Table of contents

    15 October 2011, Volume 20 Issue 10 Previous issue    Next issue
    Determination of temperature distribution and control parameter in a two-dimensional parabolic inverse problem with overspecified data
    Li Fu-Le(李福乐) and Zhang Hong-Qian(张洪谦)
    Chin. Phys. B, 2011, 20 (10):  100201.  DOI: 10.1088/1674-1056/20/10/100201
    Abstract ( 1510 )   PDF (126KB) ( 814 )  
    In this paper, we present a new algorithm to solve a two-dimensional parabolic inverse problem with a source parameter, which appears in many physical phenomena. A linearized compact difference scheme for this problem is constructed using the finite difference method. The discretization accuracy is second-order in time and fourth-order in space. We obtain the unique solvability and present an alternating direction implicit algorithm to solve this difference scheme. The results of numerical experiments are presented to demonstrate the accuracy of this algorithm.
    On the completeness of eigen and root vector systems for fourth-order operator matrices and their applications
    Wang Hua(王华), Alatancang (阿拉坦仓), and Huang Jun-Jie(黄俊杰)
    Chin. Phys. B, 2011, 20 (10):  100202.  DOI: 10.1088/1674-1056/20/10/100202
    Abstract ( 1261 )   PDF (119KB) ( 571 )  
    In this paper, we consider the eigenvalue problem of a class of fourth-order operator matrices appearing in mechanics, including the geometric multiplicity, algebraic index, and algebraic multiplicity of the eigenvalue, the symplectic orthogonality, and completeness of eigen and root vector systems. The obtained results are applied to the plate bending problem.
    Stability of the positively charged manganese centre in GaAs heterostructures examined theoretically by the effective mass approximation calculation near the $\varGamma$ critical point
    Wang Li-Guo(王丽国), Shen Chao(申超), Zheng Hou-Zhi(郑厚植), Zhu Hui(朱汇), and Zhao Jian-Hua(赵建华)
    Chin. Phys. B, 2011, 20 (10):  100301.  DOI: 10.1088/1674-1056/20/10/100301
    Abstract ( 1166 )   PDF (258KB) ( 565 )  
    This paper describes an n-i-p-i-n model heterostructure with a manganese (Mn)-doped p-type base region to check the stability of a positively charged manganese AMn+ centre with two holes weakly bound by a negatively charged 3d5(Mn) core of a local spin S=5/2 in the framework of the effective mass approximation near the Γ critical point (k~0). By including the carrier screening effect, the ground state energy and the binding energy of the second hole in the positively charged centre AMn+ are calculated within a hole concentration range from 1 × 1016 cm-3 to 1 × 1017 cm-3, which is achievable by biasing the structure under photo-excitation. For comparison, the ground-state energy of a single hole in the neutral AMn0 centre is calculated in the same concentration range. It turns out that the binding energy of the second hole in the AMn+ centre varies from 9.27 meV to 4.57 meV. We propose that the presence of the AMn+ centre can be examined by measuring the photoluminescence from recombination of electrons in the conduction band with the bound holes in the AMn+ centre since a high frequency dielectric constant of $\varepsilon_{\infty}=10.66$ can be safely adopted in this case. The novel feature of the ability to tune the impurity level of the AMn+ centre makes it attractive for optically and electrically manipulating local magnetic spins in semiconductors.
    Quantum and classical correlations for a two-qubit X structure density matrix
    Ding Bang-Fu(丁邦福), Wang Xiao-Yun(王小云), and Zhao He-Ping(赵鹤平)
    Chin. Phys. B, 2011, 20 (10):  100302.  DOI: 10.1088/1674-1056/20/10/100302
    Abstract ( 1581 )   PDF (162KB) ( 1399 )  
    We derive explicit expressions for quantum discord and classical correlation for an X structure density matrix. Based on the characteristics of the expressions, the quantum discord and the classical correlation are easily obtained and compared under different initial conditions using a novel analytical method. We explain the relationships among quantum discord, classical correlation, and entanglement, and further find that the quantum discord is not always larger than the entanglement measured by concurrence in a general two-qubit X state. The new method, which is different from previous approaches, has certain guiding significance for analysing quantum discord and classical correlation of a two-qubit X state, such as a mixed state.
    Preparation of cluster states with trapped electrons on a liquid helium surface
    Ai Ling-Yan(艾凌艳), Shi Yan-Li(石艳丽), and Zhang Zhi-Ming(张智明)
    Chin. Phys. B, 2011, 20 (10):  100303.  DOI: 10.1088/1674-1056/20/10/100303
    Abstract ( 1608 )   PDF (215KB) ( 621 )  
    We present a scheme for the preparation of one-dimensional (1D) and two-dimensional (2D) cluster states with electrons trapped on a liquid helium surface and driven by a classical laser beam. The two lowest levels of the vertical motion of the electron act as a two-level system, and the quantized vibration of the electron along one of the parallel directions (the x direction) serves as the bosonic mode. The degrees of freedom of the vertical and parallel motions of the trapped electron can be coupled together by a classical laser field. With the proper frequency of the laser field, the cluster states can be realized.
    General description of discriminating quantum operations
    Zhang Ke-Jia(张可佳), Zhu Ping(朱萍), Gao Fei(高飞), Guo Fen-Zhuo(郭奋卓), Qin Su-Juan(秦素娟), and Wen Qiao-Yan(温巧燕)
    Chin. Phys. B, 2011, 20 (10):  100304.  DOI: 10.1088/1674-1056/20/10/100304
    Abstract ( 1390 )   PDF (128KB) ( 529 )  
    The discrimination of quantum operations plays a key role in quantum information and computation. Unlike discriminating quantum states, it has some special properties which can be carried out in practice. In this paper, we provide a general description of discriminating quantum operations. Concretely speaking, we describe the distinguishability between quantum operations using a measure called operator fidelity. It is shown that, employing the theory of operator fidelity, we can not only verify some previous results to discriminate unitary operations, but also exhibit a more general discrimination condition. We further apply our results to analysing the security of some quantum cryptographic protocols and discuss the realization of our method using well-developed quantum algorithms.
    A practical two-way system of quantum key distribution with untrusted source
    Chen Ming-Juan(陈明娟) and Liu Xiang(刘翔)
    Chin. Phys. B, 2011, 20 (10):  100305.  DOI: 10.1088/1674-1056/20/10/100305
    Abstract ( 1340 )   PDF (240KB) ( 814 )  
    The most severe problem of a two-way "plug-and-play" (p & p) quantum key distribution system is that the source can be controlled by the eavesdropper. This kind of source is defined as an üntrusted source". This paper discusses the effects of the fluctuation of internal transmittance on the final key generation rate and the transmission distance. The security of the standard BB84 protocol, one-decoy state protocol, and weak+vacuum decoy state protocol, with untrusted sources and the fluctuation of internal transmittance are studied. It is shown that the one-decoy state is sensitive to the statistical fluctuation but weak+vacuum decoy state is only slightly affected by the fluctuation. It is also shown that both the maximum secure transmission distance and final key generation rate are reduced when Alice's laboratory transmittance fluctuation is considered.
    Lower bound for the security of differential phase shift quantum key distribution against a one-pulse-attack
    Li Hong-Wei(李宏伟), Yin Zhen-Qiang(银振强), Wang Shuang(王双), Bao Wan-Su(鲍皖苏), Guo Guang-Can(郭光灿), and Han Zheng-Fu(韩正甫)
    Chin. Phys. B, 2011, 20 (10):  100306.  DOI: 10.1088/1674-1056/20/10/100306
    Abstract ( 1378 )   PDF (121KB) ( 694 )  
    Quantum key distribution is the art of sharing secret keys between two distant parties, and has attracted a lot of attention due to its unconditional security. Compared with other quantum key distribution protocols, the differential phase shift quantum key distribution protocol has higher efficiency and simpler apparatus. Unfortunately, the unconditional security of differential phase shift quantum key distribution has not been proved. Utilizing the sharp continuity of the von Neuman entropy and some basic inequalities, we estimate the upper bound for the eavesdropper Eve's information. We then prove the lower bound for the security of the differential phase shift quantum key distribution protocol against a one-pulse attack with Devatak-Winter's secret key rate formula.
    Improving quantum state transfer in a general XY chain via the Dzyaloshinsky–Moriya interaction
    Zhang Jian(张剑), Shao Bin(邵彬), Zou Jian(邹健), and Li Qian-Shu(李前树)
    Chin. Phys. B, 2011, 20 (10):  100307.  DOI: 10.1088/1674-1056/20/10/100307
    Abstract ( 1294 )   PDF (187KB) ( 556 )  
    We study the state transfer of Bell states in a general XY spin chain using the Dzyaloshinsky-Moriya interaction. Two symmetries of fidelity with the anisotropy parameter are found. The maximum fidelity is shown to be significantly enhanced in cases of an odd number of sites. Enhancement of fidelity on a singlet state is greater than that on the other Bell states in such cases.
    Using a quantum dot system to realize perfect state transfer
    Li Ji(李季), Wu Shi-Hai(吴世海), Zhang Wen-Wen(张雯雯), and Xi Xiao-Qiang(惠小强)
    Chin. Phys. B, 2011, 20 (10):  100308.  DOI: 10.1088/1674-1056/20/10/100308
    Abstract ( 1443 )   PDF (547KB) ( 641 )  
    There are some disadvantages to Nikolopoulos et al.'s protocol [Nikolopoulos G M, Petrosyan D and Lambropoulos P 2004 Europhys. Lett. 65 297] where a quantum dot system is used to realize quantum communication. To overcome these disadvantages, we propose a protocol that uses a quantum dot array to construct a four-qubit spin chain to realize perfect quantum state transfer (PQST). First, we calculate the interaction relation for PQST in the spin chain. Second, we review the interaction between the quantum dots in the Heitler-London approach. Third, we present a detailed program for designing the proper parameters of a quantum dot array to realize PQST.
    A two-step quantum secure direct communication protocol with hyperentanglement
    Gu Bin(顾斌), Huang Yu-Gai(黄余改), Fang Xia(方夏), and Zhang Cheng-Yi(张成义)
    Chin. Phys. B, 2011, 20 (10):  100309.  DOI: 10.1088/1674-1056/20/10/100309
    Abstract ( 1445 )   PDF (107KB) ( 1355 )  
    We propose a two-step quantum secure direct communication (QSDC) protocol with hyperentanglement in both the spatial-mode and the polarization degrees of freedom of photon pairs which can in principle be produced with a beta barium borate crystal. The secret message can be encoded on the photon pairs with unitary operations in these two degrees of freedom independently. This QSDC protocol has a higher capacity than the original two-step QSDC protocol as each photon pair can carry 4 bits of information. Compared with the QSDC protocol based on hyperdense coding, this QSDC protocol has the immunity to Trojan horse attack strategies with the process for determining the number of the photons in each quantum signal as it is a one-way quantum communication protocol.
    Decoherence-free spin entanglement generation and purification in nanowire double quantum dots
    Peng Xue(薛鹏)
    Chin. Phys. B, 2011, 20 (10):  100310.  DOI: 10.1088/1674-1056/20/10/100310
    Abstract ( 1329 )   PDF (625KB) ( 807 )  
    We propose a deterministic generation and purification of decoherence-free spin entangled states with singlet-triplet spins in nanowire double quantum dots via resonator-assisted charge manipulation and measurement techniques. Each spin qubit corresponds to two electrons in a double quantum dot in the nanowire, with the singlet and one of the triplets as the decoherence-free qubit states. The logical qubits are immunized against the dominant source of decoherence-dephasing—while the influences of additional errors are shown by numerical simulations. We analyse the performance and stability of all required operations and emphasize that all techniques are feasible in current experimental conditions.
    Measurement-induced disturbance and nonequilibrium thermal entanglement in a qutrit–qubit mixed spin XXZ model
    Chen Li(陈丽), Shao Xiao-Qiang(邵晓强), and Zhang Shou(张寿)
    Chin. Phys. B, 2011, 20 (10):  100311.  DOI: 10.1088/1674-1056/20/10/100311
    Abstract ( 1265 )   PDF (353KB) ( 724 )  
    We investigate the dynamics of nonequilibrium thermal quantum correlation of a qutrit-qubit mixed spin system coupled to two bosonic reservoirs at different temperatures using measurement-induced disturbance. The effects of initial states of the spins and temperatures of the reservoirs on measurement-induced disturbance and entanglement are discussed. The results demonstrate that measurement-induced disturbance is more robust than entanglement against the influence of both these factors and there is no sudden death phenomenon for measurement-induced disturbance. The dependences of steady-state measurement-induced disturbance and entanglement on coupling constant and anisotropy parameter are also studied. Steady-state entanglement vanishes for a ferromagnetic qutrit-qubit model, while steady-state measurement-induced disturbance exists for both the antiferromagnetic and ferromagnetic cases. Appropriately modulating the coupling constant and anisotropy parameter can strengthen quantum correlation.
    High entanglement generation and high fidelity quantum state transfer in a non-Markovian environment
    Li Yan-Ling(李艳玲) and Fang Mao-Fa(方卯发)
    Chin. Phys. B, 2011, 20 (10):  100312.  DOI: 10.1088/1674-1056/20/10/100312
    Abstract ( 1376 )   PDF (867KB) ( 696 )  
    This paper analyses a system of two independent qubits off-resonantly coupled to a common non-Markovian reservoir at zero temperature. Compared with the results in Markovian reservoirs, we find that much higher values of entanglement can be obtained for an initially factorized state of the two-qubit system. The maximal value of the entanglement increases as the detuning grows. Moreover, the entanglement induced by non-Markovian environments is more robust against the asymmetrical couplings between the two qubits and the reservoir. Based on this system, we also show that quantum state transfer can be implemented for arbitrary input states with high fidelity in the non-Markovian regime rather than the Markovian case in which only some particular input states can be successfully transferred.
    A nearly deterministic scheme for generation of multiphoton GHZ states with weak cross-Kerr nonlinearity
    Wang Yi(王奕), Ye Liu(叶柳), and Fang Bao-Long(方保龙)
    Chin. Phys. B, 2011, 20 (10):  100313.  DOI: 10.1088/1674-1056/20/10/100313
    Abstract ( 1504 )   PDF (752KB) ( 674 )  
    We propose a scheme to generate polarization-entangled multiphoton Greenberger-Horne-Zeilinger (GHZ) states based on weak cross-Kerr nonlinearity and subsequent homodyne measurement. It can also be generalized to produce maximally N-qubit entangled states. The success probabilities of our schemes are almost equal to 1.
    Time-like geodesic structure of a spherically symmetric black hole in the brane-world
    Zhou Sheng(周盛), Chen Ju-Hua(陈菊华), and Wang Yong-Jiu(王永久)
    Chin. Phys. B, 2011, 20 (10):  100401.  DOI: 10.1088/1674-1056/20/10/100401
    Abstract ( 1103 )   PDF (174KB) ( 666 )  
    Recently Malihe Heydari-Fard obtained a spherically symmetric exterior black hole solution in the brane-world scenario, which can be used to explain the galaxy rotation curves without postulating dark matter. By analysing the particle effective potential, we have investigated the time-like geodesic structure of the spherically symmetric black hole in the brane-world. We mainly take account of how the cosmological constant α and the stellar pressure β affect the time-like geodesic structure of the black hole. We find that the radial particle falls to the singularity from a finite distance or plunges into the singularity, depending on its initial conditions. But the non-radial time-like geodesic structure is more complex than the radial case. We find that the particle moves on the bound orbit or stable (unstable) circle orbit or plunges into the singularity, or reflects to infinity, depending on its energy and initial conditions. By comparing the particle effective potential curves for different values of the stellar pressure β and the cosmological constant α, we find that the stellar pressure parameter β does not affect the time-like geodesic structure of the black hole, but the cosmological constant α has an impact on its time-like geodesic structure.
    Energy and momentum of rotating frames in tetrad gravity
    Gamal G L Nashed
    Chin. Phys. B, 2011, 20 (10):  100402.  DOI: 10.1088/1674-1056/20/10/100402
    Abstract ( 1198 )   PDF (139KB) ( 561 )  
    Within the framework of the tetrad formulation of general relativity theory, we compute the total energy and momentum of four rotating frames using the gravitational energy-momentum 3-form. We show how the effect of inertia always makes the total energy divergent. We use a natural regularization method to obtain physical values for the total energy of the system and show how it works on a number of explicit examples. We also show by calculation that inertia has no effect on the momentum components.
    A new metric for rotating charged Gauss–Bonnet black holes in AdS space
    Zou De-Cheng(邹德成), Yang Zhan-Ying(杨战营), Yue Rui-Hong(岳瑞宏), and Yu Tian-Yi(于添翼)
    Chin. Phys. B, 2011, 20 (10):  100403.  DOI: 10.1088/1674-1056/20/10/100403
    Abstract ( 1324 )   PDF (124KB) ( 541 )  
    In this paper, we study a new metric for slowly rotating charged Gauss-Bonnet black holes in higher-dimensional anti-de Sitter space. Taking the angular momentum parameter a up to second order, the slowly rotating charged black hole solutions are obtained by working directly in the action.
    Soliton dynamical properties of Bose–Einstein condensates trapped in a double square well potential
    Li Jin-Hui(李锦茴) and Li Zhi-Jian(李志坚)
    Chin. Phys. B, 2011, 20 (10):  100501.  DOI: 10.1088/1674-1056/20/10/100501
    Abstract ( 1334 )   PDF (191KB) ( 660 )  
    We first present an analytical solution of the single and double solitions of Bose-Einstein condensates trapped in a double square well potential using the multiple-scale method. Then, we show by numerical calculation that a dark soliton can be transmitted through the square well potential. With increasing depth of the square well potential, the amplitude of the dark soliton becomes larger, and the soliton propagates faster. In particular, we treat the collision behaviour of the condensates trapped in either equal or different depths of the double square well potential. If we regard the double square well potential as the output source of the solitons, the collision locations (position and time) between two dark solitons can be controlled by its depth.
    Effect of inertial mass on a linear system driven by dichotomous noise and a periodic signal
    Li Peng(李鹏), Nie Lin-Ru(聂林如), Lü Xiu-Min(吕秀敏), and Zhang Qi-Bo(张启波)
    Chin. Phys. B, 2011, 20 (10):  100502.  DOI: 10.1088/1674-1056/20/10/100502
    Abstract ( 1345 )   PDF (245KB) ( 569 )  
    A linear system driven by dichotomous noise and a periodic signal is investigated in the underdamped case. The exact expressions of output signal amplitude and signal-to-noise ratio (SNR) of the system are derived. By means of numerical calculation, the results indicate that (i) at some fixed noise intensities, the output signal amplitude with inertial mass exhibits the structure of a single peak and single valley, or even two peaks if the dichotomous noise is asymmetric; (ii) in the case of asymmetric dichotomous noise, the inertial mass can cause non-monotonic behaviour of the output signal amplitude with respect to noise intensity; (iii) the curve of SNR versus inertial mass displays a maximum in the case of asymmetric dichotomous noise, i.e., a resonance-like phenomenon, while it decreases monotonically in the case of symmetric dichotomous noise; (iv) if the noise is symmetric, the inertial mass can induce stochastic resonance in the system.
    Generalized projective synchronization between two chaotic gyros with nonlinear damping
    Min Fu-Hong(闵富红)
    Chin. Phys. B, 2011, 20 (10):  100503.  DOI: 10.1088/1674-1056/20/10/100503
    Abstract ( 1284 )   PDF (372KB) ( 1036 )  
    In this paper, the chaotic generalized projective synchronization of a controlled, noised gyro with an expected gyro is investigated by a simple control law. Based on the theory of discontinuous dynamical systems, the necessary and sufficient conditions for such a synchronization are achieved. From such conditions, non-synchronization, partial and full synchronizations between the two coupled gyros are discussed. The switching scenarios between desynchronized and synchronized states of the two dynamical systems are shown. Numerical simulations are illustrated to verify the effectiveness of this method.
    Predicting the subcellular location of apoptosis proteins based on recurrence quantification analysis and the Hilbert–Huang transform
    Han Guo-Sheng(韩国胜), Yu Zu-Guo(喻祖国), and Anh Vo
    Chin. Phys. B, 2011, 20 (10):  100504.  DOI: 10.1088/1674-1056/20/10/100504
    Abstract ( 1170 )   PDF (768KB) ( 772 )  
    Apoptosis proteins play an important role in the development and homeostasis of an organism. The elucidation of the subcellular locations and functions of these proteins is helpful for understanding the mechanism of programmed cell death. In this paper, the recurrent quantification analysis, Hilbert-Huang transform methods, the maximum relevance and minimum redundancy method and support vector machine are used to predict the subcellular location of apoptosis proteins. The validation of the jackknife test suggests that the proposed method can improve the prediction accuracy of the subcellular location of apoptosis proteins and its application may be promising in other fields.
    Comparison between two different sliding mode controllers for a fractional-order unified chaotic system
    Qi Dong-Lian(齐冬莲), Wang Qiao(王乔), and Yang Jie(杨捷)
    Chin. Phys. B, 2011, 20 (10):  100505.  DOI: 10.1088/1674-1056/20/10/100505
    Abstract ( 1364 )   PDF (229KB) ( 734 )  
    Two different sliding mode controllers for a fractional order unified chaotic system are presented. The controller for an integer-order unified chaotic system is substituted directly into the fractional-order counterpart system, and the fractional-order system can be made asymptotically stable by this controller. By proving the existence of a sliding manifold containing fractional integral, the controller for a fractional-order system is obtained, which can stabilize it. A comparison between these different methods shows that the performance of a sliding mode controller with a fractional integral is more robust than the other for controlling a fractional order unified chaotic system.
    Modified projective synchronization of a fractional-order hyperchaotic system with a single driving variable
    Wang Xing-Yuan(王兴元) and Zhang Yong-Lei(张永雷)
    Chin. Phys. B, 2011, 20 (10):  100506.  DOI: 10.1088/1674-1056/20/10/100506
    Abstract ( 1356 )   PDF (657KB) ( 821 )  
    In this paper, the modified projective synchronization (MPS) of a fractional-order hyperchaotic system is investigated. We design the response system corresponding to the drive system on the basis of projective synchronization theory, and determine the sufficient condition for the synchronization of the drive system and the response system based on fractional-order stability theory. The MPS of a fractional-order hyperchaotic system is achieved by transmitting a single variable. This scheme reduces the information transmission in order to achieve the synchronization, and extends the applicable scope of MPS. Numerical simulations further demonstrate the feasibility and the effectiveness of the proposed scheme.
    The extended auxiliary equation method for the KdV equation with variable coefficients
    Shi Lan-Fang(石兰芳), Chen Cai-Sheng(陈才生), and Zhou Xian-Chun(周先春)
    Chin. Phys. B, 2011, 20 (10):  100507.  DOI: 10.1088/1674-1056/20/10/100507
    Abstract ( 1447 )   PDF (99KB) ( 762 )  
    This paper applies an extended auxiliary equation method to obtain exact solutions of the KdV equation with variable coefficients. As a result, solitary wave solutions, trigonometric function solutions, rational function solutions, Jacobi elliptic doubly periodic wave solutions, and nonsymmetrical kink solution are obtained. It is shown that the extended auxiliary equation method, with the help of a computer symbolic computation system, is reliable and effective in finding exact solutions of variable coefficient nonlinear evolution equations in mathematical physics.
    Enhancement effect of asymmetry on the thermal conductivity of double-stranded chain systems
    Zhang Mao-Ping(张茂平), Zhong Wei-Rong(钟伟荣), and Ai Bao-Quan(艾保全)
    Chin. Phys. B, 2011, 20 (10):  100508.  DOI: 10.1088/1674-1056/20/10/100508
    Abstract ( 1263 )   PDF (337KB) ( 665 )  
    Using nonequilibrium molecular dynamics simulations, we study the thermal conductivity of asymmetric double chains. We couple two different single chains through interchain coupling to build three kinds of asymmetric double-stranded chain system: intrachain interaction, external potential, and mass asymmetric double chains. It is reported that asymmetry is helpful in improving the thermal conductivity of the system. We first propose double-heat flux channels to explain the influence of asymmetric structures on the thermal conductivity. The phonon spectral behaviour and finite size effect are also included.
    Density functional theory study of NO2-sensing mechanisms of pure and Ti-doped WO3 (002) surfaces Hot!
    Hu Ming(胡明), Wang Wei-Dan(王巍丹), Zeng Jing(曾晶), and Qin Yu-Xiang(秦玉香)
    Chin. Phys. B, 2011, 20 (10):  102101.  DOI: 10.1088/1674-1056/20/10/102101
    Abstract ( 1384 )   PDF (213KB) ( 1163 )  
    Density functional theory (DFT) calculations are employed to explore the NO2-sensing mechanisms of pure and Ti-doped WO3 (002) surfaces. When Ti is doped into the WO3 surface, two substitution models are considered: substitution of Ti for W6c and substitution of Ti for W5c. The results reveal that substitution of Ti for 5-fold W forms a stable doping structure, and doping induces some new electronic states in the band gap, which may lead to changes in the surface properties. Four top adsorption models of NO2 on pure and Ti-doped WO3 (002) surfaces are investigated: adsorptions on 5-fold W (Ti), on 6-fold W, on bridging oxygen, and on plane oxygen. The most stable and likely NO2 adsorption structures are both N-end oriented to the surface bridge oxygen O1c site. By comparing the adsorption energy and the electronic population, it is found that Ti doping can enhance the adsorption of NO2, which theoretically proves the experimental observation that Ti doping can greatly increase the WO3 gas sensor sensitivity to NO2 gas.
    Study of the excitation properties of the Si3O2 cluster under an external electric field
    Yao Dong-Yong(姚东永), Xu Guo-Liang(徐国亮), Liu Xue-Feng(刘雪峰) Zhang Xian-Zhou(张现周), and Liu Yu-Fang(刘玉芳)
    Chin. Phys. B, 2011, 20 (10):  103101.  DOI: 10.1088/1674-1056/20/10/103101
    Abstract ( 1105 )   PDF (197KB) ( 700 )  
    The structure of the Si3Ox (x=2, 3) cluster is investigated; we find that the geometry of Si3O2 is similar to that of Si3O3 except for the oxygen-deficient defect structure (Si-Si band) which exists only in the Si3O2 cluster. It is known that oxygen-deficient defects are used to explain visible luminescence (especially blue, purple and ultraviolet light) from silicon-based materials, which are directly bound up with the excited states of the molecules. Therefore the excitation properties of the two clusters are also studied. Our results show that the absorption spectrum of Si3O2 is concentrated in the visible light region. In contrast, the absorption spectrum of Si3O3 is mainly located in the ultraviolet light region. The calculations are perfectly consistent with experimental data and also support the theory of oxygen-deficient defects.
    Observation of intermolecular double-quantum coherence signal dips in nuclear magnetic resonance
    Shen Gui-Ping(沈桂平), Cai Cong-Bo(蔡聪波), Cai Shu-Hui(蔡淑惠), and Chen Zhong(陈忠)
    Chin. Phys. B, 2011, 20 (10):  103301.  DOI: 10.1088/1674-1056/20/10/103301
    Abstract ( 1164 )   PDF (818KB) ( 717 )  
    The correlated spectroscopy revamped by asymmetric Z-gradient echo detection (CRAZED) sequence is modified to investigate intermolecular double-quantum coherence nuclear magnetic resonance signal dips in highly polarized spin systems. It is found that the occurrence of intermolecular double-quantum coherence signal dips is related to sample geometry, field inhomogeneity and dipolar correlation distance. If the field inhomogeneity is refocused, the signal dip occurs at a fixed position whenever the dipolar correlation distance approaches the sample dimension. However, the position is shifted when the field inhomogeneity exists. Experiments and simulations are performed to validate our theoretic analysis. These signal features may offer a unique way to investigate porous structures and may find applications in biomedicine and material science.
    Feshbach resonances in an ultracold mixture of 87Rb and 40K
    Wang Peng-Jun(王鹏军), Fu Zheng-Kun(付正坤), Chai Shi-Jie(柴世杰), and Zhang Jing(张靖)
    Chin. Phys. B, 2011, 20 (10):  103401.  DOI: 10.1088/1674-1056/20/10/103401
    Abstract ( 1399 )   PDF (755KB) ( 723 )  
    We report the experimental preparations of the absolute ground states of 87Rb and 40K atoms (|F=1, mF=1,〉+ |F=9/2, mF=-9/2〉) by means of the radio-frequency and microwave adiabatic rapid passages, and the observation of magnetic Feshbach resonances in an ultracold mixture of bosonic 87Rb and fermionic 40K atoms between 0 T and 6.0 × 10-2 T, including 7 homonuclear and 4 heteronuclear Feshbach resonances. The resonances are identified by the abrupt trap loss of atoms induced by the strong inelastic three-body collisions. These Feshbach resonances should enable the experimental control of interspecies interactions.
    Electronic structure and infrared spectrum of a WnC0,± (n=1–6) cluster
    Zhang Xiu-Rong(张秀荣), Kang Zhang-Li(康张李), and Guo Wen-Lu(郭文录)
    Chin. Phys. B, 2011, 20 (10):  103601.  DOI: 10.1088/1674-1056/20/10/103601
    Abstract ( 1187 )   PDF (495KB) ( 677 )  
    WnC0,± (n=1-6) clusters are investigated by using the density functional theory (DFT) at the B3LYP/LANL2DZ level. We find that the neutral, anionic and cationic ground state structures are similar within the same size, and constituted by substituting a C atom for one W atom in the structures of Wn+1 clusters. The natural bond orbital (NBO) charge analyses indicate that the direction of electron transfer is from the W atom to the 2p orbital of the C atom. In addition, the calculated infrared spectra of the WnC0,± (n=2-6) clusters manifest that the vibrational frequencies of neutral, anionic and cationic clusters are similar in a range of 80 cm-1-864 cm-1. The high frequency, strong peak modes are found to be an almost stretched deformation of the carbide atom. Finally, the polarizabilities of WnC0,± (n=1-6) clusters are also discussed.
    Investigation of the diocotron instability of an infinitely wide sheet electron beam by using the macroscopic cold-fluid model theory
    Han Ying(韩莹) and Ruan Cun-Jun(阮存军)
    Chin. Phys. B, 2011, 20 (10):  104101.  DOI: 10.1088/1674-1056/20/10/104101
    Abstract ( 1135 )   PDF (221KB) ( 892 )  
    This paper investigates the diocotron instability of an infinitely wide relativistic sheet electron beam in conducting walls propagating through a uniform magnetic field by using the macroscopic cold-fluid model  theory. Assuming low-frequency perturbations with long axial wavelengths, the eigenvalue equation and the dispersion relation are acquired for a sheet electron beam with sharp boundary profile and uniform density. The results  presented in this paper has developed the use of the macroscopic cold-fluid model theory by extending the parameter of the electron cyclotron frequency $\omega _{\rm c} $ to a wider usage range, which is restricted to be much  larger than the plasma frequency $\omega _{\rm p} $ in the previous research work. Theoretical analyses and numerical calculations indicate that the transport of the sheet electron beam will be completely stabilized by  augmenting the normalized beam thickness to a conductor gap larger than a threshold $\lambda _{\rm b} $, which is greatly dependent on the parameter ${\omega _{\rm c} }/{\omega _{\rm p}}$. The larger ${\omega_{\rm c} }/  {\omega _{\rm p} }$ is, the smaller $\lambda _{\rm b} $ will be needed. Moreover, the system parameters, including the wave number $k_x $ of the perturbations and the relativistic mass factor $\gamma _{\rm b} $, will also  influence the growth rate of diocotron instability obviously.
    Half-plane diffraction of Gaussian beams carrying two vortices of equal charges
    He De(何德), Gao Zeng-Hui(高曾辉), and Lü Bai-Da(吕百达)
    Chin. Phys. B, 2011, 20 (10):  104201.  DOI: 10.1088/1674-1056/20/10/104201
    Abstract ( 1250 )   PDF (553KB) ( 565 )  
    This paper derives explicit expressions for the propagation of Gaussian beams carrying two vortices of equal charges m=±1 diffracted at a half-plane screen, which enables the study of the dynamic evolution of vortices in the diffraction field. It shows that there may be no vortices, a pair or several pairs of vortices of opposite charges m=+1, -1 in the diffraction field. Pair creation, annihilation and motion of vortices may appear upon propagation. The off-axis distance additionally affects the evolutionary behaviour. In the process the total topological charge is equal to zero, which is unequal to that of the vortex beam at the source plane. A comparison with the free-space propagation of two vortices of equal charges and a further extension are made.
    An improved fast fractal image compression using spatial texture correlation
    Wang Xing-Yuan(王兴元), Wang Yuan-Xing(王远星), and Yun Jiao-Jiao(云娇娇)
    Chin. Phys. B, 2011, 20 (10):  104202.  DOI: 10.1088/1674-1056/20/10/104202
    Abstract ( 1353 )   PDF (354KB) ( 1246 )  
    This paper utilizes a spatial texture correlation and the intelligent classification algorithm (ICA) search strategy to speed up the encoding process and improve the bit rate for fractal image compression. Texture features is one of the most important properties for the representation of an image. Entropy and maximum entry from co-occurrence matrices are used for representing texture features in an image. For a range block, concerned domain blocks of neighbouring range blocks with similar texture features can be searched. In addition, domain blocks with similar texture features are searched in the ICA search process. Experiments show that in comparison with some typical methods, the proposed algorithm significantly speeds up the encoding process and achieves a higher compression ratio, with a slight diminution in the quality of the reconstructed image; in comparison with a spatial correlation scheme, the proposed scheme spends much less encoding time while the compression ratio and the quality of the reconstructed image are almost the same.
    An efficient adaptive arithmetic coding image compression technology
    Wang Xing-Yuan(王兴元), Yun Jiao-Jiao(云娇娇), and Zhang Yong-Lei(张永雷)
    Chin. Phys. B, 2011, 20 (10):  104203.  DOI: 10.1088/1674-1056/20/10/104203
    Abstract ( 1276 )   PDF (227KB) ( 1065 )  
    This paper proposes an efficient lossless image compression scheme for still images based on an adaptive arithmetic coding compression algorithm. The algorithm increases the image coding compression rate and ensures the quality of the decoded image combined with the adaptive probability model and predictive coding. The use of adaptive models for each encoded image block dynamically estimates the probability of the relevant image block. The decoded image block can accurately recover the encoded image according to the code book information. We adopt an adaptive arithmetic coding algorithm for image compression that greatly improves the image compression rate. The results show that it is an effective compression technology.
    One- and two-photon absorption properties of two metalloporphyrin complexes
    Sun Yuan-Hong(孙元红) and Wang Chuan-Kui(王传奎)
    Chin. Phys. B, 2011, 20 (10):  104204.  DOI: 10.1088/1674-1056/20/10/104204
    Abstract ( 1096 )   PDF (499KB) ( 580 )  
    The linear and nonlinear optical properties of two metalloporphyrin complexes formed by the complementary coordination of central zinc or magnesium ions to the ligand 5, 10, 15-tri-(p-tolyl)-20-phenylethynylporphyrin are theoretically investigated by using the analytic response theory at the density functional theory level. The results indicate that the studied complexes present more symmetric geometry structures than the ligand. The charge-transfer states of the two complexes in the lower energy region are all almost degenerate but those of the ligand are well separated. The ratio of the two-photon absorption cross sections of the ligand, zinc-porphyrin and magnesium-porphyrin complexes is 1.0:1.5:1.8, demonstrating that the two-photon absorption capability can be greatly increased when the ligand is coordinated with a metal ion. Moreover, several physical micro-mechanisms including electron transitions and intramolecular charge-transfer processes are discussed to explore the differences in optical property between the ligand and two complexes.
    Simulation of continuous terahertz wave transient state thermal effects on static water
    Lü Ying-Jin(吕英进), Xu De-Gang(徐德刚), Liu Peng-Xiang(刘鹏翔), Lü Da(吕达), Wen Qi-Ye(文岐业), Zhang Huai-Wu(张怀武), and Yao Jian-Quan(姚建铨)
    Chin. Phys. B, 2011, 20 (10):  104205.  DOI: 10.1088/1674-1056/20/10/104205
    Abstract ( 1300 )   PDF (3758KB) ( 877 )  
    We report a numerical simulation of continuous terahertz beam induced transient thermal effects on static water. The terahertz wave used in this paper has a Gaussian beam profile. Based on the transient heat conduction equation, the finite element method (FEM) is utilized to calculate the temperature distribution. The simulation results show the dynamic process of temperature change in water during terahertz irradiation. After about 300 s, the temperature reaches a steady state with a water layer thickness of 5 mm and a beam radius of 0.25 mm. The highest temperature increase is 7 K/mW approximately. This work motivates further study on the interaction between terahertz wave and bio-tissue, which has a high water content.
    Temperature-dependent second harmonic generation process based on an MgO-doped periodically poled lithium niobate waveguide
    Shen Shi-Kui(沈世奎), Yang Ai-Ying(杨爱英), Zuo Lin(左林), Cui Jian-Min(崔建民), and Sun Yu-Nan(孙雨南)
    Chin. Phys. B, 2011, 20 (10):  104206.  DOI: 10.1088/1674-1056/20/10/104206
    Abstract ( 1216 )   PDF (542KB) ( 1605 )  
    The temperature dependency of a 5-mol% MgO-doped periodically poled lithium niobate waveguide was investigated in this paper. We started with the temperature-dependent refractive index equation for the waveguide. Secondly, the temperature dependency of the second harmonic generation effect was experimentally researched under different temperatures and pump powers. The quasi-phase matched wavelengths, efficiency bandwidths and peak efficiencies of the waveguide were measured. The experimental results agreed with theoretical simulations, which are indispensable in the following all-optical sampling studies based on the cascaded second harmonic generation/difference-frequency generation process in the current device.
    Light propagation properties of two-dimensional photonic crystal channel filters with elliptical micro-cavities
    Feng Shuai(冯帅) and Wang Yi-Quan(王义全)
    Chin. Phys. B, 2011, 20 (10):  104207.  DOI: 10.1088/1674-1056/20/10/104207
    Abstract ( 1241 )   PDF (934KB) ( 672 )  
    Light propagation through a channel filter based on two-dimensional photonic crystals with elliptical-rod defects is studied by the finite-difference time-domain method. Shape alteration of the defects from the usual circle to an ellipse offers a powerful approach to engineer the resonant frequency of channel filters. It is found that the resonant frequency can be flexibly adjusted by just changing the orientation angle of the elliptical defects. The sensitivity of the resonant wavelength to the alteration of the oval rods' shape is also studied. This kind of multi-channel filter is very suitable for systems requiring a large number of output channel filters.
    Optical time-domain differentiation based on intensive differential group delay
    Li Zheng-Yong(李政勇), Yu Xiang-Zhi(余向志), and Wu Chong-Qing(吴重庆)
    Chin. Phys. B, 2011, 20 (10):  104208.  DOI: 10.1088/1674-1056/20/10/104208
    Abstract ( 1182 )   PDF (225KB) ( 510 )  
    An optical time-domain differentiation scheme is proposed and demonstrated based on the intensive differential group delay in a high birefringence fibre waveguide. Results show that the differentiation waveforms agree well with the mathematically calculated derivatives. Both error and efficiency will increase when the birefringence fibre becomes longer, and the error rises up more quickly while the efficiency approaches to a maximum of ~0.25. By using a 1-m birefringence fibre a lower error of ~0.26% is obtained with an efficiency of 1% for the first-order differentiation of 10-ps Gaussian optical pulses, and the high-order optical differentiation up to 4th order is achieved with an error less than 3%. Due to its compact structure being easy to integrate and cascade into photonic circuits, our scheme has great potential for ultrafast signal processing.
    Broadband non-polarizing beam splitter based on guided mode resonance effect
    Ma Jian-Yong(麻健勇), Xu Cheng(许程), Qiang Ying-Huai(强颖怀), and Zhu Ya-Bo(朱亚波)
    Chin. Phys. B, 2011, 20 (10):  104209.  DOI: 10.1088/1674-1056/20/10/104209
    Abstract ( 1480 )   PDF (258KB) ( 690 )  
    A broadband non-polarizing beam splitter (NPBS) operating in the telecommunication C+L band is designed by using the guided mode resonance effect of periodic silicon-on-insulator (SOI) elements. It is shown that this double layer SOI structure can provide ~50/50 beam ratio with the maximum divergences between reflection and transmission being less than 8% over the spectrum of 1.4 μm~1.7 μm and 1% in the telecommunication band for both TE and TM polarizations. The physical basis of this broadband non-polarizing property is on the simultaneous excitation of the TE and TM strong modulation waveguide modes near the designed spectrum band. Meanwhile, the electric field distributions for both TE and TM polarizations verify the resonant origin of spectrum in the periodic SOI structure. Furthermore, it is demonstrated with our calculations that the beam splitter proposed here is tolerant to the deviations of incident angle and structure parameters, which make it very easy to be fabricated with current IC technology.
    Excellent polarization-independent reflector based on guided mode resonance effect
    Xu Cheng(许程), Xu Lin-Min(许林敏), Qiang Ying-Huai(强颖怀), Zhu Ya-Bo(朱亚波), Liu Jiong-Tian(刘炯天), and Ma Jian-Yong(麻健勇)
    Chin. Phys. B, 2011, 20 (10):  104210.  DOI: 10.1088/1674-1056/20/10/104210
    Abstract ( 1166 )   PDF (399KB) ( 715 )  
    A broad band polarization-independent reflector working in the telecommunication C+L band is proposed using the guided mode resonance effect of a periodic surface relief element deposited by a layer of silicon medium. It is shown that this structure can provide high reflection (R>99.5%) and wide angular bandwidth (θ ≈20°, R>98%) for both TE and TM polarizations over a wide spectrum band 1.5 μm~1.6 μm. Furthermore, it is found by rigorous coupled wave analysis that the polarization-independent reflector proposed here is tolerant of a deviation of grating thickness, which makes it very easy to fabricate in experiments.
    Acoustic longitudinal mode coupling in w-shaped Al/Ge Co-doped fibre
    Li Hong-Liang(李宏亮), Zhang Wei(张巍), Huang Yi-Dong(黄翊东), and Peng Jiang-De(彭江得)
    Chin. Phys. B, 2011, 20 (10):  104211.  DOI: 10.1088/1674-1056/20/10/104211
    Abstract ( 1280 )   PDF (304KB) ( 665 )  
    This paper proposes a novel fibre structure aiming at distributed temperature and strain sensing. Utilizing Al2O3 and GeO2 as dopants to form a w-shaped acoustic waveguide, it realizes modal coupling between longitudinal acoustic modes of its inner and outer core layers, leading to a dual-peak or multi-peak Brillouin gain spectrum. The relationship between the acoustic mode coupling properties and the fibre materials, doping concentrations and structural parameters are investigated, showing that the positions of mode coupling points in acoustic dispersion curves and the coupling intensities can be designed flexibly. A specific fibre design for the discriminative sensing of temperature and strain under a pump wavelength of 1.55 μm is given. The responses of its Brillouin gain properties on temperature and strain are analysed theoretically, demonstrating its potential for distributed fibre Brillouin sensing.
    Type of integral and reduction for a generalized Birkhoffian system
    Wu Hui-Bin(吴惠彬) and Mei Feng-Xiang(梅凤翔)
    Chin. Phys. B, 2011, 20 (10):  104501.  DOI: 10.1088/1674-1056/20/10/104501
    Abstract ( 1302 )   PDF (88KB) ( 664 )  
    This paper studies a type of integral and reduction of the generalized Birkhoffian system. An existent condition and the form of the integral are obtained. By using the integral, the dimension of the system can be reduced two degrees. An example is given to illustrate the application of the results.
    Scaling study of the combustion performance of gas–gas rocket injectors
    Wang Xiao-Wei(汪小卫), Cai Guo-Biao(蔡国飙), and Jin Ping(金平)
    Chin. Phys. B, 2011, 20 (10):  104701.  DOI: 10.1088/1674-1056/20/10/104701
    Abstract ( 1370 )   PDF (1095KB) ( 771 )  
    To obtain the key subelements that may influence the scaling of gas-gas injector combustor performance, the combustion performance subelements in a liquid propellant rocket engine combustor are initially analysed based on the results of a previous study on the scaling of a gas-gas combustion flowfield. Analysis indicates that inner wall friction loss and heat-flux loss are two key issues in gaining the scaling criterion of the combustion performance. The similarity conditions of the inner wall friction loss and heat-flux loss in a gas-gas combustion chamber are obtained by theoretical analyses. Then the theoretical scaling criterion was obtained for the combustion performance, but it proved to be impractical. The criterion conditions, the wall friction and the heat flux are further analysed in detail to obtain the specific engineering scaling criterion of the combustion performance. The results indicate that when the inner flowfields in the combustors are similar, the combustor wall shear stress will have similar distributions qualitatively and will be directly proportional to pc0.8 dt-0.2 quantitatively. In addition, the combustion peformance will remain unchanged. Furthermore, multi-element injector chambers with different geometric sizes and at different pressures are numerically simulated and the wall shear stress and combustion efficiencies are solved and compared with each other. A multi-element injector chamber is designed and hot-fire tested at several chamber pressures and the combustion performances are measured in a total of nine hot-fire tests. The numerical and experimental results verified the similarities among combustor wall shear stress and combustion performances at different chamber pressures and geometries, with the criterion applied.
    How do quantum numbers generally vary in the adiabatic transformation of an ideal gas?
    T. Yarman and A. L. Kholmetskii
    Chin. Phys. B, 2011, 20 (10):  105101.  DOI: 10.1088/1674-1056/20/10/105101
    Abstract ( 1213 )   PDF (112KB) ( 494 )  
    We continue to analyse the known law of adiabatic transformation for an ideal gas PV5/3 = Constant, where P is the pressure and V is the volume, and following the approach of non-relativistic quantum mechanics which we suggested in a previous work (Yarman et al. 2010 Int. J. Phys. Sci. 5 1524). We explicitly determine the constant for the general parallelepiped geometry of a container. We also disclose how the quantum numbers associated with molecules of an ideal gas vary through an arbitrary adiabatic transformation. Physical implications of the results obtained are discussed.
    Load optimal design for a primary test stand facility based on a zero-dimensional load model
    Zhao Hai-Long(赵海龙)$†$, Deng Jian-Jun(邓建军),Wang Gang-Hua(王刚华), and Zou Wen-Kang(邹文康)
    Chin. Phys. B, 2011, 20 (10):  105201.  DOI: 10.1088/1674-1056/20/10/105201
    Abstract ( 1140 )   PDF (208KB) ( 454 )  
    In order to couple the numerical simulation of a primary test stand driver with an optimal load design, a zero-dimensional wire array load model is designed based on the Saturn load model using PSPICE, which is an upgraded version of the Simulation Program with Integrated Circuit Emphasis (SPICE) designed by the ORCAD Corporation to perform circuit simulations. This paper calculates different load parameters and discusses factors influencing the driving current curve. With appropriate driving current curves chosen, further magneto-hydrodynamic calculations are carried out and discussed to provide the best results for experiments. The suggested optimal load parameters play an important role in experimental load design.
    Particle-in-cell investigation on the resonant absorption of a plasma surface wave
    Lan Chao-Hui(蓝朝晖) and Hu Xi-Wei(胡希伟)
    Chin. Phys. B, 2011, 20 (10):  105202.  DOI: 10.1088/1674-1056/20/10/105202
    Abstract ( 1349 )   PDF (340KB) ( 1254 )  
    The resonant absorption of a plasma surface wave is supposed to be an important and efficient mechanism of power deposition for a surface wave plasma source. In this paper, by using the particle-in-cell method and Monte Carlo simulation, the resonance absorption mechanism is investigated. Simulation results demonstrate the existence of surface wave resonance and show the high efficiency of heating electrons. The positions of resonant points, the resonance width and the spatio-temporal evolution of the resonant electric field are presented, which accord well with the theoretical results. The paper also discusses the effect of pressure on the resonance electric field and the plasma density.
    Synthesis of ZnO films with a special texture and enhanced field emission properties
    Wang Xiao-Ping(王小平), Wang Zi(王子), Wang Li-Jun(王丽军), and Mei Cui-Yu(梅翠玉)
    Chin. Phys. B, 2011, 20 (10):  105203.  DOI: 10.1088/1674-1056/20/10/105203
    Abstract ( 1216 )   PDF (180KB) ( 779 )  
    ZnO films with special textures are fabricated on Mo-coated Al2O3 ceramic substrates by the catalyst-free electron beam evaporation method, and the as-deposited films are treated by hydrogen plasma. It is found that the surface morphologies of the films are changed significantly after hydrogen plasma treatment and that the films consist of vertically standing and intersecting nanosheets. A lower turn-on field of 1.2 V/μm and an enhanced current density ~0.11 mA/cm2 at 2.47 V/μm are achieved. The low threshold field and the high emission current density are attributed primarily to the unique shape and smaller resistivity of the ZnO nanosheet films.
    Neutron diffraction study on composite compound Nd2Co7
    Yang Yu-Qi(杨育奇), Li Guan-Nan(李冠男), Wang Tong(王通), Huang Qing-Zhen(黄清镇), Gao Qing-Qing(高庆庆), Li Jing-Bo(李静波), Liu Guang-Yao(刘广耀), Luo Jun(骆军), and Rao Guang-Hui(饶光辉)
    Chin. Phys. B, 2011, 20 (10):  106101.  DOI: 10.1088/1674-1056/20/10/106101
    Abstract ( 1433 )   PDF (345KB) ( 734 )  
    The crystallographic and the magnetic structures of the composite compound Nd2Co7 at 300 K are investigated by a combined refinement of X-ray diffraction data and high-resolution neutron diffraction data. The compound crystallizes into a hexagonal Ce2Ni7-type structure and consists of alternately stacking MgZn2-type NdCo2 and CaCu5-type NdCo5 structural blocks along the c axis. A magnetic structure model with the moments of all atoms aligning along the c axis provides a satisfactory fitting to the neutron diffraction data and coincides with the easy magnetization direction revealed by the X-ray diffraction experiments on magnetically pre-aligned fine particles. The refinement results show that the derived atomic moments of the Co atoms vary in a range of 0.7 μB-1.1 μB and the atomic moment of Nd in the NdCo5 slab is close to the theoretical moment of a free trivalent Nd3+ ion, whereas the atomic moment of Nd in the NdCo2 slab is much smaller than the theoretical value for a free Nd3+ ion. The remarkable difference in the atomic moment of Nd atoms between different structural slabs at room temperature is explained in terms of the magnetic characteristics of the NdCo2 and NdCo5 compounds and the local chemical environments of the Nd atoms in different structural slabs of the Nd2Co7 compound.
    Strain-induced ferroelectric phase transitions in incipient ferroelectric rutile TiO2
    Ni Li-Hong(倪利红), Liu Yong(刘涌), Ren Zhao-Hui(任召辉), Song Chen-Lu(宋晨路), and Han Gao-Rong(韩高荣)
    Chin. Phys. B, 2011, 20 (10):  106102.  DOI: 10.1088/1674-1056/20/10/106102
    Abstract ( 1478 )   PDF (990KB) ( 919 )  
    Uniaxial strain induced ferroelectric phase transitions in rutile TiO2 are investigated by first-principles calculations. The calculated results show that the in-plane tensile strain induces rutile TiO2, paraelectric phase with P4-2/mnm (D4h) space group, to a ferroelectric phase with Pm (Cs) space group,driven by the softening behaviour of the E_u1 mode. In addition, the out-of-plane tensile strain, vertical to the ab plane, leads to a ferroelectric phase with P42nm (C4v) space group, driven by the softening behaviour of the A2u mode. The critical tensile strains are 3.7% in-plane and 4.0% out-of-plane, respectively. In addition, the in-plane compression strain, which has the same structure variation as out-of-plane tensile strain due to Poisson effect, leads the paraelectric rutile TiO2 to a paraelectric phase with Pnnm (D2h) space group driven by the softening behaviour of the B1g mode. These results indicate that the sequence ferroelectric (or paraelectric) phase depends on the strain applied. The origin of ferroelectric stabilization in rutile TiO2 is also discussed briefly in terms of strain induced Born effective charge transfer.
    Structural, electrical, and optical properties of ZnInO alloy thin films
    Cai Xi-Kun(才玺坤), Yuan Zi-Jian(原子健), Zhu Xia-Ming(朱夏明), Wang Xiong(王雄), Zhang Bing-Po(张兵坡), Qiu Dong-Jiang(邱东江), and Wu Hui-Zhen(吴惠桢)
    Chin. Phys. B, 2011, 20 (10):  106103.  DOI: 10.1088/1674-1056/20/10/106103
    Abstract ( 1313 )   PDF (290KB) ( 1249 )  
    Indium zinc oxide (IZO) thin films with different percentages of In content (In/[In+Zn]) are synthesized on glass substrates by magnetron sputtering, and the structural, electrical and optical properties of IZO thin films deposited at different In2O3 target powers are investigated. IZO thin films grown at different In2O3 target sputtering powers show evident morphological variation and different grain sizes. As the In2O3 sputtering power rises, the grain size becomes larger and electrical mobility increases. The film grown with an In2O3 target power of 100 W displays the highest electrical mobility of 13.5 cm·V-1·s-1 and the lowest resistivity of 2.4 × 10-3 Ω·cm. The average optical transmittance of the IZO thin film in the visible region reaches 80% and the band gap broadens with the increase of In2O3 target power, which is attributed to the increase in carrier concentration and is in accordance with Burstein-Moss shift theory.
    Infrared response of the lateral PIN structure of a highly titanium-doped silicon-on-insulator material
    Ma Zhi-Hua(马志华), Cao Quan(曹权), Zuo Yu-Hua(左玉华),Zheng Jun(郑军), Xue Chun-Lai(薛春来), Cheng Bu-Wen(成步文), and Wang Qi-Ming(王启明)
    Chin. Phys. B, 2011, 20 (10):  106104.  DOI: 10.1088/1674-1056/20/10/106104
    Abstract ( 1176 )   PDF (608KB) ( 734 )  
    The intermediate band (IB) solar cell is a promising third-generation solar cell that could possibly achieve very high efficiency above the Shockley-Queisser limit. One of the promising ways to synthesize IB material is to introduce heavily doped deep level impurities in conventional semiconductors. High-doped Ti with a concentration of 1020 cm-3-1021 cm-3 in the p-type top Si layer of silicon-on-insulator (SOI) substrate is obtained by ion implantation and rapid thermal annealing (RTA). Secondary ion mass spectrometry measurements confirm that the Ti concentration exceeds the theoretical Mott limit, the main requirement for the formation of an impurity intermediate band. Increased absorption is observed in the infrared (IR) region by Fourier transform infrared spectroscopy (FTIR) technology. By using a lateral p-i-n structure, an obvious infrared response in a range of 1100 nm-2000 nm is achieved in a heavily Ti-doped SOI substrate, suggesting that the improvement on IR photoresponse is a result of increased absorption in the IR. The experimental results indicate that heavily Ti-implanted Si can be used as a potential kind of intermediate-band photovoltaic material to utilize the infrared photons of the solar spectrum.
    Investigations of phase transition, elastic and thermodynamic properties of GaP by using the density functional theory
    Liu Li(刘丽), Wei Jian-Jun(韦建军), An Xin-You(安辛友), Wang Xue-Min(王雪敏), Liu Hui-Na(刘会娜), and Wu Wei-Dong(吴卫东)
    Chin. Phys. B, 2011, 20 (10):  106201.  DOI: 10.1088/1674-1056/20/10/106201
    Abstract ( 1331 )   PDF (307KB) ( 971 )  
    The phase transition of gallium phosphide (GaP) from zinc-blende (ZB) to a rocksalt (RS) structure is investigated by the plane-wave pseudopotential density functional theory (DFT). Lattice constant a0, elastic constants cij, bulk modulus B0 and the pressure derivative of bulk modulus B0' are calculated. The results are in good agreement with numerous experimental and theoretical data. From the usual condition of equal enthalpies, the phase transition from the ZB to the RS structure occurs at 21.9 GPa, which is close to the experimental value of 22.0 GPa. The elastic properties of GaP with the ZB structure in a pressure range from 0 GPa to 21.9 GPa and those of the RS structure in a pressure range of pressures from 21.9 GPa to 40 GPa are obtained. According to the quasi-harmonic Debye model, in which the phononic effects are considered, the normalized volume V/V0, the Debye temperature θ, the heat capacity Cv and the thermal expansion coefficient $\alpha$ are also discussed in a pressure range from 0 GPa to 40 GPa and a temperature range from 0 K to 1500 K.
    Effect of nanocomposite structure on the thermoelectric properties of 0.7-at% Bi-doped Mg2Si nanocomposite
    Yang Mei-Jun(杨梅君), Shen Qiang(沈强), and Zhang Lian-Meng(张联盟)
    Chin. Phys. B, 2011, 20 (10):  106202.  DOI: 10.1088/1674-1056/20/10/106202
    Abstract ( 1458 )   PDF (313KB) ( 939 )  
    Nanocomposites offer a promising approach to the incorporation of nanostructured constituents into bulk thermoelectric materials. The 0.7-at% Bi-doped Mg2Si nanocomposites are prepared by spark plasma sintering of the mixture of nanoscale and microsized 0.7-at% Bi-doped Mg2Si powders. Microstructure analysis shows that the bulk material is composed of nano- and micrograins. Although the nanograin hinders electrical conduction, the nanocomposite structure is more helpful to reduce thermal conductivity and increase the Seebeck coefficient, hence improving thermoelectric performance. A dimensionless figure of merit of 0.8 is obtained for the 0.7-at% Bi-doped Mg2Si nanocomposite with 50-wt % nanopowder, which is about twice larger than that of the sample without nanopowder.
    Critical anomaly and finite size scaling of the self-diffusion coefficient for Lennard–Jones fluids by non-equilibrium molecular dynamic simulation
    Ahmed Asad and Wu Jiang-Tao(吴江涛)
    Chin. Phys. B, 2011, 20 (10):  106601.  DOI: 10.1088/1674-1056/20/10/106601
    Abstract ( 1249 )   PDF (570KB) ( 806 )  
    We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard-Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with temperature decreases by increasing density. For density ρ* = ρσ3 = 0.84 we observe a peak at the value of the self-diffusion coefficient and the critical temperature T* = kT/ε = 1.25. The value of the self-diffusion coefficient strongly depends on system size. The data of the self-diffusion coefficient are fitted to a simple analytic relation based on hydrodynamic arguments. This correction scales as N-$\alpha$, where $\alpha$ is an adjustable parameter and N is the number of particles. It is observed that the values of α < 1 provide quite a good correction to the simulation data. The system size dependence is very strong for lower densities, but it is not as strong for higher densities. The self-diffusion coefficient calculated with non-equilibrium molecular dynamic simulations at different temperatures and densities is in good agreement with other calculations from the literature.
    Effects of V/III ratio on the growth of a-plane GaN films
    Xie Zi-Li(谢自力), Li Yi(李弋), Liu Bin(刘斌), Zhang Rong(张荣), Xiu Xiang-Qian(修向前), Chen Peng(陈鹏), and Zheng You-Liao(郑有炓)
    Chin. Phys. B, 2011, 20 (10):  106801.  DOI: 10.1088/1674-1056/20/10/106801
    Abstract ( 1424 )   PDF (238KB) ( 1627 )  
    The non-polar a-plane GaN is grown on an r-plane sapphire substrate directly without a buffer layer by metal-organic chemical vapour deposition and the effects of V/III ratio growth conditions are investigated. Atomic force microscopy results show that triangular pits are formed at a relatively high V/III ratio, while a relatively low V/III ratio can enhance the lateral growth rate along the c-axis direction. The higher V/III ratio leads to a high density of pits in comparison with the lower V/III ratio. The surface morphology is improved greatly by using a low V/III ratio of 500 and the roughness mean square of the surface is only 3.9 nm. The high resolution X-ray diffraction characterized crystal structural results show that the rocking curve full width at half maximum along the m axis decreases from 0.757° to 0.720°, while along the c axis increases from 0.220° to 0.251° with the V/III increasing from 500 μmol/min to 2000 μmol/min, which indicates that a relatively low V/III ratio is conducible to the c-axis growth of a-plane GaN.
    Partial-SOI high voltage P-channel LDMOS with interface accumulation holes
    Wu Li-Juan(吴丽娟), Hu Sheng-Dong(胡盛东), Luo Xiao-Rong(罗小蓉), Zhang Bo(张波), and Li Zhao-Ji(李肇基)
    Chin. Phys. B, 2011, 20 (10):  107101.  DOI: 10.1088/1674-1056/20/10/107101
    Abstract ( 1604 )   PDF (376KB) ( 856 )  
    A new partial SOI (silion-on-insulator) (PSOI) high voltage P-channel LDMOS (lateral double-diffused metal-oxide semiconductor) with an interface hole islands (HI) layer is proposed and its breakdown characteristics are investigated theoretically. A high concentration of charges accumulate on the interface, whose density changes with the negative drain voltage, which increase the electric field (EI) in the dielectric buried oxide layer (BOX) and modulate the electric field in drift region . This results in the enhancement of the breakdown voltage (BV). The values of EI and BV of an HI PSOI with a 2-μm thick SOI layer over a 1-μm thick buried layer are 580V/μm and -582 V, respectively, compared with 81.5 V/μm and -123 V of a conventional PSOI. Furthermore, the Si window also alleviates the self-heating effect (SHE). Moreover, in comparison with the conventional device, the proposed device exhibits low on-resistance.
    Measuring thermoelectric property of nano-heterostructure Hot!
    Lu Hong-Liang(路红亮), Zhang Chen-Dong(张晨栋), Cai Jin-Ming(蔡金明), Gao Min(高敏), Zou Qiang(邹强), Guo Hai-Ming(郭海明), and Gao Hong-Jun(高鸿钧)
    Chin. Phys. B, 2011, 20 (10):  107301.  DOI: 10.1088/1674-1056/20/10/107301
    Abstract ( 1346 )   PDF (154KB) ( 597 )  
    A method of measuring the thermoelectric power of nano-heterostructures based on four-probe scanning tunneling microscopy is presented. The process is composed of the it in-situ fabrication of a tungsten-indium tip, the precise control of the tip-sample contact and the identification of thermoelectric potential. When the temperature of the substrate is elevated, while that of the tip is kept at room temperature, a thermoelectric potential occurs and can be detected by a current-voltage measurement. As an example of its application, the method is demonstrated to be effective to measure the thermoelectric power in several systems. A Seebeck coefficient of tens of μV/K is obtained in graphene epitaxially grown on Ru (0001) substrate and the thermoelectric potential polarity of this system is found to be the reverse of that of bare Ru (0001) substrate.
    Electronic transport properties of phenylacetylene molecular junctions
    Liu Wen(刘文), Cheng Jie(程杰), Yan Cui-Xia(闫翠霞), Li Hai-Hong(李海宏), Wang Yong-Juan(王永娟), and Liu De-Sheng(刘德胜)
    Chin. Phys. B, 2011, 20 (10):  107302.  DOI: 10.1088/1674-1056/20/10/107302
    Abstract ( 1199 )   PDF (288KB) ( 812 )  
    Electronic transport properties of a kind of phenylacetylene compound— (4-mercaptophenyl)-phenylacetylene are calculated by the first-principles method in the framework of density functional theory and the nonequilibrium Green's function formalism. The molecular junction shows an obvious rectifying behaviour at a bias voltage larger than 1.0 V. The rectification effect is attributed to the asymmetry of the interface contacts. Moreover, at a bias voltage larger than 2.0 V, which is not referred to in a relevant experiment [Fang L, Park J Y, Ma H, Jen A K Y and Salmeron M 2007 Langmuir 23 11522], we find a negative differential resistance phenomenon. The negative differential resistance effect may originate from the change of the delocalization degree of the molecular orbitals induced by the bias.
    Tunable magneto–optic modulation based on magnetically responsive nanostructured magnetic fluid
    Bai Xue-Kun(白学坤),Pu Sheng-Li(卜胜利), Wang Lun-Wei(王伦唯), Wang Xiang(王响), Yu Guo-Jun(于国君), and Ji Hong-Zhu(纪红柱)
    Chin. Phys. B, 2011, 20 (10):  107501.  DOI: 10.1088/1674-1056/20/10/107501
    Abstract ( 1233 )   PDF (285KB) ( 616 )  
    Magnetic fluid is a kind of functional composite material with nanosized structure and unique optical properties. The tunable magneto-optic modulation of magnetic fluid under external magnetic field, achieved by adjusting the polarization direction of incident light, is investigated theoretically and experimentally in this work. The corresponding modulation depth and response time are obtained. The accompanying mechanisms are clarified by using the theory of dichroism of magnetic fluid and the aggregation/disintegration processes of magnetic particles within magnetic fluid when the external magnetic field turns on/off.
    Magnetization reversal in Fe48Pt34B34 magnetic foils
    Gao You-Hui(高有辉)
    Chin. Phys. B, 2011, 20 (10):  107502.  DOI: 10.1088/1674-1056/20/10/107502
    Abstract ( 1284 )   PDF (283KB) ( 586 )  
    Exchange-spring magnet L1-FePt/(Fe2B+α-Fe) is fabricated by flash annealing a melt-spun Fe48Pt34B34 foil. A coercivity of 8500 Oe (1 Oe = 79.5775 A/m), squareness (Mr/Ms) of 0.70, saturation magnetization of 10.2 kGs (1 Gs = 10-4 T) and an effective anisotropy Keff =2.0 × 107 ergs/cm3 are obtained. A two-step magnetization reversal feature is characterized in this paper. An exchange bias phenomenon is also observed in a low saturation field.
    Hot deformation in nanocrystalline Nd–Fe–B backward extruded rings
    Li An-Hua(李安华), Zhao Rui(赵睿), Lai Bin(赖彬), Wang Hui-Jie(王会杰), Zhu Ming-Gang(朱明刚), and Li Wei(李卫)
    Chin. Phys. B, 2011, 20 (10):  107503.  DOI: 10.1088/1674-1056/20/10/107503
    Abstract ( 1327 )   PDF (383KB) ( 835 )  
    Radially oriented Nd--Fe--B rings are prepared by backward extrusion of fine grained melt-spun powder. Melt-spun powder with the nominal composition of Nd$_{30.5}$Fe$_{\rm bal.}$Co$_{6.0}$Ga$_{0.6}$Al$_{0.2}$B$_{0.9}$ (wt{\%}) is used as starting material. The effects of process variables, such as deformation temperature ($T_{\rm d}$), strain rate ($\dot \varepsilon $) and height reduction  ($\Delta h% $), on the magnetic properties of the rings are investigated. A scanning electron microscope (SEM) equipped with an energy spectrum device is used to study the metallograph and microfracture of the extruded rings.  The $B_{\rm r}$ and ${(BH)}_{\rm max}$ reach the optimum values at $T_{\rm d}=800$ ${^\circ}$C, $\dot \varepsilon =0.01$ mm/s, and $\Delta h% =70$%. It is found by SEM observations that the particle boundaries, which  seemingly correspond to the interfaces of the starting melt-spun powders, emerge after the corrosion of metallography specimens. This is helpful for studying the effects of powder--powder interface on the local deformation and  deformation homogeneity in the rings. For different spatial positions of the extruded rings, there are characteristic metallographies and microfractures. The upper end of the rings has the least deformation and worst texture,  and therefore the worst magnetic properties. The magnetic properties in the radial direction increase slightly along the axis from the bottom to the middle, then steeply decrease at the upper end of the ring. The deformation  and the formation-of-texturing processes are discussed. The deformation and the texturing formation of melt-spun Nd--Fe--B alloys probably involve grain boundary sliding and grain rotation, the solution-precipitation process  and preferential growth of Nd$_{2}$Fe$_{14}$B nanograins along the easy growth $a$-axis.
    Effect of electromechanical boundary conditions on the properties of epitaxial ferroelectric thin films
    Zhou Zhi-Dong(周志东), Zhang Chun-Zu(张春祖), and Jiang Quan(蒋泉)
    Chin. Phys. B, 2011, 20 (10):  107701.  DOI: 10.1088/1674-1056/20/10/107701
    Abstract ( 1261 )   PDF (159KB) ( 601 )  
    The effects of internal stresses and depolarization fields on the properties of epitaxial ferroelectric perovskite thin films are discussed by employing the dynamic Ginzburg-Landau equation (DGLE). The numerical solution for BaTiO3 film shows that internal stress and the depolarization field have the most effects on ferroelectric properties such as polarization, Curie temperature and susceptibility. With the increase of the thickness of the film, the polarization of epitaxial ferroelectric thin film is enhanced rapidly under high internal compressively stress. With the thickness exceeding the critical thickness for dislocation formation, the polarization increases slowly and even weakens due to relaxed internal stresses and a weak electrical boundary condition. This indicates that the effects of mechanical and electrical boundary conditions both diminish for ferroelectric thick films. Consequently, our thermodynamic method is a full scale model that can predict the properties of ferroelectric perovskite films in a wide range of film thickness.
    Multipeak-structured photoluminescence mechanisms of as-prepared and oxidized Si nanoporous pillar arrays
    Xu Hai-Jun(许海军), Chan Yu-Fei(廛宇飞), and Su Lei(苏雷)
    Chin. Phys. B, 2011, 20 (10):  107801.  DOI: 10.1088/1674-1056/20/10/107801
    Abstract ( 1234 )   PDF (207KB) ( 720 )  
    Silicon dominates the electronic industry, but its poor optical properties mean that it is not preferred for photonic applications. Visible photoluminescence (PL) was observed from porous Si at room temperature in 1990, but the origin of these light emissions is still not fully understood. This paper reports that an Si nanocrystal, silicon nanoporous pillar array (Si-NPA) with strong visible PL has been prepared on a Si wafer substrate by the hydrothermal etching method. After annealing in O2 atmosphere, the hydride coverage of the Si pillar internal surface is replaced by an oxide layer, which comprises of a great quantity of Si nanocrystal (nc-Si) particles and each of them are encapsulated by an Si oxide layer. Meanwhile a transition from efficient triple-peak PL bands from blue to red before annealing to strong double-peak blue PL bands after annealing is observed. Comparison of the structural, absorption and luminescence characteristics of the as-prepared and oxidized samples provides evidence for two competitive transition processes, the band-to-band recombination of the quantum confinement effect of nc-Si and the radiative recombination of excitons from the luminescent centres located at the surface of nc-Si units or in the Si oxide layers that cover the nc-Si units because of the different oxidation degrees. The sizes of nc-Si and the quality of the Si oxide surface are two major factors affecting two competitive processes. The smaller the size of nc-Si is and the stronger the oxidation degree of Si oxide layer is, the more beneficial for the luminescent centre recombination process to surpass the quantum confinement process is. The clarification on the origin of the photons may be important for the Si nanoporous pillar array to control both the PL band positions and the relative intensities according to future device requirements and further fabrication of optoelectronic nanodevices.
    Stress and morphology of a nonpolar a-plane GaN layer on r-plane sapphire substrate
    Xu Sheng-Rui(许晟瑞), Hao Yue(郝跃), Zhang Jin-Cheng(张进成), Xue Xiao-Yong(薛晓咏), Li Pei-Xian(李培咸), Li Jian-Ting(李建婷), Lin Zhi-Yu(林志宇), Liu Zi-Yang(刘子扬), Ma Jun-Cai(马俊彩), He Qiang(贺强), and Lü Ling(吕玲)
    Chin. Phys. B, 2011, 20 (10):  107802.  DOI: 10.1088/1674-1056/20/10/107802
    Abstract ( 1454 )   PDF (883KB) ( 1852 )  
    The anisotropic strain of a nonpolar (1120) a-plane GaN epilayer on an r-plane (1102) sapphire substrate, grown by low-pressure metal-organic vapour deposition is investigated by Raman spectroscopy. The room-temperature Raman scattering spectra of nonpolar a-plane GaN are measured in surface and edge backscattering geometries. The lattice is contracted in both the c- and the m-axis directions, and the stress in the m-axis direction is larger than that in the c-axis direction. On the surface of this sample, a number of cracks appear only along the m-axis, which is confirmed by the scanning electron micrograph. Atomic force microscopy images reveal a significant decrease in the root-mean-square roughness and the density of submicron pits after the stress relief.
    Improving efficiency of organic light-emitting devices by optimizing the LiF interlayer in the hole transport layer
    Jiao Zhi-Qiang(焦志强), Wu Xiao-Ming(吴晓明), Hua Yu-Lin(华玉林), Dong Mu-Sen(董木森), Su Yue-Ju(苏跃举), Shen Li-Ying(申利莹), and Yin Shou-Gen(印寿根)
    Chin. Phys. B, 2011, 20 (10):  107803.  DOI: 10.1088/1674-1056/20/10/107803
    Abstract ( 1450 )   PDF (162KB) ( 892 )  
    The efficiency of organic light-emitting devices (OLEDs) based on N,N'-bis(1-naphthyl)-N,N'-diphenyl-N,1'-biphenyl-4,4'-diamine (NPB) (the hole transport layer) and tris(8-hydroxyquinoline) aluminum (Alq3) (both emission and electron transport layers) is improved remarkably by inserting a LiF interlayer into the hole transport layer. This thin LiF interlayer can effectively influence electrical performance and significantly improve the current efficiency of the device. A device with an optimum LiF layer thickness at the optimum position in NPB exhibits a maximum current efficiency of 5.96 cd/A at 215.79 mA/cm2, which is about 86% higher than that of an ordinary device (without a LiF interlayer, 3.2 cd/A). An explanation can be put forward that LiF in the NPB layer can block holes and balance the recombination of holes and electrons. The results may provide some valuable references for improving OLED current efficiency.
    Investigation of the Cr:LiSrAlF6 crystal by high-temperature Raman spectroscopy
    Wang Di(王迪), Wan Song-Ming(万松明), Zhang Qing-Li(张庆礼), Sun Dun-Lu(孙敦陆), Gu Gui-Xin(顾桂新), Yin Shao-Tang(殷绍唐) Zhang Guo-Chun(张国春), You Jing-Lin(尤静林), and Wang Yuan-Yuan(王媛媛)
    Chin. Phys. B, 2011, 20 (10):  108101.  DOI: 10.1088/1674-1056/20/10/108101
    Abstract ( 1231 )   PDF (927KB) ( 1107 )  
    In this paper, Cr-doped LiSrAlF6 crystals are investigated using high-temperature Raman spectroscopy and the single-crystal Raman spectra of Cr:LiSrAlF6 are analysed by factor group theory and comparison with other fluorides. The results indicate that Cr:LiSrAlF6 is stable below its melting point; Raman peaks located at 561, 322 and 250 cm-1 are assigned to the A1g modes of AlF6, SrF6 and LiF6 octachdra, respectively; with temperature increasing, Raman peaks associated with AlF6 octahedra shift towards low frequencies, while LiF6 and SrF6 octahedra are temperature-insensitive; around the crystal melting point, three new Raman peaks occur, which are associated with the AlF6 octahedral chain structure. Finally, the microstructural evolution of Cr:LiSrAlF6 from room temperature to its melting point is discussed based on its Raman spectra.
    Effect of thickness on the microstructure of GaN films on Al2O3 (0001) by laser molecular beam epitaxy
    Liu Ying-Ying(刘莹莹), Zhu Jun(朱俊), Luo Wen-Bo(罗文博), Hao Lan-Zhong(郝兰众), Zhang Ying(张鹰), and Li Yan-Rong(李言荣)
    Chin. Phys. B, 2011, 20 (10):  108102.  DOI: 10.1088/1674-1056/20/10/108102
    Abstract ( 1245 )   PDF (237KB) ( 917 )  
    Heteroepitaxial GaN films are grown on sapphire (0001) substrates using laser molecular beam epitaxy. The growth processes are in-situ monitored by reflection high energy electron diffraction. It is revealed that the growth mode of GaN transformed from three-dimensional (3D) island mode to two-dimensional (2D) layer-by-layer mode with the increase of thickness. This paper investigates the interfacial strain relaxation of GaN films by analysing their diffraction patterns. Calculation shows that the strain is completely relaxed when the thickness reaches 15 nm. The surface morphology evolution indicates that island merging and reduction of the island-edge barrier provide an effective way to make GaN films follow a 2D layer-by-layer growth mode. The 110-nm GaN films with a 2D growth mode have smooth regular hexagonal shapes. The X-ray diffraction indicates that thickness has a significant effect on the crystallized quality of GaN thin films.
    Enhanced etching of silicon dioxide guided by carbon nanotubes in HF solution
    Zhao Hua-Bo(赵华波), Ying Alex Yi-Qun(应轶群), Yan Feng(严峰), Wei Qin-Qin(魏芹芹), Fu Yun-Yi(傅云义), Zhang Yan(张岩), Li Yan(李彦), Wei Zi-Jun(魏子钧), and Zhang Zhao-Hui(张朝晖)
    Chin. Phys. B, 2011, 20 (10):  108103.  DOI: 10.1088/1674-1056/20/10/108103
    Abstract ( 1454 )   PDF (3106KB) ( 1366 )  
    This paper describes a new method to create nanoscale SiO2 pits or channels using single-walled carbon nanotubes (SWNTs) in an HF solution at room temperature within a few seconds. Using aligned SWNT arrays, a pattern of nanoscale SiO2 channels can be prepared. The nanoscale SiO2 patterns can also be created on the surface of three-dimensional (3D) SiO2 substrate and even the nanoscale trenches can be constructed with arbitrary shapes. A possible mechanism for this enhanced etching of SiO2 has been qualitatively analysed using defects in SWNTs, combined with H3O+ electric double layers around SWNTs in an HF solution.
    What happens to the initial planar instability when the thermal gradient is increased during directional solidification?
    Wang Zhi-Jun(王志军), Wang Jin-Cheng(王锦程), Li Jun-Jie(李俊杰), Yang Gen-Cang(杨根仓), and Zhou Yao-He(周尧和)
    Chin. Phys. B, 2011, 20 (10):  108104.  DOI: 10.1088/1674-1056/20/10/108104
    Abstract ( 1056 )   PDF (483KB) ( 563 )  
    The positive thermal gradient is one of the most important parameters during directional solidification. The increase of the thermal gradient usually stabilizes the planar interface in the steady state analysis. However, in the initial transient range of planar instability, the thermal gradient presents complicated effects. Time-dependent analysis shows that the increase of the thermal gradient can enhance both the stabilizing effects and the destabilizing effects on a planar interface. The incubation time first decreases and then increases with the increase of the thermal gradient. Moreover, the initial average wavelength always increases with the thermal gradient increasing, contrary to the effect of the thermal gradient on the steady cellular/dendritic spacing. This reveals the types of spacing adjustment after planar instability.
    Identification of the pressure-induced phase transition of ZnSe with the positron annihilation method
    Liu Jian-Dang(刘建党), Cheng Bin(成斌), Zhang Jie(张杰), Zhang Li-Juan(张丽娟),Weng Hui-Min(翁惠民), and Ye Bang-Jiao(叶邦角)
    Chin. Phys. B, 2011, 20 (10):  108105.  DOI: 10.1088/1674-1056/20/10/108105
    Abstract ( 1256 )   PDF (136KB) ( 617 )  
    This paper studies the pressure-induced phase transition between zincblende (B3) and NaCl (B1) structure ZnSe by using the hydrostatic pressure first-principles pseudopotential plane wave method. The energy-volume and enthalpy-pressure curves are employed to estimate the transition pressure. It is found that ZnSe undergoes a first-order phase transition from the B3 structure to the B1 structure at approximately 15 GPa derived from the energy-volume relation and 14 GPa based on deduction from enthalpy-pressure data. The pressure-related positron bulk lifetimes of the two ZnSe structures are calculated with the atomic superposition approximation method. In comparison with the 13.4% reduction in volume of ZnSe at the transition pressure, the positron bulk lifetime decreases more significantly and the relative value declines up to 22.3%. The results show that positron annihilation is an effective technique to identify and characterize the first-order phase transition and can give valuable information about changes in micro-scale, such as volume shrinkage and compressibility.
    Self-sustained target waves in excitable media with only a long-range link
    Qian Yu(钱郁), Wang Can-Jun(王参军), Shi Hu-Shan(石虎山), Mi Yuan-Yuan(弭元元), and Huang Xiao-Dong(黄晓东)
    Chin. Phys. B, 2011, 20 (10):  108201.  DOI: 10.1088/1674-1056/20/10/108201
    Abstract ( 1190 )   PDF (335KB) ( 738 )  
    In this paper we investigate spatiotemporal pattern formation in excitable media with only a long-range link. Besides the trivial solutions of spiral patterns, we find the asymptotic self-sustained target waves in the autonomous tissues. The wave source supporting this kind of new pattern is the oscillatory one-dimensional Winfree-loop self-organized under the presence of a long-range link, which is explored by the dominant phase-advanced driving method. Based on this understanding we can effectively regulate the oscillations of excitable media by suitably arranging the long-range link, including construction of self-sustained target waves with controllable period and wave length, or manipulation of system states between different patterns.
    Three-dimensional global interconnect based on a design window
    Qian Li-Bo(钱利波), Zhu Zhang-Ming(朱樟明), and Yang Yin-Tang(杨银堂)
    Chin. Phys. B, 2011, 20 (10):  108401.  DOI: 10.1088/1674-1056/20/10/108401
    Abstract ( 1234 )   PDF (156KB) ( 612 )  
    Based on a stochastic wire length distributed model, the interconnect distribution of a three-dimensional integrated circuit (3D IC) is predicted exactly. Using the results of this model, a global interconnect design window for a giga-scale system-on-chip (SOC) is established by evaluating the constraints of 1) wiring resource, 2) wiring bandwidth, and 3) wiring noise. In comparison to a two-dimensional integrated circuit (2D IC) in a 130-nm and 45-nm technology node, the design window expands for a 3D IC to improve the design reliability and system performance, further supporting 3D IC application in future integrated circuit design.
    Linear analysis of a three-dimensional rectangular Cerenkov maser with a sheet electron beam
    Chen Ye(陈晔), Zhao Ding(赵鼎), and Wang Yong(王勇)
    Chin. Phys. B, 2011, 20 (10):  108402.  DOI: 10.1088/1674-1056/20/10/108402
    Abstract ( 1242 )   PDF (278KB) ( 517 )  
    A linear theory of a rectangular Cerenkov maser (RCM) with a sheet electron beam is developed by using the field-match method. Based on the three-dimensional beam-wave interaction model proposed in this paper, a hybrid-mode dispersion equation and its analytical solution are derived for the RCM. Through numerical calculations, the effects of the beam-grating gap, beam thickness, current density, beam voltage and waveguide width on the linear growth rate are analysed. Moreover, the performance difference between the RCM with the closed transverse boundary and that with the upper open boundary is compared. The results show that the closed RCM model can avoid the effect of RF radiation on beam-wave interaction, which is more rational for practical applications.
    Improved charge trapping flash device with Al2O3/HfSiO stack as blocking layer
    Zheng Zhi-Wei(郑志威), Huo Zong-Liang(霍宗亮), Zhu Chen-Xin(朱晨昕), Xu Zhong-Guang(许中广), Liu Jing(刘璟), and Liu Ming(刘明)
    Chin. Phys. B, 2011, 20 (10):  108501.  DOI: 10.1088/1674-1056/20/10/108501
    Abstract ( 1295 )   PDF (532KB) ( 866 )  
    In this paper, we investigate an Al2O3/HfSiO stack as the blocking layer of a metal-oxide-nitride-oxide-silicon-type (MONOS) memory capacitor. Compared with a memory capacitor with a single HfSiO layer as the blocking layer or an Al2O3/HfO2 stack as the blocking layer, the sample with the Al2O3/HfSiO stack as the blocking layer shows high program/erase (P/E) speed and good data retention characteristics. These improved performances can be explained by energy band engineering. The experimental results demonstrate that the memory device with an Al2O3/HfSiO stack as the blocking layer has great potential for further high-performance nonvolatile memory applications.
    Weak avalanche multiplication in SiGe heterojunction bipolar transistors on thin film silicon-on-insulator
    Xu Xiao-Bo(徐小波), Zhang He-Ming(张鹤鸣), Hu Hui-Yong(胡辉勇) Li Yu-Chen(李妤晨), and Qu Jiang-Tao(屈江涛)
    Chin. Phys. B, 2011, 20 (10):  108502.  DOI: 10.1088/1674-1056/20/10/108502
    Abstract ( 1459 )   PDF (503KB) ( 965 )  
    In this paper, we propose an analytical avalanche multiplication model for the next generation of SiGe silicon-on-insulator (SOI) heterojunction bipolar transistors (HBTs) and consider their vertical and lateral impact ionizations for the first time. Supported by experimental data, the analytical model predicts that the avalanche multiplication governed by impact ionization shows kinks and the impact ionization effect is small compared with that of the bulk HBT, resulting in a larger base-collector breakdown voltage. The model presented in the paper is significant and has useful applications in the design and simulation of the next generation of SiGe SOI BiCMOS technology.
    Short-wavelength InAlGaAs/AlGaAs quantum dot superluminescent diodes Hot!
    Liang De-Chun(梁德春), An Qi(安琪), Jin Peng(金鹏), Li Xin-Kun(李新坤), Wei Heng(魏恒), Wu Ju(吴巨), and Wang Zhan-Guo(王占国)
    Chin. Phys. B, 2011, 20 (10):  108503.  DOI: 10.1088/1674-1056/20/10/108503
    Abstract ( 1182 )   PDF (568KB) ( 803 )  
    This paper reports the fabrication of J-shaped bent-waveguide superluminescent diodes utilizing an InAlGaAs/AlGaAs quantum dot active region. The emission spectrum of the device is centred at 884 nm with a full width at half maximum of 37 nm and an output power of 18 mW. By incorporating an Al composition into the quantum dot active region, short-wavelength superluminescent diode devices can be obtained. An intersection was found for the light power-injection current curves measured from the straight-waveguide facet and the bent-waveguide facet, respectively. The result is attributed to the conjunct effects of the gain and the additional loss of the bent waveguide. A numerical simulation is performed to verify the qualitative explanation. It is shown that bent waveguide loss is an important factor that affects the output power of J-shaped superluminescent diode devices.
    Blue InGaN light-emitting diodes with dip-shaped quantum wells
    Lu Tai-Ping(卢太平), Li Shu-Ti(李述体), Zhang Kang(张康), Liu Chao(刘超), Xiao Guo-Wei(肖国伟), Zhou Yu-Gang(周玉刚), Zheng Shu-Wen(郑树文), Yin Yi-An(尹以安), Wu Le-Juan(仵乐娟), Wang Hai-Long(王海龙), and Yang Xiao-Dong(杨孝东)
    Chin. Phys. B, 2011, 20 (10):  108504.  DOI: 10.1088/1674-1056/20/10/108504
    Abstract ( 1273 )   PDF (190KB) ( 1100 )  
    InGaN based light-emitting diodes (LEDs) with dip-shaped quantum wells and conventional rectangular quantum wells are numerically investigated by using the APSYS simulation software. It is found that the structure with dip-shaped quantum wells shows improved light output power, lower current leakage and less efficiency droop. Based on numerical simulation and analysis, these improvements on the electrical and the optical characteristics are attributed mainly to the alleviation of the electrostatic field in dip-shaped InGaN/GaN multiple quantum wells (MQWs).
    Stability of piecewise-linear models of genetic regulatory networks
    Lin Peng(林鹏), Qin Kai-Yu(秦开宇), and Wu Hai-Yan(吴海燕)
    Chin. Phys. B, 2011, 20 (10):  108701.  DOI: 10.1088/1674-1056/20/10/108701
    Abstract ( 1275 )   PDF (353KB) ( 552 )  
    This paper investigates the stability of the equilibria of the piecewise-linear models of genetic regulatory networks on the intersection of the thresholds of all variables. It first studies circling trajectories and derives some stability conditions by quantitative analysis in the state transition graph. Then it proposes a common Lyapunov function for convergence analysis of the piecewise-linear models and gives a simple sign condition. All the obtained conditions are only related to the constant terms on the right-hand side of the differential equation after bringing the equilibrium to zero.
    Micromorph tandem solar cells: optimization of the microcrystalline silicon bottom cell in a single chamber system
    Zhang Xiao-Dan(张晓丹), Zheng Xin-Xia(郑新霞), Xu Sheng-Zhi(许盛之), Lin Quan(林泉), Wei Chang-Chun(魏长春), Sun Jian(孙建), Geng Xin-Hua(耿新华), and Zhao Ying(赵颖)
    Chin. Phys. B, 2011, 20 (10):  108801.  DOI: 10.1088/1674-1056/20/10/108801
    Abstract ( 1753 )   PDF (186KB) ( 903 )  
    We report on the development of single chamber deposition of microcrystalline and micromorph tandem solar cells directly onto low-cost glass substrates. The cells have pin single-junction or pin/pin double-junction structures on glass substrates coated with a transparent conductive oxide layer such as SnO2 or ZnO. By controlling boron and phosphorus contaminations, a single-junction microcrystalline silicon cell with a conversion efficiency of 7.47% is achieved with an i-layer thickness of 1.2 μm. In tandem devices, by thickness optimization of the microcrystalline silicon bottom solar cell, we obtained an initial conversion efficiency of 9.91% with an aluminum (Al) back reflector without a dielectric layer. In order to enhance the performance of the tandem solar cells, an improved light trapping structure with a ZnO/Al back reflector is used. As a result, a tandem solar cell with 11.04% of initial conversion efficiency has been obtained.
    Thermal aspect of the diurnal variation of tropical convective and stratiform rainfall
    Cui Xiao-Peng(崔晓鹏) and Li Xiao-Fan(李小凡)
    Chin. Phys. B, 2011, 20 (10):  109201.  DOI: 10.1088/1674-1056/20/10/109201
    Abstract ( 1266 )   PDF (143KB) ( 598 )  
    The diurnal variation of radiation plays a key role in determining the diurnal variations of tropical oceanic convective and stratiform rainfall, and the examination of such a relationship requires a direct link between the radiation term in a heat budget and the surface rain rate in a cloud budget. Thus, the thermally related surface rainfall budgets derived from the combination of cloud and heat budgets are analysed with two-dimensional equilibrium cloud-resolving model simulation data to study the effects of sea surface temperature (SST) and cloud radiative, and microphysical processes on the diurnal variations of convective and stratiform rainfall. The results show that the increase in SST, the inclusion of diurnal variation of SST and the exclusion of cloud radiative processes increase negative diurnal anomalies of heat divergence over rainfall-free regions during the nighttime through changing the vertical structures of diurnal anomaly of radiation in the troposphere. The strengthened negative diurnal anomalies of heat divergence over rainfall-free regions enhance positive diurnal anomalies of heat divergence over convective regions, which intensifies the positive diurnal anomaly of convective rainfall. The exclusion of microphysical effects of ice clouds increases the negative diurnal anomaly of heat divergence over rainfall-free regions during the nighttime through reducing latent heat; this appears to enhance the positive diurnal anomaly of heat divergence over raining stratiform regions, and thus stratiform rainfall.
ISSN 1674-1056   CN 11-5639/O4
, Vol. 20, No. 10

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