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Chin. Phys. B  
  Chin. Phys. B--2008, Vol.17, No.9
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Conformal invariance and conserved quantity of Hamilton systems

Cai Jian-Le, Luo Shao-Kai, Mei Feng-Xiang
Chin. Phys. B, 2008, 17 (9): 3170-3174 doi: 10.1088/1674-1056/17/9/002
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This paper studies conformal invariance and conserved quantities of Hamilton system. The definition and the determining equation of conformal invariance for Hamilton system are provided. The relationship between the conformal invariance and the Lie symmetry are discussed, and the necessary and sufficient condition that the conformal invariance would be the Lie symmetry of the system under the infinitesimal one-parameter transformation group is deduced. It gives the conserved quantities of the system and an example for illustration.

Weak Noether symmetry for nonholonomic systems of non-Chetaev type

Xie Jia-Fang, Gang Tie-Qiang, Mei Feng-Xiang
Chin. Phys. B, 2008, 17 (9): 3175-3179 doi: 10.1088/1674-1056/17/9/003
Full Text: [PDF 155 KB] (Downloads:716)
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Based on the weak Noether symmetry proposed by Mei F X, this paper discusses the weak Noether symmetry for nonholonomic system of non-Chetaev type, and presents expressions of three kinds of conserved quantities by weak Noether symmetry. Finally, the application of this new results is showed by a practical example.

Conformal invariance and Hojman conservedquantities of first order Lagrange systems

Chen Xiang-Wei, Liu Chang, Mei Feng-Xiang
Chin. Phys. B, 2008, 17 (9): 3180-3184 doi: 10.1088/1674-1056/17/9/004
Full Text: [PDF 148 KB] (Downloads:765)
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In this paper the conformal invariance by infinitesimal transformations of first order Lagrange systems is discussed in detail. The necessary and sufficient conditions of conformal invariance and Lie symmetry simultaneously by the action of infinitesimal transformations are given. Then it gets the Hojman conserved quantities of conformal invariance by the infinitesimal transformations. Finally an example is given to illustrate the application of the results.

Simulation solution for micro droplet impingementon a flat dry surface

Sun Zhen-Hai, Han Rui-Jing
Chin. Phys. B, 2008, 17 (9): 3185-3188 doi: 10.1088/1674-1056/17/9/005
Full Text: [PDF 996 KB] (Downloads:1629)
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This paper presents a computational fluid dynamics approach for micro droplet impacting on a flat dry surface. A two-phase flow approach is employed using FLUENT VOF multiphase model to calculate the flow distributions upon impact. The contact line velocity is tracked to calculate the dynamic contact angle through user defined function program. The study showed that the treatment of contact line velocity is crucial for the accurate prediction of droplet impacting on poor wettability surfaces. On the other hand, it has much less influence on the simulation of droplet impacting on good wettability surfaces. Good fit between simulation results and experimental data is obtained using this model.

Teleportation attack on the QSDC protocol with a random basis and order

Gao Fei, Wen Qiao-Yan, Zhu Fu-Chen
Chin. Phys. B, 2008, 17 (9): 3189-3193 doi: 10.1088/1674-1056/17/9/006
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The quantum secure direct communication (QSDC) protocol with a random basis and order is analysed and an effective attack, i.e. teleportation attack, is presented. An eavesdropper can obtain half of the transmitted secret bits with the help of this special attack. It is shown that quantum teleportation can be employed to weaken the role of the order-rearrangement encryption at least in a certain circumstance. Meanwhile, a possible improvement on this protocol is proposed, which makes it secure against this kind of attack.

Indistinguishability of orthogonal time-separated bell states

Tan Yong-Gang, Cai Qing-Yu, Shi Ting-Yun
Chin. Phys. B, 2008, 17 (9): 3194-3197 doi: 10.1088/1674-1056/17/9/007
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This paper proves that it is impossible to identify orthogonally time-separated Bell states. If two qubits of a Bell state interact with the measurement apparatus at different time, any attempt to identify this state will disturb it.

A study on entanglement dynamics for a four-qubit model

Man Zhong-Xiao, Xia Yun-Jie
Chin. Phys. B, 2008, 17 (9): 3198-3202 doi: 10.1088/1674-1056/17/9/008
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In this paper, we consider the entanglement dynamics of a four-qubit model [2006 {\em Phys. Rev.} A \textbf{74} 042328] where two entangled qubits a and b locally interact with separate qubits A and B via the spin-exchange-like Hamiltonian. We study the effect of purity of initial entangled state of qubits a, b on the entanglement evolution and its relation with energy transfer. Also, we find that the total bipartite entanglement of qubits a, b plus A, B is not a constant any longer when the initial entangled state of a, b is not pure, which is a complement to the result in the paper [2007 {\em J. Phys.} B \textbf{40} S45] for the pure case.

Teleportation of arbitrary unknown two-atom statewith cluster state via thermal cavity

Zhang Wen, Liu Yi-Min, Liu Jun, Zhang Zhan-Jun
Chin. Phys. B, 2008, 17 (9): 3203-3208 doi: 10.1088/1674-1056/17/9/009
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This paper proposes a scheme for implementing the teleportation of an arbitrary unknown two-atom state by using a cluster state of four identical 2-level atoms as quantum channel in a thermal cavity. The two distinct advantages of the present scheme are: (i) The discrimination of 16 orthonormal cluster states in the standard teleportation protocol is transformed into the discrimination of single-atom states. Consequently, the discrimination difficulty of states is degraded. (ii) The scheme is insensitive to the cavity field state and the cavity decay for the thermal cavity is only virtually excited when atoms interact with it. Thus, the scheme is more feasible.

The periodic death and anabiosis of the entanglement between two moving atoms

Deng Xiao-Juan, Fang Mao-Fa
Chin. Phys. B, 2008, 17 (9): 3209-3213 doi: 10.1088/1674-1056/17/9/010
Full Text: [PDF 353 KB] (Downloads:687)
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This paper investigates the periodic death and anabiosis of the entanglement between two moving atoms interacting with the mode field, and discusses the influences of the atomic motion and the parameter of the mode field. The results show that, the atomic motion leads to the periodic death and anabiosis of the entanglement between two moving atoms, the time of the death and the amplitude of the anabiosis of the entanglement between two moving atoms depend on the initial states of two moving atoms and the parameter of the mode field.

Exact bound state solutions of the Klein--Gordonparticle in Hulth\'{e}n potential

Zhang Min-Cang
Chin. Phys. B, 2008, 17 (9): 3214-3216 doi: 10.1088/1674-1056/17/9/011
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In this paper, the Klein--Gordon equation with the spherical symmetric Hulth\'{e}n potential is turned into a hypergeometric equation and is solved in the framework of function analysis exactly. The corresponding bound state solutions are expressed in terms of the hypergeometric function, and the energy spectrum of the bound states is obtained as a solution to a given equation by boundary constraints.

Generation of four-photon W state via cavity QED

Zhong Zhi-Rong
Chin. Phys. B, 2008, 17 (9): 3217-3219 doi: 10.1088/1674-1056/17/9/012
Full Text: [PDF 162 KB] (Downloads:543)
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This paper proposes an alternative scheme for generating four-photon W state via cavity QED. The scheme bases on the resonant interaction of a \Lambda -type three level atom with two bimodal cavities. The detection of atom collapses the cavity to the desired state. Comparing with previous schemes, the advantage of this scheme is that the interaction time can be greatly shortened since it uses the resonant interaction between atom and cavities. Moreover, the proposed scheme is more experimentally feasible than the previous ones.

A quantum search algorithm of two entangled registers to realize quantum discrete Fouriertransform of signal processing

Pang Chao-Yang, Hu Ben-Qiong(
Chin. Phys. B, 2008, 17 (9): 3220-3226 doi: 10.1088/1674-1056/17/9/013
Full Text: [PDF 220 KB] (Downloads:576)
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The discrete Fourier transform (DFT) is the base of modern signal processing. 1-dimensional fast Fourier transform (1D FFT) and 2D FFT have time complexity O(N\log N)$ and O(N^{2}\log N) respectively. Since 1965, there has been no more essential breakthrough for the design of fast DFT algorithm. DFT has two properties. One property is that DFT is energy conservation transform. The other property is that many DFT coefficients are close to zero. The basic idea of this paper is that the generalized Grover's iteration can perform the computation of DFT which acts on the entangled states to search the big DFT coefficients until these big coefficients contain nearly all energy. One-dimensional quantum DFT (1D QDFT) and two-dimensional quantum DFT (2D QDFT) are presented in this paper. The quantum algorithm for convolution estimation is also presented in this paper. Compared with FFT, 1D and 2D QDFT have time complexity O(\sqrt{N}) and $O(N)$ respectively. QDFT and quantum convolution demonstrate that quantum computation to process classical signal is possible.

Kinetics investigations for holographic Bragg gratingbased on polymer dispersed liquid crystal

Zheng Zhi-Gang, Song Jing, Zhang Ling-Li, Liu Yong-Gang, Guo Fu-Zhong, Ma Ji, Li Wen-Cui, Deng Shu-Peng, Xuan Li
Chin. Phys. B, 2008, 17 (9): 3227-3235 doi: 10.1088/1674-1056/17/9/014
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This paper investigates the monomer kinetics of polymer dispersed liquid crystal (PDLC) grating. Fourier transform infrared (FTIR) spectra are used in the studies of photoreaction kinetics. The results indicate that there is a relative stable stage arises after a very short initial stage. Based on FTIR studies, the monomer diffusion equation is deduced and necessary numerical simulations are carried out to analyse the monomer conversion which is an important point to improve phase separation structure of PDLC grating. Some simulation results have a good agreement with experimental data. In addition, the effects induced by monomer diffusion constant $D$ and diffusion--polymerization-ratio rate $R$ are discussed. Results show that monomer conversion can be improved by increasing value of $D$. Besides, a good equilibrium state ($R=1$) is more beneficial to the diffusion of monomer which is important in the process of phase separation.

Thermodynamic stability of a weakly interactingFermi gas trapped in a harmonic potential

Men Fu-Dian, Liu Hui, Zhu Hou-Yu
Chin. Phys. B, 2008, 17 (9): 3236-3240 doi: 10.1088/1674-1056/17/9/015
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Based on the theoretical results derived from pseudopotential method and local approximation, this paper studies the thermodynamic stability of a weakly interacting Fermi gas trapped in a harmonic potential by using analytical method of thermodynamics. The effects of the interparticle interactions as well as external potential on the thermodynamic stability of the system are discussed. It is shown that the system is stable as for the complete average, but as for local parts, the system is unstable anywhere. This instability shows that the stability conditions of mechanics cannot be satisfied anywhere, and the stability conditions of thermostatics cannot be satisfied somewhere. In addition, the interactions and external potential have direct effects on the local stability of the system.

GEKF, GUKF and GGPF based prediction of chaotic time-series with additive and multiplicative noises

Wu Xue-Dong, Song Zhi-Huan
Chin. Phys. B, 2008, 17 (9): 3241-3246 doi: 10.1088/1674-1056/17/9/016
Full Text: [PDF 336 KB] (Downloads:566)
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On the assumption that random interruptions in the observation process are modelled by a sequence of independent Bernoulli random variables, this paper generalize the extended Kalman filtering (EKF), the unscented Kalman filtering (UKF) and the Gaussian particle filtering (GPF) to the case in which there is a positive probability that the observation in each time consists of noise alone and does not contain the chaotic signal (These generalized novel algorithms are referred to as GEKF, GUKF and GGPF correspondingly in this paper). Using weights and network output of neural networks to constitute state equation and observation equation for chaotic time-series prediction to obtain the linear system state transition equation with continuous update scheme in an online fashion, and the prediction results of chaotic time series represented by the predicted observation value, these proposed novel algorithms are applied to the prediction of Mackey--Glass time-series with additive and multiplicative noises. Simulation results prove that the GGPF provides a relatively better prediction performance in comparison with GEKF and GUKF.

Novel four-wing and eight-wing attractors using coupled chaotic Lorenz systems

Giuseppe Grassi
Chin. Phys. B, 2008, 17 (9): 3247-3251 doi: 10.1088/1674-1056/17/9/017
Full Text: [PDF 272 KB] (Downloads:723)
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This paper presents the problem of generating four-wing (eight-wing) chaotic attractors. The adopted method consists in suitably coupling two (three) identical Lorenz systems. In analogy with the original Lorenz system, where the two wings of the butterfly attractor are located around the two equilibria with the unstable pair of complex-conjugate eigenvalues, this paper shows that the four wings (eight wings) of these novel attractors are located around the four (eight) equilibria with two (three) pairs of unstable complex-conjugate eigenvalues.

One new fractional-order chaos system and its circuit simulation by electronic workbench

Zhou Ping, Cheng Xue-Feng, Zhang Nian-Ying
Chin. Phys. B, 2008, 17 (9): 3252-3257 doi: 10.1088/1674-1056/17/9/018
Full Text: [PDF 383 KB] (Downloads:1018)
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This paper proposes a new chaotic system and its fractional-order chaotic system. The necessary condition for the existence of chaotic attractors in this new fractional-order system is obtained. It finds that this new fractional-order system is chaotic for $q>0.783$ if the system parameter $m$=6. The chaotic attractors for $q$=0.8, and $q$=0.9 are obtained. A circuit is designed to realize its fractional-order chaos system for $q$=0.9 by electronic workbench.

Chaotic ferroresonance in a non-autonomous circuit

Hui Meng, Zhang Yan-Bin, Liu Chong-Xin
Chin. Phys. B, 2008, 17 (9): 3258-3263 doi: 10.1088/1674-1056/17/9/019
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Accurate description of magnetization curve has important effect on ferroresonance. In most of earlier ferroresonance studies the magnetization curve is modelled as a 3rd or 5th order polynomial. However, it is not comprehensive. This paper investigates the chaotic ferroresonance behaviour exhibited by a non-autonomous circuit which contains a nonlinear flux-controlled inductance. The ferromagnetic characteristic of this nonlinear inductance represented by a magnetization curve could be expressed as an $n$th order two-term polynomial. By varying the value of exponent $n$, the circuit can assume a diverse range of steady-state regimes including fundamental and subharmonic ferroresonance, quasi-periodic oscillations, and chaos. A detailed analysis of some simulations demonstrates that the probability of chaos increases as the exponent of the magnetization curve rises. The effect of varying the magnitude of the source voltage on the chaotic behaviour of the circuit is also studied.

Improving performance of optical fibre chaotic communication by dispersion compensation techniques

Zhang Jian-Zhong, Wang Yun-Cai, Wang An-Bang
Chin. Phys. B, 2008, 17 (9): 3264-3269 doi: 10.1088/1674-1056/17/9/020
Full Text: [PDF 238 KB] (Downloads:604)
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This paper numerically investigates the effects of dispersion on optical fibre chaotic communication, and proposes a dispersion compensation scheme to improve the performance of optical fibre chaotic communication system. The obtained results show that the transmitter--receiver synchronization progressively degrades and the signal-to-noise ratio of the recovered message deteriorates as the fibre length increases due to the dispersion accumulation. Two segments of 2.5-km dispersion-compensating fibres are symmetrically placed at both ends of a segment of 245-km nonzero dispersion-shifted fibre with low dispersion in one compensation period. The numerical results show that the signal-to-noise ratio of the extracted 1\,GHz sinusoidal message is improved from --2.92\,dB to 15.38\,dB by this dispersion compensation for the transmission distance of 500\,km.

Hyperchaos of two coupled Bose--Einstein condensates with a three-body interaction

Wang Zhi-Xia, Zhang Xi-He, Shen Ke
Chin. Phys. B, 2008, 17 (9): 3270-3275 doi: 10.1088/1674-1056/17/9/021
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We investigate the dynamics of two tunnel-coupled Bose--Einstein condensates (BECs) in a double-well potential. The effects of the three-body recombination loss and the feeding of the condensates from the thermal cloud are studied in the case of attractive interatomic interaction. An imaginary three-body interaction term is considered and a two-mode approximation is used to derive three coupled equations which describe the total atomic numbers of the two condensates, the relative population and relative phase respectively. Theoretical analyses and numerical calculations demonstrate the existence of chaotic and hyperchaotic behaviour by using a periodically time-varying scattering length.

Low-temperature heat capacities and standard molar enthalpy of formation of 4-(2-aminoethyl)-phenol (C8H11NO)

Di You-Ying, Kong Yu-Xia, Yang Wei-Wei, Tan Zhi-Cheng
Chin. Phys. B, 2008, 17 (9): 3276-3283 doi: 10.1088/1674-1056/17/9/022
Full Text: [PDF 193 KB] (Downloads:640)
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This paper reports that low-temperature heat capacities of 4-(2-aminoethyl)-phenol (C_{8}H_{11}NO) are measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 400\,K. A polynomial equation of heat capacities as a function of the temperature was fitted by the least square method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15\,K were calculated and tabulated at the interval of 5\,K. The energy equivalent, \textit{\varepsilon }_{\rm calor}, of the oxygen-bomb combustion calorimeter has been determined from 0.68\,g of NIST 39i benzoic acid to be \textit{ \varepsilon }_{\rm calor}=(14674.69\pm 17.49)J \cdot K^{ - 1}. The constant-volume energy of combustion of the compound at T=298.15\,K was measured by a precision oxygen-bomb combustion calorimeter to be \Delta _{\rm c}U=--(32374.25\pm 12.93)J \cdot g^{ - 1}. The standard molar enthalpy of combustion for the compound was calculated to be \Delta _{\rm c} H_{\rm m}^\ominus = { - }(4445.47\pm 1.77)\,{\rm kJ} \cdot \mbox{mol}^{{ - 1}} according to the definition of enthalpy of combustion and other thermodynamic principles. Finally, the standard molar enthalpy of formation of the compound was derived to be \Delta _{\rm f} H_{\rm m}^\ominus (\rm C_8 H_{11} NO,s){ = - (274.68}\pm 2\mbox{.06)\,kJ} \cdot \mbox{mol}^{{\rm - 1}}, in accordance with Hess law.

Phase transition in evolution of traffic flow with scale-free property

Shen Bo, Gao Zi-You
Chin. Phys. B, 2008, 17 (9): 3284-3288 doi: 10.1088/1674-1056/17/9/023
Full Text: [PDF 461 KB] (Downloads:613)
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This paper investigates the behaviour of traffic flow in traffic systems with a new model based on the NaSch model and cluster approximation of mean-field theory. The proposed model aims at constructing a mapping relationship between the microcosmic behaviour and the macroscopic property of traffic flow. Results demonstrate that scale-free phenomenon of the evolution network becomes obvious when the density value of traffic flow reaches at the critical point of phase transition from free flow to traffic congestion, and jamming is limited in this scale-free structure.

Study of superstructure II in multiferroic BiMnO3

Ge Bing-Hui, Li Fang-Hua, Li Xue-Ming, Wang Yu-Mei, Chi Zhen-Hua, Jin Chang-Qing
Chin. Phys. B, 2008, 17 (9): 3163-3169 doi: 10.1088/1674-1056/17/9/001
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The crystal structure of the minor phase, named superstructure II, existing in multiferroic compound BiMnO3 has been studied by electron diffraction and high-resolution transmission electron microscopy. Domains of major and minor phases coexisting in BiMnO3 were observed in high-resolution electron microscope images. The unit cell of minor phase was determined to be triclinic with the size 4\times 4\times 4 times as large as the distorted perovskite subcell. The [111] and [10\bar {1}] projected structure maps of the minor phase have been derived from the corresponding images by means of the image processing. A possible rough three-dimensional (3D) structure model was proposed based on the 3D structural information extracted from the two projected structure maps. Since there is no inversion centre in the proposed model, the minor phase may contribute to the ferroelectric property of BiMnO3.

3PF2 neutron superfluidity in neutron stars and three-body force effect

Cui Chang-Xi, Zuo Wei, H. J. Schulze
Chin. Phys. B, 2008, 17 (9): 3289-3293 doi: 10.1088/1674-1056/17/9/024
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We investigate the 3PF2 neutron superfluidity in β-stable neutron star matter and neutron stars by using the BCS theory and the Brueckner--Hartree--Fock approach. We adopt the Argonne V18 potential supplemented with a microscopic three-body force as the realistic nucleon--nucleon interaction. We have concentrated on studying the three-body force effect on the 3PF2 neutron pairing gap. It is found that the three-body force effect is to enhance remarkably the 3PF2 neutron superfluidity in neutron star matter and neutron stars.

Finite-dimensional even and odd nonlinear pair coherent states and their some nonclassical properties

Meng Xiang-Guo, Wang Ji-Suo, Liu Tang-Kun
Chin. Phys. B, 2008, 17 (9): 3350-3357 doi: 10.1088/1674-1056/17/9/034
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In this paper a new class of finite-dimensional even and odd nonlinear pair coherent states (EONLPCSs), which can be realized via operating the superposed evolution operators $D_\pm (\tau )$ on the state $\left| {q,0} \right\rangle $, is constructed, then their orthonormalized property, completeness relations and some nonclassical properties are discussed. It is shown that the finite-dimensional EONLPCSs possess normalization and completeness relations. Moreover, the finite-dimensional EONLPCSs exhibit remarkably different sub-Poissonian distributions and phase probability distributions for different values of parameters $q$, $\eta $ and $\xi $.

The dispersive properties of an excited-doubletfour-level atomic system

Hu Zheng-Feng, Deng Jian-Liao, Wang Yu-Zhu
Chin. Phys. B, 2008, 17 (9): 3358-3362 doi: 10.1088/1674-1056/17/9/035
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We have investigated the dispersive properties of excited-doublet four-level atoms interacting with a weak probe field and an intense coupling laser field. We have derived an analytical expression of the dispersion relation for a general excited-doublet four-level atomic system subject to a one-photon detuning. The numerical results demonstrate that for a typical rubidium $\rm {D1}$ line configuration, due to the unequal dipole moments for the transitions of each ground state to double excited states, generally there exists no exact dark state in the system. Close to the two-photon resonance, the probe light can be absorbed or gained and propagate in the so-called superluminal form. This system may be used as an optical switch.

Influence of patterned TiO2/SiO2 dielectric multilayers for back and front mirror facetson GaN-based laser diodes

Chen Wei-Hua, Hu Xiao-Dong, Dai Tao, Li Rui, Ye Xue-Min, Zhao Tai-Ping, Du Wei-Min, Yang Zhi-Jian, Zhang Guo-Yi
Chin. Phys. B, 2008, 17 (9): 3363-3366 doi: 10.1088/1674-1056/17/9/036
Full Text: [PDF 1927 KB] (Downloads:818)
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Ridge InGaN multi-quantum-well-structure (MQW) edge-emitting laser diodes (LDs) were grown on (0001) sapphire substrates by low-pressure metal-organic chemical vapour deposition (MOCVD). The dielectric TiO$_{2}$/SiO$_{2}$ front and back facet coatings as cavity mirror facets of the LDs have been deposited with electron-beam evaporation method. The reflectivity of the designed front coating is about 50{\%} and that of the back high reflective coating is as high as 99.9{\%}. Under pulsed current injection at room temperature, the influences of the dielectric facets were discussed. The threshold current of the ridge GaN-based LDs was decreased after the deposition of the back high reflective dielectric mirrors and decreased again after the front facets were deposited. Above the threshold, the slope efficiency of the LDs with both reflective facets was larger than those with only back facets and without any reflective facets. It is important to design the reflectivity of the front facets for improving the performance of GaN-based LDs.

Study on the optical limiting properties of the mixed liquid of carbon black suspensions and green tea solution by multi-pulse laser

Niu Yan-Xiong, Yang Hai-Lin, Zhang Peng, Shen Xue-Ju, Jiang Nan, Chen Yan, Tang Fang
Chin. Phys. B, 2008, 17 (9): 3367-3371 doi: 10.1088/1674-1056/17/9/037
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The optical limiting properties of the mixed liquid of carbon black suspensions (CBS) and green tea solution were studied by using an 8 ns laser pulse at 532\,nm. The optical limiting effects of the CBS and mixed liquid have been compared between 5 and 10\,Hz repetition frequencies with nanosecond laser pulse. The experimental results indicate that the optical limiting threshold of the sample with the incidence laser at 10\,Hz repetition frequency is lower than at 5\,Hz repetition frequency. The possible reasons for the influence of the repetition frequency on the samples are discussed. And by observing the optical radiant distributions when the laser pulse passing through different samples, a possible mechanism for the observed effects is suggested. At the same time, the result shows that the optical limiting of CBS is the dominant factor to optical limiting of the mixed liquid.

Effects of vapour bubbles on acoustic and temperature distributions of therapeutic ultrasound

Fan Ting-Bo, Zhang Dong, Zhang Zhe, Ma Yong, Gong Xiu-Fen
Chin. Phys. B, 2008, 17 (9): 3372-3377 doi: 10.1088/1674-1056/17/9/038
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This paper describes the evolution of vapour bubbles and its effect on nonlinear ultrasound propagation and temperature rise through tissues for therapeutic ultrasound. An acoustic-thermo coupling algorithm incorporating nonlinearity, diffraction, and temperature-dependent tissue properties, is employed to describe nonlinear ultrasound propagation and thermal effect. Results demonstrate that an obvious migration of peak pressure toward transducer surface is observed while the position of peak temperature changes little in liver tissue before the generation of vapour bubbles, and that the boiling region enlarges towards the surface of transducer in axial direction but increases slowly in radial direction after the generation of vapour bubbles.

The dynamic characters of excitations in aone-dimensional Frenkel--Kontorova model

Gao Xiu-Yun, Hong Xue-Ren, Wang Cang-Long, Duan Wen-Shan
Chin. Phys. B, 2008, 17 (9): 3378-3386 doi: 10.1088/1674-1056/17/9/039
Full Text: [PDF 1331 KB] (Downloads:478)
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A one-dimensional (1D) Frenkel--Kontorova (FK) model is studied numerically in this paper, and two new analytical solutions (a supersonic kink and a nonlinear periodic wave) of the Sine--Gordon (SG) equation (continuum limit approximation of the FK model) are obtained by using the Jacobi elliptic function expansion method. Taking these new solutions as initial conditions for the FK model, we numerically find there exist the supersonic kink and the nonlinear periodic wave in these systems and obtain a lot of interesting and significant results. Moreover, we also investigate the subsonic kink and the breather in these systems and obtain some new feature.

Second-order solutions for random interfacial waves in N-layer density-stratified fluid with steady uniform currents

Chen Xiao-Gang, Guo Zhi-Ping, Song Jin-Bao
Chin. Phys. B, 2008, 17 (9): 3387-3393 doi: 10.1088/1674-1056/17/9/040
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In the present paper, the random interfacial waves in $N$-layer density-stratified fluids moving at different steady uniform speeds are researched by using an expansion technique, and the second-order asymptotic solutions of the random displacements of the density interfaces and the associated velocity potentials in $N$-layer fluid are presented based on the small amplitude wave theory. The obtained results indicate that the wave--wave second-order nonlinear interactions of the wave components and the second-order nonlinear interactions between the waves and currents are described. As expected, the solutions include those derived by Chen (2006) as a special case where the steady uniform currents of the $N$-layer fluids are taken as zero, and the solutions also reduce to those obtained by Song (2005) for second-order solutions for random interfacial waves with steady uniform currents if $N = 2$.

Two-electron and one-photon transitions in highly charged nickel-like ions

Xie Lu-You, Dong Chen-Zhong, Jiang Jun, Wan Jian-Jie, Yan Jun
Chin. Phys. B, 2008, 17 (9): 3294-3299 doi: 10.1088/1674-1056/17/9/025
Full Text: [PDF 552 KB] (Downloads:575)
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This paper calculates the transition wavelengths and probabilities of the two-electron and one-photon (TEOP) transition from the $(3{\rm s}^{-1}_{1/2}4{\rm d}_{j})_{J=1,2}$ to $(3{\rm p}^{-1}_{3/2}4{\rm s}_{1/2})_{J=1}$ and the $(3{\rm p}^{-1}_{1/2}4{\rm s}_{1/2})_{J=1}$ to $(3{\rm d}^{-1}_{j}4{\rm d}_{j'})_{J=1,2}$ for highly charged Ni-like ions with atomic number $Z$ in the range $47\leq Z\leq92$. In the calculations, the multi-configuration Dirac--Fock method and corresponding program packages GRASP92 and REOS99 were used, and the relativistic effects, correlation effects and relaxation effects were considered systematically. It is found that the TEOP transitions are very sensitive to the correlation of electrons, and the probabilities will be enhanced sharply in some special $Z$ regions along the isoelectronic sequence. The present TEOP transition wavelengths are compared with the available data from some previous publications, good agreement is obtained.

Infrared-to-visible and infrared-to-violet upconversion fluorescence of rare earth doped LaF3 nanocrystals

Wang Yan, Qin Wei-Ping, Di Wei-Hua, Zhang Ji-Sen, Cao Chun-Yan
Chin. Phys. B, 2008, 17 (9): 3300-3305 doi: 10.1088/1674-1056/17/9/026
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This paper reports that hexagonal-phase LaF$_{3}$:Yb$^{3 + }_{0.20}$, Er$^{3 + }_{0.02}$ and LaF$_{3}$:Yb$^{3 + }_{0.20}$, Tm$^{3 + }_{0.02}$ nanocrystals (NCs) were synthesized via a hydrothermal method. The transmission electron microscopy, selected area electron diffraction, powder x-ray diffraction, and thermogravimetric analysis are used to characterize the NCs. Under 980 nm excitation, the Yb$^{3 + }$/Er$^{3 + }$ and Yb$^{3 + }$/Tm$^{3 + }$ codoped NCs colloidal solutions present bright green and blue upconversion fluorescence, respectively. These NCs show efficient infrared-to-violet and infrared-to-visible upconversion. The upconversion fluorescence mechanisms of LaF$_{3}$:Yb$^{3 + }_{0.20}$, Er$^{3 + }_{0.02}$ and LaF$_{3}$:Yb$^{3 + }_{0.20}$, Tm$^{3 + }_{0.02}$ NCs are investigated with a 980-nm diode laser as excitation source.

Quantum coherent effects in multi-Zeeman-sublevel atomic systems

Dong Ya-Bin, Gao Jiang-Rui, Dong You-Er
Chin. Phys. B, 2008, 17 (9): 3306-3312 doi: 10.1088/1674-1056/17/9/027
Full Text: [PDF 532 KB] (Downloads:428)
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This paper reports the experimental results on electromagnetically induced absorption (EIA) spectra observed in the system which does not satisfy completely the conditions given by Lezama {\it et al} [1999 \wx{Phys. Rev. {\rm A}}{59} 4732]. EIA signals on the transitions in the Cs $D_{2}$ line are able to be observed, where $F_{\rm g} \leftrightarrow F_{\rm e}=F_{\rm g}-1$ as open systems. Theoretical model of Lezama {\it et al} is good for the case $F_{\rm g} \leftrightarrow F_{\rm e}=F_{\rm g}+1$, considering spontaneous transfer of atomic coherences or populations this model is not able to explain our experimental results obtained in the case $F_{\rm g} \leftrightarrow F_{\rm e}=F_{\rm g}-1$. This paper offers a theoretical model which is able to well explain the case $F_{\rm g} \leftrightarrow F_{\rm e}=F_{\rm g}-1$. It also uses this theoretical model to explain the split and shift of EIA peaks, which have been obtained in experiments.

Temperature dependent phonon modes and ionicity of LiGaO2 single crystal

Ma Ji-Yun, Fang Xu, M. Kamran, Zhao Hua-Ying, Bi Cong-Zhi, Zhao Bai-Ru, Qiu Xiang-Gang
Chin. Phys. B, 2008, 17 (9): 3313-3317 doi: 10.1088/1674-1056/17/9/028
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This paper reports that polarized far-infrared reflectivity measurements have been done on LiGaO2 single crystal along two crystalline axes at different temperatures. The temperature dependent frequencies of the longitudinal and transverse optical phonon have been obtained from the real part of optical conductivity and the loss function respectively. A small Drude component is observed at frequency below 300\,cm$^{ - 1}$ which could arise from Li ions or oxygen deficiencies. The ionicity of LiGaO2 has been studied from the analysis of the Born effective charge of different ions.

Spin--orbit ab initio curves of 80Se2+ ion and theassignment of photoelectron spectra of 80Se2 molecule

Yan Bing, Pan Shou-Fu, Guo Qing-Qun
Chin. Phys. B, 2008, 17 (9): 3318-3321 doi: 10.1088/1674-1056/17/9/029
Full Text: [PDF 445 KB] (Downloads:615)
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This paper carries out {\it ab initio} calculations to study the 80Se2(X3\Sigmag-) state and 80Se2+(X2\Pig, 80Se2+(a4\Pig) states by using completed active space self-consistent field and multi-reference second order perturbation theory. The electronic curves of these states including spin--orbit coupling are calculated, and then the spectroscopic parameters are obtained. The photoelectron spectra of 80Se2 molecule in gas phase are assigned according to Franck--Condon analysis based on calculated potential energy curves. The ionization energies of 80Se2 molecule are determined by the present calculation.

Isotope effect in collision between heliumatom and hydrogen bromide molecule

Yu Chun-Ri, Cheng Xin-Lu, Yang Xiang-Dong
Chin. Phys. B, 2008, 17 (9): 3322-3328 doi: 10.1088/1674-1056/17/9/030
Full Text: [PDF 1027 KB] (Downloads:508)
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The anisotropic potential developed in our previous research and the close-coupling method are applied to the HBr--$^{3}$He ($^{4}$He, $^{5}$He, $^{6}$He, $^{7}$He) system, and the partial cross sections (PCSs) at the incident energy of 60\,meV are calculated. Based on the calculations, the influences of the isotope helium atom on PCSs are discussed in detail. The results show that the excitation PCSs converge faster than the elastic PCSs for the collision energy and the systems considered here. Also the excitation PCSs converge more rapidly for the high-excited states. The tail effect is present only in elastic scattering and low-excited states but not in high-excited states. With the increase of reduced mass of the collision system, the converging speed of the elastic and excitation PCSs slows down, and the tail effect goes up.

Energy and structure of copper clusters (n=70--150) studied by the Monte Carlo computer simulation

Pan Xiao-Dong, Gai Zhi-Gang, Gong-Ping
Chin. Phys. B, 2008, 17 (9): 3329-3335 doi: 10.1088/1674-1056/17/9/031
Full Text: [PDF 1039 KB] (Downloads:600)
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The structure and binding energy of copper clusters of the size range 70 to 150 were studied by using the embedded-atom method. The stability of the structure of the clusters was studied by calculating the average binding energy per atom, first difference energy and second difference energy of copper cluster. Most of the copper clusters of the size $n$=70--150 adopt an icosahedral structure. The results show that the trends are in agreement with theoretic prediction for copper clusters. The most stable structures for copper clusters are found at $n$=77, 90, 95, 131, 139.

First-principles calculations for titanium monoxide clusters TinO (n=1--9)

Lu Zhang-Hui, Cao Jue-Xian
Chin. Phys. B, 2008, 17 (9): 3336-3342 doi: 10.1088/1674-1056/17/9/032
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Based on the density-functional theory, this paper studies the geometric and magnetic properties of Ti$_{n}$O ($n$=1--9) clusters. The resulting geometries show that the oxygen atom remains on the surface of clusters and does not change the geometry of Ti$_{n}$ significantly. The binding energy, second-order energy differences with the size of clusters show that Ti$_{7}$O cluster is endowed with special stability. The stability of Ti$_{n}$O clusters is validated by the recent time-of-flight mass spectra. The total magnetic moments for Ti$_{n}$O clusters with $n$=1--4, 8--9 are constant with 2 and drop to zero at $n$=5--7. The local magnetic moment and charge partition of each atom, and the density of states are discussed. The magnetic moment of the Ti$_{n}$O is clearly dominated by the localized 3d electrons of Ti atoms while the oxygen atom contributes a very small amount of spin in Ti$_{n}$O clusters.

Coalescence of heteroclusters Au767 and Ag767: a molecular-dynamics study

Li Guo-Jian, Wang Qiang, Li Hu-Tian, Wang Kai, He Ji-Cheng
Chin. Phys. B, 2008, 17 (9): 3343-3349 doi: 10.1088/1674-1056/17/9/033
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This paper studies the coalescence of heteroclusters Au$_{767}$ and Ag$_{767}$ by using molecular dynamics with the embedded atom method, where layer atomic energy is employed to describe the potential energy variation of per atom in different layers along radial direction. The results show that the coalescence is driven by releasing the atomic energy of the coalesced zone. The deformation, which is induced by substitutional and vacancy diffusion during the coalescence, makes the coalesced cluster disorder. If the summation of the thermal energy and the released atomic energy is large enough to keep the disorder state, the clusters form a metastable liquid droplet; otherwise, the clusters coalesce into a solid cluster when the coalesced cluster reaches the equilibrium state, and the coalesced cluster experiences liquid to solid ordering changes during the coalescence of a solid Au$_{767}$ with a liquid Ag$_{767}$ and a liquid Au$_{767}$ with a liquid Ag$_{767}$. The centre of figure of the cluster system is shifted during the coalescence process, and higher coalescence temperature causes larger shift degree.

Surface oxidation of vanadium dioxide films prepared by radio frequency magnetron sputtering

Wang Xue-Jin, Liang Chun-Jun, Guan Kang-Ping, Li De-Hua, Nie Yu-Xin, Zhu Shi-Oiu, Huang Feng, Zhang Wei-Wei, Cheng Zheng-Wei
Chin. Phys. B, 2008, 17 (9): 3512-3515 doi: 10.1088/1674-1056/17/9/062
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This paper reports that the thermochromic vanadium dioxide films were deposited on various transparent substrates by radio frequency magnetron sputtering, and then aged under circumstance for years. Samples were characterized with several different techniques such as x-ray diffraction, x-ray photoelectron spectroscopy, and Raman, when they were fresh from sputter chamber and aged after years, respectively, in order to determine their structure and composition. It finds that a small amount of sodium occurred on the surface of vanadium dioxide films, which was probably due to sodium ion diffusion from soda-lime glass when sputtering was performed at high substrate temperature. It also finds that aging for years significantly affected the nonstoichiometry of vanadium dioxide films, thus inducing much change in Raman modes.

Phase field simulation of the columnar dendritic growth and microsegregation in a binary alloy

Li Jun-Jie, Wang Jin-Cheng, Yang Gen-Cang
Chin. Phys. B, 2008, 17 (9): 3516-3522 doi: 10.1088/1674-1056/17/9/063
Full Text: [PDF 1374 KB] (Downloads:721)
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This paper applies a phase field model for polycrystalline solidification in binary alloys to simulate the formation and growth of the columnar dendritic array under the isothermal and constant cooling conditions. The solidification process and microsegregation in the mushy zone are analysed in detail. It is shown that under the isothermal condition solidification will stop after the formation of the mushy zone, but dendritic coarsening will progress continuously, which results in the decrease of the total interface area. Under the constant cooling condition the mushy zone will solidify and coarsen simultaneously. For the constant cooling solidification, microsegregation predicted by a modified Brody-Flemings model is compared with the simulation results. It is found that the Fourier number which characterizes microsegregation is different for regions with different microstructures. Dendritic coarsening and the larger area of interface should account for the enhanced Fourier number in the region with well developed second dendritic arms.

Phase-field study for the splitting behaviour of precipitate under applied stress

Zhang Yu-Xiang, Wang Jin-Cheng, Yang Yu-Juan, Yang Gen-Cang, Zhou Yao-He
Chin. Phys. B, 2008, 17 (9): 3523-3530 doi: 10.1088/1674-1056/17/9/064
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This paper employs the phase-field method to study the splitting behaviour of a single coherent particle under an applied uniaxial stress. It finds that the splitting behaviour is greatly influenced by the initial shape of precipitates, the bulk free energy condition, the degree of supersaturation and the ratio of the interfacial energy to the elastic strain energy, etc. The simulated results demonstrate that the aspect ratio of the particle determines whether the splitting can occur and how many split plates can be obtained. The splitting of particle is sensitive to the interfacial energy, i.e.~the splitting becomes more and more difficult with increasing the ratio of the interfacial energy to the elastic strain energy. And increasing the magnitude of the applied stress is favourable to the splitting. The splitting process is also explained from the point of view of the corresponding diffusion potential.

Distribution characteristic of scattering field for an ellipsoidal target irradiated by an electromagnetic wave from an arbitrary direction

Li Ying-Le, Huang Ji-Ying, Wang Ming-Jun, Zhang Jia-Tian
Chin. Phys. B, 2008, 17 (9): 3394-3401 doi: 10.1088/1674-1056/17/9/041
Full Text: [PDF 293 KB] (Downloads:472)
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It is of great importance for engineering applications to obtain the expression of scattering field for an ellipsoidal target irradiated by an electromagnetic wave from an arbitrary direction. Literature relevant to this problem is seldom found. In this paper, the scattering field for an ellipsoidal target is presented by utilizing the scale transformation of electromagnetic field and the rotation of coordinate system, with an electromagnetic wave projecting on the target from an arbitrary direction. The obtained result is in good agreement with the solution available from the literature if we consider the scale factors to be unity. Taking a conducting ellipsoidal target for sample, we perform the partial simulations of the ellipsoidal model and a plant leaf model by choosing different scale factors. The obtained results show that the distribution characteristic of scattering field is sensitively affected by the polarization of the incident wave and varies not much with the incident wave angle but changes with the observation point. At some points the scattering energy arrives at its maximum.

Study of a rectangular coupled cavity extendedinteraction oscillator in sub-terahertz waves

Zhang Kai-Chun, Wu Zhen-Hua, Liu Sheng-Gang
Chin. Phys. B, 2008, 17 (9): 3402-3406 doi: 10.1088/1674-1056/17/9/042
Full Text: [PDF 1466 KB] (Downloads:1104)
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An extended interaction oscillator (EIO) generating 120\,GHz wave in sub-terahertz waves is studied by using the three-dimensional electromagnetic simulation software CST and PIC codes. A rectangular reentrant coupled-cavity is proposed as the slow-wave structure of EIO. By CST, the circuit parameters including frequency-phase dispersion, interaction impedance and characteristic impedance are simulated and calculated. The operation mode of EIO is chosen very close to the point where $\beta L=2\pi$ with corresponding frequency 120\,GHz, the beam voltage 12\,kV and the dimensions of the cavity with the period 0.5\,mm, the height 3\,mm and the width 1.4\,mm. Simulation results of beam--wave interaction by PIC show that the exciting frequency is 120.85\,GHz and output peak power 465\,W with 12-period coupled-cavity with the perveance 0.17\,$\mu$P. Simulation results indicate that the EIO has very wide range of the operation voltage.

Comparative spectroscopic investigation of Yb-doped YAG, YSAG and YLaO3 transparent ceramics

Jiang Ben-Xue, Huang Tong-De, Wu Yu-Song, Liu Wen-Bin, Pan Yu-Bai, Feng Tao, Yang Qiu-Hong
Chin. Phys. B, 2008, 17 (9): 3407-3411 doi: 10.1088/1674-1056/17/9/043
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Transparent Yb doped YAG, YSAG and YaLaO3 ceramics are fabricated by using the co-precipitation method. The spectral properties and thermal parameters of these Yb doped cubic phase transparent ceramics are compared, and their different and potential applications are also analysed. The absorption cross-section and the emission cross-section of these ceramics are measured and calculated. The essential properties of these materials especially for the rep-rated pulsed high-energy diode-pumped solid-state lasers are investigated. The results show that Yb doped YAG, YSAG and YaLaO$_3$ are all suitable materials used for diode-pumped solid-state lasers.

Undercooling and solidification of Ni77P23 alloy in a 52-m drop tube

Li Gong, Gao Yun-Peng, Sun Yi-Nan, Chi Zhao-Hong, Liu Ri-Ping
Chin. Phys. B, 2008, 17 (9): 3412-3416 doi: 10.1088/1674-1056/17/9/044
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This paper applies techniques of containerless processing, drop tube and glass fluxing, to undercool and solidify Ni77P23 alloys. Different diameter spheres were collected at the bottom of a 52-m long drop tube. Both crystalline and amorphous phase were formed in various size specimens due to the different cooling rate. The variation of partial undercooling with bulk undercooling is calculated for the Ni77P23 alloys. The deep undercooling and rapid solidification behaviour of Ni77P23 melts has been analysed with respect to microstructure formation and transition during fluxing and 52-m drop process of undercooled melts.

First-principles study of structural, electronic, andmagnetic properties of Mn4XGe3 (X =Fe,Co,Ni)

Zhao Yong-Hong, Liu Bang-Gui
Chin. Phys. B, 2008, 17 (9): 3417-3421 doi: 10.1088/1674-1056/17/9/045
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In order to search for promising candidates for spintronic applications, this paper systematically studies three ternary compounds based on Mn5Ge3 by using a full-potential linearized augmented plane wave method within the density functional theory. Through structure optimization and electronic structure calculations, it finds that Mn4FeGe3 and Mn4CoGe3 have much higher spin-polarization than original intermetallic compound Mn5Ge3, although the spin polarization of Mn4NiGe3 is lower than that of Mn$_{5}$Ge3. The calculated result is in agreement with experiment in the case of Mn4FeGe3. Both of them can be taken as promising candidates for spintronics applications because of their high spin-polarization and compatibility with semiconductors.

First-principles study of interphase Ni3Sn in Sn--Ni alloy for anode of lithium ion battery

Hou Xian-Hua, Hu She-Jun, Li Wei-Shan, Ru Qiang, Yu Hong-Wen, Huang Zhao-Wen
Chin. Phys. B, 2008, 17 (9): 3422-3427 doi: 10.1088/1674-1056/17/9/046
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This paper investigates the mechanism of Li insertion into interphase Ni$_{3}$Sn in Ni--Sn alloy for the anode of lithium ion battery by means of the first-principles plane-wave pseudopotential. Compared with other phases, it is found that the Ni$_{3}$Sn has larger relative expansion ratio and lower electrochemical potential, with its specific plateaus voltage around 0.3eV when lithium atoms are filled in all octahedral interstitial sites, and the relative expansion ratio increasing dramatically when the lithiated phase transits from octahedral interstitial sites to tetrahedral interstitial sites. So this phase is a devastating phase for whole alloy electrode materials.

Simulation of plasma doping process by using the localized molecular dynamics method

Ji Hui-Hui, Yu Min, Ren Li-Ming, Zhang Xing, Huang Ru, Zhang You-Guang
Chin. Phys. B, 2008, 17 (9): 3428-3432 doi: 10.1088/1674-1056/17/9/047
Full Text: [PDF 198 KB] (Downloads:563)
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Plasma doping is the candidate for semiconductor doping. Accurate simulation of the doping technology is needed for the advanced integrated circuit manufacturing. In this paper, the plasma doping process simulation is performed by using the localized molecular dynamics method. Models that involve the statistics of the implanted compositions, angles and energies are developed. The effect of the model on simulation results is studied. The simulation results about the doping concentration profile are supported by experimental data.

Common electronic band gaps and similar optical properties of ZnO nanotubes

Yang Yu-Rong, Yan Xiao-Hong, Guo Zhao-Hui, Deng Yu-Xiang
Chin. Phys. B, 2008, 17 (9): 3433-3437 doi: 10.1088/1674-1056/17/9/048
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Electronic and optical properties of single-walled zinc oxide (ZnO) nanotubes are investigated from the first-principles calculations. Electronic structure calculations show that ZnO nanotubes are all direct band gap semiconducting nanotubes and the band gaps are relatively insensitive to the diameter and chirality of tubes. The origin of the common electronic band gaps of ZnO nanotubes is explained in terms of band-folding from the two-dimensional band structure of graphite-like sheet. Moreover, the optical properties such as dielectric function and energy loss function spectra of different ZnO nanotubes are very similar, relatively independent of diameter and chirality of tubes. The calculated dielectric function and loss function spectra show a moderate optical anisotropy with respect to light polarization.

Spin-dependent tunnelling through an indirect double-barrier structure

Wang Rui, Zhang Cun-Xi, Wang Jian-Ming, Liang Jiu-Qing
Chin. Phys. B, 2008, 17 (9): 3438-3443 doi: 10.1088/1674-1056/17/9/049
Full Text: [PDF 542 KB] (Downloads:526)
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We use the transfer matrix method to study the quantum tunnelling through an indirect-band-gap double-barrier like the GaAs/AlAs/GaAs/AlAs/GaAs heterostructures along the [001] axis, which is described by the tight-binding model. The $X$-valley quasi-bound state gives rise to the Fano resonance different from the direct double-barrier transition in a resonance-tunnelling diode. The quantitative calculations demonstrate that a relatively high spin-polarization of the transmission probability can be achieved as compared with the single-barrier tunnelling case. Moreover the extension to the multi-barrier device is provided and leads to an important observation that the spin polarization increases with the number of barriers.

Cathodoluminescent and electrical properties of an individual ZnO nanowire with oxygen vacancies

He Xiao-Bo, Yang Tian-Zhong, Cai Jin-Ming, Zhang Chen-Dong, Guo Hai-Ming, Shi Dong-Xia, Shen Cheng-Min, Gao Hong-Jun
Chin. Phys. B, 2008, 17 (9): 3444-3447 doi: 10.1088/1674-1056/17/9/050
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A single ZnO nanowire with intrinsic oxygen vacancies is utilized to fabricate four-contact device with focus ion beam lithography technique. Cathodoluminescent spectra indicate strong near-UV and green emission at both room temperature and low temperatures. Experimental measurement shows the temperature-dependent conductivity of the ZnO nanowire at low temperatures (below 100\,K). The further theoretical analysis confirms that weak localization plays an important role in the electrical transport, which is attributed to the surface states induced by plenty of oxygen vacancies in ZnO nanowire.

Influence of reaction gas flows on the properties of SiGe:H thin film prepared by plasma assisted reactive thermal chemical vapour deposition

Zhang Li-Ping, Zhang Jian-Jun, Shang Ze-Ren, Hu Zeng-Xin, Geng Xin-Hua, Zhao Ying
Chin. Phys. B, 2008, 17 (9): 3448-3452 doi: 10.1088/1674-1056/17/9/051
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A new preparing technology, very high frequency plasma assisted reactive thermal chemical vapour deposition (VHFPA-RTCVD), is introduced to prepare SiGe:H thin films on substrate kept at a lower temperature. In the previous work, reactive thermal chemical vapour deposition (RTCVD) technology was successfully used to prepare SiGe:H thin films, but the temperature of the substrate needed to exceed 400\du. In this work, very high frequency plasma method is used to assist RTCVD technology in reducing the temperature of substrate by largely enhancing the temperature of reacting gases on the surface of the substrate. The growth rate, structural properties, surface morphology, photo-conductivity and dark-conductivity of SiGe:H thin films prepared by this new technology are investigated for films with different germanium concentrations, and the experimental results are discussed.

In situ infrared spectroscopic study of cubicboron nitride thin film delamination

Yang Hang-Sheng, Zhang Jian-Ying, Nie An-Min, Zhang Xiao-Bin
Chin. Phys. B, 2008, 17 (9): 3453-3458 doi: 10.1088/1674-1056/17/9/052
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This paper investigates the procedure of cubic boron nitride (cBN) thin film delamination by Fourier-transform infrared (IR) spectroscopy. It finds that the apparent IR absorption peak area near 1380\,cm$^{-1}$ and 1073\,cm$^{-1}$ attributed to the B--N stretching vibration of sp$^{2}$-bonded BN and the transverse optical phonon of cBN, respectively, increased up to 195{\%} and 175{\%} of the original peak area after film delamination induced compressive stress relaxation. The increase of IR absorption of sp$^{2}$-bonded BN is found to be non-linear and hysteretic to film delamination, which suggests that the relaxation of the turbostratic BN (tBN) layer from the compressed condition is also hysteretic to film delamination. Moreover, cross-sectional transmission electron microscopic observations revealed that cBN film delamination is possible from near the aBN(amorphous BN)/tBN interface at least for films prepared by plasma-enhanced chemical vapour deposition.

Raman analysis of defects in n-type 4H-SiC

Yang Yin-Tang, Han Ru, Wang-Ping
Chin. Phys. B, 2008, 17 (9): 3459-3463 doi: 10.1088/1674-1056/17/9/053
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This paper employs micro-Raman technique for detailed analysis of the defects (both inside and outside) in bulk 4H-SiC. The main peaks of the first-order Raman spectrum obtained in the centre of defect agree well with those of perfect bulk 4H-SiC, which indicate that there is no parasitic polytype in the round pit and the hexagonal defect. Four electronic Raman scattering peaks from nitrogen defect levels are observed in the round pit (395\,cm$^{-1}$, 526\,cm$^{-1}$, 572\,cm$^{-1}$, and 635\,cm$^{-1})$, but cannot be found in the spectra of hexagonal defect. The theoretical analysis of the longitudinal optical plasmon--phonon coupled mode line shape indicates the nonuniformity of nitrogen distribution between the hexagonal defect and the outer area in 4H-SiC. The second-order Raman features of the defects in bulk 4H-SiC are well-defined using the selection rules for second-order scattering in wurtzite structure and compared with that in the free defect zone.

The high deposition of microcrystalline silicon thin film by very high frequency plasma enhanced chemical vapour deposition and the fabrication of solar cells

Chen Yong-Sheng, Wang Jian-Hua, Lu Jing-Xiao, Zheng Wen, Gu Jin-Hua, Yang Shi-E, Gao Xiao-Yong, Guo Xue-Jun, Zhao Shang-Li, Gao Zhe
Chin. Phys. B, 2008, 17 (9): 3464-3470 doi: 10.1088/1674-1056/17/9/054
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This paper reports that the intrinsic microcrystalline silicon ($\mu $c-Si:H) films are prepared with plasma enhanced chemical vapour deposition from silane/hydrogen mixtures at 200\du\ with the aim to increase the deposition rate. An increase of the deposition rate to 0.88\,nm/s is obtained by using a plasma excitation frequency of 75\,MHz. This increase is obtained by the combination of a higher deposition pressure, an increased silane concentration, and higher discharge powers. In addition, the transient behaviour, which can decrease the film crystallinity, could be prevented by filling the background gas with H$_{2}$ prior to plasma ignition, and selecting proper discharging time after silane flow injection. Material prepared under these conditions at a deposition rate of 0.78\,nm/s maintains higher crystallinity and fine electronic properties. By H-plasma treatment before i-layer deposition, single junction $\mu $c-Si:H solar cells with 5.5{\%} efficiency are fabricated.

Self-organized GaN/AlN hexagonal quantum-dots:strain distribution and electronic structure

Liu Yu-Min, Yu Zhong-Yuan, Ren Xiao-Min, Xu Zi-Huan
Chin. Phys. B, 2008, 17 (9): 3471-3478 doi: 10.1088/1674-1056/17/9/055
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This paper presents a finite element method of calculating strain distributions in and around the self-organized GaN/AlN hexagonal quantum dots. The model is based on the continuum elastic theory, which is capable of treating a quantum dot with an arbitrary shape. A truncated hexagonal pyramid shaped quantum dot is adopted in this paper. The electronic energy levels of the GaN/AlN system are calculated by solving a three-dimension effective mass Shr\"{o}dinger equation including a strain modified confinement potential and polarization effects. The calculations support the previous results published in the literature.

Study of valence intersubband absorption in tensile strained Si/SiGe quantum wells

Lin Gui-Jiang, Lai Hong-Kai, Li Cheng, Chen Song-Yan, Yu Jin-Zhong
Chin. Phys. B, 2008, 17 (9): 3479-3483 doi: 10.1088/1674-1056/17/9/056
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The hole subband structures and effective masses of tensile strained Si/Si$_{1 - y }$Ge$_{y}$ quantum wells are calculated by using the 6$\times $6 $\bm k\cdot\bm p$ method. The results show that when the tensile strain is induced in the quantum well, the light-hole state becomes the ground state, and the light hole effective masses in the growth direction are strongly reduced while the in-plane effective masses are considerable. Quantitative calculation of the valence intersubband transition between two light hole states in a 7nm tensile strained Si/Si$_{0.55}$Ge$_{0.45}$ quantum well grown on a relaxed Si$_{0.5}$Ge$_{0.5}$ (100) substrates shows a large absorption coefficient of 8400\,cm$^{ - 1}$.

Superconductivity without dependence on valenceelectron density in Zn doped YBCO systems

Li Ping-Lin, Wang Yong-Yong, Tian Yong-Tao, Wang Jing, Niu Xiao-Li, Wang Jun-Xi, Wang Dan-Dan, Wang Xiao-Xia
Chin. Phys. B, 2008, 17 (9): 3484-3489 doi: 10.1088/1674-1056/17/9/057
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This paper reports that the YBa$_{2}$Cu$_{3 - x}$Zn$_{x}$O$_{7 - \delta }\ (x=0-0.4$) samples are researched by means of x-ray diffraction, calculations of binding energy, the positron experiments and variations of oxygen content. The results of simulated calculations, positron experiments and variations of oxygen content support the existence of cluster effect. Moreover, it is concluded that the cluster effect is an important factor on suppression of high-$T_{\rm c}$ cuprate superconductivity and the $T_{\rm c}$ does not depend on the density of valence electron directly.

Effect of magnetic field on the spin-Peierls transition in single-crystal CuGeO

Wang Qing-Bo, Xu Xiang-Fan, Tao Qian, Wang Hong-Tao, Xu Zhu-An
Chin. Phys. B, 2008, 17 (9): 3490-3494 doi: 10.1088/1674-1056/17/9/058
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This paper reports that high quality CuGeO$_{3}$ single crystals were successfully grown by floating-zone technique and the magnetic property was studied. The temperature dependence of magnetic susceptibility below the spin-Peierls (SP) transition temperature ($T_{\rm sp})$ under magnetic fields applying along both the $a$- and $c$-axis direction can be fitted well by a model of noninteracting dimmers. The spin gap derived from the fitting is consistent with other reports. There is a very weak anisotropy in the fitting parameters for different directions, which should be expected from a SP system. A small upturn in susceptibility at low temperature due to paramagnetic impurities and/or defects can be observed. A suppression of the upturn by magnetic field is first discovered in this system and the possible origins for this suppression are discussed.

Temperature-driven spin reorientation transitionof magnetron sputtered nickel thin film

Song Xiao-Hui, Zhang Dian-Lin
Chin. Phys. B, 2008, 17 (9): 3495-3498 doi: 10.1088/1674-1056/17/9/059
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The temperature-driven spin reorientation transition of magnetron sputtered Ni/Si (111) systems has been studied. The relationship between ac initial susceptibility and temperature of nickel films with different thicknesses shows that the magnetization orientation changes from in-plane to out-of-plane with the increase of temperature. The temperature dependence of magnetoelastic, magneto-crystalline, and magnetostatic anisotropies determines the direction of the reorientation transition. The temperature-driven spin reorientation transition is supported by Hall coefficient measurements which show that its temperature dependence is similar to that of susceptibility.

Anomalous magnetic properties of an iron film system deposited on fracture surfaces of α-Al2O3 ceramics

Jiao Zhi-Wei, Chen Miao-Gen, Jiang Wei-Di, Feng Chun-Mu, Ye Gao-Xiang
Chin. Phys. B, 2008, 17 (9): 3499-3504 doi: 10.1088/1674-1056/17/9/060
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An iron film percolation system is fabricated by vapour-phase deposition on fracture surfaces of α-Al2O3 ceramics. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurement reveals that the magnetic phase of the film samples evolve from a high-temperature ferromagnetic state to a low-temperature spin-glass-like state, which is also demonstrated by the temperature-dependent ac susceptibility of the iron films. The temperature dependence of the exchange bias field $H_{\rm e}$ of the iron film exhibits a minimum peak around the temperature $T$=5\,K, which is independent of the magnitude of the cooling field $H_{\rm cf}$. However, for $T > 10$\,K, (1) $H_{\rm e}$ is always negative when $H_{\rm cf}$=2\,kOe and (2) for $H_{\rm cf }$= 20\,kOe (1Oe$\approx$80\,A/m), $H_{\rm e}$ changes from negative to positive values as T increases. Our experimental results show that the anomalous hysteresis properties mainly result from the oxide surfaces of the films with spin-glass-like phase.

Theoretical investigation on near-infrared and visible absorption spectra of nanometallic aluminium with oxide coating in nanoenergetic materials: size and shape effects

Peng Ya-Jing, Zhang Shu-Ping, Wang Ying-Hui, Yang Yan-Qiang
Chin. Phys. B, 2008, 17 (9): 3505-3511 doi: 10.1088/1674-1056/17/9/061
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The effects of metal core dimension, oxide shell thickness and ellipsoid aspect ratio of Al--Al$_{2}$O$_{3}$ core-shell nanoparticles on the near-infrared and visible absorption spectra of nanocomposite Al--Al$_{2}$O$_{3}$/nitrocellulose(NC) film are investigated by numerical calculations. Both the size-dependent interband transitions and frequency-dependent free electron damping of the nanometallic aluminium are taken into account in the calculations. Oxidation effect of nanoaluminium is also analysed. It is shown that oxidation may enhance but may also reduce the optical absorption, depending on the excited light energy and initial dimension of nanoparticle. Metal core size and excited light energy dominate the absorption characteristic. The absorption ability of ellipsoidal nanoparticles is larger than that of spheroidal nanoparticles and increases by the square index as the aspect ratio increases. These calculations will provide some significant theoretical guidance for the preparation and laser ignition of nanoenergetic materials.
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