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Volume 28 Issue 6
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Organization of the Strategy Pattern in Evolutionary Prisoner's Dilemma Game on Scale-Free Networks
CHENG Hong-Yan, YANG Jun-Zhong**
Chin. Phys. Lett. 2011, 28 (6): 060201 .   DOI: 10.1088/0256-307X/28/6/060201
Abstract   PDF(pc) (615KB) ( 463 )
Based on the recently proposed concepts of asymptotic behaviors, i.e. pure cooperator, pure defector and fluctuating strategy, we explore thoroughly the dynamical organization of the strategy pattern in evolutionary prisoner's dilemma game on scale-free networks.
N-Soliton Solutions for the Four-Potential Isopectral Ablowitz–Ladik Equation
CHEN Shou-Ting**, ZHU Xiao-Ming, LI Qi, CHEN Deng-Yuan
Chin. Phys. Lett. 2011, 28 (6): 060202 .   DOI: 10.1088/0256-307X/28/6/060202
Abstract   PDF(pc) (1370KB) ( 582 )
The bilinear form of the four-potential isospectral Ablowitz–Ladik (AL) equation is derived by the dependent variable transformation. The N-soliton solutions of the equation are obtained through the Hirota method. Moreover, the double Casoratian solution is found by means of the double Casoratian technique.
A Direct Linearization Method of the Non-Isospectral KdV Equation
ZHAO Song-Lin**, ZHANG Da-Jun, CHEN Deng-Yuan
Chin. Phys. Lett. 2011, 28 (6): 060203 .   DOI: 10.1088/0256-307X/28/6/060203
Abstract   PDF(pc) (450KB) ( 472 )
Direct linearization method is used to solve the non-isospectral KdV equation. The corresponding singular linear integral equation and the time dependence of measure in the singular linear integral equation are proposed. Furthermore, the solutions to the non-isospectral modified KdV equation are also derived by using the singular linear integral equation of the non-isospectral KdV equation.
Asymptotic Behavior of Periodic Wave Solution to the Hirota–Satsuma Equation
WU Yong-Qi
Chin. Phys. Lett. 2011, 28 (6): 060204 .   DOI: 10.1088/0256-307X/28/6/060204
Abstract   PDF(pc) (462KB) ( 9325 )
The one- and two-periodic wave solutions for the Hirota–Satsuma (HS) equation are presented by using the Hirota derivative and Riemann theta function. The rigorous proofs on asymptotic behaviors of these two solutions are given such that soliton solution can be obtained from the periodic wave solution in an appropriate limiting procedure.
A New Multi-Symplectic Scheme for the KdV Equation
LV Zhong-Quan, XUE Mei, WANG Yu-Shun, **
Chin. Phys. Lett. 2011, 28 (6): 060205 .   DOI: 10.1088/0256-307X/28/6/060205
Abstract   PDF(pc) (561KB) ( 519 )
We propose a new multi-symplectic integrating scheme for the Korteweg-de Vries (KdV) equation. The new scheme is derived by concatenating spatial discretization of the multi-symplectic Fourier pseudospectral method with temporal discretization of the symplectic Euler scheme. The new scheme is explicit in the sense that it does not need to solve nonlinear algebraic equations. It is verified that the multi-symplectic semi-discretization of the KdV equation under periodic boundary conditions has N semi−discrete multi-symplectic conservation laws. We also prove that the full-discrete scheme has N full-discrete multi-symplectic conservation laws. Numerical experiments of the new scheme on the KdV equation are made to demonstrate the stability and other merits for long-time integration.
Blow-up Solutions to a Viscoelastic Fluid System and a Coupled Navier–Stokes/Phase-Field System in R2
ZHAO Li-Yun, GUO Bo-Ling, HUANG Hai-Yang**
Chin. Phys. Lett. 2011, 28 (6): 060206 .   DOI: 10.1088/0256-307X/28/6/060206
Abstract   PDF(pc) (426KB) ( 349 )
The explicit solutions to both the Oldroyd-B model with an infinite Weissenberg number and the coupled Navier–Stokes/phase-field system are constructed by the method of separation of variables. It is found that the solutions blow up in finite time.
Bilinear Bäcklund Transformation for a Variable-Coefficient Kadomtsev–Petviashvili Equation
WU Jian-Ping
Chin. Phys. Lett. 2011, 28 (6): 060207 .   DOI: 10.1088/0256-307X/28/6/060207
Abstract   PDF(pc) (755KB) ( 542 )
Resorting to the Hirota bilinear form, a bilinear Bäcklund transformation (BT) is obtained for a variable-coefficient Kadomtsev–Petviashvili equation. As applications, based on the resulting bilinear BT, single-soliton solutions and two-soliton solutions together with their soliton characteristics are presented for the equation. Furthermore, starting from the bilinear BT, a Lax pair and a new variable-coefficient (2+1)-dimensional nonlinear evolution equation is derived.
Perfect Entanglement Teleportation via Two Parallel W State Channels
WANG Mei-Yu, YAN Feng-Li**
Chin. Phys. Lett. 2011, 28 (6): 060301 .   DOI: 10.1088/0256-307X/28/6/060301
Abstract   PDF(pc) (436KB) ( 455 )
We present a scheme for perfectly teleporting a two-qubit entangled state via two parallel W state channels. The scheme consists of a positive operator valued measurement (POVM), classical communication and the corresponding local unitary operation. How to realize the POVM using unitary operation and projective measurement is explicitly designed.
Sudden Transition between Quantum Correlation and Classical Correlation: the Effect of Interaction between Subsystems
YAN Jun-Yan**, WANG Lin-Cheng, YI Xue-Xi
Chin. Phys. Lett. 2011, 28 (6): 060302 .   DOI: 10.1088/0256-307X/28/6/060302
Abstract   PDF(pc) (723KB) ( 387 )
We study the quantum discord dynamics of a bipartite composite system in the presence of a dissipative environment and investigate the effect of the interaction between the two subsystems. The results show that the interaction can influence the sudden transition between the quantum correlation and the classical correlation and for the maximally mixed marginals initial states, the sudden transition regime will always exist. The entanglements are also discussed in comparison to the quantum discord in describing the quantum correlations.
A Finite Temperature Phase Diagram in Rotating Bosonic Optical Lattices
HUANG Bei-Bing**, WAN Shao-Long
Chin. Phys. Lett. 2011, 28 (6): 060303 .   DOI: 10.1088/0256-307X/28/6/060303
Abstract   PDF(pc) (783KB) ( 390 )
A finite temperature phase diagram of the rotating Bose–Hubbard model, including the crossover between Mott insulator and the normal state, is derived on the frame of the Gutzwiller mean-field theory. In addition, we calculate the critical temperature of superfluid-normal phase transition.
Experimental Violation of Multiple-Measurement Time-Domain Bell's Inequalities
TANG Jian-Shun, LI Yu-Long, LI Chuan-Feng**, XU Jin-Shi, CHEN Geng, ZOU Yang, ZHOU Zong-Quan, GUO Guang-Can
Chin. Phys. Lett. 2011, 28 (6): 060304 .   DOI: 10.1088/0256-307X/28/6/060304
Abstract   PDF(pc) (724KB) ( 467 )
In the original time-domain Bell's inequalities (Leggett-Garg-type inequalities), the physical objective is measured at three time points. When more time points are chosen, several methods can be used to extend these inequalities. We experimentally demonstrate the violation of these extended inequalities using single photons from a self-assembled quantum dot. In general, for each extension, the quantity by which the quantum-mechanics value exceeds the classical limit becomes larger as the number of measurement time points increases. This quantity has a maximum value for the extensions that have the same number of measurement time points. Furthermore, we evaluate the noise tolerance for these extensions with a quantity that is related to the number of standard deviations by which the experimental result surpasses the classical limit.
Non-Markovian Effect on the Classical and Quantum Correlations
XU Guo-Fu**, TONG Dian-Min
Chin. Phys. Lett. 2011, 28 (6): 060305 .   DOI: 10.1088/0256-307X/28/6/060305
Abstract   PDF(pc) (627KB) ( 517 )
We evaluate the dynamics of quantum and classical correlations in the presence of non-Markovian noises. By considering an entangled pair of spins in the noise environment described by Ornstein–Uhlenbeck processes, we show that the quantum discord of some states is completely unaffected by independent Ornstein–Uhlenbeck noises for long intervals of time, and that the inevitable onset of the sudden decrease of the quantum discord can be substantially delayed by the decrease of the noise bandwidth γ, where γ−1=τc defines the environment's finite correlation time of the noise.
Thermodynamics of Charged Ideal Bose Gases in a Trap under a Magnetic Field
FAN Jing-Han, GU Qiang**, GUO Wei
Chin. Phys. Lett. 2011, 28 (6): 060306 .   DOI: 10.1088/0256-307X/28/6/060306
Abstract   PDF(pc) (456KB) ( 417 )
We investigate thermodynamic properties of the rotating Bose gas in a trap, taking the charged ideal Bose gas in a magnetic field as an example. The system is equivalent to a neutral gas in a synthetic magnetic field. It is indicated that the Bose–Einstein condensation temperature is irrelevant to the magnetic field, conflicting with established intuition that the critical temperature decreases with the field increasing. The specific heat and Landau diamagnetization also exhibit intriguing behaviors.
Control of the Entanglement between Two Josephson Charge Qubits
LIAO Qing-Hong, FANG Guang-Yu, WANG Ji-Cheng, AHMAD Muhammad Ashfaq, LIU Shu-Tian**
Chin. Phys. Lett. 2011, 28 (6): 060307 .   DOI: 10.1088/0256-307X/28/6/060307
Abstract   PDF(pc) (522KB) ( 506 )
We consider a model which consists of two coupled superconducting charge qubits by sharing a large Josephson junction. The time evolution of entanglement between two Josephson charge qubits is investigated by employing the concurrence. We examine the influence of the initial mean photon number, the relative phase and the amplitude of the two qubits on the time evolution of entanglement. The results show that the initial mean photon number, the relative phase and the amplitude of the two qubits play an important role in the evolution of entanglement.
Parameters for Cold Collisions of Lithium and Caesium Atoms
Jamieson M. J.**, Ouerdane H.,
Chin. Phys. Lett. 2011, 28 (6): 060308 .   DOI: 10.1088/0256-307X/28/6/060308
Abstract   PDF(pc) (420KB) ( 296 )
We calculate the s-wave scattering length and effective range and the p-wave scattering volume for 7Li atoms interacting with 133Cs atoms via the X1Σ+ molecular potential. The length and volume are found by fitting the log-derivative of the zero energy wave function evaluated at short range to a long range expression that accounts for the leading van der Waals dispersion potential and then incorporating the remaining long range dispersion contributions to first order. The effective range is evaluated from a quadrature formula. The calculated parameters are checked from the zero energy limits of the scattering phase shifts. We comment on ill-conditioning in the calculated s-wave scattering length.
Fractal Basins in the Lorenz Model
I. Djellit**, J. C. Sprott, M. R. Ferchichi
Chin. Phys. Lett. 2011, 28 (6): 060501 .   DOI: 10.1088/0256-307X/28/6/060501
Abstract   PDF(pc) (474KB) ( 363 )
The Lorenz mapping is a discretization of a pair of differential equations. It illustrates the pertinence of computational chaos. We describe complex dynamics, bifurcations, and chaos in the map. Fractal basins are displayed by numerical simulation.
A Rotating Pendulum Linked by an Oblique Spring
CAO Qing-Jie, **, HAN Ning, TIAN Rui-Lan
Chin. Phys. Lett. 2011, 28 (6): 060502 .   DOI: 10.1088/0256-307X/28/6/060502
Abstract   PDF(pc) (1260KB) ( 567 )
We present a novel model which comprises a rotating pendulum linked by an oblique spring pinned to its rigid support. This model provides a cylindrical dynamical system with both smooth and discontinuous regimes depending on the value of a system parameter and also the dynamics transient relying on the coupling strength between the pendulum and the linked spring. The presented system behaves with both standard (smooth) and nonstandard (discontinuous) nonlinear dynamics of equilibrium bifurcations and the periodic patterns when it is unperturbed. Complicated resonant structures of period, quasi-period and stochastic phenomena are presented for the system with unique harmonic perturbation. The chaotic behavior of the system perturbed by both viscous-damping and external excitations is also demonstrated.
Flat Crystal x-ray Spectrometer for Quantitative Spectral Measurement in the 2–5keV Region
ZHAO Yang**, WEI Min-Xi, DENG Bo, ZHU Tuo, HU Zhi-Min, XIONG Gang, SHANG Wan-Li, KUANG Long-Yu, YANG Guo-Hong, ZHANG Ji-Yan, YANG Jia-Min
Chin. Phys. Lett. 2011, 28 (6): 060701 .   DOI: 10.1088/0256-307X/28/6/060701
Abstract   PDF(pc) (634KB) ( 438 )
A technique of flat crystal x-ray spectrometer for quantitative spectral measurement is described. For the flat crystal spectrograph geometry, the quantitative reduction of relating the CCD counts back to the photon flux from the x-ray source is established. The absolute calibrations of the integral diffraction coefficients of the crystal and the CCD sensitivity make it possible to measure absolute photons flux within the energy range of 2000–5000 eV. The uncertainty analysis of the calibrations is carried out to obtain the energy resolved uncertainties of crystal and CCD. Thus, the experimental spectra with spectral resolved intensity uncertainties are available. Then, a performing experiment of laser-produced Ti plasma is carried out and the absolute x-ray spectra with intensity uncertainty less than 8.5% are obtained. The technique is promising for absolute spectral measurement of high temperature plasmas in a kilo-electron-volt region.
A New Model for Quark Mass Matrix
Chin. Phys. Lett. 2011, 28 (6): 061201 .   DOI: 10.1088/0256-307X/28/6/061201
Abstract   PDF(pc) (386KB) ( 430 )
We study the status of S3, i.e. a slightly broken symmetry of quarks and propose a new model in which the S3 symmetry among the three generation up−quarks is slightly broken into the C2 symmetry while the S3 symmetry of the down-quarks is completely broken in a different way.
KKN and KKN Molecular States with I=1/2, 3/2 and JP=1/2+ Studied with Three-Body Faddeev Calculations
JIA Er-Wei, PANG Hou-Rong
Chin. Phys. Lett. 2011, 28 (6): 061401 .   DOI: 10.1088/0256-307X/28/6/061401
Abstract   PDF(pc) (501KB) ( 337 )
Using the Akaishi–Yamazaki (AY) and Hyodo–Weise (HW) effective KK, KN, KK and KN interactions, we study possible existence of KKN and KKN molecule states with I=1/2, 3/2 and JP=1/2+ by means of three−body Faddeev equations. We find that for HW potential, KKN and KKN systems with I=1/2 both are bound hadron molecular states with about 10 MeV binding energy. The relativistic effects of kinetic energy are of the order of 4–5 MeV. AY potential would give larger binding energy because of overestimating KN interaction strength. Although there are attractive interactions in the case of I=3/2, the interaction is too weak to bind the systems.
Neutrino Mass from a Higher-Dimensional Operator
NING Guo-Zhu**, WU Yuan-Bin***
Chin. Phys. Lett. 2011, 28 (6): 061402 .   DOI: 10.1088/0256-307X/28/6/061402
Abstract   PDF(pc) (510KB) ( 425 )
We calculate the neutrino mass induced at one loop in the cascade seesaw mechanism. The ratio between the two neutrino masses, which are respectively generated from an operator of mass dimension (3+4n) occurring at one loop and an operator of dimension (5+4n) at tree level, is also given. Detailed studies show that a relatively low new physics scale could accommodate the tiny neutrino mass of desired order without demanding small couplings. We also find that the ratio will reach order one when the new physics scale is higher than several TeV and n is small. In this case, the contribution to neutrino mass from higher order quantum effects becomes important and cannot be ignored.
The influence of Multi-Step Sequential Decay on Isoscaling and Fragment Isospin Distribution in GEMINI Simulation
ZHOU Pei, TIAN Wen-Dong**, MA Yu-Gang**, CAI Xiang-Zhou, FANG De-Qing, WANG Hong-Wei
Chin. Phys. Lett. 2011, 28 (6): 062101 .   DOI: 10.1088/0256-307X/28/6/062101
Abstract   PDF(pc) (681KB) ( 320 )
Extensive calculations on isoscaling behavior with the sequential-decay model GEMINI are performed for the mediate-heavy nuclei in the mass range A=110 and at excitation energies of up to 3 MeV per nucleon. Isoscaling can still be observed after entire−step decays are considered for the light products as in the only first-step decay process case. Comparison between the products after the first-step decay and the ones after entire-step decay demonstrates that multi-step secondary sequential decay strongly influences the isoscaling parameters α, β as well as the fragment isospin distribution. After entire−step decays, the isoscaling parameters α and β are decreased and the fragment isospin distribution can better reproduce the isospin distribution shape as the experimental data.
Electronic Structures and Spectroscopic Properties of a Novel Iridium (III) Complex with an Ancillary Ligand 2-(4-Trifluoromethyl -2-Hydroxylphenyl)Benzothiazole
LEI Li-Ping, HAO Yu-Ying, **, FAN Wen-Hao, XU Bing-She
Chin. Phys. Lett. 2011, 28 (6): 063101 .   DOI: 10.1088/0256-307X/28/6/063101
Abstract   PDF(pc) (2034KB) ( 416 )
Iridium (III) complexes with 2−phenylpyridine (ppy) have been demonstrated as a type of promising phosphorescence dopant in emitting layers of organic light emitting diodes (OLEDs). In most iridium (III) complexes, there exist the strong spin−orbit coupling between π−orbitals of cyclometalated ligands and 5d orbitals of the centric iridium. We study a novel iridium (III) complex (ppy)2Ir(4−TfmBTZ) with ppy as cyclometalated ligands and 2-(4-trifluoromethyl-2-hydroxylphenyl)benzothiazole (4-TfmBTZ) as an ancillary ligand using the Gaussian 03 program. The geometries, electronic structures and spectroscopic properties of this iridium (III) complex are investigated by density functional theory (DFT) and time−dependent density functional theory (TD-DFT). The results show that the spin-orbit coupling occurs not only between ppy and iridium atom but also between 4-TfmBTZ and iridium atom in this complex. The highest occupied molecular orbital is dominantly localized on the Ir atom and 4-TfmBTZ ligand, while the lowest unoccupied molecular orbital on 4-TfmBTZ ligand. The triplet lowest-lying transition is attributed to the Ir-to-4-TfmBTZ charge-transfer (3MLCT) transition while the sub−low-lying transitions are assigned to the 3MLCT transitions of Ir(ppy)2. The nature of the lowest unoccupied orbital changes from ppy−localized to 4-TfmBTZ-localized and reveals that phosphorescent color of Ir(III) complex can be controlled by the ancillary ligand and substituent.
Improvement on Temperature Measurement of Cold Atoms in a Rubidium Fountain
LÜ, De-Sheng**, QU Qiu-Zhi, WANG Bin, ZHAO Jian-Bo, LIU Liang**, WANG Yu-Zhu
Chin. Phys. Lett. 2011, 28 (6): 063201 .   DOI: 10.1088/0256-307X/28/6/063201
Abstract   PDF(pc) (551KB) ( 514 )
The time-of-flight (TOF) method is one of the most common ways to measure the temperature of cold atoms. In the cold atomic fountain setup, the geometry of the probe beam will introduce the measurement errors to the spatial distribution of cold atomic cloud, which will lead to the measurement errors on atomic temperature. Using deconvolution, we recover the atomic cloud profile from the TOF signal. Then, we use the recovered signals other than the TOF signals to obtain a more accurate atomic temperature. This will be important in estimating the effects of cold atom collision shift and the shift due to transverse cavity phase distribution on an atomic fountain clock.
Asymmetry of Photodetachment of F by Few-Cycle Infrared Laser Fields: Laser-Intensity Effects
BAI Li-Hua**, HOU Lu-Qiang, CUI Ting-Ting, LIU Yu-Heng, WANG Yan, ZHANG Hui-Fang, DENG Dong-Mei
Chin. Phys. Lett. 2011, 28 (6): 063202 .   DOI: 10.1088/0256-307X/28/6/063202
Abstract   PDF(pc) (521KB) ( 339 )
Asymmetry of the photodetachment of F by few-cycle circularly polarized infrared laser fields is studied by using a nonperturbative quantum scattering theory. The asymmetry of photoelectrons emitted to a pair of two opposite directions for low laser peak intensities is found and the dependence of the asymmetry on the laser peak intensity is investigated. It is found that the asymmetry degree varies with the carrier-envelope (CE) phase as a sine-like pattern. The asymmetry degree, the value of the maximal asymmetry degree and the value of the CE phase corresponding to the maximal asymmetry degree vary with the laser peak intensity dramatically. At higher laser intensities, the asymmetry is still distinctive for relatively-long few-cycle pulses. It provides a possible means to measure the CE phase of laser pulses at lower intensities.
Raman Sideband Cooling of Two-Valence-Electron Fermionic Atoms
LI Guo-Hui, XU Xin-Ye**
Chin. Phys. Lett. 2011, 28 (6): 063203 .   DOI: 10.1088/0256-307X/28/6/063203
Abstract   PDF(pc) (464KB) ( 395 )
We propose a method for laser cooling two-valence-electron fermionic atoms. Our protocol employs resolved-sideband cooling on the stimulated Raman transition between the two magnetic sublevels (m=F and m=F−1) of the ground state with total angular momentum F. The optical pumping from m=F−1 to 1P1 are used to decouple atoms in the m=F−1 state. We calculate the Raman coupling generated by an engineered optical lattice. The result shows that it is possible to laser cool the two-valence-electron fermionic atoms to the ground state. The atoms in the ground state provide a new system for quantum optics.
Interferences in Photodetached Electron Spectra from a Linear Tetra-Atomic Negative Ion
A. Rahman, Iftikhar Ahmad*, A. Afaq, M. Haneef
Chin. Phys. Lett. 2011, 28 (6): 063301 .   DOI: 10.1088/0256-307X/28/6/063301
Abstract   PDF(pc) (496KB) ( 394 )
Photo-detached electron spectra from a hypothetical linear tetra-atomic negative ion is obtained. A plane polarized laser parallel to the axis of the molecular ion is used to knock off the loosely bound electron. The spectrum of the detached-electron flux shows strong interference peaks, while the number of peaks increases with the increase in the photon energy. Strong oscillations are also observed in the total photodetachment cross section spectrum. The frequency of the oscillations increases with the increase in the distance between the successive atoms d in the linear chain. These quantum interference effects vanish for very large d or very high photon energy.
Theoretical Study of the Stereodynamics of the Reaction C(3P)+CH(X2Π) and Its Isotopic Variants
WU Ji-Cheng, WANG Mei-Shan**, YANG Chuan-Lu, LI Xiao-Hu, CHEN Xiao-Qiong
Chin. Phys. Lett. 2011, 28 (6): 063401 .   DOI: 10.1088/0256-307X/28/6/063401
Abstract   PDF(pc) (1159KB) ( 348 )
Vector correlations between products and reagents of the reaction C+CH and the isotopic variant reactions are calculated by employing the quasi-classical trajectory method based on the adiabatically 12A'' double−many-body-expansion potential-energy surface computed and numerically fitted by Boggio-Pasqua et al. The normalized polarization-dependent differential cross-sections and the distributions of P(θr), P(φr) and P(θrr) at the selected collision energy are discussed in detail. The values of the product rotational alignment parameter 〈P2 (j'k)〉 are also calculated and plotted as functions of the collision energy in the range 0.005–0.5 eV. The computed results show that the rotational polarizations of the product present pronounced different characters as the mass substituted atom increasing.
Laser Cooling of 87Rb to 1.5µK in a Fountain Clock
WANG Bin, LÜ, De-Sheng**, QU Qiu-Zhi, ZHAO Jian-Bo, LI Tang, LIU Liang, **, WANG Yu-Zhu
Chin. Phys. Lett. 2011, 28 (6): 063701 .   DOI: 10.1088/0256-307X/28/6/063701
Abstract   PDF(pc) (633KB) ( 552 )
We report an experiment on the adiabatic cooling of 87Rb atoms in an atomic fountain to a temperature as low as 1.5 μK, which is roughly twice the recoil temperature. The atomic fountain has the (1,1,1) optical geometry for cooling and launching of cold atoms. The atoms are first cooled in an optical molasses of 6 beams to 3.4 μK by polarization gradient geometry and then are adiabatically cooled by decreasing the intensity of laser from 1.8Is per beam to zero in 1 ms during the launching of cold atoms. We also study the dependences of atomic temperature on different laser parameters. The method we used is useful in any cold atom physics experiment.
The research of Digital Holographic Object Wave Field Reconstruction in Image and Object Space
LI Jun-Chang**, PENG Zu-Jie, FU Yun-Chang
Chin. Phys. Lett. 2011, 28 (6): 064201 .   DOI: 10.1088/0256-307X/28/6/064201
Abstract   PDF(pc) (736KB) ( 365 )
For conveniently detecting objects of different sizes using digital holography, usual measurements employ the object wave transformed by an optical system with different magnifications to fit charge coupled devices (CCDs), then the object field reconstruction involves the diffraction calculation of the optic wave passing through the optical system. We propose two methods to reconstruct the object field. The one is that, when the object is imaging in an image space in which we reconstruct the image of the object field, the object field can be expressed according to the object-image relationship. The other is that, when the object field reaching CCD is imaged in an object space in which we reconstruct the object field, the optical system is described by introducing matrix optics in this paper. The reconstruction formulae which easily use classic diffraction integral are derived. Finally, experimental verifications are also accomplished.
The Dynamical Casimir Effect versus Collective Excitations in Atom Ensemble
ZHANG Xue, ZHENG Tai-Yu**, TIAN Tian, PAN Shu-Mei**
Chin. Phys. Lett. 2011, 28 (6): 064202 .   DOI: 10.1088/0256-307X/28/6/064202
Abstract   PDF(pc) (1872KB) ( 362 )
The Dynamical Casimir effect and collective excitations in atom ensemble are investigated in a non-stationary cavity. The results show that the dynamical Casimir effect leads to the collective excitations of atom ensemble due to absorption of the created photons. This remarkable feature indicates that the atom ensemble can serve as a detector for the process of photon production in a non-stationary cavity. Therefore by measuring the collective excitations of the atom ensemble, the dynamical Casimir effect can indirectly be verified.
Properties of the Measurement Phase Operator in Dual-Mode Entangle Coherent States
HOU Shen-Yong**, YANG Kuo
Chin. Phys. Lett. 2011, 28 (6): 064203 .   DOI: 10.1088/0256-307X/28/6/064203
Abstract   PDF(pc) (745KB) ( 352 )
A class of measurement phase operators of dual-mode is defined and their properties in a class of entangle coherent states are investigated. Numerical results indicate that the entangle coherent states display some non-classical squeezed effects.
Refraction Characteristics of Cold Plasma Thin Film as a Left-Handed Metamaterial
Cumali Sabah
Chin. Phys. Lett. 2011, 28 (6): 064204 .   DOI: 10.1088/0256-307X/28/6/064204
Abstract   PDF(pc) (391KB) ( 819 )
A methodical analysis of refraction characteristics of a plane wave with any arbitrary polarization by a cold plasma thin film as a left-handed metamaterial (CPTF-LHM) which has simultaneously negative permittivity and permeability is presented. Numerical calculations are performed by the transfer matrix method using an in-house developed simulation program code. The results strongly recommend a possibility of manufacturing anti-reflection and/or total-transmission coatings and filters for a wide frequency range and/or by tuning the fraction of thickness of the CPTF-LHM.
Terahertz Waveforms Manipulation by Two Orthogonal-Polarized Femtosecond Pulses
LI De-Hua, **, MA Jian-Jun, ZHOU Wei, LIU Sheng-Gang
Chin. Phys. Lett. 2011, 28 (6): 064205 .   DOI: 10.1088/0256-307X/28/6/064205
Abstract   PDF(pc) (469KB) ( 487 )
We present a method of terahertz generation in which both the amplitude and polarity of the terahertz pulse can be manipulated. A pair of temporally separated and orthogonally polarized collinear propagating femtosecond pulses with the same central frequencies are focused onto a (110) oriented ZnTe crystal. By adjusting the relative time delay between the pulses, the amplitude and polarity of the generated terahertz pulse based on difference frequency generation can be controlled. Theoretical derivation and simulation based on the one-dimensional propagation equation of the terahertz wave are carried out under simplified conditions of perfect phase matching, plane-wave approximation and no absorption.
A Multifrequency Cloak with a Single Shell of Negative Index Metamaterials
LI Pei-Ning, LIU You-Wen**, MENG Yun-Ji, ZHU Min-Jun
Chin. Phys. Lett. 2011, 28 (6): 064206 .   DOI: 10.1088/0256-307X/28/6/064206
Abstract   PDF(pc) (731KB) ( 518 )
We propose an invisibility multifrequency cloak with a single shell of negative index metamaterials (NIMs) based on the scattering cancellation cloaking theory. Theory and simulation results show that the cloak can reduce the total scattering cross section at multiple frequencies by exploiting the frequency dispersion of the permittivity and permeability simultaneously. It may provide a potential way to design a multifrequency cloak.
Broadband Asymmetric Conical Emission via Cascaded Second-Order Nonlinear Polarization during the Propagation of Femtosecond Laser Pulses in a BBO Crystal
WEN Jing, JIANG Hong-Bing**, YU Jing, YANG Hong, GONG Qi-Huang**
Chin. Phys. Lett. 2011, 28 (6): 064207 .   DOI: 10.1088/0256-307X/28/6/064207
Abstract   PDF(pc) (836KB) ( 351 )
We investigate the propagation of femtosecond laser pulses in a 5-mm-thick BBO crystal along the direction of type-I phase-matched second-harmonic generation. An intensity-asymmetric broadband conical emission (500–2000 nm) is demonstrated when a suitable chirp is introduced. It is generated by optical parametric amplification pumped by the second-harmonic light and seeded by the fundamental light which is broadened by cascaded nonlinear processes during second-harmonic generation.
Preprocessing-Free All-Optical Clock Recovery from NRZ and NRZ-DPSK Signals Using an FP-SOA Based Active Filter
WANG Fei, **, ZHANG Xin-Liang, YU Yu, XU En-Ming
Chin. Phys. Lett. 2011, 28 (6): 064208 .   DOI: 10.1088/0256-307X/28/6/064208
Abstract   PDF(pc) (655KB) ( 396 )
We demonstrate a simple scheme to perform all-optical clock recovery from the input nonreturn-to-zero (NRZ) and nonreturn-to-zero differential phase shifted keying (NRZ-DPSK) data, which are avoided using any preprocessing measures. A multi-quantum-well Fabry-Pérot semiconductor optical amplifier plays the dual role of the data format converter and the clock recovery device. Using this scheme, a stable and low jitter 35.80-GHz optical clock pulse sequence is directly extracted out from the input NRZ or NRZ-DPSK data. This scheme has some distinct advantages such as simple device fabrication, transparence to data format, multiwavelength operation, free preprocessing and convenient tuning. Potential powerful adaptability of this scheme is very important for next-generation optical networks, in which there exist various modulation formats and the used devices are required to be transparent to data formats.
High-Power Terahertz Radiation Based on a Compact Eudipleural THz-Wave Parametric Oscillator
LI Zhong-Yang, **, YAO Jian-Quan, LÜ, Da, XU De-Gang, WANG Jing-Li, BING Pi-Bin,
Chin. Phys. Lett. 2011, 28 (6): 064209 .   DOI: 10.1088/0256-307X/28/6/064209
Abstract   PDF(pc) (586KB) ( 396 )
Tunable high-power THz-wave radiation is achieved via a compact eudipleural THz-wave parametric oscillator. The maximum THz-wave output is 1.164 V at 1.755 THz when the pump energy is 90 mJ. In the experiments we find that the maximum output of THz-wave moves to the high frequency band as the pump energy increases and this phenomenon is reasonably explained. The polarization characteristics of the THz-wave are analyzed.
Green Upconversion Luminescence in Er3+/Yb3+ Codoped CaWO4 Polycrystals
XU Yan-Ling**, ZHAO Hong, WANG Rui, ZHANG Chun-Yu
Chin. Phys. Lett. 2011, 28 (6): 064210 .   DOI: 10.1088/0256-307X/28/6/064210
Abstract   PDF(pc) (666KB) ( 443 )
CaWO4 polycrystals with fixed Yb3+ and various Er3+ concentrations are synthesized via the high temperature solid state method. The crystal structure of the polycrystals is characterized by means of x−ray diffraction. The upconversion properties of the polycrystals under the 980 nm excitation are investigated. Intense emission bands centered at 530 nm and 552 nm correspond to the transitions 2H11/24I15/2 and 4S3/>24I15/2 of Er3+, respectively. The dependence of intensity of the green emission on the pump power and possible upconversion mechanism are discussed. Quantitative analysis of dependence of upconversion emission intensity on the pump power of a laser diode indicates that two-photon processes are responsible for both 530 nm and 552 nm green upconversion emissions.
Comparative Studies on the Laser Damage Resistance of Ta2O5 and Nb2O5 Films Performed under Different Electron Beam Currents
XU Cheng, **, XU Lin-Min, ZHANG Han-Zhuo, QIANG Ying-Huai, ZHU Ya-Bo, LIU Jiong-Tian, SHAO Jian-Da
Chin. Phys. Lett. 2011, 28 (6): 064211 .   DOI: 10.1088/0256-307X/28/6/064211
Abstract   PDF(pc) (1151KB) ( 609 )
Ta2O5 and Nb2O5 films are deposited by conventional e−beam method under different electron beam currents. The optical transmittance, chemical composition, absorption, scattering, surface topography and laser-induced damage threshold (LIDT) of the films are comparatively studied. It is shown that the increase of electron beam current results in a decrease of the optical transmittance and stoichiometry, whereas it increases the absorption, scattering and rms roughness for both Ta2O5 and Nb2O5 films. However, the LIDT increases first and then decreases with the increase of electron beam current. In addition, the annealing improves the optical transmittance, stoichiometry and LIDT for the two kinds of films. Both the effects of electron beam current and annealing on the LIDT can be mainly attributed to three factors: substoichiometric defects, structural defects and adhesive force. Furthermore, the comparative results indicate that the laser damage resistance of Ta2O5 is lower than that of Nb2O5.
A 40-Gbit/s 1-to-2 Photonic Data Distributor Employing a Single Semiconductor Optical Amplifier
ZHANG Yin, DONG Jian-Ji**, LEI Lei, HE Hao, HUANG De-Xiu, ZHANG Xin-Liang**
Chin. Phys. Lett. 2011, 28 (6): 064212 .   DOI: 10.1088/0256-307X/28/6/064212
Abstract   PDF(pc) (478KB) ( 309 )
A simple design of 1-to-2 photonic data distributor is proposed. A proof-of-concept experiment is performed at 40 Gbit/s employing four-wave mixing and cross gain modulation in a single semiconductor optical amplifier. Correct output logic signals with high extinction ratios (over 11 dB) and clear open eyes are obtained, without using any additional input light beam. The scheme would be a promising candidate for future ultrafast all-optical signal processing applications.
Entangling a Series of Trapped Ions by Moving Cavity Bus
ZHANG Miao, JIA Huan-Yu, WEI Lian-Fu, **
Chin. Phys. Lett. 2011, 28 (6): 064213 .   DOI: 10.1088/0256-307X/28/6/064213
Abstract   PDF(pc) (481KB) ( 320 )
Entangling multiple qubits is one of the central tasks of quantum information processing. We propose an approach to entangle a number of cold ions (individually trapped in a string of microtraps) by a moved cavity. The cavity is pushed to include the ions one by one with a uniform velocity and thus the information stored in former ions could be transferred to the latter ones by such a moving cavity bus. Since the positions of the trapped ions are precisely located, the strengths and durations of the ion-cavity interactions can be exactly controlled. As a consequence, by properly setting the relevant parameters, typical multi-ion entangled states, e.g., W state for 10 ions, could be deterministically generated. The feasibility of the proposal is also discussed.
Fiber Nonlinearity Post-Compensation by Optical Phase Conjugation for 40Gb/s CO-OFDM Systems
QIAO Yao-Jun**, LIU Xue-Jun, JI Yue-Feng
Chin. Phys. Lett. 2011, 28 (6): 064214 .   DOI: 10.1088/0256-307X/28/6/064214
Abstract   PDF(pc) (607KB) ( 765 )
Fiber nonlinearity impairments in a 40-Gb/s coherent optical orthogonal frequency division multiplexing (CO-OFDM) system are post-compensated for by a new method of fiber nonlinearity post-compensation (FNPC). The FNPC located before the CO-OFDM receiver includes an optical phase conjugation (OPC) unit and a subsequent 80-km-high nonlinear fiber (HNLF) as a fiber nonlinearity compensator. The OPC unit is based on a four wave mixing effect in a semiconductor optical amplifier. The fiber nonlinearity impairments in the transmission link are post-compensated for after OPC by transmission through the HNLF with a large nonlinearity coefficient. Simulation results show that the nonlinear threshold (NLT) (for Q> 10 dB) can be increased by about 2.5 dB and the maximum Q factor is increased by about 1.2 dB for the single−channel 40-Gb/s CO-OFDM system with periodic dispersion maps. In the 50-GHz channel spacing wavelength-division-multiplexing system, the NLT increases by 1.1 dB, equating to a 0.7 dB improvement for the maximum Q factor.
The Optimization of Dispersion Properties of Photonic Crystal Fibers Using a Real-Coded Genetic Algorithm
YIN Guo-Bing, LI Shu-Guang**, LIU Shuo, WANG Xiao-Yan
Chin. Phys. Lett. 2011, 28 (6): 064215 .   DOI: 10.1088/0256-307X/28/6/064215
Abstract   PDF(pc) (760KB) ( 441 )
A real-coded genetic algorithm (GA) combined with a fully vectorial effective index method (FVEIM) is employed to design structures of photonic crystal fibers (PCFs) with user defined dispersion properties theoretically. The structures of PCFs whose solid cores are doped GeO2 with zero−dispersions at 0.7–3.9 μm are optimized and the flat dispersion ranges through the R+L+C band and the negative dispersion is 1576.26 pskm−1nm−1 at 1.55 μm. Analyses show that the zero−dispersion wavelength (ZDW) could be one of many ZDWs for the same fiber structure; PCFs could alter the dispersion to be flattened through the R+L+C band with a single air-hole diameter; and negative dispersion requires high air filling rate at 1.55 μm. The method is proved to be elegant for solving this inverse problem.
A Baseline-Free Defect Imaging Technique in Plates Using Time Reversal of Lamb Waves
Hyunjo Jeong**, Sungjong Cho, Wei Wei
Chin. Phys. Lett. 2011, 28 (6): 064301 .   DOI: 10.1088/0256-307X/28/6/064301
Abstract   PDF(pc) (556KB) ( 469 )
We present an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves. We first consider the flexural wave (A0 mode) propagation in a plate containing a defect, and reception and time reversal process of the output signal at the receiver. The received output signal is then composed of two parts: a directly propagated wave and a scattered wave from the defect. The time reversal of these waves recovers the original input signal, and produces two additional sidebands that contain the time-of-flight information on the defect location. One of the side-band signals is then extracted as a pure defect signal. A defect localization image is then constructed from a beamforming technique based on the time-frequency analysis of the side band signal for each transducer pair in a network of sensors. The simulation results show that the proposed scheme enables the accurate, baseline-free imaging of a defect.
A Pair Correlation Function Characterizing the Anisotropy of Force Networks
SUN Qi-Cheng**, JI Shun-Ying
Chin. Phys. Lett. 2011, 28 (6): 064501 .   DOI: 10.1088/0256-307X/28/6/064501
Abstract   PDF(pc) (894KB) ( 394 )
Force networks may underlie the constitutive relations among granular solids and granular flows and inter-state transitions. However, it is difficult to effectively describe the anisotropy of force networks. We propose a new pair correlation function g(r,θ) to describe the characteristic lengths and orientations of force chains that are composed of particles with contact forces greater than the threshold values. A formulation g(r,θ)≈a(r)+b(r)cos2(θ−π/2) is used to fit the g(r,θ) data. The characteristic lengths and orientations of force networks are then elucidated.
Measuring Stress Distributions of Orthotropic Composite Material in Plane Stress State by the Lock-in Infrared Thermography Technique
LI Xu-Dong**, WANG Wei-Bo, LI Yong-Sheng, WU Dong-Liu
Chin. Phys. Lett. 2011, 28 (6): 064601 .   DOI: 10.1088/0256-307X/28/6/064601
Abstract   PDF(pc) (1206KB) ( 535 )
Feasibility of measuring stress distributions of orthotropic composite materials and structures in plane stress state by the lock-in infrared thermography technique is analyzed and stress distributions of a lap joint structure made of a kind of glass reinforced plastic composite lamination plates under tensile loadings are obtained by the lock-in infrared thermography technique. Feasibility and credibility of using this technique to measure stress distributions of orthotropic composite materials and structures in plane stress state are proved by comparing the results with the data given by the digital speckle correlation method.
A Void Growth Model Considering the Bauschinger Effect and Its Application to Spall Fracture
CHEN Qian-Yi, LIU Kai-Xin, **
Chin. Phys. Lett. 2011, 28 (6): 064602 .   DOI: 10.1088/0256-307X/28/6/064602
Abstract   PDF(pc) (651KB) ( 546 )
A void growth model considering the Bauschinger effect (BE) is proposed for ductile materials sustaining impact loading. Numerical simulations of two high-velocity impact problems are carried out by our newly developed Eulerian programs. The proposed model is tested by a plate impact problem and a qualitative agreement with the experiment is obtained. Then a more complicated problem, a plate impacted by a spherical projectile at a velocity of 6.0 km/s, is simulated. The numerical results are in better accordance with the experimental data when the BE is considered. The proposed model reveals that the BE has an obvious effect on the spall process.
A Numerical Study of Temporal Mixing Layer with Three-Dimensional Mortar Spectral Element Method
ZHANG Xu**, LIU Jin-Hong, Jonathan W. N.
Chin. Phys. Lett. 2011, 28 (6): 064701 .   DOI: 10.1088/0256-307X/28/6/064701
Abstract   PDF(pc) (476KB) ( 391 )
We investigate a set of well-posed interface conditions of viscous fluxes of Navier–Stokes equations, extend them to three-dimensional Navier–Stokes equations and successfully study a temporally turbulent mixing layer. The evolution of a large vortex structure and the non-dimensional statistical quantities in the mixing layer are numerically analyzed. The span-wise energy spectrum of the mixing layer exhibits wide band features, which means that the simulation generates the desired amount of small scales. These results show that too many small scales are present due to insufficient dissipation and the amount of large scales is low, indicating too much dissipation for large-scale structures.
The Effect of Mach Number on Turbulence Behaviors in Compressible Boundary Layers
WANG Li, LU Xi-Yun**
Chin. Phys. Lett. 2011, 28 (6): 064702 .   DOI: 10.1088/0256-307X/28/6/064702
Abstract   PDF(pc) (506KB) ( 496 )
The effects of Mach number on turbulence behaviors are investigated by means of direct numerical simulation of compressible turbulent boundary layers with the free-stream Mach numbers 2, 4 and 6. Some typical turbulent quantities, including the velocity and vorticity fluctuations, intermittency, sweep and ejection events and turbulent kinetic energy budget, are analyzed. The turbulence intensities are significantly decreased with the increasing Mach number. The onset of intrinsic intermittency occurs nearer the wall for a higher Mach number. The ejection event is more frequent and the sweep event becomes less frequent. Moreover, the magnitudes of turbulent kinetic energy production, diffusion and transport terms are increased and the solenoidal dissipation is slightly decreased as the Mach number is increased.
Space-Resolved Diagnosis for Electron Temperature of Laser-Produced Aluminum Plasma
ZHAO Yang**, DENG Bo, XIONG Gang, HU Zhi-Min, WEI Min-Xi, ZHU Tuo, SHANG Wan-Li, LI Jun, YANG Guo-Hong, ZHANG Ji-Yan, YANG Jia-Min
Chin. Phys. Lett. 2011, 28 (6): 065201 .   DOI: 10.1088/0256-307X/28/6/065201
Abstract   PDF(pc) (800KB) ( 369 )
The K−shell emission spectra of laser-produced aluminum plasma are measured by a space-resolved spectrometer consisting of a flat crystal spectrometer with a 20 μm wide space−resolved slit. By using the approximation of the steady collisional-radiative equilibrium model, the interstage line intensity ratios of Ly-α resonance line to He−α resonance line are given as a function of electron temperature. The spectra profiles are decomposed to resonance line and the overlapped high-order satellites manifold. Thus reliable electron temperature is deduced from the interstage line intensity ratios of the decomposed resonance lines. The results of spaced-resolved temperature are compared with the hydrodynamic simulations. The diagnostics of electron temperature for laser-produced plasma is developed.
Charge and Mass Effects on Low Energy Ion Channeling in Carbon Nanotubes
LI Yong, ZHENG Li-Ping, ZHANG Wei**, XU Zi-Jian**, REN Cui-Lan, HUAI Ping, ZHU Zhi-Yuan
Chin. Phys. Lett. 2011, 28 (6): 066101 .   DOI: 10.1088/0256-307X/28/6/066101
Abstract   PDF(pc) (558KB) ( 430 )
Channeling phenomena of He, Ne, Ar and Kr ions at energy (200–5000 eV) in single-wall carbon nanotubes (SWCNTs) are investigated by molecular dynamics simulation with analytical potentials. The critical angles for the particles to be channeled in an SWCNT are analyzed. In the incident energy range of 200–5000 eV, it is found that the ion energy dependence of the critical angle obeys an improved Lindhard equation which is closely related to the ratio of nuclear charge number to atomic mass Z/M. The critical angle for different types of ions channeling in SWCNTs is determined by both the atomic nuclear charge and mass.
Ne2+ Ion Irradiation Induced Swelling Effects in Pyrochlore Ho2Ti2O7 by Using a GIXRD Technique
LI Yu-Hong, **, XU Chun-Ping, GAO Chao, WANG Zhi-Guang
Chin. Phys. Lett. 2011, 28 (6): 066102 .   DOI: 10.1088/0256-307X/28/6/066102
Abstract   PDF(pc) (711KB) ( 561 )
We carry out 400 keV Ne2+ ion irradiation damage experiments at cryogenic temperature (about 77 K) on polycrystalline Ho2Ti2O7 pyrochlore. The irradiation fluences range from 2×1014 to 1.3×1015 ions/cm2, corresponding to the peak ballistic displacement damage of 0.075–0.487 in units of displacement per atom (dpa). The value indicates the statistical average of the fractional number of lattice atoms which have experienced a lattice displacement. Irradiation−induced structural evolution is examined by using grazing incidence x-ray diffraction (GIXRD) at x-ray angles γ=0.25° and 3°. It is found that the irradiated layer is volumetrically swelled as compared with the underlying non-irradiated substrate and the volume increase in the irradiated layer is contributed mainly to the irradiated ion fluence.
The Phase Transition of Nematic Liquid Crystal Cells Bounded by Surfactant-Laden Interfaces
ZENG Ming-Ying, CUI Wei, TAN Xiao-Qin, WU Chen-Xu**
Chin. Phys. Lett. 2011, 28 (6): 066103 .   DOI: 10.1088/0256-307X/28/6/066103
Abstract   PDF(pc) (681KB) ( 521 )
Taking into account the surface-coupling strength effect, we discuss the phase transitions of a finite thickness cell bounded by surfactant-laden interfaces in a magnetic field perpendicular to the substrate and it is compared with that of a semi-infinite system. It is found that the larger the thickness, the closer the three-dimensional phase transition surface of the finite system to that of the semi-infinite one. The simulation also shows that when a magnetic field is applied to a nematic semi-infinite sample, an orientational phase transition first takes place close to the interface and then extends to the inner space as the temperature increases.
Diameter and Temperature Dependence of Thermal Conductivity of Single-Walled Carbon Nanotubes
PAN Rui-Qin
Chin. Phys. Lett. 2011, 28 (6): 066104 .   DOI: 10.1088/0256-307X/28/6/066104
Abstract   PDF(pc) (499KB) ( 1188 )
Temperature and diameter dependence of the thermal conductivity of several armchair single-walled carbon nanotubes (SWNTs) are studied by nonequilibrium molecular dynamics method with Brenner II potential. The thermal conductivities are calculated at temperatures from 100 K to 600 K. It is found that the thermal conductivity decreases as the temperature increases and increases as the diameter of SWNT increases. The results demonstrate that these two phenomena are due to the onset of the Umklapp process.
The Effect of Atomic Vacancies and Grain Boundaries on Mechanical Properties of GaN Nanowires
XIE Shi-Feng, CHEN Shang-Da**, SOH Ai-Kah
Chin. Phys. Lett. 2011, 28 (6): 066201 .   DOI: 10.1088/0256-307X/28/6/066201
Abstract   PDF(pc) (1242KB) ( 602 )
Molecular dynamics simulations are carried out to investigate the influences of various defects on mechanical properties of wurtzite GaN nanowires by adopting the empirical Stillinger-Weber potential. Different types of vacancies and grain boundaries are considered and the uniaxial loading condition is implemented along the [001] direction. It is found that surface defects have less impact on Young's moduli and critical stresses of GaN nanowires compared with random defects. The grain boundary normal to the axial direction of a nanowire would not significantly affect Young's moduli of nanowires. However, the inversion domain grain boundaries with and without wrong bonds would significantly lower Young's moduli of GaN nanowires. In addition, the inversion domain grain boundary affects the critical stress of GaN nanowires more than the grain boundary with interface normal to the axial direction of the nanowire.
Thermal Stability and Growth Behavior of Erbium Silicide Nanowires Self-Assembled on a Vicinal Si(001) Surface
DING Tao, SONG Jun-Qiang, LI Juan, CAI Qun**
Chin. Phys. Lett. 2011, 28 (6): 066801 .   DOI: 10.1088/0256-307X/28/6/066801
Abstract   PDF(pc) (848KB) ( 378 )
Erbium silicide nanowires are self-assembled on vicinal Si(001) substrates after electron beam evaporation and post annealing at 630°C In−situ scanning tunneling microscopy investigations manifest that the nanowires will successively shrink and transform into a nanoisland with annealing prolonged. Meanwhile, a structural transition from hexagonal AlB2 phase to tetragonal ThSi2 phase is revealed with high-resolution transmission electron microscopy. It is also found that the nanowires gradually expand to embed into the substrates during the growth process, which has much influence on the shape instability of nanowires. Additionally, a multiple deposition-annealing treatment is given as a novel growth method to strengthen the controlled fabrication of nanowires.
Imaging of the Al Structure of an Ultrathin Alumina Film Grown on Cu-9 at.%Al(111) by STM
ZHANG Yun, YU Ying-Hui**, SHE Li-Min, QIN Zhi-Hui, CAO Geng-Yu
Chin. Phys. Lett. 2011, 28 (6): 066802 .   DOI: 10.1088/0256-307X/28/6/066802
Abstract   PDF(pc) (690KB) ( 435 )
An ultrathin alumina film grown on a Cu-9 at.%Al(111) substrate is investigated using low-temperature scanning tunneling microscopy and spectroscopy. The topographic images show a zigzagged corrugation characterized by the heptagonal and pentagonal organization of interfacial aluminum atoms and by a dependence on the bias voltage. Furthermore, the dI/dV maps and the spectrum reveal an unoccupied state locating at about +0.26 eV, which most likely originates from the aluminum-oxygen hybridization and is possibly responsible for the heptagonal and pentagonal arrangements of Al atoms.
Two-Dimensional Cavity Resonant Modes of Si Based Bragg Reflection Ridge Waveguide
CHEN San, **, Lu Hong-Yan, CHEN Kun-Ji**, XU Jun, MA Zhong-Yuan, LI Wei, HUANG Xin-Fan
Chin. Phys. Lett. 2011, 28 (6): 066803 .   DOI: 10.1088/0256-307X/28/6/066803
Abstract   PDF(pc) (660KB) ( 396 )
Si-based ridge-waveguides with Bragg reflectors are fabricated based on our method. Three resonant peaks could be obviously identified from the photoluminescence spectra, and field patterns of these resonant peaks, simulated by the finite difference time domain (FDTD) method, confirm that these peaks originate from cavity resonances. The resonant wavelengths and spatial angular distribution are given by the resonant models, which agree well with the experimental data. Experimentally, a simple method is proposed to testify the experimental and theoretical results. Such devices based on Bragg reflectors may have potential applications in light-emitting diodes, lasers and integrated photonic circuits.
First-Principles Calculations of the Structural, Electronic and Optical Properties of BaZrxTi1−xO3 (x=0, 0.25, 0.5, 0.75)
ZHAO Xin-Yin, WANG Yue-Hua**, ZHANG Min, ZHAO Na, GONG Sai, CHEN Qiong
Chin. Phys. Lett. 2011, 28 (6): 067101 .   DOI: 10.1088/0256-307X/28/6/067101
Abstract   PDF(pc) (1251KB) ( 568 )
The pseudo-potential plane wave (PP-PW) method with the generalized gradient approximation (GGA) is used to calculate the structural, electronic and optical properties of cubic and tetragonal BaZrxTi1−xO3(BZT) (x= 0, 0.25, 0.5, 0.75). The calculated structural parameters are found to be in good agreement with the experimental data. The energy band structure density of states (DOS) are obtained, which indicates that the Zr substitute can induce the band gap widening of BaTiO3. Furthermore, their optical properties are also calculated and analyzed in detail. It is shown that the dielectric imaginary part of BZT decreases as x (Zr concentration) increases.
A Comparative Investigation on the JT Effect in Triangular Compounds of NaMnO2, NaNiO2 and NaTiO2
OUYANG Sheng-De, QUAN Ya-Min, LIU Da-Yong, ZOU Liang-Jian**
Chin. Phys. Lett. 2011, 28 (6): 067102 .   DOI: 10.1088/0256-307X/28/6/067102
Abstract   PDF(pc) (538KB) ( 624 )
We present a study on the Jahn–Teller (JT) distortions of the TiO6, NiO6 and MnO6 complexes in NaTiO2, NaNiO2 and NaMnO2 triangular compounds with a C2/m structure. The JT vibronic normal modes are found to be Q3, Q'4 and Q6 by the group symmetry on the C2/m structure. The magnitude of the normal coordinates (Q3, Q'4, Q6) and the structural parameters of distorted octahedra MO6 (M=Ti, Ni, Mn) are obtained and in good agreement with experimental data. The energy level splitting of 3d orbitals and the highest occupied molecular orbital (HOMO) character in the MO6 complex are also calculated in accordance with the JT distortions. These results provide a first insight into the groundstate and magnetic properties of distorted triangular compounds AMO2.
Effect of Water Concentration on the Characterization of Sprayed Cd0.5Zn0.5S Films
Sur S., Ö, ztürk Z., Ö, zta&scedil, M.**, Bedir M., Ö, zdemir Y.
Chin. Phys. Lett. 2011, 28 (6): 067103 .   DOI: 10.1088/0256-307X/28/6/067103
Abstract   PDF(pc) (421KB) ( 365 )
Cd0.5Zn0.5S film samples are prepared by a spray pyrolysis technique using aqueous solutions of CdCl2, ZnCl2, SC(NH2)2 and deionized water, which are atomized using compressed air as the carrier gas onto glass substrates with different water (H2O) concentrations. H2O is used as the activator. The prepared films are characterized by means of XRD and UV−VIS spectroscopy. Experimental results reveal that the structures and properties of the films are greatly affected by the H2O content. Water in a certain range of concentrations promotes the formation of the Cd0.5Zn0.5S films and improves the properties of the films.
Voronoi Structural Evolution of Bulk Silicon upon Melting
ZHANG Shi-Liang, ZHANG Xin-Yu, WANG Lin-Min, QI Li, ZHANG Su-Hong, ZHU Yan, LIU Ri-Ping**
Chin. Phys. Lett. 2011, 28 (6): 067104 .   DOI: 10.1088/0256-307X/28/6/067104
Abstract   PDF(pc) (651KB) ( 384 )
The Voronoi structural evolution of silicon upon melting is investigated using a molecular dynamics simulation. At temperatures below the melting point, the solid state system is identified to have a four-fold coordination structure 4,0,0,0. As the temperature increases, the five−fold coordination 2,3,0,0 and six−fold coordination structures 2,2,2,0 and 0,6,0,0 are observed. This is explained in terms of increasing atomic displacement due to thermal motion and the trapping of the moving atoms by others. At temperatures above the melting point, nearly all of the four-fold coordination structures grows into multiple-fold coordination ones.
Analysis of Ground-State Zero-Field Splitting for Mn2+ in ZnNbOF56(H2O) and CoNbOF56(H2O)
LI Ju-Fen, KUANG Xiao-Yu, **
Chin. Phys. Lett. 2011, 28 (6): 067105 .   DOI: 10.1088/0256-307X/28/6/067105
Abstract   PDF(pc) (441KB) ( 437 )
The electron paramagnetic resonance spectra of trigonal Mn2+ centers in ZnNbOF5⋅6(H2O) and CoNbOF5⋅6(H2O) crystals are studied on the basis of the complete energy matrices for a d5 configuration ion in a trigonal ligand field. It is demonstrated that the local lattice structure around a trigonal Mn2+ center has an elongation distortion along the crystalline c3 axis, and when Mn2+ is doped in the ZnNbOF5⋅6(H2O) and CoNbOF5⋅6(H2O) crystals, there is a similar local distortion. From the EPR calculation, the local lattice structure parameters for trigonal Mn2+ centers in ZnNbOF5⋅6(H2O) and CoNbOF5⋅6(H2O) are determined.
Ground States and Excited States in a Tunable Graphene Quantum Dot
WANG Lin-Jun, CAO Gang, TU Tao**, LI Hai-Ou, ZHOU Cheng, HAO Xiao-Jie, GUO Guang-Can, GUO Guo-Ping**
Chin. Phys. Lett. 2011, 28 (6): 067301 .   DOI: 10.1088/0256-307X/28/6/067301
Abstract   PDF(pc) (625KB) ( 481 )
We prepare an etched gate tunable quantum dot in single-layer graphene and present transport measurement in this system. We extract the information of the ground states and excited states of the graphene quantum dot, as denoted by the presence of characteristic Coulomb blockade diamond diagrams. The results demonstrate that the quantum dot in single-layer graphene bodes well for future quantum transport study and quantum computing applications.
Magnetic Properties of a Rare-Earth Antiferromagnetic Nanoparticle Investigated with a Quantum Simulation Model
LIU Zhao-Sen**, Sechovský, Vladimir, Divi&#, Martin
Chin. Phys. Lett. 2011, 28 (6): 067302 .   DOI: 10.1088/0256-307X/28/6/067302
Abstract   PDF(pc) (598KB) ( 381 )
A Usov-type quantum model based on a mean-field approximation is utilized to simulate the magnetic structure of an assumed rare-earth nanoparticle consisting of an antiferromagnetic core and a paramagnetic outer shell. We study the magnetic properties in the presence and absence of an external magnetic field. Our simulation results show that the magnetic moments in the core region orientate antiferromagnetically in zero external magnetic field; an applied magnetic field rotates all of the magnetic moments in the paramagnetic shell completely to the field direction, and turns those in the core (which tries to maintain its original antiferromagnetic structure) towards the orientation in some degree; and the paramagnetic shell does not have a strong influence on the magnetic configuration of the core.
Tuning Electron Spin States in Quantum Dots by Spin-Orbit Interactions
LIU Yu**, CHENG Fang
Chin. Phys. Lett. 2011, 28 (6): 067303 .   DOI: 10.1088/0256-307X/28/6/067303
Abstract   PDF(pc) (533KB) ( 392 )
We theoretically investigate the influence of both Rashba spin-orbit interaction (RSOI) and Dresselhaus spin-orbit interaction (DSOI) on electron spin states, electron distribution and the optical absorption of a quantum dot. Our theoretical results show that the interplay between RSOI and DSOI results in an effective periodic potential, which consequently breaks the rotational symmetry and makes the quantum dot behave like two laterally coupled quantum dots. In the presence of RSOI and/or DSOI the spin is no longer a conserved quantity and its magnitude can be tuned by changing the strength of RSOI and/or DSOI. By reversing the direction of the perpendicular electric field, we can rotate the spatial distribution. This property provides us with a new way to control quantum states in a quantum dot by electrical means.
Effects of an InGaAs Cap Layer on the Optical Properties of InAs Quantum Dot Molecules
TIAN Peng, HUANG Li-Rong**, YUAN Xiu-Hua, HUANG De-Xiu
Chin. Phys. Lett. 2011, 28 (6): 067304 .   DOI: 10.1088/0256-307X/28/6/067304
Abstract   PDF(pc) (520KB) ( 361 )
Self-assembled InAs quantum dot molecules are grown on GaAs substrates without following any special protocols by using metal-organic chemical vapor deposition. The effects of indium composition and the thickness of the InGaAs cap layer on the optical properties of InAs quantum dot molecules are investigated by photoluminescence. With increasing indium composition and thickness of the InGaAs cap layer, the ground-state wavelength of the emission spectrum redshifts and the peak intensity decreases. In addition, the structural and optical properties of quantum dots and quantum dot molecules are comparatively studied, and the results show that when quantum dots turn into quantum dot molecules, the emission wavelength red shifts.
Characteristics of Off-Chip Millimeter-Wave Radiation from Serial Josephson Junction Arrays
WANG Zheng**, FAN Bin, ZHAO Xin-Jie, YUE Hong-Wei, HE Ming, JI Lu, YAN Shao-Lin, FANG Lan, Klushin A. M.
Chin. Phys. Lett. 2011, 28 (6): 067401 .   DOI: 10.1088/0256-307X/28/6/067401
Abstract   PDF(pc) (931KB) ( 429 )
We investigate the self-emissions from serial high-temperature superconductor bicrystal Josephson junction arrays embedded in a quasi-optical resonator. A bicrystal substrate is used as a dielectric resonator antenna, which increases the coupling strength between the junction array and the electromagnetic (EM) wave. Both three-dimension (3D) electromagnetic simulations and experiments are performed. Strong off-chip radiations are measured from the junction array at 78 GHz and 78 K. The proposed method and the experimental results are important for millimeter wave applications in junction arrays.
Fabrication and Properties of Aligned Sr0.6K0.4Fe2As2 Superconductors by High Magnetic Field Processing
GAO Zhao-Shun, ZHANG Xian-Ping, WANG Dong-Liang, QI Yan-Peng, WANG Lei, CHENG Jun-Sheng, WANG Qiu-Liang, MA Yan-Wei**, AWAJI Satoshi, WATANABE Kazuo
Chin. Phys. Lett. 2011, 28 (6): 067402 .   DOI: 10.1088/0256-307X/28/6/067402
Abstract   PDF(pc) (1015KB) ( 362 )
We fabricated a c−axis aligned Sr0.6K0.4Fe2As2 superconductor using a two−step magnetic field procedure. The effect of the magnetic fields on the structure and superconducting properties of Sr0.6K0.4Fe2As2 is investigated using x−ray diffraction and magnetic measurements. The degree of orientation of the samples is about 0.39 for the c axis and 0.51 for ab-plane orientation, as evaluated from the Lotgering factor of x-ray diffraction. This technology may be useful in a variety of potential applications, including preparing iron-based superconducting bulks and wires with high critical currents.
Spin Dynamics of B2 and L21−Ordered Co2FeAl0.5Si0.5 Heusler Alloy Films
YI Ming, CHEN Zhi-Feng, CHEN Da-Xin, Sukegawa Hiroaki, Inomata Koichiro, LAI Tian-Shu, ZHOU Shi-Ming, **
Chin. Phys. Lett. 2011, 28 (6): 067501 .   DOI: 10.1088/0256-307X/28/6/067501
Abstract   PDF(pc) (539KB) ( 421 )
Measurements of magnetization precession are performed for L21 and B2−ordered Co2FeAl0.5Si0.5 full Heusler alloy films using the time−resolved magneto-optical Kerr effect technique in the out-of-plan configuration. Dependence of the precession frequency on the external magnetic field can be fitted by the Landau–Lifshitz–Gilbert equation. The chirp parameters are close to each other for the L21 and B2 structures, and decrease with the external magnetic field increasing. The relaxation rate of the B2−ordered film is smaller than that of the L21 one.
Effect of a Boron Underlayer on the Ordering and Orientation of Sputtered FePt Film
LI Yong-Le, HUANG An-Ping, FENG Tang-Fu, CHEN Qiang, SHU Xiao-Lin, CHEN Jun-Yang, CHEN Zi-Yu, **
Chin. Phys. Lett. 2011, 28 (6): 067502 .   DOI: 10.1088/0256-307X/28/6/067502
Abstract   PDF(pc) (622KB) ( 320 )
FePt multilayer films with a boron underlayer are prepared on Si (100) substrates using magnetron sputtering and vacuum annealing is carried out to obtain the hard magnetic L10 phase. According to the microstructural and magnetic measurement results, the ordering of the FePt films is facilitated at low annealing temperatures while it is blocked at high ones by introducing boron. Moreover, (001) orientation of the samples is obviously improved by inserting a boron underlayer, which is further confirmed by the MFM analysis. The relevant mechanism is discussed by considering the diffusion of boron atoms and the consequential in-plane tensile stress.
Enhanced Magnetic and Ferroelectric Properties and Current-Voltage Hysteresis by Addition of La and Ti to BiFeO3 on 0.7%Nb−SrTiO3
CHANG Hong, **, ZHAO Yong-Gang
Chin. Phys. Lett. 2011, 28 (6): 067503 .   DOI: 10.1088/0256-307X/28/6/067503
Abstract   PDF(pc) (752KB) ( 409 )
By adding La and Ti, we improve the magnetic and ferroelectric properties of Bi0.8La0.2Fe0.92Ti0.08O3 and Bi0.8La0.2FeO3 films on 0.7%Nb−SrTiO3. In Bi0.8La0.2Fe0.92Ti0.08O3 and Bi0.8La0.2FeO3, the saturation magnetization and the coercivity are several times higher than those in BiFeO3. The La and Ti additions reduce the leakage current, and increase the remnant electric polarization. A resistance switching is observed in Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb−SrTiO3 and Bi0.8La0.2FeO3/0.7%Nb−SrTiO3 interfaces. Also, it is observed that Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb−SrTiO3 has a wider current−voltage hysteresis and a larger resistance difference than Bi0.8La0.2FeO3/0.7%Nb−SrTiO3. In the interface of Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb−SrTiO3, the ratio of high to low resistance is 103 and 105 times, at 300 K and 10 K, respectively. The voltage pulses can switch the resistance to vary in the 2 states. The transport mechanisms show that a trap−controlled space-charge-limited current induces current-voltage hysteresis and resistance switching. The current of Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb−SrTiO3 decays with the Curie–Von Schweidler law.
Ca0.5Sr0.5TiO3-Modified KNN-Based Lead-Free Piezoceramics with a Wide Temperature Usage Span
DU Juan**, WANG Jin-Feng, ZANG Guo-Zhong, YI Xiu-Jie
Chin. Phys. Lett. 2011, 28 (6): 067701 .   DOI: 10.1088/0256-307X/28/6/067701
Abstract   PDF(pc) (608KB) ( 501 )
The strong temperature dependence of dielectric and piezoelectric properties is a big 'bottleneck' for practical applications of KNN-based piezoceramics. In order to resolve this problem, Ca0.5Sr0.5TiO3 (CST) is doped into (Na0.53K0.407Li0.063)Nb0.937Sb0.063O3 (NKLNS) ceramics. The thermal stability of s11E and k31 in the temperature range from 50°C to 200°C for ceramics with 1.0 and 1.5 mol% CST is raised in comparison with ceramics without CST. Ceramics with 1.5 mol% CST exhibit high piezoelectric properties (d33=202 pC/N, kp=44%) and low dielectric loss (2%) at room temperature. The excellent piezoelectric properties, which are comparable to conventional PZT ceramics, indicate that these ceramics are promising candidates for lead-free piezoelectric applications.
Strain Effects of the Structural Characteristics of Ferroelectric Transition in Single-Domain Epitaxial BiFeO3 Films
LIU Yang**, PENG Xing-Ping
Chin. Phys. Lett. 2011, 28 (6): 067702 .   DOI: 10.1088/0256-307X/28/6/067702
Abstract   PDF(pc) (641KB) ( 451 )
Structural characteristics of phase transition in single-domain epitaxial BiFeO3 films are studied by the Landau–Devonshire theory. It is predicted that remanent polarization shows strong strain dependence for different temperatures while spontaneous polarization is almost independent of strain over a wide temperature (0–500 °C). We also obtain the thickness dependence of the c−axis lattice parameter and Curie temperature, and make a comparison between the polarization rotation angle and the angle attributed to the structural evolution in epitaxial (001)p BiFeO3 films grown on SrTiO3 substrates. The theoretical results are in agreement with recent experimental and theoretical data. Our calculations show that the clamping effect should also be taken into account in order to depict the mechanism of the polarization rotation completely.
Cathode Formed by Thermal Evaporation of Ba:Al Alloy and Estimations of Barrier Height in an Organic LED
DING Lei**, ZHANG Fang-Hui,
Chin. Phys. Lett. 2011, 28 (6): 067801 .   DOI: 10.1088/0256-307X/28/6/067801
Abstract   PDF(pc) (837KB) ( 629 )
It is demonstrated that barium and aluminum alloy synthesized by melting in a glass tube under low vacuum is applicable for organic laser emitting diodes (LEDs) as a thin film cathode. The alloy film obtained by the thermal evaporation of pre-synthesized alloy is used in a single-boat organic LED device with the structure: indium tin oxide (ITO)/4,4'-bis[N−(1-naphthyl)-N−phenylamino]biphenyl(NPB)/tris-(8-hydroxyquinoline) aluminum(Alq3)/barium:aluminum alloy. The experimental results show that devices with this alloy film cathode exhibit better current density-voltage-luminance characteristics than those with a conventional pure Al cathode, and more weight of barium in aluminum leads to better performance of the devices. Characteristics of current density versus voltage for the electron-only devices are fitted by the Richardson–Schottky emission model, indicating that the electron injection barrier has a decrease of about 0.3 eV by this alloy cathode.
Subband Light Emission from Phosphorous-Doped Amorphous Si/SiO2 Multilayers at Room Temperature
SUN Hong-Cheng, XU Jun**, LIU Yu, MU Wei-Wei, XU Wei, LI Wei, CHEN Kun-Ji
Chin. Phys. Lett. 2011, 28 (6): 067802 .   DOI: 10.1088/0256-307X/28/6/067802
Abstract   PDF(pc) (1076KB) ( 427 )
Phosphorous-doped hydrogenated amorphous Si/SiO2 multilayer structures are fabricated in a plasma enhanced chemical vapor deposition system. The microstructural and luminescence properties of the samples are characterized after annealing at various temperatures. Under the onset crystallization temperature 800–900 °C, a strong subband infrared light emission in the range 1.1–1.8 μm is observed at room temperature instead of the usually observed visible light emission. This subband infrared emission is gradually enhanced with the increase of phosphorus doping concentration, which can be ascribed to the increase of the luminescent defect states promoted by the doped phosphorous atoms.
Transmission through Ag/Organic Multilayers Using Continuous and Island Metal Films
LI Heng**, ZHENG Ning
Chin. Phys. Lett. 2011, 28 (6): 067803 .   DOI: 10.1088/0256-307X/28/6/067803
Abstract   PDF(pc) (513KB) ( 599 )
We present the results of transmission spectrum measurements of Ag/tetraphenyldiphenyldiamine periodic multilayers, as well as Ag/SiO2 in the visible and near IR spectral range. Using continuous silver films, these one-dimensional multilayers transmit visible light in controllable bands and stop IR light. Using island metal films, surface plasmon modes are excited, which exhibits broad absorption features covering the entire visible spectral range. This work successfully extends the discussion of metal-dielectric one-dimensional photonic crystals to metal-organic cases and exhibits the linear optical properties of surface plasmon modes at the island metal/organic interface.
Ultrafast Solvation Dynamics of Subtilisin-Polyethylene Glycol Interaction for Protein Crystallization
DING Qing, MENG Geng, WANG Shu-Feng**, ZHENG Xiao-Feng, YANG Hong, GONG Qi-Huang
Chin. Phys. Lett. 2011, 28 (6): 067804 .   DOI: 10.1088/0256-307X/28/6/067804
Abstract   PDF(pc) (852KB) ( 424 )
We study the ultrafast solvation dynamics of protein-precipitant complexes. Protein subtilisin carlsberg (SC) was mixed with several polyethylene glycol (PEG) precipitants for protein crystallization. Picosecond-resolved emission spectra from single intrinsic tryptophan residue (Trp-113) are recorded to construct solvation correlation functions. For precipitant concentrations with various crystallization effects, we observe drastically different solvation relaxation processes. These differences in solvation dynamics are correlated with the local protein structural integrity and water-network stability upon interaction with the precipitants. The solvation dynamics at the protein surface is proposed as a new perspective to study precipitant-protein interactions.
Monitoring Hydrogen Sulfide Using a Quantum Cascade Laser Based Trace Gas Sensing System
WANG Ling-Fang, **, SHARPLES Thomas-Roben
Chin. Phys. Lett. 2011, 28 (6): 067805 .   DOI: 10.1088/0256-307X/28/6/067805
Abstract   PDF(pc) (604KB) ( 532 )
We present the detection of hydrogen sulfide (H2S) in a quantum cascade laser (QCL) based gas sensing system employing direct laser absorption spectroscopy. The sensitivity is obtained to be 3.61×10−6 cm−1Hz−1/2 and the H2S broadening coefficient in N2 is analyzed by fitting to the plot of the Lorentzian half width at the half maximum as a function of N2 pressure is 0.1124 ±0.0031 cm−1⋅atm−1. A simulation based on data from the HITRAN database shows broad agreement with the experimentally obtained spectrum.
Efficiency-enhanced AlGaInP Light-Emitting Diodes with Thin Window Layers and Coupled Distributed Bragg Reflectors
CHEN Yi-Xin**, SHEN Guang-Di, ZHU Yan-Xu, GUO Wei-Ling, LI Jian-Jun
Chin. Phys. Lett. 2011, 28 (6): 067806 .   DOI: 10.1088/0256-307X/28/6/067806
Abstract   PDF(pc) (463KB) ( 654 )
A new structure of high-brightness light-emitting diodes (LED) is experimentally demonstrated. The thin window layer is composed of a 300-nm-thick indium-tin-oxide layer and a 500-nm-thick GaP layer for both current spreading and light anti-reflection. The two coupled distributed Bragg reflectors (DBRs) with one for reflecting normal incidence light and the other for reflecting inclined incidence light which is emitted to the GaAs substrate are employed in the LED fabrication. The coupled DBRs in the LED can provide high reflectivity with wide-angle reflection. The efficiency-enhanced AlGaInP LED has the luminance intensity increase of more than 50% compared with conventional LEDs and high reliability with the saturation current 130 mA.
Effect of Mg Doping on the Photoluminescence of GaN:Mg Films by Radio-Frequency Plasma-Assisted Molecular Beam Epitaxy
SUI Yan-Ping**, YU Guang-Hui
Chin. Phys. Lett. 2011, 28 (6): 067807 .   DOI: 10.1088/0256-307X/28/6/067807
Abstract   PDF(pc) (658KB) ( 2372 )
We investigate undoped GaN and Mg-doped GaN grown by rf plasma-assisted molecular beam epitaxy (MBE) with different Mg concentrations by photoluminescence (PL) at low temperature, Hall-effect and XRD measurements. In the PL spectra of lightly Mg-doped GaN films, a low intensity near band edge (NBE) emission and strong donor-acceptor pair (DAP) emission with its phonon replicas are observed. As the Mg concentration is increased, the DAP and NBE bands become weaker and a red shift of these bands is observed in the PL spectra. Yellow luminescence (YL) is observed in heavily Mg-doped GaN. The x-ray diffraction is employed to study the structure of the films. Hall measurement shows that there is a maximum value (3.9×1018 cm−3) of hole concentration with increasing Mg source temperature for compensation effect. PL spectra of undoped GaN are also studied under N-rich and Ga-rich growth conditions. Yellow luminescences of undoped Ga-rich GaN and heavily Mg-doped GaN are compared, indicating the different origins of the YL bands.
A Wide-Band Metamaterial Absorber Based on Loaded Magnetic Resonators
GU Chao, QU Shao-Bo, **, PEI Zhi-Bin, MA Hua, XU Zhuo, BAI Peng, PENG Wei-Dong, LIN Bao-Qin
Chin. Phys. Lett. 2011, 28 (6): 067808 .   DOI: 10.1088/0256-307X/28/6/067808
Abstract   PDF(pc) (695KB) ( 606 )
A wide-band polarization-insensitive and wide-angle metamaterial absorber based on loaded magnetic resonators is presented. The unit cell of this absorber consists of a magnetic resonator loaded with lumped resistances, a dielectric substrate and a back metal film. Theoretical and simulated results show that this absorber has a wide-band strong absorption for the incident wave from 3.87 GHz to 21.09 GHz. Simulated absorbance values under loading and unloading conditions indicate that electrocircuit's resonances are more stable than electromagnetic resonances and thus can be used to realize wide-band absorption. Simulated absorbance values under different polarization angles and different angles of incidence indicate that this absorber is polarization-insensitive and wide-angle. It may have potential applications in military fields.
Reaction Mechanism of Al and N in Diamond Growth from a FeNiCo-C System
LI Shang-Sheng, LI Xiao-Lei, MA Hong-An, SU Tai-Chao, XIAO Hong-Yu, HUANG Guo-Feng, LI Yong, ZHANG Yi-Shun, JIA Xiao-Peng, **
Chin. Phys. Lett. 2011, 28 (6): 068101 .   DOI: 10.1088/0256-307X/28/6/068101
Abstract   PDF(pc) (455KB) ( 565 )
It is significant to investigate the action of nitrogen getters, which are used to synthesize type-IIa large diamond single crystals under high pressure and high temperature (HPHT). The reaction mechanism of Al as a nitrogen getter and N in the HPHT alloy solvent is still indeterminate at present. In order to investigate the reaction of Al and N in the HPHT alloy solvent, Al and AlN are respectively added to the system of Fe55Ni29Co16−C (wt%, abbr. FeNiCo-C) for the synthesis of diamonds at about 5.5 GPa and 1600 K. The concentration of nitrogen in the diamonds is characterized by a micro Fourier transform infrared (micro-FTIR) spectrometer. The experimental results show that cN decreases when Al is added to the FeNiCo-C system. However, it increases when AlN is added. A reversible reaction confirms that Al and N can react and form AlN, simultaneously AlN can be decomposed into Al and N in the HPHT alloy solvent. Therefore the mechanism of eliminating the nitrogen of nitrogen getter Al is realized in detail.
Epitaxy of an Al-Droplet-Free AlN Layer with Step-Flow Features by Molecular Beam Epitaxy
PAN Jian-Hai, WANG Xin-Qiang**, CHEN Guang, LIU Shi-Tao, FENG Li, XU Fu-Jun, TANG Ning, SHEN Bo***
Chin. Phys. Lett. 2011, 28 (6): 068102 .   DOI: 10.1088/0256-307X/28/6/068102
Abstract   PDF(pc) (670KB) ( 512 )
We investigate epitaxy of AlN layers on sapphire substrates by molecular beam epitaxy. It is found that an atomically flat surface can be obtained under Al-rich conditions at growth temperature of 780 °C. However, the growth window to obtain an Al−droplet-free surface is too narrow to be well-controlled. However, the growth window can be greatly broadened by increasing the growth temperature up to 950 °C, where an Al-droplet-free surface with a step-flow feature is obtained due to the enhanced re-evaporization rate and migration ability of Al adatoms. The samples grown at the higher temperature also show a higher crystalline quality than those grown at lower temperatures.
Fabrication and Characterization of a Lead Zirconate Titanate Micro Energy Harvester Based on Eutectic Bonding
LI Yi-Gui**, SUN Jian, YANG Chun-Sheng, LIU Jing-Quan, SUGIYAMA Susumu, TANAKA Katsuhiko
Chin. Phys. Lett. 2011, 28 (6): 068103 .   DOI: 10.1088/0256-307X/28/6/068103
Abstract   PDF(pc) (913KB) ( 693 )
A lead zirconate titanate(PZT)-Si energy harvester cantilever with PZT bulk ceramics is fabricated by eutectic bonding, polishing and dicing processes. The feasibility of this process is studied using a successful operation of the cantilever in both actuation and harvesting modes. The first prototype made from a PZT-Au-Si cantiliever is tested. The testing results show the voltage output of 632 mV at the frequency of 815 Hz when the excitation acceleration is 0.5 g. The PZT and silicon layers are bonded together to form a sandwiched structure using a gold layer as an intermediate layer.
A Dual-Band Coaxial Waveguide Mode Converter for High-Power Microwave Applications
ZHANG Qiang**, YUAN Cheng-Wei, LIU Lie
Chin. Phys. Lett. 2011, 28 (6): 068401 .   DOI: 10.1088/0256-307X/28/6/068401
Abstract   PDF(pc) (594KB) ( 1130 )
A dual-band coaxial waveguide mode converter is investigated. In the converter, the TEM mode (Coa.TEM) and TM01 circular waveguide (Cir.TM01) mode are transformed simultaneously into TE11 coaxial waveguide (Coa.TE11) mode and TE11 circular waveguide (Cir.TE11) mode, respectively. The optimized geometrical dimensions are achieved by employing the mode coupling theory. A mode converter at 1.3 GHz and 5.0 GHz is designed, and conversion efficiencies of Coa.TEM−to-Coa.TE11 and Cir.TM01−to-Cir.TE11 are 99.88% and 99.70% at central frequency, respectively. Over the frequency ranges 1.15–1.51 GHz and 4.87–5.19 GHz, the conversion efficiency exceeds 90%. A good agreement between theoretical calculations and computer simulations is observed, demonstrating the feasibility of the dual-band mode converter.
Quantitatively Exploring the Effect of a Triangular Electrode on Performance Enhancement in a 4H-SiC Metal-Semiconductor-Metal Ultraviolet Photodetector
CHEN Bin**, YANG Yin-Tang, CHAI Chang-Chun, ZHANG Xian-Jun
Chin. Phys. Lett. 2011, 28 (6): 068501 .   DOI: 10.1088/0256-307X/28/6/068501
Abstract   PDF(pc) (604KB) ( 416 )
A model of novel triangular electrode metal-semiconductor-metal (TEMSM) and conventional electrode metal-semiconductor-metal (CEMSM) detectors is established by utilizing the ISE-TCAD simulator. By comparing the simulated results of TEMSM and CEMSM with experimental data, the model validity is verified and the TEMSM detector shows a superiority of a 113% photocurrent increase of 25.4 nA and similar low dark current of 3.16 pA at 30 V bias over the CEMSM device. Furthermore, the electrode angle α, width W and spacing S are optimized to obtain the enhanced device features including high UV−to-visible rejection ratio and large responsivity, etc. Under 30 V bias, the maximum UV-to-visible rejection ratio, comparable responsivity and external quantum efficiency at 310 nm are 13049, 0.1712 A/W and 68.48% for a TEMSM detector with device parameters of α=60°, W=3 μm and S=4 μm, respectively.
Investigation of a GaN Nucleation Layer on a Patterned Sapphire Substrate
WU Meng, **, ZENG Yi-Ping, , WANG Jun-Xi, HU Qiang
Chin. Phys. Lett. 2011, 28 (6): 068502 .   DOI: 10.1088/0256-307X/28/6/068502
Abstract   PDF(pc) (3069KB) ( 671 )
A low-temperature GaN (LT-GaN) nucleation layer is grown on a patterned sapphire substrate (PSS) using metal-organic chemical vapor deposition (MOCVD). The surface morphology of the LT-GaN is investigated and the selective nucleation phenomenon in the growth process of the LT-GaN nucleation layer is discovered. Meanwhile, effects of thickness of the LT-GaN and the annealing process on the phenomenon are also discussed. A pattern model is also proposed to analyze the possible mechanisms in atomic scale.
Theoretical Explanation and Improvement to the Flare Model of Lithography Based on the Kirk Test
CHEN De-Liang, CAO Yi-Ping**, HUANG Zhen-Fen
Chin. Phys. Lett. 2011, 28 (6): 068503 .   DOI: 10.1088/0256-307X/28/6/068503
Abstract   PDF(pc) (565KB) ( 732 )
The Kirk test has good precision for measuring stray light in optical lithography and is the usual method of measuring stray light. However, Kirk did not provide a theoretical explanation to his simulation model. We attempt to give Kirk's model a kind of theoretical explanation and a little improvement based on the model of point spread function of scattering and the theory of statistical optics. It is indicated by simulation that the improved model fits Kirk's measurement data better.
Approach of Complex Networks for the Determination of Brain Death
SUN Wei-Gang, , CAO Jian-Ting, WANG Ru-Bin**
Chin. Phys. Lett. 2011, 28 (6): 068701 .   DOI: 10.1088/0256-307X/28/6/068701
Abstract   PDF(pc) (423KB) ( 319 )
In clinical practice, brain death is the irreversible end of all brain activity. Compared to current statistical methods for the determination of brain death, we focus on the approach of complex networks for real-world electroencephalography in its determination. Brain functional networks constructed by correlation analysis are derived, and statistical network quantities used for distinguishing the patients in coma or brain death state, such as average strength, clustering coefficient and average path length, are calculated. Numerical results show that the values of network quantities of patients in coma state are larger than those of patients in brain death state. Our findings might provide valuable insights on the determination of brain death.
Effect of Cisplatin on the Flexibility of Linear DNA
JI Chao, ZHANG Ling-Yun**, HOU Xi-Miao, DOU Shuo-Xing, WANG Peng-Ye***
Chin. Phys. Lett. 2011, 28 (6): 068702 .   DOI: 10.1088/0256-307X/28/6/068702
Abstract   PDF(pc) (2802KB) ( 446 )
With the aid of an atomic force microscope (AFM), we study the interaction between linear DNA fragment and cisplatin. For different cisplatin concentrations, the AFM used to observe the conformation of DNA has a gradual change. The contour length, the end-to-end distance and the local bend angles of the linear DNA fragment can be accurately measured. The persistence length of DNA interacting with cisplatin is decreased with the increasing cisplatin concentration. Furthermore, it is demonstrated that the local bend angles of DNA chains are increased by the binding interaction of cisplatin.
Emergence of Small-World and Limitations to Its Maximization in a Macaque Cerebral Cortical Network
ZHAO Qing-Bai, LIAO Meng-Jie, CHEN Qi-Cai**
Chin. Phys. Lett. 2011, 28 (6): 068703 .   DOI: 10.1088/0256-307X/28/6/068703
Abstract   PDF(pc) (488KB) ( 352 )
We study both the emergence of small-world topology in a macaque cerebral cortical network and the limitations to maximization of small-worldness. The results show that the maximization of neural complexity leads to a small-world topology, but it also limits the maximization of small-worldness. It is suggested that the modular organization that corresponds to different functions may be a limitation. Additionally, the need for strong resilience against attacks may be another limitation.
Empirical Analysis on the Human Dynamics of a Large-Scale Short Message Communication System
ZHAO Zhi-Dan, XIA Hu, SHANG Ming-Sheng**, ZHOU Tao,
Chin. Phys. Lett. 2011, 28 (6): 068901 .   DOI: 10.1088/0256-307X/28/6/068901
Abstract   PDF(pc) (1589KB) ( 1191 )
Research on human behavior has attracted increasing attention recently because of its scientific significance and potential applications. Some empirical results have indicated that the timing of many human activities follows non-Poisson statistics. We analyze a real-life huge dataset of short message communication with 6326713 users and 37577781 records during the 2006 Chinese New Year. The results show that the number of short message sendings, the interevent time between two consecutive short message sendings and the response time all follow heavy-tailed distribution. We further observe a strongly positive correlation between the activity and the power-law exponent of the interevent time distribution. In addition, the short message communication system displays a bursty property yet no memory effects, which is in particular different from some well-studied human-activited systems such as email-sending, library-loaning and file printing.
Optimal Attack Strategy in Random Scale-Free Networks Based on Incomplete Information
LI Jun, WU Jun**, LI Yong, DENG Hong-Zhong, TAN Yue-Jin**
Chin. Phys. Lett. 2011, 28 (6): 068902 .   DOI: 10.1088/0256-307X/28/6/068902
Abstract   PDF(pc) (488KB) ( 395 )
We introduce an attack model based on incomplete information, which means that we can obtain the information from partial nodes. We investigate the optimal attack strategy in random scale-free networks both analytically and numerically. We show that the attack strategy can affect the attack effect remarkably and the OAS can achieve better attack effect than other typical attack strategies. It is found that when the attack intensity is small, the attacker should attack more nodes in the "white area" in which we can obtain attack information; when the attack intensity is greater, the attacker should attack more nodes in the "black area" in which we can not obtain attack information. Moreover, we show that there is an inflection point in the curve of optimal attack proportion. For a given magnitude of attack information, the optimal attack proportion decreases with the attack intensity before the inflection point and then increases after the inflection point.
Local Natural Connectivity in Complex Networks
Chin. Phys. Lett. 2011, 28 (6): 068903 .   DOI: 10.1088/0256-307X/28/6/068903
Abstract   PDF(pc) (397KB) ( 525 )
In network theory, a complex network represents a system whose evolving structure and dynamic behavior contribute to its robustness. The natural connectivity is recently proposed as a spectral measure to characterize the robustness of complex networks. We decompose the natural connectivity of a network as local natural connectivity of its connected components and quantify their contributions to the network robustness. In addition, we compare the natural connectivity of a network with that of an induced subgraph of it based on interlacing theorems. As an application, we derive an inequality for eigenvalues of Erdös-Rényi random graphs.
Withdrawal of Chinese Physics Letters 26 (2009) 114209
XU Shi-Xiang
Chin. Phys. Lett. 2011, 28 (6): 069901 .   DOI: 10.1088/0256-307X/28/6/069901
Abstract   PDF(pc) (171KB) ( 317 )
This paper has been retracted because Fig. 2 is copied from an earlier paper, "Interband photorefractive effect in β-BBO crystal due to multiphoton excitation by intense ultrashort optical pulses" by Shixiang Xu et al., which appeared in Optics Express 15 (2007) 10576, and its Figs. 3 and 4 also present similar data as in Figs. 3 and 4 of the same Optics Express paper though they are measured at a different pumping power. See Also: Original Article, XU Shi-Xiang et al., A Sensitive Scheme to Observe Weak Photo-Refraction Effects in Some Nonlinear Optical Crystals Pumped by Ultrashort Optical Pulses, Chin. Phys. Lett. 26 (2009) 114209
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