Chin. Phys. B

Improved delay-dependent robust H_∞ control of an uncertain stochastic system with interval time-varying and distributed delays

M. Syed Ali, R. Saravanakumar

Chin. Phys. B, 2014, 23 (12): 120201. DOI: 10.1088/1674-1056/23/12/120201

Abstract ( 702 )

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In this paper, the robust H_∞ control problem for a class of stochastic systems with interval time-varying and distributed delays is discussed. The system under study involves parameter uncertainty, stochastic disturbance, interval time-varying, and distributed delay. The aim is to design a delay-dependent robust H_∞ control which ensures the robust asymptotic stability of the given system and to express it in the form of linear matrix inequalities (LMIs). Numerical examples are given to demonstrate the effectiveness of the proposed method. The results are also compared with the existing results to show its conservativeness.

Non-probabilistic solutions of imprecisely defined fractional-orderdiffusion equations

S. Chakraverty, Smita Tapaswini

Chin. Phys. B, 2014, 23 (12): 120202. DOI: 10.1088/1674-1056/23/12/120202

Abstract ( 490 )

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The fractional diffusion equation is one of the most important partial differential equations (PDEs) to model problems in mathematical physics. These PDEs are more practical when those are combined with uncertainties. Accordingly, this paper investigates the numerical solution of a non-probabilistic viz. fuzzy fractional-order diffusion equation subjected to various external forces. A fuzzy diffusion equation having fractional order 0< α ≤ 1 with fuzzy initial condition is taken into consideration. Fuzziness appearing in the initial conditions is modelled through convex normalized triangular and Gaussian fuzzy numbers. A new computational technique is proposed based on double parametric form of fuzzy numbers to handle the fuzzy fractional diffusion equation. Using the single parametric form of fuzzy numbers, the original fuzzy diffusion equation is converted first into an interval-based fuzzy differential equation. Next, this equation is transformed into crisp form by using the proposed double parametric form of fuzzy numbers. Finally, the same is solved by Adomian decomposition method (ADM) symbolically to obtain the uncertain bounds of the solution. Computed results are depicted in terms of plots. Results obtained by the proposed method are compared with the existing results in special cases.

A conservative Fourier pseudospectral algorithm for the nonlinear Schrödinger equation

Lv Zhong-Quan (吕忠全), Zhang Lu-Ming (张鲁明), Wang Yu-Shun (王雨顺)

Chin. Phys. B, 2014, 23 (12): 120203. DOI: 10.1088/1674-1056/23/12/120203

Abstract ( 673 )

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In this paper, we derive a new method for a nonlinear Schrödinger system by using the square of the first-order Fourier spectral differentiation matrix D₁ instead of the traditional second-order Fourier spectral differentiation matrix D₂ to approximate the second derivative. We prove that the proposed method preserves the charge and energy conservation laws exactly. A deduction argument is used to prove that the numerical solution is second-order convergent to the exact solutions in ‖·‖₂ norm. Some numerical results are reported to illustrate the efficiency of the new scheme in preserving the charge and energy conservation laws.

Some new generating function formulae of the two-variable Hermite polynomials and their application in quantum optics

Zhan De-Hui (展德会), Fan Hong-Yi (范洪义)

Chin. Phys. B, 2014, 23 (12): 120301. DOI: 10.1088/1674-1056/23/12/120301

Abstract ( 854 )

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We derive some new generating function formulae of the two-variable Hermite polynomials, such as , , and . We employ the operator Hermite polynomial method and the technique of integration within an ordered product of operators to solve these problems, which will be useful in constructing new optical field states.

Wave functions of a new kind of nonlinearsingle-mode squeezed state

Fan Hong-Yi (范洪义), Da Cheng (笪诚), Chen Jun-Hua (陈俊华)

Chin. Phys. B, 2014, 23 (12): 120302. DOI: 10.1088/1674-1056/23/12/120302

Abstract ( 661 )

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We explore the theoretical possibility of extending the usual squeezed state to those produced by nonlinear single-mode squeezing operators. We derive the wave functions of exp[-(ig/2)(√1-X²P+P√1-X²)]|> in the coordinate representation. A new operator's disentangling formula is derived as a by-product.

Approximate solutions of Klein—Gordon equation with improved Manning—Rosen potential in D-dimensions using SUSYQM

A. N. Ikot, H. Hassanabadi, H. P. Obong, Y. E. Chad Umoren, C. N. Isonguyo, B. H. Yazarloo

Chin. Phys. B, 2014, 23 (12): 120303. DOI: 10.1088/1674-1056/23/12/120303

Abstract ( 729 )

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In this paper, we present solutions of the Klein–Gordon equation for the improved Manning–Rosen potential for arbitrary l state in d-dimensions using the supersymmetric shape invariance method. We obtained the energy levels and the corresponding wave functions expressed in terms of Jacobi polynomial in a closed form for arbitrary l state. We also calculate the oscillator strength for the potential.

Relativistic effect of pseudospin symmetry and tensor coupling on the Mie-type potential via Laplace transformation method Suggested by editors

M. Eshghi, S. M. Ikhdair

Chin. Phys. B, 2014, 23 (12): 120304. DOI: 10.1088/1674-1056/23/12/120304

Abstract ( 654 )

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A relativistic Mie-type potential for spin-1/2 particles is studied. The Dirac Hamiltonian contains a scalar S(r) and a vector V(r) Mie-type potential in the radial coordinates, as well as a tensor potential U(r) in the form of Coulomb potential. In the pseudospin (p-spin) symmetry setting ∑=C_ps and △ =V(r), an analytical solution for exact bound states of the corresponding Dirac equation is found. The eigenenergies and normalized wave functions are presented and particular cases are discussed with any arbitrary spin–orbit coupling number κ. Special attention is devoted to the case ∑ =0 for which p-spin symmetry is exact. The Laplace transform approach (LTA) is used in our calculations. Some numerical results are obtained and compared with those of other methods.

Preparation of optimal entropy squeezing state of atomic qubit inside the cavity via two-photon process and manipulation of atomic qubit outside the cavity

Zhou Bing-Ju (周并举), Peng Zhao-Hui (彭朝晖), Jia Chun-Xia (贾春霞), Jiang Chun-Lei (姜春蕾), Liu Xiao-Juan (刘小娟)

Chin. Phys. B, 2014, 23 (12): 120305. DOI: 10.1088/1674-1056/23/12/120305

Abstract ( 728 )

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Considering two atomic qubits initially in Bell states, we send one qubit into a vacuum cavity with two-photon resonance and leave the other one outside. Using quantum information entropy squeezing theory, the time evolutions of the entropy squeezing factor of the atomic qubit inside the cavity are discussed for two cases, i.e., before and after rotation and measurement of the atomic qubit outside the cavity. It is shown that the atomic qubit inside the cavity has no entropy squeezing phenomenon and is always in a decoherent state before the operating atomic qubit outside the cavity. However, the periodical entropy squeezing phenomenon emerges and the optimal entropy squeezing state can be prepared for the atomic qubit inside the cavity by adjusting the rotation angle, choosing the interaction time between the atomic qubit and the cavity, controlling the probability amplitudes of subsystem states. Its physical essence is cutting the entanglement between the atomic qubit and its environment, causing the atomic qubit inside the cavity to change from the initial decoherent state into maximum coherent superposition state, which is a possible way of recovering the coherence of a single atomic qubit in the noise environment.

Geometric quantum discord and Berry phase between two charge qubits coupled by a quantum transmission line

Zhu Han-Jie (朱汉杰), Zhang Guo-Feng (张国锋)

Chin. Phys. B, 2014, 23 (12): 120306. DOI: 10.1088/1674-1056/23/12/120306

Abstract ( 886 )

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Geometric quantum discord (GQD) and Berry phase between two charge qubits coupled by a quantum transmission line are investigated. We show how GQDs evolve and investigate their dependencies on the parameters of the system. We also calculate the energy and the Berry phase and compare them with GQD, finding that there are close connections between them.

Generating genuine multipartite entanglement via XY-interactionand via projective measurements

Mazhar Ali

Chin. Phys. B, 2014, 23 (12): 120307. DOI: 10.1088/1674-1056/23/12/120307

Abstract ( 671 )

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We have studied the generation of multipartite entangled states for the superconducting phase qubits. The experiments performed in this direction have the capacity to generate several specific multipartite entangled states for three and four qubits. Our studies are also important as we have used a computable measure of genuine multipartite entanglement whereas all previous studies analyzed certain probability amplitudes. As a comparison, we have reviewed the generation of multipartite entangled states via von Neumann projective measurements.

Afterpulsing characteristics of InGaAs/InP single photon avalanche diodes

Ma Hai-Qiang (马海强), Yang Jian-Hui (杨建会), Wei Ke-Jin (韦克金), Li Rui-Xue (李瑞雪), Zhu Wu (朱武)

Chin. Phys. B, 2014, 23 (12): 120308. DOI: 10.1088/1674-1056/23/12/120308

Abstract ( 950 )

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InGaAs/InP single photon avalanche diodes (SPADs) are more and more available in many research fields. They are affected by afterpulsing which leads to a poor single photon detection probability. We present an InGaAs/InP avalanche photodiode with an active quenching circuit on an application specific integrated circuit (ASIC). It can quench the avalanche rapidly and then reduce the afterpulse rate. Also this quenching circuit can operate in both free-running and gated modes. Furthermore, a new technique is introduced to characterize the influence of the higher order of afterpulses, which uses a program running on a field programmable gate array (FPGA) integrated circuit.

Block-free optical quantum Banyan network based on quantum state fusion and fission

Zhu Chang-Hua (朱畅华), Meng Yan-Hong (孟艳红), Quan Dong-Xiao (权东晓), Zhao Nan (赵楠), Pei Chang-Xing (裴昌幸)

Chin. Phys. B, 2014, 23 (12): 120309. DOI: 10.1088/1674-1056/23/12/120309

Abstract ( 638 )

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Optical switch fabric plays an important role in building multiple-user optical quantum communication networks. Owing to its self-routing property and low complexity, a banyan network is widely used for building switch fabric. While, there is no efficient way to remove internal blocking in a banyan network in a classical way, quantum state fusion, by which the two-dimensional internal quantum states of two photons could be combined into a four-dimensional internal state of a single photon, makes it possible to solve this problem. In this paper, we convert the output mode of quantum state fusion from spatial-polarization mode into time-polarization mode. By combining modified quantum state fusion and quantum state fission with quantum Fredkin gate, we propose a practical scheme to build an optical quantum switch unit which is block free. The scheme can be extended to building more complex units, four of which are shown in this paper.

A generalized Padé approximation method of solving homoclinic and heteroclinic orbits of strongly nonlinear autonomous oscillators

Li Zhen-Bo (李震波), Tang Jia-Shi (唐驾时), Cai Ping (蔡萍)

Chin. Phys. B, 2014, 23 (12): 120501. DOI: 10.1088/1674-1056/23/12/120501

Abstract ( 569 )

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An intrinsic extension of Padé approximation method, called the generalized Padé approximation method, is proposed based on the classic Padé approximation theorem. According to the proposed method, the numerator and denominator of Padé approximant are extended from polynomial functions to a series composed of any kind of function, which means that the generalized Padé approximant is not limited to some forms, but can be constructed in different forms in solving different problems. Thus, many existing modifications of Padé approximation method can be considered to be the special cases of the proposed method. For solving homoclinic and heteroclinic orbits of strongly nonlinear autonomous oscillators, two novel kinds of generalized Padé approximants are constructed. Then, some examples are given to show the validity of the present method. To show the accuracy of the method, all solutions obtained in this paper are compared with those of the Runge–Kutta method.

Multi-scale complexity entropy causality plane: An intrinsic measure for indicating two-phase flow structures

Dou Fu-Xiang (窦富祥), Jin Ning-De (金宁德), Fan Chun-Ling (樊春玲), Gao Zhong-Ke (高忠科), Sun Bin (孙斌)

Chin. Phys. B, 2014, 23 (12): 120502. DOI: 10.1088/1674-1056/23/12/120502

Abstract ( 701 )

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We extend the complexity entropy causality plane (CECP) to propose a multi-scale complexity entropy causality plane (MS-CECP) and further use the proposed method to discriminate the deterministic characteristics of different oil-in-water flows. We first take several typical time series for example to investigate the characteristic of the MS-CECP and find that the MS-CECP not only describes the continuous loss of dynamical structure with the increase of scale, but also reflects the determinacy of the system. Then we calculate the MS-CECP for the conductance fluctuating signals measured from oil–water two-phase flow loop test facility. The results indicate that the MS-CECP could be an intrinsic measure for indicating oil-in-water two-phase flow structures.

The effect of cellular aging on the dynamics of spiral waves

Deng Min-Yi (邓敏艺), Chen Xi-Qiong (陈茜琼), Tang Guo-Ning (唐国宁)

Chin. Phys. B, 2014, 23 (12): 120503. DOI: 10.1088/1674-1056/23/12/120503

Abstract ( 635 )

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Cellular aging can result in deterioration of electrical coupling, the extension of the action potential duration, and lower excitability of the cell. Those factors are introduced into the Greenberg–Hastings cellular automaton model and the effects of the cellular aging on the dynamics of spiral waves are studied. The numerical results show that a 50% reduction of the coupling strength of aging cells has a little influence on spiral waves. If the coupling strength of aging cells equals zero, the ability for the medium to maintain spiral waves will be reduced by approximately 50% when the aging cell ratio increases from 0 to 0.5, where the reduction of cell excitability plays a major role in inducing disappearance of spiral waves. When the relevant parameters are properly chosen, the cellular aging can lead to the meandering of spiral waves, the emergence of the binary spiral waves, and even the disappearance of spiral waves via the stopping rotation or shrinkage of wave. Physical mechanisms of the above phenomena are analyzed briefly.

Impulsive stabilization of a class of nonlinear system with bounded gain error

Ma Tie-Dong (马铁东), Zhao Fei-Ya (赵飞亚)

Chin. Phys. B, 2014, 23 (12): 120504. DOI: 10.1088/1674-1056/23/12/120504

Abstract ( 737 )

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Considering mechanical limitation or device restriction in practical application, this paper investigates impulsive stabilization of nonlinear systems with impulsive gain error. Compared with the existing impulsive analytical approaches, the proposed impulsive control method is more practically applicable, which includes control gain error with an acceptable boundary. A sufficient criterion for global exponential stability of an impulsive control system is derived, which relaxes the condition for precise impulsive gain efficiently. The effectiveness of the proposed method is confirmed by theoretical analysis and numerical simulation based on Chua's circuit.

Cluster synchronization of uncertain complex networks with desynchronizing impulse

Cai Guo-Liang (蔡国梁), Jiang Sheng-Qin (姜胜芹), Cai Shui-Ming (蔡水明), Tian Li-Xin (田立新)

Chin. Phys. B, 2014, 23 (12): 120505. DOI: 10.1088/1674-1056/23/12/120505

Abstract ( 679 )

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Cluster synchronization of nonlinear uncertain complex networks with desynchronizing impulse is explored. First of all, a feedback controller is employed, based on the Lyapunov stability theorem and Lipschitz condition, to guarantee that the uncertain complex networks with desynchronizing impulse synchronize with an object trajectory. Furthermore, a synchronizing impulse controller is presented, which is more efficiently and directly used to achieve the cluster synchronization. Finally, numerical examples are examined to show the effectiveness of the proposed methods.

Exact solutions of the nonlinear differential—difference equations associated with the nonlinear electrical transmission line through a variable-coefficient discrete (G'/G)-expansion method

Saïdou Abdoulkary, Alidou Mohamadou, Ousmanou Dafounansou, Serge Yamigno Doka

Chin. Phys. B, 2014, 23 (12): 120506. DOI: 10.1088/1674-1056/23/12/120506

Abstract ( 771 )

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We investigated exact traveling soliton solutions for the nonlinear electrical transmission line. By applying a concise and straightforward method, the variable-coefficient discrete (G'/G)-expansion method, we solve the nonlinear differential–difference equations associated with the network. We obtain some exact traveling wave solutions which include hyperbolic function solution, trigonometric function solution, rational solutions with arbitrary function, bright as well as dark solutions.

Research and application of regular phenomenon between periodic signals

Ye Yun-Xia (叶云霞), Xuan Zong-Qiang (宣宗强), Gu Jun-Shan (谷军闪), Xuan Yong (宣勇)

Chin. Phys. B, 2014, 23 (12): 120601. DOI: 10.1088/1674-1056/23/12/120601

Abstract ( 658 )

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The phase change between periodic signals is regular. Research on the regular phenomenon between periodic signals is helpful to improve the precision of some measurements and develop some new measurement methods. So it is necessary to analyze the characteristics of the greatest common factor frequency and the least common multiple period universally existing in periodic signals. The regulation of the quantitative phase shift resolution between periodic signals is presented. The cause of difference in phase characteristics between periodic signals is explained well. In this paper we propose different application prospects based on the regular phenomenon between periodic signals, with focusing on the methods for high precision frequency measurement and transient stability measurement. The experimental results are satisfactory.

Electronic structure and magnetic properties of (Mn, N)-codoped ZnO

Wang Qian-Jin (王前进), Wang Jin-Bin (王金斌), Zhong Xiang-Li (钟向丽), Tan Qiu-Hong (谭秋红), Liu Ying-Kai (刘应开)

Chin. Phys. B, 2014, 23 (12): 123101. DOI: 10.1088/1674-1056/23/12/123101

Abstract ( 639 )

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The electronic structures and magnetic properties of (Mn, N)-codoped ZnO are investigated by using the first-principles calculations. In the ferromagnetic state, as N substitutes for the intermediate O atom of the nearest neighboring Mn ions, about 0.5 electron per Mn²⁺ ion transfers to the N^2- ion, which leads to the high-state Mn ions (close to +2.5) and trivalent N^3- ions. In an antiferromagnetic state, one electron transfers to the N^2- ion from the downspin Mn²⁺ ion, while no electron transfer occurs for the upspin Mn²⁺ ion. The (Mn, N)-codoped ZnO system shows ferromagnetism, which is attributed to the hybridization between Mn 3d and N 2p orbitals.

Infrared diode laser spectroscopy of O₂–N₂O van der Waals complex in the ν₁ symmetric stretch region of N₂O Suggested by editors

Li Song (李松), Zheng Rui (郑锐), Duan Chuan-Xi (段传喜)

Chin. Phys. B, 2014, 23 (12): 123301. DOI: 10.1088/1674-1056/23/12/123301

Abstract ( 840 )

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The rovibrational spectrum of O₂–N₂O van der Waals complex is measured in the v₁ symmetric stretch region of N₂O monomer using a tunable diode laser spectrometer. The complex is generated by a slit-pulsed supersonic expansion with gas mixtures of O₂, N₂O, and He. Both a- and b-type transitions are observed. The effective Hamiltonian for an open-shell complex consisting of a diatomic molecule in a ³Σ electronic state and a closed-shell partner is used to analyze the observed spectrum. Molecular constants in the vibrationally excited state are determined accurately. The band-origin of the spectrum is determined to be 1284.7504(25) cm^-1, red-shifted from that of the N₂O monomer by ～ 0.1529 cm^-1.

Theoretical study of stereodynamics for the N+H₂/D₂/T₂ reactions

Li Yong-Qing (李永庆), Zhao Jin-Feng (赵金峰), Zhang Yong-Jia (张永嘉), Chi Xiao-Lin (迟晓琳), Ding Yong (丁勇), Ma Feng-Cai (马凤才)

Chin. Phys. B, 2014, 23 (12): 123401. DOI: 10.1088/1674-1056/23/12/123401

Abstract ( 641 )

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The effects of isotopic variants on stereodynamic properties for the title reactions have been investigated using a quasi-classical trajectory method based on the first excited state NH₂(1²A') potential energy surface [Li Y Q and Varandas A J C 2010 J. Phys. Chem. A 114 9644]. The forward–backward symmetry scattering of the differential cross section can be observed, which demonstrates that all these reactions follow the insertion mechanism. Three angle distribution functions P(θ_r), P(φ_r), and P(θ_r, φ_r) with different collision energies and target molecules H₂/D₂/T₂ are calculated. It is shown that the product rotational angular momentum is not only aligned, but also oriented along the direction perpendicular to the scattering plane. The title reaction is mainly governed by the “in-plane” mechanism through the calculated distribution function P(θ_r, φ_r). The observable influences on the rotational polarization of the product by the isotopic substitution of H/D/T can be demonstrated.

Quasi-classical trajectory investigation on the stereodynamics of Li+DF (v=1-6, j=0)→LiF+D reaction

Zhang Ying-Ying (张莹莹), Li Shu-Juan (李淑娟), Shi Ying (石英), Xie Ting-Xian (解廷献), Jin Ming-Xing (金明星)

Chin. Phys. B, 2014, 23 (12): 123402. DOI: 10.1088/1674-1056/23/12/123402

Abstract ( 694 )

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In this paper, the stereodynamics of Li+DF→LiF+D reaction is investigated by the quasi-classical trajectory (QCT) method on the ²A' potential energy surface (PES) at a relatively low collision energy of 8.76 kcal/mol. The scalar properties of the title reaction such as reaction probability and cross section are studied with vibrational quantum number of v=1-6. The product angular distributions P(θr) and P(ør) are presented in the same vibrational level range. Moreover, two polarization-dependent generalized differential cross sections (PDDCSs), i.e., the PDDCS₀₀ and PDDCS₂₂₊ are calculated as well. These stereodynamical results demonstrate sensitive behaviors to the vibrational quantum numbers.

Adiabatic cooling for cold polar molecules on a chip using a controllable high-efficiency electrostatic surface trap

Li Sheng-Qiang (李胜强), Xu Liang (许亮), Xia Yong (夏勇), Wang Hai-Ling (汪海玲), Yin Jian-Ping (印建平)

Chin. Phys. B, 2014, 23 (12): 123701. DOI: 10.1088/1674-1056/23/12/123701

Abstract ( 704 )

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We propose a controllable high-efficiency electrostatic surface trap for cold polar molecules on a chip by using two insulator-embedded charged rings and a grounded conductor plate. We calculate Stark energy structure pattern of ND₃ molecules in an external electric field using the method of matrix diagonalization. We analyze how the voltages that are applied to the ring electrodes affect the depth of the efficient well and the controllability of the distance between the trap center and the surface of the chip. To obtain a better understanding, we simulate the dynamical loading and trapping processes of ND₃ molecules in a|J, KM>=|1, -1> state by using classical Monte–Carlo method. Our study shows that the loading efficiency of our trap can reach ～ 88%. Finally, we study the adiabatic cooling of cold molecules in our surface trap by linearly lowering the potential-well depth (i.e., lowering the trapping voltage), and find that the temperature of the trapped ND₃ molecules can be adiabatically cooled from 34.5 mK to ～ 5.8 mK when the trapping voltage is reduced from -35 kV to -3 kV.

Determining the structural phase transition point from the temperature of ⁴⁰Ca⁺ Coulomb crystal

Chen Ting (陈婷), Du Li-Jun (杜丽军), Song Hong-Fang (宋红芳), Liu Pei-Liang (刘培亮), Huang Yao (黄垚), Tong Xin (童昕), Guan Hua (管桦), Gao Ke-Lin (高克林)

Chin. Phys. B, 2014, 23 (12): 123702. DOI: 10.1088/1674-1056/23/12/123702

Abstract ( 632 )

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We observed the linear-to-zigzag structural phase transition of a ⁴⁰Ca⁺ crystal in a homemade linear Paul trap. The values of the total temperature of the ion crystals during the phase transition are derived using the molecular-dynamics (MD) simulation method. A series of simulations revealed that the ratio of the radial to axial secular frequencies has a dependence on the total temperature that obeys different functional forms for linear and zigzag structures, and the transition point occurs where these functions intersect; thus, the critical value of the ratio of secular frequencies that drives the structure phase transition can be derived.

Backscattering from small-scale breaking wave turbulence structure generated by FLUENT

Luo Gen (罗根), Zhang Min (张民)

Chin. Phys. B, 2014, 23 (12): 124101. DOI: 10.1088/1674-1056/23/12/124101

Abstract ( 705 )

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A breaking wave can exert a great influence on the electromagnetic (EM) scattering result from sea surfaces. In this paper, the process of small-scale wave breaking is simulated by the commercial computational fluid dynamics (CFD) software FLUENT, and the backscattering radar cross section (RCS) of the turbulence structure after breaking is calculated with the method of moments. The scattering results can reflect the turbulent intensities of the wave profiles and can indicate high polarization ratios at moderate incident angles, which should be attributed to the incoherent backscatter from surface disturbance of turbulence structure. Compared with the wave profile before breaking, the turbulence structure has no obvious geometrical characteristic of a plunging breaker, and no sea spikes are present at large incident angles either. In summary, the study of EM scattering from turbulence structure can provide a basis to explain the anomalies of EM scattering from sea surfaces and help us understand the scattering mechanism about the breaking wave more completely.

A spherical higher-order finite-difference time-domain algorithm with perfectly matched layer

Liu Ya-Wen (刘亚文), Chen Yi-Wang (陈亦望), Zhang Pin (张品), Liu Zong-Xin (刘宗信)

Chin. Phys. B, 2014, 23 (12): 124102. DOI: 10.1088/1674-1056/23/12/124102

Abstract ( 683 )

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A higher-order finite-difference time-domain (HO-FDTD) in the spherical coordinate is presented in this paper. The stability and dispersion properties of the proposed scheme are investigated and an air-filled spherical resonator is modeled in order to demonstrate the advantage of this scheme over the finite-difference time-domain (FDTD) and the multiresolution time-domain (MRTD) schemes with respect to memory requirements and CPU time. Moreover, the Berenger's perfectly matched layer (PML) is derived for the spherical HO-FDTD grids, and the numerical results validate the efficiency of the PML.

Effect of electromagnetic disturbance on thepractical QKD system in the smart grid Suggested by editors

Li Fang-Yi (李芳毅), Wang Dong (王东), Wang Shuang (王双), Li Mo (李默), Yin Zhen-Qiang (银振强), Li Hong-Wei (李宏伟), Chen Wei (陈巍), Han Zheng-Fu (韩正甫)

Chin. Phys. B, 2014, 23 (12): 124201. DOI: 10.1088/1674-1056/23/12/124201

Abstract ( 696 )

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To improve the security of the smart grid, quantum key distribution (QKD) is an excellent choice. The rapid fluctuations on the power aerial optical cable and electromagnetic disturbance in substations are two main challenges for implementation of QKD. Due to insensitivity to birefringence of the channel, the stable phase-coding Faraday–Michelson QKD system is very practical in the smart grid. However, the electromagnetic disturbance in substations on this practical QKD system should be considered. The disturbance might change the rotation angle of the Faraday mirror, and would introduce an additional quantum bit error rate (QBER). We derive the new fringe visibility of the system and the additional QBER from the electromagnetic disturbance. In the worst case, the average additional QBER only increases about 0.17% due to the disturbance, which is relatively small to normal QBER values. We also find the way to degrade the electromagnetic disturbance on the QKD system.

Enhancement of four-wave mixing process in a four-level double semiconductor quantum well

She Yan-Chao (佘彦超), Zheng Xue-Jun (郑学军), Wang Deng-Long (王登龙)

Chin. Phys. B, 2014, 23 (12): 124202. DOI: 10.1088/1674-1056/23/12/124202

Abstract ( 635 )

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The time-dependent four-wave mixing (FWM) is analyzed in a four-level double semiconductor quantum well. The results show that both the amplitude and the conversion efficiency of the FWM field are enhanced with increasing the strength of two-photon Rabi frequency. Interestingly, when the one-photon detuning becomes stronger the control field corresponding to the maximum efficiency increases. Such a controlled enhanced FWM may be used to generate coherent short-wave length radiation, and it can have potential applications in quantum control and communications.

Reflection-type electromagnetically induced transparencyanalogue in terahertz metamaterials

Ding Chun-Feng (丁春峰), Zhang Ya-Ting (张雅婷), Yao Jian-Quan (姚建铨), Sun Chong-Ling (孙崇玲), Xu De-Gang (徐德刚), Zhang Gui-Zhong (张贵忠)

Chin. Phys. B, 2014, 23 (12): 124203. DOI: 10.1088/1674-1056/23/12/124203

Abstract ( 715 )

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A reflection-type electromagnetically induced transparency (EIT) metamaterial is proposed, which is composed of a dielectric spacer sandwiched with metallic patterns and metallic plane. Experimental results of THz time domain spectrum (THz-TDS) exhibit a typical reflection of EIT at 0.865 THz, which are in excellent agreement with the full-wave simulations. A multi-reflection theory is adopted to analyze the physical mechanism of the reflection-type EIT, showing that the reflection-type EIT is a superposition of multiple reflection of the transmission EIT. Such a reflection-type EIT provides many applications based on the EIT effect, such as slow light devices and nonlinear elements.

Two-photon emission in coupled biexciton quantum dot–cavity system: Phonon-assisted model Suggested by editors

Peng Yi-Wei (彭益炜), Yu Zhong-Yuan (俞重远), Liu Yu-Min (刘玉敏), Wu Tie-Sheng (伍铁生), Zhang Wen (张文)

Chin. Phys. B, 2014, 23 (12): 124204. DOI: 10.1088/1674-1056/23/12/124204

Abstract ( 649 )

PDF (381KB) ( 561 )

We theoretically analyze the steady state emission spectrum and transient temporal dynamics in a coupled biexciton quantum dot (QD)–cavity system. For steady state, a phonon-assisted biexciton–exciton cascade model under continuous wave (CW) excitation is presented to explain the asymmetric QD–cavity emission spectrum intensities (intensities of cavity, exciton, and biexciton emission peak) in off-resonance condition. Results demonstrate that the electron–phonon process is crucial to the asymmetry of emission spectrum intensity. Moreover the transient characteristics of the biexciton–exciton cascade system under pulse excitation show abundant nonlinear temporal dynamic behaviors, including complicated oscillations which are caused by the four-level structure of QD model. We also reveal that under off-resonance condition the cavity outputs are slightly reduced due to the electron–phonon interaction.

Formation mechanism of bifurcation in mode-locked class-B laser

J. Jahanpanah, M. Rezazadeh, A. A. Rahdar

Chin. Phys. B, 2014, 23 (12): 124205. DOI: 10.1088/1674-1056/23/12/124205

Abstract ( 672 )

PDF (496KB) ( 388 )

The random oscillations of many longitudinal modes are inevitable in both class –A and –B lasers due to their broadened atomic bandwidths. The destructive superposition of electric field components that are incoherently oscillating at the different longitudinal modes can be converted into a constructive one by using the mode-locking technique. Here, the Maxwell–Bloch equations of motion are solved for a three-mode class-B laser under the mode-locking conditions. The results indicate that the cavity oscillating modes are shifted by changing the laser pumping rate. On the other hand, the frequency components of cavity electric field simultaneously form the various bifurcations. These bifurcations satisfy the well-known mode-locking conditions as well. The atomic population inversion forms only one bifurcation, which is responsible for shaping the cavity electric field bifurcations.

Pump-induced carrier envelope offset frequency dynamics and stabilization of an Yb-doped fiber frequency comb Suggested by editors

Zhao Jian (赵健), Li Wen-Xue (李文雪), Yang Kang-Wen (杨康文), Shen Xu-Ling (沈旭玲), Bai Dong-Bi (白东碧), Chen Xiu-Liang (陈修亮), Zeng He-Ping (曾和平)

Chin. Phys. B, 2014, 23 (12): 124206. DOI: 10.1088/1674-1056/23/12/124206

Abstract ( 741 )

PDF (466KB) ( 385 )

In this paper, we demonstrate a carrier envelope phase-stabilized Yb-doped fiber frequency comb seeding by a nonlinear-polarization-evolution (NPE) mode-locked laser at a repetition rate of 60 MHz with a pulse duration of 191 fs. The pump-induced carrier envelope offset frequency (f₀) nonlinear tuning is discussed and further explained by the spectrum shift of the laser pulse. Through the environmental noise suppression, the drift of the free-running f₀ is reduced down to less than 3 MHz within an hour. By feedback control on the pump power with a self-made phase-lock loop (PLL) electronics the carrier envelope offset frequency is well phase-locked with a frequency jitter of 85 mHz within an hour.

Simulation studies of multi-line line-of-sight tunable-diode-laserabsorption spectroscopy performance in measuring temperature probability distribution function

Zhang Guang-Le (张光乐), Liu Jian-Guo (刘建国), Kan Rui-Feng (阚瑞峰), Xu Zhen-Yu (许振宇)

Chin. Phys. B, 2014, 23 (12): 124207. DOI: 10.1088/1674-1056/23/12/124207

Abstract ( 713 )

PDF (288KB) ( 500 )

Line-of-sight tunable-diode-laser absorption spectroscopy (LOS-TDLAS) with multiple absorption lines is introduced for non-uniform temperature measurement. Temperature binning method combined with Gauss–Seidel iteration method is used to measure temperature probability distribution function (PDF) along the line-of-sight (LOS). Through 100 simulated measurements, the variation of measurement accuracy is investigated with the number of absorption lines, the number of temperature bins and the magnitude of temperature non-uniformity. A field model with 2-T temperature distribution and 15 well-selected absorption lines are used for the simulation study. The Gauss–Seidel iteration method is discussed for its reliability. The investigation result about the variation of measurement accuracy with the number of temperature bins is different from the previous research results.

A simple model of suppressing stimulated Brillouin scattering in optical fiber with frequency-modulated laser

Hu Xiao-Yang (胡晓阳), Chen Wei (陈伟), Tu Xiao-Bo (涂晓波), Meng Zhou (孟洲)

Chin. Phys. B, 2014, 23 (12): 124208. DOI: 10.1088/1674-1056/23/12/124208

Abstract ( 732 )

PDF (317KB) ( 13090 )

A simple model is developed to study the mechanism of stimulated Brillouin scattering (SBS) suppression with frequency-modulated laser in optical fiber. By taking into account the laser frequency distribution along the fiber induced by frequency modulation, the average effective Brillouin gain is calculated to determine the SBS threshold. Experimental results show agreement with the numerical analysis. The application for SBS suppression in interferometric fiber sensing system is also discussed in this paper. The results show that the maximum input power can be increased effectively by frequency modulation method.

Radio-frequency compressed electron pulse-width characterization by cross-correlation between electron bunches and laser-induced plasma

Li Jing (李静), Pei Min-Jie (裴敏洁), Qi Da-Long (齐大龙), Qi Ying-Peng (齐迎朋), Yang Yan (杨岩), Sun Zhen-Rong (孙真荣)

Chin. Phys. B, 2014, 23 (12): 124209. DOI: 10.1088/1674-1056/23/12/124209

Abstract ( 727 )

PDF (757KB) ( 426 )

A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal evolution of 2-dimensional transverse profile of ultrafast electron bunches repelled by the formed transient electric field of laser-induced plasma on a silver needle is investigated, and the pulse-width can be obtained by analyzing these time-dependent images. This approach can characterize radio-frequency compressed ultrafast electron bunches with picosecond or sub-picosecond timescale and up to 10⁵ electron numbers.

Femtosecond parabolic pulse nonlinear compression with gas-filled hollow-core fiber

Huang Zhi-Yuan (黄志远), Leng Yu-Xin (冷雨欣), Dai Ye (戴晔)

Chin. Phys. B, 2014, 23 (12): 124210. DOI: 10.1088/1674-1056/23/12/124210

Abstract ( 773 )

PDF (854KB) ( 358 )

We study theoretically the spectral intensity evolutions of the femtosecond Gaussian and parabolic pulses with different initial pulse energies and compare the nonlinear compressions of these pulses based on a meter-long hollow-core fiber filled with neon for different initial pulse durations. The pulses are first coupled into gas-filled hollow-core fiber for spectrum broadening, then compressed by the optimal chirp compensation. The parabolic pulse possesses a shorter pulse duration, larger peak power, and cleaner wings than Gaussian pulse. The properties are useful for compressing the pulses and thus generating the high-energy, short-duration pulses.

Optical pulse shaper with integrated slab waveguide for arbitrary waveform generation using optical gradient force

Liao Sha-Sha (廖莎莎), Min Shu-Cun (闵书存), Dong Jian-Ji (董建绩)

Chin. Phys. B, 2014, 23 (12): 124211. DOI: 10.1088/1674-1056/23/12/124211

Abstract ( 648 )

PDF (567KB) ( 286 )

Integrated optical pulse shaper opens up possibilities for realizing the ultra high-speed and ultra wide-band linear signal processing with compact size and low power consumption. We propose a silicon monolithic integrated optical pulse shaper using optical gradient force, which is based on the eight-path finite impulse response. A cantilever structure is fabricated in one arm of the Mach–Zehnder interferometer (MZI) to act as an amplitude modulator. The phase shift feature of waveguide is analyzed with the optical pump power, and five typical waveforms are demonstrated with the manipulation of optical force. Unlike other pulse shaper schemes based on thermo–optic effect or electro–optic effect, our scheme is based on a new degree of freedom manipulation, i.e., optical force, so no microelectrodes are required on the silicon chip, which can reduce the complexity of fabrication. Besides, the chip structure is suitable for commercial silicon on an insulator (SOI) wafer, which has a top silicon layer of about 220 nm in thickness.

Spatial weak-light ring soliton in self-assembled quantum dots Suggested by editors

Chen Qiu-Cheng (陈秋成)

Chin. Phys. B, 2014, 23 (12): 124212. DOI: 10.1088/1674-1056/23/12/124212

Abstract ( 584 )

PDF (1190KB) ( 434 )

By using semiclassical theory combined with multiple-scale method, we analytically study the linear absorption and the nonlinear dynamical properties in a lifetime broadened Λ -type three-level self-assembled quantum dots. It is found that this system can exhibit the transparency, and the width of the transparency window becomes wider with the increase of control light field. Interestingly, a weak probe light beam can form spatial weak-light dark solitons. When it propagates along the axial direction, the soliton will transform into a steady spatial weak-light ring dark soltion. In addition, the stability of two-dimensional spatial optical solitons is testified numerically.

Calculation and analysis of the number of return photons from sodium laser beacon excited by the long pulse laser with circular polarization Suggested by editors

Liu Xiang-Yuan (刘向远), Qian Xian-Mei (钱仙妹), Li Yu-Jie (李玉杰), Rao Rui-Zhong (饶瑞中)

Chin. Phys. B, 2014, 23 (12): 124213. DOI: 10.1088/1674-1056/23/12/124213

Abstract ( 597 )

PDF (1045KB) ( 485 )

The number of return photons from sodium laser beacon (SLB) greatly suffers down-pumping, recoil, and geomagnetic field when the long pulse laser with circular polarization interacts with sodium atoms in the mesosphere. Considering recoil and down-pumping effects on the number of return photons from SLB, the spontaneous radiation rates are obtained by numerical computations and fittings. Furthermore, combining with the geomagnetic field effects, a new expression is achieved for calculating the number of return photons. By using this expression and considering the stochastic distribution of laser intensity in the mesosphere under different turbulence models for atmosphere, the number of return photons excited by the narrow-band single mode laser and that by the narrow-band three-mode laser are respectively calculated. The results show that the narrow-band three-mode laser with a specific spectrum structure has a higher spontaneous radiation rate and more return photons than a narrow-band single mode laser. Of note, the effect of the atmospheric turbulence on the number of return photons is remarkable. Calculation results indicate that the number of return photons under the HV5/7 model for atmospheric turbulence is much higher than that under the Greenwood and ModHV models.

Optical properties of phosphate glasses co-doped with Yb³⁺ and silver nanoparticles

M. A. Vallejo H., M. A. Martinez G., A. V. Kiryanov, J. L. Lucio M.

Chin. Phys. B, 2014, 23 (12): 124214. DOI: 10.1088/1674-1056/23/12/124214

Abstract ( 749 )

PDF (504KB) ( 367 )

We report the fabrication and spectroscopic characterization of Yb³⁺-doped phosphate glass, also containing silver nitrate. Scanning electron microscopy (SEM) provides the evidence of the formation of silver nano-particles (SNPs), which are formed as a consequence of melting and thermal decomposition of AgNO₃. Absorption spectra of the samples in the visible-to-near-infrared spectral range reveal the presence of bands centered at 410 nm associated with the SNP-plasmon resonance, and at 976 nm due to the Yb³⁺. Under 916-nm laser-diode pumping, the effect of the SNP reflects that: i) the fluorescence in the 950-nm–1150-nm spectral range is strongly enhanced (～30 times), while the fluorescence decay time associated with the ²F_5/2→F_7/2 transition of Yb³⁺ increases 25%, and ii) the basic lasing properties (saturation pumping intensity, the emission and absorption cross sections) are substantially improved.

A quantum efficiency analytical model for complementary metal–oxide–semiconductor image pixels with a pinned photodiode structure

Cao Chen (曹琛), Zhang Bing (张冰), Wu Long-Sheng (吴龙胜), Li Na (李娜), Wang Jun-Feng (王俊峰)

Chin. Phys. B, 2014, 23 (12): 124215. DOI: 10.1088/1674-1056/23/12/124215

Abstract ( 712 )

PDF (594KB) ( 503 )

A quantum efficiency analytical model for complementary metal–oxide–semiconductor (CMOS) image pixels with a pinned photodiode structure is developed. The proposed model takes account of the non-uniform doping distribution in the N-type region due to the impurity compensation formed by the actual fabricating process. The characteristics of two boundary PN junctions located in the N-type region for the particular spectral response of a pinned photodiode, are quantitatively analyzed. By solving the minority carrier steady-state diffusion equations and the barrier region photocurrent density equations successively, the analytical relationship between the quantum efficiency and the corresponding parameters such as incident wavelength, N-type width, peak doping concentration, and impurity density gradient of the N-type region is established. The validity of the model is verified by the measurement results with a test chip of 160× 160 pixels array, which provides the accurate process with a theoretical guidance for quantum efficiency design in pinned photodiode pixels.

Superwide-angle acoustic propagations above the critical angles of the Snell law in liquid–solid superlattice Suggested by editors

Zhang Sai (张赛), Zhang Yu (张宇), Gao Xiao-Wei (高晓薇)

Chin. Phys. B, 2014, 23 (12): 124301. DOI: 10.1088/1674-1056/23/12/124301

Abstract ( 615 )

PDF (3846KB) ( 489 )

In this paper, superwide-angle acoustic propagations above the critical angles of the Snell law in liquid–solid superlattice are investigated. Incident waves above the critical angles of the Snell law usually inevitably induce total reflection. However, incident waves with big oblique angles through the liquid–solid superlattice will produce a superwide angle transmission in a certain frequency range so that total reflection does not occur. Together with the simulation by finite element analysis, theoretical analysis by using transfer matrix method suggests the Bragg scattering of the Lamb waves as the physical mechanism of acoustic wave super-propagation far beyond the critical angle. Incident angle, filling fraction, and material thickness have significant influences on propagation. Superwide-angle propagation phenomenon may have potential applications in nondestructive evaluation of layered structures and controlling of energy flux.

Microstreaming velocity field and shear stress created by an oscillating encapsulated microbubble near a cell membrane

Wang Li (王莉), Tu Juan (屠娟), Guo Xia-Sheng (郭霞生), Xu Di (许迪), Zhang Dong (章东)

Chin. Phys. B, 2014, 23 (12): 124302. DOI: 10.1088/1674-1056/23/12/124302

Abstract ( 631 )

PDF (573KB) ( 738 )

Sonoporation mediated by microbubbles is being extensively studied as a promising technology to facilitate gene/drug delivery to cells. However, the theoretical study regarding the mechanisms involved in sonoporation is still in its infancy. Microstreaming generated by pulsating microbubble near the cell membrane is regarded as one of the most important mechanisms in the sonoporation process. Here, based on an encapsulated microbubble dynamic model with considering nonlinear rheological effects of both shell elasticity and viscosity, the microstreaming velocity field and shear stress generated by an oscillating microbubble near the cell membrane are theoretically simulated. Some factors that might affect the behaviors of microstreaming are thoroughly investigated, including the distance between the bubble center and cell membrane (d), shell elasticity (χ), and shell viscosity (κ). The results show that (i) the presence of cell membrane can result in asymmetric microstreaming velocity field, while the constrained effect of the membrane wall decays with increasing the bubble-cell distance; (ii) the bubble resonance frequency increases with the increase in d and χ, and the decrease in κ, although it is more dominated by the variation of shell elasticity; and (iii) the maximal microstreaming shear stress on the cell membrane increases rapidly with reducing the d, χ, and κ. The results suggest that microbubbles with softer and less viscous shell materials might be preferred to achieve more efficient sonoporation outcomes, and it is better to have bubbles located in the immediate vicinity of the cell membrane.

Fractional cyclic integrals and Routh equations of fractional Lagrange system with combined Caputo derivatives

Wang Lin-Li (王琳莉), Fu Jing-Li (傅景礼)

Chin. Phys. B, 2014, 23 (12): 124501. DOI: 10.1088/1674-1056/23/12/124501

Abstract ( 531 )

PDF (182KB) ( 321 )

In this paper, we develop a fractional cyclic integral and a Routh equation for fractional Lagrange system defined in terms of fractional Caputo derivatives. The fractional Hamilton principle and the fractional Lagrange equations of the system are obtained under a combined Caputo derivative. Furthermore, the fractional cyclic integrals based on the Lagrange equations are studied and the associated Routh equations of the system are presented. Finally, two examples are given to show the applications of the results.

Noether's theorems of a fractional Birkhoffian system within Riemann–Liouville derivatives Suggested by editors

Zhou Yan (周燕), Zhang Yi (张毅)

Chin. Phys. B, 2014, 23 (12): 124502. DOI: 10.1088/1674-1056/23/12/124502

Abstract ( 764 )

PDF (227KB) ( 411 )

The Noether symmetry and the conserved quantity of a fractional Birkhoffian system are studied within the Riemann–Liouville fractional derivatives. Firstly, the fractional Birkhoff's equations and the corresponding transversality conditions are given. Secondly, from special to general forms, Noether's theorems of a standard Birhoffian system are given, which provide an approach and theoretical basis for the further research on the Noether symmetry of the fractional Birkhoffian system. Thirdly, the invariances of the fractional Pfaffian action under a special one-parameter group of infinitesimal transformations without transforming the time and a general one-parameter group of infinitesimal transformations with transforming the time are studied, respectively, and the corresponding Noether's theorems are established. Finally, an example is given to illustrate the application of the results.

Dual solutions in boundary layer flow of Maxwell fluid over a porous shrinking sheet

Krishnendu Bhattacharyya, Tasawar Hayat, Ahmed Alsaedi

Chin. Phys. B, 2014, 23 (12): 124701. DOI: 10.1088/1674-1056/23/12/124701

Abstract ( 660 )

PDF (219KB) ( 919 )

An analysis is carried out for dual solutions of the boundary layer flow of Maxwell fluid over a permeable shrinking sheet. In the investigation, a constant wall mass transfer is considered. With the help of similarity transformations, the governing partial differential equations (PDEs) are converted into a nonlinear self-similar ordinary differential equation (ODE). For the numerical solution of transformed self-similar ODE, the shooting method is applied. The study reveals that the steady flow of Maxwell fluid is possible with a smaller amount of imposed mass suction compared with the viscous fluid flow. Dual solutions for the velocity distribution are obtained. Also, the increase of Deborah number reduces the boundary layer thickness for both solutions.

Orientation-dependent morphological stability of grain boundary groove Suggested by editors

Wang Li-Lin (王理林), Lin Xin (林鑫), Wang Zhi-Jun (王志军), Huang Wei-Dong (黄卫东)

Chin. Phys. B, 2014, 23 (12): 124702. DOI: 10.1088/1674-1056/23/12/124702

Abstract ( 738 )

PDF (454KB) ( 349 )

Crystal orientation influences the morphological stability of solid–liquid interface during directional solidification of alloy, resulting in the variation of solidified microstructure. In this paper, the morphological evolution near grain boundary grooves (GBGs) with different crystal orientations in a dilute succinonitrile alloy under low temperature gradient and interface velocity is observed in situ. Under experimental conditions, the macroscopic solid–liquid interface is planar and keeps stable, while in GBGs there emerge protrusion and undulation. It is found that the morphological stability of GBG is dependent on crystal orientation. Specifically, for succinonitrile with a body-centered cubic crystal structure, GBGs around the <100> crystal orientation keep stable, while those apart from the <100> crystal orientation become unstable under the same conditions. So it is concluded that <100> crystal orientation favors the morphological stability of GBG.

Effect of noncircular orifice plates on the near flow field of turbulent free jets

Xu Min-Yi (徐敏义), Tong Xing-Qing (童杏清), Yue Dan-Ting (岳丹婷), Zhang Jian-Peng (张健鹏), Mi Jian-Chun (米建春), Nathan G. J., Kalt P. A. M.

Chin. Phys. B, 2014, 23 (12): 124703. DOI: 10.1088/1674-1056/23/12/124703

Abstract ( 788 )

PDF (2880KB) ( 500 )

In this paper, we experimentally investigate the near-field flow characteristics of turbulent free jets respectively issued from circular, triangular, diamond, rectangular, and notched-rectangular orifice plates into air surroundings. All the orifice plates have identical opening areas or equivalent diameters (D_e) and their aspect ratios (AR) range from 1 to 6.5. Planar particle image velocimetry (PIV) is used to measure the velocity field at the same Reynolds number of Re= 5×10⁴, where Re= U_eD_e/ν with U_e being the exit bulk velocity and ν the kinematic viscosity of fluid. The mean and turbulent velocity fields of all the five jets are compared in detail. Results show that the noncircular jets can enhance the entrainment rate, reflected by the higher acceleration rates of mean velocity decay and spread, shorten the length of the unmixed core, expedite the increase of turbulent intensity compared with the circular counterpart shortened unmixed core, and increase turbulent intensity comparing to the circular counterpart. Among the five jets, the rectangular jet (AR= 6.5) produces the greatest decay rate of the near-field mean velocity, postpones the position at which the 鈥榓xis-switching鈥檖phenomenon occurs. This supports that axis switching phenomenon strongly depends on jet initial conditions. In addition, the hump in the centerline variation of the turbulence intensity is observed in the rectangular and triangular jets, but not in the circular jet, nor in diamond jet nor in notched-rectangular jet.

Particle path tracking method in two-and three-dimensional continuously rotating detonation engines

Zhou Rui (周蕊), Wu Dan (武丹), Liu Yan (刘岩), Wang Jian-Ping (王健平)

Chin. Phys. B, 2014, 23 (12): 124704. DOI: 10.1088/1674-1056/23/12/124704

Abstract ( 831 )

PDF (10791KB) ( 405 )

The particle path tracking method is proposed and used in two-dimensional (2D) and three-dimensional (3D) numerical simulations of continuously rotating detonation engines (CRDEs). This method is used to analyze the combustion and expansion processes of the fresh particles, and the thermodynamic cycle process of CRDE. In a 3D CRDE flow field, as the radius of the annulus increases, the no-injection area proportion increases, the non-detonation proportion decreases, and the detonation height decreases. The flow field parameters on the 3D mid annulus are different from in the 2D flow field under the same chamber size. The non-detonation proportion in the 3D flow field is less than in the 2D flow field. In the 2D and 3D CRDE, the paths of the flow particles have only a small fluctuation in the circumferential direction. The numerical thermodynamic cycle processes are qualitatively consistent with the three ideal cycle models, and they are right in between the ideal F–J cycle and ideal ZND cycle. The net mechanical work and thermal efficiency are slightly smaller in the 2D simulation than in the 3D simulation. In the 3D CRDE, as the radius of the annulus increases, the net mechanical work is almost constant, and the thermal efficiency increases. The numerical thermal efficiencies are larger than F–J cycle, and much smaller than ZND cycle.

Modified 2CLJDQP model and the second virial coefficients for linear molecules

Zhang Ying (张颖), Wang Sheng (王升), He Mao-Gang (何茂刚)

Chin. Phys. B, 2014, 23 (12): 125101. DOI: 10.1088/1674-1056/23/12/125101

Abstract ( 589 )

PDF (462KB) ( 380 )

A modified form of 2CLJDQP potential model is proposed to calculate the second virial coefficients of two-center Lennard-Jones molecules. In the presented potential model, the potential parameters σ and ε are considered as the temperature-dependent parameters in the form of hyperbolical temperature function based on the theory of temperature-dependent potential parameters. With this modified model, the second virial coefficients of some homonuclear molecules (such as O₂, Cl₂, CH₃CH₃, and CF₃CF₃) and heteronuclear molecules (such as CO, NO, CH₃F, CH₃Cl, CH₃CF₃, CH₃CHF₂, and CF₃CH₂F) are calculated. Then the Lorentz–Berthelot mixing rule is modified with a temperature-dependent expression, and the second virial coefficients of the heteronuclear molecules (such as CH₃F, CH₃Cl, and CH₃CF₃) are calculated. Moreover, CO₂ and N₂O are also studied with the modified 3CLJDQP model. The calculated results from the modified 2CLJDQP model accord better with the experimental data than those from the original model. It is shown that the presented model improves the positive deviation in low temperature range and negative deviation in high temperature range. So the modified 2CLJDQP potential model with the temperature-dependent parameters can be employed satisfactorily in large temperature range.

Charging and absorption characteristics of small particulates under alternative and electrostatic voltages in an electrostatic precipitator

Jiang Xue-Dong (姜学东), Xu He (徐鹤), Wang Xin (王昕)

Chin. Phys. B, 2014, 23 (12): 125201. DOI: 10.1088/1674-1056/23/12/125201

Abstract ( 502 )

PDF (223KB) ( 293 )

The charge quantity of small particulates such as PM2.5 plays a key role in the collection efficiency of an electrostatic precipitator (ESP). Under a single electrostatic voltage, it is difficult to charge and absorb small particulates. A new method of superimposing an alternative voltage on the electrostatic voltage is provided in this paper. Characteristics of small particulates are analyzed under alternative and electrostatic voltages. It is demonstrated that an alternative voltage can significantly improve the collection efficiency in three aspects: preventing anti-corona, increasing the charge quantity of small particulates, and increasing the median particulate size by electric agglomeration. In addition, practical usage with the superposition of alternative voltage is provided, and the results are in agreement with the theoretical analysis.

New terahertz dispersive device for single-shot spectral measurements of terahertz pulse

Wu Yin-Zhong (巫殷忠), Zhao Zong-Qing (赵宗清), Gu Yu-Qiu (谷渝秋), Wei Lai (魏来), Cao Lei-Feng (曹磊峰)

Chin. Phys. B, 2014, 23 (12): 125202. DOI: 10.1088/1674-1056/23/12/125202

Abstract ( 850 )

PDF (793KB) ( 411 )

A new terahertz dispersive device designed for single-shot spectral measurements of broadband terahertz pulses is proposed. With two-dimensional quasi-randomly distributed element design, the device exhibits approximately the dispersive property of single-order diffraction in far field. Its far-field diffraction pattern is experimentally verified employing a continuous terahertz source centered at 2.52 THz and a pyroelectric focal-plane-array camera, which is in good agreement with the numerical result. The device provides a new approach for direct single-shot spectral measurements of broadband terahertz waves.

Bipolar tri-state resistive switching characteristics in Ti/CeO_x/Pt memory device

M. Ismail, M. W. Abbas, A. M. Rana, I. Talib, E. Ahmed, M. Y. Nadeem, T. L. Tsai, U. Chand, N. A. Shah, M. Hussain, A. Aziz, M. T. Bhatti

Chin. Phys. B, 2014, 23 (12): 126101. DOI: 10.1088/1674-1056/23/12/126101

Abstract ( 609 )

PDF (743KB) ( 398 )

Highly repeatable multilevel bipolar resistive switching in Ti/CeO_x/Pt nonvolatile memory device has been demonstrated. X-ray diffraction studies of CeO₂ films reveal the formation of weak polycrystalline structure. The observed good memory performance, including stable cycling endurance and long data retention times (>10⁴ s) with an acceptable resistance ratio (～ 10²), enables the device for its applications in future non-volatile resistive random access memories (RRAMs). Based on the unique distribution characteristics of oxygen vacancies in CeO_x films, the possible mechanism of multilevel resistive switching in CeO_x RRAM devices has been discussed. The conduction mechanism in low resistance state is found to be Ohmic due to conductive filamentary paths, while that in the high resistance state was identified as Ohmic for low applied voltages and a space-charge-limited conduction dominated by Schottky emission at high applied voltages.

Effects of N doping on photoelectric properties of along different directions of ZnO bulk and nanotube

Zheng Hong-Mei (郑红梅), Fang Xiao-Yong (房晓勇), Cai Li-Xia (蔡丽霞), Yin Ai-Cha (尹爱查), Jin Hai-Bo (金海波), Yu Xiao-Xia (于晓霞), Cao Mao-Sheng (曹茂盛)

Chin. Phys. B, 2014, 23 (12): 126102. DOI: 10.1088/1674-1056/23/12/126102

Abstract ( 594 )

PDF (781KB) ( 465 )

The electronic structures and optical properties of N-doped ZnO bulks and nanotubes are investigated using the first-principles density functional method. The calculated results show that the main optical parameters of ZnO bulks are isotropic (especially in the high frequency region), while ZnO nanotubes exhibit anisotropic optical properties. N doping results show that ZnO bulks and nanotubes present more obvious anisotropies in the low-frequency region. Thereinto, the optical parameters of N-doped ZnO bulks along the [100] direction are greater than those along the [001] direction, while for N-doped nanotubes, the variable quantities of optical parameters along the [100] direction are less than those along the [001] direction. In addition, refractive indexes, electrical conductivities, dielectric constants, and absorption coefficients of ZnO bulks and nanotubes each contain an obvious spectral band in the deep ultraviolet (UV) (100 nm～ 300 nm). For each of N-doped ZnO bulks and nanotubes, a spectral peak appears in the UV and visible light region, showing that N doping can broaden the application scope of the optical properties of ZnO.

Phase field modeling of the ring-banded spherulites of crystalline polymers: The role of thermal diffusion Suggested by editors

Wang Xiao-Dong (王晓东), Ouyang Jie (欧阳洁), Su Jin (苏进), Zhou Wen (周文)

Chin. Phys. B, 2014, 23 (12): 126103. DOI: 10.1088/1674-1056/23/12/126103

Abstract ( 704 )

PDF (1896KB) ( 611 )

The ring-banded spherulite is a special morphology of polymer crystals and has attracted considerable attention over recent decades. In this study, a new phase field model with polymer characteristics is established to investigate the emergence and formation mechanism of the ring-banded spherulites of crystalline polymers. The model consists of a non-conserved phase field representing the phase transition and a temperature field describing the diffusion of the released latent heat. The corresponding model parameters can be obtained from experimentally accessible material parameters. Two-dimensional calculations are carried out for the ring-banded spherulitic growth of polyethylene film under a series of crystallization temperatures. The results of these calculations demonstrate that the formation of ring-banded spherulites can be triggered by the self-generated thermal field. Moreover, some temperature-dependent characteristics of the ring-banded spherulites observed in experiments are reproduced by simulations, which may help to study the effects of crystallization temperature on the ring-banded structures.

Temperature dependence of surface and structure properties of ZnCdO film

Lei Hong-Wen (雷红文), Yan Da-Wei (阎大伟), Zhang Hong (张红), Wang Xue-Min (王雪敏), Yao Gang (姚刚), Wu Wei-Dong (吴卫东), Zhao Yan (赵妍)

Chin. Phys. B, 2014, 23 (12): 126104. DOI: 10.1088/1674-1056/23/12/126104

Abstract ( 515 )

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Zn_1-xCd_xO films are grown on c-sapphire substrates by laser molecular beam epitaxy (LMBE) at different temperatures. Their crystallographic structures, compositions, surface electronic structures are investigated. The a-axis lattice constant of Zn_0.95Cd_0.05O is 3.20 Å. Moreover, the epitaxial relationship shows a 30°-in-plane rotation of the film with respect to the c-sapphire substrate. When the substrate temperatures arrives at 500 ℃, the in situ reflection high-energy electron diffraction (RHEED) pattern of ZnCdO film shows sharp streaky pattern. The maximum Cd content of ZnCdO film grown at low substrate temperatures increases up to about 29.6 at.%, which is close to that of the ceramic target. In situ ultraviolet photoelectron spectroscopy (UPS) measurements demonstrate that ZnCdO film exhibits intense peaks at 4.7 eV and 10.7 eV below the Fermi level, which are assigned to the O 2p and Zn 3p states. Energetic distance between Zn 3d and Cd 4d is 0.60 eV. Above 470 nm, the thin film shows excellent optical transmission.

Raman spectrum study of graphite irradiated by swift heavy ions

Zhai Peng-Fei (翟鹏飞), Liu Jie (刘杰), Zeng Jian (曾健), Yao Hui-Jun (姚会军), Duan Jing-Lai (段敬来), Hou Ming-Dong (侯明东), Sun You-Mei (孙友梅), Ewing Rodney Charles

Chin. Phys. B, 2014, 23 (12): 126105. DOI: 10.1088/1674-1056/23/12/126105

Abstract ( 749 )

PDF (832KB) ( 490 )

Highly oriented pyrolytic graphites are irradiated with 40.5-MeV and 67.7-MeV ¹¹²Sn-ions in a wide range of fluences: 1× 10¹¹ ions/cm²–1× 10¹⁴ ions/cm². Raman spectra in the region between 1200 cm^-1 and 3500 cm^-1 show that the disorder induced by Sn-ions increases with ion fluence increasing. However, for the same fluence, the amount of disorder is greater for 40.5-MeV Sn-ions than that observed for 67.7-MeV Sn-ions, even though the latter has a slightly higher value for electronic energy loss. This is explained by the ion velocity effect. Importantly, ～ 3-cm^-1 frequency shift toward lower wavenumber for the D band and ～ 6-cm^-1 shift toward lower wavenumber for the 2D band are observed at a fluence of 1× 10¹⁴ ions/cm², which is consistent with the scenario of radiation-induced strain. The strain formation is interpreted in the context of inelastic thermal spike model, and the change of the 2D band shape at high ion fluence is explained by the accumulation of stacking faults of the graphene layers activated by radiation-induced strain around ion tracks. Moreover, the hexagonal structure around the ion tracks is observed by scanning tunneling microscopy, which confirms that the strains near the ion tracks locally cause electronic decoupling of neighboring graphene layers.

Species separation of binary colloidal mixtures in the multi-Gauss potential: Effect of depletion

Sun Zong-Li (孙宗利), Kang Yan-Shuang (康艳霜), Kang Yan-Mei (康艳梅), Song Jian-Min (宋建民)

Chin. Phys. B, 2014, 23 (12): 126401. DOI: 10.1088/1674-1056/23/12/126401

Abstract ( 522 )

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For the asymmetrical colloidal mixture subject to a confining potential and an external multi-Gauss potential, the separation of species is studied based on the classical density functional theory of simple fluids. The multi-Gauss potential consists of several Gauss barriers, which are distributed along the axial direction with uniform distance. The barrier width, barrier distance, and barrier height are individually adjusted to investigate their effects on the species separation. From the numerical results, it is concluded that in each condition, the competition between the external potential and the depletion potential determines the phase equilibrium and the separation. Species separation appears only in the region where the depletion is dominant. On the contrary, both species are absent in the regions where the external potential takes the absolute advantage.

Interfacial potential approach for Ag/ZnO (0001) interfaces

Song Hong-Quan (宋宏权), Shen Jiang (申江), Qian Ping (钱萍), Chen Nan-Xian (陈难先)

Chin. Phys. B, 2014, 23 (12): 126801. DOI: 10.1088/1674-1056/23/12/126801

Abstract ( 592 )

PDF (1544KB) ( 348 )

Systematic approaches are presented to extract the interfacial potentials from the ab initio adhesive energy of the interface system by using the Chen–Möbius inversion method. We focus on the interface structure of the metal (111)/ZnO (0001) in this work. The interfacial potentials of Ag–Zn and Ag–O are obtained. These potentials can be used to solve some problems about Ag/ZnO interfacial structure. Three metastable interfacial structures are investigated in order to check these potentials. Using the interfacial potentials we study the procedure of interface fracture in the Ag/ZnO (0001) interface and discuss the change of the energy, stress, and atomic structures in tensile process. The result indicates that the exact misfit dislocation reduces the total energy and softens the fracture process. Meanwhile, the formation and mobility of the vacancy near the interface are observed.

Mechanical and thermodynamic properties of the monoclinic and orthorhombic phases of SiC₂N₄ under high pressure from first principles

Miao Nan-Xi (苗楠茜), Pu Chun-Ying (濮春英), He Chao-Zheng (何朝政), Zhang Fei-Wu (张飞武), Lu Cheng (卢成), Lu Zhi-Wen (卢志文), Zhou Da-Wei (周大伟)

Chin. Phys. B, 2014, 23 (12): 127101. DOI: 10.1088/1674-1056/23/12/127101

Abstract ( 615 )

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First principles calculations are preformed to systematically investigate the electronic structures, elastic and thermodynamic properties of the monoclinic and orthorhombic phases of SiC₂N₄ under pressure. The calculated structural parameters and elastic moduli are in good agreement with the available theoretical values at zero pressure. The elastic constants of the two phases under pressure are calculated by stress–strain method. It is found that both phases satisfy the mechanical stability criteria within 60 GPa. With the increase of pressure, the degree of the anisotropy decreases rapidly in the monoclinic phase, whereas it remains almost constant in the orthorhombic phase. Furthermore, using the hybrid density-functional theory, the monoclinic and orthorhombic phases are found to be wide band-gap semiconductors with band gaps of about 2.85 eV and 3.21 eV, respectively. The elastic moduli, ductile or brittle behaviors, compressional and shear wave velocities as well as Debye temperatures as a function of pressure in both phases are also investigated in detail.

The electronic structures, Born effective charge tensors, and phonon properties of cubic, tetragonal, orthorhombic, and rhombohedral K_0.5Na_0.5NbO₃: A first-principles comparative study

Zhou Shu-Lan (周树兰), Zhao Xian (赵显), Jiang Xiang-Ping (江向平), Han Xiao-Dong (韩晓东)

Chin. Phys. B, 2014, 23 (12): 127102. DOI: 10.1088/1674-1056/23/12/127102

Abstract ( 892 )

PDF (1295KB) ( 750 )

The electronic structures, Born effective charges (BECs), and full phonon dispersions of cubic, tetragonal, orthorhombic, and rhombohedral K_0.5Na_0.5NbO₃ are investigated by the first principles method based on density functional theory. The hybridized states of Nb 4d and O 2p states are observed in the valence band, showing the formation of a strong Nb–O covalent bond which should be responsible for the displacement of Nb and O atoms. The abnormally large BECs of Nb and O indicate the possibility of phase instability induced by the off-center displacement of Nb and O atoms. The phonon dispersions reveal that the ferroelectric instability of K_0.5Na_0.5NbO₃ is dominated by Nb and O displacements with significant Na characteristics. In addition to the ferroelectric instability, there is also rotational instability coming from the oxygen octahedra rotation around one axis. Moreover, the Γ phonon properties of orthorhombic KNbO₃, NaNbO₃, and K_0.5Na_0.5NbO₃ are also studied in detail.

Spatially nonlocal effects on optical absorption properties incoupled quantum wells with an applied electric field

Wang Chao-Yang (王晁阳), Wang Guang-Hui (王光辉)

Chin. Phys. B, 2014, 23 (12): 127103. DOI: 10.1088/1674-1056/23/12/127103

Abstract ( 739 )

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Based on the microscopic nonlocal optical response theory, the intersubband optical absorption properties in AlGaAs/GaAs couple quantum wells (CQWs) are investigated for p-polarized states. The numerical results show that spatial nonlocality of optical responses can induce a radiation shift on optical absorption spectra due to nonlocal effects. The dependence of the radiation shift on the CQW structure and the applied electric field is clarified. It is also demonstrated that the maximal radiation shift and the least optical absorbance can be obtained by adopting an appropriate CQW structure and a suitable applied electric field. This work may provide some methods of designing the nanomaterials with controllable nonlocality and observing the spatial nonlocal effects in experiment.

Effects of GaN cap layer thickness on an AlN/GaN heterostructure

Zhao Jing-Tao (赵景涛), Lin Zhao-Jun (林兆军), Luan Chong-Biao (栾崇彪), Lü Yuan-Jie (吕元杰), Feng Zhi-Hong (冯志宏), Yang Ming (杨铭)

Chin. Phys. B, 2014, 23 (12): 127104. DOI: 10.1088/1674-1056/23/12/127104

Abstract ( 762 )

PDF (532KB) ( 773 )

In this study, we investigate the effects of GaN cap layer thickness on the two-dimensional electron gas (2DEG) electron density and 2DEG electron mobility of AlN/GaN heterostructures by using the temperature-dependent Hall measurement and theoretical fitting method. The results of our analysis clearly indicate that the GaN cap layer thickness of an AlN/GaN heterostructure has influences on the 2DEG electron density and the electron mobility. For the AlN/GaN heterostructures with a 3-nm AlN barrier layer, the optimized thickness of the GaN cap layer is around 4 nm and the strained a-axis lattice constant of the AlN barrier layer is less than that of GaN.

Power dependence of terahertz carrier frequency in a plasma-based two-color generation process

Zhao Ji (赵骥), Zhang Liang-Liang (张亮亮), Luo Yi-Man (骆怡蔓), Wu Tong (吴同), Zhang Cun-Lin (张存林), Zhao Yue-Jin (赵跃进)

Chin. Phys. B, 2014, 23 (12): 127201. DOI: 10.1088/1674-1056/23/12/127201

Abstract ( 665 )

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We conduct a frequency spectrum experiment to investigate terahertz (THz) emissions from laser-induced air plasma under different laser incident powers. The frequency spectra are measured using both air-biased-coherent detection and a Michelson interferometer. The red-shift of the THz pulse carrier frequency is observed as a response to increased pump power. These phenomena are related to plasma collisions and can be explained by the plasma collision model. Based on these findings, it is apparent that the tuning of the THz carrier frequency can be achieved through regulation of the pump beam.

First-principles study of the formation and electronic structure of a conductive filament in ZnO-based resistive random access memory

Zhao Jing (赵晶), Dong Jing-Yu (董静雨), Ren Shu-Xia (任书霞), Zhang Li-Yong (张礼勇), Zhao Xu (赵旭), Chen Wei (陈伟)

Chin. Phys. B, 2014, 23 (12): 127301. DOI: 10.1088/1674-1056/23/12/127301

Abstract ( 727 )

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Oxygen vacancy plays a crucial role in resistive switching. To date, a quantitative study about the distribution of the oxygen vacancies and its effect on the resistive switching has not yet been reported. In this study, we report our first-principles calculations in ZnO-based resistive switching memory grown on a Pt substrate. We show that the oxygen vacancies prefer to be located in the ZnO (0001) plane, i.e. in the direction parallel to the film surface in the preparation process. These oxygen vacancies drift easily in the film when a voltage is applied in the SET process and prefer to form a line defect perpendicular to the film surface. An isolated oxygen vacancy makes little contribution to the conductivity of ZnO, whereas the ordering of oxygen vacancies in the direction perpendicular to the film surface leads to a dramatic enhancement of the conductivity and thus forms conductive filaments. The semiconducting characteristics of the conductive filaments are confirmed experimentally.

Annealing temperature influence on the degree of inhomogeneity of the Schottky barrier in Ti/4H–SiC contacts

Han Lin-Chao (韩林超), Shen Hua-Jun (申华军), Liu Ke-An (刘可安), Wang Yi-Yu (王弋宇), Tang Yi-Dan (汤益丹), Bai Yun (白云), Xu Heng-Yu (许恒宇), Wu Yu-Dong (吴煜东), Liu Xin-Yu (刘新宇)

Chin. Phys. B, 2014, 23 (12): 127302. DOI: 10.1088/1674-1056/23/12/127302

Abstract ( 680 )

PDF (461KB) ( 518 )

Tung's model was used to analyze anomalies observed in Ti/SiC Schottky contacts. The degree of the inhomogeneous Schottky barrier after annealing at different temperatures is characterized by the 'T₀ anomaly' and the difference (ΔФ) between the uniformly high barrier height (Ф_B⁰) and the effective barrier height (Ф_B^eff). Those two parameters of Ti Schottky contacts on 4H–SiC were deduced from I–V measurements in the temperature range of 298 K–503 K. The increase in Schottky barrier (SB) height (Ф_B) and decrease in the ideality factor (n) with an increase measurement temperature indicate the presence of an inhomogeneous SB. The degree of inhomogeneity of the Schottky barrier depends on the annealing temperature, and it is at its lowest for 500-℃ thermal treatment. The degree of inhomogeneity of the SB could reveal effects of thermal treatments on Schottky contacts in other aspects.

A novel LDMOS with a junction field plate and a partial N-buried layer ^Hot! Suggested by editors

Shi Xian-Long (石先龙), Luo Xiao-Rong (罗小蓉), Wei Jie (魏杰), Tan Qiao (谭桥), Liu Jian-Ping (刘建平), Xu Qing (徐青), Li Peng-Cheng (李鹏程), Tian Rui-Chao (田瑞超), Ma Da (马达)

Chin. Phys. B, 2014, 23 (12): 127303. DOI: 10.1088/1674-1056/23/12/127303

Abstract ( 818 )

PDF (620KB) ( 641 )

A novel lateral double-diffused metal–oxide semiconductor (LDMOS) with a high breakdown voltage (BV) and low specific on-resistance (R_on.sp) is proposed and investigated by simulation. It features a junction field plate (JFP) over the drift region and a partial N-buried layer (PNB) in the P-substrate. The JFP not only smoothes the surface electric field (E-field), but also brings in charge compensation between the JFP and the N-drift region, which increases the doping concentration of the N-drift region. The PNB reshapes the equipotential contours, and thus reduces the E-field peak on the drain side and increases that on the source side. Moreover, the PNB extends the depletion width in the substrate by introducing an additional vertical diode, resulting in a significant improvement on the vertical BV. Compared with the conventional LDMOS with the same dimensional parameters, the novel LDMOS has an increase in BV value by 67.4%, and a reduction in R_on.sp by 45.7% simultaneously.

Improved power simulation of AlGaN/GaN HEMT at class-AB operation via an RF drain–source current correction method

Pongthavornkamol Tiwat (林体元), Pang Lei (庞磊), Yuan Ting-Ting (袁婷婷), Liu Xin-Yu (刘新宇)

Chin. Phys. B, 2014, 23 (12): 127304. DOI: 10.1088/1674-1056/23/12/127304

Abstract ( 742 )

PDF (958KB) ( 514 )

A new modified Angelov current–voltage characteristic model equation is proposed to improve the drain–source current (I_ds) simulation of an AlGaN/GaN-based (gallium nitride) high electron mobility transistor (AlGaN/GaN-based HEMT) at high power operation. Since an accurate radio frequency (RF) current simulation is critical for a correct power simulation of the device, in this paper we propose a method of AlGaN/GaN high electron mobility transistor (HEMT) nonlinear large-signal model extraction with a supplemental modeling of RF drain–source current as a function of RF input power. The improved results of simulated output power, gain, and power added efficiency (PAE) at class-AB quiescent bias of V_gs= -3.5 V, V_ds= 30 V with a frequency of 9.6 GHz are presented.

Thermodynamics around magnetic phase transitions in alternating double-chain spin systems

Ding Lin-Jie (丁林杰), Zhong Yuan (钟园), Fan Shuai-Wei (樊帅伟), Zhu Li-Ya (朱丽娅)

Chin. Phys. B, 2014, 23 (12): 127401. DOI: 10.1088/1674-1056/23/12/127401

Abstract ( 766 )

PDF (1741KB) ( 363 )

The thermodynamics and quantum phase transitions of two typically alternating double-chain systems are investigated by Green's function theory. (i) For the completely antiferromagnetic (AFM) alternating double-chain, the low-temperature antiferromagnetism with gapped behavior is observed, which is in accordance with the experimental result. In a magnetic field, we unveil the ground state phase diagram with zero plateau, 1/2 plateau, and polarized ferromagnetic (FM) phases, as a result of the intra-cluster spin-singlet competition. Furthermore, the Grüneisen ratio is an excellent tool to identify the quantum criticality and testify various quantum phases. (ii) For the antiferromagnetically coupled FM alternating chains, the 1/2 magnetization plateau and double-peak structure of specific heat appear, which are also observed experimentally. Nevertheless, the M–h curve shows an anomalous behavior in an ultra-low field, which is ascribed to the effectively weak Haldane-like state, demonstrated by the two-site entanglement entropy explicitly.

Magneto-resistance and vortex phase diagram of BaNi_0.1Fe_1.9As₂ single crystal Suggested by editors

Lu Jun-Chao (鲁俊超), Yu Yi (于一), Pi Li (皮雳), Zhang Yu-Heng (张裕恒)

Chin. Phys. B, 2014, 23 (12): 127402. DOI: 10.1088/1674-1056/23/12/127402

Abstract ( 642 )

PDF (1071KB) ( 450 )

The transition from vortex glass to a liquid phase is studied in BaNi_0.1Fe_1.9As₂ single crystal with T_c=19.4 K by magneto-resistance measurements. The resistivity curves are measured in magnetic fields in a range of 0 T–13 T for H‖c and H⊥c. Good scalings for all values of resistivity ρ(H,T) and the effective pinning potential U₀(H,T) are obtained with the modified vortex glass theory by using the critical exponents s and H₀. Phase diagrams for H‖c and H⊥c are determined based on the obtained vortex glass temperature T_g, the vortex dimensionality crossover temperature T^*, and the upper critical magnetic field H_c2. Our results suggest that both below and above 5 T, single vortex pinning co-exists with collective creep, and collective creep is dominant. There is a narrower vortex liquid region for H⊥c than for H‖c in the vortex phase diagram, which may originate from a stronger pinning force.

Angle-dependent spin waves in antidot bilayers

Hu Chun-Lian (胡春莲), Liao Leng (廖棱), Stamps R

Chin. Phys. B, 2014, 23 (12): 127501. DOI: 10.1088/1674-1056/23/12/127501

Abstract ( 531 )

PDF (463KB) ( 319 )

Ferromagnetic resonance is introduced to examine the microwave frequency response of NiFe/IrMn bilayers, patterned as antidot arrays. In the experiment, field direction dependence on mode is obtained by rotating the applied magnetic field. We find that at a given resonance frequency, the dependence of the resonance field on the angle has a tendency of sinusoid/cosine variation in the experiment. From micromagnetic simulation it can be seen that spin waves are localized between dots from a given mode profile. This is caused by a demagnetization distribution with a larger value in the center of the two nearest dots than that of the next-nearest dots.

Multiple sign reversals of the exchange bias field in polycrystalline SmCr_0.9Fe_0.1O₃ Suggested by editors

Fang Yong (房勇), Yan Shi-Ming (颜士明), Gong Yuan-Yuan (龚元元), Zhu Wei-Li (朱卫利), Cao Qing-Qi (曹庆琪), Wang Dun-Hui (王敦辉), Du You-Wei (都有为)

Chin. Phys. B, 2014, 23 (12): 127502. DOI: 10.1088/1674-1056/23/12/127502

Abstract ( 602 )

PDF (1219KB) ( 497 )

We synthesize the perovskite compound SmCr_0.9Fe_0.1O₃ by the sol–gel method and investigate its exchange bias properties through thermomagnetic and isothermal magnetization measurements. The sign reversals of the exchange bias field are observed at the magnetization compensation temperatures 29.6 K and 96.2 K. It is demonstrated that the occurrence of the exchange bias originates from the antiferromagnetic coupling between the Cr-rich and Fe–Cr regions, of which the net magnetization is temperature-dependent. These results imply that there are potential applications in single systems with sign reversals of both magnetization and exchange bias.

Defect characterization and magnetic properties in un-doped ZnO thin film annealed in a strong magnetic field Suggested by editors

Ning Shuai (宁帅), Zhan Peng (战鹏), Wang Wei-Peng (王炜鹏), Li Zheng-Cao (李正操), Zhang Zheng-Jun (张政军)

Chin. Phys. B, 2014, 23 (12): 127503. DOI: 10.1088/1674-1056/23/12/127503

Abstract ( 715 )

PDF (653KB) ( 697 )

Highly c-axis oriented un-doped zinc oxide (ZnO) thin films, each with a thickness of ～ 100 nm, are deposited on Si (001) substrates by pulsed electron beam deposition at a temperature of ～ 320 ℃, followed by annealing at 650 ℃ in argon in a strong magnetic field. X-ray photoelectron spectroscopy (XPS), positron annihilation analysis (PAS), and electron paramagnetic resonance (EPR) characterizations suggest that the major defects generated in these ZnO films are oxygen vacancies. Photoluminescence (PL) and magnetic property measurements indicate that the room-temperature ferromagnetism in the un-doped ZnO film originates from the singly ionized oxygen vacancies whose number depends on the strength of the magnetic field applied in the thermal annealing process. The effects of the magnetic field on the defect generation in the ZnO films are also discussed.

Modelling self-sensing of a magnetostrictive actuator based on a terfenol-D rod Suggested by editors

Yan Bai-Ping (严柏平), Zhang Cheng-Ming (张成明), Li Li-Yi (李立毅), Tang Zhi-Feng (唐志峰), Lü Fu-Zai (吕福在), Yang Ke-Ji (杨克己)

Chin. Phys. B, 2014, 23 (12): 127504. DOI: 10.1088/1674-1056/23/12/127504

Abstract ( 737 )

PDF (779KB) ( 378 )

A simplified quasi-static computational model for self-sensing applications of magnetostrictive actuators based on terfenol-D rods is presented. Paths and angle changes in the magnetic moments rotation of Tb_0.3Dy_0.7Fe₂ alloy are studied as functions of compressive stress and magnetic field, and then used to determine the magnetization in its actuation. Then sensing of magnetic induction picked from a driving coil in an actuator is derived. The model is quick and efficient to solve moments rotation and its magnetization. Sensing results of compressive stress and magnetostriction calculated by the model are in good agreement with experiments and will be helpful in the design and control of self-sensing applications in actuators.

Synthesis, structure, optical, and electric properties of Ce-doped CuInTe₂ compound

Fu Li (付丽), Guo Yong-Quan (郭永权)

Chin. Phys. B, 2014, 23 (12): 127801. DOI: 10.1088/1674-1056/23/12/127801

Abstract ( 641 )

PDF (922KB) ( 475 )

Ce-doped CuInTe₂ (CICT) semiconducting compounds are successfully synthesized. The phase structures, optical, and electric properties are investigated using powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectrometer (XPS), Raman spectrometer, ultraviolet and visible spectrophotometer (UV-Vis), and a standard four-probe method. CuIn_1-xCe_xTe₂ crystallizes into a tetragonal structure with predominant orientation along the [112] direction. The lattice parameters are a=6.190(6) Å–6.193(0) Å and c=12.406(5) Å–12.409(5) Å. Ce prefers to occupy the 4b crystal position. According to the analysis of XPS spectra, Ce shows the mixture of valences 4+ and 3+. Raman spectra reveal that the photon vibrating model in the CICT follows A₁ mode in a wavenumber range of 123 cm^-1–128 cm^-1. UV-Vis spectra show that the band gap E_g values before and after 0.1 mole Ce doped into CuInTe₂ are 1.28 eV and 1.16 eV, respectively. It might be due to the mixture of valences for Ce. Ce doped into CuInTe₂ still shows the semiconductor characteristics.

Terahertz time-domain spectroscopy of a simulated pore structure to probe particle size and porosity of porous rock

Dong Chen (董晨), Bao Ri-Ma (宝日玛), Zhao Kun (赵昆), Xu Chang-Hong (许长虹), Jin Wu-Jun (金武军), Zhong Shou-Xian (钟寿仙)

Chin. Phys. B, 2014, 23 (12): 127802. DOI: 10.1088/1674-1056/23/12/127802

Abstract ( 696 )

PDF (605KB) ( 414 )

The particle sizes and porosities of simulated pore structures are probed by terahertz time-domain spectroscopy. A double-peak time-domain spectrum phenomenon is observed when the terahertz (THz) pulses illuminated a pore and a particle. The amplitudes of the two peaks depend strongly and monotonically on the particle size and porosity. A model is used to study the phenomenon, and the computational results agreed with the experimental measurements. These measurements indicate the terahertz spectroscopic behaviors of pores and particles, suggesting that terahertz spectroscopy can be used as a noncontact probe of porosity.

Photoluminescence characteristics and energy transfer between Bi³⁺ and Eu³⁺ in Na₂O–CaO–GeO₂–SiO₂ glass

Li Qian-Yue (黎千跃), Xu Xu-Hui (徐旭辉), Zhang Bu-Hao (张步豪), Wu Yu-Mei (吴玉梅), Qiu Jian-Bei (邱建备), Yu Xue (余雪)

Chin. Phys. B, 2014, 23 (12): 127803. DOI: 10.1088/1674-1056/23/12/127803

Abstract ( 688 )

PDF (457KB) ( 400 )

We report the photoluminescence (PL) of Eu³⁺-doped glass with Bi³⁺ as a sensitizer. The specific glass system with the strong enhancement of the red emission of Eu³⁺ is obtained by adding a small number of Bi³⁺ ions instead of increasing the Eu³⁺ concentration. The emission band of Bi³⁺ overlaps with the excitation band of Eu³⁺ and the lifetime decay curves, resulting in a very efficient energy transfer from Bi³⁺ to Eu³⁺. The probability of energy transfer is strongly dependent on Bi³⁺ concentration. In addition, the intensity of 4f–4f transition is much stronger than that of a charge-transfer (CT) band in the excitation spectrum, which indicates that the Na₂O–CaO–GeO₂-SiO₂ glass is a suitable red-emitting phosphor with high stability as a candidate for light-emitting diodes (LEDs).

Temperature dependence of the photoluminescence of MnS/ZnS core–shell quantum dots Suggested by editors

Fang Dai-Feng (房岱峰), Ding Xing (丁星), Dai Ru-Cheng (代如成), Zhao Zhi (赵智), Wang Zhong-Ping (王中平), Zhang Zeng-Ming (张增明)

Chin. Phys. B, 2014, 23 (12): 127804. DOI: 10.1088/1674-1056/23/12/127804

Abstract ( 670 )

PDF (549KB) ( 538 )

The temperature dependence of the photoluminescence (PL) from MnS/ZnS core–shell quantum dots is investigated in a temperature range of 8 K–300 K. The orange emission from the ⁴T₁ → ⁶A₁ transition of Mn²⁺ ions and the blue emission related to the trapped surface state are observed in the MnS/ZnS core–shell quantum dots. As the temperature increases, the orange emission is shifted toward a shorter wavelength while the blue emission is shifted towards the longer wavelength. Both the orange and blue emissions reduce their intensities with the increase of temperature but the blue emission is quenched faster. The temperature-dependent luminescence intensities of the two emissions are well explained by the thermal quenching theory.

Multi-band circular polarizer based on a twisted triplesplit-ring resonator Suggested by editors

Wu Song (吴松), Huang Xiao-Jun (黄晓俊), Xiao Bo-Xun (肖柏勋), Jin Yan (金彦), Yang He-Lin (杨河林)

Chin. Phys. B, 2014, 23 (12): 127805. DOI: 10.1088/1674-1056/23/12/127805

Abstract ( 773 )

PDF (1693KB) ( 420 )

A multi-band circular polarizer using a twisted triple split-ring resonator (TSRR) is presented and studied numerically and experimentally. At four distinct resonant frequencies, the incident linearly polarized wave can be transformed into left/right-handed circularly polarized waves. Numerical simulation results show that a y-polarized wave can be converted into a right-handed circularly polarized wave at 5.738 GHz and 9.218 GHz, while a left-handed circularly polarized wave is produced at 7.292 GHz and 10.118 GHz. The experimental results are in agreement with the numerical results. The surface current distributions are investigated to illustrate the polarization transformation mechanism. Furthermore, the influences of the structure parameters of the circular polarizer on transmission spectra are discussed as well.

Atomic origins of solid helium bubbles in tungsten ^Hot! Suggested by editors

Xia Min (夏敏), Guo Hong-Yan (郭洪燕), Dai Yong (戴勇), Yan Qing-Zhi (燕青芝), Guo Li-Ping (郭立平), Li Tie-Cheng (李铁成), Qiao Yi (乔祎), Ge Chang-Chun (葛昌纯)

Chin. Phys. B, 2014, 23 (12): 127806. DOI: 10.1088/1674-1056/23/12/127806

Abstract ( 863 )

PDF (3287KB) ( 523 )

Solid helium bubbles were directly observed in the helium ion implanted tungsten (W), by different transmission electron microscopy (TEM) techniques at room temperature. The diameters of these solid helium bubbles range from 1 nm to 8 nm in diameter with the mean bubble size about 3 nm. The selected area electron diffraction (SAED) and fast Fourier transform (FFT) images revealed that solid helium bubbles possess body-centered cubic (bcc) structure with a lattice constant of 0.447 nm. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images further confirmed the existence of helium bubble in tungsten. The present findings provide an atomic level view of the microstructure evolution of helium in the materials, and revealed the existence of solid helium bubbles in materials.

Mn overlayers on PbTe (111): Substitutional adsorption and interface formation

Wu Hai-Fei (吴海飞), Zhang Han-Jie (张寒洁), Lu Yun-Hao (陆赟豪), Yan Yong-Hong (鄢永红), Li Hai-Yang (李海洋), Bao Shi-Ning (鲍世宁), He Pi-Mo (何丕模)

Chin. Phys. B, 2014, 23 (12): 127901. DOI: 10.1088/1674-1056/23/12/127901

Abstract ( 611 )

PDF (420KB) ( 367 )

The formation of the Mn/PbTe (111) interface is investigated by photoemission spectrum. The core level behavior of Mn 2p is consistent with Mn substitutional adsorption during the initial Mn deposition, forming a (√3× √3)R30°-Pb_0.67Mn_0.33Te phase of the second layer. Further deposition of Mn can cause metallic Mn islands to cover the substitutional substrate. Ultraviolet photoemission measurements show that the Fermi level is shifted into the conduction band, indicating Ohmic contact formation at the Mn/PbTe (111) interface. The valence band maximum associated with the Pb_0.67Mn_0.33Te layer is located at 1.27 eV below the Fermi level, and a schematic electronic structure of the Mn/PbTe (111) interface is given. The work function of the substituted substrate with Pb-covered Mn islands is determined to be 4.16 eV, in comparison with 4.35 eV for the Pb-covered substituted substrate and 3.95 eV for the pristine PbTe (111) surface.

Liquid-phase and solid-phase microwave irradiations for reduction of graphite oxide

Zhao Na (赵娜), Wen Chen-Yu (文宸宇), Zhang David Wei (张卫), Wu Dong-Ping (吴东平), Zhang Zhi-Bin (张志滨), Zhang Shi-Li (张世理)

Chin. Phys. B, 2014, 23 (12): 128101. DOI: 10.1088/1674-1056/23/12/128101

Abstract ( 740 )

PDF (738KB) ( 478 )

In this paper, two microwave irradiation methods: (i) liquid-phase microwave irradiation (MWI) reduction of graphite oxide suspension dissolved in de-ionized water and N, N-dimethylformamide, respectively, and (ii) solid-phase MWI reduction of graphite oxide powder have been successfully carried out to reduce graphite oxide. The reduced graphene oxide products are thoroughly characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectral analysis, Raman spectroscopy, UV-Vis absorption spectral analysis, and four-point probe conductivity measurements. The results show that both methods can efficiently remove the oxygen-containing functional groups attached to the graphite layers, though the solid-phase MWI reduction method can obtain far more efficiently a higher quality-reduced graphene oxide with fewer defects. The I(D)/I(G) ratio of the solid-phase MWI sample is as low as 0.46, which is only half of that of the liquid-phase MWI samples. The electrical conductivity of the reduced graphene oxide by the solid method reaches 747.9 S/m, which is about 25 times higher than that made by the liquid-phase method.

L_g=100 nm T-shaped gate AlGaN/GaN HEMTs on Si substrates with non-planar source/drain regrowth of highly-doped n⁺-GaN layer by MOCVD Suggested by editors

Huang Jie (黄杰), Li Ming (黎明), Tang Chak-Wah (邓泽华), Lau Kei-May (刘纪美)

Chin. Phys. B, 2014, 23 (12): 128102. DOI: 10.1088/1674-1056/23/12/128102

Abstract ( 768 )

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High-performance AlGaN/GaN high electron mobility transistors (HEMTs) grown on silicon substrates by metal–organic chemical-vapor deposition (MOCVD) with a selective non-planar n-type GaN source/drain (S/D) regrowth are reported. A device exhibited a non-alloyed Ohmic contact resistance of 0.209 Ω·mm and a comprehensive transconductance (g_m) of 247 mS/mm. The current gain cutoff frequency f_T and maximum oscillation frequency f_MAX of 100-nm HEMT with S/D regrowth were measured to be 65 GHz and 69 GHz. Compared with those of the standard GaN HEMT on silicon substrate, the f_T and f_MAX is 50% and 52% higher, respectively.

An approach to controlling the fluorescence of graphene quantum dots: From surface oxidation to fluorescent mechanism ^Hot! Suggested by editors

Hu Yin (胡音), He Da-Wei (何大伟), Wang Yong-Sheng (王永生), Duan Jia-Hua (段嘉华), Wang Su-Feng (王素凤), Fu Ming (富鸣), Wang Wen-Shuo (王闻硕)

Chin. Phys. B, 2014, 23 (12): 128103. DOI: 10.1088/1674-1056/23/12/128103

Abstract ( 692 )

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We report a facile method of synthesizing graphene quantum dots (GQDs) with tunable emission. The as-prepared GQDs each with a uniform lateral dimension of ca. 6 nm have fine solubility and high stability. The photoluminescence mechanism is further investigated based on the surfacestructure and the photoluminescence behaviors. Based on our discussion, the green fluorescence emission can be attributed to the oxygen functional groups, which could possess broad emission bands within the π–π^* gap. This work is helpful to explain the vague fluorescent mechanism of GQDs, and the reported synthetic method is useful to prepare GQDs with controllable fluorescent colors.

Morphology-controlled synthesis of SrTiO₃ micro-scale particles

Cao Jia-Feng (曹加锋), Ji Yue-Xia (冀月霞)

Chin. Phys. B, 2014, 23 (12): 128104. DOI: 10.1088/1674-1056/23/12/128104

Abstract ( 637 )

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A novel and simple strategy of morphology-controlled SrTiO₃ (ST) micro-scale particle synthesis by the flux method is reported. Systematic experiments are designed to realize the tunable morphologies of the particles when the flux salt, sintering process, and the precursors are changed. The ST plates can be synthesized by plate-like Bi₄Ti₃O₁₂ (BIT) precursors in NaCl flux. However, the as-synthesized Bi₄Ti₃O₁₂ grains transform into reticular particles and finally into rods at higher temperature in NaCl and KCl compounds. Besides, cubic ST particles are also prepared using different precursors as a comparative experiment. This study provides a strategy for further investigations in designing the morphology-controlled particles and efficient anisotropic materials of perovskite structure such as ferroelectric and photocatalyst.

Synthesis of multi-walled carbon nanotubes using CoMnMgO catalysts through catalytic chemical vapor deposition

Yang Wen (杨文), Feng Yan-Yan (冯艳艳), Jiang Cheng-Fa (江成发), Chu Wei (储伟)

Chin. Phys. B, 2014, 23 (12): 128201. DOI: 10.1088/1674-1056/23/12/128201

Abstract ( 614 )

PDF (536KB) ( 471 )

The CoMgO and CoMnMgO catalysts are prepared by a co-precipitation method and used as the catalysts for the synthesis of carbon nanotubes (CNTs) through the catalytic chemical vapor deposition (CCVD). The effects of Mn addition on the carbon yield and structure are investigated. The catalysts are characterized by temperature programmed reduction (TPR) and X-ray diffraction (XRD) techniques, and the synthesized carbon materials are characterized by transmission electron microscopy (TEM) and thermo gravimetric analysis (TG). TEM measurement indicates that the catalyst CoMgO enclosed completely in the produced graphite layer results in the deactivation of the catalyst. TG results suggest that the CoMnMgO catalyst has a higher selectivity for CNTs than CoMgO. Meanwhile, different diameters of CNTs are synthesized by CoMnMgO catalysts with various amounts of Co content, and the results show that the addition of Mn avoids forming the enclosed catalyst, prevents the formation of amorphous carbon, subsequently promotes the growth of CNTs, and the catalyst with decreased Co content is favorable for the synthesis of CNTs with a narrow diameter distribution. The CoMnMgO catalyst with 40% Co content has superior catalytic activity for the growth of carbon nanotubes.

A robust power spectrum split cancellation-based spectrum sensing method for cognitive radio systems Suggested by editors

Qi Pei-Han (齐佩汉), Li Zan (李赞), Si Jiang-Bo (司江勃), Gao Rui (高锐)

Chin. Phys. B, 2014, 23 (12): 128401. DOI: 10.1088/1674-1056/23/12/128401

Abstract ( 698 )

PDF (329KB) ( 404 )

Spectrum sensing is an essential component to realize the cognitive radio, and the requirement for real-time spectrum sensing in the case of lacking prior information, fading channel, and noise uncertainty, indeed poses a major challenge to the classical spectrum sensing algorithms. Based on the stochastic properties of scalar transformation of power spectral density (PSD), a novel spectrum sensing algorithm, referred to as the power spectral density split cancellation method (PSC), is proposed in this paper. The PSC makes use of a scalar value as a test statistic, which is the ratio of each subband power to the full band power. Besides, by exploiting the asymptotic normality and independence of Fourier transform, the distribution of the ratio and the mathematical expressions for the probabilities of false alarm and detection in different channel models are derived. Further, the exact closed-form expression of decision threshold is calculated in accordance with Neyman–Pearson criterion. Analytical and simulation results show that the PSC is invulnerable to noise uncertainty, and can achive excellent detection performance without prior knowledge in additive white Gaussian noise and flat slow fading channels. In addition, the PSC benefits from a low computational cost, which can be completed in microseconds.

An analytical model for the vertical electric field distribution and optimization of high voltage REBULF LDMOS

Hu Xia-Rong (胡夏融), Lü Rui (吕瑞)

Chin. Phys. B, 2014, 23 (12): 128501. DOI: 10.1088/1674-1056/23/12/128501

Abstract ( 693 )

PDF (325KB) ( 392 )

In this paper, an analytical model for the vertical electric field distribution and optimization of a high voltage-reduced bulk field (REBULF) lateral double-diffused metal–oxide-semiconductor (LDMOS) transistor is presented. The dependences of the breakdown voltage on the buried n-layer depth, thickness, and doping concentration are discussed in detail. The REBULF criterion and the optimal vertical electric field distribution condition are derived on the basis of the optimization of the electric field distribution. The breakdown voltage of the REBULF LDMOS transistor is always higher than that of a single reduced surface field (RESURF) LDMOS transistor, and both analytical and numerical results show that it is better to make a thick n-layer buried deep into the p-substrate.

Gate-modulated generation–recombination current in n-type metal–oxide–semiconductor field-effect transistor

Chen Hai-Feng (陈海峰)

Chin. Phys. B, 2014, 23 (12): 128502. DOI: 10.1088/1674-1056/23/12/128502

Abstract ( 637 )

PDF (368KB) ( 415 )

Gate-modulated generation–recombination (GMGR) current I_GMGR induced by the interface traps in an n-type metal–oxide–semiconductor field-effect transistor (nMOSFET) is investigated. The generation current is found to expand rightwards with increasing the reversed drain PN junction bias, and the recombination current is enhanced as the forward drain bias increases. The variations of I_GMGR curves are ascribed to the changes of the electron density and hole density at the interface, N_S and P_S, under the different drain bias voltages. Based on an analysis of the physical mechanism, the I_GMGR model is set up by introducing two coefficients (m and t). The coefficients m and t can modulate the curves widths and peak values. The simulated results under reverse mode and forward mode are obviously in agreement with the experimental results. This proves that this model can be applicable for generation current and recombination current and that the theory behind the model is reasonable. The details of the relevant mechanism are given in the paper.

Fabrication and electrical properties of axial and radial GaAs nanowire pn junction diode arrays

Li Jun-Shuai (李军帅), Zhang Xia (张霞), Yan Xin (颜鑫), Chen Xiong (陈雄), Li Liang (李亮), Cui Jian-Gong (崔建功), Huang Yong-Qing (黄永清), Ren Xiao-Min (任晓敏)

Chin. Phys. B, 2014, 23 (12): 128503. DOI: 10.1088/1674-1056/23/12/128503

Abstract ( 778 )

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We report on the fabrications and characterizations of axial and radial GaAs nanowire pn junction diode arrays. The nanowires are grown on n-doped GaAs (111)B substrates using the Au-catalyzed vapor–liquid–solid mechanism by metal–organic chemical vapor deposition (MOCVD). Diethyl–zinc and silane are used as p- and n-type dopant precursors, respectively. Both the axial and radial diodes exhibit diode-like J–V characteristics and have similar performances under forward bias. Under backward bias, the axial diode has a large leakage current, which is attributed to the bending of the pn junction interface induced by two doping mechanisms in Au-catalyzed nanowires. The low leakage current and high rectification ratio make the radial diode more promising in electrical and optoelectronic devices.

Enhanced light emission from InGaN/GaN quantum wells by using surface plasmonic resonances of silver nanoparticle array

Chen Zhan-Xu (陈湛旭), Wan Wei (万巍), Zhang Bai-Jun (张佰君), He Ying-Ji (何影记), Jin Chong-Jun (金崇君)

Chin. Phys. B, 2014, 23 (12): 128504. DOI: 10.1088/1674-1056/23/12/128504

Abstract ( 671 )

PDF (726KB) ( 765 )

The effect of silver nanostructures prepared by nanosphere lithography on the photoluminescence (PL) properties of blue-emitting InGaN/GaN quantum wells (QWs) is studied. Arrays of silver nanoparticles are fabricated to yield a collective surface plasmonic resonance (SPR) near to the QWs emission wavelength. A large enhancement in peak PL intensity is observed, when the induced SPR wavelength of the nanoparticles on the QWs sample matches the QWs emission wavelength. The study proves that the SPRs could enhance the light emission efficiency of semiconductor material.

Effects of A1 site occupation on dielectric and ferroelectric properties of Sr₄CaRTi₃Nb₇O₃₀ (R=Ce, Eu) tungsten bronze ceramics

Fang Yu-Jiao (方玉娇), Gong Gao-Shang (龚高尚), Gebru Zerihun, Yuan Song-Liu (袁松柳)

Chin. Phys. B, 2014, 23 (12): 128701. DOI: 10.1088/1674-1056/23/12/128701

Abstract ( 637 )

PDF (328KB) ( 314 )

Sr₄CaRTi₃Nb₇O₃₀ (R=Ce, Eu) tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of Sr₄CaRTi₃Nb₇O₃₀ (R=Ce, Eu) tetragonal tungsten bronzes are investigated. The Sr₄CaCeTi3Nb₇O₃₀ shows a normal transition behavior due to the closer size ion occupation in A1 sites, which could suppress the distortion of B2 octahedra effectively. Sr₄CaEuTi₃Nb₇O₃₀ ceramic exhibits two dielectric anomalies, which might be related to the fact that the large radius difference between Ca²⁺ and Eu³⁺ could lead to the uneven distribution of Ca²⁺ and Eu³⁺ in A1 sites and form two slightly different kinds of compositions with different transition temperatures in the structure. Our results indicate that the ionic radius difference in A1 sites plays an important role in determining the dielectric and ferroelectric natures of the filled tungsten bronze ceramics. Polarization–electric field (P–E) curves are evaluated at room temperature and both of them show hysteresis loops. Sr₄CaCeTi₃Nb₇O₃₀ shows a fat hysteresis loop, indicating the long-range ferroelectric order in the ceramic. The current density–electric field (J–E) curves are measured at room temperature with a largest leakage current density of ～ 10^-6 A/cm², indicating that their leakage currents are rather low.

Resonance properties of THz plasmonic dipole-bowtie antenna array: The critical role of the substrate

Yang Yu-Ping (杨玉平), Ranjan Singh, Zhang Wei-Li (张伟力)

Chin. Phys. B, 2014, 23 (12): 128702. DOI: 10.1088/1674-1056/23/12/128702

Abstract ( 782 )

PDF (705KB) ( 418 )

Subwavelength arrays of dipole-bowtie antennas are designed and characterized using terahertz time-domain spectroscopy (THz-TDS) and finite element method (FEM) simulations. Two different substrates, silicon and mylar with an order of magnitude difference between their thickness values are used to study the resonance properties of the antennas. The 640-μm thick silicon substrate supports a sharper fundamental mode resonance. We discover that higher-order Fabry–Perot resonances can be excited only in 24-μm thin mylar substrates and show much higher sensitivity to dielectric changes in the environment and the geometrical parameters of the antennas than the fundamental dipole resonance.

Statistics of extreme events in Chinese stock markets Suggested by editors

Wu Gan-Hua (吴干华), Qiu Lu (邱路), Mutua Stephen, Li Xin-Li (李信利), Yang Yue (杨悦), Yang Hui-Jie (杨会杰), Jiang Yan (蒋艳)

Chin. Phys. B, 2014, 23 (12): 128901. DOI: 10.1088/1674-1056/23/12/128901

Abstract ( 769 )

PDF (414KB) ( 362 )

We investigate the impact of financial factors on daily volume recurrent time intervals in the developing Chinese stock markets. The tails of probability distribution functions (PDFs) of volume recurrent intervals behave as a power-law, and the scaling exponent decreases with the increase of stock lifetime, which are similar to those in the US stock markets, and they are typical representatives of developed markets. The difference is that the power-law exponent values remain almost the same with the changes of market capitalization, mean volume, and mean trading value, respectively. These findings enrich the results for event statistics for financial markets.

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