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  • Thermoelectric-transport in metal/graphene/metal hetero-structure

    Hu Hao, Cai Jin-Ming, Zhang Chen-Dong, Gao Min, Pan Yi, Du Shi-Xuan, Sun Qing-Feng, Niu Qian, Xie Xin-Cheng, Gao Hong-Jun
    Chin. Phys. B 2010, 19 (3): 037202
    We investigate the thermoelectric-transport properties of metal/graphene/metal hetero-structure. We use a single band tight-binding model to present the two-dimensional electronic band structure of graphene. Using the Landauer--Butticker formula and taking the coupling between graphene and the two e...

     
  • Layer resolved magnetization reversal study in SmCo5/Fe nanocomposite bilayers


    Chin. Phys. B 2010, 19 (3): 037504
    A hard/soft SmCo5/ Fe nanocomposite magnetic bilayer system is fabricated on x-ray transparent 100--200~nm thin Si3N4 films by magnetron sputtering. The microscopic magnetic domain pattern and its behaviours during magnetization reversal in the hard and the soft magnetic phases are studied separatel...

     
  • Towards an optical coupler using fine-wire: a study of the photovoltaic effect of a heterojunction formed in a single fine-wire of tungsten oxides

    Chen Shang-Hui, Chen Jian, Deng Shao-Zhi, Xu Ning-Sheng
    Chin. Phys. B 2010, 19 (3): 037803
    Nanodevices using the photovoltaic effect of a single nanowire have attracted growing interest. In this paper, we consider potential applications of the photovoltaic effect to optical signal coupling and optical power transmission, and report on the realization of a heterojunction formed between WO2...

     
Chin. Phys. B  
  Chin. Phys. B--2010, Vol.19, No.3
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GENERAL

The periodic solution to the model for the El Ni?o-Southern oscillation

Li Xiao-Jing
Chin. Phys. B, 2010, 19 (3): 030201 doi: 10.1088/1674-1056/19/3/030201
Full Text: [PDF 80 KB] (Downloads:835)
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A class of oscillator of the El Ni?o-Southern oscillation model is considered. Using Mawhin's continuation theorem, a result on the existence of periodic solutions for ENSO model is obtained.

Homotopic mapping solving method of the reduces equation for Kelvin waves

Mo Jia-Qi, Lin Yi-Hua, Lin Wan-Tao
Chin. Phys. B, 2010, 19 (3): 030202 doi: 10.1088/1674-1056/19/3/030202
Full Text: [PDF 88 KB] (Downloads:721)
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A reduces equation of the Kelvin wave is considered. By using the homotopic mapping solving method, the approximate solution is obtained. The homptopic mapping method is an analytic method, the obtained solution can analyse operations sequentially.

Chaos in the perturbed Korteweg-de Vries equation with nonlinear terms of higher order

Pan Wei-Zhen, Song Xiang-Jiong, Yu Jun
Chin. Phys. B, 2010, 19 (3): 030203 doi: 10.1088/1674-1056/19/3/030203
Full Text: [PDF 219 KB] (Downloads:774)
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The dynamical behaviour of the generalized Korteweg-de Vries (KdV) equation under a periodic perturbation is investigated numerically. The bifurcation and chaos in the system are observed by applying bifurcation diagrams, phase portraits and Poincaré maps. To characterise the chaotic behaviour of this system, the spectra of the Lyapunov exponent and Lyapunov dimension of the attractor are also employed.

Synchronisation and general dynamic symmetry of a vibrating system with two exciters rotating in opposite directions

Zhao Chun-Yu, Zhang Yi-Min, Wen Bang-Chun
Chin. Phys. B, 2010, 19 (3): 030301 doi: 10.1088/1674-1056/19/3/030301
Full Text: [PDF 158 KB] (Downloads:689)
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We derive the non-dimensional coupling equation of two exciters, including inertia coupling, stiffness coupling and load coupling. The concept of general dynamic symmetry is proposed to physically explain the synchronisation of the two exciters, which stems from the load coupling that produces the torque of general dynamic symmetry to force the phase difference between the two exciters close to the angle of general dynamic symmetry. The condition of implementing synchronisation is that the torque of general dynamic symmetry is greater than the asymmetric torque of the two motors. A general Lyapunov function is constructed to derive the stability condition of synchronisation that the non-dimensional inertia coupling matrix is positive definite and all its elements are positive. Numeric results show that the structure of the vibrating system can guarantee the stability of synchronisation of the two exciters, and that the greater the distances between the installation positions of the two exciters and the mass centre of the vibrating system are, the stronger the ability of general dynamic symmetry is.

Decomposition of almost-Poisson structure of generalised Chaplygin's nonholonomic systems

Liu Chang, Chang Peng, LiuShi-Xing, Guo Yong-Xin
Chin. Phys. B, 2010, 19 (3): 030302 doi: 10.1088/1674-1056/19/3/030302
Full Text: [PDF 97 KB] (Downloads:527)
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This paper constructs an almost-Poisson structure for the non-self-adjoint dynamical systems, which can be decomposed into a sum of a Poisson bracket and the other almost-Poisson bracket. The necessary and sufficient condition for the decomposition of the almost-Poisson bracket to be two Poisson ones is obtained. As an application, the almost-Poisson structure for generalised Chaplygin's systems is discussed in the framework of the decomposition theory. It proves that the almost-Poisson bracket for the systems can be decomposed into the sum of a canonical Poisson bracket and another two noncanonical Poisson brackets in some special cases, which is useful for integrating the equations of motion.

Symmetry of Lagrangians of nonholonomic systems of non-Chetaev's type

Wu Hui-Bin, Mei Feng-Xiang
Chin. Phys. B, 2010, 19 (3): 030303 doi: 10.1088/1674-1056/19/3/030303
Full Text: [PDF 81 KB] (Downloads:615)
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This paper studies the symmetry of Lagrangians of nonholonomic systems of non-Chetaev's type. First, the definition and the criterion of the symmetry of the system are given. Secondly, it obtains the condition under which there exists a conserved quantity and the form of the conserved quantity. Finally, an example is shown to illustrate the application of the result.

Mei symmetry and Mei conserved quantity of Appell equations for a variable mass holonomic system

Cui Jin-Chao, Zhang Yao-Yu, Yang Xin-Fang, Jia Li-Qun
Chin. Phys. B, 2010, 19 (3): 030304 doi: 10.1088/1674-1056/19/3/030304
Full Text: [PDF 86 KB] (Downloads:622)
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Mei symmetry and Mei conserved quantity of Appell equations for a variable mass holonomic system are investigated. Appell equations and differential equations of motion for a variable mass holonomic system are established. A new expression of the total first derivative of the function with respect of time t along the systematic motional track curve, and the definition and the criterion of Mei symmetry for Appell equations under the infinitesimal transformations of groups are given. The expressions of the structural equation and Mei conserved quantity for Mei symmetry in Appell are obtained. An example is given to illustrate the application of the results.

Mei symmetry and Mei conserved quantity of Nielsen equations for a non-holonomic system of Chetaev's type with variable mass

Yang Xin-Fang, Jia Li-Qun, Cui Jin-Chao, Luo Shao-Kai
Chin. Phys. B, 2010, 19 (3): 030305 doi: 10.1088/1674-1056/19/3/030305
Full Text: [PDF 87 KB] (Downloads:529)
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Mei symmetry and Mei conserved quantity of Nielsen equations for a non-holonomic, non-conservative system of Chetaev's type with variable mass are studied. The differential equations of motion of the Nielsen equation for the system, the definition and criterion of Mei symmetry, and the condition and the form of Mei conserved quantity deduced directly by Mei symmetry for the system are obtained. An example is given to illustrate the application of the results.

A connection between the (G'/G)-expansion method and the truncated Painlevé expansion method and its application to the mKdV equation

Zhao Yin-Long, Liu Yin-Ping, Li Zhi-Bin
Chin. Phys. B, 2010, 19 (3): 030306 doi: 10.1088/1674-1056/19/3/030306
Full Text: [PDF 99 KB] (Downloads:839)
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Recently the (G'/G)-expansion method was proposed to find the traveling wave solutions of nonlinear evolution equations. This paper shows that the (G'/G)-expansion method is a special form of the truncated Painlevé expansion method by introducing an intermediate expansion method. Then the generalized (G'/G)--(G'/G) expansion method is naturally derived from the standpoint of the nonstandard truncated Painlevé expansion. The application of the generalized method to the mKdV equation shows that it extends the range of exact solutions obtained by using the (G'/G)-expansion method.

A new approach of solving Green's function for wave propagation in an inhomogeneous absorbing medium

Li Wei, Liu Shi-Bing, Yang Wei
Chin. Phys. B, 2010, 19 (3): 030307 doi: 10.1088/1674-1056/19/3/030307
Full Text: [PDF 88 KB] (Downloads:800)
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A new approach is developed to solve the Green's function that satisfies the Hehmholtz equation with complex refractive index. Especially, the Green's function for the Helmholtz equation can be expressed in terms of a one-dimensional integral, which can convert a Helmholtz equation into a Schr?dinger equation with complex potential. And the Schr?dinger equation can be solved by Feynman path integral. The result is in excellent agreement with the previous work.

Measurements of a periodically driving qubit using a quantum point contact

Wang Hai-Xia, Yin Wen, Wang Fang-Wei
Chin. Phys. B, 2010, 19 (3): 030308 doi: 10.1088/1674-1056/19/3/030308
Full Text: [PDF 247 KB] (Downloads:508)
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Using the method developed by Gurvitz [1996 Phys. Rev. B 53 15932], we obtained the Bloch-type rate equations describing the entire system of a periodically driving qubit monitored by a quantum point contact detector. The results demonstrate that the isolated qubit can be kept in its initial state with a large driving frequency due to more difficult electron tunneling in qubit, and this initial state can always be measured at a small measurement-induced decoherence rate during a short time.

Entanglement dynamics of a double two-photon Jaynes-Cummings model with Kerr-like medium

Ouyang Xi-Cheng, FangMao-Fa, Kang Guo-Dong, Deng Xiao-Juan, HuangLi-Yuan
Chin. Phys. B, 2010, 19 (3): 030309 doi: 10.1088/1674-1056/19/3/030309
Full Text: [PDF 430 KB] (Downloads:916)
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In this paper, the entanglement dynamics of a double two-photon Jaynes--Cummings model with Kerr-like medium is investigated. It is shown that initial entanglement has an interesting subsequent time evolution, including the so-called entanglement sudden death effect. It is also shown analytically that the Kerr-like medium can repress entanglement sudden death and enhance the degree of atom--atom entanglement. A more interesting fact is that the Kerr effect is more obvious when each of the two cavities with have the Kerr-like medium than only one of them with the Kerr-like medium.

Controlled decoherence of three-level rf-SQUID qubit with asymmetric potential

Ji Ying-Hua, Lai Hui-Fang, Cai Shi-Hua, Wang Zi-Sheng
Chin. Phys. B, 2010, 19 (3): 030310 doi: 10.1088/1674-1056/19/3/030310
Full Text: [PDF 116 KB] (Downloads:598)
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A scheme is proposed to controll the decoherence of three-level rf-SQUID qubit with asymmetric potential by designing an external electric circuit for superconductive flux qubit. The results show that it may not only raise the gate speed but also extend decoherence time for a three-level structure.

Generation of entanglement in the atom-cavity-fibre system via adiabatic passage

Li Yan-Ling, Fang Mao-Fa
Chin. Phys. B, 2010, 19 (3): 030311 doi: 10.1088/1674-1056/19/3/030311
Full Text: [PDF 134 KB] (Downloads:612)
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A scheme, based on the system composed of three atoms separately trapped in three cavities coupled by optical fibres, for entangling two distant atoms via the adiabatic passage is proposed. It is found that the multi-particle W entangled state can also be generated. Moreover, the quantum information sharing can be implemented using this system. These results may be helpful for the implementation of quantum network and useful in quantum cryptography. This scheme is also convenient for operating since only the laser fields applied to the atoms need to be adjusted to accomplish the processes.

The propagation characteristic of the EPR entanglement for a composite non-degenerate parametric optical amplification system

Zhao Chao-Ying, Tan Wei-Han
Chin. Phys. B, 2010, 19 (3): 030312 doi: 10.1088/1674-1056/19/3/030312
Full Text: [PDF 113 KB] (Downloads:495)
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This paper applies the minimum variance V1 criterion to monitor the evolution of signal and idler modes of a composite non-degenerate optical parametric amplification (NOPA) system. The analytics and numerical calculation show the influence of the transition time, the vacuum fluctuations, and the thermal noise level on the EPR entanglement of the composite NOPA system. It finds that the entanglement and the squeezing degrade as the minimum variance V1 increases.

Distributed quantum information processing via quantum dot spins

Liu Jun, Wang Qiong, Kuang Le-Man, Zeng Hao-Sheng
Chin. Phys. B, 2010, 19 (3): 030313 doi: 10.1088/1674-1056/19/3/030313
Full Text: [PDF 237 KB] (Downloads:646)
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We propose a scheme to engineer a non-local two-qubit phase gate between two remote quantum-dot spins. Along with one-qubit local operations, one can in principal perform various types of distributed quantum information processing. The scheme employs a photon with linearly polarisation interacting one after the other with two remote quantum-dot spins in cavities. Due to the optical spin selection rule, the photon obtains a Faraday rotation after the interaction process. By measuring the polarisation of the final output photon, a non-local two-qubit phase gate between the two remote quantum-dot spins is constituted. Our scheme may has very important applications in the distributed quantum information processing.

Approximate solution for the Klein-Gordon-Schr?dinger equation by the homotopy analysis method

Wang Jia, Li Biao, Ye Wang-Chuan
Chin. Phys. B, 2010, 19 (3): 030401 doi: 10.1088/1674-1056/19/3/030401
Full Text: [PDF 3108 KB] (Downloads:860)
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The Homotopy analysis method is applied to obtain the approximate solution of the Klein--Gordon--Schr?dinger equation. The Homotopy analysis solutions of the Klein--Gordon--Schr?dinger equation contain an auxiliary parameter which provides a convenient way to control the convergence region and rate of the series solutions. Through errors analysis and numerical simulation, we can see the approximate solution is very close to the exact solution.

The series solution to the metric of stationary vacuum with axisymmetry

Gu Ying-Qiu
Chin. Phys. B, 2010, 19 (3): 030402 doi: 10.1088/1674-1056/19/3/030402
Full Text: [PDF 132 KB] (Downloads:533)
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The multipole moment method not only conduces to the understanding of the deformation of the space--time, but also serves as an effective tool to approximately solve the Einstein field equation with. However, the usual multipole moments are recursively determined by a sequence of symmetric and trace-free tensors, which is inconvenient for practical resolution. In this paper, we develop a simplified procedure to generate the series solutions to the metric of the stationary vacuum with axisymmetry, and show its validity. In order to understand the free parameters in the solution, we propose to take the Schwarzschild metric as a standard ruler, and some well- known examples are analysed and compared with the series solutions in detail.

Logit-based exit choice model of evacuation in rooms with internal obstacles and multiple exits

Guo Ren-Yong, HuangHai-Jun
Chin. Phys. B, 2010, 19 (3): 030501 doi: 10.1088/1674-1056/19/3/030501
Full Text: [PDF 835 KB] (Downloads:940)
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A logit-based discrete choice model is proposed to study the exit choice behaviour of evacuees in rooms with internal obstacles and multiple exits. Several factors influencing the exit choice behaviour, including the information obtained by evacuees, the tendency of following others, the visibility and familiarity of exits and the physical conditions of nearby exits, are considered. Evacuees are allowed to re-select their target exits for minimizing the perceived disutility during evacuation process. Numerical results from applying the model to cellular automata simulation of evacuation are presented and the effects of some model parameters on evacuation time are investigated.

Statistic properties of Fermi gas in a strong magnetic field

Men Fu-Dian, Fan Zhao-Lan
Chin. Phys. B, 2010, 19 (3): 030502 doi: 10.1088/1674-1056/19/3/030502
Full Text: [PDF 84 KB] (Downloads:1183)
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Based on the thermodynamic potential function of Fermi gas in a strong magnetic field, using the thermodynamics method, the integrated analytical expressions of thermodynamic quantities of the system at low temperatures are derived, and the effects of the magnetic field on the statistic properties of the system are analysed. It is shown that, as long as the temperature is not zero, the effects of the magnetic field on the thermodynamic quantities of the system contain both oscillatory and non-oscillatory parts. For the non-oscillatory part, compared with the situation of Fermi gas in a weak magnetic field, the influence of the magnetic field on the thermodynamic quantities is not exactly the same. For the oscillatory part, the period and amplitude of the oscillation are all related to the magnetic field. Due to the oscillation, the chemical potential may be greater than Ferim energy of the system, but the oscillation does not affect the thermodynamic stability of the system.

Stochastic resonance in the gene transcriptional regulatory system subjected to noises

Wang Can-Jun
Chin. Phys. B, 2010, 19 (3): 030503 doi: 10.1088/1674-1056/19/3/030503
Full Text: [PDF 860 KB] (Downloads:656)
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We have investigated in the adiabatic limit the phenomenon of stochastic resonance in the gene transcriptional regulatory system subjected to an additive noise, a multiplicative noise, and a weakly periodic signal. Using the general two-state approach for the asymmetry system, the analytic expression of signal-to-noise ratio is obtained. The effects of the additive noise intensity α, the multiplicative noise intensity D and the amplitude of input periodic signal A on the signal-to-noise ratio are analysed by numerical calculation. It is found that the existence of a maximum in the RSNR--α and RSNR--D plots is the identifying characteristic of the stochastic resonance phenomenon in the weakened noise intensity region. The stochastic resonance phenomena are restrained with increasing α and D, and enhanced with increasing A.

Behaviour of the current in a two-dimensional Büttiker-Landauer motor with entropic barriers

Liu Jiu-Liang, He Ji-Zhou
Chin. Phys. B, 2010, 19 (3): 030504 doi: 10.1088/1674-1056/19/3/030504
Full Text: [PDF 369 KB] (Downloads:537)
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The behaviour of the current in a two-dimensional Büttiker--Landauer motor, which is a position-dependent temperature-driven Brownian motor, is investigated in the presence of entropic and energy barriers. It is found that the motion of the Brownian particles is influenced by the shape of the channel. The existence of an entropic barrier can cause an asymmetric current as the flatness ratio of the shape varies. There exists an optimized flatness ratio (nonzero) at which the current reaches its maximum value.

Synchronising chaotic Chua's circuit using switching feedback control based on piecewise quadratic Lyapunov functions

Zhang Hong-Bin, Xia Jian-Wei, Yu Yong-Bin, Dang Chuang-Yin
Chin. Phys. B, 2010, 19 (3): 030505 doi: 10.1088/1674-1056/19/3/030505
Full Text: [PDF 150 KB] (Downloads:729)
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This paper investigates the chaos synchronisation between two coupled chaotic Chua's circuits. The sufficient condition presented by linear matrix inequalities (LMIs) of global asymptotic synchronisation is attained based on piecewise quadratic Lyapunov functions. First, we obtain the piecewise linear differential inclusions (pwLDIs) model of synchronisation error dynamics, then we design a switching (piecewise-linear) feedback control law to stabilise it based on the piecewise quadratic Laypunov functions. Then we give some numerical simulations to demonstrate the effectiveness of our theoretical results.

Wavelet threshold method of resolving noise interference in periodic short-impulse signals chaotic detection

Deng Ke, ZhangLu, Luo Mao-Kang
Chin. Phys. B, 2010, 19 (3): 030506 doi: 10.1088/1674-1056/19/3/030506
Full Text: [PDF 258 KB] (Downloads:540)
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The chaotic oscillator has already been considered as a powerful method to detect weak signals, even weak signals accompanied with noises. However, many examples, analyses and simulations indicate that chaotic oscillator detection system cannot guarantee the immunity to noises (even white noise). In fact the randomness of noises has a serious or even a destructive effect on the detection results in many cases. To solve this problem, we present a new detecting method based on wavelet threshold processing that can detect the chaotic weak signal accompanied with noise. All theoretical analyses and simulation experiments indicate that the new method reduces the noise interferences to detection significantly, thereby making the corresponding chaotic oscillator that detects the weak signals accompanied with noises more stable and reliable.

Study on eigenvalue space of hyperchaotic canonical four-dimensional Chua's circuit

Li Guan-Lin, Chen Xi-You
Chin. Phys. B, 2010, 19 (3): 030507 doi: 10.1088/1674-1056/19/3/030507
Full Text: [PDF 2947 KB] (Downloads:792)
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The eigenvalue space of the canonical four-dimensional Chua's circuit which can realize every eigenvalue for four-dimensional system is studied in this paper. First, the analytical relations between the circuit parameters and the eigenvalues of the system are established, and therefore all the circuit parameters can be determined explicitly by any given set of eigenvalues. Then, the eigenvalue space of the circuit is investigated in two cases by the nonlinear elements used. According to the types of the eigenvalues, some novel hyperchaotic attractors are presented. Further, the dynamic behaviours of the circuit are studied by the bifurcation diagrams and the Lyapunov spectra of the eigenvalues.

Controlling intracellular Ca2+ spiral waves by the local agonist in the cell membrane

Qiu Kang, Tang Jun, Ma Jun, Luo Ji-Ming
Chin. Phys. B, 2010, 19 (3): 030508 doi: 10.1088/1674-1056/19/3/030508
Full Text: [PDF 2510 KB] (Downloads:508)
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A modified spatially extended Tang--Othmer Ca2+ model is used to study intracellular Ca2+ spiral waves numerically. It is found that, as a local stimulation, the local agonist-binding on the cell membrane,which enhances the local concentration of the messenger molecule inositol 1,4,5-trisphosphate(IP3), can influence the dynamics of the spiral waves. {1}) Strong enough stimuli can change the spiral wave from a meandering to a rigidly rotating one. {2}) On the other hand, strong enough stimuli can suppress the spiral wave from the system. It provides the theoretical clue for controlling the spiral waves by stimulating the cell membrane.

Nonlinear feedback control of a novel hyperchaotic system and its circuit implementation

Wang Hao-Xiang, Cai Guo-Liang, MiaoSheng, Tian Li-Xin
Chin. Phys. B, 2010, 19 (3): 030509 doi: 10.1088/1674-1056/19/3/030509
Full Text: [PDF 895 KB] (Downloads:2885)
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This paper reports a new hyperchaotic system by adding an additional state variable into a three-dimensional chaotic dynamical system. Some of its basic dynamical properties, such as the hyperchaotic attractor, Lyapunov exponents, bifurcation diagram and the hyperchaotic attractor evolving into periodic, quasi-periodic dynamical behaviours by varying parameter k are studied. An effective nonlinear feedback control method is used to suppress hyperchaos to unstable equilibrium. Furthermore, a circuit is designed to realize this new hyperchaotic system by electronic workbench (EWB). Numerical simulations are presented to show these results.

Transient chaos in smooth memristor oscillator

Bao Bo-Cheng, Liu Zhong, Xu Jian-Ping
Chin. Phys. B, 2010, 19 (3): 030510 doi: 10.1088/1674-1056/19/3/030510
Full Text: [PDF 1803 KB] (Downloads:1691)
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This paper presents a new smooth memristor oscillator, which is derived from Chua's oscillator by replacing Chua's diode with a flux-controlled memristor and a negative conductance. Novel parameters and initial conditions are dependent upon dynamical behaviours such as transient chaos and stable chaos with an intermittence period and are found in the smooth memristor oscillator. By using dynamical analysis approaches including time series, phase portraits and bifurcation diagrams, the dynamical behaviours of the proposed memristor oscillator are effectively investigated in this paper.

Hopf bifurcation analysis of Chen circuit with direct time delay feedback

Ren Hai-Peng, Li Wen-Chao, Liu Ding
Chin. Phys. B, 2010, 19 (3): 030511 doi: 10.1088/1674-1056/19/3/030511
Full Text: [PDF 1118 KB] (Downloads:1216)
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Direct time delay feedback can make non-chaotic Chen circuit chaotic. The chaotic Chen circuit with direct time delay feedback possesses rich and complex dynamical behaviours. To reach a deep and clear understanding of the dynamics of such circuits described by delay differential equations, Hopf bifurcation in the circuit is analysed using the Hopf bifurcation theory and the central manifold theorem in this paper. Bifurcation points and bifurcation directions are derived in detail, which prove to be consistent with the previous bifurcation diagram. Numerical simulations and experimental results are given to verify the theoretical analysis. Hopf bifurcation analysis can explain and predict the periodical orbit (oscillation) in Chen circuit with direct time delay feedback. Bifurcation boundaries are derived using the Hopf bifurcation analysis, which will be helpful for determining the parameters in the stabilisation of the originally chaotic circuit.

Asymptotical p-moment stability of stochastic impulsive differential system and its application to chaos synchronization

Niu Yu-Jun, Xu Wei, Lu Zhao-Yang
Chin. Phys. B, 2010, 19 (3): 030512 doi: 10.1088/1674-1056/19/3/030512
Full Text: [PDF 244 KB] (Downloads:605)
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In this paper, the asymptotical p-moment stability of stochastic impulsive differential equations is studied and a comparison theory to ensure the asymptotical p-moment stability of the trivial solution is established, which is important for studying the impulsive control and synchronization in stochastic systems. As an application of this theory, we study the problem of chaos synchronization in the Chen system excited by parameter white-noise excitation, by using the impulsive method. Numerical simulations verify the feasibility of this method.

A fuzzy crisis in a Duffing-van der Pol system

Hong Ling
Chin. Phys. B, 2010, 19 (3): 030513 doi: 10.1088/1674-1056/19/3/030513
Full Text: [PDF 3127 KB] (Downloads:671)
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A crisis in a Duffing--van del Pol system with fuzzy uncertainties is studied by means of the fuzzy generalised cell mapping (FGCM) method. A crisis happens when two fuzzy attractors collide simultaneously with a fuzzy saddle on the basin boundary as the intensity of fuzzy noise reaches a critical point. The two fuzzy attractors merge discontinuously to form one large fuzzy attractor after a crisis. A fuzzy attractor is characterized by its global topology and membership function. A fuzzy saddle with a complicated pattern of several disjoint segments is observed in phase space. It leads to a discontinuous merging crisis of fuzzy attractors. We illustrate this crisis event by considering a fixed point under additive and multiplicative fuzzy noise. Such a crisis is fuzzy noise-induced effects which cannot be seen in deterministic systems.

A new chaotic Hopfield network with piecewise linear activation function

Zheng Peng-Sheng, Tang Wan-Sheng, Zhang Jian-Xiong
Chin. Phys. B, 2010, 19 (3): 030514 doi: 10.1088/1674-1056/19/3/030514
Full Text: [PDF 674 KB] (Downloads:631)
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This paper presents a new chaotic Hopfield network with a piecewise linear activation function. The dynamic of the network is studied by virtue of the bifurcation diagram, Lyapunov exponents spectrum and power spectrum. Numerical simulations show that the network displays chaotic behaviours for some well selected parameters.

Improvement on generalised synchronisation of chaotic systems

Zhu Hui-Bin, Qiu Fang, Cui Bao-Tong
Chin. Phys. B, 2010, 19 (3): 030515 doi: 10.1088/1674-1056/19/3/030515
Full Text: [PDF 831 KB] (Downloads:559)
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In this paper, the problem of generalised synchronisation of two different chaotic systems is investigated. Some less conservative conditions are derived using linear matrix inequality other than existing results. Furthermore, a simple adaptive control scheme is proposed to achieve the generalised synchronisation of chaotic systems. The proposed method is simple and easy to implement in practice and can be applied to secure communications. Numerical simulations are also given to demonstrate the effectiveness and feasibility of the theoretical analysis.

A new approach to detecting weak signal in strong noise based on chaos system control

Xu Yan-Chun, Yang Chun-Ling, Qu Xiao-Dong
Chin. Phys. B, 2010, 19 (3): 030516 doi: 10.1088/1674-1056/19/3/030516
Full Text: [PDF 463 KB] (Downloads:815)
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In this paper, a chaos system and proportional differential control are both used to detect the frequency of an unknown signal. In traditional methods the useful signal is obtained through the Duffing equation or other chaotic oscillators. But these methods are too complex because of using a lot of chaos oscillators. In this paper a new method is presented that uses the R?ssler equation and proportional differential control to detect a weak signal frequency. Substituting the detected signal frequency into the R?ssler equation leads the R?ssler phase state to be considerably changed. The chaos state can be controlled through the proportional differential method. Through its phase diagram and spectrum analysis, the unknown frequency is obtained. The simulation results verify that the presented method is feasible and that the detection accuracy is higher than those of other methods.

Shilnikov sense chaos in a simple three-dimensional system

Wang Wei, Zhang Qi-Chang, Tian Rui-Lan
Chin. Phys. B, 2010, 19 (3): 030517 doi: 10.1088/1674-1056/19/3/030517
Full Text: [PDF 726 KB] (Downloads:1041)
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The Shilnikov sense Smale horseshoe chaos in a simple 3D nonlinear system is studied. The proportional integral derivative (PID) controller is improved by introducing the quadratic and cubic nonlinearities into the governing equations. For the discussion of chaos, the bifurcate parameter value is selected in a reasonable regime at the requirement of the Shilnikov theorem. The analytic expression of the Shilnikov type homoclinic orbit is accomplished. It depends on the series form of the manifolds surrounding the saddle-focus equilibrium. Then the methodology is extended to research the dynamical behaviours of the simplified solar-wind-driven-magnetosphere-ionosphere system. As is illustrated, the Lyapunov characteristic exponent spectra of the two systems indicate the existence of chaotic attractor under some specific parameter conditions.

Bifurcation and chaos analysis for aeroelastic airfoil with freeplay structural nonlinearity in pitch

Zhao De-Min, Zhang Qi-Chang
Chin. Phys. B, 2010, 19 (3): 030518 doi: 10.1088/1674-1056/19/3/030518
Full Text: [PDF 386 KB] (Downloads:1175)
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The dynamics character of a two degree-of-freedom aeroelastic airfoil with combined freeplay and cubic stiffness nonlinearities in pitch submitted to supersonic and hypersonic flow has been gaining significant attention. The Poincaré mapping method and Floquet theory are adopted to analyse the limit cycle oscillation flutter and chaotic motion of this system. The result shows that the limit cycle oscillation flutter can be accurately predicted by the Floquet multiplier. The phase trajectories of both the pitch and plunge motion are obtained and the results show that the plunge motion is much more complex than the pitch motion. It is also proved that initial conditions have important influences on the dynamics character of the airfoil system. In a certain range of airspeed and with the same system parameters, the stable limit cycle oscillation, chaotic and multi-periodic motions can be detected under different initial conditions. The figure of the Poincaré section also approves the previous conclusion.

Scheduling trains on railway network using random walk method

Li Ke-Ping
Chin. Phys. B, 2010, 19 (3): 030519 doi: 10.1088/1674-1056/19/3/030519
Full Text: [PDF 524 KB] (Downloads:654)
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According to random walk, in this paper, we propose a new traffic model for scheduling trains on a railway network. In the proposed method, using some iteration rules for walkers, the departure and the arrival times of trains at each station are determined. We test the proposed method on an assumed railway network. The numerical simulations and the analytical results demonstrate that the proposed method provides an effective tool for scheduling trains. Some characteristic behaviours of train movement can be reproduced, such as train delay.

Upper bound for the time derivative of entropy for a stochastic dynamical system with double singularities driven by non-Gaussian noise

Guo Pei-Rong, Xu Wei, Liu Di
Chin. Phys. B, 2010, 19 (3): 030520 doi: 10.1088/1674-1056/19/3/030520
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A stochastic dynamical system with double singularities driven by non-Gaussian noise is investigated. The Fokker--Plank equation of the system is obtained through the path-integral approach and the method of transformation. Based on the definition of Shannon's information entropy and the Schwartz inequality principle, the upper bound for the time derivative of entropy is calculated both in the absence and in the presence of non-equilibrium constraint. The present calculations can be used to interpret the effects of the system dissipative parameter, the system singularity strength parameter, the noise correlation time and the noise deviation parameter on the upper bound.

Electrical crosstalk-coupling measurement and analysis for digital closed loop fibre optic gyro

Jin Jing, Tian Hai-Ting, Pan Xiong, Song Ning-Fang
Chin. Phys. B, 2010, 19 (3): 030701 doi: 10.1088/1674-1056/19/3/030701
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The phase modulation and the closed-loop controller can generate electrical crosstalk-coupling in digital closed-loop fibre optic gyro. Four electrical cross-coupling paths are verified by the open-loop testing approach. It is found the variation of ramp amplitude will lead to the alternation of gyro bias. The amplitude and the phase parameters of the electrical crosstalk signal are measured by lock-in amplifier, and the variation of gyro bias is confirmed to be caused by the alternation of phase according to the amplitude of the ramp. A digital closed-loop fibre optic gyro electrical crosstalk-coupling model is built by approximating the electrical cross-coupling paths as a proportion and integration segment. The results of simulation and experiment show that the modulation signal electrical crosstalk-coupling can cause the dead zone of the gyro when a small angular velocity is inputted, and it could also lead to a periodic vibration of the bias error of the gyro when a large angular velocity is inputted.
NUCLEAR PHYSICS

Numerical simulation for space charge dominated beam transport

Lü Jian-Qin
Chin. Phys. B, 2010, 19 (3): 032901 doi: 10.1088/1674-1056/19/3/032901
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To simulate the intense bunched beam transport, a computer program LEADS-3D has been developed. The particle trajectories are analysed with the Lie algebraic method. The third order approximation of the trajectory solutions is made with space charge forces off, and the second order approximation is made with space charge forces on. The particle distribution in the 3D ellipsoid is uniform or Gaussian. Most of the conventional beam optical elements are incorporated in the code. The optimization procedures are provided to fit the beam lines to satisfy the given optical conditions.

Time-and-space resolved measurements of the emission uniformity of carbon fibre cathode in high-current pulsed discharge

Liu Lie, Li Li-Min, Xu Qi-Fu, Cheng Guo-Xin, Chang Lei
Chin. Phys. B, 2010, 19 (3): 032902 doi: 10.1088/1674-1056/19/3/032902
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The remaining challenges, confronting high-power microwave (HPM) sources and pulsed power generators, stimulate the developments of robust relativistic electron beam sources. This paper presents a carbon fibre cathode which is tested in a single pulsed power generator. The distribution and the development of cathode plasma are observed by time-and-space resolved diagnostics, and the uniformity of electron beam density is checked by taking x-ray images. A quasistationary behaviour of cathode plasma expansion is observed. It is found that the uniformity of the extracted electron beam is satisfactory in spite of individual plasma jets on the cathode surface. These results show that carbon fibre cathodes can provide a positive prospect for developing a high-quality electron beam.
CLASSICAL AREAS OF PHENOMENOLOGY

Relationship between incident angle and dispersion in static large field of view polarization interference imaging spectrometer

Wu Jun-Fang, Zhang Chun-Min
Chin. Phys. B, 2010, 19 (3): 034201 doi: 10.1088/1674-1056/19/3/034201
Full Text: [PDF 132 KB] (Downloads:528)
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The static large field of the view polarization interference imaging spectrometer is based on the modified Savart polariscope. There appears a dispersion between the ordinary ray and extraordinary ray when light passes through the modified Savart polariscope. The dispersion greatly influences the intensities and the results of the interferogram and target image in the static large field of the view polarization interference imaging spectrometer. At the same time, the incident angle determines the dispersion. When the light goes through the modified Savart polariscope, the dispersion occurs in the left plate, the half-wave plate and the right plate of the modified Savart polariscope. Using the extension of Snell's law, the dispersion in the crystal is theoretically calculated and numerically simulated separately. The relationship curve between incident angle and the dispersion is obtained by simulation.

Far-field superlens for nanolithography

Chen Jian, WangQing-Kang, Li Hai-Hua
Chin. Phys. B, 2010, 19 (3): 034202 doi: 10.1088/1674-1056/19/3/034202
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A far-field optical lithography is developed in this paper. By designing the structure of a far-field optical superlens, lithographical resolution can be improved by using a conventional UV light source. The finite different time domain numerical studies indicate that the lithographic resolution at 50~nm line width is achievable with the structure shown in this paper by using 365~nm wavelength light, and the light can be transferred to a far distance in the photoresist.

Distortion of optical feedback signals in microchip Nd:YAG lasers subjected to external multi-beam interference feedback

Tan Yi-Dong, Zhang Shu-Lian, Ren Zhou, Ren Cheng, Zhang Yi-Nan
Chin. Phys. B, 2010, 19 (3): 034203 doi: 10.1088/1674-1056/19/3/034203
Full Text: [PDF 556 KB] (Downloads:539)
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This paper proposes a theoretical analysis for the characteristics of an external cavity Nd:YAG laser with feedback of multiple-beam interference, which is induced by the multi-reentrance of the light from the external Fabry--Perot cavity. The theoretical model considers the multiple beam interference of the external Fabry--Perot cavity. It is found that the optical feedback signals are distorted to pulse waveforms instead of the sinusoidal ones in conventional feedback. The experimental results are in good agreement with the theoretical analysis. The obtained theoretical and experimental results can advance the development of a laser feedback interferometer.

Surface mico-structures on amorphous alloys induced by vortex femtosecond laser pulses

Ran Ling-Ling, Qu Shi-Liang, Guo Zhong-Yi
Chin. Phys. B, 2010, 19 (3): 034204 doi: 10.1088/1674-1056/19/3/034204
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This paper investigates the generation of self-organized surface structures on amorphous alloys by vortex femtosecond laser pulses. The scanning electron microscope characterizations show that the as-formed structures are periodic ripples, aperiodic ripples, and `coral-like' structures. Optimal conditions for forming these surface structures are determined in terms of pulses number at a given pulse energy. The applicable mechanism is suggested to interpret the formation and evolution of the `coral-like' structures.

One-step implementation of an N-qubit quantum phase gate through a double Raman passage

Lü Hai-Yan, Yu Ya-Fei, Zhang Zhi-Ming
Chin. Phys. B, 2010, 19 (3): 034205 doi: 10.1088/1674-1056/19/3/034205
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We propose a scheme for controllably implementing an N-qubit phase gate by one step within a ground-state subspace of N three-state atoms trapped in a cavity through a double Raman passage. We can extend our scheme to the realisation of an arbitrary N-qubit phase gate by appropriately adjusting coupling strengths and detunings between atoms and external driving fields. The advantage of this one-step scheme is its robustness against decoherence.

Quantum fluctuation in excited states of mesoscopic LC circuits at finite temperature

Wang Ji-Suo, FanHong-Yi, Meng Xiang-Guo
Chin. Phys. B, 2010, 19 (3): 034206 doi: 10.1088/1674-1056/19/3/034206
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We discuss quantum fluctuation in excited states (named thermo number states) of mesoscopic LC circuits at a finite temperature. By introducing the coherent thermo state into the thermo field dynamics pioneered by Umezawa and using the natural representation of thermo squeezing operator we can concisely derive the fluctuation. The result shows that the noise becomes larger when either temperature or the excitation number increases.

Preparation of the four-qubit cluster states in cavity QED and the trapped-ion system

Zheng Xiao-Juan, Xu Hui, Fang Mao-Fa, Zhu Kai-Cheng
Chin. Phys. B, 2010, 19 (3): 034207 doi: 10.1088/1674-1056/19/3/034207
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This paper proposes a simple scheme to generate a four-atom entangled cluster state in cavity quantum electrodynamics. With the assistantce of a strong classical field the cavity is only virtually excited and no quantum information will be transferred from the atoms to the cavity during the preparation for a four-atom entangled cluster state, and thus the scheme is insensitive to the cavity field states and cavity decay. Assuming that deviation of laser intensity is 0.01 and that of simultaneity for the interaction is 0.01, it shows that the fidelity of the resulting four-atom entangled cluster state is about 0.9886. The scheme can also be used to generate a four-ion entangled cluster state in a hot trapped-ion system. Assuming that deviation of laser intensity is 0.01, it shows that the fidelity of the resulting four-ion entangled cluster state is about 0.9990. Experimental feasibility for achieving this scheme is also discussed.

Realization of stimulated emission-based detector and its application to antinormally ordered photodetection

Fan Dai-He, Bai Yun-Fei, ZhangHai-Long, Chen Jun-Jian, Zhang Jun-Xiang, Gao Jiang-Rui
Chin. Phys. B, 2010, 19 (3): 034208 doi: 10.1088/1674-1056/19/3/034208
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Using a stimulated parametric down-conversion process combined with a conventional detector, we theoretically propose a scheme to realize the stimulated emission-based detector, and investigate the antinormally ordered correlation function and Fano factor for the coherent field based on it. Such a detection has advantages over the normally ordered one especially when the intensity of the field is weak.

Filamentation-assisted fourth-order nonlinear process in KTP crystal

Zhang Xi-Peng, Jiang Hong-Bing, Chen Li, Jiang Ying-Ying, Yang Hong, Gong Qi-Huang
Chin. Phys. B, 2010, 19 (3): 034209 doi: 10.1088/1674-1056/19/3/034209
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We present an experimental investigation of a filamentation-assisted fourth-order nonlinear optical process in KTP crystals pumped by intense 1.53~eV (807~nm) femtosecond laser pulses. Femtosecond light pulses at 2.58~eV (480~nm) are generated by the fourth-order nonlinear polarization (P42 ) = χ 42 ,ω ,ω ,ω ,- ω 1 )E3(ω )E*1 ), where E(ω ) corresponds to the pump frequency and E(ω 1 ) to the supercontinuum generated through filamentation). If the system is seeded by a laser beam at ω 1 or ω 2 and there are spatial and temporal overlaps with the pump beam, E(ω 1 ) and E(ω 2 ) are simultaneously amplified. When the intensity of the seed laser beam exceeds a certain intensity threshold, the contribution of P4(ω ) = χ 4(ω ,ω 12 ,-ω, - ω )E(ω 1 )E(ω 2 )(E* (ω))2 becomes non-negligible, and the amplification weakens. The conversion efficiency from the pump to the signal at 2.58~eV (480~nm) attains to 0.1%.

Dispersion characteristics of two-dimensional unmagnetized dielectric plasma photonic crystal

Qi Li-Mei, Yang Zi-Qiang, Lan Feng, Gao Xi, Li Da-Zhi
Chin. Phys. B, 2010, 19 (3): 034210 doi: 10.1088/1674-1056/19/3/034210
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This paper studies dispersion characteristics of the transverse magnetic (TM) mode for two-dimensional unmagnetized dielectric plasma photonic crystal by a modified plane wave method. First, the cutoff behaviour is made clear by using the Maxwell--Garnett effective medium theory, and the influences of dielectric filling factor and dielectric constant on effective plasma frequency are analysed. Moreover, the occurence of large gaps in dielectric plasma photonic crystal is demonstrated by comparing the skin depth with the lattice constant, and the influence of plasma frequency on the first three gaps is also studied. Finally, by using the particle-in-cell simulation method, a transmission curve in the \Gamma -X direction is obtained in dielectric plasma photonic crystal, which is in accordance with the dispersion curves calculated by the modified plane wave method, and the large gap between the transmission points of 27~GHz and 47~GHz is explained by comparing the electric field patterns in particle-in-cell simulation.

Effects of granular size on stress transmission in a granular column

Abdul Qadir, Shi Qing-Fan, Liang Xuan-Wen, Sun Gang
Chin. Phys. B, 2010, 19 (3): 034601 doi: 10.1088/1674-1056/19/3/034601
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We investigate the deflection and the fluctuation of stresses due to different sizes of granular material in a cylindrical column. It is experimentally observed that the saturation mass systemically increases with granule diameter . The results indicate the shielding of vertical stress in silo is varying. We show that the ratio between the horizontal and the vertical stresses, K, decreases with the increase in grainule diameter D. In addition, it has also been found that the presence of larger granules leads to stronger stress fluctuation on the bottom plate of silo.
ATOMIC AND MOLECULAR PHYSICS

Effect of Landau-Zener tunneling by the varying sweeping rate of external field

WangJin-Bao, Tong Guo-Ping, Li Sheng
Chin. Phys. B, 2010, 19 (3): 033201 doi: 10.1088/1674-1056/19/3/033201
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We study the effect of Landau--Zener (LZ) tunneling caused by the varying sweeping rate of the external field, and solve the problem about the LZ tunneling rate among many levels. The LZ tunneling rate is essentially changed by the unsteady variation of the time-dependent sweeping field and is different from the steadily varying sweeping field, which makes the particles in lower states transit periodically to upper states within a finite time.

Exact results on cavity cooling in a system of a two-level atom and a cavity field

Zhang Yu-Qing, Tan Lei, Zhu Zhong-Hua, Liu Li-Wei
Chin. Phys. B, 2010, 19 (3): 033202 doi: 10.1088/1674-1056/19/3/033202
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Using the algebraic dynamical method, this paper investigates the laser cooling of a moving two-level atom coupled to a cavity field. Analytical solutions of optical forces and the cooling temperatures are obtained. Considering Rb atoms as an example, it finds that the numerical results are relevant to the recent experimental laser cooling investigations.

Study on wave packet dynamics of E1g+ state of Li2 with femtosecond-resolved photoelectron spectra

Liu Yu-Fang, Liu Rui-Qiong, Ding Jun-Xia
Chin. Phys. B, 2010, 19 (3): 033301 doi: 10.1088/1674-1056/19/3/033301
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Wave packet dynamics of the Li2 molecule are investigated by using the time-dependent quantum wave packet method, and the time-resolved photoelectron spectra of the Li2 molecule are calculated. The time-resolved wave packet theory is used to reasonably interpret the phenomena of the photoelectron spectra for different parameters. Our calculation shows that the loss of the wave packets in the shelf state area of E{ }^1\Sigmag^ + plays a prominent role in the process of photoionization with the increase of the delay time. Moreover, the oscillation of the wave packet on the E{ }^1\Sigmag^ + curve symbolizes a decreasing process of energy.

Relativistic density functional investigation of UX6 (X= F, Cl, Br and I)

Zhang Yun-Guang, Li Yu-De
Chin. Phys. B, 2010, 19 (3): 033302 doi: 10.1088/1674-1056/19/3/033302
Full Text: [PDF 103 KB] (Downloads:751)
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The molecular structures and the vibrational frequencies of uranium hexahalides UX_{6 } (x=F, Cl, Br and I) molecules are investigated by using local density approximation (LDA) and generalised gradient approximation (GGA) functions (BP, BLYP and RPBE) in combination with two different relativistic methods (scalar and scalar+spin--orbit relativistic effects). The calculated results show that the differences are trivial between scalar and scalar+spin--orbit relativistic methods. The vibrational frequencies are also compared with existing experimental values, and overall, the RPBE approach gives the smallest error. The bond dissociation energies (BDEs) of UX6 are computed by using the RPBE function, thereby obtaining exact vibrational frequencies. In addition, the calculated magnitudes of the spin--orbit effect on the BDE of UX_{6 } (x=F, Cl, Br, and I) are found to be approximately --0.3198, --0.3218, --0.3609 and --0.4415~eV, respectively.

Multireference calculation of lifetime of A2Пu state in nitrogen-molecule cation

Yan Bing, Feng Wei
Chin. Phys. B, 2010, 19 (3): 033303 doi: 10.1088/1674-1056/19/3/033303
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This paper utilizes multireference configuration interaction theory to calculate the lifetime of A2\Pi _{\rm u} state for nitrogen molecular ion N_{2}^{ + }. It obtains the transition moment function for A2\Pi _{\rm u} \to x2\Sigma g^{ + }, Franck--Condon factors between vibrational levels of the two states. The calculated lifetimes are 16.81, 14.62, 13.10, 12.18, 11.40, and 11.64~μ s for v'=0, 1, 2, 3, 4, 5 vibrational levels of A2\Pi _{\rm u} state, respectively, which are in excellent agreement with available experimental values.

Coherent phase control in electron-argon scattering in a bichromatic laser field

Zhou Bin, Li Shu-Min
Chin. Phys. B, 2010, 19 (3): 033401 doi: 10.1088/1674-1056/19/3/033401
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This paper theoretically investigates the coherent phase control in electron--argon scattering assisted by a bichromatic laser field. The laser field is composed of a fundamental component and its second harmonic. The incoming and out going states of electron are described by the Volkov wave functions, and the electron--target interaction is treated as a screening potential. Numerical results for differential cross section of multiphoton processes vs the phase difference between the two components of laser field are discussed for several scattering angles and impact energies.

Density functional theory study on Ni-doped MgnNi (n=1-7) clusters

Chen Xue-Feng, Zhang Yan, Qi Kai-Tian, Li Bing, Zhu Zheng-He, Sheng Yong
Chin. Phys. B, 2010, 19 (3): 033601 doi: 10.1088/1674-1056/19/3/033601
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The possible geometrical and the electronic structures of small MgnNi (n=1-7) clusters are optimised by the density functional theory with a LANL2DZ basis set. The binding energy, the energy gap, the electron affinity, the dissociation energy and the second difference in energy are calculated and discussed. The properties of MgnNi clusters are also discussed when the number of Mg atom increases.

Geometric, stable and electronic properties of Aun-2Y2 (n=3-8) clusters

Qi Kai-Tian, Mao Hua-Ping, Wang Hong-Yan, Sheng Yong
Chin. Phys. B, 2010, 19 (3): 033602 doi: 10.1088/1674-1056/19/3/033602
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Employing first-principles methods, based on the density function theory, and using the LANL2DZ basis sets, the ground-state geometric, the stable and the electronic properties of Aun-2Y2 clusters are investigated in this paper. Meanwhile, the differences in property among pure gold clusters, pure yttrium clusters, gold clusters doped with one yttrium atom, and gold clusters doped with two yttrium atoms are studied. We find that when gold clusters are doped by two yttrium atoms, the odd--even oscillatory behaviours of Aun-1Y and Aun disappear. The properties of Aun-2Y2 clusters are close to those of pure yttrium clusters.

The stability, frontier orbitals, bond character, and static linear polarizability of the fluorinated fullerene H20@C80F60

Tang Chun-Mei, Cao Qing-Song, Zhu Wei-Hua, Deng Kai-Ming
Chin. Phys. B, 2010, 19 (3): 033603 doi: 10.1088/1674-1056/19/3/033603
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This paper uses the density functional theory under generalised gradient approximation to analyse the stability, frontier orbitals, bond character, and static linear polarizability of H20@C80F60, which has not been isolated, as well as those of the synthesised H20@C80F60. The H20@C80F60 should be considerably stable by analysing its energy and aromaticity. The inside H and outside x will play different role in the chemical reaction involving H20@C80F60 (X= H and F). The covalence of C--H bond is in the order that the inside C--H bond of H20@C80F60> the inside C--H bond of H20@C80F60> the outside C--H bond of H20@C80F60, whereas the C--F bond of H20@C80F60 have both the covalent and ionic characters. The static linear polarizabilities of C80 and H20@C80X60 (X= H and F) are all isotropic.

Density functional calculations on the geometric structure and properties of the 3d transition metal atom doped endohedral fullerene M@C20F20 (M= Sc--Ni)

Tang Chun-Mei, Zhu Wei-Hua, Deng Kai-Ming
Chin. Phys. B, 2010, 19 (3): 033604 doi: 10.1088/1674-1056/19/3/033604
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This paper uses the generalised gradient approximation based on density functional theory to analyse the geometric structure and properties of the 3d transition metal atom doped endohedral fullerene M@C20F20 (M= Sc--Ni). The geometric optimization shows that the cage centre is the most stable position for M, forming the structure named as M@C20F20-4. The inclusion energy, zero-point energy, and energy gap calculations tell us that Ni@C20F20-4 should be thermodynamically and kinetically stablest. M@C20F20-4 (M= Sc--Co) possesses high magnetic moments varied from 1 to 6~μB, while Ni@C20F20-4 is nonmagnetic. The Ni--C bond in Ni@C20F20-4 contains both the covalent and ionic characters.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Two-dimensional particle-in-cell plasma source ion implantation of a prolate spheroid target

Liu Cheng-Sen, Han Hong-Ying, PengXiao-Qing, Chang Ye, Wang De-Zhen
Chin. Phys. B, 2010, 19 (3): 035201 doi: 10.1088/1674-1056/19/3/035201
Full Text: [PDF 1515 KB] (Downloads:681)
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A two-dimensional particle-in-cell simulation is used to study the time-dependent evolution of the sheath surrounding a prolate spheroid target during a high voltage pulse in plasma source ion implantation. Our study shows that the potential contour lines pack more closely in the plasma sheath near the vertex of the major axis, i.e. where a thinner sheath is formed, and a non-uniform total ion dose distribution is incident along the surface of the prolate spheroid target due to the focusing of ions by the potential structure. Ion focusing takes place not only at the vertex of the major axis, where dense potential contour lines exist, but also at the vertex of the minor axis, where sparse contour lines exist. This results in two peaks of the received ion dose, locating at the vertices of the major and minor axes of the prolate spheroid target, and an ion dose valley, staying always between the vertices, rather than at the vertex of the minor axis.

Interaction of intense laser pulses with hydrogen atomic clusters

Du Hong-Chuan, Wang Hui-Qiao, Liu Zuo-Ye, Sun Shao-Hua, Li Lu, Ma Ling-Ling, Hu Bi-Tao
Chin. Phys. B, 2010, 19 (3): 035202 doi: 10.1088/1674-1056/19/3/035202
Full Text: [PDF 180 KB] (Downloads:632)
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The interaction between intense femtosecond laser pulses and hydrogen atomic clusters is studied by a simplified Coulomb explosion model. The dependences of average proton kinetic energy on cluster size, pulse duration, laser intensity and wavelength are studied respectively. The calculated results indicate that the irradiation of a femtosecond laser of longer wavelength on hydrogen atomic clusters may be a simple, economical way to produce highly kinetic hydrogen ions. The phenomenon suggests that the irradiation of femtosecond laser of longer wavelength on deuterium atomic clusters may be easier than that of shorter wavelength to drive nuclear fusion reactions. The product of the laser intensity and the squared laser wavelength needed to make proton energy saturated as a function of the squared cluster radius is also investigated. The proton energy distribution calculated is also shown and compared with the experimental data. Our results are in agreement with the experimental results fairly well.

Analysis of diffusive coefficient of electron heat pulse based on singular value decomposition in HT-7 tokamak

Li Er-Zhong, Ling Bi-Li, Liu Yong, Ti Ang, Hu Li-Qun, Gao Xiang
Chin. Phys. B, 2010, 19 (3): 035203 doi: 10.1088/1674-1056/19/3/035203
Full Text: [PDF 713 KB] (Downloads:514)
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In this paper, singular value decomposition (SVD) as a filter-noise method is applied to electron cyclotron emission (ECE) diagnostic signals. The decomposed vectors contain the information about sawtooth such as the temporal vectors that show the sawtooth period and the spatial vectors that indicate the inverse radius. The propagation of electron heat pulse is investigated from electron cyclotron emission signals by using the perturbation method in HT-7 tokamak. The heat diffusivities are obtained at different densities in ohmic plasmas. The special result is that the heat diffusivity becomes larger as the heat pulse propagates outwards from the outside of the inverse radius.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Variations of water's local-structure induced by solvation of NaCl

Gu Bin, Zhang Feng-Shou, Huang Yu-Gai, Fang Xia
Chin. Phys. B, 2010, 19 (3): 036101 doi: 10.1088/1674-1056/19/3/036101
Full Text: [PDF 3127 KB] (Downloads:811)
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The researches on the structure of water and its changes induced by solutes are of enduring interests. The changes of the local structure of liquid water induced by NaCl solute under ambient conditions are studied and presented quantitatively with some order parameters and visualized with 2-body and 3-body correlation functions. The results show that, after the NaCl are solvated, the translational order t of water is decreased for the suppression of the second hydration shells around H2O molecules; the tetrahedral order |q| of water is also decreased and its favorite distribution peak moves from 0.76 to 0.5. In addition, the orientational freedom k and the diffusion coefficient D of water molecules are reduced because of new formed hydrogen-bonding structures between water and solvated ions.

Damage of low-energy ion irradiation on copper nanowire: molecular dynamics simulation

Zou Xue-Qing, Xue Jian-Ming, Wang Yu-Gang
Chin. Phys. B, 2010, 19 (3): 036102 doi: 10.1088/1674-1056/19/3/036102
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Physical and chemical phenomena of low-energy ion irradiation on solid surfaces have been studied systematically for many years, due to the wide applications in surface modification, ion implantation and thin-film growth. Recently the bombardment of nano-scale materials with low-energy ions gained much attention. Comared to bulk materials, nano-scale materials show different physical and chemical properties. In this article, we employed molecular dynamics simulations to study the damage caused by low-energy ion irradiation on copper nanowires. By simulating the ion bombardment of 5 different incident energies, namely, 1~keV, 2~keV, 3~keV, 4~keV and 5~keV, we found that the sputtering yield of the incident ion is linearly proportional to the energies of incident ions. Low-energy impacts mainly induce surface damage to the nanowires, and only a few bulk defects were observed. Surface vacancies and adatoms accumulated to form defect clusters on the surface, and their distribution are related to the type of crystal plane, e.g. surface vacancies prefer to stay on (100) plane, while adatoms prefer (110) plane. These results reveal that the size effect will influence the interaction between low-energy ion and nanowire.

Hydrogen storage in BC3 composite single-walled nanotube:a combined density functional theory and Monte Carlo investigation

Liu Xiu-Ying, Wang Chao-Yang, TangYong-Jian, Sun Wei-Guo, Wu Wei-Dong
Chin. Phys. B, 2010, 19 (3): 036103 doi: 10.1088/1674-1056/19/3/036103
Full Text: [PDF 2132 KB] (Downloads:908)
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This paper applies a density functional theory (DFT) and grand canonical Monte Carlo simulations (GCMC) to investigate the physisorptions of molecular hydrogen in single-walled BC3 nanotubes and carbon nanotubes. The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes. Furthermore, the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions. The present results have shown that with both computational methods, the hydrogen storage capacity of BC3 nanotubes is superior to that of carbon nanotubes. The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.

Simulation of critical behaviour on damage evolution

Qi Mei-Lan, He Hong-Liang
Chin. Phys. B, 2010, 19 (3): 036201 doi: 10.1088/1674-1056/19/3/036201
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Based on a damage evolution equation and a critical damage function model, this paper has completed the numerical simulation of ductile spall fracture. The free-surface velocity and damage distribution have been used to determine jointly the physical parameters Dl (the critical linking damage), Df (the critical fracturing damage) and k (the softening rate of critical damage function model)of the critical damage function model, which are 0.11, 0.51 and 0.57 respectively. Results indicate that the parameters determined by any of shots could be applicable to the rest of other shots, which is convincing proof for the universal property of critical damage function. In our experiments, the shock pressure is about 1~GPa to 2.5~GPa. For the reason of limited pressure range, there are still some limitations in the methods of present analysis. Moreover, according to the damage evolution characteristic of pure aluminum obtained by experiments, two critical damages are obtained, which are 0.11 and 0.51 respectively. The results are coincident with the experimental ones, which indicate that the critical growth behaviour of damage occurs in the plastic metal under dynamic loading.

Influence of AlN buffer layer thickness on structural properties of GaN epilayer grown on Si (111) substrate with AlGaN interlayer

Wu Yu-Xin, Zhu Jian-Jun, Chen Gui-Feng, Zhang Shu-Ming, Jiang De-Sheng, Liu Zong-Shun, Zhao De-Gang, Wang Hui, Wang Yu-Tian, Yang Hui
Chin. Phys. B, 2010, 19 (3): 036801 doi: 10.1088/1674-1056/19/3/036801
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We present the growth of GaN epilayer on Si (111) substrate with a single AlGaN interlayer sandwiched between the GaN epilayer and AlN buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an AlN buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.

Effects of switching pulse width and stress on properties of Bi3.25La0.75Ti3O12 thin films

Wu Xiu-Mei, Chen Hua, Zhai Ya, Lü Xiao-Mei, Liu Yun-Fei, Zhu Jin-Song
Chin. Phys. B, 2010, 19 (3): 036802 doi: 10.1088/1674-1056/19/3/036802
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Polycrystalline ferroelectric Bi3.25La0.75Ti3O12 thin films are prepared on Pt/Ti/SiO2/Si substrates by the conventional metalorganic decomposition method. It is observed that with the increase of switching pulse width, the remnant polarisation and the coercive field increase. A wider switching pulse can result in poorer fatigue properties, which comes from more charged defects diffusing to and being trapped on domain walls. On the other hand, when the compressive stress is applied to films, the fatigue properties can be improved. This phenomenon is due to the reorientation of domains under stress.

SiC epitaxial layers grown by chemical vapour deposition and the fabrication of Schottky barrier diodes

Wang Yue-Hu, Zhang Yi-Men, Zhang Yu-Ming, Zhang Lin, Jia Ren-Xu, Chen Da
Chin. Phys. B, 2010, 19 (3): 036803 doi: 10.1088/1674-1056/19/3/036803
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This paper presents the results of unintentionally doped 4H-SiC epilayers grown on n-type Si-faced 4H-SiC substrates with 8° off-axis toward the [11\overline 2 0] direction by low pressure horizontal hot-wall chemical vapour deposition. Growth temperature and pressure are 1580~°C and 104~Pa, respectively. Good surface morphology of the sample is observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) are used to characterize epitaxial layer thickness and the structural quality of the films respectively. The carrier concentration in the unintentional 4H-SiC homoepitaxial layer is about 6.4×1014~cm-3 obtained by c--V measurements. Schottky barrier diodes (SBDs) are fabricated on the epitaxial wafer in order to verify the quality of the wafer and to obtain information about the correlation between background impurity and electrical properties of the devices. Ni and Ti/4H-SiC Schottky barrier diodes with very good performances were obtained and their ideality factors are 1.10 and 1.05 respectively.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Nonadiabatic spin-torque and damping effects on vortex core switching triggered by a single current pulse

Jin Wei, Liu Yao-Wen
Chin. Phys. B, 2010, 19 (3): 037001 doi: 10.1088/1674-1056/19/3/037001
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Switching the orientation of a vortex core by spin-polarised pulse current introduces a promising concept for the reliable addressing of a single nanodisc element inside dense arrays. In this paper, micromagnetic simulations are employed to study the vortex core switching behaviour excited by a short in-plane Gaussian current pulse. We find that both the switching mechanism and the switching time are not sensitive to changes in the phenomenological parameters of spin-torque nonadiabaticity and Gilbert damping. The switching time, however, strongly depends on the current strength. In addition, we have theoretically predicted the parameter range of current pulses to achieve a single switching event.

Combined experimental and theoretical study on the effect of Nb content on martensitic transformation of NbRu shape memory alloys

Tan Chang-Long, Cai Wei, Tian Xiao-Hua
Chin. Phys. B, 2010, 19 (3): 037101 doi: 10.1088/1674-1056/19/3/037101
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The effect of Nb content on the martensitic transformation of NbRu high-temperature shape memory alloys is investigated by experiments and first-principles calculations. We calculate the lattice parameters, density of states, charge density, and heats of formation of Nb50+xRu50-x β phase. The results show that an increase in Nb content increases the stability of Nb50+xRu50-x β phase, leading to a significant decrease of the β to β' martensitic transformation temperature. In addition, the mechanism of the effects of Nb content on phase stability and martensitic transformation temperature is studied on the basis of electronic structure.

Electronic structure and optical properties of the red and yellow mercuric iodides

Xu Bin, Lü Jian
Chin. Phys. B, 2010, 19 (3): 037102 doi: 10.1088/1674-1056/19/3/037102
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With the help of the ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculations of the electronic structure and linear optical properties are carried out for red HgI2 and yellow HgI2. It is found that the red HgI2 has a direct gap of 1.22834 eV and the yellow HgI2 has an indirect gap of 2.11222 eV. For the red HgI2, the calculated optical spectra are qualitatively in agreement with the experimental data. Furthermore, the origins of the different peaks of ε 2 (ω ) are discussed. Our calculated anisotropic dielectric function of the red HgI2 is a nice match with the experimental results. Our calculated results are able to reproduce the overall trend of the experimental reflectivity spectra. Although no comparable experimental and theoretical results are available, clearly, the above proves the reliability of our calculations, suggesting that our calculations should be convincing for the yellow HgI2. Finally, the different optical properties are discussed.

Magnetic and electric properties of transition-metal doped wurtzite CdSe from first-principles calculations

Liu Jun, Chen Li, Liu Yu, Dong Hui-Ning, Zheng Rui-Lun
Chin. Phys. B, 2010, 19 (3): 037103 doi: 10.1088/1674-1056/19/3/037103
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The geometrical structures of Cd0.75TM0.25Se (TM = Ti, V, Cr and Mn) are optimized, and then their electric and magnetic properties are investigated by performing first-principles calculations within the generalized gradient approximation for the exchange--correlation function based on density functional theory. Cd0.75TM0.25Se (TM = Ti and V) are found to have high spin-polarization near 100% at the Fermi level. Cd0.75TM0.25Se (TM = Cr and Mn) are half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely +100%. The supercell magnetic moments of Cd0.75Cr0.25Se and Cd0.75Mn0.25Se are 4.00 and 5.00~μB, which arise mainly from Cr-ions and Mn-ions, respectively. The half-metallicity of Cd0.75Cr0.25Se is more stable than that of Cd0.75Mn0.25Se. The electronic structures of Cr-ions and Mn-ions are Cr eg2t2g2↑ and Mn eg2t2g3↑, respectively.

Electronic transport properties of an (8,0) carbon/boron nitride nanotube heterojunction

Liu Hong-Xia, Zhang He-Ming, Song Jiu-Xu, Zhang Zhi-Yong
Chin. Phys. B, 2010, 19 (3): 037104 doi: 10.1088/1674-1056/19/3/037104
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The structure of a heterojunction made up of an (8, 0) carbon nanotube and an (8, 0) boron nitride nanotube is achieved through geometry optimization implemented in the CASTEP package. Based on the optimized geometry, the model of the heterojunction is established. Its transport properties are investigated by combining the nonequilibrium Green's function with density functional theory. Results show that both the lowest unoccupied molecular orbital and the highest occupied molecular orbital mainly locate on the carbon nanotube section. In the current--voltage characteristic of the heterojunction, a rectification feature is revealed.

Dependence of charge trapping of fluorescent and phosphorescent dopants in organic light-emitting diodes on the dye species and current density

Wei Bin, Liao Ying-Jie, Liu Ji-Zhong, LuLin, Cao Jin, Wang Jun, Zhang Jian-Hua
Chin. Phys. B, 2010, 19 (3): 037105 doi: 10.1088/1674-1056/19/3/037105
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This paper utilizes multilayer organic light-emitting diodes with a thin layer of dye molecules to study the mechanism of charge trapping under different electric regimes. It demonstrates that the carrier trapping was independent of the current density in devices using fluorescent material as the emitting molecule while this process was exactly opposite when phosphorescent material was used. The triplet--triplet annihilation and dissociation of excitons into free charge carriers was considered to contribute to the decrease in phosphorescent emission under high electric fields. Moreover, the fluorescent dye molecule with a lower energy gap and ionized potential than the host emitter was observed to facilitate the carrier trapping mechanism, and it would produce photon emission.

High-performance n-channel organic thin-film transistors based on the dual effects of heterojunction and surface modification

Cao Jin, Hong Fei, Xing Fei-Fei, Gu Wen, Guo Xin-An, Zhang Hao, Wei Bin, Zhang Jian-Hua, Wang Jun
Chin. Phys. B, 2010, 19 (3): 037106 doi: 10.1088/1674-1056/19/3/037106
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This paper presents two n-channel organic heterojunction transistors with modified insulator by using hexadecafluorophthalocyaninatocopper (F16CuPc)/copper phthalocyanine (CuPc) and F16CuPc/pentacene as the active layers. Compared with a single-layer device, it reports that an improved field-effect mobility and a 6-fold higher drain current are observed. The highest mobility of 0.081~cm2/(V.s) was obtained from F16CuPc/CuPc heterojunction devices. This result is attributed to the dual effects of the organic heterojunction and interface modification. Furthermore, for two heterojunction devices, the performance of the F16CuPc/CuPc-based transistor is better than that of F16CuPc/pentacene. This is attributed to the morphologic match of two organic components.

Localization and delocalization of a one-dimensional system coupled with the environment

Zhu Hong-Jun, Xiong Shi-Jie
Chin. Phys. B, 2010, 19 (3): 037107 doi: 10.1088/1674-1056/19/3/037107
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We investigate several models of a one-dimensional chain coupling with surrounding atoms to elucidate disorder-induced delocalization in quantum wires, a peculiar behaviour against common wisdom. We show that the localization length is enhanced by disorder of side sites in the case of strong disorder, but in the case of weak disorder there is a plateau in this dependence. The above behaviour is the conjunct influence of the coupling to the surrounding atoms and the antiresonant effect. We also discuss different effects and their physical origin of different types of disorder in such systems. The numerical results show that coupling with the surrounding atoms can induce either the localization or delocalization effect depending on the values of parameters.

Accurate extraction of trap depth responsible for RTS noise in nano-MOSFETs

Ma Zhong-Fa, Zhang Peng, Wu Yong, Li Wei-Hua, Zhuang Yi-Qi, Du Lei
Chin. Phys. B, 2010, 19 (3): 037201 doi: 10.1088/1674-1056/19/3/037201
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This paper presents an accurate analytical model of the random telegraph signal (RTS) noise time-constant ratio (\bar {τ}c/ \bar {τ}e for RTS noise in nano-MOSFETs, in which the Coulomb-blockade effect on trapping and detrapping processes was taken into account. Based on this new model, the depth of the trap responsible for RTS noise in a sample n-type nano-MOSFET is extracted. The results show that large errors will be introduced to the calculated trap depth when the Coulomb-blockade effect is neglected.

Thermoelectric-transport in metal/graphene/metal hetero-structure Hot!

Hu Hao, Cai Jin-Ming, Zhang Chen-Dong, Gao Min, Pan Yi, Du Shi-Xuan, Sun Qing-Feng, Niu Qian, Xie Xin-Cheng, Gao Hong-Jun
Chin. Phys. B, 2010, 19 (3): 037202 doi: 10.1088/1674-1056/19/3/037202
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We investigate the thermoelectric-transport properties of metal/graphene/metal hetero-structure. We use a single band tight-binding model to present the two-dimensional electronic band structure of graphene. Using the Landauer--Butticker formula and taking the coupling between graphene and the two electrodes into account, we can calculate the thermoelectric potential and current versus temperature. It is found that in spite of metal electrodes, the carrier type of graphene determines the electron motion direction driven by the difference in temperature between the two electrodes, while for n type graphene, the electrons move along the thermal gradient, and for p type graphene, the electrons move against the thermal gradient.

Universal spin-dependent variable range hopping in wide-band-gap oxide ferromagnetic semiconductors

Dai You-Yong, Yan Shi-Shen, Tian Yu-Feng, Chen Yan-Xue, Liu Guo-Lei, Mei Liang-Mo
Chin. Phys. B, 2010, 19 (3): 037203 doi: 10.1088/1674-1056/19/3/037203
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This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the `hard gap' energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained.

Electronic transport for armchair graphene nanoribbons with a potential barrier

Zhou Ben-Hu, Duan Zi-Gang, Zhou Ben-Liang, Zhou Guang-Hui
Chin. Phys. B, 2010, 19 (3): 037204 doi: 10.1088/1674-1056/19/3/037204
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This paper studies the electronic transport property through a square potential barrier in armchair-edge graphene nanoribbon (AGNR). Using the Dirac equation with the continuity condition for wave functions at the interfaces between regions with and without a barrier, we calculate the mode-dependent transmission probability for both semiconducting and metallic AGNRs, respectively. It is shown that, by some numerical examples, the transmission probability is generally an oscillating function of the height and range of the barrier for both types of AGNRs. The main difference between the two types of systems is that the magnitude of oscillation for the semiconducting AGNR is larger than that for the metallic one. This fact implies that the electronic transport property for AGNRs depends sensitively on their widths and edge details due to the Dirac nature of fermions in the system.

Spin-dependent transport for a two-dimensional electron gas with magnetic barriers

Wang Hai-Yan, Duan Zi-Gang, Liao Wen-Hu, Zhou Guang-Hui
Chin. Phys. B, 2010, 19 (3): 037301 doi: 10.1088/1674-1056/19/3/037301
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The spin-dependent conductance and magnetoresistance ratio (MRR) for a semiconductor heterostructures consisting of two magnetic barriers with different height and space have been investigated by the transfer-matrix method. It is shown that the splitting of the conductance for parallel and antiparallel magnetization configurations results in tremendous spin-dependent MRR, and the maximal MRRs reach 5300\% and 3800\% for the magnetic barrier spaces W=81.3 and 243.9~nm, respectively. The obtained spin-filtering transport property of nanostructures with magnetic barriers may be useful to magnetic-barrier-based spintronics.

Device research on GaAs-based InAlAs/InGaAs metamorphic high electron mobility transistors grown by metal organic chemical vapour deposition

Xu Jing-Bo, Zhang Hai-Ying, Fu Xiao-Jun, Guo Tian-Yi, Huang Jie
Chin. Phys. B, 2010, 19 (3): 037302 doi: 10.1088/1674-1056/19/3/037302
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This paper applies a novel quad-layer resist and e-beam lithography technique to fabricate a GaAs-based InAlAs/InGaAs metamorphic high electron mobility transistor (HEMT) grown by metal organic chemical vapour deposition (MOCVD). The gate length of the metamorphic HEMT was 150~nm, the maximum current density was 330~mA/mm, the maximum transconductance was 470~mS/mm, the threshold voltage was -0.6~V, and the maximum current gain cut-off frequency and maximum oscillation frequency were 102~GHz and 450~GHz, respectively. This is the first report on tri-termination devices whose frequency value is above 400~GHz in China. The excellent frequency performances promise the possibility of metamorphic HEMTs grown by MOCVD for millimetre-wave applications, and more outstanding device performances would be obtained after optimizing the material structure, the elaborate T-gate and other device processes further.

A new structure and its analytical model for the vertical interface electric field of a partial-SOI high voltage device

Hu Sheng-Dong, Zhang Bo, Li Zhao-Ji, Luo Xiao-Rong
Chin. Phys. B, 2010, 19 (3): 037303 doi: 10.1088/1674-1056/19/3/037303
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A new partial-SOI (PSOI) high voltage device structure called a CI PSOI (charge island PSOI) is proposed for the first time in this paper. The device is characterized by a charge island layer on the interface of the top silicon layer and the dielectric buried layer in which a series of equidistant high concentration n+-regions is inserted. Inversion holes resulting from the vertical electric field are located in the spacing between two neighbouring n+-regions on the interface by the force with ionized donors in the undepleted n+-regions, and therefore effectively enhance the electric field of the dielectric buried layer (EI) and increase the breakdown voltage (BV), thereby alleviating the self-heating effect (SHE) by the silicon window under the source. An analytical model of the vertical interface electric field for the CI PSOI is presented and the analytical results are in good agreement with the 2D simulation results. The BV and EI of the CI PSOI LDMOS increase to 631~V and 584~V/μ m from 246~V and 85.8~V/μ m for the conventional PSOI with a lower SHE, respectively. The effects of the structure parameters on the device characteristics are analysed for the proposed device in detail.

Enhanced resistance switching stability of transparent ITO/TiO2/ITO sandwiches

Meng Yang, Zhang Pei-Jian, Liu Zi-Yu, Liao Zhao-Liang, Pan Xin-Yu, Liang Xue-Jin, Zhao Hong-Wu, Chen Dong-Min
Chin. Phys. B, 2010, 19 (3): 037304 doi: 10.1088/1674-1056/19/3/037304
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We report that fully transparent resistive random access memory (TRRAM) devices based on ITO/TiO2/ITO sandwich structure, which are prepared by the method of RF magnetron sputtering, exhibit excellent switching stability. In the visible region (400--800~nm in wavelength) the TRRAM device has a transmittance of more than 80%. The fabricated TRRAM device shows a bipolar resistance switching behaviour at low voltage, while the retention test and rewrite cycles of more than 300,000 indicate the enhancement of switching capability. The mechanism of resistance switching is further explained by the forming and rupture processes of the filament in the TiO2 layer with the help of more oxygen vacancies which are provided by the transparent ITO electrodes.

Lattice and magnetism in superconducting compounds Ca1-xKxFe2As2

Ma Huan-Feng, Pan Min, HuangZheng, Qiang Wei-Rong, Wang Long, Liang Fan-Yan, Zhao Yong
Chin. Phys. B, 2010, 19 (3): 037401 doi: 10.1088/1674-1056/19/3/037401
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Based on the density functional theory (DFT), using the scheme of the linearized augmented plane wave and the improved local orbital (APW + lo), the structure, the electronic bands and the magnetism of superconducting compounds Ca1-xkxFe2As2 (x=0, 0.25, 0.5, 0.75, 1) are optimized and calculated. The calculation results indicate that with K-doping the lengths of the A, b axes can decrease, and the length of the c axis, the volume, the energy of spin-down valence bands, and the DOS at the Fermi level can increase, which leads the magnetic moment of the system to increase.

Large magnetoresistance in metamagnetic CoMnSi0.88Ge0.12 alloy

Zhang Cheng-Liang, Wang Dun-Hui, Cao Qing-Qi, Xuan Hai-Cheng, Ma Sheng-Can, Du You-Wei
Chin. Phys. B, 2010, 19 (3): 037501 doi: 10.1088/1674-1056/19/3/037501
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The magneto-transport properties are investigated in metamagnetic CoMnSi0.88Ge0.12 alloy. By applying a magnetic field or increasing temperature, a metamagnetic phase transition from antiferromagnetic to ferromagnetic is observed in this alloy. Around the metamagnetic phase transition, CoMnSi0.88Ge0.12 alloy exhibits a large and negative magnetoresistance effect (~ 32%) under a magnetic field of 20~kOe (1~Oe = 79.5775~A/m), which is ascribed to the spin-dependent scattering of conduction electrons.

Giant magnetocaloric effect in the Gd5Ge2.025Si1.925In0.05 compound

E. Yüzüak, I. Dincer, Y. Elerman
Chin. Phys. B, 2010, 19 (3): 037502 doi: 10.1088/1674-1056/19/3/037502
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The magnetocaloric properties of the Gd5Ge2.025Si1.925In0.05 compound have been studied by x-ray diffraction, magnetic and heat capacity measurements. Powder x-ray diffraction measurement shows that the compound has a dominant phase of monoclinic Gd5Ge2Si2-type structure and a small quantity of Gd5(Ge,Si)3-type phase at room temperature. At about 270 K, this compound shows a first order phase transition. The isothermal magnetic entropy change (Δ SM) is calculated from the temperature and magnetic field dependences of the magnetization and the temperature dependence of MCE in terms of adiabatic temperature change (Δ Tad) is calculated from the isothermal magnetic entropy change and the temperature variation in zero-field heat-capacity data. The maximum Δ SM is -13.6~J.kg-1.k-1 and maximum Δ Tad is 13~K for the magnetic field change of 0--5~T. The Debye temperature (θD) of this compound is 149~K and the value of DOS at the Fermi level is 1.6 states/eV.atom from the low temperature zero-field heat-capacity data. A considerable isothermal magnetic entropy change and adiabatic temperature change under a field change of 0--5~T jointly make the Gd5Ge2.025Si1.925In0.05 compound an attractive candidate for a magnetic refrigerant.

Thermal relaxation of exchange bias field in an exchange coupled CoFe/IrMn bilayer

Qi Xian-Jin, WangYin-Gang, Zhou Guang-Hong, Li Zi-Quan, Guo Min
Chin. Phys. B, 2010, 19 (3): 037503 doi: 10.1088/1674-1056/19/3/037503
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This paper reports that a CoFe/IrMn bilayer was deposited by high vacuum magnetron sputtering on silicon wafer substrate; the thermal relaxation of the CoFe/IrMn bilayer is investigated by means of holding the film in a negative saturation field at various temperatures. The exchange bias decreases with increasing period of time while holding the film in a negative saturation field at a given temperature. Increasing the temperature accelerates the decrease of exchange field. The results can be explained by the quantitative model of the nucleation and growth of antiferromagnetic domains suggested by Xi H W et al. [2007 Phys. Rev. B 75 014434], and it is believed that two energy barriers exist in the investigated temperature range.

Layer resolved magnetization reversal study in SmCo5/Fe nanocomposite bilayers Hot!

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Chin. Phys. B, 2010, 19 (3): 037504 doi: 10.1088/1674-1056/19/3/037504
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A hard/soft SmCo5/ Fe nanocomposite magnetic bilayer system is fabricated on x-ray transparent 100--200~nm thin Si3N4 films by magnetron sputtering. The microscopic magnetic domain pattern and its behaviours during magnetization reversal in the hard and the soft magnetic phases are studied separately by element specific magnetic soft x-ray microscopy at a spatial resolution of better than 25~nm. We observe that the domain patterns for the soft and hard phases show coherent behaviours in varying magnetic fields. We derive local M(H) curves from the images of Fe and SmCo5 separately and find the switches for hard and soft phases to be the same.

Influence of Ga+ ion irradiation on the magnetisation reversal process and magnetoresistance in CoFe/Cu/CoFe/IrMn spin valves

Qi Xian-Jin, Wang Yin-Gang, Miao Xue-Fei, Li Zi-Quan, Huang Yi-Zhong
Chin. Phys. B, 2010, 19 (3): 037505 doi: 10.1088/1674-1056/19/3/037505
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Ga+ ion irradiation is performed on the surfaces of IrMn-based spin valves and the effects of ion irradiation on the magnetisation reversal process and magnetoresistance (MR) are investigated. The results show that the exchange bias field and magnetoresistance ratio of the spin valve decrease with the increase of ion dose. The width of the forward step between the free layer and the pinned layer becomes gradually smaller with the increase of ion dose whilst the recoil step tends to be narrower with ion dose increasing up to 6× 1013 ions/cm2 and the step disappears afterwards. Two peaks in the R--H curve are found to be asymmetric.

Ferroelectric and dielectric properties of La/Mn co-doped Bi4Ti3O12 ceramics

Wu Yun-Yi, Wang Xiao-Hui, Li Long-Tu
Chin. Phys. B, 2010, 19 (3): 037701 doi: 10.1088/1674-1056/19/3/037701
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La/Mn co-doped Bi4Ti3O12 ceramics, Bi3.25La0.75Ti3-xMnxO12 (x=0.02, 0.04, 0.06, 0.08), were prepared by the solid-state reaction method. The influence of manganese substitution for the titanium part in Bi3.25La0.75Ti3O12 on the sintering behaviour, microstructure, Raman spectra and electrical properties was investigated. The experimental results show that the phase composition of all samples with and without manganese doping, sintered at 1000~°C, consists of a single phase with a bismuth-layered structure belonging to the crystalline phase Bi4Ti3O12. There is no evidence of any impurity phase, but a small change in crystallographic orientation is observed. The Curie temperature of Bi3.25La0.75Ti3-xMnxO12 ceramics is steadily shifted to lower temperature with increasing Mn-doping content. Moreover, the remnant polarisation (Pr) of Bi3.25La0.75Ti3-xMnxO12 samples increases with Mn-doping content, and the Bi3.25La0.75Ti2.92Mn0.08O12 sample exhibits the largest Pr of 16.6~μ C/cm2.

White organic light-emitting diodes based on electroplex from polyvinyl carbazole and carbazole oligomers blends

Chen Fei-Peng, Xu Bin, Zhao Zu-Jin, Tian Wen-Jing, Lü Ping
Chin. Phys. B, 2010, 19 (3): 037801 doi: 10.1088/1674-1056/19/3/037801
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White organic light-emitting diodes with a blue emitting material fluorene-centred ethylene-liked carbazole oligomer (Cz6F) doped into polyvinyl carbazole (PVK) as the single light-emitting layer are reported. The optical properties of Cz6F, PVK, and PVK:Cz6F blends are studied. Single and double layer devices are fabricated by using PVK: Cz6F blends, and the device with the configuration of indium tin oxide (ITO)/PVK:Cz6F/ tris(8-hydroxyquinolinate)aluminium (Alq3)/LiF/Al exhibits white light emission with Commission Internationale de l'éclairage chromaticity coordinates of (0.30, 0.33) and a brightness of 402~cd/m2. The investigation reveals that the white light is composed of a blue--green emission originating from the excimer of Cz6F molecules and a red emission from an electroplex from the PVK:Cz6F blend films.

Structural properties of Bi1-xLaxFeO3 studied by micro-Raman scattering

Yang Yang, Liu Yu-Long, Zhu Ke, Zhang Li-Yan, Ma Shu-Yuan, Liu Jie, Jiang Yi-Jian
Chin. Phys. B, 2010, 19 (3): 037802 doi: 10.1088/1674-1056/19/3/037802
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This paper reports that La-doped BiFeO3 (Bi1-xLaxFeO3, x=0, 0.1, 0.2, 0.3, 0.6, 0.8 and 1.0) were studied by using micro-Raman spectroscopy and x-ray diffraction (XRD). The XRD patterns indicate that the structure of Bi1-xLaxFeO3 changes from rhombohedral BiFeO3 to orthorhombic LaFeO3. The results of Raman spectroscopy show good agreement with the XRD results. Strikingly, the phonon peak at around 610~cm-1 and the two-phonon peaks in the high frequency range exist in all compounds and enhance with increasing La substitution. The increasing intensity of the 610~cm-1 peak is attributed to the changes in the FeO6 octahedron during the rhombohedral--orthorhombic phase transition. The enhancements of the two-phonon peaks are associated with the breakdown of the cycloid spin configuration with the appearance of the orthorhombic structure. These results indicate the existence of strong spin--phonon coupling in Bi1-xLaxFeO3, which may provide useful information for understanding the effects of La content on the structural and magnetic properties of Bi1-xLaxFeO3.

Towards an optical coupler using fine-wire: a study of the photovoltaic effect of a heterojunction formed in a single fine-wire of tungsten oxides Hot!

Chen Shang-Hui, Chen Jian, Deng Shao-Zhi, Xu Ning-Sheng
Chin. Phys. B, 2010, 19 (3): 037803 doi: 10.1088/1674-1056/19/3/037803
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Nanodevices using the photovoltaic effect of a single nanowire have attracted growing interest. In this paper, we consider potential applications of the photovoltaic effect to optical signal coupling and optical power transmission, and report on the realization of a heterojunction formed between WO2 and WO3 in a fine-wire having a diameter on the micrometer scale. Using a laser beam of 514.5~nm as a signal source, the WO2--WO3 heterojunction yields a maximum output power of up to 37.4 pico watt per heterojunction. Fast responses (less than a second) of both photovoltaic voltage and current are also observed. In addition, we demonstrate that it is a simple and effective way to adapt a commercial Raman spectrometer for the combined functions of fabrication, material characterization and photovoltaic measurement of an optical signal coupler and optical power transmitter based on a fine-wire. Our results show an attractive perspective of developing nanowire or fine-wire elements for coupling optical signals into and for powering a nanoelectronic or nano-optoelectronic integrated circuit that works under the condition of preventing it from directly electrically connecting with the optical coupler.

Electroluminescence quenching mechanism in Rubrene doped host-guest system

Yan Guang, Zhao Su-Ling, Xu Zheng, Zhang Fu-Jun, Kong Chao, Zhu Hai-Na, Song Dan-Dan, Xu Xu-Rong
Chin. Phys. B, 2010, 19 (3): 037804 doi: 10.1088/1674-1056/19/3/037804
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In this paper, the electroluminescence quenching mechanism in a 5,6,11,12-tetraphenylnaphthacene (Rubrene) doped host--guest system is studied by utilizing a specially designed organic light-emitting diode with an emission layer consisting of a few periodic host/guest structures. Tris-(8-hydroxyquinoline) aluminium (Alq3) and Rubrene are used as the host and the guest, respectively. The thickness variation of the guest layer in each period enables the study of the effect of molecule aggregation, and the thickness variation of the host layer suggests a long range quenching mechanism of dipole--dipole interaction. The long range quenching mechanism is a F?rster process, and the F?rster radius of Rubrene is between 3 and 10~nm.
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