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Chin. Phys. B  
  Chin. Phys. B--2008, Vol.17, No.4
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A potential integration method for Birkhoffian system

Hu Chu-Le, Xie Jia-Fang
Chin. Phys. B 2008, 17 (4): 01153;  doi: 10.1088/1674-1056/17/4/001
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This paper is intended to apply the potential integration method to the differential equations of the Birkhoffian system. The method is that, for a given Birkhoffian system, its differential equations are first rewritten as 2n first-order differential equations. Secondly, the corresponding partial differential equations are obtained by potential integration method and the solution is expressed as a complete integral. Finally, the integral of the system is obtained.

New exact periodic solutions to (2+1)-dimensional dispersive long wave equations

Zhang Wen-Liang, Wu Guo-Jiang, Zhang Miao, Wang Jun-Mao, Han Jia-Hua
Chin. Phys. B 2008, 17 (4): 01156;  doi: 10.1088/1674-1056/17/4/002
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In this paper, we make use of the auxiliary equation and the expanded mapping methods to find the new exact periodic solutions for (2+1)-dimensional dispersive long wave equations in mathematical physics, which are expressed by Jacobi elliptic functions, and obtain some new solitary wave solutions (m \to 1). This method can also be used to explore new periodic wave solutions for other nonlinear evolution equations.

Implementation of n-qubit Deutsch--Jozsa algorithm using resonant interaction in cavity QED

Wang Hong-Fu, Zhang Shou
Chin. Phys. B 2008, 17 (4): 01165;  doi: 10.1088/1674-1056/17/4/003
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We propose a scheme to implement the n-qubit Deutsch--Jozsa algorithm based on resonant interaction between the atoms and a single-mode cavity. In the scheme, the resonant transitions between two ground states and one excited state of an atom are changed alternately by adjusting the cavity frequency appropriately, and the operations required to complete the algorithm can be significantly simplified following the increment of the number of qubits. The implementation of the scheme in experiment would show the full power of quantum algorithm and would be significative and important for more complicated quantum algorithm in cavity quantum electrodynamics.

Preparation of cluster state in large detuned cavity

Zou Chang-Lin, Gao Guo-Jun, Lu Yan, Li Da-Chuang, Yang Ming, Cao Zhuo-Liang
Chin. Phys. B 2008, 17 (4): 01174;  doi: 10.1088/1674-1056/17/4/004
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An experimentally realizable physical scheme for preparing multiqubit cluster states from a large detuned atom--cavity interaction is proposed. The scheme is free of any type of measurement and insensitive to the cavity decay, and the cavity field is only virtually excited so that there is no information exchanging between atom and cavity. The time required for the gate operations is very short, which is important for decoherence. We also discuss the experimental feasibility of our scheme.

Practical non-orthogonal decoy state quantum key distribution with heralded single photon source

Mi Jing-Long, Wang Fa-Qiang, Lin Qing-Qun, Liang Rui-Sheng
Chin. Phys. B 2008, 17 (4): 01178;  doi: 10.1088/1674-1056/17/4/005
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Recently the performance of the quantum key distribution (QKD) is substantially improved by the decoy state method and the non-orthogonal encoding protocol, separately. In this paper, a practical non-orthogonal decoy state protocol with a heralded single photon source (HSPS) for QKD is presented. The protocol is based on 4 states with different intensities, i.e. one signal state and three decoy states. The signal state is for generating keys; the decoy states are for detecting the eavesdropping and estimating the fraction of single-photon and two-photon pulses. We have discussed three cases of this protocol, i.e. the general case, the optimal case and the special case. Moreover, the final key rate over transmission distance is simulated. For the low dark count of the HSPS and the utilization of the two-photon pulses, our protocol has a higher key rate and a longer transmission distance than any other decoy state protocol.

Influence of dark energy on time-like geodesic motion in Schwarzschild spacetime

Chen Ju-Hua, Wang Yong-Jiu
Chin. Phys. B 2008, 17 (4): 01184;  doi: 10.1088/1674-1056/17/4/006
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In this paper we investigate the influence of the dark energy on the time-like geodesic motion of a particle in Schwarzschild spacetime by analysing the behaviour of the effective potential which appears in an equation of motion. For the non-radial time-like geodesics, we find a bound orbit when the particle energy is in an appropriate range, and also find another possible orbit, which is that the particle drops straightly into the singularity of a black hole or escapes to infinity. For the radial time-like geodesics, we find an unstable circular orbit when the particle energy is the critical value, in which case it is possible for the particle to escape to infinity.

Effect of interaction strength on gap solitons of Bose--Einstein condensates in optical lattices

Yang Ru-Shu, Yang Jiang-He
Chin. Phys. B 2008, 17 (4): 01189;  doi: 10.1088/1674-1056/17/4/007
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We have developed a systematic analytical approach to the study on the dynamic properties of the linear and the nonlinear excitations for quasi-one-dimensional Bose--Einstein condensate trapped in optical lattices. A novel linear dispersion relation and an algebraic soliton solution of the condensate are derived analytically under consideration of Bose--Einstein condensate with a periodic potential. By analysing the soliton solution, we find that the interatomic interaction strength has an important effect on soliton dynamic properties of Bose--Einstein condensate.

Parameters estimation online for Lorenz system by a novel quantum-behaved particle swarm optimization

Gao Fei, Li Zhuo-Qiu, Tong Heng-Qing
Chin. Phys. B 2008, 17 (4): 01196;  doi: 10.1088/1674-1056/17/4/008
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This paper proposes a novel quantum-behaved particle swarm optimization (NQPSO) for the estimation of chaos' unknown parameters by transforming them into nonlinear functions' optimization. By means of the techniques in the following three aspects: contracting the searching space self-adaptively; boundaries restriction strategy; substituting the particles' convex combination for their centre of mass, this paper achieves a quite effective search mechanism with fine equilibrium between exploitation and exploration. Details of applying the proposed method and other methods into Lorenz systems are given, and experiments done show that NQPSO has better adaptability, dependability and robustness. It is a successful approach in unknown parameter estimation online especially in the cases with white noises.

Breaking chaotic shift key communication via adaptive key identification

Ren Hai-Peng, Han Chong-Zhao, Liu Ding
Chin. Phys. B 2008, 17 (4): 01202
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This paper proposes an adaptive parameter identification method for breaking chaotic shift key communication from the transmitted signal in public channel. The sensitive dependence property of chaos on parameter mismatch is used for chaos adaptive synchronization and parameter identification. An index function about the synchronization error is defined and conjugate gradient method is used to minimize the index function and to search the transmitter's parameter (key). By using proposed method, secure key is recovered from transmitted signal generated by low dimensional chaos and hyper chaos switching communication. Multi-parameters can also be identified from the transmitted signal with noise.

Controlling beam halo-chaos via backstepping design

Gao Yuan, Kong Feng
Chin. Phys. B 2008, 17 (4): 01209;  doi: 10.1088/1674-1056/17/4/010
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A backstepping control method is proposed for controlling beam halo-chaos in the periodic focusing channels (PFCs) of high-current ion accelerator. The analysis and numerical results show that the method, via adjusting an exterior magnetic field, is effective to control beam halo chaos with five types of initial distribution ion beams, all statistical quantities of the beam halo-chaos are largely reduced, and the uniformity of ion beam is improved. This control method has an important value of application, for the exterior magnetic field can be easily adjusted in the periodical magnetic focusing channels in experiment.

A possible experimental observable for the determination of neutron skin thickness

Ma Chun-Wang, Fu Yao, Fang De-Qing, Ma Yu-Gang, Cai Xiang-Zhou, Guo Wei, Tian Wen-Dong, Wang Hong-Wei
Chin. Phys. B 2008, 17 (4): 01216;  doi: 10.1088/1674-1056/17/4/011
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The dependence between neutron skin thickness and neutron abrasion cross section ($\sigma_{\rm nabr}$) for neutron-rich nuclei is investigated within the framework of the statistical abrasion ablation model. Assuming that the density distributions for proton and neutron are of Fermi-type, and adjusting the diffuseness parameter of neutron density distribution in the droplet model, we find out the good linear correlation between the neutron skin thickness and the abrasion cross section $\sigma_{\rm nabr}$ for neutron-rich nuclei. The uncertainty of neutron skin thickness determined from $\sigma_{\rm nabr}$ is very small. It is suggested that $\sigma_{\rm nabr}$ can be used as a new experimental observable to extract the neutron skin thickness for neutron-rich nucleus. The scaling behaviours between neutron skin thickness and $\sigma_{\rm nabr}$, separately, for isotopes of $^{26-35}$Na, $^{44-56}$Ar, $^{48-60}$Ca, $^{67-78}$Ni are also investigated.

Femtosecond pulse laser-induced self-organized nanostructures on the surface of ZnO crystal

Zhong Min-Jian, Guo Guang-Lei, Yang Jun-Yi, Ma Ning-Hua, Ye Guo, Guo Xiao-Dong, Li Ru-Xin, Ma Hong-Liang
Chin. Phys. B 2008, 17 (4): 01223;  doi: 10.1088/1674-1056/17/4/012
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This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti:sapphire laser with a repetition rate of 250\,kHz. For a linearly polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was promoted. The period of self-organization structures is about 180\,nm. The grating orientation is adjusted by the laser polarization direction. A long range Bragg-like grating is formed by moving the sample at a speed of 10\,\mu m/s. For a circularly polarized laser beam, uniform spherical nanoparticles were formed as a result of Coulomb explosion during the interaction of near-infrared laser with ZnO crystal.

Ionization and single electron capture in collision of highly charged Ar16+ ions with helium

Wang Fei, Gou Bing-Cong
Chin. Phys. B 2008, 17 (4): 01227;  doi: 10.1088/1674-1056/17/4/013
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This paper uses the two-centre atomic orbital close-coupling method to study the ionization and the single electron capture in collision of highly charged Ar16+ ions with He atoms in the velocity range of 1.2--1.9 a.u.. The relative importance of single ionization (SI) to single capture (SC) is explored. The comparison between the calculation and experimental data shows that the SI/SC cross section ratios from this work are in good agreement with experimental data. The total single electron ionization cross sections and the total single electron capture cross sections are also given for this collision. The investigation of the partial electron capture cross section shows a general tendency of capture to larger n and l with increasing velocity from 1.2 to 1.9 a.u..

Photodetachment of H-- in an electric field between two parallel interfaces

Wang De-Hua, Yu Yong-Jiang
Chin. Phys. B 2008, 17 (4): 01231;  doi: 10.1088/1674-1056/17/4/014
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By using the closed orbit theory, the photodetachment cross section of H- in a static electric field between two parallel elastic interfaces is derived and calculated. It is found that the photodetachment cross section depends on the electric field and the distance between the ion and the elastic interface. The oscillation of the cross section becomes more complicated than in the case of H- near one elastic interface. The results show that near the detachment threshold, the influence of the additional interface can be neglected. But with the increase of the energy, its influence becomes great. At some energies, the cross sections display sharp peaks, contrasting with the staircase structure when only one interface exists. This study provides a new understanding of the photodetachment process of H- in the presence of external field and interfaces.

Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse

Li Hong-Yu, Liu Jian-Sheng, Wang Cheng, Ni Guo-Quan, Li Ru-Xin, Xu Zhi-Zhan
Chin. Phys. B 2008, 17 (4): 01237;  doi: 10.1088/1674-1056/17/4/015
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The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subclusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the case of homonuclear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuclear clusters with larger sizes are required to achieve a greater neutron yield.

Analytic solutions for degenerate Raman-coupled model

Zhang Zhi-Ming, Yu Ya-Fei
Chin. Phys. B 2008, 17 (4): 01242;  doi: 10.1088/1674-1056/17/4/016
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The Raman-coupled interaction between an atom and a single mode of a cavity field is studied. For the cases in which a light field is initially in a coherent state and in a thermal state separately, we have derived the analytic expressions for the time evolutions of atomic population difference $W$, modulus $B$ of the Bloch vector, and entropy $E$. We find that the time evolutions of these quantities are periodic with a period of $\pi $. The maxima of $W$ and $B$ appear at the scaled interaction time points $\tau = k\pi (k = 0,1,2,\ldots)$. At these time points, $E = 0$, which shows that the atom and the field are not entangled. Between these time points, $E \ne 0$, which means that the atom and the field are entangled. When the field is initially in a coherent state, near the maxima, the envelope of $W$ is a Gaussian function with a variance of $1 /{\left( {4\bar {n}} \right)}$ ($\bar {n}$ is the mean number of photons). Under the envelope, $W$ oscillates at a frequency of $\bar {n} / \pi $. When the field is initially in a thermal state, near the maxima, $W$ is a Lorentz function with a width of $1/ \bar {n}$.

Fidelity of quantum information for V-type three-level atom interacting with a number state light field in Kerr medium

Liu Su-Mei, He An-Zhi, Ji Yun-Jing
Chin. Phys. B 2008, 17 (4): 01248;  doi: 10.1088/1674-1056/17/4/017
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In this paper the evolution characteristics of the fidelity of quantum information for the V-type three-level atom interacting with number state light field in Kerr medium are investigated. It shows that the periodicity of the evolutions of fidelity of quantum information is influenced by the Kerr coefficient, the photon number of the initial field and intensity of light. The evolutions of the fidelity of quantum information are modulated by the initial number state field. The Rabi oscillation frequency and the modulation frequency of fidelity for the field and the system vary with the value of the Kerr coefficient. The evolutions of fidelity of quantum information obviously show the quantum collapse and revival behaviours in the system of atom interacting with light field.

Wigner functions and tomograms of the photon-depleted even and odd coherent states

Wang Ji-Suo, Meng Xiang-Guo
Chin. Phys. B 2008, 17 (4): 01254;  doi: 10.1088/1674-1056/17/4/018
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Using the coherent state representation of Wigner operator and the technique of integration within an ordered product (IWOP) of operators, this paper derives the Wigner functions for the photon-depleted even and odd coherent states (PDEOCSs). Moreover, in terms of the Wigner functions with respect to the complex parameter $\alpha $ the nonclassical properties of the PDEOCSs are discussed. The results show that the nonclassicality for the state $\left| {\beta ,m} \right\rangle _{\rm o} $ (or $\left| {\beta ,m} \right\rangle _{\rm e} )$ is more pronounced when $m$ is even (or odd). According to the marginal distributions of the Wigner functions, the physical meaning of the Wigner functions is given. Further, the tomograms of the PDEOCSs are calculated with the aid of newly introduced intermediate coordinate-momentum representation in quantum optics.

Security of quantum key distribution using two-mode squeezed states against optimal beam splitter attack

He Guang-Qiang, Zhu Si-Wei, Guo Hong-Bin, Zeng Gui-Hua
Chin. Phys. B 2008, 17 (4): 01263;  doi: 10.1088/1674-1056/17/4/019
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For the beam splitter attack strategy against quantum key distribution using two-mode squeezed states, the analytical expression of the optimal beam splitter parameter is provided in this paper by applying the Shannon information theory. The theoretical secret information rate after error correction and privacy amplification is given in terms of the squeezed parameter and channel parameters. The results show that the two-mode squeezed state quantum key distribution is secure against an optimal beam splitter attack.

Sideband manipulation of population inversion in a three-level Λ atomic system

Guo Hong-Ju, Niu Yue-Ping, Jin Shi-Qi, Gong Shang-Qing
Chin. Phys. B 2008, 17 (4): 01269;  doi: 10.1088/1674-1056/17/4/020
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Sideband manipulation of population inversion in a three-level $\Lambda$ atomic configuration is investigated theoretically. Compared with the case of a nearly monochromatic field, a population inversion between an excited state and a ground state has been found in a wide sideband intensity range by increasing the difference in frequency between three components. Furthermore, the population inversion can be controlled by the sum of the relative phases of the sideband components of the trichromatic pump field with respective to the phase of the central component. Changing the sum phase from 0 to $\pi$, the population inversion between the excited state and the ground state can increase within nearly half of the sideband intensity range. At the same time, the sideband intensity range that corresponds to the system exhibiting inversion $\rho_{00}>\rho_{11}$ also becomes wider evidently.

Effects of transverse mode coupling and optical confinement factor on gallium-nitride based laser diode

Jin Xiao-Ming, Zhang Bei, Dai Tao, Zhang Guo-Yi
Chin. Phys. B 2008, 17 (4): 01274;  doi: 10.1088/1674-1056/17/4/021
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We have investigated the transverse mode pattern and the optical field confinement factor of gallium nitride (GaN) laser diodes (LDs) theoretically. For the particular LD structure, composed of approximate 4 $\mu $m thick n-GaN substrate layer, the maximum optical confinement factor was found to be corresponding to the 5$^{\rm th}$ order transverse mode, the so-called lasing mode. Moreover, the value of the maximum confinement factor varies periodically when increasing the n-side GaN layer thickness, which simultaneously changes and increases the oscillation mode order of the GaN LD caused by the effects of mode coupling. The effects of the thickness and the average composition of Al in the AlGaN/GaN superlattice on the optical confinement factor are also presented. Finally, the mode coupling and optimization of the layers in the GaN-based LD are discussed.

Size-dependent optical properties and carriers dynamics in CdSe/ZnS quantum dots

Ma Hong, Ma Guo-Hong, Wang Wen-Jun, Gao Xue-Xi, Ma Hong-Liang
Chin. Phys. B 2008, 17 (4): 01280;  doi: 10.1088/1674-1056/17/4/022
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Size-dependence of optical properties and energy relaxation in CdSe/ZnS quantum dots (QDs) were investigated by two-colour femtosecond (fs) pump--probe (400/800\,nm) and picosecond time-resolved photoluminescence (ps TRPL) experiments. Pump--probe measurement results show that there are two components for the excited carriers relaxation, the fast one with a time constant of several ps arises from the Auger-type recombination, which shows almost particle size-independence. The slow relaxation component with a time constant of several decades of ns can be clearly determined with ps TRPL spectroscopy in which the slow relaxation process shows strong particle size-dependence. The decay time constants increase from 21 to 34\,ns with the decrease of particle size from 3.2 to 2.1\,nm. The room-temperature decay lifetime is due to the thermal mixing of bright and dark excitons, and the size-dependence of slow relaxation process can be explained very well in terms of simple three-level model.

Compact efficient optical parametric generator internal to a Q-switched Nd:YVO4 laser with periodically poled MgO:LiNbO3

Ji Feng, Yao Jian-Quan, Zhang Bai-Gang, Zhang Tie-Li, Xu De-Gang, Wang Peng
Chin. Phys. B 2008, 17 (4): 01286;  doi: 10.1088/1674-1056/17/4/023
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This paper demonstrates a compact efficient optical parametric generator internal to a Q-switched diode-end-pumped Nd:YVO$_{4}$ laser with periodically poled MgO:LiNbO3(PPMgLN). With the Q-switch set at a repetition rate of 25kHz and the PPMgLN crystal operated at room temperature (25\du\,), the intracavity optical parametric generator threshold was reached as a diode pump power of 0.9\,W. A maximum signal output power of 0.34W with a pulse width of 25\,ns and a beam quality factor of 1.4 was obtained at an incident diode power of 3.4\,W, leading to a conversion efficiency of 10{\%} with a slope efficiency of 14.4{\%}. By varying the crystal temperature from 25 to 200\du, the output signal wavelengths were tuned in range of 1506--1565\,nm. Over a 30-minutes interval, the instability of the signal power was measured to be less than 1{\%}. In addition, the threshold pump intensity for the intracavity optical parametric generator is theoretically investigated, and the obtained result is in good agreement with the experimental results.

Linear and nonlinear optical properties of ZnO nanorod arrays

Xiao Si, Su Xiong-Rui, Li Chun, Han Yi-Bo, Fang Guo-Jia, Wang Qu-Quan
Chin. Phys. B 2008, 17 (4): 01291;  doi: 10.1088/1674-1056/17/4/024
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Polarization-dependent linear absorption, second-harmonic generation (SHG) and 3rd-order nonlinearities of well-aligned ZnO nanorod arrays have been investigated with ps pulses. The depressed spectral width and the enhanced intensity of reflective SHG along the long axis of ZnO nanorods were observed by using p-polarized pulses, which is explained by the optical confinements. The nonlinear absorption coefficient measured with s-polarization reached the maximum 4.0$\times $10$^{4}$cm/GW at the wavelength $\sim $750\,nm, which revealed a large two-photon resonance absorption attributed to the quantum confined exciton when the polarization is vertical to the long axis of ZnO nanorod.

Observations of defect propagation in [100]-oriented opal-type photonic crystals

Jin Chong-Jun, Richard M. De La Rue, Nigel P.Johnson
Chin. Phys. B 2008, 17 (4): 01298;  doi: 10.1088/1674-1056/17/4/025
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Charged colloidal suspensions have been used as experimental models for the study of crystal nucleation. Here we propose that the technique of template-assisted colloidal self-assembly can be used to visualize the effects of defect propagation in atomic crystal films produced using epitaxial growth. Templates with periodic line defects were used to grow [100]-oriented three-dimensional photonic crystals by means of the template-assisted colloidal self-assembly method, aided by capillary and gravitational forces. The defect propagation in the [100]-oriented photonic crystal was observed using scanning electron microscopy, both at the surface of the crystal and on cleaved facets. This method is useful in the understanding of defect propagation in the growth of colloidal films on templates - and the same approach may also prove useful for the understanding of atomic crystal growth on substrates with defects. Additionally, the deliberate incorporation of line defects may prove valuable as a way of introducing waveguide channels into three-dimensional photonic crystals.

Comparison of the mechanism of gap formation for tri- and bi-component phononic crystal

Zhao Hong-Gang, Wen Ji-Hong, Liu Yao-Zong, Yu Dian-Long, Wang Gang, Wen Xi-Sen
Chin. Phys. B 2008, 17 (4): 01305;  doi: 10.1088/1674-1056/17/4/026
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Using an exact Mie scattering solution, this paper investigates the mode conversions during the Mie scattering of a single bi- or one-component sphere in unbounded epoxy. Then the formation mechanism of the first complete gap in the corresponding tri- or bi-component phononic crystal is investigated by the multiple-scattering method. It is shown that the heavy density of the scatterer plays an essential role in the Mie resonance and the formation of the gaps for both types of the phononic crystals. For the tri-component phononic crystal, the gap is mainly induced by the Mie resonance of the single scatterer. For the bi-component phononic crystal, the transverse wave (by mode-conversion during the Mie scattering under a longitudinal wave incidence) is modulated by the periodicity and governed by the Bloch theory, which induces the gap cooperatively.

Simulation study on reconstruction model of three-dimensional temperature distribution within visible range in furnace

Liu Dong, Wang Fei, Huang Qun-Xing, Yan Jian-Hua, Chi Yong, Cen Ke-Fa
Chin. Phys. B 2008, 17 (4): 01312;  doi: 10.1088/1674-1056/17/4/027
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This paper presents a reconstruction model of three-dimensional temperature distribution in furnace based on radiative energy images captured by charge-coupled device (CCD) cameras within the visible wavelength range. Numerical simulation case was used in this study and a zigzag eccentric temperature distribution was assumed to verify the model. Least square QR-factorization (LSQR) method was introduced to deal with reconstruction equation. It is found that the reconstructed temperature distributions in low-temperature areas had some fluctuations and high-temperature areas were reconstructed well. The whole reconstruction relative error was mainly due to errors in low-temperature areas and the relative error for highest-temperature reconstruction was quite small.

Theoretical analysis and numerical simulation of the impulse delivering from laser-produced plasma to solid target

Yang Yan-Nan, Yang Bo, Zhu Jin-Rong, Shen Zhong-Hua, Lu Jian, Ni Xiao-Wu
Chin. Phys. B 2008, 17 (4): 01318;  doi: 10.1088/1674-1056/17/4/028
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A plasma is produced in air by using a high-intensity Q-switch Nd:YAG pulsed laser to irradiate a solid target, and the impulses delivering from the plasma to the target are measured at different laser power densities. Analysing the formation process of laser plasma and the laser supported detonation wave (LSDW) and using fluid mechanics theory and Pirri's methods, an approximately theoretical solution of the impulse delivering from the plasma to the target under our experimental condition is found. Furthermore, according to the formation time of plasma and the variation of pressure in plasma in a non-equilibrium state, a physical model of the interaction between the pulse laser and the solid target is developed. The plasma evolutions with time during and after the laser pulse irradiating the target are simulated numerically by using a three-dimensional difference scheme. And the numerical solutions of the impulse delivering from the plasma to the target are obtained. A comparison among the theoretical, numerical and experimental results and their analyses are performed. The experimental results are explained reasonably. The consistency between numerical results and experimental results implies that the numerical calculation model used in this paper can well describe the mechanical action of the laser on the target.

Growth of β-Ga2O3 nanorods by ammoniating Ga2O3/V thin films on Si substrate

Wang Gong-Tang, Xue Cheng-Shan, Yang Zhao-Zhu
Chin. Phys. B 2008, 17 (4): 01326;  doi: 10.1088/1674-1056/17/4/029
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This paper reports that β-Ga2O3 nanorods have been synthesized by ammoniating Ga2O3 films on a V middle layer deposited on Si(111) substrates. The synthesized nanorods were confirmed as monoclinic Ga2O3 by x-ray diffraction, Fourier transform infrared spectra. Scanning electron microscopy and transmission electron microscopy reveal that the grown β-Ga2O3 nanorods have a smooth and clean surface with diameters ranging from 100nm to 200\,nm and lengths typically up to 2\mum. High resolution TEM and selected-area electron diffraction shows that the nanorods are pure monoclinic Ga2O3 single crystal. The photoluminescence spectrum indicates that the Ga2O3 nanorods have a good emission property. The growth mechanism is discussed briefly.

Existences and stabilities of bright and dark breathers in a general one-dimensional discrete monatomic Chain

Xu Quan, Tang Feng-Yun, Tian Qiang
Chin. Phys. B 2008, 17 (4): 01331;  doi: 10.1088/1674-1056/17/4/030
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A general one-dimensional discrete monatomic model is investigated by using the multiple-method. It is proven that the discrete bright breathers (DBBs) and discrete dark breathers (DDBs) exist in this model at the anti-continuous limit, and then the concrete models of the DBBs and DDBs are also presented by the multiple-scale approach (MSA) and the quasi-discreteness approach (QDA). When the results are applied to some particular models, the same conclusions as those presented in corresponding references are achieved. In addition, we use the method of the linearization analysis to investigate this system without the high order terms of $\varepsilon$. It is found that the DBBs and DDBs are linearly stable only when coupling parameter $\chi$ is small, of which the limited value is obtained by using an analytical method.

Mean-field potential calculations of high-pressure equation of state for BeO

Zhang Qi-Li, Zhang Ping, Song Hai-Feng, Liu Hai-Feng
Chin. Phys. B 2008, 17 (4): 01341;  doi: 10.1088/1674-1056/17/4/031
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A systematic study of the Hugoniot equation of state, phase transition, and the other thermodynamic properties including the Hugoniot temperature, the electronic and ionic heat capacities, and the Gr\"{u}neisen parameter for shock-compressed BeO, has been carried out by calculating the total free energy. The method of calculations combines first-principles treatment for 0\,K and finite-T electronic contribution and the mean-field-potential approach for the vibrational contribution of the lattice ion to the total energy. Our calculated Hugoniot is in good agreement with the experimental data.

Analysis of performance and optimum configuration of two-stage semiconductor thermoelectric module

Li Kai-Zhen, Liang Rui-Sheng, Wei Zheng-Jun
Chin. Phys. B 2008, 17 (4): 01349;  doi: 10.1088/1674-1056/17/4/032
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In this paper, the theoretical analysis and simulating calculation were conducted for a basic two-stage semiconductor thermoelectric module, which contains one thermocouple in the second stage and several thermocouples in the first stage. The study focused on the configuration of the two-stage semiconductor thermoelectric cooler, especially investigating the influences of some parameters, such as the current $I_1 $ of the first stage, the area $A_1 $ of every thermocouple and the number $n$ of thermocouples in the first stage, on the cooling performance of the module. The obtained results of analysis indicate that changing the current $I_1 $ of the first stage, the area $A_1 $ of thermocouples and the number $n$ of thermocouples in the first stage can improve the cooling performance of the module. These results can be used to optimize the configuration of the two-stage semiconductor thermoelectric module and provide guides for the design and application of thermoelectric cooler.

Phase transition and thermodynamic properties of SrS via first-principles calculations

Cheng Yan, Lu Lai-Yu, Jia Ou-He, Chen Xiang-Rong
Chin. Phys. B 2008, 17 (4): 01355;  doi: 10.1088/1674-1056/17/4/033
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The phase transition of SrS from NaCl structure (B1) to CsCl structure (B2) is investigated by means of ab initio plane-wave pseudopotential density functional theory, and the thermodynamic properties of the B1 and the B2 structures are obtained through the quasi-harmonic Debye model. It is found that the transition phase from the B1 to the B2 structures occurs at 17.9\,GPa, which is in good agreement with experimental data and other calculated results. Moreover, the thermodynamic properties (including specific heat capacity, the Debye temperature, thermal expansion and Gr\"{u}neisen parameter) have also been obtained successfully.

Effect of double AlN buffer layer on the qualities of GaN films grown by radio-frequency molecular beam epitaxy

Li Xin-Hua, Zhong Fei, Qiu Kai, Yin Zhi-Jun, Ji Chang-Jian
Chin. Phys. B 2008, 17 (4): 01360;  doi: 10.1088/1674-1056/17/4/034
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This paper reports that the GaN thin films with Ga-polarity and high quality were grown by radio-frequency molecular beam epitaxy on sapphire (0001) substrate with a double AlN buffer layer. The buffer layer consists of a high-temperature (HT) AlN layer and a low-temperature (LT) AlN layer grown at 800\du\ and 600\du, respectively. It is demonstrated that the HT-AlN layer can result in the growth of GaN epilayer in Ga-polarity and the LT-AlN layer is helpful for the improvement of the epilayer quality. It is observed that the carrier mobility of the GaN epilayer increases from 458 to 858\,cm$^{2}$/V$\cdot $s at room temperature when the thickness of LT-AlN layer varies from 0 to 20\,nm. The full width at half maximum of x-ray rocking curves also demonstrates a substantial improvement in the quality of GaN epilayers by the utilization of LT-AlN layer.

First-principles local density approximation (LDA)+U and generalized gradient approximation (GGA)+U studies of plutonium oxides

Sun Bo, Zhang Ping
Chin. Phys. B 2008, 17 (4): 01364;  doi: 10.1088/1674-1056/17/4/035
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The electronic structures and properties of PuO2 and Pu2O3 have been studied according to the first principles by using the all-electron projector-augmented-wave (PAW) method. The local density approximation (LDA)+U and the generalized gradient approximation (GGA)+U formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Pu 5f electrons. We discuss how the properties of PuO2 and Pu2O3 are affected by choosing the values of U and exchange-correlation potential. Also, the oxidation reaction of Pu2O3, leading to the formation of PuO2, and its dependence on U and exchange-correlation potential have been studied. Our results show that by choosing an appropriate U it is possible to consistently describe structural, electronic, and thermodynamic properties of PuO2 and Pu2O3, which enable the modelling of the redox process involving Pu-based materials.

Magnetic properties of Mn-doped ZnO diluted magnetic semiconductors

Liu Xue-Chao, Zhang Hua-Wei, Zhang Tao, Chen Bo-Yuan, Chen Zhi-Zhan, Song Li-Xin, Shi Er-Wei
Chin. Phys. B 2008, 17 (4): 01371;  doi: 10.1088/1674-1056/17/4/036
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A series of Mn-doped ZnO films have been prepared in different sputtering plasmas by using the inductively coupled plasma enhanced physical vapour deposition. The films show paramagnetic behaviour when they are deposited in an argon plasma. The Hall measurement indicates that ferromagnetism cannot be realized by increasing the electron concentration. However, the room-temperature ferromagnetism is obtained when the films are deposited in a mixed argon-nitrogen plasma. The first-principles calculations reveal that antiferromagnetic ordering is favoured in the case of the substitution of Mn$^{2 + }$ for Zn$^{2 + }$ without additional acceptor doping. The substitution of N for O (N$_{\rm O}^{ - })$ is necessary to induce ferromagnetic couplings in the Zn-Mn-O system. The hybridization between N 2p and Mn 3d provides an empty orbit around the Fermi level. The hopping of Mn 3d electrons through the empty orbit can induce the ferromagnetic coupling. The ferromagnetism in the N-doped Zn-Mn-O system possibly originates from the charge transfer between Mn$^{2 + }$ and Mn$^{3 + }$ via N$_{\rm O}^{ - }$. The key factor is the empty orbit provided by substituting N for O, rather than the conductivity type or the carrier concentration.

First-principles investigations on elastic and thermodynamic properties of zinc-blende structure BeS

Chang Jing, Chen Xiang-Rong, Zhang Wei, Zhu Jun
Chin. Phys. B 2008, 17 (4): 01377;  doi: 10.1088/1674-1056/17/4/037
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In this paper the elastic and thermodynamic properties of the cubic zinc-blende structure BeS at different pressures and temperatures are investigated by using \textit{ab initio} plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated results are in excellent agreement with the available experimental data and other theoretical results. It is found that the zinc-blende structure BeS should be unstable above 60GPa. The thermodynamic properties of the zinc-blende structure BeS are predicted by using the quasi-harmonic Debye model. The pressure-volume-temperature ($P-V-T$) relationship, the variations of the thermal expansion coefficient $\alpha$ and the heat capacity $C_{V}$ with pressure $P$ and temperature $T$, as well as the Gr\"{u}neisen parameter-pressure-temperature ($\gamma -P-T$) relationship are obtained systematically in the ranges of 0--90GPa and 0--2000K.

Spin-polarized transport through the T-shaped double quantum dots

Yang Fu-Bin, Wu Shao-Quan, Yan Cong-Hua, Huang Rui, Hou Tao, Bi Ai-Hua
Chin. Phys. B 2008, 17 (4): 01383;  doi: 10.1088/1674-1056/17/4/038
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Using the Keldysh nonequilibrium Green function and equation-of-motion technique, this paper investigates the spin-polarized transport properties of the T-shaped double quantum dots (DQD) coupled to two ferromagnetic leads. There are both Fano effect and Kondo effect in the system, and due to their mutual interaction, the density of states, the current, and the differential conductance of the system depend sensitively on the spin-polarized strength. Thus the obtained results show that this system is provided with excellent spin filtering property, which indicates that this system may be a candidate for spin valve transistors in the spintronics.

Current--voltage characteristics of an individual helical CdS nanowire rope

Long Yun-Ze, Wang Wen-Long, Bai Feng-Lian, Chen Zhao-Jia, Jin Ai-Zi, Gu Chang-Zhi
Chin. Phys. B 2008, 17 (4): 01389;  doi: 10.1088/1674-1056/17/4/039
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This paper studies the electronic transport in an individual helically twisted CdS nanowire rope, on which platinum microleads are attached by focused-ion beam deposition. The current--voltage ($I-V$) characteristics are nonlinear from 300 down to 60\,K. Some step-like structures in the $I-V$ curves and oscillation peaks in the differential conductance (d$I$/d$V-V$) curves have been observed even at room temperature. It proposes that the observed behaviour can be attributed to Coulomb-blockade transport in the one-dimensional CdS nanowires with diameters of 6--10\,nm.

Effects of deposition pressure and plasma power on the growth and properties of boron-doped microcrystalline silicon films

Chen Yong-Sheng, Yang Shi-E, Wang Jian-Hua, Lu Jing-Xiao, Gao Xiao-Yong, Gu Jin-Hua, Zheng Wen, Zhao Shang-Li
Chin. Phys. B 2008, 17 (4): 01394;  doi: 10.1088/1674-1056/17/4/040
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Using diborane as doping gas, p-doped $\mu $c-Si:H layers are deposited by using the plasma enhanced chemical vapour deposition (PECVD) technology. The effects of deposition pressure and plasma power on the growth and the properties of $\mu $c-Si:H layers are investigated. The results show that the deposition rate, the electrical and the structural properties are all strongly dependent on deposition pressure and plasma power. Boron-doped $\mu $c-Si:H films with a dark conductivity as high as 1.42\,$\Omega ^{ - 1}\cdot$cm$^{ - 1}$ and a crystallinity of above 50{\%} are obtained. With this p-layer, $\mu $c-Si:H solar cells are fabricated. In addition, the mechanism for the effects of deposition pressure and plasma power on the growth and the properties of boron-doped $\mu $c-Si:H layers is discussed.

Evaluation of electron--electron interactions in coupled quantum dots by using far-infrared spectra

Dong Qing-Rui
Chin. Phys. B 2008, 17 (4): 01400;  doi: 10.1088/1674-1056/17/4/041
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We have studied the far-infrared spectra of two-electron vertically coupled quantum dots in an axial magnetic field by exact diagonalization. The calculated results show an obvious difference in role between the interactions for spin $S=1$ and for spin $S=0$. The results support the possibility to evaluate the interactions by far-infrared spectroscopy in vertically coupled quantum dots.

A study on Al2O3 passivation in GaN MOS-HEMT by pulsed stress

Yue Yuan-Zheng, Hao Yue, Zhang Jin-Cheng, Feng Qian, Ni Jin-Yu, Ma Xiao-Hua
Chin. Phys. B 2008, 17 (4): 01405;  doi: 10.1088/1674-1056/17/4/042
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This paper studies systematically the drain current collapse in AlGaN/GaN metal--oxide--semiconductor high electron mobility transistors (MOS-HEMTs) by applying pulsed stress to the device. Low-temperature layer of A12O3 ultrathin film used as both gate dielectric and surface passivation layer was deposited by atomic layer deposition (ALD). For HEMT, gate turn-on pulses induced large current collapse. However, for MOS-HEMT, no significant current collapse was found in the gate turn-on pulsing mode with different pulse widths, indicating the good passivation effect of ALD A12O3. A small increase in Idd in the drain pulsing mode is due to the relieving of self-heating effect. The comparison of synchronously dynamic pulsed Idd-Vds characteristics of HEMT and MOS-HEMT further demonstrated the good passivation effect of ALD A12O3.

Electrothermal simulation of the self-heating effects in 4H-SiC MESFETs

Lü Hong-Liang, Zhang Yi-Men, Zhang Yu-Ming, Che Yong
Chin. Phys. B 2008, 17 (4): 01410;  doi: 10.1088/1674-1056/17/4/043
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A thermal model of 4H-SiC MESFET is developed based on the temperature dependences of material parameters and three-region $I-V$ model. The static current characteristics of 4H-SiC MESFET have been obtained with the consideration of the self-heating effect on related parameters including electron mobility, saturation velocity and thermal conductivity. High voltage performances are analysed using equivalent thermal conductivity model. Using the physical-based simulations, we studied the dependence of self-heating temperature on the thickness and doping of substrate. The obtained results can be used for optimization of the thermal design of the SiC-based high-power field effect transistors.

Dynamic Ni gettered by PSG from S-MIC poly-Si and its TFTs

Meng Zhi-Guo, Li Yang, Wu Chun-Ya, Zhao Shu-Yun, Li Juan, Man Wong, Hoi Sing-Kwok, Xiong Shao-Zhen
Chin. Phys. B 2008, 17 (4): 01415;  doi: 10.1088/1674-1056/17/4/044
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A dynamic phosphor-silicate glass (PSG) gettering method is proposed in which the processes of the gettering of Ni by PSG and the crystallizing of $\al$-Si into poly-Si by Ni take place simultaneously. The effects of PSG gettering process on the performances of solution-based metal induced crystallized (S-MIC) poly-Si materials and their thin film transistors (TFTs) are discussed. The crystallization rate is much reduced due to the fact that the Ni as a medium source of crystallization is extracted by the PSG during crystallization at the same time. The boundary between two neighbouring grains in S-MIC poly-Si with PSG looks blurrier than without PSG. Compared with the TFTs made from S-MIC poly-Si without PSG gettering, the TFTs made with PSG gettering has a reduced gate induced leakage current.

Synthesis of superconductor MgCNi3 with carbon nanotubes

Xia Qing-Lin, Yi Jian-Hong, Peng Yuan-Dong, Luo Shu-Dong, Wang Hong-Zhong, Li Li-Ya
Chin. Phys. B 2008, 17 (4): 01421;  doi: 10.1088/1674-1056/17/4/045
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MgCNi3, an intermetallic compound superconductor with a cubic perovskite crystal structure, has been synthesized using fine Mg and Ni powders and carbon nanotubes (CNTs) as starting materials by the conventional powder metallurgy method. The composition, microstructure and superconductivity are characterized using x-ray diffraction (XRD), energy dispersive x-ray (EDX) analysis, scanning electron microscopy (SEM), and superconducting quantum interference device (SQUID) magnetometer. The results indicate that the phases of the synthesized samples are MgCNi3 (major phase) and traces of C and MgO. The MgCNi3 particle sizes range from several hundreds of nanometres to several micrometres. The onset superconducting transition temperature Tc of the MgCNi3 sample is about 7.2\,K. The critical current density Jc is about 3.44×104A/cm2 calculated according to the Bean model from the magnetization hysteresis loop of the slab MgCNi3 sample at 5K and zero applied field.

Effect of heat treatment on electronic phase in underdoped La2-xSrxCuO4 single crystal

Shen Cai-Xia, Shen Xiao-Li, Lu Wei, Dong Xiao-Li, Li Zheng-Cai, Xiong Ji-Wu, Zhou Fang
Chin. Phys. B 2008, 17 (4): 01425;  doi: 10.1088/1674-1056/17/4/046
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Superconducting La2-xSrxCuO4 crystals grown by the travelling-solvent floating-zone technique were thermally treated under various temperatures and oxygen pressures for moderately adjusting the oxygen content. The response of intrinsic electronic property of the crystals to the change of hole density in La2-xSrxCuO4 in the vicinity of the magic doping of x =1/16\ (=0.0625) is studied in detail by magnetic measurements under various fields up to 1\,T. It is found that when the superconducting critical temperature (T_{\rm C}) increases with the oxygen content, there appears also a new subtle electronic state that can be detected from the differential curves of diamagnetic susceptibility d$\chi$/d$T$ of the crystal sample. In contrast with the intrinsic state, the new subtle electronic state is very fragile under the magnetic fields. Our results indicate that a moderate change in oxygen doping does not significantly modify the intrinsic electronic state originally existing at the magic doping level.

Low field microwave absorption and magnetization process in CoFeNi electroplated wires

H. García-Miquel, G. V. Kurlyandskaya
Chin. Phys. B 2008, 17 (4): 01430;  doi: 10.1088/1674-1056/17/4/047
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Ferromagnetic resonance (FMR), Ferromagnetic antirresonance (FMAR) and low field magnetoimpedance (MI) are the characteristic features of high frequency losses in applied fields. While some results on FMR and FMAR in CoFeNi electroplated wires were reported earlier, here we present microwave absorption in CuBe wires electroplated by 1\,$\mu$m FeCoNi magnetic layer at very low fields. These data are comparatively analysed together with longitudinal hysteresis loops in order to reveal the correlation between power absorption and magnetization processes. Microwave studies are made by using the cavity perturbation method at 9.65\,GHz for a DC field parallel to the sample axis, and with microwave magnetic field $h_{\rm rf}$ parallel or perpendicular to the wire axis. Two peaks have been observed in all samples, one is due to FMR, and the other is, at very low fields, related to MI. The MI peaks represent minima in power absorption. By comparing with the hysteresis loop we remark the close correspondence between the MI phenomena in the axial mode and the concomitant magnetization process.

Dephasing of quantum tunnelling in molecular nanomagnets

Zhang Shu-Qun, Chen Zhi-De
Chin. Phys. B 2008, 17 (4): 01436;  doi: 10.1088/1674-1056/17/4/048
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Dephasing mechanism of quantum tunnelling in molecular magnets has been studied by means of the spin-coherent-state path integral in a mean field approximation. It is found that the fluctuating uncompensated transverse field from the dipolar-dipolar interaction between molecular magnets contributes a random phase to the quantum interference phase. The resulting transition rate is determined by the average tunnel splitting over the random phase. Such a dephasing process leads to the suppression of quenching due to the quantum phase interference, and to the steps due to odd resonances in hysteresis loop survived, which is in good agreement with experimental observations in molecular nanomagnets Fe8 and Mn$_{12}.$

The structure dependence of exchange bias in ferromagnetic/antiferromagnetic bilayers

Xu Xiao-Yong, Wang Mao-Hua, Hu Jing-Guo
Chin. Phys. B 2008, 17 (4): 01443;  doi: 10.1088/1674-1056/17/4/049
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The structure dependence of exchange bias in ferromagnetic/antiferromagnetic (FM/AF) bilayers has been investigated in detail by extending Slonczewski's `proximity magnetism' idea. Here three important parameters are discussed for FM/AF bilayers, i.e. interfacial bilinear exchange coupling $J_{1}$, interfacial biquadratic (spin-flop) exchange coupling $J_{2}$ and antiferromagnetic layer thickness $t_{\rm AF}$. The results show that both the occurrence and the variety of the exchange bias strongly depend on the above parameters. More importantly, the small spin-flop exchange coupling may result in an exchange bias without the interfacial bilinear exchange coupling. However, in general, the spin-flop exchange coupling cannot result in the exchange bias. The corresponding critical parameters in which the exchange bias will occur or approach saturation are also presented.

X-shape oligo(thiophene)s as donor materials for vacuum-deposited organic photovoltaic cells

Wang Ya-Nan, Zhou Yin-Hua, Xu Yue, Sun Xiao-Bo, Wu Wei-Cai, Tian Wen-Jing, Liu Yun-Qi
Chin. Phys. B 2008, 17 (4): 01448;  doi: 10.1088/1674-1056/17/4/050
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The films of two $x$-shape oligo(thiophene)s, 3, 4-dibithienyl-2, 5-dithienylthiophene (7T) and 2, 5-dibithienyl-3, 4-ditrithienylthiophene (11T), which are prepared by vacuum evaporation, have been investigated as novel electron donor layers in two-layer photovoltaic cells. UV--Vis absorptions show red-shifted and broadened absorptions of the vacuum-evaporated films as compared with those of the corresponding solutions and spin-coating films, which is beneficial for photovoltaic properties. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements show that the vacuum-evaporated films are almost amorphous. Two-layer photovoltaic cells have been realized by the thermal evaporation of 7T and 11T as donors and $N$, $N'-$bis(1-ethylpropyl)-3, 4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) as an acceptor. An energy conversion efficiency (ECE) of 0.18{\%} of the cell based on 7T with an irradiation of white light at 100\,mw/cm$^{2}$ has been demonstrated by the measurements of current ($I$)- voltage ($V$) curves of the cells to be higher than the ECE of the reference system based on donor dihexylterthienyl (H3T) that is linear and without $\alpha $, $\beta $ linkage.

Comparison between photoluminescence spectroscopy and photoreflectance spectroscopy in CuGaSe2 epilayer

Zhen Guo-Yong, Jian Ao-Qun, Xu Hong-Yan, Xue Chen-Yang, Zhang Wen-Dong
Chin. Phys. B 2008, 17 (4): 01454;  doi: 10.1088/1674-1056/17/4/051
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Photoluminescence (PL) spectroscopy and photoreflectance (PR) spectroscopy are very useful techniques for studying the properties of materials. In this paper, the same material of Cu-rich metal-organic vapour phase epitaxy (MOVPE) grown CuGaSe$_{2}$ layer is investigated in a temperature range from 20 to 300\,K to compare these two techniques. Both PL and PR spectra appear red shifted, less intense and broadened. The temperature dependence of interband transitions is studied by using the Manoogian--Leclerc equation. The values of the band gap energy at $T$=0\,K and the effective phonon temperature are estimated. The temperature dependences of intensities and broadenings of PL and PR spectral lines are also analysed. Based on the results of the comparison, the features and applications of the PL and PR can be shown in detail.

All-optical switchings of 3-hydroxyflavone in different solvents

Wu Feng, Lin Lie, Li Xiang-Ping, Yu Ya-Xin, Zhang Gui-Lan, Chen Wen-Ju
Chin. Phys. B 2008, 17 (4): 01461;  doi: 10.1088/1674-1056/17/4/052
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3-hydroxyflavone (3-HF) is an organic molecule with an excited-stated intramolecular proton transfer (ESIPT) effect. All-optical switchings and beam deflections of 3-HF in three kinds of solvents (cyclohexane, ethanol and dimethyl sulfoxide) have been investigated by using the third-harmonic generation (355\,nm) of a mode-locked Nd:YAG laser as a pump beam and a continuous-wave (cw) He-Ne laser (632.8\,nm) as a probe beam. The nonlinear refractive indices of 3-HF in the three different solvents are determined by using the Z-scan technique under an ultraviolet (UV) pump beam at a wavelength of 355\,nm. It has been found that the optical switching and beam deflection effects result from the change in refractive index of 3-HF under the irradiation of the pump beam. On the basis of the analyses of absorption spectra and fluorescence spectra, we conclude that the change in refractive index of 3-HF is due to not the thermal effect but the ESIPT effect of 3-HF under the pump beam. As the ESIPT is exceedingly fast, 3-HF might be an excellent candidate for high-speed optical switching.

Field emission characteristics of nano-sheet carbon films deposited by quartz-tube microwave plasma chemical vapour deposition

Gu Guang-Rui, Jin Zhe, Ito Toshimichi
Chin. Phys. B 2008, 17 (4): 01467;  doi: 10.1088/1674-1056/17/4/053
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Nano-sheet carbon films are prepared on Si wafers by means of quartz-tube microwave plasma chemical vapour deposition (MPCVD) in a gas mixture of hydrogen and methane. The structure of the fabricated films is investigated by using field emission scanning electron microscope (FESEM) and Raman spectroscopy. These nano-carbon films are possessed of good field emission (FE) characteristics with a low threshold field of 2.6\,V/$\mu $m and a high current density of 12.6\,mA/cm$^{2}$ at an electric field of 9\,V/$\mu $m. As the FE currents tend to be saturated in a high $E$ region, no simple Fowler--Nordheim (F--N) model is applicable. A modified F--N model considering statistic effects of FE tip structures and a space-charge-limited-current (SCLC) effect is applied successfully to explaining the FE data observed at low and high electric fields, respectively.

Influence of spacer layer thickness on the current-voltage characteristics of pseudomorphic AlAs/In0.53Ga0.47As/InAs resonant tunnelling diodes

Zhang Yang, Han Chun-Lin, Gao Jian-Feng, Zhu Zhan-Ping, Wang Bao-Qiang, Zeng Yi-Ping
Chin. Phys. B 2008, 17 (4): 01472;  doi: 10.1088/1674-1056/17/4/054
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This paper investigates the dependence of current--voltage characteristics of AlAs/Insub>0.53Ga0.47As/InAs resonant tunnelling diodes (RTDs) on spacer layer thickness. It finds that the peak and the valley current density J in the negative differential resistance (NDR) region depends strongly on the thickness of the spacer layer. The measured peak to valley current ratio of RTDs studied here is shown to improve while the current density through RTDs decreases with increasing spacer layer thickness below a critical value.

The lack of carbon stars in the Galactic bulge

Zhu Chun-Hua, Lü Guo-Liang, Wang Zhao-Jun, Zhang Jun
Chin. Phys. B 2008, 17 (4): 01518;  doi: 10.1088/1674-1056/17/4/061
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In order to explain the lack of carbon stars in the Galactic bulge, we have made a detailed study of thermal pulse-asymptotic giant branch (TP-AGB) stars by using a population synthesis code. The effects of the oxygen overabundance and the mass loss rate on the ratio of the number of carbon stars to that of oxygen stars in the Galactic bulge are discussed. We find that the oxygen overabundance which is about twice as large as that in the solar neighbourhood (close to the present observations) is insufficient to explain the rareness of carbon stars in the bulge. We suggest that the large mass loss rate may serve as a controlling factor in the ratio of the number of carbon stars to that of oxygen stars.

Central black hole mass determination for blazars

Yuan Yu-Hai, Fan Jun-Hui, Huang Yong
Chin. Phys. B 2008, 17 (4): 01526;  doi: 10.1088/1674-1056/17/4/062
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In this paper, we use a method to determine some basic parameters for the $\gamma$-ray loud blazars. The parameters include the central black mass ($M$), the boosting factor ($\delta$), the propagation angle (${\it {\it\Phi}}$), the distance along the axis to the site of the $\gamma$-ray production ($d$). A sample including 32 $\gamma$-ray loud blazars with available variability time scales has been used to discuss the above properties. In this method, the $\gamma$-ray energy, the emission size and the property of the accretion disc determine the absorption effect. If we take the intrinsic $\gamma$-ray luminosity to be $\lambda$ times the Eddington luminosity, i.e. $L_{\gamma}^{\rm in}=\lambda{L_{\rm Edd}}$, then we have the following results: the mass of the black hole is in the range of $(0.59-67.99)\times10^{7}M_{\odot} \ (\lambda=1.0)$ or $(0.90-104.13)\times10^{7}M_{\odot} \ (\lambda=0.1)$; the boosting factor ($\delta$) in the range of $0.16-2.09(\lambda=1.0)$ or $0.24-2.86\ (\lambda=0.1)$; the angle (${\it\Phi}$) in the range of $9.53^{\circ}-73.85^{\circ}\ (\lambda=1.0)$ or $7.36^{\circ}-68.89^{\circ}\ (\lambda=0.1)$; and the distance ($d/R_{\rm g}$) in the range of $22.39-609.36\ (\lambda=1.0)$ or $17.54-541.88\ (\lambda=0.1)$.
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