Table of contents

15 April 2014, Volume 23 Issue 4 Previous issue    Next issue

GENERAL

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An approximation for the boundary optimal control problem of a heat equation defined in a variable domain Yu Xin (于欣), Ren Zhi-Gang (任志刚), Xu Chao (许超) Chin. Phys. B, 2014, 23 (4):  040201.  DOI: 10.1088/1674-1056/23/4/040201 Abstract ( 695 )   PDF (270KB) ( 385 )   In this paper, we consider a numerical approximation for the boundary optimal control problem with the control constraint governed by a heat equation defined in a variable domain. For this variable domain problem, the boundary of the domain is moving and the shape of the boundary is defined by a known time-dependent function. By making use of the Galerkin finite element method, we first project the original optimal control problem into a semi-discrete optimal control problem governed by a system of ordinary differential equations. Then, based on the aforementioned semi-discrete problem, we apply the control parameterization method to obtain an optimal parameter selection problem governed by a lumped parameter system, which can be solved as a nonlinear optimization problem by a Sequential Quadratic Programming (SQP) algorithm. The numerical simulation is given to illustrate the effectiveness of our numerical approximation for the variable domain problem with the finite element method and the control parameterization method.

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A class of asymptotic solution for the time delay wind field model of an ocean Zhou Xian-Chun (周先春), Shi Lan-Fang (石兰芳), Mo Jia-Qi (莫嘉琪) Chin. Phys. B, 2014, 23 (4):  040202.  DOI: 10.1088/1674-1056/23/4/040202 Abstract ( 463 )   PDF (1666KB) ( 327 )   A time delay model of a two-layer barotropic ocean with Rayleigh dissipation is built. Using the improved perturbation method, an analytic asymptotic solution of a better approximate degree is obtained in the mid-latitude wind field, and the physical meaning of the corresponding solution is also discussed.

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A meshless method based on moving Kriging interpolation for a two-dimensional time-fractional diffusion equation Ge Hong-Xia (葛红霞), Cheng Rong-Jun (程荣军) Chin. Phys. B, 2014, 23 (4):  040203.  DOI: 10.1088/1674-1056/23/4/040203 Abstract ( 785 )   PDF (514KB) ( 905 )   Fractional diffusion equations have been the focus of modeling problems in hydrology, biology, viscoelasticity, physics, engineering, and other areas of applications. In this paper, a meshfree method based on the moving Kriging interpolation is developed for a two-dimensional time-fractional diffusion equation. The shape function and its derivatives are obtained by the moving Kriging interpolation technique. For possessing the Kronecker delta property, this technique is very efficient in imposing the essential boundary conditions. The governing time-fractional diffusion equations are transformed into a standard weak formulation by the Galerkin method. It is then discretized into a meshfree system of time-dependent equations, which are solved by the standard central difference method. Numerical examples illustrating the applicability and effectiveness of the proposed method are presented and discussed in detail.

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Scheme for generating a cluster-type entangled squeezed vacuum state via cavity QED Wen Jing-Ji (文晶姬), Yeon Kyu-Hwang, Wang Hong-Fu (王洪福), Zhang Shou (张寿) Chin. Phys. B, 2014, 23 (4):  040301.  DOI: 10.1088/1674-1056/23/4/040301 Abstract ( 612 )   PDF (370KB) ( 437 )   A scheme is proposed to generate an N-qubit cluster-type entangled squeezed vacuum state (CTESVS) based on the two-photon interaction between a two-level atom and the cavity fields with the cavity QED system. The CTESVS in N separate cavities can be effectively obtained after performing a simple one-qubit measurement on the atom. The influence of cavity decay on the CTESVS is also discussed.

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Nonlocal non-Markovian effects in dephasing environments Xie Dong (谢东), Wang An-Min (王安民) Chin. Phys. B, 2014, 23 (4):  040302.  DOI: 10.1088/1674-1056/23/4/040302 Abstract ( 390 )   PDF (278KB) ( 351 )   We study the nonlocal non-Markovian effects through local interactions between two subsystems and the corresponding two environments. It has been found that the initial correlations between two environments can turn a Markovian to a non-Markovian regime with extra control on the local interaction time. We further research the nonlocal non-Markovian effects from two situations: without extra control, the nonlocal non-Markovian effects only appear under the condition that two local dynamics are non-Markovian-non-Markovian (both of the two local dynamics are non-Markovian) or Markovian-non-Markovian, but not under the condition of Markovian-Markovian; with extra control, the nonlocal non-Markovian effects can occur under the condition of Markovian-Markovian. It shows that the function of correlations between two environments has an upper bound, which makes a flow of information from the environment back to the global system beginning finitely earlier than that back to one of the two local systems, not infinitely. Then, we proposed two special ways to distribute classical correlations between two environments without initial correlations. Finally, from numerical solutions in the spin star configuration, we found that the self-correlation (internal correlation) of each environment promotes the nonlocal non-Markovian effects.

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Engineering steady-state entanglement for two atoms held in separate cavities through laser cooling Shen Li-Tuo (沈利托), Chen Rong-Xin (陈荣鑫), Wu Huai-Zhi (吴怀志), Yang Zhen-Biao (杨贞标) Chin. Phys. B, 2014, 23 (4):  040303.  DOI: 10.1088/1674-1056/23/4/040303 Abstract ( 711 )   PDF (355KB) ( 414 )   We propose a scheme to prepare the steady-state entanglement for two atoms, which are held in separate cavities that are coupled through a short optical fiber or optical resonator. The entangled steady-state with a high fidelity can be achieved even with a low cooperativity parameter, by making use of the driving laser fields. Such a cooling mechanism is based on a resonant laser pump of the unwanted ground states to the excited states, which finally decay to the desired steady-state.

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Implementation of a nonlocal N-qubit conditional phase gate using the nitrogen-vacancy center and microtoroidal resonator coupled systems Cao Cong (曹聪), Liu Gang (刘刚), Zhang Ru (张茹), Wang Chuan (王川) Chin. Phys. B, 2014, 23 (4):  040304.  DOI: 10.1088/1674-1056/23/4/040304 Abstract ( 589 )   PDF (371KB) ( 389 )   Implementation of a nonlocal multi-qubit conditional phase gate is an essential requirement in some quantum information processing (QIP) tasks. Recently, a novel solid-state cavity quantum electrodynamics (QED) system, in which the nitrogen-vacancy (NV) center in diamond is coupled to a microtoroidal resonator (MTR), has been proposed as a potential system for hybrid quantum information and computing. By virtue of such systems, we present a scheme to realize a nonlocal N-qubit conditional phase gate directly. Our scheme employs a cavity input-output process and single-photon interference, without the use of any auxiliary entanglement pair or classical communication. Considering the currently available technologies, our scheme might be quite useful among different nodes in quantum networks for large-scaled QIP.

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Analysis of dynamical properties for the two-site Bose–Hubbard model with an algebraic method Meng Xiang-Jia (孟祥佳), Feng Hai-Ran (冯海冉), Zheng Yu-Jun (郑雨军) Chin. Phys. B, 2014, 23 (4):  040305.  DOI: 10.1088/1674-1056/23/4/040305 Abstract ( 944 )   PDF (1373KB) ( 761 )   In this work, we propose an algebraic recursion method to study the dynamical evolution of the two-site Bose-Hubbard model. We analyze its properties from the viewpoints of single partite purity, energy, and trace distance, in which the model is considered as a typical bipartite system. The analytical expressions for the quantities are derived. We show that the purity can well reflect the transition between different regimes for the system. In addition, we demonstrate that the transition from the delocalization regime to the self-trapping regime with the ratio η increasing not only happens for an initially local state but also for any initial states. Furthermore, we confirm that the dynamics of the system presents a periodicity for η=0 and the period is tc=π/2J when the initial state is symmetric.

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Instability, adiabaticity, and controlling effects of external fields for the dark state in a homonuclear atom–tetramer conversion system Meng Shao-Ying (孟少英), Chen Xi-Hao (陈希浩), Wu Wei (吴炜), Fu Li-Bin (傅立斌) Chin. Phys. B, 2014, 23 (4):  040306.  DOI: 10.1088/1674-1056/23/4/040306 Abstract ( 559 )   PDF (517KB) ( 395 )   In the present paper, we investigate the instability, adiabaticity, and controlling effects of external fields for a dark state in a homonuclear atom-tetramer conversion that is implemented by a generalized stimulated Raman adiabatic passage. We analytically obtain the regions for the appearance of dynamical instability and study the adiabatic evolution by a newly defined adiabatic fidelity. Moreover, the effects of the external field parameters and the spontaneous emissions on the conversion efficiency are also investigated.

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Preparation of multi-photon Fock states and quantum entanglement properties in circuit QED Ji Ying-Hua (嵇英华), Hu Ju-Ju (胡菊菊) Chin. Phys. B, 2014, 23 (4):  040307.  DOI: 10.1088/1674-1056/23/4/040307 Abstract ( 539 )   PDF (290KB) ( 521 )   We demonstrate the controllable generation of multi-photon Fock states in circuit quantum electrodynamics (circuit QED). The external bias flux regulated by a counter can effectively adjust the bias time on each superconducting flux qubit so that each flux qubit can pass in turn through the circuit cavity and thereby avoid the effect of decoherence. We further investigate the quantum correlation dynamics of coupling superconducting qubits in a Fock state. The results reveal that the lower the photon number of the light field in the number state, the stronger the interaction between qubits is, then the more beneficial to maintaining entanglement between qubits it will be.

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Supergravity-induced interactions on thick branes Nejat T. Yılmaz Chin. Phys. B, 2014, 23 (4):  040401.  DOI: 10.1088/1674-1056/23/4/040401 Abstract ( 333 )   PDF (287KB) ( 227 )   The gravity coupling of the symmetric space sigma model is studied in the solvable Lie algebra parametrization. The corresponding Einstein equations are derived and the energy-momentum tensor is calculated. The results are used to derive the dynamical equations of the warped five-dimensional (5D) geometry for localized bulk scalar interactions in the framework of thick brane world models. The Einstein and scalar field equations are derived for flat brane geometry in the context of minimal and non-minimal gravity-bulk scalar couplings.

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Classical interpretations of relativistic precessions Sankar Hajra Chin. Phys. B, 2014, 23 (4):  040402.  DOI: 10.1088/1674-1056/23/4/040402 Abstract ( 674 )   PDF (1882KB) ( 1414 )   Relativists have exposed various precessions and developed ingenious experiments to verify those phenomena with extreme precisions. The Gravity Probe B mission was designed to study the precessions of the gyroscopes rotating round the Earth in a nearly circular near-Earth polar orbit to demonstrate the geodetic effect and the Lense-Thirring effect as predicted by the general relativity theory. In this paper, we show in a very simple and novel analysis that the precession of the perihelion of Mercury, the Thomas precession, and the precession data (on the de Sitter and Lense-Thirring precessions) collected from the Gravity Probe B mission could easily be explained from classical physics, too.

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Solution of Dirac equation around a charged rotating black hole Lü Yan (吕嫣), Hua Wei (花巍) Chin. Phys. B, 2014, 23 (4):  040403.  DOI: 10.1088/1674-1056/23/4/040403 Abstract ( 661 )   PDF (271KB) ( 367 )   The aim of this paper is to solve the radial parts of a Dirac equation in Kerr-Newman (KN) geometry. The potential is replaced by a collection of step functions, then the reflection and transmission coefficients as well as the solution of the wave equation are obtained by using a quantum mechanical method. The result shows that the waves with different values of mass will be scatted off very differently.

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Robust H∞ cluster synchronization analysis of Lurie dynamical networks Guo Ling (郭凌), Nian Xiao-Hong (年晓红), Pan Huan (潘欢), Bing Zhi-Tong (邴志桐) Chin. Phys. B, 2014, 23 (4):  040501.  DOI: 10.1088/1674-1056/23/4/040501 Abstract ( 718 )   PDF (1336KB) ( 478 )   The cluster synchronization problem of complex dynamical networks with each node being a Lurie system with external disturbances and time-varying delay is investigated in this paper. Some criteria for cluster synchronization with desired H∞ performance are presented by using a local linear control scheme. Firstly, sufficient conditions are established to realize cluster synchronization of the Lurie dynamical networks without time delay. Then, the notion of the cluster synchronized region is introduced, and some conditions guaranteeing the cluster synchronized region and unbounded cluster synchronized region are derived. Furthermore, the cluster synchronization and cluster synchronized region in the Lurie dynamical networks with time-varying delay are considered. Numerical examples are finally provided to verify and illustrate the theoretical results.

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Function projective lag synchronization of fractional-order chaotic systems Wang Sha (王莎), Yu Yong-Guang (于永光), Wang Hu (王虎), Ahmed Rahmani Chin. Phys. B, 2014, 23 (4):  040502.  DOI: 10.1088/1674-1056/23/4/040502 Abstract ( 615 )   PDF (811KB) ( 644 )   Function projective lag synchronization of different structural fractional-order chaotic systems is investigated. It is shown that the slave system can be synchronized with the past states of the driver up to a scaling function matrix. According to the stability theorem of linear fractional-order systems, a nonlinear fractional-order controller is designed for the synchronization of systems with the same and different dimensions. Especially, for two different dimensional systems, the synchronization is achieved in both reduced and increased dimensions. Three kinds of numerical examples are presented to illustrate the effectiveness of the scheme.

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Collective composite-rotating consensus of multi-agent systems Lin Peng (林鹏), Lu Wan-Ting (卢婉婷), Song Yong-Duan (宋永端) Chin. Phys. B, 2014, 23 (4):  040503.  DOI: 10.1088/1674-1056/23/4/040503 Abstract ( 431 )   PDF (303KB) ( 461 )   This paper investigates a distributed composite-rotating consensus problem of second-order multi-agent systems, where all agents move in a nested circular orbit. A distributed control law is proposed which contains two parts: the local state feedback that guarantees the circular motion and the distributed relative state feedback that guarantees the consensus of all agents. A sufficient condition is derived to drive all agents as well as ensure their circle centers make circular motion in a distributed manner. Finally, a numerical simulation is included to demonstrate our theoretical results.

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Structure identification of an uncertain network coupled with complex-variable chaotic systems via adaptive impulsive control Liu Dan-Feng (刘丹峰), Wu Zhao-Yan (吴召艳), Ye Qing-Ling (叶青伶) Chin. Phys. B, 2014, 23 (4):  040504.  DOI: 10.1088/1674-1056/23/4/040504 Abstract ( 567 )   PDF (566KB) ( 409 )   In this paper, structure identification of an uncertain network coupled with complex-variable chaotic systems is investigated. Both the topological structure and the system parameters can be unknown and need to be identified. Based on impulsive stability theory and the Lyapunov function method, an impulsive control scheme combined with an adaptive strategy is adopted to design effective and universal network estimators. The restriction on the impulsive interval is relaxed by adopting an adaptive strategy. Further, the proposed method can monitor the online switching topology effectively. Several numerical simulations are provided to illustrate the effectiveness of the theoretical results.

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Further studies on stability analysis of nonlinear Roesser-type two-dimensional systems Dai Xiao-Lin (代小林) Chin. Phys. B, 2014, 23 (4):  040701.  DOI: 10.1088/1674-1056/23/4/040701 Abstract ( 582 )   PDF (628KB) ( 597 )   This paper is concerned with further relaxations of the stability analysis of nonlinear Roesser-type two-dimensional (2D) systems in the Takagi-Sugeno fuzzy form. To achieve the goal, a novel slack matrix variable technique, which is homogenous polynomially parameter-dependent on the normalized fuzzy weighting functions with arbitrary degree, is developed and the algebraic properties of the normalized fuzzy weighting functions are collected into a set of augmented matrices. Consequently, more information about the normalized fuzzy weighting functions is involved and the relaxation quality of the stability analysis is significantly improved. Moreover, the obtained result is formulated in the form of linear matrix inequalities, which can be easily solved via standard numerical software. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed result.

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Energy dissipation of a ring-like metal rubber isolator Yan Hui (闫辉), Zhang Wen-Jing (张文静), Jiang Hong-Yuan (姜洪源), Chen Liang (陈亮) Chin. Phys. B, 2014, 23 (4):  040702.  DOI: 10.1088/1674-1056/23/4/040702 Abstract ( 637 )   PDF (326KB) ( 441 )   Metal rubber (MR) is a kind of homogeneous poroelastic damping material made of metal wire. In this paper, by analyzing the forces on the MR isolator and the MR element, the hysteresis loops of the force and deformation are studied and verified by experiments. The results show that the force and displacement hysteresis loop of the MR isolator is described by the force and deformation hysteresis loops of the MR elements. In addition, the relationship between the energy dissipation coefficient of the MR element and that of the MR isolator is derived. The energy dissipation coefficient is programmed and calculated by MATLAB using experimental data, and the results are compared with the theoretical value. It is the basis for the design and applied research of the MR isolator in a future study.

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Theoretical analysis of stack gas emission velocity measurement by optical scintillation Yang Yang (杨阳), Dong Feng-Zhong (董凤忠), Ni Zhi-Bo (倪志波), Pang Tao (庞涛), Zeng Zong-Yong (曾宗泳), Wu Bian (吴边), Zhang Zhi-Rong (张志荣) Chin. Phys. B, 2014, 23 (4):  040703.  DOI: 10.1088/1674-1056/23/4/040703 Abstract ( 721 )   PDF (574KB) ( 303 )   Theoretical analysis for an online measurement of the stack gas flow velocity based on the optical scintillation method with a structure of two parallel optical paths is performed. The causes of optical scintillation in a stack are first introduced. Then, the principle of flow velocity measurement and its mathematical expression based on cross correlation of the optical scintillation are presented. The field test results show that the flow velocity measured by the proposed technique in this article is consistent with the value tested by the Pitot tube. It verifies the effectiveness of this method. Finally, by use of the structure function of logarithmic light intensity fluctuations, the theoretical explanation of optical scintillation spectral characteristic in low frequency is given. The analysis of the optical scintillation spectrum provides the basis for the measurement of the stack gas flow velocity and particle concentration simultaneously.

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A study of transition from n-to p-type based on hexagonal WO3 nanorods sensor Wu Ya-Qiao (武雅乔), Hu Ming (胡明), Wei Xiao-Ying (韦晓莹) Chin. Phys. B, 2014, 23 (4):  040704.  DOI: 10.1088/1674-1056/23/4/040704 Abstract ( 835 )   PDF (885KB) ( 1211 )   Hexagonal WO3 nanorods are fabricated by a facile hydrothermal process at 180 ℃ using sodium tungstate and sodium chloride as starting materials. The morphology, structure, and composition of the prepared nanorods are studied by scanning electron microscopy, X-ray diffraction spectroscopy, and energy dispersive spectroscopy. It is found that the agglomeration of the nanorods is strongly dependent on the PH value of the reaction solution. Uniform and isolated WO3 nanorods with diameters ranging from 100 nm-150 nm and lengths up to several micrometers are obtained at PH=2.5 and the nanorods are identified as being hexagonal in phase structure. The sensing characteristics of the WO3 nanorod sensor are obtained by measuring the dynamic response to NO2 with concentrations in the range 0.5 ppm-5 ppm and at working temperatures in the range 25 ℃-250 ℃. The obtained WO3 nanorods sensors are found to exhibit opposite sensing behaviors, depending on the working temperature. When being exposed to oxidizing NO2 gas, the WO3 nanorod sensor behaves as an n-type semiconductor as expected when the working temperature is higher than 50 ℃, whereas, it behaves as a p-type semiconductor below 50 ℃. The origin of the n-to p-type transition is correlated with the formation of an inversion layer at the surface of the WO3 nanorod at room temperature. This finding is useful for making new room temperature NO2 sensors based on hexagonal WO3 nanorods.

ATOMIC AND MOLECULAR PHYSICS

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First-principles study on anatase TiO2 (101) surface adsorption of NO Feng Qing (冯庆), Yue Yuan-Xia (岳远霞), Wang Wei-Hua (王渭华), Zhu Hong-Qiang (朱洪强) Chin. Phys. B, 2014, 23 (4):  043101.  DOI: 10.1088/1674-1056/23/4/043101 Abstract ( 560 )   PDF (1108KB) ( 1143 )   In this paper, the stable structure and the electronic and optical properties of nitric oxide (NO) adsorption on the anatase TiO2 (101) surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV (N end adsorption), 2.6770 eV (O end adsorption), and 4.1437 eV (horizontal adsorption). The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 (101) surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 (101) surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.

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Origin of diffraction fringes in two-dimensional photoelectronmomentum distributions for single ionization of atoms in few-cycle intense laser pulses Guo Zhi-Jian (郭志坚), Chen Zhang-Jin (陈长进), Zhou Xiao-Xin (周效信) Chin. Phys. B, 2014, 23 (4):  043201.  DOI: 10.1088/1674-1056/23/4/043201 Abstract ( 469 )   PDF (1326KB) ( 409 )   We use the strong field approximation with a time window function controlling the release time of electrons to study the intra-cycle and inter-cycle interferences in few-cycle intense laser pulses impinging on He. The diffraction fringes, i.e., the vertical stripe-like structure, observed in the experimental two-dimensional photoelectron momentum distributions of Gopal et al. (2009 Phys. Rev. Lett. 103 053001) have been attributed to the interplay of the intra-and inter-cycle interferences. The pure numerical calculations by solving the time-dependent Schrödinger equation are also performed and the results are compared with the experimental measurements directly. It has been found that the position of the stripe-like structure can be used to determine the duration of the laser pulses used in experiments.

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Isolated sub-30-attosecond pulse generation using a multicycle two-color chirped laser and a static electric field Zhang Gang-Tai (张刚台) Chin. Phys. B, 2014, 23 (4):  043202.  DOI: 10.1088/1674-1056/23/4/043202 Abstract ( 513 )   PDF (1108KB) ( 723 )   We present a theoretical investigation of high-order harmonic generation in a chirped two-color laser field, which is synthesized by a 10-fs/800-nm fundamental chirped pulse and a 10-fs/1760-nm subharmonic pulse. It is shown that a supercontinuum can be produced using the multicycle two-color chirped field. However, the supercontinuum reveals a strong modulation structure, which is not good for the generation of an isolated attosecond pulse. By adding a static electric field to the multicycle two-color chirped field, not only the harmonic cutoff is extended remarkably, but also the quantum paths of the high-order harmonic generation (HHG) are modified significantly. As a result, both the extension of the supercontinuum and the selection of a single quantum path are achieved, producing an isolated 23-as pulse with a bandwidth of about 170.6 eV. Furthermore, the influences of the laser intensities on the supercontinuum and isolated attosecond pulse generation are investigated.

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Quasi-classical trajectory study of the isotope effect on the stereodynamics in the reaction H(2S)+CH(X2Π; v=0, j=1)→C(1D)+H2(X1Σg+) Wang Yun-Hui (王允辉), Xiao Chuan-Yun (肖传云), Deng Kai-Ming (邓开明), Lu Rui-Feng (陆瑞锋) Chin. Phys. B, 2014, 23 (4):  043401.  DOI: 10.1088/1674-1056/23/4/043401 Abstract ( 570 )   PDF (2252KB) ( 442 )   The isotope effect on the stereodynamic properties in the title reaction is investigated by a quasi-classical trajectory (QCT) method on the 11A' potential energy surface at a collision energy of 23.06 kcal/mol. The angular distributions P(θr), P(ør), P(θr, ør), and the polarization-dependent generalized differential cross sections are calculated, which demonstrate the observable influences on the rotational polarization of the product by the isotopic substitution of H with D.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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Electromagnetic Bloch oscillation in one-dimensional multiple microcavities composed of metamaterials Wang Tong-Biao (王同标), Liu Nian-Hua (刘念华), Yu Tian-Bao (于天宝), Deng Xin-Hua (邓新华), Xu Xu-Ming (徐旭明), Liao Qing-Hua (廖清华) Chin. Phys. B, 2014, 23 (4):  044101.  DOI: 10.1088/1674-1056/23/4/044101 Abstract ( 438 )   PDF (574KB) ( 354 )   We propose a photonic structure stacked sequentially by one-dimensional photonic crystals and cavities. The whole structure is composed of single-negative and double-negative materials. The optical Wannier-Stark ladder (WSL) can be obtained in a low frequency region by modulating the widths of the cavities in order. We simulate the dynamical behavior of the electromagnetic wave passing through the proposed photonic structure. Due to the dispersive characteristics of the metamaterials, a very narrow WSL can be obtained. The long-period electromagnetic Bloch oscillation is demonstrated theoretically to have a period on a microsecond time scale.

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Tight focusing of axially symmetric polarized vortex beams Zhou Zhe-Hai (周哲海), Guo Yang-Kuan (郭阳宽), Zhu Lian-Qing (祝连庆) Chin. Phys. B, 2014, 23 (4):  044201.  DOI: 10.1088/1674-1056/23/4/044201 Abstract ( 634 )   PDF (11097KB) ( 2031 )   Tight focusing of axially symmetric polarized vortex beams is studied numerically based on vector diffraction theory. The mathematical expressions for the focused fields are derived. Simulation results show that the focused fields and phase distributions at focus are largely influenced by both the polarization order and topological charge of the incident beams. Moreover, focal spots with flat-topped or tightly-focused patterns can be flexibly achieved by carefully choosing the polarization order and the topological charge, which confirms the potential of such beams in wide applications, such as optical tweezers, laser printing, lithography, and material processing.

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Quadripartite entangled state from cascaded second-harmonic generation Yang Rui (杨瑞), Zhai Shu-Qin (翟淑琴), Yang Rong-Guo (杨荣国) Chin. Phys. B, 2014, 23 (4):  044202.  DOI: 10.1088/1674-1056/23/4/044202 Abstract ( 730 )   PDF (262KB) ( 388 )   A generation system of continuous-variable (CV) quadripartite entangled state based on two cascaded second-harmonic generation (SHG) cavities below the threshold is investigated. Two reflected fundamental beams of the first cavity, the reflected second-harmonic beam and the output fourth-harmonic beam of the second cavity are proved to be entangled, and the dependence of the entanglement degree on the normalized frequency, pump parameter, fourth-harmonic loss parameter, and second-harmonic loss parameter is also analyzed. Due to the fact that the cavity parameters and the nonlinear crystals of the two SHG cavities can be freely chosen, the practicality of the proposed protocol is relatively perfect and the system can also be extended to the preparation of multicolor entangled states for a quantum network.

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Output three-mode entanglement via coherently prepared inverted Y-type atoms Wang Fei (王飞), Qiu Jing (邱晶) Chin. Phys. B, 2014, 23 (4):  044203.  DOI: 10.1088/1674-1056/23/4/044203 Abstract ( 479 )   PDF (593KB) ( 355 )   In this paper, the output quantum correlations of three fields interacting with inverted Y-type atoms inside a three-mode cavity are investigated. By numerically calculating the stationary noise spectra of the fields, we show that it is possible to generate the genuine tripartite continuous variable entanglement outside the cavity by coherently preparing the atoms in a superposition of the upper excited state and two ground states initially. Our numerical results demonstrate that both zero frequency entanglement and sideband frequency entanglement can be obtained under different initial coherent conditions. In addition, we investigate the thermal fluctuation effects on the quantum entanglement. It is found out that the entanglement occurring in a high frequency regime is more robust against thermal noise than the zero frequency entanglement, which may be useful for quantum communication.

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Laser-polarization-dependent spontaneous emission of the zero phonon line from single nitrogen–vacancy center in diamond Zhang Duo (张多), Li Jia-Hua (李家华), Yang Xiao-Xue (杨晓雪) Chin. Phys. B, 2014, 23 (4):  044204.  DOI: 10.1088/1674-1056/23/4/044204 Abstract ( 594 )   PDF (357KB) ( 413 )   We investigate spontaneous emission properties and control of the zero phonon line (ZPL) from a diamond nitrogen-vacancy (NV) center coherently driven by a single elliptically polarized control field. We use the Schrödinger equation to calculate the probability amplitudes of the wave function of the coupled system and derive analytical expressions of the spontaneous emission spectra. The numerical results show that a few interesting phenomena such as enhancement, narrowing, suppression, and quenching of the ZPL spontaneous emission can be realized by modulating the polarization-dependent phase, the Zeeman shift, and the intensity of the control field in our system. In the dressed-state picture of the control field, we find that multiple spontaneously generated coherence arises due to three close-lying states decaying to the same state. These results are useful in real experiments.

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Phase control of light amplification in steady and transient processes in an inverted-Y atomic system with spontaneously generated coherence Tian Si-Cong (田思聪), Tong Cun-Zhu (佟存柱), Wan Ren-Gang (万仁刚), Ning Yong-Qiang (宁永强), Qin Li (秦丽), Liu Yun (刘云), Wang Li-Jun (王立军), Zhang Hang (张航), Wang Zeng-Bin (王增斌), Gao Jin-Yue (高锦岳) Chin. Phys. B, 2014, 23 (4):  044205.  DOI: 10.1088/1674-1056/23/4/044205 Abstract ( 525 )   PDF (494KB) ( 394 )   We investigate the effects of spontaneously generated coherence (SGC) on both the steady and transient gain properties in a four-level inverted-Y-type atomic system in the presence of a weak probe, two strong coherent fields, and an incoherent pump. For the steady process, we find that the inversionless gain mainly origins from SGC. In particular, we can modulate the inversionless gain by changing the relative phase between the two fields. Moreover, the amplitude of the gain peak can be enhanced and the additional gain peak can appear by changing the detuning of the coupling field. As for the transient process, the transient gain properties can also be dramatically affected by the SGC. Compared to the case without SGC, the transient gain can be greatly enhanced with completely eliminated transient absorption by choosing the proper relative phase between the two fields. And the inverted-Y-type system with SGC can be simulated in both atomic and semiconductor quantum well systems avoiding the conditions of SGC.

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Gigahertz longitudinal acoustic phonons originating from ultrafast ligand field transitions in hematite thin films Xu Yue (徐悦), Jin Zuan-Ming (金钻明), Zhang Zheng-Bing (张郑兵), Zhang Ze-Yu (张泽宇), Lin Xian (林贤), Ma Guo-Hong (马国宏), Cheng Zhen-Xiang (程振祥) Chin. Phys. B, 2014, 23 (4):  044206.  DOI: 10.1088/1674-1056/23/4/044206 Abstract ( 505 )   PDF (928KB) ( 948 )   The creation and propagation of longitudinal acoustic phonons (LAPs) in high quality hematite thin films (α-Fe2O3) epitaxially grown on different substrates (BaTiO3, SrTiO3, and LaAlO3) are investigated using the femtosecond pump-probe technique. Transient reflection measurements (ΔR/R) indicate the photo-excited electron dynamics, and the initial decay less than 1 ps and the slow decay of ～ 500 ps are attributed to the electron-LO phonon coupling and electron-hole nonradiative recombination, respectively. LAPs in α-Fe2O3 film can be created by ultrafast excitation of the ligand field state, such as the ligand field transitions under 800-nm excitation as well as the ligand to metal charge-transfer with 400-nm excitation. The strain modulations of the sound velocity and the out-of-plane elastic properties are demonstrated in α-Fe2O3 film on different substrates.

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Extreme narrow photonic passbands generated from defective two-segment-connected triangular waveguide networks Tang Zhen-Xing (汤振兴), Yang Xiang-Bo (杨湘波), Lu Jian (卢剑), Liu Timon Cheng-Yi (刘承宜) Chin. Phys. B, 2014, 23 (4):  044207.  DOI: 10.1088/1674-1056/23/4/044207 Abstract ( 516 )   PDF (475KB) ( 432 )   In this paper, we investigate the optical transmission properties of perfect and defective two-segment-connected triangular waveguide networks (2SCTWNs) and find that after introducing defects in networks, many groups of transparent extreme narrow photonic passbands (ENPPs) will be created in the middle of the transmission spectra, the number for each group and the group number of ENPPs can be adjusted by the matching ratios of waveguide length (MRWLs), the number of defects, and the number of unit cells of 2SCTWNs. The influences of MRWL, number of defects, and number of unit cells on the number, width, and position of these ENPPs are researched and a series of quantitative rules and properties are obtained. It may be useful for the designing of high-sensitive optical switches, wavelength division multiplexers, extreme-narrowband filters, and other correlative waveguide network devices.

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Exact solutions and linear stability analysis for two-dimensional Ablowitz–Ladik equation Zhang Jin-Liang (张金良), Wang Hong-Xian (王红县) Chin. Phys. B, 2014, 23 (4):  044208.  DOI: 10.1088/1674-1056/23/4/044208 Abstract ( 797 )   PDF (5446KB) ( 521 )   The Ablowitz-Ladik equation is a very important model in nonlinear mathematical physics. In this paper, the hyperbolic function solitary wave solutions, the trigonometric function periodic wave solutions, and the rational wave solutions with more arbitrary parameters of two-dimensional Ablowitz-Ladik equation are derived by using the (G'/G)-expansion method, and the effects of the parameters (including the coupling constant and other parameters) on the linear stability of the exact solutions are analysed and numerically simulated.

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Design on a highly birefringent and nonlinear photonic crystal fiber in the C waveband Li Duan-Ming (李端明), Zhou Gui-Yao (周桂耀), Xia Chang-Ming (夏长明), Wang Chao (王超), Yuan Jin-Hui (苑金辉) Chin. Phys. B, 2014, 23 (4):  044209.  DOI: 10.1088/1674-1056/23/4/044209 Abstract ( 756 )   PDF (1078KB) ( 376 )   In this paper, a novel photonic crystal fiber (PCF) with high birefringence and nonlinearity is designed. The characteristics of birefringence, dispersion and nonlinearity are studied by using the full-vector finite element method (FVFEM). The numerical results show that the phase birefringence and nonlinear coefficient of PCF can be up to 4.51×10-3 and 32.8972 W-1·km-1 at 1.55 μm, respectively. The proposed PCF could be found to have important applications in the polarization-dependent nonlinear optics such as the pulse compress and reshaping in the C waveband.

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Novel wavelength-accurate InP-based arrayed waveguide grating Pan Pan (潘盼), An Jun-Ming (安俊明), Wang Hong-Jie (王红杰), Wang Yue (王玥), Zhang Jia-Shun (张家顺), Wang Liang-Liang (王亮亮), Dai Hong-Qing (代红庆), Zhang Xiao-Guang (张晓光), Wu Yuan-Da (吴远大), Hu Xiong-Wei (胡雄伟) Chin. Phys. B, 2014, 23 (4):  044210.  DOI: 10.1088/1674-1056/23/4/044210 Abstract ( 451 )   PDF (549KB) ( 491 )   A 13-channel, InP-based arrayed waveguide grating (AWG) is designed and fabricated in which the on-chip loss of the central channel is about-5 dB and the crosstalk is less than-23 dB in the center of the spectrum response. However, the central wavelength and channel spacing are deviated from the design values. To improve their accuracy, an optimized design is adopted to compensate the process error. As a result, the central wavelength 1549.9 nm and channel spacing 1.59 nm are obtained in the experiment, while their design values are 1549.32 nm and 1.6 nm, respectively. The route capability and thermo-optic characteristic of the AWG are also discussed in detail.

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Design optimization of highly efficient spectrum-splitting and beam-concentrating diffractive optical element for lateral multijunction solar cells Hot! Wang Jin-Ze (王进泽), Ye Jia-Sheng (叶佳声), Huang Qing-Li (黄庆礼), Xu Xin (许信), Li Dong-Mei (李冬梅), Meng Qing-Bo (孟庆波), Yang Guo-Zhen (杨国桢) Chin. Phys. B, 2014, 23 (4):  044211.  DOI: 10.1088/1674-1056/23/4/044211 Abstract ( 510 )   PDF (431KB) ( 359 )   Two improved algorithms are proposed to extend a diffractive optical element (DOE) to work under the broad spectrum of sunlight. An optimum design has been found for the DOE, with a weighted average optical efficiency of about 6.8% better than that of the previous design. The optimization of designing high optical efficiency DOEs will pave the way for future designs of high-efficiency, low-cost lateral multijunction solar cells based on such a DOE.

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Nonlinear effect of the structured light profilometry in the phase-shifting method and error correction Zhang Wan-Zhen (张万祯), Chen Zhe-Bo (陈浙泊), Xia Bin-Feng (夏彬峰), Lin Bin (林斌), Cao Xiang-Qun (曹向群) Chin. Phys. B, 2014, 23 (4):  044212.  DOI: 10.1088/1674-1056/23/4/044212 Abstract ( 579 )   PDF (812KB) ( 599 )   Digital structured light (SL) profilometry is increasingly used in three-dimensional (3D) measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measurement accuracy. In this paper, first, we review the nonlinear effects of the projector-camera system in the phase-shifting structured light depth measurement method. We show that high order harmonic wave components lead to phase error in the phase-shifting method. Then a practical method based on frequency domain filtering is proposed for nonlinear error reduction. By using this method, the nonlinear calibration of the SL system is not required. Moreover, both the nonlinear effects of the projector and the camera can be effectively reduced. The simulations and experiments have verified our nonlinear correction method.

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Application of the new pattern recognition system in the new e-nose to detecting Chinese spirits Gu Yu (谷宇), Li Qiang (李强) Chin. Phys. B, 2014, 23 (4):  044213.  DOI: 10.1088/1674-1056/23/4/044213 Abstract ( 747 )   PDF (505KB) ( 492 )   We present a new pattern recognition system based on moving average and linear discriminant analysis (LDA), which can be used to process the original signal of the new polymer quartz piezoelectric crystal air-sensitive sensor system we designed, called the new e-nose. Using the new e-nose, we obtain the template datum of Chinese spirits via a new pattern recognition system. To verify the effectiveness of the new pattern recognition system, we select three kinds of Chinese spirits to test, our results confirm that the new pattern recognition system can perfectly identify and distinguish between the Chinese spirits.

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Theory of noise in a kilo-Hz cascaded high-energy Yb-doped nanosecond pulsed fiber amplifier Liu Ming (刘明), Zhang Hai-Tao (张海涛), Gong Ma-Li (巩马理), Zhao Yue-Jin (赵跃进), Cheng Wen-Yong (程文雍), Meng Kuo (孟阔), Zheng Chao (郑超), Chen Yi-Zhu (陈倚竹) Chin. Phys. B, 2014, 23 (4):  044214.  DOI: 10.1088/1674-1056/23/4/044214 Abstract ( 572 )   PDF (320KB) ( 509 )   A theoretical analysis of noise in a high-power cascaded fiber amplifier is presented. Unlike the noise theory in low power communication, the noise of a high power system is redefined as the leaked output energy between pulses with coherent beat noise uncounted. This definition is more appropriate for high power usage in which the pulse energy receives more attention than the pulse shape integrity. Then the low power pre-amplifying stages are considered as linear amplification and analyzed by linear theory. In the high-power amplification stages, the inversion is assumed to recover linearly in the time interval between pulses. The time shape of the output pulse is different from that of the input signal because of different gains at the front and back ends of the pulse. Then, a criterion is provided to distinguish the nonlinear and linear amplifications based on the signal-to-noise ratio (SNR) analysis. Then, an experiment that shows that the output SNR actually drops off in nonlinear amplification is performed. The change in the noise factor can be well evaluated by pulse shape distortion.

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Single order soft X-ray diffraction with quasi-random radius pinhole array spectroscopic photon sieves Zhang Qiang-Qiang (张强强), Wei Lai (魏来), Yang Zu-Hua (杨祖华), Qian Feng (钱凤), Fan Quan-Ping (范全平), Zhang Bo (张博), Gu Yu-Qiu (谷渝秋), Cao Lei-Feng (曹磊峰) Chin. Phys. B, 2014, 23 (4):  044215.  DOI: 10.1088/1674-1056/23/4/044215 Abstract ( 588 )   PDF (399KB) ( 471 )   A novel single order diffraction grating in the soft X-ray region, called quasi-random radius pinhole array spectroscopic photon sieves (QRSPS), is proposed in this paper. This new grating is composed of pinholes on a substrate, whose radii are quasi-random, while their centers are regular. Analysis proves that its transmittance function across the grating bar is similar to that of sinusoidal transmission gratings. Simulation results show that the QRSPS can suppress higher-order diffraction effectively. And the QRSPS would still retain its characteristic of single order diffraction when we take the effect of X-ray penetration into account. These properties indicate that the QRSPS can be used in the soft X-ray spectra measurement.

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Magneto–optical effect of TEB30A liquid crystal doped with thulium oxides Liu Gui-Xiang (刘桂香), Jin Xiang (金香) Chin. Phys. B, 2014, 23 (4):  044216.  DOI: 10.1088/1674-1056/23/4/044216 Abstract ( 642 )   PDF (213KB) ( 366 )   The influences of an external magnetic field on the optical properties of the TEB30A nematic liquid crystal doped with thulium oxides (Gd2O3, Dy2O3, Nd2O3, Y2O3, and Sm2O3) are studied. It is shown that a magnetic field applied parallelly to the sample cell surface leads to the rotational orientation of mesogenes. All samples except for the sample doped with Sm2O3 nanoparticles undergo structural deformations. The behavior of the TEB30A/Sm2O3 differs from those of the TEB30A liquid crystal doped with other four nanoparticles. The presence of Sm2O3 nanoparticles in the TEB30A liquid crystal does not cause the structural deformation of the liquid crystal matrix. At the same time, the anchoring type of the liquid crystal molecules on the nanoparticle surface is different. The director n is parallel to the magnetic moment μ in the TEB30A/Sm2O3, and inclined to the magnetic moment μ in the TEB30A/Nd2O3, and perpendicular to the magnetic moment μ in each of TEB30A/Gd2O3, TEB30A/Dy2O3, and TEB30A/Y2O3. Besides, the dependence of the structural deformation on the critical magnetic field for the TEB30A is obtained.

TOPICAL REVIEW—Magnetism, magnetic materials, and interdisciplinary research

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Multifunctional magnetic nanoparticles for magnetic resonance image-guided photothermal therapy for cancer Yue Xiu-Li (岳秀丽), Ma Fang (马放), Dai Zhi-Fei (戴志飞) Chin. Phys. B, 2014, 23 (4):  044301.  DOI: 10.1088/1674-1056/23/4/044301 Abstract ( 651 )   PDF (1608KB) ( 9229 )   Key advances in multifunctional magnetic nanoparticles (MNPs) for magnetic resonance (MR) image-guided photothermal therapy of cancer are reviewed. We briefly outline the design and fabrication of such multifunctional MNPs. Bimodal image-guided photothermal therapies (MR/fluorescence and MR/ultrasound) are also discussed.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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Hybrid device for acoustic noise reduction and energy harvesting based on a silicon micro-perforated panel structure Wu Shao-Hua (吴少华), Du Li-Dong (杜利东), Kong De-Yi (孔德义), Ping Hao-Yue (平皓月), Fang Zhen (方震), Zhao Zhan (赵湛) Chin. Phys. B, 2014, 23 (4):  044302.  DOI: 10.1088/1674-1056/23/4/044302 Abstract ( 553 )   PDF (397KB) ( 381 )   A kind of hybrid device for acoustic noise reduction and vibration energy harvesting based on the silicon micro-perforated panel (MPP) resonant structure is investigated in the article. The critical parts of the device include MPP and energy harvesting membranes. They are all fabricated by means of silicon micro-electro-mechanical systems (MEMS) technology. The silicon MPP has dense and accurate micro-holes. This noise reduction structure has the advantages of wide band and higher absorption coefficients. The vibration energy harvesting part is formed by square piezoelectric membranes arranged in rows. ZnO material is used as it has a good compatibility with the fabrication process. The MPP, piezoelectric membranes, and metal bracket are assembled into a hybrid device with multifunctions. The device exhibits good performances of acoustic noise absorption and acoustic-electric conversion. Its maximum open circuit voltage achieves 69.41 mV.

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A thermo-fluid analysis in magnetic hyperthermia Iordana Astefanoaei, Ioan Dumitru, Alexandru Stancu, Horia Chiriac Chin. Phys. B, 2014, 23 (4):  044401.  DOI: 10.1088/1674-1056/23/4/044401 Abstract ( 515 )   PDF (1780KB) ( 489 )   In the last years, hyperthermia induced by the heating of magnetic nanoparticles (MNPs) in an alternating magnetic field received considerable attention in cancer therapy. The thermal effects could be automatically controlled by using MNPs with selective magnetic absorption properties. In this paper, we analyze the temperature field determined by the heating of MNPs, injected in a malignant tissue, subjected to an alternating magnetic field. The main parameters which have a strong influence on temperature field are analyzed. The temperature evolution within healthy and tumor tissues are analyzed by finite element method (FEM) simulations in a thermo-fluid model. The cooling effect produced by blood flow in blood vessels from the tumor is considered. A thermal analysis is conducted under different distributions of MNP injection sites. The interdependence between the optimum dose of the nanoparticles and various types of tumors is investigated in order to understand their thermal effect on hyperthermia therapy. The control of the temperature field in the tumor and healthy tissues is an important step in the healing treatment.

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Hydromagnetic flow of a Cu–water nanofluid past a moving wedge with viscous dissipation A. M. Salem, Galal Ismail, Rania Fathy Chin. Phys. B, 2014, 23 (4):  044402.  DOI: 10.1088/1674-1056/23/4/044402 Abstract ( 551 )   PDF (577KB) ( 473 )   A numerical study is performed to investigate the flow and heat transfer at the surface of a permeable wedge immersed in a copper (Cu)-water-based nanofluid in the presence of magnetic field and viscous dissipation using a nanofluid model proposed by Tiwari and Das (Tiwari I K and Das M K 2007 Int. J. Heat Mass Transfer 50 2002). A similarity solution for the transformed governing equation is obtained, and those equations are solved by employing a numerical shooting technique with a fourth-order Runge-Kutta integration scheme. A comparison with previously published work is carried out and shows that they are in good agreement with each other. The effects of velocity ratio parameter <λ, solid volume fraction ø, magnetic field M, viscous dissipation Ec, and suction parameter Fw on the fluid flow and heat transfer characteristics are discussed. The unique and dual solutions for self-similar equations of the flow and heat transfer are analyzed numerically. Moreover, the range of the velocity ratio parameter for which the solution exists increases in the presence of magnetic field and suction parameter.

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Fast synchrotron X-ray tomography study of the packing structures of rods with different aspect ratios Zhang Xiao-Dan (张晓丹), Xia Cheng-Jie (夏成杰), Xiao Xiang-Hui (肖相辉), Wang Yu-Jie (王宇杰) Chin. Phys. B, 2014, 23 (4):  044501.  DOI: 10.1088/1674-1056/23/4/044501 Abstract ( 627 )   PDF (874KB) ( 440 )   We present a fast synchrotron X-ray tomography study of the packing structures of rods with different aspect ratios. Utilizing the high flux of the X-rays generated from the third-generation synchrotron source, we can complete a high-resolution tomography scan within a short period of time, after which the three-dimensional (3D) packing structure can be obtained for the subsequent structural analysis. The image phase-retrieval procedure has been implemented to enhance the image contrast. We systematically investigated the effects of particle shape and aspect ratio on the structural properties including packing density and contact number. It turns out that large aspect ratio rod packings will have wider distributions of free volume fraction and larger mean contact numbers.

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Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads Ren Huai-Hui (任淮辉), Wang Xi-Shu (王习术) Chin. Phys. B, 2014, 23 (4):  044601.  DOI: 10.1088/1674-1056/23/4/044601 Abstract ( 475 )   PDF (2987KB) ( 359 )   This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fatigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respectively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.

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A fractal approach to low velocity non-Darcy flow in a low permeability porous medium Cai Jian-Chao (蔡建超) Chin. Phys. B, 2014, 23 (4):  044701.  DOI: 10.1088/1674-1056/23/4/044701 Abstract ( 550 )   PDF (276KB) ( 677 )   In this paper, the mechanism for fluid flow at low velocity in a porous medium is analyzed based on plastic flow of oil in a reservoir and the fractal approach. The analytical expressions for flow rate and velocity of non-Newtonian fluid flow in the low permeability porous medium are derived, and the threshold pressure gradient (TPG) is also obtained. It is notable that the TPG (J) and permeability (K) of the porous medium analytically exhibit the scaling behavior J ～ K-DT/(1 + DT), where DT is the fractal dimension for tortuous capillaries. The fractal characteristics of tortuosity for capillaries should be considered in analysis of non-Darcy flow in a low permeability porous medium. The model predictions of TPG show good agreement with those obtained by the available expression and experimental data. The proposed model may be conducible to a better understanding of the mechanism for nonlinear flow in the low permeability porous medium.

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Boundary layer flow and heat transfer of a Casson fluid past a symmetric porous wedge with surface heat flux Swati Mukhopadhyay, Iswar Chandra Mandal Chin. Phys. B, 2014, 23 (4):  044702.  DOI: 10.1088/1674-1056/23/4/044702 Abstract ( 707 )   PDF (347KB) ( 821 )   The aim of this paper is to investigate numerically the boundary layer forced convection flow of a Casson fluid past a symmetric porous wedge. Similarity transformations are used to convert the governing partial differential equations into ordinary ones. With the help of the shooting method, the reduced equations are then solved numerically. Comparisons are made with the previously published results in some special cases and they are found to be in excellent agreement with each other. The results obtained in this study are illustrated graphically and discussed in detail. The velocity is found to increase with an increasing Falkner-Skan exponent whereas the temperature decreases. With the rise of the Casson fluid parameter, the fluid velocity increases but the temperature is found to decrease in this case. Fluid velocity is suppressed with the increase of suction. The skin friction decreases with the increasing value of Casson fluid parameter. It is found that the temperature decreases as the Prandtl number increases and thermal boundary layer thickness decreases with the increasing value of Prandtl number. A significant finding of this investigation is that flow separation can be controlled by increasing the value of the Casson fluid parameter as well as by increasing the amount of suction.

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Roll stability catastrophe mechanism of a flooded ship on regular sea waves Liu Yu-Liang (刘玉良) Chin. Phys. B, 2014, 23 (4):  044703.  DOI: 10.1088/1674-1056/23/4/044703 Abstract ( 500 )   PDF (338KB) ( 294 )   Based on a typical one-free-degree ship roll motion equation, the cusp catastrophe model is built including the bifurcation set equation, splitting factor‘u’and regular factor‘v’, where both‘u’and‘v’are further expressed with typical flooded ship parameters. Then, the roll catastrophe mechanism is analyzed mainly by means of‘u’, under the given parameters of a typical trawler boat. The aim of this research is to reveal the mutagenic mechanism of the roll stability and provide a reference for improving ship roll stability.

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Large eddy simulations of a circular orifice jet with and without a cross-sectional exit plate Zhang Jian-Peng (张健鹏), Xu Min-Yi (徐敏义), Mi Jian-Chun (米建春) Chin. Phys. B, 2014, 23 (4):  044704.  DOI: 10.1088/1674-1056/23/4/044704 Abstract ( 510 )   PDF (2793KB) ( 400 )   The effect of a cross-sectional exit plane on the downstream mixing characteristics of a circular turbulent jet is investigated using large eddy simulation (LES). The turbulent jet is issued from an orifice-type nozzle at an exit Reynolds number of 5× 104. Both instantaneous and statistical velocity fields of the jet are provided. Results show that the rates of the mean velocity decay and jet spread are both higher in the case with the exit plate than without it. The existence of the plate is found to increase the downstream entrainment rate by about 10% on average over the axial range of 8-30de (exit diameter). Also, the presence of the plate enables the formation of vortex rings to occur further downstream by 0.5-1.0de. A physical insight into the near-field jet is provided to explain the importance of the boundary conditions in the evolution of a turbulent jet. In addition, a method of using the decay of the centreline velocity and the half-width of the jet to calculate the entrainment rate is proposed.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Pattern recognition and data mining software based on artificial neural networks applied to proton transfer in aqueous environments Amani Tahat, Jordi Marti, Ali Khwaldeh, Kaher Tahat Chin. Phys. B, 2014, 23 (4):  046101.  DOI: 10.1088/1674-1056/23/4/046101 Abstract ( 683 )   PDF (2713KB) ( 426 )   In computational physics proton transfer phenomena could be viewed as pattern classification problems based on a set of input features allowing classification of the proton motion into two categories: transfer‘occurred’and transfer‘not occurred’. The goal of this paper is to evaluate the use of artificial neural networks in the classification of proton transfer events, based on the feed-forward back propagation neural network, used as a classifier to distinguish between the two transfer cases. In this paper, we use a new developed data mining and pattern recognition tool for automating, controlling, and drawing charts of the output data of an Empirical Valence Bond existing code. The study analyzes the need for pattern recognition in aqueous proton transfer processes and how the learning approach in error back propagation (multilayer perceptron algorithms) could be satisfactorily employed in the present case. We present a tool for pattern recognition and validate the code including a real physical case study. The results of applying the artificial neural networks methodology to crowd patterns based upon selected physical properties (e.g., temperature, density) show the abilities of the network to learn proton transfer patterns corresponding to properties of the aqueous environments, which is in turn proved to be fully compatible with previous proton transfer studies.

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The stress field and energy of screw dislocation in smectic A liquid crystals and the mistakes of the classical solution Fan Tian-You (范天佑), Li Xian-Fang (李显方) Chin. Phys. B, 2014, 23 (4):  046102.  DOI: 10.1088/1674-1056/23/4/046102 Abstract ( 787 )   PDF (198KB) ( 387 )   The mistakes in the classical solution of a screw dislocation in smectic A liquid crystals are pointed out. A serious problem with the well-known theory is pointed, which may be named de Gennes-Kleman-Pershan paradox and has existed for many decades in the scientific community of liquid crystal study. The correct solution is given in this paper by a simplest, elementary, and straight forward method. In connection with this, the stress field and energy of dislocation are discussed in detail. The present article provides the correct stress field and dislocation energy as well.

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Hybrid plasmon waveguides with metamaterial substrate and dielectric substrate：A contrastive study Gong Hui (宫慧), Liu Yu-Min (刘玉敏), Yu Zhong-Yuan (俞重远), Wu Xiu (吴秀), Yin Hao-Zhi (尹昊智) Chin. Phys. B, 2014, 23 (4):  046103.  DOI: 10.1088/1674-1056/23/4/046103 Abstract ( 437 )   PDF (535KB) ( 454 )   Hybrid plasmon waveguides, respectively, with metamaterial substrate and dielectric substrate are investigated and analyzed contrastively with a numerical finite element method. Basic properties, including propagation length Lp, effective mode area Aeff, and energy distribution, are obtained and compared with waveguide geometric parameters at 1.55 μ. For the waveguide with metamaterial substrate, propagation length Lp increases to several tens of microns and effective mode area Aeff is reduced by more than 3 times. Moreover, the near field region is expanded, leading to potential applications in nanophotonics. Therefore, it could be very helpful for improving the integration density in optical chips and developing functional components on a nanometer scale for all optical integrated circuits.

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Single event effect in a ferroelectric-gate field-effect transistor under heavy-ion irradiation Yan Shao-An (燕少安), Tang Ming-Hua (唐明华), Zhao Wen (赵雯), Guo Hong-Xia (郭红霞), Zhang Wan-Li (张万里), Xu Xin-Yu (徐新宇), Wang Xu-Dong (王旭东), Ding Hao (丁浩), Chen Jian-Wei (陈建伟), Li Zheng (李正), Zhou Yi-Chun (周益春) Chin. Phys. B, 2014, 23 (4):  046104.  DOI: 10.1088/1674-1056/23/4/046104 Abstract ( 755 )   PDF (756KB) ( 513 )   The single event effect in ferroelectric-gate field-effect transistor (FeFET) under heavy ion irradiation is investigated in this paper. The simulation results show that the transient responses are much lower in a FeFET than in a conventional metal-oxide-semiconductor field-effect transistor (MOSFET) when the ion strikes the channel. The main reason is that the polarization-induced charges (the polarization direction here is away from the silicon surface) bring a negative surface potential which will affect the distribution of carriers and charge collection in different electrodes significantly. The simulation results are expected to explain that the FeFET has a relatively good immunity to single event effect.

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Doping effects on structural and magnetic evolutions of orthoferrite SmFe(1-x)AlxO3 Li Na-Na (李娜娜), Li Hui (李会), Tang Rui-Lian (唐瑞莲), Han Dan-Dan (韩丹丹), Zhao Yong-Sheng (赵永胜), Gao Wei (高伟), Zhu Pin-Wen (朱品文), Wang Xin (王欣) Chin. Phys. B, 2014, 23 (4):  046105.  DOI: 10.1088/1674-1056/23/4/046105 Abstract ( 584 )   PDF (1673KB) ( 1307 )   The structural and magnetic properties of SmFeO3 with B site substitution of non-magnetic atom Al are investigated. The x-ray diffraction patterns show that SmFe(1-x)AlxO3 remains an orthorhombic structure within the whole doping range, and the unit-cell volume decreases monotonically with the increase of doped Al concentration. Besides, the octahedral tilting distortions of FeO6 are found to be alleviated while the tolerance factor increases. However, the relationship between the lattice parameters and Al concentration is observed to deviate from Vegard's rule, and this may be caused by magnetostriction effects. For the doping content values in a range 0 ≤ x ≤ 0.6, the ferromagnetism, antiferromagnetism, and paramagnetism are observed to occur continuously. Moreover, the magnetization and the spin reorientation temperature (Tk) decrease monotonically as Al content value increases. With the doping content values being x = 0.8 and 1.0, these compounds only show paramagnetic behavior.

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Improving light trapping and conversion efficiency of amorphous silicon solar cell by modified and randomly distributed ZnO nanorods Jia Zhi-Nan (贾志楠), Zhang Xiao-Dan (张晓丹), Liu Yang (刘阳), Wang Yan-Feng (王延峰), Fan Jun (樊君), Liu Cai-Chi (刘彩池), Zhao Ying (赵颖) Chin. Phys. B, 2014, 23 (4):  046106.  DOI: 10.1088/1674-1056/23/4/046106 Abstract ( 603 )   PDF (1047KB) ( 894 )   Three-dimensional (3D) nanostructures in thin film solar cells have attracted significant attention due to their applications in enhancing light trapping. Enhanced light trapping can result in more effective absorption in solar cells, thus leading to higher short-circuit current density and conversion efficiency. We develop randomly distributed and modified ZnO nanorods, which are designed and fabricated by the following processes: the deposition of a ZnO seed layer on substrate with sputtering, the wet chemical etching of the seed layer to form isolated islands for nanorod growth, the chemical bath deposition of the ZnO nanorods, and the sputtering deposition of a thin Al-doped ZnO (ZnO:Al) layer to improve the ZnO/Si interface. Solar cells employing the modified ZnO nanorod substrate show a considerable increase in solar energy conversion efficiency.

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Mechanical and thermodynamic properties of cubic YH2 under high pressure：Prediction from first-principles study Li Zhen-Li (李贞丽), Cheng Xin-Lu (程新路) Chin. Phys. B, 2014, 23 (4):  046201.  DOI: 10.1088/1674-1056/23/4/046201 Abstract ( 606 )   PDF (349KB) ( 429 )   First-principles calculations are used to investigate the mechanical and thermodynamic properties of cubic YH2 at different pressures and temperatures. The generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) method is used to describe the exchange-correlation energy in the present work. The calculated equilibrium lattice constant a and bulk modulus B are in good accordance with the available experimental values. According to the Born-Huang criteria for mechanical stability, elastic constants are calculated from the strain-induced stress method in a pressure range from 0 to 67.1 GPa. Isotropic wave velocities and sound velocities are discussed in detail. It is found that the Debye temperature decreases monotonically with the increase of pressure and that YH2 has low anisotropy in both longitudinal and shear-wave velocities. The calculated elastic anisotropic factors indicate that YH2 has low anisotropy at zero pressure and that its elastic anisotropy increases as pressure increases. Through the quasi-harmonic Debye model, in which phononic effects are considered, the thermodynamic properties of YH2, such as the relations of (V-V0)/V0 to the temperature and the pressure, the dependences of heat capacity Cv and thermal expansion coefficient αon temperature and pressure ranging from 0 to 2400 K and from 0 to 65 GPa, respectively, are also discussed.

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Effects of hydrogen bonds on solid state TATB, RDX, and DATB under high pressures Guo Feng (郭峰), Zhang Hong (张红), Hu Hai-Quan (胡海泉), Cheng Xin-Lu (程新路) Chin. Phys. B, 2014, 23 (4):  046501.  DOI: 10.1088/1674-1056/23/4/046501 Abstract ( 485 )   PDF (1267KB) ( 624 )   To probe the behavior of hydrogen bonds in solid energetic materials, we conduct ReaxFF and SCC-DFTB molecular dynamics simulations of crystalline TATB, RDX, and DATB. By comparing the intra-and inter-molecular hydrogen bonding rates, we find that the crystal structures are stabilized by inter-molecular hydrogen bond networks. Under high-pressure, the inter-and intra-molecular hydrogen bonds in solid TATB and DATB are nearly equivalent. The hydrogen bonds in solid TATB and DATB are much shorter than in solid RDX, which suggests strong hydrogen bond interactions existing in these energetic materials. Stretching of the C-H bond is observed in solid RDX, which may lead to further decomposition and even detonation.

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An effective-field theory study of hexagonal Ising nanowire：Thermal and magnetic properties Yusuf Kocakaplan, Ersin Kantar Chin. Phys. B, 2014, 23 (4):  046801.  DOI: 10.1088/1674-1056/23/4/046801 Abstract ( 558 )   PDF (1714KB) ( 399 )   By means of the effective-field theory (EFT) with correlations, the thermodynamic and magnetic quantities (such as magnetization, susceptibility, internal energy, specific heat, free energy, hysteresis curves, and compensation behaviors) of the spin-1/2 hexagonal Ising nanowire (HIN) system with core/shell structure have been presented. The hysteresis curves are obtained for different values of the system parameters, in both ferromagnetic and antiferromagnetic cases. It has been shown that the system only undergoes a second-order phase transition. Moreover, from the thermal variations of the total magnetization, the five compensation types can be found under certain conditions, namely the Q-, R-, S-, P-, and N-types.

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Dynamic surface wettability of three-dimensional graphene foam Huang Wen-Bin (黄文斌), Wang Guang-Long (王广龙), Gao Feng-Qi (高凤岐), Qiao Zhong-Tao (乔中涛), Wang Gang (王刚), Chen Min-Jiang (陈闽江), Tao Li (陶立), Deng Ya (邓娅), Sun Lian-Feng (孙连峰) Chin. Phys. B, 2014, 23 (4):  046802.  DOI: 10.1088/1674-1056/23/4/046802 Abstract ( 708 )   PDF (859KB) ( 577 )   In this work, three-dimensional graphene foams (GFs) are synthesized and characterized by scanning electron microscope (SEM) and Raman spectroscopy. The SEM images indicate that after the growth of graphene, the graphene covers the surface of nickel (Ni) foam uniformly. Raman spectra show that the percentages of monolayer, bilayer, trilayer, and multilayer graphenes are ～ 58%, ～ 32%, ～ 8%, and ～ 2%, respectively. The contact angle (CA) (～ 12°) of water droplet (3 μL) on GF is found to be larger than that on Ni foam (～ 107°), indicating that graphenes have changed the surface wettability of the Ni foam. Meanwhile, the dynamic characteristics of CA of water droplet on GF are different from those on Ni foam. The mechanisms for different behaviors are discussed, which are attributed to volatilization and seepage of water droplets.

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Optical and electrical characterizations of nanoparticle Cu2S thin films M. Saadeldin, H. S. Soliman, H. A. M. Ali, K. Sawaby Chin. Phys. B, 2014, 23 (4):  046803.  DOI: 10.1088/1674-1056/23/4/046803 Abstract ( 603 )   PDF (1423KB) ( 1933 )   Copper sulfide thin films are deposited onto different substrates at room temperature using the thermal evaporation technique. X-ray diffraction spectra show that the film has an orthorhombicchalcocite (γ-Cu2S) phase. The atomic force microscopy images indicate that the film exhibits nanoparticles with an average size of nearly 44 nm. Specrtophotometric measurements for the transmittance and reflectance are carried out at normal incidence in a spectral wavelength range of 450 nm-2500 nm. The refractive index, n, as well as the absorption index, k is calculated. Some dispersion parameters are determined. The analyses of ε1 and ε2 reveal several absorption peaks. The analysis of the spectral behavior of the absorption coefficient, α, in the absorption region reveals direct and indirect allowed transitions. The dark electrical resistivity is studied as a function of film thickness and temperature. Tellier's model is adopted for determining the mean free path and bulk resistance.

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Effect of ultrathin GeOx interfacial layer formed by thermal oxidation on Al2O3 capped Ge Han Le (韩乐), Wang Sheng-Kai (王盛凯), Zhang Xiong (张雄), Xue Bai-Qing (薛百清), Wu Wang-Ran (吴汪然), Zhao Yi (赵毅), Liu Hong-Gang (刘洪刚) Chin. Phys. B, 2014, 23 (4):  046804.  DOI: 10.1088/1674-1056/23/4/046804 Abstract ( 489 )   PDF (665KB) ( 618 )   We propose a modified thermal oxidation method in which an Al2O3 capping layer is used as an oxygen blocking layer (OBL) to form an ultrathin GeOx interfacial layer, and obtain a superior Al2O3/GeOx/Ge gate stack. The GeOx interfacial layer is formed in oxidation reaction by oxygen passing through the Al2O3 OBL, in which the Al2O3 layer could restrain the oxygen diffusion and suppress the GeO desorption during thermal treatment. The thickness of the GeOx interfacial layer would dramatically decrease as the thickness of Al2O3 OBL increases, which is beneficial to achieving an ultrathin GeOx interfacial layer to satisfy the demand for small equivalent oxide thickness (EOT). In addition, the thickness of the GeOx interfacial layer has little influence on the passivation effect of the Al2O3/Ge interface. Ge (100) p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) using the Al2O3/GeOx/Ge gate stacks exhibit excellent electrical characteristics; that is, a drain current on-off (Ion/Ioff) ratio of above 1× 104, a subthreshold slope of ～ 120 mV/dec, and a peak hole mobility of 265 cm2/V· s are achieved.

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Two crucial factors influencing quality of GaAs on Ge substrate Deng Chuang (邓闯), Men Chuan-Ling (门传玲), Chen Da (陈达) Chin. Phys. B, 2014, 23 (4):  046805.  DOI: 10.1088/1674-1056/23/4/046805 Abstract ( 503 )   PDF (646KB) ( 372 )   High-quality GaAs films with fine surfaces and GaAs/Ge interfaces on Ge have been achieved via molecular beam epitaxy. The influence of low temperature annealing and low temperature epitaxy on the quality of the film when GaAs is grown on a (100) 6° offcut towards [111] Ge substrate are investigated by analyzing and comparing the GaAs films that are fabricated via three different processes. A low temperature annealing process after high temperature annealing and a low temperature epitaxy process after the initial GaAs growth play a vital role in improving the quality of GaAs film on a Ge substrate.

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An application of half-terrace model to surface ripening of non-bulk GaAs layers Liu Ke (刘珂), Guo Xiang (郭祥), Zhou Qing (周清), Zhang Bi-Chan (张毕禅), Luo Zi-Jiang (罗子江), Ding Zhao (丁召) Chin. Phys. B, 2014, 23 (4):  046806.  DOI: 10.1088/1674-1056/23/4/046806 Abstract ( 675 )   PDF (707KB) ( 442 )   In order to predict the actual quantity of non-bulk GaAs layers after long-time homoepitaxy on GaAs (001) by theoretical calculation, a half-terrace diffusion model based on thermodynamics is used to calculate the ripening time of GaAs layers to form a flat morphology in annealing. To verify the accuracy of the calculation, real space scanning tunneling microscopy images of GaAs surface after different annealing times are obtained and the roughness of the GaAs surface is measured. The results suggest that the half terrace model is an accurate method with a relative error of about 4.1%.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Structural, electronic, optical, elastic properties and Born effective charges of monoclinic HfO2 from first-principles calculations Liu Qi-Jun (刘其军), Zhang Ning-Chao (张宁超), Liu Fu-Sheng (刘福生), Liu Zheng-Tang (刘正堂) Chin. Phys. B, 2014, 23 (4):  047101.  DOI: 10.1088/1674-1056/23/4/047101 Abstract ( 749 )   PDF (609KB) ( 2491 )   First-principles calculations of structural, electronic, optical, elastic, mechanical properties, and Born effective charges of monoclinic HfO2 are performed with the plane-wave pseudopotential technique based on the density-functional theory. The calculated structural properties are consistent with the previous theoretical and experimental results. The electronic structure reveals that monoclinic HfO2 has an indirect band gap. The analyses of density of states and Mulliken charges show mainly covalent nature in Hf-O bonds. Optical properties, including the dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient, loss function, and optical conductivity each as a function of photon energy are calculated and show an optical anisotropy. Moreover, the independent elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, compressibility, Lamé constant, sound velocity, Debye temperature, and Born effective charges of monoclinic HfO2 are obtained, which may help to understand monoclinic HfO2 for future work.

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Molecular dynamics simulations of jet breakup and ejecta production from a grooved Cu surface under shock loading He An-Min (何安民), Wang Pei (王裴), Shao Jian-Li (邵建立), Duan Su-Qing (段素青) Chin. Phys. B, 2014, 23 (4):  047102.  DOI: 10.1088/1674-1056/23/4/047102 Abstract ( 620 )   PDF (868KB) ( 589 )   Large-scale non-equilibrium molecular dynamics simulations are performed to explore the jet breakup and ejecta production of single crystal Cu with a triangular grooved surface defect under shock loading. The morphology of the jet breakup and ejecta formation is obtained where the ejecta clusters remain spherical after a long simulation time. The effects of shock strength as well as groove size on the steady size distribution of ejecta clusters are investigated. It is shown that the size distribution of ejecta exhibits a scaling power law independent of the simulated shock strengths and groove sizes. This distribution, which has been observed in many fragmentation processes, can be well described by percolation theory.

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Modeling of metal-oxide semiconductor：Analytical bond-order potential for cupric oxide Li Kun (李坤), Yang Wen (杨雯), Wei Ji-Lin (魏计林), Du Shi-Wen (杜诗文), Li Yong-Tang (李永堂) Chin. Phys. B, 2014, 23 (4):  047103.  DOI: 10.1088/1674-1056/23/4/047103 Abstract ( 497 )   PDF (256KB) ( 618 )   Atomistic potentials for cupric element and cupric oxide are derived based on the analytical bond-order scheme that was presented by Brenner [Brenner D W, "Erratum: Empirical potential for hydrocarbons for use in simulating the chemical vapor deposition of diamond films", Phys. Rev. B 1992, 46 1948]. In this paper, for the pure cupric element, the energy and structural parameters for several bulk phases as well as dimmer structure are well reproduced. The reference data are taken from our density functional theory calculations and the available experiments. The model potential also provides a good description of the bulk properties of various solid structures of cupric oxide compound structures, including cohesive energies, lattice parameters, and elastic constants.

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Deposition of hexagonal boron nitride thin films on silver nanoparticle substrates and surface enhanced infrared absorption Deng Jin-Xiang (邓金祥), Chen Liang (陈亮), Man Chao (满超), Kong Le (孔乐), Cui Min (崔敏), Gao Xue-Fei (高学飞) Chin. Phys. B, 2014, 23 (4):  047104.  DOI: 10.1088/1674-1056/23/4/047104 Abstract ( 557 )   PDF (479KB) ( 451 )   Silver nanoparticle thin films with different average particle diameters are grown on silicon substrates. Boron nitride thin films are then deposited on the silver nanoparticle interlayers by radio frequency (RF) magnetron sputtering. The boron nitride thin films are characterized by Fourier transform infrared spectra. The average particle diameters of silver nanoparticle thin films are 126.6, 78.4, and 178.8 nm. The results show that the sizes of the silver nanoparticles have effects on the intensities of infrared spectra of boron nitride thin films. An enhanced infrared absorption is detected for boron nitride thin film grown on silver nanoparticle thin film. This result is helpful to study the growth mechanism of boron nitride thin film.

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Influence of the channel electric field distribution on the polarization Coulomb field scattering in In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors Yu Ying-Xia (于英霞), Lin Zhao-Jun (林兆军), Luan Chong-Biao (栾崇彪), Lü Yuan-Jie (吕元杰), Feng Zhi-Hong (冯志红), Yang Ming (杨铭), Wang Yu-Tang (王玉堂) Chin. Phys. B, 2014, 23 (4):  047201.  DOI: 10.1088/1674-1056/23/4/047201 Abstract ( 467 )   PDF (336KB) ( 478 )   By making use of the quasi-two-dimensional (quasi-2D) model, the current-voltage (I-V) characteristics of In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors (HFETs) with different gate lengths are simulated based on the measured capacitance-voltage (C-V) characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas (2DEG) with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V· s for the prepared In0.18Al0.82N/AlN/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.

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Electric field-induced hole injection-enhanced photoluminescence in a N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)-benzidine-based emitter Xu-Xie Hui-Na (许谢慧娜), Li Wen-Bin (李文彬), Peng Huan (彭欢), He Yun (何鋆), Yu Hao-Miao (于浩淼), Hou Xiao-Yuan (侯晓远) Chin. Phys. B, 2014, 23 (4):  047202.  DOI: 10.1088/1674-1056/23/4/047202 Abstract ( 632 )   PDF (438KB) ( 358 )   Non-monotonic, asymmetrical electric field dependence of photoluminescence (PL) intensity is observed in a monolayer sample of tris-(8-hydroxyquinoline) aluminum (AlQ) doped N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)-benzidine (TPD). A possible model is proposed: the charge separation from the dissociated photoexcited excitons causes energy band bending in the organic films and improves the hole injection from the electrode, which brings about the extra fluorescence. This mechanism is further verified by a series of experiments using a series of samples, variously featuring symmetrical electrodes, block layers, and hosts with lower hole mobilities.

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Direct measurement of the interfacial barrier height of the manganite p-n heterojunction Wang Mei (王妹), Wang Deng-Jing (王登京), Wang Ru-Wu (汪汝武), Li Yun-Bao (李云宝) Chin. Phys. B, 2014, 23 (4):  047301.  DOI: 10.1088/1674-1056/23/4/047301 Abstract ( 802 )   PDF (228KB) ( 484 )   A manganite p-n heterojunction composed of La0.67Sr0.33MnO3 film and 0.05 wt% Nb-doped SrTiO3 substrate is fabricated. Rectifying behavior of the junction well described by the Shockley equation is observed, and the transport properties of the interface are experimentally studied. A satisfactorily logarithmic linear dependence of resistance on temperature is observed in a temperature range of 150 K-380 K, and the linear relation between bias and activation energies deduced from the R-1/T curves is observed. According to activation energy, the interfacial barrier of the heterojunction is obtained, which is 0.91 eV.

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Simply synthesized TiO2 nanorods as an effective scattering layer for quantum dot sensitized solar cells Mahmoud Samadpour, Azam Iraji zad, Mehdi Molaei Chin. Phys. B, 2014, 23 (4):  047302.  DOI: 10.1088/1674-1056/23/4/047302 Abstract ( 475 )   PDF (2367KB) ( 547 )   TiO2 nanorod layers are synthesized by simple chemical oxidation of Ti substrates. Diffuse reflectance spectroscopy measurements show effective light scattering properties originating from nanorods with length scales on the order of one micron. The films are sensitized with CdSe quantum dots (QDs) by successive ionic layer adsorption and reaction (SILAR) and integrated as a photoanode in quantum dot sensitized solar cells (QDSCs). Incorporating nanorods in photoanode structures provided 4-to 8-fold enhancement in light scattering, which leads to a high power conversion efficiency, 3.03% (Voc=497 mV, Jsc=11.32 mA/cm2, FF=0.54), in optimized structures. High efficiency can be obtained just by tuning the photoanode structure without further treatments, which will make this system a promising nanostructure for efficient quantum dot sensitized solar cells.

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A dual-band flexible frequency selective surface with miniaturized elements and maximally flat (Butterworth) response Wang Xiu-Zhi (王秀芝), Gao Jin-Song (高劲松), Xu Nian-Xi (徐念喜), Liu Hai (刘海) Chin. Phys. B, 2014, 23 (4):  047303.  DOI: 10.1088/1674-1056/23/4/047303 Abstract ( 642 )   PDF (1171KB) ( 733 )   A dual-band flexible frequency selective surface (FSS) with miniaturized elements and maximally flat (Butterworth) response is presented in this paper. It is composed of three metallic layers, which are fabricated on thin flexible polyimide substrates and bonded together using thin bonding films. The overall thickness of the proposed structure is only about 0.3 mm, making it an attractive choice for conformal FSS applications. All the three layers can constitute a miniaturized-element FSS (MEFSS) and produce the first pass-band with miniaturization property, while the up and bottom layers can constitute a symmetric biplanar FSS and produce the second pass-band with maximally flat (Butterworth) response. The two pass-bands are independent and there is a wide band spacing up to 30 GHz between them. The principles of operation, the simulated results by using the vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.

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Frequency and voltage-dependent electrical and dielectric properties of Al/Co-doped PVA/p-Si structures at room temperature Ibrahim Yücedağ, Ahmet Kaya, Şemsettin Altındal, Ibrahim Uslu Chin. Phys. B, 2014, 23 (4):  047304.  DOI: 10.1088/1674-1056/23/4/047304 Abstract ( 569 )   PDF (570KB) ( 1429 )   In order to investigate of cobalt-doped interfacial polyvinyl alcohol (PVA) layer and interface trap (Dit) effects, Al/p-Si Schottky barrier diodes (SBDs) are fabricated, and their electrical and dielectric properties are investigated at room temperature. The forward and reverse admittance measurements are carried out in the frequency and voltage ranges of 30 kHz-300 kHz and-5 V-6 V, respectively. C-V or ε '-V plots exhibit two distinct peaks corresponding to inversion and accumulation regions. The first peak is attributed to the existence of Dit, the other to the series resistance (Rs), and interfacial layer. Both the real and imaginary parts of dielectric constant (ε ' and ε") and electric modulus (M' and M"), loss tangent (tan δ), and AC electrical conductivity (σac) are investigated, each as a function of frequency and applied bias voltage. Each of the M' versus V and M" versus V plots shows a peak and the magnitude of peak increases with the increasing of frequency. Especially due to the Dit and interfacial PVA layer, both capacitance (C) and conductance (G/w) values are strongly affected, which consequently contributes to deviation from both the electrical and dielectric properties of Al/Co-doped PVA/p-Si (MPS) type SBD. In addition, the voltage-dependent profile of Dit is obtained from the low-high frequency capacitance (CLF-CHF) method.

TOPICAL REVIEW—Plasmonics and metamaterials

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Manipulation of plasmonic wavefront and light-matter interaction in metallic nanostructures：A brief review Li Jia-Fang (李家方), Li Zhi-Yuan (李志远) Chin. Phys. B, 2014, 23 (4):  047305.  DOI: 10.1088/1674-1056/23/4/047305 Abstract ( 637 )   PDF (2894KB) ( 929 )   The control and application of surface plasmons (SPs), is introduced with particular emphasis on the manipulation of the plasmonic wavefront and light-matter interaction in metallic nanostructures. We introduce a direct design methodology called the surface wave holography method and show that it can be readily employed for wave-front shaping of near-infrared light through a subwavelength hole, it can also be used for designing holographic plasmonic lenses for SPs with complex wavefronts in the visible band. We also discuss several issues of light-matter interaction in plasmonic nanostructures. We show theoretically that amplification of SPs can be achieved in metal nanoparticles incorporated with gain media, leading to a giant reduction of surface plasmon resonance linewidth and enhancement of local electric field intensity. We present an all-analytical semiclassical theory to evaluate spaser performance in a plasmonic nanocavity incorporated with gain media described by the four-level atomic model. We experimentally demonstrate amplified spontaneous emission of SP polaritons and their amplification at the interface between a silver film and a polymer film doped with dye molecules. We discuss various aspects of microscopic and macroscopic manipulation of fluorescent radiation from gold nanorod hybrid structures in a system of either a single nanoparticle or an aligned group of nanoparticles. The findings reported and reviewed here could help others explore various approaches and schemes to manipulate plasmonic wavefront and light-matter interaction in metallic nanostructures for potential applications, such as optical displays, information integration, and energy harvesting technologies.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Enhanced light absorption of silicon in the near-infrared band by designed gold nanostructures Hot! Liu Ju (刘菊), Zhong Xiao-Lan (钟晓岚), Li Zhi-Yuan (李志远) Chin. Phys. B, 2014, 23 (4):  047306.  DOI: 10.1088/1674-1056/23/4/047306 Abstract ( 600 )   PDF (728KB) ( 588 )   A scheme to enhance near-infrared band absorption of a Si nanoparticle by placing the Si nanoparticle into a designed gold nanostructure is proposed. Three-dimensional (3D) finite-difference time-domain simulations are employed to calculate the absorption spectrum of the Si nanostructure and maximize it by generating alternate designs. The results show that in the near-infrared region over 700 nm, the absorption of a pure Si nanoparticle is very low, but when the same nanoparticle is placed within an optimally designed gold nanostructure, its absorption cross section can be enhanced by more than two orders of magnitude in the near-infrared band.

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Electronic and transport properties of V-shaped defect zigzag MoS2 nanoribbons Li Xin-Mei (李新梅), Long Meng-Qiu (龙孟秋), Cui Li-Ling (崔丽玲), Xiao Jin (肖金), Xu Hui (徐慧) Chin. Phys. B, 2014, 23 (4):  047307.  DOI: 10.1088/1674-1056/23/4/047307 Abstract ( 553 )   PDF (653KB) ( 726 )   Based on the nonequilibrium Green's function (NEGF) in combination with density functional theory (DFT) calculations, we study the electronic structures and transport properties of zigzag MoS2 nanoribbons (ZMNRs) with V-shaped vacancy defects on the edge. The vacancy formation energy results show that the zigzag vacancy is easier to create on the edge of ZMNR than the armchair vacancy. Both of the defects can make the electronic band structures of ZMNRs change from metal to semiconductor. The calculations of electronic transport properties depict that the currents drop off clearly and rectification ratios increase in the defected systems. These effects would open up possibilities for their applications in novel nanoelectronic devices.

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Magnetic properties of bulk polycrystalline Pr1-xNdx (x=0, 0.8)FeB permanent magnets He Yong-Zhou (何永周), Wu Hong-Ping (吴红平), Zou Zhi-Qiang (邹志强) Chin. Phys. B, 2014, 23 (4):  047501.  DOI: 10.1088/1674-1056/23/4/047501 Abstract ( 541 )   PDF (492KB) ( 461 )   For spin reorientation (SRT), the applications of sintering NdFeB permanent magnets are limited at low temperature. The sintering PrFeB permanent magnet (PM) presents no SRT and shows excellent magnetic properties at low temperature. The magnetic properties of bulk polycrystalline sintering Pr1-xNdxFeB (x=0 and 0.8 correspond to P42H and N50M respectively) are studied in this paper. The results show that magnetic properties and stability of N50M are better than those of 42H at room temperature. With the decrease of temperature, the parameters of Br, Hcb, and Hci of P42H present a nearly linear increasing trend; Br and Hcb of N50M first increase and then decline, Hci presents an increasing trend. At 77 K, Br, Hci, and Jr of P42H are increased by 18.7%, 308%, and 17.1% respectively over than those at 300 K; at 120 K, Br, Hci, and Jr of N50M are increased by about 16.19%, 245%, and 12.6% respectively over than those at 300 K. The magnetic properties of P42H are better than those of N50M at low temperature. The sintering PrFeB is the preferred PM in various low-temperature devices.

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Ferromagnetic resonance frequency shift model of laminated magnetoelectric structure tuned by electric field Zhou Hao-Miao (周浩淼), Chen Qing (陈晴), Deng Juan-Hu (邓娟湖) Chin. Phys. B, 2014, 23 (4):  047502.  DOI: 10.1088/1674-1056/23/4/047502 Abstract ( 556 )   PDF (330KB) ( 407 )   Based on Smith-Beljers theory and classical laminate theory, an explicit model is proposed for the ferromagnetic resonance (FMR) frequency shift of a stress-mediumed laminated magnetoelectric structure tuned by an electric field. This model can effectively predict the experimental phenomenon that the FMR frequency increases under a parallel magnetic field and decreases under a perpendicular magnetic field when the electric field ranges from-10 kV/m to 10 kV/m. Besides, this theory further shows that the FMR frequency increases monotonically as the angle between the direction of the external magnetic field and the outside normal direction of the laminated structure increases, and the frequency will increase as great as 7 GHz. In addition, when the angle reaches a certain critical value, the external electric field fails to tune the FMR frequency. When the angle is above the critical value, the increase of the electric field induces the FMR frequency to increase, and the opposite scenario happens when it is below the critical value. When the angle is 90° (parallel magnetic field), the FMR frequency is the most sensitive to the change of the electric field.

TOPICAL REVIEW—Magnetism, magnetic materials, and interdisciplinary research

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Optimizing and fabricating magnetocaloric materials Liu Jian (刘剑) Chin. Phys. B, 2014, 23 (4):  047503.  DOI: 10.1088/1674-1056/23/4/047503 Abstract ( 550 )   PDF (1698KB) ( 2160 )   The microstructural modification of existing materials for magnetic cooling applications, and mass fabrication of the modified materials are reviewed, emphasizing the maximization of magnetic entropy change and minimization of hysteresis losses, as well as the engineering problems in the actual application of promising materials. In the first part, physical rules are put forward to explore high performance magnetic refrigerants, including the enhancement of adiabatic temperature change in finite field, multi-caloric effects, and multi-layered structure. Special attention is given to non-magnetic properties. Following this, an overview of mass fabrication of magnetic refrigerants having large entropy change, small hysteresis, good mechanical properties, and high thermal conductivity is presented.

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Anomalous Hall effect in perpendicular CoFeB thin films Zhu Tao (朱涛) Chin. Phys. B, 2014, 23 (4):  047504.  DOI: 10.1088/1674-1056/23/4/047504 Abstract ( 821 )   PDF (2054KB) ( 2602 )   Our recent research achievements in the perpendicular magnetic anisotropy (PMA) properties of the CoFeB sandwiched by MgO and tantalum layers are summarized. We found that the PMA behaviors of Ta/CoFeB/MgO and MgO/CoFeB/Ta thin films are different. The larger PMA in the latter film is related to the lower magnetization of CoFeB deposited on MgO. Furthermore, we have demonstrated a large anomalous Hall effect in perpendicular CoFeB thin film. Our results show large anomalous Hall resistivity, large longitudinal resistivity, and low switching field can be achieved, all at the same time, in the perpendicular CoFeB thin film. Anomalous Hall effect with high and linear sensitivity is also found in an MgO/CoFeB/Ta thin film with a thick MgO layer, which opens a door for future device applications of perpendicular ferromagnetic thin films.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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La-doped BiFeO3：Synthesis and multiferroic property study Lin Peng-Ting (蔺鹏婷), Li Xiang (李祥), Zhang Li (张丽), Yin Jin-Hua (阴津华), Cheng Xing-Wang (程兴旺), Wang Zhi-Hong (王志宏), Wu Yu-Chuan (吴玉娟), Wu Guang-Heng (吴光恒) Chin. Phys. B, 2014, 23 (4):  047701.  DOI: 10.1088/1674-1056/23/4/047701 Abstract ( 499 )   PDF (798KB) ( 593 )   A new sol-foam-gel method was developed to fabricate La-doped BiFeO3 multiferroic materials. It was demonstrated that a gradual increase in the content of La-doped into BiFeO3 results in its structure changing from rhombohedral to orthorhombic. A study of other property changes indicates that La-doping in BiFeO3 enhances its ferromagnetism and ferroelectricity. A temperature-dependent magnetization study suggests that the magnetic property of La-doped BiFeO3 samples varied from antiferromagnetic to ferromagnetic as the content of La-doped into BiFeO3 increased from 0 to 20%. Unique temperature-dependent zero field cooling (ZFC) and field cooling (FC) magnetization behaviors were observed in 15% La-doped BiFeO3 – its ZFC temperature-dependent magnetization being ferromagnetic and its FC temperature-dependent magnetization being antiferromagnetic. A possible mechanism of such an interesting M-T behavior is discussed.

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Effects of BaCu(B2O5) addition on sintering temperature and microwave dielectric properties of Ba5Nb4O15-BaWO4 ceramics Jia Rui-Long (贾瑞龙), Su Hua (苏桦), Tang Xiao-Li (唐晓莉), Jing Yu-Lan (荆玉兰) Chin. Phys. B, 2014, 23 (4):  047801.  DOI: 10.1088/1674-1056/23/4/047801 Abstract ( 525 )   PDF (1784KB) ( 393 )   The effects of BaCu(B2O5) (BCB) addition on the microstructure, phase formation, and microwave dielectric properties of Ba5Nb4O15-BaWO4 ceramic are investigated. As a sintering aid, BaCu(B2O5) ceramic could effectively lower the sintering temperature of Ba5Nb4O15-BaWO4 ceramic from 1100 ℃ to 950 ℃ due to the liquid-phase effect. Meanwhile, BaCu(B2O5) addition effectively improves the densification of Ba5Nb4O15-BaWO4 ceramic and significantly influences the microwave dielectric properties. X-ray diffraction analysis reveals that Ba5Nb4O15 and BaWO4 coexist with no crystal phase of BaCu(B2O5) in the sintered ceramics. The Ba5Nb4O15-BaWO4 ceramics with 1.0 wt% BaCu(B2O5) sintered at 950 ℃ for 2 h presents good microwave dielectric properties of εr=19.0, high Q× f of 33802 GHz and low τf of 2.5 ppm/℃.

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Analysis and applications of a frequency selectivesurface via a random distribution method Xie Shao-Yi (谢少毅), Huang Jing-Jian (黄敬健), Liu Li-Guo (刘立国), Yuan Nai-Chang (袁乃昌) Chin. Phys. B, 2014, 23 (4):  047802.  DOI: 10.1088/1674-1056/23/4/047802 Abstract ( 525 )   PDF (1716KB) ( 903 )   A novel frequency selective surface (FSS) for reducing radar cross section (RCS) is proposed in this paper. This FSS is based on random distribution method, so it can be called random surface. In this paper the stacked patches serving as periodic elements are employed for RCS reduction. Previous work has demonstrated the efficiency by utilizing the microstrip patches, especially for the reflectarray. First, the relevant theory of the method is described. Then a sample of three-layer variable-sized stacked patch random surface with a dimension of 260 mm× 260 mm is simulated, fabricated, and measured in order to demonstrate the validity of the proposed design. For the normal incidence, the 8-dB RCS reduction can be achieved both by the simulation and the measurement in 8 GHz-13 GHz. The oblique incidence of 30° is also investigated, in which the 7-dB RCS reduction can be obtained in a frequency range of 8 GHz-14 GHz.

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Strong and broadband terahertz absorber using SiO2-based metamaterial structure Mo Man-Man (莫漫漫), Wen Qi-Ye (文岐业), Chen Zhi (陈智), Yang Qing-Hui (杨青慧), Qiu Dong-Hong (邱东鸿), Li Sheng (李胜), Jing Yu-Lan (荆玉兰), Zhang Huai-Wu (张怀武) Chin. Phys. B, 2014, 23 (4):  047803.  DOI: 10.1088/1674-1056/23/4/047803 Abstract ( 641 )   PDF (1154KB) ( 615 )   We design and experimentally demonstrate a broadband metamaterial absorber in the terahertz (THz) band based on a periodic array of aluminum (Al) squares with two different sizes. A thin silicon dioxide (SiO2) film rather than a conventional polyimide (PI) layer is used as a dielectric spacer to separate Al squares from the platinum (Pt) ground plane in our design, which significantly improves the design precision and the feasibility of the device fabrication. The combination of different sizes of Al squares gives rise to an absorption bandwidth of over 210 GHz with an absorption of over 90%. Our results also show that our device is almost polarization-insensitive. It works very well for all azimuthal angles with an absorption of beyond 80%.

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Improvement in a-plane GaN crystalline quality using wet etching method Cao Rong-Tao (曹荣涛), Xu Sheng-Rui (许晟瑞), Zhang Jin-Cheng (张进成), Zhao Yi (赵一), Xue Jun-Shuai (薛军帅), Ha Wei (哈微), Zhang Shuai (张帅), Cui Pei-Shui (崔培水), Wen Hui-Juan (温慧娟), Chen Xing (陈兴) Chin. Phys. B, 2014, 23 (4):  047804.  DOI: 10.1088/1674-1056/23/4/047804 Abstract ( 536 )   PDF (645KB) ( 451 )   Nonpolar (112 0) GaN films are grown on the etched a-plane GaN substrates via metalorganic vapor phase epitaxy. High-resolution X-ray diffraction analysis shows great decreases in the full width at half maximum of the samples grown on etched substrates compared with those of the sample without etching, both on-axis and off-axis, indicating the reduced dislocation densities and improved crystalline quality of these samples. The spatial mapping of the E2 (high) phonon mode demonstrates the smaller line width with a black background in the wing region, which testifies the reduced dislocation densities and enhanced crystalline quality of the epitaxial lateral overgrowth areas. Raman scattering spectra of the E2 (high) peaks exhibit in-plane compressive stress for all the overgrowth samples, and the E2 (high) peaks of samples grown on etched substrates shift toward the lower frequency range, indicating the relaxations of in-plane stress in these GaN films. Furthermore, room temperature photoluminescence measurement demonstrates a significant decrease in the yellow-band emission intensity of a-plane GaN grown on etched templates, which also illustrates the better optical properties of these samples.

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Electrical and optical properties of Sb-doped ZnO thin films synthesized by sol-gel method Cao Meng-Meng (曹萌萌), Zhao Xiao-Ru (赵小如), Duan Li-Bing (段利兵), Liu Jin-Ru (刘金茹), Guan Meng-Meng (关蒙萌), Guo Wen-Rui (郭文瑞) Chin. Phys. B, 2014, 23 (4):  047805.  DOI: 10.1088/1674-1056/23/4/047805 Abstract ( 542 )   PDF (585KB) ( 583 )   Sb-doped ZnO thin films with different values of Sb content (from 0 to 1.1 at.%) are deposited by the sol-gel dip-coating method under different sol concentrations. The effects of Sb-doping content, sol concentration, and annealing ambient on the structural, optical, and electrical properties of ZnO films are investigated. The results of the X-ray diffraction and ultraviolet-visible spectroscopy (UV-VIS) spectrophotometer indicate that each of all the films retains the wurtzite ZnO structure and possesses a preferred orientation along the c axis, with high transmittance (> 90%) in the visible range. The Hall effect measurements show that the vacuum annealed thin films synthesized in the sol concentration of 0.75 mol/L each have an adjustable n-type electrical conductivity by varying Sb-doping density, and the photoluminescence (PL) spectra revealed that the defect emission (around 450 nm) is predominant. However, the thin films prepared by the sol with a concentration of 0.25 mol/L, despite their poor conductivity, have priority in ultraviolet emission, and the PL peak position shows first a blue-shift and then a red-shift with the increase of the Sb doping content.

TOPICAL REVIEW—Plasmonics and metamaterials

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Control of light scattering by nanoparticles with optically-induced magnetic responses Liu Wei (刘伟), Andrey E. Miroshnichenko, Yuri S. Kivshar Chin. Phys. B, 2014, 23 (4):  047806.  DOI: 10.1088/1674-1056/23/4/047806 Abstract ( 705 )   PDF (1202KB) ( 927 )   Conventional approaches to control and shape the scattering patterns of light generated by different nanostructures are mostly based on engineering of their electric response due to the fact that most metallic nanostructures support only electric resonances in the optical frequency range. Recently, fuelled by the fast development in the fields of metamaterials and plasmonics, artificial optically-induced magnetic responses have been demonstrated for various nanostructures. This kind of response can be employed to provide an extra degree of freedom for the efficient control and shaping of the scattering patterns of nanoparticles and nanoantennas. Here we review the recent progress in this research direction of nanoparticle scattering shaping and control through the interference of both electric and optically-induced magnetic responses. We discuss the magnetic resonances supported by various structures in different spectral regimes, and then summarize the original results on the scattering shaping involving both electric and magnetic responses, based on the interference of both spectrally separated (with different resonant wavelengths) and overlapped dipoles (with the same resonant wavelength), and also other higher-order modes. Finally, we discuss the scattering control utilizing Fano resonances associated with the magnetic responses.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Enormous enhancement of electric field in active gold nanoshells Jiang Shu-Min (蒋书敏), Wu Da-Jian (吴大建), Wu Xue-Wei (吴雪炜), Liu Xiao-Jun (刘晓峻) Chin. Phys. B, 2014, 23 (4):  047807.  DOI: 10.1088/1674-1056/23/4/047807 Abstract ( 616 )   PDF (361KB) ( 528 )   The electric field enhancement properties of an active gold nanoshell with gain material inside have been investigated by using Mie theory. As the gain coefficient of the inner core increases to a critical value, a super-resonance appears in the active gold nanoshell, and enormous enhancements of the electric fields can be found near the surface of the particle. With increasing shell thickness, the critical value of the gain coefficient for the super-resonance of the active gold nanoshell first decreases and then increases, and the corresponding surface enhanced Raman scattering (SERS) enhancement factor (G factor) also first increases and then decreases. The optimized active gold nanoshell can be obtained with an extremely high SERS G factor of the order of 1019-1020. Such an optimized active gold nanoshell possesses a high-efficiency SERS effect and may be useful for single-molecule detection.

TOPICAL REVIEW—Plasmonics and metamaterials

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Manipulating electromagnetic waves with metamaterials：Concept and microwave realizations He Qiong (何琼), Sun Shu-Lin (孙树林), Xiao Shi-Yi (肖诗逸), Li Xin (李欣), Song Zheng-Yong (宋争勇), Sun Wu-Jiong (孙午炯), Zhou Lei (周磊) Chin. Phys. B, 2014, 23 (4):  047808.  DOI: 10.1088/1674-1056/23/4/047808 Abstract ( 671 )   PDF (1937KB) ( 1681 )   Our recent efforts in manipulating electromagnetic (EM) waves using metamaterials (MTMs) are reviewed with emphasis on 1) manipulating wave polarization and transporting properties using homogeneous MTMs, 2) manipulating surface-wave properties using plasmonic MTMs, and 3) bridging propagating and surface waves using inhomogeneous meta-surfaces. For all these topics, we first illustrate the physical concepts and then present several typical practical realizations and applications in the microwave regime.

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Metamaterials and plasmonics：From nanoparticles to nanoantenna arrays, metasurfaces, and metamaterials Francesco Monticone, Andrea Alú Chin. Phys. B, 2014, 23 (4):  047809.  DOI: 10.1088/1674-1056/23/4/047809 Abstract ( 1426 )   PDF (1452KB) ( 3124 )   The rise of plasmonic metamaterials in recent years has unveiled the possibility of revolutionizing the entire field of optics and photonics, challenging well-established technological limitations and paving the way to innovations at an unprecedented level. To capitalize the disruptive potential of this rising field of science and technology, it is important to be able to combine the richness of optical phenomena enabled by nanoplasmonics in order to realize metamaterial components, devices, and systems of increasing complexity. Here, we review a few recent research directions in the field of plasmonic metamaterials, which may foster further advancements in this research area. We will discuss the anomalous scattering features enabled by plasmonic nanoparticles and nanoclusters, and show how they may represent the fundamental building blocks of complex nanophotonic architectures. Building on these concepts, advanced components can be designed and operated, such as optical nanoantennas and nanoantenna arrays, which, in turn, may be at the basis of metasurface devices and complex systems. Following this path, from basic phenomena to advanced functionalities, the field of plasmonic metamaterials offers the promise of an important scientific and technological impact, with applications spanning from medical diagnostics to clean energy and information processing.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Magnetizations and magneto-transport properties of Ni-doped PrFeO3 thin films Feroz A. Mir, S. K. Sharma, Ravi Kumar Chin. Phys. B, 2014, 23 (4):  048101.  DOI: 10.1088/1674-1056/23/4/048101 Abstract ( 581 )   PDF (459KB) ( 588 )   The present study reports the magnetizations and magneto-transport properties of PrFe1-xNixO3 thin films grown by pulsed laser ablation technique on LaAlO3 substrates. From DC M/H plots of these films, weak ferromagnetism or ferrimagnetism behaviors are observed. With Ni substitution, reduction in saturation magnetization is also seen. With Ni doping, variations in saturation field (Hs), coercive field (Hc), Weiss temperature (θ), and effective magnetic moment (peff) are seen. A small change of magnetoresitance with application of higher field is observed. Various essential parameters like density of state (Nf) at Fermi level, Mott's characteristic temperature (T0), and activation energy (Ea) in the presence of and in the absence of magnetic field are calculated. The present observed magnetic properties are related to the change of Fe-O bond length (causing an overlap between the oxygen p orbital and iron d orbital) and the deviation of the Fe-O-Fe angle from 180°. Reduction of magnetic domain after Ni doping is also explored to explain the present observed magnetic behavior of the system. The influence of doping on various transport properties in these thin films indicates a distortion in the lattice structure and single particle band width, owing to stress-induced reduction in unit cell volume.

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Influences of nitrogen flow rate on the structures and properties of Ti and N co-doped diamond-like carbon films deposited by arc ion plating Zhang Lin (张林), Ma Guo-Jia (马国佳), Lin Guo-Qiang (林国强), Ma He (马贺), Han Ke-Chang (韩克昌) Chin. Phys. B, 2014, 23 (4):  048102.  DOI: 10.1088/1674-1056/23/4/048102 Abstract ( 625 )   PDF (555KB) ( 349 )   In this paper, Ti-C-N nanocomposite films are deposited under different nitrogen flow rates by pulsed bias arc ion plating using Ti and graphite targets in the Ar/N2 mixture gas. The surface morphologies, compositions, microstructures, and mechanical properties of the Ti-C-N films are investigated systematically by field emission scanning electron microscopy (FE-SEM), x-ray photoelectron spectroscopy (XPS), grazing incident x-ray diffraction (GIXRD), Raman spectra, and nano-indentation. The results show that the nanocrystalline Ti(C,N) phase precipitates in the film from GIXRD and XPS analysis, and Raman spectra prove the presence of diamond-like carbon, indicating the formation of nanocomposite film with microstructures comprising nanocrystalline Ti(C,N) phase embedded into a diamond-like matrix. The nitrogen flow rate has a significant effect on the composition, structure, and properties of the film. The nano-hardness and elastic modulus first increase and then decrease as nitrogen flow rate increases, reaching a maximum of 34.3 GPa and 383.2 GPa, at a nitrogen flow rate of 90 sccm, respectively.

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An optimized, sensitive and stable reduced graphene oxide-gold nanoparticle-luminol-H2O2 chemiluminescence system and its potential analytical application Hot! Wang Wen-Shuo (王闻硕), He Da-Wei (何大伟), Wang Ji-Hong (王继红), Duan Jia-Hua (段嘉华), Peng Hong-Shang (彭洪尚), Wu Hong-Peng (吴洪鹏), Fu Ming (富鸣), Wang Yong-Sheng (王永生), Zhang Xi-Qing (张希清) Chin. Phys. B, 2014, 23 (4):  048103.  DOI: 10.1088/1674-1056/23/4/048103 Abstract ( 479 )   PDF (826KB) ( 786 )   The chemiluminescence (CL) performance of luminol is improved using reduced graphene oxide/gold nanoparticle (rGO-AuNP) nano-composites as catalyst. To prepare this catalyst, we propose a linker free, one-step method to in-situ synthesize rGO-AuNP nano-composites. Various measurements are utilized to characterize the resulting rGO-AuNP samples, and it is revealed that rGO could improve the stability and conductivity. Furthermore, we investigate the CL signals of luminal catalyzed by rGO-AuNP. Afterwards, the size effect of particle and the assisted enhancement effect of rGO are studied and discussed in detail. Based on the discussion, an optimal, sensitive and stable rGO-AuNP-luminon-H2O2 CL system is proposed. Finally, we utilize the system as a sensor to detect hydrogen peroxide and organic compounds containing amino, hydroxyl, or thiol groups. The CL system might provide a more attractive platform for various analytical devices with CL detection in the field of biosensors, bioassays, and immunosensors.

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Synthesis and application of TiO2 single-crystal nanorod arrays grown by multicycle hydrothermal for dye-sensitized solar cells Zhu Jian-Jing (朱建晶), Zhao Yu-Long (赵宇龙), Zhu Lei (朱磊), Gu Xiu-Quan (顾修全), Qiang Ying-Huai (强颖怀) Chin. Phys. B, 2014, 23 (4):  048104.  DOI: 10.1088/1674-1056/23/4/048104 Abstract ( 511 )   PDF (702KB) ( 595 )   TiO2 is a wide band gap semiconductor with important applications in photovoltaic cells. Vertically aligned TiO2 nanorod arrays (NRs) are grown on the fluorine-doped tin oxide (FTO) substrates by a multicycle hydrothermal synthesis process. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED). It is found that dye-sensitized solar cells (DSSCs) assembled by the as-prepared TiO2 single-crystal NRs exhibit different trends under the condition of different nucleation and growth concentrations. Optimum cell performance is obtained with high nucleation concentration and low growth cycle concentration. The efficiency enhancement is mainly attributed to the improved specific surface area of the nanorod.

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Formation of ZnGa2O4 films by multilayer deposition and subsequent thermal annealing Yan Jin-Liang (闫金良), Zhao Yin-Nü (赵银女), Li Chao (李超) Chin. Phys. B, 2014, 23 (4):  048105.  DOI: 10.1088/1674-1056/23/4/048105 Abstract ( 658 )   PDF (421KB) ( 351 )   The Ga2O3/ZnO multilayer films are deposited on quartz substrates by magnetron sputtering, the thickness values of Ga2O3 layers are in a range of 19 nm-2.5 nm and the thickness of ZnO layer is a constant of 1 nm. Formation of spinel ZnGa2O4 film is achieved via the annealing of the Ga2O3/ZnO multilayer film. The influences of original Ga2O3 sublayer thickness on the optical and structural properties of Ga2O3/ZnO multilayer films and annealed films are studied. With the decrease of the thickness of Ga2O3 sublayer, the optical band-gap of Ga2O3/ZnO multilayer film decreases, the intensity of UV emission diminishes and the intensity of violet emission increases. The annealed film displays the enlarged optical band gap and the quenched violet emission. UV fluorescence bands are observed from Ga2O3 and ZnGa2O4.

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Solid solubility and photoluminescence of Y3Al5O12：Ce3+ prepared by using (Y1-xCex)2O3 as precursor Liu Si-Jia (刘思佳), Peng Tong-Jiang (彭同江), Song Zhen (宋振), Bian Liu (边柳), Song Gong-Bao (宋功保), Liu Quan-Lin (刘泉林) Chin. Phys. B, 2014, 23 (4):  048106.  DOI: 10.1088/1674-1056/23/4/048106 Abstract ( 639 )   PDF (671KB) ( 833 )   Trivalent cerium-doped yttrium aluminum garnet (YAG:Ce3+) phosphors are synthesized by solid-state reaction method through using (Y1-xCex)2O3 solid solutions as precursors. Solid solubility limits of Ce3+ replacing Y3+ in Y2O3 and YAG are determined to be 40% and 7.5%, respectively, based on the relationship between the lattice parameter and chemical composition. Using (Y1-xCex)2O3 as precursors we synthesize YAG:Ce3+single phase at 1450℃ and N2 atmosphere. However, under the same conditions using CeO2 there exists a second phase YAlO3 as impurity. The photoluminescence intensity of YAG:Ce3+ increases monotonically with the increase of Ce concentration until it reaches a maximum at solid solubility limits of Ce3+ in YAG.

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Relation between martensitic transformation temperature range and lattice distortion ratio of NiMnGaCoCu Heusler alloys Wei Jun (韦俊), Xie Ren (谢忍), Chen Le-Yi (陈乐易), Tang Yan-Mei (唐研梅), Xu Lian-Qiang (许连强), Tang Shao-Long (唐少龙), Du You-Wei (都有为) Chin. Phys. B, 2014, 23 (4):  048107.  DOI: 10.1088/1674-1056/23/4/048107 Abstract ( 485 )   PDF (360KB) ( 495 )   In order to study the relation between martensitic transformation temperature range ΔT (where ΔT is the difference between martensitic transformation start and finish temperature) and lattice distortion ratio (c/a) of martensitic transformation, a series of Ni46Mn28-xGa22Co4Cux (x= 2-5) Heusler alloys is prepared by arc melting method. The vibration sample magnetometer (VSM) experiment results show that ΔT increases when x> 4 and decreases when x< 4 with x increasing, and the minimal ΔT (about 1 K) is found at x=4. Ambient X-ray diffraction (XRD) results show that ΔT is proportional to c/a for non-modulated Ni46Mn28-xGa22Co4Cux (x= 2-5) martensites. The relation between ΔT and c/a is in agreement with the analysis result obtained from crystal lattice mismatch model. About 1000-ppm strain is found for the sample at x=4 when heating temperature increases from 323 K to 324 K. These properties, which allow a modulation of ΔT and temperature-induced strain during martensitic transformation, suggest Ni46Mn24Ga22Co4Cu4 can be a promising actuator and sensor.

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Preparation and modification of VO2 thin film on R-sapphire substrate by rapid thermal process Zhu Nai-Wei (朱乃伟), Hu Ming (胡明), Xia Xiao-Xu (夏晓旭), Wei Xiao-Ying (韦晓莹), Liang Ji-Ran (梁继然) Chin. Phys. B, 2014, 23 (4):  048108.  DOI: 10.1088/1674-1056/23/4/048108 Abstract ( 611 )   PDF (611KB) ( 570 )   The VO2 thin film with high performance of metal-insulator transition (MIT) is prepared on R-sapphire substrate for the first time by magnetron sputtering with rapid thermal process (RTP). The electrical characteristic and THz transmittance of MIT in VO2 film are studied by four-point probe method and THz time domain spectrum (THz-TDS). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and search engine marketing (SEM) are employed to analyze the crystalline structure, valence state, surface morphology of the film. Results indicate that the properties of VO2 film which is oxidized from the metal vanadium film in oxygen atmosphere are improved with a follow-up RTP modification in nitrogen atmosphere. The crystallization and components of VO2 film are improved and the film becomes compact and uniform. A better phase transition performance is shown that the resistance changes nearly 3 orders of magnitude with a 2-℃ hysteresis width and the THz transmittances are reduced by 64% and 60% in thermal and optical excitation respectively.

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Non-homogeneous SiGe-on-insulator formed by germanium condensation process Huang Shi-Hao (黄诗浩), Li Cheng (李成), Lu Wei-Fang (卢卫芳), Wang Chen (王尘), Lin Guang-Yang (林光杨), Lai Hong-Kai (赖虹凯), Chen Song-Yan (陈松岩) Chin. Phys. B, 2014, 23 (4):  048109.  DOI: 10.1088/1674-1056/23/4/048109 Abstract ( 447 )   PDF (331KB) ( 414 )   Ge condensation process of a sandwiched structure of Si/SiGe/Si on silicon-on-insulator (SOI) to form SiGe-on-insulator (SGOI) substrate is investigated. The non-homogeneity of SiGe on insulator is observed after a long time oxidation and annealing due to an increased consumption of silicon at the inflection points of the corrugated SiGe film morphology, which happens in the case of the rough surface morphology, with lateral Si atoms diffusing to the inflection points of the corrugated SiGe film. The transmission electron microscopy measurements show that the non-homogeneous SiGe layer exhibits a single crystalline nature with perfect atom lattice. Possible formation mechanism of the non-homogeneity SiGe layer is presented by discussing the highly nonuniform oxidation rate that is spatially dependent in the Ge condensation process. The results are of guiding significance for fabricating the SGOI by Ge condensation process.

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Aggregation of fullerene (C60) nanoparticle：A molecular-dynamic study He Su-Zhen (何素贞), Merlitz Holger, Wu Chen-Xu (吴晨旭) Chin. Phys. B, 2014, 23 (4):  048201.  DOI: 10.1088/1674-1056/23/4/048201 Abstract ( 734 )   PDF (356KB) ( 453 )   We present the results of molecular dynamics simulations of net positively charged fullerene nanoparticles in salt-free and salt-added solution. The aggregation of fullerene (C60)-like nanoparticle and counterion are studied in detail as a function of temperatures and a finite salt concentration. Our simulations show that the strong conformation changes as temperature changes. The net positively-charged nanoparticles do not repel each other but are condensed under proper temperatures. If salts are added, the aggregated nanoparticles will be disaggregated due to the Debye screening effect.

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Crystal structure and ionic conductivity of Mg-doped apatite-type lanthanum silicates La10Si6-xMgxO27-x(x=0-0.4 Yin Guang-Chao (尹广超), Yin Hong (殷红), Zhong Lin-Hong (仲林红), Sun Mei-Ling (孙美玲), Zhang Jun-Kai (张俊凯), Xie Xiao-Jun (谢晓君), Cong Ri-Dong (丛日东), Wang Xin (王欣), Gao Wei (高伟), Cui Qi-Liang (崔啟良) Chin. Phys. B, 2014, 23 (4):  048202.  DOI: 10.1088/1674-1056/23/4/048202 Abstract ( 452 )   PDF (717KB) ( 440 )   Lanthanum silicates La10Si6-xMgxO27-x (x= 0-0.4) were prepared by solid state synthesis to investigate the effect of Mg doping on crystal structure and ionic conductivity. Rietveld analysis of the powder XRD patterns reveals that Mg substitution on Si site results in significant enlargement of channel triangles, favoring oxide-ion conduction. Furthermore, an increase of Mg concentration significantly influences the linear density of interstitial oxygen, which plays an important role in ionic conductivity. The Arrhenius plots of La10Si6-xMgxO27-x (x=0-0.4) suggest that Mg-doped samples present higher conductivity and lower activation energy than non-doped La10Si6O27, and La10Si5.8Mg0.2O26.8 exhibits the highest conductivity with a value of 3.0× 10-2 S ·cm-1 at 700 ℃. Such conductive behavior agrees well with the refined results. The corresponding mechanism has been discussed in this paper.

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Unsteady MHD flow and heat transfer near stagnation point over a stretching/shrinking sheet in porous medium filled with a nanofluid Sadegh Khalili, Saeed Dinarvand, Reza Hosseini, Hossein Tamim, Ioan Pop Chin. Phys. B, 2014, 23 (4):  048203.  DOI: 10.1088/1674-1056/23/4/048203 Abstract ( 716 )   PDF (3312KB) ( 1013 )   In this article, the unsteady magnetohydrodynamic (MHD) stagnation point flow and heat transfer of a nanofluid over a stretching/shrinking sheet is investigated numerically. The similarity solution is used to reduce the governing system of partial differential equations to a set of nonlinear ordinary differential equations which are then solved numerically using the fourth-order Runge-Kutta method with shooting technique. The ambient fluid velocity, stretching/shrinking velocity of sheet, and the wall temperature are assumed to vary linearly with the distance from the stagnation point. To investigate the influence of various pertinent parameters, graphical results for the local Nusselt number, the skin friction coefficient, velocity profile, and temperature profile are presented for different values of the governing parameters for three types of nanoparticles, namely copper, alumina, and titania in the water-based fluid. It is found that the dual solution exists for the decelerating flow. Numerical results show that the extent of the dual solution domain increases with the increases of velocity ratio, magnetic parameter, and permeability parameter whereas it remains constant as the value of solid volume fraction of nanoparticles changes. Also, it is found that permeability parameter has a greater effect on the flow and heat transfer of a nanofluid than the magnetic parameter.

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Iron trichloride as oxidizer in acid slurry for chemical mechanical polishing of Ge2Sb2Te5 Yan Wei-Xia (闫未霞), Wang Liang-Yong (王良咏), Zhang Ze-Fang (张泽芳), Liu Wei-Li (刘卫丽), Song Zhi-Tang (宋志棠) Chin. Phys. B, 2014, 23 (4):  048301.  DOI: 10.1088/1674-1056/23/4/048301 Abstract ( 498 )   PDF (771KB) ( 719 )   The effect of iron trichloride (FeCl3) on chemical mechanical polishing (CMP) of Ge2Sb2Te5 (GST) film is investigated in this paper. The polishing rate of GST increases from 38 nm/min to 144 nm/min when the FeCl3 concentration changes from 0.01 wt% to 0.15 wt%, which is much faster than 20 nm/min for the 1 wt% H2O2-based slurry. This polishing rate trends are inversely correlated with the contact angle data of FeCl3-based slurry on the GST film surface. Thus, it is hypothesized that the hydrophilicity of the GST film surface is associated with the polishing rate during CMP. Atomic force microscope (AFM) and optical microscope (OM) are used to characterize the surface quality after CMP. The chemical mechanism is studied by potentiodynamic measurements such as Ecorr and Icorr to analyze chemical reaction between FeCl3 and GST surface. Finally, it is verified that slurry with FeCl3 has no influence on the electrical property of the post-CMP GST film by the resistivity-temperature (RT) tests.

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Computation of the locus crossing point location of MC circuit Liu Hai-Jun (刘海军), Li Zhi-Wei (李智炜), Bu Kai (步凯), Sun Zhao-Lin (孙兆林), Nie Hong-Shan (聂洪山) Chin. Phys. B, 2014, 23 (4):  048401.  DOI: 10.1088/1674-1056/23/4/048401 Abstract ( 645 )   PDF (310KB) ( 391 )   In this paper, the crossing point property of the i-v hysteresis curve in a memristor-capacitor (MC) circuit is analyzed. First, the ideal passive memristor on the crossing point property of i-v hysteresis curve is studied. Based on the analysis, the analytical derivation with respect to the crossing point location of MC circuit is given. Then the example of MC with linear memristance-versus-charge state map is demonstrated to discuss the drift property of cross-point location, caused by the frequency and capacitance value.

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Three-dimensional simulation method of multipactor in microwave components for high-power space application Li Yun (李韵), Cui Wan-Zhao (崔万照), Zhang Na (张娜), Wang Xin-Bo (王新波), Wang Hong-Guang (王洪广), Li Yong-Dong (李永东), Zhang Jian-Feng (张剑锋) Chin. Phys. B, 2014, 23 (4):  048402.  DOI: 10.1088/1674-1056/23/4/048402 Abstract ( 632 )   PDF (4613KB) ( 738 )   Based on the particle-in-cell technology and the secondary electron emission theory, a three-dimensional simulation method for multipactor is presented in this paper. By combining the finite difference time domain method and the particle tracing method, such an algorithm is self-consistent and accurate since the interaction between electromagnetic fields and particles is properly modeled. In the time domain aspect, the generation of multipactor can be easily visualized, which makes it possible to gain a deeper insight into the physical mechanism of this effect. In addition to the classic secondary electron emission model, the measured practical secondary electron yield is used, which increases the accuracy of the algorithm. In order to validate the method, the impedance transformer and ridge waveguide filter are studied. By analyzing the evolution of the secondaries obtained by our method, multipactor thresholds of these components are estimated, which show good agreement with the experimental results. Furthermore, the most sensitive positions where multipactor occurs are determined from the phase focusing phenomenon, which is very meaningful for multipactor analysis and design.

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The determination of the relative permittivity of periodic stratified media based on the iterative time-reversal method Zhang Zhi-Min (章志敏), Wang Bing-Zhong (王秉中), Liang Mu-Sheng (梁木生), Ji Qing (纪晴), Song Gang-Bing (宋钢兵) Chin. Phys. B, 2014, 23 (4):  048403.  DOI: 10.1088/1674-1056/23/4/048403 Abstract ( 583 )   PDF (1295KB) ( 430 )   In this paper, we present a new method to determine the relative permittivity of periodic stratified media using the iterative time-reversal method. Based on transmission line theory, the focal peak value of iterative time-reversal electromagnetic waves, which contain information about the periodic stratified medium, is computed in pulse-echo mode. Using the relationship between the focal peak value and the relative permittivity of the periodic stratified medium, the relative permittivity can be obtained by measuring the focal peak value. Numerical simulations are conducted, and the results demonstrate the feasibility of the proposed approach to the measurement of the relative permittivity of a periodic stratified medium.

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Charge transport in monolayer poly(3-hexylthiophene) thin-film transistors Xu Zong-Xiang (许宗祥), Roy V. A. L. Chin. Phys. B, 2014, 23 (4):  048501.  DOI: 10.1088/1674-1056/23/4/048501 Abstract ( 572 )   PDF (537KB) ( 454 )   It is found that ultrathin poly(3-hexylthiophene) (P3HT) film with a 2.5 nm-thick layer exhibits a higher mobility of 5.0× 10-2 cm2/V·s than its bulk counterpart. The crystalline structure of the as-fabricated ultrathin P3HT layer is verified by atomic force microscopy as well as grazing incidence X-ray diffraction. Transient measurements of the as-fabricated transistors reveal the influence of the interface traps on charge transport. These results are explained by the trap energy level distribution at the interface manipulated by layers of polymer film.

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A GaN–AlGaN–InGaN last quantum barrier in an InGaN/GaN multiple-quantum-well blue LED Yang Bin (杨斌), Guo Zhi-You (郭志友), Xie Nan (解楠), Zhang Pan-Jun (张盼君), Li Jing (李婧), Li Fang-Zheng (李方正), Lin Hong (林宏), Zheng Huan (郑欢), Cai Jin-Xin (蔡金鑫) Chin. Phys. B, 2014, 23 (4):  048502.  DOI: 10.1088/1674-1056/23/4/048502 Abstract ( 557 )   PDF (1099KB) ( 825 )   The advantages of a GaN-AlGaN-InGaN last quantum barrier (LQB) in an InGaN-based blue light-emitting diode are analyzed via numerical simulation. We found an improved light output power, lower current leakage, higher recombination rate, and less efficiency droop compared with conventional GaN LQBs. These improvements in the electrical and optical characteristics are attributed mainly to the specially designed GaN-AlGaN-InGaN LQB, which enhances electron confinement and improves hole injection efficiency.

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Improvement and error analysis of quantitative information extraction in diffraction-enhanced imaging Yang Hao (杨浩), Xuan Rui-Jiao (轩瑞娇), Hu Chun-Hong (胡春红), Duan Jing-Hao (段敬豪) Chin. Phys. B, 2014, 23 (4):  048701.  DOI: 10.1088/1674-1056/23/4/048701 Abstract ( 523 )   PDF (538KB) ( 366 )   Diffraction-enhanced imaging (DEI) is a powerful phase-sensitive technique that provides higher spatial resolution and supercontrast of weakly absorbing objects than conventional radiography. It derives contrast from the X-ray absorption, refraction, and ultra-small-angle X-ray scattering (USAXS) properties of an object. The separation of different-contrast contributions from images is an important issue for the potential application of DEI. In this paper, an improved DEI (IDEI) method is proposed based on the Gaussian curve fitting of the rocking curve (RC). Utilizing only three input images, the IDEI method can accurately separate the absorption, refraction, and USAXS contrasts produced by the object. The IDEI method can therefore be viewed as an improvement to the extended DEI (EDEI) method. In contrast, the IDEI method can circumvent the limitations of the EDEI method well since it does not impose a Taylor approximation on the RC. Additionally, analysis of the IDEI model errors is performed to further investigate the factors that lead to the image artifacts, and finally validation studies are conducted using computer simulation and synchrotron experimental data.

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Cardiac electrical activity imaging of patients with CRBBB or CLBBB in magnetocardiography Zhu Jun-Jie (朱俊杰), Jiang Shi-Qin (蒋式勤), Wang Wei-Yuan (王伟远), Zhao Chen (赵晨), Wu Yan-Hua (吴燕华), Luo Ming (罗明), Quan Wei-Wei (权薇薇) Chin. Phys. B, 2014, 23 (4):  048702.  DOI: 10.1088/1674-1056/23/4/048702 Abstract ( 654 )   PDF (1333KB) ( 430 )   A new method for the imaging of cardiac electrical activity in patients with complete right bundle branch block (CRBBB) or complete left bundle branch block (CLBBB) is investigated using magnetocardiographic recordings of the surface of the body. This is based on the assumption that an equivalent single-current dipole moves along the unblocked bundle branch, whose position in the measurement plane is expressed in terms of the maximum and minimum, as well as the maximum gradient value of the measured magnetic field. The trajectory of the moving dipole on the measurement plane is indicative of the excitation conduction of the CRBBB or CLBBB subject during ventricular depolarization and repolarization, which is deduced by comparing each change between the dipole moment and the maximum current density in a corresponding pseudo-current density map. In summary, this method can distinguish CRBBB from CLBBB subjects by means of the dipole depth and two dipole moment components. The possibility of visualizing the excitation conduction in a CRBBB or CLBBB subject during ventricular depolarization and repolarization is then discussed.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Early warning signals of abrupt temperature change in different regions of China over the past 50 years Tong Ji-Long (仝纪龙), Wu Hao (吴浩), Hou Wei (侯威), He Wen-Ping (何文平), Zhou Jie (周杰) Chin. Phys. B, 2014, 23 (4):  049201.  DOI: 10.1088/1674-1056/23/4/049201 Abstract ( 531 )   PDF (2298KB) ( 274 )   In this paper, the early warning signals of abrupt temperature change in different regions of China are investigated. Seven regions are divided on the basis of different climate temperature patterns, obtained through the rotated empirical orthogonal function, and the signal-to-noise temperature ratios for each region are then calculated. Based on the concept of critical slowing down, the temperature data that contain noise in the different regions of China are preprocessed to study the early warning signals of abrupt climate change. First, the Mann-Kendall method is used to identify the instant of abrupt climate change in the temperature data. Second, autocorrelation coefficients that can identify critical slowing down are calculated. The results show that the critical slowing down phenomenon appeared in temperature data about 5-10 years before abrupt climate change occurred, which indicates that the critical slowing down phenomenon is a possible early warning signal for abrupt climate change, and that noise has less influence on the detection results of the early warning signals. Accordingly, this demonstrates that the model is reliable in identifying the early warning signals of abrupt climate change based on detecting the critical slowing down phenomenon, which provides an experimental basis for the actual application of the method.