Chin. Phys. Lett.

Volume 26 Issue 8

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GENERAL

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Geometric Approach to Lie Symmetry of Discrete Time Toda Equation

JIA Xiao-Yu, WANG Na

Chin. Phys. Lett. 2009, 26 (8): 080201 . DOI: 10.1088/0256-307X/26/8/080201

Abstract

PDF(pc) (178KB) ( 789 )

By using the extended Harrison and Estabrook geometric approach, we investigate the Lie symmetry of discrete time Toda equation from the geometric point of view. Its one-dimensional continuous symmetry group is presented.

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Prisoner's Dilemma Game on Clustered Scale-Free Networks under Different Initial Distributions

LEI Chuang JIA Jian-Yuan, CHEN Xiao-Jie, CONG Rui, WANG Long,

Chin. Phys. Lett. 2009, 26 (8): 080202 . DOI: 10.1088/0256-307X/26/8/080202

Abstract

PDF(pc) (381KB) ( 534 )

The evolutionary prisoner's dilemma game is investigated under different initial distributions for cooperators and defectors on scale-free networks with a tunable clustering coefficient. It is found that, on the one hand, cooperation can be enhanced with the increasing clustering coefficient when only the most connected nodes are occupied by cooperators initially. On the other hand, if cooperators just occupy the lowest-degree nodes at the beginning, then the higher the value of the clustering coefficient, the more unfavorable the environment for cooperators to survive for the increment of temptation to defect. Thereafter, we analytically argue these nontrivial phenomena by calculating the cooperation probability of the nodes with different degrees in the steady state, and obtain the critical values of initial frequency of cooperators below which cooperators would vanish finally for the two initial distributions.

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Tripartite States Bell-Nonlocality Sudden Death under Stochastic Dephasing

ZHANG Deng-Yu, XIE Li-Jun, TANG Shi-Qing, ZHAN Xiao-Gui, GAO Feng

Chin. Phys. Lett. 2009, 26 (8): 080301 . DOI: 10.1088/0256-307X/26/8/080301

Abstract

PDF(pc) (293KB) ( 560 )

We demonstrate that the multipartite Bell-inequality violations can be fully destroyed in a finite time in three-qubit systems under decoherence induced by stochastic dephasing. It is significant that the study of tripartite systems can show fundamental characteristics which do not exist in bipartite systems.

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Polaron in Bose-Einstein-Condensation System

HUANG Bei-Bing, WAN Shao-Long

Chin. Phys. Lett. 2009, 26 (8): 080302 . DOI: 10.1088/0256-307X/26/8/080302

Abstract

PDF(pc) (293KB) ( 816 )

We consider the motion of an impurity in a Bose-Einstein condensate system at T=0K with the contact interactions for boson-boson and boson-impurity. Under the forward-scattering approximation, we obtain a Frohlich-like Hamiltonian for this system, which means that a polaron can be formed. The effective mass, the phonon number and the energy to form a polaron are obtained. We also discuss the validity of the forward-scattering approximation for this system.

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Steady State Entanglement and Saturation Effects in Correlated Spontaneous Emission Lasers

WANG Fei, HU Xiang-Ming, SHI Wen-Xing

Chin. Phys. Lett. 2009, 26 (8): 080303 . DOI: 10.1088/0256-307X/26/8/080303

Abstract

PDF(pc) (281KB) ( 580 )

It has recently been shown that correlated spontaneous emission lasers (CEL) exhibit transient entanglement in the linear regime. Here we re-examine the quantum correlations in two-photon CEL and explore the saturation effects on continuous variable entanglement. It is shown that the steady state entanglement is obtainable in the weak or moderate saturation regime, while is washed out in the deep saturation regime.

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Optimal Broadcasting of Mixed Equatorial Qubits

YU Zong-Wen

Chin. Phys. Lett. 2009, 26 (8): 080304 . DOI: 10.1088/0256-307X/26/8/080304

Abstract

PDF(pc) (174KB) ( 516 )

We derive an optimal 2→M phase-covariant quantum broadcasting of mixed equatorial qubits. This quantum broadcasting is optimal in the sense that the shrinking factor between the input and the output single qubit achieves the upper bound. The result shows that we can copy two identical mixed equatorial qubits with the same quality as those of two identical pure equatorial states.

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Spin-Orbit Splitting in Semiconductor Quantum Dots with a Two-Dimensional Ring Model

FENG Jun-Sheng, LIU Zheng

Chin. Phys. Lett. 2009, 26 (8): 080305 . DOI: 10.1088/0256-307X/26/8/080305

Abstract

PDF(pc) (291KB) ( 1091 )

We present a theoretical study of the energy levels with two-dimensional ring confining potential in the presence of the Rashba spin-orbit interaction. The features of some low-lying states in various strengths of the Rashba spin-orbit interaction are investigated. The Rashba spin-orbit splitting can also be influenced by the width of the potential barrier. The computed results show that the spin-polarized electronic states can be more easily achieved in a weakly confined dot when the confinement strength for the Rashba spin-orbit interaction is larger than a critical value.

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All Pure Two-Qudit Entangled States Generated via a Universal Yang--Baxter Matrix Assisted by Local Unitary Transformations

CHEN Jing-Ling, XUE Kang, GE Mo-Lin

Chin. Phys. Lett. 2009, 26 (8): 080306 . DOI: 10.1088/0256-307X/26/8/080306

Abstract

PDF(pc) (377KB) ( 676 )

We show that all pure entangled states of two d-dimensional quantum systems (i.e., two qudits) can be generated from an initial separable state via a universal Yang-Baxter matrix if one is assisted by local unitary transformations.

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Bifurcation of a Saddle-Node Limit Cycle with Homoclinic Orbits Satisfying the Small Lobe Condition in a Leech Neuron Model

YOOER Chi-Feng, XU Jian-Xue, ZHANG Xin-Hua

Chin. Phys. Lett. 2009, 26 (8): 080501 . DOI: 10.1088/0256-307X/26/8/080501

Abstract

PDF(pc) (281KB) ( 1264 )

Mechanism of period-adding cascades with chaos in a reduced leech neuron model is suggested as the bifurcation of a saddle-node limit cycle with homoclinic orbits satisfying the ``small lobe condition'', instead of the blue-sky catastrophe. In every spiking adding, the new spike emerges at the end of the spiking phase of the bursters.

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A Thermodynamic Analysis of the Validity of Wenzel and Cassie's Equations

TAN Shuai-Xia, LU Xiao-Ying, LI Wen, ZHAO Ning, ZHANG Xiao-Li, XU Jian

Chin. Phys. Lett. 2009, 26 (8): 080502 . DOI: 10.1088/0256-307X/26/8/080502

Abstract

PDF(pc) (403KB) ( 622 )

Wettable properties of a considered solid on its contact angle (CA) can be analyzed theoretically using the classical Wenzel and Cassie's equations. However, recent strong interest in superhydrophobic surfaces has demanded a re-examination of the applicability of the two equations. We report a thermodynamic analysis to determine the universality, in particular, the limitations of the two equations. Using some special surfaces, we demonstrate that the two equations are valid for micro-scale heterogeneous structures, however they are invalid for macro-scale heterogeneous surfaces. Furthermore, the present calculations suggest that fundamental thermodynamic analysis is the most powerful and reliable approach to determine the comprehensive wettability for various structurally patterned surfaces.

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Construction of Third-Order Diagonal Implicit Runge-Kutta Methods for Stiff Problems

Osama Yusuf Ababneh, Rokiah@Rozita Ahmad

Chin. Phys. Lett. 2009, 26 (8): 080503 . DOI: 10.1088/0256-307X/26/8/080503

Abstract

PDF(pc) (227KB) ( 530 )

We presents a new third-order diagonally implicit Runge-Kutta integration formula for stiff initial value problems, designed to be A-stable methods. The stability of the methods is analyzed and numerical results are shown to verify the conclusions.

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Darboux Transformation and Exact Solutions of the Myrzakulov-I Equation

CHEN Chi, ZHOU Zi-Xiang

Chin. Phys. Lett. 2009, 26 (8): 080504 . DOI: 10.1088/0256-307X/26/8/080504

Abstract

PDF(pc) (1049KB) ( 917 )

The Myrzakulov-I equation is a 2+1-dimensional generalization of the Heisenberg ferromagnetic equation and has a non-isospectral Lax pair. The Darboux transformation with non-constant spectral parameter is constructed and an extra constraint on the spectral parameter for the existence of the Darboux transformation is derived. Explicit expressions of the solutions of the Myrzakulov-I equation are presented.

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A New Theoretical Model of a Carbon Nanotube Strain Sensor

QIU Wei, KANG Yi-Lan, LEI Zhen-Kun, QIN Qing-Hua, LI Qiu

Chin. Phys. Lett. 2009, 26 (8): 080701 . DOI: 10.1088/0256-307X/26/8/080701

Abstract

PDF(pc) (354KB) ( 753 )

Carbon nanotubes (CNTs) are potential strain sensors due to their excellent mechanical and spectral properties. A new theoretical model of a CNT strain sensor is obtained by applying the polarized Raman properties of CNTs, which calculates the synthetic contributions of Raman spectra from the CNTs in random directions. By using this theoretical model, the analytic relationship between planar strain components and the Raman shift increment of uniformly dispersed CNTs is obtained, which is applicable for accurately characterizing the strain in random directions on the surface of a measured microsystem.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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Revisiting Chiral Extrapolation by Studying a Lattice Quark Propagator

ZHANG Yan-Bin, SUN Wei-Min, LÜ, Xiao-Fu, ZONG Hong-Shi,

Chin. Phys. Lett. 2009, 26 (8): 081101 . DOI: 10.1088/0256-307X/26/8/081101

Abstract

PDF(pc) (427KB) ( 414 )

The quark propagator in the Landau gauge is studied on the lattice, including the quenched and the unquenched results. No obvious unquenched effects are found by comparing the quenched quark propagator with the dynamical one. For the quenched and unquenched configurations, the results with different quark masses have been computed. For the quark mass function, a nonlinear chiral extrapolating behavior is found in the infrared region for both the quenched and dynamical results.

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Z' Mixing Effect in Stueckelberg Extended Effective Theory

ZHANG Ying

Chin. Phys. Lett. 2009, 26 (8): 081102 . DOI: 10.1088/0256-307X/26/8/081102

Abstract

PDF(pc) (186KB) ( 475 )

Z' gauge boson often appears in extended electroweak models. As a neutral gauge bosons, Z' mixes with electroweak bosons Z-γ in mass and kinetic parts. A general effective Lagrangian with symmetry SU(2)_LU(1)_Y U(1)' is constructed to describe Z' physics, which includes three-body mass and kinetic mixings. Z' contributions to mass eigenvalues of electroweak gauge bosons and couplings to fermions have also been discussed.

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Parameterization for Neutrino Mixing Matrix with Deviated Unitarity

LU Lei, WANG Wen-Yu, XIONG Zhao-Hua

Chin. Phys. Lett. 2009, 26 (8): 081401 . DOI: 10.1088/0256-307X/26/8/081401

Abstract

PDF(pc) (247KB) ( 1062 )

Neutrino oscillation experiments provide the first evidence on non-zero neutrino masses and indicate new physics beyond the standard model. With Majorana neutrinos introduced to acquire tiny neutrino masses, it leads to the existence of more than three neutrino species, implying that the ordinary neutrino mixing matrix is only a part of the whole extended unitary mixing matrix and thus no longer unitary. We give a parameterization for a non-unitary neutrino mixing matrix under seesaw framework and further present a method to test the unitarity of the ordinary neutrino mixing matrix.

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Solar Neutrino Oscillation Parameters after SNO Phase-III and SAGE Part-III

YANG Ping, LIU Qiu-Yu

Chin. Phys. Lett. 2009, 26 (8): 081402 . DOI: 10.1088/0256-307X/26/8/081402

Abstract

PDF(pc) (294KB) ( 543 )

We analyse the recently published results from solar neutrino experiments SNO Phase-III and SAGE Part-III and show their constraints on solar neutrino oscillation parameters, especially for the mixing angle θ₁₂. Through a global analysis using all existing data from SK, SNO, Ga&Cl radiochemical experiments and long base line reactor experiment KamLAND, we obtain the parameters Δm²₁₂=7.684^+0.212_-0.208×10^-5,eV², tan²θ₁₂=0.440^+0.059_-0.057. We also find that the discrepancy between the KamLAND and solar neutrino results can be reduced by choosing a small non-zero value for the mixing angle θ₁₃.

NUCLEAR PHYSICS

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Clarification of Confusion in Level Scheme of ¹²⁴Cs

YANG Dong, LU Jing-Bin, LIU Yun-Zuo, WANG Lie-Lin, MA Ke-Yan, YANG Chuan-Ding, HAN De-Kai, ZHAO Yan-Xin, MA Ying-Jun, ZHU Li-Hua, WUXiao-Guang, LI Guang-Sheng

Chin. Phys. Lett. 2009, 26 (8): 082101 . DOI: 10.1088/0256-307X/26/8/082101

Abstract

PDF(pc) (484KB) ( 618 )

Low-lying and high-spin states of ¹²⁴Cs are studied through the ¹¹⁶Sn¹¹B,3n)¹²⁴Cs reaction at a beam energy of 45MeV. Several new linking transitions are observed, including three transitions between the yrast and πh_11/2νd_3/2 bands and two transitions between the yrast and π h_11/2ν(d_5/2,g_7/2) bands. These transitions fix the excitation energy of the yrast band and its decay path, and confirm the existence of eight E1 linking transitions between the yrast and π h_11/2ν(d_5/2, g_7/2) bands observed before. These E1 linking transitions infer the octupole correlation in ¹²⁴Cs. The decay paths of the yrast band are investigated, and discrepancies in the level scheme of ¹²⁴Cs in the latest two studies are clarified. The reason for the discrepancies is discussed. A new decoupled band is established and temporarily assigned as the unfavored signature partner of π h_11/2νd_3/2configuration.

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Observation of Three-Quasiparticle Doublet Bands in ¹²³I: Possible Evidence of Chirality

ZHAO Yan-Xin, Komatsubara T, MA Ying-Jun, ZHANG Yu-Hu, WANG Shou-Yu, LIU Yun-Zuo, Furuno K

Chin. Phys. Lett. 2009, 26 (8): 082301 . DOI: 10.1088/0256-307X/26/8/082301

Abstract

PDF(pc) (416KB) ( 705 )

A new band in the odd proton nucleus ¹²³I is identified via in-beam γ-ray spectroscopy using the ¹⁴N+¹¹⁶Cd reaction. This band shows up as doublets with the previously assigned π g_7/2

(νh_11/2)²band. Possible configurations of the new band are discussed in the framework of the cranked shell model and the geometrical model. It is argued that the new band might be a chiral partner of the previously known π g_7/2

(νh_11/2)² band.

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Quasi-Elastic Scattering of ¹⁶C from ¹²C at 47.5 MeV/Nucleon

FAN Feng-Ying, ZHENG Tao, YE Yan-Lin, JIANG Dong-Xing, HUA Hui, LIZhi-Huan, GE Yu-Cheng, LI Xiang-Qing, LOU Jian-Ling, SHI Fan, LV Lin-Hui, CAO Zhong-Xin, NIE Peng-Xuan, LI Qi-Te, SONG Yu-Shou, LU Fei, XU Hu-Shan, HU Zheng-Guo, WANG Meng, ZHANG Xue-Ying, LI Chen, CHEN Ruo-Fu, TANG Bin, XU Zhi-Guo, YUE Ke, ZHANG Ya-Peng, ZANGYong-Dong, ZHANG Xue-Heng, YAO Xiang-Wu, CHEN Jin-Da, TU Xiao-Lin, ZHANG Jie, WU Da-Peng, BAI Zhen

Chin. Phys. Lett. 2009, 26 (8): 082501 . DOI: 10.1088/0256-307X/26/8/082501

Abstract

PDF(pc) (807KB) ( 590 )

Differential cross sections for the quasi-elastic scattering of ¹⁶C at 47.5MeV/nucleon from ¹²C target are measured. Coupled-channels calculations are carried out and the optical potential parameters are obtained by fitting the experimental angular distribution.

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Relativistic Energy Pb Projectile Fragmentation with Heavy Target Nuclei

G. Sher, M. I. Shahzad, M. A. Rana

Chin. Phys. Lett. 2009, 26 (8): 082502 . DOI: 10.1088/0256-307X/26/8/082502

Abstract

PDF(pc) (241KB) ( 632 )

We investigate the fragmentation of 158AGeV²⁰⁷Pb projectiles with Bi, Pb, Cu and Al targets using CR-39 nuclear track detectors. The exposures were made at SPS-CERN. After the etching, the detectors were scanned using an optical microscope to collect the data of etched cone diameters and lengths. We measured the partial charge-changing cross sections using the data of etched cone lengths. The predicted cross sections are compared to similar measurements reported in literature and their dependences on projectile and target mass are described.

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Isoscaling Behavior in ^48,40Ca+⁹Be Collisions at Intermediate Energy Investigated by the HIPSE Model

FU Yao, FANG De-Qing, MA Yu-Gang, CAI Xiang-Zhou, TIAN Wen-Dong, WANG Hong-Wei, GUO Wei

Chin. Phys. Lett. 2009, 26 (8): 082503 . DOI: 10.1088/0256-307X/26/8/082503

Abstract

PDF(pc) (448KB) ( 508 )

The fragment production cross sections for 140MeV/nucleon ^48,40Ca⁹Be reactions are calculated by the heavy-ion phase space exploration (HIPSE) model. Isoscaling behavior is observed. The isoscaling parameters α and β for both heavy and light fragments from the HIPSE model calculations are in good agreement with the experimental data. It is shown that the potential parameters in the HIPSE model have very little effect on the isoscaling parameters. The effect of the excitation energy and evaporation on the isoscaling behavior is also discussed.

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Probing the Dissipation Mechanism in Ternary Reactions of ¹⁹⁷Au+¹⁹⁷Au by Mean Free Path of Nucleons

TIAN Jun-Long, LI Xian, YAN Shi-Wei, , WU Xi-Zhen, LI Zhu-Xia

Chin. Phys. Lett. 2009, 26 (8): 082504 . DOI: 10.1088/0256-307X/26/8/082504

Abstract

PDF(pc) (378KB) ( 538 )

the collision of very heavy nuclei ¹⁹⁷Au+¹⁹⁷Au at 15 A MeV has been studied within the improved quantum molecular dynamics model. A class of ternary events satisfying nearly complete balance of mass numbers is selected. The experimental mass distributions for the system ¹⁹⁷Au+¹⁹⁷Au ternary fission fragments, the heaviest (A₁), the intermediate (A₂) and the lightest (A₃), are reproduced well. The mean free path of nucleons in the reaction system is studied and the shorter mean free path is responsible for the ternary fission with three mass comparable fragments, in which the two-body dissipation mechanism plays a dominant role.

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Dependence of Nucleon and Pion-Induced Fission Cross Sections on the Level Density Parameter in the Cascade-Exciton Model

Zafar Yasin

Chin. Phys. Lett. 2009, 26 (8): 082505 . DOI: 10.1088/0256-307X/26/8/082505

Abstract

PDF(pc) (338KB) ( 441 )

A new method is used to compute the fission cross sections in which a change of the ratio of the level density parameter in fission to neutron emission channels is taken into account with the change of the incident energy of the projectile. It is shown that fission cross sections induced by ucleons and pions depend on the ratio of the level density parameter in the fission and evaporation modes, i.e. a_f/a_n, respectively. We are unable to describe well the cross sections for fission without using this new method. The computed values exhibit reasonable agreement with the experimental data found in the literature across a wide range of beam energies.

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High-Power Ion Beam Characteristics of a Magnetic Multi-Pole Line-Cusp Ion Source for the HL-2A Tokomak

ZOU Gui-Qing, LEI Guang-Jiu, JIANG Shao-Feng, CAO Jian-Yong, YU Li-Ming, LU Da-Lun, YANG Li-Mei, LIU He, JIANG Tao, ZHANG Xian-Ming

Chin. Phys. Lett. 2009, 26 (8): 082901 . DOI: 10.1088/0256-307X/26/8/082901

Abstract

PDF(pc) (479KB) ( 674 )

A circular magnetic multi-pole line-cusp ion source with a nominal 45keV 25A hydrogen ion beam is developed for the neutral beam injector of the HL-2A tokomak. At present, this bucket ion source can produce a 40keV 20A hydrogen ion beam for less than 100ms on a test bed, and a 35keV 13A ion beam for 300ms on the injector of the HL-2A tokomak. The 1/e half-width of the ion beam power profile is about 6.0±0.2 cm at the position of 3.26m downstream from ion source, and the corresponding divergence degree is nearly 1.1. The optimum perveance matched conditions were obtained experimentally, and were in good agreement with the values from experiential equation of Uhlemann et al The maximum of optimum perveance reached 2.2×10^-6A/V^1.5 for 38keV beam energy. An ion beam with above 60% H⁺ species fraction can be achieved, which was measured by H_α light Doppler shift spectroscopy. According to research results, a neutral beam with a total power of more than 0.6MW was successfully injected into the plasma of the HL-2A Tokomak in 2008.

ATOMIC AND MOLECULAR PHYSICS

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Unique Magnetic Moment and Electronic Properties for Fe(MgO)_n(n=1-8) Clusters: First-Principles Calculations

GE Gui-Xian, JING Qun, YANG Zeng-Qiang, LUO You-Hua,

Chin. Phys. Lett. 2009, 26 (8): 083101 . DOI: 10.1088/0256-307X/26/8/083101

Abstract

PDF(pc) (433KB) ( 756 )

The geometries and electronic properties of Fe(MgO)_n are systematically investigated by the density functional theory. The results show that the doped Fe atom is prone to bond with the O atom, and Fe almost does not disturb the frame of (MgO)_n. The second-order energy difference, the fragmentation energies and the electron affinities show that Fe(MgO)₄ and Fe(MgO)₆ possess relatively higher stabilities. The HOMO-LUMO gaps of Fe(MgO)_n decrease obviously as compared with (MgO)_n. Almost equal unpaired electrons of the 3d state of the Fe atom in Fe(MgO)_n result in a nearly equal magnetic moment of Fe(MgO)_n.

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Excitonic Coupling between B and Q Transitions in Porphyrin Aggregates

ZHOU Mi, JIANG Yong-Heng, LU Guo-Hui, GAO Shu-Qin, LI Zuo-Wei

Chin. Phys. Lett. 2009, 26 (8): 083201 . DOI: 10.1088/0256-307X/26/8/083201

Abstract

PDF(pc) (280KB) ( 1074 )

The properties of meso-tetraphenylporphine (TPP) aggregates formed in acidic aqueous-organic solutions are investigated by UV-vis spectroscopy. According to the absorption spectra, the Q band absorption of the aggregated TPP shows red shift and intensity enhancement, and a model that includes the participation of water molecules in a porphyrin aggregation complex is proposed, then a qualitative explanation based on Gouterman's excition coupling theory is presented. Calculations including eigenenergies, eigenstates and the transition dipole strength of the coupled states are carried out.

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Structural Deformation of CO₂²⁺ in Intense Femtosecond Laser Fields

ZHANG Sheng, XIA Yuan-Qin, WANG Yu-Quan, LU Zhen-Zhong, CHEN De-Ying

Chin. Phys. Lett. 2009, 26 (8): 083202 . DOI: 10.1088/0256-307X/26/8/083202

Abstract

PDF(pc) (357KB) ( 515 )

The angular distributions of CO⁺from the dissociation of CO₂²⁺ and CO₂⁺ in intense femtosecond laser fields (45fs, about 5×10¹⁵W/cm²) are studied at a laser wavelength of 800nm based on the time-of-flight mass spectra of CO⁺ fragment ions. The experimental results show that structural deformation occurs in the charge state of CO₂²⁺ and the CO₂⁺ maintains linear geometrical structure.

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Coupled-Channels Optical Calculation for Electron Scattering from Metastable Helium

WANG Yuan-Cheng, ZHOU Ya-Jun, CHENG Yong-Jun, MA Jia

Chin. Phys. Lett. 2009, 26 (8): 083401 . DOI: 10.1088/0256-307X/26/8/083401

Abstract

PDF(pc) (309KB) ( 720 )

Coupled-channels optical calculations for total and resonance excitation integral cross sections for electron scattering on the metastable level 2^1,3S of helium are presented. The results are in agreement with other theoretical and experimental data.

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Bose-Einstein Condensates in a One-Dimensional Optical Lattice: from Superfluidity to Number-Squeezed States

WANG Xiao-Rui, YANG Lu, TAN Xin-Zhou, XIONG Hong-Wei, LÜ, Bao-Long

Chin. Phys. Lett. 2009, 26 (8): 083701 . DOI: 10.1088/0256-307X/26/8/083701

Abstract

PDF(pc) (1002KB) ( 895 )

We study the phase coherence property of Bose-Einstein condensates confined in a one-dimensional optical lattice formed by a standing-wave laser field. The lattice depth is determined using a method of Kapitza-Dirac scattering between a condensate and a short pulse lattice potential. Condensates are then adiabatically loaded into the optical lattice. The phase coherence property of the confined condensates is reflected by the interference patterns of the expanded atomic cloud released from the optical lattice. For weak lattice, nearly all of the atoms stay in a superfluid state. However, as the lattice depth is increased, the phase coherence of the whole condensate sample is gradually lost, which confirms that the sub-condensates in each lattice well have evolved into number-squeezed states.

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Realization of Green MOT for Ytterbium Atoms

ZHAO Peng-Yi, XIONG Zhuan-Xian, LONG Yun, HE Ling-Xiang, LÜ, Bao-Long

Chin. Phys. Lett. 2009, 26 (8): 083702 . DOI: 10.1088/0256-307X/26/8/083702

Abstract

PDF(pc) (571KB) ( 1387 )

We report the experimental realization of a magneto-optical trap (MOT) of ¹⁷⁴Yb atoms operating on the ¹S₀-³P₁ intercombination transition at 555.8nm. The green MOT is loaded by a Zeeman-slowed atomic beam. In order to increase the capture velocity of the MOT, we use the trapping laser beams consisting of five discrete frequency components obtained by modulating the laser light through an electro-optic modulator. The trapped atomic number of the ¹⁷⁴Yb isotope is about 6.2× 10⁵, and the temperature of the cold atomic cloud is estimated to be about 100μK. The success of the green MOT is an important step towards the goal of an ytterbium optical clock.

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Lifetime Measurement of Cold Atoms in an Integrating Sphere

ZHANG Wen-Zhuo, WANG Xu-Cheng, CHENG Hua-Dong, XIAO Ling, LIU Liang, WANG Yu-Zhu

Chin. Phys. Lett. 2009, 26 (8): 083703 . DOI: 10.1088/0256-307X/26/8/083703

Abstract

PDF(pc) (288KB) ( 907 )

We present an experimental measurement of the lifetime of the cold ⁸⁷Rb atoms in an integrating sphere. The atoms are cooled by the diffuse light which is generated by the diffuse reflection of laser beams in the integrating sphere. Our result shows that the lifetime is primarily determined by the free fall of the cold ⁸⁷Rb atoms, and its half-life can reach 40ms, which is suitable for many experiments, especially for a cold atom clock.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

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Time-Domain Techniques for Transient Scattering from Dielectric Bodies and Sea Surface Governed by Jonswap's Sea Spectra

ZHANG Min, ZHU Lei, ZHOU Ping, ZHANG Xiang-Yang

Chin. Phys. Lett. 2009, 26 (8): 084101 . DOI: 10.1088/0256-307X/26/8/084101

Abstract

PDF(pc) (421KB) ( 504 )

A time-domain surface integral equation (TDCFIE) approach is utilized to calculate the transient scattering from arbitrarily shaped, three-dimensional dielectric bodies. In conjunction with the marching-on-in-time (MOT) method, the TDCFIE-MOT method is used to derive explicit expressions for the present-time current as a function of the incident field. Sample results showing various geometries are presented and are compared with other numerical techniques. Finally, by an incident Gaussian plane tapered wave, transient scattering from the sea surface governed by Jonswap's sea spectra is computed.

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Numerical Simulation of Electromagnetic Waves Scattering by Discrete Exterior Calculus

YE Zheng, XIE Zheng, MA Yu-Jie

Chin. Phys. Lett. 2009, 26 (8): 084102 . DOI: 10.1088/0256-307X/26/8/084102

Abstract

PDF(pc) (1454KB) ( 1553 )

We show how to construct discrete Maxwell equations by discrete exterior calculus. The new scheme has many virtues compared to the traditional Yee's scheme: it is a multisymplectic scheme and keeps geometric properties. Moreover, it can be applied on triangular mesh and thus is more adaptive to handle domains with irregular shapes. We have implemented this scheme on a Java platform successfully and our experimental results show that this scheme works well.

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A Method of Analyzing Transmission Losses in Left-Handed Metamaterials

WANG Jia-Fu, QU Shao-Bo, XU Zhuo, ZHANG Jie-Qiu, MA Hua, YANGYi-Ming, GU Chao

Chin. Phys. Lett. 2009, 26 (8): 084103 . DOI: 10.1088/0256-307X/26/8/084103

Abstract

PDF(pc) (381KB) ( 899 )

A method of analyzing transmission loss in left-handed metamaterials (LHMs) is proposed. As a demonstration of this method, transmission loss of LHMs composed of split-ring resonators (SRR) and conducting wires is studied. By means of retrieving and analyzing the effective constitutive parameters, different transmission losses as well as their origins are studied. The results show that the left-handed bandwidth is narrowed because of high loss caused by the non-zero high imaginary parts of the effective permeability and permittivity. In the effective left-handed band, the radiation loss is very low and can be neglected, and the transmission losses are the sum of the substrate loss and the ohmic loss. Moreover, when the dielectric loss tangent of the substrate is greater than 0.003, the substrate loss is higher than the ohmic loss.

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Anti-Stokes Frequency Shift and Evolution in Polarization-Maintaining Photonic Crystal Fiber with Two-Zero Dispersion Wavelengths

WANG He-Lin, LENG Yu-Xin, XU Zhi-Zhan, QI Yi-Hong, HU Ming-Lie, WANGChing-Yue

Chin. Phys. Lett. 2009, 26 (8): 084201 . DOI: 10.1088/0256-307X/26/8/084201

Abstract

PDF(pc) (754KB) ( 560 )

Using the tunable pump pulses with about 100fs pulse duration and 1064nm central wavelength; the polarization-, wavelength- and power-dependent anti-Stokes lines are generated and modulated simultaneously in a polarization-maintaining photonic crystal fiber (PM-PCF) with two zero-dispersion wavelengths. By accurately controlling the polarization directions, the wavelength and the power of the pump pulse in the fiber anomalous region close to the second zero-dispersion wavelength of the PM-PCF, the output anti-Stokes pulse spectra can be tuned between 563nm and 603nm, which is in good agreement with the theoretical simulation. The color conversion of the mode image from yellow to orange is also observed with the different polarization pump pulses. These results can be attributed to the combined interaction between the fiber birefringence (including linear- and nonlinear-birefringence) and dispersion, and are attributed to phase-matching parametric four-wave mixing.

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Elimination of Gray-Tracking Effects of KTiOPO₄Crystals Using a Strong Focusing Scheme

XIANG Zhen, GE Jian-Hong, ZHAO Zhi-Gang, WANG Sha, HU Miao, LIU Chong, CHEN Jun

Chin. Phys. Lett. 2009, 26 (8): 084202 . DOI: 10.1088/0256-307X/26/8/084202

Abstract

PDF(pc) (381KB) ( 718 )

A simple method is presented to eliminate gray-tracking effects of KTP crystals using a strong focusing scheme. Experimental and theoretical studies on the gray-tracking effects are carried out. A 18W green laser is demonstrated with a 9kHz repetition rate, a beam quality factor of M²=1.6 and a conversion efficiency of 44%.

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Tunable All-Optical Filtering and Buffering in a Coupled Quantum Dot-Planar Photonic Crystal Structure

QIAN Yong, QIAN Jun, WANG Yu-Zhu

Chin. Phys. Lett. 2009, 26 (8): 084203 . DOI: 10.1088/0256-307X/26/8/084203

Abstract

PDF(pc) (268KB) ( 431 )

We theoretically investigate controlled tunable all-optical filtering and buffering of optical pulses in a hybrid nano-photonic structure, where a single quantum dot (QD) embedded in a photonic crystal nanocavity is side-coupled between a bare nanocavity and a photonic crystal waveguide. We demonstrate that there is a sharp low-loss transmission peak in the transmission spectrum under even low QD-nanocavity coupling strength and the input optical pulses can be delayed up to several hundred picoseconds within the dephasing time of the QD. The filtering regime can be shifted readily by manipulating the detuning between the QD excitonic transition frequency and resonant frequency of the nanocavity mode, which can be explored in future for on-chip all-optical logic and signal processing.

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Reversible Conformational Changes of PsbO Protein Detected by Terahertz Time-Domain Spectroscopy

CHEN Hua, CHEN Gui-Ying, LI Shu-Qin, WANG Li

Chin. Phys. Lett. 2009, 26 (8): 084204 . DOI: 10.1088/0256-307X/26/8/084204

Abstract

PDF(pc) (275KB) ( 606 )

We used a terahertz time-domain spectroscope (THz-TDS) to detect the reversible conformational changes of PsbO protein induced by N-bromosuccinimide and Guanidine Hydrochloride. The veracity and sensitivity are confirmed by the fluorescence emission spectra. The results demonstrate that THz-TDS has both advantages and disadvantages in monitoring the denaturation process of proteins, which is important in applying THz-TDS technique to studying biomolecules.

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Beam Quality and Power Scalability of Various Multicore Fiber Lasers

ZHOU Pu, WANG Xiao-Lin, MA Yan-Xing, MA Hao-Tong, XU Xiao-Jun, LIU Ze-Jin

Chin. Phys. Lett. 2009, 26 (8): 084205 . DOI: 10.1088/0256-307X/26/8/084205

Abstract

PDF(pc) (3796KB) ( 617 )

Beam quality and power scalability analyses for various multicore fiber lasers (MFL) are presented. In-phase complex amplitude and corresponding far-field intensity distribution of each type of MFL is calculated using the finite-difference time-domain method. It is revealed that the hexagonal ring-type MFL has the best performance in power handling and maintaining beam quality. Further calculation indicates that power encircled in the diffraction-bucket of L-core MFL scales with no more than 0.4L, which challenges the practical worthiness of fielding MFL with a large number of cores.

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The Self-Heating Effect of Quantum Cascade Lasers Based on a pectroscopic Method

WEI Lin, LI Ai-Zhen, ZHANG Yong-Gang, LI Yao-Yao

Chin. Phys. Lett. 2009, 26 (8): 084206 . DOI: 10.1088/0256-307X/26/8/084206

Abstract

PDF(pc) (326KB) ( 695 )

We investigate the self-heating effect of mid-infrared quantum cascade lasers by using a direct-based pulse injecting current and spectroscopy method. Based on the characterization system, the thermal characteristics of gas source MBE grown 8.4μm InP-based GaInAs/AlInAs DFB-QCLs are evaluated. The method and characterization system are also useful in evaluating the thermal characteristics of other types of mid-infrared diode lasers.

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Experimental Demonstration of Deterministic Entanglement Transformation

CHEN Geng, XU Jin-Shi, LI Chuan-Feng, GONG Ming, CHEN Lei, GUO Guang-Can

Chin. Phys. Lett. 2009, 26 (8): 084207 . DOI: 10.1088/0256-307X/26/8/084207

Abstract

PDF(pc) (336KB) ( 779 )

According to Nielsen's theorem [Phys.Rev.Lett. 83(1999)436] and as a proof of principle, we demonstrate the deterministic transformation from a maximum entangled state to an arbitrary nonmaximum entangled pure state with local operation and classical communication in an optical system. The output states are verified with a quantum tomography process. We further test the violation of Bell-like inequality to demonstrate the quantum nonlocality of the state we generated. Our results may be useful in quantum information processing.

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Theoretical Analysis of Interference Nanolithography of Surface Plasmon Polaritons without a Match Layer

WANG Jing-Quan, LIANG Hui-Min, SHI Sha, DU Jing-Lei

Chin. Phys. Lett. 2009, 26 (8): 084208 . DOI: 10.1088/0256-307X/26/8/084208

Abstract

PDF(pc) (516KB) ( 756 )

Interference nanolithography techniques based on long-range surface plasmon polaritons (LR-SPP) are hardly ever achieved by experiments at present. One key reason is that suitable liquid materials are difficult to find as the match layer connects the metal film and the resist. We redesign a Kretschmann-Raether structure for interference lithography. A polymer layer is coated under the metal film, and an air layer is placed between the polymer layer and the resist layer. This design not only avoids the above-mentioned question of the match layer, but also can form a soft contact between the polymer layer and the resist layer and can protect the exposure pattern. Simulation results confirm that a device with an appropriately thick polymer layer can form high intensity and contrast interference fringes with a critical dimension of about λ/7 in the resist. In addition, the fabrication of the device is very easy.

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Application of Equivalent Air Gap Method in Uniaxial Crystal Plate

REN Wen-Yi, ZHANG Chun-Min, MU Ting-Kui

Chin. Phys. Lett. 2009, 26 (8): 084209 . DOI: 10.1088/0256-307X/26/8/084209

Abstract

PDF(pc) (299KB) ( 589 )

The equivalent air gap method is a simple way to trace the ray propagation in an isotropic medium, but it cannot be applied to an anisotropic medium. We present the exact general expressions of the equivalent air gap thicknesses and the displacements for the plane-parallel uniaxial crystal plates. They are also suitable for the isotropic medium. This method is useful when one determines whether certain size plane-parallel plates can be fitted into the available air of an optical system, and also in the prism system design.

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High Polarization Single Mode Photonic Crystal Microlaser

CHEN Wei, XING Ming-Xin, ZHOU Wen-Jun, LIU An-Jin, ZHENG Wan-Hua

Chin. Phys. Lett. 2009, 26 (8): 084210 . DOI: 10.1088/0256-307X/26/8/084210

Abstract

PDF(pc) (814KB) ( 532 )

Generally, dipole mode is a doubly degenerate mode. Theoretical calculations have indicated that the single dipole mode of two-dimensional photonic crystal single point defect cavity shows high polarization property. We present a structure with elongated lattice, which only supports a single y-dipole mode. With this structure we can eliminate the degeneracy, control the lasing action of the cavity and demonstrate the high polarization property of the single dipole mode. In our experiment, the polarization extinction ratio of the y-dipole mode is as high as 51:1.

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Ld-Clad-Pumped All-Fiber Tm³⁺-Doped Silica Fiber Laser

ZHANG Yun-Jun, SONG Shi-Fei, TIAN Yi, WANG Yue-Zhu

Chin. Phys. Lett. 2009, 26 (8): 084211 . DOI: 10.1088/0256-307X/26/8/084211

Abstract

PDF(pc) (353KB) ( 823 )

The CW 39.4W all-fiber LD-clad-pumped Tm³⁺-doped fiber laser output is reported with a slope efficiency of 34% in respect to the pump power. The all-fiber laser is made up by progressively splicing the pigtail fiber, matched FBG fiber and Tm-doped fiber. The reflective FBG and Tm-doped fiber end fresnel reflection build up the laser resonance cavity. Due to the multi-mode FBG as the reflective mirror, the output laser spectrum is multi-peaks at high power output, whereas the total spectrum width is less than 2nm at nearly 1.94μm.

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Effects of Thickness Deviation of Elastic Plates in Multi-Layered Resonance Systems on Frequency Spectra

ZHANG Hui, ZHANG Shu-Yi, FAN Li

Chin. Phys. Lett. 2009, 26 (8): 084301 . DOI: 10.1088/0256-307X/26/8/084301

Abstract

PDF(pc) (447KB) ( 857 )

A model of high-overtone bulk acoustic resonators is used to study the effects of thickness deviation of elastic plates on resonance frequency spectra in planar multi-layered systems. The resonance frequency shifts induced by the thickness deviations of the elastic plates periodically vary with the resonance order, which depends on the acoustic impedance ratios of the elastic plates to piezoelectric patches. Additionally, the center lines of the frequency shift oscillations linearly change with the orders of the resonance modes, and their slopes are sensitive to the thickness deviations of the plates, which can be used to quantitatively evaluate the thickness deviations.

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Modeling of Nonlinear Propagation in Multi-layer Biological Tissues for Strong Focused Ultrasound

FAN Ting-Bo, LIU Zhen-Bo, ZHANG Zhe, ZHANG Dong, GONG Xiu-Fen

Chin. Phys. Lett. 2009, 26 (8): 084302 . DOI: 10.1088/0256-307X/26/8/084302

Abstract

PDF(pc) (459KB) ( 1493 )

A theoretical model of the nonlinear propagation in multi-layered tissues for strong focused ultrasound is proposed. In this model, the spheroidal beam equation (SBE) is utilized to describe the nonlinear sound propagation in each layer tissue, and generalized oblique incidence theory is used to deal with the sound transmission between two layer tissues. Computer simulation is performed on a fat-muscle-liver tissue model under the irradiation of a 1MHz focused transducer with a large aperture angle of 35°. The results demonstrate that the tissue layer would change the amplitude of sound pressure at the focal region and cause the increase of side petals.

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Characterization of Wave Dispersion in Viscoelastic Cellular Assemblies by Doublet Mechanics

JIN Yan-Fang, XIONG Chun-Yang, FANG Jing, FERRARI Mauro

Chin. Phys. Lett. 2009, 26 (8): 084601 . DOI: 10.1088/0256-307X/26/8/084601

Abstract

PDF(pc) (325KB) ( 524 )

Using the Voigt model, we analyze wave propagation in viscoelastic granular media with a monatomic lattice, planar simple cubic package and cubical-tetrahedral assembly within the context of doublet mechanics. Microstrains of elongation between the doublet particles are considered in the models. Wave dispersive relations are derived from dynamic equations of the particles involved in the media, and phase velocities and attenuations of the dispersive waves are obtained for the different assemblies. Variations in these dispersion characteristics are analyzed with the changes of cell interval, modulus, and wave frequency. The relations between micro-constants and macro-parameters are presented under the condition of non-scale continuity of the media.

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Vortex Structures and Behavior of a Flow Past Two Rotating Circular Cylinders Arranged Side-by-Side

GUO Xiao-Hui, LIN Jian-Zhong, NIE De-Ming

Chin. Phys. Lett. 2009, 26 (8): 084701 . DOI: 10.1088/0256-307X/26/8/084701

Abstract

PDF(pc) (896KB) ( 807 )

We present a study on the vortex structures and behavior of a flow past two rotating circular cylinders arranged side-by-side at a range of absolute rotational speeds (|α|≤2) for two different gap spacings g*=1.5 and 0.7 at Reynolds numbers Re=160 and 200. The results show that the flow becomes stabilized and finally steady beyond the critical rotational speed as |α| increases, regardless of the variation in Re and g*. The value of critical rotational speed increases with increasing Re. The wake patterns change in the unsteady regimes for g*=1.5 and 0.7. With increasing |α|, the time-averaged drag coefficient ^-C_D decreases and the lift coefficient ^-C_L increases, respectively. C_D at Re=160 and g*=0.7 decreases rapidly, resulting in the smallest value at the same |α| for 1≤|α|≤2. ^-C_Daugments with increasing g* at the same |α|. For g*=1.5, ^-C_D has a little disparity between the cases of Re=160 and 200. For the flow past two still cylinders, ^-C_L is inversely proportional to g* of two cylinders for a fixed |α|, and is not dependent on Re.

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Derivation of the Convective Dispersion Equation with Adsorption by Markov Random Ways

WU Jing-Chun, QIN Sheng-Gao, WANG Yang

Chin. Phys. Lett. 2009, 26 (8): 084702 . DOI: 10.1088/0256-307X/26/8/084702

Abstract

PDF(pc) (215KB) ( 771 )

The convective dispersion equation with adsorption is derived on the basis of the Chapman-Kolmogroff equation which expresses the statistical properties of the Markov transition probability. The acquired equation has the same expression as the one derived on the basis of the combination of both the mass balance equation and the particles retention kinetics equation. The probability variables that describe the random movement of solute particles have a definite physical significance associated with the parameters in the convective dispersion equation. The derivation confirms the validity of the Markov process to describe the particles movement in the process of convective dispersion.

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Direct Numerical Simulation of the Rayleigh-Taylor Instability with the Spectral Element Method

ZHANG Xu, TAN Duo-Wang

Chin. Phys. Lett. 2009, 26 (8): 084703 . DOI: 10.1088/0256-307X/26/8/084703

Abstract

PDF(pc) (853KB) ( 637 )

A novel method is proposed to simulate Rayleigh-Taylor instabilities using a specially-developed unsteady three-dimensional high-order spectral element method code. The numerical model used consists of Navier-Stokes equations and a transport-diffusive equation. The code is first validated with the results of linear stability perturbation theory. Then several characteristics of the Rayleigh-Taylor instabilities are studied using this three-dimensional unsteady code, including instantaneous turbulent structures and statistical turbulent mixing heights under different initial wave numbers. These results indicate that turbulent structures of Rayleigh-Taylor instabilities are strongly dependent on the initial conditions. The results also suggest that a high-order numerical method should provide the capability of simulating small scale fluctuations of Rayleigh-Taylor instabilities of turbulent flows.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Temperature Measurements of Condensed Gaseous Hydrogen-Helium Mixtures under Multi-Shock Compression

GU Yun-Jun, CHEN Qi-Feng, CAI Ling-Cang, CHEN Zhi-Yun, ZHENG Jun

Chin. Phys. Lett. 2009, 26 (8): 085101 . DOI: 10.1088/0256-307X/26/8/085101

Abstract

PDF(pc) (341KB) ( 924 )

Temperatures of multi-shock compressed gaseous hydrogen--helium mixtures with a mole component H₂:He=1:1.21 up to 7100K are measured at pressures up to 10GPa by means of an instantaneous optical pyrometer. The gas mixtures are shocked from environmental temperature at the initial pressure 20MPa. The measured second-shock temperature differs from the predictions of the non-dissociation model by up to 40% and is in good agreement with that of the dissociation model, indicating that a considerable amount of molecular dissociation occurs.

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One-Dimensional Fluid Model for Dust Particles in Dual-Frequency Capacitively Coupled Silane Discharges

LIU Xiang-Mei, SONG Yuan-Hong, WANG You-Nian

Chin. Phys. Lett. 2009, 26 (8): 085201 . DOI: 10.1088/0256-307X/26/8/085201

Abstract

PDF(pc) (1138KB) ( 532 )

A self-consistent fluid model, which incorporates density and flux balances of electrons, ions, neutrals and nanoparticles, electron energy balance, and Poisson's equation, is employed to investigate the capacitively coupled silane discharge modulated by dual-frequency electric sources. In this discharge process, nanoparticles are formed by a successive chemical reactions of anion with silane. The density distributions of the precursors in the dust particle formation are put forward, and the charging, transport and growth of nanoparticles are simulated. In this work, we focus our main attention on the influences of the high-frequency and low-frequency voltage on nanoparticle densities, nanoparticle charge distributions in both the bulk plasma and sheath region.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

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Comparative Study of Activity of Different Agings of Aluminum Nanopowders

YAN Zheng-Xin, DENG Jun, WANF Ya-Min, LIU Wei

Chin. Phys. Lett. 2009, 26 (8): 086101 . DOI: 10.1088/0256-307X/26/8/086101

Abstract

PDF(pc) (533KB) ( 641 )

The structure and activity of aluminum nanopowders with a 3nm oxide layer on their surface (3-nm-OLA) and 30nm oxide layers on their surface (30-nm-OLA) are investigated comparably under the same normal incident shock wave intensity. Their corresponding reaction products are characterized by x-ray diffraction, high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. The spectrum of x-ray diffraction shows that there are different phases of alumina in their products, which evidences directly the different reacting temperature in the shock tube. The x-ray photoelectron spectroscopy reveals that the oxide layer thickness is 30nm on the product surface of 30-nm-OLA, while it is only 3nm on 3-nm-OLA. Images of transmission electron microscopy present additional evidence that the agglomeration mechanism is over sintering one in the containing-30-nm-OLA system, the reversed mechanism is observed in the containing-3-nm-OLA
reaction system.

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High-Pressure Annealing Effect on Glass Transformation Temperature of Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 Bulk Metallic Glass

LI Gong, DONG Yan-Guo, HUANG Lei, HE Guo-Wei, LIU Ri-Ping, WANGWen-Kui

Chin. Phys. Lett. 2009, 26 (8): 086102 . DOI: 10.1088/0256-307X/26/8/086102

Abstract

PDF(pc) (397KB) ( 634 )

Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glasses (BMG) are annealed at a temperature of 603K under ambient and high pressures in the range of 3-6GPa. The effect of high pressure annealing on the nanocrystallization process of compressed specimens is investigated by x-ray diffraction, differential scanning calorimetry and transmission electron microscopy. Experimental results show that the grain size of the crystalline phase decreases with the increasing pressure. For the Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 BMG annealing at 603K in the pressure range of 0-6GPa, the activation energy 159.68kJ/mol and the activation volume ΔV*=0.94cm³/mol are determined. The mechanism for the effects of the high pressure on the nanocrystallization process of the BMG is discussed.

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Theoretical Investigations on the Off-Center Displacement of Co²⁺ in SrO by Analyzing Its Anisotropic g Factors

LU Guang-Duo, ZHANG Huai-Wu, TANG Xiao-Li, ZHONG Zhi-Yong, PENG Long

Chin. Phys. Lett. 2009, 26 (8): 086103 . DOI: 10.1088/0256-307X/26/8/086103

Abstract

PDF(pc) (274KB) ( 461 )

The off-center displacement of Co²⁺ ion in SrO crystal is investigated by analyzing its anisotropic g factors g_x, g_y and g_z through diagonalization of the 6×6 energy matrix within ⁴T₁ground state for a 3d⁷ ion under rhombic symmetry. In the matrix, the contributions from the admixtures of various J(=1/2, 3/2, 5/2) states and the fourth-order term D_η of rhombic crystal-fields and the ligand orbitals and spin-orbit coupling interactions, which are usually ignored in the previous studies, are considered. Both g factors (g_x=4.172, g_y=5.004 and g_z=2.133) and the off-displacement value (ΔR≈0.023nm) show good agreement with the experimental data.

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Self-Assembling of Colloidal Particles Dispersed in Mixture of Ethanol and Water at the Air-Liquid Interface of Colloidal Suspension at Room Temperature

WANG Ai-Jun, CHEN Sheng-Li, DONG Peng, ZHOU Qian, YUAN Gui-Mei, SU Gu-Cong

Chin. Phys. Lett. 2009, 26 (8): 086104 . DOI: 10.1088/0256-307X/26/8/086104

Abstract

PDF(pc) (2887KB) ( 812 )

Self-assembling of colloidal particles dispersed in a mixture of ethanol and water at the air-liquid interface of the colloidal suspension at room temperature is investigated, and a method of rapidly assembling colloidal particles is proposed. By this method, a uniform colloidal crystal thin film over ten square centimeters in area can be fabricated in 10min without special facilities and heating the suspension. SEM images and a normal incidence transmission spectrum of the sample show that the colloidal crystal film fabricated by this method is of high quality. In addition, this method is very suitable for fabricating colloidal crystal heterostructures.

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The MAEAM Model and Anharmonic Theory for the Bulk Modulus of Al Metal

LIAO Shu-Zhi, WANG Xiao-Li, ZHU Xiang-Ping, ZHANG Chun, OUYANG Yi-Fang, ZHANG Bang-Wei,

Chin. Phys. Lett. 2009, 26 (8): 086105 . DOI: 10.1088/0256-307X/26/8/086105

Abstract

PDF(pc) (321KB) ( 610 )

The modified analytic embedded atom method (MAEAM) model and the anharmonic theory are used to study the bulk modulus of fcc Al metal. The result shows that the bulk modulus can be described by a quadratic function of temperature. The result is in good agreement with the experimental data and theoretical results calculated by the first principle calculation etc. This outcome indicates that the temperature dependence of the bulk modulus for fcc Al metal can be academically studied with the MAEAM model combining with the anharmonic theory.

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Effect of Carbonized Conditions on Residual Strain and Crystallinity Quality of Heteroepitaxial Growth 3C-SiC Films

CHEN Da, ZHANG Yu-Ming, ZHANG Yi-Men, WANG Yue-Hu, TANG Xiao-Yan

Chin. Phys. Lett. 2009, 26 (8): 086106 . DOI: 10.1088/0256-307X/26/8/086106

Abstract

PDF(pc) (618KB) ( 931 )

Heteroepitaxial growth of SiC on n-Si(111) substrates is performed by a low pressure chemical vapor deposition process. The effects of different carbonized temperature and carbonized time on the crystalline quality and the residual strain of 3C-SiC films are discussed. The results show that the residual strain is obviously reduced and the crystalline quality is greatly improved at the best carbonized temperature of 1000°C and the carbonized time of 5min. Under these optimized carbonization conditions, thick epitaxial films of about 15μm with good crystalline quality and low residual strain can be obtained.

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Precipitate Contribution to the Acoustic Nonlinearity in Nickel-Based Superalloy

Chung-Seok KIM, Cliff J. LISSENDEN

Chin. Phys. Lett. 2009, 26 (8): 086107 . DOI: 10.1088/0256-307X/26/8/086107

Abstract

PDF(pc) (877KB) ( 849 )

The influence of γ' precipitate on the acoustic nonlinearity is investigated for a nickel-based superalloy, which is subjected to creep deformation. During creep deformation, the cuboidal γ' precipitate is preferentially coarsened in a direction perpendicular to the applied stress axis. The length and shape factor of the γ' precipitate increase with creep time. The increase of relative acoustic nonlinearity with increasing fraction of creep life is discussed in relation to the rafting of γ' precipitate, which is closely related to the scattering and distortion of the acoustic wave.

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Transient Reorientation of a Doped Liquid Crystal System under a Short Laser Pulse

LI Tao, XIANG Ying, LIU Yi-Kun, WANG Jian, YANG Shun-Lin

Chin. Phys. Lett. 2009, 26 (8): 086108 . DOI: 10.1088/0256-307X/26/8/086108

Abstract

PDF(pc) (393KB) ( 646 )

The transient optical nonlinearity of a nematic liquid crystal doped with azo-dye DR19 is examined. The optical reorientation threshold of a 25-μm-thick planar-aligned sample of 5CB using a 50ns pulse duration 532nm YAG laser pulse is observed to decrease from 800mJ/mm² to 0.6mJ/mm²after the addition of 1 vol% azo dopant, a reduction of three orders of magnitude. When using a laser pulse duration of 10ns, no such effect is observed. Experimental results indicate that the azo dopant molecules undergo photoisomerization from trans-isomer to cis-isomer under exposure to light, and this conformation change reorients the 5CB molecules via intermolecular coupling between guest and host. This guest-host coupling also affects the azo photoisomerization process.

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Zr-Cu Amorphous Films Prepared by Magnetron Co-sputtering Deposition of Pure Zr and Cu

JING Qin, XU Yong, ZHANG Xin-Yu, LI Gong, LI Li-Xin, XU Zhe, MA Ming-Zhen, LIU Ri-Ping

Chin. Phys. Lett. 2009, 26 (8): 086109 . DOI: 10.1088/0256-307X/26/8/086109

Abstract

PDF(pc) (421KB) ( 750 )

Zr_xCu_100-x amorphous films are prepared on Si (111) substrates by magnetron co-sputtering of pure Zr and Cu. It is found that the glass forming ability (GFA) of the films increases with x when x is in the range from 35 to 65 and with the best glass forming ability at x=65. It is therefore different from the bulk counterparts, for which only x=35 and 50 were reported to have high glass forming ability during casting. The structure of the films is sensitive to the substrate temperature and the sputtering argon pressure.

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Re-entrant-Groove-Assisted VLS Growth of Boron Carbide Five-Fold Twinned Nanowires

FU Xin, JIANG Jun, LIU Chao, YU Zhi-Yang, Steffan LEA, YUAN Jun,

Chin. Phys. Lett. 2009, 26 (8): 086110 . DOI: 10.1088/0256-307X/26/8/086110

Abstract

PDF(pc) (3034KB) ( 1025 )

We report a preferential growth of boron carbide nanowires with a five-fold twinned internal structure. The nanowires are found to grow catalytically via iron boron nanoparticles, but unusually the catalytic particle is in contact with the low-energy surfaces of boron carbide with V-shaped contact lines. We propose that this catalytical growth may be caused by preferential nucleation at the re-entrant grooves due to the twinning planes, followed by rapid spreading of atomic steps. This is consistent with the observed temperature dependence of the five-fold twinned nanowire growth.

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Tetragonal Distortion of InN Thin Films by RBS/Channeling

DING Zhi-Bo, WU Wei, WANG Kun, FA Tao, YAO Shu-De

Chin. Phys. Lett. 2009, 26 (8): 086111 . DOI: 10.1088/0256-307X/26/8/086111

Abstract

PDF(pc) (364KB) ( 1151 )

Rutherford backscattering and channeling spectrometry (RBS/C) are used to identify the crystalline quality (χ_min=4.87%) of an InN thin film as a function of depth, and make a non-destructive quantitative analysis of the structure, in order to analyze the tetragonal distortion of the InN thin film at the depth determined.

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Effect of Electrochemical Treatment in a Lithium Chloride Solution on Field Emission from Carbon Nanotubes

WANG Qiang, LI Chun, YUAN Guang, GU Chang-Zhi

Chin. Phys. Lett. 2009, 26 (8): 086112 . DOI: 10.1088/0256-307X/26/8/086112

Abstract

PDF(pc) (611KB) ( 725 )

Carbon nanotubes (CNTs) are electrochemically treated in a lithium chloride solution at a concentration 0.1mol/L. The field emission properties of the CNTs are investigated at different temperatures before and after the electrochemical treatment. After treatment, the turn-on voltage to produce field emission current of 10μA decreases from 4.2kV to 2.7kV and the field emission current increases distinctly, but the stability falls off. Based on the Fowler-Nordheim plot, the values of the work function for the CNTs are calculated, which reveals that work function decreases after the electrochemical treatment. These results are attributed to the decrease of the work function of the carbon nanotubes.

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Neutron Diffraction Measurements of a Thermally Fatigued Single Crystal Superalloy

SUN Guang-Ai, CHEN Bo, WU Er-Dong, LI Jin-Chao, T. Pirling, D. Hughes

Chin. Phys. Lett. 2009, 26 (8): 086201 . DOI: 10.1088/0256-307X/26/8/086201

Abstract

PDF(pc) (329KB) ( 775 )

The thermally fatigued single crystal superalloy DZ125L is investigated by neutron diffraction measurements. The measurements, made using the φ angle oscillating method, provide more detailed and reliable data than those with the φ angle fixed. Diffraction studies show that the influence of thermal fatigue on the lattice parameters of the alloy is very limited. The stress analysis reveals that triaxial elastic hydrostatic stress plays a major role during thermal fatigue. The magnitude of the macrostress increases with the fatigue cycles, with the stress of the γ phase increasing more significantly than that of the γ' phase, and becoming fragile after many cycles. The changes in the microstrain are dependent on the reflection planes. The microstrains at the center of the sample are released by the thermal fatigue in comparison with those at the outlying locations, which has been attributed to the advance of the dislocation slips.

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CuO Nanosheets Synthesized by Hydrothermal Process

JIANG Zhi-Ang, CHEN Jiang-Tao, WANG Jun, ZHUO Ren-Fu, YAN De, ZHANG Fei, YAN Peng-Xun

Chin. Phys. Lett. 2009, 26 (8): 086202 . DOI: 10.1088/0256-307X/26/8/086202

Abstract

PDF(pc) (2150KB) ( 2060 )

CuO nanosheets are synthesized by oxidation of commercial Cu substrates through the hydrothermal process at 150°C. The as-synthesized nanosheets are characterized by powder x-ray diffraction, transmission electron microscopy, selected area electron diffraction and x-ray photoelectron spectroscopy. For comparison, Cu substrates are also oxidized without NaOH added in precursor solution. The results show that the morphology of CuO could be controlled by NaOH, which demonstrates that NaOH can serve as a cosolvent and modifier in the reaction system. The possible mechanism of the growth of CuO nanosheets is also discussed.

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First-Principles Calculations of Elastic and Thermal Properties of Molybdenum Disilicide

ZHU Zun-Lue, FU Hong-Zhi, SUN Jin-Feng, LIU Yu-Fang, SHI De-Heng, XU Guo-Liang

Chin. Phys. Lett. 2009, 26 (8): 086203 . DOI: 10.1088/0256-307X/26/8/086203

Abstract

PDF(pc) (398KB) ( 1499 )

The first-principles plane-wave pseudopotential method using the generalized gradient approximation within the framework of density functional theory is applied to anaylse the equilibrium lattice parameters, six independent elastic constants, bulk moduli, thermal expansions and heat capacities of MoSi₂. The quasi-harmonic Debye model, using a set of total energy versus cell volume obtained with the plane-wave pseudopotential method, is applied to the study of the elastic properties, thermodynamic properties and vibrational effects. The calculated zero pressure elastic constants are in overall good agreement with the experimental data. The calculated heat capacities and the thermal expansions agree well with the observed values under ambient conditions and those calculated by others. The results show that the temperature has hardly any effect under high pressure.

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Self-Organization of Weighted Networks in Connection with the Misanthrope Process

MENG Qing-Kuan, ZHU Jian-Yang

Chin. Phys. Lett. 2009, 26 (8): 086401 . DOI: 10.1088/0256-307X/26/8/086401

Abstract

PDF(pc) (229KB) ( 513 )

From an undirected random graph, by the weight redistribution of the edges, we obtain a weighted network. The weight redistribution of the edges can be connected to the well-known Misanthrope process, in which distinguishable particles hop among different urns. Under specific conditions, the condensation phenomena can be observed, i.e., nearly all the edges connect to one vertex in the network. When there is no condensation, by adjusting the parameters, the strength distribution can be scale-free or exponentially decreasing. The numerical results fit well with the analytical ones.

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Molecular Dynamical Simulation of Water/Ice Phase Transitions within Carbon Nanotubes under Various Pressures

YIN Bing, DONG Shun-Le

Chin. Phys. Lett. 2009, 26 (8): 086402 . DOI: 10.1088/0256-307X/26/8/086402

Abstract

PDF(pc) (1503KB) ( 617 )

A molecular dynamics simulation is performed for water confined within carbon nanotubes with diameters 11.00Å and 12.38Å. Under pressures from 0.1MPa to 500MPa the simulations are carried out by cooling from 300K to 240K. Water molecules tend to transform from disordered to ordered with different configurations (square, pentagonal, hexagonal and hexagonal plus a chain). It is concluded that denser structures may appear under high pressures.

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Synchronization of Local Oscillations in a Spatial Rock-Scissors-Paper Game Model

SUN Rong-Sheng, HUA Da-Yin

Chin. Phys. Lett. 2009, 26 (8): 086403 . DOI: 10.1088/0256-307X/26/8/086403

Abstract

PDF(pc) (232KB) ( 729 )

We study a spatial rock-scissors-paper model in a square lattice and a quenched small-world network. The system exhibits a global oscillation in the quenched small-world network, but the oscillation disappears in the square lattice. We find that there is a local oscillation in the square lattice the same as in the quenched small-world network. We define σ=1/NΣ_i(d_i-<d_i>)² (where d_iis the density of a kind of species and <d_i> is the average value) as the variance of the oscillation amplitude in a certain local patch. It is found that σ decays in a power law with an increase of the local patch size R in the square lattice σ∝ R^-δ, but it remains constant with an increase of the patch size in the quenched small-world network. We can speculate that in the square lattice, superposition between the local oscillations in different patches leads to global stabilization, while in the quenched small-world network, long-range interactions can synchronize the local oscillations, and their coherence results in the global oscillation.

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Prediction and Refinement of High-Order Virial Coefficients for a Hard-Sphere System

HU Jia-Wen, YU Yang-Xin

Chin. Phys. Lett. 2009, 26 (8): 086404 . DOI: 10.1088/0256-307X/26/8/086404

Abstract

PDF(pc) (390KB) ( 550 )

The n^th virial coefficient for a hard-sphere system is expressed as the sum of n² and a remainder. When n≥3, the remainders of the virials can be accurately expressed with Pade-type functions of n. The maximum deviations are only 0.039-0.053%, which are much better than the existing approaches. By using the predicted virials, the compressibility factors of the hard-sphere system can be predicted very accurately in the whole stable fluid region, and those in the metastable fluid region can also be well predicted up to a packing fraction of 0.545. The simulated B₇ and B₁₀ are found to be inconsistent with the other known virials, and thus they are refined to be 53.2467 and 105.042, respectively.

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Tunable Anisotropic Absorption of Ag-Embedded SiO₂Thin Films by Oblique Angle Deposition

XIAO Xiu-Di, DONG Guo-Ping, SHAO Jian-Da, FAN Zheng-Xiu, HE Hong-Bo, QI Hong-Ji,

Chin. Phys. Lett. 2009, 26 (8): 086801 . DOI: 10.1088/0256-307X/26/8/086801

Abstract

PDF(pc) (1124KB) ( 504 )

Ag-embedded SiO₂ thin films are prepared by oblique angle deposition. Through field emission scanning electron microscopy (SEM), an orientated slanted columnar structure is observed. Energy-dispersive x-ray (EDX) analysis shows the Ag concentration is about 3% in the anisotropic SiO₂ matrix. Anisotropic surface plasma resonance (SPR) absorption is observed in the Ag-embedded SiO₂ thin films, which is dependent on polarization state and incidence angle of two orthogonal polarized lights and the deposition angle. This means that optical properties and anisotropic SPR absorption can be tunable in Ag-embedded SiO₂ thin films. Broadband polarization splitting is also observed and the transmission ratio T_p/T_s between p-and s-polarized lights is up to 2.7 for thin films deposited at α=70°, which means that Ag-embedded SiO₂ thin films are a promising candidate for thin film polarizers.

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A Thin Liquid Film and Its Effects in an Atomic Force Microscopy Measurement

LIN Jing, ZHENG Zhi-Jun, YU Ji-Lin, BAI Yi-Long

Chin. Phys. Lett. 2009, 26 (8): 086802 . DOI: 10.1088/0256-307X/26/8/086802

Abstract

PDF(pc) (390KB) ( 445 )

Recently, it has been observed that a liquid film spreading on a sample surface will significantly distort atomic force microscopy (AFM) measurements. In order to elaborate on the effect, we establish an equation governing the deformation of liquid film under its interaction with the AFM tip and substrate. A key issue is the critical liquid bump height y_0c, at which the liquid film jumps to contact the AFM tip. It is found that there are three distinct regimes in the variation of y_0c with film thickness H, depending on Hamaker constants of tip, sample and liquid. Noticeably, there is a characteristic thickness H* physically defining what a thin film is; namely, once the film thickness H is the same order as H*, the effect of film thickness should be taken into account. The value of H* is dependent on Hamaker constants and liquid surface tension as well as tip radius.

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Fabrication of 11-nm-Wide Silica-Like Lines Using X-Ray Diffraction Exposure

ZHU Xiao-Li, XIE Chang-Qing, ZHANG Man-Hong, LIU Ming, CHEN Bao-Qin, PAN Feng

Chin. Phys. Lett. 2009, 26 (8): 086803 . DOI: 10.1088/0256-307X/26/8/086803

Abstract

PDF(pc) (1206KB) ( 512 )

Fine silica-like lines with 11 nm width are successfully fabricated using x-ray Fresnel diffraction exposure. X-rays pass a mask of 175-nm-wide lines and 125-nm-wide spaces and form sharp peaks on a wafer coated with a layer of hydrogen silsesquioxane resist (HSQ). By precisely controlling the mask-wafer gap at 10μm using the laser interferogram method, the fine structures are defined on HSQ. Experimental images are reproduced by a simulation using the one-dimensional beam propagation method. This lithographic technique presents a novel and convenient way to fabricate fine silica-like structures and devices in nano-optical and nanoelectronic applications.

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Adsorption Mechanism of Hydrogen on Boron-Doped Fullerenes

YU Liu-Min, , SHI Guo-Sheng, WANG Zhi-Gang, JI Guang-Fu, LU Zhi-Peng,

Chin. Phys. Lett. 2009, 26 (8): 086804 . DOI: 10.1088/0256-307X/26/8/086804

Abstract

PDF(pc) (1526KB) ( 598 )

The C₃₅BH-H₂ complex and two other possible isomers, C₃₄BC_aH-H₂ and C₃₄BC_bH-H₂, are investigated using the local-spin-density approximation (LSDA) method. The results indicate that a single hydrogen molecule could be strongly adsorbed on two isomers, C₃₄BC_aH and C₃₄BC_bH, with binding
energies of 0.42 and 0.47eV, respectively, and that these calculated binding energies are suitable for reversible hydrogen adsorption/desorption near room temperature. However, it is difficult for the H₂ molecule to be firmly adsorbed on C₃₅BH. We analyze the interaction between C₃₄BC_xH (x=a, b) and the H₂ molecule using dipole moments and molecular orbitals. The charge analysis showed there was a partial charge (about 0.32e) transfer from H₂ to the doped fullerenes. These calculation results should broaden our understanding of the mechanisms of hydrogen storage using boron-doped fullerenes.

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Microstructure and Corrosion Performance of Carbonitriding Layers on Cast Iron by Plasma Electrolytic Carbonitriding

PANG Hua, LV Guo-Hua, CHEN Huan, WANG Xin-Quan, ZHANG Gu-Ling, YANG Si-Ze,

Chin. Phys. Lett. 2009, 26 (8): 086805 . DOI: 10.1088/0256-307X/26/8/086805

Abstract

PDF(pc) (907KB) ( 998 )

The surface carbonitriding of cast iron is investigated in an aqueous solution of acetamide and glycerin. Microstructure, chemical and phase composition and corrosion performance of the carbonitriding layers are investigated by scanning electron microscopy, energy dispersive spectroscopy and x-ray diffraction, as well as potentiodynamic polarization testing. X-ray diffraction results show that the carbonitriding coatings are composed of martensite, austenite(γ-Fe), Fe₂C, Fe₃C, Fe₅C₂, FeN and ε-Fe_2-3N. After the plasma electrolytic carbonitriding treatment the corrosion resistance of cast iron is clearly improved compared to the substrate, and the coatings produced at 350V for 30s give the best corrosion resistance.

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

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Theoretical Study on the Propagation of Acoustic Phonon Modes in Single-Wall Carbon Nanotubes by Different Potential Models

CAO Bing, ZHANG Wei, HUAI Ping, ZHU Zhi-Yuan

Chin. Phys. Lett. 2009, 26 (8): 087101 . DOI: 10.1088/0256-307X/26/8/087101

Abstract

PDF(pc) (400KB) ( 499 )

Propagation of a heat pulse in (10,0) zig-zag carbon nanotubes, modeled by the Brenner-II and Tersoff bond-order potentials, respectively, is investigated using a molecular dynamics simulation. The longitudinal acoustic mode, twisting phonon mode, and second sound waves are observed in the simulation. The time variations of speed and intensity of the above three phonon modes are in good agreement with the previous works based on the Brenner-I potential. Higher speed and weaker peak intensity are observed in the simulation of the Tersoff potential. The inherent over-binding of radicals and the non-local effects in Tersoff's covalent-bonding formula may play an important role in the heat pulse propagating simulation.

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First-Principles Study of Li Doping in a Double-Wall Carbon Nanotube

WEN Yan-Wei, LIU Hui-Jun, PAN Lu, TAN Xiao-Jian, SHI Jing

Chin. Phys. Lett. 2009, 26 (8): 087102 . DOI: 10.1088/0256-307X/26/8/087102

Abstract

PDF(pc) (594KB) ( 563 )

By performing first-principles calculations, we study Li doping in a double-wall carbon nanotube where a (5,0) tube is confined inside a (14,0) tube. There are three possible sites for Li doping and two of them are energetically favorable. The change of energy band structure is closely related to the doping sites and the charge transfer is investigated. Bader charge analysis indicates that Li prefers to donate its electron to the inner (5,0) tube. Moreover, the Li capacity of the system can reach LiC_4.75 which makes it a promising candidate for Li-ion battery materials.

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A Possible Structure of the Al₃₆ Cluster: Coexistence of Icosahedral and fcc-Like Structures

WANG Gui, GONG Xin-Gao

Chin. Phys. Lett. 2009, 26 (8): 087103 . DOI: 10.1088/0256-307X/26/8/087103

Abstract

PDF(pc) (1103KB) ( 417 )

We study the atomic and electronic structures of the Al₃₆ cluster using first principles total energy calculations with the local density approximation, and obtain a structure which has a HOMO-LUMO gap as large as 0.67eV, in agreement with experimental photoelectron spectroscopy. Its atomic structure is found to show the coexistence of icosahedral and fcc-based structures, which can be seen as a transition phase from icosahedral to fcc-bulk structures.

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Charge Transport and Magnetotransport Properties of Polyimide Irradiated by 80keV Co Ions

CHEN Tian-Xiang, YAO Shu-De, HUA Wei, FA Tao, LI Lin, ZHOU Sheng-Qiang

Chin. Phys. Lett. 2009, 26 (8): 087201 . DOI: 10.1088/0256-307X/26/8/087201

Abstract

PDF(pc) (444KB) ( 589 )

Charge transport properties of polyimide films implanted with 80keV Co ions at two different fluences (series I: 1.25×10¹⁷ions/cm², series II: 1.75×10¹⁷ions/cm²) are studied in detail. For series I, the temperature dependence of surface resistivity fits Mott's equation very well. It is on the insulating side of the insulator-metal transition (IMT). However, for series II, the temperature dependence of surface resistivity is not in agreement with Mott's equation. It is on the metallic side of IMT. The magnetotransport properties of these two series are also studied. No significant magnetoresistive effect is observed for series I at both 5K and 300K. For series II, an obvious magnetoresistive effect is observed at 5K, while there is no magnetoresistive effect at 300K. Rutherford backscattering spectrometry (RBS) is applied to confirm the actual fluence for these two series.

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Potential-Dependent Generalized Einstein Relation in Disordered Organic Semiconductors

LU Xiao-Hong, SUN Jiu-Xun, GUO Yang, ZHANG Da

Chin. Phys. Lett. 2009, 26 (8): 087202 . DOI: 10.1088/0256-307X/26/8/087202

Abstract

PDF(pc) (325KB) ( 643 )

The generalized Einstein relation (GER) is extended to consider the potential energy of carriers in an electric field (PDGER). It can be equivalently seen as the GER having position-dependent Fermi energy, and implies the organic semiconductor is in non-equilibrium under an electric field. The distribution of the carrier density with position is solved for two polymer layers. The numerical results are used to evaluate the PDGER. It is shown that the ratio of diffusion coefficient to mobility, μ/D, increases with Fermi energy and decreases with carrier density. The PDGER gives non-traditional values for the two polymer layers; the value of μ/D is small near the surface, and slightly increases as the position departs from the surface.

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Spin-Flip Process of Polarons in Conjugated Polymers with Magnetic Impurities

ZHAO Hui, ZHANG Xu-Ming, AN Zhong, CHEN Yu-Guang, WU Chang-Qin

Chin. Phys. Lett. 2009, 26 (8): 087203 . DOI: 10.1088/0256-307X/26/8/087203

Abstract

PDF(pc) (414KB) ( 910 )

Being driven by an external electric field, a polaron carrying both spin 1/2 and charge ±e moves at a constant speed in a polymer chain. When the polaron passes through a specific site, which couples to a magnetic impurity via spin-exchange interactions, its spin undergoes a spin-flip process if it is antiparallel to the impurity spin. Our numerical simulation shows that (a) a swap-like operation is performed between the polaron and impurity during the scattering process (b) polarons might be good candidates to be information carriers in the molecular scale.

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Bias Voltage Controlled Positive Magnetoresistance of Fe_0.05-C_0.95/Si Heterostructures

WU Li-Hua, ZHANG Xiao-Zhong, ZHANG Xin, WAN Cai-Hua, GAO Xi-Li, TAN Xin-Yu, YUAN Jun

Chin. Phys. Lett. 2009, 26 (8): 087301 . DOI: 10.1088/0256-307X/26/8/087301

Abstract

PDF(pc) (607KB) ( 606 )

Fe-doped amorphous carbon films of about 100nm in thickness are deposited on n-type silicon substrates by pulsed laser deposition (PLD), and positive magnetoresistance (MR) is observed for these Fe-doped amorphous carbon/n-Si heterostructures under current-perpendicular-to-plane configuration at forward bias. Two MR peaks are observed in the temperature range 40-120K and the positive MR varies with applied bias voltage. This bias voltage controlled MR may be related to the magnetic-field-controlled freeze out effect and recombination through the deep trapping states in the Fe-doped carbon films.

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Hydrogenic Donor in a Spherical Quantum Dot with Different Confinements

A. John Peter, K. Navaneethakrishnan

Chin. Phys. Lett. 2009, 26 (8): 087302 . DOI: 10.1088/0256-307X/26/8/087302

Abstract

PDF(pc) (231KB) ( 992 )

Binding energies of a hydrogenic donor in a spherical GaAs quantum dot surrounded by Ga_1-xAl_xAs matrix are calculated. The results are presented for realistic barrier heights corresponding to different values of x (x<0.4). The calculations are performed under two different conditions: (i) a spherical dot with square well confinement and (ii) a dot with parabolic potential well confinement. The results show that (i) the donor ionization energies are always higher under parabolic confinement as compared to a dot of the same radius under square well confinement and (ii) the oscillator strengths coupling ground state with excited states are two orders larger under parabolic confinement. Our results are in agreement with the results of other researchers.

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Robust Low Voltage Program-Erasable Cobalt-Nanocrystal Memory Capacitors with Multistacked Al₂O₃/HfO₂/Al₂O₃ Tunnel Barrier

LIAO Zhong-Wei, GOU Hong-Yan, HUANG Yue, SUN Qing-Qing, DING Shi-Jin, ZHANG Wei, ZHANG Shi-Li,

Chin. Phys. Lett. 2009, 26 (8): 087303 . DOI: 10.1088/0256-307X/26/8/087303

Abstract

PDF(pc) (839KB) ( 514 )

An atomic-layer-deposited Al₂O₃/HfO₂/Al₂O₃ (A/H/A) tunnel barrier is investigated for Co nanocrystal memory capacitors. Compared to a single Al₂O₃ tunnel barrier, the A/H/A barrier can significantly increase the hysteresis window, i.e., an increase by 9V for ±12V sweep range. This is attributed to a marked decrease in the energy barriers of charge injections for the A/H/A tunnel barrier. Further, the Co-nanocrystal memory capacitor with the A/H/A tunnel barrier exhibits a memory window as large as 4.1V for 100μs program/erase at a low voltage of ±7V, which is due to fast charge injection rates, i.e., about 2.4×10¹⁶cm^-2s^-1 for electrons and 1.9×10¹⁶cm^-2s^-1 for holes.

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Schottky Barrier Height Modulation of Nickel Germanide Schottky Diodes by the Germanidation-Induced Dopant Segregation Technique

AN Xia, FAN Chun-Hui, HUANG Ru, ZHANG Xing

Chin. Phys. Lett. 2009, 26 (8): 087304 . DOI: 10.1088/0256-307X/26/8/087304

Abstract

PDF(pc) (831KB) ( 860 )

Modulation of Schottky barrier height (SBH) is successfully demonstrated by a germanidation-induced dopant segregation technique. The barrier height of NiGe/Ge Schottky diodes is modulated by 0.06-0.15eV depending on annealing temperature. The results show the change of SBH is not attributed to the phase change of nickel germanides but to dopant segregation at the interface of germanides/germanium which causes the upward conduction energy band. In addition, we first observe a Raman peak at about 217cm^-1 corresponding to NiGe, which has not been reported till now. The surface morphology of nickel germanides can be improved by BF₂ implantation before germanidation. The results may provide guidelines for the design of Schottky source/drain germanium-based devices.

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Structural, Magnetic and Magnetocaloric Properties of La-deficient La_0.77-xSr_xCa_0.2MnO₃ Perovskites

ZHAO Xu, CHEN Wei, LI Ai-Jun, MA Li-Mei, ZONG Yun

Chin. Phys. Lett. 2009, 26 (8): 087401 . DOI: 10.1088/0256-307X/26/8/087401

Abstract

PDF(pc) (381KB) ( 592 )

La-deficient La_0.77-xCa_0.2Sr_xMnO₃ (0≤x≤0.1) polycrystalline samples are synthesized using the sol-gel technique. The crystal structures of all the samples are single orthorhombic phase with Pbnm space group. Rietveld analysis of x-ray diffraction patterns shows that the Mn-O-Mn bond angle θ_Mn-O-Mn increases whereas the Mn-O bond length d_Mn--O decreases monotonically with increasing Sr²⁺content, which results in a rich overlap between Mn 3d and O 2p orbitals and leads to a systematic increase of the Curie temperature in this compound. It is found that the magnetic entropy change has a maximum at x=0.06 in La³⁺-deficient La_0.77-xCa_0.2Sr_xMnO₃. This may result from competition between the super-exchange interactions (Mn⁴⁺-O^2--Mn⁴⁺) and double-exchange interactions (Mn³⁺-O^2--Mn⁴⁺) originating from the appearance of superfluous Mn⁴⁺ ions by substitution of Sr²⁺ for La³⁺ in this series. Large magnetic entropy changes of 2.32 and 1.83Jkg^-1K^-1 in the x= 0.06 and x= 0.1 samples at their T_Cs of 271K and 303K upon a low magnetic field (10kOe) make these materials promising candidates at near room temperature.

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Magnetoelectric Coupling Induced Electric Dipole Glass State in Heisenberg Spin Glass

LIU Jun-Ming, , CHAN-WONG Lai-Wa, CHOY Chung-Loong

Chin. Phys. Lett. 2009, 26 (8): 087501 . DOI: 10.1088/0256-307X/26/8/087501

Abstract

PDF(pc) (393KB) ( 558 )

Multiferroic behavior in an isotropic Heisenberg spin glass with Gaussian random fields, incorporated by magnetoelectric coupling derived from the Landau symmetry argument, are investigated. Electric dipole glass transitions at finite temperature, due to coupling, are demonstrated by Monte Carlo simulation. This electric dipole glass state is solely ascribed to the coupling term with chiral symmetry of the magnetization, while the term associated with the spatial derivative of the squared magnetization has no contribution.

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Crystalline and Magnetic Enhancement of Nanocrystalline MnZn Ferrites Fabricated under a High Magnetic Field

LIU Yong-Sheng, ZHONG Yun-Bo, ZHANG Jin-Cang, GU Min-An, YANG Zheng-Long, REN Zhong-Ming

Chin. Phys. Lett. 2009, 26 (8): 087502 . DOI: 10.1088/0256-307X/26/8/087502

Abstract

PDF(pc) (727KB) ( 669 )

Nanocrystalline Mn_0.6Zn_0.4Fe₂O₄ particles are synthesized under magnetic fields of 0 and 6T, and their structural and magnetic properties are investigated. The magnetic field enhances the grain size and the lattice strain. Magnetic measurements show that the majority of the 6T nanoparticles are superparamagnetic nearly from 40 to 300K. It is interesting that the saturation magnetization of the 6T sample is about 18% and 16% higher than that of the 0T sample at 120 and 300K, respectively.

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C_4v Symmetry Crystal Field and Ground State Wavefunction of the VO²⁺ Ion

Ram Kripal, Santwana Shukla

Chin. Phys. Lett. 2009, 26 (8): 087601 . DOI: 10.1088/0256-307X/26/8/087601

Abstract

PDF(pc) (219KB) ( 2878 )

The spin-Hamiltonian parameters obtained from EPR studies of the VO²⁺ ion in different diamagnetic host lattices are used to estimate the ground state wavefunctions. These are of d_xy type with admixture of the excited states d_x²-y², d_yz and d_xz. The hyperfine interaction parameter and Fermi contact term for the VO²⁺ doped crystals are determined using the coefficients of the ground state. The various parameters are correlated to the ligand properties of the complexes.

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One-on-One and R-on-One Tests on KDP and DKDP Crystals with Different Orientations

HU Guo-Hang, ZHAO Yuan-An, SUN Shao-Tao, LI Da-Wei, SUN Xun, SHAO Jian-Da, FAN Zheng-Xiu

Chin. Phys. Lett. 2009, 26 (8): 087801 . DOI: 10.1088/0256-307X/26/8/087801

Abstract

PDF(pc) (400KB) ( 1063 )

By testing a substantial number of tripler and z-cut KDP and DKDP crystals, we have observed that at 355nm, the laser induced damage threshold in the R-on-one test is higher than that in the one-on-one test. It is proved that laser conditioning is an efficient way to improve the damage resistance. The efficiency of laser conditioning becomes increasingly good with smaller ramping fluence steps. We have also found that the damage resistance of the z-cut crystal is higher than the tripler cut, and the pinpoint number is definitely less in the z-cut crystal. The reason for these observations is discussed.

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Indium-Induced Effect on Polarized Electroluminescence from InGaN/GaN MQWs Light Emitting Diodes

RUAN Jun, YU Tong-Jun, JIA Chuan-Yu, TAO Ren-Chun, WANGZhan-Guo, ZHANG Guo-Yi

Chin. Phys. Lett. 2009, 26 (8): 087802 . DOI: 10.1088/0256-307X/26/8/087802

Abstract

PDF(pc) (697KB) ( 757 )

Polarization-resolved edge-emitting electroluminescence (EL) studies of InGaN/GaN MQWs of wavelengths from near-UV (390nm) to blue (468nm) light-emitting diodes (LEDs) are performed. Although the TE mode is dominant in all the samples of InGaN/GaN MQW LEDs, an obvious difference of light polarization properties is found in the InGaN/GaN MQW LEDs with different wavelengths. The polarization degree decreases from 52.4% to 26.9% when light wavelength increases. Analyses of band structures of InGaN/GaN quantum wells and luminescence properties of quantum dots imply that quantum-dot-like behavior is the dominant reason for the low luminescence polarization degree of blue LEDs, and the high luminescence polarization degree of UV LEDs mainly comes from QW confinement and the strain effect. Therefore, indium induced carrier confinement (quantum-dot-like behavior) might play a major role in the polarization degree change of InGaN/GaN MQW LEDs from near violet to blue.

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Design of Phosphor-Free Single-Chip White Light-Emitting Diodes Using InAlGaN Irregular Multiple Quantum Well Structures

LU Hui-Min, CHEN Gen-Xiang, JIAN Shui-Sheng

Chin. Phys. Lett. 2009, 26 (8): 087803 . DOI: 10.1088/0256-307X/26/8/087803

Abstract

PDF(pc) (441KB) ( 1097 )

A novel approach for the design of phosphor-free single-chip white light-emitting diodes (LEDs) is proposed by employing InAlGaN irregular multiple quantum well (IMQW) structures. The electronic and optical properties of the designed InAlGaN IMQWs are analyzed in detail by fully considering the effects of strain, well-coupling, valence band-mixing, and quasi-bound states using the effective-mass Hamiltonian deduced from k・p theory. For comparison, three different types of InAlGaN IMQW structures with ultra-wide band spontaneous emission spectra are analyzed, and the results show that phosphor-free single-chip white light LEDs with more than 200nm emission band can be obtained using properly designed InAlGaN IMQW structures.

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High-Temperature Operation of 8.5μm Distributed Feedback Quantum Cascade Lasers

LI Yao-Yao, LI Ai-Zhen, WEI Lin, LI Hua, XU Gang-Yi, ZHANG Yong-Gang

Chin. Phys. Lett. 2009, 26 (8): 087804 . DOI: 10.1088/0256-307X/26/8/087804

Abstract

PDF(pc) (571KB) ( 851 )

We present a distributed feedback quantum cascade laser (DFB-QCL) emitting at a wavelength of 8.5μm and operating up to 420K (147°C) with a low-threshold current density in pulsed mode. The DFB-QCLs studied are based on a four-well active design; the central portion of the waveguide consists of 60 periods of lattice matched InP-based InGaAs/AlInAs. In the design of the device, an active structure with lower doping and a deep-top grating process are utilized to achieve high temperature operation with a lower-threshold current density. At 420K, a low-threshold current density of 3.28kA/cm² and a single mode peak power of 15mW are achieved on an epilayer-up mounting device with ridge width of 26μm and cavity length of 3.0mm. A side mode suppression ratio of 25dB at 420K is obtained.

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Growth Characteristics and Mechanism of Surface and Bulk Damage in KDP and DKDP Crystals

HU Guo-Hang, ZHAO Yuan-An, SUN Shao-Tao, LI Da-Wei, LIU Xiao-Feng, SUN Xun, SHAO Jian-Da, FAN Zheng-Xiu

Chin. Phys. Lett. 2009, 26 (8): 087805 . DOI: 10.1088/0256-307X/26/8/087805

Abstract

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By testing the number increase and size growth of surface and bulk laser induced damage in KDP and DKDP crystals, we observe different growth characteristics of surface and bulk damage under multiple 355nm laser irradiations. The size of the surface damage grows exponentially, but that of the bulk damage does not grow. In contrast, the bulk damage number increases, but that of surface damage does not increase significantly. We attribute the differences to the different formation of the damage initiators and the different damage testing volumes.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Novel Route to Fabrication of Metal-Sandwiched Nanoscale Tapered Structures

ZHANG Yang, YU Da-Peng

Chin. Phys. Lett. 2009, 26 (8): 088101 . DOI: 10.1088/0256-307X/26/8/088101

Abstract

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Tapered dielectric structures in metal have exhibited extraordinary performance in both surface plasmon polariton (SPP) waveguiding and SPP focusing. This is crucial to plasmonic research and industrial plasmonic device integration. We present a method that facilitates easy fabrication of smooth-surfaced sub-micron tapered structures in large scale simply with electron beam lithography (EBL). When a PMMA layer is spin-coated on previously-EBL-defined PMMA structures, steep edges can be transformed into a declining slope to form tapered PMMA structures, scaled from 10nm to 1000nm. Despite the simplicity of our method, patterns with PMMA surface smoothness can be well-positioned and replicated in large numbers, which therefore gives scientists easy access to research on the properties of tapered structures.

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Excellent Passivation of p-Type Si Surface by Sol-Gel Al₂O₃ Films

XIAO Hai-Qing, ZHOU Chun-Lan, CAO Xiao-Ning, WANG Wen-Jing, ZHAO Lei, LI Hai-Ling, DIAO Hong-Wei

Chin. Phys. Lett. 2009, 26 (8): 088102 . DOI: 10.1088/0256-307X/26/8/088102

Abstract

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Al₂O₃ films with a thickness of about 100nm synthesized by spin coating and thermally treated are applied for field-induced surface passivation of p-type crystalline silicon. The level of surface passivation is determined by techniques based on photoconductance. An effective surface recombination velocity below 100cm/s is obtained on 10Ω·cm p-type c-Si wafers (Cz Si). A high density of negative fixed charges in the order of 10¹²cm^-2 is detected in the Al₂O₃ films and its impact on the level of surface passivation is demonstrated experimentally. Furthermore, a comparison between the surface passivation achieved for thermal SiO₂ and plasma enhanced chemical vapor deposition SiN_x:H films on the same c-Si is presented. The high negative fixed charge density explains the excellent passivation of p-type c-Si by Al₂O₃.

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Effect of Phosphate on the Self-Assembly of Peptide EMK16-II

ZOU Da-Wei, TIE Zuo-Xiu, QIN Meng, LU Chun-Mei, WANG Wei

Chin. Phys. Lett. 2009, 26 (8): 088103 . DOI: 10.1088/0256-307X/26/8/088103

Abstract

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The ionic-complementary peptide EMK16-II is used to investigate the effects of hydrophobic and electrostatic interactions on the self-assembling process by atomic force microscopy and circular dichroism spectra. It is found that the increase of hydrophobicity of the peptides promotes the aggregation of fibrils in pure water. The effects of phosphate with different concentrations on electrostatic interactions are also investigated. It is found that the self-assembling process is enhanced at a low concentration of phosphate and more ordered fibrillar aggregates are formed. When the concentration of phosphate increases to a certain value (9mM), only a few fibrils are found to be formed. No fibrils but amorphous aggregates exist when the concentration further increases. A physical interpretation is presented such that one divalent anion can interact with two

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Epitaxial Growth of Graphene on 6H-SiC (0001) by Thermal Annealing

TANG Jun, LIU Zhong-Liang, KANG Chao-Yang, PAN Hai-Bin, WEI Shi-Qiang, XU Peng-Shou, GAO Yu-Qiang, XU Xian-Gang

Chin. Phys. Lett. 2009, 26 (8): 088104 . DOI: 10.1088/0256-307X/26/8/088104

Abstract

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An epitaxial graphene (EG) layer is successfully grown on a Si-terminated 6H-SiC (0001) substrate by the method of thermal annealing in an ultrahigh vacuum molecular beam epitaxy chamber. The structure and morphology of the EG sample are characterized by reflection high energy diffraction (RHEED), Raman spectroscopy and atomic force microscopy (AFM). Graphene diffraction streaks can be seen in RHEED. The G and 2D peaks of graphene are clearly observed in the Raman spectrum. The AFM results show that the graphene nominal thickness is about 4-10 layers

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Effect of Annealing Conditions on Properties of Sol-Gel Derived Al-Doped ZnO Thin Films

GAO Mei-Zhen, ZHANG Feng, LIU Jing, SUN Hui-Na

Chin. Phys. Lett. 2009, 26 (8): 088105 . DOI: 10.1088/0256-307X/26/8/088105

Abstract

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Transparent conductive Al-doped ZnO (AZO) thin films are prepared on normal glass substrates by the sol-gel spin coating method. The effects of drying conditions, annealing temperature and cooling rate on the structural, electrical and optical properties of AZO films are investigated by x-ray diffraction, scanning electron microscopy, the four-point probe method and UV-VIS spectrophotometry, respectively. The deposited films show a hexagonal wurtzite structure and high preferential c-axis orientation. As the drying temperature increases from 100°C to 300°C the resistivity of AZO films decreases dramatically. In contrast to the annealed films cooled in a furnace and in air, the resistivity of the annealed film which is cooled at -15°C is greatly reduced. Increasing the cooling rate dramatically increases the electrical conductivity of AZO films.

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Surface Micromachined Adjustable Micro-Concave Mirror for Bio-Detection Applications

KUO Ju-Nan, CHEN Wei-Lun, JYWE Wen-Yuh

Chin. Phys. Lett. 2009, 26 (8): 088501 . DOI: 10.1088/0256-307X/26/8/088501

Abstract

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We present a bio-detection system integrated with an adjustable micro-concave mirror. The bio-detection system consists of an adjustable micro-concave mirror, micro flow cytometer chip and optical detection module. The adjustable micro-concave mirror can be fabricated with ease using commercially available MEMS foundry services (such as multiuser MEMS processes, MUMPs) and its curvature can be controlled utilizing thermal or electrical effects. Experimental results show that focal lengths of the micro-concave mirror ranging from 313.5 to 2275.0μm are achieved. The adjustable micro-concave mirror can be used to increase the efficiency of optical detection and provide a high signal-to-noise ratio. The developed micro-concave mirror is integrated with a micro flow cytometer for cell counting applications. Successful counting of fluorescent-labeled beads is demonstrated using the developed method.

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The Fractal Dimensions of Complex Networks

GUO Long, CAI Xu

Chin. Phys. Lett. 2009, 26 (8): 088901 . DOI: 10.1088/0256-307X/26/8/088901

Abstract

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It is shown that many real complex networks share distinctive features, such as the small-world effect and the heterogeneous property of connectivity of vertices, which are different from random networks and regular lattices. Although these features capture the important characteristics of complex networks, their applicability depends on the style of networks. To unravel the universal characteristics many complex networks have in common, we study the fractal dimensions of complex networks using the method introduced by Shanker. We find that the average `density' <ρ(r)> of complex networks follows a better power-law function as a function of distance r with the exponent d_f, which is defined as the fractal dimension, in some real complex networks. Furthermore, we study the relation between d_f and the shortcuts N_addin small-world networks and the size N in regular lattices. Our present work provides a new perspective to understand the dependence of the fractal dimension d_f on the complex network structure.

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Evolutionary Self-Questioning Games with Local Contribution

LIU Yong-Kui, LI Zhi, CHEN Xiao-Jie, WANG Long,

Chin. Phys. Lett. 2009, 26 (8): 088902 . DOI: 10.1088/0256-307X/26/8/088902

Abstract

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We investigate the evolutionary Prisoner's Dilemma and the Snowdrift Game on small-world networks in a realistic social context where individuals consider their local contributions to their group and update their strategies by self-questioning. An individual with introspection can determine whether its current strategy is superior by playing a virtual round of the game and its local contribution is defined as the sum of all the payoffs its neighbors collect against it. In our model, the performance of an individual is determined by both its payoff and local contribution through a linear combination. We demonstrate that the present mechanism can produce very robust cooperative behavior in both games. Furthermore, we provide theoretical analysis based on mean-field approximation, and find that the analytical predictions are qualitatively consistent with the simulation results.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Secondary X-Ray Environment in the Lower Atmosphere of the Earth during Monsoon Season over Udaipur City (India) in July-September 2006

S. N. A. Jaaffrey, Shubhra Tiwari

Chin. Phys. Lett. 2009, 26 (8): 089201 . DOI: 10.1088/0256-307X/26/8/089201

Abstract

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We present a study on the secondary x-rays of energy band 2-100keV emitted by the intruded principal pollutant components (gases and minerals) brought up in the lower atmosphere by dust storms, monsoon drift and the gravitational pull on meteoritic showers. On the ground we employed a 1.5×1 inch2 NaI crystal in a scintillation detector, suitable for the energy range 2-100keV of secondary x-rays, providing better energy resolution than a larger sized crystal. In order to eliminate the radioactive background of the Earth, the detector was well shielded on all sides with the help of the lead (Pb) container, except with a small open window at the top to permit only vertically incident secondary radiation. The results from the data analysis obtained during the monsoon over Udaipur city (India) during the period from July to September (2006) have revealed a linear correlation between dust storm cum monsoon clouds and observed luminosities of secondary x-ray radiation from intruded pollutants. We found intense flux of secondary x-rays from the intruded pollutants when heavy dust and monsoon clouds were brought up by dust storms and monsoon drift in the lower atmosphere over Udaipur city as compared to normal days. Thus, secondary x-rays in the environment provide a tool for investigation of local intrusive pollutant components in the lower atmosphere.

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An Island Coalescence Scenario for Near-Earth Current Disruption in the Magnetotail

MA Zhi-Wei, LU Xing-Qiang

Chin. Phys. Lett. 2009, 26 (8): 089401 . DOI: 10.1088/0256-307X/26/8/089401

Abstract

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A current disruption and dipolarization scenario associated with island coalescences in the near-Earth region is proposed. The thin and elongated current-sheet built up during the growth phase is unstable due to a tearing mode instability that leads to formation of multiple magnetic islands (or magnetic flux ropes in the three dimensional case) in the near-Earth region. The growth rate of the tearing mode should be different in different locations because the rate is in general determined by the external driving force and the local plasma sheet properties. When the rate of the magnetic reconnection in the mid-tail region around 20R_E is much larger than that in other locations, the strong bulk earthward flows resulting from the fast reconnection in the mid-tail drive the earthward convection and the coalescence of the magnetic islands. Consequently, the cross-tail current in the near-Earth region is suddenly disrupted and the geometry of the magnetic field changes from tail-like to dipolar-like in the ideal time scale. This proposed scenario is tested by Hall MHD simulation and is compared with the observations.

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Observational Constraints on Purely Kinetic k-Essence Dark Energy Models

YANG Rong-Jia, GAO Xiang-Ting

Chin. Phys. Lett. 2009, 26 (8): 089501 . DOI: 10.1088/0256-307X/26/8/089501

Abstract

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We consider constraints on purely kinetic k-essence models from the latest observational data (including 182 gold SNIa data, the shift parameter, and the acoustic scale). We find the best-fit values of the parameters are Ω_m=0.37±m0.01 and k₀=0.064±0.013 at 68.3% confidence level. The phase transition from deceleration to acceleration is found to occur at redshift z_q=0~0.48-0.52 in 68.3% confidence level limits. By applying model-comparison statistics (F-test, AIC_c, and BIC), we find that the purely kinetic k-essence scenario is favored over the ΛCDM model by the combined data. These results are also confirmed by combined data 307 SNIa+R+l_a.

Original Articles

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Extended Analysis on New Generalized Chaplygin Gas

WANG Jun, WU Ya-Bo, WANG Di, YANG Wei-Qiang

Chin. Phys. Lett. 2009, 26 (8): 089801 . DOI: 10.1088/0256-307X/26/8/089801

Abstract

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We extend the study of the new generalized Chaplygin gas (NGCG) based on [J. Cosmol. Astropart. Phys. 0601 (2006) 003]. Specifically, we not only discuss the change rates of the energy densities and the energy transfer of this model, but also perform the Om diagnostic to differentiate the ΛCDM model from the NGCG and the GCG models. Furthermore, in order to consider the influence of dark energy on structure formation, we also present the evolution of the growth index in this scenario with interaction.

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Spatially Homogeneous Bianchi Type V Cosmological Model in the Scale-Covariant Theory of Gravitation

Shri Ram, M. K. Verma, Mohd. Zeyauddin

Chin. Phys. Lett. 2009, 26 (8): 089802 . DOI: 10.1088/0256-307X/26/8/089802

Abstract

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We discuss spatially homogeneous and anisotropic Bianchi type-V spacetime filled with a perfect fluid in the framework of the scale-covariant theory of gravitation proposed by Canuto et al. By applying the law of variation for Hubble's parameter, exact solutions of the field equations are obtained, which correspond to the model of the universe having a big-bang type singularity at the initial time t=0. The cosmological model, evolving from the initial singularity, expands with power-law expansion and gives essentially an empty space for a large time. The physical and dynamical properties of the model are also discussed.

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