中国物理B

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

M. Syed Ali

2011 (8): 80201-080201. doi: 10.1088/1674-1056/20/8/080201

摘要 ( 2034 )

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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.

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

谢利军, 张登玉, 汪新文, 詹孝贵, 唐世清, 高峰

2011 (8): 80301-080301. doi: 10.1088/1674-1056/20/8/080301

摘要 ( 1323 )

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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.

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

周凤雪, 张理达, 祁义红, 钮月萍, 张敬涛, 龚尚庆

2011 (8): 80302-080302. doi: 10.1088/1674-1056/20/8/080302

摘要 ( 1535 )

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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.

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Sudden death of entanglement of two atoms interacting with thermal fields

罗成立, 缪龙, 郑小兰, 陈子翃, 廖长庚

2011 (8): 80303-080303. doi: 10.1088/1674-1056/20/8/080303

摘要 ( 1554 )

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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.

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

葛国勤, 覃翠, 尹淼, 黄勇华

2011 (8): 80304-080304. doi: 10.1088/1674-1056/20/8/080304

摘要 ( 1248 )

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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.

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

周彦辉

2011 (8): 80305-080305. doi: 10.1088/1674-1056/20/8/080305

摘要 ( 1398 )

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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.

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Network-topology-adaptive quantum conference protocols

张盛, 王剑, 唐朝京, 张权

2011 (8): 80306-080306. doi: 10.1088/1674-1056/20/8/080306

摘要 ( 1415 )

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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.

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

姜伟, 于扬, 韦联福

2011 (8): 80307-080307. doi: 10.1088/1674-1056/20/8/080307

摘要 ( 1331 )

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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.

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

王建军, 张爱霞, 薛具奎

2011 (8): 80308-080308. doi: 10.1088/1674-1056/20/8/080308

摘要 ( 1420 )

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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.

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

孟少英, 吴炜, 陈希浩, 张静, 傅立斌

2011 (8): 80309-080309. doi: 10.1088/1674-1056/20/8/080309

摘要 ( 1363 )

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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.

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Generalized minimum information path routing strategy on scale-free networks

周思源, 王开, 张毅锋, 裴文江, 濮存来, 李微

2011 (8): 80501-080501. doi: 10.1088/1674-1056/20/8/080501

摘要 ( 1372 )

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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.

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

李志坚, 李锦茴

2011 (8): 80502-080502. doi: 10.1088/1674-1056/20/8/080502

摘要 ( 1356 )

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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.

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

张俊峰, 裴秋雨, 张晓丽

2011 (8): 80503-080503. doi: 10.1088/1674-1056/20/8/080503

摘要 ( 1449 )

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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.

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

王兴元, 谢旖欣

2011 (8): 80504-080504. doi: 10.1088/1674-1056/20/8/080504

摘要 ( 1463 )

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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.

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

司刚全, 孙志勇, 张彦斌

2011 (8): 80505-080505. doi: 10.1088/1674-1056/20/8/080505

摘要 ( 1658 )

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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.

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

王军威, 马庆华, 曾丽

2011 (8): 80506-080506. doi: 10.1088/1674-1056/20/8/080506

摘要 ( 1459 )

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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.

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

桑金玉, 杨吉, 岳立娟

2011 (8): 80507-080507. doi: 10.1088/1674-1056/20/8/080507

摘要 ( 1336 )

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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.

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

田荣刚, 孙久勋

2011 (8): 80508-080508. doi: 10.1088/1674-1056/20/8/080508

摘要 ( 1456 )

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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.

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

吴淑贞, 程荣军, 葛红霞

2011 (8): 80509-080509. doi: 10.1088/1674-1056/20/8/080509

摘要 ( 1485 )

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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.

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

杨洋, 路迪, 傅云清, 姚科, 陈卫东, 肖君, 耿志贤, Roger Hutton, 邹亚明

2011 (8): 80701-080701. doi: 10.1088/1674-1056/20/8/080701

摘要 ( 1302 )

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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.

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

田凤, 张晓光, 翁轩, 席丽霞, 张阳安, 张文博

2011 (8): 80702-080702. doi: 10.1088/1674-1056/20/8/080702

摘要 ( 1277 )

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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

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Arbitrary direction incident Gaussian beam scattering by multispheres

李正军, 吴振森, 李焕, 李海英

2011 (8): 81101-081101. doi: 10.1088/1674-1056/20/8/081101

摘要 ( 1439 )

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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.

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

胡明, 张洁, 王巍丹, 秦玉香

2011 (8): 82101-082101. doi: 10.1088/1674-1056/20/8/082101

摘要 ( 1403 )

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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.

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

胡木宏, 王治文, 曾凡伟, 王涛, 王晶

2011 (8): 83101-083101. doi: 10.1088/1674-1056/20/8/083101

摘要 ( 1339 )

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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.

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Isolated attosecond electron wave packet diffraction

余本海, 张东玲, 汤清彬

2011 (8): 83201-083201. doi: 10.1088/1674-1056/20/8/083201

摘要 ( 1208 )

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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.

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

张晖, 张诗按, 孙真荣

2011 (8): 83202-083202. doi: 10.1088/1674-1056/20/8/083202

摘要 ( 1482 )

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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.

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

葛美华, 郑雨军

2011 (8): 83401-083401. doi: 10.1088/1674-1056/20/8/083401

摘要 ( 1463 )

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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.

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

王向红, 李士本, 章林溪, 梁好均

2011 (8): 83601-083601. doi: 10.1088/1674-1056/20/8/083601

摘要 ( 1289 )

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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.

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

吴晓飞, 邓冬梅, 郭旗

2011 (8): 84201-084201. doi: 10.1088/1674-1056/20/8/084201

摘要 ( 1308 )

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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.

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

席丽霞, 李建平, 张晓光, 田凤, 张文博

2011 (8): 84202-084202. doi: 10.1088/1674-1056/20/8/084202

摘要 ( 1360 )

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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.

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Quantum mechanical photoncount formula derived by entangled state representation

胡利云, 王资生, L. C. Kwek, 范洪义

2011 (8): 84203-084203. doi: 10.1088/1674-1056/20/8/084203

摘要 ( 1308 )

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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.

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

沙鹏飞, 辛建国, 周英, 刘正帆

2011 (8): 84204-084204. doi: 10.1088/1674-1056/20/8/084204

摘要 ( 1367 )

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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.

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

樊荣伟, 姜玉刚, 夏元钦, 陈德应

2011 (8): 84205-084205. doi: 10.1088/1674-1056/20/8/084205

摘要 ( 1309 )

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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.

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

杜洪川, 王小山, 胡碧涛

2011 (8): 84206-084206. doi: 10.1088/1674-1056/20/8/084206

摘要 ( 1370 )

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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 3ω/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.

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Quantum frequency up-conversion with a cavity

白云飞, 翟淑琴, 郜江瑞, 张俊香

2011 (8): 84207-084207. doi: 10.1088/1674-1056/20/8/084207

摘要 ( 1363 )

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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.

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Optical parametric chirped pulse amplification based on photonic crystal fibre

王河林, 杨爱军, 冷雨欣, 王乘, 徐至展, 候蓝田

2011 (8): 84208-084208. doi: 10.1088/1674-1056/20/8/084208

摘要 ( 1309 )

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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.

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

黄翀, 邓鹏, 赵爽, 陈海清

2011 (8): 84209-084209. doi: 10.1088/1674-1056/20/8/084209

摘要 ( 1201 )

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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……K_n)^-1.

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

何正耀, 马远良

2011 (8): 84301-084301. doi: 10.1088/1674-1056/20/8/084301

摘要 ( 1270 )

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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.

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Acoustic dipole radiation model for magnetoacoustic tomography with magnetic induction

李宜令, 马青玉, 章东, 夏荣民

2011 (8): 84302-084302. doi: 10.1088/1674-1056/20/8/084302

摘要 ( 1321 )

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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.

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

S. B. Khasare

2011 (8): 85101-085101. doi: 10.1088/1674-1056/20/8/085101

摘要 ( 1570 )

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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 S_mⁿ(r), r ≥ d/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.

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

罗牧华, 张秋菊

2011 (8): 85201-085201. doi: 10.1088/1674-1056/20/8/085201

摘要 ( 1401 )

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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.

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

张日晨, 刘玲, 许小亮

2011 (8): 86101-086101. doi: 10.1088/1674-1056/20/8/086101

摘要 ( 1325 )

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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.

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γ radiation caused graphene defects and increased carrier density

韩买兴, 姬濯宇, 商立伟, 陈映平, 王宏, 刘欣, 李冬梅, 刘明

2011 (8): 86102-086102. doi: 10.1088/1674-1056/20/8/086102

摘要 ( 1715 )

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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.

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Study of the lateral distribution of neodymium ions implanted in silicon

秦希峰, 李洪珍, 李双, 梁毅, 王凤翔, 付刚, 季艳菊

2011 (8): 86103-086103. doi: 10.1088/1674-1056/20/8/086103

摘要 ( 1368 )

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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.

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

E. Salmani, A. Benyoussef, H. Ez-Zahraouy, E. H. Saidi

2011 (8): 86601-086601. doi: 10.1088/1674-1056/20/8/086601

摘要 ( 1311 )

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According to first-principles density functional calculations, we have investigated the magnetic properties of Mn-doped GaN with defects, Ga_1-x-yV_GxMn_y N_1-z-tV_NzO_t with Mn substituted at Ga sites, nitrogen vacancies V_N, gallium vacancies V_G 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.

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Kinetics of catalytically activated aggregation–fragmentation process

高艳, 王海锋, 林振权, 薛新英

2011 (8): 86801-086801. doi: 10.1088/1674-1056/20/8/086801

摘要 ( 1370 )

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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 a_k(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 a_k(t) satisfies the conventional scaling form. When the catalyzed fragmentation process dominates the system, the scaling description of a_k(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, a_k(t) takes the modified scaling form and the system can eventually evolve to a steady state.

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Yield strength of attached copper film

张研, 张建民

2011 (8): 86802-086802. doi: 10.1088/1674-1056/20/8/086802

摘要 ( 1419 )

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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.

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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

邵庆益, 张娟

2011 (8): 86803-086803. doi: 10.1088/1674-1056/20/8/086803

摘要 ( 1286 )

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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.

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

吴丽娟, 胡盛东, 张波, 罗小蓉, 李肇基

2011 (8): 87101-087101. doi: 10.1088/1674-1056/20/8/087101

摘要 ( 1494 )

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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 (E_I) is enhanced by these holes effectively, leading to an improved breakdown voltage (BV). The V_B and E_I 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.

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

巩龙龑, 童培庆, 周子聪

2011 (8): 87102-087102. doi: 10.1088/1674-1056/20/8/087102

摘要 ( 1344 )

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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 β_c. When β>β_c, 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.

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Phase transition and high temperature thermoelectric properties of copper selenide Cu_2-xSe (0 ≤ x ≤ 0.25)

肖星星, 谢文杰, 唐新峰, 张清杰

2011 (8): 87201-087201. doi: 10.1088/1674-1056/20/8/087201

摘要 ( 1779 )

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With good electrical properties and an inherently complex crystal structure, Cu_2-xSe is a potential “phonon glass electron crystal” thermoelectric material that has previously not attracted much interest. In this study, Cu_2-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 Cu_2-xSe were investigated in the temperature range of 300 K—750 K. The results of X-ray diffraction at room temperature show that Cu_2-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.

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

王德江, 张涛

2011 (8): 87202-087202. doi: 10.1088/1674-1056/20/8/087202

摘要 ( 1460 )

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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.

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AlGaInP–Si glue bonded high performance light emitting diodes

陈依新, 沈光地, 郭伟玲, 高志远

2011 (8): 87203-087203. doi: 10.1088/1674-1056/20/8/087203

摘要 ( 1461 )

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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.

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Magnetic plasmon mode resonance and power transmission in a nanosandwich waveguide

付非亚, 周文君, 刘安金, 陈微, 王宇飞, 晏新宇, 郑婉华

2011 (8): 87301-087301. doi: 10.1088/1674-1056/20/8/087301

摘要 ( 1375 )

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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.

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Tuning of plasmonic behaviours in coupled metallic nanotube arrays

付少丽, 李宏建, 谢素霞, 周昕, 徐海清, 夏辉

2011 (8): 87302-087302. doi: 10.1088/1674-1056/20/8/087302

摘要 ( 1315 )

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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.

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

罗煜聘, 田力耕, 蔡春鸿, 李明宪, 李丰颖

2011 (8): 87303-087303. doi: 10.1088/1674-1056/20/8/087303

摘要 ( 1279 )

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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.

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

李惟一, 茹国平, 蒋玉龙, 阮刚

2011 (8): 87304-087304. doi: 10.1088/1674-1056/20/8/087304

摘要 ( 1469 )

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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 I—V 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.

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

王悦湖, 张义门, 张玉明, 宋庆文, 贾仁需

2011 (8): 87305-087305. doi: 10.1088/1674-1056/20/8/087305

摘要 ( 1827 )

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This paper investigates the current—voltage (I—V) 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)-(qσ)²/2(kT)² versus q/kT, which is very close to the theoretical value 146 A/cm²·,K².

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Top contact organic field effect transistors fabricated using a photolithographic process

王宏, 姬濯宇, 商立伟, 刘兴华, 彭应全, 刘明

2011 (8): 87306-087306. doi: 10.1088/1674-1056/20/8/087306

摘要 ( 1382 )

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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.

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

毕志伟, 胡振华, 毛维, 郝跃, 冯倩, 曹艳荣, 高志远, 张进成, 马晓华, 常永明, 李志明, 梅楠

2011 (8): 87307-087307. doi: 10.1088/1674-1056/20/8/087307

摘要 ( 1331 )

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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.

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

任玲, 常本康

2011 (8): 87308-087308. doi: 10.1088/1674-1056/20/8/087308

摘要 ( 1490 )

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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.

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

倪牮, 张建军, 曹宇, 王先宝, 李超, 陈新亮, 耿新华, 赵颖

2011 (8): 87309-087309. doi: 10.1088/1674-1056/20/8/087309

摘要 ( 1547 )

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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 °C. 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.

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Magnetic and transport properties of bilayered manganites La_1.2Sr_1.8Mn_2-xGa_xO₇ (x=0, 0.08)^*

郑琳, 周敏, 赵建军, 成昭华, 张向群, 邢茹, 张雪峰, 鲁毅

2011 (8): 87501-087501. doi: 10.1088/1674-1056/20/8/087501

摘要 ( 1279 )

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The magnetic and electrical properties of nonmagnetic Ga⁺³ ion substitution for Mn site are investigated in the bilayer manganite La_1.2Sr_1.8Mn₂O₇. 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.

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Effects of the Mn/Co ratio on the magnetic transition and magnetocaloric properties of Mn_1+xCo_1-xGe alloys

马胜灿, 王敦辉, 轩海成, 沈凌佳, 曹庆琪, 都有为

2011 (8): 87502-087502. doi: 10.1088/1674-1056/20/8/087502

摘要 ( 1328 )

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We have investigated the magnetic transition and magnetocaloric effects of Mn_1+xCo_1-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.

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

谷晓芳, 钱轩, 姬扬, 陈林, 赵建华

2011 (8): 87503-087503. doi: 10.1088/1674-1056/20/8/087503

摘要 ( 1322 )

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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.

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Electronic and magnetic structures of V-doped zinc blende Zn_1-xV_xN_yO_1-y and Zn_1-xV_xP_yO_1-y

N. Mamouni, M. Belaiche, A. Benyoussef, A. El Kenz, H. Ez-Zahraouy, M. Loulidi, E. H. Saidi, E. K. Hlil

2011 (8): 87504-087504. doi: 10.1088/1674-1056/20/8/087504

摘要 ( 1621 )

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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.

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Multiferroic ZnO obtained by substituting oxygen with nitrogen

徐庆宇, 温峥, 高锦龙, 吴迪, 邱腾, 唐少龙, 徐明祥

2011 (8): 87505-087505. doi: 10.1088/1674-1056/20/8/087505

摘要 ( 1647 )

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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.

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

赵建果, 张伟英, 马紫微, 谢二庆, 赵阿可, 刘照军

2011 (8): 87701-087701. doi: 10.1088/1674-1056/20/8/087701

摘要 ( 1477 )

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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.

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

刘晓东, 孟冬冬, 萩原雅人, 郑旭光

2011 (8): 87801-087801. doi: 10.1088/1674-1056/20/8/087801

摘要 ( 1356 )

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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 (C_3v, C_s 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.

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

夏长明, 周桂耀, 韩颖, 侯蓝田

2011 (8): 87802-087802. doi: 10.1088/1674-1056/20/8/087802

摘要 ( 1432 )

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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.

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

叶岩溪, 胡晓云, 闫志云, 刘恩周, 樊君, 张德恺, 苗慧, 商毅博, 杨娟

2011 (8): 87803-087803. doi: 10.1088/1674-1056/20/8/087803

摘要 ( 1334 )

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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.

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

Nastaran Rezaee, Rasoul Sadighi-Bonabi, Mona Mirheydari, Homa Ebrahimi

2011 (8): 87804-087804. doi: 10.1088/1674-1056/20/8/087804

摘要 ( 1248 )

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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.

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

李婷, 于丽, 逯志欣, 宋钢, 张恺

2011 (8): 87805-087805. doi: 10.1088/1674-1056/20/8/087805

摘要 ( 1241 )

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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.

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

张翼, 鲁欣, 周木林, 林晓宣, 郑志远, 李玉同, 张杰

2011 (8): 87901-087901. doi: 10.1088/1674-1056/20/8/087901

摘要 ( 1347 )

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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.

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Influence of cesium on the stability of a GaAs photocathode

张俊举, 常本康, 付小倩, 杜玉杰, 李飙, 邹继军

2011 (8): 87902-087902. doi: 10.1088/1674-1056/20/8/087902

摘要 ( 1603 )

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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.

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Dynamic models of pest propagation and pest control

尹铭, 林振权, 柯见洪

2011 (8): 88201-088201. doi: 10.1088/1674-1056/20/8/088201

摘要 ( 1371 )

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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 M₀^A(t) and the total mass of the pest aggregates M₁^A(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.

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

陈劲丹, 温学达, 孙国柱, 于扬

2011 (8): 88501-088501. doi: 10.1088/1674-1056/20/8/088501

摘要 ( 1255 )

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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.

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

王保争, 刘杰, 吴宏滨, 张斌, 文尚胜, 杨伟

2011 (8): 88502-088502. doi: 10.1088/1674-1056/20/8/088502

摘要 ( 1489 )

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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, C^2') (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.

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

郑亮, 马寿峰, 钟石泉

2011 (8): 88701-088701. doi: 10.1088/1674-1056/20/8/088701

摘要 ( 1600 )

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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.

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A lattice traffic model with consideration of preceding mixture traffic information

李志鹏, 刘富强, 孙剑

2011 (8): 88901-088901. doi: 10.1088/1674-1056/20/8/088901

摘要 ( 1602 )

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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.

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

田川, 孙棣华, 阳树洪

2011 (8): 88902-088902. doi: 10.1088/1674-1056/20/8/088902

摘要 ( 1491 )

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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.

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Fold optics path: an improvement for an atomic fountain

魏荣, 周子超, 史春艳, 赵剑波, 李唐, 王育竹

2011 (8): 89501-089501. doi: 10.1088/1674-1056/20/8/089501

摘要 ( 1276 )

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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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