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Volume 29 Issue 12
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GENERAL
Application of the Binary Bell Polynomials Method to the Dissipative (2+1)-Dimensional AKNS Equation
LIU Na, LIU Xi-Qiang
Chin. Phys. Lett. 2012, 29 (12): 120201 .   DOI: 10.1088/0256-307X/29/12/120201
Abstract   PDF(pc) (411KB) ( 1065 )
Based on the binary Bell polynomials, the bilinear representation, bilinear B?cklund transformation and the Lax pair for the dissipative (2+1)-dimensional Ablowitz–Kaup–Newell–Segur (AKNS) equation are obtained. Moreover, the infinite conservation laws are also derived.
Wave Interaction and Resonance in a Non-Ideal Gas
Rajan Arora, Mohd. Junaid Siddiqui, V. P. Singh
Chin. Phys. Lett. 2012, 29 (12): 120202 .   DOI: 10.1088/0256-307X/29/12/120202
Abstract   PDF(pc) (388KB) ( 579 )
The method of multiple time scales is used to obtain the asymptotic solutions to the planar and non-planar flows into a non-ideal gas. The transport equations for the amplitudes of resonantly interacting high frequency waves are also found. Furthermore, the evolutionary behavior of non-resonant wave modes culminating into shock waves is studied.
Quantum Fidelity and Thermal Phase Transitions in a Two-Dimensional Spin System
WANG Bo, HUANG Hai-Lin, SUN Zhao-Yu, KOU Su-Peng
Chin. Phys. Lett. 2012, 29 (12): 120301 .   DOI: 10.1088/0256-307X/29/12/120301
Abstract   PDF(pc) (1193KB) ( 621 )
We investigate the ability of quantum fidelity in detecting the classical phase transitions (CPTs) in a two-dimensional Heisenberg–Ising mixed spin model, which has a very rich phase diagram and is exactly soluble. For a two-site subsystem of the model, the reduced fidelity (including the operator fidelity and the fidelity susceptibility) at finite temperatures is calculated, and it is found that an extreme value presents at the critical temperature, thus shows a signal for the CPTs. In some parameter region, the signal becomes blurred. We propose to use the "normalized fidelity susceptibility" to solve this problem.
Violation of Leggett–Garg Inequalities in Single Quantum Dots
SUN Yong-Nan, ZOU Yang, GE Rong-Chun, TANG Jian-Shun, LI Chuan-Feng
Chin. Phys. Lett. 2012, 29 (12): 120302 .   DOI: 10.1088/0256-307X/29/12/120302
Abstract   PDF(pc) (472KB) ( 372 )
We investigate the violation of two types of Leggett–Garg (LG) inequalities in self-assembled quantum dots under the stationarity assumption. By comparing the two types of LG inequalities, we find the better one that is easier to be tested in an experiment. In addition, we show that the fine-structure splitting, background noise and temperature of quantum dots greatly affect the violation of LG inequalities.
Quantum Stackelberg Duopoly with Continuous Distributed Incomplete Information
WANG Xia , HU Cheng-Zheng
Chin. Phys. Lett. 2012, 29 (12): 120303 .   DOI: 10.1088/0256-307X/29/12/120303
Abstract   PDF(pc) (2447KB) ( 448 )
A general model of the quantum Stackelberg duopoly is constructed by introducing the "minimal" quantum structure into the Stackelberg duopoly with continuous distributed incomplete information, where both players only know the continuous distribution of the competitor's unit cost. In this model, the cases with complete information, discrete distributed incomplete information, and continuous distributed asymmetric information are all involved. Because of different roles played by the total information uncertainty and the information asymmetry, the game exhibits some new interesting features, such as the total information uncertainty can counteract or improve the first-mover advantage according to the value of the quantum entanglement. What's more, this general model will be helpful for the government to reduce the abuses of oligopolistic competition and to improve the economic efficiency.
Propagation of Spiking and Burst-Spiking Synchronous States in a Feed-Forward Neuronal Network
ZHANG Xi, HUANG Hong-Bin, LI Pei-Jun, WU Fang-Ping, WU Wang-Jie, JIANG Min
Chin. Phys. Lett. 2012, 29 (12): 120501 .   DOI: 10.1088/0256-307X/29/12/120501
Abstract   PDF(pc) (1070KB) ( 353 )
Neuronal firing that carries information can propagate stably in neuronal networks. One important feature of the stable states is their spatiotemporal correlation (STC) developed in the propagation. The propagation of synchronous states of spiking and burst-spiking neuronal activities in a feed-forward neuronal network with high STC is studied. Different dynamic regions and synchronous regions of the second layer are clarified for spiking and burst-spiking neuronal activities. By calculating correlation, it is found that five layers are needed for stable propagation. Synchronous regions of the 4th layer and the 10th layer are compared.
Generalized Zero-Temperature Glauber Dynamics in a Two-Dimensional Square Lattice
MENG Qing-Kuan, FENG Dong-Tai, GAO Xu-Tuan, MEI Yu-Xue
Chin. Phys. Lett. 2012, 29 (12): 120502 .   DOI: 10.1088/0256-307X/29/12/120502
Abstract   PDF(pc) (541KB) ( 396 )
A new spin flipping mechanism at zero-temperature is proposed based on a node model. In a two-dimensional square lattice, at the zero-temperature, the spin flipping depends on both itself and the surroundings, while the influence from the surroundings is embodied by an adjustable parameter. With the parameter adjusting, a first order phase transition is observed.
Nonlocal Symmetry of the Lax Equation Related to Riccati-Type Pseudopotential
WANG Yun-Hu, CHEN Yong, XIN Xiang-Peng
Chin. Phys. Lett. 2012, 29 (12): 120503 .   DOI: 10.1088/0256-307X/29/12/120503
Abstract   PDF(pc) (403KB) ( 427 )
We investigate the Lax equation that can be employed to describe motions of long waves in shallow water under gravity. A nonlocal symmetry of this equation is given and used to find exact solutions and derive lower integrable models from higher ones. It is interesting that this nonlocal symmetry links with its corresponding Riccati-type pseudopotential. By introducing suitable and simple auxiliary dependent variables, the nonlocal symmetry is localized and used to generate new solutions from trivial solutions. Meanwhile, this equation is reduced to an ordinary differential equation by means of this nonlocal symmetry and some local symmetries.
Quantum Friction
Roumen Tsekov
Chin. Phys. Lett. 2012, 29 (12): 120504 .   DOI: 10.1088/0256-307X/29/12/120504
Abstract   PDF(pc) (409KB) ( 425 )
The Brownian motion of a light quantum particle in a heavy classical gas is theoretically described and a new expression for the friction coefficient is obtained for arbitrary temperature. At zero temperature it equals the de Broglie momentum of the mean free path divided by the mean free path. Alternatively, the corresponding mobility of the quantum particle in the classical gas is equal to the square of the mean free path divided by the Planck constant. The Brownian motion of a quantum particle in a quantum environment is also discussed.
Anti-Synchronization of Chaotic Systems via Adaptive Sliding Mode Control
Wafaa Jawaada, M. S. M. Noorani, M. Mossa Al-sawalha
Chin. Phys. Lett. 2012, 29 (12): 120505 .   DOI: 10.1088/0256-307X/29/12/120505
Abstract   PDF(pc) (437KB) ( 1141 )
An anti-synchronization scheme is proposed to achieve the anti-synchronization behavior between chaotic systems with fully unknown parameters. A sliding surface and an adaptive sliding mode controller are designed to gain the anti-synchronization. The stability of the error dynamics is proven theoretically using the Lyapunov stability theory. Finally numerical results are presented to justify the theoretical analysis.
Acoustic Nonlinearity of a Laser-Generated Surface Wave in a Plastically Deformed Aluminum Alloy
KIM Chung-Seok, JHANG Kyung-Young
Chin. Phys. Lett. 2012, 29 (12): 120701 .   DOI: 10.1088/0256-307X/29/12/120701
Abstract   PDF(pc) (569KB) ( 453 )
The acoustic nonlinearity of surface waves is studied to evaluate plastic deformation in aluminum alloys. A narrow-band surface wave is successfully generated by a pulsed Nd-YAG laser system consisting of a beam expander and a slit mask. Various degrees of tensile deformation are induced by interrupting the tensile tests so as to obtain aluminum specimens with different degrees of plastic damage. The normalized acoustic nonlinearity increases as a function of tensile strain. The experimental results show that the acoustic nonlinearity of a laser-generated surface wave has a good correlation with the level of tensile deformation and has a potential to evaluate microdamage induced by dislocation microplasticity.
High Performance Micro CO Sensors Based on ZnO-SnO2 Composite Nanofibers with Anti-Humidity Characteristics
YUE Xue-Jun, HONG Tian-Sheng, XIANG Wei, CAI Kun, XU Xing
Chin. Phys. Lett. 2012, 29 (12): 120702 .   DOI: 10.1088/0256-307X/29/12/120702
Abstract   PDF(pc) (821KB) ( 586 )
ZnO-SnO2 composite nanofibers are synthesized via an electrospinning method and characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Micro sensors are fabricated by spinning the nanofibers on Si substrates with Pt signal and heater electrodes. The sensors with small areas (600 μm×200 μm) can detect CO down to 1 ppm at 360°C. The corresponding sensitivity, response time, and recovery time are 3.2, 6 s, and 11 s, respectively. Importantly, the sensors can operate at high humidity conditions. The sensitivity only decreases to 2.3 when the sensors are exposed to 1 ppm CO at 95% relative humidity. These excellent sensing properties are due to combining the benefits of one-dimensional nanomaterials and the ZnO-SnO2 grain boundary in the nanofibers.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
An Anomaly Associated with Ward–Takahashi Identity for Pseudo-Tensor Current in QED
BAO Ai-Dong, SUN Yi-Qian, WANG Dan
Chin. Phys. Lett. 2012, 29 (12): 121101 .   DOI: 10.1088/0256-307X/29/12/121101
Abstract   PDF(pc) (435KB) ( 338 )
We study the quantum anomaly for the transverse Ward–Takahashi relations in the four-dimensional gauge theory QED by using Fujikawa's method in which the anomaly is fundamentally a variation of the functional integral measure under transformation. A regulator which leads to a finite result for the anomaly is proposed. It is shown that a novel anomaly associated with transverse Ward–Takahashi identity of pseudo-tensor current is derived due to a set of infinitesimal transverse transformation of field variables.
NUCLEAR PHYSICS
Photon Linear Polarization Coefficient of the Radiative Capture Process 2H(p,γ)3He at Thermal Energies
H. Sadeghi
Chin. Phys. Lett. 2012, 29 (12): 122101 .   DOI: 10.1088/0256-307X/29/12/122101
Abstract   PDF(pc) (572KB) ( 318 )
The photon polarization parameter of the proton-deuteron radiative capture process at thermal proton energies is calculated up to leading order (LO), using pionless effective field theory (EFT). In order to make a comparative study of this model, we compare our results for the photon polarization parameter with the realistic Argonne (AV14) and Argonne v18(AV18) modern nucleon-nucleon potentials and Urbana IX or Tucson-Melbourne three-nucleon interactions. The theoretical description of the 2H(p,γ)3He reaction at thermal energies is complicated by the presence of the Coulomb interaction. Only the s-wave capture contribution to the thermal energy of this reaction is calculated. Three-body currents give small but significant contributions to some of the observables in the proton-deuteron radiative capture cross section at thermal neutron energies. Our result is in good agreement with the available experimental data and potential models' calculation at this order.
Effect of Short-Range and Tensor Force Correlations on High-Density Behavior of Symmetry Energy
XU Chang, REN Zhong-Zhou
Chin. Phys. Lett. 2012, 29 (12): 122102 .   DOI: 10.1088/0256-307X/29/12/122102
Abstract   PDF(pc) (573KB) ( 365 )
The effect of short-range and tensor correlations on nuclear symmetry energy is investigated by using realistic nuclear momentum distribution n(k). For finite nuclei, the n(k) is discussed in detail within an analytical model that allows inclusion of both short-range and tensor correlation effects in a physically very transparent way. The equation of state of symmetric nuclear matter is calculated by using realistic n(k) parameterization. The tensor-force induced short-range correlations are shown to have a significant impact on the behavior of symmetry energy.
The Neutrino Energy Loss by Electron Capture of Nuclides 52,53,54,55,56Fe in Core-Collapse Supernova
LIU Jing-Jing
Chin. Phys. Lett. 2012, 29 (12): 122301 .   DOI: 10.1088/0256-307X/29/12/122301
Abstract   PDF(pc) (493KB) ( 304 )
Using the shell-model Monte Carlo method and random phase approximation theory, we carry out an estimation on neutrino energy loss (NEL) of 52,53,54,55,56Fe. We find the NEL rates increase greatly at some typical stellar conditions, and even exceed eight orders of magnitude. On the other hand, in order to compare our results of λSMMCLJ (which are calculated by using the SMMC method) with those of λFFNLJ (which are calculated by using the Fuller-Fowler-Newman (FFN) method), the error factor C, between λSMMCLJ and λFFNLJ, is discussed and shows that at higher density and temperature, the fit is fairly good for the two results (λSMMCLJ and λFFNLJ), and the maximum error is ~6.20%. However, the maximum error is ~95.50% (e.g. 53Fe) at lower density and temperature.
ATOMIC AND MOLECULAR PHYSICS
Stereodynamics Study of Li+HF/DF/TF→LiF+H/D/T Reactions on X2A' Potential Energy Surface
TAN Rui-Shan, LIU Xin-Guo, HU Mei
Chin. Phys. Lett. 2012, 29 (12): 123101 .   DOI: 10.1088/0256-307X/29/12/123101
Abstract   PDF(pc) (9400KB) ( 384 )

The product rotational polarizations of reactions Li+HF/DF/TF at different collision energies are calculated using the quasi-classical trajectory method based on a new potential energy surface constructed by Aguado and Paniagua [J. Chem. Phys. 119 (2003) 10088]. We investigate the P(θr) distributions describing the kj' correlation, the P(φr) distributions describing the kk'j' correlation, and the four polarization-dependent generalized differential cross sections. Furthermore, we compare the influences of mass factor and collision energy in detail and find that the isotope substitution has more impact on the distribution of the product's angular momentum vectors than the collision energy.

Experimental Determination (∼mHz) of the Ground-State Hyperfine Separation of Trapped 199Hg+ in a Hyperbolic Paul Trap
HE Yue-Hong, SHE Lei, CHEN Yi-He, YANG Yu-Na, LIU Hao, LI Jiao-Mei
Chin. Phys. Lett. 2012, 29 (12): 123201 .   DOI: 10.1088/0256-307X/29/12/123201
Abstract   PDF(pc) (509KB) ( 475 )
The Ramsey fringes on the ground-state hyperfine transition of 199Hg+ (ΔF=1, ΔmF=0) ions trapped in a hyperbolic Paul trap are firstly observed with the method of time-separated oscillatory fields. The full width at half maximum of central Ramsey fringes is about 25 mHz and the corresponding quality factor Q of the line is greater than 1012 for the trapped 199Hg+ microwave frequency standard. The hyperfine transition frequency shifted by magnetic field is also measured by the high-resolution Ramsey fringes. The final result is Δνhfs=40507347997.3(0.5) Hz, which is corrected to zero magnetic field.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
The 1×4 Optical Splitters Based on Silicon Photonic Crystal Self-Collimation Ring Resonators
ZHUANG Dong-Xia, CHEN Xi-Yao, LI Jun-Jun, QIANG Ze-Xuan, JIANG Jun-Zhen, CHEN Zhi-Yong, QIU Yi-Shen, LI Hui
Chin. Phys. Lett. 2012, 29 (12): 124201 .   DOI: 10.1088/0256-307X/29/12/124201
Abstract   PDF(pc) (4162KB) ( 460 )
We report 1 × 4 optical splitters (OSs) with different splitting ratios based on either rod-type or hole-type silicon photonic crystal self-collimation ring resonators (SCRRs). The four beam splitters of the OSs are formed by changing the radii of silicon rods or air holes. The light beam propagating along the SCRR can be controlled by the self-collimation effect. The transmission spectra at the through and drop ports are investigated by using the finite-difference time-domain (FDTD) method. The simulated results agree well with the theoretical calculation. For 1550-nm dropping wavelength, the free spectral ranges for rod-type and hole-type configurations are 28.8 nm and 32.5 nm, respectively, which almost cover the whole optical communication C-band window. The dimensions of these structures are only about 10 μm × 10 μm .
Ultrastable Fiber-Based Time-Domain Balanced Homodyne Detector for Quantum Communication
WANG Xu-Yang, BAI Zeng-Liang, DU Peng-Yan, LI Yong-Min, PENG Kun-Chi
Chin. Phys. Lett. 2012, 29 (12): 124202 .   DOI: 10.1088/0256-307X/29/12/124202
Abstract   PDF(pc) (2226KB) ( 784 )
We present an ultrastable fiber-based time-domain balanced homodyne detector which can be used for precise characterization of pulsed quantum light fields. A variable optical attenuator based on bending the fiber is utilized to compensate for the different quantum efficiencies of the photodiodes precisely, and a common mode rejection ratio of above 76 dB is achieved. The detector has a gain of 3.2 μV per photon and a signal-to-noise ratio above 20 dB. Optical pulses with repetition rates up to 2 MHz can be measured with a detection efficiency of 66%. The stability of the detector is analyzed via an Allan variance measurement and the detector exhibits superior stability which enables a 100-s window for measurement without calibration.
Information Transferring between a Photon's Orbital Angular Momentum and Frequency
LIU Rui-Feng, ZHANG Pei, GAO Hong, LI Fu-Li
Chin. Phys. Lett. 2012, 29 (12): 124203 .   DOI: 10.1088/0256-307X/29/12/124203
Abstract   PDF(pc) (440KB) ( 378 )
A photon's orbital angular momentum (OAM) offers a promising resource for the higher-dimensional quantum information process, which is due to the infinite values of OAM. One of the obstacles for its application is that it is difficult to transmit information encoded in OAM space in long distance quantum communication, e.g., photons with different OAMs are unsupported in optical fiber transmitting. We propose an efficient scheme to transform the information from OAM to frequency. Then the information encoded in frequency freedom can be used in fiber transmission and finally be recovered to OAM from frequency. Our scheme can be easily extended to higher-dimensional quantum information transferring between OAM and frequency.
A Switchable Multi-wavelength Erbium-Doped Photonic Crystal Fiber Laser with Linear Cavity Configuration
ZHENG Wan-Jun, CHENG Jian-Qun, RUAN Shuang-Chen**, ZHANG Min, LIU Wen-Li, YANG Xi, ZHANG Ying-Ying
Chin. Phys. Lett. 2012, 29 (12): 124204 .   DOI: 10.1088/0256-307X/29/12/124204
Abstract   PDF(pc) (1105KB) ( 432 )
A switchable multi-wavelength erbium-doped photonic crystal fiber laser with a linear cavity configuration based on a Sagnac loop mirror is proposed and demonstrated experimentally. The laser is based on saturated spectral hole burning and the polarization hole burning effects can be switched among single-wavelength, dual-wavelength, triple-wavelength and quadruple-wavelength outputs at room temperature. The wavelength period of the output spectrum is easily varied by using polarization maintaining fibers of different lengths. The proposed fiber laser has a signal-to-noise ratio of higher than 30 dB and achieves a low threshold power of 37 mW. The power fluctuations of the lasing lines are less than 0.54 dB,1.7 dB and 2.9 dB when the laser operates at single-wavelength, dual-wavelength and triple-wavelength for one hour.
Terahertz Wave Confinement in Pillar Photonic Crystal with a Tapered Waveguide and a Point Defect
WANG Chang-Hui, KUANG Deng-Feng, CHANG Sheng-Jiang, LIN Lie
Chin. Phys. Lett. 2012, 29 (12): 124205 .   DOI: 10.1088/0256-307X/29/12/124205
Abstract   PDF(pc) (628KB) ( 415 )
We demonstrate a photonic crystal cavity with a tapered waveguide and a point defect to highly confine terahertz waves. The terahertz wave is first guided into the tapered waveguide, gradually compressed to its end, and finally confined in the point defect cavity. Numerical simulations with the finite-difference time-domain method indicate that the narrow band terahertz wave is highly confined in the point defect cavity with a quality factor of 5323. The demonstrated device may be used as an antenna for enhancing light-matter interactions in the point defect cavity at terahertz frequencies and may improve the sensitivity of terahertz near-field microscopy.
A Switchable and Tunable Dual-Wavelength Actively Mode-Locked Fiber Laser Based on Dispersion Tuning
MEI Jia-Wei**, XIAO Xiao-Sheng, GUI Li-Li, XU Ming-Rui, YANG Chang-Xi
Chin. Phys. Lett. 2012, 29 (12): 124206 .   DOI: 10.1088/0256-307X/29/12/124206
Abstract   PDF(pc) (653KB) ( 360 )
A switchable and tunable dual-wavelength actively mode-locked fiber laser based on a dispersion tuning technique is proposed and demonstrated. Synchronous wavelength tuning of dual-wavelength operation with wavelength spacing of 22.9 nm can be achieved up to 23.2 nm by changing the modulation frequency. The proposed laser can operate in dual-wavelength or single-wavelength by simple adjustment of the polarization controller. Moreover, wavelength spacing can also be varied from 22 to 45 nm at the cost of a reduced tuning range by changing the harmonic order, which is determined by the modulation frequency. These experimental observations agree well with the theoretical analysis.
Three-Dimensional Hermite–Bessel–Gaussian Soliton Clusters in Strongly Nonlocal Media
JIN Hai-Qin, LIANG Jian-Chu, CAI Ze-Bin, LIU Fei, YI Lin
Chin. Phys. Lett. 2012, 29 (12): 124207 .   DOI: 10.1088/0256-307X/29/12/124207
Abstract   PDF(pc) (1490KB) ( 435 )
We analytically and numerically demonstrate the existence of Hermite–Bessel–Gaussian spatial soliton clusters in three-dimensional strongly nonlocal media. It is found that the soliton clusters display the vortex, dipole azimuthon and quadrupole azimuthon in geometry, and the total number of solitons in the necklaces depends on the quantum number n and m of the Hermite functions and generalized Bessel polynomials. The numerical simulation is basically identical to the analytical solution, and white noise does not lead to collapse of the soliton, which confirms the stability of the soliton waves. The theoretical predictions may give new insights into low-energetic spatial soliton transmission with high fidelity.
Analytic Solutions for the Spectral Responses of RCA-Grating-Based Waveguide Devices
ZENG Xiang-Kai, WEI Lai
Chin. Phys. Lett. 2012, 29 (12): 124208 .   DOI: 10.1088/0256-307X/29/12/124208
Abstract   PDF(pc) (455KB) ( 301 )
Analytic solutions (ASs) for the spectral responses of waveguide devices with raised-cosine-apodized (RCA) gratings are presented. The waveguide devices include short- and long-period RCA-gratings, RCA-grating-based interferometers as Fabry–Perot, Mach–Zehnder and Michelson interferometers. The calculations based on the analytic solutions are demonstrated and compared with those based on the transfer matrix (TM) method preferred, which has confirmed that the AS-based analysis is with enough accuracy and several thousands times the efficiency of the TM method.
The Generation Mechanism of Airy–Bessel Wave Packets in Free Space
REN Zhi-Jun, YING Chao-Fu, FAN Chang-Jiang, WU Qiong
Chin. Phys. Lett. 2012, 29 (12): 124209 .   DOI: 10.1088/0256-307X/29/12/124209
Abstract   PDF(pc) (453KB) ( 467 )

Localized optical Airy–Bessel configuration wave packets were first generated on the basis of a grating-telescope combination [Nat. Photon. 4 (2010) 103]. By studying the spatially induced group velocity dispersion effect of ultrashort pulsed Bessel beams during propagation, we find the universal physical foundation of generating Airy–Bessel wave packets (ABWs) in free space. The research results are expected to open up more common channels for generating stable linear localized ABWs.

Blue-Extended Supercontinuum Generation in Photonic Crystal Fibers with Picosecond Pulse Pumping
ZHU Xian, ZHANG Xin-Ben, CHEN Xiang, PENG Jing-Gang, DAI Neng-Li, LI Jin-Yan
Chin. Phys. Lett. 2012, 29 (12): 124210 .   DOI: 10.1088/0256-307X/29/12/124210
Abstract   PDF(pc) (569KB) ( 423 )
We report supercontinuum generation extending to the blue spectral region using pulses of 1.8 ps duration at 1040 nm in GeO2-doped core photonic crystal fibers. A spectrum in fundamental mode spanning from 415 nm to beyond 1750 nm is generated in a uniform photonic crystal fiber (PCF). A zero dispersion wavelength decreasing PCF is fabricated to optimize the parameters for deeper blue components generated by cross-phase modulation and group-velocity matching. Although the PCF is pumped at a low input power of 1.3 W in anomalous dispersion and relatively far from the zero dispersion wavelength, a flat continuum covering 406.1–671.8 nm is generated, which is of primary importance in a number of bio-photonic applications such as fluorescence imaging microscopy.
Temporal, Spectral and Spatial Characterization of High-Energy Laser Pulse with Small Bandwidth Propagating through Long Path
DENG Xue-Wei, WANG Fang, JIA Huai-Ting, XIANG Yong, FENG Bin, LI Ke-Yu, ZHOU Li-Dan
Chin. Phys. Lett. 2012, 29 (12): 124211 .   DOI: 10.1088/0256-307X/29/12/124211
Abstract   PDF(pc) (725KB) ( 576 )
Temporal, spectral and spatial characters of 0.3-nm-bandwidth high-energy laser pulse propagating through a long path are studied in detail in one newly constructed beamline of our laser facility. The evolution of propagation, pulse energy and near-field deterioration are analyzed theoretically and experimentally. Substituting argon for air is demonstrated effectively to suppress stimulated rotational Raman scattering and the experimental result provides operating criterion, and engineering parameters for the under-constructed beamlines.
Adaptive Polarization Control of Fiber Amplifier Based on SPGD Algorithm
XIONG Yu-Peng, SU Rong-Tao, LI Xiao, HOU Pu, WANG Xiao-Lin, XU Xiao-Jun
Chin. Phys. Lett. 2012, 29 (12): 124212 .   DOI: 10.1088/0256-307X/29/12/124212
Abstract   PDF(pc) (402KB) ( 462 )
We demonstrate an adaptive polarization control system of a 10.2 W non-polarization-maintaining fiber amplifier based on stochastic parallel gradient decent (SPGD) algorithm. The experimental investigation shows that the system can used to compensate for the polarization fluctuation of the fiber amplifier effectively and perform well over a long-time observation. When the adaptive polarization control system is in closed loop, the extinction ratio increases from 2.28 dB to 11.54 dB, and more than 93.4% of the total power in desired polarization direction is achieved.
Analysis of Imperfect Acoustic Cloaking Resonances
KIM Seungil
Chin. Phys. Lett. 2012, 29 (12): 124301 .   DOI: 10.1088/0256-307X/29/12/124301
Abstract   PDF(pc) (1701KB) ( 364 )
We study the resonance phenomenon arising from imperfect acoustic cloaking in 2D based on a small perturbation of the transformation acoustics. It is shown that the resonant frequencies of imperfect cloaking appearing in the total scattering cross section converge to Dirichlet eigenvalues of the concealed region as a perturbation parameter approaches zero. This theory enables us to predict the location of the resonant frequencies of imperfect cloaking and to identify the corresponding resonance modes.
Monte Carlo Simulation of Scattered Light with Shear Waves Generated by Acoustic Radiation Force for Acousto-Optic Imaging
LU Ming-Zhu, WU Yu-Peng, SHI Yu, GUAN Yu-Bo, GUO Xiao-Li, WAN Ming-Xi
Chin. Phys. Lett. 2012, 29 (12): 124302 .   DOI: 10.1088/0256-307X/29/12/124302
Abstract   PDF(pc) (778KB) ( 399 )
A Monte Carlo method of multiple scattered coherent light with the information of shear wave propagation in scattering media is presented. The established Monte-Carlo algorithm is mainly relative to optical phase variations due to the acoustic-radiation-force shear-wave-induced displacements of light scatterers. Both the distributions and temporal behaviors of optical phase increments in probe locations are obtained. Consequently, shear wave speed is evaluated quantitatively. It is noted that the phase increments exactly track the propagations of shear waves induced by focus-ultrasound radiation force. In addition, attenuations of shear waves are demonstrated in simulation results. By using linear regression processing, the shear wave speed, which is set to 2.1 m/s in simulation, is estimated to be 2.18 m/s and 2.35 m/s at time sampling intervals of 0.2 ms and 0.5 ms, respectively.
Mixed Convection Heat Transfer in Micropolar Nanofluid over a Vertical Slender Cylinder
Abdul Rehman, S. Nadeem
Chin. Phys. Lett. 2012, 29 (12): 124701 .   DOI: 10.1088/0256-307X/29/12/124701
Abstract   PDF(pc) (609KB) ( 1169 )
Analysis is carried for the problem of boundary layer steady flow and heat transfer of a micropolar fluid containing nanoparticles over a vertical cylinder. The governing partial differential equations of linear momentum, angular momentum, heat transfer and nano concentration are reduced to nonlinear coupled ordinary differential equations by applying the boundary layer approximations and a suitable similarity transformation. These nonlinear coupled ordinary differential equations, subject to the appropriate boundary conditions, are then solved by using the homotopy analysis method. The effects of the physical parameters on the flow, heat transfer and nanoparticle concentration characteristics of the model are presented through graphs and the salient features are discussed.
The Normalized Analysis of a Surface Heterogeneous Reaction of a Propane/Air Mixture into a Micro-Channel
A. Fanaee, J. A. Esfahani
Chin. Phys. Lett. 2012, 29 (12): 124702 .   DOI: 10.1088/0256-307X/29/12/124702
Abstract   PDF(pc) (474KB) ( 370 )
The effect of catalytic surface reaction on non-reactive flow in micro-channels is investigated. The hydraulic diameter of the channel is considered within the range of 0.2–1.2 mm, and the channel length is considered to be 5 mm. The whole length of the channel wall is coated with a catalyst. The sensitivity analysis shows that the effect of normalized hydraulic diameter is more than the normalized longitude coordinates in accordance with the existence of the large ratio of surface area to volume in the micro-channel. For validation of this model, the variation of fuel conversion is compared with the published experimental data and shows an acceptable agreement.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Temperature Characteristics of Cathode Sheath in High-Pressure Volume Discharge Derived from Emanating Shock Wave
YANG Chen-Guang, XU Yong-Yue, ZUO Du-Luo
Chin. Phys. Lett. 2012, 29 (12): 125201 .   DOI: 10.1088/0256-307X/29/12/125201
Abstract   PDF(pc) (563KB) ( 396 )
The temperature characteristics of cathode sheath in high-pressure volume discharge are investigated experimentally. The cathode sheath temperatures under various discharge conditions are derived from the speeds of the emanating shock waves which are measured by a Mach–Zehnder interferometry. It is found that the cathode sheath temperature and the ratio ΔT3/ΔT1 of temperature rise between cathode sheath and plasma bulk are determined by the specific energy deposition and the breakdown delay time respectively. These results are helpful for discharge stability improving and shock wave reducing.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Determination of the Lattice Parameters of a Si Nanobelt in a Tensile Test Process Using an MEMS Actuator
ZENG Hong-Jiang, LI Tie, JIN Qin-Hua, XU Fang-Fang, WANG Yue-Lin
Chin. Phys. Lett. 2012, 29 (12): 126101 .   DOI: 10.1088/0256-307X/29/12/126101
Abstract   PDF(pc) (705KB) ( 636 )
We present an experimental method for in-situ observation of the lattice behavior of a single crystal silicon nanobelt during uniaxial tensile testing. An in-situ silicon nanobelt tensile testing device for transmission electron microscopy is developed. Atomic behavior and lattice parameters of the nanobelt are studied using selected area electron diffraction. A statistical and least square methods are used for reducing the measurement errors of the lattice parameters. The results suggest that the trends of the lattice parameters during the tensile test are in agreement with the increasing tensile stress in the silicon nanobelt. Furthermore, the local strain calculated from lattice parameters and the average strain of the nanobelt are compared.
Growth of Self-Catalyzed InP Nanowires by Metalorganic Chemical Vapour Deposition
LV Xiao-Long, ZHANG Xia, YAN Xin, LIU Xiao-Long, CUI Jian-Gong, LI Jun-Shuai, HUANG Yong-Qing, REN Xiao-Min
Chin. Phys. Lett. 2012, 29 (12): 126102 .   DOI: 10.1088/0256-307X/29/12/126102
Abstract   PDF(pc) (1381KB) ( 484 )
The fabrication of self-catalyzed InP nanowires (NWs) is investigated under different growth conditions. Indium droplets induced by surface reconstruction act as nucleation sites for NW growth. Vertical standing NWs with uniform cross sections are obtained under optimized conditions. It is confirmed that the growth rate of NWs is strongly affected by the surface diffusion adatoms while contributions from the direct impingement of vapor species onto the In droplets can be negligible. The results indicate that the droplet acts as an adatom collector rather than a catalyst. Moreover, the diffusion flow rate of adatoms increases with time at the beginning of growth and stabilizes as the growth proceeds.
A Raman Study of the Origin of Oxygen Defects in Hexagonal Manganite Thin Films
CHEN Xiang-Bai, HIEN Nguyen Thi Minh, YANG In-Sang, LEE Daesu, NOH Tae-Won
Chin. Phys. Lett. 2012, 29 (12): 126103 .   DOI: 10.1088/0256-307X/29/12/126103
Abstract   PDF(pc) (482KB) ( 536 )
Oxygen defects are usually unavoidable when synthesizing oxide thin films. We study the origin of the oxygen defects in hexagonal manganite HoMnO3 epitaxial thin films through Raman scattering spectroscopy. Our results show that the oxygen defects in hexagonal HoMnO3 thin films have distinct effects on different phonon modes and on magnon scattering. Our analyses indicate that the oxygen defects in hexagonal HoMnO3 thin films mainly originate from the basal O3 and/or O4 oxygen vacancies. Furthermore, our analyses of oxygen defects predict that the Mn 3d orbitals would be more strongly hybridized with the apical O1 and/or O2 2p orbitals than the basal O3 and/or O4 2p orbitals. This prediction is consistent with our resonant Raman scattering study and earlier first-principle calculations of the electronic structures of hexagonal manganites.
A Potential Hydrogen-Storage Media: C2H4 and C5H5 Molecules Doped with Rare Earth Atoms
LEI Hong-Wen, ZHANG Hong, GONG Min, WU Wei-Dong
Chin. Phys. Lett. 2012, 29 (12): 126801 .   DOI: 10.1088/0256-307X/29/12/126801
Abstract   PDF(pc) (862KB) ( 402 )
Using first-principles calculations, we predict that a single C2H4 or C5H5 molecule can form a stable complex with two rare earth metals such as La, Eu, and Ho. The La2C2H4 complex then absorbs up to sixteen hydrogen molecules, reaching a gravimetric storage capacity of 9.5wt% by adding a rare-earth metal atom, The results show that Eu-4f electrons have little impact on the hydrogen adsorption. The nature of bonding between Eu and H2 is due to the hybridization of Eu-5d with the H-1s orbital.
Modification of Optical Band Gap and Surface Morphology of NiTsPc Thin Films
Muhamad Saipul Fakir, Zubair Ahmad Khaulah Sulaiman
Chin. Phys. Lett. 2012, 29 (12): 126802 .   DOI: 10.1088/0256-307X/29/12/126802
Abstract   PDF(pc) (753KB) ( 437 )
We demonstrate the effects of solvent treatment on the optical band gap and surface morphology of nickel (ii) phthalocyanine tetrasulfonic acid tetrasodium salt (NiTsPc) thin films. The optical band gap and surface morphology modifications are carried out by immersing the films in chloroform for different immersion times until the optimized time (60 min) is found. A Tauc plot is used to calculate the optical energy gaps, which are found to be about 2.70–2.85 eV and 1.43–1.50 eV, in the B and Q bands respectively. AFM topography shows that more granular structures have been formed upon the optimized immersion time. Photoluminescence (PL) quenching occurs in the solvent-treated NiTsPc film incorporated with a tris(8-hydroxyquinolinato)aluminium (Alq3) layer. This PL quenching indicates that the charge carrier transport is more efficient at the interface between NiTsPc/Alq3 as a result of the solvent treatment.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
New Method to Deal with Three-Dimensional Electron Gas with a Strong Correlation Effect
YU Zhi-Ming, GUO Qian, LIU Yu-Liang
Chin. Phys. Lett. 2012, 29 (12): 127101 .   DOI: 10.1088/0256-307X/29/12/127101
Abstract   PDF(pc) (562KB) ( 331 )
Similar to the bosonization method in one dimension, we divide the electron operators in phase space into two component operators, and study three-dimensional homogeneous electron gas with a strong correlation effect. We apply this method to calculate the pair distribution function g(r=0,rs) and the renormalization coefficient of the one-electron Green's function Z(kF)(ZF), and show that it has great advantages of succinctness and efficiency for studying one- and three-dimensional systems with a strong correlation effect. This method can be applied to investigate interaction quenches in ultracold atomic gases.
Influence of Oxygen Partial Pressure on the Fermi Level of ZnO Films Investigated by Kelvin Probe Force Microscopy
SU Ting, ZHANG Hai-Feng
Chin. Phys. Lett. 2012, 29 (12): 127102 .   DOI: 10.1088/0256-307X/29/12/127102
Abstract   PDF(pc) (1438KB) ( 775 )
The influence of oxygen partial pressure on the Fermi level of ZnO films prepared by pulsed laser deposition is investigated. The contact potential difference of the ZnO films fabricated under various oxygen partial pressures is studied systematically using Kelvin probe force microscopy. The Fermi level shifted by 0.35 eV as oxygen partial pressure increased. This indicates a significant change in the electronic structure and energy balance in ZnO films. This fact provides a consistent explanation that the changes in carrier concentration, resistivity and mobility of ZnO films are attributed to oxygen vacancy induced shift of the Fermi level.
Influence of Pressure on the Structural, Electronic and Mechanical Properties of Cubic SrHfO3: A First-Principles Study
FENG Li-Ping, WANG Zhi-Qiang, LIU Qi-Jun, TAN Ting-Ting, LIU Zheng-Tang
Chin. Phys. Lett. 2012, 29 (12): 127103 .   DOI: 10.1088/0256-307X/29/12/127103
Abstract   PDF(pc) (1771KB) ( 579 )
The structural, electronic and mechanical properties of cubic SrHfO3 under hydrostatic pressure up to 70 GPa are investigated using the first-principles density functional theory (DFT). The calculated lattice parameter, elastic constants and mechanical properties of cubic SrHfO3 at zero pressure are in good agreement with the available experimental data and other calculational values. As pressure increases, cubic SrHfO3 will change from an indirect band gap (Γ R) compound to a direct band gap (ΓΓ) compound. Charge densities reveal the coexistence of covalent bonding and ionic bonding in cubic SrHfO3. With the increase of pressure, both the covalent bonding (HfO) and ionic bonding (SrO) are strengthened. Cubic SrHfO3 is mechanically stable when pressure is lower than 55.1 GPa, whereas that is instable when pressure is higher than 55.1 GPa. With the increasing pressure, enthalpy, bulk modulus, shear modulus and Young's modulus increase, whereas the lattice parameter decreases. Moreover, cubic SrHfO3 under pressure has higher hardness and better ductility than that at zero pressure.
A New Method to Calculate the Rashba Spin Splitting in III-Nitride Heterostructures
LI Ming, SUN Gang, FAN Li-Bo
Chin. Phys. Lett. 2012, 29 (12): 127104 .   DOI: 10.1088/0256-307X/29/12/127104
Abstract   PDF(pc) (574KB) ( 352 )
By constructing proper basis functions, the Kane Hamiltonian is transformed to two separate Hamiltonians, and the Schr?dinger equation for conduction-band envelope functions can be obtained by eliminating the valence band components of the envelope functions. Then we decouple the up-spin and down-spin states and derive the expression for the Rashba coefficient and single-particle energy, considering the spin-orbit coupling and the nonparabolicity corrections. Finally, we calculate the Rashba spin splitting for AlxGa1?xN/GaN heterostructures by using the variational method. The Rashba spin splitting calculated here is of the same order of magnitude as in other III–V materials, showing that the internal electric field caused by the high concentration of the 2DEG is crucial for considerable Rashba spin splitting
Onset for the Electron Velocity Overshoot in Indium Nitride
Clóves G. Rodrigues
Chin. Phys. Lett. 2012, 29 (12): 127201 .   DOI: 10.1088/0256-307X/29/12/127201
Abstract   PDF(pc) (751KB) ( 334 )
A theoretical study on the electron drift velocity and electron nonequilibrium temperature of indium nitride (InN) is presented. It is based on a nonlinear quantum kinetic theory which provides a description of the dissipative phenomena developing in the system. The ultrafast time evolution of the electron drift velocity and electron nonequilibrium temperature is obtained, and overshoot effects are evidenced on both of them. The overshoot onsets are shown to occur at 4 kV/cm, electric field intensity which is considerably smaller than those recently derived by resorting to Monte Carlo simulations.
Analysis of Off-State Leakage Current Characteristics and Mechanisms of Nanoscale MOSFETs with a High-k Gate Dielectric
LIU Hong-Xia, MA Fei
Chin. Phys. Lett. 2012, 29 (12): 127301 .   DOI: 10.1088/0256-307X/29/12/127301
Abstract   PDF(pc) (646KB) ( 7106 )
The off-state leakage current characteristics of nanoscale channel metal-oxide-semiconductor field-effect transistors with a high-k gate dielectric are thoroughly investigated. The off-state leakage current can be divided into three components: the gate leakage current, the source leakage current, and the substrate leakage current. The influences of the fringing-induced barrier lowering effect and the drain-induced barrier lowering effect on each component are investigated separately. For nanoscale devices with high-k gates, the source leakage current becomes the major component of the off-state leakage current.
Laser-Induced Indium-Diffusion into Cadmium Sulfide Thin Film for Solar Cell Applications
KIM Nam-Hoon, MYUNG Kuk Do, LEE Woo-Sun
Chin. Phys. Lett. 2012, 29 (12): 127302 .   DOI: 10.1088/0256-307X/29/12/127302
Abstract   PDF(pc) (584KB) ( 810 )
Laser-induced diffusion is employed to dope indium (In) into sputtering-deposited cadmium sulfide (CdS) thin films. The increased optical band gap energy from 2.52 to 2.60 eV with maintenance of high optical transmittance about 60 nm in the 200-nm-thick films, the enhanced mobility over 42.5 cm2/V?s, and the decreased resistivity to 1.42×10?3 Ω?cm are successfully obtained to be advantageous for a window layer in solar cells.
GaSb p-Channel Metal-Oxide-Semiconductor Field-Effect Transistors with Ni/Pt/Au Source/Drain Ohmic Contacts
WU Li-Shu, SUN Bing, CHANG Hu-Dong, ZHAO Wei, XUE Bai-Qing, ZHANG Xiong, LIU Hong-Gang
Chin. Phys. Lett. 2012, 29 (12): 127303 .   DOI: 10.1088/0256-307X/29/12/127303
Abstract   PDF(pc) (740KB) ( 543 )
GaSb is an attractive candidate for future high-performance III–V p-channel metal-oxide-semiconductor-field-effect-transistors (pMOSFETs) because of its high hole mobility. The effect of HCl based-chemical cleaning on removing the non-self limiting and instable native oxide layer of GaSb to obtain a clean and smooth surface has been studied. It is observed that the rms roughness of a GaSb surface is significantly reduced from 2.731 nm to 0.693 nm by using HCl:H2O (1:3) solution. The Ni/Pt/Au ohmic contact exhibits an optimal specific contact resistivity of about 6.89×10?7 Ω?cm2 with a 60 s rapid thermal anneal (RTA) at 250°C. Based on the chemical cleaning and ohmic contact experimental results, inversion-channel enhancement GaSb pMOSFETs are demonstrated. For a 6 μm gate length GaSb pMOSFET, a maximum drain current of about 4.0 mA/mm, a drain current on-off (ION/IOFF) ratio of >103, and a subthreshold swing of ~250 mV/decade are achieved. Combined with the split CV method, a peak hole mobility of about 160 cm2/V?s is obtained for a 24 μm gate length GaSb pMOSFET.
Ultracompact Refractive Index Sensor Based on Surface-Plasmon-Polariton Interference
WANG Chen, CHEN Jian-Jun, TANG Wei-Hua, XIAO Jing-Hua
Chin. Phys. Lett. 2012, 29 (12): 127304 .   DOI: 10.1088/0256-307X/29/12/127304
Abstract   PDF(pc) (855KB) ( 413 )
Using an ultracompact groove-slit-groove (GSG) structure, a refractive index sensor with a broadband response is proposed and experimentally demonstrated. Due to the interference of surface plasmon polaritons (SPPs), the transmission spectra in the GSG structure exhibit oscillation behaviors in a broad bandwidth, and they are quite sensitive to the refractive index of the surroundings. Based on the principle, the characteristics of its refractive index sensing are demonstrated experimentally. In the experiment, the structure is illuminated with a bulk light source (not a tightly focused light source) from the back side. This decreases the difficulty of the experimental measurement and can protect strong light sources from damaging the detection samples. Meanwhile, the whole structure of the sensor can be made more ultracompact without considering the influence of the incident waves.
Enhanced Photovoltaic Properties of Gradient Doping Solar Cells
ZHANG Chun-Lei, DU Hui-Jing, ZHU Jian-Zhuo, XU Tian-Fu, FANG Xiao-Yong
Chin. Phys. Lett. 2012, 29 (12): 127305 .   DOI: 10.1088/0256-307X/29/12/127305
Abstract   PDF(pc) (631KB) ( 823 )
An optimum design of a-Si:H(n)/a-Si:H(i)/c-Si(p) heterojunction solar cell is realized with 24.27% conversion efficiency by gradient doping of the a-Si:H(n) layer. The photovoltaic properties are simulated by the AFORS-HET software. Besides the additional electric field caused by the gradient doping, the enhanced and widen spectral response also improves the solar cell performance compared with the uniform-doping mode. The simulation shows that the gradient doping is efficient to improve the photovoltaic performance of the solar cells. The study is valuable for the solar cell design with excellent performances.
Influence of Film Roughness on the Soft Magnetic Properties of Fe/Ni Multilayers
LUO Zhi-Yuan, TANG Jia, MA Bin, ZHANG Zong-Zhi, JIN Qing-Yuan, WANG Jian-Ping
Chin. Phys. Lett. 2012, 29 (12): 127501 .   DOI: 10.1088/0256-307X/29/12/127501
Abstract   PDF(pc) (640KB) ( 439 )
The influence of surface/interface roughness on the magnetic properties of Fe/Ni multilayers is investigated. Two methods are employed to tune the film roughness: one varies the substrate temperature, and the other pre-deposits a Ag underlayer on the MgO substrate. For films with higher roughness, a marked rise in coercivity is observed. Three factors are discussed to be mainly responsible for the coercivity rise, involving the formation of pinholes, the reduction of exchange coupling between Fe and Ni layers, and Fe-Ni alloying at interfaces.
Preparing Pseudo-Pure States in a Quadrupolar Spin System Using Optimal Control
TAN Yi-Peng, NIE Xin-Fang, LI Jun, CHEN Hong-Wei, ZHOU Xian-Yi, PENG Xin-Hua, DU Jiang-Feng
Chin. Phys. Lett. 2012, 29 (12): 127601 .   DOI: 10.1088/0256-307X/29/12/127601
Abstract   PDF(pc) (610KB) ( 420 )
Pseudo-pure state (PPS) preparation is crucial in nuclear magnetic resonance quantum computation. There have been some methods in spin-1/2 systems and a few attempts in quadrupolar spin systems. As optimal control via gradient ascent pulses engineering (GRAPE) has been widely used in quantum information science, we apply this technique to PPS preparation in quadrupolar spin systems. This approach shows an effective and fast quantum control method for both the state preparation and the realization of quantum gates in quadrupolar systems.
Ultrasonic Energy Transference Based on an MEMS ZnO Film Array
WU Shao-Hua, ZHAO Zhan, ZHAO Jun-Juan, GUO Li-Jun, DU Li-Dong, FANG Zhen, KONG De-Yi, XIAO Li, GAO Zhong-Hua
Chin. Phys. Lett. 2012, 29 (12): 127701 .   DOI: 10.1088/0256-307X/29/12/127701
Abstract   PDF(pc) (498KB) ( 409 )
An ultrasonic energy transference system with a ZnO square piezoelectric thin-film array (SPTFA) structure is presented. The design principle of the system is analyzed, and a device with the SPTFA structure is successfully fabricated based on MEMS processes. The characteristics of the energy transference system are investigated in detail. The experimental results reveal that the resonant frequency of the system is 13 MHz, the maximum voltage of the receiving end reaches 10.87 V when the amplitude of excitation voltage is 10 V, at that time the output power of system is 5.377 mW, and power density is 2.581 mW/cm2. The light emitting diode is lit successfully by the system in a distance of 3 mm.
A Novel Efficient Red Emitting Iridium Complex for Polymer Light Emitting Diodes
HU Zheng-Yong, YANG Jian-Kui, LUO Jing, LIANG Min, WANG Jing
Chin. Phys. Lett. 2012, 29 (12): 127801 .   DOI: 10.1088/0256-307X/29/12/127801
Abstract   PDF(pc) (714KB) ( 434 )
Photo-physical properties of iridium complexes bis(1-(2',4'-difluorobiphenyl -4-yl)isoquinoline)iridium(III)(5-(4-(bis(4-methoxyphenyl)amino)phenyl)picolinic acid) used as phosphorescent dopant in polymer light-emitting devices with a blend of poly(9,9-dioctylfluorene) and 2-tert-butyl-phenyl-5-biphenyl-1,3,4-oxadiazole as a host matrix are investigated. The iridium complex exhibits distinct UV-vis absorption bands around 300–450 nm and intense red photoluminescent emissions peaked at around 618 nm in dichloromethane. The devices display a maximum external quantum efficiency of 4.8% and luminous efficiency of 3.1 cd?A?1 at current density of 3.2 mA?cm?2 with a dominant red emission peak around 620 nm and a shoulder around 660 nm. At 100 mA?cm?2, the devices still display a maximum external quantum efficiency as high as 3.9%.
An Improvement on the Junction Temperature Measurement of Light-Emitting Diodes by using the Peak Shift Method Compared with the Forward Voltage Method
HE Su-Ming, LUO Xiang-Dong, ZHANG Bo, FU Lei, CHENG Li-Wen, WANG Jin-Bin, LU Wei
Chin. Phys. Lett. 2012, 29 (12): 127802 .   DOI: 10.1088/0256-307X/29/12/127802
Abstract   PDF(pc) (586KB) ( 428 )
The junction temperature of red, green and blue high power light emitting diodes (LEDs) is measured by using the emission peak shift method and the forward voltage method. Both the emission peak shift and the forward voltage decrease show a linear relationship relative to junction temperature. The linear coefficients of the red, green and blue LEDs for the peak shift method and the forward voltage method range from 0.03 to 0.15 nm/ °C and from 1.33 to 3.59 mV/ °C, respectively. Compared with the forward voltage method, the peak shift method is almost independent of bias current and sample difference. The variation of the slopes is less than 2% for the peak shift method and larger than 30% for the forward voltage method, when the LEDs are driven by different bias currents. It is indicated that the peak shift method gives better stability than the forward voltage method under different LED working conditions.
The Evolution of Defects in Deformed Cu-Ni-Si Alloys during Isochronal Annealing Studied by Positron Annihilation
QI Ning, JIA Yan-Lin, LIU Hui-Qun, YI Dan-Qing, CHEN Zhi-Quan
Chin. Phys. Lett. 2012, 29 (12): 127803 .   DOI: 10.1088/0256-307X/29/12/127803
Abstract   PDF(pc) (608KB) ( 479 )
The effect of isochronal annealing on the deformation-induced defects in pure Cu and Cu-Ni-Si alloys is studied by positron annihilation spectroscopy. For the cold-rolled Cu, annealing up to 900°C causes a gradual recovery of the deformation-induced defects and monotonous decrease of the hardness. This indicates that its hardening is mainly related with defects such as dislocations. However, for the hot-rolled and quenched Cu-Ni-Si alloy, although there is a partial recovery of defects after annealing below 500°C, formation of additional defects is observed after annealing above 500°C. The hardness of Cu-Ni-Si alloy has a maximum value after annealing at 500°C, which suggests that the hardening of Cu-Ni-Si alloy is not due to defects, but primarily due to the precipitation formed during annealing. Further annealing of the Cu-Ni-Si alloy above 500°C results in over-aging effect and the precipitates lose coherence with the host matrix, which leads to positron trapping by vacancy clusters in the incoherent interface region.
Origin of Ferromagnetism in Zn1−xCoxO Thin Films: Evidences Provided by Hard and Soft X-Ray Absorption Spectroscopy
XI Shi-Bo, CUI Ming-Qi, QIN Xiu-Fang, XU Xiao-Hong, XU Wei, ZHENG Lei, ZHOU Jing, LIU Li-Juan, YANG Dong-Liang, GUO Zhi-Ying
Chin. Phys. Lett. 2012, 29 (12): 127804 .   DOI: 10.1088/0256-307X/29/12/127804
Abstract   PDF(pc) (1036KB) ( 351 )
Although dilute magnetic semiconductors have promising potentials in spintronics applications, the mechanism of their ferromagnetism remains ambiguous. The extensive theoretical models and exotic experimental evidences provide self-consistent but usually contradictory explanations on its either intrinsic or extrinsic origins. We find room temperature ferromagnetism in a series of Zn1?xCoxO (0.03≤x ≤0.10) thin films prepared using magnetron co-sputtering method and treated with post-annealing at temperatures 350°C and 500°C. The origin of the ferromagnetism is investigated in terms of electronic structure combining hard x-ray absorption spectroscopy (XAS) at Zn and Co K-edge, and soft x-ray XAS at O K-edge and Co L2,3-edge. The full multiple scattering theory is employed to reinforce the interpretation of the XAS spectra, which concludes that full substitution of zinc by cobalt is responsible for the room temperature ferromagnetism due to the d states of cobalt within the framework of bound magnetic polaron. Moreover, the evidence of cobalt nanoclusters is detected at highly doped and annealed samples. The first principles calculation confirms the electronic structural evidences via the formation energy.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
The High Nitrogen Pressure Synthesis of Manganese Nitride
SI Ping-Zhan, JIANG Wei, WANG Hai-Xia, ZHONG Min, GE Hong-Liang, CHOI Chul-Jin, LEE Jung-Goo
Chin. Phys. Lett. 2012, 29 (12): 128101 .   DOI: 10.1088/0256-307X/29/12/128101
Abstract   PDF(pc) (530KB) ( 680 )
We report on the structural transformation and unique magnetic properties of manganese nitrides prepared by nitriding Mn under N2 pressures of up to 25 MPa with varying temperatures. High N2 pressure not only makes nitridation more efficient at lower temperatures, but also enhances the N-content in the nitride lattices, which were expanded with increasing N-content. The N-rich nitrides, including ε-Mn4N, ζ-Mn6N2.58 and η-Mn3N2, exhibit unique thermal behaviors. The N-rich ε-phase exhibits much larger coercivity and lower saturation magnetization in comparison with the ε-phase prepared under ambient N2 pressures. The coercivity of the N-rich ζ-phase reaches up to 45054 A/m. A saturation magnetization as large as 31 Am2/kg is observed in the N-rich η-phase. Both are quite different from the conventional antiferromagnetic ζ- and η-phase obtained under ambient N2 pressures. We ascribe the unconventional magnetic properties of the nitrides to the lattice distortion originating from the N-enrichment.
The Synthesis and Characterization of Peach-Like ZnO
A. Kamalianfar, S. A. Halim, Siamak Pilban Jahromi, M. Navasery, Fasih Ud Din, K. P. Lim, S. K. Chen, J. A. M. Zahedi
Chin. Phys. Lett. 2012, 29 (12): 128102 .   DOI: 10.1088/0256-307X/29/12/128102
Abstract   PDF(pc) (1797KB) ( 444 )
Peach-like ZnO microstructures are synthesized using vapor phase transport on MgO (001) substrates with a copper oxide (60 nm) buffer layer. The structure and morphology of the product are investigated using an x-ray diffractometer (XRD) and a field-emission scanning electron microscope. The peaches have an average diameter of 3 μm and a wurtzite structure. To study the optical properties, photoluminescence (PL) and Raman spectroscopy are employed. A strong UV emission at 380 nm in the PL spectra is observed, and a sharp and dominant peak at 437 cm?1 in the Raman spectrum can be assigned to the good crystallization of obtained product. In addition, the growth mechanism of the peach-like ZnO structure is tentatively investigated based on the EDX analysis and growth time.
The Effects of Heating Mechanism on Granular Gases with a Gaussian Size Distribution
LI Rui, XIAO Ming, LI Zhi-Hao, ZHANG Duan-Ming
Chin. Phys. Lett. 2012, 29 (12): 128103 .   DOI: 10.1088/0256-307X/29/12/128103
Abstract   PDF(pc) (572KB) ( 326 )
Two-dimensional event-driven simulations are employed to gain insight into the granular energy and segregation in granular gases with a Gaussian particle size distribution when exposed to a differential heating mechanism. It is found that the bulk value of the temperature ratio depends on the choice of differential boundary heating, while the segregation behavior is insensitive to the differential heating mechanism. Moreover, by studying the numerical model without spatial degrees of freedom, differential boundary heating is found to affect nonequipartition in the bulk of the system even where heating events are rare compared to collisions.
Independently Tunable Multichannel Filters Based on Graphene Superlattices with Fractal Potential Patterns
ZHANG Hui-Yun, ZHANG Yu-Ping, GAO Ying, YIN Yi-Heng
Chin. Phys. Lett. 2012, 29 (12): 128401 .   DOI: 10.1088/0256-307X/29/12/128401
Abstract   PDF(pc) (747KB) ( 428 )
An independently tunable multichannel filter based on graphene superlattices with fractal potentials is theoretically studied. It is found that such fractal structures with a defect layer possess an unusual tunneling state occurring inside the forbidden gap, and the defect modes can be modulated by changing the width of the defect layer. The facts that the wave functions of defect states do not overlap and their bases are orthogonal lead to the result of the independency among the defect modes. The modulation of energy, energy interval and number of the defect modes may lead to potential applications in graphene-based electronic devices.
The Structural and Electrical Properties of Al/Pb(Zr0.52Ti0.48)O3/Al2O3/Si with an Al2O3 Layer Prepared by using the Molecular Atomic Deposition Method
YANG Yi, ZHOU Chang-Jian, PENG Ping-Gang, XIE Dan, REN Tian-Ling, PAN Xiao, LIU Jing-Song
Chin. Phys. Lett. 2012, 29 (12): 128501 .   DOI: 10.1088/0256-307X/29/12/128501
Abstract   PDF(pc) (1079KB) ( 410 )
The structural and electrical properties of a metal-ferroelectric-insulator-semiconductor (MFIS) structure with an Al2O3 layer prepared by using the molecular atomic deposition method and Pb(Zr0.52Ti0.48)O3 (PZT) deposited by the radio frequency magnetron sputtering method are investigated. PZT exhibits a very smooth surface and (110) orientation of the perovskite phase. The MFIS structure shows well-behaved clockwise capacitance-voltage hysteresis loops due to the ferroelectric polarization under a sweep voltage up to ±40 V. Memory windows of 1.9 V and 18.14 V in conjunction with leakage current density of 2.42×10?7 A/cm2 and 8.28×10?7 A/cm2 are obtained under sweep voltages of ±5 V and ±20 V, respectively.
A 50–60 V Class Ultralow Specific on-Resistance Trench Power MOSFET
HU Sheng-Dong, ZHANG Ling, CHEN Wen-Suo, LUO Jun, TAN Kai-Zhou, GAN Ping, ZHU Zhi, WU Xing-He
Chin. Phys. Lett. 2012, 29 (12): 128502 .   DOI: 10.1088/0256-307X/29/12/128502
Abstract   PDF(pc) (636KB) ( 600 )
A 50–60 V class ultralow specific on-resistance (Ron,sp) trench power MOSFET is proposed. The structure is characterized by an n+-layer which is buried on the top surface of the p-substrate and connected to the drain n+-region. The low-resistance n+-layer shortens the motion-path in high-resistance n? drift region for the carriers, and therefore, reduces the Ron,sp in the on-state. Electrical characteristics for the proposed power MOSFET are analyzed and discussed. The 50–60 V class breakdown voltages (VB) with Ron,sp less than 0.35 mΩ?cm2 are obtained. Compared with several power MOSFETs, the proposed power MOSFET has a significantly optimized dependence of Ron,sp on VB.
Topological and Spectral Perturbations in Complex Networks
YAN Xin, WU Yang
Chin. Phys. Lett. 2012, 29 (12): 128901 .   DOI: 10.1088/0256-307X/29/12/128901
Abstract   PDF(pc) (481KB) ( 722 )
Recently many network perturbation techniques, mainly involving topological and spectral perturbations, have been employed to analyze and improve the robustness of complex networks. However, to the best of our knowledge, the relationship between topological perturbation and spectral perturbation has not been studied intensively so far. We introduce a new robustness measure, subgraph centrality defined by eigenvalue spectrum, to investigate the impact of topological perturbation on eigenvalue spectrum. A specific definition of spectral perturbation is given, such that we can examine the impact of spectral perturbation on topological property by a measure of topological performance: global efficiency. Our main finding is that the spectral perturbations we define are equivalent to the conventional topological perturbations, especially for scale-free networks
Pheromone Static Routing Strategy for Complex Networks
HU Mao-Bin, Henry Y.K. Lau, LING Xiang, JIANG Rui
Chin. Phys. Lett. 2012, 29 (12): 128902 .   DOI: 10.1088/0256-307X/29/12/128902
Abstract   PDF(pc) (641KB) ( 536 )
We adopt the concept of using pheromones to generate a set of static paths that can reach the performance of global dynamic routing strategy [Phys. Rev. E 81 (2010) 016113]. The path generation method consists of two stages. In the first stage, a pheromone is dropped to the nodes by packets forwarded according to the global dynamic routing strategy. In the second stage, pheromone static paths are generated according to the pheromone density. The output paths can greatly improve traffic systems' overall capacity on different network structures, including scale-free networks, small-world networks and random graphs. Because the paths are static, the system needs much less computational resources than the global dynamic routing strategy.
Self-Similarity in Game-Locked Aggregation
WANG Chao, XIONG Wan-Ting, WANG You-Gui
Chin. Phys. Lett. 2012, 29 (12): 128903 .   DOI: 10.1088/0256-307X/29/12/128903
Abstract   PDF(pc) (431KB) ( 333 )
A collective game is studied via agent-based modeling approach, where a group of adaptive learning players seek for their best positions on a vertical line. The movements of players are driven by benefits obtained from interactions. The game falls into an evolutionary stable state, at which aggregations of players on the line emerge. The pattern of these aggregates exhibits self-similarity at different scales with a fractal dimension of 0.58. The underlying mechanism of this aggregation is unique in that aggregates are resulted from mutual lock-in of players. This game-locked aggregation, in contrast with the diffusion limited aggregation, is applicable to a broader scope of aggregation processes.
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