Chin. Phys. B

Bandgap characteristics of 2D plasma photonic crystal with oblique incidence：TM case

Xie Ying-Tao (谢应涛), Yang Li-Xia (杨利霞)

Chin. Phys. B, 2011, 20 (6): 060201. DOI: 10.1088/1674-1056/20/6/060201

Abstract ( 1768 )

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A novel periodic boundary condition (PBC), that is the constant transverse wavenumber (CTW) method, is introduced to solve the time delay in the transverse plane with oblique incidence. Based on the novel PBC, the FDTD/PBC algorithm is proposed to study periodic structure consisting of plasma and vacuum. Then the reflection coefficient for the plasma slab from the FDTD/PBC algorithm is compared with the analytic results to show the validity of our technique. Finally, the reflection coefficients for the plasma photonic crystals are calculated using the FDTD/PBC algorithm to study the variation of bandgap characteristics with the incident angle and the plasma parameters. Thus it has provided the guiding sense for the actual manufacturing plasma photonic crystal.

The relation between Hardy's non-locality and violation of Bell inequality

Xiang Yang (向阳)

Chin. Phys. B, 2011, 20 (6): 060301. DOI: 10.1088/1674-1056/20/6/060301

Abstract ( 1289 )

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We give an analytic quantitative relation between Hardy's non-locality and Bell operator. We find that Hardy's non-locality is a sufficient condition for the violation of Bell inequality, the upper bound of Hardy's non-locality allowed by information causality just corresponds to Tsirelson bound of Bell inequality and the upper bound of Hardy's non-locality allowed by the principle of no-signaling just corresponds to the algebraic maximum of Bell operator. Then we study the Cabello's argument of Hardy's non-locality (a generalization of Hardy's argument) and find a similar relation between it and violation of Bell inequality. Finally, we give a simple derivation of the bound of Hardy's non-locality under the constraint of information causality with the aid of the above derived relation between Hardy's non-locality and Bell operator.

Atomic N00N state generation in distant cavities by virtual excitations

Yang Rong-Can (杨榕灿), Li Gang (李刚), Li Jie (李杰), Zhang Tian-Cai (张天才)

Chin. Phys. B, 2011, 20 (6): 060302. DOI: 10.1088/1674-1056/20/6/060302

Abstract ( 1656 )

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A general scheme of generating N00N states of virtually-excited 2N atoms is proposed. The two cavities are fibre-connected with N atoms in each cavity. Although we focus on the case of N=2, the system can be extended to a few atoms with N>2. It is found that all 2N atoms can be entangled in the form of N00N states if the atoms in the first cavity are initially in the excited states and atoms in the second cavity are all in the ground states. The feasibility of the scheme is carefully discussed, it shows that the N00N state with a few atoms can be generated with good fidelity and the scheme is feasible in experiment.

A new theorem relating quantum tomogram to the Fresnel operator

Xie Chuan-Mei (谢传梅), Fan Hong-Yi (范洪义)

Chin. Phys. B, 2011, 20 (6): 060303. DOI: 10.1088/1674-1056/20/6/060303

Abstract ( 1232 )

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According to Fan-Hu's formalism (Fan Hong-Yi and Hu Li-Yun 2009 Opt. Commun. 282 3734) that the tomogram of quantum states can be considered as the module-square of the state wave function in the intermediate coordinate-momentum representation which is just the eigenvector of the Fresnel quadrature phase, we derive a new theorem for calculating quantum tomogram of density operator, i.e., the tomogram of a density operator ρ is equal to the marginal integration of the classical Weyl correspondence function of F⁺ρF, where F is the Fresnel operator. Applications of this theorem to evaluating the tomogram of optical chaotic field and squeezed chaotic optical field are presented.

Non-Markovian dynamics of a qubit in a reservoir: different solutions of non-Markovian master equation

Ding Bang-Fu (丁邦福), Wang Xiao-Yun (王小云), Tang Yan-Fang (唐艳芳), Mi Xian-Wu (米贤武), Zhao He-Ping (赵鹤平)

Chin. Phys. B, 2011, 20 (6): 060304. DOI: 10.1088/1674-1056/20/6/060304

Abstract ( 1455 )

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We present a non-Markovian master equation for a qubit interacting with a general reservoir, which is derived according to the Nakajima-Zwanzig and the time convolutionless projection operator technique. The non-Markovian solutions and Markovian solution of dynamical decay of a qubit are compared. The results indicate the validity of non-Markovian approach in different coupling regimes and also show that the Markovian master equation may not precisely describe the dynamics of an open quantum system in some situation. The non-Markovian solutions may be effective for many qubits independently interacting with the heated reservoirs.

Generation of squeezed TEMM₀₁ modes with periodically poled KTiOPO₄ crystal

Yang Rong-Guo(杨荣国), Sun Heng-Xin(孙恒信), Zhang Jun-Xiang(张俊香), and Gao Jiang-Rui(郜江瑞)

Chin. Phys. B, 2011, 20 (6): 060305. DOI: 10.1088/1674-1056/20/6/060305

Abstract ( 1480 )

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Spatial quantum optics and quantum information based on the high order transverse mode are of importance for the super-resolution measurement beyond the quantum noise level. We demonstrated experimentally the transverse plane TEM₀₁ Hermite-Gauss quantum squeezing. The squeezed TEM₀₁ mode is generated in a degenerate optical parametric amplifier with the nonlinear crystal of periodically poled KTiOPO₄. The level of 2.2-dB squeezing is measured using a spatial balance homodyne detection system.

Implementation of quantum controlled phase gate and preparation of multiparticle entanglement in cavity QED

Wu Xi(吴熙), Chen Zhi-Hua(陈志华), Zhang Yong(张勇), Chen Yue-Hua(陈悦华), Ye Ming-Yong(叶明勇), and Lin Xiu-Min(林秀敏)

Chin. Phys. B, 2011, 20 (6): 060306. DOI: 10.1088/1674-1056/20/6/060306

Abstract ( 1446 )

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Schemes are presented for realizing quantum controlled phase gate and preparing an N-qubit W-like state, which are based on the large-detuned interaction among three-state atoms, dual-mode cavity and a classical pulse. In particular, a class of W states that can be used for perfect teleportation and superdense coding is generated by only one step. Compared with the previous schemes, cavity decay is largely suppressed because the cavity is only virtually excited and always in the vacuum state and the atomic spontaneous emission is strongly restrained due to a large atom-field detuning.

Composite-fermionization of the mixture composed of Tonks gas and Fermi gas

Hao Ya-Jiang(郝亚江)

Chin. Phys. B, 2011, 20 (6): 060307. DOI: 10.1088/1674-1056/20/6/060307

Abstract ( 1304 )

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This paper investigates the ground-state properties of the mixture composed of the strongly interacting Tonks-Girardeau gas and spin polarized Fermi gas confined in one-dimensional harmonic traps, where the interaction between the Bose atoms and Fermi atoms is tunable. With a generalized Bose-Fermi transformation the mixture is mapped into a two-component Fermi gas. The homogeneous Fermi gas is exactly solvable by the Bethe-ansatz method and the ground state energy density can be obtained. Combining the ground-state energy function of the homogeneous system with local density approximation it obtains the ground-state density distributions of inhomogeneous mixture. It is shown that with the increase in boson-fermion interaction, the system exhibits composite-fermionization crossover.

Tunneling of Boseben–Einstein condensate and interference effect in a harmonic trap with a Gaussian energy barrier

Hua Wei (花巍), Li Bin (李彬), Liu Xue-Shen (刘学深)

Chin. Phys. B, 2011, 20 (6): 060308. DOI: 10.1088/1674-1056/20/6/060308

Abstract ( 1359 )

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The tunneling effect of Bose-Einstein condensate (BEC) in a harmonic trap with a Gaussian energy barrier is studied in this paper. The initial condensate evolves into two separate moving condensates after the tunneling time under certain conditions. The interference pattern between the two moving condensates is given as a comparison and as a further demonstration of the existence of the global phase.

Spectroscopic investigations on NO$^{ + }$($X^{1}\varSigma ^{ + }$, $a^{3}\varSigma ^{ + }$, $A^{1}\varPi$) ion using multi-reference configuration interaction method and correlation-consistent sextuple basis set augmented with diffuse functions #br#

Zhang Jin-Ping (张金平), Cheng Xin-Lu (程新路), Zhang Hong (张红), Yang Xiang-Dong (杨向东)

Chin. Phys. B, 2011, 20 (6): 060401. DOI: 10.1088/1674-1056/20/6/060401

Abstract ( 1395 )

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Three low-lying electronic states ($X^{1}\varSigma ^{ + }$, $a^{3}\varSigma ^{ + }$, and $A^{1}\varPi$) of NO$^{ + }$ ion are studied using the complete active space self-consistent-field (CASSCF) method followed by highly accurate valence internally contracted multi-reference configuration interaction (MRCI) approach in combination of the correlation-consistent sextuple basis set augmented with diffuse functions, aug-cc-pV6Z. The potential energy curves (PECs) of the NO$^{ + }$($X^{1}\varSigma ^{ + }$, $a^{3}\varSigma ^{ + }$, $A^{1}\varPi$) are calculated. Based on the PECs, the spectroscopic parameters $R_{\rm e}$, $D_{\rm e}$, $\omega _{\rm e}$, $\omega _{\rm e}\chi _{\rm e}$, $\alpha _{\rm e}$, $B_{\rm e}$, and $D_{0}$ are reproduced, which are in excellent agreement with the available measurements. By numerically solving the radial Schr\"{o}dinger equation of nuclear motion using the Numerov method, the first 20 vibrational levels, inertial rotation and centrifugal distortion constants of NO$^{ + }$($X^{1}\varSigma ^{ + }$, $a^{3}\varSigma ^{ + }$, $A^{1}\varPi$) ion are derived when the rotational quantum number $J$ is equal to zero ($J = 0$) for the first time, which accord well with the available measurements. Finally, the analytical potential energy functions of these states are fitted, which are used to accurately derive the first 20 classical turning points when $J = 0$. These results are compared in detail with those of previous investigations reported in the literature.

Impact of neutron star crust on gravitational waves from the axial w-modes

Wen De-Hua(文德华), Fu Hong-Yang(付宏洋), and Chen Wei(陈伟)

Chin. Phys. B, 2011, 20 (6): 060402. DOI: 10.1088/1674-1056/20/6/060402

Abstract ( 1243 )

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The imprints of the neutron star crust on the gravitational waves emitted from the axial w-modes are investigated by adopting two typical equations of state (EOSs) of the crust matter and two representative EOSs of the core matter. It is shown that there is a significant effect of the crust EOSs on the gravitational waves from the axial w-mode oscillation for a stiff core EOS.

Resonance response of a single-degree-of-freedom nonlinear vibro-impact system to a narrow-band random parametric excitation

Su Min-Bang (苏敏邦), Rong Hai-Wu (戎海武)

Chin. Phys. B, 2011, 20 (6): 060501. DOI: 10.1088/1674-1056/20/6/060501

Abstract ( 1270 )

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The resonant response of a single-degree-of-freedom nonlinear vibro-impact oscillator with a one-sided barrier to a narrow-band random parametric excitation is investigated. The narrow-band random excitation used here is a bounded random noise. The analysis is based on a special Zhuravlev transformation, which reduces the system to one without impacts, thereby permitting the applications of random averaging over "fast" variables. The averaged equations are solved exactly and an algebraic equation of the amplitude of the response is obtained for the case without random disorder. The methods of linearization and moment are used to obtain the formula of the mean-square amplitude approximately for the case with random disorder. The effects of damping, detuning, restitution factor, nonlinear intensity, frequency and magnitude of random excitations are analysed. The theoretical analyses are verified by numerical results. Theoretical analyses and numerical simulations show that the peak response amplitudes will reduce at large damping or large nonlinear intensity and will increase with large amplitude or frequency of the random excitations. The phenomenon of stochastic jump is observed, that is, the steady-state response of the system will jump from a trivial solution to a large non-trivial one when the amplitude of the random excitation exceeds some threshold value, or will jump from a large non-trivial solution to a trivial one when the intensity of the random disorder of the random excitation exceeds some threshold value.

Parameter estimation for chaotic systems with and without noise using differential evolution-based method

Li Nian-Qiang (李念强), Pan Wei (潘炜), Yan Lian-Shan (闫连山), Luo Bin (罗斌), Xu Ming-Feng (徐明峰), Jiang Ning (江宁)

Chin. Phys. B, 2011, 20 (6): 060502. DOI: 10.1088/1674-1056/20/6/060502

Abstract ( 1477 )

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We present an approach in which the differential evolution (DE) algorithm is used to address identification problems in chaotic systems with or without delay terms. Unlike existing considerations, the scheme is able to simultaneously extract (i) the commonly considered parameters, (ii) the delay, and (iii) the initial state. The main goal is to present and verify the robustness against the common white Guassian noise of the DE-based method. Results of the time-delay logistic system, the Mackey-Glass system and the Lorenz system are also presented.

Cluster synchronization in a network of non-identical dynamic systems

Wu Jian-She(吴建设), Jiao Li-Cheng(焦李成), and Chen Guan-Rong(陈关荣)

Chin. Phys. B, 2011, 20 (6): 060503. DOI: 10.1088/1674-1056/20/6/060503

Abstract ( 1273 )

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Cluster synchronization in a network of non-identical dynamic systems is studied in this paper, using two-cluster synchronization for detailed analysis and discussion. The results show that the common intercluster coupling condition is not always needed for the diffusively coupled network. Several sufficient conditions are obtained by using the Schur unitary triangularization theorem, which extends previous results. Some numerical examples are presented for illustration.

Robust H_∞ observer-based control for synchronization of a class of complex dynamical networks

Zheng Hai-Qing(郑海青) and Jing Yuan-Wei(井元伟)

Chin. Phys. B, 2011, 20 (6): 060504. DOI: 10.1088/1674-1056/20/6/060504

Abstract ( 1593 )

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This paper is concerned with the robust H_∞ synchronization problem for a class of complex dynamical networks by applying the observer-based control. The proposed feedback control scheme is developed to ensure the asymptotic stability of the augmented system, to reconstruct the non-measurable state variables of each node and to improve the H_∞ performance related to the synchronization error and observation error despite the external disturbance. Based on the Lyapunov stability theory, a synchronization criterion is obtained under which the controlled network can be robustly stabilized onto a desired state with a guaranteed H_∞ performance. The controller and the observer gains can be given by the feasible solutions of a set of linear matrix inequalities (LMIs). The effectiveness of the proposed control scheme is demonstrated by a numerical example through simulation.

The synchronization of a fractional order hyperchaotic system based on passive control

Wu Chao-Jun(吴朝俊), Zhang Yan-Bin(张彦斌), and Yang Ning-Ning(杨宁宁)

Chin. Phys. B, 2011, 20 (6): 060505. DOI: 10.1088/1674-1056/20/6/060505

Abstract ( 1412 )

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This paper investigates the synchronization of a fractional order hyperchaotic system using passive control. A passive controller is designed, based on the properties of a passive system. Then the synchronization between two fractional order hyperchaotic systems under different initial conditions is realized, on the basis of the stability theorem for fractional order systems. Numerical simulations and circuitry simulations are presented to verify the analytical results.

Soliton excitations and chaotic patterns for the (2+1)-dimensional Boiti–Leon–Pempinelli system

Yang Zheng (杨征), Ma Song-Hua (马松华), Fang Jian-Ping (方建平)

Chin. Phys. B, 2011, 20 (6): 060506. DOI: 10.1088/1674-1056/20/6/060506

Abstract ( 1373 )

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By improved projective equation approach and a linear variable separation approach, a new family of exact solutions of the (2+1)-dimensional Boiti-Leon-Pempinelli (BLP) system is derived. Based on the derived solitary wave solution, some dromion and solitoff excitations and chaotic behaviours are investigated.

Phase diagrams in mixed spin-3/2 and spin-2 Ising system with two alternative layers within the effective-field theory

Bayram Deviren, Yasin Polat, and Mustafa Keskin

Chin. Phys. B, 2011, 20 (6): 060507. DOI: 10.1088/1674-1056/20/6/060507

Abstract ( 1279 )

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The phase diagrams in the mixed spin-3/2 and spin-2 Ising system with two alternative layers on a honeycomb lattice are investigated and discussed by the use of the effective-field theory with correlations. The interaction of the nearest-neighbour spins of each layer is taken to be positive (ferromagnetic interaction) and the interaction of the adjacent spins of the nearest-neighbour layers is considered to be either positive or negative (ferromagnetic or antiferromagnetic interaction). The temperature dependence of the layer magnetizations of the system is examined to characterize the nature (continuous or discontinuous) of the phase transitions and obtain the phase transition temperatures. The system exhibits both second- and first-order phase transitions besides triple point (TP), critical end point (E), multicritical point (A), isolated critical point (C) and reentrant behaviour depending on the interaction parameters. We have also studied the temperature dependence of the total magnetization to find the compensation points, as well as to determine the type of behaviour, and N-type behaviour in Néel classification nomenclature existing in the system. The phase diagrams are constructed in eight different planes and it is found that the system also presents the compensation phenomena depending on the sign of the bilinear exchange interactions.

Heat transport in coupled inhomogeneous chains

Hu Tao (胡涛), Bai Meng (白萌), Hu Ke (胡柯), Tang Yi (唐翌)

Chin. Phys. B, 2011, 20 (6): 060508. DOI: 10.1088/1674-1056/20/6/060508

Abstract ( 1084 )

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We first investigate the heat transport in a network model consisting of two coupled dimerized chains. Results indicate that the thermal resistance of each chain increases with the decrease of the mass ratio $\gamma$ of the two types of atoms. Then, we find, when a light impurity or a heavy one is added in the two coupled homogeneous chains and coupled with a particle of another chain, the interface thermal resistances $R_{\rm int}^l$ and $R_{\rm int}^r$ present different dependences on the mass ratio $\gamma'$. Finally, a persistent circulation of energy current is observed in coupled inhomogeneous chains with two pairs of interchain coupling.

Effect of unequal injection rates on asymmetric exclusion processes with junction

Xiao Song(肖松), Liu Ming-Zhe(刘明哲), Wang Jian-Jun(王建军), and Wang Hua(王华)

Chin. Phys. B, 2011, 20 (6): 060509. DOI: 10.1088/1674-1056/20/6/060509

Abstract ( 1325 )

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In this paper, we investigate the effect of unequal injection rates on totally asymmetric simple exclusion processes (TASEPs) with a 2-input 1-output junction and parallel update. A mean-field approach is developed to deal with the junction that connects two sub-chains and the single main chain. We obtain the stationary particle currents, density profiles and phase diagrams. Interestingly, we find that the number of stationary-state phases is changeable depending on the value of $\alpha_1$ ($\alpha_1$ is the injection rate on the first sub-chain). When $\alpha_1$ > 1/3, there are seven stationary-state phases in the system, however when $\alpha_1$ < 1/3, only six stationary-state phases exist in the system. The theoretical calculations are shown to be in agreement with Monte Carlo simulations.

Fabrication and electromagnetic wave absorption properties of amorphous Ni–P nanotubes

Lu Hai-Peng(陆海鹏), Han Man-Gui(韩满贵), Cai Li(蔡黎), and Deng Long-Jiang(邓龙江)

Chin. Phys. B, 2011, 20 (6): 060701. DOI: 10.1088/1674-1056/20/6/060701

Abstract ( 1267 )

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Amorphous Ni-P nanotubes are fabricated through electroless chemical deposition inside an anodic aluminum oxide template. The hysteresis loops of Ni-P nanotube arrays are each found to exhibit an unusual isotropic behaviour, which is believed to be due to the competition results between the shape anisotropy and the magnetostatic interaction among nanotubes. The dynamic dependence of permittivity on the frequency spectrum is fitted to the Lorentzian-type dispersion law. The permeability dispersion behaviours have been fitted based on the Kittel equation. Electromagnetic wave absorption properties of Ni-P nanotubes/paraffin composites with different values of thickness (t) are clearly shown by a three-dimensional graph. Furthermore, the bandwidths of composites with different “t ”values can be well presented by a two-dimensional contour graph, which is a novel presentation form. The results show that the composites each have a good microwave absorption performance with t larger than 5.5 mm and with the frequency around 8 gigahertz.

A k-band broadband monolithic distributed frequency multiplier based on nonlinear transmission line ^Hot!

Huang Jie(黄杰), Dong Jun-Rong(董军荣), Yang Hao(杨浩), Zhang Hai-Ying(张海英), Tian Chao(田超), and Guo Tian-Yi(郭天义)

Chin. Phys. B, 2011, 20 (6): 060702. DOI: 10.1088/1674-1056/20/6/060702

Abstract ( 1532 )

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A fabrication technology of GaAs planar Schottky varactor diode (PSVD) is successfully developed and used to design and manufacture GaAs-based monolithic frequency multiplication based on 23-section nonlinear transmission lines (NLTLs) consisting of a coplanar waveguide transmission line and periodically distributed PSVDs. The throughout design and optimization procedure of 23-section monolithic NLTLs for frequency multiplication in the k-band range is based on a large signal equivalent model of PSVD extracted from small-signal S-parameter measurements. This paper reports that the distributed SPVD exhibits a capacitance ratio of 5.4, a normalized capacitance of 0.86 fF/μ² and a breakdown voltage in excess of 22 V. The integrated 23-section NLTLs fed by 20-dBm input power demonstrates a 26-GHz peak second harmonic output power of 14-dBm with 25.3% conversion efficiency in the second harmonic output frequency range of 6 GHz-26 GHz.

Spin-weighted spheroidal equation in the case of s=1

Sun Yue(孙越), Tian Gui-Hua(田贵花), and Dong Kun(董锟)

Chin. Phys. B, 2011, 20 (6): 061101. DOI: 10.1088/1674-1056/20/6/061101

Abstract ( 1350 )

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We present a series of studies to solve the spin-weighted spheroidal wave equation by using the method of super-symmetric quantum mechanics. We first obtain the first four terms of super-potential of the spin-weighted spheroidal wave equation in the case of s=1. These results may help summarize the general form for the n-th term of the super-potential, which is proved to be correct by means of induction. Then we compute the eigen-values and the eigen-functions for the ground state. Finally, the shape-invariance property is proved and the eigen-values and eigen-functions for excited states are obtained. All the results may be of significance for studying the electromagnetic radiation processes near rotating black holes and computing the radiation reaction in curved space-time.

Spin symmetry in the relativistic modified Rosen–Morse potential with the approximate centrifugal term

Chen Wen-Li (陈文利), Wei Gao-Feng (卫高峰)

Chin. Phys. B, 2011, 20 (6): 062101. DOI: 10.1088/1674-1056/20/6/062101

Abstract ( 1093 )

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By applying a Pekeris-type approximation to the centrifugal term, we study the spin symmetry of a Dirac nucleon subjected to scalar and vector modified Rosen-Morse potentials. A complicated energy equation and associated two-component spinors with arbitrary spin-orbit coupling quantum number k are presented. The positive-energy bound states are checked numerically in the case of spin symmetry. The relativistic modified Rosen-Morse potential cannot trap a Dirac nucleon in the limiting case $\alpha$→ 0.

Structural, electronic and vibrational properties of indium oxide clusters

Xu Mao-Jie (徐茂杰), Niquad Yi (倪一), Li Zhen-Qing (李振庆), Wang Sheng-Li (王胜利), Liu Xiao-Hui (柳效辉), Dou Xiao-Ming (窦晓鸣)

Chin. Phys. B, 2011, 20 (6): 063101. DOI: 10.1088/1674-1056/20/6/063101

Abstract ( 1310 )

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Geometric, electronic and vibrational properties of the most stable and energetically favourable configurations of indium oxide clusters In_mO_n (1≤m, n≤4) are investigated using density functional theory. The lowest energy geometries prefer the planar arrangement of the constituent atoms with a trend to maximize the number of ionic In-O bonds. Due to the charge transfer from In to O atoms, the electrostatic repulsion occurs between the atoms with the same kind of charge. The minimization of electrostatic repulsion and the maximization of In-O bond number compete between each other and determine the location of the isometric total energy. The most stable linear In-O-In-O structure of In₂O₂ cluster is attributed to the reduced electrostatic repulsive energy at the expense of In-O bond number, while the lowest energy rhombus-like structure of In₂O₃ cluster reflects the maximized number of In-O bonds. Furthermore, the vibrational frequencies of the lowest energy clusters are calculated and compared with the available experimental results. The energy gap and the charge density distribution for clusters with varying oxygen/indium ratio are also discussed.

Geometrical structures, vibrational frequencies, force constants and dissociation energies of isotopic water molecules (H₂O, HDO, D₂O, HTO, DTO, and T₂O) under dipole electric field

Shi Shun-Ping(史顺平), Zhang Quan(张全), Zhang Li(张莉), Wang Rong(王蓉), Zhu Zheng-He(朱正和), Jiang Gang(蒋刚), and Fu Yi-Bei(傅依备)

Chin. Phys. B, 2011, 20 (6): 063102. DOI: 10.1088/1674-1056/20/6/063102

Abstract ( 1356 )

PDF (243KB) ( 1929 )

The dissociation limits of isotopic water molecules are derived for the ground state. The equilibrium geometries, the vibrational frequencies, the force constants and the dissociation energies for the ground states of all isotopic water molecules under the dipole electric fields from -0.05 a.u. to 0.05 a.u. are calculated using B3P86/6-311++G(3df,3pf). The results show that when the dipole electric fields change from -0.05 a.u. to 0.05 a.u., the bond length of H-O increases whereas the bond angle of H-O-H decreases because of the charge transfer induced by the applied dipole electric field. The vibrational frequencies and the force constants of isotopic water molecules change under the influence of the strong external torque. The dissociation energies increase when the dipole electric fields change from -0.05 a.u. to 0.05 a.u. and the increased dissociation energies are in the order of H₂O, HDO, HTO, D₂O, DTO, and T₂O under the same external electric fields.

Multi-configuration Dirac–Hartree–Fock (MCDHF) calculations for Zn-like sequence from Z=48 to 54

Hu Feng (胡峰), Jiang Gang (蒋刚), Yang Jia-Min (杨家敏), Wang Chuan-Ke (王传珂), Zhao Xue-Feng (赵学峰), Zang Hua-Ping (臧华萍)

Chin. Phys. B, 2011, 20 (6): 063103. DOI: 10.1088/1674-1056/20/6/063103

Abstract ( 1243 )

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The 4s4p excitation energies and the 4s²-4s4p E1 transitions for zinc-like ions from Z=48 to 54 are calculated by the multi-configuration Dirac-Hartree-Fock (MCDHF) method in this paper. The results for fine-structure energy levels, wavelengths and lifetimes between Z=48 (Cd) and Z=54 (Xe) are presented and compared with other theoretical and experimental results. The calculated values including core-valence correlation are found to be very similar to other theoretical and experimental values. We believe that our calculated values can guide experimentalists in identifying the fine-structure levels in their future work.

Theoretical study of stereodynamics for the reaction O(³P) +D₂ (v=0, j=0) $\to$ OD+D and isotope effect

Xu Zeng-Hui(许增慧) and Zong Fu-Jian(宗福建)

Chin. Phys. B, 2011, 20 (6): 063104. DOI: 10.1088/1674-1056/20/6/063104

Abstract ( 1453 )

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Quasi-classical trajectory (QCT) calculations have been performed to study the product polarization behaviours in the reaction ${\rm O({ }^3P) + D_2}$ ($v = 0$, $j = 0) \to$ OD + D. By running trajectories on the $^{3}$A$^\prime $ and $^{3}$A$''$ potential energy surfaces (PESs), vector correlations such as the distributions of the polarization-dependent differential cross sections (PDDCSs), the angular distributions of $P(\theta _r $) and $P(\phi _r $) are presented. Isotope effect is discussed in this work by a comprehensive comparison with the reaction ${\rm O({ }^3P) + H_2}$ ($v = 0$, $j = 0) \to$ H + H. Common characteristics as well as differences are discussed in product alignment and orientation for the two reactions. The isotope mass effect differs on the two potential energy surfaces: the isotope mass effect has stronger influence on $P(\theta _r $) and PDDCSs of the $^{3}$A$^\prime $ PES while the opposite on $P(\phi _r $) of the $^{3}$A$''$ potential energy surface.

Miniaturized optical system for atomic fountain clock ^Hot!

Lü De-Sheng (吕德胜), Qu Qiu-Zhi (屈求智), Wang Bin (汪斌), Zhao Jian-Bo (赵剑波), Li Tang (李唐), Liu Liang (刘亮), Wang Yu-Zhu (王育竹)

Chin. Phys. B, 2011, 20 (6): 063201. DOI: 10.1088/1674-1056/20/6/063201

Abstract ( 1433 )

PDF (255KB) ( 903 )

Using modularized components, we have built a miniaturized optical system for ⁸⁷Rb atomic fountain clock that is fitted on an 80 cm×60 cm optical breadboard. Compared with the conventional optical setup on the table, our system is more compact, more robust and miniaturized. Taking advantage of this system, laser beams are transmitted through eight optical fibre patch cords from the optical breadboard to an ultra high vacuum system. This optical setup has operated for five months in our fountain system and required no alignment.

Laser-induced quadrupole–quadrupole collisional energy transfer in Xe–Kr

Lu Zhen-Zhong (鲁振中), Chen De-Ying (陈德应), Fan Rong-Wei (樊荣伟), Xia Yuan-Qin (夏元钦)

Chin. Phys. B, 2011, 20 (6): 063202. DOI: 10.1088/1674-1056/20/6/063202

Abstract ( 1068 )

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By considering the relative velocity distribution function and multipole expansion interaction Hamiltonian, a three-state model for calculating the cross section of laser-induced quadrupole-quadrupole collisional energy transfer is presented. Calculated results in Xe-Kr system show that in the present system, the laser-induced collision process occurs for ~4 ps, which is much shorter than the dipole-dipole laser-induced collisional energy transfer (LICET) process. The spectrum of laser-induced quadrupole-quadrupole collisional energy transfer in Xe-Kr system has wider tunable range in an order of magnitude than the dipole-dipole LICET spectra. The peak cross section decreases and moves to the quasi-static wing with increasing temperature and the full width at half peak of the profile becomes larger as the system temperature increases.

Photoionization microscopy of hydrogen atom near a metal surface

Yang Hai-Feng (杨海峰), Wang Lei (汪磊), Liu Xiao-Jun (柳晓军), Liu Hong-Ping (刘红平)

Chin. Phys. B, 2011, 20 (6): 063203. DOI: 10.1088/1674-1056/20/6/063203

Abstract ( 1489 )

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We have studied the ionization of Rydberg hydrogen atom near a metal surface with a semiclassical analysis of photoionization microscopy. Interference patterns of the electron radial distribution are calculated at different scaled energies above the classical saddle point and at various atom-surface distances. We find that different types of trajectories contribute predominantly to different manifolds in a certain interference pattern. As the scaled energy increases, the structure of the interference pattern evolves smoothly and more types of trajectories emerge. As the atom approaches the metal surface closer, there are more types of trajectories contributing to the interference pattern as well. When the Rydberg atom comes very close to the metal surface or the scaled energy approaches the zero field ionization energy, the potential induced by the metal surface will make atomic system chaotic. The results also show that atoms near a metal surface exhibit similar properties like the atoms in the parallel electric and magnetic fields.

Even-parity states of the Sm atom with stepwise excitation

Li Ming(李鸣), Dai Chang-Jian(戴长建), and Xie Jun(谢军)

Chin. Phys. B, 2011, 20 (6): 063204. DOI: 10.1088/1674-1056/20/6/063204

Abstract ( 1238 )

PDF (350KB) ( 506 )

Two-colour stepwise excitation and photoionization schemes are adopted to study the spectra of high-lying states of the Sm atom. These bound even-parity states are excited with three different excitation paths from the 4f⁶6s6p⁷D_J (J=1, 2, 3) intermediate states, respectively. They are probed by photoionization process with an extra photon driving them to the continuum states. In this experiment, 270 states are detected in an energy range from 36160 cm^-1 to 42250 cm^-1, 109 of which are newly discovered, while the rest of them are confirmed to be the energy levels reported previously. Furthermore, based on the J-momentum selection rules of three excitation paths, a unique assignment of J-momentum for all observed states is determined, eliminating all remaining ambiguities in the literature. Finally, 53 single-colour transitions originating from the scanning laser are also identified. For all the relevant transitions, the information about their relative intensities is also given in the paper.

Magnetic field effect in photodetachment from negative ion in electric field near metal surface

Tang Tian-Tian (唐田田), Wang De-Hua (王德华), Huang Kai-Yun (黄凯云), Wang Shan-Shan (王姗姗)

Chin. Phys. B, 2011, 20 (6): 063205. DOI: 10.1088/1674-1056/20/6/063205

Abstract ( 1319 )

PDF (243KB) ( 710 )

Based on the closed-orbit theory, the magnetic field effect in the photodetachment of negative ion in the electric field near a metal surface is studied for the first time. The results show that the magnetic field can produce a significant effect on the photodetachment of negative ion near a metal surface. Besides the closed orbits previously found by Du et al. for the H^- in the electric field near a metal surface (J. Phys. B 43 035002 (2010)), some additional closed orbits are produced due to the effect of magnetic field. For a given ion-surface distance and an electric field strength, the cross section depends sensitively on the magnetic field strength. As the magnetic field strength is very small, its influence can be neglected. With the increase of the magnetic field strength, the number of the closed orbits increases greatly and the oscillation in the cross section becomes much more complex. Therefore we can control the photodetachment cross section of the negative ion by changing the magnetic field strength. We hope that our results may guide future experimental studies for the photodetachment process of negative ion in the presence of external fields and surfaces.

Geometries, stabilities, and electronic properties of Be-doped gold clusters: a density functional theory study

Chen Dong-Dong(陈冬冬), Kuang Xiao-Yu(邝小渝), Zhao Ya-Ru(赵亚儒), Shao Peng(邵鹏), and Li Yan-Fang(李艳芳)

Chin. Phys. B, 2011, 20 (6): 063601. DOI: 10.1088/1674-1056/20/6/063601

Abstract ( 1206 )

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We have systematically investigated the geometrical structures, relative stabilities and electronic properties of small bimetallic Au_nBe (n=1, 2, ..., 8) clusters using a density functional method at BP86 level. The optimized geometries reveal that the impurity beryllium atom dramatically affects the structures of the Au_n clusters. The averaged binding energies, fragmentation energies, second-order difference of energies, the highest occupied-lowest unoccupied molecular orbital energy gaps and chemical hardness are investigated. All of them exhibit a pronounced odd-even alternation, manifesting that the clusters with even number of gold atoms possess relatively higher stabilities. Especially, the linear Au₂Be cluster is magic cluster with the most stable chemical stability. According to the natural population analysis, it is found that charge-transferring direction between Au atom and Be atom changes at the size of n=4.

Complete leaky mode coupling in dual-core photonic crystal fibre based on the coupled-mode theory

Yuan Jin-Hui(苑金辉), Yu Chong-Xiu(余重秀), Sang Xin-Zhu(桑新柱), Zhang Jin-Long(张锦龙), Zhou Gui-Yao(周桂耀), and Hou Lan-Tian(侯蓝田)

Chin. Phys. B, 2011, 20 (6): 064101. DOI: 10.1088/1674-1056/20/6/064101

Abstract ( 1254 )

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This paper theoretically investigates the dependence of leaky mode coupling between inner core fundamental mode and outer core defect mode on phase and loss matching in pure silica dual-core photonic crystal fibres with the multi-pole method. The complete mode coupling can take place when both the phase and loss matching conditions are satisfied at the avoided anti-crossing wavelength. It shows the influences of cladding structure parameters including the diameters of cladding air holes d₁, diameters of outer core holes d₂ and hole to hole pitch $\varLambda$ on the characteristics of leaky modes coupling. The coupled-mode theory is used to analyse the mode transition characteristics and the complete coupling can be clearly indicated by comparing the real and imaginary parts of propagation constant of the leaky modes.

Second harmonic generation in inhomogeneous MgO:LiNbO₃ waveguides

Li Guo-Hui(李国辉), Jiang Hai-Ling(蒋海灵), and Xu Xin-Ye(徐信业)

Chin. Phys. B, 2011, 20 (6): 064201. DOI: 10.1088/1674-1056/20/6/064201

Abstract ( 1471 )

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A fibre laser at 1111.6 nm is frequency doubled by two inhomogeneous MgO:LiNbO$_{3}$ waveguides and the output powers of 85 mW and 49 mW at 555.8 nm have been generated with the conversion efficiencies of 47% and 27% respectively. By analysing the second harmonic generation temperature tuning curves, we investigate the influence of the optical inhomogeneities upon the conversion efficiency. The final result shows that the efficiency difference is mainly affected by the optical inhomogeneities in our case.

Broadband tunable external cavity laser using a bent-waveguide quantum-dot superluminescent diode as gain device

Wu Jian(吴剑), Lü Xue-Qin(吕雪芹), Jin Peng(金鹏), Meng Xian-Quan(孟宪权), and Wang Zhan-Guo(王占国)

Chin. Phys. B, 2011, 20 (6): 064202. DOI: 10.1088/1674-1056/20/6/064202

Abstract ( 1428 )

PDF (280KB) ( 802 )

A broadband tunable grating-coupled external cavity laser is realized by employing a self-assembled InAs/GaAs quantum-dot (QD) superluminescent diode (SLD) as the gain device. The SLD device is processed with a bent-waveguide structure and facet antireflection (AR) coating. Tuning bandwidths of 106 nm and 117 nm are achieved under 3-A and 3.5-A injection currents, respectively. The large tuning range originates essentially from the broad gain spectrum of self-assembled QDs. The bent waveguide structure combined with the facet AR coating plays a role in suppressing the inner-cavity lasing under a large injection current.

Investigation of the guided-mode characteristics of hollow-core photonic band-gap fibre with interstitial holes

Yuan Jin-Hui(苑金辉), Yu Chong-Xiu(余重秀), Sang Xin-Zhu(桑新柱), Zhang Jin-Long(张锦龙), Zhou Gui-Yao(周桂耀), Li Shu-Guang(李曙光), and Hou Lan-Tian(侯蓝田)

Chin. Phys. B, 2011, 20 (6): 064203. DOI: 10.1088/1674-1056/20/6/064203

Abstract ( 1464 )

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This paper investigates the guided-mode characteristics of hollow-core photonic band-gap fibre (HC-PBGF) with interstitial holes fabricated by an improved twice stack-and-draw technique at visible wavelengths. Based on the simulation model with interstitial holes, the influence of glass interstitial apexes on photonic band-gaps is discussed. The existing forms of guided-mode in part band gaps are shown by using the full-vector plane-wave method. In the experiment, the observed transmission spectrum corresponds to the part band gaps obtained by simulation. The fundamental and second-order guided-modes with mixture of yellow and green light are observed through choosing appropriate fibre length and adjusting coupling device. The loss mechanism of guided-modes in HC-PBGF is also discussed.

Photon counts modulation in optical time domain reflectometry

Wang Xiao-Bo(王晓波), Wang Jing-Jing(王晶晶), Zhang Guo-Feng(张国锋), Xiao Lian-Tuan(肖连团), and Jia Suo-Tang(贾锁堂)

Chin. Phys. B, 2011, 20 (6): 064204. DOI: 10.1088/1674-1056/20/6/064204

Abstract ( 1398 )

PDF (523KB) ( 723 )

The quantum fluctuation of photon counting limits the field application of optical time domain reflection. A method of photon counts modulation optics time domain reflection with single photon detection at 1.55 μm is presented. The influence of quantum fluctuation can be effectively controlled by demodulation technology since quantum fluctuation shows a uniform distribution in the frequency domain. Combined with the changing of the integration time of the lock-in amplifier, the signal to noise ratio is significantly enhanced. Accordingly the signal to noise improvement ratio reaches 31.7 dB compared with the direct photon counting measurement.

Application of Tikhonov regularization method to wind retrieval from scatterometer data II: cyclone wind retrieval with consideration of rain

Zhong Jian(钟剑), Huang Si-Xun(黄思训), Fei Jian-Fang(费建芳) Du Hua-Dong(杜华栋), and Zhang Liang(张亮)

Chin. Phys. B, 2011, 20 (6): 064301. DOI: 10.1088/1674-1056/20/6/064301

Abstract ( 1266 )

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According to the conclusion of the simulation experiments in paper I, the Tikhonov regularization method is applied to cyclone wind retrieval with a rain-effect-considering geophysical model function (called GMF+Rain). The GMF+Rain model which is based on the NASA scatterometer-2 (NSCAT2) GMF is presented to compensate for the effects of rain on cyclone wind retrieval. With the multiple solution scheme (MSS), the noise of wind retrieval is effectively suppressed, but the influence of the background increases. It will cause a large wind direction error in ambiguity removal when the background error is large. However, this can be mitigated by the new ambiguity removal method of Tikhonov regularization as proved in the simulation experiments. A case study on an extratropical cyclone of hurricane observed with SeaWinds at 25-km resolution shows that the retrieved wind speed for areas with rain is in better agreement with that derived from the best track analysis for the GMF+Rain model, but the wind direction obtained with the two-dimensional variational (2DVAR) ambiguity removal is incorrect. The new method of Tikhonov regularization effectively improves the performance of wind direction ambiguity removal through choosing appropriate regularization parameters and the retrieved wind speed is almost the same as that obtained from the 2DVAR.

The power spectrum and correlation of flow noise for an axisymmetric body in water

Li Xue-Gang (黎雪刚), Yang Kun-De (杨坤德), Wang Yong (汪勇)

Chin. Phys. B, 2011, 20 (6): 064302. DOI: 10.1088/1674-1056/20/6/064302

Abstract ( 1200 )

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Understanding the physical features of the flow noise for an axisymmetric body is important for improving the performance of a sonar mounted on an underwater platform. Analytical calculation and numerical analysis of the physical features of the flow noise for an axisymmetric body are presented and a simulation scheme for the noise correlation on the hydrophones is given. It is shown that the numerical values of the flow noise coincide well with the analytical values. The main physical features of flow noise are obtained. The flow noises of two different models are compared and a model with a rather optimal fore-body shape is given. The flow noise in horizontal symmetry profile of the axisymmetric body is non-uniform, but it is omni-directional and has little difference in the cross section of the body. The loss of noise diffraction has a great effect on the flow noise from boundary layer transition. Meanwhile, based on the simulation, the noise power level increases with velocity to approximately the fifth power at high frequencies, which is consistent with the experiment data reported in the literature. Furthermore, the flow noise received by the acoustic array has lower correlation at a designed central frequency, which is important for sonar system design.

Thermal resistance matrix representation of thermal effects and thermal design in multi-finger power heterojunction bipolar transistors

Jin Dong-Yue(金冬月), Zhang Wan-Rong(张万荣), Chen Liang(陈亮), Fu Qiang(付强), Xiao Ying(肖盈), Wang Ren-Qing(王任卿), and Zhao Xin(赵昕)

Chin. Phys. B, 2011, 20 (6): 064401. DOI: 10.1088/1674-1056/20/6/064401

Abstract ( 1467 )

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The thermal resistance matrix including self-heating thermal resistance and thermal coupling resistance is presented to describe the thermal effects of multi-finger power heterojunction bipolar transistors. The dependence of thermal resistance matrix on finger spacing is also investigated. It is shown that both self-heating thermal resistance and thermal coupling resistance are lowered by increasing the finger spacing, in which the downward dissipated heat path is widened and the heat flow from adjacent fingers is effectively suppressed. The decrease of self-heating thermal resistance and thermal coupling resistance is helpful for improving the thermal stability of power devices. Furthermore, with the aid of the thermal resistance matrix, a 10-finger power heterojunction bipolar transistor (HBT) with non-uniform finger spacing is designed for high thermal stability. The optimized structure can effectively lower the peak temperature while maintaining a uniformity of the temperature profile at various biases and thus the device effectively may operate at a higher power level.

Effect of acceleration threshold on the phase transition in a cellular automaton traffic flow model

Jin Cheng-Jie(金诚杰), Wang Wei(王炜), Gao Kun(高坤), and Jiang Rui(姜锐)

Chin. Phys. B, 2011, 20 (6): 064501. DOI: 10.1088/1674-1056/20/6/064501

Abstract ( 1422 )

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In this paper, we incorporate new parameters into a cellular automaton traffic flow model proposed in our previous paper [Jin et al. 2010 J. Stat. Mech. 2010 P03018]. Through these parameters, we adjust the anticipated velocity and the acceleration threshold separately. It turns out that the flow rate of synchronized flow mainly changes with the anticipated velocity, and the F→S phase transition feature mainly changes with the acceleration threshold. Therefore, we conclude that the acceleration threshold is the major factor affecting the F→S phase transition.

Scaling of heat transfer in gas–gas injector combustor

Wang Xiao-Wei(汪小卫), Cai Guo-Biao(蔡国飙), and Gao Yu-Shan(高玉闪)

Chin. Phys. B, 2011, 20 (6): 064701. DOI: 10.1088/1674-1056/20/6/064701

Abstract ( 1260 )

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The scaling of heat transfer in gas–gas injector combustor is investigated theoretically, numerically and experimentally based on the previous study on the scaling of gas–gas combustion flowfield. The similarity condition of the gas–gas injector combustor heat transfer is obtained by conducting a formulation analysis of the boundary layer Navier–Stokes equations and a dimensional analysis of the corresponding heat transfer phenomenon. Then, a practicable engineering scaling criterion of the gas–gas injector combustor heat transfer is put forward. The criterion implies that when the similarity conditions of inner flowfield are satisfied, the size and the pressure of gas–gas combustion chamber can be changed, while the heat transfer can still be qualitatively similar to the distribution trend and quantitatively correlates well with the size and pressure as q ∝ p_c^0.8d_t^-0.2 . Based on the criterion, single-element injector chambers with different geometric sizes and at different chamber pressures ranging from 1 MPa to 20 MPa are numerically simulated. A single-element injector chamber is designed and hot-fire tested at seven chamber pressures from 0.92 MPa to 6.1 MPa. The inner wall heat flux are obtained and analysed. The numerical and experimental results both verified the scaling criterion in gas–gas injector combustion chambers under different chamber pressures and geometries.

Landau damping of longitudinal oscillation in ultra- relativistic plasmas with nonextensive distribution

Liu San-Qiu (刘三秋), Xiao-Chang (陈小昌)

Chin. Phys. B, 2011, 20 (6): 065201. DOI: 10.1088/1674-1056/20/6/065201

Abstract ( 1370 )

PDF (436KB) ( 1069 )

The generalized dispersion equation for longitudinal oscillation in an unmagnetized, collisionless, isotropic and relativistic plasma is derived in the context of nonextensive q-distribution. An analytical expression for the Landau damping is obtained in an ultra-relativistic regime, which is related to q-parameter. In the limit q → 1, the result based on the relativistic Maxwellian distribution is recovered. It is shown that the interactions between the wave and particles are stronger and the waves are more strongly damped for lower values of q-parameter. The results are explained by the increased number of superthermal particles or low velocity particles contained in the plasma with the nonextensive distribution.

Shock wave velocity measurement in the Al₂O₃ under ultrahigh pressure

Wang Feng (王峰), Peng Xiao-Shi (彭晓世), Liu Shen-Ye (刘慎业), Li Yong-Sheng (李永升), Jiang Xiao-Hua (蒋小华), Ding Yong-Kun (丁永坤)

Chin. Phys. B, 2011, 20 (6): 065202. DOI: 10.1088/1674-1056/20/6/065202

Abstract ( 1366 )

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In indirect-drive experiment, the blank effect caused by X-rays from Hohlraum will show the dark area in time scale of optical streak camera (OSC). This blank effect, which was a serious problem in indirect-drive shock wave experiments, has been explained by the semiconductor model. The X-rays cause the band to band transition and the probe laser is absorbed by the intraband transition, which leads to a dark region in time scale of the OSC image. In the experiment, the reflectivity of shock wave front was measured to be about 50% at shock wave velocity 32 km/s and was compared to the theoretical calculations with the Drude free electron model. From the experimental data, it is found that the blank effect can be avoided at radiation temperature of 170 eV if the Al layer is thicker than 60 μm.

Growth of deuterium clusters in a gas jet and ion energy spectrum of clusters in ultra-short laser field

Liu Hong-Jie (刘红杰), Gu Yu-Qiu (谷渝秋), Zhou Wei-Min (周维民), Gao Yu-Lin (高宇林), Shan Lian-Qiang (单连强), Zhu Bin (朱斌), Wu Yu-Chi (吴玉迟), Jiao Chun-Ye (焦春晔), Li Fang (李芳), Cao Lei-Feng (曹磊峰), Zhang Bao-Han (张保汉), Zheng Zhi-Jian (郑志坚)

Chin. Phys. B, 2011, 20 (6): 065203. DOI: 10.1088/1674-1056/20/6/065203

Abstract ( 1336 )

PDF (393KB) ( 586 )

Large deuterium clusters are generated using a cryogenic pulse valve with a cone nozzle (21 mm long, 4° open angle). Rayleigh scattering experiment is carried out to obtain the scaling relation between scattering signal S_R and backing pressure P₀. A method using the Coulomb explosion model is proposed to verify that the clusters continue to grow after their leaving the nozzle. Our experiments suggest a tentatively optimized position for laser cluster interaction.

On characteristics of sheath damping near a dielectric wall with secondary electron emission

Yu Da-Ren(于达仁), Qing Shao-Wei(卿绍伟), Yan Guo-Jun(闫国军), and Duan Ping(段萍)

Chin. Phys. B, 2011, 20 (6): 065204. DOI: 10.1088/1674-1056/20/6/065204

Abstract ( 1328 )

PDF (312KB) ( 959 )

A preliminary investigation is conducted to study the characteristics of sheath damping near a dielectric wall with secondary electron emission (SEE). Making use of the linear analysis of the sheath stability, we have found two major contributions to the sheath damping, one similar to the Landau damping in uniform plasmas and another determined by local electric field and electron density of the steady-state sheath. It indicates that in a classical sheath regime the damping in the sheath region monotonically increases towards the wall and decreases with the enhancement of SEE effect. In order to verify the theoretical analysis, sheath oscillation processes induced by an initial disturbance are simulated with a time-dependent one-dimensional (1D) sheath model. Numerical results obtained are consistent with the theoretical analysis qualitatively.

Driving frequency effects on the mode transition in capacitively coupled argon discharges

Liu Xiang-Mei(刘相梅), Song Yuan-Hong(宋远红), and Wang You-Nian(王友年)

Chin. Phys. B, 2011, 20 (6): 065205. DOI: 10.1088/1674-1056/20/6/065205

Abstract ( 1295 )

PDF (600KB) ( 1233 )

A one-dimensional fluid model is employed to investigate the discharge sustaining mechanisms in the capacitively coupled argon plasmas, by modulating the driving frequency in the range of 40 kHz-60 MHz. The model incorporates the density and flux balance of electron and ion, electron energy balance, as well as Poisson's equation. In our simulation, the discharge experiences mode transition as the driving frequency increases, from the $\gamma$ regime in which the discharge is maintained by the secondary electrons emitted from the electrodes under ion bombardment, to the $\alpha$ regime in which sheath oscillation is responsible for most of the electron heating in the discharge sustaining. The electron density and electron temperature at the centre of the discharge, as well as the ion flux on the electrode are figured out as a function of the driving frequency, to confirm the two regimes and transition between them. The effects of gas pressure, secondary electron emission coefficient and applied voltage on the discharge are also discussed.

Surface modification of polytetrafluoroethylene film using single liquid electrode atmospheric- pressure glow discharge

Zhou Lan(周澜), Lü Guo-Hua(吕国华), Chen Wei(陈维), Pang Hua(庞华), Zhang Gu-Ling(张谷令), and Yang Si-Ze(杨思泽)

Chin. Phys. B, 2011, 20 (6): 065206. DOI: 10.1088/1674-1056/20/6/065206

Abstract ( 1548 )

PDF (3789KB) ( 1297 )

Polytetrafluoroethylene films are treated by room temperature helium atmospheric pressure plasma plumes, which are generated with a home-made single liquid electrode plasma device. After plasma treatment, the water contact angle of polytetrafluoroethylene film drops from 114° to 46° and the surface free energy increases from 22.0 mJ/m² to 59.1 mJ/m². The optical emission spectrum indicates that there are reactive species such as O₂⁺, O and He in the plasma plume. After plasma treatment, a highly crosslinking structure is formed on the film surface and the oxygen element is incorporated into the film surface in the forms of -C-O-C-, -C=O, and -O-C=O groups. Over a period of 10 days, the contact angle of the treated film is recovered by only about 10°, which indicates that the plasma surface modification is stable with time.

In situ high-pressure X-ray diffraction experiments and ab initio calculations of Co₂P

Zhang Qian(张倩), Wu Xiang(巫翔), and Qin Shan(秦善)

Chin. Phys. B, 2011, 20 (6): 066101. DOI: 10.1088/1674-1056/20/6/066101

Abstract ( 1354 )

PDF (354KB) ( 779 )

In situ high-pressure experiments of Co₂P are carried out by means of angle dispersive X-ray diffraction with diamond anvil cell technique. No phase transition is observed in the present pressure range up to 15 GPa at room temperature, even at high temperature and 15 GPa. Results of compression for Co₂P are well presented by the second-order Birch-Murnaghan equation of state with V₀ = 130.99(2) Å³ (1 Å=0.1 nm) and K₀ = 160(3) GPa. Axial compressibilities are described by compressional modulus of the axis: K_a = 123(2) GPa, K_b = 167(8) GPa and K_c = 220(7) GPa. Theoretical calculations further support the experimental results and indicate that C23-type Co₂P is stable at high pressure compared with the C22-type phase.

Icosahedral medium-range order formed in Mg₇₀Zn₃₀ metallic glass: a larger-scale molecular dynamics simulation

Hou Zhao-Yang(侯兆阳), Liu Rang-Su(刘让苏), Tian Ze-An(田泽安), and Wang Jin-Guo(王晋国)

Chin. Phys. B, 2011, 20 (6): 066102. DOI: 10.1088/1674-1056/20/6/066102

Abstract ( 1289 )

PDF (1656KB) ( 1191 )

A larger-scale Mg₇₀Zn₃₀ alloy system including 100000 atoms has been simulated by using the molecular dynamics method to investigate the icosahedral medium-range order (IMRO) formed in the Mg₇₀Zn₃₀ metallic glass. It is found that the simulated pair distribution function of Mg₇₀Zn₃₀ metallic glass is in good agreement with the experimental results. The glass transition temperature T_g is near 450 K under the cooling rate of 1×10¹² K/s. The icosahedral local structures play a critical role in the formation of metallic glass, and they are the dominant local configurations in the Mg₇₀Zn₃₀ metallic glass. The IMRO in the Mg₇₀Zn₃₀ metallic glass is characterized by certain types of extended icosahedral clusters combined by intercross-sharing atoms in the form of chains or dendrites. The size distributions of these IMRO clusters present a magic number sequence of 19, 23, 25, 27, 29, 31, 33, 35, 37, 39,..., and the magic clusters can be classified into three types according to their compactness. The IMRO clusters grow rapidly in a low-dimensional way with cooling, but this growth is limited near T_g.

Morphology and microstructure of Ag islands of aggregated atoms on oil surfaces

Zhang Chu-Hang(张初航), Lü Neng(吕能), Zhang Xiao-Fei(张晓飞), Saida Ajeeb, Xia A-Gen(夏阿根), and Ye Gao-Xiang(叶高翔)

Chin. Phys. B, 2011, 20 (6): 066103. DOI: 10.1088/1674-1056/20/6/066103

Abstract ( 1352 )

PDF (1192KB) ( 805 )

The morphology evolution of silver islands on silicone oil surfaces is measured and the microstructure of the islands is studied. The deposited Ag atoms diffuse and aggregate on the oil surface and then Ag islands with the width of the order of 10²-nm form. After the samples are removed from the vacuum chamber, the immediate measurement shows that the apparent Ag coverage of the total area decays with the magnitude up to (23.0±3.8)% in few minutes. In the following two hours, the samples are kept in the ambient atmosphere and several unexpected results are detected: 1) as the topological structure of the islands evolves, the total area of each island decreases gradually and the maximum decrement measured is around 20%; 2) if an island breaks and becomes two small pieces, the total area decreases obviously; 3) however, if two small islands meet and stick together, a sudden increment of the total area is observed. These phenomena, mirroring the evolution process of the island microstructure, are resulted from both the diffusion of the atoms and the combination of the defects inside the islands.

Sb complexes and Zn interstitials in Sb-implanted ZnO epitaxial films ^Hot!

Liu Yao-Ping (刘尧平), Ying Min-Ju (英敏菊), Mei Zeng-Xia (梅增霞), Li Jun-Qiang (李俊强), Du Xiao-Long (杜小龙), A. Yu. Kuznetsov

Chin. Phys. B, 2011, 20 (6): 066104. DOI: 10.1088/1674-1056/20/6/066104

Abstract ( 1261 )

PDF (414KB) ( 770 )

In the present work, post-annealing is adopted to investigate the formation and the correlation of Sb complexes and Zn interstitials in Sb-ion implanted ZnO films, by using Raman scattering technique and electrical characterizations. The damage of Zn sublattice, produced by ion bombardment process is discerned from the unrecovered E₂ (L) peak in annealed high Sb⁺ dose implanted samples. It is suggested that the Zn sublattice may be strongly affected by the introduction of Sb dopant because of the formation of Sb_Zn-2V_Zn complex acceptor. The appearance of a new peak at 510 cm^-1 in the annealed high dose Sb⁺ implanted samples is speculated to result from (Zn interstitials-O interstitials) Zn_i-O_i complex, which is in a good accordance with the electrical measurement. The p-type ZnO is difficult to obtain from the Sb⁺ implantation, however, which can be realized by in-situ Sb doping with proper growth conditions instead.

Electronic structure of twinned ZnS nanowires

Li Deng-Feng(李登峰), Li Bo-Lin(李柏林), Xiao Hai-Yan(肖海燕), and Dong Hui-Ning(董会宁)

Chin. Phys. B, 2011, 20 (6): 067101. DOI: 10.1088/1674-1056/20/6/067101

Abstract ( 1226 )

PDF (2400KB) ( 1034 )

The electronic properties of twinned ZnS nanowires (NWs) with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal (2H) stacking inside the cubic (3C) stacking has no effect on the electronic properties of thin ZnS NWs.

Research on high-voltage 4H–SiC P–i–N diode with planar edge junction termination techniques

Zhang Fa-Sheng (张发生), Li Xin-Ran (李欣然)

Chin. Phys. B, 2011, 20 (6): 067102. DOI: 10.1088/1674-1056/20/6/067102

Abstract ( 1392 )

PDF (473KB) ( 1148 )

The planar edge termination techniques of junction termination extension (JTE) and offset field plates and field-limiting rings for the 4H-SiC P-i-N diode were investigated and optimized by using a two-dimensional device simulator ISE-TCAD10.0. By experimental verification, a good consistency between simulation and experiment can be observed. The results show that the reverse breakdown voltage for the 4H-SiC P-i-N diode with optimized JTE edge termination can accomplish near ideal breakdown voltage and much lower leakage current. The breakdown voltage can be near 1650 V, which achieves more than 90 percent of ideal parallel plane junction breakdown voltage and the leakage current density can be near 3×10^-5 A/cm².

Properties of ground state and anomalous quantum fluctuations in one-dimensional polaron–soliton systems—the effects of electron-two-phonon interaction and non-adiabatic quantum correlations

Luo Zhi-Hua(罗质华), Cao Xi-Jin(曹锡金), and Yu Chao-Fan(余超凡)

Chin. Phys. B, 2011, 20 (6): 067103. DOI: 10.1088/1674-1056/20/6/067103

Abstract ( 1186 )

PDF (320KB) ( 898 )

Based on the Holstein model Hamiltonian of one-dimensional molecular crystals, by making use of the expansion approach of the correlated squeezed-coherent states of phonon instead of the two-phonon coherent state expansion scheme, the properties of the ground state and the anomalous quantum fluctuations are investigated in a strongly coupled electron-phonon system with special consideration of the electron-two-phonon interaction. The effective renormalization (ã_i) of the displacement of the squeezed phonons with the effect of the squeezed-coherent states of phonon and both the electron-displaced phonon and the polaron-squeezed phonon correlations have been combined to obtain the anomalous quantum fluctuations for the corrections of the coherent state. Due to these non-adiabatic correlations, the effective displacement parameter ã_i is larger than the ordinary parameter α_i⁽⁰⁾. In comparison with the electron-one-phonon interaction (g) corrected as ã_i, we have found the electron-two-phonon interaction (g₁) corrected as ã_i²g₁ is enhanced significantly. For this reason, the ground state energy (E₀⁽²⁾) contributed by the electron-two-phonon interaction is more negative than the single-phonon case (E₀⁽¹⁾) and the soliton solution is more stable. At the same time, the effects of the electron-two-phonon interaction greatly increase the polaron energy and the quantum fluctuations. Furthermore, in a deeper level, we have considered the effect of the polaron-squeezed phonon correlation (f-correlation). Since this correlation parameter f>1, this effect will strengthen the electron-one and two-phonon interactions by fã_ig and f²ã_i²g₁, respectively. The final results show that the ground state energy and the polaron energy will appear more negative further and the quantum fluctuations will gain further improvement.

Spin-dependent Breit–Wigner and Fano resonances in photon-assisted electron transport through a semiconductor heterostructure

Hu Li-Yun(胡丽云) and Zhou Bin(周斌)

Chin. Phys. B, 2011, 20 (6): 067201. DOI: 10.1088/1674-1056/20/6/067201

Abstract ( 1240 )

PDF (316KB) ( 1018 )

We theoretically investigate the electron transmission through a seven-layer semiconductor heterostructure with the Dresselhaus spin-orbit coupling under two applied oscillating fields. Numerical results show that both of the spin-dependent symmetric Breit-Wigner and the asymmetric Fano resonances appear and that the properties of these two types of resonance peaks are dependent on the amplitude and the relative phases of the two applied oscillating fields. The modulation of the spin-polarization efficiency of transmitted electrons by the relative phase is also discussed.

Donor-bound electron states in a two-dimensional quantum ring under uniform magnetic field

Jia Bo-Yong(贾博雍), Yu Zhong-Yuan(俞重远), Liu Yu-Min(刘玉敏), Han Li-Hong(韩利红), Yao Wen-Jie(姚文杰), Feng Hao(冯昊), and Ye Han(叶寒)

Chin. Phys. B, 2011, 20 (6): 067301. DOI: 10.1088/1674-1056/20/6/067301

Abstract ( 1238 )

PDF (576KB) ( 843 )

The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring. The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.

Effect of compensation doping on the electrical and optical properties of mid-infrared type-II InAs/GaSb superlattice photodetectors

Wang Yong-Bin (王永宾), Xu Yun (徐云), Zhang Yu (张宇), Yu Xiu (迂修), Song Guo-Feng (宋国峰), Chen Liang-Hui (陈良惠)

Chin. Phys. B, 2011, 20 (6): 067302. DOI: 10.1088/1674-1056/20/6/067302

Abstract ( 1397 )

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This paper presents a theoretical study on the electrical and optical properties of mid-infrared type-II InAs/GaSb superlattices with different beryllium concentrations in the InAs layer of the active region. Dark current, resistance-area product, absorption coefficient and quantum efficiency characteristics are thoroughly examined. The superlattice is residually n-type and it becomes slightly p-type by varying beryllium-doping concentrations, which improves its electrical performances. The optical performances remain almost unaffected with relatively low p-doping levels and begin to deteriorate with increasing p-doping density. To make a compromise between the electrical and optical performances, the photodetector with a doping concentration of 3 × 10¹⁵cm^-3 in the active region is believed to have the best overall performances.

Thermal stability of tungsten and tungsten nitride Schottky contacts to AlGaN/GaN

Liu Fang(刘芳), Qin Zhi-Xin(秦志新), Xu Fu-Jun(许福军), Zhao Sheng(赵胜), Kang Xiang-Ning(康香宁), Shen Bo(沈波), and Zhang Guo-Yi(张国义)

Chin. Phys. B, 2011, 20 (6): 067303. DOI: 10.1088/1674-1056/20/6/067303

Abstract ( 1600 )

PDF (279KB) ( 1843 )

Thin tungsten nitride (WN_x) films were produced by reactive DC magnetron sputtering of tungsten in an Ar-N₂ gas mixture. The films were used as Schottky contacts on AlGaN/GaN heterostructures. The Schottky behaviours of WN_x contact was investigated under various annealing conditions by current-voltage (I-V) measurements. The results show that the gate leakage current was reduced to 10^-6 A/cm² when the N₂ flow is 400 mL/min. The results also show that the WN_x contact improved the thermal stability of Schottky contacts. Finally, the current transport mechanism in WN_x/AlGaN/GaN Schottky diodes has been investigated by means of I-V characterisation technique at various temperatures between 300 K and 523 K. A TE model with a Gaussian distribution of Schottky barrier heights (SBHs) is thought to be responsible for the electrical behaviour at temperatures lower than 523 K.

Kink effect in AlGaN/GaN high electron mobility transistors by electrical stress

Ma Xiao-Hua(马晓华), Ma Ji-Gang(马骥刚), Yang Li-Yuan(杨丽媛), He Qiang(贺强), Jiao Ying(焦颖), Ma Ping(马平), and Hao Yue(郝跃)

Chin. Phys. B, 2011, 20 (6): 067304. DOI: 10.1088/1674-1056/20/6/067304

Abstract ( 1518 )

PDF (450KB) ( 1972 )

The kink effect is studied in an AlGaN/GaN high electron mobility transistor by measuring DC performance during fresh, short-term stress and recovery cycle with negligible degradation. V_dg plays an assistant role in detrapping electrons and short-term stress results in no creation of new category traps but an increase in number of active traps. A possible mechanism is proposed that electrical stress supplies traps with the electric field for activation and when device is under test field-assisted hot-electrons result in electrons detrapping from traps, thus deteriorating the kink effect. In addition, experiments show that the impact ionization is at a relatively low level, which is not the dominant mechanism compared with trapping effect. We analyse the complicated link between the kink effect and stress bias through groups of electrical stress states: V_ds=0-state, off-state, on-state (on-state with low voltage, high-power state, high field state). Finlly, a conclusion is drawn that electric field brings about more severe kink effect than hot electrons. With the assistance of electric field, hot electrons tend to be possible to modulate the charges in deep-level trap.

Selection of isolated and individual single-walled carbon nanotube from a film and its usage in nanodevices

Wang Gong-Tang(王公堂)

Chin. Phys. B, 2011, 20 (6): 067305. DOI: 10.1088/1674-1056/20/6/067305

Abstract ( 1447 )

PDF (3178KB) ( 543 )

Individual and isolated single-walled carbon nanotubes (SWNTs) are important for fabricating relevant nanodevices and studying the properties of the SWNT devices. In this work, we demonstrate that individual and isolated SWNT can be selected and obtained from a film containing a huge number of SWNTs. By using both the polymethylmethacrylate (PMMA) as a negative resist and the electron beam lithography, the selected SWNT can be fixed on a substrate, while the other SWNTs in the film can lift off. The selected SWNT can be used to fabricate nanodevice and a gas sensor of oxygen is demonstrated in this work.

Glassy behaviour of random field Ising spins on Bethe lattice in external magnetic field

Khalid Bannora, Galal Ismail, and Wafaa Hassan

Chin. Phys. B, 2011, 20 (6): 067501. DOI: 10.1088/1674-1056/20/6/067501

Abstract ( 1337 )

PDF (881KB) ( 856 )

The thermodynamics and the phase diagram of random field Ising model (RFIM) on Bethe lattice are studied by using a replica trick. This lattice is placed in an external magnetic field ($B$). A Gaussian distribution of random field $( {h_{\rm i} } )$ with zero mean and variance $\langle {{h}_{\rm i}^{\rm 2} } \rangle = { H}_{{\rm RF}}^{\rm 2} $ is considered. The free-energy ($F$), the magnetization ($M$) and the order parameter ($q$) are investigated for several values of coordination number ($z$). The phase diagram shows several interesting behaviours and presents tricritical point at critical temperature $T_{\rm C} = J / k$ and when $H_{\rm RF} = 0$ for finite $z$. The free-energy ($F$) values increase as $T$ increases for different intensities of random field ($H_{\rm RF} $) and finite $z$. The internal energy ($U$) has a similar behaviour to that obtained from the Monte Carlo simulations. The ground state of magnetization decreases as the intensity of random field $H_{\rm RF} $ increases. The ferromagnetic (FM)--paramagnetic (PM) phase boundary is clearly observed only when $z \to \infty $. While FM--PM-spin glass (SG) phase boundaries are present for finite $z$. The magnetic susceptibility ($\chi $) shows a sharp cusp at $T_{\rm C} $ in a small random field for finite $z$ and rounded different peaks on increasing $H_{\rm RF}$.

Hydrogenation, structure and magnetic properties of La(Fe_0.91Si_0.09)₁₃ hydrides and deuterides

Wang Zhi-Cui(王志翠), He Lun-Hua(何伦华), F. Cuevas, M. Latroche, Shen Jun(沈俊), and Wang Fang-Wei(王芳卫)

Chin. Phys. B, 2011, 20 (6): 067502. DOI: 10.1088/1674-1056/20/6/067502

Abstract ( 1350 )

PDF (394KB) ( 649 )

Hydrogenation, crystal structure and magnetic properties of La(Fe_0.91Si_0.09)₁₃H(D)_y have been studied by pressure-composition isotherms (PCI), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and magnetization measurements. The maximum absorption capacity is found to be 1.9 H(D) atoms per formula unit as a solid solution. All hydrides and deuterides crystallize in the NaZn₁₃-type cubic structure with the lattice parameter increasing linearly with H(D) concentration. The H(D) absorption enhances the Curie temperature significantly. The magnetic entropy change of the highly H-absorbed compound La(Fe_0.91Si_0.09)₁₃H_1.81 reaches ~26 J/kg·K under a magnetic field change of 5 T near the Curie temperature T_C=350 K. No observable isotope effect seems to imply that only the magnetovolume effect is responsible for the strong interplay between magnetism and lattice.

Magnetoelectric effect in layered composites with arc shape

Bi Ke (毕科), Wu Wei (吴玮), Wang Yin-Gang (王寅岗)

Chin. Phys. B, 2011, 20 (6): 067503. DOI: 10.1088/1674-1056/20/6/067503

Abstract ( 1421 )

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Magnetoelectric (ME) layered Ni/PZT/Ni composites with arc shape have been prepared by using electroless deposition. The ME effect is measured by applying both constant and alternating magnetic fields in longitudinal and transverse directions. The longitudinal ME voltage coefficient is much larger than the transverse one. With the increase of arc length or decrease of curvature, the resonance frequency of layered arc Ni/PZT/Ni composites gradually decreases, while the maximum of the ME voltage coefficient of the composites increases monotonously. The influence of the arc length and the curvature on ME coupling is discussed. The flat interface between the ferromagnetic and the piezoelectric phases in layered ME composites is believed to provide large ME voltage coefficient.

Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K_0.5Na_0.5NbO₃–0.04LiSbO₃ lead-free piezoelectric ceramics

Zhao Jing-Bo(赵静波), Du Hong-Liang(杜红亮), Qu Shao-Bo(屈绍波), Zhang Hong-Mei(张红梅), and Xu Zhuo(徐卓)

Chin. Phys. B, 2011, 20 (6): 067701. DOI: 10.1088/1674-1056/20/6/067701

Abstract ( 1290 )

PDF (6647KB) ( 831 )

Effects of A-site non-stoichiometry on the structural and electrical properties of 0.96K_{0.5 + x}Na_{0.5 + x}NbO₃-0.04LiSbO₃ lead-free piezoelectric ceramics were examined for 0 ≤ x ≤ 0.02. The piezoelectric coefficients exhibited a maximum, d₃₃= 187 pC/N at x=0.0075, coinciding with the maximum of the grain size and the apparent density at x=0.0075. The apparent density and the piezoelectric coefficients decreased with increasing x at higher x which was likely due to the crystal geometrical distortion of 0.96K_{0.5 + x}Na_{0.5 + x}NbO₃-0.04LiSbO₃. In addition, super-large grains were found and this may be due to liquid phase sintering. Excess (K⁺+Na⁺) attracted a sum of space charges to keep the charge neutral, resulting in charge leakage during the course of ceramic polarization, influencing the piezoelectric and ferroelectric properties. These findings are of importance for guiding the design of K_0.5Na_0.5NbO₃-based lead-free ceramics with enhanced electrical properties.

Photoabsorption cross sections of the alkaline-earth-metal elements under strong interaction conditions

Liu Meng-Meng (刘萌萌), Ma Xiao-Guang (马晓光)

Chin. Phys. B, 2011, 20 (6): 067801. DOI: 10.1088/1674-1056/20/6/067801

Abstract ( 1217 )

PDF (1301KB) ( 611 )

The strong interatomic interaction effects on photoabsorption cross sections of a private atom have been interpreted by the contribution of both the real and imaginary parts of atomic polarizability in the present work. Some unresolved differences between the photoabsorption cross sections of isolated atoms and those of condensed atoms, especially near thresholds and resonances, probably could be interpreted by the competition between the imaginary and real parts of atomic frequency-dependent polarizabilities.

Electromagnetic chirality-induced negative refraction with the same amplitude and anti-phase of the two chirality coefficients

Zhao Shun-Cai (赵顺才), Liu Zheng-Dong (刘正东), Zheng Jun (郑军), Li Gen (黎根)

Chin. Phys. B, 2011, 20 (6): 067802. DOI: 10.1088/1674-1056/20/6/067802

Abstract ( 1299 )

PDF (1249KB) ( 668 )

This paper suggests a scheme of electromagnetic chirality-induced negative refraction utilizing magneto-electric cross coupling in a four-level atomic system. The negative refraction can be achieved with the two chirality coefficients having the same amplitude but the opposite phase, without requiring the simultaneous presence of an electric-dipole and a magnetic-dipole transition near the same transition frequency.

Studies on selected polymeric materials using the photoacoustic spectroscopic technique

Hukum Singh

Chin. Phys. B, 2011, 20 (6): 067803. DOI: 10.1088/1674-1056/20/6/067803

Abstract ( 1278 )

PDF (660KB) ( 670 )

Polymethylmethacrylate-graft-polybisphenol-A-carbonate (PMMA-G-PC) with 50% grafting is synthesized. The graft co-polymerization of methylmethacrylate (0.036 mol·lit^-1) onto polybisphenol-A-carbonate (0.5 g) in the presence of a redox couple formed from potassium persulphate (40 mol·lit^-1) and thio-urea (30 mmol·lit^-1) in aqueous nitric acid (0.18 M, 100 ml) in air at (45±2)°C for 3.0 h. Condensation of (PMMA-G-PC) with N- [p-(carboxyl phenyl amino acetic acid)] hydrazide (PCPH) affords polybisphenol-A-carbonate-graft-polymethylmethacrylate hydrazide (PCGH). The photoacoustic (PA) spectra of (PCGH) are recorded in a wavelength range from 200 nm to 800 nm at a modulation frequency of 22 Hz, and compared with those of pure polybisphenol-A-carbonate (PC), (PMMA-G-PC) and (PCPH). In the present work, a non-destructive and non-contact analytical method, namely the photoacoustic technique, is successfully implemented for optical and thermal characterization of selected polymeric materials. The indigenous PA spectrometer used in the present study consists of a 300-W xenon arc lamp, a lock-in amplifier, a chopper, a (1/8)-m monochromator controlled by computer and a home-made PA cell.

Photoluminescence spectroscopy of defects in ZnO nano/microwires

Sun Xiang-Bing(孙香冰), Feng Lin(冯林), and Jiao Xian-Wei(焦现炜)

Chin. Phys. B, 2011, 20 (6): 067804. DOI: 10.1088/1674-1056/20/6/067804

Abstract ( 1320 )

PDF (549KB) ( 913 )

Photoluminescence spectroscopy is used to study defects found in single ZnO nano/microwires at 90 K. The defect, acting as binding site for bound exciton (BX) transition, is represented by B_F, the fractional intensity of the BX peak in the whole near-band edge ultraviolet (UV) luminescence. The concentration of defects as origins of the visible emissions is proportional to the intensity fraction D_F, i.e., the intensity fraction of visible emissions in the sum total of all UV and visible luminescences. By comparing B_F and D_F, it is concluded that the two defects are not correlated to each other. The former kind of defect is considered to be related to the blueshift of the near-band edge peak as the radius of the nano/microwires decreases at room temperature.

Expanding the bandwidth of planar MNG materials with co-directional split-ring resonators

Tang Ming-Chun(唐明春), Xiao Shao-Qiu(肖绍球), Wang Duo(王多), Ge Guang-Ding(葛广顶), Bai Yan-Ying(柏艳英), Zhang Jun-Rui(张俊睿), and Wang Bing-Zhong (王秉中)

Chin. Phys. B, 2011, 20 (6): 067805. DOI: 10.1088/1674-1056/20/6/067805

Abstract ( 1275 )

PDF (780KB) ( 900 )

An effective approach to expand the bandwidth of negative permeability of small-sized planar materials is proposed. Based on qualitative analysis of equivalent circuit models, the fractional bandwidth of an μ-negative (MNG) material is expanded from 3.53% up to 12.87% by adding split-ring resonators (SRRs) and arranging them by proposed steps. Moreover, the experimental results validate the effectiveness of bandwidth-expanding methods, which is promising for the extensive application of metamaterials in the microwave field.

Splitting the surface wave in metal/dielectric nanostructures

Zhu Song(祝颂), Wu Jian(吴坚)

Chin. Phys. B, 2011, 20 (6): 067901. DOI: 10.1088/1674-1056/20/6/067901

Abstract ( 1322 )

PDF (1390KB) ( 765 )

We investigate a modified surface wave splitter with a double-layer structure, which consists of symmetrical metallic grating and an asymmetrical dielectric, using the finite-difference time-domain (FDTD) simulation method. The metal/dielectric interface structure at this two-side aperture can support bound waves of different wavelengths, thus guiding waves in opposite directions. The covered dielectric films play an important role in the enhancement and confinement of the diffraction wave by the waveguide modes. The simulation result shows that the optical intensities of the guided surface wave at wavelengths of 760-nm and 1000-nm are about 100 times and 4～5 times those of the weaker side, respectively, which means that the surface wave is split by the proposed device.

Adsorption of sodium ions and hydrated sodium ions on a hydrophobic graphite surface via cation-$\pi$ interactions

Shi Guo-Sheng(石国升), Wang Zhi-Gang(王志刚), Zhao Ji-Jun(赵纪军), Hu Jun(胡钧), and Fang Hai-Ping(方海平)

Chin. Phys. B, 2011, 20 (6): 068101. DOI: 10.1088/1674-1056/20/6/068101

Abstract ( 1640 )

PDF (3011KB) ( 22597 )

Using density functional theory computation, we show that sodium ions and hydrated sodium ions can be strongly adsorbed onto a hydrophobic graphite surface via cation-$\pi$ interactions. The key to this cation-π interaction is the coupling of the delocalized $\pi$ states of graphite and the empty orbitals of sodium ions. This finding implies that the property of the graphite surface is extremely dependent on the existence of the ions on the surface, suggesting that the hydrophobic property of the graphite surface may be affected by the existence of the sodium ions.

Thickness optimization of Mo films for Cu(InGa)Se₂ solar cell applications

Li Wei (李微), Zhao Yan-Min (赵彦民), Liu Xing-Jiang (刘兴江), Ao Jian-Ping (敖建平), Sun Yun (孙云)

Chin. Phys. B, 2011, 20 (6): 068102. DOI: 10.1088/1674-1056/20/6/068102

Abstract ( 1351 )

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Mo thin films are deposited on soda lime glass (SLG) substrates using DC magnetron sputtering. The Mo film thicknesses are varied from 0.08 μm to 1.5 μm to gain a better understanding of the growth process of the film. The residual stresses and the structural properties of these films are investigated, with attention paid particularly to the film thickness dependence of these properties. Residual stress decreases and yields a typical tensile-to-compressive stress transition with the increase of film thickness at the first stages of film growth. The stress tends to be stable with the further increase of film thickness. Using the Mo film with an optimum thickness of 1 μm as the back contact, the Cu(InGa)Se₂ solar cell can reach a conversion efficiency of 13.15%.

Strained and strain-relaxed epitaxial Ge_1-xSn_x alloys on Si(100) substrates

Wang Wei (汪巍), Su Shao-Jian (苏少坚), Zheng Jun (郑军), Zhang Guang-Ze (张广泽), Zuo Yu-Hua (左玉华), Cheng Bu-Wen (成步文), Wang Qi-Ming (王启明)

Chin. Phys. B, 2011, 20 (6): 068103. DOI: 10.1088/1674-1056/20/6/068103

Abstract ( 1385 )

PDF (3808KB) ( 1356 )

Epitaxial Ge_1-xSn_x alloys are grown separately on a Ge-buffer/Si(100) substrate and directly on a Si(100) substrate by molecular beam epitaxy (MBE) at low temperature. In the case of the Ge buffer/Si(100) substrate, a high crystalline quality strained Ge_0.97Sn_0.03 alloy is grown, with a $\chi_{\min}$ value of 6.7% measured by channeling and random Rutherford backscattering spectrometry (RBS), and a surface root-mean-square (RMS) roughness of 1.568 nm obtained by atomic force microscopy (AFM). In the case of the Si(100) substrate, strain-relaxed Ge_0.97Sn_0.03 alloys are epitaxially grown at 150℃-300℃, with the degree of strain relaxation being more than 96%. The X-ray diffraction (XRD) and AFM measurements demonstrate that the alloys each have a good crystalline quality and a relatively flat surface. The predominant defects accommodating the large misfit are Lomer edge dislocations at the interface, which are parallel to the interface plane and should not degrade electrical properties and device performance.

Circuit-field coupled finite element analysis method for an electromagnetic acoustic transducer under pulsed voltage excitation

Hao Kuan-Sheng(郝宽胜), Huang Song-Ling(黄松岭), Zhao Wei(赵伟), and Wang Shen(王珅)

Chin. Phys. B, 2011, 20 (6): 068104. DOI: 10.1088/1674-1056/20/6/068104

Abstract ( 1319 )

PDF (719KB) ( 1311 )

This paper presents an analytical method for electromagnetic acoustic transducers (EMATs) under voltage excitation and considers the non-uniform distribution of the biased magnetic field. A complete model of EMATs including the non-uniform biased magnetic field, a pulsed eddy current field and the acoustic field is built up. The pulsed voltage excitation is transformed to the frequency domain by fast Fourier transformation (FFT). In terms of the time harmonic field equations of the EMAT system, the impedances of the coils under different frequencies are calculated according to the circuit-field coupling method and Poynting's theorem. Then the currents under different frequencies are calculated according to Ohm's law and the pulsed current excitation is obtained by inverse fast Fourier transformation (IFFT). Lastly, the sequentially coupled finite element method (FEM) is used to calculate the Lorentz force in the EMATs under the current excitation. An actual EMAT with a two-layer two-bundle printed circuit board (PCB) coil, a rectangular permanent magnet and an aluminium specimen is analysed. The coil impedances and the pulsed current are calculated and compared with the experimental results. Their agreement verified the validity of the proposed method. Furthermore, the influences of lift-off distances and the non-uniform static magnetic field on the Lorentz force under pulsed voltage excitation are studied.

Measurement accuracy analysis of the free carrier absorption determination of the electronic transport properties of silicon wafers

Zhang Xi-Ren(张希仁), Gao Chun-Ming(高椿明), Zhou Ying(周鹰), and Wang Zhan-Ping(王占平)

Chin. Phys. B, 2011, 20 (6): 068105. DOI: 10.1088/1674-1056/20/6/068105

Abstract ( 1250 )

PDF (272KB) ( 760 )

By introducing the random and systematic errors in simulated data computed from conventional frequency-scan and laterally resolved modulated free carrier absorption theory models, we investigate the relative determination sensitivities of three electronic transport properties, namely, carrier lifetime, carrier diffusivity and front surface recombination velocity of silicon wafers determined by frequency-scan and laterally resolved techniques. The phase and amplitude data with random errors as functions of the modulation frequency at zero pump-probe-beam separation or of the two-beam separation at four different modulation frequencies are simultaneously fitted to an appreciated carrier diffusion model to extract three transport parameters. The statistical results and fitted accuracies of the transport parameter determined by both techniques are theoretically analysed. Corresponding experimental results are carried out to compare to the simulated results. The simulated and experimental results show that the determination of the transport properties of silicon wafers by the laterally resolved technique are more accurate, as compared with that by the frequency-scan technique.

Viscosity of aluminum under shock-loading conditions

Ma Xiao-Juan (马小娟), Liu Fu-Sheng (刘福生), Zhang Ming-Jian (张明建), Sun Yan-Yun (孙燕云)

Chin. Phys. B, 2011, 20 (6): 068301. DOI: 10.1088/1674-1056/20/6/068301

Abstract ( 1272 )

PDF (987KB) ( 865 )

A reliable data treatment method is critical for viscosity measurements using the disturbance amplitude damping method of shock waves. In this paper the finite difference method is used to obtain the numerical solutions for the disturbance amplitude damping behaviour of the sinusoidal shock front in a flyer-impact experiment. The disturbance amplitude damping curves are used to depict the numerical solutions of viscous flow. By fitting the experimental data to the numerical solutions of different viscosities, we find that the effective shear viscosity coefficients of shocked aluminum at pressures of 42, 78 and 101 GPa are (1500±100) Pa·s, (2800±100) Pa·s and (3500±100) Pa·s respectively. It is clear that the shear viscosity of aluminum increases with an increase in shock pressure, so aluminum does not melt below a shock pressure of 101 GPa. This conclusion is consistent with the sound velocity measurement.

An interconnecting bus power optimization method combining interconnect wire spacing with wire ordering

Zhu Zhang-Ming (朱樟明), Hao Bao-Tian (郝报田), En Yun-Fei (恩云飞), Yang Yin-Tang (杨银堂), Li Yue-Jin (李跃进)

Chin. Phys. B, 2011, 20 (6): 068401. DOI: 10.1088/1674-1056/20/6/068401

Abstract ( 1090 )

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On-chip interconnect buses consume tens of percents of dynamic power in a nanometer scale integrated circuit and they will consume more power with the rapid scaling down of technology size and continuously rising clock frequency, therefore it is meaningful to lower the interconnecting bus power in design. In this paper, a simple yet accurate interconnect parasitic capacitance model is presented first and then, based on this model, a novel interconnecting bus optimization method is proposed. Wire spacing is a process for spacing wires for minimum dynamic power, while wire ordering is a process that searches for wire orders that maximally enhance it. The method, i.e., combining wire spacing with wire ordering, focuses on bus dynamic power optimization with a consideration of bus performance requirements. The optimization method is verified based on various nanometer technology parameters, showing that with 50% slack of routing space, 25.71% and 32.65% of power can be saved on average by the proposed optimization method for a global bus and an intermediate bus, respectively, under a 65-nm technology node, compared with 21.78% and 27.68% of power saved on average by uniform spacing technology. The proposed method is especially suitable for computer-aided design of nanometer scale on-chip buses.

Effects of the insulated magnetic field and oblique incidence of electrons on the multipactor in MILO

Fan Jie-Qing(范杰清) and Hao Jian-Hong(郝建红)

Chin. Phys. B, 2011, 20 (6): 068402. DOI: 10.1088/1674-1056/20/6/068402

Abstract ( 1300 )

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The theoretical analysis and actual performance of the single-surface multipactor discharge model in the presence of a magnetic field are conducted through simulations. The effects of the magnitude of the insulated magnetic field and the oblique incidence of electrons on the multipactor are analysed. The results show that the multipactor susceptibility region shrinks gradually as the magnetic field increases when the electron cyclotron frequency is close to the RF frequency of the electric field. As a result, the evolution of the multipactor discharge will reach saturation earlier and become saturated at a higher level than the case when the magnetic field is absent, but the change of evolution and saturation as the insulated magnetic field increases is not obvious.

First principles simulation technique for characterizing single event effects

Zhang Ke-Ying (张科营), Guo Hong-Xia (郭红霞), Luo Yin-Hong (罗尹虹), Fan Ru-Yu (范如玉), Chen Wei (陈伟), Lin Dong-Sheng (林东生), Guo Gang (郭刚), Yan Yi-Hua (闫逸华)

Chin. Phys. B, 2011, 20 (6): 068501. DOI: 10.1088/1674-1056/20/6/068501

Abstract ( 1281 )

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This paper develops a new simulation technique to characterize single event effects on semiconductor devices. The technique used to calculate the single event effects is developed according to the physical interaction mechanism of a single event effect. An application of the first principles simulation technique is performed to predict the ground-test single event upset effect on field-programmable gate arrays based on 0.25 μm advanced complementary metal-oxide-semiconductor technology. The agreement between the single event upset cross section accessed from a broad-beam heavy ion experiment and simulation shows that the simulation technique could be used to characterize the single event effects induced by heavy ions on a semiconductor device.

Fabrication of 160-nm T-gate metamorphic AlInAs/GaInAs HEMTs on GaAs substrates by metal organic chemical vapour deposition

Li Hai-Ou(李海鸥), Huang Wei(黄伟), Tang Chak Wah(邓泽华), Deng Xiao-Fang(邓小芳), and Lau Kei May(刘纪美)

Chin. Phys. B, 2011, 20 (6): 068502. DOI: 10.1088/1674-1056/20/6/068502

Abstract ( 1451 )

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The fabrication and performance of 160-nm gate-length metamorphic AlInAs/GaInAs high electron mobility transistors (mHEMTs) grown on GaAs substrate by metal organic chemical vapour deposition (MOCVD) are reported. By using a novel combined optical and e-beam photolithography technology, submicron mHEMTs devices have been achieved. The devices exhibit good DC and RF performance. The maximum current density was 817 mA/mm and the maximum transconductance was 828 mS/mm. The non-alloyed Ohmic contact resistance R_c was as low as 0.02 Ωmm. The unity current gain cut-off frequency (f_T) and the maximum oscillation frequency (f_max) were 146 GHz and 189 GHz, respectively. This device has the highest f_T yet reported for a 160-nm gate-length HEMTs grown by MOCVD. The output conductance is 28.9 mS/mm, which results in a large voltage gain of 28.6. Also, an input capacitance to gate-drain feedback capacitance ratio, Cgs/Cgd, of 4.3 is obtained in the device.

Imaging properties of a tetra wedge readout

Liu Yong-An (刘永安), Yan Qiu-Rong (鄢秋荣), Sai Xiao-Feng (赛小锋), Wei Yong-Lin (韦永林), Sheng Li-Zhi (盛立志), Yang Hao (杨颢), Hu Hui-Jun (胡慧君), Zhao Bao-Sheng (赵宝升)

Chin. Phys. B, 2011, 20 (6): 068503. DOI: 10.1088/1674-1056/20/6/068503

Abstract ( 1317 )

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The decoding principle of a tetra wedge anode, which is a development of the wedge and strip anode, is described. The influence of charge cloud size on decoding accuracy is studied using the Monte Carlo method. Simulation results show that the decoding error is large when the size of charge clouds collected by the anode is small. Thus, the charge clouds collected by the tetra wedge anode should reach a necessary size to ensure accurate decoding. Finally, using the ultraviolet photon counting imaging system, the linearity and the spatial resolution of the system are tested. Experimental results show that the system has a good linearity and the spatial resolution is better than 100 μm.

Performance improvement of MEH-PPV:PCBM solar cells using bathocuproine and bathophenanthroline as the buffer layers

Liu Xiao-Dong(刘晓东), Zhao Su-Ling (赵谡玲), Xu Zheng(徐征), Zhang Fu-Jun(张福俊), Zhang Tian-Hui(张天慧), Gong Wei(龚伟), Yan Guang(闫光), Kong Chao(孔超), Wang Yong-Sheng(王永生), and Xu Xu-Rong(徐叙瑢)

Chin. Phys. B, 2011, 20 (6): 068801. DOI: 10.1088/1674-1056/20/6/068801

Abstract ( 1501 )

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In this work, bathocuproine (BCP) and bathophenanthroline (Bphen), commonly used in small-molecule organic solar cells (OSCs), are adopted as the buffer layers to improve the performance of the polymer solar cells (PSCs) based on poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV): [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) bulk heterojunction. By inserting BCP or Bphen between the active layer and the top cathode, all the performance parameters are dramatically improved. The power conversion efficiency is increased by about 70% and 120% with 5-nm BCP and 12-nm Bphen layers, respectively, when compared with that of the devices without any buffer layer. The performance enhancement is attributed to BCP or Bphen (i) increasing the optical field, and hence the absorption in the active layer, (ii) effectively blocking the excitons generated in MEH-PPV from quenching at organic/aluminum (Al) interface due to the large band-gap of BCP or Bphen, which results in a significant reduction in series resistance (R_s), and (iii) preventing damage to the active layer during the metal deposition. Compared with the traditional device using LiF as the buffer layer, the BCP-based devices show a comparable efficiency, while the Bphen-based devices show a much larger efficiency. This is due to the higher electron mobility in Bphen than that in BCP, which facilitates the electron transport and extraction through the buffer layer to the cathode.

Generalized unscented Kalman filtering based radial basis function neural network for the prediction of ground radioactivity time series with missing data

Wu Xue-Dong(伍雪冬), Wang Yao-Nan(王耀南), Liu Wei-Ting(刘维亭), and Zhu Zhi-Yu(朱志宇)

Chin. Phys. B, 2011, 20 (6): 069201. DOI: 10.1088/1674-1056/20/6/069201

Abstract ( 1264 )

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On the assumption that random interruptions in the observation process are modeled by a sequence of independent Bernoulli random variables, we firstly generalize two kinds of nonlinear filtering methods with random interruption failures in the observation based on the extended Kalman filtering (EKF) and the unscented Kalman filtering (UKF), which were shortened as GEKF and GUKF in this paper, respectively. Then the nonlinear filtering model is established by using the radial basis function neural network (RBFNN) prototypes and the network weights as state equation and the output of RBFNN to present the observation equation. Finally, we take the filtering problem under missing observed data as a special case of nonlinear filtering with random intermittent failures by setting each missing data to be zero without needing to pre-estimate the missing data, and use the GEKF-based RBFNN and the GUKF-based RBFNN to predict the ground radioactivity time series with missing data. Experimental results demonstrate that the prediction results of GUKF-based RBFNN accord well with the real ground radioactivity time series while the prediction results of GEKF-based RBFNN are divergent.

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