Table of contents

15 July 2011, Volume 20 Issue 7 Previous issue    Next issue

GENERAL

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Binary nonlinearization of the super classical-Boussinesq hierarchy Tao Si-Xing(陶司兴), Wang Hui(王惠), and Shi Hui(史会) Chin. Phys. B, 2011, 20 (7):  070201.  DOI: 10.1088/1674-1056/20/7/070201 Abstract ( 1594 )   PDF (135KB) ( 830 )   The symmetry constraint and binary nonlinearization of Lax pairs for the super classical-Boussinesq hierarchy is obtained. Under the obtained symmetry constraint, the n-th flow of the super classical-Boussinesq hierarchy is decomposed into two super finite-dimensional integrable Hamiltonian systems, defined over the super-symmetry manifold with the corresponding dynamical variables x and tn. The integrals of motion required for Liouville integrability are explicitly given.

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Conservation laws for variable coefficient nonlinear wave equations with power nonlinearities Huang Ding-Jiang(黄定江), Zhou Shui-Geng(周水庚), and Yang Qin-Min(杨勤民) Chin. Phys. B, 2011, 20 (7):  070202.  DOI: 10.1088/1674-1056/20/7/070202 Abstract ( 1401 )   PDF (120KB) ( 789 )   Conservation laws for a class of variable coefficient nonlinear wave equations with power nonlinearities are investigated. The usual equivalence group and the generalized extended one including transformations which are nonlocal with respect to arbitrary elements are introduced. Then, using the most direct method, we carry out a classification of local conservation laws with characteristics of zero order for the equation under consideration up to equivalence relations generated by the generalized extended equivalence group. The equivalence with respect to this group and the correct choice of gauge coefficients of the equations play the major roles for simple and clear formulation of the final results.

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The approximate conserved quantity of the weakly nonholonomic mechanical-electrical system Liu Xiao-Wei(刘晓巍), Li Yuan-Cheng(李元成), and Xia Li-Li(夏丽莉) Chin. Phys. B, 2011, 20 (7):  070203.  DOI: 10.1088/1674-1056/20/7/070203 Abstract ( 1536 )   PDF (96KB) ( 564 )   We study the approximate conserved quantity of the weakly nonholonomic mechanical-electrical system. By means of the Lagrange—Maxwell equation, the Noether equality of the weakly nonholonomic mechanical-electrical system is obtained. The multiple powers-series expansion of the parameter of the generators of infinitesimal transformations and the gauge function is put into a generalized Noether identity. Using the Noether theorem, we obtain an approximate conserved quantity. An example is provided to prove the existence of the approximate conserved quantity.

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Lie–Mei symmetry and conserved quantities of the Rosenberg problem Liu Xiao-Wei(刘晓巍) and Li Yuan-Cheng(李元成) Chin. Phys. B, 2011, 20 (7):  070204.  DOI: 10.1088/1674-1056/20/7/070204 Abstract ( 1578 )   PDF (83KB) ( 590 )   The Rosenberg problem is a typical but not too complicated problem of nonholonomic mechanical systems. The Lie—Mei symmetry and the conserved quantities of the Rosenberg problem are studied. For the Rosenberg problem, the Lie and the Mei symmetries for the equation are obtained, the conserved quantities are deduced from them and then the definition and the criterion for the Lie—Mei symmetry of the Rosenberg problem are derived. Finally, the Hojman conserved quantity and the Mei conserved quantity are deduced from the Lie—Mei symmetry.

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Asymptotic solution for the Eiño time delay sea–air oscillator model Mo Jia-Qi(莫嘉琪), Lin Wan-Tao(林万涛), and Lin Yi-Hua(林一骅) Chin. Phys. B, 2011, 20 (7):  070205.  DOI: 10.1088/1674-1056/20/7/070205 Abstract ( 1538 )   PDF (102KB) ( 871 )   A sea—air oscillator model is studied using the time delay theory. The aim is to find an asymptotic solving method for the El Ni no-southern oscillation (ENSO) model. Employing the perturbed method, an asymptotic solution of the corresponding problem is obtained. Thus we can obtain the prognoses of the sea surface temperature (SST) anomaly and the related physical quantities.

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A meshless method for the compound KdV-Burgers equation Cheng Rong-Jun(程荣军) and Cheng Yu-Min(程玉民) Chin. Phys. B, 2011, 20 (7):  070206.  DOI: 10.1088/1674-1056/20/7/070206 Abstract ( 1728 )   PDF (616KB) ( 1090 )   The element-free Galerkin (EFG) method for numerically solving the compound Korteweg—de Vries—Burgers (KdVB) equation is discussed in this paper. The Galerkin weak form is used to obtain the discrete equation and the essential boundary conditions are enforced by the penalty method. The effectiveness of the EFG method of solving the compound Korteweg—de Vries—Burgers (KdVB) equation is illustrated by three numerical examples.

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A new approach to obtaining positive-definite Wigner operator for two entangled particles with different masses Fan Hong-Yi(范洪义), Xu Xue-Xiang(徐学翔), Yuan Hong-Chun(袁洪春), Wang Shuai(王帅), Wang Zhen(王震), Xu Peng(许朋), and Jiang Nian-Quan(姜年权) Chin. Phys. B, 2011, 20 (7):  070301.  DOI: 10.1088/1674-1056/20/7/070301 Abstract ( 1355 )   PDF (111KB) ( 655 )   Based on our previously proposed Wigner operator in entangled form, we introduce the generalized Wigner operator for two entangled particles with different masses, which is expected to be positive-definite. This approach is able to convert the generalized Wigner operator into a pure state so that the positivity can be ensured. The technique of integration within an ordered product of operators is used in the discussion.

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Spin symmetric solutions of Dirac equation with Pöschl–Teller potential Ferhat Tacskhin and Gökhan Koccak Chin. Phys. B, 2011, 20 (7):  070302.  DOI: 10.1088/1674-1056/20/7/070302 Abstract ( 1342 )   PDF (107KB) ( 794 )   The approximate analytical solutions of the Dirac equation with the P?schl—Teller potential is presented for arbitrary spin-orbit quantum number $\kappa$ within the framework of the spin symmetry concept. The energy eigenvalues and the corresponding two Dirac spinors are obtained approximately in closed forms. The limiting cases of the energy eigenvalues and the two Dirac spinors are briefly discussed.

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Entanglement dynamics of a moving multi-photon Jaynes–Cummings model in mixed states Tan Lei(谭磊), Zhang Yu-Qing(张玉青), and Zhu Zhong-Hua(朱中华) Chin. Phys. B, 2011, 20 (7):  070303.  DOI: 10.1088/1674-1056/20/7/070303 Abstract ( 1315 )   PDF (3699KB) ( 648 )   Using the algebraic dynamical method, the entanglement dynamics of an atom-field bipartite system in a mixed state is investigated. The atomic center-of-mass motion and the field-mode structure are also included in this system. We find that the values of the detuning and the average photon number are larger, the amplitude of the entanglement is smaller, but its period does not increase accordingly. Moreover, with the increase of the field-mode structure parameter and the transition photon number, the amplitude of the entanglement varies slightly while the oscillation becomes more and more fast. Interestingly, a damping evolution of the entanglement appears when both the detuning and the atomic motion are considered simultaneously.

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Avoiding the decay of entanglement for coupling two-qubit system interacting with a non-Markov environment Ji Ying-Hua(嵇英华), Liu Yong-Mei(刘咏梅), and Wang Zi-Sheng(王资生) Chin. Phys. B, 2011, 20 (7):  070304.  DOI: 10.1088/1674-1056/20/7/070304 Abstract ( 1568 )   PDF (126KB) ( 668 )   The entanglement evolution of the coupled qubits interacting with a non-Markov environment is investigated in terms of concurrence. The results show that the entanglement of the quantum systems depends not only on the initial state of the system but also on the coupling between the qubit and the environment. For the initial state (|00〉± | 11〉) /√2, the coupled qubits will always been in the maximum entangled state under an asymmetric coupling. For the initial state (|01〉± | 10〉) /√2, in contrast, the entangling degree of the coupled qubits is always equal to unity and does not depend on the evolving time under the symmetric coupling. We find that the stronger the interaction between the qubits is, the better the struggle against the entanglement sudden death is.

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Eavesdropping on the quantum dialogue protocol in lossy channel Liu Heng(刘恒), Zhang Xiu-Lan(张秀兰), and Lü Hui(吕辉) Chin. Phys. B, 2011, 20 (7):  070305.  DOI: 10.1088/1674-1056/20/7/070305 Abstract ( 1586 )   PDF (108KB) ( 1460 )   We present an improved eavesdropping scheme on the quantum dialogue protocol in lossy channel, which is based on the strategies of Wójcik [Phys. Rev. Lett. 90 157901 (2003)] and ZML [Phys. Lett. A 333 46 (2004)] attack schemes. We show that our attack scheme doubles the domain of Eve's eavesdropping and Eve can gain more information of the communication with less risk of being detected. Finally, a possible improvement for the dialogue protocol security is proposed.

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Entanglement distribution using three-mode separable state with imperfect equipments Song Ting-Ting(宋婷婷), Zhang Jie(张劼), Gao Fei(高飞), and Wen Qiao-Yan(温巧燕) Chin. Phys. B, 2011, 20 (7):  070306.  DOI: 10.1088/1674-1056/20/7/070306 Abstract ( 1473 )   PDF (143KB) ( 561 )   We show a scheme to distribute the entanglement by using three-mode separable Gaussian state prepared with imperfect equipments. The scheme achieves the aim that the entanglement is distributed between two distant parties with only Gaussian operations and linear optics elements. Moreover, we analyse the logarithmic negativity of the entanglement shared between the two parties when the systems are imperfect and arrive at the conclusion that the logarithmic negativity is asymptotically stable with fluctuations within a certain space range.

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Landau damping of collective mode in a quasi-two-dimensional repulsive Bose–Einstein condensate Ma Xiao-Dong(马晓栋), Yang Zhan-Jin(杨占金), Lu Jun-Zhe(路俊哲), and Wei Wei(魏蔚) Chin. Phys. B, 2011, 20 (7):  070307.  DOI: 10.1088/1674-1056/20/7/070307 Abstract ( 1369 )   PDF (159KB) ( 781 )   We investigate the Landau damping of the collective mode in a quasi-two-dimension repulsive Bose—Einstein condensate by using the self-consistent time-dependent Hatree—Fock—Bogoliubov approximation and a complete and orthogonal eigenfunction set for the elementary excitation of the system. We calculate the three-mode coupling matrix element between the collective mode and the thermal excited quasi-particles and the Landau damping rate of the collective mode. We discuss the dependence of the Landau damping on temperature, on atom number in the condensate, on transverse trapping frequency and on the length of the condensate. The energy width of the collective mode is taken into account in our calculation. With little approximation, our theoretic calculation results agree well with the experimental ones and are helpful for deducing the damping mechanics and the inter-particle interaction.

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A note on teleparallel Killing vector fields in Bianchi type VIII and IX space–times in teleparallel theory of gravitation Ghulam Shabbir, Amjad Ali, and Suhail Khan Chin. Phys. B, 2011, 20 (7):  070401.  DOI: 10.1088/1674-1056/20/7/070401 Abstract ( 2036 )   PDF (98KB) ( 1333 )   In this paper we classify Bianchi type VIII and IX space—times according to their teleparallel Killing vector fields in the teleparallel theory of gravitation by using a direct integration technique. It turns out that the dimensions of the teleparallel Killing vector fields are either 4 or 5. From the above study we have shown that the Killing vector fields for Bianchi type VIII and IX space—times in the context of teleparallel theory are different from that in general relativity.

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An efficient chaotic source coding scheme with variable-length blocks Lin Qiu-Zhen(林秋镇), Wong Kwok-Wo(黄国和), and Chen Jian-Yong(陈剑勇) Chin. Phys. B, 2011, 20 (7):  070501.  DOI: 10.1088/1674-1056/20/7/070501 Abstract ( 1593 )   PDF (169KB) ( 688 )   An efficient chaotic source coding scheme operating on variable-length blocks is proposed. With the source message represented by a trajectory in the state space of a chaotic system, data compression is achieved when the dynamical system is adapted to the probability distribution of the source symbols. For infinite-precision computation, the theoretical compression performance of this chaotic coding approach attains that of optimal entropy coding. In finite-precision implementation, it can be realized by encoding variable-length blocks using a piecewise linear chaotic map within the precision of register length. In the decoding process, the bit shift in the register can track the synchronization of the initial value and the corresponding block. Therefore, all the variable-length blocks are decoded correctly. Simulation results show that the proposed scheme performs well with high efficiency and minor compression loss when compared with traditional entropy coding.

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The $\mathscr{H}_{\infty}$ synchronization of nonlinear Bloch systems via dynamic feedback control approach D.H. Ji, J.H. Koo, S.C. Won, and Ju H. Park Chin. Phys. B, 2011, 20 (7):  070502.  DOI: 10.1088/1674-1056/20/7/070502 Abstract ( 1423 )   PDF (164KB) ( 583 )   We consider an $\mathscr{H}_{\infty}$ synchronization problem in nonlinear Bloch systems. Based on Lyapunov stability theory and linear matrix inequality formulation, a dynamic feedback controller is designed to guarantee asymptotic stability of the master-slave synchronization. Moreover, this controller reduces the effect of an external disturbance to the $\mathscr{H}_{\infty}$ norm constraint. A numerical example is given to validate the proposed synchronization scheme.

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Generalized synchronization of two unidirectionally coupled discrete stochastic dynamical systems Yuan Zhi-Ling(袁志玲), Xu Zhen-Yuan(徐振源), and Guo Liu-Xiao(过榴晓) Chin. Phys. B, 2011, 20 (7):  070503.  DOI: 10.1088/1674-1056/20/7/070503 Abstract ( 1507 )   PDF (172KB) ( 777 )   The existence of two kinds of generalized synchronization manifold in two unidirectionally coupled discrete stochastic dynamical systems is studied in this paper. When the drive system is chaotic and the modified response system collapses to an asymptotically stable equilibrium or asymptotically stable periodic orbit, under certain conditions, the existence of the generalized synchronization can be converted to the problem of a Lipschitz contractive fixed point or Schauder fixed point. Moreover, the exponential attractive property of generalized synchronization manifold is strictly proved. In addition, numerical simulations demonstrate the correctness of the present theory. The physical background and meaning of the results obtained in this paper are also discussed.

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Universal critical properties of the Eulerian bond-cubic model Ding Cheng-Xiang(丁成祥), Yao Gui-Yuan(姚桂元), Li Song(李崧), Deng You-Jin(邓友金), and Guo Wen-An(郭文安) Chin. Phys. B, 2011, 20 (7):  070504.  DOI: 10.1088/1674-1056/20/7/070504 Abstract ( 1666 )   PDF (3964KB) ( 696 )   We investigate the Eulerian bond-cubic model on the square lattice by means of Monte Carlo simulations, using an efficient cluster algorithm and a finite-size scaling analysis. The critical points and four critical exponents of the model are determined for several values of n. Two of the exponents are fractal dimensions, which are obtained numerically for the first time. Our results are consistent with the Coulomb gas predictions for the critical O(n) branch for n < 2 and the results obtained by previous transfer matrix calculations. For n=2, we find that the thermal exponent, the magnetic exponent and the fractal dimension of the largest critical Eulerian bond component are different from those of the critical O(2) loop model. These results confirm that the cubic anisotropy is marginal at n=2 but irrelevant for n<2.

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Bias dependence of a deep submicron NMOSFET response to total dose irradiation Liu Zhang-Li(刘张李), Hu Zhi-Yuan(胡志远), Zhang Zheng-Xuan(张正选), Shao Hua(邵华), Chen Ming(陈明), Bi Da-Wei(毕大炜), Ning Bing-Xu(宁冰旭), and Zou Shi-Chang(邹世昌) Chin. Phys. B, 2011, 20 (7):  070701.  DOI: 10.1088/1674-1056/20/7/070701 Abstract ( 1440 )   PDF (1358KB) ( 1011 )   Deep submicron n-channel metal-oxide-semiconductor field-effect transistors (NMOSFETs) with shallow trench isolation (STI) are exposed to ionizing dose radiation under different bias conditions. The total ionizing dose radiation induced subthreshold leakage current increase and the hump effect under four different irradiation bias conditions including the worst case (ON bias) for the transistors are discussed. The high electric fields at the corners are partly responsible for the subthreshold hump effect. Charge trapped in the isolation oxide, particularly at the Si/SiO2 interface along the sidewalls of the trench oxide creates a leakage path, which becomes a dominant contributor to the off-state drain-to-source leakage current in the NMOSFET. Non-uniform charge distribution is introduced into a three-dimensional (3D) simulation. Good agreement between experimental and simulation results is demonstrated. We find that the electric field distribution along with the STI sidewall is important for the radiation effect under different bias conditions.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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Low frequency asymptotics for the spin-weighted spheroidal equation in the case of s=1/2 Dong Kun(董锟), Tian Gui-Hua(田贵花), and Sun Yue(孙越) Chin. Phys. B, 2011, 20 (7):  071101.  DOI: 10.1088/1674-1056/20/7/071101 Abstract ( 1406 )   PDF (146KB) ( 556 )   The spin-weighted spheroidal equation in the case of s=1/2 is thoroughly studied by using the perturbation method from the supersymmetric quantum mechanics. The first-five terms of the superpotential in the series of parameter β are given. The general form for the n-th term of the superpotential is also obtained, which could also be derived from the previous terms Wk, k < n. From these results, it is easy to obtain the ground eigenfunction of the equation. Furthermore, the shape-invariance property in the series of parameter β is investigated and is proven to be kept. This nice property guarantees that the excited eigenfunctions in the series form can be obtained from the ground eigenfunction by using the method from the supersymmetric quantum mechanics. We show the perturbation method in supersymmetric quantum mechanics could completely solve the spin-weight spheroidal wave equations in the series form of the small parameter β.

ATOMIC AND MOLECULAR PHYSICS

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The influence of interface modifier on photodetachment of negative ions in an electric field near a metal surface Huang Kai-Yun(黄凯云) and Wang De-Hua(王德华) Chin. Phys. B, 2011, 20 (7):  073201.  DOI: 10.1088/1674-1056/20/7/073201 Abstract ( 1346 )   PDF (203KB) ( 716 )   Based on closed-orbit theory, the influence of an interface modifier on the photodetachment of H - in an electric field near a metal surface is studied. It is demonstrated that the interface strengthens the oscillations in the photodetachment cross section. However, when the electric field environments are different, the strengthening oscillations are caused by different sources. When the electric field direction is upward, the interface enhances the oscillations by shortening the period and the action of the closed orbit. When the electric field direction is downward, the interface strengthens the oscillations either by extending the coherent energy range or by increasing the total number of the closed orbits. We hope that our results will be conducive to the understanding of the photodetachment process of negative ions near interfaces, cavities and ion traps.

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Generation-channel interference of high-order harmonics of an anharmonic oscillator driven by bi-chrime laser fields and its mechanism Wang Li-Ming(王黎明), Cai Jun(蔡俊), and Qiao Hao-Xue(乔豪学) Chin. Phys. B, 2011, 20 (7):  073202.  DOI: 10.1088/1674-1056/20/7/073202 Abstract ( 1401 )   PDF (373KB) ( 593 )   A method to describe the generation channels of high-order harmonics is proposed. According to this method, the mechanism of generation-channel interference of high-order harmonics is revealed clearly. We take the anharmonic oscillator driven by bi-chrome fields as an example to illustrate that this method can be used to understand the effect of generation-channel interference.

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Extending a release-and-recapture scheme to single atom optical tweezer for effective temperature evaluation He Jun(何军), Yang Bao-Dong(杨保东), Zhang Tian-Cai(张天才), and Wang Jun-Min(王军民) Chin. Phys. B, 2011, 20 (7):  073701.  DOI: 10.1088/1674-1056/20/7/073701 Abstract ( 1493 )   PDF (1282KB) ( 665 )   By recording the fluorescence fraction of the cold atoms remaining in the magneto-optical trap (MOT) as a function of the release time, the release-and-recapture (R&R) method is utilized to evaluate the effective temperature of the cold atomic ensemble. We prepare a single atom in a large-magnetic-gradient MOT and then transfer the trapped single atom into a 1064-nm microscopic optical tweezer. The energy of the single atom trapped in the tweezer is further reduced by polarization gradient cooling (PGC) and the effective temperature is evaluated by extending the R&R technique to a single atom tweezer. The typical effective temperature of a single atom in the tweezer is improved from about 105 μK to about 17 μK by applying the optimum PGC phase.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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Effects of self-fields on electron trajectory and gain in two-stream electromagnetically pumped free-electron laser with ion channel guiding S. Saviz, Farzin M. Aghamir, H. Mehdian, and M. Ghorannevis Chin. Phys. B, 2011, 20 (7):  074101.  DOI: 10.1088/1674-1056/20/7/074101 Abstract ( 1566 )   PDF (1151KB) ( 655 )   A theory for the two-stream free-electron laser with an electromagnetic wiggler (EMW) and an ion channel guiding is developed. In the analysis, the effects of self-fields have been taken into account. The electron trajectories and the small signal gain are derived. The stability of the trajectories, the characteristics of the linear gain and the normalized maximum gain are studied numerically. The dependence of the normalized frequency $\hat{\omega}$ corresponding to the maximum gain on the ion-channel frequency is presented. The results show that there are seven groups of orbits in the presence of the self-fields, which are similar to those reported in the absence of the self-fields. It is also shown that the normalized gains of 2 groups decrease while the rest increase with the increasing normalized ion-channel frequency. Furthermore, it is found that the two-stream instability and the self-field lead to a decrease in the maximum gain except for group 4.

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Terahertz coherent transition radiation based on an ultrashort electron bunching beam Liu Wen-Xin(刘文鑫), Huang Wen-Hui(黄文会), Du Ying-Chao(杜应超), Yan Li-Xin(颜立新), Wu Dai(吴岱), and Tang Chuan-Xiang(唐传祥) Chin. Phys. B, 2011, 20 (7):  074102.  DOI: 10.1088/1674-1056/20/7/074102 Abstract ( 1389 )   PDF (4449KB) ( 938 )   The experimental result of terahertz (THz) coherent transition radiation generated from an ultrashort electron bunching beam is reported. During this experiment, the window for THz transmission from ultrahigh vacuum to free air is tested. The compact measurement system which can simultaneously test the THz wave power and frequency is built and proofed. With the help of improved Martin—Puplett interferometer and Kramers—Krong transform, the longitudinal bunch length is measured. The results show that the peak power of THz radiation wave is more than 80 kW, and its radiation frequency is from 0.1 THz to 1.5 THz.

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Conformal optical system design with a single fixed conic corrector Song Da-Lin(宋大林), Chang Jun(常军), Wang Qing-Feng(王庆丰), He Wu-Bin(何伍斌), and Cao Jiao(曹娇) Chin. Phys. B, 2011, 20 (7):  074201.  DOI: 10.1088/1674-1056/20/7/074201 Abstract ( 1433 )   PDF (3513KB) ( 1571 )   A conformal optical system refers to the one whose first optical surface conforms to both aerodynamic and imaging requirements. Appropriate correction is required because a conformal dome induces significant aberrations. This paper intends to explain that an effective solution to the easy-fabrication conic surface corrector compensates aberrations induced by a coaxial aspheric dome. A conformal optical system with an ellipsoid MgF2 conformal dome, which has a fineness ratio of 2.0, is designed as an example. The field of regard angle is $\pm30$  degrees with a $\pm2$ degree instantaneous field of view. The system's ultimate value of modulation transfer function is close to the diffraction limit, which indicates that the performance of the conic conformal optical system with a fixed conic corrector meets the imaging requirements.

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Sunlight loss for femtosecond microstructured silicon with two impurity bands Fang Jian(方健), Chen Chang-Shui(陈长水), Wang Fang(王芳), and Liu Song-Hao(刘颂豪) Chin. Phys. B, 2011, 20 (7):  074202.  DOI: 10.1088/1674-1056/20/7/074202 Abstract ( 1391 )   PDF (924KB) ( 808 )   Black silicon, produced by irradiating the surface of a silicon wafer with femtosecond laser pulses in the presence of a sulfur-bearing gas, is widely believed to be a potential material for efficient multi-intermediate-band silicon solar cells. Taking chalcogen as an example, we analyse the loss of sunlight for silicon with two impurity bands and we find that loss of the sunlight can be minimized to 0.332 when Te0(0.307 eV) and Te + (0.411 eV) are doped into microstructured silicon. Finally, problems needed to be resolved in analysing the relationship between conversion efficiency of the ideal four-band silicon solar cell and the position of the introduced two intermediated bands in silicon according to detailed balance theory are pointed out with great asis.

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Far-field divergence of a vectorial plane wave diffracted by a circular aperture from the vectorial structure Zhou Guo-Quan(周国泉) Chin. Phys. B, 2011, 20 (7):  074203.  DOI: 10.1088/1674-1056/20/7/074203 Abstract ( 1547 )   PDF (349KB) ( 581 )   Based on the vectorial structure of an electromagnetic wave, the analytical and concise expressions for the TE and TM terms of a vectorial plane wave diffracted by a circular aperture are derived in the far-field. The expressions of the energy flux distributions of the TE term, the TM term and the diffracted plane wave are also presented. The ratios of the power of the TE and TM terms to that of the diffracted plane wave are examined in the far-field. In addition, the far-field divergence angles of the TE term, the TM term and the diffracted plane wave, which are related to the energy flux distribution, are investigated. The different energy flux distributions of the TE and TM terms result in the discrepancy of their divergence angles. The influences of the linearly polarized angle and the radius of the circular aperture on the far-field divergence angles of the TE term, the TM term and the diffracted plane wave are discussed in detail. This research may promote the recognition of the optical propagation through a circular aperture.

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Time evolution of distribution functions in dissipative environments Hu Li-Yun(胡利云), Chen Fei(陈菲), Wang Zi-Sheng(王资生), and Fan Hong-Yi(范洪义) Chin. Phys. B, 2011, 20 (7):  074204.  DOI: 10.1088/1674-1056/20/7/074204 Abstract ( 1430 )   PDF (129KB) ( 607 )   By introducing the thermal entangled state representation, we investigate the time evolution of distribution functions in the dissipative channels by bridging the relation between the initial distribution function and the any time distribution function. We find that most of them are expressed as such integrations over the Laguerre—Gaussian function. Furthermore, as applications, we derive the time evolution of photon-counting distribution by bridging the relation between the initial distribution function and the any time photon-counting distribution, and the time evolution of R-function characteristic of nonclassicality depth.

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Effective Bose–Hubbard interaction with enhanced nonlinearity in an array of coupled cavities Zhou Ling(周玲), Liu Zhong-Ju(刘忠菊), Yan Wei-Bin(闫伟斌), and Mu Qing-Xia(穆青霞) Chin. Phys. B, 2011, 20 (7):  074205.  DOI: 10.1088/1674-1056/20/7/074205 Abstract ( 1433 )   PDF (162KB) ( 732 )   An array of coupled cavities, each of which contains an N four-level atom, is investigated. When cavity fields dispersively interact with the atoms, an effective Bose—Hubbard model can be achieved. By numerically comparing the full Hamiltonian with the effective one, we find that within the parameters region, the effective Hamiltonian can completely account for the Mott-insulator as well as the phase transition from the similar Mott-insulator to superfluid. Through jointly adjusting the classical Rabi frequency and the detuning, the nonlinearity can be improved.

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Enhanced or suppressed six-wave mixing in a five-level atomic system Song Yue(宋悦), Dai Guo-Xian(代国宪), Fu Yu-Xin(付雨欣), Zhao Jin-Yan(赵金燕), Wang Zhi-Guo(王志国), and Zhang Yan-Peng(张彦鹏) Chin. Phys. B, 2011, 20 (7):  074206.  DOI: 10.1088/1674-1056/20/7/074206 Abstract ( 1580 )   PDF (592KB) ( 520 )   We show the enhancement and suppression of a six-wave mixing (SWM) signal in the electromagnetically induced transparency in a five-level 85Rb atomic system. The results show the Autler—Townes splitting and the enhancement or suppression of SWM, which are caused respectively by a self-dressing effect and by an external dressing effect in the presence of mutual dressing between two SWM signals. In addition, we observe the polarization dependence of the enhancement and suppression of the SWM signals.

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An optical rotation sensor based on dispersive slow-light medium Wang Nan(王楠), Zhang Yun-Dong(掌蕴东), and Yuan Ping(袁萍) Chin. Phys. B, 2011, 20 (7):  074207.  DOI: 10.1088/1674-1056/20/7/074207 Abstract ( 1387 )   PDF (950KB) ( 790 )   Slow light supported by electromagnetically induced transparency effect in dispersive medium is extremely susceptible with respect to Doppler detuning. In this paper, the Doppler effect induced by rotating dispersive medium was considered and the effect of the velocity of rotating dispersive medium on the group velocity was studied. Based on a dispersive slow-light medium, a high sensitive optical rotation sensor for measuring absolute rotation is proposed and analysed. The sensitivity of the rotation sensor is the group delay between the counterpropagationed wave packets in the device, and scales directly with square of the group index which can reach 102—108 orders of magnitude by selecting a proper dispersive medium.

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A large bandwidth photonic delay line using passive cascaded silicon-on-insulator microring resonators Hu Ying-Tao(胡应涛), Xiao Xi(肖希), Li Zhi-Yong(李智勇), Li Yun-Tao(李运涛), Fan Zhong-Chao(樊中朝), Han Wei-Hua(韩伟华), Yu Yu-De(俞育德), and Yu Jin-Zhong(余金中) Chin. Phys. B, 2011, 20 (7):  074208.  DOI: 10.1088/1674-1056/20/7/074208 Abstract ( 1470 )   PDF (1758KB) ( 822 )   This paper investigated the design and the characterization of a photonic delay line based on passive cascaded silicon-on-insulator (SOI) microrings. We considered the compromise of group delay, bandwidth and insertion loss. A 3-stage double channel side-coupled integrated spaced sequence of resonator (SCISSOR) device was optimized by shifting the resonance of each microring and fabricated with electron beam lithography and dry etching. The group delay was measured to be 17 ps for non-return-to-zero signals at different bit rates and the bandwidth of 78 GHz was achieved. The experiment result agreed well with our simulation.

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Numerical simulation of the modulation to incident laser by the repaired damage site in a fused silica subsurface Li Li(李莉), Xiang Xia(向霞), Zu Xiao-Tao(祖小涛), Wang Hai-Jun(王海军), Yuan Xiao-Dong(袁晓东), Jiang Xiao-Dong(蒋晓东), Zheng Wan-Guo(郑万国), and Dai Wei(戴威) Chin. Phys. B, 2011, 20 (7):  074209.  DOI: 10.1088/1674-1056/20/7/074209 Abstract ( 1552 )   PDF (1006KB) ( 828 )   One of the main factors of laser induced damage is the modulation to incident laser which is caused by the defect in the subsurface of the fused silica. In this work, the repaired damage site irradiated by CO2 laser is simplified to a Gaussian rotation according to the corresponding experimental results. Then, the three-dimensional finite-difference time-domain method is employed to simulate the electric field intensity distribution in the vicinity of this kind of defect in fused silica front subsurface. The simulated results show that the modulation is notable, the Emax is about 2.6 times the irradiated electric field intensity in the fused silica with the damage site (the width is 1.5 μm and depth is 2.3 μm) though the damage site is repaired by CO2 laser. The phenomenon and the theoretical result of the annular laser enhancement existed on the rear surface are first verified effectively, which agrees well with the corresponding experimental results. The relations between the maximal electric field intensity in fused silica with defect depth and width are given respectively. Meanwhile, the corresponding physical mechanism is analysed theoretically in detail.

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A compact in-plane photonic crystal channel drop filter Zhao Yi-Nan(赵铱楠), Li Ke-Zheng(李科铮), Wang Xue-Hua(王雪华), and Jin Chong-Jun (金崇君) Chin. Phys. B, 2011, 20 (7):  074210.  DOI: 10.1088/1674-1056/20/7/074210 Abstract ( 1594 )   PDF (2242KB) ( 957 )   This paper presents a novel in-plane photonic crystal channel drop filter. The device is composed of a resonant cavity sandwiched by two parallel waveguides. The cavity has two resonant modes with opposite symmetries. Tuning these two modes into degeneracy causes destructive interference in bus waveguide, which results in high forward drop efficiency at the resonant wavelength. From the result of numerical analysis by using two-dimensional finite-difference time-domain method, the channel drop filter has a drop efficiency of 96% and a Q value of over 3000, which can be used in dense wavelength division multiplexing systems.

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The disorder effect on the performance of novel waveguides constructed in two-dimensional amorphous photonic materials Chen Xiao(陈笑) and Wang Yi-Quan(王义全) Chin. Phys. B, 2011, 20 (7):  074211.  DOI: 10.1088/1674-1056/20/7/074211 Abstract ( 1354 )   PDF (639KB) ( 551 )   On the basis of two-dimensional amorphous photonic materials, we have designed a novel waveguide by inserting thinner cylindrical inclusions in the centre of basic hexagonal units of the amorphous structure along a given path. This waveguide in amorphous structure is similar to the coupled resonator optical waveguides in periodic photonic crystals. The transmission of this waveguide for S-polarized waves is investigated by a multiple-scattering method. Compared with the conventional waveguide by removing a line of cells from amorphous photonic materials, the guiding properties of this waveguide, including the transmissivity and bandwidth, are improved significantly. Then we study the effect of various types of positional disorder on the functionality of this device. Our results show that the waveguide performance is quite sensitive to the disorder located on the boundary layer of the waveguide, but robust against the disorder in the other area in amorphous structure except the waveguide border. This disorder effect in amorphous photonic materials is similar to the case in periodic photonic crystals.

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CMOS compatible highly efficient grating couplers with a stair-step blaze profile Zhou Liang(周亮), Li Zhi-Yong(李智勇), Hu Ying-Tao(胡应涛), Xiong Kang(熊康), Fan Zhong-Chao(樊中朝), Han Wei-Hua(韩伟华), Yu Yu-De (俞育德), and Yu Jin-Zhong (余金中) Chin. Phys. B, 2011, 20 (7):  074212.  DOI: 10.1088/1674-1056/20/7/074212 Abstract ( 1484 )   PDF (595KB) ( 852 )   A novel grating coupler with a stair-step blaze profile is proposed. The coupler is a CMOS process compatible device and can be used for light coupling in optical communication. The blaze profile can be optimized to obtain a high efficiency of 66.7% for the out-of-plane coupling at the centre wavelength of 1595 nm with a 1 dB bandwidth of 41 nm. Five key parameters of the stair-step blaze grating and their effects on the coupling are discussed for the application in L band telecommunication.

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The diffracted sound field from the transition region of 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 (7):  074301.  DOI: 10.1088/1674-1056/20/7/074301 Abstract ( 1393 )   PDF (801KB) ( 760 )   Understanding the physical features of the diffracted sound field on the surface of an axisymmetric body is important for predicting the self-noise of a sonar mounted on an underwater platform. The diffracted sound field from the transition region of an axisymmetric body was calculated by the geometrical theory of diffraction. The diffraction ray between the source point and the receiving point on the surface of an axisymmetric body was calculated by using the dynamic programming method. Based on the diffracted sound field, a simulation scheme for the noise correlation of the conformal array was presented. It was shown that the normalized pressure of the diffracted sound field from the transition region reduced with the increases of the frequency and the curvature of the ray. The flow noises of two models were compared and a rather optimum fore-body geometric shape was given. Furthermore, it was shown that the correlation of the flow noise in the low frequencies was stronger than that in the high frequencies. And the flow noise received by the acoustic array on the curved surface had a stronger correlation than that on the head plane at the designed center frequency, which is important for sonar system design.

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A unique circular path of moving single bubble sonoluminescence in water Rasoul Sadighi-Bonabi, Mona Mirheydari, Homa Ebrahimi, Nastaran Rezaee, and Lida Nikzad Chin. Phys. B, 2011, 20 (7):  074302.  DOI: 10.1088/1674-1056/20/7/074302 Abstract ( 1515 )   PDF (1347KB) ( 739 )   Based on a quasi-adiabatic model, the parameters of the bubble interior for a moving single bubble sonoluminescence (m-SBSL) in water are calculated. By using a complete form of the hydrodynamic force, a unique circular path for the m-SBSL in water is obtained. The effect of the ambient pressure variation on the bubble trajectory is also investigated. It is concluded that as the ambient pressure increases, the bubble moves along a circular path with a larger radius and all bubble parameters, such as gas pressure, interior temperature and light intensity, increase. A comparison is made between the parameters of the moving bubble in water and those in N-methylformamide. With fluid viscosity increasing, the circular path changes into an elliptic form and the light intensity increases.

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Designing power heterojunction bipolar transistors with non-uniform emitter finger lengths to achieve high thermal stability Jin Dong-Yue(金冬月), Zhang Wan-Rong(张万荣), Fu Qiang(付强), Chen Liang(陈亮), Xiao Ying(肖盈), Wang Ren-Qing(王任卿), and Zhao Xin(赵昕) Chin. Phys. B, 2011, 20 (7):  074401.  DOI: 10.1088/1674-1056/20/7/074401 Abstract ( 1578 )   PDF (3052KB) ( 730 )   With the aid of a thermal-electrical model, a practical method for designing multi-finger power heterojunction bipolar transistors with finger lengths divided in groups is proposed. The method can effectively enhance the thermal stability of the devices without sacrificing the design time. Taking a 40-finger heterojunction bipolar transistor for example, the device with non-uniform emitter finger lengths is optimized and fabricated. Both the theoretical and the experimental results show that, for the optimum device, the peak temperature is lowered by 26.19 K and the maximum temperature difference is reduced by 56.67% when compared with the conventional heterojunction bipolar transistor with uniform emitter finger length. Furthermore, the ability to improve the uniformity of the temperature profile and to expand the thermal stable operation range is strengthened as the power level increases, which is ascribed to the improvement of the thermal resistance in the optimum device. A detailed design procedure is also summarized to provide a general guide for designing power heterojunction bipolar transistors with non-uniform finger lengths.

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The effect of rotation on plane waves in generalized thermo-microstretch elastic solid with one relaxation time for a mode-I crack problem Kh. Lotfy and Mohamed I. A. Othman Chin. Phys. B, 2011, 20 (7):  074601.  DOI: 10.1088/1674-1056/20/7/074601 Abstract ( 1428 )   PDF (374KB) ( 900 )   The present paper is aimed at studying the effect of rotation on the general model of the equations of the generalized thermo-microstretch for a homogeneous isotropic elastic half-space solid, whose surface is subjected to a Mode-I crack problem. The problem is studied in the context of the generalized thermoelasticity Lord—cShulman's (L—S) theory with one relaxation time, as well as with the classical dynamical coupled theory (CD). The normal mode analysis is used to obtain the exact expressions for the displacement components, the force stresses, the temperature, the couple stresses and the microstress distribution. The variations of the considered variables through the horizontal distance are illustrated graphically. Comparisons of the results are made between the two theories with and without the rotation and the microstretch constants.

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Analytical investigation on mean and turbulent velocity fields of a plane jet Mi Jian-Chun(米建春) and Feng Bao-Ping(冯宝平) Chin. Phys. B, 2011, 20 (7):  074701.  DOI: 10.1088/1674-1056/20/7/074701 Abstract ( 1311 )   PDF (218KB) ( 837 )   This paper analyses the downstream developments of the mean and the turbulent velocity fields of a plane jet. Based on the conservation of mass and the conservation of momentum, the mean-velocity half width (reflecting the jet spread rate) and the relative mass flow rate (jet entrainment) are related to the decay rate of the centreline mean velocity. These relations are not subject to self-preservation. Both analytical and experimental results suggest that the jet spread rate (K1) and the entrainment rate (K3) (and thus the decay rate K2) can be well estimated from the centreline velocity, i.e., K1 ≈ 0.6K2 and K3 ∝ K2. The effect of initial mean velocity and RMS velocity profiles on the downstream mean velocity field appears to be embodied in the constants K1 K2 and K3. The analytical relationship for the self-preserving Reynolds shear stress, obtained for the first time, works well.

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Turing pattern selection in a reaction–diffusion epidemic model Wang Wei-Ming(王玮明), Liu Hou-Ye(刘厚业), Cai Yong-Li (蔡永丽), and Li Zhen-Qing (李镇清) Chin. Phys. B, 2011, 20 (7):  074702.  DOI: 10.1088/1674-1056/20/7/074702 Abstract ( 1537 )   PDF (2249KB) ( 1420 )   We present Turing pattern selection in a reaction--diffusion epidemic model under zero-flux  boundary conditions. The value of this study is twofold. First, it establishes the amplitude equations for  the excited modes, which determines the stability of amplitudes towards uniform and inhomogeneous  perturbations. Second, it illustrates all five categories of Turing patterns close to the onset of Turing  bifurcation via numerical simulations which indicates that the model dynamics exhibits complex pattern  replication: on increasing the control parameter $\nu$, the sequence ``$H_0$ hexagons $\rightarrow$  $H_0$-hexagon-stripe mixtures $\rightarrow$ stripes $\rightarrow$ $H_{\pi}$-hexagon-stripe mixtures  $\rightarrow$ $H_{\pi}$ hexagons" is observed. This may enrich the pattern dynamics in a diffusive epidemic model.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Luminescence properties of InxGa1 - xN (x ～ 0.04) films grown by metal organic vapour phase epitaxy Zhao Wei(赵维), Wang Lai(汪莱), Wang Jia-Xing(王嘉星), and Luo Yi(罗毅) Chin. Phys. B, 2011, 20 (7):  076101.  DOI: 10.1088/1674-1056/20/7/076101 Abstract ( 1494 )   PDF (6656KB) ( 819 )   InxGa1 - xN (x ～ 0.04) films are grown by metal organic vapour phase epitaxy. For the samples grown on GaN directly, the relaxation of InGaN happens when its thickness is beyond a critical value. A broad band is observed in the luminescence spectrum, and its intensity increases with the increasing degree of relaxation. Secondary ion mass spectrometry measurement rules out the possibility of the broad band originating from impurities in InGaN. The combination of the energy-dispersive X-ray spectra and the cathodeluminescence measurements shows that the origin of the broad band is attributed to the indium composition inhomogeneity caused by the phase separation effect. The measurement results of the tensile-strained sample further demonstrate the conclusions.

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Interface of quasicrystal and crystal Fan Tian-You(范天佑), Xie Ling-Yun(解凌云), Fan Lei(范蕾), and Wang Qing-Zhao(王清昭) Chin. Phys. B, 2011, 20 (7):  076102.  DOI: 10.1088/1674-1056/20/7/076102 Abstract ( 1503 )   PDF (877KB) ( 757 )   A model on the coexisting phase of quasicrystal-crystal is proposed, with which we concretely investigate the interface effects for coexisting phases of one-dimensional orthorhombic quasicrystal-isotropic crystal and three-dimensional icosahedral quasicrystal-cubic crystal. The phason strain fields which play an important role in some processes are determined. Some factors affecting the strain fields, e.g., the material constants of phonon, phason, phonon—phason coupling of the quasicrystal and the elastic modulus and the size of the crystal are also explored.

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Surface-enhanced Raman scattering properties of highly ordered self-assemblies of gold nanorods with different aspect ratios Shi Xue-Zhao(时雪钊), Shen Cheng-Min(申承民), Wang Deng-Ke(王登科), Li Chen(李晨), Tian Yuan(田园), Xu Zhi-Chuan(徐桎川), Wang Chun-Ming(王春明), and Gao Hong-Jun(高鸿钧) Chin. Phys. B, 2011, 20 (7):  076103.  DOI: 10.1088/1674-1056/20/7/076103 Abstract ( 1508 )   PDF (2893KB) ( 767 )   Gold nanorods with aspect ratios of from 1 (particles) to 31.6 were synthesized by the seed-mediated method and packed in a highly ordered structure on a large scale on silicon substrates through capillary force induced self-assembly behaviour during solvent evaporation. The gold nanorod surface exhibits a strong enhancing effect on Raman scattering spectroscopy. The enhancement of Raman scattering for two model molecules (2-naphthalenethiol and rhodamine 6G) is about 5—6 orders of magnitude. By changing the aspect ratio of the Au nanorods, we found that the enhancement factors decreased with the increase of aspect ratios. The observed Raman scattering enhancement is strong and should be ascribed to the surface plasmon coupling between closely packed nanorods, which may result in huge local electromagnetic field enhancements in those confined junctions.

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Atomistic simulation of site preference, Curie temperature, and lattice vibration of Nd2Co7 - xFex Qian Ping(钱萍), Liu Jiu-Li (刘九丽), Hu Yao-Wen(胡耀文), Bai Li-Jun(白丽君), and Shen Jiang(申江) Chin. Phys. B, 2011, 20 (7):  076104.  DOI: 10.1088/1674-1056/20/7/076104 Abstract ( 1759 )   PDF (602KB) ( 719 )   The effects of Fe substitution for Co on the structural stability and the site preference of  intermetallics Nd$_{2}$Co$_{7 - x}$Fe$_{x}$ with a hexagonal Ce$_{2}$Ni$_{7}$-type structure are studied by  using a series of interatomic pair potentials. In Nd$_{2}$Co$_{7 - x}$Fe$_{x}$, Fe atoms are substituted for  Co atoms with a strong preference for the 6h sites and the order of site preference is 6h, 4e, 4f, 2a, and  12k. Calculated lattice parameters are found to be consistent with the reported results in the literature.  The variation behaviour of the Curie temperature of Nd$_{2}$Co$_{7 - x}$Fe$_{x}$ is explained qualitatively  by the exchange interaction model. The properties related to lattice vibration, such as phonon density of  states and Debye temperature, are first evaluated for the Nd$_{2}$Co$_{7 - x}$Fe$_{x}$ compounds.

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Structural modification of C60 films induced by 300-keV Xe-ion irradiation Yao Cun-Feng (姚存峰), Jin Yun-Fan(金运范), Wang Zhi-Guang(王志光), Pang Li-Long(庞立龙), Shen Tie-Long(申铁龙), and Zhu Ya-Bin(朱亚滨) Chin. Phys. B, 2011, 20 (7):  076105.  DOI: 10.1088/1674-1056/20/7/076105 Abstract ( 1439 )   PDF (3306KB) ( 654 )   The structural modification of C60 films induced by 300-keV Xe-ion irradiation was investigated. The irradiated C60 films were analysed using Fourier transform infrared spectroscopy, the Raman scattering technique, ultraviolet/visible spectrophotometry and atomic force microscopy. The analysis results indicate that the Xe-ion irradiation induces polymerization and damage of the C60 molecule and significantly modifies the surface morphology and the optical property of the C60 films. The damage cross-section for the C60 molecule was also evaluated.

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Electrostatic interaction between a rod-like macromolecule and a circular orifice/disk in an electrolyte solution Lian Zeng-Ju(连增菊) Chin. Phys. B, 2011, 20 (7):  076401.  DOI: 10.1088/1674-1056/20/7/076401 Abstract ( 1378 )   PDF (630KB) ( 653 )   We present the solutions of the interaction energy for a colloid system with a charged rod-like macromolecule immersed in a bulk electrolyte and moving along the axis of a circular orifice or disk (orifice/disk). The calculation requires a numerical computation of the surface charge profiles, which result from a constant surface potential on the macromolecule and the orifice/disk. In the calculation, remarkable divergences of the surface charge emerge on the edges of the macromolecule and the orifice/disk, which are well-known edge effects. The anisotropic distribution of the surface charge (effective dipole) results in an attraction between these two charged objects. This attraction is enhanced with the increase of the screening length of the system for both the orifice and the disk systems. However, the sizes of the orifice and the disk reduce to different effects on the interaction energy.

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Phase relations in the ZnO-V2O5-K2O system Hot! Chen Ye-Qing(陈业青), Li Lei(李蕾), Ren Qi(任其), Zhu Hang-Tian(朱航天), Liang Jing-Kui(梁敬魁), Luo Jun(骆军), Li Jing-Bo(李静波), and Rao Guang-Hui(饶光辉) Chin. Phys. B, 2011, 20 (7):  076402.  DOI: 10.1088/1674-1056/20/7/076402 Abstract ( 1509 )   PDF (615KB) ( 1420 )   The subsolidus phase relations of a ZnO-V2O5-K2O system are investigated by X-ray powder diffraction. There is 1 ternary compound, 11 binary compounds and 14 three-phase regions in this system. The phase diagrams of V2O5-K2O with the K2O content ranging from 0 to 71 mol% and pseudo-binary system of ZnO-K2ZnV2O7 are also studied by X-ray powder diffraction and differential thermal analysis methods.

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Quantum diffusion in bilateral doped chains Jin Fu-Bao(金福报), Zhang Kai-Wang(张凯旺), and Zhong Jian-Xin(钟建新) Chin. Phys. B, 2011, 20 (7):  076701.  DOI: 10.1088/1674-1056/20/7/076701 Abstract ( 1486 )   PDF (1757KB) ( 682 )   In this paper, we quantitatively study the quantum diffusion in a bilateral doped chain, which is randomly doped on both sides. A tight binding approximation and quantum dynamics are used to calculate the three electronic characteristics: autocorrelation function C(t), the mean square displacement d(t) and the participation number P(E) in different doping situations. The results show that the quantum diffusion is more sensitive to the small ratio of doping than to the big one, there exists a critical doping ratio q0, and C(t), d(t) and P(E) have different variation trends on different sides of q0. For the self-doped chain, the doped atoms have tremendous influence on the central states of P(E), which causes the electronic states distributed in other energy bands to aggregate to the central band (E=0) and form quasi-mobility edges there. All of the doped systems experience an incomplete transition of metal-semiconductor-metal.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Magnetic properties of several potential rocksalt half-metallic ferromagnets based on the first-principles calculations Liu Jun(刘俊), Zhan Rui(詹瑞), Li Li(李丽), and Dong Hui-Ning(董会宁) Chin. Phys. B, 2011, 20 (7):  077101.  DOI: 10.1088/1674-1056/20/7/077101 Abstract ( 1528 )   PDF (1467KB) ( 742 )   Several rocksalt Sr4X3N (X=O, S, Se, and Te) are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their magnetic properties, such as the half metallicity and the crystal-cell magnetic moments are investigated. The Sr4X3N possibly have higher Curie temperatures and have more stable half metallicity than the Sr4X3C. Their crystal-cell magnetic moments are all 1.00 μB. The crystal-cell magnetic moments and the half metallicity arise mainly from the N ions. The main mechanism is the strong covalent interaction leading to the sp2 hybridized orbitals in the Sr4X3N. Then two Sr-5s and three N-2p electrons enter into three sp2 hybridized orbitals. Among these five electrons, four electrons are paired and one is unpaired, so there are three spin-up electrons and two spin-down electrons in these sp2 hybridized orbitals.

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Structural, electronic, and magnetic properties of CrN under high pressure Lin He(蔺何) and Zeng Zhi(曾雉) Chin. Phys. B, 2011, 20 (7):  077102.  DOI: 10.1088/1674-1056/20/7/077102 Abstract ( 1492 )   PDF (176KB) ( 1247 )   The structural, electronic and magnetic properties of CrN under high pressure are investigated by first-principles calculations. The antiferromagnetic orthorhombic structure is identified to be the preferred ground state structure. It possesses a bulk modulus of 252.8 GPa and the nonzero magnetic moment of 2.33 μB per Cr ion, which agree well with the experimental results. CrN undergoes structural and magnetic transitions from an antiferromagnetic rocksalt structure to a non-magnetic Pnma phase at 132 GPa. Under compression, the magnetic moment of the Cr ion reduces rapidly near the equilibrium and phase transition point, and the distribution of the density of states is broadened, but the form of overlap between the orbitals of Cr d and N p remains unchanged. The broadening of the band induces spin flipping, which consequently results in the smaller magnetic moment of the Cr ion.

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MgO-decorated carbon nanotubes for CO2 adsorption: first principles calculations Hot! Zhu Feng(朱峰), Dong Shan(董珊), and Cheng Gang(承刚) Chin. Phys. B, 2011, 20 (7):  077103.  DOI: 10.1088/1674-1056/20/7/077103 Abstract ( 1491 )   PDF (974KB) ( 1227 )   The global greenhouse effect makes it urgent to deal with the increasing greenhouse gases. In this paper the performance of MgO-decorated carbon nanotubes for CO2 adsorption is investigated through first principles calculations. The results show that the MgO-decorated carbon nanotubes can adsorb CO2 well and are relatively insensitive to O2 and N2 at the same time. The binding energy arrives at 1.18 eV for the single-MgO-decorated carbon nanotube adsorbing one CO2 molecule, while the corresponding values for O2 and N2 are 0.55 eV and 0.06 eV, respectively. In addition, multi-molecule adsorption is also proved to be very satisfactory. These results indicate that MgO-decorated carbon nanotubes have great potential applications in industrial and environmental processes.

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Radiative life time of an exciton confined in a strained GaN/Ga1-xAlxN cylindrical dot: built-in electric field effects Chang Woo Lee, A. John Peter Chin. Phys. B, 2011, 20 (7):  077104.  DOI: 10.1088/1674-1056/20/7/077104 Abstract ( 1467 )   PDF (277KB) ( 1132 )   The binding energy of an exciton in a wurtzite GaN/GaAlN strained cylindrical quantum dot is investigated theoretically. The strong built-in electric field due to the spontaneous and piezoelectric polarizations of a GaN/GaAlN quantum dot is included. Numerical calculations are performed using a variational procedure within the single band effective mass approximation. Valence-band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. The exciton oscillator strength and the exciton lifetime for radiative recombination each as a function of dot radius have been computed. The result elucidates that the strong built-in electric field influences the oscillator strength and the recombination life time of the exciton. It is observed that the ground state exciton binding energy and the interband emission energy increase when the cylindrical quantum dot height or radius is decreased, and that the exciton binding energy, the oscillator strength and the radiative lifetime each as a function of structural parameters (height and radius) sensitively depend on the strong built-in electric field. The obtained results are useful for the design of some opto-photoelectronic devices.

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Dynamic electron transport theory for multiprobe mesoscopic structures Quan Jun(全军), Tian Ying (田英), Zhang Jun(张军), and Shao Le-Xi(邵乐喜) Chin. Phys. B, 2011, 20 (7):  077201.  DOI: 10.1088/1674-1056/20/7/077201 Abstract ( 1413 )   PDF (149KB) ( 567 )   Using the linear response theory and random phase approximation, we develop a general dynamic electron transport theory for multiprobe mesoscopic structures in an arbitrarily time-dependent external field. In this case, the responses of the dynamic current, charge and internal potential to the external fields can be determined self-consistently. Without loss of generality, charge (current) conservation and gauge invariance under a potential shift are satisfied. As an example, we employ a quantum wire with a single barrier to discuss the response of the internal potential.

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Numerical study of strained InGaAs quantum well lasers emitting at 2.33 μm using the eight-band model Wang Ming(汪明), Gu Yong-Xian(谷永先), Ji Hai-Ming(季海铭), Yang Tao(杨涛), and Wang Zhan-Guo(王占国) Chin. Phys. B, 2011, 20 (7):  077301.  DOI: 10.1088/1674-1056/20/7/077301 Abstract ( 1369 )   PDF (1146KB) ( 821 )   We investigate the band structure of a compressively strained In(Ga)As/In0.53Ga0.47As quantum well (QW) on an InP substrate using the eight-band k·p theory. Aiming at the emission wavelength around 2.33 μm, we discuss the influences of temperature, strain and well width on the band structure and on the emission wavelength of the QW. The wavelength increases with the increase of temperature, strain and well width. Furthermore, we design an InAs /In0.53Ga0.47As QW with a well width of 4.1 nm emitting at 2.33 μm by optimizing the strain and the well width.

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Spin current and its heat effect in a multichannel quantum wire with Rashba spin–orbit coupling Song Zhan-Feng(宋占锋), Wang Ya-Dong(王亚东), Shao Hui-Bin(邵慧彬), and Sun Zhi-Gang(孙志刚) Chin. Phys. B, 2011, 20 (7):  077302.  DOI: 10.1088/1674-1056/20/7/077302 Abstract ( 1509 )   PDF (163KB) ( 587 )   Using the perturbation method, we theoretically study the spin current and its heat effect in a multichannel quantum wire with Rashba spin–orbit coupling. The heat generated by the spin current is calculated. With the increase of the width of the quantum wire, the spin current and the heat generated both exhibit period oscillations with equal amplitudes. When the quantum-channel number is doubled, the oscillation periods of the spin current and of the heat generated both decrease by a factor of 2. For the spin current js,xy, the amplitude increases with the decrease of the quantum channel; while the amplitude of the spin current js,yx remains the same. Therefore we conclude that the effect of the quantum-channel number on the spin current js,xy is greater than that on the spin current js,yx. The strength of the Rashba spin—orbit coupling is tunable by the gate voltage, and the gate voltage can be varied experimentally, which implies a new method of detecting the spin current. In addition, we can control the amplitude and the oscillation period of the spin current by controlling the number of the quantum channels. All these characteristics of the spin current will be very important for detecting and controlling the spin current, and especially for designing new spintronic devices in the future.

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Identification and elimination of inductively coupled plasma-induced defects in AlxGa1 - xN/GaN heterostructures Lin Fang(林芳), Shen Bo(沈波), Lu Li-Wu(卢励吾), Liu Xin-Yu(刘新宇), Wei Ke(魏珂), Xu Fu-Jun(许福军), Wang Yan(王彦), Ma Nan(马楠), and Huang Jun(黄俊) Chin. Phys. B, 2011, 20 (7):  077303.  DOI: 10.1088/1674-1056/20/7/077303 Abstract ( 1423 )   PDF (399KB) ( 802 )   By using temperature-dependent Hall, variable-frequency capacitance—voltage and cathodoluminescence (CL) measurements, the identification of inductively coupled plasma (ICP)-induced defect states around the AlxGa1 - xN/GaN heterointerface and their elimination by subsequent annealing in AlxGa1 - xN/GaN heterostructures are systematically investigated. The energy levels of interface states with activation energies in a range from 0.211 to 0.253 eV below the conduction band of GaN are observed. The interface state density after the ICP-etching process is as high as 2.75 × 1012 cm - 2·eV - 1. The ICP-induced interface states could be reduced by two orders of magnitude by subsequent annealing in N2 ambient. The CL studies indicate that the ICP-induced defects should be Ga-vacancy related.

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Compound buried layer SOI high voltage device with a step buried oxide Wang Yuan-Gang(王元刚), Luo Xiao-Rong(罗小蓉), Ge Rui(葛锐), Wu Li-Juan(吴丽娟), Chen Xi（陈曦), Yao Guo-Liang(姚国亮), Lei Tian-Fei(雷天飞), Wang Qi(王琦), Fan Jie(范杰), and Hu Xia-Rong(胡夏融) Chin. Phys. B, 2011, 20 (7):  077304.  DOI: 10.1088/1674-1056/20/7/077304 Abstract ( 1526 )   PDF (1859KB) ( 871 )   A silicon-on-insulator (SOI) high performance lateral double-diffusion metal oxide semiconductor (LDMOS) on a compound buried layer (CBL) with a step buried oxide (SBO CBL SOI) is proposed. The step buried oxide locates holes in the top interface of the upper buried oxide (UBO) layer. Furthermore, holes with high density are collected in the interface between the polysilicon layer and the lower buried oxide (LBO) layer. Consequently, the electric fields in both the thin LBO and the thick UBO are enhanced by these holes, leading to an improved breakdown voltage. The breakdown voltage of the SBO CBL SOI LDMOS increases to 847 V from the 477 V of a conventional SOI with the same thicknesses of SOI layer and the buried oxide layer. Moreover, SBO CBL SOI can also reduce the self-heating effect.

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Transport properties through double-magnetic-barrier structures in graphene Wang Su-Xin(王素新), Li Zhi-Wen(李志文), Liu Jian-Jun(刘建军), and Li Yu-Xian(李玉现) Chin. Phys. B, 2011, 20 (7):  077305.  DOI: 10.1088/1674-1056/20/7/077305 Abstract ( 1797 )   PDF (182KB) ( 1014 )   We study electrons tunneling through a double-magnetic-barrier structure on the surface of monolayer graphene. The transmission probability and the conductance are calculated by using the transfer matrix method. The results show that the normal incident transmission probability is blocked by the magnetic vector potential and the Klein tunneling region depends strongly on the direction of the incidence electron. The transmission probability and the conductance can be modulated by changing structural parameters of the barrier, such as width and height, offering a possibility to control electron beams on graphene.

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Effect of proportion on rectification in organic co-oligomer spin rectifiers Hu Gui-Chao(胡贵超), Wang Hui(王辉), and Ren Jun-Feng(任俊峰) Chin. Phys. B, 2011, 20 (7):  077306.  DOI: 10.1088/1674-1056/20/7/077306 Abstract ( 1570 )   PDF (168KB) ( 696 )   The rectification behaviours in organic magnetic/nonmagnetic co-oligomer spin rectifiers are investigated theoretically. It is found that both the charge current and the spin current through the device are rectified at the same time. By adjusting the proportion between the magnetic and nonmagnetic components, the threshold voltage and the rectification ratio of the rectifier are modulated. A large rectification ratio is obtained when the two components are equal in length. The intrinsic mechanism is analysed in terms of the asymmetric localization of molecular orbitals under biases. The effect of molecular length on the rectification is also discussed. These results will be helpful in the future design of organic spin diodes.

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Formation energies and electronic structures of native point defects in potassium dihydrogen phosphate Wang Kun-Peng(王坤鹏) and Huang Ye(黄烨) Chin. Phys. B, 2011, 20 (7):  077401.  DOI: 10.1088/1674-1056/20/7/077401 Abstract ( 1487 )   PDF (1103KB) ( 682 )   The formation energies and the equilibrium concentration of vacancies, interstitial H, K, P, O and antisite structural defects with P and K in KH2PO4 (KDP) crystals are investigated by ab initio total-energy calculations. The formation energy of interstitial H is calculated to be about 2.06 eV and we suggest that it may be the dominant defect in KDP crystal. The formation energy of an O vacancy (5.25 eV) is much higher than that of interstitial O (0.60 eV). Optical absorption centres can be induced by defects of O vacancies, interstitial O and interstitial H. We suggest that these defects may be responsible for the lowering of the damage threshold of the KDP. A K vacancy defect may increase the ionic conductivity and therefore the laser-induced damage threshold decreases.

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A method based on magnetic moment measurement to identify the structural transition of quenched Fe1 -xGax (x = 0.15–0.30) alloys Zhu Xiao-Xi(朱小溪), Liu Jing-Hua(刘敬华), Xu Xiang(徐翔), and Jiang Cheng-Bao(蒋成保) Chin. Phys. B, 2011, 20 (7):  077501.  DOI: 10.1088/1674-1056/20/7/077501 Abstract ( 1302 )   PDF (326KB) ( 637 )   A method based on the measurement of Fe average atomic magnetic moment to identify the structural transition caused by the increase of Ga content in quenched Fe1 - xGax alloys (0.15 ≤ x ≤ 0.30) is proposed. The quenched Fe1 - xGax alloys show a change of the Fe average atomic magnetic moment from 2.25 μB to 1.78 μB and then to 1.58 μB, which corresponds to the structural transition from A2 to D03 and then to B2. The relationship between the structure and the magnetostriction is clarified, and the maximum magnetostriction appears in the A2 phase. The variation tendency of the magnetostriction is well characterized, which also reflects the structural transition.

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Multiferroic properties of sol–gel derived Bi5Fe1-xCoxTi3O15 thin films Wang Wei(王伟), Wu Xin-Hua(武鑫华), Mao Xiang-Yu(毛翔宇), and Chen Xiao-Bing(陈小兵) Chin. Phys. B, 2011, 20 (7):  077701.  DOI: 10.1088/1674-1056/20/7/077701 Abstract ( 1672 )   PDF (5259KB) ( 1184 )   Co-doped Bi$_{5}$FeTi$_{3}$O$_{15}$ thin films (BFCT-$x$,  Bi$_{5}$Fe$_{1-x}$Co$_{x}$Ti$_{3}$O$_{15}$) were prepared using a sol--gel technique. XRD patterns confirm  their single phase Aurivillius structure, and the corresponding powder Rietveld analysis indicates the change  of space group around $x=0.12$. The magnetic hysteresis loops are obtained and ferromagnetism is therefore  confirmed in BFCT-$x$ thin films. The remanent magnetization ($M_{\rm r}$) first increases and reaches the  maximum value of 0.42 emu/cm$^{3}$ at $x=0.12$ due to the possible Fe$^{3+}$--O--Co$^{3+}$ ferromagnetic  coupling. When $x = 0.25$, the $M_{\rm r}$ increases again because of the dominant Fe$^{3+}$--O--Co$^{3+}$  ferromagnetic coupling. The remanent polarization ($2P_{\rm r}$) of BFCT-0.25 was measured to be as high as  62 $\mu $C/cm$^{2}$, a 75% increase when compared with the non-doped BFCT-0 films. The $2P_{\rm r}$  remains almost unchanged after being subjected to $5.2\times 10^{9}$ read/write cycles. Greatly enhanced ferroelectric properties are considered to be associated with decreased leakage current density.

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Raman and mid-infrared spectroscopic study of geometrically frustrated hydroxyl cobalt halides at room temperature Liu Xiao-Dong(刘晓东), Meng Dong-Dong(孟冬冬), Hagihala Masato(萩原雅人), Zheng Xu-Guang(郑旭光), and Guo Qi-Xin(郭其新) Chin. Phys. B, 2011, 20 (7):  077801.  DOI: 10.1088/1674-1056/20/7/077801 Abstract ( 1338 )   PDF (2583KB) ( 1125 )   Mid-infrared absorption and Raman spectra of the geometrically frustrated material series, hydroxyl cobalt halides β -Co2(OH)3Cl and β -Co2(OH)3Br, are first, to the best of our knowledge, measured at room temperature, to study the corresponding relationship between their vibrational spectral properties and crystal microstructures. Through the comparative analysis of the four spectra we have categorically assigned the OH-related vibration modes of hydroxyl groups in the trimeric hydrogen bond environment (Co3 ≡ OH)3 ··· Cl/Br, and tentatively suggested vibration modes of O—Co—O, Co—O and Cl/Br—Co—Cl/Br units. These results can also become the basis for analysing their low-temperature spectral properties, which can help to understand the underlying physics of their exotic geometric frustration phenomena around phase transition temperatures.

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Evolution of infrared spectra and optical emission spectra in hydrogenated silicon thin films prepared by VHF-PECVD Hou Guo-Fu(侯国付), Geng Xin-Hua(耿新华), Zhang Xiao-Dan(张晓丹), Sun Jian(孙建), Zhang Jian-Jun(张建军), and Zhao Ying(赵颖) Chin. Phys. B, 2011, 20 (7):  077802.  DOI: 10.1088/1674-1056/20/7/077802 Abstract ( 1538 )   PDF (582KB) ( 989 )   A series of hydrogenated silicon thin films with varying silane concentrations have been deposited by using very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The deposition process and the silicon thin films are studied by using optical emission spectroscopy (OES) and Fourier transfer infrared (FTIR) spectroscopy, respectively. The results show that when the silane concentration changes from 10% to 1%, the peak frequency of the Si—H stretching mode shifts from 2000 cm - 1 to 2100 cm - 1, while the peak frequency of the Si—H wagging—rocking mode shifts from 650 cm - 1 to 620 cm - 1. At the same time the SiH*/Hα intensity ratio in the plasma decreases gradually. The evolution of the infrared spectra and the optical emission spectra demonstrates a morphological phase transition from amorphous silicon (a-Si:H) to microcrystalline silicon (μc-Si:H). The structural evolution and the μc-Si:H formation have been analyzed based on the variation of H$\alpha$ and SiH* intensities in the plasma. The role of oxygen impurity during the plasma process and in the silicon films is also discussed in this study.

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Amplified spontaneous emission from metal-backed poly[2-methoxy-5-(2'-ethylhexyloxy)-1, 4-phenylenevinylene] film Zhang Bo (张波), Hou Yan-Bing (侯延冰), Teng Feng (滕枫), Lou Zhi-Dong (娄志东), Liu Xiao-Jun (刘小君), Hu Bing (胡兵), Wu Wen-Bin (武文彬) Chin. Phys. B, 2011, 20 (7):  077803.  DOI: 10.1088/1674-1056/20/7/077803 Abstract ( 1605 )   PDF (307KB) ( 777 )   We investigate the amplified spontaneous emission (ASE) from an Ag-backed poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) film with different film thicknesses. The ASE characteristics of Ag-backed MEH-PPV films with different thicknesses show that increasing the film thickness can reduce the influence of the Ag cladding. The threshold, the gain, and the loss of the device with a thickness of 170 nm are comparable to those of a metal-free device. The lasing threshold of this device is about 7.5 times that of a metal-free device. Our findings demonstrate that Ag-backed MEH-PPV film with an appropriate thickness can still be a good polymer gain material for the fabrication of solid-state lasers.

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Simulation of the light extraction efficiency of nanostructure light-emitting diodes Zhu Ji-Hong(朱继红), Wang Liang-Ji(王良吉), Zhang Shu-Ming(张书明), Wang Hui(王辉), Zhao De-Gang(赵德刚), Zhu Jian-Jun(朱建军), Liu Zong-Shun(刘宗顺), Jiang De-Sheng(江德生), and Yang Hui(杨辉) Chin. Phys. B, 2011, 20 (7):  077804.  DOI: 10.1088/1674-1056/20/7/077804 Abstract ( 1579 )   PDF (654KB) ( 1347 )   The light extraction efficiencies have been calculated for various InGaN/GaN multiple quantum well nanostructure light-emitting diodes including nanopillar, nanorough of P-GaN surface, coreshell and nano-interlayer structure. From the calculated results we can see that the light extraction efficiency is remarkably improved in the nanostructures, especially those with an InGaN or AlGaN nano-interlayer. With a 420-nm luminescence wavelength, the light extraction efficiency can reach as high as 65% for the InGaN or AlGaN nano-interlayer structure with appropriate In or Al content while only 26% for the planar structure.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Novel photoluminescence properties of InAlO3(ZnO)m superlattice nanowires Liu Xin(刘欣), Huang Dong-Liang(黄东亮), Wu Li-Li(武立立), Zhang Xi-Tian(张喜田), and Zhang Wei-Guang(张伟光) Chin. Phys. B, 2011, 20 (7):  078101.  DOI: 10.1088/1674-1056/20/7/078101 Abstract ( 1705 )   PDF (1647KB) ( 883 )   One-dimension InAlO3(ZnO)m superlattice nanowires were successfully synthesized via chemical vapor deposition. Transmission electron microscopy measurements reveal that the nanowires have a periodic layered structure along the 〈0001〉 direction. The photoluminescence properties of InAlO3(ZnO)m superlattice nanowires are studied for the first time. The near-band-edge emissions exhibit an obvious red shift due to the formation of the localized tail states. The two peaks centered at 3.348 eV and 3.299 eV indicate a lever phenomenon at the low-temperature region. A new luminescence mechanism is proposed, combined with the special energy band structure of InAlO3(ZnO)m.

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Real-time observation of template-assisted colloidal aggregation and colloidal dispersion under an alternating electric field Hot! Li Chao-Rong(李超荣), Li Shu-Wen(李书文), Mei Jie(梅洁), Xu Qing(徐庆), Zheng Ying-Ying(郑莹莹), and Dong Wen-Jun(董文钧) Chin. Phys. B, 2011, 20 (7):  078102.  DOI: 10.1088/1674-1056/20/7/078102 Abstract ( 1403 )   PDF (9333KB) ( 531 )   A fascinating colloid phenomenon was observed in a specially designed template-assisted cell under an alternating electrical field. Most colloidal particles experienced the processes of aggregation, dispersion and climbing up to the plateaus of the patterns pre-lithographed on the indium tin oxide glass as the frequency of the alternating electrical field increased. Two critical frequencies fcrit1 ≈ 15 kHz and fcrit2 ≈ 40 kHz, corresponding to the transitions of the colloid behaviour were observed. When f < 15 kHz, the particles were forced to aggregate along the grooves of the negative photoresist patterned template. When 15 kHz < f < 40 kHz, the particle clusters became unstable and most particles started to disperse and were blocked by the fringes of the negative photoresist patterns. As the frequency increased to above 40 kHz, the majority of particles started to climb up to the plateaus of the patterns. Furthermore, the dynamics analysis for the behaviour of the colloids was given and we found out that positive or negative dielectrophoresis force, electrohydrodynamic force, particle—particle interactions and Brownian motion change with the frequency of the alternating electric field. Thus, changes of the related forces affect or control the behaviour of the colloids.

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Growth of gem-grade nitrogen-doped diamond crystals heavily doped with the addition of Ba(N3)2 Huang Guo-Feng(黄国锋), Jia Xiao-Peng(贾晓鹏), Li Yong(李勇), Hu Mei-Hua(胡美华), Li Zhan-Chang(李战厂), Yan Bing-Min(颜丙敏), and Ma Hong-An(马红安) Chin. Phys. B, 2011, 20 (7):  078103.  DOI: 10.1088/1674-1056/20/7/078103 Abstract ( 1471 )   PDF (1811KB) ( 1027 )   Additive Ba(N3)2 as a source of nitrogen is heavily doped into the graphite—Fe-based alloy system to grow nitrogen-doped diamond crystals under a relatively high pressure (about 6.0 GPa) by employing the temperature gradient method. Gem-grade diamond crystal with a size of around 5 mm and a nitrogen concentration of about 1173 ppm is successfully synthesised for the first time under high pressure and high temperature in a China-type cubic anvil high-pressure apparatus. The growth habit of diamond crystal under the environment with high degree of nitrogen doping is investigated. It is found that the morphologies of heavily nitrogen-doped diamond crystals are all of octahedral shape dominated by {111} facets. The effects of temperature and duration on nitrogen concentration and form are explored by infrared absorption spectra. The results indicate that nitrogen impurity is present in diamond predominantly in the dispersed form accompanied by aggregated form, and the aggregated nitrogen concentration in diamond increases with temperature and duration. In addition, it is indicated that nitrogen donors are more easily incorporated into growing crystals at higher temperature. Strains in nitrogen-doped diamond crystal are characterized by micro-Raman spectroscopy. Measurement results demonstrate that the undoped diamond crystals exhibit the compressive stress, whereas diamond crystals heavily doped with the addition of Ba(N3)2 display the tensile stress.

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Ionic conductivity study on electron beam irradiated polyacrylonitrile–polyethylene oxide gel Ma Yi-Zhun (马艺准), Pang Li-Long(庞立龙), Zhu Ya-Bin(朱亚滨), Wang Zhi-Guang(王志光), and Shen Tie-Long(申铁龙) Chin. Phys. B, 2011, 20 (7):  078104.  DOI: 10.1088/1674-1056/20/7/078104 Abstract ( 1604 )   PDF (287KB) ( 764 )   Different mass percent polyacrylonitrile (PAN)–polyethylene oxide (PEO) gels were prepared and irradiated by an electron beam (EB) with energy of 1.0 MeV to the dose ranging from 13 kGy to 260 kGy. The gels were analysed by using Fourier transform infrared spectrum, gel fraction and ionic conductivity (IC) measurement. The results show that the gel is crosslinked by EB irradiation, the crosslinking degree rises with the increasing EB irradiation dose (ID) and the mass percents of both PAN and PEO contribute a lot to the crosslinking; in addition, EB irradiation can promote the IC of PAN–PEO gels. There exists an optimum irradiation dose, at which the IC can increase dramatically. The IC changes of the PAN–PEO gels along with ID are divided into three regions: IC rapidly increasing region, IC decreasing region and IC balanced region. The cause of the change can be ascribed to two aspects, gel capturing electron degree and crosslinking degree. By comparing the IC–ID curves of different mass percents of PAN and PEO in gel, we found that PAN plays a more important role for gel IC promotion than PEO, since addition of PAN in gel causes the IC–ID curve sharper, while addition of PEO in gel causes the curve milder.

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Enhancement of photoluminescence in Sr2CeO4 phosphors by doping with non-rare earth impurities Xue Shu-Wen(薛书文), Wang En-Guo(王恩过), and Zhang Jun(张军) Chin. Phys. B, 2011, 20 (7):  078105.  DOI: 10.1088/1674-1056/20/7/078105 Abstract ( 1382 )   PDF (161KB) ( 832 )   Non-rare earth impurity doped Sr2CeO4:X (X=,Zn, Hg, Al, Ag, Cr) phosphors are prepared by using the combustion method. The structural and photoluminescent properties of the as-prepared phosphors are investigated by X-ray diffraction (XRD) and photoluminescence at room temperature. Experimental results show that zinc addition and firing processing can effectively enhance the photoluminescence of Sr2CeO4 phosphors.

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Stereodynamics of the O(3P) with H2 (D2) ($\nu$=0, j=0) reaction Liu Yu-Fang(刘玉芳), He Xiao-Hu(和小虎), Shi De-Heng(施德恒), and Sun Jin-Feng(孙金锋) Chin. Phys. B, 2011, 20 (7):  078201.  DOI: 10.1088/1674-1056/20/7/078201 Abstract ( 1768 )   PDF (170KB) ( 705 )   Quasi-classical trajectory theory is used to study the reaction of O(3P) with H2 (D2) based on the ground 3A'' potential energy surface (PES). The reaction cross section of the reaction O+H2 → OH+H is in excellent agreement with the previous result. Vector correlations, product rotational alignment parameters 〈P2 (j'·k)〉 and several polarized-dependent differential cross sections are further calculated for the reaction. The product polarization distribution exhibits different characteristics that can be ascribed to different motion paths on the PES, arising from various collision energies or mass factors.

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Nonlinear time-dependent simulation of helix traveling wave tubes Peng Wei-Feng(彭维峰), Yang Zhong-Hai(杨中海), Hu Yu-Lu(胡玉禄), Li Jian-Qing(李建清), Lu Qi-Ru(陆麒如), and Li Bin(李斌) Chin. Phys. B, 2011, 20 (7):  078401.  DOI: 10.1088/1674-1056/20/7/078401 Abstract ( 1527 )   PDF (241KB) ( 732 )   A one-dimensional nonlinear time-dependent theory for helix traveling wave tubes is studied. A generalized electromagnetic field is applied to the expression of the radio frequency field. To simulate the variations of the high frequency structure, such as the pitch taper and the effect of harmonics, the spatial average over a wavelength is substituted by a time average over a wave period in the equation of the radio frequency field. Under this assumption, the space charge field of the electron beam can be treated by a space charge wave model along with the space charge coefficient. The effects of the radio frequency and the space charge fields on the electrons are presented by the equations of the electron energy and the electron phase. The time-dependent simulation is compared with the frequency-domain simulation for a helix TWT, which validates the availability of this theory.

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The p recombination layer in tunnel junctions for micromorph tandem solar cells Yao Wen-Jie(姚文杰), Zeng Xiang-Bo(曾湘波), Peng Wen-Bo(彭文博), Liu Shi-Yong(刘石勇), Xie Xiao-Bing(谢小兵), Wang Chao(王超), and Liao Xian-Bo(廖显伯) Chin. Phys. B, 2011, 20 (7):  078402.  DOI: 10.1088/1674-1056/20/7/078402 Abstract ( 1457 )   PDF (153KB) ( 1071 )   A new tunnel recombination junction is fabricated for n—i—p type micromorph tandem solar cells. We insert a thin heavily doped hydrogenated amorphous silicon (a-Si:H) p+ recombination layer between the n a-Si:H and the p hydrogenated nanocrystalline silicon (nc-Si:H) layers to improve the performance of the n—i—p tandem solar cells. The effects of the boron doping gas ratio and the deposition time of the p-a-Si:H recombination layer on the tunnel recombination junctions have been investigated. The current-voltage characteristic of the tunnel recombination junction shows a nearly ohmic characteristic, and the resistance of the tunnel recombination junction can be as low as 1.5 Ω·cm2 by using the optimized p-a-Si:H recombination layer. We obtain tandem solar cells with open circuit voltage Voc= 1.4 V, which is nearly the sum of the Vocs of the two corresponding single cells, indicating no Voc losses at the tunnel recombination junction.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Circulation system complex networks and teleconnections Gong Zhi-Qiang(龚志强), Wang Xiao-Juan(王晓娟), Zhi Rong(支蓉), and Feng Ai-Xia(冯爱霞) Chin. Phys. B, 2011, 20 (7):  079201.  DOI: 10.1088/1674-1056/20/7/079201 Abstract ( 1540 )   PDF (2490KB) ( 845 )   In terms of the characteristic topology parameters of climate complex networks, the spatial connection structural complexity of the circulation system and the influence of four teleconnection patterns are quantitatively described. Results of node degrees for the Northern Hemisphere (NH) mid-high latitude (30°N—90°N) circulation system (NHS) networks with and without the Arctic Oscillations (AO), the North Atlantic Oscillations (NAO) and the Pacific—North American pattern (PNA) demonstrate that the teleconnections greatly shorten the mean shortest path length of the networks, thus being advantageous to the rapid transfer of local fluctuation information over the network and to the stability of the NHS. The impact of the AO on the NHS connection structure is most important and the impact of the NAO is the next important. The PNA is a relatively independent teleconnection, and its role in the NHS is mainly manifested in the connection between the NHS and the tropical circulation system (TRS). As to the Southern Hemisphere mid-high latitude (30°S—90°S) circulation system (SHS), the impact of the Antarctic Arctic Oscillations (AAO) on the structural stability of the system is most important. In addition, there might be a stable correlation dipole (AACD) in the SHS, which also has important influence on the structure of the SHS networks.

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Constraints on the unified model of dark matter and dark energy Lü Jian-Bo(吕剑波), Wu Ya-Bo(吴亚波), Xu Li-Xin(徐立昕), and Wang Yu-Ting(王钰婷) Chin. Phys. B, 2011, 20 (7):  079801.  DOI: 10.1088/1674-1056/20/7/079801 Abstract ( 1409 )   PDF (182KB) ( 603 )   Using recently observed data: the Constitution dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the measurement results of baryon acoustic oscillation (BAO) from the Sloan Digital Sky Survey (SDSS) and the Two Degree Field Galaxy Redshift Survey (2dFGRS), and the current cosmic microwave background (CMB) data from the five-year Wilkinson Microwave Anisotropy Probe (WMAP), we apply the Markov Chain Monte Carlo method to investigate the observational constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy. For this unified model, the constraints on GCG mixture are discussed by considering the different expressions of current matter density or considering constraints as being independent of the matter quantity Ωm.