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Volume 28 Issue 4
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GENERAL
A Field Integration Method for a Nonholonomic Mechanical System of Non-Chetaev's Type
XIA Li-Li
Chin. Phys. Lett. 2011, 28 (4): 040201 .   DOI: 10.1088/0256-307X/28/4/040201
Abstract   PDF(pc) (333KB) ( 480 )
A field integration method for a nonholonomic mechanical system of non-Chetaev's type is studied. The differential equations of the motion of the system are established. The solution of the corresponding holonomic system for the nonholonomic system is obtained by the field method. The restriction of nonholonomic constrained to initial conditions is added and the solution of the nonholonomic mechanical system of non-Chetaev's type is provided. An example is presented to illustrate the application of the results.
A Modification of Extended Homoclinic Test Approach to Solve the (3+1)-Dimensional Potential-YTSF Equation
M. T. Darvishi**, Mohammad Najafi
Chin. Phys. Lett. 2011, 28 (4): 040202 .   DOI: 10.1088/0256-307X/28/4/040202
Abstract   PDF(pc) (692KB) ( 691 )
By means of the extended homoclinic test approach (EHTA) one can solve some nonlinear partial differential equations (NLPDEs) in their bilinear forms. When an NLPDE has no bilinear closed form we can not use this method. We modify the idea of EHTA to obtain some analytic solutions for the (3+1)-dimensional potential-Yu-Toda-Sasa-Fukuyama (YTSF) equation by obtaining a bilinear closed form for it. By comparison of this method and other analytic methods, like HAM, HTA and three-wave methods, we can see that the new idea is very easy and straightforward.
Perturbation to Noether Symmetry and Noether adiabatic Invariants of Discrete Mechanico-Electrical Systems
WANG Peng
Chin. Phys. Lett. 2011, 28 (4): 040203 .   DOI: 10.1088/0256-307X/28/4/040203
Abstract   PDF(pc) (396KB) ( 387 )
Perturbation to Noether symmetry of discrete mechanico-electrical systems on an uniform lattice is investigated. First, Noether theorem of a system is presented. Secondly, the criterion of perturbation to Noether symmetry of the system is given. Based on the definition of adiabatic invariants, Noether adiabatic invariants of the system are obtained. Finally, An example is given to support these results.
Jacobi Last Multiplier Method for Equations of Motion of Constrained Mechanical Systems
CHEN Xiang-Wei, MEI Feng-Xiang**
Chin. Phys. Lett. 2011, 28 (4): 040204 .   DOI: 10.1088/0256-307X/28/4/040204
Abstract   PDF(pc) (345KB) ( 516 )
The Jacobi last multiplier method for holonomic and nonholonomic mechanical systems is studied and some examples are given to attempt applications of the method.
Simultaneous Synchronization and Anti-Synchronization of Two Identical New 4D Chaotic Systems
GUO Rong-Wei
Chin. Phys. Lett. 2011, 28 (4): 040205 .   DOI: 10.1088/0256-307X/28/4/040205
Abstract   PDF(pc) (387KB) ( 465 )
We investigate the synchronization and anti-synchronization of the new 4D chaotic system and propose a same adaptive controller in the form which not only synchronizes, but also anti-synchronizes two identical new 4D chaotic systems. Numerical simulations verify the correctness and the effectiveness of the proposed theoretical results.
Multipartite Spin Entangled States in Quantum Dots with a Quantum Databus Based on Nano Electro-Mechanical Resonator
ZHU Zhi-Cheng, TU Tao**, GUO Guo-Ping
Chin. Phys. Lett. 2011, 28 (4): 040301 .   DOI: 10.1088/0256-307X/28/4/040301
Abstract   PDF(pc) (411KB) ( 428 )
We propose an efficient method to create multipartite spin entangled states in quantum dots coupled to a nano electro-mechanical resonator array. Our method, based on the interaction between electron spins confined in quantum dots and the motion of magnetized nano electro-mechanical resonators, can enable a coherent spin-spin coupling over long distances and in principle be applied to an arbitrarily large number of electronic spins.
Photon Distribution of a Squeezed Chaotic State
FAN Hong-Yi, ZHOU Jun, **, XU Xue-Xiang, HU Li-Yun
Chin. Phys. Lett. 2011, 28 (4): 040302 .   DOI: 10.1088/0256-307X/28/4/040302
Abstract   PDF(pc) (456KB) ( 544 )
We investigate the photon number distribution of squeezed chaotic field (SCF) (a mixed state), by converting the density operator of SCF into its normally ordered bivariate distribution form we find that it is a Legendre distribution. This is a remarkable result.
A Three-Node QKD Network Based on a Two-Way QKD System
HAN Jia-Jia, SUN Shi-Hai, LIANG Lin-Mei**
Chin. Phys. Lett. 2011, 28 (4): 040303 .   DOI: 10.1088/0256-307X/28/4/040303
Abstract   PDF(pc) (698KB) ( 421 )
We demonstrate a three-node active quantum key distribution (QKD) network with our previous two-way QKD system. An optical switch is used as a router to connect the two nodes. Adjacent nodes are connected by a 25 km optical fiber. The test over 11 h shows that our system can reduce the Raleigh backscattering efficiently in the absence of the storage fiber. Furthermore, the obtained average sifted key is about 1.2 kbps in the network, with high visibility and low quantum bit error rate in the long-time test.
Effect of the Velocity-Dependent Potentials on the Bound State Energy Eigenvalues
O. Bayrak**, A. Soylu, I. Boztosun
Chin. Phys. Lett. 2011, 28 (4): 040304 .   DOI: 10.1088/0256-307X/28/4/040304
Abstract   PDF(pc) (401KB) ( 427 )
We investigate the effect of isotropic velocity-dependent potentials on the bound state energy eigenvalues for the first time for any quantum states of the Coulomb and harmonic oscillator potentials within the framework of the asymptotic iteration method. When the velocity-dependent term is selected as a constant parameter ρ0, we present that the energy eigenvalues can be obtained analytically for both Coulomb and harmonic oscillator potentials. However, when the velocity−dependent term is considered as a harmonic oscillator type ρ0r2, taking the velocity−dependent term as a perturbation, we present how to obtain the energy eigenvalues of the Coulomb and harmonic oscillator potentials for any n and quantum states by using perturbation expansion and numerical calculations in the asymptotic iteration method procedure.
High-Capacity Quantum Secure Direct Communication Based on Quantum Hyperdense Coding with Hyperentanglement
WANG Tie-Jun, , LI Tao, DU Fang-Fang, DENG Fu-Guo**
Chin. Phys. Lett. 2011, 28 (4): 040305 .   DOI: 10.1088/0256-307X/28/4/040305
Abstract   PDF(pc) (416KB) ( 638 )
We present a quantum hyperdense coding protocol with hyperentanglement in polarization and spatial-mode degrees of freedom of photons first and then give the details for a quantum secure direct communication (QSDC) protocol based on this quantum hyperdense coding protocol. This QSDC protocol has the advantage of having a higher capacity than the quantum communication protocols with a qubit system. Compared with the QSDC protocol based on superdense coding with d-dimensional systems, this QSDC protocol is more feasible as the preparation of a high-dimension quantum system is more difficult than that of a two-level quantum system at present.
Cosmological Dynamics of de Sitter Gravity
AO Xi-Chen**, LI Xin-Zhou, XI Ping
Chin. Phys. Lett. 2011, 28 (4): 040401 .   DOI: 10.1088/0256-307X/28/4/040401
Abstract   PDF(pc) (503KB) ( 343 )
A new cosmological model based on the de Sitter gravity is investigated by dynamical analysis and numerical discussions. Via some transformations, the evolution equations of this model can form an autonomous system with 8 physical critical points. Among these critical points there exist one positive attractor and one negative attractor. The positive attractor describes the asymptotic behavior of late-time universe, which indicates that the universe will enter the exponential expansion phase, finally. Some numerical calculations are also carried out, which convince us of this conclusion derived from the dynamical analysis.
Effects of Time Delay on Stability of an Unstable State in a Bistable System with Correlated Noises
LI Chun, MEI Dong-Cheng, **
Chin. Phys. Lett. 2011, 28 (4): 040501 .   DOI: 10.1088/0256-307X/28/4/040501
Abstract   PDF(pc) (446KB) ( 362 )
Effects of time delay on stability of an unstable state in a time-delayed bistable system are investigated. The analytic expression of the transition rate W(xu,τ) from unstable state xu to stable state x+ is derived. The numerical calculation results of W(xu,τ) indicate that W(xu,τ) decreases with the increasing multiplicative noise intensity, the additive noise intensity and the strength of correlations between the multiplicative and the additive noise increase, but W(xu,τ) increases with increasing delay time. Namely, the multiplicative noise, the additive noise and the correlations between the multiplicative and the additive noises enhance the stability of the unstable state in the time-delayed bistable system but the stability is weakened by time delay.
Weak Signal Frequency Detection Method Based on Generalized Duffing Oscillator
SHI Si-Hong, YUAN Yong, WANG Hui-Qi, LUO Mao-Kang**
Chin. Phys. Lett. 2011, 28 (4): 040502 .   DOI: 10.1088/0256-307X/28/4/040502
Abstract   PDF(pc) (946KB) ( 608 )
The sensitive characteristic to the initial value of chaos system sufficiently demonstrates the superiority in weak signal parameters detection. Analyzing the current chaos-based frequency detection method, a novel generalized Duffing equation is proposed to detect weak signal frequency. By choosing a suitable adjusting factor, when the outside driving force frequency is equal to that of the detected signal, the generalized Duffing oscillator is in great period state, which can obtain the frequency information of the detected signal. The simulation results indicate this method is rapidly convenient and shows better accuracy.
Stable Flocking of Multiple Agents Based on Molecular Potential Field and Distributed Receding Horizon Control
ZHANG Yun-Peng, DUAN Hai-Bin, **, ZHANG Xiang-Yin
Chin. Phys. Lett. 2011, 28 (4): 040503 .   DOI: 10.1088/0256-307X/28/4/040503
Abstract   PDF(pc) (422KB) ( 320 )
A novel distributed control scheme to generate stable flocking motion for a group of agents is proposed. In this control scheme, a molecular potential field model is applied as the potential field function because of its smoothness and unique shape. The approach of distributed receding horizon control is adopted to drive each agent to find its optimal control input to lower its potential at every step. Experimental results show that this proposed control scheme can ensure that all agents eventually converge to a stable flocking formation with a common velocity and the collisions can also be avoided at the same time.
Chaos Control in Random Boolean Networks by Reducing Mean Damage Percolation Rate
JIANG Nan**, CHEN Shi-Jian
Chin. Phys. Lett. 2011, 28 (4): 040504 .   DOI: 10.1088/0256-307X/28/4/040504
Abstract   PDF(pc) (452KB) ( 494 )
Chaos control in random Boolean networks is implemented by freezing part of the network to drive it from chaotic to ordered phase. However, controlled nodes are only viewed as passive blocks to prevent perturbation spread. We propose a new control method in which controlled nodes can exert an active impact on the network. Controlled nodes and frozen values are deliberately selected according to the information of connection and Boolean functions. Simulation results show that the number of nodes needed to achieve control is largely reduced compared to the previous method. Theoretical analysis is also given to estimate the least fraction of nodes needed to achieve control.
Time Evolution of a Harmonic Chain with Fixed Boundary Conditions
LU Hong**, BAO Jing-Dong
Chin. Phys. Lett. 2011, 28 (4): 040505 .   DOI: 10.1088/0256-307X/28/4/040505
Abstract   PDF(pc) (543KB) ( 383 )
We investigate the time evolution of a coupled harmonic-oscillator chain under two boundary conditions: two ends fixed and one end fixed. The dynamics of the coupled chain and the steady variances of the coordinates are explicitly analyzed by the entire Hamiltonian using a diagonalization approach. Our result shows the desirable symmetry for the case with two ends fixed. In particular, a Langevin simulation technique is proposed to sample the harmonic chain across the entire equilibrium distribution.
Influence of Fabricating Process on Gas Sensing Properties of ZnO Nanofiber-Based Sensors
XU Lei, WANG Rui**, LIU Yong, DONG Liang
Chin. Phys. Lett. 2011, 28 (4): 040701 .   DOI: 10.1088/0256-307X/28/4/040701
Abstract   PDF(pc) (836KB) ( 596 )
ZnO nanofibers are synthesized by an electrospinning method and characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Two types of gas sensors are fabricated by loading these nanofibers as the sensing materials and their performances are investigated in detail. Compared with the sensors based on traditional ceramic tubes with Au electrodes (traditional sensors), the sensors fabricated by spinning ZnO nanofibers on ceramic planes with Ag-Pd electrodes (plane sensors) exhibit much higher sensing properties. The sensitivity for the plane sensors is about 30 to 100 ppm ethanol at 300 °C, while the value is only 13 for the traditional sensors. The response and recovery times are about 2 and 3 s for the plane sensors and are 3 and 6 s for the traditional sensors, respectively. Lower minimum-detection-limit is also found for the plane sensors. These improvements are explained by considering the morphological damage in the fabricating process for traditional sensors. The results suggest that the plane sensors are more suitable to sensing investigation for higher veracity.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Peak of Chiral Susceptibility and Chiral Phase Transition in QED3
ZHOU Yu-Qing**, YANG Yong-Hong
Chin. Phys. Lett. 2011, 28 (4): 041101 .   DOI: 10.1088/0256-307X/28/4/041101
Abstract   PDF(pc) (562KB) ( 356 )
A general expression for the scalar susceptibility in QED3 is given. We adopt the Dyson–Schwinger equation for the fermion propagator to solve χc within a range of the number of fermion flavors, N, in chiral symmetry breaking phase. We show that the scalar susceptibility has a peak and the corresponding N is less than the critical number of fermion flavors for chiral symmetry.
Associated Production of a Neutral Top-Higgs with Top Quark Pairs at the LHC within the TC2 model
LI Bing-Zhong, HAN Jin-Zhong
Chin. Phys. Lett. 2011, 28 (4): 041201 .   DOI: 10.1088/0256-307X/28/4/041201
Abstract   PDF(pc) (557KB) ( 349 )
Within the context of the topcolor-assisted technicolor (TC2) model we investigate the associated production of the neutral top-higgs ht0 with a pair of top quarks, i.e.pp →ttht0 at the Large Hadron Collider (LHC), which proceeds through the partonic processes qqttht0 and gg →ttht0. We calculate the production rate and show the distributions of the transverse momenta of ht0. It is found that the cross section of pp →ttht0 can reach a few hundred fb in the most part of the allowed parameter space and even a few tens of pb for the light top−higgs. Due to the large cross section of ttht0 production and the top−charm decay mode of ht0 for mh(_o^t)<2mt, the process pp →ttht0 can play an important role in the probe of neutral top-higgs and the test of the TC2 model.
NUCLEAR PHYSICS
174Hf and 174Yb by the Projected Shell Model with Improved 4-quasiparticle basis
CHEN Fang-Qi, ZHOU Xian-Rong**
Chin. Phys. Lett. 2011, 28 (4): 042101 .   DOI: 10.1088/0256-307X/28/4/042101
Abstract   PDF(pc) (462KB) ( 387 )
The rare-earth nuclei 174Hf and 174Yb are studied in the framework of the projected shell model. The calculations are carried out with an improved version of code which contains all types of four−quasiparticle basis in the configuration space. Both the yrast band and the multi-quasiparticle excited bands can be well reproduced. Compared with the experimental data, our calculations improve the previous results, especially for high spin states. This improvement suggests that the newly added configurations are important. In 174Yb, a new possible configuration is suggested for the observed Kπ=14+ band, and the decay of the Kπ=6+ isomeric state to the yrast band is discussed.
ATOMIC AND MOLECULAR PHYSICS
Lifetime Measurement for 6snp Rydberg States of Barium
SHEN Li, WANG Lei, YANG Hai-Feng, LIU Xiao-Jun, LIU Hong-Ping**
Chin. Phys. Lett. 2011, 28 (4): 043101 .   DOI: 10.1088/0256-307X/28/4/043101
Abstract   PDF(pc) (532KB) ( 377 )
We present a simple and efficient method for measuring the atomic lifetimes in order of tens of microseconds and demonstrate it in the lifetime determination of barium Rydberg states. This method extracts the lifetime information from the time-of-flight spectrum directly, which is much more efficient than other methods such as the time-delayed field ionization and the traditional laser induced fluorescence. The lifetimes determined with our method for barium Rydberg 6snp (n=37–59) series are well coincident with the values deduced from the absolute oscillator strengths of barium which were given in the literature [J. Phys. B 14 (1981) 4489, 29 (1996) 655] on experiments.
Elastic Scattering between Ultracold 23Na and 85Rb Atoms in the Triplet State
HU Qiu-Bo, ZHANG Yong-Sheng, SUN Jin-Feng, YU Ke
Chin. Phys. Lett. 2011, 28 (4): 043201 .   DOI: 10.1088/0256-307X/28/4/043201
Abstract   PDF(pc) (591KB) ( 368 )
The elastic scattering properties between ultracold 23Na and 85Rb atoms for the triplet state (a3u+) are researched. The s−wave scattering lengths of 23Na and 85Rb are calculated by the Numerov and semiclassical method with two kinds of interatomic potentials, which are the interpolation potential and Lennard–Jones potential (LJ12,6) by the same phase ϕ. Shape resonances appear clearly in the l=5 partial waves for the a3u+ state. Moreover, the s-wave scattering cross section, total cross section and energy positions of shape resonances are also discussed.
Field-Free Molecular Orientation Induced by Nonresonant Square Laser Pulses
XU Shu-Wu**, HUANG Yun-Xia, JI Xian-Ming
Chin. Phys. Lett. 2011, 28 (4): 043301 .   DOI: 10.1088/0256-307X/28/4/043301
Abstract   PDF(pc) (542KB) ( 422 )
We propose a scheme to achieve field-free molecular orientation by a nonresonant square laser pulse. Using CO molecules as an example, we show that, differing from the conventional Gaussian pulse, field-free molecular orientation excited by square pulses can be realized in both nonadiabatic and adiabatic cases. We also show that the maximum degree of the molecular orientation can be further enhanced by separating one square pulse into two time delayed subpulses and by applying the second subpulse at the beginning of the rotational wave packet rephrasing created by the first subpulse and the optimal intensity ratio between the two subpulses is about I1/I2 =1:1.5.
Measurement of Absolute Atomic Collision Cross Section with Helium Using 87Rb Atoms Confined in Magneto-Optic and Magnetic Traps
WANG Ji-Cheng, ZHOU Ke-Ya, WANG Yue-Yuan, LIAO Qing-Hong, LIU Shu-Tian**
Chin. Phys. Lett. 2011, 28 (4): 043401 .   DOI: 10.1088/0256-307X/28/4/043401
Abstract   PDF(pc) (1099KB) ( 988 )
We present the measurements and calculations of the absolute total collision cross sections for a room-temperature gas of helium using 87Rb atoms confined in either a magneto-optic or a magnetic quadrupole trap. The loss rates from the magneto-optic trap and the pure magnetic trap are compared and show significant differences. The collision cross sections as a function of trap depth for helium gas are obtained. These findings are significant for extracting the information about the different cross sections when the trap depth is changed.
Second Harmonic Generation in Scanning Probe Microscopy for Edge Localization
HU Xiao-Gen**, LI Yu-He**, LIN Hao-Shan, WANG Dong-Sheng, QI Xin
Chin. Phys. Lett. 2011, 28 (4): 043402 .   DOI: 10.1088/0256-307X/28/4/043402
Abstract   PDF(pc) (670KB) ( 326 )
We present an approach of second harmonic generation for edge localization of nano-scale defects measurement, based on the impact of the oscillating tip on the sample that induces higher harmonics of the excitation frequency. The harmonic signals of tip motion are measured by the heterodyne interferometry. The edge amplitude ratio for the edge characterization can be calculated by a mechanics model and the threshold of edge localization is experimentally determined by second harmonic profiles. This approach has been successfully utilized to measure the pitch of a standard sample. The results show that the second harmonic is sensitive to locating the edge of nano-scale defects with high accuracy.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Temperature Compensation for Threshold Current and Slope Efficiency of 1.3µm InAs/GaAs Quantum-Dot Lasers by Facet Coating Design
XU Peng-Fei, YANG Tao**, JI Hai-Ming, CAO Yu-Lian, GU Yong-Xian, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (4): 044201 .   DOI: 10.1088/0256-307X/28/4/044201
Abstract   PDF(pc) (542KB) ( 323 )
We demonstrate a technique of temperature compensation for 1.3 µm InAs/GaAs quantum-dot (QD) lasers by facet coating design. The key point of the technique is to make sure that the mirror loss of the lasers decreases as the temperature rises. To realize this, we design a type of facet coating by shifting the central wavelength of the facet coating from 1310 nm to 1480 nm, whose reflectivity increases as the emission wavelength of the lasers red-shifts. Consequently, the laser with the new facet coating exhibits a characteristic temperature doubled in size and a more stable slope efficiency in the temperature range from 10°C to 70°C, compared with the traditional one with a temperature-independent mirror loss.
Suppression Impact of Group-Velocity Dispersion on the Cell of Pulse Cleaning
LI Jing, DENG Ying, WANG Jian-Jun, LI Ming-Zhong, XU Dang-Peng, LIN Hong-Huan, ZHU Na, ZHANG Rui, JING Feng**
Chin. Phys. Lett. 2011, 28 (4): 044202 .   DOI: 10.1088/0256-307X/28/4/044202
Abstract   PDF(pc) (703KB) ( 442 )
In order to improve the signal-to-noise ratio of an all-fiber front-end system for high-energy pete-watt (PW) laser devices, we propose a method to restrain the noise by optical Kerr effect. In terms of analytical calculation, it is found that the signal-to-noise ratio can be increased by three orders of magnitude with the cell of pulse cleaning for the pulses, with the full width at half maximum T FWHM larger than 100 ps. However, numerical calculation indicates that the group−velocity dispersion (GVD) may have a marked effect on the pulses with TFWHM smaller than 100 ps but larger than 5 ps, with the help of self-phase modulation (SPM). This would debase the performance of the cell of pulse cleaning. Meanwhile, we study the methods of restraining the distortion for the pulses with different peak powers to improve the performance of an all-fiber front-end system for high-energy PW laser devices, These results are of benefit to the experiments and the improvement of signal-to-noise ratio for high-energy PW laser devices.
Sensitive Detection of Individual Neutral Atoms in a Strong Coupling Cavity QED System
ZHANG Peng-Fei, ZHANG Yu-Chi, LI Gang, DU Jin-Jin, ZHANG Yan-Feng, GUO Yan-Qiang, WANG Jun-Min, ZHANG Tian-Cai**, LI Wei-Dong
Chin. Phys. Lett. 2011, 28 (4): 044203 .   DOI: 10.1088/0256-307X/28/4/044203
Abstract   PDF(pc) (929KB) ( 360 )
We experimentally demonstrate real-time detection of individual cesium atoms by using a high-finesse optical micro-cavity in a strong coupling regime. A cloud of cesium atoms is trapped in a magneto-optical trap positioned at 5 mm above the micro-cavity center. The atoms fall down freely in gravitation after shutting off the magneto-optical trap and pass through the cavity. The cavity transmission is strongly affected by the atoms in the cavity, which enables the micro-cavity to sense the atoms individually. We detect the single atom transits either in the resonance or various detunings. The single atom vacuum-Rabi splitting is directly measured to be Ω=2π×23.9 MHz. The average duration of atom-cavity coupling of about 110 µs is obtained according to the probability distribution of the atom transits.
Theoretical Revision and Experimental Comparison of Quantum Yield for Transmission-Mode GaAlAs/GaAs Photocathodes
SHI Feng, , ZHANG Yi-Jun, CHENG Hong-Chang, ZHAO Jing, XIONG Ya-Juan, CHANG Ben-Kang**
Chin. Phys. Lett. 2011, 28 (4): 044204 .   DOI: 10.1088/0256-307X/28/4/044204
Abstract   PDF(pc) (450KB) ( 454 )
The quantum yield formula for uniform-doping GaAlAs/GaAs transmission-mode photocathodes is revised by taking into account the light absorption in the window layer. By using the revised quantum yield formula, the domestic and ITT's experimental quantum yield curves are fitted and the fitted curves match well with the experimental curves. In addition, the fit results show that the integral sensitivity and quantum yield of domestic image intensifier tube has achieved 2130 µA/lm and 45%, nearly reaching ITT's third generation level in 2002, whereas the discrepancy in cathode performance is mainly embodied in the electron diffusion length and back interface recombination velocity.
A Successive Scans Method of Adjusting Scan-Time for Injection Electroluminescent Display Panels
OU Peng, YANG Gang**, JIANG Quan, WANG Jun, HU Jian-Hua, WU Qi-Peng, LUO Kai-Jun**
Chin. Phys. Lett. 2011, 28 (4): 044205 .   DOI: 10.1088/0256-307X/28/4/044205
Abstract   PDF(pc) (640KB) ( 421 )
Aiming at the problem of luminance uniformity for injection electroluminescent display panels, we present a new scan method for display panels according to successive scans theory. First, on the basis of the number of pixels requiring light emitting in one frame period, we adjust the scan time for each row. Secondly, for ensuring image transmission synchronization, the frame period must to be a constant. We adopt a 64×32 LED display panel as an example to expound the new scan method and we obtain the good result that the reduce amplitude of luminance non-uniformity is 31.34% and the increase amplitude of the average luminance value is 7.8258%.
Q-Switched Thulium-Doped Domestic Silica Fiber Laser
HU Hui, DU Ge-Guo**, YAN Pei-Guang, ZHAO Jun-Qing, GUO Chun-Yu, RUAN Shuang-Chen
Chin. Phys. Lett. 2011, 28 (4): 044206 .   DOI: 10.1088/0256-307X/28/4/044206
Abstract   PDF(pc) (545KB) ( 396 )
We report a cladding-pumped Tm3+-doped domestic silica fiber laser operated at 2 µm and actively Q-switched with an acousto-optic modulator. Pulse trains are obtained as pumped by a 785 nm laser diode. The maximum average output power is 1.27 W. Peak power up to 4.2 kW and pulse energy up to 840 µJ are obtained with the pulse duration of 200 ns produced at a repetition rate of 1 kHz. The laser performance is studied under different repetition rates and pump powers. Lastly, we give some discussion.
Coupling Frequency Band of the In-Phase Locked Gain Waveguide Array Lasers
SHA Peng-Fei, XIN Jian-Guo**, FANG Li-Ping, LIU Zheng-Fan, ZHOU Ying, YU Song-Lin, WEN Jian-Guo
Chin. Phys. Lett. 2011, 28 (4): 044207 .   DOI: 10.1088/0256-307X/28/4/044207
Abstract   PDF(pc) (611KB) ( 340 )
A coupling frequency band of an in-phase locked sliced gain waveguide array laser is experimentally investigated. The experimental data show that for an in-phase locked single peak intensity distribution output without side lobes of the sliced gain waveguide array laser, there exists a coupling frequency band and the coupling frequency band increases as the transmissivity of the laser output coupler decreases.
Polarized Spatial Splitting of Four-Wave Mixing Signal in Multi-Level Atomic Systems
FU Yu-Xin, ZHAO Jin-Yan, SONG Yue, DAI Guo-Xian, HUO Shu-Li, ZHANG Yan-Peng**
Chin. Phys. Lett. 2011, 28 (4): 044208 .   DOI: 10.1088/0256-307X/28/4/044208
Abstract   PDF(pc) (664KB) ( 458 )
We illustrate our experimental observation of the periodic changes of spatial splitting of the generated four-wave mixing (FWM) signal induced by different polarization states of one of the dressing beams. It is pointed out that the changes of intensity of the dressing beam and the FWM signal have influences on the spatial splitting and their influences compete with each other. The differences between p- and s-polarized FWM beams are demonstrated. The influences of the dressing beams, which lead to the larger spatial splitting with different polarization states or frequency detuning, are observed as well.
Suppression of FM-to-AM Conversion in Broadband Third-Harmonic Generation of Nd:Glass Laser
CHEN Ying, QIAN Lie-Jia**, ZHU He-Yuan, FAN Dian-Yuan
Chin. Phys. Lett. 2011, 28 (4): 044209 .   DOI: 10.1088/0256-307X/28/4/044209
Abstract   PDF(pc) (687KB) ( 405 )
Frequency modulation to amplitude modulation (FM-to-AM) conversion is important for controlling temporal shapes of high-power Nd:glass lasers in the application of fusion ignition. To suppress this FM-to-AM conversion effect in the process of broadband third-harmonic generation of Nd:glass laser, we report an efficient frequency-tripling scheme based on mixing narrowband and broadband pulses. Numerical results show that the FM-to-AM conversion in frequency conversion process can be suppressed effectively. For a required third-harmonic bandwidth of 1 THz, the defined relative modulation α in pulse intensity is as large as 180% in the conventional baseline design, while it will be reduced to only about 20% by using our proposed scheme.
Hysteretic Nonlinearity of Sub-harmonic Emission from Ultrasound Contrast Agent Microbubbles
QIU Yuan-Yuan, ZHENG Hai-Rong, ZHANG Dong**
Chin. Phys. Lett. 2011, 28 (4): 044301 .   DOI: 10.1088/0256-307X/28/4/044301
Abstract   PDF(pc) (588KB) ( 423 )
Sub-harmonic contrast imaging promises to improve ultrasound imaging quality by taking advantage of increased contrast to tissue signal. The aim of this study is to examine the hysteretic nonlinearity of sub-harmonic component emitted from microbubbles. Two kinds of microbubble solutions, i.e. Sonovue® and a self-developed contrast agent, are utilized in the study. The hysteretic curves for increasing and decreasing acoustic pressure are theoretically predicted by the Marmottant model and confirmed by measurements. The results reveal that for both microbubble solutions, the development of the rising ramp undergoes three stages, i.e. occurrence, growth and saturation; while hysteresis effect appears in the descending ramp. SonoVue® microbubbles exhibit better sub-harmonic performance over the self-developed UCAs microbubbles due to the difference of elastic properties of the shell.
Heat Transfer Analysis for Peristaltic Mechanism in Variable Viscosity Fluid
T. Hayat, **, F. M. Abbasi, Awatif A. Hendi
Chin. Phys. Lett. 2011, 28 (4): 044701 .   DOI: 10.1088/0256-307X/28/4/044701
Abstract   PDF(pc) (420KB) ( 559 )
An analysis is carried out for a peristaltic flow of a third-order fluid with heat transfer and variable viscosity when no-slip condition does not hold. Perturbation solution is discussed and a comparative study between the cases of constant and variable viscosities is presented and analyzed.
Flow of a Viscoelastic Fluid through a Porous Channel with Expanding or Contracting Walls
SI Xin-Hui**, ZHENG Lian-Cun, ZHANG Xin-Xin, SI Xin-Yi, YANG Jian-Hong
Chin. Phys. Lett. 2011, 28 (4): 044702 .   DOI: 10.1088/0256-307X/28/4/044702
Abstract   PDF(pc) (590KB) ( 850 )
The flow of a viscoelastic fluid in porous channels with expanding or contracting walls is investigated. Using a similar transformation, the governing equations are reduced to a nonlinear fifth-order differential equation. The homotopy analysis method is employed to obtain the expression for velocity fields. The analytical solutions are influenced by the permeation Reynolds number Re, the wall expansion ratio α and viscoelastic parameter ω. Graphs are sketched and the effects of some values of parameters, especially the expansion ratio, on the velocity fields are discussed in detail.
Spectral Characteristics of CN Radical (B→X) and Its Application in Determination of Rotational and Vibrational Temperatures of Plasma
PENG Zhi-Min, DING Yan-Jun**, ZHAI Xiao-Dong, YANG Qian-Suo, JIANG Zong-Lin
Chin. Phys. Lett. 2011, 28 (4): 044703 .   DOI: 10.1088/0256-307X/28/4/044703
Abstract   PDF(pc) (900KB) ( 326 )
The aim is to resolve the difficulties of measurement of temperature at several thousands of Celsius degrees for some unstable non-equilibrium gas flows. Based on the molecular spectroscopy theory and inherent molecular structure characteristics of the CN radical, the dependence of the spectral profile on the rotational temperature (RT), vibrational temperature (VT) and optical apparatus function are numerically explored within some certain ranges. Meanwhile, by comparing the numerically calculated spectra with the experimental spectra of the CN radical, the corresponding RT and VT of the plasma induced by the interaction of the laser pulse from an oscillated Nd:YAG laser with the coal target are determined, respectively. In addition, a short discussion on the thermodynamic state and the energy transfer process of the CN radical is also given.
Effective Shear Viscosity of Iron under Shock-Loading Condition
MA Xiao-Juan**, LIU Fu-Sheng, SUN Yan-Yun, ZHANG Ming-Jian, PENG Xiao-Juan, LI Yong-Hong
Chin. Phys. Lett. 2011, 28 (4): 044704 .   DOI: 10.1088/0256-307X/28/4/044704
Abstract   PDF(pc) (597KB) ( 377 )
We combine the flyer-impact experiment and improve the finite difference method to solve whether the shear viscosity coefficient of shock iron is more reliable. We find that the numerical simulated profile agrees well with the measured one, from which the determined effective shear viscosity coefficients of shocked iron are 3000±100 Pas and 4000±100 Pas, respectively, at 103 GPa and 159 GPa. These values are more than 2000±300 Pas of Li Y L et al.[Chin. Phys. Lett. 26 (2009) 038301] Our values are more reasonable because they are obtained from a comprehensive simulation for the full-shocked perturbation evolving process.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Numerical Reproduction of Spatio-Temporal Evolution of Surface Plasmon Polaritons at Dielectric-Plasma Interface
CHEN Zhao-Quan, **, LIU Ming-Hai***, ZHOU Qi-Yan, HU Ye-Lin, YANG An, ZHU Long-Ji, HU Xi-Wei
Chin. Phys. Lett. 2011, 28 (4): 045201 .   DOI: 10.1088/0256-307X/28/4/045201
Abstract   PDF(pc) (746KB) ( 497 )
Discharges in planar-type overdense plasmas caused by resonant excitation of surface plasmon polaritons (SPPs) are presented. The spatio-temporal evolution of surface waves of SPPs at the dielectric-plasma interface is reproduced numerically. It is found that different discharge light patterns are excited by different spatio-temporal wave fields. Moreover, the corrugation surface included in the proposed plasma sources plays a significant role in producing large-area uniform plasmas.
Non Planar Electrostatic Solitary Wave Structures in Negative Ion Degenerate Plasma
S. Hussain, * N. Akhtar, Saeed-ur-Rehman
Chin. Phys. Lett. 2011, 28 (4): 045202 .   DOI: 10.1088/0256-307X/28/4/045202
Abstract   PDF(pc) (438KB) ( 346 )
Theoretical and numerical studies are performed for quantum ion acoustic solitons in planar and non-planar geometries in an unmagnetized homogenous plasma consisting of warm positive and negative ions with nonthermal electrons. A deformed Korteweg de Vries (DKdV) equation is derived by using the reductive perturbation method. The numerical solution to the DKdV equation indicates that the quantum parameter, temperatures of positive ions, temperture of negative ions and electron density blatantly influence the propagation speed and the structure of quantum ion acoustic solitons. The geometrical effects on the structure of quantum ion acoustic wave are discussed. It is shown that the amplitude and propagation speed in spherical geometry is larger as compared to cylinderical and planar geometries for different values of the above-mentioned parameters.
Spatial-Temporal Patterns in a Dielectric Barrier Discharge under Narrow Boundary Conditions in Argon at Atmospheric Pressure
LI Xue-Chen**, JIA Peng-Ying, ZHAO Na
Chin. Phys. Lett. 2011, 28 (4): 045203 .   DOI: 10.1088/0256-307X/28/4/045203
Abstract   PDF(pc) (792KB) ( 524 )
Pattern formation phenomena are investigated in a dielectric barrier discharge under narrow boundary conditions in argon at atmospheric pressure. The discharge shows various scenarios with the increasing applied voltage. This is the first observation of alternating single spot and pair spots pattern and of a moving striation pattern in a dielectric barrier discharge system. The spatial-temporal correlations between discharge filaments in these patterns are measured by an optical method. The results show that the zigzag pattern is an interleaving of two sub-structure patterns, which ignites once for each sub-pattern per half cycle of the applied voltage. There is a temporal sequence inversion in consecutive half-cycles for the two sub-patterns. The pattern of alternating single spot and pair spots is also an interleaving of two sub-structure patterns. However, the pair spots sub-pattern ignites twice and the single spot sub-pattern ignites once per half cycle of the applied voltage.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Pressure-Induced Anomalous Phase Transitions and Colossal Enhancements of Piezoelectricity in Ground-State BaTiO3
DUAN Yi-Feng**, QIN Li-Xia, SHI Li-Wei, TANG Gang
Chin. Phys. Lett. 2011, 28 (4): 046101 .   DOI: 10.1088/0256-307X/28/4/046101
Abstract   PDF(pc) (579KB) ( 474 )
Rhombohedral BaTiO3 under hydrostatic pressure is investigated by first principles calculations. Our results show that just like tetragonal perovskites, as pressure increases, this material first becomes para-electric at low pressures, then transfers to another ferroelectric phase at much higher pressures. We also find a giant enhancement of piezoelectricity near the phase-transition regions, due to large atomic displacements along different directions in response to the applied pressures.
Monte Carlo Simulation of the Potts Model on a Dodecagonal Quasiperiodic Structure
WEN Zhang-Bin, HOU Zhi-Lin, FU Xiu-Jun**
Chin. Phys. Lett. 2011, 28 (4): 046102 .   DOI: 10.1088/0256-307X/28/4/046102
Abstract   PDF(pc) (576KB) ( 357 )
By means of a Monte Carlo simulation, we study the three-state Potts model on a two-dimensional quasiperiodic structure based on a dodecagonal cluster covering pattern. The critical temperature and exponents are obtained from finite-size scaling analysis. It is shown that the Potts model on the quasiperiodic lattice belongs to the same universal class as those on periodic ones.
Improving the Quality of the Deteriorated Regions of Multicrystalline Silicon Ingots during General Solar Cell Processes
WU Shan-Shan, WANG Lei**, YANG De-Ren
Chin. Phys. Lett. 2011, 28 (4): 046103 .   DOI: 10.1088/0256-307X/28/4/046103
Abstract   PDF(pc) (883KB) ( 383 )
The behavior of wafers and solar cells from the border of a multicrystalline silicon (mc-Si) ingot, which contain deteriorated regions, is investigated. It is found that the diffusion length distribution of minority carriers in the cells is uniform, and high efficiency of the solar cells (about 16%) is achieved. It is considered that the quality of the deteriorated regions could be improved to be similar to that of adjacent regions. Moreover, it is indicated that during general solar cell fabrication, phosphorus gettering and hydrogen passivation could significantly improve the quality of deteriorated regions, while aluminum gettering by RTP could not. Therefore, it is suggested that the border of a mc-Si ingot could be used to fabricate high efficiency solar cells, which will increase mc-Si utilization effectively.
Molecule Statistical Thermodynamics Simulation of Nanoindentation of Single Crystal Copper with EAM Potential
TAN Hao, WANG Hai-Ying**, XIA Meng-Fen, KE Fu-Jiu, BAI Yi-Long
Chin. Phys. Lett. 2011, 28 (4): 046201 .   DOI: 10.1088/0256-307X/28/4/046201
Abstract   PDF(pc) (700KB) ( 385 )
The quasistatic nanoindentation process of a spherical indenter in a single crystal copper is investigated with the molecular statistical thermodynamics (MST) method based on the embedded atom method (EAM) potential. The indentation modulus obtained in the MST simulation is 129.9 GPa, which agrees well with the theoretical prediction (129 GPa). In the elastic regime, the obtained maximum displacement of the indenter is two times the contact depth and the contact area is qualitatively proportional to the contact depth, which agrees well with Hertzian elastic theory of contact. The MST simulation can reproduce the nucleation of dislocation as well. Moreover, the efficiency of the MST method is about 8 times higher than that of traditional MD simulations.
Surface Effects on the Postbuckling of Nanowires
LI Bin, **, LI Chuan-Xi, WEI Cheng-Long,
Chin. Phys. Lett. 2011, 28 (4): 046202 .   DOI: 10.1088/0256-307X/28/4/046202
Abstract   PDF(pc) (480KB) ( 595 )
A core-shell model that accounts for surface effects is suggested to investigate the postbuckling behavior of nanowires. The corresponding critical load, buckling wavenumber and amplitude incorporated in the surface effects are analytically derived. The results demonstrate that the surface effects have a strong influence on the buckling amplitude of each order. This study can not only shed light on the postbuckling of nanowires but also provide an method for measuring the physical parameters of nanowires used in nano-devices.
Effect of the Viscosity of Silicone Oil on the Aggregation Behavior of C:F Clusters on a Silicone Oil Liquid Substrate
DENG Yan-Hong, YE Chao**, YUAN Yuan, LIU Hui-Min, CUI Jin
Chin. Phys. Lett. 2011, 28 (4): 046601 .   DOI: 10.1088/0256-307X/28/4/046601
Abstract   PDF(pc) (483KB) ( 465 )
We investigate the effect of silicone oil viscosity on the aggregation behavior of C:F clusters deposited on silicone oil liquid substrates with viscous coefficients of 100, 350 and 500 mm2/s by C4F8 dual−frequency capacitively coupled plasma. The aggregated C:F clusters all exhibit a branch-like fractal structure. However, the fractal dimension decreases from 1.67 to 1.45 with the silicone oil viscous coefficient increasing from 100 mm2/s to 500 mm2/s. Owing to the fractal dimension of 1.67 and 1.45, corresponding to the diffusion-limited-aggregation (DLA) model and the cluster-cluster-aggregation (CCA) model respectively, the results show that the increase of silicone oil viscosity can lead to the change of C:F clusters aggregating on a silicone oil liquid substrate from DLA to CCA growth.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Ideal Strengths and Bonding Properties of PuO2 under Tension
WANG Bao-Tian, ZHANG Ping**
Chin. Phys. Lett. 2011, 28 (4): 047101 .   DOI: 10.1088/0256-307X/28/4/047101
Abstract   PDF(pc) (761KB) ( 423 )
We perform a first-principles computational tensile test on PuO2 based on density−functional theory within a local density approximation (LDA)+U formalism to investigate its structural, mechanical, magnetic and intrinsic bonding properties in four representative directions: [001], [100], [110] and [111]. The stress−strain relations show that the ideal tensile strengths in the four directions are 81.2, 80.5, 28.3 and 16.8 GPa at strains of 0.36, 0.36, 0.22 and 0.18, respectively. The [001] and [100] directions are prominently stronger than the other two directions since more Pu–O bonds participate in the pulling process. By charge and density of state analysis along the [001] direction, we find that the strong mixed ionic/covalent character of the Pu–O bond is weakened by tensile strain and PuO2 will exhibit an insulator-to-metal transition after tensile stresses exceeding about 79 GPa.
Rectifying Properties of a Nitrogen/Boron-Doped Capped-Carbon-Nanotube-Based Molecular Junction
ZHAO Peng**, LIU De-Sheng, ZHANG Ying, WANG Pei-Ji, ZHANG Zhong
Chin. Phys. Lett. 2011, 28 (4): 047301 .   DOI: 10.1088/0256-307X/28/4/047301
Abstract   PDF(pc) (804KB) ( 414 )
Based on the non-equilibrium Green's function method and first-principles density functional theory calculations, we investigate the electronic transport properties of a nitrogen/boron-doped capped-single-walled carbon-nanotube-based molecular junction. Obvious rectifying behavior is observed and it is strongly dependent on the doping site. The best rectifying performance can be carried out when the nitrogen/boron atom dopes at a carbon site in the second layer. Moreover, the rectifying performance can be further improved by adjusting the distance between the C60 nanotube caps.
Electronic Density Decay Lengths of Pb Films from First Principles Calculations
LI Meng, JIN Hong-Bo, LI Jin-Ming, SUN Qiang, JIA Yu**
Chin. Phys. Lett. 2011, 28 (4): 047302 .   DOI: 10.1088/0256-307X/28/4/047302
Abstract   PDF(pc) (636KB) ( 330 )
The electronic density decay lengths of freestanding Pb films are investigated by first-principles calculations. The results show that, like surface energy and work function, the electronic density decay length λ exhibits pronounced oscillatory behavior as a function of film thickness and this is expected to have an impact on surface chemical reactivity. For freestanding Pb(111) films, λ oscillates following a bilayer pattern interrupted by crossovers, and the separation between two neighbor crossovers is 9 monolayers. For the films on Si(111) substrates, the oscillations of the decay lengths are similar to those of freestanding films except for an extra phase shift.
Deflection Reduction of GaN Wafer Bowing by Coating or Cutting Grooves in the Substrates
SUN Tao, WANG Ming-Qing, SUN Yong-Jian, WANG Bo-Ping, ZHANG Guo-Yi, TONG Yu-Zhen, DUAN Hui-Ling**
Chin. Phys. Lett. 2011, 28 (4): 047303 .   DOI: 10.1088/0256-307X/28/4/047303
Abstract   PDF(pc) (527KB) ( 761 )
GaN films on sapphire substrates are obtained using the metal-organic chemical vapor deposition growth technique. We present two methods to reduce the GaN wafer bowing caused by the mismatch of the thermal expansion coefficients (TECs) between the film and the substrate. The first method is to use coating materials on the back side of the substrate whose TECs are smaller than that of the GaN films. The second is to cut grooves on the back side of the sapphire substrate and filling the grooves with appropriate materials (e.g., tungsten, silicon nitride). For each method, we minimize wafer bowing and even reduce it to zero. Moreover, the two methods can reduce stress concentration and suppress the propagation of cracks in the GaN/sapphire structure.
Electronic Properties of Bilayer Zigzag Graphene Nanoribbons: First Principles Study
OUYANG Fang-Ping, **, CHEN Li-Jian, XIAO Jin, ZHANG Hua
Chin. Phys. Lett. 2011, 28 (4): 047304 .   DOI: 10.1088/0256-307X/28/4/047304
Abstract   PDF(pc) (644KB) ( 627 )
Based on the density functional theory, we calculate the dependence of the band structures of bilayer zigzag-edged graphene nanoribbons (BZGNRs) upon ribbon width, interlayer distance and stacking styles. Unlike monolayer zigzag GNR, whose energy gap is always zero under different ribbon widths, the gap of BZGNR varies greatly with the ribbon width or the interlayer distance. The greatest gaps for AA-stacking and AB-stacking BZGNRs are about 0.22 eV and 0.12 eV, respectively, which implies that gap-tuning of AA-BZGNRs is more effective than that of AB-BZGNRs. These results present a way to tune the band structures of BZGNRs and also provide theoretical guidance for the fabrication of GNR-based piezoelectric devices.
Heat Transport in Graphene Ferromagnet-Insulator-Superconductor Junctions
LI Xiao-Wei
Chin. Phys. Lett. 2011, 28 (4): 047401 .   DOI: 10.1088/0256-307X/28/4/047401
Abstract   PDF(pc) (500KB) ( 454 )
We study heat transport in a graphene ferromagnet-insulator-superconducting junction. It is found that the thermal conductance of the graphene ferromagnet-insulator-superconductor (FIS) junction is an oscillatory function of the barrier strength χ in the thin−barrier limit. The gate potential U0 decreases the amplitude of thermal conductance oscillation. Both the amplitude and phase of the thermal conductance oscillation varies with the exchange energy Eh. The thermal conductance of a graphene FIS junction displays the usual exponential dependence on temperature, reflecting the s-wave symmetry of superconducting graphene.
Energy Gap Dependence on Mn Content in a Diluted Magnetic Quantum Dot
P. Nalini, A. John Peter**
Chin. Phys. Lett. 2011, 28 (4): 047501 .   DOI: 10.1088/0256-307X/28/4/047501
Abstract   PDF(pc) (546KB) ( 371 )
Positively charged donor exciton binding energy is computed as a function of quantum-dot size within the single band effective mass approximation for different Mn contents in Cd1−xin MnxinTe/Cd1−x outMnxoutTe. The exciton bound polaron is computed for 0≤x≤0.08, on the Mn mole fraction. We determine the energy gap using the mean field approximation and incorporate the exchange interaction between the carrier and the magnetic impurity. The interband emission energy is studied with the height and radius of the cylindrical quantum dot. Valence-band anisotropy is included in our theoretical model using different hole masses in different spatial directions. Spin polaronic shifts as functions of quantum-dot radius and Mn concentration are estimated using the mean field theory. It is found that (i) the energy gap depends on the Mn mole fraction, (ii) it increases linearly with an increase in Mn content, and (iii) the effect is more pronounced for a narrow dot, showing the quantum size effects. Our results are in good agreement with other recently published reports.
Spectral Resolution Effects on the Lineshape of Photoreflectance
MA Li-Li, SHAO Jun**, LÜ, Xiang, GUO Shao-Ling, LU Wei**
Chin. Phys. Lett. 2011, 28 (4): 047801 .   DOI: 10.1088/0256-307X/28/4/047801
Abstract   PDF(pc) (505KB) ( 377 )
Spectral resolution effects on the lineshape of photoreflectance (PR) spectroscopy is experimentally investigated. PR measurements are performed on HgCdTe epilayer and InAs/GaAs quantum dot (QD) low-dimensional samples at low temperatures in a spectral resolution range from 8 to 0.5 meV. The results indicate that the resolution affects not only the identification of narrow PR features, but also the determination of critical-point energies of identified PR features, and a spectral resolution of as high as 0.5 meV may be necessary for low-dimensional semiconductors. The spectral resolution is indeed a crucial parameter, for which the step-scan Fourier transform infrared spectrometer-based PR technique is preferable.
Multilayer Antireflection Coating for Triple Junction Solar Cells
ZHAN Feng**, WANG Hai-Li, HE Ji-Fang, WANG Juan, HUANG She-Song, NI Hai-Qiao, NIU Zhi-Chuan
Chin. Phys. Lett. 2011, 28 (4): 047802 .   DOI: 10.1088/0256-307X/28/4/047802
Abstract   PDF(pc) (1954KB) ( 1519 )
According to the theory of optical films, we simulate the reflectivity of antireflection coatings (ARCs) for solar cells of Ga0.5In0.5P/GaAs/Ge based on an optical transfer matrix. In order to provide sufficient consideration of the refractive index dispersion effect of multilayer ARCs, we use multi−dimensional matrix data for reliable simulation. After the reflection curves are obtained, the effective average reflectance Re is introduced to optimize the film system by minimizing Re. Optimization of single layer (Al2O3), double layer (MgF2/ZnS) and triple layer (MgF2/Al2O3/ZnS) ARCs is realized by using this method for space and terrestrial applications. Effects of these ARCs are compared after optimization. These theoretical parameters can be used to guide experiments.
Improved Hole-Blocking and Electron Injection Using a TPBI Interlayer at the Cathode Interface of OLEDs
LIAN Jia-Rong**, NIU Fang-Fang, LIU Ya-Wei, ZENG Peng-Ju
Chin. Phys. Lett. 2011, 28 (4): 047803 .   DOI: 10.1088/0256-307X/28/4/047803
Abstract   PDF(pc) (488KB) ( 815 )
The effect of a benzimidazole derivative (TPBI) electron injection layer (EIL) on the performance of Alq3 based organic light−emitting devices (OLEDs) with a Cs2CO3/Al cathode is investigated. An increasing current density from 71.9 mA/cm2 to 188.3 mA/cm2, and an enhanced electroluminescence (EL) efficiency from 3.2 cd/A to 3.64 cd/A at 9 V are found when a thin TPBI layer (5 nm) is inserted at the Alq3/Cs2CO3 interface. After further increasing the TPBI thickness to 10 nm, OLEDs display a further increase in EL efficiency to 4.53 cd/A. Our experiment suggests that the TPBI thin layer at the Alq3/Cs2CO3 interface facilitates the electron injection and is also involved with hole-blocking and exciton confinement.
Femtosecond Time-Resolved Resonance-Enhanced CARS of Gaseous Iodine at Room Temperature
HE Ping, FAN Rong-Wei, XIA Yuan-Qin, YU Xin, YAO Yong, CHEN De-Ying, **
Chin. Phys. Lett. 2011, 28 (4): 047804 .   DOI: 10.1088/0256-307X/28/4/047804
Abstract   PDF(pc) (520KB) ( 431 )
Time-resolved resonance-enhanced coherent anti-Stokes Raman scattering (CARS) is applied to investigate molecular dynamics in gaseous iodine. 40 fs laser pulses are applied to create and monitor the high vibrational states of iodine at room temperature (corresponding to a vapor pressure as low as about 35 Pa) by femtosecond time-resolved CARS. Depending on the time delay between the probe pulse and the pump/Stokes pulse pairs, the high vibrational states both on the electronically ground states and the excited states can be detected as oscillations in the CARS transient signal. It is proved that the femtosecond time-resolved CARS technique is a promising candidate for investigating the molecular dynamics of a low concentration system and can be applied to environmental and atmospheric monitoring measurements.
Preparation of Gd2O2S:Yb,Ho Phosphor via Thermolysis of Sulfur−Contained (Gd,Yb,Ho)[S2CN(C4H8)]3 Phen Complexes
ZHONG Hai-Yang, LUO Xi-Xian**, MA Lu-Bin, ZHANG Ming, XING Ming-Ming, FU Yao
Chin. Phys. Lett. 2011, 28 (4): 047805 .   DOI: 10.1088/0256-307X/28/4/047805
Abstract   PDF(pc) (469KB) ( 662 )
A novel handy single-source precursor method is adopted to prepare Gd2O2S:Yb,Ho up−conversion phosphors. Pure Gd2O2S:Yb0.06Ho0.02 phosphors are prepared via thermolysis of the air−stable ternary solid complexes RE[S2CN(C4H8)]3phen (RE=Gd, Yb, Ho) in a nitrogen atmosphere with certain amount of oxygen at 600–1100 °C. The as−prepared Gd2O2S:Yb0.06Ho0.02 exhibits a strong green up−conversion luminescence under 980 nm IR excitation. The intensity of the green emission component is 37.4 and 53.4 times more than that of the red and NIR emissions, respectively. It is indicated that the material is of excellent color purity. Under an IR excitation density of 34.75 mW/mm2 with a laser beam diameter of 1 mm, the material exhibits an up−conversion luminescence brightness of 43.68 Cd/m2.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Stress Control in GaN Grown on 6H-SiC by Metalorganic Chemical Vapor Deposition
CHEN Yao**, JIANG Yang, XU Pei-Qiang, MA Zi-Guang, WANG Xiao-Li, WANG Lu, JIA Hai-Qiang, CHEN Hong
Chin. Phys. Lett. 2011, 28 (4): 048101 .   DOI: 10.1088/0256-307X/28/4/048101
Abstract   PDF(pc) (537KB) ( 555 )
The strain in GaN epitaxial layers grown on 6H-SiC substrates with an AlN buffer by metalorganic chemical vapor deposition is investigated. It is found that the insertion of a graded AlGaN layer between the GaN layer and the AlN buffer can change the signs of strain. A compressive strain in an overgrown thick (2 µm) GaN layer is obtained. High-resolution x-ray diffraction, Raman spectroscopy and photoluminescence measurements are used to determine the strain state in the GaN layers. The mechanism of stress control by inserting graded AlGaN in subsequent GaN layers is discussed briefly.
Growth of 2 µm Crack-Free GaN on Si(111) Substrates by Metal Organic Chemical Vapor Deposition
WEI Meng**, WANG Xiao-Liang, XIAO Hong-Ling, WANG Cui-Mei, PAN Xu, HOU Qi-Feng, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (4): 048102 .   DOI: 10.1088/0256-307X/28/4/048102
Abstract   PDF(pc) (580KB) ( 1141 )
A 2 µm high quality crack-free GaN film was successfully grown on 2-inch Si(111) substrates by metal organic chemical vapor deposition with a high temperature AlN/graded-AlGaN multibuffer and an AlN/GaN superlattice interlayer. It is found that the structures, as well as the thicknesses of the multibuffer and interlayer, are crucial for the growth of a crack-free GaN epilayer. The GaN(0002) XRD FWHM of the crack-free sample is 479.8 arcsec, indicating good crystal quality. An AlGaN/GaN heterostructure was grown and tested by Van der Pauw Hall measurement. The electron mobility of two-dimensional electron gas increases from 1928 cm2/Vs to 12277 cm2/Vs when the test-temperature decreases from room temperature to liquid nitrogen temperature. The electron mobility is comparable to that of AlGaN/GaN heterostructures grown on sapphire, and the largest value is obtained for an AlGaN/GaN/Si(111) heterostructure grown by metal organic chemical vapor deposition.
A Monte Carlo Simulation of a Monomer Dimer CO-O2 Catalytic Reaction on the Surface and Subsurface of a Face-centered Cubic Lattice
K. Iqbal, A. Basit**
Chin. Phys. Lett. 2011, 28 (4): 048201 .   DOI: 10.1088/0256-307X/28/4/048201
Abstract   PDF(pc) (477KB) ( 333 )
The presence of oxygen in the subsurface in monomer-dimer reactions (CO-O2 and NO−CO) is observed experimentally. The effect of subsurface oxygen on a CO-O2 catalytic reaction on a face-centered cubic (FCC) lattice is studied using Monte Carlo simulation. The effect of adding subsurface neighbours on the phase diagram is also extensively explored. It is observed that the subsurface oxygen totally eliminates the typical second order phase transition. It is also shown that the introduction of the diffusion of O atoms and the subsurface of the FCC lattice shifts the single transition point towards the stoichiometric ratio.
Thermoelectric Properties of Te-Doped Ba0.32Co4Sb12−xTexPrepared at HPHT
REN Guo-Zhong, LIU Yang, MA Hong-An, SU Tai-Chao, LIN Le-Jing, DENG Le, JIANG Yi-Ping, ZHENG Shi-Zhao, JIA Xiao-Peng**
Chin. Phys. Lett. 2011, 28 (4): 048401 .   DOI: 10.1088/0256-307X/28/4/048401
Abstract   PDF(pc) (712KB) ( 399 )
Polycrystalline skutterudites Ba0.32Co4Sb12−xTex (nominally x=0.1–0.7) are synthesized by the high pressure and high temperature (HPHT) method. The influence of Te substitution on electrical transport properties are investigated in the temperature range of 300–710 K. All the samples show n−type conduction. It is found that the presence of Te substantially decreases electrical resistivity without any detrimental effect on the Seebeck coefficients, which improves the power factor. Among all the samples, Ba0.32Co4Sb11.5Te0.5 shows the highest thermoelectric figure of merit of 0.76 at 710 K.
Scale-Free Brain Networks Based on the Event-Related Potential during Visual Spatial Attention
LI Ling**, JIN Zhen-Lan
Chin. Phys. Lett. 2011, 28 (4): 048701 .   DOI: 10.1088/0256-307X/28/4/048701
Abstract   PDF(pc) (476KB) ( 332 )
The human brain is thought of as one of the most complex dynamical systems in the universe. The network view of the dynamical system has emerged since the discovery of scale-free networks. Brain functional networks, which represent functional associations among brain regions, are extracted by measuring the temporal correlations from electroencephalogram data. We measure the topological properties of the brain functional network, including degree distribution, average degree, clustering coefficient and the shortest path length, to compare the networks of multi-channel event-related potential activity between visual spatial attention and unattention conditions. It is found that the degree distribution of the brain functional networks under both the conditions is a power law distribution, which reflects a scale-free property. Moreover, the scaling exponent of the attention condition is significantly smaller than that of the unattention condition. However, the degree distribution of equivalent random networks does not follow the power law distribution. In addition, the clustering coefficient of these random networks is smaller than those of brain networks, and the shortest path length of these random networks is large and comparable with those of brain networks. Our results, typical of scale-free networks, indicate that the scaling exponent of brain activity could reflect different cognitive processes.
DNA Conformational Variations Induced by Stretching 3'5'-Termini Studied by Molecular Dynamics Simulations
QI Wen-Peng, LEI Xiao-Ling**
Chin. Phys. Lett. 2011, 28 (4): 048702 .   DOI: 10.1088/0256-307X/28/4/048702
Abstract   PDF(pc) (508KB) ( 351 )
Investigating the interaction between protein and stretched DNA molecules has become a new way to study the protein DNA interaction. The conformations from different stretching methods give us a further understanding of the interaction between protein and DNA. We study the conformational variations of a 22-mer DNA caused by stretching both 3'− and 5'−termini by molecular dynamics simulations. It requires 250 kJ/mol to stretch the DNA molecule by 3'5'−termini for 3.5 nm and the force plateau is at 123.8 pN. The stretching 3'5'−termini leads to large values of the angle opening and the dihedral propeller between bases in one base pair, the double helix untwists from 34° to 20° and the successive base pairs rolls to the side of the DNA major groove. The distances between successive base pairs increases from 3.2 Å to 5.6 Å.
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