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  • Open-circuit voltage analysis of p–i–n type amorphous silicon solar cells deposited at low temperature

    Ni Jian, Zhang Jian-Jun, Cao Yu, Wang Xian-Bao, Li Chao, Chen Xin-Liang, Geng Xin-Hua, Zhao Ying
    Chin. Phys. B 2011, 20 (8): 087309
    This paper identifies the contributions of p–a–SiC:H layers and i–a–Si:H layers to the open circuit voltage of p–i–n type a–Si:H solar cells deposited at a low temperature of 125 ℃. We find that poor quality p–a–SiC:H films under regular con...

     
  • Laser propulsion with a high specific impulse using a thin film propellant

    Zhang Yi, Lu Xin, Zhou Mu-Lin, Lin Xiao-Xuan, Zheng Zhi-Yuan, Li Yu-Tong, Zhang Jie
    Chin. Phys. B 2011, 20 (8): 087901
    A new laser propulsion scheme with a high specific impulse is proposed in this paper. An extremely thin polyimide film is used as the propellant to eliminate thermal diffusion and sputter from the target material. It is found that a high specific impulse of 1520 s can be achieved at 1011 -W/cm2 lase...

     
  • Landau–Zener–Stückelberg interference in a multi-anticrossing system

    Chen Jin-Dan, Wen Xue-Da, Sun Guo-Zhu, Yu Yang
    Chin. Phys. B 2011, 20 (8): 088501
    We propose a universal analytical method of studying the dynamics of a multi-anticrossing system subjected to driving by a single large-amplitude triangle pulse, within a time scale smaller than the dephasing time. Our approach can explain the main features of the Landau—Zener—Stück...

     
Chin. Phys. B  
  Chin. Phys. B--2011, Vol.20, No.8
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GENERAL

Robust stability analysis of Takagi–Sugeno uncertain stochastic fuzzy recurrent neural networks with mixed time-varying delays

M. Syed Ali
Chin. Phys. B, 2011, 20 (8): 080201 doi: 10.1088/1674-1056/20/8/080201
Full Text: [PDF 166 KB] (Downloads:585)
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In this paper, the global stability of Takagi—Sugeno (TS) uncertain stochastic fuzzy recurrent neural networks with discrete and distributed time-varying delays (TSUSFRNNs) is considered. A novel LMI-based stability criterion is obtained by using Lyapunov functional theory to guarantee the asymptotic stability of TSUSFRNNs. The proposed stability conditions are demonstrated through numerical examples. Furthermore, the supplementary requirement that the time derivative of time-varying delays must be smaller than one is removed. Comparison results are demonstrated to show that the proposed method is more able to guarantee the widest stability region than the other methods available in the existing literature.

Tripartite states Bell-nonlocality sudden death in a spin environment with multisite interaction

Xie Li-Jun, Zhang Deng-Yu, Wang Xin-Wen, Zhan Xiao-Gui, Tang Shi-Qing, Gao Feng
Chin. Phys. B, 2011, 20 (8): 080301 doi: 10.1088/1674-1056/20/8/080301
Full Text: [PDF 190 KB] (Downloads:578)
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This paper demonstrates that multipartite Bell-inequality violations can be fully destroyed in a finite time in three-qubit states coupled to a general XY spin-chain with a three-site interaction environment. The Mermin—Ardehali—Belinksii—Klyshko inequality is used to detect the degree of nonlocality, as measured by the extent of their violations. The effects of system-environment couplings, the size of degrees of freedom of the environment and the strength of the three-site interaction on the Bell-inequality violations are given. The results indicate that the Bell-inequality violations of the tripartite states will be completely destroyed by decoherence under certain conditions for the GHZ state. The decoherence-free subspaces of our model are identified and the entanglement of quantum states is also discussed.

Entanglement dynamics of two qubits coupled by Heisenberg XY interaction under a nonuniform magnetic field in a spin bath

Zhou Feng-Xue, Zhang Li-Da, Qi Yi-Hong, Niu Yue-Ping, Zhang Jing-Tao, Gong Shang-Qing
Chin. Phys. B, 2011, 20 (8): 080302 doi: 10.1088/1674-1056/20/8/080302
Full Text: [PDF 2036 KB] (Downloads:747)
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This paper investigates the entanglement dynamics of a Heisenberg XY model for a two-spin system in the presence of a nonuniform magnetic field. The master equations and the concurrence evolution equations for the initial α state are derived and analysed. It is shown that for the symmetric initial α state, only the nonuniform field can play a role in entanglement dynamics while the uniform field and the bath will not play such a role. For the asymmetric α state, the nonuniform field leads to the beat pattern oscillation of the concurrence evolution. The inhomogeneity of the field can enhance the entanglement by suppressing the decoherence effects of both the spin—orbit interaction and the spin bath.

Sudden death of entanglement of two atoms interacting with thermal fields

Luo Cheng-Li, Miao Long, Zheng Xiao-Lan, Chen Zi-Hong, Liao Chang-Geng
Chin. Phys. B, 2011, 20 (8): 080303 doi: 10.1088/1674-1056/20/8/080303
Full Text: [PDF 747 KB] (Downloads:678)
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We investigate the entanglement dynamics of two initially entangled atoms each interacting with a thermal field. We show that the two entangled atoms become completely disentangled in a finite time and that the lost information cannot return to the atomic system when the mean photon number of the thermal field exceeds a critical value (3.3584), even though the whole system is lossless. Then we study how the detuning between the atomic transition frequency and the field frequency and the disparity between two coupling rates would affect the evolution of the entanglement of the atomic system.

Structure formation of entanglement entropy in a system of two superconducting qubits coupled with an LC-resonator

Ge Guo-Qin, Qin Cui, Yin Miao, Huang Yong-Hua
Chin. Phys. B, 2011, 20 (8): 080304 doi: 10.1088/1674-1056/20/8/080304
Full Text: [PDF 250 KB] (Downloads:875)
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This paper investigates theoretically the evolutions of the entanglement entropy of a system of two coupled-charge-qubits interacting with an LC-resonator. It is found that when the initial states of the two qubits are prepared in a given superposition excited state, the evolution of the von Neumann entropy of the system depends significantly on the coupling strength between the two Josephson charge qubits. With the variation of the coupling strength, the evolution of the entanglement entropy of the system forms some structures, especially the periodically bistable properties, which are the first discovered for such a system to our knowledge. It is found that the relative entropy entanglement of the system is also sensitive to the variation of the coupling strength between the two charge qubits, some novel 'collective oscillations' of the relative entropy are found for the system.

Quantum logic networks for cloning a quantum state near a given state

Zhou Yan-Hui
Chin. Phys. B, 2011, 20 (8): 080305 doi: 10.1088/1674-1056/20/8/080305
Full Text: [PDF 113 KB] (Downloads:410)
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Two quantum logic networks are proposed to simulate a cloning machine that copies the states near a given one. Probabilistic cloning based on the first network is realized and the cloning probability of success based on the second network is 100%. Therefore, the second network is more motivative than the first one.

Network-topology-adaptive quantum conference protocols

Zhang Sheng, Wang Jian, Tang Chao-Jing, Zhang Quan
Chin. Phys. B, 2011, 20 (8): 080306 doi: 10.1088/1674-1056/20/8/080306
Full Text: [PDF 124 KB] (Downloads:501)
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As an important application of the quantum network communication, quantum multiparty conference has made multiparty secret communication possible. Previous quantum multiparty conference schemes based on quantum data encryption are insensitive to network topology. However, the topology of the quantum network significantly affects the communication efficiency, e.g., parallel transmission in a channel with limited bandwidth. We have proposed two distinctive protocols, which work in two basic network topologies with efficiency higher than the existing ones. We first present a protocol which works in the reticulate network using Greeberger—Horne—Zeilinger states and entanglement swapping. Another protocol, based on quantum multicasting with quantum data compression, which can improve the efficiency of the network, works in the star-like network. The security of our protocols is guaranteed by quantum key distribution and one-time-pad encryption. In general, the two protocols can be applied to any quantum network where the topology can be equivalently transformed to one of the two structures we propose in our protocols.

Quantum nondemolition measurements of a flux qubit coupled to a noisy detector

Jiang Wei, Yu Yang, Wei Lian-Fu
Chin. Phys. B, 2011, 20 (8): 080307 doi: 10.1088/1674-1056/20/8/080307
Full Text: [PDF 1365 KB] (Downloads:554)
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We theoretically study the quantum nondemolition measurements of a flux qubit coupled to a noisy superconducting quantum interference device (SQUID). The obtained analytical results indicate that the measurement probability is frequency-dependent in a short time scale and has a close relationship with the measurement-induced dephasing. Furthermore, when the detuning between the driven and bare resonator equals the coupling strength, we can obtain the maximum measurement rate that is determined by the character of the noise in the SQUID. Finally, we analysed the mixed effect caused by coupling between the non-diagonal term and the external variable. It is found that the initial information of the qubit is destroyed due to quantum tunneling between the qubit states.

Impurity-induced localization of Bose-Einstein condensates in one-dimensional optical lattices

Wang Jian-Jun, Zhang Ai-Xia, Xue Ju-Kui
Chin. Phys. B, 2011, 20 (8): 080308 doi: 10.1088/1674-1056/20/8/080308
Full Text: [PDF 194 KB] (Downloads:576)
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The impurity-induced localization of two-component Bose—Einstein condensates loaded into deep one-dimensional optical lattices is studied both analytically and numerically. It is shown that, the analytical criteria for self-trapping and moving soliton/breather of the primary-component condensate are modified significantly by an admixture of an impurity component (the second component). The realization of the self-trapped state and the moving soliton/breather states of the primary-component becomes more easy with the minor admixture of the impurity-component, even if the two components are partly overlapped.

Dynamical instability of the dark state in the conversion of Bose–Fermi mixtures into stable molecules

Meng Shao-Ying, Wu Wei, Chen Xi-Hao, Zhang Jing, Fu Li-Bin
Chin. Phys. B, 2011, 20 (8): 080309 doi: 10.1088/1674-1056/20/8/080309
Full Text: [PDF 321 KB] (Downloads:458)
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In this paper, we investigate the dynamical instability of the dark state in the conversion of Bose—Fermi mixtures into stable molecules through a stimulated Raman adiabatic passage aided by Feshbach resonance. We analytically obtain the regions where the dynamical instability appears and find that such instability in the Bose—Fermi mixture system is caused not only by bosonic interparticle interactions but also by Pauli blocking terms, which is different from the scenario of a pure bosonic system where instability is induced by nonlinear interparticle collisions. Taking a 40K—87Rb mixture as an example, we give the unstable regions numerically.

Generalized minimum information path routing strategy on scale-free networks

Zhou Si-Yuan, Wang Kai, Zhang Yi-Feng, Pei Wen-Jiang, Pu Cun-Lai, Li Wei
Chin. Phys. B, 2011, 20 (8): 080501 doi: 10.1088/1674-1056/20/8/080501
Full Text: [PDF 231 KB] (Downloads:558)
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This paper presents a new routing strategy by introducing a tunable parameter into the minimum information path routing strategy we proposed previously. It is found that network transmission capacity can be considerably enhanced by adjusting the parameter with various allocations of node capability for packet delivery. Moreover, the proposed routing strategy provides a traffic load distribution which can better match the allocation of node capability than that of traditional efficient routing strategies, leading to a network with improved transmission performance. This routing strategy, without deviating from the shortest-path routing strategy in the length of paths too much, produces improved performance indexes such as critical generating rate, average length of paths and average search information.

Controlling the collision between two solitons in the condensates by a double-barrier potential

Li Zhi-Jian, Li Jin-Hui
Chin. Phys. B, 2011, 20 (8): 080502 doi: 10.1088/1674-1056/20/8/080502
Full Text: [PDF 219 KB] (Downloads:441)
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We present an analytical solution of two solitons of Bose—Einstein condensates trapped in a double-barrier potential by using a multiple-scale method. In the linear case, we find that the stable spots of the soliton formation are at the top of the barrier potential and at the region of barrier potential absence. For weak nonlinearity, it is shown that the height of the barrier potential has an important effect on the dark soliton dynamical properties. Especially, in the case of regarding a double-barrier potential as the output source of the solitons, the collision spots between two dark solitons can be controlled by the height of the barrier potential.

A new kind of nonlinear phenomenon in coupled fractional-order chaotic systems: coexistence of anti-phase and complete synchronization

Zhang Jun-Feng, Pei Qiu-Yu, Zhang Xiao-Li
Chin. Phys. B, 2011, 20 (8): 080503 doi: 10.1088/1674-1056/20/8/080503
Full Text: [PDF 191 KB] (Downloads:605)
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In this paper, we have found a kind of interesting nonlinear phenomenon—-hybrid synchronization in linearly coupled fractional-order chaotic systems. This new synchronization mechanism, i.e., part of state variables are anti-phase synchronized and part completely synchronized, can be achieved using a single linear controller with only one drive variable. Based on the stability theory of the fractional-order system, we investigated the possible existence of this new synchronization mechanism. Moreover, a helpful theorem, serving as a determinant for the gain of the controller, is also presented. Solutions of coupled systems are obtained numerically by an improved Adams—Bashforth—Moulton algorithm. To support our theoretical analysis, simulation results are given.

Cryptanalysis of a chaos-based cryptosystem with an embedded adaptive arithmetic coder

Wang Xing-Yuan, Xie Yi-Xin
Chin. Phys. B, 2011, 20 (8): 080504 doi: 10.1088/1674-1056/20/8/080504
Full Text: [PDF 175 KB] (Downloads:541)
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In this paper, we analyse a new chaos-based cryptosystem with an embedded adaptive arithmetic coder, which was proposed by Li Heng-Jian and Zhang J S (Li H J and Zhang J S 2010 Chin. Phys. B 19 050508). Although this new method has a better compression performance than its original version, it is found that there are some problems with its security and decryption processes. In this paper, it is shown how to obtain a great deal of plain text from the cipher text without prior knowledge of the secret key. After discussing the security and decryption problems of the Li Heng-Jian et al. algorithm, we propose an improved chaos-based cryptosystem with an embedded adaptive arithmetic coder that is more secure.

A general method for synchronizing an integer-order chaotic system and a fractional-order chaotic system

Si Gang-Quan, Sun Zhi-Yong, Zhang Yan-Bin
Chin. Phys. B, 2011, 20 (8): 080505 doi: 10.1088/1674-1056/20/8/080505
Full Text: [PDF 369 KB] (Downloads:785)
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This paper investigates the synchronization between integer-order and fractional-order chaotic systems. By introducing fractional-order operators into the controllers, the addressed problem is transformed into a synchronization one among integer-order systems. A novel general method is presented in the paper with rigorous proof. Based on this method, effective controllers are designed for the synchronization between Lorenz systems with an integer order and a fractional order, and for the synchronization between an integer-order Chen system and a fractional-order Liu system. Numerical results, which agree well with the theoretical analyses, are also given to show the effectiveness of this method.

A novel mixed-synchronization phenomenon in coupled Chua's circuits via non-fragile linear control

Wang Jun-Wei, Ma Qing-Hua, Zeng Li
Chin. Phys. B, 2011, 20 (8): 080506 doi: 10.1088/1674-1056/20/8/080506
Full Text: [PDF 274 KB] (Downloads:936)
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Dynamical variables of coupled nonlinear oscillators can exhibit different synchronization patterns depending on the designed coupling scheme. In this paper, a non-fragile linear feedback control strategy with multiplicative controller gain uncertainties is proposed for realizing the mixed-synchronization of Chua's circuits connected in a drive-response configuration. In particular, in the mixed-synchronization regime, different state variables of the response system can evolve into complete synchronization, anti-synchronization and even amplitude death simultaneously with the drive variables for an appropriate choice of scaling matrix. Using Lyapunov stability theory, we derive some sufficient criteria for achieving global mixed-synchronization. It is shown that the desired non-fragile state feedback controller can be constructed by solving a set of linear matrix inequalities (LMIs). Numerical simulations are also provided to demonstrate the effectiveness of the proposed control approach.

Complete synchronization of double-delayed R"ossler systems with uncertain parameters

Sang Jin-Yu, Yang Ji, Yue Li-Juan
Chin. Phys. B, 2011, 20 (8): 080507 doi: 10.1088/1674-1056/20/8/080507
Full Text: [PDF 167 KB] (Downloads:514)
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In this paper, we investigate complete synchronization of double-delayed R"ossler systems with uncertain parameters as the master system is in chaotic synchronization. The uncertain parameters can be nonlinearly expressed in the system. The analysis and proof are given by means of the Lyapunov stability theorem. Based on theoretical analysis, some sufficient conditions of complete synchronization are proved. In order to validate the proposed scheme, numerical simulations are performed and the numerical results show that our scheme is very effective.

Five-parameter equation of state for solids correctly incorporating cohesive energy data

Tian Rong-Gang, Sun Jiu-Xun
Chin. Phys. B, 2011, 20 (8): 080508 doi: 10.1088/1674-1056/20/8/080508
Full Text: [PDF 1028 KB] (Downloads:868)
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A five-parameter equation of state (EOS) is proposed to correctly incorporate the cohesive energy data in it without physically incorrect oscillations. The proposed EOS is applied to 10 selected metals. It is shown that the calculated compression curves are in good accordance with the experimental data. The values of the bulk modulus and its derivative with respect to pressure extracted from the proposed EOS remain almost unchanged while the data range used is varied.

The time-dependent Ginzburg–Landau equation for the two-velocity difference model

Wu Shu-Zhen, Cheng Rong-Jun, Ge Hong-Xia
Chin. Phys. B, 2011, 20 (8): 080509 doi: 10.1088/1674-1056/20/8/080509
Full Text: [PDF 148 KB] (Downloads:644)
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A thermodynamic theory is formulated to describe the phase transition and critical phenomenon in traffic flow. Based on the two-velocity difference model, the time-dependent Ginzburg—Landau (TDGL) equation under certain condition is derived to describe the traffic flow near the critical point through the nonlinear analytical method. The corresponding two solutions, the uniform and the kink solutions, are given. The coexisting curve, spinodal line and critical point are obtained by the first and second derivatives of the thermodynamic potential. The modified Korteweg de Vries (mKdV) equation around the critical point is derived by using the reductive perturbation method and its kink—antikink solution is also obtained. The relation between the TDGL equation and the mKdV equation is shown. The simulation result is consistent with the nonlinear analytical result.

Electron beam density study using a portable slit imaging system at the Shanghai Electron Beam Ion Trap

Yang Yang, Lu Di, Fu Yun-Qing, Yao Ke, Chen Wei-Dong, Xiao Jun, Geng Zhi-Xian, Roger Hutton, Zou Ya-Ming
Chin. Phys. B, 2011, 20 (8): 080701 doi: 10.1088/1674-1056/20/8/080701
Full Text: [PDF 183 KB] (Downloads:586)
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In this work, a portable slit imaging system is developed to study both the electron beam diameter and the profile of the newly developed Shanghai Electron Beam Ion Trap (Shanghai EBIT). Images are detected by a charge coupled device (CCD) sensitive to both X rays and longer wavelength photons (up to visible). Large scale ray tracings were conducted for correcting the image broadening effects caused by the finite slit width and the finite width of the CCD pixels. A numerical de-convolution method was developed to analyse and reconstruct the electron beam density distribution in the EBIT. As an example of the measured beam diameter and current density, the FWHM (full width at half maximum) diameter of the electron beam at 81 keV and 120 mA is found to be 76.2 μm and the density 2.00 × 103 A·cm-2, under a magnetic field of 3 T, including all corrections.

High-speed polarization mode dispersion compensation in a 43-Gb/s RZ-DQPSK transmission system over 1200 km of standard single-mode fibre

Tian Feng, Zhang Xiao-Guang, Weng Xuan, Xi Li-Xia, Zhang Yang-An, Zhang Wen-Bo
Chin. Phys. B, 2011, 20 (8): 080702 doi: 10.1088/1674-1056/20/8/080702
Full Text: [PDF 312 KB] (Downloads:680)
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This paper reports that the designed optical polarization mode dispersion compensator shows a good performance under the real-time variation of differential group delay, state of polarization and principal state of polarization in a (40 × 43)-Gb/s dense-wavelength-multiplexing, 1200-km enhanced return-to-zero differential-quadrature-phase-shift-keying (RZ-DQPSK) system. The polarization mode dispersion tolerance of the system is improved by 26 ps using the optical polarization mode dispersion compensator. The short and long time stabilities are tested with the bit error ratio recorded.vspace1mm
NUCLEAR PHYSICS

Ab-initio density functional theory study of a WO3 NH3-sensing mechanism

Hu Ming, Zhang Jie, Wang Wei-Dan, Qin Yu-Xiang
Chin. Phys. B, 2011, 20 (8): 082101 doi: 10.1088/1674-1056/20/8/082101
Full Text: [PDF 259 KB] (Downloads:1674)
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WO3 bulk and various surfaces are studied by an ab-initio density functional theory technique. The band structures and electronic density states of WO3 bulk are investigated. The surface energies of different WO3 surfaces are compared and then the (002) surface with minimum energy is computed for its NH3 sensing mechanism which explains the results in the experiments. Three adsorption sites are considered. According to the comparisons of the energy and the charge change between before and after adsorption in the optimal adsorption site O_1c, the NH3 sensing mechanism is obtained.
CLASSICAL AREAS OF PHENOMENOLOGY

Propagation of optical vortex solitons due to the Gouy phase in strongly nonlocal nonlinear media

Wu Xiao-Fei, Deng Dong-Mei, Guo Qi
Chin. Phys. B, 2011, 20 (8): 084201 doi: 10.1088/1674-1056/20/8/084201
Full Text: [PDF 311 KB] (Downloads:639)
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In this paper, we present a study on the propagation of the symmetrical optical vortices formed by two collinear Laguerre—Gauss solitons in strongly nonlocal nonlinear media. The optical vortices, which move along the beam axis as the light propagates, result in a rotation of the beam's transverse profile. This physical reason of the rotation is the Gouy phase acquired by the component beams.

Factors affecting the performance of a multi-tone carrier source based re-circulating frequency shifter

Xi Li-Xia, Li Jian-Ping, Zhang Xiao-Guang, Tian Feng, Zhang Wen-Bo
Chin. Phys. B, 2011, 20 (8): 084202 doi: 10.1088/1674-1056/20/8/084202
Full Text: [PDF 331 KB] (Downloads:601)
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Generation of single-sideband (SSB) multi-carrier source based on a recirculating frequency shifter (RFS) is analysed theoretically and realized experimentally. The effects of affecting factors originating from the deviation from the right operation bias voltage and unbalanced amplitude, and the phase of the radio frequency (RF) drive signals on the performance of the multi-tone source are discussed in detail. Based on the theoretical analysis, high-quality 50-tone output is successfully realized. Experiments under some implementation imperfections are also carried out. The imperfect and low-quality output results are in good agreement with theoretical analysis.

Quantum mechanical photoncount formula derived by entangled state representation

Hu Li-Yun, Wang Zi-Sheng, L. C. Kwek, Fan Hong-Yi
Chin. Phys. B, 2011, 20 (8): 084203 doi: 10.1088/1674-1056/20/8/084203
Full Text: [PDF 124 KB] (Downloads:471)
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By introducing the thermo entangled state representation, we derive four new photocount distribution formulas for a given light field density operator. It is shown that these new formulas, which are convenient to calculate the photocount, can be expressed as integrations over a Laguerre-Gaussian function with a characteristic function, Wigner function, Q-function and P-function, respectively.

Output mode characteristics of an in-phase locked gain waveguide array CO2 laser

Sha Peng-Fei, Xin Jian-Guo, Zhou Ying, Liu Zheng-Fan
Chin. Phys. B, 2011, 20 (8): 084204 doi: 10.1088/1674-1056/20/8/084204
Full Text: [PDF 282 KB] (Downloads:547)
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In this paper, experimental and theoretical studies of the output mode characteristics of an in-phase locked gain waveguide array CO2 laser are reported. The experimental results of the optical oscillation mode frequency, the far-field intensity distribution and the burnt pattern of the sliced waveguide array laser are obtained. A revised mode expression of the rectangle waveguide, which is suited for this waveguide array CO2 laser, is proposed. The theoretical simulation results based on the revised mode expression are shown to be in good agreement with the experimental results.

Enhanced laser characteristics of pyrromethene 650 using modified PMMA as solid hosts

Fan Rong-Wei, Jiang Yu-Gang, Xia Yuan-Qin, Chen De-Ying
Chin. Phys. B, 2011, 20 (8): 084205 doi: 10.1088/1674-1056/20/8/084205
Full Text: [PDF 181 KB] (Downloads:896)
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Solid-state samples based on modified polymethyl methacrylate (MPMMA) with methanol doped with the dye pyrromethene 650 (PM650) are prepared. The effects of a volume percentage of methanol on the laser characteristics of the sample, including spectra properties, slope efficiency, photostability and tunable properties, are investigated. The broadband dye laser output wavelength is around 655 nm and a highest slope efficiency of 32.23% is achieved. Pumping the samples at a repetition rate of 5 Hz with a pulse energy of as high as 100 mJ (the fluence is 0.26 J/cm2), the longest lifetime (168000 shots) is obtained in the sample (MMA:methanol=18:2), and the corresponding normalized photostability reaches 109.19 GJ/mol. When the sample (MMA:methanol=18:2) is placed in a Shoshan-type oscillator, the narrow-linewidth operation is a continuous tuning range (up to 64 nm). The results indicate that the laser characteristics of solid-state dyes can be greatly enhanced by using modified PMMA with methanol serving as the solid host.

boldmath Broadband water window supercontinuum generation with a ω+3ω/2 multicycle two-colour pulse

Du Hong-Chuan, Wang Xiao-Shan, Hu Bi-Tao
Chin. Phys. B, 2011, 20 (8): 084206 doi: 10.1088/1674-1056/20/8/084206
Full Text: [PDF 423 KB] (Downloads:471)
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We propose a method to generate a high-efficiency broadband water window supercontinuum with a ω+3ω/2 multicycle two-colour pulse. Our results reveal that the /2 laser pulse can simultaneously modulate the acceleration step and the ionization step, which not only broadens the bandwidth but also enhances the yield of the generated supercontinuum. An ultra-broadband supercontinuum from 290 eV to 555 eV covering the whole water window is generated. Using this method, we expect that an isolated 62-as pulse with a minor pre-pulse can be directly obtained.

Quantum frequency up-conversion with a cavity

Bai Yun-Fei, Zhai Shu-Qin, Gao Jiang-Rui, Zhang Jun-Xiang
Chin. Phys. B, 2011, 20 (8): 084207 doi: 10.1088/1674-1056/20/8/084207
Full Text: [PDF 197 KB] (Downloads:472)
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The quantum state transfer from subharmonic frequency to harmonic frequency based on asymmetrically pumped second harmonic generation in a cavity is investigated theoretically. The performance of noise-free frequency up-conversion is evaluated by the signal transfer coefficient and the conversion efficiency, in which both the quadrature fluctuation and the average photon number are taken into consideration. It is shown that the quantum property can be preserved during frequency up-conversion via operating the cavity far below the threshold. The dependences of the transfer coefficient and the conversion efficiency on pump parameter, analysing frequency, and cavity extra loss are also discussed.

Optical parametric chirped pulse amplification based on photonic crystal fibre

Wang He-Lin, Yang Ai-Jun, Leng Yu-Xin, Wang Cheng, Xu Zhi-Zhan, Hou Lan-Tian
Chin. Phys. B, 2011, 20 (8): 084208 doi: 10.1088/1674-1056/20/8/084208
Full Text: [PDF 448 KB] (Downloads:613)
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A compact two-stage optical parametric chirped pulse amplifier based on photonic crystal fibre is demonstrated. A 1064-nm soliton pulse is obtained in a home-made photonic crystal fibre (PCF) with femtosecond pulse pumping and then amplified to 2 mJ in an Nd:YAG regenerative amplifier. After the amplified pulses pass through the LBO crystal, the 532-nm double-frequency light with an energy of 0.8 mJ and a duration of over 100 ps at 10-Hz repetition rate is generated as a pump source in the following two-stage optical parametric amplification (OPA). The 850-nm chirped signal light gain from the stretcher is 1.5 × 104 in the first-stage OPA while it is 120 in the second-stage OPA. The total signal gain of optical parametric chirped pulse amplification (OPCPA) can reach 1.8 × 106.

Attenuation characteristics of a light attenuator combined by polarizers with different extinction ratios

Huang Chong, Deng Peng, Zhao Shuang, Chen Hai-Qing
Chin. Phys. B, 2011, 20 (8): 084209 doi: 10.1088/1674-1056/20/8/084209
Full Text: [PDF 949 KB] (Downloads:554)
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This paper deals with a systematical analysis and an algorithm of attenuation characteristics of a light attenuator combined by n pieces of polarizers (n-LACP) whose extinction ratios are different from each other. The attenuation ratio expression of a two-LACP is deduced. We find that the monotonic attenuation interval depends on the first polarizer and that the attenuation range depends on the second one. For the three-LACP, a method for obtaining a monotonic attenuation interval is proposed. Moreover, the attenuation ratio expression is demonstrated. Analysis and experiment show that when the initial status of the three-LACP is at the maximum output, if the second or third polarizer rotates alone, the minimum attenuation ratios can reach K2-1 and K3-1, respectively, and if the first polarizer rotates, a minimum attenuation ratio of K2-1K3-1 can be obtained (K1, K2 and K3 represent the extinction ratios of the three polarizers in turn). Furthermore, the attenuation ratio expression of n-LACP and the relevant attenuation characteristics are proposed. The minimum attenuation ratio of an n-LACP is (K2K3……Kn)-1.

Advantage analysis of PMN–PT material for free-flooded ring transducers

He Zheng-Yao, Ma Yuan-Liang
Chin. Phys. B, 2011, 20 (8): 084301 doi: 10.1088/1674-1056/20/8/084301
Full Text: [PDF 780 KB] (Downloads:1666)
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The acoustic radiation characteristics of free-flooded ring transducers made of PZT4 and PMN—PT materials are calculated and compared. First, the theoretical formulae for free-flooded ring transducers are studied. The resonant frequencies of a transducer made of PZT4 and PMN—PT materials are calculated. Then, the transmitting voltage responses of the free-flooded ring transducers are calculated using the finite element method. Finally, the acoustic radiation characteristics of the free-flooded ring transducers are calculated using the boundary element method. The calculated results show that the resonant frequencies of the free-flooded ring transducer made of PMN—PT are greatly reduced compared with those made of PZT4 with the same size. The transmitting voltage response of the transducer made of PMN—PT is much higher than that of the transducer made of PZT4. The calculated 3-dB beamwidth of the acoustic radiated far-field directivity of the free-flooded ring transducer made of PZT4 at the resonant frequency 1900 Hz is 63.6° and that of the transducer made of PMN—PT at the resonant frequency 1000 Hz is 64.6°. The comparison results show that the free-flooded ring transducer made of PMN—PT material has many advantages over that made of PZT4. The PMN—PT is a promising material for improving the performance of free-flooded ring transducers.

Acoustic dipole radiation model for magnetoacoustic tomography with magnetic induction

Li Yi-Ling, Ma Qing-Yu, Zhang Dong, Xia Rong-Min
Chin. Phys. B, 2011, 20 (8): 084302 doi: 10.1088/1674-1056/20/8/084302
Full Text: [PDF 261 KB] (Downloads:771)
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An acoustic dipole radiation model for magnetoacoustic tomography with magnetic induction (MAT-MI) is proposed, based on the analyses of one-dimensional tissue vibration, three-dimensional acoustic dipole radiation and acoustic waveform detection with a planar piston transducer. The collected waveforms provide information about the conductivity boundaries in various vibration intensities and phases due to the acoustic dipole radiation pattern. Combined with the simplified back projection algorithm, the conductivity configuration of the measured layer in terms of shape and size can be reconstructed with obvious border stripes. The numerical simulation is performed for a two-layer cylindrical phantom model and it is also verified by the experimental results of MAT-MI for a tissue-like sample phantom. The proposed model suggests a potential application of conductivity differentiation and provides a universal basis for the further study of conductivity reconstruction for MAT-MI.
ATOMIC AND MOLECULAR PHYSICS

Energy levels of 1s2nd (n ≤ 9) states for lithium-like ions

Hu Mu-Hong, Wang Zhi-Wen, Zeng Fan-Wei, Wang Tao, Wang Jing
Chin. Phys. B, 2011, 20 (8): 083101 doi: 10.1088/1674-1056/20/8/083101
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The full-core plus correlation method with multi-configuration interaction wave functions is extended to the calculation of the non-relativistic energies of 1s2nd (n ≤ 9) states for the lithium isoelectronic sequence from Z = 11 to 20. Relativistic and mass-polarization effects on the energy are calculated as the first-order perturbation correction. The quantum-electrodynamics correction is also included. The fine structure splittings are determined from the expectation values of spin—orbit and spin—other-orbit interaction operators in the Pauli—Breit approximation. Combining the term energies of lowly excited states obtained with the quantum defects calculated by the single channel quantum defect theory, each of which is a smooth function of energy and approximated by a weakly varying function of energy, the ion potentials of highly excited states (n ≤ 6) are obtained with the semi-empirical iteration method. The results are compared with experimental data in the literature and found to be closely consistent with the regularity.

Isolated attosecond electron wave packet diffraction

Yu Ben-Hai, Zhang Dong-Ling, Tang Qing-Bin
Chin. Phys. B, 2011, 20 (8): 083201 doi: 10.1088/1674-1056/20/8/083201
Full Text: [PDF 162 KB] (Downloads:509)
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Wave-particle duality is one of the most fundamental and mysterious natures of matters. Here, we present an interesting scheme of isolated electron wave packet diffraction with a few-cycle laser pulse and an extreme ultraviolet (XUV) pulse. The diffraction fringes are clearly present in the laser dressed XUV photoelectron spectra, strongly resembling the Airy diffraction pattern of optical waves. This phenomenon suggests a great potential of attosecond diffractometry. According to this scheme we also propose a simple method to determine the XUV pulse duration from the photoelectron spectra with a rather high resolution.

Highly selective population of two excited states in nonresonant two-photon absorption

Zhang Hui, Zhang Shi-An, Sun Zhen-Rong
Chin. Phys. B, 2011, 20 (8): 083202 doi: 10.1088/1674-1056/20/8/083202
Full Text: [PDF 131 KB] (Downloads:582)
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A nonresonant two-photon absorption process can be manipulated by tailoring the ultra-short laser pulse. In this paper, we theoretically demonstrate a highly selective population of two excited states in the nonresonant two-photon absorption process by rationally designing a spectral phase distribution. Our results show that one excited state is maximally populated while the other state population is widely tunable from zero to the maximum value. We believe that the theoretical results may play an important role in the selective population of a more complex nonlinear process comprising nonresonant two-photon absorption, such as resonance-mediated (2+1)-three-photon absorption and (2+1)-resonant multiphoton ionization.

Quasi-classical trajectory study of the stereodynamics of a Ne+H2+→NeH++H reaction

Ge Mei-Hua, Zheng Yu-Jun
Chin. Phys. B, 2011, 20 (8): 083401 doi: 10.1088/1674-1056/20/8/083401
Full Text: [PDF 325 KB] (Downloads:620)
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We have carried out a quasi-classical trajectory calculation for the reaction of Ne + H2+ (v=0, j=1) → NeH+ + H on the ground state (12A') using the LZHH potential energy surface constructed by Lü et al. [Lü S J, Zhang P Y, Han K L and He G Z 2010 J. Chem. Phys. 132 014303]. Differential cross sections at many collision energies indicate that the reaction is dominated by forward-scattering. In addition, the NeH+ product shows rotationally hot and vibrationally cold distributions. Stereodynamical results indicate that the products are strongly polarized in the direction perpendicular to the scattering plane and that the products rotate mainly in planes parallel to the scattering plane.

Surface-field-induced effects on morphologies of lamella-forming diblock copolymers in nanorod arrays

Wang Xiang-Hong, Li Shi-Ben, Zhang Lin-Xi, Liang Hao-Jun
Chin. Phys. B, 2011, 20 (8): 083601 doi: 10.1088/1674-1056/20/8/083601
Full Text: [PDF 2571 KB] (Downloads:590)
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The surface-induced effect on the morphologies of lamella-forming diblock copolymers in nanorod arrays is studied by using the self-consistent field theory. In the simulation study, a rich variety of novel morphologies are observed by variations in the strength of the surface field for the diblock copolymers. Different surface-field-induced effects are examined for the diblock copolymers in the arrays with distinct preferential surfaces. It is observed that the majority-block preferential surfaces have more obvious induced effects than those of minority-block preferential surfaces. The strong surface fields exhibit different behaviours from those observed in the weak surface fields, by which the morphologies possess cylindrical symmetries. Results from this research deepen the knowledge of surface-induced effects in a confinement system, which may aid the fabrication of polymer-based nanomaterials.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Arbitrary direction incident Gaussian beam scattering by multispheres

Li Zheng-Jun, Wu Zhen-Sen, Li Huan, Li Hai-Ying
Chin. Phys. B, 2011, 20 (8): 081101 doi: 10.1088/1674-1056/20/8/081101
Full Text: [PDF 528 KB] (Downloads:1071)
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Based on spherical vector wave functions and their coordinate rotation theory, the field of a Gaussian beam in terms of the spherical vector wave functions in an arbitrary unparallel Cartesian coordinate system is expanded. The beam shape coefficient and its convergence property are discussed in detail. Scattering of an arbitrary direction Gaussian beam by multiple homogeneous isotropic spheres is investigated. The effects of beam waist width, sphere separation distance, sphere number, beam centre positioning, and incident angle for a Gaussian beam with two polarization modes incident on various shaped sphere clusters are numerically studied. Moreover, the scattering characteristics of two kinds of shaped red blood cells illuminated by an arbitrary direction incident Gaussian beam with two polarization modes are investigated. Our results are expected to provide useful insights into particle sizing and the measurement of the scattering characteristics of blood corpuscle particles with laser diagnostic techniques.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

A comprehensive approach to an equation of state for hard spheres and Lennard–Jones fluids

S. B. Khasare
Chin. Phys. B, 2011, 20 (8): 085101 doi: 10.1088/1674-1056/20/8/085101
Full Text: [PDF 117 KB] (Downloads:498)
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We present a simple method of obtaining various equations of state for hard sphere fluid in a simple unifying way. We will guess equations of state by using suitable axiomatic functional forms (n = 1, 2, 3, 4, 5) for surface tension Smn(r), rd/2 with intermolecular separation r as a variable, where m is an arbitrary real number (pole). Among the equations of state obtained in this way are Percus—Yevick, scaled particle theory and Carnahan—Starling equations of state. In addition, we have found a simple equation of state for the hard sphere fluid in the region that represents the simulation data accurately. It is found that for both hard sphere fluids as well as Lennard—Jones fluids, with m = 3/4 the derived equation of state (EOS) gives results which are in good agreement with computer simulation results. Furthermore, this equation of state gives the Percus—Yevick (pressure) EOS for the m = 0, the Carnahan—Starling EOS for m = 4/5, while for the value of m = 1 it corresponds to a scaled particle theory EOS.

Generation of a single attosecond pulse from an overdense plasma surface driven by a laser pulse with time-dependent polarization

Luo Mu-Hua, Zhang Qiu-Ju
Chin. Phys. B, 2011, 20 (8): 085201 doi: 10.1088/1674-1056/20/8/085201
Full Text: [PDF 204 KB] (Downloads:600)
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The influence of time-dependent polarization on attosecond pulse generation from an overdense plasma surface driven by laser pulse is discussed analytically and numerically. The results show that the frequency of controlling pulse controls the number and interval of the generated attosecond pulse, that the generation moment of the attosecond pulse is dominated by the phase difference between the controlling and driving pulses, and that the amplitude of the controlling pulse affects the intensity of the attosecond pulse. Using the method of time-dependent polarization, a “single” ultra-strong attosecond pulse with duration τ ≈ 8.6 as and intensity I ≈ 3.08 × 1020 W·cm-2 can be generated.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Synthesis and characteristics of multifunctional Fe3O4–SiO2–CdS magnetic-fluorescent nanocomposites

Zhang Ri-Chen, Liu Ling, Xu Xiao-Liang
Chin. Phys. B, 2011, 20 (8): 086101 doi: 10.1088/1674-1056/20/8/086101
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A luminescent superparamagnetic nanocomposite with an Fe3O4—SiO2—CdS structure is synthesised. Coated with a silica shell, Fe3O4 nanoparticles and CdS quantum dots (QDs) are successfully assembled together. Analysed from the test results of X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), hysteresis loop, and photoluminescence (PL) spectrum, these nanocomposites exhibit superparamagnetic and photoluminescent properties.

γ radiation caused graphene defects and increased carrier density

Han Mai-Xing, Ji Zhuo-Yu, Shang Li-Wei, Chen Ying-Ping, Wang Hong, Liu Xin, Li Dong-Mei, Liu Ming
Chin. Phys. B, 2011, 20 (8): 086102 doi: 10.1088/1674-1056/20/8/086102
Full Text: [PDF 218 KB] (Downloads:992)
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We report on a micro-Raman investigation of inducing defects in mono-layer, bi-layer and tri-layer graphene by γ ray radiation. It is found that the radiation exposure results in two-dimensional (2D) and G band position evolution with the layer number increasing and D and D' bands rising, suggesting the presence of defects and related crystal lattice deformation in graphene. Bi-layer graphene is more stable than mono- and tri-layer graphene, indicating that the former is a better candidate in the application of radiation environments. Also, the DC electrical property of the mono-layer graphene device shows that the defects increase the carrier density.

Study of the lateral distribution of neodymium ions implanted in silicon

Qin Xi-Feng, Li Hong-Zhen, Li Shuang, Liang Yi, Wang Feng-Xiang, Fu Gang, Ji Yan-Ju
Chin. Phys. B, 2011, 20 (8): 086103 doi: 10.1088/1674-1056/20/8/086103
Full Text: [PDF 126 KB] (Downloads:739)
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Due to the need to reduce electronic device sizes, it is very important to consider the depth and lateral distribution of ions implanted into a crystalline target. This paper reports that Nd ions with energies of 200 keV to 500 keV and dose of 5 × 1015 ions/cm2 are implanted into Si single crystals at room temperature under the angles of 0°, 30°, and 45°, respectively. The lateral spreads of 200 keV—500 keV Nd ions implanted in Si sample are measured by Rutherford backscattering technique. The results show that the measured values are in good agreement with those obtained from the prediction of SRIM2010 codes.

Magnetic properties of Mn-doped GaN with defects: ab-initio calculations

E. Salmani, A. Benyoussef, H. Ez-Zahraouy, E. H. Saidi
Chin. Phys. B, 2011, 20 (8): 086601 doi: 10.1088/1674-1056/20/8/086601
Full Text: [PDF 2190 KB] (Downloads:1119)
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According to first-principles density functional calculations, we have investigated the magnetic properties of Mn-doped GaN with defects, Ga1-x-yVGxMny N1-z-tVNzOt with Mn substituted at Ga sites, nitrogen vacancies VN, gallium vacancies VG and oxygen substituted at nitrogen sites. The magnetic interaction in Mn-doped GaN favours the ferromagnetic coupling via the double exchange mechanism. The ground state is found to be well described by a model based on a Mn3+—d5 in a high spin state coupled via a double exchange to a partially delocalized hole accommodated in the 2p states of neighbouring nitrogen ions. The effect of defects on ferromagnetic coupling is investigated. It is found that in the presence of donor defects, such as oxygen substituted at nitrogen sites, nitrogen vacancy antiferromagnetic interactions appear, while in the case of Ga vacancies, the interactions remain ferromagnetic; in the case of acceptor defects like Mg and Zn codoping, ferromagnetism is stabilized. The formation energies of these defects are computed. Furthermore, the half-metallic behaviours appear in some studied compounds.

Kinetics of catalytically activated aggregation–fragmentation process

Gao Yan, Wang Hai-Feng, Lin Zhen-Quan, Xue Xin-Ying
Chin. Phys. B, 2011, 20 (8): 086801 doi: 10.1088/1674-1056/20/8/086801
Full Text: [PDF 138 KB] (Downloads:385)
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We propose a catalytically activated aggregation—fragmentation model of three species, in which two clusters of species A can coagulate into a larger one under the catalysis of B clusters; otherwise, one cluster of species A will fragment into two smaller clusters under the catalysis of C clusters. By means of mean-field rate equations, we derive the asymptotic solutions of the cluster-mass distributions ak(t) of species A, which is found to depend strongly on the competition between the catalyzed aggregation process and the catalyzed fragmentation process. When the catalyzed aggregation process dominates the system, the cluster-mass distribution ak(t) satisfies the conventional scaling form. When the catalyzed fragmentation process dominates the system, the scaling description of ak(t) breaks down completely and the monodisperse initial condition of species A would not be changed in the long-time limit. In the marginal case when the effects of catalyzed aggregation and catalyzed fragmentation counteract each other, ak(t) takes the modified scaling form and the system can eventually evolve to a steady state.

Yield strength of attached copper film

Zhang Yan, Zhang Jian-Min
Chin. Phys. B, 2011, 20 (8): 086802 doi: 10.1088/1674-1056/20/8/086802
Full Text: [PDF 119 KB] (Downloads:661)
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Variation of stress in attached copper film with an applied strain is measured by X-ray diffraction combined with a four-point bending method. A lower slope of the initial elastic segment of the curve of X-ray measured stress versus applied strain results from incomplete elastic strain transferred from the substrate to the film due to insufficiently strong interface cohesion. So the slope of the initial elastic segment of the X-ray stress (or X-ray strain directly) of the film against the substrate applied strain may be used to measure the film-substrate cohesive strength. The yield strength of the attached copper film is much higher than that of the bulk material and varies linearly with the inverse of the film thickness.

Revision of single atom local density and capture number varying with coverage in uniform depletion approximation and its effect on coalescence and number of stable clusters

Shao Qing-Yi, Zhang Juan
Chin. Phys. B, 2011, 20 (8): 086803 doi: 10.1088/1674-1056/20/8/086803
Full Text: [PDF 921 KB] (Downloads:438)
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In vapour deposition, single atoms (adatoms) on the substrate surface are the main source of growth. The change in its density plays a decisive role in the growth of thin films and quantum size islands. In the nucleation and cluster coalescence stages of vapour deposition, the growth of stable clusters occurs on the substrate surface covered by stable clusters. Nucleation occurs in the non-covered part, while the total area covered by stable clusters on the substrate surface will gradually increase. Carefully taking into account the coverage effect, a revised single atom density rate equation is given for the famous and widely used thin-film rate equation theory, but the work of solving the revised equation has not been done. In this paper, we solve the equation and obtain the single-atom density and capture number by using a uniform depletion approximation. We determine that the single atom density is much lower than that evaluated from the single atom density rate equation in the traditional rate equation theory when the stable cluster coverage fraction is large, and it goes down very fast with an increase in the coverage fraction. The revised equation gives a higher value for the 'average' capture number than the present equation. It also increases with increasing coverage. That makes the preparation of single crystalline thin film materials difficult and the size control of quantum size islands complicated. We also discuss the effect of the revision on coalescence and the number of stable clusters in vapour deposition.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

A–188 V 7.2 Ω·mm2, P-channel high voltage device formed on an epitaxy-SIMOX substrate

Wu Li-Juan, Hu Sheng-Dong, Zhang Bo, Luo Xiao-Rong, Li Zhao-Ji
Chin. Phys. B, 2011, 20 (8): 087101 doi: 10.1088/1674-1056/20/8/087101
Full Text: [PDF 307 KB] (Downloads:650)
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This paper proposes a new n+-charge island (NCI) P-channel lateral double diffused metal—oxide semiconductor (LDMOS) based on silicon epitaxial separation by implantation oxygen (E-SIMOX) substrate. Higher concentration self-adapted holes resulting from a vertical electric field are located in the spacing of two neighbouring n+ -regions on the interface of a buried oxide layer, and therefore the electric field of a dielectric buried layer (EI) is enhanced by these holes effectively, leading to an improved breakdown voltage (BV). The VB and EI of the NCI P-channel LDMOS increase to —188 V and 502.3 V/μm from -75 V and 82.2 V/μm of the conventional P-channel LDMOS with the same thicknesses SOI layer and the buried oxide layer, respectively. The influences of structure parameters on the proposed device characteristics are investigated by simulation. Moreover, compared with the conventional device, the proposed device exhibits low special on-resistance.

Electronic properties of one-dimensional systems with long-range correlated binary potentials

Gong Long-Yan, Tong Pei-Qing, Zhou Zi-Cong
Chin. Phys. B, 2011, 20 (8): 087102 doi: 10.1088/1674-1056/20/8/087102
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We study numerically the electronic properties of one-dimensional systems with long-range correlated binary potentials. The potentials are mapped from binary sequences with a power-law power spectrum over the entire frequency range, which is characterized by correlation exponent β. We find the localization length ξ increases with β. At system sizes N→∞, there are no extended states. However, there exists a transition at a threshold βc. When β>βc, we obtain ξ>0. On the other hand, at finite system sizes, ξ ≥ N may happen at certain β, which makes the system “metallic”, and the upper-bound system size N*(β) is given.

Phase transition and high temperature thermoelectric properties of copper selenide Cu2-xSe (0 ≤ x ≤ 0.25)

Xiao Xing-Xing, Xie Wen-Jie, Tang Xin-Feng, Zhang Qing-Jie
Chin. Phys. B, 2011, 20 (8): 087201 doi: 10.1088/1674-1056/20/8/087201
Full Text: [PDF 420 KB] (Downloads:1593)
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With good electrical properties and an inherently complex crystal structure, Cu2-xSe is a potential “phonon glass electron crystal” thermoelectric material that has previously not attracted much interest. In this study, Cu2-xSe (0 ≤ x ≤ 0.25) compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition and thermoelectric properties of Cu2-xSe were investigated in the temperature range of 300 K—750 K. The results of X-ray diffraction at room temperature show that Cu2-xSe compounds possess a cubic structure with a space group of Fm3m (#225) when 0.15 < x le 0.25, whereas they adopt a composite of monoclinic and cubic phases when 0 ≤ x ≤ 0.15. The thermoelectric property measurements show that with increasing Cu content, the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu2Se compound achieves the highest ZT of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.

Noise analysis and measurement of time delay and integration charge coupled device

Wang De-Jiang, Zhang Tao
Chin. Phys. B, 2011, 20 (8): 087202 doi: 10.1088/1674-1056/20/8/087202
Full Text: [PDF 233 KB] (Downloads:1484)
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Time delay and integration (TDI) charge coupled device (CCD) noise sets a fundamental limit on image sensor performance, especially under low illumination in remote sensing applications. After introducing the complete sources of CCD noise, we study the effects of TDI operation mode on noise, and the relationship between different types of noise and number of the TDI stage. Then we propose a new technique to identify and measure sources of TDI CCD noise employing mathematical statistics theory, where theoretical analysis shows that noise estimated formulation converges well. Finally, we establish a testing platform to carry out experiments, and a standard TDI CCD is calibrated by using the proposed method. The experimental results show that the noise analysis and measurement methods presented in this paper are useful for modeling TDI CCDs.

AlGaInP–Si glue bonded high performance light emitting diodes

Chen Yi-Xin, Shen Guang-Di, Guo Wei-Ling, Gao Zhi-Yuan
Chin. Phys. B, 2011, 20 (8): 087203 doi: 10.1088/1674-1056/20/8/087203
Full Text: [PDF 726 KB] (Downloads:1201)
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We propose a new method of using conductive glue to agglutinate GaAs based AlGaInP light emitting diodes (LEDs) onto silicon substrate, and the absorbing GaAs layer is subsequently removed by grinding and selective wet etching. It was found that AlGaInP—Si glue agglutinated LEDs have larger saturation current and luminous intensity than the conventional LEDs working at the same injected current. The luminous intensity of the new device is as much as 1007.4 mcd at a saturation current of 125 mA without being encapsulated, while the conventional LEDs only have 266.2 mcd at a saturation current of 105 mA. The luminescence intensity is also found to increase by about 3.2% after working at 50 mA for 768 h. This means that the new structured LEDs have good reliability performance.

Magnetic plasmon mode resonance and power transmission in a nanosandwich waveguide

Fu Fei-Ya, Zhou Wen-Jun, Liu An-Jin, Chen Wei, Wang Yu-Fei, Yan Xin-Yu, Zheng Wan-Hua
Chin. Phys. B, 2011, 20 (8): 087301 doi: 10.1088/1674-1056/20/8/087301
Full Text: [PDF 753 KB] (Downloads:575)
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The magnetic plasmon (MP) modes in the metal—dielectric—metal nanosandwich structure are investigated numerically, and the principle of energy resonance in such a resonator is proposed. An equivalent inductance capacitance circuit analysis method is proposed and the results are in agreement with the numerical simulations. Based on the MP resonance in such a structure, a nanosandwich chain waveguide is designed. Gold and silver are chosen as the metal materials. The power transmission efficiency of the nanosandwich waveguide can be as high as 0.546 in a specific nanosandwich unit cell, even when the metal absorption loss is large, which is the perspective of the new waveguides and lasers based on MP modes.

Tuning of plasmonic behaviours in coupled metallic nanotube arrays

Fu Shao-Li, Li Hong-Jian, Xie Su-Xia, Zhou Xin, Xu Hai-Qing, Xia Hui
Chin. Phys. B, 2011, 20 (8): 087302 doi: 10.1088/1674-1056/20/8/087302
Full Text: [PDF 204 KB] (Downloads:553)
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We theoretically investigate the influence of the shape of nanoholes on plasmonic behaviours in coupled elliptical metallic nanotube arrays by the finite-difference time-domain (FDTD) method. We study the structure in two cases: one for the array aligned along the minor axis and the other for the array aligned along the major axis. It is found that the optical properties and plasmonic effects can be tuned by the effective surface charges as a result of the variation in the minor axis length. Based on the localized nature of electric field distributions, we also clearly show that the presence of localized plasmon resonant modes originates from multipolar plasmon polaritons and a large magnitude of opposing surface charges build up in the gap between adjacent nanotubes.

Dependence of the electrical properties of defective single-walled carbon nanotubes on the vacancy density

Luo Yu-Pin, Tien Li-Gan, Tsai Chuen-Horng, Lee Ming-Hsien, Li Feng-Yin
Chin. Phys. B, 2011, 20 (8): 087303 doi: 10.1088/1674-1056/20/8/087303
Full Text: [PDF 344 KB] (Downloads:593)
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The relationship between the electric properties and the vacancy density in single-walled carbon nanotubes has been investigated from first principles as well as the dependence of the influencing range of a vacancy in the nanotube on the nanotube chirality. Compared with the long-range interaction of the vacancies in a single-walled carbon nanotube with non-zero chiral angle, a much shorter interaction was found between vacancies in a zigzag single-walled carbon nanotube. In this study, we investigated the bandstructure fluctuations caused by the nanotube strain, which depends on both the vacancy density and the tube chirality. These theoretical results provide new insight to understand the relationship between the local deformation of a defective single-walled carbon nanotube and its measurable electronic properties.

Trapezoid mesa trench metal–oxide semiconductor barrier Schottky rectifier: an improved Schottky rectifier with better reverse characteristics

Li Wei-Yi, Ru Guo-Ping, Jiang Yu-Long, Ruan Gang
Chin. Phys. B, 2011, 20 (8): 087304 doi: 10.1088/1674-1056/20/8/087304
Full Text: [PDF 7700 KB] (Downloads:2128)
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An improved structure of Schottky rectifier, called a trapezoid mesa trench metal—oxide semiconductor (MOS) barrier Schottky rectifier (TM-TMBS), is proposed and studied by two-dimensional numerical simulations. Both forward and especially better reverse IV characteristics, including lower leakage current and higher breakdown voltage, are demonstrated by comparing our proposed TM-TMBS with a regular trench MOS barrier Schottky rectifier (TMBS) as well as a conventional planar Schottky barrier diode rectifier. Optimized device parameters corresponding to the requirement for high breakdown voltage are given. With optimized parameters, TM-TMBS attains a breakdown voltage of 186 V, which is 6.3% larger than that of the optimized TMBS, and a leakage current of 4.3 × 10-6 A/cm2, which is 26% smaller than that of the optimized TMBS. The relationship between optimized breakdown voltage and some device parameters is studied. Explanations and design rules are given according to this relationship.

Al/Ti/4H–SiC Schottky barrier diodes with inhomogeneous barrier heights

Wang Yue-Hu, Zhang Yi-Men, Zhang Yu-Ming, Song Qing-Wen, Jia Ren-Xu
Chin. Phys. B, 2011, 20 (8): 087305 doi: 10.1088/1674-1056/20/8/087305
Full Text: [PDF 164 KB] (Downloads:1208)
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This paper investigates the current—voltage (IV) characteristics of Al/Ti/4H—SiC Schottky barrier diodes (SBDs) in the temperature range of 77 K—500 K, which shows that Al/Ti/4H—SiC SBDs have good rectifying behaviour. An abnormal behaviour, in which the zero bias barrier height decreases while the ideality factor increases with decreasing temperature (T), has been successfully interpreted by using thermionic emission theory with Gaussian distribution of the barrier heights due to the inhomogeneous barrier height at the Al/Ti/4H—SiC interface. The effective Richardson constant A*=154 A/cm2·,K2 is determined by means of a modified Richardson plot ln(I0/T2)-()2/2(kT)2 versus q/kT, which is very close to the theoretical value 146 A/cm2·,K2.

Top contact organic field effect transistors fabricated using a photolithographic process

Wang Hong, Ji Zhuo-Yu, Shang Li-Wei, Liu Xing-Hua, Peng Ying-Quan, Liu Ming
Chin. Phys. B, 2011, 20 (8): 087306 doi: 10.1088/1674-1056/20/8/087306
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This paper proposes an effective method of fabricating top contact organic field effect transistors by using a photolithographic process. The semiconductor layer is protected by a passivation layer. Through photolithographic and etching processes, parts of the passivation layer are etched off to form source/drain electrode patterns. Combined with conventional evaporation and lift-off techniques, organic field effect transistors with a top contact are fabricated successfully, whose properties are comparable to those prepared with the shadow mask method and one order of magnitude higher than the bottom contact devices fabricated by using a photolithographic process.

Investigation of passivation effects in AlGaN/GaN metal–insulator–semiconductor high electron-mobility transistor by gate–drain conductance dispersion study

Bi Zhi-Wei, Hu Zhen-Hua, Mao Wei, Hao Yue, Feng Qian, Cao Yan-Rong, Gao Zhi-Yuan, Zhang Jin-Cheng, Ma Xiao-Hua, Chang Yong-Ming, Li Zhi-Ming, Mei Nan
Chin. Phys. B, 2011, 20 (8): 087307 doi: 10.1088/1674-1056/20/8/087307
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This paper studies the drain current collapse of AlGaN/GaN metal—insulator—semiconductor high electron-mobility transistors (MIS-HEMTs) with NbAlO dielectric by applying dual-pulsed stress to the gate and drain of the device. For NbAlO MIS-HEMT, smaller current collapse is found, especially when the gate static voltage is -8 V. Through a thorough study of the gate—drain conductance dispersion, it is found that the growth of NbAlO can reduce the trap density of the AlGaN surface. Therefore, fewer traps can be filled by gate electrons, and hence the depletion effect in the channel is suppressed effectively. It is proved that the NbAlO gate dielectric can not only decrease gate leakage current but also passivate the AlGaN surface effectively, and weaken the current collapse effect accordingly.

Modulation transfer function characteristic of uniform-doping transmission-mode GaAs/GaAlAs photocathode

Ren Ling, Chang Ben-Kang
Chin. Phys. B, 2011, 20 (8): 087308 doi: 10.1088/1674-1056/20/8/087308
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The resolution characteristic can be obtained by the modulation transfer function (MTF) of a GaAs/GaAlAs photocathode. After establishing the theoretical model of GaAs(100)-oriented atomic configuration and the formula for the ionized impurity scattering of the non-equilibrium carriers, this paper calculates the trajectories of photoelectrons in a photocathode. Thus the distribution of photoelectron spots on the emit-face is obtained, which is namely the point spread function. The MTF is obtained by Fourier transfer of the line spread function obtained from the point spread function. The MTF obtained from these calculations is shown to depend heavily on the electron diffusion length, and enhanced considerably by decreasing the electron diffusion length and increasing the doping concentration. Furthermore, the resolution is enhanced considerably by increasing the active-layer thickness, especially at high spatial frequencies. The best spatial resolution is 860 lp/mm, for the GaAs photocathode of doping concentration 1 × 1019 cm-3, electron diffusion length 3.6 μm and the active-layer thickness 2 μm, under the 633-nm light irradiated. This research will contribute to the future improvement of the cathode's resolution for preparing a high performance GaAs photocathode, and improve the resolution of a low light level image intensifier.

Open-circuit voltage analysis of p–i–n type amorphous silicon solar cells deposited at low temperature Hot!

Ni Jian, Zhang Jian-Jun, Cao Yu, Wang Xian-Bao, Li Chao, Chen Xin-Liang, Geng Xin-Hua, Zhao Ying
Chin. Phys. B, 2011, 20 (8): 087309 doi: 10.1088/1674-1056/20/8/087309
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This paper identifies the contributions of p–a–SiC:H layers and i–a–Si:H layers to the open circuit voltage of p–i–n type a–Si:H solar cells deposited at a low temperature of 125 ℃. We find that poor quality p–a–SiC:H films under regular conditions lead to a restriction of open circuit voltage although the band gap of the i-layer varies widely. A significant improvement in open circuit voltage has been obtained by using high quality p–a–SiC:H films optimized at the “low-power regime” under low silane flow rates and high hydrogen dilution conditions.

Magnetic and transport properties of bilayered manganites La1.2Sr1.8Mn2-xGaxO7 (x=0, 0.08)*

Zheng Lin, Zhou Min, Zhao Jian-Jun, Cheng Zhao-Hua, Zhang Xiang-Qun, Xing Ru, Zhang Xue-Feng, Lu Yi
Chin. Phys. B, 2011, 20 (8): 087501 doi: 10.1088/1674-1056/20/8/087501
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The magnetic and electrical properties of nonmagnetic Ga+3 ion substitution for Mn site are investigated in the bilayer manganite La1.2Sr1.8Mn2O7. When the Mn is substituted by Ga, the ferromagnetic property obviously weakens, the magnetic transition temperature decreases and a spin-glass behaviour occurs at low temperature. Meanwhile, doping causes the resistivity to dramatically increase, the metal–insulator transition temperature to disappear, and a greater magneto-resistance effect to occur at low temperature. These effects result from the fact that Ga substitution dilutes the magnetic active Mn–O–Mn network and weakens the double exchange interaction, and further suppresses ferromagnetic ordering and metallic conduction.

Effects of the Mn/Co ratio on the magnetic transition and magnetocaloric properties of Mn1+xCo1-xGe alloys

Ma Sheng-Can, Wang Dun-Hui, Xuan Hai-Cheng, Shen Ling-Jia, Cao Qing-Qi, Du You-Wei
Chin. Phys. B, 2011, 20 (8): 087502 doi: 10.1088/1674-1056/20/8/087502
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We have investigated the magnetic transition and magnetocaloric effects of Mn1+xCo1-xGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature. Further increasing the content of Mn (x=0.11) gives rise to a single second-order magnetic transition. Interestingly, large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys. The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper.

Determining the sign of g factor via time-resolved Kerr rotation spectroscopy with a rotatable magnetic field

Gu Xiao-Fang, Qian Xuan, Ji Yang, Chen Lin, Zhao Jian-Hua
Chin. Phys. B, 2011, 20 (8): 087503 doi: 10.1088/1674-1056/20/8/087503
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Time-resolved Kerr rotation spectroscopy is used to determine the sign of the g factor of carriers in a semiconductor material, with the help of a rotatable magnetic field in the plane of the sample. The spin precession signal of carriers at a fixed time delay is measured as a function of the orientation of the magnetic field with a fixed strength B. The signal has a sine-like form and its phase determines the sign of the g factor of carriers. As a natural extension of previous methods to measure the (time-resolved) photoluminescence or time-resolved Kerr rotation signal as a function of the magnetic field strength with a fixed orientation, such a method gives the correct sign of the g factor of electrons in GaAs. Furthermore, the sign of carriers in a (Ga, Mn)As magnetic semiconductor is also found to be negative.

Electronic and magnetic structures of V-doped zinc blende Zn1-xVxNyO1-y and Zn1-xVxPyO1-y

N. Mamouni, M. Belaiche, A. Benyoussef, A. El Kenz, H. Ez-Zahraouy, M. Loulidi, E. H. Saidi, E. K. Hlil
Chin. Phys. B, 2011, 20 (8): 087504 doi: 10.1088/1674-1056/20/8/087504
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Electronic and magnetic structures of zinc blende ZnO doped with V impurities are studied by first-principles calculations based on the Korringa—Kohn—Rostoker (KKR) method combined with the coherent potential approximation (CPA). Calculations for the substitution of O by N or P are performed and the magnetic moment is found to be sensitive to the N or P content. Furthermore, the system exhibits a half-metallic band structure accompanied by the broadening of vanadium bands. The mechanism responsible for ferromagnetism is also discussed and the stability of the ferromagnetic state compared with that of the paramagnetic state is systematically investigated by calculating the total energy difference between them by using supercell method.

Multiferroic ZnO obtained by substituting oxygen with nitrogen

Xu Qing-Yu, Wen Zheng, Gao Jin-Long, Wu Di, Qiu Teng, Tang Shao-Long, Xu Ming-Xiang
Chin. Phys. B, 2011, 20 (8): 087505 doi: 10.1088/1674-1056/20/8/087505
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N-doped ZnO films were prepared in nitrogen plasma by pulsed laser deposition. Clear room temperature ferromagnetism has been observed in the film prepared at a substrate temperature of 500 °C. The structural characterizations of X-ray diffraction, Raman, and X-ray photoelectron spectroscopy confirm the substitution of O by N in ZnO, which has been considered to be the origin of the observed ferromagnetism. Furthermore, ferroelectricity has been observed at room temperature by piezoelectric force microscopy, indicating the potential multiferroic applications.

Structure and photoluminescence properties of Er3+-doped TiO2–SiO2 powders prepared by sol–gel method

Zhao Jian-Guo, Zhang Wei-Ying, Ma Zi-Wei, Xie Er-Qing, Zhao A-Ke, Liu Zhao-Jun
Chin. Phys. B, 2011, 20 (8): 087701 doi: 10.1088/1674-1056/20/8/087701
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Er3+-doped TiO2—SiO2 powders are prepared by the sol—gel method, and they are characterized by high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) spectra, and Raman spectra of the samples. It is shown that the TiO2 nanocrystals are surrounded by an SiO2 glass matrix. The photoluminescence (PL) spectra are recorded at room temperature. A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm. The intensity of the emission, which is related to the defect states, is strongest at the annealing temperature of 800 °C. The PL intensity of Er3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO2 particles and Er3+ ions.

Microstructured hydroxyl environments and Raman spectroscopy in selected basic transition-metal halides

Liu Xiao-Dong, Meng Dong-Dong, Hagihala Masato, Zheng Xu-Guang
Chin. Phys. B, 2011, 20 (8): 087801 doi: 10.1088/1674-1056/20/8/087801
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Raman vibrational spectra of the selected basic (hydroxyl OH and deuteroxyl OD) transition-metal halides, geometrically frustrated material series α-, β-, γ-Cu2(OH)3Cl, α-Cu2(OH)3Br, β-Ni2(OH)3Cl, β-Co2(OH)3Cl, β-Co2(OH)3Br, γ-Cu2(OD)3Cl, and β-Co2(OD)3Cl are measured at room temperature and analysed to investigate the relationship between the microstructured OH environments and their respective Raman spectra. Among these selected samples, the last two are used to determine the OH stretching vibration region (3600 cm-1—3300 cm-1) and OH bending vibration region (1000 cm-1—600 cm-1) of OH systems in the spectra. Through the comparative analysis of the distances d(metal—O), d(O—halogen), and d(OH), the strong metal—O interaction and trimeric hydrogen bond (C3v, Cs or C1 symmetry) are found in every material, but both determine simultaneously an ultimate d(OH), and therefore an OH stretching vibration frequency. According to the approximately linear relationship between the OH stretching vibration frequency and d(OH), some unavailable d(OH) are guessed and some doubtful d(OH) are suggested to be corrected. In addition, it is demonstrated in brief that the OH bending vibration frequency is also of importance to check the more detailed crystal microstructure relating to the OH group.

Photoluminescence of an Yb3+/Al3+-codoped microstructured optical fibre

Xia Chang-Ming, Zhou Gui-Yao, Han Ying, Hou Lan-Tian
Chin. Phys. B, 2011, 20 (8): 087802 doi: 10.1088/1674-1056/20/8/087802
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An Yb3+/Al3+-codoped microstructured optical fibre is prepared based on photonic crystal fibre technology. The characteristic spectra of preforms and fibres are experimentally investigated. The results show that under a 971 nm excitation, besides the known infrared fluorescence luminescence around 1050 nm, a blue luminescence peak at 486 nm is obtained. Moreover, an unexpected emission peak at 730 nm is also observed. The photoluminescence mechanism of an Yb3+/Al3+-codoped microstructured optical fibre is discussed. The emission peak at 486 nm is attributed to the cooperative upconversion resulting from pairs of Yb3+ ions, and the emission peak around 730 nm is ascribed to the stimulated Raman scattering because of nonlinear effects of microstructured optical fibre. The Yb3+/Al3+-codoped microstructured optical fibre is promising for varieties of applications from laser printing and optical recording to cancer treatments, such as photodynamic therapy.

Preparation of NaYF4:Er3+/TiO2 composite and up-conversion luminescence properties under visible light excitation

Ye Yan-Xi, Hu Xiao-Yun, Yan Zhi-Yun, Liu En-Zhou, Fan Jun, Zhang De-Kai, Miao Hui, Shang Yi-Bo, Yang Juan
Chin. Phys. B, 2011, 20 (8): 087803 doi: 10.1088/1674-1056/20/8/087803
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The up-conversion luminescence composite NaYF4:,Er3+/TiO2 is prepared using the sol—gel method. The specimen has good crystallinity and two shapes, i.e., viereck and round, while the sizes of viereck and round particles are both micron-sized. The TiO2 has an anatase structure, while the NaYF4 has a hexagonal phase, which can be hardly obtained through the common sol—gel method. Due to the big particle size and the high crystallinity of pure NaYF4:,Er3+, the composite has a small specific surface area that is less than Degussa P25 TiO2. The NaYF4:,Er3+/TiO2 composite shows several emission peaks at 211, 237, and 251 nm under the excitation of 388 nm, at 395 nm and 411 nm under the excitation of 500 nm, and at 467, 481, 492, and 508 nm under the excitation of 570 nm.

Investigation of a mutual interaction force at different pressure amplitudes in sulfuric acid

Nastaran Rezaee, Rasoul Sadighi-Bonabi, Mona Mirheydari, Homa Ebrahimi
Chin. Phys. B, 2011, 20 (8): 087804 doi: 10.1088/1674-1056/20/8/087804
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This paper investigates the secondary Bjerknes force for two oscillating bubbles in various pressure amplitudes in a concentration of 95% sulfuric acid. The equilibrium radii of the bubbles are assumed to be smaller than 10 μm at a frequency of 37 kHz in various strong driving acoustical fields around 2.0 bars (1 bar=105 Pa). The secondary Bjerknes force is investigated in uncoupled and coupled states between the bubbles, with regard to the quasi-adiabatic model for the bubble interior. It finds that the value of the secondary Bjerknes force depends on the driven pressure of sulfuric acid and its amount would be increased by liquid pressure amplitude enhancement. The results show that the repulsion area of the interaction force would be increased by increasing the driven pressure because of nonlinear oscillation of bubbles.

Controlling optical properties of periodic gold nanoparticle arrays by changing the substrate, topologic shapes of nanoparticles, and polarization direction of incident light

Li Ting, Yu Li, Lu Zhi-Xin, Song Gang, Zhang Kai
Chin. Phys. B, 2011, 20 (8): 087805 doi: 10.1088/1674-1056/20/8/087805
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The effects of various parameters including thickness and dielectric constants of substrates, shapes of nanoparticles, and polarization direction of incident light, on the extinction spectra of periodic gold nanoparticle arrays are investigated by the full-vectorial three-dimensional (3D) finite difference time domain (FDTD) method. The calculated results show that the substrate affects the extinction spectra by coupling the fields co-excited by the substrate and gold nanoparticles. Extinction spectra are influenced by the shapes of the nanoparticles, but there are no obvious changes in extinction spectra for similar shapes. The polarization direction of incident light has a great influence on the extinction spectra. The implications of these results are discussed.

Laser propulsion with a high specific impulse using a thin film propellant Hot!

Zhang Yi, Lu Xin, Zhou Mu-Lin, Lin Xiao-Xuan, Zheng Zhi-Yuan, Li Yu-Tong, Zhang Jie
Chin. Phys. B, 2011, 20 (8): 087901 doi: 10.1088/1674-1056/20/8/087901
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A new laser propulsion scheme with a high specific impulse is proposed in this paper. An extremely thin polyimide film is used as the propellant to eliminate thermal diffusion and sputter from the target material. It is found that a high specific impulse of 1520 s can be achieved at 1011 -W/cm2 laser intensity because of economic use of the propellant. The influences of the laser intensity and the ablation area on the specific impulse are also studied in the experiment.

Influence of cesium on the stability of a GaAs photocathode

Zhang Jun-Ju, Chang Ben-Kang, Fu Xiao-Qian, Du Yu-Jie, Li Biao, Zou Ji-Jun
Chin. Phys. B, 2011, 20 (8): 087902 doi: 10.1088/1674-1056/20/8/087902
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The stability of a reflection-mode GaAs photocathode has been investigated by monitoring the photocurrent and the spectral response at room temperature. We observe the photocurrent of the cathode decaying with time in the vacuum system under the action of Cs current, and find that the Cs atoms residing in the vacuum system are helpful in prolonging the life of the cathode. We examine the evolution and analyse the influence of the barrier on the spectral response of the cathode. Our results support the double dipolar model for the explanation of the negative electron affinity effect.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Dynamic models of pest propagation and pest control

Yin Ming, Lin Zhen-Quan, Ke Jian-Hong
Chin. Phys. B, 2011, 20 (8): 088201 doi: 10.1088/1674-1056/20/8/088201
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This paper proposes a pest propagation model to investigate the evolution behaviours of pest aggregates. A pest aggregate grows by self-monomer birth, and it may fragment into two smaller ones. The kinetic evolution behaviours of pest aggregates are investigated by the rate equation approach based on the mean-field theory. For a system with a self-birth rate kernel I(k)=Ik and a fragmentation rate kernel L(i,j)=L, we find that the total number M0A(t) and the total mass of the pest aggregates M1A(t) both increase exponentially with time if L ≠ 0. Furthermore, we introduce two catalysis-driven monomer death mechanisms for the former pest propagation model to study the evolution behaviours of pest aggregates under pesticide and natural enemy controlled pest propagation. In the pesticide controlled model with a catalyzed monomer death rate kernel J1(k)=J1k, it is found that only when I<J1B0 (B0 is the concentration of catalyst aggregates) can the pests be killed off. Otherwise, the pest aggregates can survive. In the model of pest control with a natural enemy, a pest aggregate loses one of its individuals and the number of natural enemies increases by one. For this system, we find that no matter how many natural enemies there are at the beginning, pests will be eliminated by them eventually.

Landau–Zener–Stückelberg interference in a multi-anticrossing system Hot!

Chen Jin-Dan, Wen Xue-Da, Sun Guo-Zhu, Yu Yang
Chin. Phys. B, 2011, 20 (8): 088501 doi: 10.1088/1674-1056/20/8/088501
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We propose a universal analytical method of studying the dynamics of a multi-anticrossing system subjected to driving by a single large-amplitude triangle pulse, within a time scale smaller than the dephasing time. Our approach can explain the main features of the Landau—Zener—Stückelberg interference patterns recently observed in a tripartite system [Nature Communications 1 51 (2010)]. In particular, we focus on the effect of the size of the anticrossing on interference and compare the calculated interference patterns with numerical simulations. In addition, a Fourier transform of the patterns can extract the information about the energy level spectrum.

Highly efficient polymer phosphorescent light-emitting devices based on a new polyfluorene derivative as host

Wang Bao-Zheng, Liu Jie, Wu Hong-Bin, Zhang Bin, Wen Shang-Sheng, Yang Wei
Chin. Phys. B, 2011, 20 (8): 088502 doi: 10.1088/1674-1056/20/8/088502
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Several highly efficient iridium-complex polymer light-emitting devices (PLEDs) are fabricated, with a newly synthesized blue conjugated polymer, poly[(9,9-bis(4-(2-ethylhexyloxy)phenyl)-fluorene)-co-(3,7-dibenziothiene-S,S-dioxide15)] (PPF-3,7SO15), chosen as host. High luminous efficiencies of 7.4 cd·A-1 and 27.4 cd·A-1 are achieved in red and green PLEDs, respectively, by optimizing the doping concentrations of red phosphorescent dye iridium bis(1-phenylisoquinoline) (acetylacetonate) (Ir(piq)) and green phosphorescent dye iridium tris(2-(4-tolyl)pyridinato-N, C2') (Ir(mppy)3). Furthermore, highly efficient white PLEDs (WPLEDs) with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.35, 0.38) are successfully produced by carefully controlling the doping concentration of the iridium complex. The obtained WPLEDs show maximal efficiencies of 14.4 cd·A-1 and 10.1 lm·W-1, which are comparable to those of incandescent bulbs. Moreover, the electroluminescent spectrum of the white device with an initial luminance of about 1000 cd·m-2 is stable, subject to constant applied current stress, indicating that good device stability can be obtained in this system.

Influence of lane change on stability analysis for two-lane traffic flow

Zheng Liang, Ma Shou-Feng, Zhong Shi-Quan
Chin. Phys. B, 2011, 20 (8): 088701 doi: 10.1088/1674-1056/20/8/088701
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This paper deals mainly with the influence of lane changing behaviours on the stability of two-lane traffic flow under a periodic boundary condition. Following the description of an optimal velocity model for two vehicle groups and the derivation of their stability conditions, the feedback signals, which involve information about vehicles from both lanes acting on the two-lane traffic system, are introduced into the optimal velocity model. The control signals play a role in alleviating the traffic jam only if the traffic state is in congestion, and their role will vanish if the traffic state is in the steady state. The numerical simulations show that lane changing behaviours can break the steady state of two-lane traffic flow and aggravate the traffic disturbance, but the control method would successfully suppress the traffic jam eventually, which implies that the conclusions obtained here have certain theoretical and practical significance.

A lattice traffic model with consideration of preceding mixture traffic information

Li Zhi-Peng, Liu Fu-Qiang, Sun Jian
Chin. Phys. B, 2011, 20 (8): 088901 doi: 10.1088/1674-1056/20/8/088901
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In this paper, the lattice model is presented, incorporating not only site information about preceding cars but also relative currents in front. We derive the stability condition of the extended model by considering a small perturbation around the homogeneous flow solution and find that the improvement in the stability of traffic flow is obtained by taking into account preceding mixture traffic information. Direct simulations also confirm that the traffic jam can be suppressed efficiently by considering the relative currents ahead, just like incorporating site information in front. Moreover, from the nonlinear analysis of the extended models, the preceding mixture traffic information dependence of the propagating kink solutions for traffic jams is obtained by deriving the modified KdV equation near the critical point using the reductive perturbation method.

A new lattice hydrodynamic traffic flow model with a consideration of multi-anticipation effect

Tian Chuan, Sun Di-Hua, Yang Shu-Hong
Chin. Phys. B, 2011, 20 (8): 088902 doi: 10.1088/1674-1056/20/8/088902
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We present a new multi-anticipation lattice hydrodynamic model based on the traffic anticipation effect in the real world. Applying the linear stability theory, we obtain the linear stability condition of the model. Through nonlinear analysis, we derive the modified Korteweg-de Vries equation to describe the propagating behaviour of a traffic density wave near the critical point. The good agreement between the simulation results and the analytical results shows that the stability of traffic flow can be enhanced when the multi-anticipation effect is considered.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Fold optics path: an improvement for an atomic fountain

Wei Rong, Zhou Zi-Chao, Shi Chun-Yan, Zhao Jian-Bo, Li Tang, Wang Yu-Zhu
Chin. Phys. B, 2011, 20 (8): 089501 doi: 10.1088/1674-1056/20/8/089501
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A fold optical path is utilized to capture and launch atoms in the atomic fountain. This improved technique reduces the laser power needed by 60 percent, facilitates suppression of the laser power fluctuations, and leads to a more simple and stable system.
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