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Chin. Phys. B  
  Chin. Phys. B--2013, Vol.22, No.11
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New homotopy analysis transform method for solving the discontinued problems arising in nanotechnology

M. M. Khader, Sunil Kumar, S. Abbasbandy
Chin. Phys. B 2013, 22 (11): 110201 ;  doi: 10.1088/1674-1056/22/11/110201
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We present a new reliable analytical study for solving the discontinued problems arising in nanotechnology. Such problems are presented as nonlinear differential–difference equations. The proposed method is based on the Laplace transform with the homotopy analysis method (HAM). This method is a powerful tool for solving a large amount of problems. This technique provides a series of functions which may converge to the exact solution of the problem. A good agreement between the obtained solution and some well-known results is obtained.

Exact solutions of nonlinear fractional differential equations by (G’/G)-expansion method

Ahmet Bekir, Özkan Güner
Chin. Phys. B 2013, 22 (11): 110202 ;  doi: 10.1088/1674-1056/22/11/110202
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In this paper, we use the fractional complex transform and the (G’/G)-expansion method to study the nonlinear fractional differential equations and find the exact solutions. The fractional complex transform is proposed to convert a partial fractional differential equation with Jumarie’s modified Riemann–Liouville derivative into its ordinary differential equation. It is shown that the considered transform and method are very efficient and powerful in solving wide classes of nonlinear fractional order equations.

Invariance of Painlevé property for some reduced (1+1)-dimensional equations

Zhi Hong-Yan, Chang Hui
Chin. Phys. B 2013, 22 (11): 110203 ;  doi: 10.1088/1674-1056/22/11/110203
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We study the Painlevé property of the (1+1)-dimensional equations arising from the symmetry reduction for the (2+1)-dimensional ones. Firstly, we derive the similarity reduction of the (2+1)-dimensional potential Calogero–Bogoyavlenskii–Schiff (CBS) equation and Konopelchenko–Dubrovsky (KD) equations with the optimal system of the admitted one-dimensional subalgebras. Secondly, by analyzing the reduced CBS, KD, and Burgers equations with Painlevé test, respectively, we find both the Painlevé integrability, and the number and location of resonance points are invariant, if the similarity variables include all of the independent variables.

Finite-time consensus for leader-following multi-agent systems over switching network topologies

Sun Feng-Lan, Zhu Wei
Chin. Phys. B 2013, 22 (11): 110204 ;  doi: 10.1088/1674-1056/22/11/110204
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Finite-time consensus problem of the leader-following multi-agent system under switching network topologies is studied in this paper. Based on the graph theory, matrix theory, homogeneity with dilation, and LaSalle’s invariance principle, the control protocol of each agent using local information is designed, and the detailed analysis of the leader-following finite-time consensus is provided. Some examples and simulation results are given to illustrate the effectiveness of the obtained theoretical results.

Stochastic responses of Duffing–Van der Pol vibro-impact system under additive colored noise excitation

Li Chao, Xu Wei, Wang Liang, Li Dong-Xi
Chin. Phys. B 2013, 22 (11): 110205 ;  doi: 10.1088/1674-1056/22/11/110205
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A response analysis procedure is developed for a vibro-impact system excited by colored noise. The non-smooth transformation is used to convert the vibro-impact system into a new system without impact term. With the help of the modified quasi-conservative averaging, the total energy of the new system can be approximated as a Markov process, and the stationary probability density function (PDF) of the total energy is derived. The response PDFs of the original system are obtained using the analytical solution of the stationary PDF of the total energy. The validity of the theoretical results is tested through comparison with the corresponding simulation results. Moreover, stochastic bifurcations are also explored.

Exact solution of Schrödinger equation with q-deformed quantum potentials using Nikiforov–Uvarov method

Falaye B. J., Oyewumi K. J., Abbas M.
Chin. Phys. B 2013, 22 (11): 110301 ;  doi: 10.1088/1674-1056/22/11/110301
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In this paper, we present the exact solution of the one-dimensional Schrödinger equation for the q-deformed quantum potentials via the Nikiforov–Uvarov method. The eigenvalues and eigenfunctions of these potentials are obtained via this method. The energy equations and the corresponding wave functions for some special cases of these potentials are briefly discussed. The PT-symmetry and Hermiticity for these potentials are also discussed.

Minimum detection efficiency for the loophole-free confirmation of quantum contextuality

Xiang Yang, Hong Fang-Yu
Chin. Phys. B 2013, 22 (11): 110302 ;  doi: 10.1088/1674-1056/22/11/110302
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Klyachko–Can–Binicio?lu–Shumovsky (KCBS) inequality is a Bell-like inequality, the violation of which can be used to confirm the existence of quantum contextuality. However, the imperfection of detection efficiency may cause the so-called loophole in actual KCBS’s experiments. We derive an alternative KCBS inequality to deal with the loophole in actual KCBS’s experiments. We prove that if the experimental data violate this KCBS inequality, the loophole-free violation of the original KCBS inequality will occur. We show that the minimum detection efficiency needed for a loophole-free violation of the KCBS inequality is about 0.9738.

Efficient electronic entanglement concentration assisted by single mobile electrons

Sheng Yu-Bo, Zhou Lan
Chin. Phys. B 2013, 22 (11): 110303 ;  doi: 10.1088/1674-1056/22/11/110303
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We present an efficient entanglement concentration protocol (ECP) for mobile electrons with charge detection. This protocol is quite different from other ECPs for one can obtain a maximally entangled pair from a pair of less-entangled state and a single mobile electron with a certain probability. With the help of charge detection, it can be repeated to reach a higher success probability. It also does not need to know the coefficient of the original less-entangled states. All these advantages may make this protocol useful in current distributed quantum information processing.

Deterministic assisted clone of an unknown four-particle entangled cluster-type state

Ma Song-Ya, Luo Ming-Xing, Sun Ying
Chin. Phys. B 2013, 22 (11): 110304 ;  doi: 10.1088/1674-1056/22/11/110304
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Two deterministic schemes are proposed to realize the assisted clone of an unknown four-particle entangled cluster-type state. The schemes include two stages. The first stage requires teleportation via maximal entanglement as the quantum channel. In the second stages of the protocols, two novel sets of mutually orthogonal basis vectors are constructed. With the assistance of the preparer through a four-particle or two-step two-particle projective measurement under these bases, the perfect copy of an original state can be produced. Comparing with the previous protocols which produce the unknown state and its orthogonal complement state at the site of the sender, the proposed schemes generate the unknown state deterministically.

Implementation of quantum partial search with superconducting quantum interference device qudits in cavity QED

Li Hong-Yi, Wu Chun-Wang, Chen Yu-Bo, Lin Yuan-Gen, Chen Ping-Xing, Li Cheng-Zu
Chin. Phys. B 2013, 22 (11): 110305 ;  doi: 10.1088/1674-1056/22/11/110305
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We present a method to implement the quantum partial search of the database separated into any number of blocks with qudits, D-level quantum systems. Compared with the partial search using qubits, our method needs fewer iteration steps and uses the carriers of the information more economically. To illustrate how to realize the idea with concrete physical systems, we propose a scheme to carry out a twelve-dimensional partial search of the database partitioned into three blocks with superconducting quantum interference devices (SQUIDs) in cavity QED. Through the appropriate modulation of the amplitudes of the microwave pulses, the scheme can overcome the non-identity of the cavity–SQUID coupling strengths due to the parameter variations resulting from the fabrication processes. Numerical simulation under the influence of the cavity and SQUID decays shows that the scheme could be achieved efficiently within current state-of-the-art technology.

Novel exact solutions of coupled nonlinear Schrödinger equations with time–space modulation

Chen Jun-Chao, Li Biao, Chen Yong
Chin. Phys. B 2013, 22 (11): 110306 ;  doi: 10.1088/1674-1056/22/11/110306
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We construct various novel exact solutions of two coupled dynamical nonlinear Schrödinger equations. Based on the similarity transformation, we reduce the coupled nonlinear Schrödinger equations with time-and space-dependent potentials, nonlinearities, and gain or loss to the coupled dynamical nonlinear Schrödinger equations. Some special types of non-travelling wave solutions, such as periodic, resonant, and quasiperiodically oscillating solitons, are used to exhibit the wave propagations by choosing some arbitrary functions. Our results show that the number of the localized wave of one component is always twice that of the other one. In addition, the stability analysis of the solutions is discussed numerically.

Effects of effective attractive multi-body interaction on quantum phase and transport dynamics of a strongly correlated bosonic gas across the superfluid to Mott insulator transition Hot!

Sun Jian-Fang, Cui Guo-Dong, Jiang Bo-Nan, Qian Jun, Wang Yu-Zhu
Chin. Phys. B 2013, 22 (11): 110307 ;  doi: 10.1088/1674-1056/22/11/110307
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We theoretically investigate quantum phases and transport dynamics of ultracold atoms trapped in an optical lattice in the presence of effective multi-body interaction. When a harmonic external potential is added, several interesting phenomena are revealed, such as the broadening and the emergence of a central insulator plateau and the phase transition between superfluid and Mott insulator phase. We also study the transport of the system which runs across the superfluid–insulator transition after ramping up the lattice, and predict a slower relaxation which is attributed to the influence of the multi-body interaction on the mass transport.

Skyrmion crystals in pseudo-spin-1/2 Bose–Einstein condensates

Zhang Cong, Guo Wen-An, Feng Shi-Ping, Yang Shi-Jie
Chin. Phys. B 2013, 22 (11): 110308 ;  doi: 10.1088/1674-1056/22/11/110308
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Exact two-dimensional solutions are constructed for the pseudo-spin-1/2 Bose–Einstein condensates, which are described by the coupled nonlinear Gross–Pitaevskii equations where the intra-and inter-species coupling constants are assumed to be equal. The equations are decoupled by means of re-combinations of the nonlinear terms of the hyperfine states according to the spatial dimensions. The stationary solutions form various spin textures which are identified as skyrmion crystals. In a special case, a crystal of skyrmion–anti-skyrmion pairs is formed in the soliton limit.

Quantum phase transitions of fermionic atoms in an anisotropic triangular optical lattice

Bao An, Chen Yao-Hua, Zhang Xiao-Zhong
Chin. Phys. B 2013, 22 (11): 110309 ;  doi: 10.1088/1674-1056/22/11/110309
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The effect of anisotropy caused by a confining potential on the properties of fermionic cold atoms in a triangular optical lattice is systematically investigated by using the dynamical cluster approximation combined with the continuous time quantum Monte–Carlo algorithm. The quantum phase diagrams which reflect the temperature–interaction relation and the competition between the anisotropic parameter and the interaction are presented with full consideration of the anisotropy of the system. Our results show that the system undergoes a transition from Fermi liquid to Mott insulator when the repulsive interaction reaches a critical value. The Kondo effect also can be observed in this system and the pseudogap is suppressed at low temperatures due to the Kondo effect. A feasible experiment protocol to observe these phenomena in an anisotropic triangular optical lattice with cold atoms is proposed, in which the hopping terms are closely related to the lattice confining potential and the atomic interaction can be adjusted via the Feshbach resonance.

Invariant expression for tunneling rate under canonical transformations

Ren Jun, Jia Meng-Wen, Wei Yi-Huan
Chin. Phys. B 2013, 22 (11): 110401 ;  doi: 10.1088/1674-1056/22/11/110401
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The original formula to calculate the tunneling rate through event horizons is apparently dependent on the type of coordinates used. In this paper, we propose an invariant expression under canonical transformations to study the tunneling effect. Moreover, the problem of factor 2 is solved naturally. As an application of this expression, we obtain the same tunneling rate both in the Schwarzschild and the Painlevé coordinates. It is shown that once the suitable formula to calculate tunneling rate is correctly identified, the tunneling method is manifestly covariant.

Symmetrical dynamical characteristic of peak and valley current-mode controlled single-phase H-bridge inverter

Liu Hong-Chen, Li Fei, Su Zhen-Xia, Sun Li-Shan
Chin. Phys. B 2013, 22 (11): 110501 ;  doi: 10.1088/1674-1056/22/11/110501
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Complex dynamical phenomenon was studied in the single phase H-bridge inverter which was controlled by either a peak current or a valley current. The state functions and the discrete iterative map equations were established to analyze the dynamical phenomenon in the single phase H-bridge inverter. The dynamical characteristics of the single phase H-bridge inverter, such as time domain waveform diagram, bifurcation diagram, and folding map, were obtained by using the numerical calculation when the circuit parameters varied in specific range. Moreover, the simulation results were obtained by using the OrCAD-PSpice software to validate the numerical calculation. Both the numerical calculation and the circuit simulation show that the symmetrical dynamical phenomenon occurs in the single phase H-bridge inverter controlled by the peak current or the valley current.

Existence of heteroclinic orbits in a novel three-order dynamical system

Hu Yu, Min Le-Quan, Zhen Ping
Chin. Phys. B 2013, 22 (11): 110502 ;  doi: 10.1088/1674-1056/22/11/110502
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In this paper, we design a novel three-order autonomous system. Numerical simulations reveal the complex chaotic behaviors of the system. By applying the undetermined coefficient method, we find a heteroclinic orbit in the system. As a result, the Ši’lnikov criterion along with some other given conditions guarantees that the system has both Smale horseshoes and chaos of horseshoe type.

A secure key agreement protocol based on chaotic maps

Wang Xing-Yuan, Luan Da-Peng
Chin. Phys. B 2013, 22 (11): 110503 ;  doi: 10.1088/1674-1056/22/11/110503
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To guarantee the security of communication in the public channel, many key agreement protocols have been proposed. Recently, Gong et al. proposed a key agreement protocol based on chaotic maps with password sharing. In this paper, Gong et al.’s protocol is analyzed, and we find that this protocol exhibits key management issues and potential security problems. Furthermore, the paper presents a new key agreement protocol based on enhanced Chebyshev polynomials to overcome these problems. Through our analysis, our key agreement protocol not only provides mutual authentication and the ability to resist a variety of common attacks, but also solve the problems of key management and security issues existing in Gong et al.’s protocol.

H synchronization of chaotic neural networks with time-varying delays

O. M. Kwon, M. J. Park, Ju H. Park, S. M. Lee, E. J. Cha
Chin. Phys. B 2013, 22 (11): 110504 ;  doi: 10.1088/1674-1056/22/11/110504
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In this paper, we investigate the problem of H synchronization for chaotic neural networks with time-varying delays. A new model of the networks with disturbances in both master and slave systems is presented. By constructing a suitable Lyapunov–Krasovskii functional and using a reciprocally convex approach, a novel H synchronization criterion for the networks concerned is established in terms of linear matrix inequalities (LMIs) which can be easily solved by various effective optimization algorithms. Two numerical examples are given to illustrate the effectiveness of the proposed method.

Bounded consensus tracking of second-order multi-agent systems with sampling delay under directed networks

Li Li, Fang Hua-Jing
Chin. Phys. B 2013, 22 (11): 110505 ;  doi: 10.1088/1674-1056/22/11/110505
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The bounded consensus tracking problems of second-order multi-agent systems under directed networks with sampling delay are addressed in this paper. When the sampling delay is more than a sampling period, new protocols based on sampled-data control are proposed so that each agent can track the time-varying reference state of the virtual leader. By using the delay decomposition approach, the augmented matrix method, and the frequency domain analysis, necessary and sufficient conditions are obtained, which guarantee that the bounded consensus tracking is realized. Furthermore, some numerical simulations are presented to demonstrate the effectiveness of the theoretical results.

Analyses of the endoreversible Carnot cycle with entropy theory and entransy theory

Wang Wen-Hua, Cheng Xue-Tao, Liang Xin-Gang
Chin. Phys. B 2013, 22 (11): 110506 ;  doi: 10.1088/1674-1056/22/11/110506
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The endoreversible Carnot cycle is analyzed based on the concepts of entropy generation, entropy generation number, entransy loss, and entransy loss coefficient. The relationships of the cycle output power and heat-work conversion efficiency with these parameters are discussed. For the numerical examples discussed, the preconditions of the application for these concepts are derived. When the inlet temperatures and heat capacity flow rates of hot streams and environment temperature are prescribed, the results show that the concepts of entropy generation and entransy loss are applicable. However, in the presence of various inlet temperatures of streams, larger entransy loss rate still leads to larger output power, while smaller entropy generation rate does not. When the heat capacity flow rates of hot streams are various, neither larger entransy loss rate nor smaller entropy generation rate always leads to larger output power. Larger entransy loss coefficient always leads to larger heat-work conversion efficiency for the cases discussed, while smaller entropy generation number does not always.
TOPICAL REVIEW—Quantum information

Towards quantum-enhanced precision measurements:Promise and challenges

Zhang Li-Jian, Xiao Min
Chin. Phys. B 2013, 22 (11): 110310 ;  doi: 10.1088/1674-1056/22/11/110310
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Quantum metrology holds the promise of improving the measurement precision beyond the limit of classical approaches. To achieve such enhancement in performance requires the development of quantum estimation theories as well as novel experimental techniques. In this article, we provide a brief review of some recent results in the field of quantum metrology. We emphasize that the unambiguous demonstration of the quantum-enhanced precision needs a careful analysis of the resources involved. In particular, the implementation of quantum metrology in practice requires us to take into account the experimental imperfections included, for example, particle loss and dephasing noise. For a detailed introduction to the experimental demonstrations of quantum metrology, we refer the reader to another article ‘Quantum metrology’ in the same issue.

Quantum cloning machines and their implementation in physical systems

Wu Tao, Fang Bao-Long, Ye Liu
Chin. Phys. B 2013, 22 (11): 110311 ;  doi: 10.1088/1674-1056/22/11/110311
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We review the basic theory of approximate quantum cloning for discrete variables and some schemes for implementing quantum cloning machines. Several types of approximate quantum clones and their expansive quantum clones are introduced. As for the implementation of quantum cloning machines, we review some design methods and recent experimental results.

Disorder and decoherence in coined quantum walks

Zhang Rong, Qin Hao, Tang Bao, Xue Peng
Chin. Phys. B 2013, 22 (11): 110312 ;  doi: 10.1088/1674-1056/22/11/110312
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This article aims to provide a review on quantum walks. Starting form a basic idea of discrete-time quantum walks, we will review the impact of disorder and decoherence on the properties of quantum walks. The evolution of the standard quantum walks is deterministic and disorder introduces randomness to the whole system and change interference pattern leading to the localization effect. Whereas, decoherence plays the role of transmitting quantum walks to classical random walks.

Progress in superconducting qubits from the perspective of coherence and readout

Zhong You-Peng, Li Chun-Yan, Wang Hao-Hua, Chen Yu
Chin. Phys. B 2013, 22 (11): 110313 ;  doi: 10.1088/1674-1056/22/11/110313
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Superconducting qubits are Josephson junction-based circuits that exhibit macroscopic quantum behavior and can be manipulated as artificial atoms. Benefiting from the well-developed technology of microfabrication and microwave engineering, superconducting qubits have great advantages in design flexibility, controllability, and scalability. Over the past decade, there has been rapid progress in the field, which greatly improved our understanding of qubit decoherence and circuit optimization. The single-qubit coherence time has been steadily raised to the order of 10 to 100 μs, allowing for the demonstration of high-fidelity gate operations and measurement-based feedback control. Here we review recent progress in the coherence and readout of superconducting qubits.

Quantum metrology

Xiang Guo-Yong, Guo Guang-Can
Chin. Phys. B 2013, 22 (11): 110601 ;  doi: 10.1088/1674-1056/22/11/110601
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The statistical error is ineluctable in any measurement. Quantum techniques, especially with the development of quantum information, can help us squeeze the statistical error and enhance the precision of measurement. In a quantum system, there are some quantum parameters, such as the quantum state, quantum operator, and quantum dimension, which have no classical counterparts. So quantum metrology deals with not only the traditional parameters, but also the quantum parameters. Quantum metrology includes two important parts: measuring the physical parameters with a precision beating the classical physics limit and measuring the quantum parameters precisely. In this review, we will introduce how quantum characters (e.g., squeezed state and quantum entanglement) yield a higher precision, what the research areas are scientists most interesting in, and what the development status of quantum metrology and its perspectives are.

Review of cavity optomechanical cooling

Liu Yong-Chun, Hu Yu-Wen, Wong Chee Wei, Xiao Yun-Feng
Chin. Phys. B 2013, 22 (11): 114213 ;  doi: 10.1088/1674-1056/22/11/114213
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Quantum manipulation of macroscopic mechanical systems is of great interest in both fundamental physics and applications ranging from high-precision metrology to quantum information processing. For these purposes, a crucial step is to cool the mechanical system to its quantum ground state. In this review, we focus on the cavity optomechanical cooling, which exploits the cavity enhanced interaction between optical field and mechanical motion to reduce the thermal noise. Recent remarkable theoretical and experimental efforts in this field have taken a major step forward in preparing the motional quantum ground state of mesoscopic mechanical systems. This review first describes the quantum theory of cavity optomechanical cooling, including quantum noise approach and covariance approach; then, the up-to-date experimental progresses are introduced. Finally, new cooling approaches are discussed along the directions of cooling in the strong coupling regime and cooling beyond the resolved sideband limit.

Graphene-like physics in optical lattices

Mei Feng, Zhang Dan-Wei, Zhu Shi-Liang
Chin. Phys. B 2013, 22 (11): 116106 ;  doi: 10.1088/1674-1056/22/11/116106
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Graphene has attracted enormous attention over the past years in condensed matter physics. The most interesting feature of graphene is that its low-energy excitations are relativistic Dirac fermions. Such feature is the origin of many topological properties in graphene-like physics. On the other hand, ultracold quantum gas trapped in an optical lattice has become a unique setting for quantum simulation of condensed matter physics. Here, we mainly review our recent work on quantum simulation of graphene-like physics with ultracold atoms trapped in a honeycomb or square optical lattice, including the simulation of Dirac fermions and quantum Hall effect with and without Landau levels. We also present the related experimental advances.

Quantitative analysis of the self-absorption and reemission effects on the emission spectrum of photoluminescence in right-angle excitation–detection configuration

Wang Zhen-Hua, Wu Yu-E, Zhang Xin-Zheng, Yun Zhi-Qiang, Li Wei, Xu Jing-Jun
Chin. Phys. B 2013, 22 (11): 113301 ;  doi: 10.1088/1674-1056/22/11/113301
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A theoretical approach based on differential radiative transport is proposed to quantitatively analyze the self-absorption and reemission effects on the emission spectrum for right angle excitation–detection photoluminescence measurements, and the wavelength dependence of the reemission effect is taken into account. Simulations and experiments are performed using rhodamine 6G solutions in ethanol as model samples. It is shown that the self-absorption effect is the dominant effect on the detected spectrum by inducing pseudo red-shift and reducing total intensity; whereas the reemission effect partly compensates for signal decrease and also results in an apparent signal gain at the wavelengths without absorption. Both effects decrease with the decrease in the sample concentration and the propagation distance of the emission light inside the sample. We therefore suggest that diluted solutions are required for accurate photoluminescence spectrum measurements and photoluminescence-based measurements.

Product polarization and mechanism of Li+HF(v=0, j=0)→LiF (v’, j’)+H collision reaction

Yue Xian-Fang
Chin. Phys. B 2013, 22 (11): 113401 ;  doi: 10.1088/1674-1056/22/11/113401
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A state-to-state dynamics analysis for the Li+HF (v = 0, j = 0)→LiF (v’, j’)+H collision reaction has been performed through quasiclassical trajectory (QCT) calculations. It is found that the differential cross section (DCS) of the LiF products from the title reaction is preferentially backward scattering for v’=0, yet forward scattering for v’=1 and 2. For v’=3, the DCS exhibits forward, backward, and sideways scatterings. The variation of the internuclear distances and angles along the propagation time reveals that more than 99.08% of reaction trajectories undergo the direct reaction mechanism. The values of the polarization parameters a1-{1} and a0{2} demonstrate that the product rotational angular moment j’ is not only aligned perpendicular to the reagent relative velocity vector k, but also oriented along the negative y axis. These product polarization results agree well with the recent quantum mechanical studies. The mechanism of these results was proposed and discussed in detail.

Charge state effect on the K-shell ionization of iron by xenon ions near the Bohr velocity

Zhou Xian-Ming, Zhao Yong-Tao, Ren Jie-Ru, Cheng Rui, Lei Yu, Sun Yuan-Bo, Xu Ge, Wang Yu-Yu, Liu Shi-Dong, Xiao Guo-Qing
Chin. Phys. B 2013, 22 (11): 113402 ;  doi: 10.1088/1674-1056/22/11/113402
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Fe K-shell ionization cross sections induced by 2.4–6.0 MeV Xe20+ are measured and compared with different binary-encounter-approximation (BEA) models. The results indicate that the BEA model corrected both by the Coulomb repulsion and by the effective nuclear charge (Zeff) agrees well with the experimental data. Comparison of Fe K-shell X-ray emission induced by 5 MeV xenon ions with different initial charge states (20+, 22+, 26+, 30+) verifies the applicability of the effective nuclear charge (Zeff) correction for the BEA model. It is found that Zeff correction is reasonable to describe direct ionization induced by xenon ions with no initial M-shell vacancies. However, when the M shell is opened, the Zeff corrected BEA model is unable to explain the inner-shell ionization, and the electron transfer by molecular-orbital promotion should be considered.

Enhanced optical transmission by V-shaped nanoslit in metal film

He Meng-Dong, Ma Wang-Guo, Wang Xin-Jun
Chin. Phys. B 2013, 22 (11): 114201 ;  doi: 10.1088/1674-1056/22/11/114201
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In this paper, we reveal that the enhanced transmission through a perforated metal film can be further boosted up by a V-shaped nanoslit, which consists of two connected oblique slits. The maximum transmission at resonance can be enhanced significantly by 71.5% in comparison with the corresponding vertical slit with the same exit width. The value and position of transmission resonance peak strongly depend on the apex angle of the V-shaped slit. The optimum apex angle, at which the transmission is maximal, is sensitive to the slit width. Such phenomena can be well explained by a concrete picture in which the incident wave drives free electrons on the slit walls. Moreover, we also simply analyze the splitting of the transmission peak in the symmetry broken V-shaped slit, originating from the resonances of different parts of the V-shaped slit. We expect that our findings will be used to design the nanoscale light sources based on the metal nanoslit structures.

A new near-field phase-correction method for superlens

Wang Ying-Qi, Ye Jia-Sheng, Liu Shu-Tian, Zhang Yan
Chin. Phys. B 2013, 22 (11): 114202 ;  doi: 10.1088/1674-1056/22/11/114202
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A new phase-correction method in a realistic loss superlens imaging system is theoretically predicted. The image resolution is enhanced using the near-field active phase-correction method. Resolvable separation between two slits has been significantly improved to λ/20 for the symmetrical superlens system and λ/12 for unsymmetrical system.

Slow light via four-wave mixing in a hot rubidium vapour

Ding Dong-Sheng, Zhou Zhi-Yuan, Shi Bao-Sen
Chin. Phys. B 2013, 22 (11): 114203 ;  doi: 10.1088/1674-1056/22/11/114203
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In this work, we report on an off-resonant four-wave mixing experiment via a ladder-type configuration in a hot rubidium atomic vapour. We find for the first time, to the best of our knowledge, that the generated light is delayed compared with the reference. At the same time, the seeded signal beam is also delayed, though the delay time is not as so large as the one that the generated light has. Both delayed times can be adjusted experimentally by controlling the two-photon detuning. The experimental results are in good agreement with our theoretical predictions. Our results may be important for storing telecom-band photons.

Enhanced Kerr nonlinearity in a left-handed three-level atomic system driven by a bichromatic field

Yang Xiao-Yu, Jiang Yong-Yuan
Chin. Phys. B 2013, 22 (11): 114204 ;  doi: 10.1088/1674-1056/22/11/114204
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Enhanced Kerr nonlinearity in a left-handed atomic system consisting of three levels driven by a bichromatic field is presented in this paper. Based on bichromatic field coherence, the real parts of the permittivity and permeability can obtain negative values simultaneously in the same detuning frequency region. By adjusting the frequency difference and the Rabi frequencies of the bichromatic field, the multi-band left-handed behavior of the presented atomic metamaterial is exhibited. Meanwhile, the enhanced Kerr nonlinearity can be realized in this multi-band left-handed three-level atomic system. It is shown that the third-order susceptibility possesses focusing or defocusing properties in the same frequency band.

Dynamics of Rabi model under second-order Born–Oppenheimer approximation

Wang Zhi-Hai, Zhou Duan-Lu
Chin. Phys. B 2013, 22 (11): 114205 ;  doi: 10.1088/1674-1056/22/11/114205
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We apply the second-order Born–Oppenheimer (BO) approximation to investigate the dynamics of the Rabi model, which describes the interaction between a two-level system and a single bosonic mode beyond the rotating wave approximation. By comparing with the numerical results, we find that our approach works well when the frequency of the two-level system is much smaller than that of the bosonic mode.

Quantum interferometer with two-mode squeezed vacuum:Ŝz2 measurement

Zhang Yuan-Ming, Li Xin-Wei, Jin Guang-Ri
Chin. Phys. B 2013, 22 (11): 114206 ;  doi: 10.1088/1674-1056/22/11/114206
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Quantum interferometric strategy with input two-mode squeezed vacuum [Phys. Rev. Lett. 104 103602] is reexamined for both parity and Ŝz2 measurements. Unlike the previous scheme, we find that phase sensitivity obtained with the Ŝz2 measurement is minimized at phase origin, which may be useful to estimate a small phase shift at high precision. For the phase deviated from zero, the sensitivity increases more slowly than that of the parity detection.

Energy transfer in solid-state dye lasers based on methyl methacrylate co-doped with sulforhodamine B and crystal violet

R. G. Geethu Mani, M. Basheer Ahamed
Chin. Phys. B 2013, 22 (11): 114207 ;  doi: 10.1088/1674-1056/22/11/114207
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Laser action in methyl methacrylate (MMA) co-doped with sulforhodamine B and crystal violet dyes was investigated. The dye mixture was incorporated into a solid polymeric matrix and was pumped by a 532-nm Nd:YAG laser. Distributed feedback dye laser (DFDL) action was induced in the dye mixture using a prism arrangement both in the donor and acceptor regions by an energy transfer mechanism. Theoretically, the characteristics of acceptor and donor DFDLs, and the dependence of their pulse widths and output powers on acceptor–donor concentrations and pump power, were studied. Experimentally, the output energy of DFDL was measured at the emission peaks of donor and acceptor dyes for different pump powers and different acceptor–donor concentrations. Tuning of the output wavelength was achieved by varying the period of the gain modulation of the laser medium. The laser wavelength showed continuous tunability from 563 nm to 648 nm.

Theoretical study of power amplification in tapered fiber with multi-seed parallel injection

Xiao Qi-Rong, Ren Hai-Cui, Li Dan, Gong Ma-Li, Yan Ping
Chin. Phys. B 2013, 22 (11): 114208 ;  doi: 10.1088/1674-1056/22/11/114208
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We proposed the concept of parallel injection power amplification. A tapered fiber amplifier with multi-seed sources by the way of parallel injection was studied. The lower-order modes are excited and more than 90% of the input signal power remains in the fiber core if optimal injection and taper design are set. The power in the doped-core is amplified with high optical-optical efficiency. When light is propagating along the fiber, the higher-order modes are filtered which results in the high output beam quality. Incoherent combination of multi-seed lights launched through the wide end gives rise to the output power of several kW.

Physical origin of observed nonlinearities in Poly (1-naphthyl methacrylate):Using a single transistor–transistor logic modulated laser beam

Qusay M. A. Hassan, Hussain A. Badran, Alaa Y. AL-Ahmad, Chassib A. Emshary
Chin. Phys. B 2013, 22 (11): 114209 ;  doi: 10.1088/1674-1056/22/11/114209
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A thermal lens technique is adopted using a single modulated continuous wave (cw) 532-nm laser beam to evaluate the nonlinear refractive index n2, and the thermo-optic coefficient dn/dT, in polymer Poly (1-naphthyl methacrylate) (P-1-NM) dissolved in chloroform, tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO) solvents. The results are compared with Z-scan and diffraction ring techniques. The comparison reveals the effectiveness and the simplicity of the TTL modulation technique. The physical origin is discussed for the obtained results.

Ultrafast population transfer in a Λ-configuration level system driven by few-cycle laser pulses

Zhang Wen-Jing, Xie Xiao-Tao, Jin Lu-Ling, Bai Jin-Tao
Chin. Phys. B 2013, 22 (11): 114210 ;  doi: 10.1088/1674-1056/22/11/114210
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The feasibility of population transfer from a populated level via an intermediate state to the target level driven by few-cycle pulses is theoretically discussed. The processes of on-or far-resonance stimulated Raman scattering with sequential or simultaneous ultrashort pulses are investigated respectively. We find that the ultrashort pulses with about two optical cycles can be used to realize the population operation. This suggests that the population transfer can be completed in the femtosecond time scale. At the same time, our simulation shows that the signal of the carrier-envelope-phase-dependent effect can be enlarged due to quantum interference in some conditions. Our theoretic study may promote the research on the coherent control via ultrashort pulses in the related fields.

Six-bit all-optical quantization using photonic crystal fiber with soliton self-frequency shift and pre-chirp spectral compression techniques

Kang Zhe, Yuan Jin-Hui, Li Sha, Xie Song-Lin, Yan Bin-Bin, Sang Xin-Zhu, Yu Chong-Xiu
Chin. Phys. B 2013, 22 (11): 114211 ;  doi: 10.1088/1674-1056/22/11/114211
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In this paper, we propose an optical quantization scheme for all-optical analog-to-digital conversion that facilitates photonics integration. A segment of 10-m photonic crystal fiber with a high nonlinear coefficient of 62.8 W-1/km is utilized to realize large scale soliton self-frequency shift relevant to the power of the sampled optical signal. Furthermore, a 100-m dispersion-increasing fiber is used as the spectral compression module for further resolution enhancement. Simulation results show that 317-nm maximum wavelength shift is realized with 1550-nm initial wavelength and 6-bit quantization resolution is obtained with a subsequent spectral compression process.

Acoustic beam splitting in a sonic crystal around a directional band gap

Ahmet Cicek, Olgun Adem Kaya, Bulent Ulug
Chin. Phys. B 2013, 22 (11): 114301 ;  doi: 10.1088/1674-1056/22/11/114301
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Beam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size, which facilitates circumvention of a directional band gap. Experiments reveal that two distinct beams emerge at crystal output, in agreement with the numerical results obtained through the finite-element method. Beam splitting occurs at sufficiently-small source sizes comparable to lattice periodicity determined by the spatial gap width in reciprocal space. Split beams propagate in equal amplitude, whereas beam splitting is destructed for oblique incidence above a critical incidence angle.

Exact solutions for the flow of Casson fluid over a stretching surface with transpiration and heat transfer effects

Swati Mukhopadhyay, Krishnendu Bhattacharyya, Tasawar Hayat
Chin. Phys. B 2013, 22 (11): 114701 ;  doi: 10.1088/1674-1056/22/11/114701
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The effects of transpiration on forced convection boundary layer non-Newtonian fluid flow and heat transfer toward a linearly stretching surface are reported. The flow is caused solely by the stretching of the sheet in its own plane with a velocity varying linearly with the distance from a fixed point. The constitutive relationship for the Casson fluid is used. The governing partial differential equations corresponding to the momentum and energy equations are converted into non-linear ordinary differential equations by using similarity transformations. Exact solutions of the resulting ordinary differential equations are obtained. The effect of increasing Casson parameter, i.e., with decreasing yield stress (the fluid behaves as a Newtonian fluid as the Casson parameter becomes large), is to suppress the velocity field. However, the temperature is enhanced as the Casson parameter increases. It is observed that the effect of transpiration is to decrease the fluid velocity as well as the temperature. The skin-friction coefficient is found to increase as the transpiration parameter increases.

Effects of thermal radiation on Casson fluid flow and heat transfer over an unsteady stretching surface subjected to suction/blowing

Swati Mukhopadhyay
Chin. Phys. B 2013, 22 (11): 114702 ;  doi: 10.1088/1674-1056/22/11/114702
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The unsteady flow of a Casson fluid and heat transfer over a stretching surface in presence of suction/blowing are investigated. The transformed equations are solved numerically by using the shooting method. The exact solution corresponding to the momentum equation for the steady case is obtained. Fluid velocity initially decreases with the increase of unsteadiness parameter. Due to an increasing Casson parameter the velocity field is suppressed. Thermal radiation enhances the effective thermal diffusivity and the temperature rises.

Imaging of supersonic flow over a double elliptic surface

Zhang Qing-Hu, Yi Shi-He, He Lin, Zhu Yang-Zhu, Chen Zhi
Chin. Phys. B 2013, 22 (11): 114703 ;  doi: 10.1088/1674-1056/22/11/114703
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The coherent structures of flow over a double elliptic surface are experimentally investigated in a supersonic low-noise wind tunnel at Mach number 3 using nano-tracer planar laser scattering (NPLS) and particle image velocimetry (PIV) techniques. High spatiotemporal resolution images and velocity fields of both laminar and turbulent inflows over the test model are captured. Based on the time-correlation images, the spatial and temporal evolutionary characteristics of the coherent structures are investigated. The flow structures in the NPLS images are in good agreement with the velocity fluctuation fields by PIV. From statistically significant ensembles, spatial correlation analysis of both cases is performed to quantify the mean size and the orientation of coherent structures. The results indicate that the mean structure is elliptical in shape and the structural angles in the separated region of laminar inflow are slightly smaller than that of turbulent inflow. Moreover, the structural angles of both cases increase with their distance away from the wall.

Multi-relaxation time lattice Boltzmann simulation of inertial secondary flow in a curved microchannel

Sun Dong-Ke, Xiang Nan, Jiang Di, Chen Ke, Yi Hong, Ni Zhong-Hua
Chin. Phys. B 2013, 22 (11): 114704 ;  doi: 10.1088/1674-1056/22/11/114704
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The inertial secondary flow is particularly important for hydrodynamic focusing and particle manipulation in biomedical research. In this paper, the development of the inertial secondary flow structure in a curved microchannel was investigated by the multi relaxation time lattice Boltzmann equation model with a force term. The numerical results indicate that the viscous and inertial competition dominates the development of secondary flow structure development. The Reynolds number, Dean number, and the cross section aspect ratio influence significantly on the development of the secondary vortexes. Both the intensity of secondary flow and the distance between the normalized vortex centers are functions of Dean numbers but independent of channel curvature radius. In addition, the competition mechanism between the viscous and inertial effects were discussed by performing the particle focusing experiments. The present investigation provides an improved understanding of the development of inertial secondary flows in curved microchannels.

High-speed and broad optical bandwidth silicon modulator

Xu Hao, Li Xian-Yao, Xiao Xi, Li Zhi-Yong, Yu Yu-De, Yu Jin-Zhong
Chin. Phys. B 2013, 22 (11): 114212 ;  doi: 10.1088/1674-1056/22/11/114212
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A high-speed silicon modulator with broad optical bandwidth is proposed based on a symmetrically configured Mach–Zehnder interferometer. Careful phase bias control and traveling-wave design are used to improve the high-speed performance. Over a broadband wavelength range, high-speed operation up to 30 Gbit/s with a 4.5 dB–5.5 dB extinction ratio is experimentally demonstrated with a low driving voltage of 3 V.

Coupling-matrix approach to the Chern number calculation in disordered systems Hot!

Zhang Yi-Fu, Yang Yun-You, Ju Yan, Sheng Li, Shen Rui, Sheng Dong-Ning, Xing Ding-Yu
Chin. Phys. B 2013, 22 (11): 117312 ;  doi: 10.1088/1674-1056/22/11/117312
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The Chern number is often used to distinguish different topological phases of matter in two-dimensional electron systems. A fast and efficient coupling-matrix method is designed to calculate the Chern number in finite crystalline and disordered systems. To show its effectiveness, we apply the approach to the Haldane model and the lattice Hofstadter model, and obtain the correct quantized Chern numbers. The disorder-induced topological phase transition is well reproduced, when the disorder strength is increased beyond the critical value. We expect the method to be widely applicable to the study of topological quantum numbers.

Nonlinear Landau damping of high frequency waves in non-Maxwellian plasmas

M. N. S. Qureshi, Sumbul Sehar, J. K. Shi, H. A. Shah
Chin. Phys. B 2013, 22 (11): 115201 ;  doi: 10.1088/1674-1056/22/11/115201
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Space plasmas often possess non-Maxwellian distribution functions which have a significant effect on the plasma waves. When a laser or electron beam passes through a dense plasma, hot low density electron populations can be generated to alter the wave damping/growth rate. In this paper, we present theoretical analysis of the nonlinear Landau damping for Langmuir waves in a plasma where two electron populations are found. The results show a marked difference between the Maxwellian and non-Maxwellian instantaneous damping rates when we employ a non-Maxwellian distribution function called the generalized (r, q) distribution function, which is the generalized form of the kappa and Maxwellian distribution functions. In the limiting case of r = 0 and q→∞, it reduces to the classical Maxwellian distribution function, and when r = 0 and qk +1, it reduces to the kappa distribution function.

Effects of bi-kappa distributed electrons on dust-ion-acoustic shock waves in dusty superthermal plasmas

M. S. Alam, M. M. Masud, A. A. Mamun
Chin. Phys. B 2013, 22 (11): 115202 ;  doi: 10.1088/1674-1056/22/11/115202
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The basic properties of dust-ion-acoustic (DIA) shock waves in an unmagnetized dusty plasma (containing inertial ions, kappa distributed electrons with two distinct temperatures, and negatively charged immobile dust grains) are investigated both numerically and analytically. The hydrodynamic equation for inertial ions has been used to derive the Burgers equation. The effects of superthermal bi-kappa electrons and ion kinematic viscosity, which are found to modify the basic features of DIA shock waves significantly, are briefly discussed.

Drift-wave fluctuation in an inviscid tokamak plasma

Yang Jian-Rong, Mao Jie-Jian, Tang Xiao-Yan
Chin. Phys. B 2013, 22 (11): 115203 ;  doi: 10.1088/1674-1056/22/11/115203
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In order to describe the characterization of resistive drift-wave fluctuation in a tokamak plasma, a coupled inviscid two-dimensional Hasegawa–Wakatani model is investigated. Two groups of new analytic solutions with and without phase shift between the fluctuant density and the fluctuant potential are obtained by using the special function transformation method. It is demonstrated that the fluctuant potential shares similar spatio–temporal variations with the density. It is found from the solutions without phase shift that the effect of the diffusion and adiabaticity on the fluctuant density is quite complex, and that the fluctuation may be controlled through the adiabaticity and diffusion. By using the typical parameters in the quasi-adiabatic regime in the solutions with phase shift, it is shown that the density gradient becomes larger as the contours become dense toward the plasma edge and the contours have irregular structures, which reveal the nonuniform distribution in the tokamak edge.

Diagnostic technique for measuring fusion reaction rate for inertial confinement fusion experiments at Shen Guang-III prototype laser facility

Wang Feng, Peng Xiao-Shi, Kang Dong-Guo, Liu Shen-Ye, Xu Tao
Chin. Phys. B 2013, 22 (11): 115204 ;  doi: 10.1088/1674-1056/22/11/115204
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A study is conducted using a two-dimensional simulation program (Lared-s) with the goal of developing a technique to evaluate the effect of Rayleigh–Taylor growth in a neutron fusion reaction region. Two peaks of fusion reaction rate are simulated by using a two-dimensional simulation program (Lared-s) and confirmed by the experimental results. A neutron temporal diagnostic (NTD) system is developed with a high temporal resolution of ~ 30 ps at the Shen Guang-III (SG-III) prototype laser facility in China, to measure the fusion reaction rate history. With the shape of neutron reaction rate curve and the spherical harmonic function in this paper, the degree of Rayleigh–Taylor growth and the main source of the neutron yield in our experiment can be estimated qualitatively. This technique, including the diagnostic system and the simulation program, may provide important information for obtaining a higher neutron yield in implosion experiments of inertial confinement fusion.

Changes of the electron dynamics in hydrogen inductively coupled plasma

Gao Fei, Liu Wei, Zhao Shu-Xia, Zhang Yu-Ru, Sun Chang-Sen, Wang You-Nian
Chin. Phys. B 2013, 22 (11): 115205 ;  doi: 10.1088/1674-1056/22/11/115205
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Changes of the electron dynamics in hydrogen (H2) radio-frequency (RF) inductively coupled plasmas are investigated using a hairpin probe and an intensified charged coupled device (ICCD). The electron density, plasma emission intensity, and input current (voltage) are measured during the E to H mode transitions at different pressures. It is found that the electron density, plasma emission intensity, and input current jump up discontinuously, and the input voltage jumps down at the E to H mode transition points. And the threshold power of the E to H mode transition decreases with the increase of the pressure. Moreover, space and phase resolved optical emission spectroscopic measurements reveal that, in the E mode, the RF dynamics is characterized by one dominant excitation per RF cycle, while in the H mode, there are two excitation maxima within one cycle.

Three different low-temperature plasma-based methods for hydrophilicity improvement of polyethylene films at atmospheric pressure

Chen Guang-Liang, Zheng Xu, Huang Jun, Si Xiao-Lei, Chen Zhi-Li, Xue Fei, Sylvain Massey
Chin. Phys. B 2013, 22 (11): 115206 ;  doi: 10.1088/1674-1056/22/11/115206
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Three different low-temperature plasma-based methods were used to improve the surface hydrophilicity of polyethylene (PE) films, and all the modification processes were carried out by employing an atmospheric pressure plasma jet (APPJ) system. (a) PE films were directly modified by APPJ using a gas mixture of He and O2. (b) Acrylic acid (AA) was introduced into the system and a polymer acrylic acid (PAA) coating was deposited onto the PE films. (c) AA was grafted onto the PE surface activated by plasma pre-treatment. It was found that the hydrophilicity of the PE films was significantly improved for all the three methods. However, the samples modified by Process (a) showed hydrophobicity recovery after a storage time of 20 days while no significant change was found in samples modified by Process (b) and Process (c). The Fourier transform infrared spectroscopy (FTIR) results indicated that the most intensive C=O peak was detected on the PE surface modified by Process (c). According to the X-ray photoelectron spectroscopy (XPS) analysis, the ratios of oxygen-containing polar groups for samples modified by Process (b) and Process (c) were higher than that modified by Process (a).

Generalized 2D problem of icosahedral quasicrystals containing an elliptic hole

Li Lian-He
Chin. Phys. B 2013, 22 (11): 116101 ;  doi: 10.1088/1674-1056/22/11/116101
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The generalized 2D problem of icosahedral quasicrystals containing an elliptic hole is considered by using the extended Stroh formalism. The closed-form solutions for the displacements and stresses are obtained under general loading conditions. The solution of the Griffith crack problem as a special case of the results is also observed. The stress intensity factor and strain energy release rate are given. The effect of the phonon–phason coupling elastic constant on the mechanical behavior is also discussed.

Misfit-layered compound PbTiS3 with incommensurate modulation:Transmission electron microscopy analysis and transport properties

Shen Xi, Cheng Dan, Zhao Hao-Fei, Yao Yuan, Liu Xiao-Yang, Yu Ri-Cheng
Chin. Phys. B 2013, 22 (11): 116102 ;  doi: 10.1088/1674-1056/22/11/116102
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The microstructural characteristic of the misfit-layered compound PbTiS3 has been studied with transmission electron microscopy. All the incommensurate modulation-induced satellite spots and main diffraction spots of basic sublattices can be indexed systematically with a superspace group method. Finally, the relationship between the electronic transport properties and the crystal structure is discussed.

Critical size of iron nanoparticles on liquid substrates

Lü Neng, Pan Qi-Fa, Cheng Yi, Yang Bo, Ye Gao-Xiang
Chin. Phys. B 2013, 22 (11): 116103 ;  doi: 10.1088/1674-1056/22/11/116103
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We study the iron atomic aggregates deposited on silicone oil surfaces by using atomic force microscopy. The aggregates are composed of disk-shaped nanoparticles with the mean diameter Φc≈31.7 nm and height Hc≈4.5 nm, which are nearly independent of the nominal film thickness. The experiment shows that a material condensation process must occur in the nanoparticles during the growth period. The anomalous phenomenon is explained.

Ground-state structure determination and mechanical properties of palladium seminitride

Zhang Gang-Tai, Bai Ting-Ting, Zhao Ya-Ru, Lu Cheng
Chin. Phys. B 2013, 22 (11): 116104 ;  doi: 10.1088/1674-1056/22/11/116104
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Combining first-principles calculations with the particle swarm optimization (PSO) algorithm, we have explored the ground-state structure of Pd2N, whose structure is in debate although it is the first synthesized binary platinum group nitride. The ground-state structure is predicted to be tetragonal with space group P4m2, which is energetically more favorable than the previously proposed orthorhombic Co2N-type structure. The stability is confirmed by the subsequent calculations on the phonon dispersion curves and elastic constants. Furthermore, the calculated mechanical properties indicate that Pd2N has low incompressibility and is a common hard material.

Micro-track structure analysis for 100 MeV Si ions in CR-39 by using atomic force microscopy

Fang Mei-Hua, Wei Zhi-Yong, Zhang Zi-Xia, Zhu Li, Fu Yu, Shi Miao, Li Guang-Wu, Guo Gang
Chin. Phys. B 2013, 22 (11): 116105 ;  doi: 10.1088/1674-1056/22/11/116105
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To analyze the micro-track structure of heavy ions in a polymer material, parameters including bulk etch rate, track etch rate, etch rate ratio, and track core size were measured. The pieces of CR-39 were exposed to 100 MeV Si ions with normal incidence and were etched in 6.25N NaOH solution at 70 ℃. Bulk etch rate was read out by a profilemeter after several hours of etching. The other parameters were obtained by using an atomic force microscope (AFM) after a short time of etching. We have measured the second etch pits and minute etch pits to obtain the track growth curve and three dimension track structures to track the core size and etch rate measurements. The local dose of the track core was calculated by the δ-ray theory. In our study, we figure out that the bulk etch rate Vb=(1.58±0.022) μm/h, the track etch rate Vt=(2.90±0.529) μ/h, the etch rate ratio V=1.84±0.031, and the track core radii r≈4.65 nm. In the meantime, we find that the micro-track development violates the traditional track-growth model. For this reason, a scenario is carried out to provide an explanation.

Pressure-induced phase transitions in single-crystalline Cu4Bi4S9 nanoribbons

Hu Jing-Yu, Li Jing, Zhang Si-Jia, Zhao Hao-Fei, Zhang Qing-Hua, Yao Yuan, Zhao Qing, Shi Li-Jie, Zou Bing-Suo, Li Yan-Chun, Li Xiao-Dong, Liu Jing, Zhu Ke, Liu Yu-Long, Jin Chang-Qing, Yu Ri-Cheng
Chin. Phys. B 2013, 22 (11): 116201 ;  doi: 10.1088/1674-1056/22/11/116201
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In situ angle dispersive synchrotron X-ray diffraction and Raman scattering measurements under pressure are employed to study the structural evolution of Cu4Bi4S9 nanoribbons, which are fabricated by using a facile solvothermal method. Both experiments show that a structural phase transition occurs near 14.5 GPa, and there is a pressure-induced reversible amorphization at about 25.6 GPa. The electrical transport property of a single Cu4Bi4S9 nanoribbon under different pressures is also investigated.

Effects of the trimodal random field on the magnetic properties of a spin-1 Ising nanotube

H. Magoussi, A. Zaim, M. Kerouad
Chin. Phys. B 2013, 22 (11): 116401 ;  doi: 10.1088/1674-1056/22/11/116401
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In this work, the hysteresis behavior of a nanotube, consisting of a ferromagnetic core of spin-1 atoms surrounded by a ferromagnetic shell of spin-1 atoms with ferro-or anti-ferromagnetic interfacial coupling is studied in the presence of a random magnetic field. Based on a probability distribution method, the effective-field theory has been used to investigate the effects of the random magnetic field, the interfacial coupling constant, and the temperature on the hysteresis loops of the nanotube. Some characteristic behaviors have been found, such as the existence of double or triple hysteresis loops for appropriate values of the system parameters. The remanent magnetization and the coercive field, as functions of the temperature, are examined.

Improved light extraction of organic light emitting diodes with a nanopillar pattering structure

Gao Zhi-Xiang, Wang Hua, Hao Yu-Ying, Miao Yan-Qin, Xu Bing-She
Chin. Phys. B 2013, 22 (11): 116801 ;  doi: 10.1088/1674-1056/22/11/116801
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We have investigated the properties of organic light emitting diodes (OLEDs) with a nanopillar patterning structure at organic–metal or organic–organic interfaces. The results demonstrate that the introduction of a nanopillar structure can improve the light extraction efficiency greatly. We also find that the number, height, and position of nanopillars all affect the light extraction of OLEDs. The maximum power efficiency of a device with an optimized nanopillar patterning mode can be improved to 2.47 times that of the reference device. This enhancement in light extraction originates from the improved injected carriers, the broadened charge recombination zone, and the intensified wave guiding effects.

Simple statistical model for predicting thermal atom diffusion on crystal surfaces

Yu Wei-Feng, Lin Zheng-Zhe, Ning Xi-Jing
Chin. Phys. B 2013, 22 (11): 116802 ;  doi: 10.1088/1674-1056/22/11/116802
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A simple model based on the statistics of single atoms is developed to predict the diffusion rate of thermal atoms in (or on) bulk materials without empirical parameters. Compared with vast classical molecular-dynamics simulations for predicting the self-diffusion rate of Pt, Cu, and Ar adatoms on crystal surfaces, the model is proved to be much more accurate than the Arrhenius law and the transition state theory. Applying this model, the theoretical predictions agree well with the experimental values in the presented paper about the self-diffusion of Pt (Cu) adatoms on the surfaces.

Effects of high temperature rapid thermal annealing on Ge films grown on Si(001) substrate

Liu Zhi, Cheng Bu-Wen, Li Ya-Ming, Li Chuan-Bo, Xue Chun-Lai, Wang Qi-Ming
Chin. Phys. B 2013, 22 (11): 116804 ;  doi: 10.1088/1674-1056/22/11/116804
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Tensile strain, crystal quality, and surface morphology of 500 nm thick Ge films were improved after rapid thermal annealing at 900 ℃ for a short period (< 20 s). The films were grown on Si(001) substrates by ultra-high vacuum chemical vapor deposition. These improvements are attributed to relaxation and defect annihilation in the Ge films. However, after prolonged (>20 s) rapid thermal annealing, tensile strain and crystal quality degenerated. This phenomenon results from intensive Si–Ge mixing at high temperature.

Effect of buoyancy-driven convection on steady state dendritic growth in a binary alloy

Chen Ming-Wen, Wang Bao, Wang Zi-Dong
Chin. Phys. B 2013, 22 (11): 116805 ;  doi: 10.1088/1674-1056/22/11/116805
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The effect of buoyancy-driven convection on the steady state dendritic growth in an undercooled binary alloy is studied. For the case of the moderate modified Grashof number, the uniformly valid asymptotic solution in the entire region of space is obtained by means of the matched asymptotic expansion method. The analytical results show that the buoyancy-driven convection has a significant effect on the needle-like interface of dendritic growth. Due to the buoyancy-driven convection, the needle-like interface shape of the crystal is changed. When the Peclet number that is not affected by the buoyant flow is less than a certain critical value, the interface shape of the dendrite becomes thinner as the Grashof number increases; when it is larger than the critical value, the interface shape becomes fatter as the Grashof number increases. In the undercooled binary alloy the morphology number plays an active role in the interface shape and leads to the buoyancy effect that is different from the situation for the pure melt. The smaller the morphology number is, the more significant change the interface shape has. As the Peclet number further increases, the effect of buoyancy on the interface diminishes eventually.
SPECIAL TOPIC --- Non-equilibrium phenomena in soft matters

A comparison study on the electronic structures, lattice dynamics and thermoelectric properties of bulk silicon and silicon nanotubes

Lu Peng-Xian, Qu Ling-Bo, Cheng Qiao-Huan
Chin. Phys. B 2013, 22 (11): 117101 ;  doi: 10.1088/1674-1056/22/11/117101
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In order to investigate the mechanism of the electron and phonon transport in a silicon nanotube (SiNT), the electronic structures, the lattice dynamics, and the thermoelectric properties of bulk silicon (bulk Si) and a SiNT have been calculated in this work using density functional theory and Boltzmann transport theory. Our results suggest that the thermal conductivity of a SiNT is reduced by a factor of 1, while its electrical conductivity is improved significantly, although the Seebeck coefficient is increased slightly as compared to those of the bulk Si. As a consequence, the figure of merit (ZT) of a SiNT at 1200 K is enhanced by 12 times from 0.08 for bulk Si to 1.10. The large enhancement in electrical conductivity originates from the largely increased density of states at the Fermi energy level and the obviously narrowed band gap. The significant reduction in thermal conductivity is ascribed to the remarkably suppressed phonon thermal conductivity caused by a weakened covalent bonding, a decreased phonon density of states, a reduced phonon vibration frequency, as well as a shortened mean free path of phonons. The other factors influencing the thermoelectric properties have also been studied from the perspective of electronic structures and lattice dynamics.

Energy transfer between two aggregates in light-harvesting complexes

Wang Xiao-Lian, Li Hong-Rong, Zhang Pei, Li Fu-Li
Chin. Phys. B 2013, 22 (11): 117102 ;  doi: 10.1088/1674-1056/22/11/117102
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Energy transfer processes between two aggregates in a coupled chromophoric-pigment (protein) system are studied via the standard master equation approach. Each pigment of the two aggregates is modeled as a two-level system. The excitation energy is assumed to be transferred from the donor aggregate to the acceptor aggregate. The model can be used to theoretically simulate many aspects of light-harvesting complexes (LHCs). By applying the real bio-parameters of photosynthesis, we numerically investigate the efficiency of energy transfer (EET) between the two aggregates in terms of some factors, e.g., the initial coherence of the donor aggregate, the coupling strengthes between the two aggregates and between different pigments, and the effects of noise from the environment. Our results provide evidence for that the actual numbers of pigments in the chromophoric rings of LHCs should be the optimum parameters for a high EET. We also give a detailed analysis of the effects of noise on the EET.

Electronic structure and optical properties of Al and Mg co-doped GaN

Ji Yan-Jun, Du Yu-Jie, Wang Mei-Shan
Chin. Phys. B 2013, 22 (11): 117103 ;  doi: 10.1088/1674-1056/22/11/117103
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The electronic structure and optical properties of Al and Mg co-doped GaN are calculated from first principles using density function theory with the plane-wave ultrasoft pseudopotential method. The results show that the optimal form of p-type GaN is obtained with an appropriate Al:Mg co-doping ratio rather than with only Mg doping. Al doping weakens the interaction between Ga and N, resulting in the Ga 4s states moving to a high energy region and the system band gap widening. The optical properties of the co-doped system are calculated and compared with those of undoped GaN. The dielectric function of the co-doped system is anisotropic in the low energy region. The static refractive index and reflectivity increase, and absorption coefficient decreases. This provides the theoretical foundation for the design and application of Al–Mg co-doped GaN photoelectric materials.

Interfacial electronic structure at a metal–phthalocyanine/graphene interface:Copper–phthalocyanine versus iron–phthalocyanine

Ye Wei-Guo, Liu Dan, Peng Xiao-Feng, Dou Wei-Dong
Chin. Phys. B 2013, 22 (11): 117301 ;  doi: 10.1088/1674-1056/22/11/117301
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The energy level alignment of CuPc and FePc on single-layer graphene/Ni(111) (SLG/Ni) substrate was investigated by using ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS). The highest occupied molecular orbitals (HOMOs) in a thick layer of CuPc and FePc lie at 1.04 eV and 0.90 eV, respectively, below the Fermi level of the SLG/Ni substrate. Weak adsorbate–substrate interaction leads to negligible interfacial dipole at the CuPc/SLG/Ni interface, while a large interfacial dipole (0.20 eV) was observed in the case of FePc/SLG/Ni interface, due to strong adsorbate–substrate coupling. In addition, a new interfacial electronic feature was observed for the first time in the case of FePc on SLG/Ni substrate. This interfacial state can be attributed to a charge transfer from the SLG/Ni substrate to unoccupied orbitals of FePc.

Near-field optical observations of surface plasmon wave interference at subwavelength hole arrays perforated in Au film

Li Jiang-Yan, Gan Lin, Li Zhi-Yuan
Chin. Phys. B 2013, 22 (11): 117302 ;  doi: 10.1088/1674-1056/22/11/117302
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We image optical near-field patterns at subwavelength circular hole arrays in Au film by using scanning near-field optical microscopy in near-infrared wavelengths. Periodical oscillation features are found in the near-field images at the air/Au interface and exhibit two typical kinds of standing wave oscillation forms at the wavelengths corresponding to the transmission minimum and maximum in the transmission spectrum, and the latter one originates from the excitation and interference of a surface plasmon wave at the metallic hole arrays. Our work indicates that monitoring optical near-field patterns can help to reveal many interesting properties of surface plasmon waves at metallic nanostructures and understand their underlying physical mechanisms.

Thermoelectric transport through a quantum dot with a magnetic impurity

Yu Zhen, Guo Yu, Zheng Jun, Chi Feng
Chin. Phys. B 2013, 22 (11): 117303 ;  doi: 10.1088/1674-1056/22/11/117303
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We study the thermoelectric effect in a small quantum dot with a magnetic impurity in the Coulomb blockade regime. The electrical conductance, thermal conductance, thermopower, and the thermoelectrical figure of merit (FOM) are calculated by using Green’s function method. It is found that the peaks in the electrical conductance are split by the exchange coupling between the electron entering into the dot and the magnetic impurity inside the dot, accompanied by the decrease in the height of peaks. As a result, the resonances in the thermoelectric quantities, such as the thermal conductance, thermopower, and the FOM, are all split, opening some effective new working regions. Despite of the significant reduction in the height of the electrical conductance peaks induced by the exchange coupling, the values of the FOM and the thermopower can be as large as those in the case of zero exchange coupling. We also find that the thermoelectric efficiency, characterized by the magnitude of the FOM, can be enhanced by adjusting the left–right asymmetry of the electrode–dot coupling or by optimizing the system’s temperature.

Coupling strength effect on shot noise in boron devices

Li Gui-Qin, Guo Yong
Chin. Phys. B 2013, 22 (11): 117304 ;  doi: 10.1088/1674-1056/22/11/117304
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The shot noise properties in boron devices are investigated with a tight-binding model and the non-equilibrium Green’s function. It is found that the shot noise and Fano factors can be tuned by changing the structures, the size, and the coupling strength. The shot noise is suppressed momentarily as we switch on the bias voltage, and the electron correlation is significant. The Fano factors are more sensitive to the ribbon width than to the ribbon length in the full coupling context. In the weak-coupling context, the Fano factors are almost invariant with the increase of length and width over a wide bias range.

Transition from the Kondo effect to a Coulomb blockade in an electron shuttle

Zhang Rong, Chu Wei-Dong, Duan Su-Qing, Yang Ning
Chin. Phys. B 2013, 22 (11): 117305 ;  doi: 10.1088/1674-1056/22/11/117305
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We investigate the effect of the mechanical motion of a quantum dot on the transport properties of a quantum dot shuttle. Employing the equation of motion method for the nonequilibrium Green’s function, we show that the oscillation of the dot, i.e., the time-dependent coupling between the dot’s electron and the reservoirs, can destroy the Kondo effect. With the increase in the oscillation frequency of the dot, the density of states of the quantum dot shuttle changes from the Kondo-like to a Coulomb-blockade pattern. Increasing the coupling between the dot and the electrodes may partly recover the Kondo peak in the spectrum of the density of states. Understanding of the effect of mechanical motion on the transport properties of an electron shuttle is important for the future application of nanoelectromechanical devices.

Electric field driven plasmon dispersion in AlGaN/GaN high electron mobility transistors

Tan Ren-Bing, Qin Hua, Zhang Xiao-Yu, Xu Wen
Chin. Phys. B 2013, 22 (11): 117306 ;  doi: 10.1088/1674-1056/22/11/117306
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We present a theoretical study on the electric field driven plasmon dispersion of the two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistors (HEMTs). By introducing a drifted Fermi–Dirac distribution, we calculate the transport properties of the 2DEG in the AlGaN/GaN interface by employing the balance-equation approach based on the Boltzmann equation. Then, the nonequilibrium Fermi–Dirac function is obtained by applying the calculated electron drift velocity and electron temperature. Under random phase approximation (RPA), the electric field driven plasmon dispersion is investigated. The calculated results indicate that the plasmon frequency is dominated by both the electric field E and the angle between wavevector q and electric field E. Importantly, the plasmon frequency could be tuned by the applied source–drain bias voltage besides the gate voltage (change of the electron density).

Influence of a drain field plate on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor

Zhao Sheng-Lei, Chen Wei-Wei, Yue Tong, Wang Yi, Luo Jun, Mao Wei, Ma Xiao-Hua, Hao Yue
Chin. Phys. B 2013, 22 (11): 117307 ;  doi: 10.1088/1674-1056/22/11/117307
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In this paper, the influence of a drain field plate (FP) on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor (HEMT) is investigated. The HEMT with only a gate FP is optimized, and breakdown voltage VBR is saturated at 1085 V for gate–drain spacing LGD ≥ 8 μm. On the basis of the HEMT with a gate FP, a drain FP is added with LGD=10 μm. For the length of the drain FP LDF ≤ 2 μm, VBR is almost kept at 1085 V, showing no degradation. When LDF exceeds 2 μm, VBR decreases obviously as LDF increases. Moreover, the larger the LDF, the larger the decrease of VBR. It is concluded that the distance between the gate edge and the drain FP edge should be larger than a certain value to prevent the drain FP from affecting the forward blocking voltage and the value should be equal to the LGD at which VBR begins to saturate in the first structure. The electric field and potential distribution are simulated and analyzed to account for the decrease of VBR.

Low voltage program-erasable Pd-Al2O3-Si capacitors with Ru nanocrystals for nonvolatile memory application

Lan Lan, Gou Hong-Yan, Ding Shi-Jin, Zhang Wei
Chin. Phys. B 2013, 22 (11): 117308 ;  doi: 10.1088/1674-1056/22/11/117308
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Pd-Al2O3-Si capacitors with Ru nanocrystals are fabricated and electrically characterized for nonvolatile memory application. While keeping the entire insulator Al2O3 thickness fixed, the memory window has a strong dependence on the tunneling layer thickness under low operating voltages, whereas it has weak dependence under high operating voltages. As for the optimal configuration comprised of 6-nm tunneling layer and 22-nm blocking layer, the resulting memory window increases from 1.5 V to 5.3 V with bias pulse increasing from 10-5 s to 10-2 s under ±7 V. A ten-year memory window as large as 5.2 V is extrapolated at room temperature after ±8 V/1 ms programming/erasing pulses.

A high performance HfSiON/TaN NMOSFET fabricated using a gate-last process

Xu Gao-Bo, Xu Qiu-Xia, Yin Hua-Xiang, Zhou Hua-Jie, Yang Tao, Niu Jie-Bin, Yu Jia-Han, Li Jun-Feng, Zhao Chao
Chin. Phys. B 2013, 22 (11): 117309 ;  doi: 10.1088/1674-1056/22/11/117309
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A gate-last process for fabricating HfSiON/TaN n-channel metal-oxide-semiconductor-field-effect transistors (NMOSFETs) is presented. In the process, a HfSiON gate dielectric with an equivalent oxide thickness of 10 Å was prepared by a simple physical vapor deposition method. Poly-Si was deposited on the HfSiON gate dielectric as a dummy gate. After the source/drain formation, the poly-Si dummy gate was removed by tetramethylammonium hydroxide (TMAH) wet-etching and replaced by a TaN metal gate. Because the metal gate was formed after the ion-implant doping activation process, the effects of the high temperature process on the metal gate were avoided. The fabricated device exhibits good electrical characteristics, including good driving ability and excellent sub-threshold characteristics. The device’s gate length is 73 nm, the driving current is 117 μA/μm under power supply voltages of VGS=VDS=1.5 V and the off-state current is only 4.4 nA/μ. The lower effective work function of TaN on HfSiON gives the device a suitable threshold voltage (~ 0.24 V) for high performance NMOSFETs. The device’s excellent performance indicates that this novel gate-last process is practical for fabricating high performance MOSFETs.

Temperature-dependent dielectric properties of Au/Si3N4/n-Si (metal–insulator–semiconductor) structures

T. Ataseven, A. Tataroğlu
Chin. Phys. B 2013, 22 (11): 117310 ;  doi: 10.1088/1674-1056/22/11/117310
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The dielectric properties of Au/Si3N4/n-Si (MIS) structures are studied using the admittance measurements (C–V and G/ω–V) each as a function of temperature in a range from 80 K to 400 K for two frequencies (100 kHz and 1 MHz). Experimental results show that both the dielectric constant (ε’) and the dielectric loss (ε") increase with temperature increasing and decrease with frequency increasing. The measurements also show that the ac conductivity (σac) increases with temperature and frequency increasing. The lnσac versus 1000/T plot shows two linear regions with different slopes which correspond to low (120 K–240 K) and high (280 K–400 K) temperature ranges for the two frequencies. It is found that activation energy increases with frequency and temperature increasing.

Effects of stress conditions on the generation of negative bias temperature instability-associated interface traps

Zhang Yue, Pu Shi, Lei Xiao-Yi, Chen Qing, Ma Xiao-Hua, Hao Yue
Chin. Phys. B 2013, 22 (11): 117311 ;  doi: 10.1088/1674-1056/22/11/117311
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The exponent n of the generation of an interface trap (Nit), which contributes to the power-law negative bias temperature instability (NBTI) degradation, and the exponent’s time evolution are investigated by simulations with varying the stress voltage Vg and temperature T. It is found that the exponent n in the diffusion-limited phase of the degradation process is irrelevant to both Vg and T. The time evolution of the exponent n is affected by the stress conditions, which is reflected in the shift of the onset of the diffusion-limited phase. According to the diffusion profiles, the generation of the atomic hydrogen species, which is equal to the buildup of Nit, is strongly correlated with the stress conditions, whereas the diffusion of the hydrogen species shows Vg-unaffected but T-affected relations through the normalized results.

Simulation of the magnetoresistance of Heisenberg spin lattices using the resistor–network model

Lin Ling-Fang, Huang Xin, Dong Shuai
Chin. Phys. B 2013, 22 (11): 117313 ;  doi: 10.1088/1674-1056/22/11/117313
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The magnetism and conductance of two-dimensional Heisenberg spin lattices are investigated by using Monte Carlo simulations to qualitatively understand a fascinating magnetoresistance effect observed in magnetic materials and their artificial multilayers. Various magnetic profiles, including a pure ferromagnetic, a pure antiferromagnetic, two phase competitive cases, and an artificial sandwich junction, are simulated, and their conductances are calculated based on an extended resistor–network model. Magnetoresistance is observed in some lattices, which is prominent when the system is near phase boundaries. Compared with real manganites, the absence of colossal magnetoresistance in our simulation implies the essential role of charge ordered phase which is not included in our pure spin model. However, our model provides an intuitive understanding of the spin-dependent conductance in large scale.

Reversible alternation between bipolar and unipolar resistive switching in La-SrTiO3 thin films

Xu Ding-Lin, Xiong Ying, Tang Ming-Hua, Zeng Bai-Wen, Xiao Yong-Guang, Wang Zi-Ping
Chin. Phys. B 2013, 22 (11): 117314 ;  doi: 10.1088/1674-1056/22/11/117314
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The alternation from bipolar to unipolar resistive switching is observed in perovskite La0.01Sr0.99TiO3 thin films. These two switching modes can be activated separately depending on the compliance current (Icomp) during the electroforming process: with a higher Icomp (5 mA) the unipolar resistance switching behavior is measured, while the bipolar resistance switching behavior is observed with a lower Icomp (1 mA). On the basis of I–V characteristics, the switching mechanisms for the URS and BRS modes are considered as being a change in the Schottky-like barrier height and/or width at the Pt/La-SrTiO3 interface and the formation and disruption of conduction filaments, respectively.

Paraconductivity study in ErBa2Cu3-xMxO7-δ (M = Zn, Fe) superconductors

A. Sedky, S. B. Mohamed
Chin. Phys. B 2013, 22 (11): 117401 ;  doi: 10.1088/1674-1056/22/11/117401
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We report here the paraconductivity of ErBa2Cu3-xMxO7-δ (M = Zn and Fe) superconductors. The logarithmic plots of excess conductivity Δσ and reduced temperature C reveal two different exponents corresponding to crossover temperature as a result of shifting the order parameter from 2 to 3. The first exponent in the normal field region is close to 1, in which the order parameter dimensionality (OPD) is 2. The second exponent in the critical field region is close to 0.5, in which the OPD is 3. The coherence length, interlayer coupling, interlayer separation and carrier concentration decrease with increasing doping content, and their values for Fe samples are different from those of Zn samples. While anisotropy is increased with increasing doping content, it is generally higher for a Zn sample than that for an Fe sample. We also estimate several physical parameters such as upper critical magnetic fields in the a–b plane and along the c axis (Bab and Bc), and critical current density J at 0 K. Although Bab and Bc are generally increased with doping content increasing, the value of Bab is found to be twice more than that of Bc. A similar behavior is obtained for J (0 K) and its value is higher in the Fe sample than that in the Zn sample. These results are discussed in terms of oxygen deficiency, localization of carriers, and flux pinning, which are produced by doping.

Analytical thermodynamical properties of a two-dimensional electron gas in a magnetic field

Chen Jin-Wang, Pan Xiao-Yin
Chin. Phys. B 2013, 22 (11): 117501 ;  doi: 10.1088/1674-1056/22/11/117501
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Analytical expressions for the thermodynamical properties of a two-dimensional electron gas in a perpendicular magnetic field are derived. This is accomplished by first deriving the general expression for the thermodynamical potential, and then employing this result to obtain the corresponding expression for the two-dimensional gas. The chemical potential and magnetization are studied as a function of temperature and magnetic field, and shown to be in agreement with prior work. It is also shown that the results are close to those obtained by assuming a Gaussian density of states for the Landau levels.

A quantum explanation of the magnetic properties of Mn-doped graphene

Lei Tian-Min, Liu Jia-Jia, Zhang Yu-Ming, Guo Hui, Zhang Zhi-Yong
Chin. Phys. B 2013, 22 (11): 117502 ;  doi: 10.1088/1674-1056/22/11/117502
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Mn-doped graphene is investigated using first-principles calculations based on the density functional theory (DFT). The magnetic moment is calculated for systems of various sizes, and the atomic populations and the density of states (DOS) are analyzed in detail. It is found that Mn doped graphene-based diluted magnetic semiconductors (DMS) have strong ferromagnetic properties, the impurity concentration influences the value of the magnetic moment, and the magnetic moment of the 8×8 supercell is greatest for a single impurity. The graphene containing two Mn atoms together is more stable in the 7×7 supercell. The analysis of the total DOS and partial density of states (PDOS) indicates that the magnetic properties of doped graphene originate from the p–d exchange, and the magnetism is given a simple quantum explanation using the Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange theory.

Thermal activation of magnetization in Pr2Fe14B ribbons

Li Zhu-Bai, Shen Bao-Gen, Niu E, Liu Rong-Ming, Zhang Ming, Sun Ji-Rong
Chin. Phys. B 2013, 22 (11): 117503 ;  doi: 10.1088/1674-1056/22/11/117503
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The aftereffect field of thermal activation, which corresponds to the fluctuation field of a domain wall, is investigated via specific measurements of the magnetization behavior in Pr2Fe14B nanocrystalline magnets. The thermal activation is a magnetization reversal arising from thermal fluctuation over an energy barrier to an equilibrate state. According to the magnetic viscosity and the field sweep rate dependence of the coercivity, the calculated values of the fluctuation field are lower than the aftereffect field and in a range between those of domain walls and individual grains. Based on these results, we propose that the magnetization reversal occurs in multiple ways involving grain activation and domain wall activation in thermal activation, and the thermal activation decreases the coercivity by ~ 0.2 kOe in the Pr2Fe14B ribbons.

Effects of charge and dipole on flatband voltage in an MOS device with a Gd-doped HfO2 dielectric

Han Kai, Wang Xiao-Lei, Yang Hong, Wang Wen-Wu
Chin. Phys. B 2013, 22 (11): 117701 ;  doi: 10.1088/1674-1056/22/11/117701
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Gd-doped HfO2 has drawn worldwide interest for its interesting features. It is considered to be a suitable material for N-type metal-oxide-semiconductor (MOS) devices due to a negative flatband voltage (Vfb) shift caused by the Gd doping. In this work, an anomalous positive shift was observed when Gd was doped into HfO2. The cause for such a phenomenon was systematically investigated by distinguishing the effects of different factors, such as Fermi level pinning (FLP), a dipole at the dielectric/SiO2 interface, fixed interfacial charge, and bulk charge, on Vfb. It was found that the FLP and interfacial dipole could make Vfb negatively shifted, which is in agreement with the conventional dipole theory. The increase in interfacial fixed charge resulting from Gd doping plays a major role in positive Vfb shift.

Optical study of Ba(MnxTi(1-x)O3) thin films by spectroscopic ellipsometry

Zhang Ting, Yin Jiang, Ding Ling-Hong, Zhang Wei-Feng
Chin. Phys. B 2013, 22 (11): 117801 ;  doi: 10.1088/1674-1056/22/11/117801
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Stoichiometric Ba(MnxTi(1-x)O3) (BMT) thin films with various values of x were deposited on Si(111) substrates by the sol-gel technique. The influence of Mn content on the optical properties was studied by spectroscopic ellipsometry (SE) in the UV–Vis–NIR region. By fitting the measured ellipsometric parameter (Ψ and Δ) with a four-phase model (air/BMT+voids/BMT/Si(111)), the key optical constants of the thin films have been obtained. It was found that the refractive index n and the extinction coefficient k increase with increasing Mn content due to the increase in the packing density. Furthermore, a strong dependence of the optical band gap Eg on Mn/Ti ratios in the deposited films was observed, and it was inferred that the energy level of conduction bands decreases with increasing Mn content.

Nonlinear optical characterization of phosphate glasses based on ZnO using the Z-scan technique

Masoumeh Shokati Mojdehi, Wan Mahmood Mat Yunus, Khor Shing Fhan, Zainal Abidin Talib, N. Tamchek
Chin. Phys. B 2013, 22 (11): 117802 ;  doi: 10.1088/1674-1056/22/11/117802
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The nonlinear optical properties of a phosphate vitreous system [(ZnO)x-(MgO)30-x-(P2O5)70], where x=8, 10, 15, 18, and 20 mol% synthesized through the melt-quenching technique have been investigated by using the Z-scan technique. In the experiment, a continuous-wave laser with a wavelength of 405 nm was utilized to determine the sign and value of the nonlinear refractive (NLR) index and the absorption coefficient with closed and opened apertures of the Z-scan setup. The NLR index was found to increase with the ZnO concentration in the glass samples by an order of 10-10 cm2·W-1. The real and imaginary parts of the third-order nonlinear susceptibility were calculated by referring to the NLR index (n2) and absorption coefficient (β) of the samples. The value of the third-order nonlinear susceptibility was presented by nonlinear refractive or absorptive behavior of phosphate glasses for proper utilization in nonlinear optical devices. Based on the measurement, the positive sign of the NLR index shows a self-focusing phenomenon. The figures of merit for each sample were calculated to judge the potential of phosphate glasses for application in optical switching.

The subwavelength tuned magneto-optical Kerr effect in L10-FePt films with perpendicular magnetic anisotropy

Zhang Xia, Shi Lei, Li Jing, Xia Yun-Jie, Shi Zhong, Zhou Shi-Ming
Chin. Phys. B 2013, 22 (11): 117803 ;  doi: 10.1088/1674-1056/22/11/117803
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For L10-FePt films with strong perpendicular anisotropy covered by arrays of hexagonal close-packed polystyrene spheres (PSSs), fine structures are observed in magneto-optical Kerr rotation spectra in the visible spectral range. The reflection minima are found to be located at the same wavelengths as the Kerr rotation peaks. The Kerr rotation enhancement is attributed to the excitation of both the surface plasmon polariton in the dielectric PSS/metal interface and the guide waves (guide mode) in the PSS array. The two-dimensional PSSs/SiO2/FePt system exhibiting a tunable magneto-optical Kerr effect and a high perpendicular magnetic anisotropy will be helpful for designing and fabricating magneto-optics devices.

Degradation behaviors of high power GaN-based blue light emitting diodes

Zhong Can-Tao, Yu Tong-Jun, Yan Jian, Chen Zhi-Zhong, Zhang Guo-Yi
Chin. Phys. B 2013, 22 (11): 117804 ;  doi: 10.1088/1674-1056/22/11/117804
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The degradation mechanism of high power InGaN/GaN blue light emitting diodes (LEDs) is investigated in this paper. The LED samples were stressed at room temperature under 350-mA injection current for about 400 h. The light output power of the LEDs decreased by 35% during the first 100 h and then remained almost unchanged, and the reverse current at-5 V increased from 10-9 A to 10-7 A during the aging process. The power law, whose meaning was re-illustrated by the improved rate equation, was used to analyze the light output power-injection current (L–I) curves. The analysis results indicate that nonradiative recombination, Auger recombination, and the third-order term of carriers overflow increase during the aging process, all of which may be important reasons for the degradation of LEDs. Besides, simulating L–I curves with the improved rate equation reveal that higher-than-third-order terms of carriers overflow may not be the main degradation mechanism, because they change slightly when the LED is stressed.

Optimization of a poly(p-phenylene benzobisoxazole)-based light-emitting device with a complex cathode structure

Zhang Xiao-Jin, He Zhi-Qun, Wang Jing, Mu Lin-Ping, Zhao Huan, Liang Chun-Jun, Zhuang Qi-Xin, Han Zhe-Wen
Chin. Phys. B 2013, 22 (11): 117805 ;  doi: 10.1088/1674-1056/22/11/117805
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In this work, we report the preparation of a series of electroluminescent (EL) devices based on a high-performance polymer, poly(p-phenylene benzobisoxazole) (PBO), and their optoelectronic properties, which have been rarely explored. The device structure is optimised using a complex cathode structure of tris-(8-hydoxyquinoline) aluminium (Alq3)/LiF/Al. By tuning the thickness of the Alq3 layer, we improve the device efficiency dramatically in an optimized condition. Further analysis reveals that the Alq3 layer in the complex cathode structure acts as a hole blocker in addition to its electron-injection role. A green light emission with a maximum brightness of 8.7×103 cd/m2 and a moderate current efficiency of 4.8 cd/A is obtained. These values are the highest ever reported for PBO devices. The high operational stability demonstrated by the present device makes it a promising tool for display and lighting applications. A new material is added to the selection of polymers used in this field up to now.

Polarization characteristics of chiral photonic crystal fibers with an elliptical hollow core

Li She, Li Jun-Qing, Cao Yu-Sheng
Chin. Phys. B 2013, 22 (11): 117806 ;  doi: 10.1088/1674-1056/22/11/117806
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The theoretical study of dielectric-chiral photonic crystal fiber (PCF) with an elliptical hollow core is presented. The band structure of chiral photonic crystal (PhC) is calculated by using a modified plane-wave expansion (PWE) method. By examining the out-of-plane photonic bandgaps (PBGs) of chiral PhC, a kind of chiral PCF with a hollow core is designed and their eigenstates are calculated. The distributions of mode field and polarization state are demonstrated, and how the structural asymmetry of the core together with the chirality in the background affects the modal polarization is discussed. The dependences of birefringence on chirality for different ellipticities of core are investigated.

Optical total reflection and transmission with mode control in a dielectric subwavelength nanorod chain

Li Hao, Li Wei, Du Jun-Jie, Wu Ai-Min, Qiu Chao, Sheng Zhen, Wang Xi, Zou Shi-Chang, Gan Fu-Wan
Chin. Phys. B 2013, 22 (11): 117807 ;  doi: 10.1088/1674-1056/22/11/117807
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We report a polarization dependent reflection phenomenon beyond the normal incidence with a subwavelength nanorod chain. Light waves of the transverse electric mode will be totally reflected while those of the transverse magnetic mode will transmit through. The total reflection or transmission phenomenon can be seen as a constructive or destructive interference of the incident field with the transverse mode field of the chain. With the low-loss feature and the ultra-compact characteristic, this structure may find applications in photonic circuits.

Suppressing the mechanical quadrature error of a quartz double-H gyroscope through laser trimming

Zhao Ke, Feng Li-Hui, Wang Qian-Qian, Liu Ming-Zhi, Wang Ben-Guo, Cui Fang, Sun Yu-Nan
Chin. Phys. B 2013, 22 (11): 117901 ;  doi: 10.1088/1674-1056/22/11/117901
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In this paper, we introduce a z-axis quartz gyroscope using a double-H tuning fork, which has a high sensitivity. However, it also causes a large mechanical quadrature error. The laser trimming method is used to suppress this error at quartz level. The trimming law is obtained through the finite element method (FEM). A femtosecond laser processing system is used to trim the gold balancing masses on the beams, and experimental results are basically consistent with the simulated ones. The mechanical quadrature error is suppressed by 96%, from 26.3° s-1 to 1.1° s-1. Nonlinearity changes from 1.48% to 0.30%, angular random walk (ARW) is reduced from 2.19° h-1/2 to 1.42° h-1/2, and bias instability is improved by a factor of 7.7, from 197.6° h-1 to 25.4° h-1.

Aluminium phthalocyanine chloride thin films for temperature sensing

Muhammad Tariq Saeed Chani, Abdullah M. Asiri, Kh. S. Karimov, Atif Khan Niaz, Sher Bhadar Khan, Khalid. A. Alamry
Chin. Phys. B 2013, 22 (11): 118101 ;  doi: 10.1088/1674-1056/22/11/118101
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This study presents the fabrication and temperature sensing properties of sensors based on aluminium phthalocyanine chloride (AlPcCl) thin films. To fabricate the sensors, 50-nm-thick electrodes with 50-μ gaps between them are deposited on glass substrates. AlPcCl thin films with thickness of 50–100 nm are deposited in the gap between electrodes by thermal evaporation. The resistance of the sensors decreases with increasing thickness and the annealing at 100 ℃ results in an increase in the initial resistance of sensors up to 24%. The sensing mechanism is based on the change in resistance with temperature. For temperature varying from 25 ℃ to 80 ℃, the change in resistance is up to 60%. Simulation is carried out and results obtained coincide with experimental data with an error of ±1%.

Physical model for the exotic ultraviolet photo-conductivity of ZnO nanowire films

Pan Yue-Wu, Ren Shou-Tian, Qu Shi-Liang, Wang Qiang
Chin. Phys. B 2013, 22 (11): 118102 ;  doi: 10.1088/1674-1056/22/11/118102
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Employing a simple and efficient method of electro-chemical anodization, ZnO nanowire films are fabricated on Zn foil, and an ultraviolet (UV) sensor prototype is formed for investigating the electronic transport through back-to-back double junctions. The UV (365 nm) responses of surface-contacted ZnO film are provided by I–V measurement, along with the current evolution process by on/off of UV illumination. In this paper, the back-to-back metal–seconductor–metal (M–S–M) model is used to explain the electronic transport of a ZnO nanowire film based structure. A thermionic-field electron emission mechanism is employed to fit and explain the as-observed UV sensitive electronic transport properties of ZnO film with surface-modulation by oxygen and water molecular coverage.

Scaling effects of single-event gate rupture in thin oxides

Ding Li-Li, Chen Wei, Guo Hong-Xia, Yan Yi-Hua, Guo Xiao-Qiang, Fan Ru-Yu
Chin. Phys. B 2013, 22 (11): 118501 ;  doi: 10.1088/1674-1056/22/11/118501
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The dynamics of the excess carriers generated by incident heavy ions are considered in both SiO2 and Si substrate. Influences of the initial radius of the charge track, surface potential decrease, external electric field, and the LET value of the incident ion on internal electric field buildup are analyzed separately. Considering the mechanisms of recombination, impact ionization, and bandgap tunneling, models are verified by using published experimental data. Moreover, the scaling effects of single-event gate rupture in thin gate oxides are studied, with the feature size of the MOS device down to 90 nm. The value of the total electric field decreases rapidly along with the decrease of oxide thickness in the first period (12 nm to 3.3 nm), and then increases a little when the gate oxide becomes thinner and thinner (3.3 nm to 1.8 nm).

High-voltage SOI lateral MOSFET with a dual vertical field plate Hot!

Fan Jie, Zhang Bo, Luo Xiao-Rong, Li Zhao-Ji
Chin. Phys. B 2013, 22 (11): 118502 ;  doi: 10.1088/1674-1056/22/11/118502
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A new silicon-on-insulator (SOI) power lateral MOSFET with a dual vertical field plate (VFP) in the oxide trench is proposed. The dual VFP modulates the distribution of the electric field in the drift region, which enhances the internal field of the drift region and increases the drift doping concentration of the drift region, resulting in remarkable improvements in breakdown voltage (BV) and specific on-resistance (Ron,sp). The mechanism of the VFP is analyzed and the characteristics of BV and Ron,sp are discussed. It is shown that the BV of the proposed device increases from 389 V of the conventional device to 589 V, and the Ron,sp decreases from 366 mΩ·cm2 to 110 mΩ·cm2.

High bandwidth surface-illuminated InGaAs/InP uni-travelling-carrier photodetector

Li Chong, Xue Chun-Lai, Li Chuan-Bo, Liu Zhi, Cheng Bu-Wen, Wang Qi-Ming
Chin. Phys. B 2013, 22 (11): 118503 ;  doi: 10.1088/1674-1056/22/11/118503
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Uni-traveling-carrier photodiodes (UTC-PDs) with ultrafast response and high saturation output are reported. A gradient doping layer and a narrow InP cliff layer were introduced to enhance the saturation and bandwidth characteristics. We measured the dark current, photo response, bandwidth, and saturation current of the fabricated UTC devices. For a 15-μm-diameter device, the dark current was 3.5 nA at a reverse bias of 1 V, and the 3-dB bandwidth was 17.2 GHz at a reverse bias of 5 V, which are comparable to the theoretically values. The maximum responsivity at 1.55 μm was 0.32 A/W. The saturation output current was over 19.0 mA without bias.

Efficiency enhancement of an InGaN light-emitting diode with a p-AlGaN/GaN superlattice last quantum barrier

Xiong Jian-Yong, Zhao Fang, Fan Guang-Han, Xu Yi-Qin, Liu Xiao-Ping, Song Jing-Jing, Ding Bin-Bin, Zhang Tao, Zheng Shu-Wen
Chin. Phys. B 2013, 22 (11): 118504 ;  doi: 10.1088/1674-1056/22/11/118504
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In this study, the efficiency droop of an InGaN light-emitting diode (LED) is reduced significantly by using a p-AlGaN/GaN superlattice last quantum barrier. The reduction in efficiency droop is mainly caused by the decrease of electron current leakage and the increase of hole injection efficiency, which is revealed by investigating the light currents, internal quantum efficiencies, energy band diagrams, carrier concentrations, carrier current densities, and radiative recombination efficiencies of three LED structures with the advanced physical model of semiconductor device (APSYS).

Monitoring the reaction between AlCl3 and o-xylene by using terahertz spectroscopy

Jin Wu-Jun, Li Tao, Zhao Kun, Zhao Hui
Chin. Phys. B 2013, 22 (11): 118701 ;  doi: 10.1088/1674-1056/22/11/118701
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Terahertz time-domain spectroscopy (THz-TDS) is used to study the interaction between AlCl3 and o-xylene in a temperature range from 300 K to 368 K. For comparison, the three isomers of o-, m-, and p-xylene are measured by using THz-TDS. The o-xylene carries out isomerization reaction in the presence of catalyst AlCl3. The absorption coefficient of the mixed reaction solution is extracted and analyzed in the frequency range from 0.2 THz to 1.4 THz. The temperature dependence of the absorption coefficient, which is influenced by both the dissolution of AlCl3 and the production of the two other isomer resultants, is obtained, and it can indicate the process of the isomerization reaction. The results suggest that THz spectroscopy can be used to monitor the isomerization reaction and other reactions in chemical synthesis, petrochemical and biomedical fields.

Effects of annealing rate and morphology of sol–gel derived ZnO on the performance of inverted polymer solar cells

Yu Xuan, Hu Zi-Yang, Huang Zhen-Hua, Yu Xiao-Ming, Zhang Jian-Jun, Zhao Geng-Shen, Zhao Ying
Chin. Phys. B 2013, 22 (11): 118801 ;  doi: 10.1088/1674-1056/22/11/118801
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The effects of annealing rate and morphology of sol–gel derived zinc oxide (ZnO) thin films on the performance of inverted polymer solar cells (IPSCs) are investigated. ZnO films with different morphologies are prepared at different annealing rates and used as the electron transport layers in IPSCs. The undulating morphologies of ZnO films fabricated at annealing rates of 10 ℃/min and 3 ℃/min each possess a rougher surface than that of the ZnO film fabricated at a fast annealing rate of 50 ℃/min. The ZnO films are characterized by atomic force microscopy (AFM), optical transmittance measurements, and simulation. The results indicate that the ZnO film formed at 3 ℃/min possesses a good-quality contact area with the active layer. Combined with a moderate light-scattering, the resulting device shows a 16% improvement in power conversion efficiency compared with that of the rapidly annealed ZnO film device.
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