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Volume 30 Issue 7
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Dynamical Decomposition of Markov Processes without Detailed Balance
AO Ping, CHEN Tian-Qi, SHI Jiang-Hong
Chin. Phys. Lett. 2013, 30 (7): 070201 .   DOI: 10.1088/0256-307X/30/7/070201
Abstract   PDF(pc) (619KB) ( 1540 )
We introduce a dynamical decomposition view in dealing with Markov processes without detailed balance. This work generalizes a previous decomposition framework on continuous-state Markov processes and explicitly gives its correspondence in discrete-state case. We investigate the dynamical roles of decomposed parts by studying the evolution of relative-entropy-like functions. We find a special definition of relative entropy to unify the dynamical roles played by the detailed balance part and the breaking detailed balance part. The evolution of the relative entropy naturally bounds the convergence of the process.
Multisymplectic Scheme for the Improved Boussinesq Equation
CAI Jia-Xiang, QIN Zhi-Lin, BAI Chuan-Zhi
Chin. Phys. Lett. 2013, 30 (7): 070202 .   DOI: 10.1088/0256-307X/30/7/070202
Abstract   PDF(pc) (470KB) ( 604 )
We first note that the improved Boussinesq equation has a multisymplectic structure. Based on it, a multisymplectic scheme is proposed. Dispersion relations analysis and linear stability analysis show that the proposed scheme has excellent properties. Numerical results confirm the excellent long-term behavior of the proposed scheme.
Infrared Spectra of PH3 and NF3: An Algebraic Approach
Joydeep Choudhury, Nirmal Kumar Sarkar, Ramendu Bhattacharjee
Chin. Phys. Lett. 2013, 30 (7): 070301 .   DOI: 10.1088/0256-307X/30/7/070301
Abstract   PDF(pc) (391KB) ( 551 )
Molecular spectroscopy is a branch of physics which deals with the interaction of electromagnetic radiation with matter. Using the new theoretical approach, i.e., Lie algebraic approach, we calculate the infrared spectra of phosphine in the range from 3000 cm?1 to 9500 cm?1 and nitrogen trifluoride in the range from 900 cm?1 to 4500 cm?1. The model Hamiltonian constructed seems to describe the P–H and N–F stretching modes accurately with only four numbers of parameters. The present calculation not only predicts the higher overtones but also shows good agreement with the few observed data.
Deterministic Three-Copy Entanglement Concentration of Photons through Direct Sum Extension and Auxiliary Degrees of Freedom
ZHAO Jie, LI Wen-Dong, GU Yong-Jian
Chin. Phys. Lett. 2013, 30 (7): 070302 .   DOI: 10.1088/0256-307X/30/7/070302
Abstract   PDF(pc) (527KB) ( 431 )
The schematic optical realization of deterministic multicopy (three-copy) entanglement concentration under local operations and classical communication (LOCC) is presented, which can resort to the linear optical elements, controlled-NOT gate that uses weak cross-Kerr nonlinearity effect and entangled qudits with different degrees of freedom. This concentration is based on Nielsen's theorem, which in principle quantifies the unit success probability. In addition, the required positive operator-valued measurement (POVM) is implemented through direct sum extension, because the least number of ancillary dimensions is demanded. The construction of POVM is systematically formulated, which results in the feasibility to generate the protocol to n-copy (n>3) cases.
Canonical Ensemble Model for the Black Hole Quantum Tunneling Radiation
Chin. Phys. Lett. 2013, 30 (7): 070401 .   DOI: 10.1088/0256-307X/30/7/070401
Abstract   PDF(pc) (380KB) ( 388 )
A canonical ensemble model for the black hole quantum tunneling radiation is introduced. With this model the probability distribution function corresponding to the emission shell is calculated. Comparing with this function, we investigate the statistical significance of the quantum tunneling radiation spectrum of black holes. Moreover, by calculating the entropy of the emission shell, a discussion about the mechanism of information flowing out from the black hole is given out.
Brownian Motion and the Temperament of Living Cells
Roumen Tsekov, Marga C. Lensen
Chin. Phys. Lett. 2013, 30 (7): 070501 .   DOI: 10.1088/0256-307X/30/7/070501
Abstract   PDF(pc) (410KB) ( 473 )
The migration of living cells usually obeys the laws of Brownian motion. While the latter is due to the thermal motion of the surrounding matter, the locomotion of cells is generally associated with their vitality. We study what drives cell migration and how to model memory effects in the Brownian motion of cells. The concept of temperament is introduced as an effective biophysical parameter driving the motion of living biological entities in analogy with the physical parameter of temperature, which dictates the movement of lifeless physical objects. The locomemory of cells is also studied via the generalized Langevin equation. We explore the possibility of describing cell locomemory via the Brownian self-similarity concept. An heuristic expression for the diffusion coefficient of cells on structured surfaces is derived.
Adaptive Synchronization and Anti-Synchronization of a Chaotic Lorenz–Stenflo System with Fully Unknown Parameters
M. Mossa Al-sawalha
Chin. Phys. Lett. 2013, 30 (7): 070502 .   DOI: 10.1088/0256-307X/30/7/070502
Abstract   PDF(pc) (443KB) ( 485 )
An adaptive control scheme is developed to study the synchronization and the anti-synchronization behaviors between two identical Lorenz–Stenflo systems with unknown parameters. This adaptive controller is designed based on Lyapunov stability theory and an analytic expression of the controller with its adaptive laws of parameters is shown. Theoretical analysis and numerical simulations are shown to verify the results.
Cusp Bursting and Slow-Fast Analysis with Two Slow Parameters in Photosensitive Belousov–Zhabotinsky Reaction
LI Xiang-Hong, BI Qin-Sheng
Chin. Phys. Lett. 2013, 30 (7): 070503 .   DOI: 10.1088/0256-307X/30/7/070503
Abstract   PDF(pc) (7489KB) ( 268 )
By introducing weakly periodic perturbation given by light, the three-variable model of photosensitive Belousov–Zhabotinsky reaction with two time scales may possess two slow processes. The codimension-2 bursting called cusp bursting is novel, especially the phenomenon that is of the transiently quiescent state mixed among repetitively large amplitude oscillations. The slow-fast dynamics analysis with two slow parameters, based on overlapping the codimension-2 bifurcation diagram of the fast subsystem with the 3-dimensional transition phase portrait of the whole system, is proposed to reveal the bifurcation mechanism of bursting oscillation with two slow variables. The adjustment behavior of slow parameters is used to explain the transformation between the spiking state and quiescent state.
Stochastic Resonance for a Time-Delayed Metapopulation System Driven by Multiplicative and Additive Noises
WANG Kang-Kang, LIU Xian-Bin
Chin. Phys. Lett. 2013, 30 (7): 070504 .   DOI: 10.1088/0256-307X/30/7/070504
Abstract   PDF(pc) (472KB) ( 461 )
The stochastic resonance (SR) phenomenon induced by the periodic signal in a metapopulation system which is driven by noises and contains a time delay is investigated. Under the condition of small delay time, the analytical expression of signal-to-noise ratio (SNR) is derived in the adiabatic limit. Via numerical calculations, each effect of the additive noise intensity, the multiplicative noise intensity and the delay time upon the SNR is discussed, respectively. It is shown that both the additive noise intensity and the multiplicative noise intensity can play a role in restraining the SR phenomenon, and for the additive noise, even a very small intensity can excite the SR phenomenon. For the delay time, the different role upon the SR phenomenon is discovered finally.
Function Projective Synchronization for Two Gyroscopes under Specific Constraints
MIN Fu-Hong
Chin. Phys. Lett. 2013, 30 (7): 070505 .   DOI: 10.1088/0256-307X/30/7/070505
Abstract   PDF(pc) (588KB) ( 450 )
The function projective synchronization between two coupled gyroscope systems is investigated under the sinusoidal constraints. From the theory of discontinuous dynamical systems, the necessary and sufficient conditions of such synchronization are given, and the parameter map is developed. Numerical simulations for the function synchronization of two coupled gyroscopes are illustrated to verify the effectiveness of this method.
Enhancement of the Neuronal Dynamic Range by Proper Intensities of Channel Noise
WANG Lei, ZHANG Pu-Ming, LIANG Pei-Ji, QIU Yi-Hong
Chin. Phys. Lett. 2013, 30 (7): 070506 .   DOI: 10.1088/0256-307X/30/7/070506
Abstract   PDF(pc) (553KB) ( 343 )
The capability of a biological neuron to discriminate the intensity of external stimulus is measured in its dynamic range. In previous studies, a few factors have been reported to be able to enhance the dynamic range, e.g., electrical coupling and active dendrites. Here we numerically show that intrinsic channel noise within neurons has a subtle effect in neuronal dynamic range modulation. Our simulation results indicate that for relatively weak noise intensity, the dynamic range of the neuron is enhanced significantly. However, as the noise intensity becomes stronger, the dynamic range of the neuron is weakened. Further investigation suggests that sodium channel noise and potassium channel noise play opposite roles in modulating the dynamic range. Consequently, the model results suggest a new function of channel noise, that is, a proper value of noise intensity could optimize the dynamic range of neurons.
Enhanced Electron-Positron Pair Production of a Vacuum in a Strong Laser Pulse Field by Frequency Variation
LI Zi-Liang, SANG Hai-Bo, XIE Bai-Song
Chin. Phys. Lett. 2013, 30 (7): 071201 .   DOI: 10.1088/0256-307X/30/7/071201
Abstract   PDF(pc) (573KB) ( 391 )
Effects of frequency variation on vacuum electron-positron pair production in strong pulsed laser fields are investigated in the framework of a quantum kinetic method. It is found that the slowly varying frequency can influence the pair production to some extent, while rapid varying frequency can increase the pair creation rate a few orders if the time lies within a narrow time window, in which frequency jump occurs. The possible physical mechanism behind the pair enhancement phenomenon is discussed briefly.
Extraction of Mechanical-Reactivity Influences from Neutron Noise Spectra at the IBR-2 Reactor
M. Dima, Yu. Pepelyshev
Chin. Phys. Lett. 2013, 30 (7): 072801 .   DOI: 10.1088/0256-307X/30/7/072801
Abstract   PDF(pc) (1177KB) ( 397 )
Neutron noise spectra in nuclear reactors are a convolution of multiple-induced reactivities. For the IBR-2 pulsed reactor (JINR-Dubna), one part is represented by the reactivities induced by the two moving reflectors, and the other part by other sources that are moderately stable. In the present study, using recordings of the mechanical noise of the two moving reflectors, their non-linear correlations into the power spectra of the reactor are extracted using statistical analysis. The remaining noise sources are moderately stable noise and can be further monitored by other automated reactor diagnoses.
Theoretical Calculation of Vector Correlations of the Reaction D'(2S)+DS(X1 Σ+)S(1D)+D2
WEI Qiang
Chin. Phys. Lett. 2013, 30 (7): 073101 .   DOI: 10.1088/0256-307X/30/7/073101
Abstract   PDF(pc) (2253KB) ( 379 )
The vector correlations in the title reaction at collision energies of 0.4–1.6 eV are studied by using the quasi-classical trajectory method on an accurate 1A' potential energy surface (PES) to gain insight into the alignment and the orientation of the product molecules. The calculated results are compared with those on 3A" PES and different properties of vector correlations have been found. The influences of the PES and the collision energy on the product vector correlations as well as the reaction mechanism are discussed. The results demonstrate that the deep potential well and the collision energy display large effect on the product vector correlations. The title reaction occurring on 1A' PES is dominantly controlled by indirect insertion mechanism.
The Dynamics of Rubidium Atoms in THz Laser Fields
JIA Guang-Rui, ZHAO Yue-Jin, ZHANG Xian-Zhou, LIU Yu-Fang, YU Kun
Chin. Phys. Lett. 2013, 30 (7): 073201 .   DOI: 10.1088/0256-307X/30/7/073201
Abstract   PDF(pc) (635KB) ( 339 )
By using B-spline basis set combined with model potential, energy levels and wave functions of rubidium atoms are obtained. Using a time-dependent multi-level approach, we study the dependence of the population of rubidium atoms excited from a low lying state to a target state on the parameters of a single or two broadband terahertz laser pulses. The population redistribution between the states n=23 and n=24 due to the interaction with terahertz pulses is analyzed in detail. Population oscillation in the initial and final states as a function of the time delay between two half cycle pulses is shown, and the oscillation period is the same as the Kepler period of the selected states. The calculation results agree well with the experiment and can be explained by the semiclassical picture.
Effect of Electron Initial Longitudinal Velocity on Low-Energy Structure in Above-Threshold Ionization Spectra
WU Ming-Yan, WANG Yan-Lan, LIU Xiao-Jun, LI Wei-Dong, HAO Xiao-Lei, CHEN Jing
Chin. Phys. Lett. 2013, 30 (7): 073202 .   DOI: 10.1088/0256-307X/30/7/073202
Abstract   PDF(pc) (1116KB) ( 383 )
Using a semiclassical model, we investigate the effect of the initial longitudinal velocity of the tunnel-ionized electron on low-energy structure (LES) in above-threshold ionization (ATI) spectra. Our analysis shows that the effect (reduction or enhancement) of the initial longitudinal velocity pz0 on the LES is dependent on the direction of the initial longitudinal velocity. For the initial longitudinal velocity along the direction of the laser electric field at the moment of tunneling (i.e., pz0>0), the Coulomb interaction between the photoelectron and ion core is enhanced, while for the initial longitudinal velocity in the opposite direction (i.e., pz0<0), the Coulomb effect is reduced. Our work provides solid evidence that the initial electron longitudinal velocity has considerable effect on the photoelectron dynamics in the ATI process.
Electronic Excitation of H2 by Electron Impact Using Multichannel Static-Exchange-Optical Method
WANG Yuan-Cheng, MA Jia, ZHOU Ya-Jun
Chin. Phys. Lett. 2013, 30 (7): 073401 .   DOI: 10.1088/0256-307X/30/7/073401
Abstract   PDF(pc) (699KB) ( 344 )
The momentum-space multichannel static-exchange-optical model is applied to the electron-H2 collision at the two-state close-coupling level. Differential cross sections for X1Σg to b3Σu transition at the energies of 20 and 30 eV are reported. Results are compared with other theoretical results and experimental data. Elastic scattering cross sections are also presented and compared with other work.
Observation of Photoassociation Spectra of Ultracold 174Yb Atoms at 1S03P1 Inter-Combination Line
LONG Yun, XIONG Zhuan-Xian, ZHANG Xi, ZHANG Meng-Jiao, LÜ Bao-Long, HE Ling-Xiang
Chin. Phys. Lett. 2013, 30 (7): 073402 .   DOI: 10.1088/0256-307X/30/7/073402
Abstract   PDF(pc) (631KB) ( 347 )
Photoassociation (PA) of cold atoms is a key tool widely used for accurate determination of long-range molecular potentials, measurement and tuning of interatomic interactions, as well as creation of desired cold molecules. We report the observation of PA spectra of ultracold ytterbium (Yb) atoms at the 1S03P1 inter-combination line by detecting the resonant loss of atoms trapped in a crossed far-off-resonance trap (crossed-FORT). Eight vibrational levels in the 10+u molecular state are observed for PA laser detunings up to 1 GHz with respect to the atomic resonance. The photoassociation resonances have a Lorentzian shape and sub-MHz linewidths due to the ultra low temperature of the atoms, and the resonance positions agree well with that predicted by the semiclassical formula.
Manipulation of Ions in Microscopic Surface-Electrode Ion Traps
WAN Wei, CHEN Liang, WU Hao-Yu, XIE Yi, ZHOU Fei, FENG Mang
Chin. Phys. Lett. 2013, 30 (7): 073701 .   DOI: 10.1088/0256-307X/30/7/073701
Abstract   PDF(pc) (1021KB) ( 404 )
The spatial manipulation of ionic qubits in a fast and precise fashion is one of the foremost issues in scalable quantum information processing with trapped ions. We report our recent efforts toward precise manipulation of trapped ions, including separation, recombination and reordering of the ions, in our home-made microscopic surface-electrode trap. We also demonstrate the micromotion compensation for the trapped ions by rf-photon cross-correlation, which ensures the cooling of the ions down to the temperature 23.3 mK.
Enhancement of Photodetector Responsivity and Response Speed Using Cascaded-Cavity Structure with Subwavelength Metallic Slit
DU Ming-Di, SUN Jun-Qiang, QIN Yi, LIAO Jian-Fei
Chin. Phys. Lett. 2013, 30 (7): 074201 .   DOI: 10.1088/0256-307X/30/7/074201
Abstract   PDF(pc) (538KB) ( 427 )
A cascaded-cavity photodetector with subwavelength metallic slit is proposed to enhance responsivity and response speed simultaneously. Responsivity enhancement depends on light transmittance increased by using a subwavelength metallic slit plasmonic mode resonant cavity; it also relies on quantum efficiency improved by adopting a resonant cavity enhanced structure. Response speed improvement is due to low capacitance of metal-slit-metal and thin absorption layers. In the cascaded-cavity structure, the subwavelength metallic slit plays a vital role in performance improvements. Simulation results show that, for the optimized slit structure, responsivity enhancement of 80 times can be achieved compared to the conventional structure. In addition, response bandwidth of the optimized structure can reach 150 GHz.
High Power Quasi-Continuous-Wave Diode-End-Pumped Nd:YAG Slab Amplifier at 1319 nm
ZHENG Jian-Kui, BO Yong, XIE Shi-Yong, ZUO Jun-Wei, WANG Peng-Yuan, GUO Ya-Ding, LIU Biao-Long, PENG Qin-Jun, CUI Da-Fu, LEI Wen-Qiang, XU Zu-Yan
Chin. Phys. Lett. 2013, 30 (7): 074202 .   DOI: 10.1088/0256-307X/30/7/074202
Abstract   PDF(pc) (703KB) ( 623 )
We report a high power high beam quality quasi-continuous-wave (QCW) diode-end-pumped Nd:YAG slab amplifier at 1319 nm. The strongest 1064 nm parasitic oscillation has been successfully suppressed by reasonable coating design. In a five-pass configuration, the amplifier yields a 42.3 W linearly polarized 1319 nm output at repetition rate of 1 kHz with pulse duration of 75 μs and beam quality factors of Mx2=1.13 and My2=2.16 in the orthogonal directions. The fluctuation of the amplifier output power is measured to be ±0.6 %. Furthermore, a computational model of QCW pulse amplification is employed to examine the amplification process.
Ptychographical Imaging Algorithm with a Single Random Phase Encoding
SHI Yi-Shi , WANG Ya-Li, LI Tuo, GAO Qian-Kun, WAN Hao, ZHANG San-Guo, WU Zhi-Bo
Chin. Phys. Lett. 2013, 30 (7): 074203 .   DOI: 10.1088/0256-307X/30/7/074203
Abstract   PDF(pc) (1029KB) ( 400 )
A single random phase encoding is introduced into ptychography for the first time. Since the diffractive wave front is encoded with the random phase modulator, the information of the sample cooperated with each probe can be uniformly distributed onto an entire diffraction pattern. It leads to the much faster convergent speed of the iterative algorithm for ptychographical imaging. It is more important for practice that the robustness to resist the noises and especially the transverse shift errors of probes are considerably improved compared with the conventional ptychographic algorithm.
Tuning Properties of External Cavity Violet Semiconductor Laser
LV Xue-Qin, CHEN Shao-Wei, ZHANG Jiang-Yong, YING Lei-Ying, ZHANG Bao-Ping
Chin. Phys. Lett. 2013, 30 (7): 074204 .   DOI: 10.1088/0256-307X/30/7/074204
Abstract   PDF(pc) (550KB) ( 1175 )
A tunable grating-coupled external cavity (EC) laser is realized by employing a GaN-based laser diode as the gain device. A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved. Detailed investigations reveal that the injection current strongly influences the performance of the EC laser. Below the free-running lasing threshold, EC laser works stably. While above the free-running lasing threshold, a Fabry–Pérot (F-P) resonance peak in the emission spectrum and a smooth kink in the output power-injection current characteristic curve are observed, suggesting the competition between the inner F-P cavity resonance and EC resonance. Furthermore, the tuning range is found to be asymmetric and occurs predominantly on the longer wavelength side. This is interpreted in terms of the asymmetric gain distribution of GaN-based quantum well material.
End-Output Coupling Efficiency Measurement of Silicon Wire Waveguides Based on Correlated Photon Pair Generation
LV Ning, ZHANG Wei, GUO Yuan, ZHOU Qiang, HUANG Yi-Dong, PENG Jiang-De
Chin. Phys. Lett. 2013, 30 (7): 074205 .   DOI: 10.1088/0256-307X/30/7/074205
Abstract   PDF(pc) (550KB) ( 400 )
A method to measure the end-output coupling efficiencies between silicon wire waveguides (SWWs) and optical fibers is proposed and demonstrated. The end-output coupling efficiency is calculated through four measured counting rates based on the correlated photon pair generation in the SWW. It provides a way to investigate and optimize the coupling processes at the input and output end of the optical waveguides separately.
Gain Improvement of Fiber Parametric Amplifier via the Introduction of Standard Single-Mode Fiber for Phase Matching
ZHU Hong-Na, LUO Bin, PAN Wei, YAN Lian-Shan, ZHAO Jian-Peng, WANG Ze-Yong, GAO Xiao-Rong
Chin. Phys. Lett. 2013, 30 (7): 074206 .   DOI: 10.1088/0256-307X/30/7/074206
Abstract   PDF(pc) (440KB) ( 450 )
We investigate and experimentally demonstrate the gain improvement of single-pump fiber parametric amplifiers by using a suitable length of standard single-mode fiber (SSMF) inserted between two high-nonlinear fibers (HNLFs). The SSMF with different dispersion properties from the HNLF is employed for phase matching of the parametric processes, and the signal gain is improved as compared with the absence of the SSMF with experiment results. Furthermore, the effect of the input pump power and the fiber length of the SSMF on the output signal gain are discussed with experimental investigation.
End-Pumped Slab Yb:YAG Crystal Emitting 1030 nm Laser at Room Temperature
XU Liu, ZHANG Heng-Li, MAO Ye-Fei, DENG Bo, HE Jing-Liang, XIN Jian-Guo
Chin. Phys. Lett. 2013, 30 (7): 074207 .   DOI: 10.1088/0256-307X/30/7/074207
Abstract   PDF(pc) (412KB) ( 4475 )
We demonstrate a 1030-nm laser with end-pumped slab Yb:YAG geometry at room temperature. A maximum power of 86 W output at the pump power of 323 W is obtained. The optical-optical efficiency is about 26.6% and the slope efficiency is 31%.
Modeling 2D Gyromagnetic Photonic Crystals by Modified FDTD Method
LI Qing-Bo, WU Rui-Xin, YANG Yan, SUN Hui-Ling
Chin. Phys. Lett. 2013, 30 (7): 074208 .   DOI: 10.1088/0256-307X/30/7/074208
Abstract   PDF(pc) (573KB) ( 554 )
The band structures of two-dimensional (2D) gyromagnetic photonic crystals (PCs) are analyzed by a modified finite difference time domain (FDTD) method. A special implementation is used to tackle the magnetic constitution equation. This method avoids the discretizing complexity in the time domain caused by nonlinear frequency dependence of anisotropy permeability tensor, and therefore keeps the fully explicit nature of the original FDTD method. Our implementation is proved by the band structure calculations using other methods and the transmission measurements of 2D gyromagnetic PC involving circular ferrite rods and square rods.
Phonon Lifetime Measurement by Stimulated Brillouin Scattering Slow Light Technique in Optical Fiber
CHEN Wei, MENG Zhou, ZHOU Hui-Juan
Chin. Phys. Lett. 2013, 30 (7): 074209 .   DOI: 10.1088/0256-307X/30/7/074209
Abstract   PDF(pc) (400KB) ( 566 )
Phonon lifetime is a significant parameter in the process of stimulated Brillouin scattering (SBS). In the present study, SBS slow light technique is used to measure phonon lifetime. Brillouin bandwidth is divided into natural, spontaneous and stimulated bandwidth. Compared with the traditional heterodyne-detection and pump-probe techniques, the natural Brillouin bandwidth can be obtained by SBS slow light technique, which equals the reciprocal of phonon lifetime and has no relations with the pump power. Another advantage of this technique is that the effect of polarization can be excluded. The natural Brillouin bandwidth is measured to be 50 MHz and the phonon lifetime 3.2 ns in the conventional single-mode fiber (SMF) at room temperature and zero strain. The obtained results are guidable in applications where the phonon lifetime information is a requisite such as phase conjugation and pulse compression.
Numerical Solution of Range-Dependent Acoustic Propagation
QIN Ji-Xing, LUO Wen-Yu, ZHANG Ren-He, YANG Chun-Mei
Chin. Phys. Lett. 2013, 30 (7): 074301 .   DOI: 10.1088/0256-307X/30/7/074301
Abstract   PDF(pc) (855KB) ( 343 )
The direct global matrix approach can be applied to modeling of range-dependent sound propagation in order to achieve numerically stable and accurate solutions. By solving the global system directly, this method features high efficiency as well as accuracy by avoiding error accumulation. It is an important issue to solve linear systems numerically in the direct global matrix approach, especially for the large-scale problems. An efficient and memory-saving algorithm is developed for solving the global system, in which the global coefficient matrix is treated as a block pentadiagonal matrix. As a result, this numerical model has the ability to solve large-scale problems on regular computers. Numerical examples are also presented to demonstrate the accuracy and efficiency of this method.
Modeling of Shock Wave Generated from a Strong Focused Ultrasound Transducer
CHEN Tao, QIU Yuan-Yuan, FAN Ting-Bo, ZHANG Dong
Chin. Phys. Lett. 2013, 30 (7): 074302 .   DOI: 10.1088/0256-307X/30/7/074302
Abstract   PDF(pc) (642KB) ( 418 )
A combined time and frequency domain method is developed for the calculation of a shock wave induced by a strong focused ultrasound transducer in the oblate spheroidal coordinate system. The spheroidal beam equation (SBE) is utilized to describe the nonlinear sound propagation; the diffraction and attenuation effects are calculated in the frequency-domain, while the nonlinear effect is calculated in the time-domain. Compared with the traditional frequency-domain method, this method could calculate the shock wave effectively without oscillation at the shock front and with less computation time. When the harmonic number is 200, the computation time by this method is about 1/16 of that used by the traditional frequency-domain method.
Surface Tension Gradients on Mixing Processes after Coalescence of Binary Equal-Sized Droplets
LIU Dong, GUO Yin-Cheng, LIN Wen-Yi
Chin. Phys. Lett. 2013, 30 (7): 074701 .   DOI: 10.1088/0256-307X/30/7/074701
Abstract   PDF(pc) (818KB) ( 570 )
Numerical simulations on coalescence of binary equal-sized droplets with surface tension gradients are carried out by using the front tracking method. Mixing process of the fluid from each droplet is investigated. The tangential flow caused by the Marangoni effect and the interface replacement by the fluid with small surface tension coefficient are simulated successfully. Asymmetry caused by the surface tension gradients can generate some extent of mixing within the coalesced droplet. The effects of the surface tension gradients and viscosity on the tangential velocity, replacement time of interface and mixing are investigated.
An Immersed Boundary-Lattice Boltzmann Simulation of Particle Hydrodynamic Focusing in a Straight Microchannel
SUN Dong-Ke, JIANG Di, XIANG Nan, CHEN Ke, NI Zhong-Hua
Chin. Phys. Lett. 2013, 30 (7): 074702 .   DOI: 10.1088/0256-307X/30/7/074702
Abstract   PDF(pc) (576KB) ( 523 )
An immersed boundary (IB)-lattice Boltzmamm method (LBM) coupled model is utilized to study the particle focusing in a straight microchannel. The LBM is used to solve the incompressible fluid flow over a regular Eulerian grid, while the IB method is employed to couple the bead-spring model which represents the fluid-particle interaction. After model validation, the simulations for hydrodynamic focusing of the single and multi particles are performed. The particles can be focused into the equilibrium positions under the pressure gradient and self-rotation induced forces, and the particle radius and Reynolds number are the key parameters influencing the focusing dynamics. This work demonstrates the potential usefulness of the IB-LBM model in studying the particle hydrodynamic focusing.
Observation of Electron Fishbone-Like Instabilities in EAST Heavy Impurity Ohmic Plasma
XU Li-Qing, HU Li-Qun, EAST team
Chin. Phys. Lett. 2013, 30 (7): 075201 .   DOI: 10.1088/0256-307X/30/7/075201
Abstract   PDF(pc) (1714KB) ( 286 )
The transient burst of an internal kink mode is first observed in EAST heavy impurity ohmic plasma. The features of the electron fishbone-like mode are presented, and the fishbone-like instabilities are found to be driven by the trapped supra-thermal electrons. The processional frequency of the trapped supra-thermal electrons is calculated with different discharge parameters. The results indicate that the calculated processional frequency is consistent with the experimental observations. Furthermore, we also find that the frequency chirping of the long-lived mode is related to the evolution of the safety factor profile.
A Polymer-Rich Re-deposition Technique for Non-volatile Etching By-products in Reactive Ion Etching Systems
A. Limcharoen, C. Pakpum, P. Limsuwan
Chin. Phys. Lett. 2013, 30 (7): 075202 .   DOI: 10.1088/0256-307X/30/7/075202
Abstract   PDF(pc) (666KB) ( 1613 )
Re-deposition is a non-volatile etching by-product in reactive ion etching systems that is well known to cause dirt on etching work. In this study, we propose a novel etching method called the polymer-rich re-deposition technique, used particularly for improving the etched sidewall where the re-deposition is able to accumulate. This technique works by allowing the accumulated re-deposition on the etched sidewall to have a higher polymer species than the new compounds in the non-volatile etching by-product. The polymer-rich re-deposition is easy to remove along with the photo-resist mask residual at the photo-resist strip step using an isopropyl alcohol-based solution. The traditional, additional cleaning process step used to remove the re-deposition material is not required anymore, so this reduces the overall processing time. The technique is demonstrated on an Al2O3-TiC substrate by C4F8 plasma, and the EDX spectrum confirms that the polymer re-deposition has C and F atoms as the dominant atoms, suggesting that it is a C–F polymer re-deposition.
A Band-Gap Energy Model of the Quaternary Alloy InxGayAl1−x−yN using Modified Simplified Coherent Potential Approximation
ZHAO Chuan-Zhen,ZHANG Rong , LIU Bin, LI Ming, XIU Xiang-Qian, XIE Zi-Li, ZHENG You-Dou
Chin. Phys. Lett. 2013, 30 (7): 076101 .   DOI: 10.1088/0256-307X/30/7/076101
Abstract   PDF(pc) (531KB) ( 385 )
Based on modification of the simplified coherent potential approximation, a model for the band-gap energy of InxGayAl1?x?yN is developed. The parameters of the model are obtained by fitting the experimental band-gap energy of their ternary alloys. It is found that the results agree with the experimental values better than those reported by others, and that the band-gap reduction of InxGayAl1?x?yN with increasing In or Ga content is mainly due to enhanced intraband coupling within the conduction band, and separately within the valence band.
Low-Dose 1 MeV Electron Irradiation-Induced Enhancement in the Photoluminescence Emission of Ga-Rich InGaN Multiple Quantum Wells
ZHANG Xiao-Fu, LI Yu-Dong, GUO Qi, LU Wu
Chin. Phys. Lett. 2013, 30 (7): 076102 .   DOI: 10.1088/0256-307X/30/7/076102
Abstract   PDF(pc) (546KB) ( 541 )
We investigate the photoluminescence (PL) emission from InGaN/GaN multiple quantum-well structures before and after 1 MeV electron irradiation. The PL peak intensity exhibits a slight enhancement after low-dose electron irradiation (2×1013 e/cm2), and then decreases with the cumulative electron dose. Meanwhile, the full width at half maximum of the PL spectrum narrows after low-dose electron irradiation and widens when the irradiation dose is relatively high. With respect to the yellow photoluminescence, there is no significant change until the electron fluence has accumulated up to 1014 e/cm2.
The Anomalous Temperature Effect on the Ductility of Nanocrystalline Cu Films Adhered to Flexible Substrates
HU Kun, CAO Zhen-Hua, WANG Lei, SHE Qian-Wei, MENG Xiang-Kang
Chin. Phys. Lett. 2013, 30 (7): 076201 .   DOI: 10.1088/0256-307X/30/7/076201
Abstract   PDF(pc) (4774KB) ( 357 )
The effect of temperature, T, on the ductility of nanocrystalline (NC) Cu films of different thicknesses on flexible substrates is studied by uniaxial tension. It is found that the NC Cu films will fracture more easily with increasing T, exhibiting the anomalous T effect compared with that of bulk NC metals and freestanding films. Moreover, the T dependence of ductility becomes stronger for thinner films due to the larger decrement of the interfacial strength in thinner films. T-induced softening of the stretchable substrate reduces the interface constraint ability for suppressing strain localization, leading to the anomalous T effect.
The Material Behavior and Fracture Mechanism of a Frangible Bullet Composite
LI Jian, RONG Ji-Li, ZHANG Yu-Ning, XU Tian-Fu, LI Bin
Chin. Phys. Lett. 2013, 30 (7): 076202 .   DOI: 10.1088/0256-307X/30/7/076202
Abstract   PDF(pc) (1267KB) ( 880 )
The quasi-static and dynamic compressive mechanical properties of a bullet composite are investigated using the scattered spot technique, an electronic universal testing machine, and a Split–Hopkinson pressure bar. The stress-strain curves under static and dynamic loading are also obtained, and the strain rate effect is analyzed. The rupture structure is observed under a scanning electron microscope, and the microscopic damage mechanism of the bullet composite is examined. Results show that the composite is sensitive to the strain rate, such that the compressive strength of the composite increases with increased strain rate. The relationship of the compressive strength and elastic modulus with the logarithmic strain rate is nonlinear.
Harnessing Light and Single Masks to Create Multiple Patterns in a Ternary Blend with Photoinduced Reaction
PAN Jun-Xing, ZHANG Jin-Jun, WANG Bao-Feng, WU Hai-Shun, SUN Min-Na
Chin. Phys. Lett. 2013, 30 (7): 076401 .   DOI: 10.1088/0256-307X/30/7/076401
Abstract   PDF(pc) (1003KB) ( 336 )
Using cell dynamics system simulation, we provide a simple way to form differently ordered patterns in a photosensitive, immiscible ABC ternary blend. The first pattern is established by irradiating the sample through a mask, which serves to pin the non-photoactivity C regions and thereby promotes the self-assembly of A and B into ordered domains. When the mask is removed, the photoactivity of the AB blend leads to different periodic patterns. Thus, the use of one mask permits the creation of multiple ordered morphologies, which can be stable for a long time by quenching the system at the appropriate time or choosing a suitable composition ratio and mask shape. Furthermore, the influence on the morphology of the composition ratio, the shape of the mask, and the illumination intensity are studied systematically.
Partial Order in Potts Models on the Generalized Decorated Square Lattice
QIN Ming-Pu, CHEN Jing, CHEN Qiao-Ni, XIE Zhi-Yuan, KONG Xin, ZHAO Hui-Hai, Bruce Normand, XIANG Tao
Chin. Phys. Lett. 2013, 30 (7): 076402 .   DOI: 10.1088/0256-307X/30/7/076402
Abstract   PDF(pc) (719KB) ( 429 )
We explore the Potts model on the generalized decorated square lattice, with both nearest (J1) and next-nearest (J2) neighbor interactions. Using the tensor renormalization-group method augmented by higher order singular value decompositions, we calculate the spontaneous magnetization of the Potts model with q = 2, 3, and 4. The results for q = 2 allow us to benchmark our numerics using the exact solution. For q = 3, we find a highly degenerate ground state with partial order on a single sublattice, but with vanishing entropy per site, and we obtain the phase diagram as a function of the ratio J2/J1. There is no finite-temperature transition for the q = 4 case when J1 = J2, whereas the magnetic susceptibility diverges as the temperature goes to zero, showing that the model is critical at T = 0.
The Structural, Electronic and Elastic Properties, and the Raman Spectra of Orthorhombic CaSnO3 through First Principles Calculations
A. Yangthaisong
Chin. Phys. Lett. 2013, 30 (7): 077101 .   DOI: 10.1088/0256-307X/30/7/077101
Abstract   PDF(pc) (544KB) ( 1565 )
First principles calculations based on the density functional theory of the electronic structure, elastic and lattice vibrational properties of orthorhombic CaSnO3 are carried out using standard functional approximation and density functional perturbation theory. The results show that CaSnO3 is an insulator with an indirect local density approximation and generalized gradient approximation gap of 3.10(2.69) eV. In addition, the Raman vibration modes of CaSnO3 are determined by the calculated phonon frequencies at the gamma point, where the prominent peaks of the Raman spectra of CaSnO3 coinciding with the calculated frequencies can be assigned.
A Density Functional Study of the Gold Cages MAu16 (M = Si, Ge, and Sn)
TANG Chun-Mei, ZHU Wei-Hua, ZHANG Ai-Mei, ZHANG Kai-Xiao, LIU Ming-Yi
Chin. Phys. Lett. 2013, 30 (7): 077102 .   DOI: 10.1088/0256-307X/30/7/077102
Abstract   PDF(pc) (806KB) ( 332 )
Relativistic density functional calculations are performed to explore the promise of MAu16(M=Si, Ge, and Sn) clusters as magic clusters and building blocks in developing cluster-assembled materials. C1 and Cs, two isomers of SiAu16, GeAu16 and SnAu16 with M (Ge or Sn) at the center of the cage, named, respectively, as SiAu16–C1, SiAu16–Cs, GeAu16-center, and SnAu16-center, are calculated to be the most stable. The Au–M bond should have both ionic and covalent characteristics. Their static linear polarizabilities and first-order hyperpolarizabilities are found to be sensitive to the delocalization of the valence electrons of the M atom, as well as their structures and shapes.
Enhanced Performance and Stability in Polymer Photovoltaic Cells Using Ultraviolet-Treated PEDOT:PSS
XU Xue-Jian, YANG Li-Ying, TIAN Hui, QIN Wen-Jing, YIN Shou-Gen, ZHANG Fengling
Chin. Phys. Lett. 2013, 30 (7): 077201 .   DOI: 10.1088/0256-307X/30/7/077201
Abstract   PDF(pc) (859KB) ( 1200 )
We investigate the effects of ultraviolet (UV) irradiation treatment with varying irradiation intensities for different treatment times of poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film on the performance and stability of polymer solar cells (PSCs) based on regioregular poly(3-hexylthiophene) (P3HT) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend. Ultraviolet-visible transmission spectra, x-ray photoelectron spectroscopy, contact angle measurement, atomic force microscopy and the Kelvin probe method are conducted to characterize the UV-treated PEDOT:PSS film. The results demonstrate that UV treatment can improve the power conversion efficiency (PCE) and stability of PSCs effectively. The best performance is achieved under 1200 μW/cm2 UV treatment for 50 min. Compared to the control device, the optimized device exhibits enhanced performance with a Voc of 0.59 V, Jsc of 12.3 mA/cm2, fill factor of 51%, and PCE of 3.64%, increased by 3.5%, 33%, 8.7% and 50%, respectively. The stability of the PSCs is enhanced by 2.5 times simply through the UV treatment on the PEDOT:PSS buffer layer. The improvement in the device performance and stability is attributed to the improvement in the wettability property and the increase in the work function of the PEDOT:PSS film by UV treatment, while the impact of UV treatment on the transparency of the PEDOT:PSS film is negligible. The strategy of using UV treatment to improve device performance and stability is attractive due to its simplicity, cost-effectiveness, and because it is suitable for large-scale commercial production.
The Effect of Intraband Transitions on the Optical Spectra of Metallic Carbon Nanotubes
T. Movlarooy
Chin. Phys. Lett. 2013, 30 (7): 077301 .   DOI: 10.1088/0256-307X/30/7/077301
Abstract   PDF(pc) (548KB) ( 883 )
First-principles calculations of the electronic structure and linear optical properties of metallic carbon nanotubes are carried out using the full-potential linear-augmented plane-wave method. The effect of intraband transition and electric-field polarization on the optical spectra of (5,2) chiral, (15,0) zigzag, and (8,8) armchair metallic carbon nanotubes are investigated. The optical spectra are calculated for both electric-field polarizations, parallel and perpendicular to the axis of the tube. It is revealed that the optical spectra are anisotropic along these two polarizations. For the parallel polarization to the tube axis, adding the intraband transition contributions shows that the dielectric function has singularity at zero frequency due to the screening effect in metallic carbon nanotubes.
The Nuclear Dark State under Dynamical Nuclear Polarization
YU Hong-Yi, LUO Yu, YAO Wang
Chin. Phys. Lett. 2013, 30 (7): 077302 .   DOI: 10.1088/0256-307X/30/7/077302
Abstract   PDF(pc) (619KB) ( 388 )
We analyze aspects of nuclear dark states. The formation of the dark states prevents the further establishment of nuclear polarizations, while inhomogeneous nuclear spin precessions can result in leakage from these states. An optimal efficiency for pumping nuclear polarization is achieved when the dynamical nuclear polarization (DNP) cycling rate is comparable to the dark-state leakage rate. When the DNP rate is much larger, the nuclear spin bath can be locked on the dark states. We propose schemes where the inhomogeneous precessions can be suppressed for the realization of large-scale dark states. As the dark states correspond to low transverse nuclear field fluctuations, they can be used to suppress the decoherence of the electron induced by the nuclear spins.
Room-Temperature Multi-Peak NDR in nc-Si Quantum-Dot Stacking MOS Structures for Multiple Value Memory and Logic
QIAN Xin-Ye, CHEN Kun-Ji, HUANG Jian, WANG Yue-Fei, FANG Zhong-Hui, XU Jun, HUANG Xin-Fan
Chin. Phys. Lett. 2013, 30 (7): 077303 .   DOI: 10.1088/0256-307X/30/7/077303
Abstract   PDF(pc) (744KB) ( 403 )
Room-temperature negative differential resistance (NDR) characteristics are observed in a nanocrystalline Si quantum dot (nc-Si QD) floating-gate MOS structure, which is fabricated by plasma-enhanced chemical vapor deposition. Clear multi-NDR peaks for the electrons and holes, shown in the IV curves, which are significant for the application of multiple value memory and logic, are proved to be induced by electron and hole resonant tunneling into the nc-Si QDs from the substrate. The calculation results indicate that these NDR characteristics should be associated with the Coulomb blockade effect and the quantum confinement effect of the nc-Si QDs. Furthermore, low-temperature IV characteristics are also investigated to confirm the room-temperature results.
Quantum Size and Doping Concentration Effects on the Current-Voltage Characteristics in GaN Resonant Tunneling Diodes
Hassen Dakhlaoui
Chin. Phys. Lett. 2013, 30 (7): 077304 .   DOI: 10.1088/0256-307X/30/7/077304
Abstract   PDF(pc) (514KB) ( 328 )
We theoretically investigate the effects of quantum size and doping concentration on the current-voltage characteristics of GaN resonant tunneling diodes. The results show a marked dependence of the peak current density on the emitter and collector spacers, and the existence of some thickness in the emitter, for which the electric current density reaches its maximum with a large peak-to-valley ratio. We also study the effect of the doping concentration in the emitter and collector layers. It is found that the doping concentration can greatly affect the current-voltage characteristics. In particular, it increases the peak of the current density and displaces the position of the maxima of the current dependence on the applied bias voltage. The effects of aluminum concentration and temperature are also presented. Finally, it is demonstrated that it is possible to have a symmetrical current for applying bias voltage in both directions by adjusting the thickness of the collector spacer.
The Unconventional Transport Properties of Dirac Fermions in Graphyne
LIN Xin, WANG Hai-Long, PAN Hui, XU Huai-Zhe
Chin. Phys. Lett. 2013, 30 (7): 077305 .   DOI: 10.1088/0256-307X/30/7/077305
Abstract   PDF(pc) (778KB) ( 493 )
A two-band Hamiltonian for β-graphyne is derived by the k?p method. The energy dispersions around the Dirac points are analytically obtained depending on the relative amplitude of the hopping terms t1/t2, and the Dirac cones are elliptical when ?2t1/t2j. This interesting feature is useful for direction-dependent wave filter devices.
The CV and G/ωV Electrical Characteristics of 60Co γ-Ray Irradiated Al/Si3N4/p-Si (MIS) Structures
S. Zeyrek, A. Turan, M. M. Bülbül
Chin. Phys. Lett. 2013, 30 (7): 077306 .   DOI: 10.1088/0256-307X/30/7/077306
Abstract   PDF(pc) (610KB) ( 372 )
The influence of 60Co (γ-ray) irradiation on the electrical characteristics of Al/Si3N4/p-Si (MIS) structures is investigated using capacitance-voltage (CV) and conductance-voltage (G/ωV) measurements. The MIS structures are exposed to a 60Co γ radiation source at a dose of 0.7 kGy/h, with a total dose range of 0–100 kGy. The CV and G/ωV properties are measured before and after 60Co γ-ray irradiation at 500 kHz and room temperature. It is found that the capacitance and conductance values decrease with the increase in the total dose due to the irradiation-induced defects at the interface. The results also indicate that γ radiation causes an increase in the barrier height ?B, Fermi energy EF and depletion layer width WD. The interface state density (Nss), using the Hill–Coleman method and dependent on radiation dose, is determined from the CV and G/ωV measurements and decreases with an increase in the radiation dose. The decrease in the interface states can be attributed to the decrease in the recombination centers and the passivation of the Si surface due to the deposition insulator layer (Si3N4). In addition, it is clear that the acceptor concentration NA decreases with increasing radiation dose. The profile of series resistance Rs for various radiation doses is obtained from forward and reverse-biased CV and G/ωV measurements, and its values decrease with increasing radiation dose, while it increases with increasing voltage in the accumulation region
The Effect of Multiple Interface States and nc-Si Dots in a Nc-Si Floating Gate MOS Structure Measured by their GV Characteristics
SHI Yong, MA Zhong-Yuan, CHEN Kun-Ji, JIANG Xiao-Fan, LI Wei, HUANG Xin-Fan, XU Ling, XU Jun, FENG Duan
Chin. Phys. Lett. 2013, 30 (7): 077307 .   DOI: 10.1088/0256-307X/30/7/077307
Abstract   PDF(pc) (872KB) ( 389 )
An nc-Si floating gate MOS structure is fabricated by thermal annealing of SiNx/a-Si/SiO2. There are nc-Si dots isolated by a-Si due to partial crystallization. Conductance-voltage (GV) measurements are performed to investigate the effect of multiple interface states including Si-sub/SiO2, a-Si related (as-deposited sample) and nc-Si (annealed sample) in a charge trapping/releasing process. Double conductance peaks located in the depletion and weak inversion regions are found in our study. For the as-deposited sample, the Si-sub/SiO2 related GV peak with weak intensity shifts to the negative as test frequency increases. The a-Si related GV peak with strong intensity shifts slightly with the increasing frequency. For the annealed sample, little change appears in the intensity and shift of Si-sub/SiO2 related GV peaks. The position of a-Si/nc-Si related peak is independent of frequency, and its intensity is weaker compared to that of the as-deposited sample. It is also found that as the size of nc-Si becomes larger, the a-Si/nc-Si related peak shifts to the depletion region due to the size effect of nc-Si.
Fano-Resonance of a Planar Metamaterial
Chin. Phys. Lett. 2013, 30 (7): 077308 .   DOI: 10.1088/0256-307X/30/7/077308
Abstract   PDF(pc) (526KB) ( 701 )
We demonstrate experimentally a intriguing Fano-resonance in a perforated planar metamaterial with hole and slit pairs. The transmission strength of the Fano-resonance is modulated by interference between the composite diffracted evanescent wave and the direct transmission field instead of by the coupling between two plasmonic modes. Our metamaterials might have potential applications in future designs of plasmonic devices.
An Insight into the Structural, Electronic and Transport Characteristics of XIn2S4 (X = Zn, Hg) Thiospinels using a Highly Accurate All-Electron FP-LAPW+Lo Method
Masood Yousaf, M. A. Saeed, Ahmad Radzi Mat Isa, H. A. Rahnamaye Aliabad, M. R. Sahar
Chin. Phys. Lett. 2013, 30 (7): 077402 .   DOI: 10.1088/0256-307X/30/7/077402
Abstract   PDF(pc) (741KB) ( 607 )
The highly accurate full-potential linearized augmented plane wave plus local orbital method is employed to calculate the structural, electronic and transport properties of HgIn2S4 and ZnIn2S4. For ZnIn2S4, the calculated In–S bond length is in good agreement with the experimental data. Bulk moduli results suggest that ZnIn2S4 can afford more compressional effects than HgIn2S4. The present study confirms that both HgIn2S4 and ZnIn2S4 are indirect band gap materials with band gap values of 0.705 eV and 1.533 eV respectively. The localized region existing in the most bottom valance band of both materials splits into states by 1 eV energy difference under the spin orbital coupling effect. Contour plots of charge density predict that chemical bonding in these compounds is a mixture of ionic and covalent characteristics. Effective mass results reveal that mobility of charge carriers in ZnIn2S4 is greater than that in HgIn2S4.
The Optical Study of Single Crystalline Cs0.8(Fe1.05Se)2 with High Néel Temperature
YUAN Rui-Hua, DONG Tao, WANG Nan-Lin
Chin. Phys. Lett. 2013, 30 (7): 077403 .   DOI: 10.1088/0256-307X/30/7/077403
Abstract   PDF(pc) (622KB) ( 370 )
We report an optical spectroscopy study on an iron-selenide single crystal of insulating Cs0.8(Fe1.05Se)2 with relatively high Néel temperature. The resistivity and magnetization measurements reveal a semiconductor behavior with TN=492 K. The sample has been examined in the temperature range from 10 K up to 500 K by using infrared measurement. The low frequency optical measurement implies an insulating response with a major absorption near 0.31 eV. The double-peak structure in the mid-infrared region and the low-frequency phonon modes support the presence of the blocked anti-ferromagnetism. The infrared measurement reveals no signature of SDW-type energy gap formation below the anti-ferromagnetic-order temperature.
The Finite Temperature Effect on Josephson Junction between an s-Wave Superconductor and an s±-Wave Superconductor
WANG Da, LU Hong-Yan, WANG Qiang-Hua
Chin. Phys. Lett. 2013, 30 (7): 077404 .   DOI: 10.1088/0256-307X/30/7/077404
Abstract   PDF(pc) (973KB) ( 408 )
We investigate a Josephson junction between a one-band and a multi-band s-wave superconductor. When the multi-band lead is an s±-wave superconductor, we find that the critical Josephson current may change its sign when the temperature changes. Our result confirms that this is a widespread effect of the s±-wave superconductor, independent of the type of the junction, the ratios of the gaps and superconducting transition temperatures, as long as the tunneling matrix elements have suitable values. This novel effect comes directly from the opposite gap signs. We propose that the observation of this phenomena can be used to detect the s±-wave pairing symmetry in iron-based superconductors.
Synthesis and Characterization of Alkaline-Earth Metal (Ca, Sr, and Ba) Doped Nanodimensional LaMnO3 Rare-Earth Manganites
Asma Khalid, Saadat Anwar Siddiqi, Affia Aslam
Chin. Phys. Lett. 2013, 30 (7): 077501 .   DOI: 10.1088/0256-307X/30/7/077501
Abstract   PDF(pc) (860KB) ( 579 )
The substitution of divalent cations of alkaline-earth elements in nanodimensional structures of rare-earth manganites produces advanced materials with potential electrical and magnetic functionalities. A systematic investigation of La0.65A0.35MnO3 (A = Ca, Sr, Ba) materials synthesized with a modified citrate route adopting ethanol dehydration has been undertaken. The structural and morphological analyses are carried out by using x-ray diffraction and scanning electron microscopy, respectively. Resistivity measurements are performed in variation with temperature to study the electrical transport properties which are found to vary with the size of the A-site cationic radius. Room temperature magnetic measurements are carried out to investigate the type of magnetic phase present in materials. The stability of the magnetic phase and coercivity are found to be dependent on the size of nanocrystallites.
A First-Principles Investigation of the Carrier Doping Effect on the Magnetic Properties of Defective Graphene
LEI Shu-Lai, LI Bin, HUANG Jing, LI Qun-Xiang, YANG Jin-Long
Chin. Phys. Lett. 2013, 30 (7): 077502 .   DOI: 10.1088/0256-307X/30/7/077502
Abstract   PDF(pc) (830KB) ( 415 )
The carrier doping effects on the magnetic properties of defective graphene with a hydrogen chemisorbed single-atom vacancy (H-GSV) are investigated by performing extensive spin-polarized first-principles calculations. Theoretical results show that the quasi-localized pz-derived states around the Fermi level are responsible for the weakened magnetic moment (MM) and magnetic stabilized energy (MSE) of the H-GSV under carrier doping. The mechanism of reduced MSE in the carrier doped H-GSV can be well understood by the Heisenberg magnetic coupling model due to the response of these pz-derived states to the carrier doping. Within the examined range of carrier doping concentration, the total MM of H-GSV is always larger than 1.0μB with μB representing the Bohr magneton, which is mainly contributed by the localized sp2 states of the unsaturated C atom around the vacancy. These findings of H-GSV provide fundamental insight into defective graphene and help to understand the related experimental observations.
Room-Temperature d0 Ferromagnetism in Nitrogen-Doped In2O3 Films
SUN Shao-Hua, WU Ping, XING Peng-Fei
Chin. Phys. Lett. 2013, 30 (7): 077503 .   DOI: 10.1088/0256-307X/30/7/077503
Abstract   PDF(pc) (765KB) ( 507 )
N-doped In2O3 films were deposited on fused quartz substrates by radio-frequency magnetron sputtering with different N2 flux. X-ray diffraction patterns, x-ray photoelectron spectroscopy and the optical transmittance spectra indicate that nitrogen has incorporated into the In2O3 lattice. Room-temperature d0 ferromagnetism is observed in all the films. The saturation magnetization increases from 0.73 to 3.5 emu/cm3 when the N2 flux varies from 0 to 10 sccm. The concordant results in structural, compositional, optical and magnetic properties suggest that this d0 ferromagnetism is associated with the N incorporation and may be mediated by the long-range pp interaction between the N 2p states.
Wafer-Scale Flexible Surface Acoustic Wave Devices Based on an AlN/Si Structure
ZHANG Cang-Hai, YANG Yi, ZHOU Chang-Jian, SHU Yi, TIAN He, WANG Zhe, XUE Qing-Tang, REN Tian-Ling
Chin. Phys. Lett. 2013, 30 (7): 077701 .   DOI: 10.1088/0256-307X/30/7/077701
Abstract   PDF(pc) (1455KB) ( 1114 )
Wafer-scale flexible surface acoustic wave (SAW) devices based on AlN/silicon structure are demonstrated. The final fabricated devices with a 50μm-thickness silicon wafer exhibit good flexibility with a bending curvature radius of 8 mm. Measurements under free and bending conditions are carried out, showing that the central frequency shifts little as the curvature changes. SAW devices with central frequency about 191.9 MHz and Q-factor up to 600 are obtained. The flexible technology proposed is directly applied to the wafer silicon substrate in the last step, providing the potential of high performance flexible wafer-scale devices by direct integration with mature CMOS and MEMS technology.
Magnetic-Field-Induced Stress-Birefringence in Laminate Composites of Terfenol-D and Polycarbonate
LUO Xiao-Bin, WU Dong, ZHANG Ning
Chin. Phys. Lett. 2013, 30 (7): 077801 .   DOI: 10.1088/0256-307X/30/7/077801
Abstract   PDF(pc) (489KB) ( 360 )
The laminate composites that can show the magneto-birefringence effect are suggested and fabricated by the product of magnetostriction and stress-birefringence. Under a magnetic field no stronger than 1900 Oe, a phase difference of 3.3π is observed for a trilayer composite Tb1?xDyxFe2?y/polycarbonate/Tb1?xDyxFe2?y with a polycarbonate layer at a size of 5 × 2.75 × 20 mm3 at room temperature, resulting in a half-wave magnetic field of no greater than 270 Oe.
The Fano-Like Resonance in Self-Assembled Trimer Clusters
ZHANG Mei, LI Liang-Sheng ZHENG Ning, SHI Qing-Fan
Chin. Phys. Lett. 2013, 30 (7): 077802 .   DOI: 10.1088/0256-307X/30/7/077802
Abstract   PDF(pc) (874KB) ( 431 )
We illustrate that three identical nanocylinders self-assembled into a trimer with a small interparticle gap separation support strong Fano-like interference. The asymmetry line shape of the Fano-like resonance can be controlled by modifying the cluster structures, and a narrow linewidth between a peak and a dip is displayed in the line trimer. The resonant behaviors of the trimers could be strengthened by increasing the permittivity of the nanorods, and the asymmetry resonance is highly sensitive to the angle of the incident wave due to the orientation-dependent coupling between the cylinders in the cluster. The present study provides a way to investigate the environmental change caused by the reshaped asymmetry line, which can be applied to future high-performance resonance sensors.
Overcoming Decomposition with Order-Reversed Quenching Obtained by Flash Melting
SI Ping-Zhan, XIAO Xiao-Fei, FENG He, YU Sen-Jiang, GE Hong-Liang
Chin. Phys. Lett. 2013, 30 (7): 078101 .   DOI: 10.1088/0256-307X/30/7/078101
Abstract   PDF(pc) (468KB) ( 754 )
We report on an order-reversed quenching phenomenon in manganese nitrides under flash melting, which prevents the thermodynamically favorable phase transformations from occurring at high temperatures by providing a narrow window of time. The Mn-N kept un-decomposed at high temperatures generated by current up to 339 MA/m2 within 60 ms. After flash melting, the Mn-N shows a significantly enhanced coercivity and a decreased crystalline size. The Mn-N samples decompose rapidly at temperatures above 1100 K with time. The order-reversed quenching technique is potentially useful in processing and preventing phase transformations of meta-stable materials at high temperatures.
A Low Specific on-Resistance SOI Trench MOSFET with a Non-Depleted Embedded p-Island
FAN Jie, ZHANG Bo, LUO Xiao-Rong, LI Zhao-Ji
Chin. Phys. Lett. 2013, 30 (7): 078501 .   DOI: 10.1088/0256-307X/30/7/078501
Abstract   PDF(pc) (762KB) ( 363 )
A novel silicon-on-insulator (SOI) trench metal-oxide-semiconductor field effect transistor (MOSFET) with a reduced specific on-resistance (Ron, sp) is presented. It features an oxide-filled trench and a non-depleted embedded p-type island (p-SOI). The oxide trench folds the drift region into a U-shape, resulting in a reduction in cell pitch and Ron, sp. The non-depleted p-island is employed to further reduce Ron, sp by increasing the optimized doping concentration of the drift region without deteriorating the breakdown voltage (BV). The simulation results show that the p-SOI decreases the Ron, sp to 10.2 mΩ?cm2 from 17.4 mΩ?cm2 of the conventional SOI MOSFET at the same BV.
High-Efficiency InGaN/GaN Nanorod Arrays by Temperature Dependent Photoluminescence
WANG Wen-Jie, CHEN Peng, YU Zhi-Guo, LIU Bin, XIE Zi-Li, XIU Xiang-Qian, WU Zhen-Long, XU Feng, XU Zhou, HUA Xue-Mei, ZHAO Hong, HAN Ping, SHI Yi, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2013, 30 (7): 078502 .   DOI: 10.1088/0256-307X/30/7/078502
Abstract   PDF(pc) (600KB) ( 461 )
We report on the photoluminescent characteristics of InGaN/GaN multiple quantum well (MQW) nanorod arrays with high internal quantum efficiency. The InGaN/GaN MQWs are grown by metalorganic chemical vapor deposition on c-plane sapphire substrates, and then the MQW nanorod arrays are fabricated by using inductively coupled plasma etching with self-assembled Ni nanoparticle mask with low-damage etching technique. The typical diameter of the nanorods is from 200 nm to 300 nm and the length is around 800 nm, which almost is dislocation free. At room temperature, an enhancement of 3.1 times in total integrated photoluminescence intensity is achieved from the MQW nanorod arrays, in comparison to that of the as-grown MQW structure. Based on the temperature-dependent photoluminescence measurements, the internal quantum efficiency of the nanorod structure is 59.2%, i.e., 1.75 times of as-grown MQW structure (33.8%). Therefore, the nanorod structure with a significant reduction of defects can be a very promising candidate for highly efficient light emitting devices.
A Distributed Phase Shifter Using Bi1.5Zn1.0Nb1.5O7/Ba0.5Sr0.5TiO3 Thin Films
LI Ru-Guan, JIANG Shu-Wen, GAO Li-Bin, LI Yan-Rong
Chin. Phys. Lett. 2013, 30 (7): 078503 .   DOI: 10.1088/0256-307X/30/7/078503
Abstract   PDF(pc) (553KB) ( 331 )
We report the demonstration of a monolithic phase shifter employing Bi1.5Zn1.0Nb1.5O7 (BZN)/Ba0.5Sr0.5TiO3 (BST) thin films on sapphire substrates. The BST and BZN thin films are successively deposited by radio?frequency magnetron sputtering. A distributed phase shifter with a coplanar?waveguide transmission line periodically loaded with the BZN/BST capacitors is fabricated. The return loss of the circuit is better than -13 dB from 1 to 12 GHz, and it provides 65° phase shift with an insertion loss of -4 dB at 12 GHz. The results show that BZN/BST thin films are promising candidate dielectrics for rf/microwave tunable applications.
Optimization of Metal Coverage on the Emitter in n-Type Interdigitated Back Contact Solar Cells Using a PC2D Simulation
ZHANG Wei, CHEN Chen, JIA Rui, Janssen G. J. M., ZHANG Dai-Sheng, XING Zhao, Bronsveld P. C. P., Weeber A. W., JIN Zhi, LIU Xin-Yu
Chin. Phys. Lett. 2013, 30 (7): 078801 .   DOI: 10.1088/0256-307X/30/7/078801
Abstract   PDF(pc) (837KB) ( 1184 )
In interdigitated back contact (IBC) solar cells, the metal-electrode coverage on a p-type emitter is optimized by a PC2D simulation. The result shows that the variation of the metal coverage ratio (MCR) will affect both the surface passivation and the electrode-contact properties for the p-type emitter in IBC solar cells. We find that when Rc ranges from 0.08 to 0.16Ω?cm2, the MCR is optimized with a value of 25% and 33%, resulting in a highest energy-conversion efficiency. The dependences of both Voc and fill factor on MCR are simulated in order to explore the mechanism of the IBC solar cells.
Comment on "Improvement of Controlled Bidirectional Quantum Direct Communication Using a GHZ State" [Chin. Phys. Lett. 30 (2013) 040305]
LIU Zhi-Hao, CHEN Han-Wu
Chin. Phys. Lett. 2013, 30 (7): 079901 .   DOI: 10.1088/0256-307X/30/7/079901
Abstract   PDF(pc) (297KB) ( 397 )
The problem of definite information leakage existing in the controlled bidirectional quantum direct communication protocol using GHZ states [Chin. Phys. Lett. 23 (2006) 1680] was pointed out by Ye and Jiang [Chin. Phys. Lett. 30 (2013) 040305]. Then, they proposed two strategies to improve this security bug. However, if the revised versions are analyzed from the viewpoint of information theory, it can be found that they still have the problem of information leakage. That is, three quarters and one half of the information interchanged by the communication parties are leaked out unknowingly in the first and second revised protocols, respectively.
Reply to the Comment on "Improvement of Controlled Bidirectional Quantum Direct Communication Using a GHZ State" [Chin. Phys. Lett. 30 (2013) 040305]*
YE Tian-Yu, JIANG Li-Zhen
Chin. Phys. Lett. 2013, 30 (7): 079902 .   DOI: 10.1088/0256-307X/30/7/079902
Abstract   PDF(pc) (300KB) ( 388 )
Most recently, Liu and Chen [Chin. Phys. Lett. 30 (2013) 079901] used the tool of information theory to analyze the security of our two improved versions of the MX protocol [Chin. Phys. Lett. 30 (2013) 040305], and they found out that our two improved versions still have the information leakage problem. After revisiting them with the tool of information theory again, with respect to the security, we draw the same conclusion as Liu and Chen. In addition, we point out that how to use a single quantum state as the sole quantum resource to design a bidirectional quantum secure direct communication protocol without information leakage is still a big challenge that needs to be solved.
Comment on "Cryptanalysis and Improvement of a Quantum Network System of QSS-QDC Using χ-Type Entangled States" [Chin. Phys. Lett. 29 (2012) 110305]
LIU Zhi-Hao, CHEN Han-Wu
Chin. Phys. Lett. 2013, 30 (7): 079903 .   DOI: 10.1088/0256-307X/30/7/079903
Abstract   PDF(pc) (326KB) ( 287 )
We point out that the quantum secret sharing (QSS) protocol proposed by Gao et al. [Chin. Phys. Lett. 29 (2012) 110305] has some defects. Thus, some strategies are given to mend them.
Reply to the Comment on "Cryptanalysis and Improvement of a Quantum Network System of QSS-QDC Using χ-Type Entangled States" [Chin. Phys. Lett. 29 (2012) 110305]
GAO Gan, FANG Ming, CHENG Mu-Tian
Chin. Phys. Lett. 2013, 30 (7): 079904 .   DOI: 10.1088/0256-307X/30/7/079904
Abstract   PDF(pc) (336KB) ( 350 )

We first make a small modification to the improved protocol in order to enhance its efficiency. Secondly, the explanation that our improved protocol can prevent Trent from using the {|Ψ±2>,|Φ±2>} basis is given.

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