesoscopic Radio-Frequency Single Electron Transistor

A. H. Phillips, N. A. I. Aly, K. Kirah, H. E. El-Sayes

Chin. Phys. Lett. 2008, 25 (1): 250-253 .

Abstract

PDF(pc) (235KB) ( 630 )

The transport property of a quantum dot under the influence of external time-dependent field is investigated. The mesoscopic device is modelled as semiconductor quantum dot coupled weakly to superconducting leads via asymmetric double tunnel barriers of different heights. An expression for the current is deduced by using the Landauer--Buttiker formula, taking into
consideration of both the Coulomb blockade effect and the magnetic field. It is found that the periodic oscillation of the current with the magnetic field is controlled by the ratio of the frequency of the applied ac-field to the electron cyclotron frequency. Our results show that the present device operates as a radio-frequency single electron transistor.

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Simulation of Inelastic Electron Tunnelling Spectroscopy on Different Contact Structures in 4,4'-Biphenyldithiol Molecular Junctions

ZOU Bin, LI Zong-Liang, SONG Xiu-Neng, WANG Chuan-Kui

Chin. Phys. Lett. 2008, 25 (1): 254-257 .

Abstract

PDF(pc) (1180KB) ( 788 )

A first-principles computational method is developed to study the inelastic electron tunnelling spectroscopy (IETS) of 4,4'-biphenyldithiol molecular junction with three different contact structures between the molecule and electrodes in the nonresonant regime. The obtained distinct IETS can be used to resolve the geometrical structure of the molecular junction. The computational results demonstrate that the IETS has certain selection
rule for vibrational modes, where the longitudinal modes with the same direction as the tunnelling current have greatest contribution to the IETS. The thermal effect on the IETS is also displayed.

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AlGaN-Based Solar-Blind Schottky Photodetectors Fabricated on AlN/Sapphire Template

SANG Li-Wen, QIN Zhi-Xin, CEN Long-Bin, SHEN Bo, ZHANG Guo-Yi, LI Shu-Ping, CHEN Hang-Yang, LIU Da-Yi, KANG Jun-Yong, CHENG Cai-Jing, ZHAO Hong-Yan, LU Zheng-Xiong, DING Jia-Xin, ZHAO Lan, SI Jun-Jie, SUN Wei-Guo

Chin. Phys. Lett. 2008, 25 (1): 258-261 .

Abstract

PDF(pc) (424KB) ( 807 )

We report AlGaN-based back-illuminated solar-blind Schottky-type ultraviolet photodetectors with the cutoff-wavelength from 280nm to 292nm without bias. The devices show low dark current of 2.1i×10^-6A/cm² at the reverse
bias of 5V. The specific detectivity D* is estimated to be 3.3×10¹²cmHz^1/2W^-1 . To guarantee the performance of the photodetectors, the optimization of AlGaN growth and annealing condition for Schottky contacts were performed. The results show that high-temperature annealing method for Ni/Pt Schottky contacts is effective for the reduction of leakage current.

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A Novel Super-Junction Lateral Double-Diffused Metal--Oxide--Semiconductor Field Effect Transistor with n-Type Step Doping Buffer Layer

CHENG Jian-Bing, ZHANG Bo, DUAN Bao-Xing, LI Zhao-Ji

Chin. Phys. Lett. 2008, 25 (1): 262-265 .

Abstract

PDF(pc) (270KB) ( 1160 )

A novel super-junction lateral double-diffused metal--oxide--semiconductor field effect transistor (SJ-LDMOSFET) with n-type step doping buffer layer is proposed. The step doping buffer layer almost completely eliminates the
substrate-assisted depletion effect, modulates lateral electric field and achieves nearly uniform surface field. On the other hand, the buffer layer also provides another conductive path and reduces on-state resistance. In short, the proposed LDMOSFET improves trade-off performance between breakdown voltage (BV) and specific on-state resistance R_on,sp. Compared with the conventional SJ-LDMOSFET, the simulation results indicate that the BV of the
SSJ-LDMOSFET is increased from saturation voltage 121.7V to 644.9V; at the same time, the specific on-state resistance is decreased from 0.314Ω•cm² to
0.14Ω•cm² by virtue of 3D numerical simulations using ISE when the drift region length and the step number are taken as 48μm and 3, respectively.

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Hydrogen Sensors Based on AlGaN/AlN/GaN Schottky Diodes

WANG Xin-Hua, WANG Xiao-Liang, FENG Chun, XIAO Hong-Ling, YANG Cui-Bai, WANG Jun-Xi, WANG Bao-Zhu, RAN Jun-Xue, WANG Cui-Mei

Chin. Phys. Lett. 2008, 25 (1): 266-269 .

Abstract

PDF(pc) (480KB) ( 1017 )

Pt/AlGaN/AlN/GaN Schottky diodes are fabricated and characterized for hydrogen sensing. The Pt Schottky contact and the Ti/Al/Ni/Au ohmic contact are formed by evaporation. Both the forward and reverse currents of the device increase greatly when exposed to hydrogen gas. A shift of 0.3V at 300K is obtained at a fixed forward current after switching from N₂ to 10%H₂+N₂. The sensor responses under different concentrations from 50ppm H₂ to 10%H₂+N₂ at 373K are investigated. Time dependences of the device forward current at 0.5V forward bias in N₂ and air atmosphere at 300 and 373K are compared. Oxygen in air accelerates the desorption of the hydrogen and the recovery of the sensor. Finally, the decrease of the Schottky barrier height and sensitivity of the sensor are calculated.

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Mechanism of Carbon Nanotubes Aligning along Applied Electric Field

MA Shao-Jie, GUO Wan-Lin

Chin. Phys. Lett. 2008, 25 (1): 270-273 .

Abstract

PDF(pc) (240KB) ( 1013 )

The mechanism of single-walled carbon nanotubes (SWCNTs) aligning in the direction of external electric field is studied by quantum mechanics calculations. The rotational torque on the carbon nanotubes is proportional to the difference between the longitudinal and transverse polarizabilities and varies with the angle of SWCNTs to the external electric field. The longitudinal polarizability increases with second power of length, while the transverse polarizability increases linearly with length. A zigzag SWCNT has larger longitudinal and transverse polarizabilities than an armchair SWCNT with the same diameter and the discrepancy becomes larger for longer tubes.

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Plasmon-Assisted Phase-Matched Second- and Third-Harmonic Generation in Single-Negative Heterostructures

YU Xiao-Qiang, ZHOU Lin, ZHU Yong-Yuan, ZHU Shi-Ning

Chin. Phys. Lett. 2008, 25 (1): 274-277 .

Abstract

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Dispersion relations of surface plasmon polaritons (SPPs) in sandwiched optical systems are studied. The system is actually a kind of SPP waveguides, with two kinds of single negative material (SNG) as core and cladding layers,
respectively. Since both TM and TE polarized SPPs can be excited in the structure, the dispersion of SPPs becomes more abundant and leads to colorful nonlinear optical properties. The authors demonstrate the effective phase-matched second and third-harmonic generation (SHG, THG) assisted by the coupled SPPs. A cascaded second-order nonlinear process can also be achieved in the structure when the thickness of the core layer is properly selected, leading to the simultaneous SHG and THG. Further investigations show that much easier phase-matching can be fulfilled in the SNG waveguide
array. Our results would be of potential use for surface-enhanced frequency conversion device such as light emitters or lasers.

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Asymmetric Magnetization Reversal Probed by Recoil Loop Measurements inan Exchange Biased La_0.67Sr_0.33MnO₃/La_0.33Ca_0.67MnO₃ Bilayer Film

WANG Zhi-Hong, H. -U. HABERMEIER, G. CRISTIANI, SUN Ji-Rong, SHEN Bao-Gen

Chin. Phys. Lett. 2008, 25 (1): 278-281 .

Abstract

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We exploit the recoil loop measurements to study the asymmetric magnetization reversal in an exchange-biased La_0.37Sr_0.33MnO₃/La_0.33Ca_0.67MnO₃ bilayer film. It is found that the recoil curve encloses a marked area only in the second quadrant of the hysteresis loop, and the recoil susceptibility in the descending branch of the major loop is evidently higher than that in the ascending branch. The study indicates that the exchange anisotropy of a unidirectional nature and an orientation deviated from the easy axis of the ferromagnetic layer plays a crucial role in creating the reversal asymmetry.

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Magnetic and Distribution of Magnetic Moments in Amorphous Fe_89.7P_10.3 Alloy Nanowire Arrays

SHI Hui-Gang, XUE De-Sheng

Chin. Phys. Lett. 2008, 25 (1): 282-285 .

Abstract

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Binary amorphous Fe_89.7P_10.3alloy nanowire arrays in diameter of about 40nm and length of about 3μm have been fabricated in an anodic aluminium oxide template by electrodeposition. Magnetic properties of the samples are
investigated by mean of vibrating sample magnetometer, transmission
Mossbauer spectroscopy and conversion electron Mossbauer spectroscopy at room temperature. It is found that the nanowire arrays have obvious perpendicular magnetic anisotropy, and are ferromagnetic at room temperature, with its Mossbauer spectra consisting of six broad lines. The average angles between the Fe magnetic moment and the wire axis are about 14° inside and 28° at the end of the amorphous Fe_89.7P_10.3 alloy
nanowire arrays, respectively. The magnetic behaviour is decided by the shape anisotropy and the dipolar interaction between wires. In addition, the magnetic moments distribution is theoretically demonstrated by using the symmetric fanning mechanism of the spheres chain model.

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Impacts of Refraction Index Mismatch on Performance of Target Detection and Imaging by Using Flat LHM Lens

FANG Jie-Ran, GONG Yu, DONG Xiao-Ting, WANG Gang

Chin. Phys. Lett. 2008, 25 (1): 286-289 .

Abstract

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Refraction index mismatch between flat left-handed metamaterial (LHM) lens and its surrounding medium generally destroys the focusing of flat LHM lens and degrades the performance of near-field target detection by using flat LHM lens. For LHM lens of refraction index mismatch within ±30%, numerical simulations demonstrate that lenses with large refraction index may suffer less resolution degradation than lenses with small refraction index, and the enhancement of refocused microwave backscattered from target can be subsided by up to approximately 5.5dB. The refraction index mismatch will also shift the target position in the reconstructed image so that theoretical prediction of target position needs to be modified.

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Polarized Micro-Raman Study of the Temperature-Induced Phase Transition In0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃

SUN Jing-Ya, YANG Yang, ZHU Ke, LIU Yu-Long, SIU G. G., XU Z. K.

Chin. Phys. Lett. 2008, 25 (1): 290-293 .

Abstract

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Polarized Raman spectra of ferroelectric relaxor 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (0.67PMN-0.33PT) single crystal are systematically investigated in a wide temperature range from -196 to 600°C by micro-Raman scattering technique. The results clearly reveal that there are two structural phase transitions in such composite ferroelectric relaxor: the rhombohedral-tetragonal (R-T) phase transition and the tetragonal-cubic (T-C) phase transition. The former occurs at about T_R-T=34°C, corresponding to the vanishing of the soft A₁ mode at 106cm^-1 recorded in the parallel polarization. The latter appears at about T_T-C=144°C, which can be verified with the vanishing of mode at 780cm^-1measured in the crossed polarization.

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Influence of Dopant Concentration on Electroluminescent Performance of Organic White-Light-Emitting Device with Double-Emissive-Layered Structure

WU Xiao-Ming, , HUA Yu-Lin, , YIN Shou-Gen, , ZHANG Li-Juan, , WANG Yu, , HOU Qing-Chuan, , ZHANG Jun-Mei

Chin. Phys. Lett. 2008, 25 (1): 294-297 .

Abstract

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A novel phosphorescent organic white-light-emitting device (WOLED) with configuration of ITO/NPB/CBP: TBPe:rubrene/Zn(BTZ)₂:Ir(piq)₂(acac)/Zn(BTZ)₂/Mg:Ag is fabricated successfully, where the phosphorescent dye bis (1-(phenyl)isoquinoline) iridium (III) acetylanetonate (Ir(piq)₂(acac)) doped into bis-(2-(2-hydroxyphenyl) benzothiazole)zinc (Zn(BTZ)₂) (greenish-blue emitting material with electron transport character) as the red emitting layer, and fluorescent dye 2,5,8,11-tetra-tertbutylperylene (TBPe) and 5,6,11,12-tetraphenyl-naphthacene (rubrene) together doped into 4,4'-N,N'-dicarbazole-biphenyl (CBP) (ambipolar conductivity material) as the blue-orange emitting layer, respectively. The two emitting layers are sandwiched between the hole-transport layer N,N'-biphenyl-N, N'-bis (1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) and electron-transport layer (Zn(BTZ)₂). The optimum device turns on at the driving voltage of 4.5V. A maximum external quantum efficiency of 1.53% and brightness 15000cd/m² are presented.
The best point of the Commission Internationale de l'Eclairage (CIE) coordinates locates at (0.335, 0.338) at about 13V. Moreover, we also discuss how to achieve the bright pure white light through optimizing the doping concentration of each dye from the viewpoint of energy transfer process.

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Surface Polaritons in a Wire Medium with Spatial Dispersion

LIU Zheng, GONG Qi-Huang

Chin. Phys. Lett. 2008, 25 (1): 298-301 .

Abstract

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The dispersion relations of the surface polariton in a semi-infinite wire medium with spatial dispersion are analysed. In comparison with the traditional spatial dispersive medium there only exists one branch instead of multibranch for the dispersion curve. The possibility of the experimentally observing the surface polaritons by attenuated total reflection is simulated numerically.

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Homoepitaxial Growth and Optical Properties of ZnO Polar Nanoleaves

ZHANG Chun-Zhi, GAO Hong, ZHANG Di, ZHANG Xi-Tian,

Chin. Phys. Lett. 2008, 25 (1): 302-305 .

Abstract

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Using a mixture of ZnO and Te powders as the source material, ZnO nanoleaves with high yield and uniform morphology are fabricated by thermal evaporation. Each nanoleaf is constructed with a nanowire and a nanodisc on one side of the nanowire near the top. The polygonal nanodisc is in symmetric
distribution in relation to the nanowires and has polar planes ±(0001) as surfaces. A local homoepitaxial growth mechanism of ZnO polar nanodiscs induced by Te is proposed. With thin nanodiscs, the ZnO nanoleaves could be used in nanolasers, sensors, and photoelectronic nanodevices. Room-temperature photoluminescence result implies good crystalline quality of the ZnO nanoleaves.

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Long-Term Thermal Stability of Binary Cu_50.3Zr_49.7Bulk Metallic Glass

DING Ding, XIA Lei, SHAN Shao-Tai, DONG Yuan-Da

Chin. Phys. Lett. 2008, 25 (1): 306-309 .

Abstract

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We investigate the kinetics and thermal stability of a simple Cu_50.3Zr_49.7 binary bulk metallic glass (BMG). The long-term thermal stability of Cu_50.3Zr_49.7 BMG is evaluated by a newly developed method from an extension of Vogel--Fulcher--Tammann analysis. The method has been proven to be valid in Cu_50.3Zr_49.7 or even other BMGs.

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Pt/Ti Electrodes of PZT Thin Films Patterning by Novel Lift-Off Using ZnO as a Sacrificial Layer

LI Jun-Hong, WANG Cheng-Hao, XU Lian, XIE Shu

Chin. Phys. Lett. 2008, 25 (1): 310-313 .

Abstract

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We achieve a successful novel lift-off of patterning Pt/Ti electrodes on SiO₂/Si substrates by employing ZnO sacrificial layer deposition and patterning, successive uniform Pt/Ti deposition and final lift-off. Then we deposit PZT thin films on the electrodes. Compared with the conventional lift-off processes for the electrodes, this novel process does not need post-annealing, which must be performed after conventional lift-off process. It is demonstrated that the electrodes patterned by the novel lift-off process have stronger adhesion. The electrodes and the PZT films on the electrodes are more compact and smoother than those by the conventional lift-off process.

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Grand Canonical Ensemble Monte Carlo Simulation of Depletion Interactions in Colloidal Suspensions

GUO Ji-Yuan, XIAO Chang-Ming

Chin. Phys. Lett. 2008, 25 (1): 314-316 .

Abstract

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Depletion interactions in colloidal suspensions confined between two parallel plates are investigated by using acceptance ratio method with grand canonical ensemble Monte Carlo simulation. The numerical results show that both the depletion potential and depletion force are affected by the confinement from the two parallel plates. Furthermore, it is found that in the grand canonical ensemble Monte Carlo simulation, the depletion interactions are strongly affected by the generalized chemical potential.

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Kinetics of Liquid Structure Transition of Sn--(40wt%)Bi Melt

LI Xian-Fen, CHEN Hong-Sheng, ZU Fang-Qiu, CHEN Zhi-Hao, SUN Qi-Qiang, GUO Lei-Lei

Chin. Phys. Lett. 2008, 25 (1): 317-320 .

Abstract

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The kinetics of temperature-induced liquid--liquid structure transition (TI-LLST) process in Sn--(40wt%)Bi melt is investigated in isothermal and continuous
heating experiments with electrical resistivity method. The time evolution pattern of the electrical resistivity suggested the transition mechanism of TI-LLST for Sn--(40wt%)Bi melt in accordance with the autocatalytic reaction model, which is an indication of nucleation-growth type. With the calculated reaction rate constant K_T and apparent activation energy ΔE, we deduce the
reason for the characteristics of TI-LLST. The present result may be beneficial for further understanding of the nature of TI-LLST.

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Monte Carlo Simulation on Coordinated Movement of Kinesin and Dynein Motors

WANG Hong, DOU Shuo-Xing, WANG Peng-Ye

Chin. Phys. Lett. 2008, 25 (1): 321-324 .

Abstract

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Kinesin and dynein are two important classes of molecular motors which are responsible for active organelle trafficking and cell division. They can work together to carry a cargo, moving along the microtubule in a coordinated way. We use Monte Carlo method to simulate the dynamics of this coordinated
movement. Based on four essential assumptions, our simulations reproduce some features of the recent in vivo experiments. The fast moving speed of the cargo is simulated and the speed distribution is presented.

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Interleaving Gradient Magnetic Field Method for Diffusion Weighted Spectroscopy

GAO Song, ZU Zhong-Liang, BAO Shang-Lian

Chin. Phys. Lett. 2008, 25 (1): 325-328 .

Abstract

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Diffusion-weighted magnetic resonance spectroscopy (DWS) has considerable potential in clinical and research applications. However, it is seldom implemented in conventional magnetic resonance imaging (MRI) scanners due to the strict hardware requirements. We propose an interleaving gradient magnetic field (IGMF) method based on point resolved spectroscopy (PRESS). Four interlaced powerful diffusion sensitive gradient magnetic fields are positioned around the two π refocusing rf pulses in the PRESS sequence. This method utilizes the interval time in the PRESS pulse sequence, doubles the duration time of the diffusion sensitive gradient magnetic field and decreases the detrimental effect of the induced eddy current. The results of theoretical analysis and experimental observation demonstrate that the IGMF method is suitable for conventional MRI scanners

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Observing Nanometre Scale Particles with Light Scattering for Manipulation Using Optical Tweezers

ZHOU Jin-Hua, QU Lian-Jie, Yao Kun, ZHONG Min-Cheng, LI Yin-Mei

Chin. Phys. Lett. 2008, 25 (1): 329-331 .

Abstract

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Nanometre-scale particles can be manipulated using optical tweezers, but cannot be directly observed. We present a simple method that nanoparticles can be directly observed using optical tweezers combined with dark field microscopy. A laser beam perpendicular to a tightly focused laser beam for trap illuminates specimen and does not enter objective, nanoparticles in focal plane all can be directly observed in dark field because of light scattering. It is implemented that the polystyrene beads of diameter 100nm can be directly observed and trapped.

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A Strength Softening Phase Transition Observed in Shocked (Mg_0.92,Fe_0.08)SiO₃ Perovskite at About 83GPa

HE Lin, GONG Zi-Zheng, JING Fu-Qian,

Chin. Phys. Lett. 2008, 25 (1): 332-335 .

Abstract

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We report the experimental data of Hügoniot longitudinal sound velocity V_L for natural (Mg_0.92,Fe_0.08)SiO₃enstatite sample at about 40--140GPa, consisting of three new data and five previously reported data but revised by our new Hügoniot equation of state parameters. Three segments, separated by two discontinuities, appear in the V_L--pH (shock pressure) plot. Analyses show that the first discontinuity at about 64GPa, with a sharp increase of V_L of about 21%, is judged to be a phase transition from enstatite to Pbnm perovskite (PV); while the second one at about 83GPa, with a dramatic decrease of V_L of about 23%, is likely caused by a subtle structural change from Pbnm PV to tetragonal PV, accompanied by material strength softening due to melting of oxygen sublattices. This strength softening evidence is obtained first from shock wave experiments, and probably has profound implications for probing into the origin of low seismic velocity anomaly in the Earth's lower mantle and thus constraining the geophysical and geochemical models for the Earth's lower mantle.

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Second-Order Resonant Interaction of Ring Current Protons with Whistler-Mode Waves

XIAO Fu-Liang, CHEN Liang-Xu, HE Hui-Yong, ZHOU Qing-Hua

Chin. Phys. Lett. 2008, 25 (1): 336-339 .

Abstract

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We present a study on the second-order resonant interaction between the ring current protons with Whistler-mode waves propagating near the quasi electrostatic limit following the previous second-order resonant theory. The
diffusion coefficients are proportional to the electric field amplitude E, much greater than those for the regular first-order resonance, which are proportional to the electric field amplitudes square E². Numerical calculations for the pitch angle scattering are performed for typical energies of protons
E_k=50keV and 100keV at locations L=2 and L=3.5. The timescale for the loss process of protons by the Whistler waves is found to approach one hour, comparable to that by the EMIC waves, suggesting that Whistler waves may also contribute significantly to the ring current decay under appropriate
conditions.

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A Three-Dimensional Ray-Tracing Study of R-X Mode Waves during High Geomagnetic Activity

XIAO Fu-Liang, CHEN Lun-Jin, ZHENG Hui-Nan, WANG Shui, GUO Jun

Chin. Phys. Lett. 2008, 25 (1): 340-343 .

Abstract

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We further present a three-dimensional (3D) ray-tracing study on the propagation characteristic of the superluminous R-X mode waves during high geomagnetic activity following our recent two-dimensional results [J. Geophys. Res. 112(2007)A10214]. We perform numerical calculations for this mode which originates at specific altitude r=2.0R_E in the source cavity along a 70° night geomagnetic field line. We demonstrate that the ray path of the R-X mode is essentially governed by the azimuthal angle of the wave vector k. Ray paths starting with azimuthal angle 180° (or in the meridian plane) can reach the lowest latitude, but stay at relatively higher latitudes with the azimuthal angles other than 180° (or off the meridian plane). The results further supports the previous finding that the R-X mode may be physically
present in the radiation belts under appropriate conditions.

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Theoretical Constraint on Purely Kinetic k-Essence

YANG Rong-Jia, ZHANG Shuang-Nan,

Chin. Phys. Lett. 2008, 25 (1): 344-346 .

Abstract

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Purely kinetic k-essence models in which the Lagrangian contains only a kinetic factor and does not depend explicitly on the field itself are considered, and a theoretical constraint is obtained: F_x=F₀a^-3. Under this theoretical constraint, we discuss a kind of purely k-essence with form F(X)=-(1+2Xⁿ)^1/2n, which can be considered as the generalized tachyon field, and find that this kind of k-essence is not likely a candidate of dark energy to describe the present accelerated expansion of the Universe. This is contrary to a previous suggestion that k-essence with such a form may be used to describe phantom cosmologies.

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Dynamical Attractor of Modified Chaplygin Gas

HE Jing, WU Ya-Bo, FU Ming-Hui

Chin. Phys. Lett. 2008, 25 (1): 347-350 .

Abstract

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The dynamical attractor of the modified Chaplygin gas (MCG) model is studied. The dynamical analysis indicates that the phase ω_MCG=-1 is a
dynamical attractor and the equation of state of the MCG approaches it from either ω_MCG> -1 or ω_MCG<-1, independent of the choice of its initial densityparameter and the ratio of pressure to critical energy density. Therefore our universe will not end up with Big Rip in the future. Moreover, the evolutions of the density parameters Ωγ and Ω_MCG are quite different. For
different initial values of x and y, Ωγ decreases and Ω_MCG increases as time increases, and they will eventually approach Ωγ=0 and Ω_MCG=1, i.e., de Sitter phase. This implies that when there is not the interaction (i.e., the energy transfer) between the barotropic background fluid and modified Chaplygin gas (MCG), the behaviour of the MCG will be similar to λCDM in the future.

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Comment on `Five-Dimensional Cosmological Model with Variable

Arbab Ibrahim Arbab

Chin. Phys. Lett. 2008, 25 (1): 351-352 .

Abstract

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This comment corrects the small errors in the Letter of Baysal and Yilmaz [Chin. Phys. Lett. 24(2007)2185], where the case of n=1 was ignored. Meanwhile, the discussion in this comment on the case of n=-3 is novel, which
shows a potential reason why today the effect of the extra dimension has not been observed.

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