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Vol. 57, No. 2 (2008)

2008-01-20
GENERAL

EDITOR'S SUGGESTION

Stability and convergence analysis of incompatible numerical manifold method
Feng Wei, Gao Hong-Fen, Li Kai-Tai, Wei Gao-Feng
2008, 57 (2): 639-647. doi: 10.7498/aps.57.639
Abstract +
The incompatible numerical manifold method (INMM) is developed on the basis of numerical manifold method (NMM). The advantages of INMM are that the calculation accuracy and computing efficiency can be greatly increased without adding generalized degrees of freedom. The expressions of element strain matrix and element stiffness matrix are given based on eliminating the internal parameters. On the basis of least potential energy theory the stability and convergence are analyzed and discussed in Hilbert space, and the basic condition ensuring uniqueness and convergence of solution is given. The theorization of INMM is perfected. To illustrate the stability and convergence of the present approach, numerical examples are provided. It is shown that this method produces highly accurate and convergent results.
Experimental and numerical investigations on the electro-magnetic control of hydrofoil wake
Chen Yao-Hui, Fan Bao-Chun, Chen Zhi-Hua, Zhou Ben-Mou
2008, 57 (2): 648-653. doi: 10.7498/aps.57.648
Abstract +
The Lorentz force generated in the low-conduction fluid can be used to control the boundary layer effectively. In the present paper, experimental and numerical investigations have been performed to suppress the flow separation of a hydrofoil with a certain attack angle in the low-conduction fluid. Both experimental and numerical results show that the Lorentz force parallel to the moving fluid can suppress the flow separation and thus remove the von Karman street. However, when Lorentz forces are applied opposite to the moving fluid of the surface of the foil, the separation point cannot be suppressed, instead, it would move reversely to the leading edge and the vortex street of the downstream acts as in the cases with a large attack angle.
Porosity inversion of 1-D two-phase medium with wavelet multiscale method
Liu Jia-Qi, Liu Ke-An, Zhang Xin-Ming
2008, 57 (2): 654-660. doi: 10.7498/aps.57.654
Abstract +
Based on the idea of multiscale approximation, a wavelet multiscale method is proposed by combining the wavelet analysis and multiscale inversion strategy, and applied to the inversion of porosity in the two-phase medium. The inverse problem is decomposed to multiple scales with wavelet transform and hence the original inverse problem is re-formulated to a set of sub-inverse problem corresponding to different scales and is solved successively according to the size of scale from the smallest to the largest. On each scale, regularized Gauss-Newton method is carried out, which is stable and fast, until the optimum solution of original inverse problem is found. The wavelet multiscale method is described as the combination of three operators: the restriction operator, the relaxation operator and the prolongation operator. And then the flow of wavelet multiscale method is outlined and the restriction operator matrix and the prolongation operator matrix obtained by adapting the compactly supported orthonormal wavelet Daubechies wavelets are deduced. The inversion results obtained by wavelet multiscale method are compared with those with traditional regularized Gauss-Newton method, the results of numerical simulation demonstrated that the method is an effective and widely convergent optimization method.
Phase transition and entanglement entropy of Bose-Einstein condensates in double-well trap under periodic modulation
Yang Li-Yun, Fang Yong-Cui, Yang Zhi-An
2008, 57 (2): 661-666. doi: 10.7498/aps.57.661
Abstract +
Dynamical phase transition of Bose-Einstein condensates (BEC) in double-well trap with external periodic modulation applied to the interaction term is investigated in this paper. Particularly, phase transition to chaos is studied. It is found that, when resonance between the modulation frequency and the natural frequency of the system happens, the system turns to instability (chaos) at certain values of the parameters. In the chaotic region, distribution of particles is random, and the average of population difference fluctuates around zero. Especially, chaos can be manifested by the entanglement entropy. In the chaotic zone, both of the average entanglement entropies approach to their maxima.
Irregular spin tunneling for Bose-Einstein condensates in a sweeping magnetic field
Liu Hong, Wang Guan-Fang
2008, 57 (2): 667-673. doi: 10.7498/aps.57.667
Abstract +
With a mean-field treatment, the spin tunneling of spin-1 Bose-Einstein condensates in a linearly sweeping magnetic field is investigated. We focus on a typical alkali Bose atoms 87Rb condensate and study its tunneling dynamics under different sweeping rates of external magnetic field. In the adiabatic (i.e., slowly sweeping) and sudden (i.e., fast sweeping) limits, no tunneling is observed. In the case of moderate sweeping rates, the tunneling dynamics is found to be very sensitive to the sweeping rate, showing a chaotic-like tunneling regime. By magnifying the apparently chaotic regime, however, we find interestingly that the plot becomes resolvable at a resolution of 10-8T/s where the tunneling probability with respect to the sweeping rate shows a regular pseudo-periodic pattern. Moreover, a conserved quantity standing for the magnetization in experiments is found which can dramatically affect the above picture of the spin tunneling. Theoretically, we give a reasonable interpretation to the above findings.
The Cartesian momentum and the kinetic operators on curved surfaces
Liu Quan-Hui
2008, 57 (2): 674-677. doi: 10.7498/aps.57.674
Abstract +
For describing particles moving on the two dimensional curved surfaces, we can use either the intrinsic local coordinates or the Cartesian coordinates. The representation of the momentum operators differs from each other in these two kinds of coordinates, the former ones depend on the intrinsic geometrical quantities, but the latter case depend on a geometrical invariant, namely the mean curvature. Taking the operator-ordering problem into consideration, the kinetic operator for the former case can be expressed in a possibly unique way, while that for latter case can be expressed in two different ways.
Decoy state quantum key distribution with dual detectors heralded single photon source
Mi Jing-Long, Wang Fa-Qiang, Lin Qing-Qun, Liang Rui-Sheng, Liu Song-Hao
2008, 57 (2): 678-684. doi: 10.7498/aps.57.678
Abstract +
Decoy state has recently been proved as a useful method for substantially improving the performance of quantum key distribution (QKD). Considering the imperfect extinction ratio and the spontaneous emission of the practical Laser, vacuum states are not prepared easily. So in this paper, the optimal situation of the decoy state protocol applied to the QKD system with heralded single photon source (HSPS) is complemented and extended. The two weak decoy state protocol and the one decoy state protocol are proposed. At last, the theory of “dual detectors" is combined with the QKD system with HSPS. In the simulation, the secure distance is up to 2215 km, which is approximately 50 km more than that of the on-off detectors.
Analysis of differential-phase-shift keying protocol for a two-way quantum-key-distribution system
Jiao Rong-Zhen, Feng Chen-Xu
2008, 57 (2): 685-688. doi: 10.7498/aps.57.685
Abstract +
The performance of a two-way quantum-key-distribution (QKD) system are analyzed using the differential-phase-shift keying (DPSK) protocol. The comparison is based on the secure communication rate as a function of distance for three QKD protocols: the Bennett-Brassard 1984, the Bennett-Brassard-Mermin 1992, and the coherent differential-phase-shift keying protocols. We discussed the security of DPSK protocol against any type of individual photon splitting attack and concluded that the simple and efficient DPSK protocol allows for more than 200km of secure communication distance with high communication rates.
Robust quantum computation of the quantum kicked Harper model and dissipative decoherence
Gu Bin-Jie, Ye Bin, Xu Wen-Bo
2008, 57 (2): 689-695. doi: 10.7498/aps.57.689
Abstract +
The effects of the dissipative decoherence on the quantum computation of the quantum kicked Harper (QKH) model are investigated using the quantum trajectory approach and the quantum Monte Carlo method. The simulation shows that the dynamical localization for the QKH model and the stochastic web in phase space are destroyed by moderate levels of dissipation. Taking the phase damping channel as the noise model, the universal law for fidelity decay and the timescales of reliable computation are analyzed. Compared with the static imperfections, the timescales for reliable computation of the dissipative system drop more quickly with the increase of the number of qubits when the decay rate is under a certain threshold. While above the threshold, the timescales drop more quickly in the presence of static imperfections.
Approach of continuous time random walk model to anomalous diffusion
Lin Fang, Bao Jing-Dong
2008, 57 (2): 696-702. doi: 10.7498/aps.57.696
Abstract +
A numerical method based on the continuous time random walk (CTRW) theory is developed to study the normal diffusion and anomalous diffusion including both sub-diffusion and super-diffusion. The probability density functions for both the jump distance and the residence time in the CTRW model are determined as well as the Metropolis sampling method in the periodic potential has been improved. The directional transport of a Brownian motor in both a flashing ratchet potential and a rocking ratchet potential is investigated. Our results have shown that the maximum of directional current occurs in the case of super-diffusion in a flashing ratchet and in the case of ballistic diffusion in a rocking ratchet.
T-S fuzzy system design by chaotic ant swarm algorithm
Li Li-Xiang, Peng Hai-Peng, Yang Yi-Xian
2008, 57 (2): 703-708. doi: 10.7498/aps.57.703
Abstract +
essful application of the algorithm to the problem of designing fuzzy system that matches the desired input-output pairs. The resulting CAS-designed fuzzy systems models can be used to achieve the identification and adaptive control of dynamical systems. Simulation results show that the proposed method is effective.
Division time chaos switch-synchronization for a class interrelated chaotic systems
Lin Chang-Sheng, Jiang Chang-Sheng, Liu Yang-Zheng
2008, 57 (2): 709-713. doi: 10.7498/aps.57.709
Abstract +
The method of division time chaos switch-synchronization for a class of interrelated chaotic systems is proposed. The division time chaos switch-synchronization between each chaotic subsystem and its duplicate system is achieved via linear feedback control. Based on the theory of stability of time-varying systems, the range of feedback gain for synchronization of these interrelated chaotic systems is derived. Numerical simulation shows the effectiveness and feasibility of the method.
On the application of non-stationary time series prediction based on the SVM method
Wang Ge-Li, Yang Pei-Cai, Mao Yu-Qing
2008, 57 (2): 714-719. doi: 10.7498/aps.57.714
Abstract +
The nonstationary behaviors of complex system and their applications to the climate prediction present a significant and forward-looking study. Up to now, its importance is not yet well understood. In reality, climate is just a normal nonstationary system. However, almost all the current theories for climate prediction, including the ones in statistics and nonlinear science, are based on one assumption that the process is stationary which is contrary to the nature of the climate process. Probably, this contradictory is an important cause resulting in the climate prediction being at a low reliability level. Therefore, it is theoretically important in climate prediction to start with how to reduce the nonstationary degree of time series. In this paper, support vector machine (SVM) method based on an idea of dimension raising is presented to study the time series prediction analysis, and prediction experiments are performed using some nonstationary time series from the Lorenz model and logistic system with changing control parameter, as well as two realistic climatic time series. The prediction results suggest that the SVM method can perform well in predicting nonstationary time series, which may be due to that the SVM method can map the input space into a higher dimensional feature space through nonlinear mapping and can reduce to some extent the nonstationary degree of the system.
A class of nonlinear phenomena resulting from saturation
Zou Jian-Long, Ma Xi-Kui
2008, 57 (2): 720-725. doi: 10.7498/aps.57.720
Abstract +
Based on a power-factor-correction (PFC) boost converter, a class of nonlinear phenomena are described when the system switches between saturated and non-saturated states alternately. Their characteristics and origination are analyzed. According the piecewise differential equations derived, we simulate the system's dynamical behavior. The simulating results demonstrate that period-doubling bifurcation and chaos may occur in this system. Moreover, border-collision bifurcation and transition from chaos to period-1 may also appear. These nonlinear phenomena result from the abrupt change of the system's qualitative behavior when the rectified input current runs into its saturation border. The nonlinear phenomena caused by saturation and the related analysis are verified by the experimental results.
Linear and nonlinear generalized synchronization of autonomous chaotic systems
Wang Xing-Yuan, Meng Juan
2008, 57 (2): 726-730. doi: 10.7498/aps.57.726
Abstract +
The generalized synchronization of autonomous chaotic systems is investigated. A new approach is proposed based on the modified state observer method and the pole placement technique, which have a wide scope of applications. The linear and nonlinear generalized synchronizations of autonomous chaotic systems are achieved by using the proposed method. According to the state observer theory, some sufficient conditions of global asymptotic generalized synchronization between the drive and response systems are obtained. Numerical simulations further illustrate the effectiveness of the proposed scheme.
Chaotic control of the coupled Logistic map
Wang Xing-Yuan, Wang Ming-Jun
2008, 57 (2): 731-736. doi: 10.7498/aps.57.731
Abstract +
Based on the stability criterion of discrete systems, state feedback is used to stabilize unstable low-periodic orbits of the coupled Logistic map, and a new scheme is proposed to change the parameter value of the first bifurcation point of this dynamic system optionally. Numerical simulations show the effectiveness of our methods.
Synchronization of Julia sets of complex systems
Liu Shu-Tang, Zhang Yong-Ping
2008, 57 (2): 737-742. doi: 10.7498/aps.57.737
Abstract +
Julia set, being a fractal set in the literature of nonlinear physics, has significance for the engineering applications. In this work, we are the first to define the synchronization of Julia sets between different systems and introduce a nonlinear coupling method to realize the synchronization of Julia sets of the same systems but with different parameters. We also illustrate the effectiveness of our method by the synchronization of Julia sets of polynomial and trigonometric functions respectively.
A modified digraph cell mapping method
He Qun, Xu Wei, Li Shuang, Xiao Yu-Zhu
2008, 57 (2): 743-748. doi: 10.7498/aps.57.743
Abstract +
By introducing new concepts, this paper presents a new classification of transient cells for the digraph cell mapping dynamical system. Based on this new classification, the approximation problem of the invariant manifolds of dynamical system is discussed in detail. In order to improve the efficiency and speed of computing, an effective algorithm is given to complete the above classification. As an illustrative example, Henon map is taken to demonstrate the validity of the modified digraph cell mapping method.
Fitz hugh-nagumo neural system driven by colored noises
Wang Chao-Qing, Xu Wei, Zhang Na-Min, Li Hai-Quan
2008, 57 (2): 749-755. doi: 10.7498/aps.57.749
Abstract +
We investigated the phase transition and the mean first-passage time of a Fitz hugh-nagumo neural system driven by colored noises, and the expressions of the stationary probability distribution and the mean first-passage time were obtained. The conclusions show that the parameters α,τ and β can induce phase transition, and there is a locking phenomenon in the system. Each parameter affects the system's mean first-passage time quite differently.
Impact of edges for new nodes on scale-free networks
Guo Jin-Li
2008, 57 (2): 756-761. doi: 10.7498/aps.57.756
Abstract +
This paper analyses the impact of edges for new nodes on scale-free networks. Although non-stationary average degree distribution of a sub-linearly growing network follows the power law, the stationary average degree distribution of the network does not. This paper proposes a random growth model whose node arrival process is a renewal process and the number of new edges is a random variable with binomial distribution. The result shows that the stationary average degree distribution of the model follows the power law under an appropriate condition, and the condition is found.
Temperature measurement with one dimensional defect photonic crystal
Tong Kai, Cui Wei-Wei, Li Zhi-Quan, Wang Mei-Ting
2008, 57 (2): 762-766. doi: 10.7498/aps.57.762
Abstract +
Si and SiO2 were used as materials to build the one-dimension (1D) defect photonic crystal and the medium of detect layer is Si. Using transfer matrix method, the optical transmission properties in 1D defect photonic crystals was analyzed, and the band gap property of 1D photonic crystal was obtained. Because of the defect, the defect peak appears in the transmission spectra. According to thermo-optical effect and thermal-expansion effect the optical depth and index of the materials and the defect of photonic crystal vary when the temperature changes. So the temperature can be measured by the wavelength shift value of the defect peak. Using 1D defect photonic crystal an experimentation system was set up for temperature measurement. The result showed that there is a linear relationship between the temperature of photonic crystal and the wave-length of the peak. And the sensitivity of this measuring system is 0207nm/℃ and the measurement range is -20—120℃.
Fabrication of MnSb/Sb functionally graded materials by high gradient magnetic fields
Gao Ao, Wang Qiang, Wang Chun-Jiang, Liu Tie, Zhang Chao, He Ji-Cheng
2008, 57 (2): 767-771. doi: 10.7498/aps.57.767
Abstract +
Mn-898wt%Sb alloys were solidified in the absence or presence of high magnetic fields of 88 T with various gradients to investigate the effects of high magnetic fields on the structures of the alloys. It was found that both of the two primary phases, i.e. MnSb and Sb appeared simultaneously in MnSb/Sb eutectic matrix and the MnSb and Sb phase-rich layers were aggregated in different domains under high gradient magnetic field conditions. It was also found that the volume fraction of these two primary phases increased with the increase of the field gradient. This process was attributed to that the alloying element clusters with different susceptibility in molten state were driven along or opposite to the direction of magnetic forces when subjected to high gradient magnetic fields and thus resulted in a layered microstructure with compositional gradient. The results of present study suggest that adjastment of high gradient magnetic field may potentially be used to tailor functionally graded materials.
Autofluorescence lifetime imaging of lipofuscin and oxidized melanin in retinal pigment epithelium cells
Sun Yi-Wen, Qu Jun-Le, Zhao Ling-Ling, Niu Han-Ben, Xu Gai-Xia, Ding Zhi-Hua
2008, 57 (2): 772-777. doi: 10.7498/aps.57.772
Abstract +
We report on our investigation of the spatial distribution and autofluorescence lifetime characterization of lipofuscin and oxidized melanin in the retinal pigment epithelium cells of the pig eye using a two-photon excitation fluorescence lifetime imaging microscopy (TPE-FLIM) system, which that is based on a time-correlated single photon counting technique. In particular, we analyzed the difference of autofluorescence lifetimes of these pigment granules in light-induced oxidizing environment. The experimental results showed that the fluorescence lifetime imaging can provide an effective differentiation of multi-component fluorophores, and fluorescence decay can be used to distinguish normal from abnormal fluorescence. TPE-FLIM has the potential to provide a high sensitive imaging instrument for the clinical diagnosis and pathological studies in ophthalmology, and is also of significance to the study of aging mechanism of cells in the fundus.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Probing R-parity violating interactions from top quark polarization at LHC
Li Xiang, Lu Gong-Ru, Li Pei-Ying
2008, 57 (2): 778-783. doi: 10.7498/aps.57.778
Abstract +
In minimal supersymmetric standard model, the R-parity violating interactions can induce anomalous top pair productions at the LHC through the t-channel process dRdR→tLtL by exchanging a slepton or the u-channel process dRdR→tRtR by exchanging a squark. Such top pair productions with certain chirality cause top quark polarization in the top pair events. We found that at the LHC, due to the large statistics, the statistical significance of the polarization observable and thus the probing ability for the corresponding R-parity violating couplings are much higher than at the Tevatron Upgrade.
NUCLEAR PHYSICS
Development of a system of measuring 37Ar by spectrum method
Xiang Yong-Chun, Gong Jian, Li Wei, Bian Zhi-Shang, Hao Fan-Hua, Wang Hong-Xia, Wang Qian, Xiong Zong-Hua
2008, 57 (2): 784-789. doi: 10.7498/aps.57.784
Abstract +
A portable system of measuring 37Ar has been developed. Measurement of 37Ar is realized by the proportional counter and spectrum analysis method. Plateau length, plateau slope and background have been analyzed. Compared with traditional counting method, the present method has the advantages of visibility, longer plateau length and smaller plateau slope. background is reduced by an order of magnitude which decreases the detection limit. Working gas of 10% methane improves the peak shape. Greater concentration of methane is not necessary because it does not make the peak shape better but needs higher working voltage.
ATOMIC AND MOLECULAR PHYSICS
The characteristics of terahertz radiation from InAs irradiated with femtosecond optical pulses of different wavelengths
Sun Hong-Qi, Zhao Guo-Zhong, Zhang Cun-Lin, Yang Guo-Zhen
2008, 57 (2): 790-795. doi: 10.7498/aps.57.790
Abstract +
The characteristics of terahertz (THz) radiation from the surface of an (100)p-InAs crystal excited by fs laser pulses of different wavelengths (from 750 to 850nm) are investigated experimentally. The terahertz radiation can be interpreted as being emited from accelerated photo-carriers in the Dember field and be detected by using the free-space electro-optic sampling method. A (110) ZnTe crystal was used as detector. The results of experiment show that the Dember field in the surface of InAs, concentration of excited carriers, intervalley scattering and the concentration of excited carriers of different states, all changed when the wavelength of excited pulse changed, so the radiant efficiency and the effective spectral width of terahertz wave were different. This investigation will be useful to the measure of time domain spectrum of samples and the optimization of experimental system. It also gives better physieal insight into the ultra-fast process of terahertz wave radiation from InAs excited by femtosecond pulses.
Rovibronic spectrum of N2O+ ion at the A2Σ+ state
Wang Hua, Liu Shi-Lin, Liu Jie, Wang Feng-Yan, Jiang Bo, Yang Xue-Ming
2008, 57 (2): 796-802. doi: 10.7498/aps.57.796
Abstract +
The rotational structures of the photofragment excitation spectrum of N2O+(A2Σ+) at high vibrational levels have been studied experimentally. The parent N2O+(X2Π) ions were prepared by (3+1) resonance-enhanced multiphoton ionization of jet-cooled N2O molecules by 36055nm laser beam,and were excited by another laser to the predissociative A2Σ+ state in the range of 280—320nm. Two types of rotational transition,i.e.,2Σ+←2Π and 2Π←2Π,have been clearly observed for a series of vibronic transitions. The rotational constants and spin splitting constants have been obtained from the spectral analysis.
X-ray spectra produced by interaction of Ar16+ and Ar17+ with Zr
Cui Ying, Zhang Hong-Qiang, Shao Jian-Xiong, Du Juan, Liu Yu-Wen, Chen Xi-Meng, Zhang Xiao-An, Yang Zhi-Hu, Song Zhang-Yong, Ruan Fang-Fang, Zhu Ke-Xin, Shao Cao-Jie, Lu Rong-Chun, Yu De-Yang, Cai Xiao-Hong
2008, 57 (2): 803-807. doi: 10.7498/aps.57.803
Abstract +
The 10—20qkeV Ar16+ and Ar17+ ions produced by SECRAL enter on metallic surface of Zr. In this interaction,the multi-electron excitation possibly occurred in the neutralization of the highly charged Ar16+ ions,which produced vacancy in the K shell. Electron of the high n state de-excited to K vacancy gives off X-ray. The experimental results show that X-ray intensities for the Ar hollow atom decrease with increase of incidence energy,and Lβ X-ray intensities of target atom Zr increase with increasing incidence energy. Kα X-ray yield per ion for Ar17+ was five orders of magnitude greater than that for Ar16+.
The absolute rotation measurement of atom interferometer by phase modulation
Zhu Chang-Xing, Feng Yan-Ying, Ye Xiong-Ying, Zhou Zhao-Ying, Zhou Yong-Jia, Xue Hong-Bo
2008, 57 (2): 808-815. doi: 10.7498/aps.57.808
Abstract +
In the paper,a measurement method of absolute rotation of atom interferometer is proposed. Generally,there are π/2-π-π/2 phase gratings in an atom interferometer in the space domain. We add three special phases to the three gratings,then,we modulate the special phases to change the detector signal of atom interferometer,and Fourier transform is performed on the detector signal,to obtain the absolute rotation of atom interferometer. The results are the discussed in the paper.
Analytical potential energy function for the electronic states X2Σ+,A2Π and B2Σ+ of MgH molecule
Zhou Xun, Linghu Rong-Feng, Yang Xiang-Dong, Zhu Zheng-He, Lü Bing
2008, 57 (2): 816-821. doi: 10.7498/aps.57.816
Abstract +
The equilibrium geometries of three electronic states X2Σ+,A2Π and B2Σ+ of MgH molecule have been calculated using the SAC-CI and QCISD (T) methods with the basis sets cc-pVQZ,aug-cc-pVTZ,6-311++G and 6-311++G(3df,2pd). Comparing the above mentioned four basis sets,the conclusion is obtained that the basis set 6-311++G (3df,2pd) is the most suitable for the energy calculation of MgH molecule. The whole potential curves for three electronic states are further scanned using QCISD (T)/6-311++G (3df,2pd) method for the ground state and SAC-CI/6-311++G (3df,2pd) method for the excited states. The potential energy functions and relevant spectrum constants ωe,ωexe,Be,αe of these states are obtained by fitting to the Murrell-Sorbie function and the modified Murrell-Sorbie+C6 function,respectively. The results showed that the spectral constants derived from the modified Murrell-Sorbie+C6 function are in very good agreement with the experimental data,and the modified Murrell-Sorbie+C6 function can correctly describe the potential energy function of the ground state and the first degenerate state of MgH molecule.
CLASSICAL AREA OF PHENOMENOLOGY
Novel miniaturized planar left-handed metamaterial transmission lines verified by the backward wave property
Wu Ming-Feng, Meng Fan-Yi, Fu Jia-Hui, Wu Qun, Wu Jian
2008, 57 (2): 822-826. doi: 10.7498/aps.57.822
Abstract +
Based on the technique of reducing working frequency of split ring resonators (SRR),this paper presents a miniaturized left-handed metamaterial transmission line unit,and retrieves the effective permittivity and permeability parameters from the transmission and reflection data. To verify the presence of the left-handed frequency band,3D numerical simulation is conducted to an array of left-handed metamaterials including eight units,which demonstrates that the left-handed metamaterial microstrip line can support unique backward wave property very well. Compared with conventional left-handed microstrip lines,this structure has been reduced by 60% in electrical sizes,and would be more convenient for fabrication in applications as miniaturized planar circuit components.
Design of reflection resonant grating filters
Jin Yun-Xia, Zhao Yuan-An, Shao Jian-Da, Fan Zheng-Xiu, Ma Jian-Yong, Liu Shi-Jie, Wei Chao-Yang, Xu Cheng
2008, 57 (2): 827-832. doi: 10.7498/aps.57.827
Abstract +
Resonant grating filters based on grating abnormality have attracted much attention in recent years owing to their high peak reflectivity,low sideband reflection and controllable line width of central wavelength. Some special characteristics which are hard to be achieved by multilayer stack alternated with high and low refractive indices can be realized with guide-mode resonance of sub-wavelength gratings whose line width of central wavelength can be compressed to less than one nanometer under the condition of weak modulation of gratings. However,the sideband reflections near or far from the central wavelength are still somewhat high due to Fresnel reflection between air and material. According to the effective medium theory (EMT),sub-wavelength waveguide gratings can be viewed as thin films. In this paper,the sideband reflections of resonant grating filters are effectively reduced through antireflection design based on thin film theory and narrow band resonant filters are attained in the range of visible wavelength with good characteristics.
Electromagnetic scattering by multi-layered spheres in a 2-D Gaussian beam
Li Hai-Ying, Wu Zhen-Sen
2008, 57 (2): 833-838. doi: 10.7498/aps.57.833
Abstract +
Based on formula of vector wave functions in spherical and cylindrical coordinates and their transformation relations,a new method to solve beam coefficients of a two dimensions (2-D) on-axis Gaussian beam is provided. An analyzical expansion of beam coefficients is obtained. With the help of generalized Lorentz Mie theory,electromagnetic scattering by multi-layered spheres in a 2-D Gaussian beam is deduced. Distribution of scattering intensity changing with scattering angle are simulated. A comparison of scattering intensity with results of incident plane wave is given.
A hybrid analytical-numerical algorithm for scattering from a 3-D target above a randomly rough surface
Ye Hong-Xia, Jin Ya-Qiu
2008, 57 (2): 839-846. doi: 10.7498/aps.57.839
Abstract +
This paper presents a hybrid iterative algorithm of analytic KA-numerical MOM for scattering computation from a 3-dimensional (3-D) perfect conducting target above a randomly rough surface. The coupled integral equations (IEs) are derived for difference scattering computation. The method of moment (MoM) with the conjugate gradient (CG) approach is used to solve the target's IE,and the Kirchhoff approximation (KA) is applied to scattering from the rough surface. The coupling iteration takes account of the interactions between the target and the underlying rough surface. The convergence of this hybrid algorithm of KA-MoM is numerically validated. Since there is only one numerical integral along the rough surface performed for KA computation,memory and CPU time are significantly reduced. Numerical results of bistatic scattering from a PEC ellipsoid or cubic target above a Gaussian rough surface produced by Monte Carlo method are obtained.
Gray-image information hiding based on kinoform
Zhai Hong-Chen, Wang Ming-Wei, Yang Xiao-Ping
2008, 57 (2): 847-852. doi: 10.7498/aps.57.847
Abstract +
In this paper,a new method of hiding gray-images in a host image by using double-random phase encryption method based on kinoform iterative is presented,through which not only the volume to be hidden can be compressed,but also the optical efficiency in the information extracting can be improved. The decoding process of which will not rely on the original host image,and this method can also be applied to the hiding of binary-images. In the last part of this paper,the efficiency and the robustness of this method is analyzed. Computer simulations are presented to illustrate the effectiveness of this method.
Effect of partial coherence laser arrays on far-field output properties
Xiao Rui, Hou Jing, Jiang Zong-Fu
2008, 57 (2): 853-859. doi: 10.7498/aps.57.853
Abstract +
Quantitative details about coherence are important for determining the performance of laser arrays. In this paper,we deduce the analytical equation of the far-field intensity distribution in partially coherent combining of fiber laser arrays and investigate its effects on the far-field patterns, the FWHM of the central far-field lobe, strehl ratio and power in the bucket. The master oscillator-power amplifier scheme was used to realize phase control of three ytterbium fiber amplifiers, and the experimental results are presented.
Experimental study of the generation of Laguerre-Gaussian beam using a computer-generated amplitude grating
Li Feng, Gao Chun-Qing, Liu Yi-Dong, Gao Ming-Wei
2008, 57 (2): 860-866. doi: 10.7498/aps.57.860
Abstract +
Laguerre-Gaussian (LG) beams attratts much attention in the fields of rotating micro-particle manipulation and information processing due to their special phase structures and related orbital angular momentum. In this paper the generation of LG beam by an amplitude grating was theoretically studied and the LG beams with azimuthal number of ±1 were obtained by the amplitude grating produced by the computer-generated hologram (CGH). Influences of main factors on the beam transformation were discussed.
Design and implementation of a PRML detection system for HD-DVD
Yuan Hai-Bo, Xu Duan-Yi, Ma Jian-She
2008, 57 (2): 867-872. doi: 10.7498/aps.57.867
Abstract +
A PRML detector suitable for high-density DVD (HD-DVD) system is developed in this paper. After comparing the spectrum characteristics of the linear optical channel model with various PR polynomials (memory length from 4 to 7),the criteria of determining memory length and coefficients of target PR is given. The simulated SNR-BER curves show that the Viterbi detector's performance is much better when the memory length of PR is seven. The architecture of a Viterbi detector in PRML system is also described. By computer simulation and experiments,it is proved that the performance and speed of the PRML system with memory length seven can completely satisfy the requirements of the HD-DVD system.
Entropy squeezing of the optical field in k-photon Jaynes-Cummings model
Ren Min, Kang Dong-Peng, Liu Zheng-Jun, Liu Shu-Tian, Ma Ai-Qun, Qian Yan
2008, 57 (2): 873-879. doi: 10.7498/aps.57.873
Abstract +
We investigated the field entropy squeezing of k-photon Jaynes-Cummings model,discuss the influence of the photon number k and the initial state of the atom on the entropy squeezing. The results show that with the photon numberk increasing,the position entropy squeezing will be enhanced and the momentum entropy squeezing reduced. When k≥3,the position entropy is always squeezed. The initial state of the atom also shows some influence on the entropy squeezing.
Generations of coherent states of single trapped cold ion beyond the Lamb-Dicke limit
Zhang Miao, Jia Huan-Yu
2008, 57 (2): 880-886. doi: 10.7498/aps.57.880
Abstract +
Based on the quantum dynamics of laser-ion interaction beyond the Lamb-Dicke limit,we discuss how to superpose a series of vibrational number states from motional ground state by sequentially applying laser beams. The Q function,Wigner distribution function,and the nonclassical properties such as squeezing effect and anti-bunching effect of the generated superposition states are investigated in detail by numerical method. It is shown that,by controlling the durations of the applied laser pulses,these quantum states could well approach to the well-known coherent states.
Entanglement transfer via cross-Kerr nonlinearity
Ren Min, Yang Jian, Yu Ya-Fei, Zhang Zhi-Ming, Liu Song-Hao
2008, 57 (2): 887-891. doi: 10.7498/aps.57.887
Abstract +
We propose a scheme for realizing entanglement transfer based on the cross-Kerr nonlinear interaction between field-modes. By using this scheme the entanglement can be transferred from the field-states with discrete variables to the field-states with continuous variables. By suitably choosing the amplitude of the initial coherent states,we can obtain the maximum entangled coherent states.
Highly precise active-synchronization between two independent femotosecond Ti: sapphire oscillators
Zhao Huan, Zhao Yan-Ying, Tian Jin-Rong, Wang Peng, Zhu Jiang-Feng, Ling Wei-Jun, Wei Zhi-Yi
2008, 57 (2): 892-896. doi: 10.7498/aps.57.892
Abstract +
We demonstrate the highly precise active-synchronization between two independent Ti: sapphire femtosecond oscillators. A combination of three phase locked loops, is used to control the synchronization between two laser pulses,which gives a RMS timing jitter less than 30fs. With the technique of cavity length monitoring and autocontrol by a computer,this highly precise synchronization can be retained for more than 40 minutes.
The performance of phase-only liquid crystal spatial light modulator used for generating Zernike terms
Ling Ning, Jiang Wen-Han, Cai Dong-Mei
2008, 57 (2): 897-903. doi: 10.7498/aps.57.897
Abstract +
The liquid crystal spatial light modulators (LC-SLM) are recently emerging as wavefront aberration correctors for use in low cost adaptive optics system (AO). As a novel aberration corrector,the wavefront generation performance of a phase-only LC-SLM is a governing factor that determines its ability for wave-front correction in an AO system. In this article,the performance of wave-front generation of LC-SLM is demonstrated by the production and quantification of the first 36 Zernike terms with different values. The factors,such as the fill factor,fringe field effect,pixel structure,the phase wrapping method and different phase strokes to impact wave-front generation are analyzed.
Ultrabroadband continuum spectrum generated in Ar gas
Zhang Li-Ping, Li Hai-Ning, Wu Hong, Li Xian, Ding Liang-En
2008, 57 (2): 904-908. doi: 10.7498/aps.57.904
Abstract +
We observed the supercontinuum in Ar during the propagation of a femtosecond pulse with wavelength of 800nm,repetition rate of 10Hz and pulse duration of 30fs. We studied the supercontinuum when changing the chirp of the pulse,pulse energy,pressure in the cell and the focal length to find the optimal conditions. And we observed the steady broadest supercontinuum extending up to 200nm with the pulse of 20mJ energe,29×104fs2 chirps when the focal length was 500mm and the pressure of the cell was 23×105Pa. We measured the far-field pattern of the continuum and found the divergence angle of the white light to be 31mrad.
A tunable wavelength routing scheme based on the sum-and difference-frequency generation with double pass configuration and its applications
Yu Song, Zhang Hua, Shen Jing, Zhang Yong-Jun, Gu Wan-Yi
2008, 57 (2): 909-916. doi: 10.7498/aps.57.909
Abstract +
A tunable wavelength routing scheme based on sum- and difference- frequency generation (SFG+DFG) is proposed, where the concept of double pass configuration is employed. An arbitrary channel can be dropped from a WDM signal and added to another WDM signal at arbitrary wavelength. Therefore, the tunable wavelength conversion and wavelength routing are integrated together in this scheme. The theoretical expression of the input signal wave and the converted wave are derived under the assumption of “small signal" when the phase is matched perfectly. Numerical calculations were performed which showed that the cross-talk can be suppressed provided the spacing of the WDM channels is greater than 02nm (25GHz). If the input or output of this device is changed, this scheme can be utilized as tunable wavelength add multiplexer, tunable wavelength drop multiplexer, wide tunable wavelength filter or tunable wavelength converter. A wavelength interchange cross connection (WIXC) unit can also be realized by employing two devices of this scheme.
Experimental research of supercontinuum generation by femtosecond pulse in highly nonlinear photonic crystal fiber
Liu Wei-Hua, Peng Qin-Jun, Xu Zu-Yan, Song Xiao-Zhong, Wang Yi-Shan, Liu Hong-Jun, Zhao Wei, Liu Xue-Ming
2008, 57 (2): 917-922. doi: 10.7498/aps.57.917
Abstract +
We pumped a 1m long highly nonlinear photonic crystal fiber by a Ti: sapphire laser and generated a supercontinuum with the wavelength extension form 420—1700nm,of which the output power was about 170mW and we conversion efficiency was above 20%. The experiment result was particularly analyzed and compared with calculated result,and we consider the main reasons of supercontinuum generation was fission of high-order solitons and four-wave mixing. We also researched the supercontinuum generation under different pump power and wavelength conditions. With the pump power increased gradually in the same fiber,the output spectrum can be divided into initial broadening stage,dramatic broadening stage and saturation broadening stage. When the output spectrum is in the initial broadening stage or saturation broadening stage,there exists some residual pump,when the output spectrum is in the dramatic broadening stage,the highest conversion efficiency is obtained. When the pump wavelength is in the anomalous dispersion reion of the fiber,the spectrum width is far broader than that in the zero dispersion region,but the shapes of the spectra are very similar. These conclusions provide valuable reference for supercontinuum system optimization and control.
Kerr-type spatial optical solitons in planar waveguides with finite width and the design of all optical devices
Guo Qi, Xiao Yi
2008, 57 (2): 923-933. doi: 10.7498/aps.57.923
Abstract +
The propagation of paraxial light beams injected at an inclined angle in a planar waveguide with finite width is studied by numerical method. The soliton beams with different wavelength and same width,if their incident point and incident slanting angle are the same,will propagate along the same periodic Z-type route in the planar waveguide. With the power of the beam increasing,the distance between two adjacent reflecting points will become longer and longer with the propagation distance and the Z-type route will lose its periodicity. When the power of a beam become fairly strong,the beam will propagate along z direction of the waveguide,and will no longer be reflected back and forth between the two boundaries of the planar waveguide. Using the characteristic that a beam injected at an inclined angle in the waveguide will propagate along different route with different power,a power switch and an optical time division demultiplexer are designed.
The thick ring resonators to achieve negative permeability and its left-handed behavior in perpendicular propagation
Liu Ya-Hong, Song Juan, Luo Chun-Rong, Fu Quan-Hong, Zhao Xiao-Peng
2008, 57 (2): 934-939. doi: 10.7498/aps.57.934
Abstract +
We experimentally investigated the microwave transmittance properties of the thick ring resonators in a rectangular waveguide for propagation perpendicular to the plane of the ring resonators. Our ring resonators are different from the conventional split ring resonators which have the certain thickness. It is found that a transmission dip occurs at 145GHz and the transmission phase has a shift at the resonance frequency for the thick ring resonators. Furthermore,we calculated the permeability of the thick ring resonators applying bianisotropic composite modeling and found the negative permeability near the resonance transmission dip. We measured the left-handed peak and phase advance by using the thick ring resonators combined with wires which have transmission pass bandwidth of 15GHz and transmission value of -21dB.
Molecular dynamics simulation of shock-induced collapse in single crystal copper with nano-void inclusion
Zhang Guang-Cai, Xu Ai-Guo, Zhao Yan-Hong, Yang Qi-Li, Li Ying-Jun
2008, 57 (2): 940-946. doi: 10.7498/aps.57.940
Abstract +
The evolution of preexisting nano-voids of different size in single crystal copper is investigated by means of molecular dynamics (MD) simulations. The results show that void collapse depends upon the size of the void. Numerous dislocation loops emerge for large void and phase transformation takes place in the sample. When the shock wave passes the void from left to right,dislocation loop emerges in the right of the void first for small void. However,loops emerge in the right and the left at the same time when the size of the void increases to a critical size,which is decided by the distribution of the stress near the void. Once dislocation loop emerges and grows,the frontal dislocation loop in the right of void grows faster than that in the left for the same void. When the size of the void increases,the velocity of frontal dislocation loops is essentially unvaried,and the angle between the direction leading from the centre of the void to the initial position of collapse and the direction of impact increases.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Quantum-mechanical calculations of vibrationally resolved cross sections for non-dissociative charge transfer of O3+ with H2
Wu Yong, Liu Ling, Wang Jian-Guo
2008, 57 (2): 947-956. doi: 10.7498/aps.57.947
Abstract +
Charge transfer due to collisions of ground state O3+(2s22p 2P) ions with molecular hydrogen is investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) method,and electronic and vibrational state-selective cross sections along with the corresponding differential cross sections are calculated for projectile energies of 100,500,1000 and 5000eV/u at the orientation angles of 25°,45° and 89°. The adiabatic potentials and radial coupling matrix elements utilized in the QMOCC calculations were obtained with the spin-coupled valence-bond approach. The infinite order sudden approximation (IOSA) and the vibrational sudden approximation (VSA) are utilized to deal with the rotation of H2 and the coupling between the electron and the vibration of H2. It is found that the distribution of vibrationally resolved cross sections with the vibrational quantum number v′ of H+2(v′) varies with the increment of the projectile energy; and the electronic and vibrational state-selective differential cross sections show similar behaviors: there is a highest platform within a very small scattering angle,beyond which the differential cross sections decrease as the scattering angle increases and lots of oscillating structures appear,where the scattering angle of the first structure decreases as E-1/2p with the increment of the projectile energy Ep; and the structure and amplitude of the differential cross sections are sensitive to the orientation of molecule H2,which provides a possibility to identify the orientations of molecule H2 by the vibrational state-selective differential scattering processes.
Modelling the universal dielectric response in heterogeneous materials using 3-D RC networks
Peng Jin-Hui, Xiao Zhe, Wu Yue-Feng, Huang Ming
2008, 57 (2): 957-961. doi: 10.7498/aps.57.957
Abstract +
In this paper,a three-dimensional RC networks model has been developed,and the RC networks has been coded,modeled and simulated based on Matlab and C programming language. The complex permittivity of this model has been calculated. The dielectric properties of RC networks containing 54,144,300,540 and 882 components have been computed. It was found that these properties exhibit the anomalous power law dependence on frequency known as the ‘universal dielectric response’ (UDR). The UDR is stable for RC networks containing 300 or more components. When the capacitor is 100nF,10nF,1nF and 100pF,respectively,the simulation results of normalized complex permittivity versus angular frequency for RC networks containing 540 components have been obtained. The relation between normalized complex permittivity and angular frequency for the RC networks containing 540 components in the ratios 4% R-96% C,7% R-93% C,10% R-90% C,16% R-84% C,33% R-67% C have been simulated. The results show that the UDR in heterogeneous materials can be modelled and simulated by 3-D RC networks,and has non-Debye nature.
Study of three dimensional zonal flows characteristic and novel probe design in HL-2A
Hong Wen-Yu, Yan Long-Wen, Zhao Kai-Jun, Dong Jia-Qi, Cheng Jun, Qian Jun, Luo Cui-Wen, Xu Zheng-Yu, Huang Yuan, Yang Qing-Wei, Lan Tao, Yu Chang-Xuan, Liu A-Di
2008, 57 (2): 962-968. doi: 10.7498/aps.57.962
Abstract +
Three dimensional(3-D) features of geodesic acoustic mode zonal flows (GAMZF) were first determined with novel three-step zonal flow probes (TSZFP) at the edge of the HL-2A Tokamak plasmas. Three arrays of TSZFP were located 65mm and 800mm apart. The poloidal mode (m~0) and toroidal mode (n~0) of electric potential and field perturbations were simultaneously determined for the first time. Corresponding frequencies were estimated as 7kHz,which are in good agreement with theoretical prediction. The radial scale lengths of ZF were 24—42cm. The formation mechanism of the flows is identified to be nonlinear three wave coupling between high frequency turbulent fluctuations and the flows. The regulating effect of the flows on the ambient turbulent fluctuations was also demonstrated. The Reynolds stress driven by edge fluctuation is one of the main reasons driving the poloidal flow. It is also verified that the radial gradient of Reynolds stress can drive zonal flows.
The characteristics of the spectrum emitted from dielectric barrier-discharge plasmas
Li Gang, Nie Chao-Qun, Li Yu-Tong, Zhang Yi, Zhang Jie, Li Han-Ming, Li Ying-Jun, Cheng Tao
2008, 57 (2): 969-974. doi: 10.7498/aps.57.969
Abstract +
In order to optimize the parameters of dielectric barrier-discharge plasmas, the emission spectrum of second transition line of oxygen and nitrogen under normal temperature and pressure was measured with a grating spectrometer. The results show that the intensity of the emission spectrum of the plasma increases with the voltage, and the best frequency range to generate the plasma spectrum is 39—41kHz. Meanwhile, the introduction of helium gas increases the intensity to a high extent. In combination with the theoretical analysis, the feasibility of spectral method in the study of dielectric barrier discharge plasma is verified.
A proposed high electrical efficiency and high current intensity radial split-cavity oscillator
Zhang Yun-Jian, Meng Fan-Bao, Fan Zhi-Kai, Luo Xiong
2008, 57 (2): 975-979. doi: 10.7498/aps.57.975
Abstract +
Using the structure of the coaxial vircator oscillator, a new kind of compact radial split-cavity oscillator is presented. The characteristic of the oscillator is that the input current can be intense, and this is the main reason for the output microwave power to be high. Taking into consideration all kinds of factor, under the condition of the voltage of 410kV and the beam current of 35kA, the numerical simulation gives an average output microwave power of about 50GW at the microwave frequency of 146GHz, and the electronic efficiency is 348%.
Study on the electrical potential signals induced by laser plasma in the target with bias-voltage
Ji Yun-Jing, Bian Bao-Min, Tong Chao-Xia, Lu Jian
2008, 57 (2): 980-984. doi: 10.7498/aps.57.980
Abstract +
The electrical potential signals induced by laser-plasma generated on a copper target with bias-voltage using a Nd:YAG laser (7ns) were detected, and the effect of the additional voltage on the potential signals was mainly studied. The experimental results show a single-peak distribution in the temporal profile, which is positive for negative bias voltage and negative peak when with positive bias voltage. Taking into account the effect of plasma charging and the electric field produced by the target bias-voltage, a clear explanation of the observed effect is given.
Absorption experiments on radiatively heated Al plasma
Xu Yan, Yan Jun, Meng Guang-Wei, Zhang Ji-Yan, Yang Jia-Min, Yang Guo-Hong, Ding Yao-Nan, Wang Yan
2008, 57 (2): 985-989. doi: 10.7498/aps.57.985
Abstract +
K-shell absorption spectroscopy of radiatively heated Al sample is reported. The experiment was conducted on Shenguang-Ⅱ Laser facility. Eight main beams of the facitliy are injected into a conical gold cavity to produce high-temperature X-ray heating source. This X-ray source is then used to irradiate an Al foil located in the center of the cavity, and heat the foil to temperature of tens of electronvolt. After a time delay, a ninth short-pulsed laser beam is focused on a gold disk to generated an X-ray point-backlighter. By measuring the spectra both directly from backlighter and attenuated by the heated sample in the wavelength range of 075—085nm, the K-shell absorption spectrum of Al is obtained. By fitting the experimental spectrum with theoretical calculation, electron temperature of the heated sample is determined.
The initiation phase of pseudospark discharge in a hollow cathode via PIC/MCC simulation
Zheng Fei-Teng, Yang Zhong-Hai, Jin Xiao-Lin
2008, 57 (2): 990-995. doi: 10.7498/aps.57.990
Abstract +
We have developed a theoretical and computational model to study the initiation phase of pseudospark discharges in a hollow cathode via a quasi-three-dimensional electrostatic particle-in-cell plus Monte Carlo collision(PIC/MCC) method. The numerical results clearly identified different processes of ionization growth. It has been found that the ionization processes are determined by hollow cathode effect and local electric field. The growth is dependent on α ionization multiplication due to local space charge in the stage from initial ionization growth to the onset of the hollow cathode effect, and then the hollow cathode effect becomes the leading factor.
The research on half-analytical method in calculating the magnetic field of unbalanced magnetron sputtering
Han Liang, Zhao Yu-Qing, Zhang Hai-Bo
2008, 57 (2): 996-1000. doi: 10.7498/aps.57.996
Abstract +
Half-analytical method is a new method of calculating electromagnetic field. In this paper, this method is applied to analyzing magnetic field in unbalanced magnetron sputtering system. There are less unknown variables with this method in the solving process and the result has high accuracy. This method is better the oretically founded compared with the equivalent source method. The expression of scalar potential function is an analytic series, which favors calculating field intensity and optimization.
Study on the transition from filamentary to uniform discharge in dielectric barrier discharge
Li Xue-Chen, Jia Peng-Ying, Liu Zhi-Hui, Li Li-Chun, Dong Li-Fang
2008, 57 (2): 1001-1007. doi: 10.7498/aps.57.1001
Abstract +
The transition from filamentary discharge to uniform discharge in a device with water electrodes is studied in air by electrical method and emission spectroscopy. Results show that discharge can transit from filamentary mode to uniform mode by increasing the applied voltage or decreasing the gas pressure. The discharge mechanism at high pressure is the streamer and that at low pressure is glow discharge. The relations of the number of high-energy electons and experimental parameters were studied by optical emission spectroscopy. The results show that high-energy electrons increases in number with decreasing gas pressure and decreases with increasing applied voltage. The experimental results are explained qualitatively based on the theory of wall charge. The results are of value for the study of uniform discharge in dielectric barrier discharge.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Mesoscopic impedivity of Fe-based nanocrystalline alloy and its application
Yang Yi, Xu Qi-Ming, Fang Yun-Zhang, Yang Quan-Min
2008, 57 (2): 1008-1012. doi: 10.7498/aps.57.1008
Abstract +
We put forward an physical concep for the mesoscopic impedivity of Fe-based nanocrystalline alloy for the first time, and its formula ρ=-μ{A}/{t}/Δ×His obtained by using Maxwell system of equations. The formula shows that the mesoscopic impedivity ρ of Fe-based nanocrystalline alloy depends on the mesoscopic magnetic field intensity H, mesoscopic magnetic vector potential A, and mesoscopic permeability μ. The mesoscopic magnetic vector potential A is caused by the effect of quantum mechanics with the mesoscopic structure in the studied material, and is determined by the microcosmic structure of the studied material. Magneto-resonance frequency shift of nanocrystalline Fe735Cu1Nb3Si135B9 powder for its giant magneto-impedance(GMI) effect and frequency resonance magnetic field intensity shift of nanocrystalline Fe730Cu10Nb15V20Si135B90 microwire with the multilayer structure for its GMI effect are explained successfully by the formula.
The stress characteristics of metal nanowires: an atomistic simulation study
Wen Yu-Hua, Zhu Zi-Zhong, Shao Gui-Fang
2008, 57 (2): 1013-1018. doi: 10.7498/aps.57.1013
Abstract +
In this paper, we have used molecular statics calculations with the quantum corrected Sutten-Chen type many-body force field to study the stress distribution characteristic of nickel nanowires with [100], [110] and [111] crystallographic orientations in equilibrium state. The simulated results show that tensile stress on the surface of the nanowires causes them to contract along the length. It can be seen that the stress is tensile in surface region while compressive in core region. With the increasing of diameter, the average stress in core region is compressive and strongly decreased to approach to zero, while the surface tensile stress first increases, and then tends to a non-zero constant. The contraction ratio of length, and average stress in core and surface are always largest for [100] nanowire and smallest for [111] nanowire.
Pressure control model for transport of liquid mercury in carbon nanotubes
Zhang Zhong-Qiang, Zhang Hong-Wu, Wang Lei, Zheng Yong-Gang, Wang Jin-Bao
2008, 57 (2): 1019-1024. doi: 10.7498/aps.57.1019
Abstract +
Carbon nanotubes have a significant application in nanotechnology as nanopipes conveying fluids. In this paper, a pressure control model for transport of liquid mercury through carbon nanotubes using classical molecular dynamics simulations in conjunction with an atomistic model is presented. Wetting of single-walled carbon nanotubes by mercury occurs above a threshold pressure of liquid mercury. The liquid mercury can be transported through carbon nanotubes with the continuous increase of its internal pressure. Also, we show that single-walled carbon nanotubes can transport liquid mercury discontinuously when a periodical pressure is applied on the liquid.
Relaxation resulting from atomic defects in quenched Fe-Al alloys
Zhou Zheng-Cun, Zhao Hong-Ping, Gu Su-Yi, Wu Qian
2008, 57 (2): 1025-1029. doi: 10.7498/aps.57.1025
Abstract +
Two relaxational internal friction peaks in quenched Fe-Al alloys with different Al content have been investigated using a computer-controlled automatic inverted torsion pendulum through free-decay and forced vibration method. It has been shown that the two peaks (P1, 180℃ and P2, 340℃) appear only in the heating process and do not appear in subsequent in-situ cooling process. It is suggested that P1 resulted from the stress-induced reorientation of di-vacancies, which consists of the reorientation of nearest neighbour Fe-vacancies on the α and β (or γ) sublattice sites. The relaxation strength of P1 varies im-monotonicly with Al content and there is a maximum at about 25% Al(atomic percent). There is no P1 peak in the Fe-Al alloys with lower Al content since vacancies exist in the form of isolated vacancies. When Al content is over 25%, the number of vacancies on β and γ sites is reduced. Therefore, the nearest neighbour di-vacancies are decreased and the height of P1 peak declines. P2 originates from the stress-induced reorientation of FeAl-VFe dipoles under. P2 does not appear in the Fe-Al alloys with Al less than 22% since no FeAl anti-site atoms and FeAl-VFe dipoles are produced.
Study of acoustical properties of supercritical carbon dioxide using liquid acoustical theory
Lu Yi-Gang, Peng Jian-Xin
2008, 57 (2): 1030-1036. doi: 10.7498/aps.57.1030
Abstract +
Molar sound velocity, molar adiabatic compressibility and Van der Waals constant of gaseons, liquid and supercritical carbon dioxide at different temperature and pressure are calculated using liquid acoustical models and data of sound velocity, density, molar volume and adiabatic compressibility of carbon dioxide provided by National Institute of Standards and Technology, USA. The results show that the liquid acoustical models can be used in study acoustical property of supercritical carbon dioxide in wide ranges of temperature and pressure. The surface tension, conglutination and diffusivity at different temperatures and pressures are calculated. And the mutative rules of these physical quantities are analyzed. The data can provide reference for supercritical liquid technique.
Effect of ramping from low temperatures on oxygen precipitation in Czochralski silicon
Ma Xiang-Yang, Yang De-Ren, Cui Can
2008, 57 (2): 1037-1042. doi: 10.7498/aps.57.1037
Abstract +
Czochralski (CZ) silicon wafers were firstly subjected to a variety of ramping annealing from low temperatures to 750℃, and then subjected to a prolonged anneal at 750℃ for up to 64 h. It was revealed that the prior ramping anneal from low temperature lead to strong enhancement of oxygen precipitation in the subsequent annealing, and the lower the starting temperature the stronger the enhancement. It is considered that at low temperatures (450—650℃) the diffusion of oxygen was greatly enhanced and therefore the nucleation of oxygen precipitation was facilitated. Moreover, the slow ramping rate could also increase the stability as well as facilitate the growth of the oxygen precipitate nuclei formed at low temperature. A novel internal gettering (IG) process based on ramping anneal from low temperature has been developed, which can reduce the annealing time and therefore the thermal budget. However, the ramping anneal from low temperature is not available for the application of magic denude zone (MDZ) process.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
The electronic structure of the microstructure of Mg-Zr alloys
Liu Gui-Li
2008, 57 (2): 1043-1047. doi: 10.7498/aps.57.1043
Abstract +
The electronic structure parameters (such as the structure energy, atomic binding energy of α-Mg and α-Zr phase; the interface energy of Mg/Zr; the surface energy of Mg; the interacting energy between Zr atoms or impurity atoms; the density of state and the charge variety of Mg and Zr in auoys) were calculated by recursion method. The calculated results show that: the shape of the density of states of Zr is different from Mg in the cryctal grain, but is similar to the Mg at the Mg/Zr interface, which means the electronic structure environment of the interface of Mg/Zr is similar for Zr and Mg, which provides the condition for Mg to nucleate on the surface of Zr. The structure energy and the atomic binding energy of α-Zr phase are lower than that of α-Mg, and the interface energy of Mg/Zr is lower than the surface energy of Mg. This explains from energy point of view the experiment phenomenon that Zr precipitates from Mg liquid before α-Mg solidifies, and it acts as good centers for heterogeneous nucleation to refine α-Mg grains. The interacting energy between atoms indicated that Zr atoms attracts each other, so they can form Zr atom clusters in Mg easily, and may combine with impurity atoms to form compounds, which will weaken the effect of the refinement of Mg grains. But it cleans the Mg alloys and improves the performances of Mg alloys. The charge transfer between Mg and Zr produces the ionic bond, which reduces the coefficient of diffusion of Mg. This makes the growing of α-Mg grain difficult, and leads to the refinement of α-Mg grain.
First-principles calculations on the electrical structures and vibration frequencies of β-Si3N4
Zhu Ying-Tao, Yang Chuan-Lu, Wang Mei-Shan, Dong Yong-Mian
2008, 57 (2): 1048-1053. doi: 10.7498/aps.57.1048
Abstract +
Both unit cell parameters and fractional atomic coordinates of β-Si3N4 have been fully relaxed using Crysta106 program that adopts all-electron gauss-type basis sets and the density functional theory (PW91 and B3LYP). The geometrically optimized results are in excellent agreement with experiment. The band structure and density of states are also calculated. Based on the optimized geometries, the vibration frequencies have been calculated at Γ point using PW91 and B3LYP method with symmetry assignment. The 11 Raman mode frequencies are compared with experiment and other theoretical results, and the missing Ag mode frequency is assigned to 459cm-1. The present calculation shows that the results of B3LYP are better than those of PW91 In the intermediate and low-frequency region, the largest differences from experimental results are 2 and 17cm-1, while in the high-frequency region the largest differences are 16 and 35cm-1 respectively. For IR frequencies, the symmetries of the experimental data are assigned by comparing them with the present theoretical results.
First principles study of optical properties of wurtzite ZnO with Mn-doping
Chen Kun, Fan Guang-Han, Zhang Yong
2008, 57 (2): 1054-1060. doi: 10.7498/aps.57.1054
Abstract +
The electronic structures of pure and Mn-doped wurtzite ZnO have been calculated by first-principles ultra-soft pseudo-potential approach of the plane wave based upon the density functional theory, and the structure change, bandstructure, density of state and the difference charge density were studied. The calculated results were revealed that Mn-doping changed the band gap of the films, which increased with the increase of the Mn content. Moreover, the absorbence in strong UV absorption band of ZnO increased too.
Effect of rotation on photonic band gap of two-dimensional square lattice photonic crystal with hollow rod
Zhao Ming-Ming, Lü Yan-Wu, Yu Jia-Xin, Pang Xu-Qian
2008, 57 (2): 1061-1065. doi: 10.7498/aps.57.1061
Abstract +
The plane-wave expansion method is used to calculate TE and TM mode band gaps for two-dimensional square lattice photonic crystal with hollow anisotropic tellurium (Te) rods under three different rotation operations. The effect of rotation on TE and TM mode band gaps and absolute band gap is investigated. The calculated results show that the high order band gaps of TM mode have a close relationship with structure rotation symmetry, and the rotation symmetry and the distribution of Te in x-y plane together influence TE mode band gaps.
First-principles study of electronic structure for Cd-doped wurtzite ZnO
Zhao Ji-Jun, Tang Xin, Ma Chun-Yu, Zhang Qing-Yu, Lü Hai-Feng
2008, 57 (2): 1066-1072. doi: 10.7498/aps.57.1066
Abstract +
Using the density-functional theory (DFT) combined with the projector augumented wave (PAW) method, we have investigated the electronic structure of Cd-doped wurtzite ZnO. Analysis of the band structures, density of states (DOS) and partial density of states (PDOS) of CdxZn1-xO shows that the valence band maximum (VBM) is determined by O-2p states and the conduction band minimum (CBM) is occupied by the hybrid Cd-5s and Zn-4s orbital. The energy of CBM decreases and the energy of VBM increases with increasing Cd-doped concentrations. Both effects lead to narrowing of the band gap. Furthermore, it was found that Cd-doped can cause tensile strain in the crystal structure, which also reduces the band gap.
First-principles study of electronic structure and transport properties of zigzag graphene nanoribbons
Ouyang Fang-Ping, Xu Hui, Wei Chen
2008, 57 (2): 1073-1077. doi: 10.7498/aps.57.1073
Abstract +
By performing first-principles electronic structure and transport calculations, we have demonstrated the electronic structure and transport properties of single layer zigzag graphene nanoribbons with armchair edges and the effect of edge-vacancy defects. It is shown that perfect zigzag graphene nanoribbons are semiconductor with certain energy gaps which will become smaller due to the edge-vacancy defects combining with semiconductor-metal transition. This result may contribute to the electronic structure sewing of the graphene nanoribbons in the energy-band engineering.
First-principles calculation on the electronic structure and absorption spectrum of the wurtzite Zn1-xMgxO alloys
Guo Jin, Li Guang-Xu, Huang Dan, Shao Yuan-Zhi, Chen Di-Hu
2008, 57 (2): 1078-1083. doi: 10.7498/aps.57.1078
Abstract +
The electronic structure and absorption spectrum of the wurtzite Zn1-xMgxO(x=0, 00625, 0125, 025) alloys have been calculated by means of the first-principles method. The doping of magnesium leads to an apparent change of the electronic structure of ZnO. The electron density of the oxygen atoms near the magnesium atom increases obviously, and the oxygen atoms transfer some of the electrons to Zn atoms nearby. This weakens the interactions between zinc and oxygen atoms, the band gap becomes broader, which has been validated by the extent of shift of Zn 4s in the same alloys. Theoretical calculation also reveals a blue shift in the absorption spectrum of Mg-doped ZnO, and the absorption edges were located at 379,366,357 and 333nm, respectively, with increasing doping of magnesium in ZnO. The results are discussed in detail.
Phase-field model of isothermal solidification of binary alloy with multiple grains
Feng Li, Lu Yang, Zhu Chang-Sheng, Wang Zhi-Ping
2008, 57 (2): 1084-1090. doi: 10.7498/aps.57.1084
Abstract +
A new phase-field model for dendrite growth of multiple grains is developed based on the Ginzberg-Landau theory and phase-field model of single grains. Taking Al-2mole-Cu alloy for example, in connection with the concentration field, we simulated the dendritic growth process of multiple grains during isothermal solidification. The simulation showed dendritic competitive growth of multiple grains, and reproduced the process of dendrite growth in practical solidification.
Electronic structure in GaAs/AlxGa1-xAs spherical quantum dots
Wang Chuan-Dao
2008, 57 (2): 1091-1096. doi: 10.7498/aps.57.1091
Abstract +
In this paper, how the dots’ radius, Al concentration and external electric field affect the single electron energy states in GaAs/AlxGa1-xAs spherical quantum dots are discussed in detail. Furthermore, the modification of the energy states is calculated when the difference in effective electron mass in GaAs and AlxGa1-xAs are considered. In addition, both the analytical method and the plane wave method are used in calculation and the results are compared, showing that they are in good agreement with each other. The results and methods can provide useful information for the future research and potential applications of quantum dots.
Photo-thermal ionization spectroscopy of shallow acceptors in high purity germanium
Yu Li-Bo, Zhang Bo, Li Ya-Jun, Lu Wei, Shen Xue-Chu, Yu Chen-Hui
2008, 57 (2): 1097-1101. doi: 10.7498/aps.57.1097
Abstract +
The results of high sensitivity photo-thermal ionization spectroscoic (PTIS) investigation of shallow acceptors in high purity p-type germanium sample with room temperature resistivity of about 50Ω·cm, at temperature above liquid helium by Fourier transform spectrometer and associated magneto-optical measurement systems, are reported. The optimum photo-thermal ionization temperature range for the shallow impurities in high purity germanium is determined experimentally. At temperatures within this range, the PTIS spectra of this sample were measured. Boron and aluminum are found to be the main shallow acceptors in the sample. The causes of line splits of spectra, rapid recombination of compensating impurity and random strain, are analyzed and discussed.
Compensating impurity in high purity silicon single crystal investigated by photo-thermal ionization spectroscopy
Yu Li-Bo, Zhang Bo, Li Ya-Jun, Lu Wei, Shen Xue-Chu, Yu Chen-Hui
2008, 57 (2): 1102-1108. doi: 10.7498/aps.57.1102
Abstract +
The optimum photo-thermal ionization range near liquid helium temperature for the shallow impurities in n type high purity silicon single crystal was determined experimentally. At temperature within this range, the high resolution photo-thermal ionization spectra (PTIS) of this sample were measured. Positive PTIS responses from the majority residual impurity phosphor (P) and compensating impurity boron (B) were observed by simultaneously irradiating the sample with far infrared and band-edge light. Under action of applied external magnetic fields, the positive response from compensating impurity B changes to negative response. The posibility of these phenomena being the result of temperature effect was excluded, which revealed the deficiency of Darken model and supported the model of rapid recombination of minority carriers for PTIS response of compensating impurity in elemental semiconductors.
Ab initio studies of CiCs and CiOi defects in Si1-xGex alloys
Yang Fu-Hua, Tan Jin, Zhou Cheng-Gang, Luo Hong-Bo
2008, 57 (2): 1109-1116. doi: 10.7498/aps.57.1109
Abstract +
Ab initio total-energy calculations were used to investigate the behaviors of CiCs and CiOi defects in Si and Si1-xGex alloys. It was found that in Si1-xGex alloys with different Ge contents, both CiCs and CiOi defects have good stability, and direct Ge—C or Ge—O bonds are unlikely to be formed. The A and B type structures of CiCs defects have similar characters in the alloys. The formation energy of A type configuration decreases with increasing Ge content. But the formation energy of B type decreases at first and then increases with the Ge content. The energy differences of A and B type configuration defects are between 0235 and 0220eV with lower Ge contents, and decrease sharply to around 01eV for higher Ge contents. The formation energy of CiOi pair displays a complex feature. Under isothermal annealing at 1000K and above, the structure of A type CiCs defect in pure Si was destroyed and transformed to B type defect. During annealing, the behavior of A type CiCs defect in Si1-xGex alloys depended on the annealing temperature, Ge content in the alloy, and the sites of Ge atoms.
Injection and transport of the charge carriers in metal/impurity polymer/metal structure
Li Hai-Hong, Li Dong-Mei, Liu Wen, Li Yuan, Liu Xiao-Jing, Xie Shi-Jie, Liu De-Sheng
2008, 57 (2): 1117-1122. doi: 10.7498/aps.57.1117
Abstract +
Using the tight-binding Su-Schrieffer-Heeger (SSH) model and a nonadiabatic dynamical evolution method, the dynamic process of the charge carrier injection and transport through metal/ polymer/metal structure was studied, for which the polymer chain contains an impurity ion. The electron wave function was described by the time-dependent Schrdinger equation, while the polymer lattice was treated classically by the Newtonian equations of motion. It was found that the impurity ion acts as a control gate on the charge carriers, while the state of the control gate is determined by the strength of the electric field and the magnitude of the bias voltage.
A new method to measure the electrical conductivity of metals in electric exploding
Jiang Ji-Hao, Wang Gui-Ji, Yang Yu
2008, 57 (2): 1123-1127. doi: 10.7498/aps.57.1123
Abstract +
The electrical conductivity is an important transport coefficient for electric exploding. A new method to measure the electrical conductivity is designed using the experiment of electric gun. The electrical conductivity of copper is calculated using the data of electric gun. The electrical conductivity change exponentially with of the density.
Properties of p-type GaN etched by inductively coupled plasma and their improvement
Lü Ling, Gong Xin, Hao Yue
2008, 57 (2): 1128-1132. doi: 10.7498/aps.57.1128
Abstract +
Our preseut research was focused on the surface properies of the p-type gallium nitride (p-GaN) etched by inductively coupled plasma (ICP). Different methods were used to process the etched surface. The surface condition was investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The current voltage measurement was used to show the I-V characteristics of Ni/Au contacts on the sample. The experimental result demonstrated that the NaOH treatment is effective in improving the material surface and the ohmic contact properties.
Effect of sapphire substrate pre-treatment on the growth of ZnO films
Liu Ming, Liu Zhi-Wen, Gu Jian-Feng, Qin Fu-Wen, Ma Chun-Yu, Zhang Qing-Yu
2008, 57 (2): 1133-1140. doi: 10.7498/aps.57.1133
Abstract +
Using the reactive radio-frequent magnetron sputtering method, ZnO thin films were deposited on pretreated (100) sapphire substrates. The effect of substrate pretreatments on the growth of ZnO films was studied with the structural and morphological characterization using atomic force microscopy, reflection high-energy electron diffraction and X-ray diffraction. It was found that both the original substrate and the substrates annealed in vacuum (8×10-4 Pa), nitrogen atmosphere (40 Pa), and oxygen atmosphere (40 Pa) at 750℃ for 4h have the same surface structure that can be indexed to be α-Al2O3 (001). The surface morphologies of the substrates are different from each other. All the ZnO films grown on the substrates are highly c-axis textured. Their morphologies, however, are related to the pretreatment. For the substrate annealed in vacuum, the film has the morphology with -c and +c epitaxial islands, similar to ZnO grown on the untreated substrate. For the substrate annealed in nitrogen, the film has the morphology with only -c epitaxial islands and has quite large grains and surface roughness. For the substrate annealed in oxygen, the films also has the morphology with -c epitaxial islands, but the surface is much smoother. The surface roughness is as small as 15nm.
Fabrication of ZnO nanowire-based diodes and their light-emitting properties
Wang Yan-Xin, Zhang Qi-Feng, Sun Hui, Chang Yan-Ling, Wu Jin-Lei
2008, 57 (2): 1141-1144. doi: 10.7498/aps.57.1141
Abstract +
A Schottky type light-emitting diode of ZnO nanowire was fabricated based on the principle of luminescence of Schottky barrier heterojunction. Driven by a voltage of above 6 V, an EL spectrum was obtained. The spectrum consisted of two peaks: one is centered at a wavelength of the ultraviolet 392nm, and the other at the visible 525nm. The mechanism of electroluminescence of this device was analyzed according to the rectifying I-V curve and the energy band structure.
Preparation and characteristics of p-type ZnO by treated gaseous ammonia annealing
Tang Li-Dan, Zhang Yue
2008, 57 (2): 1145-1149. doi: 10.7498/aps.57.1145
Abstract +
The p-type ZnO:Al films deposited by RF/DC magnetron sputtering at room temperature were treated by gaseous ammonia annealing. The characteristics were examined by XRD, FESEM and Hall measurement. The results showed that the films crystallized in the wurzite phase with a preferential orientation along the c-axis and the surfaces are smooth and dense without visible pores and defects over the film, and the grain size was about 40—60nm at the annealing temperature of 700℃. The Hall measurement showed p-type conduction with the high carrier concentration of 8346×1018 cm-3 and low resistivity of 25014 Ω·cm when the annealing temperature was 700℃.
Properties of white organic electroluminescent device with double light-emitting layers based upon different hosts
Wu Xiao-Ming, Hua Yu-Lin, Yin Shou-Gen, Zhang Guo-Hui, Hui Juan-Li, Zhang Li-Juan, Wang Yu
2008, 57 (2): 1150-1154. doi: 10.7498/aps.57.1150
Abstract +
A novel phosphorescent white organic light-emitting device (WOLED) with configuration of ITO/NPB/CBP:TBPe:rubrene/BAlq:Ir(piq)2(acac)/BAlq/Alq3/Mg:Ag was fabricated successfully, where the phosphorescent dye Ir(piq)2(acac) was doped into BAlq (electron transport material) as the red emitting layer, and fluorescent dye TBPe and together with rubrene was doped into CBP (ambipolar conductivity material) as the blue and orange emitting layer, respectively. The emitting layers were sandwiched between the undoped NPB and BALq layers. We also discussed how to achieve the bright pure white light with high stability through optimizing the doping concentration of each dopant and employing the balanced charges distribution for the introduction of the heterojunctions between the different hosts in detail. This device turns on at the driving voltage of 42 V. It presents a maximum external quantum efficiency and brightness of 15% and 15000 cd/m2, respectively. The Commission Internationale de l'Eclairage (CIE) coordinates varies from (0368, 0389) at 10 V to (0314, 0327) at 15 V, and the best point is located at (0334, 0339) at 13 V. With the good EL performance,this kind of WOLED are particular suited for working as the backlight in LCD in combination with color filters to achieve the full color display.
The effect of the inserted AlGaAs films on the behaviors of InAs quantum dot detector
Xiao Jun, Zhang Shu, Yang Yu, Wang Chong, Liu Zhao-Lin, Li Tian-Xin, Chen Ping-Ping, Cui Hao-Yang, Lu Wei
2008, 57 (2): 1155-1160. doi: 10.7498/aps.57.1155
Abstract +
Two InAs quantum dot samples have been grown by the solid source molecular beam epitaxy (MBE) and fabricated to detectors. AlGaAs thin films have been inserted into the source region for one of the two devices. The structural features of the two samples have been studied by using the transmission electron microscope (TEM). The photoelectric properties of them have been measured by the photoluminescence (PL) and photocurrent (PC) spectra. The experimental results indicated that the AlGaAs films have profound effects on the properties of the detector. According to the calculations based on effective mass approximation, the origins of the photocurrent peaks of the two devices have been identified.
Boundary alternating current characteristics of an ideal p-n junction diode
Halimulati, Abai, Baishan, Aimaiti
2008, 57 (2): 1161-1165. doi: 10.7498/aps.57.1161
Abstract +
According to basic assumptions about the ideal operating state of p-n junction diode, deducing the relation of the time dependence of constant on the parameters such as diode size, diffusion length, carrier lifetime and alternating current frequency etc. at the base and near the p-n junction interface when diode is working under the applied alternating current. From the results,we discovered that in the two kinds of states of low and high current frequencies, the diode characteristics act on the time constants differently. In the low frequency state, the time constant is related to the material characteristics but not to applied current frequency. But in high frequency state, the time constant has no relation with the material characteristics, and was only related to the applied current frequency.
Photo-induced effect of Mn site Fe doping in La0.67Sr0.33FexMn1-xO3 thin films
Tang Jing, Chen Chang-Le, Jin Ke-Xin, Zhao Sheng-Gui
2008, 57 (2): 1166-1170. doi: 10.7498/aps.57.1166
Abstract +
The compounds and films of La067Sr033FexMn1-xO3(x=0, 005, 010, 015) were prepared by the sol-gel technique and pulsed laser deposition method, respectively. The effect of Fe doping on the transport and photo-induced properties of La067Sr033FexMn1-xO3 film was investigated. Experimental results indicate that the Fe doping lowers the insulator-metal transition temperature, but increases the resistance. The photo-induced relative change in resistance increases initially with increasing temperature, then followed by a decrease.The maximum value of the relative change in resistance increases with increasing x, it reaching 38% when x =015 The intriguing mechanism of photo-induced effect on the resistance was discussed in connection with lattice effect.
Electronic structures of hydrogenated and oxygenated boron-doped diamond films
Liu Feng-Bin, Wang Jia-Dao, Chen Da-Rong
2008, 57 (2): 1171-1176. doi: 10.7498/aps.57.1171
Abstract +
The hydrogenated and oxygenated boron-doped diamond films have been prepared by hydrogen-plasma treatment and boiling in the strong acids, respectively. By means of the X-ray photoelectron spectroscopy and contact angle measurements, the two surface-terminated diamond films have been evaluated. The scanning tunneling spectra have been measured by scanning probe microscope. The results indicated that for the hydrogenated diamond surface, the surface energy bands bend downwards and there exists a shallow acceptor above the valence band maximum. However, the surface energy bands for the oxygenated film bends upwards and its band gap is wide and clean. The conduction mechanisms for the two surface-terminated diamond films have been discussed.
The property of third-order optical nonlinear susceptibility of water soluble CdTe quantum dots
Wu Wen-Zhi, Zheng Zhi-Ren, Liu Wei-Long, Yang Yan-Qiang, Su Wen-Hui, Zhang Jian-Ping, Jin Qin-Han, Yan Yu-Xi
2008, 57 (2): 1177-1182. doi: 10.7498/aps.57.1177
Abstract +
The property of optical nonlinear susceptibility of the CdTe quantum dots (QDs) has been studied by using Z-scan and optical Kerr effect technique. Laser-induced sign reversal of the nonlinear refractive index of CdTe quantum dots appears under femtosecond and picosecond pulse excitation. Two-phonon absorption and free carrier absorption in the nanometer-sized CdTe are the possible origins of the nonlinear absorption. This material has the ultrafast response time of less than 400 fs in optical switching operation, and the peak Kerr transmittance is found to be 32 times greater than that of the standard CS2 liquid Kerr medium.
Strain effect on microwave surface resistance of YBa2Cu3O7-δ/LaAlO3 and Tl2Ba2CaCu2O8/LaAlO3 high temperature superconducting thin films
Zhang Guo-Hua, Shi Li-Bin, Zheng Yan, Ren Jun-Yuan, Li Ming-Biao
2008, 57 (2): 1183-1189. doi: 10.7498/aps.57.1183
Abstract +
YBa2Cu3O7-δ (YBCO) thin films were prepared by thermal coevaporation on (LaAlO3) LAO substrates,and Tl2Ba2CaCu2O8 (TBCCO) thin films were synthesized by magnetron sputtering method on LAO substrates. We obtained the strain from the results of XRD of the films,which had the values of ΔCY=48483×10-3 and ΔCT=85272×10-5. We found that the strain in YBCO was larger than that in TBCCO. In addition, the curve of surface resistance of the films as a funttion of temperature was obtained by coplanar resonator technique, which showed the resistance of YBCO was larger than that of TBCCO at the same reduced temperature. In the paper, we also analyzed the strain effect on the surface resistance of the films.
Thermoelectric transport properties of Zn-doped n-type Ba8Ga16-2xZnxGe30+x clathrates
Xiong Cong, Deng Shu-Kang, Tang Xin-Feng, Qi Qiong, Zhang Qing-Jie
2008, 57 (2): 1190-1196. doi: 10.7498/aps.57.1190
Abstract +
The single-phase Zn-doped n-type Ba8Ga16-2xZnxGe30+x clathrates were prepared by melting reaction method combined with spark plasma sintering (SPS). Influences of substituting Zn for Ga on the thermoelectric transport properties of the compounds were investigated. Research results indicate that the electrical conductivity of n-type Ba8Ga16-2xZnxGe30+x compounds increases gradually with the increasing of Zn substitution fraction x. The Seebeck coefficient decreases gradually with the increasing of x. When Zn replaces Ga entirely, the electrical conductivity of Ba8Zn8Ge38 compound drops rapidly and its Seebeck coefficient increases suddenly. Zn substitution fraction x dependence of the thermal conductivity and lattice thermal conductivity are similar in the temperature range from 300 to 1000 K.When xx,lattice thermal conductivity decreases gradually. When x>4, with the increase of x,lattice thermal conductivity increases gradually.In all n_type Ba8Ga16-2xZnxGe30+x clathrates, Ba8Ga8Zn4Ge34 compound has the greatest ZT value, and its maximal ZT value reaches 085 at about 1000K.
Tunneling magnetoresistance of Fe3O4 compacts prepared in magnetic field
Wang Jing-Ping, Meng Jian
2008, 57 (2): 1197-1201. doi: 10.7498/aps.57.1197
Abstract +
The magnetite particles were prepared in magnetic field in order to improve the surface crystallinity and reduce the lattice defests of particles. The magnetotransport properties of as-prepared magnetite compact were investigated and compared with that prepared without magnetic field. Spin polarization tunneling and high order hopping conductance were the main conduct mechanisms. The resistance decreased almost exponentially with increasing temperature, and was noncollinearity dependent on the voltage. Magnetoresistance vs magnetic field curves were butterfly-like, which was characteristic of tunneling magnetoresistance. The results showed that the sample prepared in magnetic field had lower resistance and higher magnetoresistance, maybe due to the particles having better crystallinty in the surface and less lattice defect. Magnetoresistance of both samples decreased slowly with increasing temperature.
The microstructure and impact toughness of sintered Nd-Fe-B magnets
Lian Fa-Zeng, Hu Zhi-Hua, Zhu Ming-Gang, Li Wei
2008, 57 (2): 1202-1206. doi: 10.7498/aps.57.1202
Abstract +
The effects of Nb on the microstructure and impact toughness of sintered Nd-Fe-B magnets as well as their inter relation have been investigated. The results show that the addition of Nb improves the microstructure, and increases impact toughness of sintered magnets. When Nb content of the sintered magnets without Co is 15 at%,the maximum impact toughness is obtained. But for the sintered magnets with the Co addition, the variation of impact toughness of the magnets is not obvious, and the magnets have lower impact energy than the magnets with the Co addition. The microstructure of sintered magnets has been studied. It was found that many factors affect the impact toughness of sintered magnets, but the main factor is the width and shape of grain boundary of sintered magnets.
Optimization of seed layer of PbTiO3/PbZr0.3Ti0.7O3/PbTiO3 sandwich structure ferroelectric thin film
Wang Long-Hai, Yu Jun, Wang Yun-Bo, Gao Jun-Xiong, Zhao Su-Ling
2008, 57 (2): 1207-1213. doi: 10.7498/aps.57.1207
Abstract +
The PT/PZT/PT and PZT thin films were prepared by sol-gel method. Different Pb content (x) (x=0, 005, 010, 015, 020) were added in excess to the PT precursor to optimize PT seed layer. The XRD and AFM results show that the crystalline phase and microstructure of the films were greatly affected by the excess Pb content (x) in PT layers. The pure perovskite structure PT/PZT/PT films with dense, void-free and uniform fine grain size were obtained for the proper choice of excess Pb content (x=010—015). EDX results showed that, in the interlayer and surface regions, the Pb deficiently and Pb abandance are obvious for the samples of x=0 and x=02, respectively. The ferroelectric, fatigue and leakage current properties of the films are not obviously relate to the change of excess Pb content (x), but correlate obviously with the crystalline behavior of PT layers. A well-saturated hysteresis loop with high remnant polarization, excellent fatigue properties and low leakage curremt were obtained for the films of excess Pb content x= 010 and 015. The excess Pb content (x) in PT layers affects the crystallization of PT layer, which will act as a nucleation site or seeding layer for PZT films and affect the perovskite phase formation of the PZT films. The optimized seed layer with excess Pb content x=010—015 improves not only the microstructure, but also the electric properties.
Built-in electric field and a new type of charged excitons observed in modulation-doped ZnSe/BeTe type-Ⅱ quantum well
Akimoto Ryoichi, Chen Jin-Xiang, Ji Zi-Wu, Takeyama Shojiro, Lu Yun, Mino Hirofumi
2008, 57 (2): 1214-1219. doi: 10.7498/aps.57.1214
Abstract +
We report results of the photoluminescence, photoluminescence excitation, and magneto-photoluminescence spectra measurements performed on modulation doped ZnSe/BeTe/ZnSe type-Ⅱ quantum well structures at low temperature (2—5 K). The non-doped sample showed two distinct peaks, while the doped one showed one peak only. The linear polarization degree measured in both photoluminescence and the photoluminescence excitation spectroscopy indicates that photoluminescence transitions of an indirect type takes place at respective heterointerfaces. The peak splitting in the non-doped sample was caused by a built-in electric field resulting from the spatial separation of charges along the growth axis. We found optical Shubinkov-de Hass oscillations in both the photoluminescence intensity and the transition energy under a high magnetic field perpendicular to the well. These features and the additional absorption (or reflection) spectra measurements demonstrated that two-dimensional electron gas of a high concentration was formed in the doped samples. All these present the signature of charged excitons and also of a correlated excitonic phase of type-Ⅱ quantum wells.
Dependence of properties of GaN-based light emitting diodes on the surface InGaN thickness
Gu Xiao-Ling, Guo Xia, Wu Di, Li Yi-Bo, Shen Guang-Di
2008, 57 (2): 1220-1223. doi: 10.7498/aps.57.1220
Abstract +
GaN-based light emitting diodes (LEDs) with InGaN as the capping layer was designed in our experiment. The forward voltage at the typical driving current of 20mA was obviously changed by adjusting the thickness of the InGaN layer. We were concerned with the effect of polarization and solved the concentration and the tunneling probability of the two dimensional hole in the triangular potential well at the surface InGaN/GaN interface and obtained the minimal forward voltage. The calculation results were consistent with the experimental data.
Preparation of tetrapod-shaped ZnO nanomaterial field emission cathodes by deposition method
Qin Hua-Fang, Guo Tai-Liang
2008, 57 (2): 1224-1228. doi: 10.7498/aps.57.1224
Abstract +
Tetrapod-shaped ZnO nanomaterial field emission cathode was preparated by deposition method. To the high-vacuum flat capsulation with phosphor screen and cathode was applied a voltage to test the cathode emission current and the phosphor screen brightness. For the cathode with total area 13×15 cm2, the test results showed that when the volume percentage of K2SiO3 ranged from 50 × 10-3 to 83× 10-3, concentration of Ba(NO3)2 arranged from 50 × 10-4 to 77×10-4 M, and concentration of tetrapod-shaped ZnO arranged from 82×10-4 to 12×10-3M, the cathode emission current was the largest, and phosphor screen at peak brightness could reach 60 cd/cm2 The average brightness was 48 cd/cm2
RF magnetron sputtering deposition growth of highly orientated strontium barium niobate thin films
Li Yue-Fu, Ye Hui, Fu Xing-Hai
2008, 57 (2): 1229-1235. doi: 10.7498/aps.57.1229
Abstract +
The ferroelectric potassium ion doped Sr075Ba025Nb2O6(SBN75) buffer layers were fabricated on Si(100) substrate by the sol-gel method, and the highly c-axis preferentially orientated SBN thin films on the KSBN buffer layers were obtained by the RF magnetron sputtering deposition. For the deposition of films, the corresponding preparation parameters have been optimized. It was found that the KSBN buffer layers can reduce the mis-match of crystalline lattices between the SBN film and the substrate effectively. When the ratio of O2/Ar pressure reached 1∶2, the working pressure was 10 Pa, and the sputtering power was 300W, the temperature of substrate was 300℃ and the post-annealing temperature was adjusted to 800℃, the c-axis highly preferentially orientated growth of SBN thin film can be realized. The microstructure of the thin films was investigated by XRD and AFM, and the p-n junction effect was found in our ITO/SBN/KSBN/Si structures, which is characteristic of semiconductor materials. The intensity of the junction effect was closely related to the presence of the buffer layer as well as the crystalline properties of SBN thin films.

EDITOR'S SUGGESTION

Epitaxial growth of high quality TiN thin film on Si by laser molecular beam epitaxy
He Meng, Liu Guo-Zhen, Qiu Jie, Xing Jie, Lü Hui-Bin
2008, 57 (2): 1236-1240. doi: 10.7498/aps.57.1236
Abstract +
TiN thin films have been successfully epitaxially grown on Si substrates by laser molecular-beam epitaxy using the two-step method. The thin film has a smooth surface with a root-mean-square roughness of 0842nm over a 10μm×10μm area. Hall measurement shows that the resistivity of the TiN film is 36×10-5 Ω·cm and the mobility is up to 5830 cm2/V·S at room temperature,which implies that TiN thin film is an excellent electrode material. The X-ray diffraction (XRD) θ—2θ scan result together with the very high mobility show that the TiN film has high quality. The result that SrTiO3 thin film can be subseguently epitaxially grown on TiN/Si substrate indicates that the TiN thin film on Si substrate not only has good thermal stability, but also can be used as buffers or bottom electrode for epitaxial growth of other thin films or multilayer films.
The adhesives strength of nanostructured AT13 ceramic coatings characterized by fractal dimension
Zhang Wu, Hua Shao-Chun, Wang Han-Gong, Wang Liu-Ying, Liu Gu
2008, 57 (2): 1241-1245. doi: 10.7498/aps.57.1241
Abstract +
Fractal dimension has been applied to study the interface of nanostructured AT13 coatings deposited by micro-plasma spraying. The result shows that the higher the spraying current, the greater the fractal dimension and adhesive strength. Fractal dimension and adhesive strength increase firstly and then decrease with increase of Ar flow rate. Fractal dimension can be used to characterize adhesive strength of the coatings. Adhesive strength increases with rising of fractal dimension. There is a proximate linear relationship between the logarithm of adhesive strength and fractal dimension: ln(σ)=176D-262.
The asymptotic analysis of interfacial stability with surface tension anisotropy for directional solidification of alloys
Wang Zhi-Jun, Wang Jin-Cheng, Yang Gen-Cang
2008, 57 (2): 1246-1253. doi: 10.7498/aps.57.1246
Abstract +
An asymptotic analysis of interfacial stability with the surface tension anisotropy is derived for directional solidification of alloys. The zero and first order solution for multi-scale and the zero order solution for single-scale are obtained. The dispersion relation adapted to all wave-length is presented by combining the short and the long wave-length solutions. It was concluded that the zero order asymptotic solution is equivalent to constitutional undercooling theory and the first order solution is consistent with M-S theory. The instability zone of control parameter enlarges with the surface tension anisotropy,especially for the high temperature gradient and high pulling velocitycases.
Study of nucleation of void-induced phase transformation under shock compression
Shao Jian-Li, Wang Pei, Qin Cheng-Sen, Zhou Hong-Qiang
2008, 57 (2): 1254-1258. doi: 10.7498/aps.57.1254
Abstract +
Molecular dynamics simulations have been used to study the nucleation and growth of void-induced phase transformation of single crystal Fe under shock-wave loading along the [001] direction and effects of initial temperature on the process. It was found that: 1) phase transformation nucleates firstly on the (110) and (110) planes around the void and grows along the [110],[110] and [110],[110] directions, respectively, and then grow along 〈111〉 directions of the (110) and (110) planes, and ultimately “V" shaped grains form; 2) under the same shock compression, grains at initial temperature 300 K are smaller than those at 60 K, and at the same time, many embryos appear around the grains. These phenomena indicate that void-induced phase transformation nucleates and grows along certain directions, and increasing the initial temperature can diversify the action. Finally, we calculate the statictics of pressure-volume tensor and energy distributions, and give a preliminary analysis of the nucleation and growth of phase transformation.
Neuron excitability changes induced by low-power laser irradiation
He Bing-Jun, Dong You-Er, Qiao Xiao-Yan, Li Gang
2008, 57 (2): 1259-1265. doi: 10.7498/aps.57.1259
Abstract +
The change in excitability induced by low-power laser was investigated for freshly dissociated rat hippocampal CA3 pyramidal neuron using the whole-cell patch clamp technique. The experimental results indicate that the activation potential of Na+ channel shifted towards a more negative potential, the peak amplitude of INa increased in a voltage-dependent and reversible manner, the steady-state activation curve and inactivation curve of INa were significantly shifted, the half-activation voltage and the half-inactivation voltage respectively changed from (-4414±528)mV to (-5655±614)mV(n=8,Pn=8, P+ channel, further affect the depolarizing and firing of action potential, and finally be involved in adjusting the excitability of neurons.
Non-ionizing energy loss of low energy proton in semiconductor materials Si and GaAs
He Xin-Fu, Luo Wen-Yun, Zha Yuan-Zi, Wang Chuan-Shan, Tang Xin-Xin, Wang Chao-Zhuang, Fan Sheng, Huang Xiao-Long
2008, 57 (2): 1266-1270. doi: 10.7498/aps.57.1266
Abstract +
The displacement damage due to non_ionizing energy loss (NIEL) is the main reason of device-malfunction in spatial radiation environments. In the low energy range where the Coulombic interaction dominates, Mott-Rutherford differential cross section is usually used in its creatment. However, electrostatic screening of nuclear charges of interacting particles is not accounted for. The NIEL induced by low energy proton in Si and GaAs have been calculated using analytical method and Monte-Carlo code (SRIM). Thin_target approximation was used when calculating NIEL by SRIM code and the result compared with that of other authors' . The results show that thin_target approximation is reasonable and NIEL scaling is feasible. The NIEL values become lower after taking into account the screening effect. The results by SRIM code are 30% and 20% of Summers's results for Si and GaAs at 1 keV, respectively. The result is very important for spacecraft design.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Polarization properties of partially coherent flat-topped light beams diffracted through a regular polygonal aperture
Fu Wen-Yu, Ma Shu-Yi
2008, 57 (2): 1271-1277. doi: 10.7498/aps.57.1271
Abstract +
Based on the beam coherence-polarization matrix and the propagation law, the polarization properties of partially coherent flat-topped light beams diffracted through a regular polygonal aperture are studied systematically. The expression for the degree of polarization of partially coherent flat-topped light beams is derived. And according to that, the expression for the degree of polarization of Gaussian Schell-model beams and the propagation of partially coherent flat-topped light beams in the free space are obtained. It is shown that the polarization properties of partially coherent flat-topped light beams diffracted through a rectangular aperture depends on the truncation parameter, spatial coherence parameters, diffraction angle, propagation distance and the order of flat-topped light beams.
Hawking radiation of Dirac particles in a rectilinearly accelerating Kinnersley black hole
Yang Bo
2008, 57 (2): 1278-1284. doi: 10.7498/aps.57.1278
Abstract +
In a uniformly accelerating space time, the coupling Dirac equation can be simplified to the second-order equation. Using new tortoise coordinates, we further simplify the equation to the standard wave-equation near the horizon and get the temperature function of radiation and the Hawking radiation spectrum.
The relationship between FWHM and duration of single peaked GRB light curves
Deng Jia-Gan, Huang Ren-Tang
2008, 57 (2): 1285-1289. doi: 10.7498/aps.57.1285
Abstract +
We explored the relation between FWHMs of single pulses in a sample of GRB (Gamma-Ray Burst) light curves and durations of the GRBs. Based on a sample of 108 single_peaked GRB light curves, we fitted these sample data with Kocevski, Ryde & Liang (2003) model. A sub-sample containing 59 pulses with χ2T≈BWa, where T is the duration, W is the FWHM, a and B are constants. Our result shows that there does exist a proportional correlation between the logarithm of FWHMs and the logarithm of T90 (duration containing from 5% to 95% of the total fluence of a GRB) of GRB light curves with a correlation coefficient R=072.The proportional correlation between the logarithm of FWHMs and the logarithm of T50 (duration containing from 25% to 75% of the total fluence of a GRB) is more tight with a larger correlation coefficient R=093.Our finding shows that the light curve structure is correlated to the GRB duration. A larger FWHM corresponds to a longer GRB.