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Chin. Phys. B  
  Chin. Phys. B--2015, Vol.24, No.6
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Degree distribution and robustness of cooperativecommunication network with scale-free model

Wang Jian-Rong, Wang Jian-Ping, He Zhen, Xu Hai-Tao
Chin. Phys. B 2015, 24 (6): 060101;  doi: 10.1088/1674-1056/24/6/060101
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With the requirements of users enhanced for wireless communication, the cooperative communication will become a development trend in future. In this paper, a model based on complex networks with both preferential attachment is researched to solve an actual network CCN (Cooperative Communication Network). Firstly, the evolution of CCN is given by four steps with different probabilities. At the same time, the rate equations of nodes degree are presented to analyze the evolution of CCN. Secondly, the degree distribution is analyzed by calculating the rate equation and numerical simulation. Finally, the robustness of CCN is studied by numerical simulation with random attack and intentional attack to analyze the effects of degree distribution and average path length. The results of this paper are more significant for building CCN to programme the resource of communication.

The consistent Riccati expansion and new interaction solution for a Boussinesq-type coupled system

Ruan Shao-Qing, Yu Wei-Feng, Yu Jun, Yu Guo-Xiang
Chin. Phys. B 2015, 24 (6): 060201;  doi: 10.1088/1674-1056/24/6/060201
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Starting from the Davey–Stewartson equation, a Boussinesq-type coupled equation system is obtained by using a variable separation approach. For the Boussinesq-type coupled equation system, its consistent Riccati expansion (CRE) solvability is studied with the help of a Riccati equation. It is significant that the soliton–cnoidal wave interaction solution, expressed explicitly by Jacobi elliptic functions and the third type of incomplete elliptic integral, of the system is also given.

Reweighted ensemble dynamics simulations: Theory, improvement, and application

Gong Lin-Chen, Zhou Xin, Ouyang Zhong-Can
Chin. Phys. B 2015, 24 (6): 060202;  doi: 10.1088/1674-1056/24/6/060202
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Based on multiple parallel short molecular dynamics simulation trajectories, we designed the reweighted ensemble dynamics (RED) method to more efficiently sample complex (biopolymer) systems, and to explore their hierarchical metastable states. Here we further present an improvement to depress statistical errors of the RED and we discuss a few keys in practical application of the RED, provide schemes on selection of basis functions, and determination of the free parameter in the RED. We illustrate the application of the improvements in two toy models and in the solvated alanine dipeptide. The results show the RED enables us to capture the topology of multiple-state transition networks, to detect the diffusion-like dynamical behavior in an entropy-dominated system, and to identify solvent effects in the solvated peptides. The illustrations serve as general applications of the RED in more complex biopolymer systems.

Solutions of the D-dimensional Schrödinger equation with Killingbeck potential: Lie algebraic approach

H. Panahi, S. Zarrinkamar, M. Baradaran
Chin. Phys. B 2015, 24 (6): 060301;  doi: 10.1088/1674-1056/24/6/060301
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Algebraic solutions of the D-dimensional Schrödinger equation with Killingbeck potential are investigated using the Lie algebraic approach within the framework of quasi-exact solvability. The spectrum and wavefunctions of the system are reported and the allowed values of the potential parameters are obtained through the sl(2) algebraization.

Quantum correlation dynamics in a two-qubit Heisenberg XYZ model with decoherence

Yang Guo-Hui, Zhang Bing-Bing, Li Lei
Chin. Phys. B 2015, 24 (6): 060302;  doi: 10.1088/1674-1056/24/6/060302
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Quantum correlation dynamics in an anisotropic Heisenberg XYZ model under decoherence is investigated by making use of concurrence C and quantum discord (QD). Firstly, we show that both the concurrence and QD exhibit oscillation with time whereas a remarkable difference between them is presented: there is an “entanglement intermittently sudden death” phenomenon in the concurrence but not in the QD, which is valid for all the initial states of this system. Also, the interval time of entanglement sudden death is found to be strongly dependent on the initial states, the inhomogeneous magnetic field b and the anisotropic parameter . Then, it implies that the steady concurrence and QD can be obtained in the long-time limit, which means that the environmental decoherence cannot entirely destroy the quantum correlation, the variation of the uniform magnetic field B and the anisotropic parameter can change the magnitude of the steady concurrence and QD evidently whereas the parameter b cannot. In addition, based on the analysis of the steady concurrence and QD with t→∞, we give the reason why the magnitude of the steady concurrence and QD is so complicated with the change of the parameters B and D, whereas the parameter b is independent of the steady concurrence and QD.

Statistical analysis of the temporal single-photon response of superconducting nanowire single photon detection

He Yu-Hao, Lü Chao-Lin, Zhang Wei-Jun, Zhang Lu, Wu Jun-Jie, Chen Si-Jing, You Li-Xing, Wang Zhen
Chin. Phys. B 2015, 24 (6): 060303;  doi: 10.1088/1674-1056/24/6/060303
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A new method to study the transient detection efficiency (DE) and pulse amplitude of superconducting nanowire single photon detectors (SNSPD) during the current recovery process is proposed–statistically analyzing the single photon response under photon illumination with a high repetition rate. The transient DE results match well with the DEs deduced from the static current dependence of DE combined with the waveform of a single-photon detection event. This proves that static measurement results can be used to analyze the transient current recovery process after a detection event. The results are relevant for understanding the current recovery process of SNSPDs after a detection event and for determining the counting rate of SNSPDs.

Effects of systematic phase errors on optimized quantum random-walk search algorithm

Zhang Yu-Chao, Bao Wan-Su, Wang Xiang, Fu Xiang-Qun
Chin. Phys. B 2015, 24 (6): 060304;  doi: 10.1088/1674-1056/24/6/060304
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This study investigates the effects of systematic errors in phase inversions on the success rate and number of iterations in the optimized quantum random-walk search algorithm. Using the geometric description of this algorithm, a model of the algorithm with phase errors is established, and the relationship between the success rate of the algorithm, the database size, the number of iterations, and the phase error is determined. For a given database size, we obtain both the maximum success rate of the algorithm and the required number of iterations when phase errors are present in the algorithm. Analyses and numerical simulations show that the optimized quantum random-walk search algorithm is more robust against phase errors than Grover's algorithm.

Oscillation of the spin-currents of cold atoms on a ring due to light-induced spin-orbit coupling

Xie Wen-Fang, He Yan-Zhang, Bao Cheng-Guang
Chin. Phys. B 2015, 24 (6): 060305;  doi: 10.1088/1674-1056/24/6/060305
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The evolution of two-component cold atoms on a ring with spin–orbit coupling has been studied analytically for the case with N noninteracting particles. Then, the effect of interaction is evaluated numerically via a two-body system. Two cases are considered: (i) Starting from a ground state the evolution is induced by a sudden change of the laser field, and (ii) the evolution starting from a superposition state. Oscillating persistent spin-currents have been found. A set of formulae have been derived to describe the period and amplitude of the oscillation. Based on these formulae the oscillation can be well controlled via adjusting the parameters of the laser beams. In particular, it is predicted that movable stripes might emerge on the ring.

Analysis of field coupling to transmission lines with random rotation over the ground

Xie Hai-Yan, Li Yong, Qiao Hai-Liang, Wang Jian-Guo
Chin. Phys. B 2015, 24 (6): 060501;  doi: 10.1088/1674-1056/24/6/060501
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In this paper we analyze plane wave coupling to transmission lines rotating randomly over an infinite and perfectly conducting ground and present an efficient method to calculate average voltage. Under the assumption of small rotation quantity, the factors affecting the induced voltage and their effects are analyzed and then an efficient method to calculate the average voltage is presented when the distribution of the random rotation angles is uniform in [-π, π]. The results show that voltage variation is mainly due to the change of the source term. The effects of the source term increase linearly with the magnitude of the incident wave, change periodically with the rotation angle, and are larger in the high frequency range than in the low frequency range. The results show that the average voltages obtained by the proposed method agree well with those via the Monte Carlo method and the proposed method is much more efficient. The results also imply that the effect of random rotation is more important than that of random translation.

Moment stability for a predator-prey model with parametric dichotomous noises

Jin Yan-Fei
Chin. Phys. B 2015, 24 (6): 060502;  doi: 10.1088/1674-1056/24/6/060502
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In this paper, we investigate the solution moment stability for a Harrison-type predator–prey model with parametric dichotomous noises. Using the Shapiro–Loginov formula, the equations for the first-order and second-order moments are obtained and the corresponding stable conditions are given. It is found that the solution moment stability depends on the noise intensity and correlation time of noise. The first-order and second-order moments become unstable with the decrease of correlation time. That is, the dichotomous noise can improve the solution moment stability with respect to Gaussian white noise. Finally, some numerical results are presented to verify the theoretical analyses.

Study on a new chaotic bitwise dynamical system and its FPGA implementation

Wang Qian-Xue, Yu Si-Min, C. Guyeux, J. Bahi, Fang Xiao-Le
Chin. Phys. B 2015, 24 (6): 060503;  doi: 10.1088/1674-1056/24/6/060503
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In this paper, the structure of a new chaotic bitwise dynamical system (CBDS) is described. Compared to our previous research work, it uses various random bitwise operations instead of only one. The chaotic behavior of CBDS is mathematically proven according to the Devaney's definition, and its statistical properties are verified both for uniformity and by a comprehensive, reputed and stringent battery of tests called TestU01. Furthermore, a systematic methodology developing the parallel computations is proposed for FPGA platform-based realization of this CBDS. Experiments finally validate the proposed systematic methodology.

A circular zone counting method of identifying a Duffing oscillator state transition and determining the critical value in weak signal detection

Li Meng-Ping, Xu Xue-Mei, Yang Bing-Chu, Ding Jia-Feng
Chin. Phys. B 2015, 24 (6): 060504;  doi: 10.1088/1674-1056/24/6/060504
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Identifying state transition and determining the critical value of the Duffing oscillator are crucial to indicating external signal existence and have a great influence on detection accuracy in weak signal detection. A circular zone counting (CZC) method is proposed in this paper, by combining the Duffing oscillator's phase trajectory feature and numerical calculation for quickly and accurately identifying state transition and determining the critical value, to realize a high-efficiency weak signal detection. Detailed model analysis and method construction of the CZC method are introduced. Numerical experiments into the reliability of the proposed CZC method compared with the maximum Lyapunov exponent (MLE) method are carried out. The CZC method is demonstrated to have better detecting ability than the MLE method, and furthermore it is simpler and clearer in calculation to extend to engineering application.

A joint image encryption and watermarking algorithm based on compressive sensing and chaotic map

Xiao Di, Cai Hong-Kun, Zheng Hong-Ying
Chin. Phys. B 2015, 24 (6): 060505;  doi: 10.1088/1674-1056/24/6/060505
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In this paper, a compressive sensing (CS) and chaotic map-based joint image encryption and watermarking algorithm is proposed. The transform domain coefficients of the original image are scrambled by Arnold map firstly. Then the watermark is adhered to the scrambled data. By compressive sensing, a set of watermarked measurements is obtained as the watermarked cipher image. In this algorithm, watermark embedding and data compression can be performed without knowing the original image; similarly, watermark extraction will not interfere with decryption. Due to the characteristics of CS, this algorithm features compressible cipher image size, flexible watermark capacity, and lossless watermark extraction from the compressed cipher image as well as robustness against packet loss. Simulation results and analyses show that the algorithm achieves good performance in the sense of security, watermark capacity, extraction accuracy, reconstruction, robustness, etc.

Dynamical characteristics of an HP memristor based on an equivalent circuit model in a chaotic oscillator

Yuan Fang, Wang Guang-Yi, Wang Xiao-Yuan
Chin. Phys. B 2015, 24 (6): 060506;  doi: 10.1088/1674-1056/24/6/060506
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To develop real world memristor application circuits, an equivalent circuit model which imitates memductance (memory conductance) of the HP memristor is presented. The equivalent circuit can be used for breadboard experiments for various application circuit designs of memristor. Based on memductance of the realistic HP memristor and Chua's circuit a new chaotic oscillator is designed. Some basic dynamical behaviors of the oscillator, including equilibrium set, Lyapunov exponent spectrum, and bifurcations with various circuit parameters are investigated theoretically and numerically. To confirm the correction of the proposed oscillator an analog circuit is designed using the proposed equivalent circuit model of an HP memristor, and the circuit simulations and the experimental results are given.

A new piecewise linear Chen system of fractional-order: Numerical approximation of stable attractors

Marius-F. Danca, M. A. Aziz-Alaoui, Michael Small
Chin. Phys. B 2015, 24 (6): 060507;  doi: 10.1088/1674-1056/24/6/060507
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In this paper we present a new version of Chen's system: a piecewise linear (PWL) Chen system of fractional-order. Via a sigmoid-like function, the discontinuous system is transformed into a continuous system. By numerical simulations, we reveal chaotic behaviors and also multistability, i.e., the existence of small parameter windows where, for some fixed bifurcation parameter and depending on initial conditions, coexistence of stable attractors and chaotic attractors is possible. Moreover, we show that by using an algorithm to switch the bifurcation parameter, the stable attractors can be numerically approximated.

Mittag-Leffler synchronization of fractional-order uncertain chaotic systems

Wang Qiao, Ding Dong-Sheng, Qi Dong-Lian
Chin. Phys. B 2015, 24 (6): 060508;  doi: 10.1088/1674-1056/24/6/060508
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This paper deals with the synchronization of fractional-order chaotic systems with unknown parameters and unknown disturbances. An adaptive control scheme combined with fractional-order update laws is proposed. The asymptotic stability of the error system is proved in the sense of generalized Mittag–Leffler stability. The two fractional-order chaotic systems can be synchronized in the presence of model uncertainties and additive disturbances. Finally these new developments are illustrated in examples and numerical simulations are provided to demonstrate the effectiveness of the proposed control scheme.

An efficient three-party password-based key agreement protocol using extended chaotic maps

Shu Jian
Chin. Phys. B 2015, 24 (6): 060509;  doi: 10.1088/1674-1056/24/6/060509
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Three-party password-based key agreement protocols allow two users to authenticate each other via a public channel and establish a session key with the aid of a trusted server. Recently, Farash et al. [Farash M S, Attari M A 2014 “An efficient and provably secure three-party password-based authenticated key exchange protocol based on Chebyshev chaotic maps”, Nonlinear Dynamics 77(7): 399–411] proposed a three-party key agreement protocol by using the extended chaotic maps. They claimed that their protocol could achieve strong security. In the present paper, we analyze Farash et al.'s protocol and point out that this protocol is vulnerable to off-line password guessing attack and suffers communication burden. To handle the issue, we propose an efficient three-party password-based key agreement protocol using extended chaotic maps, which uses neither symmetric cryptosystems nor the server's public key. Compared with the relevant schemes, our protocol provides better performance in terms of computation and communication. Therefore, it is suitable for practical applications.

Optimization of combined endoreversible Carnot heat engines with different objectives

Cheng Xue-Tao, Liang Xin-Gang
Chin. Phys. B 2015, 24 (6): 060510;  doi: 10.1088/1674-1056/24/6/060510
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Taking the output power, thermal efficiency, and thermo-economic performance as the optimization objectives, we optimize the operation parameters of a thermodynamic system with combined endoreversible Carnot heat engines in this paper. The applicabilities of the entropy generation minimization and entransy theory to the optimizations are discussed. For the discussed cases, only the entransy loss coefficient is always agreeable to the optimization of thermal efficiency. The applicabilities of the other discussed concepts to the optimizations are conditional. Different concepts and principles are needed for different optimization objectives, and the optimization principles have their application preconditions. When the preconditions are not satisfied, the principles may be not applicable.

Theoretical models for designing a 220-GHz folded waveguide backward wave oscillator

Cai Jin-Chi, Hu Lin-Lin, Ma Guo-Wu, Chen Hong-Bin, Jin Xiao, Chen Huai-Bi
Chin. Phys. B 2015, 24 (6): 060701;  doi: 10.1088/1674-1056/24/6/060701
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In this paper, the basic equations of beam-wave interaction for designing the 220 GHz folded waveguide (FW) backward wave oscillator (BWO) are described. On the whole, these equations are mainly classified into small signal model (SSM), large signal model (LSM), and simplified small signal model (SSSM). Using these linear and nonlinear one-dimensional (1D) models, the oscillation characteristics of the FW BWO of a given configuration of slow wave structure (SWS) can be calculated by numerical iteration algorithm, which is more time efficient than three-dimensional (3D) particle-in-cell (PIC) simulation. The SSSM expressed by analytical formulas is innovatively derived for determining the initial values of the FW SWS conveniently. The dispersion characteristics of the FW are obtained by equivalent circuit analysis. The space charge effect, the end reflection effect, the lossy wall effect, and the relativistic effect are all considered in our models to offer more accurate results. The design process of the FW BWO tube with output power of watt scale in a frequency range between 215 GHz and 225 GHz based on these 1D models is demonstrated. The 3D PIC method is adopted to verify the theoretical design results, which shows that they are in good agreement with each other.

In-situ measurement of magnetic field gradient in a magnetic shield by a spin-exchange relaxation-free magnetometer

Fang Jian-Cheng, Wang Tao, Zhang Hong, Li Yang, Cai Hong-Wei
Chin. Phys. B 2015, 24 (6): 060702;  doi: 10.1088/1674-1056/24/6/060702
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A method of measuring in-situ magnetic field gradient is proposed in this paper. The magnetic shield is widely used in the atomic magnetometer. However, there is magnetic field gradient in the magnetic shield, which would lead to additional gradient broadening. It is impossible to use an ex-situ magnetometer to measure magnetic field gradient in the region of a cell, whose length of side is several centimeters. The method demonstrated in this paper can realize the in-situ measurement of the magnetic field gradient inside the cell, which is significant for the spin relaxation study. The magnetic field gradients along the longitudinal axis of the magnetic shield are measured by a spin-exchange relaxation-free (SERF) magnetometer by adding a magnetic field modulation in the probe beam's direction. The transmissivity of the cell for the probe beam is always inhomogeneous along the pump beam direction, and the method proposed in this paper is independent of the intensity of the probe beam, which means that the method is independent of the cell's transmissivity. This feature makes the method more practical experimentally. Moreover, the AC-Stark shift can seriously degrade and affect the precision of the magnetic field gradient measurement. The AC-Stark shift is suppressed by locking the pump beam to the resonance of potassium's D1 line. Furthermore, the residual magnetic fields are measured with σ+- and σ--polarized pump beams, which can further suppress the effect of the AC-Stark shift. The method of measuring in-situ magnetic field gradient has achieved a magnetic field gradient precision of better than 30 pT/mm.

Globally accurate ab initio based potential energy surface of H2O+(X4A")

Song Yu-Zhi, Zhang Yuan, Zhang Lu-Lu, Gao Shou-Bao, Meng Qing-Tian
Chin. Phys. B 2015, 24 (6): 063101;  doi: 10.1088/1674-1056/24/6/063101
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A globally accurate potential energy surface is reported for the electronic ground-state H2O+. The ab initio energies utilized to map the potential energy surface are calculated at the multireference configuration interaction method employing the aug-cc-pVQZ basis set and the full valence complete active space wave function as reference. In order to improve accuracy of the resulting raw ab initio energies, they are then extrapolated to the complete basis set limit and most importantly to the full configuration-interaction limit by semiempirically correcting the dynamical correlation using the double many-body expansion-scaled external correlation method. The topographical features of the current potential energy surface were examined in detail, which agree nicely with those of other theoretical work.

Two-photon spectrum of 87Rb using optical frequency comb

Wang Li-Rong, Zhang Yi-Chi, Xiang Shao-Shan, Cao Shu-Kai, Xiao Lian-Tuan, Jia Suo-Tang
Chin. Phys. B 2015, 24 (6): 063201;  doi: 10.1088/1674-1056/24/6/063201
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The high precision two-photon excitation measurements for 5S1/2 (Fg = 2) to 5D5/2 (Fe = 4 to 1) of 87Rb are performed by using an optical frequency comb. The two counter-propagating femtosecond pulses (5S1/2→5P3/2 at 780 nm, and 5P3/2→5D5/2 at 776 nm) act on 87Rb vapor, and the Doppler broadened background signal is effectively eliminated. The temperature and power dependences of the two-photon spectrum are studied in this paper.

Exploring photocurrent output from donor/acceptor bulk-heterojunctions by monitoring exciton quenching

Wang Xin-Ping, He Zhi-Qun, Liang Chun-Jun, Qiu Hai-An, Jing Xi-Ping
Chin. Phys. B 2015, 24 (6): 063301;  doi: 10.1088/1674-1056/24/6/063301
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In this work, a series of polymer bulk-heterojunctions is fabricated based on the combinations of different donors (Ds) (P3HT and PCPDTBT) and acceptors (As) (PCBM, ICBA, and F8BT). Exciton quenching efficiencies of the D–A pairs are obtained in order to quantify charge-transfer between the donor and the acceptor via a modified approach developed in conjunction with experimental results of optical absorption and photoluminescence spectra. It is discovered that the exciton quenching efficiency in the combination of PCPDTBT:PCBM and P3HT:PCBM reaches 70% and over, but in PCPDTBT:ICBA it is about 12%. A relatively high ΔLUMOdonor-acceptor results in a relatively high exciton quenching efficiency, which is responsible for better charge separation. The results agreed well with the photocurrent effect of the heterojunction layers. The work offers a convenient way to predict a potentially promising photovoltaic material with a selected D–A pair.

Ramsey-CPT spectrum with the Faraday effect and its application to atomic clocks

Tian Yuan, Tan Bo-Zhong, Yang Jing, Zhang Yi, Gu Si-Hong
Chin. Phys. B 2015, 24 (6): 063302;  doi: 10.1088/1674-1056/24/6/063302
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A method that obtains the Ramsey-coherent population trapping (CPT) spectrum with the Faraday effect is investigated. An experiment is implemented to detect the light polarization components generated from the Faraday effect. The experimental results agree with the theoretical calculations based on the Liouville equation. By comparing with the method without using the Faraday effect, the potential of this method for a CPT-based atomic clock is assessed. The results indicate that this method should improve the short-term frequency stability by several times.

Rydberg excitation of neutral nitric oxide molecules instrong UV and near-IR laser fields

Lv Hang, Zhang Jun-Feng, Zuo Wan-Long, Xu Hai-Feng, Jin Ming-Xing, Ding Da-Jun
Chin. Phys. B 2015, 24 (6): 063303;  doi: 10.1088/1674-1056/24/6/063303
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Rydberg state excitations of neutral nitric oxide molecules are studied in strong ultraviolet (UV) and near-infra-red (IR) laser fields using a linear time-of-flight (TOF) mass spectrometer with the pulsed electronic field ionization method. The yield of Rydberg molecules is measured as a function of laser intensity and ellipticity, and the results in UV laser fields are compared with those in near-IR laser fields. The present study provides the first experimental evidence of neutral Rydberg molecules surviving in a strong laser field. The results indicate that a rescattering-after-tunneling process is the main contribution to the formation of Rydberg molecules in strong near-IR laser fields, while multi-photon excitation may play an important role in the strong UV laser fields.

Photodetachment microscopy of H- in the magnetic field near different dielectric surfaces

Tang Tian-Tian, Zhang Min, Zhang Chao-Min
Chin. Phys. B 2015, 24 (6): 063401;  doi: 10.1088/1674-1056/24/6/063401
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We study the photo-detachment interference patterns of a hydrogen negative ion in the magnetic field near different dielectric surfaces with a semi-classical open orbit theory. We give a clear physical picture describing the photo-detachment of H- in this case. The electron flux distributions are calculated at various dielectric surfaces with unchanged magnetic field strength. It is found that the electron flux distributions of H- are very different in a magnetic field near different dielectric surfaces, namely the dielectric surface has a great influence on the photo-detachment interference pattern of the negative ion. Therefore, the interference pattern in the detached-electron flux distribution can be controlled by changing the dielectric constant. We hope that our studies may guide the future experimental research in photo-detachment microscopy.

Scaling law of single ion-atom impact ionization cross sections of noble gases from He to Xe at strong perturbative energies

Ren Ping-Yuan, Zou Xian-Rong, Shao Jian-Xiong, Wang Shi-Yao, Zhou Man, Zhou Wang, Yang Ai-Xiang, Yan Peng-Xun, Chen Xi-Meng
Chin. Phys. B 2015, 24 (6): 063402;  doi: 10.1088/1674-1056/24/6/063402
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We extend our previous work of a classical over-barrier ionization (COBI) model to calculate the single ionization cross sections of noble gases ranging from He to Xe at strong perturbative energies. The calculation results are in good agreement with extensive experimental data. The scaling law of single ion–atom impact ionization cross sections of noble gases on projectile charge q and energy E, also on target ionization energy I is drawn from the model.

Multiple ionization of Ne induced by 10 keV/u-500 keV/u Cq+ (q=1-3) ions

Liu Wen-Biao, Niu Shu-Tong, Yang Ai-Xiang, Han Cheng-Zhi, Hu Wei, Chen Lin, Shao Jian-Xiong, Chen Xi-Meng
Chin. Phys. B 2015, 24 (6): 063403;  doi: 10.1088/1674-1056/24/6/063403
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The values of cross-section ratio Rk1 of direct k-fold ionization cross section (σk) to direct single ionization cross section (σ1) of Ne impacted by Cq+ (q=1–3) ions in an energy range of 10 keV/u–500 keV/u are measured in this work. The experimental data are compared with the results from our multi-electron classical over-barrier ionization (ME-COBI) model, showing that the model can give a good estimate to the experimental data.

Conditions for formation and trapping of the two-ion Coulomb cluster in the dissipative optical superlattice

I. V. Krasnov
Chin. Phys. B 2015, 24 (6): 063701;  doi: 10.1088/1674-1056/24/6/063701
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Conditions have been studied under which a polychromatic optical superlattice can form and trap the Coulomb cluster of two strongly interacting ions. In our previous work (Krasnov I V and Kamenshchikov L P 2014 Opt. Comm. 312 192) this new all-optical method of obtaining and confining the Coulomb clusters was demonstrated by numerical simulations for special values of the optical superlattice parameters and in the case of Yb ions. In the present paper the conditions are explicitly formulated, under which the long-lived two-ion cluster in the superlattice cell is formed. The peculiarity of these conditions is the renormalization of the ion–ion Coulomb interaction. Notably, the renormalized Coulomb force is determined by the effective charge which depends on the light field parameters and can strongly differ from the “bare” ion charge. This result can be accounted for by the combined manifestation of the quantum fluctuations of optical forces, nonlinear dependence of these forces on the velocity, and non-Maxwellian (Tsallis type) velocity distribution of the ions in the optical superlattice. Explicit analytical formulas are also obtained for the parameters of the optical two-ion cluster.


Achieving a multi-band metamaterial perfect absorber via a hexagonal ring dielectric resonator

Li Li-Yang, Wang Jun, Du Hong-Liang, Wang Jia-Fu, Qu Shao-Bo
Chin. Phys. B 2015, 24 (6): 064201;  doi: 10.1088/1674-1056/24/6/064201
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A multi-band absorber composed of high-permittivity hexagonal ring dielectric resonators and a metallic ground plate is designed in the microwave band. Near-unity absorptions around 9.785 GHz, 11.525 GHz, and 12.37 GHz are observed for this metamaterial absorber. The dielectric hexagonal ring resonator is made of microwave ceramics with high permittivity and low loss. The mechanism for the near-unity absorption is investigated via the dielectric resonator theory. It is found that the absorption results from electric and magnetic resonances where enhanced electromagnetic fields are excited inside the dielectric resonator. In addition, the resonance modes of the hexagonal resonator are similar to those of standard rectangle resonators and can be used for analyzing hexagonal absorbers. Our work provides a new research method as well as a solid foundation for designing and analyzing dielectric metamaterial absorbers with complex shapes.

Improved autonomous star identification algorithm

Luo Li-Yan, Xu Lu-Ping, Zhang Hua, Sun Jing-Rong
Chin. Phys. B 2015, 24 (6): 064202;  doi: 10.1088/1674-1056/24/6/064202
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The log–polar transform (LPT) is introduced into the star identification because of its rotation invariance. An improved autonomous star identification algorithm is proposed in this paper to avoid the circular shift of the feature vector and to reduce the time consumed in the star identification algorithm using LPT. In the proposed algorithm, the star pattern of the same navigation star remains unchanged when the stellar image is rotated, which makes it able to reduce the star identification time. The logarithmic values of the plane distances between the navigation and its neighbor stars are adopted to structure the feature vector of the navigation star, which enhances the robustness of star identification. In addition, some efforts are made to make it able to find the identification result with fewer comparisons, instead of searching the whole feature database. The simulation results demonstrate that the proposed algorithm can effectively accelerate the star identification. Moreover, the recognition rate and robustness by the proposed algorithm are better than those by the LPT algorithm and the modified grid algorithm.

Electrically tunable holographic polymer templated blue phase liquid crystal grating

He Zheng-Hong, Chen Chao-Ping, Zhu Ji-Liang, Yuan Ya-Chao, Li Yan, Hu Wei, Li Xiao, Li Hong-Jing, Lu Jian-Gang, Su Yi-Kai
Chin. Phys. B 2015, 24 (6): 064203;  doi: 10.1088/1674-1056/24/6/064203
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In this paper, we demonstrate an alternative approach to fabricating an electrically tunable holographic polymer templated blue phase liquid crystal grating. This grating is obtained by preforming a polymer template comprised of periodic fringes, and then refilling it with a blue phase liquid crystal. Compared with conventional holographic polymer dispersed liquid crystal gratings, our grating can remarkably reduce its switching voltage from 200 V to 43 V while maintaining a sub-millisecond response time. The holographic polymer templated blue phase liquid crystal (HPTBPLC) grating is free from electrode patterning, thus leading to a lower cost and more flexible applications.

Algebraic and group treatments to nonlinear displaced number statesand their nonclassicality features: A new approach

N Asili Firouzabadi, M K Tavassoly, M J Faghihi
Chin. Phys. B 2015, 24 (6): 064204;  doi: 10.1088/1674-1056/24/6/064204
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Recently, nonlinear displaced number states (NDNSs) have been manually introduced, in which the deformation function f(n) has been artificially added to the previously well-known displaced number states (DNSs). Indeed, just a simple comparison has been performed between the standard coherent state and nonlinear coherent state for the formation of NDNSs. In the present paper, after expressing enough physical motivation of our procedure, four distinct classes of NDNSs are presented by applying algebraic and group treatments. To achieve this purpose, by considering the DNSs and recalling the nonlinear coherent states formalism, the NDNSs are logically defined through an algebraic consideration. In addition, by using a particular class of Gilmore–Perelomov-type of SU(1,1) and a class of SU(2) coherent states, the NDNSs are introduced via group-theoretical approach. Then, in order to examine the nonclassical behavior of these states, sub-Poissonian statistics by evaluating Mandel parameter and Wigner quasi-probability distribution function associated with the obtained NDNSs are discussed, in detail.

Multiple frequency conversion via atomic spin coherence of storing a light pulse

Wang Lei, Luo Meng-Xi, Sun Jia-Xiang, Sun Yuan-Hang, Chen Yi, Wei Xiao-Gang, Kang Zhi-Hui, Wang Hai-Hua, Gao Jin-Yue
Chin. Phys. B 2015, 24 (6): 064205;  doi: 10.1088/1674-1056/24/6/064205
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We experimentally demonstrate multiple frequency conversion via atomic spin coherence of storing a light pulse in a doped solid. The essence of this multiple frequency conversion is four-wave mixing based on stored atomic spin coherence. Through electromagnetically induced transparency, an input probe pulse is stored into atomic spin coherence by modulating the intensity of the control field. By using two different control fields to interact with the coherently prepared medium, the stored atomic spin coherence can be transformed into three different information channels. Multiple frequency conversion is implemented efficiently by manipulating the spectra of the control fields to scatter atomic spin coherence. This multiple frequency conversion is expected to have potential applications in information processing and communication network.

Electromagnetic field quantization and input-output relation for anisotropic magnetodielectric metamaterial

Dong Yun-Xia, Liu Chun-Ying
Chin. Phys. B 2015, 24 (6): 064206;  doi: 10.1088/1674-1056/24/6/064206
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A phenomenological quantization of electromagnetic field is introduced in the presence of the anisotropic magnetodielectric metamaterial. For a single layer structure with the anisotropic metamaterial, input–output relations of quantized radiation are derived using the Green-function approach. Based on these relations, the reflectance of the linearly polarized wave through this structure is calculated. The results show that different resonant peaks of reflectance appear for different polarized waves and indicate the use of the anisotropic metamaterial as a reflector for a certain polarized wave. Furthermore it is found that such a structure can realize the resonant gap with the increase of the thickness. Finally the effects of the absorption are considered and we find that the above properties do not change with the introduction of the absorption.

A scheme for two-photon lasing with two coupled flux qubits in circuit quantum electrodynamics

Huang Wen, Zou Xu-Bo, Guo Guang-Can
Chin. Phys. B 2015, 24 (6): 064207;  doi: 10.1088/1674-1056/24/6/064207
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We theoretically study the system of a superconducting transmission line resonator coupled to two interacting superconducting flux qubits. It is shown that under certain conditions the resonator mode can be tuned to two-photon resonance between the ground state and the highest excited state while the middle excited states are far-off resonance. Furthermore, we study the steady-state properties of the flux qubits and resonator, such as the photon statistics, the spectrum and squeezing of the resonator, and demonstrate that two-photon laser can be implemented with current experimental technology.

High coupling efficiency and low signal light loss (2+1)× 1 coupler

Chen Xiao, Xiao Qi-Rong, Jin Guang-Yong, Yan Ping, Gong Ma-Li
Chin. Phys. B 2015, 24 (6): 064208;  doi: 10.1088/1674-1056/24/6/064208
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The coupling efficiency of the pump coupler determines the pump light injection capacity of a laser system. Experimental analysis of the influences of different factors on the pump coupling efficiency is in accordance with this conclusion. We use two Nufern fibers (400 μm/440 μm with NA = 0.22) as pump arm, one Nufern fiber (20 μm/400 μm with NA = 0.06/0.46) as a main fiber to make a side-pumping (2+1)× 1 coupler. The experimental result shows that the total output power of this (2+1)× 1 coupler is about 1160 W, corresponding to a coupling efficiency as high as 98.6%. The loss of signal light is less than 1%.

A long-term frequency-stabilized erbium-fiber-laser-based optical frequency comb with an intra-cavity electro-optic modulator

Zhang Yan-Yan, Yan Lu-Lu, Zhao Wen-Yu, Meng Sen, Fan Song-Tao, Zhang Long, Guo Wen-Ge, Zhang Shou-Gang, Jiang Hai-Feng
Chin. Phys. B 2015, 24 (6): 064209;  doi: 10.1088/1674-1056/24/6/064209
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We demonstrate an optical frequency comb based on an erbium-doped-fiber femtosecond laser with the nonlinear polarization evolution scheme. The repetition rate of the laser is about 209 MHz. By controlling an intra-cavity electro-optic modulator and a piezo-transducer, the repetition rate can be stabilized with a high-bandwidth servo in a frequency range of 3 kHz, enabling long-term repetition rate phase-locking. The in-loop frequency stability of repetition rate is about 1.6× 10-13 in an integration time of 1 s, limited by the measurement system; and it is inversely proportional to integration time in the short term. Furthermore, using a common path f–2f interferometer, the carrier envelope offset frequency of the comb is obtained with a signal-to-noise ratio of 40 dB in a 3-MHz resolution bandwidth. Stabilized carrier envelope offset frequency exhibits a deviation of 0.6 mHz in an integration time of 1 s.

Single, composite, and ceramic Nd:YAG 946-nm lasers

Lan Rui-Jun, Yang Guang, Wang Zheng-Ping
Chin. Phys. B 2015, 24 (6): 064210;  doi: 10.1088/1674-1056/24/6/064210
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Single, composite crystal and ceramic continuous wave (CW) 946-nm Nd:YAG lasers are demonstrated, respectively. The ceramic laser behaves better than the crystal laser. With 5-mm long ceramic, a CW output power of 1.46 W is generated with an optical conversion efficiency of 13.9%, while the slope efficiency is 17.9%. The optimal ceramic length for a 946-nm laser is also calculated.

Graded doping low internal loss 1060-nm InGaAs/AlGaAsquantum well semiconductor lasers

Tan Shao-Yang, Zhai Teng, Zhang Rui-Kang, Lu Dan, Wang Wei, Ji Chen
Chin. Phys. B 2015, 24 (6): 064211;  doi: 10.1088/1674-1056/24/6/064211
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Internal loss is a key internal parameter for high power 1060-nm InGaAs/AlGaAs semiconductor laser. In this paper, we discuss the origin of internal loss of 1060-nm InGaAs/GaAs quantum well (QW) AlGaAs separate confinement heterostructure semiconductor laser, and the method to reduce internal loss. By light doping the n-cladding layer, and stepwise doping the p-cladding layer combined with the expanded waveguide layer, a broad area laser with internal loss of 1/cm is designed and fabricated. Ridge waveguide laser with an output power of 350 mW is obtained. The threshold current and slope efficiency near the threshold current are 20 mA and 0.8 W/A, respectively.

Stability analysis for flow past a cylinder via lattice Boltzmann method and dynamic mode decomposition

Zhang Wei, Wang Yong, Qian Yue-Hong
Chin. Phys. B 2015, 24 (6): 064701;  doi: 10.1088/1674-1056/24/6/064701
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A combination of the lattice Boltzmann method and the most recently developed dynamic mode decomposition is proposed for stability analysis. The simulations are performed on a graphical processing unit. Stability of the flow past a cylinder at supercritical state, Re=50, is studied by the combination for both the exponential growing and the limit cycle regimes. The Ritz values, energy spectrum, and modes for both regimes are presented and compared with the Koopman eigenvalues. For harmonic-like periodic flow in the limit cycle, global analysis from the combination gives the same results as those from the Koopman analysis. For transient flow as in the exponential growth regime, the combination can provide more reasonable results. It is demonstrated that the combination of the lattice Boltzmann method and the dynamic mode decomposition is powerful and can be used for stability analysis for more complex flows.

Experimental study on spectrum and multi-scale nature of wall pressure and velocity in turbulent boundary layer

Zheng Xiao-Bo, Jiang Nan
Chin. Phys. B 2015, 24 (6): 064702;  doi: 10.1088/1674-1056/24/6/064702
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When using a miniature single sensor boundary layer probe, the time sequences of the stream-wise velocity in the turbulent boundary layer (TBL) are measured by using a hot wire anemometer. Beneath the fully developed TBL, the wall pressure fluctuations are attained by a microphone mechanism with high spatial resolution. Analysis on the statistic and spectrum properties of velocity and wall pressure reveals the relationship between the wall pressure fluctuation and the energy-containing structure in the buffer layer of the TBL. Wavelet transform shows the multi-scale natures of coherent structures contained in both signals of velocity and pressure. The most intermittent wall pressure scale is associated with the coherent structure in the buffer layer. Meanwhile the most energetic scale of velocity fluctuation at y+= 14 provides a specific frequency f9 ≈ 147 Hz for wall actuating control with Reτ= 996.

A novel simulation method for positive corona current pulses

Liu Yang, Cui Xiang, Lu Tie-Bing, Li Xue-Bao, Wang Zhen-Guo, Xiang Yu, Wang Xiao-Bo
Chin. Phys. B 2015, 24 (6): 065201;  doi: 10.1088/1674-1056/24/6/065201
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A novel two-dimensional (2D) simulation method of positive corona current pulses is proposed. A control-volume-based finite element method (CV-FEM) is used to solve continuity equations, and the Galerkin finite element method (FEM) is used to solve Poisson's equation. In the proposed method, photoionization is considered by adopting an exact Helmholtz photoionization model. Furthermore, fully implicit discretization and variable time step are used to ensure the time-efficiency of the present method. Finally, the method is applied to a positive rod-plane corona problem. The numerical results are in agreement with the experimental results, and the validity of the proposed method is verified.

High-order optical vortex harmonics generated by relativistic femtosecond laser pulse

Han Yu-Jing, Liao Guo-Qian, Chen Li-Ming, Li Yu-Tong, Wang Wei-Min, Zhang Jie
Chin. Phys. B 2015, 24 (6): 065202;  doi: 10.1088/1674-1056/24/6/065202
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Harmonics generated by an intense femtosecond Gaussian laser pulse normally incident on a spiral-shaped thin foil target were studied. By using two-dimensional (2D) particle-in-cell (PIC) simulation, we observed evident odd harmonics signals in the reflection direction and found that the reflected field has a helical structure determined by the target shape. This method provides a new way to generate an intense ultraviolet vortex with high-order topological charge by use of ultrahigh intense laser-driven harmonics.

Two-dimensional numerical study of an atmospheric pressurehelium plasma jet with dual-power electrode

Yan Wen, Liu Fu-Cheng, Sang Chao-Feng, Wang De-Zhen
Chin. Phys. B 2015, 24 (6): 065203;  doi: 10.1088/1674-1056/24/6/065203
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In this paper, the characteristics of an atmospheric pressure helium plasma jet generated by a dual-power electrode (DPE) configuration are investigated by using a two-dimensional fluid model. The effect of a needle electrode on the discharge is studied by comparing the results of the DPE configuration with those of the single ring electrode configuration. It is found that the existence of the needle leads to the generation of a helium plasma jet with a higher propagation velocity, higher species density, and larger discharge width. Furthermore, the influences of the needle radius and needle-to-ring discharge gap on the generation of a plasma jet are also studied. The simulation results indicate that the needle electrode has an evident influence on the plasma jet characteristics.

Effect of deposition parameters on structural and mechanicalproperties of niobium nitride synthesized by plasma focus device

Jamil Siddiqui, Tousif Hussain, Riaz Ahmad, Nida Khalid
Chin. Phys. B 2015, 24 (6): 065204;  doi: 10.1088/1674-1056/24/6/065204
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Effects of deposition angle and axial distance on the structural and mechanical properties of niobium nitride synthesized by a dense plasma focus (DPF) system are studied. The x-ray diffraction (XRD) confirms that the deposition parameters affect the growth of multi-phase niobium nitride. Scanning electron microscopy (SEM) shows the granular surface morphology with strong thermally assisted coagulation effects observed at the 5-cm axial distance. The non-porous granular morphology observed at the 9-cm distance along the anode axis is different from those observed at deposition angles of 10° and 20°. Energy dispersive x-ray (EDX) spectroscopy reveals the maximum nitrogen content at the shortest (5 cm) axial position. Atomic force microscopy (AFM) exhibits that the roughness of coated films varies for coatings synthesized at different axial and angular positions, and the Vickers micro-hardness test shows that a maximum hardness value is (08.44± 0.01) GPa for niobium nitride synthesized at 5-cm axial distance, which is about 500% more than that of a virgin sample.

Current-voltage characteristics of hydrogen DC plasma torches with different sizes in an external axial magnetic field

Ma Jie, Wen Guang-Dong, Su Bao-Gen, Yang Yi-Wen, Ren Qi-Long
Chin. Phys. B 2015, 24 (6): 065205;  doi: 10.1088/1674-1056/24/6/065205
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Current–voltage (I–V) characteristics of hydrogen DC plasma torches with different sizes in an external axial magnetic field under atmospheric pressure are reported. Three anodes with different diameters are adopted in a 50-kW torch: 25 mm, 30 mm, and 35 mm, respectively. Two different diameters of anodes, that is, 100 mm and 130 mm, are adopted in a 1-MW plasma torch. The arc voltage shows a negative trend with the increase of arc current under the operating regimes. On the contrary, arc voltage shows a positive trend as the flow rate of carrier gas increases, and a similar trend is found with increasing the external magnetic flux density. A similarity formula is constructed to correlate the experimental data of the torches mentioned above. Linear fitting shows that the Pearson correlation coefficient is 0.9958.

Evolution of magnetically rotating arc into large area arc plasma

Wang Cheng, Li Wan-Wan, Zhang Xiao-Ning, Zha Jun, Xia Wei-Dong
Chin. Phys. B 2015, 24 (6): 065206;  doi: 10.1088/1674-1056/24/6/065206
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An arc channel tends to shrink due to its conductivity increasing with the increase of temperature. In this study, to generate large area arc plasma, we construct a magnetically rotating arc plasma generator, which mainly consists of a lanthanide tungsten cathode (13 mm in diameter), a concentric cylindrical graphite anode chamber (60 mm in diameter) and a solenoid coil for producing an axial magnet field. By controlling the cold gas flow, the magnetically rotating arc evolves from constricted mode to diffuse mode, which almost fills the whole arc chamber cross section. Results show that the diffuse arc plasma has better uniformity and stability. The formation mechanism of large area arc plasma is discussed in this paper.

Implicit electrostatic particle-in-cell/Monte Carlo simulation for the magnetized plasma: Algorithms and application in gas-inductive breakdown

Wang Hong-Yu, Sun Peng, Jiang Wei, Zhou Jie, Xie Bai-Song
Chin. Phys. B 2015, 24 (6): 065207;  doi: 10.1088/1674-1056/24/6/065207
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An implicit electrostatic particle-in-cell/Monte Carlo (PIC/MC) algorithm is developed for the magnetized discharging device simulation. The inductive driving force can be considered. The direct implicit PIC algorithm (DIPIC) and energy conservation scheme are applied together and the grid heating can be eliminated in most cases. A tensor-susceptibility Poisson equation is constructed. Its discrete form is made up by a hybrid scheme in one-dimensional (1D) and two-dimensional (2D) cylindrical systems. A semi-coarsening multigrid method is used to solve the discrete system. The algorithm is applied to simulate the cylindrical magnetized target fusion (MTF) pre-ionization process and get qualitatively correct results. The potential application of the algorithm is discussed briefly.

Band structures of elastic waves in two-dimensional eight-fold solid-solid quasi-periodic phononic crystals

Chen A-Li, Liang Tong-Li, Wang Yue-Sheng
Chin. Phys. B 2015, 24 (6): 066101;  doi: 10.1088/1674-1056/24/6/066101
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Combined with the supercell method, band structures of the anti-plane and in-plane modes of two-dimensional (2D) eight-fold solid–solid quasi-periodic phononic crystals (QPNCs) are calculated by using the finite element method. The influences of the supercell on the band structure and the wave localization phenomenon are discussed based on the modal distributions. The reason for the appearance of unphysical bands is analyzed. The influence of the incidence angle on the transmission spectrum is also discussed.

Low-temperature phase transformation from nanotube to sp3 superhard carbon phase

Xu Ning, Li Jian-Fu, Huang Bo-Long, Wang Bao-Lin
Chin. Phys. B 2015, 24 (6): 066102;  doi: 10.1088/1674-1056/24/6/066102
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Numerous new carbon allotropes have been uncovered by compressing carbon nanotubes based on our computational investigation. The volume compression calculations suggest that these new phases have a very high anti-compressibility with a large bulk modulus (B0). The predicted B0 of new phases is larger than that of c-BN (373 GPa) and smaller than that of diamond (453 GPa). All of the predicted structures are superhard transparent materials with a larger band gap and possess the covalent characteristics with sp3-hybridized electronic states. The simulated results will help us better understand the structural phase transition of cold-compressed carbon nanotubes.

Structural and magnetic transition in stainless steel Fe-21Cr-6Ni-9Mn up to 250 GPa

Liu Lei, Hou Qi-Yue, Zhang Yi, Jing Qiu-Min, Wang Zhi-Gang, Bi Yan, Xu Ji-An, Li Xiao-Dong, Li Yan-Chun, Liu Jing
Chin. Phys. B 2015, 24 (6): 066103;  doi: 10.1088/1674-1056/24/6/066103
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Stainless steel Fe-21Cr-6Ni-9Mn (SS 21-6-9), with ~ 21% Cr, ~ 6% Ni, and ~ 9% Mn in weight percentage, has wide applications in extensive fields. In the present study, SS 21-6-9 is compressed up to 250 GPa, and its crystal structures and compressive behaviors are investigated simultaneously using the synchrotron angle-dispersive x-ray diffraction technique. The SS 21-6-9 undergoes a structural phase transition from fcc to hcp structure at ~ 12.8 GPa with neglectable volume collapse within the determination error under the quasi-hydrostatic environment. The hcp structure remains stable up to the highest pressure of 250 GPa in the present experiments. The antiferromagnetic-to-nonmagnetic state transition of hcp SS 21-6-9 with the changes of inconspicuous density and structure, is discovered at ~ 50 GPa, and revealed by the significant change in c/a ratio. The hcp SS-21-6-9 is compressive anisotropic: it is more compressive in the c-axis direction than in the a-axis direction. Both the equations of states (EOSs) of fcc and hcp SS 21-6-9, which are in accordance with those of fcc and hcp pure irons respectively, are also presented. Furthermore, the c/a ratio of hcp SS 21-6-9 at infinite compression, R, is consistent with the values of pure iron and Fe–10Ni alloy.

Room temperature damping correlated to the microstructures in Cu-20.4Al-8.7Mn

Hao Gang-Ling, Wang Xin-Fu, Wang Hui, Li Xian-Yu
Chin. Phys. B 2015, 24 (6): 066104;  doi: 10.1088/1674-1056/24/6/066104
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The damping capacity of the shape memory alloy Cu–20.4Al–8.7Mn (at.%) at room temperature is investigated by an internal friction technique. Results indicate that the alloy exhibits higher damping capacity in the Martensitic condition than that in the austenitic condition due to the latter having lower intrinsic damping capacity and pinning effect coming from the precipitate particles. The maximum damping capacity is obtained in the coexistence condition of Martensite and austenite. The condition can be achieved when processing an isothermal ageing for the as-cast sample at temperatures of 100 ℃–150 ℃. Three possible mechanisms are considered to account for the maximum damping capacity. They are listed as much increased interfaces between twin boundaries, owing to the thinning of martensitic plates, martensitic transformation induced by the applied stress during internal friction measurements, phase transformation itself based on the coexistence of martensitic and austenitic phases with a macroscopic amount. However, the contribution of the first mechanism is predominant.

Dynamic strength behavior of a Zr-based bulk metallic glassunder shock loading

Yu Yu-Ying, Xi Feng, Dai Cheng-Da, Cai Ling-Cang, Tan Ye, Li Xue-Mei, Wu Qiang, Tan Hua
Chin. Phys. B 2015, 24 (6): 066201;  doi: 10.1088/1674-1056/24/6/066201
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Dynamic strength behavior of Zr51Ti5Ni10Cu25Al9 bulk metallic glass (BMG) up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments. Particle velocity profiles measured at the sample/LiF window interface were used to estimate the shear stress, shear modulus, and yield stress in shocked BMG. Beyond confirming the previously reported strain-softening of shear stress during the shock loading process for BMGs, it is also shown that the softened Zr-BMG still has a high shear modulus and can support large yield stress when released or reloaded from the shocked state, and both the shear modulus and the yield stress appear as strain-hardening behaviors. The work provides a much clearer picture of the strength behavior of BMGs under shock loading, which is useful to comprehensively understand the plastic deformation mechanisms of BMGs.

Synthesis mechanism of nanoporous Sn3O4 nanosheets by hydrothermal process without any additives

Zhao Jun-Hua, Tan Rui-Qin, Yang Ye, Xu Wei, Li Jia, Shen Wen-Feng, Wu Guo-Qiang, Zhu You-Liang, Yang Xu-Feng, Song Wei-Jie
Chin. Phys. B 2015, 24 (6): 066202;  doi: 10.1088/1674-1056/24/6/066202
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Nanoporous anorthic-phase Sn3O4 nanosheets are successfully fabricated via a hydrothermal process without any additives. With the pH value of the precursor increasing from 2.0 to 11.8, the valence of the precursor changes from mixed valence (the ratio of Sn2+ to Sn4+ is 2.7:1) to pure bivalent, and the product transformed from Sn3O4 to SnO mesocrystals. When doping SbCl3 to the alkaline precursor, the valence of the precursor shows mixed valence with the ratio of Sn2+ to Sn4+ being 2.6:1 and Sn3O4 is synthesized after the hydrothermal process. The valence state of Sn species in the precursor is the key factor of the formation of Sn3O4. The synthesis mechanism is discussed and proposed. These experimental results expand the knowledge base that can be used to guide technological applications of intermediate tin oxide materials.

Mechanical properties of copper nanocube under three-axial tensile loadings

Yang Zai-Lin, Zhang Guo-Wei, Luo Gang
Chin. Phys. B 2015, 24 (6): 066203;  doi: 10.1088/1674-1056/24/6/066203
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The mechanical properties of copper nanocubes by molecular dynamics are investigated in this paper. The [100], [110], [111] nanocubes are created, and their energies, yield stresses, hydrostatic stresses, Mises stresses, and the relationships between them and strain are analyzed. Some concepts of the microscopic damage mechanics are introduced, which are the basis of studying the damage mechanical properties by molecular dynamics. The [100] nanocube exhibits homogeneity and isotropy and achieves a balance easily. The [110] nanocube presents transverse isotropy. The [111] nanocube shows the complexity and anisotropy because the orientation sizes in three directions are different. The broken point occurs on a surface, but the other two do not. The [100] orientation model will be an ideal model for studying the microscopic damage theory.

Properties of sound attenuation around a two-dimensional underwater vehicle with a large cavitation number

Ye Peng-Cheng, Pan Guang
Chin. Phys. B 2015, 24 (6): 066401;  doi: 10.1088/1674-1056/24/6/066401
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Due to the high speed of underwater vehicles, cavitation is generated inevitably along with the sound attenuation when the sound signal traverses through the cavity region around the underwater vehicle. The linear wave propagation is studied to obtain the influence of bubbly liquid on the acoustic wave propagation in the cavity region. The sound attenuation coefficient and the sound speed formula of the bubbly liquid are presented. Based on the sound attenuation coefficients with various vapor volume fractions, the attenuation of sound intensity is calculated under large cavitation number conditions. The result shows that the sound intensity attenuation is fairly small in a certain condition. Consequently, the intensity attenuation can be neglected in engineering.

Linear and nonlinear optical properties of Sb-doped GeSe2 thin films

Zhang Zhen-Ying, Chen Fen, Lu Shun-Bin, Wang Yong-Hui, Shen Xiang, Dai Shi-Xun, Nie Qiu-Hua
Chin. Phys. B 2015, 24 (6): 066801;  doi: 10.1088/1674-1056/24/6/066801
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Sb-doped GeSe2 chalcogenide thin films are prepared by the magnetron co-sputtering method. The linear optical properties of as-deposited films are derived by analyzing transmission spectra. The refractive index rises and the optical band gap decreases from 2.08 eV to 1.41 eV with increasing the Sb content. X-ray photoelectron spectra further confirm the formation of a covalent Sb–Se bond. The third-order nonlinear optical properties of thin films are investigated under femtosecond laser excitation at 800 nm. The results show that the third-order nonlinear optical properties are enhanced with increasing the concentration of Sb. The nonlinear refraction indices of these thin films are measured to be on the order of 10-18 m2/W with a positive sign and the nonlinear absorption coefficients are obtained to be on the order of 10-10 m/W. These excellent properties indicate that Sb-doped Ge–Se films have a good prospect in the applications of nonlinear optical devices.
TOPICAL REVIEW—III-nitride optoelectronic materials and devices

Progress in bulk GaN growth

Xu Ke, Wang Jian-Feng, Ren Guo-Qiang
Chin. Phys. B 2015, 24 (6): 066105;  doi: 10.1088/1674-1056/24/6/066105
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Three main technologies for bulk GaN growth, i.e., hydride vapor phase epitaxy (HVPE), Na-flux method, and ammonothermal method, are discussed. We report our recent work in HVPE growth of GaN substrate, including dislocation reduction, strain control, separation, and doping of GaN film. The growth mechanisms of GaN by Na-flux and ammonothermal methods are compared with those of HVPE. The mechanical behaviors of dislocation in bulk GaN are investigated through nano-indentation and high-space resolution surface photo-voltage spectroscopy. In the last part, the progress in growing some devices on GaN substrate by homo-epitaxy is introduced.

Design of patterned sapphire substrates for GaN-based light-emitting diodes

Wang Hai-Yan, Lin Zhi-Ting, Han Jing-Lei, Zhong Li-Yi, Li Guo-Qiang
Chin. Phys. B 2015, 24 (6): 067103;  doi: 10.1088/1674-1056/24/6/067103
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A new method for patterned sapphire substrate (PSS) design is developed and proven to be reliable and cost-effective. As progress is made with LEDs' luminous efficiency, the pattern units of PSS become more complicated, and the effect of complicated geometrical features is almost impossible to study systematically by experiments only. By employing our new method, the influence of pattern parameters can be systematically studied, and various novel patterns are designed and optimized within a reasonable time span, with great improvement in LEDs' light extraction efficiency (LEE). Clearly, PSS pattern design with such a method deserves particular attention. We foresee that GaN-based LEDs on these newly designed PSSs will achieve more progress in the coming years.

Metal-organic-vapor phase epitaxy of InGaN quantum dots and their applications in light-emitting diodes

Wang Lai, Yang Di, Hao Zhi-Biao, Luo Yi
Chin. Phys. B 2015, 24 (6): 067303;  doi: 10.1088/1674-1056/24/6/067303
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InGaN quantum dot is a promising optoelectronic material, which combines the advantages of low-dimensional and wide-gap semiconductors. The growth of InGaN quantum dots is still not mature, especially the growth by metal–organic–vapor phase epitaxy (MOVPE), which is challenge due to the lack of 、itin-situ monitoring tool. In this paper, we reviewed the development of InGaN quantum dot growth by MOVPE, including our work on growth of near-UV, green, and red InGaN quantum dots. In addition, we also introduced the applications of InGaN quantum dots on visible light emitting diodes.

Progress in research of GaN-based LEDs fabricated on SiC substrate

Xu Hua-Yong, Chen Xiu-Fang, Peng Yan, Xu Ming-Sheng, Shen Yan, Hu Xiao-Bo, Xu Xian-Gang
Chin. Phys. B 2015, 24 (6): 067305;  doi: 10.1088/1674-1056/24/6/067305
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The influence of buffer layer growth conditions on the crystal quality and residual stress of GaN film grown on silicon carbide substrate is investigated. It is found that the AlGaN nucleation layer with high growth temperature can efficiently decrease the dislocation density and stress of the GaN film compared with AlN buffer layer. To increase the light extraction efficiency of GaN-based LEDs on SiC substrate, flip-chip structure and thin film flip-chip structure were designed and optimized. The fabricated blue LED had a maximum wall-plug efficiency of 72% at 80 mA. At 350 mA, the output power, the Vf, the dominant wavelength, and the wall-plug efficiency of the blue LED were 644 mW, 2.95 V, 460 nm, and 63%, respectively.

Status of GaN-based green light-emitting diodes

Liu Jun-Lin, Zhang Jian-Li, Wang Guang-Xu, Mo Chun-Lan, Xu Long-Quan, Ding Jie, Quan Zhi-Jue, Wang Xiao-Lan, Pan Shuan, Zheng Chang-Da, Wu Xiao-Ming, Fang Wen-Qing, Jiang Feng-Yi
Chin. Phys. B 2015, 24 (6): 067804;  doi: 10.1088/1674-1056/24/6/067804
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GaN-based blue light emitting diodes (LEDs) have undergone great development in recent years, but the improvement of green LEDs is still in progress. Currently, the external quantum efficiency (EQE) of GaN-based green LEDs is typically 30%, which is much lower than that of top-level blue LEDs. The current challenge with regard to GaN-based green LEDs is to grow a high quality InGaN quantum well (QW) with low strain. Many techniques of improving efficiency are discussed, such as inserting AlGaN between the QW and the barrier, employing prestrained layers beneath the QW and growing semipolar QW. The recent progress of GaN-based green LEDs on Si substrate is also reported: high efficiency, high power green LEDs on Si substrate with 45.2% IQE at 35 A/cm2, and the relevant techniques are detailed.

Transient thermal analysis as measurement method for IC package structural integrity

Alexander Hanß, Maximilian Schmid, E Liu, Gordon Elger
Chin. Phys. B 2015, 24 (6): 068105;  doi: 10.1088/1674-1056/24/6/068105
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Practices of IC package reliability testing are reviewed briefly, and the application of transient thermal analysis is examined in great depth. For the design of light sources based on light emitting diode (LED) efficient and accurate reliability testing is required to realize the potential lifetimes of 10^5 h. Transient thermal analysis is a standard method to determine the transient thermal impedance of semiconductor devices, e.g. power electronics and LEDs. The temperature of the semiconductor junctions is assessed by time-resolved measurement of their forward voltage (Vf). The thermal path in the IC package is resolved by the transient technique in the time domain. This enables analyzing the structural integrity of the semiconductor package. However, to evaluate thermal resistance, one must also measure the dissipated energy of the device (i.e., the thermal load) and the k-factor. This is time consuming, and measurement errors reduce the accuracy. To overcome these limitations, an innovative approach, the relative thermal resistance method, was developed to reduce the measurement effort, increase accuracy and enable automatic data evaluation. This new way of evaluating data simplifies the thermal transient analysis by eliminating measurement of the k-factor and thermal load, i.e. measurement of the lumen flux for LEDs, by normalizing the transient Vf data. This is especially advantageous for reliability testing where changes in the thermal path, like cracks and delaminations, can be determined without measuring the k-factor and thermal load. Different failure modes can be separated in the time domain. The sensitivity of the method is demonstrated by its application to high-power white InGaN LEDs. For detailed analysis and identification of the failure mode of the LED packages, the transient signals are simulated by time-resolved finite element (FE) simulations. Using the new approach, the transient thermal analysis is enhanced to a powerful tool for reliability investigation of semiconductor packages in accelerated lifetime tests and for inline inspection. This enables automatic data analysis of the transient thermal data required for processing a large amount of data in production and reliability testing. Based on the method, the integrity of LED packages can be tested by inline, outgoing inspection and the lifetime prediction of the products is improved.

GaN substrate and GaN homo-epitaxy for LEDs: Progress and challenges

Wu Jie-Jun, Wang Kun, Yu Tong-Jun, Zhang Guo-Yi
Chin. Phys. B 2015, 24 (6): 068106;  doi: 10.1088/1674-1056/24/6/068106
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After a brief review on the progresses in GaN substrates by ammonothermal method and Na-flux method and hydride vapor phase epitaxy (HVPE) technology, our research results of growing GaN thick layer by a gas flow-modulated HVPE, removing the GaN layer through an efficient self-separation process from sapphire substrate, and modifying the uniformity of multiple wafer growth are presented. The effects of surface morphology and defect behaviors on the GaN homo-epitaxial growth on free standing substrate are also discussed, and followed by the advances of LEDs on GaN substrates and prospects of their applications in solid state lighting.

Phosphor-free white light-emitting diodes

Guo Xia, Liu Qiao-Li, Li Chong, Liu Bai, Dong Jian, Shen Guang-Di
Chin. Phys. B 2015, 24 (6): 068505;  doi: 10.1088/1674-1056/24/6/068505
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The multiple color-matching schemes that could improve the color rendering index for phosphor-free white LEDs are discussed. Then we review a few of the recent research directions for phosphor-free white LEDs, which include the development of monolithic GaN-based white LEDs and hybrid integrated GaN-based and AlGaInP-based white LEDs. These development paths will pave the way toward commercial application of phosphor-free white LEDs in the coming years.

Progress and prospects of GaN-based LEDs using nanostructures

Zhao Li-Xia, Yu Zhi-Guo, Sun Bo, Zhu Shi-Chao, An Ping-Bo, Yang Chao, Liu Lei, Wang Jun-Xi, Li Jin-Min
Chin. Phys. B 2015, 24 (6): 068506;  doi: 10.1088/1674-1056/24/6/068506
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Progress with GaN-based light emitting diodes (LEDs) that incorporate nanostructures is reviewed, especially the recent achievements in our research group. Nano-patterned sapphire substrates have been used to grow an AlN template layer for deep-ultraviolet (DUV) LEDs. One efficient surface nano-texturing technology, hemisphere-cones-hybrid nanostructures, was employed to enhance the extraction efficiency of InGaN flip-chip LEDs. Hexagonal nanopyramid GaN-based LEDs have been fabricated and show electrically driven color modification and phosphor-free white light emission because of the linearly increased quantum well width and indium incorporation from the shell to the core. Based on the nanostructures, we have also fabricated surface plasmon-enhanced nanoporous GaN-based green LEDs using AAO membrane as a mask. Benefitting from the strong lateral SP coupling as well as good electrical protection by a passivation layer, the EL intensity of an SP-enhanced nanoporous LED was significantly enhanced by 380%. Furthermore, nanostructures have been used for the growth of GaN LEDs on amorphous substrates, the fabrication of stretchable LEDs, and for increasing the 3-dB modulation bandwidth for visible light communication.


Structural, electronic, and magnetic properties in FeAlAun (n=1-6) clusters: A first-principles study

Zhang Jian-Fei, Zhang Meng, Zhao Yan-Wei, Zhang Hong-Yu, Zhao Li-Na, Luo You-Hua
Chin. Phys. B 2015, 24 (6): 067101;  doi: 10.1088/1674-1056/24/6/067101
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The geometries, electronic and magnetic properties of the trimetallic clusters FeAlAun (n=1–6) are systematically investigated using density functional theory (DFT). A number of new isomers are obtained to probe the structural evolutions. All doped clusters show larger relative binding energies than pure Aun+2 partners, indicating that doping with Fe and Al atoms can stabilize the Aun clusters. The highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps, vertical ionization potentials and vertical electron affinities are also studied and compared with those of pure gold clusters. Magnetism calculations demonstrate that the magnetic moments of FeAlAun clusters each show a pronounced odd–even oscillation with the number of Au atoms.

First principles study on d0 half-metallic properties of full-Heusler compounds RbCaX2 (X=C, N, and O)

Gao Yong-Chun, Wang Xiao-Tian, Habib Rozale
Chin. Phys. B 2015, 24 (6): 067102;  doi: 10.1088/1674-1056/24/6/067102
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A first-principles approach is employed to study the structural, electronic, and magnetic properties of RbCaX2 (X=C, N, and O) full-Heusler compounds. It is observed that RbCaN2 and RbCaO2 are new d0 half-metals with an integer magnetic moment of 3 μB and 1 μB in their ferrimagnetic ground states, respectively, while RbCaC2 is a common metallic compound. Analysis of the density of states of these compounds indicates that the magnetic moment and furthermore, the half-metallicity primarily originate from the spin-polarization of the p-like states of N and O atoms. The half-metallic (HM) gaps of RbCaN2 and RbCaO2 are notably large; thus, the half-metallicity is robust against lattice distortion. Such materials are suitable to be grown on various semiconductor substrates. In addition, for RbCaN2 and RbCaO2, four possible terminations of the surface are also calculated.

Low-temperature physical properties and electronic structures of Ni3Sb, Ni5Sb2, NiSb2, and NiSb

Luo Xiao-Ning, Dong Cheng, Liu Shi-Kai, Zhang Zi-Ping, Li Ao-Lei, Yang Li-Hong, Li Xiao-Chuan
Chin. Phys. B 2015, 24 (6): 067201;  doi: 10.1088/1674-1056/24/6/067201
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We report the results of low temperature resistivity and magnetization measurements on polycrystalline samples of four Ni–Sb compounds, Ni3Sb, Ni5Sb2, NiSb, and NiSb2. Resistivity measurements revealed that these compounds exhibit a metallic type of electrical conductivity. Temperature dependences of the resistivities were well fitted by the generalized Bloch–Grüneisen formula with an exponent of n=3, indicating that the s–d interband scattering is the dominant scattering mechanism. The magnetic susceptibilities of Ni5Sb2, NiSb, and NiSb2 are almost independent of temperature (above 150 K), exhibiting Pauli paramagnetic behavior. The temperature dependences of the susceptibilities were fitted using the Curie–Weiss law. Ni3Sb was found to have a paramagnetic–ferromagnetic phase transition at 229 K.
First-principles calculations have been performed to investigate the electronic structures and physical properties of these Ni–Sb alloys. The calculation of the band structure predicted that Ni3Sb, Ni5Sb2, NiSb, and NiSb2 have characteristics of metal, and the ground state of Ni3Sb is ferromagnetic. The electrical and magnetic properties observed experimentally are consistent with that predicted by the first-principle electronic structure calculations.

Influences of spark plasma sintering temperature on the microstructures and thermoelectric properties of (Sr0.95Gd0.05)TiO3 ceramics

Li Liang-Liang, Qin Xiao-Ying, Liu Yong-Fei, Liu Quan-Zhen
Chin. Phys. B 2015, 24 (6): 067202;  doi: 10.1088/1674-1056/24/6/067202
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(Sr0.95Gd0.05)TiO3 (SGTO) ceramics are successfully prepared via spark plasma sintering (SPS) respectively at 1548, 1648, and 1748 K by using submicron-sized SGTO powders synthesized from a sol–gel method. The densities, microstructures, and thermoelectric properties of the SGTO ceramics are studied. Though the Seebeck coefficient shows no obvious difference in the case that SPS temperatures range from 1548 K to 1648 K, the electrical conductivity and the thermal conductivity increase remarkably due to the increase in grain size and density. The sample has a density higher than 98% theoretical density as the sintering temperature increases up to 1648 K and shows average grain sizes increasing from ~ 0.7 μm to 7 μm until 1748 K. As a result, the maximum of the dimensionless figure of merit of ~ 0.24 is achieved at ~ 1000 K for the samples sintered at 1648 K and 1748 K, which was ~ 71% larger than that (0.14 at ~ 1000 K) for the sample sintered at 1548 K due to the enhancement of the power factor.

Effect of de-trapping on carrier transport process in semi-insulating CdZnTe

Guo Rong-Rong, Jie Wan-Qi, Zha Gang-Qiang, Xu Ya-Dong, Feng Tao, Wang Tao, Du Zhuo-Tong
Chin. Phys. B 2015, 24 (6): 067203;  doi: 10.1088/1674-1056/24/6/067203
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The effect of de-trapping on the carrier transport process in the CdZnTe detector is studied by laser beam-induced transient current (LBIC) measurement. Trapping time, de-trapping time, and mobility for electrons are determined directly from transient waveforms under various bias voltages. The results suggest that an electric field strengthens the capture and emission effects in trap center, which is associated with field-assisted capture and the Poole–Frenkel effect, respectively. The electron mobility is calculated to be 950 cm2/V·s and the corresponding electron mobility-lifetime product is found to be 1.32× 10-3 cm2/V by a modified Hecht equation with considering the surface recombination effect. It is concluded that the trapping time and de-trapping time obtained from LBIC measurement provide direct information concerning the transport process.

Formation of two-dimensional electron gas at AlGaN/GaN heterostructure and the derivation of its sheet density expression

He Xiao-Guang, Zhao De-Gang, Jiang De-Sheng
Chin. Phys. B 2015, 24 (6): 067301;  doi: 10.1088/1674-1056/24/6/067301
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Models for calculating the sheet densities of two-dimensional electron gas (2DEG) induced by spontaneous and piezoelectric polarization in AlGaN/GaN, AlGaN/AlN/GaN, and GaN/AlGaN/GaN heterostructures are provided. The detailed derivation process of the expression of 2DEG sheet density is given. A longstanding confusion in a very widely cited formula is pointed out and its correct expression is analyzed in detail.

Disorder-enhanced nuclear spin relaxation at Landau level filling factor one Hot!

Guan Tong, Benedikt Friess, Li Yong-Qing, Yan Shi-Shen, Vladimir Umansky, Klaus von Klitzing, Jurgen H. Smet
Chin. Phys. B 2015, 24 (6): 067302;  doi: 10.1088/1674-1056/24/6/067302
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The nuclear spin relaxation rate (1/T1) is measured for GaAs two-dimensional (2D) electron systems in the quantum Hall regime with an all-electrical technique for agitating and probing the nuclear spins. A “tilted plateau” feature is observed near the Landau level filling factor ν=1 in 1/T1 versus ν. Both the width and magnitude of the plateau increase with decreasing electron density. At low temperatures, 1/T1 exhibits an Arrhenius temperature dependence within the tilted plateau regime. The extracted energy gaps are up to two orders of magnitude smaller than the corresponding charge transport gaps. These results point to a nontrivial mechanism for the disorder-enhanced nuclear spin relaxation, in which microscopic inhomogeneities play a key role for the low energy spin excitations related to skyrmions.

Finite size effects on the quantum spin Hall state in HgTe quantum wells under two different types of boundary conditions

Cheng Zhi, Chen Rui, Zhou Bin
Chin. Phys. B 2015, 24 (6): 067304;  doi: 10.1088/1674-1056/24/6/067304
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The finite size effect in a two-dimensional topological insulator can induce an energy gap Eg in the spectrum of helical edge states for a strip of finite width. In a recent work, it has been found that when the spin–orbit coupling due to bulk-inversion asymmetry is taken into account, the energy gap Eg of the edge states features an oscillating exponential decay as a function of the strip width of the inverted HgTe quantum well. In this paper, we investigate the effects of the interface between a topological insulator and a normal insulator on the finite size effect in the HgTe quantum well by means of the numerical diagonalization method. Two different types of boundary conditions, i.e., the symmetric and asymmetric geometries, are considered. It is found that due to the existence of the interface between topological insulator and normal insulator this oscillatory pattern on the exponential decay induced by bulk-inversion asymmetry is modulated by the width of normal insulator regions. With the variation of the width of normal insulator regions, the shift of the Dirac point of the edge states in the spectrum and the energy gap Eg closing point in the oscillatory pattern can occur. Additionally, the effect of the spin–orbit coupling due to structure-inversion asymmetry on the finite size effects is also investigated.

Enhanced ultraviolet photoresponse based on ZnO nanocrystals/Pt bilayer nanostructure

Tong Xiao-Lin, Xia Xiao-Zhi, Li Qing-Xia
Chin. Phys. B 2015, 24 (6): 067306;  doi: 10.1088/1674-1056/24/6/067306
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The development of solution strategies for Zinc oxide (ZnO) quantum dots provides a pathway to utilizing ZnO nanocrystal thin films in optoelectronic devices. In this work, quasi-spherical ZnO quantum dots with a diameter of 5 nm are synthesized by using ethanol as a solvent. ZnO nanocrystal thin film is obtained by spin-coating ZnO quantum dots on a Au interdigital electrode (IDE)/Al2O3 substrate and annealing at different temperatures in order to yield the optimal photosensitive on/off ratio of ZnO. For further enhancing the responsivity, ion sputtering is utilized to deposit Pt nanoparticles on the surface of ZnO nanocrystal thin film, the responsivity of the ZnO/Pt bilayer nanostructure increases from 0.07 A/W to 54 A/W, showing that the metal/inorganic nanocrystal bilayer nanostructure can be used to improve the performance of optoelectronic devices. The excellent properties of ZnO/Pt bilayer nanostructure have important applications in future electronic and optoelectronic devices.

Stability of conductance oscillations in carbon atomic chains

Yu Jing-Xin, Hou Zhi-Wei, Liu Xiu-Ying
Chin. Phys. B 2015, 24 (6): 067307;  doi: 10.1088/1674-1056/24/6/067307
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The conductance stabilities of carbon atomic chains (CACs) with different lengths are investigated by performing theoretical calculations using the nonequilibrium Green's function method combined with density functional theory. Regular even–odd conductance oscillation is observed as a function of the wire length. This oscillation is influenced delicately by changes in the end carbon or sulfur atoms as well as variations in coupling strength between the chain and leads. The lowest unoccupied molecular orbital in odd-numbered chains is the main transmission channel, whereas the conductance remains relatively small for even-numbered chains and a significant drift in the highest occupied molecular orbital resonance toward higher energies is observed as the number of carbon atoms increases. The amplitude of the conductance oscillation is predicted to be relatively stable based on a thiol joint between the chain and leads. Results show that the current–voltage evolution of CACs can be affected by the chain length. The differential and second derivatives of the conductance are also provided.

Possible magnetic structures of EuZrO3

Hu Ai-Yuan, Qin Guo-Ping, Wu Zhi-Min, Cui Yu-Ting
Chin. Phys. B 2015, 24 (6): 067501;  doi: 10.1088/1674-1056/24/6/067501
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A comprehensive research of the antiferromagnetic (AFM) structures of perovskite-type EuZrO3 is carried out by use of the double-time Green's function. Two possible types of AFM configurations are considered, and theoretical results are compared with experimental results to extract the values of parameters J1, J2, and D. The obtained exchanges are employed to calculate the magnetic susceptibility, which is then in turn compared with the experimental one. Therefore, we think that the magnetic structure of EuZrO3 may be an isotropic G-type structure or an anisotropic A-type structure.

Influences of P doping on magnetic phase transition and structure in MnCoSi ribbon

Du Qian-Heng, Chen Guo-Fu, Yang Wen-Yun, Hua Mu-Xin, Du Hong-Lin, Wang Chang-Sheng, Liu Shun-Quan, Han Jing-Zhi, Zhou Dong, Zhang Yan, Yang Jin-Bo
Chin. Phys. B 2015, 24 (6): 067502;  doi: 10.1088/1674-1056/24/6/067502
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The structure and magnetic properties of MnCoSi1-xPx (x=0.05–0.50) are systematically investigated. With P content increasing, the lattice parameter a increases monotonically while both b and c decrease. At the same time, the temperature of metamagnetic transition from a low-temperature non-collinear ferromagnetic state to a high-temperature ferromagnetic state decreases and a new magnetic transition from a higher-magnetization ferromagnetic state to a lower-magnetization ferromagnetic state is observed in each of these compounds for the first time. This is explained by the changes of crystal structure and distance between Mn and Si atoms with the increase of temperature according to the high-temperature XRD result. The metamagnetic transition is found to be a second-order magnetic transition accompanied by a low inversed magnetocaloric effect (1.0 J·kg-1·K-1 at 5 T) with a large temperature span (190 K at 5 T) compared with the scenario of MnCoSi. The changes in the order of metamagnetic transition and structure make P-doped MoCoSi compounds good candidates for the study of magnetoelastic coupling and the modulation of magnetic phase transition.

Radio-frequency-heating capability of silica-coated manganese ferrite nanoparticles

Qiu Qing-Wei, Xu Xiao-Wen, He Mang, Zhang Hong-Wang
Chin. Phys. B 2015, 24 (6): 067503;  doi: 10.1088/1674-1056/24/6/067503
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MnFe2O4 nanoparticles (NPs) with various sizes and tight size-distribution were synthesized by a chemical solution-phase method. The as-synthesized NPs were coated with a silica shell of 4 nm–5 nm in thickness, enabling the water-solubility and biocompatibility of the NPs. The MnFe2O4 NPs with a size of less than 18 nm exhibit superparamagnetic behavior with high saturated magnetization. The capacity of the heat production was enhanced by increasing particle sizes and radio frequency (RF) field strengths. MnFe2O4/SiO2 NPs with 18-nm magnetic cores showed the highest heat-generation ability under an RF field. These MnFe2O4/SiO2 NPs have great potentiality to cancer treatments, controlled drug releases, and remote controls of single cell functions.

Preparation and piezoelectric properties of potassium sodium niobate glass ceramics

Jiang Shan, Wang Xuan-Ming, Li Jia-Yu, Zhang Yong, Zheng Tao, Lv Jing-Wen
Chin. Phys. B 2015, 24 (6): 067701;  doi: 10.1088/1674-1056/24/6/067701
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This paper describes the preparation of a piezoelectric glass ceramic material from potassium sodium niobate (K0.5Na0.5NbO3; KNN) using a novel melting method. The effects of the subsequent heat-treatment on the optical, thermal, electrical, and mechanical properties of the material are carefully examined, and its crystal structure and surface morphology are characterized respectively by x-ray diffraction and scanning electron microscopy. This new material has a much higher piezoelectric coefficient (163 pC·N-1) than traditional piezoelectric ceramics (131 pC·N-1). On this basis therefore, a strategy for the future study and development of lead-free KNN-based piezoelectric glass ceramics is proposed.

Magnetic and ferroelectric properties of Zn and Mn co-doped BaTiO3

Sangram Keshari Das, Binod Kumar Roul
Chin. Phys. B 2015, 24 (6): 067702;  doi: 10.1088/1674-1056/24/6/067702
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This paper reports an approach to obtaining multiferroic properties in co-doped (Zn:Mn) BaTiO3 near room temperature. Interestingly, an unusual magnetic hysteresis loop is observed in the co-doped compositions in which the central portion of the loop is squeezed. However, in the composition Ba0.9Zn0.1Ti0.9Mn0.1O3, a broad magnetic hysteresis loop is observed. Such a magnetic effect is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system. The observation of the above type of magnetic properties is likely to be due to the presence of exchange interactions between Mn ions. A lossy-type of ferroelectric hysteresis loop is also observed in co-doped ceramic compositions near room temperature.

Hydrothermal synthesis of Yb3+, Tm3+ co-doped Gd6MoO12 and its upconversion properties

Di Qiu-Mei, Sun Yu-Mei, Xu Qi-Guang, Han Liu, Xue Bing, Sun Jia-Yue
Chin. Phys. B 2015, 24 (6): 067801;  doi: 10.1088/1674-1056/24/6/067801
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Yb3+, Tm3+ co-doped Gd6MoO12 phosphors with different morphologies are prepared by the hydrothermal method. The dendrites present different morphologies (including hexagonal prisms, spindles, and spheres) after changing the pH value and edetate disodium (EDTA) usage. It is found that each of the two factors plays a crucial role in forming different morphologies.#br#The up-conversion (UC) luminescence is studied. Under 980-nm semiconductor laser excitation, relatively strong blue emission and weak red emission are observed. Finally, the effect of pumping power on the UC luminescence properties and the level diagram mechanism of Gd6MoO12:Yb3+/Tm3+ phosphor are also discussed.

2.0-μm emission and energy transfer of Ho3+/Yb3+ co-doped LiYF4 single crystal excited by 980 nm

Yang Shuo, Xia Hai-Ping, Jiang Yong-Zhang, Zhang Jia-Zhong, Jiang Dong-Sheng, Wang Cheng, Feng Zhi-Gang, Zhang Jian, Gu Xue-Mei, Zhang Jian-Li, Jiang Hao-Chuan, Chen Bao-Jiu
Chin. Phys. B 2015, 24 (6): 067802;  doi: 10.1088/1674-1056/24/6/067802
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Ho3+/Yb3+ co-doped LiYF4 single crystals with various Yb3+ concentrations and ~ 0.98 mol% Ho3+ concentration are grown by the Bridgman method under the conditions of taking LiF and YF3 as raw materials and a temperature gradient (40 ℃/cm–50 ℃/cm) for the solid–liquid interface. The luminescent performances of the crystals are investigated through emission spectra, infrared transmittance spectrum, emission cross section, and decay curves under excitation by 980 nm. Compared with the Ho3+ single-doped LiYF4 crystal, the Ho3+/Yb3+ co-doped LiYF4 single crystal has an obviously enhanced emission band from 1850 nm to 2150 nm observed when excited by a 980-nm diode laser. The energy transfer from Yb3+ to Ho3+ and the optimum fluorescence emission around 2.0 μm of Ho3+ ions are investigated. The maximum emission cross section of the above sample at 2.0 μm is calculated to be 1.08× 10-20 cm2 for the LiYF4 single crystal of 1-mol% Ho3+ and 6-mol% Yb3+ according to the measured absorption spectrum. The high energy transfer efficiency of 88.9% from Yb3+ to Ho3+ ion in the sample co-doped by Ho3+ (1 mol%) and Yb3+ (8 mol%) demonstrates that the Yb3+ ions can efficiently sensitize the Ho3+ ions.

Effects of the ion-beam voltage on the properties of the diamond-like carbon thin film prepared by ion-beam sputtering deposition

Sun Peng, Hu Ming, Zhang Feng, Ji Yi-Qin, Liu Hua-Song, Liu Dan-Dan, Leng Jian
Chin. Phys. B 2015, 24 (6): 067803;  doi: 10.1088/1674-1056/24/6/067803
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Diamond-like carbon (DLC) thin film is one of the most widely used optical thin films. The fraction of chemical bondings has a great influence on the properties of the DLC film. In this work, DLC thin films are prepared by ion-beam sputtering deposition in Ar and CH4 mixtures with graphite as the target. The influences of the ion-beam voltage on the surface morphology, chemical structure, mechanical and infrared optical properties of the DLC films are investigated by atomic force microscopy (AFM), Raman spectroscopy, nanoindentation, and Fourier transform infrared (FTIR) spectroscopy, respectively. The results show that the surface of the film is uniform and smooth. The film contains sp2 and sp3 hybridized carbon bondings. The film prepared by lower ion beam voltage has a higher sp3 bonding content. It is found that the hardness of DLC films increases with reducing ion-beam voltage, which can be attributed to an increase in the fraction of sp3 carbon bondings in the DLC film. The optical constants can be obtained by the whole infrared optical spectrum fitting with the transmittance spectrum. The refractive index increases with the decrease of the ion-beam voltage, while the extinction coefficient decreases.

Influence factors and mechanism of emission of ZnS:Cu nanocrystals

Chu Xue-Ying, Wang Xin-Nong, Li Jin-Hua, Yao Dan, Fang Xuan, Fang Fang, Wei Zhi-Peng, Wang Xiao-Hua
Chin. Phys. B 2015, 24 (6): 067805;  doi: 10.1088/1674-1056/24/6/067805
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Copper-doped ZnS (ZnS:Cu) nanocrystals are synthesized by the sol–gel method. The average size of the ZnS:Cu nanocrystals is 3.1 nm. The x-ray diffraction indicates that increasing the Cu-dopant concentration results in a large shift in the diffraction angle. The effects of the dopant concentration, the reactant ratio, and aging temperature on the optical properties of the ZnS:Cu nanocrystals are also investigated. The fluorescence emission mechanism is analyzed by peak deconvolution using Gaussian functions. We find that the emission of the ZnS:Cu nanocrystal is composed of different luminescence centers at 430, 470, 490, 526, and 560 nm. The origins of these emissions are discussed and demonstrated by controlled experiments.

The influence of phonon bath on the control of single photon

Zhang Wei, Lu Hai-Tao
Chin. Phys. B 2015, 24 (6): 067806;  doi: 10.1088/1674-1056/24/6/067806
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The influence of vacuum fluctuation and phonon bath on the probability of single photon emission are both considered in the two-level system model theoretically; by using the master equations and generating function method we get the analytical expression of the second-order fluorescence correlation function, probability of single photon emission, and Mandel's Q parameter. The results manifest that the coupling between the phonon bath and single photon source destroys the superposition state induced by the square laser pulse, the Rabi oscillation damped rapidly with the increasing of temperature. Theoretically, when the structure parameter of arsenide quantum dots α scaled to 0.1 times of the sample, the critical coherence-temperature will rise up to hundreds of Kelvin, which means a step forward to the realization of coherent control of single photon source at room temperature.

Giant enhancement of Kerr rotation in two-dimensional Bismuth iron garnet/Ag photonic crystals

Liang Hong, Liu Huan, Zhang Qiang, Fu Shu-Fang, Zhou Sheng, Wang Xuan-Zhang
Chin. Phys. B 2015, 24 (6): 067807;  doi: 10.1088/1674-1056/24/6/067807
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Kerr effects of two-dimensional (2D) Bismuth iron garnet (BIG)/Ag photonic crystals (PCs) combined magnetic and plasmonic functionalities is investigated with the effective medium theory. An analytical expression of Kerr rotation angles is derived, in which the effects of the surface pasmons polaritons (SPP) on magneto–optical (MO) activities are reflected. The largest enhancement of Kerr rotation up to now is demonstrated, which is improved three orders of magnitude compared with that of BIG film. When λ< 750 nm all of the reflection are over 10% for the arbitrary filling ratio f1, in addition, the enhancement of Kerr rotation angles are at least one order of magnitude.

Electronic structure of transition metal dichalcogenides PdTe2 and Cu0.05PdTe2 superconductors obtained by angle-resolved photoemission spectroscopy Hot!

Liu Yan, Zhao Jian-Zhou, Yu Li, Lin Cheng-Tian, Hu Cheng, Liu De-Fa, Peng Ying-Ying, Xie Zhuo-Jin, He Jun-Feng, Chen Chao-Yu, Feng Ya, Yi He-Mian, Liu Xu, Zhao Lin, He Shao-Long, Liu Guo-Dong, Dong Xiao-Li, Zhang Jun, Chen Chuang-Tian, Xu Zu-Yan, Weng Hong-Ming, Dai Xi, Fang Zhong, Zhou Xing-Jiang
Chin. Phys. B 2015, 24 (6): 067401;  doi: 10.1088/1674-1056/24/6/067401
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The layered transition metal chalcogenides have been a fertile land in solid state physics for many decades. Various MX2-type transition metal dichalcogenides, such as WTe2, IrTe2, and MoS2, have triggered great attention recently, either for the discovery of novel phenomena or some extreme or exotic physical properties, or for their potential applications. PdTe2 is a superconductor in the class of transition metal dichalcogenides, and superconductivity is enhanced in its Cu-intercalated form, Cu0.05PdTe2. It is important to study the electronic structures of PdTe2 and its intercalated form in order to explore for new phenomena and physical properties and understand the related superconductivity enhancement mechanism. Here we report systematic high resolution angle-resolved photoemission (ARPES) studies on PdTe2 and Cu0.05PdTe2 single crystals, combined with the band structure calculations. We present in detail for the first time the complex multi-band Fermi surface topology and densely-arranged band structure of these compounds. By carefully examining the electronic structures of the two systems, we find that Cu-intercalation in PdTe2 results in electron-doping, which causes the band structure to shift downwards by nearly 16 meV in Cu0.05PdTe2. Our results lay a foundation for further exploration and investigation on PdTe2 and related superconductors.

Toward the complete relational graph of fundamental circuit elements Hot!

Shang Da-Shan, Chai Yi-Sheng, Cao Ze-Xian, Lu Jun, Sun Young
Chin. Phys. B 2015, 24 (6): 068402;  doi: 10.1088/1674-1056/24/6/068402
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A complete and harmonized fundamental circuit relational graph with four linear and four memory elements is constructed based on some newly defined elements, which provides a guide to developing novel circuit functionalities in the future. In addition to resistors, capacitors, and inductors, which are defined in terms of a linear relationship between charge q, current i, voltage v, and magnetic flux φ, Chua proposed in 1971 a fourth linear circuit element to directly relate φ and q. A nonlinear resistive device defined in memory i–v relation and dubbed memristor, was later attributed to such an element and has been realized in various material structures. Here we clarify that the memristor is not the true fourth fundamental circuit element but the memory extension to the concept of resistor, in analogy to the extension of memcapacitor to capacitor and meminductor to inductor. Instead, a two-terminal device employing the linear ME effects, termed transtor, directly relates φ and q and should be recognized as the fourth linear element. Moreover, its memory extension, termed memtranstor, is proposed and analyzed here.

Curvature-induced lipid segregation

Zheng Bin, Meng Qing-Tian, Robin L. B. Selinger, Jonathan V. Selinger, Ye Fang-Fu
Chin. Phys. B 2015, 24 (6): 068701;  doi: 10.1088/1674-1056/24/6/068701
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We investigate how an externally imposed curvature influences lipid segregation on two-phase-coexistent membranes. We show that the bending-modulus contrast of the two phases and the curvature act together to yield a reduced effective line tension. On largely curved membranes, a state of multiple domains (or rafts) forms due to a mechanism analogous to that causing magnetic-vortex formation in type-II superconductors. We determine the criterion for such a multi-domain state to occur; we then calculate respectively the size of the domains formed on cylindrically and spherically curved membranes.


Gate-dependent photoresponse in self-assembled graphene p-n junctions

Yin Wei-Hong, Wang Yu-Bing, Han Qin, Yang Xiao-Hong
Chin. Phys. B 2015, 24 (6): 068101;  doi: 10.1088/1674-1056/24/6/068101
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The intrinsic photocurrent generation mechanism of a self-assembled graphene p–n junction operating at 1.55 μ is investigated experimentally. It is concluded that both a photovoltage effect and a photothermoelectric effect contribute to the final photocurrent. The photocurrent signal at the p–n junction was found to be dominated by photothermoelectric current, arising from different self-assembled doping levels.

Silicon nanowire formed via shallow anisotropic etching Si-ash-trimming for specific DNA and electrochemical detection

Tijjani Adam, U. HAshim, Th S. Dhahi
Chin. Phys. B 2015, 24 (6): 068102;  doi: 10.1088/1674-1056/24/6/068102
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A functionalized silicon nanowire field-effect transistor (SiNW FET) was fabricated to detect single molecules in the pM range to detect disease at the early stage with a sensitive, robust, and inexpensive method with the ability to provide specific and reliable data. The device was designed and fabricated by indented ash trimming via shallow anisotropic etching. The approach is a simple and low-cost technique that is compatible with the current commercial semiconductor standard CMOS process without an expensive deep reactive ion etcher. Specific electric changes were observed for DNA sensing when the nanowire surface was modified with a complementary captured DNA probe and target DNA through an organic linker (–OCH2CH3) using organofunctional alkoxysilanes (3-aminopropyl) triethoxysilane (APTES). With this surface modification, a single specific target molecule can be detected. The simplicity of the sensing domain makes it feasible to miniaturize it for the development of a cancer detection kit, facilitating its use in both clinical and non-clinical environments to allow non-expert interpretation. With its novel electric response and potential for mass commercial fabrication, this biosensor can be developed to become a portable/point of care biosensor for both field and diagnostic applications.

Wavelength-tunable prism-coupled external cavity passively mode-locked quantum-dot laser

Wu Yan-Hua, Wu Jian, Jin Peng, Wang Fei-Fei, Hu Fa-Jie, Wei Heng, Wang Zhan-Guo
Chin. Phys. B 2015, 24 (6): 068103;  doi: 10.1088/1674-1056/24/6/068103
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A wavelength-tunable mode-locked quantum dot laser using an InAs/GaAs quantum-dot gain medium and a discrete semiconductor saturable absorber mirror is demonstrated. A dispersion prism, which has lower optical loss and less spectral narrowing than a blazed grating, is used for wavelength selection and tuning. A wavelength tuning range of 45.5 nm (from 1137.3 nm to 1182.8 nm) under 140-mA injection current in the passive mode-locked regime is achieved. The maximum average power of 19 mW is obtained at the 1170.3-nm wavelength, corresponding to the single pulse energy of 36.5 pJ.

Modeling the reactive sputter deposition of Ti-doped VOx thin films

Wang Tao, Yu He, Gu De-En, Guo Rui, Dong Xiang, Jiang Ya-Dong, Hu Rui-Lin
Chin. Phys. B 2015, 24 (6): 068104;  doi: 10.1088/1674-1056/24/6/068104
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In this paper an original numerical model, based on the standard Berg model, is used to simulate the growth mechanism of Ti-doped VOx deposited with changing oxygen flow during reactive sputtering deposition. Ti-doped VOx thin films are deposited using a V target with Ti inserts. The effects of titanium inserts on the discharge voltage, deposition rate, and the ratio of V/Ti are investigated. By doping titanium in the vanadium target, the average sputtering yield decreases. In this case, the sputter erosion reduces, which is accompanied by a reduction in the deposition rate. The ratio between V content and Ti content in the film is measured using energy-dispersive x-ray spectroscopy (EDX). A decrease in the vanadium concentration with the increasing of the oxygen flow rate is detected using EDX. Results show a reasonable agreement between numerical and experimental data.

Theoretical investigation on isomer formation probability and free energy of small C clusters

Lin Zheng-Zhe
Chin. Phys. B 2015, 24 (6): 068201;  doi: 10.1088/1674-1056/24/6/068201
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Molecular dynamics simulations and free energy calculations are employed to investigate the evolution, formation probability, detailed balance, and isomerization rate of small C cluster isomer at 2500 K. For C10, the isomer formation probability predicted by free energy is in good agreement with molecular dynamics simulation. However, for C20, C30, and C36, the formation probabilities predicted by free energy are not in agreement with molecular dynamics simulations. Although the cluster systems are in equilibrium, detailed balance is not reached. Such results may be attributed to high transformation barriers between cage, bowl, and sheet isomers. In summary, for mesoscopic nanosystems the free energy criterion, which commonly holds for macroscopic systems in dynamic equilibrium, may not provide a good prediction for isomer formation probability. New theoretical criterion should be further investigated for predicting the isomer formation probability of a mesoscopic nanosystem.

A theoretical exploration of the influencing factors for surface potential

Liu Xin-Min, Yang Gang, Li Hang, Tian Rui, Li Rui, Ding Wu-Quan, Yuan Ruo
Chin. Phys. B 2015, 24 (6): 068202;  doi: 10.1088/1674-1056/24/6/068202
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Although it has been widely used to probe the interfacial property, dynamics, and reactivity, the surface potential remains intractable for directly being measured, especially for charged particles in aqueous solutions. This paper presents that the surface potential is strongly dependent on the Hofmeister effect, and the theory including ion polarization and ionic correlation shows significant improvement compared with the classical theory. Ion polarization causes a strong Hofmeister effect and further dramatic decrease to surface potential, especially at low concentration; in contrast, ionic correlation that is closely associated with potential decay distance overestimates surface potential and plays an increasing role at higher ionic concentrations. Contributions of ion polarization and ionic correlation are respectively assessed, and a critical point is detected where their contributions can be exactly counteracted. Ionic correlation can be almost neglected at low ionic concentrations, while ion polarization, albeit less important at high concentrations, should be considered across the entire concentration range. The results thus obtained are applicable to other interfacial processes.

Generic meminductive characteristics ofswitched reluctance machines

Liang Yan, Chen Hao, Liu Hua-Jian, Shi Jiao-Tong
Chin. Phys. B 2015, 24 (6): 068401;  doi: 10.1088/1674-1056/24/6/068401
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The meminductive system can be regarded as the generalization of the meminductor. This paper focuses on exploring the generic meminductive characteristics of the switched reluctance machine (SRM). The dynamical equations of SRM systems are derived and discussed in comparison with the typical constitutive relation equations of the meminductive system. Memory ability and pinched hysteresis loop (PHL) are taken as the indicative fingerprints to draw forth the theoretically comparative analysis. Based on the theoretical analysis, in addition to simulation and experimental confirmation, it can be concluded that from the viewpoint of circuit, SRM can be considered as a generic meminductive system.

High efficiency, large-active-area superconducting nanowire single-photon detectors

Gu Min, Zhang La-Bao, Kang Lin, Zhao Qing-Yuan, Jia Tao, Wan Chao, Xu Rui-Ying, Yang Xiao-Zhong, Wu Pei-Heng, Zhang Yong, Xia Jin-Song
Chin. Phys. B 2015, 24 (6): 068501;  doi: 10.1088/1674-1056/24/6/068501
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Niobium nitride superconducting nanowire single-photon detectors were fabricated on thermally oxidized silicon substrates with large active areas of 30 μm × 30 μm. To achieve non-constricted detectors, we improved the film growth and electron beam lithography process to fabricate uniform 100-nm wide NbN nanowires with a fill factor of 50%. The devices showed 72.4% system detection efficiency (SDE) at 100-Hz dark count rate (DCR) and 74-ps timing jitter, measured at the fiber communication wavelength of 1550 nm. The highest SDE which is 81.2% when the DCR is ~700 c/s appears at the wavelength of 1650 nm.

Non-ideal effect in 4H—SiC bipolar junction transistor with double Gaussian-doped base

Yuan Lei, Zhang Yu-Ming, Song Qing-Wen, Tang Xiao-Yan, Zhang Yi-Men
Chin. Phys. B 2015, 24 (6): 068502;  doi: 10.1088/1674-1056/24/6/068502
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The non-ideal effect of 4H–SiC bipolar junction transistor (BJT) with a double Gaussian-doped base is characterized and simulated in this paper. By adding a specific interface model between SiC and SiO2, the simulation results are in good agreement with the experiment data. An obvious early effect is found from the output characteristic. As the temperature rises, the early voltage increases, while the current gain gradually decreases, which is totally different from the scenario of silicon BJT. With the same effective Gummel number in the base region, the double Gaussian-doped base structure can realize higher current gain than the single base BJT due to the built-in electric field, whereas the early effect will be more salient. Besides, the emitter current crowding effect is also analyzed. Due to the low sheet resistance in the first highly-doped base epilayer, the 4H–BJT with a double base has more uniform emitter current density across the base-emitter junction, leading to better thermal stability.

Influences of stress on the properties of GaN/InGaN multiple quantum well LEDs grown on Si (111) substrates

Liu Ming-Gang, Yang Yi-Bin, Xiang Peng, Chen Wei-Jie, Han Xiao-Biao, Lin Xiu-Qi, Lin Jia-Li, Luo Hui, Liao Qiang, Zang Wen-Jie, Wu Zhi-Sheng, Liu Yang, Zhang Bai-Jun
Chin. Phys. B 2015, 24 (6): 068503;  doi: 10.1088/1674-1056/24/6/068503
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The influences of stress on the properties of InGaN/GaN multiple quantum wells (MQWs) grown on silicon substrate were investigated. The different stresses were induced by growing InGaN and AlGaN insertion layers (IL) respectively before the growth of MQWs in metal–organic chemical vapor deposition (MOCVD) system. High resolution x-ray diffraction (HRXRD) and photoluminescence (PL) measurements demonstrated that the InGaN IL introduced an additional tensile stress in n-GaN, which released the strain in MQWs. It is helpful to increase the indium incorporation in MQWs. In comparison with MQWs without the IL, the wavelength shows a red-shift. AlGaN IL introduced a compressive stress to compensate the tensile stress, which reduces the indium composition in MQWs. PL measurement shows a blue-shift of wavelength. The two kinds of ILs were adopted to InGaN/GaN MQWs LED structures. The same wavelength shifts were also observed in the electroluminescence (EL) measurements of the LEDs. Improved indium homogeneity with InGaN IL, and phase separation with AlGaN IL were observed in the light images of the LEDs.

Investigation of L10 FePt-based soft/hard composite bit-patterned media by micromagnetic simulation

Wang Ying, Wei Dan, Cao Jiang-Wei, Wei Fu-Lin
Chin. Phys. B 2015, 24 (6): 068504;  doi: 10.1088/1674-1056/24/6/068504
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The soft/hard composite patterned media have potential to be the next generation of magnetic recording, but the composing modes of soft and hard materials have not been investigated systematically. L10 FePt-based soft/hard composite patterned media with an anisotropic constant distribution are studied by micromagnetic simulation. Square arrays and hexagonal arrays with various pitch sizes are simulated for two composing types: the soft layer that encloses the hard dots and the soft layer that covers the whole surface. It is found that the soft material can reduce the switching fields of bits effectively for all models. Compared with the first type, the second type of models possess low switching fields, narrow switching field distributions, and high gain factors due to the introduction of inter-bit exchange coupling. Furthermore, the readout waveforms of the second type are not deteriorated by the inter-bit soft layers. Since the recording density of hexagonal arrays are higher than that of square arrays with the same center-to-center distances, the readout waveforms of hexagonal arrays are a little worse, although other simulation results are similar for these two arrays.

Design and optimization of terahertz directional coupler based on hybrid-cladding hollow waveguide with low confinement loss

Yu Ying-Ying, Li Xu-You, Sun Bo, He Kun-Peng
Chin. Phys. B 2015, 24 (6): 068702;  doi: 10.1088/1674-1056/24/6/068702
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We propose a design and optimization for directional coupling in terahertz hybrid-cladding hollow waveguide. It is composed of two square hollow waveguides which touch each other and are surrounded by a metallic layer. By employing the finite element method, the coupling performance and loss property are numerically investigated. Numerical results indicate that this directional coupler with hybrid-cladding can realize ultra-narrow-band coupling; it provides a low confinement loss performance: the confinement loss can reach as low as 6.27× 10-5 cm-1. Moreover, the further analyses of configuration and performance show that confinement loss and frequency range shift for the low-confinement-loss frequency regime can be realized and optimized by appropriately tuning the thickness values of the metallic and dielectric layer. In addition, through the further analysis of coupling performance, the possibilities of realizing ultra-narrow-band couplings in different frequency ranges are demonstrated. It is a powerful candidate for high precision optical fiber sensing, and communication in terahertz splitting fields.

Experimental research on the feature of an x-ray Talbot-Lau interferometer versus tube accelerating voltage

Wang Sheng-Hao, Margie P. Olbinado, Atsushi Momose, Han Hua-Jie, Hu Ren-Fang, Wang Zhi-Li, Gao Kun, Zhang Kai, Zhu Pei-Ping, Wu Zi-Yu
Chin. Phys. B 2015, 24 (6): 068703;  doi: 10.1088/1674-1056/24/6/068703
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X-ray Talbot–Lau interferometer has been used most widely to perform x-ray phase-contrast imaging with a conventional low-brilliance x-ray source, and it yields high-sensitivity phase and dark-field images of samples producing low absorption contrast, thus bearing tremendous potential for future clinical diagnosis. In this work, by changing the accelerating voltage of the x-ray tube from 35 kV to 45 kV, x-ray phase-contrast imaging of a test sample is performed at each integer value of the accelerating voltage to investigate the characteristic of an x-ray Talbot–Lau interferometer (located in the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan) versus tube voltage. Experimental results and data analysis show that within a range this x-ray Talbot–Lau interferometer is not sensitive to the accelerating voltage of the tube with a constant fringe visibility of ~ 44%. This x-ray Talbot–Lau interferometer research demonstrates the feasibility of a new dual energy phase-contrast x-ray imaging strategy and the possibility to collect a refraction spectrum.

Cosine fitting radiography and computed tomography

Li Pan-Yun, Zhang Kai, Huang Wan-Xia, Yuan Qing-Xi, Wang Yan, Ju Zai-Qiang, Wu Zi-Yu, Zhu Pei-Ping
Chin. Phys. B 2015, 24 (6): 068704;  doi: 10.1088/1674-1056/24/6/068704
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A new method in diffraction-enhanced imaging computed tomography (DEI-CT) that follows the idea developed by Chapman et al. [Chapman D, Thomlinson W, Johnston R E, Washburn D, Pisano E, Gmur N, Zhong Z, Menk R, Arfelli F and Sayers D 1997 Phys. Med. Biol. 42 2015] in 1997 is proposed in this paper. Merged with a “reverse projections” algorithm, only two sets of projection datasets at two defined orientations of the analyzer crystal are needed to reconstruct the linear absorption coefficient, the decrement of the real part of the refractive index and the linear scattering coefficient of the sample. Not only does this method reduce the delivered dose to the sample without degrading the image quality, but, compared with the existing DEI-CT approaches, it simplifies data-acquisition procedures. Experimental results confirm the reliability of this new method for DEI-CT applications.

Stair evacuation simulation based on cellular automataconsidering evacuees' walk preferences

Ding Ning, Zhang Hui, Chen Tao, Peter B. Luh
Chin. Phys. B 2015, 24 (6): 068801;  doi: 10.1088/1674-1056/24/6/068801
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As a physical model, the cellular automata (CA) model is widely used in many areas, such as stair evacuation. However, existing CA models do not consider evacuees' walk preferences nor psychological status, and the structure of the basic model is unapplicable for the stair structure. This paper is to improve the stair evacuation simulation by addressing these issues, and a new cellular automata model is established. Several evacuees' walk preference and how evacuee's psychology influences their behaviors are introduced into this model. Evacuees' speeds will be influenced by these features. To validate this simulation, two fire drills held in two high-rise buildings are video-recorded. It is found that the simulation results are similar to the fire drill results. The structure of this model is simple, and it is easy to further develop and utilize in different buildings with various kinds of occupants.

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